System Aspects of Black Liquor Gasification a Review of Existing Reports

System Aspects of Black Liquor Gasification A review of existing reports

ER 2008:25 Acknowledgement The author wishes to express his gratitude to Niklas Berglin, STFI-Packforsk AB, Anna von Schenck (Isaksson), STFI, Tomas Ekbom, Nykomb Synergetics, Gunnar Modig, LTH, Karin Pettersson, Chalmers, Eva Andersson, Chalmers, Lillemor Madeyski, Chalmers, and Lil Falkensson, Chalmers for valuable help and discussions. The Author also wishes to thank the Swedish Energy Agency for financial support.

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ER 2008:25

ISSN 1403-1892 Forord Energimyndigheten har under 2000-talet finansierat teknisk forskning om svartlutsforgasning inom programmet Svartlutsforgasning. Samtidigt har myndigheten uppmarksammat behovet av mer systeminriktade insatser inom detta omrade. Under hosten 2005-varen 2006 genomfordes projektet ” System Aspects on Black Liquor Gasification ”, vid Chalmers tekniska hogskola. Projektet omfattade en litteraturgenomgang av projekt med denna inriktning, som har genomforts under perioden 1996-2005.

Projektets slutrapport sags som sa intressant att den borde komma till kannedom for en vidare krets, varfor Energimyndigheten ger ut den i sin rapportserie.

Svartlutsforgasning ar ett teknikomrade som utifran olika utgangspunkter har varit intressant under en langre tid. Mojligheten att ersatta sulfatmassafabrikernas soda- pannor med sakrare teknik (undvika explosionsrisken), liksom potentialen att vasentligt hoja elproduktionen vid bruket har varit betydelsel^lla drivkral^er. Pa senare ar har mojligheten att framstalla fornybara drivmedel fran gasen vackt stort intresse.

Rapporten ar skriven pa engelska och riktar sig till beslutsfattare, forskare, konsulter och ovriga aktorer som har ett intresse for systemutvecklingen inom svartlutforgasningsomradet.

Rapporten har skrivits av professor Thore Berntsson, Chalmers tekniska hogskola.

Birgitta Palmberger Avdelningschef Preface The Swedish Energy Agency has financed technical research regarding black liquor gasification within the programme Black Liquor Gasification (BLG programme). The agency has also identified a need for systems related studies within this field. In the years 2005-2006, the project “System Aspects on Black Liquor Gasification ” was carried out at Chalmers Institute of Technology. The project included a literature review of completed projects directed to this aim, which had been carried out during the decade 1996-2005.

The final report of the project was considered to be of interest for a wider audi ence and therefore the Swedish Energy Agency has decided to publish it in its report series.

Black liquor gasification is a technology which for several reasons has been of interest for a long time. The possibility to replace the furnace of kraft pulp mills with a more secure technology (avoiding explosion risk) and also to increase the potential to produce electricity at the mill have been important driving forces. In later years the option to produce renewable motor fuels from the gas has aroused significant interest.

The report is written in English and is intended for decision makers, governmental agencies, researchers, consultants and other stakeholders, with an interest in this field.

The principal author of the report is professor Thore Berntsson, Chalmers Institute of Technology.

Birgitta Palmberger f Head of department Swedish Energy Agency Contents

1 Introduction 7 1.1 Background ...... 7 1.2 Aims...... 7 1.3 C ontents of the Report ...... 7 1.4 Projects with System Aspects of BLG...... 8

2 Basics and Principles for the high-temperature BLG technology 9 2.1 Introduction ...... 9 2.2 BLGCC...... 9 2.3 Process integration ...... 11 2.4 Performance ...... 12 2.5 BLGMF...... 12

3 Important System Aspects 15 3.1 Process Integration ...... 15 3.2 System consequences in a pulp mill and a pulp and paper mill, respectively ...... 15 3.3 Product or mix of products from a BLG...... 16 3.4 Environmental aspects ...... 16 3.5 COz Capture (CCS)...... 16 3.6 Economy ...... 16

4 Potentials for energy efficiency in pulp mills 17

5 BLG Programme 19

6 Efficient Upgrading of Biofuel by Integrated Biorefinery Operations in Future Pulp Mills 21 6.1 Introduction ...... 21 6.2 Aim...... 21 6.3 Reference mill...... 22 6.4 Environmental evaluation ...... 24 6.5 Economic evaluation ...... 25

7 Black Liquor Gasification - an Assessment from the perspective of the Pulp and Paper Industry 27

8 Black Liquor Gasification with Motor Fuel Production - BLGMFII 33

9 System Aspects of Black Liquor Gasification - Consequences for both Industry and Society 37 10 A Cost-Benefit Assessment of Biomass Gasification Power Generation in the Pulp and Paper Industry 45 10.1 Reference mill...... 45 10.2 Black liquor gasification plants ...... 46 10.3 Steam conditions ...... 46 10.4 Energy balances ...... 47 10.5 Environmental evaluation ...... 48 10.6 Economic evaluation ...... 48 10.7 Regional and national impacts ...... 49

11 The KAM Programme (2003) 51 11.1 Effects on recausticizing ...... 52 11.2 Energy balances ...... 53 11.3 Black Liquor Gasification Combined Cycle Systems...... 58 11.4 Investment and Operating Costs...... 60 11.5 Conclusions...... 63

12 Pulp Mill Energy Systems with Black Liquor Gasification - a Process Integration Study 65

13 Flexible and Efficient Biomass Energy Systems in the Pulp Industry and opportunities for Efficient Use of Biomass in the Pulp and Paper Industry 73 13.1 Introduction ...... 73 13.2 Power Generation Using advanced Gas Turbine Technologies...... 73 13.3 Potential Power Production Using Black Liquor and Bark...... 74 13 .4 Transportation fuel production with black liquor gasification...... 75 13.5 C02 Reduction ...... 78 13.6 Comparison of combined Cycle and Steam-Injected Gas Turbine Cycle...... 81

14 Synthesis of earlier work 83

15 Need for Further Work 89

References 91

Attachment: Historical development of BLG technologies 95 1 Introduction

1.1 Background Black liquor gasification (BLG) is one of the high-prioritized R&D areas in Sweden. Research work is going on in the national program BLG-Programmet. The first period of this Program ended in December 2005. In this program R&D on system aspects of BLG is very limited. At the same time several projects have been carried out, in which system aspects on different system levels have been studied. They have been performed as individual projects or as part of other R&D programs. From the Swedish Energy Agency (e.g. Lars Tegner) and from the BLG Program participants, a high interest to include more system oriented research in the new period of the program, if financing for this period can be achieved, and to summarize earlier work in this area has been expressed. For these reasons the Swedish Energy Agency has granted a senior project for Thore Berntsson, Heat and Power Technology, Chalmers.

1.2 Aims The main aims with the project are to: • Identify larger projects dealing with energy oriented system aspects of BLG • Make a synthesis on system aspects results in these projects • Identify need for further work, e.g. as a part of a second period of the BLG Programme

Due to the limited budget of the project, 150 000 SEK, no new work or calcula tions have been performed. The aim has been only to compile and draw conclu sions from existing information.

The focus has been on system studies. Most of the research on BLG has been technically, chemically and component oriented. These areas are not included in this report.

1.3 Contents of the Report In Chapter 2 basics for BLG are presented and in Chapter 3 important system aspects of this technology are discussed. Future opportunities for energy savings in mills are crucial for a BLG system, both technically and economically. Therefore present knowledge for such opportunities is presented in Chapter 4.

In section 1.4 the report/projects included in this report are introduced and in Chapter 5-13 Summaries, especially on system aspects, of these reports are given. In order to keep the report at a reasonable size only major projects dealing with system aspects during the last 10 year period have been included.

7 In Chapter 14 a synthesis of system aspects dealt with in the different reports is presented and in Chapter 15 suggestions for further work are given. In Chapter 16 references are given and finally in the Attachment a brief overview of different BLG technologies is presented.

1.4 Projects with System Aspects of BLG The following projects are included in this report and analyzed:

• BLG Programme (2006) A national R&D programme with Richard Gebart, ETC Pitea as coordinator

• Efficient Upgrading of Biofuel by Integrated Biorefinery Operations in Future Pulp Mills, three papers (2004), (2004) and (2005) A Ph. D. project at Heat and Power Technology, Chalmers by Eva Andersson and supervisor Simon Harvey. A project in the Swedish national programme Program Energisystem • Black Liquor Gasification -An assessment from the Perspective of the Pulp and Paper Industry (2005). A licentiate thesis from LTH by Gunnar Modig • Black Liquor Gasification with Motor Fuel Production (2005). An EU report by Tomas Ekbom, Niklas Berlin and Sara Logdberg • System Aspects of Black Liquor Gasification - Consequences for both Industry and Society (2001). A licentiate thesis by Hakan Eriksson, Heat and Power Technology, Chalmers • A Cost-Benefit Assessment of Biomass Gasification Power Generation in the Pulp and Paper Industry (2003) A report by Eric Larson, Stefano Consonni, Ryan Katofsky The principal author Eric Larsen is at Princeton University, US • KAM “Ecocyclic Pulp Mill” ( 2003) Two national R&D programs dealing with new technologies and systems solutions for chemical pulp and paper mills. Principal author of BLG parts in these programmes has been Niklas Berglin, STFI-Packforsk • Pulp Mill Energy System with Black Liquor Gasification - A Process Integration study (1996) Licentiate thesis by Niklas Berglin, Heat and Power Technology, Chalmers • Opportunities for Efficient use of Biomass in the Pulp and Paper Industry and Flexible and Efficient Biomass Energy Systems in the Pulp Industry - two licentiates theses at Energy Processes, Royal Institute of Technology, (1999) and (2000), by Katarina Maunsbach and Anna Isaksson (These theses are treated together, as they are rather closely linked together)

8 2 Basics and Principles for the high- temperature BLG technology

2.1 Introduction The description in this chapter has been taken from ”Black Liquor Gasification with Motor Fuels production - BLGMF”, by Tomas Ekbom, Mats Lindblom, Niklas Berglin, Peter Ahlvik (2003). It deals with the Chemrec technology, as this technology is the most commonly used in the system studies. An overview of different technologies is done in the Attachment.

Gasification of black liquor is an alternative recovery technology that has gone through a step-wise development since its early predecessor was developed in the 1960s. The currently most commercially advanced BLG technology is the Chemrec® technology, which is based on entrained-flow gasification of the black liquor at temperatures above the melting point of the inorganic chemicals.

In a BLG system, the recovery boiler is replaced with a gasification plant. The evaporated black liquor is gasified in a pressurised reactor under reducing condi tions. The generated gas is separated from the inorganic smelt and ash. The gas and smelt are cooled and separated in the quench zone below the gasifier. The smelt falls into the quench bath where it dissolves to form green liquor in a manner similar to the dissolving tank of a recovery boiler.

The raw fuel gas exits the quench and is further cooled in a counter-current condenser. Water vapour in the fuel gas is condensed, and this heat release is used to generate steam. Hydrogen sulphide is removed from the cool, dry fuel gas in a pressurised absorption stage. The resulting gas is a nearly sulphur-free synthesis gas (syngas) consisting of mostly carbon monoxide, hydrogen and carbon dioxide.

2.2 BLGCC Most of the development of large-scale systems for BLG has been aimed at using the syngas to fire a gas turbine in which power is generated. The hot flue gas from the gas turbine is then used to generate steam in a waste heat boiler, and the generated high-pressure steam is used in a steam turbine for additional power generation. The concept is known as BLGCC (Black Liquor Gasification Com bined Cycle). It is described here to provide background information. The alter nate route for the use of the syngas, i.e. synthesis of motor fuels, is what has been investigated in the present project. The new concept, Black Liquor Gasification with Motor Fuels Production, (BLGMF) is described in next chapter.

The use of BLGCC, as compared to a recovery boiler system, increases the poten tial to generate power and reduces the heat surplus of the mill. Because a large

9 amount of the sulphur can be separated from the smelt the possibility to generate liquors with different sulphidity increases. This is of interest to be able to further optimise the kraft cook. For example, it is easier to divide the sulphur between different white liquor streams for modified cooking. It is also straightforward to produce elemental sulphur from the H2S gas if the plant is integrated with a Claus reactor. Sulphur can be mixed with cooking liquors to produce polysulphide and then returned for use in impregnation.

The gasification process is described in Figure 2.1. At the heart of the process is an oxygen-blown, entrained-flow gasifier. The gasifier can be either ceramic-lined or have water-cooled walls.

HRSG 4.5 bar ^LP Sleann 10 bar (Bypsss supplementary firing)

25 bar GASIFIER

Sulfur

Nitraaen

Figure 2.1 Black liquor gasification combined cycle (BLGCC) with air separation unit (ASU), gasifier and syngas cooler, acid gas removal (AGR), sulphur recovery unit (SRU), gas turbine (GT), heat recovery steam generator (HRSG) and steam turbine (ST).

The alkali smelt, with a relatively low content of sulphide, from the gasification plant is dissolved and forms green liquor. The green liquor is causticised in the conventional manner before the separately recovered H2S sulphur is returned to the white liquor. Hydrogen sulphide removal from the gas is preferably done by physical absorption in a conventional acid gas treatment plant. Some C02 is absorbed both when the gas and smelt are quenched with weak wash and when the H2S is reabsorbed in the white liquor. The causticising plant is of a conventional type, but it requires a larger amount of lime from the lime kiln due to the higher fraction of alkali present as carbonate in the green liquor. A more detailed description is given in Berglin et al. (1999).

10 2.3 Process integration The cleaned pressurised gas is fired in a gas turbine of industrial, heavy-duty type. The gas turbine model chosen is representative of large machines currently being used for cogeneration as well as in stand-alone combined-cycle power plants. There is also considerable experience from operating these on gasified coal and oil. Black liquor syngas is similar in composition to the one obtained from coal or oil gasification.

The expanded flue gas is cooled in a boiler producing HP, MP, LP, and LLP steam. The high-pressure steam is passed through a back-pressure steam turbine before it is used by mill consumers. The steam turbine is smaller than in a recov ery boiler system because the steam production is lower and a large fraction of the MP and LP steam is generated directly in the gasification plant.

The incineration of malodorous weak gases calls for another solution than in the conventional mill where they are destroyed in the recovery boiler. The strong gases can be burned in a dedicated incinerator or in the lime kiln. Between 2 and 3 percent of the sulphur captured in the gas cleaning unit will also leave with tail gases from the sulphur recovery unit, adding to the amount of strong gases.

Since precipitator ash is not generated, purging of potassium and chloride would call for another process, e.g., evaporation and crystallization of a part of a green or white liquor stream. On the other hand, control of the sodium and sulphur bal ances would be facilitated by the fact that Na and S are enriched in separate streams.

If the H2S is reabsorbed to make conventional green liquor there is no effect on the pulp properties. However, there is a potential to use modified cooking liquors with different sulphide contents, in particular a polysulphide liquor. Polysulphide impregnation improves yield by retaining more hemicellulose. Because wood represents the dominant operating cost in a pulp mill, a higher yield can provide a substantial economic benefit. On the other hand, pulps rich in hemicellulose sometimes exhibit lower tear strength than conventional kraft pulps, which may reduce their value in some applications.

Combustion in the gas turbine takes place at a high pressure and temperature, which are conditions that promote the formation of thermal-NO X. Conventional low-NOX burners cannot be used for synthesis gas, because the flame propagation speed is too high. The main methods to prevent NOX formation are therefore steam or nitrogen injection. In addition to this, the nitrogen in the black liquor will form ammonia that may increase NOX emissions if it is incinerated with the sulphur-containing gases.

The physical absorption system used to remove H2S is designed so that SO2 emis sions are on par with those from the recovery boiler. Higher removal efficiencies can be achieved but at a higher cost. To minimise CO2 absorption, some H2S will

11 be allowed to slip through the reabsorption system. These gases are burned with the weak gases.

2.4 Performance The power generation in the gas turbine corresponds to about 138 MW for a model mill producing 2000 ADt/day, and the total power generated is 2070 kWh/ADt. The auxiliary power consumption is also much higher, however, than in the Reference Mill, mainly because of the compression requirements for air separation. Nevertheless, the amount of excess power that can be sold to the grid nearly doubles compared to the same mill with a recovery boiler system.

A general disadvantage of a black liquor gasification combined cycle process is the limited flexibility of the gas turbine. It is only possible to purchase units with fixed capacities i.e. they cannot be tailor-made as is possible with steam turbines, and they are not very flexible, from an operational point of view. Their efficiency decreases significantly when they are operated at part load. It is normal that a pulp mill capacity increases considerably during its first five to ten years after start-up. At different times there will therefore be a mismatch between the amount of gas produced and the amount of gas that can be fired in the gas turbine. If the gas turbine is undersized relative to the amount of gas, some of the gas will be burned in the heat recovery steam generator; this leads to a decrease in power generation efficiency, but the overall efficiency increases. If there is another gas turbine fuel available, the gas turbine can be oversized relative to the fuel gas flow only.

2.5 BLGMF A novel concept here developed from the BLGCC is the Black Liquor Gasifi cation with Motor Fuels production (BLGMF) system is an alternative for processing black liquor and is intended to replace the conventional recovery boiler. A schematic drawing of the BLGMF system is shown in figure 2.2. The gasifier/quench system is analogous to the recovery boiler system in the respect that it converts black liquor into green liquor. But rather than burning the black liquor to form steam, the BLGMF system partially converts (gasifies) the liquor with oxygen to produce a synthesis gas and a molten salt smelt. The gas and smelt are cooled and separated in the quench zone below the gasifier. The smelt falls into the quench bath where it dissolves to form green liquor in a manner similar to the dissolving tank of a recovery boiler.

12 BFW

Steam

Gas cooling Distillation Methanol Gasifier i— Gas cleaning DME

Auto-Thermal Quench reformer Compression Power, & motor fuel Steam synthesis

Figure 2.2 Black liquor motor fuel system (here with optional auto-thermal reformer).

The raw fuel gas exits the quench and is cooled in a counter-current condenser. Water vapour in the fuel gas is condensed, and this heat release is used to generate steam. Hydrogen sulphide is removed from the cool, dry fuel gas in a gas cleaning stage and the synthesis gas is compressed and converted into methanol or alterna tively DME in a synthesis reactor.

The raw methanol/DME is further distilled and a clean product is obtained. Addi tional steam and power are needed for the compression, synthesis and distillation units. This is foreseen at being produced in an adjacent power boiler, which is fed with extra biomass. With this process scheme, almost 70 % of the extra biomass energy is transformed to methanol/DME, giving an exergy efficiency about twice that of a recovery boiler system. The extraordinary methanol/DME output of a black liquor motor fuel system offers the potential to significantly reduce fossil fuels used for transport. In short, “green ” methanol/DME from biomass and black liquor replaces fossil fuel-based energy.

Aside from energy-related advantages, a black liquor motor fuel system offers improved environmental performance and safety compared to a recovery boiler. Efficient sulphur removal from the fuel gas before the synthesis results in signifi cantly lower levels of reduced sulphur compounds exiting the system, thus elimi nating the disturbing pulp mill smell. The lack of a smelt bed in the gasification reactor also means that there is no risk for a deadly smelt-water explosion inherent with recovery boilers.

13 14 3 Important System Aspects

In this chapter different important system aspects, included in the synthesis of earlier work mentioned in Chapter 1 are discussed

3.1 Process Integration Process integration aspects should be seen on at least two levels:

• Integration between a BLG and a mill in order to make best use of possible synergy effects from e.g. an energy point of view, for example use of excess heat from the BLG in the mill • Process integration in the mill for creating an excess of biomass fuel

The importance of the first level is obvious. The second level is of very high im portance for the BLG technology, as the economy and environmental performance are highly influenced by the degree of energy efficiency in a mill. The higher energy efficiency, the less external biomass is needed for the energy balance. With a high degree of energy efficiency a BLG can perform well without any import of biomass to the mill. Thereby the investment costs for process integra tion must be compared with the operational costs for imported biomass. With reasonable investment costs, the economic benefits of not having to import biomass can be substantial. The environmental implications are also large. The external biomass not needed in the mill can instead be used for replacing fossil fuels in other parts of society.

3.2 System consequences in a pulp mill and a pulp and paper mill, respectively With the aid of BLG the electricity production can be considerably increased or biomass based motor fuels can be produced in a rational way. In future market pulp mill an excess of internal fuel can be achieved and this excess can be increased by process integration (see above). The incentives for more advanced process integration could be increased if a BLG is considered in a mill.

In a future pulp and paper mill there will be an excess of internal biofuel only in very extreme cases, but the economic situation for a BLG can be considerably improved if the need for imported biomass fuel can be minimized. Also in a situation with internal excess, it can be of interest to import biomass fuel in order to the black liquor even for production of electricity or motor fuels.

All these opportunities/combinations, combined with process integration poten tials, are important system aspects. Identification of both technical, economic and environmental opportunities must be considered.

15 3.3 Product or mix of products from a BLG One important aspect is what a BLG shall produce. The two obvious routes are electricity or motor fuels. These are two very different approaches seen in a system perspective for both a mill and society. Aspects to take into account are e.g.: • Future efficiencies for electricity or motor fuel productions systems • Future process for electricity, biomass fuel and different types of motor fuel • Future policy instruments regarding e.g. CO2 trading, green certificates for electricity and/or motor fuels • Car market development and thereby future demands for different types of motor fuel • Future development into a possible hydrogen society • Global environmental consequences of different production routes, especially differences in global CO2 emissions between electricity or motor fuel production

3.4 Environmental aspects An introduction of a BLG will give several different environmental consequences, such as changes in emissions of NOx, SOx and CO2. Of these the CO2 ones are of course the most important and will also probably influence the economy to a high extent, due to future policy instruments. Different system solutions for and pro ducts (see above) from a BLG will also influence the environmental performance. For CO2 the global consequences must be considered, i.e. external consequences such as decrease or increase in electricity production in the marginal production technology in society (e.g. the Northern European System). Biomass as a limited resource which alternatively can be used in other parts of society for fossil fuel replacement, etc, must also be taken into account.

3.5 CO2 Capture (CCS) Gasification technology offers an opportunity of removing CO2 as a by-product together with water vapour and can easily be removed from such a mixture, transported and stored. For e.g. methanol and DME production the amount of CO2 produced is approximately 20 % compared with the total number of carbon atoms but in a possible future hydrogen society, hydrogen can be produced by the BLG and in this case at least 90 % of the coal is transferred to CO2 which can easily be removed. This opportunity can be of high importance for both the economic and environmental consequences of using BLG.

3.6 Economy The overall economy for different BLG system solutions and products is also an important system aspect. Investment costs, future scenarios regarding energy prices, policy instruments, availability of external biomass fuel, infrastructure of pulp and paper industry, etc must be taken into account.

16 4 Potentials for energy efficiency in pulp mills

Within the FRAM programme (2004), two models of average Scandinavian mills producing bleached market pulp have been analysed from an energy perspective. The aim was to explore the opportunities for heat integration in order to create a steam surplus. The steam surplus gives opportunities for increased power genera tion or lignin extraction. The technical and economic consequences of using the steam surplus in this way are explored in a continuation of this project. In FRAM other areas than BLG have been investigated and this work is therefore not sum marized in this report.

Two different approaches for creating a steam surplus have been investigated: 1) conventional measures and 2) process-integrated evaporation (PIvap). The former approach includes improved heat integration and new equipment. The latter approach means that excess heat from the mill is used for evaporation to partly replace live steam.

The two model mills created within FRAM differ in the level of water usage, since it is expected that the amount of excess heat for PIvap will increase with decreasing water usage. They are called HWU (high water usage) and LWU (low water usage).

Conventional measures consist of the following ones: Solving pinch violations (deleting heat exchange with very high AT, heating at low temperatures or cooling at high temperatures), new equipment (e.g. shoe press in the dryer and increasing the dry solids content of the heavy liquor from 73 % to 80 % and compiling the surplus, blow out steam. The resulting total steam surplus and associated invest ment costs are shown in Table.4.1.

Table 4.1 Resulting steam surplus and investment costs for conventional measures.

Inv. Spec. Steam saving Steam surplus cost inv. measure [MW] [GJ/ADt] [M€] [€/W] Pinch violations 17.4 1.51 4.3 0.25 New evap. plant 21.8+6.0 2.40 6.4 0.23 Shoe press 6.2 0.53 5.2 0.85 Blow off 8.2 0.71 0 0 Total 59.6 5.15 15.9 0.3 This Table is approximately valid for both the HWU and LWU case.

When using PIvap for creating a large steam surplus the amount of water, as the amount of available excess heat above 95oC in the plant (in the PIvap solution) is influenced. To collect the excess heat for the evaporation a new hot and warm

17 water system (HWWS) must be designed. The resulting steam savings and associated I investment cost are shown in Table 4.2, where different number of evaporation effects are included (Convap 7+ is the conventional design):

Table 4.2 Steam surplus and costs for the approach with PIvap.

Steam surplus [MW] Steam saving PIvap6 PIvap7 PIvap8 Con- measure HWU LWU HWU LWU HWU LWU vap7+ Evap. plant 17.1 23.1 25.0 30.9 30.3 33.6 21.7 Increased DS 6.0 6.0 6.0 6.0 6.0 6.0 6.0 hw/ww prod 6.4 6.4 6.4 6.4 6.4 6.4 6.4 Wood yard 1.6 1.6 1.6 1.6 1.6 1.6 1.6 Blow out 8.2 8.2 8.2 8.2 8.2 8.2 8.2 Total surplus 39 45 47 53 52 56 44

Costs [M€] Evap. plant 2.7 3.9 5.7 7.0 8.0 9.3 6.4 New HWWS* 2.5 2.2 2.5 2.2 2.5 2.2 0.6 Total 5.3 6.2 8.3 9.3 10.5 11.5 7.0 * New HWWS solves pinch violations (and gives excess heat for PIvap)

To summarize, by investing 11 M€ in conventional measures it is possible to cre ate a steam surplus of 53 MW (about 26 % of the total consumption), independent of the level of water usage. For the PIvap approach, the level of water usage mat ters, since there is more excess heat for PIvap in the mill with lower water usage. As a result, the total steam surplus with the PIvap approach differs in the two mills: up to 52 and 56 MW, respectively. Hence, the steam savings for the PIvap approach are similar to those in the approach with conventional measures; and so are the investments needed (10-12 M€). Even though the two approaches give approximately the same savings with the same investment, the PIvap approach might be easier to implement in an existing mill.

Similar studies within the KAM programme (2003) have shown even higher steam saving potentials. In the KAM programme only greenfield mills were studied. For a Greenfield market pulp mill possible steam saving potentials, compared with today's average mill, are 35-50 %, depending on the conditions.

18 5 BLG Programme

This is a national Swedish programme with Rikard Gebart, ETC Pitea, as coordinator. Parts of this program are also included in the IEA project Industrial Energy Technologies and Systems, Annex VI. The coordinator has made a summary of the projects in the first period, 2004-2006. It is shown in the table below: Table 5.1 Projects in the BLG Program 2004-2006.

Project name Project leader Description

0. Synthesis of results Prof. Rikard Coordination of sub projects, participation in the and project coordination Gebart, ETC IEA Annex 15 Technical Review Committee, for the BLG Program synthesis and dissemination of project results, workshops for technology transfer.

1. Modelling, simulation Rikard Gebart, ETC Development and validation of a computer model and optimisation of a for the hot parts of the gasifier. The model shall be black liquor gasification validated by comparison to the DP1 reactor and reactor then be used for studies of scale-up effects.

2. Validation of models Ass.prof. Lars Development and validation of a computer model for the quench and the Westerlund, Lulea for the quench cooler and counter current con counter current University of denser. The model shall be validated by compari condenser in a black Technology son to the DP1 reactor and then be used for liquor gasifier studies of scale-up effects.

3. Gas phase reactions, Prof. Anders Nordin Detailed studies of reaction kinetics for the in smelt formation and & prof. Bjorn organic reactions between smelt, water spray and green liquor quality in Warnqvist, Umea syngas. Determination of fundamental thermo pressurized black liquor University chemical data that are needed as input to gasification computer models. 4. The kinetics of the Ass. prof. Tobias Detailed studies of reaction kinetics for the gasifi gasification of black Richards, Chalmers cation reactions (drying, pyrolysis and char gasifi liquor cation). Theoretical and experimental studies of swelling of black liquor droplets during gasification. Determination of fundamental data and reduced models that can be implemented in computer models.

5. Borate Dr Ingrid Nohlgren, Evaluate possibilities for borate autocausticization autocausticizing and ETC during black liquor gasification conditions. Borates chemical recovery of follow the pulping liquor through the pulping cycle. sulphur-free pulping The objective is to eliminate the need for in processes creased causticization capacity, and thereby the demand for redesigning the existing lime kilns when introducing black liquor gasification in the pulping process.

19 Project name Project leader Description

6. Pulps produced with Dr Leelo Olm, STFI The increased control of process chemistry, which liquors from new is made possible by introduction of black liquor recovery systems gasification, opens the possibility to implement modified pulping processes. This project is focused on investigation of the yield increase with so called ZAP pulping when combined with black liquor gasification.

7. Kidneys in a kraft pulp Tekn. Lie. Niklas In the recovery boiler process there is a natural mill with a pressurized Berglin, STFI purging mechanism for non-process elements black through the electrostatic precipitator dust. No natural purging liquor gasification system mecha nism exists in the black liquor gasifier. Alternative methods for control of accumulation of non process elements will be studied in this project.

8. Material investigation Dr Lars Troselius In the recovery boiler, green liquor is produced in green liquor with a temperature that is controlled by the boiling point of the green liquor. In pressurized black liquor gasification the green liquor temperature will be increased with more than 100°C, which will severely increase the corrosion rate of the materi als in contact with green liquor. The knowledge of the impact on the materials is very limited since the process is new. In this project, materials suit able for contact with hot green liquor will be identi fied by experimental studies of stress corrosion.

As shown in the table, none of the projects have dealt with the system aspects discussed in Chapter 3.

20 6 Efficient Upgrading of Biofuel by Integrated Biorefinery Operations in Future Pulp Mills

People involved in the project Eva Andersson and Dr Simon Harvey Project financing Swedish Energy Agency

6.1 Introduction This work is conducted within the interdisciplinary graduate school Energy Sys tems. The national Energy Systems Programme aims at creating competence in solving complex energy problems by combining technical and social sciences. The research programme analyses processes for the conversion, transmission and utilisation of energy, combined in order to fulfil specific needs.

6.2 Aim The project aims at evaluating the benefits of biofuel upgrading integrated with a pulp mill. The evaluation includes net CO2 emissions and economics. Coherent energy reference systems, corresponding to different possible future energy market scenarios, are used to evaluate the resulting energy flows.

The first part of the project investigated possibilities to produce pellets by inte grating the biofuel drying process with the pulp mill process. The evaluation was made assuming integration with the Eco-Cyclic Pulp Mill (a reference mill assumed to incorporate the best available technology built and commercially used in the Swedish and Finnish pulp industry today). A systems analysis was performed to evaluate the net effect on CO2 emissions taking into account the changes in electricity production and biofuel use.

Secondly, hydrogen production from gasified black liquor was evaluated by comparing its net CO2 emissions with the net emissions associated with other possible future uses of black liquor, such as electric power production in a black liquor gasification combined cycle (BLGCC) powerhouse unit, or methanol production. Excess heat at different temperature levels from the hydrogen production process was matched with the demand in the pulp mill. Hydrogen production requires that electricity and biomass be imported to the mill. The systems evaluation considers different reference energy systems for electricity production, road transportation and biofuel use.

21 Ongoing work includes evaluation of hydrogen production from gasified bio mass integrated with a natural gas fired combined cycle CHP unit in the district heating sector, compared to production from gasified biomass in a stand-alone unit. Evaluation of the net CO2 emissions consequences if excess heat can be delivered to a district heating system and if CO2 is captured and stored is included. The project also includes an economic evaluation and consequences of different policy instruments.

A summary of the work from the following articles:

• Andersson, Eva; Harvey, Simon: System analysis of hydrogen production for gasified black liquor. Proceedings of the 17th International Conference onEfficiency, Cost, Optimization, Simulation and Environmental Impact of Energy and Process Systems, ECOS 2004, Guanajuato, Mexico July 7-9, 2004 • Andersson, Eva; Harvey, Simon: Pulp-mill integrated biorefineries: a framework for assessing net CO2 emission consequences. Proceedings, AIChE 2004 Fall Annual Meeting. Nov 7-12, 2004, Austin, Texas, USA • Andersson, Eva; Harvey, Simon: Comparison of pulp-mill integrated hydrogen production from gasified black liquor with stand-alone production from gasified biomass. Proceedings of ECOS 2005

Hydrogen production from gasified black liquor is evaluated in the papers above. Hydrogen production integrated with a market pulp mill is evaluated on the basis of energy use and CO2 emissions. Hydrogen production is compared with other options for black liquor use, such as recovery boiler, BLGCC and methanol pro duction; but also with hydrogen production from gasified biomass. Net changes in CO2 emissions are calculated using marginal technology for electricity produc tion, transportation service technology and alternative biofuel use in different futures with more or less ambitious targets for CO2 emissions.

6.3 Reference mill The market pulp mill used in the calculations is the KAM 2 model mill, Table 6.1. It produces 2000 ADt pulp per day. It is a model mill from a study “Eco Cyclic Pulp Mill” in 2001, based on best technology available in Swedish and Finish pulp industry. The recovery boiler at the reference mill produces more steam than the process requires and a condensing turbine produces extra power. The mill has a surplus of electricity and biofuel (bark).

The net heat demand in the KAM 2 mill is 10.4 GJ/ADt compared to the average Swedish pulp mill in 2000 15.4 GJ/ADt.

22 Table 6.1 Input data for the KAM2a Mill. Capacity ADt pulp/day 2000 Wood consumption tonnes/day (dry) 4148 Black liquor solids (BLS) per tonne of pulp tonnes/tonne 1.71 BLS available tonnes/day 3420 MW 487 Dry Solids content of BL % 80 Bark available (air dried) tonnes/day 362.5 a KAM2 refers to 2nd model developed in the KAM program

Table 6.2 Steam system at KAM mill.

Pressure Temperature Steam demand[t/hr] HP steam 141 bar 545 oC IP steam 30 bar MP steam 10.5 bar 135 tonnes/h LP steam 4.5 bar 220.5 tonnes/h

Black liquor gasification All the available black liquor in the KAM 2 mill is gasified in a Chemrec pressur ized gasifier. The process data for the gasification and syngas composition and is given by Berglin. The hydrogen production from syngas is modeled and mass and energy balances are calculated. Steam levels in the hydrogen production plant are chosen to facilitate integration with the pulp mill, Table 6.2. The steam demand of the pulp mill is not covered by excess heat from the hydrogen production unit and a biofuel boiler is used for heat production. The hydrogen production unit requires steam of higher pressure than produced as excess heat. The biofuel boiler also covers this.

Sulfur is recovered by re-absorption in white liquor. More steam is required in the limekiln with the gasification process so the bark consumption for this is increased.

Electricity is co-produced in the biofuel boiler, where steam can be produced at higher pressure and temperature than in the recovery boiler. But electricity still has to be purchased from the grid. Biofuel must be purchased to the biofuel boiler. Energy rich waste gas from the hydrogen production unit is also fired in the boiler.

Hydrogen production from gasified black liquor is compared with alternative use of black liquor, such as recovery boiler, black liquor gasification combined cycle and methanol production from gasified black liquor, Table 6.3.

23 Table 6.3 Results for pulp mill co-production systems: hydrogen production (H2) recovery boiler with condensing steam turbine unit (RB), Black liquor gasification with gas turbine combined cycle (BLGCC) and black liquor gasification with methanol production (MeOH).

RB BLGCC MeOH H2 Pulp Mill Pulp production ADt/day 2000 2000 2000 2000

Wood consumption dry, tonnes /day 4148 4148 4148 4148

Bark available tonnes DS/day 362.5 362.5 362.5 362.5

Black liquor available tonnes DS/day 3420 3420 3420 3420

BL energy content LHV MW 486.9 486.9 486.9 486.9

Steam Net production BL unit tonnes/h 476.3 404.3 199.3 123.6

Mill Consumption tonnes/h 353.5 356.2 355.5 355.5

Steam to turbine/deficit tonnes/h 122.8 48.1 -156.2 -231.9

Bark Bark to lime kilna tonnes DS/day 187.5 247.5 265 265

Bark to bark boiler tonnes DS/day 0 0 801 765

Bark available, net tonnes DS/day 175.0 115.0 -703.5 -667.1

Import/Export (-/+) MW 32.4 21.3 -130.3 -123.5

Power Produced MW 104.4 172.7 42.2 32.2

Consumed in BL unit MW 5 30.1 32.0 32.8

Consumed in Mill MW 54.3 56.1 56.1 56.1

Import/Export (-/+) MW 45.1 86.5 -45.9 -56.7

Fuel Fuel production t/day 1183 188.0

Fuel production (LHV) MW 0 0 271.1 261.0

Driving distance b Gm/year 4834 6934

Heat Excess heat MW 45.4 50.0 a H2S formation in the gasification process will increase the load in the limekiln. The increase depends on themethod for H2S recovery [16]. Here the re-absorption route is chosen. b Updated numbers for energy output from FCV and distribution losses. Hydrogen 0.84 MJ/km and methanol1.48 MJ/km. Distribution losses: hydrogen 18 % and methanol 3 %.

Generation of excess heat for district heating is calculated for the BLGCC case and the hydrogen production case.

6.4 Environmental evaluation The environmental evaluation of the alternative uses of black liquor is only car ried out for CO2 emissions. The evaluation includes changes in the surrounding energy system affected by changes in energy balance of the hydrogen production and the pulp mill.

The evaluation is based on the following assumptions: • Biofuel is a limited resource. Excess biofuel will be used in another application. • The grid electricity demand is assumed to be constant. Increased demand at the mill will increase production of the same amount. • Hydrogen is used in fuel cell vehicles. • Heat will replace biofuel. Biofuel will be used in other application.

24 Choice of technology for electricity generation, biofuel use and technology for replaced transportation is based on assumptions of future development of these technologies. The scenarios develop in different ways influenced by more or less ambitious targets for green house gas emission reductions, Table 6.4. Results from paper “Pulp-mill integrated biorefineries: a framework for assessing net CO2 emission consequences ” is presented in Figure 6.1

Net CO, em issions reduction

900 800 □ RB ■ BLGCC □ MeOH ■ H2 l. 700 ■I,600 0 500 % 400 I 1 300 2 200 100 0 ll ll .1 .1 I Near future Business as usual III Moderate change IVa Sustainable A IVb Sustainable B

Figure 6.1 Reduction of C02 [ktonnes/year] for the different biorefinery concepts, assuming the five different reference energy systems described in Table 6.4

Table 6.4 Example of scenarios used forC0 2 evaluation

I II III IVa IVb CO2 emissions -5 -5 -25 -50 -50 reduction target[%l Electric power Coal Advanced NGCC Adv. coal Adv. coal production 1 coal with C02— with C02— (g C02 /MJ) (224) (209) (102) sep sep (32) (32) Transportation^ Gasoline in Gasoline in a Gasoline in a NG- NG- [16] today’s cars hybrid hybrid hydrogen in hydrogen in (g C02/km) (196) vehicle vehicle fuel cell fuel cell (140) (140) vehicles vehicles (83) (83) Biomass use' Oil Oil Co-firing in BIGCC Transportatio substitution substitution coal power n fuel (g C02 /MJ plant biomass) (68) (68) (91) (12) (44)

6.5 Economic evaluation Economic evaluation of hydrogen production will be performed with different scenarios for future energy market prices. The investment cost used for the hydrogen production unit is the incremental cost for investing in this instead of a new Tomlinson boiler.

25 26 7 Black Liquor Gasification - an Assessmentfrom the perspective of the Pulp and Paper Industry

In this licentiate thesis by Gunnar Modig, LTH (2002) the main aim was to gain insight into the development and diffusion of gasification technology and assess the prospects for introducing BLG in the pulp and paper industry. Among other things quantitative an qualitative data are combined to explore the future of BLG given the present circumstances concerning energy policy, technical maturity and economic drivers for changing energy recovery technology in a complex and heavy industry - pulp and paper. This thesis is therefore investigating the compe tition between the future technological alternatives for black liquor - existing but refined recovery boiler combustion technique or gasification with possible some new end products like motor fuels.

In addition to giving a good background and history of BLG, Gunnar Modig discusses in the thesis opportunities technically and economically for BLG as well as obstacles, reasons for slow (or non-existing) implementation, reliability and availability for gasification, environmental aspects, competition situations in Sweden and the overall situation for pulp and paper industry. For this report the techno-economic discussions and comparisons as well as the environmental aspects and competition between production of electricity and motor fuels are of special interest. A big part of the comparisons in the thesis is between BLG and RB (recovery boiler) for maximal electricity production

One important factor in such a comparison is the differences in efficiencies, both ntot and pel (and of course nheat which is equal to %ot - Pel). The author has com piled many data from different sources, both for BLG(HT) and BLG(LT). HT and LT mean high temperature and low-temperature gasification respectively (see Gunnar Modig's licentiate thesis). The results, given as A%ot (BLG - RB), are shown in Figures 7.1 and 7.2.

27 Difference in Total Efficiency between RB and BLG(HT) at Various Process Heat Demand and Steam Pressure Level

Aritot 60 bar

Q 100 bar

GJ/ADt

Figure 7.1: The dotted line indicates how the difference in total efficiency varies with process heat demand.

This graph shows that the difference in calculated total thermal efficiency is small between the HT and RB processes if the pulp mill consumes steam corresponding to 13-17 GJ/ADt. Then the HT total efficiency is only about 0-4 % higher than RB. If at low heat demand (10-12 Gj/ADt) a condensing turbine is also installed with the RB for using the surplus steam, efficiency difference will rise to 5-10 % in about absolute terms.

The explanation is that the latent heat in the low pressure steam from the condens ing turbine outlet is wasted to the cooling water in the condenser. The LT process will not show a similar surplus of steam as the alpha value is higher meaning less total steam available, but more power.

A similar graph is obtained when RB and LT efficiencies are compared concer ning the total energy efficiency:

28 Difference in Total Efficiency between RB and BLG(LT) at Various Process Heat Demand and Steam Pressure Level

Aritot b k. 60 bar

Q 100 bar

GJ/ADt

Figure 7.2: The corresponding relationship for the LT process. No significant difference in this respect between the two BLG processes.

From Figures 7.1 and 7.2 it is possible to draw the conclusion that the difference in total efficiency is marginal (0-4 %) in the heat demand range of 13-17 GJ/ADt where almost all kraft pulp mills in Sweden and other countries are operating today [43].

It is therefore evident that the potential improvement in total efficiency for gasifi cation technology compared to RB is highly dependent on the specific heat de mand of the pulp process. Only at very low specific heat demands, 10-12 GJ/ADt, can a significant difference regarding the benefit of HT/LT gasification alterna tives be observed.

Investment costs from two studies, (Eric Larson and KAM, also included in this report) were compared and the author found that they gave costs in relatively good agreement with each other. In both cases the additional cost, compared with a new RB, for 2000 ADt/d pulp mill was around 600 MSEK, with an uncertainty interval of ± 30 %

The author finds that a Swedish average mill with the size 2000 ADt/d would produce 35 MW more electricity with BLG(HT) compared with RB and would need 40 MW extra biomass fuel for the energy balance. Two levels of elec tricity price, 500 SEK/MWh and 350 SEK/MWh and one for biomass fuel, 120 SEK/MWh were used. This gives a price ratio of 4.17 and 2.92, respectively.

29 In Figure 7.3, the economic revenues of extra electricity production compared with annual capital charge at two different annuity factors, 0.20 and 0.25, is shown. The figure shows that with the assumed data, BLG (HT) cannot compete with RB economically.

Economic Result from a Simulation of a 2000 ADt/d Pulp Mill when Comparing HT with RB

MSEK/year

180 Annual capital 160 charge at a = 0.25 140

120 a = 0.20

100 A

60 A ^ Ratio Pe|IPfc>io 2.92 4.17

Figure 7.3: Graphical illustration of how the revenues from extra power match capital cost of the higher investment needed for building a HT unit.

The author argues that the necessary biomass fuel amount cannot be reduced significantly in existing mills but, based on KAM results, be eliminated in future, greenfield plants. In that case the economy for a BLG(HT) would be improved, see Figure 7.4.

30 Economic Result from a Simulation of a 2000 ADt/d pulp Mill when Comparing HT with RB No Extra Biomass Needed

MSEK/year

180 Annual capital 160 Charge at a = 0.25 140 A

120 a = 0.20

100 A

60 ^ Ratio Pei/Pbio 2.92 4.17

Figure 7.4: The graph shows a higher net revenue when no extra biomass is needed for HT operation. The capital charge levels are, however, still not reached in this example.

In the figure it can be seen that in this case it would be possible to achieve reasonable economy for BLG (HT), if the annuity factor is clearly below 0.25.

One important aspect, discussed by the author, is the differences in reliability and availability between a BLG and an RB. A comparison between availability for RB:s and for gasification plants (not black liquor gasification) showed that RB:s have typically an availability of 97-98 % whereas modern gasification plants have 85-90 %, which is a significant difference. For gas turbines the corresponding figure is 86-87 %.

In the environmental discussions consequences for SOx, NOx and HCL are included but not for global CO2 emissions.

Motor fuels are discussed more in general terms. Based on assumptions already discussed above for electricity production, the author can show that motor fuels (methanol, DME) can be produced for 7 SEK per liter gasoline equivalent, to be compared with 11 SEK/liter for gasoline (assuming no tax on the biomass motor fuel).

31 The author concludes that there are several important benefits with BLG, such as: • Simplifying capture and sequestration of CO2 from fossil feedstocks • Lower emissions (mainly from coal) thanks to advanced gas cleanup before combustion • Possible use of chemical synthesis routes for producing motor fuels or other chemicals • Conversion of low value residual products (asphalt, petcoke, municipal waste) into useful and profitable energy products (electricity, hydrogen, steam etc.) but also major problems, such as: • High investment cost • Poor operational reliability • No technical guarantees can be given yet by technology suppliers - risk are considered too high by investors

32 8 Black Liquor Gasification with Motor Fuel Production - BLGMFII

By Tomas Ekbom, Niklas Berglin, Sara Logdberg (2005)

The project focuses on the technical and economic feasibility with material and energy balances to produce synthetic Fischer-Tropsch diesel (FTD) as transport fuel based on black liquor gasification. In a previous project from 2003 the same type of study was performed for the production of methanol (MeOH) and dim ethyl ether (DME). In this project an update of the economical results from that study is included for a base comparison.

The results show that alternative fuels produced in conjunction with the produc tion of pulp and paper may with small fiscal and other incentives may be com petitive even with fossil automotive fuels as traded on a free open market.

Using black liquor as a raw material for synthetic fuel production would have the following advantages: • Biomass logistics are extremely simplified as the raw material for fuel making is handled within the ordinary operation of the pulp and paper plant. • The process is easily pressurised, which enhances fuel production efficiency. • The produced syngas has a low methane content, which optimises fuel yield. • Pulp mill economics becomes less sensitive to pulp prices as the economics are diversified with another product. • Gasification capital cost is shared between recovery of chemicals, steam production and syngas production.

Based on the ecocyclic pulp mill reference (KAM2 model mill), where all energy and by-products are recovered with today ’s most efficient technology, a BLGMF concept was designed and calculated. The results are thus based on a comparison with a reference mill with a capacity of 2000 ADt/day of pulp and with a modern recovery boiler (RB) producing electricity for export.

The principle of BLGMF plant are shown in Figure 8.1.

33 Wood for pulping Falling bark

Biomass Steam Biomass CHP Pulping Steam operation Power Purge gas

Only in Power from external biomass power plant Black liquor BLGMF Syngas derived Green liquor plant motor fuels

Figure 8.1 Basic flow sheet fora pulp mill with a BLGMF plant

The gasification process considered in this project is the CHEMREC® high tem perature gasification process, which is based on entrained-flow gasification of the black liquor at temperatures above the melting point of the inorganic chemicals. The syngas from the gasification process is then compressed and converted into synthetic fuels in a synthesis reactor. The raw fuel products MeOH/DME are further distilled and for FTD further upgraded and a clean product is obtained. When FTD is synthesised, naphtha is also produced as a by-product.

In all cases the BLGMF plant has an excess of steam. Steam is mainly produced when the syngas from the gasifier is cooled and at the exothermic fuel synthesis. The steam production from the FTD synthesis is more than three times bigger than from the MeOH/DME synthesis. This, together with the fact that FTD pro duction doesn ’t include a distillation step, is the main reason why the excess of steam is bigger in the FTD case (see 8.1). The excess steam from the BLGMF plant is used in the mill. The remaining steam demand of the mill is covered by firing falling bark, imported biomass and purge gas from the BLGMF plant in a biomass boiler.

The biomass boiler also produces electricity, which in the MeOH and DME cases, actually covers the fuel production unit ’s electricity need almost exactly. In the FTD case, however, additional electricity must be purchased to balance the need of the fuel production unit. In all three cases, external electricity must be pur chased to cover the electricity need of the pulp mill. The external electricity is produced in a biomass fired power boiler with an assumed electrical efficiency of 40 %. In order to calculate the biomass to fuel efficiency for the BLGMF cases they must produce the same amount of electricity as the reference case. Therefore, the same amount of electricity that is exported from the mill in the reference case is now produced in the external power boiler. In Table 8.1 the mass and energy balances for the different BLGMF cases is shown.

34 Table 8.1 Mass and energy balances for the BLGMF cases in a market pulp mill. Ref BLGMF BLGMF BLGMF RB MeOH DME FTD Steam Net steam produced in [t/h] RB-system/BLGMF 476,3 182,8 171,8 306,5 plant 1 Steam consumed in mill [t/h] -353,5 -355,5 -355,5 -355,5 Excess steam [t/h] 122,8 -172,7 -183,7 -49,0 Steam produced in [t/h] - 172,7 183,7 49,0 biomass boiler Power Net power generated [MW] 99,4 0,0 0,7 -27,0 Power consumed in mill [MW] -54,3 -56,1 -56,1 -56,1 Excess power [MW] 45,1 -56,1 -55,4 -83,1 Incremental power [MW] base -101,2 -100,6 -128,2 generated Biomass Biomass used for [MW] base 253,0 251,4 320,4 incremental power Biomass production [MW] 67,0 67,0 67,0 67,0 (falling bark) Biomass consumed in [MW] -34,7 -49,1 -49,1 -48,8 lime kiln Biomass consumed in [MW] - -146,6 -142,4 -43,8 biomass boiler Sold/purchased [MW] 32,3 -128,7 -124,5 -25,6 biomass Incremental biomass [MW] base 161,0 156,8 57,9 used in mill Total incremental [MW] base 414 408 378 biomass consumed Product MeOH/DME/FTD [MW] - 272 275 2442 Fuel production, total [kt/year] " 411 286 166 System efficiency (LHV) Biomass to fuel [%] - 66 67 65

Accordingly, the total incremental biomass consumed is the sum of the biomass used in the external power boiler to produce the deficit of electricity for the whole plant and the amount of electricity exported in the reference case plus the differ ence in consumed biomass at the plant between the BLGMF cases and the ref erence case.

All configurations are based and calculated on the same black liquor capacity (487 MW). The resulting biomass-to-fuel energy efficiency when only biomass is used as an external energy source was 43 % for FTD, or 65 % for FT products, compared with 66 % for methanol and 67 % for DME. The FTD calculation is considerably more complicated and based on assumptions rather than the vendor ’s calculations used for methanol and DME cases. Therefore, the uncertainty is significantly higher for the FTD case.

1 Includes the steam produced in the biomass boiler with purge gas from the BLGMF plant. 2 The sum of the produced FTD (162 MW) and naphtha (82 MW).

35 The plant economics are based on an additional investment cost with incremental production costs. This is the normal procedure, as in this case the host (the pulp mill owner) can choose between investing in the same technology - a new recov ery boiler - or in a new technology, a gasification plant (BLGMF). Thus, the investment decision would normally be based on a comparison between the two alternatives: a) reference mill with a recovery boiler and b) same type of mill with a BLGMF plant. It should therefore be noted that the results in this report are based on a comparison and that additional investment and production costs are calculated.

In order to estimate the potential revenues a selling price of the fuels at the mill gate was calculated by assuming that the cost for the consumer should be the same as for petrol (MeOH) and diesel (DME, FTD). A cash flow Internal Rate of Return (IRR) analysis was carried out for the cases, considering the additional investment and operating costs for the BLGMF system relative to a new recovery boiler investment. The results are shown in Table 8.2.

Table 8.2 Results on return on investment, where the FTD and naphtha are added. BLGMF BLGMF BLGMF BLGMF MeOH DME FT-diesel FT-naphtha Additional investment cost3 [MEUR] 174 190 205 Total incremental operating [MEUR/year] 66,3 66,1 68,2 cost Production volume4 [m3 /year] 260600 238900 145350 81700 Production cost5 [E UR/I iter] 0,26 0,27 0,32 0,29 Selling price [EUR/liter] 0,51 0,62 0,68 0,39 Margin [EUR/liter] 0,25 0,35 0,36 0,10 Margin [MEUR/year] 66,5 82,3 52,3 8,2 Payback time [years] 2,6 2,9 3,4 IRR [%] 40 45 30

In conclusion, there are necessary recourses and potential for large-scale methanol (or DME, FTD) production and substantial economic incentive for making plant investments and achieving competitive product revenues.

3 The total investment for the recovery boiler was 171 MEUR. 4 Pctrol/dicscl equivalent m3 where methanol and naphtha are petrol fuels and the other diesel fuels. 5 The annuity factor is 11,1 %

36 9 System Aspects of Black Liquor Gasification - Consequences for both Industry and Society

This licentiate thesis by Hakan Eriksson, Heat and Power Technology, Chalmers (2001) deals with different ways of using a limited future resource of biomass fuel in Sweden. The main goal of the theses was to identify how available black liquor and other biomass should be used which a mill and/or in e.g. district heating CHP plants configurations in order to maximize the electricity production from this given amount of biomass. Some general assumptions are:

• Availability of biofuel at a reasonable price is assumed to be limited, therefore increased import/export to/from the mill is assumed to correspond to de creased/increased usage elsewhere; • Biofuel usage elsewhere is assumed to follow the same target as biofuel usage at the mill site, namely high electricity production with high total efficiency; • Biofuel is particularly attractive for low temperature heat load applications (e.g. district heating), because it is a wet fuel and high total efficiency values can be achieved if a flue gas condenser unit is used. A district heating system (including CHP units) is therefore retained as the reference alternative biofuel user for this study; • The reference alternative biofuel user is assumed to also have access to natural gas fuel; • The mills are assumed to be equipped to handle large quantities of biomass. It is therefore assumed that they will cover their energy demands exclusively with biofuel; • Since the focus of the study is on high performance electricity production, it is important to make assumptions regarding the most likely technology for new grid electric power generation capacity additions. Given that BLG technology is only likely to be commercially mature within 10 to 15 years, high perform ance natural gas fired combined cycle technology (60 % electric efficiency) is retained as the reference technology for added grid capacity.

Finally, it should be noted that this study focuses on biomass energy conversion potential, thus investment costs and other economic aspects are not explicitly taken into account. However, given the assumptions listed above, biofuel usage is primarily focused on CHP, either at the mill site, or in the reference external en ergy system. Given that the investment and running costs for biofuel CHP are to a certain extent comparable for the different technologies and configurations con sidered, not directly considering economic aspects should therefore not severely bias the results in favour of certain configurations in relation to others.

37 It is also assumed that Biofuels are available at the mill in the form of bark and black liquor fuels. Excess biofuel can be exported from the mill to the district heating system in the form of bark or lignin. Biofuel can also be imported to the mill but this will result in a corresponding decrease in biofuel usage in the district heating system.

Natural gas is currently only available on the West coast of Sweden. In this study it is assumed that the natural gas grid is extended and is thus an available fuel option for most district heating systems. As discussed previously, it is assumed that natural gas is not an available option for most pulp mill locations. Natural gas can also be used for electric power generation in high efficiency combined cycle (NGCC) condensing power plants.

Heat Heat Electricity (fixed) Electricity Electricity

H°mill+AHmill E°mill+AEmill DH E dh +AEdh E NGCC +AEngcc

Biofuel Natural gas Internal (fixed) (fixed) Biomass (fixed) Figure 9.1 Overview of fuel and energy flows for the mill and reference energy systems.

The fuel and energy flows for the mill and reference energy systems considered in this study are shown in 9.1. The different flows and related assumptions are dis cussed below:

38 • B0miii is the fixed amount of internal biomass at the mill site in the form of black liquor and falling bark; • B0biomass is the fixed biofuel resource that is available primarily as fuel for the district heating network; • ABexport is the amount of biofuel that is exported from the mill-site. If it is negative, it means that biofuel is imported to the mill; • B0biomass+ABexport is the total flow of biofuel to the district heating system. For the case where biofuel is imported to the mill (ABexport <0), the amount of bio fuel available for the district heating system is therefore decreased compared to B0 biomass ;

• F0ng is the fixed amount of natural gas that can be used in the district heating system for CHP or in the NGCC power plant for electricity production; • H0mill+AHmill is the mill heat consumption that is fixed for each of the three mill types, as defined in Section 5.4. To account for the different heat demand in three mill types, the heat demand has been divided into two parts, one fixed reference level (H0mm) and one part that varies with mill type (AH^m); • E0mill+AEmill is the net electricity production at the mill powerhouse (i.e. the powerhouse internal electricity consumption is deducted). To show the differ ent electricity productions in the different mill powerhouse configurations, the mill electricity production has been divided into two parts, one fixed reference level (E0min) and one part that varies with powerhouse configuration (AEmm);

• H0dh is the fixed heat demand in the district heating system;

• E0dH+AEdH is the electricity production from the district heating system CHP plant. E0dH is the reference level of electricity production when no biofuel is exported from the mill to the district heating system and AEdH accounts for the change in electricity production that relates to the exported biofuel from the mill site. When fuel is imported to the mill, the electricity production in the district heating system is reduced, and AEdH is negative;

• E0ngcc +AEngcc is the electricity production from the NGCC power plant.

E0ngcc is the reference level of electricity production when no biofuel is exported from the mill and AENGCC accounts for the change in electricity production in the NGCC power plant that relates to the exported biofuel from the mill site.

Since the goal is to maximise the total electricity production from the system shown in Figure 9.1 with a fixed amount of fuel (i.e. B0mm+ B0biomass+ F0ng ), the goal function for this function is defined as:

Goal function = E°mm+AEmm+ E°dh +AEdh +E°ngcc +AEngcc

For the use of biomass in district heating CHP plants, the following two situations were considered: • ?7el,marginal=49 %; corresponds to a situation in which CHP is fully built out in the alternative energy system’s district heating plant, using natural gas fired

39 CHP technology. Biofuel exported to the district heating system is used to increase the share of biomass based CHP, thereby decreasing the share of natural gas based CHP. The natural gas no longer required for CHP is used to increase electricity production in the NGCC power plant. • ?7el,marginal =105 %; corresponds to a district heating system in which CHP has not been implemented to full capacity, i.e. a fraction of the heat load that could potentially be used for CHP is covered by a heat-only biofuel boiler. Export biofuel is used to increase the degree of biomass CHP in the district heating network.

The results for total electricity production potential for BLG in Sweden are shown in Table 9.1:

Table 9.1 Total electricity production potential (TWh/year) in Sweden, based on limited biofuel resource shared between mills and district heating systems.

Average 2000 mill Average 2000 mill

(nel,marginal-49%) (nel,marginal 105%) market integ market integ

Heat demand GJ/Adt 15.20 18.82 15.20 18.82 Fuel import, mill GJ/Adt 1.76 7.02 1.76 7.02 Electricity production, mill kWh/Adt 538 371 538 371 Electricity production, mill TWh/year 1.91 1.35 1.91 1.35 Electricity production, change outside mill TWh/year -0.85 -3.49 -1.82 -7.48 Electricity production TWh/year 1.06 -2.14 0.09 -6.13 Total electricity production TWh/year -1.07 -6.04

BLG CC BP BLG CC BP BLG NO-GT BLG NO-GT

(n el,marginal=49%) (nel,marginal=105%) (nel,marginal=49%) (nel,marginal 105%) market integ market integ market integ market integ

Heat demand GJ/Adt 8.00 15.80 8.00 15.80 8.00 15.80 8.00 15.80 Fuel import, mill GJ/Adt -11.60 7.20 -11.60 4.02 -15.40 -7.60 -15.40 -7.60 Electricity production, mill kWh/Adt 396 2302 396 1833 -334 -331 -334 -331 Electricity production, mill TWh/year 1.41 8.41 1.41 6.70 -1.19 -1.21 -1.19 -1.21 Electricity production, change outside mill TWh/year 5.62 -3.58 12.03 -4.28 7.46 3.78 15.98 8.10 Electricity production TWh/year 7.02 4.83 13.44 2.41 6.27 2.57 14.79 6.89 Total electricity production TWh/year 11.86 15.86 8.84 21.68

The following abbreviations are used: BP = backpressure, i.e. no condensing power part NOGT = no gas turbine, only BLG plant

Statistics from a Swedish mill survey for the year 2000 were used to estimate the size, heat demand, electricity production and fuel import for the average Swedish bleached market pulp mill and for the average integrated fine paper mill. The total electric power output for the powerhouse configurations considered is then esti mated assuming that the pulp production and paper production (given in ADt pulp) corresponds to the total production in Sweden for the year 2000. The elec tricity production, heat consumption and biofuel import vary according to the powerhouse configuration selected. It is important to restate that for this assess ment, it is assumed that all market pulp mills and all integrated pulp and paper mills in Sweden adopt the same powerhouse technology.

40 The different cases considered are as follows:

1 Average 2000 mill (n„r maroi„ai=49 %): the results presented are based on pub lished energy statistics for an average bleached kraft pulp mill and an average integrated fine paper mill, based on operating data for Swedish mills in the year 2000. Conventional recovery boilers and bark boilers are used for steam and electricity production and all fuel including imported fuel is used for heat and power production at the mill site, including possible electric power gen eration in condensing steam turbine units. The available statistics concern on site electric power production. This data was then adapted to account for limited availability of biofuel and the corresponding change in off-site elec tricity production based on a marginal electric power generation efficiency for alternative biofuel usage of 49 %; 2 Average 2000 mill (n,,i mar.,nai=105 %): as in case (1) but with a marginal electric power generation efficiency for alternative biofuel usage of 105 %; 3 BLG CC BP (n,,i mar.,nai=49 %): the process heat and power requirements are selected equal to the values for the process integrated pulp mill and the inte grated pulp and paper mill. On-site power generation is accomplished in a CHP plant that is assumed sized according to the mill heat demand. This implies that the market pulp mills will export excess biofuel and the integrated pulp and paper mill will import biofuel. The change in off-site electricity pro duction due to biofuel import/export to/from mills are accounted for with a marginal electric power generation efficiency of 49 %. The mill powerhouse configuration was selected so as to maximise the total electricity production given the marginal electrical efficiency for alternative biofuel usage. The selected configurations were the BLG CC LE configuration for the market pulp mill and the BLG/BIG CC B configuration for the integrated pulp and paper mill. 4 BLG CC BP (nei mar.,nai=105 %): as in case (3), but with a marginal electric power generation efficiency of 105 %. The selected mill powerhouse con figuration was the BLG CC LE configuration for the market pulp mill and the BLG CC L configuration for the integrated pulp and paper mill. 5 BLG NO-GT (in mar.,nai=49 %): as in case (3), but fuel usage at the mills is restricted to the amounts necessary to satisfy the heat demand only (i.e. the NO-GT configurations). All excess fuel is exported and used for additional off-site electric power generation with a marginal efficiency of 49 %. 6 BLG NO-GT (m marg,w=105 %): as in case (5), but with a marginal efficiency of 105 %. The 2000 average market pulp mill imported 1.76 GJ/ADt of fuel (assumed to be biofuel only in this study) and produced 538 kWh/ADt of electricity. The com bined electricity production from all market pulp mills can then be extrapolated to 1.91 TWh/year based on the total production of pulp. Similarly, for the integrated pulp and fine paper mill, the electricity production is 371 kWh/ADt pulp and the consumption of imported fuel is 7.02 GJ/ADt. The annual electricity production at the integrated pulp and fine paper mills can thus be estimated at 1.35 TWh. With a

41 marginal electrical efficiency of 49 % for the imported fuel, the decrease due to the import of fuel to the market pulp mills is 0.85 TWh. Similarly, the decrease can be estimated at 3.49 TWh/year for the integrated pulp and paper mills. This results in a total electricity production of -1.07 TWh for a marginal electrical efficiency of 49 %. If the marginal electrical efficiency is 105 %, the total elec tricity production will drop to -6.04 TWh, because of the large fuel import and small electricity production at the mill. These figures should be compared to statistics from the industry showing a total electricity production of 3.2 TWh, not taking into account the decrease in electricity production outside the mill, related to the import of biofuel.

For the BLG CC BP cases, the CHP plant is assumed to be exactly sized to cover the mill’s steam demand. This means that the market pulp mill has excess biofuel available for export whilst the integrated pulp and paper mills must import fuel. Depending on the marginal efficiency for alternative biofuel usage, different powerhouse configurations are used in the mills for maximising the total elec tricity production. For the 49 % marginal efficiency the total electricity production amounts to 11.9 TWh and for a marginal electrical efficiency of the 105 %, the production is 15.9 TWh.

If no electricity is produced at the mill sites, as in the BLG NO-GT cases, large amounts of biofuel can be exported from both types of mill. If this biofuel can be put to alternative use for increasing production of electricity in CHP plants in district heating networks, a marginal electric power generation efficiency for the exported biofuel as high as 105 % can be achieved. In this case, the total electric ity production related to implementation of black liquor gasification and large scale export of lignin extracted from the black liquor fuel to district heating for CHP power generation can be as high as 21.68 TWh/year. This potential drops to 8.84 TWh/year if the marginal electrical efficiency for alternative biofuel usage is 49 %.

Finally, it should be again noted that when large amounts of biofuel are exported from the mill, the total electricity generation potential is very sensitive to the assumed marginal efficiency for electric power generation from the exported fuel. For the BLG NO-GT cases the total electricity potential can vary from 21.65 TWh/year for %margmai=105 % to 8.84 TWh/year for %marg,nai=49 %, i.e. a difference of 12.8 TWh per year! The difference between potential for total electricity production with %marginai=49 % and %marg,nai=105 % decreases if more electricity is produced at the mill site (BLG CC BP cases) and less fuel is transferred between the mills and alternative fuel users.

42 The results of the studies can be summarized as follows:

• Black liquor gasification technology performs better than conventional and ad vanced recovery boiler technology in all cases considered; • For both market pulp mills and integrated pulp and paper mills, excess biomass fuel export is the best way to achieve high total electricity production if the marginal electricity generation efficiency for the exported fuel is higher than that for on site usage (~50 % for condensing power generation). This is the case if biofuel exported from the mill can be used to increase the degree of CHP in a district heating system. Biofuel usage at the mill site should then be restricted to the amount necessary to satisfy the mill’s heat load, i.e. CHP should be avoided. For the process integrated market pulp mill for example, 178.4 MW of biofuel can be exported and used to cogenerate 173 MWe off-site in district heating CHP plant, assuming a marginal electrical efficiency value of 105 % for biofuel usage in the district heating plant. If all fuel is instead used on-site (which would include condensing power generation) at most 80 MWe can be produced with the BLG CC technology. • For market pulp mills, all internal mill biofuel should be used to fuel a black liquor gasification combined cycle if the marginal electricity generation efficiency for exported biofuel is lower than that for on-site usage (~50 %). This is the case for example if CHP is fully built out in the reference district heating system, based on natural gas fuel. Exported biofuel can be used to partly replace natural gas fired CHP with biofuel CHP, and the natural gas no longer needed for CHP in the district heating plant can be used for electric power generation in a natural gas combined cycle condensing power plant instead. • For the integrated pulp and paper mills, fuel can be imported to the mill for use in a black liquor gasification CHP powerhouse configuration, provided that the incremental marginal electric power generation efficiency for each additional unit of imported fuel is higher than that achieved by the alternative energy system. Since the marginal electrical efficiency is between 60-70 % for the black liquor gasification based CHP powerhouses compared to heat-only powerhouse configurations, biofuel should be imported if %marginai=49 % for the alternative energy system (the highest total electricity production that can be achieved is in this case equal to 55 MWe for the BLG/BIG CC B case).

These conclusions are clearly only valid for the conditions assumed in this study. The district heating system chosen in this study for alternative usage of biofuel was chosen as relevant for a future situation in Sweden, but in other countries with other resources and different energy policies, a totally different alternative biofuel user may well be more relevant. It is important to point out for example that the results of this study are in part due to the assumption that an alternative use for biomass is combustion in a district heating system with a very high efficiency (due mainly to flue gas condensation that is possible given the low temperature level of the district heating heat demand).

43 The results of this study can be used to estimate the potential for maximal increase in total electricity production in Sweden assuming the following:

• All market kraft pulp mills reduce their heat demand to the levels corresponding to the process integrated KAM pulp mill; • Similarly, all kraft pulp based integrated pulp and paper mills reduce their heat demand to the level considered in this study; • Black liquor gasification replaces recovery boiler technology in all mills; • The total pulp production and paper production remain equal to their current values; • Biofuel is used where it is most effective. In this study the most effective alternative usage considered is CHP power generation in a district heating system; • Excess biofuel can be exported from the mills and used elsewhere.

Under these conditions, the potential for total electricity production in Sweden related to implementation of black liquor gasification was estimated to be 21 TWh/year.

Finally, it is important to note that this study was restricted to energy aspects of fuel usage. In practise, economic aspects will play an important role in determin ing the choice of technology configuration.

44 10 A Cost-Benefit Assessment of Bio mass Gasification Power Genera tion in the Pulp and Paper Industry

Eric D. Larson, Stefano Consonni, Ryan E. Katofsky Final report 8 Oct 2003 Principal author Erik Larson, Princeton university, US

The study examines the prospective technical and financial feasibility of black liquor gasification based systems at kraft pulp mills. The Tomlinson recovery boiler will be fully replaced by the black liquor gasification system. It includes mill level cost - benefit assessments and assessment of potential regional and national energy and environmental impacts of the implementation of black liquor gasification technology under different future market penetration scenarios.

10.1 Reference mill The study compares the replacement of an old recovery system at a reference mill with either a Tomlinson recovery boiler or a black liquor gasification recovery system. The reference mill has the process characteristics representative of ex pected typical mills in the Southeastern US in the 2010 time frame. It is an inte grated pulp and paper mill producing 1725 machine-dry metric tons/day uncoated freesheet paper from a 65/35 mix of hardwood and softwood. To include future improvements in energy efficiency of the pulp mill, the steam demand is assumed to be 10 % less then “best practice ” today.

Two different Tomlinson boilers are modeled: BASE -expected state of the art, business as usual HERB - high efficiency recovery boiler, marginal improvements such as higher pressure and temperature in recovery boiler, higher black liquor dry solids concentration

Reference case study mill parameter assumptions are given in Table 10.1.

45 Table 10.1 Reference case study mill parameters for Tomlinson boilers with two perform ances and for gasification plants.

Power/recovery system Tomlinson Gasification BASE HERB Pulping chemistry Conventional Polysulfide Machine-dry metric Product flow tones/day 1725 Wood to process Bone dry short 3434 3208 Hog fuel tons/d 340 317 BL flow rate Tonnes BLS/hr 113.4 102.4 Black liguor solids cone. % solids 80 85 80 Mill steam use, 3.8 bar MWth 142.8 141.8 135.3 Mill steam use, 12.1 bar MWth 69.3 71.5 64.8 Total process steam MWth 212.1 213.3 200.2 Mill electricity use kWh/mt paper 1,407 1,406 1,407

The paper production in the reference mill is the same in all cases. Polysulfide is formed in the gasification plants and is used in a new pulping chemistry, poly sulfide pulping, which gives a higher digester yield. This means that less wood is needed for the same paper production. Less hog fuel will also be available.

10.2 Black liquor gasification plants Three different BLGCC plants at a comparably level of technological maturity as the Tomlinson systems are included in the study. It assumes that the all research and development needs are met and that a reliable Black liquor gasification com bined cycle can replace the Tomlinson technology.

The gas turbines selected are commercially available, which means that the size is fixed. The first two BLGCC plants have a “mill scale” gas turbine that match the syngas flow available from the gasification plant. One plant is a low-temperature gasifier and the other is a high-temperature gasifier. The third plant is a high tem perature gasifier with a larger, “utility scale”, gas turbine. It will generate more electricity and steam than the “mill scale” plants. The fuel is a mix of syngas from the gasifier and natural gas. The “utility scale” plant includes a condensing turbine since the steam production exceeds the internal demand.

10.3 Steam conditions The steam data, Table 10.2, for the HERB Tomlinson boiler is higher than in the BASE case. For the BLGCC plants it is possible to have an even higher steam pressure and temperatures since the combustion products are cleaner.

46 Table 10.2 Steam data for the Tomlinson boilers and gasification plants

Tomlinson Gasification High-T Base HERB Low-T High-T utility scale HP steam pressure [bar] 87.2 104.5 130.0 130.0 130.0 HP steam temperature [°C] 480 520 540 540 565 MP steam pressure [bar] 13.1 Bark boiler (hog fuel) , pressure 87.2 87.2 87.2 87.2 87.2 [bar] temperature [°C] 480 480 480 480 480 Bark input [MWth] 71.2 71.2 100 100 66.6

10.4 Energy balances The mass and energy balances and overall performance of each configuration were predicted by a computer code called GS (Gas-Steam cycles) developed at Politecnico di Milano and Princeton University.

Details of the energy balance are given in Table 10.3. Due to the higher digester yield with polysulfide pulping, less black liquor must be processed and the mill steam is decreased in the BLGCC plants compared to the Tomlinson case. There is also less hog fuel available for steam generation.

Table 10.3 Energy balances for the two Tomlinson boilers and the three gasification configu rations.

Tomlinson BLGCC [MW] HHV BASE HERB Low-temp High-temp High-temp gasifier gasifier gasifier Mill-scale Mill-scale Utility-scale GT GT GT Mill by-product fuels 508.8 508.8 457.7 457.7 457.7 Black liquor 437.6 437.6 391.1 391.1 391.1 Hog fuel 71.2 71.2 66.6 66.6 66.6 Purchased fuels 33.1 33.1 148.7 85.9 301.2 Wood 33.4 33.4 Natural gas to GT 263.0 Natural gas to duct burner 67.6 14.3 Lime kiln fuel oil 33.1 33.1 47.7 38.2 38.2 Total fuels 541.9 606.4 543.6 758.9 Total process steam 212.1 213.3 200.2 200.2 200.2 Net power production 64.3 88.6 122.1 114.7 225.8 Excess power available for -35.8 -11.5 22.0 14.6 125.7

The higher pressure in the HERB Tomlinson recovery boiler gives a higher elec tricity production than in the BASE Tomlinson boiler. But there is still a need to purchase electricity from the grid. The BLGCC plants have a higher output of electricity and they all produce more electricity than needed at the site.

47 The BLGCC plants will all produce more electricity but additional fuel must be used to produce process steam. The “mill scale” plants have a duct burner fired with some syngas and natural gas and they also have to purchase hog fuel to the hog fuel boiler to produce enough steam. The “utility scale” plant will generate excess steam that can be used for generation of electricity in a condensing turbine. No hog fuel must be imported to the “utility scale” plant and it does not need additional fuel to a duct burner.

The BLGCC system will increase the limekiln load and the need for limekiln fuel. In this case the fuel is fuel oil. The increase of limekiln load is higher in the low- temperature BLGCC process.

Considering the black liquor, hog fuel, purchased wood residues, natural gas, and lime kiln fuel as energy inputs, the net electricity generating efficiency of the BLGCC systems are 20.0 %, 21.1 % and 29.8 % respectively, which is substan tially higher than for the Tomlinson BASE case. The efficiencies of incremental purchased fuel use for electricity generation (relative to Tomlinson BASE) are 50 %, 96 % and 60 % (HHV basis).

10.5 Environmental evaluation The most significant effluent differences between BLGCC and Tomlinson sys tems are expected to be in air emissions, more detailed analysis of air emissions was carried out as part of this study. The emissions included are CO2, SO2, NOx, CO, VOC, PM and TRS (total reduced sulfur).

The average mix of electricity production to grid was used to calculate change in emissions due to grid offsets. After a long discussion about what kind of elec tricity is offset by the changes in electricity production the average mix with the following CO2 emissions where chosen: Emissions of CO2 from South East US 2008- 612 kg/MWh, 2020- 577 kg/MWh, 2035-544 kg/MWh.

10.6 Economic evaluation To assess the prospective economics of BLGCC technology at the mill level, a cash flow analysis was carried out assuming that an investment would be made in a new power/recovery system to replace an existing Tomlinson system (character ized by the Tomlinson BASE system described earlier) that had reached the end of its working life. The internal rate of return (IRR) and net present value (NPV) of the incremental investment required for a BLGCC over a new Tomlinson sys tem were calculated. Calculations were done both without and with consideration of the potential economic value of environmental benefits of the advanced recov ery systems.

48 Table 10.4 Financial result.

Total net cash flow relative Tomlinson BASE Including environmental benefits a IRR %/yr NPV IRR %/yr NPV (M$) (M$) Tomlinson HERB 14.2 9.0 37.8 58.2 BLGCC - Low T Gasifier, mill scale 8.9 -6.0 20.9 73.0 BLGCC - High T Gasifier, mill scale 18.5 44.9 34.8 138.5 BLGCC - High T Gasifier, utility scale 20.1 83.1 35.1 216.2 a) Renewable electricity premium of 2.5 0/kWh, renewable electricity production tax credit eq to 1.8 0/kWh for 10 years

10.7 Regional and national impacts Other impacts of an introduction of black liquor gasification technology are dis cussed. These are national fossil fuel savings, introduction of electricity genera tion facilities in a region with an increasing electricity demand, contribution to renewable electricity generation, emissions reductions, fuel diversity and energy security.

These are discussed with three possible market penetration scenarios, from “low ” to “aggressive” market penetration.

49 50 11 The KAM Programme (2003)

In the ”Ecocyclic Pulp Mill” research programme (“KAM”), detailed design-point performance estimates for black liquor gasification gas turbine cogeneration sys tems were presented and compared to estimates for conventional recovery boiler systems, including possible future developments. All calculations were based on full-mill energy balances including lime kiln fuel use, for two types of kraft mills with different energy situations: (A) a bleached market pulp mill, and (B) an inte grated bleached pulp and fine paper mill where all the pulp is used for paper pro duction. Material and energy balances for the mills stem from a reference mill used in the KAM programme. The results show that the market pulp mill can be a significant exporter of power (up to 1.3 MWh/ADt) without using more fuel than is already available at the site. The integrated mill will remain a net buyer of fuel if maximum power generation is sought, but it was also shown that an integrated mill can reach a balance where all power consumed can be generated internally using only fuels originating from the wood brought into the mill. Such a mill would then be neither a buyer nor seller of power or fuel.

Background data for the reference mill include calculations for one recovery boiler, generating steam at 79 bar(a), 485°C. Recovery boiler performance was calculated with a model derived from the model used for the black liquor gasifier, to ensure consistency in thermodynamic data between the boiler and gasifier mod els and to allow changes in input also to the recovery boiler model. The studied systems centered around a high-temperature oxygen-blown gasifier, implied to approximate the systems being developed by Chemrec. Gasifier performance was estimated with an inhouse chemical equilibrium model based on Gibbs energy minimization [11]. The remaining system - air separation, gas and smelt cooling, acid gas removal and recovery, gas turbine, heat recovery steam generator, and steam cycle - were modelled in the process simulator HYSYS. Heat losses and pressure drops were estimated for each unit operation. Auxiliary calculations for the chemical recovery cycle and the bark boiler were carried out in a spreadsheet model. Figure 11.1 shows the approximate match between gasifier recovery capacity and some gas turbine models from the major manufacturers.

51 APPROXIMATE BLACK LIQUOR FUEL REQUIREMENT (tDS/d) 0 1000 2000 3000 4000 5000 6000

General Electric/ Nuovo Pig none 2500

ABB/Alstom 11N2 13E2

Siemens KWU V64.3A V84.2 V84.3A/V94.2

Siemens Westing house/ 501D5 501 F 501G Mitsubishi

Figure 11.1 Estimated match between gasifier black liquor solids capacity and some specific gas turbine models. Gas turbines that have been modified for use in integrated gasification combined cycle (IGCC) applications are represented by shaded boxes.

11.1 Effects on recausticizing In the gasifier, a large fraction of the sulfur in the black liquor is converted to hydrogen sulfide. There are three principal routes to convert the concentrated H2S stream from the acid gas removal system to sulfur in a useful form in the pulping liquor:

• reabsorption in green or white liquor • recirculation to the gasifier • conversion to liquid sulfur, which is dissolved to give a polysulfide liquor

The first two routes will yield a white liquor with essentially the same composi tion as a conventional liquor, while the third route can be utilized for pulping modifications as described below. The first route does also make it possible to prepare white liquors with different sulfidities, if desired.

Operating variables may also be used to control the amount of hydrogen sulfide formation. Gasifier pressure and temperature, and black liquor solids content all affect the equilibrium (reaction 1 below). The effect of a 100°C increase in temperature has been included in the calculations.

Although the sulfur split may be put to an advantage in the pulping process, it also leads to an increased load on the lime kiln. The primary reason is that as hydrogen sulfide rather than sodium sulfide is formed, according to the overall reaction 1, the effective alkali contribution from hydrolysis of sulfide ions (reaction 2) decreases.

Na2S +H20 +C02 H2S +Na2C03 (1)

S-- + H20 -> HS + OH (2)

52 Thus, for every mole of hydrogen sulfide formed, one mole of hydroxide ions is lost from the green liquor, corresponding to 0.5 moles of calcium oxide that need to be produced in the lime kiln.

If the hydrogen sulfide is reabsorbed in green or white liquor, hydroxide ions will be consumed in reaction 3 and in the simultaneous coabsorption of CO2 (reaction 4):

H2S + OHHS- + H2O (3)

CO2 + 2 OH CO32" + H2O (4 )

Qualitatively, the reabsorption route will have the largest impact on lime con sumption, requiring a minimum of one additional mole of CaO for every mole of H2S formed in the gasifier. In contrast, the recirculation route will shift the equi librium in the gasifier (reaction 1) from hydrogen sulfide towards sodium sulfide, until the smelt has the same composition as that from a recovery boiler, and there will therefore be no difference in lime consumption. The disadvantage is that the sodium/sulfur split cannot be utilized and that the recompression of H2S to the gasifier pressure reduces the net power output of the plant.

The Claus route will avoid reactions 3 and 4. However, alkali will be consumed in the formation of polysulfide ions (reaction 5) and as polysulfide ions decompose during impregnation and cooking (reaction 6):

HS"+ OH" + n S0 ^ SnS2- + H2O (5)

SnS2"+ (n -1) OH " + (1 -n) H2O (1+ 2) HS" + 4 s2O32" (6)

Since one mole of elemental sulfur is generated for each mole of H2S, reactions 5 and 6 indicate that the maximum increase in lime consumption is one mole of CaO per mole of H2S formed in the gasifier. The actual increase is slightly lower when accounting for the decreased wood consumption per ton of pulp with poly sulfide impregnation and the rate of reaction 6. It was estimated in the study that about 80 % of the polysulfide ions will decompose as the cook proceeds.

11.2 Energy balances The market pulp mill has a surplus of fuel for all systems. It is assumed that all the black liquor and bark is used for power and steam generation at the mill and that the surplus steam is fed to a condensing turbine. The performance of different systems can be compared by looking at the net power generated as presented in Table 11.1 and 11.2. It thus represents the amount of power that is possible to generate from the fixed amount of internal fuels.

53 Baseline performance for the reference mill recovery boiler is given in the first column of Table 11.1. Net electricity from the powerhouse amounts to 52 MW or 1250 kWh/ADt, which is considerably more than the mill requirements of 700 kWh/ADt. With this recovery boiler, the market pulp mill would therefore generate a surplus of electric power amounting to 23 MW or 550 kWh/ADt, which could be sold to the grid. About 13 MW emanate from the condensing turbine.

Steam Data. Steam pressure is the most important variable affecting electric power generation in the recovery boiler systems. The steam pressure is, however, limited by the maximum allowable superheater temperature and the necessity to avoid condensation in the back-pressure turbine. Superheater corrosion becomes severe if carryover ash deposits melt on the tube surface. Current recovery boiler designs use a maximum steam temperature of 490-495°C. The ash composition and, consequently, the melting point can vary widely from boiler to boiler - and for different operating conditions - depending on black liquor composition, lower furnace temperature, flow patterns, boiler load, etc. Of particular importance are potassium and chloride which lower the ash melting point. A complication is that both these elements tend to increase in concentration as a result of mill closure.

54 Table 11.1 Calculated performance for the recovery boiler systems in the market pulp mill (at 1000 ADt/d).

Case Description Base Advanced Future Reheat HP/Reheat Steam Pressure bar(a} 79 90 110 120/79 HP/Reheat Steam Temperature °C 4B5 500 530 485/485

ELECTRIC POWER Producers Back-Pressure Turbine MWe 43.08 45.06 48.28 47.76 Condensing Turbine MWe 12.74 12.27 11.50 11.64 Consumers Fans MWe -1.55 -1.55 -1.55 -1.55 ESP MWe -0.60 -0.60 -0.60 -0.60' BFW Pumps MWe -1.13 -1.27 -1.52 -1.66 Liquor Pumps MWe -0.22 -0.22 -0.22 -0.22 Mi sc MWe -0.20 -0.20 -0.20 -0.20' Summary Power Generated. Gross MWe 55.3 57.3 59.8 59.4 Power Generated, Net MWe 52.1 53.5 55.7 55.2 Power Consumed in Mill MWe -20.2 -29.2 -29.2 -29.2 Excess Power for Ex do rt MWe 22.3 24.3 26.5 28.0' Power Generated, Gross kWh/ADt 1340 1376 1435 1426 Power Generated, Net kWh/ADt 1251 1284 1337 1324 Power Consumed in Mill kWh/ADt -701 -701 -701 -701 Excess Power for Export kWh/ADt 550 583 536 623

STEAM Producers Recovery Boiler Vh 230.2 287.8 282.5 282.3 Bark Boiler t''h 17.5 17.3 17.0 17.8 MP Condensate Flash Vh 0.3 0.9 0.9 0.9 Desuperheaters Vh 3.3 8.3 8.3 8.6 Internal Consumers Sootblowers Vh -15.0 -15.0 -15.0 -15.0 Air Preheaters Vh -22.1 -22.1 -22.1 -22.1 Deaerator Vh -20.8 -20.5 -19 9 -20.0' Net Steam Produced 253.4 256.6 251.7 252.5 Mill Consumers LP steam to Mill Vh 102.7 102.7 102.7 102.7 MP steam to Mill Vh 75.4 75.4 75.4 75.4 LP Steam to Cond Turbine Vh 81.3 78.4 73.5 74.3 Total Steam Consumed Vh 253.4 256.6 251.7 252.5

HEAT TO STEAM SYSTEM Producers Recovery Boiler, HP GJ/ADt 19.32 19.32 13.32 13.32 Bark Boiler, HP GJ/ADt 1.16 1.16 1.16 1.16 Soot blowing, IP GJ/ADt -1.00 -1.00 -1.00 -1.00 Air Preheaters, MP GJ/ADt -0.43 -0.43 -0.43 -0.43 Air Preheaters, LP GJ/ADt -0.73 -0.73 -0.73 -0.73 Mill, Make-Up GJ/ADt 0.37 0.37 0.37 0.37 Mill. Turbine Condensate GJ/ADt 0.42 0.40 0.38 0.38 Total Produced GJ/ADt 19.11 19.09 13.07 19.07 Consumers Mill. MP GJ/ADt 4.30 4.30 4.30 4.30' Mill. LP GJ/ADt 5.68 5.38 5.68 5.68 Back-Pressure Turbine GJ/ADt 3.91 4.03 4.35 4.34 Condensing Turbine GJ/ADt 5 21 5.02 4.71 4.76 Total Consumed GJ/ADt 19.11 19.09 13.07 19.07

55 Salmenoja measured ash melting points in the superheater section of one recov ery boiler operating with a steam temperature of 480°C. As a side result of the measurements, it was concluded that it would have been possible to increase the steam temperature to as high as 530°C without risking molten phase corrosion for this particular boiler under its present operating conditions. This result can not be generalized because of the factors mentioned above, but it could be taken as an estimate of steam temperatures that could be allowed in a future boiler with care fully controlled operating conditions and where smaller margins are accepted.

Advanced boilers. Three more cases are included in Table 11.1 to reflect the im pact that advanced recovery boiler technology would have on electricity genera tion. Case 2 assumes that the recovery boiler will generate steam at 90 bar, 500°C, which is on par with or slightly higher than the most advanced boilers in operation in Scandinavia today. Electricity generation increases by about 35 kWh/ADt. Case 3 represents a future boiler that utilizes a steam temperature of 530°C, and a cor responding maximum steam pressure of 110 bar. Compared to the baseline case, an additional 85 kWh/ADt can be generated. Case 4 utilizes reheat to avoid going to very high steam temperatures. By reheating the steam after the high pressure turbine the steam pressure can be increased to 120 bar while the steam tempera ture remains at 485°C. The advantage compared to the base case is about 65 kWh/ADt.

Table 11.2 Calculated performance for the BLGCC systems in the market pulp mill (at lOOOADt/d).

FWno .Watfiresfcrt Csnvsnt'smtl a Spi t S.1 Ifiditv Ccm. Paly sulfide Case L2 Gasifier Temperature *c 950 950 1050 1050 1050 1050 950 950 1050 1050 1050 Gasifier Pressure barfaj 25 32 32 32 32 38 32 32 32 32 38 H2S Recovery * Reabs Fla ids Flaaas Raabs Rsabs Fla las Re-circ. Claus Claus Claus Claus ASU Integration ** N2 N2 N2 N2 Full N2 M2 N2 N2 N2 N2 Gss Turbine 6 FA 6FA 6 FA 6 FA 6FA 7G 6FA 6 FA 6 FA 6 FA 7G HP Steam Pressure barfai 70 79 79 110 70 1 10/30 70 79 79 110 110/30 HP Steam Temperature *c 485 485 485 530 485 530/370 485 485 485 530 530/370 ELECTRIC POWER Produsars Gas Turbine MWe 71.0 71.2 68.0 68.0 64.6 76.4 68.9 66.4 64.7 64.7 72.6 Back-Pressure Steam Turto. MWe 13.7 15.5 16.1 17.5 18.2 16.0 15.8 14.8 15.6 16.9 15.1 Condensing Steam Turb. MWe 6.0 5.6 7.3 6.9 9.5 5.3 6.9 4.7 6.7 6.3 5.0 Air Exaardar MWe 0.0 0.0 0.0 0.0 1.3 0.0 0.0 0.0 0.0 0.0 0.0 Consumers ASU MWe -7.13 -7.04 -7.74 -7.74 0.00 -7.71 -7.48 -6.58 -7.35 -7.35 -7.33 32 ConiDrssssr MWe -2.73 -2.94 -3.23 -3.23 -2.35 43.41 -3.13 -2.75 -3.07 -3.07 43.24 M2 Csmprassar MWe 43.14 -3.48 -2.91 -2.91 -11.92 43.20 -2.66 -3.25 2.77 -2.77 43.02 LLP Compressor MWe -0.91 J0.52 -0.47 -0.47 -0.82 4)28 -0.54 -0.48 -0.45 -0.45 -0.26 BFW Pumps MWe -0.42 4)42 -0.41 -0.52 -0.46 4)45 -0.41 -0.39 -0.39 -0.50 -0.42 Liquor Pumps MWe -0.50 4).57 -0.57 -0.57 -0.57 4).64 -0.57 -0.54 -0.54 -0.54 -0.60 A GR Claus MWe -0.42 jQ.33 -0.30 -0.30 -0.26 4).32 -1.73 -0.38 -0.34 -0.34 -0.36 Misc MWe -0.20 4)20 -0.20 -0.20 -0.20 4)20 -0.20 -0.20 -0.20 -0.20 -0.20 Summary Fewer Generated. Gross MWe 90.7 92.3 91.5 92.5 93.6 97.8 91.6 85.9 86.9 87.9 92.7 Fewer Generated. Net MWe 75.3 76.8 75.7 76.6 77.0 81.6 74.9 71.4 71.8 72.7 77.2 Fewer Consumed in Mill MWe 430.0 -30.0 -29.7 -29.7 -29.7 -29.7 -29.2 -29.6 -29.4 -29.4 -29.4 Exsass Paws r far Exes a MWe 45.3 40 40 46.3 47.3 51.3 45.7 41.S 424 43.3 47.3 Fewer Generated. Gross kWh-'ADt 2177 2215 2196 2220 2247 2347 2198 2063 2086 2109 2224 Rower Gene rated, Net kWh/ADt 1806 1843 1816 1838 1849 1958 1797 1713 1723 1744 1653 Fewer Consumed in Mill kWh-ADt -719 -720 -713 -713 -714 -713 -701 -709 -705 -705 -705 Excess Power kWh/ADt 1087 1123 1103 1125 1135 1246 1096 1004 1018 1039 1149

56 STEAM Producers HRSG t-'h 122.7 122.9 118.4 116.8 129.1 106.1 120.0 114.7 112.5 111.0 100.8 Baht Boiler t-'h 11.2 10.6 13.5 13.1 13.0 12.7 17.4 10.7 13.5 13,1 12.8 Gasifier Island t-'h 90.8 90.3 103.6 103.6 103.3 103,3 97.8 84.3 98.5 98.5 98.4 Claus Plant t-'h 3.3 5.3 3.3 3.3 3.3 3.3 3.3 3.3 £.3 £.3 £.5 MR Condensate Flash t-'h 1.7 1.6 1.5 1.5 1.4 1.4 2,0 I. I 1.2 1.2 1.1 Desuperheaters t-'h 6.7 3.8 2.5 22 3,0 2.4 4,3 3.4 2.3 2,0 2.7 Internal Consumers AGP t-'h -9.2 -7.7 -6.8 -6.8 -6.5 -6.2 -11,5 -7,1 -6.5 -6,5 -5.9 Fuel gas heater t-'h -3.6 -3.6 -3.4 -3,4 0.0 -3,5 -3,5 -3,4 -3,3 -3,3 -3,3 Bark Boibr t-'h -1.0 -0.9 -1.2 -1.2 -1.1 -1.1 -1.5 -0.9 -1.2 -1.2 -1.1 Deaerator t-h -2.7 -2.7 -3.1 -3,1 -3,5 -2.7 -2.9 -2.6 -3,3 -3,2 -2.7 Net Steam Produced 216.5 214.2 224.9 222.7 238.8 212,3 222.0 203.5 216.0 213.9 295.1 Mill Consumers LP steam to Mill t-'h 102.7 102.7 102.7 102.7 102.7 102.7 102.7 100.8 100.8 100.8 100.8 MP steam to Mill t-'h 75.4 75.4 7 5.4 75.4 75.4 75.4 75.4 7£.e 72.6 7£.6 7£.6 LP Stsamta Cand. Tint. th 39.4 16.3 46.7 44.4 63.6 34.£ 43.6 33.1 426 43.4 31.7 Total Steam Consumed ti'h 216.6 214.1 224.9 222.6 238.8 212,3 222.0 203.5 216.0 213.8 205.1

HEAT TO STEAM SYSTEM Producers HRSG. HP GJ/ADt 6.97 6.98 6.74 6.53 7.71 5.46 6.84 6.52 6.41 6.20 5.19 HRSG. MP GJ/ADt 0.62 0.82 0.78 0.99 0.62 0.88 0.78 0.76 0.74 0.94 0.84 HRSG. LP GJ/ADt 023 0.23 0.22 0.23 0.19 0.74 0.22 0.22 0.21 0.22 0.70 Bark Boiler. HP GJ/ADt 0.76 0.72 0.91 0.91 0.88 0.88 1.18 0.73 0.91 0.91 0.89 Barit Boiler. MP GJ/ADt -0.02 -0.02 -0.02 -0.02 -0.02 -0.02 -0.03 -0.02 -0.02 -0.02 -0.02 Barit Boiler. LP GJ/ADt -0.03 -0.03 -0.04 -0.04 -0.04 -0.04 -0.05 -0.03 -0.04 -0.04 -0.04 Syngas Cooler, MP GJ/ADt 0.13 2.29 3.15 3.15 3.12 3.90 2.48 2.14 2.99 2.99 3.17 Syngas Gaoler. LP GJ/ADt 3.96 2.04 1.94 1.94 1.95 1.29 2.22 1.91 1.84 1.84 1.76 Syngas Cssler. LLP GJ/ADt 066 0.45 0.42 0.42 0.42 0.32 0.49 0.42 0.40 0.40 0.31 Syngas Cooler, Make-Up GJ/ADt 016 0.18 0.18 0,18 0.18 0.18 0.18 0.17 0.17 0.17 0.17 Syngas Cooler. Turb. Cond. GJ/ADt 0.14 0.13 0.17 0.16 0.21 0.12 0.16 0.11 0.15 0.14 0.11 Gas Heater. LLP GJ/ADt -0.19 -0.19 -0.18 -0.16 0.00 -0.19 -0.19 -0.16 -0.18 -0.18 -0.16 Steam Campresaar. LP GJ/ADt 0.07 0.04 0.04 0.04 0.07 0.02 0.05 0.04 0.04 0.04 0.02 Mill, Make-Up GJ/ADt 026 0.28 0.28 0.28 0.28 0.28 0.28 0.28 0.23 0.28 0.28 Mill. Turbine Condensate GJ/ADt 020 0.18 0.24 0.23 0.31 0.17 0.22 0.15 0.22 0.21 0.16 Total Produced GJfADt 14.17 14.11 14.82 14.60 15.88 14.00 14.84 13.22 14,13 14.12 13.37 Consumers AGR. IP GJ/ADt 044 0.37 0.33 0.33 0.31 0.30 0.55 0.19 0.20 020 0.16 Mill. MP GJ/ADt 4.30 4.30 4.30 4.30 4.30 4.30 4.30 4.16 4.16 4.16 4.16 Mill. LP GJ/ADt 5.66 5.63 5.68 5.66 5.68 5.68 5.68 5.57 5.57 5.57 5.57 Back-Pressure Turbine GJ/ADt 1.26 1.43 1.49 1.61 1.68 1.48 1.45 1.36 1.43 1.55 1.39 Condena in a Turbine GJ/ADt £.49 2.35 3.3£ £.87 3.31 £.£ 1 £.04 1.34 £.75 £.61 £.35 Total Consumed GJ/ADt 14.17 14.11 14.82 14.60 15.88 13.97 14.83 13.22 14,12 14.10 13.34 PULPING Wood Consumption tDW/ADt 2.10 2.10 2.10 2,10 2.10 2.10 2.10 2.01 2.03 2.03 2.03 CaO from Lime Kiln kayADt 304 310 277 277 283 282 232 290 263 263 267 Lime Kiln Capacity/Reference " 1.31 1.34 1.20 1.20 1.22 1.22 1.00 1.25 1.13 1.13 1.15 FUEL Black Liquor Produced/Consumed GJ/ADt 21.75 21.75 21.75 21.75 21.75 21.75 21.75 20.31 20.67 20.67 20.67 Bark Consumed in Lime Kiln GJ/ADt -2.05 -2.09 -1.87 -1.87 -1.91 -1.90 -1.57 -1.96 -1.78 -1.78 -1.80 Consumed in Bark Boiler GJ/ADt -0.66 -0.52 -1.04 -1.04 -1.00 -1.01 -1.34 -0.83 -1.04 -1.04 -1.01 Produatian GJ/ADt £.91 £.01 £.91 £.91 £.31 £.31 £.31 £.73 £.82 £.9£ £.9£ Purchased GJ/ADt ooo 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Tall Gil Produced/Sold GJ/ADt 1.37 1.37 1.37 1.37 1.37 1.37 1.37 1.31 1.32 1.32 1.32 OTHER CHARACTERISTICS Mill Size Matching GT **** ADtd 1171 1169 1214 1214 1054 1 202 1252 1276 1276

* Reabs = reabsorption of H2S in green or white liquor: Recirc= recirculation of H2S to the gasifier; Claus = conversion of H2S to liquid sulfur ** N2 = the fuel gas is assumed to be diluted with nitrogen to a lower heating value of 7.5 MJ/kg in order to suppress NOx formation. Full = air to the ASU is bled from the gas turbine compressor. *** Indicates how much lime kiln load changes compared to the recovery boiler cases. **** The calculations were done for agas turbine of fixed size (the General Electric 6FA); the results in the table have been scaled to the gen 1000 ADt d mill. Data in the indicated row shew the mill production rate that would exactly match the gas turbine fuel requirement at the desk point (given the specific black liquor flows in table 3). The next generation gas turbine is based on data for the larger GE 7G. If a "6G* **versior *** **** developed, it could be expected to be about 50% larger than the 6FA.

57 In principle, it should be possible to go to much higher pressures when reheat is employed. However, when the steam pressure increases, less heat is needed to evaporate the steam but more heat must be transferred in the superheater and economizer sections. As a consequence, less heat is transferred in the furnace and the flue gases will enter the superheater section at a higher temperature. Tube metal temperatures will increase and lead to a higher risk of molten phase corro sion. Also, because of the higher gas side temperatures, more of the ash will be in its ”sticky” (partly molten) state which may lead to increased plugging, and, in turn to greater requirements for sootblowing steam. Obviously, the flue gas tem perature at the superheater inlet is an important parameter, and it has therefore been estimated for the different cases in Table 11.1.

11.3 Black Liquor Gasification Combined Cycle Systems A large number of configurations and operating parameters were tested as outlined above. For all the studied black liquor gasification combined cycle (BLGCC) systems, electric power generated net of the powerhouse ranges from 1700-2000 kWh/ADt, i.e. 450-750 kWh/ADt more than the reference recovery boiler at the same fuel consumption (or lower, for the poly-sulfide cases). Table 11.2 summarizes the predicted performance of the BLGCC systems in the market pulp mill

Pressure. The GE 6FA gas turbine requires a minimum gasifier pressure of about 25 bar to compensate for pressure drop in the gas cooling and gas clean-up sys tems and across the fuel control valve. The gasifier pressure may be increased beyond this to improve heat recovery and allow medium pressure steam genera tion in the syngas cooler. Less extraction steam is then needed from the steam turbine which leads to about 2 % higher net power generation (40 kWh/ADt), even after accounting for increased power consumption in the oxygen and nitrogen compressors. Although the increase in power is marginal, raising the pressure will have the added advantage of reducing the size or increasing the capacity of the gasification system.

Since the BLGCC systems may increase the amount of generated power from black liquor by up to a 1000 kWh/ADt, the increase in overall efficiency is not sufficient to avoid an increase in fuel consumption, as has been shown in the report (Figure 11.2) The incremental efficiency ranges from 80-140 %, which is higher than for the recovery boiler systems at about 70 %.

58 Biomass Cons, at 1000 ADt/d (MW) 25 50 75 100 125

Q < o % o o TO CLI O 1 0. o o HI

Figure 11.2 An overview of how different cogeneration systems affect power generated and fuel consumed. Note that the black liquor (20.3-21.8 GJ/ADt) is not included in the fuel consumption on the x-axis. Symbols: diamonds - systems with H2S real)sorption; triangles - H2S recirculation; squares - Claus /polysulfide. Lines connect systems with varying amounts of bypass supplementary firing.

In many mills, the incentive to save steam by improved heat integration or other measures reaches a threshold when all steam can be raised from internal fuels, because it is difficult to realize economic benefits from further savings. To in crease power generation it is then necessary to consider a condensing turbine, but due to seasonal load variations it is difficult to size a small condensing turbine so that it runs at near-optimal conditions all the time, and its small size makes the specific investment cost high. Also, the steam surplus tends to be larger in the summer when electricity prices (in Scandinavia) are lower than in the winter.

An inherent drawback of condensing turbines is that the fuel is used at a low overall efficiency, as most of the energy is removed in the condenser. If there is a market for the surplus fuel to be used in other cogeneration plants, the fuel will be used at higher overall efficiencies and the specific investment cost for power generation is likely to be lower. Surplus fuel is sold by some mills today, but this route is currently limited to tall oil and bark. Lignin precipitation may be a future alternative, but it must be developed, e g. to avoid chemical losses.

With BLGCC systems, steam savings may in effect allow more power to be generated. Figure 11.3 shows net power generation for BLGCC systems in the

59 integrated mill, if fuel consumption is fixed at the amount of internal fuels avail able (including tall oil). For example, a steam saving of about 3 GJ/ADt would allow up to 800-1000 kWh/ADt to be extracted from the system at constant fuel consumption. The same steam saving would allow about 200 kWh/ADt to be generated in a condensing turbine, so, clearly, the BLGCC systems benefit more than the recovery boiler systems from a reduction in process steam consumption.

Steam Available for Mill (GJ/ADt) 10.8 12.8 14.8 16.8 2400 H------'------'------'------'------■------'------1- 100

Integrated Mill Steam Consumption

C 1800 - - 75

Internal | 1200 - - 50 £ % 0) 0) Desired Steam LU LU 600 - Saving - 25

Steam : Steam _ Deficit Surplus 0 0 -5 -4 -3-2-10 1 2 Steam Surplus (GJ/ADt)

Figure 11.3 Net power and steam generation in the integrated mill at fixed fuel consumption. Symbols: diamonds - BLG systems; circles - recovery boiler systems.

11.4 Investment and Operating Costs The extra investment for the gasification plant, including air separation, gas clean up and the combined cycle, in comparison with a recovery boiler, is estimated to be about 580 MSEK for the case with conventional pulping and about 550 MSEK for the case with polysulfide pulping (Table 11.3). The plant incorporates some redundancy in the gasifier island (3 x 50 % gasifier) to ensure an availability equal to that of a recovery boiler. The extra investment also includes a higher capacity lime kiln and some changes to the size of the equipment on the turbine and steam side.

The obvious operation benefit is the increase in power surplus, approximately 500 kWh/ADt more than that for the Reference Mill. Differences in operation costs are primarily due to increased maintenance. When electricity is sold at 0.25 SEK/kWh, the net operating benefit is estimated to reach 84 SEK/ADt with conventional pulping. Note that the latter number includes the generation of poly sulfide liquor to improve pulp yield and reduce wood costs. It has been assumed that the polysulfide pulp can be sold at the same price as the reference pulp, al though the differences in pulp properties may warrant a different price in reality.

60 As of 2003, electricity from renewable sources will be valued higher in Sweden due to a system with mandatory trading of “green certificates”. Electricity from such sources could therefore be sold at a minimum premium of 0.175 SEK/kWh, thus increasing the net operating benefit for the cases above by approximately 90 SEK/ADt.

In order to determinate when these schemes could be profitable, the production cost of electricity was calculated. If all extra capital costs and operating costs (in cluding changes in wood consumption) are allocated to the electricity produced, the resulting electricity production costs are 0.28 SEK/kWh and 0.11 SEK/kWh, respectively for the “conventional ” and “PS” cases.

61 Table 11.3 Investment and operating costs for the BLGCC model mills in comparison with the Reference Mill. In the “Conventional” case, the H2S is reabsorbed to make a conven tional white liquor. In the “PS” (polysulfide) case, the H2S is converted to elemental sulphur, which is used to produce a PS liquor. The calculations assume that the yield improvement from PS impregnation is 2.5 % (on wood). Wood consumption thus decreases by 5.4 % and the black liquor flow rate by 6.5 %, reducing the required investment for the chemical recovery cycle.

Incremental Investment (TIC|\ MSEK BLGCC BLGCC Conv PS Air separation unit 230 219 Gasification & gas cooling 508 488 Gas clean-up (Selexol) 129 124 Sulfur handling (H2S Reabsorption or Claus plant) 80 125 Gas turbine 345 331 HRSG 118 113 Balance of plant 100 66 Recovery boiler -345 -845 Steam turbine -118 -121 Lime kiln + bark dryer 35 24 NET INCREMENTAL INVESTMENT MSEK 582 555

Incremental Operating Costs, MSEK/a

Reduced wood consumption^ 0 -55 Biofuels 5 7 8 Maintenance (Gas turbine) 4 14 13 Maintenance (Other) 4 5 4 Labor 5 4 4 NET INCREMENTAL OPERATING COST MSEK/a 29 -26

Total Incremental Cost for Power Generation

Incremental Capital Coslb MSEK/a 58 55 Incremental Operating Cost MSEK/a 29 -26 Incremental Cost, Total MSEK/a 87 29 Incremental Electricity Produced GWh/a 313 243 COST OF INCREMENTAL POWER SEKJMWh 278 119

1 Total Installed Cost Indudes site preparation, buildings, electrical, piping, instrumentalkin, engineering, and license tees. Estimated costs have been scaled fnocn several sources with an initial accuracy of +A 30 %. Scaling adds an additional uncertainty ot +A10 tt. 2 330 SEKitti3*ub 3 80 SEfOMWh for sold bark 4 2 % of TIC annually (4 % for gas turbine) 5 2 operators per shift 6 at an annuity factor of 0.1

62 11.5 Conclusions • A market pulp mill can export about 550 kWh/ADt with a modern recovery boiler system (79 bar, 485°C) and a condensing turbine for surplus steam. A future boiler with very advanced steam data (110 bar, 530°C) may add about 90 kWh/ADt. A BLGCC system with a modern gas turbine would increase the excess power to about 1100 kWh/ADt, and with a next-generation gas turbine to about 1250 kWh/ADt. All numbers assume a fixed amount of available fuel and include lime kiln fuel use. • Utilizing the BLGCC concept in conjunction with polysulfide impregnation in the cook could reduce wood costs by 3.3-4.3 % while adding 450-600 kWh/ADt of exported power compared to the recovery boiler case. Total fuel consumption and required black liquor processing capacity is lower in these cases because of the reduced wood consumption. • Also the integrated mill may become a net exporter of power with a BLGCC system. Up to about 500 kWh/ADt may be sold, compared to the 360 kWh/ADt that must be bought in the reference case. However, purchased fuel must be brought into the system when the increase in generated power exceeds approxi mately 400 kWh/ADt. Bypass supplementary firing can be used to reduce or eliminate the need for purchased fuel. The integrated mill’s need for steam and power can be very closely balanced using only internal fuels if about one third of the gas is used in the HRSG. • With BLGCC systems, reductions in steam use bring possibilities to increase power generation, which is possible for the recovery boiler systems only if condensing turbines are used. With a 3 GJ/ADt reduction in steam use - corre sponding to about 20 % - the net power generation could be increased by up to 1000 kWh/ADt with the BLGCC systems. • The investment cost for a BLGCC system is higher than that for a recovery boiler, approximately 550-580 MSEK. • The electricity production cost of a BLGCC is on a competitive level, 0.11-0.28 SEK/kWh.

63 64 12 Pulp Mill Energy Systems with Black Liquor Gasification - a Process Integration Study

Process integration aspects of black liquor gasification in kraft pulp mills were studied between 1993 and 1998 in a research project at the Department of Heat and Power Technology, Chalmers, with Niklas Berglin as the principal investiga tor. The research was carried out within the Swedish Recovery Boiler Commit tee’s research program Kraft recovery/Black liquor gasification. Between 1997 and 1998 the project was partially funded by Nykomb Synergetics and by the KAM program.

The realization of the energy recovery potential of black liquor gasification is strongly connected to the implementation of changes in the pulp mill’s system for cogeneration of heat and electric power. To design an efficient and cost-effective energy system for the mill, it is necessary to be able to predict the effects of these changes ahead of detailed design. It is also desirable to identify possibilities for energy savings that can result from increased integration between the gasification plant and other parts of the mill.

In a licentiate thesis (Berglin 1996), the potential impact of a number of combina tions of gasification and cogeneration systems on the energy balances of several actual mills were studied and compared to the conventional technology. Data from the mills have been collected and analyzed to provide an accurate background for the remaining analysis. The possibilities for process integration have been studied through pinch analysis. Mass and energy balance models have been developed in the process simulation tool HYSIM/HYSYS for the important parts of the gasi fication-based cogeneration system, viz. the gasifier, the heat recovery system, the gas turbine, and the steam cycle (see Figure 12.1).

65 Figure 12.1 Overview of the HYSYS model of the BLGCC plant.

Low- 40% - Temp BLG/CC O) X _l High- CD > 30% - Temp i -OW- ▲ BLG/CC _i 1 emp 0 BLG/GT *1 £ 20% - ■ IBS* •i© High- Recover) 5% Temp 1CL 10% - ' <35% 7 Boilers BLG/GT

0% 40% 50% 60% 70% 80% Heat (% of LHVbls)

Figure 12.2 Electric power generation vs. heat generation for conventional and advanced recovery boilers, high-temperature (950 C) and low-temperature (700 C) BLG systems with combined cycles (CC) and single cycle gas turbines (GT). (Berglin 1996)

The results show that the flexibility in meeting the specific demands for heat and electric power of a particular mill is much greater with a gasification and gas turbine based recovery system, with possibilities to design systems with power-to- heat ratios from 0.25 to 1.1, whereas that of the conventional system does not exceed 0.3 (Figure 12.2). It is confirmed that the ultimate potential for power gen eration is up to 2.5 times that of the conventional system. Some systems with high power-to-heat ratios will yield less heat than the existing system, and it will

66 therefore be necessary to supply extra fuel in mills where steam consumption cannot be reduced correspondingly. In the extreme case, the need for extra fuel corresponds to twice the falling bark.

It has been found that substantial savings in the mill’s steam consumption can be made by considering the process integration aspects, viz. through the recovery of low-temperature heat from the gasification plant, and that such heat can be of particular use in a mill employing closed-cycle operation. It is pointed out that a simple gas turbine cycle with process heat recovery can be a better alternative than a combined cycle in a mill with a large heat demand.

GIBBSGAS, a chemical equilibrium model of a gasifier was developed to be used in the analysis of pulp and paper mill energy systems with black liquor gasifica tion. (Berglin and Berntsson 1999) The model was used to quantify the impact of important process variables — temperature, pressure, dry solids content, liquor composition, and type of oxidant — on the cold gas efficiency, on latent heat recovery, and on the fraction of sulfur found in gaseous species. The results show that for a high-temperature oxygen-blown gasifier the cold gas efficiency will typically be about 70 % based on the net heating value of the black liquor solids. The most important process variables which affect the cold gas efficiency are dry solids content and gasifier temperature. At moderate to high pressures a consider able share of the latent heat of water in the gas can be recovered as steam suitable for the pulping process. The model is not in itself sufficient to guide the design of the gasifier, but it gives important information on how the system downstream is affected by changes in the gasifier process conditions, e g. Figure 12.3 shows the split of sulfur in the black liquor between the gas and the smelt leaving the gasifier.

100%

65%DS Oxygen 75%DS — 85%DS

Oxygen-Blown Gasifiers (950°C)

PRESSURE (bar)

Figure 12.3 Fraction of sulfur in the black liquor solids that leaves in the gas phase, mainly as H2S . Calculated with the GIBBSGAS model (Berglin and Berntsson 1999).

67 A high pressure in the gasifier allows excess heat from the gasifier to be recovered at high temperatures, i.e. as process steam. Figure 12.4 shows that at a gasifier pressure of 15 bar more than half of the heat can be recovered as low pressure steam. At higher pressures a large fraction can be recovered as medium pressure steam. Heat at temperatures lower than low pressure steam can, e g., replace low pressure steam in boiler feedwater preheating or be used to heat white liquor to the digester.

(MW) (GJ/ADt) 70 - 6 Heat to 40°C Heat to 120°C ILP Steam IMP Steam

1 (MISTRA Ref Mill) 0 2 5 10 15 20 25 30 35 40 45 50 Gasifier Pressure (bar)

Figure 12.4 Heat recovered in the syngas cooler as a function of the gasifier pressure. Calculations for the KAM 1000 ADt/d reference mill with a high-temperature gasifier and quench cooler (Stigsson and Berglin 1999).

A detailed pinch analysis with heat exchanger network design showed that the only pinches in the system are caused by the utilities (Berglin and Bemtsson 1998a). If weak wash and condensate are to be heated before the quench they should be heated to the cold pinch temperature of the desired utility level in the waste heat boiler. Gas reheat improves the electric efficiency of the system by up to 6 %, but leads to a small decrease in the total CHP efficiency. Similarly, oxygen-blown systems will increase power generation. The gain in power output is on the order of 10 %. The study showed that manageable heat exchanger networks can be designed to meet the targets outlined by the pinch analysis, Figure 12.5.

68 ^\\\\\\\\\\\\^^^ 54 MW 42 MW

220

200

180

160

140 4 bar steam

120

100

0 Q (MW)

Figure 12.5 The amount of steam available from the syngas cooler can be increased by appropriate heat exchange between green liquor and weak wash (Berglin and Berntsson 1998a).

Gasification systems will include new low-to-medium temperature heat sources, and it is attractive to integrate these sources well with heat sinks in the mill to further reduce steam and cooling water use. The potential for process integration in the chemical recovery loop, including the digester, was examined by Berglin and Berntsson (1998b). Using pinch analysis, two opportunities were identified which could increase the amount of steam available for operations outside this loop. In the evaporator plant, a relatively simple arrangement with five flash tanks to pre-evaporate black liquor, using heat from the gasification plant, could reduce steam use by about 25 % or 0.8-0.9 GJ/ADt in a design suitable for retrofit. The capacity could possibly increase, by 7-8 %, but it is likely that this will be coun teracted by reduced heat transfer coefficients. In the digester area, heating of white liquor with heat from the gasification plant, could reduce steam use by about 0.6 GJ/ADt. Either of the two alternatives could be designed to use all of the excess low-temperature heat from the gasification plant studied, and they are therefore mutually exclusive.

There are currently 21 kraft mills in operation in Sweden, black liquor being fired in 33 recovery boilers. In 1997, the total kraft pulp production amounted to 6.3 million tons (FAO, 1999). In order to estimate the amount of electricity that could be generated from black liquor in the future, it is desirable to attempt a prediction of how much black liquor will be available and at which rate existing recovery boilers could be expected to be replaced, either with new boilers or with gasifiers.

69 Figure 12.6 shows how kraft pulp production in Sweden has increased since 1965. The growth in production is approximately linear over longer periods of time, although the influence of the 5-7 year long business cycles is evident. An attempt has been made to estimate future production levels by assuming that the average future growth will be equal to the average growth between 1965 and 1997, i.e. about 95000 tons/year. This assumption leads to a projected total production of approximately 9.5 million tons in the year 2025.

There are of course uncertainties in extrapolating this far into the future. For example, it can be assumed that some of the growth in kraft pulp production is due to conversion from sulfite pulping to kraft pulping, a change that took place mostly in the years 1965-1980. Between 1975 and 1990, production of mechani cal pulp grew almost twofold, presumably to some extent at the expense of invest ments in kraft mills. Nevertheless, basing the prediction on other assumptions such as total growth for chemical pulps (including sulfite) or on the slower growth in more recent years does not change the prediction by more than 10 %. An accu racy of this order is sufficient for the present purpose.

As is evident from Figure 12.6 production of unbleached kraft pulp has been relatively constant throughout the 1965-1997 period, and based on the linear growth assumption above, production of unbleached pulp would be expected to remain at close to 2.4 million tons per year. As a consequence, the entire growth in production would be expected to fall on bleached pulp, leading to an estimated production rate of approximately 7 million tons per year of bleached kraft pulp in the year 2025.

Figure 12.7 contains an estimate of black liquor production rates based on the pulp production estimates. The specific black liquor production rate (expressed as tDS/ADt) can vary widely between different mills, but for the simplified analysis here was assumed to be a constant for each pulp category. The values used were 1.7 tDS/ADt and 1.2 tDS/ADt for bleached and unbleached pulp, respectively. The error introduced by these assumptions is estimated to a maximum of 15 %. The corresponding energy content was estimated by assuming a lower heating value of 12 MJ/kgDS for all the black liquor produced, which should fall within 5 % of the actual value. Based on these assumptions, the 1997 black liquor pro duction was about 10 million tons of dry solids, corresponding to an energy content of 120 PJ (33 TWh), which is close to the value based on information from the mills (NUTEK, 1998).

70 Kraft Pulp Production (5wed an)

1965 1975 1975 1980 1955 19HD 1095 2DOO ZD95 3D 1U 2015 jOliO 2035

Figure 12.6 Annual production of bleached and unbleached kraft pulp in Sweden. Historical data 1965-1997 from (FAO, 1999). Projection based on assumption of linear growth.

Estimated Black Liquor Production (Sweden!

£ ;oa) ido QEr O Cr=1

Figure 12.7 Annual black liquor production estimated from pulp production in Figure 12.6 and assuming an average of 1.7 tDS/ADt (bleached pulp) and 1.2 tDS/ADt (unbleached pulp). Energy content estimated from assumed average lower heating value of 12 MJ/kgDS.

Based on the calculations of design-point performance for BLGCC and advanced recovery boiler systems as presented in Berglin et al (1999), the total potential for electricity generation from black liquor in Sweden was estimated. Figure 12.8 shows that the ultimate potential in the year 2025 is about 16 TWh via BLGCC with advanced gas turbines.

71 Pole mini for Electrify Generation from Black Liquor (Sweden) 20 20 — — Max Pciinniiai OL.Clf r IS 16 " Men PutarflaJ Mew Reonwy BalMm te Curreii Pjbed wary BollMI 16

14 14

% 12 j 12 2 EU to t 10 OH ? 5 . ^ —- 8 v ..." E 6 6 J£u Lit — d 4 4 2 2

i9/i. imo i&as i otio ims ;md 2004 2010 201 & 2020 202s 20:1(1 2031. ?oio

Figure 12.8 Potential for electricity generation from black liquor in Sweden, based on the estimated black liquor production in Figure 12.7.

72 13 Flexible and Efficient Biomass Energy Systems in the Pulp Industry and opportunities for Efficient Use of Biomass in the Pulp and Paper Industry

Two licentiate theses by Katarina Maunsbach and Anna Isaksson, KTH (1999 and 2000)

13.1 Introduction The licentiate theses have five main topics:

• Energy consequences of increased pulp yield (through e.g. polysulfide cooking) • Technologies for power production using waste heat • Power generation with black liquor gasification using advanced gas turbine technologies • Transportation fuel production coupled to black liquor gasification (energy efficiencies and opportunities for greenhouse gas reduction) • Energy balances for market pulp and paper mills

The three first topics were performed as part of the KAM programme (KAM, 2000). Some parts of this work, especially the opportunities with polysulfate cooking, are therefore reported in Chapter 11. The topic on technologies for power production using waste heat is not connected to black liquor gasification. Therefore the third, fourth and fifth topics are reported in this chapter.

The description of basics, conditions etc, are common for the thesis, the results in 13.3-13.5 are from Anna Isaksson and 15.6 is from Katarina Maunsbach.

13.2 Power Generation Using advanced Gas Turbine Technologies Increasing closure of the pulp mills will result in a reduced process steam demand. This gives an opportunity to use the biofuel for increased power production. Several studies have shown that black liquor gasification in combination with combined cycles increase the power production significantly compare to the traditional recovery process used today (Berglin and Berntsson, 1997; Larson et al., 1998a; Maunsbach et al., 1999a). It is of interest to investigate the potential of

73 power production when the new generation of gas turbine systems is applied together with black liquor gasification.

In Figure 13.1, the basic configuration of the STIG cycle is shown. The STIG cycle involves a preheater, and a steam boiler to produce process steam. A part of the steam is overheated in a superheater to be injected in the high pressure area of the gas turbine. This configuration enables higher efficiencies than the simple gas turbine cycle. For cogeneration of power and heat, steam can partially be drawn off to be used in the process. STIG has the advantage over a combined cycle, in having a lower investment cost because steam turbines are not needed. This makes it suitable for smaller installations. It also has a flexibility with regard to variations in the heat load, which makes it suitable for integration into pulp mills. The STIG cycle is already a commercially available technology.

Compressor Expander

<°J Combustor r r Air Fuel Steam Superheat i

Process.____ steam Preheater and steam hntler Water Exhausts

Figure 13.1 The configuration of a STIG cycle.

13.3 Potential Power Production Using Black Liquor and Bark The base case is the reference mill where a conventional recovery boiler and a bark boiler connected to a back pressure turbine and condensing steam turbine are used for steam and power production. In the first case, a black liquor gasifier re places the recovery boiler and the bark is gasified in a biomass gasifier. A STIG cycle and a Combined Cycle (CC) has been compared using gasified black liquor and bark as fuel. Here, only half of the bark has been used to fuel the gas turbine since the other half is used in the lime kiln as in the reference mill.

In the future, the pulp mill steam demand will probably decrease due to increased closure, an improved heat exchange network and changes in process design. Therefore, different cases have been simulated where the steam demand has been decreased compared to the reference mill. In case A, the steam demand is kept at the reference mill level, in Cases B and C it is decreased by 25 % and 50 %

74 respectively. In the case of the CC, the steam data in the HRSG is 60 bar and 450oC and for the case of the STIG cycle it is 30 bar and 450oC. The results of the simulated cases are shown in Table 13.1. The results of Table 13.1 are based on a pulp production of 2000 ADt/d.

As shown in Table 13.1, only the STIG cycle (case A) can generate enough steam to satisfy the mill steam demand. The CC system requires a reduction in steam demand, presumably by way of process integration and new technologies. If using a CC system, the steam data in the HRSG must be lowered to 14 bar and 268 oC in order to fulfill the steam demand. This indicates that it would be more appropriate to use some kind of gas turbine system with a process steam generator instead of a steam turbine (Maunsbach et al., 1999b). The lower power efficiencies obtained for the STIG cycle can be explained by a higher heat loss with the exhaust gas as it contains more water.

Table 13.1 Comparison of CC and STIG cycle integrated with a BLG.

System Ref. Mill B2 C3 A1 B2 C3 CC CC STIG STIG STIG Fuel Input 4 (MW)/(GJ/ADt) 581/25.1 581/25.1 581/25.1 581/25.1 581/25.1 581/25.1 Process Steam (MW)/(GJ/ADt) 231/10.0 174/7.5 116/5.0 231/10.0 174/7.5 116/5.0 Power Production 117/1400 187/2236 204/2447 158/1895 177/2118 194/2327 (MW)/(kWh/ADt) Power Surplus (MW)/(kWh/ADt) 55/660 125/1496 142/1707 96/1155 115/1378 132/1587 Steam Injection (water/air inlet%) 0 0 0 1.9 9.8 20 Power Eff (%) 20.1 32.1 35.1 27.2 30.4 33.4 Total Eff. (%) 59.8 62.0 55.0 67.0 60.3 53.3 1) The reference mill steam demand is produced 2) The reference mill steam demand is reduced by 25 % 3) The reference mill steam demand is reduced by 50 % 4) The energy content in black liquor and bark based on LHV

Equipment price levels for the gas turbines are US$ 357/kW for LM 2500 STIG. The turnkey plant equipment cost is for the combined cycle based on LM 2500 US$ 800k/W (Gas Turbine World, 1998-1999)

13.4 Transportation fuel production with black liquor gasification Cogeneration of biomass fuel, power and heat from gasified black liquor has been studied. The potential production of three different transportation fuels, i.e. metha nol, biomass-based diesel and hydrogen has been investigated. The simulations

75 have been performed in ASPEN PLUS™ Engineering Equation Solver (EES). Brief descriptions of the processes are given below.

Case 1: Methanol Production Methanol is the simplest alcohol, containing one carbon atom. It is a colourless, tasteless liquid with a very faint odor and is commonly known as “wood alcohol ”. Methanol is one of a number of fuels that could substitute for gasoline in passen ger cars.

The simulated methanol reactor is based on a commercially available technique, the Air Products & Chemicals ’ Liquid Phase Methanol Reactor, LPMEOH™ (Tijm et al, 1997). In the reactor, there are two reactions taking place: a shift reaction (Eq. 13.1), and the methanol synthesis reaction (Eq.13.2). The heat evolved in the methanol synthesis is utilized to generate LP steam.

CO + H2O ^ ^ CO2 + H2 Water Shift Reaction (13.1)

CO + 2H2 ( ^ CHj OH Methanol Synthesis Reaction (13.2)

After the methanol reactor, the gas is cooled and flashed to separate the liquid methanol from the unreacted gases, which are then used for power and steam generation in a gas turbine HRSG system.

Case 2; Diesel and Fuel Oil Production Just like fossil diesel, biomass-based diesel operates in compression-ignition en gines, and essentially no engine modifications are required. The use of biomass- based diesel in a conventional diesel engine results in substantial reduction of unbumed hydrocarbons, carbon monoxide, and particulate matter (National Bio diesel Board, 2000). In Fischer-Tropsch conversion, hydrocarbons are synthesized from carbon monoxide (CO) and hydrogen (H2) using iron- or cobolt-based catalysts/Eq. 13.3).

CO + 2H2< CH2- +H20 Fischer-Tropsch Reaction (13.3)

The reaction is exothermic and the heat evolved is used for LP steam production. The products out of the reactor consists of a mix of different paraffins with vary ing molecular weight. By distillation, this mixture may be separated into fractions according to their boiling point intervals: light hydrocarbons (naphta), diesel oil and waxes. Here, two cases are studied: case 2A, where only the diesel oil is used as a substitute for fossil diesel; and case 2B, where in addition naphta and waxes are considered as replacement for fossil fuel oil. Unreacted gases leaving the Fischer-Tropsch reactor are used for steam production.

Case 3: Hydrogen Production Hydrogen can be extracted from the synthesis gas by water shift reaction (Eq. 13.1). The hydrogen is then separated from the gaseous mixture by Pres

76 sure Swing Adsorption (PSA). In this process the unreacted gases have a lower energy content as compared to the cases of methanol and diesel production. Two cases are therefore studied; case 3 A, where the gases are used for power and steam production and case 3B, where only steam is produced.

The three cases with cogeneration of fuel, power and steam have been compared to the original reference mill, and a reference mill utilizing Black Liquor Gasifica tion Combined Cycle (BLGCC). Both the reference mill alternatives deliver a power surplus.

Results from the system performance simulations are summarized in Table 13.2. The calculations are based on LHV of the black liquor and the transportation fuels. The net process steam production represents LP and MP steam production. In the gasifier, steam at 2 bar can also be produced.

Table 13.2 Cogeneration performance results for a pulp production of 2000ADt/d

System Case 1 Case 2 - Paraffins Case 2 - Hydrogen

A Ba A B - Methanol - Diesel - Diesel - Power - Steam and fuel oil and Steam Only Fuel Input 6 (MW)/(GJ/ADt) 507/21.9 507/21.9 507/21.9 507/21.9 507/21.9 Transportation Fuel Production 156/6.7 86/3.7 181/7.8 262/11.3 262/11.3 (MW)/(GJ/ADt)

Net Process Steam Production 240/10.4 234/10.1 234/10.1 142/6.1 223/9.6 (MW)/(GJ/ADt)

Net Power Production 0 33/396 27/324 27/324 -7A84 -44A528 (MW)/(kWh/ADt) (-29A348) (-35/-420) (-35/-420) (-69A828) (-106/-1272) Product Efficiency0 (%) 37.3 22.3 41.0 50.3 43.0 Overall Energy Efficency® (%) 84.6 68.4 87.2 78.3 87.0

In addition to the diesel produced, case 2 also yields around 28 MW naphta and 67 MW waxes. Case 2 B includes those products. The black liquor/transportation fuel energy content based on LHV. The numbers in parenthesis include the pulp and mill power demand of 62 MW. The products are defined as the transportation fuel, and net power produced. Product efficiency is then defined as the energy content in these products divided by the black liquor energy content (LHV). Overall efficiency defined as the energy content in the transportation fuel, net power, and net process steam produced divided by the black liquor energy content (LHV).

In addition to the transportation fuel produced, cases 1 (methanol) and 2 (paraf fins) also result in a net power production that may be used towards the power requirement of the pulping process (62 MW). However the power produced is not sufficient to meet this power requirement. Cases 3 A and 3 B (hydrogen) do not produce enough power to meet the power requirement of the hydrogen process. When including the power requirement of the pulping process, the deficiency becomes even larger. Cases 1 and 2 produce enough process steam to satisfy the

77 pulping process steam demand (230 MW). However, case 2 generate a surplus of LP steam but cannot generate enough MP steam. The reference mill excess bark (approximately 80 MW) has not been considered in the present study. This bark can be used for steam production so that enough MP steam is generated in case 2. Under these circumstances case 3B also fulfills the mill steam demand.

13.5 CO2 Reduction Transportation fuel production via BLG will reduce the potential for power pro duction. Whether it, from a greenhouse gas emission ’s point of view, is best to generate biomass-based power or transportation fuel depends on the mode of power generation that would be replaced by the biomass-based power.

Hence, a comparison of the three cases with the original reference mill, and a reference mill utilizing BLGCC has been carried out. For this comparison, it is assumed that the power replaced originates from a 50/50 mix of natural gas com bined cycle (NGCC) and coal-fired condensing power plant. With this mixture, the CO2-emissions are approximately 618 kg CO2/MWh el (Audus, 1993). As Swedish nuclear power is being phased out, it is realistic to assume that such a 50/50 mix will be used to replace it, unless there is an increase in biomass-based power generation in the future.

To quantify how much kg CO2-reduction is obtained by replacing conventional transportation fuel with the biofuel from the present study, the following assumptions have been made:

• The methanol is used as gasoline replacement in a conventional Otto engine, and the ratio of the volume of methanol to the volume of gasoline for a certain driving distance is about 1.7. • The ratio, on an energy basis, of biomass-based diesel to conventional diesel is 1.0 and is used in a diesel engine • The hydrogen is used in a fuel cell vehicle (FCV) with a “fuel-to-shaft ” efficiency, n FCV=50 %. A hydrogen-fuelled FCV will replace a conventional gasoline fuelled vehicle with an efficiency n GFV=25 %.

In addition, the CO2-emissions when combusting one liter of gasoline and one liter of diesel are 2.35 kg CO2/l and 2.60 kg CO2/l, respectively. In case 2B, the paraffins produced (except diesel) are assumed to replace fuel oil. The CO2- emissions from fossil fuel oil are 74 g CO2/MJfuel. Figure 13.2 shows the CO2- reductions obtained for the different cases. The results are given per tonne air dry pulp produced to allow for easy applicability to mills of different sizes.

78 2000 □ Reduction due to transportation fuel (and fuel oil in Case 2B)

□ Reduction due to power surplus

□ Total reduction

Figure 13.2 Comparison of the C02-reduction (kg C02/ADt pulp) for the different cases.

Here the power produced replaces a 50/50 mix of natural gas and coal. A power production totally based on coal would increase the C02-reductions for the reference mill and BLFGCC cases, and decrease it for cases 1-3.

Figure 13.3 shows the total C02-reduction on a national basis. In Sweden the total C02-emissions are 60Mt/year. If all Swedish chemical pulp mills with a produc tion level of 6.6 MADt pulp/year would apply the systems simulated herein, the C02-emissions could be reduced by 4 % for case 1 (methanol) and by 15 % for case 3 A (hydrogen). Case 2A (diesel) would not give a significant contribution to the C02-reduction. However, Case 2B (diesel and fuel oil) gives a C02-reduction of around 3.5 %. The reference mill, with its power surplus, would give about the same effect as in the case of methanol production. If a BLGCC would be inte grated into the reference mill the contribution to C02-reduction would increase to about 7 %. For the case of United States, with a chemical pulp production of 45 MADt/year, the reduction in case 3 A would only represent a little more than 1 % of the US total C02-emissions (5490 Mt C02/year).

79 Figure 13.3 Total C02-reduction on a national basis.

The results show that there is a good potential for cogeneration of biofuels, power and heat by means of black liquor gasification. Overall efficiencies ranging from 65 to 87 % (based on the black liquor and transportation fuel LHV) have been obtained. This should be compared with the traditional recovery boiler that has a total efficiency of around 60-65 %. Even in the case of a black liquor gasifier with power and steam generation in a combined cycle, the total efficiency is about the same as for the recovery boiler (Maunsbach et ah, 1999a). In the cases of methanol, and diesel and fuel oil, a steam surplus is generated. If steam would be produced just enough to fulfil the reference steam demand the total efficiency decreases to 83 and 86 %, respectively. However, the extra steam could be used in the paper mill in the case of an integrated pulp and paper mill.

Hydrogen production is the case that results in the largest C02-reduction, with a reduction of almost 15 % (case 3 A) based on Swedish total C02-emissions. The large fuel production on an energy basis (MW), and the high “fuel-to-shaft ” efficiency in FCV can explain this. However, in case 3A, the pulp mill steam demand is not fulfilled. Case 3B is therefore more realistic. The C02-reduction is then 12 % and the steam demand is supplied by using the excess bark. Diesel production gives the lowest C02-reduction. However, in this case, biomass-based fuel oil is also produced, which if used to replace fossil fuel oil will also contribute towards additional C02-reduction as the reference mill.

80 13.6 Comparison of combined Cycle and Steam-Injected Gas Turbine Cycle The combined cycle (CC) is compared to the STIG cycle with constant biomass intake and varying steam demand. By reducing the process steam demand, the amount of steam available for use in the condensing turbine in the combined cycle is increased. An alternative use of excess steam could be to increase the steam injection in the STIG cycle. The energy demands of the reference kraft pulp mill and the integrated pulp and paper mil are based on the KAM reference mills, see Chapter 11 and the thesis of Katarina Maunsbach.

Integration in a Kraft Pulp Mill Three different steam demand levels are considered. The steam demand levels are considered. The steam demand is reduced to three quarters of the reference pulp mill steam demand and half of the reference pulp mill steam demand. When using the combined cycle, the process steam generation cannot be kept at the reference pulp mill steam demand level and still generate steam in the HRSG at the level of 60 bar and 450oC. However, in the case using a STIG cycle, it is possible to satisfy the process steam demand by lowering the amount of steam injected.

The next power efficiency is somewhat higher for the combined cycle compared to the steam injected gas turbine. This caused by an increased heat loss with the exhaust gas that contains higher water content in the STIG case. The surplus of power for the cases and the reference kraft mill steam demand, together with the cases for the integrated pulp and paper mill, are shown in Figure 13.4.

Integration in an Integrated Pulp and Paper Mill The steam demand is, in this comparison, either almost the same as the reference integrated pulp and paper mill level, or reduced to the level where it is possible to deliver the required process steam in the combined cycle, keeping the steam data in the HRSG at the level of 60 bar and 450oC. In the case with steam demand being the same as in the reference mill, no steam injection is possible since all the flue gas heat is needed for process steam production. It was found that the use of a STIG turbine was not possible in this case. Instead, a gas turbine without steam injection is needed. The results are shown in Figure 13.4.

The surplus of power for the cases different cases versus the variation of the reference pulp and paper mill steam demand, together with the cases for the kraft mill, are shown in Figure 13.4.

81 140U eve Inn mill S3 STIG t>cle trail itiiU □ STIG IniEgintd mil D C V IniajpaiEd imU HKifcTcuie krafl null □ RtfertTL'c diicgntcti mil

Figure 13.4 Steam demand vs. power surplus in the kraft pulp mill and the integrated pulp and paper mill.

As shown in Figure 13.4, the STIG cycle system has better characteristics for increasing the power production, while keeping process steam demand constant compared to the combined cycle system.

82 14 Synthesis of earlier work

Process integration Eva Andersson: Process Integration between the BLG plant and the mill has been studied. No studies have been carried out on opportunities for process integration in the mill for a better match of the total fuel needed in the combined plant. The KAM2 reference mill has been used in all calculations.

Gunnar Modig: Different levels of steam demand in the mill are studied but no calculations technically or economically, on how to achieve these levels were carried out.

BLGMF: No process integration studies have been carried out for the mill. The KAM2 reference model has been used.

Hakan Eriksson: No process integration studies have been carried out. The calcu lations are based on a Swedish average market pulp and pulp and paper mill, respectively.

Eric Larson: All calculations are based on a pulp and paper mill with 10 % less steam consumption then today ’s US average.

KAM: The KAM reference mill has been used as a base and no process integration studies have been performed.

Niklas Berglin: Detailed process integration between BLGCC and a mill has been performed. No studies, however, have been carried out on optimal levels of pro cess integration within the mill when BLGCC is introduced.

Anna Isaksson, Katarina Maunsbach: The same approach as Gunnar Modig

It can be concluded that process integration has not been a major part in the studies (except for Niklas Berglin). Integration between the BLG and the mill and needs/benefits of reducing steam consumption in the mill when introducing a BLG have been studied in some but optimal levels of steam reduction and how to achieve this has not been included.

System consequences Eva Andersson: Energy regarding results of energy balance calculations for several different system solutions and comparisons between hydrogen and recovery boiler, BLGCC, BLGMF (methanol) and hydrogen (including need for imported biomass fuel) from biomass standalone plants are included.

83 Gunnar Modig: The main comparisons are on system consequences technically and economically (including need for imported biomass fuel) when introducing a BLGCC compared with a recovery boiler. Also reliability and availability of the new versus the traditional technology are also studied and quantified.

BLGMF: Different motor fuel products and balances, needs for imported biomass fuel, etc, are studied in detail for different system solutions and conditions.

Hakan Eriksson: The project has mainly dealt with system consequences of alternative use for electricity production of a restricted amount of biomass fuel (internal in the mill and external) in a BLG plant or in CHP plants in society.

Eric Larson: Energy balances for different system solutions of BLG and recovery boiler including alternatives including effect on these and on wood consumption of polysulfide cooking are included. Also regional and national impacts have been discussed.

KAM: Energy balances for both market pulp and pulp and paper mills have been discussed. Consequences of polysulfide cooking are included. Different system solutions of BLGCC and recovery boiler systems are included, including effects of possible future improvements of both these technologies.

Niklas Berglin: Conventional and advanced recovery boilers have been compared with BLG Systems for electricity production. Furthermore, an estimate of the Swedish potential for electricity production with BLG has been performed at different assumptions for future conditions.

Anna Isaksson, Katarina Maunsbach: Comparisons have been done between an advanced gas turbine cycle (STIG) and a conventional one in a BLGCC. Conse quences of production of methanol, diesel or hydrogen.

It can be concluded that energy balances, needs for imported biomass fuel, etc, for different system solutions have been well covered in the projects. The conse quences of polysulfide cooking is discussed in three of them but the important aspects of reliability and availability are only discussed in one report. The base for comparisons (reference mill, etc, see under Process Integration) and system solutions are partly different, which makes direct comparisons difficult.

More advanced gas turbine cycles have only been discussed in two reports. From then it can be concluded that the STIG cycle seems to have a higher electricity efficiency than the combined one.

With polysulfide impregnation wood consumption can be reduced (3-4 %) and electricity output can be increased.

84 The total potential for electricity production in Sweden from BLG including imported fuel depends highly on the assumptions made, but in the reports levels between 16 and 21 TWh/a have been mentioned.

Product or mix of products from a BLG plant Eva Andersson: Hydrogen production in a BLG and comparisons with electricity, methanol and hydrogen biomass standalone production are discussed. So far the global environmental aspects (CO2 mitigation) have been included but studies on economic consequences are now carried out.

Gunnar Modig: Electricity production in a BLGCC compared with a recovery boiler is mainly discussed. Some cost calculations of DME/methanol production is carried out but no comparisons with BLGCC have been carried out.

BLGMF: Different motor fuel products have been compared, i.e. methanol, DME and Fischer Tropsch diesel.

Hakan Eriksson: Only BLGCC systems have been considered.

KAM: Same as Eriksson. (In KAM system studies with methanol production were performed, but the results were very similar to the ones reported in the BLGMF study and therefore not included in Chapter 11)

Niklas Berglin: Only electricity production through BLG has been included

Anna Isaksson, Katarina Maunsbach: Both electricity production and motor fuels (methanol, diesel or hydrogen) have been studied.

Most projects have dealt with either electricity or motor fuel production. Only in two projects comparisons between electricity and motor fuel productions have been made (Eva Andersson and Anna Isaksson). Comparisons between different motor fuels have been carried out in Gunnar Modig's, Eva Andersson ’s, the BLGMF and Anna Isaksson ’s project.

Different bases and conditions for comparisons in the different projects makes it impossible to make comparisons between the results in the reports without detailed further calculations and studies. Conditions for energy prices, policy instruments etc, have a very high influence on the results.

Environmental aspects Eva Andersson: Global CO2 consequences for both BLGCC and different motor fuels (including hydrogen) have been studied.

Gunnar Modig: Some aspects of SOx, NOx and HCC are discussed but CO2 mitigation is not included.

85 BLGMF: No explicit discussions of environmental consequences are included.

Hakan Eriksson: The aim has been to maximize the electricity production for a given amount of biomass, i.e. no direct CO2 consequences are included

Erik Larson: Studies of several consequences, i.e. SOx, NOx, CO, VOC, PM, TRS (total reduced sulphur) and, not the least, CO2 are included.

KAM: No explicit discussions on environmental aspects are included.

Niklas Berglin: No detailed studies on environmental consequences are included.

Anna Isaksson, Katarina Maunsbach: Consequences of CO2 emissions when producing different motor fuels are analyzed.

The global environmental consequences of BLG, i.e. CO2 mitigation, are included in several of the studies but in some of them no attentions to these aspects have been paid. The studies have shown that substantial reduction in CO2 emissions can be achieved by using BLG but that the system boundary and external mar ginal electricity production technology play important roles for the results. Under some conditions it will be more advantageous from an environmental point of view to export biomass to society for use in CHP plants than to use it internally for electricity production.

When producing transport biofuels, the total Swedish CO2 emissions can be reduced by 4 % (methanol production) up to 15 % (hydrogen production).

Local environmental aspects, e.g. SOx and NOx, are discussed in two of the reports.

CO2 Capture (CSS) Opportunities for CO2 sequestration in pulp and paper mills have not been dis cussed in any of the reports.

Economy Eva Andersson: Economic comparisons of different system solutions and products are so far not available but are included in the ongoing work in this project.

Gunnar Modig: Detailed economic comparisons between BLGCC and recovery boiler have been carried out. Also some calculations on possible future costs for DME/methanol production are included, but no specific discussions of impacts of possible future policy instruments.

BLGMF: A major part of the study is directed towards economic comparisons between different motor fuels. Possible future alternative policy instruments are a part of the study.

86 Hakan Eriksson: No economic calculations or comparisons are included.

Eric Larson: Detailed studies of the economy for different alternative BLGCC and recovery boiler systems are included. A part of the studies deal with economic consequences as a function of how quickly the BLG concept can be introduced in the pulp and paper industry. No discussions on consequences of different future policy instrument are included.

KAM: Detailed studies on investment and operation costs are included for BLGCC and recovery boiler systems. From these reasonable electricity production costs with BLGCC have been calculated.

Niklas Berglin: Economy has not been included

Anna Isaksson, Katarina Maunsbach: Same as Hakan Eriksson

Economic aspects have been extensively studied in several of the projects. How ever, the importance of how policy instruments are introduced in the future is only studied in one of the projects (BLGMF).

The results concerning possible economic advantages of using BLG depend to a high extent on the conditions chosen, such as energy prices, future costs for CO2 emissions, annuity factor level and investment costs. It is therefore, as for other aspects discussed in this chapter, impossible to draw general conclusions of the results and make comparisons between different reports, types of BLG products, etc without going into more detailed calculations and studies. The reports, how ever, form an excellent base for further such studies as they contain very valuable and important information on technical, economic and environmental characteris tics for different system solutions with BLG.

Based on assumptions used in the projects, it can be concluded that the investment cost for BLGCC is considerably higher than for an RB. According to Chapter 7, the investment cost is estimated to be approximately 550-600 MSEK higher in both KAM (2003) and Eric Larson et al (2003). The higher efficiency makes it possible, however, to produce electricity in a BLGCC to a cost of 0.11-0.28 SEK/kWh (according to KAM (2003)).

According to BLGMF II (2005) it should be possible to produce motor fuels to a price of 2.4 - 2.8 SEK/l, depending on the type of fuel. Calculations by Gunnar Modig (2005) showed that methanol can be produced at a cost of 7 SEK/l gasoline equivalent. The latter figure is based on a much higher annuity factory than the BLGMF one (0.2 compared with 0.11) and with some other assumptions that make them not directly comparable.

87 88 15 Need for Further Work

Process Integration One of the important aspects of BLG, both economically and environmentally, is the steam balance for the mill, i.e. the amount of excess internal biomass available for upgrading to electricity or motor fuels. When introducing a BLG, the optimal level of process integration, i.e. energy efficiency, in a mill, will most probably be higher than in a plant with recovery boiler. The reason is that thereby more inter nal biomass can be used and the production capacity of the BLG can be increased and/or the amount of imported biomass can be decreased.

This means, in turn, that the economy for a BLG can be improved considerably with increased process integration in a mill. For example, according to the results of the BLGMF project, the total potential for methanol production in Sweden via BLG is approximately 20 TWh/year but 20 TWh/year biomass must be imported to the mills. With a higher degree of process integration and using potentials from the KAM programme, 5-10 TWh/year of the imported biomass could be saved and the economy for methanol production would be improved. Important im provements would be achieved also for production of electricity, DME, hydrogen and diesel.

These aspects have so far not been studied. The knowledge of process integration methods of opportunities in pulp mills and of BLG systems should be combined in further research.

System Consequences Several system consequences have been studied. There are, however, several other areas of interest to study, which are discussed below.

Cogasification of black liquor and biomass is important in systems needing imported biomass for the steam balance. By cogasification the output from the gasification plant, both in terms of products(s) and heat, can be increased and thereby the necessary steam can be produced. This aspect should be studied both on technical and system levels. The technical problems can be high when mixing these two types of biomass both in terms of gasification conditions, kinetics, etc and of achieving an appropriate liquor to be reused by the mill.

Energy combines with other types of industry should also be looked into. One example of an energy combine would be to use BLG for production of a motor fuel (methanol, DME, diesel, hydrogen) and use the cellulose content of the wood for production of ethanol instead of pulp. There should be high opportunities for energy efficiency and thereby in economy in such a combination of motor fuel production.

89 The consequences and opportunities of using BLG in integrated mills (pulp and paper production) should be further explored. In Niklas Berglin ’s and Katarina Maunsbach ’s projects these aspects have been partly studied but there is much more to be done in this area. This is important for future considerations of this technology, as there is a development towards more integrated mills.

Another important area is the most rational usages of biomass in Sweden under different future conditions. In system studies on an aggregated system level on this topic, BLG should be included as one of several options and be evaluated and compared with other ways of using biomass in different future scenarios.

Product or mix of products The most rational way of using BLG, electricity or motor fuel production, for different future conditions have been studied in some of the projects but new knowledge of electricity certificates, CO2-trading, voluntary agreements (FPE), etc have not been taken into account properly. Studies at different future scenarios should be performed in a more systematic way.

The knowledge of differences technically, economically and environmentally of producing different motor fuels should be improved through system studies.

Environmental aspects The environmental consequences of using the excess biomass internally via BLG or export for use in society have been studied for some special conditions but an improved knowledge on this is important for our understanding of how this biomass should be used in the future. Studies at different future conditions and scenarios should be carried out.

Another area for further studies, also mentioned above, is the rational use of this biomass internally, electricity or motor fuel production, and the global environ mental consequences of this.

CO2 Capture (CCS) With BLG a part (methanol, DME, diesel) or practically all (hydrogen) of the CO2 could be removed from the system prior to the use of the product, i.e. in the gasifi cation stage. This important environmental aspect has not been looked into so far. Further studies in this area should be carried out. Such studies should include transport (infrastructure) and storing of CO2.

Economy Although economy has been an important part of several of the projects, the importance of future policy instruments and how they are introduced should be studied further. The future of the BLG technology will to a high extent depend on policy instruments and on future energy prices. The knowledge on how these parameters influence the economy should be further studied and different future scenarios should be used in these studies.

90 References

Andersson E, Harvey S, “Comparison of pulp-mill integrated hydrogen production from gasified black liquor with stand-alone production from gasified biomass ”, Proceedings of ECOS 2005, 3 pp. 1131-1138. ISBN/ISSN: ISBN 82-519-2041-8, 2005;

Andersson E, Harvey S, “Pulp-mill integrated biorefineries: a framework for assessing net CO2 emission consequence ”, Proceedings, AIChE 2004 Fall Annual Meeting, Nov 7-12, 2004, Austin, Texas, USA, pp. p 203-208, 2004;

Andersson, E, Harvey S, “System analysis of hydrogen production from gasified black liquor”, Proceedings of the 17th International Conference on Efficiency, Cost,Optimization, Simulation and Environmental Impact of Energy and Process Systems, ECOS 2004, Guanajuato, Mexico July 7-9, 2004 , Edited. by R. Rivero et al., pp. pp 1435-1445. ISBN/ISSN: 968-489 027-3, 2004;

Audus H, “Green Gas Releases from Fossil Fuel Power Stations ”, IEA Greenhouse gas R&D program, IEAGHG/SR1, Cheltenham, 1993;

Berglin N, “Pulp Mill Energy System with Black Liquor Gasification - a Process Integration study”, Lic thesis, Chalmers University of Technology, Division of Heat and Power Technology, Goteborg, 1996;

Berglin N, Berntsson T, “Thermodynamic Model and Analysis of Energy Conversion in Black Liquor Gasification ”, to be submitted for publication, 1999;

Berglin N, Berntsson T, ”Energisystemkonsekvenser och processintegrations- aspekter av svartlutsforgasning ” (Energy System Consequences and Process Integration Aspects of Black Liquor Gasification), Slutrapport till forsk- ningsprogram Sulfatatervinning/Svartlutsforgasning, ISSN 1103-2952, Stockholm, 1997 (report in swedish);

Berglin N, Berntsson T, ”Pulp Mill Heat Integration of Black Liquor Gasifiers”, TAPPI/CPPA 1998, International Chemical Recovery Conference, Tampa, FL, June 1-June 4, 1998;

Delin L, Berglin N, Lundstrom A, Samuelsson A, Backlund B, Sivard A, “Bleached market kraft pulp mill - Reference and type mill”, FRAM Final Report, Report FRAM 9 CW 241, Dec 2004;

91 “Ecocyclic Pulp Mill - “KAM””, Final Report 1996-2002, KAM Report A100, Stockholm, Jun 2003;

Ekbom T, Berglin N, Logdberg S, ”Black Liquor Gasification with Motor Fuel Production - BLGMF II”, Stockholm, Dec 2005;

Ekbom T, Lindblom M, Berglin N, Ahlvik P, “Technical and Commercial Feasi bility Study of Black Liquor Gasification with Methanol/DME Production as Motor Fuels for Automotive Uses - BLGMF”, Stockholm, Dec 2003;

Eriksson H, “System Aspects of Black Liquor Gasification - Consequences for both Industry and Society ”, Lic thesis, Chalmers University of Technology, Division of Heat and Power Technology, Goteborg, 2001;

Isaksson A, “Flexible and Efficient Biomass Energy Systems in the Pulp Indus try”, Lic thesis, Royal Institute of Technology, Department of Chemical Engineering and Technology, Energy Processes, Stockholm, 2000;

Larson E, Consonni S, Katofsky R. A., “Cost-Benefit Assessment of Biomass Gasification Power Generation in the Pulp and Paper Industry ”, Final Report, Navigant Consulting, Inc., Princeton University and Politecnico di Milano, 8 October 2003;

Larson E, Kreutz T, Consonni S, ”Combined Biomass and Black Liquor Gasi fier/Gas Turbine Cogeneration and Pulp and Paper Mills”, Proceedings of International Gas Turbine and Aeroengine Congress & Exhibition, Stockholm, June 2-5, 1998a;

Maunsbach K, “Opportunities for Efficient use of Biomass in the Pulp and Paper Industry ”, Lic thesis, Royal Institute of Technology, Department of Chemical Engineering and Technology, Energy Processes, Stockholm, 1999;

Maunsbach K, Martin V, Svedberg G, “Gasification of Black Liquor and Biomass in Pulp Mill for Increased Power Generation ”, Proceedings of the 6th Inter national conference on new available technologies, SPCI, Stockholm, June 1-4, 1999a;

Modig G, “Black Liquor Gasification - An Assessment from the Perspective of the Pulp and Paper Industry ”, Lic Thesis, Lund University, Department of Environmental and Energy System Studies, Lund, Sep 2005;

”Pulp and Paper Capacities, 1999 - 2004”, Food and Agriculture Organization of the United Nations (FAO), 1999;

92 Stigsson L, Berglin N, ”Black liquor gasification - Towards improved pulp and energy yields”, 6th New Available Technologies and Current Trends Conference, World Pulp and Paper Week, SPCI’99, Stockholm, June 1-4, 1999;

Tijm P J A, Brown W R, Heydorn E C, Moore R B, “Advances in Liquid Phase Technology ”, American Chemical Society Meeting, San Francisco, California, April 13-17, 1997;

93 94 Attachment: Historical development of BLG technologies

This attachment is in its entirety based on Chapter 5 in Gunnar Modig's licentiate thesis. The most recent development, after 2005, is therefore not included.

A1 Overview In the search for alternative ways of recovering the cooking chemicals, gasifica tion techniques have been thoroughly examined several times. In total more than twenty different technologies have been investigated over the years.

DARS NSP SCA-Billerud Chemrec Copeland TRI SKF Chemrec DARS SCA-Billerud TRI A Ahl Copeland ABB Weyerhaeuser Tampella Paprican VTT KBR NSP Noell UCAL Rockw Bab&Wil

1960 1970 1980 1990 2000 2005

Figure A1: Illustration of the different process alternatives which have been suggested and tested as a replacement to RB over the years.

In most of the proposed designs the recovery process was split into multiple unit operations to achieve higher energy efficiency. A number of the development efforts were only directed to non-sulfur pulp processes, like the sulphite one, which nowadays is used only by a small number of pulp producers. Technical challenges, lack of funding and poor market interest have shelved all proposed technologies with the exception of the TRI and Chemrec designs.

The following technologies have reached the demonstration scale status at pulp mills.

95 SCA-Billerud SCA-Billerud process was developed during the 1960s. The first plant was built in Sweden 1968 and was later followed by four more in Japan and the US. These plants were installed at pulp mills using non-sulfur processes.

The black liquor was injected into a downwards-flowing reactor heated with an oil burner at the top. The reactor operated below the melting point of the ash and the product gas (syngas) was burned without cleaning in a power boiler.

Copeland The Copeland recovery process was based on a bubbling fluidized bed consisting of black liquor ash and often silica sand. It was operated below the melting point of the ash but usually at stoichiometric conditions, i.e. not in reducing mode.

Some plants were built in the 1970s at sulphite pulp mills and at least one for the kraft process. The Copeland process became uncompetitive when the conventional recovery boiler's performance improved.

NSP The Swedish NSP-process (Ny Sodahus Process) was built around a cyclone gasi fier in which the reaction between black liquor and air took place under reducing conditions. The fuel gas was then fired in a boiler similar to an ordinary RB with additional air injected.

One pilot unit was built and operated for a few years in the beginning of the 1980s. Technical difficulties and lack of funding discontinued the project.

DARS The Direct Alkali Recovery Systems (DARS) used in in-situ causticizing agent (iron oxide) which was added prior to combustion. The DARS process could only be used in non-sulfur pulping as unrecoverable compounds were otherwise formed between iron and reduced sulphur.

One plant was built in 1986 with a fluidized bed combustion zone combined with a counter-current reactor for leaching the chemicals. The operation was finally shut down by the late 1990s due to the economic problems and technical difficulties.

ABB ABB developed a gasification method for black liquor during the early 1990s where the liquid was injected into a circulating fluidized bed under atmospheric or pressurized conditions. The bed material consisted of titanium compounds. The idea was to let the titanium dioxide react with sodium carbonate (Na2CO3) and form Na2O.TiO2 after the carbonate had released the CO2. The main advantage was to get a direct in-situ autocaustization without the need for a separate loop with an energy consuming lime kiln. A pilot plant was built in Vasteras, Sweden

96 and remained in operation until 1993. In 1998 the decision was taken to withdraw from further development work.

The two gasification technologies for black liquor, which are still in an active development phase, are based on two different principles and a brief description of the characteristic features is necessary to understand the technical and economic evaluations.

A2 Steam reforming BLG process - Low Temperature (LT) The steam reforming technology is suited to convert a variety of fluid or solid organic feedstocks, including black liquor, into hydrogen rich syngas.

The reformer is a bubbling bed, fluidized with superheated steam and heated in directly with pulsed jet heater modules. The operation takes place in the absence of air or oxygen at fairly low temperature (-600° C). The steam has a dual func tion - as a fluidizing medium and as a reactant for steam reforming of the organic constituents. Steam Reformer BLG process

► Hydrogen rich syngas

Pulsed jet heater

- Flue gas

Fluidizing steam

Pulsed jet heater One characteristic feature of the technology is the usage of pulse-combustor heat exchange tubes immersed in the fluidized bed. It is claimed to enhance the heat transfer considerably by the resonance effect (velocity fluctuations) and by also creating a uniform heat flux along the tubes.

97 Thermodynamic considerations The basic idea behind the design and the relatively low chosen temperature is to maximize the calorific value of the syngas, reduce the sensible heat and thereby minimizing the increase in entropy. With the moderate temperature maintained in the reactor, the condensed material (sodium carbonate) leaves as a dry solid from the bottom. Hydrogen content of up to 65 % by volume can be reached and the inventors indicate that it is possible to alter the H2:CO ratio within a wide range.

This stem reformer technology has been under development by the firm Thermo- chem Recovery International (TRI) since the mid 1980s with financial support from DOE. Pilot runs have been conducted to date at four different mills during fairly short periods. At present two fairly small plants are in operation or under commissioning in Canada (Ontario) and USA (Virginia). More than 30 million USD has been spent on R&D activities so far.

A3 Entrained flow reactor - High Temperature (HT) The origin of this high-temperature gasification process comes from two inventors and is a spin-off from plasma gas technology development by SKF in Sweden during the 1970s. Together with some other actors Chemrec (established 1989) has conducted development work and erected a number of pilot plants during the last fifteen years.

Gasification concept for HT process Concentrated black liquor is pumped at high pressure to the top of the vertical reactor and through nozzles into the downward mixed flow of liquid and air or oxygen. A partial oxidation takes place and the temperature is raised adiabatically to around 950o C. After a short residence time the slurry has reached the lower part of the reactor where a rapid cooling occurs in the quench zone with water or weak wash liquor. The syngas leaves the reactor for cleaning and the recovered chemicals (smelt) are tapped from the bottom. Elevated pressure and oxygen instead of air can give the most favourable energy efficiency performed.

98 Entrained Flow Reactor - High Temperature

Black liquor

Air/oxygen

Syngas for cooling and cleaning Weak wash Gas cooling and dissolving of chemicals

Green liquor

Figure A3: Principle operation of a gasifier with downward flow of black liquor. Rapid cooling takes place at the bottom part of the reactor.

Table 2: BLG(HT) pilot plants tests to date Start year Location Capacity tDS/day 1987 SKF, Motors 2 1991 AssiDoman, Frovi 75 1994 Stora Enso, Skoghall 6 (later 10) 1996 Weyerhaeuser, USA 300 2005 Kappa Kraftliner, Pitea 20

The latest pilot plant with HT technology in Pitea is expected to be in operation during the second half of 2005. The test facilities are linked to a kraftliner pro ducer in the northern part of Sweden. This unit will be pressurized (30 bar) and oxygen blown. No comprehensive gas cleaning or energy recovery is planned as focus will be on suitable materials of construction for the refractory lined reactor and various process chemistry investigations.

Some important technical differences between the two technologies Due to the different approaches for gasifying black liquor, the process data down stream of the reactors are not directly comparable but some important features are listed below:

99 Table 3: Different properties between BLG(LT) and BLG(HT) Property LT (TRI) HT (Chemrec) Heating In-directly (syngas) Directly (black liquor) Chemicals recovered Solid phase Smelt Sulfur split (gas(smelt) 90/10 50/50 Syngas composition High H2-conc. Moderate H2-conc. Syngas energy content High Low

Contrary to RB where essentially all of the sulphur circulating in the kraft process leaves the boiler in the smelt, gasification processes give a partitioning of the sulphur between the gas phase (as hydrogen sulfide H2S) and the smelt/solid bed leaving the reactor.

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