Straw for Energy Production

Technology - Environment - Economy

The Centre for Biomass Technology 1998 Straw for Energy Production has been prepared in 1998 by The Centre for Biomass Technology (www.sh.dk/~cbt ) on behalf of the Danish Energy Agency. The publication can be found on the web site: www.ens.dk . The paper edition can be ordered through the Danish Energy Agency or The Centre for Biomass Technology at the following addresses:

• Danish Energy Agency 44 Amaliegade DK-1256 Copenhagen K Tel+45 33 92 67 00 Fax +45 33 11 47 43 www.ens.dk • Danish Technological Institute Teknologiparken DK-8000 Aarhus C Tel +45 89 43 89 43 Fax +45 89 43 85 43 www.dti.dk • dk-TEKNIK 15 Gladsaxe Mellevej DK-2860 Soborg Tel +45 39 55 59 99 Fax +45 39 69 60 02 www.dk-teknik.dk • Research Centre Bygholm 17 Schiittesvej DK-8700 Horsens Tel +45 75 60 22 11 Fax +45 75 62 48 80 www.agrsci.dk

Authors: Lars Nikolaisen (Editor) Carsten Nielsen Mogens G. Larsen Villy Nielsen Uwe Zielke Jens Kristian Kristensen Birgitte Holm-Christensen

Cover photo: Lars Nikolaisen, Danish Technological Institute and M. Carrebye, SK Energi Layout: BioPress Printed by: Trojborg Bogtryk. Printed on 100% recycled paper ISBN: 87-90074-20-3 DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. Straw for Energy Production

Technology - Environment - Economy

Second Edition

The Centre for Biomass Technology

1998 Contents Foreword...... 5 1 Danish Energy Policy...... 6 2 Straw as Energy Resource...... 9 3 Annual Energy Crops...... 13 4 Handling of Straw ...... 15 5 Boiler Plants for Farms ...... 19 6 Neighbour Heating ...... 24 7 District Heating Plants ...... 26 8 CHP- and Power Plants ...... 34 9 Gasification and Pyrolysis...... 43 10 Other Technologies for Electric Power Generation...... 45 11 Residual Products ...... 47 12 Further Information ...... 48 13 Table of References...... 49 14 List of Manufacturers ...... 51 15 Survey of Straw-Fired Plants in Operation...... 52 Foreword This publication illustrates how Denmark has succeeded in utilising straw, a former surplus product, for an environmentally desirable and C02 neutral energy production. It further illustrates the recent Danish advances in the field of using straw as an energy option with respect to both technology, environment, and economy.

At the United Nations Climate Change Conference in Kyoto, Japan, in December 1997, the emis­ sion of greenhouse gases was an issue of great concern. For the first time ever, legally binding emission reduction target levels of greenhouse gas emissions by developed nations were estab ­ lished. Total emissions must be reduced by 5.2% by 2012, and the European Union has under ­ taken the major reduction of 8% compared to the 1990 level.

One of the tools for a reduction of the emission of greenhouse gases is to increase the renewable energy share of total energy production. Today, only 6% of the European Union’s energy consump­ tion is covered by renewable energy, but that will change over the next years. The EU Commission Renewable Energy White Paper that was published in December 1997, prescribes a doubling of the share of renewable energy by 2010. Biomass is the sector that is to be developed most and most rapidly. By 2010, it should contribute by 74% of the total EU consumption of renewable energy.

Energy 21, the governmental plan for a sustainable energy development in Denmark, also gives renewable energy high priority. In a long-term perspective, it is the intention to develop an energy system in which a steadily growing part of the energy consumption is covered by renewable energy. This presupposes that a constant and gradual adaptation takes place concurrently with the techno­ logical and financial potentialities.

The Danish government is aiming towards an enlargement of 1% per annum on average. This means that the renewable energy share increases to 35% in 2030. The enlargement will primarily be in the form of an increased use of energy based on biomass and wind energy, and biomass will therefore contribute considerable to Denmark ’s energy production in the next decades.

There are great potentialities for the use of biomass - both in Denmark and internationally, and the experience gained in Denmark so far is already extensive. We have made great achievements both in respect of individual energy supply and collective energy supply systems. Denmark ’s strongholds are particularly in the fields of collective energy supply and decentralised combined heat and power (CHP) supplies, areas of great potentialities for the Danish energy industry - also in the export market.

Svend Auken Minister for the Environment and Energy Danish Energy Policy 1. Danish Energy Policy

Danish energy policy is in a con­ tain the existing objective of Energi stant process of change. The gov­ 2000 to the effect that Denmark must ernment’s Energy Action Plan of reduce its C02 emission by 20% by 1996, Energi 21, is the forth in a se­ the end of 2005 compared to the 1988 ries of plans that all have or have level, and that the emission by the had as their objective to optimise end of 2000 shall be stabilised under the Danish energy sector to the the 1990 level. In addition, interna ­ present national and international tional climate change negotiators will conditions in the field of energy. advocate that the industrialised coun­ tries by 2030 halve their emissions of C02 compared to the 1990 level. At The Four Energy Plans the UN Climate Change Conference The objective of the first energy plan, in Kyoto in 1997, the EU reduction Danish Energy Policy 1976 (Dansk was fixed at 8% by the end of 2012 Energipolitik 1976), was to safeguard compared to the 1990 level. Denmark against supply crises like Energi 21 estimates that renew­ the energy crisis of 1973 174. able energy covers 10% of the coun­ The second energy plan, Energi- try’s total energy consumption in plan 81, attached increased impor­ 2000. This is equal to 75 peta joule tance to socio-economic and environ­ (PJ) and the increase is primarily a mental considerations, thereby con­ consequence of the centralised power tinuing the efforts of reducing the de­ Energy 21 shall contribute to a sus­ plants ’ increased use of straw and pendence on the importation of fuels. tainable development of the Danish wood chips (see the section on the Through the 1980s, the oil and gas society. The energy sector shall con­ Biomass Agreement). An increased fields in the North Sea were heavily tinue being a financially, vigorously, use of biomass and landfill gas also extended, and also the nation-wide and technologically efficient sector contributes to achieving the objective natural gas net was established. The that forms part of a dynamic develop­ of 75 PJ. first subsidy schemes for the utilisa ­ ment of society. Thus the initiatives in the field of tion of straw and wood chips were im­ biomass are directed towards the fol­ plemented via increasing taxes on • Increase the consumption of lowing subsidiary targets of Energi 21: fossil fuels (oil and coal), thereby renewable energy by 100% making it possible to make biomass • Reduce the consumption of coal • Increased use of straw and wood competitive as a fuel. See Figure 1. by 45% chips at centralised power plants. The first CHP plants based on straw • Reduce the consumption of oil • Increased enlargement of decentral ­ were constructed, and the number of by 40% ised CHP generation based on straw-fired district heating plants and • Reduce the COz emission straw, wood chips, biogas and land­ farm plants gathered momentum. by not less than 20% fill gas. The third energy plan in the se­ • Reduce the S02 emission • Conversion, to the greatest possible ries is the action plan Energi 2000 of by 60% extent, of 350 block heating units 1990. This plan is an ambitious at­ • Reduce the NOx emission above 250 kW in rural districts from tempt to increase the use of environ­ by 50% fossil fuels to biofuels. mentally desirable fuels. At the same • Right to establish biofuel plants that time, the objective of a sustainable The objectives are achieved by were formerreserved for natural gas. development of the energy sector is means of a wide range of activities: • Accomplishing of a demonstration introduced. In Energi 2000, the envi­ Energy savings, tax on C02 emis­ and developmentscheme that can ronmentally desirable fuels are de­ sions, conversion to the use of envi­ illustrate future use of energy crops fined as natural gas, solar heat, wind, ronmentally desirable fuels by CHP (including cereal grain, rape etc.) in biomass (straw, wood, liquid manure, generation, subsidised schemes for the energy supply. and household waste). The use of bio ­ the construction and operation of dis ­ • Accomplishing of a minor pilot proj­ mass is based on the fact that it is trict heating systems, financial sup ­ ect for the purpose of demonstrating C02 neutral, that it saves foreign cur­ port for the establishing of biofuel boil ­ the basis of the production and the rency, that it creates Danish jobs, and ers in rural districts etc. use of liquid biofuels. that it utilises waste products from ag­ The forth and last energy plan is riculture, forestry, households, and Energi 21/ref. 1/that was introduced in Figure 2 illustrates the distribution of trade and industry. The ambitious 1996. According to Energi 21, it is the individual renewable energy objective of Energi 2000 is that com­ planned that the “household” with its sources. It shows, e.g., that the full pared to the year 1988, Denmark resources shall have a central role. utilisation of straw and wood chips is shall achieve the following aims by The energy sector is still dominated planned to be achieved already in 2005: by our consumption of depletable, fos­ 2000, and the use of energy crops sil energy sources, and the emissions (annual or perennial) begins in 2005 • Reduce energy consumption resulting from the consumption and and increases until the year 2030 by 15% energy production burden the atmos ­ when the energy crops are planned to • Increase the consumption of natural phere and the environment. The im­ be approx. 45 PJ that is equal to ap ­ gas by 170% portant clue of Energi 21 is to main­ prox. 3,000,000 tonnes of straw. Danish Energy Policy

EU Influence version to environmentally desirable of conversion to more environmentally fuels to selected municipalities and desirable fuels. The target was that EU Commission Renewable Energy owners of plants. In addition, “Letters the Minister of Energy could then White Paper 1997/ref. 28/ fixes an in­ of General Preconditions” that de­ counteract the consumers being crease in the EU use of renewable en­ scribe the prospect of voluntary con­ charged higher heating prices due to ergy from 6% to 12% up to the year verting from coal and oil to more envi­ the conversion. 2010. It is estimated that the biomass ronmentally desirable fuels were cir­ The three acts are Act Nos. 2, 3 sector will be the fastest growing sec­ culated to all Danish municipalities. and 4/1992 and the titles are: tor within the renewable energy tech­ The conversion was immediately nologies. The use of agricultural land implemented. Phase 1 was during the • “State-Subsidised Promotion of De­ is closely connected to the EU agricul ­ period from 1990-1994 and included centralised Combined Heat and tural policy. In the most recent EU pro­ the conversion of a number of coal- Powerand Utilisation of Biomass posal in respect of future agricultural and natural gas-fired district heating Fuels Act”. Under this act, it is possi­ policies, it is estimated that the legal plants that should be converted from ble to receive subsidies up to 50% obligation to fallow land will be abol­ natural gas to decentralised CHP for the construction works. In prac­ ished, and there will be one rate for plants. Phase 2 was during the period tice, the subsidies given have been subsidies no matter the choice of crop. from 1994-1996 and included the re­ in the range of 20-30% of the cost of That will affect the farmers’ manage ­ maining coal- and natural gas-fired dis­ construction. In 1997, the scheme ment also with regard to growing energy trict heating plants that are converted was prolonged until 2000. crops on land voluntarily left fallow. to natural gas-fired, decentralised CHP • “State-Subsidised Electrical Power plants. In addition, minor district heat­ Generation Act". A subsidy of DKK ing plants outside of the large district 0. 10/kWh is given for electrical The Heat Supply Act heating nets are converted to biofuels. power generation based on natural For the purposes of implementing the Phase 3 began in 1996 and is not gas and DKK 0.27/kWh for electrical activities suggested in Energi yet accomplished. It was estimated power generation based on straw 2000/ref. 5/, the Heat Supply Act of that small, gas-fired district heating and wood chips. The scheme has June 13,1990, was passed by the plants be converted to natural gas- no time limit. However, on January Danish parliament “Folketinget". This fired, decentralised CHP plants and 1, 1997, an Executive Order was put Act gave the Minister of Energy wide that the remaining district heating into forcewhich, e.g., requires an powers to control the choice of fuel in plants be converted to biofuels. See 80% overall efficiency of the bio ­ block heating units, district heating also the section on the Biomass mass plant in order for it to receive plants and decentralised CHP plants. Agreement and the adaptation of the maximum subsidy. This was carried into effect by means progress of the phase. • “State-Subsidised Completion of of the so-called “Letters of Specific District Heating Nets”. Under this and General Preconditions” that were act, up to 50% of the cost of con­ circulated to municipalities and own­ The C02 Acts struction could be subsidised. The ers of plants in three staggered The Heat Supply Act was followed by scheme expired at the end of 1997. phases. The “Letters of Specific Pre­ three new acts offering the prospec­ conditions" describe in details the con­ tive of receiving grants for the process The Scheme for Renewable 0re/kWh Energy and the Biomass 45 Committee In 1991, the Minister of Energy set up the “Committeefor Biomass for En­ ergy Purposes” as an advisory body. The committee has, e.g., drafted two 3-year development programmes. The "Bioenergy development programme” (Bioenergi Udviklingsprogram (BUP- 95))/ref.35/ is a 3-year development programme for the period of 1995-97 describing activities for the promotion of the technological development of biomass-based plants. In the pro­ gramme, e.g., the following activities are recommended:

• The developmentof CHP technolo­ Gas oil Fuel oil Natural gas Coal Wood Wood Chips Straw gies on the basis of straw and wood pellets chips as fuels. The technologies are steam, gasification, and Stirling en­ gine. Price without tax □ Energy tax □ C02 tax • District heating plants should focus on fuels flexibility and an environ­ Figure 1: Fuel prices at the beginning of 1998 for heating purposes including mentally desirable handling of fuels. taxes but exclusive of VAT. Coal and oil for electrical power generation are not • Environmentally desirable boiler taxed. The natural gas price for electrical power generation is 13 ore/kWh. The plants should be developed for pri­ consumers are billed for the tax imposed on electrical power. vate houses.

Straw for Energy Production Page 7 Danish Energy Policy

• Energy crops should be investigated PJ/per annum with a view to the growing, handling and use of them. 0 Wind energy

The Danish Energy Agency’s scheme □ Geothermic energy titled “Development Scheme for Re­ newable Energy” supports projects for the promotion of biomass in the en­ □ Ambient heat ergy supply and uses, e.g., “BUP-95” as background material when consid ­ ■ Solar heat ering applications.

□ Biogas The Biomass Agreement In order to safeguard the achievement □ Waste of the targets laid down in Energi 2000, the government, the Conserva­ □ Energy crops tive Party, the Liberal Party, and the Socialist People’s Party entered into an agreementon June 14, 1993 on an □ Wood increased use of biomass in the en­ ergy supply with a special viewto use □ Straw at the centralised power plants. The main points of the agreement are as follows: 1. A gradual increase in the use of biomass at power plants should Figure 2: The Energy 21 proposal for the use of renewable energy sources up to take place resulting in a consump­ 2030. tion by 2000 amounting to 1.2 mil­ consumption of 120,000 tonnes of • seven towns in Phase 3 may con­ lion tonnes of straw and 0.2 million straw and 30,000 tonnes of wood tinue the present district heating tonnes of wood chips annually chips annually. Sjaallandske Kraft- supply until a conversion to equal to 19.5 PJ. vaarker (Electricity Utility Group) has biomass-based CHP is technically 2. Eleven towns in natural gas dis ­ constructed a straw- and wood chips- and financially appropriate. tricts that have not converted to fired CHP plant at Masnedo, and a natural gas-fired CHP within plant at Maribo is being planned. Phase 1 or Phase 2 may make a On July 1,1997, the political par ­ Political Harmony choice between biofuels and natu­ ties to the Biomass Agreement drafted It is characteristic that since the mid­ ral gas as fuels. It is possible to a supplementary agreement with the dle of the 1980s, changing govern­ wait until 2000 in order to, e.g., intention to improve the possibilities of ments, parliamentary majority, and await the development and com­ adapting biomass to the energy sup ­ ministers of energy have persisted in mercialisation of technologies in ply. The supplementary agreement the importance of an active energy the field of biomass. implies, in principle, that policy thereby increasingly weighting 3. Phase-2 towns outside the natural the resource-based and environmen­ gas area may postpone converting • the centralised power plants are tally acceptable line. The conversion until 1998 if they choose biomass- freer to choose among straw, wood to the use of renewable energy based CHP. chips, and willow chips, since there sources may seem very costly, but 4. Six towns in Phase 3 may post­ will be transformed 1.0 million ton­ with the knowledge gained so far in pone converting to biomass-based nes of straw, 0.2 million tonnes of the field of global circulation and the CHP until 2000. wood chips, and for the remainder, greenhouse effect, it is imperative. 5. Approx. 60 small towns in Phase 3 there will be freedom of choice, Denmark has a leading position in the should be converted to biomass- though, in a way so that the total field of several renewable energies, based district heating by the end of amount makes out 19.5 PJ. and it is the target of Energi 21 that 1998. • biomass-based CHP plants are per­ this position be maintained. The agreement has resulted in Son- mitted in natural gas areas. derjyllands Hojspsendingsvserk (elec­ • the municipalities shall give priority tricity utility) constructing a biomass- to CHP based on biogas, landfill based power plant in Aabenraa with a gas, and other gasified biomass. Straw as Energy Resource 2. Straw as Energy Resource

Straw is a by-product resulting from agriculture. In addition, an amount Farm-scale boilers (420) the growing of commercial crops, agreed upon according to crop deliv­ primarily cereal grain. Straw from ery contract is sold to district heating rape and other seed-producing plants and power plants for energy crops is also included in the total production. The straw left after deduc ­ production. Agriculture’s choice of tions for these applications, is for the crops - and thus also the amount of major part chaffed and ploughed back the production of straw - depends and is thereby used for soil ameliora ­ in the first instance on agronomy, tion. Thus this is a straw surplus i.e., the science of cultivation of which - with the annually weather- land, soil management, and crop dependent variations - makes out a production, and on financial mat­ potential fuel reserve. ters affecting the management of Of a total straw harvest of 6 mil­ Other (775) Not possible to gather in (600) the entire agricultural area. lion tonnes, an amount of approx. 15% was used for energy purposes in Figure 4: Of a total straw harvest of 6 1996. In 1997-98, it is estimated that million tonnes, an amount of approx. the consumption of straw at power 15% was used for energy purposes in plants and CHP plants will rise to ap­ 1996 /ref. 25 and29/ “Other ” is bed ­ prox. 400,000 tonnes. ding, clamps etc. (Thousandsof Based on the Biomass Agree­ tonnes). ment of June 14, 1993, the Electricity Utility Group ELSAM and ELKRAFT three different scenarios including a Power Company Ltd in co-operation range of possible developments in the with the Farmers’ Union, specialists theoretically accessible surplus that is from relevant research institutes, and possible to gather in as a consequence the Danish Energy Agency carried of a transformation of the agricultural through an investigation of the exist­ production, larger livestock, change in ing and future amounts of straw /ref. environmental and agrarian political 6/. The purpose of that was to estab ­ matters etc. lish an assessment of what amounts The investigation concludes that, Figure 3: Straw harvest in 1996. Of will be available in the future for a de­ in theory, sufficient amounts of straw the total of approx. 6 million tonnesof velopment of the straw-based electri­ will be available. However in years straw that can be gathered in, wheat cal power and heat generation in Den­ with extremely poor harvest, straw and barley make out more than 80% mark. This investigation operateswith may be in short supply. /ref. 30/. (Thousands of tonnes).

The annual straw production is influ ­ enced by the framework stipulated by the EU agricultural policies, including developments in cereal prices, thefal ­ low of land etc. The straw quality and the amount of straw that can be gath ­ ered in, are also influenced by the weather during growing and harvest. In 1996, the Danish area with ce­ real grain amounted to 1.55 million ha /ref. 25/. The cereal grain yield was 9.17 million tonnes of cereal grain, and the amount of straw was 6 million tonnes. The straw production in a year with average harvest is estimated at 6.3 million tonnes, but may vary up to 30% due to climatic conditions during the period of growing and gathering in. skott

Straw Applications biopress/torben Of the total straw production, only a minor part is used for energy pur­ poses. The major part is used in agri ­ photo: culture’s own production, i.e., as bed­ Straw is a waste product from cereal grain production. The picture shows the ding in livestock housing systems etc. combine harvester chaff cutter having chaffed the straw so that it can be ploughed Also a considerable amount of straw back. The area behind the combine harvester is fallow land. is used for heating, grain drying etc. in

Straw for Energy Production Page 9 Straw as Energy Resource

kg C02/GJ to thefertility of the earth, a mainte­ nance of this fertility requires a current 120 application of crop remains or other organic matter. Though the optimal or critical levels for the carbon contentof 95 100 the earth is not known. Experiments carried out since 1920 at the Danish 74 Institute of Agricultural Sciences 80 Askov Experimental Station have shown that the carbon contentof the earth has dropped no matter whether 60 57 LI commercial fertiliser (NPK) or animal manure is applied. As is the case with liquid manure, 40 sludge and other crop remains, ploughed back straw may contribute to increasing the carbon content of 20 cultivated land on a long view as is the case also with grass after grain 0 0 0 crops. The gain by removing straw from the field for energy purposes is Coal Gas oil Natural gas Waste Straw Wood that it substitutes fossil fuels. Most of the carbon in the ploughed back straw Figure 5: Fuel emissions. Burning coalemits, e.g., 95 kg C02 per GJ coal, while is released in the form of CO2, and al ­ the biofuels are C02 neutral. The C02 values are average values for the fuel together less C02 is emitted to the at­ types mentioned /ref. 58/. mosphere if straw is removed for the purpose of substituting fossil fuels. Straw Market • Provisions concerning the regulation of the basic price Trading in straw for energy purposes • Provisions concerning arbitration Straw as a Fuel among producers and the energy sec­ The most important argument for us ­ tor is in principle determined by crop ing straw for energy purposes is that delivery contracts for several years, Plough Back of Straw this fuel is C02 neutral and therefore concluded between the individual Land that has been cultivated for sev­ does not contribute to increasing the straw producer or an association of eral years has a lowercarbon content C02 content of the atmosphere, straw producers and the purchaser. than has uncultivated land. Thus thereby resulting in an aggravation of The purchasers are straw-fired when cultivating land, carbon is re­ the greenhouse effect. district heating plants and CHP plants moved from the soil in the form of C02 Straw used for fuel purposes that by entering into long-term crop being released to the atmosphere. usually contains 14-20% water that delivery contracts for straw make sure The carbon content is of importance vaporises during burning. The dry that they can perform their duty to supply heat and energy to the con­ sumers. Not all straw is traded ac­ Unit Yellow Grey Wood Coal Natural straw straw chips gas cording to crop delivery contracts. By purchasing straw in the spot market, Water content % 10-20 10-20 40 12 0 e.g., at machine pools, or at the Volatile components % >70 >70 >70 25 100 places of other middlemen, the plants may often achieve an advantageous Ash % 4 3 0.6-1.5 12 0 price for part of their annual consump­ Carbon % 42 43 50 59 75 tion of straw. Hydrogen % 5 5.2 6 3.5 24 The crop delivery contract for straw may include the following terms Oxygen % 37 38 43 7.3 0.9 and conditions: Chloride % 0.75 0.2 0,02 0.08 -

Nitrogen % 0.35 0.41 0.3 1 0.9 • Term of contract and notice of termi­ nation Sulphur % 0.16 0.13 0.05 0.8 0 • The amount of straw agreed upon, Calorific Value, Water/Ash-Free MJ/kg 18.2 18.7 19.4 32 48 including provisions in the eventof increase/decrease in the consump­ Calorific value, actual MJ/kg 14.4 15 10.4 25 48 tion of straw, non-delivery due to Ash softening temperature °C 800 950 1000 1100 decrease in crop yield etc. -1000 -1100 -1400 -1400 • Terms of delivery, including the type Table 1: Fuel data at a typically occurring water content/ref. 11 and 32/. In /ref. of bale, the dimensions and weight 33/, leaching experiment on barley straw has been carried out. The result of bales, water content, and other showed that after 150 mm rain, the chloride content had dropped from 0.49% to grade determinations below 0.05%, and for potassium from 1.18% to 0.22%. At the same time, the • Basic price and the regulation of straw had turned grey. Straw may turn grey (colonies of funguses) due to night price in proportion to water content dew and hot weather without leaching taking place. and time of delivery Straw as Energy Resource

matter left consists of less than 50% Percentage in dry flue gas Figure 6: Ideal carbon, 6% hydrogen, 42% oxygen, combustion of straw and small amounts of nitrogen, sul ­ is performed by phur, silicon and other minerals, e.g., excess air of alkali (sodium and potassium) and between 1.4 and chloride. Combustion takes places in 1.6. As an example, 4 phases. During phase 1, the free 7.5% oxygen is water vaporises. In phase 2, the pyro­ measured in the flue lysis (gasification) occurs, during ------"<---- gas. The curve which combustible gases are pro­ illustrates the duced depending on the temperature. presence of approx. There will always be a certain content 13% carbon dioxide of carbon monoxide (CO), hydrogen with excess air (H2), methane (CH4), and other hydro ­ being 1.5%. carbons. Phase 3 is the combustion of gases. If sufficient oxygen is supplied, a complete combustion occurs where the residual products are carbon diox­ 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 ide (C02) and water. Wherethe oxy­ Lambda gen supply is insufficient, carbon mon­ oxide, soot (finely divided carbon), —Carbon dioxide C02 = Oxygen 02 tar, and unburnt hydrocarbons are produced. During phase 4, the char ­ coal burns. By complete combustion, ever, it has even been demonstrated Straw Pellets carbon dioxide is produced. By re­ that the ash may become viscid al ­ duced supply of oxygen, monoxide is ready at 600°C /ref. 31/. This is of im­ Experiments have been carried out on produced. Finally, there is only ash portance, in particular, at power plants the use of straw pellets, i.e., commi­ that consists of incombustible inor­ where a high steam temperature is nuted straw that has been pressed ganic matter. By incomplete combus ­ desired in order to achieve a great ef­ into pellets of a diameter of 8 or 10 tion, the ash may also contain unburnt ficiency. This requires a high super­ mm/ref. 131. The experiments showed straw residues. heater temperature, thereby risking that straw pellets can be used as a The air that is supplied in excess extensive deposits on the superheater fuel in large boilers, whereas ash and of that theoretically required for com­ tubes. particularly slagging problems make plete combustion is called excess air. Where a combination of straw straw pellets less suitable for use in A certain amount of excess air is nec­ and coal is used as a fuel, the pres­ small boiler plants. Straw pellets can essary in order to secure sufficient air ence of alkaline matter in the ash indi­ be pressed with molasses as a bind­ all over the area where the gases are cates that - contrary to pure carbon ing agent thereby admixing an anti ­ to burn although the gas/air mixture is ash - it cannot be used as a filler in slagging agent, e.g., kaolin, in order to never quite uniform. The ratio be­ building materials, but must be make them more stable during trans ­ tween the air supplied and that theo­ dumped at controlled disposal site. port and in order to counteract the retically required is called the excess air ratio (lambda). . _ air supplied K air required Through boiler walls and fire tubes, the major proportion of the combus ­ tion heat is absorbed by the water in the boiler, while the remainder disap ­ pears through the chimney as a mix­ ture of carbon dioxide, vapour, and small amounts of carbon monoxide and other gases, e.g., tar and com­ pounds of chlorine. In addition, the flue gas contains small particles of ash and alkaline salts. The presence of chlorine and al ­ kali in the flue gas is problematic, since these matters undergo chemi­ cal reactions into sodium chloride and rukolaisen potassium chloride that are extremely tars corrosive in respect of the steel of boiler and tubes, particularly at high temperatures. photo: The ash is not without problems Straw pellets of a diameter of 10 mm mixed with molasses and kaolin and the either, since its softening temperature resulting ash content of 8-10%. Kaolin prevents the ash from forming clinker. is relatively low in proportion to other Molasses makes the pellets stable during transport fuels, beginning at 800-850°C. How­

Straw for Energy Production Page 11 Straw as Energy Resource

tendency of the ash to become viscid in connection with turning, baling, and form clinker. The calorific value of Turning (8) gathering in, and costs of storage and the pellets is 16.3 MJ/kg at 8% water, transport to heating plant. In addition and the volume weight is 4 times to that, lost fertiliser value, insurance, larger than that of straw baled into big and the producer’s risk covering, i.e., bales, i.e., approx. 550 kg/m3. due to shrinkage caused by bad weather conditions during the period of harvest and shrinkage during stor­ Washing of Straw age. It has been known for a long time that A term that is now and then used straw that has been lying in thefield is the “socio-economic straw price”. and has been exposed to rain has a That is a price that is cleaned for di­ reduced content of the corrosive mat­ rect and indirect taxes so that it re­ ter, chlorine and potassium. Contrary flects the actual cost of producing it. to “yellow” straw, this “grey" straw is The socio-economic price is used, more lenientto the boiler, since part of Figure 7: In April 1997, The National e.g., for a comparison between prices the matter that corrodes boiler wall Department of Farm Buildings and of various domestic and imported fu ­ and tubes has been removed. Grey Machinery calculated the cost price of els and is more a planning tool than a straw also has a somewhat higher straw for energy purposes at DKK price calculation for use in the day-to- calorific value than yellow straw. 466.00 per tonne. Add to this the day trading. This price is fixed by the In order to reduce the corrosive costs of transport to plant /ref .27/. (In Danish Energy Agency and was re­ effect of straw upon the boiler plant, p.s.). ported in 1994 to be DKK 240/tonne the ELSAM - Electricity Utility Group delivered on the plant. Of this amount, of Jutland-Funen implemented in the ers. With demands by the large elec­ DKK 43/tonne accounted for the cost spring of 1996 experiments on the re­ trical power producers steadily in­ of transport and DKK 197/tonne ac ­ moval of the unwanted components creasing over the recentyear due to counted for other cost of production. by boiling the straw at 160°C. Later it the Biomass Agreement, the market was demonstrated that chlorine and has been characterised by a certain potassium can also be washed out at increase in prices. Thus the cost price Transport Energy lower temperatures. At present, it is is not only an expression of the cost of Admittedly, the great number of trucks considered most economical to wash producing the straw and the profit, but transporting straw to plants or trans ­ the straw at 50-60°C. So far, straw it is also part of the parties' strategy in port over great distances emit C02 to washing has only been tested at small respect of performing the Biomass the atmosphere caused by the en­ plants. According to ELSAM, a plant Agreement. Consequently, price fluc ­ gines of the trucks. that can treat 125-150,000 tonnes of tuations in the range of DKK 360 to A truck travels 2-3 km on one litre straw per annum will most probably DKK 500 per tonne are seen. In 1997, of diesel oil, thereby emitting 2.7 kg cost about DKK 200 million/ref. 26/. the “span in price" between the pro­ C02. Therefore, the C02 emission can The energy losses caused by ducers of straw and the power plants ’ be estimated at approx. 1 kg per km washing, drying and the leaching of purchasers of straw was above DKK travelled. A truck load of straw with a organic matter make out approx. 8% 80 per tonne, i.e. DKK 466 and DKK calorific value of 14.5 GJ/tonne of the calorific value of the straw. This 380, respectively. Tenders for straw weighs 11-12 tonnes and represents cost is offsetthough by the prolonged were invited by district heating plants an amount of energyof approx. 170 life of the boilers, because corrosion east of the Great Belt in 1997 and GJ. Since the C02 emission from coal problems are avoided. Washing of 1998 with a tender result of DKK 350- is approx. 100 kg/GJ, then the straw straw is also expected to give advan ­ 400/tonne delivered to the plant. corresponds to a C02 emission of ap­ tages in respectof the subsequent ap­ West of the Great Belt, the straw prox. 17 tonnes subject to coal being plication of the fly ash, since straw price according to the most recent burnt instead of straw. ash that does not contain alkaline crop delivery contracts for straw has That means that the truck should salts and other impurities can be used been in the range of DKK 320-370/ travel 17,000 km with a load of straw as a filler in building materials. tonne, also delivered to the plant. in order to emit the same amount of The producer’s straw price in­ C02 that is saved by using the truck cludes in addition to return on invest­ load of straw as a fuel instead of coal. Straw Price ment and depreciation on the machin ­ It can also be expressed by saying The market price of straw for energy ery used in connection with the gath ­ that the C02 saving is reduced by ap­ purposes is still being intensely nego­ ering in of straw and a range of other prox. 0.6% per 100 km transport dis­ tiated among suppliers and purchas- elements, e.g., wages and cost of fuel tance travelled. ______Annual Energy Crops______3. Annual Energy Crops Biomass that is grown for the pur ­ pose of energy production contrary to, e.g., straw that is a residual product/by-product from cereal pro­ duction is called energy crops. An­ nual energy crops may be cereal grain or rape alone or cereal grain/ rape and straw harvested together, e.g., by swathing. Perennial energy crops may be willow, elephant grass, and reed canary grass.

Burning of cereal grain in boiler plants larger than 250 kW is prohibited. This appears from the Danish Energy Agency Follow Directions in connection with the Heat Supply Act of June 13, hinge 1990. The prohibition is laid down in a letter of September 13,1990/ref. 24/ jorgen that has been circulated to all munici­ palities, and it says in the letter that it is photo: not allowed to either wholly or partly burn fish oil, surplus butter, cereal Triticale left in swaths without having been combined. The swath is too wide for grain etc. The prohibition may be the big baler and should be raked before baling. The raking results in grain rooted in ethical considerations in re­ losses. The stiff, unthreshed triticale stalks are difficult to bale into big bales. The spect of burning food in a starving picture is from the test at Djursland. world. The provisions do not apply to sume. Rape can only be used as co­ other boilers may also be suitable for plants below 250 kW. This means that firing in small amounts together with, burning cereal grain, but the efficiency a farmer with own farm-scale boiler e.g., cereal grain or wood pellets, e.g. and emission through the chimney has may legally burn cereal grain or rape. because the boiler firing system is not been documented, and it cannot However, it must be a crop deriving adapted to fuel with less energy con­ be recommended to burn cereal grain from the ordinary agricultural produc­ tent (the lower calorific value of rape in a boiler that is not designed to it. tion. If thecrop has been grown on is approx. 24 MJ/kg at approx. 10% fallow land, then according to the EU water). Usually pure rape firing results Full-scale Tests on Cereal Directions, it must not be used for own in so much energy being fed that the heating purposes, nor be “traded ” with boiler bottom “is covered with” oil, re­ Grain Burning the neighbour if he is a grain grower, sulting in danger of fire and malfunc ­ During the period from 1995-97, full- too. tion. About ten boilers for cereal grain scale tests on the burning of cereal firing have been type approved by the grain were carried out at 5 locations, Cereal Grain and Rape Test Laboratory for small Biofuel Boil­ i.e., Bornholm, Lolland, Langeland, ers (see Section 5). Then the boilers Djursland, and Haunstrup near Hern- for Small Boilers can be state-subsidised and they are ing. The individual heating and CHP It is difficult to estimate how much ce­ of a good standard in terms of the plants had filed applications to the real grain and rape small boilers con- combustion of cereal grain. Certain Danish Energy Agency for an exemp-

Plant MWheat MWeiec. Plant type Fuels Tonnes Holeby 3.1 0 D. H./grate Wheat and triticale in big bales 394 Tullebdlle 1.6 0 D. H ./whole bales Triticale in big bales 169

Lohals 1.4 0 D. H./sliced bales Triticale in big bales 51 Haunstrup 0.5 0 D. H ./stoker Rye grains 222 Rudkobing 7 2.3 Steam/grate Triticale in big bales 380 Studstrup 1 0 150 Steam/pulverised fuel Triticale in big bales 1100

Grena 60 18.6 Steam/fluidized bed Triticale in big bales 2000 Bornholm 35 16 Steam/spreader stoker Wheat grains 781

Table 2: Survey of plants carrying out combustion tests in 1995-96. D. H. = District Heating.

Straw for Energy Production Page 13 Annual Energy Crops

NO concentration (ppm) in flue gas at 10% oxygen • Emissions and efficiencies are more or less the same for energygrain (cereal grain and straw) as for wheat straw. However, a marked rise in the Wheat straw Triti cale NO emission could be seen at few of the plants, since the protein content of the grain during burning releases nitrogen (N) /ref. 7, 8, 36, and 37/.

Energy Crop Programme 1997-2000 In 1997, a large demonstration pro­ gramme was implemented concerning the production and use of energy crops. It is a 4-year programme and shall pave the way for a large-scale consumption of energy crops after the year 2005. In Energy 21, it is esti­ mated that the consumption of energy crops rises from 0 tonnes in 2005 to almost 3 million tonnes in 2030 (see 16:00 20:48 01:36 06:24 11:12 16:00 20:48 Figure 2). The purpose of the project November 15 and 16, 1995 is to develop and demonstrate an opti­ mal operating economy and an envi­ Figure 8: At Holeby Halmvarmevaerk (straw-fired heating plant), a heavy increase ronmentally sound production of en­ in the NO emission is seen by firing with cereal grain. At the same time, a halv ­ ergy crops. The greatest importance ing of the CO emission was measured. has been attached to the use of rye, triticale and afforestation. Of other fu ­ tion from the prohibition of burning ce­ strup, Studstrup 1, Grenaa, and els that form part of the programme real grain, and EU-approved crop de­ 0stkraft (Bornholm) participated. can be mentioned willow, elephant livery contracts for the supply of ce­ In summary, it can be concluded grass, reed canary grass, and hemp. real crops from fallow land areas were that the tests demonstrated: The programme includes subsidi ­ concluded between the farmers and ary programmes consisting of: the plants. During the growing and • that rye and triticale are better than • Establishing and growing harvesting period, large-scale regis­ wheat due to reduced grain losses • Harvesting, storage, and transport tration of the application of fertilisers, and reduced requirement for the ap ­ • Importance of choice of species pesticides and insecticides, harvest­ plication of fertilisers, pesticides and • Fuel characterising and combustion ing technique (swath forming mower), insecticides. tests baling into big bales and storage on • Particularly in dry seasons, the straw • Impact on the aquatic environment the farm was made. Unthreshed grains is suitable for swathing, but the stiff • Flora and fauna conditions and straw were used except for Born­ straw/stalks may be difficult to bale • Landscape visualising holm and Haunstrup. into homogeneous big bales. In wet • Carbon balance of the earth Table 2 shows the plants that car ­ crop years, there is a great risk of • Financial analyses ried out combustion tests during sprouting of the crop left in swaths. 1995- 96. • The heating plants had problems in The programme is carried through by During the heating season of lifting the heavy energy grain bales seven research institutions and one 1996- 97, the plants Holeby, Haun­ (600-700 kg). electrical power producer /ref. 38/. Handling of Straw 4. Handling of Straw nikolaisen lars

photo: The loader tractor ready to load the truck and trailer up with 24 big bales. In this case, the bales are transported directly to Grenaa Kraftvarmevaerk (CHP plant) where they are unloaded, 12 bales at a time, by an automatic crane.

Large-scale straw handling for en­ • Small baler cm. The average bale weight is 244 ergy purposes has developed into • Round baler kg, and the bale density is approx. an independent discipline in agri­ • Medium-size baler 110 kg/m3 /ref. 17/. There is also a culture with attachments in which • Big baler type of baler designed for round bales particularly large farms and ma­ • Chaff cutter of 150 cm width and 180 cm diameter. chine pools invest. That was the type that was first mar­ The small baler typically has a tunnel keted, but now it is only seldom seen. dimension of 46 x 36 cm and a bale The interest for the round baler was After combine harvesting, the straw is length of 80 cm. The weight of the great when it was marketed, but has lefton the earth in swaths. The straw bale is approx. 12 kg, and the bale declined over the last many years. should be removed as quickly as pos­ density is 90-100 kg/m3 /ref. 17/. Pre­ The round baler is primarily used for sible so that the treatment of the soil viously, is was the most widely used baling of straw for feeding and bed­ preparation can begin thereby estab ­ type of baler, but is now used only to a ding purposes, and for burning in lishing next year’s crop. The thickness small extent for baling of straw for straw-fired farm-scale boilers. of the straw swath has increased con­ bedding and for burning in small The medium-size baler has siderable over the recentyears, be­ farm-scale boilers. gained a firm foothold in agriculture cause the combine harvester swath The round baler has been in the for the baling of straw for feeding and width has been considerably in­ market for approx. 25 years. The com­ bedding purposes, and for burning in creased. This is an immediate advan ­ monest type of baler bales into a farm-scale boilers. It was marketed tage in respectof the baling capacity, width of 120 cm and a diameter of 150 some years after the big baler, proba ­ but it may be problematic to dry the bly because the bale dimension is straw after rainfall. Tonnes/hour more suitable for agricultural pur ­ The following calculation is based poses. The baler tunnel dimension is on a straw yield of 3 tonnes per ha, a typically 80 x 80 cm and the bale field size of 4 ha, and a transport dis­ length is 240 cm. Theweight of the tance of 1,000 m from thefield to the bale is approx. 235 kg, and the den­ farmer’s storage. Big bales are cur­ sity is approx. 140 kg/m3. However, rently delivered from the storage to balers with other tunnel dimensions district heating plants etc. during the and bale lengths from 120 to 200 cm year depending on crop delivery con­ are also manufactured. The baler of ­ tracts. Straw that has not been baled ten is equipped with a chaff cutter, into big bales is used primarily in the thereby increasing the bale density to farmer’s farm-scale boiler. Low capacity Average capacity High capacity approx. 165 kg/m3. Chaffed straw is a better bedding material, and this is the Baling/Chaff cutting of | Small baler □ Round baler Q Medium-size major reason why the baler is equip­ □ Big baler □ Chaff cutter baler ped with a chaff cutter. Straw The big baler has been in the The following baling/chaff cutters are Figure 9: Gross capacity by baling or market for approx. 20 years. It is the examples of baling/cutting types used chaff cutting of straw. only bale size that is accepted by the in agriculture: district heating-, CHP-, and power

Straw for Energy Production Page 15 photo: bygholm from the the tion The weight A out conform be chaff in ments, of of and density cutter They a density opment years at length introduction been boilers. power important directly approx. bulk has bale prox. road bale length plants. 170 baler

bale self-propelled value/ref. the straw heating-,

used.

farms field cover

of

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photo: bygholm Handling of Straw

Man-minutes per tonne 30 Big bales are loaded and unloaded by manpower required for the handling of front-end loader, trencher, loader trac ­ small bales is thus 72 minutes per 25 tor, telescope loader or the like. The tonne when loading unloading by telescope loader is suitable for un­ hand. This is almost 3 times as much 20 loading, because it can reach high up as required for the handling of round when storing in stacks. The front-end bales and 5% times more than re­ 15 loader is the commonest. Depending quired for the handling of big bales, on the front-end loader equipment and see Figure 10. By mounting a bale 10 lifting capacity, the tractor load capac ­ chute on the bailer and by loading di ­

5 ity and stability, and the local condi ­ rectly on to the transporting vehicle, tions, one or two bales are handled at the manpower may be reduced, 0 a time. The capacity is highest, when though, to approx. 45 minutes per Round Medium- Big Chaff bales sized bales bales cutter handling two bales at a time, but it is a tonne for small bales. severe load on the tractor front axle, The manpower required for chaff (Baling | [Loading | [Transporting | (unloading and the stability of thetractor is de­ cutting of the straw or for the handling creased dramatically if not a balancing of medium-sized bales is the same, Figure 10: Manpower required for weight is mounted on the back of the i.e., 17 minutes per tonne. By hand ­ pressing/chaff cutting of straw and tractor. ling of big bales, the manpower re­ transportingto storage. Reconstructed trucks or truck quired is only 13 minutes per tonne, trailers are widely used. The size of though. This very drastic reduction of the load varies from 6 to 18 bales. Tonnes/hour the manpower required and the great 20 |------Over long distances, the tractor is of­ physical labour saving is the principal ten towing two trailers so that the size cause of small bales having been al ­ I of the truckload attains 24 bales per most outdistanced by round bales, 15 trail /ref. 17 and 19/. medium-sized bales, and big bales.

im Manpower Required Delivery to Plant The manpower required for the bailing During the heating season, the straw and transport of the straw to the stor­ is usually delivered to the plant in ac­ age on the farm varies with the type of cordance with a crop delivery con­ bale and technique that is used during tract. It may be a direct agreement Small Round Medium- Big Chaff loading, unloading, and transport. The with the farmer, an association of bales bales sized bales bales cutter Figure 11: Capacity during transport­ ing of straw to storage. for unloading in the storage. The front-end loader is the most used ma­ chine both in field and in storage. Depending on the front-end loader design, lifting capacity, and the local conditions, one or two bales are handled at a time. Most often, only one bale is handled at a time. For transport, reconstructed trucks or truck trailers are used, but also ordi ­ nary farm trailers or specially de ­ signed vehicles are used. Usually, the tractor is only towing one trailer, and it will contain from 8 to 14 bales /ref. 17/. Medium-sized bales are loaded and unloaded by front-end loader, trencher, loader tractor or the like. The front-end loader is the most used ma­ chine for both loading in the field and

for unloading in the storage or at the hojspaendingsvaork straw stack. One or two bales are handled at a time depending on the front-end loader equipment and lifting

capacity. Reconstructed trucks, truck sonderjyllands trailers, flat cars, or specially designed vehicles are used for the transport. photo: The size of the loads varies from 12 to 45 bales, but most often load will hold approx. 24 bales.

Straw for Energy Production Page 17 thoto. byaholm may persons, the transports truck farmer tractor, ten volved there the the dates, agreement straw by by crane Figure bly mounting in ling loads delivery around tracted man-minutes/tonne age plant

transporting — —

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lower

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by

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where is are

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seen sizes

Tractor, Tractor, Transport

distances. distributed accurately

particularly

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This re­ often

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Boiler Plants for farms 5. Boiler Plants for farms

The present use of straw firing in agriculture expanded heavily due to the energy crisis in the 1970s with the following subsidy schemes and easy terms concerning depre­ ciation on straw-fired boilers. In the middle of the 1980s, approx. 14,000 straw-fired boilers had been in­ stalled. In 1997, it is estimated that there are approx. 10,000 straw-fired boilers in agriculture. The reason for the drop in numbers is that the early installed boilers were small, primitive boilers designed for batch firing that have not all of them faust been substituted by a straw-fired boiler.

There are two types of boilers, the maskinfabnkken

batch-fired and the automatically fed boilers. The batch-fired boilers are al­ photo' ways installed in combination with a “Tractor firing". The tractor feeds a round bale into a batch-fired boiler. The boiler storage tank that can absorb the heat is located inside the house in a way that offers easy access for the tractor both energy from one firing (1-4 bales). for firing and for the removal of ash. Thereby, the energy contentof the straw is utilised better, because the boiler can operate at full boiler load. to three big bales in the combustion Control of Air Supply for Automatically fed boilers are fed by a chamber. The most widely used boiler conveyor that, e.g., is loaded with size is a boiler for one medium-sized Combustion straw approx, once every24 hours. bale or alternatively 8-10 small Today, all batch-fired boilers are The conveyor feeds bales into the bales. equipped with combustion air fans, boiler automatically, concurrently with When disregarding firing with where the amount of air and the distri ­ the consumption of heat. small bales, firing and the removal of bution of air between primary and Over the recent 10-15 years, ash are usually performed by a tractor secondary air is controlled by an elec­ great technological advances have with front-end loader. tronic control unit. Theflue gas tem­ been made in respectof these boilers perature and oxygen content are used with a view to achieving a greater as a control parameter. In addition, efficiency and reducing the smoke the boiler has refractory linings of fire­ nuisance. Greatest technological ad­ bricks round the walls of the combus ­ vances have been in the field of tion chamber in the upper part in order batch-fired boilers, where the effi­ to secure a high combustion tempera­ ciency has increased from 35-40% in ture. 1980 to 77-82% in 1997. This can be Measuring of theflue gas tem­ ascribed, in particular, to a better con­ perature secures that the boiler output trol of the air supply required for com­ is kept within certain determined lim­ bustion. The smoke nuisance is re­ its, as, e.g., a high flue gas tempera­ duced considerably with increased ture is an expression of the boiler be­ combustion quality. ing overloaded, i.e., the combustion produces more heat than can be ab ­ sorbed by thewater in the boiler. Simi­ Batch-fired Boilers larly a too low flue gas temperature Whereas the small straw bales earlier is an expression of a too low boiler dominated the market, most batch- output. fired boilers are to-day designed for Measuring of the oxygen in the big bales (round bales, medium-sized flue gas is used for adjusting the com­ bales, or big bales). The boilers are bustion excess air by opening and often built together with a storage tank closing the primary and secondary air. as an all-in-one unit for outdoor loca­ The ideal target is an oxygen percent­ tion. The outdoor location highly re­ Batch-fired boiler for round bales or age in the flue gas of 6-7% which is duces the danger of fire. big bales located in a separate equal to an excess air, lambda, of ap­ The batch-fired boilers are pro­ housing, thereby eliminating the prox. 1.5. duced in a wide range of sizes, con­ danger of fire in respect of the farm The oxygen content is measured taining from one medium-sized bale buildings. continuously by an oxygen probe of

Straw for Energy Production Page 19 Boiler Plants for farms almost the same type as that used for The gate is open to the controlling the petrol injection in mod­ combustion chamber of ern car engines. The electronic con­ an automatically fed fire trol unit converts the signals from the tube boiler. The straw is probe into air-inlet-open- and shut-off fed by screw stoker impulses to the motor-driven air valve. behind the flames, and If the oxygen percentage is too high, a the flue gas passes small amount of primary air is allowed though the four tubes and to enter, thereby shutting off a bit the further through the boiler secondary air inlet. Similarly, the pri­ vessel. Below on the mary air inlet shuts off a bit, and the right, the gear motor of inlet of secondary air opens a bit if the the ash conveyor is seen. oxygen content decreases too much. It is important that the electronic control unit is capable of keeping the oxygen percentage constant, since fluctuations in the oxygen percentage result in too high CO values and too low boiler efficiency. Therefore ongo­ ing developments aim at improving the straw-fired boilers by developing a very accurate and reliable control sys­ tem with oxygen probe. In addition, it is also important that the air nozzles are designed and positioned so that the proper turbulence is created in the combustion zone. In order to attain a good combus ­ tion with a low CO content in the flue gas, it is also of decisive importance poor combustible properties (see Sec­ tained in the combustion chamber. that the straw that is used is of a good tion 2). This is equal to the temperature in the quality. That means first and foremost In order for the boiler to keep a storage tank increasing 30-40°C at that the straw should be dry before stable rate of combustion at maximum the time of firing if not simultaneously baling and be stored in a dry place. boiler load without interruptions heat is drawn from the tank. The stor­ But also, the straw should be well field throughout all combustion stages, all age tank is typically a separate tank cured (i.e. it has been left in the field batch-fired boilers designed for straw that is located on top of the boiler, but exposed to rain and has turned grey) are equipped with a storage tank. The the boiler may also be built into the before baling, since the too early storage tank will usually contain 60-80 storage tank. Figure 15 illustrates the gathered “yellow” straw normally has litres of water per kg of straw con­ principle of separate tank. reka maskmfabnkken maskmfabnkken

graphic Figure 14: Automatic boiler. The straw is being shredded by a slow-speed shredder and fed via screw stoker on to the grate where the combustion takes place. The forward and backward movements of the grate pushes the ash towards the ash chute and further out with the ash conveyor. The flue gases are cooled by passing several passes where the fire tubes are surrounded by boiler water. The photo• hnka maskinfabrik that transmission eration, called system. in shredder greatest flexibility firing, The Automatically An perature. and the with the reduced boiler blower a shredder ter. by veyor batch-fired small primarily separated batch-fired more against fan cyclone tube From ing straw the straw the consuming veyed valve contain

worm addition,

means

automatic

device The blower boiler is screw cyclone

reacts thereby

first Continuous most At straw

of

stable there, bales, under into is the seen by of, the towards

system, automatic

the

backfire/burn-back 2-4

conveyor controlled

transport and sucked The

smoke boilers

a ease e.g.,

in and

straw and widely

screw stoker of the

from bales were

worm system on

boilers. boilers cyclone. than it on

small

relation exit the a combustion the

since a is straw

gives is

boiler. the

boiler. the the

higher efficiency 10-20 the the

rotating

dosed the

adjusted

since

the is nuisance with bales into cyclone air.

developed

firing is

stoker. once

used conveyor,

firing, bales.

or boiler that system by boiler shredder. being

the work back by could the is

is boiler.

a The

transport

to Fired The

the a The The automatic m

positioning The good fed more

a it

via passes are results every originally the blower system worm

shredder/cut

length offers thermostat

boiler

of may of a water lower,

disintegrated

down straw often in by

upper

into chaffed

a flue

between Before compared

bale

slowly

boiler, firing the

security energy the

rotary between

in often on/off

Boilers

However, 24

conveyor be

the air

in

the gas system.

order

heat the

is boiler. only is tem on is bright

con­ boiler

feed

tube and hours. simple a with either

filled

in of the

con­ the and

to op

­

the the the

­ ­

to

is to

­

chamber contain Figure gen gen this at starting amount type oxygen-controlled tion, tion 7%. under is means boilers straw order be boiler. In Control gas

automatically

short order adapted

Boiler

level air is content content Traditionally, If the of

to being

the batch recorded The

15:

are that that oxygen

the

and intervals. of to secure amount

will considerably,

oxygen

straw The achieve therefore oxygen of

energy the

is to fed, stopping of fired in

Plants hold.

introduced the

the Firing the

principle

probe amount

a adjusted by the is of

boilers, the constant amount

content amount

screw flue

flue

thus generated content means straw a

newest

equipped

good

the aim that for

gas from gas the

of adjusted in

stoker

to fired screw by and

is

exceeds is straw of of

a farms combus screw

in of

the

an automatic a described

batch-fired

combus the

the

approx. the by

fan. should

with

Straw

oxy oxy

which stoker

fired the

same combustion by flue

In ­ ­ ­ of

­

for

boiler fuel Type flue will solid So tions automatic gen stoker to 7%. stoker rough the nuisance Denmark multaneously, proved by intervals.

Energy

stopping a

of

far,

try

oxygen gas content starts level Then The By

fuels

for the

Boilers operates

estimate,

stops to there

Testing by

using

is

the

storage from

straw keep

far for

If

the

boiler, 5-10 - reduced,

Production

the content

except

the

combustion completely, type has below

oxygen

automatic

the

the this

that oxygen

Expansion percentage screw because uninterruptedly

the tank been

testing CO of

boiler rising

oxygen

from

7%, the drops

and efficiency

Small control is

content stoker

no

content combustion

the

big

boilers step the are again. is until

tank of the tradition to

Storage firebricks tion door Water-cooled Refractory Combus Fire

reduced. percentage

point boilers screw

enough smoke Page

about better.

condi at at function the

of air Bio tube drops is

for an short until

the on im

oxy tank ­

­

in

for ­

21 Si­ ­

to

a ­

Boiler Plants for farms

straw that have been tested at Re­ Fuel Firing CO-emission CO-emission Dust emission search Centre Bygholm, Horsens, in at 10% 02.30% at 10% 02 at 10% 02 connection with previous subsidy schemes. The market for small boilers boiler load nominal output has been uncontrolled, i.e., so far Firewood, pel­ Batch 0.50% 0.50% 300 mg/Nm3 there have been no statutory require­ lets,cuttings, (manual) ments in respect of type testing of en­ ergy-, environmental-, or safety prop­ wood chips, erties. The only statutory require­ cereal grain ments are safety requirements that Firewood, pel­ Automatic 0.15% 0.10% 300 mg/Nm3 are laid down in the Directory of La ­ bour Inspection Publication No. 42 lets,cuttings, dealing with safety systems for hot- wood chips, water boilers including requirements cereal grain for pressure testing. 600 mg/Nm3 With the introduction of general Straw Batch 0.80% 0.80% subsidies for small biofuel boilers in Straw Automatic 0.40% 0.30% 600 mg/Nm3 1995, type testing became of great immediate interest to the manufactur ­ Table 3: Maximum allowable CO emission and dust emission at normal output ers. That was because the Danish En­ and at low boiler load during type testing. ergy Agency required as a precondi­ tion for subsidies being granted that the boiler should be type approved, stated by the manufacturer and is an • Maximum allowable surface tem­ thereby complying with a wide range expression of the optimal point of op­ peratures of requirements for emission and en­ eration when the efficiency is high and • Leakage tightness to prevent flue ergy utilisation. The type testing was emissions low. gas leakage in the room carried out at the Test Laboratory for In addition to testing at nominal • Documentation, e.g., technical infor­ small Biofuel Boilers in accordance output, the type testing also includes mation, operational instructions, in­ with testdirections setting out the testing at low values, i.e., 30% of the stallation manual etc. guidelines for testing and the require­ nominal output. The requirements in ments to comply with in order to respect of dust- and CO emissions The subsidy scheme applies to biofuel achieve a type approval. Thedirec ­ are stated in Table 3, whereas the effi­ boilers, including straw-fired boilers tions are drafted on the basis of sug­ ciency should at least be as that that are installed in areas without dis ­ gestions for a joint European standard stated in Figure 16. trict heating supply. The subsidy per­ for solid fuel systems. However, the Other important requirements are: centage is calculated on the basis of requirements in respect of efficiency the testing result, and the sum is cal­ and emissions have been restricted • Securing against backfire/burn-back culated in proportion to the con­ and grouped according to firing tech­ in storage (e.g. mechanical damper sumer’s expensesfor boiler and in­ nology (batch or automatic) and fuel or by spraying with water) stallations. The subsidy scheme is ad- type (straw or wood). The require­ ments are established in a joint col­ laboration between the manufacturers of biofuel boilers, the Test Laboratory for small Biofuel Boilers, the Danish Automatic be Her Energy Agency, and the Danish Envi­ (wood, cere? I gr< ronmental Protection Agency. The type testing can be carried Batch-fired (manually out on the basis of various fuels, e.g.: boiler (wood, Forest wood, straw, wood pellets, wood chips, cereal grain or saw Automatic be iler stre w) dust/cuttings. The type approval does only apply for the fuel that was used during the testing. The scheme ap ­ plies to automatic boilers up to 200 kW and for batch-fired boilers up to Batch-fired b 400 kW. By raising the level to 400 kW, a reasonable combustion time is achieved for big bales. The list of type-approved boliers can be seen in /ref.39/.

Testing Requirements 10 20 40 60 80 100 200 400 600 8001000 Output (kW) The values for CO emission, dust emission, and efficiency are deter­ Figure 16: Efficiency minimum values depending on the type of boiler. For an mined by type testing as the mean automatic straw-fired boiler of 40 kW to be approved, a minimum efficiency of value over 2x6 hours at nominal 67% is required. boiler load. The nominal load is often Boiler Plants for farms

ministered by the Danish Energy Agency.

Experiences and Future Developmental Require­ ments Since implementing the systematic type testing in 1995, a wide range of experience has been gained in the field of small boilers. It was evident at the beginning that many manufactur ­ ers marketed boilers whose output far exceeds the requirement for typical in­ stallations. This meant that therewas an obvious disparity between the sup ­ ply of boilers with an output of less than 20 kW and the consumers’ actual demand. However, this has changed tremendously since then, and today most manufacturers offer systems with an output in the range of 10-20 kW or are developing new boilers. The small boilers are often designed The engineer responsible for the testing is preparing the boiler for type testing for wood pellets or perhaps boilers for at the Test Laboratory for small Biofuel Boilers at Danish Technological Institute grain. in Aarhus. There are still a need for improv­ ing the efficiency of boilers designed dust emission does not always de­ several boilers have advanced con­ for straw firing. There are several pos­ pend on the combustion. Variations trols with several output options and sibilities, e.g.: in straw quality may result in varying in a few cases oxygen control which emission levels. to a high extent has regard to the • Improving the boiler convection unit, • Improvements on devices for the variations in consumption in a typical so that the flue gas temperature can cleaning of the fire tubes and for the central heating installation. For this be reduced from the present removal of ash. reason, the Danish Energy Agency 250-300°C to 150-200°C. • Improvements on the boiler control is funding a research and develop­ • Improved lining and design of air equipment so as to ensure an opti­ ment project with the objective to de­ nozzles, thereby keeping the excess mal environmentally desirable and velop a cheap, universal oxygen air and the CO contentof theflue energy efficient operation with a high control unit adaptable for most small gas constant, thereby contributing to user comfort where the time con­ boilers in the market. reducing the dust emission. How­ sumed by the weekly attendance is ever, it should be mentioned that the minimal. It should be mentioned that

Straw for Energy Production Page 23 Neighbour Heating 6. Neighbour Heating

By “neighbour heating” is under­ • Ellehavegaard is centrally located in the boiler output can service. The stood a farm-scale boiler that in ad­ relation to Horreby. With several project has been approved by the Mu ­ dition to supplying heating to the large municipal heating consumers nicipal Housing and Building Agency, farm also supplies heating to one as “safe” customers, the heating but since the nominal output is less or several neighbours. sale was secured on beforehand than 1 MW, no environmental ap­ and the prospects of extending the proval is required. According to the Heat Supply Act, distribution net with connections to The existing straw-based heating neighbour heating plants larger than several private heating clients were plant has been replaced by a new 250 kW are under the obligation to re­ good. complete plant including the following: port, e.g., the heating prices to the • there were good prospects in re­ Gas- and Heating price Committee, spect of achieving public subsidies • Transport system for straw to the thereby specifying the method of the for the cost of construction via the boiler price calculation. Danish Energy Agency, and the mu­ • Feed system and boiler The difference between an actual nicipality had a positive attitude to­ • System for the removal of ash and district heating plant and a neighbour wards the idea. slag heating plant larger than 250 kW is • Flue gas cleaning and control sys­ first and foremost the size and the Organisation and tem type of ownership. A district heating plant is typically larger than 1 MW and Technique The plant has been designed so as to organised in the form of a (Danish) The plant that is organised in the form cope with peak loads, but in case of private limited liability company of a partnership with Peter Palle and suspension of operations of the (A.m.b.a.) (see Section 7), or in the his wife as the owners was started up straw-fired boiler, an oil-fired boiler form of a publicly owned company in January 1996 and is financed by has been established as a stand-by where the plant is not liable to pay tax approx. 50% via a mortgage loan, boiler. subject to the condition that the heat 25% subsidies by the Danish Energy can be supplied to anyone living in the Agency, and the remaining 25% by area. the owner’s own funds. User Agreement The relatively few neighbour At the time of starting up the plant An agreement was made between the heating plants established in Denmark and in addition to supplying heating Stubbekobing Kommune (municipal ­ - smaller than 1 MW - are typically for the farmer’s own farm, contracts ity) and the owner to the effect that owned by the farmer or perhaps es­ for heating supplies to a total of 5 mu­ the municipal buildings/undertakings tablished in the form of a (Danish) nicipal large-scale consumers and an pay a basic heating price that is equal partnership (I/S) with one or two part­ independent kindergarten institution to the oil price the municipality is pay­ ners. had been concluded. The distribution ing at the time of being connected to net is dimensioned so that a further 50 the district heating system. Thus, the private consumers can be connected basic price is fixed at DKK 400 per Horreby without major piping changes. With a MWh exclusive of VAT which is equal As an example of a modern neighbour peak load on a cold winter morning of to an oil price of DKK 3,200 per 1,000 heating plant, Peter Palle’s plant “Elle- approx. 0.6 MW with the present heat­ litres. The actual heating price is cal ­ havegaards Varmeforsyning I/S” in ing clients, there are limits, though, to culated as a variable charge accord ­ Horreby, Falster, will be described. how many more private connections ing to the heat consumption metered, In 1995, a project plan was drafted for the Danish Energy Agency on the establishing of a neighbour heating plant at Ellehavegaard. Apart tndslev from the owner's interest in proving that small-scale straw-based district Norr^ff fsli heating in a village could be estab ­ lished and operated satisfactorily both CO r ifkitetrup on the part of the ownerof the plant :Skils/rup and the heating clients, the back­ Horbaiev ground of the initiative was, e.g., that: St/bberup r

Horreby • the owner was experienced in straw

firing and as a supplier of straw for a Ellohavogirds large straw-based heating plant for Varmeforsyning I/S several years, he had the relevant

straw-handling equipment, storage Sr 0rsl« facilities, and straw resources at his Idestrlip disposal. • Stubbekobing Municipality ’s heating planning included the precondition Horreby is situated at Falster, Stubbekobing Kommune (municipality). There are that Horreby should be supplied with 114 houses and several public institutions biomass-based district heating. photo: hnka maskinfabrik production where Ash that The the quarterly tion fertiliser/manure. The on the a plied lated Krengerup Flue Manufacturer: General manner manure Multicyclone. LINKA The Typical

few

international

oil basic

between a expenditure dry handling: Centre

gas

by on

years price

prise the

Maskinfabrik. straw

with and ask/slag Kuwait the

cleaning: price price.

size

often Estate

agreement for Data

may may basis

spread the

income boiler

of

of Biomass

It Petroleum

price

net increases for fluctuate

result

is ordinary

the is at of

mixed

for

the

straw-fired on index

Funen. the

and charge conditions.

neighbour in like to experience

Technology average

thefield

a expenditure.

with fuel depending whereas

based in that dispropor

is a

oil

liquid

regu regular heat within

sup on heating.

like

of ­

­ ­

tems, Heat water Throughout the 25% Distribution boiler: Straw-fired Boiler institution 5 with ternal days Period consumers exchanger Only mm, Distribution Length: Consumer Cyclone,

municipal farm

the

consumers: 076 of the

for

Neighbour

farmhouse, is central output:

0.75

of

gross

1,100 district exchanged

maintenance.

are school

rotary mm, operation, plus

installation: where

boiler: have loss: MW. net: institutions

the connected.

heating heat

m. 050 livestock

heating year valve has

direct

Pipe the and

0.7

production. mm,

with straw:

installed except

Heating

system. district and

MW. 2

Diameter:

and connections

water

040 housing dwellings that

screw

Oil-fired

1

for

mm. heating of

a private circulat All

Straw heat 4-5 the

sys stoker 088 other

on

in ­

­ ­

for are DKK Approx. tent) tonnes tem. the the The sumer and Straw Fuel ing consumers prox. nicipality): Boiler cluding lations: is nance Cost Approx. Operating

seen Energy

handled

in operationalisation, distribution service

plant

consumption: per

300,000. of DKK the

installations consumption: etc.:

to to

(at

straw construction: DKK 3,000 DKK

annum.

the the

internal

runs

costs: approx. DKK 2.2 by Production DKK

have pipes:

80,000. left. consumers

the 430,000 expenditure.

litres million Electrical satisfactorily,

net. 220,000.

800,000.

Oil been The partnership. central

DKK 11-12%

(paid

per Approx.

consumption:

Distribution (in picture

per more connected

annum. 820,000. ’

power instal

1995 by

heating boiler Totalling annum Buildings:

Mainte­ water

the

Page private and 500-550 is

prices).

room from mu

since net con­ sys

Con­ to in ap­

­ 25 ­

­ ­ photo biopress/torben skott have (space ways The fired There amount coldest supplied of The All verted pressure shifting and Straw-fired container. heating the 3.7 perature duction Paae or cently Sabro 3.2 piping put Boiler average generation. 7. generation.

the closed

plants dimensions of MW. MW. term boiler 58

combined

refers been

maximum 9

Halmvarmevserk loss have

26

3

to heating day plants but requirements

can

MW

to The bale

to is of District Size The is

“ are

other district

The rating down

without

in 120°C the natural

6 constructed them

The of to

district be been

and

largest plant straw Straw bar. the weight designed

the

plants

annual are

distribution and divided

2.4

fuels

maximum heat heat

is

the in distribution

heating

The have and year.

61

fixed now electrical storage x gas connection hot

with heating

is smallest

1.2 for

plants,

amount to consumption of and

average (wood the

520

into for

water) been The

(straw-fired and in the

on

x since

plant

Enerav

heat

has maximum

big power operation. net boiler

1.3

the kg. is seen the

houses

heat

waste-

power net. plants

con but

chips)

0.6

bales ” and on an m.

pro­

size net basis 1980,

al

be with

tem

The ­ ­ the re­ The MW. out

on Production

heating of

is

of

­

­

straw

the Heating

for stated. straw-fired ties days of sum Heating established. corresponding Ordningen)) Control be heat quirement ex ple, heat normal houses. lated. 1995/96, 11,200 right,

plant)

hot is

Of

plant used a

District

where the

approx. The Maximum ” of

production, town production

this, on This water (ELO

these The year MWh/per

Scheme west maximum

Association

is

as the distribution the .

where of 40.7 the

is district

distribution a

average is is Of of 4,000 and left

In 400-450 distribution of equal to

guide

the

Heating

straw-fired 10%. to 3,112

the

Aarhus. TJ/per this, two

ex

output the

the and (EnergiLedelses- with annum the

acronym

heating district

tonnes.

Danish x plant. to

in

figures boiler These

statistics distribution loss

heat “ the small

space a the ELO single-family respect

x

annum

distribution

= The loss

can losses

consumption

As is

heating heating

plants Plants production ------house,

plants 3.2

District

degree communi figures of yields 30%

plant an

heating be from

and Plants Energy of or x

of exam

calcu 6,720 loss

are a of

are

load control

re­ the

was 37

hot

can net the

­

8,760

­ ­

makes

water constructed MWh

room, There was /ref. year. selected straw-fired stalled illustrated peak hours load requirement plant requirement ure loss put Figure normal loss 1995/96,

hours

make for can +

60% 40/. The The 28% being Normally, is

(here

The workshop load loads,

4,480

of

were

thus the so 17.

year. be

the in for

factor straw-fired

and

with

= 8760 as by throughout

42% out 66% maximum

calculated boiler.

1991

30% 3,300 6,720 repair, 60-70%

year. on of The

to a MWh

the

the a 3

40%

duration 3.2 and cover hours the and equal

oil-fired

when and MW

average maximum A highest degree

or = is MWh.

coldest

a district the boiler

of

=

damage the

3 space has an to the room on is to .

4,480 correcting the ......

MW

curve, lowest the be

boiler 2 empirical

the

year an entire

days distribution

distribution is MW).

for maximum

heating day used number heating boiler

usually output basis

MWh

of can is see the

16%. in of

output

With

at in the

to

the out fig

­ ash of be

of a of ­

­

District Heating Plants

this boiler size, the summer load of • The summer consumption is only (see Section 14). The main compo­ 0.5 MW will be approx. 25% of 2 MW, distribution loss and hot water. The nents are both manufactured by them­ which can yield a reasonable summer output requirement is 0.5 MW. That selves or they purchase sub-contracts operation in terms of combustion. is the lower part of the curve on the in the form of filters, chimney, crane, When the boiler is selected for 2 MW, right, and the summer load lasts and electric equipment etc. it is capable of operating at the maxi­ 8,760 - 6,500 = 2,260 hours. Three All boiler plants consist of the mum load for more than 1,000 hours weeks suspension of operations dur ­ same main components: per annum. ing summer for service purposes is The duration curve is created by shown. During that period, oil is • Straw storage with straw scales plotting the hourly load over the year used. • Straw crane and straw conveyor (totalling 8,760 hours) with the heavi­ (straw table) est load on the left and then the other Plant statistics show that the straw • Chaff cutter/shredder/slicer (the 3 one according to decreasing values. share of the total heat production is in first-mentioned types) The duration curve illustrates the the range of 85 - 93% /ref. 91. • Firing system and boiler following points: • Combustion air fans • Flue gas cleaning and ash/slag • The total area under the curve is Types of Boiler Plants conveyor equal to the annual production of The various types of boiler plants • Chimney and flue gas fan 11,200 MWh. have different firing principles that re­ • Control and regulation equipment • The Yellow area is equal to the straw- quire different equipment for transport fired boiler production. It makes out of straw and handling of straw from Boiler Plant Designed 93% of the area under the curve, storage to boiler. for Chaffed and Shredded equal to 10,400 MWh or 37,400 GJ. The 58 plants can be grouped in With an annual boiler efficiency of 5 typical systems/ref. 9 and 10/: Straw 84% and a calorific value of 14.5 This section also describes those GJ/t for straw, the requirement will • Boiler plant for chaffed straw: 7 parts of the boiler plants that are com­ be approx. 3,000 tonnes of straw per plants mon for the 5 boiler types. annum. • Boiler plant for shredded straw: 24 • The heat production based on oil is plants Storage approx. 800 MWh distributed on 550 • Boiler plant for sliced bales: 3 plants The storage is space consuming. On MWh at peak load and 250 MWh • Boiler plant for cigar firing: 11 plants average, the plants have storage fa ­ during 3 weeks suspension of op­ • Boiler plant for whole bales: 13 cilities for 8 days operation at full load erations during the summer season plants which for the average plant is equal to for service purposes, the brown 3.7 MW or more than 400 big bales. area. The energy consumption is There are 2-3 manufacturers in the The aggregate storage floor space in­ 87,000 litres of oil per annum. market that deliver all-in-one systems cluding driveway etc. for this amount of straw is approx. 600 m2. The straw supplier delivers the straw to the plant Output requirement expressed in MW by truck or tractor-towed trailers. The plant takes care of unloading by fork­ lift truck. The bales are weighed on unloading, and the water content is determined. The plants receive straw with up to approx. 20% water content. F eak loa Bales with a water content higher than that are returned, since combustion would thereby be too uneven, espe­ cially at part load. Working in the straw storage creates the risk of breathing in straw dust containing allergy promoting fun ­ gus spores and micro-organisms. As a guide in respectof permitted limit spension of operations values, the Directory of Labour In­ summer s spection Report No. 10/1990 on work­ oil-firing raw-firing ing environment problems in connec­ tion with waste management can be used.

Weighing and Water Content The weighing takes place eitheron a weighbridge or a platform scales. It is illegal to settle with the suppliers via Operating hours: Thousand hours a weighing cell mounted on the truck. The weighbridge is the fastest, since Figure 17: The duration curve fora 3 MW boiler plant with a 2 MW straw-fired only 2 weighing operations shall be boiler. Peak load and stand-by load by a 3 MW oil-fired boiler carried out (gross and tare of the truck).

Straw for Energy Production Page 27 District Heating Plants

placed. The bales are conveyed on to achieved. The grate can simultane ­ the straw table, the strings are cut, ously make a forward and backward and the bales continue to a chaff cut­ movement, whereby the burning straw ter or shredder. is transported through the boiler to­ wards the ash outlet. The energy con­ Chaff Cutting, Shredding, and Firing tent of the straw consists to a great The chaff cutter has a higher electrical extent of volatile gases (approx. 70%) powerconsumption, and the costs of that are driven out during heating for maintenance are also higher than burning in the combustion chamber those of the shredders and is there­ (furnace) over the grate. In order to fore substituted at existing plants as secure combustion air to the gases, time goes on. secondary air is introduced via many The purpose of the shredder is to nozzles in the boiler wall. The nozzle try to bring the straw back to the con­ air speed should be high so as to se­ dition before the baling. The bales are cure a good mixture of gases and conveyed towards the shredder that combustion air. If there is insufficient revolves at up to 30 rev./min. The out­ secondary air in the system, the result put can be varied from 15-1,000 kg/h. is high percentages of carbon monox­ A different type of shredder is ide and smell (unburnt hydrocarbons) called “straw-divider ”. The bales are in the flue gas. This results in pooref ­ conveyed towards a set of upward ficiency, since the unburnt gases dis ­ and downward moving racks that tear appear through the chimney. Measuring the water content in big apart the straw. It falls through a hop­ From the combustion chamber, bales at the heating plant. per on to a screw stoker or ram stoker theflue gases pass to the convector that passes the straw into the boiler. unit. The convector unit usually con­ It applies to all firing systems that sists of vertical rows of tubes through The platform scales is used by the a fireproof tunnel is established in which the flue gases pass. Most boiler truck driving on to the platform with front of the boiler. It should prevent plants are equipped with an econo­ the front wheels and is weighed every fire from starting outside the boiler miser, i.e., a heat exchanger posi­ time a bale is unloaded. This results in (backfire/burn-back). tioned after the convector unit. There a slower flow of work. A weighbridge theflue gases give off further heat to is 2-3 times more expensive than a Boiler the boiler water resulting in a higher platform scales, so the choice be­ The straw is passed via a screw overall efficiency. tween the two options is a matter of stoker or ram stoker into the bottom of increased investment against in­ the boiler. The boiler bottom consists Boiler Plants for Sliced creased working time. The scales of a grate that is a heavy cast-iron should be calibrated every 4 years by construction on which the combustion Bales a DANAK-approved laboratory. takes place. The grate is normally di ­ The whole bale is sliced by a hydrau ­ DANAK is short for Dansk Akkrediter- vided into several combustion zones lic knife, and the slice is pushed into ing, and the approval should secure admitting combustion air through the the boiler by a ram stoker. Before slic­ the quality of the calibration. grate (primary air). The combustion ing, the bale is raised to a vertical po­ For the determination of the wa ­ can be controlled in each zone, and a sition, and the knife slices from the ter content, a measuring instrument good burning of the straw can be “bottom” of the bale. equipped with a spear for insertion into the straw bale is used. The resis­ tance over two electrodes is meas­ ured and converted into water per­ centage on an indicator. Normally, three measurements are taken of the same bale, and on the basis of that, the average water content is calcu­ lated. Depending on practice and the wording of the contract, acceptance may be refused of eithera few bales or the whole load. The limit for refusal of straw is normally 20%.

Crane All large plants are equipped with an automatic crane that lifts the bales from storage to straw table. The crane is programmed to pick up the bales in a certain order, and it is therefore im­ portant that the truck driver/forklift driver places the bales in marked sec­ The forklift truck places the big bales in marked sections so that the automatic tions when unloading. Some of the crane can find them. Stacking in a height of 4 bales. The automatism sees to it small plants do not have cranes but a that the crane places a bale on the straw table from where the bale is conveyed long conveyoron which the bales are to the shredder. The

graphic: volund Then pushed that The Whole burns burner to and a the towards from feeder endless ting/shredding ous bale the oxygen troduction most ber box proof towards straw introduced from bustion. stoker end. bales mounted ing partly bale In the combustion Instead Boiler Boiler "Cigar basis

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Page 29 field, on elec­ the gas Price/m bags

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District Heating Plants

• Flue gas scrubber: The flue gas the requirements by the authority in • Peak load morning and evening dur ­ passes through a showerso that the question. The Danish Environmental ing the winter season can be particles are trapped/caught in the Protection Agency Directions No. 6 smoothed out, thereby avoiding oil water. and 9/1990 “Industrial Air Pollution firing. • Flue gas condensation: The flue gas Control Guidelines” apply to straw- • During suspension of operations, the is cooled to below the dew point, fired plants. The directions also in­ heat consumption can be drawn and the particles are absorbed/trap ­ struct how to calculate the heights of from the storage tank, thereby ped by the dew. chimneys /ref. 42/. avoiding oil firing. A 400 m3 tank can supply heat for 7 hours at full load at The normal equipment is a multicy- an average plant. clone to serve as spark arrester and Ash • At off-peak load during summer, the for coarse particles followed by a bag Straw contains 3-5% ash. Part of the boiler can operate at full load for a filter. The multicyclone cleans the flue ash falls off the grate into a hopper short period while the storage tank is gas from 1,000-2,000 mg dust/Nm 3 to under the boiler and passes via the filled, and then boiler is closed. The 500-600 mg/Nm3. Much of the fly ash chain scraper to the ash container. result is improved efficiency and from straw firing is so fine-grained The chain scraper usually lies in a lower emissions compared to con­ (below 0.01 mm) that the filter bags water bath where an automatic water tinuous operating at off-peak load. are the best and cheapest solution for addition takes place simultaneously • The personnel’s roster becomes complying with the requirement of 40 with the water evaporating and being more flexible, since, e.g., the boiler mg dust/ Nm3. The particle content of carried together with the ash to the can be closed over the week-end the dust after filter is under normal op­ container. Wet transport of the ash is during summer. eration 20-30 mg dust/ Nnfwith bags the most normal procedure at the without cracks. See also the section plants, and a water bath in the chain The drawbacks are increased ex­ on environmental conditions. scraper is an efficient trap so as to pensesfor investment and mainte­ Electrostatic filters may give prevent the introduction of false air to nance of the tank, and also straw problems in connection with straw- the boiler through the ash conveyor should be purchased in order to cover fired plants. Two plants that originally system. the tank heat loss. had electrostatic filters have replaced The fly ash consists of the sus ­ them with bag filters. pended solids that follow the flue gas Control, Regulation and The dust particles are difficult to through the boiler and are separated ionise in the electrostaticfilter, and it in cyclone and filter. From there, the Monitoring/Supervision is difficult to make them leave the particles are transported via worm Control, regulation and monitoring/su­ electrodes and fall off to the ash sys­ conveyors to the chain scraper. The pervision of the plant is called the tem due to the very small mass. Some application of the ash as fertiliser is SRO system (Styring, Regulering and of the particles therefore condense described under Section 11. Overvagning). The system usually and deposit like coating in the chim­ consists of two computers: ney, and, in particular, when the plant is started up, lumps of soot are carried Storage Tank • A PLC (Programmable Logic Com­ along and fall down in the neighbour­ Storage tanks have been installed at puter) that collects operating data hood of the plant. 23 heating plants. The average tank is from the plant and keeps the plant to A few heating plants have in­ 400 m3. This size of tank costs ap­ chosen values for pressure, tem­ stalled a flue gas scrubber. The princi­ prox. DKK 1 million (1995 prices). perature, flow etc. ple is that the flue gas passes The advantages of installing a • An ordinary PC that shows the op­ through a “waterfall ” of atomised wa ­ tank are the following: erator the actual data from the PLC ter, thereby absorbing the dust parti­ cles, thereby transporting them with the water. This method creates a waste-water problem for the plant in­ stead of an ash deposition problem. As something new, the district heating plant Hals Fjernvarme has in­ stalled a flue gas condenser. Experi­ ences gained over the first years are good despite the low water contentof straw. The operating costs for electri­ cal power are approx. 5% lower for the entire plant. The costs of mainte­ nance are 1/3-1/4 compared to the fil­ ter bags.

Chimney A district heating plant with cigar-fired boiler. The automatic crane places the big The cleaned flue gas is released bales in the feeder box, and the bales are passed on for combustion. The flue through the chimney to the atmos ­ gases pass through the 4 empty passes and out into the convector unit that phere. There is a separate flue gas consists of vertical fire tubes. The ash falls via hoppers off to the ash container. tube for each of the boilers. In each The flue gas passes through the bag filter, and via the flue gas fan in the individual case, the heightof the chim­ basement, the cleaned flue gas is released through the chimney. All fans are ney should be decided on the basis of located in the basement for noise considerations.

Page 30 Straw for Energy Production District Heating Plants

on a visual display screen and via ences in emission depending on vari ­ Sulphur dioxide (S02) is formed on printouts. The chosen values can be ous firing principles were found /ref. the basis of thefuel contentof sul ­ changed on the PC, and the plant 11, Videnblad 61/. phur. S02 causes: operating conditions can be In Table 5, the CO value of 1,200 changed via the PLC. mg/Nm3 is equal to 0.096% which is • Acidification of the atmosphere above the Danish Environmental Pro­ • Corrosion in boiler and filter by for­ The system is divided into three main tection Agency’s limit value of 0.05%. mation of sulphuric acid. functions covering the following: The CO content in the flue gas de­ pends on how good the combustion Both S02 and NOx can be removed • The control takes care that the entire is. The content should be as low as from the flue gases, but the processes process takes place in a pre-set se­ possible, since are too expensivefor small plants like quence. The crane, e.g., is pro­ district heating plants. Measurements grammed not to pick up a new straw • CO is poisonous at 2 district heating plants have shown bale until the preceding bale has • CO is a flammable gas. A high that an amount of 57-65% of the sul ­ been fed into the boiler and the CO content decreases the effici­ phur is released through the chimney. boiler working thermostat calls for ency The remainder is bound in the ash more heat. • high CO value and odour nuisance /ref.59/. • The regulation takes care that the from the chimney go together Hydrogen chloride (HCI) also values chosen for pressure, tem­ • high CO value and the presence of contributes to S02 acidification of the perature etc. are maintained. PAH and dioxin in the flue gas atmosphere and corrosion in the • The monitor signals malfunctions. probably go together boiler plant. The chlorine content of The alarm can via a bleep be trans ­ straw may probably be due to the use mitted to the person on duty in or It is desired for the NOxformation to of fertiliser and pesticides. outside the plant. Usually the plant is be reduced, since the presence of PAH (polyaromatic hydrocarbons) manned from 08:00 -16:00 hours NO* contributes to is a genericterm for a long range of during the 5 working days of the hydrocarbon compounds character ­ week. • the formation of "smog" in the at­ ised by smelling. Dioxin is also a ge­ mosphere neric termfor substances that contain • acid deposits carbon, oxygen, hydrogen, and chlo­ Environmental Conditions rine. PAH and dioxins are formed by The authorities and the public debate The NOx is formed by the nitrogen incomplete combustion and are haz­ are very concerned about the impact content of the air and thefuel and de­ ardous to health. A connection be­ on the environment by energy produc ­ pends on how the combustion takes tween a high CO content and the for­ tion. Straw is C02 neutral, and that is place in the combustion chamber. Of mation of PAH and dioxins has been the major reason why it is a political important parameters for a low NOx demonstrated /ref. 44, 45 and 46/. desire to promote the use of straw in emission can be mentioned: the energy supply. In the period from 1987-93, a se­ • low excess air Noise ries of emission measurements was • low flame temperature In connection with public approval of made at 13 plants (Table 5). No differ­ • rapid cooling of the flue gases the heating plant, the following levels can be established: Parameter Mg/Nm3 at 10% 02 Mg/MJ • Noise limit in boundaries: 40 dB (A) • Noise limit in existing housing areas: Particles1’ (dust) 80 (5 - 200) 40 (3-100) - 45 dB(A) Monday - Friday from 07:00-18:00 hours and Saturdays CO (carbon monoxide) 1200 (240-2300) 600 (120-1150) from 07:00-14:00 hours - 40 dB (A) Monday - Friday from NOx (nitrogen oxides)2’ 180 (80-300) 90 (40-150) 18:00-22:00 and Saturdays from S02 (Sulphur oxides)3’ 260 (200 -340) 130 (100-170) 14:00-22:00 and Sundays and non-working days from 07:00-22:00 HCI (hydrogen chloride) 80 (30-150) 40 (15-80) - 35 dB (A) all days from 22:00 - 07:00. PAH 0,35 (0,20 - 0,60) 0,18(0,10-0,30) As a comparison, the background Dioxin (Nordic tox. eqv.)4’ (0,01‘lo^-o,4*10"6) (0,005*10'6-4*1 O'6) noise in a housing area is 31-32 dB (A). An efficient way of controlling the (0,8*10"6-8*1 O'6) (0,4*10"6-4*1 O'6) Dioxin (PCDD + PCDF)4’ noise from noise sources is to place fans, hydraulic engines etc. in a base­ 1) The figures apply to plants with bag filter ment. 2) Calculated as NOz equivalents 3) The figure is determined by calculation on the basis of the sulphur content of straw (20 straw ana ­ lyses). Measurements in 1997 have shown that 35-43% of the sulphur is bound in the ash /ref. 59/. Safety 4) Measurements have been conducted at two plants, one value per plant In-plant safety includes fire safety and Table 5: In the period from 1987-93 a series of emission measurements has personnel safety. The plant must be been made at 13 district heating plants. The figures in bold are mean values, approved by the local fire authorities and the figures in brackets show at which interval it can be expected to find before starting up. The plant should approx. 90% of the measuring results. Dust- and carbon monoxide emissions be divided into fireproof sections, e.g., are beyond the Danish Environmental ProtectionAgency ’s limit values. as follows:

Straw for Energy Production Page 31 District Heating Plants

• Straw storage • Straw feeding • Boiler room • Other rooms: Offices, canteen, workshop etc.

The greatest risks are fire in the straw storage or explosions in the flue gas. If flue gases leak to the rooms, e.g. due to malfunction of the feeder sys­ tem, sparks from electric switches, or from the boiler itselfmay ignite the flue gases thereby causing an explo­ sion. Usually the section around the feeder system should be equipped with explosion relief doors in order to reduce the damage caused by a flue gas explosion. The Danish Directory of Labour Inspection shall approve the person­ nel safety. It includes safety from suf ­ fering scalding, burn, poisoning with flue gas or dust, and injuries caused by cranes, conveyors, shredders etc.

Co-firing with Other Fuels 0 1 23456789 10 As mentioned under the section on MW output rating, all plants are equipped with oil-fired peak and stand-by load boiler Figure 18: Cost of construction by the million (DKK) per MW installed output, capable of supplying the entire heat adjusted to the price level of 1995. The price includes site, land development, requirements of the net. buildings, installation of machinery, and projecting. The information is based on 40 plants that only use straw. The price spread can be explained by different The debate over the recent years size of storage, the general quality of the plant, fluctuations of the market in the in respectof straw resources and the period from 1983-1995, and that individual plants have included a storage tank meagre straw year 1993 occasioning local shortage of straw has resulted in in the price. 11 plants having upgraded the stor­ age, feeder system and boiler for co­ firing with wood. It is primarily dry machinery and projecting. All prices Heat production: 11,200 MWh waste wood from the wood industry or are 1995 prices so that they are com­ Heat production, straw-based: 93% wood pellets that are used. At four parable. Only veryfew plants have Heat production, oil-based: 7% plants, it is possible to mix fatty sludge storage tank included in the price. Fig­ Maximum output requirement: 3 MW and straw/ref. 47 and 48/. ure 18 illustrates the prices for the in­ Straw-based boiler output: 2 MW Manager District Heating Plant is dividual plants as a function of the one of the plants that has been con­ straw boiler output. For a densely built-up town, the distri ­ verted into burning both waste wood As an example, the cost of con­ bution loss for a year with 3,112 En­ and straw. The plant has a 6 MW bio ­ struction will be set out in detail for a ergy Control Scheme degree days fuel boiler and has had the following town where both a new plant and a (“ELO degree days ”) is approx. 30%. fuel consumption during 1995: new distribution net is established. It If the area is sparsely built over or in is important for a new project to get“ a case of small towns connected via Straw: 4,944 tonnes head start ”. Therefore, at least 80% of transmission piping, the distribution Wood: 1,310 tonnes Oil: 57.4 m3 the oil-fired boilers and all public loss rises to above 35%. large-scale consumers should join it The investment is as follows: Oil share in relation to the total heat right from the beginning. Public large- production of 23,200 MWh is only 2%. scale consumers are municipality of­ million DKK fices, schools, sports centres, etc. The heating plant 9.0 Contrary to earlier practice, industrial Distribution net 10.0 Investment and Operating enterprises and liberal professions will Consumer service pipes 4.0 not be reimbursed for energy and en­ Consumer house installations 4.0 Construction Investment vironmental taxes in connection with Unforeseen expenses 1.0 For the purpose of the report space heating and are therefore also Total cost of construction 28.0 “Anlsegs- og driftsdata for halmfyrede a target group. Possible subsidies 4.8 varmevserker. 1996” (data on the con­ The data of the example are partly Loan requirement 23.2 struction and operation of straw-fired from Figure 17 and are per annum: heating plants) /ref. 9 and 10/, infor­ The cost of construction can be fi­ mation has been collected about initial 260 consumers: 4,550 MWh nanced fully by means of index-linked expenditures in respectof site, land 10 large-scale cons.: 3,300 MWh loan. Index-linked loan is a loan that is development, buildings, installation of Net losses in percent: 30% repaid by annual payments that in-

Pane 32 Straw fnr Fnprnv Prnrli mtirin District Heating Plants crease concurrently with inflation. It is With regard to accounting practice, Fuel (35%) Capital costs (41%) a cheaper type of loan than the ordi ­ the straight line method of deprecia ­ nary loans, repayable by equal semi­ tion, which charges each year an annual instalments or annuity loans, equal sum, reflects in a better way the as long as inflation is below 7% per partial using-up of the life of the plant annum. The structure of index-linked than does the other practice where loan is set out in more detail in /ref. the depreciation is booked as being 41/. Applications for subsidies from equal to the instalments on the loan. the Danish Energy Agency can be By the last-mentioned method, the ex­ filed until and including the year 2000. penses will increase as the instal ­ ments rise over the period of repay­ Operating ment. Indexation of instalments is the and mainten-' Operating Profit and Loss ance (9%) expensefor the annual appreciation of Electrical Personnel and Other power ,00/. administration The heating plant income derives from instalments with the index of net and chem-costs /o) (11 %) the sale of heat and is distributed on prices. The remaining debt also is re­ icals (2%) standard and variable prices for the valued with the index of net prices. heating. The tariff for the sale of heat This item is booked in an exchange Figure 19: Distribution of costs in to the consumers may e.g. be: equalisation fund under the equity percentages concerning the example capital /ref. 11, Videnblad 117/. illustrated/calculated. The costs in Variable charge DKK 350/MWh connection with repayment of loan Fixed annual charge DKK 1,000/con Forms of Organisation (capital costs) and the purchase of Capacity charge, private DKK 30/m2 Straw-fired heating plants can be es­ straw and oil make out 76% of the Capacity charge, industry DKK 30/m2 tablished as privately owned compa ­ plant’s costs. nies: In addition to that, VAT shall be in­ liable only for the capital for which cluded. For a private consumer in a • Co-operative societywith limited li­ they have subscribed shares. house of 120-130 m2 with an average ability (A.m.b.a.) Straw-based plants shall not be consumption of 17.5 MWh, the heat­ • Private limited liability company liable to pay tax if the heat can be ing expense will amount to DKK (ApS) supplied to everyone living in the area 13,800 per annum. This expense is • Limited liability company (A/S) they supply. Therefore it would not be more or less equal to the operating appropriate to form a partnership (I/S), costs in respectof oil firing: Oil, chim­ or publicly owned companies. since it would not normally be possi­ ney sweeping, and maintenance. The ble to exploitthe tax benefits. On the tariff will yield the following income: The persons behind such company contrary, the partners are jointly and may be either: severally liable to the full extent of Thousand DKK their property. This means that credi­ Sale of heat, 7,840 MWh 2,748 • a group of farmers tors may levy execution against all Fixed annual charge 270 • an association of straw suppliers partners in the event that the com­ Capacity charge, private 1,014 • an existing district heating company pany goes bankruptcy. Capacity charge, industry 350 • a group of consumers Total income 4.442 • a municipality

The expenses are as follows: If a straw-based heating plant is pri­ vately owned, it would be appropriate Thousand DKK to organise it as a co-operative soci­ Purchase of straw, DKK 430/t 1,235 ety with limited liability (A.m.b.a.). The Purchase of oil, 87,000 litres 295 owners shall only be personally liable Maintenance, plant 200 for their contribution, and each con­ Maintenance distribution net 200 sumer has one vote at the general Electrical power, chemicals 100 meeting. In addition, theform of com­ Othercosts (insurance etc.) 75 pany is already known to many peo­ Personnel and administration 500 ple. Almost all straw-based heating Depreciation, 20 years 1,160 plants in Denmark are privately owned Indexation of instalments 23 co-operative societies with limited li­ Interest and contribution 620 ability. A partnership may also be the Total expenses 4,408 form chosen, or a limited liability com­ Net result 14 pany where the participants also are

Straw for Energy Production Page 33 CHP- and Power Plants 8. CHP- and Power Plants In 1986, the Danish Government entered into an energy policy agreement including, e.g., that de­ centralised CHP plants with a total power output of 450 MW fired with domestic fuels like straw, wood, waste, biogas, and natural gas shall be constructed up to 1995. In 1990, the government entered into another agreement on increased use of natural gas and biofuels, pri marily by constructing new CHP plants and converting the existing coal- and oil-fired district heating plants to natural gas and biomass- energi

based CHP production. wain

& CHP Plant Principle At a traditional coal-fired power plant burmeister (condensation), 40-45% of the energy input is converted into electrical power. The remaining energy is not photo: utilised. It vanishes with the hot flue Masned0 Kraftvarmevaerk (CHP plant) was started up in 1996 and consumes gas from the boiler through the chim­ approx. 40,000 tonnes of straw per annum. In addition, an amount of approx. ney into thin air and with the cooling 8,000 tonnesof wood chips is consumed. water out into the sea (see Figure 20). At a CHP plant, electrical power district heating production achieve as trical power and heat production is is generated in the same way as at a high electrical powerefficiency, i.e., changed, but in principle, the greater power plant, but instead of discharg ­ the ratio between the electrical power heating requirement the more steam ing the condensation heat from the generated and the energy input, as can be cooled by the district heating steam together with the cooling water that of a power plant. The electrical water, and the more steam can be into the sea, the steam is cooled by power efficiency for a straw-fired plant produced by the boiler with the sub ­ means of the recycling water from a is 20-30%. sequently greater electrical power district heating distribution net which By operating a CHP plant, the an­ generation. At a power plant, there in turn is heated. nual electrical power efficiency (on av­ is not this dependence, since there is The advantages of a CHP plant erage over a year) is not necessarily always sufficient cooling capacity in is, e.g., that is does not require sea an expression of what is technically the sea. In order to make the electri­ water for cooling and can therefore be possible. Requirements in respectof cal power generation at a CHP plant located near large towns (decentral ­ process steam supply, priority of dis ­ more independent of the district heat­ ised) where there is a sufficiently trict heating supply, and electrical ing requirement, all plants are great requirementfor district heating powergeneration according to certain equipped with a storage tank where and a distribution net. Another advan ­ tariffs result in a lower efficiencythan the condensation heat can be stored tage is that the energy generated by the full-load electrical power effi­ when the district heating requirement the fuel can be utilised up to 85-90% ciency. See Table 6. is low. (see Figure 20). At the CHP plant, it is possible Combined heat and power pro­ On the other hand, it is not possi­ to with certain limits regulate the tur ­ duction is given high priority in Den­ ble to at a CHP plant together with bine so that the ratio between elec­ mark, also when it comes to power

- --4#% Heat production 85%

..Losi

Figure 20: By separate electrical power generation and heat production at a power plant and a district heating plant, the losses are much larger than by combined heat and power production at a CHP plant. Losses include own consumption at the plant CHP- and Power Plants

Rudkobing Haslev Slagelse Masnedo Grena Mabjerg Maribo/ Sakskobing Electrical power output (net) 2.3 MW 5.0 MW 11.7 MW 8.3 MW 18.6 MW 28 MW 9.3 MW Heat output 7.0 MJ/s 13.0 MJ/s 28.0 MJ/s 20.8 MJ/s 60.0 MJ/s 67 MJ/s 20.3 MJ/s Full load electrical efficiency (net) 21% 23% 27% 26% 18% 27% 29% Electrical efficiency per annum 17% 17% 22% 23% 14% 20% 26%

Table 6: Electrical power output, heat output, and electrical power efficiency for the seven decentralised CHP plants. As explained in the text, the annual electrical power efficiency is lower than the efficiency at full load. The annual electrical power efficiency is calculatedon the basis of production figures for 1997 except for Maribo/Sakskobing that is an esti ­ mated figure. The high figures for Slagelse are caused by the fact that the steam from the waste boiler plant is not included in the boiler loss. The low figures for Grenaa Kraftvarmevaerk (CHP plant) are caused by supplies of process steam for in­ dustrial purposes. All figures stated are net figures, i.e., the plant’s own consumption of electrical power has been de ­ ducted. See also Table 7. plants located near large cities like Rudkobing, Haslev, The plants are owned and run by the Copenhagen, Aarhus, Aalborg, Slagelse, Masnede, and electrical powercompanies: I/S Sjael- Odense and others. At these power landske Kraftvaerker, SK Energi, and plants, part of the loss of approx. 60% Maribo/Sakskebing I/S Fynsvaerket. The electricity gener­ as shown in Figure 20 is utilised for The CHP plants in Haslev and Rud- ated is supplied to the public utility district heating production. kobing were started up in 1989 and companies’ main distribution network, The six straw-fired decentralised 1990 and are Denmark’s and probably and the heat is supplied to the district CHP plants that are already in opera­ the world ’s first electrical power gen­ heating systems of the towns. tion and the planned plant in Mar- erating plants exclusively fired with ibo/Sakskobing are all based on the straw. The plant at Masnedo near Size of Plant CHP principle described. As the Vordingborg that was started up in The outputs at the plants of Rudke- plants are partly constructed as dem­ 1996 is also exclusively straw-fired, bing, Haslev, and Masnede are: 2.3, onstration plants for the purpose of but at the same time designed for 5, and 8.3 MW electrical power (MW demonstrating the straw-based tech­ wood chips up to 20% of the total in­ electricity). With a heat output of 7.0, nologies, they are rather different in put. The plant near Maribo/Sak- 13, and 20.8 MJ/s respectively, the construction design. Comparable data skobing is planned to start up at the annual consumption of straw is ap­ on the seven plants appear from Ta ­ beginning of the year 2000 and is ex­ prox. 12,500, 25,000, and 40,000 ton­ bles 6, 7, 8, and 9. clusively straw-fired. nes. Electrical output and heat output

Boiler

District heating Slag container Feed water tank heat exchanger

Condenser

Storage tank

Figure 21. Simplified diagram of Rudkobing Kraftvarmevaerk (CHP plant). The flue gas passes through the combustion chamber to the superheater section and further through an economiser and air preheater and is cleaned in a bag filter before being released through the chimney at 110°C. CHP- and Power Plants

are net figures, i.e., the plants ’ own Firing and Combustion System which for each of the three firing sys­ consumption of electrical powerand At the plant in Slagelse, two automatic tems consist of three screws. The heat are deducted. cranes handle the transport of the big screw stokers press the straw through As the plant in Slagelse is a com­ bales from the rows in the storage to the feeding tunnel on to the grate that bination between a waste-fired and a three parallel feeding system. The consists of an inclined movable push straw-fired boiler that produces steam bales are passed via a closed fire­ grate followed by a short horizontal for the same turbine, the data in Ta ­ proof tunnel system (that prevents a push grate. After burning out, the bles 6 and 7 for the entire plant are possible backfire/burn-back from ash/slag falls via a slag hopper into a 11.7 MW electrical powerand 28 MJ/s spreading to the straw storage) to­ slag bath filled with water from where heat, respectively. An amount of 65- wards the straw shredder of the same a conveyorsystem conveys the wet 70% of the production output is based type as that used at Grenaa Kraftvar- ash/slag to containers. on straw which is equal to an annual mevaerk (CHP plant). The strings that At Rudkebing Kraftvarmevserk consumption of straw of approx. hold the bales together are automati ­ (CHP plant) with a firing capacity of 25.000 tonnes. cally cut and removed. 10.7 MW, only one firing system is re­ The plant near Maribo/Sak- The shredder consists of three quired. After shredding, the straw falls skobing is designed for an electrical rotating cylinders positioned above down into a stokersystem consisting power output of 9.3 MW and a heat each otherequipped with kind of a of one single rectangular ram stoker production of 20.3 MJ/s. The annual disc separator. The loose straw falls that by forward and backward move­ consumption of straw is approx. off the shredder on to a rotary valve ments pushes the straw through a 40.000 tonnes. and from there to the screw stokers water-cooled feeding tunnel on to the

Data Unit Rud- Haslev Slagelse3* Masnedo Grena Mabjerg 1* Maribo kebing Saks- kobing Electrical power (net) MW 2.3 5.0 11.7 4) 8.3 18.6 282) 9.3 Heat output MJ/s 7.0 13 284) 20.8 60.05) 67 2) 20.3 Steam pressure bar 60 67 67 92 92 67 93 Steam temp. °C 450 450 450 522 505 410/520 542 Max. Steam flow tonnes/h 13.9 26 40.5 43.2 104 125 43.2 Storage tank m3 2,500 3,200 3.500 5,000 4,000 5,000 5,600 Flue gas flow, max. kg/s 6.8 9.9 13.4 14 39 71 14 Flue gas temp. °c 110 120 120 120 135 110 110 Straw storage tonnes 350 350 550 1,000 1,100 432 1,000 Straw consumption tonnes/year 12,500 25,000 25,000 40,000 55,000 35,000 40,000 Water content, straw % 10-25 10-25 10-25 max 25 10-23 10-25 max 25 Filter type Bag filter Bag filter Elec, filter Elec, filter Elec, filter Bag filter Bag filter Firing system Shredded/ Cigar Shredded/ Shredded/ Shredded/ Cigar Shredded/ stoker burner stoker stokerpneumatic burner stoker Boiler plant costs DKK 64 mill. 100 mill. 1406) mill. 240 mill. 365 mill. 600 mill. 240 mill. Started up year 1990 1989 1990 1996 1992 1993 2000

Specific 1995-price2* DKK/MWe, 30 mill. 23 mill. 21 mill. 28 mill. 21 mill. 22 mill. 23 mill.

1): The plant consists of two waste-fired and one straw/wood chips-fired boiler that produces steam for the same turbine. 2) : Data are the total production output of electrical power and heat of the straw/wood chips- and the waste-fired boilers of which the straw/wood chips-fired boiler produces approx. 27%. 3) :The plant consists of a waste-fired and a straw-fired boiler that produces steam for the same turbine. 4) : Data are the total production of electrical power and heat of the straw- and waste-fired boilers of which the straw-fired boiler generates/produces approx. 66%. 5) : Distributed between district heating (max. 32 MJ/s) and process steam (max. 53 MJ/s). 6) : The cost of construction only for the straw-boiler. 7) : The specific price is only normative, since it varies how much the cost of construction shall include. As a comparison with other types of CHP plants, it should be informed that here the net output has formed the basis of the calculation of the specific price and not the gross electrical power output (gross figures include own consumption at the plant). Table 1: Data for the seven straw-fired, decentralised CHP plants. CHP- and Power Plants

grate. By means of the ram stoker movements, the straw is pressed to­ gether in the feeding tunnel to a gas ­ proofplug that prevents backfire/ burn-back. The straw burns out on a vibrating grate, and the ash/slag falls into a water-cooled slag bath from where it passes to the container. At Haslev Kraftvarmevasrk (CHP plant), the big bales are fired without shredding in four parallel cigar burner systems. The cigar burner is de­ scribed under Section 7 on district heating plants. At Masnedo Kraftvarmevaerk (CHP plant), the straw is stored and handled to the firing system via crane and feeding lines. A completely new system has been developed for the feeding of the straw whereby the straw bale is pushed against two verti­ cal screws which by means of their ro­ tation shred the straw and pass it to a horizontal set of screw stokers that by means of counter rotation press the A water tube boiler of a CHP plant is being welded. The tubes are equipped with straw into theform of a gas-proof plug small longitudinal fins so that they can be welded together to a gas-proof wall through an almost rectangular feeding making out the sides, top and bottom of the boiler. tunnel and then on to the grate. With two of these systems, the plant is ca­ pable of at full load consuming 19 big the boiler. From the steam drum the free movement of the flue gas to bales, equal to 10 tonnes of straw, per where water and steam are sepa­ an extent that the negative pressure hour. Each of the two firing systems rated, the steam passes to the super­ and thus the load on the boiler cannot have been designed so as to be fed heaters which, e.g., can be clustered be maintained. At the plants in Haslev, wood chips simultaneously with the either like festoons vertically from the Slagelse, and Rudkobing, it has been straw. Preliminary experiments show ceiling or be set in vertical banks of tried to avoid these problems by limit­ that the wood chips can make out up pipes in independent superheater ing the superheater temperature to a to 40% of the overall energy input. passes after the combustion chamber. maximum of 450°C. In Haslev and The plant has been designed for 20% After the superheater passes, there is Slagelse, this has been done by pull ­ wood chips. a pass with the economiserand the ing the superheater sectionsthat far air preheater where thefeed water back in the boiler system that theflue Ash and Slag Handling and combustion air are heated. Due to gas temperature is reduced to approx. At all plants, the slag and ash from the the relative high content of alkali met­ 650-700°C before its contact with the bottom of the boiler are separated als in the straw ash (potassium and first superheater section. from the fly ash from the filter. The sodium) and chlorine, the flue gas is At Masnedo Kraftvarmevaerk slag and ash from the bottom of the corrosive, particularly at high tempera­ (CHP plant), the steam temperature boiler are returned to the farmer so as tures (above 450°C), and thus as a has been increased to 522°C as an to be applied as a manure/fertiliser consequence of the low ash tempera­ experiment. As mentioned, the higher supplement whereas the fly ash due ture of fusion, the ash particles may temperature increases the risk of to its too high content of heavy metals cause slagging problems in the boiler. heavy corrosion and slagging prob­ may either be deposited on a con­ If the slag becomes solid and viscid, it lems. The superheaterand the top trolled waste disposal site or be used is difficult to remove during operating of the boiler is therefore constructed for mixing with fertilisers. For further and will obstruct the heat transfer from so that it is relatively easy to replace details, see under Section 11 “Resid­ theflue gas to the steam in the tubes, possible corroded superheater ual Products ”. and in severe cases, it may shut off tubes.

Boiler Output, Steam Data, and Other Unit Masnedo Grena Mabjerg Slagelse Heat Storage fuels All the boilers are water tube boilers with steam drum and natural circula ­ Waste tonnes/year - - 150,000 20,000 tion in the vaporiser system. For rea­ sons of plant efficiency, it is necessary Coal tonnes/year - 40,000 - - with a high electrical power genera­ Gas Nm3/year - - 4 million - tion. This preconditions a high steam pressure and steam temperature. In Wood chips tonnes/year 8,000 - 25,000 - order for the boiler to withstand the high pressure, the boiler water passes Table 8: Four of the plants are designed for co-firing with other fuels. through water/steam tubes that make out the walls (and top and bottom) of

Straw for Energy Production Page 37 CHP- and Power Plants

At the planned CHP plant in Mar- ing with combinations of straw and The fluidized bed principle is seen in a ibo/Sakskobing that will be started up other fuels. variety of types, but roughly there are at the beginning of the year 2000, the two main principles: steam temperature will be designed to The CHP Plant in Grenaa • Bubbling fluidized bed (BFB) 542°C. A range of experiments will The CHP plant in Grenaa is coal- and • Circulating fluidized bed (CFB) show how serious the corrosion prob­ straw-fired, and in addition to electri­ lems will be. cal power, it shall together with a mu­ The boiler in Grenaa is a circulating The prospects for Danish trade nicipality run refuse incineration plant, fluidized bed type. From the fluidized and industry gaining a foothold in for­ and waste heat from the industrial en­ bed section, the heated flue gas circu ­ eign markets with straw-fired CHP terprises nearby, cover 90% of the lates together with solid particles into plants preconditions high electrical district heating consumption in Gre­ an separator cyclone where the solid power efficiencies and thus high naa and 90% of the process steam particles are extracted and re­ steam data in the range of 580°C as consumption by the industrial enter­ circulated in the fluidized bed. The at the most recently constructed pul­ prise Danisco Paper. As from 1997, flue gas passes from the cyclone to a verised coal-fired power plants. At the industrial steam system is devel­ pass where the economiserand air temperatures that high, it will, in addi ­ oped so as to also cover the process preheater are positioned. Between the tion to the problems in connection with steam consumption by Danisco Distill­ cyclone outlet and the economiser, corrosion and slag deposits, also be ers. So far being the only biomass- theflue gas passes 2 tube sections necessary to equip the plant with tur ­ fired plant in Denmark, the boiler type which together with a bank of pipes in bines of a different and more expen­ used in Grenaa is designed as a cir­ the bed itself make out the superhea­ sive quality than that previously used culating fluidized bed system. ter. In 1996, the superheater was ex­ on the CHP plants described in the tended with a section positioned in the above sections. Fluidized Bed ash re-circulation system. A fluidized bed boiler consists of a cy­ lindrical vertically setcombustion Grenaa and Maabjerg chamber where air passes through Handling and Firing System The CHP plants in Grenaa and Maa­ the solid particles consisting of fuel At the CHP plant in Grenaa as with bjerg near Holstebro are owned and and a fluidizing medium, e.g., sand, the other plants, the straw is delivered run by the electricity utility companies thereby fluidizing the mixture (the bed) in theform of big bales. With an an­ I/S Midtkraft and I/S Vestkraft. and thus attain properties as a liquid. nual supply of 55,000 tonnes of straw, The Grenaa plant was started up An advantage of the fluidized bed it has been necessary to automate in 1992, and the plant in Maabjerg in boiler is that it is suitable for firing with weighing and measuring of the water 1993. Both plants are designed for fir­ co-fuels. content on delivery to the plant. An

i skott

biopress/torben

• photo Maabjergvserket (CHP plant). On the left, the storage tank of 5,000 m3 . The straw storage is the low building on the right. Outermost on the right the outdoor woodchips storage. CHP- and Power Plants

automatic crane is equipped with grip-hooks that can lift 12 bales at a time off the truck. By means of micro- waves that are sent through the bales from one grip-hook to the other one, and by means of a weighing cell be­ tween grip-hooks and crane, the aver­ age water content and the weight are being measured and recorded by a computer. From the storage, the bales are picked up by a crane and unloaded on to 4 feeding lines. The straw is shred­ ded by a relatively low energy con­ sumption (1.8 kWh per MWh fired). The shredded straw is conveyed from the 4 lines via rotary valves to 2 feed­ ing systems. Via the feeding systems, the straw is blown on to the ash circu ­ lation system from where it passes on to the bed. After having been pulver­ ised to a grain size of maximum 8 mm, the coal is fed either via screw stokers in the bottom of the boiler or via rotary valves on to the ash circula ­ The operationsmanager at Grenaa Kraftvarmevserk (CHP plant) standsby the tion system. straw shredder that is opened for inspection.

Other Data is cleaned for solid particles by means filter, and in respectof thewaste-fired The boiler in Grenaa has been de­ of an electrostatic filter. boilers, the flue gas cleaning system signed for firing with coal and straw in is supplemented by a scrubber sys­ a mixture of 50% straw on energy ba ­ The CHP Plant in Maabjerg tem in order to reduce hydrogen chlo­ sis. At full load (100%), the boiler pro­ In Maabjerg near Holstebro, I/S ride-, hydrogen fluoride-, and sulphur duces 104 tonnes of steam per hour Vestkraft ( electricity utility) has con­ oxide emissions. The scrubber system at 505°C and 92 bar. Of this amount, structed a CHP plant that is fired with separates at the same time heavy met­ between 37 and 77 tonnes of steam waste, straw, wood chips, and natural als from the fly ash to a certain extent. are drawn off per hour at 210°C and gas. The plant is divided into 3 boiler The straw/wood chips-fired boiler 8.3 bar for process steam for the in­ lines, 2 for waste and 1 for straw and can operate at full load on either straw dustrial enterprises Danisco Paper wood chips. or wood chips, or on combinations of and Danisco Distillers. In addition to All 3 boilers are equipped with straw and wood chips. The boiler out­ 55.000 tonnes of straw, approx. separate natural gas-fired superheater put is 12 tonnes of straw per hour. 40.000 tonnes of coal are consumed that raises the steam temperature Further data are set out in Tables 6, 7, per annum. The coal storage is capa ­ from 410°C to 520°C at a pressure of 8, and 9. ble of supplying coal for 20 days and 67 bar. The straw is fired in theform nights at 100% pure coal firing, and of whole big bales into 6 cigar burn ­ Environmental the straw storage is capable of sup ­ ers, installed 3 and 3 opposite each plying straw for the consumption of other. By means of a pneumatic feed­ Requirements 4.2 days and nights at 50/50% fuel ing system, thewood chips are thrown In the Danish Environmental Protec­ mixture. Like the other CHP plants, on to a vibrating grate where unburnt tion Agency Directions No. 6 and the boiler plant is equipped with a straw and wood chips burn out. The 9/1990 on "Industrial Air Pollution heat storage tank, and like the plants flue gas generated by the straw/wood Control Guidelines” /ref. 42/, emission in Slagelse and Masnedo, the flue gas chips-fired boiler is cleaned in a bag levels that are intended as a guide for

Emission Unit Rudkobing Haslev Slagelse Grena Aabenraa Mabjerg Masnede Maribo/ Sakskebing CO volume % 0.2 at 0.05 at 0.2 at None None 0.05 at 0.05 at 0.05 at dry flue gas 12% CC2 10 % o2 12% COz 10%O22) 10% 02 10% 02 Dust mg/Nm3 50 50 50 50 50 40 40 40 NO, mg/Nm3 350 340 340 160 400 None 200 400 S02 mg/Nm3 None 300 300 280 2,0001) None None None Table 9: Maximum emissions from the 7 decentralised CHP plants and the power plant at Aabenraa. The figures are from the environmental approvalsof the individual plants. 1) : The emission is 100-200 mg SO/Nm3 when operating 2): Calculated on the basis of 650 mg/Nm 3 .

Straw for Energy Production Page 39 CHP- and Power Plants straw-fired boiler plants larger than 1 price forming the basis of Table 7 is amounts of straw at power plants to a MW input are for dust and CO sug ­ based on the net output and not on critical analysis. Among the important gested at 40 mg/Nm3 and 0.05% CO the gross output. The gross output in­ issues in that respect were: (volume % at 10% 02 in the flue gas), cludes the plant ’s own consumption of respectively. However, concerning the power. The status of being pilot and • High-temperature corrosion of su­ CHP plants described here, the envi­ demonstration plant also contributes perheaters at high steam tempera­ ronmental approvals in question stipu ­ to an increase in the cost of construc­ tures late individual requirements to be met, tion which contributes to confusing the • Industrial application of mixed ash see Table 9. price. by co-firing of straw and coal The volumetric calorific value of • Flue gas cleaning by co-firing of Cost of Construction and straw is a factor 10-15 times lower straw and coal than that of coal at the same time of • Resource statements and straw sup ­ Operating Costs straw being physically more difficult to ply safety The cost of construction for the de­ handle, thus the costs for storage, • Costs centralised biomass-fired CHP plants handling and firing systems contribute is relatively higher than that of con­ to increasing the plants ’ high specific There are several overall concepts for ventional coal-fired power plants cost of construction. With a straw solutions: measured by the million (DKK) per in­ price of approx. DKK 0.45 per kg or stalled MW electrical power output. approx. DKK 0.11 per kWh, straw is 1. Separate firing: Straw fired in a For the seven plants, the specific con­ three times as expensive as coal for separate biomass-based boiler struction investment is in the range of electrical power production, see Fig­ that supplies steam for the coal- approx. DKK 21 and 30 million per ure 1, Section 1. fired boiler. MW electrical power. As will appear 2. Co-firing: Straw and coal fired to­ from Table 7, the cost of construction gether in power plant boiler is price index-linked to the 1995 level, Straw at Power Plants 3. Coupled-gasifier-combustor. Gasi­ thereby making it suitable to be com­ In 1993, the Danish parliament fication of straw, the gas burns in a pared. The relatively high cost of con­ “Folketinget” ordered the Danish boiler that may be designed for struction depends first and foremost power plants to use 1.2 million tonnes co-firing of straw gas and pulver­ on the size of the plant, (the smaller of straw (it was later decided that 0.2 ised coal. This concept is undergo­ the plant, the higher the specific cost million tonnes of wood chips can be ing further development. of construction). By technological ad­ substituted by wood or willow chips) vances in respectof a certain type of and 0.2 million tonnes of wood chips By separate firing, problems in re­ plant, the specific price will drop for as fuels at the centralised power spect of high-temperature corrosion new plants compared to older plants plants not later than 2000 as a result are avoided because the steam tem­ of the same size. The specific price of the energy policy target in respect perature in the biomass boiler is kept should be understood as a guide, of C02 reduction. under a critical level. Industrial appli ­ since the cost of construction varies The Electricity Utility Group EL- cation of ash from the coal boiler is no with the items included, see Table 7. SAM and ELKRAFT Power Company problem because the ash from the two By a comparison with other types of Ltd. therefore implemented a wide boilers are not mixed. The drawback CHP plants, it should be mentioned range of activities in order to subject to separate firing is first and foremost that the calculation of the specific the problems of firing very large the high cost of construction. By co­ firing, solutions should be found to the problems of high-temperature corro­ sion and industrial application of mixed ash. At power plants that are equipped with desulphurization- and nitrogen reduction units (deNOx plants), the content of alkali metals (potassium and sodium) and chlorine in the straw ash causes operating problems. A major advantage of co­ firing is the low cost of construction. The interest for coupled-gasifier- combustors is due to both the low cost of construction and the prospects of low alkali and chlorine contents in the gas. So far, a straw-fired boiler plant has been established at a power plant within a framework managed by the Electricity Utility Group ELSAM. In the autumn of 1997, Sonderjyllands Hoj- spasndingsvasrk (electricity utility) has started up a separate biomass-fired boiler at the Enstedvserket (power plant) running parallel with the pulver­ 3 of 4 feeding lines at Enstedvserket (power plant). The big bales are collected ised coal-fired Unit 3 of the Ensted- via a conveyor belt in the storage and are distributed to the 4 lines via a vaerket. Since 1995, I/S Midtkraft ( traversing vehicle. electricity utility) has carried out ex- electrical 6.6%

tralised graphic sondeijyllands hojspsandingsvsBrk duces wood tonnes vaerket The larger biomass-fired power generated ing mated pressure heated straw-fired superheating a MJ/s, in straw Company Enstedvaerket Enstedvaerket power power pulverised periments the Figure 470°C, 630

straw-fired a

39.7

amount separate MW biomass-fired In

of

the chips, at

than

88

annual

Zealand, 22: of steam and Unit

biomass-fired

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CHP- and Power Plants

grate-fired stoker plant of 70 MW elec­ trical power, during the period from 1992-1994. The purpose of the ex­ periments was to investigate the gen­ erally known problematic issues in connection with straw-firing at power plants, including: • Handling and firing of straw in a power plant boiler that is simultane ­ ously fired with coal • Consequences for the boiler output and flue gas emissions • Corrosion of superheaters and slag ­ ging problems • Mixed ash problems • Straw influence on flue gas cleaning systems The experiments have resulted in the carrying though of a 2-year demon­ stration projectduring 1996/97 with co-firing of straw and coal at the pul­ verised coal-fired the power plant (Unit 1) 150 MW electrical powerof Straw being unloaded from a truck at the Enstedvaerket. The crane lifts 12 bales the Stud stru p vas rket. at a time. At the same time, the bales are being weighed, and the water content The plant at Studstrupvaerket is measured via microwave equipment mounted in the grip-hooks. designed for a maximum straw input of 20% of the total input energy. A the establishing of storage, handling been planned that can produce steam straw storage is established with equipment, and firing systems at 300 bar and 580°C. The steam space for 1,100 big bales and a total amounts to approx. DKK 90 million. passes to the main boiler steam tur ­ of 4 feeding lines each consisting of a bine. If it is not possible to attain the shredder and a hammer mill that Avedorevaerket high steam temperaturewithout too crushes the shredded straw stalks. In connection with the construction of severe corrosion problems, arrange ­ The straw is together with the pulver­ a new power plant unit (Unit 2) at the ments will be made for part of the su­ ised coal blown into the combustion power plant Avedorevaerket, a perheating to take place in a natural chamber. biomass-fired plant with an input of gas-fired superheater. With the plan­ The boiler is designed for an out­ 150,000 tonnes of biomass per an ­ ned construction projectand the high put of 500 tonnes of steam per hour at num of which the majority will be steam temperature, an electric power a steam pressure of 143 bar and a su ­ straw. Based on experiences gained efficiency of the biomass-based unit of perheater temperature of 540°C. The at the plant in Masnedo, a separate 43% is estimated. The plant is plan­ cost of construction in connection with straw-/wood chips-fired boiler has ned for starting up at the end of 2001. Gasification and Pyrolysis 9. Gasification and Pyrolysis

Gasification of straw is interesting with a view to substitution fossil fu­ els with biomass at small power plants of an output of 0.2-3 MW electrical power and at power plants of a size of 50-100 MW elec­ trical power. The gas from a small gasifier can be used so as to drive an engine that drives a generator that generates electrical power. The cooling water supplies hot water to a district heating distribution net. At a power station, the gas can be burnt in a high-pressure boiler where the steam drives a tur­ bine/generator.

From 1988, various experiments on gasification of straw were carried out, e.g., at Kyndbyvaerket (power plant). The experimentswere financed by ELKRAFT Power Company Ltd , Dan­ ish Energy Agency, and Ansaldo Volund A/S. These experiments have The pyrolysis plant at Haslev Kraftvarmevaerk (CHP plant). The pyrolysis plant revealed certain problems associated has been coupledto the plant as a demonstration facility and therefore not struc­ with the special properties of straw turally fitted into the entire design. when used as a fuel. By updraft gasifi ­ cation (the gas rises through the in­ coming straw), problems were dem­ wood charcoal make this fuel consid ­ plants where the low alkali and onstrated within the following areas: erably suitable for gasification pur­ chlorine contents of the gas make poses. it possible to burn it in a high- • Feeding of fuel With the gasifier at Kyndbyvaerket pressure boiler. The concept is • Non-homogeneity of layers of fuels (power plant) as the prototype, an up­ called a coupled-gasifier-combus- with straw compacting in cold zones draft gasifier has been constructed at tor and has been developed for • Unburnt straw charcoal blown out of Harboore wherewood chips are used wood in Finland. the gasifier as the fuel due to more experience having been gained. The “Kyndby ga ­ The feeding of fuel resulted in many sifier” was closed down after finishing Haslev Pyrolysis Plant problems with plugs in thefuel feed­ the experimental programme. It was The high chlorine and alkali contents ing system. A discontinuous feeding dismantled in 1997 along with the of straw make it unsuitable for direct of fuel affect the gasification process demolition of Kyndbyvaerket ’s old unit. burning in boilers with high steam negatively, since it increases burning At the Technical University of data. High steam data are necessary through tendencies with a poor gas Denmark (DTU), a two-staged gasifier in order to be able to achieve high quality and great variations in the gas has been developed. During the pe­ electrical powerefficiency. By pyroly­ composition as the result. riod from 1994-98, the effort has been sis, the major part of the chlorine and Attempts were made so as to concentrated on wood gasification, alkali is retained in the charcoal if the remedy non-homogeneity by means since it is now easier to upscale wood temperature is kept at a maximum of of a stirring system which did not gasifiers from small to larger test 550°C. Furthermore, particles from solve the problem, though. Perhaps plants. Long-range experiments on the hot gas are separated in a cy­ the stirrer contributed to pyrolysed gasification of briquette fuel have clone. Thus, the pyrolysis gas can be straw charcoal being pulverised to been carried out. used to superheat steam without any finely divided powder that is fluidized From 1998, straw gasification has major risk of corrosion, erosion, and in hot zones and blown out of the ga ­ been given priority. The developing deposits on the superheater. sifier. In cold zones, the straw com­ work is aiming at two boiler plant In the spring of 1992, it was de­ pacted in wet lumps more or less im­ types: cided to construct a full-scale demon­ pervious to gas. Thereby the heat stration plant designed for pyrolytic transfer into the fuel was interrupted 1. Small gasifiers of a size of 0.2-3 gasification of straw in connection with so that an evenly distributed glow bed MW electrical power with a heat Haslev Kraftvarmevaerk (CHP plant). could not be built up. production of 0.5-8 MW that can In addition to ELKRAFT Power Com­ Experiments on gasification of substitute existing boilers at district pany Ltd., the EU “Thermie Pro­ wood chips made in the same boiler heating plants where there is no gramme”, the Danish Energy Agency, for a shorter period have shown that electrical power generation today. Ansaldo Volund A/S, and COWI Con­ the granular structure of the wood 2. Large gasifiers of a size of 50-100 sulting Engineers have supported the chips and the formation of a stable MW electrical powerat power project financially.

Straw for Energy Production Page 43 Gasification and Pyrolysis

Figure 23: Simplified diagram of the pyrolysis plant at Haslev Kraft- varmevserk (CHP plant).

12-26 t/h 65 bar

Turbine (fy Generator Straw- based Air preheater boiler

l Superheater

District ICyklone heating

Straw

Pyrolysis unit Boundary line for pyrolysis plant

Flue gas Charcoal

The overall objective of the project is hours of operation of which 200 being MW. The remaining 1.7 MW is recov­ to demonstrate the function of the based on gas produced by pyrolysis, ered in the charcoal that is utilised in main components and the conceptas the plant was retrofitted and optimised the boiler. such, since it can improve the effi­ in several respects. In addition to straw, the pyrolysis ciency of waste- and biomass-fired in the separate superheater, see unit can be fed dried sludge, and the CHP plants. Figure 23, the gas heats a partial charcoal can be used as auxiliary fir­ Already in 1987 in ELKRAFT steam flow from approx. 430°C to ap ­ ing and thereby replace natural gas Power Company Ltd. ’s brainstorm prox. 480°C, the flue gas then passes and oil. Straw charcoal can also be competition on gasification technol­ to the pyrolysis unit double jacket, used in order to regulate variations in ogy, COWI was awarded the first prize thereby transferring energy to the pro­ the straw quality, thereby keeping a for the above-mentioned concept. cess. The pyrolysis unit is a worm- constant boiler load. A partial flow of The project started up in 1989 with based pyrolysis unit where the maxi­ the charcoal can also be used in the laboratory tests carried out at the mum jacket temperature is kept at ap­ flue gas cleaning system thus reduc­ Technical University of Denmark prox. 600°C. The maximum tempera­ ing the purchase of activated char ­ (DTU). Then a pilot plant was con­ ture in the pyrolysis unit can thereby coal. structed also at the Technical Univer­ be kept at approx. 550°C. The flue At new plants, the concept may sity of Denmark (DTU) where the gas is further cooled in an air prehea­ increase the electrical power output plant in 1991 operated for a total of ter and then released through the by 10-15% at a given heating basis, 1,000 hours producing an extremely chimney. The charcoal from the pyro­ equal to an improvementof 2-3 per­ promising result. This formed the ba ­ lysis process is lead to the straw- centage point in electrical powereffi­ sis for the decision to construct a py­ based boiler and burns together with ciency. In Haslev, the interplay be­ rolysis plant in Haslev. the straw. The pyrolysis plant has a tween the boiler and the pyrolysis unit Test operation at the pyrolysis capacity of 675 kg straw per hour, is not yetfinally optimised, since it is plant in Haslev commenced in the equal to an input of approx. 2.7 MW. still being a pilot plant with an ex­ autumn of 1996, and after approx. 800 The pyrolysis gas output is approx. 1 pected limited life. ______Other Technologies for Electric Power Generation 10. Other Technologies for Electric Power Generation

For small-scale CHP production, for alternative applications as co-firing adapted to experiences gained from i.e., district heating plants, institu­ at power plants. In terms of finance, the use of biomass in large steam tions, and farm-scale plants, there this solution is not attractive, though, boiler plants. In addition, the engine is is a potential market both domesti­ when considering the present prices hermetically sealed, since the genera­ cally and internationally. There are of straw and wood chips. tor is built into a pressurised crank ­ several development projects cur­ case. By at the same time using lubri­ rently underway aiming at small- cated, sealed bearings, the problem of scale electrical power generation Stirling Engine leakage of theworking mediums gas based on biomass with acceptable The design of the Stirling engine and oil in the working volumes is electrical power efficiencies. Of makes it particularly suitable for diffi ­ solved. these, flash pyrolysis, Stirling en­ cult fuels, because the combustion The temperature in the engine gine, and steam engine will be de­ does not take place in the cylinders heating surfaces should be as high as scribed. but externally as in a boiler. Depend­ possible in order to achieve a good ef­ ing on the design of the engine and ficiency. This means in practice that the design of the firing equipment, it is the temperature of the heating sur ­ Flash Pyrolysis thereby possible to use both gaseous, faces should be at least 650-700°C. By pyrolysis of biomass, the volatile liquid, and solid fuels. It is therefore The temperature of the flue gas leav­ compounds of straw (75-80% of the an obvious possibility to apply the ing the heating surfaces will be high. calorific value) are converted to gases technology to biomass-fired CHP Therefore, an air preheater is used by heating in the absence of oxygen. plants. that preheats the combustion air by If the pyrolysis process is very fast At the Technical University of means of the hot flue gas. The hot with subsequent rapid quenching of Denmark, development work is cur­ combustion air does not constitute the gases developed, a very high out­ rently taking place in order to develop any great problem in a natural gas put (typically 60-70%) is achieved of three engines generating electrical burner, but with wood chips or straw an oily product, pyrolysis oil. power outputs of 150, 35, and 9 kW, being fired instead, there is a risk of For some years, ELKRAFT respectively. Developmentand testing the high temperatures causing the ash Power Company Ltd. has participated of the three engine types are carried to fuse and deposit on the heat trans ­ in several pyrolysis projects in Can ­ out in several projects. The 150 kW ferring surfaces. An important part of ada and Finland, and under the aus­ electrical power project is financially the Danish Stirling engine activities pices of the EU in order to both inves­ supported by ELKRAFT PowerCom­ are therefore the development of an tigate the suitability of the process for pany Ltd. and the Danish Energy efficient combustion system. pyrolysis of straw, and also to investi­ Agency and is based on gasification The 150 kW electrical power and gate the applicability of the pyrolysis technology. The 35 kW electrical 35 kW electrical powerengines are oil (technically and financially) in die­ powerengine is supported by the designed with regard to being used for sel engines and boilers. So far, results Danish Energy Agency via two proj­ biomass as the energy source, either have shown that straw can be con­ ects, and the work is carried out in via combustion or gasification. This verted to pyrolysis oil without prob ­ co-operation with the industrial enter­ results in the combustion chamber lems in the process itself, but that fur ­ prises REKA A/S and PlanEnergi A/S. and the boiler sections being much ther developmentof methods for The 9 kW electrical power engine is larger than those of a Stirling engine separating solid particles from the gas supported financially by Naturgas for natural gas or oil. The burnout time before condensing it is necessary. In Midt-Nord and the Danish Energy for solid fuel is longer than those of oil Finland and England, short-term ex­ Agency. This engine is designed for and gas, and the particle content ne­ periments have been carried out on gaseous fuels and is not described in cessitates a great distance between pyrolysis oil as a fuel in diesel engines more detail. It is necessary to develop tubes and fins of the Stirling engine in the size of 60, 250, and 1,500 kW. Stirling engines for direct use of bio ­ heating surfaces. The heating load in In terms of combustion, the pyrolysis mass in stationary plants for electrical the heater is approx. 50 kW/m2 which oil is unproblematic in behaviour, but it powergeneration. This means that is equal to the heat load in a steam will be necessary with modifications of the engine heating surfaces are boiler for wood chips, but it is only all components that are in contact with the pyrolysis oil due to its low pH Unit Stirling 35 Stirling 150 Sunpower Inc value (3-4). Other experiments show that the pyrolysis oil is relatively easy Electrical power output kW 33 142 2.5 to use in both small and large boilers. Heat output kW 102 350 Unknown CHP production based on pyroly­ sis oil could, e.g., consist of a central Electrical power effic., net - 21 26 20 flash pyrolysis plant and a distribution Specific cost of constr. DKK/kWei 20,000 15-20,000 20,000 system (tankers) and several small CHP plants that, e.g., consist of an Table 10: Stirling engine. Electrical power efficiency at full load. The annual unattended diesel engine. The low efficiency will be lower depending on operating conditions. The cost of contents of ash, chlorine, and alkali in construction is budgeted price. The data stated are based on test results and on pyrolysis oil also make it interesting wood chips being the fuel.

Straw for Energy Production Page 45 Other Technologies for Electric Power Generation

1/4-1/5 of the load in a gas-fired Stir­ The prototype of a ling engine. The development projects Danish manufac­ are primarily based on wood chips be­ tured steam engine ing the fuel, but straw is also a possi­ installed for testing. ble fuel. The chlorine and alkali con­ The steam tubes tents of straw result in corrosion of the supply steam for heating surfaces, but washing of the the high-pressure straw offers the possibility of reducing cylinder and after­ the aggressive components (see Sec­ wards for the big ­ tion 2) /ref. 3 and 49/. ger low-pressure The American enterprise Sun- cylinder. The hy ­ power Inc. in Ohio manufactured in draulic valves can 1996 six prototypes of an 2.5 kW be seen in the up­ per left corner be ­ electrical power Stirling engine with a hind the low-pres­ linear generator directly connected to sure cylinder. the piston without a crank. The fuels being wood, bagasse, rice hulls, straw etc. By an annual production of 10,000 engines, the price has been fixed at US$ 6,000, equal to approx. DKK 20,000/kW electrical power.

Steam Engines Steam engines can be an alternative at CHP plants up to approx. 1 MW electrical power, i.e., small plants that can cover the heating requirements in small towns up to 500 houses. The advantages of the steam engine are:

• that this size of steam engine is ca­ • that the conventional slider valve satisfactory testing of the prototype, it pable of competing with the steam system yields a lower efficiencythan is planned to construct a steam en­ turbine in respect of price and effi­ that of modern hydraulic valve gine running at 70 bar and 550°C. ciency, guide. A commercialised product of a • that the technology is relatively sim­ ple, size of 1 MW electrical power and With a viewto developing a modern with a net electrical power efficiency • that the working medium is steam steam engine, a two-cylinder proto­ that is produced in a boiler capable type with a steam pressure of 24 bar of almost 20% may be commercial­ of running on vario biofuels. and a steam temperature of 380°C ised and marketed during 2000- with oil-free piston rings of carbon fi­ 2005. The specific cost of construc­ The disadvantages of the steam en­ bres and with hydraulic valves has tion is estimated at DKK 20-25 mil­ gine (or the development requirement) been constructed. The steam engine lion per MW electrical power/ref. 3, are: is capable of generating an output of 12, 50/. 500 kW electrical power. The project • that an engine should be developed is being carried out by dk-TEKNIK and that does not have to be lubricated the engineering firm Milton Andersen with lubricating oil, since oil leakage and is financially supported by the EU to cylinders destroy the steam quality, and the Danish Energy Agency. After ■______Besldwal Products 11. Residual Products Straw typically contains 3-5% ash. Part of the ash is taken out in the Limit values in force Limit values in force bottom of the boiler and is called 01.10.1996-30.06.2000 01.07.2000 bottom ash while the remainder is Heavy metals mg per kg mg per kg mg per kg mg per kg whirled round in the boiler with the dry matter total phosphorus dry matter total phosphorus combustion air and further out in a Cadmium 0.8 200 0.4 100 flue gas cleaning system. This part Mercury 0.8 200 0.8 200 of the ash is called fly ash. In the Lead 120 10,000 120 10,000 flue gas cleaning system, the major part of the fly ash is separated, Nickel 30 2,500 30 2,500 while the remainder is released Chromium 100 100 through the chimney in the form of Zinc 4,000 4,000 particle emission. Flue gas clean­ Copper 1,000 1,000 ing systems are described in more detail under Sections 7 and 8. Table 11: Limit values for heavy metals, e.g., in ash for agricultural applications, The collected bottom ash and see Executive Order No. 823 of September 16, 1996. fly ash from the straw-fired boiler are considered residual products and should pursuant to the (Dan­ investigated. The Danish Environmen­ straw (bottom) ash to start fusing al­ ish) Environmental Act be dis­ tal Protection Agency is preparing an ready at temperatures about 800- posed of in a safe way. Disposal Executive Order that, e.g., includes 900°C (see Section 2). The slagging may include recycling or storage. ash from straw and wood for agricul ­ tendency may vary, though, depend ­ tural applications. ing on the type of straw and the grow­ ing conditions. A great proportion of Ash Recycling for Cement and the potassium contentof straw is re­ Concrete Applications moved (washed out) by rain if the Recycling for Agricultural In Denmark, applications for a large straw is left in the field after being har­ Applications. proportion of the residual products (fly vested. The problems of slagging and Straw ash contains nutrients, primarily ash from coal) from the energy pro­ condensing are therefore very much potassium and othersoil amelioration duction have been found in the ce­ reduced when using straw that has matter like magnesium, phosphorus, ment and concrete industry. The re­ been washed out in the field /ref. 33/. and calcium and can therefore be ap ­ quirements applying to fly ash in con­ Together with advisers, the power plied in agriculture as fertiliser. Agri­ crete are set out in /ref. 23/. Straw ash companies have carried out success­ cultural application of ash requires will result in a too high content of al ­ ful experiments on straw being sub ­ permission from the county. Applica ­ kali metals (potassium and sodium) jected to a more controlled washing tions submitted to the County are con­ and chloride in cement. Alkali metals process. In the subsequent energy sidered, thereby having regard to the constitute a problem because they application of the washed straw, the Department of the Environmentand can react to flint stone particles in the energy utilisation can be controlled so Energy Executive Order No. 823 of gravel aggregate with which the ce­ that the increased water content of the September 16, 1996 on residual prod­ ment is mixed during concrete manu ­ washed straw does not give rise to ucts for agricultural applications. This facturing. Thereby combinations can any considerable energy loss. ' means, e.g., that the content of heavy be formed that absorb water from the During the combustion of straw, metals in the ash should not exceed surroundings. This results in volume part of the potassium content of straw the limit values stated in the Executive expansions, formation of cracks, and is liberated along with the major pro­ Order. The Danish Environmental problems with the freezing and thaw ­ portion of chlorine and sulphur to the Protection Agency may however grant ing properties. A high chloride content flue gas. When cooling the flue gas an exemption. It is optional whether is problematic because it may result in later on, greyish depositing results the content of heavy metals in the ash corrosion of the reinforcement bars. whose thickness is currently in­ is calculated on the basis of the dry creased, thereby reducing the heat matter contentof the ash or its phos­ transfer in the heating surfaces. The phorus content. Slagging and Condensing depositing may be so serious that fre­ At the beginning of 1998, an in­ Usually, straw has a serious slagging quent cleaning of the heating surfaces vestment is being carried out so as to tendency, i.e., a concretion or fusion being required. In addition, submi ­ clarify whether or not heavy metals of the ash. This may occur, e.g., lo­ crons (particles of diameter less than can be concentrated in some smaller cally on the grate in case of grate fir­ 1/1000 mm) are produced consisting ash fractions by a separation of the ing or in the combustion chamber of potassium chloride and potassium ash flow from the grate, cyclone and where the temperatures are so high sulphate that are carried with the flue filter sections. Thereby some fractions that the ash fuses wholly or partly. gas to the particle filter. Boilerdesign of the ash will get a lower heavy metal The hard, vitreous slag may be very (superheaterpositioning, distance be­ content, primarily of cadmium. In addi ­ difficult to remove. The slagging ten­ tween the tubes etc.) may however tion, the distribution of the ash nutri ­ dency of straw is due to its relatively prevent some of these nuisances. ents among the ash fractions will be high content of potassium that causes Further Information 12. Further Information The centres, institutes, and authori­ Danske Fjernvarmevasrkers ELSAM ties listed below can provide fur­ Forening 45 Overgade ther information and directions in Danish District Heating Association, Electricity Utility Group ELSAM respect of using straw as a source 44 Galgebjervej, DK-6000 Kolding DK-7000 Fredericia of energy. Tel: +45 7630 8000, fax +45 7552 8962 Tel: +45 7622 2000, fax: +45 7622 2009 E-mail: [email protected] E-mail: [email protected]

Videncenter for Halm- og Flisfyring Energistyrelsen ELKRAFT Centre for Biomass Technology Danish Energy Agency ELKRAFT Power Company Ltd. can be found at the following ad ­ 44 Amaliegade Electricity Utility Group dresses: DK-1256 Copenhagen K 5 Lautruphoj Tel: +45 3392 6700, fax +45 3311 4743 DK-2750 Ballerup Dansk Teknologisk Institut E-mail: [email protected] Tel: +45 4466 0022, fax: +45 4465 6104 Danish Technological Institute E-mail: [email protected] Teknologiparken Milj0styrelsen DK-8000 Aarhus C Danish Environmental Protection Dansk BioEnergi (magazine) Tel: +45 8943 8556, fax: +45 8943 8543 Agency Forlaget BioPress E-mail: [email protected] 29 Strandgade 8 Vestre Skovvej dk-TEKNIK DK-1401 Copenhagen K DK-8240 Risskov 15 Gladsaxe Mollevej Tel: +45 3266 0100, fax +45 3266 0479 Tel: +45 8617 3407, fax: +45 8617 8507 E-mail: [email protected] E-mail: [email protected] DK-2860 S0borg Tel: + 45 3955 5999, fax +45 3969 6002 E-mail: [email protected] Statens Jordbrugs- og Fiskeriokono- Non-food Sekretariatet miske Institut The Non-food Secretariat Danmarks JordbrugsForskning Danish Institute of Agricultural and Danish Directorate for Development Forskningscenter Bygholm Fisheries Economics 29 Toldbodgade Afdeling for Jordbrugsteknik 1-3 Gl. Koge Landevej, DK-2500 Valby DK-1253 Copenhagen K Danish Institute of Agricultural Sciences Tel: +45 3644 2080, fax: +45 3644 1110 Tel: +45 3363 7300, fax +45 3363 7333 Research Centre Bygholm E-mail: [email protected] E-mail: [email protected] Dept, of Agricultural Engineering 17 Schuttesvej Danske Halmleverandorer Provestationen for mindre DK-8700 Horsens Danish Straw Suppliers Biobraendselskedler Tel: +45 7560 2211, fax +45 7562 4880 Chairman: Hans Stougaard Test Laboratory for small E-mail: [email protected] 68 Langgade Biofuel Boilers Forskningscentret for Skov & DK-5620 Glamsbjerg Danish Technological Institute Landskab Tel: +45 6472 1901, fax: +45 6472 2244 Teknologiparken Danish Forest and Landscape DK-8000 Aarhus C Research Institute Landbrugets Halmudvalg. Tel: +45 8943 8556, fax: +45 8943 8543 11 Hersholm Kongevej Agricultural Council for Utilization of DK-2970 Horsholm Surplus Straw Danmarks JordbrugsForskning Tel: +45 4576 3200, fax +45 4576 3233 15 Udksersvej, Skejby Forskningscenter Foulum E-mail: [email protected] DK-8200 Aarhus N Afdeling for Plantevsekst og Jord Tel: +45 8740 5000, fax: +45 8740 5010 Danish Institute of Agricultural E-mail: [email protected] Sciences Research Centre Foulum Foreningen for Producenter af Dept, of Crops Physiology and Informationssekretariatet for fastbraendsels Anlseg (FOFA) Soil Science Vedvarende Energi. DTI Energi Association of Danish Manufactures P.O. Box 50, DK-8830 Tjele Renewable Energy Information of Biomass Boilers Tel: +45 8999 1900, fax: +45 8999 1619 Centre. DTI Energy c/o Haandvaerksraadet E-mail: [email protected] RO. Box 141, DK-2630 Taastrup 31 Amaliegade Tel: +45 4399 6065, fax +45 4399 1799 DK-1256 Copenhagen K Danmarks JordbrugsForskning E-mail: [email protected] Tel: +45 3393 2000, fax: +45 3332 0174 Forskningscenter Flakkebjerg E-mail: [email protected] Afdeling for Plantebiologi Samvirkende Energi- og Milj0kontorer Danish Institute of Agricultural Associated Energy and Environmental Landskontoret for Bygninger og Sciences Office Maskiner Research Centre Flakkebjerg 8 Dumpen The National Department of Farm Dept, of Plant Biology DK-8800 Viborg Buildings and Machinery DK-4200 Slagelse Tel: +45 8661 2322, fax +45 8661 4146 15 Udksersvej, DK-8200 Aarhus N Tel: +45 5811 3300, fax: +45 5811 3301 (refers to Energy and Environmental Tel: +45 8740 5000, fax: +45 8740 5010 E-mail: johannes.jorgensen offices in the individual counties) E-mail: [email protected] @agrsci.dk Table of References 13. Table of References The table of references contains ti­ 13. Halm- og traapillers anvendelighed 28. Energi for fremtiden: Vedvarende tles etc. of recent reports and infor­ som braendsel i mindre fyring- energikilder. Hvidbog vedrorende mation material. Further refer­ sanlasg. Dansk Teknologisk Insti­ en strategi og handlingsplan pa ences, table of books, prices etc. tut, marts 1994. fsellesskabsplan. Kommissionen can be requested through The for de europasiske faallesskaber, Centre for Biomass Technology. 14. Biomasse: Breendsels- og 1997. fyringskarakteristika med saerlig 1. Energi 21. Regeringens energi- relation til anvendelse som braend ­ 29. Energistyrelsens energistatistik handlingsplan 1996. Miljo- og sel i decentrale kraftvarmeanlasg. 1996 Energiministeriet, 1996. dk-TEKNIK, august 1991. 30. Halmprognose 1997 (indeholder 2. Danmarks energifremtider. Milje- 15. Forbraendingsberegninger. Dansk tal for produktionen i 1996). og Energiministeriet, 1995. Teknologisk Institut, marts 1991. Landskontoret for Planteavl.

3. Teknologidata for vedvarende en- 16. Brandteknisk vejledning nr. 22. 31 .Undersegelse af aske fra halm. ergianleeg, del 2: Biomassetek- Dansk Brandteknisk Institut, juli 1996. Notat 12.6.1991 fra Haslev Kraft- nologier. Milje- og Energiminister­ varmevaerk. iet, januar 1996. 17. Halmhandtering. Smaballer, rund- baller, storballer, snittet. Arbejds- 32. Halms fyringstekniske egenskaber 4. Milje og okonomi for udvalgte ved­ behov og kapacitet. Beretning nr. (med bilag). dk-TEKNIK, 1991. varende energianlaeg. Energisty- 25. Statens Jordbrugstekniske relsen, november 1991. Forsog, 1985. 33. Unders0gelse af halms kemiske sammensaetning med relation til 5. Energi 2000. Handlingsplan for en 18. Halmbjaergning -1993. Storballer. forbreending og forgasning. Bio- baeredygtig udvikling (med bilag). Intern rapport. Statens Jordbrug ­ teknologisk Institut, 1994. Energiministeriet, 1990. stekniske Forsog, 1994. 34. Optimering af halmvarmeveerker. 6. Halmressourcer i Danmark pa 19. “DRIFT”. Et program for beregning dk-TEKNIK, 1994. laengere sigt. ELSAM og ELK­ af arbejdsbehov, arbejdskapacitet, RAFT i samarbejde med De dan ­ arbejdsbudget, arbejdsprofil. Be­ 35. Bioenergi Udviklingsprogram. En- ske Landboforeninger og Ener- retning nr. 53. Statens Jordbrug ­ ergistyrelsen, 1995. gistyrelsen,juni 1994. stekniske Forsog, 1993. 36. Dyrknings- og fyringsforseg med 7. Dyrknings- og fyringsforseg med 20. Handtering af halm. Intern rapport, energikorn 1996/97. Dansk energikorn i stor skala, 1995. delrapport 1. Statens Jordbrug ­ Teknologisk Institut, 1998. Dansk Teknologisk Institut m.fl. stekniske Forsog, 1993. Der er udarbejdet en 24 minutters 37. Energikorn i storballer. Host og video: “Energikorn” 21 .Transport af snittet halm til var- handtering. DJF-rapport nr. 4, mevaarker m.m. Intern rapport. 1998. Danmarks Jordbrugs- 8. Host og handtering af energikorn i Delrapport nr. 2. Statens Jordbrug ­ forskning. storballer. Forskningscenter Byg­ stekniske Forsog, 1993. holm, 1996. 38. Demonstrations- og udviklingspro­ 22. Restprodukter fra CFB-anlaag. An­ gram vedrorende produktion og an­ 9. Anlasgs- og driftsdata for halmfy- vendelse af restprodukter fra vendelse af energiafgreder 1997- rede varmevasrker. Videncenter for multi-cirkulerende fluid bed. 2000. Statens Jordbrugs- og Fisk- Halm- og Flisfyring, april 1996. EFP-90, 1993. eriokonomiske Institut, 1997.

10.Straw Fired District Heating Plants 23. DS/EN 450. Flyveaske i beton 39. Typegodkendte og tilskudsberetti- in Denmark - Facts and Figures. gede biobr$ndselsanlaeg. Udsen­ Centre for Biomass Technology, 24. Energiministerens skrivelse af 13. des ca. 5 gange om aret. Dansk maj 1996. September 1990 om gene- Teknologisk Institut. relle og specifikke forudsastninger 11. Videnblade. Informationsblade om for braandselsvalg og samproduk- 40. Forsyningskataloget 1988. Styre- halm og trae til energiformal. Der tion i fjernvarmevaerker. gruppen for Forsyningskataloget udsendes 3-4 videnblade ca. hver 3. maned. Abonnement kan 25. Danmarks Statistik. Statistiske Efter- 41. Forsyningskataloget , supplement rekvireres hos Videncenter for retninger, Landbrug nr. 10,1997. ‘86. Finansiering af energiprojek- Halm- og Flisfyring. Indholdsfor- ter, nye muligheder. tegnelse i kapitel 16 i den dan ­ 26. Kogt halm kan lette biomasseaf- ske version talen. ELSAM-posten nr. 9/1996. 42. Vejledning nr. 6 og 9: Begraens- ning af luftforurening fra virksom- 12.Sma halmkraftvarmevaarker 100- 27. Priser pa halm til kraftvarme. heder. Miljostyrelsen 1990. Nr. 9 er 1000 kWei. 3 delrapporter. dk- Landskontoret for Bygninger og den engelske version: Industrial TEKNIK, 1991. Maskiner, april 1997 Air Pollution Control Guidelines.

Straw for Energy Production Page 49 photo lors nikolaisen 43. 46. 45. 44. 48. 47.

Emission pavirkninger. Teknologisk TEKNIK. Tekstilfiltres dk-TEKNIK sen TEKNIK ders0gelse. dk-TEKNIK Dioxin-udslip PAH ders0gelse. brendsel 1989. halm/slam 1987. Pilotfors0gene Udnyttelse

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List of Manufacturers 14. List of Manufacturers Large Boiler Plants Small Boiler Plants Manufacturers, suppliers, and re­ Manufacturers, suppliers, and re­ Pilevang Smede- og pairers of large automatic feeding pairers of boiler plants below 1 MW Maskinvserksted Aps (T) systems and boiler plants for straw for straw firing. Some of the com­ 57 Havrebjergvej firing. The companies also supply panies also supply boiler plants for DK-4100 Ringsted plants for other biofuels. other biofuels. Tel: +45 53 61 19 56

Weiss A/S Aunslev Smede- og Maskinfabrik Sanderum Smede- og Maskinfabrik 13 Plastvaenget 12 Nederbyvej 31 Holkebjergvej DK-9560 Hadsund DK-5800 Nyborg DK-5350 Odense SV Tel: +45 96 52 04 44 Tel: +45 65 36 12 40 Tel:+45 66 17 02 72

Ansaldo Volund A/S CN Maskinfabrik Skelhoje Maskinfabrik A/S (T) 2 Falkevej 236 Kongevej, Tiset 8 Laesovej DK-6705 Esbjerg 0 DK-6510 Gram DK-8800 Viborg Tel: +45 75 14 11 11 Tel: +45 74 82 19 19 Tel: +45 86 61 16 44

Danstoker A/S J.O.S. Smede- og Maskinfabrik Skeltek Ing. og Handelsfirma (T) 13 Industrivej Nord 18 Kaersangervej 74 Aalborgvej DK-7400 Kerning DK-8870 Langa DK-9280 Storvorde Tel: +45 97 12 64 44 Tel: +45 86 46 11 88 Tel: +45 98 31 16 26

DanTrim A/S KF Halmfyr (T) Smith, Holm & Co A/S 2 Islandsvej 16 Skaeveledvej 24 Bryggervej DK-7480 Vildbjerg DK-9252 Dybvad DK-8240 Risskov Tel: +45 97 13 34 00 Tel: +45 98 86 45 99 Tel: +45 86 21 55 22

LINKA Maskinfabrik LINKA Maskinfabrik (T) Smedem. Hans Schmidt (T) 38 Nylandsvej 38 Nylandsvej 6 Smedetoft, Avnbol DK-6940 Lem DK-6940 Lem DK-6400 Sonderborg Tel: +45 97 34 16 55 Tel: +45 97 3416 55 Tel: +45 74 46 11 11

B&W Energi A/S Maskinfabrikken Cormall A/S Stalservice Fyn ApS (T) 25 Teknikerbyen 3 Tronholmen 109-115 Bojdenvej DK-2830 Virum DK-6400 Sonderborg DK-5750 Ringe Tel: +45 45 85 71 00 Tel: +45 74 48 61 11 Tel: +45 62 27 21 80

Hollensen Kedler ApS Maskinfabrikken Faust (T) Jens Moos Aps 22 Drejervej 2 Vester Fjordvej 4 Dalsgardvej DK-7451 Sends DK-9280 Storvorde DK-6300 Grasten Tel: +45 97 14 20 22 Tel:+45 98 31 10 55 Tel: +45 74 65 07 24

Passat Energi A/S Maskinfabrikken REKA A/S (T) (T) =supplier of straw-fired boilers with 36 Vestergade, 0rum 7 Vestvej type approval (o. January 1998). DK-8830 Tjele DK-9600 Ars Tel: +45 86 65 21 00 Tel: +45 98 62 40 11

EuroTherm A/S Overdahl Kedler (T) 25A S. Nymarksvej 21 Hjallerupvej DK-8270 Hojbjerg DK-9320 Hjallerup Tel: +45 86 29 92 99 Tel: +45 98 28 16 06

IF Energy Systems A/S Passat Energi A/S 88 Avedore Holme 36 Vestergade, 0rum DK-2650 Hvidovre DK-8830 Tjele Tel: +45 36 78 66 33 Tel: +45 86 65 21 00

Straw for Energy Production Page 51 Survey of Straw-Fired Plants in Operation 15. Survey of Straw-Fired Plants in Operation

District Heating Plants The list includes heating plants that supply heat for district heating systems primarily using straw as a fuel. Information about boiler equipment, fuel consumption etc. is set out in detail in /ref. 9 and 10/.

Straw-fired Plant Address Postal code/Town Telephone Als Fjernvarme 26 Rorsangervej DK-9560 Hadsund +45 98 58 17 00 Auning Varmevaerk 18 Energivej DK-8963 Auning +45 86 48 38 89 Borup Halmvarmevaerk 60 Baekgardsvej DK-4140 Borup +45 57 52 64 94 Davinde Energiselskab 54 Udlodgyden, Davinde DK-5220 Odense S0 +45 65 97 29 30 Frederiksvaerk kommunale Vserker 8 Havnevej DK-3300 Frederiksvaerk +45 47 77 10 22 Fuglebjerg Fjernvarmevaerk 16&31A Sandvedvej DK-4250 Fuglebjerg +45 55 45 36 88 Gedser Halmvarmevaerk 3 Borsholmvej DK-4871 Gedser +45 53 87 92 78 Gjerlev Varmevaerk 12 Merkurvej DK-8983 Gjerlev +45 86 47 47 16

Hadsten Varmevaerk 32A Toftegardsvej DK-8370 Hadsten +45 89 98 11 55

Hals Fjernvarme 9-11 Bygmestervej DK-9370 Hals +45 98 25 24 11 Harlev, 0stjydsk Halmvarme 32 Lilleringvej DK-8462 Harlev +45 86 94 24 55 Havndal Fjernvarme 4 Laursensvej DK-8970 Havndal +45 86 47 09 15 Hinnerup Fjernvarme 15 Fanovej DK-8382 Hinnerup +45 86 98 53 40 Holeby Halmvarmevaerk 7 Industrivej DK-4960 Holeby +45 53 90 62 73 Hvidbjerg Fjernvarme 2 Handveerkervej DK-7790 Thyholm +45 97 87 15 35 Hvidebaek Fjernvarmeforsyning 37A Hovvej DK-4490 Jerslev Sj. +45 53 49 56 38 Hong Varmevaerk 8 Banemarken DK-4270 Hong +45 58 85 24 32 Horby Varmevaerk 101 Hjorringvej DK-9300 Saeby +45 98 46 63 20 Klemensker Fjernvarmevaerk 6 Industrivej DK-3782 Klemensker +45 56 96 67 46 Kolind Halmvarmevaerk 18 Engvej DK-8560 Kolind +45 86 39 25 20 Kvaerndrup Fjernvarme 22B Bojdenvej DK-5772 Kvaerndrup +45 62 27 13 19 Lobbaek, Aakirkeby Kommune 5 Ravnsgade DK-3720 Aakirkeby +45 56 97 20 32 Lohals Varmeforsyning 3 Bremleveenget DK-5953 Tranekaar +45 62 55 15 59 Logstor Fjernvarme 8 Blekingevej DK-9870 Logstor +45 98 87 12 58 Lojt Kirkeby Fjernvarmeselskab 44 Skovbyvej, Lojt Kirkeby DK-6200 Abenra +45 74 61 78 87 Manager Fjernvarmevaerk 5 Klostermarken DK-9550 Manager +45 98 54 13 01 Nakskov Fjernvarme 5 Strandpromenaden DK-4900 Nakskov +45 53 92 28 66 Nexo Halmvarmevaerk 2 Halmvaenget DK-3730 Nexo +45 56 49 45 55 Norre Alslev Fjernvarmevaerk 4 Peter L. Jensensvej DK-4840 Nr. Alslev +45 53 85 55 67 Nysted Halmvarmevaerk 1 Egevanget DK-4880 Nysted +45 53 87 10 80 Ringsted Halmvarmevaerk 1 Jaettevej DK-4100 Ringsted +45 53 61 33 99 Roslev Fjernvarmeselskab 1 Mollebuen DK-7870 Roslev +45 97 57 13 19 Survey of Straw-Fired Plants in Operation

Ryomgard Fjernvarmevaerk 1 Frederikslundvej DK-8550 Ryomgard +45 86 39 49 80 R@dby Varmevaerk 5 Herredsfogedvej DK-4970 Rodby +45 54 60 14 92 R0dbyhavn Fjernvarme 1 Jencksvej DK-4970 Rodby +45 54 60 53 37 Ronde By's Fjernvarmevark 9C Skejrupvej DK-8410 Rende +45 86 37 17 51

Sabro, 0stjysk Halmvarme 1 Sabrovej DK-8471 Sabro +45 86 94 94 55 Saksk0bing Fjernvarmeselskab 10 Maltrup Vaenge DK-4990 Sakskobing +45 53 89 47 39 Simmelkaer Varmevaerk 10 Enghavevej DK-7400 Kerning +45 99 26 82 11 Solbjerg, 0stjysk Halmvarme 1 Solbjerg Hedevej DK-8355 Solbjerg +45 86 92 60 55 St. Merl0se Varmevark 11 Tastrupvej DK-4730 St. Merlose +45 53 60 12 51 Stege Fjernvarme 35 Kobbelvej DK-4780 Stege +45 55 81 50 88 Svendborg Halmvarmevaerk 1 Bodevej DK-5700 Svendborg +45 62 22 83 66 Sydlangeland Fjernvarme 2B 0sterskovvej DK-5932 Humle +45 62 56 10 56 Sellested Fjernvarmeselskab 25 Jernbanegade DK-4920 Sollested +45 53 94 14 84 Terndrup Fjernvarme 30 Industriparken DK-9575 Terndrup +45 98 33 66 33 Thorsager Fjemvarmevaerk 26 Nerregade DK-8410 Ronde +45 86 37 95 66 Tinggarden 101 Tinggarden DK-4681 Herfolge +45 53 67 53 82 Tommerup By’s Fjv.forsyning 6 Stadionvaenget DK-5690 Tommerup +45 64 76 10 03 Tranebjerg Varmevaerk (ARKE) 20 Marsk Stigsvej DK-8305 Samso +45 87 39 04 04

Tullebolle Fjernvarme 4 Industrivej DK-5953 Tranekaer +45 62 50 16 79 Vester Nebel Varmecentral Hygumvej DK-6715 Esbjerg N +45 75 14 44 33 Sydfalster Varmevaerk 16 Handvaerkervaenget DK-4873 Vaeggerlose +45 53 87 42 00 /Eraskebing Fjernvarme 23 Lerbaekken DK-5970 /Eroskobing +45 62 52 29 09 0rsted Fjernvarme 61D Rougsevej DK-8950 0rsted +45 86 48 86 72 0sterHornum Varmevaerk 11 Tingager DK-9530 Stovring +45 98 38 58 55 0. Toreby Varmevaerk 3 Agrovej DK-4800 Nykobing F +45 54 86 00 66 Aabybro Fjernvarmeforsyning 40 Industrivej DK-9440 Aabybro +45 98 24 23 20

CHP Plants and Power Plants Rudkobing Kraftvarmevaerk 147D Spodsbjergvej DK-5900 Rudkobing +45 62 51 44 77 Haslev Kraftvarmevaerk 27 Slagterivej DK-4690 Haslev +45 56 31 23 33 Slagelse Kraftvarmevaerk 1 Assensvej DK-4200 Slagelse +45 58 50 11 56 Masnedo Kraftvarmevaerk 10 Brovejen DK-4760 Vordingborg +45 53 77 07 77 Mabjergvaerket 2 Energivej DK-7500 Holstebro +45 97 40 60 80 Grena Kraftvarmevaerk 11 Kalorievej DK-8500 Grenaa +45 86 32 78 22

Studstrupvaerket 14 Ny Studstrupvej DK-8541 Skodstrup +45 86 99 17 00 Sonderjyllands Hojspaendingsvaerk 185 Flensborgvej DK-6200 Aabenraa +45 74 31 41 41

Straw for Energy Production Page 53