Reducing CO2 Through the Integration of Renewable Energy and Hydrogen Into the German Steel Industry

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Article Power-to-Steel: Reducing CO2 through the Integration of Renewable Energy and Hydrogen into the German Steel Industry

Alexander Otto 1,2, Martin Robinius 1,2,*, Thomas Grube 1,2, Sebastian Schiebahn 1,2, Aaron Praktiknjo 3,4 and Detlef Stolten 1,2,5 1 JARA-ENERGY, 52425 Jülich, Germany; [email protected] (A.O.); [email protected] (T.G.); [email protected] (S.S.); [email protected] (D.S.) 2 Institute of Energy and Climate Research: Electrochemical Process Engineering IEK-3, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany 3 JARA-ENERGY, 52074 Aachen, Germany; [email protected] 4 Institute for Future Energy Consumer Needs and Behavior (FCN), RWTH Aachen University, Mathieustr. 10, D-52074 Aachen, Germany 5 Chair of Fuel Cells, RWTH Aachen University, c/o Institute of Electrochemical Process Engineering (IEK-3), Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Str., D-52428 Jülich, Germany * Correspondence: [email protected]; Tel.: +49-2461-61-3077

Academic Editor: Bin Chen Received: 13 February 2017; Accepted: 17 March 2017; Published: 1 April 2017

Abstract: This paper analyses some possible means by which renewable power could be integrated into the steel manufacturing process, with techniques such as blast furnace gas recirculation (BF-GR), furnaces that utilize carbon capture, a higher share of electrical arc furnaces (EAFs) and the use of direct reduced iron with hydrogen as reduction agent (H-DR). It is demonstrated that these processes could lead to less dependence on—and ultimately complete independence from—coal. This opens the possibility of providing the steel industry with power and heat by coupling to renewable power generation (sector coupling). In this context, it is shown using the example of Germany that with these technologies, reductions of 47–95% of CO2 emissions against 1990 levels and 27–95% of primary energy demand against 2008 can be achieved through the integration of 12–274 TWh of renewable electrical power into the steel industry. Thereby, a substantial contribution to reducing CO2 emissions and fuel demand could be made (although it would fall short of realizing the German government’s target of a 50% reduction in power consumption by 2050).

Keywords: power-to-steel; CO2 reduction in steel industry; sector coupling; renewable energy for steelmaking; alternative steelmaking processes

1. Introduction The growth of the global economy and population is strongly associated with a continuous increase in primary energy demand. In 2012, 81% of energy was generated by fossil fuels, which emitted around 30.2 billion tons of CO2 [1]. In its World Energy Outlook 2012 [1], the International Energy Agency (IEA) outlines in the “450 Scenario” that the average increase of global temperature ◦ could be limited to 2 C if CO2 emissions could be reduced to 22 billion tons a year by 2035. This would mean that annual global CO2 emissions must be reduced by approximately 30% from the year 2012 until 2035. As a worldwide leader in climate protection-focused policy, the targets of the German government are more ambitious. In its energy concept 2010/2011, it set out the goal of reducing greenhouse gas emissions in Germany by 80–95% by 2050 against 1990 levels, with a simultaneous reduction of electrical power demand by 25% and primary energy demand by 50% by 2050 against

Energies 2017, 10, 451; doi:10.3390/en10040451 www.mdpi.com/journal/energies Energies 2017, 10, 451 2 of 21

2008Energies levels. 2017 The, 10, primary 451 means foreseen for achieving this is the expansion of renewable2 energies,of 21 which are intended to provide 60% of final energy consumption and 80% of power production by 20502008 [2]. Therefore,levels. The theprimary German means landscape foreseen for has achiev seening a continuous this is the expansion expansion of of renewable wind turbines energies, during 2003which to 2015 are from intended 14 to to 45 provide GW and 60% photovoltaic of final energy installations consumption in theand same 80% of time power from production 0.5 to 39 GWby for 2050 [2]. Therefore, the German landscape has seen a continuous expansion of wind turbines during power production [3]. 2003 to 2015 from 14 to 45 GW and photovoltaic installations in the same time from 0.5 to 39 GW for However, both technologies are characterized by fluctuating electrical power provision due to the power production [3]. volatile natureHowever, of wind both andtechnologies solar radiation, are characterized so that thereby fluctuating are times electrical when supply power ofprovision electricity due isto scare and timesthe volatile when nature it is abundant. of wind and To integratesolar radiation, a high so proportion that there are of windtimes andwhen solar supply power of electricity into the energyis system,scare a large-scaleand times when storage it is abundant. solution is To required integrate to a high compensate proportion for of the wind temporal and solar imbalances power into betweenthe productionenergy system, and demand. a large-scale For thisstorage task, solution power-to-gas is required technologies to compensate that for convertthe temporal surplus imbalances power into otherbetween forms of production final energy and such demand. as thermal For this or task, chemical power-to-gas energy (e.g.,technologies hydrogen that or convert synthetic surplus methane) are suitable,power into even other though forms of electrical final energy power such has as ther themal highest or chemical degree energy in energy (e.g., hydrogen [4–6]. The or production synthetic of gasesmethane) using excess are suitable, electrical even power though at electrical times when power more has electricitythe highest than degree needed in energy is produced [4–6]. The offers production of gases using excess electrical power at times when more electricity than needed is different opportunities. On the one hand, the gas can be reconverted into electrical power with gas produced offers different opportunities. On the one hand, the gas can be reconverted into electrical turbinespower or with fuel gas cells turbines during or periodsfuel cells whenduring demandperiods when for electricaldemand for power electrical is higherpower is than higher production. than On theproduction. other hand, On conventionalthe other hand, gas co powernventional plants gas can power be usedplants for can backup be used power for backup to compensate power to gaps in electricitycompensate production, gaps in electricity with the production, gases produced with the beinggases produced used in otherbeing applications,used in other applications, such as fuel for transportationsuch as fuel or for for transportation heating in several or for heating sectors in [ 5several,7,8]. The sectors direct [5,7,8]. or indirectThe direct use or ofindirect electrical use of power fromelectrical renewable power energies from renewable to provide energies heat, cold to provi andde operating heat, cold power and operating across allpower sectors across is alsoall sectors known as sectoris couplingalso known [9], as which sector is coupling shown in[9], simplified which is shown form inin Figuresimplified1. Furthermore, form in Figure synthetic 1. Furthermore, methane or hydrogensynthetic can methane be used directlyor hydrogen as a can feedstock be used in directly the chemical as a feedstock industry in the [10 ].chemical The integration industry [10]. of renewable The integration of renewable energies into different shapes, applications and sectors can lead to a energies into different shapes, applications and sectors can lead to a reduction in CO2 emissions beyond reduction in CO2 emissions beyond the power sector [6,11,12]. Although the step of converting the power sector [6,11,12]. Although the step of converting hydrogen to methane incurs additional hydrogen to methane incurs additional energy (η = 80%) [4,5], an advantage of synthetic methane is η energythat ( it= can 80%) be fed [4,5 directly], an advantage into the natural of synthetic gas grid methane so that existing is that infrastructure it can be fed and directly technologies into the for natural gas gridheat so generation that existing can be infrastructure used. and technologies for heat generation can be used.

Figure 1. Principle of sector coupling, description from [9]. Figure 1. Principle of sector coupling, description from [9]. However, renewable power is not always directly convertible, especially in certain industrial However,processes. This renewable is exemplified power by is the not steel always industry, directly which convertible, is mainly dependent especially on incoal certain or coke, industrial not processes.only as This an energy is exempliﬁed source but by also the for steel necessary industry, process which engineering is mainly dependent[13]. In a conventional on coal or blast coke, not onlyfurnace, as an energy coal or sourcecoke serves but as also a reducing for necessary agent, heat process provider engineering and ensures [13 the]. Inmechanical a conventional stability blast furnace,of the coal different or coke layers serves of ascoke a reducingand iron ore agent, inside heat the provider furnace (see and also ensures Section the 4.1). mechanical For the need stability to of reduce CO2 emissions is particularly acute in steelmaking, as it constitutes one of the most energy- the different layers of coke and iron ore inside the furnace (see also Section 4.1). For the need to reduce and carbon dioxide-intensive industrial processes worldwide; Germany, serving as a case study in CO2 emissions is particularly acute in steelmaking, as it constitutes one of the most energy- and carbon dioxide-intensive industrial processes worldwide; Germany, serving as a case study in this paper, is no Energies 2017, 10, 451 3 of 21 exception (see Section3)[ 14]. The literature contains many studies that deal with the overall potential of CO2 reduction in the steel industry in terms of increasing efficiency [15–18]. Fujii and Managi (2015) [19] for example proposed and measured optimal production resource reallocation using data envelopment analysis. Their research clarifies the effect of optimal production resource reallocation on CO2 emissions reduction, focusing on regional and industrial characteristics [19]. Nevertheless, studies that specifically pertain to alternative processes and the potential to integrate renewable power are lacking. In a bid to contribute to ﬁlling this gap, this study evaluates blast furnace gas recirculation (BF-GR) [20,21], blast furnace carbon capture (BF-CC) [20,21], the possibility of a higher share of steelmaking being conducted with electrical arc furnaces (EAFs) [22] and the direct reduction of iron ore with renewable hydrogen (H-DR) [23] technologies and methods that not only have the potential to reduce sector CO2 emissions, but also to shift the steel industry’s energy demand away from coal to other energy carriers that can be provided by renewable energies. Therefore, the objective of the present study is to determine whether it is possible to integrate renewably-generated power into the conventional coal-based steel industry via alternative manufacturing technologies or measures and to analyze the effect on CO2 emissions. Additionally, the above-mentioned aims of the German Government regarding the simultaneous reduction of CO2 emissions, as well as electrical power and primary energy demand are also taken into account and analyzed. As the German Government did not publish particular objectives of CO2 and energy reduction for special sectors or processes, it is assumed at this point that the steel industry should achieve an 80–95% CO2 reduction on 1990 levels by 2050 and simultaneously a reduction in electrical power demand by 25% and primary energy demand by 50% against 2008 by 2050. While this analysis is conducted within the context of Germany, the methodology and data on the technologies could be applied to similar analyses focused elsewhere, as the steel industry is similarly constructed around the world (see Section3).

2. Method and Procedure To achieve the objectives of the present study, the state-of-the-art conventional method of steelmaking is first described and its energy demand determined using data from the literature. On the basis of this data and the specific emission factors of fuels, feedstocks and electrical power, energy-related emissions are calculated. Emissions arising from plant construction, fuel procurement and maintenance are not considered. For the calculation of the energy as well as process-related emissions, only CO2 was included because the greenhouse gas emissions of the relevant energy carriers consist of 98.8% CO2 and the process emissions of steel manufacturing of CO2 only [24,25]. Secondly, selected measures and alternative processes that have the potential to reduce CO2 emissions and incorporate renewable energy into the integrated steelworks are considered. These potential CO2-reduction technologies were analyzed in the same manner as conventional processes to determine energy demand and CO2 emissions. Finally, a comparison of the energy demand and CO2 emissions between the conventional processes and alternative processes should indicate if it is possible to achieve the emission and energy consumption reduction aims of the German government, first without (Sections 6.1–6.3) and then with (Section 6.4) the integration of renewable energies into the steelmaking process. For this comparison, not only were blast furnaces investigated in isolation, but also connected processes, like coking plants, sinter production and blast furnace gas utilization processes were analyzed for their energy demand and CO2 emissions. A detailed outline of the analytical framework can be found in Section6. The method used in this study is based on common CO2 and energy balance calculations derived from data in the literature. Table1 shows the CO 2 emission factors of the most important energy carriers and gases that are used for steelmaking. For the analyses of CO2 emissions in Sections 4.1, 4.2, 5.1–5.4 and 6.1–6.3, the electricity use assumed is based on the German electricity mix from 2012, which had a CO2 emission factor of 160 kgCO2/GJ. Energies 2017, 10, 451 4 of 21

Table 1. CO2 emission factors of fuels, electrical power and feedstocks [4,24,26–28].

Energy Carrier/Gases Description/Assumptions CO2 Emission Factor

Natural gas (NG) - 56 kgCO2/GJ

Blast furnace gas (BF gas) - 257.8 kgCO2/GJ

Coke - 105.0 kgCO2/GJ

Hard coal - 94.2 kgCO2/GJ

Coke oven gas (COG) - 40.0 kgCO2/GJ

Basic oxygen furnace gas (BOF gas) - 257.8 kgCO2/GJ

German electricity mix 2012 - 160 kgCO2/GJ

Energy demand of O2 provision 119.2 kgCO2/tH2 Oxygen by cryogenic air separation: (powered by the German 0.745 MJel/kgO2 [27] electricity mix 2012)

Energy demand of N2 provided by 92.18 kgCO2/tH2 Nitrogen cryogenic air separation: (powered by the German 0.576 MJel/kgO2 [28] electricity mix 2012) Hydrogen produced through the 66.64 kg/GJ η = 84% [29] =>1.190 GJNG/GJH2 steam reforming of natural gas (NG) (8000 kgCO2/tH2) Hydrogen produced through water 119 kg/GJ electrolysis powered by the German η = 70% [4] =>1.428 GJ /GJ el H2 (27,418 kg /t ) electricity mix 2012 CO2 H2 Used in Section 6.4 only Only energy-related CO Renewable electrical power 2 0.0 kg /GJ emissions are considered CO2 Hydrogen produced by water 0.0 kg/GJ electrolysis powered by renewable η = 70% [4] =>1.428 GJ /GJ el H2 (0.0 kg /t ) electrical power CO2 H2 Electrolyzer: η = 70% [4] Synthetic methane produced via Methanation: η = 80% [4] power-to-gas with hydrogen from =>1.785 MJ /MJ el CH4 0.0 kg/GJ water electrolysis powered by Energy demand and CO2 renewable electrical power emissions of CO2 provision are not considered

Two different cases based on the use of hydrogen are also considered. In the ﬁrst of these, hydrogen was produced by steam reforming [29], with an energy demand of 1.190 MJNG/MJH2 and related CO2 emissions of 66.64 kgCO2/GJH2, while in the other case it was sourced by water electrolysis powered by the electricity mix [4] In Section 6.4, which deals with the integration of renewable energies, it is assumed that electrical power is exclusively provided by renewable sources such as solar cells or wind turbines. Hence, zero CO2 emissions are assumed because only the energy-related CO2 emissions are considered in this study. In this case, the CO2 emissions arising from hydrogen provided via water electrolysis are zero as well. Furthermore, natural gas is substituted by synthetic natural gas, which is produced by a methanation process that entails the hydrogenation of CO2, in which the necessary hydrogen is provided by water electrolysis powered by renewable electricity, as shown in Figure1. Since the provision of CO 2 is not considered at this point, it is assumed that the CO2 emission factor of the synthetic methane is also zero. Synthetic methane is considered for heat provision in this study because it can directly substitute natural gas without a change in the combustion technologies. At this point, a detailed description of the different technologies is omitted, because this would be beyond the scope of the present study. More information about the technologies can be found in Schiebahn et al. [4,5] and Agostinha et al. [29].

3. Global and German Steel Industry In 2012, the global production of crude steel exceeded 1560 million tons [30], produced mainly in oxygen blast furnaces (BF-BOF) (70.49%) by iron ore and in EAFs with iron metal scrap (28.62%) [31]. Other crude steel production routes, such as open hearth furnaces (OHF), smelting reduction (SR) or Energies 2017, 10, 451 5 of 21

directEnergies reduction 2017, 10 (DR), 451 contributed only a minor portion to this, with a share of less than 1% of5 of the 21 total amount produced [31]. Indirect 2012, reduction crude steel (DR) manufacturingcontributed only constituted a minor portion 5.5% to of this, global with primary a share energyof less than demand 1% of andthe was total amount produced [31]. the source of 8.0% of total global CO2 emissions (data based on Table2). The largest manufacturer of In 2012, crude steel manufacturing constituted 5.5% of global primary energy demand and was crude steel is China, whose share amounts to approximately 47% followed by Japan, the USA, India the source of 8.0% of total global CO2 emissions (data based on Table 2). The largest manufacturer of and Russiacrude steel (see is Figure China,2 ).whose share amounts to approximately 47% followed by Japan, the USA, India Althoughand Russia its(see production Figure 2). quantity is relatively low compared to China, Germany is the eighth largest producerAlthough in its the production world (see quantity Figure is 2relatively). In 2012, low it compared produced to 42.7 China, million Germany tons is of the crude eighth steel, similarlargest to the producer globalaverage in the world of 67.67% (see Figure produced 2). In through 2012, it theproduced BF-BOF 42.7 method million and tons 32.32% of crude via steel, the EAF route,similar with ato primary the global energy average demand of 67.67% of produced 762.76 PJ through and CO the2 emissions BF-BOF method of 57.84 and million 32.32% tons,via the which EAF route, with a primary energy demand of 762.76 PJ and CO2 emissions of 57.84 million tons, which corresponds to 5.67% of primary overall German energy consumption and 7.01% of German CO2 emissionscorresponds (see Table to 5.67%2). The of steel primary industry’s overall manufacturingGerman energy processesconsumption are and the 7.01% most energy-of German and CO carbon2 emissions (see Table 2). The steel industry’s manufacturing processes are the most energy- and carbon dioxide-intensive in Germany, accounting for approximately 24% of thermal energy demand and 28% dioxide-intensive in Germany, accounting for approximately 24% of thermal energy demand and of CO2 emissions in German industry, although this is only “one” product of “millions” [32]. 28% of CO2 emissions in German industry, although this is only “one” product of “millions” [32].

 China Japan  USA  India   Russia

 South Korea  Germany Brazil  Ukranine Italy  Other   Figure 2. Share of countries in total steel production in 2012 [31]. The ten largest steel manufacturers Figure 2. Share of countries in total steel production in 2012 [31]. The ten largest steel manufacturers in in the world (2012). Total global production: 1560 million tons of crude steel. the world (2012). Total global production: 1560 million tons of crude steel. Table 2. Data from the year 2012 used for calculation to classify the steel industry. Table 2. Data from the year 2012 used for calculation to classify the steel industry. Steel Industry Global Ref. Germany Ref. Primary energy demand (EJ/a) 559.82 [33] 13.45 [25] Steel Industry Global Reference Germany Reference Net power consumption (TWH/a) 22,668 [33] 540 [25] Primary energyCO2 demand emissions (EJ/a) (million t/a) 559.82 35,083 [33 [34]] 818 13.45 [35] [25] Net power consumption (TWH/a) 22,668 [33] 540 [25] Manufacturing Process Crude Steel CO2 emissions (million t/a) 35,083 [34] 818 [35] Output (million t/a) 1560 [30] 42.7 [30] Manufacturing Process Crude Steel Average primary energy demand (GJth/tCrude steel) 20.0 [30] 17.88 [36] OutputAverage (million CO2 emissions t/a) (tCO2/tCrude steel) 1560 1.8 [30[30]] 1.356 42.7 [37] [30] Average primary energy demand (GJth/tCrude steel) 20.0 [30] 17.88 [36] Average CO2 emissions (tCO2/tCrude steel) 1.8 [30] 1.356 [37] The above-mentioned CO2 emissions already include process-related emissions. The reduction of iron ore (Fe2O3) to pig iron, directly with coke (Equation (1)) or indirectly with carbon monoxide The(Equation above-mentioned (2)), which is COformed2 emissions in situ with already oxygen include inside process-related of oxygen blast emissions.furnace (simplified The reduction in of ironEquation ore (Fe (1)),2O3 )produces to pig iron, reaction-related directly with CO coke2 emissions. (Equation The(1)) specific or indirectly process-related with carbonemissions monoxide are (Equationtypically (2)), 0.588 which tCO2/t ispig formediron [35]. in situ with oxygen inside of oxygen blast furnace (simpliﬁed in

Equation (1)), produces reaction-relatedFeO CO +2 1.5Cemissions. → 2Fe + 1.5COThe speciﬁc process-related emissions(1) are typically 0.588 t /t [35]. CO2 pig iron (2) FeO +3CO→2Fe+3CO

Fe2O3 + 1.5C → 2Fe + 1.5CO2 (1) 4. Conventional Steelmaking Processes

In this section, the steel/iron industryFe2O3 + is3CO analyz→ed,2Fe beginning+ 3CO2 with a description of conventional (2) steelmaking processes using blast furnaces, which is the most energy-intensive part of the 4. Conventionalsteelmaking process, Steelmaking followed Processes by steel production in an electric arc furnace. The SR and DR are not Inconsidered this section, here thebecause steel/iron these methods industry make is analyzed, up only a beginningnegligible proportion with a description of the global of conventionaltotal and steelmaking processes using blast furnaces, which is the most energy-intensive part of the steelmaking Energies 2017, 10, 451 6 of 21 process, followed by steel production in an electric arc furnace. The SR and DR are not considered here because these methods make up only a negligible proportion of the global total and are not practiced in the German steel industry (see Section3). The second part of this presents an analysis of measures and alternativeEnergies 2017, 10 processes, 451 that have the potential to reduce CO2 emissions and integrate a higher6 of 21 share of renewable energy into steelmaking. are not practiced in the German steel industry (see Section 3). The second part of this presents an 4.1. Conventionalanalysis of measures Blast Furnace and alternative Route processes that have the potential to reduce CO2 emissions and integrate a higher share of renewable energy into steelmaking. Figure3 schematically displays a typical blast furnace for steelmaking. Before the feedstock iron ore is4.1. fed Conventional into the top Blast of Furnace the blast Route furnace, it is pretreated in a sinter or pellet plant and mixed with additives such as limestone (CaCO ) and dolomite (CaMg(CO ) ). This mixture of sinter, pellets and Figure 3 schematically displays3 a typical blast furnace for steelmaking.3 2 Before the feedstock iron additivesore is isfed referred into the totop as of the the burden. blast furnace, In the it blast is pretreated furnace, in the a sinter iron ofor thepellet burden, plant and which mixed comprises with a mixtureadditives of hematite such as (Felimestone2O3) and (CaCO magnetite3) and dolomite (Fe3O4), (CaMg(CO is reduced3)2). and This the mixture resulting of sinter, iron melted.pellets and For the separationadditives of is oxygen referred and to as iron the inburden. conventional In the blast blast furnace, furnaces, the iron coke of the and burden, coal dust which are comprises typically a used as reductionmixture of agents. hematite The (Fe burden2O3) and andmagnetite coke are(Fe3 fedO4), intois reduced the top and of the the resulting furnace iron in alternatingmelted. For the batches, whileseparation at the same of oxygen time coal and dust iron andin conventional hot air, enriched blast furnaces, with oxygen, coke and are coal injected dust are into typically the lower used part of the furnaceas reduction (see Figureagents.3 The). The burden blast and furnace coke are is a fed continuously into the top operatedof the furnace shaft in furnace alternating that batches, works on a countercurrentwhile at the principle.same time coal The dust reducing and hot agents air, enri cokeched and with coal oxygen, react are with/burn injected into the the oxygen lower topart mainly of the furnace (see Figure 3). The blast furnace is a continuously operated shaft furnace that works produce carbon monoxide (CO) and heat. The CO reduces the iron ore to metal iron, producing CO on a countercurrent principle. The reducing agents coke and coal react with/burn the oxygen to 2 (Equation (1)). The blast furnace gas leaves the furnace at the top, while the molten metal and slug are mainly produce carbon monoxide (CO) and heat. The CO reduces the iron ore to metal iron, collected in the hearth at the bottom, where both are discharged at regular intervals. The BF gas, which producing CO2 (Equation (1)). The blast furnace gas leaves the furnace at the top, while the molten is undermetal pressure and slug (1.25–3.5 are collected bar) andin the still hearth has aat heat the value,bottom, is where ﬁrst expanded both are discharged over a turbine at regular to recover electricalintervals. power The (18 BF kWh/t gas, whichpig iron is) andunder then pressure a portion (1.25–3.5 of it (1.536 bar) and GJ/t stillpig ironhas) isa heat used value, to heat is upfirst the air, whichexpanded is then ledover to a the turbine furnace. to recover The main electrical part of power the BF (18 gas kWh/t is thereafterpig iron) and exported then a toportion other processesof it of the(1.536 integrated GJ/tpig iron steelworks) is used to heat [38,39 up]. the The air, energy which demandis then led of to an the average furnace. blastThe main furnace part (seeof the Figure BF 3) gas is thereafter exported to other processes of the integrated steelworks [38,39]. The energy demand is 15.95 GJ/tpig iron. Considering the export of blast furnace gas (4.719 GJ/tpig iron), the net energy of an average blast furnace (see Figure 3) is 15.95 GJ/tpig iron. Considering the export of blast furnace requirement is 11.4 GJ/tpig iron. These values include the power demand for the O2 and N2 provision gas (4.719 GJ/tpig iron), the net energy requirement is 11.4 GJ/tpig iron. These values include the power via cryogenic air separation, but not the energy demand for coke and burden production, which are demand for the O2 and N2 provision via cryogenic air separation, but not the energy demand for coke additional processes and considered in Section6. For the calculations of the CO emissions—through and burden production, which are additional processes and considered in Section 6. For2 the calculations the use of emission factors from Table1 and the energy data from Figure3—only the upstream chain of the CO2 emissions—through the use of emission factors from Table 1 and the energy data from of N2Figureand O 3—only2, as well the asupstream the used chain electrical of N2 and power, O2, as are well considered. as the used electrical power, are considered.

Energy demand per ton of pig iron [39] Coke 10.303 GJ Coal dust 4.67 GJ Net power demand 0.202 GJ Power demand for N2 and O2 allocation 0.119 GJ To hot-blast stoves Natural Gas (NG) 0.213 GJ Coke oven gas (COG) 0.284 GJ Oxygen steel furnace gas (BOF gas) 0.168 GJ Total energy demand 15.95 GJ Export of blast furnace gas 4.719 GJ Net energy demand (overall demand minus 11.24 GJ export of blast furnace gas) CO2 emissions of the blast furnace per ton of pig iron Directly from the process 514 kgCO2

Inclusive CO2 in exported BF gas 1099 kgCO2 Data per ton pig iron

Figure 3. Simplified scheme of a blast furnace based on average data from UBA 2012 [39]. Figure 3. Simpliﬁed scheme of a blast furnace based on average data from UBA 2012 [39].

The CO2 emissions of the process are 514 kgCO2/tpig iron as a result of burning a part of the BF gas (462The kg COCO22 /temissionspig iron) for preheating of the process the air are and 514 the kg emissionsCO2/tpig irongeneratedas a result by the of electrical burning power a part demand of the BF gas (462 kgof CO2the /tprocesspig iron and) for the preheating N2 and CO the2 provision air and the(51.5 emissions kgCO2/tpig iron generated). However, by thea large electrical proportion power of demandthe of theCO process2, which and is formed the N 2insideand the CO blas2 provisiont furnace,(51.5 exits kgtheCO2 process/tpig in iron the). form However, of exported a large BF proportion gas. The of CO2 concentration in the gas is 21% and when this is also considered in the CO2 balance, CO2 emissions are 1099 kgCO2/tpig iron. Moreover, the process-related CO2 emissions accruing from iron ore

Energies 2017, 10, 451 7 of 21

the CO2, which is formed inside the blast furnace, exits the process in the form of exported BF gas. The CO2 concentration in the gas is 21% and when this is also considered in the CO2 balance, CO2 emissions are 1099 kgCO2/tpig iron. Moreover, the process-related CO2 emissions accruing from iron ore reduction are already a part of the BF gas. As shown in Figure3, the largest part of the conventional blast furnace’s energy demand is provided by coke and coal (94%), hence the integration of renewable energies to achieve a large reduction of CO2 emissions is not possible.

4.2. Electrical Arc Furnace In an EAF, materials that contain iron, such as scrap, are melted directly through the use of electrical power. The resulting product from this process is liquid steel rather than pig iron, as in blast furnaces. Initially, a natural gas burner assists with the melting process. For process engineering and metallurgical reasons, oxygen nitrogen and coal are inserted into the liquid steel [39]. The energy demand and resultant CO2 emissions entailed by the production of one ton of crude steel are shown in Table3. The speciﬁc energy demand, including the electrical power demand for the provision of N2 and O2, is 3.34 GJ/tLS, which is only 30% of blast furnace energy demand. The CO2 emissions are 508 kg/tLS, which also includes the emissions for electrical power (German electricity mix) and N2, O2 provision and process-related CO2 emissions caused by decarburization processes and electrode burn-off [39].

Table 3. Energy demand (average values based on UBA 2012 [39]) and calculated CO2 emissions of an EAF.

Energy Demand per Ton of Liquid Steel Electrical power 2.07 GJ a Natural gas 0.78 GJ b N2 8 kg (4.6 MJel) b O2 50 kg (37.3 MJel) Coal 0.45 GJ Overall energy demand 3.34 GJ

CO2 Emissions per Ton of Liquid Steel Process-related: Decarburization 83.9 kg and electrode burn-off Total CO emissions 2 508 kg including N2 and O2 provision Notes: a German electricity mix (2012); b see also Table1.

In contrast to blast furnaces, EAFs not only have the potential to reduce CO2 emissions through lower energy demand, but also through the use of renewable electricity and synthetic methane instead of natural gas. Therefore, a higher share of steelmaking in EAF is discussed as an alternative means of CO2 reduction and the integration of renewable energies in Sections 5.3 and6.

5. Alternative Processes for Steelmaking

In this section, the following selected CO2-reduction technologies or routes are evaluated for use in the steel industry: (Section 5.1) Blast furnaces with gas recirculation (BF-GR) [20,21]; (Section 5.2) blast furnaces with carbon capture capability (BF-CC) [20,21]; (Section 5.3) a higher share of steelmaking using EAFs at constant steel production volume [22]; and (Section 5.4) the direct reduction of iron ore using hydrogen as the reduction agent (Circored Process) [23]. These technologies were selected by the authors because all of them have the potential to reduce a huge amount of CO2 through the implementation of one measure or technology, and all have already attained commercialization potential, or are on the verge thereof [20,40]. In addition, these technologies would enable greater independence from coal, such that energy demand can be met by other, less CO2-intensive fossil sources Energies 2017, 10, 451 8 of 21 like natural gas or directly with emission-free renewable sources such as renewable electrical power or renewable gases like synthetic methane or hydrogen. Furthermore, the CO2 reduction potential of a higher share of steelmaking in EAFs at constant steel production is also considered in Section 5.3, because this could lead to a relatively simple reduction in CO2 emissions without the implementation of new technologies. The analysis of other technologies like the electrochemical cleavage of iron [41] ore are not considered, because these technologies are still at the basic research stage and unlikely to be marketableEnergies 2017, 10 before, 451 2040 [20]. Furthermore, many possible efﬁciency measures relating8 of 21 to the whole integrated steelworks, which are described in Santos 2013 [21], for example, are not considered, still at the basic research stage and unlikely to be marketable before 2040 [20]. Furthermore, many becausepossible one of efficiency the targets measures of this relating study isto tothe illuminate whole integrated technologies steelworks, and which measures are described that lead in to large reductionsSantos in 2013 CO2 [21],emissions for example, and to are determinate not considered, the possibilitybecause one ofof integratingthe targets of renewable this study energies.is to illuminate technologies and measures that lead to large reductions in CO2 emissions and to 5.1. Blastdeterminate Furnace withthe possibility Blast Furnace of integrating Gas Recirculation renewable energies.

Figure5.1. Blast4 outlines Furnace awith blast Blas furnacet Furnace withGas Recirculation BF-GR. Ultra-Low Carbon Dioxide Steelmaking (ULCOS), a consortium of 48 European companies and organizations [41], has developed and evaluated this Figure 4 outlines a blast furnace with BF-GR. Ultra-Low Carbon Dioxide Steelmaking (ULCOS), technology [20,21,42,43]. BF-GR is intended as a replacement of air (hot blast) by nearly pure oxygen a consortium of 48 European companies and organizations [41], has developed and evaluated this and pretreatedtechnology BF [20,21,42,43]. gas. At BF-GR the pretreatment is intended as a stage, replacement the BF of air gas (hot is blast) separated by nearly in pure a CO oxygen2-rich and a CO-rich-gasand pretreated by vacuum BF gas. pressure At the pretreatment swing adsorption stage, the BF (VPSA).gas is separated The CO-richin a CO2-rich gas and stream a CO-rich-gas is fed into the furnaceby and vacuum the CO pressure2-rich swing stream, adsorption which still (VPSA). contains The CO-rich CO and gas H 2stream(see Figureis fed into5), isthe used furnace for preheatingand the CO-richthe CO stream.2-rich stream, Due which to the still recycling contains of CO CO and to H the2 (see furnace, Figure 5), coke is used demand for preheating drops bythe 45%CO-rich compared stream. Due to the recycling of CO to the furnace, coke demand drops by 45% compared to the to the conventional blast furnace (Figure3). conventional blast furnace (Figure 3).

Energy demand per ton of pig iron [20,21,42] Coke 5.64 GJ Coal dust 4.89 GJ Total Power consumption inclusive of N2 and O2 allocation and VPSA; 0.78 GJ (assumption based on [20,21,27,39,43]) Hot-blast stoves Coke oven gas (COG) 0.29 GJ Total energy demand 11.6 GJ Export of blast furnace gas 0 GJ Net energy demand (overall demand minus export of 11.6 GJ blast furnace gas) CO2 emissions of the blast furnace per ton of pig iron Directly at the process (inclusive electrical power 1065 kgCO2 demand) Data per ton of pig iron VPSA = Vacuum pressure swing adsorption

Figure 4. Simplified scheme of a blast furnace with blast furnace gas recirculation based on average Figuredata 4. Simpliﬁed from Danloy scheme 2009, Santos of a blast2013 [20,21]. furnace with blast furnace gas recirculation based on average data from Danloy 2009, Santos 2013 [20,21]. The reason for the reduction in coke demand is that CO, as well as coke, can act as a fuel and reduction agent of iron ore (see Equation (2)). With the help of data from Danloy 2009, Santos 2013 The reason for the reduction in coke demand is that CO, as well as coke, can act as a fuel and and Danloy 2008 [20,21,42], the net energy demand of the BF-GR, inclusive of the provision of N2 and reduction agent of iron ore (see Equation (2)). With the help of data from Danloy 2009, Santos 2013 and O2, was determined to be 11.6 GJ/tpig iron. The reason for the reduction in coke demand is that CO, as Danloywell 2008 as [coke,20,21 can,42 ],act the as a net fuel energy and reduction demand agent of of the iron BF-GR, ore (see inclusive Equation of(2)). the With provision the help of of data N2 and O2, was determinedfrom Danloy to be2009, 11.6 Santos GJ/t 2013pig iron and. The Danloy reason 2008 for [20,21,42], the reduction the net energy in coke demand demand of isthe that BF-GR, CO, as well as coke,inclusive can act of as the a fuel provision and reduction of N2 and agent O2, was of determined iron ore (see to Equationbe 11.6 GJ/t (2)).pig iron With. Although the help the ofcoke data from Danloydemand 2009, Santos is less than 2013 in and the Danloyconventional 2008 process, [20,21 ,42net], energy the net demand energy is demandslightly higher, of the because BF-GR, the inclusive conventional process exports the largest part of the BF gas, which is used in this technology. of the provision of N and O , was determined to be 11.6 GJ/t . Although the coke demand is Moreover, the electrical2 energy2 demand increases due to the lackpig of ironpower recovery due to BF gas less thanexpanding in the conventional and the additional process, energy net demand energy for demand VPSA and is slightlythe higher higher, amount because of necessary the conventional pure processoxygen. exports These the largest circumstances part of lead the BFto the gas, result which that is CO used2 emissions in this technology. (calculated with Moreover, the emission the electrical energyfactors demand of Table increases 1 and due data to from the Figure lack of 4) power arisingrecovery directly from due blast to BF furnaces gas expanding with gas recirculation and the additional (1065 kg/tpig iron) are higher than for the conventional process (514 kg/tpig iron). However, when the CO2 content of the exported BOF gas is also taken into account in the context of the conventional blast

Energies 2017, 10, 451 9 of 21 energy demand for VPSA and the higher amount of necessary pure oxygen. These circumstances lead to the result that CO2 emissions (calculated with the emission factors of Table1 and data from Figure4) arising directly from blast furnaces with gas recirculation (1065 kg/t pig iron) are higher than for the conventional process (514 kg/tpig iron). However, when the CO2 content of the exported BOF gas is also taken into account in the context of the conventional blast furnace, the emissions of the blast furnace with gas recirculation is slightly less (1065 kg/t vs. 1099 kg/t ). At this point, it Energies 2017, 10, 451 pig iron pig iron 9 of 21 should be pointed out again that the CO2 emissions are only based on the combustions of fuels, and that COfurnace,2 emissions the emissions for building of the blast the facilitiesfurnace with were gas not recirculation considered. is Theslightly extent less to(1065 which kg/t thepig iron complete vs. CO2 1099reduction kg/tpig iron potential,). At this aspoint, well it asshould the potential be pointed to out integrate again that renewable the CO2 emissions energy, is are due only to based the reduction on of cokethe andcombustions the lack of fuels, exported and that blast CO furnace2 emissions gas becomesfor building apparent the facilities under were consideration not considered. ofthe The entire integratedextent to steelwork which the process, complete which CO2 reduction is analyzed potential, in detail as well in Section as the potential6. to integrate renewable energy, is due to the reduction of coke and the lack of exported blast furnace gas becomes apparent 5.2. Blastunder Furnace consideration with Carbon of the entire Capture integrated steelwork process, which is analyzed in detail in Section 6.

5.2.Figure Blast5 Furnaceshows with a schematic Carbon Capture of a blast furnace with BF gas recirculation and carbon capture (BF-CC). This concept is also developed by ULCOS [21,44]. The main difference to the BF-GR is that Figure 5 shows a schematic of a blast furnace with BF gas recirculation and carbon capture the BF(BF-CC). gas is separatedThis concept by is chemical also developed scrubbing by ULCOS in an almost[21,44]. The pure main CO 2differencestream (>99.99%) to the BF-GR and is a that CO-rich streamthe isBF led gas back is separated to the blastby chemical furnace. scrubbing Because in thean almost CO2-rich pure streamCO2 stream has (>99.99%) no heat value, and a CO-rich it cannot be usedstream for preheating is led back the to the CO-rich blast furnace. stream Because as in the the case CO2 above-rich stream (see Figurehas no 4heat). Therefore, value, it cannot natural be gas is usedused for for the preheating preheating the ofCO-rich the stream, stream asas wellin the as ca forse above the additional (see Figure thermal 4). Therefore, energy natural demand gas is of the CO2-separationused for the unitpreheating via chemical of the stream, scrubbing. as well To as avoid for the CO additional2 emissions thermal to the energy air, the demand pure CO of 2thestream mustCO be2-separation geologically-stored unit via chemical or used scrubbing. as a feedstock To avoid for CO chemical2 emissions products to the air, or the synthetic pure CO2 gasesstream [ 5,10]. must be geologically-stored or used as a feedstock for chemical products or synthetic gases [5,10]. According to the data on ULCOS (see Figure5), the coke demand drops to 7.26 GJ/t pig iron, which is According to the data on ULCOS (see Figure 5), the coke demand drops to 7.26 GJ/tpig iron, which is 30% lower than in the conventional process. The coke drop is not as high as with the BF-GR, because 30% lower than in the conventional process. The coke drop is not as high as with the BF-GR, because part of the CO-rich stream (1.69 GJ/t ) is exported. The net energy demand of the blast furnace part of the CO-rich stream (1.69 GJ/tpigpig ironiron) is exported. The net energy demand of the blast furnace withwith carbon carbon capture capture is higher is higher than than for for both both thethe otherother cases cases above above (Figures (Figures 3 and3 and 4) 4because) because of the of lack the lack of BFof gas BF forgas preheating for preheating the airthe or air the or recirculatedthe recirculat gas,ed gas, and and the the additional additional thermal thermal and and electrical electrical energy demandenergy of thedemand CO2 ofseparation the CO2 separation unit. However, unit. However, the direct the CO direct2 emissions CO2 emissions from thefrom furnace the furnace are veryare low (382 kgveryCO2 low/tpig (382 iron kg)CO2 because/tpig iron) ofbecause the separation of the separation of 867 kgof CO2867 /tkgpigCO2/t ironpig .iron Even. Even taking taking into into accountaccount the the CO2 contentCO of2 content the exported of the BFexported gas, the BF emissions gas, the emissions are 392 kg CO2are /t392pig kg ironCO2and/tpig iron thus and less thus than less in athan conventional in a conventional blast furnace and the BF-GR. The entire CO2 reduction potential, due to the reduction blast furnace and the BF-GR. The entire CO2 reduction potential, due to the reduction of coke and the less exportedof coke and BF the gas, less as exported well as BF the gas, potential as well toas integratethe potential renewable to integrate energy, renewable becomes energy, apparent becomes under apparent under consideration of the entire integrated steelworks, which are analyzed in detail in consideration of the entire integrated steelworks, which are analyzed in detail in Section6. Section 6.

Energy demand per ton of pig iron [21,44] Coke 7.26 GJ Coal dust 4.39 GJ

2 Total power consumption inclusive of N 1.07 GJ and O2 allocation and chemical scrubbing Hot blast stoves Natural gas (NG) 3.59 GJ Total energy demand 16.31 GJ Export of blast furnace gas 1.69 GJ Net energy demand (overall demand minus the export of 14.62 GJ blast furnace gas) CO2 emissions of the blast furnace per ton of pig iron Directly at the process 382 kgCO2 (inclusive power demand)

Data per ton of pig iron Inclusive CO2 in exported BF gas 392 kgCO2

Figure 5. Simplified scheme of a blast furnace with gas recirculation and carbon capture based on Figure 5. Simpliﬁed scheme of a blast furnace with gas recirculation and carbon capture based on average data from Santos 2009 and UNIDO 2010 [21,44]. average data from Santos 2009 and UNIDO 2010 [21,44]. 5.3. A Higher Share of Steelmaking in EAF

Energies 2017, 10, 451 10 of 21

5.3. A Higher Share of Steelmaking in EAF

As was already shown in Section 4.2, steel manufacturing in an EAF is less energy and CO2-intensive than in a blast furnace, because iron ore reduction is not necessary due to the use of scrap as feedstock. In additional, thermal and electrical energy demand can be easily substituted by renewable energies without changes in technology. Under the assumption that German steel production remains constant, it would be possible to reduce the energy demand by 12.61 GJ/tS and the CO2 emissions by 507 kg/tS

(relatedEnergies to the 2017 CO, 102 ,emissions 451 of the blast furnace inclusive CO2 content in the BF gas), which10 of 21 is more produced in an EAF. However, the available quantity of scrap is limited. In the study “climate protectionrenewable scenario energies 2050”, without which changes was conducted in technolo ongy. behalf Under of the assumption German Federal that German Government steel [22], production remains constant, it would be possible to reduce the energy demand by 12.61 GJ/tS and the potential for additional steel production in EAF is limited to 6.1 Mt/a. Furthermore, with respect the CO2 emissions by 507 kg/tS (related to the CO2 emissions of the blast furnace inclusive CO2 content to the energyin the BF and gas), CO which2-reduction is more produced potential in mentionedan EAF. However, above, the there available is a quantity broader of reduction scrap is limited. in both due to the lackIn the of cokestudy and“climate sinter protection as feedstocks. scenario These 2050”, effects which arewas alsoconducted analyzed on behalf in Section of the6 .German Federal Government [22], the potential for additional steel production in EAF is limited to 6.1 Mt/a. 5.4. DirectFurthermore, Reduction with of Iron respect Ore Usingto the energy Hydrogen and (CircoredCO2-reduction Process) potential mentioned above, there is a broader reduction in both due to the lack of coke and sinter as feedstocks. These effects are also The Circored process [23,45] produces direct reduced iron briquettes from iron ore fines and uses analyzed in Section 6. pure hydrogen as a reduction agent. The first commercial-scale plant has operated in Trinidad since 1999 and5.4. has Direct a capacity Reduction of Iron 65 t/a.Ore Using During Hydrogen the process,(Circored Process) iron ore fines are dried and heated through ◦ the combustionThe Circored of natural process gas at[23,45] temperatures produces direct of up re toduced 850–900 iron briquettesC. Finally, from it isiron reduced ore fines by and hydrogen produceduses via pure natural hydrogen gas as reforming. a reduction Usingagent. The hydrogen first commercial-scale as a reducing plant agent has operated leads to in the Trinidad formation of water (seesince Equation 1999 and has (3)) a rather capacity than of 65 CO t/a.2 Duringas a byproduct the process, (seeiron ore Equation fines are (2)). dried and heated through the combustion of natural gas at temperatures of up to 850–900 °C. Finally, it is reduced by hydrogen produced via natural gas reforming. Using hydrogen as a reducing agent leads to the formation of Fe2O3 + 3H2 → 2Fe + 3H2O (3) water (see Equation (3)) rather than CO2 as a byproduct (see Equation (2)).

The product of the Circored processFe isO not +3H pig iron,→2Fe+3H but a solidO iron sponge in the form of(3) briquettes or fines withThe a metallizationproduct of the ofCircored approximately process is not 95%, pig which iron, but can a besolid added iron sponge to the chargein the form of an of EAF to producebriquettes steel. The or fines reason with for a metallization the reduction of approxim of the ironately ore 95%, fines which by can hydrogen be added isto thethe productscharge of of the Circoredan process EAF to produce contain steel. nocarbon. The reason Therefore, for the reduction an injection of the iron of coal ore fines into by the hydrogen iron bath is the of products the EAF is also necessaryof the for Circored metallurgical process contain reasons, no particularlycarbon. Therefore, when an theinjection charge of coal of theinto EAF the iron has bath a share of the higherEAF than 40% of directis also necessary reduction for iron metallurgical [45]. Figure reasons,6 shows particularly a simplified when the scheme charge of of the the EAF Circored has a share process higher and the than 40% of direct reduction iron [45]. Figure 6 shows a simplified scheme of the Circored process subsequentand the treatment subsequent of iron treatment sponge of iniron EAF. sponge The in data EAF. on The the data Circored on the processCircored areprocess from are Elmquist from 2002 and NubertElmquist 2006 2002 [23, 45and], while,Nubert for 2006 the [23,45], EAF part, while, the for same the valuesEAF part, as forthe thesame conventional values as for process the were used. Anconventional additional process amount were of used. coal (0.574An additional GJ/tLS )amount is also of assumed coal (0.574 and GJ/t isLS) needed is also assumed for injection and is into the iron bathneeded to achieve for injection a carbon into the content iron bath of 2%to achieve and 100% a carbon charge content of sponge of 2% and iron 100% in charge the EAF. of sponge iron in the EAF.

Circored process [23,45] Electric arc furnace (EAF) Energy demand per 1.03 ton of hot briquetted iron (HBI) Energy demand per ton of liquid steel Electrical power 0.46 GJ Electrical power 2.07 GJ Natural gas for heat provision 5.62 GJ Natural gas 0.78 GJ Natural gas for H2 provision 8.31 GJ (58.17 kgH2)a N2 8 kg (4.6 MJel) a - - O2 50 kg (37.3 MJel) a - - Coal 1.024 GJ b Total energy demand 14.39 GJ Total energy demand 3.91 GJ Total energy demand of the Circored process + EAF 18.3 GJ/tLS Total CO2 emissions of the Circored process + EAF (including N2 and 1.206 kgCO2/tLS O2 provision inclusive of process-related emissions (83.9 kg/t))

Figure 6. Simplified scheme of the Circored process connected with an electrical arc furnace. a Figure 6.a ForSimpliﬁed more informatio schemen, see of Table the Circored1. b Additional process coal to connected achieve 2% withcarbon an content electrical in steel arc and furnace. 100% For b more information,charge of sponge see Tableiron in1. the AdditionalEAF. coal to achieve 2% carbon content in steel and 100% charge of sponge iron in the EAF. The energy demand of the Circored process, together with the following EAF process, is 18.3 GJ/tLS and the corresponding CO2 emissions are 1.206 kg/tLS. Both the total energy demand and CO2 emissions are higher than for pig iron manufacturing in the conventional blast furnace (15.95 GJ/tpig iron,

Energies 2017, 10, 451 11 of 21

The energy demand of the Circored process, together with the following EAF process, is 18.3 GJ/tLS and the corresponding CO2 emissions are 1.206 kg/tLS. Both the total energy demand and CO2 emissions are higher than for pig iron manufacturing in the conventional blast furnace (15.95 GJ/tpig iron, 1099 kgCO2/tpig iron) inclusive CO2 in exported BF gas, (see Figure3). However, the Circored process has the advantage that no energy-intensive upstream processes such as a coke oven are necessary and no CO2-intensive gases like BF gas are exported. The effects on energy demand and CO2 emissions of the whole integrated steelworks with the use of fossil against renewable energies is also discussed in Section6.

5.4.1. Direct Reduction of Iron Ore with Hydrogen from Electrolysis In the Circored process, the requisite hydrogen is produced from natural gas by an external steam reformer (Section 5.4). It is also possible that the hydrogen is produced by water electrolysis. However in the case that the electrical energy demand of 12.5 GJ/tLS (Table4) is provided by the German electricity mix and only the heat is provided by natural gas, the CO2 emissions total 2407 kg/tLS, which are two-times higher than in the case with hydrogen production via the steam reforming of natural gas. Furthermore, the energy demand is higher due to the lower efﬁciency of the electrolyzer (η = 70%) compared to a steam reformer (η = 84) (Table1). To achieve a major reduction in CO2 emissions, it is necessary that the electrical power is fully supplied by renewable sources. In this case, the CO2 emissions are only 409 kg/tLS and thus much lower than for the process via hydrogen from steam reforming. A further reduction in CO2 could be achieved with the substitution of natural gas by synthetic methane for heat supply (Section 6.4).

Table 4. Energy demand and CO2 emissions of the Circored process connected to an EAF for the hydrogen production via water electrolysis.

Circored Process [23,45] Energy demand per 1.03 tons of hot briquetted iron (HBI) Electrical power for plant operation 0.46 GJ [23,45] a Electrical power for hydrogen production 9.97 GJ (58.17 kgH2) Natural gas for heat provision 5.62 GJ [23,45] Overall energy demand 16.05 GJ Total energy demand inclusive of further processing in EAF 19.96 GJ

CO2 emissions per ton of liquid steel (Circored process + EAF) CO emissions using electrical power from the German electricity mix 2 2407 kg and natural gas for the heat supply CO emissions using renewable electrical power and natural gas for the 2 409 kg heat supply CO emissions using renewable electrical power and synthetic methane 2 94 kg for the heat supply Note: a Efﬁciency of the electrolyzer = 70%.

6. Evaluation of Alternative Processes under Consideration for the Integrated Steelworks In the first part of this section, a balancing area of the most important processes in an average conventional integrated steelworks is defined. An example of the procedure and basic conditions for the evaluation of the alternative processes (see Section5) is then defined in the context of the integrated steelworks outlined. In the second part, the effects on energy demand and CO2 emissions, first by the use of conventional fossil fuels and the German electricity mix, and then with the integration of renewable energy sources, are investigated. Energies 2017, 10, 451 12 of 21

6.1. Definition of the Reference Case The reference case of the conventional integrated steelworks, which is shown in Figure7, was defined by the authors with the help of data from Sun 2012, UBA 2014 and Hensmann 2010 [25,35,46] and Section 4.1. The parts considered are the coke oven, sinter plant, blast furnace, a power plant for house requirements and export, as well as heat generation for export. The oxygen furnace is not considered a reason for the relatively low energy demand compared to the other processes, as well as for simplification of the balance area. Further processes in the integrated steelworks are considered with the export of heat and electricity over the balance area beyond. In the defined integrated steelworks (Figure7), the incoming energy flows comprise coal and natural gas for the coke oven, sinter plant and Energies 2017, 10, 451 12 of 21 blast furnace. Becausewith the export coke demandof heat and in electricity Germany over is notthe completelybalance area producedbeyond. In the by defined own coking integrated plants, coke importedsteelworks as an energy (Figure input 7), the is incoming also part energy of the flows balance comprise area. coal The and energynatural gas flows for the inside coke theoven, integrated sinter plant and blast furnace. steelworks are shown in Figure7. For example, the coke oven uses BF gas as an energy input, but Because the coke demand in Germany is not completely produced by own coking plants, coke exports cokeimported oven asgas an energy (COG) input to theis also hot part stoves of the of balance the blast area. furnace.The energy The flows blast inside furnace the integrated and coke oven internallysteelworks produce are more shown gas in than Figure is 7. needed. For example, the coke oven uses BF gas as an energy input, but Theexports surplus coke gas oven is usedgas (COG) to generate to the hot powerstoves of and the blast heat furnace. for export The blast to other furnace parts and coke of the oven integrated steelworks,internally for example produce more rolling gas mills,than is orneeded. to the public power or heating grid. As shown in Figure7, The surplus gas is used to generate power and heat for export to other parts of the integrated 0.5 GJ electricalsteelworks, power for example and 3.9 rolling GJ heat mills, per or tonto the of public pig iron power are or exported. heating grid.The AsCO shown2 emissions in Figure considered7, are also shown0.5 GJ electrical in Figure power7. Forand 3.9 example, GJ heat per during ton of thepig iron production are exported. of 10The GJ CO coke,2 emissions the coke considered oven emitted 165 kgCO2are/t pigalso iron shown. All in emissions Figure 7. For that example, are inside during of the production balance are of 10 attributed GJ coke, the to coke pig ironoven production.emitted The 165 kgCO2/tpig iron. All emissions that are inside of the balance are attributed to pig iron production. CO2 emissions of the exported power and heat are divided into two parts. All CO2 emissions that exceed The CO2 emissions of the exported power and heat are divided into two parts. All CO2 emissions that the German power mix or heat provision by natural gas are included in the pig iron production, because exceed the German power mix or heat provision by natural gas are included in the pig iron the high COproduction,2 emission because factor the of high the CO BF2 gasemission (Table factor1) leads of the to BF heat gas and(Table power 1) leads with to heat a very and power high CO with2 footprint. Witha respectvery high to CO the2 footprint. balance area considered, the production of one ton of pig iron has a total energy demand of 19.18With GJ;respect however, to the balance 4.4 GJ area are considered, exported inthe the production form of of electrical one ton of powerpig iron and has heat.a total The CO2 energy demand of 19.18 GJ; however, 4.4 GJ are exported in the form of electrical power and heat. emissions that relate to the balance area are 1732 kgCO2/tpig iron and the remaining 299 kg CO2/tpig iron The CO2 emissions that relate to the balance area are 1732 kgCO2/tpig iron and the remaining 299 kg CO2/tpig iron relates torelates the exported to the exported energy energy that that is not is not attributed attributed to the the balance balance area. area.

Figure 7. Defined balancing area of the integrated steelworks using data from Sun 2012, UBA 2014 Figure 7.andDefined Hensmann balancing 2010 [25,35,46] area of and the Section integrated 4.1. All steelworks data relating using to the production data from of Sun a ton 2012, of pig UBA iron. 2014 and Hensmann 2010 [25,35,46] and Section 4.1. All data relating to the production of a ton of pig iron. 6.2. Example of the Procedure and Basic Conditions 6.2. Example ofIn thethis Proceduresection, the andinfluences Basic of Conditions the alternative processes on the integrated steelworks are shown in Figure 8 for the case that the blast furnace is equipped with a BF-GR (Section 5.1). Through the BF gas In thisrecirculation, section, the coke influences demand drops of theby 45% alternative compared processesto the conventional on the blast integrated furnace. steelworksAssuming that are shown in Figure8the for coke the import case is that first the terminated blast furnace (in order is to equipped use the capacity with of a own BF-GR plants) (Section leads to 5.1 a reduction). Through of the BF gas recirculation,coke oven cokeproduction demand of 31%. drops The byreduction 45% compared of coke production to the conventionalleads in turn to blastless production furnace. of Assuming that the cokeCOG, import which is is used first for terminated heat and power (in orderproduction. to use Under the capacitythe condition of ownthat the plants) export leads of electrical to a reduction power and heat out of the balance area is constant, the lack of COG must be replaced by a substitute of coke ovenlike natural production gas. of 31%. The reduction of coke production leads in turn to less production of COG, which is used for heat and power production. Under the condition that the export of electrical power and heat out of the balance area is constant, the lack of COG must be replaced by a substitute like natural gas.

Energies 2017, 10, 451 13 of 21

Figure 8. Considered balancing area of the integrated steelworks with a blast furnace with BF gas Figure 8. Considered balancing area of the integrated steelworks with a blast furnace with BF gas recirculation using data from Sun 2012, UBA 2014 and Hensmann 2010 [25,35,46] and Section 5.1. All recirculationdata usingrelate to data the production from Sun of a 2012, ton pig UBA iron. 2014 and Hensmann 2010 [25,35,46] and Section 5.1. All data relate to the production of a ton pig iron. Furthermore, the blast furnace with BF-GR does not have a gas export. As a result, this missing gas has also been replaced by a substitute gas (Figure 8). The electrical power that is generated in the Furthermore,integrated power the blast plant furnace and used withwithin BF-GR the balance does area not is also have kept a constant. gas export. The saving As a of result, electrical this missing gas has alsopower been at the replaced coke oven by is a used substitute to cover the gas higher (Figure electrical8). The power electrical demand power of the blast that furnace is generated with in the integratedBF power gas recirculation. plant and The used part within that cannot the balance be covered area by is this also power kept is constant. provided Theby the saving German of electrical electricity mix (0.45 GJel/tpig iron). power at the cokeThe changes oven is in used the energy to cover demand the higherof the blast electrical furnace powerand coke demand oven, as well of the as the blast additional furnace with BF gas recirculation.energy demand The part for the that provision cannot of bethecovered substitute byfuels this to assure power a constant is provided export byof electrical the German power electricity mix (0.45 GJ(0.5el/ GJtelpig/tpig iron iron)). and heat (3.9 GJth/tpig iron), yields a total energy demand of 19.01 GJ/tpig iron. This figure The changesis approximately in the energyas high as demand the energy of demand the blast of the furnace conventional and coke integrated oven, steelworks, as well as but the the additional energy input shifts from coal to natural gas and a higher share of electrical power. This opens up the energy demandoptions to for meeting the provision the energy demand of the substitutewith either conventional fuels to assure energy acarriers constant or completely export by of electrical power (0.5renewables. GJel/tpig Even iron) if and natural heat gas (3.9 and GJtheth German/tpig iron electricity), yields mix a are total used, energy the CO demand2 emissions of of 19.01the GJ/tpig iron. Thisbalance ﬁgure area is are approximately 1336 kgCO2/tpig iron as and high hence as 23% the lower energy than in demand the reference of the case conventional of the integrated integrated steelworks,steelworks. but the energyTherefore, input as already shifts me fromntioned coal above, to natural the effect gas of and the aCO higher2 reduction share potential of electrical by power. alternative technologies is only apparent by considering the integrated steelworks in its entirety, This opensespecially up the because options the to isolated meeting analysis the energyin Section demand 5 could create with the either impression conventional that the energy energy carriers or completelydemand by and renewables. CO2 emissions Even of the if naturalblast furnace gas with and BF the gas German recirculation electricity are higher mix than are for used, the the CO2 emissionsconventional of the balance process. area are 1336 kgCO2/tpig iron and hence 23% lower than in the reference case of the integrated steelworks. Therefore, as already mentioned above, the effect of the CO reduction 6.3. Alternative Processes with Conventional Energy Provision 2 potential by alternative technologies is only apparent by considering the integrated steelworks in According to the same method as described in Section 6.2, the other alternative processes its entirety, especially because the isolated analysis in Section5 could create the impression that the (Section 5) were analyzed with consideration to the integrated steelworks. Figure 9 shows on the left energy demandside the andtotal COenergy2 emissions demand and of on the the blastright side, furnace the CO with2 emissions BF gas for recirculation the production areof 27.048 higher t than for the conventionalof pig iron process. by means of the conventional blast furnace and alternative processes. The production volume correlates with the amount produced in German blast furnaces in 2012 [35]. Pig iron 6.3. Alternativeproduction Processes was chosen with Conventionalas a basis for the Energy comparison Provision because the idea of this study is to replace the blast furnace as the most energy-intensive part of steelmaking, even if processes such as the Circored Accordingprocess toor EAF the directly same produce method steel. as Figure described 9 also shows in Section energy demand6.2, the in the other year alternative2008 and CO2 processes (Section5)emissions were analyzed from the withyear 1990. consideration These values to were the extrapolated integrated with steelworks. the help of Figuredata from9 shows 2012 and on the left the corresponding years [21,25]. Total energy demand has decreased by 8% since 2008 and CO2 side the total energy demand and on the right side, the CO emissions for the production of 27.048 t of emissions by 30% since 1990. The values of 2008 and 1990 2were added to address one target of the pig iron bystudy, means namely of the to indicate conventional whether blastit is possible furnace to achieve and alternative a reduction in processes. electrical power The demand production by volume correlates25% with and the primary amount energy produced demand inby 50% German against blast 2008 furnacesby 2050 and in simultaneously 2012 [35]. Pig GHG iron emissions production was chosen asby a basis80–95% for against the comparison 1990 by 2050. becauseTherefore, thethe re idealative of change this study of fuelis demand to replace to the the alternative blast furnace as processes is also shown in Figure 9. the most energy-intensive part of steelmaking, even if processes such as the Circored process or EAF directly produce steel. Figure9 also shows energy demand in the year 2008 and CO 2 emissions from the year 1990. These values were extrapolated with the help of data from 2012 and the corresponding years [21,25]. Total energy demand has decreased by 8% since 2008 and CO2 emissions by 30% since 1990. The values of 2008 and 1990 were added to address one target of the study, namely to indicate whether it is possible to achieve a reduction in electrical power demand by 25% and primary energy demand by 50% against 2008 by 2050 and simultaneously GHG emissions by 80–95% against 1990 by 2050. Therefore, the relative change of fuel demand to the alternative processes is also shown in Figure9. Energies 2017, 10, 451 14 of 21

Energies 2017, 10, 451 14 of 21 In Figure9, the bars of the energy demand of the alternative processes are divided into three different kindsIn Figure of energy9, the bars input. of the Firstly, energy conventional demand of the fuels alternative that are processes needed forare thedivided process; into three secondly, additionaldifferent electrical kinds of power, energy whichinput. Firstly, is not coveredconvention byal the fuels integrated that are needed power for plants; the process; and thirdly, secondly, the fuel that isadditional needed electrical to replace power, missing which COG is not and covered BF gas by the to keepintegrated the powerpower plants; and heat and productionthirdly, the fuel output that is needed to replace missing COG and BF gas to keep the power and heat production output of of the integrated steelworks constant (see Sections 6.1 and 6.2). In a similar manner, CO2 emissions the integrated steelworks constant (see Sections 6.1 and 6.2). In a similar manner, CO2 emissions (Figure9, right side) are divided into three different types, namely CO 2 emissions from fuel combustion, (Figure 9, right side) are divided into three different types, namely CO2 emissions from fuel process-relatedcombustion, emissions process-related and indirect emissions emissions and indirect through emissions the use through of electrical the use power of electrical fromthe power German powerfrom gird. the German power gird.

Change of 80 -8% -10% +5% -20% +5% -35% fuel demand 66.9 Mt -1% 800 +22% 60 +15% +8% -30% 600 566 PJ -8% -41% -8% -46% -18% 40 -46% 400 -68%

emissions, Mt/a 20 2 200 CO 0

Energy demand, PJ/a 1990 2012 1 2345 0 Cases 2008 2012 1 2 3 4 5 Cases Case 2: 23.45 Mt/a CO2 are separated Fuel Substitute fuel (NG) Electrical power Process related Cases Defined integrated steelworks (see Section 6.1) with: 2008: Conventional blast furnace in 2008 only for comparison of the energy demand 1990: Conventional blast furnace in 1990 only for comparison of the CO2 emissions 2012: Conventional blast furnace in 2012 1: Blast furnace with blast furnace gas recirculation (see Section 5.1) 2: Blast furnace with blast furnace gas recirculation and carbon capture (see Section 5.2) 3: Reduced conventional blast furnace production and 6.1 Mt/a more steel production by EAF (see Section 5.3) 4: Circored process with EAF using hydrogen produced by natural gas (see Section 5.4) 5: Circored process wit EAF using hydrogen produced by electrolysis (see Section 5.4.1)

Figure 9. Energy demand and CO2 emissions depending on the considered cases. Figure 9. Energy demand and CO2 emissions depending on the considered cases. Case 1: Blast Furnace with Gas Recirculation Case 1: Blast Furnace with Gas Recirculation The energy demand of the conventional integrated steelworks in 2012 (corresponding to the Thedefinition energy in Section demand 6.1 ofand the defined conventional as case 2012), integrated as well as steelworkssteelworks with in 2012a BF-GR (corresponding (see Section 5.1), to the deﬁnitionis 8% inlower Section than 6.1in 2008. and However, deﬁned as in case the case 2012), with as BF well gas as recirculation, steelworks the with energy a BF-GR demand (see consists Section 5.1), is 8%of lower not only than fuels in 2008. such However,as coke, but in also the electrical case with power BF gas and recirculation, a relatively hi thegh energyamount demandof substitute consists of notfuel only to ensure fuels such power as and coke, heat but generation also electrical for own power use and and export. a relatively Thus, the high missing amount BF gas of is substitute replaced fuel by a substitute fuel (natural gas) with a lower emission factor, achieving a CO2 reduction of 46% on to ensure power and heat generation for own use and export. Thus, the missing BF gas is replaced by 1990. However, the saving in fuel is relatively low, with 10% against 2008 and additional power from a substitutethe grid fuel needed. (natural gas) with a lower emission factor, achieving a CO2 reduction of 46% on 1990. However, the saving in fuel is relatively low, with 10% against 2008 and additional power from the grid needed.Case 2: Blast Furnace with Blast Furnace Gas Recirculation and Carbon Capture In Case 2 (Figure 9), when the blast furnace is equipped with a BF gas recirculation and CO2 Caseseparation 2: Blast Furnace (see Section with 5.2), Blast total Furnace energy Gas demand Recirculation is 8% higher and than Carbon in 2008, Capture but as a reason for the separation of 23.45 MtCO2/a and simultaneous reduction of coke, the CO2 emissions are 68% lower In Case 2 (Figure9), when the blast furnace is equipped with a BF gas recirculation and CO than in 1990. Moreover, the remaining BF gas, which is used for heat and power production, has a 2 separation (see Section 5.2), total energy demand is 8% higher than in 2008, but as a reason for the lower emission factor due to the lower CO2 concentration as a reason for the CO2 separation (see separationFigure of5). 23.45 As in Mt CaseCO2 /a1, the and substitution simultaneous of GF reduction gas by natural of coke, gas the also CO leads2 emissions to a reduction are 68% in lower than inCO 1990.2 emissions. Moreover, the remaining BF gas, which is used for heat and power production, has a lower emission factor due to the lower CO 2 concentration as a reason for the CO2 separation (see Figure5). As in Case 1, the substitution of GF gas by natural gas also leads to a reduction in CO2 emissions.

Energies 2017, 10, 451 15 of 21

Case 3: Reduced Conventional Blast Furnace Production and 6.1 Mt/a More Steel Production by EAF The production of 6.1 million tons more steel per year in an EAF instead of a blast furnace (see Section 5.3) leads to a total energy reduction of 18% and a reduction in fuel demand of 20% against 2008 (Figure9). The slight increase in electrical power demand is caused by the EAF itself, which needs four-times more electrical power for the production of one ton of steel/pig iron than the integrated steelworks that use a conventional blast furnace. Nevertheless, the CO2 emissions are 41% lower than in 1990. In this case, it is also assumed that the power plant produces a constant amount of electricity for export and own use, as well as a constant amount of heat. It is for this reason that substitute fuel is still needed.

Case 4: Circored Process with EAF Using Hydrogen Produced by Natural Gas In Case 4 (Figure9), the iron ore is reduced by hydrogen via the Circored process, followed by further processing in an EAF (see Section 5.4). The necessary hydrogen is produced by the steam reforming of natural gas. Although the sinter plant, coke oven and conventional blast furnace are not necessary, the total energy demand increases by 15% and fuel demand, inclusive of substitute fuel, by 5%. The higher energy demand is primarily due to the hydrogen supply. Nevertheless, it is possible to achieve a CO2 reduction of 46% against 1990, because the main part of the energy is provided by natural gas instead of coal or BF gas. Nevertheless, the process is not free of process-related CO2 emissions, because these kinds of emissions occur during the steam reforming of natural gas for hydrogen production.

Case 5: Circored Process Wit EAF Using Hydrogen Produced by Electrolysis From a technical point of view, Case 5 is very similar to Case 4 (see above), but as shown in Figure9, the kind of energy used and the resulting CO 2 emission levels are very different. In Case 5, the energy demand is dominated by electrical power for hydrogen production via electrolysis (see Section 5.4.1). In spite of a reduction of fuel demand by 35% against 2008, the total energy demand is higher because of the high demand for electrical power. As a result of the relatively high CO2 footprint of the German electricity mix, CO2 emissions are only 1% lower than in the year 1990, but higher than in 2012.

6.4. Alternative Processes with the Integration of Renewable Power In this section, as already suggested above, the feasibility and inﬂuence of insertion of renewable electrical power for the same cases as in Section 6.3 are investigated. At the conventional steelworks, coke is not only used as an energy carrier, but is also necessary for the correct operation of the blast furnace, because coke is also a reducing agent and responsible for the gas permeability and stability of the layers inside the furnace and cannot be easily replaced. The alternative processes are less dependent on coke, but more dependent on electrical power and a substitute fuel for COG and BG gas to ensure electricity and heat export beyond the balance limit (see Figures7 and9). Although in Section 6.3 and Figure9 natural gas is used to ensure the production of electricity, at this point synthetic natural gas is not used to substitute this part of the natural gas. The reason for this is that from an energetic point of view, it makes no sense to convert electrical power into synthetic methane and directly back into electrical power unless the synthetic methane is used as a large energy storage medium for excess power from ﬂuctuating renewable sources (see Section1). Since the focus of the present study is on the integrated steelworks and not on a possible energy supply system for Germany, it is assumed that the missing output of the power plant, due to the lack of BF and COG gas, is directly replaced by renewable electrical power without the detour via synthetic methane or the methanation process. However, the provision of heat is still based on gas, which is substituted by synthetic methane. The impact on energy demand and CO2 emissions through the use of renewable electricity, either directly or via synthetic methane or hydrogen, is shown in Figure 10. Energies 2017, 10, 451 16 of 21 Energies 2017, 10, 451 16 of 21

Change of -9% -36% -27% -28% -95% -95% 80 fuel demand 1200 66.9 Mt +79% 60 1000 +56% -31% 800 40 +19% -47% 566 PJ -2% 600 -7.5% -61% -20% emissions, Mt/a emissions, 20 400 2 -82%

CO -95% -95% 200 0

Energy demand, PJ/a 1990201212345 0 Cases 2008 2012 1 2 3 4 5 Cases Case 2: 23.45 Mt/a CO2 are separated

Fuel Electrical power for H2 and CH4 provision Electrical power Process related Cases Defined integrated steelworks (see Section 6.1) with: 2008: Conventional blast furnace in 2008 for the comparison of energy demand 1990: Conventional blast furnace in 1990 for the comparison of CO2 emissions 2012: Conventional blast furnace in 2012 1: Blast furnace with gas recirculation (see Section 5.1) 2: Blast furnace with gas recirculation and carbon capture (see Section 5.2) 3: Reduced conventional blast furnace production and 6.1 Mt/a more steel production by EAF (see Section 5.3) 4: Circored process with EAF using hydrogen produced by natural gas (see Section 5.4) 5: Circored process with EAF using hydrogen produced by electrolysis (see Section 5.4.1)

Figure 10. Energy demand and CO2 emissions of the different cases using as much renewable electrical Figure 10. Energy demand and CO emissions of the different cases using as much renewable electrical power as possible directly and in2directly for the provision of synthetic methane and hydrogen. power as possible directly and indirectly for the provision of synthetic methane and hydrogen. Figure 10 also shows for this case the potential to integrate renewable power. It is only possible Figureto substitute 10 also a relatively shows for small this amount case the of potential natural gas to integrate(0.214 GJ/t renewablepig iron) by synthetic power. methane It is only used possible in to the coke oven and sinter plant. All other energy carriers are not replaceable by renewables, because substitute a relatively small amount of natural gas (0.214 GJ/tpig iron) by synthetic methane used in they are a conversion product of the coal used and must be burned for heat and electrical power the coke oven and sinter plant. All other energy carriers are not replaceable by renewables, because generation. Given the electricity demand for the production of synthetic methane (see also Table 1) they are a conversion product of the coal used and must be burned for heat and electrical power and a production volume of 27 Mt pig iron per year, 5.8 PJ of natural gas could be replaced with 2.86 TWh generation.of renewable Given electricity the electricity in the demandconventional for theprocess. production This would of synthetic lead to an methane increase (seeof 0.5% also of Tableenergy1) and a productiondemand and volume a CO of2 reduction 27 Mt pig of irononly perone year,percent 5.8 (compare PJ of natural Figures gas 9 and could 10). be replaced with 2.86 TWh of renewableIn Cases electricity 1–5, the in integration the conventional of renewable process. energy This technologies would lead hadto a signi an increaseficantly higher of 0.5% impact of energy demandon CO and2 emissions. a CO2 reduction In Cases 4 of and only 5, a one CO percent2 reduction (compare of 95% against Figures 19909 and is achievable. 10). However, the Intotal Cases energy 1–5, demand the integration increased ofby renewable79% and 56%, energy respecti technologiesvely, so higher had than a significantly in the use of higherconventional impact on energy sources (see Figure 9), because the provision of synthetic methane has an electrical energy CO2 emissions. In Cases 4 and 5, a CO2 reduction of 95% against 1990 is achievable. However, the total energydemand demand of 1.785 increased MJel/MJ byCH4 79%. Furthermore, and 56%, at respectively, this point Case so higher4 does thannot make in the sense, use ofbecause conventional the necessary hydrogen is first produced via electrolysis and then converted into methane, and finally energy sources (see Figure9), because the provision of synthetic methane has an electrical energy reconverted into hydrogen. This leads to a higher energy demand than in Case 5, where hydrogen is demand of 1.785 MJ /MJ . Furthermore, at this point Case 4 does not make sense, because the directly used. In bothel cases,CH4 the energy demand is almost completely covered by renewable power, necessary hydrogen is first produced via electrolysis and then converted into methane, and finally and so the higher energy demand of Case 4 has no influence on CO2 emissions, resulting in a reconvertedreduction into of 95% hydrogen. against 1990 This in leads both tocases. a higher energy demand than in Case 5, where hydrogen is directly used.Only in In Case both 2 cases,does the the energy energy demand demand decrease is almost compared completely to the results covered in Section by renewable 6.3, because power, and sothe the direct higher use energyof renewable demand power of Case instead 4 has of noa substitute influence gas on CObypasses2 emissions, the efficiency resulting losses in aof reduction the of 95%power against plant. 1990 in both cases. Only in Case 2 does the energy demand decrease compared to the results in Section 6.3, because 7. Discussion the direct use of renewable power instead of a substitute gas bypasses the efficiency losses of the power plant.Table 5 summarizes the different cases, with and without the integration of renewable power sources (Sections 6.3 and 6.4). Even with the conventional energy supply, a significant reduction of 7. DiscussionCO2 is possible through the use of alternative technologies. The only exception is Case 5, which presents the Circored process that uses hydrogen produced by electrolysis. In this case, only CO2 Tableemissions5 summarizes are 1% less thethan different those of cases,conventional with and integrated without steelworks the integration in 1990, ofbecause renewable the high power sources (Sections 6.3 and 6.4). Even with the conventional energy supply, a significant reduction of CO2 is possible through the use of alternative technologies. The only exception is Case 5, which presents the Circored process that uses hydrogen produced by electrolysis. In this case, only CO2 Energies 2017, 10, 451 17 of 21 emissions are 1% less than those of conventional integrated steelworks in 1990, because the high electricity demand is provided by the German electricity mix. However, this case achieves the highest reduction in fuel demand, because the main share of the energy demand is supplied by electrical power. The greatest CO2 reduction using conventional fuels is achievable by using a blast furnace with blast furnace gas recirculation and carbon capture (Case 2, −68%). However, in this case the gross reduction is lower, because 23.45 MtCO2 per 27 Mtpig iron are separated, which must be further treated to prevent it from entering the atmosphere, such as by means of geological storage, even if such storage is legally limited to 4 Mt/a in Germany [47]. Nevertheless, in countries such as Germany, the separated CO2 can be reused as a feedstock in the chemical industry [10] or for the production of synthetic methane. In all analyzed cases, the CO2 (−80 to −95% vs. 1990) and energy reduction targets (electrical power −25% and primary energy demand −50% vs. 2008) of the German government (see Section1) are not achievable by using conventional energy carriers. In all cases, the electrical power demand increases. Only in Case 2 (a higher share of EAF) is a relatively high reduction of CO2 emissions and a simultaneous reduction in energy demand achievable, because steel production in the integrated steelworks decreases and the additional production in EAFs needs less energy and emitted less CO2. In addition, the technical effort is relatively low compared to the other alternative processes, and so the production of more steel in an EAF can lead to a significant reduction in CO2 and energy saving in the steel industry in the short term. However, the availability of scrap is limited, so that other technologies are also necessary to achieve further CO2 reductions.

Table 5. Changes in thermal and electrical energy demand of the conventional steelworks in 2012 and

the steelworks with alternative processes against 2008, as well as the changes in terms of CO2 emissions towards 1990, with and without the integration of renewable energies.

Results with Conventional Energy Provision Results with Integration of Renewable Energies Electrical Energy Electrical Energy Case Fuel Demand CO Emissions Fuel Demand CO Emissions Demand against 2 Demand against 2 against 2008 against 1990 against 2008 against 1990 2008 2008 2012 (Conventional 0 TWh −8% −30% +3 TWh −9% −34% steelworks in 2012) 1 (Blast furnace with gas +3 TWh −10% −46% +54 TWh −36% −61% recirculation) 2 (BF gas recirculation +6 TWh +5% −68% +72 TWh −27% −82% with CO2 separation) 3 (Reduced conventional blast furnace production +3 TWh −20% −41% +12 TWh −28% −47% and 6.1 Mt/a more steel production by EAF) 4 (Direct reduction of iron +16 TWh +5% −46% +274 TWh −95% −95% ore with H2 produced by steam reforming) 5 (Direct reduction of iron +90 TWh −35% −1% +237 TWh −95% −95% ore with H2 produced by electrolysis)

The application of alternative technologies not only has the potential to reduce CO2 emissions, but also opens a way to using renewable energy sources instead of coal, so that the effect of CO2 reduction can be increased. With the integration of renewable energies, either directly by electrical power or indirectly by synthetic methane or hydrogen as a reduction agent, CO2 emissions signiﬁcantly decrease in all cases (see Table5). Both the Circored processes (Cases 4 and 5) and the integration of a blast furnace with BF gas recirculation and CO2 separation achieve the CO2 reduction targets of the German government. At the same time, the fuel demand decreases by 82–95% against 2008. As already mentioned above, by using renewable power sources, Case 4 does not make sense, because Energies 2017, 10, 451 18 of 21 the necessary hydrogen can be delivered directly by an electrolyzer without additional methanation and reforming steps, which only leads to unnecessary additional energy demand (Figure 10). Nevertheless, the huge reduction in fuel demand leads to a strong additional demand for electrical power for heat (via synthetic methane) and hydrogen provision, which is contrary to the electrical power saving targets of the German government. Apart from this, the required renewable electrical energy demand (237 TWh) is higher than that generated (194 TWh) in Germany in 2015 [48]. This, along with the high present cost of synthetic methane and hydrogen [4], are from today's perspective a factor that makes instant implementation implausible. However, in numerous studies, such as Sternberg 2015, Robinius 2015, ETG-Task-Force 2012, DLR 2012 and Prognos AG 2012, about the future energy system in Germany, it is assumed that both the massive expansion of renewable power generation and the availability of large quantities of excess power will also lead to a reduction in costs [8,49–53]. Through the use of alternative technologies for steelmaking, future energy systems could also be supported because the released power generation capacity of the integrated steelworks could be used as backup power to ensure security of supply in a strong share of ﬂuctuating renewable energies for power generation.

8. Conclusions and Outlook

This study demonstrates that it is possible to reduce CO2 emissions by up to 95% through the integration of renewable electrical power into the currently coal-based steel industry by using alternative technologies. Both the possibility to integrate renewable power and CO2 reduction is mainly achieved by an increase or complete discontinuation of coal or the resulting BF gas, which is usually burned for power and heat production in order to avoid release into the atmosphere. With less or no BF gas production, there is an opportunity to use lower-emission fossil fuels or even renewable energies for heat and electricity provision. The latter would allow the coupling of renewable electricity and the steel industry, which could also be seen as “Power-to-Steel”. However, to achieve the CO2 reduction targets of the German government in the steel industry, a major extension of renewable electrical power generation is necessary for providing the processes with energy. Thereby, a large reduction in CO2 emissions would only be enabled by an increase in electrical power demand and a simultaneous reduction of both is not possible. Nevertheless, the mere substitution of steel production in blast furnaces with the direct reduction via hydrogen could reduce current CO2 emissions in Germany by about 5%. Further questions that must be resolved are, for example, how the integration of renewable energies and hydrogen into the steel-making process can be introduced, such as through a speciﬁc subsidy regime or by considering carbon pricing. Nevertheless, steel is an internationally-traded product and must therefore be cost-competitive, which necessitates concerted international action.

Acknowledgments: This work was supported by the Helmholtz Association under the Joint Initiative “EnergySystem 2050—A Contribution of the Research Field Energy”. Additionally, it was performed in the frame of the TESA (Technology based energy systems analysis) Seed Fund financed by JARA Energy (Jülich Aachen Research Alliance Energy) to promote science and research at German universities and research units. Author Contributions: Alexander Otto and Martin Robinius proposed the research topic and the structure of the paper. Alexander Otto designed the model and analyzed the results. Martin Robinius and Aaron Praktiknjo added the context of sector coupling. Martin Robinius took care of the reviewer comments. Thomas Grube and Sebastian Schiebahn took part in validating the idea. Detlef Stolten took part in validating the idea and revising the paper. Conflicts of Interest: The authors declare no conflict of interest. Energies 2017, 10, 451 19 of 21

Abbreviations

Abbreviations and symbols BF-CC Blast furnace with carbon capture BF gas Blast furnace gas BF-GR Blast furnace gas recirculation BOF gas Basic Oxygen Furnace gas CaCO3 Limestone CaMg(CO3)2 Dolomite CH4 Methane CO Carbon monoxide CO2 carbon dioxide COG Coke oven gas DR Direct reduction EAF Electrical arc furnace Fe2O3 Hematite Fe3O4 Magnetite H2 Hydrogen η Efﬁciency HBI Hot briquetted iron H-DR Direct reduced iron with hydrogen as reduction agent IEA International Energy Agency N2 Nitrogen NG Natural gas OHF Open hearth furnaces SR Smelting reduction ULCOS Ultra-Low Carbon Dioxide Steelmaking VPSA Vacuum pressure swing adsorption Subscripts el Electrical LS Liquid steel S Steel th Thermal

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