- Email: [email protected]
CO2 removal in competition with other options for reducing CO2 emissions
Energy Convers. Mgmt Vol. 33, No. 5-g. pp. 737-745. 1992
0196-8904/92 $5.00+0.00 Copyright© 1992PergamonPressLtd
Primedin GreatBritain.All rights reserved
CO2 REMOVAL IN COMPETITION WITH OTHER OPTIONS FOR REDUCING CO2 EMISSIONS
P.A. OKKEN, P. LAKO, D. GERBERS, T. KRAM and J.R. YBEMA
ESC/Energy Studies, Netherlands Energy Research Foundation ECN, PO Box 1, 1755 ZG, Petten, the Netherlands
ABSTRACT CO2-reduction scenarios are calculated with the MARKAL-model in a bottom-up analysis of the evolution of the Netherlands energy system for the period 2000-2040. In these calculations moderate fuel price increases, stringent environmental constraints, steady improvements in energy efficiency and major energy alternatives are taking into account. Preliminary results indicate a strong potential for CO2 removal from fossil fuels in combination with electricity and hydrogen production, at severe CO2 emission constraints.
KEYWORDS Coal gasification, carbon dioxide, cost, forecasting, hydrogen, M codes, recovery, removal, storage.
INTRODUCTION The unit ESC-Energy Studies of ECN performs energy and environmental studies to support the Netherlands government and international agencies. Long term CO 2 reduction targets have not yet been agreed upon by governments. Critical issues are the cost sharing amongst nations, and the potential for energy technology development. In order to detect cost-effective international CO 2 reduction strategies a complete array of new energy technologies is incorporated in EMS (Energy and Materials Scenarios to reduce emissions of CO2 and other greenhouse gases). EMS is implemented at ESC with cooperation from KEMA Amhem and the universities of Groningen and Utrecht, within the framework of the IEA Energy Technology Systems Analysis Programme (ETSAP), sponsored by the Ministry of Economic Affairs energy directorate and the Netherlands national research programme on global air pollution and climate change.
INTEGRATED ASSESSMENT OF CO 2 EMISSION REDUCING OPTIONS Many energy technology options for reducing CO2 emissions are available. Normally, the contribution of individual options to CO2 reduction is calculated in a simple way starting from a constant reference situation and without considering interactions between different options. However, on longer term, the reference situation will change. Therefore, fuel price paths, future energy demand projections, environmental measures and reference technology efficiency improvements must be taken into account. Moreover, future CO 2 reducing options should be evaluated in relation with other future options to uncover
737
738
OKKEN et al.: CO2 REMOVALIN COMPETITIONWITH OTHEROPTIONS
potential conflicts and synergies. Energy technology systems analysis provides a tool for the design of cost-effective long term CO2 reduction strategies.
Model The model used in EMS, the MARKet ALlocation (MARKAL) model, is a standard linear programming software package which is used to represent energy systems. The model is currently operated in 12 IEA countries including the United States, Japan and the European Community. Using detailed compilations of data characterising available and prospective energy technologies, and incorporating projections and assumptions about the costs and availability of fuels M A R K A L configures an optimal mix of technologies to satisfy the specified useful energy demands. The model includes detailed data for the Netherlands energy system, like fuel prices, costs and energy efficiency indicators for several hundreds of different energy conservation and -supply technologies, emission coefficients and emission abatement techniques. The model is used in a national costs minimizing mode with exogenous national maximum allowable annual emissions of NOx, SO2 and CO 2 ('bubble' concept). The model optimizes the energy system for the period 2000 to 2040 simultaneously in steps of 5 years each. This dynamic simultaneous optimization is referred to as 'perfect foresight', reflecting the activities of policy-makers as they are supposed to 'know the future'. Dynamic modelling is of vital importance for testing structural changes in the energy system under environmental constraints. Gradual efficiency improvements of existing energy technologies are incorporated, and several new energy technologies are projected to be available at fixed points in the future, thus reflecting the promises of ongoing energy and environmental R&D. The model enables testing of such new technologies in a future energy system under various external constraints ('technology assessment'). Few institutional and market barriers are assumed. On the other hand bounds are imposed on the speed of market penetration for new energy technologies to prevent unrealistic solutions, and there-are lower bounds to ensure that older technologies will not be phased out too rapidly. The model optimizes with a 5% discount rate. In an earlier scenario study (Okken et al 1991) with MARKAL for the Netherlands energy system on mid-term up to the year 2020 cost-effective contributions from CO: reducing options were calculated: renewable energy (e.g. wind, solar) nuclear energy savings on conversion (e.g. combined heat and power) savings on end-use (e.g. building insulation) intra-fossil fuel switch (e.g. from coal to gas) - recycling (e.g. waste plastics) CO: removal (e.g. at coal power stations) -
-
In this paper scenario calculations are reported for the Netherlands energy system on longer term, the period 2000 to 2040, with moderate fossil fuel price increases and stringent constraints for NO, and SO2 emissions. To detect cost-effective strategies for drastic CO2 reduction calculations are performed with variable CO 2 constraints.
CO? calculation The Netbeflands CO 2 budget differentiates actual and potential emissions. In the porto-chemical industries a significant amount of fossil fuel carbon is sequestered into solid materials (e.g. plastics). These solid carbonaceous materials represent "potential emissions" only: CO 2 is emitted just in case the material becomes oxidized, e.g. in a municipal waste combustion plant. The production rate of potential emissions in the Netherlands is relatively high, being equivalent to 13% of the national CO 2 emission, whereas the world average is 2%. Most of the plastics is exported. Re-use of plastics, in
OKKEN et al.: CO2 REMOVAL IN COMPETITIONWITH OTHER OPTIONS
739
stead of burning them, reduces CO z emissions, In order to quantify the exact fossil fuel CO z emission rate for carbon cycle studies, and to address waste management policy opportunities for CO a reduction, a methodology for the calculation of "actual emissions" was proposed by Okken and Kram (1990). COz emissions are calculated from the carbon content of fuels and the national energy balance; the so-called "feedstocks" in the balance are subtracted, unless these feedstocks are inevitable oxidized (e.g. natural gas feedstocks in nitrogen fertilizer production); furthermore the inland COz emission due to combustion of carbonaceous materials of fossil fuel origin (e.g. plastics in MSW combustion) are added. COs emissions from international marine bunkers in the Netherlands are equivalent to 22 % of the national emissions. Again this is an exceptional situation (the world average is 1.5%) due to the geographical location. CO2 emissions from international aviation bunkers in the Netherlands are equivalent to 2.8% of the national emissions; this is about the same as the world average (Okken et al 1991). This paper reports on actual national COs emissions and international aviation bunkers. The CO 2 emissions from international aviation bunkers in the Netherlands are expected to increase from 4 in 1990 to 7 MtCO2 in 2000, as a result of planned extensions of passenger air traffic. The actual national CO 2 emission rate is expected to decrease from 160 in 1990 to 154 MtCO z in 2000; in accordance with the official governmental COz emission reduction target of 3 to 5% by the year 2000.
TECHNO-ECONOMIC ASSUMPTIONS All cost figures are in Ecu's of 1990. (1 Ecu --- 1,26 $ = 2,33 Dfl). The scenario's for economic development, useful energy demand, fuel prices and NO, and SO z constraints are taken from Kram et al (1991), adjusted for the most recent population projection and implemented energy and environmental policies regarding the year 2000. The fuel price is projected to increase linearly during the period 2000 to 2040 as follows: coal from 1.9 to 3.2 Ecu/GJ, crude oil from 4.4 to 8.9 Ecu/GJ, gas from 4.0 to 8.2 Ecu/GJ (or 10.2 at 25% higher price). An obvious strategy to reduce CO2 emissions is fuel switching from coal to natural gas (table 1). In order to reflect scarcity in the international gas markets when global CO 2 constraints would become reality, a 25% price increase is assumed for those natural gas requirements exceeding the base case gas demand. Table 1.
Hard coal Oil Natural gas Uranium, renewables
CO: emission coefficients of combustion of fossil fuels, at lower heating value (lhv) in kgCO2/GJ,
94 73 56 0
NO, and SO 2 constraints are imposed as maximum allowable annual emissions, resulting in a 85% reduction in acidificadon-equivalents in 2030, as compared to 1980. This is in accordance with present environmental policy. The model incorporates emission abatement technologies and fuel switch options to reduce NO, and SO2. The four scenarios include high growth (2%/y) export oriented and low growth (1.5%/y) economic developments; with and/or without nuclear energy. This paper discusses the high growth scenario without nuclear energy. The energy demand is primarily met with coal, gas and oil; not surprisingly the resulting base case annual CO2 emission increases from 161 MtCO2 in 2000 to 240 MtCO2 in 2040. In order to detect cost-effective strategies for drastic CO 2 reduction this scenario was recalculated with variable maximum allowable annual CO2 emissions (see figure 1).
740
OKKEN et al.:
CO 2 REMOVAL IN COMPETITION WITH OTHER OPTIONS
EMISSIOH[MTOH CO2/YEAR] 250
BASE
200
....
180
+ _ ++
-40%
100
-50% -60% 50
• .....
1
I
I
1990
2000
2010
I
2020
• ..........................
70%
"'.. .........................
-80%
I
I
2030
2040
[YEAR]
Fig 1.
Netherlands CO2 emission rate 2000-2040; Base case and CO2 constrained calculations.
Technologies for reducing COt emissions In the 2020 study a significant potential for CO2 removal in combination with electrification (electric heatpumps and vehicles) was identified. Other technologies for CO 2 reduction in the 2020 study include biogas, geothermal, solar, wind, nuclear power, natural gas-fh-ed heatpumps and fuel ceils, methanol and ethanol vehicles, energy end-use conservation, etc. (Okken et al 1991). In the 2030 study several new coal conversion options and solid coal waste emissions were added (Kram et al 1991). In the 2040 study reported in this paper the above mentioned options in the model are extended with: CO 2 removal coupled with synfuel production, hydrogen end-use, detailed electricity and energy conservation options in every energy demand category, biomass (bio-ethanol, rape seed, miscanthus, short rotation forestry, methanol from ligno-cellulose) and other prospective energy supply options (e.g. thermo photovolatic residential boilers, solar heating with seasonal storage). Although cost-effective energy conservation options are included in the base case calculation, a stepwise energy end-use conservation potental in different sectors varying from 20% to 50% (in specific industrial sub-sectors resp. for residential space heating) still remains for further reducing CO2 emissions. The renewable energy potential reflects local possibilities within the Netherlands, e.g. 8 GWe wind-turbines (of which 5 off-shore) for electricity generation, 500000 ha land area available for energy crops, an unlimited potential for solar PV electricity generating capacity (1100 h/y, investment costs 0.85 Ecu/pWe). For more details see Okken et al (1992). In this paper CO2 removal options are considered.
CO~ recovery COz removal = CO2 recovery + CO z storage outside the atmosphere. The array of COz-removal options, considered in this study in competition with all other options for CO z reduction, is shown in figure 2. Performance data in the model for future CO2 recovery technologies are summarized in table 2. The data characterization builds upon recent literature and projections of performance improvements within the chemical industries ( e.g. gradual replacement of conventional steam reforming by catalytic partial oxidation processes).
OKKEN et al.: CO2 REMOVALIN COMPETITIONWITH OTHER OPTIONS
gasoline.................--l---~M-~-~st_~-hydrogen . . . . . . . . . . . . . . . . . J
coal . . . . . . . . 1. . . . . . .
~
i~o2
SNG hydrogen
'
methanol
I
~_~_..... ~ - s ~ r
oil residue
car
-~co=
....... ~-H~,ng--~ r---I '. . . . ~ c o : ~ | ii2/.. ---J
gas--
741
[-;~,m,~,
r----~~ J ~ x ~2.- ' -
electricity -N-fertilizer
. "co~
---hydrogen ..,,,.,./,~. ,,,,
Fig. 2.
CO 2 removal options considered in the Netherlands energy system MARKAL model 2000-2040. Abbreviations see text.
Table 2.
CO 2 recovery options, energetic efficiency and recovery rate, target year 2020+
Proces
Input
Eft. (lhv)
Output(s)
Rec. rate
Ref.
F cost Ecu/GJ
IGCC power plant IGMCFC (fuel cell) Gas STAG power plant N-fertilizer plant Adv. gas reformer Partial oxidation Hybrid/hydride car Coal gasification Coal gasification Coal gasification
coal coal nat.gas nat,gas nat,gas oilres. oil/coal coal coal coal
38% 47% 46% nc 80% 75% nc 71% 74% 63%
electricity electricity electricity NH4NO3 H2 H2 transport 53H2 +18CI-I4 63H2 +1 IIFG methanol
88% 97% 88% 98% 98% 98% 90% 83% 78% 49%
H O,L H,L L L L S L L L
6.4 8.2 4.7 1.6 4.1 5.6 5.4 5.8
H (Hendriks, Blok and Turkenburg 1989), L (Lako and Okken 1992), O (Oudhuis, Janssen and van der Laag 1991), S (Seifritz 1990). CO 2 recovery decreases the efficiency of the plant. The electric efficiency of an integrated coal gasification combined cycle (IGCC) power plant drops from 44 to 38% CHendriks et al 1989). In a recent design study of Oudhuis et al (1991) the electric efficiency loss, from 52 to 47%, is reduced by incorporating a molten carbonate fuel cell (MCFC) for hydrogen pre-separation in the IGCC power plant. CO2 recovery by amine washing integrated in a high efficiency (ceramic turbine) gas steam and gasturbine (STAG) power plant, reduces the efficiency from 54 to 46%. In the production of synfuels (hydrogen, industrial & flare gas (IFG), methanol (gasf/met) or synthetic natural gas (SNG)) the costs and efficiency losses are small, when adding CO2 recovery. Partial oxydation (POX) of heavy oil residues is currently implemented to satisfy the increasing demands for hydrogen in oil-refining. A novel option is a hybride (gasoline/hydrogen) car with MgH z storage and CO2 absorption in MgCO3, coupled with a centralized system for regeneration of spent MgCO 3 with CO2 recovery (Seifritz 1990).
742
OKKEN et
al.:
CO2 REMOVAL IN COMPETITIONWITH OTHER OPTIONS
Costs per GJ output of final energy carriers (electricity, H 2 etc.) can be estimated according to the equation: C --- F + P/eft. where F = fixed costs of the production process including CO2 recovery (table 2, Ecu/GJ, assuming 6570 operating h/y for electric power plants and 7450 operating h/y for synfuels production); P = fossil fuel price (Ecu/GJ, see previous section); eff. = energy conversion efficiency (table 2). In the case of electricity CO s recovery increases the production costs by 15 to 25%, i.e. ca. 0.01 Ecu/kWh. Cost figures in the equation apply to plant gate; whereas costs for delivery of final energy carders (electricity, hydrogen, etc) and for CO2-tmnspcrt and -storage are taken into account separately by the model. Cost figure F excludes NOx and SO2 abatement technologies; these are accounted for separately in the model to comply with the exogenous 85% acidification reduction constraint.
CO7 storage The availability of COs storage is a sine qua non for CO s removal. In the Netherlands storage is considered in depleted underground natural gas reservoirs. The storage capacity is related to the initial amount of natural gas (CH4) in the reservoir. The maximum COs storage capacity in depleted natural gas reservoirs in the Netherlands is presented in table 3 (Harst and Nieuwland 1989). Enhanced recovery of gas is a positive side benefit: carefully planned CO s storage in an almost depleted natural gas reservoir (at the abandonment stage) may increase cumulative gas production. Other options for CO s storage include underground aquifers and depleted oil wells. The ultimate capacity however is uncertain, e.g. the theoretical storage capacity in underground aquifers in the Netherlands of ca. 100 GtCO2 is likely to decrease when geological, geochemical and safety limitations are taken into account. The large Groningen gasfield is probably not yet available for CO 2 storage before 2040. In the modelcalculations for the period 2000-2040 two storage reservoirs are considered with cumulated capacities of 0.7 and 2.0 GtCO2 at costs of 3 and 7 Ecu/tCO2 respectively. The first reservoir represents half of the small on-shore gasfields with transport and storage costs according to Harst and Nieuwland (1989).The second reservoir represents a mix of off-shore gasfields and aquifers, at costs twice as high. Electricity-inputs for compression, drying, pipe-line transport and field-injection (50 to 100 kWh/tCO 2, depending upon the initial CO2 pressure) are taken into account separately in the model. Table 3.
CO2 storage capacity (GtCO2) in the Netherlands
Gas reservoirs Groningen Other on-shore Off-shore
7.7 1.3 1.5
Aquifers Depleted oil wells
> 1 pm
The CO2 removal technologies in table 2 reflect a broad array of thinkable options, removal of solid carbon was not considered in this study however. In case of solid carbon- in stead of CO2-removal, the energy efficiency loss is greater and the storage costs are expected to be higher. The costs for solid coal waste disposal in the Netherlands are as high as 67 Ecu/t (Kram et al 1991); the ass~ciated costs for solid carbon-storage would increase the fuel costs by 2 Ecu/GJ (about doubling the coal price).
O K K E N et al.:
CO 2 REMOVAL
IN COMPETITION
WITH OTHER OPTIONS
743
RESULTS AND DISCUSSION
Primary energy
supply
The impact from the imposed maximum allowable national CO: emission rate (see figure 1) on the calculated Netherlands primary energy supply in 2040 is shown in figure 3. PetaJoule / year RENEWABLES .
3.000
~ :-'-T;~!
2.500
:
.
.
_
.
i ~
I!
+
i:-
i~i i!~i il ~ i~!
:
t
....?::::
500
5':S
i!~!+~++~¸¸ !
!iiii!i!i++i
~
ii?+iiii+i:ii+~
0 base
constant
[]
OIL
iil;i!!!+~ii~:
1.500 :}
NATURAL GAS COAL
~~i
2.000
1.000
[]
20%
40%
. ' : . . :.. :
J
•
4
'_7t
50%
60%
7O%
.
.:::
< :~,:? :
80%
1202 r e d u c t i o n (%) Fig. 3.
Primary energy supply (PJ/y) 2040, impact of CO 2 constraints
In the base case scenario in 2040 the primary energy requirement is largely met by coal, gas and oil. With stabilizationon of CO2 emissions to constant and with 20% reduction the primary energy supply decreases as a result of energy conservation and efficiency improvement efforts. Coal consumption decreases in favour of oil and renewables. This is the result of several underlying fuel and technology switches (e.g. from coal-methanol to diesel in the transport sector, from coal power generation to natural gas combined heat and power stations and off-shore windturbines, etc.). The residual coal power generating capacity is equiped with CO2 removal. At 40 to 50% CO2 reduction (figure 3) the consumption of natural gas increases. This is a net result of continuing energy conservation efforts on one hand, and on the other hand the introduction of hydrogen production from natural gas with CO2 removal. Hydrogen is used for stationary purposes (e.g. direct steam generation and fuel cells for combined heat and power generation in industry) as well as selected automotive transport applications (e.g. airplanes). At 60 to 80% CO2 reduction (figure 3) the contributions from coal and oil decrease in favour of natural gas and renewables. At these severe CO2 constraints the most expensive renewable energy options are introduced (e.g. solar photovoltaic electricity generation, biofueis in road transport). The contribution from oil decreases as the transport sector switches from oil to biofuels, electric vehicles and hydrogen. The increased natural gas supply is mainly used for hydrogen production. The resulting final energy consumption of hydrogen increases in 2040 from 500 (at 40% CO2 reduction) to 1500 PJ/y (at 80% CO2 reduction). Despite the implementation of energy consuming CO2 removal techniques, the total primary energy supply hardly increases, going from the constant case to 80% CO2 reduction. This is a net result from two compensating features: Ca. 15-20% energy loss occurs when CO2 removal is introduced, e.g. in coal power stations or with natural gas reforming to hydrogen (see table 2). On the other hand the primary energy supply decreases as a result of ongoing energy conservation, coupled with the increase
744
OKKEN et al.: CO2 REMOVAL IN COMPETITION WITH OTHER OPTIONS
in end-use efficiency due to the introduction of hydrogen (high efficiency fuel cells, reduction in airplane take-off weight, etc.) (Okken et al 1992).
CO~ storage caoacitv The storage capacity for CO2 in the Netherlands depleted gas fields and aquifers during the period 2000-2040 is restricted to 2.7 GtCO 2 (see previous section). At mild CO2 constraints (constant'88 and 20% reduction) the capacity is mainly utilized for storage of CO 2 recovered in N-fertilizer production and coal gasification (power stations and methanol production). At severe CO 2 constraints (>40% reduction) the storage capacity restriction is a bottleneck, and MARKAL seeks cost-effective ways to fill the storage reservoir. The amount of CO s in producing hydrogen from natural gas (70 g CO2/MJ Hz) is considerably less compared to electricity production from coal IGMCFC (200 gCOJMJe). The CO2 storage capacity restriction, assumed in the model-calculation, contributes to the preference for hydrogen production from natural gas at severe CO 2 constraints, resulting in a switch over in storage capacity utilization (see figure 4). cumulative period 2000 - 2 0 4 0
Mt C 0 2 /- f--~---~'~
2.500
/] J
,.,t
2.000
m-used capacity
.,.
1.500
/
t
' :1[ ] [ []
hydrogen from natural gas IGMCFC coal power plant
~ []
IGCCcoal power plant hydrogen + syngas from coal
[]
methanol from coal
[ ~ gas STAG power plant 1.000
[]
N-ferUllzer plant
500
0
base case
constant
20%
40% 50% 60% 70% 80%
CO2 reduction (%) eme/ellc/ecn 1992
Fig. 4.
Cumulated CO2 storage capacity utilization, at various CO2 constraints
Costs MARKAL calculates the total system costs. By comparing undiscounted total system costs in alternate CO2 constrained calculations the incremental CO2 reduction costs are calculated (per tCO2 from 40 to 50, to 60, to 70% etc.). The incremental costs increase as the most expensive CO2 reducing options are introduced (figure 5). The average CO 2 reduction costs are below 100 Ecu per tonne of CO 2 reduced. The average costs in the period 2000-2040 to achieve 80% COs reduction by the year 2040 would consume 2.2% of the expected Netherlands gross national product (GNP) during this period.
OKKEN et al.:
CO 2 REMOVAL IN COMPETITION WITH OTHER OPTIONS
745
E cu / t C 02 (1Ecu = 1.265 = 2.33fl) ino'~m~m~l costs Q
average
30¢
-°--4---
250
2OO 15¢ 100 .@ o.4p o"
50 .....e
0 baao~
....
) 0
- o-
0---'''
20
40
emission reduction Fig. 5.
60
8O
100
(%)
CO2 reduction costs, Netherlands energy system 2000-2040
FINAL REMARKS The rapid rate of technological change, coupled with changes in industry and society, make it difficult to assess the future market penetration of new energy technology options. Although energy technology systems analysis identifies a cost-effective future technology mix; cost and efficiency estimates for new energy technologies often appear too optimistic, and there may be hidden barriers to prevent their market penetration. On the other hand unexpected new technologies may emerge that were not considered in the systems analysis. The results obtained in this scenario-study should thus not be regarded as predictions of what will happen in the future. The scenario is just a present-day conditional "what if" prospective integrated cost-effective CO2 reduction strategy, including CO 2 removal options.
REFERENCES Harst, A.C. van der, A.J.F.M. van Nieuwland (1989). Disposal of carbon dioxide in depleted natural gas reservoirs. In: Climate and Energy (P.A. Okken, R.J. Swart and S. Zwerver eds.) pp. 178-188. Kluwer Academic Publishers, Dordr¢cht, Boston, London Hendriks, C.A., K. Blok and W.C. Turkenburg (1989). The recovery of carbon dioxide from power plants. In" Climate and Energy (P.A. Okken, R.J. Swart and S. Zwerver eds.) pp. 125142. Kluwer Academic Publishers, Dordrecht, Boston, London Kram, T., P.A. Okken, D. Gerbers, P. Lako, M. Rouw and D.N. Tiemersma (1991). Koleninzet studie (in Dutch). Report nr. ECN-C-91-072, Petten, the Netherlands Lako, P. and P.A. Okken (1992). Technologic karakterisatie CO2 verwijdering en H 2 optics (in Dutch). ECN, Petten, the Netherlands Okken, P.A., T. Kram (1990). Calculation of actual CO 2 emissions. Report hr. ECN-RX-90-048, Petten, the Netherlands Okken, P.A., J.R. Ybema, D. Gerbers, T. Kram and P. Lako (1991). The challenge of drastic CO2 reduction. Report nr. ECN-C-91-009, Petten, the Netherlands Okken, P.A., T. Kram, J.R. Ybema, J. v. Doom, D. Gerbers, P. Lako (1992). Future energy systems under CO 2 constraints; an integrated assessment of options for reducing CO 2 emissions in the Netherlands energy system up to 2040. ECN, Petten, the Netherlands. Oudhuis, A.BJ., D. Jansen and P.C. van der Laag (1991). Concept for coal fuelled fuel-cell power plant with CO 2 removal. Modern Power Systems, 12 nr. 11, pp.25-29 Seifritz, W. (1990). A new hybrid hydrogen/gasoline driven motor-car with a CO 2 trap. Int. J. Hydrogen Energy, 15 pp.757-762
0196-8904/92 $5.00+0.00 Copyright© 1992PergamonPressLtd
Primedin GreatBritain.All rights reserved
CO2 REMOVAL IN COMPETITION WITH OTHER OPTIONS FOR REDUCING CO2 EMISSIONS
P.A. OKKEN, P. LAKO, D. GERBERS, T. KRAM and J.R. YBEMA
ESC/Energy Studies, Netherlands Energy Research Foundation ECN, PO Box 1, 1755 ZG, Petten, the Netherlands
ABSTRACT CO2-reduction scenarios are calculated with the MARKAL-model in a bottom-up analysis of the evolution of the Netherlands energy system for the period 2000-2040. In these calculations moderate fuel price increases, stringent environmental constraints, steady improvements in energy efficiency and major energy alternatives are taking into account. Preliminary results indicate a strong potential for CO2 removal from fossil fuels in combination with electricity and hydrogen production, at severe CO2 emission constraints.
KEYWORDS Coal gasification, carbon dioxide, cost, forecasting, hydrogen, M codes, recovery, removal, storage.
INTRODUCTION The unit ESC-Energy Studies of ECN performs energy and environmental studies to support the Netherlands government and international agencies. Long term CO 2 reduction targets have not yet been agreed upon by governments. Critical issues are the cost sharing amongst nations, and the potential for energy technology development. In order to detect cost-effective international CO 2 reduction strategies a complete array of new energy technologies is incorporated in EMS (Energy and Materials Scenarios to reduce emissions of CO2 and other greenhouse gases). EMS is implemented at ESC with cooperation from KEMA Amhem and the universities of Groningen and Utrecht, within the framework of the IEA Energy Technology Systems Analysis Programme (ETSAP), sponsored by the Ministry of Economic Affairs energy directorate and the Netherlands national research programme on global air pollution and climate change.
INTEGRATED ASSESSMENT OF CO 2 EMISSION REDUCING OPTIONS Many energy technology options for reducing CO2 emissions are available. Normally, the contribution of individual options to CO2 reduction is calculated in a simple way starting from a constant reference situation and without considering interactions between different options. However, on longer term, the reference situation will change. Therefore, fuel price paths, future energy demand projections, environmental measures and reference technology efficiency improvements must be taken into account. Moreover, future CO 2 reducing options should be evaluated in relation with other future options to uncover
737
738
OKKEN et al.: CO2 REMOVALIN COMPETITIONWITH OTHEROPTIONS
potential conflicts and synergies. Energy technology systems analysis provides a tool for the design of cost-effective long term CO2 reduction strategies.
Model The model used in EMS, the MARKet ALlocation (MARKAL) model, is a standard linear programming software package which is used to represent energy systems. The model is currently operated in 12 IEA countries including the United States, Japan and the European Community. Using detailed compilations of data characterising available and prospective energy technologies, and incorporating projections and assumptions about the costs and availability of fuels M A R K A L configures an optimal mix of technologies to satisfy the specified useful energy demands. The model includes detailed data for the Netherlands energy system, like fuel prices, costs and energy efficiency indicators for several hundreds of different energy conservation and -supply technologies, emission coefficients and emission abatement techniques. The model is used in a national costs minimizing mode with exogenous national maximum allowable annual emissions of NOx, SO2 and CO 2 ('bubble' concept). The model optimizes the energy system for the period 2000 to 2040 simultaneously in steps of 5 years each. This dynamic simultaneous optimization is referred to as 'perfect foresight', reflecting the activities of policy-makers as they are supposed to 'know the future'. Dynamic modelling is of vital importance for testing structural changes in the energy system under environmental constraints. Gradual efficiency improvements of existing energy technologies are incorporated, and several new energy technologies are projected to be available at fixed points in the future, thus reflecting the promises of ongoing energy and environmental R&D. The model enables testing of such new technologies in a future energy system under various external constraints ('technology assessment'). Few institutional and market barriers are assumed. On the other hand bounds are imposed on the speed of market penetration for new energy technologies to prevent unrealistic solutions, and there-are lower bounds to ensure that older technologies will not be phased out too rapidly. The model optimizes with a 5% discount rate. In an earlier scenario study (Okken et al 1991) with MARKAL for the Netherlands energy system on mid-term up to the year 2020 cost-effective contributions from CO: reducing options were calculated: renewable energy (e.g. wind, solar) nuclear energy savings on conversion (e.g. combined heat and power) savings on end-use (e.g. building insulation) intra-fossil fuel switch (e.g. from coal to gas) - recycling (e.g. waste plastics) CO: removal (e.g. at coal power stations) -
-
In this paper scenario calculations are reported for the Netherlands energy system on longer term, the period 2000 to 2040, with moderate fossil fuel price increases and stringent constraints for NO, and SO2 emissions. To detect cost-effective strategies for drastic CO2 reduction calculations are performed with variable CO 2 constraints.
CO? calculation The Netbeflands CO 2 budget differentiates actual and potential emissions. In the porto-chemical industries a significant amount of fossil fuel carbon is sequestered into solid materials (e.g. plastics). These solid carbonaceous materials represent "potential emissions" only: CO 2 is emitted just in case the material becomes oxidized, e.g. in a municipal waste combustion plant. The production rate of potential emissions in the Netherlands is relatively high, being equivalent to 13% of the national CO 2 emission, whereas the world average is 2%. Most of the plastics is exported. Re-use of plastics, in
OKKEN et al.: CO2 REMOVAL IN COMPETITIONWITH OTHER OPTIONS
739
stead of burning them, reduces CO z emissions, In order to quantify the exact fossil fuel CO z emission rate for carbon cycle studies, and to address waste management policy opportunities for CO a reduction, a methodology for the calculation of "actual emissions" was proposed by Okken and Kram (1990). COz emissions are calculated from the carbon content of fuels and the national energy balance; the so-called "feedstocks" in the balance are subtracted, unless these feedstocks are inevitable oxidized (e.g. natural gas feedstocks in nitrogen fertilizer production); furthermore the inland COz emission due to combustion of carbonaceous materials of fossil fuel origin (e.g. plastics in MSW combustion) are added. COs emissions from international marine bunkers in the Netherlands are equivalent to 22 % of the national emissions. Again this is an exceptional situation (the world average is 1.5%) due to the geographical location. CO2 emissions from international aviation bunkers in the Netherlands are equivalent to 2.8% of the national emissions; this is about the same as the world average (Okken et al 1991). This paper reports on actual national COs emissions and international aviation bunkers. The CO 2 emissions from international aviation bunkers in the Netherlands are expected to increase from 4 in 1990 to 7 MtCO2 in 2000, as a result of planned extensions of passenger air traffic. The actual national CO 2 emission rate is expected to decrease from 160 in 1990 to 154 MtCO z in 2000; in accordance with the official governmental COz emission reduction target of 3 to 5% by the year 2000.
TECHNO-ECONOMIC ASSUMPTIONS All cost figures are in Ecu's of 1990. (1 Ecu --- 1,26 $ = 2,33 Dfl). The scenario's for economic development, useful energy demand, fuel prices and NO, and SO z constraints are taken from Kram et al (1991), adjusted for the most recent population projection and implemented energy and environmental policies regarding the year 2000. The fuel price is projected to increase linearly during the period 2000 to 2040 as follows: coal from 1.9 to 3.2 Ecu/GJ, crude oil from 4.4 to 8.9 Ecu/GJ, gas from 4.0 to 8.2 Ecu/GJ (or 10.2 at 25% higher price). An obvious strategy to reduce CO2 emissions is fuel switching from coal to natural gas (table 1). In order to reflect scarcity in the international gas markets when global CO 2 constraints would become reality, a 25% price increase is assumed for those natural gas requirements exceeding the base case gas demand. Table 1.
Hard coal Oil Natural gas Uranium, renewables
CO: emission coefficients of combustion of fossil fuels, at lower heating value (lhv) in kgCO2/GJ,
94 73 56 0
NO, and SO 2 constraints are imposed as maximum allowable annual emissions, resulting in a 85% reduction in acidificadon-equivalents in 2030, as compared to 1980. This is in accordance with present environmental policy. The model incorporates emission abatement technologies and fuel switch options to reduce NO, and SO2. The four scenarios include high growth (2%/y) export oriented and low growth (1.5%/y) economic developments; with and/or without nuclear energy. This paper discusses the high growth scenario without nuclear energy. The energy demand is primarily met with coal, gas and oil; not surprisingly the resulting base case annual CO2 emission increases from 161 MtCO2 in 2000 to 240 MtCO2 in 2040. In order to detect cost-effective strategies for drastic CO 2 reduction this scenario was recalculated with variable maximum allowable annual CO2 emissions (see figure 1).
740
OKKEN et al.:
CO 2 REMOVAL IN COMPETITION WITH OTHER OPTIONS
EMISSIOH[MTOH CO2/YEAR] 250
BASE
200
....
180
+ _ ++
-40%
100
-50% -60% 50
• .....
1
I
I
1990
2000
2010
I
2020
• ..........................
70%
"'.. .........................
-80%
I
I
2030
2040
[YEAR]
Fig 1.
Netherlands CO2 emission rate 2000-2040; Base case and CO2 constrained calculations.
Technologies for reducing COt emissions In the 2020 study a significant potential for CO2 removal in combination with electrification (electric heatpumps and vehicles) was identified. Other technologies for CO 2 reduction in the 2020 study include biogas, geothermal, solar, wind, nuclear power, natural gas-fh-ed heatpumps and fuel ceils, methanol and ethanol vehicles, energy end-use conservation, etc. (Okken et al 1991). In the 2030 study several new coal conversion options and solid coal waste emissions were added (Kram et al 1991). In the 2040 study reported in this paper the above mentioned options in the model are extended with: CO 2 removal coupled with synfuel production, hydrogen end-use, detailed electricity and energy conservation options in every energy demand category, biomass (bio-ethanol, rape seed, miscanthus, short rotation forestry, methanol from ligno-cellulose) and other prospective energy supply options (e.g. thermo photovolatic residential boilers, solar heating with seasonal storage). Although cost-effective energy conservation options are included in the base case calculation, a stepwise energy end-use conservation potental in different sectors varying from 20% to 50% (in specific industrial sub-sectors resp. for residential space heating) still remains for further reducing CO2 emissions. The renewable energy potential reflects local possibilities within the Netherlands, e.g. 8 GWe wind-turbines (of which 5 off-shore) for electricity generation, 500000 ha land area available for energy crops, an unlimited potential for solar PV electricity generating capacity (1100 h/y, investment costs 0.85 Ecu/pWe). For more details see Okken et al (1992). In this paper CO2 removal options are considered.
CO~ recovery COz removal = CO2 recovery + CO z storage outside the atmosphere. The array of COz-removal options, considered in this study in competition with all other options for CO z reduction, is shown in figure 2. Performance data in the model for future CO2 recovery technologies are summarized in table 2. The data characterization builds upon recent literature and projections of performance improvements within the chemical industries ( e.g. gradual replacement of conventional steam reforming by catalytic partial oxidation processes).
OKKEN et al.: CO2 REMOVALIN COMPETITIONWITH OTHER OPTIONS
gasoline.................--l---~M-~-~st_~-hydrogen . . . . . . . . . . . . . . . . . J
coal . . . . . . . . 1. . . . . . .
~
i~o2
SNG hydrogen
'
methanol
I
~_~_..... ~ - s ~ r
oil residue
car
-~co=
....... ~-H~,ng--~ r---I '. . . . ~ c o : ~ | ii2/.. ---J
gas--
741
[-;~,m,~,
r----~~ J ~ x ~2.- ' -
electricity -N-fertilizer
. "co~
---hydrogen ..,,,.,./,~. ,,,,
Fig. 2.
CO 2 removal options considered in the Netherlands energy system MARKAL model 2000-2040. Abbreviations see text.
Table 2.
CO 2 recovery options, energetic efficiency and recovery rate, target year 2020+
Proces
Input
Eft. (lhv)
Output(s)
Rec. rate
Ref.
F cost Ecu/GJ
IGCC power plant IGMCFC (fuel cell) Gas STAG power plant N-fertilizer plant Adv. gas reformer Partial oxidation Hybrid/hydride car Coal gasification Coal gasification Coal gasification
coal coal nat.gas nat,gas nat,gas oilres. oil/coal coal coal coal
38% 47% 46% nc 80% 75% nc 71% 74% 63%
electricity electricity electricity NH4NO3 H2 H2 transport 53H2 +18CI-I4 63H2 +1 IIFG methanol
88% 97% 88% 98% 98% 98% 90% 83% 78% 49%
H O,L H,L L L L S L L L
6.4 8.2 4.7 1.6 4.1 5.6 5.4 5.8
H (Hendriks, Blok and Turkenburg 1989), L (Lako and Okken 1992), O (Oudhuis, Janssen and van der Laag 1991), S (Seifritz 1990). CO 2 recovery decreases the efficiency of the plant. The electric efficiency of an integrated coal gasification combined cycle (IGCC) power plant drops from 44 to 38% CHendriks et al 1989). In a recent design study of Oudhuis et al (1991) the electric efficiency loss, from 52 to 47%, is reduced by incorporating a molten carbonate fuel cell (MCFC) for hydrogen pre-separation in the IGCC power plant. CO2 recovery by amine washing integrated in a high efficiency (ceramic turbine) gas steam and gasturbine (STAG) power plant, reduces the efficiency from 54 to 46%. In the production of synfuels (hydrogen, industrial & flare gas (IFG), methanol (gasf/met) or synthetic natural gas (SNG)) the costs and efficiency losses are small, when adding CO2 recovery. Partial oxydation (POX) of heavy oil residues is currently implemented to satisfy the increasing demands for hydrogen in oil-refining. A novel option is a hybride (gasoline/hydrogen) car with MgH z storage and CO2 absorption in MgCO3, coupled with a centralized system for regeneration of spent MgCO 3 with CO2 recovery (Seifritz 1990).
742
OKKEN et
al.:
CO2 REMOVAL IN COMPETITIONWITH OTHER OPTIONS
Costs per GJ output of final energy carriers (electricity, H 2 etc.) can be estimated according to the equation: C --- F + P/eft. where F = fixed costs of the production process including CO2 recovery (table 2, Ecu/GJ, assuming 6570 operating h/y for electric power plants and 7450 operating h/y for synfuels production); P = fossil fuel price (Ecu/GJ, see previous section); eff. = energy conversion efficiency (table 2). In the case of electricity CO s recovery increases the production costs by 15 to 25%, i.e. ca. 0.01 Ecu/kWh. Cost figures in the equation apply to plant gate; whereas costs for delivery of final energy carders (electricity, hydrogen, etc) and for CO2-tmnspcrt and -storage are taken into account separately by the model. Cost figure F excludes NOx and SO2 abatement technologies; these are accounted for separately in the model to comply with the exogenous 85% acidification reduction constraint.
CO7 storage The availability of COs storage is a sine qua non for CO s removal. In the Netherlands storage is considered in depleted underground natural gas reservoirs. The storage capacity is related to the initial amount of natural gas (CH4) in the reservoir. The maximum COs storage capacity in depleted natural gas reservoirs in the Netherlands is presented in table 3 (Harst and Nieuwland 1989). Enhanced recovery of gas is a positive side benefit: carefully planned CO s storage in an almost depleted natural gas reservoir (at the abandonment stage) may increase cumulative gas production. Other options for CO s storage include underground aquifers and depleted oil wells. The ultimate capacity however is uncertain, e.g. the theoretical storage capacity in underground aquifers in the Netherlands of ca. 100 GtCO2 is likely to decrease when geological, geochemical and safety limitations are taken into account. The large Groningen gasfield is probably not yet available for CO 2 storage before 2040. In the modelcalculations for the period 2000-2040 two storage reservoirs are considered with cumulated capacities of 0.7 and 2.0 GtCO2 at costs of 3 and 7 Ecu/tCO2 respectively. The first reservoir represents half of the small on-shore gasfields with transport and storage costs according to Harst and Nieuwland (1989).The second reservoir represents a mix of off-shore gasfields and aquifers, at costs twice as high. Electricity-inputs for compression, drying, pipe-line transport and field-injection (50 to 100 kWh/tCO 2, depending upon the initial CO2 pressure) are taken into account separately in the model. Table 3.
CO2 storage capacity (GtCO2) in the Netherlands
Gas reservoirs Groningen Other on-shore Off-shore
7.7 1.3 1.5
Aquifers Depleted oil wells
> 1 pm
The CO2 removal technologies in table 2 reflect a broad array of thinkable options, removal of solid carbon was not considered in this study however. In case of solid carbon- in stead of CO2-removal, the energy efficiency loss is greater and the storage costs are expected to be higher. The costs for solid coal waste disposal in the Netherlands are as high as 67 Ecu/t (Kram et al 1991); the ass~ciated costs for solid carbon-storage would increase the fuel costs by 2 Ecu/GJ (about doubling the coal price).
O K K E N et al.:
CO 2 REMOVAL
IN COMPETITION
WITH OTHER OPTIONS
743
RESULTS AND DISCUSSION
Primary energy
supply
The impact from the imposed maximum allowable national CO: emission rate (see figure 1) on the calculated Netherlands primary energy supply in 2040 is shown in figure 3. PetaJoule / year RENEWABLES .
3.000
~ :-'-T;~!
2.500
:
.
.
_
.
i ~
I!
+
i:-
i~i i!~i il ~ i~!
:
t
....?::::
500
5':S
i!~!+~++~¸¸ !
!iiii!i!i++i
~
ii?+iiii+i:ii+~
0 base
constant
[]
OIL
iil;i!!!+~ii~:
1.500 :}
NATURAL GAS COAL
~~i
2.000
1.000
[]
20%
40%
. ' : . . :.. :
J
•
4
'_7t
50%
60%
7O%
.
.:::
< :~,:? :
80%
1202 r e d u c t i o n (%) Fig. 3.
Primary energy supply (PJ/y) 2040, impact of CO 2 constraints
In the base case scenario in 2040 the primary energy requirement is largely met by coal, gas and oil. With stabilizationon of CO2 emissions to constant and with 20% reduction the primary energy supply decreases as a result of energy conservation and efficiency improvement efforts. Coal consumption decreases in favour of oil and renewables. This is the result of several underlying fuel and technology switches (e.g. from coal-methanol to diesel in the transport sector, from coal power generation to natural gas combined heat and power stations and off-shore windturbines, etc.). The residual coal power generating capacity is equiped with CO2 removal. At 40 to 50% CO2 reduction (figure 3) the consumption of natural gas increases. This is a net result of continuing energy conservation efforts on one hand, and on the other hand the introduction of hydrogen production from natural gas with CO2 removal. Hydrogen is used for stationary purposes (e.g. direct steam generation and fuel cells for combined heat and power generation in industry) as well as selected automotive transport applications (e.g. airplanes). At 60 to 80% CO2 reduction (figure 3) the contributions from coal and oil decrease in favour of natural gas and renewables. At these severe CO2 constraints the most expensive renewable energy options are introduced (e.g. solar photovoltaic electricity generation, biofueis in road transport). The contribution from oil decreases as the transport sector switches from oil to biofuels, electric vehicles and hydrogen. The increased natural gas supply is mainly used for hydrogen production. The resulting final energy consumption of hydrogen increases in 2040 from 500 (at 40% CO2 reduction) to 1500 PJ/y (at 80% CO2 reduction). Despite the implementation of energy consuming CO2 removal techniques, the total primary energy supply hardly increases, going from the constant case to 80% CO2 reduction. This is a net result from two compensating features: Ca. 15-20% energy loss occurs when CO2 removal is introduced, e.g. in coal power stations or with natural gas reforming to hydrogen (see table 2). On the other hand the primary energy supply decreases as a result of ongoing energy conservation, coupled with the increase
744
OKKEN et al.: CO2 REMOVAL IN COMPETITION WITH OTHER OPTIONS
in end-use efficiency due to the introduction of hydrogen (high efficiency fuel cells, reduction in airplane take-off weight, etc.) (Okken et al 1992).
CO~ storage caoacitv The storage capacity for CO2 in the Netherlands depleted gas fields and aquifers during the period 2000-2040 is restricted to 2.7 GtCO 2 (see previous section). At mild CO2 constraints (constant'88 and 20% reduction) the capacity is mainly utilized for storage of CO 2 recovered in N-fertilizer production and coal gasification (power stations and methanol production). At severe CO 2 constraints (>40% reduction) the storage capacity restriction is a bottleneck, and MARKAL seeks cost-effective ways to fill the storage reservoir. The amount of CO s in producing hydrogen from natural gas (70 g CO2/MJ Hz) is considerably less compared to electricity production from coal IGMCFC (200 gCOJMJe). The CO2 storage capacity restriction, assumed in the model-calculation, contributes to the preference for hydrogen production from natural gas at severe CO 2 constraints, resulting in a switch over in storage capacity utilization (see figure 4). cumulative period 2000 - 2 0 4 0
Mt C 0 2 /- f--~---~'~
2.500
/] J
,.,t
2.000
m-used capacity
.,.
1.500
/
t
' :1[ ] [ []
hydrogen from natural gas IGMCFC coal power plant
~ []
IGCCcoal power plant hydrogen + syngas from coal
[]
methanol from coal
[ ~ gas STAG power plant 1.000
[]
N-ferUllzer plant
500
0
base case
constant
20%
40% 50% 60% 70% 80%
CO2 reduction (%) eme/ellc/ecn 1992
Fig. 4.
Cumulated CO2 storage capacity utilization, at various CO2 constraints
Costs MARKAL calculates the total system costs. By comparing undiscounted total system costs in alternate CO2 constrained calculations the incremental CO2 reduction costs are calculated (per tCO2 from 40 to 50, to 60, to 70% etc.). The incremental costs increase as the most expensive CO2 reducing options are introduced (figure 5). The average CO 2 reduction costs are below 100 Ecu per tonne of CO 2 reduced. The average costs in the period 2000-2040 to achieve 80% COs reduction by the year 2040 would consume 2.2% of the expected Netherlands gross national product (GNP) during this period.
OKKEN et al.:
CO 2 REMOVAL IN COMPETITION WITH OTHER OPTIONS
745
E cu / t C 02 (1Ecu = 1.265 = 2.33fl) ino'~m~m~l costs Q
average
30¢
-°--4---
250
2OO 15¢ 100 .@ o.4p o"
50 .....e
0 baao~
....
) 0
- o-
0---'''
20
40
emission reduction Fig. 5.
60
8O
100
(%)
CO2 reduction costs, Netherlands energy system 2000-2040
FINAL REMARKS The rapid rate of technological change, coupled with changes in industry and society, make it difficult to assess the future market penetration of new energy technology options. Although energy technology systems analysis identifies a cost-effective future technology mix; cost and efficiency estimates for new energy technologies often appear too optimistic, and there may be hidden barriers to prevent their market penetration. On the other hand unexpected new technologies may emerge that were not considered in the systems analysis. The results obtained in this scenario-study should thus not be regarded as predictions of what will happen in the future. The scenario is just a present-day conditional "what if" prospective integrated cost-effective CO2 reduction strategy, including CO 2 removal options.
REFERENCES Harst, A.C. van der, A.J.F.M. van Nieuwland (1989). Disposal of carbon dioxide in depleted natural gas reservoirs. In: Climate and Energy (P.A. Okken, R.J. Swart and S. Zwerver eds.) pp. 178-188. Kluwer Academic Publishers, Dordr¢cht, Boston, London Hendriks, C.A., K. Blok and W.C. Turkenburg (1989). The recovery of carbon dioxide from power plants. In" Climate and Energy (P.A. Okken, R.J. Swart and S. Zwerver eds.) pp. 125142. Kluwer Academic Publishers, Dordrecht, Boston, London Kram, T., P.A. Okken, D. Gerbers, P. Lako, M. Rouw and D.N. Tiemersma (1991). Koleninzet studie (in Dutch). Report nr. ECN-C-91-072, Petten, the Netherlands Lako, P. and P.A. Okken (1992). Technologic karakterisatie CO2 verwijdering en H 2 optics (in Dutch). ECN, Petten, the Netherlands Okken, P.A., T. Kram (1990). Calculation of actual CO 2 emissions. Report hr. ECN-RX-90-048, Petten, the Netherlands Okken, P.A., J.R. Ybema, D. Gerbers, T. Kram and P. Lako (1991). The challenge of drastic CO2 reduction. Report nr. ECN-C-91-009, Petten, the Netherlands Okken, P.A., T. Kram, J.R. Ybema, J. v. Doom, D. Gerbers, P. Lako (1992). Future energy systems under CO 2 constraints; an integrated assessment of options for reducing CO 2 emissions in the Netherlands energy system up to 2040. ECN, Petten, the Netherlands. Oudhuis, A.BJ., D. Jansen and P.C. van der Laag (1991). Concept for coal fuelled fuel-cell power plant with CO 2 removal. Modern Power Systems, 12 nr. 11, pp.25-29 Seifritz, W. (1990). A new hybrid hydrogen/gasoline driven motor-car with a CO 2 trap. Int. J. Hydrogen Energy, 15 pp.757-762