SINTEF Energy Research Jens Hetland a , Ping Yowargana b , Sylvain Leduc b , Florian Kraxner b a SINTEF Energy Research, Kolbjorn Hejesvei 1A, N-7465 Trondheim, Norway, b Ecosystems Services and Management (ESM), International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria Carbon-negative biopower via direct conversion and co-firing: Systemic impacts of capture and storage of CO 2 applied to Indonesia TCCS-8 16-18 June 2015, Trondheim, Norway Corresponding author's e-mail address: [email protected]
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SINTEF Energy Research Jens Hetland a, Ping Yowargana b, Sylvain Leduc b, Florian Kraxner b a SINTEF Energy Research, Kolbjorn Hejesvei 1A, N-7465 Trondheim,
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a SINTEF Energy Research, Kolbjorn Hejesvei 1A, N-7465 Trondheim, Norway, b Ecosystems Services and Management (ESM), International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria
Carbon-negative biopower via direct conversion and co-firing: Systemic impacts of capture and storage
About half of the scenarios of the IPCC, constraining the atmospheric concentration of greenhouse gases to 430-480 ppm CO2 equivalents, feature bioenergy with CCS (BECCS) (1).
As these scenarios jointly account for more than 5% of the global primary energy supply (2), it is necessary to further assess the potential for CO2 mitigation from a systemic perspective.
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(1) Cf. the 5th assessment report of the IPCC (WG 3)(2) Fuss, S., Canadell, J. G., Peters, G. P., Tavoni, M., Andrew, R. M., Ciais, P., Yamagata, Y. (2014).
Betting on negative emissions. Nature Clim. Change, 4(10), 850–853.
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Components to consider
Localisation and size of the plant vis-à-vis the biomass feedstock and grid connection Life-cycle emissions
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Case-specific studies conducted from the perspective of biomass availability and technology selection are required, pursuant to local and regional demands for electricity as well as affordable pricing.
Primary energy/feedstock
Primary/secondary conversion Market / end usage
• Biomass sources• Other feedstock
• Plant size• Power cycle technology; dedicated BECCS or co-firing with coal• CO2 intensity and life-cycle emission• Carbon pricing
in the vicinity of the plant Would require 700 tonne biomass per hour (1) 24 lorries per hour, 30 tonne each
200 000 deliveries per year From a logistic point of view, deployment of such plants is a challenge Additional firing options will be needed to offset investments ( co-firing)
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(1) Air dried biomass with [C,H,O,N,S,moisture,ash]=[0.3028,0.0352,0.2563,0.0704,0.0000,0.4014,0.00352] with LHV 10.55 MJ/kg
BECCSCoal
Oil
Natural gas
Gasification/
reforming
Water shift
reaction
CO2 capture
(H2
separation)
Power cycle
Hydrogen-
enriched fuel
Power cycle
Air separtion
unit(de-nitrogenation)
Water
removal
(condenser)
Power cycle CO2 capture
(scrubbing)
CO2
conditioning,
compression
and transport
H2 + CO H2 + CO2
H2
O2
CnHm + O2 <=> nCO2 + m/2 H2O
Exhaust, 0.3-0.5% CO2
Exhaust, 0.1-0.5% CO2
SINTEF Energy Research/
Jens Hetland 2006
CO2 storage
(geological
formations,
EOR/EGT)
2
3
1
Water
Biomass
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Trajectories depending on plant size (net power output)
Co-firing of biomass in modern coal power plants offers higher efficiency than smaller biopower plants.
Replacing a portion of coal with biomass seems to be the most economic near-term solution for employing biopower at large.
Biopower plant efficiency without CCS Resulting efficiency of co-fired biomass and biopower with CCS (BECCS)
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Combustion characteristics and typical feedstock compositions of Indonesian biomass sources
The biomass is converted either in existing large-scale coal power plants available for co-firing, or in smaller decentralised BECCS.
Studies carried out by the GIZ(1) conclude that residues of palm oil, rice paddy and sugar cane are the most dominant resources of bioenergy feedstock in Indonesia, due to the large volume of crops production.
Hydrogen (H) and oxygen contents (O) as well as carbon (C) of the Indonesian palm kernel shell (left), and reference coal (right, Pittsburg No. 8), presented in accordance with van Krevelen.c
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0
0,5
1
1,5
2
2,5
3
3,5
4
0 0,2 0,4 0,6 0,8 1
H/C
O/C
0
0,5
1
1,5
2
2,5
3
3,5
4
0 0,2 0,4 0,6 0,8 1
H/C
O/C
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Power plant assumptions Assessments are based on independent biomass-fired power plants and co-firing of biomass
in conventional coal power plants, comparable to the current Indonesian situation. The efficiency of biopower plants forming the basis for BECCS has been assumed to follow
three efficiency trajectories (low, medium and high), essentially corresponding to three classes of biopower capacity: 10, 50 and 100 MWe.
For the co-firing alternative, a conventional 660 MWe coal power plant with an initial efficiency of 38% (LHV) has been chosen (i.e. sub-critical steam conditions).
Generic bituminous coal (Pittsburgh No.8) is used for co-firing with Indonesian biomass (palm kernel shell). Up to 16% biomass can be co-fired without essential modifications of the plant. The condenser pressure is assumed to be similar for the BECCS and the coal-power plant (0.003 bara, 36°C).
The flue gas is cleaned via an absorption process using an amine-based solvent requiring 3.24 GJ/tonne CO2 to be regenerated. For both alternatives, the heat is provided by steam extracted from the medium-pressure turbine at 5 bara and 160°C. The captured CO2 is compressed to meet a pipeline pressure of 146 bara for delivery in dense phase at the wellhead.
The estimation of the coal-power plant is made on the assumption that the plant is fully equipped with environmental control systems (ECS) removing 99% of the sulphur contained in the flue gas, whereas the BECCS alternative is without ECS.
The calculations are based on ISO conditions.
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Impact of biomass depending on technology and feed rate
The combustion is provided with 5% excess oxygen. Estimations are based on complete reactions, and typically 85% full operational availability.
The initial plant efficiency (without CCS) and the rate of CO2 capture has been used as parameters characterising the fully integrated CCS-based power cycle.
Impact on power generation plant efficiency The power generation efficiency will drop by roughly 10%-points (essentially the same
whether CCS is applied to the coal power plant or to the smaller dedicated BECCS plant).
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Results (assessing the impact of biomass per se)
Concentration of species resulting from the two alternatives using the same feed rate for biomass.
It has been assumed that the biomass per se is completely dry, which is usually not correct. The true humidity of the fuel will affect the dew point.
GWh denotes net power output.
g/g denotes mass fraction of species in the flue gas.
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Co-firing BECCS Net el. power without CCS [MWe] 67.681 49.87
Net el. power with CCS [MWe] 49.95
32.14
Plant efficiency / no CCS [%] 38.00 28.00 Plant efficiency with CCS [%] 28.04 18.04 Biomass demand (kg/s) 10.927 10.927 Flue gas composition formed (referred to base plant without CCS)
CO2 126.4 0.0238 196,4 0,0280 H2O 311.0 0.0519 483,4 0,0690 SO2 0.029 4.898E-05 4,4 0,0006 O2 275.2 0.0608 427,7 0,0611 N2 3724.5 0.8478 5788,7 0,8262 Ar 67.9 0.0155 105,6 0,0151 Elementary sulphur removal (g S/kWh) 9.2 0 Acid dew point (°C, Okke) 140.1 155.1 Acid dew point (°C, Verhoff) 146.8 162.8 Water dew point [°C) 39.4 44.4
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Negative carbon emission resulting from the two plants in g/kWh net power output
The table compares the impact on emissions termed neutral and negative. Since the conversion of biomass by definition is carbon neutral, the amount of CO2 released to the atmosphere is deducted from the plant's emissions. With CCS, the amount of CO2 generated from biomass and permanently stored represents negative emissions.
With BECCS, an additional amount of 37% CO2 must be captured and stored than the CO2 captured and stored from the co-firing alternative.
Due to the higher efficiency, the emission of CO2 from co-fired biomass is lower than that of a biopower plant.
With reference to the net electric energy supplied to the grid, the neutral and negative emissions from the BECCS plants will be from 27% to 75% higher than those from a very large power plant equipped with CCS, where the biomass is co-fired with coal. The reason is that the efficiency ratio between the co-firing and the BECCS options ranges from 1.27 for the largest and most efficient BECCS plant (100 MWe) to 1.75 for the smallest and less efficient BECCS plant (10 MWe).
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Co-firing with biomass BECCS Comments Neutral emission (g/kWh) 126.4 196.4 Released to the atmosphere Negative emission (g/kWh) 778.6 1069.6 Captured and stored
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Conclusion
1. Significant advantages of co-firing over independent bioenergy power plants when CCS is applied. Provided that an operational coal-power plant is at hand, more net electric energy can be
generated from the biomass than would be the case in a dedicated BECCS plant, although the amount of CO2 captured and stored will be identical.
2. Independent bioenergy power plants with the same electric energy must burn roughly 27-75% more biomass and will generate a corresponding amount of additional CO2 (dependent on the size and complexity of the plant).
Nevertheless, in the context of Indonesia, where the feedstock mainly comes from existing agriculture residues, biopower plants are still seen as an attractive option despite the lower efficiency. This interest is backed by resource availability and limited access to electrification in areas with dominant agriculture activities.
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Conclusion
3. Without a high initial efficiency, CCS will not become economically viable, simply because of the limited amount of electricity to sell.
Most likely, a sufficiently high efficiency can only be ensured in large plants with advanced steam parameters (preferably in super-critical steam power cycles). Future material development is expected to enhance the efficiency considerably, which may have an impact also on smaller plants, whereby the range of differences may become smaller.
4. When it comes to safeguarding the energy supply, which is important in countries with power
scarcity such as Indonesia, the use of available biomass resources for co-firing in coal power plants will be preferable. Clearly, this has a considerable limitation as concerns the logistics of providing the required
biomass feedstock.
5. In a regulatory regime with a sufficient price on carbon emissions, independent biopower plants may be preferred to the co-firing alternative mainly due to the CO2 which is accountable either as negative or neutral emission.
In this case, an accounting system capable of handling negative CO2 emissions is mandatory.
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Concluding remark
The above insights should lead to further investigations, especially to cost-benefit analyses pertaining to electricity tariffs, and carbon pricing within a limited national context. Such analyses will be useful for the identification of patterns maximising carbon emission reduction.