Study finds co-producing FT fuels and electricity from coal and biomass with CCS delivers low GHG synfuels at lower cost and with less biomass than cellulosic ethanol
A detailed study by researchers from China and the US has concluded that Fischer-Tropsch synthetic liquid fuels (FTL) are typically less costly to produce when electricity is generated as a major coproduct than when the plants are designed to produce mainly liquid fuels.
Furthermore, coproduction systems that utilize a co-feed of biomass and coal (CBTL) and incorporate CO2 capture and storage (CCS) in the design offer attractive opportunities for decarbonizing both liquid fuels and power generation simultaneously. Such co-production systems, when considered as power generators, can provide decarbonized electricity at lower costs than is feasible with new stand-alone fossil fuel power plants under a wide range of conditions, according to the study by Liu et al. published in the ACS journal Energy & Fuels.
At a plausible GHG emissions price of $50/t CO2eq under a future US carbon mitigation policy, such co-production systems competing as power suppliers would be able to provide low-GHG-emitting synthetic fuels at the same unit cost as for coal synfuels characterized by ten times the GHG emission rate that are produced in plants having three times the synfuel output capacity and requiring twice the total capital investment. Moreover, the low-GHG-emitting synfuels produced by such systems would be less costly and require only half as much lignocellulosic biomass (or less) to produce as would cellulosic ethanol.
This strategy depends on the viability of CCS as a major carbon mitigation option, but all system components for the first generation of the required conversion technologies (including carbon capture components) are proven technologically, so that commercial-scale projects for co-production plants with CCS that have modest biomass input rates (~ 10%) could be demonstrated during this decade.—Liu et al.
The team used detailed process simulations, lifecycle greenhouse gas emissions analyses, and cost analyses in a comprehensive analytical framework to assess 16 alternative system configurations that involve gasification-based coproduction of Fischer-Tropsch liquid (FTL) fuels and electricity from coal and/or biomass, with and without capture and storage of byproduct CO2.
The analysis found that 9 of the systems in the study—including two cellulosic ethanol systems (with and without CCS) have greenhouse gas index (GHGI) numbers of less than 0.20, and represent low-carbon transportation fuel options. The GHGI represents lifecycle GHG emissions associated with the facility divided by lifecycle emissions for production and use of an LHV-equivalent amount of fossil fuel-derived products displaced—i.e., a GHGI of 1 would represent lifecycle GHG emissions equivalent to that of fossil-fuel derived products.
The study also found that both BTL-RC-CCS (biomass-to-liquids, with recycling of unconverted syngas to maximize FTL output and CCS) and cellulosic ethanol with CCS (EtOH-CCS) have negative GHGI emission values that can be exploited to offset GHG missions from difficult to decarbonize energy sources such as transportation fuels derived from crude oil.
The team also observed that GHG Avoided [GHGA = (1 - GHGI)·(lifecycle GHG emissions for the displaced fossil fuels] for BTL-RC-CCS is 56% higher than that of EtOH-CCS largely because 56% of the biomass carbon is stored underground for BTL-RC-CCS compared to only 15% for EtOH-CCS.
Guangjian Liu, Eric D. Larson, Robert H. Williams, Thomas G. Kreutz and Xiangbo Guo (2010) Making Fischer-Tropsch Fuels and Electricity from Coal and Biomass: Performance and Cost Analysis. Energy Fuels, Article ASAP doi: 10.1021/ef101184e