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Amreica’s Enery Future: Technology and Transformation
MTG technology is considered by the committee to be commercially deployable today; a number of projects are in fact moving toward commercial deployment. Meanwhile, several variations on the technology, which could provide improvements, are ready for commercial demonstration.
While the technologies involved in thermochemical conversion of coal have all been commercialized and their operators have logged years of experience, geologic storage of CO2 has not been adequately developed and demonstrated. For power generation from coal, most of the costs for CCS are in the CO2 capture part of the process, and this technology has been demonstrated on a large scale. However, geologic storage of CO2 in the subsurface has not been developed and demonstrated, except for use in enhanced oil recovery, and so there is insufficient confidence in its efficiency and long-term efficacy for commercial application at required scales. This is an important consideration for coal-to-liquid-fuels technology, as its CO2 emissions are high because of the high carbon content of coal (about twice the carbon content of oil). Even with geologic storage of CO2, the well-to-wheel emissions from coal-to-liquid fuels are about the same as those of gasoline because, as for any hydrocarbon fuel, CO2 is released when the fuel is combusted in vehicles.
Inclusion of biomass in the feedstock with coal decreases the greenhouse gas life-cycle emissions because the biomass takes up atmospheric CO2 during its growth. Thus, it is possible to optimize the biomass-plus-coal indirect liquefaction process to produce liquid fuels that have somewhat lower life-cycle greenhouse gas emissions than does gasoline, and even to make carbon-neutral liquid fuels if geologic storage of CO2 is used. Although the notion of gasifying mixtures of coal and biomass to produce liquid fuels is relatively new and commercial experience is limited, several demonstration units are currently running in Europe. The committee judges that the technology for co-feeding biomass and coal is close to being ready for commercial deployment.
Gasifiers for biomass alone, designed around limited biomass availability, operate on a smaller scale than those for coal and thus will be more costly because of the diseconomies of scale of small plants. However, the fuels produced from such plants can have greenhouse gas life-cycle emissions that are close to zero without geologic storage of CO2, and they can have highly negative carbon emissions if geologic storage of CO2 is employed. The committee judges that standalone biomass gasification technology is probably 5–8 years away from commercial scale-up.
Working with the Princeton Environmental Institute, the committee analyzed the costs and CO2 balances for thermochemical conversion of coal and biomass.