Tenth Year Annual Report:
Carbon Capture: 2000-2010 Accomplishments
Paths to a Hydrogen Economy
The original goal of Bob Williams and colleagues was to find opportunities for lowering the costs of the "hydrogen economy," focusing on generation of hydrogen and electricity at coal plants with CCS. The group's initial studies on novel hydrogen separation membrane reactors gave way to research on similar plants that employ "commercially ready" gas separation technologies, as it was found that the advanced technology offered little or no economic benefit. Using existing technology, the researchers showed that hydrogen produced via coal gasification and with CCS could be cost-competitive with hydrogen from natural gas. The team also showed that the economics of CCS could be improved by co-storage of other acid gases (especially H2S) with CO2. However, the researchers also found that high infrastructure investments needed to shift from gasoline and diesel to hydrogen as a transportation fuel suggest that, at best, hydrogen use in transportation is an option for the very long term.
Reducing Emissions of Coal-Based Synfuels
Early work by the Williams Group in collaboration with Chinese colleagues highlighted the climate change risks associated with making synfuels from coal—showing that if the CO2 generated at coal synfuels plants is vented, greenhouse gas emissions would be almost double the rates for hydrocarbon fuels derived from crude oil. However, over the years the team identified strategies for producing dimethyl ether and Fischer-Tropsch liquid fuels and gasoline with CCS that halved their net emissions, making them comparable to those of crude oil-derived fuels, and showed that the cost penalty for CCS is likely to be modest. The team also showed that plants that produce coal synfuels with CCS would be able to offer CO2 for enhanced oil recovery (EOR) at much lower prices than could power plants with CCS, and that CO2 EOR applications would significantly improve the economics of synfuels production.
Exploiting Negative Emissions from Biomass Gasification with CCS
Another focus of the Williams Group has been finding economical ways to exploit the "negative" emissions made possible by using thermochemical biomass conversion strategies with CCS. Work by Eric Larson and colleagues has shown that large-scale biomass gasification plants that make fuels and electricity with CCS can provide dramatic reductions in GHG emissions. The biomass gasification strategy the group has evolved can be carried out with technology that is close to being commercially available and would likely be economically viable with a GHG emission price ~ $100 per tonne CO2eq.
Hybrid Fossil Fuel-Biomass Systems for Making Fuels and Electricity
The promising results of the Williams Group's studies on coal synfuels and biomass prompted the researchers to examine strategies that exploit simultaneously the low price of coal, the scale economies of coal energy conversion, and the negative emissions potential of thermochemical biomass conversion with CCS. As a result, Williams and colleagues have built up an extensive and unique capacity for modeling hybrid energy systems producing both fuels and electricity from a combination of coal and biomass feedstocks, and they have recently extended the analysis to include combining natural gas and biomass.
The group's results show that, under a wide range of circumstances, synfuels can be produced at lower cost in systems that produce electricity as a major co-product than in systems that make mainly liquid fuels. Moreover, such systems co-processing ~ 30% biomass can provide electricity with 90% reduction in greenhouse gas emissions at lower cost than can stand-alone power plants in a world with $90 a barrel oil and a GHG emissions price of $40 a tonne of CO2eq, The decarbonized synthetic transportation fuels so produced would be less costly than and would require less than 40% as much biomass per unit of low-C fuel as would next-generation biofuels such as cellulosic ethanol.
Coupling Wind and Natural Gas via Compressed Air Energy Storage
For several years the Williams Group explored the prospects for making low-carbon baseload power from wind plus natural gas-fired compressed air energy storage systems that would simultaneously address the intermittency of wind power and enable, via high-voltage, longdistance transmission lines, exploitation of abundant wind resources that are remote from electricity demand centers. Such systems would enable both wind and natural gas to compete in baseload power markets. Their results show that that these baseload power systems are likely to be competitive with coal electricity with CCS when GHG emissions prices are high enough to make the latter cost-competitive, and that locations of high-quality wind resources and deep aquifers for air storage are well correlated. The major uncertainty in this area is the extent of storage reservoirs that are truly suitable for air storage in windy regions.