A team at Stanford University is proposing using solid oxide fuel cells as the basis for a method for electricity production from oil shale with in situ carbon capture (EPICC) as a means to provide transportation services from oil shale with greatly reduced CO2 emissions.
Oil shale contains large amounts of stored chemical energy: over 1 trillion barrels of oil equivalent is present in the Green River formation of the United States alone. Unfortunately, extraction of energy from oil shale generally releases significant quantities of greenhouse gases (GHGs). Liquid hydrocarbon (HC) fuels derived from oil shale have 1.2−1.75 times the fuel cycle GHG emissions of HC fuels produced from conventional oil. This paper proposes a concept that could provide transportation services from oil shale with significantly reduced carbon emissions, called electricity production with in situ carbon capture (EPICC). EPICC reduces CO2 emissions by (1) utilizing waste heat to retort shale; (2) retorting shale beyond the point of liquid hydrocarbon production, converting much of the organic carbon in oil shale to char which is left in the subsurface; and (3) using the produced HC gas to generate electricity, which provides transportation services with no tailpipe emissions. The resulting life cycle GHG emissions from EPICC amount to ≈110 g of CO2 per km, ≈0.5 times those of conventional fuel cycles or ≈0.33 times those from other proposed in situ oil shale conversion processes. Potential drawbacks of EPICC include uncertain operation of subsurface fuel cells, potential geophysical impacts without pressure management, and economic concerns associated with the value of stranded energy left in the formation and the long time period of retorting.
EPICC is designed to maintain, to the extent possible, a bulk shale temperature below that at which significant carbonate mineral decomposition to CO2 occurs, since this would render it impossible to produce low-CO2 electricity. Because of the volumes of produced gases generated during retorting and cracking of HCs, EPICC is in most cases a self-fueled process.
A key factor in the efficiency and low-CO2 nature of EPICC is the “rearrangement” of the order of the conventional transportation fuel cycle. The chemical energy contained in the shale is converted to work (e.g., electricity) in the subsurface, rather than in distributed internal combustion engines, allowing waste heat from work conversion to supply the heat of retorting. In other words, retorting thermal demands are provided by the waste heat that is unavoidably generated with any conversion of chemical energy to work. Also, conversion to work occurs in a centralized location, enabling easier control of resulting CO2 emissions (although this is not explored here).
EPICC should not be viewed as a method to produce natural gas from shale: such methods would consume significant amounts of primary energy and result in a lower value product than the oil that was destroyed to produce gas. Instead, EPICC produces gas as an intermediate product, and the waste heat output from conversion of this gas to electricity provides the driving heat for kerogen decomposition and cracking of hydrocarbons. Thus, the heat integration with electricity production is a fundamental part of the EPICC concept.
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