Coal Energy Conversion with Aquifer-Based Carbon Sequestration: An Approach to Electric Power Generation with Zero Matter Release to the Atmosphere Investigators Reginald E. Mitchell (PI), Associate Professor, Mechanical Engineering; Christopher Edwards, Associate Professor, Mechanical Engineering; Scott Fendorf, Associate Professor, Department of Geological and Environmental Sciences; Adam Berger, Byunghang Ha, John (J.R.) Heberle, BumJick Kim, Andrew Lee, and Paul Mobley, Graduate Researchers, Stanford University Abstract This project has the objective of providing the information needed to develop a coal- based electric power generation process that involves coal conversion in supercritical water (SCW) with CO 2 capture and storage. In efforts to date, we have constructed a system-level model of the proposed plant that can be used to evaluate the viability of the overall concept in terms of efficiency. In the thermodynamic analysis, the coal composition is based on that of a sub-bituminous coal. The combustion products stream is treated as an ideal solution of real fluids (water, oxygen, carbon dioxide, and nitrogen), with property data computed using a linear mixing rule. The Brayton cycle helium heat engine is modeled as an ideal gas. The work requirement for the air separation unit used to obtain process oxygen is taken from the literature. Aquifer conditions and well pressure losses used to calculate the work requirements of the aquifer water pumps are also taken from the literature. Representative state-of-the-art values are used for other component performance parameters. The model was used to calculate the power balance for a 500 MW power plant. For a combustor outlet temperature of 1650 K and a Brayton compressor inlet pressure of 79.5 bar, overall efficiency, after energy penalties for oxygen separation, carbon sequestration, and non-ideal components, is just over 42% on a lower heating value basis. The model indicates that the overall efficiency of the system increases with combustor outlet temperature. For a selected outlet temperature, the overall efficiency usually increases with the Brayton inlet pressure, however at certain inlet pressures, the combination of conditions in the SCW system loop causes decreased efficiency. Also to date, the reactor that will be used in tests to characterize coal extraction, devolatilization and gasification in SCW environments has been designed and built. It provides up to 125 s of reaction time under isothermal conditions. A base-case coal for study has been selected and the models that will be developed to predict coal extraction and devolatilization rates in the reformer have been identified. Development of a reaction mechanism that describes the rate-limiting reaction pathways during reaction between char and water vapor has also been initiated. The major hardware for the supercritical water combustor experiments has been identified and an experimental facility that will permit various burner geometries to be tested has been planned. A high-pressure stack consisting of a reactant preheater, a supercritical combustor, an experimental heat exchanger, and a cooling section has been designed.