Design and Thermo-Economic Analyses of Solid Oxide Fuel Cell-Gas Turbine Hybrid Systems with Water Recovery
Highly efficient electric power systems are crucial for the reduction of carbon emissions from fossil fuels, as well as, in a circular economy where renewable fuels like biogas, biomass and hydrogen need to be converted to electricity in an efficient manner to minimize the environmental footprint. Moreover, current thermoelectric electricity generation requires enormous amounts of water, primarily for cooling or heat rejection, which creates tensions and interdependencies between the electricity sector and the water sector. To address these concerns, this dissertation focuses on the design of highly efficient, economically viable solid oxide fuel cell (SOFC)-gas turbine (GT) hybrid systems to minimize the environmental impact of electricity generation including the water use, and further addresses the system integration and the economics of flue gas water recovery technologies.Two of the greatest challenges to widespread adoption of SOFC technology are thermal cell management and costs. Applying a unique bottom-up SOFC cost approach, cell design parameters are identified that synergistically reduce thermal gradients and specific SOFC stack cost. Using this optimized cell design, the SOFC stack is integrated into a SOFC-GT hybrid system. Through research of this SOFCGT hybrid system over a wide range of pressure conditions, fuel utilization factors, and operating voltages, cost-competitive operating points and major cost driving factors contributing to the cost of electricity are identified while considering thermal SOFC and GT aerodynamics constraints associated with SOFC-GT systems. Based upon the results of the hybrid system design study, multiple water recovery technologies, such as an air-cooled condenser, a direct contact condenser, a LiBr absorption system, a monoethylene glycol absorption system and a transport membrane condenser, are integrated into the hybrid and studied in combination with various fuel types at numerous scales. In the studied configurations, the direct contact condenser and the transport membrane condenser suffer from low water recovery rates, while the air-cooled condenser’s large pressure drop leads to substantial system integration losses. The absorption systems achieve the highest water recovery rates and the LiBr absorption system exhibits the most favorable economics. The absorption systems are particularly advantageous in biogas scenarios where the latent heat can be upgraded and made available to the digester.