The impact of fuel properties on SOFC-based power systems

The goal of this dissertation research is to investigate the effects of fuel properties on the performance of SOFC-based power systems through detailed thermodynamic analyses and experiments including the study of (1) SOFC system behavior; (2) integrated SOFC/Gas Turbine hybrid system behavior; (3) effects of fuel type (natural gas, landfill and digester gas, distillate fuel, and coal derived syngas); and (4) effects of impurities (e.g., ammonia) on SOFC system performance and emissions.; For the experimental part, a particular integrated 25kW SOFC reformer system located in National Fuel Cell Research Center is enabled to operate on various fuels such as natural gas, distillate fuel reformate, digester biogas, and gases derived from biomass or coal gasification. The fuel streams consist of some or all of the following species: hydrogen, carbon monoxide, carbon dioxide, methane, nitrogen and impurities (e.g., ammonia). Based on the theoretical understanding, simulation results and previous operating experience, detailed test procedures are designed and the required additional equipment is added into the current 25kW SOFC system to achieve the test goals. The integrated system performance and emissions characteristics of tubular SOFC systems with tolerance to a wide range of contaminants (CO, NH3, etc.) are then analyzed on the bases of system operation results and modeling.; Finally, the conclusions and recommendations from this study of the impact of fuel properties on SOFC-based power systems are developed and provided. The major conclusions include: (1) Both theoretical and experimental studies show operation of SOFC system on digester gas or diesel reformate is feasible and leads to system performance close to that of natural gas operation; (2) Operation of the SOFC system on coal derived syngas is much more challenging, however, leading to lower system efficiency at the design point and significant system thermal management challenges; (3) SOFC operation on various fuels does not result in any changes in the emission levels of major criteria pollutants (e.g., NOx, THC); (4) Operation of a SOFC/GT hybrid on various fuel sources is feasible. The SOFC module contributes to major exergy loss, but fuel cell exergy loss remains much smaller than that of a combustor used in a typical Brayton cycle. The major recommendations include: (1) further work on experimental study of NH3 performance as a contaminant in SOFC system, (2) experimental tests of SOFC system on coal syngas, (3) further theoretical study (e.g. transient performance study) and experimental tests of SOFC/GT hybrid system for operating on various fuel types. (Abstract shortened by UMI.)...