Numerical investigation of a dual-stage off-gas burner to support high pressure and high temperature solid oxide fuel cell/gas turbine (SOFC/GT) hybrid systems

Abstract

The objective of this study is to investigate the challenges associated with burning these off-gases and to develop a simple yet efficient combustor to support solid oxide fuel cell/gas turbine hybrid power systems. As a result of operating of the fuel cell under conditions of high fuel utilization, a solid oxide fuel cell produces high temperature exhaust gases on the anode side that are of low heating value, and depleted air with low oxygen content on the cathode side. Anode off-gases characterized by heating values less than 2 MJ/m3 and cathode off-gases with as little as 9 vol % oxygen concentration present a challenge for achieving stable combustion. In this study, the focus is on the development of a dual-stage combustor for low-calorific solid oxide fuel cell off-gases at combustor inlet temperatures up to 1100 K. In addition to taking advantage of high temperature off-gases to support the stable combustion of these low heating value off-gases, the influence of elevated-pressure combustor operation (set by the solid oxide fuel cell operating pressure) is investigated. Initially, a chemical reactor network is developed and used to simulate mixing and flow characteristics of a typical gas turbine combustor operating on the aforementioned fuel/air mixtures at the elevated operating conditions. These results are then used to inform a dual-stage burner design in the form of a computational fluid dynamics model for simulations incorporating both flow and combustion dynamics. The final parameters that are used to evaluate the final design are criteria pollutant emissions such as carbon monoxide and oxides of nitrogen, as well as suitable temperature profiles across the burner.