Dynamic analysis of a micro CHP system based on flame fuel cells

Micro combined heat and power (CHP) systems based on flame fuel cells (FFCs) are promising technologies for residential applications due to their simple setup and rapid startup. A dynamic model was developed in this paper for a micro FFC-based CHP system which consists of an FFC and a heat exchanger. At first, the operation conditions at the design point (system AC power output is 1.1 kW) and the part-load point (system AC power output is 0.7 kW) were determined respectively at steady state. An exergy assessment was conducted for each component and the whole system. It is found that at the design point, the heat exchanger accounts for the majority of the exergy losses. Then, the transient responses of the system components as well as the electrical and heat dynamics of the whole system were investigated when the operation conditions of the system ramped from the values at the design point to those at the part-load point. The electrical dynamic response of the CHP system, in terms of the output AC power shows a time delay of less than 50 s, while the thermal dynamic response, in terms of the generated heat shows a time delay of 300 s. The electrical dynamic response of the system is limited by the dynamics of the gas supply process of the fuel-rich burner. The thermal settling time of the system is governed by the thermal settling time of both the SOFC stack and the heat exchanger. The relatively slow thermal response under a transient electrical demand indicates that an additional heat storage is necessary in the FFC-CHP system.