Combined dry and steam reforming of biogas for generation of H2 and CO rich fuel gas for SOFC

摘要

Biogas as renewable energy carrier offers great potential for the generation of electrical power. As a new approach a system including combined dry and steam reforming and a high temperature Solid Oxide Fuel Cell (SOFC) can improve the efficiency of electrical power generation from biogas at varying gas qualities when using the anode off-gas for supplying the necessary heat of the reforming reaction. Biogas mainly consists of methane and carbon dioxide with fluctuating concentrations. Therefore the dry reforming of biogas using the CO2 seems to be the most interesting reforming reaction. However, due to potential carbon formation during reforming at given biogas compositions, additional steam as oxygen carrier is necessary resulting in a combined dry and steam reforming. This paper is focused on the design and performance data of a reformer module that has been developed for reforming cleaned biogas from a sugar plant waste water facility for coupling with a SOFC with an electrical power output of 1 kW. The reformer module consists of an evaporator, a super heater and a reformer/burner reactor. To obtain a high heat transfer metallic structures have been chosen for the reformer/burner reactor. Thermodynamic simulations have been made with focus on the boundary conditions of carbon formation at different CH4 concentrations. Based on these data the reformer module has been designed and characterised. Tests have been performed at different O/C ratios resulting in a good agreement between thermodynamic simulations and experimental results. No carbon formation could be detected in the reformer. Simulation results, thermodynamic calculations, system design and integration as well as experimental results regarding gas qualities and temperature profiles of the reformer module will be presented in this paper.