Farm-based biogas production, processing and use in PEM fuel cells

The use of biogas as an energy source in polymer electrolyte membrane fuel cells (PEMFC) with combined heat and power generation provides a clean and reliable option to replace conventional power generation with fossil fuels. From the point of view of energy and ecological policy, it has the advantage both of being a comparatively cost effective domestic regenerative energy source, as well as being a technology that unites high electrical efficiency with low pollution emission. The investigative experiments carried out confirm the fundamental suitability of cogeneration from Biogas with a modified fuel cell system for residential energy supply. The fuel cell system consists of the PEM fuel cell unit and a steam reformer with two stage shift converter and selective oxidation and is supplied with biogas from two solid state fermenters. The substrate used is a mixture of manure and corn silage. By adding manufactured gases, the methane content of the biogas is varied. Biogas with a methane content of about 60% is generated by solid state anaerobic digestion of cattle manure and corn silage. Biogas processing in a steam reformer results in a reformate gas with a hydrogen purity of more than 50% which is sufficient for an efficient and stable operation of a PEM fuel cell stack. The hydrogen concentration is dependent on the quality of biogas. The operation of the fuel cell at a current density of 0.2 A/cm2 offers a cell efficiency of more than 58%. The influence of the biogas methane concentration on the cell efficiency is slight in the range of low power density needed to achieve high efficiency.