Entwicklung eines autothermen Methanol-Gasprozessorsystems für PEM-Brennstoffzellen

Abstract

Fuel cells (FC) show great prospect for clean generation of electricity from chemically bound energy. Commonly hydrogen is used as fuel. In cases of high or prolonged energy needs without access to H2 distribution lines, reforming of hydrocarbons or alcohols to hydrogen rich gas shows great potential to circumvent most technical issues. Methanol is considered as a prime H2-carrier due to its high energy density and relatively moderate process parameters for its conversion. Especially the field of portable power generation can benefit from this alternative source of H2. In this thesis the process for generation of hydrogen rich reformate is further developed to satisfy the restrictive needs of portable systems of up to 1,2 kWel. Autothermal reforming (ATR) of methanol is considered the most promising approach for simple and rugged gas processor systems. By partial shift towards steam reforming, the efficiency of the reforming process can be enhanced. The basic principle of ATR in porous plates was therefore expanded by integration of heat supplied from anode off-gas combustion. Reactant and heat distributions of the reformer/heat exchanger module were enhanced by transfer of manifold and flowfield structures known from fuel cells, into equivalent geometries within the reformer. In order to achieve a sufficiently low CO concentration for FC usage an internally cooled cleanup stage for preferential oxidation (PrOx) was developed. The integration of the vaporizer for the liquid reactants methanol and water kept the PrOx catalyst in a nearly ideal temperature range, so that a significantly shortened catalyst bed could be achieved. The modules were first investigated separately, then in conjunction as a gas processor system optimized for portable applications.