Development of an Autothermal Biogas Processor for Hydrogen Production

摘要

In this paper a novel concept for biogas reforming is presented. Major novelties are the utilization of an autothermal or oxidative steam reforming in combination with a subsequent catalytically coated soot trap for soot retention and oxidation as well as enhancement of the water gas shift reaction. The plant design of the BioRobur (Biogas robust processing with combined catalytic reformer and trap) processor has been realized on the basis of ASPEN PLUS? mass and energy flow modeling. The system efficiency depends on the reforming route (catalytic partial oxidation, steam reforming or autothermal reforming), the level of heat integration, the preheating temperature of the mixed reactants, the steam-to-carbon- and oxygen-to-carbon ratio as well as the usage of the off-gas from pressure swing adsorption (PSA). The highest efficiency is achieved with an autothermal reforming in the first place. Through the energetic usage of the PSA off-gas in an extra burner and a sophisticated heat integration a system efficiency up to nearly 70% is realizable. Without the two mentioned possibilities the efficiency trops down to 50%. In addition, detailed numerical simulations of the transient gas flow inside the catalyst have been conducted in order to evaluate the performance of different geometries for the catalyst support regarding their ability to support the catalytic conversion process at a moderate pressure loss. Exemplary results of a sensitivity analysis based on calculations in ASPEN PLUS? are shown. Furthermore, the results of CFD and FEM simulations on different catalyst support geometries are presented. Structures composed of Kelvin cells were found to be the best catalyst support due to their enhanced dispersion coefficient while at the same time featuring lower pressure loss as compared to the modified octet cells. Additionally, the Kelvin cell shows both high effective thermal conductivity and relatively high specific surface area.