Studies on the energy demand of two-stage fermentative hydrogen production from biomass in a factory equipped with fuel-cell based power plant

A conceptual factory to produce hydrogen from starchy biomass is considered. The production plant comprises a pretreatment unit for starchy raw material, a bioreactor for dark fermentation, a photobioreactor for photofermentation and gas upgrading & compression units, and is supplied with the necessary heat and power from the power plant. In the power plant, a part of the stream of raw gas produced in bioreactors is burned in a steam boiler and in addition some product gas from the upgrading unit is directed to fuel cells from which waste gas flows to a catalytic oxidizer. The demand for process heat is covered by steam generation in the boiler and oxidizer, and the power demand is covered by electricity generation in the fuel cells. The energy demand is studied as a function of selected process parameters; among them, CO2 content in the product gas is of key importance. Conclusions are presented regarding the practicability of using own-produced hydrogen for the energy supply.