A new process concept for highly efficient conversion of sewage sludge by combined fermentation and gasification and power generation in a hybrid system consisting of a SOFC and a gas turbine

Abstract

Sewage sludge can be disposed of by fermentation, incineration or gasification. Conversion of the resulting biogas, combustion heat or gasification gas into electricity is often employed. Since sewage sludge cannot be fermented completely and due to the significant heat requirements for drying it in the incineration plant or before the gasifier, the electrical output in all cases is very low. Consequently, this work seeks to investigate a combination of fermentation and gasification in which dried fermentation waste is converted in a gasifier. With the aim of combining these two biomass conversion processes with power generation in an efficient manner, a hybrid system consisting of a SOFC and a gas turbine is investigated. This combination of a biogas plant and a gasifier has the advantage that waste heat can be used as a heat source in drying the fermentation waste. Another advantage is the combined conversion of biogas and gasification gas in the SOFC. As steam from gasification gas is used for internal reforming of methane out of biogas at the anode of the SOFC, the complexity of the plant is reduced and the efficiency is increased. A configuration including a pressurized gasification process was identified as most efficient in terms of electrical output.