CO2-neutral co-produced gas utilization for deep geothermal applications

Abstract

The purpose of this paper is to identify a suitable and CO2-neutral geothermal co-produced gas utilization for a use case in the German Molasse Basin. Therefore, different approaches, based on gas engines, are compared to each other. The investigations are based on heating values from existing measurements of the actual co-produced gas composition. An oxyfuel-based concept with flue gas recirculation has been determined to be the best suitable option, since it allows the reinjection of the entire flue gas into the geothermal brine. The approach for the technological adaption of the gas engine is based on the adiabatic flame temperature in order to identify comparable operational regimes and the necessary flue gas recirculation rate. Necessary reinjection pressures are calculated based on hydrogeochemical equilibrium calculations, showing general feasibility of the reinjection as well. An analysis of the energy balance and the resulting energy streams shows an electric power output of 94.9 kW and an additional heat output of at least 256.2 kW, when the power consumption for the air separation unit is taken into account as well.