Improving Energy Utilization in Anaerobic Digester Power Systems

Abstract

This study investigates a 50 kW anaerobic digestion system to identify practical ways of improving energy utilization within the system. This digester system is operated with heat provided only from the biogas combusted in the engine-generator. Energy utilization in this study is thus considered as how best to apply this produced heat to overcome deficient operating temperatures in the colder winter months. A computer model was developed to simulate the system and was used to investigate outcomes of various design improvements. The most significant improvements could be obtained by increasing the heat recovered from the digester effluent and removing condensation from the biogas prior to combustion. The simulation results show that increasing the waste heat recovery unit effectiveness to 0.4 or higher allows for year-round performance without the need for supplemental heating. In addition, conditioning the biogas by chilling it from 35C to 20C (thus removing a portion of the moisture content) increases output energy from the engine-generator by almost 10%.