Energy and Exergy Analysis of Biogas-Powered Power Plant from Anaerobic Co-Digestion of Food and Animal Waste

Abstract

Despite the research that has been conducted on biogas production from different waste materials through the anaerobic digestion process, there are still limited studies on their application for thermal systems. This paper presents an energetic and exergetic analysis of a multigeneration system comprising a micro-gas turbine, an organic Rankine cycle (ORC), an absorption chiller, and a water heater. It uses energy from biogas combustion produced through anaerobic co-digestion of food and animal waste. The reported biogas yield from 3 different studies was used in designing the fuel input for the system. The results showed that substrate combination of poultry manure and food waste (Biogas-A) needs 35.07 tons of volatile solids (tons-VS/day) of waste compared to 33.11 tons-VS/day for Biogas-B (Cattle manure and food waste), and 81.87 tons-VS/day for Biogas-C (swine manure and corn straw). For an increase in the methane content from 40% to 60%, the substrate amounts were reduced by 42.3% for Biogas-A, 45.3% for Biogas-B, and 42.7% for Biogas-C. Likewise, for an increase in recuperator effectiveness from 65% to 95%, the substrate amounts reduced by 31.6% for Biogas-A, 30.3% for Biogas-B, and 31.4% for Biogas-C. Increasing the ambient temperature was shown to have an adverse effect on the performance of the system. The energy efficiency of the system reduced from 47.8% to 39.8% and the exergy efficiency reduced from 63% to 60% for an increase from 5◦C to 40◦C. The total exergy destruction of the system also increased from 1760 kW to 1885 kW. The results from this study will give an overview for future practical design for electricity production from waste and the choice of biomass materials to be utilized.