Energy balance and efficiency analysis for power generation in internal combustion engine sets using biogas

Abstract

This paper presents an example of the energy balance and the efficiency analysis for power generation in internal combustion engine sets using biogas. Water-cooled engine can effectively reduce the cylinder wall temperature. Therefore, the working conditions of the cylinder components could be improved. Result of energy balance and efficiency calculation show that the engine set can generate electricity of 70.0kW under a biogas yield of 34.84m3/h in the standard state with the energy efficiency of 28.45% and the exergy efficiency correspond to 27.36%. The energy consumption of electricity generated was 432g coal equivalent (kce) per each kWh. The thermal energy dissipated from the engine exhaust was the greatest of all and it was accounting for 40.34%. Whereas the recoverable thermal energy dissipated from the water in the cylinder jacket was approximately 26.86%. Thermal energy dissipated by radiation and convection from the engine only accounted for 2.99% of total energy input. How to improve the energy efficiency of biogas processed was discussed in this paper, for example, the biogas purification (removal of CO2 and H2S) to enrich methane in biogas, can be used for the power fuel, meanwhile, it enhances the efficiency of power generation. A CHP efficiency of over 80% can be achieved if heat of both the exhaust gas and water heated within the cylinder jacket is utilized.