Performance and efficiency of a biogas CHP system utilizing a stirling engine

Abstract

A Stirling engine utilizes external combustion to produce heat and electricity. Due to the external combustion chamber, the engine can utilize a multitude of fuels including biogas or natural gas. The system used in this study is capable of producing about 7 kW of heat and 1 kW of electricity. Nitrogen is used as the “working fluid” in the engine. The heat from the combustion chamber is circulated through a cooling system making use of the thermal energy. The system includes a battery bank for energy storage and has been equipped with various instruments used to measure temperatures, pressures and flow rates of the fuel, the combustion air and the coolant. The engine is operated using natural gas as well as biogas and the engine characteristics for each are compared. The data collected is used to determine the system performance, thermal and electrical power outputs, individual and overall efficiencies, as well as exhaust emissions (O2, CO, CO2, NOx and HC). This paper will present a detailed description of the CHP system, the instrumentation, the test procedures, the test data, analysis of the results and comparison of the biogas and natural gas test results.