Previously published studies have addressed modifications to the engines when operating with biogas, i.e. a low heating value (LHV) fuel. This study focuses on mapping out the possible biogas share in a fuel mixture of biogas and natural gas in micro combined heat and power (CHP) installations without any engine modifications. This contributes to a reduction in CO2 emissions from existing CHP installations and makes it possible to avoid a costly upgrade of biogas to the natural gas quality as well as engine modifications. Moreover, this approach allows the use of natural gas as a “fallback” solution in the case of eventual variations of the biogas composition and or shortage of biogas, providing improved availability. In this study, the performance of a commercial 100kW micro gas turbine (MGT) is experimentally evaluated when fed by varying mixtures of natural gas and biogas. The MGT is equipped with additional instrumentation, and a gas mixing station is used to supply the demanded fuel mixtures from zero biogas to maximum possible level by diluting natural gas with CO2. A typical biogas composition with 0.6 CH4 and 0.4 CO2 (in mole fraction) was used as reference, and corresponding biogas content in the supplied mixtures was computed. The performance changes due to increased biogas share were studied and compared with the purely natural gas fired engine. This paper presents the test rig setup used for the experimental activities and reports results, demonstrating the impact of burning a mixture of biogas and natural gas on the performance of the MGT. Comparing with when only natural gas was fired in the engine, the electrical efficiency was almost unchanged and no significant changes in operating parameters were observed. It was also shown that burning a mixture of natural gas and biogas contributes to a significant reduction in CO2 emissions from the plant.
A micro gas turbine for UK domestic combined heat and power
