A Biogas Fuelled Micro Gas Turbine: Energetic Performance and Environmental Impact Analysis.

The use of biogas in micro gas turbines (MGTs) generally requires invasive structural modifications to fuel compression units, control valves and combustor. Costs associated with the modifications significantly reduce the benefits of a rational and sustainable exploitation of energy resources of lower value as the biogas. In order to overcome this aspect, in a recent paper the authors proposed a dual fuel approach, identifying a structurally non-invasive and cost-effective technical solution to increase the CO2 concentration in the fuel and to extend the operation domain of the MGT when low calorific value fuels are used. In that study, it has been evaluated, implemented and tested an innovative management strategy of fuel feeding and combustion. Experimental preliminary tests validated the idea of a new supply strategy for exceeding the current limits of biogas exploitation as MGT fuel. With this approach the MGT operating domain has been extended, increasing more than twice the CO2 concentration limit than experimentally validated limit available in literature. In this study the authors present a more extensive investigation concerning the energetic performance and the environmental impact of a 100 kWe MGT Turbec T100 when fuelled with a mixture of natural gas and carbon dioxide (synthesis biogas) in the dual fuel approach, by varying CO2 concentration in the fuel at part load condition. The data acquired by an extensive experimental campaign, in terms of thermodynamic parameters and gaseous exhaust emissions, are presented and compared with the results of numerical simulations. A 3D CFD analysis of the combustion process is also presented. Initial and boundary conditions of the numerical approach were obtained from a previous validated 0D thermodynamic matching model. The synergistic activity between numerical modeling and experimental work allows to analyze and explain the overall behavior of the micro gas turbine in the dual fuel mode with biogas fuel. The study shows that the micro gas turbine can stably operate in a dual fuel mode until the CO2 content rises above 25%.