MICRO-GAS TURBINE CYCLE CONFIGURATIONS FOR BIOMASS COMBINED HEAT AND POWER PLANTS

The potential of integrating micro-gas turbine systems into biomass micro-Combined Heat and Power (CHP) units is investigated, following a thermodynamic analysis. Various cycle configurations are elaborated, utilising the producer gas of an existing biomass gasification CHP unit, with a capacity of 30 kWe. The reference CHP unit consists of a fluidised bed gasifier coupled with a gas treatment unit, a gas cooler and an Internal Combustion Engine (ICE). The gas cooler operation is entailed with environmental issues, concerning tar condensation and removal. In this paper, alternative approaches of direct fuel combustion, at elevated temperatures, through micro-gas turbine systems are investigated. Five configurations, based on the internally-fired (simple and recuperative mu-GT) or the externally-fired gas turbine ( mu-EFGT), as well an additional reheated micro-gas turbine (mu-RHGT) are considered. The mu-EFGT is investigated for two cases: unfiltered (UF) and filtered (F) producer gas fuel. Each configuration is optimised, using in-house solvers, while the components are modelled using turbomachinery and heat exchanger detailed designs. The recuperative mu-rGT and the unfiltered mu-EFGT/UF show a similar electrical efficiency of around 31.5%, while the overall efficiencies are 63% and 74.8% respectively, which is improved by 5%, compared to the ICE. Challenges related to fuel compression, mainly due to the high rotational speed, are expected in the mu-rGT case, while fouling is expected to be a serious challenge in the mu-EFGT/UF case. Both challenges can be addressed by the filtered mu-EFGT, however, this results in lower electrical efficiency, around 26.5%, which is -12% compared to the ICE.