Simulation of externally fired gas turbine configurations for micro-scale biomass applications

Abstract

Most rural communities in South Africa are forced to rely on alternative energy resources such as biomass, gas, liquid fuels and waste materials for the provision of energy to fulfil their lighting and cooking needs since electrification in rural areas is problematically low. Biomass as a source of renewable energy is a promising, ecological and sustainable solution for electricity generation. A micro-scale externally fired gas turbine (EFGT) fuelled by biomass provides a suitable solution for electricity generation in rural areas. The EFGT holds the advantage of being able to operate with poor quality and a variety of biomass fuels since the combustion gasses is not in direct contact with the working fluid of the cycle. The purpose of this study is to evaluate different EFGT configurations using thermal-fluid simulation models developed for micro-scale EFGT biomass applications, typically with an electricity generation capacity in the region of 5 kW that will be suitable for a small rural community. The conceptual simulation models can be used to assist farming and rural communities, who are interested and capable of implementing micro-scale generation to fulfil their basic electricity needs, to gain practical insight into different cycle configurations and its operating conditions. Verification was done by comparing the results of the simple EFGT cycle configuration against that found in the literature of a similar biomass cycle. The comparative results were within 5% correlation. Within this study, four different system configurations of a micro-scaled EFGT cycle were modelled with different levels of complexity, but with rural applications in mind. The different cycle configurations were evaluated for different operating conditions and component efficiencies. The performance of the EFGT cycles was investigated to evaluate the effect of varying parameters such as turbine inlet temperature, mass flow of air, combustion heat and COP of the pre-cooling unit respectively. The individual models showed promising results, such as cycle efficiencies ranging from 12.58% for the simple cycle 30.07% for the heat recovery cycle with pre-cooled air.