A Comparative Exergy Analysis of Advanced Power Cycles Using Biomass Fuel

This paper describes a design point study of different power generation systems using the gasification of sugar cane bagasse, which produces a low calorific value fuel. The biomass gasification is viewed as a process of drying the solid fuel and heating it up before the gasification reactions take place. The process is represented by equilibrium conditions. Varying pressure, temperature and feed composition in the gasifier controls the fuel gas composition. Five alternative arrangements of an integrated gasification combined cycle (IGCC) power plant have been analysed using the exergy method. These alternatives comprise a combined gas / steam cycle using a simple gas turbine and also a reheat gas turbine, a combined gas / air cycle using a simple gas turbine and also a reheat gas turbine, and a combined gas / air / freon cycle using a reheat gas turbine. The combined gas / steam cycles are more efficient rather than the combined gas / air cycles. Using a reheat gas turbine at the topping cycle of the combined cycles analysed contribute to increase the overall plant exergetic efficiency. The exergy analysis has been carried out along with the performance assessment of power plants and takes into account the irreversibility of their components and the exhaust losses. The gasifier is the component of the power plant that destroys maximum exergy. Three computer codes have been developed. One of them has the ability of simulating the thermodynamic properties of the low calorific value fuel in the gasification process and the other two are related to the performance analysis of the different power cycles using the exergy method. The production of energy from the gasification of sugar cane bagasse has been of increasing importance to the Brazilian energetic matrix. This paper has been focused on the GEOPHILES - αlfa Programme, a project to train Latin America engineers on biomass gasification for power generation. The Commission of Energy of the European Community has supported this project.