The Use of Biomass Fuels in Gas Turbine Combined Cycles: Gasification jvs. Externally Fired Cycle

The use of biomass as gas turbine combined cycle fuels is broadly seen as one of the alternatives to diminish greenhouse gas emissions, mainly CO2, due to the efficiency delivered by such systems and the renewable characteristic of biomass itself. Integrated gasification cycles, BIGGT, are the current technology available, however the gasification system severely penalizes the power plant in terms of efficiency and demands modifications in the engine to accommodate the large fuel mass flow. This gives an opportunity to improvements in the current technologies and implementation of new ones. This paper intends to analyze new alternatives to the use of solid fuels in gas turbines through the use of external combustion, EFGT, discussing its advantages and limitations over the current technology. A study of the use of intercooled and recuperated cycles in conjunction with integrated gasification and external combustion is also carried out.

The results show that the intercooled and recuperated cycles are the best systems in terms of efficiency. However due to their complexity and given the already high costs of BIGGT and EFGT cycles their intercooled/recuperated counterparts are not likely to come into operation in the near future. On the other hand, the inherently recuperative characteristic of the EFGT gas turbine engine makes it well suited to the biomass market. The thermal efficiency of this cycle is much higher than the BIGGT system. Furthermore, its fuel flexibility is another advantage that makes it an interesting option for the Brazilian market.

Sandro Barros Ferreira, Pericles Pilidis, Marco A. R. do Nascimento