Considering the expected climate change biomass is one of the promising energy sources for the future; however, burning and only producing low temperature heat means wasting exergy. To utilize this renewable fuel highly efficient cogeneration plants are required. Existing small and medium sized power generation systems using gas turbines have either complicated flow sheets or problems with charging pressurized combustion chambers, which are not yet solved.
This project deals with the investigation and the development of an atmospheric biomass combustion chamber combined with an inverted gas turbine cycle followed by a steam cycle. The system consists of a combustor with a wood grate firing working at atmospheric pressure. A gas turbine expands the hot particle loaded exhaust gas with a temperature of about 800 to 1000°C from atmospheric pressure down to a pressure of about 0.35 bar. The exhaust gas of the turbine is used for operating a single-pressure steam generator, the steam is mainly utilized for power generation in a steam turbine, a part stream is used to control the gas turbine inlet temperature depending on the moisture content of the fuel. The gas outlet temperature of the steam generator is about 186°C (Fig. 1, p6) at a pressure of 0.3 bar, one part is used for preheating the air required for combustion, the other part is cooled down by water injection, whereby ashes and particles are separated. The cleaned gas is compressed to atmospheric pressure again (Moser, 1995).
Such a system can achieve an efficiency of up to 40 % in the MW electricity range using components, which are available on the market, and at the same time it demonstrates the possibility of highly efficient biomass utilization.