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 utilise this renewable fuel, highly efficient cogeneration plants are requierd. Existing, small and medium sized power generation systems using gas turbines, have, either complicated flow schemes, or problems with fuel charging of pressurised combustion chambers, which are yet to be solved.

Here is a solution is presented requiring no preparation of the biomass fuel. In several publications (Jericha 1991, Fesharaki 1995, Fesharaki 1996) the inverted gas turbine cycle has been presented. This project deals with the investigation and the development of an atmospheric biomass combustion chamber, combined with an inverted gas turbine cycle. The system consists of a combustor with wood grate firing, working at atmospheric pressure. The exhaust gas from the combustor, with a temperature of 1050 °C, is cooled by water or steam injection, to a temperature of 730 °C. The exhaust gas is purified in a cyclone and expanded in a gas turbine to a pressure of 0.3 to 0.4 bar. The exhaust gas of the turbine can be used for operating a single-pressure steam generator, and for district heating. The exhaust gas is purified again by condensing the moisture in the exhaust gas, which stems from the biomass and the steam, or water injection after the combustion chamber. The purified gas is recompressed to atmospheric pressure, which is used for combustion-air preheating. With such a system a high electrical efficiency can be achieved, dependent upon the turbo machines, and the use of an additional bottoming steam cycle.

Considering the Austrian situation a feasibility study is being carried out. Special attention has been paid to:

Turbine design,

Exhaust gas purification,

and the cycle control. The feasibility study shows, that this concept is practicable, and that several biomass existing heating systems in Austria could be converted for production of electricity.

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