Pneumatic Fuel Feeding of a Directly Wood Particle Fired Gas Turbine Under Special Consideration of Low Conveying Air Ratio

Abstract

In order to reduce the production of green house gases, the combustion of biomass has been gaining importance in electricity generation. Especially the direct combustion of biomass in gas turbines of a few MW output would offer a very attractive option because of low investment costs and high operational flexibility. Therefore, since 1991 the Institute of Thermal Turbomachines and Powerplants at the Vienna University of Technology has been working on realising a wood particle fired gas turbine with direct combustion. With reference to earlier studies (c.f. Hamrick (1991), Fredriksson and Kallner (1993)), it had been concluded that the design and the operating characteristics of the fuel feed system would strongly influence the combustion and so would be a very important part of the whole facility. Following an overview of the planned gas turbine test facility including the combustion chamber and the recently installed pneumatic fuel feed system, the paper will deal with three basic requirements of fuel feeding in the case of a directly fired gas turbine: feeding against back pressure, continuous fuel flow rate and a low conveying air ratio, which is the ratio of fuel conveying air to total combustion air of the combustion chamber. While the first two requirements, i.e. feeding against back pressure and continuous feeding, are briefly considered, the minimisation of the conveying air ratio is discussed in detail. For instance, important parameters affecting the conveying air ratio are fuel moisture, combustion air ratio and, in particular, techniques. Following theoretical estimation of the conveying air ratio, results of fuel feeding measurements are presented and conclusions drawn with respect to system integration.