Most of the processes using wood fuels in gas turbine applications that are presently being studied are based on gasification of the wood fuel and operating the gas turbine with the product gas. An alternative is running the gas turbine with the hot gas from a wood combustor — the directly wood particle fired gas turbine. This technique offers the possibility to realise efficient and cost effective small scale power generation systems in the low power range (1–2 MWe). For realizing a directly wood particle fired gas turbine, the Institute of Thermal Turbomachines and Powerplants at the Vienna University of Technology developed a two stage combustor. Solid and liquid fuels require relatively long residence times and good mixing with the oxidant to be completely burned. This can be achieved in the primary stage designed as a cyclone combustor/gasifier. In the cyclone chamber, burning fuel particles are suspended, according to their size, caused by centrifugal and drag forces. This cyclone effect of the flow offers the possibility that big particles remain in the cyclone combustor until they have been completely burned. Using a two stage combustor, the combustion process can be divided into two zones: A primary zone for fuel-rich pyrolysed-gasified-combustion and a secondary zone where the gasification products from the primary zone are oxidized with excess air. Staged combustion has the potential to reduce NOx (NO, NO2 and N2O), CO and total hydrocarbons CnHm concentrations in the exhaust. A large series of test runs was carried out with 3 different fuels, numerous fuel feed rates and equivalence ratios in the cyclone combustor resulting in stable operating conditions and almost total carbon burn-out. The main purpose of the test runs was to investigate the effect of air staging and temperature on the emissions of CO, CnHm and NOx.

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