Tars and the combustion of biomass derived low calorific value gas in a gas turbine combustor

At the end of 2001 until mid 2002, fourteen full day experiments were successfully performed with an air blown pressurized fluidized bed gasifier of 1.5 MW_th. Three fuels were used: wood, miscanthus and brown coal. The fuel gas was cleaned with high efficiencies (>99.67%) with honeycomb ceramic filters operated above 880 K. Tar concentrations were analyzed before and after the filters. Poly-Aromatic Hydrocarbon species concentrations of 1.6 to 7.9 g/m_n³ were found. Stable combustion of the fuel gas with a heating value (HHV) between 1.88 and 4.64 MJ/m_n³ was accomplished because of fuel temperatures higher than 850 K. Because of these temperatures the tars seemed to give no condensation problems during integrated PFBG, gas cleaning and combustor operation. Also, no fouling of alkalis was found inside the equipment of the gas turbine combustor after more than 100 hours of operation. On average the emissions for carbon monoxide were lower than 50 ppmv and the emissions for nitrogen oxide were between 40 and 220 ppmv both calculated at 15% oxygen. At the lowest ammonia concentrations the conversion to nitrogen oxide reached 100% but at higher ammonia concentrations the conversion dropped to 30%.