Optical Measurements of a LCV-Combustor Operated in a Micro Gas Turbine With Various Fuel Compositions

Abstract

In a recent joint research project, a new FLOX®-combustion system was developed to couple a fixed-bed gasifier with a micro gas turbine. Product gases from biomass gasification exhibit low calorific values and varying compositions of mainly H2, CO, CO2, N2 and CH4. Furthermore, combustion characteristics differ significantly compared to the commonly used natural gas. As the FLOX®-technology is considered as efficient and fuel-flexible featuring low emissions of hazardous pollutants, the design of the LCV-combustor is based on it. It contains a two-staged combustor consisting of a jet-stabilized main stage adapted from the FLOX®-concept combined with a swirl stabilized pilot stage. The combustor was operated in a Turbec T100 test rig using an optically accessible combustion chamber, which allowed OH*-chemiluminescence and OH-PLIF measurements for various fuel compositions. In particular, the hydrogen content in the synthetically mixed fuel gas was varied from 0 % to 30 %. The exhaust gas composition was additionally analysed regarding CO, NOx and unburned hydrocarbons. The results provide a comprehensive insight into the flame behaviour during turbine operation. Efficient combustion and stable operation of the micro gas turbine was observed for all fuel compositions, while the hydrogen showed a strong influence. It is remarkable, that with hydrogen contents higher than 9 % no OH radicals were detected within the inner recirculation zone, while they were increasingly entrained below hydrogen contents of 9 %. Without hydrogen, the inner recirculation zone was completely filled with OH radicals and the highest concentrations were detected there. Therefore, the results indicate a different flame behaviour with low and high hydrogen contents. Although the flame shape and position was affected, pollutant emissions remained consistent below 10 ppm based on 15% O2. Only in case of 0% hydrogen, CO-emissions increased to 43 ppm, which is still meeting the emission limits. Thus, the combustor allows operation with syngases having hydrogen contents from 0% to 30%.