Extended operability of a commercial air-staged burner using a synthetic mixture of biomass derived gas for application in an externally fired micro gas turbine

• A two staged diffusion burner was used for combustion tests of simulated biomass derived gas.
• Benzene was injected at two concentrations in the fuel tested to represent tar.
• An optimum equivalence ratio was found for minimum emissions of CO and UHC.
• NOX emissions increased with the addition of benzene in the fuel gas.

Biomass gasification converts solid biomass into a gaseous fuel that is more versatile and can be used in many applications. However, biomass gasification gas contains some contaminants and inert compounds. The contaminants can cause several problems in the downstream equipment and undesirable emissions while the inert compounds can affect the lower heating value of the gas. Because of these characteristics, there have been difficulties in finding a conversion technology using biomass gasification gas for heat and power generation. In this regard, externally fired gas turbines open a possibility for this combustible gas since due to its configuration, combustion takes place outside the conventional gas turbine cycle. For this reason, combustion studies of biomass derived gas are important. In this work the operability of a commercial air-staged natural gas burner is shown in terms of CO, UHC, and NOX emissions using a synthetic mixture of biomass gasification gas. Two fuel gas mixtures simulating the composition of biomass gasification gas are injected in the combustor. Each fuel gas contains different injection rates of benzene in order to represent tars and to understand their effect on the combustion performance. Additionally, the equivalence ratio is varied in a range of lean conditions in order to find an optimum operation point for the burner studied. The results showed that the presence of polyaromatic hydrocarbons such as benzene reduced the CO concentrations in the exhaust gas while it increased the concentrations of unburned hydrocarbons (UHC) at equivalence ratios lower than 0.68. Additionally, NOX emissions showed a relatively constant trend over the range of equivalence ratios studied for both fuels. It was also observed that NOX emissions increase with the addition of benzene in the fuel gas. An optimum point with regards CO and UHC concentrations was found for the fuels tested.