Catalytic Combustion in Gas Turbines : Experimental Study on Gasified Biomass Utilization

Abstract: Environmental and geopolitical concerns encourage societies towards the utilization of renewable energy sources (RES). Photovoltaic and wind power can produce electricity directly, although their intermittent characteristic negatively affects the security and safety of the energy supply chain; moreover, in order to be viable it is necessary to establish energy storage systems and to find mechanisms to adapt the power distribution grid to larger production variability. In contrast, biomass (a carbon neutral fuel if adequately managed) can be stored, is relatively widely available, and after simple treatments can be gasified and ready to be used for power production. Correspondingly, gas turbines are a well-established technology that first became relevant in industrial applications and power production since 1940’s. The use of biomass in gas turbines is an important step forward towards more sustainable power production; however, this combination presents some technical challenges that have yet to be overcome.Gasified biomass is generally a gas with low or medium heating value that is usually composed of a mixture of gases such as CO, H2, CH4, CO2, and N2 as well as other c60'6nents in small fractions. Its firing in standard gas turbine combustors might be unstable at certain load conditions. Moreover, gasified biomass contains undesirable compounds; in particular the nitrogen-containing compounds that may produce elevated NOx emissions once the biomass is burned.Catalytic combustion is an alternative for using gasified biomass in a gas turbine, and it is investigated in this study. Using catalytic combustion is possible to burn such a mixture of gases under very lean conditions, extending the normal flammability limits, reducing the maximum temperature of the reaction zone, and thus reducing the thermal NOx formation. It also reduces the vibration levels, and it is possible to avoid fuel-NOx formation using alternative catalytic techniques, such as Selective Catalytic Oxidation (SCO).In the present study the feasibility of using catalytic combustion in a gas turbine combustor is evaluated. The tests performed indicate the necessity of using hybrid combustion chamber concepts to achieve turbine inlet temperatures levels of modern gas turbines. The different catalytic burning characteristic of H2, CO and CH4 was evaluated and different techniques were applied to equalize their burning behaviour such as the diffusion barrier, and partially coated catalyst. Fuel-NOx is another subject treated in this work, where a Selective Catalytic Oxidation (SCO) technique is applied reaching up to 42% of fuel NOx reduction. Finally, the use of Catalytic Partial Oxidation (CPO) of methane was experimentally investigated.In this study, two one-of-a-kind test facilities were used directly, namely the high-pressure test facility and the pilot scale test facility. This gives a unique characteristic to the study performed. Finally, the catalytic combustion approach allows the utilization of gasified biomass with some restrictions depending on whether it is a Catalytic Lean, Catalytic Rich or Catalytic Partial Oxidation (CPO) approach.