Development of a zero-emission gas-turbine combustor adapting premixed oxy-combustion technology

Carbon dioxide is the main contributor to the global warming because of combustion of fossil fuels. These emissions could be reduced using renewable energies including wind, solar and wave energies. However, most of these energies are not yet economically visible especially in the developing countries. Legislation and public awareness led to strict policies for control of the emissions of greenhouse gases. At this stage, the world is forced to use fossil fuels while following the policies for greenhouse gas emission control. In Saudi Arabia, fossil fuel is expected to be in use for a long time for energy production. In the power sector, Saudi Arabia is the biggest world user of gas turbines (GTs) for power generation. These GTs are working mainly on diffusion flame type using air as an oxidizer. Diffusion type of air-flames results in high-temperature spots within the flame zone and, as a result, high NOx emissions will be generated. Also, the concentrations of CO2 in the exhaust are reduced making its separation very hard and the associated cost for separation is increased. In this study, the conversion of gas turbine to work on partially or fully premixed controlled temperature flame instead of diffusion flame will be investigated experimentally and numerically aiming at complete control of NOx and CO2 emissions at the lowest cost. To achieve such objective, two approaches will be examined considering a gas turbine combustor fueled by natural gas. In the first approach, fully premixed emission-reduced temperature-controlled air combustion flame will be investigated. Fully premixing of the combustion reactants will prevent the creation of high-temperature spots in the flame zone and, accordingly, NOx emissions will be fully controlled. However, this kind of flames may encounter a range of unstable flame operation. So, the flame characteristics will be studied to identify stable flame operation range under premixing conditions. In the second approach, a range of flames, from partially premixed to fully non-premixed (diffusion), will be investigated under oxy-combustion conditions. Using oxygen instead of air for combustion will result in complete elimination of NOx emissions and the combustion products will be mainly CO2 and H2O enabling complete capture of CO2. Also, the concentrations of CO2 in the exhaust flue gas will be increased facilitating its separation. However, oxy-combustion results in extreme temperature rise in the case of non-premixed flames. Different flames will be examined to specify a premixing range through which moderate combustion temperature can be encountered for safe operation of GT. The application of the first approach will result in no additional cost; however, the combustion temperature and, accordingly, turbine power will be reduced. The application of the second approach results in increase in the combustion temperature and, accordingly, the turbine power will be increased; however, it requires the use of air separation unit for oxygen separation which requires additional powering. GT performance will be evaluated and compared considering both approaches targeting its proper application of the technology in the energy sector.