Development of a syngas-fueled micromixing gas-turbine combustor for zero-emission power plants

At the present stage, the world is largely dependent on fossil energy, yet combustion of fossil fuels emits the primary greenhouse-gas carbon dioxide (CO2) causing global warming. Fossil fuels are expected to remain the primary source of energy in Saudi Arabia for a long time; more than 95% of the Kingdoms electricity has been produced with fossil energy in 2017 using gas turbines (GTs). The fact that KSA is on the world-top-10 list of countries producing electricity (311 TWh in 2017) and generating CO2 emissions (589 MtCO2 in 2017) makes KSA the largest user of GTs worldwide and highlights the critical need to implement efficient carbon capture and sequestration. Over the past five decades, GT manufacturers switched from traditional diffusion combustion to lean premixed (LPM) combustion technologies to reduce NOx emissions; General Electric successfully developed the micromixer (MM) LPM technology in their F-class utility GTs (TRL of 9). The use of air as oxidizer is, however, not beneficial from a carbon-capture perspective, as unreacted nitrogen from air forms the primary constituent of GT exhaust, which reduces the CO2 concentration in it, thus complicating the CO2 separation process and increasing the associated costs of CO2 capture. Oxy-fuel combustion (i.e., burning fuel in oxygen instead of air), on the other hand, produces CO2 and H2O as primary exhaust constituents, so once the latter is condensed out, the former can readily be captured at the lowest cost. This study thus proposes the development of a MM-based oxy-fuel combustor, fueled by syngas. Syngas is a fuel gas mixture consisting primarily of H2, CO, and some CO2 and is produced in many industries and from the gasification of various fuels and wastes. Gasification offers the extra advantage of easy pre-combustion capture of CO2 from syngas, and if the water-shift reaction is implemented, most CO is converted to CO2 and captured as well, resulting in high-H2 syngas to be burned in a low-carbon-footprint Integrated Gasification Combined Cycle (IGCC). However, the combustion of high-H2 syngas is technically challenging because of the extreme temperatures and super-fast reaction kinetics. Oxy-combustion of high-H2 fuels in MMs has never been examined in past studies, which is the novelty of this proposed work. Exhaust-Gas Recirculation (EGR) will be implemented to control the flame temperature and reaction kinetics. The effects of fuel H2 content, CO2 percentage, and equivalence ratio will be examined both numerically and experimentally, in addition to the effects of MM design geometry. The developed MM technology and corresponding intellectual property are of strategic value to international GT manufacturers for the development of next-generation, zero-emission, and fuel-flexible GTs. The primary beneficiary institutions in KSA are Saudi Electric Company (SEC), SABIC, and Saudi Aramco as main emitters of CO2. These institutions are already investing substantially in carbon-capture and sequestration and will benefit greatly from the enhanced energy efficiency, reduced carbon-capture costs, and improved fuel flexibility of a GT fleet implementing this developed MM technology. The Saudi society will benefit from reduced energy costs (because of enhanced efficiency), as well as cleaner environment.