Development and Testing of a Low NOx Hydrogen Combustion System for Heavy Duty Gas Turbines

Abstract

Interest in hydrogen as a primary fuel stream in heavyduty gas turbine engines has increased as precombustion carbon capture and sequestration (CCS) has become a viable option for integrated gasification combined cycle (IGCC) power plants. The U.S. Department of Energy has funded the Advanced IGCC/Hydrogen Gas Turbine Program since 2005 with an aggressive plantlevel NOx target of 2 ppm at 15% O2 for an advanced gas turbine cycle. Approaching this NOx level with highly reactive hydrogen fuel at the conditions required is a formidable challenge that requires novel combustion technology. This study begins by measuring entitlement NOx emissions from perfectly premixed combustion of the highhydrogen fuels of interest. A new premixing fuel injector for highhydrogen fuels was designed to balance reliable flashbackfree operation, reasonable pressure drop, and low emissions. The concept relies on smallscale jetincrossflow mixing that is a departure from traditional swirlbased premixing concepts. Single nozzle rig experiments were conducted at pressures of 10 atm and 17 atm, with air preheat temperatures of about 650 K. With nitrogendiluted hydrogen fuel, characteristic of carbonfree syngas, stable operation without flashback was conducted up to flame temperatures of approximately 1850 K. In addition to the effects of pressure, the impacts of nitrogen dilution levels and amounts of minor constituents in the fuel—carbon monoxide, carbon dioxide, and methane—on flame holding in the premixer are presented. The new fuel injector concept has been incorporated into a fullscale, multinozzle combustor can with an energy conversion rate of more than 10 MW at Fclass conditions. The fullcan testing was conducted at full gas turbine conditions and various fuel compositions of hydrogen, natural gas, and nitrogen. This combustion system has accumulated over 100 h of fired testing at full load with hydrogen comprising over 90% of the reactants by volume. NOx emissions (ppm) have been measured in the single digits with hydrogennitrogen fuel at target gas turbine pressure and temperatures. Results of the testing show that smallscale fuelair mixing can deliver a reliable, lowNOxsolution to hydrogen combustion in advanced gas turbines.