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 heavy-duty gas turbine engines has increased as pre-combustion carbon capture and sequestration (CCS) has become a viable option for integrated gasification combined cycle (IGCC) power plants. The US Department of Energy has funded the Advanced IGCC/Hydrogen Gas Turbine Program since 2005 with an aggressive plant-level NOx target of 2 ppm @ 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 high-hydrogen fuels of interest. A new premixing fuel injector for high-hydrogen fuels was designed to balance reliable, flashback-free operation, reasonable pressure drop, and low emissions. The concept relies on distributed, small-scale jet-in-crossflow mixing that is a departure from traditional swirl-based premixing concepts. Single nozzle rig experiments were conducted at pressures of 10 atm and 17 atm, with air preheat temperatures of about 650K. With nitrogen-diluted hydrogen fuel, characteristic of carbon-free syngas, stable operation without flashback was conducted up to flame temperatures of approximately 1850K. In addition to the effects of operating pressure, the impact of minor constituents in the fuel — carbon monoxide, carbon dioxide, and methane — on flame holding in the premixer is presented. The new fuel injector concept has been incorporated into a full-scale, multi-nozzle combustor can with an energy conversion rate of more than 10 MW at F-class conditions. The full-can 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 hours of fired testing at full-load with hydrogen comprising over 90 percent of the reactants by volume. NOx emissions (ppm) have been measured in the single digits with hydrogen-nitrogen fuel at target gas turbine pressure and temperatures. Results of the testing show that small-scale fuel-air mixing can deliver a reliable, low-NOx solution to hydrogen combustion in advanced gas turbines.