Combustion emissions from nh3 fuel gas turbine power generation demonstrated

A massive influx of renewable energy is required in order to mitigate global warming. Although H₂ is a renewable medium, its storage and transportation in large quantities has some problems. NH₃ fuel, however, is an H₂ energy carrier and carbon-free fuel, and its storage and transportation technology is already established. Although NH₃ fuel combustion was studied in the 1960s in the USA, the development of an NH₃ fuel gas turbine had been abandoned because the combustion efficiency was unacceptably low. The recent demand for H₂ energy carriers has revived the interest of NH₃ fuel; however an actual design setup for NH₃ fuel gas turbine power generation has not been attempted. The National Institute of Advanced Industrial Science and Technology (AIST) in Japan, in collaboration with Tohoku University successfully achieved NH₃-kerosene gas turbine power generation in 2014, and NH₃ fuel gas turbine power generation in 2015. The facility consists of an NH₃ fuel-supply system, NH₃ gas compressor, 50 kWe-class micro gas turbine, Selective Catalytic Reduction (SCR) NOx-reduction apparatus, and loading equipment. The micro gas turbine utilizes a diffusion combustor to stabilize the flame and a regenerative heat exchanger to improve the thermal efficiency of the gas turbine cycle. Considering that the laminar burning velocity of NH₃/air is one-fifth that of CH₄/air, the combustion intensity of NH₃/air is very low. In addition, NH₃ has been thought of as a fuel N additive in the study of NOx formation. Although NOx reduction is desirable in the combustion process, low NOx combustion technology is difficult because NH₃ has been thought of as the source of fuel-NO. Hence, in order to evaluate the performance of NH₃ fuel gas turbine power generation, it is important to focus on the combustion stability and combustion emissions. Earlier, we have reported the combustion emission characteristics of NH3 fuel gas turbines; in the case of NH₃/air, concentrations of NO and unburnt NH₃ strongly depend on the combustor inlet temperature, and in the case of NH₃/CH₄/air, the concentration of NO at a constant electric power output depends on the NH₃ ratio in the mixture. This report additionally shows that other than NO, the combustion emissions of NO₂ and N₂O also decrease considerably at high electric power output. These results arise from the restriction of the eigen balance of fuel, air, and heat, because the compressor and turbine are connected by a single shaft in the gas turbine. In the next step, the element test was carried out using a combustor test rig to develop a low NOx combustor. It is difficult to characterize combustion emissions with the former parameters in the case of a combustor test rig, because there is no restriction of the quantity of fuel, air, and combustor inlet temperature. Thus, this paper reports the combustion emissions of NH₃ fuel gas turbine re-characterized with respect to the other parameters, such as fuel flow rate, overall equivalence ratio, combustor pressure, and combustion temperature.