Achieving high flame stability with low NO And Zero N2O and NH3 emissions during liquid ammonia spray combustion with gas turbine combustors

Liquid ammonia spray direct injection is more desirable than gaseous ammonia injection in large scale gas turbine combustors because it enables a larger volumetric energy density and allows a reduction in cost and size of the fuel supply system. However, previous studies have shown that the large evaporative cooling effects of liquid ammonia droplets vaporization impair flame stabilization, and inhibit efficient control of emissions such as NO, N2O and unburned fuels. This article reports the development and testing of a novel two-stage gas turbine combustor for pure liquid ammonia spray, which achieves approximately zero N2O and unburned fuel emissions with NO emissions as low as 282 ppmv (@16% O2) in a 50 kW micro gas turbine combustor test rig. The combustor design focused on optimization of the secondary injection holes to prevent the dilution of the primary zone (PZ) by air injected into the secondary zone; improving mixture formation using a multi-nozzle twin-fluid atomizer; and elongation of the combustor length to allow sufficient fluid residence time for N2O reduction as well as droplets vaporization and combustion. It was found that the mitigation of PZ dilution resulted in a significant increase in the combustion temperature thereby encouraging efficient combustion of the liquid droplets. On the other hand, the multi-nozzle twin fluid atomizer resulted in a more uniform combustor wall temperature, a more efficient combustion and lower NOx emissions than a single-nozzle pressure swirl atomizer. It is considered that the multi-nozzle injector allowed for an improved droplets dispersion, which is necessary to mitigate large local heat extraction from the flame. These features of the combustor enabled a substantial improvement in liquid ammonia spray flame stability and a better simultaneous control of NO, N2O and unburned fuel emissions never reported before.