Liquid ammonia spray combustion in two-stage micro gas turbine combustors at 0.25 MPa; Relevance of combustion enhancement to flame stability and NOx control

Abstract

The development of liquid ammonia spray combustion technology is expected to reduce the cost and size of gas turbines otherwise fueled with gaseous ammonia. However, successful studies on this topic are scarce due to the difficulty in flame stabilization. In this study, the flame stability and emissions control in liquid ammonia spray combustion is studied for the first time for input thermal power up to 230 kW using novel two-stage gas turbine combustors with and without slot film cooling at 0.25 MPa. The experiments were conducted in a micro gas turbine combustor test facility originally developed for gaseous ammonia combustion. The results show that the injection of liquid ammonia spray into a methane-air flame encouraged rapid cooling of the combustor liner head, enhancing flame blowoff. The blowoff limit based on ammonia fraction in the fuel showed a strong dependence on the combustor temperature, hence the combustor without slot film cooling extended the blowoff limit allowing the successful stabilization of pure liquid ammonia spray flame. Result of emissions analysis showed that two-stage rich-lean combustion is effective in controlling emissions from the flames, however, requires further enhancement of the flame in the primary combustion zone. An increase in combustor inlet temperature and a decrease in combustor wall heat loss, both of which enhanced the combustion of the liquid spray, resulted in a decrease in the emissions of NO, NO2, N2O, NH3, HCN and CO from liquid ammonia co-fired with methane. Conversely, pure liquid ammonia spray combustion resulted in higher emissions of NH3, NO and N2O than did the co-combustion with methane, encouraged by inhomogeneity in droplets distribution and larger heat transfer to the liquid droplets.