Impact of ammonia as a fuel / co-fuel on NOx emissions


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Ammonia is a hydrogen-based, carbon-free energy carrier. It has good energy density (22.5 MJ/kg) and can be liquefied (about 10 bar at 298 K). With the increasing demand to lower the CO2 emissions worldwide, pure ammonia combustion or co-combustion with a conventional fuel is an alternative solution in turbines, gas engines, power plants, furnaces, and cement kilns. The major challenges with the use of ammonia as a fuel are lowered heat flux and increased NOx emissions. These parameters were analyzed in Linde’s lab-scale tests with pure ammonia as well as mixtures of ammonia and natural gas.

Tests were conducted with ammonia mixed with natural gas from 0 – 100% ammonia at different stoichiometric ratios. Further, oxygen content in the oxidant was varied from 0 – 100% by mixing pure oxygen with air. The tests were conducted in a pipe-in-pipe burner placed inside a quartz tube. The entire setup was enclosed in an insulated furnace. Combustion temperatures and corresponding NOx emissions were measured. Other gas components from ammonia / natural gas combustion like H2, H2O, N2, CO, CO2 and residual NH3, O2 and CH4 were also measured with Fourier Transform Infrared (FTIR) spectroscopy and a micro-gas chromatograph (GC). A large scale of fuel and oxidant compositions were used to facilitate fair comparison of results.