Numerical and experimental investigation of natural gas injection effects on NOx reburning at the rotary cement kiln exhaust

Thermal NOx formation is very high in the rotary cement kiln due to high-temperature flame. Essentially all NOx emissions associated to the cement manufacturing are formed in cement kilns. In this paper, the effects of natural gas injection into calciner exhaust, i.e., rotary kiln inlet, on NOx reburning by CO and CH radicals is numerically and experimentally investigated. A 3D model of turbulent combustion flow to stimulate the NOX reburning on an industrial scale is developed by the finite volume method. The results show that the NOx reduction can be reached 30 % and 70 % by 950 m3/h and 2750 m3/h natural gas injection, respectively. Furthermore, by increasing natural gas injection flow rate and reaction time, NOx reduction rate is abruptly decreased. The experimental results imply 65 % NOx reduction by natural gas injection from walls of rotary furnace channel inlet where good agreement by numerical results is well proved. Obtaining results also prove that the NOx return in swirling region is highly increased and NOx concentration remarkably reduced.