Effects of gas compositions on NOx reduction by selective non-catalytic reduction with ammonia in a simulated cement precalciner atmosphere

• Effects of gas compositions on SNCR were investigated in precalciner atmosphere.
• H2O, O2 and CO have different and significant effects on NOx reduction.
• The effect of SO2 on NOx reduction is negligible.
• O and OH are crucial to SNCR process and can be affected by gas compositions.
• The presence of H2O, O2, SO2 and CO can reduce NH3 slip below 900 °C.

The effects of gas compositions on NOx reduction and NH3 slip by selective non-catalytic reduction (SNCR) with NH3 were investigated in a simulated cement precalciner atmosphere. The results show that the presence of H2O improves NOx reduction and widens the reduction temperature window significantly. O2 is indispensable for reducing NOx. The optimum reduction temperature decreases and the temperature window widens to a lower temperature with the increase of O2 content. In addition, the increase of O2 content also results in a decrease of the maximum NOx reduction efficiency. The effect of SO2 on NOx reduction is negligible in the simulated precalciner atmosphere. To increase CO concentration makes NO reduction take place at relatively low temperatures. However, NH3 will tend to be oxidized into NO instead of reducing NO after entering the stream containing O2 at high temperatures if it is initially blended with a high concentration of CO in an oxygen-free environment. The increase of H2O, O2, SO2 or CO concentration is helpful to reduce NH3 slip in the temperature region below 900 °C. These effects are resulted from the fact that the generation and consumption of O and OH radicals which are crucial to NO reduction and formation can be influenced by the four gas compositions. In industrial operation of SNCR for cement precalciner, these effects should be taken into account to increase NOx reduction efficiency and avoid NH3 slip.