Experimental Investigation of Cutting Nitrogen Oxides Emission from Cement Kilns using Coal Preheating Method

The large consumption of coal in cement industry leads to a significant nitrogen oxide (NOx) emission, which has caused severe atmospheric pollution due to the existing low-efficiency denitration technologies. In this research, a fuel pretreatment method on the concept of coal preheating was proposed to reduce NOx emission from cement kilns. A special bench-scale experiment was designed to verify the feasibility of the proposed method. Experimental results showed that the proposed method could achieve high combustion efficiency, steady operation and low NOx emission. The maximum reduction efficiency of primary NO in kiln gas reached 91.4% while the lowest NOx emission was 145 mg/m3 (@10% O2) during the experiment. The effects of key parameters on NOx emission and primary NOx reduction efficiency were comprehensively investigated. It was found that primary and secondary air ratios determined the oxygen content in the flue gas and the reaction temperature, which multiply affected the fuel-NOx formation and activity of reductants. Increasing the length of the reducing zone could not only enhance the primary NOx reduction efficiency, but also lower the combustion efficiency. In addition, cement raw material could greatly accelerate the formation of fuel-NOx while its catalytic action on NOx reduction was limited.