Research on the dynamic process of NO heterogeneous and homogeneous reduction with cement raw meal in vertical tubular reactor

Abstract

A certain amount of coal is supplied at the outlet of cyclone suspension preheater C5 to reduce NOx through homogenous and heterogenous reduction. Subsequently, char enters into precalciner and burnt out, while volatiles are burnt out after being exposed to over-fire air. Such process, i.e. the high-order reduction of NOx, has been verified as a high-efficiency control mean for NOx emission in cement industry. The dynamic processes of NO reduction by volatiles and coal in absence of O2 have been studied in the vertical tubular reactor. The effects of cement raw meal and reaction temperature on NO heterogenous and homogeneous reduction were analyzed. The results suggested that the reactions were classified into two types (the homogeneous and the heterogeneous reactions), characterizing the reactions in the gas phase and the reactions between the gas phase and the particle surfaces, respectively. Homogeneous reduction was the critical mechanism during the earlier stage of reaction. Then, the char reduction mechanism became more efficient. Raw meal could promote NO heterogeneous reduction because CaO, as the carrier, could accelerate the transfer of oxygen atom. However, raw meal could significantly inhibit NO homogeneous reduction. CaO, as reactant, could change the pathways of cleavage reaction; the products of new reaction path contained a neutral molecule and an anion, instead of unstable free radicals which are actually vital to reduce NO in the gas phase. High temperature could facilitate homogeneous and heterogenous NO reduction. The catalysis of CaO on heterogenous had the optimum temperature (850 °C), and it could restrain the effect of heat inactivation. And CaO could significantly inhibit NO homogeneous reduction at the whole operation temperature.