Cement kiln NOX control

Control of NO_X emissions from combustion sources has become an important issue in recent years, particularly in the ozone nonattainment areas of California. Cement kilns represent an important source of NO_X emissions, and they either have already been regulated or are being considered for future regulations. This paper presents the results of a critical analysis of the state-of-the-art in cement kiln NO_X control. A survey of current and anticipated cement kiln NO_X regulations, NO_X formation mechanisms, and common NO_X control technologies (as applied to boilers) is presented. Cement kiln features relating to NO_X control, such as a combustion characteristics and temperature and residence time profiles, are outlined. A comparison is made of NO_X control technologies applicable to cement kilns; these include combustion modifications, low NO_X burners, staged combustion, selective noncatalytic reduction, and selective catalytic reduction. The criteria for comparing these NO_X control technologies include the principle of operation, technical feasibility, potential NO_X reduction, relative cost, and, most importantly, the potential effects on clinker quality. Finally, conclusions and future directions in cement kiln NO_X control are discussed