Cement Kiln NOX Control

Abstract

Control of NO x emissions from combustion sources hbas 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. The development of NO x controls for cement kilns is not a trivial problem, and many different control methods have been tried over the last 15-20 years, many of which have failed. However, recently progress has been made, and additional novel ideas are being pursued. 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