REDUCTION OF NOX EMISSIONS FROM A DRY PROCESS PREHEATER KILN WITH CALCINER THROUGH THE USE OF THE UREA-BASED SNCR PROCESS

The post combustion reduction of NOx using urea has proven to be an ef fective method in controlling NOx from various combustion sources. Suc h a reduction process has been successfully demonstrated in a week-lon g test at Ash Grove's dry process cement kiln system located in Seattl e. This system is equipped with planetary coolers; a 5-stage preheater and an air-through-the-kiln calciner. Testing was done under ten diff erent kiln/calciner operating conditions. Using three to four injector s, NOx was efficiently reduced from 350-600 lb per hour lb/ton of clin ker) to less than 100 lb per hour. This calculates to a NOx reduction of greater than 80% for most cases. Chemical utilization was greater t han 50% percent. A high degree of mixing and a long residence time at an appropriate temperature present in the preheater tower contributed to these excellent results. An average ammonia slip was four ppm above a baseline level at a normalized stoichiometric ratio of 1. This demo nstration confirms expectations that dry process cement kilns with 4preheater stages are an ideal application for the selective noncatalyt ic reduction of NOx with urea, NOx was efficiently and effectively red uced with minimal byproduct emissions and virtually no effect on plant operations.