Reduction of NO/sub x/ emissions from a dry process preheater kiln with calciner through the use of the urea-based SNCR process

The post combustion reduction of NO/sub x/ using urea has proven to be an effective method in controlling NO/sub x/ from various combustion sources, such a reduction process has been successfully demonstrated in a week-long test at Ash Grove's dry process cement kiln system located in Seattle. This system is equipped with planetary coolers, a 5-stage preheater and an air-through-the-kiln calciner. Testing was done under ten different kiln/calciner operating conditions. Using three to four injectors, NO/sub x/ was efficiently reduced from 350-600 lb per hour lb/ton of clinker to less than 100 lb per hour. This calculates to a NO/sub x/ reduction of greater than 80% for most cases. Chemical utilization was greater than 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 demonstration confirms expectations that dry process cement kilns with 4+ preheater stages are an ideal application for the selective noncatalytic reduction of NO/sub x/ with urea. NO/sub x/ was efficiently and effectively reduced with minimal byproduct emissions and virtually no effect on plant operations.