NOX REMOVAL ON A COAL-FIRED UTILITY BOILER BY SELECTIVE NONCATALYTIC REDUCTION

A plant for Selective Non-catalytic Reduction (SNR) of NOx emissions by NH3 (ammonia) injection has been designed, installed and successfully tested on a 135 MW(e) coal-fired utility boiler. The final 2000 hours test was performed with the plant automatically controlled. The NOx level in the untreated flue gas is typically 400-700 ppm, and NH3 is injected at a molar ratio to NO between 0.6 and 1.8. Through most of the load range 50-70% reduction of the NOx emission was achieved. The temperature window for the process is 850-1050-degrees-C, with an optimum at 950-degrees-C. In order to minimize the emission of unburnt NH3, natural gas was added in a molar ratio to NOx of about 1 in part of the load range. The plant met a demand of no more than 15 ppm NH3 in the flue gas. The research and development work needed for adoption of the SNR-process to coal-firing has been in progress through five years in a cooperation between Aalborg Ciserv International, The Technical University of Denmark, and the Danish power plant association ELSAM. The research program included basic laboratory research on the chemical kinetics of the process, pilot scale research on the reducing capacity and emissions of ammonia and urea, testing in laboratory scale and pilot scale of several additives for widening the temperature window and minimizing the NH3 emission, and development of nozzles for good mixing of NH3 into the flue gas. The resulting concept is applicable for NOx-removal on several types of boilers.