NOx Control for Utility Boiler OTR Compliance

Babcock & Wilcox Power Generation Group (B&W) and Fuel Tech, Inc. (Fuel Tech) teamed to evaluate an integrated solution for NO{sub x} control comprised of B&W's DRB-4Z{reg_sign} low-NO{sub x} pulverized coal (PC) burner technology and Fuel Tech's NO{sub x}OUT{reg_sign}, a selective non-catalytic reduction (SNCR) technology, capable of meeting a target emission limit of 0.15 lb NO{sub x}/10{sup 6} Btu. In a previous project sponsored by the U.S. Department of Energy (DOE), promising results were obtained with this technology from large-scale testing in B&W's 100-million Btu/hr Clean Environment Development Facility (CEDF) which simulates the conditions of large coal-fired utility boilers. Under the most challenging boiler temperatures at full load conditions, NO{sub x} emissions of 0.19 lb/10{sup 6} Btu were achieved firing Powder River Basin coal while controlling ammonia slip to less than 5 ppm. At a 40 million Btu/hr firing rate, NO{sub x} emissions were as low as 0.09 lb/10{sup 6} Btu. Improved performance with this system was proposed for this new program with injection at full load via a convective pass multiple nozzle lance (MNL) in front of the superheater tubes or in the convective tube bank. Convective pass lances represent the current state-of-the-art in SNCR and needed to be evaluated in order to assess the full potential of the combined technologies. The objective of the program was to achieve a NO{sub x} level below 0.15 lb/10{sup 6} Btu (with ammonia slip of less than 5 ppm) in the CEDF using PRB coal and B&W's DRB-4Z{reg_sign} low-NO{sub x} pulverized coal (PC) burner in combination with dual zone overfire air ports and Fuel Tech's NO{sub x}OUT{reg_sign} System. Commercial installations of B&W's low-NO{sub x} burner, in combination with overfire air ports using PRB coal, have demonstrated a NO{sub x} level of 0.15 to 0.2 lb/10{sup 6} Btu under staged combustion conditions. The proposed goal of the combustion system (no SNCR) for this project is a NO{sub x} level at 0.15 lb/10{sup 6} Btu. The NO{sub x} reduction goal for SNCR is 25% from the low-NO{sub x} combustion emission levels. Therefore, overall NO{sub x} emissions would approach a level of 0.11 lb/10{sup 6} Btu in commercial installation. The goals of the program were met. At 100% load, using the MNL for very low baseline NO{sub x} (0.094 to 0.162 lb/10{sup 6} Btu depending on burner stoichiometry), an approximately 25% NO{sub x} reduction was achieved (0.071 to 0.124 lb/10{sup 6} Btu) while maintaining NH{sub 3} slip less than 6.4 ppm. At 60% load, using MNL or only wall-injectors for very low baseline NO{sub x} levels, more than 30% NO{sub x} reduction was achieved. Although site specific economic evaluation is required for each unit, our economic evaluation of DRB-4Z{reg_sign} burner and SNCR for a 500 MW{sub e} plant firing PRB shows that the least cost strategy is low-NO{sub x} burner and OFA at a cost of $210 to $525 per ton of NO{sub x} removed. Installation of SNCR allows the utilities to sell more NO{sub x} credit and it becomes economical when NO{sub x} credit cost is more than $5,275 per ton of NO{sub x}