OCR Text |
Show 19 A165E738.T • load changes induce wide variations in NOx, and NOx changed more rapidly than the temporary SNCR system could respond: these together limited how closely NOx could be controlled. Nalco Fuel Tech and RJM both believe that improvements (reductions in response time) can be included in a commercial injection and control system. • over control of NOx at loads below 100 MW will help compensate for the inability to control NOx at high levels of excess air and load over a 24-hour period • air heater fouling from the deposition of ammonium bisulfate increases regardless of setpoint or injector configuration; an acceptable, and controllable, level of ammonia slip appears to be less than 10 ppm but needs to be tested further. Air heater fouling during the test periods was probably exacerbated by low ambient air temperatures and failure of the steam coil air heater. • flyash reinjection eliminates problems associated with elevated NH3 content of the fly ash • the low level of slip that can be tolerated will limit reagent usage and overall NOx control cost Based on the test results, none of the injection configurations are capable of controlling NOx below a 0.90 Ib/MMBtu setpoint without impacting the boiler reliability. All configurations tested increased the rate of air heater fouling and caused elevated concentrations of NH3 on the fly ash. The system could not maintain NOx setpoints below 0.82 without sacrificing excess O2 , load or NH3 slip. Upward adjustments of excess O2 and/or conditions of high baseline NOx generally resulted in periods in which the setpoint could not be maintained. Such instances of high NOx were observed in seven of the eight periods, with each exhibiting controlled NOx levels approaching 0.9 Ib/MMBtu. SNCR OPERATING COSTS The costs involved with the procurement, operation, and maintenance of the SNCR system may be divided into several categories. They are the capital costs incurred for the design and installation of the system, the chemical costs required for system operation, costs associated with the operation of the urea heater, injection pumps, and associated equipment, labor costs for required maintenance, and costs due to boiler efficiency penalties. To determine the cost associated with each category, the following assumptions and operating parameters were used. Based on baseline data collected since the CEMS was installed in November of 1993, the uncontrolled NOx concentration is assumed to be 1.3 Ib/MMBtu while operating at full load. |