OCR Text |
Show 17 A16SE738.T ammonium sulfate and bisulfate fonnation and possibly increased ash cohesiveness due to the elevated NH3 levels on the ash. The air heater fouling was likely compounded by low air temperatures exiting the steam coils during periods of low ambient air temperature ( < 20°F) and periods when the steam coil air heater was out of operation. Sootblowing did not appear to reduce the air heater fouling after an increase in the pressure drop was noticed. Optimizing the frequency of sootblowing and steam pressure to the sootblowers may have the potential to improve the time between air heater washes, but is not expected to improve the ability to remove deposits in the intennediate air heater baskets and deep within the cold-end air heater baskets. During air heater washes, a significant amount of ammonium compounds are transferred to the waste water treatment plant. Modifications to the plant may be necessary before the treated water can be discharged or fed to the flue gas scrubber. Increased air heater pressure drop exacerbates the existing problem with fan capacity. Increases in fan horsepower and parasitic loss of power will be an added cost and impact of SNCR for NOx control. SUMMARY NOx Reduction Over the course of the long tenn SNCR demonstration, four NOx setpoints and two levels of injection were utilized to test the ability of SNCR to control NOx at B.L. England Unit 1. The different injection modes and setpoints were used in response to either the inability of the SNCR system to control to the given NOx setpoint or to boiler impacts, primarily air heater fouling, reSUlting from the NH3 slip. The primary variable affecting the ability to control the level of NOx was the boiler O2, with higher 02'S leading to higher NOx values. Of secondary importance was the injection elevation, with multiple levels providing increased NOx control without a quantifiable penalty in NH3 slip. The following is a summary of the perfonnance along with any associated boiler impacts. • the system was able to maintain an average reduction of 30 % during the test while maintaining NH3 slip at less than 10 ppmv. For a representative baseline 1.3 Ib/MMBtu, one could expect to maintain an average emission rate of 0.9 Ib/MMBtu under dispatch conditions as one approach to minimize ammonia slip and air heater impacts. • the SNCR system was unable to control to tested NOx setpoints below 0.9 Ib/MMBtu at loads above 120 MW with stack O2 levels in excess of 9.6% while simultaneously maintaining NH3 slip at less than 10 ppmv. |