OCR Text |
Show 11 A16SE738.T As previously mentioned, the longer-term test took place from December 1993 through March 1994. During December, only baseline testing was done with urea injection limited to setting injection pressures and flows. Urea injection under automatic control was begun in early January, and the unit was left on economic dispatch for the bulk of the test period. To accomplish the test goal and due to an increased frequency of air heater fouling with the unit operating under area regulation several injector configurations and NOx setpoints were evaluated. A summary of these test conditions is presented in Table 1. TABLE 1 Injection NOx Setpoint Period Date Configuration (lb/MMBtu) Boiler Conditions 1 Jan. 6-Jan. 21 2 Levels 0.75 Low O2 2 Jan. 25-Feb. 8 1 Level 0.82 Low O2 3 Feb. 9-Feb. 16 1 Level 0.75 Low O2 4 Feb. I7-Mar. 2 1 Level 0.68 Low O2 5 Mar. 2-Mar. 9 1 Level 0.61 Design O2 6 'Mar. 9-Mar. 15 1 Level 0.61 60-100 ~ Design O2 0.68 100-132 ~ 7 Mar. I5-Mar. 26 2 Levels 0.68 Design O2 8 Mar. 26-Mar. 29 2 Levels 0.82 Design O2 RESULTS NOx Emissions The stack NOx emission value that could be maintained was found to be dependent on several parameters. These include: (1) the ability of the SNCR control system to react to changing unit conditions and hold a given setpoint; (2) combustion conditions such as fuel-to-air ratios, flue gas temperatures, CO and S03; (3) secondary effects such as NH3 slip, ammonia/ash recycle, ambient conditions and air heater fouling. The ability to control to a NOx emission rate was limited to a few controllable process variables. SNCR process variables including injector location, style and nozzle tip orientation, dilution water flow rate and atomization pressure were optimized and flxed for the test condition. The real time, controllable parameter remaining was reagent injection rate to either or both injection levels. Reagent injection rates were determined by the controls based on setpoint, NOx, steam flow (load), and O2• The test period was split into eight operating periods, characterized |