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Show Economic Cost Function For the BPL output, a formula was developed to calculate the approximate performance changes (percent boiler efficiency and/or heat rate) from certain parameters. Effects of the following parameters were included: UBC, O2, dry gas loss, main steam temperature, and hot reheat steam temperature. BPL was included in a formula called "Pain" which was used for optimizing the process. The following parameters or assumptions were included in this formula: • Projected cost for 10w-NOx burners and expected NOx levels. • The expected annual rate of return on capital investments. • A baseline BPL. • Average coal ash content. • Average fuel cost for Unit 3. • No change in air heater leakage rate and fuel moisture content during the test. While this formula was specific to Unit 3, it can be tailored to fit any unit with a few modifications to coefficients and constants. NOz and Cost Improvements A total of 85 test runs were performed under SPO software advice. NOx emissions were lowered by as much as 300/0 but improvements varied due to fluctuating load levels (Figure 6). Pain, the function being minimized, also showed variation due to load. Figure 7 shows that the first week of the test produced the largest improvement by lowering the Pain by $700,000. The second week of the test averaged a $400,000 improvement compared with baseline. The emissions account for about 80% of the improvement, and the BPL for about 20%. Models for all outputs except UBC and steam temperatures exhibited high predictive accuracy. The software suggested that gross load (an uncontrolled input) had the greatest impact on NOx, BPL and Pain. Among controlled inputs, mill bias, excess O2, BFG/COG damper positions and air register settings also had significant influence. Optimum input settings to minimize Pain are calculated from the software model. Table 2 compares the optimum provided by the program with the initial (Run 1) settings. Table 2 - Comparison of Optimum Settings vs. Baseline Inputs Units Initial Optimum Lower Mill Bias % 0 8.33 Middle Mill Bias % -2.70 -1.33 Tert. Air Reg. % 6.30 7.08 Upper Air Reg. Scale 5.90 4.98 Middle Air Reg. Scale 6.10 4.00 Lower Air Reg. Scale 6.00 7.57 Excess 02 % 2.93 2.00 Gas Fuel % 8.48 9.00 BFG/COG Damper POSe % 45.8 40 Gross Load MW 287 290 Outputs Heat Rate Ib/MBtu 0.97 0.68 NOx $ 1,007 298 6 |