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Show other variables including ambient air temperature and humidity, excess O2 in the flue gas (or Figure 1. Efficiency loss In Coftrtng as a Function of Wood Percentage In Blend 1.8 1.6 iii 0 1.4 u !.,. .5 1.2 ti ." C"D E 1 e ~ ." ." 0 .J 0.8 >- U C., U 0.6 m c., .~, 0.4 IL 0.2 0 0 2 4 6 y c 0.OO2X2 + 0.0375x ~c 0.8558 • 8 10 12 Percent Wood In Fuel Blend 14 16 18 20 stoichiometric ratio), gas temperature exiting the air heater, air heater in-leakage, and unburned carbon in the flyash and slag. It is significant that the excess O2 and the gas temperature exiting the air heater are parameters managed in the control room. Neither the excess O2 nor the gas temperature exiting the air heater were increased as a function of cofiring or trifiring. The O2 was held to a constant level well below 3 percent, and variability was ±G. 1 percent. The air heater exit temperature was held to about 290«>P to 300«>P regardless of the fuel blend when firing western coals at or near full capacity. Unburned carbon in the flyash appeared to vary significantly, however the variation could not be correlated to the level of wood in the fuel mix or the level of cofiring or trifiring being practices. The efficiency loss from the baseline can be expressed as an equation derived from the curve fitting calculation is as follows: ELoIo = .002W2 + 0.0375W [1] Where ELoIo is the percentage loss in efficiency when practicing cofiring or trifiring and W is the percentage of wood in the fuel blend. At 10 percent wood in the mix, there is an estimated efficiency loss of 0.58 percent, at 15 percent wood in the mix, there is an estimated efficiency loss of 1.01 percent, and at 20 percent wood in the mix, there is an estimated efficiency loss of 1.55 percent. The dominant factor governing these efficiency losses is the moisture content of the wood. These efficiency losses translate into increases in net station heat rate. Economically the 8 |