Keywords: mercury control, coal-fired boilers, SO2, NOx control
Flue gas Hg measurements from coal-fired boilers equipped with wet scrubbers
The U.S. EPA has indicated they are considering additional SO2 and NOx emission reductions, and EPA is under a consent agreement to propose mercury reduction regulations by 2004 for the utility industry. The boiler manufacturers and the utility industry have developed improved combustion modification techniques to reduce NOx emissions. These advanced combustion modification techniques, plus selective catalytic reduction (SCR), offer the potential to reduce NOx emissions at reduced cost. Wet and dry FGD systems have been shown to reduce SO2 emissions by up to 95%. CONSOL has shown that conventional wet FGD and ESP systems can remove an average of 67±6% of the inlet mercury. These data show that utility boilers equipped with ESP-scrubber combinations are removing two-thirds of the mercury in the as-fired coal at no added cost. The mercury speciation data show that 80 to 95% of the oxidised mercury, as determined by the Ontario Hydro method, is removed by the scrubber. The average mercury material balance closure at the six plants was 103±8%. The mercury removed from the scrubber reported to the scrubber by-product. Standard leachate testing conducted on fixated and unfixated scrubber by-product from one test showed no mercury leaching. Mercury volatility was evaluated by heating the scrubber by-product 140°F for eleven weeks. After eleven weeks, no loss of mercury was reported. Based on these findings, there may be combinations of environmental control systems that can achieve significant SO2, NOx, and mercury reductions at lower cost than the conventional approach of three add-on processes FGD for SO2 control, selective catalytic reduction for NOx control, and carbon injection for mercury control.