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• ash dewatering bins. Excess water is recycled as ash sluice water and is also used for coal and fly ash dust <br />suppression. Control of particulates (fy ash) is accomplished with an electrostatic precipitator on Units 1 and <br />2 and a baghouse on Unit 3. All three stacks are approximately 600 feet in height. The precipitators and the <br />baghouse are designed to remove 99.9 percent of the fly ash, resulting in a particulate emission of 0.1 <br />pounds per 106 Btu. Fly ash from Units 1 and 2 is transferred pneumatically from the precipitator to storage <br />silos. From the storage silos, it can be either utilized or disposed of. <br />Peabody wet limestone scrubbers are used on Units 1 and 2. The scrubbing efficiency expected on the wet <br />scrubbers is 85 percent. The wet scrubber systems uses eight six -stage spray towers with countercurrent <br />flue gas flow. The wet scrubber liquid -togas ratio is about 50 gallons of scrubber liquor per 100 actual cubic <br />feet per minute. Adjustment of the pH and the concentration of recirculating solids control gypsum seating. <br />Under normal operating conditions the recycle slurry is about 15 percent solids and is increased to 35 percent <br />solids in the thickener underflow. This is further dewatered to 60 percent solids by centrifuges prior to <br />disposal. <br />The Unit 3 dry scrubbing system utilizes dry limestone in four absorbers, twelve mixers per absorber. The <br />design SO2 removal is 87 percent. The manufacturer is Babcock and Wilcox. <br />4.3.4.2 Waste Characteristics <br />• Utility wastes consist of three primary products, i.e. fly ash, bottom ash and scrubber sludge, along with small <br />volumes of other miscellaneous non -hazardous solid wastes. Fly ash and bottom ash are the products that <br />remain after the combustion of the coal. Fly ash is a fine dry material similar in texture to Portland cement. <br />During the combustion of the coal, light particulates (fly ash) rise up the emissions stacks. To prevent them <br />from being dispersed into the atmosphere, electrostatic precipitators are used to collect the particles as they <br />travel up the slacks. The resulting waste is fly ash. Bottom ash is the waste product that remains in the <br />boiler after the combustion of coal. It is a coarse material similar in texture to a mixture of sand and fine <br />gravel. <br />• <br />4-27 <br />Revision: "(2-10 <br />Approved: FF -R 2 ?999 <br />