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<br />OD112~ <br /> <br />Draft - 9/81 <br /> <br />A hybrid cooling system, consisting of both the wet cooling <br />tower and dry cooling tower systems, is an intermediate step in <br />cooling technology which may recei~e some attention in the fu- <br />ture. Rough estimates suggest that the capital costs of this <br />combined system may be about twice as much as those for either. <br />cooling ponds or wet cooling towers alone. It is estimated, how- <br />ever, that a hybrid cooling system would consume 20 to 30 percent <br />less water than either the cooling pond or wet cooling tower <br />methods. <br />Ash Transport of Water <br />Water is required in coal-fired plants to transport ash from <br />the hopper to a disposal site and to wet down fly ash captured <br />during electrostatic precipitation. (Fly ash, as the name <br />implies, is that portion of the ash left after combustion which <br />attempts to escape up the stack. Bottom ash, by contrast, <br />remains at the bottom of the stack.) Literature estimates of the <br />amount of water required for ash transport range from 1,000 to <br />10,000 acre-feet per year in a 1,000 MW plant assumed to operate <br />at 80 to 85 percent capacity. This range is large because the <br />exact quantity of water consumed depends on the ash content and <br />the bottom ash to fly ash ratio, which varies with the type of <br />coal and combustion process utilized (Old West Regional Commis- <br />sion, 1974, p. 55). Public Service Company of Colorado estimates <br />that its Pawnee plant, operating at a capacity factor of 80 to 85 <br />percent, will consume approximately 78 acre-feet per year for ash <br />transport purposes (Parsons, Ed, 1977). <br /> <br />4 <br /> <br />) <br />......... <br />