Cooling Water

Water Conservation Using Closed-Loop, Evaporative Systems for Process and Power Applications

By Peter G. Demakos, P.E., and Brian Demers

COOLING CONSERVATION PHARMACEUTICALS POWER REUSE WASTEWATER

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Abstract

Power generation accounts for a significant amount of fresh water use in the United States. There will be increased competition from agricultural, residential, and commercial users. With limitations on water availability and the importance of water quality, closed-loop, evaporative cooling systems can be a cost-effective technology for both heat transfer and water conservation. Wet surface air cooler (WSAC) coolers and condensers are used in a wide variety of industries, including simple and combined cycle power plants. Applications include auxiliary fluid loop cooling, direct steam condensing, and inlet air chilling system refrigerant condensing. Principle of Operation The basic operating principle of a WSAC system is that heat is rejected by means of latent (evaporative) heat transfer (see Figure 1). The fluid/vapor to be cooled or condensed flows through tube bundles as part of a closed-loop system. A large quantity of water (generally 7 to 10 gallons per minute per square feet [gpm/ft2] of coil face area) from the unit basin is sprayed downward over the tube surface. Simultaneously, fans induce air over the bundles in a co-current direction. Evaporative cooling takes place at the exterior tube surfaces. The saturated air stream leaving the tube bundle then makes two 90ᄚ turns into the unitメs fan plenum at a lower velocity, dropping most of the large water droplets back into the basin. The air is then discharged out of the unit through the fan stacks.

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