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<br />~,
<br />~
<br />w
<br />C"J)
<br />
<br />DRIFT'O.7CFS~
<br />CONDENS ,., ,
<br />C!RC'727CFS
<br />
<br />rEVAP021.8CFS
<br />
<br />TOWER
<br />
<br />
<br />BLOW-
<br />MAKEUP. 24.5CFS DOWN' it eFS
<br />$ALliN" SALT OUT
<br />MAKEUP DRIFT + SLOWDOWN
<br />
<br />Figure 15.
<br />
<br />Typical water flow rates in the
<br />conventional cooling water loop
<br />of a 1000 MWe power plant.
<br />
<br />The notion of cooling with low quality
<br />water seems to be gaining momentum with an
<br />impressive rate of technological advancement.
<br />The study has certainly not considered every
<br />possible strategy for using saline water in
<br />power plant cooling, but attempts have been
<br />made to evaluate some of the more promising
<br />options.
<br />
<br />The modeling associated with this study
<br />assumed a hypothetical 1,000 MWe power plant
<br />oper at i ng at 40 percent therrna 1 e f f ie i ency.
<br />This is roughly equivalent to a 1,000 MWe
<br />J)lant operating at 35 percent thermal ef-
<br />ficiency and 80 percent load factor.
<br />
<br />Table 6. Concentration of constituents in
<br />cooling tower makeup waters.
<br />
<br />The Cooling Tower-Condenser Loop
<br />
<br />Wet cooling towers reject the energy
<br />acquired in the condenser to the atmosphere
<br />by evaporating part of the coo].lng water,
<br />thus enabling the remaining cooling water to
<br />be cycled back through the system supple-
<br />mented by makeup water (Figure 16.) In the
<br />conventional wet tower, the warmed cooling
<br />water leaving the condenser is introduced at
<br />the top of the tower through distributing
<br />nozzles and falls through a series of trays,
<br />plates or baffles, which expose large wetted
<br />surface areas to the air moving through the
<br />tower, thus enhancing evaporation.
<br />
<br />The relatively small amount of entrained
<br />water lost as fine liquid droplets in the
<br />upwelling air stream is referred to as drift
<br />loss. For mechanical draft towers, drift
<br />los ses of 0.1 percent to 0.3 percent of the
<br />circulating water flow rate are considered
<br />typical.
<br />
<br />
<br />The nonvolatile minerals and ions
<br />present in the makeup water become in-
<br />creasingly concentrated in the recirculating
<br />cooli ng water as evaporat ion proceeds. The
<br />total dissolved solids (TDS) level, as well
<br />as the level of suspended solids thus builds
<br />up. Keeping these concentration levels below
<br />the maximum limi ts that can be tolerated by
<br />physical hardware necessitates the removal of
<br />some of the circulating water from the
<br />system. This discharged water is referred to
<br />as blowdown.
<br />
<br />In order to examine the impact on these
<br />flow rates of using waters of various sa-
<br />linity levels for cooling tower makeup, the
<br />following procedures were developed.
<br />
<br />An energy balance across the cooling
<br />tower is written,
<br />
<br />Q = Mlhf1 - M2hf2
<br />
<br />(1)
<br />
<br /> Sample 1 Sample 2 Sample 3
<br />Constituent TOS = TOS TDS '"
<br /> 1000 to 3000 to > 10,000
<br /> 3000 mg/l 10,000 mg!1 mg/l
<br />Al 0.25 0.72 1.14
<br />B 0,1 0.5 0,7 MevllP,
<br />Ca 156, 343, 312,
<br />C03 117, 361. 550, M, 1 ("'.'"
<br />CI 592, 138, 4880.
<br />F 0.17 0.68 0,46 )~(
<br />Fe <0.02 <0.02 <0.02
<br />Hg 48, 267. 109,
<br />Hn <0.01 0.25 0,50 0
<br />N03-N <0.04 0,50 1.02
<br />0- P04 0,71 0,72 0.98
<br />K 4, 20, 102, /' ",
<br />Si02 11- 22. 35, Mbd
<br /> MlIir
<br />Nil 458, 620, 4300,
<br />S04 700, 2740. 2770. MmlJ
<br />TDS 2220. 4640, 13180,
<br />pH 7,6 8,3 7,8
<br />
<br />
<br />Figure 16. Basic elements of the cooling tower.
<br />
<br />17
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