Chilled water mechanical refrigeration

FIG. 24-65 Mechanical refrigeration TIC systems utilizing chilled water for cooling turbine inlet air, and cooling towers to reject the waste heat into the environment, account for the majority of refrigeration TIC systems sold. 

The optical chilled-mirror dew point technique is a fundamental measurement, because the saturation temperature determines the saturation partial pressure of the water vapor. A temperature element is then placed in thermal contact with the mirror, and the mirror temperature is utilized directly as the dew point or saturation temperature. The cooling of the mirror surface in the past was done by acetone and dry ice, liquid C02, mechanical refrigeration, and later by thermoelectric heat pumps. The thermoelectrically cooled, optically observed dew point hygrometer probe is illustrated in Figure 3.26. 

Precooling — As discussed in the previous section, it may be necessary to chill the air before entering the adsorbers. This may be accomplished with an in-line mechanical refrigeration unit, a water chiller using evaporative cooling from waste gas from the plant, or a combination of both. 

Two tyjjes of coolants are used (1) water from a cooling tower (CTW), and (2) chilled mixtures of glycols and water, or of soluble salts and water. The mixtures are called "brines" (Box 1.5), and are produced by mechanical refrigeration. 

Despite this concern, some users of Ciass II cosolvent machines do not use chilled brine. Obviously, these users will experience reduced energy costs and required investment, and also experience increased costs of solvent loss. Certainly, chilled brine is not required for effective cleaning. In Table 1.5 is tabulated a comparison of cooling tower performance vs. that of mechanical refrigeration of "brine." The choice between chilled brine and cooling tower water is simply one of optimization. 

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