Closed loop control, also known as feedback control, is the most widely used type of…
Closed Loop Water Cooling
Closed loop water cooling is used where the coolant temperatures must be maintained over a certain temperature to avoid solidifying the process stream (“tempered water cooling”), or for high process temperature applications that would exceed the temperature limits of treated cooling tower water or sea water discussed above.
Closed loop water is usually boiler quality and either inhibited with chromate or nitrogen blanketed. Chromate is effective if tube temperatures are below the water boiling point. If tube temperature could exceed the water boiling point, nitrogen blanketing without inhibitor is recommended.
Heavy oils may freeze or become immobile at temperatures above normal coolant temperature. Cooling such fluids is usually accomplished with “tempered water cooling,” as illustrated in Figure 300-4. The coolant temperature should be controlled about 10°F above the freezing/pour point temperature of the stock being cooled.
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