Reducing the Load on Cooling Towers through Revamping of Individual Coolers

The engineering of cooling water systems involves a consideration of both hydraulic and thermal behaviour. Unfortunately this is often ignored. For instance when engineers seek to reduce the thermal load on cooling towers they will often opt for increased heat recovery (via improved heat integration) but will ignore the effect that such action has upon the performance of the individual coolers forming the cooling water network. Improved heat recovery leads to reduced inlet temperatures to the coolers. This, in turn, leads to over-performance of the coolers (with the process streams being cooled to lower temperatures than previously accepted).

The over performance of these coolers can be corrected in a number of ways: reducing the flow of cooling water through the exchanger (by using either a bypass or by throttling a valve), operating a bypass on the hot side of the exchanger, or by plugging some of the tubes in the exchanger. These options can be used in combination.

This paper presents a systematic procedure for identifying all of the effective options.

Using a case study it is shown that failure to modify the coolers following an improvement in heat recovery can result in reduction in the thermal load on the cooling tower being just 70 % of what is possible.