High concentration ratios in atmospheric cooling

In the 1970s, this process was the subject of much speculation in the professional literature. First a very high number of cycles was mentioned, 50 for instance or even more, in order to achieve zero blowdown discharge . 

In refinery or petrochemical plant processes, there is diversity in exchanger shapes and models and the conditions they are used under, plus the geographical dispersion on the site. This explains why expectations for concentration values do not usually exceed the still ambitious figure of eight to ten times. 

Nevertheless, some power plants in the U.S. state they achieve concentration ratios in excess of 20 times in systems equipped with side-scream treatments in combination with reverse osmosis or an evaporator creating the blowdown. 

Even at these levels, the system must be run so as to prevent precipitation of silica (maximum solubility of around 140 to 160 mgT ). Additionally, conventional chemical purification of the make up water alone must be replaced by side-stream treatment of the main system water itself (Fig. 40), theoretically advantageous as to size and cost. This treatment provides for chemical precipitation of the calcic bicarbonate alkalinity and silica. 

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