Open cooling system

Nitrite formulations are employed for both hot and cold water closed loops (and also occasionally for open cooling systems). Unfortunately, nitrite is easily oxidized to nitrate and is very susceptible to microbiological attack (by Nitrobacter agilis and other microorganisms). Nevertheless, it is a good low-cost passivating inhibitor. 

Interpretation of Corrosion Rates in Open Cooling Systems ... 

Molybdate is never used on its own in open cooling systems, as the dose rate for protection of steel is on the order of 75 to 150 ppm Mo. It tends to be formulated primarily with various organic corrosion inhibitors in alkaline solution, and certain synergistic ratios permit the molybdenum content to be reduced so that the reserve of Mo in the cooling water is only 3 to 10 ppm. 

Polysilicates, incorporated in various formulations that may include P-P04 or molybdate and phosphonates/TTA/polymer, have found application for smaller, light duty, open cooling systems and closed-loop circuits, especially where naturally soft or ion-exchange-softened makeup waters have been used. The reported effectiveness of such programs has been mixed. 

As with cleaning closed-loop systems, it is always necessary to first identify the basic types of foulants and problems likely to be found in any new open cooling system and to then select both an appropriate chemical treatment and a cleaning process. 

Nitrite is suitable as an initial passivator in open cooling systems, but it requires dosing at 1000 to 1500 ppm NaN(>2 to compensate for the loss of nitrite in the system, due to conversion to nitrate. 

Fig. 9.1 Sales aid to demonstrate that daily manual addition of chemical inhibitor to an open cooling system consistently fails to maintain reserves within prescribed levels, resulting in either overdosing (higher costs), or underdosing (inadequate protection).

Dosing and Control Equipment for Open Cooling Systems to Meet Current Basic Needs... 

For most open cooling systems, the samples that will need to be taken most regularly will include the recirculating cooling water and the immediate makeup water source(s). If the makeup is a blend of waters or has been subjected to pretreatment processes that can alter its natural characteristics, such as softening, additional samples will need to be taken, albeit probably less frequently. 

With an open cooling system (see Fig. G-11), the incoming air is to be filtered. 

With an open cooling system, a housing with filter cassettes is mounted on one side of the exciter housing for the incoming cooling air. The cooling air exit is directed downward under the exciter housing. 

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