Control cooling system water treatment

Some pioneers in cooling system water treatment attempted to control corrosion by Saturation Index adjustments alone, without addition of chemical inhibitors. Unfortunately, most cooling systems include heat exchangers with wide temperature variations. A cooling... 

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Most microbes in cooling systems can be controlled by chlorine or bromine treatment if exposed to a sufficient residual for a long enough time. A free chlorine residual of 0.1—0.5 ppm is adequate to control bulk water organisms if the residual can be maintained for a sufficient period of time. 

Open recirculating systems These are more amenable to inhibition since it is possible to maintain a closer control on water composition. Corrosion inhibition in these systems is closely allied to a number of other problems that have to be considered in the application of water treatment. Most of these arise from the use of cooling towers, ponds, etc. in which the water is subject to constant evaporation and contamination leading to accumulation of dirt, insoluble matter, aggressive ions and bacterial growths, and to variations in pH. A successful water treatment must therefore take all these factors into account and inhibition will often be accompanied by scale prevention and bactericidal treatments. 

Because of their surfactant and filming properties fatty amines such as coco-alkylamine acetate (and more especially diamines, such as tallow propylenediamine) are also occasionally employed in other types of water treatment programs. For example, they may be used as corrosion inhibitors for steel cooling systems, especially those smaller units where minimal operational control is provided. The amines must be continuously dosed to ensure good film formation (and thus corrosion protection), typically at 5 to 10 ppm active amine. They also tend to have good biostatic control properties, which provide a benefit of algal and bacterial control at no extra cost. 

The quantity of deposit control water treatment chemical required to be added to a cooling system per unit time (and hence the cost of the chemical program) is a function of the volume of makeup water added to the system and the cycles of concentration, or concentration factor of dissolved solids within the recirculating water. 

Most chemical treatment programs have not in the past specifically focused on controlling silica levels in cooling water, and as a consequence almost all analyses of scales and deposits taken from the waterside of cooling systems, especially from heat exchangers, have shown the presence of small percentages of silica. Research over the last five years or so has led to the introduction of silica-specific deposit control polymers and has also led, with some success, to the reevaluation and promotion of some established calcium carbonate polymer products for effective silica control. 

When extremely poor control is exercised over lime-soda softening, the pH of the treated water can often rise and fall, and may rise to exceed pH 11.0 to 11.5 on occasion. This is clearly unacceptable and will dramatically increase the risk of carbonate fouling, thus tending to make subsequent treatment and control of the cooling system extremely difficult (on the premise that chemical and services treatment programs can be developed for almost any quality of cooling system makeup water, as long as the water quality remains reasonably consistent). 

The fact is that sulfuric acid is an excellent low cost method of reducing the risk of carbonate scaling and often permits higher cycles of concentration in a cooling system than might otherwise be available. These features of sulfuric acid have benefits such as lower system stress, reduced water and chemical treatment consumption, and probably a lower maintenance cost. To achieve these benefits, good control over acid dosing and pH is required, as discussed above. 

An early standard treatment method, used up to the mid 1950s and based on first identifying the precise cooling water CaCC>3 solubility equilibrium point for any system, then using sulfuric acid to control the Langelier Saturation Index (LSI) to approx. +0.6 (M alkalinity of approx. 80 ppm CaCC>3). Primarily employed for cooling systems with makeup water of a... 

In the United States, the European Union, and many other countries, as has been mentioned earlier, there are regulations that control the use of biocides and other types of chemicals in industrial situations. Successful efforts to clean up rivers, improve working environments, and remove pollutants from being discharged cannot just be ignored or overridden. The cooling system operator often has a duty to review all water treatment chemicals, including biocides, prior to their potential use on-site. The owner may have rules in place over what biocides are or are not acceptable in the workplace. 

Cooling systems are dynamic and therefore need various control and monitoring systems. Among them are systems for injection of acid or specialty chemicals, real-time monitoring and recording of the water treatment program performance, and the control of pH, TDS, oxidation reduction potential (ORP), suspended solids (SS), etc. 

There are no commercially viable inhibitor treatments commonly available that can provide complete waterside protection under any and all water chemistry and operational conditions Vendors generally design inhibitor products for only a limited range of the cooling water spectrum. Therefore, for any particular cooling system, careful product selection and control is necessary to ensure adequate coverage and protection. 

A feature of modem water treatment inhibitor manufacture is the trend to formulate products with an increasing bias toward All Organic Programs. However, this development coupled with cooling system users demands for increased product performance (to match higher stress production process operating conditions) has tended to exacerbate problems of accurate field product testing and control. 

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