Cooling water system types

Metal surfaces in a well-designed, well-operated cooling water system will establish an equilibrium with the environment by forming a coating of protective corrosion product. This covering effectively isolates the metal from the environment, thereby stifling additional corrosion. Any mechanical, chemical, or chemical and mechanical condition that affects the ability of the metal to form and maintain this protective coating can lead to metal deterioration. Erosion-corrosion is a classic example of a chemical and mechanical condition of this type. A typical sequence of events is ... 

The subject of weld defects is quite extensive, and complete coverage is well beyond the scope of this chapter. Therefore, this chapter will focus on specific types of weld defects of general concern in cooling water systems. Defects of seam-welded tubes are considered under material defects in Chap. 14. 

Finally, although the basic development and nature of boiler water plant problems may be similar to those arising in other types of water systems (such as cooling water systems), the extremely high steam-water temperatures and heat-flux densities generally encountered impart a much higher level of intensity. This in turn creates the need for more highly focused and effective solutions to boiler plant problems. 

Figure 8-3 Three basic types of cooling water systems. Top the once-through system where the cooling water is used once and then discharged. Middle the open recirculation system where the water is cooled and recycled through a system in which it comes in direct contact with air. Bottom a closed recirculation system where the water is cooled and recycled without coming in direct contact with the atmosphere.

Apart from sodium hypochlorite and sodium bromide solutions, almost all other liquid biocides (or biocide intermediates) are nonoxidizer types. Most nonoxidizers are manufactured by specialist chemical companies, who sell these branded products for scores of different sanitizing or disinfection applications, of which cooling water system treatment is only one. These chemicals may be merely renamed (according to subregistration permits) or they may be blended with other biocides or inhibitors to form new and different products with accordingly modified properties. Some biocides may only be available from the primary manufacturer, often as extremely concentrated and hazardous materials. These chemicals will then usually require some form of dilution, stabilization, and quality verification before being incorporated into a service company s product line. 

During the last 20 years, the use of programs based on bromine chemistry has become standard practice. Bromine/chlorine-based biocides have become internationally accepted as mainstream products for all types of cooling water systems, brewery pasteurizers, and many other... 

The fact is that for almost all cooling water system situations, there are several potential routes to a satisfactory solution. There are usually several possible types of chemical treatment programs, each with particular features, benefits, and price ranges. 

Buyers need to assure themselves that the representative and the employer can provide all the particular services, facilities, and expertise that may be necessary for the size, type, and complexity of cooling water system under consideration, and also that the vendor has the financial resources relative to the contract requirements. 

The Eederal Clean Air Act requires the U.S. Environmental Protection Agency to establish hazardous air pollutant emission criteria per unit of production. These standards have been promulgated and range from 0.2 to 0.25 kg for 100 kg of oilseeds processed, for specihc categories of extraction and oilseed type. Attainment of this hgure requires a properly designed vent and cooling water system with minimal intermptions to the operations. 

Fig. 2 Crevice corrosion under seal in Type SS316 sieve from steam condenser cooling water system exposed to flowing seawater for 2 years at less than 40 °C [1].

Open recirculated cooling water systems remove the heat picked up in plant by evaporative cooling. This may be done by a spray pond, for example, combining air conditioning needs with aesthetic considerations in industrial parks. The most common type of evaporative cooling, however, is effective in cooling towers of one type or another (Fig. 8.11). 

Cooling water systems may be either recirculating or once-through types. In closed recirculating systems, oxygen can be excluded, and corrosion often can be controlled by adjusting the pH to an alkaline value. 

Microbiological corrosion in the process industries is most often found in three areas cooling water systems, aqueous waste treatment, and gronndwater left in new equipment or piping systems after testing. Nearly all confirmed cases of MIC have been accompanied by characteristic deposits. These are usually discrete mounds. Deposit color can also be an indication of the types of micro-organisnis that are active in the system. For example, iron bacteria deposits on stainless steel, such as those produced by Gallionella, are often reddish. 

The cooling of the inter-stage compressor air by injecting water is also another very effective way for getting more power from the gas turbine. The problem in most units is that there is no convenient place to inject the water. The gas turbines would require substantial modification to install such a system. Care would have to be taken that any modification would not affect the integrity of the system. This type of a system is very effective in units where there is a low and high-pressure compressor, providing a very convenient place to inject the water. This type of compressor are mostly available in aeroderivative units. 

Figure 9 shows the details of a typical horizontal tube-type ozone generator. This unit is preferred for larger systems. Water-cooled plate units are often used in smaller operations. However, these require considerably more floor space per unit of output than the tube-type units. The air-cooled Lowther plate type is a relatively new design. It has the potential for simplifying the use of ozone-generating equipment. However, it has had only limited operating experience in water treatment facilities. 

---