Recirculating Cooling Water Systems

When the use of fresh cold water is limited, or environmental regulations limit the heat rejection to rivers, canals, lakes and the sea, then air cooling or recirculating cooling water systems must be used. Recirculating cooling 

Many different designs of cooling tower are available. These can be broken down into two broad classes as follows. 

Natural draft. Natural draft cooling towers consist of an empty shell, usually constructed in concrete. The upper, empty portion of the shell merely serves to increase the draft. The lower portion is fitted with the packing. The draft is created by the difference in density between the warm humid air within the tower and the denser ambient air. 

The type of packing used can be as simple as splash bars but is more likely to be packing similar in form to that used in absorption and distillation towers. The temperature limitation of the packing needs careful attention. Plastic packing has severe temperature limitations, as far as the cooling water return temperature is concerned. If the 

Chemicals are added to the circulation system to prevent fouling. Dispersants are added to prevent deposit of solids, corrosion inhibitors to prevent corrosion and biocides to inhibit biological growth. 

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Improved service water reliability by elimination of rubber expansion joints in the recirculated cooling water system and minimization of their use in the raw service water systems... 

Amine salts of ether carboxylates inhibit internal corrosion of oil storage tanks and pipelines [230]. Furthermore it is possible to use ether carboxylates as corrosion and scale inhibitors for industrial recirculating cooling water systems, metalworking fluids, and hydraulic fluids [28,231-233]. 

Lichen is in fact a symbiose between a weed and a fungus. They are not found in swimming pools. Mostly they are present in open recirculating cooling water systems. 

Chemical additives are needed at some plants with recirculating cooling water systems in order to prevent corrosion and scaling. Chemical additives are also occasionally used at plants with once-through cooling water systems for corrosion controls. 

Chlorine and hypochlorite are used to control biofouling in both once-through and recirculating cooling water systems. The addition of chlorine to the water causes the formation of toxic compounds and chlorinated organics, which may be priority pollutants. 

Plant 1226 is a bituminous coal-, oil-, and gas-fired electricity plant [1]. The recirculator cooling water system influent was sampled from a stream taken from the river and the effluent from the cooling tower blowdown stream. The effluent stream is used again in the ash sluice stream. Table 7 presents the data. The following additives are combined with the cooling tower influent ... 

This product has long been available for use in recirculating cooling water systems but has failed to gain much market share. Over the years, there have been periodic attempts to market peracetic acid and renewed attempts are being made as a result of the difficulties associated with chlorine in some markets. The product most commonly available is an equilibrium mixture of approximately 5% peroxyacetic acid and 22% hydrogen peroxide. Peracetic acid is a strong oxidant and is also corrosive. 

See also Chapter 9, Section 4, and the notes on Process Contamination in Section 10.8.28). Techniques for the on-line cleaning of open recirculating cooling water systems are often similar to those for preoperational cleaning in that generally there is a two-stage approach ... 

Almost all open recirculating cooling water systems operate within a pH range of 6.5 to 9.5. Occasionally this may be as low as 6.0 or as high as 10.0. Typically, however, water treatment programs are designed to function within only a narrow pH band of 0.5 to 1.0 pH unit or less. The specific... 

Rice, R.G. and Wilkes, J.F., 1991, Fundamental aspects of ozone chemistry in recirculating cooling water systems. Corrosion 91 Paper 205, Nat. Assn. Cor. Engnrs. Houston. 

FIGURE 16.1. A simplified fiow diagram of a recirculating cooling water system. Sources of water and application are presented in Table 16.1. 

SERVICE WATER SYSTEMS CSA Class 6 These systems remov c heat from equipment including saictv related equipment and transfer this heat to the ultimate heat sink The sy stems are compnsed of a recirculated cooling water system (closed loq>) and a raw service water system (once-ihrough) connected to the ultimate heat sink... 

Figure 1 Diagram of recirculating cooling water system.

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). 

Corrosion inhibition in recirculated cooling water systems historically depended on the oxidizing inhibitors such as chromates and nitrites. These days are gone since nitrites have been found to be highly conducive to organic growths and chromates have been phased out for environmental toxicity reasons. 

It has been weU-established that ozone is an efficient microbiological control agent in open recirculating cooling-water systems (cooling towers). It has also been reported that commonly encountered scales have not been observed in ozonated cooling systems under conditions where scale would otherwise be expected. The water chemistry of 13 ozonated... 

This is an area worthy of further research, as Cu alloys are widely used in recirculating cooling water systems to which corrosion inhibitors are added. 

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