Cooling water Fouling

Cooper, A.,J. W. Suitor, andj. D. Usher, Cooling Water Fouling in Plate Heat Exchangers, Heat Transfer Eng, V. 1, No. 3, Jan.-March (1980). 

Zuniga, Patricia O. Miller, Kenneth Winters, Michael. A Cooling Water Fouling Monitor Senses Upsets, Evaluates Changes. Reprinted from Chemical Processing, April 1990. 

Comparison of plate heat exchanger area requirements with two different cooling water fouling resistances... 

Tributyl(tetradecyl)phosphonium chloride was developed specifically (26,27) as a broad-spectmm biocide for the control of biological fouling in cooling water systems where it is particularly effective (see Industrialantimicrobialagents). 

Other energy considerations for cooling towers include the use of two-speed or variable-speed drives on cooling-tower fans, and proper cooling-water chemistry to prevent fouling in users (see Water, industrial water treatment). Air coolers can be a cost-effective alternative to cooling towers at 50—90°C, just below the level where heat recovery is economical. 

Foulants enter a cooling system with makeup water, airborne contamination, process leaks, and corrosion. Most potential foulants enter with makeup water as particulate matter, such as clay, sdt, and iron oxides. Insoluble aluminum and iron hydroxides enter a system from makeup water pretreatment operations. Some well waters contain high levels of soluble ferrous iron that is later oxidized to ferric iron by dissolved oxygen in the recirculating cooling water. Because it is insoluble, the ferric iron precipitates. The steel corrosion process is also a source of ferrous iron and, consequendy, contributes to fouling. 

Removal of Particulate Matter. The amount of particulate entering a cooling system with the makeup water can be reduced by filtration and/or sedimentation processes. Particulate removal can also be accompHshed by filtration of recirculating cooling water. These methods do not remove all of the suspended matter from the cooling water. The level of fouling experienced is influenced by the effectiveness of the particular removal scheme employed, the water velocities in the process equipment, and the cycles of concentration maintained in the cooling tower. 

A test water box was installed during a 2-week trial to monitor corrosion and fouling in a utility cooling water system. A baffle plate from the test box was removed after the test. Small, hollow incipient tubercles dotted surfaces (Fig. 3.28). Small amounts of carbonate were present atop and around each tubercle. Each tubercle capped a small depression no deeper than 0.005 in. (0.013 cm) (Fig. 3.29). This indicated local average corrosion rates were as high as 130 mihy (3.3 mm/y). 

Silt, sand, concrete chips, shells, and so on, foul many cooling water systems. These siliceous materials produce indirect attack by establishing oxygen concentration cells. Attack is usually general on steel, cast iron, and most copper alloys. Localized attack is almost always confined to strongly passivating metals such as stainless steels and aluminum alloys. 

Maintenance may be reduced due to elimination of water fouling characteristics which could require frequent cleaning of water cooled heat exchangers... 

Figure 10-41. For many cooling waters, the fouling resistance increases rapidly, then decreases, and finally approaches an asymptotic value. (Used by permission Knudsen, J. G., Chemical Engineering Progress. V. 87, No. 4, 1991. American Institute of Chemical Engineers. All rights reserved.)...

In some instances (e.g. cooling water circuits), chemicals can be added to the heat transfer fluids to inhibit fouling. The chemicals added to inhibit fouling and the means of cleaning depend on the nature of the fouling. Fouling can be classified as ... 

Assume the fouling coefficients to be 10,000 W-m-2-K 1 and 5000 W rn 2 K 1 for isopropanol and cooling water respectively. For an assumed cooling water velocity of 1 m-s 1, estimate the heat transfer area for ... 

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