About Cooling Towers

Introduction

Cooling waters are widely used in industry, especially in conventional or nuclear power plants for condensation of vapors; in the chemical and petrochemical industries for condensing distillates and for cooling products undergoing exothermic reactions; in the metallurgical industry for cooling turbines, motors, compressors, blast furnaces; etc

Many types of waters, including both fresh and salt water or seawater, are used for cooling purposes. Depending on the raw water quality and the type of cooling system, most waters will require a certain degree of treatment before they can be used. Adequate cooling water treatment is often the bottleneck of successful plant operation.

Cooling Water Treatment

General

Successful cooling water treatment programs must control corrosion, scale and deposit formation, and microbiological fouling. All of these problems are interrelated, and no one problem can be isolated from the others.

For example : scaling occurs more rapidly in a corroding system, while under-deposit corrosion can lead to rapid failure of otherwise un-attacked metal.

Microbiological growth on a metal surface will be facilitated by the presence of deposits or rust, and (additional) microbiologically induced corrosion may result.

Cooling water treatment technology has undergone profound changes over the years. New chemicals have been developed that permit new methods of chemical treatment, and environmental regulations now require strict control of the composition and quantity of cooling water discharged to receiving streams.

Water treatment programs and processes

The definition of an adequate water treatment program is highly dependent on specific circumstances, like :

• type of cooling water circuit
• materials of construction used
• type and quality of the raw (untreated) cooling water
• temperatures
• nature of the process stream to be cooled (e.g., risk of accidental leakages restricts the choice of treatment chemicals in case of cooling of food or beverage products), etc

Furthermore, an extremely wide range of treatment chemicals is available on the market. An optimal selection requires skilled personnel and experience.

All this makes water treatment a highly specialized field, which is not further covered in the present information system.

Types of Cooling water Systems

Three basic types of cooling water systems are in use today, singly or in combination. They are known as "once-through", "closed recirculating", and "open recirculating" systems. The recirculating types are the most widely used, and the open recirculating system - in which the water gets exposed to the atmosphere - poses the most severe treatment problems (to avoid fouling and corrosion).

Once-through systems

feature single-pass flow through heat-exchange equipment. Used mostly by large plants with abundant water supply, this is the simplest system, but it contaminates large water volumes.

Recirculating systems

are water-conservative but are more complicated

Closed recirculating systems

meet small-volume needs, as for chillers, generators, diesel engines, etc. Fewest treatment problems are encountered here.

Open recirculating systems

are most commonly found at utilities, chemical plants, etc. The greatest treatment problems occur here because solids are concentrated and water is aerated (in - polluted - atmospheres  ).

Compound systems

combine the features of both (once-through and recirculating). They are, for example, encountered in many chemical and petrochemical plants where energy recovery is critical for efficiency. Water-cooled nuclear power stations also feature different types of cooling systems. The primary and secondary loop are of the closed recirculating type, the tertiary circuit is either an open recirculating or a once-through system.