Overview
- Introduction
- Cooling Water Treatment
-
General
Water Treatment Programs and Processes
- Types of Cooling Water Systems
- Once Through Systems
Recirculating Systems
Closed Recirculating Systems
Open Recirculating Systems
Compound Systems
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.
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
unattacked 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.
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.
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