COOLING WATER TREATMENT. "ENVIRONMENTAL SOLUTIONS. Specializing in Industrial & commercial water treatment, Environmental Consultants".

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Usual method of corrosion prevention is by the use of an inhibitor which passivates the metal of the circulating water circuit. This inhibiting chemical reacts with the metals and in effect, it encourages a touch metal oxide or other film to form on the metal surface, chromate are generally used to inhibit corrosion of iron and steel in water systems.

ENVIRONMENTA SOLUTIONS has the corrosion inhibitors to get the best performance of the cooling towers, among them:

- LA9CT

- LA11CT

- AB4PC

These inhibitors are applied to open and closed recirculating cooling water systems:

-Cooling water circuits utilizing cooling towers

-Chilled water circuits for air conditioning systems

Scaling:

Calcium bicarbonate is the main scaling agent in local cooling water systems.

The two methods used by us for the prevention of scaling are:

-Soft water control

-pH control

Soft water control is the application of the water softener to remove calcium hardness from the feed water before entering to the cooling water system.

pH control is the application of sulphuric acid to create a conversion from bicarbonate to sulphate, alkalinity should be reduced not eliminated.

Microbiological growth (slime & algae):

The inherent operation of a cooling tower is conducive to the growth of algae, fungi and bacteria in the circulating water. Generally, the mayor contributing cause of biological fouling is an algae growth of some type and so we normally talk in terms of algicides for cooling tower water, even though the fouling may be a combination of three causes listed above. Since water is recirculated and air is drawn through it by the fans, air borne contamination is continually drawn into the water is usually warmed and exposed to sunlight, thereby affording and ideal environment of microbes.

Some biocides supplied by us are:

- B11CT

- B30CT

- CTB4009CT

- CT4612L

Cycles of Concentration:

Total dissolved solid, such as, hardness and alkalinity are affected by three inter-related factors; evaporation, make up water and bleed off rates. Water when it evaporates, leaves the system in a pure state, leaving behind all dissolved matters. Water volume of open recirculating cooling systems are held at relatively constant figure through the use of float valves.

Fresh make up water brings with it dissolved material which has evaporated.

Theoretically, assuming that all the water leaves the system by evaporation and system volume stays constant, concentration will continue to increase indefinitely. Dissolved solids it would seem, are on a one way street into a system with no way out. It is for this reason that a bleed-off is installed on open recirculating cooling tower systems, therefore allowing the total dissolved solids to be maintained at prescribed limit.

The control of concentration, the bleed-off removes a portion of the concentrated circulating water, which is then replaced with fresh make up water, which is lower in dissolved solids. This lowers the solids concentration in the system. Either continuous or intermittent bleed-off is used. A flow control valve on a separate line to waste, controls the bleed-off flow rate. Varying the valve setting cycles of concentration within safe limits and prevents scale formation.

Closed recirculatating systems:

Closed systems are those recirculating systems in which losses and make up are at minimum, The air conditioning chilled water systems falls into this category.

Carbonate scale is not a problem unless excessive losses occur, resulting in high make up. Corrosion is usually the main concern. Treatment is usually applied by means of a pot feeder which dosage in proportion to the amount of water in the system, after the initial dosage, it is unlikely that additional treatment will be necessary for several months, unless leakage is excessive. No bleed-off is necessary not should it be permitted, therefore, once a body of water is treated, no additional treatment is necessary unless more water is added to the system.

Cooling water analysis:

The analysis is allowing us to look directly into the cooling water, to determine whether the cooling water is scale forming, corrosive or over concentrating, so that we can take the necessary steps to advert these occurrences. It should never be taken for granted or neglected.

There are five tests always done on cooling water systems, serviced by us. there are:

-Calcium hardness:

Calcium bicarbonate in feed water is converted to calcium sulphate, a more soluble salt, if solubility exceed 1000 ppm, very hard calcium sulphate will be formed in condenser or other type heat exchangers, which is very difficult to remove.

The calcium hardness test determine the level of calcium present in cooling water systems, whether in the carbonate or sulphate form.

-Total “M”Alkalinity:

Detection of alkalinity due to carbonates and bicarbonates, shows the tendence of cooling water to be scale forming or corrosive. Limits 50-100 (criterion for chloride test).

-Chlorides:

The main purpose is for the detection of chlorides to determine cycles of concentration and bleed-off rates. High concentration of chlorides are corrosive, again chlorides allows control. Limits 3 to 5 cycles of concentration. Chlorides should never exceed 1500 ppm.

-Chromium or Molybdenum:

They are added to inhibit corrosion for optimum chromate or molybdenum performance it is essential, therefore, that the concentration be controlled within prescribed limits. Results are expressed as ppm Cr. or Mo. Limits 30-60 ppm.

-pH: Indicates whether cooling water has scale forming or corrosive tendencies. Limits 6.5-7.0.

Habits for a good cooling water treatment:

-For soft water program, ensure that soft water always enter the cooling water system.

-Always monitor cooling water treatment tank closely, identify reasonable low level mark, at this point, new batch of treatment should be made up, preventing possibility of running out of treatment.

-Always order treatment before stock on hand runs out.

-Always monitor bleed-off.

-Do all tests recommended , pay careful attention to results of the analysis, make corrective adjustment immediately as indicated by analysis.

-Always flush cooling tower basin from the high flow sump drain, every week, for the removal of sand, dirt and other foreign matter that is washed from the air that flows through the tower.

-Religiously add all biocides to cooling tower sump or upper basin, as instructed.

Solution to problems encountered in cooling water systems.

Corrosion:

There are four basic caused of corrosion, first of which is oxygen, since the water circulating through a cooling tower is continually aerated, it is saturated with oxygen.

This condition is conducive to oxygen corrosion of any iron or steel piping and equipment in the system. With certain water this type of corrosion is so severe as to cause almost complete plugging of condenser tubes and piping by iron oxide particles. Galvanic action causes another form of corrosion, this take place where dissimilar metals are placed in contact with one another. Biological organisms are still another cause of corrosion, some types of slime living in dark sections are capable of eating or digesting metals. Erosion in still another cause of corrosion, which is the hitting and wearing away of pipe and condenser metal loss by either entrained gases, solid particles or the water it self travelling at high velocity.

The last cause of corrosion is the poor control of scale prevention chemical treatment. If too munch treatment is fed, the pH is lowered sufficiently to cause corrosion of the system, piping and condenser tubes or heat exchanger, even the cooling tower can be damaged, specially metal towers, very low pH will strip the galvanized coating on the tower’s structure.

There are two types of cooling water systems commonly used locally:

-The open recirculating.

-The closed systems.

The principal problems encountered in open recirculating cooling water systems are the following:

-Corrosion - Microbiological Growth (Slime & algae)

-Scaling - Cycles of Concentration

The functioning of a cooling water systems is to remove the heat from a process or equipment. Heat transfer is accomplished by one medium of lower temperature absorbing heat from another medium of a higher temperature. E.g. as in the condenser water, lower temperature absorbing heat from the refrigerant, higher temperature, thus increase the temperature of the condenser water and cooling the refrigerant. This increased temperature affect the balance of the minerals (impurities) present in the water.

In this country, feed water for most cooling water systems are taken from the municipal water supply (city mains). There are a few processing plants that utilizes canal water for various cooling functions.