WATER       [ GOTO TOP]

          Water is tasteless, odorless, colorless, and liquid in its pure form.  It is the only inorganic material that occurs in three forms (Ice, Water, Vapors) within the earth’s natural temperature range.  Because water is converted to steam at convenient temperature, it is ideal of generating power or steam, or conducting heat.

CHEMICAL COMPOSITION OF WATER        [ GOTO TOP]

           The common formula is H2O however there are several hybrid forms of water in all supplies.  Water contains about 300 PPM of deuterium oxide D2O or heavy water.  This does not quenched thirst or makes plant grow.  But in pure form it has found use in moderating nuclear reactor.  Another form of water is tritium oxide T2O is made radioactive by cosmic rays.  For all practical purpose though only ordinary water H2O is considered for use in Boilers, Cooling Tower, Chilling Plants, Heat Exchangers etc.

TYPES OF IMPURITIES IN WATER   (Impurities in natural waters may classified as)         [ GOTO TOP]

1. Dissolved solids
2. Dissolved gases.
3. Suspended matter.
4. Microbiological contamination

      Water is a universal solvent, it dissolves the rocks and soil it contacts.  It dissolves gases from the air and gases given of from organic in the soil. It picks up suspended matter from the earth.  It is also subject to contamination with industrial waste, oils, and process material in general the type of impurities water contains depend on what it contacts, the amount of impurities depends of the contact time.

KINDS of DISSOLVED SOLIDS IN WATER      [ GOTO TOP]

     The minerals that water picks up from rock consist chiefly of calcium carbonate (limestone), magnesium carbonate (dolomite), calcium sulfate (gypsum), silica (sand), magnesium sulfate (Epsom salt), sodium chloride (salt), Hydrate sodium sulfate and small quantities of iron, manganese, fluorides, aluminum, and other substances.  Waste from mines and certain industrial processes make some surface waters very acid, while minerals in the earth make some ground waters very alkaline, sometimes nitrates and phosphate found in water and in many cases can be associated with sewage contamination.

HARDNESS      [ GOTO TOP]

     Water contains large amount of calcium and magnesium minerals are hard to wash with.  The calcium and magnesium compounds react with soap to form a curd in the water.  The compounds are referred to as water hardness.  These amounts of hardness in natural water may vary from several 00 PPM to 500 PPM.  Because calcium and magnesium compound are relatively insoluble in water they tend to precipitate out causing scale and deposit problems.  The hardness of the water source is an important consideration in determination suitability of the water for steam generation & Cooling purpose. Hardness is perhaps the most troublesome of all water impurities. It may cause scale formation in your system. Hardness is due to soluble compounds of calcium and magnesium in the form of calcium carbonate and magnesium carbonate.

pH      [ GOTO TOP]

        Control of pH is critical for the majority of cooling water treatment programs. In general, when pH is below recommended ranges, the chance of corrosion increases and when pH is above recommended ranges the chance of scale formation increases.  The effectiveness of many biocides also depends on pH therefore high or low pH may allow growth and development of microbiological problems. A good control point is 8.2 to 8.5.

T.D.S.     [ GOTO TOP]

         When raw water from its source is high in its TDS contents, it is desirable to remove it in pretreatment preferably since cooling water concentrate by 3-5 times even normal blow-down are maintained. When TDS crosses the prescribed limit for a cooling tower, it should be controlled by blow down if necessary more than a shift as cooling water blows down is the only direct method of lowering concentration of solids.

ALKALINITY     [ GOTO TOP]

         Alkalinity and pH are related because increase in pH indicates in alkalinity and vice versa. As with pH, alkalinity below-recommended ranges increases the chances for corrosion, those above-recommended ranges increase the chances for scale formation.  When corrosion and scale problems exist, fouling will also be a problem.

DISSOLVED GASES     [ GOTO TOP]

      Water dissolved varying amount of air, which is composed of 21% oxygen, 78% nitrogen 1% other (including 0.03%-0.06% carbon dioxide) Oxygen is soluble up to 9 PPM in water at room temperature and at atmospheric pressure.  The solubility of oxygen decreases as the temperature of the water increases.  But water under pressure can hold larger quantities of dissolved oxygen.  Although nitrogen is dissolved in natural water, it is an inert gas and has little effect on the water used in boilers & cooling system.

SCALE DEPOSITS      [ GOTO TOP]

         Scale can be defined as the deposit of sparingly soluble inorganic minerals on the metal surface.  These deposits or scales are typically dense, non-conducting, hard, tightly bound particles that tenaciously adhere to the metallic surface. Scales such as calcium carbonate and calcium sulphates are formed on the heat transfer surface since these substances possess inverse solubility that is these substances are more soluble in cold water than in hot.

      The factors that determine the scaling tendencies of water are temperature, alkalinity, pH, hardness and dissolved solids.  If any of these changes, scaling tendencies also will change.  For example increase in pH or alkalinity can increase calcium carbonate scale formation, while silica scales decrease under these conditions.  Scale results when the amount of scale forming materials dissolved in the water exceeds its saturation level, other dissolved solids in water also influence the scale forming tendencies.  In general, the higher the level of scale forming dissolved solids, the greater the chances of scale formation.

SCALE DEPOSIT CONTROL      [ GOTO TOP]

        Scale can be effectively controlled in a re-circulation cooling system by one or more of the following methods.

1. Limiting the cycles of concentration.
2. Physical removal of scaling impurities (external treatment)
3. Chemical treatment.

ALGAE     [ GOTO TOP]

          Primitive plants, manufacture their own food by photosynthesis from water carbon-di-oxide, using chlorophyll as a catalyst.  Algae growth usually occurs in sections of the cooling tower to the sun.

FUNGI      [ GOTO TOP]

       Fungi include all simple plants not containing chlorophyll in industrial cooling system.  Fungi growth is generally encountered above the water level.

BACTERIA      [ GOTO TOP]

      Bacteria are the smallest, yet the most prolific and trouble some forms of life in a cooling water system. Bacteria multiply at an awesome rate by cell division.

BIO-FOULING CONTROL     [ GOTO TOP]

       Microorganisms present in the cooling system are controlled by the periodic application of micro-biocides. Factor which influence the effectiveness of the biocides are (a) choice of biocide (b) concentration of the biocide per application, (c) contact time, (d) application point and (e) frequency of addition.

CURRENT METHOD OF TREATMENT AND CONTROL      [ GOTO TOP]

      A cooling water treatment program for all system can never be standardized.  Cooling systems differ widely from a simple central air-conditioning or diesel engine cooling system to complex fertilizer plants.  The quality varies depending on its cooling water supply from lake, river, bore-well or sea.  The heat load, cooling range, material of construction also differ widely.  System design, plant layout, metallurgy of the equipment contaminants from the process and environment, make up and re-circulating water chemistry and microbiology are the important factors influencing the design of a suitable water treatment program.

    Although the problem of corrosion, scale, general fouling and bio fouling have been discussed separately, in practice all four problems occur together, but in different degrees.  Therefore, a versatile and complete treatment program design is very essential to achieve satisfactory results.  For this reason, Comet™ Water Treatment program are designed to include:

1. Mixed corrosion inhibitors that is effective over multi-metal systems.
2. Scale control additives to prevent calcium carbonate and other deposits.
3. Anti-foulants to prevent sedimentation fouling.
4. Low toxicity additives for easy handling and minimal disposal problems.
5. Compatibility with biocides applied

OPERATING MECHANISM OF THE TREATMENT PROGRAM     [ GOTO TOP]

          Comet™ Cooling water treatment programs are non-toxic and are based on polymer inhibitors.  They are effective in treating a wide range of severely corrosive to severely scaling water (re-circulating water LSI from-1.5 to +1.5)
                                   
         Polymer based inhibitor treatment inhibits corrosion through combined action of cathodic and anodic inhibitors formulated in a synergistic mixture.  In an operating cooling system, the inhibitors are removed from the solution by the metal surfaces.  The anodic inhibitor combines with the oxidized film to form a protective barrier while the cathodic inhibitor as absorbed directly into the metal.  The net effect is the retardation of the corrosion process.

        In addition to inhibiting corrosion, poly functional inhibitor treatments prevent mineral deposition and fouling.  This protection is achieved by combining the inhibitor with an organic sequestering agent and polymeric anti fouling such as homo polymer Comet™.  Where water quality dictates, pH control can be used without adversely affecting inhibitor performance.

CONCLUSION     [ GOTO TOP]

        Effective scale/corrosion/fouling prevention will only be achieved if the correct treatment is prescribed and applied.  Therefore, for any cooling system and approval of the plant, water quality and problems (degree to which each problem prevails) is essential.  This is best done by a careful plant survey prior to introduction of any treatment program.  The program designed should be balanced blend of correct operation practices augmented by the use of chemical inhibitors combined with a simple but effective schedule of monitoring and control.  The proper selection and application of micro-biocides are essential if the integrity and efficiency of the cooling system is to be maintained.

       The effectiveness of the microbiological control program should be monitored by regular visual inspection of exposed cooling tower surfaces and by periodic microbiological analysis of the re-circulating water.

    Cooling water management in essence is specialized job and can be done effectively only by companies with expertise in water treatment who can supply not only plant and chemicals but also service by regular visits to monitor and control the treatment program implemented and train the staff in correct plant operation and control.