Metito Cooling Systems Treatment Program

Scale deposition is a fundamental problem in cooling water systems as it reduces the heat transfer efficiency by forming insoluble deposits on heat exchanger tubes and surfaces. The formation of scale can result in under deposit corrosion, restriction in water flow and an increase in water consumption thereby reducing plant productivity and increasing operational and maintenance cost.  Typical deposits are calcium carbonate, calcium sulfate, calcium phosphate, magnesium silicate, silica compounds and mixtures of these.

In addition to mineral scale, the formation of sludge and organic foulants also contribute to the challenges related to deposits formation in the cooling system equipment. These foulants are introduced through the silt and debris in the air, corrosion bi-products, bio-mass deposits and process contamination.

Solutions for Scale and Deposit Control
Prevention of scale deposition is accomplished by controlling the water chemistry below the saturation point of mineral scale. This includes the use of pH adjustment, phosphonate sequestrants, and polymer dispersants.  The use of scale inhibitors is mainly intended for open systems, since closed systems mainly use soft or demineralised water.

Optional Treatments

• Increase the Solubility of Minerals
  Every mineral in water has a solubility limit effected by ion concentration, pH and temperature. The use of scale inhibitors increase the solubility of mineral scale but it must be noted that there is a limit for the inhibition property of different grades of inhibitors that are typically organic phosphonates and polymers.
• Crystal Modification
  This approach works on the deposits after it is formed by changing its morphology and structure by forming non-adherent form of crystals that are released from the system with the regular blowdown.
• Dispersion
  The use of dispersants to break up the particles of mineral scale.  Another type of dispersants is surfactant based which is effective in the prevention of bio-mass formation and organic foulant agglomeration.

Corrosion damages the key components (pipes, pumps, heat exchangers and other metallic components) in the cooling system and reduces its original strength leading to reduction in its life and resulting in process leaks and equipment failures in the recirculating cooling system network.

Corrosion is caused by the reversion of the metal surface to its original oxide state, which can be observed by general uniform metal loss, localised or pitting corrosion, galvanic, under deposit and micro-bio induced corrosion (known as MIC).  Metito has as comprehensive line of corrosion inhibitors (Cathodic and Anodic) ranging for zinc based, phosphate, non-phosphate and filming type.

Corrosion control is also achieved via different mechanisms in addition to the application of proper chemicals as corrosion monitoring is essential for every cooling system regardless of its size. Metito utilises corrosion coupons and/or online monitoring equipment to monitor this critical factor. Computer modeling is then used to define the type of corrosion inhibitors needed based on water quality and system design.

Range of Products:

• Inorganic and poly phosphates
• Organic phosphonates
• Polymers
• Molybdate
• Nitrites
• Silicates
• Azoles
• Filmers

Microbiological problems commonly exist in cooling water systems. These living organisms are present in the air, soil and water. Under the proper conditions, they grow into large bio-mass that block water flow, obstruct heat transfer, induce corrosion, impose health risks and cause offensive odors. If left uncontrolled, microbiological growth will result in fast deterioration of the cooling system pipes, packing, heat exchangers, nozzles and other parts.

Micro Bio-Control Solutions

• Oxidising Biocides
  Chlorine and hypochlorite are the most common used oxidisers in the industry.  In some cases their effectiveness is hindered and the use of enhancers such as brominating agents is needed.  The use of a stabilised form of chlorine based biocides is also considered in areas with elevated ambient temperature. Chlorine dioxide has a high level of performance under different conditions and in situations where there maybe process leaks.
• Non-Oxidising Biocides (NOB)
  The use of NOBs is intended to support the oxidisers or replace them in case of limitation in the use of chlorine or other regulatory rules, such as discharge requirements. The selection of the best NOB or combination of two different types depends on the chemistry used in the cooling system and the system operating parameters.
• Enhancers
  Dispersants (surface active agents) are used to enable the biocide penetrate into bio-mass layers and to assure proper disinfection of the system.

Bio-control is considered the most essential part in allowing the effective treatment program to deliver its results.  Improper bio-control can result in the failure of the best chemical treatment program to deliver the expected results.