Cooling water impurities and treatment
- Posted by: María García
- Category: Process Engineering
An open recirculating cooling system uses the same water repeatedly to cool process equipment. Heat absorbed from the process must be dissipated to allow reuse of the water. Cooling towers, spray ponds, and evaporative condensers are used for this purpose.
Fresh water is being added to cooling water towers to replace water lost through leaks or evaporation. But this makeup water contains minerals, dirt, debris and other impurities that build up and insulate the metal surfaces.
Open recirculating cooling systems are inherently subject impurities-related problems such as:
- cooling by evaporation increases the dissolved solids concentration in the water, raising corrosion and deposition tendencies
- the relatively higher temperatures significantly increase corrosion potential
- the longer retention time and warmer water in an open recirculating system increase the tendency for biological growth
- airborne gases such as sulfur dioxide, ammonia or hydrogen sulfide can be absorbed from the air, causing higher corrosion rates
- microorganisms, nutrients, and potential foulants can also be absorbed into the water across the tower
Main problems of the cooling water circuits are corrosion, scale, fouling and microbial growth. They can lead to flow restrictions, reduced operating efficiency, higher maintenance costs and unscheduled outages. These four problems do not happen in isolation and they can occur simultaneously.
Nowadays, the programs used for proper treatment address these four harms together. Then, a specific treatment to remove damaging impurities from cooling water systems is essential in cooling water systems.
Treatment of the cooling water is broken down into two major categories, external and internal:
- External treatment encompasses any treatment given to the cooling tower makeup.
- Internal treatment is the addition of chemical directly to the recirculated cooling water
Corrosion inhibitors, hardness stabilizers, dispersants and microbiocides should be used for conditioning purposes. Treatment shall be selected to eliminate or at least reducing the mechanical contaminations and prevent microorganism´s growth in the Cooling system.
Nevertheless, a proper treatment is not only the ability to apply the right chemistries and the right dose, but also to constantly monitor and control water quality to keep it balanced at all times, by monitoring pH, water temperature, electrical conductivity, microbiological activity, corrosion, chemistry levels and other variables in the system.
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