By P. Thyse, technical manager at Allmech

Cooling towers require water treatment systems to ensure they operate optimally and last their designed service life.

An example of corrosion that has occurred on a cooling tower. Image credit: Allmech

An example of corrosion that has occurred on a cooling tower. Image credit: Allmech

Without water treatment, cooling tower water may be affected by organic growth, fouling, scaling, and corrosion. This can reduce plant productivity, cause downtime, and increase maintenance and repair costs significantly. The key is water treatment optimisation: the ability to not only apply the right chemistries but also to constantly monitor and control water quality and to keep it balanced at all times.

By monitoring pH, water temperature, electrical conductivity, microbiological activity, corrosion, chemistry levels and other variables you are able to increase production, reduce downtime, lower operating and chemical costs and reduce your operation’s impact on the planet. To control scale, corrosion, microbiological fouling, and foaming; water quality must be maintained at all times, and the right microbicides must also be applied in the right doses.

Water treatment products can generally be divided into three groups: scale and corrosion inhibitors for open circuits, scale and corrosion inhibitors for closed circuits, and micro biocides. Solutions across these categories exist and are designed for each specific requirement.

Scale and corrosion inhibitors

When it comes to scale and corrosion inhibitors for open circuits, versatile products are on the market that control scale and corrosion equally well. These products are particularly effective where system control is erratic and when plant operating conditions tend to fluctuate. A wide variety of deposits can be controlled over an extensive pH range. Specially formulated solutions designed to reduce corrosion and scale formation in cooling and boiler water systems should be used. These are also useful in other systems where calcium carbonate scale and mild steel corrosion need to be prevented.

For closed circuits, other inhibitors are designed to control the corrosion of metals in such systems and are best for treating process cooling, hot water and chilled water systems, as well as glycol water systems. Such products contain steel and copper corrosion inhibitors to provide multi-metal corrosion control, plus pH buffering to minimise the effects of acidic conditions from ethylene glycol breakdown or acidic process leaks. Hardness salts are controlled to a maximum level of 225ppm by means of a formulated dispersant and antiscalants. It can be used with ethylene glycol in winterised systems, thereby eliminating the incompatibility problems of chromates.

Micro biocides

Meeting certain water quality standards requires testing for Legionella bacteria. SANS 893-1 provides guidelines for the risk management of Legionella bacteria in any undertaking, while SANS 893-2 focuses on requirements for designing and managing hot- and cold-water systems that could create and transmit water droplets (and thus Legionella bacteria).

Experience has shown us that cooling towers, evaporative condensers as well as hot- and cold-water systems in a wide variety of workplaces present a risk of exposure to Legionella bacteria. Corrosion, scaling, fouling and biofouling are all inter-related and if not treated correctly can lead to inefficient processes, higher water and energy usage and increased plant maintenance costs.

Different micro biocide products are available

  • Broad-spectrum biocide for use in RO, UF and NF systems where bacteria and biofilm are expected to be present. It provides microorganism control (including Legionella) and clean systems. It can be used alone or with other biocides on a rotation basis.
  • Broad-spectrum algaecide and biocide are especially effective for the control of algae and slime in industrial water systems, air evaporative condensers and air conditioning units.
  • Broad-spectrum biocide for closed circuits.
  • Low-cost algaecide and biocide when combined with other treatment products.

Businesses with cooling towers should also consider additional water filtration to remove suspended solids, organics, and silt particles in their cooling systems. Reducing fouling and biological growth in the cooling systems helps to control other issues in the system, such as scaling and corrosion. Side stream filtration is an effective tool for the control of deposition and fouling in a cooling water system.

Allmech is a South African manufacturer of boilers and supplier of water treatment components.

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