What are the Best Practices of Cooling Tower Water Treatment?

With water cooling treatment such an integral part of operations for a range of industries, scale, corrosion, fouling and microbiological contamination can be costly both in terms of productivity and product quality.

Water: The Universal Solvent

Water is a highly efficient heat transfer medium that has the ability to dissolve many substances. As a result, it can cause unwelcome corrosion in water cooling towers, and dissolved ions can concentrate and form scale. Bacterial growth, encouraged by water’s life-giving properties, may cause fouling. Add in the risk of legionella bacteria, the cause of the often-fatal Legionnaire’s disease that grows in locations where water is present, and water treatment and maintenance becomes necessary and often vital.

Preventing Legionella

As open circuit systems, water towers are particularly susceptible to the development of legionella. Ongoing risk assessments and treatment are best practice when it comes to cooling tower maintenance. Failure to comply with legionella control guidance is a public health risk, and failure to follow accepted best practice may be used in criminal proceedings as proof of negligence.

Once a risk assessment has been completed, all findings must be detailed and logged, and a prevention and treatment scheme must be implemented either by chemical, or preferably non-chemical means, thus lessening the environmental impact.

Guidance on the control of legionella is detailed in the Health and Safety Executive’s Approved Code of Practice L8 2013 – The Control of Legionella Bacteria in Water Systems (ACoP L8).

Corrosion and Scaling

Although some increase in the concentration factor of dissolved minerals can help to guard against corrosion, there is also the risk of scaling and fouling, which should be controlled by periodic replacement of the cooling water with less concentrated water through a controlled and systematic bleed-off process.

The creation of limescale can have a range of damaging effects, from impairing heat transfer to becoming a breeding ground for legionella. Scale should be controlled by the use of a water softener or a scale inhibitor, lowering the pH and alkalinity by dosing with sulphuric acid, or ensuring that salts remain soluble by limiting the system concentration factor.

Best practice in cooling tower water treatment allows the chemical balance of the water work to inhibit the formation of scale whilst running an elevated concentration factor to guard against corrosion. Close control of the concentration cycles coupled with an effective corrosion inhibitor suited to the metallurgy of the cooling tower is an effective deterrent to corrosion.

Fouling

Fouling can be caused by factors such as scale, microbial slime, and sediment from the incoming water supply. Left untreated, it causes a myriad of problems including reduced flow, inefficient heat transfer and corrosion. Best practice includes the use of filtration systems on the incoming water supply and the use of a polymer dispersant to keep suspended solids mobile.

Cooling tower water treatment is essential to extend plant life, keep energy costs down and ensure that vital equipment remains both reliable and safe.