By Eamonn Ryan, from a TechTalk hosted by SAIRAC Cape Town Centre.
In a recent technical talk, Pieter de Jager, owner of Procontrol, a leading provider of water treatment solutions, shed light on the critical importance of effective water treatment in cooling systems. This is Part 1 of a 5-part series.
With over three decades of experience in the field, De Jager emphasises that neglecting this crucial aspect can lead to a cascade of operational and economic problems.
De Jager highlights the four major challenges that necessitate proactive water treatment:
- Scaling: The precipitation of calcium and other salts can form insulating deposits on heat exchange surfaces, drastically reducing efficiency and increasing energy consumption. He points out that scale not only acts as an insulator but also narrows pipes, restricts flow and roughens tube surfaces. In refrigeration systems, this translates to higher pressures and increased power demands.
- Corrosion: Chemical reactions between the water and the system’s metallic components can lead to corrosion, weakening the system and potentially causing leaks and failures.
- Biological growths: The uncontrolled proliferation of bacteria, algae and fungi results in biofilm formation on heat exchanger surfaces. De Jager stresses that biofilm’s unique hydrodynamic and insulating properties make it even more detrimental to heat transfer efficiency than scale or corrosion of equivalent thickness.
- Sludge: The accumulation of suspended solids and other particulate matter can foul heat exchangers and impede flow.
While pH control is generally less of an issue with municipal water, de Jager notes its importance in systems utilising alternative water sources like borehole, river or rainwater, where alkalinity and pH levels can be more variable.
To combat scaling and corrosion, de Jager explains the widespread use of organophosphonate-based products. These chemicals are typically dosed proportionally to the make-up water entering the system, often controlled by a water meter with a pulse output connected to a dosing pump. He highlights the convenience of on-site titration tests to monitor organophosphonate levels.
Addressing the problem of biological growth, de Jager advocates for the use of biocides over chlorine or chlorine derivatives. He cautions against chlorides, noting that many chiller manufacturers explicitly exclude warranty claims if chloride levels are too high. Biocides, unlike chlorine, do not contribute to chloride levels and are applied as a ‘slug dose’ – a concentrated amount added periodically to effectively eliminate microorganisms.
De Jager then tackles the crucial aspect of conductivity control. He points out that many cooling towers come equipped with a manual bleed valve, which, without proper management, can lead to inefficient water usage and poor water quality.