MOST cooling and heating system failures happen because of the same mistakes or oversights. Anelia Hough, water treatment consultant at Allmech, says that in boilers and cooling towers, these issues include skimping on water pre-treatment or on ongoing maintenance.
“There are four common problems that can occur in boilers and cooling towers that damage effectiveness: corrosion, fouling, biological contamination, and scaling,” she says. “Companies often select not to do water treatment, including pre-filtration, on their cooling and heating systems to reduce operating costs and to meet production demands. This, however, often has the opposite effect and the company might land up losing money. Skipping water treatment doesn’t just result in higher energy costs; customers risk a complete boiler or cooling tower shut down or replacement. That’s far more costly than the initial water treatment equipment and monthly water treatment services.”
Stages of water treatment
Effective water treatment requires treatment before and after introduction of water into the boiler or cooling tower.
The selection of pre-treatment option depends upon the quality of the water source, chemical characteristics of the water, the quantity of make-up feed water required, plant operating practices, etc.
“Raw water sources contain varying amounts of suspended and dissolved impurities,” says Hough.
“Specific water treatment processes will vary depending on the requirements of the system (cooling / heating) and the quality/chemistry of the feed and/or circulation water.”
She says that in boiler operations, poor water quality results in poor quality steam. Feedwater must therefore be pre-treated. The aim is to remove impurities to control deposition, carryover, and corrosion in the boiler system, which affect the boiler’s effectiveness and, in the long run, can cause costly down time and unplanned repairs.
“Within cooling towers’ makeup water, we focus on the water-replacing bleed, and evaporated and leaked water from the cooling tower,” says Hough. “If makeup water is not treated in cooling towers, we almost always see scale and corrosion taking place, which decrease the efficiency of the system. Microbiological fouling is another concern, as it often causes the problems in the tower as organisms settle on the surface and secrete a polysaccharide layer for protection. This film then will collect silt from the water, thus growing thicker and further reducing heat transfer.”
After-treatment involves the addition of chemicals. Specific chemicals must be used depending on the application. For example, Allmech offers a range of SANS 1827 food-grade chemicals for boilers, which are safe for food, beverage, pharmaceutical and agricultural uses. For cooling towers, the company supplies chemicals that act as scale and corrosion inhibitors (for open and closed systems), micro biocides, dispersants and cleaning agents.
Maintenance and testing
“One of the best ways to stay on top of the health of your boiler or cooling tower is to schedule regular maintenance checks,” says Hough.
Allmech ensures operators are maintaining their cooling and heating systems correctly and regularly by completing water treatment checklists and logs during the monthly water treatment services they provide. “These checklists and reports provide continuous updates and feedback to the customer, ensuring the water treatment programme is effective and the boiler or cooling tower is maintained correctly,” says Hough.
