Online monitoring helps keep cooling tower water scale-free
Cooling tower (CT) systems chill industrial products and equipment by circulating water. This chilled water is passed through a heat exchanger which raises the temperature of the water from the CT, then re-chills it through evaporation. This evaporation process builds up a concentration of hard minerals, which, over time, results in scaling. The challenge for operators is to avoid this scale polluting the water, while also avoiding corrosion or bio-contamination caused by cleaning. Traditional treatments are increasingly problematic. As chemical additives are often hazardous, many are banned under strict regulations. So-called ‘blowdowns’ (using steam pressure to blow out water residue) are often unaffordable, as water is increasingly regarded as a precious resource. However, electrochemical partial electrolysis has the potential to be an inexpensive and clean option, but its widespread adoption has been hampered by a lack of reliable monitoring systems. EU funding for the I-SOFT project helped host company UET further fine-tune its scale removal technology. The I-SOFT extension monitors heat exchanger conditions by transmitting information about scale formation to UET’s computer, so that the scale can be removed without contamination. UET’s treatment deliberately produces scale compounds in its reactors, instead of them building up within water systems. The technology also helps dissolve pre-existing scale into water, then reconstituting it within the UET reactors.
The scale monitoring loop
In the I-SOFT project, two temperature elements were connected to the heat exchanger – one to the inlet and one to the outlet. When scale built up in the heat exchanger, the outlet temperature dropped from its set-point. This temperature change altered the UET controller’s amperage, which in turn changed the power supply to the heat exchanger, so that scale could be re-dissolved from the heat exchanger and released back into the water. The process of electrolysis produces an excess of hydroxide which breaks down the scale deposits. “We were inspired by nature, in which hard minerals react with dissolved gases by forming scale on readily accepting surfaces. We followed the same principle by concentrating scaling in the reactors themselves, so they don’t contaminate the water,” says project coordinator David Sherzer. After connecting the heat exchanger inlet and outlet temperature elements and regulating the power supply according to different temperature changes, trials showed that the heat exchanger temperature remained stable. This means that it was maintaining its cooling function effectively.
Ensuring a supply of clean drinking water
At a time of increased concerns about access to clean water, one of the implications of I-SOFT is that the European drinking water table is less likely to be contaminated by overflow from the wastewater table. “I’m proud to have realised that scale, corrosion and bio-contamination can be countered without chemical additives, to help maintain clean drinking water, thereby benefitting everyone,” says Sherzer. At the moment, the I-SOFT technology is still in development. The next step will be to implement the system across the operations of a few customers (where it can be retrofitted) and to monitor the results, before rolling out the technology more widely.
Keywords
I-SOFT, cooling towers, descale, scale, water, pollution, contamination, partial electrolysis, corrosion, temperature, amperage