Installing a side-stream filtration system to cleanse cooling tower water helps maintain water efficiency across facilities, as the U.S. Office of Energy Efficiency & Renewable Energy has demonstrated. Although this applies to many applications throughout a range of industries, systems that are exposed to a large amount of airborne particulate are at a greater risk for compromised efficiency and system failure.

Cooling towers are an essential aspect of many refrigeration systems. In HVAC applications, for example, they provide temperature regulation for comfort in workplaces, residences and service centers.

In industrial facilities, they provide process cooling in a range of applications found in manufacturing processes and power generation, among others. For instance, pharmaceutical and biomedical production facilities require effective cooling systems. Cooling towers in these facilities may protect ancillary equipment in the manufacturing process, including condensers, chillers and heat exchangers.

During the COVID-19 health crisis, biomedical facilities are at the forefront, developing plasma therapies until a vaccine is available. The plasma recovered from COVID-19 donors contains antibodies that are specific against SARS-CoV-2, the virus that causes COVID-19. Convalescent plasma can be used for direct transfusion as well as to develop medicines.

In one Los Angeles biomedical facility, production of plasma therapies, immunoglobulin medicines and screening tests has become a top priority. The fortunate addition of cooling tower filtration is allowing the facility to operate at optimum cooling.

In 2019, the facility’s director of maintenance noticed that dirty cooling tower water was causing adverse effects on chiller performance, requiring increased maintenance on the heat exchangers. He contacted a cooling tower filtration provider to help address the problems being caused by the dirty cooling tower water. The facility needed a reliable way to keep the cooling water clean. The proper and uninterrupted function of the chillers and heat exchangers relied on it.

The biomedical facility needed a filter to integrate with a straight 8” pipe flowing 380 gal/min of cooling tower water at 40 psi. Taking into consideration all of the application data, a filter with a 200-micron screen was recommended.

Cooling Towers Play Key Role in Keeping Processes Online

Cooling towers are located at the point in a cooling system where unwanted heat is released into to the atmosphere through evaporation. Keeping the heat transfer surfaces of a cooling tower system clean is widely recognized as the best way to ensure efficient operation.

Because of the operating environment of cooling towers as well as the nature of their technology, cooling towers are vulnerable to the elements. They are susceptible to a variety of particulates that are introduced by the wind. As air quality and wind conditions change, cooling towers undergo wide variations in particulate loading.

Operation can be affected significantly by the quality of the water making up the system. Atmospheric particulate matter can originate from dust storms, living vegetation, fires and industrial processes, all of which may, at various times, contribute to patterns of particle loading in cooling towers. The mineral dusts of airborne soils/sand, ash and cement — comprised of oxides and carbonates — can contribute to higher particle loading in cooling tower water.

It is commonly known that poor water quality, including high particle loading, can lead to problems within an open-recirculating cooling tower system, including corrosion, scaling, fouling and microbiological activity. These problems are interdependent to the extent that prevention of one may help reduce the magnitude of the others.

Self-cleaning strainers can remove unwanted particles from a water source in the 5- to 4,000-micron range.

Biomedical Facility Adds Cooling Tower Filtration

Utilizing samples from the Los Angeles biomedical facility’s cooling tower water, the filtration system supplier recommended a system to address the airborne particulate. The filter screen needed to be fine enough to capture the debris of concern without being so fine that it wasted too much cooling tower water through excessive backwash.

To properly size the system, the filtration system supplier conducted an in-house sieve test on biomedical facility’s cooling tower water. The sieve test takes a representative 1 to 2 gal sample to simulate filter operations across a small area of screen. Filter design engineers take note of the interval required to create differential pressure. In addition, they conduct an analysis of the debris present before and after the sample test. Debris collected on a 200-micron screen shows the efficacy of that screen for the water source.

Typically, filter screens are selected with margins to allow for a reduction in screen pore size, if desired, over time. Once an installation has an established performance baseline, including a recorded average-backwash frequency, field adjustments may be made to size the screen up or down. In some cases, spare screens are kept on hand for seasonal variation.

Based on results from the cooling tower water test for the biomedical facility, the filtration system provider recommended a 200-micron screen to address the cooling tower fouling problem.

The complete solution recommended included a filter to integrate with a straight 8” pipe flowing 380 gal/min of cooling tower water at 40 psi. Taking into consideration all of the application data, a filter with a 200-micron screen was installed. The filter was brought online in August of 2019 and evaluated against a rigorous list of inspection points.

Debris collected on a 200-micron screen shows the efficacy of that screen for the cooling water at the biomedical facility.

The assessment included a confirmation of adequate flush piping, proper wiring and installation of pressure gauges. Of particular importance was a review confirming proper hydraulics to avoid excessive pressure loss to other sensitive equipment in the system. Flush duration was set to 16 sec to match the timing of the hydraulic piston stroke. Once the system became fully operational on a 24-hour basis, the performance baseline was determined at an average of five backwashes per day.

At the biomedical facility, the onsite maintenance team reports that the overall system has improved since installation of the self-cleaning filter. In June of 2020, the facility’s director of maintenance cited performance of the chilling equipment and recent heat exchanger inspections as revealing surprisingly clean results.

The filtration system has reduced both maintenance and labor costs in the facility at a time when efficient production in biomedical facilities such as this one is more important than ever. PC