Jan 08, 2016

Cooling Towers: Chemical Treatment for Cooling Towers

University implements chemical treatment program to address scale & biofouling

Cooling Towers: Chemical Treatment for Cooling Towers
Cooling Towers: Chemical Treatment for Cooling Towers
Cooling Towers: Chemical Treatment for Cooling Towers
Cooling Towers: Chemical Treatment for Cooling Towers
Cooling Towers: Chemical Treatment for Cooling Towers

Like cooling tower owners across the U.S., the facilities managers/system owners at a major Midwest university are facing continuing pressure to optimize the performance of their cooling tower/chiller systems under limited and sometimes decreasing budgets. This situation is further complicated by the recent publication of ANSI/ASHRAE Standard 188-2015, Legionellosis: Risk Management for Building Water Systems, which requires extensive review and planning, and potential changes in water treatment programs. University-wide teams are being formed to comprehensively address a wide range of water issues while experts with responsibility for affected facilities are reviewing options and collecting vital information to address their requirements.

The preliminary results from a trial of an new treatment program at the university have confirmed a new option that tower owners and water treatment professionals can employ to meet anticipated operational, health and safety requirements. The chemical treatment program proved effective on multiple sources of fouling, offered reductions in maintenance resources committed and improved worker safety.  

Corrosion rates were controlled and total bacteria counts were well below allowable levels. The low toxicity of the chemical also provided a green profile attractive to the university. The initial trial will continue, and planning is under way for installations in several other campus facilities in 2016. While research continues at the university to document its site-specific results, this technology has been deployed over the past seven years in cooling towers in dozens of locations in the U.S. with similar results.

Background & Trial Design

In keeping with the university’s research tradition and the need to address specific system problems, over the years the facilities program conducted trials of treatment programs including chemicals and mechanical devices. In early 2015, an eight-month trial of the Mexel 432/0 chemical treatment program was commissioned to determine its efficacy on the existing challenges in the water circuits. With the developing attention to ANSI/ASHRAE 188-2015, the results were also to be evaluated for inclusion in future treatment program design. Typical problems included scaling of the towers and chillers associated with the variable, elevated hardness of the municipal makeup water, and difficulty maintaining acceptable corrosion levels for copper and mild steel within the systems. The calculated hardness ranged from 92 to 180 and corrosion rates were above acceptable industry standards using a bromine and phosphate polymer treatment program.  

A 40,000-gal cooling tower/chiller system composed of two 1,200-ton centrifugal chillers, one 650-ton chiller and two cooling towers was selected for the trial. The treatment consisted of injection of a single emulsion of filming amines to achieve a residual level of 2 to 2.5 ppm for 30 minutes per day. The emulsion replaced all other chemicals previously used for treatment of the system. 

The treatment coats the interior wetted surfaces with a protective layer at the molecular level to prevent fouling rather than treating the entire water column. The coating controls biofouling, scaling and corrosion. It has a mild detergent/dispersant action that provides some remediation of existing deposits. A single metering pump was attached to the existing controller, and corrosion coupon racks were installed to allow bimonthly coupon testing along with more frequent Corater readings. Dip slides tracked total bacteria counts.

Preliminary Results

At the beginning of the trial, the towers were inspected and found to contain significant accumulation of mud and biological fouling. Substantial amounts of scale also had accumulated on the tower fill, but resource limitations did not allow for cleaning prior to the cooling season.  During the season, conductivity control over the towers was lost several times due to equipment failures. After repairs, system balances were restored and monitored parameters returned to expected levels.

Cooling Tower Conditions Prior to Trial

During the trial, university staff monitored performance on a weekly basis. The dosing equipment performed consistently throughout, providing chemical at the required rate with only minor adjustments to maintain preferred residual levels for efficacy. Corrator readings were consistently below 3 mils per year (mpy) for mild copper and 0.3 mpy during normal operations. Total aerobic bacteria counts remained within good control in keeping with Cooling Tower Institute standards and decreased to low levels as the season progressed. Scaling on the tower fill was reduced, and planned condenser inspections were expected to show similar results.

When reviewing the preliminary data, university staff noted that the simplicity of the treatment would improve operations and maintenance resource requirements. Because the dosing did not require frequent adjustments with changes in water chemistry, monitoring requirements would be reduced. The concentrated formula reduced transportation, storage and handling requirements.

With effective control of scaling during the season, reduced chiller cleaning also was anticipated, along with increased efficiency of heat transfer in the tower and chiller throughout the season. Another concern was worker and public safety.  Recent testing for U.S. Environmental Protection Agency registration showed the product to be non-toxic to humans and have low toxicity to aquatic organisms when discharged, providing a green profile for its use. The product does not burn, explode or volatilize, making it safe for service personnel.

While final results will be evaluated in the future, university staff are not waiting to move forward in implementing and assessing this technology in a broader range of cooling tower applications. If future results confirm the initial findings, more extensive adoption across the campus is expected.

About the author

Mary Wolter Glass is president of Mexel USA. Glass can be reached at [email protected] or 703.349.3347.

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