Cooling Towers: Benefits of a Cold Eyes Review

Cooling Towers: Benefits of a Cold Eyes Review


One key decision that often needs to be made is repair vs. replace. When has a cooling tower arrived at the point where a new tower should be considered? Maintenance costs, overall tower condition, environmental constraints, and performance optimization are all factors that need to be evaluated.

If a new cooling tower is justified, how are the specifications for performance selected? What range, fan horsepower, approach to wet bulb, and water flow rate should be specified to best match plant requirements? The range is the difference between the hot water (return) temperature and the cold water (supply) temperature. The approach to wet bulb is due to the fact that, if the cooling tower were infinite in size, the cold water temperature would be at the wet bulb temperature. However, just like a shell and tube heat exchanger with a temperature difference between two streams, a finite cooling tower results in some approach to the wet bulb temperature. There is also a trade-off between plan area (footprint) and fan horsepower; you can have a smaller tower with high fan HP or a larger tower with lower fan HP to achieve the same approach to wet bulb. What materials of construction and fabrication techniques should be utilized? Do these conform to accepted industry standards?

For an existing cooling tower, there are options for improving performance. The items to be optimized include:

  • Air distribution through the tower.
  • Water distribution through the tower.
  • Bypassing of either air or water in the tower.
  • Significantly lower or higher water flow than the tower was designed for.
  • Fans not pulling maximum air through the tower.
  • Actual vs. design heat load (this is usually a constraint dictated by demands of the process).

Below are specific examples of conditions which contribute to some of the above factors:

  • Over flow of water from the hot water distribution pans, (hot water bypassing) on cross flow towers resulting in thermal contamination of the cold water basin.
  • Plugging of orifice nozzles in hot water pans (cross flow towers) or clogged spray nozzles in counter flow towers resulting in mal distribution of water, thereby not allowing for proper distribution of water over the fill. 
  • Plugging of drift eliminators with algae, dirt, scale, etc. causing increased resistance to airflow.
  • Fans not pitched properly to draw (near) maximum amps resulting in lower airflow through the tower. 
  • Defective plenum air seals resulting in air bypassing the fill.

These 5 items are usually lower cost items to fix. Moreover, they are almost always worth doing to achieve whatever percentage of lost design capability that can be recovered. Larger (capital) investments to increase tower performance include such items as changing the fill, (orientation, spacing, and type of fill), higher efficiency fans,  addition of a cell or helper tower (if real estate permits). These type items probably would require a further cost/benefit analysis.

Whether a new tower or improvement of an existing tower is under consideration,  in order to evaluate the efficacy by cost/benefit analysis, the value of colder water should be known in terms of its benefit to the process.

A Becht SME can work with the plant to thoroughly assess all of these things and develop the most cost effective solutions.

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About The Author

Allen Feltzin has over 30 years of experience in process engineering, maintenance, operations, and construction in large scale industrial plants based on his long career with BOC Gases, Murray Hill, New Jersey. He developed world class, state of the art cooling systems which were installed at over 80 sites in North America. He was responsible for every aspect associated with cooling towers: design, specification, erection, inspection, testing, retrofits, upgrades, and demolition. Al developed and presented training courses on cooling water treatment and cooling system equipment, both in North America and globally. He conducted a comprehensive audit achieving cost reductions and optimizations on a 360,000 gpm seawater cooled system at a 360 MW combined cycle power plant. As an Advisor with Becht, Al has worked with a European refinery to control calcium phosphate deposition and Legionella. He provided consultation to a US Gulf Coast Refinery on cooling tower life cycle optimization: repair vs. replace, review of inspection reports, thermal performance assessment, oversight of contractors, and asbestos abatement. He has built strong professional organizational affiliations, authored numerous technical papers and made presentations to various industry groups including the Cooling Technology Institute, American Chemical Society, National Association of Corrosion Engineers, Compressed Gas Association, and American Institute of Chemical Engineers. Mr. Feltzin has the following professional affiliations: Cooling Technology Institute, American Chemical Society, National Association of Corrosion Engineers, Compressed Gas Associations, and American Institute of Chemical Engineers. Mr. Feltzin holds a Bachelor of Science degree in Chemistry from the University of Delaware.

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