[pullquote]The approach of summer is a good time to check the performance and, more importantly, the physical condition of your cooling towers. After all, it’s easier to repair a tower when weather conditions don’t put a strain on its cooling capacity.
A cooling tower passes air over tiny droplets or the exposed surface of a water film. In both cases, a small amount of water is vaporized, drawing the latent heat from the remaining liquid water, reducing its temperature. Splash fill continuously breaks up droplets of water dropping down the tower; the fill is arranged so the droplets fall from one splash bar to the next, avoiding agglomeration. Film fill spreads the liquid out on highly wetted plastic, exposing the maximum surface area to the air stream. The amount of water vaporized depends on the airflow over the droplets or film and the ambient wet bulb temperature. As the wet bulb temperature approaches the sensible temperature, the capacity of the air to absorb vapor reduces. This, in turn, increases the temperature of water leaving the tower.
You often can observe the condition of the fill from the face of the tower. Concentrations of flow can indicate water maldistribution, which can stem from either blockage or missing distribution devices. Sagging or missing fill may be visible as well.
Along the Gulf Coast, ambient weather conditions may strain a cooling tower even in the winter; a poorly functioning tower could pose significant issues in the summer. A walk-around followed by a quick performance test can avoid summer headaches.
Learn From Jake
It was a very hot August in Texas. Jake had been called in to help diagnose a condenser problem. The plant made a component used in a downstream facility and a drop in its output was curtailing production downstream.
Jake took a quick look at the condenser operator screen. The unit condensed the exhaust steam from the process compressor’s steam turbine drive. The compressor was experiencing reduced flow, decreasing plant production. Jake immediately recognized that the inlet cooling tower water significantly exceeded design temperature. Ambient conditions were high but the temperature was much greater than the design approach temperature. A quick check at the local weather bureau confirmed his expectation.
As Jake set up temperature loggers, calibrated the night before, he also surveyed the condition of the fill. The plant engineer assigned to help him indicated that upgrading the splash fill to a new design was in process. That design, suggested in a recent research paper, promised to drop the approach temperature. The splash fill bars would be installed parallel instead of perpendicular to the flow. The tower was a cross-flow design, meaning the air flowed perpendicular to the down flow of the water droplets. Jake thought the idea made sense.
As they made their survey, Jake noted that he was puzzled by the lack of fill in the front face of the tower. The plant engineer responded that the installer had said the more-efficient design required less fill. That seemed questionable to Jake; a performance test of the three cells verified the tower was the problem. One unconverted cell was at design performance. Fortunately, available performance records confirmed the tower had performed to design in the past.
Jake then contacted the author of the research paper, who indicated the same amount of fill was needed to achieve the desired approach.
The threat of a lawsuit persuaded the installer to complete the installation with the right amount of fill. Temporary cooling towers were brought in to get the plant through the August/September hot spell. Production was increased and no downstream sales were lost.
So, check the performance and condition of your towers right now. If you’ve upgraded or even replaced the fill, ensure you got what’s required. Also, it’s a good idea to spend time with the installer’s team to verify they understand the job and to ensure quality. Contact reputable sources for information if you don’t understand what they are doing or proposing.
Active in both, the American Society of Mechanical Engineers and the American Society of Heating, Ventilating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), Clark was chairman of ASHRAE's task group on Halocarbon Emissions and served on the committee that created ASHRAE SPG3 - Guideline for Reducing Halocarbon Emissions. He has written numerous papers on CFC alternatives and retrofitting CFC chillers. He was awarded a U.S. patent on a method for reducing emissions from refrigeration equipment. He has served as technical resource for several others.
You can email him at [email protected]