Field-erected evaporative “wet” cooling towers, combined with heat exchangers, are an economical and efficient method to dissipate large heat loads at oil and gas refineries and chemical processing plants – as long as they’re free of harmful debris. Yet many cooling towers at these facilities are highly susceptible to poor performance and costly downtime due to problems associated with debris buildup and potential for debris to pass by traditional stationary water screens during the cleaning process, clogging heat exchangers.
Fortunately, traveling water screens systems used in place of stationary water screens give plants the ability to more efficiently and safely remove debris, often saving the operation hundreds of thousands of dollars in lost production and maintenance costs.
The Importance of Cooling Tower Efficiency
Evaporative cooling towers encountering issues with debris and found at chemical plants and refineries include counterflow and crossflow configurations, as well as natural-draft, induced-draft, and forced-draft towers.
A wet cooling tower uses an evaporation process in combination with shell-and-tube heat exchangers to provide cooling water to processes within the plant. The tower also typically includes one or more water screens installed in the cold-water basin at the bottom of the tower. The screens filter out large debris, in turn, protecting pumps, heat exchangers and downstream systems by filtering out debris that finds its way into the cold-water basin.
The efficiency of cooling towers is critical to maintaining production given the large-scale heat transfer necessary to provide cooling water to the plant. Of the utmost importance is optimal performance of the cooling process within the heat exchanger since it plays a vital role in the overall tower cooling cycle.
Problems Add up with Clogged Heat Exchangers
With a shell and tube heat exchanger, cold water flows through a set of metal tubes while a second heat transfer fluid passes through a sealed shell surrounding them, allowing heat to pass from one fluid to another. If the cooling water from the cold-water basin contains debris that is larger in diameter than the diameter of the heat exchanger tubes used for cooling water circulation, the debris can obstruct the flow of the cooling water and diminish the device’s ability to transfer heat. The volume and type of debris in the water will determine the severity of the problem. As debris continues to build up and obstruct the flow rate of cooling water through the heat exchangers, the more severe the problem.
When cleaning stationary water screens on cooling towers, debris is commonly pulled into the tower’s recycling pump and on to the tower’s heat exchanger.
The volume and type of debris entering a cooling tower basin is directly impacted by the age and condition of the cooling tower. Towers with the highest risk are aging towers that are 15 or more years old, as well as damaged towers. In aging or damaged cooling towers, larger fragments of wood, plastic or other material are more prone to come loose and fall into the cold-water basin.
Also impacting the severity of the debris problem is the environment around the tower. Debris problems are the result of a variety of debris sources, such as cotton wood tree fuzz, leaves, bugs, and pieces of trash. It’s not uncommon for natural debris to be pulled into the cold-water basin by the force of the fans located at the top of induced- and forced-draft towers. New towers operating in clean environments are less likely to encounter problems with debris.
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