Clean your ACCs and eliminate vacuum leaks to assure top performance

Gary Fischer knows a thing or two about heat transfer. The Conco Services executive, recently elected chairman of the ASME Heat Transfer Committee, has years of experience on how to maintain Rankine cycle heat-rejection systems in top condition to meet performance expectations. He shared some of that knowledge with owner/operators last week on a webinar dedicated to Effective Cleaning, Testing, and Inspection of Air-Cooled Condensers, hosted by CCJ ONscreen.

With the onset of triple-digit temperatures in some areas, he urged users who had not maintained their ACCs during spring outages to quickly schedule cleanings to assure peak performance this summer. Free flow of air across all heat-transfer surfaces is critical, Fischer said: A 20% reduction in air flow because of fouling and debris nestled in an ACC’s finned tubes will increase turbine backpressure by 33%. That decreases electrical output, reducing revenue.

Pushing fans to their maximum to reduce the impact of fouling only exacerbates the negative impact on financials because auxiliary load increases. You wind up consuming more power at a time when you’re making less.

Fischer showed several photos to illustrate the extreme fouling that can be created by pollen, dust, leaves, insects, plastic bags, bird carcasses, etc, picked up by fans, entrained in the air stream, and forced through the tightly spaced finned-tube bundles. It was a wakeup call for those who might not have inspected their ACCs lately.

Fischer went on to describe offline cleaning options—such as fire hose, high-pressure hand lance, and chemicals or foam—noting the advantages and disadvantages of each and the safety concerns of having O&M personnel climb on the ACC to operate these manual solutions. A big disadvantage of cleaning offline unless you’re in a planned outage, is loss of electric production.

The automated online cleaning systems described next offer the advantages of high water volume at pressures that will not damage fin and tube surfaces; plus no scaffolding is required. A focused array of water jets mounted on a trolley distribute water deep into the bundle with the opportunity to adjust the jets to optimize the washing effect. The typical carriage holds a nominal one-dozen jets and travels at constant speed across the tubes, assuring effective cleaning in one or two passes.

The pump skid for a large ACC delivers about 60-70 gpm of water to the spray nozzles at 1500 to 1600 psig. Water pressure may go to 2000 psig if necessary. Fischer showed webinar participants how to gauge cleaning effectiveness.

Testing for, and minimizing air inleakage, was another part of the presentation. Recall that if air inleakage exceeds the capability of your air removal system, backpressure increases and output is reduced.

The webinar was recorded and is available to registered users online 24/7/365. In addition to the best practices and lessons learned provided on cleaning and on detecting vacuum leaks, Fischer covered basic design and operating principles of ACCs—good for training of those unfamiliar with these heat exchangers.

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