Figure 2 -- Elevation issue: Hot air from distant lower exchanger degraded performance of higher exchanger. Click on illustration for a larger image.
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Another air-fin exchanger example underscores the importance of field work. A natural-gas processing complex used multiple air fins for heat rejection. Two large units ended up at different elevations. Even though the distance between the units exceeded 100 yards, the prevailing wind direction and velocity pushed large quantities of hot air from the lower exchanger to the upper exchanger (Figure 2). So, the upper exchanger’s service suffered from severe capacity limits. The centralized support office, despite extensive efforts, couldn’t find the source of this problem. A relatively short plant visit quickly identified it. Some straightforward windbreaks along the ground between the two exchangers significantly reduced the amount of hot air forced into the second exchanger.
Field observation and application of fundamentals are key to solving many “inexplicable” plant problems. Get out into the field, talk to the operators, verify the unit configuration and gain the experience to be able to say “that doesn’t look right” when you see something new. Engineering is about building things that work and keeping them working, not about calculating things that should work.
Andrew Sloley is a contributing editor to Chemical Processing. You can e-mail him at [email protected].