Process Puzzler: Combat Column Contamination

Readers suggest how to tackle a troublesome tower.

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Eliminate the common causes: 1) sample the preheater to ensure it's not spitting liquid; 2) check the reboiler temperature control; 3) do a gamma scan, or sample trays to reveal leaky bubble caps or sidewalls; and 4) vent the condenser of inerts. My bet is on the column ― it's the one link, besides the preheater, between the simultaneous contamination of the bottoms and the overhead.
Dirk Willard, consultant
Wooster, Ohio

The online version of Process Puzzler, "Guard Against Gas," (, contained an incorrect formula in Dirk Willard's response. The correct formula is: 4e- + 4 H+(aq) +O2(aq) → 2 H2O(l)

We use a centrifugal pump for tank truck loading. It's driven by a standard fixed-speed induction motor operating at 3,600 rpm. We have no controls on pump flow. The pump runs out on the pump curve during tank loading. An upset condition could cause a very high pressure at the pump suction. The piping system can handle the pressure but we have a concern about relief valve capacity downstream of the pump. The relief valve and downstream piping were designed based on flow being limited by pump capacity. But suction pressure can rise so high that the flow rate, if the pump weren't present, would exceed pump run-out capacity. Can the pump motor be forced to speed up to accommodate a higher flow rate by high pump suction pressure? Or will the motor and pump act as a brake on the system?

Send us your comments, suggestions or solutions for this question by February 12, 2010. We'll include as many of them as possible in the March 2010 issue and all on Send visuals — a sketch is fine. E-mail us at or mail to Process Puzzler, Chemical Processing, 555 W. Pierce Road, Suite 301, Itasca, IL 60143. Fax: (630) 467-1120. Please include your name, title, location and company affiliation in the response. And, of course, if you have a process problem you'd like to pose to our readers, send it along and we'll be pleased to consider it for publication.

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