Keep Catalyst From Overheating

Readers react to a fouling problem in an exchanger.

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Let's consider the chemical analysis of the tubeside again. Traces of silicon could indicate insulation material but we would expect to see alumina, too. The potash is a mystery. To resolve this you must review the components of the material balance and the catalyst manufacturer assay.

Now, let's consider inspection. Think carefully about your tools when you open up the exchanger for an inspection. If possible, pull the unit and install a spare so the exchanger can undergo a shop inspection. Use a borescope to check tight corners in the shell and the tubing. Don't read too much into a borescope picture; the best tools in the hands of someone not an expert with them won't help you. A good history of the process is the best tool.
Dirk Willard, contract staff engineer
Hemlock Semiconductor, Hemlock, Mich.

Our decanter for separating a mixture of C10, C20, C30 and C40 compounds from a water/toluene solution isn't performing right. To save space, we opted for a 3-ft-diameter vertical unit with a length/diameter ratio of about 3:1. The flows are 6,000 pounds per hour (PPH) of organic and 2,500 PPH of aqueous phase. The viscosities are: 300 cP for the organic; 0.8 cP for the water. The specific gravities are: 0.8 for the organic; 0.99 for the water. Feed is at about 50% of the straight side length and we use a dispersion layer of about 5%. Although the decanter is designed to capture 100 micron (µ) droplets, the carbon filter that's supposed to serve as a water polishing filter actually is removing them. We've had to change it out every 30 hours at a cost of $250/500 pounds. On examination, we discovered that during construction 1-in. high-flow packing was dumped into the decanter. It fills the bottom third of the column. How can we fix the decanter? Should we be happy with 100 µ? How can we reduce our carbon costs?

Send us your comments, suggestions or solutions for this question by October 15, 2010. We'll include as many of them as possible in the November 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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