Process Puzzler: Make Solid Progress

Readers suggest ways to improve crystallizer controls.

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To do the job you need two four-wire RTDs connected to a single differential transmitter. Another way to reduce lead wire error is with a constant current source whereby the resistance bridge is replaced by a digital voltage meter. Avoiding contact problems by using gold contacts also would help. Although this solution requires careful wiring, it might be the best option to meet customer requirements for large crystals.
Dirk Willard, consultant
Wooster, Ohio

Gas temperature is gradually rising at the exit of our waste heat exchanger; the gas goes to a reactor and threatens to raise its catalyst bed temperature above the allowable limit. The exchanger extracts heat for steam from gas exiting a steam reformer (see Figure 1), whose feed rate of hydrogen and liquefied petroleum gas is steady. De-mineralized water is on the shellside; hot water, H2S, H2, CO2, CO are on the tubeside. An analysis of the shellside condensate shows traces of iron and phosphate; an analysis of the tubeside shows traces of iron, potash and silicon. There are some similarities with the analysis of the desulfurization catalyst but our supplier denies the possibility of broken catalyst. What's causing the fouling? How can we solve the problem?

Send us your comments, suggestions or solutions for this question by August 13, 2010. We'll include as many of them as possible in the September 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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