June Process Puzzler: Forestall furnace foibles

Readers suggest how to address a hard-running vaporizer in this month's Process Puzzler.

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Install dampers

This really isn’t my area of expertise but my guess would be that the draft in the vaporizer is such that the heat from the burner(s) is pretty much bypassing the vaporizer coils and damaging the economizer. The solution would seem to be to slow the passage of the combustion products down and/or increase their contact rate with the coils. As a result of this situation, there also may be an excess of air. I would suggest increasing the retention time by adding an exhaust damper and at the same adding  angled inlet dampers to increase the swirl inside of the combustion chamber to increase the contact rate of the flame with the coils. Increasing the fuel rate or steam injection may be used to reduce flame temperature and limit NOx while maintaining adequate heat to provide the required vaporization rate.

Patrick Richards, sr. instrument designer
Fluor Canada, Saint John, N.B.

August's Puzzler

Our fractionating column is notorious for its problems. Oil is injected into heated feed to separate an impurity (Figure 2). This approach eliminates the impurity well, perhaps too well. A sludge collects in the bottom of the reboiler feed tank, clogs the sieve column and plugs the reboiler and pre-heater. There is some concern that separation efficiency is affected by plugging of the trays but the main problem is frequent fouling of the heaters, which have fixed heads and are difficult to bore out. The reboiler pump fails often and we must call in a vacuum truck frequently and unexpectedly to clean out the reboiler feed tank. Start-up is often a problem because the steam plant is far away. The oil frequently burns, which adds to our fouling woes. What can you recommend to reduce sludge build-up in the trays, heaters and reboiler feed tank?

Figure 1. A variety of problems lead to excessive downtime.

Figure 2. A variety of problems lead to excessive downtime.

Send us your comments, suggestions or solutions for this question by July 6, 2007. We’ll include as many of them as possible in the August 2007 issue and all on CP.com. Send visuals — a sketch is fine. E-mail us at ProcessPuzzler@putman.net or mail to ProcessPuzzler, Chemical Processing, 555 W. Pierce Rd., 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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