August 2008: Designing a desulfurization process

June 1, 2008
How would you improve this design?

We are designing a desulfurization process for a client overseas. The client produces a wet coke gas that must be treated for COS, H2S, and HCN before it can be used to make chemicals. A knock-out pot serves double duty — collecting the circulating spent slurry and vapor from the client’s gasification plant (Figure 1). The vapor flow in is 50,000 lb/hr and the liquid flow is 519 gal/min. The pot operates at 200°F and 560 psig with a barometric pressure of only 12 psia. A k of 0.27 was used with a velocity allowance of 0.15 to size the tank for vapor separation. The residence time is set at 30 minutes. The calculated diameter is 13 ft. with a length/diameter ratio of 3.4. The vapor passes through a mesh pad mist eliminator that is only partially used because of low vapor flow. Several problems are anticipated with the design: the liquid drains to atmospheric; foaming sometimes occurs, disrupting level measurement; the mesh pad fouls every four months; and the process water used on a timer to keep the pad clean may contain particulates. How would you improve the design?

Send us your comments, suggestions or solutions for this question by July 11, 2008. We’ll include as many of them as possible in the August issue and all on Send visuals — a sketch is fine. E-mail us at [email protected] or mail to ProcessPuzzler, 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.