Process Puzzler: Choose a pump wisely

Readers offer tips about how to choose the best pump for slurry service.

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 QUESTION FROM MARCH’S CHEMICAL PROCESSING

We need to pump a reactor effluent stream. The stream is a slurry that is highly aerated by an agitator in the reactor. We estimate that 10% to 15% of the pump suction volume is gas. The total volume at the pump suction is about 1,200 gpm (including gas) at a head of around 70 psi (200 ft). What kind of pump is best for this service?


Adequate suction head is essential
For this service you need a properly designed centrifugal pump, but a reciprocating pump would work best. Adequate NPSH is essential. Although you have a great deal of head, it is important to have sufficient static and velocity head in the vessel above the pump inlet piping; minimal pump inlet/head losses due to constricting suction pipe diameters and fittings; and optimized suction specific speed and impeller design for the pump itself.
Ron Johnson, process engineer
Alpharma Pharmaceuticals, Baltimore

Positively the best
A positive displacement pump with a diaphragm might be the solution if your slurry is not very abrasive.
George Constantinescu, design engineer
Nitrochem Corp., Maitland, Ontario

Try a rotary disc pump
You should consider using a rotary disc pump; they work.
This type of pump uses a series of rotating parallel plates to create a boundary layer and viscous drag force. The plates allow the pump to transfer the liquid as needed.
Girish Malhotra, P.E.
EPCOT International, Pepper Pike, Ohio

 

 

 

 MAY'S PUZZLER

We are experiencing variations in both our raw materials and finished product. We chemically analyze the raw materials using an online vertical analyzer, but the data from the raw materials do not correspond to those for the finished product. We have experienced hangups and segregation in our feed silos, which might be exacerbated when the raw materials are mixed and then transported on a belt conveyor. We suspect the variation in analyzer readings could be due to increased moisture in the raw materials after leaving the feed silos, but we don't know why. Is the difference in readings due to segregation or to moisture?

Send us your comments, suggestions or solutions for this question by May 30. We’ll include as many of them as possible in the July 2005 issue. Send visuals, too — 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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