May Process Puzzler: Quick fix needed!

Readers recommend solutions for a pump control problem in this month's Chemical Processing Process Puzzler.

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Girish Malhotra, president
EPCOT International, Pepper Pike, Ohio

Use a baffle

To avoid early kill of the pump, you can add a baffle to the inside of the tank, just before the “high level switch.” Another alternative would be to put a 60°downwards elbow and nipple at the end of the pump outlet into the tank.

Emilio Malaguti, technical manager
Chemtron, Hialeah, Fla.

Go with a programming solution

Without a through detailed examination of the system, a quick test to eliminate electrical noise and/or splash during the initial operation of the feed pump, a quick solution/test would be to put a 2 to 3-sec. delay on the overflow sensor during pump start up. This would eliminate any potential electrical noise being generated by the pump or physical motion as well as liquid splashing on to the over flow sensor.

Mike Bender, project sales engineer
Millipore, Stafford, Va.

Add a time delay

A time delay, on start-up only, should take care of the problem.

Ben Mickler, president
Benchmark Electric, Inc., Raleigh, N.C.

Consider all the options

I am assuming that this is a batch process and it appears that the pump flow is splashing onto the high level sensor. Options to consider: reduce flow rate into the tank by lowering the output from the VFD or by throttling with a valve or an orifice plate; direct the flow away from the high level sensor or re-pipe the nozzle to direct it downward to avoid splashing the sensor; relocate the sensor to prevent it from being splashed — orient it parallel to the flow; and, use a different type of sensor, shorter or one less susceptible to the splashing, install a baffle (still well) around the high level sensor to protect it. There’s a last resort to be considered. If the system absolutely must be operational, can you run it without the high level sensor being on? You could use known flow rate to estimate quantity of liquid in the tank and drive the process by dead reckoning. This method could be augmented by a timer with an alarm. With this approach, the tank volume couldn’t be safely used to full capacity.

John Tashijan, president
T-Squared Associates, Kansas City, Kan.

Install a guard

Place a guard on the pump side of the switch. This will avoid false alarms during pump start by keeping the turbulence away from the switch.

Rick Hildebrand, senior engineer
V2 Bio-Consulting, South San Francisco Calif.

Submerged discharge

Install a 90° elbow and a sub-surface tube on the pump inlet. These two simple pieces of equipment combined would allow the water to enter the tank along the side, below the liquid surface, eliminating splashing. If installed correctly they could remain there as a permanent corrective action.

Kevin M. Nowak, associate scientist
Mentholatum, Orchard Park, N.Y.

Why not gravity feed?

Although I don't understand why the plant is pumping into the decanter.  It would be preferable to gravity flow into the decanter to minimize turbulence and promote settling. The feed should be introduced around the interface - perhaps a dip tube can be added - to maximize separation of water from the organic and organic from the organic. Although there are no outlets shown, I assume there will be excess organics in the water phase because of the inlet arrangement. A baffle can be added in front of the level switch to prevent impingement and false readings. A tee or elbow can be added to the inlet to mitigate splashing.

David Greene, Sr. director of bioprocess engineering
PS&S, Warren, N.J.

July's Puzzler

A corrosive material is transported by vacuum pneumatic conveyor from a dryer to silo (Figure 2). The condition at the discharge of the dryer is about 90°F and 75% relative humidity. Since commissioning, during the summer, the blower has suffered reliability problems: seal corrosion, bearing failure, motor trips and noisy operation. In particular, bearing failure has been the number one problem with this blower. Failures are worse in the fall and winter than in the summer. Current readings on the blower tend to increase slightly during the winter but the draw seems normal until sudden failure of the seals or bearings. What is the likely cause and what can we do to reduce reliability problems?

Figure 2. Blower, receivers and baghouse are located outside.

Figure 2. Blower, receivers and baghouse are located outside.

Send us your comments, suggestions or solutions for this question by June 8, 2007. We’ll include as many of them as possible in the July 2007 issue and all on Send visuals — a sketch is fine. E-mail us at 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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