Chemical Processing - February 2008 - (Page 42)

>> PROCESS PUZZLER Switch the leads Switch the leads to the motor in the starter bucket. However, due diligence is required before you switch leads to reverse the rotation, since some equipment is not amenable to reverse rotation. I would review the manuals that came with the motor, agitator and gearboxes. If there is a problem, my hunch is that the vendor will put a warning label in the documentation. G. C. Shah, HSE project manager Mustang Engineers, Sunnyvale, Calif. What do the vendors say? It looks fairly simple to rework the motor fan, assuming other items don’t preclude reversing rotation. This may involve changing the motor fan for one with a reverse pitch. All this should be taken up with the agitator vendor and motor representative. “Can the shaft seals be changed and run in the reverse directions?” This will require consultation with a seals expert. I am not a mechanical engineer, but I think the most likely problem with my suggestion would be the gearbox. With all the dimensions of this dilemma, I am not certain where to go. I hope my thoughts stimulate someone else to come up with a workable solution. Steven Walker, senior process engineer, Eli Lilly, Clinton, Ind. Reverse the rotation If the motor is three phase, isn’t it feasible to simply reverse the rotation of the motor? This would allow the agitator to spin in the correct rotation without disassembling of the agitator after draining the storage tank. Donald Acker, manager of construction, CH2M Hill, Dallas Do what you can This sounds so simple to correct. There must be something more to the puzzle. Reverse the motor leads and rotate the shaft counterclockwise. We have and use equipment that can be reversed. With some equipment it helps prolong equipment life by periodically changing direction. If the agitator is a long-lead item, can you find gearboxes and motors in other areas of the plant that can be swapped out with these and rotate the opposite direction? Or, perhaps you can borrow one from another company in your area until a counterclockwise impeller comes in? Look around for something that can be used to reverse the rotation. Be creative! In the worst case, go ahead and destroy the gearbox and motor over the time it takes to get the new agitator. It might be a lower cost option and be worthwhile if you get your 42 • February 2008 process back on line. Idle processes usually cost a lot more than equipment. Glen Oswald, engineer advisor, Mosaic Phosphates, Plymouth, Minn. First check about damage First check with the agitator manufacturer about possible damage due to reverse operation. Then, if the manufacturer OKs it, have your electrician interchange two of the power wires to the motor. This assumes that the motor is three phase, which is reasonable for the stated size of the tank. Michael Wisdom, senior project manager, Contour Global, Houston Pay attention to four things I see no problem with changing the shaft rotation from clockwise to counterclockwise. There are four things to worry about in changing the shaft rotation: the impeller, the motor, the seals and the gearbox. Our firm uses a line of gearboxes that allow rotation in both directions. Motors may need to be de-rated, but it depends on loads if run in reverse. Many seals can run both directions. Also, I remember the problem saying that there was not enough time to have an impeller to be fabricated. He would have plenty of time if he worked with our mixer company. David Bowlin, president, Engineered Products & Services, Inc., Sammamish, Wash. >> APRIL’S PUZZLER A viscous ingredient is pumped through a heat exchanger to raise it to a sufficient temperature so that a reaction can occur when it then goes to a batch reactor. The pump is interlocked with the temperature control loop. Unfortunately, frequent nuisance alarms and trips are associated with this system. Typically, start-up requires the operator’s full attention with all controls in manual mode. Can you suggest some ways to reduce or eliminate these nuisances while assuring a heated exit stream? Send us your comments, suggestions or solutions for this question by March 7, 2008. We’ll include as many of them as possible in the April 2008 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 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. www.chemicalprocessing.com http://CP.com http://www.chemicalprocessing.com

Table of Contents Feed for the Digital Edition of Chemical Processing - February 2008

Chemical Processing - February 2008 Contents From the Editor ChemicalProcessing.com Field Notes In Process Energy Saver Compliance Advisor Nanoparticle Safety Raises Questions Take the Pressure Off Vacuum Systems Achieve Optimum Centrifugal Pump Performance Rethink Batch-Manufacturing Alarm Systems Dr. Gooddata Orlando Plant Pioneers HMI Migration Strategy Process Puzzler Plant InSites Equipment & Services Ad Index Product Spotlight/Classifieds End Point

Chemical Processing - February 2008

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