Chemical Processing - February 2008 - (Page 44)

>> PLANT INSITES the suction and discharge conditions of all the pumps is identical, the pressure change between the suction and pressure must be the same. So, analysis must start by putting the two pump curves on the same basis and then drawing a horizontal line across the pump curves at the known pressure (Figure 2). The intersection of this line with each pump curve gives the flow rate through that pump. Here, at 2,300 ft. of head, 292 gpm goes to the old pump and 556 gpm to new pump for a total of 848 gpm. For two pumps to operate in parallel, their TDHs must overlap. At zero flow the original pumps have a differential head of 2,619 ft. At discharge pressures higher than this, reverse flow may damage the pump and reduce overall system capability. Here, the new pump has the capability to deliver the higher head. In such cases when operating different pumps in parallel, make sure that reverse flow doesn’t occur. Of course, most pumps start having reliability problems well before zero flow rates actually are reached. The hydrotreater pumps were very poorly matched. When Get troubleshooting insights online Full-text archives of previous Plant InSites columns are available at ChemicalProcessing.com. You also can find numerous answers to questions related to plant operations and design in the “Ask the Experts” feature there. It covers pumps — as well as compressors, heat exchangers, instrumentation, solids processing and more than twenty other topics. Not only can you see what others have asked, but you can pose your own questions. operating the new pump and one of the original pumps in parallel, the smaller pump was forced to operate at very low loads, far from its best efficiency point (~375 gpm). The longterm solution required modifying the new pump and replacing the original spares with a single unit fit for the service. CP Andrew Sloley, contributing editor ASloley@putman.net Conference: May 5–8, 2008 Exhibition: May 6–8, 2008 Donald E. Stephens Convention Center Rosemont (Chicago), IL For information on attending or exhibiting, visit Please use Promo Code: AB 8335_CH_PTXi Produced and managed by: CANON COMMUNICATIONS LLC 11444 W. Olympic Blvd. • Los Angeles, CA 90064-1549 • tel: 310/445-4200 • fax: 310/996-9499 44 • February 2008 www.chemicalprocessing.com http://www.chemicalprocessing.com http://processtechexpo.com http://processtechexpo.com http://www.chemicalprocessing.com

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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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