Chemical Processing - February 2008 - (Page 43) PLANT INSITES < > Pump curve 2,800 2,600 Total dynamic head, ft. 2,400 2,200 2,000 1,800 1,600 1,400 0 100 Two pumps running One pump running 200 300 400 Gallons per minute 500 600 Parallel operation may make a pump run at low efficiency. When putting two pumps in parallel, always bear in mind that even “identical” pumps don’t necessarily have the same performance. as a previous column has covered (www.chemicalprocessing.com/articles/2007/053.html), their pump curves can differ due to dissimilar maintenance histories, tolerances and wear — and piping and layout differences also can have an impact. running the two pumps on the hydrotreater meant no spare was available. hence, when one pump required maintenance unit capacity dropped. This eventually led to adding a third, larger pump. (figure 2 includes the pump curves for the original pumps and the new pump.) The plan was to use the new unit as the main pump and keep the originals as spares — because the smaller pumps would run at low percentages of design flow and thus at low efficiency. The idea was to keep the higher efficiency pump in service. over time, operation rates continued to be pushed and an attempt was made to use one of the old pumps in parallel with the new pump. however, this led to frequent maintenance problems on the smaller pump. analysis of non-identical pumps in parallel can be difwww.chemicalprocessing.com Figure 1. Using two identical pumps to handle the same flow significantly boosts total dynamic head generated. >> Larger pump added 3,200 3,000 2,800 2,600 Maximum discharge pressure, two pumps operating New pump curve Total dynamic head, ft. 2,400 2,200 2,000 1,800 1,600 1,400 0 100 Old pump’s curve 200 300 400 Gallons per minute 500 600 split operation 848 gpm Figure 2. Parallel operation forced the older, smaller pump to run far from its best efficiency point. ficult. The key concept to keep in mind is that any connected flow path between two points must have equal pressure differentials between those two points. Because february 2008 • 43 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 Chemical Processing - February 2008 - Chemical Processing - February 2008 (Page Cover1) Chemical Processing - February 2008 - Chemical Processing - February 2008 (Page Cover2) Chemical Processing - February 2008 - Chemical Processing - February 2008 (Page 3) Chemical Processing - February 2008 - Chemical Processing - February 2008 (Page 4) Chemical Processing - February 2008 - Contents (Page 5) Chemical Processing - February 2008 - Contents (Page 6) Chemical Processing - February 2008 - From the Editor (Page 7) Chemical Processing - February 2008 - ChemicalProcessing.com (Page 8) Chemical Processing - February 2008 - Field Notes (Page 9) Chemical Processing - February 2008 - In Process (Page 10) Chemical Processing - February 2008 - In Process (Page 11) Chemical Processing - February 2008 - Energy Saver (Page 12) Chemical Processing - February 2008 - Compliance Advisor (Page 13) Chemical Processing - February 2008 - Nanoparticle Safety Raises Questions (Page 14) Chemical Processing - February 2008 - Nanoparticle Safety Raises Questions (Page 15) Chemical Processing - February 2008 - Nanoparticle Safety Raises Questions (Page 16) Chemical Processing - February 2008 - Nanoparticle Safety Raises Questions (Page 17) Chemical Processing - February 2008 - Nanoparticle Safety Raises Questions (Page 18) Chemical Processing - February 2008 - Nanoparticle Safety Raises Questions (Page 19) Chemical Processing - February 2008 - Take the Pressure Off Vacuum Systems (Page 20) Chemical Processing - February 2008 - Take the Pressure Off Vacuum Systems (Page 21) Chemical Processing - February 2008 - Take the Pressure Off Vacuum Systems (Page 22) Chemical Processing - February 2008 - Take the Pressure Off Vacuum Systems (Page 23) Chemical Processing - February 2008 - Achieve Optimum Centrifugal Pump Performance (Page 24) Chemical Processing - February 2008 - Achieve Optimum Centrifugal Pump Performance (Page 25) Chemical Processing - February 2008 - Achieve Optimum Centrifugal Pump Performance (Page 26) Chemical Processing - February 2008 - Achieve Optimum Centrifugal Pump Performance (Page 27) Chemical Processing - February 2008 - Achieve Optimum Centrifugal Pump Performance (Page 28) Chemical Processing - February 2008 - Rethink Batch-Manufacturing Alarm Systems (Page 29) Chemical Processing - February 2008 - Rethink Batch-Manufacturing Alarm Systems (Page 30) Chemical Processing - February 2008 - Rethink Batch-Manufacturing Alarm Systems (Page 31) Chemical Processing - February 2008 - Rethink Batch-Manufacturing Alarm Systems (Page 32) Chemical Processing - February 2008 - Rethink Batch-Manufacturing Alarm Systems (Page 33) Chemical Processing - February 2008 - Rethink Batch-Manufacturing Alarm Systems (Page 34) Chemical Processing - February 2008 - Rethink Batch-Manufacturing Alarm Systems (Page 35) Chemical Processing - February 2008 - Rethink Batch-Manufacturing Alarm Systems (Page 36) Chemical Processing - February 2008 - Dr. Gooddata (Page 37) Chemical Processing - February 2008 - Dr. Gooddata (Page 38) Chemical Processing - February 2008 - Orlando Plant Pioneers HMI Migration Strategy (Page 39) Chemical Processing - February 2008 - Orlando Plant Pioneers HMI Migration Strategy (Page 40) Chemical Processing - February 2008 - Process Puzzler (Page 41) Chemical Processing - February 2008 - Process Puzzler (Page 42) Chemical Processing - February 2008 - Plant InSites (Page 43) Chemical Processing - February 2008 - Plant InSites (Page 44) Chemical Processing - February 2008 - Equipment & Services (Page 45) Chemical Processing - February 2008 - Ad Index (Page 46) Chemical Processing - February 2008 - Product Spotlight/Classifieds (Page 47) Chemical Processing - February 2008 - Product Spotlight/Classifieds (Page 48) Chemical Processing - February 2008 - Product Spotlight/Classifieds (Page 49) Chemical Processing - February 2008 - End Point (Page 50) Chemical Processing - February 2008 - End Point (Page Cover3) Chemical Processing - February 2008 - End Point (Page Cover4)
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