Chemical Processing - August 2007 - (Page 42) After condenser Raffinate flash tower >> PLANT Steam Raffinate Extract flash tower INSITES Steam Extract Condensate to water treating Condensed water/ NMP to solvent recovery >> 160 140 120 Torr (mm Hg) 100 80 60 40 20 0 Saturation temperature versus pressure 3.0 2.5 Lower condensing pressure limit imposed by cooling water temperature 2.0 1.5 B 1.0 Cooling water temperature required imposed by actual 0.5 operating pressure 70 90 110 Temperature, °F 130 0.0 150 psia A 30 50 Figure 2. Too high a vacuum made it impossible for the available cooling water to condense solvent. However, I must plead guilty here, I’ve put control valves on ejector steam supply to control the ejector. Ejector sensitivity varies depending upon the exact operating point and specific ejector. For a particular case, throttling steam to the ejector may work well enough but don’t count on it — be prepared to vary the load to control ejector suction pressure if required. In this case, steam throttling wouldn’t work. The required operating point is so far away from the current operation that major changes are needed. Either the load had to be changed or the ejector replaced. If a process operates for years and years far way from the operating point, replacement with a smaller ejector is a very attractive option. Ejector suction pressure control by changing the load requires either recycling some of the discharge to the suction or adding extra load by steam injection into the ejector suction. Either will work here. Take care with multiple-stage ejector systems. Pick a good recycle location to make sure that non-condensible gas doesn’t choke any of the ejectors. Check them all, not just the first one. CP By Andrew W. Sloley, contributing editor ASloley@putman.net O 3000 WAYS TO V E R SAY YES North SPARES WAREHOUSE American With over 3,000 ways to say yes, we can help when municipal or industrial applications fail! For service problems with ANY mixer drive, PMSL is available 24/7. Whether your drive is Philly, Lightnin, Chemineer, Falk, Flender, Hansen, Sumitomo, Ekato or virtually any other brand, we have an answer. If the exact item is not in stock, we can quickly design an adapter plate to marry an appropriately sized mixer drive to the vessel. Or we can supply a replacement drive to the destination before your failed one is removed! CALL TODAY TO LEARN MORE 1-800-95-MIXERS www.philamixers.com http://www.philamixers.com http://www.philamixers.com
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