7/27/2019 Canned Motor Pumps in Refinery.pdf

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FLUID FLOW AND ROTATING EQUIPMENT SPECIALREPORT

Canned motor pumps makeimportant inroads in refinery serviceDifficult applications drive increased uses. D. FEGAN, Hermetic Pumps Inc., Houston, Texas

M gncric drive and cann ed motor pumps have had relatively low acceptance rates in refineries, especially inth e US, even though thousands of these uni ts are successfu lly operating in hydrocarbon se rvices around the wo rld.The importance of these pumps is well recognized in the efforcsof the American Petroleum Institute (AP I). A worki ng comm ittee was fo rmed in 1990 to compile data for a documenc covering sealless pumps in refinery services . Th e res ulting standard(API-685) was formally adopred in 2000 and a revision to thisstandard is due for publication in 2008.Initially slow acceptance overcome. In a typical cannedmotor pump (Fig. I) the ma[Qr rotor shares its shaft with thepump impeller or impellers. The stator portion of the mo tor isse parated from this rotor by a (hin containm ent can and is thusnot contacted by the pumpage. In a cann ed motor pump, (hebearings usually receive lubrication from the fluid being pumpedand clean fluids are obviously preferred. However, contam inatedfluid s can be easily accomm odated by first filter ing and thenreinjecting a fluid si de stream . Relevan t pro vis ions are incorporated in many canned motor pumps .

Until recen tly one of the major drawbacks in ap p lying"canned moto r" style sealless pumps to refi nery services hasbeen the lack of larger than 150 hp motors. Even though largercanned mo tors have been advertised, they were not consideredcommercially viable due their cost and lack of operating experience. In addition, there has been the occasional perception thatsealless pumps were not rel iable, or tha t th ey were d ifficult, orex pensive, or im possible to repa ir. Another sweeping (bu t inaccu rate) judgment simply consid ered them a bad investment.T hanks to a large number of successful and relatively trouble-free installations, this perception has certainly been proveninco rrect.Product-lubricated bearings. On e of the st rongestimpediments to the more widespread use and applicatio n ofsea lless pumps in oi l refine ri es is that they will incorporateproduct-lubricated bearings and that abrasives in certain productstreams can cause accelerated bearing wear. This is actual ly anappl ication issue, since there are designs and materials availableto ensure successful operation and relatively long life, even underthe most seve re operating cond itions. The issue is not un like thatwith mechanical seals, where certain app lications require a suitable ope rating env ironment. Th e same consideration logicallyexists for a sealless pump where the operating environment must

I FIC.1ypical 1lIgh-pre ss ure canned motor pump (source_ Herm etic Inc , Gundelfingen, Germany)accommodate the needs of the bearings. Sealless pump componems may add heat to the fluid cont act ing the bearings. Th isaddition may now affect the vapor pressure and fluid viscosity;both must st ill be suitable for the app li cation .

Cooperation between pump user and manu factu rer is veryimportant. Th e pump manufactu rer must be given as muchinformation about th e application and physical properties ofthe pumped fluid as possible. Sim ilarl y, information about theplanned operation of canned mOtOr pumps is also important. Itincludes data on the number of starts and stops an ticipated fora given period, sta rtup conditions (co ld sta rt), as we I.! as environmental issues such as coo ling water qual ity, wh ich could bea big facto r in the overaIl success of a given insta llat ion and thetype of pump offered.A telling case history. About seven years ago, the auth orreceived an inquiry about a pump app lication handling 750Fdi es el fuel at 1,000 psi suction pressure and sa turated w ithhydrogen. W hen he indicated that wou ld not pose a problem,he was immediately asked if he would be willing to pu t thatresponse in wri ting. He was then told it was possible thar thefluid stream contained some catalys t fines.

Th e potential for hav ing abrasives in the stream prompted acloser review of the pump requirements fo r handling the ap pl ication. Prefilling the motor section with clean diesel fuel solved

HYDROCARBON PROCESSING AUGUST 2008 r 51

7/27/2019 Canned Motor Pumps in Refinery.pdf

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FLUID FLOW AND ROTATING EQUIPMENT SPECIALREPORTlem. This 100 hp unit was successfu lly commissionedand has been operating successfully since then. Two

were subsequ ent ly commi ss ioned in other refineriesmilar operating co nditions. Tn other instances, the vented ro lise a mete ring pump ro inject a cl ea n compatible

the maw r as a barrier fluid [Q prevent damage to thegs .

S. Dennis (Denny) Fegan has over 40 years' experience inrotating equipment including pumps, compressors, and steam andgas turbines. His career has included design, application. installation and troubleshooting of this equ ipment to the HVAC, powergeneration. petroleum refining, chemical processing and the refrig

eration markets. Mr. Fegan 's work history includes Ingersoll Rand Corporation, PacificPump Division of Dresser Industries, Teikoku USA Inc. and Hermetic Pumps Inc. He isan active member of the American Society of Mechanical Engineers (A SME) and theAmerican Institute of Chemical Engineers (AIChE). Mr. Fegan is a member and pastchair of the Equipment Testing Procedures Committee of the AIChE and a discussiongroup leader for sea!1ess pumps at the Texas A&M Pump Symposium . He holds severalpatents on sealless pump design and has published a number of papers on seallesspump design and appl ications.

r units in successful operation . Sin ce theseun its we re sold, a need fo r larger units arose requi ring

n 200 hp and 300 hp and flows between 2,000 gpm andgpm, Th e total developed heads ranged between 300 ft

ft, with working pressures up Ii r=:i i i i i i i i i i i i i i . i i i i i i i i i i i i i i i i i . i i i i i ; ; ; ; ~ : = ~ i i . i i i i i i0 psi. Some of these units are beingin ultra-low-sulfur refining appH

s and others in light hydrocarbonble interna l p ressu re profil esimary reason for canned mowr

pumps being uc il ized in these andstrenuous services. At no point inmbined pump and mOtor geomes the fluid have w be reduced toheric pressure. In fact, most ca nneddesigns inc rease rhe internal pres

rta in that two-phase flow do escur. Analytical programs al low

s with pressurelremperacu re profilesll ascertain that a pure liquid phase

under al l operat ing cond itions.refinery insta llatio ns require t hat

be furn ished with an explolabel. Although that currently

the available motor nameplate rat350 hp , steps have been initiated to

this to 700 hp by late 2008,a final point, axial th rust contro l

represent one of the major chalin producing large horse powerpumps. This challenge was com

wh enever a wide range of fI uvarying ph ys ical properti es had

accommodated, as would be th er units with low net positive suc-d req ui red (N PSHR) and steeppre ss ure cur ves. The re have bee nti c improvements in the ability ofpumps to control axial thrust and

ava ilabi lity of instrumentation tohis thrust. "Real-time" bearing

ing has had a maj or beneficialo n the increased reliability of

machin es and the reduced cost ofp.

t certainly, canned motOr pum psrning of age. Th eir ran ge of app li-ha s been greatly extended and

rve to be con sidered by forwarduser co mpani es in the hyd rocar

ing an d many other indus-HP

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