Processing, June 2018

services for many processing plants and facilities e operation of the plant or facility usually depends on these seawater pumps Dual ush utility water and seawater connection for mechanical seal flushing should be speci ed for such a seawater pump Such a pump system is provided with an automatic switchover dual flush system utility and seawater in the event of loss of utility water e same method can be used for services in liquid hydrocarbon chemical liquids and others For example instead of the ushing with a di cult pumped liquid a clean liquid will be used for normal ushing with the capability of switchover to the pumped liquid if the external source of clean liquid is interrupted Bearing lubrication system Pump bearings and their lubrication have usually been the source of problems A sophisticated lubrication system should be provided Bushings in vertical pumps are usually lubricated by the liquid pumped Alternative methods of lubrication should be used if the pumped liquid is not suitable for this application Bearing details such as type sizing and life calculation and lubrication system details should be reviewed carefully to ensure the reliability and long trouble free operation of vertical pumps Rolling bearings are still widely used in vertical pumps and vertical motors as it is common to see vertical motors as large as 600 kilowatts kW or even larger equipped with spherical or taper roller bearings Therefore bearing life expectation and calculation are usually topics for discussion and challenges Any bearing life expectation less than four years say 32000 hours at worst conditions is often discouraged although unfortunately many manufacturers still use traditional life values of 16000 hours or 20000 hours for the bearing sizing and selection Case study Large vertical seawater pump installation In a series of identical vertical seawater pumps at a large processing plant pumps are vertically suspended type VS1 e pump capacity and discharge pressure is 8300 m h and 44 Barg respectively ree pumps operate in parallel to provide the seawater requirement for the plant e rated hydraulic power of each pump is around 1 megawatt MW the rated electric motor power is about 14 MW The electric motor is sized for the end of curve therefore suitable margins and factors on power rating are provided e BEP ow of the pump is around 8750 m h the rated point ow is about 95 percent of the BEP ow e pump e ciency at rated point is estimated around 85 percent which is relatively high for a vertical pump e head rise to shuto is estimated at around 26 percent which is assessed as suitable for this service e pump speed is 750 rpm and a direct drive vertical electric motor is used no gear unit e pump is wet pit a vertically suspended single casing diffuser pump with discharge through the column e discharge nozzle of each pump is 40 inch ASME B165 150 ange e overall vertical pump train is more than 14 meters m long e column section is furnished in parts not exceeding nominal length of 32 m to ease transportation and installation Sections are connected by anges and each pump train weight is more than 27 tons T e seawater was considered dirty and polluted for this location therefore all materials of construction in contact with seawater are considered super duplex stainless steel Line shaft bearings thrust bearings and mechanical seal are provided with dual flush system utility water and seawater the automatic switchover capability from utility water flushing to seawater ushing and vice versa are provided In normal operation clean utility water is used for ushing and it can switch over to seawater automatically if the clean utility water is interrupted In addition an operator can switch over from one to another e pump package is provided with two accelerometers X Y for the electric motor radial bearings NDE and DE three accelerometers X Y Z for pump thrust bearing one key phaser and one duplex RTD per bearing for an e ective vibration condition monitoring A sophisticated seawater intake package is provided for each pump to lter the seawater and protect each pump e seawater intake system is a self cleaning vertical traveling type This is a complex and multistage seawater ltration package including Bar screen 50 millimeter mm ltration level band screen system and screen wash system to wash accumulated trash and solids e screen washing is accomplished by using ltered and treated seawater Amin Almasi is a senior rotating machinery consultant in Australia He is a chartered professional engineer of Engineers Australia and IMechE and holds bachelors and masters degrees in mechanical engineering and RPEQ He is an active member of Engineers Australia IMechE ASME and SPE and has authored more than 100 papers and articles dealing with rotating equipment condition monitoring offshore subsea and reliability JUNE 2018 www processingmagazine com 47 1988 2018 30th Celebrating 30 Years of Thermal Mass Flow Meter Excellence Eldridge Products 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