low flow high head

8/13/2019 Low Flow High Head

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A LONG

TIME AGO IN

A REFINERY FAR

FAR AWAY. . . A GALACTIC

WAR RAGES BETWEEN PUMP

MANUFACTURERS AND THE EVIL

EMPIRE OF PROCESS ENGINEERS.

FROM THIS PRESENTATION YOU WILL LEARN

THE SECRETS OF THE “ DARK SIDE ” OF LOWFLOW / HIGH HEAD PUMPS AND LEARN HOW

TO USE THE FORCE TO . . . . “CHOOSE WISELY”



25,000

RPM

8000

RPM

3600

RPM



Presentation

Why do we need “low flow,high head”

LF / HH pumps?• Centrifugal Pump Fundamentals

• Types of low flow / high head pumps

• Considerations and factors that impactyour pump selection choices

• Summary



Classification of PumpsHy d rau l ic In s t i tu te A PI-610

OH1; OH2

OH3

Ov erh u n g 1- an d 2- s tag e OH4

Im p el ler OH5

OH6

R o t o d y n a m i c

(Cent r i fuga l ) B etw een 1- an d 2- s tag e B B 1

B ear in g s B B 2

Mu l t is tag e B B 3

B B 4

Ver t ic al ly B B 5

Supended

Kine t icReg en erat iv e Ov erh u n g Per ip h eral

Tu rb in e B etw een S id e Ch an n el

B ear ings

Sp ec ial E f fec t Ro tat in g Cas in g (p ito t )

P u m p s

Di rec t Ac t i ng S imp lex, Dup lex, e tc

Rec ip roca t i ng Power F rame API-674

Po si t i v e Co ntro lled Vo lu m e D iaphragm API-675

Disp lacmen t

Gear

Rotary Screw API-676

Vane

L o b e



Reciprocating Pumps



2. Centrifugal Pump Fundamentals

• Head vs. Tip Speed, Torque vs. HP• Affinity Laws

• Specific Speed—ns

• Suction Specific Speed—S

• NPSH



Head vs. Tip Speed … Torque vs. HpTheoretical head is defined by the formula:

Where: HT = Theoretical Head (Ft.)

U = Impeller Tip Speed (ft./sec.)

g = Acceleration = 32.3 ft./sec2.

HT = U2

g

Tip speed (U) is found by the formula:

Where: D = Impeller Diameter (in.)

N = Speed (RPM)U =229

DN



Constant

Speed

Q2 /Q

1= D

2 /D

1D=Impeller

Diameter

H2 /H1 = (D2 /D1)2

BHP2 /BHP1 = (D2 /D1)3



Constant

ImpellerDiameter Q

2 /Q

1= N

2 /N

1 Q = capacityN = speed

H2 /H1 = (N2 /N1)2 H = head

BHP=brake

horse power

BHP2 /BHP1 = (N2 /N1)3



Specific Speed ns

Where: Q = Flow (gpm) @ BEPN = Speed (RPM)

H = Head (per stage)

3/4s

H

Q Nn

x=



Impeller Design vs. Specific Speed

D2/D1 > 2 D2/D1 = 1.5-2. D2/D1 < 1.5 D2/D1 = 1.

(D2 = Vane O.D. D1 = Vane I.D.)



Pump Specific Speed ns

• Dimensionless number based on the affinity

laws used to select the impeller geometry formaximum efficiency.

• ns between 200 and 1000 = Barske

• ns between 1000 and 5000 = Francis vane

• ns between 5000 and 15000 = axial flow

pump (inducer)



ns vs. Impeller Design, Curve Shape



Curve Characteristics vs. ns

10,000 nsTypical

Axial Flow Machine

4000 nsTypical Mixed Flow



Efficiency vs. ns by Pump Types



Suction Specific Speed S

Where: Q = Flow (gpm) @ BEP“per eye”

N = Speed (RPM)

NPSHR = Net Positive Suction Head“required” by the pump

( ) 4/3R NPSHQ NS ×

=



NPSH

• Net Positive Suction Head is the

amount of energy available in the fluidat the pump suction flange.

• Successful pump operation resultswhen the suction fluid has sufficientenergy to push liquid into the pumpfaster than the pump can pump it away.



What Does NPSH Have To Do WithPump Maintenance?

• Inducer, impeller, cover , diffuser and pumpcase can suffer metal loss via “cavitation”

• Prevent Cavitation

by:

Increase NPSHA

(of the system)

Decrease NPSHR

(of the pump)



NPSHA

• NPSHA = ABSOLUTE PRESSURE HEAD(Barometric Pressure +/- Fluid Vapor

Pressure converted to head)- VAPOR PRESSURE HEAD (Temp. at

Suction Flange)

- LINE LOSSES (Frictional Loss)

+/- STATIC HEAD (Difference in Elevationfrom the Liquid Level to Pump Centerline)

+ VELOCITY HEAD (Small, Often Negligible)

• Consistent Units of Feet or Meters

• Pump suction gage improves accuracy



How To Increase NPSHA

• Increase Suction Vessel Pressure

• Decrease Vapor Pressure

(Decrease Suction Temperature)• Decrease Line Losses

• Increase Static Head



How To Decrease NPSHR

• Add Inducers

• Operate unit near BEP

• Select lower speed unit

Typical S =18,000 to

23,000



3. Types of Low Flow/ High Head Pumps

• Hydraulic Envelope• Sectional Views

• Methods for Handling Axial Thrust

• Ways to Handle Radial Loads



Hydraulic EnvelopeLow Flow/High Head

• Product options are available

• Over-lap of product performance envelopes does

occur—you do have choices

• Understand your system requirements

• Gather details and discuss with the pump supplier



Single Stage

3600 RPM



Two stage3600 RPM

Pitot



Single Stage

Medium Speed

Gearbox

Single Stage

Medium SpeedVFD



Pitot

3600-5000 RPM



Multi-stage

Between Bearings3600 RPM



Single Stage

Integral High Speed

Gearbox



Multi-stage Barske

3600 RPM



Two Stage Barske

Integral High SpeedGearbox



Three Stage BarskeIntegral High Speed

Gearbox



Barske – single stage @ 3600 rpm

Pitot @ 3600 – 5000 RPM

or

Barske – two stage @ 3600 RPM

Barske – Single stage or two stage

• Gearbox @ 6000 – 17000 RPM

• VFD @ 8000 RPM

Pitot @ 3600 – 5000 RPM

Multi-stage barrel @ 3600 RPM

Barske – single stage

Gearbox @ 9000 – 25,000 RPM

Barske– multi-stage (barrel) @ 3600 RPM

Barske – two stage

Gearbox @ 9000 – 25,000 RPM

Barske – Three-Stage

Gearbox @ 9000 –25,000 RPM

A

C

H

I

G

F

E

D

B

Low Flow, High Head Pumps



Two-stage Barske

M l i H i l d



Multi-stage Horizontal and

Vertical Options



Gearbox Driven Multi-stagePump with Barske Impellers



Pitot Pump Sectional



Pitot Principles of Operation

Pick-Up Tube

Generates 50% of Head

Rotor Assembly

Mechanical Seal on Suction Side Suction

Discharge

Centrifugal Rotor Cover

Generates 50% of Head



Methods for Handling Axial Thrust

Pump-out vanes• Balance holes

• Wear rings

• Balance Drum

• Back-to-back Impellers

• Special Bearing Arrangements



Multi-radial-blade Impellers

Shroud

HydraulicBalance Holes

Blades



Closed Impeller

LABYRINTH STEPS (wear ring)



Methods for Handling Radial Loads

• Volute Designs (circular vs. constantvelocity)

• Diffusers

Radial Load Trends



Radial Load Trends

Principles of Developing Head in Diffuser Pumps



A B C

P R E S S U R E

A B C

V E L O C I T Y

PUMP CASING

IMPELLER

DIFFUSERTHROAT

CONICALDIFFUSER

A BC

Principles of Developing Head in Diffuser Pumps

KMC B i



KMC Bearings

Flexure Pivot™ Radial and Thrust



4. Considerations & Factorsfor Your Pump Selection Choices

• Footprint

• NPSH

• Pump / System Interaction

• Life Cycle CostEfficiency Operational Flexibility MTBPM

Maintenance Practices Equipment Desirability

Service Support Personal Preference

Price & Delivery ISO 13709 (API 610) Compliance

• Equipment Field Experience



ISO 13709 (API 610) Compliance

• Classifications OH3, OH4, OH5, OH6

• Pressure Containment

• Temperature Limits

• Mechanical Seal Designs

• Hydrocarbon Applications

• Handling Solids

• Pump Bearing Housing



5. Summary• Do your homework to understand the

process system requirements• Select a pump type to fit your system for

normal and any upset conditions

• Evaluate the true benefit of any pump’s“special features”

• Evaluate Life Cycle Cost

Bottom Line… Choose Wisely



Questions and Answers

low flow high head

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