Pump Design

1
Pump Design Selection

• Dick Hawrelak
• Presented to UWO CBE 497
• 16 Oct 01

2
Good Design References

• Flow of Fluid Through Valves and Fittings by
  Crane. Technical Paper No. 410-C.
• Centrifugal Pumps and System Hydraulics,
  Chem Engg, 4 Oct 82, p-84, by Karassik.
• Chem Eng Handbook, Perry 6, Sections 5 and 6
• Primer software by Durco http//www.durcopump.com
  
• PumpSel 6.2 (rev .07) by Durco
  http//www.durcopump.com

3
Pump Design Stages

• Phase 2 Process alternatives optimization.
• Phase 3 PIDs, preliminary layout, approx
  design, specification, pre-selection, cost
  estimate.
• Phase 4 detailed design.
• Final layout check piping elevations.
• Final detailed hydraulic design selection.
• Suitability (NPSH, SSS, Re-circulation).
• Final cost estimate.

4
Excel Pump Design Program

• Plant Design Programs on CD-ROM
• Quick Pump Design V1.3
• Contains Following Features
• Line Sizing
• Control Valve Sizing
• Check Valve Sizing
• Orifice Plate Sizing
• NPSH, NS, SSS, HP calculations
• System Head Curve
• Limited Pump Selection
• Used along with Durcos PUMPSEL and PRIMER

5
Draw Sketch of Pump System

• Collect physical property data (density,
  viscosity, vapor pressure).
• Show line details, size, schedule or wall thk,
  check valves, control valves, block valves,
  reducers/expanders (may have to take a WAG).
• Show origin (min.) and destination pressures
  (max.).
• Show origin and destination elevations for static
  head.
• Combine services where practical economical.

6
Typical Pump Sketch
7
Size Suction and Discharge Lines

• Break lines into sizable sections. There may be
  different sizes in any one branch. Eg 4, 6 and
  8 sections.
• Estimate the number of elbows, block valves,
  fittings, etc. (WAG in Ph 2). Fitting pgm in
  Phase III.
• Expand line sizing routine for record keeping.
  This will simplify phase 4 checking.

8
Line Size Equations

• Re No. 6.31 ( W ) / ( d ) / ( cP )
• Darcy friction factor f 4 ( f Fanning )
  f Darcy by all-in-one
  Chen Equation
• DP100 0.000336 ( f )( W )2 / ( DL ) / ( d )5
• Max Dp100 usually limited to 1.0 psi per 100 ft.
• K ( f ) ( L / D ) for pipe
• K ( f Turb ) ( L / D ) for valves and fittings
• K total K pipe K valves fittings
• DP 2.8E-07 ( K total )( W )2 / ( DL ) / ( d
  )4
• Abs roughness e 0.00015 for clean pipe, ft.
• Abs roughness e 0.0004 for dirty pipe, ft.

9
Size Check Valves in Each Discharge Line Branch

• Line sizing program built-into Pump pgm.
• Check pipe spec for type of check valve.
• Check minimum line velocity to keep ChV in open
  position. Prolonged operation at reduced rates
  may cause ChV chatter and damage to ChV.
• Operation with damaged ChV is extremely
  hazardous.

10
Typical Check Valve Equation

• For a Swing Check Valve (see Crane, page A-27)
• K 100 ( f Turb ) for pressure drop
• Minimum Velocity, fps 35 / ( DL )

11
Size Orifice Plates in Each Branch

• See Line sizing routine.
• Orifice Plate pressure drop usually in three
  ranges.
• Typically 0.5, 1.0 or 2.0 psi

12
Typical Orifice Equation

• Beta d1 / d2 should be in range 0.2 to 0.7
• d1 orifice dia., d2 pipe dia., inches
• Re No. based on d2, the pipe diameter
• W 1891 ( d1 )2 ( C ) (( DP )( DL))0.5
• C Flow Coefficient for square edged orifices
  (see Crane, page A-20)
• C Function of Re No. and Beta ratio
• C should be in range 0.6 to 0.8

13
Control Valves

• Select each branch with control valves and use
  line size routine to size control valves assuming
  Fisher Equal Percentage type valves.
• Poor CV selection no control, pump running on
  by-passmay need two control valves.
• If too large DP taken across control valve, it
  may be better to trim impeller, save CV wear
  energy.
• Pump program should use CV in controlling line.
• DP CV / (DP CV DP fric) approx 0.1 to 0.3.
  Default DP control valve 10 psi.

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Typical Control Valve Equations

• Cv ( USGPM )( SG / DP )0.5
• Cv Liquid Sizing Coefficient.
• SG Specific Gravity.
• DP Pressure Drop (10 psi default)
• Typical control valve is an equal percentage type
  valve.
• Cv depends on valve size, valve opening, and
  flow.

15
Blocked-in Operation.

• Determine features required for blocked-in
  operation.
• Low flow shut-down.
• High temperature shut-down.
• Recycle plus cooling.
• Pumps can explode in a short period of time if
  left running while blocked-in and no high
  temperature shut-down is provided.
• Pump explodes, pieces rocket 275m, hits truck,
  kills driver.
• Pump leaks under high pressure, liquid catches
  fire and destroys plant.

16
Suction Conditions

• Determine NPSH available.
• NPSH SP VP HL DP friction all in ft of
  liq.
• Boiling liquids, SP VP. Raise height or reduce
  DP.
• Poor NPSH causes pump cavitation, high vibration
  ultimately pump failure (hazard).
• Pump fails to perform as designed without NPSH
  available greater than NPSH required.
• Typically, NPSH avail 12 ft. vs 10 ft. reqd.
• Pump Vendor will tell you NPSH required based on
  pumps selection.

17
System Head Curve

• Determine Controlling Branch I.e the one that
  requires the maximum differential head.
• Determine the system curve for all items except
  the control valve.
• For Dp at reduced USGPM, assume DP is
  proportional to the square of the flow.
• Include static head.

18
Pump Selection

• Hundreds of pumps to select from.
• Which selection is best?
• Which RPM to use?
• What HP size type of motor to select, explosion
  proof, TEFC?
• Download Durco PUMPSEL and PRIMER on internet
  (program is free).
• http//www.durcopump.com

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Durco PUMSEL Program Input

• From Quick Pump Design V1.3 enter
• Design USGPM
• System head, in ft.
• Specific Gravity
• Pumping temp, Deg F
• Viscosity in Centipoise
• NPSH available in ft.
• 3 points from system curve.

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PUMPSEL Output

• Selects all available pumps
• Gives Impeller sizes
• Gives HP and NPSH Required
• Gives a cost estimate (PRIMER)
• Gives options for types of pumps
• Gives all kinds of help on all features.
• PUMPSEL is a must for any design group.
• Program also available from Gould.

21
Typical Pump Head Curves
22
Selected Pump
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Suction Specific Speed, SSS

• SSS is an Index number descriptive of the suction
  charateristics of a pump impeller.
• SSS (rpm)(Q _at_ BEP)0.5 / (NPSH _at_ BEP)0.75
• Pumps operating at SSS greater than 11,000 had a
  high failure frequency (hazard).
• Low capacity operation causes inlet
  recirculation, impeller erosion, shaft
  deflections, bearing failures and seal problems
  which lead to leakage.
• Pump program predicts recirculation as of SSS.

24
Dissolved Gases

• Absorbed gas follows Henrys Law xa (pp / Pt) /
  H.
• Dissolved gases are like entrained bubbles.
  Residence time in suction vessel may be too
  short.
• Dissolved gases causes problems similar to NPSH
  cavitation.
• Prevent vapor entrainment with vortex breakers.

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Material Transfer

• Need multiple checks on quantity of material
  transferred to storage.
• Weigh scales, level checks, mass (flow
  rate)(time) on computer.
• Time control EBVs to minimize Water Hammer
  problems.

26
Excess Flow Protection

• Pumps cannot be allowed to run out on the
  impeller curve, may burnout motor if motor not
  selected for runout.
• May need excess flow protection.

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Repeat Design in Phase IV

• All of the above details are checked again in
  Phase IV Engineering.
• Necessary to have good documentation.
• Poor Phase III Design Selection means rework
  during expensive Phase IV stage.