1. Pump Design & Selection n Dick Hawrelak n Presented to UWO CBE 497 n 16 Oct 01

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

3. Pump Design Stages n Phase 2 – Process alternatives & optimization. n Phase 3 – P&IDs, preliminary layout, approx design, specification, pre-selection, cost estimate. n Phase 4 – detailed design. u Final layout – check piping & elevations. u Final detailed hydraulic design & selection. u Suitability (NPSH, SSS, Re-circulation). u Final cost estimate.

4. Excel Pump Design Program n Plant Design Programs on CD-ROM n Quick Pump Design V1.3 n Contains Following Features F Line Sizing F Control Valve Sizing F Check Valve Sizing F Orifice Plate Sizing F NPSH, NS, SSS, HP calculations F System Head Curve F Limited Pump Selection n Used along with Durco’s PUMPSEL and PRIMER

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

6. Typical Pump Sketch

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

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

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

10. Typical Check Valve Equation n For a Swing Check Valve (see Crane, page A-27) n K = 100 ( f Turb ) for pressure drop n Minimum Velocity, fps = 35 / ( DL )

11. Size Orifice Plates in Each Branch n See Line sizing routine. n Orifice Plate pressure drop usually in three ranges. n Typically 0.5, 1.0 or 2.0 psi

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

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

14. Typical Control Valve Equations n Cv = ( USGPM )( SG / DP )^0.5 n Cv = Liquid Sizing Coefficient. n SG = Specific Gravity. n DP = Pressure Drop (10 psi default) n Typical control valve is an equal percentage type valve. n Cv depends on valve size, % valve opening, and flow.

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

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

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

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

19. Durco PUMSEL Program Input n From Quick Pump Design V1.3 enter: F Design USGPM F System head, in ft. F Specific Gravity F Pumping temp, Deg F F Viscosity in Centipoise F NPSH available in ft. F 3 points from system curve.

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

21. Typical Pump Head Curves

22. Selected Pump

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

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

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

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

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