1 / 20

Where We Go Wrong In Pump Design

Where We Go Wrong In Pump Design. Dick Hawrelak Presented to ES317Y in 1999 at UWO. Introduction. 5% of large property damage losses are caused by failures in pumps. Average Trended Loss was $19.2MM, the lowest of all unit operations. Typical Pump Sketch. Poor Mass Balances.

aria
Télécharger la présentation

Where We Go Wrong In Pump Design

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Where We Go Wrong In Pump Design Dick Hawrelak Presented to ES317Y in 1999 at UWO

  2. Introduction • 5% of large property damage losses are caused by failures in pumps. • Average Trended Loss was $19.2MM, the lowest of all unit operations.

  3. Typical Pump Sketch

  4. Poor Mass Balances • Normal mass balance. • Start-up, shut down or upset. • Recycle conditions on EBV closure. • Pump design for multiple services are tricky.

  5. Multi-Discipline Design • Line sizing. • Check valve sizing. • Control valve sizing. • Orifice plate sizing. • Viscosity corrections. • Light density hydrocarbon corrections.

  6. Control Valves • Poor CV selection - pump running on by-pass…may need two CVs. • If too large DP taken across control valve, it may be better to trim impeller, save CV wear & energy.

  7. Blocked-in Operation. • Pumps can explode in a short period of time if left running while blocked-in. • Pump explodes, pieces rocket 275m, hits truck, kills driver. • Pump leaks, liquid catches fire and destroys plant.

  8. Suction Conditions • Poor NPSH causes pump cavitation, high vibration & ultimately pump failure. • Pump fails to perform as designed without suitable NPSH.

  9. Suction Specific Speed • SSS = rpm(Q)^0.5 / (NPSH@ BEP)^0.75 • Pumps operating at SSS greater than 11,000 had a high failure frequency. • Low capacity operation causes inlet recirculation, impeller erosion, shaft deflections, bearing failures and seal problems which lead to leakage.

  10. Maintenance • Poor alignment causes bearing problems and ultimately pump failure. • If seal leakage rate too high, select better mechanical seal (single, double, triple). • Require a good preventative maintenance (PM) program.

  11. Check Valves • If Check Valve designed properly, it will prevent back flow. • If Check Valve not designed properly, it will chatter continuously and destroy seal seat faces in a short period of time. • Without back flow protection, hazardous flooding conditions can occur on pump shut-down.

  12. Phase 4 Design Checks • Preliminary Phase 2 & 3 pump calculations not confirmed in Detailed Design, Phase 4. • Pumps fail to perform as designed. • Corrections costly during start-up.

  13. 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 on internet (program is free).

  14. Typical Pump

  15. Selected Pump

  16. Dissolved Gases • Absorbed gas follows Henry’s 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.

  17. 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.

  18. 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.

  19. Possible Exam Questions • What is the problem of running a pump while it is blocked in? • What is the hazard created by poor pump alignment? • What is the hazard created by poor mechanical seal selection for a pump? • What is the hazard created by low capacity operation of the pump? • Why is it necessary to provide adequate NPSH for a pump?

  20. Summary • This short list is indicative of some of the problems caused by poor engineering discipline in pump design. • Recommend you obtain a copy of the Chemical Plant Design programs and follow the procedures built into the pump design spreadsheets.

More Related