Where We Go Wrong - With Compressors

1. Where We Go Wrong - With Compressors Dick Hawrelak Presented to ES-317y in 1999 at UWO

2. Introduction • 5% of large property damage losses are caused by failures in pumps and compressors. • When a major failure takes place, the average trended Loss is $19.2MM. • C3H6 compressor,driver & spares in a world scale ethylene plant costs $17MM purchased.

3. Compressors Costs FS LHC#1 • Cost Summary By Elliott RAH Estimated • CG K-201/K-321 $17,239,800 $17,472,331 • Propylene K-601 $8,667,000 $6,674,797 • Ethylene K-651 $6,014,000 $5,478,011 • $31,920,800 $29,625,139 • 1.077 1.000

4. Compressor Problems • The following are some of the problems found in compressor design and operation. • The compressor train includes; compressors, drivers, KO Pots, exchangers and storage vessels.

5. ComplexCompSystemsCan BeFoundIn AnEthylenePlant

6. Mass Balance Problems • Process start-up, shut down or upset conditions not well defined. • Refrigerant mass balances. • Steam driver mass balances • Hot gas turbine mass balance. • Designers did not consider all problems associated with recycle for turn-down or false-load conditions.

7. Typical Steam Balance

8. Pressure / Temperature • Operating points not well located. • Poor data from the field. • Poor data is useless for determining compressor performance.

9. Interstage Conditions • If low stage pressure drops are higher than designed, final stage discharge pressure may not be achieved. • See NCOMP example for demonstration.

10. NCOMP Results

11. Discharge Conditions • Discharge temperatures higher than allowable limits. Indicates lower efficiency and pending trouble. • See NCOMP example for demonstration.

12. Composition • Actual plant feed stock differs from design feed stock. • Condensate compositions differ from one oil field to another. • Design for 100% ethane cracking but operate with mixed HC feeds.

13. Physical Properties • Vendor and customer did not agree on physical properties. • Non-ideal vapor / liquid systems. • VCM plant operates at 50% of capacity.

14. Vendor Offering • Vendors often quote unusually high compressor efficiency to try and win the contract. • Many customers are gullible enough to swallow the offering. • Difficult to pin vendor down on final performance. Too many degrees of wiggle freedom.

15. Follow-up • Customer fails to up-date material and energy balance after vendor shop tests confirm projected adiabatic compression efficiency.

16. Prototypes • Customer accepts vendor prototype offering with blind faith. • Ford Edsel example.

17. Spare Parts • Customer fails to request a spare rotor. 6 months to fabricate. • Customer orders a spare rotor but stores it incorrectly. • Rotor must be balanced in a coffin, turned regularly and the coffin nitrogen purged under positive pressure.

18. Shop Tests • Customer goes the cheap route and specifies only a “one point” shop test. • Customer fails to witness construction and final shop test.

19. Fabrication • Customer accepts vendor without shop visit. • Poor fabrication techniques.

20. Interstage Seals • Poor seal selection. • Mechanical seal. • Hot gas seal. • Water seal.

21. Vibrations • Vendor fails to identify all critical speeds. • Vendor makes a poor vibration corrections. • Poor vibration monitors and trip system.

22. Bearings • Poor fabrication. • Poor alignment. • Poor maintenance.

23. Anti-surge Control • High vibrations on approaching stonewall point. • Anti-surge control does not respond as required.

24. Shut-down Trip Systems • Cheap trip systems do not identify what tripped the compressor by a “first out” diagnostics trip system. • Poor trip systems do not permit good diagnostics following a compressor trip.

25. Lube Oil Systems • Insufficient lube oil reservoir capacity for roll-down. • Lube oil lines not cleaned before start-up. • Poor lube oil supply. • Non union lube oil system reassembled by local union.

26. Field Inspection • Customer fails to inspect lines after contractor finishes job. • Contractor hammer wrecks compressor on start-up.

27. Compressor Gears • Poor gear design. • High noise. • Poor alignment on maintenance. • Poor lubrication.

28. Compressor Configuration • Over-hung lines on compressors are poor for maintenance. • Bottom-hung lines on compressors are good for maintenance but require taller compressor building.

29. Typical Configuration

30. 3 Case C3H6 Compressor

31. Foundations • Poor soil bearing tests fail to disclose soil loading problems. • Compressor experiences settling. • Alignment suffers and compressor wrecks. • One project manager doubles all foundation specifications to be on the safe side.

32. Inlet Piping • Inlet lines too small. • Inlet vanes do not receive design flow due to poor flow distribution.

33. Driver Selection • Electrical motor. • Diesel motor. • Gas turbines. • Steam turbines. • Drivers require as much attention as the compressor.

34. Possible Exam Questions • In a multi-stage compressor, if the low stage pressure drops are higher than designed, how will the final final discharge pressure be affected? • What is the problem of running a compressor with a very high discharge temperature? • Why do we install vibration monitors and high vibration trips on centrifugal compressors? • ***