Where We Go Wrong - With Compressors

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Where We Go Wrong - With Compressors

• Dick Hawrelak
• Presented to ES-317y in 1999 at UWO

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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.

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Compressors Costs FS LHC1

• 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

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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.

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ComplexCompSystemsCan BeFoundIn
AnEthylenePlant
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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.

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Typical Steam Balance
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Pressure / Temperature

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

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Interstage Conditions

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

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NCOMP Results
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Discharge Conditions

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

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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.

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Physical Properties

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

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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.

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Follow-up

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

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Prototypes

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

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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.

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Shop Tests

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

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Fabrication

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

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Interstage Seals

• Poor seal selection.
• Mechanical seal.
• Hot gas seal.
• Water seal.

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Vibrations

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

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Bearings

• Poor fabrication.
• Poor alignment.
• Poor maintenance.

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Anti-surge Control

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

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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.

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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.

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Field Inspection

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

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Compressor Gears

• Poor gear design.
• High noise.
• Poor alignment on maintenance.
• Poor lubrication.

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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.

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Typical Configuration
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3 Case C3H6 Compressor
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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.

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Inlet Piping

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

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Driver Selection

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

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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?