1.6b compressors slides

8/13/2019 1.6b Compressors Slides

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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 damagelosses are caused by failures inpumps and compressors.

When a major failure takes place,the average trended Loss is$19.2MM.

C3H6 compressor,driver & spares

in a world scale ethylene plantcosts $17MM purchased.


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Compressors Costs FS LHC#1

Cost Summary By Elliott RAHEstimated

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


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Compressor Problems

The following are some of the

problems found in compressordesign and operation.

The compressor train includes;compressors, drivers, KO Pots,

exchangers and storage vessels.


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ComplexComp

SystemsCan BeFound

In AnEthylenePlant


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Mass Balance Problems

Process start-up, shut down orupset conditions not well defined.

Refrigerant mass balances.

Steam driver mass balances

Hot gas turbine mass balance.

Designers did not consider allproblems associated with recycle

for turn-down or false-loadconditions.


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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 stagedischarge pressure may not beachieved.

See NCOMP example fordemonstration.


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NCOMP Results


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Discharge Conditions

Discharge temperatures higher

than allowable limits. Indicateslower efficiency and pendingtrouble.

See NCOMP example fordemonstration.


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Composition

Actual plant feed stock differs fromdesign feed stock.

Condensate compositions differfrom 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% ofcapacity.


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Vendor Offering

Vendors often quote unusuallyhigh compressor efficiency to tryand win the contract.

Many customers are gullibleenough to swallow the offering.

Difficult to pin vendor down on finalperformance. Too many degrees ofwiggle freedom.


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Follow-up

Customer fails to up-date materialand energy balance after vendorshop tests confirm projectedadiabatic compression efficiency.


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Prototypes

Customer accepts vendorprototype offering with blind faith.

Ford Edsel example.


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Spare Parts

Customer fails to request a sparerotor. 6 months to fabricate.

Customer orders a spare rotor butstores it incorrectly.

Rotor must be balanced in a coffin,turned regularly and the coffinnitrogen purged under positivepressure.


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Shop Tests

Customer goes the cheap routeand specifies only a one point

shop test.

Customer fails to witnessconstruction 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 criticalspeeds.

Vendor makes a poor vibrationcorrections.

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 identifywhat 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 reservoircapacity for roll-down.

Lube oil lines not cleaned beforestart-up.

Poor lube oil supply.

Non union lube oil systemreassembled by local union.


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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 compressorsare good for maintenance butrequire 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 todisclose soil loading problems.

Compressor experiences settling. Alignment suffers and compressor

wrecks.

One project manager doubles all

foundation specifications to be onthe 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.

P ibl E


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Possible ExamQuestions

In a multi-stage compressor, if the low stagepressure drops are higher than designed, how

will the final final discharge pressure beaffected?

What is the problem of running a compressorwith a very high discharge temperature?

Why do we install vibration monitors and highvibration trips on centrifugal compressors?

***

1.6b compressors slides

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