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

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

Compressors Costs FS LHC#1 Cost Summary By Elliott RAH Estimated CGK-201/K-321$17,239,800 $17,472,331 PropyleneK-601$8,667,000 $6,674,797 EthyleneK-651$6,014,000 $5,478,011 $31,920,800 $29,625,

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

Complex Comp Systems Can Be Found In An Ethylene Plant

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

Typical Steam Balance

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

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

NCOMP Results

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

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

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

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

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

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

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

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

Fabrication n Customer accepts vendor without shop visit. n Poor fabrication techniques.

Interstage Seals n Poor seal selection. n Mechanical seal. n Hot gas seal. n Water seal.

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

Bearings n Poor fabrication. n Poor alignment. n Poor maintenance.

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

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

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

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

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

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

Typical Configuration

3 Case C3H6 Compressor

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

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

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

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