Compressor control , operation and maintenance

Control System

1

Field Control room

front real

COMPRESSOR HAZARD

• MOVING PARTS

• HOT SURFACE

• NOISY

• LEAKS FROM THE GAS SYSTEM

• FLAMMABLE EXPLOSIVE GASES (SPARK PRODUCING

EQUIPMENT SHOULD NEVER BE USED)

ACCESSORIES

• LUBRICATION

• COOLING

• FILTERING

LUBRICATION SYSTEM

• MAIN FUNCTION IS TO REDUCE FRICTION BETWEEN THE MOVING PARTS

• LUBRICATION HELPS COOLING THE COMPRESSOR MOVING PARTS AND HELP PREVENT THE LEAKING GAS OUT OF COMPRESSOR.

DESCRIPTION

• OIL FROM THE COMPRESSOR FLOWS INTO THE OIL PUMP.THE OIL

IS THEN PUMPED THROUGH FILTER WHICH REMOVES ANY SOLID

PARTICLE FROM THE OIL.

• OIL FLOWS THROUGH THE HEAT EXCHANGER WHERE IT IS COOLED

• FROM HEAT EXCHANGER MOST OF THE OIL FLOWS DIRECTLY TO

COMPRESSOR LUBRICATION.

• REST OF THE OIL GOES TO OILER.

• OILER SUPPLIES A SMALL AMOUNT OF OIL TO THE

COMPRESSOR CYLINDER

• THE OIL LUBRICTES THE PISTON RINGS AND HELPS SEAL

THE SPACE BETWEEN THE CYLINDER WALL AND THE RING.

COOLING • WHEN A GAS IS COMPRESSED HEAT IS PRODUCED THIS

HEAT CAN CAUSE TWO PROBLEM

1. EXCESS HEAT CAN BREAK DOWN OIL CAUSING IT TO BE

LOOSE ITS LUBRICATING CHARECTORSTIC

2. GASED EXPAND WHEN THEY ARE

HEATED SINCE COMPRESSOR IS DESINGED TO COMPRESS

GASES THE EFFECT CREATE ADDITIONAL FORCE WHICH

COMPRESSOR MUST OVERCOME.

HEAT REMOVAL

• AIR COOLING AND WATER COOLING ARE TWO TECHNIQUES

1. AN AIR COOLED COMPRESSOR

EASILY IDENTIFIED BY MEAL FINS

ON ITS CASING THE FINS PROVIDE INCREASED SURFACE

AREA.

2. ANOTHER WAY TO REMOVE THE

EXCESS HEAT IS TO COOL THE GAS AFTER THE

COMPRESSION IS COMPLETE, THE DEVICE THAT

DOES THIS IS AN AFTERCOOLER OR INTERCOOLER

• DEPENDING UPON ITS LOCATION THESE EXCHANGERS

ARE CLASSIFIED AS INTERCOOLER OF AFTER COOLER.

Compressor INSTRUMENTATION AND CONTROL

Compressor control

‘Compressor controls’’ have different definitions

among users, designers, and suppliers.

These can be, but are not limited to:

1. Machinery protection

a. Simple alarm system for several parameters

b. Simple shutdown system for several parameters

2. Safety shutdown system monitoring multiple parameters for

machinery protection

and safety of personnel

3. Same as 2, with loading/capacity control

4. Same as 3 with communications and remote monitoring. Computer

monitoring

provides enhanced automation and energy management in addition to

the capability

to store and manipulate data for maintenance and diagnostic purposes.

Compressor control cont.

Compressor control cont.2

• 5. Environmental regulations have made the addition of emissions controls on compressors and engine drivers necessary for certain geographical areas.

SYSTEM CONSIDERATIONSSYSTEM CONSIDERATIONSThe control system must be selected to suit the machine, the operator,

and the application. These considerations include, but are not limited to:

1. Is this machine part of a critical process?2. What is the cost/benefit ratio to be provided by controls?3. What are the personnel hazards?4. Is this machine in a hazardous area?5. What codes such as NEC, API, NFPA, OSHA, EPA or other regulatory

agencies apply?

6. What degree of complexity is required for safety shutdown, capacity control, loading control, remote start-stop capability, and communications?

7. Should the safety devices be monitored by the information/operations/capacity

controls system or should safety monitoring be in a separate stand alone system?

8. Will the system be maintained by:a. Mechanics and/or operatorsb. Instrument techniciansc. Electronics techniciansd. Communications technicianse. Users or contract personnel9. Will the system require expansion at a later date?

SYSTEM CONSIDERATIONS

INSTRUMENTATION AND CONTROL

• THE PROPER OPERATION OF COMP. DEPENDS UPON

INSTRUMENTAITON AND CONTROL DEVICES

• THESE DEVICES ALLOWS THE COMPRESSOR TO BE STARTED

AND STOPPED.

• THEY PROVIDE INFORMATION ABOUT THE COMPRESSOR

OPERATING CONDITIONS

• THEY MAINTAIN THE VALUES OF PROCESS VARIABLES

• THEY KEEP THE COMPRESSOR OPERATION STABLE

• THEY CAN SHUT DOWN THE COMPRESSOR IF

UNSAFE CONDTITON OCCURED

• CONTROL PANEL MAY HAVE CONTROL TO REGULATE

THE SPEED

• CONTROL PANEL ME ALSO CONTAIN ALARMS THAT

LET THE PERSONNEL KNOW WHEN ABNORMAL AND

POTENTIAL DAMAGING CONDITION EXISTS

• PRESSURE CONTROLLER CONTROLS THE DISCHARGE

PRESSUR AND IF IT DEVIATES CONTROLLER

MANUPULATE THE INLET FLOW

SURGE CONTROL

• FOR A GIVEN DISCHARGE PRESSURE A COMPRESSOR HAS A

CERTAIN MINIMUM FLOW RATE. BELOW THIS FLOW RATE

THE COMPRESSOR BECOME UNSTABLE. A DECREASE IN FLOW

BELOW THE MINIMUM FLOW CAN CAUSE A SERIES OF

MOMENTARY REVERSAL OF FLOW THROUGH THE

COMPRESSOR. THIS SITUATIION IS CALLED SURGE

• SURGING RESULTS IN VIOLENT FLUCTUATIONS IN

DISCHARGE PRESSURE.

• WHEN AN ELECTRIC MOTOR IS USED AS DRIVER SURGING

CAN CAUSE EXTREME VARIANTION IN MOTOR CURRENT.

• SYMPTOMS OF SURGING ARE LOW GAS FLOW, EXCESSIVE

VIBRATION AND BANGING SOUND INSIDE COMPRESSOR

• TO PREVENT THE SURGING THE FLOW RATE OF THE

GAS THRU THE COMPRESSOR MUST BE KEPT ABOVE

THE MINIMUM STABLE FLOW RATE OR SURGE POINT

• WHEN THE DEMAND IS LOW FLOW RATE IS

MAINTAINED BY RECIRCULATING THE PORTION

FROM DISCHARGE TO BACK TO COMPRESSOR.

SURGE CURVE

P= p2 /p1 Q 1 FLOW RATE

START UP

• PREPARING THE COMPRESSOR FOR STARTUP

• WARMING UP THE COMPRESSOR

• STARTING THE GAS FLOW THRU COMPRESSOR

• COMPRESSORS GAS SUPPLY IS AVAILABLE, CONTROLS ARE

SET IN POSITIONS.

• VALVE LINE UP MEANS ALL THE VALVE ARE PROPERLY SET.

• START THE COMPRESSOR AUXILARIES AND MAKE SURE

THEY ARE OPERATING PROPERLY.

• OPERATOR MUST CHECK THE COMPRESSOR AND MAKE

SURE THAT NO ABNORMAL CONDITION EXISTS.

• IF THE COMPRESSOR HANDLES THE FLAMMABLE GAS IT MUST

BE PURGE WITH AN INERT GAS LIKE NITORGEN.

• ONCE PURGED IT CAN BE STARTED AND KEPT IN WARMING UP.

• ONCE THE COMPRESSOR AND ITS PARTS RUNS FOR A WHILE AT

A LOW SPEED THE COMPRSSOR CAN BE BROUGHT UP TO

NORMAL SPEED.

• THIS INVOLVES THE INCREASE OF SPEED AT CERTAIN RATE

CALLED RAMP RATE

• CRITICAL SPEED – FOR CETRUFUGAL COMPRSSOR CERTAIN

ROTATIONAL SPEED CAUSE SEVERE VIBRATION, IT IS CALLED

CRITICAL SPEED.

• IT IS DUE TO PHYSICAL CHARECTORSTIC OF MOVING PARTS OF

COMPRESSOR.

• WHEN A CRITICAL SPEED IS REACHED THE RAMP SPEED IS

USUALLY INCREADED TO PASS THROUGH THE CRITICAL SPEED.

OPERATION

• ONCE STARTED COMPRESSOR SHOULD BE CHECKED

ROUTINELY.

• WHILE CHECKING A COMPRSSOR OPERATOR MUST KEEP IN

MIND THAT IT OPERATES AT VERY HIGH SPEED.

• AN IMPORTANT PART OF CHECKING A COMPRSSOR IS TO

LISTEN TO THE ABNORMAL SOUND.

• IT IS IMPORTANT TO CHECK THE COMPRESSOR BEARING FOR

EXCESSIVE VIBRATION AND OVERHEATING IT INDICATE

PROBABLE BEARING FAILURE.

• COMPRESSOR AUXILIARY CHECK IS IMPORTANT DURING

OPERATION OF COMP. LIKE OIL LEVEL IS IN NORMAL

RANGE,OIL IS CLEAR AND NOT MILKY.

• OIL PRESSURE IS IMPORTANT PARAMETER TO CHECK,

INIDCATE MALFUNCTION OF OIL PUMP OR OIL LEAK IN

SYSTEM.

• OIL PARAMETER IS CRITICAL PARAMETER, HIGHER

THAN NORMAL OIL PRESSURE INDICATES THE

CLOGGING OF SOME PART IN OIL LUBRICATION

SYSTEM.

Five Valve Loading Sequence Machine Not RunningBlowdown valve openBypass valve openSuction valve closedDischarge valve closedPurge valve closedPrior to start—1. Close bypass valve.2. Open purge valve.3. After time delay for pressurized purge, open bypass.Start machine—1. After warm-up or appropriate time, initiate load sequence.2. Open purge valve (pressurize compressor and confirm pressure).3. Close purge valve.4. Open discharge valve.5. Open suction valve.6. Close bypass valve to begin flow through the compressor. (Bypass valve can beused to control flow through the machine.)Five Valve Unloading Sequence1. Open bybass valve.2. Open blowdown valve (optional)3. Close suction valve.4. Close discharge valve.

• RECIPROCATING COMPRESSOR MONITORING

Monitoring systems have progressed to measuring many

parameters beyond those required for basic safety. These

include capacity, pressure, volume, time, vibration ,

calculations of gas, rod load, power, fuel consumption and

efficiency.

The industry is also rapidly moving to a ‘‘predictive

maintenance’’ mode as compared to ‘‘preventive

maintenance.’’ Monitoring systems must be more complex to

accomplish predictive maintenance.

Centrifugal/Axial Compressor Monitoring

- Centrifugal and axial compressors are less forgiving than slower speed reciprocating

machines because of the operating speeds.

- The controls for centrifugal machines must have very quick response times in

order to prevent catastrophic failures and are much more complex than the systems

required for reciprocating compressors.

- Real time on-line performance monitoring and trending is now commonplace

because of available high speed computer systems.

- Surge control on axial and centrifugal machines is essential to prevent damage

in the event of rapidly changing flow conditions. Bearing vibration monitoring in

three planes and axial trip sensors, along with bearing trip monitors, are common

practice on centrifugal machinery.