compressor instrument and control -1
DESCRIPTION
Compressor Instrument and ControlTRANSCRIPT
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.