COMPRESSOR%20BASICS

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COMPRESSOR BASICS
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TYPES OF COMPRESSORS

• POSITIVE DISPLACEMENT COMPRESSOR
• CENTRIFUGAL COMPRESSOR

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POSITIVE DISPLACEMENT COMPRESSOR

• PD COMPRSSOR WORK BY TRAPPING A CERTAIN AMOUNT OF
  GAS AND FORCING IT INTO A SMALLER VOLUME
• A COMMON TYPE OF PD COMPR. IS RECIPROCATING
  COMPRESSOR.
• TWO OF THE MAIN PARTS OF RECIPROCATING COMP. ARE
  CYLINDER AND A PISTON

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• GAS ENTERS THE CYLINDER AND IS TRAPPED INSIDE THE
  CYLINDER. THE GAS IS THEN FORCED INTO A SMALLER
  SPACE BY THE ACTION OF THE PISTON.
• FORCING THE GAS IN SMALLER SPACE INCREASES THE
  PRESSURE, THE COMPRESSED GAS IS THEN DISCHARGED.

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CENTRIFUGAL COMPRESSOR

• IT USES A DEVICE CALLED IMPELLER TO SPIN THE GAS
  AROUND
• THE ACTION OF THE IMPELLER ACCELERATE OR
  INCREASES THE SPEED OF THE GAS FLOW. IT GIVES THE
  GAS ENERGY.
• AS THE GAS FLOWS OUT IT SPEED OUT AND SLOW DOWN
  AND ITS ENERGY IS CONVERTED INTO PRESSURE

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SHARING CHARACTERSTICS

• COMPRSSORS ARE RATED FOR DISCHARGE PRESSUR AND
  FLOW RATE
• ALL COMPRESSORS REQUIRE SOME FORM OF DRIVE
  MECHANISM
• ELECTRIC MOTORS ARE COMMONLY USED DRIVES.

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COMPRESSOR HAZARD

• MOVING PARTS
• HOT SURFACE
• NOICY
• LEAKS FROM THE GAS SYSTEM
• FLAMMABLE EXPLOSIVE GASES (SPARK PRODUCING
  EQUIPMENT SHOULD NEVER BE USED)

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ACCESSORIES

• LUBRICATION
• COOLING
• FILTERING

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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.

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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.

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• 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.

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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.

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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.

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• 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.

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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

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• 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

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• 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

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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

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• 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

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• 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.

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START UP

• PREPARING THE COMPRESSOR FOR STARTUP
• WARMING UP THE COMPRESSOR
• STARTING THE GAS FLOW THRU COMPRESSOR

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• 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.

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• 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

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• 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.

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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.

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• 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.

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• OIL PARAMETER IS CRITICAL PARAMETER, HIGHER THAN
  NORMAL OIL PRESSURE INDICATES THE CLOGGING OF
  SOME PART IN OIL LUBRICATION SYSTEM.