SYED ASGHAR ABBAS NAQVI

1
RECIPROCATING COMPRESSORS

• By
• SYED ASGHAR ABBAS NAQVI

2
CLASSIFICATION
3
Reciprocating Compressor

• In a reciprocating compressor, a volume of gas is
  drawn into a cylinder, it is trapped, and
  compressed by piston and then discharged into the
  discharge line. The cylinder valves control the
  flow of gas through the cylinder these valves
  act as check valves. There are two types of
  reciprocating compressor.

4
Reciprocating CompressorTypes

• Single Acting compressor
• It is a compressor that has one discharge per
  revolution of crankshaft.
• Double Acting Compressor
• It is a compressor that completes two discharge
  strokes per revolutions of crankshaft. Most
  heavy-duty compressors are double acting..

5
Reciprocating Compressor
6
Reciprocating Compressor

• Different parts of double acting compressor are
  listed below.
• Suction valve.
• Suction gas jacket.
• Piston.
• Cylinder.
• Discharge valve.
• Discharge gas jacket

7
Reciprocating Compressor
8
Construction of Reciprocating Compressors

• Reciprocating compressors can be divided into two
  main groups.
• Gas end.
• Power end.

9
Gas End

• GAS END
• Parts of the reciprocating compressor that handle
  process gas are grouped in this category.

10
(No Transcript)
11
Cylinder Liner

• Piston reciprocates inside a cylinder. To provide
  for reduced reconditioning cost, the cylinder may
  be fitted with a liner or sleeve. A cylinder or
  liner usually wears at the points where the
  piston rings rub against it. Because of the
  weight of the piston, wear is usually greater at
  the bottom of a horizontal cylinder. A cylinder
  liner is usually counter bored near the ends of
  the outer ring travel i.e. counter bores are made
  just ahead of the points where the end piston
  rings stop and reverse direction. Shoulders may
  form in the liner where the rings travel stops
  unless counter bores are provided.

12
Piston

• For low speed compressors (upto 330 rpm) and
  medium speed compressors (330-600 rpm), pistons
  are usually made of cast iron.
• Upto 7 diameter cast iron pistons are made of
  solids. Those of more than 7 diameters are
  usually hollow (to reduce cost).
• Carbon pistons are sometimes used for compressing
  oxygen and other gases that must be kept free of
  lubricant.

13

• As the compressor reaches operating temperature,
  the piston and rod expand more than
  liner/cylinder does. In order to prevent seizure
  adequate clearance should be provided, at the
  same time clearance must be close enough to
  permit adequate support of piston rings.
  Similarly end clearance is also important.
• A cold piston is usually installed with one third
  of its end clearance on the crank end and two
  third of its end clearance on the head end.

14
PISTON ROD AND PISTON

• Generally, the piston rod is fastened to the
  piston by means of special nut that is prevented
  from unscrewing. The surface of the rod has
  suitable degree of finish designed to minimize
  wear on the sealing areas as much as possible.
  The piston is provided with grooves for piston
  rings and rider rings.

15
PISTON ROD AND PISTON
16
Piston rod packing

• Piston rod packing ensures sealing of the
  compressed gas. The piston rod packing consists
  of series of cups each containing several seal
  rings side by side. The rings are built of three
  sectors, held together by a spring installed in
  the groove running around the outside of the
  ring.
• The entire set of cups is held in place by stud
  bolts. Inside channels are there for cooling, gas
  recovery and lubrication of the piston rod
  packing.

17
Piston rod packing
18
Piston rod packing
19
Piston rod packing
20
Piston rod packing
21
Oil Seal

• An arrangement of scraper rings serves to keep
  the oil, entrained by piston rod, from leaking
  out of the crankcase. The oil scraped is returned
  to the crankcase reservoir.

22
Oil Seal

• An arrangement of scraper rings serves to keep
  the oil, entrained by piston rod, from leaking
  out of the crankcase. The oil scraped is returned
  to the crankcase reservoir.

23
Piston Rings

• Piston rings provide a seal that prevents or
  minimizes leakage through piston and liner. Metal
  piston rings are made either in one piece, with a
  gap or in several segments. Gaps in the rings
  allow them to move out or expand as the
  compressor reaches operating temperature. Rings
  of heavy piston are sometimes given bronze,
  Babbitt or Teflon expanders or riders.
  Lubrication is a must for metallic rings. Teflon
  rings with Teflon rider bands are sometimes used
  to support the piston when the gas do not permit
  use of a lubricant.

24
Piston Rings
25
Head

• The ends of cylinder are equipped with removable
  heads, these heads may contain water/liquid
  jacket for cooling. One end is called head-end
  head and other crank-end head. The crank-end
  contains packing (a set of metallic packing
  rings) to prevent gas leakage around piston rod.
• Valves
• There are normally three types of valves, these
  are
• Plate valve.
• Channel valve.
• Poppet valve.

26
Plate Valve

• Heavy-duty compressors use a form of plate valve.
  The part that closes against a valve seat is a
  flat metal plate. The plates are held tightly
  against the seat by a set of springs.

27
Channel Valve

• These valves use channel shaped plates instead of
  flat plates. Above each channel is a bowed, steel
  tension spring. Spring pushes from the stop plate
  and channels cover the slots in the valve seat.

28
Poppet Valve

• These are shaped like the valves in an automobile
  engine. These are separate, round poppets to
  seat against holes in the valve seats. Poppets
  are made of low friction material (e.g.
  Bakelite), they provide a low-pressure drop and
  are often used when ratios of compression are low
  and also for high flow rates.

29
Valves

• The valves are of automatic type. They open due
  to the effect of the differential pressure
  between cylinder and the suction or discharge
  chambers, and close due to the force of springs
  acting on the plates plus the differential
  pressure across the valves.

30
Major Components of Valves

• Seat
• The main body of valve that withstands the
  differential pressure when the valve is closed

31
Major Components of Valves contd.

• Counter seat
• The valve component that limits the lift and
  contains the springs
• Rings
• The element that withstands the differential
  pressure, ensuring gas seal
• Spring
• The element that acts on the rings, causing valve
  closing
• Shim
• The element that determines the valve lift.
• Stud bolt, nut pin
• These elements fasten all the components
  together.

32
Power End

• Parts of reciprocating compressor that assist in
  transferring power and converting rotary motion
  into reciprocating motion are grouped in this
  category.

33
Crank Case

• Crank case supports the crankshaft. All bearing
  supports are bored under setup condition to
  ensure perfect alignment. Crankcase is provided
  with easy removable covers on the top for
  inspection and maintenance. The bottom of the
  crankcase serves as the oil reservoir. A main
  pump for lubrication of the crank mechanism is
  placed on the shield mounted on the side opposite
  the coupling and is driven by compressor.

34
(No Transcript)
35
Crankshaft
The crankshaft is built in a single piece. On the
inside of the shaft are holes for passage and
distribution of lube oil.

• Main Bearings
• The main bearings are built in two halves, made
  of steel, with inner coating of antifriction
  metal.

36
Connecting Rods

• The connecting rod has two bearings. The big end
  bearing is built in two halves. It is made of
  metal with inner coating of antifriction metal.
  The connecting rod small end bearing is build of
  steel, with inner coating of antifriction metal.
  A hole runs through the connecting rod for its
  entire length, to allow passage of oil from the
  big end to the small end bush.

37
Connecting Rods
38
Connecting Rods
39
Crosshead

• Crosshead fastens piston rod to the connecting
  rod. The sliding surfaces of crosshead are coated
  with antifriction metal i.e. babbited shoes.
  These are of interchangeable type. That permits
  it to slide back and forth within the crosshead
  guides. The shoes have channels for the
  distribution of lube oil. The lubrication is
  obtained under pressure it comes out from the
  two guides of the crosshead slide body.
• Connection between connecting rod and crosshead
  is realized by means of a gudgeon pin. The piston
  rod is connected to the crosshead by nut
  arrangement, tightened by means of hydraulic
  device.

40
Crosshead
41
Crosshead
42
Lubrication

• Lubricants reduce friction and therefore wear
  between moving compressor parts. Lubricant also
  serves as a coolant.

43
Lubrication Systems

• Generally, two types of systems are uses to
  lubricate the positive displacement compressors.
• SPLASH SYSTEM
• It is used in older machines. A supply is
  maintained in the crankcase. Oil is splashed up
  by the rotation of the crank and the counter
  weight into the collecting ring. Centrifugal
  force throws the oil outward through an oil
  passage to the crank pin.

44
Splash Lubrication
45
Forced Feed System

• Oil is pumped under pressure to the required
  parts. Following are the main parts of system
• STRAINER
• Oil from the crankcase first passes through a
  coarse strainer. The strainer is removable so
  that chips or broken off pieces can be cleaned
  out of the strainer.

46
Forced Feed System
47
Bypass Relief Valve

• The compressor will be completely damaged if the
  oil flow is appreciably reduced or stopped by a
  plugged filter. In order to prevent this damage,
  forced feed system is fitted with a bypass relief
  valve, a low-pressure alarm and bypass shutdown.
• If this filter becomes plugged, inlet pressure to
  the filter increases. If the inlet pressure
  exceeds spring pressure, the bypass valve opens
  allowing oil to return to the crankcase. Oil
  pressure in the system falls, the low-pressure
  alarm causes the compressor to shutdown.

48
Oil Circulation System

• To keep bearings lubricated, oil is supplied
  under pressure to the bearings. The lubrication
  system keeps a supply of cool and clean oil
  flowing to the system. A sufficient quantity of
  oil is stored in a reservoir.

49
Oil Cooler

• Oil flows from the pump to cooler. The oil in the
  cooler flows through the tubes. The cooling water
  on the shell side absorbs heat from the oil.
  Generally, oil temperature is kept between 40
  50?C. Oil cooler than 40?C can lead to
  condensation of water inside the crank case.
  Moisture can promote sludging of oil. Temperature
  of oil higher than 50 C can decrease strength of
  bearing materials (Babbitt), that can lead to
  premature failure.
• In order to maintain the desired temperature
  range, the oil system has a bypass valve upstream
  the cooler that is controlled by a thermostat.

50
CO2 Compressor

• In a reciprocating compressor, a volume of gas is
  drawn into a cylinder, it is trapped, and
  compressed by piston and then discharged into the
  discharge line. The cylinder valves control the
  flow of gas through the cylinder these valves
  act as check valves.
• The compressor, which has been selected, is used
  to compress CO2 gas. It is driven by electric
  motor and is manufactured by M/s Nuovo Pignone,
  Italy. It is a multistage, double acting
  reciprocating compressor of four stages.
• The crankshaft is directly coupled to the
  electric motor and flywheel.

51
Oil Cooler
52
Interstage Cooler
53
Cylinder Cooling
54
Lubricated Piston/Packing
55
Outboard Bearing
56
Clearance Pocket
57
Packing Lubrication
58
Piston Lubrication
59
(No Transcript)
60
Maintenance Procedure
Periodic Maintenance (Every 4000 hours of
operation)
61
Maintenance Procedure
62
Maintenance Procedures Safety

• Recommendations Precautionary Measures
• Gather all tools necessary for service in a
  container near the machine.
• Use the set of special tools and instruction
  supplied by manufacturer.
• Isolate the compressor from the process gas.
• Make sure that the driver cannot be started.
• During assembly, fully comply with assembly
  drawings.
• Follow bolt torque sequence and torque values
  given in instruction manual.
• When hoisting systems are used, ensure that they
  are perfect.

63
Maintenance Procedures Safety (contd.)

• After maintenance, machine shall be rotated
  slowly for at leas on revolution to ensure no
  interference.
• Whenever a component is disassembled. Make sure
  of the absence of defects before re-using.
• The person responsible for maintenance should
  ensure that all parts installed are perfectly
  clean.
• After, maintenance on cylinders and sealing rings
  ensure that all the lube oil pipes are filed with
  oil. This could be checked by loosening the
  pipefitting. Tighten the pipe fitting again.

64
Maintenance Procedures Safety (contd.)

• Do not use a chisel to remove gaskets attached to
  the surface. Carefully slide a blade between
  gasket and surface. Damaging to the
  compressor-sealing surface can be avoided in this
  way.
• If the bearings are found damaged, perform
  thorough cleaning to avoid further damage due to
  contamination of oil by metallic particles.

65
Problems Troubleshooting
66
Problems Troubleshooting contd.