Recip. Comp ECDP

8/12/2019 Recip. Comp ECDP

1/51

1

Date : July, 04, 2008

Lecturer : D. S. KIM


2/51

CONTENTS

INTRODUCTION PURPOSE & GOVERNING STANDARD TYPES OF RECIPROCATING COMPRESSORS COMPONENTS / AUXILIARY SYSTEMS UNBALANCED FORCES IN RECIPROCATING COMPRESSORS CAPACITY CONTROL (LOADING & UNLOADING) REFERENCE

2


3/51

INTRODUCTION

COMPRESSOR :Any machine which uses external energy to

increase the pressure of a gas/ mixture of gases is called a compressor.

Compressors are broadly classified into the following two categories-

Positive Displacement Type

Dynamic Type

Positive Displacement type compressors are those in which

successive volumes of gas are confined within some type of

enclosure (compression chamber) and elevated to a higher

pressure. Eg. Reciprocating compressors, screwcompressors, sliding vane compressors etc.

Dynamic compressors accelerate a continually flowing gas stream and subsequently

convert the velocity head into pressure. Eg.: Centrifugal Compressors, axial flow

compressors, mixed flow compressors etc.

3


4/51

INTRODUCTION

INTRODUCTION : Reciprocating compressors are positive

displacement machines with a piston compressing the gas in a

cylinder. As the piston moves forward it compresses the gas into a

smaller space, thus raising its pressure. There are two types of

reciprocating compressors, called "lube" type with oil injection and

"non lube" as oil-free.

3


5/51

INTRODUCTION

3


6/51

PURPOSE & GOVERNING STANDARD

PURPOSE: For producing pressurized air/gas at required outlet

conditions.

(Generally for high pressure applications with capacity as a

constraint between Centrifugal & Reciprocating compressors).

Governing standards:

API 618 - Specification for Reciprocating compressor.

3


7/51

TYPES OF RECI. COMPRESSOR

I. Based on the mounting & cylinder arrangement1. Horizontal

2. Vertical

3. V configuration

4. Y configuration

5. L configuration

6. Radial

7. Balanced opposed

8. Tandem type

II. Based on no. of cylinders in series1. Single stage

2. Two stage

3. Multi-stage

4


8/51


III. Based on no. of cylinders per stage

1. Simplex

2. Duplex

3. Triplex and so on

IV. Based on the Lubrication

1. Lubricated R.C

2. Non-lubricated R.C

V. Based on compression sides

1. Single acting2. Double acting

5


9/51


6

Horizontal Vertical L-Type V-Type

Y-Type RadialSingle stage

Inlet Outlet Inlet Outlet

Double stage

Balanced Opposed Tandem arrangement


10/51


7

4

3

1

2

P

V

1-2 Adiabatic(Polytropic) compression

2-3 Constant pressure Discharge

3-4 Adiabatic (Polytropic) expansion

4-1 Constant pressure Suction

P-V Diagram :

Single acting Double acting

Discharge

Suction

Discharge

Suction

DischargeSuction


11/51

COMPONENTS

8

Sectional View ofsimple Reciprocating compressor:


12/51

COMPONENTS

9

Sectional View ofsimple Reciprocating compressor:


13/51

COMPONENTS

10

Cylinder:

The Cylinders will be one of the following types

a. Single acting

b. Double acting

c. Tandem single or double acting

d. Fitted with tail rods ( For high pressure services)

The cylinders may be lubricated or non-lubricated, vertical or

horizontal.In the case of non-lubricated cylinders, a distance piece is inserted

between the cross-head and cylinder to ensure the part of the

piston rod adjacent to the cross head (which is lubricated) does

not enter the non-lubricated cylinder packing.The distance piece is often fitted with a wiper ring and may have one

or more compartments which are pressurized or purged with

inert gas and vented if the compressor is used on toxic gas service.


14/51

COMPONENTS

11

Cylinder:Cylinders may be fitted with air cooling fins, but are usually water

cooled. In the case of cryogenic service, the water passages are

often filled with a static supply of anti-freeze supplied from a

header tank, with the objective of minimizing temperaturegradients within the cylinder casting.

Cylinders are sometimes fitted with replaceable liners, either of wet

or dry type. The material is invariably cast iron or steel

depending on the application, but Ni-Resist is sometimes used onnon-lubricated service. The bore of the cylinder is honed with

PTFE when this material is used for the piston rings. Cylinders

for oxygen service are sometimes immersed in water tanks to

maintain a low working temperature.

Cylinders head can be fitted with clearance pockets to increase the

cylinder clearance and thus reduce the volume flow through the

cylinder. The pockets can be of fixed OR variable volume and

operated manually or pneumatically.


15/51

COMPONENTS

12

Typical views of reciprocating compressors:

Fig: Cylinder with wet liner

Fig: Non-lubricated cylinder


16/51

COMPONENTS

13


Fig: Double acting Cylinder

Fig: Piston with tail rod


17/51

COMPONENTS

14


Fig: Balanced opposed (lubricated) cylinder arrangement


18/51

COMPONENTS

15


Fig: Balanced opposed (Oil free) cylinder arrangement


19/51

COMPONENTS

16

Typical views for cylinder cooling:

Fig: Valves on cylinder head & tail ends

Fig: Valves on sides of cylinder walls


20/51

COMPONENTS

17

Valves:

Compressors usually have automatic valves which operate when aset set pressure differential exists across the valve. To functionproperly a valve must seat uniformly and tightly against its seat,yet must not have snap-action on opening or closing. Until

pressure builds up to the discharge point the valve must remainclosed, open at discharge pressure, and then reset as the pressurein the cylinder drops below the discharge value. The same type ofaction is required for the suction valves.

Valves must be made of fatigue resistant carbon or alloy steel orstainless steel, depending upon the service. The stainless steel &carbon steel is often used for corrosive and/or high temperatureservice. Any springs, as in the plate type valves, are either carbonor nickel steel.

Valves passages must be smooth, streamlined and as large aspossible. Cylinder efficiency depends to a certain extent upon theproper selection and sizing of the valves. Valves must beadequately cooled, so provision is usually made for water jackets

immediately adjacent to the valves, particularly the dischargevalves.

CO O S


21/51

COMPONENTS

18

Valves:Valve lift should be kept to a minimum to prolong valve life, but this

will of course reduce the flow area and increase the gas velocityand subsequently the losses through the valve. Suction valves areoften fitted with un-loaders to facilitate compressor starting.

These can take the form of a fork actuated either manually orpneumatically to hold the valve off its seat.

Common causes of sudden valve failure are due to compression ofwet or dirty gas, and the formation of condensate within the

cylinder. Solid or liquid particles settling on the valve seat cancause failure of the plate at that point. Delivery valves shouldtherefore be located at the bottom of the cylinder to preventaccumulation of solids or condensate.

In lubricated cylinder service the design of valve pockets should besuch that oil cannot collect in the pocket. Compressor dischargetemperatures are often above the flash point of the oil used andfire explosion can occur as results of carbon or oil accumulationin the vicinity of the valves. Suction and delivery valve assemblies

should be designed to ensure they cannot be interchanged duringassembly.

COMPONENTS


22/51

COMPONENTS

19

Types of Valves:

1. Feather type valves

2. Plate type valves

3. Channel type valves

4. Ring channel valves, etc

The valves may be channel or reed type, but are usually concentric

circular plates or ported plate type.

The operations of concentric circular plates are assisted by helical

springs bearing on the plate and a dampener plate may be located

over the valve plate to reduce flutter. Adjacent concentric plates

tend to open out of phase in relation to each other and an

alternative ported plate design with an integral central leaf spring

gives better performance. The ported plate type can also have a

dampener plate and helical springs located around the plate edge.

COMPONENTS


23/51

COMPONENTS

20

Fig: Valves & valves details

Plate type valves

Ring channel valvesChannel type valves

COMPONENTS


24/51

COMPONENTS

21

Fig: Valves & details

COMPONENTS


25/51

COMPONENTS

22

Piston, Piston rod & Packing:

Pistons are usually manufactured from cast iron or aluminium in order

to balance the masses on successive throws of the crankshaft. Large

diameter pistons are often produced in segments bolted together.

Single acting pistons are sometimes fitted with cooling fins cast

under the crown. First stage large diameter pistons are often of

welded construction.

Piston rings are normally manufactured from cast iron for lubricatedcylinders, but in non-lubricated cylinders, they are either carbon or

PTFE. Solid carbon rings are used with segmented pistons, but

segmented carbon rings are a common alternative. Carbon relies on

moisture for its strength and should therefore not be used on verydry gas service.

PTFE has a lower permissible operating temperature than carbon

(about 180C). Above this temperature the wear rate increasesrapidly. Split PTFE rings are flexible and easily assembled over solid

COMPONENTS


26/51

COMPONENTS

23


pistons, however, because of their flexibility, a steel garter spring ring

is sometimes inserted behind the sealing ring. Solid PTFE bearer

rings are usually located centrally on the piston to transmit the

weight of the piston on to the lower cylinder wall. Runningclearances are a function of operating and wall temperatures. When

checking the cylinder design ensures that the pressure rings do not

span the valve pockets as this causes distortion and uneven wear of

the rings, leading to premature failure.Labyrinth pistons do not touch the cylinder wall at any point. The

piston rod is carried on a piston guide which runs on lubricated pads

above the cross-head. The piston sides are machined with

circumferential grooves and there is no contact with the cylinderwalls. Leakage is greater with labyrinth pistons than with pressure

rings, but by increasing the piston length the loss can be reduced to

an acceptable amount. Labyrinth pistons are particularly suitable

for oxygen and clean gas service.

COMPONENTS


27/51

COMPONENTS

24

Piston Cylinder

Labyrinth piston

COMPONENTS


28/51

COMPONENTS

25


A compromise between the labyrinth and self-lubricating ring design is

the captive ring and piston. This arrangement is fitted with PTFE

rings and a piston guide. The inner edge of the ring is retained by a

flange. After an initial wear period, no contact exists between therings and cylinder. Clearances are smaller than can be

accomplished with the labyrinth design and momentary contact is

harmless.

The piston rod, where it enters the cylinder, is sealed by spring loaded

segmented sealing rings. These are PTFE or carbon in non-

lubricated machines, but can be metallic in lubricated cylinders.

The packing box is sometimes water-cooled and can be vented atsome point along its length. Purging with inert gas or high-pressure

gas is used for special applications. The pressure seal between the

cylinder pressure and the crank case or atmosphere is maintained by

a packing gland.

COMPONENTS


29/51

COMPONENTS

26

Pulsation dampers:

Pulsations generated by reciprocating pistons cause vibration and

pulsations in the gas lines on both inlet and outlet sides of the

compressor. These have an adverse effect on the valves and on any

measuring instruments fitted to the gas lines, and cause vibration in

the piping and support structures. These effects can be reduced by

fitting a large volume bottle or vessel as close to the cylinder as

possible. Pulsations can thus be reduced to 2% of the line pressure.

In large installations, it is necessary to conduct a study of the piping

in the vicinity of the compressor to ensure that harmful vibrations or

pulsations do not exists. This study is conducted by an analog

computer programmed to produce a model of the piping and

indicate where pulsations might occur. The study should be

performed at all expected part load flow rates.

AUXILIARY SYSTEM


30/51

AUXILIARY SYSTEM

27

Auxiliary Systems

1. Filters

2. Coolers

3. Drivers

4. Piping, instrumentation & controlsFilters:

Filters will be used to avoid entering of dust particles, moisture etc intothe compressor cylinder, in order to get better efficiency and to meet

the system output requirements. Depending upon the moisturecontent of the fluid, separators are provided before somecompression stages to ensure that no moisture is entrained in the gasflow to the cylinders.

Coolers:Where the overall compression ratio is so high that the discharge gas

temperature is unacceptable, it is necessary to effect the compressionin stages. Delivery from the first stage is cooled to somewhere near

the initial suction temperature before passing to the next stage.Inter-coolers can be mounted directly on the cylinders, along withany necessary pulsation bottles and separators.

AUXILIARY SYSTEM


31/51

AUXILIARY SYSTEM

28

Drivers:

Drivers for Reciprocating compressors are

Electric motors

Diesel engines or Gas engines

Turbines

The driver may be connected to reciprocating compressors by means of

Coupling

Rigid

Flexible

Constant or Variable speed arrangement

Belt

Gear box

Fluid coupling, etc.

AUXILIARY SYSTEM


32/51

AUXILIARY SYSTEM

29

Fluid (Hydraulic) Coupling:The fluid or hydraulic coupling is a device used for transmitting power

from driving shaft to driven shaft with the help of fluid. There is nomechanical connection between the two shafts. It consists of a radial

pump impeller mounted on a driving shaft and a radial flow reactionturbine mounted on the driven shaft. Both the impeller and runnerare identical in shape and they together form a casing which iscompletely enclosed and filled with oil.

In the beginning, both the shafts are at rest. When the driving shaftrotates, the oil starts moving from the inner radius to the outerradius of the pump impeller . The pressure and kinetic energy of theoil increases at the outer radius of the pump impeller. This oil ofincreased energy enters the runner of the reaction turbine at theouter radius of the turbine runner and flows inwardly to the innerradius of the turbine runner. The oil, while flowing through therunner, transfers its energy to the blades of the runner and makesthe runner to rotate. The oil from the runner then flows back into

the pump impeller, thus having a continuous circulation.

AUXILIARY SYSTEM


33/51

AUXILIARY SYSTEM

30

Fluid (Hydraulic) Coupling:

In usual practice the speed of the driven shaft will be 2% less than the speedof the driver shaft.

Efficiency of the hydraulic coupling:

inputPower

outputPowerEfficiency =

UNBALABCED FORCES


34/51

UNBALABCED FORCES

31

Unbalanced forces in Reciprocating Compressors:

In a single cylinder, single crank arrangement, the primary forces set

up by the out-of-balance weight of the piston can be reduced to

half the maximum value by placing a counter weight on the crank

throws, though the secondary force, having twice the frequency of

the primary force, will remain unbalanced.

With a two crank vertical arrangement the primary forces are

balanced, but the secondary forces are twice those produced in a

single crank machine and cannot be economically balanced. With

this arrangement, a primary couple, due to the distance between

piston centerlines (d) and equal to half the primary force

multiplied by the distance (d), if the machine is fitted withcounterweights, then is also present.

Two cylinder horizontally opposed arrangements have no out-of-

balance forces or couples and are preferred where space permits.

V and L cylinder arrangements have balanced primary forces,but the secondary forces are not balanced.

CAPACITY CONTROL


35/51

CAPACITY CONTROL

32

Capacity control (Loading & Unloading) in Reciprocating Compressor:

Types:

Variable speed

Suction throttling

Bypass control

Receiver pressure Start/Stop method

Adjusting (Screwing) the piston rod further into or out of the cross

head, for some single acting units

Suction valve un-loaders

Clearance pocket un-loaders

Fixed clearance pocket Variable clearance pocket

Combination of Suction valve & Clearance pocket un-loaders

CAPACITY CONTROL


36/51

CAPACITY CONTROL

33

Variable speedCapacity control can be achieved with the help of Variable speed

drives like variable speed motors, Hydraulic converter, etc.

Suction throttlingCapacity control can be achieved by throttling the flow in the suction

line.

Bypass control

With the help of bypassing the amount of air (which is not exactly

required or which is a excess of flow at that particular operating

point) back to the suction line capacity control can be obtained, but

the bypassing air needs to be cooled before passing into the suctionline.

CAPACITY CONTROL


37/51

C C CON O

34

Receiver pressure Start/Stop method

In this method the compressor will be loaded OR unloaded

depending on the receiver pressure control switches. But the

compressor will be subjected to frequent start & stop.

By Adjusting (Screwing) the piston rodfurther into or out of the cross

head (only in case of single acting units) capacity control can be

achieved.

Suction valve un-loadersIn this method when compressor un-loading is required then the

suction valve will be kept open for complete cycle, that means with in

the cylinder there will not be any compression. What ever the air its

sucks into the cylinder will be discharged through the suction valvewithout compressing it to a higher valve. In this type depending on

the cylinder arrangement capacity can be control in steps of

CAPACITY CONTROL


38/51

35

a) 0%, 100% (for single stage)

b) 0%, 50% & 100%. ( for double acting )

c) 0%, 25%, 50%, 75% & 100% (for combination of double

acting & Duplex cylinder arrangement)

Clearance pocket un-loadersBy increasing the clearance volume at the cylinder head end capacitycan be controlled. There are two types of clearance pockets

Fixed clearance pocket

Variable clearance pocketFixed clearance pocket : In this type of clearance pocket capacity

can be controlled in steps depending on the cylinder arrangement.

The steps of control may be

a) 0%, 100% (for single stage)

b) 0%, 50% & 100%. ( for double acting )

c) 0%, 25%, 50%, 75% & 100% (for combination of double

acting & Duplex cylinder arrangement)

CAPACITY CONTROL


39/51

36

Variable clearance pocket : In this type of clearance pocket capacitycan be controlled in a wide range depending on the area of the

clearance pocket. If the area of the clearance pocket is sized for

1) The complete piston displacement in case of single acting

cylinder arrangement2) Half the piston displacement in case of double acting or duplexcylinder arrangement

3)1/4th of the piston displacement in case of combination of double

acting & duplex arrangement

then the capacity control range will be from 0% to 100% of

compressor discharge capacity.

Combination of Suction valve un-loaders & Clearance pocket un-loaders

By using combination of suction valve un-loaders and clearance

pocket un-loaders the capacity can be controlled to a great extent

with out providing excessive clearance pocket area.

CAPACITY CONTROL


40/51

37

Figures: Capacity control

Using two clearance pockets each having50% area of piston displacement

Using single clearance pockets with

100% area of piston displacement

CAPACITY CONTROL


41/51

38

Pneumatic control schematic

Fixed clearance pocket

Variable clearance pocket

CAPACITY CONTROL


42/51

39

5-Step capacity control: Using clearance pockets only

Combination of suction valve un-loaders & clearance

pockets

REFERENCE


43/51

40

API 618 - Specification for Reciprocating Compressors:

This specification covers the minimum requirements for reciprocating

compressors and their drivers used in petroleum, chemical and gas

industry services for handling process gas or air with wither

lubricated or non-lubricated cylinders.

This specification covers Compressors which are of moderate to low speed

and in critical services. This specification also covers the related

lubricating systems, controls, instrumentation, inter-coolers, after-

coolers, pulsation suppression devices and other auxiliary equipment.This specification does not cover

a. Integral gas engine driven compressors with single acting trunk type

(automotive type) pistons that also serve as crossheads and

b. Either plant or instrument-air compressors that discharge at a gauge

pressure of 9 bar (125 pounds per square inch) or less.

Requirements for packaged high speed reciprocating compressors for

oil and gas production services are covered in API-11P.Requirements for packaged reciprocating plant and instrument-air

compressors are covered in API-680.

REFERENCE


44/51

41


Following are the minimum requirements to be complied as

per API-618 Specification for Reciprocating

compressors:

Design requirements:

General :

1. Minimum service life shall be 20 years and uninterrupted

operation shall at least be 3 years.

2. The capacity at the normal operating point shall have no negative

tolerance.

3. The maximum predicted discharge temperature shall not exceed1500C(3000F)

4. In case of high pressure hydrogen (or those with molecular weight

of 12 or less) OR applications requiring non lubricated cylinders ,

the predicted discharge temperature shall not exceed 1350C(2750F).

REFERENCE


45/51

42


5. The Maximum Allowable Working Pressure (MAWP) shall be at

least 10% more than rated discharge pressure or 1.7 bar

(25pounds per square inch), which ever is greater.

6. The cylinder shall have replaceable, dry type liner, not contactedby the coolant. The liner shall be at least 9.5 millimeters thick for

piston diameters up to & including 254 millimeters (10 inches).

For pistons diameters larger than 254 millimeters, the minimum

liner thickness shall be 12 millimeters.7. Replaceable, precision-bored shell (sleeve) crank-pin bearings and

main bearings shall be used; however tapered roller type anti-

friction bearings are acceptable for main bearings in compressors

with nominal frame ratings of 150 kW or less. Cylindrical orroller or ball bearings are unacceptable.

8. All tapered roller-type anti-friction bearings shall be suitable for

belt drives and shall give an L10 -rated life of either 50,000 hours

with continuous operation at rated conditions or 25,000 hours at

maximum axial & radial load & rated speed.

REFERENCE


46/51

43


9. The frame lubrication system shall be a pressurized system;

however, splash lubrication systems may be used on horizontal

compressors with anti-friction journal bearings when the

compressors nominal frame rating is 150 kW or less.

10. The crankcase oil temperature shall not exceed 700C for

pressurized oil systems and 800C for splash systems.

11. Cooling coils shall not be used in crankcase or oil reservoirs.12. If not specified the capacity shall not have negative tolerance.

13. The driver nameplate power should be selected to be a minimum

of 110% (for electric motor) or 120% (for turbines) of the greatesttotal power required.

14. The power required by the compressor at the normal operating

point shall not exceed the stated power by more than 3 percent.

15. Air cooled cylinders shall not be furnished.

REFERENCE


47/51

44


16. The walls of cylinders without liners shall be thick enough to

provide for re-boring to a total of 3.2 mm (1/8 inch) increase over

the original diameter without encroaching on either the MAWP,

or the maximum allowable continuous gas load, or the maximumallowable combined rod loading.

17. To prevent the gas condensation in the cylinder Coolant inlet

temperature shall be at a minimum of 6K (100F) above the inlet

gas temperature.18. Coolant exit temperature should not exceed 16K (300F) above the

gas inlet temperature to avoid capacity reduction.

19. The coolant circulated shall be controlled to maintain a rise in

coolant temperature across any individual cylinder, including the

cylinder heads between 5K (100F) & 10K (200F).

20. Pneumatically operated un-loaders shall be used for capacity

control.

REFERENCE


48/51

45


21. If hollow pistons are used, they shall be continuously self-venting;

that is, they shall de-pressure when the cylinder is de-pressured.

22. All piston rods, regardless of base material, shall be continuously

coated from the piston-rod packing to the oil wiper packing travelareas with a wear resistant material.

23. Cross-head packing boxes shall employ wiper packing to

effectively minimize oil leakage from the crankcase.

24. Lubricators shall have provisions for pre-lubrication of the

compressor start-up.

25. Lubrication oil reservoir shall be adequate for 30 hours of

operation at normal flow.

REFERENCE


49/51

45

P & ID HAND OUT

THE END


50/51

45

Q & A

THANKS


51/51

Recip. Comp ECDP

Documents