Dynamic Compressors
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Transcript of Dynamic Compressors
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Ejector Dynamic
Intermittent flow
COMPRESSORS
Continuous flow
Positive displacement
Radial flow
Mixed flow
Axial flow
Rotary Reciprocating
•Helical lobe
•Straight lobe
•Sliding vans
• Liquid piston
Mechanical piston
DYNAMIC COMPRESSORS
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Ejector Dynamic
Intermittent flow
COMPRESSORS
Continuous flow
Positive displacement
Radial flow
Mixed flow
Axial flow
Rotary Reciprocating
•Helical lobe
•Straight lobe
•Sliding vans
• Liquid piston
Mechanical piston
DYNAMIC COMPRESSORS
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Centrifugal compressor
DYNAMIC COMPRESSORS
Diffuser
Impeller
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Centrifugal compressor
DYNAMIC COMPRESSORS
Centrifugal compressors or radial flow compressors are second only to reciprocating compressors in numbers of machines in service.
The centrifugal compressor has been around for quite a long time. Originally it was used in process applications at
relatively low pressure, high volume service .
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An Introduction to Pumping Equipment
2
20
200
102 103 104 105 106
Multistage Reciprocating
Single stage Recip.
Flow rate (CFM)
Pre
ssu
re r
atio
Rotary compressors
Multistage Centrifugal
Single S Cen.
Multistage Axial
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Centrifugal compressor
DYNAMIC COMPRESSORS
Classification
Classification can be established by how the machine casing is constructed:
Horizontal split.
Vertical split.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Classification
Single stage, vertically split, overhung style centrifugal
compressor.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Classification
Multistage barrel type compressor.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Classification
an overhung style machine mounted on a gearbox and uses the gear pinion shaft
extension to mount an impeller .
The casing is also attached to the gearbox.
This style is built in both the single and multistage
configuration.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
The overhung style is, on very rare occasions, constructed in
the multistage form, usually overhanging no more than two
impellers.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
Careful application must be made because the overhung
impeller configuration is more sensitive to unbalance than the
between-bearing design. If impeller fouling is anticipated,
this design may not be acceptable.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
A beam type single-stage is a less common form of the single-stage. In
this form, the impeller is located between two bearings as is the
multistage.
The flow enters and leaves in a tangential direction with the nozzles
located in the horizontal plane.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
The between-bearing, single-stage is found most commonly in pipe line booster service where the inherent
rigidity of the two outboard bearings is desirable.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
The integrally geared compressor. As shown, it consists of three impeller,
the first located on one pinion, which would have a lower speed than the other pinion which has mounted
the remaining two impellers.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
This arrangement is common to the plant air
compressor. Configurations such as this are used in
other air and gas services, with the number of stages
set to match the application.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
The flow path is straight through the compressor,
moving through each impeller in turn. This type of centrifugal compressor
is probably the most common of any found in
process service, with applications ranging from
air to gas.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
In the double-flow compressor , the flow enters the case at two points, is compressed by a single impeller at each
end and then enters the double-flow wheel.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
The flow enters the case and is divided to each side of the double flow impeller and then joins at the impeller exit
prior to entering the diffuser.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
If a number of options are open for a given application, the
double-flow option should not be the first choice.
Although it should be evaluated as there are successful
applications in service indicating that with careful design, the
compressor will perform satisfactorily.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
The back-to-back arrangement is normally considered useful in solving difficult thrust balance problems where
the conventional thrust bearing and balance drum size are inadequate or become excessively large.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
The flow is removed part way through the compressor and reintroduced at the opposite end, then allowed to exit at
the center.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
The obvious use is for applications generating high thrusts, higher than can be readily controlled by a normal
size thrust bearing and balance drum.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
An evaluation of the cross leakage between the two discharge nozzles must be made and compared to the
balance drum leakage to determine the desirability of the "back to back".
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
The sidestream compressor is the very common compressor design used in the chemical industry,
particularly in large refrigeration systems.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Arrangement
The properties of the gas stream are modified at the mixing point, as the sidestream is rarely at the same temperature as the stream from the second impeller.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
All centrifugal compressors' casings were initially of cast construction, particularly in the smaller sizes.
Casings
Casing materials are, in most cases, cast of iron or nodular iron and steel.
Casings are, on occasion, made of austenitic stainless steel or one of the high nickel alloys.
Fabricated casings are generally made of carbon or alloy steel.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
For low temperature, suction applications a low nickel alloy may be used
Casings
API Standard 617 includes material guidelines in its appendix.
The vertically-split, multistage barrel compressor is generally constructed of steel or steel alloy. It may be
cast, fabricated or for very high pressure service it may be forged.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
The vertically-split should always be used when the gas contains hydrogen at or above a partial pressure of 200
psig.
Casings
It may also be required in those services where the overall pressure is too high for the horizontal-split joint
compressor.
This occurs when the horizontally-split joint deforms too much at the operating pressure to maintain a gas tight
seal.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
They are the stationary members located inside a multistage casing.
Diaphragms
The function of the diaphragm is to act as a diffuser for the impeller and a channel to redirect the gas into the
following stage.
The diaphragm also acts as the carrier for the impeller eye seal and the interstage shaft seal.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
The diaphragm are split, located with matching grooves in the upper and lower half casing and pinned to upper half
for maintenance ease.
Diaphragms
Diaphragms are hand fitted to center them to the rotating element.
It is important for the horizontal joint to match well, to keep the joint leakage to a minimum
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
On barrel compressors, the diaphragm assembly makes
up an inner barrel.
Diaphragms
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
The assembly and rotor are removed from the barrel casing as a unit using a
special fixture. The diaphragm assembly is split to permit the removal of the
rotor and the diaphragms are generally constructed the
same as those of the horizontally split compressor.
Diaphragms
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
Casing inlet and outlet nozzles are normally flanged.
Casing Connections
Most of the auxiliary connections on these machines will be screwed fittings.
It is desirable to use standard flanges throughout the connections on the casing. However, for space reasons,
on rare occasions, a nonstandard flange arrangement may become necessary.
It is quite important to have the equipment vender furnish all mating flanges and associated hardware.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
The impeller is the most highly stressed compressor component .
Impellers
Impellers are made of low alloy steel for most compressors in process service, either chrome-moly or
chrom-moly-nickel.
Because of the high strength to weight ratio, many of the high head, integrally geared units use aluminum.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
Austenitic stainless, Monel and titanium are some of the other materials used for impellers in certain special
applications, generally with corrosive gases involved.
Impellers
Although not universal, on most multistage compressors, the impellers are axially located by shaft sleeves.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
Shafts are made of material ranging from medium carbon to low alloy steel and are usually heat-treated.
Shafts
Shafts require the good finish achieved by grinding or honing.
The shaft is the foundation for good mechanical performance to keep the rotor dynamics in control and
maintain good balance.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
The requirements are that the shaft must be round and all turns must be concentric to the journals.
Shafts
The tighter the tolerance, the closer to perfection, the more expensive that particular manufacturing step.
However, some added expense at this point will save time in subsequent rotor balancing providing the user with a
rotor, which can be more easily maintained.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
Radial bearings or journal bearings are usually pressure lubricated.
Radial Bearings
Most compressors use two bearings on opposite ends of the
rotor assembly.
Or on the overhung design, located adjacent to each other
between the drive coupling and the impeller.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction:
Radial bearings or journal bearings are usually pressure lubricated.
Radial Bearings
On centrifugal compressors the bearings size is not a function of the load but rather it is dictated by critical
speed considerations.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction: Radial Bearings
Straight cylindrical bearings are the most simple in concept.
Because of low resistance to bearing induced problems, this bearing is limited to centrifugal compressors.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction: Radial Bearings
It is found normally in very large compressors with
relatively heavy rotors and low operating speeds.
They are also used in the fluorocarbon refrigerant compressors, where speeds are low because of high
molecular weight and where relatively short rotors are used.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction: Radial Bearings
As a minimum, most compressors with sleeve
bearings use a modified sleeve bearing, such as the dam type
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction: Radial Bearings
The tilting pad bearings is the bearing most often found in centrifugal compressors, which is inherently stable. The
bearing also known as the tilting shoe bearing.
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Centrifugal compressor
DYNAMIC COMPRESSORS
Construction: Thrust Bearings
Centrifugal compressor impellers, with the exception of the open impeller, are thrust unbalanced.
The machine also has a requirement for a location device to maintain axial clearance.
For these reasons, all centrifugal compressors use some form of thrust bearing.
API 617 recognizes the need for the compressor thrust design to take into account peripheral factors such as the
coupling.