Dynamic Compressors

DYNAMIC COMPRESSORS

DYNAMIC COMPRESSORS

COMPRESSORS Intermittent flow

Continuous flow

Positive displacement Reciprocating Mechanical piston

Dynamic

Rotary •Helical lobe •Straight lobe •Sliding vans • Liquid piston

Radial flow

Mixed flow

Ejector Axial flow

DYNAMIC COMPRESSORS

COMPRESSORS Intermittent flow

Continuous flow

Positive displacement Reciprocating Mechanical piston

Dynamic

Rotary •Helical lobe •Straight lobe •Sliding vans • Liquid piston

Radial flow

Mixed flow

Ejector Axial flow

DYNAMIC COMPRESSORS

Centrifugal compressor

DYNAMIC COMPRESSORS

Centrifugal compressor

Diffuser Impeller

DYNAMIC COMPRESSORS

Centrifugal compressor 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

An Introduction to Pumping Equipment

Pressure ratio

200

Multistage Reciprocating 20

Single stage Recip.

Multistage Centrifugal

Rotary compressors 2

Multistage Axial

.Single S Cen 102

103

104 )Flow rate )CFM

105

106

DYNAMIC COMPRESSORS

Centrifugal compressor Classification Classification can be established by how the machine casing is constructed: Horizontal split. Vertical split.

DYNAMIC COMPRESSORS

Centrifugal compressor Classification Single stage, vertically split, overhung style centrifugal compressor.

DYNAMIC COMPRESSORS

Centrifugal compressor Classification Multistage barrel type compressor.

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor Arrangement The overhung style is, on very rare occasions, constructed in the multistage form, usually overhanging no more than two impellers.

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor Arrangement

DYNAMIC COMPRESSORS

Centrifugal compressor Arrangement

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor Arrangement The flow is removed part way through the compressor and reintroduced at the opposite end, then allowed to exit at the center.

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor 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".

DYNAMIC COMPRESSORS

Centrifugal compressor Arrangement The sidestream compressor is the very common compressor design used in the chemical industry, particularly in large refrigeration systems.

DYNAMIC COMPRESSORS

Centrifugal compressor 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.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Casings

All centrifugal compressors' casings were initially of cast construction, particularly in the smaller sizes. Casing materials are, in most cases, cast of iron or nodular iron and steel. Fabricated casings are generally made of carbon or alloy steel. Casings are, on occasion, made of austenitic stainless steel or one of the high nickel alloys.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Casings

For low temperature, suction applications a low nickel alloy may be used 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.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Casings

The vertically-split should always be used when the gas contains hydrogen at or above a partial pressure of 200 psig. 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.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Diaphragms

They are the stationary members located inside a multistage casing. 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.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Diaphragms

The diaphragm are split, located with matching grooves in the upper and lower half casing and pinned to upper half for maintenance ease. 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

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Diaphragms

On barrel compressors, the diaphragm assembly makes up an inner barrel.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Diaphragms

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.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Casing Connections

Casing inlet and outlet nozzles are normally flanged. 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.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Impellers

The impeller is the most highly stressed compressor component . 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.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Impellers

Austenitic stainless, Monel and titanium are some of the other materials used for impellers in certain special applications, generally with corrosive gases involved. Although not universal, on most multistage compressors, the impellers are axially located by shaft sleeves.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Shafts

Shafts are made of material ranging from medium carbon to low alloy steel and are usually heat-treated. 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.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Shafts

The requirements are that the shaft must be round and all turns must be concentric to the journals. 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.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Radial Bearings

Radial bearings or journal bearings are usually pressure lubricated. 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.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Radial Bearings

Radial bearings or journal bearings are usually pressure lubricated. On centrifugal compressors the bearings size is not a function of the load but rather it is dictated by critical speed considerations.

DYNAMIC COMPRESSORS

Centrifugal compressor :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.

DYNAMIC COMPRESSORS

Centrifugal compressor :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.

DYNAMIC COMPRESSORS

Centrifugal compressor :Construction

Radial Bearings

As a minimum, most compressors with sleeve bearings use a modified sleeve bearing, such as the dam type

DYNAMIC COMPRESSORS

Centrifugal compressor :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.

DYNAMIC COMPRESSORS

Centrifugal compressor :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.