Centrifugal Compressor

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Transcript of Centrifugal Compressor

The need to move gases has been arequirement of industry.In virtually all systems that require the movement of gas, there must be a means of producing a driving force, the higher pressure. The equipment that raises a gas to a higher pressure is called a compressor. Pressure in gas is developed by pressing molecules of gas.

FAN AND BLOWER Low pressure (1 atm)and low P (0.010.15 kg/cm2) for FAN. Blower P (0.15-1.5 kg/cm2) High volume flow to 500 std m3/s Efficiencies of 65-80%

Principle of operation:(a) Compression by decreasing volume: Required pressure is developed by trapping a gas in a chamber, reducing the volume of the chamber and increasing the pressure of the gas by the ratio of initial chamber to the final volume. (b) Compression by accelerating fluid : The second method of compressing gases is based on the conversion of kinetic energy into the potential energy. Accelerating fluid to a higher velocity and then decelerating it by changing its direction of flow transforms the accumulated energy into potential energy

Classification of Compressors:-


Capacity Suction pressure Suction temperature Discharge pressure Gas composition Type of driver Utilities like cooling water, steam, N2, electricity etc.

Selection results in calculation Type of compressor Number of casing / phases Number of impellers in each phase Speed of compressor Compressor BKW Driver rating Operating range

Application Range of Various Compressors105

Discharge Pressure (Psia)




Axial Reciprocating







Inlet Flow (Acfm)

CENTRIFUGAL COMPRESSORS: Centrifugal compressor works on the principle i.e.accelerating a gas to a high velocity and converting its KINETIC ENERGY (velocity) into POTENTIAL ENERGY (pressure) by decelerating the gas. The gas enters the eye of the impeller and is accelerated to the outward edge of the impeller as it rotates. It then enters a diffuser where its direction is changed, causing deceleration. This deceleration converts the KE into the PE, pressure. If the gas is to be further compressed, then a return chamber directs it from the diffuser to the eye of the next impeller in series. The gas enters a collector or volute when it is to leave the compression stage. It is discharged to the process through a discharge nozzle.

DESIGN FEATURES: 1)Based on the type of casing design,centrifugal compressors are classified into two types: Horizontally split casing design(MCL/MCH type):- This design is used for low working pressure below 40ata.These casings are in two halves with horizontal parting plane. DMCL Compressor have two stages of compression in parallel in a single casing.The solution is most balanced.The other aspects of construction are the same as for the MCL Compressor. Verically Split Casing design (BCL/BCH type):-This design is made of barrel construction closed on the sides by end covers with help of studs.This type of construction is suitable for high pressure operations upto 750kg/cm2 Another type of compressor is the PCL(Pipeline compressor),which has casing in the form of a cup with a single closing flange in the vertical plane instead of two as with the BCL.


Horizontally split type Compressor

Vertically Split Type Compressor

Example of Designation of BCL Compressor:Example : 2BCL407/b 2 BCL 40 7 / b Pr. rating (up to 350 ata) No. Of impellers (7 impellers on rotor) Nominal dia. of impeller (Impeller dia. of 40 cms appx.) Constructional feature (Barrel design) Functional feature (2 Compressor stages in series)

Compressor Components Casing Counter Casing (If Applicable) Diaphragm End Cover (If Applicable) Shaft Impellers Shaft Seals Journal Bearing Thrust Bearing Coupling


Construction of centrifugal compressor:

Every centrifugal compressor consist of

two parts:- An impeller which forces the gas into the rotary motion by the action of blades, and the casing which directs the gas to the eye of the impeller and then leads it away from the impeller perimeter at a higher pressure. For most multistage compressors, shaft end seals are located inboard of the bearings. The internal passages are formed by a set of diaphragms.

Cross-section of a BCL Compressor


Rotor Assembly

Assembly of Diaphragms in Counter Casing

Assembly of Journal Bearing

Assembly of Thrust Bearing

BALANCING DRUMThere exists some amount of thrust generated at each impeller because of the differntial pressure prevailing across it. The cumulative thrust generated across all the impellers is huge and it needs to be supported by the thrust bearing. The thrust bearing size becomes huge if all the gas thrust has to act on the bearing. For this purpose a rotating element called Balancing Drum is incorporated on the rotor. The drum is acted upon by a pressure differential which pushes the rotor in a direction opposite to that of the gas thrust. The thrust so generated balances the thrust produced by the impellers. Amount of balancing depends upon the size of the drum and pressure differential created across it. The pressure differentiated is maintained by an efficient seal placed over the balancing drum.

Types of Compressor End Sealing Systems Labyrinth Sealing Floating Oil Seals Oil Mechanical Seals Air Injection Sealing System Injection / Extraction Sealing Dry Gas Seals

Compressor Drives STEAM TURBINE For variable speed operation In process plants like fertilizers and refineries

ELECTRIC MOTOR For constant speed operation Wherein uninterrupted electricity from captive power plants is ensured

GAS TURBINE For variable speed operation Applications where gas availability is ensured

Advantages of Centrifugal Compressors

High degree of balancing Pulsation free delivery Easy maintenance Standby not required Best suited for part load operations Lower noise level Compact

Industrial Applications of Centrifugal CompressorsType of Plant Gas Compressed CO2, Nitrogen Fertilisers Syn Gas, NH3, Air, Nat gas, Refineries Air, Wet Gas, Hydrogen Petrochemical Plants Ethylene. Metallurgical Plants O2, Air, Gas Propane, Propylene,