What is Compressor? …… a device used for pumping... compressible fluids i.e, air, gas & steam

PRIMEMOVER COMPRESSOR

HEAT REJECTED

HEAT SOURCE

HEAT TO RADIATION AND COOLANT

LOW PRESSURE AIR COMPRESSED AIR

Compression Process

•The below picture shows the classification of different types of compressors.

CLASSIFICATION OF COMPRESSORS

CLASSIFICATION: •Compressors are classified in many

ways out of which the common one is the classification based on the principle of operation.

TYPES OF COMPRESSORS:

1. Positive Displacement

2. Roto-Dynamic Compressors.

Positive displacement compressors

In this type the volume of the cylinder is reduced mechanically to compress the gas.

Roto-dynamic compressors

• In this type the centrifugal force or the velocity of the moving gas is used for producing compression of gas.

• Positive displacement compressors can be further divided into Reciprocating and rotary compressors. • Under the classification of reciprocating compressors, we have

1. In-line compressors, 2. “V”-shaped compressors, 3. Single-acting compressors, 4. Double-acting compressors, 5. Diaphragm compressors.

•The rotary compressors are divided into Screw compressors,

1. Vane type compressors, 2. Lobe and scroll compressors

and other types.

•Under the Roto-dynamic compressors, we have

1. Centrifugal compressors, 2. Axial flow compressors.

TYPES OF RECIPROCATING COMPRESSORS: SINGLE-ACTING COMPRESSORS: •Single-stage compressors are generally used for pressures in the range of 70 psig to 100 psig. •They have piston working on air only in one direction. •The other end of the piston is free or open which does not perform any work. •The air is compressed only on the top part of the piston. •The bottom of the piston is open to crankcase and not utilized for the compression of air.

SINGLE-ACTING COMPRESSORS: Arrangement of single acting Reciprocating Compressor

SINGLE-ACTING COMPRESSORS: P-V Diagram

SINGLE ACTING RECIPROCATING COMPRESSOR

DOUBLE-ACTING COMPRESSORS: •Two-stage compressors are generally used for higher pressures in the range of 100 psig to 250 psig. •They have two sets of intake and delivery valves on both sides of the piston. •As the piston moves up and down, both sides of piston is utilized in compressing the air.

DOUBLE-ACTING COMPRESSORS:

•The intake and delivery valves operate corresponding to the stroke of the compressor. • The compressed air delivery is comparatively continuous when compared to a single-acting air compressor. •Both sides of the pistons are effectively used in compressing the air.

ADVANTAGES •It has flexibility in capacity and pressure range. •It is highly adaptability to low speed drive. •It is suitable for low, medium and high pressures and low and medium gas volumes. •It has high delivery pressure.

DISADVANTAGES •Its operating speed is low. •The air supply is pulsating. •Cyclic vibrations occur. •Has complicated lubrication system. •The air compressor size is large for a given discharge.

ROTARY AIR COMPRESSOR: •Air is compressed by two rotating or inter meshing rotors. • According to the type of construction Rotary Compressor can be further classified as

(a) Rotary Screw Compressor,

(b) Rotary Vane Compressor.

(a) ROTARY SCREW COMPRESSOR.

•Air is compressed between two rotating screw and a casing. •The compression takes place by gradually reducing space between these two parts.

ROTARY SCREW COMPRESSOR

(b) ROTARY VANE COMPRESSOR. •Air is compressed between casing & rotating rotor by the help of movable rotor blade. •This type of Air Compressor can be further classified as Single Stage or Double Stage Rotary Air Compressor.

ROTARY VANE COMPRESSOR

•This type of compressor is further classified as

(a) Centrifugal Air Compressor

(b) Axial Flow Air Compressor

Rota-Dynamic Compressors

(a) CENTRIFUGAL AIR COMPRESSOR.

•In a Centrifugal Air Compressor, an Impeller is mounted on a shaft and positioned within housing, consisting of an inlet duct, a volute and a Diffuser. • The velocity to the air can be imparted by the high speed rotation of Impeller. •The Diffuser surrounds the Impeller and act to convert the Kinetic energy of air into potential energy at a higher pressure level.

CENTRIFUGAL AIR COMPRESSOR

•The centrifugal air compressor is a dynamic compressor which depends on transfer of energy from a rotating impeller to the air. •Centrifugal compressors produce high-pressure discharge by converting angular momentum imparted by the rotating impeller (dynamic displacement). In order to do this efficiently, centrifugal compressors rotate at higher speeds than the other types of compressors.

ADVANTAGES

•Pressure is high about 4.5:1. •More flexible during operation. •Part load performance is better. •Low starting torque required. •Delivery pressure is about 400 bar.

(b) AXIAL FLOW AIR COMPRESSOR. •The Axial Flow Type Air Compressor is essentially a large capacity, high speed machine with characteristics quite different from the centrifugal air compressor. • Each stage consist of two row of blades, one row rotating & the next row of blade is stationery. •The rotor blades impart velocity and pressure to the air as the motor turns, the velocity being converted to pressure in stationery blades.

•Axial compressors are rotating, airfoil based compressors in which the working fluid principally flows parallel to the axis of rotation. •Axial flow compressors produce a continuous flow of compressed gas, and have the benefits of high efficiencies and large mass flow capacity, particularly in relation to their cross-section. •Axial compressors are widely used in gas turbines, such as jet engines, high speed ship engines, and small scale power stations.

AXIAL FLOW AIR COMPRESSOR

ADVANTAGES

•Pressure ratio per stage is 1.2:1. •Frontal area is smaller. •More suitable for multistaging. •Delivery pressure is about 20 bar.

(C) ROOTS BLOWER COMPRESSOR:

•This type is generally called as blower.

•The discharge air pressure obtained from this type of machine is very low.

•The Discharge Pressure of 1 bar can be obtained in Single Stage and pressure of 2. 2 bar is obtained from Double Stage.

•The discharge pressure achieved by two rotors which have separate parallel axis and rotate in opposite directions.

•This is the example of Positive Displacement Compressor in Rotary Type Air Compressor.

ROOTS BLOWER AIR COMPRESSOR