Introduction: A compressor is a device used to reduce the volume of a gas or air by increasing its pressure. In other words, it compresses a gas or air into a smaller space, which increases its density and energy. Compressors are commonly used in air conditioning systems, refrigeration units, gas pipelines, and manufacturing processes.
Compressors used in industrial applications are available in various types and sizes, ranging from small portable units to large ones. Compressors can be powered by different sources, like electricity, gas, or diesel, depending on the application and requirements.
Types of Compressor:
- Piston type Compressor
- Screw Type Compressor
- Centrifugal Compressor
- Jet Compressor
Piston-Type Compressor: A piston-type compressor is a positive displacement compressor that uses the reciprocating piston mechanism to compress gas or air.
Construction: A piston compressor consists of the following components:
1. Cylinder: A cylindrical chamber inside compression takes place.
2. Piston: A piston is basically a reciprocating component that moves back and forth inside the cylinder and compresses the gas.
3. Crankshaft: A crankshaft that converts the linear motion of the piston into rotary motion due to its rotation (rotating component)
4. Connecting rod: A component that connects the piston to the crankshaft.
5. Intake valve: A one-way valve that allows gas to enter the cylinder during the intake stroke.
6. Discharge valve: A one-way valve that allows compressed gas to exit the cylinder during the compression stroke.
Working: The working of a piston compressor is as follows:
1. Piston moves downwards during the intake stroke which creates a low-pressure region in the cylinder This causes the intake valve to open, and atmospheric air is drawn into the cylinder.
2. Piston moves upwards during the compression stroke, In this stroke compressing the air inside the cylinder. The discharge valve remains closed during the compression stroke.
3. When the pressure inside the cylinder reaches the preset level, the discharge valve opens, allowing the compressed air to exit the cylinder and flow into a storage tank or a downstream system.
4. Piston moves downwards during the intake stroke again which creates a low-pressure region in the cylinder This causes the intake valve to open, and atmospheric air is drawn into the cylinder, repeating the cycle. Hence, the mentioned process is repeated with the piston moving back and forth to compress the gas.
Screw Compressor: A screw compressor is a positive displacement rotary compressor that compresses gas or air using two helical rotors which are interlocked, and rotate in the opposite direction. Gas is compressed as it moves through the compression chamber formed between the rotors and the compressor casing.
The compression process in a screw compressor is continuous and steady, which makes it more efficient and reliable compared to other types of compressors.
The compressor output depends on the factors such as the speed of the rotors, varying the speed & changing the size of the compressor
Working: The working of a screw compressor can be broken down into the following steps:
1. Inlet: The gas enters the compressor with the help of the inlet valve and flows into the space or construction between the rotors.
2. Compression: due to the rotation of rotors the gas gets trapped between the rotors and the casing of the compressor. Gas is compressed by decreasing the volume created by the rotors.
3. Discharge: The compressed gas is discharged through the outlet valve.
4. Oil Injection: Oil injection in the compressor is required to minimize the friction between the rotors and to seal the compression chamber. This injected oil helps to cool down the compressed gas and also lubricates the bearings and other moving parts.
5. Oil Separation: After the compression, the mixture of gas and oil is fed to the oil separator, where the oil is separated and returned to the compressor. The gas is then discharged into the system.
Centrifugal Compressor: Centrifugal compressors are treated as a type of dynamic compressor which works on the principle of converting kinetic energy into pressure energy.
- Inlet: Primarily gas enters the compressor through the inlet nozzle and flows into the rotating impeller which consists of a series of blades.
- Impeller: The impeller is mounted on a shaft. As the impeller rotates at high speed it imparts kinetic energy to the gas and accelerates it to a high velocity.
- Diffuser: This high-velocity of gas leaves the impeller into a stationary diffuser that converts the kinetic energy into pressure energy. The diffuser consists of a series of stationary vanes that decreases the gas velocity and moves into the volute casing which is continuously expanding as the gas moves forward.
- Volute casing: The collection of compressed gas takes place in the spiral-shaped chamber called volume casing and finally gas exits the outlet nozzle. As the gas flows through the volute casing, its velocity decreases, and its pressure increases (As the volume casing expands).
- Outlet: In the last step of compression, high-pressure compressed gas exits the compressor through the outlet nozzle.
Jet Compressor: Hydraulic jet compressors, also called as Ejectors, work on the Venturi effect principle to compress a gas or Vapour. The compressor has no moving parts and is driven by liquid or gas which contains high pressure.
- Inlet: The gas or vapor enters the compressor through the inlet nozzle.
- Mixing chamber: Mixing chamber inside which the gas to be compressed is mixed with driven fluid high-pressure liquid or gas.
- Converging nozzle: The mixture of gas or vapor and high-pressure liquid or gas passes or flows through a converging section, which reduces the path for flow (area) and increases the velocity of the mixture.
- Throat: The throat is simply a point where construction is the narrowest point of the converging section. Thus the maximum velocity of the mixture has attained, and the pressure of the mixture gets decreases due to the Venturi effect.
- Diffuser: After flowing through the throat, this mixture flows into a diffuser section increasing the flow area and reducing the velocity of the mixture because of its expanding construction.
- Outlet: As the compressed gas or vapor passed through the throat. High-pressure gas finally exits via the outlet nozzle.
The high-pressure liquid or gas used to drive the hydraulic jet compressor can come from a pump or a compressed gas source. The efficiency of the compressor depends on the pressure and flow rate of the driving fluid and the operating conditions of the compressor, such as the inlet pressure and the compression ratio. Hydraulic jet compressors are commonly used in industrial applications such as refrigeration systems, vacuum pumps, and gas handling systems.