Centrifugal Compressor

Introduction

A centrifugal compressor is a type of dynamic compressor. Dynamic compressors work under a fixed and constant pressure and their performance is affected by several external factors, such as changes in temperature, etc. In a centrifugal compressor, air is drawn towards the centre of a radical blade, and this air is pushed towards the centre by centrifugal force. In this way, the kinetic energy is converted into pressure by passing it through a diffuser and volute. However, ultra-high-speed electric motors are used to drive the impeller in modern centrifugal air compressors.

Centrifugal Compressors

In aerospace engineering, centrifugal compressors are considered an important element. 

The principle of centrifugal compression according to the theory of aerodynamics is shown in steps.

At first, the air reaches the centre of the impeller. 

Then the air is driven outward by centrifugal force. 

Then the diffuser is used to reduce the air velocity. 

Finally, the wind velocity is converted to high pressure. 

One of the things that is considered for the centrifugal compressors is their efficiency at full load. In the plant, air consumption is usually fluctuating. For this reason, resonant capacity control is needed to ensure the stability of the compressor. For this, an inlet guide vane (IGV) is installed before the air passage of the first compression stage to supply air with constant discharge pressure. 

Centrifugal compressor types

There are different types of centrifugal compressors available. The various types of centrifugal compressors are, 

Single stage compressor: A single stage compressor is one of the most commonly found centrifugal compressors available. This type of compressor has a single impeller to drive the air in a specific direction. It also has connected guide vanes and a diffuser. The flow capacities of this kind of compressor range between 1000 and 3000 cfm. 

Overhung single-stage centrifugal compressor: This is a very useful and effective type of centrifugal compressor. It is used for high-volume and low-pressure applications. The impeller is set on the non-drive portion of the shaft. They have a greater level efficiency and a wide range of applications due to their suction nozzle of axial flow. This compressor can take care of around 60,000 m3 per hour of gas flow. 

Integrally Geared Single-stage centrifugal compressor: This is another kind of single-stage centrifugal compressor. It does have an overhung half-open impeller. The impeller is set inside the speedy shaft of the gearbox. This compressor can handle the gas flow up to 300,000 cubic metres per hour and it can support the ratio of pressure up to 3.5. It can also handle discharge pressures of up to 50 bar. 

Multi-stage compressor: Another kind of centrifugal compressor is the multi-stage compressor. This compressor passes the gas throughout several stages for different purposes. This is more effective for keeping up with the expected requirements of pressure as the single-stage compressor has a single impeller. Multi-stage compressors contain various impellers on the rotor. In this kind of compressor, each impeller diffuses the gas to the next level. Multi-level compressors are also categorised into different types, such as

Centrifugal compressors which are multi-staged in nature horizontal split casting: this kind of centrifugal compressor is also quite popular. These compressors can handle pressures of up to 60 bar. It contains two portions of a cylindrical case. These two halves are connected by a bolt. This type of compressor is effective in high-pressure applications. 

Centrifugal compressors which are multi-staged in nature vertical split-It also looks like a cylinder which is also known as a “barrel”. These kinds of compressors are effective in high-pressure applications. This can handle pressure of around 680 bars. 

Multi-stage centrifugal compressors with bell casing: they are named after the bell-shaped case. This case uses shear rings instead of bolts. These compressors are also effective in high-pressure applications. 

Pipe line multi-stage compressors: these kinds of centrifugal compressors also have a bell-shaped case, but they contain one vertical cover. The delivery nozzle and the side suctions are placed facing each other, and these types of compressors are effective for installation on pipelines of gas. These compressors can handle pressures of up to 100 bars. These kinds of compressors are suitable for the transportation of natural gas and other similar purposes. 

Integrally geared multi-stage compressors: These integrally geared multi-stage compressors are suitable for both high pressure and low-pressure applications, as well as high and low flow applications. Each shaft of a compressor has the capability of hosting two impellers. These compressors are very efficient as they have the ability to inter-cool compression stages as well as an distinguished impeller speed. 

Conclusion

Different kinds of centrifugal compressors are used in engineering. These concepts are important for GATE aspirants.