Centrifugal Compressor is a machine in which a particular
gas or vapor is compressed by a radial acceleration by an impeller with the
help of a surrounding case. It can then be arranged multistage for greater
proportions of compression. The compression is largely influenced by a
centrifugal pump.
In this article we will cover each and every point related
to centrifugal compressor or sometimes called as radial compressor.
So let's get started with it's principle.
Centrifugal Compressor:
Principle:
The compression principle of centrifugal compressor is quite
different from that of reciprocating or rotary type compressor.
When the air passes through the rotating
impeller it experiences force or work which is performed by centrifugal forces
. The work input takes place as an increase in pressure and velocity or speed
of the air flow through the impeller. The air flow looses it's velocity after
entering in the diffuser section. The diffuser is actually a fixed or static component
that escorts the air flow when it leaves the impeller. This loss in velocity
eventually results in an additional increase of pressure. The impeller and the
diffuser contributes about 65% and 35% of the total pressure developed or
produced in the compressor.
Construction:
A centrifugal compressor generally consists of four
components named inlet , impeller,diffusor and
collector.
1.Casing and inlet .
The above mentioned components are usually protected or
guarded by a casing or housing . A case house consists of number of bearings in
order to provide radial and axial support of the rotor. The case also contain
nozzles along with inlets and discharge flow connections in order to introduce
and extract flow from the compressor.
Casing are of two types :-
a.) Horizontally split
b.) Vertically split
A case is generally build of cast iron or steel.
2. Impellers.
The impellers are assembled or mounted on a steel shaft and
this assembly is known as compressor rotor (mostly in multi stage compressors).
The rotor provide velocity to the gas with blades that are attached to a
rotating disc. These blades can be forward-leaning , radial or backward-leaning
depending upon the desired output . Most of the multistage compressors use
backward-leaning blades as they provide the widest range of efficiency.
3. Diffuser.
The impeller extracts the gas with great velocity into a
diffuser passage. The diffuser usually compromise two walls which form a radial
channel. Because of these arrangements the velocity of the gas decreases and
dynamic pressure is converted into static pressure.
The diffuser passages are small space between adjacent
diaphragms which generally turns the gas flow 180° in order to direct it
towards the next impeller.
4. Collector.
Following the last stage impeller the gas must be collected
and delivered to the discharge flange. The component used to collect the gas
discharged through the diffuser is called as collector. It may also be termed
as volute or scroll. The collector may also contain valves and other
instrumentation in order to control the compressor.
Types:
There are two types of it :-
1. Single stage centrifugal compressor
2. Multi stage centrifugal compressor
Both of these compressor work on the same principle but they
do have some drastic difference in their construction and working.
So let's study each of them separately.
1. Single stage compressor.
Single stage compressors consist of only a single impeller
and it is use for moving the air or other gases up to 3 to 1 compression ratio
for either pressure or vacuum duty. These type of compressors are considered to have a beam
design or an overhung impeller arrangement. In this type of arrangement the
impeller is at the non-driving end of the shaft. One major advantage of it over
the multistage compressor is that it provides high efficiency and the delivered
gas is totally oil and surge free.
2. Multistage compressor.
Multistage compressors consists of 1-10 impellers and it can
be arranged in a variety of flow path configurations. Throughout each and every
stage the temperature and the compression ratio are assumed to be constant.
Multistage compressor can be arranged in straight-through, compound, and double
flow configurations. Multistage compressor are also considered to have
beam-type design but the impellers are located between the radial bearings .
Applications of centrifugal compressor:
1. Compressed gas or air:
Centrifugal compressor is one of the most simple and
efficient way to obtain or produce compressed air. They are best suited when
the demand of air or gas is constant and excessive.
2. Food Industry:
Food processing industry depends highly on this type of compressor as it can provide oil free compressed air which are necessary for
some sensitive petitions.
3. Gas turbines:
Gas turbines use either or both axial and centrifugal
compressor to provide the necessary compression.
Centrifugal compressors are mostly used in gas turbines such as :-
a.) Turboshaft
b.) Turboprop
c.) Micro turbines and
d.) Auxiliary power units
4.) Oil refiners , petrochemical and chemical plants:
The centrifugal
compressors used for the above purposes generally have a horizontally split
casing and most of them are multistage compressors. These type of compressors
are generally operated by over-sized steam engines and gas turbines.
5. Refrigeration and air control:
Centrifugal Compressors support a wide variety of
refrigerants and thermodynamics and are also able to supply compression in
water chiller cycles due to which it has a high demand for usage in
refrigerators and air conditioners.
Advantages and Disadvantages:
Advantages
- a.) When compared to other compressors, it is relatively agile and easy to manufacturer.
- b.) As this compressor does not require any special foundation it is highly energy efficient and reliable.
- c.) They consist of a small number of rubbing parts and are absolutely oil free in nature.
- d.) It generates a higher pressure ratio per stage than the axial flow compressor.
Disadvantages.
- a.) They produce a limited amount of pressure and are not suitable for very high compression.
- b.) As they work at relatively high speed an enlightened or worldly mounting is required.
- c.) They are very sensitive towards problems such as stalling and choking.
This is all about centrifugal compressor principle, working, construction, types, advantages, disadvantages with its application. If you have any query regarding this article, ask by commenting. If you like this article, don't forget to share it on social network. Subscribe our website for more informative articles.