What is a Boiler? Different Types of Boiler

In this article, we will study what is a boiler? Different types of boiler (steam). The boilers are used in power plants for the generation of steam. They are crucial for the working of a power plant. They are mostly used in power plants where steam turbines are used for electricity generation. Knowledge of the boiler is very essential if you are a mechanical engineer.

What is a Boiler?

what is a boiler

A boiler is a closed vessel which is used to convert the water into high pressure steam. The high pressure steam so generated is used to generate power. The high pressure steam is made to strike on the turbine blades and as the turbine blades rotates it rotates the generator attached to the turbine shaft. The Rotation of the generator produces electricity that we use for doing various works.

Working Principle of a Boiler

principle of boiler

The boiler works on the same principle as the water is heated in a closed vessel and due to heating, the water changes into steam. This steam possesses high-pressure kinetic energy. The boiler contains water. The water is heated to its boiling temperature by the use of heat from the furnace. Due to the heating of water, it gets converted into high-pressure steam. The steam generated is passed through the steam turbines. As the high-pressure steam strikes the turbine, it rotates the turbine. A generator is attached to the turbine and the generator also starts to rotate with the turbine and produces electricity.

We spoke to a representative from 2nd city gas plumbing and heating, a company that offers boiler services in Dudley, and they said, “ There are different types of boilers and they are classified according to  several factors such as the pressure and temperature, fuel type form of heating, heating method, draft net, size/capacity, etc. However the fuel type is the most common and it uses gas, oil, or electricity to operate. Gas and oil boilers operate in the same way. When oil burns inside the combustion chamber and heats up the heat exchanger, which in turn heats the water. On the other hand, electric boilers are preferred in homes where gas and oil are scarce, and the electric boiler operates differently from the gas and oil boiler as they use electrical power to heat elements.” If you need a new boiler, check out this website.

Different Types of Boiler

Boilers can be classified on a different basis but here I am discussing the only important basis of boiler classification.

1. According to the Contents in the Tubes

According to the contents in the tubes, the boilers can be classified as fire tube boiler and water tube boiler.

(i) Fire Tube Boiler:

In a fire tube boiler the fire or hot gas is present inside the tubes and water surrounds these fire tubes. Since fire is inside the tubes and hence it is named as fire tube boiler. The heat from the hot gases is conducted through the walls of the tube to the water.

(ii). Water Tube Boiler:

In water tube boilers, the water is present inside the tubes and the fire or hot gases surrounds these water tubes.

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2. According to the Number of Tubes

According to the no of tubes, the boilers are classified as single tube boiler and multitubular boilers.

(i). Single Tube Boilers:

The boilers which contain one fire tube or water tube are called a single tube boiler.

  • The examples of single tube boilers are Cornish boiler and simple vertical boiler.

(ii). Multitubular Boiler:

The boilers which has two or more water tube or fire tubes are called multi-tubular boilers.

  • Lancashire boiler, Locomotive boiler, Cochran boiler, Babcock and Wilcox boilers are multitubular boilers.

3. According to the Position of the Furnace

According to the position of the furnace, the steam boilers are classified as internally fired boilers and externally fired boilers.

(i). Internally Fired Boilers:

The boilers in which the furnace is located inside the boiler shell are called internally fired boilers.

  • Among all the fire tube boilers, most of the boilers are internally fired boilers.

(ii). Externally Fired Boilers:

In externally fired boilers, the furnace is located outside the boiler shell. In this the furnace is arranged underneath in brick work setting.

  • Water tube boilers are always externally fired boilers.

4. According to the Axis of the Shell

According to the axis of the shell, the boilers are classified as vertical boilers and horizontal boilers.

(i). Vertical Boilers:

The boilers in which the axis of the shell is vertical are called vertical boilers.

  • Examples of vertical boilers are: simple vertical boiler and Cochran boiler.

(ii). Horizontal Boilers:

When the axis of the shell in a boiler is found horizontal than it is called a horizontal boiler.

5. According to the Methods of Circulation of Water and Steam

According to the method of circulation of water and steam, the steam boilers are divided into natural circulation boilers and forced circulation boilers.

(i). Natural Circulation Boilers:

In natural circulation boilers, the circulation of water takes place naturally by the convection currents that set ups during the heating of water.

  • In most of the boilers there is a natural circulation of water such as Lancashire boiler, Cochran boiler etc.

(ii). Forced Circulation Boilers:

In this type of steam boilers, the water circulation takes place with the help of a centrifugal pump driven by some external power. Here the circulation is forced by some external agency.

6. According To The Use

According to the use, the boilers are classified as stationary boilers and mobile boilers

(i). Stationary Boilers:

These are the boilers that are stationary and cannot be moved from one place to another. Once they are installed, they cannot be transported to another destination.

  • These boilers are used in power plants and in industrial
    process works.

(ii). Mobile Boilers:

These are the steam boilers that can be moved from one place to another.

  • Locomotive and marine boilers are mobile boilers.

If you need a new boiler check out this website:


In this article, we have studied what is a boiler? different types of boiler. I hope you have grasp everything discusses here. If you really enjoyed the post then don’t forget to like and share it.

4 thoughts on “What is a Boiler? Different Types of Boiler”

  1. Love what you said about “What is a Boiler? Different Types of Boiler”
    Its a perfect article to get all information about Boiler Mechanical Systems.

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