Steam Boilers: Parts, Working Principle, Types, Uses (PDF)

In this article, you’ll learn what is a steam boiler. Its classification, parts, working principle, application, and types of steam boilers.

You can download the PDF file of this article at the end of it.

What is a Steam Boiler?

The steam boiler, also known as the steam generator, is usually a closed vessel made of steel. In a steam boiler, the water is converted into steam by applying heat. Fuels commonly used in boilers are coal, oil, and gas for producing heat.

The steam generated by the boiler is used in various Industries for processing, heating, and running steam turbines in power plants.

The steam produced may be supplied:

1. To an external combustion engine, i.e. steam engines and turbines,
2. At low pressure for industrial process work in cotton mills, sugar factories, breweries, etc., and
3. For producing hot water, which can be used for heating installation at much lower pressures.

Important Terms for Steam Boilers

The following are important terms used in steam boilers:

1. Boiler Shell
2. Combustion Chamber
3. Grate
4. Furnace
5. Heating surface
6. Mountings
7. Accessories

#1 Boiler Shell

It is made up of steel plates bent into a cylindrical form and riveted or welded together.

The ends of the shell are closed through the endplates. A boiler shell must have sufficient capacity to carry water and steam

#2 Combustion Chamber

It is the space, usually below the boiler shell, intended for burning fuel to produce steam from the water contained in the shell.

#3 Grate:

The grate is a platform, in the combustion chamber, on which fuel like coal or wood is burnt.

It consists of cast iron bars that are spaced apart so that air can pass through them. The surface area of the grate, over which the fire takes place, is called the grate surface.

#4 Furnace:

It is the space, above the grate and below the boiler shell, in which the fuel is burnt. The furnace is also called a firebox.

#5 Heating Surface:

It is that part of the boiler surface, which is exposed to the fire or hot gases from the fire.

#6 Mountings:

Some fittings are mounted on the boiler for its proper functioning. Mountings are water level indicators, safety valves, pressure gauges, etc. It may be noted that a boiler cannot function safely without the mountings.

Read also: The complete list of Boiler Mountings and Accessories

#7 Accessories:

There are the devices, which form an integral part of a boiler but are not mounted on it. They include a superheater, economized, feed pump, etc. It may be noted the accessories help in controlling and running the boiler efficiently.

Types of Steam Boilers

Following are the types of steam boilers classified according to their uses:

Fire Tube Boiler

In fire tube boilers the hot gases produced by the combustion of fuel pass through the tubes, which are surrounded by water. The heat from the gases in conduction through the walls of the tubes to the surrounding water.

The following are examples of fire tube boilers:

#1 Cornish Fire Tube Boiler

This type of boiler has a plain cylindrical shell with a single heat pipe running through its center. Its single heat pipe is coupled to a single exhaust flue.

#2 Lancashire Fire Tube Boiler

The Lancashire boiler is constructed similarly to the Cornish boiler, with the exception of two interior fire tubes and two exhaust flues.

#3 Locomotive Fire Tube Water

The locomotive boiler is an outdated design. The combustion chamber, sometimes known as the furnace, was used to burn coal or wood in steam locomotives. This equipment was sturdy and had a large steam capacity. It had a horizontal tube construction.

#4 Vertical Fire Tube Boiler

A vertical tube boiler is a basic boiler with a vertical cylinder configuration. It contains cross tubes, and the furnace is positioned at the bottom of the boiler. The flue allows combustion gases to exit the boiler through the top.

#5 Cochran Fire Tube Boiler

The Cochran boiler is a vertical, multi-tubular boiler. It features several horizontal fire tubes.

#6 Immersion Fire Tube Boiler

This type of boiler has a single-pass horizontal design. Flames are directed into the appropriate small-diameter tubes. Individual small-diameter tubes are immersed in water. Every flame nozzle has its tube.

#2 Water Tube Boiler

Water tube boilers are an advancement in the technology used to produce steam. This technology reduces fuel costs by utilizing a large containment space to distribute heat more evenly and efficiently compared to fire tube technology.

There are several water-filled tubes inside the chamber. These tubes run the entire length of the boiler. Since each tube is sealed, it can resist pressure on its own without impacting the tubes next to it. The water passing through the metallic tubes receives heat from them.

The following are examples of water tube boilers:

#1 Babcock and Wilcox Boiler

In 1967, the Babcock and Wilcox Boiler was founded by George Herman Babcock and Stephen Wilcox. This is a water tube boiler generally used for steam power plants. These types of steam boilers circulate hot gases over the tubes as water flows inside of them.

#2 LaMont Boiler

LaMont boilers are a type of forced circulation water-tube boiler in which the boiler water circulates via an external pump through long, closely spaced tubes with small diameters.

In steam and hot water boilers, a mechanical pump is used to ensure sufficient and positive circulation.

#3 Loeffler Boiler

The Loeffler Boiler is a forced circulation and high-pressure water tube boiler with an internal furnace. In this boiler, the water is evaporated using 65% superheated steam.

In the evaporating drum, everything occurs. All the process is accomplished with the help of a mixing nozzle. The remaining 35% of superheated steam is used by two steam turbines.

#4 Benson Boiler

The Benson Boiler is a type of high-pressure, supercritical water boiler that produces steam directly from compressed water at supercritical pressure, eliminating the formation of bubbles. In 1922, Mark Benson discovered the Benson boiler.

Advantages and disadvantages of water tube boilers over fire tube boilers:

Advantage:

1. Steam can be raised more quickly.
2. Steam at higher pressure can be produced.
3. Higher rate of evaporation.
4. Sediment deposition is less.
5. Suitable for any type of fuel and method of firing,
6. More effective heat transfer.
7. Failure of water tubes will not affect the working of the boiler.
8. Occupies less space.
9. Easy maintenance.
10. Easy transportation.

Disadvantage:

1. Not suitable for ordinary water.
2. Not suitable for mobile applications.
3. High initial cost and hence not economical.

#3 Internally Fired Boilers

In an internally fired boiler, the furnace is inside the boiler shell. Most fire tube steam boilers are internally fired.

#4 Externally Fired Boilers

In externally fired boilers, the furnace is arranged underneath in a brickwork setting. Water tube steam boilers are externally fired.

#5 Vertical Boiler

In vertical boilers, the axis of the shell is vertical. Simple vertical boilers and Cochran boilers are vertical boilers.

#6 Horizontal Boiler

In horizontal boilers, the axis of the shell is horizontal. Babcock and Wilcox boiler, Locomotive boiler, and Lancashire boiler are horizontal boilers.

#7 Natural Circulation Boilers

In natural circulation boilers, the circulation of water is by natural convection currents, which are set up during the heating of water. In most steam boilers, there is a natural circulation of water.

#8 Forced Circulation Boilers

In forced circulation boilers, there is a forced circulation of water by a Centrifugal pump, which is driven by some external power.

These types of steam boilers use forced circulars made in high-pressure boilers such as La-Mount boilers, Benson boilers, and Loeffler boilers.

#9 Single Tube Boilers

Single-tube steam boilers have only one fire tube or water tube. Simple vertical boilers and Cornish boilers are single-tube boilers.

#10 Multi Tubular Boilers

In a multi-tubular steam boiler, there are two or more fire tubes or water tubes.

#11 Stationary Boilers

Stationary boilers are mainly used in power plants and industrial process work. These are called stationary because they do not move from one place to another.

#12 Mobile Boilers

The mobile steam boilers are those that move from one place to another. These boilers are locomotive and marine.

#13 Source of Heat Boilers

The steam boilers may also be classified according, to the source of heat supplied for producing steam.

These sources may be the combustion of solid, liquid, or gaseous fuel, electrical energy or nuclear energy, hot waste gases as by-products of other chemical processes, etc.

Read Also: What Are The Different Types of Generators and Their Uses?

Advantages of Steam Boiler

The following are the advantages of steam boilers:

1. Steam boilers are highly efficient, producing a lot of energy from a small amount of fuel. They are therefore economical and safe for the environment.
2. When compared to other heating systems, steam boilers require extremely little maintenance.
3. Because they contain fewer moving parts, fewer parts are prone to corrosion or failure.
4. Steam boilers are intended to endure and can resist the high pressures and temperatures required to produce steam.
5. Steam boilers have numerous uses, including producing power and heating industrial operations.

Disadvantages of Steam Boiler

The following are the disadvantages of steam boilers:

1. If steam boilers aren’t properly maintained and controlled, they could be hazardous. They can blow up if they are not maintained properly and run at high temperatures and pressures.
2. Steam boilers are made to run at a particular temperature and pressure. This indicates that they are not particularly good at regulating the water’s or steam’s temperature.
3. Steam boilers may lose energy owing to system leaks or inadequate heat transfer. This can lead to increased energy costs and decreased efficiency.
4. It may take some time for steam boilers to heat up and produce steam. This could be a problem when steam is required right away.

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Read next:

• Thermodynamic Cycle: Its Classification, Working.
• Important Terms Used In Thermodynamics

External resources:

• Steam Boiler|Researchgate.net

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