Cornish Boiler: Working Principle, Parts, Construction, & Applications

Cornish boiler is one of the most common types of fire tube boilers. This article deeply describes the Cornish boiler working, parts, construction, and applications.

What is a Cornish Boiler?

The Cornish boiler is an internally fired horizontal boiler that produces steam by burning fuel (i.e., coal). This output steam is then used in steam turbines and industries like sugar mills, textile mills, etc.

Cornish Boiler

Cornish boilers consist of a cylindrical shell that is fixed in the horizontal direction. The diameter of this cylindrical shell length is between 4 to 7 meters while the shell has a diameter between 1.25 and 1.7 meters. The first Cornish boiler was designed by Richard Trevithick in 1812.

The Cornish boiler is designed like the Lancashire boiler, but the Lancashire boiler is more efficient compared to the Cornish boiler. The steam generation rate is about 9000 kg per hour of the Lancashire boiler, and its pressure is about 16 bars. On the other hand, the steam generation rate of the Cornish boiler is about 6500 kg per hour, and the steam pressure is about 10.5 bars.

Cornish boilers are most usually used for textile industries, sugar mills, and steam turbines.

Working Principle of Cornish Boiler

The Cornish boiler works as per the principle of thermal conduction. The heat of hot flue gases is transferred to the surrounding water, which creates steam.

Cornish boiler working

Here is the proper working of the Cornish boiler:

  • The fuel is drawn onto the grate and then burned. As a result of this combustion, hot flue gases are released.
  • The grate is placed in equal spaces for the complete combustion of the air with the fuel. Heat is produced as a result of this combustion process, and hot flue gases are produced.
  • These hot flue gases pass through the fire tube from the grate. Heat is then transferred to the water surrounding the tubes from these hot flue gases.
  • These gases then enter the bottom flue.
  • The surrounding water in the shell heats up from the bottom and sides. The bottom flue heats the water from the bottom, and the side flue heats the water from the sides and the center of the tube.
  • These heated gases raise the temperature of the tube walls, resulting in a rise in the water temperature inside the tube.
  • After the continuous transfer of heat, the water starts boiling and converting into steam.
  • These hot flue gasses then left the system through the chimney after passing from the bottom flue.

Parts of a Cornish Boiler

The Cornish boiler has the following major parts:

  • Shell
  • Furnace
  • Grate
  • Fire Tube
  • Water Level Indicator
  • Smoke Box
  • Manhole
  • Pressure Gauge
  • Ash Pit
  • Safety Valve
  • Stop Valve
  • Chimney

1) Shell

One of the important components of the Cornish boiler is the shell. It protects the internal components of the boilers.

The shell is the external part of the boiler that has water and the tube inside it. The heat is transferred to the water with the help of this shell.

2) Furnace

The furnace is the place where the combustion in the boiler happens. The furnace is used to burn all the solid fuel. Heat is produced due to the burning of the fuel, which is then transferred into the flue gases. These hot flue gases then go into the combustion chamber.

3) Grate

An internal part of the Cornish boiler is placed at the bottom of the furnace. This part carries out the combustion process as the solid fuel is present in that grate. The grates are made of cast iron.

The design of the grate is so unique that it allows the air to pass to the furnace to help in the burning process. The grate is wide enough to send the ash or unburnt soil to the ash pit.

4) Fire Tube

This tube is usually used in fire tube boilers. There is only one fire tube present in the Cornish boiler. The fire tube has hot flue gases, and the water surrounds that fire tube. The heat is transferred from the hot flue gases to the surrounding water through the walls of the fire tube.

As the water gets hotter, it starts boiling and converting the water into steam. Hence, fire tubes are a vital part of the Cornish boiler that majorly converts the water into steam.

5) Water Level Indicator

A water level indicator shows the water level inside the boiler. This indicates the water level when it crosses its minimum or maximum limit.

6) Smoke Box

The smoke is generated as a result of the fuel-burning process. All this smoke is forwarded into the smoke box. This smoke box sends that smoke out into the atmosphere through the chimney.

7) Manhole

The manhole is the passage made for the workers to enter the boiler. This opening is used for the repair and cleaning of the boiler from the inside.

8) Pressure Gauge

The pressure gauge measures the internal pressure of the Cornish boiler. This is installed with the boiler. It indicates several readings of the internal pressure.

So, in case of excessive pressure, the boiler can be protected from explosion by limiting that internal pressure by observing the gauge readings and following some safety procedures.

9) Ash Pit

All the unburned fuel and the ashes were collected in this ash pit. The grate moves the unburnt fuel and the ash into the ash pit.

10) Safety Valve

The safety valve mainly protects the Cornish boiler from explosions in case of extreme steam pressure. This valve works automatically.

Whenever the steam pressure inside the boiler exceeds its internal limit, this valve opens, removes the extra steam from the boiler, and then maintains the internal pressure accordingly.

11) Stop Valve

It’s a one-way valve. This valve acts as the steam regulator.

12) Chimney

The chimney is used to collect the unburnt gases and smoke of the burnt fuel. All of the unburned fuel and the smoke come out from the boiler into the atmosphere through the chimney.

Read More: Boiler Mountings and Accessories 

Construction of a Cornish Boiler

The shortest component of the Cornish boiler is its exterior shell, which acts as the external component and surrounds its various internal components. It also protects the other parts of the boiler.

A furnace is present in the boiler that burns the solid fuel. The furnace is an internal component of the boiler that has a fire hole. The fire hole is the opening from where the fuel is inserted into the furnace.

In the center of the water, the fire watch is present. There is a brick arc that stops the ash from going into the flue or the fire tube.

Cornish boiler construction

One flue tube in the Cornish boiler is present at its bottom. It is known as the bottom flue. Similarly, the two flue tubes installed on the side of the boilers are known as the side flue tubes. A grip tube is also present, known as the main grip tube.

The hot flue gases pass through all of these tubes and then discharge from the chimney. The chimney releases these gases into the air outside.

A safety valve is also present in the boiler, which is an automatic spring-loaded valve. In some cases, when the internal pressure is higher than the required pressure, this valve protects the boiler from an explosion. It automatically opens, releases the excessive steam from the boiler, and then closes. It then maintains the required internal pressure of the boiler.

The flow of the steam is controlled by the stop valve in the steam pipes. This valve is present at the top of the boiler.

The feed pump pumps the water into the boiler and acts as the external part of the boiler. Different pumps, like the piston pump, reciprocating pump, submersible pump, and centrifugal pump, are used to feed the water into the boiler.

The water is transferred to the reservoir using the feed pipe. This feed pipe is controlled by the feed valve. It’s a one-way valve that blocks the backflow of the water.

All the contamination from the bottom of the boiler is eliminated with the help of the blow-off coke. This is also known as the manhole. This manhole is used by the workers and the engineers to repair, inspect, and clean the boiler from the inside.

Read More: Cochran Boiler Working and Construction

 Advantages of Cornish Boilers

  • It has a simple design.
  • These boilers have low maintenance costs.
  • It is very easy to construct.
  • It has small size and lightweight.
  • The Cornish boiler can be easily shifted from one location to another.
  • It has the ability to overcome load variations during its operation.

Disadvantages of Cornish Boilers

  • These boilers have a very low rate of steam production (i.e., 1350 kg/hour). Therefore, Cornish boilers can’t be used in large power plants.
  • They may be dangerous if not operated properly, mainly if the pressure gauges and safety valves are faulty.
  • They are less efficient compared to other types of boilers.
  • They need a large floor area for installation.
  • They require regular cleaning and maintenance.

Applications of Cornish Boilers

  • Cornish boilers are usually used for several industries, including sugar, mill, chemical, and paper industries.
  • They are employed in the Marines.
  • They also use to run steam turbines.

Cornish Boiler VS Lancashire Boiler

Cornish BoilerLancashire Boiler
Cornish boiler has a single flue.The Lancashire boiler has two flues.
It has small size and lightweight.It is larger and heavier than the Cornish boiler.
It has low steam production rate than the Lancashire boiler.It has a faster rate of steam production.
It has less pressure capacity than the Lancashire boilerIt has a higher pressure capacity i.e., 200 psi.
It is less fuel-efficient.It is more fuel-efficient.
The Cornish boiler is hard to clean and maintain.It is easy to maintain because of its large size.

FAQ Section

Who invented the Cornish Boiler?

The first Cornish boiler was designed by Richard Trevithick in 1812.

What are the components of Cornish Boiler?

  • Stop Valve
  • Shell
  • Chimney
  • Furnace
  • Grate
  • Ash Pit
  • Fire Tube
  • Water Level Indicator
  • Safety Valve
  • Smoke Box
  • Manhole
  • Pressure Gauge

What is the pressure range of Cornish boiler?

Cornish boiler has the ability to generate steam at the rate of 1350 kg/hr and can take a maximum pressure of about 12 bar.

Which boiler has highest efficiency?

Condensing boilers are considered to have the highest efficiency.

Read More

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