Cornish Boiler – Parts, Construction and Working

Cornish boiler is a horizontal fire tube boiler which has an internal fire tube. Cornish Boiler was first time fabricated in the year 1812 by Richard Trevithic.
Cornish boiler has a long horizontal cylindrical shell. This boiler has only one firetube running from front to rear. This firetube is not concentrically fixed inside the shell. This firetube is offset from the centre. This firetube is offset from the centre because the shell is never fully filled with water, some space of the upper part of shell is left for steam and the firetube is placed in such a way that it almost in the middle of the water filled area.
Length of the shell in cornish boiler varies from 4 to 7 metres and diameter of the shell varies from 1.25 to 1.75 m.

Parts Of Cornish Boiler :-

1) Shell :-
It is the outermost covering of the cornish boiler. This is the container which contains water as well as fire tube. Heat transfer between hot gases and water takes place here.

2) Grate and Furnace :-
This is the place in the firetube where coal will be placed and burned. Furnace is the part where the coal or fuel enters and burn inside it. Grate is the part where heat is developed with the help of fuel burning in it.

3) Combustion Chamber :-
It is used to supply the heat generated in the grate to the fire tube which transfer heat to water.

4) Ash Pit:-
Ash pit contains the ashes of the fuel after they are burnt completely.

5) Firetube :-
This is present in the centre of the water area of the cornish boiler and the hot gases from grate flows through this tube.

6) Side Flue :-
Flue are the tubes in which the hot gases enters after passing from firetube. Flue present in the side of the horizontal shell is known as side flue.

7) Bottom Flue :-
Bottom flue is present at the bottom of the horizontal shell. It takes the smoke from the side flue to the chimney.

8) Chimney
A chimney is a long vertical tube which takes the smoke from the bottom flue and passes it to the atmosphere with the help of a smoke box.

9) Brick arc
Brick arc is provided to prevent the ash from entring into the tubes.

10) Water Feed Pump
It is used to supply water to the boiler.

Apart from these parts three mountings are present in the cornish boiler. These are :-

1) Water Level Indicator
It is used to identify water level in the boiler and used to send signals when eater level is too high or too low.

2) Steam Stop Valve
It is used to regulate the fow of steam from the boiler.

3) Safety Valve
Safety Valves are used to stop the steam pressure from exceeding the maximum limit.

Construction Of Cornish Boiler :-

The buggest part of the boiler is a long cylindrical exernal shell. It is the outermost part of the Cornish Boiler which contains other boiler parts. Inside the shell there is one internal fire tube palced near bottom side of the boiler. Firetube is placed in such a way that it is in the center of the water area of the cornish boiler.
The furnace and grate is present in the front side of the boiler. Coal is intriduced to the grate through a fire hole. A brick arc is also provided to prevent the ashes from burning coal to enter into fire tube and flue tube.
Two flue tubes are present in the two side of the boiler and are called side flues and one is npresent in the bottom of the boiler and is known as bottom flue. There is another flue tube which is called main flue tube. Through this main flue tube the flue gases reaches the chimney.
This chimney is used to pass the flue gases and smoke from the main flue tube to the environment.
Apart from these parts some mountings are mounted on this boiler. A safety valve which is spring loaded is mounted on the boiler to release the excess steam pressure whenever there is high steam pressure inside the boiler.
Another mounting is stop valve and it is used to regulate the generated steam between the steam pipe and the boiler.t is located at the top of the boiler. A high steam low water safety valve is also provided near the stop valve and is used to release the generated steam when the water level falls below a certain level.
Water feed pipe is there to feed water inside the boiler. This feed pipe is controlled by feed valve. Steam generated inside the boiler contains a large quantity of water in the steam spaces and is called priming. An anti pripme pipe is provided to seperate water as far as possible. A blow-off cock is used to remove mud present inside the bottom of the boiler. This blow-off cock can be used to completely drain water from the boiler for ispection. A main hole is also present that is used to inspect inside the boiler.
A pressure guage is also attached inside the boilers which is used to know the amount of pressure present inside the boiler when it is under operation.
Dampers are located at two side of the boiler which are used to regulate the flow of air and it also controls the steam generation.

Working Of Cornish Boiler

• At first, the fuel start to burn inside the furnace and flue gas is generated. This flue gas passes through the boiler internal firetube. This firetube is placed in the center of the water area of the boiler. So the heat transfers from the flue gases inside the firetube to the water. As the water is heated by the flue gases,steam is generated.
• The steam generated by heating water using flue gas then goes through the priming pipe to the engine.
• The flue gas from the internal firetube then goes to the side flue and then to the bottom flue.
• The flue gases from the bottom flue goes to the main flue which takes the flue gases to chimney where it is passed to the atmosphere.

Application of Cornish Boiler

• Cornish Boilers are used in many industries like sugar, paper, tyre, chemical etc.
• Cornish Boilers are also used to produce steam to run steam turbine.
• It is also found in many marine industries.

Advantages of Cornish Boiler

• Cornish Boiler have very simple design and easy construction.
• It is a compact and portable boiler.
• This boiler can overcome load fluctuation during operation.
• Construction and maintenance cost of this boiler is very low.

Disadvantages of Cornish Boiler

• Low steam production rate of nearly 1350 kg/hr.
• It can take maximum steam pressure of 10.5 bar.
• Need more ground due to horizontal structure.