Cochran Boiler || Definition, Main Parts, Working, Features, & Advantages

Cochran Boiler The Cochran boiler was founded by Cochran & Co. of Annan. It is a vertical multi -rounded kettle…

By admin , in THERMODYNAMICS , at March 3, 2020

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Cochran Boiler

The Cochran boiler was founded by Cochran & Co. of Annan.
It is a vertical multi -rounded kettle and having various level fire tubes.
It is the modification of simple vertical evaporator where the heating surface has been increased by means of a number of fire tubes.
The productivity of this evaporator is obviously superior to the straightforward vertical heater.

Definitions of Cochran Boiler

Cochran Boiler is one of the best types of vertical multi- tubular boiler and has a number of horizontal fire tubes.
They have cylindrical shell with a dome shape top where the space is provided for steam.

Main Parts of Cochran Boiler

Fig. Cochran Boiler line Diagram.

1. Shell

A shell is the main body of the boiler.
They having vertical axis cylindrical drum with hemispherical dome type shell at the top.
This hemisphere gives higher volume to increase steam capacity.

2. Grate

It is the stage on which the strong fuel is singed.

3. Combustion chamber

The consuming of fuel happens in the burning chamber.

4. Fire tubes

The fire tubes helps in the trading of warmth from the hot vent gases to the water.

5. Fire hole

It is the hole through which fuel is fire inside the furnace.

6. Furnace (Fire box)

Furnace is the place where combustion of all the fuel is take place.
It lies at the bottom of the boiler.
It terms as fire box.

7. Ash pit

It is the place where ash of the burning fuel is collected.

8. Chimney

The chimney is attached with the smoke box.
And it releases smoke into the atmosphere.

9. Fire brick lining

It helps in the combustion of the fuel and present in combustion chamber.

10. Man hole

It is a hole on the boiler shell for the purpose of either cleaning, inspection and maintenance.

11. Flue pipe

It is a small passage which connected with the fire box and combustion chamber.
The hot gases enter into the combustion chamber through the pipework.

Also read : Boiler Definition, Parts, Components , etc.

Working of Cochran boiler

Fuel is placed at the grate through fire hole.
Air comes into the combustion chamber through atmosphere.
Fuel is burn through fire hole.
Then, the hot flue gases emerge out and start flowing into hemispherical dome shaped combustion chamber.
This hot flue gases further moves into the fire pipes.
The hot flue gases inside the fire tubes exchange the heat from the hot gases to the water.
Due to the exchange of heat, the steam produced. And it rises upward to collect into the upper side of the shell.
When the required pressure generated, the flue gases goes to the chimney through fire box where it leaves to the atmosphere.
Hence, this process repeats and run continuously.

Features

In Cochran boiler, any types of fuel may be used.
It gives 70% to 75% of thermal efficiency with coal and oil firing.
It is well suitable for small capacity requirement.
The ratio of grate area to the heating surface area varies from 10:1 to 20:1.

Specification of the Cochran boiler

Height	5.75 m
Efficiency	70 – 75 %
Shell diameter	2.75 m
Steam capacity	3500 kg/hr (max. 4000 kg/hr)
Working pressure	6.5 bar( max. 15 bar)
Heating surface area	120 m

Advantages

It occupies less floor space.
Initial cost of boiler is less.
It is easy to operate.
Low initialization cost.
They having higher volume to area ratio.
Easy to clean and inspect.
It’s easy to transport from one place to another.

Limitations

Maintenance and inspection are difficult due to narrow space inside for entering.
They having limited pressure range.
Steam generation rate is low.
Due to it’s vertical design, high room head is required for its installation.

Different types of Mounting used in Cochran boiler

The Mountings are those mechanical appliances which are considered essential for operating a boiler smoothly and safety. Which are normally mounted on the outside of a heater.

The following are the important mountings of a boiler:

1. Safety valves 2. Fusible plug

3. Pressure gauge 4. Water level indicator

5. Blow off cock 6. Feed check valve

7. Steam stop valve

1. Safety valves

It is utilized to forestall blast because of extreme inward weight.
Safety valves are attached on the chest of the boiler.
General, there are two safety valves are present on a boiler.

2. Fusible plug

The function of a fusible plug is to ensure safety to the boiler from begin damaged by overheating due to water level falling very low in the boiler.

3. Pressure gauge

It application is to measure the pressure of the steam which is present inside the boiler.
It’s also present in front of the boiler.

4. Water level indicator

It shows the immediate degree of water that’s accessible within the steam evaporator.

5. Blow off cock

It is situated at the bottom of the boiler drum.

Purpose of Blow off cock:

i. To empty the boiler.

ii. To discharge the dimensions, mud and sediments.

6. Feed check valve

It regulates the supply of water that is pumped into the boiler by feed pump.

7. Steam stop valve

It is normally fitted on the most noteworthy piece of the heater with the assistance of a spine.

The main functions are as follows:

i. To regulate the flow of steam from the boiler to the moststeam line.

ii. To fully shut off the steam provide.

Different types of Accessories used in Cochran boiler

1. Economizer

2. Feed pump

3. Super heater

4. Air preheater

1. Economizer

It improves the economy of the boilers.
It is used to heat the feed water by the application of heat from the hot fuel gases before it leaves the chimney.

Advantages of Economizer:

The long life of the boiler.
To increase in the evaporative capacity of the boiler.

2. Feed pump

It use to deliver water to the boiler.

There are mainly two types of feed pump:

i. Reciprocating feed pump

This is positive displacement type pumps. The most popular types of reciprocating feed pump used in a boiler is a duplex feed pump.
It consists of a steam engine and a water pump side by side.

ii. Rotary feed pump

It is a high speed centrifugal pump that is used to deliver a large quantity of water into the boiler.
It consists of impeller and casing.

3. Super heater

It is a heat exchanger in which products of the heat of combustion is utilized to dry the wet steam and to make super heated by increasing it’s temperature.
During this process, pressure remains constant and it’s volume and temperature increase. It consists of a set of small diameter U – tube in which steam flows and takes up the heat from hot flue gases.

Advantages: