Cochran Boiler | Cochran Boiler Construction, Types and Working

The boilers are used for generating steam. This generated steam is used for different purposes. The popularity of the boilers is increasing day by day because of their excellent functionality. The boilers have different types that are designed according to different applications, and the Cochran boiler is one of them. The Cochran boiler is a type of fire tube boiler. This article mainly describes the different aspects of the Cochran boiler. 

What is a Cochran Boiler? 

Types of Pipes | Classification of ...
Types of Pipes | Classification of Pipes (PDF)

The Cochran boiler is a solid fuel-fired, multi-tubular, low pressure, natural draft, natural circulation, vertical drum shaft, fire tube boiler. It has an internally fired furnace.

Cochran boiler

This type of boiler is an improved version of the simple vertical boiler. It has fire tubes in the horizontal direction.  It has higher efficiency than the efficiency of a simple vertical boiler.

The Cochran boilers are available in different evaporation capacities (i.e., from 140 to 3100 kg/hour) and up to 15 bar working pressure.

In the construction of the Cochran boiler, there is a combustion chamber, grate, fire door, and a cylindrical outer shell. The combustion chamber and shell have a hemispherical shape.  The hemispherical crown of the shell provides the utmost area and intensity to survive the steam pressure. The combustion chamber’s hemispherical crown helps to withstand against high heat.

The combustion chamber and the firebox are linked by a short pipe. A series of tubes are used to move the flue gases from the combustion chamber into the smokebox. As the gases pass by the smokebox, they enter the chimney from where they go into the atmosphere.

The boiler has a manhole used for the boiler cleaning. A grate is located at the bottom of the combustion chamber, which uses to fed the coal in the combustion chamber.  

Cochran Boiler Working Principle

The working of the Cochran boiler is the same as other types of boilers. A Cochran boiler works in the following way:

Cochran Boiler Working

  • First of all, the coal fuel is placed on the grate via a firebox.
  • The air introduces into the furnace.
  • A spark of fire is provided to the coal via a fire hole.
  • As the coal receives fire spark in the presence of air, the fuel combustion process starts.
  • Due to the combustion of fuel, heat produces inside the furnace, which is transferred to the flue gases.
  • As the flue gases get heat, their temperature increases, and they start flowing from the furnace into the combustion chamber (or burner) through a flue pipe.
  • When the hot flue gases reach into the combustion chamber, they go into the fire tubes. The boiler water surrounds to these fire tubes.
  • The hot flue gases transfer their heat to the fire tube, which is further transferred to the water.
  • The heat transfer process occurs due to the thermal consuction process.
  • As the water receives heat, its temperature increases; due to that, it converts into steam.
  • The yielded steam starts rising in an upward direction which is stored in the hemispherical dome.
  • The Cochran boilerhas an anti-priming pipe. This pipe uses to separate the steam from the wet steam and convert it into dry form.
  • The dry steam uses to drive the steam turbine, and the flow of steam is controlled via a steam stop valve. As the steam strikes the turbine blades, the blades start rotating, which further rotates the generator coal and produces electricity. The steam turbine operates according to the Rankine cycle.
  • During the coal combustion process into the boiler furnace, the smoke and hot gasses are released. After exchanging the heat of the hot gases, the smoke and useless hot gases are sent into the smokebox, from where they are discharged into the atmosphere via a chimney.
  • There is also an ash pit used to collect the ash of the burnt fuel.

Fow a better understanding, watch the following video:

Read More: Working and Construction of Locomotive Boiler

Components of Cochran Boiler

The Cochran boiler has the following components:

  1. Boiler Shell
  2. Combustion Chamber
  3. Safety Valve
  4. Flue Pipe
  5. Grate
  6. Fire Door
  7. Fire Tubes
  8. Chimney
  9.  Manhole
  10. Stop Valve
  11. Feed Pump
  12. Water Level Indicator
  13. Feed Check Valve
  14. Pressure Gauge

Cochran boiler components

1) Boiler Shell

The boiler shell has a cylindrical shape which is constructed of steel plates. It has an adequate space to contain the steam and water. All the internal parts of the Cochran boiler are located inside the shell. It ensures the safety of all internal parts due to any external load.

2) Combustion Chamber

A combustion chamber or furnace uses to burn the fuel. The solid fuel introduces from the outside into the combustion chamber. It burns the fuel due to that heat is produced. This produced heat is supplied to the flue gases, which further heats the water and generates steam.

Read Also: Different types of Fire Tube Boilers

3) Grate

The grate acts as a door used to place the fuel. It is made of iron bars. It is divided into sections, and each section has 3 to 4 bars.  These bars have space for airflow. This air uses for the burning process of the combustion chamber. The area where the combustion process occurs is known as a great surface.

4) Fire Door

This component of the boiler uses to introduce fire into the combustion chamber for starting the combustion process.

5) Fire Tubes

The fire tubes are installed horizontally between the furnace. As the flue gases get heat from the combusted fuel, they start flowing inside the fire tubes. The water is flowing outside the fire tubes.

These tubes get heat from the flue gases and transfer it to the outer water and convert it into steam. These tubes are also used to move the useless flue gases from the furnace to the smokebox.

Read Also: Different types of Boilers

6) Chimney

It is located on the top of the boiler. This component of the boiler links with the smokebox. It uses to remove the waste flue gases into the atmosphere. The waste gases firstly go into the smokebox via fire tubes. After passing through the smokebox, it enters the chimney from where it discharges.

 7) Manhole

As the name represents, it is a hole through which a person can easily enter into the boiler to repair, change, or clean the different parts of the Cochran boiler.

8) Flue Pipe

The flue pipe connects with the burner and firebox of the boiler. This pipe uses to flow the hot flue gases from the grate into the burner.

 9) Water Level Indicator

A water level indicator is the most important component of the boiler. It indicates the water level inside the boiler. It ensures the safe operation of the Cochran boiler. The water level indicator has different marks which indicate the water level.

10) Pressure Gauge

It shows the steam pressure inside the boiler. It installs in the boiler front.

11) Safety Valve

This valve uses to prevent the boiler from explosion due to excess steam pressure. As the steam pressure inside the boiler increases, the safety valve opens and removes the extra steam. In this way, it ensures the safety of the boiler.

Read Also: Different types of Valves

12) Feed Check Valve

It is a one-way valve. It uses to regulate the water flow from the feed pump to the boiler. The check valve forces the water to flow in only one direction. In this way, this valve stops the backflow of the water.

This valve is used because when you turn off the feed pump, the water starts moving backward from the boiler to the feed pump, and a check valve uses to stop backflow.

13) Feed Pump

This pump is used to transfer the water from the reservoir to the Cochran boiler. There are different types of feed pumps such as centrifugal pump, reciprocating pump, plunger pump, diaphragm pump, gear pump, etc.

Read More: Different types of Pumps

14) Stop Valve

The main purpose of the stop valve is to control or completely stop the flow of water or steam according to requirements.

Advantages and Disadvantages of Cochran Boiler

The Cochran boiler has the following advantages and disadvantages:

Advantages of Cochran Boiler

  • It has a low installation cost.
  • This type of boiler has a small size
  • It has an easy operation.
  • The Cochran boiler needs less floor area for installation.
  • These boilers can use all types of fuels.
  • You can easily transport it from one place to another.
  • This boiler has a high volume to area ratio.

Cochran Boiler Disadvantages

  • This boiler has a low steam generation rate.
  • It can generate steam pressure up to a limited range.
  • This boiler requires high room in a vertical direction for installation.
  • It has difficult maintenance and inspection.

 Cochran Boiler Application

The main applications of Cochran Boiler are:

  • These fire-tube boilers are used in many refinery units.
  • These are used in small hydropower plants.
  • These are used for chemical processing units.
  • The Cochran boiler also uses for paper manufacturing units.

 Cochran Boiler Specification

The Cochran Boiler has the following Specification:

  • This boiler has up to 75% efficiency.
  • It has working pressure from 7 to 15 bar.
  • This boiler has a 120 square meter heating surface.
  • The height of the boiler is 5.75 m, and the shell diameter is 2.76 m.

FAQ Section

Who Invented the Cochran Boiler?

Mr. Edward Crompton was designed the first Cochran boiler.

How Cochran boiler works?

In a Cochran boiler, sold fuel is placed on the grate of the furnace. The atmospheric air introduces into the furnace from the atmosphere. The fire hole uses to introduce fire into the furnace.

When the fuel-burning process starts, the heat rejects from the fuel, which transfers to the flue gases. After getting heat, the flue gases move into the fire tubes, which further heats the water. Due to increasing water temperature, the water transforms into steam. In this way, a Cochran boiler works.

How many number of Fire tubes are in a Cochran Boiler?

The Cochran boiler has 165 fire tubes.

Read More
  1. Types of Boilers
  2. Different types of Fire-tube Boilers
  3. Working of Locomotive Boiler
  4. Working of Lancashire Boiler

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