Elements of MechanicalEngineering

COCHRAN BOILER & LANCASHIRE BOILER

Index:

Here _ words means hyperlink & cons. Means construction.

COCHRAN BOILER

General

It is one of the best types of vertical multi-tube type boiler. It is fire tube type boiler. It is popular portable boiler. It consist of very small floor area.

Specifications

Shell diameter = 2.75m

Height = 5.75m

Working pressure = 6.5bar(max = 15bar)

Steam capacity = 3500 kg/hr(max = 4000 kg/hr)

Heating surface area = 120 m²

Efficiency = 70% to 75%

Characteristics It is vertical. It is portable. It is a fire tube boiler. It’s multi tube boiler. It is internally fired. Solid as well as liquid fuel can be burnt. It has natural circulation. It’s low pressure boiler.

Construction & Working The boiler consist of a

cylindrical shell, hemispherical fire box, fire tubes & chimney.

The top of the shell having

hemispherical shaped crown. The hemispherical crown of boiler gives good strength to withstand pressure of steam inside the boiler.

The grate is placed at the bottom of furnace and ash pit is located below the grate.

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The furnace and the combustion chamber are connected by short flue pipe.

The wall of the combustion chamber is lined with the fire bricks.

The ash pit is located below the grate.

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Working The water is supplied to the boiler through feed

check valve. The coal is introduced to the grate through the fire

door. The hot gases produced from furnace enters

combustion chamber through flue pipe. This hot gases enters into horizontal fire tubes.

Convection heat transfer take place from flue gases passing inside the tubes to water surrounded the tubes.

The flue gases coming from of fire tubes enter into smoke box.

Finally they discharge to atmosphere through a chimney. The ash formed is collected in ash pit.

The steam is collected through antiprimming pipe on top of the shell.TOP

Mountings

Steam pressure gauge Water level indicator Dead weight safety valve Feed check valve Blow-off cock Steam stop valve Man hole Fusible plug Antipriming pipeTOP

Advantages

It is compact and portable boiler therefore minimum floor area is required.

Initial cost of boiler is less.

It can be moved and set up readily in different locations.

Quick and easy installation.

Any type of fuel can be used(coal or oil).

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Disadvantages

Steam raising capacity is less due to vertical design.

Water along with steam may enter the steam pipe under heavy load due to small steam space.

Efficiency is poor in smaller size.

Difficulty in cleaning and inspection due to vertical design.

The boiler require high head room.

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Lancashire Boiler

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General

It’s simple in design, easy to operate and less operating and maintenance cost. It’s one of the most commonly used stationary boilers. It’s normally used in sugar mills, textile industries where power generation as well as process heating is required.

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Specifications

Shell diameter = 2 to 3 m

Length of the shell = 7 to 9 m

Working pressure = 16 bar

Steam capacity = 9000 kg/hr

Efficiency = 50% to 70%

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Characteristics It is horizontal. It is stationary. It is a fire tube boiler. It’s multi tubes boiler. It is internally fired. It has natural circulation. Solid as well as liquid fuel can be burnt. It’s medium pressure boiler.

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Construction

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WorkingThe coal is introduced to the

grate through fire holes. The combustion of coal takes place in presence of air which is regulated by damper. The combustion will produce hot gases.

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Mountings

Steam pressure gauge Water level indicator Dead weight safety valve Feed check valve Blow-off cock Steam stop valve Low water & high steam safety valve Man hole Fusible plug Antipriming pipe

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Advantages

Due to three passes of flue gases , the heating surface area per unit volume of boiler is large.

The fluctuations in load can be easily met by this boiler due to large reservoir.

By use of economizer and superheater , maximum heat of flue gases is utilized, so efficiency of boiler can be increased.

Easy operation, low maintenance costs, easy to clean and inspect.

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Disadvantages

Maximum working pressure is limited to 16 bars.

Due to brick work, more floor area is required.

Response of pressure build up is less.

The furnace is inside the tubes therefore the grate area is restricted.

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Thank You

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