Lancashire Boiler – Parts, Construction, Working, Advantages, Disadvantages, and Applications:
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LANCASHIRE BOILER |
Specifications of the Lancashire boiler are as under:
Shell
diameter = 2 to 3 m (Most commonly used is 2.74 m)
Length of
the shell = 7 to 9 m (Most commonly used is 9 m)
Maximum
working pressure = 16 bar
Steam
generating capacity = 8000-9000 Kg/hr
Efficiency
= 50 to 70%
Characteristics
of the boiler :
1. It is
horizontal.
2. It is
stationary.
3. It is a fire-tube type.
4. It is
internally fired.
5. It is a
multi-tube boiler (has two fire or flue tubes).
6. It has a natural circulation of hot gases.
7. It burns
solid fuel.
8. It is a
medium pressure boiler.
Construction of Lancashire Boiler:
(1)
Boiler Shell: The boiler shell is made of steel plates. The steel plates are
of 10 mm to 12.5 mm in thickness. The plate is bent into a circular form and
then welded or riveted together
by lap joints. The cylinder is placed above the brick structure.
(2) Brick
structure: The brick structure provides for certain channels (known as flue
paths or flues). The flue gases flow through the channels in the required
direction. The channel made at the bottom of the shell is called bottom flue
and the sides are called side flues. Inside the boiler shell, two furnace tubes
are known as main flue pipes. They are placed longitudinally. These tubes are
approximately 1 m in diameter.
The diameter of these tubes is broader at the front end and at the rear end, they are tapered. The diameter is made broader at the front end in order to accommodate grate. The tapering at the end will increase the velocity of the hot gases coming out of the main flue pipes. All the space of the boiler shell surrounding these furnace tubes is filled with water.
The diameter of these tubes is broader at the front end and at the rear end, they are tapered. The diameter is made broader at the front end in order to accommodate grate. The tapering at the end will increase the velocity of the hot gases coming out of the main flue pipes. All the space of the boiler shell surrounding these furnace tubes is filled with water.
(3) Grate: At the front end of these furnace tubes, two grates are provided. The coal is
placed on the grates and then burnt. The coal is added to the grate through two
fire holes.
(4) Fire
brick Arch: At the end of each grate, a fire brick arch is built to reflect
the path of the hot gases so that they pass through the horizontal main flue
tubes. This arch also stops the entry of any un-burnt coal or ashes into the fire tubes.
(5)
Dampers and Damper doors: The dampers and damper doors are placed at the
beginning and at the end of the fire tubes. The dampers control the air
entering the joint and damper doors control it at the rear. The dampers and
damper doors can be operated by a chain from outside. The hot gases after passing
through various passages, discharge to a chimney.
Mountings
of the boiler :
The
following mountings are fitted on this boiler:
- Feed check valve
- Water level indicator
- Pressure gauge
- Deadweight safety valve
- Manhole
- Blow-off cock
- Anti-priming pipe
- Steam stop valve
- Fusible plug
Name of Mounting used in Lancashire Boiler:
- Feed check valve - For filling water into the boiler
- Water level indicator - For indicating the water level in the boiler
- Pressure gauge - To read boiler pressure
- Deadweight safety valve - For safety
- Manhole - For periodic inspection
- Blow-off cock - For taking out mud and other impurities.
- Anti-priming pipe - To separate suspended moisture and allow the passage of dry saturated steam through the steam stop valve.
- Steam stop valve - To stop or allow the flow of steam from the boiler.
- Fusible plug - To stop firing if the water level falls below the safe level.
Working of Lancashire Boiler:
The water
is fed into the boiler shell through the feed-check valve. The level of the
water is adjusted with the help of a water level indicator. Coal is added to the
grate through the fire hole. The coal is then burnt. The position of the damper is
adjusted in such a way that the necessary air required for combustion of the
coal will be supplied. The combustion will produce hot gases. They move along
the main flue tubes.
They are
deflected by the fire brick arch. They are made to pass all among the length of
the main flue (MF) tubes. At the back of the main flues, they have deflected again and made to pass through the bottom flue (BF) of the boiler. At the front
side of the boiler shell, the gases in the bottom flue are divided into two side
flues (SF) and sent back. From the side flues, the gases enter the smokebox
and then finally go to the chimney. The path of the gas is shown in the figure.
The gases
passing through the main flues heat the water in the boiler centrally, from
below (bottom flues) from the side (side flues) and thus transferring maximum heat
to the water. The water is then converted into steam. The steam is collected in
the steam collecting pipe from where it can be taken out for further use with
the help of a steam stop valve. If superheated steam is required then a
super-heater unit is arranged with the boiler.
Application of Lancashire Boiler:
This type
of boilers are used in sugar mills and textile industries where the steam is
required for power generation as well as for the process work. This boiler is
also used in chemical industries.
Advantages
and Disadvantages of Lancashire Boiler:
Advantages
:
- Due to large reservoir capacity, the load fluctuations can be easily be met by this boiler.
- It is easy to clean and inspect and maintain.
- The heating surface area/unit volume of the boiler is considerably large.
- The availability of steam is high and maintenance costs are low.
- It is reliable. Water capacity is high & priming is not required.
- Its operation is easy. It has corrugated fire tubes & cross tubes.
- The steam generation rate is high.
Disadvantages
:
- Due to shell construction the maximum pressure is limited to about 20 bar.
- More floor area is required due to brickwork settings.
- Cracks in setting, due to large temperature differences inside and outside cause leakage.
- Due to large water capacity, for developing more pressures, the boiler takes high time for required pressure.
- Since the furnace is inside the tubes the grate area is restricted.
- Heat energy loss occurs due to cracks in the brick setting.
Applications of Lancashire Boiler:
1. It is used in locomotives
2. It is commonly used to drive
steam turbines.
3. It also employed in sugar mills,
textile mills, etc.
LANCASHIRE BOILER: CONSTRUCTION AND WORKING PRINCIPLE OF LANCASHIRE BOILER
Reviewed by Harish
on
August 13, 2020
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