LANCASHIRE BOILER: CONSTRUCTION AND WORKING PRINCIPLE OF LANCASHIRE BOILER

Lancashire Boiler – Parts, Construction, Working, Advantages, Disadvantages, and Applications:

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.

(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:

1. Feed check valve
2. Water level indicator
3. Pressure gauge
4. Deadweight safety valve
5. Manhole
6. Blow-off cock
7. Anti-priming pipe
8. Steam stop valve
9. Fusible plug

Name of Mounting used in Lancashire Boiler:

1. Feed check valve - For filling water into the boiler
2. Water level indicator - For indicating the water level in the boiler
3. Pressure gauge - To read boiler pressure
4. Deadweight safety valve - For safety
5. Manhole - For periodic inspection
6. Blow-off cock - For taking out mud and other impurities.
7. Anti-priming pipe - To separate suspended moisture and allow the passage of dry saturated steam through the steam stop valve.
8. Steam stop valve - To stop or allow the flow of steam from the boiler.
9. Fusible plug - To stop firing if the water level falls below the safe level.

Related Article: Boiler Mountings and Functions

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 :

1. Due to large reservoir capacity, the load fluctuations can be easily be met by this boiler.
2. It is easy to clean and inspect and maintain.
3. The heating surface area/unit volume of the boiler is considerably large.
4. The availability of steam is high and maintenance costs are low.
5. It is reliable. Water capacity is high & priming is not required.
6. Its operation is easy. It has corrugated fire tubes & cross tubes.
7. The steam generation rate is high.

 Disadvantages :

1. Due to shell construction the maximum pressure is limited to about 20 bar.
2. More floor area is required due to brickwork settings.
3. Cracks in setting, due to large temperature differences inside and outside cause leakage.
4. Due to large water capacity, for developing more pressures, the boiler takes high time for required pressure.
5. Since the furnace is inside the tubes the grate area is restricted.
6. 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.

4. It is also used in marines.

Also Read: Cochran Boiler