DEPARTMENT OF MECHANICAL ENGINEERING

STEAM ENGINES LABORATORY

Object: To study the working and construction of a Lancashire Boiler .

BOILERS (introduction):-

A closed metallic vessel in which the water is heated beyond the boiling temperature by the application of heat by the combustion of fuels to convert it into steam. The function of the boiler is to supply the steam at constant pressure with desired quality by maintaining the steam generation rate and the steam flow rate equal.

Classification of Boiler:

Based upon relative position of water and flue gas (hot gas) carrying tubes,1) Fire tube boiler 2)Water tube boiler

Based upon location of furnace,1) Externally fired boiler 2) Internally fired boiler

Based upon method of water circulation,1) Natural circulation 2)Forced circulation

Based upon direction of principle axis of the shell,1) Horizontal axis boiler 2)Vertical axis boiler 3) Inclined axis boiler

Based upon pressure of the steam produced,1) High pressure boiler 2)Low pressure boiler

Based upon usage,1) Stationary boiler 2) Portable boiler 3) Locomotive boiler 4) Marine boiler

Fire tube Boiler:In the fire tube boiler, the hot gases produced by the combustion of fuel are passed through tubes around which the water circulates as shown in the figure 1Example: Lancashire boiler, Cornish boiler.

Water tube Boiler:In water tube boiler, the water circulates inside the tubes while hot gases produced by the combustion of fuel flows around the water tubes externally as shown in the figure 2

Example: Babcock and Wilcox boiler, Stirling boiler.

Comparison of Fire tube and Water tube boiler:

Description Water tube Fire tube

1 Passage of hot gases and water circulation

Here water circulates through the tubes and the hot flue gases surround them externally

Here the hot flue gases passes through tubes which are surrounded by water circulation

2 Position of furnace Furnace is situated outside the boiler

Furnace is situated within the boiler

LANCASHIRE BOILER

Lancashire Boiler is a fire tube, internally fired, horizontal smoke tube boiler. The size of the boiler ranges from a shell 2m. dia.× 6m. long to 3m. dia. × 10 m. long. The working pressure are up to 19.6 bar. Though the general range is from 6.86 – 14.7 bar. The ratio of heating surface to grate area varies from 24 – 30.

Figure 1 Fire Tube Boiler Figure 2 Water Tube Boiler

History:

It is generally considered to be the invention of William Fairbairnin 1844, although his patent was for the method of firing the furnaces alternately, so as to reduce smoke, rather than the boiler itself. The Lancashire boiler is similar to the Cornish, but has two large flues containing the fires instead of one. His Lancashire boiler had twin furnace tubes side-by-side, which gave it a much larger heating surface than that of the Cornish boiler.

Usage: The boiler is very popular due to its reliability, simplicity of design, ease of operation and

less operating and maintenance cost. Commonly used in sugar mills and textile industries, where along with the power steam for

the process is also needed. In addition, this boiler is used where larger reserve of water and steam are needed.Advantages & disadvantage One of the disadvantages of the Lancashire boiler was that repeated heating and cooling

of the boiler, with the resultant expansion and contraction that occurred, upset the brickwork setting and ducting. This resulted in the infiltration of air, which upset the furnace draught. 

Conical shaped cross tubes known as Galloway tubes present in the Lancashire Boiler, may be fitted inside the furnace tubes to increase their heating surfaces and circulation of water. But these tubes are now become obsolete for their considerable cost of fitting.

These boilers would now be very expensive to produce, due to the large amounts of material used and the labour required to build the brick setting.

Construction details(as per the model):1. Boiler Shell 12. Main Steam Supply to Engines2. Furnace Tubes 13.Combined Low Water Alarm and Second3. Furnace Doors Safety Valve4. Fire Bars 14.Boiler Inspection Manhole5. Bridge & Bridge Plate 15.Furnace Damper Mechanism6. Cross Water Tubes 16.Boiler Feed Water Supply7. Lever Safety Valve 17.Boiler Blow Down Valve8. Chemical Dosing Pot 18.Blow Down Pit9. Return Leg from Engine 19.Sole Flue Cylinder Jackets Heating 20.Side Flue Circuit. 10. Main Steam Valve 21.Main Flue to Chimney11. Steam Receiver 22.Arrows indicating path of Flue Gases

Figure 3 Side & Front views of Lancashire boiler

Figure 4 Installed Lancashire Boiler ( look at the brick work)

Working:

Several rings of steel plates are either welded or riveted to make the cylindrical shell of sustainable dimensions. The boiler has two parallel flues, which run throughout the entire length of the horizontal shell of the boiler. The flue tubes built in short lengths are flanged. Further to reduce the internal amount of internal bracing, the flue tubes are sometimes corrugated. To accommodate a grate of sufficient area and minimum length, the flue tubes are larger in diameter at the front of the shell.

Each of the flue tubes has its own furnace with grate arranged at the front end of the shell. Through the fire door, the coal is fed to the grates where its combustion takes place. The flue gases rising from the furnace pass over the fire-bridge and transverse over the horizontal path. At the rear end the gases enter the bottom common flue, travel backwards to near front of the boiler where they bifurcate and pass into two side flues.

Thereafter the gases into two streams enter the main flue and are finally discharged to the atmosphere through the chimney.

The need to produce the gas flow and to control the amount of air entering the grate is regulated by dampers, which are placed in the path of the flue gas. These dampers are operated by means of chains passing over the pulleys to the front of boiler.Openings are in the boiler for inspection, steam exit and for necessary mountings and accessories.

Questions:

1. What is a Boiler? Describe common applications.2. How are Boilers classified?3. Give common differences b/w Fire Tube and Water Tube boilers.4. Describe the common features of a Lancashire Boiler.5. Write down the common usage of a Lancashire Boiler. Also write down the disadvantages.6. Draw the diagram of a Lancashire Boiler showing the different components.7. Draw the diagram of a Lancashire Boiler showing its working.8. Describe the working of the Lancashire Boiler.