Lancashire Boiler: Definition, Parts, Operation, Merits, Demerits

Lancashire Boiler is a type of steam boiler with a double fire tube or furnace tube. It is a modified version of its Cornish counterpart with improved boiler efficiency, increased steaming quality, and performance in general. It is a stationary boiler.

It differs from the Cornish boiler with respect to the number of flue tubes: There are two flue tubes or furnace tubes in the Lancashire boiler compared to the Cornish boiler, which has just one.

It is labeled below with its front (a) and top (b) views.

front view and top view of Lancashire Boiler

It is a fire-tube stationary boiler in which hot gases or the products of the combustion pass through two furnace tubes surrounded by water, thereby boiling it by heat transfer and generating steam as a consequence, which is to be used for industrial applications such as for expanding in the steam engine or steam turbine for the production of useful work.

In its construction, it is a horizontal shell-type boiler with two flat ends as well as two side flues and one bottom flue formed by brickwork setting as shown.

The difference between the Cornish and the Lancashire boiler is also governed by the path traveled by the hot flue gases: The furnace gases emanate from the grate during the combustion process at the front end of the boiler, and from there they travel through two flue tubes to the rear end of the boiler.

Now, the gases dip down and, via. one bottom flue, return to the front end again. Finally, they split into two streams and pass through two side flues to exit at the back end of the boiler via. Chimney or stack into the atmosphere.

Lancashire boiler is sufficient to produce up to 10,000 kg of steam per hour and is designed to operate at pressures up to 13 bar.

Main Parts of the Lancashire Boiler

The main parts of the Lancashire boiler are mentioned below:

1. Shell

It is the horizontal cylinder or the main body of the Lancashire boiler (or any other shell-type steam boiler) which retains water and the furnace tubes. Its length usually varies between 8.5 to 12 meters. However, shell length may vary according to need.

2. Fire Tubes

There are two fire tubes or furnace tubes in the Lancashire boiler, which are located off-center of the shell center line. Combustion gases pass through these fire tubes and, by convection, transfer heat to the water, thereby elevating its thermal value up to the required temperature.

3. Furnace

It is positioned at one end of the boiler. Its prime purpose is to burn fuel, usually coal, and produce extremely hot gases that are directed to pass through the fire tubes to transfer heat to the water for the production of steam.

One of the added benefits of the Lancashire boiler is that it can run with moderate to low-quality fuels.

4. Grate

It is typically designed to be at the bottom of the furnace, similar to a Cornish boiler. It supports the combustion process by maximizing the oxidation of the coal to be burned in the furnace.

5. Ashpit

It collects the burned gas residue in the form of ash at the bottom of the grate, just like in the Cornish boiler. Special holes and doors are provided for cleaning and washing.

6. Combustion Chamber

Likewise, the Cornish boiler is the key area of the furnace in which actually the combustion of fuel takes place, as a result of which hot gases produced are destined to flow through the furnace tubes.

It is designed to be at the front end of the boiler next to the firebox.

7. Side Flue and Bottom Flue

There are two side flues and one bottom flue in the Lancashire boiler.

side view of Lancashire boiler

Combustion gases rise above the grate and collect at the trailing end of the boiler, having transferred heat to the water via. two fire tubes.

They continue to flow into the one bottom flue and, by passing through it, now accumulate at the front end of the boiler to pass through the two side flues and finally exit via. chimney into the atmosphere. It is shown in the figure above.

8. Galloway Tubes

These are the special tubes that are fitted with the furnace tubes in a criss-cross fashion, as shown in the figure above. Their purpose is to improve the flowability of the circulated water. Few of them are oriented vertically, while others are diagonal, as in the Cornish boiler.

Moreover, they permit the diversion or spread of the current of flue gases flowing in them with extended surface area for heat transfer and cause scrubbing action of the gases at the outer surface of the tube.

9. Water Space

It is an area within the boiler shell which stores water to be converted into steam. The water level in the water space is monitored continuously for the smooth operation of the cornish boiler with the help of glass indicators for visual inspection.

10. Safety Valve/s

As in the Cornish boiler, safety valves are the pressure relief valves for releasing excess pressure of steam that is gradually built up in the shell due to certain missed safety checks for preventing any explosions in case pressure goes off limits.

11. Chimney

Like any industrial boiler, flue gases leave the Lancashire boiler by passing through a vertical pipe called a chimney or stack. Its counterpart in the water-tube boiler is uptake.

12. Brick Arc

It serves to prevent the admission of ash into the shell tubes and miscellaneous internal parts of the boiler.

13. Blow-off Valve

As self-explanatory by its name, it is used to purify water-space from the impurities deposited over time by blowing water at high speed and driven by the steam flow. This valve is common in both boilers.

14. Water Level Indicator

It is a glass gauge indicator that is used to determine the water level in a drum or shell. According to the manufacturer’s design, two or three glass tubes are mounted at the outer casing of the Lancashire boiler. Internally, they are linked to the various shell positions to determine the actual water level.

As in the Cornish boiler, glass level indicators are programmed to turn the feed water pump on once the level of water drops dangerously low until it reaches the minimum design level. It is considered a safety feature of any boiler to prevent dry-firing as well as water over-filling conditions.

15. Feed Water Pump

It pumps water into the boiler via. external sources such as water tanks, lakes, and reservoirs for the steady generation of steam.

Operation

In principle, the operation of the Lancashire boiler is similar to that of the Cornish. The fuel, for instance, raw coal, is burned in the combustion chamber of the furnace.

As a result of the oxidation of the fuel or by firing coal, the hot gases thus produced in the chamber are directed to flow through two furnace tubes submerged in the water.

In the water space, due to heat transfer from the hot gases, the water converts into hot steam, which collects above the water space and is used to perform key operations such as rotating the shaft of the steam turbine for electricity generation and so forth. The hot gases then follow the route in flues, as explicitly mentioned above.

Merits

The merits of using a Lancashire boiler are mentioned below:

  • Robust and compact engineering design
  • Improved reliable operation compared with its Cornish counterpart
  • Easy preventive maintenance
  • Relatively higher steaming rate
  • Extended surface area for convention due to the addition of optimally fitted Galloway tubes with the furnace tubes
  • Ease of operation with the fluctuating loads (compatible with the variable steaming rates)
  • Fireable with multiple solid fuels: coal and others
  • Resilient in operation in harsh industrial environments due to its sturdier construction

Demerits

In industrial settings, there are certain demerits  of using Lancashire boilers, which are articulated below:

  • Relatively lower steam pressure compared with modern steam generators with the latest boiler technology used on the controls and instrumentation level
  • Large footprint, that is, more space-consuming
  • Relatively higher fuel consumption compared with its modern counterpart
  • Less adaptable with liquid or gaseous fuels
  • Though there is a large capacity for water, there is little room for circulation, especially between the furnace tubes and the bottom of the shell, thereby limiting the steaming capacity from cold water and fluctuating loads.
  • Expensive brickwork setting: higher capital investment and costlier repair maintenance
  • Congested grate area due to the large size of furnace or flue tubes
  • There is a higher risk of accidents or boiler explosion due to large heating surfaces as well as external flues.
  • Manually controlled operations and consequently less automation
  • Unfriendly from an environmental perspective due to coal-firing
  • Almost obsolete in modern industrial settings due to reasons aforementioned

Applications

They were used in the late nineteenth and early twentieth century. Its few applications were in:

  • Textile industry for running various textile operations, for instance, dyeing, weaving, and others
  • Paper industry for drying paper pulp
  • Food processing industry for cooking and other related operations 
  • Chemical industry for carrying out large-scale chemical processes 
  • Heating large buildings such as schools, hospitals, and others during cold weather 
  • The sugar industry drives various processes in sugar production, such as extraction,  evaporation, crystallization, and others.
  • Iron and Steel industry for executing processes such as metal forging, rolling, heat treatment process, and others

Modern Boilers as Stand-ins of Lancashire Boilers

Today, Lancashire boilers are almost obsolete in industrial settings owing to their low efficiency, less reliability, higher maintenance cost, reduced steaming rate, and so forth.

Modern boilers have replaced Lancashire boilers due to their radically improved adaptability with fluctuating steam demands, modernized data analytics, sync with cogeneration and combined heat and power systems, modular and compact shell design, fluidized bed combustion, and many others.