What is Scotch Marine Boiler?- Parts, And Working

What is Scotch Marine Boiler?

“Scotch” marine boiler (or simply Scotch boiler) is a design of steam boiler best known for its use on ships.

The general layout is that of a squat horizontal cylinder. One or more large cylindrical furnaces are in the lower part of the boiler shell. Above this are many small-diameter fire tubes. Gases and smoke from the furnace pass to the back of the boiler, then return through the small tubes and up and out of the chimney. The ends of these multiple tubes are capped by a smokebox, outside the boiler shell.

The Scotch boiler is a fire-tube boiler, in that hot flue gases pass through tubes set within a tank of water. As such, it is a descendant of the earlier Lancashire boiler, and like the Lancashire, it uses multiple separate furnaces to give greater heating area for a given furnace capacity.

It differs from the Lancashire in two respects: many small-diameter tubes typically 3 or 4 inches (76.2 or 101.6 mm) diameter each are used to increase the ratio of heating area to cross-section. Secondly, the overall length of the boiler is halved by folding the gas path back on itself.

Parts of a Scotch Marine Boiler

The following are important construction parts of Scotch marine boiler:

Engineering Choice The Biggest Learning Platform
  1. Furnace: It is the space, above the grate and below the boiler, It is employed to burn solid fuel inside the boiler. A single-ended boiler is fired with four furnaces. The furnaces are usually corrugated for strength. In type this boiler, each furnace has its own combustion chamber.
  2. Combustion Chamber: It is the space, commonly below the boiler shell, meant for burning fuel in order to generate steam from the water held in the shell. The combustion chamber consists of fine plates, which need to be staying i.e., top plate, backplate, two side plates and tube plate.
  3. Smoke Box: The smoking box has several smoke tubes placed horizontally and attaches the combustion chamber to the chimney. The smoke passes through these smoke tubes and eventually enters into the chimney.
  4. Chimney: The chimney It is used to drain out the smoke and burnt gases from the boiler. The flue gases are released into the atmosphere by means of the chimney.
  5. Boiler Shell: It is made up of steel plates bent into a cylindrical form and riveted or welded together. The boiler shell should have enough ability to contain water and steam. This protects the inner parts of the boiler. All the necessary fittings of the boiler are adjusted on the boiler shell.

Construction of Scotch Marine Boiler

This boiler consists of some basic components like another boiler. I am going to give you more details about each element. If I missed any of it then please let me know in a comment.

First of all, it’s Furnace, and like other boilers, it used to burn the fuel inside the boiler. We already know that a single-ended scotch marine boiler is fired with four furnaces. But each of the furnaces has its own combustion chamber with it.

Now come to another component which is a combustion chamber. It is one of the parts of the boiler where the fuel combustion normally takes place. You will also find plates in the combustion chamber. 

It requires staying the top plate, backplate, two side plates, and the tube plate. There are some smokes tubes placed horizontally. All those smoked tubes connect the combustion chamber to the chimney.

The next component is the smokebox. This boiler has a number of smoke tubes. We already know that all are tubes placed horizontally and connect each other from the combustion chamber to the chimney. After fuel combustion, burned smoke passes through smokes tubes, and then it enters the chimney.

Like others, a boiler Chimney is used to exhaust the burned gases and smoke out of the boiler during operation. Exhaust gases release into the environment by the chimney. Another important component is the Boiler shell.

scotch marine boiler

Working of Scotch Marine Boiler

Water is surrounded by the tube. The heat generated is much high and due to that, even the tube gets hot. Due to the heated tubes, the water starts getting heated and its phase is 1st water to saturated steam and saturated steam to superheated steam.

Working on the boiler is very simple. It will take the fuel, burn it in the combustion chamber and water will be heated. After then heated water becomes steam. For this reason, at first, fuel is inserted into the furnace. The fuel passes through the furnace by a fire hole.

When there is fuel in the furnace then it ignites through the fire hole. After that burnt fuel enters the combustion chamber and this is the place where the combustion of the fuel takes place. Now come to the heat transfer procedure.

When the heat is generated into the combustion chamber then it is used to heat the water surrounding the combustion chamber. Again, it is the basic heat transfer procedure for a regular fire tube boiler.

When water becomes steam, then it supplies to the steam turbine. Here we have some burnt flue gases and smoke that are created during the fuel combustion procedure and it needs to release into the environment. For this step, the exhaust gases pass through the smoke tubes and reach the boiler chimney.

Then the chimney releases all smoke and exhaust gases into the atmosphere. In this boiler, water uses to surround the furnace, combustion chamber, and smoke tubes. For this reason, it provides a greater heating surface to the water during boiler operation.

Types of Scotch Marine Boiler

There are two main types of Scotch Marine Boilers:

  • Single Finished Scotch Marine Boiler.
  • Double Ended Scotch Marine Boiler.

1. Single Finished Scotch Marine Boiler

This boiler consists of a circular boiler shell of a large diameter and a short length. Single-end Scotch boilers have a distance of up to 3.5 meters. It consists of one to four furnaces, and these furnaces enter from the front end of the boiler. The Scotch boiler was a very common marine boiler used in steamships in many countries.

  • Single-end steam boilers can have a length of up to 3.5 meters.
  • Single-end steam boilers consist of one to four furnaces, and these furnaces enter from the front end of the boiler.

2. Double Ended Scotch Marine Boiler

Older double-ended Scotch Marine boilers typically had vertical Galloway tubes manufactured in the combustion chamber. They were meant to promote the circulation of water in the boiler and thus contribute to reducing stresses in the material.

  • A double-ended steam boiler has a length of up to 6.5 meters.
  • In double-end Scotch Marine boilers, the furnaces are present at both ends of them. And the numbers of furnaces vary from 2 to 4 at each end.

Advantages of Scotch marine boiler

  • The size of the boiler is not so big comparatively another boiler.
  • The boiler efficiency is great.
  • A cost-effective boiler.
  • It can generate steam with the use of any type of water which is a major advantage.

Disadvantages of Scotch Marine Boiler

  • It cannot be used for large plants. Used for limited or small plants
  • This is a fire tube boiler so the steam formation or generation quality is not much good comparatively water tube boiler.
  • For output, more floor area is required.
  • Load variation cannot be controlled easily.

Application of scotch marine boiler

  • It is used at marine works.
  • Or we can say it is used on ships.