They are popularly known as Shell boilers since in these boilers all the surfaces contributing towards heat transfer are enclosed inside a shell made up of steel. They can be also called as Smoke tube boilers. As the name suggests, in Fire Tube Boiler systems, the hot exhaust gases emanating out of combustion reaction are passed through the boiler tubes. These tubes are in turn surrounded by the water which needs to be heated. Heat is then transferred to the circulating water via the hot gases produced by the burner. In firetube boilers, the combustion gases pass inside boiler tubes, and heat is transferred to water on the shell side. In this way the water gets converted into steam for utilization into various process applications. The most widely used boilers for industrial applications are Scotch marine boilers.
Scotch Marine Boiler
Scotch marine boilers are typically cylindrical shells with horizontal tubes configured such that the exhaust gases pass through these tubes, transferring energy to boiler water on the shell side.
This type of fire tube boiler is considered to be an industry workhorse owing to its several advantages. Most common of them include:
- They are highly proficient and strong.
- Their use proves to be very economical because they involve very low initial price.
- These types of boilers usually hold quite huge quantities of water due to which they are capable of retorting to load changes occurring with reasonably small variations in pressure.
However, this category of boilers suffers from few limitations too which are listed below:
- Since, these types of boilers consist of large amount of water; they consume somewhat extra time to set off steaming operation and put up with variations occurring in steam pressure.
- In these types of boilers steam generation takes place in the shell portion which offers a big surface area. Due to this fact, the quantity of pressure generation tends to be less.
- Typically, the use of Scotch marine boilers is not recommended in areas requiring high pressures (normally beyond 300 psig).
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