Steam Generators

2 Types of Boiler - Fire Tube Boiler

Types of Boiler

There are mainly two types of boiler – water tube boiler and fire tube boiler.

In fire tube boiler, there are numbers of tubes through which hot gases are passed and water surrounds these tubes.
Water tube boiler is reverse of the fire tube boiler. In water tube boiler the water is heated inside tubes and hot gasses surround these tubes.

These are the main two types of boiler but each of the types can be sub divided into many which we will discuss later.

Fire Tube Boiler

As it indicated from the name, the fire tube boiler consists of numbers of tubes through which hot gasses are passed. These hot gas tubes are immersed into water, in a closed vessel. Actually in fire tube boiler one closed vessel or shellcontains water, through which hot tubes are passed. These fire tubes or hot gas tubes heated up the water and convert the water into steam and the steam remains in same vessel. As the water and steam both are in same vessel a fire tube boiler cannot produce steam at very high pressure. Generally it can produce maximum 17.5 kg/cm2 and with a capacity of 9 Metric Ton of steam per hour.

Types of Fire Tube Boiler

There are different types of fire tube boiler likewise, external furnace and internal furnace fire tube boiler.
External furnace boiler can be again categorized into three different types-

1) Horizontal Return Tubular Boiler.

2) Short Fire Box Boiler.

3) Compact Boiler.

Again, internal furnace fire tube boiler has also two main categories such as horizontal tubular and vertical tubular fire tube boiler.

Normally horizontal return fire tube boiler is used in thermal power plant of low capacity. It consists of a horizontal drum into which there are numbers of horizontal tubes. These tubes are submerged in water. The fuel (normally coal) burnt below these horizontal drum and the combustible gasses move to the rear from where they enter into fire tubes and travel towards the front into the smoke box. During this travel of gasses in tubes, they transfer their heat into the water and steam bubbles come up. As steam is produced, the pressure of the boiler developed, in that closed vessel.

Advantages of Fire Tube Boiler

1) It is quite compact in construction.

2) Fluctuation of steam demand can be met easily.

3) It is also quite cheap.

Disadvantages of Fire Tube Boiler

1) As the water required for operation of the boiler is quite large, it requires long time for rising steam at desired pressure.

2) As the water and steam are in same vessel the very high pressure of steam is not possible.

3) The steam received from fire tube boiler is not very dry.