There are mainly two types of industry boilers – there are water tube boiler and fire tube boiler if divided from inner structure.These are the main two types of boiler but each of the types can be sub divided into many different types of boiler.
In fire tube boiler, there are numbers of tubes through which hot gases are passed and water surrounds these tubes.
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 shell contains 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.
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.A water tube boiler is such kind of boiler where the water is heated inside tubes and the hot gasses surround them.
This is the basic definition of water tube boiler. Actually this boiler is just opposite of fire tube boiler where hot gasses are passed through tubes which are surrounded by water.