Water Tube Boiler

Water Tube Boiler:

    ➥ A water tube boiler is such kind of a boiler, where the water is heated inside the tubes and the hot gases surrounded them. 
    ➥ It is the opposite of Fire tube boiler, where hot gasses are passed through the tubes which are surrounded by water. 

Working Principle of Water tube boiler:

    ➥ The working principle of water tube boiler is very simple. 
    ➥ It consists of mainly two drums, one is upper drum called steam drum and other is lower drum called mud drum. 
    ➥ These upper drum and lower drum are connected with two tubes namely down-comer and riser tubes as shown in the figure.
Water Tube Boiler
    ➥ Water in the lower drum and in the riser connected to it, is heated and steam is produced in them which comes to the upper drums naturally. 
    ➥ In the upper drum the steam is separated from water naturally and stored above the water surface. 
    ➥ The colder water is fed from feed water inlet at upper drum and as this water is heavier than the hotter water of lower drum and that in the riser, the colder water push the hotter water upwards through the riser. 
    ➥ So there is one convectional flow of water in the boiler system.
    ➥ More and more steam is produced the pressure of the closed system increases which obstructs this convectional flow of water and hence rate production of steam becomes slower proportionately. 
    ➥ Again if the steam is taken trough steam outlet, the pressure inside the system falls and consequently the convectional flow of water becomes faster which result in faster steam production rate. 
    ➥ In this way the water tube boiler can control its own pressure.
    ➥ Hence this type of boiler is referred as self controlled machine.

Types of Water Tube Boiler:

    ◨ Babcock & Wilcox boiler

    ◨ Stirling boiler
    ◨ La-Mont boiler
    ◨ Benson boiler
    ◨ Yarrow boiler
    ◨ Loeffler boiler

Advantage of Water tube boiler:

There are many advantages of water tube boiler due to which these types of boiler are essentially used in large thermal power station.

    ⚬ Larger heating surface can be achieved by using more numbers of water tubes.
    ⚬ Due to convectional flow, movement of water is much faster than that of fire tube boiler, hence rate of heat transfer is high which results into higher efficiency.
    ⚬ Very high pressure in order of 140 kg/cm2 can be obtained smoothly.

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