Steam boiler and its various types
Boiler feed water treatment
Water Tube Boiler
Water Tube Boiler
In this lesson, we will discuss the water tube boiler.
A water tube boiler is such a kind of boiler where the water is heated inside tubes and the hot gasses surround them. This is the basic definition of a water tube boiler. Actually, this boiler is just the opposite of a fire tube boiler where hot gasses are passed through tubes that are surrounded by water.
Advantages of Water Tube Boiler
There are many advantages of the water tube boiler due to which these types of boiler are essentially used in large thermal power stations.
- The larger heating surface can be achieved by using more numbers of water tubes.
- due to convectional flow, the movement of water is much faster than that of the fire tube boiler, hence the rate of heat transfer is high which results in higher efficiency.
- very high pressure in the order of 140 kg/cm2 can be obtained smoothly.
Working Principle of Water Tube Boiler
The working principle of a water tube boiler is very interesting and simple.
Let us draw a very basic diagram of a water tube boiler.
It consists of mainly two drums, one is an upper drum called steam drum other is a lower drum called mud drum.
These upper drums and lower drums are connected with two tubes namely down-comer and riser tubes as shown in the picture.
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 the upper drum and as this water is heavier than the hotter water of lower drum and that in the riser, the colder water pushes 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 results in a faster steam production rate.
In this way, the water tube boiler can control its own pressure. Hence this type of boiler is referred to as a self-controlled machine.
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