Circulation of water in the pipes/tubes in steam boiler is a very important thing to be designed. Boiler must be designed in such a way that avoided the formation of steam and out of the water wall tubes from steam drum. In other words, should not be going back-flow.
To get even warming on all parts of the boiler, especially in boiler water tubes, then the perfect water circulation must be maintained to prevent air bubbles and steam in the wall tubes and termination expenses of steam from tubes. The occurrence of bubbles on the wall tubes and the cessation of vaporization can lead to corrosion and salt concentrations which can damage the wall tubes.
The circulation of water and steam in the boiler occurs because:
1. Difference of density between water and steam.
2. The existence of mixture of water and steam.
The type of water circulation in the steam boiler can be classified into two types, namely:
- Natural Circulation
In this circulation, the water flowing from upper drums through downcomers which is located in the boiler is relatively cold, flow down to mud drum. From mud drum, water flow back into the steam drum after passing through the evaporator tubes.
- Forced circulation
In this forced circulation, fluid is pumped through the evaporator. This causes the boiler can work with very high pressures.