Steam-Water Circulation in Boilers

Abstract

Circulation refers here to the flow of water, steam, or their mixture around the steam—water circuit in a boiler. In early days of boilers, steam was generated in a large vessel. The vessel was heated from outside, which would create a convective current within the large body of water. This process did not pose any threat to the safety of the boiler. So a detailed knowledge of steam—water circulation or flow pattern was not important. Modern water tube boilers, on the other hand, are subjected to increasingly higher levels of heat flux, temperature, and pressure. So the designers can no longer ignore the process of circulation of water and steam in the boilers. Inadequate circulation of water would fail to remove heat from the tube surface at a sufficient rate, which may lead to increased tube wall temperature. The allowable stress of the metal reduces with increasing metal temperature. In an extreme case the tube may rupture. An adequate circulation of steam—water is also essential for proper separation of steam from water. Without a good circulation the quality of steam would suffer.