High Pressure Boiler : Powertherm Model
Before converting to steam, water circulates multiple times from shell (water drum) to water tubes and then back to shell. During the circulation, the temperature of water increases as it comes in indirect contact with flue gases that transfer heat through tubes.
Water circulation continues until it’s vapor pressure exceeds the vapor pressure of steam at the top of the drum. At this pressure, water gets converted to saturated steam.
Overall, Circulation Ratio is an important factor in designing of water tube boilers. Based on circulation there are 2 basic designs of water tube boilers: Natural Circulation Boilers and Forced Circulation Boilers
Natural Circulation Boilers are the type of boilers where water circulates naturally that is due to the density difference. The difference in density is created with the difference in temperature of cold and hot water. Circulation ratio is an important factor in designing of natural circulation boilers so as to prevent the overheating or bursting of tubes.