Numerical Simulation Research On Flow Distribution Of Utility Boiler Tee-Junction Header System

In large utility boilers, tube rupture, which is caused by overheating from thermal deviations, often occurs in the complex system of superheaters and reheaters. Unreasonable flow distribution is one of the major causes for this phenomenon. In order to avoid tube rupture, it is quite necessary to eliminate safety incipient faults due to unreasonable flow distribution and to improve the reliability and economy of the superheating and reheating systems. Reasonable flow distribution in Tee-junction header system should be assured when superheaters and reheaters are designed. The assurance comes from the accurate understanding of static pressure distribution in Tee-junction system, and of the influence of back flow areas near Tee-junction on flow distribution. As to the radial leading-in and leading-out Tee-junction, the flow distribution is greatly influenced by the existence of back flow areas near Tee-junction. The importance of this kind of influence is often ignored by available calculation methods of flow distribution.In this paper, numerical simulation was adopted for the radial leading-in and leading-out Tee-junction headers of superheaters and reheaters in utility boiler. Static pressure distribution features, flow mechanics, influence of flow patterns near Tee-junction areas on flow distribution, and static pressure distribution on bus bars were analyzed using FLUENT for the radial leading-in and leading-out Tee-junction structure under stable working conditions.The numerical simulation research on radial leading-in and leading-out Tee-junction indicates that there was an abrupt change of flow field near Tee-junction. Three back flow areas existed obviously, all of which determine the influence pattern of Tee-junction effect. The influenced areas of back flow were within 2D (D is the diameter of the radial leading-in tube). For those areas far away from Tee-junction structures, steam flow becomes stable gradually. The research results indicates that Tee-junction effect of Tee-junction structures is a common phenomenon, however, the range of Tee-junction effect influence is limited. The strength of the influence is related to Tee-junction structure patterns. By reasonable improvement of Tee-junction structures, the influence of back flow areas near Tee-junction structures on flow distribution could be weakened. Two ways to improve the Tee-junction structures---spherical Tee-junction structures and arc Tee-junction structures are presented. The flow features of the two Tee-junction structure patterns were researched and the results demonstrate that both of the two improved Tee-junction structures could greatly optimize the flow fields near Tee-junction structures and the influence of back flow areas on flow distribution. The two improved Tee-junction structures have great practical application values.