CFD study of using a tube insert and an air blowing system to prevent tube failure in the Bisotoun Power Plant boiler

In this study attempts to find a theoretical solution to prevent tube explosion of the tubes placed in the superheater region of the Bisotoun Power Plant boiler, Iran. The boiler has three types of tube and the tube failure was occurred in the long length type of these tubes. A three dimensional Computational Fluid Dynamics (CFD) modeling was carried out for this purpose. The result of modeling of the boiler shows that the long tubes are working in a temperature higher than the designed value. In the present work in order to solve this problem, two different ways was proposed and theoretically investigated. Using of a tube insert in the tube for heat transfer enhancement which increases the cooling performance of the steam inside the tube was the first one. The ability of the tube insert to increasing the heat transfer coefficient and reducing the tube wall temperature was observed from the CFD modeling. However, this way was not accepted due to probability of separating a part of the welded parts and the consequent danger of the steam turbine placed after the boiler in the plant layout. Using the air blowing system which locally cools the tube in the placed of explosion was also studied. The results show that by this method it is possible to reduce the tube wall temperature to a safe value for the tube. The relation between the air mass flow rate and the temperature at place of damage is also predicted in this study