Three-dimensional Numerical Simulation Of Finishing Super-heater Tube Screen In Supercritical Boilers

The high temperature heating surface of supercritical and ultra-supercritical power plant boiler is arranged in the high temperature gas region. Qvertemperature tube-burst accident which affects the safe operation of the unit seriously often occurs on because of highest temperature steam. Contrary to the defect of conventional analysis of thermal deviation, using the numerical method to study temperature distribution of metal, thermal deviation of high temperature heating surface and its impact on the distribution and fall-off situation of oxide scale has great significance for improving the security of high-temperature heating surface significantly.This paper chooses the finishing super-heater of a 600MW boiler as the research project. Based on the analysis of factors affecting thermal deviation and features of conventional analysis of thermal deviation, using CFD numerical method to analyze distribution of thermal deviation and thermal parameters of a single tube screen. Based on its original size,using RNG k-ε flow model to establish the heat transfer model of gas horizontally sweeping the finishing super-heater tube bundle, using the Workbench internal software for meshing. Then completing the steady-state’s numerical simulation in Fluent software platform by 50%,75% and 100% load conditions and comparing the results with boiler thermodynamic calculation results integrally to determine the validity of the established model. On this basis, using the datas of calculation to analyze steam temperature, metal temperature and flue gas temperature distribution of the finishing super-heater tube screen and features of each tube’s heat transfer and thermal deviation, to obtain the growth law of the steam side oxide scale on each tube in the same screen. The results show that comparing with conventional analysis of thermal deviation the numerical model reflects the distribution of thermal parameters and heat transfer more acurratly. It’s an important method to analyze the safety of supercritical and ultra-supercritical boiler’s temperature heating surface.For analyzing the falling off of steam side oxide scale on high-temperature heating surface, the study based on steady-state calculation results taking appropriate simplified assumptions to the model in accordance with analysis of dynamic characteristics. Simulating the the metal wall temperature’s dynamic response along the tube length direction of each tube which in the same screen,the simulation is in three cases which using steam inlet temperature disturbances, flue gas inlet temperature disturbances and steam inlet flow disturbances as parameters. Dynamic calculations reflect that inlet steam temperature perturbations has the most impacts on each tube screen tube wall metal temperature changes. The temperature change of the steam outlet, the inner wall of the metal and the steam inlet is substantially equal. There are some differences between different tubes, flue gas inlet temperature disturbances and steam inlet flow disturbances have less impacts. When the inlet steam temperature disturbances, closer to the inlet the metal temperature of the inner wall change faster. Therefore, in actual operation we should analyze the possibility of the falling off of steam side oxide scale on high-temperature heating surface combining with the thickness distribution and different disturbance conditions.The calculated data and distribution of the parameters in the papers provides important data for further study on growth and fall off of similar boiler’s steam side oxide scale on high-temperature heating surface, but also for on-site optimization operation mode and providing guidance to ensure the safe operation of high temperature heating surface.