Fluid Dynamic Simulation Of Gas Mixed With Ash In 600MW Supercritical CFB Boiler

In the boiler furnace, which is a main part of a thermal generator set, the flue gas flow is a typical gas-solid two phase turbulent flow. The pressure fluctuation of the two phase flow may cause the oscillation, even resonance phenomenon, of the complex internal structure, which will affect the operation safety of the boiler. With the development of computer technology, it becomes an important step during the boiler design process to check the safety through numerical simulation method.Aiming at a novel 600MW supercritical boiler designed by Dong Fang Boiler Group, this article investigates the fluid dynamics problems relevant to the safety, which is caused by the pressure fluctuation of the two phase flow in the boiler. To be more specific, the research contents and results are listed as follows.â‘ According to geometric parameters of the boiler, the three-dimensional model is established. Based on the design operation parameters of the boiler, the physical model of the fluid in the boiler is simplified, and the equivalent density is developed to simplify the two phase flow in the boiler. The turbulent flow in the boiler is simulated by the Large Eddy Simulation (LES) method. Besides, the frequency of pressure fluctuation in the boiler, especially in the critical regions near the middle hanging walls, is analyzed. The results show that under design parameters, the oscillation amplitude of the middle hanging walls due to the oscillating gas flow is very small, and the oscillating gas flow cannot generate the resonance phenomenon when the main oscillation frequency is about 0.195Hz.â‘¡The gas-solid two phase flow model is also adopted to simulate the flow field in the boiler. It is founded that the distribution of the pressure field and the velocity field is generally consistent with the results computed by the proposed equivalent density model. The mixed density of the two phase fluid is uniform in the most internal regions of the boiler, which validates the hypothesis that it is reasonable to employ the equivalent density model to deal with the relevant problems in this research. The frequency of the fluid fluctuation in the boiler, particularly near the middle walls, and the frequency of oscillatory convection between the two sides of the middle walls are both lower than the numerical results simulated by the equivalent density model. Compared to the two phase flow model, the equivalent density model is more dependable to evaluate the safety of the middle hanging walls in the boiler.