A Study On Structure Optimization And Flow Field Simulation Of Semi-dry Deacidification Of Flue Gas In Waste Incineration

With the economic development and population growth of urban, the amount of municipal waste increased significantly, which made the environmental pollution more serious. As the traditional treatment of landfill disposal can not meet the capacity in the current circumstances, the waste incineration method has become the main development direction of municipal solid waste, but the incineration gas will cause secondary pollution to the environment. For the acid gases (HCl, SO2, etc.) in the flue gas, the current common approach is Semi-dry spray drying process. But with the increasing scale and complication of the gas purification system, the experimental research needs to add more costs. Therefore, establishing mathematical models for system design and optimization of process conditions has become a preferred method to guide the practical operation in domestic and foreign.In this research, based on the structure characteristics and the actual design needs, three geometric models of the deacidfication spray drying tower were established, which were called Model 1, Model 2 and Model 3 respectively. Firstly, using computational fluid dynamics method and FLUENT software, the continuous phase flow field was simulated by Reynolds-Averaged N-S control equations and Renormalization Group (RNG) k-εturbulence model. The results showed the existence of irrational for the flue gas entrance structure of Model 1 and Model 2, which could lead to the phenomenon of wall-sticking in the tower, or can not flow around the tower with a stable state. In the optimization process, the inlet guide vanes were added to improve the entrance structure, which founded Model 3.For Model 3, under the Eulerian-Lagrangian coordinates, the Realizable k-εturbulence model, discrete phase model (DPM) and stochastic model were used to couple the continuous phase and discrete phase through repeated iteration, which to simulate the two-phase flow field inside the tower. The results showed that: the inlet gas flow equalization level was better, which could form a visible flow state around the tower. The best inlet gas flow rate was 1m/s, and the residence time was 20.91s; When the nozzle diameter d=1mm and the spray half-angelθ=60°, an optimal spray condition was determined; Between entrance and the area near spraying nozzle, the gas contacted with the slurry spray drops, which resulted a strong turbulent flow and promoted the mass transfer and chemical reaction process. So it's speculated that the main drying and deacidfication reaction occurred between 8m to 11m. Followed by the constant exposure of gas-liquid two-phase and the continuously settlement of the flue gas, the velocity magnitude in the tower tended to uniform gradually. These simulation results can be used to provide a quantitative basis and theoretical reference for the design of deacidfication tower and the actual working conditions.