Numerical Simulation Of Full-loop Gas-solid Circulating Fluidized Bed System And Parameter Analysis

The ful-loop gas-solid circulating fluidized bed systems are widely used in industrial applications.Compared to simulation of a single operating unit,mathemat ica l modeling and accurate simulation of the complex ful-loop system can reveal interactions between different operating components in the ful-loop system,thus having a more significant influence in guiding practical operation,The ful-loop system realizes the organic combination of each component in the system through the particle transport.For capturing the main characteristics of the ful-loop systems such as coexistence of multiple flow regimes,dense particle conveying and higher particle friction stress in the dense particle conveying,the following studies are conducted.The Chapter 1 is the literature review which has an emphasis in summarizing the main flow features in ful-loop gas-solid circulating fluidized bed system and the research progress in simulations of full-loop systems.In Chapter 2,a series of full-loop simulations of the VPE unit and related parameter analysis are conducted.The simulations use the two fluid model where the gas-solid drag employs the EMMS/matrix model and Gidaspow model and Gidaspow model,and the solid pressure and solid viscosity are closed by Kinetic Theory of Granular Flow(KTGF).Then,the influence of the solid inventory,superficial gas velocity,drag force model and valve opening on the simulation results are investigated.The simulation results show that the resistance in the horizontal pipeline has significant influence on the ful-loop simulation.The increase of resistance can reduce or avoid the fictitious periodic fluctuation of riser pressure drop.Therefore,accurate simulation of dense flows in the conveying pipeline is key to successful simulation of gas-solid ful-loop system.In Chapter 3,the L-shaped conveying pipe was simulated where the applicability of different particle stress models are examined through the analyzing the repose angle of static particle material.Then,the influence of the wall condition through adjusting the particle-wall collision restitution coefficient and specularity coefficient on the repose angle are investigated,for trying to find the suitable particle stress model and particle wall condition for successful simulation of the gas-solid ful-loop system.Simula t io n results show that the frictional term in the traditional particle stress model was highly under-evaluated and in the dense particle convey region,the frictional term and the particle-wall interaction have big influence on the particle flow behaviors.Therefore,reasonable modeling of solid frictional pressure and frictional viscosity is critical to successful simulation of dense particle conveying in full-loop simulation.The last chapter summarizes the whole study and provides the suggestions for the future work.