Study On Collision Characteristics And Breakage Model Of Oxygen Carrier Particles In Chemical Looping Process

Reducing carbon dioxide emissions is the key to solving the climate crisis.Among the existing CO₂ capture technologies,chemical looping combustion technology is one of the most promising combustion technologies due to its advantages in CO₂ separation and low cost.High-performance oxygen carriers are the key in chemical looping technology,but they are severely abrasion during the long-term operation,and fresh oxygen carriers need to be continuously replenished.Due to the small particle size and the complex fluidization process,it is currently difficult to use experimental methods to deeply study the particle abrasion problem.In terms of numerical simulation,it is difficult to study the breakage of solid particles by using the existing gas-solid two-phase flow model.In this thesis,a realistic irregular polyhedral oxygen carrier particle geometry is constructed and 36 kinds of particles with different sizes and aspect ratios are put into the fluidized bed,and an Ab-T₁₀ breakage model based on computer graphics is proposed.The CFD-DEM two-ways coupling calculation method has obtained the characteristics of particle velocity,particle surface collision frequency distribution,particle surface stress distribution and collision energy in the fluidized bed,revealing the single particle breakage process and the children particle distribution and evolution characteristics.The following is the specific research content of this thesis:First,particles with 10,20,30 and 40 vertices were established,respectively.And the particle geometry with 20 vertices was determined by comparing the particle surface collision frequency distribution.After inputting 36 kinds of particles with different aspect ratios and particle sizes,the particle velocity,collision frequency and impact power during the generation,development and collapse of bubbles in the fluidized bed was compared and analyzed.It is found that the velocity difference between particles is the root cause of the impact power reaching a maximum value.The surface collision frequency and stress distribution characteristics at three moments near the impact power of a single particle reach the maximum value are further analyzed.Second,using the Ab-T₁₀ breakage model and Voronoi diagram segmentation algorithm based on computer graphics,the evolution of the particle size of the children particles during the whole process from the first fragmentation to the complete elutriation of a single particle was tracked,and three important fragmentation stages were selected for further analysis.By counting the breakage heights of particles with different sizes,it is found that the region 1.5-2.5 times height of the bed material is the region where the particles are most prone to breakage.Finally,the breakage model was applied to all the particles in the fluidized bed,and the particle size distribution in the fluidized bed at 20 instants was obtained,as well as the evolution of the overall number of particle breakage with time.The quality and quantity of separated particles in the top area of the fluidized bed was counted,and it was found that the elutriation phenomenon gradually increased with time.As the particles continue to break up,the particle size distribution of 60-340μm approximates a bimodal curve,which is the result of the combined action of abrasion and fracture.This thesis has 46 figures,4 tables,and references 116.