Study On Particle Attrition Modle And Effect Factors During Fluidization Processes

Fluid Catalytic Cracking(FCC)is an important secondary processing technology for the conversion of heavy oil to light oil in China’s petroleum refining and chemical industry.As a typical fluidization technology,FCC process is faced with the problem of catalyst particle wear and breakage,which leads to a series of problems such as increased cost,product pollution and safety hazards.However,due to its small particle size and the complex flow process in the FCC unit,it is difficult to study the flow,impact and breakage characteristics of catalyst particles through experimental methods.The numerical simulation method can make up for the deficiency of the experiment and obtain the information of fluid and particle size which is difficult to obtain in the experiment,and predict the experimental results,guide the experimental and even industrial progress.In this thesis,by using CFD-DEM coupling numerical simulation method,the geometric modeling of the FCC unit was built,the flow,impact and breakage characteristics of catalyst particles in FCC unit were studied,and the influencing factors of catalyst particle collision process were revealed.The main research contents include the following aspects:(1)By studying the impact frequency and power of particles,the main type of particle impact was determined,and the most severe impact area within the device was clarified.The impact frequency and of particles with different particle sizes was explored separately in the FCC device to obtain the impact characteristics of particles with different particle sizes.The cyclone separator was divided into 10 areas from top to bottom,and the variation trend of particle velocity in different regions was revealed.On this basis,the differences in the flow state of particles with different particle sizes in different areas of the cyclone separator were explored.(2)A complex gas-solid flow particle breakage model based on computational graphics was constructed by coupling flow and fragmentation.Abt10 breakage model for a single particle was established to track the particle breakage process.The type of attrition was determined based on the particle size distribution after breakage.The path of particle energy conversion was determined based on the energy of particles before and after breakage.A breakage model for all particles was established,and the parameters of the breakage model were set separately to obtain the distribution of breakage times in different areas and PSD before and after breakage,thus the type of attrition was determined.(3)The factors affecting the impact characteristics of catalyst particles were studied using DEM method.The relationship between the impact and dissipation power and the impact angle was obtained.Particles of different shapes were established,geometric parameters were chaged,thus the effects of factors such as length-diameter ratio,superquadric degree,particle size,and velocity on particle impact characteristics were clarified.