Research On Mixing And Flowing Characteristics Of Cold Solid-solid Particles In A Two-dimensional Moving Bed

In order to provide reliable design basis and operation parameters for industrial reactor and process operation,the mixing characteristics and industrial feasibility of mixing device and the flow characteristics of pyrolysis device were studied,based on solving the mixing and flowing bottlenecks of circulating ash heat carrier pyrolyzer in the coal pyrolysis/circulating fluidized bed combustion classification conversion process.The main contents include the following two aspects:Firstly,the mixing characteristics of the high temperature ash and coal particles and industrial feasibility of the baffle-gravity-mixing device were investigated by the cold simulation.The cold baffle-gravity-mixing device was designed and the suitable simulated material(silica gel and quartz sand)were used,to explore the influence of baffle angle,baffle numbers,baffle placement and material mixing ratio on the mixing effect and clear the mixing mechanism.Compared with the related mechanical mixing experiment,the applicability and feasibility of the home-made baffle-mixing-device to the coupling process were verified.Secondly,the flow characteristics of pyrolysis raw material(high temperature ash/coal)in a pyrolyzer were investigated by cold simulation.A two-dimensional moving bed equipped with insert was built to serve as pyrolyzer and the suitable simulated material(quartz sand)was used,to investigate the influence of heat carrier,insert angle and material mixing ratio on the flow characteristics(flow pattern,velocity distribution and mixing degree)and predict the residence time distribution of coal particles in the pyrolyzer,and the basic flow laws of particles in moving bed were obtained.The main conclusions of this study are as follows:(1)The mixing effect of 300 baffle is better than that of 400 and 50°and the mixing effect of rotating baffle is better than opposite baffle.Synchronously,with the increasing of baffle numbers and the proportion of quartz sand(simulated heat carrier),the mixing uniformity is gradually improved.The main performance of the initial meeting of the baffle mixer is convective mixing,when flow through the baffle,the convective and shear mixing acts together.For the opposite baffle,it is mainly convective mixing at this time,and the shear mixing is the dominant mechanism,when the baffle is rotating.The mixing state of a two phase particle at a certain moment is usually the effect of the common action of convection,shear and diffusion.The mixing effect of the baffle-gravity-mixing is similar to that of the mechanical mixing.But the structure of the baffle-gravity-mixing is structural simple and low in cost,and it can meet the requirements of the mixing standard of ash/coal in a certain operating range.Therefore,the baffle-gravity-mixing can be used the mixing device of the pyrolyzer.(2)The flow characteristics of ?2=20° is better than that of other angles,and with the increase of the content of quartz sand,the flow characteristics of the mixture gradually become better.The optimized insert can improve the flow performance of the pyrolysis raw material,increase the velocity uniformity,reduce the secondary separation between the high temperature ash and coal,and improve the heat transfer efficiency and the pyrolysis efficiency,which is helpful for the stable operation of pyrolyzer.Using tracer technique,through the investigation of the residence time of tracer particles in a cold two-dimensional flow device to predict the residence time distribution of coal particle in moving bed pyrolysis reactor and further to explore the relationship between residence time in different area of the pyrolysis reactor,accurately predict the actual state of the pyrolysis reactor for coal pyrolysis.