Study On Cyclone And Interception To Collect Fine Dust Particles

Cyclone separator is a dry-type gas-solid separation device that uses centrifugal force generated by rotated gas to separate the solid particle from the gas.Because of its simple structure, no moving parts,low manufacture and installation investment,conveniently operated and maintenanced,stable performance,less impacted by dust gas concentrations and temperature,low pressure drop and power consumption,they are widely used in industry,air sampling,separation, heat exchange and so on.However,the capture efficiency of micro dust particles(10 microns or less) in cyclone is so low that its applications are limited by a large extent.So,taking necessary measures to cut down its pressture drop and improve efficiency is an urgent problem.There were great difficulty in theoretical research of cyclone separator,and the theory developed slowly because the gas flow with solid particles in the cyclone separator was a kind of complex three-dimensional revolving turbulent flow with two-phase separation motion and many physical phenomena including interaction between gas and solid,collide,coagulate,and static electricity.It would cost much time and expenditure to optimize the performance of cyclone merely by experiments because of the limitations of experiment conditions.The numerical simulation on the cyclone separator has carried out by using the commercial CFD software-FLUENT in this thesis.After choosing the suitable method of numerical simulation and contrasting with the experimental results,the velocity and pressure field of gas phase,paths and classification efficiency of particles and separation efficiency of cyclone separator under several circumstances had been simulated.We designed the intergral cyclone filter dust collector by combining cyclone and interception,by large amount of study on numerical simulation,the following conclusion was obtained.1) Established numerical simulation methods that are most suitable for thegas field in the cyclone separator-RSM model for turbulent flow,QUICK format for difference scheme,PRESTO format for pressure discretization and SIMPLEC for pressure-velocity coupling.2) The main flow in cyclone separator is double vortex.The exterior is the revolved flow downwards and the interior is the revolved flow upwards.They have the same revolved direction. The tangential velocity shows the characteristic of compound vortex.The central area is the forced vortex and the outside area is the norm free vortex.3) The static pressure on the radial direction in the cyclone separator is reduced when the radial dimension is reduced.At the boundary surface-CS of forced vortex and norm free vortex, the dynamic pressure is largest.The total pressure losses include static pressure loss and dynamic pressure loss.4) The motion of particles in the cyclone separator is very complicated,we use DPM Model to track its trajectory.Generally speaking,particles that injected on the outer flank and underside of the inlet are more easily separated than particles that injected on the inner flank and upside of the inlet.ln the radial direction of cyclone separation space,the concentration filed can be divided into the middle low-concentration area and the high concentration area near the wall;particles concentration showed helix solid strand distribution in the collecting zone;there are ash rings in the annular space and the dust hopper,and the ash ring are uneven;the short-circuit flow exsit in exhaust pipe:there is a clear back-mixing near the dust port in the lower part of the separation space;the strongly swirling flow at the top of Dust port has a significant role in the secondary separation.When the solid phase is composed by particles with different diameter,the total separation efficiency could be obtained by fitting the Rosin-Rammler distribution:and its collection efficiency simulation results were basically consistent with the experimental results for particles larger than 5 microns.5) The cyclone pressure drop and separation efficiency increase in pace with increasing the inlet velocity and decreasing the exhatist pipe diameter;different forms of the entrance also have an impact on its performance,scroll-type entrance is slightly better than the tangential,the performance of the different angle's scroll-type entrance need further study.6) simulation and experiment to optimize the the intergral cyclone filter dust collector,by using the porous medium model,we compared the results with ordinary cyclone,collect efficiency is improved at least 10%,up to 95%,and the pressure loss was increased up to 400Pa when inlet velocity was less than 25m / s,no more than 25%.That is a new approach to cut down its pressure drop and improve efficiency for cyclone.Further study is needed on how to increase the filter area without too much additional cost.