Numerical Simulation Of Underwater Pelletizer And Structure Optimization

Granulation equipment is important resin processing equipment in petrochemical processing industry. As the new processing machines in the granulation equipment, the underwater pelletizer has the advantages of high production and good quality particles. In the face of the rapid development of petrochemical processing industry, the underwater pelletizer tends to be more large-scale to further improve the yield. While, unreasonable design or improper operation parameters are exist, which resulting in various problems, and even the units'chain parking, bring huge economic losses.The wear or fracture of cutter, diced accumulation, wrap cutter and other issues were discussed in this paper. By using FLUENT software and Realizable k-epsilon model, the numerical simulation is carried out. In the simulation processing, the particle trajectory is tracked and residence time is analyzed with the discrete phase model (DPM), the influence of the inlet and outlet structure on the convective field and cut grain discharge is also been studied. In addition, drilling hole on knife plate is been putted forward and design and analysis are carried out. Finally, the tangential force and axial force of the cutting knife and cutting wheel is been analyzed, providing theoretical basis for the operation parameters and structural optimization the underwater pelletizer.The main research contents and results are as follows:(1)Jet flow is formed in the inlet of granulating chamber. In order to explore the influence of different jet position on the flow field and the particle trajectory, three different flow inlets are putted forward. Through the numerical simulation analysis, it is found that the design of radial inlet can make the efficiency of particle removal more efficient, and it is not easy to detain.(2)It is found that indoor water vortex is not conducive to cut grain discharge by contrasting granulation discharge conditions and the flow field of all kinds of data. High external and low internal tangential velocity make the external pressure to be high and the internal pressure to be small in the water outdoor, leading to the granulation bear the gradient force towards the center of the water chamber, and it is also not conducive to the discharge of the granule; In addition, the high turbulence intensity is beneficial to the granule dispersion and discharge of the granule. Therefore, when designing the structure of water chamber, how to prevent the emergence of the maelstrom, and disturbing external and low internal tangential velocity distribution by turbulence flow could be a way.(3)It is found that the effect of the change of the flow outlet angle has little influence on the efficiency of the particle removal through the analysis of the flow field in the granulating chamber.(4)If there are no openings on cutter head, low pressure area will form in the middle region of cutter head and template, then part of the cut grain will be brought together to this the region in the gradient force and eddy current effect, making it is unable to discharge. Thus, three types spiral hole is designed on the cutter, so that the water can be directly flow through the opening region, which disturbs originally eddy current to a certain extent, and it is good for transporting, making granulation cannot enter the cutter plate from around clearance.(5)The tangential force of the cutter bore at work is small and it is not the main reason for the fracture of the cutter. The cutter wear and damage has direct relationship with the size of the feeding pressure. In this paper, the numerical simulation of the axial force of the cutter and the cutter in the work is carried out, and the relationship between the speed and the axial force is obtained, providing an important theoretical basis for the correction of feed pressure.