Numerical Simulation Of The Gas-solid Multiphase Flow In The Stripping Process Of Spray Granulation Tower

The processing of the heavy oil has become an important part of today's world oil refining process.A new technology for heavy oil processing is the process of heavy oil deep stage separation.As one of the key equipment in this process,the optimal design and operation of the new spray granulation tower have a direct effect on the solvent reclamation and asphalt granulation in the process.The fluidization and gas stripping of the deoiled asphalt particles is an important part of the spray granulation system.Fundamentally speaking,the improvement of the structure and operating conditions in gas stripping are both based on the comprehensive understanding of the internal gas-solid two-phase flow.In this thesis,CFD is used to conduct numerical simulations and experimental verifications on deoiled asphalt particles' particulate fluidization and the characteristics of gas stripping.Then another numerical simulation is conducted on gas-solid two-phase flow in separation space of granulation tower and the flow field after gas stripping.Firstly,the influence of different feeding ways on its separation performance and the particles' concentration is explored.The result shows that asphalt particle uniform distribution in the bottom when direct injection.the particle concentration is higher,under the gas stripping,the particle accumulates in the bottom.oblique feeding not only has higher separation efficiency,but also has a symmetrical pressure distribution in the isolated space,due to the dual function of centrifugation and gravity sedimentation.After a long computing period,there is no particle packing in the bottom.Secondly,based on Euler Model,the gas-solid two-phase flow model in fluidized bed is built after modifying the Drag Model,taking into account that the deoiled asphalt particles easily aggregate.By using the model,the process of the particulate fluidization of deoiled asphalt particles in fluidized bed is investigated and its characteristics are as follows.When the gas velocity is less than the minimum fluidization velocity,the fixed bed turns into particulate fluidization which is similar to the conventional liquid-solid system.The bed pressure drop increases evenly as the gas velocity increases.As the fluidization gas velocity continues to increase,the bed expands evenly,so that gas passes through the particle clearance that is bigger than that of the fixed bed without any bubbles.Based on this,the influence of gas stripping and gas velocity on stripping performance is studied.The result shows that when the linear velocity of gas stripping is smaller than 0.06m/s,gas stripping efficiency is greatly influenced by the linear velocity of gas stripping.When the linear velocity of gas stripping is over 0.06m/s,the increase of stripping efficiency becomes unobvious.Lastly,the influence of gas stripping on flow field and separation performance in separation space is computed by investigating two different feeding ways,which are direct injection and 45° oblique spray.The result indicates that gas stripping has great influence on the separation efficiency of direct injection.As the gas stripping rate increases from 1.8% to 7.2%,the separation efficiency decreases by 4%.Comparatively,for the granulation tower with 45° oblique spray,the separation efficiency just decreases by 0.8%.