Fine Design Of Flow Field And Product Control In DTB Crystallizer

This research focus on a kind of widely used DTB(Draft tube and Baffle)crystallizer,using CFD(computational fluid dynamics)to simulate the single and multi-phase flow in the crystallizer.Ammonium sulfate is used as the crystallize system.Several key structure is optimized to enhance the hydrodynamic properties by a fine strategy and a control strategy of crystalline via design of flow field is raised.Firstly,a small jet circulation DTB crystallizer model with a length to diameter ratio of 4 was established.The single-phase and multi-phase flow simulations for the model were completed using the RNG k-? turbulence model and the Euler multiphase flow model,and the simulation results were performed.Verification.The verification results show that the development process of the jet in the guide tube conforms to the development law of the circular jet.The radial velocity distribution accords with the Gaussian positive distribution,and the jet velocity characteristic half thickness decay also meets the reference value.The flow property is determined to determine the optimal jet incident velocity.At 3m/s,the jet velocity can complete the liquid circulation and have relatively low vorticity and energy consumption.The distribution and flow state of particles with different particle sizes in the crystallizer are studied by multiphase flow data,and the particle phase circulation is found.The outflow ratio and deposition rate are important parameters that affect whether the crystallizer can stably operate the particle phase.Then the bottom shape and baffle position are selected as key structural parameters.The influence of the above structural parameters on the flow in the mold is studied by investigating the important flow parameters such as circulation flow rate,circulation outflow ratio and deposition rate.The results show that the structural design conforming to the bottom streamline can reduce the accumulation of solid particles at the bottom and enhance the ability of the jet entrainment particles to enter the liquid circulation,but has little effect on the overall flow characteristics in the mold;Both the diameter and the baffle position have a strong influence on the liquid flow.By optimizing the combination,the maximum circulating flow rate is increased by 29%,and the particle phase circulation outflow ratio is reduced by up to 62%.In addition,pulsed jet is used to enhance the power of regular jet in this study.The influence of using sine pulse to the flow field and suspension of the crystal particles.The results shows that,compared with a constant jet,pulsed jet will generate a periodically change in the downside of the draft tube and fade away during the development of flow,which means the flow field at the top of the crystallizer is rarely change.Pulsed jet is able to enhance the suspension of the particles in the crystallizer than a constant jet,and the amount of cycled particles has a maximum during the increase of the frequency of the pulse,which lead to a optimized pulsed frequency.