| Chinese phosphate rock resources are abundant,however,medium and low grade phosphate rock accounts for the majority.Therefore,How to rationally and fully exploit phosphate rock resources is become a primary problem to be resolved.Phosphoric acid stirred reactor is one of the key equipment in the wet process phosphoric acid.The main purpose is to keep the slurry flowing in a specific direction and velocity,to ensure that solid particles are not deposited on the bottom and solid-liquid two phases are sufficient mixing.The traditional stirred reactor is easy to form a symmetrical flow field,which directly affects the mixing effect of solid-liquid mixing.Reasonable design and optimization of stirring impeller is an important means to strengthen the solid-liquid mixing in stirred tank in the experiment.In this paper,rigid-flexible impeller was used to enhance the suspension and leaching of phosphate rock particles,and to improve the crystallization process of phosphogypsum,which was of great value in improving the efficiency of phosphoric acid stirred reactor.In this thesis,the flow field characteristics of solid-liquid two-phase in a stirred tank were studied by Computational Fluid Dynamics（CFD）numerical simulation method.Flow field structure and motion law of dispersed phase were analyzed.Secondly,torque value of impeller was collected by the experimental data acquisition system,and the maximum Lyapunov exponent（LLE）was calculated by Matlab,which reflects the suspension degree of solid-liquid two-phase in the stirred tank.Finally,the strengthening law of phosphate rock leaching by rigid-flexible impeller was discussed.The effects of impeller type,off-bottom clearance,stirring speed,length and width of flexible piece and electric field on phosphate leaching were investigated.Phosphate leaching rate and phosphogypsum were analyzed,The results showed that:（1）CFD numerical simulation showed that rigid-flexible impeller can effectively break the circulation through the multi-body movement of flexible piece,improve turbulent energy in the stirred tank,improve axial velocity of particle,and strengthen solid-liquid two-phase mixing;（2）Rigid-flexible impeller can effectively break the flow field symmetry circulation and improve the chaotic mixing.At the stirring speed is 225 r·min-1,the LLE of rigid-flexible impeller is increased by 25.07%compared with rigid impeller.chaotic mixing characteristic parameter and stirring speed are regular;rigid impeller:LLE=-2.0*10-6N2+9.54*10-4N-0.036;rigid-flexible impeller:LLE=-2.4*10-6N2+11.2*10-4N-0.040.（3）Rigid-flexible impeller can accelerate the“indicative renewal”of the phosphogypsum compared with traditional rigid impeller and improve the crystal growth of the phosphogypsum.At leaching time 120 min,impeller speed is 225 r·min-1,off-bottom clearance C=0.25T（T is impeller spacing）,and width of flexible piece S=1.25R（R is diameter of stirring shaft）,and length of flexible piece L=1.33T（T is impeller spacing）,phosphate leaching rate of rigid-flexible impeller is increased by24.55%,which effectively enhanced particle suspension;（4）Phosphate rock leaching rate increased by 2.98%with electric field compared with no electric field condition.The electric field can reduce apparent activation energy of phosphate rock leaching reaction,improve charge distribution on the surface of the phosphate rock particles effectively,promote effective contact between the hydrogen ions and the particles,increase phosphate rock leaching rate,and shorten leaching time of phosphate rock.In summary,rigid-flexible impeller can enhance phosphate rock leaching rate and improve crystallization process of phosphogypsum.Experimental research provides some theoretical guidance for industrial application of rigid-flexible imepller. |
