| At present, there are two main kinds of discharging structures at the bottom of the downflow tower for high consistency pulp bleaching: one is the high consistency pulp to be discharged directly, the other is diluted pulp to be discharged. More energy consumption and larger space will be caused in the direct one, however in the indirect one the pulp can not be diluted uniformly to influence the bleaching effect because of the fixed diluted-site. So in the paper, the flow field of diluted zone and its key parts were studied to optimize their structures , with the aim of discharging and bleaching uniformly, which is belonged to the rotating diluted system. Now the system has been applied for invention patent in disclosed state.The flow field of diluted zone at the bottom of the high consistency bleaching tower, was simulated by means of the two process from different directions: the constant pressure process and the stability process of the continuous production. The main researches are as follow:1. It showed that there was critical value W in the fitted regression curves for(?-?o)and P by means of studying the bulk density of high consistency pulp, in which(?-?o)was the difference between the packed density and aerated bulk density, P was caused by the weigh of the piled high consistency pulp. When P was within a scope of 0 to W,(?-?o)and P was showed linear relationships; When P was over W, it was showed power function relationships. By means of determining the sizes of engineering towers, it showed that there was maximum pressure 69000Pa over the diluted zone, and the flow field of experiment system in the diluted zone was studied in turbulent flow.2. By means of PIV system and its experiment results, It showed that the images of tracers and pulp fiber particles were separated to gain the exact flow field information respectively by way of mask technique and threshold values.3. By means of velocity analysis and numerical computation for the three kinds of water spray pipe such as straight pipe, spindle-shaped pipe, waist- shaped pipe, it showed that the spindle-shaped water spray pipe can be better to be used in equal consistency spraying. In the spray pipe, it was full of secondary flow such as vortex and reflux, and the water flow can be away from the pipe wall because of the higher rotational speed.4. The pulp fiber particles as cylinder particles in the flow field, can be acted upon by Stokes force, additional mass force, Basset force. The pulp suspension as two phase flow can be simulated by Eulerian particle flow model combining with sliding grid. It showed that S-shaped discharger can be quicker and more uniform than the straight discharger, and more turbulent energy to keep the pulp suspension not be flocculated, S-shaped discharger with edge-ellipse section, which was characterized by discharging more quickly and uniformly, and more turbulent energy and dissipation rate. From the pulp volume percentage, Particles diameter, viscosity and density had small effect on discharging, however the rotational speed had marked influence on it.From the above research, by way of measuring the flow field of water and 0.01% pulp, and doing some experiments of discharging effect and velocity magnitude for 3-4% low consistency pulp, The results indicated that it was suitable to go on numerical computation in the flow field of water spray pipe by using realizable k-?model combining with PISO computation and quadratic upwind scheme; It was reliable that Eulerian particle flow model combining with sliding grid and dispersed turbulence model to simulate the flow field of discharger and diluted zone; The S-shaped discharger with edge-ellipse section, and spindle -shaped water spray pipe were structural optimization in the rotating diluted system. |
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