| Wastewater problem has been one of the most urgent issues to be solved. Currently,anaerobic wastewater treatment has good development prospect, because it is a technologythat integrates energy recovery, environment protection and ecological circulation. UASB(Up-flow Anaerobic Sludge Bed/Blaket)has many advantages such as high volumetricloading rate, large processing capacity, low cost investment, less occupied area, quickstartup, stable operation, etc, and becomes the good solution to the problem of theseparation of gas and liquid from solid, so it is widely used in high concentration organicwastewater treatment. But many domestic and foreign researchers just considered the effectof changing the biochemical process of typical anaerobic wastewater treatment on UASBreactor processing capacity, and ignored the impact of condition of fluid flow on theprocessing capacity of UASB reactor. Thus, it is necessary to discuss the handling capacityof wastewater treatment of UASB reactor from the hydraulics standpoint.The method of the numerical simulation was introduced. It can correctly describe theinner flow condition on the core area of the UASB reactor by using the liquid-solidtwo-phase flow model. Firstly, based on the wastewater anaerobic process experiment andstructure parameters, the geometry was divided into several cells in the shape of2D-grids.Steady state simulation was adopted under different conditions of HRT. Then theinformation such as velocity field and volume fraction of solid phase was obtained andanalyzed. Furthermore, three-dimensional grid which consists of unstructured tetrahedralmeshes on the selected UASB reactor was generated, and stirrer was added into the reactionarea so that the two phases blended well. Local grid refinement was made in the area of thestirrer rotating part. Governing equations was three-dimensional steady ReynoldsNavier-Stokes equations. The standard k-ε turbulence model was chosen. The boundaryconditions of solid wall, blender, impeller surface and other solid walls was wasadiabatic,rotation no-slip,respectively. According to the results of numerical studies of thetypical bioreactor under different structural styles and operating parameters, flow structurewas analyzed with different conditions of HRT, hydraulics conditions wasoptimized.Further more the performance optimization of UASB was solved。 Simulation results showed that there are large "dead zones" in the reaction zone, whichresult in the semi-mixture between wastewater and sludge particles, thereby affecting theeffluent quality of UASB reactor. To improve the structure of the UASB reactor in thereaction zone by adding the blender, it will be conducive to a mixture of wastewater andsludge particles, even eliminating the dead zone. Smaller "dead zone" inlet velocities were0.4m/h and0.8m/h, steady-state simulation was proceeded under6different stirrer rotationrate,50r/min,70r/min,90r/min,110r/min,130r/min and150r/min. The analysis of velocityfield and the solid phase volume fraction showed that stirrer improved the flow fieldconditions in the reactor and eliminated the "dead zone". Under the same rotation rate andinlet velocity was0.8m/h, the smaller dead zone,the better wastewater and sludge particlesmixed; under the same inlet velocity, the greater rotation rate of stirrer, the smaller "deadzone" and the better wastewater and sludge particles mixed. In summary, the optimumprocess conditions were that inlet velocity was0.8m/h, stirrer rotation rate was150r/min,under which conditions "dead zone" in the reaction zone would be decreased, wastewaterand sludge particles mixed best, and the UASB reactor performed best. |
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