| The bauxite slurry after high pressure digestion of alumina refinery plant are usually flashed down to atmosphere temperature and pressure.And then pumped to red mud separation and washing.Flash tank is the key equipment that accomplished decrease the high temperature and high pressure slurry.With alumina refinery design towards large-scale,modern development,flash tank specifications become bigger and bigger,the processing capacity is also growing fast.Some flash tank in operation in the process of vibration occurred in a cyclical vibration will cause some damage to pipeline and long time vibration may appear pipe weld cracking,flange leakage,serious when need to stop tank maintenance,directly affects the flash capacity and production safety.Flash tank is a pressured vessel,during the operation,the internal of flash tank processing heat and mass transfer.Gas,liquid,solid three-phase composition of the slurry flow in the flash tank is complex,it can not be detected by conventional means.In order to deeply know the inside bauxite slurry,flashed steam flow of the flash tank and the influence of them on the equipment vibration,the self compiler UDF program is loaded into the FLUENT software simulation of gas-flash evaporation process of liquid two-phase system and to self evaporator multiphase flow characteristics were analyzed.The main results are as follows:(1)The velocity and concentration field research results show that:from the upper part of the evaporator is gas phase region,below the liquid level of the evaporator area is 100%liquid phase region.near the orifice is gas and liquid mixing zone.In the gas-liquid mixed phase gas phase concentration from top to the bottom decreased gradually;The fluid flow near the orifice fluctuate is larger,the gas speed above the orifice zone is zero.(2)The results of pressure field study show that the pressure distribution in the gas phase is uniform,and the pressure of the gas liquid mixing zone is slightly higher than that of the gas phase.The pressure of liquid zone is increased from down to up gradually(3)The temperature filed results show that:the orifice around is the highest temperature.With solution go down to the bottom while the temperature of solution decreased gradually.(4)The flash process analysis of the factors affecting the results show that:self evaporator in initial meniscus height will have an impact on the process of flash,in a certain range,the higher level the slower flash speed.The worse to flashing.lt may cause flash tank vibrate;the inlet slurry initial temperature higher,the larger amount of steam generated;When the orifice diameter too small,the inlet piping energy consumption will be large,the steam out of flash tank will be less.Due to the orifice near the speed difference and an orifice distance from the flash tank wall distance changes will cause different levels of flash tank vibration difference.Through the analysis of the simulation results,it can be controlled by the process conditions are as follows:the height of the liquid level control in about 2.21m,the maximum not more than 2.47m;orifice diameter should be to increase to 356 x 10,resulting from the view of hydrodynamics weakened the vibration of the flash tank.Orifice which inside of the flash tank will be severe vibration source,orifice plate driven pipeline vibration,and flash tank produce resonance,affecting the normal operation of equipment,one selection is reinforce inlet pipeline,of self evaporator was improved from the aspects of process equipment,so as to achieve to eliminate vibration. |
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