Falling film evaporation is to add the liquid to the upper tube of the heating chamber of the falling film evaporator.Through the liquid distribution and film forming device,it is evenly distributed into the heat exchange tubes.Under the action of gravity and vacuum induction and air flow,it forms a uniform film.Flow from top to bottom.During the flow,it is heated and vaporized by the shell-side heating medium,and the generated steam and the liquid phase enter the separation chamber of the evaporator.The vapor-liquid is sufficiently separated,and the steam enters the condenser for condensation (single-effect operation)or enters the next-effect evaporator.The medium is heated to achieve multi-effect operation,and the liquid phase is discharged from the separation chamber.
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The process flow has four forms: downstream (cocurrent),countercurrent,mixed flow (crossflow)and advection.
(1)The feed liquid of the falling film evaporator is added from the top of the evaporator,and descends along the wall of the tube under the action of gravity,and is concentrated by evaporation in the process,and a concentrated liquid is obtained at the bottom.The falling film evaporator can evaporate materials with higher concentration and higher viscosity.
(2)Since the solution flows in a film in a single-pass evaporator,the heat transfer coefficient is high.
(3)The residence time is short,it is not easy to cause material deterioration,and it is suitable for handling heat sensitive materials.
(4)The liquid hold-up amount is small,and the falling film evaporator can be operated quickly according to changes in energy supply,vacuum degree,feed amount,concentration,and the like.Near constant,
(5)Since the process fluid flows only under the action of gravity rather than by the high temperature difference,low temperature differential evaporation can be used.
(6)Falling film evaporator is suitable for evaporation and concentration of foaming materials.Because the liquid liquid evaporates in the heating tube,it forms vapor-liquid separation.At the bottom of the effect body,most of the liquid is pumped away.A small part of the feed liquid and all the secondary steam enter the separator to strengthen the separation,and the liquid preparation process does not form too much impact,avoiding the formation of foam.