升膜式蒸发器与降膜式蒸发器的比较

Comparison of Climbing Film Evaporator and Falling Film Evaporator

料液在升膜与降膜式蒸发器中均以膜的形式沿着管壁边流动边与管外加热介质进行热的交换并蒸发。两者都不适合浓度较高的易结垢结焦或在蒸发过程中有结晶析出的料液的蒸发;不同点前者料液是在高速的二次蒸汽流及真空的作用下在管壁成膜并向上运动,蒸发后料液与二次蒸汽从蒸发器顶部进入分离器,实现蒸发后料液与二次蒸汽的分离,而降膜式蒸发器则是在料液分布器的作用下将来料均匀的分配给每根降膜管并以膜的状态沿着管壁在自身重力及二次蒸汽流的作用下自上而下流动,蒸发后的料液与二次蒸汽在蒸发器底部进入分离器中实现蒸发后料液与二次蒸汽的彻底分离。升膜式蒸发器要求加热温差较大,操作不易控制,易造成跑料等现象的发生。因此,近些年来很少应用。

In both of climbing film evaporator and falling film evaporator, fluid flows along the wall of tubes to finish the exchange of heat and evaporation. However, concentrated fluids with the properties of easy forming of scale and coke and separation of crystals are not applicable for both evaporators. In the former, the fluids form of the wall of tube and move upward under the action of second steam flow and vacuum condition, and the fluids and second steam, then, enter the separator from the top of evaporator after evaporation so as to realize the separation of fluids and second steam. But in the latter, from distributor, the fluids are uniformly distributed to each tube and flow on the wall of tubes downward with the form of film and under the action of self weight and second steam, the fluids and second steam enter the separator from the bottom of evaporator to carry out the separation of fluids and second steam. In climbing film evaporator, it is needed to have large temperature difference, so the operation is uneasily controlled and material run easily occur. Thus, in recent years, it has been seldom applied.