How is the process flow of falling film evaporator carried out?

Falling film evaporation is to add the material liquid from the upper tube box of the heating chamber of falling film evaporator, distribute it evenly to each heat exchange tube through the liquid distribution and film forming device, and flow from top to bottom in a uniform film shape under the effect of gravity, vacuum induction and air flow In the process of flow, the steam generated is heated and vaporized by the shell side heating medium, and enters the separation chamber of the evaporator together with the liquid phase After full separation, the steam enters the condenser for condensation (single effect operation) or enters the next effect evaporator as the heating medium, so as to realize multi effect operation The liquid phase is discharged from the separation chamber Process flow: the process flow of falling film evaporator has four forms: forward flow (parallel flow), reverse flow, mixed flow (cross flow) and horizontal flow: forward flow: the flow direction of solution and steam is the same, from the first effect sequence to the final effect The feed liquid is pumped into the first effect, and automatically flows into the next effect depending on the pressure difference between each effect The liquid is pumped out from the final effect (generally operated under negative pressure) Because of the low pressure of the first effect and the low boiling point of the solution, when the solution enters the first effect from the front effect, it will flash some water and generate more secondary steam Because the concentration of the second effect is higher than that of the first effect and the operating temperature is lower, the heat transfer coefficient of the second effect is often much higher than that of the last effect The downstream process is generally suitable for the treatment of heat sensitive materials in the case of high concentration Countercurrent: the raw material is pumped from the end effect to the front effect in turn, the finished liquid is discharged from the first effect, and the material liquid and steam flow in reverse Generally, it is suitable to deal with the solution whose viscosity changes greatly with the temperature and concentration, and it is not easy to deal with the heat sensitive materials Mixed flow: it is a combination of upstream and downstream flow, and has the advantages of upstream and downstream flow to avoid its disadvantages, but the operation is complex and requires a high degree of self-control Advection: each effect is fed with finished liquid, and each effect has crystallization, which can separate crystallization in time, generally used for evaporation of saturated solution Characteristics of falling film evaporator: (1) l / D = 100-250; (2) heat transfer coefficient k = 1000-3000 kcal / (M2 * c *); (3) it can handle materials with high concentration and poor fluidity; (4) it has small heat transfer temperature difference and has no influence of hydrostatic pressure of liquid column.