Evaporator equipment in the design should pay attention to what problems

Evaporators are widely used in chemical, food, light industry and other industries. It mainly carries out liquid evaporation and crystallization. If the design of the evaporator is reasonable, the life of the evaporator can be extended and the evaporator can be operated stably.

Therefore, the evaporator equipment should pay attention to the following issues in the design:
1. Forward and reverse cycles. Generally, the direction of the material cycle of the evaporator is the same as that of the steam cycle, and sometimes the direction of the material cycle of the evaporator is opposite to that of the steam cycle. Regardless of which cycle is chosen, the principle followed by evaporative crystallization is that the material in the heating tube should not boil.

2, secondary steam overheating. In the evaporator design calculation, the designer usually takes the temperature of the secondary steam as the saturated water vapor temperature at the pressure of the evaporation chamber. In some cases, it doesn't fit. When the solution boils, the vapor in the bubble has a similar temperature. At the temperature of the solution, the steam in the bubble overheats due to the increase in the boiling point of the solution. Especially for the concentration of materials with a large increase in boiling point (such as NaOH, MgCL2, KOH, CaCL2, etc.), if the concentration of the material is large, the superheat of the secondary steam is larger. The greater the superheat of secondary steam, the more serious the reduction of heat transfer coefficient. Therefore, in the design of the evaporator, it is necessary to consider simple measures to eliminate the overheating of the secondary steam, and the effect of reducing corrosion, enhancing heat transfer and recovering heat energy can be obtained.

3. Factors affecting crystal size. How to control the size and particle size distribution of salt particles is also an important problem that cannot be ignored. An important principle to follow in the design process is that the supersaturation of the solution must be strictly controlled so that the crystallization process takes place in a metastable zone with the lowest possible supersaturation. The design should correctly select the amount of solution circulation, the amount of flash evaporator circulation, and prevent the feed flash.

4. Parts and methods for discharging non-condensable gas. When the material is concentrated, it releases gas and evaporates. Each effect heating steam also contains a small amount of non-condensable gas. If the discharge position of the non-condensable gas in the heating chamber is designed incorrectly, the improper discharge method will cause the non-condensable gas to gradually accumulate in the heating chamber and increase. If the non-condensable gas can not be discharged in time, the heat transfer coefficient of the condensate will decrease sharply, and the production capacity of the evaporator will decrease. Therefore, attention should be paid to the location and method of non-condensable discharge when designing the evaporator.