Working Principle：

       In industrial production, it is often necessary to evaporate a large amount of water and consume a large amount of energy to heat the water to produce steam, which is then condensed to achieve the purpose of evaporating water. This steam contains a lot of latent heat, so it should be recycled and used. If the secondary steam is passed into the heating chamber of another evaporator, as long as the operating pressure of the latter and the boiling point of the solution are lower than the pressure and boiling point of the secondary steam, the secondary steam can still be used for heating. The operation mode is multi-effect evaporation.

       Each evaporator in multi-effect evaporation is called an effect. The evaporator that adds raw steam is called the first effect, and the evaporator that uses the secondary steam generated by the first effect as the heat source is called the second effect, and so on. Multi-effect evaporation is an evaporation system in which several single-effect evaporators are operated in series. For example, the secondary steam of the first effect is used as the heating steam of the second-effect evaporator. Similarly, the second-effect evaporator newly generates secondary steam It can also be used as the heating steam of the third effect evaporator, and so on. Due to the repeated use of heat energy, the amount of raw steam is significantly reduced, the cost is greatly reduced, and the efficiency is also increased. Connect multiple evaporators to operate together to form a multi-effect evaporation system.

       In a typical three-effect evaporation operation process (see the figure below), the first effect uses raw steam as heating steam, the second and third effects use the second steam of the previous effect as heating steam, and the last effect condenses the condenser condenses, thereby greatly reducing the amount of raw steam.

Main Feature：

a) Several evaporators are connected to operate, and the secondary steam generated during the evaporation in the previous effect evaporator is used as the heating steam of the latter effect evaporator.

b) Heat energy has been reused many times, significantly reducing heat energy consumption.

c) The main types of evaporators are: single-effect evaporator, double-effect evaporator, three-effect evaporator, four-effect evaporator, five-effect evaporator, etc. The number of effects depends on the nature of the material, equipment investment and operating cost consider.

d) According to the characteristics of materials, downstream, countercurrent, advection, and cross-flow processes can be used flexibly.

Multi-effect Evaporation Operation Process Design：

 1、Downstream process：

   Process: The flow direction of steam and material liquid are the same, from the first effect to the last effect. As shown below：

Advantage：

 ● The pressure of each effect evaporation chamber decreases in order of effect, and the material liquid can automatically flow into the next effect by the pressure difference of the adjacent two effects, without the need for pumping.

 ● The boiling point of the material liquid decreases in the order of effect. When the pre-effect material liquid enters the after-effect, it releases sensible heat, which will cause self-evaporation, which can vaporize a part of the water.

 ● The concentration of the material liquid increases in order of effect. The high-concentration material liquid evaporates at low temperature, which is beneficial to heat-sensitive materials.

 ● The viscosity of the material liquid generally increases in order of effect, and the heat transfer coefficient decreases in order of the effect number. The degree of decrease depends on the degree of change in the viscosity of the material liquid with temperature.

 ● The finishing liquid is discharged at the last effect, and its temperature is the lowest, so the total heat consumption is lower.

 ● The operation is relatively simple and easy to stabilize.

Disadvantage:The concentration gradually increases in the order of effect along the flow direction of the material liquid, but the boiling point gradually decreases, resulting in a rapid increase in the viscosity of the solution and a decrease in the heat transfer coefficient, which will lead to a decrease in the production capacity of the entire evaporation device or an increase in the heat transfer area.

2、Countercurrent Flow：

Reverse flow: The flow direction of the material liquid and the steam is opposite. The raw material enters from the last effect and is pumped to the front effect in sequence. The finished liquid is output from the bottom of the first effect. The flow direction of the heating steam is still from the first effect to the last effect. As shown below:

Advantage:

 ● The higher concentration of the material liquid evaporates at a higher temperature, and the effects of the concentration and temperature of each effect on the viscosity of the solution are roughly offset, and the heat transfer coefficient of each effect is about the same. This process is suitable for viscosity changes with concentration and temperature the larger solution evaporates. 

Disadvantage: 

 ● The material and liquid must be pumped. 

 ● The material liquid flows from low temperature to high temperature in the effect, the feed of each effect is relatively cold liquid, there is no self-evaporation, the amount of secondary steam generated is less than the downstream process, which will consume more heat.

 ● The temperature and concentration of the first effect are high, which is easy to cause coking.

 ● The finished liquid is discharged in the first effect, and its temperature is higher, which takes away more heat and is not conducive to the evaporation of heat-sensitive liquid.

3、Advection Process：

The raw material liquid is added to each effect separately, the finished liquid is also output from the bottom of each effect, and the steam flow direction is still from the first effect to the last effect. This process is suitable for treating the solution accompanied by crystallization during the evaporation process. As shown below:

4、Mixed Flow Process：

When the number of effects is large, it can also use the operation of co-current and counter-current. This process can coordinate the advantages and disadvantages of the two processes, and is suitable for the evaporation and concentration of very high viscosity liquids.

Application Scope:

The multi-effect evaporator designed by Jiangsu Heide will make full use of various heat sources according to the actual needs of customers. It has many advantages such as high evaporation capacity, energy saving, low investment, and low operating cost. It has been widely used in medicine, food, Evaporative concentration and wastewater treatment of water or solution in chemical, light industry and other industries.