The multi-effect evaporator adopts multi-stage evaporation and multi-stage compression technologies to minimize energy consumption and reduce wastewater discharge, which has a good environmental protection effect.

Definition and Principle:
Multiple-effect evaporator is a device used to evaporate concentrated solutions. It uses steam to improve energy efficiency by multiple utilization. Its basic principle is that in multiple evaporators connected in series, the secondary steam generated by the previous effect evaporator is used as the heating steam for the next effect evaporator, thereby achieving multiple evaporations and reducing the consumption of fresh steam.
Taking the double-effect evaporator as an example, in the first effect evaporator, the raw material liquid boils and evaporates under the action of the heating steam, and the secondary steam generated enters the second effect evaporator as heating steam, so that the solution in the second effect continues to evaporate. Since the operating pressure of the second effect evaporator is lower than that of the first effect, the secondary steam of the first effect can be used as heating steam in the second effect. This method can make full use of the latent heat of steam and reduce energy consumption.

Main components:
Evaporator body:
Including heating chamber and evaporation chamber. The heating chamber is the part that uses steam or other heat sources to heat the solution, usually composed of a shell-and-tube heat exchanger or a plate heat exchanger. In a shell-and-tube heat exchanger, steam flows between the tubes, and the solution flows in the tubes, and heat is transferred through the tube wall. The evaporation chamber is where the solution boils and evaporates to produce steam. Its structural design should be conducive to the separation of steam and liquid to prevent droplets from being entrained by steam.

Separator:
It is used to separate the steam and concentrated liquid produced during the evaporation process. It can be a gravity separator, a centrifugal separator or other forms of separators. The gravity separator relies on the density difference between steam and liquid to make the steam flow upward and the concentrated liquid flow downward in the separator to achieve separation. The centrifugal separator uses the centrifugal force to separate the liquid and steam during the rotation process.

Condenser:
The secondary steam generated by the last-effect evaporator is condensed to turn the steam into liquid. The condenser is usually water-cooled or air-cooled. The water-cooled condenser uses cooling water to absorb the latent heat of steam and condense the steam into liquid; the air-cooled condenser uses the flow of air to take away the heat of the steam to achieve condensation.

Vacuum pump (optional):
If evaporation operation needs to be performed at a lower pressure, a vacuum pump is required to maintain the vacuum degree of the system. The vacuum pump can extract the non-condensable gas in the system, reduce the pressure in the evaporator, and make the solution boil and evaporate at a lower temperature, which is very important for handling heat-sensitive solutions.

Pipeline system and valve:
Used to connect various components, transport steam, solution, condensed water and concentrated liquid, etc. The valve is used to control the flow, pressure and flow direction of the fluid to ensure the normal operation of the evaporator.

Workflow:
Feeding:
First, the raw material liquid to be concentrated is transported to the heating chamber of the first effect evaporator through the feed pump. During the feeding process, the feed rate, temperature and other parameters can be controlled according to the properties of the solution and the requirements of the evaporator.

Evaporation and concentration:
In the first effect evaporator, the heating steam enters the heating chamber and transfers heat to the solution through the tube wall, causing the solution to boil and evaporate. The secondary steam generated enters the heating chamber of the second effect evaporator as heating steam. The concentrated liquid in the first effect evaporator is transported to the second effect evaporator through the liquid level difference or pump to continue evaporation and concentration. In the multi-effect evaporator, this process will be carried out in each evaporator in turn until the predetermined concentration multiple is reached.

Steam condensation and recovery:
The secondary steam generated by the last effect evaporator enters the condenser for condensation. The condensed liquid (usually distilled water) can be collected and reused as pure water, or it can be treated in other ways as needed. During the steam condensation process, a certain amount of condensed water will be produced, which can be recycled and used for preheating raw liquid or other purposes.

Concentrated liquid discharge:
The concentrated liquid after multi-effect evaporation is discharged from the bottom of the last effect evaporator. According to the properties and subsequent uses of the concentrated liquid, it can be further treated, such as crystallization, drying, etc.

Performance characteristics:
Energy saving and high efficiency:
The biggest advantage of the multi-effect evaporator is energy saving. Since the secondary steam of the previous effect is used by the next effect, the amount of fresh steam is greatly reduced compared with the single-effect evaporator. For example, the double-effect evaporator can save about 50% of the steam consumption, and the triple-effect evaporator can save more. In theory, as the number of effects increases, the steam consumption will gradually decrease, but too many effects will also increase the equipment cost and operation complexity.

Can handle a variety of solutions:
It can be used to evaporate and concentrate various solutions, including chemical solutions (such as brine, acid and alkali solutions, etc.), juice and milk in the food industry, and liquid medicine concentration in the pharmaceutical industry. Different solutions can choose the appropriate evaporator type and operating conditions according to their properties (such as boiling point increase, heat sensitivity, corrosiveness, etc.).

Flexible operation:
The evaporation process can be controlled by adjusting parameters such as the pressure of the heating steam, the feed rate, and the number of evaporator effects. For example, for heat-sensitive solutions, the pressure of the heating steam can be reduced and the vacuum pump's suction capacity can be increased to reduce the evaporation temperature of the solution and reduce the damage to the effective components in the solution.

High product quality:
During the evaporation concentration process, through reasonable separator design and operation, the steam and the concentrate can be effectively separated to obtain high-quality concentrated products. For example, in the food and pharmaceutical industries, the purity and quality of the concentrated products can be guaranteed to meet the relevant product standards.

Application areas:
Chemical industry:
Used for brine concentration in salt chemical industry, solution concentration in fertilizer production, and organic solvent recovery in organic chemical industry. For example, in the chlor-alkali industry, the multi-effect evaporator can concentrate the brine after electrolysis, increase the concentration of the brine, and meet the requirements of subsequent processes.

Food industry:
Widely used for the concentration of fruit juice, vegetable juice, milk, sugar solution, etc. In juice concentration, the water in the original juice can be evaporated to obtain concentrated juice while maintaining the flavor and nutrients of the juice. In milk processing, multi-effect evaporators can be used to produce dairy products such as milk powder.

Pharmaceutical industry:
Used for the concentration of drug extracts to ensure the stability of the active ingredients of the drugs during the concentration process. For example, in the concentration process of Chinese medicine extracts, the decomposition and denaturation of drug ingredients can be prevented by controlling the evaporation temperature and pressure.

Environmental protection industry:
Used to treat industrial wastewater and sewage, evaporate the water in the wastewater, achieve wastewater reduction and salt concentration. For example, when treating high-salinity printing and dyeing wastewater, the multi-effect evaporator can concentrate the wastewater, reduce the volume of the wastewater, and recover the salt and water resources in it.