Today, as industrial production continues to pursue high efficiency, energy saving and environmental protection, MVR evaporator, as an advanced evaporation equipment, is gradually emerging and is widely used in many fields. MVR is the abbreviation of Mechanical Vapor Recompression. This technology greatly reduces the dependence on external energy by cleverly recycling the secondary steam energy generated by itself, bringing significant economic and environmental benefits to enterprises. Next, let us take a deeper look at the working principle, unique advantages and rich application scenarios of MVR evaporator. ​

I. Working principle of MVR evaporator​

(I) Basic principle​

The core principle of MVR evaporator is to use compressor to compress the secondary steam generated during evaporation. When the material is heated and evaporated in the evaporator, a large amount of low-temperature and low-pressure secondary steam will be generated. These steams contain a certain amount of energy, but cannot be directly used to heat the material again. At this time, the compressor plays a key role. It sucks in the low-temperature and low-pressure secondary steam and compresses it through mechanical work, which significantly increases the temperature and pressure of the steam, and the enthalpy value also increases accordingly, thereby converting it into high-temperature and high-pressure steam. This part of compressed steam is sent back to the heating chamber of the evaporator and used as a heat source to heat the material. In the process of releasing latent heat, the steam condenses into liquid water and is discharged, completing the reuse of energy. In addition, the sensible heat of the condensed water can be further used to preheat the material to be evaporated, realizing the multi-level utilization of energy and greatly improving the thermal efficiency. ​

(II) Detailed explanation of the work process ​

Material evaporation: The material to be processed first enters the evaporation chamber of the evaporator, where the material is heated (the initial heating can usually be done by a small amount of fresh steam, etc.), and the solvent (such as water) begins to evaporate, generating secondary steam. As the evaporation process continues, the solute in the material gradually concentrates. ​

Steam compression: The secondary steam generated from the evaporation chamber enters the compressor. Compressors generally include centrifugal and Roots types. Taking the centrifugal compressor as an example, it uses a high-speed rotating impeller to do work on the steam, increasing the speed and pressure of the steam, thereby achieving a temperature increase. For example, the saturated water vapor from the evaporator is compressed from the suction state p1 = 1.9bar, t1 = 119℃ to p2 = 2.7bar, t2 = 161℃ (compression ratio Π = 1.4). ​

Heat exchange and condensation: The compressed high-temperature and high-pressure steam enters the heating chamber of the evaporator and exchanges heat with the material in the evaporation chamber. The steam releases latent heat, and the material absorbs heat and continues to evaporate. After releasing heat, the steam gradually condenses into liquid water and is discharged through the condensate outlet. ​

Circulation and control: During the entire process, the temperature, pressure, liquid level and other parameters in the system are monitored in real time through sensors. The control system automatically adjusts the power of the compressor, the flow rate of the steam, and the feeding and discharging speed of the material according to these parameters to ensure the stable operation of the evaporation system. For example, when the liquid level in the evaporation chamber is too high, the discharge pump flow rate is automatically increased; when the temperature in the heating room is too low, the compressor is adjusted to increase the steam temperature.

II. Key components of MVR evaporator

(I) Compressor

The compressor is the core component of the MVR evaporator, and its performance directly affects the operating efficiency and energy consumption of the entire system. Common types of compressors include centrifugal compressors and Roots compressors.

Centrifugal compressor: It has the advantages of large volume flow, compact structure, and smooth operation. It uses the high-speed rotation of the impeller to enable the steam to obtain energy under the action of centrifugal force and achieve pressure and temperature increase. It is suitable for large-scale evaporation systems and can handle a large amount of secondary steam.

Roots compressor: It is a positive displacement compressor with high efficiency in a lower compression ratio range. It uses two synchronously rotating rotors to push the steam from the air inlet to the air outlet to achieve steam compression. Roots compressors are widely used in some occasions where the compression ratio is not high and the flow rate is relatively small.

(II) Evaporator

The evaporator is the place where the material evaporates, and its structural design directly affects the evaporation efficiency and product quality. Common types of evaporators include falling film evaporators, forced circulation evaporators, etc.
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Falling film evaporator: The material enters from the liquid distributor at the top of the evaporator, and forms a uniform liquid film along the inner wall of the heat exchange tube under the action of gravity and flows downward. The heating steam heats the material outside the tube, and the material gradually evaporates during the flow. The falling film evaporator has the advantages of high heat transfer efficiency and short material residence time, and is suitable for the evaporation of heat-sensitive materials. ​

Forced circulation evaporator: The material circulates at high speed in the evaporator through a circulation pump. After the material is heated in the heating tube, it enters the evaporation separation chamber for gas-liquid separation. The forced circulation evaporator can handle high-viscosity and easy-to-crystallize materials, and the power provided by its circulation pump can effectively prevent the material from scaling and clogging in the heating tube. ​

(III) Heat exchanger ​

The heat exchanger plays a key role in transferring heat in the MVR evaporator. The compressed high-temperature steam exchanges heat with the material to be evaporated in the heat exchanger, transfers heat to the material, and condenses itself into liquid water. The heat transfer efficiency of the heat exchanger directly affects the energy utilization rate of the system. Common types of heat exchangers include plate heat exchangers and tube heat exchangers. ​

Plate heat exchanger: It is composed of a series of corrugated metal plates stacked together, with fluid channels formed between the plates. It has the advantages of high heat transfer efficiency, small footprint, easy cleaning and maintenance. ​

Tube heat exchanger: It is composed of tube bundles, shells, tube sheets and other components. The material and heating medium flow in the tube side and shell side respectively, and heat exchange is carried out through the tube wall. The tube heat exchanger has a sturdy structure and is suitable for high temperature, high pressure and highly corrosive working conditions. ​

(IV) Control system ​

The control system is the guarantee for the stable operation of the MVR evaporator. It monitors the temperature, pressure, liquid level, flow rate and other parameters in the system in real time through various sensors, and automatically adjusts the compressor speed, steam valve opening, material pump flow rate and other actuators according to the preset control strategy to ensure that the system operates under the best working conditions. The advanced control system also has remote monitoring and data recording functions, which facilitates operators to grasp the equipment operation status in real time and analyze historical data to provide a basis for the optimization and maintenance of the equipment.

III. Advantages of MVR evaporator

(I) High energy efficiency

One of the biggest advantages of MVR evaporator is its extremely high energy efficiency. Traditional evaporation equipment usually requires a large amount of external heat source (such as steam) to maintain the evaporation process, while MVR evaporator greatly reduces the demand for external energy by recycling the latent heat of secondary steam. According to statistics, MVR evaporator can save 50% - 80% of energy consumption compared with traditional multi-effect evaporation equipment. With the rising energy prices today, this undoubtedly brings significant cost savings to enterprises. For example, in the production process of a chemical enterprise, after adopting MVR evaporator, the annual steam consumption cost was reduced by millions of yuan.

(II) Low operating cost

Due to the significant reduction in energy consumption, the operating cost of MVR evaporator has also dropped significantly. In addition, MVR evaporator usually adopts a control system with a high degree of automation, which reduces the workload of manual operation and maintenance, and further reduces labor costs. At the same time, its compact structural design makes the footprint smaller, reducing the cost of plant construction and leasing. Overall, the MVR evaporator can save a lot of operating costs for enterprises during long-term operation. ​

(III) Good environmental performance​

Lower energy consumption means less greenhouse gas emissions. During operation, the MVR evaporator reduces its dependence on external heat sources (such as steam generated by coal-fired and oil-fired boilers), greatly reducing the emission of pollutants such as carbon dioxide and sulfur dioxide, which meets the strict requirements of today's society for environmental protection. For example, in some pharmaceutical and food industries with extremely high environmental protection requirements, MVR evaporators are widely used due to their excellent environmental performance. ​

(IV) High product quality​

During the evaporation process, the MVR evaporator uses a lower temperature difference for heat exchange, which can effectively avoid the quality degradation of the material due to overheating. This advantage is particularly obvious for some heat-sensitive materials (such as medicines, fruit juices, etc.). Under low-temperature evaporation conditions, the effective ingredients in the material can be better retained, thereby ensuring the quality and taste of the product. For example, in the process of fruit juice concentration, the use of MVR evaporators can retain the vitamins and aroma components in the juice to the greatest extent, making the concentrated juice taste closer to fresh juice.​

(V) Simple operation and high degree of automation​

The MVR evaporator is equipped with an advanced control system. The operator only needs to set the relevant parameters on the control interface, and the equipment can run automatically. The system can automatically adjust the operating status according to the real-time monitored parameters to ensure the stability and efficiency of the evaporation process. At the same time, the equipment also has fault diagnosis and alarm functions. Once an abnormal situation occurs, the operator can be notified in time for processing, which greatly reduces the difficulty of operation and labor intensity.

IV. Application scenarios of MVR evaporators

(I) Chemical industry

Wastewater treatment: A large amount of high-salt, high-concentration organic wastewater is generated during the chemical production process. MVR evaporators can evaporate and concentrate these wastewaters, separate the salt and organic matter in the wastewater, and achieve standard discharge or reuse of wastewater. For example, in the chlor-alkali chemical industry, MVR evaporators can be used to treat wastewater containing salts such as sodium chloride and sodium hydroxide, recover useful substances in it, and reduce the cost of wastewater treatment.

Salt crystallization: When recovering inorganic salts such as sodium chloride, sodium sulfate, and ammonium sulfate from chemical wastewater, the MVR evaporator can make the solution reach a supersaturated state through evaporation and concentration, thereby achieving crystallization and precipitation of salts. Compared with traditional evaporation and crystallization processes, this method has lower energy consumption and higher crystallization efficiency.

Organic solvent recovery: In chemical production, many organic solvents (such as ethanol, acetone, etc.) need to be recycled and reused. MVR evaporator can evaporate and separate mixed liquids containing organic solvents, concentrate and recycle organic solvents, reduce production costs, and reduce environmental pollution caused by organic solvents.
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(II) Pharmaceutical Industry​

Concentration of Chinese medicine extracts: Chinese medicine extracts contain a large amount of water and need to be concentrated to increase the concentration of active ingredients. The low-temperature evaporation characteristics of the MVR evaporator can prevent the heat-sensitive components in Chinese medicine from being destroyed during the concentration process, ensuring the efficacy of Chinese medicine. For example, MVR evaporators have been widely used in the concentration process of Chinese medicine extracts such as ginseng and angelica. ​

Concentration of fermentation broth: In the fermentation production process of drugs such as antibiotics and amino acids, the fermentation broth needs to be concentrated. MVR evaporator can efficiently concentrate the fermentation broth while maintaining the activity and purity of the fermentation product and improving product quality. ​

Solvent recovery: A large amount of organic solvents, such as ethanol and methanol, are used in the pharmaceutical process. MVR evaporator can be used to recover these organic solvents, reduce production costs, and meet the environmental protection requirements of drug production.
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(III) Food Industry​

Juice Concentration: MVR evaporator can concentrate juice at low temperature, retaining the flavor, color and nutrients of the juice to the greatest extent. After being concentrated by MVR evaporator, the juice has a richer taste and is easy to store and transport. For example, in the production process of orange juice, apple juice and other juices, MVR evaporator has become the mainstream concentration equipment. ​

Dairy Processing: In the concentration process of dairy products such as milk and whey, MVR evaporator can avoid the damage of high temperature to the nutrients such as protein and fat in dairy products, and ensure the quality of dairy products. At the same time, through concentration, the shelf life of dairy products can be extended and the added value of products can be increased. ​

Sugar Liquid Concentration: For the concentration of sugar liquids such as syrup and honey, MVR evaporator can operate at a lower temperature to prevent the sugar liquid from caramelizing due to overheating, which affects the product quality. The concentrated sugar liquid has a higher concentration, which is convenient for subsequent processing and packaging.​

(IV) Environmental protection industry​

Leachate treatment: Leachate contains a large amount of organic matter, ammonia nitrogen, heavy metals and other pollutants, which is difficult to treat. MVR evaporator can evaporate and concentrate leachate, reduce the volume of leachate, and reduce the load of subsequent treatment. At the same time, part of the water resources can be recovered through evaporation and concentration, and resources can be recycled. ​

Electroplating wastewater treatment: Electroplating wastewater contains a large amount of heavy metal ions (such as chromium, nickel, copper, etc.) and cyanide and other harmful substances. MVR evaporator can evaporate and concentrate electroplating wastewater, separate heavy metal ions and other pollutants, and realize wastewater reuse and heavy metal recovery. For example, in chrome plating wastewater treatment, MVR evaporator can concentrate and recover chromium ions in wastewater for electroplating production again. ​

Printing and dyeing wastewater treatment: Printing and dyeing wastewater contains a large amount of pollutants such as dyes, auxiliaries and inorganic salts, with dark color and high COD. MVR evaporator can evaporate and concentrate printing and dyeing wastewater, remove salt and dyes from wastewater, make wastewater meet reuse standards, and reduce water resource consumption and wastewater discharge of printing and dyeing enterprises. ​

(V) Seawater desalination and resource recovery​

Reverse osmosis concentrated water treatment: Reverse osmosis is a commonly used technology in seawater desalination and wastewater treatment, but it will produce a certain amount of concentrated water. MVR evaporator can further concentrate reverse osmosis concentrated water, recover water resources in it, and improve the utilization rate of water resources. At the same time, the volume of concentrated concentrated water is reduced, which is convenient for subsequent treatment and disposal. ​

Lithium extraction from salt lake: Salt lake brine contains rich lithium resources, but the concentration of lithium is low, so it needs to be concentrated and extracted. MVR evaporator plays an important role in the process of lithium extraction from salt lake. By evaporating and concentrating salt lake brine, the concentration of lithium is increased, providing more favorable conditions for subsequent lithium extraction process.

V. Comparison between MVR evaporator and other evaporators

In order to understand the characteristics of MVR evaporator more intuitively, we compare it with traditional multi-effect evaporator and thermal vapor recompression (TVR) evaporator. The specific comparison is shown in the following table:

As can be seen from the comparison table, MVR evaporator has obvious advantages in energy consumption, operating costs, environmental protection performance and product quality, and is especially suitable for industries and application scenarios that are sensitive to energy costs and have high requirements for product quality. ​

VI. Conclusion​

As an innovative evaporation technology, MVR evaporator has shown broad application prospects in many industries such as chemical, pharmaceutical, food, and environmental protection due to its many advantages such as high efficiency and energy saving, environmental protection, high product quality, and simple operation. With the increasing attention paid to energy issues and environmental protection requirements, MVR evaporator will surely play a more important role in future industrial production and provide strong support for enterprises to achieve sustainable development. When choosing MVR evaporator, enterprises should consider the performance, investment cost and operating cost of the equipment according to their own production needs, material characteristics, energy supply and other factors, and choose the most suitable equipment and process solutions. At the same time, with the continuous advancement of science and technology, MVR evaporator technology is also constantly developing and improving, and it is expected to be applied in more fields in the future and achieve better economic and social benefits.