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1. Principle of MVR

Mechanical Vapor Recompression ( Mechanical Vapor Recompression, abbreviated as MVR, technology can be widely used in chemical, pharmaceutical, and environmental protection industries to concentrate or crystallize solutions. The working principle of a conventional evaporator is shown in Figure 1. Fresh steam produced by a boiler is used as the heat source. The solution is heated to its boiling point through a heat exchanger and then further heated to boil and evaporate, producing secondary steam. The water in the solution evaporates and separates as steam, concentrating the solution itself. The secondary steam generated during evaporation is condensed into condensate by cooling water. The heat energy in the secondary steam is transferred to the cooling water and then dissipated into the air, causing heat energy waste and cooling water consumption. The working principle of the Mechanical Vapor Recompression (MVR) evaporator is shown in Figure 2. It uses a compressor to compress the secondary steam generated by the evaporator, increasing its pressure and temperature, then uses it as the heat source for the evaporator instead of fresh steam. This realizes the reuse of heat energy in the secondary steam, enabling heat energy recycling in the evaporator. Only a small amount of electricity is needed to drive the compressor, and no fresh steam is required to recycle the evaporator's heat energy for continuous evaporation. In thermodynamics, the MVR evaporator can also be understood as an open heat pump. The compressor's role is not to generate the heat required for evaporation but to transport the evaporator's heat to form a heat cycle. The MVR evaporator is a new generation of evaporator technology and is an energy-saving and environmentally friendly high-tech solution.

2. Common MVR Devices

( 1) MVR Forced Circulation Evaporation Device: Used for liquids that need to evaporate close to saturation concentration, where evaporation and crystallization occur simultaneously. A forced circulation pump is used to create turbulent flow of the liquid inside the heater tubes. The heated liquid boils and evaporates in the evaporation chamber, and crystals precipitate. A salt leg is set at the bottom of the evaporation chamber to continuously discharge the salt solution to a centrifuge separator. The electricity consumption per ton of evaporated water is less than 60KW, and no additional heat is required.

( 2) MVR Falling (Rising) Film Evaporation Device: When the evaporated liquid does not require crystallization, due to the high heat transfer coefficient of falling (rising) film heat exchangers and low power consumption, single-effect or multiple-effect MVR evaporator devices are mostly used. The electricity consumption per ton of evaporated water is less than 30KW, and no additional heat is required.

( 3) MVR Falling (Rising) Film Enhanced Forced Circulation Evaporation Crystallization Device: When the evaporated liquid has not reached saturation concentration but crystallization is needed, a falling (rising) film enhanced forced circulation evaporation crystallization device is used. The falling (rising) film heat exchanger pre-concentrates the liquid to near saturation before entering the forced circulation evaporation crystallization device. This improves the overall efficiency of the device. Because the boiling point elevation and evaporation characteristics of the feed liquid during pre-concentration are more stable, the performance of the entire device is also more stable. The choice of single-effect or multiple-effect falling (rising) film heat exchangers for pre-concentration depends on the concentration and boiling point elevation data of the liquid to be evaporated. The electricity consumption per ton of evaporated water is less than 45KW, and no additional heat is required.

( 4) MVR Plus Multiple-Effect Evaporation Device: For certain liquids that, after reaching a certain concentration, have a large boiling point elevation exceeding the temperature rise capacity of the steam compressor, and where multi-stage steam compression is not economical, an MVR plus multiple-effect evaporation device can be used. The MVR part is used for pre-concentration, and after the boiling point elevation, new steam multiple-effect evaporation continues the concentration. When no crystallization occurs, the evaporator uses falling (rising) film heat exchangers; when crystallization occurs, forced circulation heat exchangers or flash evaporators are used.

( 5) MVR Acid (Solvent) Evaporation Device: For certain acidic liquids (or solvents), the steam generated after evaporation can cause corrosion and safety issues if it enters the compressor. Moreover, steam compressors are usually designed and manufactured based on water steam models, which complicates compressor design. Our company uses two-effect body technology to solve these problems, has applied for related patents, and has promoted its application.