Comparison of three evaporation concentration technologies: MEE, TVR & MVR

Evaporation concentration, evaporation crystallization, distillation and drying devices are high energy consumption process.
Energy consumption accounts for a large proportion of the operating costs of these devices. Therefore, the reduction and optimization of unit energy consumption is crucial to reduce the whole operation cost.
At present, there are three main technologies to minimize the specific energy consumption, which can be applied alone or in combination:

• Multiple Effect Evaporator (MEE)
• Thermal Vapor Recompression (TVR)
• Mechanical Vapor Recompression (MVR)

Among the three evaporation technologies, MVR Evaporator is the lowest energy consumption technology at present.

 

1) Multiple Effect Evaporator (MEE)

In a multi effect evaporator, the secondary steam produced by the first effect does not enter the condenser, but will be reused as heating medium for second effect. The new steam consumption can be effectively reduced by about 50%. The new steam consumption can be further reduced by using this principle repeatedly.
The maximum heating temperature of the first effect and the minimum boiling point temperature of the last effect form the total temperature difference, and distributed in each effect. As a result, the temperature difference of each effect decreases with the increase of the effect number.
Therefore, the heating area must be increased to achieve the specified evaporation rate. The preliminary estimation shows that the effective heating area increases with the increase of efficiency, so that the cost of steam is reduced gradually. Meanwhile, the investment cost is increased significantly.

 

2) Thermal Vapor Recompression (TVR)

According to the heat pump principle, the steam from the boiling chamber is compressed to the higher pressure in the heating chamber; that is, the energy is added to the steam.
Because the saturated steam temperature corresponding to the pressure of the heating chamber is higher, the steam can be reused for heating. Steam jet compressor is used for this purpose.
They are operated according to the principle of jet pump, without moving parts, the design is simple and effective, and can ensure the highest reliability. Using a thermal steam compressor has the same saving steam / energy result as adding a single effect evaporator.
The operation of a thermal steam compressor requires a certain amount of new steam, the so-called power steam.
The steam must be delivered to the next effect or sent to the condenser as the residual steam. The residual energy contained in the residual steam is approximately equal to the energy supplied by the power steam.

 

3) Mechanical Vapor Recompression (MVR)

MVR is called Mechanical Vapor Re-compression. It use the centrifugal compressor to re-compress the secondary vapor (low temperature and low pressure) which is evaporated from the liquid material to rise its temperature and pressure, so as to reuse it as heating source to evaporate the liquid material again. The process is to convert a small amount of electric energy to more heat energy.
Theoretically, compared with multi-effect evaporator, it can save more than 50%~80% energy consumption and 90% cooling water. Among the three evaporation technologies, MVR is the lowest energy consumption technology at present.

 

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