MVR Falling Film Evaporator
MVR Falling Film Evaporator
MVR is the abbreviated form of the mechanical vapor recompression. This is a technology that recovers the energy of the secondary vapor it generates and therefore reduces the demand for external energy. As early as in 1960s, Germany and France have applied this technology successfully to chemical, pharmaceutical, paper-making, waste water treatment and desalination fields.
MVR Technical Principle:
When mechanical vapor is recompressed, the mechanically driven compressor will compress the secondary vapor generated by the evaporator to form a higher pressure. In this sense, the compressor acts as a heat pump to increase energy to the vapor. In another word, in this process, the low-temperature vapor is compressed by the compressor to improve its temperature and pressure and increase its enthalpy and then flow into the heat exchanger for heat exchange and condensation so as to make use of the latent heat of the secondary vapor. Except machine startup, no generation of additional vapor is required during the entire evaporation process.
MVR Falling Film Evaporator Principle:
The material enters the top part of the falling-film evaporator through the material circular pump and flows in a membranous manner by means of the distribution plate. The primary vapor is the fresh steam heated outside the pipe, boiling the solution to generate the secondary vapor which then is sucked in by the compressor. After pressurization, the secondary vapor has its temperature increased and flows into the heating chamber as a heating source to join the circulating evaporation process. When normally started up, the compressor will suck in the secondary vapor and heat the vapor by means of pressurization. It is in this way that the circular evaporation cycle is then permanently maintained. The moisture evaporated eventually becomes the condensate water and get discharged. No supplement of additional fresh steam is required when the system reach a stable state.
Advantages of MVR Falling-film Evaporator:
1. Short retention time, no aroused degradation of heat sensitive materials.
2. Bigger heat transfer coefficient during evaporation due to the film like contour and faster fluid flow-rate.
3. Small pressure drop and therefore nearly constant pressure and temperature at the heat exchange side, requiring almost no or only minimal sensible heat.
4. An even lower difference in temperature is allowed as the process stream flows only under the gravity rather than temperature difference.
5. Less retentate in the plant.
6. Convective boiling, subject to little effect of the tube surface state on the boiling process.
1. Low energy consumption, low operating costs.
2. Small space occupation.
3. Require fewer public utilities and less total investment.
4. Stable operation and high degree of automation.
5. Require no primary steam.
6. Short retention time due to frequently used single effect.
7. Simple process, high practicability and excellent service performance at some loads.
8. Low operation costs.
9. Capable of evaporating at and below 40 degree without refrigerating plant and particularly suitable for heat sensitive materials.
Design and Function:
Vapor compressor currently used for MVP technology has two forms:the positive displacement type and the centrifugal type
Among positive displacement compressors,the most commonly used compressor is the Roots compressor which compresses gas by bringing two or three lobed rotors to relative motions in the cylinder.This kind of compressor keeps two rotors engaged with each other by relying on synchromesh gears located on the rotor axle ends;the curved surface of each concave on the rotor,together with the inside wall of the cylinder,forms a working displacement,which carries away the gas from the gas suction port during rotor rotation,when the carried gas moves to the vicinity of the exhaust port,the pressure in the working displacement will abruptly pick up at the moment,It is to connect with the exhaust port due to the return of gas at higher pressure,and the gas then is delivered to the exhaust passage.This compressor has a large pressure ratio and a small sucking rate.
Centrifugal compressors provide gas energy by means of high-speed rotation of impeller blades.In these compressors,the gas is accelerated and then passes through the diffuser at downstream of the impller to decelerate.In doing so,the kinetic energy is transformed into pressure energy.According to the direction of fluids passing through the impller ,these compressors are named axial flow,mixed flow,or centrifugal compressors respecitively.They are renowed for large pressure ratio,big flow rate,and good stability.
Whichever is the most suitable compressor depends on specific operating conditions and the economy of the entire system.Critical parameter s include the pressure rise to be achieved and volume flow of steam to be compressed.
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