Key Words: Centrifuge, Evaporator, CBD
Evaporation and crystallization technologies are used to concentrate liquid solutions, with dissolved solids, or to precipitate and recover materials dissolved in solution as products. There a number of different evaporator configurations used in different industries based on the unique characteristics of the materials being concentrated. This is especially true in the food industry.
Mechanical vaporization re-compression system, which is called MVR which principle is to compress the second steam generated by evaporator by high efficiency steam compressor; this process transfers electric energy to heating energy and higher the pressure and temperature of second steam. The second steam with higher temperature will be sent to evaporation room to heat the product for evaporation. So the latent heat of vaporization of the second steam can be circularly used. Making use of less energy which is the mechanical energy of compressor blade wheel as the compression heat pump, energy is added into the heating medium and is circularly used in heating process. Under this circumstance, no need to add first steam as heating medium.
Compress secondary steam by using steam centrifugal compressor or other steam compression device to make sure its physical properties meet with the requirements for heating steam ; evaporation that uses it as heating steam only requires fresh steam supply when the machine is started. After entering normal operation, there is no need to supply new steam and no (or very little) secondary steam needs condensation. Therefore MVR evaporation substantially cuts down steam demand but consumes more power.
Multi-effect Evaporation Steam Consumption
（t steam/ t water)
1）Main driven power of MVR evaporation system is electric energy. Electric energy transfer to mechanical energy and improve the quality of second steam which is more economic than produce or purchase fresh steam.
2）Under most of the evaporation process, system no need fresh steam during operation. Only need some steam compensation for pre-heating the raw material when heat energy from product discharged or mother liquid cannot be recycled due to process requirement.
3）No need independent condenser for second steam condensation, so no need circulating cooling water. Water resource and electric energy will be saved.
4）Compared with traditional evaporators, MVR evaporator temperature difference is much smaller, can achieve moderate evaporation, greatly improve product quality and reduce fouling.
5）Evaporation temperature of system can be controlled and very suitable for evaporation an concentration of thermal sensitive product.
6）Lowest energy consumption and operation cost,electricity consumption of one ton water's evaporation is 2.2ks/C.
Excellent condensate segregation
Temperature difference is small ,heating is gentle ,the loss of product is less
Compact structure and lower building cost,plant area is 50% less than that of traditional evaporator
Surrounding is friendly,no gas and no steam
Good adaptability in low loading condition,flexibility of operation is good and has a longer service life
Consumptio of circular water is low and energy saving is obvious
No fresh steam or cooling water required
Evaporation can be carried out under 40degree and equipment need not to be frozen,specially suitable for thermal activity products
No condenser or one with small heat exchange area required
Applied to multiple areas, such as: "zero release" solution for industrial waste water, Evaporation and concentration for process industry, food fermentation (aginomoto, citric acid, starch and sugar), pharmacy (traditional Chinesemedicine preparation, low temperature concentration of western medicine), fine chemical (pesticide, synthetic dyes, organic pigments, paints, spice and essence, cosmetic), chlorine chemical (salt water concentration), seawater desalt and metallurgical industry, etc.
Especially in the following industries, MVR is widely used.
1) Seawater desalination
At present, the main methods of seawater desalination are reverse osmosis and distillation. The distillation method mainly includes multistage flash, low-temperature multi-effect distillation and pressure steam distillation technology. According to various comparative studies, MVR heat pump circulating system is the most energy-saving solution for seawater desalination system.
Many sugar factories have seen capacity expansions and process additions. As a result of this growth, existing steam boilers have been pushed to maximum capacity limits. Therefore, use of energy saving techniques is considered a viable option. A system of mechanical vapor recompression units for initial concentration to remove large quantities of water followed by multiple-effect, steam heated units to finish evaporate the process streams is an excellent solution for the project requirements.
In China, multiple-effect evaporation facilities are widely used in salt production process while in Europe MVR salt producing method is more widely applied. The MVR salt making technology can effectively reduce energy consumption in this era with the increasing cost of energy.
In chemical, chemical fertilizer, pesticide, textile and some other industries, waste-water usually contains a large number of non-organic salts, such as sodium chloride and sodium sulfate, etc. If the high-salt waste-water is discharged directly without treatment, it will not only pollute the environment but also cause the soil salinization.
At present, waste-water treatment methods include physical and chemical filtration, MVR evaporation and concentration, multiple-effect evaporation, membrane purification and so on. Compared with other methods, MVR evaporation and concentration has obvious advantages in terms of lower energy consumption and reduced running cost.