The Rinciples And Types Of Evaporator

The Rinciples and Types of Evaporator

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Evaporator is an equipment by heating the solution to make it concentrated or precipitate grains from it . Evaporator is mainly composed of two parts of the heating chamber and the evaporation chamber . The heating chamber provides heat which is needed for the liquid to make it boiling and vaporized while the evaporation chamber makes the gas-liquid phase get separated completely . The steam which is generated in the heating chamber comes with a large amount of liquid foam , and when it gets into the evaporation chamber which is relatively larger , the liquid depends on the condensation of itself or the demister or something esle to separate from the vapor . The demister usually located in the top of the evaporation chamber .

The basic form of the evaporator :

Mechanical vapor recompression (MVR evaporator)

The secondary steam from the evaporator undergoes compression by the compressor , pressure, temperature , enthalpy increases, then goes into the heating chamber of the evaporator to be used as the heating steam so that the material boiling state was maintained , while the heating steam itself condensed into water . Thus , the original waste steam has been made full use of which not only recycles the latent heat , but also improves the thermal efficiency , raw steam economy equivalent of 30 multi-effect evaporation effect . To make the manufacturing of the evaporation device as simple as possible and ensure the convenience of operation , the single-effect centrifugal compressor is often used , and the high pressure positive blower or the turbocompressor are also be OK. The volume flow of these machines is higher when they are in a compression ratio of 1:1.2 to 1:2 . For low evaporation rate , the piston compressor , the sliding vane compressor or the screw compressor can be used . Evaporation equipment is compact, small footprint , and the required space is small as well . Cooling system can be omitted . For those existing factories which need to expand the evaporation equipment but are lack of steam , water supply capacity and the site of the plant is not enough , especially the occasions in which the low temperature evaporation needs freezing water for condensation , you can not only save the investment but also achieve the better energy efficiency .


Thermal vapor recompression (TVR)

Part of the secondary steam from the separator goes into the eductor and get mixed evenly in the driven of high pressure work steam , then comes into the heating chamber to be used as the heating steam to heat the feed solution . Another part enters the condenser , and discharges after condensated . The heating steam condenses into water in the heating chamber and then discharges . The tube solution was heated into steam and get concentrated by heating steam, and discharges after meeting the requirements , the steam jet pump has a simple structure, stable operation, low price and so on. Steam jet pump , representing an increase of an effect on the performance of the evaporator .


Falling Film Evaporator

In falling film evaporator , the liquid and the vapor flow down . The feed solution is preheated to the boiling temperature by the preheater and formed into a uniform film via the top liquid distribution means , then goes into the heating pipe and partially evaporated in the tube. The secondary steam and the concentrated liquid in the pipe flow down . The feed liquid stays a short time in the evaporator so that it is able to adapt to the evaporation of heat-sensitive solution . In addition , falling film evaporator is also suitable for high -viscosity solution with a viscosity in the range of 0.05-0.4Pas. Falling film evaporator could easily make the tube foam rupture , hence applicable to evaporate easily foam materials. Due to the falling film heat transfer of the falling film evaporator , so the heat transfer coefficient is higher than other forms of evaporators ; addition , a falling film evaporator has no static pressure of the liquid column so temperature difference is significantly higher than the evaporation of other forms. Therefore you can get good heat transfer effect, and the minimum time investment makes it the select evaporator forms for the owners .


Forced Circulation Evaporator

Such evaporators use external power ( circulation pump ) to send the circulation pipe decreasing solution and a part of the origin feed solution into the heating chamber . Greatly accelerate the circulation speed. The size of the circulation rate can be controlled by adjusting the flow rate of the pump . Generally the circulation rate is 2.5m / s or more. When the circulation liquid flowing through the heat exchanger it will be heated and then evaporated partly when the pressure is reduced in the separator , thereby cooling the liquid to the boiling point of the it should be under this pressure , especially for materials crystallize . 


Natural Circulation Evaporator

In the natural circulation evaporator , the liquid is heated and evaporated in the heater , the secondary steam generated goes into the separation chamber by the top , discharge the liquid after separating it . The separated liquid flows back to the evaporator through the circulation pipe , and goes into the evaporator heaterby the role of the thermosyphon heat . Thus it has formed a closed loop . The higher the temperature difference between the heater and the separator , the more vapor bubbles will be generated . This enhanced thermal siphon effect and increase the flow rate to obtain a better heat transfer effect . Natural circulation evaporator circulating pump doesn't need the circulating pump and has a lower operating costs.

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