At present, vacuum technology is more and more widely used in vacuum evaporation, crystallization, distillation, sublimation, drying, negative pressure concentration, dehydration, chemical reaction absorption and vacuum conveying of materials in petroleum, chemical, pharmaceutical and other industries. Vacuum technology can save energy, reduce consumption, accelerate reaction speed and improve the efficiency of various processing processes. There is a consensus on product quality and economic benefits, but vacuum technology is a frontier science. China’s vacuum industry developed on the basis of digesting and absorbing products from the former Soviet Union, the United States, Japan and Germany after liberation, although the number of vacuum equipment manufacturers in China has mushroomed in recent years. However, many manufacturers are not clear about how to select the type of vacuum pump produced by them in different processes, which brings great inconvenience to the selection of users.
How to apply chemical vacuum pump in the process of chemical production is introduced by the manufacturer of EVP vacuum pump.
Several Vacuum Pumps in Chemical Industry and Their Advantages and Disadvantages
1. Several kinds of vacuum pumps commonly used in chemical industry-common vacuum pumps in chemical industry can be simply divided into variable-volume vacuum pumps and jet vacuum pumps. Variable-volume vacuum pumps are devices that use the periodic change of pump chamber volume to complete suction and exhaust, reciprocating vacuum pumps, rotary vane vacuum pumps, slide valve vacuum pumps and water rings. Vacuum pump and Roots vacuum pump belong to variable volume vacuum pump. Jet vacuum pump is a momentum transfer pump that uses the high-speed jet generated by the pressure drop of Venturi effect to transport gas to the outlet. Water jet vacuum pump, steam jet vacuum pump, steam-water series jet vacuum pump and steam-water combined jet vacuum pump belong to the same kind of jet vacuum pump.
2. Working Principle and Advantages and Disadvantages of Variable Volume Vacuum Pump
(1) Reciprocating vacuum pump, rotary vane vacuum pump, slide valve vacuum pump and Roots vacuum pump inhale, compress and discharge gas by reciprocating motion or rotation of piston. Their advantage is that the vacuum degree of the new pump is relatively high, but the piston is a running part, so the wear of the piston is inevitable. With the increase of maintenance times, the working vacuum degree will continue to decline until it can not meet the production requirements. This kind of pump has the disadvantage of high working noise, high fuel consumption and high failure rate. Generally, it needs to open a spare one, which invisibly increases the cost of equipment investment and operation. In addition, if this kind of pump is used to pump condensable gases such as suction steam, lubricating oil will be emulsified, so it can only be used to suck non-condensable (air) gases, nor can it suck medium with granular shape, which limits its scope of application.
(2) The water ring vacuum pump rotates by an eccentric rotor with multiple blades in the pump shell, throwing water into the pump shell to form a water ring concentric with the pump shell, and the water ring and the rotor blade form a volume periodic change, thus inhaling, compressing and discharging gas. It has the advantages of large suction capacity at low vacuum and direct suction of condensable gases such as water vapor. Its shortcomings are low vacuum, inability to suck granular media, high-speed rotation of the rotor is not easy to do anti-corrosion treatment, so it can not suck corrosive media.
3. The working principle and advantages and disadvantages of jet vacuum pump is a momentum transfer pump, which uses the high-speed jet generated by the pressure drop of Venturi effect to transport gas to the outlet. It is divided into water jet vacuum pump, steam jet vacuum pump, steam-water series jet vacuum pump, steam-water combination jet vacuum pump. Jet vacuum pump has been widely used in various processes of chemical operation for its advantages of wide vacuum range, direct suction of condensable gases such as suction steam and granular media, simple structure, easy operation, small maintenance of non-operating components, energy saving and consumption reduction, etc. Working principle.
(1) The working principle and structure sketch of the water jet vacuum pump are shown in its structure sketch. The working principle of the water jet vacuum pump is that the water in the circulating water tank produces certain pressure and velocity after the circulating water pump works. Water with certain pressure and velocity enters the catchment chamber of the water ejector, and many water enters the catchment chamber of the water ejector through the orifice plate. Laval nozzle injection, the formation of a high-speed jet ejector mixing chamber to create a vacuum, the medium is pumped into the ejector mixing chamber under the action of vacuum, in the mixing chamber and high-speed water flow fully mixed, Venturi tube speed down, pressurization and discharged into the circulating water tank, non-condensable gas precipitation, condensable vapor overflow from the water tank. The outlet overflowed, so repeated work. It has the advantage of low-level whole machine type, higher vacuum than water ring vacuum pump. Replacing W-type reciprocating vacuum pump, it can cancel the pre-condenser and save one-time equipment investment and operation costs.
(2) The working principle and structure sketch of the steam-water series jet vacuum pump The steam-water series jet vacuum pump is one or more stages in series in front of the ejector of the water-jet vacuum pump, i.e. the steam-water series jet vacuum pump. The structure of the steam-water series jet vacuum pump can be seen. Its working principle is that saturated or superheated vapor at a certain pressure enters the mixing chamber of the steam ejector after decompression and acceleration through the Laval nozzle, which makes the mixing chamber produce vacuum, and the extracted medium is sucked into the mixing chamber to mix with the working vapor. After mixing, the fluid passes through the diffuser, the velocity decreases and the pressure rises until it reaches the next level. The first stage suction inlet pressure is discharged into the next stage steam jet pump or water jet pump. It is a low-level whole machine type with relatively high vacuum, which can replace the water ring-Roots unit and the rotary blade-Roots unit to directly suck condensable vapor. However, the amount of non-condensable gas pumped in high vacuum is limited.
(3) The working principle and process flow chart of a new type of high efficiency steam jet vacuum pump The new type of high efficiency steam jet vacuum pump is composed of one or more stage steam jet pumps and high efficiency condensers. Saturated or superheated vapor at a certain pressure enters the mixing chamber of the steam ejector after reducing pressure and increasing speed through the Laval nozzle to produce the mixing chamber. In the raw vacuum, the extracted medium is sucked into the mixing chamber to mix with the working steam. After mixing, the fluid passes through the diffuser, the velocity decreases and the pressure rises until it reaches the pressure of the next suction port and is discharged into the next steam ejector. After the mixed fluid discharged by the steam ejector in front of the condenser enters the high efficiency condenser, the condensable vapor body is cooled to liquid and non-condensable gas and discharged out of the condenser with the cooling water (see the process flow chart of the new high efficiency steam ejection vacuum pump). It can be installed at any height, and the amount of non-condensable gas in the medium suitable for suction is relatively small. Most of the process is condensable vapor body. It can save more than 60% of the working steam instead of the traditional multi-stage steam jet vacuum pump.
(4) The working principle and flow chart of the steam-water combined jet vacuum pump are composed of a steam-water combined jet vacuum pump in series behind the first condenser of the traditional steam jet pump. The working principle of the steam-water combined jet vacuum pump is shown in the flow chart of the steam-water combined jet vacuum pump. It overcomes the shortcomings of steam-jet vacuum pump and water-jet vacuum pump, and gives full play to their advantages. It can not only achieve a higher working vacuum, but also have a larger pumping capacity. Compared with the traditional multi-stage steam-jet vacuum pump, it can save more than 50% of the working steam, 30% of the cooling water, and it does not need to be equipped with start-up pump and pumping. The empty tower has a short time.
(5) The advantages of the multi-stage steam jet vacuum pump are simple structure, convenient use, stable and reliable operation, but the disadvantages are large steam consumption (high operating costs), which must be installed above 11 meters height, and inconvenient maintenance.
In the process of chemical production, the vacuum pump can be selected reasonably according to the working pressure required by the specific process and the nature of the suction gas. Generally, the working pressure required by the specific process is determined first, and the vacuum required by the negative pressure distillation, distillation and sublimation is high (working pressure is low). The vacuum required for vacuum evaporation, drying, concentration, crystallization, dehydration, decolorization, chemical reaction absorption and vacuum conveying of materials is low (high working pressure). After the working pressure is determined, the chemical vacuum pump can be reasonably selected according to the size of the pumping volume and the nature of the pumped gas.