Application of Jet Vacuum Pump in Chemical Industry
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. The application of vacuum technology in various processing processes can save energy, reduce consumption, accelerate reaction speed, improve product quality and increase economic benefits. Understanding, but vacuum technology is a frontier science. China's vacuum industry was 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, many manufacturers are not clear about how to apply and select vacuum pumps produced by them in different processes (more). Not to mention the design of new products according to the process parameters provided by users, which brings great inconvenience to the selection of customers. Based on the production, development and matching experience of our company for more than 30 years, this paper expounds how to reasonably select jet vacuum pumps for several typical processes in the chemical industry.
I. Some Concepts of Vacuum Pump
How to apply vacuum pump well in the process of chemical production needs to clarify the following concepts:
1. The concept of "vacuum": "vacuum" refers to the state of a gas below an atmospheric pressure in a given space, that is, the gas molecular density in the space is lower than the atmospheric pressure in the region. The space state in which there is no gas at all is called absolute vacuum.
2. Vacuum pumps: devices used to generate, improve and maintain vacuum.
3. Pumping capacity: the flow rate of the suction gas per unit time under the working pressure of the vacuum pump. Unit: kg/h or m3/h;
4. Limit pressure (vacuum degree): The absolute pressure that a vacuum pump can achieve when the extraction capacity is zero. Units: Pa, KPa, MPa or mmHg (the local atmospheric pressure is the ultimate vacuum under extreme absolute pressure);
5. Working Pressure (Vacuum): Absolute Pressure of Jet Pump at Rated Pumping Volume. SETTING: Pa, KPa, MPa or mmHg (working vacuum for working absolute pressure reduction of local atmospheric pressure);
6. Working Steam Pressure: Working Steam Pressure of Steam Jet Vacuum Pump. Unit: MPa or kgf/cm2;
7. Working Steam Consumption: Steam Consumption per Unit Time of Steam Jet Vacuum Pump. Unit: kg/h;
8. Cooling water temperature: circulating water temperature of water jet pump or condenser circulating water temperature of steam jet vacuum pump. SETTING: OC;
9. Cooling water circulation: the circulating water flow through the condenser of water ejector or steam ejector pump per unit time. Unit: kg/h;
2. Several Vacuum Pumps in Chemical Industry and Their Advantages and Disadvantages
1. Several kinds of vacuum pumps commonly used in chemical industry-the 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, water ring vacuum pumps and Roots vacuum pumps belong to variable-volume vacuum pumps. Type 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. Working Principle and Advantages and Disadvantages of Jet 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. 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 chemical operation because of its wide vacuum range, direct suction of condensable gases such as water vapor and granular media, simple structure, easy operation, small maintenance of non-operating components, energy saving and consumption reduction. The working principles of various jet vacuum pumps are described below.
(1) Working Principle and Structure of Water Jet Vacuum Pump
The equipment composition of the water jet vacuum pump is shown in its structure sketch. Its working principle 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 is ejected through multiple Laval nozzles on the orifice plate. The high-speed jet forms a vacuum in the mixing chamber of the ejector, and the medium is pumped in vacuum. Enter the ejector mixing chamber, mix fully with the high-speed water flow in the mixing chamber and discharge to the circulating water tank after Venturi tube reduces speed and boosts pressure. The non-condensable gas is released, and the condensable vapor overflows from the overflow outlet of the water tank, so work is done repeatedly. 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.