A vacuum pump is a conveying machine that pumps air under negative pressure and generally exhausts at atmospheric pressure. Its purpose is to create and maintain the vacuum required by the process system. The commonly used vacuum pumps in oil refining and petrochemical production include reciprocating vacuum pumps, water ring vacuum pumps and jet vacuum pumps.
(1) reciprocating vacuum pump
Structure and function principle of reciprocating vacuum pump and reciprocating compressor basic same, cylinder inside and outside differential pressure is small, but its compression ratio is very big (for example, for 95% of the vacuum degree, the compression ratio is about 20 or so). Therefore, the reciprocating vacuum pump suction and discharge valve must be light and flexible, easy to open and close; The remaining gap volume must be very small, at the same time, in order to reduce residual gas in xiao yu gap of the vacuum pump gas rate of adverse effects, often at the end of the vacuum pump cylinder wall has connected balance on either side of the piston in the airway. At the end of the exhaust gas phase, the balancing air duct allows for a brief period of communication between the clearance and the other side of the piston, so that residual gas in the clearance is passed through the balancing airway to the other side of the piston, so as to reduce the pressure of the gas in the clearance, thereby enhancing the suction efficiency, i.e. the coefficient of the volume is increased. The ultimate vacuum produced by reciprocating vacuum pump can reach about 2kPa (absolute pressure). Reciprocating vacuum pump to the gas should not contain liquid, such as the gas contains a lot of steam, must put condensable gas to remove (generally USES condensation) and then into the vacuum pump, reciprocating vacuum pump belongs to the dry vacuum pump.
(2) water ring vacuum pump
Water ring vacuum pump in the inhalation can allow a small amount of water, belong to the wet vacuum pump. Water ring vacuum pump structure is simple and compact, no valve, safe and reliable. However, the vacuum it can produce is not high, up to 85%, and because the rotor rotates in water, it will cause additional friction loss, so the efficiency is low, about 30%~50%. When the water ring vacuum pump is running, it is necessary to continuously replenish water to maintain the liquid seal inside the pump and also play the role of cooling the pump body.
If the inlet of the water ring vacuum pump is connected with the atmosphere, when the outlet is connected with the equipment, it can be used as a blower, and the wind pressure produced shall not exceed 98kPa(table pressure).
(3) rotary vane vacuum pump
If you want to get a high degree of vacuum, it is advisable to use oil-sealed rotary vane vacuum pump. The exhaust valve is immersed in the tank to prevent the gas from flowing back into the cylinder. Water jacket is arranged outside the cylinder to cool the cylinder wall.
Rotary vane vacuum pump can reach a high vacuum degree (the ultimate pressure can reach 0.06Pa), but the extraction rate is relatively small, suitable for the extraction of dry or a small amount of condensable vapor. It is not suitable for the removal of dust and chemicals from lubricating oil.
(4) jet vacuum pump
Jet vacuum pump belongs to a fluid mechanical role type, it is the use of high speed fluid jet pressure can convert the kinetic energy caused by the vacuum to send fluid absorption, both can be used to send gas absorption, also can be used to send liquid absorption. If the working fluid of jet pump is steam, it is steam jet pump. If the working fluid is water or other liquid, it is called water or liquid jet pump.