Cryogenic liquid pumps (referred to as cryogenic pumps) are special pumps used to transport cryogenic liquids (such as liquid oxygen, liquid nitrogen, liquid argon, liquid hydrocarbons and liquefied natural gas) in petroleum, air separation and chemical plants. In air separation, it is mainly used to transport liquid products, such as liquid oxygen pump, liquid nitrogen pump and liquid argon pump and other product pumps.
Process pumps are also set in the air separation process, for example: liquid oxygen circulation pump in the main cooling explosion-proof system; when the upper and lower towers are separated, the liquid oxygen at the bottom of the upper tower is sent to the main condensation evaporator at the top of the lower tower; The crude argon column is divided into crude argon column I and crude argon column II, and a liquid argon pump is arranged between the two columns. According to different working principles, cryopumps are mainly divided into two types: reciprocating and centrifugal.
Its purpose is to transport cryogenic liquids from low pressure locations to high pressure locations. With the development of air separation technology, cryogenic liquids have been widely used and developed. Its only function in the air separation plant is: for liquid circulation; or to extract liquid from the storage tank and press it into the vaporizer, and then send it to the user after vaporization.
The working principle of centrifugal cryogenic liquid pump is the same as that of centrifugal water pump. Centrifugal pumps rely on the rotating impeller to perform work on the liquid and transfer the mechanical energy of the prime mover to the liquid. When the pump is filled with liquid, due to the high-speed rotation of the impeller, the liquid generates centrifugal force under the action of the impeller, which drives the liquid to flow from the impeller inlet to the outlet. It can be further converted into pressure energy and then output. Brief summary: The working principle of the centrifugal pump is: when the centrifugal pump is working, the liquid is continuously sucked into the pump by the pressure difference inside and outside the pump, and the liquid obtains kinetic energy by the high-speed rotation of the impeller; The kinetic energy of the liquid is converted into pressure energy.
The working principle of the reciprocating cryopump is similar to that of the reciprocating compressor, and it is a positive displacement compressor. It reciprocates the piston (plunger) in the working chamber of the liquid cylinder, so that the volume of the working chamber changes periodically to realize the whole process of suction-compression-discharge.
When the piston (plunger) moves to the right, the volume of the pump cylinder increases and the pressure decreases accordingly. When the liquid pressure in the inlet pipe is greater than the pressure in the pump cylinder, the suction valve opens and the liquid flows into the pump cylinder. When the crank rotates 180°, when the piston (plunger) moves to the left, the volume of the pump cylinder decreases. Because the liquid is an incompressible fluid, the pressure will rise rapidly. When the pressure rises to open the discharge liquid, the high pressure The liquid is discharged through the discharge valve, which is a working cycle of the reciprocating liquid pump.
It can be seen that the flow of the reciprocating pump is pulsating and discontinuous. The number of pulsations is determined by the rotational speed. The discharge pressure of the reciprocating pump is determined by the characteristics of the pipeline, because the discharge valve can only be opened when the pressure of the liquid in the pump cylinder is higher than the pressure of the discharge pipe. Because of this, as long as the motor power is sufficient and the pump has good sealing performance, the discharge pressure of the reciprocating pump can meet the pressure requirements of various pipeline networks of low, medium and high pressure.