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 pumps, liquid nitrogen pumps, liquid argon pumps, and other product pumps. A process pump is also installed in the air separation process, for example, a liquid oxygen circulation pump in the main cold 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 condensing evaporator at the top of the lower tower; The crude argon tower is divided into crude argon tower I and crude argon tower II, and a liquid argon pump is installed between the two towers.
According to different working principles, cryopumps are mainly divided into two types: reciprocating and centrifugal.
Cryogenic liquid pump function
Its purpose is to transport cryogenic liquids from places of low pressure to places of high pressure. With the development of air separation technology, cryogenic liquid has been widely used and developed. Its main 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 send it to the user after vaporization.
Working principle of cryogenic liquid pump
Centrifugal cryogenic liquid pumps work on the same principle as centrifugal water pumps. The centrifugal pump relies on the rotating impeller to do 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 increase in pressure and velocity in the process of flowing from the impeller inlet to the outlet, and then in the diffuser chamber. 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 between the pump and the outside, and the liquid is obtained 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 volumetric compression machine. It uses a piston (plunger) to reciprocate in the working chamber of the hydraulic 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 turns 180°, when the piston (plunger) moves to the left, the volume of the pump cylinder decreases because the liquid is an incompressible fluid, so the pressure will rise rapidly, and when the pressure rises to the point where the liquid can be opened to discharge 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 rate of the reciprocating pump is pulsating and discontinuous. The number of pulses 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 is well sealed, the discharge pressure of the reciprocating pump can meet the pressure requirements of various pipe networks with low, medium, and high pressure.
Cryogenic Liquid Pump Features
The cryopump is different from general-purpose pumps. It needs to keep a low temperature during the liquid delivery process to minimize cold loss, otherwise, the cryopump will not work due to the vaporization of the liquid. Because it works under low-temperature conditions, its pump material, structure, operation, installation, etc. are different from general pumps.
Cryogenic liquid pump classification
A cryogenic liquid pump is a machine used to transport cryogenic liquid and increase its pressure. According to the principle of action, cryopumps can be divided into two categories: vane type and reciprocating type. The vane types are centrifugal, mixed flow, and axial flow. The reciprocating type has a plunger type and a piston type.
Centrifugal pumps are the most commonly used type of vane pump. The centrifugal type is divided into single-stage and multi-stage. The plunger pump is the most commonly used type of reciprocating pump, which can be divided into single-row and multi-row.
Centrifugal cryopumps are mostly used for low and medium-pressure delivery. Column cryopumps are used in systems with high pressure and low flow.