Cryogenic liquid pumps are a special type of pump that is often used in petroleum, air separation and chemical plants. As the name suggests, cryogenic liquid pumps are used to transport cryogenic liquids, such as liquid oxygen, liquid nitrogen, liquid argon, liquid hydrocarbons, and liquefied natural gas. Since the medium of the cryogenic liquid pump is cryogenic liquid, if it absorbs more heat from the surrounding of the pump, the cryogenic liquid in the pump will vaporize in large quantities and produce gas, which will affect the work of the pump. Therefore, cryogenic pumps have special requirements in terms of structure, materials, installation and operation to achieve the purpose of conveying cryogenic liquids.
First, the working principle
1. The reciprocating cryogenic pump is composed of two parts: the main body of the pump and the prime mover, of which the main body of the pump can be divided into two parts: the hydraulic end and the transmission end.
2. The function of the hydraulic end (also known as the pump head) is to compress the cryogenic liquid in the pump body, so that the mechanical energy is converted into the liquid internal energy, and the pressure of the discharged liquid increases.
3. The function of the transmission end is to input the power of the prime mover through the deceleration mechanism, and convert the rotary motion into reciprocating motion through the connecting rod mechanism.
4. When the live cold (or plunger) moves from left to right, the volume in the pump cylinder increases, the pressure decreases, and the liquid pressure entering the pipeline is greater than the pressure in the pump cylinder, and the liquid opens the suction valve and enters the pump cylinder under the action of pressure difference. The crank of the gearbox is turned 180º and the live cold moves to the left. Since cryogenic liquids are essentially incompressible, cryogenic liquids are immediately compressed by the piston and the pressure rises rapidly. Until the liquid pressure in the pump cylinder is high enough to open the discharge valve, the cryogenic liquid is discharged through the discharge valve to the drain pipe. When the piston is pulled by the crank and moves to the right, repeat the process.
5. The first half of the cycle of the reciprocating cryogenic pump is to suck in the cryogenic liquid, and the cryogenic liquid is discharged in the second half of the cycle. Discharge is intermittent and discontinuous.
6. The hydraulic end mainly includes the suction valve (or suction window), discharge valve, pump cylinder and cylinder liner, piston (plunger), sealer, various connecting pipes and tonic tubes.
2. Precautions for installation
The liquid medium conveyed by the reciprocating cryogenic pump is cryogenic liquefied gas, and the temperature range is -183~-196°C. Therefore, in addition to the commonality of ordinary reciprocating cryogenic pumps, it also has the characteristics that are closely related to low-temperature operation
1 Fluid end (pump head) section
(1) The hydraulic end is in a low temperature environment, the materials used are copper and stainless steel or solid lubricating materials, and the contact surface requires high precision, so be careful not to be bruised.
(2) The parts used for assembly must be strictly removed from grease and moisture to prevent dust from entering the pump.
(3) For the low temperature part, it is necessary to do a good job of thermal insulation and cold insulation, and try to avoid the invasion of external heat. The vacuum jacket must not be damaged.
(4) The exhaust pipe should be unobstructed and the diameter should be large enough, so that the vaporized gas can be discharged in time to avoid the gas from entering the pump cylinder.
(5) The sealing surface of the inlet and discharge valves should be carefully and evenly sealed, and there should be no serious leakage after the air tightness test. You can also use a simple kerosene test, which is better not to leak, and the grease must be removed after the test.
(6) Do not damage the piston, guide ring and piston rod when installing it
