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DEAR air separation:What is stage cooling? What are its advantages and disadvantages?

When the high pressure of the heat exchanger rises to near the maximum starting pressure, open the throttle-1 valve, keep the medium pressure in the range of 0.4 ~ 0.5MPa, and the gas is discharged from the valve sleeve of throttle-3 and throttle-4. When the high-pressure pressure is lower than the normal working pressure, THE-1 valve can be temporarily opened, and the air can be blown after the high-pressure pressure rises until there is no impurity in the blown gas;Generally, the temperature of the waste nitrogen from the reversible heat exchanger (or cold accumulator) is 27 ~ 28 ℃, and the relative humidity is about 30%. In the water cooling tower, the temperature of the hot water from the air cooling tower is 35 ~ 45 ℃. Therefore, the nitrogen in the tower will absorb heat when it meets the hot water spraying, which will reduce the temperature of the water.When the full low pressure oxygen generator encounters an emergency power failure, the first task is to quickly open the vent valve at the end of the air compressor and close the valve of the air entering the rectification tower, so as to avoid the failure of the check valve at the outlet of the air compressor causing the compressed air to reverse and burn the bearing.
Some molecular sieves (such as carbon molecular sieves) have strong adsorption properties for oxygen, so that nitrogen molecules can pass through, so nitrogen with high purity can be obtained. Due to the limited adsorption capacity of adsorbent, when the adsorption of a certain molecule reaches saturation, there is no ability to continue adsorption. It is necessary to drive away the adsorbed substances in order to restore the adsorption capacity. This process is called regeneration.There are two ways of blowing: continuous blowing and intermittent blowing. The so-called "continuous blowing" is the blowing method that the blowing valve is always open for a period of time. The so-called "intermittent blowing" means that the blowing valve is closed and opened when it is closed, and then it is suddenly opened after holding high pressure when it is closed and repeated. This method has a good effect on removing solid impurities and free water. Because the pressure difference increases when the pressure is held, the air flow speed increases when the blow off valve is opened, and the impact entrainment effect is enhanced.
The heating and blowing before the start-up of the oxygen generator and the operation in the start-up stage also directly affect the operation cycle. This situation often occurs: due to eager oxygen production, incomplete heating and blowing, residual water in the tower, resulting in excessive resistance of the cold accumulator or reversible heat exchanger after start-up, and sometimes the resistance of the distillation tower is too large, resulting in frequent flooding.The diameter of casing should be 10-20 mm larger than that of oxygen pipe. There should be no welded joint in the oxygen pipe section in the casing. At the two ends of the casing, the gap between the oxygen pipe and the casing shall be filled with asbestos or other non combustible fibrous materials;The method of intermediate extraction is to open the ventilation and extraction valves for 4-5 turns, and then slowly open the regulating valve-7. A part of the air can be extracted from the middle, and combined with the low-temperature air from the ventilation valve-4 to enter the carbon dioxide adsorber. When the middle part can not be pumped out temporarily, it means that the resistance of the central extraction pipeline is large, the air only goes through - 2 valve and - 4 valve, and the automatic valve of the central extraction can not be opened.
When parking, it is not easy to produce convection when it is cold at the bottom and hot at the top. The cold gas in the tower goes through low temperature first and then high temperature, so the cold loss is less. Its disadvantage is that the hot pipe is on the top, which is not convenient for pressure test. In addition, when the air cooling tower fails and the water enters the molecular sieve system, and then enters the plate fin heat exchanger, the water will enter the low temperature zone, so it is troublesome to heat and thaw.If the refrigerating capacity is too much, for example, when the working pressure of the medium pressure device is too high, the moisture content of the air entering the lower tower will increase, the heat load of the main cooler will decrease, the evaporation capacity of liquid oxygen will decrease, and the liquid oxygen level will rise. Therefore, whether the cooling capacity of the device is balanced or not is first reflected in the change of the main cooling liquid level.