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.DEAR Air separation equipment.The temperature of the gas returning to the cold end of the switching heat exchanger will not be too low, which is not only conducive to the self cleaning of the switching heat exchanger, but also will not cause supercooling of the switching heat exchanger. Moreover, the pressure of the upper tower will rise slightly when the expanded air is sent to the upper tower, which is also beneficial to the accumulation of liquid.DEAR Air separation equipment.The longitudinal grooves on the condensation side increase the heat transfer area, and the surface tension on the condensation side can be used to enhance the laminar film condensation heat release on the vertical wall. When saturated nitrogen comes into contact with the wave crest of the longitudinal groove on the circumference of the pipe, the steam condenses at the wave crest first, and the condensate film flows from the wave crest to the wave trough under the action of surface tension, which makes the condensate film on both sides of the wave crest and groove very thin and reduces the thermal resistance of the liquid film.
When boiling water, we can see that at atmospheric pressure, the temperature rises to 100 ℃, and the water begins to boil. However, water does not turn into steam all at once, but with the absorption of heat, the amount of steam increases. The coexistence of vapor and liquid is called saturation state. The steam in this state is called "saturated steam" and the water is called "saturated water". In the whole vaporization stage, steam and water have the same temperature, so it is also called "saturation temperature".At the pressure of 0.59mpa, the liquefying temperature is - 173 ℃. For medium pressure oxygen generator, the general working pressure is about 2.45mpa. Therefore, when the air is cooled to - 150 ℃, it is lower than the temperature at which liquefaction begins, and some liquid air will be produced. For the low-pressure oxygen generator, the working pressure is about 0.59mpa, so it is still in gas state when it is cooled to - 171 ℃ in the main heat exchanger.DEAR Air separation equipment.When l / di increases 5 times, the boiling heat transfer coefficient increases almost 2 times. Therefore, the condensing evaporators boiling in tubes are long tubes. However, the boiling heat transfer coefficient decreases with the increase of L / Di, and tends to be stable after L / di > 500, so it is generally taken as L / di < 500. Considering the manufacturing process, in fact, the pipe length is about 3M. At this time, the influence of static pressure of liquid oxygen column is still not great.
DEAR Air separation equipment.In the switching heat exchanger of the air separation unit, the air temperature decreases continuously. Although the relative humidity of the air is always 100%, the absolute humidity decreases continuously. Finally, the moisture in the air can be separated out completely, almost without moisture.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.DEAR Air separation equipment.The fundamental purpose of setting nitrogen water precooler is to reduce the temperature of air entering the air separation column and avoid the temperature fluctuation. Because the inlet air temperature directly affects the working conditions of the switching heat exchanger and the distillation column, as well as the economy of the whole air separation unit.
