DEAR Liquid air separation unit.The gasification process of water in air can be divided into evaporation and boiling. Evaporation is carried out on the surface of water, and boiling is a process of simultaneous gasification in the liquid. Under a certain pressure, when the liquid temperature rises to boiling temperature, it is called "boiling point ts".DEAR Liquid air separation unit.If the automatic valve is not closed tightly, the medium and low pressure blowby will be caused, which will increase the air flow and decrease the air pressure. This phenomenon is the same as that of the forced valve. To distinguish between automatic valve failure and forced valve failure, it can be judged from the following three aspects: if the automatic valve is not closed tightly, the gas in the upper tower will be difficult to be discharged, and the pressure of the low-pressure system will rise, and the influence will be greater.A number of interlayers are overlapped or arranged properly to form a number of parallel channels. At the two ends of the channels, the guide plates for the inlet and outlet of cold and hot fluids are equipped, and they are welded together by brazing method to form a group of plate bundles (or units). Combined with the head and pipe joint of fluid flow in and out, a complete plate fin heat exchanger is formed.
Although the temperature and pressure remain unchanged before and after mixing, the two states are different, and the state can not be explained by temperature and pressure alone. When two objects with different temperatures contact each other, the high temperature object will spontaneously transfer heat to the low temperature object, and finally the two objects reach the same temperature.DEAR Liquid air separation unit.The dew point can be measured by a special dew point meter. For example, the dew point of air after drying is - 50 ℃. According to table 8, the saturated moisture content corresponding to - 50 ℃ is 0.038g/m3, which indicates that the air still contains these moisture. If the dew point is - 60 ℃, the saturated moisture content is 0.011g/m3. The lower the dew point, the higher the degree of drying.DEAR Liquid air separation unit.The refrigeration capacity of the expander is determined according to the cooling capacity demand of the whole air separation unit. In the start-up stage, in order to make the device cool and accumulate liquid as soon as possible, an additional expander is often used to increase the expansion air volume to increase the total cooling capacity.
The temperature in the lower tower is the saturation temperature corresponding to the lower tower pressure; after throttling to the upper tower, the temperature drops to the saturation temperature corresponding to the upper tower pressure, and some liquid gasifies. The temperature of tap water is far lower than the saturation temperature corresponding to the water pressure, because the saturation temperature of water at atmospheric pressure is 100 ℃, so the general water is in the supercooled state lower than the saturation temperature. For pressure water, the minimum pressure after throttling is atmospheric pressure, and it is still impossible to reach saturation state, so it is impossible to produce gasification phenomenon, and the temperature will not decrease.DEAR Liquid air separation unit.If we don't pay attention to the liquefying effect of liquefier and liquid air subcooler in the liquid accumulation stage, and don't pay attention to using liquid nitrogen subcooler to recover the cold capacity, it will cause too much cold capacity to be brought to the cold accumulator (or switching heat exchanger) by the backflow gas, which will cause the "supercooling" of the cold accumulator, expand the temperature difference at the hot end and increase the cold loss.
At present, the air cooling tower of large-scale air separation plant in our country adopts the upper section as the packed tower with new plastic rings, and the lower section as the sieve plate tower (aperture 12mm, spacing 24mm), which has achieved good results. The heat transfer temperature difference at the top is only 0.5 ℃, and the scaling problem is completely solved. The air cooling tower in the nitrogen water precooler of the air separation unit is also made into a non mixed type (tubular type), which is connected with the terminal cooler of the air compressor.DEAR Liquid air separation unit.For the same substance, higher saturation pressure corresponds to higher saturation temperature. Increasing the pressure can increase the liquefaction temperature and make the gas easy to liquefy. That is, at a certain temperature, it can be liquefied by increasing the pressure. However, for every substance, when the temperature exceeds a certain value, no matter how high the pressure is, it is impossible to liquefy it. This temperature is called critical temperature.
