What are the types of dry filters for DEAR air separation units? What are the pros and cons of each?
The heat transfer coefficient K increases with the increase of fluid velocity. However, increasing the flow rate will increase the flow resistance and increase the energy consumption of conveying fluid, so we can not unilaterally emphasize increasing the flow rate. The strength of heat conduction through the wall is not only related to the material and thickness of the wall, but also related to the pollution of the wall.Its temperature can be lower than that of the cooled medium (chilled water, etc.), so it can absorb heat Q2 from the cooled medium in evaporator 4, and the refrigerant will evaporate into low-pressure steam and return to the compressor for circulation. Therefore, compared with the refrigeration in the oxygen generator, the common point of the refrigeration in the refrigerator is that the compressor needs to consume work.The heat capacity of the plate fin heat exchanger is small, and the start-up time of the DEAR air separation unit is short, at the level of 30-36 h; the start-up time of the DEAR air separation unit with the stone cold accumulator is 48-60 H. As far as operation is concerned, it is necessary to master the operation essentials: prevent moisture and carbon dioxide from entering the tower; strictly control the temperature difference between the cold end and the hot end; pay attention to the cooling of the main cooler; strictly control the temperature difference between the cold end and the hot end;
The method is to observe the regularity of escaping gas. It is mainly used to judge the leakage of the switching channel of the switching heat exchanger. For the alternately used containers, the leakage position can be further determined by switching use.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.Because the temperature difference at the cold end is not limited by self clearing, it is much larger than that of the switching heat exchanger. Therefore, the liquefier is not needed in this process, but the pure nitrogen and waste nitrogen from the upper tower are recycled by subcooler as far as possible. The task of liquefier is completed by the cold section of the heat exchanger.
In order to have a preliminary judgment on the leakage position and leakage before shutdown for maintenance, and to shorten the shutdown time, many units have explored some effective methods in practice.The automatic valve is actually a kind of one-way valve, which is installed at the cold end and central extraction of the switching heat exchanger. It is matched with the forced valve. When the positive flow air is used, the air (and intermediate air extraction) automatic valve will open and the sewage nitrogen (or oxygen, nitrogen) automatic valve will close; when the backflow air is used, the sewage nitrogen automatic valve will open and the air automatic valve will close.In severe cases, the dust net of the adsorber will be broken, and the molecular sieve powder will be brought into the heat exchanger channel, causing blockage; the spray cooling tower will carry water. When the air velocity through the spray cooling tower is too high, the water mist will be brought into the adsorber, which greatly increases the load of water removal by the adsorber. The content of water and carbon dioxide in the outlet air exceeds the standard and is brought into the main heat exchanger to freeze, which increases the resistance.