DEAR Liquid air separation unit.The removal amount of waste nitrogen (or distillate) is too large, the opening of liquid air and liquid nitrogen control valves is improper, and the working condition of lower tower is not adjusted properly. Poor heat exchange of main cooling system. Insufficient heat exchange surface of the main cooler or more non condensable gas on the nitrogen side affect the heat transfer of the main cooler and reduce the evaporation of liquid oxygen.DEAR Liquid air separation unit.Before the automatic valve is installed in the automatic valve box, it must be removed and cleaned and degreased with clean alcohol. If it has been used, the automatic valve must grind the sealing surface, and then use the special tool to test the pressure. According to the manufacturing requirements, the leakage is less than 0.1l/min under the pressure of 0.6MPa.The bypass valve can be opened step by step when the switching heat exchanger is cooled. However, in order to get through the freezing zone as soon as possible, some people are used to using the bypass valve when the cold end temperature drops below - 45 ℃. For the process with start-up dryer, because the start-up dryer adsorbs the moisture in the air, there is no need to control the temperature difference at the cold end after the moisture freezing stage, so the bypass valve should not be used first.
DEAR Liquid air separation unit.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.Due to the hard work of valve opening and closing, the valve stem is often twisted and the hand wheel is broken. Therefore, after the maintenance of the valve, the packing should be installed evenly and tightly, and the compression nut should be tightened. During the overall leakage test of air separation unit, the leakage at the valve rod packing should also be checked, and this problem should be solved before cold start-up.There are many kinds and types of low temperature valves. Taking the low temperature stop valve as an example, the failure occurred on the top of the valve. The valve top (valve head) of the valve is movably connected with the valve stem, so that the two sealing surfaces can be "automatically aligned" when the valve is closed. After long-term use, sometimes the locking nut is loose due to the damage of anti retreat gasket, and finally the valve top falls off when opening the valve.
DEAR Liquid air separation unit.After adopting the supercharged turbine process, the expander is used to drive the supercharger to compress the expansion air from the air compressor, which can increase the inlet pressure of the expander to about 1.0MPa and increase the unit cooling capacity. Under the condition of a certain total cooling capacity, the amount of expansion air can be reduced, which is conducive to the distillation of upper tower.DEAR Liquid air separation unit.Expander is the gas through the adiabatic expansion of external work, internal energy reduction (enthalpy reduction), in order to achieve the purpose of cooling, refrigeration. In the ideal adiabatic expansion process, the enthalpy decreases the most, and the larger the unit cooling capacity is, the greater the temperature drop is.DEAR Liquid air separation unit.Compared with switching purification process, the air separation unit of molecular sieve purification process has simple start-up operation and easy control because the air is adsorbed by molecular sieve to remove impurities such as water and carbon dioxide. It does not need to consider the complex effects such as the self removal of water and carbon dioxide, the precipitation of water and carbon dioxide in the expander and so on. The attention of the start-up process is mainly focused on giving full play to the refrigeration capacity of the expander, reasonably distributing the cooling capacity, and comprehensively cooling the equipment.
