Air separation plant.In the start-up stage, the time of passing through the water and carbon dioxide freezing zone is prolonged, and the temperature difference at the cold end of the switching heat exchanger is not controlled within the allowable range (in the start-up stage, the temperature range gradually decreases with the decrease of temperature), which will cause the increase of water and carbon dioxide impurities into the air separation tower. If the start-up process of an air separation unit is interrupted or started for many times, the temperature of the accumulator or the switching heat exchanger will rise and a large amount of carbon dioxide will be brought into the tower, thus shortening the operation cycle.In the start-up stage of air separation unit, with the cooling of switching heat exchanger, in order to ensure self cleaning, the switching cycle must be shortened. The shortening of switching period is beneficial to the removal of frozen water and carbon dioxide. But the air switching loss is large at this time.
If the nitrogen content of the argon fraction is too much, the purity of the crude argon will be reduced, and the temperature difference of the crude argon condenser will be reduced, or even zero, and the crude argon tower will stop working. Moreover, too much nitrogen in the crude argon will bring difficulties to the production of refined argon, so the argon fraction should be located in the place with as little nitrogen as possible.If it is serious, it must stop running and reheat. Once the chiller stops running, the argon production will stop immediately. In order to avoid the blockage of the air separation system, the air volume can be appropriately reduced during the failure of the refrigerator to reduce the load of the adsorber;In order to realize the separation of oxygen and nitrogen in the air separation unit, it is necessary to liquefy the air, which must be reduced to the liquefying temperature. The absolute pressure of the lower column of the air separation column is about 0.6MPa, and the temperature at which the air begins to liquefy is about - 172 ℃. Therefore, in order to liquefy the air, there must be a lower temperature cold fluid to cool the air.
Due to the large heat capacity of the accumulator, when the temperature of the cold end reaches - 60 ℃, the temperature of the intermediate extraction is still above 0 ℃ after the water freezing stage. Therefore, for the process of intermediate extraction, in addition to the problem that the air at the cold end of the accumulator has passed through the freezing stage of moisture and carbon dioxide, there is also the problem that the intermediate extraction air has passed through the freezing stage of moisture.It can be seen that in this case, it is better to stop an expander, which can not only reduce the impact of expansion on distillation conditions, but also make the switching heat exchanger work under normal conditions, so as to prevent cold end supercooling or low temperature after expander.Air separation plant.High pressure blow off: when the purifier pressure rises to near the maximum start-up pressure, open the high-pressure air main inlet valve, and then open the air inlet valves of oxygen, nitrogen and distillate compartments intermittently and blow off repeatedly until the blown gas is clean. When the high-pressure pressure is lower than the normal working pressure, the blowing should be stopped temporarily, and the blowing should be started when it is close to the maximum starting pressure.
