DEAR Liquid air separation unit.In the process of putting the crude argon column into operation, firstly, the argon fraction is extracted to pre cool the crude argon column, and then the liquid air is gradually sent to the crude argon condenser. With the cooling of the crude argon column, the distillation condition of the crude argon column is gradually established. The sign is that the resistance of crude argon tower, the purity of crude argon and the extraction amount of argon fraction continue to increase until the normal index is reached. At the beginning, the main cooling liquid level may drop slightly, and with the establishment of crude argon column distillation, the main cooling liquid level will recover.When the liquid air throttling in the lower tower reaches the upper tower, the temperature will decrease from - 173 ℃ to - 191 ℃; when the liquid nitrogen throttling reaches the upper tower, the temperature will decrease from - 177 ℃ to - 193 ℃. However, when the tap water flows out from the valve, the phenomenon of temperature drop can not be seen. This is mainly because the throttled liquid in the air separation column is "saturated liquid", while the tap water is "supercooled liquid".
DEAR Liquid air separation unit.If the molecular sieve bed is uneven and the thickness of the bed through which the airflow passes is different, the maximum temperature will not be reached at the same time at the outlet. Several peaks may appear after mixing, or the whole peak may be relatively flat, the peak temperature will decrease, and the shape of the cold blowing curve will also become "short and fat". In this case, heating and cold blowing to the specified temperature often takes longer.DEAR Liquid air separation unit.When the temperature of the backflow gas out of the accumulator decreases, the temperature difference at the hot end will be larger. The cooling capacity absorbed by positive flow air is more than that absorbed by return flow and positive flow air, so the temperature of air out of the accumulator decreases, resulting in the reduction of temperature difference at the cold end.There is a flow resistance when the gas flows through the switching heat exchanger. The resistance is usually expressed by the pressure drop of backflow gas, which is about 10KPA. The resistance is not only related to the amount of gas flow, but also related to the manufacturing quality of the equipment and the accumulation of water or carbon dioxide. Air leakage in the automatic valve box will also increase the resistance.
At the beginning, the amount of air that can be fed into the air separation tower is very small, because the liquid air, liquid nitrogen pipeline and control valve are considered according to the flow rate of liquid, and the specific volume of gas is much larger than that of liquid, so the ability to pass through gas is limited. With the accumulation of liquid, when there is liquid in the main cooling, the condensing evaporator will start to work, and part of the rising steam in the lower tower will condense into liquid in the main cooling.DEAR Liquid air separation unit.In the actual operation process, according to the inlet and outlet pressure and temperature of the expander, the efficiency can be estimated by using the thermodynamic property diagram of the gas, and the change of its performance can be checked. It is more convenient to use enthalpy entropy diagram. According to the expander inlet temperature T and pressure P1, the corresponding specific enthalpy H1 can be found from the ordinate.
DEAR Liquid air separation unit.The main heat exchanger and condensing evaporator play a key role in the production of liquid in air separation plant. The main heat exchanger uses the low-temperature and low-pressure gas after expansion as the backflow gas of the heat exchanger to cool the high-pressure positive flow air, so that its temperature before expansion is gradually reduced. At the same time, the temperature after expansion will gradually decrease to a lower level until the temperature required for liquefaction is reached, which makes the positive air partially liquefied. The cooling process of air separation unit in the start-up stage is such a gradual cooling process.DEAR Liquid air separation unit.The cooling water is preferably softened. It is easy to use magnetic water softener for softening treatment, and the effect is acceptable. Sedimentation tank should be set up to remove suspended solids. If the cooling water is recycled, it is conducive to the softening of water quality, but it covers a large area and has a large capital investment.
