It is not as safe as submerged evaporator. Therefore, in order to improve the safety and reliability of the equipment, we prefer to reduce some heat transfer effect, and do not advocate the use of membrane evaporator at present. For the liquid oxygen pump that has been used, attention should be paid to ensure the liquid oxygen circulation volume of the liquid oxygen pump.For the medium pressure process air separation unit, the high pressure air is divided into two channels after passing through the first heat exchanger: one is cooled continuously through the second heat exchanger, and then throttled to enter the lower tower; the other is expanded by the expander, and then enters the lower tower. The expansion amount has no direct relationship with the oxygen extraction rate.DEAR Air separation plant.According to the expander outlet temperature T2 and pressure P2, the corresponding specific enthalpy H2 can be found from the ordinate. The ideal adiabatic expansion process should be isentropic expansion process. The ideal specific enthalpy value when expanding to the same outlet pressure P2 can draw a vertical line through the state point 1 at the inlet to obtain the intersection 2T of the isobaric line with the outlet pressure P2, which is the outlet state point of ideal expansion. Its specific enthalpy h 2T can be found on the ordinate.
DEAR Air separation plant.The feed gas and cold source of crude argon tower come from the main tower and return to the main tower, so the crude argon tower and the main tower are closely related and interact with each other. The operation of the crude argon column needs the following conditions: 1) stable working condition of the main column; 2) the output and quality of oxygen and nitrogen products are close to or reach the normal value; 3) the argon content of the argon fraction is close to normal; 4) the main cooling liquid level is high and there is sufficient cooling capacity.DEAR Air separation plant.First, increase the circulating current to keep the front of the machine at a higher temperature (e.g. - 120 ℃), so that the carbon dioxide content in front of the machine is in an unsaturated state. After expansion, carbon dioxide is not easy to precipitate in the machine. When the temperature of the cold end reaches - 150 ℃, the amount of carbon dioxide brought into the expander is very small, so the bypass and circulation can be cut off temporarily, so that the temperature in front of the expander can be reduced rapidly, and the expander will not be blocked if it is forced to cross the carbon dioxide freezing zone in about 10 minutes.
The load regulation range of low-pressure air separation unit is related to the regulation performance of raw material air compressor, expander and the structural characteristics of distillation column. At present, the flow regulation range of turbine air compressor with inlet guide vane is 75% ～ 100%, and that of turbine expander with adjustable nozzle is 65% ～ 100%. The key is how to adjust the distillation column.Part of the liquid air is sent to the condensing evaporator of the crude argon tower and evaporated completely, then the steam is sent to the upper tower. Its characteristics are opposite to the first one. Generally, the third way between the two ways is adopted, that is, part of the liquid air passes through the crude argon tower, but not all of it evaporates. This can not only ensure the normal operation of the crude argon column, but also reduce the impact on the main column.Special attention should be paid to the liquid discharge pipeline to prevent the increasing cold loss caused by the continuous gasification of liquid. The outlet pipe should be inclined upward, and an upward bend should be made within 800mm near the cold insulation box, with the height of about 6-10 times of the diameter, but not less than 200 mm. When the valve is closed, a liquid seal is formed, and the liquid will not continuously flow to the valve side for gasification. Some of the liquid discharge pipe with heating sleeve, in order to prevent freezing.
