In order to condense the required amount of nitrogen, it is necessary to increase the pressure of the lower tower to increase the heat transfer temperature difference, which will increase the energy consumption of the air separation unit. Neon and helium purge pipes are installed on the top of condensing evaporator. During operation, it is necessary to open neon and helium purge valves regularly to discharge them. When air liquefies in the liquefier, there will also be accumulation of neon and helium non condensable gases, so neon and helium purging pipes are installed on the upper part of the liquefier for regular discharge. The converter steelmaking of air separation plant requires high purity oxygen with oxygen content more than 99.5%. At the same time, there are certain requirements for pressure, the working pressure is greater than 1.3mpa. The oxygen consumption per ton of steel is 50 ~ 60m3 / T. Oxygen enriched blast furnace. Increasing oxygen content in blast furnace blast can increase pulverized coal injection and pig iron production. When the amount of coal injection per ton of iron reaches 200kg / T, the oxygen content of blast is required to be 25% - 29%.
When the temperature of the cold end of the switching heat exchanger reaches - 60 ～ - 150 ℃, the circulation can be used. The function of the circulation is to reduce the temperature difference at the cold end. When passing through the water freezing stage before - 60 ℃, it is easy to ensure the temperature difference of water self-cleaning (between 12 ℃ and 28 ℃), so the circulating current can not be used. In particular, the central cooling method can accelerate the cooling of the cold end of the switched heat exchanger. The moisture and carbon dioxide in the gas after circulation reheating are in unsaturated state, which is also conducive to preventing moisture and carbon dioxide from separating out in the expander. In a word, it is more advantageous to use circulation in advance, and it must be used before the cold end temperature of the switching heat exchanger reaches - 150 ℃.
The boiling point of 0.932% argon in the air is between oxygen and nitrogen, and the content is the highest in the middle of the upper column of the air separation unit, which is called argon fraction. At the same time of separating oxygen and nitrogen, the argon fraction is extracted for further separation and purification, and the argon by-product can also be obtained. For all low pressure air separation units, 30% - 35% argon in the process air can be obtained as a product (the latest process has increased the argon extraction rate to more than 80%)“ "Cooling capacity" is a kind of idiom in the field of refrigeration. Because in order to get a lower temperature than the environment, it depends on the power consumption of refrigeration. That is to say, there is a price to be paid to remove heat from cold objects. Because its temperature is lower than the ambient temperature, it has the ability to spontaneously absorb heat from the environment.
Some air separation processes are different. There is no butterfly valve at the nitrogen outlet of the upper tower. At the same time, the expanded air is only sent to the liquefier without going through the cooler. For such a process, gas can be sent to the upper tower at the beginning of liquid accumulation. Because it can make full use of low temperature gas to cool the upper tower, and the cooling capacity of the gas discharged from the upper tower can be fully recovered in the subcooler and liquefier. With a large amount of condensation of oxygen, the oxygen content in gas phase decreases and the argon condensation increases relatively. Therefore, the argon content in gas phase decreases gradually and only 0.0% after reaching the tower top. Because oxygen and argon are difficult to volatilize to nitrogen, they condense into liquid phase more than nitrogen, so the concentration of oxygen and argon in liquid phase is higher than that in gas phase.
When the butterfly valve is opened to a certain extent by the air separation plant manufacturer, and then the valve opening is changed, the influence on the flow rate is small. When the butterfly valve is just opened, due to the decrease of the passage at the disc, the fluid flow shrinks, and the eddy current is generated behind the disc, resulting in a large flow resistance. With the increase of valve opening, the eddy current weakens, the resistance decreases more, and the flow increases faster. In order to improve the extraction rate of argon, the content of argon in oxygen and nitrogen must be reduced. When the content of argon in nitrogen is more than 0.3% and the content of argon in product oxygen is 0.7%, the extraction rate of argon cannot exceed 60%. Therefore, the number of plates in the main tower with argon tower is more than that without argon tower.
