Oxygen extraction rate of lithium molecular sieve air separation equipment

When lithium molecular sieve is used to prepare oxygen by air separation method, lithium molecular sieve always hopes to separate the oxygen in the processing air as product as much as possible. In order to evaluate the completeness of separation, lithium-type molecular sieves introduce the concept of oxygen extraction rate.

        The oxygen extraction rate of lithium molecular sieve is expressed by the ratio of the total oxygen in the product oxygen to the total oxygen in the processing air entering the tower. That is, in the formula ψ-the extraction rate of oxygen;

       Vo2, Vk-- Lithium molecular sieve oxygen output and processing air volume, m3/h;

       yo2, yk-the volume fraction of oxygen in lithium molecular sieve product and oxygen in the air.

       It can be seen from the above formula: The oxygen content in the air is basically unchanged for a certain location of lithium molecular sieve. When the amount of air entering the tower and the purity of the product oxygen are constant, the oxygen extraction rate depends on the oxygen output. The amount of lithium-type molecular sieve and oxygen output is mainly determined by the level of oxygen in the polluted nitrogen under the condition of a certain air intake for a full-pressure oxygen generator. Now take the 3200m3/h air separation plant as an example. When the inlet air is 18100m3/h, the waste gas nitrogen amount is 60.2% of the processing air volume, and the volume fraction of oxygen in the waste nitrogen is 5.5%, the oxygen output is 3200m3/h , The oxygen purity is 99.6%. It can be calculated that the oxygen extraction rate at this time

       ψ=3200×99.6/(18100×20.9)=0.842, which is 84.2%

        Lithium molecular sieve can also calculate the amount of oxygen running away with polluted nitrogen as 18100 (m3/h)×60.2/%×5.5%=599.2m3/h. If the oxygen content in the polluted nitrogen increases to 7.5%, the amount of oxygen running away with the polluted nitrogen is: 18100(m3/h)×60.2%×7.5%=817.2m3/h

        From this it can be seen that the oxygen output will be reduced by (817.2-599.2) m3/h=218m3/h, that is, the oxygen output will be (3200-218) m3/h=2982m3/h. At this time, the oxygen extraction rate is ψ=2982×99.6/(18100×20.9)=0.718=71.8%.

        Therefore, efforts should be made to reduce the oxygen content in the polluted nitrogen. In this way, lithium molecular sieves can produce more oxygen and increase the oxygen extraction rate. The oxygen extraction rate of the lithium-type molecular sieve all-low-pressure rectification tower was only 80%-85% before, and now it has increased to 90%-95%, and the most advanced ones can even reach about 99%.