There are many ways to classify air separation units. According to the product output (oxygen products), there are three types: large, medium and small. The oxygen production of large-scale air separation plant is greater than or equal to 10000 cubic meters per hour; the oxygen production of medium-sized air separation plant is greater than or equal to 1000 cubic meters per hour; the oxygen production of small-scale air separation plant is less than 1000 cubic meters per hour.