Why is the pressure in the lower tower of the air separation equipment higher than that in the upper tower?

Why does steelmaking require air separation equipment?

  Since 1956 China began to have an air separation equipment manufacturing industry, and constantly meet the growing demand for industrial gases from all walks of life, in view of the then poor technology and manufacturing capacity of gas separation equipment manufacturing products, many departments rely on imported equipment to develop the national economy, in the 1950s and 1960s China mainly imported ...