In the working condition of air separation distillation, the reflux ratio is the core operation control parameter of the air separation distillation column, which specifically refers to the ratio of the downflow liquid flow rate flowing from top to bottom in the distillation column to the rising steam flow rate flowing from bottom to top. Air separation relies on gas-liquid two-phase countercurrent contact heat transfer in the tower to realize the separation of oxygen and nitrogen components, and the reflux liquid is the basic condition to ensure the normal mass transfer and heat transfer of distillation.
The reflux ratio directly determines the separation effect, product purity and equipment energy consumption of air separation distillation, and the effect is most significant when the number of trays is fixed. When the reflux ratio is increased, the amount of liquid phase materials in the lower stream of the tower increases, the gas-liquid contact heat transfer is more sufficient, the purification effect of high volatile components such as nitrogen is improved, and the purity of gas-phase nitrogen at the top of the tower is significantly increased; However, too much will increase the load of condensing and evaporating equipment, increase the energy consumption of the unit, and even cause flooding in the tower, damaging the distillation condition.
When the reflux ratio is reduced, the proportion of rising steam is increased, which is conducive to enriching liquid oxygen components and improving the purity of liquid oxygen product at the bottom of the tower; However, too small reflux ratio will lead to insufficient gas-liquid mass transfer, incomplete separation of nitrogen and oxygen, and the purity of both products is not up to standard. In industrial air separation production, it is necessary to match the process conditions of upper and lower towers, set the optimal reflux ratio, balance product purity, production energy consumption and unit operation stability, and ensure the continuous and efficient production of qualified oxygen and nitrogen products by air separation equipment.
