1. Expansion air into the lower tower requires that the pressure of air out of the air compressor is much higher. 5 MPa (g), which is generally used in external compression process; The pressure of the air compressor in the down tower process is between 0.85 ~ 1.0 MPa (g), which is generally used in the internal compression process, and the corresponding liquid output is more. 2. Although the process of expanding air into the lower column does not make full use of the distillation potential of the upper column, argon basically enters into the liquid air, and then is sent to the upper column, so the argon extraction rate can be very high, up to 90 ~ 92%. But only 83% can be obtained in the up tower process.
