Method and device for producing air gases in a gaseous and liquid form with a high flexibility and by cryogenic distillation

A method of producing at least one air gas using cryogenic distillation in a system of columns comprising at least one medium-pressure column operating at a medium pressure and a low-pressure column operating at a low pressure, said at least one median pressure column and low-pressure column being thermally coupled to one another, wherein in a first operating mode and a second operating mode, the method comprises the steps of:

• a) pressurizing a compressed air stream to a main pressure that is at least 5 bar above the pressure of the medium-pressure column, and purifying said compressed air stream at this main pressure to produce a main pressure air stream;
• b) cooling the main pressure air stream in a heat exchange line to an intermediate temperature T1;
• c) removing a first part of the main pressure air stream from the heat exchange line at temperature T1;
• d) further cooling a second part of the main pressure air stream within the heat exchange line to a temperature TL to form a liquefied air stream and sending the liquefied air stream to the system of columns for separation;
• e) introducing the first part of the main pressure air stream to a cold supercharger, wherein the first part of the main pressure air stream is pressurized to a high pressure that is greater than or equal to the main pressure to form a supercharged stream;
• f) cooling the supercharged stream in the heat exchange line to a temperature T3 that is warmer than temperature T1;
• g) removing a first part of the supercharged stream from the heat exchange line at temperature T3;
• h) further cooling a second part of the supercharged stream within the heat exchange line before introducing the second part of the supercharged stream to the system of columns for separation;
• i) introducing the first part of the supercharged stream to a first turbine, wherein the first part of the supercharged stream is expanded to a pressure that is greater than or equal to the medium pressure to form a first expanded stream;
• j) introducing at least a portion of the first expanded stream to the system of columns;
• and
• k) vaporizing a press zed liquid product from the system of columns in the heat exchange line,
• wherein in the first operating mode, the method further comprises the steps of:
• l) warming a second portion of the first expanded stream in the heat exchange line to form a warned stream;
• m) introducing the warmed stream to an auxiliary turbine and expanding the warmed stream to form an expanded auxiliary stream;
• and
• n) warming said expanded auxiliary stream in the heat exchange line and discharging said warm expanded auxiliary stream into the atmosphere,
• wherein in the second operating mode, the method further comprises the steps of:
• o) reducing the flow rate of the second portion of the first expanded stream processed in the auxiliary turbine as compared to the first mode;
• and
• p) decreasing the production of liquid by way of end product by comparison with the production of liquid by way of end product in the first mode,
• wherein the flow rate of the compressed air stream is reduced, during the second mode by a flow rate at least equal to the reduction in the flow rate of the portion of the first expanded stream sent to the auxiliary turbine during the second mode.