Distillation column system and plant for production of oxygen by cryogenic fractionation of air

A distillation column system for obtaining oxygen by cryogenic fractionation of air, comprising

• a high-pressure column and a low-pressure column,
• a main condenser, which is a condenser-evaporator, having a liquefaction space in flow connection with a top of the high-pressure column,
• an argon column which is in flow connection with an intermediate point in the low-pressure column, said argon column having a line for withdrawing an argon-enriched stream, and an argon column top condenser which is a condenser-evaporator and is in flow connection with a top of the argon column,
• wherein the low-pressure column has an upper mass transfer region, a lower mass transfer region and a middle mass transfer region,
• wherein the middle mass transfer region has at least one first mass transfer space which is in fluid communication with the upper mass transfer region and is in fluid communication with the lower mass transfer region,
• wherein the upper mass transfer region has a liquid collector at a bottom end of the upper mass transfer region,
• wherein the first mass transfer space of the middle mass transfer region has a liquid distributor at a top of the first mass transfer space of the middle mass transfer region,
• wherein the argon column top condenser is arranged within the low-pressure column between the upper mass transfer region and the middle mass transfer region, and the argon column top condenser is a forced-flow evaporator, having a liquefaction space and an evaporation space, the evaporation space having an inlet at a bottom end of the evaporation space and an outlet at a top end of the evaporation space, and the outlet of the evaporation space is connected to the liquid distributor of the first mass transfer space of the middle mass transfer region,
• the system further comprising
• a conduit from the liquid collector beneath the upper mass transfer region to the inlet of the evaporation space of the argon column top condenser, whereby liquid from the liquid collector beneath the upper mass transfer region can flow into the evaporation space of the argon column top condenser,
• a vessel having an inlet and an outlet,
• a two-phase conduit which is connected to the outlet of the evaporation space of the argon condenser and to the inlet of the vessel,
• a gas conduit connected to the outlet of the vessel for drawing off gas from the vessel, said gas conduit including a control valve, and
• a liquid conduit from the vessel to the liquid distributor at the top of the middle mass transfer section, whereby liquid from the vessel can flow to the liquid distributor at the top of the middle mass transfer section.