A method and device used to variably obtain a compressed-gas product by means low-temperature separation of air in a distillation column system. In a first operating mode, a first amount of first compressed-gas product is obtained, and, in a second operating mode, a second, smaller amount is obtained. In the first operating mode, a first amount of air is compressed in the main air compressor, and in the second operating mode, a second, larger amount is compressed in the main air compressor.

A method for cryogenic separation of air uses an air separation plant, wherein, in a mass transfer column, a liquid first fluid and a gaseous second fluid are subjected to mass transfer with one another. A gaseous third fluid is removed from the column and is at least partly discharged from the air separation plant. A liquid fourth fluid is removed from the column and is at least partly fed into a low-pressure column. The first fluid is formed using at least a part of an oxygen-rich liquid removed from the low-pressure column. The second fluid is formed using an oxygen-enriched liquid removed from a high-pressure column. The oxygen-enriched liquid removed from the high-pressure column and bottom liquid of the mass transfer column are mixed and partly evaporated in a condenser-evaporator. A liquid fifth fluid is removed from the mass transfer column between a feed point for the first fluid and a feed point for the oxygen-enriched liquid, and is at least partly fed into the low-pressure column. The fifth fluid or a fraction thereof is fed into the low-pressure column below the fourth fluid or a fraction thereof.

The method and the device arc used for the cryogenic decomposition of air in a distillation column system for separating nitrogen and oxygen, said system having a first high-pressure column (23), a low-pressure column (25, 26), and three condenser-evaporators, namely a high-pressure column head condenser (27), a low-pressure column bottom evaporator (28), and an auxiliary condenser (29; 228).

A portion of feed air is expanded and cooled in front of a main heat exchanger, and is used as cold for precooling the remaining unexpanded feed air inside the main heat exchanger. A portion of the feed air precooled inside the main heat exchanger is removed to outside the main heat exchanger, expanded and cooled, and used as cold to cool the remaining unexpanded precooled feed air inside the main heat exchanger.

A method for controlling a coupled heat exchanger system having a first heat exchanger block and a second heat exchanger block. A first fluid stream is divided into a first partial current and a second partial current both flowing through the heat exchanger system. A second fluid stream flows through the first heat exchanger block counter to the first partial current. A third fluid stream flows through the second heat exchanger block counter to the second partial current. An intermediate temperature is measured on one of the heat exchanger blocks. The amount of the first partial current and the second partial current is controlled based on the current value of the intermediate temperature. This control reduces the strain on the heat exchangers by changing loads while keeping fluctuations of the intermediate temperature low.

In a method for separating air by cryogenic distillation in a system of columns comprising a first column operating at a first pressure and a second column operating at a second pressure which is lower than the first column, the temperature T1 at which an airflow leaves, after cooling, the heat exchanger by rising towards the cold end of said heat exchanger and enters the first column is at least 1? C., preferably at least 2? C., higher than the dew point of the airflow.

A method and a device used to variably obtain a compressed-gas product by means of the low-temperature separation of air in a distillation column system. In a first operating mode, a first amount of first compressed-gas product is obtained, and, in a second operating mode, a second, smaller amount is obtained. In the first operating mode, a first amount of high-pressure column nitrogen is compressed in a nitrogen compressor and in the second operating mode, a second, larger amount is compressed in the nitrogen compressor.

Feed air is compressed to a first pressure in a main air compressor. A first sub-stream of the air compressed to the first pressure is cooled and fed at least in part to the distillation column system. A second sub-stream of the air compressed to the first pressure is cooled and at least partially liquefied in a low-pressure column bottom evaporator. The at least partially liquefied second sub-stream is introduced at least in part into the distillation column system. A liquid oxygen-enriched fraction is introduced into the evaporation chamber of a high-pressure top condenser. An argon-containing oxygen stream from an intermediate point in the low-pressure column is introduced into an argon column. The second sub-stream is introduced at least in part into an argon top condenser and partially evaporated therein. The second sub-stream is then introduced at least in part into the high-pressure column and/or into the low-pressure column.

The method and device according to the invention provide for recovery of high-pressure oxygen and high-pressure nitrogen by low-temperature separation of air in a distillation-column system. This system comprises a high-pressure column, a low-pressure column, and a main condenser. A first air feed stream is cooled at a first subcritical pressure in a main heat exchanger to approximately dew point and introduced at least partially into the high-pressure column. A second air feed stream is brought to a second, supercritical, pressure, cooled, depressurized, and introduced at least partially into the distillation-column system. A first partial stream of the second air feed stream is cooled in the main heat exchanger, and a second partial stream is cooled in a high-pressure heat-exchanger system. The first and second partial streams are then merged and work-expanded in a liquid turbine.

A method is provided for production of gaseous oxygen at high pressures by splitting a main air feed into at least three separate streams, with the first stream being fed to a heat exchanger and then a column system for rectification; the second stream being further compressed in a warm booster, partially cooled in the heat exchanger, expanded in a turbine coupled to the warm booster and then fed to the column system; the third stream being expanded in a warm expander before being introduced to the heat exchanger and introduced to the column system. In certain embodiments, substantially all of the main air feed is eventually introduced to the column system for rectification, resulting in reduced sizing of a main air compressor and improved product recoveries.