Patent ID: 12196485

InFIG.1a, compressed and cleaned feed air arrives via line1. The initial stages of an air compressor, a pre-cooler and an air cleaner, are not illustrated here and are embodied in a known manner in the exemplary embodiments. The air is cooled almost to its dew point in the main heat exchanger2and flows with a certain amount of superheating into the bottom of the high- pressure column4of the distillation column system via line3. The distillation column system also has a main condenser5, a low-pressure column6and a low-pressure-column top condenser7. The two condensers are in the form of condenser-evaporators; their evaporation spaces are each operated as forced-flow evaporators.

According to the invention, the high-pressure column4has a barrier-plate section8, which is arranged immediately above the point at which the feed air, via air feed line3, is introduced. It consists for example of one to five, preferably of two to three conventional rectifier plates. Alternatively, a section with structured packing of for example one to five, preferably two to three theoretical plates can also be used. This section retains high-boiling constituents of the air, in particular propane, which are withdrawn with a purge stream9A (Purge) from the bottom of the high-pressure column4and are removed therewith from the distillation column system. To this end, the purge stream9B can, as illustrated, be introduced in a warm waste stream via line10.

Above the barrier-plate section8, an oxygen-enriched liquid stream11is withdrawn from the high-pressure column4, cooled in a counter-current subcooler12and fed to the low-pressure column6at an intermediate point via line13. This stream is virtually free of propane and other high-boiling components. This then also goes for all other oxygen-rich fractions in the low-pressure column, in particular for the bottoms liquid, which can be evaporated without risk both in the main condenser5(via line14) and in the low-pressure-column top condenser7(via the lines15and16). Complete evaporation can be carried out without problems in the low-pressure-column top condenser7. With two theoretical plates in the barrier-plate section, given a propane content of 0.0075 ppm in the air downstream of the air cleaner (with an exemplary assumption for propane retention in the molecular sieve of the air cleaner of about 85%), 99.8% of the propane is removed with the purge stream. In the process, 84% of the N2O is also separated out (relative to the N2O quantity which passes through the air cleaner). The degrees of separation of other components are 69% for C2H6, 15% for C2H4and about 2.5% for methane, which is less critical.

In the main condenser5, a part18of the nitrogen tops gas17from the high-pressure column4is condensed. The liquid nitrogen19obtained in the process is returned to the high-pressure column4as a recirculation flow. The low-pressure-column top condenser liquefies tops gas20from the low-pressure column6. Liquid nitrogen21generated in the process is returned to the low-pressure column6. A part thereof is immediately drawn off from the low-pressure column6again as a liquid nitrogen stream22. (Alternatively, this stream could also be withdrawn directly from the liquefaction space of the low-pressure-column top condenser7). A pump23brings the liquid nitrogen stream22to approximately high-pressure-column pressure. The pressure liquid24is supplied to the top of the high-pressure column4via the counter-current subcooler12and line25A/25B.

A gaseous nitrogen stream from the top of the high-pressure column4is withdrawn via line17/26A/26B and initially warmed according to the invention in the counter-current subcooler12. Subsequently, the nitrogen27is warmed in the main heat exchanger to around ambient temperature and can be drawn off at28as gaseous pressurized nitrogen product under high-pressure-column pressure. In this example, however, it is compressed even further by one or for example two nitrogen compressors29,30in each case with intermediate cooling or postcooling, such that the final pressurized nitrogen product31(PGAN) exhibits a pressure of for example 120 or 150 bar here.

As a result of the evaporation of the low-pressure-column bottoms liquid16in the low-pressure-column top condenser7, a residual gas32is generated, which is initially warmed in the counter-current subcooler12. Subsequently, it flows via line33to the main heat exchanger2, in which it is warmed to an intermediate temperature. Subsequently, it is expanded in a work-performing manner in a residual-gas turbine35with a bypass37. The turbine35is decelerated by a generator36. The expanded residual gas is reintroduced in two parts into the main heat exchanger and warmed to around ambient temperature. A first part38is fed as regeneration gas to the air cleaner via line39. The rest40is discharged into the atmosphere (ATM) via line10.

A part41of the tops gas of the low-pressure column6is discharged via the lines42and43and through the counter-current subcooler12and the main heat exchanger2as sealing gas (Seal).

The line44shows the balancing group around the distillation column system. It intersects the purge gas line9A, the residual gas line33and the sealing gas line41and especially the feed air line3and the pressurized nitrogen line27(illustrated in bold here). H_Luft means the enthalpy of the air stream, H_Prod the enthalpy of the product streams, WPump the heat introduced by the pump23.

FIG.1bdiffers fromFIG.1aonly in that a part125C of the liquid nitrogen22warmed in the counter-current subcooler12is drawn off as liquid product LIN. Alternatively, the entire stream25A can be guided via line125C; the entire gaseous nitrogen product, which comes from the low-pressure column6, is then drawn off from the low-pressure column6via line41.

FIG.2differs fromFIG.1aonly in that the turbine35is decelerated by a compressor236. The latter brings the part39of the warmed expanded residual gas to the pressure that is required in order to employ it as regeneration gas in the air cleaner. As a result, the pressure in the distillation column system and at the outlet of the air compressor (not illustrated) can be reduced and the energy can be saved directly at the air compressor. For example, the pressure at the MAC is lowered by about 500 mbar or even more in this case.

InFIG.3, in contrast toFIG.2, the entire expanded and warmed residual gas339is compressed in the turbine-driven compressor236. A first part340of the compressed residual gas is used, as inFIG.2, as regeneration gas; the rest341is expanded in a throttle valve and let out into the atmosphere (Atm).

In the method inFIG.4, in contrast to the preceding exemplary embodiments, no liquid nitrogen is pumped out of the low-pressure column6into the high-pressure column. Rather, the entire nitrogen product of the low-pressure column6is withdrawn directly in gas form via line41/42and brought to high-pressure-column pressure in the warm state in a further nitrogen compressor429. It can then be admixed to the nitrogen product28from the high-pressure column or be drawn off separately via line43.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

The entire disclosures of all applications, patents and publications, cited herein and of corresponding German application No. 102018000842.9, filed Feb. 2, 2018, are incorporated by reference herein.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.