Method and device for generating gaseous compressed nitrogen

Abstract

Method and device for generating gaseous compressed nitrogen by the low-temperature separation of air in a distillation column system, having a pre-column, a high-pressure column and a low-pressure column. The feed air is compressed, purified in a purification apparatus and cooled. A first sub-flow of the cooled feed air is introduced in a predominantly liquid state into the distillation column system. A gaseous fraction from the pre-column in introduced into the liquefaction chamber of a pre-column head condenser with liquid formed therein fed as reflux into the pre-column. A first gaseous nitrogen product fraction is drawn from the high-pressure column, heated, and obtained as first gaseous compressed nitrogen product. At least a part of the second sub-flow is introduced into the evaporation chamber of the pre-column head condenser. A third sub-flow of the cooled feed air is expanded to perform work and subsequently introduced into the liquefaction chamber.

Claims

1. A method for generating gaseous compressed nitrogen by low-temperature separation of air in a distillation column system having a pre-column which has a pre-column head condenser/evaporator having a liquefaction chamber and an evaporation chamber, a high-pressure column and a low-pressure column, said process comprising: compressing input air in a main air compressor to form compressed input air, cleaning the compressed input air in a cleaning device to form cleaned input air, cooling the cleaned input air in a main heat exchanger to form cooled input air, feeding a first partial stream of the cooled input air in gaseous form into the pre-column, feeding a second partial stream of the cooled input air in a predominantly liquid state into the distillation column system, feeding a gaseous fraction from an upper region of the pre-column into the liquefaction chamber of the head condenser/evaporator wherein liquid is formed in said liquefaction chamber, and returning at least part of the liquid formed in the liquefaction chamber to the pre-column, wherein said low-pressure column has a low-pressure column sump condenser/evaporator which has a liquefaction chamber and an evaporation chamber, withdrawing a first nitrogen product fraction from the high-pressure column in gaseous form, warming said first nitrogen product fraction in the main heat exchanger, and removing warmed first nitrogen product fraction from the main heat exchanger to form a first gaseous compressed nitrogen product, feeding at least a first substream of the second partial stream into the evaporation chamber of the pre-column head condenser/evaporator, subjecting a third partial stream of the cooled input air to pressure reduction whereby work is performed, wherein, after said pressure reduction, the third partial stream has a pressure which is higher than an operating pressure of the low-pressure column, wherein, after said pressure reduction, the third partial stream is fed into the liquefaction chamber of the low-pressure column sump condenser/evaporator and is at least partly liquefied there to form liquefied third partial stream, feeding at least a substream of the liquefied third partial stream into the low-pressure column, wherein said sub stream of the liquefied third partial stream is liquefied air, wherein the low-pressure column has an intermediate condenser/evaporator having a liquefaction chamber and an evaporation chamber, evaporating at least part of an intermediate liquid of the low-pressure column in the evaporation chamber of the intermediate condenser/evaporator, liquefying at least part of a gaseous head fraction from the high-pressure column in the liquefaction chamber of the intermediate condenser/evaporator to form liquid, and returning at least part of the liquid formed in the liquefaction chamber of the intermediate condenser/evaporator to the high-pressure column, and wherein said first gaseous compressed nitrogen product is more than 35 mol % of said input air.

2. The method as claimed in claim 1, wherein a second gaseous nitrogen product fraction is withdrawn from the pre-column in gaseous form, warmed in the main heat exchanger and removed from the main heat exchanger to form a second gaseous compressed product.

3. The method as claimed in claim 1, wherein less than 30 mol % of said input air is fed in the liquid state into the distillation column system.

4. The method as claimed in claim 1, wherein the quantity of oxygen-enriched streams fed in the liquid state from the pre-column and the evaporation chamber of the pre-column head condenser/evaporator into the high-pressure column and the low-pressure column is less than 14 mol % of said input air.

5. The method as claimed in claim 1, wherein the second partial stream is compressed, before being cooled in the main heat exchanger, to a pressure that is higher than an operating pressure of the pre-column, and is liquefied or pseudo-liquefied in the main heat exchanger, and a liquid stream is removed from the distillation column system, brought to an elevated pressure in the liquid state, evaporated or pseudo-evaporated in the main heat exchanger.

6. The method as claimed in claim 1, wherein a gaseous fraction from the evaporation chamber of the pre-column head condenser/evaporator is fed, in the form of a gaseous input stream, into the high-pressure column.

7. The method as claimed in claim 1, wherein at least some sump liquid of the pre-column is fed into the evaporation chamber of the pre-column head condenser/evaporator.

8. The method as claimed in claim 1, wherein the third partial stream is further compressed before being cooled in the main heat exchanger.

9. The method as claimed in claim 1, wherein, after said reducing, the pressure of the third partial stream is lower than an operating pressure of the high-pressure column.

10. The method as claimed in claim 4, wherein the total quantity of oxygen-enriched streams fed in the liquid state from the pre-column and the evaporation chamber of the pre-column head condenser/evaporator into the high-pressure column and the low-pressure column is less than 1 mol % of said input air.

11. The method as claimed in claim 1, wherein more than 45 mol % of the input air, in the form of the first nitrogen product fraction, is withdrawn in gaseous form from the high-pressure column and warmed in the main heat exchanger.

12. The method as claimed in claim 1, wherein the second partial stream is compressed, before being cooled in the main heat exchanger, to a pressure that is higher than an operating pressure of the pre-column, and is liquefied or pseudo-liquefied in the main heat exchanger, and a liquid oxygen stream is removed from the distillation column system, brought to an elevated pressure in the liquid state, and evaporated or pseudo-evaporated in the main heat exchanger.

13. The method according to claim 1, wherein the pre-column has a head, the low-pressure column has a head, and the high-pressure column has a head, and an operating pressure at the head of the pre-column is 6 to 9 bar, an operating pressure at the head of the high-pressure column is 3 to 6 bar, and an operating pressure at the head of the low-pressure column is 1.25 to 1.7 bar.

14. A method for generating gaseous compressed nitrogen by low-temperature separation of air in a distillation column system having a pre-column which has a pre-column head condenser/evaporator having a liquefaction chamber and an evaporation chamber, a high-pressure column and a low-pressure column, said process comprising: compressing input air in a main air compressor to form compressed input air, cleaning the compressed input air in a cleaning device to form cleaned input air, cooling the cleaned input air in a main heat exchanger to form cooled input air, feeding a first partial stream of the cooled input air in gaseous form into the pre-column, feeding a second partial stream of the cooled input air in a predominantly liquid state into the distillation column system, feeding a gaseous fraction from an upper region of the pre-column into the liquefaction chamber of the head condenser/evaporator wherein liquid is formed in said liquefaction chamber, and returning at least part of the liquid formed in the liquefaction chamber to the pre-column, wherein said low-pressure column has a low-pressure column sump condenser/evaporator which has a liquefaction chamber and an evaporation chamber, withdrawing a first nitrogen product fraction from the high-pressure column in gaseous form, warming said first nitrogen product fraction in the main heat exchanger, and removing warmed first nitrogen product fraction from the main heat exchanger to form a first gaseous compressed nitrogen product, feeding at least a first substream of the second partial stream into the evaporation chamber of the pre-column head condenser/evaporator, subjecting a third partial stream of the cooled input air to pressure reduction whereby work is performed, wherein, after said pressure reduction, the third partial stream has a pressure which is higher than an operating pressure of the low-pressure column, wherein, after said pressure reduction, the third partial stream is fed into the liquefaction chamber of the low-pressure column sump condenser/evaporator and is at least partly liquefied there to form liquefied third partial stream, feeding at least a substream of the liquefied third partial stream into the low-pressure column, wherein said sub stream of the liquefied third partial stream is liquefied air, wherein the low-pressure column has an intermediate condenser/evaporator having a liquefaction chamber and an evaporation chamber, evaporating at least part of an intermediate liquid of the low-pressure column in the evaporation chamber of the intermediate condenser/evaporator, liquefying at least part of a gaseous head fraction from the high-pressure column in the liquefaction chamber of the intermediate condenser/evaporator to form liquid, and returning at least part of the liquid formed in the liquefaction chamber of the intermediate condenser/evaporator to the high-pressure column, wherein said first gaseous compressed nitrogen product is more than 35 mol % of said input air, and wherein less than 30 mol % of said input air is fed in the liquid state into the distillation column system.

15. A method for generating gaseous compressed nitrogen by low-temperature separation of air in a distillation column system having a pre-column which has a pre-column head condenser/evaporator having a liquefaction chamber and an evaporation chamber, a high-pressure column and a low-pressure column, said process comprising: compressing input air in a main air compressor to form compressed input air, cleaning the compressed input air in a cleaning device to form cleaned input air, cooling the cleaned input air in a main heat exchanger to form cooled input air, feeding a first partial stream of the cooled input air in gaseous form into the pre-column, feeding a second partial stream of the cooled input air in a predominantly liquid state into the distillation column system, feeding a gaseous fraction from an upper region of the pre-column into the liquefaction chamber of the head condenser/evaporator wherein liquid is formed in said liquefaction chamber, and returning at least part of the liquid formed in the liquefaction chamber to the pre-column, wherein said low-pressure column has a low-pressure column sump condenser/evaporator which has a liquefaction chamber and an evaporation chamber, withdrawing a first nitrogen product fraction from the high-pressure column in gaseous form, warming said first nitrogen product fraction in the main heat exchanger, and removing warmed first nitrogen product fraction from the main heat exchanger to form a first gaseous compressed nitrogen product, feeding at least a first substream of the second partial stream into the evaporation chamber of the pre-column head condenser/evaporator, subjecting a third partial stream of the cooled input air to pressure reduction whereby work is performed, wherein, after said pressure reduction, the third partial stream has a pressure which is higher than an operating pressure of the low-pressure column, wherein, after said pressure reduction, the third partial stream is fed into the liquefaction chamber of the low-pressure column sump condenser/evaporator and is at least partly liquefied there to form liquefied third partial stream, feeding at least a substream of the liquefied third partial stream into the low-pressure column, wherein said sub stream of the liquefied third partial stream is liquefied air, wherein the low-pressure column has an intermediate condenser/evaporator having a liquefaction chamber and an evaporation chamber, evaporating at least part of an intermediate liquid of the low-pressure column in the evaporation chamber of the intermediate condenser/evaporator, liquefying at least part of a gaseous head fraction from the high-pressure column in the liquefaction chamber of the intermediate condenser/evaporator to form liquid, and returning at least part of the liquid formed in the liquefaction chamber of the intermediate condenser/evaporator to the high-pressure column, wherein said first gaseous compressed nitrogen product is more than 35 mol % of said input air, and wherein, after said reducing, the pressure of the third partial stream is lower than an operating pressure of the high-pressure column.

16. The method as claimed in claim 1, further comprising splitting said second partial stream of the cooled input air, before being introduced into the distillation column system, into said first substream of the second partial stream and a second substream of the second partial stream, and feeding said second substream of the second partial stream into the pre-column.

17. The method as claimed in claim 1, further comprising removing a liquid flushing stream from the evaporation chamber of the pre-column head condenser/evaporator, warming the liquid flushing stream in a heat exchanger, and then feeding the flushing stream into the low-pressure column.

Description

(1) The “regulating apparatus” comprises complex open-loop and closed-loop control devices that, in cooperation, enable the corresponding process parameters to be achieved at least partly automatically, for example by means of a correspondingly programmed operating control system.

(2) The operating pressures in the distillation column system of the invention (in each case at the head) are: Pre-column: for example 6 to 9 bar, preferably 6 to 7.5 bar High-pressure column: for example 3 to 6 bar, preferably 3.5 to 4.5 bar Low-pressure column: for example 1.25 to 1.7 bar, preferably L3 to 1.5 bar

(3) The invention and further details of the invention will be explained in more detail below with reference to exemplary embodiments illustrated schematically in FIGS. 1 to 5.

(4) The system illustrated in FIG. 1 has a distillation column system having a pre-column 41, a high-pressure column 42, a low-pressure column 43, a pre-column head condenser 44, a low-pressure column sump evaporator 45 and a low-pressure column intermediate evaporator 46. The operating pressures, in each case at the head, are: Pre-column: 7.3 bar High-pressure column: 4.1 bar Low-pressure column: 1.37 bar

(5) Compressed, pre-cooled and cleaned input air 1 enters at a pressure of 7.6 bar. The main air compressor 103, which draws atmospheric air in by way of line 101 and a filter 102 and compresses it to the said pressure, and pre-cooling and cleaning of the air (104) are carried out in a known manner and are illustrated only schematically in the drawing.

(6) A “first partial current”10 of input air is cooled in a main heat exchanger 2, approximately to dew point, and enters the pre-column 41 in a gaseous state by way of line 11.

(7) Using external energy, a “second partial current” 20 is post-compressed, approximately to a high-pressure of approximately 70 bar, in two post-compressor stages 3, 5 having aftercoolers 4, 6. (This pressure is very strongly dependent on the desired oxygen product pressure, which in the example is about 50 bar.) The second partial current enters the main heat exchanger 2 at this high pressure and is cooled and pseudo-liquefied there. The second partial current 21 that exits from the main heat exchanger 2 is let down in a liquid turbine 22, such that work is performed, approximately to the operating pressure of the pre-column 41, and a first part 23 thereof is fed into the evaporation chamber of the pre-column head condenser 44. The remainder 24 flows into the pre-column 41. The liquid turbine 22 is braked by a generator 25.

(8) A “third partial current” 30 is branched off upstream of the second post-compressor stage 5 and its pressure is bought to about 16 bar in a turbine-driven post-compressor 31 having an aftercooler 32. It enters the main heat exchanger 2 at the warm end, by way of line 33. It is removed again at an intermediate temperature by way of line 34, and is let down such that work is performed, in an air turbine 35. The third partial current 36 which has been let down such that work was performed is at least partly, preferably entirely or substantially entirely, liquefied in the liquefaction chamber of the low-pressure column sump evaporator 45. The liquefied third partial current 37 is further cooled in a supercooling countercurrent exchanger 7 and fed to an intermediate position in the low-pressure column by way of line 38.

(9) The entirety of the sump liquid 50 of the pm-column is fed into the evaporation chamber of the pm-column head condenser 44. In the liquefaction chamber thereof, a first part 51 of the gaseous head nitrogen of the pre-column is condensed. A first part 53 of the liquid nitrogen 52 that is generated during this is returned to the pre-column 41, and a second part 54 is delivered to the high-pressure column 42. The gaseous fraction 55 that is formed in the evaporation chamber of the pre-column head condenser is fed into the high-pressure column 42 as a gaseous input current. In the exemplary embodiment, it forms in particular the single gaseous input current of the high-pressure column 42. A small liquid flushing current 105/106 is drawn off from the evaporation chamber of the pre-column head condenser 44, continuously or from time to time, and is warmed in the supercooling countercurrent exchanger 7 (the flow of the flushing current from the evaporation chamber of the pre-column head condenser 44 to the supercooling countercurrent exchanger 7 is represented by the symbols {circle around (3)}) and fed into the low-pressure column by way of line 107 the flow from line 107 into the low-pressure column 43 is represented by the symbols {circle around (5)}).

(10) Taken as an average over time, this flushing quantity is less than 14 mol %, in particular less than 1 mol %, of the input air quantity.

(11) After being cooled in the supercooling countercurrent exchanger 7, the sump liquid 56/57 of the high-pressure column is fed into the low-pressure column 43. A first part 58 of the gaseous head nitrogen of the high-pressure column is at least partly, preferably entirely or substantially entirely, liquefied in the intermediate evaporator 46 of the low-pressure column 42. A first part 60 of the liquid nitrogen 59 that is generated during this is returned to the high-pressure column 42. After being cooled in the supercooling countercurrent exchanger 7, a nitrogen-rich liquid 61/62 from an intermediate position in the high-pressure column 42 is returned to the head of the low-pressure column 43. Gaseous impure nitrogen 63 from the head of the low-pressure column 43 is warmed, approximately to ambient temperature, in the supercooling countercurrent exchanger 7 and further in the main heat exchanger 2. The warm, unpressurized impure nitrogen 64 may be used as the regeneration gas in the cleaning apparatus (104) for the input air, or be expelled to the atmosphere.

(12) A second part of the gaseous head nitrogen of the high-pressure column 42 forms the “first nitrogen product fraction” 65 and is warmed, approximately to ambient temperature, in the main heat exchanger 2. The warm high-pressure column nitrogen 66 is obtained either directly (by way of line 67) or after further compression in the product compressors 68, 69 as a gaseous compressed nitrogen product (PLAN or HPGAN). In the exemplary embodiment, the quantity of the first nitrogen fraction is approximately 49 mol % of the input air quantity.

(13) A second part of the gaseous head nitrogen of the pre-column 41 forms the “second nitrogen product fraction” 70 and is warmed, approximately to ambient temperature, in the main heat exchanger 2. The warm pre-column nitrogen 71 is obtained either directly (MPGAN) or after further compression in the product compressor 69 (HPGAN) as a gaseous compressed nitrogen product.

(14) Moreover, in the exemplary embodiment two compressed product fractions (GOX IC and GAN IC) are obtained by internal compression.

(15) The quantities of the second nitrogen product fraction and the compressed product fraction that is internally compressed are, in the exemplary embodiment, in each case less than 20 mol % of the input air quantity, in particular less than 10 mol % of the input air quantity.

(16) Liquid oxygen 72 is removed from the low-pressure column 43 (or to be more precise, from the evaporation chamber of the low-pressure column sump evaporator 45), brought to an elevated pressure of 50 bar in a liquid state by means of an oxygen pump 73, guided by way of line 74 to the main heat exchanger 2, pseudo-evaporated and finally obtained as a gaseous compressed product 75.

(17) A second part 76 of the liquid nitrogen 59 from the low-pressure column intermediate evaporator 46 is brought to an elevated pressure in the liquid state by means of a nitrogen pump 77, guided by way of line 78 to the main heat exchanger 2, evaporated or pseudo-evaporated and finally obtained as a gaseous compressed product 79.

(18) In the exemplary embodiment of FIG. 1, the material exchange elements in the pre-column 41 and in the high-pressure column 42 are formed by sieve bases and in the low-pressure column 43 by ordered packing. All three condenser/evaporators 44, 45, 46 take the form of bath evaporators.

(19) As an alternative to this, the material exchange elements in the pre-column 41 and/or in the high-pressure column 42 may also be formed by ordered packing. Similarly, it is possible to equip one of these columns or both columns 41, 42 partly with bases, in particular sieve bases, and partly with ordered packing.

(20) The exemplary embodiment of FIG. 2 corresponds largely to the variant in FIG. 1, with use exclusively of ordered packing in the columns. As a further difference, the three condenser/evaporators 44, 45, 46 take the form of forced-flow evaporators.

(21) FIG. 3 differs from FIG. 2 in that the low-pressure column intermediate evaporator 46 takes the form of a falling-film evaporator.

(22) In FIG. 4, the low-pressure column has, in addition to that shown in FIG. 3, a pure nitrogen section 400. This additionally allows liquid nitrogen 401 (LIN) and pure low-pressure nitrogen 402/403/LPGAN to be obtained as products.

(23) FIG. 5 illustrates an exemplary embodiment in which the material exchange elements in the pre-column 41 and the high-pressure column 42 are formed by sieve bases. In contrast to FIG. 1, this is a high-pressure method (HAP—high air pressure); thus, all the air is compressed to a pressure that is at least 1 bar higher than the highest operating pressure in the distillation column system, which in the exemplary embodiment are approximately 17 bar. For this purpose, the use of post-compressors that are driven by external energy may be dispensed with here.

(24) The exemplary embodiment according to FIG. 5 further differs from FIG. 1 in the use of two gas expansion turbines, a first air turbine 35a and a second air turbine 35b, In the first air turbine 35a, as before the third partial current 34 is let down such that work is performed, and it is then guided to the liquefaction chamber of the low-pressure column sump evaporator 45 by way of line 36. The first partial current 11a is sent through the second air turbine 35b and, after being let down such that work is performed, is fed into the pre-column 41 entirely or substantially in gaseous form, by way of line 11b. In the exemplary embodiment, the two air turbines 35a, 35b are at the same entry pressure (approximately 17 bar) and the same entry temperature, and for this reason the first and the third partial current are jointly fed to the main heat exchanger by way of line 10a and are removed again by way of line 10b. As an alternative, the two turbines 35a, 35b may be at different entry temperatures and where appropriate different entry pressures.

(25) The method according to FIG. 5 is in particular suitable for a supercritical oxygen product pressure (GOX IC) (in the example illustrated, approximately 50 bar), in particular in the case of low compressed nitrogen production (GAN IC) and low liquid production (LOX, where appropriate LIN, if a pure nitrogen section according to FIG. 4 is used). The term “low” here is understood to mean a molar content of the respective products in the entire input air quantity of less than 2 mol %, in particular less than 1 mol %.