Method and apparatus for obtaining a compressed gas product by cryogenic separation of air

Abstract

A method and the apparatus for obtaining a compressed gas product by means of cryogenic separation of air in a distillation column system which has a high-pressure column and a low-pressure column. All of the feed air is compressed in a main air compressor to a first pressure which is at least 4 bar higher than the operating pressure of the high-pressure column. A first partial flow of the feed air compressed in the main air compressor is cooled to an intermediate temperature in a main heat exchanger and is expanded so as to perform work in a first air turbine. At least a first part of the first partial flow expanded so as to perform work is introduced into the distillation column system.

Claims

1. A method for obtaining a compressed gas product by means of cryogenic separation of air in a distillation column system which has a high-pressure column, a low-pressure column, and a main condenser, said method comprising: compressing all of a feed air in a main air compressor to a first pressure which is at least 4 bar higher than an operating pressure of the high-pressure column, cooling a first partial flow of the feed air compressed in the main air compressor to a first intermediate temperature in a main heat exchanger to produce a cooled first partial flow, and expanding the cooled first partial flow to perform work in a first air turbine to produce an expanded first partial flow, introducing at least a first part of the expanded first partial flow into the distillation column system, compressing a second partial flow of the feed air compressed in the main air compressor in a first booster compressor, which is driven by the first air turbine, to a second pressure which is higher than the first pressure, cooling the second partial flow in the main heat exchanger to a second intermediate temperature to form a cooled second partial flow, compressing the cooled second partial flow in a second booster compressor, which is driven by a second air turbine, to a third pressure which is higher than the second pressure, to produce a further compressed second partial flow, cooling said further compressed second partial flow in the main heat exchanger and then expanding said further compressed second partial flow to produce an expanded second partial flow, and introducing said expanded second partial flow into the distillation column system, cooling a third partial flow of the feed air compressed in the main air compressor in the main heat exchanger to a third intermediate temperature to produce a cooled third partial flow, expanding said cooled third partial flow to perform work in the second air turbine to produce an expanded third partial flow, and introducing at least a first part of the expanded third partial flow into the distillation column system, removing a first product flow in liquid form from the distillation column system and pressurizing the first product flow to a first product pressure, evaporating or pseudo-evaporating the first product flow at the first product pressure in the main heat exchanger and heating evaporated or pseudo-evaporated first product flow in the main heat exchanger to form said compressed gas product, and removing a second product flow from the high-pressure column or from the main condenser, pressurizing the second product flow to a second product pressure, heating the second product flow in the main heat exchanger at the second product pressure to form a further compressed gas product, wherein: wherein the main condenser provides heat exchange between gas from an upper region of the high-pressure column and liquid from a bottom region of the low-pressure column, the cooled third partial flow is expanded in the second air turbine to a pressure which is at least 1 bar higher than the operating pressure of the high-pressure column, an inlet pressure of the first air turbine is at least 1 bar lower than the third pressure, and before being introduced into the distillation column system, said at least a first part of the expanded third partial flow is cooled and liquefied in the main heat exchanger and then expanded.

2. The method according to claim 1, further comprising cooling a fourth partial flow of the air compressed in the main air compressor in the main heat exchanger at the first pressure to produce a cooled fourth partial flow, expanding said cooled fourth partial flow, and introducing expanded fourth partial flow into the distillation column system.

3. The method according to claim 1, wherein the third partial flow, together with the second partial flow, is compressed in the first booster compressor to the second pressure before the third partial flow is introduced into the second air turbine at the second pressure.

4. The method according to claim 1, wherein the third partial flow is introduced into the second air turbine at the first pressure.

5. The method according to claim 1, wherein a second part of the expanded third partial flow is not introduced into the main heat exchanger, and wherein said second part of the expanded third partial flow is introduced into a liquefaction space of a sump evaporator of the high-pressure column which is a condenser-evaporator and at last partially condensed therein.

6. The method according to claim 5, wherein the second part of the expanded third partial flow that is at least partially condensed in the sump evaporator is introduced into the high-pressure column at an intermediate point thereof.

7. An apparatus for obtaining a compressed gas product by means of cryogenic separation of air comprising: a distillation column system which has a high-pressure column, a low-pressure column, and a main condenser wherein the main condenser provides heat exchange between gas from an upper region of the high-pressure column and liquid from a bottom region of the low-pressure column, a main air compressor for compressing all of a feed air to a first pressure which is at least 4 bar higher than an operating pressure of the high-pressure column, a line for introducing a first partial flow of the feed air compressed in the main air compressor into a main heat exchanger, a line for removing the first partial flow, cooled to a first intermediate temperature, from the main heat exchanger, a line for introducing the first partial flow cooled to the first intermediate temperature into a first air turbine where the first partial flow is expanded to perform work, a line for introducing the first partial flow from the first air turbine into the distillation column system, a first booster compressor, driven by the first air turbine, for further compressing a second partial flow of the feed air compressed in the main air compressor to a second pressure, which is higher than the first pressure, to produce a further compressed second partial flow, a line for introducing the further compressed second partial flow into the main heat exchanger, and a line for removing the further compressed second partial flow from the main heat exchanger at a second intermediate temperature, a second booster compressor, driven by a second air turbine, for compressing the second partial flow, removed from the main heat exchanger at the second intermediate temperature, to a third pressure which is higher than the second pressure, and wherein the first partial flow of the feed air is introduced into the first air turbine at an inlet pressure which is at least 1 bar lower than the third pressure, a line for introducing the second partial flow at the third pressure into the main heat exchanger, a line for removing the second partial flow at the third pressure from the main heat exchanger, means for expanding the second partial flow removed from the main heat exchanger to produce an expanded second partial flow, and a line for introducing the expanded second partial flow into the distillation column system, a line for introducing a third partial flow of the feed air compressed in the main air compressor into the main heat exchanger, and a line for removing the third partial flow from the main heat exchanger at a third intermediate temperature, a second air turbine for work-performing expansion of the third partial flow removed from the main heat exchanger at the third intermediate temperature to produce an expanded third partial flow at a pressure which is at least 1 bar higher than the operating pressure of the high-pressure column, a line for introducing the expanded third partial flow into the main heat exchanger wherein the expanded third partial flow is cooled and liquified, means for expanding the liquefied third partial flow, and a line for introducing the expanded liquefied third partial flow into the distillation column system, a line for removing in liquid form a first product flow from the distillation column system, a pump for pressurizing the first product flow removed from the distillation column system to a first product pressure, a line for introducing the first product flow at the first product pressure into the main heat exchanger wherein the first product flow is evaporated or pseudo-evaporated to form said compressed gas product, a line for removing the compressed gas product from the main heat exchanger, a line for removing in liquid form a second product flow from the high-pressure column or from the main condenser, a further pump for pressurizing the second product flow removed from the distillation column system the high-pressure column or from the main condenser to a second product pressure, a line for introducing the second product flow at the second product pressure into the main heat exchanger wherein the second product flow is heated to form a further compressed gas product, and a line for removing the further compressed gas product from the main heat exchanger.

8. The method according to claim 1, wherein the third partial flow, together with the second partial flow and the first partial flow, is compressed in the first booster compressor to the second pressure before the third partial flow is introduced into the second air turbine at the second pressure.

9. The method according to claim 1, wherein the second intermediate temperature which is higher than the first intermediate temperature.

10. The method according to claim 1, wherein said further compressed second partial flow is introduced into the main heat exchanger at a further intermediate temperature which is higher than the second intermediate temperature.

11. The method according to claim 1, wherein the third intermediate temperature which is higher than the first intermediate temperature.

12. A method for obtaining a compressed gas product by means of cryogenic separation of air in a plant having a main heat exchanger and a distillation column system having a high-pressure column and a low-pressure column, said method comprising: compressing all of a feed air in a main air compressor to form compressed feed air at a first pressure which is at least 4 bar higher than an operating pressure of the high-pressure column, compressing a first partial steam of the compressed feed air in a first booster compressor to a second pressure and introducing the first partial stream of the compressed feed air into the main heat exchanger at the second pressure, which is higher than the first pressure, removing a first part of the first partial flow of the compressed feed air from the main heat exchanger at a first intermediate temperature, and expanding the first part of the first partial flow to perform work in a first air turbine to produce an expanded first part of the first partial flow, wherein the first air turbine drives the first booster compressor introducing at least a portion of the expanded first part of the of the first partial flow into the distillation column system, removing a second part of the first partial flow of the compressed feed air from the main heat exchanger at a second intermediate temperature, compressing the second part of the first partial flow in a second booster compressor, which is driven by a second air turbine, to a third pressure which is higher than the second pressure, to produce a further compressed second part of the first partial flow, cooling said further compressed second part of the first partial flow in the main heat exchanger and then expanding said further compressed second partial flow to produce an expanded second partial flow, and introducing said expanded second partial flow into the distillation column system, cooling a further partial flow of the feed air compressed in the main air compressor in the main heat exchanger to a third intermediate temperature to produce a cooled further partial flow, expanding said cooled further partial flow to perform work in the second air turbine to produce an expanded further partial flow, and introducing at least a first part of the expanded further partial flow into the distillation column system, removing a first product flow in liquid form from the distillation column system and pressurizing the first product flow to a first product pressure, and evaporating or pseudo-evaporating the first product flow at the first product pressure in the main heat exchanger and heating evaporated or pseudo-evaporated first product flow in the main heat exchanger to form said compressed gas product, wherein: the cooled further partial flow is expanded in the second air turbine to a pressure which is at least 1 bar higher than the operating pressure of the high-pressure column, an inlet pressure of the first air turbine is at least 1 bar lower than the third pressure, and before being introduced into the distillation column system, said at least a first part of the expanded further partial flow is cooled and liquefied in the main heat exchanger and then expanded.

13. The method according to claim 12, wherein the further partial flow of the feed air compressed in the main air compressor is introduced into the main heat exchanger at the second pressure.

14. The method according to claim 12, wherein the further partial flow of the feed air compressed in the main air compressor is introduced into the main heat exchanger at the first pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention, and further details of the invention, is explained in more detail below with reference to exemplary embodiments of the inventive air separation plant represented schematically in FIGS. 1, 2 and 3.

DETAILED DESCRIPTION OF THE INVENTION

(2) In FIG. 1, atmospheric air (AIR) is drawn in, via a filter 1, by a main air compressor 2. The main air compressor has, in the example, five stages and compresses the entire air flow to a “first pressure” of for example 19.7 bar. The entire air flow 3 downstream of the main air compressor 2 is cooled at the first pressure in a pre-cooler 4. The pre-cooled entire air flow 5 is purified in a purification unit 6 which in particular consists of a pair of switchable molecular sieve-adsorbers. A first part 8 of the purified entire air flow 7 is post-compressed, in a hot-operated air post-compressor 9 with a post-cooler 10, to a “second pressure” of for example 24 bar and is then split into a “first partial flow” 11 (first turbine air flow) and a “second partial flow” 12 (first throttle flow).

(3) The first partial flow 11 is cooled in a main heat exchanger 13 to a first intermediate temperature of approx. 135 K. The cooled first partial flow 14 is expanded so as to perform work in a first air turbine 15, from the second pressure to approximately 5.5 bar. The first air turbine 15 drives the hot air post-compressor 9. The first partial flow 16 expanded so as to perform work is introduced into a separator (phase separator) 17. The liquid fraction 18 is introduced, via the lines 19 and 20, into the low-pressure column 22 of the distillation column system.

(4) The distillation column system comprises a high-pressure column 21, the low-pressure column 22 and a main condenser 23 as well as common argon production 24 with a crude argon column 25 and a pure argon column 26. The main condenser 23 is designed as a condenser-evaporator, in the concrete example as a cascade evaporator. The operating pressure at the top of the high-pressure column is in this example 5.3 bar; that at the top of the low-pressure column is 1.35 bar.

(5) The second partial flow 12 of the feed air is cooled in the main heat exchanger 13 to a second intermediate temperature which is higher than the first intermediate temperature, is fed via line 27 to a cold compressor 28 where it is post-compressed to a “third pressure” of approx. 35 bar. The post-compressed second partial flow 29 is reintroduced, at a third intermediate temperature which is higher than the second intermediate temperature, into the main heat exchanger 13 where it is cooled to the cold end. The cold second partial flow 30 is expanded in a throttle valve 31 to close to the operating pressure of the high-pressure column and is fed via line 32 to the high-pressure column 21. One part 33 is removed again, is cooled in a counter-current subcooler 34 and is injected via lines 35 and 20 into the low-pressure column 22.

(6) A “third partial flow” 436 of the feed air is introduced at the second pressure into the main heat exchanger 13 where it is cooled to a fourth intermediate temperature, which in the example is somewhat higher than the first intermediate temperature. The cooled first partial flow 37 is expanded so as to perform work in a second air turbine 38, from the first pressure. The turbine flow 339 expanded so as to perform work is at a pressure which is at least 1 bar, in particular 4 to 10 bar, above the operating pressure of the high-pressure column, and a temperature which is at least 10 K, in particular 15 to 40 K, above the inlet temperature of the low-pressure nitrogen flows 55, 61 at the cold end of the main heat exchanger. This flow is then cooled further in the cold part of the main heat exchanger. The further cooled third partial flow 340 is expanded as third throttle flow in a throttle valve 341 to near high-pressure column pressure and is introduced via line 32 into the high-pressure column. This permits further optimization of the heat-exchange process in the main heat exchanger, in particular in the case of relatively low GAN-IC pressures of for example 7 to 15 bar, in particular approximately 12 bar.

(7) The second air turbine 38 drives the cold compressor 28. The gas fraction from separator 17 is fed via line 40 to the sump of the high-pressure column 21.

(8) (The division into the partial flows at identical pressure could also, in contrast to the representation in the drawing of FIG. 1, be carried out within the main heat exchanger 13.)

(9) A “fourth partial flow” 41 (second throttle flow) flows through the main heat exchanger 13 from the hot to the cold end, at the first pressure. The cold fourth partial flow 42 is expanded in a throttle valve 43 to close to the operating pressure of the high-pressure column and is fed via line 32 to the high-pressure column 21.

(10) The oxygen-enriched sump liquid 44 of the high-pressure column 21 is cooled in the counter-current subcooler 34 and is introduced into the optional argon production 24. Gas 44 and residual liquid 45 produced thereby are injected into the low-pressure column 22.

(11) A first part 49 of the top nitrogen 48 of the high-pressure column 21 is entirely or essentially entirely liquefied in the liquefaction space of the main condenser 23 counter to liquid oxygen from the sump of the low-pressure column evaporating in the evaporation space. A first part 51 of the liquid nitrogen 50 generated in this manner is given up as return flow to the high-pressure column 21. A second part 52 is cooled in the counter-current subcooler 34 and is fed via line 53 into the low-pressure column 22. At least one part of the liquid low-pressure nitrogen 53 serves as return flow in the low-pressure column 21; another part 54 can be obtained as liquid nitrogen product (LIN).

(12) Gaseous crude nitrogen 61 is drawn off from an intermediate location in the low-pressure column 22 and is heated in the counter-current subcooler 34 and in the main heat exchanger 13. The hot crude nitrogen 62 can be vented (63) into the atmosphere (ATM) and/or can be used as regeneration gas 64 for the purification device 6. Gaseous nitrogen 55 from the top of the low-pressure column 22 is also heated in the counter-current subcooler 34 and in the main heat exchanger 13 and is drawn off via line 56 as low-pressure nitrogen product (GAN).

(13) The lines 67 and 68 (so-called argon transition) connect the low-pressure column 21 to the crude argon column 25 of the argon production 24.

(14) A first part 70 of the liquid oxygen 69 from the sump of the low-pressure column 21 is drawn off as “first product flow”, is raised in an oxygen pump 71 to a “first product pressure” of for example 37 bar, is evaporated at the first product pressure in the main heat exchanger 13 and finally is obtained via line 72 as “first compressed gas product” (GOX IC—internally compressed gaseous oxygen).

(15) A second part 73 of the liquid oxygen 69 from the sump of the low-pressure column 21 is, where appropriate, cooled in the counter-current subcooler 34 and obtained via line 74 as liquid oxygen product (LOX).

(16) In the example, also a third part 75 of the liquid nitrogen 50 from the high-pressure column 21 or from the main condenser 23 undergoes internal compression, in that it is raised in a nitrogen pump 76 to a second product pressure of for example 12 bar, is pseudo-evaporated at the second product pressure in the main heat exchanger 13 and finally is obtained via line 77 as internally compressed gaseous nitrogen product (GAN IC).

(17) A second part 78 of the gaseous top nitrogen 48 of the high-pressure column 21 is heated in the main heat exchanger and obtained via line 79 either as gaseous intermediate-compressed product or—as shown—used as seal gas for one or more of the process pumps shown.

(18) FIG. 2 differs from FIG. 1 in that the third partial flow 36 of the feed air is introduced at the first pressure into the main heat exchanger 13 and the second turbine 38 thus has an accordingly lower inlet pressure.

(19) In the exemplary embodiment of FIG. 3, the high-pressure column has a sump evaporator 351. This sump evaporator is then used in particular if, at least occasionally, a particularly low liquid production or even pure gas operation is desired. The turbine 38 of the preceding exemplary embodiments cannot be run with its maximum throughput as, in that case, too much air as third partial flow would have to be run through the cold end of the main heat exchanger and the operation of the main heat exchanger would thus be less efficient.

(20) In FIG. 3, it is now possible in the case of particularly low liquid production for one part 350 of the third partial flow from the turbine 38 to be guided past the main heat exchanger. The turbine 38 (and thus the coupled cold compressor) can now be run with full throughput without burdening the heat-exchange process in the main heat exchanger. The flow 350 is at least partially condensed in the evaporation space of the sump evaporator 351 and is then fed via line 352 to an intermediate location of the high-pressure column. It thus reinforces the distillation in the lower part of the high-pressure column.

(21) Notwithstanding the representation in FIG. 3, the flow 350 can also be cooled in the main heat exchanger to the dew state prior to introduction into the sump evaporator. This can take place in a separate passage, but also by means of an intermediate takeoff at a suitable location and corresponding rerouting.