METHOD FOR OBTAINING AN AIR PRODUCT IN AN AIR SEPARATION PLANT AND AIR SEPARATION PLANT

Abstract

A method for obtaining an air product from an air separation plant having a distillation column system and a tank system. The tank system includes a first tank and a second tank. Cryogenic liquid is withdrawn from the distillation column system, stored in the tank system, and used as the air product. The cryogenic liquid is supplied to the first tank and withdrawn from the second tank during a first period, and is supplied to the second tank and withdrawn from the first tank during a second period. The tank system has a third tank to which cryogenic liquid withdrawn from the first tank and the second tank is transferred unheated. The air product is withdrawn from the third tank in liquid state, vaporized and discharged. Alternatively, the cryogenic liquid can be withdrawn from the third tank and stored in the liquid state in a fourth tank.

Claims

1. Method for obtaining an air product using an air separation plant having a distillation column system and a tank system with a first tank and a second tank, in which a cryogenic liquid is withdrawn from the distillation column system, is stored at least in part in the tank system, and is then used at least in part as the air product, wherein the cryogenic liquid is supplied to the first tank and not to the second tank during a first period, and is supplied to the second tank and not to the first tank during a second period, and is withdrawn from the second tank and not from the first tank during the first period, and from the first tank and not from the second tank during the second period, characterized in that the tank system comprises an additional third tank, and in that the cryogenic liquid which is withdrawn from the second tank during the first period, and from the first tank during the second period, is transferred at least partially unheated into the third tank, and in that the air product is provided at least in part by using the cryogenic liquid transferred, unheated, into the third tank, or part of this, wherein the cryogenic liquid from the third tank used for providing the air product is withdrawn from the third tank in the liquid state, is vaporized or converted from the liquid to the supercritical state, and is discharged from the air separation plant, and/or wherein the cryogenic liquid from the third tank used for providing the air product is withdrawn from the third tank in the liquid state and is stored in the liquid state in a fourth tank.

2. Method according to claim 1, in which the cryogenic liquid is supplied to the first tank and to the second tank at a first pressure level, and/or in which the cryogenic liquid is stored in the third tank at a second, higher pressure level.

3. Method according to claim 2, in which the first pressure level is between 1.3 and 7 bar, and the second pressure level is between 2 and 100 bar.

4. Method according to claim 2, in which the cryogenic liquid is raised, in the liquid state and using a pump, from the first pressure level to the second pressure level prior to introduction into the first tank and into the second tank.

5. Method according to claim 1, in which the cryogenic liquid undergoes, in the first tank and in the second tank, pressurization vaporization to the second pressure level.

6. Method according to claim 1, in which a purity of the cryogenic liquid, which is supplied to the first tank during the first period and to the second tank during the second period, is determined in the respective tank.

7. Method according to claim 6, in which the cryogenic liquid is transferred from the second tank to the third tank during the first period, and from the first tank to the third tank during the second period, only if its purity corresponds to a setpoint value.

8. Method according to claim 7, in which, if the purity of the cryogenic liquid does not correspond to the setpoint value, the fluid is returned, from the second tank during the first period and from the first tank during the second period, to the distillation column system.

9. Method according to claim 1, in which the third tank retains a quantity of the cryogenic liquid that is at least as large as a quantity of the cryogenic liquid, that can be stored in the first tank and/or in the second tank.

10. Method according to claim 1, in which the distillation column system comprises a first separation column and a second separation column, the first separation column being used to generate a fluid stream which is enriched to a first oxygen content and which is used in the second separation column to generate pure liquid oxygen that is withdrawn from the second separation column at least in part as the cryogenic liquid.

11. Method according to claim 10, in which the first separation column is further used to generate a fluid stream enriched to a second oxygen content and a fluid stream enriched to a third oxygen content, and to heat these to different temperatures, wherein the heated fluid stream that is enriched to the second oxygen content is at least in part compressed in a compressor coupled to an expansion machine, cooled and returned to the first separation column, and part of the heated fluid stream enriched to the third oxygen content is used to drive the expansion machine.

12. Method according to claim 1, in which a main heat exchanger of the air separation plant and/or a vaporizer is used for heating the cryogenic liquid.

13. Air separation plant, which is designed for obtaining an air product, having a distillation column system and a tank system with a first tank and a second tank, means which are designed to withdraw a cryogenic liquid from the distillation column system, to store at least part of this liquid in the tank system, and then use at least part of this as the air product, and means which are designed to supply the cryogenic liquid to the first tank and not to the second tank during a first period, and is supplied to the second tank and not to the first tank during a second period, and to withdraw the liquid from the second tank and not from the first tank during the first period, and from the first tank and not from the second tank during the second period, characterized, in that the tank system comprises an additional third tank, and in that there are provided means which are designed to transfer the cryogenic liquid which is withdrawn from the second tank during the first period, and from the first tank during the second period, at least temporarily and at least partially unheated into the third tank, and to provide the air product at least in part by using the cryogenic liquid transferred, unheated, into the third tank, or part of this, wherein there are provided means which are designed to withdraw, from the third tank in the liquid state, the cryogenic liquid from the third tank used for providing the air product, to vaporize or convert this cryogenic liquid from the liquid to the supercritical state, and to discharge it from the air separation plant, and/or which are designed to withdraw, from the third tank in the liquid state, the cryogenic liquid from the third tank used for providing the air product, and to store this in the liquid state in a fourth tank.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 shows an air separation plant according to one embodiment of the invention, in the form of a schematic plant diagram.

[0039] FIG. 2 shows a tank system according to one embodiment of the invention, in the form of a schematic plant diagram.

[0040] FIG. 3 shows a tank system according to one embodiment of the invention, in the form of a schematic plant diagram.

DETAILED DESCRIPTION OF THE DRAWINGS

[0041] In the figures below, mutually corresponding elements are indicated with identical reference signs, and explanations will not be repeated, for the sake of clarity. In that context, FIGS. 2 and 3 respectively show tank systems as can be integrated into an air separation plant according to FIG. 1, or an air separation plant of a different design. In that context, the integration of the tank system is given by the elements also indicated in FIG. 1.

[0042] FIG. 1 shows, schematically, in the form of a schematic plant diagram, an air separation plant according to one embodiment of the present invention. The air separation plant is provided, as a whole, with the label 100.

[0043] Atmospheric air 1 (AIR) is drawn in, via a filter 2, by an air compressor 3 where it is compressed to an absolute pressure of between 6 and 20 bar, preferably approximately 9 bar. After flowing through an after-cooler 4 and a water separator 5 for separating off water (H2O), the compressed air 6 is purified in a purification apparatus 7 which has a pair of containers filled with adsorption material, preferably a molecular sieve. The purified air 8 is cooled to near dew point, and partially liquefied, in a main heat exchanger 9. A first part 11 of the cooled air 10 is introduced, via a throttle valve 51, into a first separation column 12. The injection preferably takes place several actual or theoretical trays above the sump.

[0044] The operating pressure of the single column 12 (at the top) is between 6 and 20 bar, preferably approximately 9 bar. Its top condenser 13 is cooled with a fluid stream 18 and a fluid stream 14. The fluid stream 18 is drawn off from an intermediate point which is several actual or theoretical trays above the air injection, or which is at the same height as the latter, and the fluid stream 14 is drawn off from the sump of the first separation column 12. In the context of the above explanations, the fluid stream 18 has been labelled a fluid stream enriched to a second oxygen content, and the fluid stream 14 has been labelled a fluid stream enriched to a third oxygen content.

[0045] Gaseous nitrogen 15, 16 is drawn off at the top of the first separation column 12 as the main product of the first separation column 12, is heated in the main heat exchanger 9 to approximately ambient temperature, and is finally drawn off via line 17 as a pressurized gas product (PLAN). Further gaseous nitrogen is fed through the top condenser 13. A part 53 of the condensate 52 obtained in the top condenser 13 can be obtained as liquid nitrogen product (PLIN); the remainder 54 is delivered to the top of the first separation column 12 as return flow.

[0046] The fluid stream 14 is vaporized in the top condenser 13 at a pressure of between 2 and 9 bar, preferably approximately 4 bar, and flows in gaseous form via a line 19 to the cold end of the main heat exchanger 9. It is withdrawn from the latter, at an intermediate temperature, in the form of the stream 20 and, in an expansion machine 21 which in the example shown takes the form of a turboexpander, is expanded, so as to perform work, to approximately 300 mbar above atmospheric pressure. The expansion machine 21 is mechanically coupled to a (cold) compressor 30 and to a brake device 22 which in the example shown takes the form of an oil brake. The expanded fluid stream 23 is heated in the main heat exchanger 9 to approximately ambient temperature. The hot fluid stream 24 is vented, as fluid stream 25, to the atmosphere (ATM) and/or is used as regeneration gas 26, 27, possibly after heating in the heating device 28.

[0047] The fluid stream 18 is vaporized in the top condenser 13 at a pressure of between 2 and 9 bar, preferably approximately 4 bar, and flows in gaseous form via a line 29 to the compressor 30 in which it is re-compressed to approximately the operating pressure of the first separation column 12. The re-compressed fluid stream 31 is cooled, in the main heat exchanger 9, back to the column temperature and finally fed, via the line 32, back to the sump of the first separation column 12. The treatment of the fluid streams 14 and 18 as described corresponds to the already-mentioned SPECTRA method.

[0048] A fluid stream 36, previously labelled a fluid stream enriched to a first oxygen content, which is essentially free from heavy volatile contaminants, is drawn off in the liquid state from an intermediate point of the first separation column 12, which point is arranged 5 to 25 theoretical or actual trays above the air injection point. Where appropriate, the fluid stream 36 is sub-cooled in a sump vaporizer 37 of a second separation column 38, designed as a pure oxygen column, and is then delivered, via a line 39 and a throttle valve 40, to the top of the pure oxygen column 38. The operating pressure of the pure oxygen column 38 (at the top) is between 1.3 and 4 bar, preferably approximately 2.5 bar.

[0049] The sump vaporizer 37 of the second separation column 38 is also operated using a second part 42 of the cooled feed air 10. The feed air stream 42 is then at least partially, for example entirely, condensed and flows via a line 43 to the first separation column 12 where it is introduced approximately at the height of the injection of the remaining feed air 11, or into the column sump.

[0050] Pure oxygen is withdrawn as a cryogenic liquid 41 from the sump of the second separation column 38, is optionally raised by means of a pump 55 to an increased pressure of between 2 and 100 bar, preferably approximately 12 bar, and is introduced into a tank arrangement 70 which is shown in the subsequent FIGS. 2 and 3, After intermediate storage in the tank arrangement 70, the cryogenic liquid is fed via a line 56 to the cold end of the main heat exchanger 9 where it is vaporized at the increased pressure and is heated to approximately ambient temperature, and is finally obtained via line 57 as a gaseous product (GOX-IC).

[0051] A top gas 58 of the second separation column 38 is mixed into the previously mentioned expanded second fluid stream 23 (cf. connection A). Where relevant, part of the feed air is guided via a bypass line 59 to the inlet of the cold compressor 30 for surge prevention of the latter (what is referred to as anti-surge control).

[0052] When necessary, it is possible to withdraw from the air separation plant 100, upstream and/or downstream of the pump 55, liquid oxygen as liquid fraction (labelled LOX in the drawing). In addition, an external liquid, for example liquid argon, liquid nitrogen or liquid oxygen, also from a liquid tank, can be vaporized in the main heat exchanger 9 in indirect exchange of heat with the feed air (not shown in the drawing).

[0053] FIG. 2 shows, in the form of a schematic plant diagram, a tank system according to one embodiment of the invention, which can be used in an air separation plant 100 as illustrated in FIG. 1 and which as a whole is provided with the label 70.

[0054] The pump 55, already explained with reference to FIG. 1, is used to bring the cryogenic liquid of the fluid stream 41 from a first pressure level to a second pressure level. The first pressure level can in particular correspond to a pressure level at which a second separation column 38 (pure oxygen column) of an air separation plant 100, as shown in FIG. 1, can be operated. The second pressure level is for example 2 to 100 bar.

[0055] The pressurized fluid stream 41 is supplied to a first tank 71 or to a second tank 72. As explained many times, the tanks 71 and 72 are supplied with the cryogenic liquid of the fluid stream 41 in alternation with respect to one another, i.e. during a first period the cryogenic liquid of the fluid stream 41 is supplied to the first tank 71, and not to the second tank 72, and during a second period to the second tank 72, and not to the first tank 71. It is for example possible to provide a tank control 80 for controlling valves 71a and 72a used for this purpose.

[0056] As also explained many times, cryogenic liquid is always withdrawn from that tank 71, 72 which at that moment is not Supplied with cryogenic liquid of the fluid stream 41. This liquid is transferred, unheated, into a third tank 73. As already explained, it can also be provided, for example in the event of the third tank 73 being completely full, and as illustrated here by means of a line 74, to directly forward the corresponding fluid and supply it to heating. Heating of the fluid can, as also mentioned, take place for example in a main heat exchanger 9 of a corresponding air separation plant, for example the air separation plant 100 according to FIG. 1, and/or in an additional vaporizer 90.

[0057] FIG. 3 illustrates a tank system according to another embodiment of the invention, in the form of a schematic plant diagram. The tank system of FIG. 3 is also labelled 70, The tank system 70, which is illustrated in FIG. 3, is equipped with a pressurization vaporization device 75. A pump 55, as in the tank system 70 of FIG. 2 and/or in the air separation plant 100 of FIG. 1, is optionally provided here. In the case of pressurization vaporization, a corresponding pump 55 is generally omitted and the cryogenic liquid of the stream 41 is injected at the distillation pressure in the pure oxygen column 38, which corresponds to the first pressure level, into the tanks 71 or, respectively, 72. The pressurization vaporization device 75 vaporises a fraction of the cryogenic liquid of the stream 41 which is withdrawn in liquid form from the tanks 71 or, respectively, 72. The vaporized and pressurized gas is fed to a top space of the tanks 71 or, respectively, 72. It is thus possible to dispense with the pump 55, and it is possible to use only pressurization vaporization.

[0058] As shown here, the cryogenic liquid used to provide the liquid air product is withdrawn in the liquid state from the third tank 73 and is vaporized in the main heat exchanger 9 and/or in the additional vaporizer 90, or is converted from the liquid to the supercritical state and is discharged from the air separation plant. The cryogenic liquid used to provide the liquid air product can however also be withdrawn in the liquid state from the third tank 73 and stored in liquid form in a fourth tank 76 until it is used. The details have already been explained. Further withdrawal points upstream and/or downstream of the third tank 73 are also possible.