Patent Application
20230043513
The present invention relates to a method for providing an oxygen product and to a corresponding plant in accordance with the respective preambles of the independent claims.
The production of air products in the liquid or gaseous state by cryogenic fractionation of air in air separation plants is known and described, for example, in H.-W. Häring (editor), Industrial Gases Processing, Wiley-VCH, 2006—in particular, Section 2.2.5, “Cryogenic Rectification.”
Oxygen in the liquid or gaseous state is usually produced by cryogenic fractionation of air in corresponding air separation plants with distillation column systems known per se. These can be designed, for example, as single-column or two-column systems—in particular, as classic double-column systems, but also as three-column or multi-column systems. In the context of the present invention, it is possible in particular to use a distillation column system which has a distillation column primarily configured for providing nitrogen and which is referred to here as a “nitrogen column.” A corresponding method is also referred to as a SPECTRA method and is explained in more detail below.
In this embodiment, liquid is withdrawn from the nitrogen column, expanded, vaporized in a top condenser of the nitrogen column against condensing top gas—which is then partly returned to the nitrogen column as a return flow and can be partially conducted out of the plant—subsequently recompressed, and returned into the nitrogen column. Further liquid from the nitrogen column can also be expanded in this embodiment, vaporized in the top condenser of the nitrogen column against the condensing top gas of the nitrogen column, further expanded, and conducted out of the plant.
In addition to the nitrogen column, in a corresponding embodiment of the present invention, an additional column for generating (pure or high-purity) oxygen is provided. This can be fed directly from the nitrogen column or with fluid withdrawn from the nitrogen column and processed further in at least one further distillation column. Furthermore, devices, e.g., distillation columns, for obtaining further air components—in particular, the noble gases helium, neon, krypton, xenon, and/or argon—can be provided in the aforementioned distillation column systems.
Oxygen, but also other air products, can be subjected to what is known as internal compression. In the case of internal compression, a gaseous, pressurized air product is conventionally formed in that a cryogenic liquid air product is withdrawn from the distillation column system used, subjected to a pressure increase to a product pressure, and transferred to the gaseous or supercritical state at the product pressure by heating. For example, gaseous pressurized oxygen of any purity, gaseous pressurized nitrogen, and/or gaseous pressurized argon can be generated by means of conventional internal compression. The internal compression offers a range of advantages over an alternative possible external compression and is explained, for example, in Häring (see above), section 2.2.5.2, “Internal Compression.” In addition, methods and systems for cryogenic fractionation of air in which internal compression is used are shown in US 2007/0209389 A1 and in WO 2015/127648 A1.
To increase the pressure of air products in air separation plants, what is known as pressurization vaporization is known and described, for example, in DE 676 616 C and EP 0 464 630 A1. As disclosed, for example, in U.S. Pat. No. 6,295,840 B1, an air product can also be brought to pressure by means of a partial flow of compressed feed air in a tank arrangement.
WO 2014/173496 A2 discloses a method for obtaining oxygen in the sense explained below in an air separation plant, in which a liquid fraction is obtained from feed air and is used at least in part to provide the oxygen. The liquid fraction is temporarily stored in a tank arrangement with at least two tanks, wherein the liquid fraction is supplied to at least one of the tanks and/or is withdrawn from at least one of the tanks for providing the air product, and is not supplied and withdrawn from any of the tanks at the same time. The composition of the liquid fraction in the tank is determined in each case before the liquid fraction is withdrawn from one of the tanks. EP 3 193 114 A1 discloses a further method with pressurization vaporization.
There is a need for improved methods for providing oxygen—in particular, using the air separation plants explained—which in particular ensure a better yield than in the prior art.
Against this background, the invention proposes a method for providing an oxygen product and a corresponding plant according to the respective preambles of the independent claims. Embodiments are the subject matter of the dependent claims and of the description below.
Before explaining the features and advantages of the present invention, further principles are first explained, and terms used in the present application are defined.
In principle, “oxygen” is to be understood here to mean any liquid or gaseous fluid which has more than 80% oxygen. The term, “oxygen,” is therefore not limited to pure or high-purity oxygen as a basis for the underlying understanding, but pure or high-purity oxygen can also be provided. The term, “high purity,” is to be understood below as oxygen with at least 99.9 mole percent purity. The oxygen is conducted out of a corresponding plant as an oxygen product, wherein a “product” no longer is returned to the plant and participates in plant-internal circuits.
If a “SPECTRA process” is mentioned here, this term, as already mentioned in the introduction, stands for a method with a focus on the production of nitrogen, in which a liquid is withdrawn from an air-fed distillation column, expanded, vaporized in a top condenser of the distillation column against condensing top gas of the distillation column—which is partly returned to the distillation column as a return flow—then recompressed and returned to the distillation column.
Features and advantages of the invention
In the processes of the prior art mentioned at the outset, pressurization vaporization is carried out in what are called run tanks. In this case, usually, one tank is filled, during which the pressurization, a determination of the purity, and subsequently an emptying (“draining”) are carried out in the other tank. In other words, a tank system with several tanks is used in which a first tank or a first group of the several tanks, but not a second tank or a second group of the several tanks, is filled in a first time period. Accordingly, the second tank or the second group of the tanks, but not the first tank, is filled in a second time period. The same applies to the emptying, which can take place at the same time as the filling of a respective other tank or a respective other group of tanks. Thus, in the first or a third time period, the second tank or the second group of tanks, but not the first tank or the first group of tanks, and, in the first time period, the first tank or the first group of tanks, but not the second tank or the second group of tanks, can be emptied. If a “first tank” or a “second tank” is referred to below, this can also stand, in simplified form, for the first or second group of tanks. Corresponding groups of tanks comprise tanks operated in parallel operation, so that in each case at least one first or one second tank (from the first or second group) is operated accordingly.
After the draining or emptying of the pressurized liquid from a corresponding tank (the pressure generated in the pressurization vaporization is in particular at approximately 8 to 16 bara), a residual gas is still present in the tank. This residual gas (blow-off gas) is conventionally blown off into the atmosphere and is thereby lost. A central aspect of the present invention is to make use of this residual gas. This results in considerable efficiency advantages, as explained below.
Corresponding pressurization systems can be used in particular in such plants in which products are, advantageously, not subjected to conveying or pressurization by means of pumps or compressors—for example, high-purity air products, which could become contaminated in this way. For example, such pressurization systems can be used in SPECTRA plants with oxygen production. In these, the production of liquid oxygen is comparatively energy-intensive. When blowing off the blow-off gas, however, about 5 to 15% of the amount of liquid oxygen produced is discarded, depending upon the feed amount and the run time. A use of this amount therefore results in considerable energy savings, since the net amount of liquid oxygen to be produced can be reduced.
The present invention achieves these advantages by utilizing the blow-off gas, which has hitherto been blown off to the atmosphere, from a pressurization system, wherein the utilization can take place in different ways. In particular, a re-liquefaction and a material utilization of the oxygen molecules contained in the blow-off gas can take place.
Overall, the present invention proposes a method for providing an oxygen product using an air separation plant with a distillation column system, in which a cryogenic liquid is withdrawn from the distillation column system, wherein a first portion of the cryogenic liquid is subjected to pressurization vaporization by vaporizing a second portion of the cryogenic liquid, and the oxygen product is provided using at least a part of the first portion of the cryogenic liquid. The pressurization vaporization takes place, as explained above, in corresponding tanks, from which the first portion of the cryogenic liquid is periodically withdrawn. After withdrawal of the first portion of the cryogenic liquid from the respective tank, the second portion of the cryogenic liquid is also discharged from the tank, at least partially, before the tank is refilled, and the tank is expanded in this way to the discharge pressure, as a result of which the aforementioned blow-off gas is provided.
The cryogenic liquid can be formed at 1 to 4 bara, e.g., about 3 bara, in particular in a pure oxygen column of a SPECTRA method, as also indicated below, and transferred via a gradient into tanks which are used in the pressurization vaporization. The pressurization vaporization delivers a pressure of, for example, about 8 to 16 bara or higher. After draining, the second portion of the cryogenic liquid is, conventionally, not present in any further utilization.
The present invention now proposes that at least a part of the vaporized second portion of the cryogenic liquid be supplied to a utilization for providing the oxygen product. In this way, the advantages already mentioned can be achieved. The correspondingly vaporized cryogenic liquid is at least not completely lost to the method.
In the method according to the invention, the utilization can comprise, in particular, a material utilization and/or a thermal utilization and/or a pressure utilization. Material utilization is present in particular when oxygen molecules contained in the second portion are converted into the ultimately liquid oxygen product—in particular, by liquefaction and optionally feeding into a column used to form the oxygen product or directly to the oxygen product. Thermal utilization can be present in particular when the second fraction is used as a cooling or heating medium, e.g., in a sump vaporizer (sump boiler) of a rectification column or for cooling a different material flow—for example, of nitrogen. However, thermal utilization can also be present when the second portion is expanded, and “cold is produced” or heat is dissipated in this way. This can take place, for example, by means of suitable expansion devices, such as turbines, which can be coupled, for example, with brakes of any type. On a cooled and expanded flow formed in this way, heat of one or more of any other flows can be transmitted. Pressure utilization can comprise, in particular, the expansion of a corresponding flow in an expansion turbine, which is coupled either to a generator or to a booster for compressing a further flow.
A particularly preferred embodiment of the invention comprises conducting the corresponding gas back into the air separation plant and liquefying it in a sump boiler of a distillation column in which the cryogenic liquid is formed. Subsequently, the liquid of the cryogenic liquid thus obtained is supplied in the distillation column (or the cryogenic liquid withdrawn from the distillation column) and conveyed back to the pressurization vaporization. In this way, the net amount of liquid oxygen to be produced can be reduced, or more liquid oxygen can be produced in total. Further details are explained in a corresponding embodiment below.
As mentioned, the present invention is particularly suitable in conjunction with a SPECTRA method and develops its particular advantages there due to the comparatively complex oxygen production. However, the present invention can in principle also be used with other methods of air separation. As mentioned, a SPECTRA method is characterized in that the distillation column system comprises a first distillation column, wherein liquid is withdrawn from the first distillation column, expanded, and vaporized against condensing top gas of the first distillation column, which is at least partially returned to the first distillation column, wherein the vaporized liquid is at least partially recompressed and fed back into the first distillation column. In a SPECTRA method, further liquid can in particular also be withdrawn from the first distillation column, expanded, vaporized against the condensing top gas of the first distillation column, and at least partially discharged from the air separation plant.
In a version of a SPECTRA method used in the present invention, the distillation column system can comprise, for example, a second distillation column fed from the first distillation column, wherein the second distillation column is operated using a sump boiler, and the cryogenic liquid is withdrawn from the second distillation column. However, the present invention can also comprise any versions thereof in which, for example, an additional high-purity oxygen column is used, and/or plants with argon production, in which a side flow is withdrawn from one of the columns used and converted to an argon column or a column system for argon generation. In general, the cryogenic liquid can be withdrawn from any further distillation column downstream of the first distillation column, i.e., fed in turn directly from the first distillation column or with fluid which was withdrawn from the first distillation column and processed further in at least one other distillation column. The withdrawal of the cryogenic liquid can take place in particular in the form of high-purity oxygen from a further distillation column, which is not the second distillation column mentioned, but is downstream of it.
If a material utilization takes place here, the vaporized second portion of the cryogenic liquid, or the part thereof which is supplied to the further utilization for providing the oxygen product, can be fed—in particular, at least partially—into the second distillation column. However, it is also possible to feed the vaporized second portion of the cryogenic liquid, or the part thereof which is supplied to the further utilization for providing the oxygen product, at least partially into the cryogenic liquid withdrawn from the second distillation column before the pressurization vaporization. In particular, liquefaction takes place before the feeding, so that a complete material utilization of the oxygen in the gas can be present, as explained below. In principle, however, a gaseous feed into a corresponding distillation column and liquefaction there can also take place.
A particularly preferred embodiment of the invention comprises, as already mentioned in principle, that the vaporized second portion of the cryogenic liquid, or the part thereof which is supplied to the further utilization for providing the oxygen product, is at least partially cooled in the sump boiler of the second distillation column.
As mentioned, approximately 15% loss arises during the pressurization. Up to about 93% of this amount can be made usable. This reduces the total loss to only about 1%. This limit can be explained by the design of the sump boiler. As a rule, these sump boilers are designed with a minimum temperature difference between flows to be vaporized and condensed of >1 K. Since the gas (the second portion or a part thereof) is liquefied by liquid oxygen (in the sump of the distillation column), the minimum pressure of the liquid oxygen in the sump boiler is about 300 mbar above the pressure in the sump of the distillation column. The minimum pressure of the gas is limited to a value of about 500 or at least 400 mbar above the column sumps by further line and valve pressure loss on the path from the tanks in the pressurization vaporization to the sump boiler. This means that the second portion can be made usable at a corresponding pressure value during an expansion of, for example, 11 bara. Accordingly, the gas at a lower pressure level must continue to be blown out into the atmosphere.
In a further embodiment of the present invention, the vaporized second portion of the cryogenic liquid, or the part thereof which is supplied to the further utilization for providing the oxygen product, can be cooled at least partially in a further heat exchanger of the air separation plant.
The further heat exchanger can, in particular, be a heat exchanger, which liquid nitrogen, which is formed from top gas of the first distillation column, is supercooled to provide a liquid nitrogen product. In this way, liquefied oxygen can be supplied to the cryogenic liquid. When a sump boiler is used in a second distillation column of the type explained, the minimum pressure can be lowered here to a value of about 200 mbar above the pressure in the sump of the distillation column plus the heat exchanger pressure loss. This corresponds to the line and valve pressure losses. The energy saving is, for an the aforementioned case example, 101 kW (1.4%).
In principle, however, cooling in the main heat exchanger, with comparable savings effects, is also possible. In this way, the present invention can be implemented with minimal interventions in the overall system of the air separation plant.
If a thermal utilization is provided, the second portion is likewise guided at least partially through a heat exchanger for the transfer of heat to the latter, but is heated in the process. This can also take place in a separate heat exchanger or in the main heat exchanger. The second portion can be heated separately (i.e., without being mixed with further fluid) or together with further fluid, e.g., residual gas from the air separation plant or another fluid which can in particular be present at a lower pressure level than the second portion.
The present invention is suitable in particular for methods for producing cryogenic liquid and an oxygen product having an oxygen content of more than 99 mole percent—in particular, more than 99.5 or 99.9 mole percent.
Only for the sake of completeness is it again stated here that, in a corresponding method in the pressurization vaporization, a tank system with one or more alternately filled and emptied tanks is advantageously used, wherein in each case the filled tank is pressurized by vaporization of the second portion of the cryogenic liquid, and the second portion of the cryogenic liquid is discharged from the respectively emptied tank. This operation results in a surge-like or pulsating occurrence of the second portion of the cryogenic liquid, i.e., the liquefying gas. This can therefore advantageously be temporarily stored—in particular, in a buffer tank.
The present invention also extends to an air separation plant, with regard to which reference is expressly made to the corresponding independent claim. A corresponding air separation plant, which is preferably configured to carry out a method as has been explained above in different embodiments, benefits from the aforementioned advantages in the same way.
The invention is described below in more detail with reference to the accompanying drawings, which illustrate preferred embodiments of the present invention.
In the figures, elements corresponding to one another are indicated by identical reference signs and are not explained repeatedly for the sake of clarity. If method steps are described below, these also apply to the devices used for these method steps and vice versa.
In
The air separation plant 100 is supplied with air from the atmosphere A in the form of an input air flow a via a filter 1, which air is compressed in a main air compressor 2, cooled in a post-cooler (not denoted separately) and a direct contact cooler with water W, dried and freed of carbon dioxide in an adsorber station 4, supplied to a main heat exchanger 5 at the warm side, guided in the main heat exchanger 5 nearly to the cold end, and fed into a first distillation column 11 of a distillation column system 10. The feeding takes place in part without further cooling in the form of a material flow a1, partly after cooling in a sump boiler 121 in the sump of a second distillation column 12 of the distillation column system 10.
The air separation plant 100 is designed to carry out a SPECTRA process, for which purpose two liquid material flows b and c are withdrawn from the first distillation column 11 at different positions, i.e., via a side draw and from the sump, in each case supercooled in the main heat exchanger 5, expanded, and vaporized in a heat exchanger 111 against condensing top gas of the first distillation column 11. Liquid nitrogen can, for example, be fed from a store I. The material flow b is thereafter recompressed at least in part in a compressor 6 coupled to an expansion machine 7 and a brake (not separately denoted), cooled again in the main heat exchanger 5, and fed back into the first distillation column 11. The material flow c is at least partly heated in the main heat exchanger 5, expanded in the expansion machine 7, and discharged from the air separation plant 100.
The top gas is withdrawn from the first column 11 in the form of a material flow c, which is then divided into a partial flow c1, which is conducted into the heat exchanger 111 and liquefied there, and a partial flow c2, which is discharged from the air separation plant 100 as product N1, N2. After liquefaction, the material flow c1 is partly returned to the first column 11 as a return flow. A further portion can be cooled after supercooling in a heat exchanger 8 against a part of itself and can be discharged as liquid nitrogen product C. A part can be discharged from the air separation plant 100 as a purge flow P.
The second distillation column 12 is fed with a liquid side flow d from the first distillation column 11, which is supercooled in the sump boiler 121 and then dispensed to the second distillation column 12 at the top. An oxygen product is formed by cryogenic, oxygen-rich liquid which is withdrawn from the sump of the second distillation column 12 in the form of a material flow e. After feeding in a further material flow (see below), the material flow e is supplied as liquid oxygen to a pressurization vaporization 20 (see the details below and link E in
From the top of the second distillation column, impure nitrogen in the form of a material flow f is drawn off and, after combining with, inter alia, the expanded flow c, is heated in the main heat exchanger 5 and emitted to the atmosphere A and/or used as regeneration gas in the adsorber station 4.
Further treatment of the liquid oxygen of the material flow e takes place in the pressurization vaporization 20, illustrated in a greatly simplified manner. For details, reference is also made to
While, in the embodiment according to
It is understood that the features shown in
An essential component of the pressurization vaporization 20 is a double-tank system, which here is denoted as 70 overall, and includes the two tanks 71 and 72. By means of a pump 55, the pressure of the cryogenic liquid of the fluid flow e, denoted here as 41, can be increased. However, the pump 55 is not absolutely necessary if the pressurization by vaporization alone is sufficient. In the case of pressurization vaporization 20, pump 55 is regularly omitted, and the cryogenic liquid of the flow 41 is fed into the tanks 71 and 72 at distillation pressure in second distillation column 12.
The tank system 70 is equipped with a pressurization vaporization device 75. In the pressurization vaporization device 75, a portion of the cryogenic liquid of the flow 41 withdrawn in liquid form from the tanks 71 or 72 is vaporized. The vaporized gas present under an increased pressure is supplied to a headspace of the tanks 71 or 72. In this way, the pump 55 can be omitted, and only a pressurization vaporization can be used. However, it becomes apparent that part of the product is converted into the gas phase in doing this. If the cryogenic liquid is withdrawn from the respective tank 71, 72, the gas phase remains. In conventional methods, this is blown off to the atmosphere, as illustrated here and previously with V. Instead, the embodiment of the invention illustrated here provides that a part in the form of material flow h be used, as explained above.
The pressure-elevated fluid flow 41 is supplied to either the tank 71 or the tank 72 and is then pressurized. In this case, the tanks 71 and 72 are alternately charged with the cryogenic liquid of the fluid flow 41, i.e., during a first time period, the cryogenic liquid of the fluid flow 41 is supplied to the first tank 71 and not to the second tank 72, and, during a second time period, to the second tank 72 and not to the first tank 71. To control correspondingly used valves 71a and 72a, a tank control 80 can be provided, for example.
Furthermore, cryogenic liquid is always withdrawn from the tank 71, 72 which is currently not being supplied with the fluid flow 41. This liquid can generally be discharged directly after withdrawal. In the embodiment shown, however, this is transferred unheated into a further tank 73. For example, when the further tank 73 is completely filled, it can also be provided, as illustrated here by means of a line 74, for corresponding fluid to be conducted onwards directly and to be supplied to heating. The heating of the fluid can, as also mentioned, take place, for example, in a main heat exchanger 5 of a corresponding air separation plant, e.g., the air separation plant 100 according to
However, the cryogenic liquid can also be withdrawn from the further tank 73 in the liquid state and stored in liquid state in a storage tank 76 until use. Further withdrawals upstream and/or downstream of the further tank 73 are also possible in principle.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19020722.5 | Dec 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/025522 | 11/19/2020 | WO |
