Patent Application
20240382894
The invention relates to a method and a system for separating a gas mixture according to the respective preambles of the independent patent claims.
Pressure swing adsorption (PSA) is generally used to separate gaseous substance mixtures. With PSA, the different strengths of adsorption forces of the individual gas molecules or atoms against the employed adsorbent are exploited.
PSA and variants thereof, as well as other adsorption methods and the corresponding technical principles, are described extensively in the technical literature, for example in the article of H.-J. Bart and U. v. Gemmingen, “Adsorption,” in Ullmann's Encyclopedia of Industrial Chemistry, online publication 2012, DOI: 10.1002/14356007.b03_09.pub2.
The substance mixture identified in Table 1 is merely an example of a problem underlying the present invention:
One widespread use of PSA is the recovery of the weaker or the weakest adsorbable component(s) in enriched or pure form, i.e. hydrogen in the example of the gas mixture indicated in Table 1. In other cases, in contrast, the recovery of the stronger or most strongly adsorbable component(s) in enriched or pure form, i.e. carbon dioxide in the example of the gas mixture indicated in Table 1, is of interest.
The present invention is not limited to the use of the gas mixture indicated in Table 1 or comparable gas mixtures. It is also suitable for other gas mixtures which have more strongly and weakly adsorbable components, as explained further below.
In a typical PSA method, which is shown highly schematized in
The outlet flow 2 (generally referred to as a “high-pressure product” and hereinafter also referred as a “high-pressure extraction flow”) is extracted from the PSA 10 approximately at the inlet pressure. In contrast, the outlet flow 3 (generally referred to as a “low-pressure product” and hereinafter also referred to as “low-pressure extraction flow”) is extracted from the PSA at a significantly lower pressure, namely at a desorption pressure. The desorption pressure can also be subatmospheric; this is referred to as a “vacuum” PSA (VPSA).
Where “a PSA” is referred to here and below, it should be understood to mean both a corresponding method or a corresponding method step and a technical device designed to carry out such a method or method step, or a corresponding apparatus or corresponding system component.
Adsorption takes place during PSA typically using porous adsorbents. The adsorbed shares of the adsorbable components depend in particular on the pressure of the inlet flow supplied to the PSA, i.e. the adsorption pressure, and on the selectivity of the adsorbent. The adsorbent used in the PSA is located in corresponding adsorption containers.
If one wishes to obtain hydrogen in pure form for the previously selected example, i.e. the gas composition according to Table 1, the typical split factors indicated in Table 2 can be used, again with reference to the highly schematized arrangement shown in
In the example in Table 2, the components carbon monoxide, carbon dioxide and water are present in higher concentrations in the outlet flow 3 than in the outlet flow 2 for the split factor used here. In contrast, the outlet flow 2 comprises substantially hydrogen, which is desired in this embodiment.
However, it is often not of interest for a component such as hydrogen in the case of Table 2 to be particularly pure in the outlet flow 2. If, for example, the carbon dioxide of the mixture according to Table 2 is to be particularly concentrated by means of a PSA process, the mode of operation of the PSA can be adapted such that the values indicated in Table 3 result.
For this purpose, the split factor can be adjusted accordingly (see the table lines “Amount” in Tables 2 and 3).
In the example in Table 3, the carbon dioxide content, in comparison with the starting mixture of the inlet flow 1 (15 mol. %), can be increased about fivefold (75 mol. %) in the outlet flow 3.
If the achieved concentration of a medium-to-highly adsorbable component of the inlet flow 1 by a corresponding method is not quite sufficient, a so-called circulation mode can be used in which a part of the outlet flow 3 is mixed back into the fresh inlet flow 1. A corresponding circuit mode is shown in a highly schematic manner in
Here, the low-pressure product is first extracted from the PSA 10 in the form of an outlet flow 3′. A recycled share is shown in the form of a material flow 4. This is compressed by means of a compressor 11 downstream from an aftercooler 12, guided through a (droplet) separator 13, and supplied as a material flow 4′ together with the inlet flow 1 in the form of a collective flow 1′ of the PSA 10. The share of the outlet flow 3′ that is not returned, i.e., for example, an exported low-pressure product, is designated with 3 as previously in
By means of a corresponding circuit mode, the concentration of the carbon dioxide in the outlet flow 3 can further increase when the previously described mixture is used. A further advantage results from the often desired higher yield of the weakly adsorbable components in the direction of the outlet flow 2. Even with high circulation rates of 70% (i.e. a ratio of 0.7 of material flow 4 to material flow 3′), the concentration of carbon dioxide cannot, however, be increased as desired. A corresponding situation is illustrated in Table 4. It can also be seen from Table 4 that, although the concentration of the carbon dioxide in the outlet flow 3 is stronger, the “loss” of carbon dioxide in the direction of the outlet flow 2 simultaneously also increases in principle, however.
A further increase in concentration is possible in principle with a series connection of two or more PSA units with intermediate compression, as is not illustrated separately here. However, a minimum amount of weakly adsorbable components in the inlet flow to the PSA is also always required since the pressure build-up can only be carried out in this way.
The last stage of a multistage PSA is thereby defined in principle. The
content of weakly to very weakly adsorbable components must be in the range from 15 to 35 mol. % at the inlet thereto. If it were less, the PSA process itself would collapse. An arbitrarily high content of the desired components in the outlet flow 3 or an outlet flow then correspondingly formed cannot be achieved in this way either.
As a result, from a technical point of view, not just any number of PSA units can be connected in series to achieve an arbitrarily high concentration of the medium-to-strongly adsorbable component in the low-pressure product.
It is also known to supply a extraction flow 3′, as shown in
A corresponding variant is illustrated in
The object of the present invention is to improve methods and systems for adsorptive concentration of strongly adsorbable components using a PSA.
This object is achieved by a method and a system for the separation of a gas mixture having the features of the respective independent patent claims. Embodiments are the subject matter of the dependent claims and of the following description.
The proposed method according to the invention serves for the separation of a starting gas mixture which comprises a first component or component group (in particular one or more “light” components which adsorb more weakly in the PSA and at the same time have a lower boiling point) and a second component or component group (in particular one or more “heavy” components which adsorb more strongly in the PSA and at the same time have a lower boiling point).
As is known in this respect for PSA methods, a feed flow is also formed within the scope of the present invention using at least part of the starting gas mixture, which is referred to here as the “first” separation feed flow for the sake of better differentiation, and which contains the first component or component group and the second component or component group. The separating feed flow is fed to a PSA, i.e. pressure swing adsorption separation, at feed pressure.
From the pressure swing adsorption separation, a high-pressure extraction flow at a pressure in a first pressure range and a low-pressure extraction flow are extracted at a pressure in a second pressure range below the first pressure range, wherein the first component or component group from the first separating feed flow in the pressure swing adsorption separation is transferred to a greater extent into the high-pressure extraction flow and to a lesser extent into the low-pressure extraction flow, and wherein the second component or component group from the first separating feed flow in the pressure swing adsorption separation is transferred to a lesser extent into the high-pressure extraction flow and to a greater extent into the low-pressure extraction flow.
Within the scope of the invention, at least a part of the low-pressure extraction flow is subjected to compression at a pressure in a third pressure range and used to form a material flow which is referred to here for better differentiation as a “second separation feed flow.” The latter is subjected to a thermal separation (low-temperature separation) at the pressure in the third pressure range.
In the thermal separation, at least a part of the second separation feed flow is subjected by cooling to the pressure in the third pressure range to partial condensation to obtain a first gas phase and a first condensate (hereinafter also referred to as a “first liquid phase”). Furthermore, a second gas phase and a second condensate (“second liquid phase”) are formed in the thermal separation by expanding (“flashing”) at least a part of the first condensate, in particular from the pressure in the third pressure range to a pressure in a fourth pressure range below the third pressure range.
According to the invention, a first share of the second condensate is now liquid-pressurized and discharged from the process. Before the first liquid-pressurized share of the second condensate is discharged from the process, it can either be vaporized, as explained again below and illustrated in
By the expansion and recirculation of the second share of the second condensate proposed according to the invention, cold for low-temperature separation can be generated in a particularly advantageous manner in accordance with the principle of a heat pump. The returned share, like a refrigerant in a refrigerant circuit, is initially present in a condensed state, vaporized in counterflow to the second separating feed flow as it cools, then recompressed when the second separating feed flow is formed, and again subjected to condensation in the thermal separation unit.
The pressurization of the first share of the second condensate in the liquid state makes it possible to dispense with a gaseous compression, and thereby facilitates the structural implementation of the method according to the invention.
In particular, in the thermal separation, at least a part of the second separating feed flow is subjected to a partial condensation using counterflow cooling and obtaining a two-phase mixture, wherein at least a part of the two-phase mixture is subjected to a first phase separation while obtaining the first gas phase and the first condensate. The second condensate and the second gas phase are formed in particular without further cooling in a heat exchanger, but only by expansion (and possibly associated cooling) of the first condensate.
At least a part of the first and optionally second gas phase can be used here to form a return fraction, in principle as illustrated in
The counterflow cooling is carried out in particular in a counterflow to at least a part of the first and optionally second gas phase and to at least a part of the second share of the second liquid phase. Furthermore, either the first liquid-pressurized share of the second liquid phase, a part thereof, and/or a suitable separate refrigerant is used.
In other words, the cooling of at least a part of the second separation feed flow at the pressure in the third pressure range to its partial condensation in low-temperature separation can be carried out within the scope of the present invention, in particular using a counterflow heat exchanger in which at least a part of the first gas phase is heated, and at least a part of the second share of the second condensate is vaporized.
As mentioned above, the first condensate is depleted with respect to the second separating feed stream, in particular of the first component or component group, and enriched with the second component or component group, and the second condensate is depleted with respect to the first condensate, in particular of the first component or component group, and enriched with the second component or component group.
As already mentioned, the recirculation according to the invention achieves improved operation of the thermal separation in accordance with the principle of a heat pump. In this case, the vaporized second share of the second condensate used during the formation of the second separating feed flow is subjected to compression at the pressure in a third pressure range, in particular at least in part with the low-pressure extraction flow or a part thereof.
In the method proposed according to the invention, the second separating feed flow can be formed, in particular, using at least a part of the low-pressure extraction flow which is processed in a suitable manner and is freed from interfering components, for example.
Within the scope of the present invention, the third pressure range can be in particular 10 to 80 bar. The adsorption pressure in the PSA can be selected in a suitable manner. Within the scope of the present invention, a PSA operated at an superatmospheric desorption pressure, but also a VPSA explained at the outset, can be used.
Within the scope of the invention, the counterflow cooling and the expansion of at least a part of the first condensate to form the second condensate can in particular be carried out in such a way that the second liquid phase is present at a temperature and a pressure which are such that the second condensate can be completely vaporized during the corresponding heating. The person skilled in the art selects the specific values taking into account the respective composition of the relevant substance mixtures. A particularly advantageous adaptation of the heat exchange diagram can be achieved through two-stage vaporization.
Within the scope of the present invention, the counterflow cooling can in particular be carried out to a temperature of −30 to −100° C., and the expansion of at least a part of the first condensate to form the second two-phase mixture can be carried out in particular at an (absolute) pressure of from 1 to 40 bar, in particular from 1 to 10 or 1 to 15 bar. This pressure depends in particular also on the third pressure level.
In the proposed method according to the invention, the first component or component group comprises at least one of the components hydrogen, methane, nitrogen, oxygen and/or carbon monoxide, or represents a corresponding component, and the second component or component group comprises in particular at least one of the components carbon dioxide, ethane, ethylene, propane or butane, or represents such a component.
Within the scope of the present invention, the thermal separation can be carried out without an additional refrigerant so that corresponding refrigerant circuits and the like can be dispensed with. In this case, as mentioned, the liquid-pressurized first share of the second condensate can be vaporized in the thermal separation or the aforementioned counterflow heat exchanger before it is discharged from the process and thereby used as a refrigerant. Alternatively, the use of a separate refrigerant in the thermal separation is also possible. A combination of both alternatives is also possible.
In addition, within the scope of the present invention, the counterflow cooling is in particular not supplied with any more feed flows than the second separating feed flow, for example with no feed flows from a carbon dioxide removal.
In general, within the scope of the present application, if used, the terms “enriched” and “depleted” should generally refer to a content in a starting fluid from which the relevant fluid is obtained. The fluid is referred to as enriched if it contains at least 1.1 times, 1.5 times, 2 times, 5 times, 10 times, 100 times or 1,000 times the content of a corresponding component in relation to the starting fluid. Accordingly, the fluid is referred to as depleted if it contains at most 0.9 times, 0.5 times, 0.1 times, 0.01 times or 0.001 times the content of a corresponding component in relation to the starting fluid.
With regard to the system provided according to the invention and its features, reference is expressly made to the respective independent device claim and the above explanations of the method according to the invention, since these likewise concern a corresponding device. The same applies in particular to an embodiment of a corresponding device which is advantageously configured for carrying out a corresponding method in any embodiment.
The invention is further explained below with reference to the figures, which illustrate an embodiment of the present invention in comparison with the prior art.
In the further description above and in the following, systems and, on the basis thereof, corresponding method steps not according to the invention and those formed according to embodiments of the invention have been or are described. Merely for the sake of simplicity and to avoid unnecessary repetition, in this case the same reference signs and explanations have been or are used for method steps and system components (for example, a cooling step and a heat exchanger used for this purpose). In the figures, identical reference signs are used for identical or comparable components, and these are not explained repeatedly simply for the sake of clarity.
The apparatuses shown in
In the arrangements illustrated in
In the embodiments in
According to
According to
According to
A first part of the second condensate C′ is liquid-pressurized in a pump 56 and used to provide a method product P, and a second share is expanded at the valve 55, then vaporized in the plate heat exchanger 51, and returned to the compressor 11 and used again in this way to form the second separation feed stream S.
The embodiments according to
The achievable advantage within the scope of the invention is in particular
that, even with circulation rates of 0.7 to 1.0, the content of strongly adsorbable components in the circuit does not increase arbitrarily since these can condense out and can thus be discharged in a targeted and selective manner. In this method, the yield of slightly adsorbable components increases to almost 100%.
The advantages of the last described embodiment of the invention can be explained with the aid of Table 4 below, in which F represents the gas mixture subjected to the method, C the high-pressure outlet flow, L the low-pressure outlet flow and C′ the export flow formed from the additional liquid phase (with the same reference signs according to
All previously made statements can be transferred to similar substance mixtures with stronger and weaker adsorbing components. In all explanations and in practical use, carbon dioxide can therefore be replaced by ethane or propane. Table 5 below presents the corresponding adsorption forces and boiling points.
Common to all methods is the desire to enrich a highly to strongly adsorbable component, which usually also has a higher boiling point than the less adsorbable components.
A specific example from technology is the extraction of gaseous carbon dioxide for so-called enhanced oil recovery from known steam reforming (SMR, steam methane reforming) which serves to generate hydrogen from hydrocarbons. In this case, carbon dioxide can be removed by means of PSA in accordance with the invention both in the residual gas flow and in the feed gas flow to the hydrogen PSA already present.
Table 6 below illustrates the case of the arrangement in the feed gas flow to the already present hydrogen PSA (for the designation of the flows, see explanations relating to Table 4).
| Number | Date | Country | Kind |
|---|---|---|---|
| 21020448.3 | Sep 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/025414 | 9/5/2022 | WO |
