METHOD AND SYSTEM FOR SEPARATING A GAS MIXTURE

Abstract

Separating a starting gas mixture using pressure swing adsorption. In this, at least part of a low-pressure extraction flow from the pressure swing adsorption is subjected to a thermal separation, wherein a return fraction is formed in the thermal separation which is returned to the pressure swing adsorption separation. In the thermal separation, counterflow cooling takes place to obtain a two-phase mixture, wherein at least part of the two-phase mixture is subjected to phase separation to obtain a gas phase and a condensate. At least a part of the gas phase is used to form the return fraction, and counterflow cooling is carried out using at least a part of the gas phase and at least a part of one or more fluid flows which are formed by expansion of at least a part of the liquid phase.

Claims

1. A method for separating a starting gas mixture which contains a first component or component group and a second component or component group, wherein using at least a part of the starting gas mixture, a first separating feed flow is formed which contains the first component group and the second component or component group, and which is supplied to a pressure swing adsorption separation, 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, 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, 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, at least a part of the low-pressure extraction flow subjected to a compression at a pressure in a third pressure range and used to form a second separating feed flow is subjected to a thermal separation at the pressure in the third pressure range, in the thermal separation, at least a share of the second separating feed flow is subjected by cooling to the pressure in the third pressure range of a partial condensation to obtain a first gas phase and a first condensate, and in the thermal separation, a second gas phase and a second condensate are formed by expanding at least a share of the first condensate, wherein a first share of the second condensate is liquid-pressurized and is discharged from the method, and a second share of the second condensate is vaporized and used in the formation of the second separation feed flow.

2. The method according to claim 1, in which the first condensate is depleted of the first component or component group compared to the second separating feed flow and is enriched with the second component or component group, and in which the second condensate is depleted of the first component or component group relative to the first condensate and is enriched with the second component or component group.

3. The method according to claim 1, in which the cooling of at least a share of the second separating feed flow at the pressure in the third pressure range to its partial condensation in the thermal separation is carried out using a counterflow heat exchanger in which at least a share of the first gas phase is warmed, and at least a share of the second share of the second condensate is vaporized.

4. The method according to claim 1, in which the vaporized second share of the second condensate used during the formation of the second separation feed flow is subjected to the pressure in a third pressure range at least in part with the low-pressure extraction flow or a part thereof of the compression.

5. The method according to claim 1, wherein the third pressure range is 10 to 80 bar.

6. The method according to claim 1, wherein the cooling at the pressure in the third pressure range is performed to a temperature of ?30 to ?100? C., and wherein the expansion of at least a part of the first condensate is performed to a pressure of 1 to 40 bar, in particular 1 to 10 bar, 15 bar.

7. The method according to claim 1, wherein the first component or component group comprises or represents at least one of the components hydrogen, nitrogen, oxygen, methane and/or carbon monoxide, and in which the second component or component group comprises or represents at least one of the components carbon dioxide, ethane, ethylene, propane, or butane.

8. The method according to claim 1, wherein the thermal separation is carried out without an additional refrigerant, wherein the first share of the second condensate liquid-pressurized in the thermal separation is vaporized at least to a part, or wherein the thermal separation is performed using an additional refrigerant.

9. The method according to claim 1, wherein the thermal separation is fed with no further feed flows than the second separation feed flow.

10. A system for separating a starting gas mixture, which contains a first component or component group and a second component or component group, wherein the system is configured using at least a part of the starting gas mixture, to form a first separating feed flow which contains the first component group and the second component or component group, and to supply it to a pressure swing adsorption separation, to remove a high-pressure extraction flow from the pressure swing adsorption separation at a pressure in a first pressure range and a low-pressure extraction flow at a pressure in a second pressure range below the first pressure range, wherein the first component or component group is transferred from the first separating feed flow in the pressure swing adsorption separation to a greater share into the high-pressure extraction flow and to a lower share into the low-pressure extraction flow, wherein the second component or component group is transferred from the first separating feed flow in the pressure swing adsorption separation to a lower share into the high-pressure extraction flow and to a greater share into the low-pressure extraction flow, subjecting at least a part of the low-pressure extraction flow (L) to a compression at a pressure in a third pressure range and using it to form a second separating feed flow, and subjecting it to a thermal separation at the pressure in the third pressure range, in the thermal separation, to subject at least a part of the second separation feed stream to a partial condensation by cooling to the pressure in the third pressure range to obtain a first gas phase and a first condensate, and in the thermal separation, by expanding at least a part of the first condensate, to form a second gas phase and a second condensate, wherein means that are configured: to liquid-pressurize a first share of the second condensate and to discharge it from the method, and to vaporize a second share of the second condensate and use it in the formation of the second separation feed flow.

11. (canceled)

12. A system for separating a starting gas mixture, which contains a first component or component group and a second component or component group, wherein the system is configured using at least a part of the starting gas mixture, to form a first separating feed flow which contains the first component group and the second component or component group, and to supply it to a pressure swing adsorption separation, to remove a high-pressure extraction flow from the pressure swing adsorption separation at a pressure in a first pressure range and a low-pressure extraction flow at a pressure in a second pressure range below the first pressure range, wherein the first component or component group is transferred from the first separating feed flow in the pressure swing adsorption separation to a greater share into the high-pressure extraction flow and to a lower share into the low-pressure extraction flow, wherein the second component or component group is transferred from the first separating feed flow in the pressure swing adsorption separation to a lower share into the high-pressure extraction flow and to a greater share into the low-pressure extraction flow, subjecting at least a part of the low-pressure extraction flow to a compression at a pressure in a third pressure range and using it to form a second separating feed flow, and subjecting it to a thermal separation at the pressure in the third pressure range, in the thermal separation, to subject at least a part of the second separation feed stream to a partial condensation by cooling to the pressure in the third pressure range to obtain a first gas phase and a first condensate, and in the thermal separation, by expanding at least a part of the first condensate, to form a second gas phase and a second condensate, wherein means that are configured: to liquid-pressurize a first share of the second condensate and to discharge it, and to vaporize a second share of the second condensate and use it in the formation of the second separation feed flow, whereas the system is configured to perform the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0051] FIGS. 1 to 3 show arrangements not according to the invention.

[0052] FIG. 4 shows an arrangement according to an embodiment of the invention.

[0053] FIG. 5 shows an arrangement according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0054] 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.

[0055] FIGS. 1 to 3 have already been explained above.

[0056] FIGS. 4 and 5 illustrate methods according to embodiments of the invention and are denoted overall by 100 or 200.

[0057] The apparatuses shown in FIGS. 4 and 5 bear the same reference signs as those illustrated in FIGS. 1 to 3. A PSA is indicated by 10, a container arranged on the suction side of a compressor 11 by 14, an aftercooler by 15, a further container arranged downstream therefrom by 16 and a treatment device, for example for removing unwanted components, by 30. Low-temperature separation is indicated as 50 in FIG. 3, but illustrated here with details according to embodiments of the invention. The low-temperature separation 50 comprises a counterflow or plate heat exchanger 51, separator 52 and 53 and expansion valves 54 and 55.

[0058] In the arrangements illustrated in FIGS. 4 and 5, a freshly supplied gas mixture is also designated E (previously 1), an inlet flow formed therefrom into the PSA 10, i.e. a first separation inlet flow, is designated by F (previously 1), a high-pressure outlet flow by C (previously 2), a low-pressure outlet flow by L (previously 3), a second separation insert flow by S (previously also 3) and return flows by R, R and R (previously 4). In FIGS. 4 and 5, M denotes a first two-phase mixture with M being a second two-phase mixture, C a first condensate, and Ca second condensate.

[0059] In the embodiments in FIGS. 4 and 5, the flow L will partially condense due to the compression in the compressor L, in contrast to flow 1, as a result of comparatively moderate cooling. In principle, such a partial condensation is always possible in the described cases since the strongly adsorbable components also have a comparatively high boiling point compared to the only slightly adsorbable components. In this case, this results in a strong concentration of the strongly adsorbable component(s) in the condensates C and C. In contrast, the concentration of the weakly adsorbable components(s) of the gas phases V and V is again high.

[0060] According to FIGS. 4 and 5, the low-pressure outlet flow L is supplied to the compressor 11 at least in part and is compressed therein. The corresponding second separating feed flow S, possibly obtained after additional treatment in the unit 30, is further treated as explained below.

[0061] According to FIGS. 4 and 5, the separating feed flow S is cooled in the plate heat exchanger 51 to obtain the first two-phase flow M which is fed into the separator 52. A first gas phase V and a first liquid phase C are removed from the separator 52, wherein the first gas phase V is fed back into the PSA 10 in the form of the return flow R, i.e. is used to form the inlet flow F.

[0062] According to FIGS. 4 and 5, the first condensate C is expanded to form a second two-phase mixture M at the expansion valve 54, and a second condensate C and a second gas phase V are formed in the separator 53. At least a part of the second gas phase V is then advantageously used as a further return flow which is denoted by R in FIGS. 4 and 5. The further return flow R can either, if the pressures permit, be subjected again to the PSA 10 (as illustrated) or, together with the low-pressure outlet flow L or its correspondingly used part, again be subjected to compression in the compressor 11 and then to partial condensation.

[0063] 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.

[0064] The embodiments according to FIGS. 4 and 5 differ in that in the embodiment according to FIG. 4, the first part of the second condensate C liquid-pressurized in the pump 56 is vaporized in the counterflow heat exchanger to form a material flow P, i.e. this material flow is used as refrigerant, and in the embodiment according to FIG. 5, the first part of the second condensate C liquid-pressurized in the pump 56 is discharged in liquid form, and a separate refrigerant in the form of a material flow Q is used instead.

[0065] The achievable advantage within the scope of the invention is in particular

[0066] 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%.

[0067] 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 FIGS. 4 and 5).

TABLE-US-00005 TABLE 4 Unit F C L C Quantity Nm.sup.3/h* 10000.0 8648.2 2137.9 1321.4 Pressure Bar 24.0 23.50 0.10 39.00 Temperature ? C. 40.0 41.0 28.5 40.0 Yield: Hydrogen Mol. % 74.700 86.3664 14.5574 0.0411 99.99% Carbon monoxide Mol. % 10.000 11.4996 6.3435 0.4125 99.45% Carbon dioxide Mol. % 15.000 2.1341 77.6965 99.5463 12.30% Water Mol. % 0.3000 0.0000 1.4032 0.0000 0.00% *Standard cubic meters per hour

[0068] 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.

TABLE-US-00006 TABLE 5 Concentration Adsorption Boiling point [K] Component [mol. %] force at 1 bar Hydrogen 74.700 Very weak 20 Carbon monoxide 10.000 Weak to medium 102 Carbon dioxide 15.000 Strong 195 (sublimation) Ethane Strong 184 Propane Strong 231 Water 0.3000 Very strong 373

[0069] 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.

[0070] 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.

[0071] 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).

TABLE-US-00007 TABLE 6 Unit F C L C Quantity Nm.sup.3/h* 10000.0 8646.4 2202.8 1323.6 Pressure bar 24.0 23.50 0.10 39.00 Temperature ? C. 40.0 41.0 28.4 40.0 Yield: Hydrogen Mol. % 74.700 86.3895 14.1289 0.0333 99.99% Carbon monoxide Mol. % 5.000 5.7557 3.0808 0.1767 99.53% Carbon dioxide Mol. % 15.000 2.1663 76.5272 99.1738 12.49% Methane Mol. % 5.0000 5.6884 4.9013 0.6162 98.37% Water Mol. % 0.3000 0.0000 1.3619 0.0000 0.00% *Standard cubic meters per hour