METHOD AND SYSTEM FOR SEPARATING A FEED FLOW

Abstract

A method and a system for separating a feed flow which contains at least hydrogen and a hydrocarbon with three or four carbon atoms per molecule, in particular propane, propylene, propadiene, butane, 1-butene, 2-butene, and/or 1,3-butadiene. The condensed feed flow is cooled over multiple cooling steps in at least two heat exchangers and is then separated into a condensate and a residual gas flow after each cooling step. The at least two heat exchangers are operated at least two different temperature levels, wherein a hot heat exchanger is operated at an average temperature level, and a cold heat exchanger is operated at a lower temperature level. An internal refrigerant which is made of a part of one of the condensate flows and a part of one of the residual gas flows, is used to dispense a part of the heat from the cold heat exchanger.

Claims

1. A method for separating a feed flow which contains at least hydrogen and a hydrocarbon with three to four carbon atoms per molecule, which feed flow is formed from a raw material flow, wherein the feed flow is partially liquefied in the compressed state using at least two coolers which are operated at different temperature levels, via at least two cooling steps, to obtain at least two condensate flows and at least two residual gas flows, wherein the residual gas flow of a cooling step is respectively fed into the subsequent cooling step, and wherein each condensate flow is depleted in hydrogen and enriched in the hydrocarbon with respect to the feed flow and each residual gas flow is enriched in hydrogen and depleted in hydrocarbon with respect to the feed flow, wherein a part of at least one of the condensate flows is combined with a part of at least one of the residual gas flows under expansion and used as internal refrigerant for at least one of the cooling steps or coolers and is at least partially recycled to the feed flow.

2. The method according to claim 1, wherein at least a first cooling step takes place at an average temperature level in a range from −40° C. to +10° C., preferably from −40° C. to −10° C., and at least a second cooling step takes place at a low temperature level in a range from −130° C. to −80° C., preferably from −110° C. to −90° C.

3. The method according to claim 2, wherein only material flows formed from the raw material flow are used to achieve at least the low temperature level.

4. The method according to claim 2, wherein a refrigerant which is not provided internally in the process is used to achieve the average temperature level.

5. The method according to claim 2, wherein the first and second cooling steps are performed by counterflow heat exchange.

6. The method according to claim 2, wherein the residual gas flow of the second cooling step is subjected to at least one expansion to obtain further condensate flows and residual gas flows.

7. The method according to claim 1, wherein the internal refrigerant is formed of a part of at least one of the condensate flows and a part of at least one of the residual gas flows, wherein the condensate flow is formed in a step which takes place upstream of the step in which the residual gas flow is formed.

8. The method according to claim 1, wherein a plurality of or all condensate flows are each at least partially combined to form a combined flow, and the combined flow is subjected to a gas separation to form a flash gas and a liquid product flow.

9. The method according to claim 1, wherein the liquid product flow, a predominantly hydrogen-containing gas product flow, formed from a part of at least one of the residual gas flows, and the flash gas are heated to a temperature level corresponding to the temperature level of the feed flow.

10. The method according to claim 1, wherein the flash gas is at least partially recycled into the feed flow.

11. A system for separating a feed flow which contains at least hydrogen and a hydrocarbon with three to four carbon atoms per molecule, having at least two heat exchangers, of which at least one can be operated at an average temperature level and at least one can be operated at a low temperature level, and which are configured to cool the feed flow according to the counterflow principle, and having at least two phase separation devices, which are each configured to split a partially liquefied flow into a condensate flow and a residual gas flow, wherein means configured to combine a part of at least one of the condensate flows with a part of at least one of the residual gas flows under expansion, and to feed the internal refrigerant to at least one of the heat exchangers.

12. The system according to claim 11, also having means which enable the system to carry out a method for separating a feed flow which contains at least hydrogen and a hydrocarbon with three to four carbon atoms per molecule, which feed flow is formed from a raw material flow, wherein the feed flow is partially liquefied in the compressed state using at least two coolers which are operated at different temperature levels, via at least two cooling steps, to obtain at least two condensate flows and at least two residual gas flows, wherein the residual gas flow of a cooling step is respectively fed into the subsequent cooling step, and wherein each condensate flow is depleted in hydrogen and enriched in the hydrocarbon with respect to the feed flow and each residual gas flow is enriched in hydrogen and depleted in hydrocarbon with respect to the feed flow, wherein a part of at least one of the condensate flows is combined with a part of at least one of the residual gas flows under expansion and used as internal refrigerant for at least one of the cooling steps or coolers and is at least partially recycled to the feed flow.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0030] FIG. 1 schematically shows a preferred embodiment of a system according to the invention.

EMBODIMENTS OF THE INVENTION

[0031] FIG. 1 schematically illustrates a system 100, which is configured to carry out a method according to the invention. The system 100 comprises, among other things, a hot heat exchanger 120, a cold heat exchanger 130 and a plurality of gas separators 142, 144, 146, 148.

[0032] Furthermore, in the example shown, the system 100 comprises a provision unit 110 which is designed to generate a feed flow 1 which contains at least hydrogen and a hydrocarbon with three or four carbon atoms per molecule (here and in the following, the latter is also referred to as C3 in relation to three carbon atoms per molecule, for example). In particular, the carbon is propene. The provision unit 110 can, for example, be designed as a reactor which is configured to carry out a propane dehydrogenation reaction. For this purpose, the reactor 110 is equipped with a catalyst and is charged with one or more raw material flows 18, 19 which supply at least propane to the reactor.

[0033] In the provision unit 110, the dehydrogenation reaction typically takes place at low pressure such as, for example, 50 kPa to −500 kPa. The feed flow is compressed upstream of the heat exchanger 120 with a compressor, which can be part of the provision system 110, to a final pressure of 1 MPa to 1.8 MPa. There may also be some fine purification steps of the gas, for example the removal of H2S, water and chlorine.

[0034] Irrespective of the origin thereof, the feed flow 1 comprising at least hydrogen and C3 is fed to the hot heat exchanger 120 and cooled therein against other material flows. For example, the feed flow 1 is fed to the hot heat exchanger 120 at a high temperature level which substantially corresponds to a natural ambient temperature of, for example, between 10° C. and 40° C., in particular between 15° C. and 25° C. and is withdrawn therefrom at an average temperature level in a range from −10° C. to −40° C., for example at an average temperature level of −15° C., −25° C. or −35° C., as a cooled feed flow 2. As a result of the cooling in the heat exchanger 120, part of the components of the feed flow 1 condenses so that the cooled feed flow is a mixture of at least one liquid and a gas. The cooled feed 2 is fed to a gas separator 142 and is separated there into a first residual gas flow 3 and a first condensate flow 7. Due to the different vapor pressures of hydrogen and C3, the first residual gas flow 3 is enriched in hydrogen and depleted in C3 with respect to the feed flow 1, while the first condensate flow 7 behaves exactly vice versa. The first residual gas flow 3 is fed to the cold heat exchanger 130 and is cooled there from the average temperature level to a low temperature level (also referred to as low temperature level within the scope of the disclosure), which is, for example, in a range from −80° C. to −110° C. In this case, a part of the components of the first residual gas flow 3 is again condensed and a supercooled residual gas flow 4 is thus withdrawn from the cold heat exchanger 130, which contains at least one liquid phase and a gas phase.

[0035] The supercooled residual gas flow 4 is separated in a second gas separator 144 into a second residual gas flow 5 and a second condensate flow 8. The second residual gas flow 5 is enriched with hydrogen and depleted in C3 in relation to the first residual gas flow 3, while the second condensate flow 8 is depleted in hydrogen and enriched in C3 with respect to the first residual gas flow 3.

[0036] In the example shown, the second residual gas flow 5 is supplied to an expander or a turbine, which in this case is designed for example as a turbine 150. An expanded residual gas flow 6 is withdrawn from the turbine 150, which flow is in turn partially liquefied due to the energy released in the turbine 150. In a third gas separator 146, the expanded residual gas flow 6 is again separated into a third residual gas flow 11 and a third condensate flow 9. The third condensate flow 9 is again depleted in hydrogen and enriched in C3 with respect to the second residual gas flow 5, the third residual gas flow 11 is accordingly enriched in hydrogen and depleted in C3 with respect to the second residual gas flow 5. According to the invention, however, the use of the expander is optional. Alternatively, the turbine 150, the gas separator 146 and the condensate flow 9 are omitted. Accordingly, the residual gas flows 5 and 11 would be identical. As a further alternative, the expander 150 could simply be designed as a throttle valve.

[0037] The three different condensate flows 7, 8 and 9 are combined, with heating, if appropriate, in the cold heat exchanger 130, at the average temperature level, into a fourth gas separator 148, in which a fourth residual gas flow, which evaporates at the set conditions, which is here referred to as flash gas flow 12, is separated. A liquid product flow 10, which consists essentially of C3, is withdrawn on the side of the liquid phase and conveyed via a pump 149 at least through the hot heat exchanger 120.

[0038] A part of the third residual gas flow 11, which consists primarily of hydrogen, is heated by the cold and hot heat exchanger 130, 120 and withdrawn as a gas product 20. In some embodiments, part of the gas product 20 can be returned to the provision unit, in particular for purging purposes, for example during a catalyst regeneration. A further part 14 of the third residual gas flow 11 is backmixed with a part 13 of the second condensate flow 8 under expansion of the two flows, heated/evaporated as internal refrigerant 15 via the cold heat exchanger 130 and backmixed upstream of the hot heat exchanger 120 with the flash gas 12 and further heated as mixed flow 17 in the hot heat exchanger 120. The mixed flow 17 is preferably recycled into the feed flow 1 in order to increase the overall yield of C3 in the liquid product flow 10.

[0039] As already mentioned, the reactor 110 requires a raw material flow 19 which contains propane. In the example shown, this raw material flow is initially provided as a liquid raw material flow 18. The liquid raw material flow 18 is cooled in the hot heat exchanger 120 and optionally also in the cold heat exchanger 130 and mixed with a third part 16 of the third residual gas flow 11 before it is heated again as a mixed raw material flow 19 via the hot heat exchanger 120 or both heat exchangers 130 and 120 and fed into the reactor 110. In particular, the liquid raw material flow 18 is expanded after the supercooling in the hot heat exchanger 120 and/or the cold heat exchanger 130, for example via one or more throttle valves. As a result of the expansion of the supercooled liquid raw material flow 18 and the addition of residual gas flow (16) at low temperature, thermal energy from the liquid raw material flow 18 is converted into volume work so that the mixed raw material flow 19 is at a temperature level that is substantially lower than that of the corresponding supercooled liquid raw material flow 18, before the heating in the respective heat exchanger 120, 130. The evaporation heat of the liquid raw material flow 18 is thus used as the main cold source for the partial condensation of the feed flow 1 and the first residual gas flow 3. The additional useful cooling of the internal refrigerant 15 is decisive for the cold heat exchanger 130, but evaporation heat can also be withdrawn here by the supercooled liquid raw material flow 18.

[0040] The liquid raw material flow can be provided, for example, at a pressure level in a range from 1.5 MPa to 2.5 MPa. Downstream of the heat exchanger(s), the gaseous raw material flow 19 is, for example, at a pressure level in the range from 200 kPa to 500 kPa.

[0041] Downstream of the reactor and upstream of the compressor of the provision unit 110, the feed flow 1 is present, for example, at a pressure level in the range of about 100 kPa to 200 kPa, downstream of the compressor and upstream of the hot heat exchanger 120 at a pressure level in the range of, for example, 1 MPa to 1.8 MPa.

[0042] In principle, all flows have a correspondingly higher pressure upstream of valves due to pressure losses through the respective valve than the respective flows downstream of the respective valve. In particular, an explicitly described pressure drop or a pressure drop resulting from the different pressure levels of flows transferred into one another is realized by the respective valve.

[0043] Overall, at least the cold heat exchanger 130 operates without an externally cooled refrigerant. The cooling power required here is thus provided via the pressure difference between feed flow 1 (or the residual gas flow 3 remaining from it) on one side and the mixed raw material flow 19 and the internal refrigerant 15 on the other side. To increase the pressure of feed flow 1, one or more compressors can be provided upstream of the hot heat exchanger 120 ( ).

[0044] If necessary, an external refrigerant 21 can be used at the average temperature level. In this way, variable amounts and/or temperatures of the feed flow 1 or of the liquid raw material flow 18 can be compensated.

[0045] As already mentioned, the system 100 can also be used to separate a feed flow which comprises at least hydrogen and a hydrocarbon (C4) comprising four carbon atoms per molecule, in particular 1-butene, 2-butene, 1,3-butadiene and/or butane. The features and advantages of system 100 described above, which apply to the separation of a feed flow 1 comprising C3, correspondingly apply to C4. However, the set temperature levels can differ.

[0046] It should be mentioned that multiple exchangers can also be used in each cooling step, depending on the energy balance and demand, i.e., the respective flows to be cooled and heated can also be distributed to 2, 3, 4 or more exchangers.

[0047] Furthermore, it should be noted that the method is not limited to the two cooling steps explained here, i.e., one, two or more intermediate temperature levels (such as at about −50° C. to −90° C.) and one, two or more additional heat exchangers and corresponding separation device can be additionally used.