Process for separating a component mixture and separation apparatus

Abstract

A process for separating a component mixture comprising essentially hydrocarbons having two or two or more carbon atoms, methane and hydrogen using a distillation apparatus (10) is proposed. Fluid (a, c, e, g, i) from the component mixture is cooled stepwise to a first pressure level, with separation of first condensates (b, d, f, h, j) out of the fluid (a, c, e, g, i) in each case. Fluid (k) from the component mixture that remains in gaseous form thereafter is expanded to a second pressure level in an expander, giving a second condensate (l). Fluid from the first condensates (b, d, f, h, j) is expanded from the first pressure level to the second pressure level and fed together with the fluid from the second condensates into the distillation apparatus (10) which is being operated at the second pressure level. The present invention likewise provides a corresponding separation apparatus.

Claims

1. A process for separating a component mixture (C2minus) comprising essentially hydrocarbons having two or two or more carbon atoms, methane and hydrogen using a distillation apparatus (10), in which a first fluid from the component mixture (C2minus) at a first pressure level is cooled down stepwise from a first temperature level via two or more intermediate temperature levels to a second temperature level, with separation of condensates (b, d, f, h, j) out of the first fluid at each of the intermediate temperature levels, a second fluid from the component mixture (C2minus) that remains in gaseous form at the second temperature level is cooled down by expanding from the first pressure level to a second pressure level below the first pressure level, forming a biphasic stream (l) comprising a liquid and a gaseous part, fluids from the condensates (b, d, f, h, j) and fluid from the biphasic stream (l) is fed into the distillation apparatus (10) which is being operated at the second pressure level, where a liquid stream of matter (o) comprising essentially hydrocarbons having two or two or more carbon atoms and a gaseous stream of matter (n) comprising essentially methane and hydrogen are obtained in the distillation apparatus (10) and are drawn off from the distillation apparatus (10), characterized in that the second temperature level is −125 to −150° C., the distillation apparatus (10) has a first distillation unit (11), a second distillation unit (12), and a condenser (13), wherein the first distillation unit (11) is operated with a third temperature level at its top which is below the second temperature level, the second distillation unit (12) is operated at a fourth temperature level at its top which is below the second temperature level, and the condenser is operated a temperature level above the second temperature level, a liquid part of the biphasic stream is at least partially fed into the first distillation unit (11), and a gaseous stream of matter (m) is drawn off from the second distillation unit (12) of the distillation apparatus (10), cooled down in the condenser (13) and used to provide a liquid return stream to the second distillation unit (12).

2. The process according to claim 1, wherein the separated condensates (b, d, f, h, j) are fed at least partly into the first and the second distillation units (11, 12) of the distillation apparatus (10).

3. The process according to claim 1, wherein the liquid stream of matter (o) is expanded from the second pressure level to a pressure level below the second pressure level.

4. The process according to claim 1, wherein the first fluid from the component mixture (C2minus) is cooled down using an ethane and/or ethylene coolant at different pressure levels from the first temperature level via the intermediate temperature levels to the second temperature level.

5. The process according to claim 1, wherein the intermediate temperature levels include an intermediate temperature level at −48 to −53° C. and/or an intermediate temperature level at −74 to −79° C. and/or an intermediate temperature level at −95 to −100° C. and/or an intermediate temperature level at −120 to −125° C. and/or an intermediate temperature level at −140 to −145° C.

6. The process according to claim 1, wherein the gaseous stream of matter (m) is cooled down in the condenser (13) by an ethylene coolant.

7. The process according to claim 1, wherein the condenser (13) is disposed between the first distillation unit (11) and the second distillation unit (12).

8. The process according to claim 1, in which fluid from the gaseous stream of matter (n) which is drawn off from the distillation apparatus (10) is used at least to cool down the first fluid from the component mixture (C2minus) from the first temperature level via the intermediate temperature levels to the second temperature level.

9. The process according to claim 1, wherein the fluid from the gaseous stream of matter (n) which is drawn off from the distillation apparatus (10) is expanded in an expander (21) to a third pressure level below the second pressure level.

10. The process according to claim 9, wherein the fluid from the gaseous stream of matter (n) which is drawn off from the distillation apparatus (10), after use for cooling down the first fluid from the component mixture (C2minus), is compressed, using compressors coupled to expanders (20, 21) for compression.

11. The process according to claim 1, which is used for separation of the component mixture (C2minus) which is obtained from a cracked gas obtained by means of a steam cracking process.

12. A process for separating a component mixture (C2minus) comprising essentially hydrocarbons having two or two or more carbon atoms, methane and hydrogen using a distillation apparatus (10), in which a first fluid from the component mixture (C2minus) at a first pressure level is cooled down stepwise from a first temperature level via two or more intermediate temperature levels to a second temperature level, with separation of condensates (b, d, f, h, j) out of the first fluid at each of the intermediate temperature levels, a second fluid from the component mixture (C2minus) that remains in gaseous form at the second temperature level is cooled down by expanding from the first pressure level to a second pressure level below the first pressure level, forming a biphasic stream (l) comprising a liquid and a gaseous part, fluids from the condensates (b, d, f, h, j) and fluid from the biphasic stream (l) is fed into the distillation apparatus (10) which is being operated at the second pressure level, where a liquid stream of matter (o) comprising essentially hydrocarbons having two or two or more carbon atoms and a gaseous stream of matter (n) comprising essentially methane and hydrogen are obtained in the distillation apparatus (10) and are drawn off from the distillation apparatus (10), characterized in that the second temperature level is −125 to −150° C., the distillation apparatus (10) has a first distillation unit (11), and a second distillation unit (12) wherein the first distillation unit (11) is operated with a third temperature level at its top which is below the second temperature level and the second distillation unit (12) is operated at a fourth temperature level at its top which is below the second temperature level, a liquid part of the biphasic stream is at least partially fed into the first distillation unit (11), and the liquid stream of matter (o) is expanded from the second pressure level to a pressure level below the second pressure level.

13. A separation apparatus (100) set up for separation of a component mixture comprising essentially hydrocarbons having two or two or more carbon atoms, methane and hydrogen, wherein the separation apparatus (100) comprises: one or more indirect heat exchangers (1, 2, 3, 4, 5) which are adapted to cool down a first fluid from the component mixture (C2minus) at a first pressure level stepwise from a first temperature level via two or more intermediate temperature levels to a second temperature level, and one or more liquid separators (31, 32, 33, 34, 35) which are adapted to separate condensates (b, d, f, h, j) out of the first fluid at each of the intermediate temperature levels, one or more expanders (20) which is or are adapted to cool down a second fluid from the component mixture (C2minus) that remains in gaseous form at the second temperature level by expanding from the first pressure level to a second pressure level below the first pressure level, thereby forming a biphasic stream (l) comprising a liquid part and a gaseous part, a distillation apparatus (10) and feed lines which are adapted to feed fluid from the condensates (b, d, f, h, j) and fluid from the biphasic stream (l) into the distillation apparatus (10), wherein the distillation apparatus (10) is arranged to operate at the second pressure level and to form a liquid stream of matter (o) comprising essentially hydrocarbons having two carbon atoms and a gaseous stream of matter (n) comprising essentially methane and hydrogen, wherein a withdrawal line is provided which is adapted to draw the gaseous stream of matter (n) off from the distillation apparatus (10), characterized in that the distillation apparatus (10) has a first distillation unit (11), a second distillation unit (12), and a condenser (13), wherein the first distillation unit (11) is arranged to be operated at its top with a third temperature level below the second temperature level, the second distillation unit (12) is arranged to be operated at its top at a fourth temperature level above the second temperature level, and the condenser (13) is operated a temperature level above the second temperature level, a reflux line is provided which is adapted to feed a liquid part of the biphasic stream at least partially as a reflux to the first distillation unit (11), and a gaseous stream of matter (m) is drawn off from the second distillation unit (12) of the distillation apparatus (10), cooled down in the condenser (13) and used to provide a liquid return stream to the second distillation unit (12).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a separation apparatus for separation of a component mixture according to the prior art.

(2) FIG. 2 shows a separation apparatus for separation of a component mixture in one embodiment of the invention.

(3) FIG. 3 shows a separation apparatus for separation of a component mixture in a second embodiment of the invention.

(4) FIG. 4 shows a separation apparatus for separation of a component mixture in a third embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) In the figures, corresponding elements bear identical reference signs and, for the sake of clarity, are not elucidated repeatedly. In the figures which follow, the invention is described with reference to a separating treatment of a component mixture including essentially hydrocarbons having two carbon atoms and methane and hydrogen. However, it is suitable in the same way for separating treatment of a component mixture including essentially hydrocarbons having two or more carbon atoms and methane and hydrogen.

(6) FIG. 1 shows a separation apparatus for separation of a component mixture in a non-inventive embodiment. The separation apparatus is collectively labelled 200 and is set up to separate a component mixture including essentially hydrocarbons having two carbon atoms, methane and hydrogen (i.e. a C2minus fraction). The C2minus fraction is fed to the separation apparatus 200 in the form of a stream of matter a.

(7) The separation apparatus 200 comprises a first heat exchanger 1, a second heat exchanger 2 and a third heat exchanger 3. Stream of matter a is first guided through the first heat exchanger 1 and cooled therein. It is subsequently fed into a first liquid separator 31. The cooling in the first heat exchanger 1 is effected by separating out a liquid condensate in the first liquid separator 31. This is drawn off at the base of the first liquid separator 31 as stream of matter b. The further use of stream of matter b is elucidated below.

(8) A fraction of stream of matter a that has remained in gaseous form in the first liquid separator 31 is guided as stream of matter c through the second heat exchanger 2 and then fed into a second liquid separator 32. In the latter as well, a liquid condensate separates out at the base and is drawn off in the form of stream of matter d. A fraction of stream of matter c that has still remained in gaseous form is guided as stream of matter e through a third heat exchanger 3 and then fed into a third liquid separator 33. In the latter as well, a liquid condensate separates out at the base and is drawn off in the form of stream of matter f. A fraction of stream of matter e that has still remained in gaseous form is guided into an expander 20 as stream of matter k, expanded and at least partly liquefied. A biphasic stream formed in this way is provided in the form of a stream of matter l.

(9) The separation apparatus 200 further comprises a rectification column 50 which is operated with a reboiler 14 which is not elucidated any further, the heat exchanger of which is operated, for example, with a propylene stream that comes from other plant components. Also assigned to the rectification column 50 are two plate exchangers 15, 16, the operation of which is elucidated below. The rectification column 50 has two sections 51, 52.

(10) Owing to the successive cooling of streams of matter a, c, e and k, the condensates obtained correspondingly, which are obtained in the form of streams of matter b, d, f, l, have different contents of hydrocarbons having two carbon atoms, methane and hydrogen. More particularly, stream of matter l has a higher methane and hydrogen content than stream of matter f, stream of matter f has a higher methane and hydrogen content than stream of matter d, and stream of matter d has a higher methane and hydrogen content than stream of matter b.

(11) Streams of matter b, d, f and l are therefore fed into the rectification column 50 at different heights, which has application devices suitable for the purpose between the trays, which are shown here in highly schematic form.

(12) A gaseous stream of matter n is drawn off from the top of rectification column 50 and expanded in an expander 21 and significantly cooled or at least partly liquefied as a result. Stream of matter n comprises predominantly methane and hydrogen (it is thus a “C1minus” fraction). The liquefied stream of matter n is guided through the two plate exchangers 15, 16 and used for cooling therein. Subsequently, stream of matter n is guided through heat exchanger 2 and used for cooling of gaseous stream of matter c, and guided through heat exchanger 1 and used for cooling of gaseous stream of matter a. Subsequently, stream of matter n, especially after use in a preliminary cooling unit 99, is guided through two boosters 22, 23 coupled to the expanders 20 and 21, and discharged from the plant as tail gas.

(13) In the bottom of rectification column 50, a liquid condensate separates out, essentially consisting of hydrocarbons having two carbon atoms (this is a “C2” fraction). The condensate is drawn off in the form of stream of matter o, heated in the first heat exchanger 1 and then, for example, sent to a further separation apparatus such as a C2 splitter.

(14) A gaseous stream of matter m1 is withdrawn in gaseous form from rectification column 50 at a first position, cooled down in the plate exchanger 16 and hence at least partly liquefied and sent to rectification column 50 as return stream at a second position, i.e. guided back into rectification column 50 by gravity. A further gaseous stream of matter m2 is withdrawn in gaseous form from rectification column 50 at a third position, cooled down in the plate exchanger 15 and hence at least partly liquefied and sent to rectification column 50 as return stream at a fourth position, i.e. guided back into rectification column 50 by gravity, where the first position is below the second position, the second position is below the third position and the third position is below the fourth position. As mentioned above, in plate exchangers 15, 16, the liquefied stream of matter n is used for cooling of streams of matter m1 and m2, and has to be transported in a complex manner to the plate exchangers that are at a great height. The installation of these plate exchangers 15, 16 at the top of rectification column 50 is inconvenient and costly.

(15) FIG. 2 shows a separation apparatus 100 in one embodiment of the invention. The separation apparatus 100 comprises the essential components of separation apparatus 200 shown in FIG. 1. These will not be elucidated again.

(16) In separation apparatus 100 as well, a rectification column with two sections is provided. This is referred to hereinafter as distillation apparatus 10. The two sections thereof are referred to hereinafter as first distillation unit 11 and second distillation unit 12. The separation apparatus is assigned a condenser 13. In separation apparatus 100, the first distillation unit 11 is disposed above the second distillation unit 12. The condenser 13 is additionally disposed above the first distillation unit 11. In a departure from the separation apparatus 200 shown in FIG. 1, however, the plate exchangers 15, 16 have been dispensed with here. A stream of matter m corresponding to stream of matter m1 in separation apparatus 100 is cooled by means of ethylene coolant in the condenser 13 and at least partly liquefied. The gaseous stream of matter m is withdrawn from the upper portion of the second distillation unit 12 and fed into the lower portion of the first distillation unit 11. Since the first distillation unit 11 and the second distillation unit 12 are separated from one another by means of a liquid backup tray, the recycled stream of matter m serves for provision of a return stream to the second distillation unit 12. There is no stream of matter here corresponding to stream of matter m2 in separation apparatus 100. A return stream to the first distillation unit 11 is instead provided as elucidated hereinafter.

(17) The successive cooling of the C2minus stream a is extended by a heat exchanger 4 for cooling of a gaseous stream of matter g, and by a heat exchanger 5 for cooling of a gaseous stream of matter i. In addition to the condensates or streams of matter b, d, f and l, condensates or streams of matter h and j are separated out in further liquid separators 34, 35. Fractions that remain in gaseous form in each case are guided through the heat exchangers 4 and 5 in the form of streams of matter g and i and cooled down to the intermediate temperature levels at −120 to −125° C. (stream g) or −140 to −145° C. (stream i). Since stream of matter j has a higher methane and hydrogen content than stream of matter h, and stream of matter h has a higher methane and hydrogen content than stream of matter f, these are fed to distillation apparatus 10 at different heights.

(18) Stream of matter l is formed in separation apparatus 200 in a comparable manner to stream of matter l in separation apparatus 100, but is at a much lower temperature owing to the further cooling in heat exchangers 4 and 5. Owing to the further cooling, it is especially possible to use streams of matter j and l as return stream to the first distillation unit 11. Liquefaction of a stream of matter m2 as in separation apparatus 100 is therefore not required, and so, as mentioned, it is possible to dispense with the heat exchangers 15, 16.

(19) Since, in the present invention, the gaseous stream of matter n which is withdrawn at the top of the distillation apparatus does not have to be used for cooling in the plate exchangers 15, 16, it can be used for cooling in the heat exchangers 1, 2, 3, 4, 5. In this way, the low temperatures mentioned can be achieved.

(20) FIG. 3 shows a separation apparatus 300 in a further embodiment of the invention. In this case, the separation apparatus according to the prior art has been extended only by a heat exchanger 4 and a liquid separator 34.

(21) In FIGS. 1 to 3, heat exchangers 1 to 3 are each cooled using further streams of matter u, v, w and x. Streams of matter u, v and w are ethylene coolant at different pressure levels; stream of matter x is, for example, a recycled ethane stream. An ethylene coolant stream w through the condenser 13 is correspondingly specified.

(22) FIG. 4 shows the distillation unit 40 in a further embodiment of the invention. In this case, the condenser 13 is disposed between the first distillation unit 11 and the second distillation unit 12, with the first distillation unit 11 disposed above the condenser, and the condenser 13 above the second distillation unit 12. Mass transfer is effected in the form of a stream of matter p and a stream of matter q.

(23) In addition, it would be possible to directly integrate the condenser 13 into the distillation unit 40, for example in the form of a shell-and-tube apparatus or a block between the first distillation unit 11 and the second distillation unit 12. Correspondingly, internals such as the liquid seal would be dispensed with.

(24) The table below gives temperatures of selected streams of matter. The figures in brackets are each preferred temperature ranges; the value after the bracket is a preferred example.

(25) TABLE-US-00001 Separation apparatus 200 100 300 Stream of matter a (−25 to −35° C.) (−25 to −35° C.) (−25 to −35° C.) upstream of heat −32° C. −32° C. −32° C. exchanger 1 Stream of matter a (−45 to −55° C.) (−45 to −55° C.) (−45 to −55° C.) downstream of −51° C. −51° C. −51° C. heat exchanger 1 Stream of matter c (−70 to −80° C.) (−74 to −80° C.) (−74 to −80° C.) downstream of −76° C. −76° C. −76° C. heat exchanger 2 Stream of matter e (−95 to −100° C.) (−95 to −100° C.) (−95 to −100° downstream of −97° C. −97° C. C.) −97° C. heat exchanger 3 Stream of matter g (−115 to −125° C.) (−135 to −145° downstream of −122° C. C.) −143° C. heat exchanger 4 Stream of matter i (−135 to −145° C.) downstream of −143° C. heat exchanger 5 Stream of matter l (−112 to −118° C.) (−155 to −165° C.) (−155 to −165° downstream of −115° C. −162° C. C.) −162° C. expander 20 Stream of matter n (−150 to −155° C.) (−150 to −155° C.) (−150 to −155° after withdrawal −152° C. −153° C. C.) −153° C. Stream of matter o (−35 to −45° C.) (−35 to −45° C.) (−35 to −45° C.) after withdrawal −36° C. −36° C. −36° C.