Apparatus for separating a mixture of carbon monoxide, hydrogen, and methane by cryogenic distillation

Abstract

Title of the invention: Apparatus for separating a mixture of carbon monoxide, hydrogen and methane by cryogenic distillation. An apparatus for separating a mixture of carbon monoxide, hydrogen and methane (SG) by cryogenic distillation comprises a distillation column (K3) including a condenser and a reboiler (R3), a refrigeration cycle including a cycle compressor, a first heat exchanger (E1), a second heat exchanger (E2), means for sending the gas mixture to be cooled in the first heat exchanger, means for separating the cooled gas mixture in the first heat exchanger and for sending a fluid produced by the separation to the distillation column, a thermally insulated enclosure containing the first and second heat exchangers,means for sending a cycle gas from the distillation column to the second heat exchanger and then to the first heat exchanger to be reheated, means for sending a liquefied cycle gas to the reboiler to be cooled in the second heat exchanger, and means for sending the liquefied and cooled cycle gas from the second heat exchanger to the condenser. Figure from the abstract: Fig 1,

Description

Title of the invention: Apparatus for separating a mixture of carbon monoxide, hydrogen and methane by cryogenic distillation

[0001] The present invention relates to an apparatus for separating a mixture of carbon monoxide, hydrogen and methane by cryogenic distillation.

[0002] It is known to separate a mixture of carbon monoxide, hydrogen, and methane by cryogenic distillation using a methane scrubbing column, a stripping column, and a CO / CH4 distillation column that produces methane for the scrubbing column. The equipment necessary for a cryogenic separation unit for a synthesis gas containing a mixture of hydrogen, carbon monoxide, methane, and optionally nitrogen and / or argon, is contained within a closed enclosure filled with thermal insulation.

[0003] The enclosure can be built on site or transported in one or more packages.

[0004] The heat exchange line generally comprises several exchangers.

[0005] The arrangement of these heat exchangers thus determines the size of the package containing them. It is therefore necessary to find the best arrangement that respects the constraints of the process and results in the smallest possible amount of structure to reduce costs.

[0006] To heat the stripping column and / or the distillation column, it is known to use a cycle fed by the head of the CO / CH4 column.

[0007] The mixture to be separated is cooled in at least one heat exchanger upstream of the washing column.

[0008] One object of the present invention is to use a plurality of heat exchangers arranged in a thermally insulated enclosure, in order to be able to choose more freely the final dimensions of the enclosure.

[0009] Another object of the invention is to arrange the heat exchangers in the enclosure in such a way as to make it more compact.

[0010] According to one aspect of the invention, an apparatus for separating a mixture of carbon monoxide, hydrogen, and methane by cryogenic distillation is provided, comprising at least one distillation column including a top condenser and a tank reboiler, a refrigeration cycle including a cycle compressor, a first heat exchanger, a second heat exchanger, optionally a third heat exchanger, and means for sending the gaseous mixture to be cooled in at least the first heat exchanger and optionally in the third heat exchanger, means for separating the cooled gas mixture in at least the first heat exchanger and for sending a fluid produced by the separation to at least one distillation column, a thermally insulated enclosure which contains the first and second heat exchangers and optionally the third heat exchanger but no washing or distillation column, means for sending a cycle gas from the at least one distillation column to the second heat exchanger to be heated and then to the first heat exchanger to be heated, means for sending a liquefied cycle gas in the tank reboiler to be cooled in the second heat exchanger, and means for sending the liquefied and cooled cycle gas in the second heat exchanger to the head condenser.

[0011] According to other optional features: • In use, the enclosure is positioned with its length vertical. • The first heat exchanger is positioned above the second heat exchanger. • The first heat exchanger is positioned next to the second heat exchanger. • the second heat exchanger has a first end and a second end and is connected so that in operation at least one fluid to be heated is sent to the first end and exits from the second end and / or at least one fluid to be cooled is sent to the second end and exits from the first end, the first end being at a geodesic height greater than that of the second end. • -The first heat exchanger has a first end at a first geodetic height and a second end at a second geodetic height lower than the first geodetic height, and is connected so that in operation at least one fluid to be heated is sent to the end at the second height and exits from the end at the first height and / or at least one fluid to be cooled is sent to the end at the first height and exits from the end at the second height • a pipe is connected to the second end of the second heat exchanger and to the end of the first exchanger at the second geodesic height to transfer a fluid to be heated from the second exchanger to the first exchanger. • a pipe is connected to the second end of the second heat exchanger and to the end of the first exchanger at the second geodesic height to transfer a fluid to be cooled from the first exchanger to the second exchanger. • the second end of the second interchange is substantially at the second geodetic height. • the first end of the second interchange is at a geodetic height between the first and second geodetic heights. • The first and second exchangers are in use in an upper part of the enclosure, and the third heat exchanger and possibly other elements of the device that must operate at a cryogenic temperature are located in a lower part of the enclosure.

[0012] According to another object of the invention, a process for separating a mixture of carbon monoxide, hydrogen and methane by cryogenic distillation is provided in an apparatus according to one of the preceding claims, wherein the gaseous mixture is cooled in at least the first heat exchanger and is separated forming a fluid, the fluid produced by the separation is sent to at least one distillation column, a cycle gas from at least one distillation column is heated in the second heat exchanger, the cycle gas heated in the second exchanger is reheated in the first heat exchanger, liquefied cycle gas is sent to the tank reboiler to be cooled in the second heat exchanger, and the liquefied and cooled cycle gas from the second heat exchanger is sent to the head condenser.

[0013] The invention will be described in more detail with reference to the figures where:

[0014] [Fig-1] shows a separation apparatus according to the invention

[0015] [Fig.2] shows heat exchangers of the separation device arranged in an enclosure according to the invention.

[0016] [Fig.3] shows heat exchangers of the separation device arranged in an enclosure according to the invention.

[0017] In [Fig. 1], a mixture of carbon monoxide, hydrogen, and methane SG is separated by cryogenic distillation. The gaseous mixture SG is first cooled from a temperature above 0°C in a heat exchanger E1, from its hottest end to its coldest end, to an intermediate temperature, and then in a heat exchanger E3, from its hottest end to its coldest end, to a temperature below -170°C. The cooled SG flow is then sent to the tank of a methane scrubbing column K1, which is fed at the top with a flow of liquid methane 14. A heat exchanger E4 provides cooling to intermediate levels of the scrubbing column K1, which operates at a pressure between 15 and 30 bar abs. The heat exchanger E4 is cooled by a portion of the cycle gas.

[0018] A hydrogen-rich overhead gas 5 is drawn from the top of column Kl and heated in exchangers E3, El, and the tank liquid 3 is sent to the top of the Stripping column K2. Stripping column K2 has a tank reboiler R2 and operates at between 7 and 15 bar absolute pressure. A methane-depleted and hydrogen-enriched flow 9 is drawn off at the top of column K2 and heated in heat exchanger E2 and then in heat exchanger E1. The tank liquid 7 from column K2 is heated in heat exchanger E3 and then split in two. Part 9 is expanded and sent to the top of column K3, and part 11 is expanded and sent to an intermediate level of a distillation column K3. Column K3, having a tank reboiler R3 and an overhead condenser, operates at between 1.5 and 4 bar absolute pressure.

[0019] Methane-rich tank fluid 14 from column K3 is pressurized by a pump P and sent to the scrubbing column Kl as scrubbing fluid after cooling in the heat exchanger E3. The remaining fluid 13 is vaporized in the heat exchanger EL

[0020] A carbon monoxide-rich overhead gas 15 from column K3 serves as the cycle gas and is first heated in the heat exchanger E2 and then in the heat exchanger El as gas 23. The gas 23 is compressed in a cycle compressor (not shown) to a higher pressure (e.g. 28 bar) and then cooled in the heat exchanger El as gas 25. A portion 27 of the gas 25 is expanded in a turbine T to provide cooling and then rejoins the gas 23 at an intermediate temperature in the heat exchanger EL. The remaining 27 of the gas leaves the heat exchanger El at -140°C and is used to heat at least one of the reboilers R2, R3 thus being cooled and condensed. In the figure, the two liquid parts 29, 31 of the flow 27 enter the exchanger E2 downstream of the reboilers R2, R3 where they are cooled down to -180°C.Then the flow 29 and the flow 31 are expanded, mixed, sent partly as liquid flow 33 to the top condenser of column K3 and partly as liquid flow 35 to the exchanger E3 to be vaporized and join the flow 25 coming from the cycle compressor.

[0021] The gas 17 from the condenser of column K3 joins the cycle gas 15 forming the flow 23.

[0022] Gas from cycle 33 condenses in the top condenser of column K3 and the resulting liquid is sent to the top of column K3. Another part 21 of the condenser liquid is vaporized in the exchanger E3, mixes with the gas coming from the exchanger E4 forming gas 19 and rejoins the rest of the cycle 15, 17, 23.

[0023] In summary, the heat exchanger E2 cools the liquid flows 29, 31 from -147°C and -151°C down to -180°C by exchanging heat with the head gas 9, which is a mixture of carbon monoxide, methane, and hydrogen intended to serve as fuel, and with the cycle gas 23, which is to be heated for compression into the cycle gas. Neither fluid undergoes a phase change.

[0024] According to the invention, the heat exchangers E1, E3 and optionally E2 are located in the same thermally insulated enclosure B, as illustrated in [Fig. 2]. However, no column is located in this enclosure.

[0025] A phase separator S is fixed to the outside of the enclosure B. The exchanger E3 and a thermosiphon TS are located in a lower part of the enclosure which is arranged with its length vertical.

[0026] In the upper part are the heat exchanger E1, composed of two identical bodies arranged side by side, and the heat exchanger E2, which is located at a geodetic level lower than the heat exchanger E1. At least one pipe C connects the heat exchanger E2 to each body of the heat exchanger E1 to send a gas heated in the heat exchanger E2 to be reheated in the heat exchanger E1. Similarly, there is at least one pipe (not shown) to send a fluid cooled in the bodies of the heat exchanger E1 to the heat exchanger E2 to be cooled further. Obviously, the heat exchanger E1 may comprise a single body or more than two bodies.

[0027] It will be noted that the height of enclosure B is greater than the sum of the heights of the exchangers El, E2 and E3, which may lead to problems in transporting the enclosure.

[0028] In this variant, the heat exchangers El and E2 are conventionally oriented with their cold end EF downwards and their hot end EC upwards. Therefore, the pipe C must be longer than the height of the heat exchanger E2 to bring the gas to be heated towards the heat exchanger El. Thus, the circulation of at least one heat source is downward and the reverse for at least one cold fluid.

[0029] This variant is well suited for the case where at least one fluid has to change phase in the exchanger E2, either by condensing at least partially for a gas or by vaporizing at least partially for a liquid.

[0030] No part of the synthesis gas SG is cooled in the exchanger E2.

[0031] According to a variant of the invention, it is planned to reverse the direction of fluid flow in one of the exchangers in order to reduce the size of the package and thus reduce the amount of structure.

[0032] The reversible heat exchanger(s) shall comprise heat exchangers and refrigerants in the form of a gas or liquid that does not change state (gas or liquid) through the exchanger. Typically, the heat exchangers are liquids to be subcooled and the refrigerants are gases to be heated.

[0033] This allows the length of the pipes between the different exchangers to be reduced and consequently the price of the piping and the size of the package to be reduced.

[0034] In this case, El and E3 are arranged with the heat exchanger El, possibly composed of several bodies, above the heat exchanger E3, if present. Optionally, the heat exchanger E2 may be located below the heat exchanger E3. Thus, heat exchangers El and E2, and possibly E2, are arranged in the thermally insulated enclosure with their lengths aligned along a vertical axis of the enclosure. Therefore, the cold end of heat exchanger El is located opposite the cold end of heat exchanger E2, with columns K1 to K3 located in at least one other thermally insulated enclosure.

[0035] Usually, as illustrated in [Fig.2], all heat exchangers are arranged with their hot end upwards and their cold end downwards, so that the fluids flow in a generally vertical direction.

[0036] According to a variant of the invention, illustrated in [Fig. 3], the arrangement of these exchangers is modified to reduce the size of the package containing them. It is then necessary to find the best arrangement that respects the constraints of the process and results in the smallest possible amount of structure to reduce costs.

[0037] According to this variant, the exchanger E2 is arranged with its cold end EF upwards and its hot end EC downwards, so that the fluids flow in an overall vertical direction, but at least one liquid that is cooling flows upwards and the gases that are heating up flow downwards.

[0038] In this case, it is possible to place the heat exchanger El and the heat exchanger E2 side by side so that a pipe bringing a heated gas from the hot end of the heat exchanger E2 to the cold end of the heat exchanger El forms a U and is much shorter than it would be if the hot end were at the top for the heat exchanger E2. Since the heat exchanger E2 is no longer below the heat exchanger El, the enclosure B of the heat exchangers becomes much shorter, facilitating transport.

[0039] Moreover, as enclosure B includes other elements below the exchanger El, R2 which occupy a certain width, the arrangement of the exchanger E2 next to the exchanger El does not substantially change the width of the enclosure, or even does not change it.

[0040] These other elements may be the exchanger E3 and / or a phase separator S and / or a thermosiphon TS.

[0041] Here it is essentially the heights of the exchangers El and E3 which determine the height of the enclosure B, which will be shorter than for the variant of [Fig.2].

[0042] The exchanger E3 and the thermosiphon TS are not necessarily present in enclosure B.

[0043] In this case, it is preferable that no fluid undergoes a phase change in the heat exchanger E2, either by condensing at least partially for a gas that is cooling or by vaporizing at least partially for a liquid that is heating up. Preferably, the heat exchanger is designed so that the fluids that exchange heat indirectly within it are all gases. Optionally, at least one liquid may also be cooled within it.

[0044] No part of the synthesis gas SG is cooled in the exchanger E2.

[0045] The enclosure of [Fig.3] typically occupies at most 90% of the volume of that of the [Fig.2] and its height is reduced by 20%.

Claims

Demands

1. Apparatus for separating a mixture of carbon monoxide, hydrogen and methane (SG) by cryogenic distillation comprising at least one distillation column (K3) including a top condenser and a tank reboiler (R3), a refrigeration cycle including a cycle compressor, a first heat exchanger (E1), a second heat exchanger (E2), optionally a third heat exchanger (E3), means for sending the gas mixture to be cooled in at least the first heat exchanger and optionally in the third heat exchanger, means for separating the cooled gas mixture in at least the first heat exchanger and for sending a fluid produced by the separation to at least one distillation column, a thermally insulated enclosure (B) which contains the first and second heat exchangers and optionally the third heat exchanger but no washing or distillation column,means for sending a cycle gas from at least one distillation column to the second heat exchanger to be heated and then to the first heat exchanger to be heated, means for sending a liquefied cycle gas from the reboiler to be cooled in the second heat exchanger, and means for sending the liquefied and cooled cycle gas from the second heat exchanger to the overhead condenser.

2. Apparatus according to claim 1 in which, in use, the enclosure (B) is arranged with its length vertical.

3. Apparatus according to claim 2 in which the first heat exchanger (E1) is arranged above the second heat exchanger (E2).

4. Apparatus according to claim 2 in which the first heat exchanger (E1) is arranged next to the second heat exchanger (E2).

5. Apparatus according to claim 4 in which the second heat exchanger (E2) has a first end and a second end and is connected such that in operation at least one fluid to be heated is sent to the first end and exits from the second end and / or at least one fluid to be cooled is sent to the second end and exits at the first end, the first end being at a geodesic height greater than that of the second end.

6. Apparatus according to any one of the preceding claims, wherein the first heat exchanger (E1) has a first end at a first geodesic height and a second end at a second geodesic height lower than the first geodesic height, and is connected such that in operation at least one fluid to be heated is sent to the end at the second height and exits from the end at the first height and / or at least one fluid to be cooled is sent to the end at the first height and exits from the end at the second height

7. Apparatus according to claims 5 and 6 in which a conduit is connected to the second end of the second heat exchanger (E2) and to the end of the first exchanger (El) at the second geodesic height to transfer a fluid to be heated from the second exchanger to the first exchanger.

8. Apparatus according to claims 5 and 6 in which a conduit is connected to the second end of the second heat exchanger (E2) and to the end of the first heat exchanger (El) at the second geodesic height to transfer a fluid to be cooled from the first heat exchanger to the second heat exchanger.

9. Apparatus according to any one of claims 5, 7 or 8 wherein the second end of the second exchanger (E2) is substantially at the second geodesic height.

10. Apparatus according to any one of the preceding claims wherein the first and second exchangers (E1, E2) are in use in an upper part of the enclosure (B) and the third heat exchanger (E3) and possibly other elements (TS) of the apparatus to operate at a cryogenic temperature are in a lower part of the enclosure.

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