PROCESS AND APPARATUS FOR PRODUCTION OF CARBON MONOXIDE BY PARTIAL CONDENSATION

Abstract

A process for separating a mixture of hydrogen, methane and carbon monoxide by cryogenic distillation. The mixture is cooled in a first heat exchanger and is partially condensed in at least one second heat exchanger which is a bottom reboiler of a first or second column of the column system and at least one portion of the liquid produced by the partial condensation is sent to an intermediate level of the first column.

Claims

1. A process for separating a mixture of hydrogen, methane and carbon monoxide by cryogenic distillation in a column system comprising a first column and a second column, comprising: i. cooling the mixture in a first heat exchanger and partially condensing at least one portion thereof in at least one second heat exchanger which is a bottom reboiler of the second column of the column system and at least one portion of the liquid produced by the partial condensation, or a liquid derived therefrom, by at least one step of partial condensation is sent to an intermediate level of the first column, only the at least one portion of the mixture and bottom liquid from the second column exchanging heat in the second heat exchanger, the vaporized bottom liquid being sent back to the column from which it originates, ii. withdrawing a hydrogen-enriched overhead gas from the first column and reheating the hydrogen-enriched overhead gas in the first heat exchanger, iii. withdrawing a liquid enriched in carbon monoxide and in methane from the bottom of the first column and sending it to at least one intermediate level of the second column, iv. withdrawing a methane-rich liquid from the bottom of the second column and withdrawing a fluid rich in carbon monoxide from the top of the second column, and v. producing refrigeration to keep the process cold by means of a refrigeration cycle.

2. The process according to claim 1, in which a portion of the cooled mixture is sent to the second heat exchanger which is a reboiler of the first column.

3. The process according to claim 1, in which at least one portion of the cooled mixture is sent to be cooled to the second exchanger which is a reboiler of the second column and then the at least one portion of the cooled mixture is sent to a third exchanger which is a reboiler of the first column.

4. The process according to claim 1, in which at least one portion of the cooled mixture is sent to be partially condensed in the second exchanger which is a reboiler of the second column to produce a gas and a liquid, then the gas is sent to a third exchanger which is a reboiler of the first column and at least one portion of the liquid produced by at least partial condensation of the gas in the third exchanger is sent to the intermediate point of the first column.

5. The process according to claim 1, in which a condensed portion produced following at least one step of partial condensation of the mixture, is sent to the top of the first column of the column system.

6. The process according to claim 1, in which the first column has a bottom reboiler and has no overhead condenser.

7. The process according to claim 1, in which the mixture is cooled in the first heat exchanger to an intermediate temperature thereof and then leaves the first heat exchanger before being sent to the reboiler.

8. The process according to claim 1, in which the fluid rich in carbon monoxide from the top of the second column and/or the hydrogen-enriched overhead gas from the first column is (are) cooled in the first heat exchanger from the cold end of the first heat exchanger.

9. An apparatus for separating a mixture of hydrogen, methane and carbon monoxide by cryogenic distillation, said apparatus comprising a column system comprising a first column and a second column, a first heat exchanger, a second heat exchanger, a means for sending the mixture to be cooled to the first heat exchanger, a means for sending the cooled mixture to be partially condensed to at least the second heat exchanger which is a bottom reboiler of the second column, a means for sending to an intermediate level of the first column at least one portion of the liquid produced by the partial condensation or a liquid derived from this liquid by at least one step of partial condensation, only the mixture and bottom liquid from the second column exchanging heat in the second heat exchanger, a means for sending the vaporized bottom liquid back to the second column, a means for withdrawing a hydrogen-enriched overhead gas from the first column, a means for sending the overhead gas to be reheated to the first heat exchanger, a means for withdrawing a liquid enriched in carbon monoxide and in methane from the bottom of the first column, a means for sending the liquid enriched in carbon monoxide and in methane to at least one intermediate level of the second column, a means for withdrawing a methane-rich liquid from the bottom of the second column, a means for withdrawing a fluid rich in carbon monoxide from the top of the second column and a refrigeration cycle to produce refrigeration to keep the process cold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

[0049] FIG. 1 is a schematic representation of a process for separating a gas mixture, in accordance with one embodiment of the present invention . . . .

[0050] FIG. 2 is another schematic representation of a process for separating a gas mixture, in accordance with one embodiment of the present invention . . . .

[0051] FIG. 3 is another schematic representation of a process for separating a gas mixture, in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] FIG. 1 describes a process for separating a gas mixture, such as a synthesis gas, according to the invention. The two reboilers in parallel with a shared vessel at the outlet of the two reboilers, the resulting gas is cooled in the exchange line and the liquid fraction is sent to the intermediate part of the stripping column, A gas mixture 1 containing at least carbon monoxide, hydrogen and methane is cooled in the first section 3 of a heat exchanger that has two sections 3, 9.

[0053] The cooled mixture is split into two portions 5, 7. The portion 5 is partially condensed by cooling it in a bottom reboiler 13 of a column K1, which is a stripping column. The portion 7 is partially condensed by cooling it in a bottom reboiler of a column K2, which is a CO/CH4 distillation column. The partially condensed flows are mixed in a phase separator 15.

[0054] The gas produced is cooled in the section 9 of the exchanger where it is partially condensed and is sent to a phase separator S2. The gas 63 from the phase separator S2 is reheated in the sections 9, 3. The liquid from the phase separator S2 is sent to the top of the column K1.

[0055] The liquid 17 from the phase separator 15 is expanded then mixed with another flow to form a two-phase flow 19. The flow 19 is separated in a phase separator to form a gas 21 and a liquid 23, the two being sent to an intermediate level of the column K1.

[0056] A portion 45 of the liquid from the phase separator 15 is cooled in the section 9 of the heat exchanger where it is partially condensed before being sent to a phase separator S1.

[0057] The bottom liquid from the phase separator S2 is split into two. One portion 61 is sent as liquid to the top of the column K1. The remainder 43 is expanded and feeds the phase separator S1. The liquid 41 formed in the separator S1 is vaporized in the section 9 to form a gas mixture with the gas from the separator S1 and the flow formed 45 is mixed with the flow 17 from the separator 15.

[0058] The overhead gas 21 from the column K1 is reheated in the two sections 9, 3 to form a hydrogen-rich gas 63.

[0059] Bottom liquid from the column K1 is vaporized in the reboiler 13 and sent back to the column K1.

[0060] The column K1 operates at a pressure between 13 and 16 bar abs and the overhead gas 21 has the following composition: [0061] CO: 20-35 mol % [0062] H2: 65-80% [0063] CH4: 0.1% [0064] N2: 0.5% [0065] Ar: 0.1%

[0066] Bottom liquid from the column K1 is split into two to form two expanded liquid flows 27, 31. The expanded flow 31 is sent to an intermediate level of the second column K2 and the expanded flow 27 is partially reheated in the section 9 in order to be sent to an intermediate level of the second column K2 lower than that of the inlet of the flow 31.

[0067] A bottom liquid 21 is sent to the reboiler 11, is vaporized and is sent back to the column K2, which operates at a pressure above 6 bar abs.

[0068] Another bottom liquid 23 from the column K2 is reheated in the section 3 to form a methane-rich product.

[0069] An overhead gas 37 from the column K2 is reheated in the sections 9, 3 to form a carbon monoxide-rich product.

[0070] The overhead condenser C of the CO/CH4 column K2 is fed with liquid by a nitrogen cycle, comprising two compressors V1, V2 and with two levels of vaporization at different pressures in the section 9. This cycle is completely independent of remainder of the process and may be replaced by a different refrigeration cycle.

[0071] FIG. 2 describes a process for separating a gas mixture according to the invention, similar to that of FIG. 1. The two reboilers 11, 13 are in series. Thus, the mixture 1 cooled in the section 3 solely arrives as the flow 5 in the first reboiler 11, vaporizes the bottom liquid 21 and is partially condensed thereby. The partially condensed mixture is sent to the separator vessel 15 which is at the outlet of the first reboiler 11. The liquid 17 from the vessel 15 is sent to a vessel 65, the liquid 67 of which is sent to an intermediate part of the column K1. The gas 77 from the vessel 15 is partially condensed in the second reboiler 13. A second vessel 65 is at the outlet of the second reboiler 13. The vapor fraction of the second vessel 65 is cooled in the exchange line 9 whilst the liquid fractions 17, 67 of the two vessels 15, 65, at the reboiler outlet respectively are sent to an intermediate part of the column K1.

[0072] The solution should be selected from those of the two figures as a function of the pressure of the incoming synthesis gas 1 and the content of CO in the incoming synthesis gas 1.

[0073] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.