METHOD FOR SEPARATING A SYNTHESIS GAS

Abstract

A method for separating a synthesis gas containing carbon monoxide and hydrogen including compressing a flow of synthesis gas received from a source of synthesis gas in a compressor, purifying the compressed synthesis gas in a purification unit to purify it of water and/or carbon dioxide, cooling the compressed and purified flow of synthesis gas, separating the cooled flow of synthesis gas by washing and/or distillation at a cryogenic temperature and optionally by adsorption in a separating unit, and producing at least the following three gases in the separating unit: a carbon monoxide-enriched gas, a hydrogen-enriched gas, a residual gas containing carbon monoxide and hydrogen that is less pure with respect to carbon monoxide than the carbon monoxide-enriched gas and less pure with respect to hydrogen than the hydrogen-enriched gas.

Claims

1.-15. (canceled)

16. A method for separating a synthesis gas containing carbon monoxide and hydrogen comprising: i) compressing a flow of synthesis gas received from a source of synthesis gas in a compressor, ii) purifying the compressed synthesis gas in a purification unit to purify it of water and/or carbon dioxide, iii) cooling the compressed and purified flow of synthesis gas, iv) separating the cooled flow of synthesis gas by washing and/or distillation at a cryogenic temperature and optionally by adsorption in a separating unit, and v) producing at least the following three gases in the separating unit: a carbon monoxide-enriched gas, a hydrogen-enriched gas, a residual gas containing carbon monoxide and hydrogen that is less pure with respect to carbon monoxide than the carbon monoxide-enriched gas and less pure with respect to hydrogen than the hydrogen-enriched gas and optionally also a methane-enriched gas, and/or a nitrogen-enriched gas, and vi) sending at least one part of each of the following gases downstream of the source, only if the flow of synthesis gas received from the source and sent to the compressor is below a threshold or zero, the carbon monoxide-enriched gas, the hydrogen-enriched gas, and the residual gas containing carbon monoxide and hydrogen, to be purified in the purification unit and separated in the separating unit, wherein the at least one part of the three gases is sent upstream of the compressor to be compressed in the compressor upstream of the purification.

17. The method as claimed in claim 16, further comprising: a) storing compressed synthesis gas while the flow of synthesis gas received from the source is above the threshold, and b) sending at least one part of the compressed synthesis gas, previously stored, as well as at least one part of at least each of the first three gases in step v), downstream of the source.

18. The method as claimed in claim 16, wherein at least one part of at least each of the three gases in step v) downstream of the source and upstream of the compressor only if the flow of synthesis gas received from the source is below the threshold, or even if no flow is received from the source.

19. The method as claimed claim 16, wherein only x% of the carbon monoxide-enriched gas, y% of the hydrogen-enriched gas and z% of the residual gas are sent to the separating unit when the flow of synthesis gas received from the source is below a threshold, x, y and z differing by at most 5%.

20. The method as claimed in claim 16, wherein a part of the carbon monoxide-enriched gas is stored in a storage facility and the rest of the carbon monoxide-enriched gas is sent to a customer if the flow of synthesis gas received from the source is above the threshold and the carbon monoxide-enriched gas received from the storage facility is sent to the customer if the flow of synthesis gas is below the threshold.

21. The method as claimed in claim 20, wherein if the flow of synthesis gas received from the source is below the threshold, all the carbon monoxide-enriched gas sent to the customer comes from the storage facility is sent upstream of the compressor and downstream of the source.

22. The method as claimed in claim 16, wherein the synthesis gas is a residual gas from an acetylene production unit.

23. The method as claimed in claim 16, wherein if the flow of synthesis gas received from the source is above the threshold, part of the synthesis gas is stored in a storage facility and if the flow of synthesis gas received from the source is below the threshold, synthesis gas is sent from the storage facility to the compressor.

24. The method as claimed in claim 16, wherein if the flow of synthesis gas received from the source is zero, the separating unit is only supplied with gases produced by the separating unit.

25. The method as claimed in claim 16, wherein the carbon monoxide-enriched gas is compressed in a product compressor and is sent to the customer and if the flow of synthesis gas received from the source is below the threshold and the flow of carbon monoxide-enriched gas to be compressed is below another threshold, gaseous nitrogen is sent to the product compressor to be compressed with the carbon monoxide-enriched gas.

26. The method as claimed in claim 16, wherein if the flow of synthesis gas received from the source is below a threshold, a gas rich in a component of the synthesis gas received from another source, which is not the separating unit, is sent to the separating unit.

27. The method as claimed in claim 16, wherein the carbon monoxide-enriched gas is compressed in a product compressor, then split into two, one compressed part serving as a product and one compressed part being recycled downstream of the source and/or the hydrogen-enriched gas is compressed in a product compressor, then split into two, one compressed part serving as a product and one compressed part being recycled downstream of the source.

28. The method as claimed in claim 16, wherein the residual gas contains methane.

29. The method as claimed in claim 16, wherein the total percentage of hydrogen and carbon monoxide in the residual gas is below 98 mol %.

30. The method as claimed in claim 16, wherein the at least one part of each of the following three gases: the carbon monoxide-enriched gas, the hydrogen-enriched gas and the residual gas containing carbon monoxide and hydrogen are only compressed in the compressor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] 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:

[0053] FIG. 1 illustrates a schematic representation in accordance with one embodiment of the present invention.

[0054] FIG. 2 illustrates a schematic representation in accordance with one embodiment of the present invention; and

[0055] FIG. 3 illustrates a schematic representation in accordance with one embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0056] In FIG. 1, a synthesis gas 1 is received from a synthesis gas generating unit, for example a reforming unit, such as an SMR or an ATR or a partial oxidation unit, which for example produces acetylene. The synthesis gas 1 contains carbon monoxide, carbon dioxide, hydrogen and optionally methane and nitrogen.

[0057] The gas 1 is compressed by a compressor 3 to form a compressed gas 5. The compressed gas 5 is sent to a hydrogenation treatment unit 7 for removing the oxygen and the unsaturated hydrocarbons, producing a flow 9. The flow 9 is sent to a CO.sub.2 purification unit 13, for example by washing with amines, producing a purge flow rich in CO.sub.2 11 and a flow of synthesis gas depleted of CO.sub.2 15. The flow 15 is sent to a unit for CO.sub.2 purification by adsorption 17 for removing the remaining CO.sub.2. The synthesis gas purified of CO.sub.2 19 is sent to a cryogenic distillation unit 21, where the synthesis gas is cooled and then separated in at least one distillation column, comprising for example a step of washing with methane and/or partial condensation and/or washing with carbon monoxide.

[0058] The cryogenic distillation unit 21 produces a carbon monoxide-enriched gaseous flow 26, a hydrogen-rich gas 27 and a residual gas 23 containing carbon monoxide and hydrogen, less pure with respect to carbon monoxide than the gas 26 and less pure with respect to hydrogen than the gas 27. The residual gas 23 preferably contains methane and optionally nitrogen and/or argon. Preferably the total percentage of hydrogen and carbon monoxide in the residual gas is below 98 mol %.

[0059] The carbon monoxide-enriched gaseous flow 26 is compressed in a compressor 33. A gaseous flow 31 received from the outlet of the compressor 33 is returned to the cryogenic distillation unit 21. The flow 37 represents losses of the carbon monoxide-enriched gases from the compressor 33. The gas from an intermediate stage of the compressor 33 forms a product in part 39.

[0060] If the flow of synthesis gas received from the source of synthesis gas is zero, the whole of these three products 23, 27, 39 is returned to purification. Hydrogen and the residual gas must be compressed in compressor 3 but the carbon monoxide may be compressed to the required pressure in compressor 33 and recycled downstream of the compressor 3. Thus, gases 23 and 27 must be sent upstream of compressor 3 whereas gas 26 may be recycled upstream or downstream of compressor 3.

[0061] If the flow of synthesis gas received from the source is not zero but is below a threshold, a percentage of x% of the carbon monoxide-rich gas, y% of the hydrogen-rich gas and z% of the residual gas may be returned to the purification unit and then to cryogenic separation. The percentages x, y and z are preferably identical but may differ by less than 5%.

[0062] When at least one part of the carbon monoxide from compressor 33 is recycled, gaseous nitrogen 35 may be injected at an intermediate level or at the intake of compressor 33 to compensate the leaks from the compressor.

[0063] FIG. 2 differs from FIG. 1 in that the hydrogen-enriched flow 30 is sent from the adsorption unit 17, which removes the water and the CO.sub.2, to an apparatus for purification by adsorption 41. This apparatus 41 produces a hydrogen-rich gas 43.

[0064] The gas depleted of hydrogen 47 received from apparatus 41 is mixed with the residual product 49 from apparatus 21 and compressed in a compressor 53 to supply a residual gas under pressure.

[0065] Thus, if the synthesis gas 1 from the source is no longer produced or is produced in reduced amount, at least some products from the cryogenic distillation apparatus 21 are recycled upstream of the compressor 3, optionally after an additional treatment step. In addition to the rest 51 of the gas from the intermediate stage of the compressor 33 or in place of gas 51, at least one part 45 of the hydrogen-rich product 43 and/or at least one part 55 of the residual gas received from the compressor 53 may be recycled upstream of the compressor 3.

[0066] The residual gas 55 preferably contains methane and optionally nitrogen and/or argon. Preferably the total percentage of hydrogen and carbon monoxide in the residual gas is below 98 mol %.

[0067] FIG. 3 differs from FIG. 1 in that a part 4 of the synthesis gas is taken at an intermediate pressure of the compressor 3 for part 4 and at the final pressure of the latter for part 4 and are not treated in units 7, 13, 17, 21. The part 4 is sent from the final pressure of the compressor 3 to an adsorption separating unit called PSA 16 where it is purified to form a hydrogen-rich flow 52. The residual product 18 from the adsorption separating unit 16 depleted of hydrogen is mixed with the residual gas 49 from the cryogenic apparatus 21 and the mixture is compressed in a compressor 22 to form a gaseous fuel 20. The part 12 of synthesis gas may be mixed with the gaseous fuel 20.

[0068] If the synthesis gas 1 received from the source is no longer produced or is produced in reduced amount, below a threshold, at least the following three gases are recycled, downstream of the source of the synthesis gas and optionally upstream of the compressor 3:

[0069] i) At least one part 51 of the carbon monoxide-enriched gas 39 received from the cryogenic distillation apparatus 21.

[0070] ii) At least one part 45 of the hydrogen-enriched gas received from the adsorption separating unit 16.

[0071] iii) At least one part 14 of a residual gas containing hydrogen and/or carbon monoxide received from the cryogenic distillation apparatus and/or adsorption separating unit 16, less pure with respect to carbon monoxide than gas 51 and less pure with respect to hydrogen than gas 45, and optionally also

[0072] iv) A part 6 of the compressed synthesis gas taken downstream of the compressor 3, stored in a storage facility 8 while the flow of synthesis gas is above the threshold and returned via pipe 10 and a valve.

[0073] The residual gas 14 preferably contains methane and optionally nitrogen and/or argon. Preferably the total percentage of hydrogen and carbon monoxide in the residual gas is below 98 mol %.

[0074] Preferably the percentages of the recycled gases differ little, for reconstituting the synthesis gas by mixing the different products 45, 51, 14.

[0075] To ensure that there is sufficient carbon monoxide for the customer, it is possible to use a liquid carbon monoxide tank 24 within the distillation apparatus 21 and/or a gaseous carbon monoxide tank 38 fed from the compressor 33 via pipe 36 for supplying the carbon monoxide that is lacking. The liquid from storage facility 24 is vaporized in the vaporizer 25.

[0076] In particular, if a large part or all of the carbon monoxide produced in real time is destined for recycling, the carbon monoxide stored in tanks 24 or 38 may make it possible to supply the customer. Thus, for example, valve 40 will be opened to supply carbon monoxide from the storage facility 38 to the customer if there will be a shortage of synthesis gas 1.

[0077] In a preferred variant, which may be used for all the methods in FIGS. 1 to 3 using pipelines that are present or by adding the necessary storage facilities, recycling is carried out as follows.

[0078] Firstly, the flow of synthesis gas falls below a threshold or stops. First of all, we begin to open recycling valves for at least two fluids produced by treating the synthesis gas.

[0079] The synthesis gas is recycled from the storage facility 8 (or from the pipe downstream of compressor 3 if its volume and its pressure allow this) to upstream of compressor 3.

[0080] Once the recycling valves are open, at least the following three gases are recycled, downstream of the source of the synthesis gas and optionally upstream of compressor 3:

[0081] i) At least one part 51 of the carbon monoxide-enriched gas 39 received from the cryogenic distillation apparatus 21.

[0082] ii) At least one part 45 of the hydrogen-enriched gas received from the adsorption separating unit 16.

[0083] iii) At least one part 14 of a residual gas containing hydrogen and/or carbon monoxide received from the cryogenic distillation apparatus and/or adsorption separating unit 16, less pure with respect to carbon monoxide than gas 51 and less pure with respect to hydrogen than gas 45, and optionally also

[0084] iv) A part 6 of the compressed synthesis gas taken downstream of compressor 3, stored in a storage facility 8 while the flow of synthesis gas is above the threshold and returned via pipe 10 and a valve.

[0085] In certain cases, the entire production of the separating apparatus consisting of the separating apparatus by washing and/or distillation and optionally by the adsorption unit is recycled upstream of the synthesis gas compressor.

[0086] It is also possible, for all the figures, to recycle the carbon monoxide-enriched gas 51 downstream of the synthesis gas compressor 3. The gas 51 may in this case be taken at the outlet pressure of compressor 3.

[0087] It is also possible to recycle at least two products and also send a gas 2 rich in a component of the synthesis gas obtained from an external source, other than the separating apparatus, upstream or downstream of the synthesis gas compressor. This gas 2 may be natural gas obtained from a pipeline or a synthesis gas from another source.

[0088] 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.