Process and apparatus for the production of a synthesis gas
By integrating high-pressure hydrogen into the CO2 capture unit through heat exchanger mixing, the process reduces compression work and energy consumption, optimizing synthesis gas production.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Applications
- Current Assignee / Owner
- LAIR LIQUIDE SA POUR LETUDE & LEXPLOITATION DES PROCEDES GEORGES CLAUDE
- Filing Date
- 2024-11-25
- Publication Date
- 2026-05-29
AI Technical Summary
Existing methods for producing synthesis gas require significant compression work to combine CO2 and hydrogen at high pressures, leading to high energy consumption and equipment size requirements.
Integrate high-pressure hydrogen into the CO2 capture unit by cooling it in a heat exchanger and mixing it with pressurized CO2-rich liquid, allowing vaporization at reaction pressures, thereby reducing the need for separate compression and energy consumption.
This approach reduces the size and energy requirements of the CO2 compressor, optimizing the process by integrating hydrogen and CO2 at reaction pressures, thus enhancing efficiency and reducing energy consumption.
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Abstract
Description
Title of the invention: Process and apparatus for the production of a synthesis gas
[0001] The present invention relates to a method and apparatus for the production of a synthesis gas.
[0002] It relates to the production of a synthesis gas which is a mixture of CO2 and hydrogen. The ratio between the two components varies depending on the final product to be formed by the reaction of the synthesis gas.
[0003] It relates to CO2 capture units by partial condensation and distillation producing CO2 intended for the synthesis of a product, for example methanol, methane or carbon monoxide.
[0004] One of the proposed ways to utilize captured CO2, for example from large industrial emitters, is to use it as a feedstock for the synthesis of methanol, ideally using decarbonized hydrogen. This methanol can then be used as a feedstock for industry or as an alternative fuel.
[0005] The synthesis reaction is based on the following reaction:
[0006] [Chem.l] CO2 + 3H2 → CH3OH + H2O
[0007] It is also possible to valorize the captured CO2 as a raw material for the synthesis of carbon monoxide with the following reaction:
[0008] [Chem.2] CO2 + H2 → CO + H2O
[0009] It is also possible to valorize the captured CO2 as a raw material for the synthesis of methane with a methanation reaction (Sabatier reaction):
[0010] [Chem.3] CO2+4H2-ÆH4+2H2O
[0011] The methanol production reaction takes place at relatively high pressure, typically between 80 and 90 bar. [Fig. 1] shows a methanol synthesis gas production process in which hydrogen is produced by water electrolysis E and CO2 is produced by partial condensation and distillation CC. The CO2 is taken as tank liquid from the distillation column and is vaporized at at least two different pressures, lower than the pressure required for the reaction. It is therefore necessary to compress the CO2 and hydrogen separately in a compressor VCO2 before entering the reaction loop S, which produces methanol MEOH. Indeed, cryogenic CO2 capture units produce CO2 at relatively low pressure, typically 5 and 10 bara. Hydrogen is compressed in a VH2 hydrogen compressor upstream of the S loop before being mixed with the CO2.
[0012] The described invention aims to reduce the compression work by integrating the reactive hydrogen into the CO2 capture unit.
[0013] A CO2 capture unit by partial condensation and distillation processes a gas rich in CO2 (>50mol%, ideally >65mol% or even >80mol%), also containing light gases (typically H2, CO, CH4, N2, Ar, O2).
[0014] The gas undergoes partial condensation at high pressure (25-60 bara) in a heat exchanger, generating a liquid rich in CO2 (>95 mol%). This liquid is then purified of its light impurities in a distillation column.
[0015] Typically, the liquid obtained at the bottom of the column is then vaporized at several pressures, in order to generate the cold necessary for partial condensation.
[0016] The invention proposes to modify the process by incorporating the following steps: 1. The hydrogen required for the reaction, for example available at high pressure (80-90 bara) and at a temperature above -40°C, or even at 0°C, is cooled in the heat exchanger. 2. The purified CO2 available at the bottom of the distillation column is pumped up to the pressure of hydrogen, then mixed with the latter, generating a two-phase mixture. 3. The liquid present in the two-phase mixture is vaporized in the heat exchanger, providing the cold necessary for partial condensation.
[0017] The advantage of this invention lies in the fact that, instead of being vaporized at 5 or 10 bar, the CO2 is vaporized at a higher pressure, even at the pressure required for the reaction to synthesize methanol, which makes it possible to reduce the size of the CO2 compressor, or even eliminate it altogether. This also results in reduced energy consumption, since pressurizing a liquid consumes less energy than compressing an equivalent gas.
[0018] It is known from EP2692411 and EP2656898 to pressurize a CO2-rich liquid flow from a partial condensation or distillation separation process and to vaporize the pressurized flow in a heat exchanger against the flow to be separated, which cools there. No flow containing at least 90 mol% hydrogen is present.
[0019] The presence of hydrogen lowers the partial pressure of the mixture and allows for non-isothermal vaporization, with a large temperature glide that follows the condensation curve of the feed gas relatively well.
[0020] [Fig. 3] shows the diagram of the exchange of the device according to the invention (in solid lines), compared to the conventional diagram (in dashed lines) with heat Heat exchange is represented on the ordinate and temperature T on the abscissa. Vaporization of the H2 / CO2 mixture allows for very satisfactory thermal integration in a single vaporization step.
[0021] The two-phase mixture can be introduced into the exchanger via a dedicated device, or directly without special equipment.
[0022] Depending on the CO2 content of the gas to be purified, the process may or may not be autothermal. If it is not, all or part of the high-pressure non-condensables can be expanded in a turbine to generate the necessary additional cooling. Additional cooling can also be provided by an external mechanical refrigeration unit or by the cooling from the vaporization of a liquid external to the process.
[0023] According to one object of the invention, a process for producing a synthesis gas is provided in which: a. A feed gas containing more than 10 mol% CO2, typically more than 50 mol% CO2, preferably more than 65 mol% or even more than 80 mol% CO2, as well as at least one compound lighter than CO2 chosen from the group H2, CO, CH4, N2, Ar, and O2, is cooled in a heat exchanger and separated by partial condensation and / or distillation, generating a CO2-rich liquid, typically greater than 95 mol% CO2, and a CO2-poor gas. b. A gas containing at least 90 mol% hydrogen is cooled in the heat exchanger and mixed with the CO2-rich liquid, forming a two-phase fluid. c. The two-phase fluid heats up in the heat exchanger, forming a gaseous mixture of hydrogen and carbon dioxide and d. The gaseous mixture constitutes a synthesis gas.
[0024] According to other optional aspects: • The CO2-rich liquid is pressurized to the pressure of the gas containing at least 90% mol of hydrogen cooled in the heat exchanger before being mixed with the gas containing at least 90% mol of hydrogen cooled in the heat exchanger. • the gas containing at least 90% mol of hydrogen enters the heat exchanger at a pressure equal to or greater than 20 bars, preferably greater than or equal to 40 bars. • the gas containing at least 90% mol of hydrogen enters the heat exchanger at a pressure equal to or greater than 80 bars, preferably less than or equal to 90 bars. • the feed gas is separated by distillation in a column system comprising at least one distillation column generating a CO2-rich liquid in the distillation column tank. Part of the liquid produced in the column tank is vaporized in the heat exchanger, without having been pressurized, and returned to the column in gaseous form. Part of the liquid produced in the column tank is vaporized, without being pressurized, by heat exchange with the hydrogen cooled in the heat exchanger and returned to the column in gaseous form either in the heat exchanger or in another dedicated heat exchanger. the synthesis gas is at least a methanol synthesis gas and is sent to a methanol synthesis unit, preferably without having been compressed downstream of the heat exchanger. Synthesis gas is at least a synthesis gas from a methanation process and is sent to a methane synthesis unit, preferably without having been compressed downstream of the heat exchanger. Synthesis gas is at least a synthesis gas from a reverse water gas reaction and is sent to a carbon monoxide synthesis unit, preferably without having been compressed downstream of the heat exchanger. all or part of a CO2-depleted gas generated by partial condensation and / or distillation is heated in the heat exchanger, expanded in a turbine and heated again in the heat exchanger. all or part of the gas containing at least 90% mol of hydrogen is cooled by a mechanical refrigeration unit external to the process. Hydrogen and / or carbon dioxide is added to the gas mixture downstream of the heat exchanger. The gas mixture contains hydrogen and CO2 in a 1:1 ratio at the outlet of the heat exchanger. The gas mixture contains hydrogen and CO2 in a 3:1 ratio at the outlet of the heat exchanger. The gas mixture contains hydrogen and CO2 in a 4:1 ratio at the outlet of the heat exchanger. The gas mixture contains hydrogen and CO2 in a 1:1 ratio once mixed with hydrogen and / or CO2 downstream of the heat exchanger. The gas mixture contains hydrogen and CO2 in a 3:1 ratio once mixed with hydrogen and / or CO2 downstream of the heat exchanger. The gas mixture contains hydrogen and CO2 in a 4:1 ratio once mixed with hydrogen and / or CO2 downstream of the heat exchanger. • the gas containing at least 90 mol% hydrogen arrives in the heat exchanger at a temperature above 0°C • The gas containing at least 90 mol% hydrogen enters the heat exchanger at a temperature equal to or lower than 0°C • the gas containing at least 90 mol% hydrogen arrives in the heat exchanger at a temperature equal to or less than 0°C from a unit separating carbon monoxide and hydrogen by cryogenic distillation from which it has been extracted at a temperature equal to or less than 0°C • the gas containing at least 90 mol% hydrogen arrives in the heat exchanger at a temperature equal to or less than 0°C from a hydrogen liquefier from which it has been extracted at a temperature equal to or less than 0°C.
[0025] According to another object of the invention, a synthesis gas production apparatus is provided, comprising a heat exchanger, a separation apparatus by partial condensation and / or distillation, means for sending a feed gas containing more than 10% mol CO2, typically more than 50 mol% CO2, preferably more than 65% or even more than 80 mol% CO2, as well as at least one compound lighter than CO2 selected from the group H2, CO, CH4, N2, Ar and O2, to be cooled in a heat exchanger and then separated by partial condensation and / or distillation in the separation apparatus, generating a liquid rich in CO2, typically greater than 95 mol% CO2, and a gas poor in CO2, means for sending a gas containing at least 90% mol hydrogen to be cooled in the heat exchanger and then mixed with the liquid rich in CO2, forming a two-phase fluid,means of sending the two-phase fluid to be heated in the heat exchanger, forming a gaseous mixture of hydrogen and carbon dioxide; this gaseous mixture constitutes a synthesis gas.
[0026] Preferably, the device includes a pump for compressing the CO2-rich liquid upstream of the heat exchanger.
[0027] Preferably, the apparatus includes means for mixing the gas containing at least 90% mol of hydrogen and the CO2-rich liquid downstream of the pump.
[0028] The invention will be described in more detail with reference to the figures where:
[0029] [Fig.2] represents at least certain features of a method according to the invention
[0030] [Fig.4] represents at least certain characteristics of another process according to the invention.
[0031] In [Fig. 2] in a process according to the invention, a feed flow 1 containing more than 10% mol CO2 typically more than 50 mol% CO2, preferably more than 65% or even more than 80 mol% CO2 as well as at least one compound lighter than CO2 selected from the group H2, CO, CH4, N2, Ar and O2 is cooled in a heat exchanger E to an intermediate exchanger temperature, for example -35°C, where it partially condenses; the two-phase flow is separated in a phase separator SI, forming a CO2-depleted gas 3 and a CO2-enriched liquid 5. The gas 3 is cooled in the exchanger E to the cold end, partially condensing, and then separated in a second phase separator S2 at a cold temperature, for example -52.5°C, forming a CO2-depleted gas 9 containing between 15 and 25 mol% CO2 and a liquid 10 enriched in CO2 relative to gas 3. The liquid 10 is mixed with the liquid 5, forming a liquid 11 containing approximately 95 mol% CO2.
[0032] Liquid 11 is expanded and sent to the top of a distillation column C as the sole feed stream, where it separates, forming a head gas containing approximately 65 mol% CO2 and a tank liquid containing more than 95 mol% CO2. The liquid is divided into two, forming a liquid 15 and a liquid 17. Liquid 15 is not pressurized, vaporizes in the heat exchanger E, which it enters at an intermediate temperature, and is returned as a gas to the tank of column C as a reboiling gas.
[0033] The liquid 17 is pressurized to a pressure greater than or equal to 20 bar, preferably greater than or equal to 40 bar, or even greater than or equal to 80 bar, possibly less than 90 bar by a pump P. The exchanger E is designed to withstand such a pressure.
[0034] A flow 19 containing at least 90 mol% hydrogen, for example from a water electrolysis unit, enters the heat exchanger at its hot end and is cooled to an intermediate temperature while remaining gaseous (flow 21). The flow 21 mixes with the pressurized flow 17, forming a two-phase flow 23 which is heated from the cold end of the exchanger E, in which the liquid portion vaporizes. The proportions of the flow rates 17 and 19 are chosen so that the mixture 25 exiting the exchanger E contains 25% CO2 and 75% hydrogen, so that the mixture can serve as the synthesis gas for methanol. Alternatively, it is also possible to add gaseous CO2 and / or gaseous hydrogen downstream of the exchanger E to obtain the desired percentages.
[0035] Preferably the pressures of the flow rates 17, 19 are chosen so that the mixture 25 exiting the exchanger E can be sent directly to a synthesis unit S, for example a methanol synthesis unit without having been pressurized downstream of the exchanger E. However, the presence of a compressor is not excluded.
[0036] Preferably the pump outlet pressure P is equal to the hydrogen pressure 21.
[0037] The reboiling of the column is represented in [Fig.2] as being integrated into the main exchange line.
[0038] However, this reboiling could be carried out in a separate heat exchanger R, as seen in [Fig. 4], for example using hydrogen 19 as the hot fluid. Thus, the hydrogen cooled in heat exchanger E and then in heat exchanger R is mixed with the liquid CO2 from pump P. The remainder of [Fig. 4] corresponds to [Fig. 2].
[0039] The process according to the invention may be advantageous given the high operating pressure of the heat exchanger E: limiting the number of fluids and heads, in particular the number of vaporizations, can simplify the thermomechanical design of the exchanger.
[0040] Depending on the CO2 content of the gas to be purified, the process may or may not require a cooling input. If a cooling input is required, all or part of the high-pressure non-condensables 9, 13 may be heated in the heat exchanger, expanded in a turbine, and reheated in the heat exchanger to generate the necessary additional cooling. Additional cooling may also be provided by an external mechanical refrigeration unit or by the cooling from the vaporization of a liquid external to the process.
[0041] The invention has been described in the context of the production of a methanol synthesis gas.
[0042] It will be understood that by varying the ratios between hydrogen and CO2 it is possible to form a methanation synthesis gas with a ratio of 4:1 or a synthesis gas from the reverse reaction of the gas to water (called in English "reverse water gas shift reaction").
[0043] The methanation reaction takes place at between 5 and 30 bars abs, or even between 15 and 30 bars abs or up to 50 bars abs, it will therefore be necessary to mix the pressurized CO2 and hydrogen at a pressure equal to or less than the pressure of the methanation synthesis gas.
[0044] The reverse reaction of the gas with water takes place at a pressure between 1 and 50 bars abs, preferably between 12 and 50 bars abs.
[0045] It is possible to produce a mixture of hydrogen and CO2 which does not exactly correspond to the desired proportions, not containing enough hydrogen, and to add hydrogen to the mixture downstream of the heat exchanger to obtain the desired proportions.
[0046] It is also possible to produce a mixture having the proportions desired for one type of synthesis and to add hydrogen downstream of the exchanger to obtain a synthesis gas for another type of synthesis, in addition to or instead of the other gas.
[0047] In all cases, heat generated by the reaction of the synthesis gas to form methanol, methane or carbon monoxide can be used to preheat the water for electrolysis.
[0048] For example, one could produce methanol synthesis gas according to the invention and add hydrogen downstream of the heat exchanger to obtain in addition (or instead) a methanation synthesis gas.
[0049] It is possible to take hydrogen for Figures 2 and 4 at a temperature below ambient, for example by taking hydrogen at a temperature below 0°C taken from a unit separating a mixture of carbon monoxide and hydrogen by cryogenic distillation or from a hydrogen liquefier.
Claims
Demands
1. A process for producing a synthesis gas in which: a) a feed gas (1) containing more than 10 mol% CO2, typically more than 50 mol% CO2, preferably more than 65 mol% or even more than 80 mol% CO2, and at least one compound lighter than CO2 selected from the group H2, CO, CH4, N2, Ar, and O2, is cooled in a heat exchanger (E) and separated by partial condensation and / or distillation, generating a liquid (17) rich in CO2, typically greater than 95 mol% CO2, and a gas (13) poor in CO2; b) a gas (19) containing at least 90 mol% hydrogen is cooled in the heat exchanger and mixed with the CO2-rich liquid, forming a two-phase fluid (23); c) the two-phase fluid is heated in the heat exchanger, forming a gaseous mixture (25) of hydrogen and carbon dioxide and d) the gaseous mixture constitutes a synthesis gas.
2. A method according to claim 1 wherein the CO2-rich liquid is pressurized to the pressure of the gas containing at least 90% mol of hydrogen cooled in the heat exchanger (E) before being mixed with the gas (21) containing at least 90% mol of hydrogen cooled in the heat exchanger.
3. A method according to claim 1 or 2 wherein the gas containing at least 90% mol of hydrogen (19) enters the heat exchanger at a pressure equal to or greater than 20 bar, preferably greater than or equal to 40 bar.
4. A method according to claim 3 wherein the gas containing at least 90 mol% hydrogen (19) enters the heat exchanger (E) at a pressure equal to or greater than 80 bar, preferably less than or equal to 90 bar.
5. A method according to any one of the preceding claims wherein the feed gas (1) is separated by distillation in a column system comprising at least one distillation column (C) generating a CO2-rich liquid in the distillation column tank.
6. A method according to claim 5, wherein a portion of the liquid produced in the column tank (15) is vaporized in the exchanger of heat (E), without having been pressurized, and returned to the column in gaseous form.
7. A method according to claim 5 or 6 wherein a portion of the liquid produced in the column tank is vaporized, without having been pressurized, by heat exchange with hydrogen cooled in the heat exchanger and returned to the column (C) in gaseous form either in the heat exchanger (E) or in another dedicated heat exchanger (R).
8. A method according to any one of the preceding claims wherein the synthesis gas (25) is at least a methanol synthesis gas and is sent to a methanol synthesis unit (S), preferably without having been compressed downstream of the heat exchanger.
9. A process according to any one of the preceding claims wherein the synthesis gas is at least one synthesis gas (25) from a methanation process and is sent to a methane synthesis unit, preferably without having been compressed downstream of the heat exchanger.
10. A method according to any one of the preceding claims wherein the synthesis gas (25) is at least a synthesis gas from a reverse water gas reaction and is sent to a carbon monoxide synthesis unit, preferably without having been compressed downstream of the heat exchanger.