Process and apparatus for the production of ammonia synthesis gas
A multi-stage cryogenic separation process effectively recycles carbon monoxide and methane in ammonia synthesis, reducing CO2 emissions by minimizing their combustion, thereby improving the environmental footprint of ammonia production.
Patent Information
- Application Number
- FR2024003780
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2024-04-11
- Publication Date
- 2026-03-06
- Estimated Expiration
- 2044-04-11
AI Technical Summary
Existing ammonia synthesis processes produce significant amounts of CO2 emissions due to the combustion of residual gases containing high levels of carbon monoxide and methane, which are not effectively recycled or utilized.
A multi-stage cryogenic separation process using liquid nitrogen washing and multiple separation columns to separate and recycle carbon monoxide and methane, reducing their presence in residual gases before combustion, thereby minimizing CO2 emissions.
The process significantly reduces CO2 emissions by recycling at least 50-70% of carbon monoxide and methane back into the reformer, decreasing the amount sent to combustion, thus enhancing the efficiency and environmental impact of ammonia synthesis.
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Abstract
Description
Title of the invention: Process and apparatus for the production of ammonia synthesis gas
[0001] The present invention relates to a method and apparatus for producing a synthesis gas of ammonia. It uses a hydrogen purification process by nitrogen washing with methane recovery.
[0002] The ammonia synthesis units are fed by a stoichiometric H2 / N2 mixture.
[0003] Certain compounds such as argon, methane, oxygen, CO, CO2 or others are considered as inert or as poisons of catalysts for the synthesis of ammonia.
[0004] It is therefore necessary to purify the hydrogen which can be produced by a steam reforming reactor, by an autothermal reactor or by a coal gasification reactor to name only the most common.
[0005] One of the processes for purifying this hydrogen operates by cryogenic means and is known as liquid nitrogen washing where the impure hydrogen is treated in a counter-current flow in a column where it is sent to a tank while the column is fed at the top by a flow of liquid nitrogen.
[0006] Impure hydrogen produced by a steam reforming or coal gasification reactor is initially treated in an acid gas removal unit such as CO2, H2S, before being sent to an adsorption purification unit to remove components that can solidify in the cold box.
[0007] At the exit of this adsorption, the impure hydrogen is treated in a cold box.
[0008] This hydrogen is cooled to a temperature around -182°C / -190°C to supply the tank of a washing column where liquid nitrogen is injected at the top.
[0009] This liquid nitrogen can be produced by an air separation unit in gaseous form and liquefied in the main exchanger.
[0010] The liquid from the washing column tank containing the impurities CO, Ar and CH4 is vaporized in the main exchanger before being used, for example, as fuel.
[0011] In the case where the CH4 content in the impure hydrogen is on the order of several molar %, it is known from WO 2012 / 097497 to separate the liquid phase created before entering the nitrogen washing column and thus produce a fluid richer in CH4.
[0012] A pure H2+N2 mixture is thus produced at the top of the scrubbing column for the synthesis of NH3. A fluid rich in CH4 can be recycled upstream or used to supply an H2 production unit, as well as a so-called residual fluid, used as fuel. containing a mixture of CO and Ar with residual levels of CH4, H2, and N2.
[0013] The waste fluid is used as fuel and, for example, is burned in a combustion unit, such as a combustion unit where combustion takes place in a closed chamber, with the heat of combustion transferred to air by indirect heat transfer (also known as an indirect-fired heater). The heat can also be transferred by direct heat exchange. This combustion unit can generate heat for a reformer producing a mixture of carbon monoxide and hydrogen, for example, a self-heating reformer. However, it generates flue gases containing CO2, emitted in particular by the combustion of the CO contained in the waste fluid.
[0014] One object of the invention is to reduce the production of CO2 from this combustion unit by modifying the composition of the residual fluid used as fuel to reduce its carbon monoxide and / or methane content.
[0015] According to one aspect of the invention, a process for producing a synthesis gas of ammonia is provided in which a gaseous mixture containing hydrogen, argon, carbon monoxide, carbon dioxide and methane is obtained from a reformer, the mixture being treated to remove the carbon dioxide it contains before being cooled and separated in a cryogenic separation unit in a thermally insulated chamber, the mixture being separated in a first liquid nitrogen scrubbing column to produce at the top of the column a first gas which is the synthesis gas of ammonia and in the tank a first liquid containing nitrogen, hydrogen, argon, carbon monoxide and methane, the liquid is separated in a second separation column to produce a second column top gas enriched in hydrogen and a second liquid depleted in hydrogen and enriched in methane and argon,The second hydrogen-depleted liquid is sent to a third separation column which produces a third methane-enriched liquid and a third overhead gas in a tank. This third liquid is then sent to a fourth separation column which produces an argon-enriched liquid and a fourth overhead gas in a tank. The fourth gas is then sent to a fifth column which produces a fifth carbon monoxide-rich liquid and a fifth nitrogen-rich gas. The fourth liquid is vaporized and sent as fuel to a combustion unit which produces flue gases containing CO2 and heat, which is used in the gas mixture production process.
[0016] According to other optional features: • the third and / or fifth liquid is vaporized and sent upstream of the reformer. • A fuel, for example natural gas, is optionally treated in a desulfurization unit, then sent to a pre-reformer and the reformer producing a gas which is treated by at least one shift operation producing the mixture containing hydrogen, argon, carbon monoxide, carbon dioxide and methane. • the third and / or fifth liquid is sent upstream of the pre-reformer or upstream of the desulfurization unit. • no part of the fourth liquid is sent upstream of the reformer. • at least 50%, or even at least 70%, of the carbon monoxide present in the gas mixture at the inlet of the thermally insulated enclosure is recycled upstream of the reformer. • at least 50%, or even at least 70%, of the methane present in the gas mixture at the inlet of the thermally insulated enclosure is recycled upstream of the reformer. • less than 50% or even less than 30% of the carbon monoxide present in the gas mixture at the inlet of the thermally insulated enclosure is sent to the combustion unit. • less than 50% or even less than 30% of the methane present in the gas mixture at the inlet of the thermally insulated enclosure is sent to the combustion unit. • the first, second, third, fourth and fifth columns are located inside a single thermally insulated enclosure.
[0017] According to another object of the invention, an apparatus for the production of a synthesis gas of ammonia is provided, comprising a cryogenic separation unit including a first liquid nitrogen washing column, a second separation column, a third separation column, a fourth separation column and a fifth column, a thermally insulated enclosure, means for treating a gaseous mixture containing hydrogen, argon, carbon monoxide, carbon dioxide and methane from a reformer, to remove the carbon dioxide it contains, means for cooling the carbon dioxide-purified mixture, means for sending the cooled and purified mixture to separate in the cryogenic separation unit in the thermally insulated enclosure,in the first liquid nitrogen scrubbing column to produce at the top of the column a first gas which is ammonia synthesis gas and in the tank a first liquid containing nitrogen, hydrogen, argon, carbon monoxide and methane, means for sending the first liquid to separate in the second separation column to produce a second column top gas enriched in hydrogen and a second liquid depleted in hydrogen and enriched in methane and argon, means for sending the second liquid depleted in hydrogen to the third separation column which produces in the tank a third liquid enriched in methane and a third, head gas, means for sending the third head gas to the fourth separation column which produces in a tank a fourth liquid enriched in argon and a fourth head gas, means for sending the fourth gas to a fifth column which produces a fifth liquid rich in carbon monoxide and a fifth gas rich in nitrogen, means for vaporizing the fourth liquid and means for sending the vaporized fourth liquid as fuel to a combustion unit which produces fumes containing CO2 and heat which is used to produce the gas mixture.
[0018] The invention will be described in more detail with reference to the figures in which:
[0019] [Fig. 1] schematically represents a process for the production of ammonia synthesis gas.
[0020] [Fig.2] represents the cryogenic separation of the gaseous mixture used to produce ammonia synthesis gas.
[0021] [Fig. 1] represents a process for producing ammonia synthesis gas (NH3) in which a flow of hydrocarbons (NG), for example natural gas, is sent to an optional desulfurization unit (HD). The gas is then sent to a pre-reformer (PR) and a reformer (R), for example of the autothermal type, heated by the heat from a combustion unit (H) fueled by hydrocarbons (NG), for example natural gas. The reformer produces a gas consisting mainly of hydrogen, carbon monoxide, carbon dioxide, methane, and argon. This gas is heated in a unit (B), and then some of the carbon monoxide it contains is converted to carbon dioxide in two shift units (SH1, SH2). Acid gases such as carbon dioxide are partially removed in a scrubbing unit (M), for example by a Rectisol®-type process using methanol scrubbing.The purified gas, now acidic, is then sent to an adsorption purification unit (not shown) to remove components that may solidify during cryogenic separation.
[0022] The mixture 1 entering the cryogenic chamber CB still contains hydrogen, carbon monoxide, carbon dioxide, methane, and argon. The mixture is separated by cryogenic separation comprising a liquid nitrogen wash in a separation unit CB, which produces ammonia synthesis gas 2 containing nitrogen and hydrogen. Gas 2 is sent to an ammonia production unit S.
[0023] An air separation device ASU produces nitrogen N for nitrogen scrubbing in unit CB and oxygen O for the reformer.
[0024] A gas 15 containing argon is sent to a combustion unit H and a gas 21 containing carbon monoxide and / or methane is sent upstream of the reformer R (or upstream of the pre-reformer PR or upstream of the desulfurization unit HD). The combustion unit H produces
[0025] [Fig.2] represents a thermally insulated enclosure CB containing two heat exchangers of heat 3.5, a first separation column K1 which is a liquid nitrogen washing column, a second separation column K2, a third separation column K3, a fourth separation column K4 and a fifth separation column K5.
[0026] The mixture 1, at the outlet of the adsorption, containing hydrogen, carbon monoxide, carbon dioxide, methane, and argon, is cooled in heat exchangers 3, 5 to a temperature around -182°C / -190°C. Nitrogen N from the air separation also liquefies in these exchangers. The cooled mixture 1 is sent to the tank of the scrubbing column K1, and the liquefied nitrogen is sent to the top, so that an ammonia synthesis gas 2 is produced at the top of column KL. The tank liquid containing nitrogen, hydrogen, carbon monoxide, methane, and argon is sent to the second column K2 to reduce its hydrogen content, a hydrogen-enriched flow 8 exiting the top of column K2, and a liquid 9 containing proportionally less hydrogen than the liquid 7 exiting the tank of column K2.Liquid 9 is sent to a third column which produces in a tank a liquid enriched in methane 13 compared to liquid 7 and a head gas 11 depleted in methane compared to liquid 7. Gas 11 is sent to a fourth column which produces in a tank a liquid enriched in argon 15 compared to gas 11 and a head gas 17 depleted in argon and methane compared to gas 11.
[0027] The gas 17 is separated in a fifth column K5 to produce at the top a flow 19 enriched in nitrogen and depleted in carbon monoxide compared to the gas 17 and in the tank a liquid 21 enriched in carbon monoxide and depleted in nitrogen compared to the fluid 17.
[0028] The argon-enriched liquid 15 is sent as fuel to the combustion unit H. Since some of the methane has already been removed in the column K3, the liquid 15 contains less methane than it would if the column K3 were not present.
[0029] The liquid 13 enriched in methane and / or the liquid 21 enriched in carbon monoxide are vaporized and sent either just upstream of the reformer R between the reformer R and the pre-reformer PR, or just before the pre-former PR or just before the desulfurization unit HD.
[0030] Thus, by successive separation using columns Kl to K5 containing internals allowing mass transfer between the liquid and gas phases, the thermally insulated enclosure CB containing the nitrogen scrubbing column Kl is capable of producing an H2+N2 mixture for the synthesis of NH3, a gas rich in CO, CH4 containing H2 and N2 that can be recycled upstream of unit R which generates the H2-rich fluid which is treated in the isolated CB enclosure as well as a residual gas (produced by vaporizing liquid 15) which contains the majority of the argon which cannot be recycled.
[0031] The majority of the CO and / or CH4 is then separated and recycled upstream, which reduces their quantity in the argon-rich fluid and thus considerably reduces the amount of CO2 emitted by combustion of the argon-rich fluid.
[0032] At least 50%, or even at least 70%, of the carbon monoxide present in the gas mixture 1 at the inlet of the thermally insulated enclosure is recycled upstream of the reformer R.
[0033] At least 50%, or even at least 70%, of the methane present in the gas mixture 1 at the inlet of the thermally insulated enclosure CB is recycled upstream of the reformer R.
[0034] Less than 50%, or even less than 30%, of the carbon monoxide present in the gas mixture at the inlet of the thermally insulated enclosure CB is sent to the combustion unit H associated with the reformer R.
[0035] Less than 50%, or even less than 30%, of the methane present in the gas mixture at the inlet of the thermally insulated enclosure CB is sent to the combustion unit H associated with the reformer R.
Claims
Demands
1. A process for producing a synthesis ammonia gas in which a gaseous mixture containing hydrogen, argon, carbon monoxide, carbon dioxide, and methane is obtained from a reformer (R), the mixture (1) being treated to remove the carbon dioxide it contains before being cooled (3, 5) and separated in a cryogenic separation unit in a thermally insulated chamber (CB), the mixture being separated in a first liquid nitrogen scrubbing column (1) to produce at the top of the column a first gas (2), which is the synthesis ammonia gas, and in a tank a first liquid (7) containing nitrogen, hydrogen, argon, carbon monoxide, and methane, the liquid being separated in a second separation column (K2) to produce a second column-top gas enriched in hydrogen (8) and a second liquid (9) depleted in hydrogen and enriched in methane and argon,The second hydrogen-depleted liquid is sent to a third separation column (K3) which produces in a tank a third liquid (13) enriched in methane and a third overhead gas (11) which is sent to a fourth separation column (K4) which produces in a tank a fourth liquid (15) enriched in argon and a fourth overhead gas (17), the fourth gas being sent to a fifth column (K5) which produces a fifth liquid (21) rich in carbon monoxide and a fifth gas (19) rich in nitrogen, the fourth liquid being vaporized and sent as fuel to a combustion unit (H) which produces fumes containing CO2 and heat which is used in the process of producing the gas mixture.
2. A method according to claim 1 wherein the third and / or fifth liquid (13, 21) is vaporized and sent upstream of the reformer (5).
3. A process according to any one of the preceding claims wherein a fuel (NG), for example natural gas, is optionally treated in a desulfurization unit (HD), then sent into a pre-reformer (PR) and reformer (R) producing a gas which is treated by at least one shift operation (SH1, SH2) producing the mixture containing hydrogen, argon, carbon monoxide, carbon dioxide and methane (1).
4. A method according to claims 2 and 3 wherein the third and / or the fifth liquid (13, 21) is sent upstream of the pre-reformer (PR) or upstream of the desulfurization unit (HD).
5. A method according to any one of the preceding claims in which no part of the fourth liquid (15) is sent upstream of the reformer (R).
6. A method according to any one of the preceding claims wherein at least 50%, or even at least 70%, of the carbon monoxide present in the gas mixture (1) at the inlet of the thermally insulated enclosure (CB) is recycled upstream of the reformer (R).
7. A process according to any one of the preceding claims wherein at least 50%, or even at least 70%, of the methane present in the gas mixture (1) at the inlet of the thermally insulated enclosure (CB) is recycled upstream of the reformer (R).
8. A method according to any one of the preceding claims wherein less than 50% or even less than 30% of the carbon monoxide present in the gas mixture (1) at the inlet of the thermally insulated enclosure (CB) is sent to the combustion unit (H).
9. A method according to any one of the preceding claims wherein less than 50% or even less than 30% of the methane present in the gas mixture (1) at the inlet of the thermally insulated enclosure (CB) is sent to the combustion unit (H).
10. Apparatus for the production of a synthesis gas of ammonia comprising a cryogenic separation unit including a first liquid nitrogen scrubbing column (K1), a second separation column (K2), a third separation column (K3), a fourth separation column (K4) and a fifth column (K5), a thermally insulated enclosure (CB), means (M) for treating a gaseous mixture (1) containing hydrogen, argon, carbon monoxide, carbon dioxide and methane from a reformer (R), to remove the carbon dioxide it contains, means (3,5) for cooling the carbon dioxide-purified mixture, means for sending the cooled and purified mixture to separate in the cryogenic separation unit in the thermally insulated enclosure,in the first liquid nitrogen washing column to produce at the top of the column a first gas (2) which is the ammonia synthesis gas and in the tank a first liquid (7) containing nitrogen, hydrogen, argon, carbon monoxide and methane, means for sending the first liquid to separate in the second se- column, means for producing a second hydrogen-enriched column head gas (8) and a second hydrogen-depleted liquid (9) enriched in methane and argon, means for sending the second hydrogen-depleted liquid to the third separation column which produces in a tank a third methane-enriched liquid (13) and a third head gas (11), means for sending the third head gas to the fourth separation column which produces in a tank a fourth argon-enriched liquid (15) and a fourth head gas (17), means for sending the fourth gas to a fifth column which produces a fifth carbon monoxide-rich liquid (21) and a nitrogen-rich fifth gas (19), means for vaporizing the fourth liquid and means for sending the vaporized fourth liquid as fuel to a combustion unit (H) which produces fumes containing CO2 and heat which is used to produce the mixture.