Method for producing low-carbon ammonia from natural gas

Abstract

The invention relates to the field of ammonia synthesis technologies which use natural gas as feedstock. On a process line, natural gas is subjected to primary and secondary reforming. The obtained converted gas is sent for the conversion of carbon dioxide and the subsequent methanation of the purified synthesis gas, after which ammonia synthesis is carried out. On a fuel line, natural gas and steam are heated and subjected to primary and secondary reforming, the obtained converted gas is sent for the conversion of carbon dioxide and the purified synthesis gas is used on the fuel and process lines. The technical result is that of making it possible to use the entire volume of synthesis gas on a process line for the synthesis of ammonia.

Description

[0001] METHOD FOR PRODUCING LOW-CARBON AMMONIA FROM NATURAL GAS

[0002] Field of technology

[0003] The invention relates to the field of ammonia synthesis technologies that use natural gas as raw material.

[0004] State of the art

[0005] A method for producing ammonia from conventional natural gas includes a stage of converting natural gas into synthesis gas containing hydrogen and nitrogen, and a stage of synthesizing ammonia, in which said synthesis gas reacts at high pressure to form ammonia.

[0006] At the conversion stage, natural gas is sent to preparation, where gas is obtained that is purified from undesirable impurities. Then, the prepared natural gas is sent to the reforming stage, where converted gas is obtained, mainly containing nitrogen, hydrogen, carbon monoxide CO and carbon dioxide CO2. Then, the synthesis gas is sent to the CO conversion stage, where carbon monoxide is oxidized to carbon dioxide CO2. Carbon dioxide CO2 is removed from the resulting gas mixture and the synthesis gas is sent to the final purification stage - methanation.

[0007] At the ammonia synthesis stage, the synthesis gas is compressed and sent to the synthesis stage, where converted synthesis gas is obtained, mainly containing ammonia, nitrogen and hydrogen. The resulting mixture is sent to the ammonia extraction stage.

[0008] When using the method of producing ammonia from natural gas of the conventional type, the most common method is reforming, which takes place in two stages: preliminary steam reforming (primary reforming) and secondary reforming of the resulting gas with the addition of a steam-oxygen or steam-air-oxygen mixture (secondary reforming). In this method, the heat required for the primary reforming reaction is obtained by burning part of the natural gas in a reforming furnace. In this case, it is envisaged to use a fire heater to heat the process media and / or generate high-pressure steam for the needs of the ammonia production plant.

[0009] The above-described furnaces and fired heaters in conventional natural gas ammonia production plants are a source of carbon dioxide (CO2) emissions into the atmosphere due to the use of natural gas as a fuel.

[0010] A method is known for producing ammonia from natural gas, including compression, heating and purification of natural gas from sulfur compounds, two-stage catalytic conversion of methane under pressure, including steam conversion in the first stage and steam-air conversion in the second stage, using the heat of the gas converted in the second stage, as well as a portion of the natural gas, purge and tank gases additionally burned on a burner to carry out the conversion in the first stage of the conversion process, catalytic conversion of carbon monoxide contained in the converted gas to obtain a nitrogen-hydrogen mixture, its purification from carbon dioxide, purification from oxygen-containing compounds by methanation, compression of the purified nitrogen-hydrogen mixture, synthesis of ammonia in a closed cycle and separation of the obtained ammonia with its subsequent delivery to the consumer, as well as the utilization of the heat of flue gases and their release into the environment (RU 2445262 C1, Published 20.03.2012).

[0011] The disadvantage of this method is the use of heat from natural gas burned in a burner, which causes carbon dioxide emissions into the atmosphere. The closest to the proposed method is a method for producing ammonia from natural gas, characterized by low levels of CO2 emissions into the atmosphere, which consists in the fact that natural gas and steam are heated in a furnace (VSP) and converted into synthesis gas containing H2, CO and CO2 in preparatory (primary) reforming (PDR) and autothermal (secondary) reforming (ATR) units; the ATR operates using an oxygen-enriched air flow or oxygen; the synthesis gas is converted in the conversion reaction section (CRS) and then CO2 is removed in the decarbonization section (DCS) to obtain lean synthesis gas; part of the lean synthesis gas is used as fuel in the VSP furnace; the remaining part of the synthesis gas depleted in carbon dioxide is processed in a methanation unit (MET).the nitrogen leaving the air separation section (ASS) is added to the synthesis gas fraction leaving the MET and sent to the ammonia synthesis section (ASS), where ammonia and purge gas are obtained; hydrogen is extracted from the purge gas (H2O) and added to the nitrogen and synthesis gas stream before being fed to the ASS; the off-gas obtained in the H2O is added to a portion of the carbon dioxide-depleted synthesis gas stream sent as fuel to the VSP; the ASS section also produces a stream of oxygen-enriched air or oxygen, which is used in the ATR (RU 2759379 C2, publ. 12.1 1.2021).;

[0012] In this method, natural gas is not used as a fuel, so the method is characterized by a low level of carbon dioxide emissions into the atmosphere. However, part of the synthesis gas is used as a fuel and is not used for the synthesis of ammonia, which reduces the productivity of the method. The essence of the invention

[0013] The technical problem solved by the proposed method is the production of low-carbon ammonia without reducing the productivity of the ammonia process line.

[0014] The technical result achieved by the invention consists in ensuring the possibility of using the entire volume of synthesis gas on the process line for the synthesis of ammonia.

[0015] The technical result is achieved by a method for producing ammonia from natural gas, which consists in the fact that natural gas and steam are heated and subjected to primary reforming on a process line, the obtained converted gas is subjected to secondary reforming using a steam-air-oxygen mixture, after which the obtained converted gas is sent for carbon monoxide conversion, the obtained synthesis gas is purified from carbon dioxide, then the purified synthesis gas is methanated, after which ammonia is synthesized, and the purge gas from the ammonia synthesis process is used as fuel for heating natural gas and steam, wherein according to the invention, natural gas and steam are heated and subjected to primary reforming on a fuel line, the obtained converted gas is subjected to secondary reforming using a steam-air-oxygen mixture, after which the obtained converted gas is sent for carbon monoxide conversion,the resulting synthesis gas is purified from carbon dioxide, then the pressure of the purified synthesis gas is reduced and part of it is used as fuel for heating natural gas and steam on the fuel line and another part of it together with the purge gas as fuel for heating natural gas and steam on the process line. In addition, it is advisable to carry out primary reforming on the process line using the heat of the converted gas leaving after secondary reforming.

[0016] It is also advisable to carry out primary reforming on the fuel line using the heat of the converted gas leaving after secondary reforming.

[0017] In addition, it is preferable to also use the purified synthesis gas after pressure reduction as fuel for generating steam, which is used in the process and fuel lines.

[0018] Thus, the technical result is achieved due to the fact that the entire volume of synthesis gas produced on the process line is directed to the synthesis of ammonia, and low-carbon fuel, which ensures a reduction in CO2 emissions, is produced on a separate fuel line.

[0019] List of drawings

[0020] Fig. 1 shows a diagram of the implementation of the proposed method for producing low-carbon ammonia.

[0021] Examples of implementation of the invention

[0022] The method for producing low-carbon ammonia from natural gas, which has received the conventional name “Decarbonized Ammonia-3000” (“AmDek-3000”), is carried out as follows.

[0023] The diagram shown in the drawing represents a separate process line for the synthesis of ammonia and a separate line for the production of a nitrogen-hydrogen mixture for use as fuel for heating process flows - a fuel line.

[0024] Technological line

[0025] Raw natural gas 101 enters the sulfur compound cleaning line 1, where gas purified from undesirable impurities is obtained. Water vapor 103 is added to purified natural gas 102 and sent to the fire heater 2. The steam-gas mixture 107 heated to the temperature of the start of the steam reforming reaction enters the reaction tubes of the primary reforming reactor 3, where the primary reforming process takes place due to the heat of the converted gas 110 leaving the secondary reforming reactor 4. Then the converted gas 108 enters the secondary reforming reactor 4.

[0026] Atmospheric air 106 enters the process air compression line 5, water vapor 104 and oxygen 105 are added to the compressed air and sent to the fire heater 2. The heated steam-air-oxygen mixture 109 enters the secondary reforming reactor 4, where converted gas is obtained, containing mainly nitrogen, hydrogen, water vapor, carbon monoxide and carbon dioxide.

[0027] The converted gas stream 111 enters the carbon monoxide conversion line 6, where in the presence of water vapor, catalytic conversion of carbon monoxide into carbon dioxide occurs with the formation of hydrogen. The synthesis gas 112 containing carbon dioxide obtained as a result of the conversion is sent to the stage of purification from carbon dioxide 7 by the amine purification method. Carbon dioxide 113 separated from the synthesis gas is sent for disposal.

[0028] Carbon dioxide-depleted synthesis gas 114 is sent to methanation reactor 8, where catalytic conversion of traces of carbon dioxide remaining after carbon dioxide purification stage 7 occurs. Next, synthesis gas stream 115 enters ammonia synthesis line 9, where product ammonia 116 is produced. Purge gas 117 from ammonia synthesis stage 9, containing mainly nitrogen, hydrogen and ammonia, is added to carbon-free fuel 118 from expander unit of fuel line 17. Flue gases 119 from fire heater 2, containing mainly nitrogen and water vapor, are sent to the atmosphere.

[0029] Fuel line

[0030] Raw natural gas 120 enters the desulfurization line 10, where gas purified from undesirable impurities is obtained. Water vapor 122 is added to purified natural gas 121 and sent to the fire heater 11. The steam-gas mixture 123 heated to the temperature of the start of the steam reforming reaction enters the reaction tubes of the primary reforming reactor 12, where the primary reforming process takes place due to the heat of the converted gas 126 leaving the secondary reforming reactor 13. Then the converted gas 124 enters the secondary reforming reactor 13.

[0031] Atmospheric air 127 enters the process air compression line 14, water vapor 128 and oxygen 129 are added to the compressed air and sent to the fire heater 11. The heated steam-air-oxygen mixture 125 enters the secondary reforming reactor 13, where converted gas is obtained, containing mainly nitrogen, hydrogen, water vapor, carbon monoxide and carbon dioxide.

[0032] The converted gas stream 130 enters the carbon monoxide conversion line 15, where in the presence of water vapor, catalytic conversion of carbon monoxide into carbon dioxide occurs with the formation of hydrogen. The synthesis gas 131 containing carbon dioxide obtained as a result of the conversion is sent to the stage of purification from carbon dioxide 16 by the amine purification method. The carbon dioxide 132 separated from the synthesis gas is sent for utilization. The synthesis gas 133 depleted in carbon dioxide, containing mainly nitrogen and hydrogen, enters the pressure reduction unit 17, which can be a throttle or an expander unit, where the energy of excess gas pressure is used to generate cold and electricity. The resulting low-pressure synthesis gas is intended for use as fuel.In the proposed scheme, fuel synthesis gas is sent to the fire heater 2 of the process line - flow 118, to the fire heater 11 of the fuel line - flow 134 and to the fire heater of the steam generation unit 18 - flow 135. Flue gases 136 from the fire heater 11, containing mainly nitrogen and water vapor, are sent to the atmosphere.

[0033] Steam from steam generation unit 18 is directed into the process line - streams 103, 104; into the fuel line - streams 122, 128, and also, if necessary, to third-party consumers - stream 137. Flue gases 138 from the fire heater of steam generation unit 18, containing mainly nitrogen and water vapor, are directed into the atmosphere.

[0034] The extraction of carbon dioxide 113, 132 for subsequent utilization, together with the absence of carbon dioxide in the flue gases, ensures a low level of CO2 emissions, amounting to less than 0.2 t / t (the number of tons of CO2 calculated per 1 ton of ammonia produced), which corresponds to a CO2 capture level of more than 90%.

[0035] The present method for producing low-carbon ammonia can be used in methods and installations intended for producing hydrogen, urea, ammonium sulfate, ammonium chloride, ammonium nitrate, nitric acid and other derivatives of synthetic ammonia.

Claims

Invention formula 1. A method for producing ammonia from natural gas, which consists in the fact that natural gas and steam are heated and subjected to primary reforming in a process line, the resulting converted gas is subjected to secondary reforming using a steam-air-oxygen mixture, after which the resulting converted gas is sent to the conversion of carbon dioxide, the resulting synthesis gas is purified to remove carbon dioxide, then the purified synthesis gas is methanated, after which ammonia is synthesized, and the purge gas from the ammonia synthesis process is used as fuel for heating natural gas and steam, characterized in that natural gas and steam are heated and subjected to primary reforming in a fuel line, the resulting converted gas is subjected to secondary reforming using a steam-air-oxygen mixture, after which the resulting converted gas is sent to the conversion of carbon dioxide,the resulting synthesis gas is purified to remove carbon dioxide, then the pressure of the purified synthesis gas is reduced and part of it is used as fuel for heating natural gas and steam on the fuel line and the other part of it together with the purge gas is used as fuel for heating natural gas and steam on the process line.

2. The method according to paragraph 1, characterized in that on the process line, primary reforming is carried out using the heat of the converted gas exiting after secondary reforming.

3. The method according to paragraph 1, characterized in that primary reforming on the fuel line is carried out using the heat of the converted gas exiting after secondary reforming.

4. The method according to paragraph 1, characterized in that after reducing the pressure of the purified synthesis gas, it is also used as fuel for generating steam, which is used on the process and fuel lines.

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