Ammonia Cracking: A method for producing low-carbon hydrogen from ammonia using "Ammonia Cracking Technology-3000," and a plant for implementing the same.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- PUBLICHNOE AKTSIONERNOE OBSHCHESTVO NOVATEK
- Filing Date
- 2024-01-12
- Publication Date
- 2026-05-29
Smart Images
Figure 2026517434000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a technique for generating low-carbon hydrogen from ammonia by ammonia cracking for further use of low-carbon hydrogen as a carbon-neutral fuel or for compression of low-carbon hydrogen for delivery to end-users via a mainline fuel system.
Background Art
[0002] There are many well-known methods for generating hydrogen by ammonia cracking, which involve the use of fuels that generate carbon dioxide during combustion.
[0003] The drawback of such methods and plants is that carbon dioxide is released into the atmosphere when ammonia is cracked using a fuel that generates carbon dioxide during combustion.
[0004] There are also methods for generating low-carbon hydrogen by ammonia cracking using ammonia and mixtures of nitrogen and hydrogen as fuels that do not generate any carbon dioxide during combustion (International Publication No. 2021 / 257944 with a publication date of December 23, 2021, International Publication No. 2022 / 265648 with a publication date of December 22, 2022, International Publication No. 2022 / 265651 with a publication date of December 22, 2022, Chinese Patent Application Publication No. 111137853 with a publication date of May 12, 2020, Chinese Patent Application Publication No. 111957270 with a publication date of November 20, 2020).
[0005] The method most closely related to the proposed method is characterized by the production of low-carbon hydrogen by ammonia cracking, in which ammonia cracking is performed by separating liquid ammonia feedstock into ammonia fuel and ammonia feedstock, pressurizing them with two pumps, and then superheating the liquid ammonia feedstock to over 250°C by heating and evaporating it in a heat exchanger and recovering waste heat from the flue gas and mixture of nitrogen and hydrogen (NHM), and then feeding the superheated gaseous ammonia to an ammonia cracking reactor, in which ammonia is decomposed into nitrogen and hydrogen in an endothermic reaction, with heat from the combustion of carbon-neutral fuel gas (a mixture of ammonia fuel and flue gas from a pressure swing adsorption (PSA) unit) being used as an energy source for the normal occurrence of the endothermic reaction. Downstream of the reactor, a mixture of nitrogen and hydrogen with a residual ammonia content is supplied (preferably via an air cooler) to a PSA unit to recover hydrogen, while the flue gas downstream of the heat exchanger is discharged. Although a single heat exchanger is shown in the drawing, a series of heat exchangers would be used in practical applications. Different heat sources, such as water or ambient air, can be used for preheating and evaporation of the compressed ammonia feedstock (International Publication No. 2021 / 265649, published December 22, 2022).
[0006] A plant for implementing the method described above, which is closest to the proposed plant, includes a heat exchanger (or a series of heat exchangers), an ammonia cracking reactor, an ammonia feedstock line, an ammonia fuel line, an air supply line, a nitrogen-hydrogen mixture (NHM) line, and a flue gas line. The ammonia feedstock line connects in series a liquid ammonia feedstock pump, the first heat exchange space of the heat exchanger (or a series of heat exchangers), and a conduit for supplying superheated ammonia to the reactor. The ammonia fuel line connects in series a liquid ammonia fuel pump, the second heat exchange space of the heat exchanger, a mixer, and a reactor furnace. The air supply line includes a compressor, the third heat exchange space of the heat exchanger, and a reactor furnace. The NHM line includes the fourth heat exchange space of the heat exchanger, an air cooler, a pressure swing adsorption (PSA) unit, an off-gas conduit for gases that are not the target products of the PSA unit, the fifth heat exchange space of the heat exchanger, a mixer, and a reactor furnace. A mixer-free option is available in which each component is supplied to the reactor as a separate flow for combustion. The PSA unit has connections to a hydrogen discharge line and a flue gas line, and comprises a sixth heat exchange space of the heat exchanger and a flue gas discharge conduit (International Publication No. 2021 / 265649, published December 22, 2022).
[0007] Known methods and plants are characterized by the following drawbacks: Because the flue gas cooled in a multiflow heat exchanger is very hot, the use of a flue gas extractor to send the flue gas for further processing results in higher energy consumption because the volumetric flow rate of the flue gas is higher when the flue gas is hot. In other words, at a constant mass flow rate, the hotter the gas, the larger the volume it occupies and therefore the more energy is required to move the gas.
[0008] Furthermore, the use of multi-flow heat exchangers, which are characterized by phase transitions (evaporation of ammonia feedstock and ammonia fuel), can cause high vibration loads and compromise the overall process reliability. [Prior art documents] [Patent Documents]
[0009] [Patent Document 1] International Publication No. 2021 / 257944 [Patent Document 2] International Publication No. 2022 / 265648 [Patent Document 3] International Publication No. 2021 / 265651 [Patent Document 4] Chinese Patent Application Publication No. 111137853 Specification [Patent Document 5] Chinese Patent Application Publication No. 111957270 Specification [Patent Document 6] International Publication No. 2021 / 265649 [Overview of the project] [Problems that the invention aims to solve]
[0010] The technical challenges to be addressed by the proposed low-carbon hydrogen technology are improving the overall efficiency of the low-carbon hydrogen process and enhancing its ability to produce distilled water as a by-product. [Means for solving the problem]
[0011] The technical problem is a method for producing hydrogen from ammonia, the method comprising pressurizing liquid ammonia, heating and evaporating the liquid ammonia feedstock, superheating the gaseous ammonia feedstock supplied to the ammonia cracking reactor, cooling the mixture of nitrogen and hydrogen produced from ammonia cracking and recovering hydrogen from the mixture, heating and evaporating ammonia fuel, superheating the gaseous ammonia fuel, mixing it with tail gas produced from hydrogen recovery, supplying the resulting fuel gas to the ammonia cracking reactor for combustion along with high-temperature air, and increasing the temperature of the ammonia feedstock, air, and fuel gas using heat from the flue gas. According to the present invention, the ammonia cracking reactor is paired with a heat-reclaiming equipment (HRE) that utilizes heat from the flue gas, the temperature of the liquid ammonia feedstock is increased upstream of the HRE flue gas outlet using heat from the flue gas, then the used flue gas is pressurized and cooled, condensed distilled water is extracted from the flue gas, and the dehydrated flue gas is discharged.
[0012] Furthermore, the ammonia supply material is evaporated and superheated in each recovery heat exchanger that utilizes heat from a mixture of nitrogen and hydrogen, and then the gaseous ammonia supply material is heated using heat from the flue gas.
[0013] Furthermore, the ammonia fuel is evaporated and superheated in each of the other recovery heat exchangers using a heating medium that utilizes heat from the flue gas.
[0014] Hydrogen recovery from a mixture of nitrogen and hydrogen can be achieved by pressure swing adsorption.
[0015] Another option for hydrogen recovery is membrane extraction.
[0016] A preferred option is the separation of the ammonia flow into liquid ammonia feedstock and liquid ammonia fuel after pressurizing the liquid ammonia.
[0017] It is also desirable to neutralize nitrogen oxides by adding a portion of the gaseous ammonia fuel to the flue gas supplied to the shell side of the HRE.
[0018] The technical challenge is a plant for producing hydrogen from ammonia, comprising a liquid ammonia pump, an ammonia feedstock heating line, an ammonia fuel heating line, an ammonia cracking reactor paired with a heat regeneration unit (HRE), an air heating line, and a purification line, wherein the ammonia feedstock heating line includes an HRE liquid ammonia feedstock heating coil, a first recovery heat exchanger, i.e., an ammonia feedstock evaporator, a second recovery heat exchanger, i.e., an ammonia feedstock superheater, and an HRE gaseous ammonia feedstock heating coil, the ammonia feedstock heating line is connected to the reaction tube of the ammonia cracking reactor, and the ammonia fuel heating line includes a third recovery heat exchanger, i.e., a liquid ammonia fuel heater, and a fourth recovery heat exchanger, i.e., an ammonia fuel evaporator. The plant is resolved by an ammonia fuel heating line, which is connected to an HRE gaseous ammonia fuel heating coil connected to an ammonia cracking reactor burner, the outlet of which is connected to a second recovery heat exchanger and a first recovery heat exchanger, and a purification line, which includes at least one air cooler and a hydrogen recovery unit, the hydrogen recovery unit having a tail gas outlet connected to the ammonia fuel heating line upstream of the HRE gaseous ammonia fuel heating coil, the air heating line includes an air feeder and an HRE air heating coil connected to an ammonia cracking reactor burner, and furthermore, an HRE liquid ammonia feed material heating coil located upstream of the HRE fuel gas outlet, the HRE fuel gas outlet being connected in series to a flue gas extractor, at least one other air cooler, and a distilled water separator.
[0019] Furthermore, a third recuperative heat exchanger, namely a liquid ammonia fuel heater, and a fourth recuperative heat exchanger, namely an ammonia fuel evaporator, are connected in parallel to the heating medium circuit, which includes an HRE heating medium heating coil connected to these heat exchangers and a heating medium circulation pump.
[0020] A shell and tube heat exchanger is preferred as the recuperative heat exchanger.
[0021] One option for the hydrogen recovery unit is a pressure swing adsorption unit.
[0022] Another option for the hydrogen recovery unit is a membrane hydrogen recovery unit.
[0023] A parallel connection to the liquid ammonia pump outlet is desirable for the ammonia feedstock and ammonia fuel heating lines.
[0024] A flue gas branch line connected to the shell side of the HRE is also desirable for the ammonia fuel heating line.
[0025] The technical result of the proposed method and plant is to enable the extraction of distilled water as a by - product from the flue gas by cooling the outgoing flue gas to approximately +60°C in the heat regeneration facility unit.
Brief Description of the Drawings
[0026] [Figure 1] It is a diagram showing the layout of the proposed plant.
Modes for Carrying Out the Invention
[0027] A plant for producing low - carbon hydrogen includes a liquid ammonia feedstock heating line, an ammonia cracking reactor paired with an HRE (heat regeneration facility unit), an ammonia fuel heating line, an air heating line, a purification line, and a water condensation line.
[0028] The liquid ammonia supply raw material heating line includes a liquid ammonia pump 1, an HRE coil 12, a recovery heat exchanger (liquid ammonia evaporator) 2, a recovery heat exchanger (gas ammonia superheater) 3, and an HRE coil 8 connected in series.
[0029] The ammonia cracking reactor 4, having a reaction tube 5, is equipped with a nitrogen-hydrogen burner 6. The air heating line includes a blower 7 and an HRE coil 9 connected to the burner 6. The HRE is connected to the flue gas outlet of the reactor 4 and, upstream of the HRE flue gas outlet, houses a gaseous ammonia heating coil 8, an ammonia fuel heating coil 9, an air heating coil 10, a heating medium heating coil 11, and a liquid ammonia heating coil 12 in a series layout.
[0030] The ammonia fuel heating line connects a third recovery heat exchanger (liquid ammonia fuel heater) 13 and a fourth recovery heat exchanger (liquid ammonia fuel evaporator) 14, as well as a pressure reducer 15, in series. The heater 13 and evaporator 14 are part of a heating medium (preferably oil) circuit, which includes an HRE coil 11 connected to the heater 13 and evaporator 14, and a heating medium circulation pump 16.
[0031] The purification line includes an air cooler(s) 17, a pressure swing adsorption (PSA) hydrogen recovery unit 18, and an off-gas depressurizer 19 for tail gases that are not the target product of the PSA unit 18. The purification line and the ammonia fuel heating line form a single line connected to the HRE coil 9. A compressor 23 is an additional design option for compressing low-carbon hydrogen downstream of the PSA unit 18 when low-carbon hydrogen needs to be delivered over long distances.
[0032] As an alternative plant design, the refining line includes a downstream air cooler(s)17 for releasing compression heat, at least one nitrogen-hydrogen compressor and at least one air cooler, and a membrane hydrogen recovery unit (not shown in the drawing) as a replacement for the PSA unit, which also eliminates the need for a low-carbon hydrogen compressor 23 by enabling the production of market-grade high-pressure low-carbon hydrogen.
[0033] Prior to contact with the refining line, the ammonia fuel heating line has a branch pipeline connected to the shell side of the HRE.
[0034] The water condensation line includes one or more air coolers 21 connected to the HRE outlet and a separator 22 for bringing in distilled water and dehydrated flue gas.
[0035] The proposed drive unit for the liquid ammonia pump 1, the heating medium circulation pump 16, and the low-carbon hydrogen compressor 23 is an electric motor powered by a wind power plant, but this is not the only drive option. Any carbon-neutral or "green" power source or gas turbine engine can serve as the power source.
[0036] The method for producing low-carbon hydrogen from ammonia is carried out as follows:
[0037] Liquid ammonia is supplied to liquid ammonia pump 1, where it is pressurized to approximately 2.5-4.0 MPa and then separated into ammonia fuel and ammonia feedstock in ratios of 5-10% and 90-95%, respectively. Next, the heat recovery unit coil 12 uses the heat recovered from the flue gas to heat the liquid ammonia feedstock to just below its boiling point at pressures 2-10°C below the ammonia boiling point. Then, the liquid ammonia feedstock is evaporated in evaporator 2 and superheated by 2-10°C using the heat from the nitrogen-hydrogen mixture. After that, the gaseous ammonia feedstock is superheated to approximately +360°C in superheater 3 using the heat from the nitrogen-hydrogen mixture (NHM). Next, superheated gaseous ammonia is supplied to the HRE coil 8, heated to approximately +400°C, and sent to the reaction tube 5 of the ammonia cracking reactor 4, where the ammonia is decomposed into nitrogen and hydrogen in an endothermic reaction at approximately 2-3.5 MPa and approximately +450-1,000°C. For the normal occurrence of this reaction, heat from the combustion of fuel gas is used as the energy source. Suitable catalysts are selected from, but are not limited to, Ru / Al2O3, Ni / Al2O3, Ru / CeO2, and Ni / CeO2.
[0038] Downstream of the ammonia cracking reactor 4, a mixture of nitrogen and hydrogen having a residual ammonia content of approximately 0.9 mol% at approximately 2 to 3.5 MPa and approximately +450 to 1,000°C is supplied to the recovery heat exchanger system (superheater 3, evaporator 2) and the air cooler 17. In the air cooler 17, the mixture is cooled to approximately +35°C by heat transfer to the ammonia feed material and ambient air, and then sent to the PSA unit 18 (or membrane hydrogen recovery unit) for the recovery of hydrogen with a purity of 99.97 mass%.
[0039] Tail gas from the PSA unit 18, containing nitrogen, hydrogen, and ammonia, is reduced to approximately 0.16 MPaG with the help of a pressure reducer 19 and sent for mixing with gaseous ammonia fuel upstream of the HRE coil 9. Liquid ammonia fuel is supplied to a heat exchanger 13, where it is heated to just below the ammonia boiling point at each pressure by an oil-type heating medium, then evaporated in an evaporator 14, and superheated by 2 to 10°C by an oil-type heating medium, coming out at a temperature of approximately +76°C. The superheated ammonia fuel is then gradually reduced to 0.16 MPaG with the help of a pressure reducer 15 and mixed with tail gas from the PSA unit 18 upstream of the HRE coil 9. As the fuel gas passes through the coil 9, it is heated to approximately +600°C and supplied to a burner 6 to release the energy required for the normal occurrence of the endothermic ammonia cracking reaction.
[0040] The blower 7 supplies ambient air to the HRE coil 10 to heat it to approximately +300°C. The air is then sent to the burner 6 for the combustion of a carbon-neutral fuel containing (but not limited to) ammonia, nitrogen, hydrogen, and trace amounts of water.
[0041] A heating medium (e.g., oil) at approximately 50 kPaG and approximately +190°C is supplied to the heating medium circulation pump 16, pressurized to the heating medium circuit operating pressure, and then simultaneously sent to the heater 13 and the evaporator 14 in a ratio of approximately 34% / 66%, where it is cooled to approximately +170°C, and then sent to the HRE coil 11 for reheating to approximately +190°C.
[0042] Flue gas at approximately +450 to +1,000°C from ammonia cracking reactor 4 is supplied to the shell side of the HRE, cooled to approximately +60°C by passing through coil 8, then coil 9, then coil 10, then coil 11, then coil 12, and with the help of flue gas extractor 20, is sent to air cooler 21 for water condensation, after which the condensed distilled water is extracted in separator 22. Downstream of separator 22, flue gas consisting of nitrogen, residual water, and air impurities is discharged, while trace amounts of NOx are neutralized by supplying gaseous ammonia fuel to the shell side of the HRE, thus making the process carbon neutral or low carbon.
[0043] Unlike the prototype, condensation in the air cooler 21 utilizes the flue gas to produce distilled water as a byproduct, which is a result of the combustion of carbon-neutral fuel. The higher the heat transfer from the flue gas to the liquid ammonia feedstock in the HRE coil 12, where the flue gas cools to approximately +60°C, the more it is possible to produce distilled water as a byproduct by pressurizing the flue gas in the flue gas extractor and condensing water from the flue gas through ambient cooling. In the prototype, the temperature becomes higher as a result of heat recovery, which means that using a flue gas extractor with higher inlet and outlet temperatures results in higher energy consumption because the volumetric flow rate of the flue gas is higher when the flue gas is at a higher temperature. In other words, at a constant mass flow rate, the higher the temperature of the gas, the larger the volume it occupies and therefore the more energy is required to move the gas. Unlike the prototype, the proposed method and plant process for liquid ammonia is performed in stages: the ammonia feedstock is heated in an HRE coil 12 using heat from the flue gas, then evaporated in a separate heat exchanger 2 using heat from a nitrogen-hydrogen mixture, superheated in a heat exchanger 3 using heat from the nitrogen-hydrogen mixture, and heated to just above the reaction point temperature in an HRE coil 8. The evaporation of the ammonia feedstock in a separate heat exchanger transferring heat from the nitrogen-hydrogen mixture means that a simple shell and tube design with an evaporation space can be used, the process design is less hardware-intensive, and there is no need for a multi-flow heat exchanger featuring a phase transition, which can cause high vibration loads and compromise the overall process reliability. The simple shell and tube design also allows for process line extensions, which are not possible with the multi-flow heat exchanger seen in the prototype, and are created by installing the same number of exchangers in parallel as required for such extensions.Furthermore, by using a nitrogen-hydrogen stream to evaporate and superheat the ammonia feedstock, more heat can be recovered from the flue gas. This heat then translates into increased energy efficiency for the plant as the ammonia feedstock is heated to just below its reaction point temperature. This means that less heat is consumed in the ammonia feedstock to reach its reaction point temperature, thus reducing overall ammonia fuel consumption.
[0044] The proposed design also differs in that the ammonia fuel is heated in a separate heating medium (preferably oil-type) circuit, and therefore, the use of a system of recovery heat exchangers connected separately in series for the ammonia feedstock flow and the ammonia fuel flow allows for lower unit capacities of individual equipment items on the one hand, and higher overall plant capacities on the other hand, so the method and plant are no longer limited to small-scale applications but can be used for large-scale applications.
Claims
1. A method for producing hydrogen from ammonia, the method comprising pressurizing liquid ammonia, heating and evaporating liquid ammonia feedstock, superheating gaseous ammonia feedstock supplied to an ammonia cracking reactor, cooling a mixture of nitrogen and hydrogen produced from ammonia cracking and recovering hydrogen from the mixture of nitrogen and hydrogen, heating and evaporating liquid ammonia fuel, superheating gaseous ammonia fuel, mixing it with tail gas produced from the recovery of hydrogen, supplying the resulting fuel gas together with high-temperature air to the ammonia cracking reactor for combustion, and increasing the temperature of the ammonia feedstock, air, and fuel gas using heat from the flue gas, wherein the ammonia cracking reactor is paired with a heat regeneration unit (HRE) that utilizes the heat from the flue gas, increasing the temperature of the liquid ammonia feedstock upstream of the HRE flue gas outlet using the heat from the flue gas, then pressurizing and cooling the utilized flue gas, extracting condensed distilled water from the flue gas, and discharging the dehydrated flue gas.
2. The method according to claim 1, characterized in that the ammonia supply raw material is evaporated and superheated in each recovery heat exchanger using the heat from the mixture of nitrogen and hydrogen, and then the gaseous ammonia raw material is heated using the heat from the flue gas.
3. The method according to claim 1, characterized in that the ammonia fuel is evaporated and superheated in each of the other recovery heat exchangers using a heating medium that utilizes the heat from the flue gas.
4. The method according to claim 1, characterized in that the recovery of hydrogen from the mixture of nitrogen and hydrogen is achieved by pressure swing adsorption.
5. The method according to claim 1, characterized in that the recovery of hydrogen is achieved by membrane recovery.
6. The method according to claim 1, wherein, after pressurizing the liquid ammonia, the ammonia flow is separated into a liquid ammonia supply flow and a liquid ammonia fuel flow.
7. The method according to claim 1, characterized in that a portion of the gaseous ammonia fuel is added to the flue gas supplied to the shell side of the HRE to neutralize nitrogen oxides.
8. A plant for producing hydrogen from ammonia, comprising a liquid ammonia pump, an ammonia feedstock heating line, an ammonia fuel heating line, an ammonia cracking reactor paired with a heat regeneration unit (HRE), an air heating line, and a purification line, wherein the ammonia feedstock heating line includes an HRE liquid ammonia feedstock heating coil, a first recovery heat exchanger, i.e., an ammonia feedstock evaporator, a second recovery heat exchanger, i.e., an ammonia feedstock superheater, and an HRE gaseous ammonia feedstock heating coil, the ammonia feedstock heating line is connected to the reaction tube of the ammonia cracking reactor, and the ammonia fuel heating line includes a third recovery heat exchanger, i.e., a liquid ammonia fuel heater, and a fourth recovery heat exchanger, i.e., an ammonia fuel evaporator, and the ammonia A plant comprising a fuel heating line connected to an HRE gaseous ammonia fuel heating coil connected to an ammonia cracking reactor burner, the outlet of the reaction tube connected to the second recovery heat exchanger and the first recovery heat exchanger, and the purification line, the purification line comprising at least one air cooler and a hydrogen recovery unit, the hydrogen recovery unit having a tail gas outlet connected to the ammonia fuel heating line upstream of the HRE gaseous ammonia fuel heating coil, the air heating line comprising an air supplyer and an HRE air heating coil connected to the ammonia cracking reactor burner, and further comprising an HRE liquid ammonia feedstock heating coil located upstream of the HRE fuel gas outlet, at which the HRE fuel gas outlet is connected in series to a flue gas extractor, at least one other air cooler, and a distilled water separator.
9. The plant according to claim 8, wherein the third recovery heat exchanger, i.e., a liquid ammonia fuel heater, and the fourth recovery heat exchanger, i.e., an ammonia fuel evaporator, are connected in parallel to a heating medium circuit, the heating medium circuit including an HRE heating medium heating coil connected to these heat exchangers and a heating medium circulation pump.
10. The plant according to claim 8, wherein the recovery heat exchanger is of shell and tube type.
11. The plant according to claim 8, wherein the hydrogen recovery unit is a pressure swing adsorption unit.
12. The plant according to claim 8, wherein the hydrogen recovery unit is a membrane hydrogen recovery unit.
13. The plant according to claim 8, wherein the ammonia supply raw material heating line and the ammonia fuel heating line are connected in parallel to the outlet of the liquid ammonia pump.
14. The plant according to claim 8, wherein the ammonia fuel heating line has a flue gas branch pipeline connected to the shell side of the HRE.