Autothermal ammonia decomposition process
The process addresses the inefficiencies of autothermal ammonia decomposition by using non-catalytic partial oxidation and condensation to remove unconverted ammonia, enhancing safety and efficiency in hydrogen production.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- LAIR LIQUIDE SA POUR LETUDE & LEXPLOITATION DES PROCEDES GEORGES CLAUDE
- Filing Date
- 2024-07-11
- Publication Date
- 2026-07-21
AI Technical Summary
Existing autothermal ammonia decomposition processes require significant heat and energy, leading to unconverted ammonia in the effluent gas, which can be toxic and harmful to downstream equipment and applications like fuel cells.
A process involving non-catalytic partial oxidation of ammonia with an oxidant gas to generate steam, followed by endothermic decomposition and condensation to remove unconverted ammonia through absorption, using moderator vapor to control ammonia and nitrogen oxide levels.
The process effectively reduces unconverted ammonia in the effluent gas to almost zero, minimizing toxicity and equipment harm, while optimizing energy use and product purity.
Smart Images
Figure 2026524164000001_ABST
Abstract
Description
Technical Field
[0001] [1] The field of the present invention is the field of processes for producing hydrogen by the endothermic decomposition reaction of an ammonia feed stream.
Background Art
[0002] [2] The production of an effluent gas containing hydrogen and nitrogen by the endothermic decomposition reaction of an ammonia feed stream can generally be carried out at a high temperature of 500°C to 850°C in a catalytic reactor. Such units typically comprise a metal shell, a catalyst, and a heat source for providing heat to the endothermic reaction. In the autothermal ammonia decomposition process, the heat is provided directly by the partial oxidation of a portion of the reactor feed. These autothermal processes enable large-scale hydrogen production from ammonia. However, this process requires a large amount of heat and energy, and an unconverted portion of the ammonia feed stream still remains in the effluent gas. This unconverted ammonia can be toxic for some uses of the produced hydrogen, such as in fuel cells, and can be harmful to downstream equipment, such as a purification / separation unit for the effluent gas containing nitrogen and hydrogen.
Summary of the Invention
[0003] [3] The object of the present invention is to overcome these problems and provide a process for efficiently removing unconverted ammonia after the ammonia decomposition reaction.
[0004] [4] For this purpose, the present invention proposes a process for producing hydrogen from an ammonia feed stream, the process comprising: - subjecting the ammonia feed stream to non-catalytic partial oxidation with an oxidant gas, thereby generating steam from the partial oxidation, wherein the remaining amount of ammonia is not oxidized; - subjecting a portion of the remaining amount of ammonia to endothermic decomposition conversion, thereby generating a decomposition gas containing hydrogen, nitrogen, and some unconverted ammonia; - A step of mixing the decomposition gas with the vapor produced from partial oxidation, thereby obtaining the effluent gas, - The process comprises a step of condensing the vapor produced from partial oxidation (condensation step), thereby removing at least a portion of the unconverted ammonia from the effluent gas by absorption.
[0005] [5] By absorbing the unconverted ammonia into the water produced as vapor from the partial oxidation, the need to introduce additional water downstream of the endothermic decomposition conversion is reduced. The resulting effluent gas contains almost no unconverted ammonia.
[0006] [6] In one embodiment, the oxidizing gas is an oxygen-containing gas, such as air, an oxygen-containing gas having more than 21% oxygen, or pure oxygen.
[0007] [7] In one embodiment, the endothermic decomposition conversion is carried out by contact with a catalyst, such as a nickel-containing catalyst.
[0008] [8] In one embodiment, the non-catalytic partial oxidation and endothermic decomposition transformations occur in a single reaction vessel. The endothermic decomposition transformation, which occurs by contact with a catalyst, typically takes place in the catalytic reaction zone of the reaction vessel downstream of the non-catalytic partial oxidation.
[0009] [9] In one embodiment, the process comprises the steps of providing a liquid ammonia feedstock and vaporizing the liquid ammonia feedstock to obtain a gaseous vaporized ammonia feedstock, which is an ammonia feedstock.
[0010]
[10] In one embodiment, the process comprises a step of preheating an ammonia feed stream, in particular a vaporized ammonia feed, at a feed preheating temperature before non-catalytic partial oxidation. In particular, the feed preheating temperature is adjusted to control the amount of vapor produced from the partial oxidation.
[0011]
[11] In one embodiment, the reaction vessel is equipped with a burner, and non-catalytic partial oxidation of the ammonia feed stream is carried out by partially burning the ammonia feed stream in particular in gaseous form with the burner. In particular, the burner is equipped with a burner nozzle, and the oxidizing gas is introduced into the reaction vessel from the burner nozzle.
[0012]
[12] In one embodiment, the process comprises the steps of introducing moderator steam into the reaction vessel to protect the burner nozzle from overheating, and mixing the moderator steam with the exhaust gas. Specifically, the oxidizing gas is introduced centrally from the burner nozzle, and the moderator steam is introduced concentrically around the oxidizing gas from the burner nozzle.
[0013]
[13] In one embodiment, moderator vapor is mixed in the effluent with vapor produced from partial oxidation to obtain a water steam fraction of the effluent, which is condensed in a condensation step to remove at least a portion of the unconverted ammonia from the effluent by absorption.
[0014]
[14] In one embodiment, the process comprises the step of adjusting the amount of vapor produced from partial oxidation or the amount of water vapor fraction in the effluent, thereby adjusting the amount of vapor in the effluent that is available for condensation and removal of unconverted ammonia depending on the amount of unconverted ammonia.
[0015]
[15] In one embodiment, an unconverted ammonia solution containing absorbed unconverted ammonia is produced by condensing the vapor generated from partial oxidation, or by condensing the water vapor fraction.
[0016]
[16] In one embodiment, the process comprises the step of adjusting the amount of moderator vapor introduced into the reaction vessel to control the concentration of unconverted ammonia in an unconverted ammonia solution. In particular, the process comprises the steps of measuring the concentration of unconverted ammonia in an unconverted ammonia solution, comparing the measured concentration to a predetermined first threshold for the unconverted ammonia concentration, and increasing the amount of moderator vapor introduced into the reaction vessel if the measured concentration exceeds the first threshold. In particular, the process comprises the steps of comparing the measured concentration to a predetermined second threshold for the unconverted ammonia concentration, and decreasing the amount of moderator vapor introduced into the reaction vessel if the measured concentration falls below the second threshold. The first and second thresholds may be the same value.
[0017]
[17] In one embodiment, the process comprises a step of discharging the effluent gas from the reaction vessel before condensing the vapor produced from partial oxidation or before condensing the water vapor fraction.
[0018]
[18] In one embodiment, non-catalytic partial oxidation of an ammonia feedstream generates nitrogen oxides mixed in the effluent gas, and the process comprises the step of adjusting the amount of moderator vapor introduced into the reaction vessel to control the amount of nitrogen oxides in the effluent gas. In particular, the process comprises the steps of measuring the concentration of nitrogen oxides in the effluent gas, in particular in the discharged effluent gas; comparing the measured concentration to a predetermined first threshold of nitrogen oxide concentration; and increasing the amount of moderator vapor introduced into the reaction vessel if the measured concentration exceeds the first threshold. In particular, the process comprises the steps of comparing the measured concentration to a predetermined second threshold of nitrogen oxide concentration; and decreasing the amount of moderator vapor introduced into the reaction vessel if the measured concentration falls below the second threshold. The first and second thresholds may be the same value.
[0019]
[19] In one embodiment, the effluent, in particular the discharged effluent, has a water content of 10-40%.
[0020]
[20] In one embodiment, the process comprises the steps of providing a secondary ammonia feed stream and performing secondary endothermic decomposition of at least a portion of the secondary ammonia feed stream in a secondary decomposer heated by the discharged effluent gas, thereby producing a secondary effluent gas containing hydrogen and nitrogen. The secondary effluent gas can be combined with the effluent gas discharged from the reaction vessel. The secondary ammonia feed stream can be derived from the ammonia feed stream.
[0021]
[21] In one embodiment, the process comprises the step of endothermally pre-decomposing an ammonia feed stream before non-catalytic partial oxidation, thereby generating a pre-decomposed ammonia feed stream containing hydrogen, nitrogen, and undecomposed ammonia, and the step of non-catalytic partial oxidation of the ammonia feed stream comprising non-catalytic partial oxidation of the pre-decomposed ammonia feed stream. In particular, the endothermally pre-decomposition conversion is carried out in a pre-decomposer heated by the exhaust gas. Alternatively, the endothermally pre-decomposition conversion is carried out in an adiabatic pre-decomposer.
[0022]
[22] In one embodiment, the process comprises a step of pre-cooling the effluent gas before condensing the vapor produced from partial oxidation. In particular, the step of pre-cooling the effluent gas is performed after the step of discharging the effluent gas from the reaction vessel. The step of pre-cooling the effluent gas can be performed by direct water quenching. In particular, direct water quenching can be performed in a quenching vessel directly connected to the reaction vessel.
[0023]
[23] In one embodiment, condensation of the vapor produced from partial oxidation or the water vapor fraction is carried out by cooling the effluent gas, for example by water cooling, by air cooling, by heat exchange between the effluent gas and the liquid ammonia feedstock, by cooling the effluent gas in the reboiler, or by a combination of these options. Direct water quenching may further cool the effluent gas after precooling, thereby condensing the vapor produced from partial oxidation.
[0024]
[24] In one embodiment, the condensation of the vapor generated from partial oxidation or the condensation of the water vapor fraction is carried out in a wash column. In particular, the condensation of the vapor generated from partial oxidation or the condensation of the water vapor fraction is carried out at the top of the wash column. Alternatively, the condensation of the vapor generated from partial oxidation or the condensation of the water vapor fraction is carried out upstream of the wash column.
[0025]
[25] In one embodiment, no additional water is introduced into the wash column. Alternatively, some additional water is introduced into the wash column. The additional water, as a side effect, dilutes the condensed unconverted ammonia solution. In particular, the additional water is sprayed into the wash column.
[0026]
[26] In one embodiment, a part of the unconverted ammonia is removed from the effluent gas by absorption by condensation of the vapor generated from partial oxidation or by condensation of the water vapor fraction, and the remaining part of the unconverted ammonia is removed by further absorption in the wash column. A higher purity of the effluent gas can be achieved. In particular, the further absorption is carried out by recycling a part of the unconverted ammonia solution back into the wash column. In particular, the remaining part of the unconverted ammonia is removed by further absorption by contact with means in the wash column that increase mass transfer and heat transfer, such as random packing, structured packing, at least one bottom sieve or tray.
[0027]
[27] In one embodiment, the unconverted ammonia removed from the effluent gas by absorption is recovered in gaseous form. In particular, the unconverted ammonia removed by absorption is recovered in gaseous form, for example, by distillation of the unconverted ammonia solution after discharging the unconverted ammonia solution from the wash column. The unconverted ammonia recovered in gaseous form can be recycled to the non-catalytic partial oxidation step. In particular, the unconverted ammonia recovered in gaseous form is recycled, for example, after compression, as part of the ammonia feed stream.
[0028]
[28] In one embodiment, at least a portion of the unconverted ammonia solution is vaporized and introduced into the reaction vessel as moderator vapor. In particular, at least a portion of the unconverted ammonia solution is pumped before being vaporized. The unconverted ammonia solution can be vaporized by heat exchange with an external heat source such as flue gas or gas turbine exhaust gas.
[0029]
[29] In one embodiment, a first portion of the unconverted ammonia solution is vaporized and introduced into the reaction vessel as moderator vapor, and the unconverted ammonia of the second portion of the unconverted ammonia solution is recovered in gaseous form, particularly by distillation of the second portion. The unconverted ammonia of the second portion of the unconverted ammonia solution can be recycled to the step of non-catalytic partial oxidation. In particular, the unconverted ammonia recovered in gaseous form is recycled as part of the ammonia feed stream, for example after compression.
[0030]
[30] In one embodiment, the off-gas with little unconverted ammonia is purified, for example by pressure swing adsorption, thereby producing a hydrogen product stream.
Brief Description of the Drawings
[0031] [Figure 1]
[31] It is a schematic diagram of a reaction vessel suitable for implementing the process according to the present invention. [Figure 2] It is an enlarged view of the burner nozzle of the autothermal decomposer of FIG. 1. [Figure 3] It is a schematic diagram of the process in the first modification according to the first embodiment. [Figure 4] It is a schematic diagram of the process in the second modification according to the first embodiment. [Figure 5] It is a schematic diagram of the process according to the second embodiment.
Modes for Carrying Out the Invention
[0032]
[32] The following describes embodiments of the present invention. The scope of the present invention is not limited by these specific embodiments.
[0033]
[33] Figure 1 is a schematic diagram of a reaction vessel 1 for carrying out a self-thermal ammonia decomposition reaction. An ammonia supply stream is supplied from the reaction vessel inlet 1 to the burner section 3 of the reaction vessel 1. A gaseous ammonia supply stream can be obtained by vaporizing the liquid ammonia supply material. The gaseous ammonia supply stream can be preheated to a feed preheating temperature of approximately 100°C.
[0034]
[34] Air is supplied as an oxidizing gas from the nozzle 2 of burner 3. A portion of the ammonia feedstream, along with the oxidizing gas, acts as a reactant for non-catalytic oxidation, that is, the ammonia feedstream is partially oxidized non-catalyzably. Burner 3 is configured as a mixer for the reactants. The combustion reaction produces vapor, i.e., water vapor, nitrogen, and heat. In some cases, the combustion reaction also produces nitrogen oxides (NOx). The remaining ammonia feedstream is not burned. The heat produced acts as a heat input for the endothermic decomposition conversion of a portion of the unburned remaining ammonia. The endothermic decomposition conversion takes place in the catalytic reaction zone 4 of the reaction vessel 1 downstream of burner 3. The catalytic reaction zone 4 contains a catalyst, such as a nickel-containing catalyst. The endothermic decomposition conversion produces a decomposition gas containing hydrogen, nitrogen, and some unconverted ammonia.
[0035]
[35] Figure 2 is a magnified view of nozzle 2. The nozzle comprises two coaxially arranged air supply conduits. The central conduit 6 supplies air to the burner 3 as an oxidizer. The outer conduit, together with the central conduit 6, forms an annular gap 7 for introducing moderator vapor into the reaction vessel. The moderator vapor acts as a shield 8 surrounding the flow of oxidizer gas, thereby causing the oxidizer gas to flow out of the burner nozzle 2 and then come into contact with only a portion of the ammonia supply flow for combustion. The combustion flame is not in the immediate vicinity of the burner nozzle; it is rather "pushed away" by the moderator vapor shield 8.
[0036]
[36] The vapor produced from partial oxidation is mixed with the decomposition gas and moderator vapor in the reaction vessel. The mixture, called the effluent, typically has a water content of 10–40%, for example, about 18%, and about 0.5% unconverted ammonia. The effluent is discharged from reaction vessel 1 at a temperature of about 700°C. The total vapor contained in the effluent consists of the vapor produced from partial oxidation and the moderator vapor, which are mixed together in the effluent as the water vapor fraction of the effluent.
[0037]
[37] The effluent is cooled, and the water vapor fraction of the effluent is condensed into liquid water in a downstream condenser. Some of the unconverted ammonia is absorbed by the liquid water, thereby separating the unconverted ammonia solution from the effluent. The water content of the effluent leaving the condenser is reduced to 0.3%, and its unconverted ammonia content is reduced to 0.09%. Before condensation, the effluent can also be pre-cooled, for example, by direct water quenching, that is, the quenched water comes into direct contact with the effluent and cools it.
[0038]
[38] The unconverted ammonia solution is advantageously vaporized and introduced into the reaction vessel 1 as moderator vapor. In this way, the unconverted ammonia can be recycled to the non-catalytic partial oxidation step much more energy-efficiently and also acts as a protective shield 8 against overheating of the burner nozzle. The vaporized unconverted ammonia solution is immediately at a pressure level suitable for use as moderator vapor. Compression is not required, and there is no need to reduce the pressure of the unconverted ammonia solution.
[0039]
[39] There are several ways of adjusting the amount of vapor produced from partial oxidation or the amount of water vapor fraction in the effluent gas, thereby adjusting the amount of vapor available for condensing and removing unconverted ammonia, depending on that amount.
[0040]
[40] For example, the feed preheating temperature can be adjusted to control the amount of vapor produced from partial oxidation. A higher feed preheating temperature means less vapor is produced from non-catalytic partial oxidation. This is because a higher feed preheating temperature requires less additional heat to heat the feed to the decomposition conversion temperature, which may result in less non-catalytic partial oxidation and therefore less vapor produced by partial oxidation.
[0041]
[41] Alternatively, the amount of moderator vapor introduced into the reaction vessel 1 may be adjusted. This can be done by a suitable controller (not shown) that measures the concentration of unconverted ammonia in the ammonia solution and adjusts the amount of moderator vapor introduced accordingly. This allows the total amount of water vapor fraction available from the process to be adjusted to meet the amount of unconverted ammonia to be removed by absorption in the condensation step, without wasting too much energy during moderator vapor generation. The concentration of unconverted ammonia in the ammonia solution can also be controlled in this way.
[0042]
[42] Since moderator vapor also has the effect of reducing the flame temperature, the formation of nitrogen oxides can be controlled by a suitable controller (not shown) that measures the concentration of nitrogen oxides in the exhaust gas and adjusts the amount of moderator vapor introduced accordingly.
[0043]
[43] In the embodiments of Figures 3 and 4, a secondary ammonia feed stream is derived from the ammonia feed stream and supplied to a secondary cracker. The secondary cracker is a gas-heated cracker (GHC) that is heated by the discharged effluent gas. The secondary cracker produces a secondary effluent gas containing hydrogen and nitrogen. In the embodiments of Figures 3 and 4, the secondary effluent gas is combined with the effluent gas discharged from the reaction vessel 1, and the secondary cracker is arranged in fluid parallel with the reaction vessel.
[0044]
[44] In the embodiment shown in Figure 5, the ammonia feed stream is subjected to a pre-decomposition endothermic reaction, and a portion of the ammonia feed stream is immediately decomposed in the pre-decomposition unit into a pre-decomposed ammonia feed stream containing hydrogen, nitrogen, and undecomposed ammonia before entering the reaction vessel 1. The pre-decomposition unit is a gas-heated pre-decomposition unit (GHC) that is fluidly connected upstream of the reaction vessel 1 and heated by the high-temperature effluent gas discharged from the reaction vessel 1. The hydrogen from the pre-decomposed ammonia feed stream stabilizes the non-catalytic partial oxidation and increases the combustibility within the reaction vessel 1.
[0045]
[45] A gas pyrolysis unit or gas pre-pyrolysis unit may be a heat exchanger having an outlet gas circulation section or a secondary ammonia supply flow circulation section arranged in a heat exchange relationship with an ammonia supply flow. The ammonia supply flow or secondary ammonia supply flow circulation section includes a catalyst to facilitate the endothermic conversion of secondary or pre-pyrolysis. In Figure 3 of the first modification, the secondary outlet gas is combined with the outlet gas upstream of the outlet gas circulation section of the gas pyrolysis unit (GHC). In doing so, the high-temperature secondary outlet gas also contributes to heating the gas pyrolysis unit. The secondary outlet gas may be combined with the outlet gas downstream of the outlet gas circulation section of the gas pyrolysis unit, as shown in Figure 4 of the second modification.
Claims
1. A process for generating hydrogen from an ammonia feed stream, - The ammonia supply stream is subjected to non-catalytic partial oxidation with an oxidizing gas, thereby generating vapor from the non-catalytic partial oxidation, and in this step, the remaining amount of ammonia is not oxidized. - A step of endothermally decomposing a portion of the remaining ammonia to produce a decomposition gas containing hydrogen, nitrogen, and some unconverted ammonia, - A step of mixing the decomposition gas with the vapor produced from the non-catalytic partial oxidation, thereby obtaining an outlet gas, - A step of condensing the vapor generated from the non-catalytic partial oxidation, thereby removing at least a portion of the unconverted ammonia from the effluent gas by absorption, A process that includes [the following].
2. The process according to claim 1, wherein the non-catalytic partial oxidation and the endothermic decomposition conversion are carried out in a single reaction vessel (1) equipped with a burner (3), the non-catalytic partial oxidation of the ammonia supply stream is carried out by partially burning the ammonia supply stream with the burner (3), the burner is equipped with a burner nozzle (2), and the oxidizing gas is introduced into the reaction vessel from the burner nozzle (2).
3. - A step of introducing moderator steam into the reaction vessel (1) in order to protect the burner nozzle (2) from overheating, - A step of mixing the moderator vapor with the exhaust gas, - A step of mixing the moderator vapor with the vapor generated from the non-catalytic partial oxidation in the effluent gas, thereby obtaining a water vapor fraction of the effluent gas, - A step of condensing the water vapor fraction and thereby removing at least a portion of the unconverted ammonia from the effluent gas by absorption, The process according to claim 2, comprising:
4. The process according to claim 3, wherein an unconverted ammonia solution containing the absorbed unconverted ammonia is produced by condensing the water vapor fraction.
5. The process according to claim 4, wherein at least a portion of the unconverted ammonia solution is vaporized and introduced into the reaction vessel (1) as the moderator vapor.
6. The process according to claim 5, wherein the first portion of the unconverted ammonia solution is vaporized and introduced into the reaction vessel (1) as moderator vapor, and the unconverted ammonia in the second portion of the unconverted ammonia solution is recovered in gaseous form, particularly by distillation of the second portion.
7. The process according to claim 6, wherein the unconverted ammonia of the second portion of the unconverted ammonia solution is recycled to the non-catalytic partial oxidation step.
8. The process according to any one of claims 4 to 7, further comprising the step of adjusting the amount of moderator vapor introduced into the reaction vessel (1) in order to control the concentration of unconverted ammonia in the unconverted ammonia solution.
9. The process according to any one of claims 3 to 8, wherein the non-catalytic partial oxidation of the ammonia supply stream generates nitrogen oxides mixed in the effluent gas, and the process comprises the step of adjusting the amount of moderator vapor introduced into the reaction vessel (1) to control the amount of nitrogen oxides in the effluent gas.
10. The process according to any one of claims 1 to 9, comprising the step of endothermally pre-decomposing the ammonia feed stream before the non-catalytic partial oxidation, thereby generating a pre-decomposed ammonia feed stream containing hydrogen, nitrogen, and undecomposed ammonia, wherein the step of non-catalytic partial oxidation of the ammonia feed stream comprises non-catalytic partial oxidation of the pre-decomposed ammonia feed stream.
11. The process according to any one of claims 1 to 10, comprising the step of adjusting the amount of vapor produced from the non-catalytic partial oxidation, or the step of adjusting the amount of the water vapor fraction of the effluent gas.
12. The process according to any one of claims 1 to 11, comprising the steps of preheating the ammonia feed stream to a feed preheating temperature before the non-catalytic partial oxidation, and adjusting the feed preheating temperature to control the amount of vapor produced from the non-catalytic partial oxidation.
13. The process according to any one of claims 1 to 12, wherein the condensation of the vapor generated from the non-catalytic partial oxidation is carried out in a scrubbing tower.
14. The process according to claim 13, wherein a portion of the unconverted ammonia is removed from the effluent gas by absorption through condensation of the vapor generated from the non-catalytic partial oxidation, and the remaining portion of the unconverted ammonia is removed by further absorption within the washing tower.
15. The process according to claim 12 or 13, wherein no additional water is introduced into the washing tower.