DE102023206108B4 - Ammonia production plant - Google Patents

Abstract

A process for producing ammonia, wherein in one step a mixed gas comprising carbon dioxide, hydrogen and nitrogen is produced by means of steam reforming, which mixed gas then flows into an amine system (9), wherein in the amine system (9) the carbon dioxide is separated from the mixed gas, wherein the synthesis gas consisting of nitrogen and hydrogen produced from the amine system (9) is fed to a synthesis gas compressor (15), wherein after the synthesis gas compressor (15) the synthesis gas is fed to an ammonia reactor (2) where nitrogen and hydrogen react chemically to form ammonia, wherein the thermal energy produced in the synthesis gas compressor (15) is used to produce steam in a synthesis gas waste heat steam generator (16), which steam is fed to the amine system (9).

Description

The invention relates to a plant for producing ammonia, comprising an ammonia reactor designed for the chemical reaction of hydrogen with nitrogen to form ammonia, a device for steam methane reforming for producing hydrogen, the device having a natural gas supply line for natural gas and an air supply line for air, the device having an outlet line, the outlet line containing a mixed gas of hydrogen, carbon dioxide and nitrogen, further comprising an amine system fluidically connected to the outlet line and designed to separate the carbon dioxide from the mixed gas, the amine system having a steam access line for supplying steam, the amine system comprising a synthesis gas outlet line for synthesis gas, the synthesis gas comprising hydrogen and nitrogen, a synthesis gas compressor being arranged in the synthesis gas outlet line and designed to compress the synthesis gas.

Furthermore, the invention relates to a process for producing ammonia, wherein in one step a mixed gas comprising carbon dioxide, hydrogen and nitrogen is produced by means of steam reforming, which mixed gas then flows into an amine system, wherein in the amine system the carbon dioxide is separated from the mixed gas, wherein the synthesis gas consisting of nitrogen and hydrogen produced from the amine system is fed to a synthesis gas compressor, wherein after the synthesis gas compressor the synthesis gas is fed to an ammonia reactor where nitrogen and hydrogen react chemically to form ammonia.

The invention is based on the aspect of transporting hydrogen over long distances. Ammonia is perceived as a rapidly growing application as a hydrogen energy carrier, especially when hydrogen needs to be transported in liquid form over long distances.

This is because the liquefaction of ammonia requires significantly less energy than the liquefaction of hydrogen. Similar to hydrogen, carbon-free ammonia, which can also be referred to as clean ammonia, can be produced either green or blue, determined by the method of hydrogen production. If the hydrogen is produced by electrolysis, i.e. "green," the ammonia is also "green," whereas if natural gas is reformed with subsequent carbon capture, the hydrogen is "blue." For blue ammonia, steam methane reforming is typically used as the reforming process because the resulting syngas consists primarily of hydrogen, carbon dioxide, and nitrogen. After carbon dioxide sequestration, hydrogen and nitrogen can be fed directly into ammonia synthesis without the need for an additional nitrogen source.

However, the gas produced during steam methane reforming typically has a relatively low carbon dioxide concentration, which is why an amine system is required to capture the carbon dioxide from the other components. An amine system requires comparatively large amounts of low-pressure steam, which requires an additional heat source, such as a natural gas-fired boiler. This leads to high gas consumption and additional carbon dioxide emissions. On the other hand, there are several compressors used in a blue ammonia plant. Downstream of the carbon capture system, there is a carbon dioxide compressor, a syngas compressor for compressing the hydrogen and nitrogen syngas to the required synthesis pressure, an ammonia refrigerant compressor for liquefying the ammonia, an air compressor for compressing the process air to the required reforming pressure, and a natural gas compressor that fulfills the same requirement as the process air compressor, namely bringing the natural gas to the required reforming pressure.

The heat required to reboil the low-pressure steam for the amine plant is provided by an alternative heat source, such as natural gas combustion. This results in additional fuel and energy consumption and carbon dioxide emissions when using a fossil fuel.

Further state of the art can be found, for example, in the publications US 2017 / 0 283 371 A1 and EP 3 730 456 A1 revealed.

Against this background, the invention aims to provide a plant and a process with which ammonia can be produced in a more energy-efficient manner.

This object is achieved by a plant for producing ammonia comprising an ammonia reactor which is designed for the chemical reaction of hydrogen with nitrogen to form ammonia, a device for steam methane reforming for the production of hydrogen, wherein the device has a natural gas supply line for natural gas and an air supply line for air, wherein the device has an outlet line, wherein the outlet line contains a mixed gas of hydrogen, carbon dioxide and nitrogen, further comprising an amine system which is fluidically connected to the outlet line and is designed to separate the carbon dioxide from the mixed gas, wherein the amine system has a steam access line for the supply of steam, wherein the amine system comprises a synthesis gas outlet line for synthesis gas, wherein the synthesis gas comprises hydrogen and nitrogen, wherein a synthesis gas compressor is arranged in the synthesis gas outlet line and is designed to compress the synthesis gas, with a synthesis gas heat recovery steam generator which is designed such that the thermal energy of the synthesis gas heated by the synthesis gas compressor is used to generate steam, wherein the steam generated in the synthesis gas heat recovery steam generator flows into the steam access line into the amine system.

Furthermore, the object is also achieved by a process for producing ammonia, wherein in one step a mixed gas comprising carbon dioxide, hydrogen and nitrogen is produced by means of steam reforming, which mixed gas then flows into an amine system, wherein in the amine system the carbon dioxide is separated from the mixed gas, wherein the synthesis gas consisting of nitrogen and hydrogen produced from the amine system is fed to a synthesis gas compressor, wherein after the synthesis gas compressor the synthesis gas is fed to an ammonia reactor where nitrogen and hydrogen react chemically to form ammonia, wherein the thermal energy generated in the synthesis gas compressor is used to generate steam in a synthesis gas heat recovery steam generator, which steam is fed to the amine system.

The invention thus describes a concept that utilizes the compression heat generated within the air compressor, the synthesis gas compressor, the carbon dioxide compressor and the refrigerant compressor.

The heat from the synthesis gas and air compressor is recovered by using fewer charge air coolers, thus bringing the process gas to the temperature level usable for low-pressure steam preparation in the following charge and aftercoolers.

A new approach is being taken to recover heat from the condensing cycle. The temperatures reached at the compressor outlet are typically too low to directly generate steam at the required pressure and temperature levels. However, steam can be generated at a lower pressure than actually required for the amine process and then subsequently boosted in a steam compressor to increase its temperature and pressure to meet the requirements of the amine system. The generated steam, which comes from the various compressors and an additional steam source (e.g., a fossil-fuel-fired boiler), is then fed into a common steam header, which is fed into the amine system.

The invention thus enables more energy-efficient operation, as heat generated in a compression process is utilized.

The invention is based on the idea that this heat can be used to generate steam for the steam reforming process. This means that less, and ideally no, fossil fuel needs to be used to generate steam.

Advantageous further developments are specified in the subclaims.

An advantage of the system according to the invention is that cooling water for the compressors can be saved, since feed water is usually used for cooling or intermediate cooling of the gases.

The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

Identical components or components with the same function are marked with the same reference symbols.

Embodiments of the invention are described below with reference to the drawings. These are not intended to represent the embodiments to scale; rather, where useful for explanation, the drawings are presented in a schematic and/or slightly distorted form. For supplements to the teachings immediately apparent in the drawings, reference is made to the relevant prior art.

• 1 eine schematische Darstellung einer Ausführungsform einer erfindungsgemäßen Einrichtung
• 2 eine schematische Darstellung

They show:

• 1 a schematic representation of an embodiment of a device according to the invention
• 2 a schematic representation

The 1 shows a schematic representation of an embodiment of the invention.

In particular, the 1 a plant 1 for the production of ammonia. Plant 1 has an ammonia reactor 2, which is designed for the chemical reaction of hydrogen with nitrogen to produce ammonia.

First, natural gas or a similarly combustible gas is fed into a natural gas compressor 3 via a supply line 4. In the natural gas compressor 3, the natural gas is brought to the required pressure for steam reforming. Hydrogen is generated in the steam methane reformer 5. For this purpose, the steam methane reformer 5 has an air supply line 6. An air compressor 7 is arranged in the air supply line 6, which increases the air pressure. Air flows into the air compressor 7 via a line 8.

The steam methane reformer 5 is designed for the production of hydrogen, with an outlet line 10 provided. The outlet line 10 contains a mixed gas consisting of hydrogen, carbon dioxide, and nitrogen. The mixed gas is then passed via the outlet line 10 to an amine system 9. The amine system 9 is designed to separate the carbon dioxide from the mixed gas.

For this purpose, the amine system 9 has a steam inlet line 11 for supplying steam. A comparatively large amount of steam is required for the operation of the amine system 9. The carbon dioxide separated from the mixed gas flows via a carbon dioxide outlet line 12 into a carbon dioxide compressor 13, which is designed to compress the carbon dioxide.

The amine system 9 has a synthesis gas outlet line 14 for synthesis gas, wherein the synthesis gas comprises hydrogen and nitrogen. A synthesis gas compressor 15 is arranged in the synthesis gas outlet line 14 and is designed to compress the synthesis gas.

After the synthesis gas compressor 15, the compressed synthesis gas is fed to the ammonia reactor 2, where ammonia is produced by a chemical reaction.

Heat is generated during the compression of the synthesis gas. This heat is used to generate steam for the amine system 9.

For this purpose, a synthesis gas heat recovery steam generator 16 is arranged, which is designed such that the thermal energy of the synthesis gas heated by the synthesis gas compressor 15 is used to generate steam, wherein the steam generated in the synthesis gas heat recovery steam generator 16 flows into the steam access line 11 into the amine system 9.

When producing ammonia, it is not possible to achieve a complete chemical reaction stoichiometrically due to the process. Therefore, unreacted synthesis gas is fed back to the synthesis gas compressor 15 via a recycle line 17 and from there back to the ammonia reactor 2.

The heat generated during air compression is also used to generate steam for the amine system 9.

For this purpose, the air compressor 7, which is designed to compress the air, is arranged in the air supply line 6, wherein an air waste heat steam generator 18 is arranged, which is designed such that the thermal energy of the air heated by the air compressor 7 is used to generate steam.

The steam generated in the air heat recovery steam generator 18 flows into the steam access line 11 into the amine system 9.

The heat generated during the compression of carbon dioxide is also used to generate steam for the amine system 9.

For this purpose, the amine system 9 has the carbon dioxide outlet line 12, in which the carbon dioxide compressor 13 is arranged, which is designed to compress the carbon dioxide. A carbon dioxide heat recovery steam generator 19 is arranged such that the thermal energy of the carbon dioxide heated by the carbon dioxide compressor 13 is used to generate steam. The steam generated in the carbon dioxide heat recovery steam generator 19 flows into the steam inlet line 11 in the amine system.

After the ammonia reactor 2, gaseous ammonia flows into an ammonia liquefaction plant 21 via an ammonia outlet line 20. The ammonia outlet line 20 is thus fluidly connected to the ammonia liquefaction plant 21. The ammonia liquefaction plant 21 is designed to liquefy the gaseous ammonia.

When ammonia is liquefied, thermal energy is generated, which is also used to generate steam for the amine system 9.

The ammonia liquefaction plant 21 is therefore designed in such a way that thermal energy is generated during the liquefaction of the ammonia.

The conversion of the thermal energy generated in the ammonia liquefaction plant 21 is carried out with the help of the 2 described.

In the ammonia liquefaction plant 21, a rapid steam generator 22 is arranged, which is designed such that the thermal energy generated by the liquefaction of the ammonia is used to generate steam.

The steam generated in the flash steam generator 22 flows into the steam access line 11 into the amine system 9.

The 2 essentially shows a heat pump cycle. Ammonia is used as the refrigerant. However, other refrigerants can also be used.

The temperature of the refrigerant is increased with the help of a refrigerant compressor 23. The thermal energy gained in this process is used, as described above, in a flash steam generator 22 to generate steam 25 from feedwater 24. After the flash steam generator 22, the refrigerant is further cooled in a cooling unit 26. The refrigerant is further cooled by an expansion valve 27. Finally, in a heat exchanger 28, the warm gaseous ammonia 29 is converted into liquid ammonia 30.

In the event that the steam emerging from the ammonia liquefaction plant 21 does not have a suitable pressure, a steam compressor 31 is used. The steam generated by the ammonia liquefaction plant 21 flows through the steam compressor 31, wherein the steam compressor 31 is designed to increase the pressure of the steam.

The steam then flows to the steam access line 11 into the amine system 9.

The steam access line 11 is fluidly connected to a steam collector 33. The steam collector 33 is designed to collect steam, with the steam access line 11 being provided on the outlet side of the steam collector 33.

The steam coming from the heat recovery steam generators 18, 19, and 16, as well as the steam coming from the ammonia liquefaction plant 21 via the steam compressor 31, is collected in the steam collector 33 and fed to the amine system 9. If the steam collected in the steam collector 33 is insufficient for the operation of the amine system 9, an external steam source 34 is connected to the steam collector 33.

Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variants can be derived by those skilled in the art without departing from the scope of the invention.

Claims (14)

Plant (1) for producing ammonia, comprising an ammonia reactor (2) designed for the chemical reaction of hydrogen with nitrogen to form ammonia, a device for steam methane reforming (5) for producing hydrogen, wherein the device has a natural gas supply line (4) for natural gas and an air supply line (8) for air, wherein the device has an outlet line (10), wherein the outlet line (10) contains a mixed gas of hydrogen, carbon dioxide and nitrogen, further comprising an amine system (9) which is fluidically connected to the outlet line (10) and is designed to separate the carbon dioxide from the mixed gas, wherein the amine system (9) has a steam access line (11) for supplying steam, wherein the amine system (9) comprises a synthesis gas outlet line (14) for synthesis gas, wherein the synthesis gas comprises hydrogen and nitrogen, wherein in the synthesis gas outlet line (14) a A synthesis gas compressor (15) is arranged, which is designed to compress the synthesis gas, characterized by a synthesis gas waste heat steam generator (16) which is designed such that the thermal energy of the synthesis gas heated by the synthesis gas compressor (15) is used to generate steam, wherein the steam generated in the synthesis gas waste heat steam generator (16) flows into the steam access line (11) into the amine system (9). Annex (1) to Claim 1 , wherein an air compressor (7) is arranged in the air supply line (8), which is designed to compress the air, wherein an air heat recovery steam generator (18) is arranged, which is designed such that the thermal energy of the air heated by the air compressor (7) is used to generate steam, wherein the steam generated in the air heat recovery steam generator (18) flows into the steam access line (11) into the amine system (9). Annex (1) to Claim 1 or 2 , wherein the amine system (9) has a carbon dioxide outlet line (12) and a carbon dioxide compressor (13) is arranged in the carbon dioxide outlet line (12), which is designed to compress the carbon dioxide, wherein a carbon dioxide heat recovery steam generator (19) is arranged, which is designed such that the thermal energy of the carbon dioxide heated by the carbon dioxide compressor (13) is used to generate steam, wherein the steam generated in the carbon dioxide heat recovery steam generator (19) flows into the steam access line (11) in the amine system (9). Plant (1) according to one of the preceding claims, wherein the ammonia reactor (2) has an ammonia outlet line (20) for gaseous ammonia, wherein the ammonia outlet line (20) is fluidly connected to an ammonia liquefaction plant (21), wherein the ammonia liquefaction plant (21) is designed to liquefy the gaseous ammonia, wherein the ammonia liquefaction plant (21) is designed such that thermal energy is generated during the liquefaction of the ammonia, wherein the ammonia liquefaction plant (21) has a flash steam generator (22) designed such that the thermal energy generated by the liquefaction of the ammonia is used to generate steam, wherein the steam generated in the flash steam generator (22) is fed into the steam access line (11) in the amine system (9). flows. Annex (1) to Claim 4 , wherein the steam generated by the ammonia liquefaction plant (21) flows through a steam compressor (31), wherein the steam compressor (31) is designed to increase the pressure of the steam. Plant (1) according to one of the preceding claims, with a steam collector (33) which is designed to collect steam, wherein the steam collector (33) has the steam access line (11) on the outlet side. Plant (1) according to one of the preceding claims, wherein the ammonia liquefaction plant (21) is designed as a refrigerant circuit, wherein the refrigerant is heated by means of a refrigerant compressor (23), wherein the thermal energy generated by the refrigerant compressor (23) is used to generate steam in the flash steam generator (22). Annex (1) to Claim 7 , with ammonia being used as the refrigerant. A process for producing ammonia, wherein, in one step, a mixed gas comprising carbon dioxide, hydrogen, and nitrogen is produced by steam reforming, which then flows into an amine system (9), wherein the carbon dioxide is separated from the mixed gas in the amine system (9), wherein the synthesis gas consisting of nitrogen and hydrogen produced from the amine system (9) is fed to a synthesis gas compressor (15), wherein, after the synthesis gas compressor (15), the synthesis gas is fed to an ammonia reactor (2), where nitrogen and hydrogen chemically react to form ammonia, wherein the thermal energy generated in the synthesis gas compressor (15) is used to generate steam in a synthesis gas heat recovery steam generator (16), which is fed to the amine system (9). Procedure according to Claim 9 , wherein the steam reforming is connected to an air supply line (8) in which an air compressor (7) is arranged, wherein the thermal energy generated in the air compressor (7) is used to generate steam in an air heat recovery steam generator (18), which steam is fed to the amine system (9). Procedure according to Claim 9 or 10 , wherein the amine system (9) has a carbon dioxide outlet line (12) in which a carbon dioxide compressor (13) is arranged, wherein the thermal energy generated in the carbon dioxide compressor (13) is used to generate steam in a carbon dioxide waste heat steam generator (19), which steam is fed to the amine system (9). Method according to one of the Claims 9 until 11 , wherein the gaseous ammonia flowing from the ammonia reactor (2) is liquefied in an ammonia liquefaction plant (21) and the thermal energy generated in the ammonia liquefaction plant (21) is used to generate steam for the amine system (9). Procedure according to Claim 12 , wherein the ammonia liquefaction plant (21) has a refrigerant circuit which has a flash steam generator (22) through which the refrigerant heated by a compressor (23) flows, the thermal energy of the refrigerant being used to generate steam for the amine system (9) in the flash steam generator (22). Procedure according to Claim 13 , using ammonia as the refrigerant.

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