BE1029787B1 - Process for the synthesis of ammonia and plant for the production of ammonia - Google Patents

Abstract

The invention relates to a method for producing ammonia, in which a hydrocarbon mixture and steam are fed to a primary reformer (1), the hydrocarbon mixture and the steam in the primary reformer (1) being at least partially converted into carbon monoxide and hydrogen, the gas mixture from the primary reformer ( 1) is passed into a secondary reformer (2), wherein the secondary reformer (2) is supplied with process air, at least comprising oxygen and nitrogen, so that unreacted hydrocarbon is converted into carbon monoxide and hydrogen, in a method in which the firing capacity of the primary reformer is increased is provided that the oxygen content of the process air is reduced before the process air is fed into the secondary reformer (2).

Description

t BE2021/5747

Process for the synthesis of ammonia and plant for the production of ammonia

The invention relates to a process for the production of ammonia, wherein a

Hydrocarbon mixture and water vapor are fed to a primary reformer, wherein the hydrocarbon mixture and the water vapor are at least partially converted into carbon monoxide and hydrogen in the primary reformer, the gas mixture from the

Primary reformer is passed into a secondary reformer, the secondary reformer

Process air, at least comprising oxygen and nitrogen, is supplied so that unreacted hydrocarbon is converted into carbon monoxide and hydrogen.

In addition, the invention relates to a plant for the production of ammonia, with at least one primary reformer for converting a hydrocarbon mixture and steam at least partially to carbon monoxide and hydrogen, with a secondary reformer for

Conversion of unreacted hydrocarbon to carbon monoxide and hydrogen, wherein the secondary reformer is fluidically connected to the primary reformer, wherein the secondary reformer is fluidically connected to a supply of process air, the process air comprising at least oxygen and nitrogen.

Ammonia is one of the most important raw materials. Annual world production is currently around 170 million tons. Most of the ammonia is used to make fertilizers. Large-scale production today largely uses that of Haber and

At the beginning of the 20th century, Bosch developed high-pressure synthesis in fixed-bed reactors with iron as the main catalytic component, based on a stoichiometrically composed synthesis gas with the main components hydrogen and nitrogen. The

Synthesis gas is mainly generated via the natural gas route. The large amounts of carbon dioxide produced are disadvantageous here.

Due to the exothermic character of the ammonia formation reaction arise in the

Process course relatively large amounts of heat. For a good specific

energy consumption of the overall process, they must be used as efficiently as possible.

In general, the use of waste heat is associated with thermodynamically unavoidable losses. There has therefore been no lack of attempts to find alternatives to the Haber-Bosch

To develop processes that work without the high temperatures and pressures. in the haber

Bosch process, the fundamental difficulty of activating the very inert nitrogen molecule through the use of specifically very active catalysts in

combination with relatively high temperatures. An alternative for the

Providing the required activation energy is the use of electrical energy.

? BE2021/5747

To save carbon dioxide there are considerations, the raw materials, in particular

Hydrogen cannot be obtained, or not completely, via the natural gas route. For example, EP 2 589 426 A1 discloses a method for producing ammonia in which hydrogen is obtained from the electrolysis of water. For example, nitrogen can be obtained from a cryogenic air separation plant. The substances are mixed together and compressed to a pressure in the range from 80 to 300 bar.

The invention deals with the process in which part of the hydrogen is obtained via the natural gas route and another part from an external source. The problem with this is that the amount of hydrogen to be produced in the production of synthesis gas in the so-called

Although the front end of an ammonia plant decreases, the amount of nitrogen to be added increases

Process air, which contains at least nitrogen and oxygen, but must remain constant in the secondary reformer as a first approximation. However, this means that too much oxygen is supplied to the secondary reformer, which leads to the undesired combustion of freshly obtained oxygen

hydrogen leads. To counteract this, the proportion of unreformed methane in the

Secondary reformer can be increased by greatly reducing the primary reformer's firing capacity. As a result, the reforming process is strongly from the primary reformer in the

Secondary reformer moved. However, with the amount of heat now available and the resulting temperature level, it is no longer possible to combine all flows in one

To heat the flue gas duct in the front end as intended.

The invention is therefore based on the object of specifying a method for the production of ammonia and an ammonia plant in which the firing capacity of the

Primary reformers also reduce the number of items to be produced in the frontend

Amount of hydrogen remains almost unchanged.

This object is first achieved by the features of claim 1 in that the oxygen content of the process air is reduced before the process air in the

Secondary reformer is directed. Depletion of oxygen in the process air reduces the amount of heat released in the secondary reformer. At constant

Outlet temperature of the secondary reformer, it is therefore possible to reduce the outlet temperature of the

To increase primary reformer, on the one hand by the greater firing capacity, but also by the amount of heat available and the temperature level in the aforementioned

flue gas duct. The oxygen content of the process air flow can, for example, by a

Nitrogen pressure swing adsorption can be reduced.

3 BE2021/5747

In a first embodiment of the method according to the invention, it is provided that the

Gas mixture from the secondary reformer is fed to a reactor after further processing, that nitrogen and hydrogen are at least partially converted into ammonia in the reactor and that external hydrogen is additionally fed into the reactor.

The external hydrogen does not have to be introduced directly into the reactor. It is also conceivable that the gas mixture from the secondary reformer is combined with the external hydrogen after further purification and the entire mixture is then introduced into the reactor. A further mixing unit can be provided for this purpose, which is arranged upstream of the reactor. However, this is not absolutely necessary.

In a further embodiment of the method according to the invention, it is advantageously provided that the external hydrogen is produced by means of electrolysis. the through

Hydrogen produced by electrolysis can improve the environmental balance of the

Process or the operation of an ammonia plant contribute, provided that the

Using electrolysis greener and cheaper electricity is available. Another advantage of the inventive method is that a certain hybrid driving style

ammonia plant is possible. If clean electricity is available, the

Hydrogen can be produced by electrolysis, for example, right next to an ammonia plant. Accordingly, the depletion of the oxygen content of the

Process air can be adjusted to the hydrogen content available from the electrolysis or to the reduced hydrogen content in the front end of the ammonia plant.

In a further embodiment of the inventive method it is provided that the process air upstream of the secondary reformer in at least a first

Partial flow and a second partial flow is divided that the oxygen content of the first

Partial flow is reduced and that the first partial flow and the second partial flow are merged upstream of the secondary reformer. This way he can

Oxygen content of the process air flow can be set ideally. For existing plants, the second partial flow can follow the original flow path, while only one

Branch must be installed in the existing piping system to the first

to treat partial flow.

In order to operate the method as advantageously as possible, in a further embodiment of the

Invention provides that the proportion of nitrogen in the first partial flow with respect to the

Total amount of nitrogen in the reactor at least 43% of the proportion of external

hydrogen in relation to the total amount of hydrogen in the reactor. To one

° BE2021/5747 to ensure adequate firing of the primary reformer, it is recommended that the

Capacity of the proportion of nitrogen in the first partial flow of the total nitrogen requirement, in the make-

Up stream to the syngas compressor, must be at least half the proportion of external (green) hydrogen. So, as an example, 30% of the hydrogen from the

Replaced front end with external hydrogen, the capacity of the nitrogen portion is the first

Partial flow at least 13.3% of the total nitrogen.

In addition, it is provided in a further embodiment of the method according to the invention that a multi-stage compression of the process air is provided and that the

Process air is divided between two compression stages in at least the first partial flow and the second partial flow. The first partial flow is therefore after a relation to the

Pressure levels appropriate stage of the process air compressor branched off to realize a depletion of oxygen.

Between the compression stages is preferably in a further embodiment of the

Invention provided that the process air is divided at a pressure range of 5 to 15 bara in at least the first partial flow and the second partial flow.

Next can be provided in a further embodiment of the method that the first

Partial flow and the second partial flow are brought together again before the last compression stage. After the last compression stage, the nitrogen-enriched air is dem

Supplied to secondary reformer.

In a particularly advantageous embodiment of the method according to the invention, it is provided that the first partial flow is fed to a nitrogen pressure swing adsorption.

In the physical separation process of pressure swing adsorption (PSA), individual

Gases isolated from a gas mixture. The principle is based on the fact that gas molecules can attach themselves to solid bodies. This solid body, also called adsorbent, is designed for the respective application so that only the component that is important in the application is adsorbed or can penetrate the adsorbent. In the

Nitrogen pressure swing adsorption of process air, which may be, for example, ambient air and contains at least nitrogen and oxygen, the larger nitrogen molecule can permeate the adsorbent while the smaller oxygen molecule in the pores permeates the pores of the adsorbent. In this case, the adsorbent can preferably be a

Carbon molecular sieve can be used.

> BE2021/5747

Pressure swing adsorption can be broken down into four cyclical steps.

First, the raw gas is fed under pressure into an adsorbent bed. Oxygen accumulates on the surface of the adsorbent or penetrates into the pores.

Nitrogen can pass through the bed. This accumulation can until reaching a

equilibrium. Subsequently, the pressure is lowered, creating a

Regeneration of the adsorbent is initiated. By lowering the pressure, the adsorbed oxygen can be released and discharged. In a further step, the adsorbent is flushed with the product gas. This is followed by a new one

Pressure builds up until the necessary conditions for adsorption are met again.

In a further embodiment of the method, it is advantageously provided that the first partial flow after the nitrogen pressure swing adsorption has a mass fraction of nitrogen in the range from 0.9 to 1.0, preferably from 0.95 to 0.99.

The above object is also achieved by a system for the production of

Ammonia, with at least one primary reformer for implementing a

Hydrocarbon mixture and water vapor at least partially to carbon monoxide and

Hydrogen, with a secondary reformer to convert unreacted

Hydrocarbon to carbon monoxide and hydrogen, wherein the secondary reformer is fluidly connected to the primary reformer, wherein the secondary reformer is fluidly connected to a supply of process air, the process air comprising at least oxygen and nitrogen. In addition, the secondary reformer is fluidically connected to a device for depleting oxygen from the process air.

The secondary reformer does not have to be directly fluidly connected to the device

Be connected depletion of oxygen from the process air. It is conceivable that other facilities in the flow path between the device for the depletion of

Oxygen from the process air and the secondary reformer are arranged.

With the system according to the invention it is possible to carry out a method according to one of claims 1 to 10. The above statements regarding the invention

Methods apply analogously to the system according to the invention

Production of Ammonia.

The plant can accordingly additionally have a reactor for converting nitrogen and

Have hydrogen at least partially to ammonia. In addition, the plant over

° BE2021/5747 be supplied to a corresponding flow path of external hydrogen. the external

Hydrogen does not have to be introduced directly into the reactor. It is also conceivable that

Gas mixture from the secondary reformer after further processing with the external

Hydrogen is brought together and the total mixture is then introduced into the reactor. For this purpose, a further mixing unit can be provided upstream of the

Reactor is arranged. However, this is not absolutely necessary.

In a first embodiment of the system according to the invention, it is provided that the

Device for the depletion of oxygen from the process air at least one nitrogen

Includes pressure swing adsorption. Thus, the depletion of oxygen from the

Process air are carried out advantageously.

In particular, there are a number of possibilities for embodying and developing the method according to the invention and the system according to the invention. For this purpose, reference is made both to the patent claims subordinate to patent claims 1 and 11 and to the following description of preferred exemplary embodiments in conjunction with the drawing. Show in the drawing

Fig. 1 is a schematic representation of a method according to the invention for

Production of ammonia or synthesis gas and

2 shows a schematic representation of an exemplary embodiment of a method for producing ammonia.

Fig. 1 shows a schematic representation of the implementation of a method for producing ammonia, or for producing synthesis gas for further conversion to ammonia. A primary reformer 1 and a secondary reformer 2 are shown in the so-called front end of an ammonia plant. The synthesis gas can later be fed to a reactor 3, not shown in FIG.

The primary reformer 1 is initially used, in particular in the production of ammonia, to produce hydrogen. This will usually be a

Hydrocarbon mixture, often methane, and water vapor are used as raw materials. When using natural gas, the main component of which is methane, there are others

contain hydrocarbons. The natural gas is desulfurized beforehand and fed into the primary reformer. At temperatures between 700 to 850°C, methane is reacted with water under pressure on a nickel catalyst, so that carbon monoxide and hydrogen

7 BE2021/5747 arise. The carbon monoxide also reacts with water vapor to form carbon dioxide.

A mixture of hydrogen, carbon monoxide,

Carbon dioxide, unreacted hydrocarbons and water vapor.

The secondary reformer 2 is used to provide nitrogen for the ammonia synthesis. The gas mixture from the primary reformer is mixed with compressed process air in the secondary reformer 2. The process air is preferably

Ambient air, which primarily contains nitrogen and oxygen

Air reacts with the gas mixture that is fed to the secondary reformer 2, as a result of which the unreacted methane or the hydrocarbon mixture is converted.

The nitrogen contained in the process air does not react with the other substances and remains in the gas mixture. By controlling the amount of air introduced, a desired

Ratio between hydrogen and nitrogen can already be set in the secondary reformer 2.

If for later reactions, especially the reaction of hydrogen and nitrogen

Ammonia, additional hydrogen, for example green hydrogen, are used, is the required amount of hydrogen from the primary reformer 1 or the

Secondary reformer 2 lower. However, the amount of nitrogen from the process air remains approximately constant. If the amount of oxygen in the air fed to the secondary reformer also remains unchanged, the reforming process has to move strongly from the primary reformer 1 to the

Secondary reformer 2 are moved. For this, the firing capacity of the

Primary reformer 1 greatly decrease. With the amount of heat that is now available, it is not possible to sufficiently heat all the additional flows that are required.

Therefore, in this exemplary embodiment of the method according to the invention, it is provided that the process air is divided into a first partial flow 4 and a second partial flow 5 before it is fed into the secondary reformer 2 via a feed 6 . The first partial flow 4 is fed to a device 7 for the depletion of oxygen. In this way, the firing capacity of the primary reformer 1 is increased. The first partial flow 4 and the second

Partial stream 5 are brought together again before entering the secondary reformer 2.

Fig. 2 shows another embodiment of the implementation of a method for

Production of Ammonia. In addition to the primary reformer 1 and the

Secondary reformer 2 also a device 7 for the depletion of oxygen from the

Process air provided. The process air is multi-stage compression on the for

© BE2021/5747 the secondary reformer 2 compresses the pressure required. Between a first

Compression stage 8 and a second compression stage 9, the first partial flow 4 is branched off from the second partial flow 5 and fed to the device 7 for the depletion of oxygen from the process air. The second compression stage 9 is the last

Compression stage in the process shown.

In this exemplary embodiment, the device 7 for depleting oxygen from the process air is a nitrogen pressure swing adsorption. With a nitrogen

Pressure swing adsorption (PSA) is used to isolate individual gases from a gas mixture. The principle is based on the fact that gas molecules can attach themselves to solid bodies. This

Solids, also known as adsorbents, are designed for the respective application so that only the components that are important in the application are adsorbed or can penetrate the adsorbent. In the nitrogen pressure swing adsorption of

Process air, ambient air in this embodiment, can be larger

Nitrogen molecule penetrate the adsorbent, while the smaller oxygen molecule in the pores penetrates the pores of the adsorbent. In this case, an adsorbent is used

Carbon molecular sieve used.

Since the nitrogen can flow through the adsorbent, the nitrogen

Pressure swing adsorption obtained a purified stream of nitrogen. In this

Embodiment is the purity of the nitrogen pressure swing adsorption left

nitrogen at 95% to 100%. By adjusting the volume flows of the first partial flow 4 and the second partial flow 5, the total nitrogen content can thus be adjusted accordingly.

The synthesis gas thus produced in the secondary reformer 2 is first processed before the ammonia synthesis can be carried out. For this purpose, a conversion of the carbon oxides is carried out in the designated with reference numeral 10 block, otherwise as

Catalyst poisons work and make the catalysts useless in the synthesis. The remaining carbon monoxide is converted to carbon dioxide using water vapor. The

Carbon dioxide is then separated from the raw gas, e.g. by scrubbing or absorption. Then all oxygen-containing components (carbon monoxide,

carbon dioxide, water), which are considered harmful to the catalyst in the ammonia synthesis, is reduced to a minimum and the so-called make-up gas is reduced to the synthesis

pressure compressed.

3 BE2021/5747

In the subsequent synthesis of ammonia in reactor 3, hydrogen and nitrogen are converted into ammonia. In addition to the hydrogen from the reforming, i.e. the

Primary reformer 1 and the secondary reformer 2, additional hydrogen is fed into reactor 3 from an external source. In this exemplary embodiment, the additional hydrogen is generated from an electrolysis 11 of water

Hydrogen. The electrolysis 11 can be used when cheap electricity to

is available so that the ammonia plant can be used economically.

In order to operate the process as advantageously as possible, the proportion of nitrogen in the first partial stream 4 in relation to the total amount of nitrogen in the reactor 3 corresponds to at least 43% of the proportion of external hydrogen in relation to the total amount of hydrogen in the reactor

Reactor 3. In order to ensure sufficient firing of the primary reformer, it is recommended that the capacity of the nitrogen content in the first partial stream 4 am

Total nitrogen requirement must be at least 43% of the proportion of external (green) hydrogen. So, as an example, 30% of the hydrogen from the front end with external

Hydrogen replaced electrolysis 11, the capacity of the nitrogen portion is the first

Partial flow at least 13.3% of the total nitrogen.

LIST OF REFERENCE NUMERALS (1) Primary reformer (2) Secondary reformer

(3) reactor (4) first substream (5) second substream (6) feed

(7) Device for depleting oxygen (8) First compression stage (9) Second compression stage (10) Processing (11) Electrolysis

Claims (12)

patent claims 1. A process for producing ammonia, in which a hydrocarbon mixture and steam are fed to a primary reformer (1), the hydrocarbon mixture and the steam in the primary reformer (1) being at least partially converted into carbon monoxide and hydrogen, the gas mixture from the primary reformer (1) is conducted into a secondary reformer (2), wherein the secondary reformer (2) is supplied with process air, at least comprising oxygen and nitrogen, so that unreacted hydrocarbon is converted into carbon monoxide and hydrogen, characterized in that the oxygen content of the process air is reduced before the Process air is fed into the secondary reformer (2). 2. The method according to claim 1, characterized in that the gas mixture from the secondary reformer (2) after further processing is mixed with external hydrogen and fed to a reactor (3) in which nitrogen and hydrogen are at least partially converted into ammonia. 3. The method according to claim 2, characterized in that the external hydrogen is produced by means of electrolysis. 4. The method according to any one of claims 2 to 4, characterized in that the process air upstream of the secondary reformer (2) is divided into at least a first partial flow (4) and a second partial flow (5), that the oxygen content of the first partial flow (4 ) is reduced and that the first partial flow (4) and the second partial flow (5) are combined upstream of the secondary reformer (2). 5. The method according to any one of claims 2 to 4, characterized in that the proportion of nitrogen in the first partial stream (4) in relation to the total amount of nitrogen in the reactor (3) is at least 43% of the proportion of external hydrogen in relation to the total amount of hydrogen in the reactor (3) corresponds. 6. The method according to claim 4 or 5, characterized in that a multi-stage compression of the process air is provided and that the process air is divided between two compression stages in at least the first partial flow (4) and the second partial flow (5). 7. The method according to claim 6, characterized in that the process air is divided at a pressure range of 5 to 15 bara in at least the first partial flow (4) and the second partial flow (5). 8. The method according to claim 6 or 7, characterized in that the first partial flow (4) and the second partial flow (5) are brought together again before the last compression stage. 9. The method according to any one of claims 4 to 7, characterized in that the first partial flow (4) is fed to a nitrogen pressure swing adsorption. 10. The method according to claim 9, characterized in that the first partial flow (4) after the nitrogen pressure swing adsorption has a mass fraction of nitrogen in the range from 0.9 to 1.0, preferably 0.95 to 0.99. 11. Plant for the production of ammonia, with at least one primary reformer (1) for converting a hydrocarbon mixture and water vapor at least partially into carbon monoxide and hydrogen, with a secondary reformer (2) for converting unreacted hydrocarbon into carbon monoxide and hydrogen, the secondary reformer (2 ) is fluidically connected to the primary reformer (1), the secondary reformer (2) being fluidically connected to a supply (6) of process air, the process air comprising at least oxygen and nitrogen, characterized in that the secondary reformer (2) is fluidically connected to a Device (7) for the depletion of oxygen from the process air is connected. 12. Plant according to claim 11, characterized in that the device (7) for the depletion of oxygen from the process air comprises at least one nitrogen pressure swing adsorption.