DE102022204104A1 - Ammonia converter for fluctuating partial load operation - Google Patents

Abstract

The present invention relates to an ammonia converter 10, wherein the ammonia converter 10 has a shell 20, wherein the ammonia converter 10 has a reactant inlet 30 and a product outlet 40, wherein the ammonia converter 10 has at least a first catalyst bed 50 and a second catalyst bed 60, wherein the first catalyst bed 50 and the second catalyst bed 60 are flowed through radially from the outside towards the center, the ammonia converter 10 having at least one first heat exchanger, the first heat exchanger being designed as a first tube bundle heat exchanger, the first tube bundle heat exchanger having a central tube 70 and a plurality of heat exchange tubes 80 , wherein the heat exchange tubes 80 are arranged parallel to the central tube 70 and around the central tube 70, the first tube bundle heat exchanger having a deflection device 90, the deflection device 90 being arranged between the central tube 70 and the heat exchange tubes 80, the first tube bundle heat exchanger being annular the first catalyst bed 50 is surrounded, characterized in that the educt inlet 30 is connected directly to the heat exchange tubes 80 in terms of gas flow, the central tube 70 being connected directly to the space between the shell 20 and the first catalyst bed 50 in terms of gas flow.

Description

The invention relates to an ammonia converter that is designed to function reliably even with fluctuating utilization. Fluctuating loads occur, for example, when the hydrogen is produced using renewable energy via electrolysis and the available educts are therefore subject to large fluctuations depending on the weather conditions.

From the EP 3 497 392 B2 the use of a plate heat exchanger and a synthesis device for the production of ammonia in particular is known.

From the EP 3 497 058 B1 a synthesis device and a process for producing ammonia in particular are known.

During ammonia synthesis, energy is released through the conversion. The higher the temperature, the further the equilibrium shifts towards the reactants. And if the temperature exceeds a certain level, damage to the device can of course occur. Therefore, implementation usually takes place in two or more stages. Between two stages, the excess energy is transferred to cooler incoming educt using a heat exchanger.

For a normal synthesis, the heat exchanger is designed for maximum efficiency, as it can be made particularly small, which in turn allows more catalyst in the converter, which in turn increases conversion.

If a conventional converter is now confronted with a fluctuating educt stream, it can happen that the educt stream cools the product stream to such an extent that it is no longer warm enough at the next stage, for example below 370 °, to be further implemented, the reaction comes to a standstill. However, if the heat exchanger were to be made smaller, either the cold incoming gas would not be heated sufficiently, so that the reaction would come to a standstill, or the converter could overheat at full load because the gas emerging from the previous stage is not cooled down sufficiently.

The object of the invention is to provide a converter that works reliably both at full load and at the lowest possible partial loads.

This task is solved by the ammonia converter with the features specified in claim 1. Advantageous further developments result from the subclaims, the following description and the drawing.

The ammonia converter according to the invention has a shell. The shell is relevant for the high pressures typical for ammonia synthesis and at the same time must be designed for the hydrogen-containing atmosphere and elevated temperatures. The ammonia converter also has an educt inlet and a product outlet. Further by-product inlets can be provided in order, for example, to be able to supply cool educt gas mixture directly to the second catalyst bed, for example in order to be able to regulate the temperature with it. The mixture of hydrogen and nitrogen (possibly with other components such as ammonia or argon) is fed in through the educt inlet. The product gas mixture of ammonia, hydrogen and nitrogen is removed from the ammonia converter via the product outlet. The ammonia converter has at least a first catalyst bed and a second catalyst bed. Within the catalyst beds, the conversion of hydrogen and nitrogen to ammonia takes place on the surface of the catalyst. The first catalyst bed and the second catalyst bed are flowed through radially from the outside towards the center. The gas mixture to be converted is therefore fed to the catalyst bed from the outside from a space between the shell and the catalyst bed. The gap between the shell and the catalyst bed serves to distribute the gas mixture along the catalyst bed. The ammonia converter has at least a first heat exchanger. The first heat exchanger is designed as a first tube bundle heat exchanger. The first tube bundle heat exchanger has a central tube and a plurality of heat exchange tubes. The heat exchange tubes are flowed through in the opposite direction to the flow through the central tube. The heat exchange tubes are arranged parallel to the central tube and around the central tube. The heat exchange tubes thus surround the central tube. The first tube bundle heat exchanger has a deflection device.

The deflection device is fluidly arranged between the central tube and the heat exchange tubes and guides the gas flow from one to the other. The first tube bundle heat exchanger is surrounded in a ring by the first catalyst bed, and is therefore arranged in the inner core of the first catalyst bed. As a result, the gas mixture heated by the reaction in the first catalyst bed is fed to the tube bundle heat exchanger and thus heats the gas mixture inside the tubes.

According to the invention, the educt inlet is directly connected to the heat exchange tube in terms of gas flow ren connected and the central tube is connected directly to the space between the shell and the first catalyst bed in terms of gas flow. The fact that the educt inlet is directly connected to the heat exchange tubes in terms of gas flow means in particular that the central first tube is not arranged between the educt inlet and the heat exchange tubes. This also means that the central tube is connected directly to the space between the casing and the first catalyst bed in terms of gas flow technology, and that between the central pipe and the space between the casing and the first catalyst bed is not connected via the heat exchange tubes. This means that the first heat exchanger is a co-current heat exchanger . In conventional converters, the heat exchanger is operated as a countercurrent heat exchanger, as this reduces the size of the heat exchanger, which in turn increases the amount of catalyst and thus increases the maximum system capacity. Therefore, a direct current heat exchanger appears inefficient. However, the direct current heat exchanger has a technical advantage. Due to the direct current, both gas streams have the same temperature at the outlet with maximum heat transfer. This means that not too much heat can be transferred; both gas streams have the temperature that is required to further convert each of the gas streams when fed to the next catalyst bed and thus maintain the reaction. This achieves maximum flexibility for partial loads at the expense of a certain proportion of the maximum capacity, making the ammonia converter ideal for use in producing so-called green ammonia using renewable energy.

In a further embodiment of the invention, the ammonia converter has a third catalyst bed. The third catalyst bed is arranged between the first catalyst bed and the second catalyst bed. The first heat exchanger has a first partial heat exchanger and a second partial heat exchanger. The first partial heat exchanger is surrounded in a ring shape by the first catalyst bed and the second partial heat exchanger is surrounded in a ring shape by the third catalyst bed. The path of the gas flow is therefore from the educt inlet through the first heat exchanger, more precisely through the heat exchange tubes of the first partial heat exchanger, then through the heat exchange tubes of the second partial heat exchanger, then through the central tube. From there the gas stream is passed between the shell and the first catalyst bed and then through the first catalyst bed. From there it passes through the first heat exchanger between the shell and the third catalyst bed and is then guided through the third catalyst bed. From there it passes through the first heat exchanger between the shell and the second catalyst bed and is then guided through the second catalyst bed. The gas stream is then passed through the product outlet.

In a further embodiment of the invention, the entire surface of the heat exchange tubes is designed for sufficient heat transfer for a partial circulation gas quantity of 10% of the maximum circulation gas quantity at full load. The lower the possible partial load, the larger the heat exchanger can be. On the other hand, the ammonia converter can continue to be operated even with very small amounts of available renewable energy, so that switch-off times are reduced, which in turn avoids start-ups with high losses.

In a further embodiment of the invention, the ammonia converter has a maximum system capacity of 50 to 700 tons of ammonia per day. The invention is therefore particularly preferred for comparatively small systems for ammonia synthesis. Conventional systems achieve a capacity of 3,000 tons per day and more. However, if you want to use renewable energies, they are subject to change over time. On the other hand, production is also regularly limited, for example due to the space available for solar or wind turbines. It can therefore be assumed that systems planned to produce green ammonia will require comparatively small converters. However, there is a synergy with the invention here. Since the converter is built in a pressure-stable shell, these are usually of certain sizes. This means that in comparatively small systems there is additional space in the converter. The disadvantage of the increased space requirement for the first heat exchanger according to the invention is therefore not a disadvantage.

In a further embodiment of the invention, radially arranged guide elements are arranged on the side around which the gas emerging from the first catalyst bed flows around the first heat exchanger in order to generate a flow crossing the heat exchange tubes. This zigzag guidance optimizes the exchange.

• 1 Ammoniakkonverter

The ammonia converter according to the invention is explained in more detail below using an exemplary embodiment shown in the drawing.

• 1 Ammonia converter

In 1 an exemplary ammonia converter 10 is shown in schematic cross section. The illustration is not to scale and serves to illustrate the invention.

A mixture of hydrogen and nitrogen is supplied via an educt inlet 30. The gas mixture is passed into the heat exchange tubes 80 and flows downwards and is heated in the process. The heated gas mixture is brought together from the heat exchange tubes 80 by means of the deflection device 90 and into the central tube 70. There the gas mixture flows upwards and then reaches the gap between the shell 20 and the first catalyst bed 50 via the upper region. There the gas stream is guided radially through the first catalyst bed 50, converted there and heated up in the process. The gas stream emerging from the first catalyst bed 50 releases its excess heat to the heat exchange tubes 80 and is guided into the gap between the shell 20 and the third catalyst bed 100. There the gas stream is guided radially through the third catalyst bed 100, converted there and heats up in the process. The gas stream emerging from the third catalyst bed 100 releases its excess heat to the heat exchange tubes 80 and is guided into the gap between the shell 20 and the second catalyst bed 60. There the gas stream is guided radially through the second catalyst bed 60, converted there and heats up in the process. The gas stream emerging from the second catalyst bed 60 is led to the product outlet 40.

Reference symbols

10

Ammonia converter

20

Covering

30

Educt inlet

40

Product outlet

50

first catalyst bed

60

second catalyst bed

70

central pipe

80

Heat exchange tube

90

Deflection device

100

third catalyst bed

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 3497392 B2 [0002]
• EP 3497058 B1 [0003]

Claims (5)

Ammonia converter (10), wherein the ammonia converter (10) has a shell (20), wherein the ammonia converter (10) has a reactant inlet (30) and a product outlet (40), wherein the ammonia converter (10) has at least a first catalyst bed (50) and a second catalyst bed (60), wherein the first catalyst bed (50) and the second catalyst bed (60) are flowed through radially from the outside towards the center, the ammonia converter (10) having at least one first heat exchanger, the first heat exchanger being the first A tube bundle heat exchanger is designed, wherein the first tube bundle heat exchanger has a central tube (70) and a plurality of heat exchange tubes (80), the heat exchange tubes (80) being arranged parallel to the central tube (70) and around the central tube (70), the The first tube bundle heat exchanger has a deflection device (90), the deflection device (90) being arranged between the central tube (70) and the heat exchange tubes (80), the first tube bundle heat exchanger being surrounded in a ring by the first catalyst bed (50), characterized in that the educt inlet (30) is connected directly to the heat exchange tubes (80) in terms of gas flow, the central tube (70) being connected directly to the space between the shell (20) and the first catalyst bed (50) in terms of gas flow. Ammonia converter (10). Claim 1 , characterized in that the ammonia converter (10) has a third catalyst bed (100), the first heat exchanger having a first partial heat exchanger and a second partial heat exchanger, the first partial heat exchanger being surrounded in a ring by the first catalyst bed (50), the second partial heat exchanger is surrounded in a ring by the third catalyst bed (100). Ammonia converter (10) according to one of the preceding claims, characterized in that the entire surface of the heat exchange tubes (80) is designed for sufficient heat transfer for a partial circulation gas quantity of 10% of the maximum circulation gas quantity at full load. Ammonia converter (10) according to one of the preceding claims, characterized in that the ammonia converter (10) has a maximum system capacity of 50 to 700 tons of ammonia per day. Ammonia converter (10) according to one of the preceding claims, characterized in that the first heat exchanger has radially arranged guide elements for generating a flow crossing the heat exchange tubes (80) on the side around which the gas emerging from the first catalyst bed (50) flows.

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