DE102022204105A1 - Heat exchanger with integrated start-up heating - Google Patents

Abstract

The present invention relates to a gas-gas heat exchanger 10, wherein the gas-gas heat exchanger 10 has a first gas side and a second gas side, the first gas side having a first gas inlet 20 and a first gas outlet 30, the second gas side having a second gas inlet 40 and a second gas outlet 50, wherein the first gas side has a first gas distribution region 60 connected to the first gas inlet 20, the first gas side having a first gas collection region 70 connected to the first gas outlet 30, the first gas distribution region 60 and the first gas collection region 70 are connected to one another via a plurality of first heat exchange gas ducts 100, the first heat exchange gas ducts 100 being in thermal contact with the second gas side, characterized in that at least one first electrical heating element 120 is arranged in the first gas collection region 70.

Description

The invention relates to a heat exchanger with an integrated heater for warming up a system.

Many chemical processes, for example and in particular the synthesis of ammonia from nitrogen and hydrogen, release heat, which is used to heat the educts supplied. However, when starting up such a chemical plant, the plant is initially too cold for the reaction and the reaction therefore does not provide the required heat. It is therefore common practice to provide the required energy, particularly using a natural gas burner. In most cases today, the hydrogen for ammonia synthesis is produced from natural gas, so natural gas is available in such plants.

However, there is increasing interest in reducing CO ₂ emissions. Therefore, alternative sources of hydrogen are being sought that do not require the production of CO ₂ . One source, for example, is electrolysis using electricity generated from renewable sources. However, this means that natural gas is no longer necessarily available for the start-up process, for example. On the other hand, the emission of CO ₂ should also be avoided in such processes. There is therefore a need to heat the starting materials differently in order to reach the minimum temperature in the catalyst bed necessary for the reaction.

Two solutions in particular are currently being used. On the one hand, an electrical preheater is built between the heat exchanger and the converter. However, since pressures well over 100 bar (up to 400 bar) prevail in the recirculation circuit of ammonia synthesis, the housing for the electrical preheating must be correspondingly stable and therefore complex and expensive. On the other hand, the preheating is integrated directly into the converter. Although this eliminates the need for a separate housing, the space requirement reduces the amount of catalyst in the converter and thus reduces the maximum production output.

From the EP 2 116 296 A1 a start-up heater for an ammonia reactor is known.

From the DE 10 2019 202 893 A1 a process for producing ammonia is known.

From the EP 3 623 343 A1 a process for producing ammonia is known.

A method for heating an ammonia converter is known from WO 2017/186 613 A1.

From the EP 3 730 456 A1 The use of renewable energies for ammonia synthesis is known.

From the CN 107188197 A a method for using nitrogen to heat an ammonia synthesis catalyst is known.

The use of renewable energy for the synthesis of ammonia is known from WO 2020/150 245 A1.

The object of the invention is to enable regenerative preheating, which avoids the problems of the two known solutions.

This task is solved by the gas-gas heat exchanger with the features specified in claim 1, the chemical plant with the features specified in claim 12 and the method with the features specified in claim 15. Advantageous further developments result from the subclaims, the following description and the drawings.

The gas-gas heat exchanger according to the invention has a first gas side and a second gas side. In regular operation, thermal energy in the gas-gas heat exchanger is transferred from the gas flowing through the second gas side to the gas flowing in the first gas side. In particular, the heat generated during the conversion of the gas is used to heat the inflowing educts. The first gas side has a first gas inlet and a first gas outlet. At the first gas flow, the gas stream to be heated is fed to the first gas side and the heated gas stream is then released again at the gas outlet. The second gas side accordingly has a second gas inlet and a second gas outlet. The gas that is to give off heat is introduced through the second gas inlet and leaves the gas-gas heat exchanger cooled through the second gas outlet. The first gas side has a first gas distribution area connected to the first gas inlet and a first gas collection area connected to the first gas outlet. The first gas distribution area and the first gas collection area are connected to one another via a plurality of first heat exchange gas ducts. The heat exchange gas ducts can, for example and preferably, be designed in a plate-shaped or tubular manner. By dividing it into several heat exchange gas ducts, the surface area is increased and heat transfer is improved. The number of the plural depends depends on the embodiment. If, for example, this is plate-shaped (plate heat exchanger), then 10 to 25 heat exchange gas ducts are common. If the embodiment is, for example, tubular (tube bundle heat exchanger), 20 to 250 heat exchange gas ducts are more common. The person skilled in the art will therefore choose the number of the majority according to the designs common in the prior art. The The first heat exchange gas guides are in thermal contact with the second gas side. This allows heat transfer to take place. According to the invention, at least one first electrical heating element is arranged in the first gas collection area. In regular operation, the first electrical heating element is switched off. This only heats up when starting up from the cold state. The The arrangement is chosen in such a way that the gas initially flows through the first gas side, is heated electrically at the end, and from there is fed into a reaction reactor. However, no reaction takes place there due to the temperature being too low. The gas then flows back into the Gas-gas heat exchanger, this time on the second gas side. Here the gas gives off the electrically generated heat to the incoming gas stream of the first gas side, which is then further heated electrically by the first electrical heating element at the end of the first gas side after being heated by the backflowing gas and is thus brought to a higher temperature. In this way, both the gas stream and the reaction reactor are heated continuously until a threshold temperature is reached, for example 370 ° C in ammonia synthesis, so that the reaction begins in the reaction reactor and generates additional energy. From this point on, the system is no longer dependent on the supply of external energy from the first electrical heating element. The first electrical heating element can either be switched off completely or slowly turned down until the target temperature is reached.

Due to the arrangement in the gas-gas heat exchanger, neither its own pressure-stable housing is required, nor is the space for the catalytic converter reduced in the converter, so that the problems known from the prior art can be solved in this way.

In a further embodiment of the invention, the first gas collection region has a first subregion and a second subregion. The first portion is connected to the first heat exchange gas ducts and the second portion is connected to the first gas outlet. The first electrical heating element is arranged in the second portion. The effect is that the gas on the first gas side in the first subregion has approximately the temperature of the gas flowing into the second gas side and this is further increased in a separate second subregion. This also allows, for example, the extraction of gas streams at two different temperature levels.

In a further embodiment of the invention, the second portion is thermally insulated from the second gas side. This prevents the hotter gas entering the second gas side from being further heated by the first electrical heating element. The heating by the first electrical heating element is thus limited to the colder gas on the first gas side. For example, the thermal insulation of the second portion can be achieved by a double tube, provided the second portion is tubular. The space in the double tube then acts as insulation and prevents heat generated by the first electrical heating element from being released to the second gas side.

In a further embodiment of the invention, the first gas side has a third gas outlet. The third gas outlet is connected to the first gas collection area.

This is particularly preferred if the first gas collection area has different temperature levels.

In a further embodiment of the invention, the third gas outlet can be closed. The third gas outlet is particularly preferably closed during regular operation and is only opened in a specific phase of the start-up process. In particular, the third gas outlet can be closed with a valve.

In a further embodiment of the invention, the third gas outlet is connected to the first portion.

In a further embodiment of the invention, a second electrical heating element is arranged in the first subregion.

In a further embodiment of the invention, the gas-gas heat exchanger is designed as a plate heat exchanger. In this embodiment, the second gas side has a second gas distribution region connected to the second gas inlet and a second gas collection region connected to the second gas outlet. The second gas distribution area and the second gas collection area are connected to one another via a plurality of second heat exchange gas ducts. First heat exchange gas ducts and second heat exchange gas ducts are each arranged alternately next to one another and adjacent to one another.

In a further alternative embodiment of the invention, the gas-gas heat exchanger is designed as a tube bundle heat exchanger. There are two other important alternative embodiments. In a first exemplary embodiment, the second gas side can be designed as a large, continuous area in which the tubular first heat exchange gas guides run and are surrounded by the gas from the second gas side. In a second exemplary embodiment, the second gas side may have a second gas distribution region connected to the second gas inlet and a second gas collection region connected to the second gas outlet. The second gas distribution area and the second gas collection area are connected to one another via a plurality of second heat exchange gas ducts. First heat exchange gas ducts and second heat exchange gas ducts are each arranged parallel next to one another.

Preferably, the second gas side in the area of the first heat exchange gas ducts is flowed through in the direction opposite to the gas duct in the first heat exchange gas ducts (countercurrent heat exchanger).

In a further embodiment of the invention, the gas-gas heat exchanger has a pressure housing.

In a further aspect, the invention relates to a chemical plant with a gas-gas heat exchanger according to the invention. The chemical plant has a conversion reactor. The reaction reactor has an educt input and a product output. The first gas outlet is connected to the educt inlet and the product outlet is connected to the second gas inlet. Particularly preferably, the chemical plant is an ammonia synthesis device and the reaction reactor is a converter. The gas-gas heat exchanger according to the invention is thus integrated in the recirculation circuit of the ammonia synthesis.

In a further embodiment of the invention, the reaction reactor has a first sub-reactor and a second sub-reactor. A secondary educt inlet is arranged between the first sub-reactor and the second sub-reactor. The third gas outlet is connected to the secondary educt inlet. Thus, in particular, a less preheated gas can cool the gas stream heated by the reaction that starts. As a result, the full electrical heating power is available for the first reaction stage in the first sub-reactor and the second sub-reactor is heated with the incipient heat of reaction from the first sub-reactor.

1. a) Einleiten von kaltem Eduktgasgemisch in den ersten Gaseinlass,
2. b) Erwärmen des Eduktgasgemisches mit der ersten elektrischen Heizung,
3. c) Erfasse der Temperatur im Umsetzungsreaktor und/oder des den Produktausgang verlassenen Produktgasgemisches,
4. d) Ermitteln des Beginns der chemischen Umsetzung im Umsetzungsreaktor anhand der in Schritt c) erfassten Temperatur,
5. e) Nach dem Beginn der chemischen Umsetzung Reduktion der Heizleistung der ersten elektrischen Heizung.

In a further aspect, the invention relates to a method for starting up a chemical plant according to the invention. The procedure includes the following steps:

1. a) introducing cold educt gas mixture into the first gas inlet,
2. b) heating the educt gas mixture with the first electrical heater,
3. c) record the temperature in the reaction reactor and/or the product gas mixture leaving the product outlet,
4. d) determining the start of the chemical reaction in the reaction reactor based on the temperature recorded in step c),
5. e) After the start of the chemical reaction, reduction of the heating output of the first electric heater.

The recording in step c) can take place directly or indirectly. For example, the heat released in another heat exchanger can also be recorded here, for example via the temperature of the heat exchange medium.

• f) Öffnen der Verbindung zwischen dem dritten Gasauslass und dem Nebenedukteinlass,
• g) Ermitteln des Beginns der chemischen Umsetzung im zweiten Teilreaktor des Umsetzungsreaktor anhand der in Schritt c) erfassten Temperatur,
• h) Nach dem Beginn der chemischen Umsetzung im zweiten Teilreaktor Trennen der Verbindung zwischen dem dritten Gasauslass und dem Nebenedukteinlass.

In a further embodiment of the invention, the method additionally has the following steps between step d) and step e):

• f) opening the connection between the third gas outlet and the secondary educt inlet,
• g) determining the start of the chemical reaction in the second sub-reactor of the reaction reactor based on the temperature recorded in step c),
• h) After the start of the chemical reaction in the second sub-reactor, disconnecting the connection between the third gas outlet and the secondary reactant inlet.

In a further embodiment of the invention, the proportional start of the implementation is determined in step d) and the heating output of the first electrical heater is reduced proportionately. The advantage of this is that, on the one hand, it is possible to heat up to operating temperature as quickly as possible, but on the other hand, overshooting the temperature can be prevented. This is particularly important because an increased temperature shifts the equilibrium in ammonia synthesis to the side of the educts and temperatures that are too high lead to material damage.

• 1 erste beispielhafte Ausführungsform
• 2 zweite beispielhafte Ausführungsform
• 3 dritte beispielhafte Ausführungsform
• 4 vierte beispielhafte Ausführungsform
• 5 fünfte beispielhafte Ausführungsform

The gas-gas heat exchanger according to the invention is explained in more detail below using exemplary embodiments shown in the drawings.

• 1 first exemplary embodiment
• 2 second exemplary embodiment
• 3 third exemplary embodiment
• 4 fourth exemplary embodiment
• 5 fifth exemplary embodiment

In the 1 , 2 and 3 Three exemplary plate heat exchangers are shown in the 4 and 5 Two exemplary raw bundle heat exchangers are shown. The same parts are therefore provided with the same reference numbers

In 1 a first exemplary embodiment of the gas-gas heat exchanger 10 according to the invention is shown. The gas mixture flows in through the first gas inlet 20, which is present twice in the mirror-symmetrical structure shown. This is still cold when the system starts. From there, the gas mixture reaches the first gas distribution area 60 and is distributed there to the first heat exchange gas ducts 100 (three shown here as an example). The first heat exchange gas guides 100 are plate-shaped in the example shown. In regular operation, the gas mixture is heated in countercurrent in the second heat exchange gas ducts 110. However, when starting, the gas on the second gas side is still cold, so there is little or no heating when starting. The gas mixture then reaches the first gas collection area 70 and is heated here by means of the first electrical heating element 120. In regular operation, the first electrical heating element 120 is switched off. The heated gas mixture is released via the first gas outlet 30 and transferred to a reaction reactor (not shown), for example a converter for ammonia synthesis. The gas mixture coming from the reaction reactor, which is warmer in regular operation due to the reaction taking place there than the gas mixture flowing into the gas-gas heat exchanger 10, is returned to the gas-gas heat exchanger 10 through the second gas inlet 40. From the second gas inlet 40, the gas mixture enters the second gas distribution area 80 and from there into the second heat exchange gas guides 110, in the example shown four plate-shaped heat exchange gas guides 110. The first heat exchange gas guides 100 and the second heat exchange gas guides 110 are arranged alternately. From the second heat exchange gas guides 110, the gas mixture then reaches the second gas collection area 90 and is discharged from there via the second gas outlet 50.

The second exemplary embodiment, which in 2 is shown, differs from the first exemplary embodiment in that a third gas outlet 130 is arranged at the first gas collection area 70. Therefore, one can mentally divide the first gas collection area 70 into a first subarea (bottom, adjacent to the third gas outlet 130) and a second subarea (top, adjacent to the first gas outlet 30, with the first electrical heating element 120). In the 3 The third exemplary embodiment shown differs in that a second electrical heating element 140 is arranged in this imaginary first partial area.

In 4 a second exemplary embodiment of the gas-gas heat exchanger 10 according to the invention is shown. The gas mixture flows in through the first gas inlet 20. This is still cold when the system starts. From there, the gas mixture reaches the first gas distribution area 60 and is distributed there to the first heat exchange gas ducts 100 (four shown here as an example). The first heat exchange gas ducts 100 are tubular in the example shown. In regular operation, the gas mixture is heated in countercurrent in the second heat exchange gas ducts 110. However, when starting, the gas on the second gas side is still cold, so there is little or no heating when starting. The gas mixture then reaches the first subregion 72 of the first gas collection region 70 (in 4 and 5 marked separately). From there, the gas mixture reaches the second subregion 74 of the first gas collection region 70. The first electrical heating element 120, which heats the gas stream, is arranged in the second subregion 74. In regular operation, the first electrical heating element 120 is switched off. The heated gas mixture is released via the first gas outlet 30 and transferred to a reaction reactor (not shown), for example a converter for ammonia synthesis. The gas mixture coming from the reaction reactor, which is warmer in regular operation due to the reaction taking place there than the gas mixture flowing into the gas-gas heat exchanger 10, is returned to the gas-gas heat exchanger 10 through the second gas inlet 40. From the second gas inlet 40, the gas mixture enters the second heat exchange gas ducts 110, in the example shown a tubular second heat exchange gas duct 110, in which the first tubular heat exchange gas ducts 100 (four in the cross section shown) are arranged. This allows heat to be transferred across all wall surfaces of the first heat exchange gas ducts 100 into the second heat exchange gas duct 110. From the second heat exchange gas guides 110, the gas mixture then reaches the second gas outlet 50 and is released there.

In the 5 The fifth exemplary embodiment shown differs from the fourth exemplary embodiment in that in the first th subregion 72 a third gas outlet 130 is arranged.

Reference symbols

10

Gas-gas heat exchanger

20

first gas inlet

30

first gas outlet

40

second gas inlet

50

second gas outlet

60

first gas distribution area

70

first gas collection area

72

first section

74

second section

80

second gas distribution area

90

second gas collection area

100

first heat exchange gas supply

110

second heat exchange gas guide

120

first electric heating element

130

third gas outlet

140

second electric heating element

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 2116296 A1 [0005]
• DE 102019202893 A1 [0006]
• EP 3623343 A1 [0007]
• EP 3730456 A1 [0009]
• CN 107188197 A [0010]

Claims (17)

Gas-gas heat exchanger (10), wherein the gas-gas heat exchanger (10) has a first gas side and a second gas side, the first gas side having a first gas inlet (20) and a first gas outlet (30), the second Gas side has a second gas inlet (40) and a second gas outlet (50), the first gas side having a first gas distribution region (60) connected to the first gas inlet (20), the first gas side having a first gas outlet (30) connected to the first gas outlet (30). Gas collection area (70), wherein the first gas distribution area (60) and the first gas collection area (70) are connected to one another via a plurality of first heat exchange gas ducts (100), the first heat exchange gas ducts (100) being in thermal contact with the second gas side, thereby characterized in that at least one first electrical heating element (120) is arranged in the first gas collection area (70). Gas-gas heat exchanger (10). Claim 1 , characterized in that the first gas collection area (70) has a first sub-area (72) and a second sub-area (74), the first sub-area (72) being connected to the first heat exchange gas ducts (100) and the second sub-area (74). is connected to the first gas outlet (30), the first electrical heating element (120) being arranged in the second portion (74). Gas-gas heat exchanger (10) according to one of the preceding claims, characterized in that the first gas side has a third gas outlet (130), the third gas outlet (130) being connected to the first gas collection area (70). Gas-gas heat exchanger (10). Claim 3 , characterized in that the third gas outlet (130) can be closed. Gas-gas heat exchanger (10). Claim 2 in combination with one of the Claims 3 until 4 , characterized in that the third gas outlet (130) is connected to the first portion (72). Gas-gas heat exchanger (10). Claim 5 , characterized in that a second electrical heating element (140) is arranged in the first subregion (72). Gas-gas heat exchanger (10) according to one of the preceding claims, characterized in that the gas-gas heat exchanger (10) is designed as a plate heat exchanger. Gas-gas heat exchanger (10) according to one of the Claims 1 until 6 , characterized in that the gas-gas heat exchanger (10) is designed as a tube bundle heat exchanger. Gas-gas heat exchanger (10) according to one of the preceding claims, characterized in that the gas-gas heat exchanger (10) has a pressure housing. Gas-gas heat exchanger (10) according to one of the preceding claims, characterized in that the second portion (74) is thermally insulated from the second gas side. Gas heat exchanger (10). Claim 10 , characterized in that the second portion (74) is designed in the form of a double tube. Chemical plant with a gas-gas heat exchanger (10) according to one of the preceding claims, wherein the chemical plant has a reaction reactor, the reaction reactor having an educt inlet and a product outlet, the first gas outlet (30) being connected to the educt inlet and the product outlet to the second gas inlet (40) is connected. chemical plant Claim 12 , characterized in that the chemical plant is an ammonia synthesis device and the reaction reactor is an ammonia converter. Chemical plant according to one of the Claims 12 until 13 , characterized in that the reaction reactor has a first sub-reactor and a second sub-reactor, a secondary reactant inlet being arranged between the first sub-reactor and the second sub-reactor, the third gas outlet (130) being connected to the secondary reactant inlet. Method for starting up a chemical plant according to one of the Claims 12 until 14 , wherein the method comprises the following steps: a) introducing cold educt gas mixture into the first gas inlet (20), b) heating the educt gas mixture with the first electrical heater, c) recording the temperature in the reaction reactor and / or the product gas mixture leaving the product outlet, d) Determining the start of the chemical reaction in the reaction reactor based on the temperature recorded in step c), e) After the start of the chemical reaction, reduction of the heating power of the first electrical heater. Procedure according to Claim 15 , characterized in that the method additionally has the following steps between step d) and step e): f) opening the connection between the third gas outlet (130) and the secondary reactant inlet, g) determining the start of the chemical reaction in the second sub-reactor of the reaction reactor based on the temperature recorded in step c), h) after the start of the chemical reaction in the second sub-reactor, separating the connection between the third gas outlet (130) and the secondary educt inlet. Procedure according to one of the Claims 15 until 16 , characterized in that in step d) the proportional start of the implementation is determined and the heating output of the first electrical heater is reduced proportionately.

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