BE1030484A1 - 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

1 BE2022/5309

Heat exchanger with integrated start-up heating

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

Many chemical processes, for example and especially 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...

However, the reaction 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 is used for the

Ammonia synthesis is made from natural gas, so natural gas is available in such plants.

However, there is increasing interest in reducing CO2 emissions. Therefore, alternative sources of hydrogen are being sought that do not require the production of CO2. One source, for example, is electrolysis using renewable energy sources

Electricity. However, this means that natural gas is no longer necessarily suitable for the

Start-up process is available. On the other hand, the emission of CO should also be avoided in such processes. The need therefore arises,

Educts have to be heated 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. There in

However, if pressures far exceed 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.

A start-up heater for an ammonia reactor is known from EP 2 116 296 A1.

2 BE2022/5309

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

A process for producing ammonia is known from EP 3 623 343 A1.

From WO 2017/186 613 A1 there is a method for heating an ammonia

Converter known.

From EP3730456A1 the use of renewable energies for

Ammonia synthesis is known.

From 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

Problems of the two known solutions are avoided.

This task is solved by the gas-gas heat exchanger with the features specified in claim 1, the chemical plant with those specified in claim 12

Features and the method with the features specified in claim 15.

Advantageous further developments result from the subclaims below

Description and 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 that in the first

Gas flowing on the gas side is transferred. In particular, when implementing the

Heat generated by the gas is used to heat the inflowing educts. The first

Gas side has a first gas inlet and a first gas outlet. At first

The gas stream to be heated is fed to the first gas side in a wet gas state and the heated gas stream is then released again at the gas outlet. The second gas side points

3 BE2022/5309 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 increase the surface area and thus the

Heat transfer improved. The number of plural depends on the embodiment. For example, if this is plate-shaped (plate heat exchanger), then there are 10 to 25

Heat exchange gas ducts are common. For example, if the embodiment is tubular (tube bundle heat exchanger), 20 to 250 heat exchange gas ducts are more common.

The person skilled in the art will therefore select the number of the majority according to the designs common in the prior art. The first heat exchange gas ducts are with the second

Gas side in thermal contact. This allows heat to be transferred.

According to the invention, there is at least a first electrical gas collection area in the first gas collection area

Heating element arranged. During regular operation, the first electrical heating element is switched off. This only heats up when starting up from a cold state.

The arrangement is chosen such that the gas initially flows through the first gas side, is heated electrically at the end, and from there is fed into a conversion reactor. However, there is still none there due to the temperature being too low

reaction takes place. 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 the ammonia synthesis, so that the reaction can take place in

Implementation reactor begins and generates additional energy. From this point on, that is

System no longer relies on the supply of external energy through the first electrical

Heating element required. The first electric heating element can either be complete

4 BE2022/5309 can be switched off or slowly reduced until the target temperature is reached.

The arrangement in the gas-gas heat exchanger does not create its own pressure-stable heat exchanger

Housing is required, nor is the space for the catalyst in the converter reduced, 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 electric heating element is in the second

Partial area is arranged. The effect is that the gas on the first gas side in the first

Partial area has approximately the temperature of the gas flowing into the second gas side and this is further increased in a separate second partial area. This also allows, for example, the extraction of gas streams in two different ways

Temperature levels.

In a further embodiment of the invention, the second portion is thermally insulated from the second gas side. This prevents this from happening in the second

Hotter gas entering the gas side is 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 section can be achieved by a double pipe, provided the second

Partial area is tubular. The space in the double pipe 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 on. The third gas outlet is connected to the first gas collection area.

This is particularly preferred if the first gas collection area is 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 is 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 subregion.

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 as

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 over a plurality of second

Heat exchange gas ducts connected to each other. 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 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 can have a second gas inlet connected to the second gas inlet

Gas distribution area and a second connected to the second gas outlet

Have gas collection area. The second gas distribution area and the second

Gas collection areas 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 arranged parallel to each other.

Preferably, the second gas side in the area of the first heat exchange gas ducts is opposite the gas duct in the first heat exchange gas ducts

Direction flows through (countercurrent heat exchanger).

6 BE2022/5309

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 one

Implementation reactor. The reaction reactor has one reactant inlet and one

Product output. The first gas outlet is connected to the educt inlet and the

Product outlet is connected to the second gas inlet. This is particularly preferred

Chemical plant is an ammonia synthesis device and the reaction reactor is a

Converter. The gas-gas heat exchanger according to the invention is therefore in

Integrated recirculation circuit for 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. This means that the full electrical heating output is the first

Reaction stage in the first sub-reactor is available and the second sub-reactor is heated with the incipient heat of reaction from the first sub-reactor.

In a further aspect, the invention relates to a method for starting up a chemical plant according to the invention. The method includes the following steps: a) introducing cold educt gas mixture into the first gas inlet, 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 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.

7 BE2022/5309

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.

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

Implementation 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 and the secondary educt inlet.

In a further embodiment of the invention, the proportionate 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,

Temperature overshoot 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.

Below is the gas-gas heat exchanger according to the invention based on in the

Drawings illustrated embodiments explained in more detail.

Fig. 1 first exemplary embodiment

Fig. 2 second exemplary embodiment

Fig. 3 third exemplary embodiment

Fig. 4 fourth exemplary embodiment

Fig. 5 fifth exemplary embodiment

Three exemplary plate heat exchangers are shown in FIGS. 1, 2 and 3, and two exemplary raw bundle heat exchangers are shown in FIGS. 4 and 5. Same

Parts are therefore given the same reference numbers

8 BE2022/5309

1 shows a first exemplary embodiment of the gas-gas system according to the invention.

Heat exchanger 10 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 there for the first time

Heat exchange gas guides 100 (three shown here as an example) are distributed. The first

Heat exchange gas guides 100 are plate-shaped in the example shown. In the

In regular operation, the gas mixture is fed into the second one in countercurrent

Heat exchange gas guides 110 heated. However, when starting up, the gas on the second gas side is still cold, so there is little or no warming up

Starting takes place. The gas mixture then enters 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 in

Due to the reaction taking place there, regular operation is warmer than the gas-gas

The gas mixture flowing into the 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, four plate-shaped in the example shown

Heat exchange gas guide 110. The first heat exchange gas guides 100 and the second heat exchange gas guides 110 are arranged alternately. From the second

The gas mixture then reaches the second heat exchange gas guides 110

Gas collection area 90 and is released from there via the second gas outlet 50.

The second exemplary embodiment, which is shown in FIG. 2, differs from the first exemplary embodiment in that a third gas outlet 130 is arranged at the first gas collection region 70. Therefore you can do the first

Gas collection area 70 mentally divided into a first subarea (bottom, adjacent to the third gas outlet 130) and a second subarea (top, adjacent to the first

Gas outlet 30, share with the first electrical heating element 120). The third exemplary embodiment shown in Fig. 3 differs in that in this

9 BE2022/5309 mental first subarea a second electrical heating element 140 is arranged.

4 shows a second exemplary embodiment of the gas-gas system according to the invention.

M heat exchanger 10 shown. The gas mixture flows in through the first gas inlet 20. This is still cold when the system starts. That's where it comes from

Gas mixture into the first gas distribution area 60 and is there for the first time

Heat exchange gas guides 100 (four shown here as an example) are distributed. The first

Heat exchange gas ducts 100 are tubular in the example shown. In regular operation, the gas mixture is fed into the second one in countercurrent

Heat exchange gas guides 110 heated. However, when starting up, the gas on the second gas side is still cold, so there is little or no warming up

Starting takes place. The gas mixture then reaches the first subregion 72 of the first gas collection region 70 (marked separately in FIGS. 4 and 5). 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 discharged via the first gas outlet 30 and into 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 guides 110, in the example shown a tubular second one

Heat exchange gas guide 110, in which the first tubular heat exchange gas guides 100 (four in the cross section shown) are arranged. This is a

Heat transfer over all wall surfaces of the first heat exchange gas ducts 100 into the second heat exchange gas duct 110 is possible. From the second

Heat exchange gas guides 110, the gas mixture then reaches the second gas outlet and is released there.

10 BE2022/5309

The fifth exemplary embodiment shown in FIG. 5 differs from the fourth exemplary embodiment in that in the first portion 72 there is a third

Gas outlet 130 is arranged.

Reference symbols

Gas-gas heat exchanger 20 first gas inlet 30 first gas outlet 40 second gas inlet 10 50 second gas outlet 60 first gas distribution area 70 first gas collection area 72 first sub-area 74 second sub-area 80 second gas distribution area 90 second gas collection area 100 first heat exchange gas guide 110 second heat exchange gas guide 120 first electrical heating element 130 third gas outlet 140 second electric heating element

Claims (17)

11 BE2022/5309 patent claims 1. 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), wherein 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 first 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), wherein the first heat exchange gas ducts (100) are 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 area (70). 2. Gas-gas heat exchanger (10) according to claim 1, characterized in that the first gas collection area (70) has a first partial area (72) and a second partial area (74), the first partial area (72) having the first heat exchange gas guides (100) is connected and the second portion (74) is connected to the first gas outlet (30), wherein the first electrical heating element (120) is arranged in the second portion (74). 3. 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). 4. Gas-gas heat exchanger (10) according to claim 3, characterized in that the third gas outlet (130) can be closed. 5. Gas-gas heat exchanger (10) according to claim 2 in combination with one of claims 3 to 4, characterized in that the third gas outlet (130) is connected to the first portion (72). 12 BE2022/5309 6. Gas-gas heat exchanger (10) according to claim 5, characterized in that a second electrical heating element (140) is arranged in the first portion (72). 7. 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. 8. Gas-gas heat exchanger (10) according to one of claims 1 to 6, characterized in that the gas-gas heat exchanger (10) is designed as a tube bundle heat exchanger. 9. 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. 10. 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. 11. Gas heat exchanger (10) according to claim 10, characterized in that the second portion (74) is designed in the form of a double tube. 12. 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 is connected to the second gas inlet (40). 13. Chemical plant according to claim 12, characterized in that the chemical plant is an ammonia synthesis device and the reaction reactor is an ammonia converter. 14. Chemical plant according to one of claims 12 to 13, characterized in that the reaction reactor has a first sub-reactor and a second 13 BE2022/5309 sub-reactor, wherein a secondary educt inlet is arranged between the first sub-reactor and the second sub-reactor, the third gas outlet (130) being connected to the secondary educt inlet. 15. A method for starting up a chemical plant according to one of claims 12 to 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) Record the temperature in the reaction reactor and/or the product gas mixture leaving the product outlet, d) Determine 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, reduce the heating power of the first electrical heater. 16. The method 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 educt inlet, g) determining the start of the chemical Implementation in the second sub-reactor of the implementation 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 reactant inlet. 17. The method according to any one of claims 15 to 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.