BE1030221B1 - Process and plant for the production of hydrogen from ammonia - Google Patents

Abstract

The present invention relates to a process for producing hydrogen by splitting ammonia, in which ammonia is split into hydrogen and nitrogen in the presence of a catalyst, with the splitting of the ammonia without preceding non-catalytic oxidation in the absence of an oxidizing agent being carried out only by supplying heat in presence of the catalyst takes place. According to one of several alternatively possible process variants, the splitting of the ammonia is carried out in a reactor (18) analogously to a primary reformer, the catalyst being arranged in at least one tube through which ammonia flows. A mixture of ammonia and hydrogen is preferably burned in the combustion chamber of the reactor (18), the nitrogen formed in the reaction being an inert component which serves as an additional heat carrier. A mixture of hydrogen and ammonia is advantageous because it has a medium flame temperature, has better combustion properties than pure ammonia and, depending on the mixing ratio, emits less NOx than the two pure substances.

Description

Process and plant for the production of hydrogen from ammonia

The present invention relates to a method and a system for the production of

Hydrogen by splitting ammonia, in which ammonia is produced in the presence of a

Catalyst is split into hydrogen and nitrogen.

The splitting of ammonia, also known in technical language as “ammonia decomposition” or “ammonia cracking”, takes place according to the procedure described below

Reaction equation: 2 NH3 > N2+3 Hz

The reaction is endothermic and therefore requires the supply of energy in order to take place. Your balance shifts to the side of products at higher

temperatures and at low pressures.

In a CO2-free energy economy, the problem arises of the spatial separation of efficient production of renewable energies and their sources and their energetic or material use. Due to its low boiling temperature, hydrogen as an energy source can only be transported with great effort at extremely high pressures. Intermediaries such as methane or

Ammonia is much easier and cheaper to transport. It therefore makes sense to temporarily store hydrogen produced from renewable sources in an intermediate such as ammonia.

In order to recover the hydrogen at the destination, it must be removed from the intermediate again. Ammonia as a buffer has the advantage of not releasing any CO during re-splitting. The process for splitting the ammonia not only has to

Catalytically splitting ammonia into hydrogen and nitrogen and separating the two from each other, but also includes an efficient form of energy integration

Heat losses are clearly reflected in the efficiency of the process due to the low calorific value of ammonia and hydrogen.

US 2020/0123006 A1 describes a process for cracking ammonia in an autothermal ammonia cracking reactor, in which a non-catalytic partial oxidation of the ammonia takes place with an oxygen-containing gas, whereby a process gas is obtained which contains nitrogen, Contains water, portions of nitrogen oxides and remaining portions of ammonia, after which at least part of the remaining

Proportions of ammonia with hydrogen and nitrogen in the process gas through contact with a

Nickel-containing catalyst is split and proportions of nitrogen oxides are broken down by reaction

Hydrogen, which is formed during the fission process, is reduced to nitrogen and water. In this known process, the partial non-catalytic oxidation step and the ammonia splitting step can be carried out in the same reactor. Air can be used as the oxygen-containing gas for the partial oxidation of the ammonia in the first step.

An adiabatic reaction with an internal energy supply, such as in a secondary or autothermal reformer with an external combustion chamber, requires preheating of the feed and subsequent combustion of parts of the feed to generate the energy necessary for the reaction. Since the possible preheating temperature is limited by material properties and therefore a lot at the same time with a low yield of hydrogen purification

Energy from the combustion of the residual gas cannot be incorporated and a significant amount of ammonia has to be burned to generate the heat of reaction, a completely autothermal solution only achieves low yields of hydrogen. in one

Application example with a hydrogen purification yield of, for example, 86%, the waste heat from flue gas combustion cannot be fully utilized, so that it leaves the process at a temperature of 660 °C. On the other hand, so much ammonia has to be burned in the process stream that the overall material yield of the process is only 72%.

Further disadvantages of the method known from US 2020/0123006 A1 are that poor energy recovery results from water in the process gas. Since ammonia is dissolved in the condensate, recovery is made more difficult. In addition, they form

Nitrogen oxides (NOx) that need to be removed.

Based on the above-mentioned state of the art, the task of the present one is

Invention is to provide a process for producing hydrogen by splitting ammonia with the features mentioned above, in which a higher

Yield and a better energy balance can be achieved.

The solution to the aforementioned problem provides a process for producing hydrogen from ammonia with the features of claim 1.

According to the invention, the ammonia is split without any upstream non-catalytic

Oxidation in the absence of an oxidizing agent only by supplying heat in the presence of the catalyst. In contrast to the method known from US 2020/123006 A1, an external energy supply is therefore provided according to the invention.

The ammonia cracking according to the method according to the invention preferably comprises a five-stage process with the following steps: ammonia evaporation, ammonia cracking, heat recovery, ammonia recovery, hydrogen purification.

Ammonia evaporation is necessary because ammonia is usually liquid

Educt is present at atmospheric pressure and a temperature below its boiling point of -33.5 ° C. Ammonia evaporation requires significant amounts of energy.

For each MW of energy input, around 2.4 /h of ammonia can be preheated and evaporated at a pressure of 30 bar.

Ammonia cracking is the actual reaction, which also takes place thermally but is accelerated by the use of a catalyst. The reaction can be different

Conditions and with different interconnections with different types of reactors, the clever combination of which was the focus of the developments that led to the present invention. In the context of the present application, various advantageous variants for such interconnections in systems for

Ammonia cracking demonstrated.

Heat recovery is an essential aspect as the reaction occurs at increased

temperature takes place. In all preferred ones presented in the present application

Concepts use a burner system to thermally use waste gases from product purification so that hot flue gas is available as an energy source and, in parallel, the hot process gas. Process steam is still preferably used as an internal energy source, so that the heat recovery is able to fulfill the following tasks: — preheating of the feed gas stream — steam generation — combustion air preheating — boiler feed water preheating.

Since driving a turbine with process steam would be disadvantageous from an energy perspective, the process steam does not have to be overheated. Within the scope of the present invention, there are various options for the arrangement of the system parts for heat recovery

Combination options available.

Ammonia recovery serves to separate ammonia that has not been converted in the reaction from the process gas and for further use as fuel or feed gas

To make available. Ammonia can be separated technically in a variety of ways, including membrane separation, adsorption and condensation, but these processes require high pressures and are therefore energy intensive. The absorption of

Ammonia in water can be carried out at process pressures, but requires the application of steam to carry the mixture of ammonia and water through

To be able to separate rectification. Since ammonia has to be burned to produce the steam, this leads to a reduction in the hydrogen yield of the process. If the reaction is carried out skillfully, ammonia recovery can also be dispensed with if necessary. This is possible by choosing the reaction parameters so that the conversion is as high as possible and thus the amount of remaining ammonia is as small as possible. This is not possible through a high reaction temperature alone, as the

The equilibrium temperature would then have to be 900 °C or higher. But small amounts of ammonia can also be separated, for example, in a pressure swing adsorption, which combines the recovery of ammonia and the purification of hydrogen into one step.

The type of hydrogen purification depends on the technical use of the product, which in turn determines the quality requirements. Technical hydrogen can remain relatively impure and, for example, have a purity of around 99.7%. However, if the hydrogen were intended for use in fuel cells, significantly higher purities in the range of, for example, around 99.96% would be necessary. The

For example, hydrogen can be purified by partial condensation, analogous to air separation. However, this requires the use of a compressor to generate the high required inlet pressures of, for example, around 230 bar. Furthermore, upstream adsorptive drying is then necessary to remove traces of ammonia and water and the separation unit itself is also required. Since this concept is very costly in terms of investment and operation, alternatives are to be preferred. Through

Hydrogen and nitrogen are difficult to separate from each other in membranes, and a high inlet pressure must also be created here. An adsorptive separation in one

Pressure swing adsorption is therefore preferred in the context of the present invention, since it takes place at moderate pressures and also achieves high purities of up to over 99.9%,

with a hydrogen yield of 85%. In addition, pressure swing adsorption (PSA) can also capture residual amounts of ammonia and water in the same work step.

According to a first possible preferred variant of the invention, the splitting of the ammonia is carried out in a reactor analogous to a primary reformer, the

Catalyst is arranged in at least one tube through which ammonia flows.

In a reactor according to the invention, which is designed analogously to a primary reformer, the catalyst can be arranged, for example, in one or more tubes through which ammonia flows, for example, from top to bottom. A mixture of ammonia and hydrogen is preferably burned in the combustion chamber of the reactor, with the nitrogen formed in the reaction being an inert component that acts as an additional

Heat transfer medium is used. A mixture of hydrogen and ammonia is advantageous because it has a medium flame temperature and better combustion properties than pure ammonia and, depending on the mixing ratio, it emits less NOx than the two

Pure substances. The generated by the combustion process in the combustion chamber of the reactor

Energy is used to heat the pipe or pipes through which the material to be split

Ammonia gas is passed through.

Various materials can be used as catalysts for the catalytic splitting of ammonia in the context of the present invention. For example, nickel or a nickel-containing catalyst can be used. The temperature at which the reaction takes place is determined in particular by the choice of catalyst system. With a nickel catalyst, for example, higher temperatures are required, for example in the range from about 650 ° C to about 900 ° C. However, these high temperatures cause a high

Sales of, for example, up to over 98%, in particular around 98.5% and a low residual ammonia content in the product gas. The use of a nickel catalyst is more complex despite the higher operating temperature and the associated costs

Energy integration advantageous. Due to the high turnover, a separate separation of the

Ammonia is not required, but it can be in the form of, for example

Pressure swing absorption can be combined with hydrogen purification into one process step.

Alternatively, for example, ruthenium or a ruthenium-containing catalyst is active

Component can be used at temperatures of, for example, about 450 ° C to about 500 ° C, although somewhat lower conversions of, for example, about 95% can be achieved here. With

Ruthenium as the active component can therefore start the reaction at lower temperatures

temperatures take place.

Alternatively, other catalysts can also be used at even lower levels

temperatures are used. Basically, the lower the reaction temperature, the lower the conversion and the more ammonia has to be separated from the product gas and recycled. The selective deposition of ammonia can in particular be carried out adsorptively or absorptively, with deposition using water as the absorbent being advantageous in view of the considerable quantities. The recovery of the

Ammonia from the wash water requires significant amounts of steam to reach the high levels

To achieve vapor deposition rates for a high degree of separation. The production of steam, in turn, requires the combustion of additional ammonia and is therefore disadvantageous in terms of

Hydrogen yield of the process...

The temperature of the reaction determines the equilibrium conversion. For example, at 900 °C and 20 bar pressure, the reaction takes place almost quantitatively. At 650 °C the conversion is

Ammonia about 98.5%, at 500 °C only about 95%. A lower reaction temperature, made possible by more active catalysts, is therefore not always advantageous because at low

Sales require more complex steps to separate the remaining ammonia.

Basically, the optimal operating point is with regard to the energy industry and the

Ammonia conversion in particular in the operating temperature range of around 630 °C to 640 °C.

The reaction pressure is determined in particular by the execution of the hydrogen

Purification. The stoichiometry of the reaction increases the specific volume of the gas stream, therefore increased pressure has a negative effect on conversion. On the other hand, it makes sense to operate a technical process at higher pressures in order to limit the container volume and thus the investment costs. At 1 bar pressure the reaction reaches

Temperatures from 400 °C over 99% conversion. However, since 1 bar only makes sense for small systems, systems on a normal industrial scale should be operated at higher pressures, even if this means accepting a certain loss in sales. Ultimately, the reaction pressure is also determined by the execution of the hydrogen purification.

In the case of pressure swing absorption (PSA) as a joint deposition of

Ammonia and hydrogen, which can be operated effectively in a range of around 15 bar to around 25 bar, for example, the ammonia should preferably be delivered at the “battery limit” at a pressure of around 30 bar a. With a pressure at the reactor outlet of, for example, around 20 bar, both the PSA requirements can be satisfied and the negative influence of the pressure on sales can be limited.

According to the invention, the ammonia splitting reaction can basically take place in different types of reactors. In adiabatic processes the internal energy of the

Reaction gas used as an energy source for the reaction. Examples of this are the autothermal reformer mentioned at the beginning and the secondary reformer, which has internal

Energy production work. Air is added to the process gas and part of the feed stream is burned to increase the temperature of the gas so that the desired temperature prevails at the reactor outlet. The disadvantage of this process is the presence of the water produced during combustion in the process gas, which must be removed by condensation. During this condensation, some of the unreacted ammonia dissolves and is lost to the process. In addition, the high temperatures lead to significant

Amount of nitrogen oxides in the process gas that need to be removed in-line.

In the process management according to the invention with external energy generation, the two aforementioned disadvantages are avoided by physically separating the fuel and exhaust gas and the process gas from one another.

In isothermal reaction procedures, the temperature of the gas remains largely unchanged.

They therefore require a permanent supply of energy, for example by firing one

Primary reformer or an electric heater.

Mixed forms of the above-mentioned process control variants are possible. A fired one

Primary reformer with an upstream fixed bed reactor combines, for example, an adiabatic and an isothermal reaction step. Even purely adiabatic systems do not have to be powered by internal energy generation. A reactor horde or cascade feeds the feed gas into an alternating series of heating steps, each followed by

Reaction steps to use the externally supplied energy as an energy source.

According to a preferred development of the method according to the invention, this is

Ammonia feed gas is preheated before being introduced into the reactor or into a catalyst bed and enters the reactor at a temperature of at least about 600 ° C and up to about 850 ° C, preferably at least about 630 ° C and up to about 820 ° C into the catalyst bed. With optimized energy integration, the feed gas flow occurs at a temperature in

The reaction temperature in the tube (the

Pipes) of the reactor, which (accommodate) the catalyst and through which the ammonia feed gas is passed, is at about 630 ° C to about 670 ° C, preferably at about 650 ° C, preferably the Outlet pressure from the reactor is in the order of about 15 bar to about 25 bar, preferably about 20 bar.

According to an advantageous possible alternative variant of the invention

In the process, the ammonia feed gas is first introduced into the reactor

Once preheated and then fed upstream of the reactor to a pre-reformer in which an intermediate cooling occurs, the ammonia feed gas is then heated again to the temperature intended for entry into the reactor, which is, for example, in a range from approximately 620 ° C to is about 680 ° C, preferably on the order of about 650 ° C. The ammonia feed gas is then fed into the for the further cleavage reaction

Reactor initiated. In this alternative variant, the inlet temperature into the reactor is lower than in the previously mentioned variant, which has the advantage that nitriding of the pipelines only occurs to a lesser extent. Here you take one twice

Heating of the ammonia feed gas before, preferably with an intermediate one

Pre-reformer. In this variant, the preheating of the ammonia feed gas stream is limited, for example to a temperature in the above-mentioned range, whereby the

The service life of the steel is also increased in contact with the ammonia. The one entering

Ammonia gas stream is first preheated to a specified temperature, then part of the cracking reaction is carried out in the pre-reformer and then the partially split feed gas is preheated again to the intended temperature and fed into the primary reformer, where the remaining reaction takes place.

The energy integration must bring the ammonia feed gas to the reactor inlet temperature, where it is advantageous to preheat and evaporate demineralized water and boiler feed water and also preheat the combustion air. Since the

Process heat is present in two strands, the process gas on the one hand and the exhaust gas on the one hand

Reactor (reformer), on the other hand, the heat exchangers can be arranged in different variants according to the invention. At an inlet temperature of the feed gas

Current in the order of, for example, around 650 ° C, you can, for example, arrange a steam generator behind the reactor outlet in order to avoid hydrogen embrittlement. Also the arrangement of a gas-gas heat exchanger, preferably in one

Position downstream of the aforementioned steam generator can be advantageous. Since after the cooling that has already taken place in the gas-gas heat exchanger, the temperature of the

Process gas flow is already comparatively low, it is advantageous to have a preheater for demineralized water, which is used in the system for steam generation

Flow path to be arranged downstream of the aforementioned steam generator and particularly preferably also downstream of the aforementioned gas-gas heat exchanger.

For example, it is also possible in the exhaust gas duct/flue gas duct of the reactor

To use an evaporator coil, which provides at least some of the energy for the

Contributes to steam generation. This increases the performance of the gas-gas heat exchanger and reduces the performance of the said steam generator. Since here only energy transfer from one

Heat exchanger is moved to the other, with such an arrangement the outlet temperatures in the process gas, steam and in the ammonia feed gas stream do not change. At low reactor outlet temperatures, such as around 500 ° C, the enthalpy flow of the process gas is significantly lower and it is therefore advantageous to generate steam largely or completely with flue gas from the reactor

energy source to carry out. This variant of connecting the components for the

Heat recovery has the disadvantage of a lower temperature gradient between

Flue gas and boiler feed water in the evaporator coil, but this is due to a significantly larger

Evaporator coil or a reduction in pressure level can be compensated.

This is done according to a preferred development of the method according to the invention

Heating the ammonia feed gas by means of at least one heat exchanger, wherein

Heat is absorbed from the product gas stream downstream of the reactor and / or the ammonia feed gas is heated by means of at least one heat exchanger, which is arranged in the flow path of a flue gas duct, with heat being absorbed from an exhaust gas stream of a combustion chamber of the reactor or a residual gas combustion.

According to a preferred development of the method according to the invention

Provision of the ammonia feed gas is based on liquid ammonia, which is included

With the help of the thermal energy of hot steam, this hot steam is obtained by means of at least one heat exchanger connected in the system, through which hot product gas flows downstream of the reactor or the residual gas combustion or which is arranged in the flow path of a flue gas duct, whereby

Heat is absorbed from a flue gas stream of a combustion chamber of the reactor or an exhaust gas stream from the residual gas combustion. The use of process steam for the

Evaporation of ammonia is advantageous in terms of safety compared to the otherwise possible direct use of flue gas or process gas as a heat source, because, for example, if a pipe is damaged, ammonia could flow into the exhaust gas and thus into the atmosphere or get into the process stream. Electric evaporation would lead to high energy consumption and “corresponding costs.

From a safety and economic perspective, steam is therefore the preferred heat source

Solution. Since the ammonia has to be preheated, the ammonia evaporation preferably consists of at least two heat exchangers in which ammonia is only released up to

Boiling point is preheated and then evaporated.

According to a preferred development of the method according to the invention

Combustion chamber of the reactor or the residual gas combustion process air is supplied, which is preheated in the system before being introduced into the combustion chamber or the residual gas combustion by means of at least one heat exchanger, which is in the flow path of a

Flue gas duct is arranged, with heat being absorbed from a flue gas stream of the combustion chamber of the reactor or an exhaust gas stream from the residual gas combustion. This means that excess process heat generated in the process can also be used for preheating

Process air can be used.

According to a preferred development of the invention, the reaction of

Ammonia splitting is preferably carried out isothermally, quasi-isothermally or in a mixed form of isothermal and adiabatic process control.

Preferably, in the process according to the invention, the thermal energy contained in the flue gas stream of the reactor and/or in the exhaust gas stream of the residual gas combustion is divided into at least three, preferably at least four, particularly preferably at least five

Flow direction of the flue gas flow or exhaust gas flow arranged one behind the other

Heat exchangers, preferably used for various sub-processes of the process.

According to a possible alternative variant of the method according to the invention

Splitting the ammonia not in the tubes of a reactor but in at least two in

Catalyst beds connected in series in the direction of flow, whereby after the process gas has cooled through the reaction in a first catalyst bed, the process gas is heated again downstream of this first catalyst bed by means of at least one heat exchanger, which is preferably in one

Flue gas duct is arranged, which is fed by the exhaust gas from residual gas combustion.

Preferably, in the aforementioned variant of the method according to the invention,

Residual gas combustion is arranged separately from the catalyst beds and is connected to the

Residual gas after separation of hydrogen from the process gas using at least one

Separating device operated, the separating device preferably being one

Pressure swing adsorption includes and wherein the residual gas combustion is preferably supplied with combustion air from outside the system in addition to the residual gas.

According to a further possible alternative variant of the method according to the invention, at least one electrical heating device is preferably used to support this

To heat up process gas, in particular to heat the process gas when using several in

To bring the direction of flow of catalyst beds connected in series to the entry temperature intended for this before entering the next catalyst bed. According to the invention, part of the heating power can be supplied by electrical current. This creates the possibility, for example, of using fresh ammonia as fuel

To avoid this and instead only use the exhaust gas from hydrogen purification as fuel. In particular, the number of catalyst beds used can be reduced by supplying electrical energy. The electrical heating elements can be inserted directly into the gas space and ensure the temperature increase to the intended inlet temperature into the next catalyst bed. Here, for example, a temperature increase of up to 200 °C can be effected via electrical heating elements, for example one cooled to around 450 °C to around 650 °C

Process gas is heated electrically to temperatures of around 650 °C to around 850 °C.

The increased temperature is not a problem in terms of materials, since the heating can, for example, take place in a channel lined with heat protection lining instead of in a pipeline, which means that the actual pressure jacket is protected from the high temperatures.

The subject of the present invention is also a system for the production of

Hydrogen by splitting ammonia, comprising a splitting device with a

Reactor or at least one catalyst bed for the catalytic splitting of ammonia

Hydrogen and nitrogen with the supply of heat, an evaporation device being arranged upstream of the splitting device, in which liquid ammonia is heated and evaporated, the evaporation device according to the invention being at least two

Heat exchanger includes, wherein at least a first heat exchanger is designed as a preheater to preheat the ammonia and at least a second, the first

Heat exchanger in the flow path downstream heat exchanger is designed as an evaporator and at least one of these heat exchangers is used as steam for operation

Heat source is supplied, which is in a steam generating device of the system by means

Process heat is generated. The use of steam from the system as a heat source

Preheating and evaporation of the ammonia, which is initially in liquid form, is economically and safety-wise advantageous, with steam generated in the system and

Steam condensate is preferably passed through the heat exchanger in countercurrent.

If there is another steam consumer in the process, for example an ammonia wash reboiler, it may be advantageous to extend the chain with a third heat exchanger, as this steam consumer reduces the amount of steam available and increases the amount of available condensate. In this case it can

Ammonia, for example, is evaporated in two heat exchangers connected in parallel.

It is also conceivable to preheat the ammonia with warm cooling water, which would add another heat exchanger to the chain and process steam and thus burnt

would save ammonia.

According to a preferred development of the invention, the system comprises at least one

Steam drum, which serves as a steam generating device, which is in operative connection with a heat exchanger which is arranged downstream of a splitting device in a line through which hot process gas flows. The process heat in the hot

Process gas which leaves the cracking reactor or the catalyst bed is therefore preferably taken up by a heat exchanger and used to heat steam in a steam drum, this steam drum being fed with preferably demineralized water, which is fed into a line system of the system. The steam generated in this way is then fed into the heat exchanger arranged in the area of the front end of the system, which serves to evaporate the ammonia, which is then preheated and fed to the reactor or the catalyst bed.

According to a preferred development of the invention, the system further comprises others

Heat recovery units and/or ammonia recovery devices and/or hydrogen purification devices. Heat, which enables recovery, is available in two strands in a system according to the invention, one being the

Process heat from the process of catalytic splitting of ammonia, which includes a larger mass flow, but is usually lower in temperature and on the other hand, the heat contained in the flue gas from combustion, which is usually significantly higher in temperature, but typically has a lower mass flow.

Efficient heat integration increases the overall yield of the process.

According to a preferred development of the invention, a further unit can be used

Heat recovery, for example, at least one gas-gas heat exchanger

Line system can be arranged downstream of the reactor or a catalyst bed, which on the one hand is flowed through by the hot process gas of the reactor or catalyst bed and which on the other hand is flowed through by the ammonia to be heated.

Feed gas stream flows through, which is fed to the reactor or catalyst bed.

In this variant, heat recovered from the process heat is used to heat up fresh process gas.

Alternatively or additionally, at least one heat exchanger in a flue gas duct downstream can be used as a further unit for heat recovery

Combustion chamber of the reactor or downstream of a residual gas combustion of the system can be arranged. With such a measure, heat is extracted from the flue gas

Combustion used.

Finally, the subject of the present invention is the use of a system with the above-mentioned features in a process for producing hydrogen

Cleavage of ammonia as previously described.

The present invention is explained below using exemplary embodiments

Reference to the accompanying drawings explained in more detail. Show it

Figure 1 shows a flow diagram of a plant for splitting ammonia according to a first exemplary embodiment of the present invention;

Figure 2 is an enlarged view of part of an alternative system according to the invention in which the evaporation of ammonia takes place;

Figure 3 shows a flow diagram of a plant for splitting ammonia according to a second exemplary embodiment of the present invention;

Figure 4 shows a flow diagram of a plant for splitting ammonia according to a third exemplary embodiment of the present invention;

Figure 5 shows a flow diagram of a plant for splitting ammonia according to a fourth exemplary embodiment of the present invention.

A first exemplary flow diagram of a plant for splitting ammonia is explained below with reference to FIG. Liquid ammonia from one

Ammonia tank 10, which is at low temperature and increased pressure, is supplied via the

Line 11 is passed through the preheater 13 by means of the pump 12 and heated, in which

Evaporator 14 evaporates and flows via line 15 at a temperature of, for example, approximately 58 ° C to a branch 16, where a division of the

Ammonia gas stream is divided into two partial streams. Starting from this branch 16, a first part of the ammonia gas is fed into the combustion chamber via line 17

Reactor 18, which is constructed analogously to a primary reformer. A second

Partial flow is carried out from branch 16 via line 19 through a first

Heat exchanger 20 and then flows further via line 21 through a second

Heat exchanger 22, where the ammonia gas is heated further and then flows via line 23 into the tubes 24 of the reactor 18 (primary reformer), in which the catalyst is located, so that the catalytic reaction of ammonia splitting takes place in these tubes 24. The tubes 24 extend in the combustion chamber, with the flow through the tubes 24 preferably from top to bottom. The reaction that takes place in the pipes

Ammonia splitting is endothermic and is necessary to maintain the reaction

Heat is generated by burning the tubes 24 in the combustion chamber

Ammonia can be heated.

Despite the supply of heat, the temperature of the process gas passed through the tubes 24 drops and, when it exits the reactor 18 via line 25, is, for example, about 150 ° C lower than when the ammonia gas enters the tubes via line 23. This

Process gas after the ammonia splitting flows through another in the line

Heat exchanger 26, then flows through the heat exchanger 20 in cross flow, flows through line 27 and flows through another heat exchanger for further cooling and

Preheater 28, which is operated, for example, with demineralized water at, for example, 40 ° C. Finally, the process gas is further cooled by means of a process cooler 29 to a temperature of, for example, 35 ° C and is then fed via a line 30 to a pressure swing adsorption 31 (PSA: pressure swing adsorption), where a

The gas mixture is separated under pressure by adsorption. The one that was separated

Hydrogen leaves the PSA 31 via line 32, is brought to an increased pressure via a first compressor 33, flows through a heat exchanger 34 and a second

Compressor 35 for further increasing the pressure, a second heat exchanger 36 and is derived from the system at a pressure of, for example, approximately 70 bar via line 37.

That remaining in the pressure swing adsorption 31 after the hydrogen has been separated off

Residual gas mixture contains nitrogen, water, residual ammonia and residual hydrogen and is returned via the return line 38 at a comparatively low temperature of, for example, in the order of 40 ° C and via the branching line 39

Combustion chamber of the reactor 18 is supplied so that energy contained in the residual gas mixture can be used to heat the combustion chamber.

The combustion air for the combustion process in the reactor 18 is supplied to the system via a

Filter 40 is supplied cleaned, compressed by means of the compressor 41, passed via line 42 through the heat exchanger 43 and heated, then flows via line 44 and through a further heat exchanger 45, is heated further there and then flows via line 46 and the two Branch lines 47 and 48 branching off from this into the combustion chamber of the

Reactor 18, where the combustion air is supplied via line 17 to the partial flow of the

Ammonia is supplied in order to burn it and thus heat up the combustion chamber.

The hot exhaust gas mixture from the combustion in the reactor 18 is first passed through the

Heat exchanger 22 cooled, thereby providing energy for heating the pipes 24

Reactor 18 supplied process gas is obtained. The flue gas is then passed through a flue gas duct 49 via the heat exchanger 45, by means of which the

Combustion air is preheated and then flows through the flue gas denitrification unit 50, by means of which the flue gas stream is cleaned of nitrogen oxides (NOx). Then it flows through

Flue gas via line 51 another heat exchanger 52, whereby heat is supplied

Heating water is obtained, and then flows through the further heat exchanger 43, which also serves to warm up the combustion air. The flue gas is then compressed in the end region of the flue gas duct 49 by means of the flue gas compressor 53 and leaves the system via a chimney 54.

Demineralized water for steam generation is supplied via line 55 with a

Temperature of, for example, around 40 °C is fed into the system and over the

Preheater 28 is passed and is then passed at a temperature of, for example, about 135 ° C into a deaerator 56 (degasser), in which air and other gases dissolved in the water are removed. Using the pump 57, the water is pumped through the line 58

Heat exchanger 52 and thereby heated to a temperature of, for example, about 230 ° C. The heat exchanger 52 serves to transport the flue gases from the reactor

To cool the flue gas duct 49, with the thermal energy contained in the flue gas being used

Superheating of the steam is used, which then passes through the

Heat exchanger 52 is passed via line 59 into a steam drum 60. From this

Steam drum 60 can be fed boiler feed water through the heat exchanger 26 via line 61 and thereby absorb further heat energy in order to then be returned to the steam drum via line 62. The heat exchanger 26 is arranged in line 25 downstream of the reactor 18 and serves to cool the process gas after leaving the reactor. The thermal energy gained can therefore be used to generate additional steam.

The steam generated in the steam drum 60, for example at around 240 ° C, is passed over the

Line 63 is introduced into the evaporator 14 shown in the upper part of the drawing.

The energy is obtained through the condensation of the steam, the preheated ammonia

To evaporate. . After flowing through the evaporator 14, the condensate is passed over the

Line 64 is fed to the preheater 13, which serves to preheat the ammonia so that the energy contained in the steam is used in two stages to heat the ammonia feed. After flowing through the heat exchanger 13, the condensate can

Temperatures of, for example, 40 ° C are derived from the system.

A second exemplary embodiment of a system according to the invention for splitting ammonia into hydrogen and nitrogen is explained in more detail below with reference to FIG. In this variant of the method, a number of system parts are identical to the corresponding system parts of the variant of Figure 1 and are therefore not explained again in detail, but reference is made to the statements above.

The same system parts are designated with the same reference numbers. The area of the front end, in which the originally liquid ammonia is heated and evaporated, remains unchanged, as does the area downstream

Pressure swing adsorption after separation of the hydrogen (top right in the drawing).

In deviation from the variant of Figure 1, a total of five heat exchangers are now arranged in the flue gas duct 49 instead of four. Here too, line 21 leads for the

Heating of the ammonia feed stream from the gas-gas heat exchanger 20 to the im

Exhaust duct 49 arranged heat exchanger 22. However, after flowing through the heat exchanger 22, the ammonia gas feed stream is passed through a pre-reformer 65, whereby the feed stream cools from, for example, approximately 650 ° C to, for example, approximately 500 ° C and the feed stream is then passed over the Line 66 leads to a further heat exchanger 67, which is arranged in the exhaust duct 49 upstream of the heat exchanger 22. There the feed gas stream is warmed up again, for example to a temperature of

Order of magnitude of approximately 650 ° C and is then introduced via line 23 into the pipe(s) of the reactor 18. The combustion air for the combustion chamber is heated in the same way as described above in Figure 1, initially by heating via the

Heat exchanger 43 and then by further heating via the heat exchanger 45, both heat exchangers 43 and 45 being arranged in the flue gas duct 49. The heating and evaporation of the demineralized water supplied to the system for the

Steam drum 60 via the preheater 28 and the heat exchanger 52, which is arranged in the flue gas duct 49, takes place in principle in the same way as in the variant of FIG. 1. In the alternative variant according to FIG

As seen from the flue gas - the five heat exchangers 67, 22, 45, 52 and 43 are arranged one behind the other in the flue gas duct 49.

The crucial difference in the reaction procedure according to FIG. 3 compared to that of FIG. 1 is that the feed gas preheating is limited to lower temperatures of, for example, approximately 650 ° C, which increases the service life of the reactor steel even in contact with the ammonia. For this purpose, the incoming gas stream is first preheated to, for example, around 650 ° C and then in the pre-reformer 65

Part of the reaction carried out. The feed gas stream with the partially already split ammonia is then heated again, for example again to a temperature of approximately 650 ° C, and fed into the reactor 18, which is constructed analogously to a primary reformer, where the remaining reaction takes place.

A further variant of the method according to the invention will be explained in more detail below with reference to FIG. 4. With this variant you can use an adiabatic

Achieve reaction control, but with external energy supply. Here too, the material problem mentioned above (rapid corrosion of the pipe material due to nitriding) can be avoided by adding the heat to the feed gas stream successively in stages and using it in several catalyst beds to supply the reaction with energy. The

The beds can be arranged either as a tray reactor in which all

Catalyst beds are stacked one on top of the other, as shown in Figure 4, or alternatively several reactors can be designed as separate containers. A

Burner system preferably burns the residual gas from the hydrogen processing and, if necessary, additional ammonia if necessary. The smoke of this

Burner system serves as an energy source for the reaction.

4, the ammonia feed gas preheated in the gas-gas heat exchanger 22 and then further heated in the further heat exchanger 69 to the intended reaction temperature of, for example, approximately 650 ° C, is introduced into a first catalyst bed 70 and partially split there, the temperature drops to, for example, about 400 to 450 ° C as a result of the reaction. The slightly cooled process gas is passed through a heat exchanger 71 and there it is warmed up again to the intended reaction temperature of, for example, approximately 650 and introduced into the second catalyst bed 72, where at least a portion of the ammonia contained in the feed gas stream is again split. The

Heat exchanger 71 is arranged in a flue gas duct 49 so that the hot flue gas serves to heat up the feed gas stream. The feed gas, which has cooled slightly after the reaction in the second catalyst bed, is passed again through a heat exchanger 73, which is located in the flue gas duct 49, heated there again and then into the third

Catalyst bed 74 initiated. A third will be added accordingly

Heat exchanger 75, a fourth catalyst bed 76, a fourth heat exchanger 77 and a fifth catalyst bed 78 flows through and after leaving the fifth catalyst bed 78, the still hot process gas flows via line 79 through the heat exchanger 26, which is used to generate steam, then flows through the gas Gas heat exchanger 20 and from there to the pressure swing adsorption 31, in which hydrogen is separated from the product gas stream. With an arrangement of, for example, five connected in series

Catalyst beds according to the variant of Figure 4 can achieve the same conversion as in an isothermal reaction. The preheating of the feed stream is limited, for example, to approximately 650 ° C in order to reduce the nitriding of the steel used, with the outlet temperatures of the catalyst beds increasing, for example, from approximately 450 ° C to approximately 600 ° C.

Those separated after the hydrogen has been separated off in the pressure swing adsorption 31

Gases, namely residual ammonia, nitrogen, water and residual hydrogen, are fed into the residual gas combustion 68 and burned there together with the combustion air supplied via the line, leaving the residual gas combustion

Flue gas can have a comparatively high temperature of more than 1000 ° C, in particular of over 1100 ° C, in particular of over 1200 ° C, in particular of over 1300 ° C, particularly preferably of more than 1400 ° C, so that the flue gas is sufficient

Contains thermal energy in order to have a sufficient temperature, even after flowing through the cascade of heat exchangers 77, 75, 73, 71 arranged in the flue gas duct, in order to reduce the ammonia feed gas stream supplied via line 19 in the fifth heat exchanger 69 of the cascade to a level for the reaction in first catalyst bed 70 to warm up to sufficient temperature.

In the variant according to Figure 4, a total of seven heat exchangers are arranged in the flue gas duct 49, with the combustion air also being heated via a heat exchanger 43, which, similar to the variant from Figure 1, is the last heat exchanger beyond the cascade of heat exchangers described above in the downstream located

End region of the flue gas duct 49 is arranged. The heat exchanger 52, which adjoins the heat exchanger 43 upstream in the flue gas duct, serves to heat the steam and corresponds in principle to the heat exchanger 52 in Figure 1, which is also in the

Flue gas duct 49 is arranged. Since the temperature of the flue gas depends on the

Residual gas combustion 68 is significantly higher than in the previously described variants of Figures 1 and 2, a larger number of heat exchangers can be arranged in the flue gas duct 49 in the variant of Figure 4. The temperature differences after

Flowing through one heat exchanger in the flue gas duct can, for example, be around 100 ° C to around 220 ° C or more, so that the flue gas temperature before flowing through the last heat exchanger 43 is still on the order of over 300 ° C and is therefore sufficient to heat the combustion air, which after their

Heating is introduced into the residual gas combustion 68. Unlike those two

1 and 3, in the variant of Figure 4, the residual gas combustion 68 is used as an energy source for a gradual heating of individual catalyst beds 70, 72, 74, 76, 78 and the reaction in these catalyst beds takes place virtually spatially separated from the residual gas combustion 68. In the variant of Figure 1, however, this takes place

Combustion of residual gas, if necessary in a mixture with fresh ammonia and the

Combustion air in a reactor 18, through whose pipe (pipes) the feed stream of

Ammonia gas flows through, so that the ammonia gas feed stream is heated directly in the reactor 18 by this combustion process.

A further exemplary embodiment is described below with reference to FIG

Invention explained in more detail. In this variant, part of the heating output can be provided electrically

Electricity can be introduced. In extreme cases, no fresh ammonia is used as fuel, but only the exhaust gas from hydrogen purification. In this case, the maximum possible amount of hydrogen is produced, which is only determined by the yield

Hydrogen purification. In this variant, however, this advantage is offset by the requirement that significant amounts of electrical energy must be used. Figure 5 shows an exemplary process concept according to the invention with a four-stage reactor cascade and additional electrical heating.

Similar to the variant of Figure 4 described above, in the exemplary embodiment according to Figure 5 a residual gas combustion 68 is provided, in the flue gas duct 49 of which

Row of heat exchangers is arranged. The ammonia splitting reaction takes place in a total of four catalyst beds 70, 72, 74, 76 connected in series, with the

Feed gas flow of ammonia first through the gas-gas heat exchanger 20 and the

Heat exchanger 69 is passed in the flue gas duct 49 and then via an electrical

Heating device 88 is further heated to the intended entry temperature into the first catalyst bed 70 of, for example, approximately 650 ° C. The electric heating device can only be used as a support, which means that the preheating takes place before further electric heating

Heating, for example, can already achieve heating to a temperature of over 600 °C. The reaction in the first catalyst bed 70 causes the catalyst to cool down

Process gas, for example, to a temperature in the range of approximately 450 ° C and the cooled process gas can then be used via line 80 for reheating

Heat exchanger 77 is supplied and from there is then introduced into the second catalyst bed 72. Unlike the exemplary embodiment of FIG. 4, this first heat exchanger 77 after the flow through the first catalyst bed is the heat exchanger which is arranged immediately downstream of the residual gas combustion 68. After

Flowing through the second catalyst bed 72, the process gas is warmed up again by being passed through the heat exchanger 75 in the flue gas duct 49. In addition, a further electrical heating device 81 can be provided to heat the process gas in front of the

Introduction into the third catalyst bed 74 to be heated to the intended inlet temperature, which can, for example, be higher than in the first and second catalyst beds 70, 72 and in particular can be from 700 ° C to over 800 ° C, for example around 850 ° C.

After passing through the third catalyst bed 74, the process gas can be passed through a further heat exchanger 73 in the flue gas duct 49 and then heated electrically via the electrical heating device 82 to a temperature that is intended for entry into the fourth catalyst bed 76 and which in turn can be higher than in the first and second catalyst beds. For example, the

Entry temperature into the fourth catalyst bed 76 at more than 700 - 800 ° C, for example at about 840 ° C. In this way, several, for example three electrical

Heating devices 79, 81, 82 for heating the process gas to the appropriate level

The inlet temperature provided for the catalyst bed can be used to provide support, although, as in the examples described above, the heat from the exhaust gas is largely used

Residual gas combustion can be used for heating the process gas through several heat exchangers 73, 75, 77 arranged in the flue gas duct 49. After passing through the fourth catalyst bed 76, the hot process gas can again be passed via line 79 through the heat exchanger 26, by means of which steam is heated.

Figure 2, to which reference is made below, shows a detailed section

Front end area of a system according to the invention, in which the ammonia is heated and evaporated. The illustration according to Figure 2 shows an alternative embodiment of this part of the system. Unlike the variant of evaporation described above in connection with FIG. 1, two evaporators 14, 83 are provided here instead of just one, which can be connected in parallel. The ammonia from the ammonia tank 10 is conveyed through the preheater 13 by means of the pump 12 and then via two mutually parallel lines 84, 85 into the first evaporator 14 and into the second

Evaporator 83 is introduced, the second evaporator 83 being able to be fed with steam via line 86, while the first evaporator 14 can be supplied with steam via line 87

Steam condensate is supplied. After flowing through the first evaporator 14, the condensate reaches the preheater 13 via line 64 and also flows through it, releasing heat. The evaporated ammonia gas can be fed via line 15 to a plant for splitting ammonia, as described in Figures 1, 3, 4 or 5.

List of reference symbols 10 ammonia tank 11 line 12 pump 13 preheater 14 evaporator 15 line 16 branch 17 line 18 reactor 19 line 20 gas-gas heat exchanger 21 line 22 heat exchanger 23 line 24 pipes of the reactor 25 outlet line from the reactor 26 further heat exchanger 27 line 28 preheater 29 Process cooler 30 line 31 pressure swing adsorption, separation device 32 line 33 compressor 34 heat exchanger 35 compressor 36 heat exchanger 37 output line for hydrogen 38 return line 39 branch line 40 filter for combustion air 41 compressor 42 line 43 heat exchanger 44 line

45 Heat exchanger 46 Line 47 Branch line 48 Branch line 49 Flue gas duct, exhaust duct 50 Flue gas denitrification unit 51 Line 52 Heat exchanger 53 Flue gas compressor 54 Chimney 55 Line for feeding water 56 Deaerator 57 Pump 58 Line 59 Line 60 Steam drum 61 Line 62 Line 63 Line 64 Line 65 Pre- Reformer 66 line 67 further heat exchanger 68 residual gas combustion 69 heat exchanger 70 first catalyst bed 71 heat exchanger 72 second catalyst bed 73 heat exchanger 74 third catalyst bed 75 heat exchanger 76 fourth catalyst bed 77 heat exchanger 78 fifth catalyst bed 79 line 80 line 81 electrical heating device

82 electrical heating device 83 further evaporator 84 line 85 line 86 line 87 line 88 electrical heating device

Claims (18)

Patent claims 1. Process for producing hydrogen by splitting ammonia, in which ammonia is split into hydrogen and nitrogen in the presence of a catalyst, characterized in that the splitting of the ammonia without upstream non-catalytic oxidation in the absence of an oxidizing agent only by supplying heat Presence of the catalyst takes place. 2. The method according to claim 1, characterized in that the splitting of the ammonia is carried out in a reactor (18) analogous to a primary reformer, the catalyst being arranged in at least one tube through which ammonia flows. 3. The method according to any one of claims 1 or 2, characterized in that the ammonia feed gas is preheated before introduction into the reactor (18) or into a catalyst bed (70) and at a temperature of at least about 600 ° C and up to about 850 ° C, preferably from at least about 630 ° C and up to about 820 ° C, enters the reactor (18) or the catalyst bed (70). 4. The method according to any one of claims 1 to 3, characterized in that the ammonia feed gas is first preheated for the first time before being introduced into the reactor (18) or a catalyst bed and a pre-reformer (65) upstream of the reactor (18). is supplied, in which the ammonia is partially split into hydrogen and nitrogen and in which intermediate cooling occurs and that the ammonia feed gas is then heated again to the temperature intended for entry into the reactor (18) or the catalyst bed, and is introduced into the reactor (18) or the catalyst bed for the further cleavage reaction. 5. The method according to any one of claims 3 or 4, characterized in that the ammonia feed gas is heated by means of at least one heat exchanger (20), heat being absorbed from the product gas stream downstream of the reactor (18) and/or the ammonia being heated -Feed gas takes place by means of at least one heat exchanger (22, 69), which is arranged in the flow path of a flue gas duct (49), heat being absorbed from a flue gas stream of a combustion chamber of the reactor (18) or from a residual gas combustion (68). 6. The method according to any one of claims 1 to 5, characterized in that liquid ammonia is used to provide the ammonia feed gas, which is evaporated with the help of the thermal energy of hot steam, this hot steam being obtained by means of at least one heat exchanger (26, 52) connected in the system, through which hot product gas flows downstream of the reactor (18) or the residual gas combustion (68), or which is arranged in the flow path of a flue gas duct (49), heat being absorbed from a flue gas stream of a combustion chamber of the reactor (18) or an exhaust gas stream from the residual gas combustion (68). 7. The method according to one of claims 1 to 6, characterized in that the combustion chamber of the reactor (18) or the residual gas combustion (68) is supplied with process air, which is in the system before being introduced into the combustion chamber or the residual gas combustion (68) by means of at least one Heat exchanger (43, 45) is preheated, which is arranged in the flow path of a flue gas duct (49), heat being absorbed from a flue gas stream of the combustion chamber of the reactor (18) or an exhaust gas stream from the residual gas combustion (68). 8. The method according to any one of claims 1 to 7, characterized in that the reaction is carried out isothermally, quasi-isothermally or in a mixed form of isothermal and adiabatic process control. 9. The method according to any one of claims 1 to 8, characterized in that the thermal energy contained in the flue gas stream of the reactor (18) and / or in the exhaust gas stream of the residual gas combustion (68) is divided into at least three, preferably at least four, particularly preferably at least five Flow direction of the flue gas flow or exhaust gas flow of heat exchangers (67, 22, 45, 52, 43) arranged one behind the other, preferably for various sub-processes of the method, is used. 10. The method according to any one of claims 1 to 9, characterized in that the splitting of the ammonia takes place in at least two catalyst beds (70, 72, 74, 76, 78) connected one behind the other in the direction of flow, after the process gas has been cooled by the reaction in In a first catalyst bed downstream of this first catalyst bed, the process gas is heated again by means of at least one heat exchanger (71, 73, 75, 77), which is preferably arranged in a flue gas duct (49) which is fed by the exhaust gas from a residual gas combustion (68). becomes. 11. The method according to claim 10, characterized in that the residual gas combustion (68) is arranged separately from the catalyst beds (70, 72, 74, 76, 78) and with the residual gas after separation of hydrogen from the Process gas is operated by means of at least one separation device (31), the separation device preferably comprising a pressure swing adsorption (31) and wherein the residual gas combustion (68) is preferably supplied with combustion air from outside the system in addition to the residual gas. 12. The method according to any one of claims 3 to 11, characterized in that at least one electrical heating device (88, 81, 82) is used to provide support in order to heat up the process gas, in particular to heat the process gas when using several catalyst beds (70) connected one behind the other in the direction of flow. 72, 74, 76) before entering the next catalyst bed to the intended entry temperature. 13. Plant for producing hydrogen by splitting ammonia, comprising a splitting device with a reactor (18) or at least one catalyst bed (70) for the catalytic splitting of ammonia into hydrogen while supplying heat, an evaporation device being arranged upstream of the splitting device, in the liquid ammonia is heated and evaporated, characterized in that the evaporation device comprises at least two heat exchangers (13, 14), at least a first heat exchanger (13) being designed as a preheater in order to preheat the ammonia and at least a second, the first heat exchanger in Flow path downstream heat exchanger is designed as an evaporator (14) and for the operation of at least one of these heat exchangers (13, 14) steam is supplied as a heat source, which is generated in a steam generating device (60) of the system by means of process heat. 14. Plant for producing hydrogen according to claim 13, characterized in that it comprises at least one steam drum (60) as a steam generating device, which is in operative connection with a heat exchanger (26) which is downstream of a splitting device (18) in a line (25). is arranged, through which hot process gas flows. 15. Plant for the production of hydrogen according to claim 13 or 14, characterized in that it further comprises further units for heat recovery and / or devices for ammonia recovery and / or devices for hydrogen purification. 16. Plant for producing hydrogen according to claim 15, characterized in that at least one gas-gas heat exchanger (20) is arranged in the line system (21) downstream of the reactor (18) or a catalyst bed (70) as a further unit for heat recovery, which, on the one hand, is flowed through by the hot process gas of the reactor (18) or catalyst bed and which, on the other hand, is flowed through by the ammonia feed gas stream to be heated, which is fed to the reactor (18) or catalyst bed (70). 17. Plant for producing hydrogen according to one of claims 15 or 16, characterized in that as a further unit for heat recovery at least one heat exchanger (22, 45, 52, 43) in a flue gas duct (49) downstream of a combustion chamber of the reactor (18) or is arranged downstream of a residual gas combustion (68) of the system. 18. Use of a plant for producing hydrogen according to one of claims 13 to 17 in a method according to one of claims 1 to 12.