DE102011013271A1 - Process and plant for the reduction of nitrogen oxide emissions during steam reforming - Google Patents

Abstract

To reduce nitrogen oxides in steam reforming, wherein a gaseous carbon support, preferably natural gas, and water are reacted in a reactor to a synthesis gas containing hydrogen, carbon monoxide and carbon dioxide, hydrogen, carbon monoxide and / or carbon dioxide are separated from the synthesis gas and the resulting in the reactor Flue gas passed over at least one catalyst stage and subjected there to a selective catalytic reduction. A portion of the gaseous carbon support, a portion of a mixture of the gaseous carbon support and water, a portion of a gaseous fuel used for heating, a portion of the synthesis gas, a portion of the depleted synthesis gas and / or a portion of the separated hydrogen is / are in the catalyst stage used as a reducing agent.

Description

The present invention relates to a process and a plant for the reduction of nitrogen oxides in steam reforming, wherein a gaseous carbon support and water are reacted in a reactor to a synthesis gas containing hydrogen, carbon monoxide and carbon dioxide, wherein hydrogen, carbon monoxide and / or carbon dioxide separated from the synthesis gas is passed and the resulting flue gas in the reactor via at least one catalyst stage and there is subjected to a selective catalytic reduction.

Nitrogen oxides (NO _x ) is a collective term for gaseous oxides of nitrogen. Due to the many oxidation states of nitrogen, there are a number of nitrogen-oxygen compounds, the most important being nitric oxide (NO), nitrogen dioxide (NO ₂ ) and di-nitric oxide (N ₂ O, nitrous oxide). Nitrogen oxides are the source of a multitude of environmental pollution, which is why they attracted early environmental attention. They are among the main causes of acid rain, are the cause of the so-called summer smog with the associated environmental pollution and act as strong greenhouse gases. In particular, the nitrous oxide also contributes significantly to the destruction of the ozone layer.

The main source of nitrogen oxides are combustion processes, especially in motor vehicle traffic and in large-scale stationary applications. To reduce nitrogen oxide emissions, selective catalytic reduction (SCR) has been developed. In this case, a reducing agent, usually ammonia (NH ₃ ), the exhaust gas admixed, resulting in a heterogeneous catalyst to a Komproportionierung the nitrogen oxides comes as a result of water and nitrogen. Ammonia has the advantage that it is a readily available and cheaply procurable substance. Because ammonia is liquid at ordinary ambient temperatures, it can be easily stored and transported.

In the development of the SCR technology, in addition to ammonia, further reducing agents were investigated, which, however, have a lower reduction potential. That's how it describes DE 11 2006 003 078 T5 the selective catalytic reduction of nitrogen oxide with a mixture of hydrogen and carbon monoxide over a catalyst having a palladium content of 0.1 to 2.0%, a vanadium pentoxide content (V ₂ O ₅ ) of 0.1 to 7% and an oxide support material having a has a large surface. However, with this catalyst, only NO can be effectively reduced.

The US 2010/0092360 A1 describes a novel catalyst for the selective catalytic reduction of NO and partly also NO ₂ with hydrogen, the catalyst consisting of a mixture of platinum and palladium, which is in contact with a solid carrier material mixed with magnesium oxide and cerium oxide. The reaction of NO takes place under strictly observed oxidizing conditions in a helium atmosphere.

The US 2009/0285740 A1 describes a selective catalytic reduction on a palladium catalyst deposited on a zirconia sulfate. Hydrogen is also used as the reducing agent, wherein water and hydrogen are injected into the exhaust gas stream and a molar ratio of hydrogen and NO _x must be set within a range of 10 to 100, which requires very large amounts of hydrogen.

All these methods have in common that they can be carried out successfully only under certain, well-defined conditions. In addition, often only NO, sometimes also NO ₂ , but not N ₂ O successfully reduced. In addition, there are difficulties in the hydrogen storage and the hydrogen transport, which is why hydrogen has hardly been able to prevail as a reducing agent in industrial application.

Another reducing agent studied in academia is methane. That's how it describes WO 2008/026002 A1 the conversion of nitrogen monoxide (NO) to nitrogen dioxide on a metal zeolite catalyst, wherein a hydrocarbon is used as a reducing agent. An implementation of other nitrogen oxides is not described.

The publication in "Mechanistic study of SCR-NO with methane over Pd-loaded BEA zeolite" by Yong-Ki Park et. al., published in Journal of Molecular Catalysis A, Chemical 158, 2000, pp. 173-179 describes a SCR process with methane, in which a likewise nitrogen monoxide-containing gas is reacted on a palladium-loaded BEA zeolite.

These two methods have in common that only nitrogen monoxide (NO) can be reduced with them. A reduction of other nitrogen oxides, in particular nitrous oxide, is also not described in these reducing agents.

The classic SCR catalyst with NH ₃ as the reducing agent is a doped vanadium pentoxide catalyst, which is applied to titanium dioxide. With this at least nitrogen monoxide and nitrogen dioxide can be converted into dinitrogen and dioxygen with sufficiently high conversions. Problematic in this conventional Catalyst system is, however, that the catalyst has only a low high temperature resistance and therefore it comes to the unwanted phase transformation of the V ₂ O ₅ from the anatase to the rutile modification and also to the sublimation of vanadium. On the other hand, V ₂ O _{5 is} toxic. Another disadvantage is the relatively high price and the high price volatility of the vanadium raw material. The actual and potential risks of vanadium emission from sublimation and other undesirable side reactions are only partially covered. Due to the described problems of conventional catalytic systems, these are no longer permitted, for example, in the Japanese and partly also in the US automotive industry. It is therefore to be expected that the use of vanadium will no longer be permitted in stationary applications in the future.

In part, zeolitic systems are now being used. The EP 0 955 080 B1 describes a process for preparing a catalyst material by incorporating a metallic component in a synthetic zeolite material. However, this catalyst is so active that it already works without the introduction of an additional reagent, which is why in industrial processes a number of side reactions is to be feared.

The WO 03/105998 describes a method and apparatus for reducing the NO _x content relative to all components, wherein the exhaust gas to be purified is passed over two catalyst beds, both of which are filled with old loaded zeolites. The reducing agent used is ammonia.

The publication "Uhde EnviNOx® Technology for NOx and N2O abatement - A contribution to reducing emissions from nitric acid plants". M. Groves, A. Sasonow, Fifth International Symposium on Non-CO2 Greenhouse Gases, 30.6-3.7.2009, Wageningen describes a method in which for effective reduction, the SCR system is also divided into two parts. In a first step, the nitrogen oxides are reduced with ammonia as a reducing agent and then further lowered in a second step using hydrocarbons.

Nitrogen oxides are basically also produced in all processes in which air is heated to temperatures of more than 1000 ° C. in at least one step, as a result of which radical reactions of the N ₂ molecules contained in the air are intensified. One of these processes is the so-called steam reforming (also called "steam reforming"), in which a carbon support is heterogeneously catalysed with water to give synthesis gas of hydrogen (H ₂ ) and carbon monoxide (CO) and carbon dioxide (CO ₂ ).

The WO 2009/080937 A2 proposes a method for the selective catalytic reduction of nitrogen oxides in combustion exhaust gases, including from the steam reforming, in which ammonia is used as a reducing agent. In a first step, a reactor is heated by a hot gas and in a second step, the exhaust gas produced in the furnace is selectively reduced. For this purpose, part of the gas intended for heating is branched off and mixed with the reducing agent before it is introduced into the catalyst stage. This allows accurate temperature control. By this method, at least the content of NO and N ₂ O can be lowered significantly.

However, the use of ammonia as a reducing agent has a number of disadvantages in flue gas denitration of steam reforming. On the one hand, an ammonia provision and dosage is basically necessary. On the other hand, ammonia is classified as a toxic and environmentally hazardous substance, with the use of special safety equipment (ventilation, emergency showers, etc.) are required. A minor emission of unreacted ammonia can not be excluded, which limits the performance of these systems and poses a potential environmental impact. In addition, the storage of the reducing agent in an ammonia tank requires additional space in the system, whereby the space requirement can be further increased by possibly to be maintained safety distances due to explosion protection zones. The regular filling of the ammonia tank represents a significant risk at the prevailing operating temperatures.

It is therefore an object of the invention to provide a method for the selective reduction of nitrogen oxides, in particular also nitrous oxide, in the purification of the flue gases from a steam reformer system, which does not work with ammonia as a reducing agent, but all nitrogen oxides contained in the exhaust gas equally can be implemented.

This object is achieved with the features of claim 1, after which a gaseous carbon support and preferably vaporous H ₂ O are reacted in a reactor to a synthesis gas containing hydrogen, carbon monoxide and carbon dioxide. The reaction is an allothermic reaction, which is why the reactor must either be indirectly heated or fired directly. To heat the reactor, another gaseous fuel is used. Both the gaseous carbon carrier and the other fuel are preferably methane or natural gas. The synthesis gas formed in the reactor is then divided into its components hydrogen, carbon monoxide and carbon dioxide or it is set a defined mixture of these components. The resulting flue gas is also passed over at least one catalyst stage where it is subjected to selective catalytic reduction. The reducing agent used in this catalyst stage is part of the gaseous carbon support, part of a mixture of the gaseous carbon support with the water or steam, part of the gaseous fuel used for heating the reactor, part of the (depleted) synthesis gas and / or a part of the separated hydrogen used. The mentioned disadvantages of ammonia as a reducing agent omitted. In addition, such a process is easy to maintain, since the filling of an ammonia tank is eliminated.

The flue gas preferably has a CO ₂ content of 15 to 20 mol%, an H ₂ O content of 15 to 20 mol%, an O ₂ content of 0.5 to 5 mol%, an argon content of about 1 mol% and a NO _x content of 50 to 250 mg / m ³ .

In a favorable embodiment of the catalyst stage, this contains a metallic component of one or more metals and / or metal oxides of the group Cr, Cu, Mn, Mo, Fe, Co, Pd, Ru, Pt, Rh, Ti, Zr, V, W, preferably palladium, ruthenium and platinum. By using palladium, ruthenium and / or platinum in pure or oxidic form, disadvantages of a vanadium-containing catalyst can be avoided. In addition, the preparation of a metallic catalyst is simpler than that of a zeolitic one.

Furthermore, it is favorable if the catalyst stage contains a zeolite in whose structure atoms of one or more metals (s) and / or metal oxides (s) of the group Cr, Cu, Mn, Mo, Fe, Co, Pd, Ru , Pt, Rh, Ti, Zr, V, W, preferably iron, copper or cobalt. According to the invention, zeolite is understood as meaning a crystalline substance from the group of aluminosilicates having a uniform spatial ring structure of SiO ₄ / AlO ₄ tetrahedra linked via hydrogen atoms. Any zeolite may be used, but preference is given to zeolites in a ten or twelve ring structure and zeolites of the MFI, FER, MOR and BEA types. The zeolite used is additionally characterized by the replacement of one or more metals or metal oxides. As exchange metals, for example copper, iron or cobalt and a doping with one or more transition or precious metals are used. The metals are typically located in the zeolitic ring structure at characteristic centers, the alpha, beta or gamma positions. The invention involves metals exchanged at all three positions, preferably with an exchange content of between 2.5 and 15% by weight, irrespective of whether this exchange takes place in the liquid or solid phase. The exchanged metal can be present in metallic form or as metallic oxides or in any possible mixture and as monomer or dimer.

The significant advantage of the zeolitic catalyst over the metallic catalyst system is its higher temperature stability, allowing for a wider design temperature regime and leading to greater system insensitivity to unwanted or unusual operating conditions. Furthermore, zeolitic catalysts have a higher DeNOx activity, resulting in a wider temperature window for the operating condition as well as a potentially smaller catalyst volume and correspondingly smaller reactors. In addition, zeolites have a simplified, fully synthetic raw material base, which is why there is an environmentally friendly catalyst composition (pollutant, noble and transition metal-free) and lower raw material prices. Another advantage of zeolites as catalysts for SCR reactions is lower catalytic activity for undesired side reactions. In particular, vanadium-based products produce the undesirable nitrous oxide, sulfur trioxide and gaseous vanadium in the classic SCR reaction conditions. In particular, the formation of the nitrogen oxide N ₂ O to be degraded is to be regarded as highly disadvantageous.

Since temperatures in the range 850-1200 ° C, preferably 900 to 1050 ° C, in particular about 970 ° C prevail in the reactor, the flue gas exits the reactor at temperatures of 150 ° to 200 ° C above the reactor temperature. In order to recover at least part of the heat of the flue gas, the gaseous carbon support used as one of the starting materials and / or the water, which is preferably introduced into the reactor in a vaporized manner, are conducted in heat exchange with the flue gas. Thus, the gaseous carbon carrier and / or the water or the steam can be further warmed up. Based on the water, the amount of energy contained in the flue gas can also be used to evaporate the water. The temperature of the flue gas entering the catalyst stage is then between 200 and 500 ° C; a preferred range for the SCR reactions for the entry of the gas into the catalyst bed is 200 to 350 ° C when using NH ₃ , and 150 to 250 ° C when using H ₂ as the reducing agent.

Since the flue gas may contain other impurities, it is also beneficial that Flue gas to subject at least one further purification step. Such a cleaning step may be, for example, a desulfurization, or the filtration of the particles contained in the exhaust gas. In order not to unnecessarily burden the catalyst for the SCR process, it may be useful to switch both the desulfurization and the filtration before the SCR catalyst stage. However, this has the disadvantage, in particular with integrated heat recovery of the flue gas, that the temperature of the flue gas can drop so sharply that it is no longer high enough to allow the SCR process to run completely. The advantage of an arrangement in which the SCR process is switched in the second or even in the first position of the exhaust gas aftertreatment therefore has the advantage that it is possible to work with relatively high temperatures. However, it takes a catalyst damage in purchasing, which has a negative effect on the lifetime, especially in metallic catalysts.

In order to achieve a sufficient distribution of the gaseous reducing agent, it has been found to be particularly favorable to divert a portion of the flue gas upstream of the catalyst stage, to meter the reducing agent into this partial stream and then to feed this mixture into the catalyst stage. This prevents locally high concentrations of the reducing agent and undesirable storage processes.

The invention further includes a plant for the reduction of nitrogen oxides in a steam reforming, which is suitable for carrying out the method according to the invention and having the features of claim 8. This plant comprises a reactor into which opens either a conduit for the supply of a mixture of H ₂ O and a carbon carrier or two separate lines for the separate introduction of H ₂ O and a carbon carrier. The synthesis gas formed in the reactor is fed via a discharge of a separator. In addition, an exhaust gas line leads into a catalyst stage, wherein a metering device for introducing a reducing agent is provided before or in the catalyst stage. The exhaust pipe is led directly out of the reactor. The metering device is connected via a line to one of the feed lines of the reactor, a further feed line for a gaseous fuel for heating the reactor, the discharge for the formed (depleted) synthesis gas and / or the discharge for the separated hydrogen. The connection of the metering device with the discharge can be provided both before and after the separation device for the separation of the reaction products of the steam reforming.

According to the invention, the metering device is designed so that it is suitable for introducing a gas. It differs from the dosing devices of classical SCR systems, which are operated with ammonia as a reducing agent, since the ammonia is introduced as a liquid either in its pure form or, as for example in the vehicle sector, as a urea solution.

Furthermore, it has proven to be particularly advantageous that the metering device is provided in a partial flow line which branches off from the exhaust gas line and opens into the catalyst stage.

It has also been found to be favorable to use the catalyst either as a bulk material of extruded cylindrical Vollkörperextrudaten or as a honeycomb catalyst modules depending on the process-side allowed pressure loss. Systematic advantages of the honeycomb catalyst modules are the improved mechanical properties, a significantly reduced process-side pressure drop and a simplified reactor filling and emptying. In addition, when using honeycomb modules, the replacement of parts of the catalyst bed is possible and a scale-up easier because here, similar to the microreaction technique, only a numbering-up must be done.

Further developments, advantages and applications of the invention will become apparent from the following description of an embodiment and the drawing. All described and / or illustrated features alone or in any combination form the subject matter of the invention, regardless of their combination in the claims or their dependency.

The sole FIGURE shows the diagram of a steam reforming plant according to the invention with a downstream SCR catalyst stage;

In a reactor according to the invention 10 will be over line 1 and 1' preferably with the compressor 2 introduced compressed methane. In principle, however, other carbon-containing gaseous carbon carriers, such as natural gas, mineral spirits or methanol as well as biogas, are also conceivable here. However, methane has the advantage that only a few impurities are introduced into the system. Previous purification steps, such as the removal of acid gases, e.g. As AGR-acid gas removal or the Rectisol process can be omitted.

Via wire 3 and 3 ' Water is preferably introduced into the reactor as steam 10 brought in. It is therefore beneficial to have the water over one heat exchangers 4 to lead. In order to achieve complete mixing of the two educts, methane and water, it may be advantageous to combine the two starting materials first in a common line, if necessary in addition to mix and then together in the reactor 10 feed. Optionally, the water or water vapor can be partially or completely before or after the compressor 2 are admixed to the carbon carrier and the entire starting material mixture via line 1' in the reactor 10 be guided. Usually, the starting material mixture or the individual educts before entering the reactor 10 in a heat exchanger 8th warmed up.

In the reactor 10 it is preferably a fired tube furnace. This tube furnace is operated with a fuel gas, preferably natural gas or methane or depleted synthesis gas (tail gas / off gas), via the supply line 5 and 5 ' in the reactor 10 is introduced. About the heat exchanger 6 the fuel gas can also be previously heated. However, other directly fired reactors are conceivable as well as indirectly heated, in particular the steam reforming can also be carried out in microreactors.

About a derivation 7 it will be in the reactor 10 resulting synthesis gas removed. This synthesis gas is then processed in one or more purification steps. To separate the products H ₂ , CO and CO ₂ comes as the last stage of a separation process 40 for carrying out a catalytic, adsorptive, absorptive or cryogenic separation process or combinations of such processes, preferably a process of pressure swing absorption, for use. Via wire 41 the resulting carbon monoxide is removed, via line 42 the carbon dioxide and via pipe 43 the hydrogen. Alternatively, a defined mixture of all components mentioned is taken as product (synthesis gas mixture).

The over line 11 exhausted flue gas from the fired furnace undergoes one or more incomplete heat recovery steps. Preferably, the flue gas can be used to heat water, methane and / or the fuel gas.

Via wire 15 The exhaust gas still loaded with nitrogen oxides then enters an SCR catalytic converter stage 20 , where possibly the exhaust gas is heated to the ideal operating temperature of 150 to 350 ° C. In this catalyst stage 20 will be over line 22 ' a reducing agent is fed, wherein the amount of the reducing agent via the metering device 21 can be controlled or regulated. As a reducing agent, the hydrogen from the treated product stream behind the separator 40 be removed. In principle, however, it is also conceivable to use the depleted synthesis gas stream 22 divert.

The reducing agent can either via line 22 ' directly into the catalyst stage 20 be introduced or optional parts of the exhaust stream to be cleaned via line 15 ' branched off, with the line 22 ' connected is. This forms a bypass in which the metering device 21 is positioned.

Not only hydrogen but also methane and natural gas can be used as reducing agents. This must be done from the feed line of the educt 1 and / or the fuel 5 a line to the metering device 21 be guided. The use of the educt or the fuel gas has the advantage that the yield of hydrogen or synthesis gas is not reduced by the exhaust gas purification process.

Several reducing agents can also be mixed. Although all of these reducing agents have a lower reduction potential than NH ₃ within a system with vanadium catalyst, they have the advantage that they are already present in the system.

Via wire 23 The purified exhaust gas is then in a chimney 30 guided and escapes as electricity 31 ,

example

A typical steam reforming plant with a production of 45,000 Nm ³ / h of hydrogen has a flue gas quantity of 173,000 m ³ / h. With pure natural gas firing, a NO _x content of 200 mg / m ³ (0.00667 mol / m ³ ) in the exhaust gas is to be expected. The amount of substance in firing is typically composed of about 95 mol% NO and 5 mol% NO ₂ . In addition, N ₂ O concentrations are found between 2 to 500 ppm by volume, in particular between 20 and 80 ppm by volume. A typical emission limit value for the total nitrogen oxide load is about 100 mg / m ³ , so that about 548 mol / h of NO, 29 mol / h of NO ₂ and the N ₂ O must be as completely as possible implemented. The stoichiometric hydrogen demand according to the reaction equations: 2NO + 2H ₂ → N ₂ + 2H ₂ O and 2NO ₂ + 4H ₂ → N ₂ + 4H ₂ O is thus 606 mol / h or 13.6 m ³ / h, which corresponds to 0.03% of the production amount.

In the flue gas of a furnace of a steam reforming reactor is expected to be about 1.2 vol .-% oxygen. These 2076 m ³ / h of oxygen are about 12.8 m ³ / h of hydrogen. The proportion of hydrogen in oxygen of 0.6% falls below the lower explosion limit, which is 4% in air and 19% in pure oxygen. The use of hydrogen as a reducing agent thus does not lead to an explosive atmosphere.

LIST OF REFERENCE NUMBERS

1, 1 '

management

2

compressor

3, 3 ', 3' '

management

4

heat exchangers

5, 5 '

supply line

6

heat exchangers

7

derivation

8th

heat exchangers

10

reactor

11

management

13

management

15, 15 '

management

20

SCR catalyst stage

21

metering

22, 22 '

management

23

management

30

fireplace

31

management

40

separating device

41

management

42

management

43

management

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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

• DE 112006003078 T5 [0004]
• US 2010/0092360 A1 [0005]
• US 2009/0285740 A1 [0006]
• WO 2008/026002 A1 [0008]
• EP 0955080 B1 [0012]
• WO 03/105998 [0013]
• WO 2009/080937 A2 [0016]

Cited non-patent literature

• "Mechanistic study of SCR-NO with methane over Pd-loaded BEA zeolite" by Yong-Ki Park et. al., published in the Journal of Molecular Catalysis A, Chemical 158, 2000, pp. 173-179 [0009]
• "Uhde EnviNOx® Technology for NOx and N2O abatement - A contribution to reducing emissions from nitric acid plants". M. Groves, A. Sasonow, Fifth International Symposium on Non-CO2 Greenhouse Gases, 30.6.3.7.2009, Wageningen [0014]

Claims (10)

A process for the reduction of nitrogen oxides in steam reforming, wherein a gaseous carbon support, preferably natural gas, and water are reacted in a reactor to a synthesis gas containing hydrogen, carbon monoxide and carbon dioxide, wherein hydrogen, carbon monoxide and / or carbon dioxide are separated from the synthesis gas and wherein the in the reactor resulting flue gas is passed through at least one catalyst stage and there subjected to a selective catalytic reduction, characterized in that a part of the gaseous carbon support, a part of a mixture of the gaseous carbon support and water, a part of a used for heating gaseous fuel, a part of the synthesis gas, a portion of the depleted synthesis gas, and / or a portion of the separated hydrogen in the catalyst stage is used as the reducing agent. A method according to claim 1, characterized in that the flue gas has a CO ₂ content of 15 to 20 mol%, an H ₂ O content of 15-20 mol%, an O ₂ content of 0.5 to 5 mol having%, an Ar content of about 1 mol% and a NO _x content of 50 to 250 mg / Nm ³ -. A method according to claim 1 or 2, characterized in that the catalyst stage is a metallic component of one or more metals and / or metal oxides of the group Cr, Cu, Mn, Mo, Fe, Co, Pd, Ru, Pt, Rh, Ti, Zr , V, W contains. Method according to one of the preceding claims, characterized in that the catalyst stage contains a zeolite in the structure of atoms of one or more metals (s) and / or metal oxides (s) of the group Cr, Cu, Mn, Mo, Fe, Co, Pd, Ru, Pt, Rh, Ti, Zr, V, W. Method according to one of the preceding claims, characterized in that the flue gas is at least partly used for heating the gaseous carbon support and / or H ₂ O. Method according to one of the preceding claims, characterized in that the flue gas is subjected to at least one further cleaning step. Method according to one of the preceding claims, characterized in that a part of the flue gas is branched off, mixed with the reducing agent and fed into the catalyst stage. Plant for the reduction of nitrogen oxides in steam reforming, in particular for carrying out a process according to one of the preceding claims, with at least one reactor ( 10 ), into which at least one line ( 1' ) for a mixture consisting of water and a carbon support, preferably natural gas, with one of the reactor ( 10 ) outgoing derivative ( 7 ), by the formed synthesis gas via at least one separating device ( 40 ) is conducted to the separation of hydrogen, carbon monoxide and / or carbon dioxide from the synthesis gas, and with a catalyst stage ( 20 ) in an exhaust pipe ( 15 ) of the reactor ( 10 ), wherein before and / or in the catalyst stage a metering device ( 21 ) is provided for introducing a reducing agent, characterized in that the metering device ( 21 ) with a line ( 1 . 3 ) for introducing the carbon carrier or a mixture of the carbon carrier with water, a supply line ( 5 ) for a gaseous fuel, the derivative ( 7 ) for the synthesis gas, the derivative ( 22 ) for the depleted synthesis gas and / or the derivative ( 43 ) is connected to the separated hydrogen. Plant according to claim 8, characterized in that the metering device ( 21 ) is suitable for the introduction of a gas. Plant according to claim 8 or 9, characterized in that the metering device ( 21 ) is provided in a bypass, which by the from the exhaust pipe ( 15 ) branching line ( 15 ' ) and the supply line for the reducing agent ( 22 ' ) is formed.

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