DE102019202893A1 - Process for the production of ammonia - Google Patents

Abstract

The present invention relates to a process for the production of ammonia by catalytic conversion of a nitrogen and hydrogen-containing synthesis gas mixture, the ammonia synthesis catalyst being heated in a start-up phase when the reaction is started in order to generate the required activation energy for the ammonia synthesis reaction and, according to the invention, a hot process gas for this heating is used, which is obtained in one of the process steps of the production process upstream of the ammonia synthesis reaction (36). For this purpose, a hot process gas generated in a carbon monoxide converter (11) of the system or, alternatively, a hot process gas generated in a methanation unit (30) of the system can be used. The invention makes it possible to save a start-up furnace in the ammonia synthesis, since the necessary activation energy for the ammonia reaction is provided from existing sources within the ammonia process.

Description

The present invention relates to a method for producing ammonia by catalytic conversion of a nitrogen and hydrogen-containing synthesis gas mixture, the ammonia synthesis catalyst being heated in a start-up phase when the reaction is started in order to generate the required activation energy for the ammonia synthesis reaction, a hot process gas being used for this heating which is obtained in one of the process steps of the manufacturing process preceding the ammonia synthesis reaction.

An elementary component in the process of ammonia production, based on the well-known Haber-Bosch process, is the exothermic reaction of hydrogen and nitrogen to form ammonia in an approximate ratio of 3: 1. An iron-containing catalyst is usually used.

In order to start the exothermic ammonia reaction and thus be able to guarantee continued operation, the activation energy required for the reaction must first be provided. This is usually done by an externally heated start-up furnace. The heat to be provided in the start-up furnace is usually provided by burning hydrocarbons.

The operation and especially the starting of the start-up furnace turn out to be difficult in practice in many cases and are often fraught with problems. In addition, the start-up furnace only fulfills the task of warming up the ammonia synthesis catalyst and is then switched off again. The warm-up process of the ammonia synthesis catalyst takes several hours. There is no permanent use.

The U.S. 4,171,343 A describes a start-up procedure for the synthesis of ammonia in a plant that includes a primary reformer, a secondary reformer, two carbon monoxide conversion units, a device for removing carbon dioxide, methanation and an ammonia synthesis converter. In this known method, the primary reformer and the secondary reformer are heated with steam and the device for low-temperature CO conversion is heated with preheated desulfurized hydrocarbon gas. In a subsequent phase, the process in the reformers is started up with preheated hydrocarbon gas and steam or oxygen and the gas from the reformers is used to preheat the high-temperature CO conversion. In addition, the device for removing carbon dioxide is preheated with exhaust gas from the low-temperature CO conversion and a proportion of gas from the high-temperature CO conversion. Subsequently, a process gas stream from the two reformers is passed through both CO conversion units and through the device for removing CO ₂ for methanation in order to preheat them. Finally, the process gas flow from the methanation is fed into the preheated ammonia synthesis converter. In this process, the various parts of the system are heated up in a rather cumbersome manner in several phases. In this known system, no separate heat exchanger is provided by means of which the heat from the process gas from the high-temperature CO conversion unit could be used to directly heat the synthesis gas supplied to the ammonia unit without having to pass it through all the other system parts beforehand. The parts of the system are connected to one another in a purely sequential manner. In the warming-up phase, in principle in each step the downstream part of the installation is heated with a process gas previously generated in the upstream part of the installation.

In the US 2004/0219088 A1 a mini ammonia plant is described which is intended to be used for the in situ production of small amounts of ammonia. The system includes methanation and the process gas emerging from this is then brought to the process pressure required for ammonia synthesis by means of a compressor. Downstream of the compressor there is an electric gas heater (trim heater), which is also used as a preheater (start-up heater) in the start-up phase of the system. This preheater is located in the flow path between the compressor and a first ammonia converter and the process gas flowing out of the methanation always flows through it. In this known system, no separately flow-through line loop is provided, through which flow is only in the start-up phase. A heat exchange with a hot process gas, which occurs in other parts of the plant upstream of the methanation, for example after the CO conversion, is also not provided here. In addition to the "trim heater", the ammonia converters are preceded by a further heat exchanger, which, however, only provides for heat exchange with the hot product gases that arise during the ammonia reaction in the converters.

The object of the present invention is to provide an improved method for the synthesis of ammonia with preheating of the ammonia synthesis catalyst with the features of the type mentioned above, which makes it possible to save the start-up furnace in the ammonia synthesis and the necessary To provide activation energy elsewhere from existing sources within the ammonia process.

The solution to the aforementioned object is provided by a method of the type mentioned at the beginning with the features of claim 1.

According to the invention, it is provided that the hot process gas is passed through a device designed in the manner of a heat exchanger for preheating, which is integrated into a separate line circuit through which the synthesis gas supplied to the ammonia synthesis reaction does not flow during regular operation of the plant.

The general approach to solving the problem at hand is the use of hot process gas from one or more process steps preceding the ammonia synthesis. Since a process-side temperature of at least about 400 ° C. should be present to provide the necessary activation energy for ammonia synthesis, two sources from the previous process steps are particularly suitable for performing this task.

The method according to the invention preferably comprises at least one steam reforming and at least one carbon monoxide conversion downstream of the steam reforming, the hot process gas generated in the carbon monoxide conversion being passed downstream of this through the device designed as a heat exchanger for preheating, through which a colder gas flow is passed in countercurrent and is heated, which is used to warm up the ammonia synthesis catalyst in the ammonia converter.

As the first option preferred within the scope of the present invention (variant 1 ) the use of the hot process gas downstream of a carbon monoxide conversion, in particular downstream of the high-temperature carbon monoxide conversion (HTS) to warm up the ammonia synthesis catalyst, is possible. In terms of process technology, the carbon monoxide conversion is arranged after the steam reforming step.

In steam reforming, a feed gas stream containing hydrocarbons (usually natural gas) is reacted with steam in the primary reformer according to the reaction equation listed below ( 1 ): CH ₄ + H ₂ O → CO + 3 H ₂ (1)

The task of the carbon monoxide conversion is to convert the carbon monoxide (CO) in the process gas to carbon dioxide and hydrogen by means of a catalytic reaction with water vapor, according to the following reaction equation ( 2 ): CO + H ₂ O → CO ₂ + H ₂ (2)

The aforementioned reaction is exothermic.

A possibly possible modification of this variant of the method according to the invention provides that the hot process gas generated in the carbon monoxide conversion is divided downstream of it and only a partial flow of this hot process gas is used to warm up the ammonia synthesis catalyst in the ammonia converter.

The hot process gas which leaves the carbon monoxide conversion and is used for heating up the ammonia synthesis catalyst can in particular have a temperature of 400.degree. C. to 500.degree.

In the first variant of the method, the gas can thus be passed completely or only partially at a temperature of, for example, between about 400 ° C and 500 ° C through a heat exchanger, through which the relatively colder gas flows on the other side to warm up the ammonia synthesis catalyst.

Usually there is waste heat utilization behind the high-temperature carbon monoxide conversion, for example in the form of a boiler feed water preheater, which generates heat from the exothermic carbon monoxide conversion according to reaction ( 2 ) by preheating boiler feed water or other media. This is done in order to set the inlet temperature for the subsequent low-temperature carbon monoxide conversion (LTS) to approximately 200 ° C., for example. The heating of the boiler feed water serves in the further course of the energy use to generate high pressure steam with which various drive machines in the ammonia plant are driven after subsequent overheating. According to a preferred variant of the method according to the invention, the lack of energy for boiler feed water preheating due to the preheating of the ammonia synthesis catalyst can be provided in another way, for example by using an external auxiliary boiler, which in most applications is already present in an ammonia plant.

For the common ammonia production capacities between, for example, approximately 1000 and approximately 3300 tons per day, the energy to be provided for heating the ammonia synthesis catalyst ranges from approximately 7 to approximately 20 Megawatt. In this variant of the invention, no noteworthy changes in the process management are necessary.

According to a second preferred variant of the invention, the method comprises at least one methanation and the hot process gas resulting from the methanation is wholly or only partially passed downstream of the methanation through the device designed as a heat exchanger for preheating, through which a colder gas flow is passed and heated in countercurrent , which is used to warm up the ammonia synthesis catalyst in the ammonia converter.

An alternative possibility within the scope of the present invention to provide the corresponding activation energy for the catalyst in the ammonia synthesis is thus to use the exothermic reaction energy from the methanation. The task of methanation is to remove the residual traces of carbon monoxide (CO) and carbon dioxide (CO ₂ ) from the process gas, which are harmful for the subsequent ammonia reaction. This happens through a catalytic reaction in which the proportions of CO and CO ₂ remaining in the process gas with the hydrogen H ₂ in the process gas according to the following reaction equations ( 3 ) and ( 4th ) react to methane. This reaction takes place exothermically and the amount of heat released can be influenced by the amount of CO ₂ and CO in the process gas. CO + 3 H ₂ → CH ₄ + H ₂ O (3) CO ₂ + 4 H ₂ → CH ₄ + 2 H ₂ O (4)

In the process according to the invention, the hot process gas exiting from the methanation which can be used for heating the ammonia synthesis catalyst has a temperature of at least 390 ° C., preferably a temperature of at least 400 ° C., particularly preferably a temperature of at least 410 ° C. The hot gas emerging from the methanation can be used entirely or only partially in a heat exchanger in order to preheat the cold gas flowing on the other side of the heat exchanger to heat the ammonia synthesis catalyst. In this case, part of the heat of reaction from the methanation can be used for the start-up process of the ammonia synthesis cycle.

Usually, according to the state of the art, the gas exiting the methanation with a temperature of, for example, approx. 330 ° C is used in a gas-gas heat exchanger (GGT) to preheat the process gas entering the methanation to the required activation temperature of the methanation reaction. The required activation temperature for methanation is approximately 300 ° C. As a result of the warming up of the ammonia synthesis catalyst, less energy would be available for setting the inlet temperature in the methanation.

In the method according to the invention, the process gas entering the methanation has a minimum temperature of 300 ° C, preferably a minimum temperature of 320 ° C, particularly preferably a minimum temperature of 330 ° C.

According to a further development of the method according to the invention, a start-up preheater connected upstream of the methanation in the flow path is preferably used for setting the inlet temperature of the process gas into the methanation. Since the exothermic reaction energy from the methanation is usually not sufficient to provide the required 300 ° C at the start of the methanation even in normal plant operation with a fresh catalyst in the methanation, a start-up preheater is connected upstream of the methanation reactor in a preferred design of the plant according to the invention. The start-up preheater provides the heat for setting the methanation inlet temperature in most cases through the condensation of high-pressure steam, which can be taken from the steam drum from the upstream process steps. This method can also be used if part of the heat from the methanation reaction is to be used to preheat the catalyst in the ammonia synthesis.

According to a preferred development of the method according to the invention, the hot process gas emerging from the methanation is at least partially passed through a gas / gas heat exchanger assigned to the methanation and used to preheat the process gas fed to the methanation.

A start-up preheater upstream of the methanation in the flow path can also be used to set the inlet temperature of the process gas in the methanation.

Particularly preferably, the process gas is first passed through a gas / gas heat exchanger and then through a start-up preheater before entering the methanation.

The temperature at the methanation outlet is under normal process conditions for example about 330 ° C to 340 ° C and is influenced by the content of carbon monoxide and carbon dioxide in the gas entering the methanation. Under normal process conditions, the CO content of the inlet gas entering the methanation is, for example, about 0.3% by volume and the CO ₂ content there is, for example, about 0.05% by volume. The CO content is set in the upstream (usually multi-stage) step of CO conversion and the CO ₂ content is set in the upstream step of CO ₂ cleaning. The reactions of CO and CO ₂ to methane and water that take place in methanation according to the above reaction equations ( 3 ) and (4) usually lead to the above-mentioned outlet temperatures from the methanation of, for example, about 330 ° C to about 340 ° C.

According to a preferred development of the invention, the method comprises at least one method step for removing carbon dioxide (CO ₂ scrubbing) from the process gas in a device provided for this purpose before the process gas is introduced into the ammonia converter and upstream of the methanation, with a partial flow of the process gas directly from the Methanation is supplied bypassing this facility for removing carbon dioxide. Since ideally a preheating temperature of, for example, about 380 ° C should be present for preheating the ammonia synthesis catalyst, an exit temperature from the methanation of around 400 ° C is advantageous, taking into account a moderate heat exchange surface in the heat exchanger between the methanation and ammonia catalyst preheater. In order to achieve the required exit temperature from the methanation, a part of the process gas (preferably about 5 to 10% of the molar amount) is preferably passed around the CO ₂ scrubbing in order to artificially reduce the CO ₂ content in the process gas before the methanation to increase. As a result, the exothermic reaction in the methanation can be intensified and the outlet temperature from the methanation can be adjusted accordingly to the required temperature.

In the alternative variants for preheating the ammonia synthesis catalyst described herein, the duration of the preheating of the synthesis catalyst is a relevant influencing factor. In the cold state of the ammonia converter at the beginning of the preheating, the process gas temperature in the device for preheating (start-up heater) for the ammonia synthesis catalyst is, for example, about 50 ° C to about 80 ° C. At an approximate rate of, for example, about 80 ° C. to about 100 ° C. per hour, the process of preheating the ammonia synthesis catalyst takes, on average, about 4 to about 6 hours, for example. During this period, the requirements for the start-up heater performance of the ammonia synthesis also change over time. The warmer the catalyst, the less heat has to be provided by the start-up heater for the ammonia synthesis. These changing requirements for the start-up heater for ammonia synthesis can be taken into account in different ways in the preferred process alternatives listed in the present application.

With the variant according to 1 As a consequence of the constantly increasing inlet temperature of the ammonia synthesis gas in the preheater of the ammonia synthesis, the required performance of the heat exchanger between the high-temperature CO conversion and the downstream boiler feed water preheater, for example, would continue to decrease and thus more heat would be available again for boiler feed water preheating. In this case, the additional heat required from an auxiliary boiler that may have to be used would decrease over time.

With the variant according to 2 It is not possible at this point to minimize the amount of process gas passed around the CO ₂ scrubber, since the CO ₂ content at the entry into the methanation must be kept high, around the required temperature of around 380 ° C, for example to provide for the ammonia converter catalyst. Since the performance of the preheater for ammonia synthesis decreases with increasing duration, the inlet temperature in the gas-gas exchanger increases and thus also the inlet temperature in the steam-operated preheater for methanation. The inlet temperature into the methanation should preferably not exceed a temperature of about 300 ° C. In the case of a process gas temperature of over 300 ° C upstream of the methanation preheater, a corresponding heat removal would have to take place in the preheater. This can be done, for example, by evaporating boiler feed water, whereby the steam generated in the process can be used for preheating purposes elsewhere in the process (for example in the process capacitor stripper).

The present invention also relates to a plant for the production of ammonia comprising at least one ammonia converter and units upstream of this in the flow path for generating and processing a synthesis gas to be fed into the ammonia converter comprising at least one reformer section, at least one carbon monoxide conversion downstream of this in the flow path and at least one device for preheating the ammonia synthesis catalyst in one Start-up phase when starting the reaction in order to generate the necessary activation energy for the ammonia synthesis reaction, whereby according to the invention at least one device designed as a heat exchanger for preheating is provided as a device for preheating the ammonia synthesis catalyst, which device is arranged downstream of the carbon monoxide conversion and on the one hand is flowed through by a hot process gas and which, on the other hand, is in operative connection on the input side with at least one line for a colder gas stream of synthesis gas processed in the plant, in heat exchange with the hot process gas, and on the output side in operative connection with the ammonia converter via at least one line.

An essential element of the solution according to the invention is that the device for preheating the ammonia synthesis catalyst is integrated into its own separate line circuit, which can preferably be shut off via valves or the like, so that hot process gas, which is produced in a system part upstream of this device, is in a start-up phase can pass through this device and the synthesis gas fed to the ammonia converter in the start-up phase for the purpose of preheating by heat exchange can also be passed through this device. In normal operation of the plant, on the other hand, the above-mentioned separate line circuit can optionally be shut off and the synthesis gas generated in the plant can be fed directly to the ammonia synthesis reactor, since preheating is no longer necessary.

Another advantage of the invention is that the device for preheating can optionally be connected to different system parts in which hot process gases arise, for example with a carbon monoxide conversion or with a device for methanation. These are system parts that are usually present in an ammonia system and in which process gases with possibly different temperatures occur on the outlet side, so that the thermal energy stored in these process gases is targeted and variable for preheating the synthesis gas that is fed to the ammonia converter, as required, can be used.

The aforementioned separate line circuit for the device for preheating is preferably integrated into the line system of the plant in such a way that the synthesis gas can flow into this separate line circuit downstream of the synthesis gas compressor and is then fed to the ammonia synthesis reactor after being preheated in the device. This separate line circuit is generally only flowed through by the synthesis gas in the start-up phase of the plant, while this can flow through at least one alternative line from the synthesis gas compressor directly to the ammonia synthesis reactor in regular operation.

According to a preferred embodiment of the invention, the device for preheating is arranged downstream of a first carbon monoxide conversion of the system and a hot process gas generated in the first carbon monoxide conversion flows through it, the device for preheating being arranged upstream of a second carbon monoxide conversion of the system . In this variant of the design of the system, the heating of the process gas that occurs in the first carbon monoxide conversion can be used to preheat the synthesis gas before it gets into the ammonia converter. The first carbon monoxide conversion can work, for example, at a comparatively higher temperature, while the second carbon monoxide conversion, arranged downstream of this, is preferably a low-temperature CO conversion, in which an additional water-gas shift reaction takes place. Systems for processing the synthesis gas for an ammonia reaction often include two such carbon monoxide conversions, which are connected in series and work at different temperatures.

In a variant of the system according to the invention, the device for preheating is arranged downstream of a methanation of the system and a hot process gas generated in the methanation flows through it. In this variant, instead of the hot process gas flow from the carbon monoxide conversion, the heat of a process gas flow from the methanation, which is usually part of an ammonia plant, is used.

The system according to the invention preferably further comprises at least one device for removing carbon dioxide from the process gas, which is preferably arranged upstream of the methanation, wherein at least one line is also provided through which the process gas can flow, bypassing the device for removing carbon dioxide, before the Process gas enters the methanation. As a rule, so-called CO ₂ scrubbing is present in ammonia plants, which has the task of at least largely removing the CO ₂ generated during the previous CO shift. If part of the process gas (preferably about 5 to 10% of the molar amount) is passed around the CO ₂ scrubbing, the CO ₂ content in the process gas can be artificially increased before the methanation. This can intensify the exothermic reaction in the methanation and the exit temperature from the methanation adjusted accordingly to the required temperature.

The system according to the invention preferably further comprises a line leading back from the device for preheating on the output side to a gas / gas heat exchanger of the methanation unit, wherein preferably a line through which hot process gas from the methanation flows also leads to the gas / gas heat exchanger. The gas / gas heat exchanger assigned to the methanation is used to preheat the process gas supplied to the methanation. If the process gas flowing in the aforementioned return line still has a sufficiently high temperature after flowing through the device for preheating, this heat can be used to heat the process gas in the gas / gas heat exchanger, which is fed to the methanation.

On the output side with respect to the process gas stream that cools during the heat exchange, the gas / gas heat exchanger is preferably in operative connection with the ammonia converter via a line, with a synthesis gas compressor usually being connected upstream of the ammonia converter in order to bring the process gas to the pressure required for the ammonia reaction. The temperature-controlled synthesis gas then either enters the ammonia converter directly during regular operation of the plant or, in the start-up phase, the process gas coming from the gas / gas heat exchanger initially flows through the preheating device described above and is then fed to the ammonia converter.

• 1 eine schematisch vereinfachte Darstellung einer beispielhaften, für das erfindungsgemäße Verfahren verwendbaren Anlage gemäß einer ersten möglichen Ausführungsvariante der vorliegenden Erfindung;
• 2 eine schematisch vereinfachte Darstellung einer beispielhaften, für das erfindungsgemäße Verfahren verwendbaren Anlage gemäß einer zweiten möglichen Ausführungsvariante der vorliegenden Erfindung.

The present invention is explained in more detail below on the basis of exemplary embodiments with reference to the accompanying drawings. Show:

• 1 a schematically simplified representation of an exemplary plant that can be used for the method according to the invention according to a first possible embodiment variant of the present invention;
• 2 a schematically simplified representation of an exemplary plant that can be used for the method according to the invention according to a second possible embodiment variant of the present invention.

In the following, first with reference to the 1 the basic structure of a plant for the production of ammonia is explained in which, according to the invention, the catalyst for the ammonia reaction is preheated with the aid of a hot process gas from one of the upstream process steps. In 1 only the system parts of an ammonia system that are essential for understanding the present invention are shown. This usually includes a reformer section 10 , which can comprise different reformers, for example a combination of a primary reformer and a secondary reformer connected downstream of this. Alternatively, for example, an autothermal reformer or combinations of various reformers of the type mentioned can be used. In the case of using a primary reformer, steam reforming of a hydrocarbon-containing feed gas stream, for example natural gas, takes place in this, with carbon monoxide and hydrogen being generated according to the reaction equation given below ( 5 ): CH ₄ + H ₂ O → CO + 3 H ₂ (5)

Following this reaction, if a secondary reformer is used, a further conversion of hydrocarbons in the presence of oxygen or air can be provided, with further hydrogen being generated according to the reaction equation given below ( 5 a): 2 CH ₄ + O ₂ → 2 CO + 4 H ₂ (5 a)

In this way in the reformer section 10 Synthesis gas is then generated via the pipe 12 a first facility 11 supplied for carbon monoxide conversion, also referred to as a water gas shift reaction, the task of which is to convert the carbon monoxide (CO) in the process gas by means of a catalytic reaction with water vapor to carbon dioxide and hydrogen according to the following reaction equation ( 6th ): CO + H ₂ O → CO ₂ + H ₂ (6)

The aforementioned reaction is exothermic. In many cases, two consecutive CO conversions are made with the first setup set in the 1 with the reference number 11 is provided, a high temperature carbon monoxide conversion (also called HTS) can be. The process gas prepared in this way then reaches the branch during normal operation of the system 13 branching line 14th and the open valve 15th as well as the junction 16 into the line 17th to a boiler feed water preheater 18th , in which excess heat from the heating of the process gas can be used, for example, in heat exchange to preheat boiler feed water.

In the warm-up phase of the system, however, according to the invention, this is the high-temperature CO conversion 11 leaving syngas mixture at the junction 13 via the open valve 45 and the line 44 as hot process gas the facility 39 supplied for preheating, which is flowed through in countercurrent by the cooler synthesis gas, which the ammonia converter 36 is supplied to this synthesis gas in the start-up phase and warm-up phase of the plant in the facility 39 to preheat. The function of this facility 39 for preheating is explained in more detail below.

In the following, the other components of the in 1 illustrated system and its function in regular operation. After flowing through the boiler feed water preheater 18th the process gas passes through the pipe 19th into a second CO conversion, a so-called low-temperature CO conversion 20th , in which a water gas shift reaction takes place again at a lower temperature according to equation (2) given above. After that, the process gas is over the line 21st another heat exchanger 22nd supplied, in which a heat recovery takes place. The process gas is then passed through the line 23 a facility 24 supplied, in which a CO ₂ scrubbing takes place, which serves to at least partially remove the carbon dioxide previously formed in the water-gas shift reaction from the gas mixture. Over the line 25th The process gas that has been treated in this way then first enters a gas / gas heat exchanger 26th , then over the line 27 in a start-up preheater 28 for methanation and is then over the line 29 methanation 30th fed.

In the methanation, the residual proportions of carbon dioxide and possibly carbon monoxide still contained in the process gas are determined according to the reaction equations already mentioned in the application ( 7th ) and (8) removed by conversion to methane. CO + 3 H ₂ → CH ₄ + H ₂ O (7) CO ₂ + 4 H ₂ → CH ₄ + 2 H ₂ O (8)

Since this reaction is exothermic, it occurs in the methanation 30th to a renewed heating of the process gas and you can use the heat of the heated process gas for a heat exchange by removing the gas mixture from the methanation 30th over the line 31 the gas / gas heat exchanger 26th feeds and thus leads in countercurrent to the process gas flow, which the gas / gas heat exchanger 26th over the line 25th is fed and then via the lines 27 and 29 into methanation 30th got. After flowing through the gas / gas heat exchanger 26th the process gas flows through the line 32 to a synthesis gas compressor 33 , by means of which it is brought to the process pressure intended for the reaction and can then be used in the regular operation of the system via the line 34 and the open valve 35 directly to the ammonia converter 36 be supplied in which the synthesis gas containing nitrogen and hydrogen is converted to ammonia.

In the start-up phase of the plant, however, it is necessary to preheat the synthesis gas because the catalyst requires a certain minimum temperature for the ammonia reaction. In this case, therefore, is the valve 35 initially closed and the valve 38 is instead opened so that the syngas is on the line 37 first the device for preheating 39 is fed through which it flows in countercurrent to hot process gas, which is from the high-temperature CO conversion 11 coming over the open valve and the line 44 the device for preheating 39 is fed. In this way, in the start-up phase, the line is used 37 supplied compressed synthesis gas in the facility 39 preheated and can then over the line 40 and the open valve 41 the ammonia converter 36 are fed. The CO conversion is used for this warming up 11 Heated gas flow is used, i.e. heat that was generated in the process itself and it is therefore no longer necessary to have a separate burner-operated heating device for preheating the ammonia reactor 36 to use supplied synthesis gas.

The administration 37 , the establishment 39 for preheating and the line 40 form their own separate and lockable pipeline circuit that is used by the synthesis gas compressor 33 incoming process gas can optionally be flowed through in the start-up phase. In the regular operation of the plant, if no preheating of the synthesis gas is required upstream of the ammonia reactor, the device for preheating 39 bypassed by the valve 45 is closed and thus that of the high-temperature CO conversion 11 incoming process gas via the branch and the open valve 15th directly through the line 14th into the line 17th can flow in order to then go through the process cycle described above. Also for the colder synthesis gas after the synthesis gas compressor 33 the separate pipeline circuit can be bypassed by opening the valve 38 closed and the valve 35 opened when the synthesis gas no longer needs to be preheated.

In the following, with reference to the 2 an alternative embodiment of the present invention is illustrated. The same system parts are in 2 denoted by the same reference numerals as in FIG 1 and the system parts already described there and their function are not described again here. Rather, only the differences to the one previously described are shown here Design variant outlined. That from the high temperature CO conversion 11 incoming process gas is here directly by the pipe 17th and thus reaches the boiler feed water preheater 18th . The device for preheating 39 the variant of 2 there is no flow through the system at this point.

The system area with the boiler feed water preheater 18th , the low temperature CO conversion 20th , the heat exchanger 22nd for heat recovery and the CO ₂ scrubbing 24 is designed in the same way as in the previous one based on 1 described variant. However, it differs from this one via a valve 47 lockable line 46 provided by the line 23 branches off upstream of the CO ₂ scrubber so that the CO ₂ scrubber can be bypassed and the process gas through the line shown in dashed lines 46 straight into the line 25th that can flow to the gas / gas heat exchanger 26th leads. The administration 25th is via another valve 48 lockable. When the valve 47 in the bypass line 46 is closed, the process gas can, however, via the line 23 can be fed directly to the CO ₂ scrubber.

With the valve open 48 the process gas enters the gas / gas heat exchanger 26th and then, after preheating as described above, flows into the methanation 30th . In contrast to the variant described above, in the embodiment according to FIG 2 the process gas flow, which the methanation 30th leaves, in the start-up phase of the plant operation for preheating the synthesis gas in the facility 39 used. For this purpose, there is an optional cable that is shown in dashed lines 49 provided by methanation 30th to the device for preheating 39 leads and possibly via another valve 50 is lockable. This hot process gas stream from the methanation is used here to dissipate that from the synthesis gas compressor 33 compressed synthesis gas, which in the start-up phase of the plant via the line 37 through the device for preheating 39 flows, preheat and then after preheating over the line 40 the ammonia converter 36 feed to preheat the catalyst there.

With the variant according to 2 is another shown in dashed lines and via a valve 52 lockable line 51 provided that a return of the somewhat cooled process gas after flowing through the device 39 for preheating when the valve is open 52 to the gas / gas heat exchanger 26th methanation made possible. After the gas / gas heat exchanger 26th was flowed through, can over the line 32 the process gas to the synthesis gas compressor 33 and then, depending on whether preheating is provided in the start-up phase, either via the line 34 directly to the ammonia converter 36 be supplied or via the line 37 through the establishment 39 directed to preheating and then over the line 40 the ammonia converter 36 are fed. A major difference in the variant according to 2 is therefore that instead of the process gas after the high-temperature CO conversion 11 a hot process gas from methanation 30th for preheating in the facility 39 used. As the process gas comes out of the pipe 49 when flowing through the facility 39 cools down to preheat it is over the line 51 returned, this line 51 at a junction 54 into the line 31 upstream of the gas / gas heat exchanger 26th joins. It is thus also possible to control the process gas flow that is in the methanation 30th has heated and then over the line 31 to the gas / gas heat exchanger 26th flows, with the process gas from the line 51 to mix in order to make an optimized setting of the temperature at this point if necessary.

List of reference symbols

10

Reformer section

11

High temperature CO conversion

12

Line / operative connection

13

Junction

14th

management

15th

Valve

16

Junction

17th

management

18th

Boiler feed water preheater

19th

management

20th

Low temperature CO conversion

21st

management

22nd

Heat exchanger for heat recovery

23

management

24

CO ₂ washing

25th

management

26th

Gas / gas heat exchanger

27

management

28

Start-up preheater for methanation

29

management

30th

Methanation

31

management

32

management

33

Syngas compressor

34

management

35

Valve

36

Ammonia converter

37

management

38

Valve

39

Device for preheating in the start-up phase / heat exchanger

40

management

41

Valve

42

management

43

Valve

44

management

45

Valve

46

management

47

Valve

48

Valve

49

management

50

Valve

51

management

52

Valve

53

Valve

54

Junction

QUOTES INCLUDED IN THE DESCRIPTION

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

Patent literature cited

• US 4171343 A [0005]
• US 2004/0219088 A1 [0006]

Claims (18)

Process for the production of ammonia by catalytic conversion of a nitrogen and hydrogen-containing synthesis gas mixture, wherein in a start-up phase when starting the reaction, the ammonia synthesis catalyst is heated in order to generate the necessary activation energy for the ammonia synthesis reaction, a hot process gas being used for this heating, which in a the process steps of the production process upstream of the ammonia synthesis reaction, characterized in that the hot process gas is passed through a device (39) designed in the manner of a heat exchanger for preheating, which is integrated into a separate line circuit (37, 40) which is in regular operation of the Plant is not traversed by the synthesis gas supplied to the ammonia synthesis reaction. Procedure according to Claim 1 , characterized in that the method comprises at least one steam reforming (10) and at least one carbon monoxide conversion (11) downstream of the steam reforming, wherein the hot process gas generated in the carbon monoxide conversion (11) downstream of this through the device designed as a heat exchanger ( 39) is passed for preheating, through which a colder gas flow (37) is passed and heated in countercurrent, which is used to warm up the ammonia synthesis catalyst in the ammonia converter (36). Procedure according to Claim 2 , characterized in that the hot process gas generated in the carbon monoxide converter (11) is divided downstream of this (13) and only a partial flow (44) of this hot process gas is used to heat the ammonia synthesis catalyst in the ammonia converter (36). Method according to one of the Claims 1 to 3 , characterized in that the hot process gas leaving the carbon monoxide conversion and used for warming up the ammonia synthesis catalyst has a temperature of 400 ° C to 500 ° C. Method according to one of the Claims 1 to 4th , characterized in that the method comprises at least one methanation (30) and the hot process gas resulting from the methanation is passed downstream of the methanation entirely or only partially through the device for preheating (39) designed as a heat exchanger, through which a colder gas flow is countercurrent (37) is passed and heated, which is used to warm up the ammonia synthesis catalyst in the ammonia converter (36). Procedure according to Claim 5 , characterized in that the process gas entering the methanation has a temperature of at least 300 ° C, preferably a temperature of at least 320 ° C, particularly preferably a temperature of at least 330 ° C. Method according to one of the Claims 5 or 6th , characterized in that the hot process gas emerging from the methanation is at least partially passed through a gas / gas heat exchanger (26) assigned to the methanation and is used to preheat the process gas fed to the methanation. Procedure according to Claim 7 , characterized in that a start-up preheater (28) upstream of the methanation (30) in the flow path is used to set the inlet temperature of the process gas into the methanation. Procedure according to Claim 8 , characterized in that the process gas before entering the methanation (30) is first passed through the gas / gas heat exchanger (26) and then through the start-up preheater (28). Method according to one of the Claims 5 to 9 characterized in that this comprises at least one method step (24) for removing carbon dioxide from the process gas in a device (24) provided for this purpose before the process gas is introduced into the ammonia converter (36) and upstream of the methanation (30) and a partial flow of the process gas the methanation is fed by bypassing this device (24). Method according to one of the Claims 5 to 10 , characterized in that the process gas emerging from the methanation has a minimum temperature of 390 ° C, preferably a minimum temperature of 400 ° C, particularly preferably a minimum temperature of 410 ° C. Method according to one of the Claims 5 to 11 , characterized in that at least one device for lowering the temperature of the process gas is provided in the flow path before entering the methanation, with a start-up preheater (28) connected upstream of the methanation (30) being used for this purpose. Plant for the production of ammonia comprising at least one ammonia converter (36) and units upstream of this in the flow path for generating and processing a synthesis gas to be introduced into the ammonia converter comprising at least one reformer section (10), at least one of these in the flow path downstream carbon monoxide converter (11) and at least one device for preheating the ammonia synthesis catalyst in a start-up phase when starting the reaction in order to generate the required activation energy for the ammonia synthesis reaction, characterized in that the device for preheating the ammonia synthesis catalyst is at least one device designed as a heat exchanger (39 ) is provided for preheating, which is arranged downstream of the carbon monoxide converter (11) and on the one hand is traversed by a hot process gas and on the other hand is in operative connection on the inlet side with at least one line (37) for a colder gas flow of synthesis gas processed in the plant, in the heat exchange with the hot process gas, and is in operative connection on the output side via at least one line (40) with the ammonia converter (36). Plant after Claim 13 , characterized in that the device for preheating (39) is arranged downstream of a first carbon monoxide converter (11) of the system and is flowed through by a hot process gas generated in the first carbon monoxide converter (11) and the device for preheating (39) is arranged upstream of a second carbon monoxide conversion (20) of the system. Plant after Claim 13 , characterized in that the device for preheating (39) is arranged downstream of a methanation (30) of the plant and a hot process gas generated in the methanation flows through it. Plant after Claim 15 , characterized in that it comprises at least one device (24) for removing carbon dioxide from the process gas, which is preferably arranged upstream of the methanation (30), wherein at least one line (46) is furthermore provided, which flows from the process gas by bypassing the Device (24) for removing carbon dioxide can be flowed through before the process gas reaches the methanation. Plant after Claim 15 or 16 , characterized in that it further comprises a line (51) leading back from the device for preheating (39) on the outlet side to a gas / gas heat exchanger (26) of the methanation unit, wherein preferably also a line through which hot process gas from the methanation flows ( 31) leads to the gas / gas heat exchanger (26). Plant after Claim 17 , characterized in that the gas / gas heat exchanger (26) is in operative connection on the output side via a line (32) with the ammonia converter (36).

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