DE19902926A1 - Steam reforming apparatus used in a fuel cell system comprises a pyrolysis reactor connected to a shift reactor - Google Patents

Abstract

Steam reforming apparatus comprises a pyrolysis reactor (5) connected to a shift reactor (10). The pyrolysis reactor carries out a splitting process and the shift reactor carries out a hydrogen gas shift reaction on the product gas containing carbon monoxide from the pyrolysis reactor. An Independent claim is also included for a process for steam reforming methanol comprising splitting methanol in the pyrolysis reactor at 400-480 deg C in the presence of a catalyst into carbon monoxide and hydrogen, and carrying out a catalytic low temperature shift reaction at not more than 250 deg C on the carbon monoxide contained in the product gas from the pyrolysis reactor or a catalytic high temperature shift reaction at 400-450 deg C to form carbon dioxide and hydrogen.

Description

The invention relates to a plant for steam refor a hydrocarbon or hydrocarbon derivative Feedstock through a reforming reaction process, the one pyrolysis reaction associated with the formation of carbon monoxide and includes the water gas shift reaction as sub-processes, so as for a method of operating such a facility Steam reforming of methanol.

Plants of this type and operating procedures for this are in vie All types known. More recently, their ver considered in fuel cell vehicles, wherein mostly methanol is used. Usual facilities of this Kind especially for such a mobile application include egg NEN evaporator in which a feed / water mixture is riding, as well as a one or multi-stage reform Actuator for the implementation of the feed / water-steam mixed in a hydrogen-containing gas mixture. So z. B. in conventional methanol reforming plants in the evaporator rode methanol / water vapor mixture into a reforming freak initiation room and there using a CuO / ZnO Catalyst material according to the steam reforming reaction in one hydrogen-rich reformate gas converted, this Refor mation reaction process two parallel, in the reforming reaction onsraum includes sub-processes, on the one hand methanol cleavage in synthesis gas, d. H. into a coal mono xid / hydrogen mixture, by means of pyrolysis and the other Implementation of the carbon monoxide formed with the water of the supplied  led methanol / water vapor mixture according to the water gas Shift reaction in carbon dioxide and hydrogen. The thereby he generated hydrogen can then, for example, a fuel cell lens system are supplied as fuel.

To increase the hydrogen yield and to reduce the Carbon monoxide content of the reformate gas generated is known this through a CO shift stage where the carbon monoxide about the water gas shift reaction with water to additional what hydrogen and carbon dioxide is implemented. Furthermore, it is known, the hydrogen contained in the reformate gas by means of egg selectively separate a suitable hydrogen separation membrane, why the separation membrane in the reforming reaction space itself or a downstream gas cleaning stage can. The evaporator and the endothermic reforming reaction performing reforming reactor are suitably heated, for. B. by an electric heater, a gas burner or a ka talytical burner device with one in the plant self-generated fuel can be fed. Plants and Operating methods of these types are e.g. B. in the patent document ten FR 1.417.757, FR 1.417.758 and US 4,981,676 and the Offen documents DE 44 23 587 A1 and EP 0 615 949 A2.

It is made of Dy especially for use in vehicle technology namik and space problems desirable, the components of the Reformer system to be as small and light as possible. At the same time, a high level of efficiency is sought, and it will be tries to get by with as few components as possible, especially in particular with as few regulation and control units as possible and to be built-in housings with high heat capacity. With Ver There is also use of the reformate gas for fuel cells the requirement that the carbon monoxide content is very low, typi should be below 50 ppm, in order to to avoid signs of deterioration in the fuel cells.

The invention is a technical problem of providing a steam reforming plant and an associated Be  drive process of the type mentioned at the beginning, which Also suitable for mobile applications and a low Ge important, a compact design, a simple rule and egg ne high hydrogen yield with low carbon monoxide concentration enable.

The invention solves this problem by providing a Steam reforming system with the features of claim 1 and an operating procedure for this with the features of the An Proverbs 6

Characteristically, the system according to claim 1 separates the Reforming reaction process in the pyrolysis reaction and Water gas shift reaction carried out in series Subprocesses by using a pyrolysis reactor, which the one Substitute is supplied for the purpose of pyrolytic cleavage, and egg NEN includes this downstream shift reactor, which the Product gas of the pyrolysis reactor together with that for the water gas shift reaction water is supplied. The Shiftre Depending on the application, actuator can be in a common Connect the unit with the pyrolysis reactor directly to it or can be implemented as a separate unit from this. By the separation of the pyrolysis reaction and the water gas shift reaction the relevant components, i. H. the pyrolysis reactor and the shift reactor, ideal for carrying out the respective Sub-process of the entire reform reaction process be placed. It turns out that a system constructed in this way, Depending on the application, supplemented by additional, optional systems gene components, a simple regulation of reforming with ho forth hydrogen yield with sufficiently low carbon monoxide allows concentration and the system is compact and with ge low weight.

In a system developed according to claim 2 is in the Py rolysis reactor and / or in the shift reactor a respective What Integrated hydrogen separation membrane. So that in each Reactor formed hydrogen directly at the point of origin  pulled what the reaction equilibrium in question further shifted in favor of hydrogen production and thereby to one complete conversion of the input material as possible and Lich contributes to a high hydrogen yield. In particular, lets the pyrolysis reactor is also made very small.

In a system developed according to claim 3, a Ver steamer to provide water vapor for the shift reactor from an internal catalytic burner unit and / or with heat from the pyrolysis reactor or the shift reactor heated, so that a further external heating of the same mostly can be omitted.

In a system developed according to claim 4 is a Ver steamer intended for the feed from a plant internally powered, catalytic burner unit and / or from egg ner electric heater is heated. The electrical Heating device can be activated especially for cold starts be in order as quickly as possible vaporous feed for the To have a pyrolysis reaction available.

A system developed according to claim 5 has a connection line from the product gas outlet of the pyrolysis reactor to the this heating, catalytic burner unit, these Connection line can be opened and closed controllably can, and / or an oxygen supply line via which a oxygen-containing gas are passed into the pyrolysis reactor can. For this purpose, this line can mün directly into the pyrolysis reactor or upstream thereof, for example in the methanol ver Steam boat. This oxygen supply can be particularly in the case of a Cold start are used initially in the pyrolysis reactor Partially oxidize the fabric to heat with this exothermic Response to bring the system up to operating temperature more quickly. The mentioned connecting line can also serve this purpose, by initially ge at least partially during the cold start is opened and thereby emerging from the pyrolysis reactor Product gas directly from the catalytic heating the pyrolysis reactor  the burner unit. In warmed up operation can then the connecting line completely or at least largely getting closed.

According to the method of claim 6, methanol as a feedstock in the pyrolysis reactor at a temperature above 350 ° C is catalytically split into CO and H ₂ , and the carbon monoxide is then in the shift reactor with water by a catalytic low-temperature shift reaction at a temperature of at most 380 ° C or by a catalytic high-temperature shift reaction at a temperature of more than 380 ° C in CO ₂ and further hydrogen. It can be seen that with these process conditions, a largely complete methanol reaction with high hydrogen yield and low CO concentration can be achieved in the product gas of the shift reactor.

An operating method developed according to claim 7 is suitable up for an installation according to claim 4 or 5 and includes partial cold start measures in order to get the system to its faster bring normal operating temperature. You can use a or serve several of the following three measures. First, one can electrical heating of the methanol evaporator may be provided. Second, in the pyrolysis reactor there can initially be a partial one Methanol oxidation can be carried out if this in addition to metha an oxygen-containing gas is also supplied. Third can the product gas of the pyrolysis via the corresponding connec cable, if present, directly into the catalytic burner nereinheit for the pyrolysis reactor are passed so that this can contribute very quickly to heating the pyrolysis reactor.

An advantageous embodiment of the invention is in the Drawing shown and is described below.

The single figure shows a block diagram of a steam generator formation plant.  

The system shown is suitable for steam reforming nes hydrocarbon or hydrocarbon derivative, in particular that of methanol, and can, for example, in a fuel cell vehicle to be installed there for the fuel cells to provide the required hydrogen. The simplicity for the sake of convenience, the system will subsequently be used without restriction of the general described in use for methanol reforming.

The system contains a methanol tank 1 , from which the methanol stored there can be fed to a methanol evaporator 3 via a pump 2 . Optionally, an oxygen supply line 4 also opens into the methanol evaporator 3 , as indicated by dotted lines. The evaporator outlet side is connected to the inlet side of a pyrolysis reactor 5 , which contains a suitable methane nolfission catalyst, for. B. platinum. In the pyrolysis reactor 5 , a first hydrogen separation membrane 6 is integrated, which forms a delimiting wall of the pyrolysis reaction space and to which on the opposite side of the pyrolysis reaction space adjoins a first hydrogen discharge space 7 , from which hydrogen can be drawn off via an outlet line 8 , which is in the pyrolysis reaction space generated and diffused selectively through the What serstoffabtrennmembran 6 into the hydrogen discharge space 7 .

The product gas formed in the pyro lysis reactor 5 passes into a downstream shift reactor 10 via a corresponding product gas line 9 . In the product gas line 9 opens a water vapor line 12 coming from egg nem water evaporator 11 , so that 5 water vapor can be added to the product gas of the pyrolysis reactor. The water required is removed from a water tank 13 and fed to the water evaporator 11 via a pump 14 . In the shift reactor 10 , a second hydrogen separation membrane 15 is integrated, which forms a delimiting wall of the shift reaction space and separates it from a second hydrogen discharge space 16 , from which hydrogen can be drawn off via an outlet line 17 , which passes from the shift reaction space through the second hydrogen separation membrane 15 into the second water fume hood 16 diffuses. The shift reaction space contains a suitable shift catalyst material for catalyzing the water gas shift reaction, e.g. B. A CuO / ZnO catalyst material on Al ₂ O _{3 support} : Optionally, the methanol evaporator 3 can also be heated by an electric heating device 24 , as indicated by dotted lines.

Furthermore, the system includes a three-unit catalytic burner device, of which a first burner unit 18 a with the water evaporator 11 , a second burner unit 18 b with the pyrolysis reactor 5 and a third burner unit 18 c with the methanol evaporator 3 is in thermal contact. The three catalytic burner units 18 a, 18 b, 18 c can be flowed through serially in the order mentioned by the residual gas emerging from the shift reactor 10 , for which purpose this can be fed into the first burner unit 18 a from the shift reactor outlet via a corresponding residual gas line 19 . The there unused residual gas fraction passes through a first Brennerver connecting line 20 a to the central burner unit 18 b, with the output of the third burner unit 18 c through a second connecting line burner 20 is connected b. The exhaust gas 23 emerging from the last burner unit 18 c is suitably discharged.

In addition, a connection or bypass line 21 is optionally provided, as indicated by dots, which connects the pyrolysis reactor output directly to the input of the second burner unit 18 b which is in thermal contact with the pyrolysis reactor 5 . Furthermore, optionally, as also indicated by dots, a heat exchanger 22 in thermal contact with the shift reactor 10 , alternatively in thermal contact with the gas emerging from it, is provided, which in a manner not shown by the water stream flowing from the water tank 13 to the product gas line 9 can be streamed. The heat exchanger 22 can, depending on the application, replace the water evaporator 11 or be connected in series to it in the water flow path.

The mode of operation of the system shown is discussed in more detail below. Starting from a cold start, methanol is fed from the methanol tank 1 to the methanol evaporator 3 via the metering pump 2 . In the starting phase, this is also primarily heated by the electrical heating device 24 , if present, otherwise by the associated catalytic burner unit 18 c. The methanol, which has a low enthalpy of vaporization, is thereby evaporated and overheated to a temperature of over 350 ° C., preferably to a temperature between 400 ° C. and 480 ° C. The superheated, gaseous methanol then enters the pyolysis reactor 5 , in which it is pyrolysed according to the reaction equation

CH ₃ OH ↔ CO + 2.H ₂

is split into carbon monoxide and hydrogen, the free enthalpy of this endothermic reaction being 129 kJ / mol. The heat required for this endothermic reaction is generated by the associated, second catalytic burner unit 18 b. To this end, in the starting phase is emerging from the pyrolysis reactor 5 product gas via the bypass line 21, if present, directly this burner unit 18 b to the combustion of the non reactor in the pyrolysis of 5 unreacted methanol and may not hindurchdiffundierten by the Wasserstoffabtrennmembran 6 hydrogen supplied. Possibly unconverted fuel in this burner unit 18 b can be used in the subsequent burner unit 18 c which is in thermal contact with the methanol evaporator 3 for heat generation.

Optionally, for even faster heating of the system for the starting process, an oxygen-containing gas, such as air, can be passed through the oxygen supply line 4 , if present, into the pyrolysis reactor 5 . More specifically, the oxygen-containing gas is fed upstream of the pyrolysis reactor 5 parallel to the methanol in the methanol evaporator 3 and mixed and heated there with it. Since the methanol cleavage catalyst, e.g. B. platinum, in the presence of oxygen also catalyzes the partial methane oxidation, this reactor then runs in the pyrolysis reactor instead of the methanol cleavage reaction, as long as the oxygen supply is maintained. The heat generated by the exothermic partial oxidation reaction can bring the pyrolysis reactor 5 to operating temperature in a very short time. At the same time, it already supplies hydrogen, which, with increasing heating of the hydrogen separation membrane 6 , is able to diffuse through it and is available, for example, for supplying fuel cells. With this operating mode, partial load operation of a connected fuel cell system and thus a corresponding motor vehicle drive is already possible if required.

In order to bring the shift reactor 10 and what the server steamer 11 largely to normal operating temperature even in the starting phase, provision may be made for not all of the product gas emerging from the pyro lysis reactor 5 via the bypass line 21 directly. second burner unit 18 b, but at least part of it to feed the shift reactor 10 in order to heat it through this process gas heat transport and to implement gas monoxide contained in the feed process with increasing heating via the water gas shift reaction. The product gas formed in the shift reactor 10 is then supplied to the first catalytic burner unit 18 a, which, in turn, causes the heating of the water evaporator 11 , except for the increasing heating of the hydrogen separation membrane 15 there through this selectively withdrawn hydrogen. This unused fuel can be used in the subsequent burner units 18 b, 18 c.

As soon as the various system components have essentially reached their normal operating temperature, the system is switched to normal operation. For this purpose, the possible supply of oxygen to the pyrolysis reactor 5 is stopped, and the electrical heating device 24 can be switched off in most applications. At the same time, the optional bypass line 21 is completely or at least largely closed.

When the oxygen supply is terminated, the partial methanol oxidation which may be activated in the pyrolysis reactor 5 is ended , and the methanol which is then supplied exclusively is cleaved catalytically into carbon monoxide and hydrogen. The hydrogen formed can be drawn off from the pyrolysis reaction space through the associated hydrogen separation membrane 6 , which shifts the equilibrium of the methanol cleavage reaction in favor of the products. A complete methanol conversion is achieved by even with a shorter residence time, so that a rela tively short run length of the reaction mixture and thus a relatively small volume of the pyrolysis reactor 5 are sufficient. To the fact that the pyrolysis reactor 5 can be built small, also contributes to the fact that it is operated in a relatively high temperature range of over 350 ° C, in which the conventional methanol cleavage catalysts have a high activity. In addition, the permeability of the hydrogen vent membrane 6 at this temperature is turbereich higher than at low temperatures, so that more hydrogen can be selectively separated.

The product gas of the pyrolysis reactor 5 , in the normal operation of the system mainly carbon monoxide and possibly not separated ter hydrogen, is fed via the product gas line 9 to the shift actuator 10 , with evaporated and superheated water being supplied to it via the steam line 12 , which is prepared by the water evaporator 11 becomes. Alternatively or additionally, the water withdrawn from the water tank 13 via the pump 14 can be evaporated via the heat exchanger 22 by the gas mixture in the shift reactor 10 or by the residual gas emerging therefrom.

In the shift reactor 10 , the carbon monoxide then becomes catalytic via the water gas shift reaction

CO + H ₂ O ↔ CO ₂ + H ₂

implemented with water to carbon dioxide and further hydrogen, this reaction being endothermic with a free enthalpy of 3 kJ / mol. For the temperature in the shift reactor 10 , a low temperature range up to at most about 400 ° C, preferably less than 250 ° C, z. B. in the order of 200 ° C, egg nem high temperature range with shift reaction temperatures in the order of 400 ° C and more, preferably between 400 ° C and 480 ° C. For the low-temperature variants, it is normally sufficient to use only the water evaporator 11 or the heat exchanger 22 for steam preparation. For the high-temperature variant, both components are preferably seen before, in which case the water vapor from the water evaporator 11 can be overheated by the product or residual gas from the shift reactor 10 via the heat exchanger 22 .

The hydrogen additionally formed in the shift reactor 10 is selectively drawn off via the hydrogen discharge membrane 15 there, which in turn allows the reaction equilibrium of the water gas shift reaction to be shifted to the product side, which further improves the hydrogen yield. The light exiting the shift reactor 10 residual gas from unseparated hydrogen, unconverted carbon monoxide and water is successively seri the economic catalytic burner units 18 a, b 18, c 18, and supplied there catalytically burnt completely under heat.

It goes without saying that in addition to the example shown and here in addition to the variants mentioned above, further implementations of the invention possible are. The door is characteristic of each the entire reform process of the Koh hydrogen or hydrocarbon derivative in the pyrolyti cleavage reaction without the presence of water and the after switched water gas shift reaction. Obviously the Heat requirement of the overall endothermic reforming process entirely or at least largely internally through catalytic Incineration of the input material or the product obtained from it be covered. By using a respective water material separation membrane, the reaction equilibrium for both processes in favor of hydrogen production and thus a complete conversion of the input material  move fes. Possibly not split in the pyrolysis reactor Methanol can still in the shift reactor with what is there steam can be reformed, which with the help of the catalytic converter there door material is possible.

As is clear from the realizations mentioned, the Invention a steam reforming plant for Hydrogen Ge available, which is compact and light in weight can build, including in particular the shift of the reacti equilibria due to the separation membranes in the two reacts contributes gates, which results in a relatively short barrel length can be placed. The selected feed material can be filled constantly and with high hydrogen yield at high hydrogen Selectivity greater than 99.99999% for use in particular re convert into fuel cells. The separation of pyrolysis reac tion and water gas shift reaction and the self-regulating, largely internal heating of the system components with heat may allow a relatively simple regulation of the entire An location.

Claims (7)

1. Plant for steam reforming a hydrocarbon or hydrocarbon derivative feedstock by a refor mation reaction process which includes a pyrolysis reaction associated with the formation of carbon monoxide and the water gas shift reaction as sub-processes, characterized in that

• - It has a pyrolysis reactor ( 5 ), to which the feed can be fed for the purpose of cleavage by a pyrolysis reaction, and a downstream shift reactor ( 10 ) which, for the purpose of carrying out the water gas shift reaction, contains the product gas from the pyrolysis reactor and water.

2. Steam reforming system according to claim 1, further characterized in that in the pyrolysis reactor ( 5 ) and / or in the shift reactor ( 10 ) egg ne respective hydrogen separation membrane ( 6 , 15 ) is integrated. 3. Steam reforming system according to claim 1 or 2, further characterized by a water evaporator ( 11 ) which is heated by a system-internally fed, most catalytic burner unit ( 18 a) and / or with heat from the shift reactor ( 10 ). 4. Steam reforming system according to one of claims 1 to 3, further characterized by a feedstock evaporator ( 3 ) which is heated by an internal system-fed, catalytic burner unit ( 18 c) and / or by an electric heating device ( 24 ). 5. Steam reforming system according to claim 4, further characterized by a controllably openable and closing connecting line ( 21 ) from the product gas outlet of the pyrolysis reactor ( 5 ) to which the heating catalytic burner unit ( 18 b) and / or egg ne oxygen supply line ( 4 ) for supply of an oxygen-containing gas to the pyrolysis reactor. 6. A method for operating a system according to one of claims 1 to 5 for steam reforming of methanol, characterized in that

• - In the pyrolysis reactor ( 5 ) supplied methanol at a temperature of over 350 ° C, preferably between 400 ° C and 480 ° C, is catalytically split into carbon monoxide and hydrogen and
• - In the shift reactor ( 10 ), the carbon monoxide contained in the supplied product gas of the pyrolysis reactor with supplied water by a low-temperature catalytic shift reaction at a temperature of at most 380 ° C, preferably at most 250 ° C, or by a high-temperature catalytic shift reaction at one temperature of more than 380 ° C, preferably between 400 ° C and 450 ° C, is converted to carbon dioxide and hydrogen.

7. The method according to claim 6 for operating a system for steam reformation of methanol according to claim 4 or 5, further characterized in that when the system is cold started before the transition to normal operation with the system warmed up, the electrical heating device ( 24 ) of the feedstock evaporator ( 3rd ) activated and / or a partial oxidation of the feedstock in the pyrolysis reactor by supplying an oxygen-containing gas via the oxygen supply line ( 4 ) and / or at least part of the product gas of the pyrolysis reactor ( 5 ) via the associated connecting line, which we at least partially keep open ( 21 ) into the catalytic burner unit ( 18 b) which heats the pyrolysis reactor.