EP1957399A2

EP1957399A2 - Diesel fuel reforming method and reactor

Info

Publication number: EP1957399A2
Application number: EP06818821A
Authority: EP
Inventors: Axel Maurer; Klaus Wanninger; Herbert Wancura
Original assignee: Alpps Fuel Cell Systems GmbH; Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; Sued Chemie AG
Current assignee: Alpps Fuel Cell Systems GmbH; Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; Sued Chemie AG
Priority date: 2005-11-25
Filing date: 2006-11-24
Publication date: 2008-08-20
Also published as: US20090053562A1; DE102005056363A1; WO2007060001A2; WO2007060001A3

Abstract

The invention relates to a method and device for reforming a diesel fuel into a H2-and-CO-containing gas product, wherein the inventive method consists in mixing the diesel fuel with an O2-containing gas mixture at a first premixing stage, in subsequently mixing the thus obtained mixture with the O2-containing gas mixture and a gas flow-containing mixture at a second premixing stage and in exposing the thus obtained mixture to hydrocarbon oxidation in a reactor provided with a catalyst.

Description

Process for the reforming of diesel fuel and reactor for this purpose

The present invention relates to a process for converting diesel fuel into a product gas containing H ₂ and CO and a corresponding reactor.

In particular, stationary fuel cells are supplied today, and in the foreseeable future most economically with hydrogen, which is generated by reforming carbonaceous energy sources. Natural gas is an option for reforming, as it is technically the easiest to reform. If natural gas is not available on site, other sources of energy such as propane / butane or gasoline can also be used.

In this context, it is technically particularly demanding to reform media which are a mixture, which contains hydrocarbon compounds, especially when mixed with difficult-to-evaporate aromatics.

Such a liquid mixture of hydrocarbon compounds and difficult-to-evaporate aromatics is for example diesel.

For the above-described reforming of hydrocarbons, in particular diesel fuels, various processes have become known in the prior art for this purpose.

For one thing, the steam reforming should be mentioned here, i. the reforming with water, the second possibility relates to the so-called. Partial oxidation (POX) and the third possibility is the so-called. Autothermal reforming, i. a reforming with air and water.

For a mobile application, however, steam reforming is not suitable because of its high water consumption. The partial oxidation (POX) of diesel fuel is unfavorable because of the risk of soot formation. The autothermal reforming therefore represents, at the present state of knowledge, the only possibility of reforming diesel for mobile application. For autothermal reforming e.g. Diesel is usually used with an air ratio of 0.3 to 0.4 and a S / C ratio (steam to carbon) of 1.5 to 2.5. But especially the S / C

Ratio is particularly problematic for a mobile application of the method. Large amounts of water must be carried along in the vehicle and condensed, which would mean a high procedural, financial and spatial effort. Based on this, it is therefore an object of the present invention to provide a method and a reactor for reforming diesel fuel, which is inexpensive and can be operated with little effort, which is particularly required that the process must be feasible if possible without liquid water.

The object of the present invention is solved by the features of claim 1 with respect to the method and the features of claim 15 with respect to the reactor. The dependent claims show advantageous developments.

According to the invention, it is thus proposed to subject diesel fuels (educts) before the hydrocarbon oxidation in the reactor to a specific two-stage premix. It is essential to the invention that the educts in the second premixing stage are not mixed with water as in the prior art, but that in the second premixing stage an oxygen-containing gas and an H ₂ O, N ₂ and CO ₂ containing waste gas mixture is added. In the method according to the invention, therefore, it is no longer necessary to add liquid water, which thus has advantageous effects on the process management, namely in such a way that now a simple method is possible because the weight of the entire system can be reduced and what at the same time too low Costs leads. In the method according to the invention is further emphasized that despite the admixture of the water in the form of a H ₂ O, N ₂ and CO ₂ exhaust gas mixture was found in the resulting product gas that only small amounts of higher hydrocarbons in the reforming process according to the invention in comparison to the Reforming processes in the state of the art, in which work is carried out with large amounts of liquid water arise.

In the method according to the invention, it is preferred if in the second premixing stage the exhaust gas mixture containing H ₂ O, N ₂ and CO ₂ is the exhaust gas from a diesel combustion. This has the decisive advantage that low costs are associated with this, since it is possible to work with simple exhaust gases, for example with the exhaust gas of an engine. The waste gas mixture used in the second premixing stage may preferably contain 10 to 15% by volume of CO ₂ , 10 to 13% by volume of water, 0 to 5% by volume of O ₂ and 73 to 75% by volume of nitrogen contain. It is furthermore advantageous if the oxygen provided for the second premix stage is supplied in the form of air, particularly preferably in the form of ambient air. This also applies to the oxygen-containing gas supplied in the first premix stage, in which likewise preferably air, more preferably ambient air, is used.

In the process according to the invention, it has proven useful to add the gas mixture provided for the first premix stage with an air ratio "lambda" between 0.28 and 0.43, preferably between 0.31 and 0.41 actual amount of oxygen delivered divided by the amount of oxygen required for total oxidation.

The gas mixture for the second premix stage is mixed with an S / C ratio (= molar mass of water vapor in the gas mixture fed in / molar amount of carbon atoms in the fueluct) between 0.1 and 0.9, preferably between 0.25 and 0, 5 added. Further favorable process conditions for the process according to the invention are in relation to the temperature, if the educts before the mixing in the first stage have a feed temperature of 10 to 70 ^° C., preferably 40 to 60 ^° C. With respect to the gas mixture for the first premix stage has proved to be advantageous when the temperature 0 to 50 ⁰ C, preferably 15 to 25 ⁰ C, is. At the temperature for the second premix 350 to 600 ⁰ C, in particular 400 to 500 ⁰ C are favorable.

For carrying out the hydrocarbon oxidation in the reactor, as is well known in the prior art, 850 to 1000 ⁰ C and 0 to 10 bar pressure required.

The invention further relates to a reactor for carrying out a method as described above.

The reactor according to the invention is constructed so that it has a two-fluid nozzle, which results in a first premix and a second premix, said two-fluid nozzle downstream of a reactor space in which then the hydrocarbon oxidation takes place.

In the following, developments of the reactor according to the invention will be explained.

In this case, the supply of starting materials can be effected in a simplified manner, for example by means of a tubular supply line.

In terms of manufacturing technology, it is particularly simple that the feed of the educts has one or more lateral Having openings with which the O ₂ -containing first gas mixture of the first premix stage is initiated.

As a result, the allocation, which is provided with a lateral opening, becomes the "first premixing stage". At the end of this first premixing stage, a nozzle is preferably present, which is oriented towards the second premixing stage, which is located at the beginning of the reactor chamber.

The educt, preferably diesel, is thus injected into the reactor by means of the two-component nozzle. In a special embodiment of the reactor, which is designed as a pressure vessel and is made for example of a stainless steel, will be discussed again below.

The second premixing stage adjoining the beginning of the reactor space preferably has around it a peripheral space or an annular space which serves to distribute the gas mixture for the second premix stage (which contains O ₂ and a mixture of CO ₂ , N ₂ and H ₂ O) , In this case, the surrounding circumferential space preferably has radially distributed mixing nozzles which allow a uniform inflow of the second gas mixture into the second premix stage. In this case, it is advantageous that (in the sense of a uniform distribution of the second gas mixture into the second mixing stage) a tangential feed is provided for the second gas mixture containing O ₂ and H ₂ O, CO ₂ and N ₂ .

In the adjoining reactor space is preferably a cladding made of ceramic (for example aluminum oxide), which is preferably tubular. is designed, provided. The reactor space is in this case preferably produced as a pressure housing, in which case a two-layeredness is advantageous. In the first shell, for example, the ceramic tube is provided, around which a stainless steel housing is constructed. This stainless steel housing or the reactor space can be held with at least one flange.

A catalyst is preferably provided on the side of the reactor chamber which repels the second premix stage, for example a noble metal catalyst which contains a metallic or ceramic carrier.

Optionally, various elements may be provided subsequent to the reactor space or the catalyst, for example CO-Schift / CO fine cleaning etc.

For example, gas cleaning is not absolutely necessary for high-temperature fuel cells.

The invention will be explained in more detail with reference to 6 figures. Show it:

1 shows a cross section through the structure of a reactor according to the invention,

FIG. 2 shows a flow chart for a preferred embodiment of the method,

FIG. 3 shows the proportion of higher hydrocarbons in the product gas,

Figure 4 shows the proportion of VoI-% of the residues of higher hydrocarbons in the product gas, and FIG. 5 shows the product gas fractions of the gases obtained on the basis of an exemplary embodiment.

Figure 6 is another flow diagram for a preferred method.

FIG. 1 shows a reactor 1 for reforming hydrocarbons 15 in the form of a liquid mixture. The reactor 1 has a feed 2 for the educt. In addition, a first mixing stage 3 for the supply of an O ₂ enthal-border mixture and mixing with the reactant 15 is provided. Thereafter, a second mixing stage 4 is provided for the supply of a mixture containing O ₂ and H ₂ O, N ₂ and CO ₂ and a reactor chamber 5 arranged downstream of the second mixing stage for the catalytic oxidation of the mixture obtained in the second mixing stage. In this case, the second mixing stage 4 forms the space essentially shown in the truncated cone section in FIG. 1 and is therefore located at the upper end of the reactor space. Finally, downstream of the reactor chamber is an outlet 6, which serves to remove the reaction products.

1 shows a feed 2 for the educt 15 in the direction of the arrow (see FIG. 1), the feed being designed as a tubular feed line with a diameter of 6 mm. This has at least one lateral opening 7, through which, for example, ambient air can be introduced. This results in a mixture of educt and ambient air in the first premix, which is thus essentially formed by the tubular supply line. At the end of the first premixing stage, a nozzle 8 is provided, which is sealed off with heat-resistant copper seals. is sealed. It can therefore be said that, for example, the educt, such as diesel, can be sprayed into the reactor through the "two-fluid nozzle" shown here.

Around the second premix stage 4 (the second mixing stage is assumed to be only in the interior of the upper section above the reaction space) is a feed line for the O ₂ - and H ₂ O, N ₂ and CO ₂ containing (second) gas mixture in Given shape of a circumferential space. This is preferably designed as an annular space 9, wherein this annular space to the second mixing stage 4 toward preferably radially distributed mixing nozzles 10 (perforated ring). The supply of the O ₂ - and H ₂ O, N ₂ and CO ₂ containing mixture takes place here by a TangentialZuführung 11, which allows a uniform distribution of the sprayed gas mixture over the circumference of the annular space 9.

The reactor chamber 5 and the second mixing stage 4 are in this case surrounded by a ceramic tube 12, so that here results in a radial temperature distribution and the most continuous process temperature. The reactor space is in this case constructed of two shells, around the ceramic tube 12 around a further (pressure-tight) shell is provided from a stainless steel, so that the reaction chamber 5 is pressure-tight overall.

At the lower end of the reaction space a catalyst 14 is provided, which is preferably designed as a noble metal catalyst on a metallic or ceramic support.

Subsequently, an outlet 6 for gas purification and / or direct access to a fuel cell arrangement is given. Now that the basic structure of the reactor has been explained, the implementation of the method according to the invention will be discussed below.

This is a process for reforming a hydrocarbon compound-containing liquid mixture.

Here, the educt 15 is first mixed with a first O ₂ -containing gas mixture in the first stage 3, wherein the O ₂ -containing gas mixture in the present case is ambient air, which is introduced through the lateral opening 7. The mixture obtained in the first stage is then mixed in the second premixing stage 4 with a gas mixture containing O ₂ and H ₂ O, N ₂ and CO ₂ (in the present case ambient air introduced via the annular space 9 via a perforated rim, which is mixed with steam) and subsequently the mixture obtained in the second mixing stage 4, preferably catalytically reformed.

Preferably, the educt 15 is diesel fuel. At present, the educt is introduced before mixing in the first stage 3 with a temperature of 50 ⁰ C under a low pressure. The temperature of the supplied through the side opening 7 the gas mixture (in the present case ambient air) in this case is 20 ⁰ C (ambient temperature). In the present case, the ratio between the educt 15 and the ambient air, preferably expressed by the air ratio "lambda", is 0.33. (The air ratio "lambda" is the actual amount of oxygen supplied divided by the amount of oxygen required for total oxidation second mixing stage 4 supplied gas mixture Ambient air and H ₂ O, N ₂ and CO ₂ is introduced at 400 ⁰ C, so that after the mixture, a temperature of about 300 ⁰ C results in this area. In this case, the second gas mixture flows through the perforated ring into the second mixing stage (top of the reactor) and evaporates there the droplet-shaped diesel. Subsequently, the resulting mixture continues to flow into the catalyst, which in the present case sits 150 mm below the nozzle 8 in the reactor (based on the upper edge of the catalyst).

The ratio of the educt 15 to the second gas mixture containing O ₂ and H ₂ O, N ₂ and CO ₂ is preferably 0.25, expressed by the S / C ratio (= molar mass of water vapor in the gas mixture / molar quantity supplied) Carbon atoms in fuel product). It is particularly advantageous to operate the process with low S / C ratios of, for example, 0.2. Overall, the preferably catalytic treatment is driven by the catalyst 14 at temperatures of, for example, constant 1000 ⁰ C.

In this case, the lining of the reactor chamber 5 with the ceramic tube 12 avoids heat losses to the environment through the walls of the reactor. Keeping these losses small, in addition to energetic reasons, also has the effect that the radial temperature difference in the catalyst is kept low. It is important that there is no cooling of the catalyst on the surface layers, otherwise there arises soot.

The inner reactor wall should therefore consist of a material which is not damaged by temperatures higher than the process temperature of 1,000 ⁰ C. In the design of the reactor were from a Temperature of 1,300 ⁰ C assumed. Other properties that the material of the reactor must meet is the chemical inertness with respect to hydrocarbon oxidation. In this case, for example, steel containers can support catalytically undesirable reactions as wall material, which is why the present ceramic interior lining makes sense.

FIG. 2 now shows a flow chart of the method according to the invention. The scheme shown in Figure 2 shows the simple and inexpensive construction of the method according to the invention. In the example according to FIG. 2, diesel oil 15 is used as the hydrocarbon mixture. For the first premixing stage 3, air is used which is introduced into the reactor 1 into the two-substance nozzle 20 via a corresponding valve. As a gas mixture for the second premixing stage 4 while air and diesel are provided, which is burned by an additional burner 26, so that a corresponding exhaust gas containing CO ₂ , H ₂ O and N ₂ is formed. In the exemplary embodiment according to FIG. 2, the method according to the invention is connected directly to a fuel cell 25. As a fuel cell here all known in the art and in the art fuel cells can be used, such as SOFC as well as MCFC fuel cells.

The advantage of the method according to the invention can be seen in particular in the fact that now the gas exiting from the reactor no longer needs to be aftertreated, but can be used directly for the corresponding fuel cells. It should also be emphasized that in the evaporation of the educt here diesel without flame formation and liquid residues in the evaporation chambers is realized. The fact that no liquid water is needed is the Process technically simple and inexpensive to carry out and the weight of the entire system is to keep low.

Figure 3 now shows the proportions of higher hydrocarbons, which are formed in the additional addition of CO ₂ and nitrogen to water vapor in the product gas.

In the measurement results shown in Figure 3, a theoretical composition of a combustion exhaust gas of water vapor, CO ₂ and N _{2 was added} with a share of 13% by volume of CO ₂ , 13% by volume of water and 74% by volume of nitrogen. In order to achieve a high quality process for a fuel cell based on the addition of water by means of exhaust gas, a low S / C = 0.25 was used. This can reduce the dilution with CO ₂ and N ₂ . In addition, the space velocity is halved. In addition, the fact is exploited that the temperature at the catalyst in the second premixing stage by the addition of CO ₂ and N ₂ decreases. Therefore, Lamba could be increased to 0.14 and the maximum temperature still be kept below 1000 ⁰ C. Positive effects of increasing the air number on the higher hydrocarbons could be proven in experiments (see FIG. 3). With additional CO ₂ - and N ₂ addition with otherwise the same settings are found in comparison (Figure 4) more higher hydrocarbons in the product gas than in a pure water. However, the sum of the proportions of the higher hydrocarbons is well below 0.1% by volume. The concentrations of the higher hydrocarbons are so low that there is no risk of soot formation. FIG. 4 also shows values of the concentration of the higher hydrocarbons in the product gas of a partial oxidation for comparison (POX), under otherwise identical conditions. It shows the clear advantage of the method according to the invention.

By using the gas mixture according to the invention in the second premix stage in the form of a gas mixture of water, CO ₂ and nitrogen, a dilution of the product gas occurs. However, this leads only insignificantly to a reduction in the concentration of usable gases (see FIG. 5).

Except for residual methane, the composition corresponds to the thermodynamic equilibrium.

FIG. 6 shows a further flow chart for a preferred method.

FIG. 6 shows an example in which the reactor 1 according to the invention is arranged in bypass to a line 30 which leads from an internal combustion engine 31 to a device for the selective catalytic reduction of nitrogen oxides 32 (SCR device). The flow chart of Figure 6 thus shows the application case in which the reactor according to the invention is used so that the product gases obtained from CO and H ₂ for the reduction of nitrogen oxides in a

Internal combustion engine to be used with diesel fuel. For this purpose, it is favorable if, as already explained above, the reactor is switched in the bypass, that is, only a partial flow of the exhaust gas flows out of the internal combustion engine 31. Furthermore, it has proven to be advantageous if, for gas cleaning still in the exhaust pipe 30, a soot filter 33 is connected in between. It has now been found that, in particular, this arrangement is outstandingly suitable for the exhaust gas purification of diesel fuels. In the method according to the invention and the corresponding Arrangement, as shown in Figure 6, of course, then after the apparatus for the catalytic reduction of nitrogen oxides, a Dieseloxi- dationskatalysator 34 for the reduction of residual CO and hydrocarbons are connected downstream.

Claims

claims

A process for reforming diesel fuel into H ₂ and CO or a product gas containing H ₂ and CO, wherein:

a) the diesel fuel in a first premixing stage with an O ₂ -containing

Mixed gas mixture and then

b) the mixture thus obtained is mixed in a second premix stage with an O ₂ -containing gas mixture and with an exhaust gas mixture from a hydrocarbon combustion comprising an H ₂ O, N ₂ and CO ₂ gas mixture and subsequently

c) this mixture is subjected to a hydrocarbon oxidation in a reactor with a catalyst.

2. The method according to claim 1, characterized in that the exhaust gas mixture (step b) is an exhaust gas mixture from a combustion of diesel fuel.

3. The method according to claim 1 or 2, characterized in that the exhaust gas mixture (step b) 10 to 15 vol .-% CO ₂ , 10 to 13 vol .-% water, 0 to 5 vol .-% O ₂ and 73 to Contains 75 vol .-% N ₂ .

4. The method according to any one of claims 1 to 3, characterized in that for the second Premix stage provided O ₂ in the form of air, preferably ambient air, is supplied.

5. The method according to at least one of claims 1 to 4, characterized in that the diesel fuel before mixing in the first stage, a feed temperature of 10 to 70 ⁰ C, preferably 40 to 60 ⁰ C having.

6. The method according to at least one of claims 1 to 5, characterized in that the space provided for the first premix O ₂ gas mixture air, preferably ambient air, is.

7. The method according to at least one of claims 1 to 6, characterized in that the temperature of the O ₂ -containing gas mixture of the first premix 0 to 50 ⁰ C, preferably 15 to 25 ⁰ C, is.

8. The method according to at least one of claims 1 to 7, characterized in that the temperature of the O ₂ and H ₂ O and N ₂ and CO ₂ containing exhaust gas mixture of the second premix 350 to 600 ⁰ C, preferably 400 to 500 ⁰ C. , is.

9. The method according to at least one of claims 1 to 8, characterized in that the kohlenstoff- serstoffoxidation in the reactor at 850 to 1000 ⁰ C and 0 to 10 bar pressure is carried out.

10. The method according to at least one of claims 1 to 9, characterized in that the ratio between the diesel fuel and the O ₂ -containing gas mixture for the first premixing stage is defined by the air ratio lambda (= actually supplied amount of oxygen / amount of oxygen required for total oxidation), between 0.28 and 0 , 43, preferably between 0.31 and 0.41.

11. The method according to at least one of claims 1 to 10, characterized in that the ratio of the diesel fuel to the provided for the second premix O ₂ and H ₂ O, CO ₂ and N ₂ containing exhaust gas mixture by an S / C ratio (= Molar mass of water vapor in the supplied gas mixture / amount of carbon atoms in the diesel fuel), this ratio being between 0.1 and 0.9, preferably between 0.25 and 0.5.

12. The method according to at least one of claims 1 to 11, characterized in that the ratio s: c (steam to carbon) for both stages a total of 0.1: 0.9, preferably 0.2: 0.5 ,.

13. The method according to at least one of claims 1 to 12, characterized in that the resulting H ₂ / CO gas or H ₂ / CO contained product gas is supplied to a fuel cell.

14. The method according to at least one of claims 1 to 12, characterized in that the obtained H ₂ / CO gas or H ₂ / CO product gas is used for the reduction of nitrogen oxides.

15. Reactor (1) for carrying out a conversion of diesel fuel according to at least one of claims 1 to 12, which

a) a two-fluid nozzle (20), the first

Premix stage (3) and a second premix stage (4) pretends and b) one of the two-fluid nozzle downstream

Reactor space (5) for oxidation and a c) the reactor chamber (5) downstream outlet

(6).

16. Reactor according to claim 15, characterized in that the two-substance nozzle

(20) a preferably tubular feed line (2).

17. Reactor according to claim 16, characterized in that the feed line (2) has at least one lateral opening (7) for the gas mixture provided for the first premix stage.

18. Reactor according to one of claims 15 to 17, characterized in that at the end of the first premixing stage (3) to the second premixing stage (4) oriented towards the nozzle is given.

19. A reactor according to any one of claims 15 to 18, characterized in that around the second premixing stage (4) around the supply line for the gas mixture of the second premix stage in the form of a

Given circumferential space, preferably an annular space (9), said peripheral space to the Having second mixing stage (4) preferably radially distributed mixing nozzles (10).

20. Reactor according to claim 19, characterized in that the peripheral space has a tangential feed (11).

21. Reactor according to one of claims 15 to 20, characterized in that the reactor space

(5) is lined with ceramic (12).

22. Reactor according to one of claims 15 to 21, characterized in that the reactor space

(5) is constructed at least two-shelled.

23. Reactor according to one of claims 15 to 22, characterized in that the reactor space (5) is held by at least one flange (13).

24. Reactor according to one of claims 15 to 23, characterized in that on the side facing away from the second mixing stage (4) of the reactor chamber (5), a catalyst, preferably a noble metal catalyst, is provided on a metallic or ceramic support.

25. A reactor for carrying out a conversion of diesel fuel according to claim 13, characterized in that the outlet (6) has a direct access to a high-temperature fuel cell arrangement (HZ).

26. Reactor according to claim 25, characterized in that the outlet (6) is connected to a gas purification.

27 reactor for performing a conversion of diesel fuel according to claim 14, characterized in that the reactor is arranged in the region of a motor vehicle in the bypass to the exhaust gas flow and that the outlet (6) has access to a device for the reduction of nitrogen oxides (SCR).

28. Reactor according to claim 27, characterized in that the reactor has a connection to a soot filter at the entrance.