EP2537199A2

EP2537199A2 - Catalytic burner for fuel cell exhaust gas

Info

Publication number: EP2537199A2
Application number: EP10785365A
Authority: EP
Inventors: Kai Kuchenbuch; Patrick Mangold; Gert Hinsenkamp
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2010-02-17
Filing date: 2010-12-04
Publication date: 2012-12-26
Also published as: WO2011101008A3; CN102763256A; WO2011101008A2; CN102763256B; JP5721748B2; JP2013519861A; US20130004878A1; DE102010008209A1

Abstract

The invention relates to a catalytic burner (1), comprising a catalyst body (2) and a line element (3) for supplying a gas mixture (A) to the catalyst body (2). In addition, the catalytic burner (1) has a transition area (9) between the line element (3) and the catalyst body (2). A swirl element (8) is arranged in the area of the flow and upstream of the catalyst body (2) in the flow direction.

Description

Catalytic burner

The invention relates to a catalytic burner according to the further defined in the preamble of claim 1. Art Furthermore, the invention relates to the use of such a catalytic burner.

Catalytic burners can be used to convert flammable starting materials without open flame. For example, from the field of

Fuel cell systems catalytic burners for the afterburning of

Residual hydrogen in the exhaust gas and / or for the targeted combustion of hydrogen or another fuel for generating thermal energy known. Such catalytic burners generally have a catalyst body, which is formed for example as a porous or honeycomb-like material or as a bed of pellets or the like. The material used in the catalyst body is at least partially provided with a catalytically active substance, such as platinum, palladium or the like. In order to fully implement the starting materials used on such a catalytic burner, which is particularly in the

Afterburning unwanted residues in exhaust gases or the like is one of the main objectives for the use of the catalytic burner, it is necessary to offer an appropriate size of the catalytic burner to implement all existing in the gas mixture combustible combustibles can. This requires a correspondingly large space and thus a comparatively large catalyst body. Since the materials typically used as catalysts, such as platinum, are extremely expensive, such a correspondingly large catalyst body is always associated with considerable costs. The length of the catalyst body used has in particular with the

Uniform distribution of the flowing gas mixture to the catalyst body to do. If this improves, then a more uniform reaction in the provided flow-through cross-sectional area of the catalyst body can be achieved, whereby it can be made correspondingly shorter and thus smaller and more cost-effective. From this point of view it is known from DE 10 2008 031 060 A1, for the uniform distribution of an exhaust gas flow in an exhaust pipe in

Flow direction extending internals to provide as baffles, which despite a space often necessary curvature of the exhaust pipe is a relatively uniform

Distribution of the exhaust gas flow over the entire cross section of the exhaust pipe

to ensure. This construction allows for curved duct elements, which lead the gas mixture in the region of the catalyst body, quite an improvement, but they can not be for such a uniform flow of the

durchströmbaren cross-section of the catalyst body ensure that this can be shortened sustainable in its length expansion.

From the further general state of the art in the form of US 2003/0096204 A1, a catalytic burner is known in which, unlike in the prior art, an additional fuel is not introduced via an annular nozzle, but in which a very complex structure is formed which inflowing gas and a metered fuel in its flow direction repeatedly reverse, so a very good

To achieve thorough mixing. The gas mixture then flows correspondingly mixed in the region of the catalyst body. Again, only a very good mixing is achieved, a uniform flow of the catalyst body can not be realized by the structure. In addition, the structure is extremely complex due to a large number of very small and filigree components and leads to a very costly mixing area in front of the catalyst body.

For further general state of the art, reference should also be made to US 2005/0172547 A1. In this document, a device for mixing gases is described, in which swirl elements are used to mix two independently flowing into the region of the swirl elements gas flows as best as possible with each other. It is now the object of the present invention to provide a catalytic burner, which with minimal effort in terms of components in a simple and compact design, the best possible homogeneous flow of the

Catalyst body allowed, so that it can be shortened sustainably in its overall length.

According to the invention this object is achieved by the features mentioned in the characterizing part of claim 1. Further advantageous embodiments of

catalytic burner according to the invention will become apparent from the dependent claims. A particularly preferred use of the catalytic burner according to the invention is specified in claim 8. Advantageous developments of this use emerge from the dependent claims.

According to the invention is thus in the flow direction in front of the catalyst body

Swirl element arranged in the region of the flow. Such a swirl element, which according to a very advantageous development can be formed with a plurality of guide vanes, ensures minimum installation space seen in the direction of flow that clearly homogenizes both the fuel gas distribution and the velocity profile of the gas mixture over the catalyst body in different load cases. This has been clearly demonstrated by simulations of the flow. The swirl element, in particular if it is formed with a plurality of guide vanes, fan out the flow of the gas mixture before the catalyst body by radial deflection and thus ensures the very uniform and homogeneous flow of the catalyst body. Thus, the gas mixture over the entire available area of

Catalyst body with a very homogeneous velocity profile distributed. The catalyst body or the catalytically active substance present in it can thus be ideally utilized and the catalyst body can be correspondingly minimized with regard to the installation space required by it, and here in particular with regard to the required overall length. This results in a very compact construction, which also allows a significant saving of the generally very expensive catalytically active substance.

According to a particularly favorable and advantageous development of

According to the construction of the invention, it is provided that the catalyst body is cylindrical and the swirl element with respect to the flow-through cross-section of the Catalyst body is arranged centrally. A cylindrical catalyst body has the advantage that it can be easily integrated into a conduit element or a piece of piping. The central arrangement of the swirl element makes it possible, a best possible distribution of the inflowing gas mixture on the

durchströmbaren cross-section of the cylindrically shaped catalyst body, which is then formed accordingly as a round cross-section.

In a particularly advantageous embodiment of the catalytic burner according to the invention, it is further provided that the swirl element occupies the entire cross-section of the conduit element and is arranged at its end facing the transition region. According to this embodiment, therefore, the swirl element occupies the entire flow-through cross-section, so that the entire gas mixture for the swirl element is set into a rotational movement and deflected radially. This achieves the best possible fanning out of the flow of the gas mixture. Due to the arrangement in the region of the line element, which faces the transition region and thus the catalyst body, a very simple structure is created, since the swirl element can be easily introduced as termination of the line element between the transition region and the line element.

In a further very favorable and advantageous embodiment of the catalytic burner according to the invention, it is further provided that the flow-through cross section widens between the swirl element and the catalyst body. This extension, which can take place in particular in the transition region, can typically take place in the manner of a funnel, so that a comparatively large cross-sectional area of the catalyst body which can be flowed through can be flowed through uniformly. In addition, the velocity of the gas mixture is reduced due to the extension of the cross section at the same volume flow, so that the

Flow rate and thus the residence time of the gas mixture in the region of the catalyst body can be increased. This also serves to reduce the size and the amount of catalytically active substance in the region of the catalyst body. By means of the swirl element, the flow of the gas mixture is fanned out so that a very even distribution of the gas over the entire cross-section of the catalyst body takes place in the area of the expanding flow-through cross section since, as already mentioned several times, this is fanned out accordingly by the swirl element. In a very advantageous embodiment of the catalytic burner according to the invention, it is also provided that in the region of the cross-sectional widening on radially outer walls guide elements and / or openings for discharging liquid are provided. The gas mixture may optionally carry liquid which impinges in the region of the catalyst body and wets parts of the active surface so that the reaction of the gas is hindered. Due to the radial fanning of the gas flow, however, this is given a twist, with which this flows through the region of the cross-sectional widening. As a result, any entrained liquid droplets are thrown outward due to the centrifugal force and accumulate in the region of the walls of the cross-sectional widening. Here, corresponding guide elements and / or openings can be provided, through which the collecting liquid can flow. For example, in the walls before the

Catalyst body be introduced a corresponding groove in which liquid collects and is discharged from the region of the cross-sectional widening.

In an advantageous development of the catalytic burner according to the invention, it can also be provided that the line element is divided by at least two parallel sub-line elements in the direction of flow in front of the swirl element in the direction of flow. This installation of guide elements, as it is also described in the aforementioned prior art, in particular in curved conduit elements, which the gas mixture in the range of

Swirl elements lead, be used to equalize the flow of the swirl element and thus ultimately make the fanned flow much more homogeneous. If such internals extending in the direction of flow, which divide the line element into at least two parallel sub-line elements, are not used, then a curved line element could lead to an uneven flow of the swirl element, which would then result in a likewise non-uniform flow of the catalyst body.

A particularly preferred use of the catalytic burner according to the invention in one of the embodiments described above is the use for the thermal conversion of combustible radicals in the exhaust gases of a fuel cell. This particularly preferred use of the catalytic burner according to the invention enables the conversion of residues in the exhaust gases of a fuel cell, which typically have hydrogen. Due to the fact that no hydrogen should reach the environment in order to prevent any ignitable or explosive mixtures from escaping from the fuel cell system, the complete implementation of the combustible radicals in the exhaust gases of a fuel cell is particularly high

To make a request. Therefore, correspondingly large catalyst body are necessary to ensure safe and reliable in all operating situations. However, the inventive construction of the catalytic burner can now be the

Size of the catalyst body, as mentioned above several times, reduce.

This plays a decisive role, in particular for use in a fuel cell, since it minimizes this with regard to installation space and costs

However, a reliable and reliable complete conversion of all flammable residues in the exhaust gases can be achieved with catalytic burners. If the fuel cell or the fuel cell system equipped with it is also used for providing electric drive power in vehicles, as is known from the general state of the art, then the corresponding cost savings and the usual numbers of motor vehicles, which in the long run surely also of fuel cell vehicles be achieved, a clear

Savings in costs and raw materials in the range of the catalytic burner allows.

In a further very favorable and advantageous embodiment of the use, it is further provided that additional fuel is supplied to the exhaust gas. In the fuel cell system so the starting material for generating a

hydrogen-containing gas for the fuel cell or during operation of the fuel cell with hydrogen, this hydrogen supplied to the gas mixture. The supply can be done for example by a Ringsindüsung, which is known from the aforementioned prior art per se. The gas mixture can then be conducted via the line element and possibly running in this internals to the swirl element and can be so together with the existing gas mixture, which is typically an exhaust stream from a cathode region of the fuel cell and optionally a hydrogen-containing residual gas from the

Anode area of the fuel cell will be mixed. Overall, this results in a gas mixture which has comparatively large amounts of fuel and so, if the thermal energy of the catalytic burner is needed for other applications, can provide them sufficiently. In a particularly favorable and advantageous development of this use of the catalytic burner, it is provided that the hot exhaust gases after the

be relaxed in a turbine catalytic burner. Such a turbine for the recovery of pressure energy and thermal energy in the exhaust gases of

Fuel cell systems are also known from the general state of the art. In this case, the turbine can be connected either directly or indirectly to a compressor for the process air delivered to the fuel cell. It is also conceivable to couple the turbine and / or the compressor also in an electric machine. Then arises a structure, which is also referred to as an electric turbocharger (Electric Turbo Charger) or ETC. In this design, the residual energy from the region of the fuel cell can be utilized via the catalytic burner and converted into usable mechanical energy via the turbine. This then drives - at least partially - the compressor for the process air. Any remaining required power is supplied via the electric machine in motor operation. If more power is provided via the turbine than the compressor requires, the electric machine can also be used as a generator to convert this power into electrical power. Thus, a highly dynamic operation of a vehicle can be realized by temporarily hot gases are generated by the additional injection of fuel in the catalytic burner, which then provide so much energy through the turbine that the electric machine as a generator additional electrical energy for driving the vehicle when, for example, the

Fuel cell provides no or no sufficient electrical power can be provided.

Further advantageous embodiments of the catalytic burner according to the invention will become apparent from the embodiment, which is explained in more detail below with reference to the figures.

Showing:

1 shows a principle cross section through a catalytic burner according to the invention. and

Fig. 2 is a plan view of a swirl element according to the invention.

In the representation of FIG. 1, a cross section indicated by way of principle is represented by a catalytic burner 1. This consists essentially of one

Catalyst body 2 and a line member 3, which is a gas mixture with flammable or convertible starting materials leads to the catalyst body 2. The starting materials, for example, in the exhaust gases from a

Cathode space and an anode compartment of a fuel cell contained substances, in particular so be residual oxygen and residual hydrogen. In principle, however, the implementation of other combustible substances, such as those of hydrocarbons or the like is conceivable. The conduit element 3, which in the illustrated here

Embodiment is curved, has in the flow direction extending internals 4, which ensures that despite the curvature of the

Conduit element 3 is a uniform distribution of the inflowing gas mixture on the cross section of the conduit member 3 after the curvature. The gas mixture flowing in according to the arrow A can for example be a mixture of the exhaust gases A from a cathode space and an anode space of a fuel cell. This gas mixture, which is already combustible in itself, can also be introduced via an annular nozzle 5

Fuel B are additionally supplied. This fuel B is introduced via the known per se ring nozzle 5 in the gas mixture A, that flows from an annular space 6 of the fuel B via distributed around the circumference of the power element 3 openings 7 in the mixture. The gas mixture A, to which optionally the fuel B has been supplied, then flows through the conduit element 3 and from the internals 4

uniformly guided by the curvature of the conduit member 3 in the region of a swirl element 8 and from there through a transition region 9 in the catalyst body. 2

The swirl element 8 is, as can be seen in the plan view of Figure 2, formed with a plurality of vanes 10 so that a radial deflection of the flowing through the swirl element 8 gas mixture A occurs. The gas mixture A is thereby fanned out accordingly and can be very homogeneous and uniformly over the through ström bare surface of the expanding cross section in the cross-section 9

Catalyst body 2 are distributed. The swirl element 8 is very small and simple in construction and can be manufactured according to cost. In

Flow simulations could be confirmed that this gas distribution and the velocity profile over the catalyst body 2 could be significantly made uniform in different load cases by this simple and efficient swirl element 8. Thus, the available catalyst body 2

or the available in the catalyst body 2 through-flowable cross-sectional area ideally flows and optimally utilized. The catalyst body 2 can thus be made very small and efficient. This is in terms of Installation space and the cost and in terms of the required catalytically active material is a decisive advantage.

Should liquid in the form of liquid droplets be present in the flow of the gas mixture, they would at least partially wet and render ineffective at least part of the surface of the catalyst body 2. To prevent this, it can be optionally provided that in the transition region 9 in the region of the walls, for example in the region of the walls immediately before this on the

Catalyst body 2 meet, corresponding guide elements 11 and / or openings are provided. In the through the swirl element 8 on the cross-sectional area of

Catalyst body 2 fanned out flow of the gas mixture, there is a movement of the droplets outward due to the centrifugal force. As a result, the liquid can be deposited very efficiently in the area of the walls of the transitional area 9 via the guide elements 11 and, if appropriate, drain openings not shown here, and removed from the area of the catalytic burner 1.

All in all, this results in a very efficient and compact construction, which enables the best possible flow of the available flow-through cross-sectional area of the catalyst body 2 with very simple and cost-effective means, and thus a very short and thus cost-effective construction in the flow direction

Catalyst body 2 allowed.

Claims

claims

1. A catalytic burner with a catalyst body and a conduit element for supplying a gas mixture to the catalyst body, and a

Transition region between the conduit element and the catalyst body, characterized in that

in the flow direction in front of the catalyst body (2) a swirl element (8) is arranged in the region of the flow.

2. The catalytic burner according to claim 1,

characterized in that

the catalyst body (2) is cylindrical and the swirl element (8) with respect to the flow-through cross-section of the catalyst body (2) is arranged centrally.

3. A catalytic burner according to claim 1 or 2,

characterized in that

the swirl element (8) occupies the entire cross-section of the conduit element (3) and is arranged at its end facing the transition region (9).

4. A catalytic burner according to claim 2 or 3,

characterized in that

the swirl element (8) has a plurality of guide vanes (10).

5. The catalytic burner according to one of claims 1 to 4,

characterized in that the flow-through cross section widens between the swirl element (8) and the catalyst body (2).

6. The catalytic burner according to claim 5,

characterized in that

In the region of the cross-sectional widening on radially outer walls, guide elements (11) and / or openings for discharging liquid are provided.

7. The catalytic burner according to one of claims 1 to 6,

characterized in that

the conduit element (3) is subdivided into at least two parallel subconducting elements in the flow direction upstream of the swirl element (8) by means of internals (4) running in the direction of flow.

8. Use of the catalytic burner according to one of claims 1 to 7

for the thermal conversion of combustible residues in the exhaust gases (A) of a fuel cell.

9. Use according to claim 8,

characterized in that

the exhaust gases (A) additional fuel (B) is supplied.

10. Use according to claim 8 or 9,

characterized in that

the hot gases after the catalytic burner (1) are relaxed in a turbine.