This application claims priority under 35 U.S.C. § 119 to Swiss application number 2002 0737/02, filed May 2, 2002.
The invention relates to a catalytic burner at or for a combustion chamber, in particular of a power plant.
JP 61 276 627 A discloses a catalytic burner of this type which has an annularly arranged catalyst, through which the flow passes when the burner is in operation, and a swirl generator, through which the flow passes when the burner is in operation. In this case, the swirl generator is designed as an axial swirl generator, through which the flow passes in the axial direction and which at the same time acts with a swirl upon the flow. The axial swirl generator is in this case arranged concentrically within the catalyst, so that the flow passes in parallel through the catalyst and swirl generator.
The present invention is concerned with the problem of specifying, for a catalytic burner of the type initially mentioned, an improved embodiment in which, in particular, combustion stability in the combustion chamber is increased.
The invention is based on the general notion of using, for acting with a swirl upon the burner flow, a radial swirl generator, that is to say a swirl generator through which the flow passes radially and which at the same time generates a swirl flow emerging axially. In the case of a radial swirl generator, for the same outlet cross section, the flow resistance is lower than with an axial swirl generator. Correspondingly, in the burner according to the invention, there is a smaller pressure drop, this being particularly advantageous here, since the throughflow of the catalyst or catalysts is always accompanied by a pressure drop.
It is particularly advantageous to have a version in which the swirl generator and the catalyst or catalysts are arranged in the same flow path, so that the entire flow lead through the catalyst or catalysts is or becomes acted upon by the swirl. This leads to intensive intermixing even before entry into the combustion chamber.
According to a preferred embodiment, the radial swirl generator may have a plurality of rectilinear swirl generator ducts which in each case are inclined with respect to the radial direction in the circumferential direction and which connect a radially outer inflow space to a radially inner outflow space. This form of construction possesses relatively low throughflow resistance. The rectilinear swirl generator ducts possess, in their longitudinal direction, a constant cross section which, in particular, makes it possible to insert especially simply constructed and therefore cost-effective catalysts into the swirl generator ducts. For example, conventional monolithic catalysts with rectilinear and parallel catalyst ducts or cells may be used. It is thereby possible to resort to standard components, this being particularly cost-effective. Instead of monolithic catalysts, it is also possible to use catalysts which are produced from zigzag-folded or corrugated metal sheets by multiply folding, layering or winding.
It is particularly important, in this case, that the catalysts are integrated into the radial swirl generator, thus resulting in an especially compact construction for the burner according to the invention.
Further features and advantages of the burner according to the invention may be gathered from the drawings and from the accompanying figure description with reference to the drawings.
Preferred exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, the same reference symbols relating to identical or similar or functionally identical components. In the drawings, in each case diagrammatically,
In
A transition 10 between the outflow space 8 and the combustion space 3 possesses here, a cross-sectional widening 11 which, in particular, may be formed abruptly. By virtue of this cross-sectional widening 11, the swirl flow generated in the burner 1 can virtually burst open in the combustion space 3, as a result of which, on the one hand, a first vortex system 12 is generated in the region of the cross-sectional widening 11 and, on the other hand, a central second vortex system 13 is generated in the combustion space 3. With the aid of the second vortex system 13, a central recirculation zone 14 is generated in the combustion chamber 2 and anchors and stabilizes a flame front 15 in the combustion chamber 2 in what is known as the “plenum”, that is to say in the vicinity of the burner 1.
According to
Expediently, the swirl generator ducts 16 are of rectilinear design with a cross section which is constant in their longitudinal direction. It is thereby possible to insert particularly simply constructed catalysts 5 into the swirl generator ducts 16. For example, the individual catalysts 5 consist of ceramic monoliths which are catalytically coated in a suitable way. It is likewise possible to construct the catalysts 5 by means of a stack or a winding of corrugated or zigzag-folded sheet metal webs which are likewise catalytically activated by means of a suitable coating. The catalysts 5 in each case contain a multiplicity of catalyst ducts, not designated in any more detail, which in each case run parallel to one another and parallel to the swirl generator ducts 16. In order to avoid an overheating of the catalysts 5 when the burner is in operation, it may be expedient to carry out the coating of the individual catalyst ducts in such a way that not all the catalyst ducts, for example only every second catalyst duct, is designed to be catalytically active. In a construction of this type, no combustion reaction takes place in the catalytically inactive catalyst ducts, so that the flow carried in them serves for cooling the adjacent catalyst ducts in which combustion reactions occur. A catalyst construction of this type is basically known from U.S. Pat. No. 5,202,303 and therefore does not have to be explained in any more detail.
By the individual catalysts 6 being inserted into the swirl generator ducts 16, the catalysts 5 or the catalyst arrangement 4 are integrated into the swirl generator 6. It is particularly important, in this case, that, in this construction, the flow led through the catalysts 5 is acted upon simultaneously with the desired swirl.
Since the catalysts 5 are arranged in the radial swirl generator 6, they are positioned on a radius which is larger than the radius of the outlet cross section 17. Correspondingly, a smaller pressure drop is obtained from the throughflow of the catalysts 5 than in the case of a comparable arrangement with a straightforward axial throughflow. The flow velocity in the catalyst ducts and the pressure loss of the catalysts 5 can be set, on the one hand, via the length of the catalysts 5 and via their cell density and also by means of the axial extent of the catalysts 5 or of the swirl generator ducts 16 and therefore of the swirl generator 6. Expediently, the burner 1 is designed in such a way that, when the burner is in operation, at least in the outflow space 8, the flow velocity is higher than a turbulent flame velocity at which the flame front 15 may be propagated toward the burner 1. A propagation of the flame front 15 into the outflow space 8 can be avoided by means of this measure. Alternatively or additionally, the burner 1 is designed in such a way that, when the burner is in operation, a dwell time of the flow in the outflow space 8 is shorter than a time delay up to the autoignition of the partially reacted hot fuel/oxidizer mixture flowing into the outflow space 8. By virtue of this measure, the hot gas generation provided for the combustion space 3 can be kept away from the outflow space 8. Said measures in each case contribute to the fact that an overheating of the catalysts 5 or of the swirl generator 6 can be avoided.
According to
Moreover, according to
With the aid of the secondary injection device 22, sufficient combustion in the combustion chamber 2 can be implemented for the purpose of starting the burner 1 or for transient operating states. A “pilot mode” of this type is necessary, for example, when the catalysts 5 have not yet reached a sufficiently high operating temperature. The introduction of secondary fuel may be advantageous not only in the transient operating states during the run-up of the burner 1, but also in part-load states, in order to increase the operating reliability of the burner.
Furthermore, it is basically possible to introduce liquid fuel via the secondary injection device 22, without said liquid fuel coming into contact with the catalysts 5. Additional aging of the catalysts 5 due to the supply of liquid fuel can thereby be avoided.
Whereas, in the embodiment of
In the embodiment of
Whereas, in the embodiments shown hitherto, at least one catalyst 5 is arranged in each swirl generator duct 16,
Although, in the embodiment of
Whereas, in the embodiments shown hitherto, the catalyst arrangement 4 has in each case only one catalyst 5 for each swirl generator duct 16, in the embodiment according to
In the embodiments of
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