Patent Grant
6901760
The invention relates to a burner for a heat generator.
From EP 0 321 809 (US equivalent U.S. Pat. No. 4,932,861), EP 0 780 629 (US equivalent U.S. Pat. No. 5,735,687), WO 93/17279 (US equivalent U.S. Pat. No. 5,402,633), and EP 0 945 677 (US equivalent U.S. Pat. No. 6,178,752), premixing burners are known in which a combustion air flow is introduced tangentially into a burner interior by means of a swirl generator and is mixed with fuel. At the burner outlet, the resulting vortex flow bursts open at a jump in cross section, inducing a recirculation zone which serves to stabilize the flame in operation of the burner.
The axial position of the recirculation zone which arises is of critical importance for the stabilization of the flame, and in its turn is substantially determined by the axial flow in the center of the burner. If this axial flow is too weak, the recirculation zone, and with it the flame, migrates into the burner interior. The danger then exists of a flashback of the flame and a gradual overheating of the burner. If, on the other hand, the axial flow is too strong, the recirculation zone can detach from the burner outlet and become unstable. The consequence can be strong, damaging, combustion pulsations or even an extinction of the flame.
Summarizing, the axial flow in the center of a burner of the aforementioned kind is thus of great importance for stable and safe operation. It is therefore also known to produce a defined axial central flow in such burners by means of a central air injection. Nevertheless, a more or less favorable position of the recirculation zone results even in these burners in different states of operation. Thus, at full load, an axial flow is desirable which is strong enough to hold the flame safely outside the burner. In contrast, at lower loading of the burner the axial flow has to be prevented from driving the recirculation zone impermissibly far from the burner mouth; the axial impulse of the central flow thus has to be smaller.
Solutions known from the state of the art are not capable of setting an optimum axial position of the recirculation zone under all operating conditions.
According to a first aspect of the invention, a burner for a heat generator comprises a swirl generator for receiving and swirling at least part of a combustion air flow, the swirl generator defining a central burner axis and having an internal space, the swirl generator configured and arranged for tangentially introducing the combustion air flow into the internal space, the internal space defining a cross sectional throughflow area, and means for the introduction of at least one fuel into the combustion air flow; means at a downstream end of the swirl generator for forming an abrupt widening of the cross sectional throughflow area; and an injection device configured and arranged for the introduction of an axial central air flow along the central burner axis, the injection device including an adjustable element configured and arranged for altering a throughflow cross section of the injection device and for the control of the mass flow of the axial central air flow.
According to a second aspect of the invention, a process for operating a burner comprises the steps of providing a burner as described above, and throttling the axial central air flow based upon the burner load, the central flow being strongly throttled at low burner load, and the central flow being little throttled or not throttled at high burner load.
According to a third aspect of the invention, a process of operating a gas turbine comprises the steps of providing a plurality of burners as described above, throttling the axial central air flow based upon the burner load, the central flow being strongly throttled at low burner load, and the central flow being little throttled or not throttled at high burner load; measuring combustion pulsations; and controlling the central flow of each of the plurality of burners depending on the measured combustion pulsations.
The invention will provide a remedy here. The invention has as an object to provide a burner of the kind mentioned above with a central injection device so that the axial impulse of the central air flow is adjustable in all regions of operation to an optimum stabilization and positioning of the flame.
This is attained according to the invention in that the injection device has displaceable elements for changing a flow cross section of the injection device.
An aspect of the invention is thus to provide the burner with a variable geometry of the central injection. It is possible in this manner to match the axial impulse of the central flow to the operating conditions at any given time. This makes it possible to affect the position and intensity of the recirculation zone in a targeted manner. It is thereby possible in a particularly advantageous manner to reduce the amount of air introduced centrally at a low burner load, such that the recirculation zone forms very near to the burner mouth or even partially within the burner interior, so that a superior flame stability results. At high load and high flame temperatures, in contrast, high stability is already intrinsically inherent in the flame. Here the centrally introduced amount of air can be increased such that the recirculation zone comes to be reliably situated a distance downstream of the burner mouth. Thermal overloading of the burner is thereby prevented.
The use of a burner according to the invention is also particularly advantageous when the flow field of the combustion air flow varies due to changing mass flows or temperatures. Precisely such conditions are present in the combustion chambers of gas turbines when the load varies. The states at the compressor outlet and the inflow conditions at the combustion chamber entrance vary considerably, due to different intake air mass flows and compressor outlet pressures. Variations of the position of the recirculation zone thereby arising can be compensated in a burner according to the invention by an adjustment of the geometry of the central injection device.
The invention is concerned with premixing burners, which are well known and familiar per se to the skilled person from the state of the art in the above-cited documents. One aspect of the invention is that it can be immediately combined with all the constructional kinds of swirl generators and burners which are disclosed in the documents cited herein and developed from these documents, and are familiar per se to the skilled person.
The control of the central air flow can be appropriately carried out according to different criteria. Worth mentioning and advantageous here is, for example, a control in dependence on the burner load or on a measured material temperature.
A further operating method results with advantageous operation in the combustion chamber in gas turbines. Here the variable central geometry in combination with the operating concepts of gas turbines with premixers, which are familiar to the skilled person, furthermore serves to ensure operation which is low in pollutants and at the same time stable and free from pulsation. Finally, a variation of the conditions can be set for individual burners in a targeted manner, in order to prevent acoustic resonances in the combustion chamber by a detuning of individual burners.
Still other objects, features, and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of embodiments constructed in accordance therewith, taken in conjunction with the accompanying drawings.
The invention of the present application will now be described in more detail with reference to preferred embodiments of the apparatus and method, given only by way of example, and with reference to the accompanying drawings, in which:
a illustrates portions of the burner of
b illustrates an end view of the portions of a burner illustrated in
Referring to the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures.
As a first preferred embodiment of the invention, a premixing burner is shown in
Again referring to
A fuel is supplied in a suitable manner to the combustion air flow in the swirl generator. In the embodiment example, fuel ducts 111 are arranged along the partial members in the region of the tangential inlet slots 121, in the axial direction of the swirl generator. Rows of fuel outlet bores 1111 can be seen in the embodiment example. A fuel 142 is supplied via the fuel ducts 111, and flows via the fuel outlet openings 1111 into the interior space 122 of the swirl generator 100. This kind of fuel admixing is frequently and preferably used for gaseous fuels. Intensive mixing of the fuel 142 with the tangentially inflowing combustion air 141 takes place in the interior space of the swirl generator. A very homogeneous mixture of air and fuel is present in the swirl flow 144 at the outlet from the burner into the combustion space 50.
A flame from the premixed air-fuel mixture can be stabilized in the region of the recirculation zone 123. Due to the good premixing of air and fuel, this flame can be operated, with the prevention of stoichiometric zones and the accompanying formation of “hot spots”, with a quite high air excess: as a rule, air numbers of two and more are found at the burner itself. Because of the comparatively cool combustion temperatures, very low emissions of nitrogen oxides can be attained with such burners without expensive exhaust gas after-treatment. Because of the good premixing of the fuel with the combustion air and a good flame stabilization by means of the recirculation zone, a good degree of oxidation furthermore occurs in spite of the low combustion temperatures, and thus also low emissions of partially and completely uncombusted fuel, and in particular of carbon monoxide and uncombusted hydrocarbons, but also other undesired organic compounds. Furthermore, the purely aerodynamic flame stabilization due to the breakdown of the vortex flow 144 (“vortex breakdown”) is found to be advantageous. Because mechanical flame baffles are dispensed with, no mechanical components come into contact with the flame. The feared failure of mechanical flame baffles due to overheating, with possible subsequent serious accidents to machine sets, is thus excluded. Furthermore, apart from radiation, the flame loses no heat to cold walls. This additionally contributes to equalization of the flame temperature and thus low pollutant emissions and good combustion stability.
A critical factor for the operating performance of such a burner, as given in the Figure, is the position of the recirculation zone 123. This is furthermore essentially determined by the swirl number, roughly speaking, the ratio of the peripheral component to the axial component of the vortex flow 144: if the rotational speed of the vortex flow 144 is large, a wide recirculation zone is formed. Under these conditions, a robust recirculation zone is formed, situated near the burner opening, and thus a stable combustion zone is formed in operation. These are conditions which are desired in the interest of a good flame stability at low burner loads and thus high burner air numbers, and which also are necessary for the stabilization of the flame, burning at comparatively low temperatures. On the other hand, at high swirl numbers of the combustion air flow, a region of low pressure forms along the burner axis and, as it were, sucks the recirculation zone, and with it the flame, into the burner interior. This is, however, undesired at high burner loads. At full load of this burner, this operates with air numbers in a region of 2, in the extreme case, even still under fuel-rich conditions, for example with air numbers of 1.7, 1.5 or even 1.3, but air numbers being attained in each case in the region between 2.5 and 2, preferably about 2.3. The combustion zone therefore clearly has higher temperatures than in the partial load region, in which burner air numbers of 3 or 4 appear, and is itself substantially more stable. A recirculation zone which is so pronounced is thus not required at high loads. There exists on the contrary the danger that hot gas is sucked out of the combustion zone along the burner axis and into the burner. Such a flashback can on the one hand endanger the integrity of the burner, and in the extreme case that of a whole machine set. On the other hand, a flip-flop effect of the flame between two combustion modes inside and outside the burner can build up. Furthermore, a combustion zone spread over a larger space is desired for a high load.
Summarizing, it would thus be established that here a smaller swirl number of the vortex flow 144 is desirable and realizable, which however again limits the operating region to small loads. In order to reduce the danger of flame flashback, it is also known to introduce an axial air flow centrally into the burner, again negatively affecting the partial load behavior of the burner, since the recirculation zone is driven out of the burner mouth. Lastly, the constructionally predetermined flow parameters of the combustion air flow must always represent a compromise, not least because of the fact that, for example, when used in gas turbines the inflow conditions of the combustion air to the burner vary strongly with respect to the mass flow, the temperature, and the pressure, so that in any case it is difficult to provide a defined combustion air flow.
Here the invention proposes to introduce an axial central flow 145 into the center of the burner, along the burner axis or the swirl generator axis 100a. The central flow is made variable for matching to the operating conditions. In a first preferred variant, an injection device 112 is situated centrally on the head end of the burner, thus at the upstream end. The injection device shown here includes a throughflow member 1121. This is substantially a hollow-bored cylinder with an open end and an end which has a floor 1124. The floor 1124 has an opening 1125 whose diameter is smaller than the internal diameter of the cylinder bore. The throughflow member 1121 ends with the blunt open side at an inflow, that is, upstream, end of the burner or of the swirl generator 100, while the floor 1124 faces with its opening toward the interior 122 of the burner.
An air stream which flows from the inflow side toward the burner is hereby largely conducted through the tangential inlet slots 121 tangentially into the burner as combustion air 141; however, a partial stream, dependent on the throughflow cross section of the injection device, flows as an axial air flow 145 along the burner axis 100a into the center of the burner, and by the additional axial impulse affects the axial position of the recirculation zone 123. An adjustable central member 1122 is inserted coaxially into the throughflow member 1121. This member 1122 tapers at one end with a cone 1123. This cone projects at least in an axial position of the central member into the opening of the floor of the throughflow member. The cone 1123 obstructs the opening to different extents by an axial adjustment of the central member 1122, and thus defines the narrowest throughflow cross section of the injection device 112. The axial central flow 145 can be controlled by an axial adjustment of the central member, which serves as a control member, and thereby also the position and intensity of the recirculation zone 123 can be altered. The embodiment according to the invention of the premixing burner, known per se, thus makes it possible to match the central flow to the operating conditions of the burner. The stable and safe operating region of the burner is thus once more substantially widened.
In the premixing burners to which the invention preferably finds application, fuel is frequently also supplied centrally, this fuel supply then finding application both as an alternative and as a supplement to the above-described fuel supply via the ducts 111. Such a burner is shown in FIG. 4. In essential elements, particularly with respect to the swirl generator 100 and the supply of the fuel 142, the burner is completely identical to the burner shown in
Usually in the real embodiment of such a burner, as shown in
A further preferred embodiment is shown in FIG. 6. The burner 1 is arranged on a combustion chamber 20, for example, of a gas turbine, and opens into a combustion space 50. Air flows from a compressor (not shown) into an air chamber 60, which is enclosed by a housing 4. A burner hood 5 is arranged within the housing 4, and further encloses the burner 1. A plenum 55 is formed within the burner hood, and is in fluid connection with the air chamber 60. A combustion air flow 141 flows out of the air chamber 60 into the plenum 55, and from there through tangential inlet slots into the interior of the burner 1, where this air forms a swirl flow in the manner described hereinabove, and is mixed with fuel. The burner is provided with a central injection device 112 in the manner described hereinabove. The central injection device is connected to a central air supply duct 1129. The air chamber 60 is provided with a bypass duct 61. The bypass duct 61 and the central air supply duct 1129 are connected together such that a central air flow 145 can flow from the bypass duct 61 to the central air supply duct 1129. An adjustable throttle element 62 is arranged in this flow path as a control element for the central air flow 145. Thus the central air flow can likewise be varied as described above, and can be matched to the load conditions of the burner. In contrast to the embodiments of the controllable central air injection shown in
A special embodiment of the central air supply with a control element is shown in FIG. 7. Both the air bypass 61 and also the central air supply duct 1129 open into an fluid conduit space 66. A throttle valve 64 is arranged within the fluid conduit space. This is mounted to rotate around an axis, as indicated by the arrow in the drawing. The free flow cross section of the fluid conduit space can be changed by a rotation of the throttle valve 64, resulting in a variation of the central air flow 145.
Based on the radial pressure equilibrium which is given by the known equation:
w2/r=ρ·dp/dr
where w is the circumferential speed, r is the distance from the axis of a swirl flow, and p is the static pressure, there is always a reduced pressure in the center of a swirl flow. Embodiments without a burner hood 5 would therefore also be conceivable in principle.
Burners are familiar to the skilled person in different constitutions, which differ in specific embodiment from the burners shown in
It is known from U.S. Pat. No. 5,735,687 (which is in the patent family including EP 0 780 629), which document is incorporated into the present application by reference in its entirety, to arrange a mixing pipe downstream of the swirl generator of a burner. The embodiment of the invention with such a burner is shown by way of example in
Based on the uniform preparation of an ignitable mixture over the whole flow cross section of the mixing pipe, the danger exists of a flame flashing back along the low-impulse wall boundary layers in the mixing pipe. The mixing pipe is therefore provided with wall film bores 231 running at an acute angle to the burner axis. An air mass 150 flows through these into the mixing pipe and forms a wall film there. This flashback is effectively prevented by the acceleration or diminution of the wall boundary layers on the one hand, and the displacement of ignitable mixture from the low-impulse regions on the other hand. The mixing pipe 230 is provided at the opening into the combustion space 50 with a breakaway edge 232 which likewise stabilizes the form and position of the recirculation zone 123 forming at the burner mouth. The mixing pipe is fastened to a front segment 108 which at the same time forms a combustion space wall and which in this example is impact cooled by means of impact cooling sheets 109 and impact cooling air 149.
Besides the danger of flashback along the wall boundary layers, there also exists here the danger of a flashback of the flame along the burner axis 100a under high load, or the danger of the recirculation zone 123 floating away with flame instabilities at low load. In order to prevent this, the burner shown in
Burners are likewise known from WO 93/17279 and EP 0 945 677, and have cylindrical swirl generators with tangential combustion air inlets. In this connection it is also known to arrange a displacement member, tapering toward the burner mouth, in the interior of a cylindrical swirl generator. The favorable criterion given above for the axial throughflow cross section of the swirl generator, namely that the axial throughflow cross section increases in the axial throughflow direction, is fulfilled by means of such a swirl generator internal member. Embodiments of such burners are shown in
The burner can of course also be provided with a cylindrical swirl generator with a mixing section following downstream of the swirl generator, without departing from the present invention.
The use of a swirl generator with a central displacement member also makes it possible to shape the swirl generator itself as convergent to the mouth, but to nevertheless shape the axial throughflow cross section of the swirl generator internal space as divergent. This variant, shown in
Swirl generators with tangential combustion air inlets can be constructed in different ways. Besides the construction from several partial members shown in cross section in
The embodiment examples described hereinabove are in no way to be understood as limiting the present invention. They are on the contrary to be understood as illustrative and as a sketch of the multifarious possible embodiments within the scope of the invention as characterized in the claims.
Preferred methods for the operation of a burner according to the invention will be apparent to the skilled person from the specific use.
A first method of operation, easy to manipulate, is shown in FIG. 14. The burner 1 is operated with a fuel 142. The mass flow of this fuel is determined at a measurement point 2. The resulting mass flow signal X{dot over (m)} is processed in a control unit 3, and is converted into a control signal Y for the adjustment mechanism of the axial central air injection of the burner 1.
A second embodiment, shown in
A gas turbine set with a compressor 10, a turbine 30, and a generator 40 arranged on a common shaft is again shown in FIG. 16. The combustion chamber 20 is shown in longitudinal section as an annular combustion chamber which is operated with at least one burner 1 according to the invention. The burner 1 is provided with a temperature measurement point for the determination of the material temperature, producing a temperature signal XT. The combustion chamber 20 is provided with a pulsation measuring device for the determination of the combustion air pressure fluctuations, producing a pulsation signal XPuls. The signals XT and XPuls are passed to a control unit 3 which generates a control signal Y for the control of the intensity of the axial central flow. When the material temperature exceeds a given threshold value, the central injected mass flow is increased so that the flame is driven a little away from the burner mouth, reducing the heat loading of the burner. On the other hand this can lead to an undesired reduction of flame stability. This is determined by the pulsation measuring point. When the pulsation signal XPuls increases, the central injected mass flow can be reduced, in order to increase the stability of combustion and to counter the increase of combustion pressure fluctuations. The central injection can be controlled in this manner in dependence on relevant measured data.
It goes without saying that the given operating processes also represent portions of substantially more complex, superordinate control designs and can be integrated into these.
It is furthermore conceivable to provide only one burner of a multi-burner system with the central air supply according to the invention, or to operate the burners with different central air flows. Symmetry-breaking can thereby be attained in a targeted manner in multi-burner systems, and can be used for the reduction or complete prevention of, in particular, azimuthal acoustic vibrations.
The statements hereinabove serve to the skilled person as illustrative examples for the numerous possible embodiments of the burner according to the invention characterized in the claims, and for their advantageous manner of operation.
While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. Each of the aforementioned documents is incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 100 50 248 | Oct 2000 | DE | national |
This application is related and claims priority under 35 U.S.C. § 119 to German Patent Application No. 100 50 248.2, filed Oct. 11, 2000, the entire contents of which are incorporated by reference herein. In addition, this application is a divisional of U.S. patent application Ser. No. 09/973,868 filed on Oct. 11, 2001, now abandoned, the entire contents of which are incorporated by reference herein.
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| Number | Date | Country | |
|---|---|---|---|
| 20040139748 A1 | Jul 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09973868 | Oct 2001 | US |
| Child | 10665569 | US |
