EP0931979A1 - Method and apparatus for supressing flame and pressure fluctuations in a furnace - Google Patents

Abstract

The flame (7) has a higher flow speed in its spreading direction (13) than its outer area. A screen (15) surrounds the gas outlet aperture (9) with radial distance around the burner outlet and separates a flue gas recirculation area (16) connected to the combustion chamber (8) from the gas (9). The screen is of the single or double shell type and in the latter case the gas flows through it. The screen extends parallel to the flame spreading direction. It can be cylindrical and concentric with the burner or can have a conical shape. It can be made of high temperature-resistant steel or of ceramic material.

Description

The invention relates to a device for suppressing flame / pressure vibrations with a furnace with at least one Burners for generating a flame and a combustion chamber in which the flame is directed, the furnace at least one gas outlet has, from which gas flows, the flame encloses a jacket and a higher flow rate in the flame propagation direction than the outer regions of the Flame, as well as a gas turbine using such a device is issued.

In industrial combustion plants such as gas turbines, combustion chambers, Hot water heaters, residue incineration plants or industrial furnaces, but also for small furnaces such as gas boilers or boilers in the domestic use area occur under certain through the firing parameters such as thermal performance conditions and unstable operating conditions on, which is characterized by time-period changes in the flame that are accompanied by changes in particular the static Pressure in the combustion chamber and in this upstream or downstream Plant parts. These unstable states also occur in furnaces whose flames are caused by known measures such as Swirl currents, bluff bodies etc. are sufficiently stabilized by ignition.

The occurrence of these combustion instabilities often causes changed behavior compared to the stationary operation of the system and causes not only an increased noise pollution but also an increased one mechanical and / or thermal stress on the combustion chamber or the combustion chamber lining. Such flame / pressure vibrations can under unfavorable conditions up to Destruction of the system in which they occur, so much effort is driven to such flame / pressure vibrations avoid. For example, you can change the geometry of the combustion chamber through special fittings, which often only results in a shift of the occurring vibration frequencies and therefore not contributes to a general solution to the problem. Otherwise special when flame / pressure vibrations occur Measures taken on an empirical basis.

EP-A-0 754 908 accordingly describes a device as specified above proposed in which the flame of a burner with a Flow from gas is encased as closely as possible, the gas flow a higher speed in the direction of flame propagation has as the outer or edge areas of the flame or main burner flow containing fuel.

Außenbereichen der Flamme" gesprochen wird, werden hierunter die reagierenden bzw. reaktionsfähigen Schichten einer Brennstoff bzw. Brenngas/Luftströmung verstanden. Auf diese Schichten wird dann durch den Gasmantelstrom eine Übertragung von Axialimpuls bewirkt.As far as here in the following from the

Outside regions of the flame "is spoken here, the reacting or reactive layers of a fuel or fuel gas / air flow are understood. A transmission of axial impulse is then effected on these layers by the gas jacket flow.

With The main direction of propagation in the axial extent of a flame is to be referred to here, which in this respect is to be distinguished from the radial direction of propagation of the flame.

The principle of the invention is based on the knowledge that the vibrations essentially by themselves in the edge area of the Flame periodic ring vortices caused or intensified become. This ring vortex created by rolling up the edge areas of the fuel-containing burner flow arise, close at their Education is hot, already burned out, no longer reactive Flue gases with a, which also quickly heats up the Ring vortex contained fuel / air mixture and therefore a pulse-like, pressure vibration-stimulating reaction of the fuel cause.

To prevent this ring vortex formation, the procedure is as described above the flame with the smallest possible radial distance to the flame or to the main burner flow Surround the gas jacket flow, which has a higher flow rate in the flame propagation direction than the outer or Edge areas of the flame. So it comes between the jacket flow and flame or fuel gas / air flow for an axial pulse exchange, an acceleration of the free flame or flow boundary layer of the fuel / air mixture, with which the Effective formation of reactive vortices in this area is counteracted.

So much for the boundary layer between the gas jacket flow and the surrounding medium (in the included case in general Flue gases) corresponding ring vortices occur again, it is on cheapest if the gas jacket flow contains no fuel, since the (fuel-free) jacket flow does not result in any fuel-enclosing flows Vortices that can form a periodic Abreaction of fuel and thus to excite flame / pressure vibrations can lead, as with an unclad Flame or fuel / air flow occur.

It is preferably the non-fuel-containing one Gas the jacket flow around air everywhere in sufficient quantities is available. But it is also conceivable to use an inner gas to use, which however results in a certain cost disadvantage would have.

This results in particular in the case of internal gas Task to develop a device as described such that a lower gas flow or a smaller amount of gas per unit of time is necessary to achieve the desired effect. But also when using air one is interested in having little air for to have to provide the jacket flow in order for this purpose do not provide too much compressor power or otherwise to have to branch off.

This object is achieved in that a Gas outlet opening more extensive, with a radial distance around the Burner outlet extending screen is provided, through which a the flue gas recirculation area connected to the combustion chamber is separated from said gas.

It has been found that due to the spatial separation of the fuel / air mixture and the jacket-like enclosing Gases from the outer recirculation flow are hotter, burned out Flue gases using the screen improve the jacket flow is protected against lateral distraction and therefore with regard is less distracted in their direction. This is enough also lower pulse current densities or gas velocities Jacket flow to ensure that the jacket flow with sufficient impulse, that is to say with sufficient overspeed towards the edge areas of the flame reached downstream of the burner outlet where the above-mentioned periodic formation of reactive, that is, fuel-enclosing ring vortices can be avoided should.

This results in a considerable amount through the use of the screen Saving of the required gas, air mass or air pulse flow.

By the flue gas recirculation area from the exit point of the Gas jacket flow and thus the gas jacket flow is separated, there will still be an interference of hot flue gases from this area of the combustion chamber in the jacket flow prevented. Such Interference otherwise causes a strong reduction in the flow rate the jacket flow, the jacket flow itself heated up accordingly at the same time.

The design of the gas jacket flow is thereby dependent on that surrounding it remaining design of the furnace more independent. Especially with several, possibly mutually influencing Burners, this is another advantage of the invention. The screen itself can be single-shell, with which it is already in existing furnaces can be retrofitted relatively easily.

The radial distance between the screen and the burner outlet is so to choose that the jacket flow is not due to a friction Adhesion to the wall undesirably slowed down too much becomes. It must be ensured that the jacket flow can reach the places where they form the formation of ring vortices should prevent.

In particular, it takes into account the fact that they are from their exit to strive to expand the gas jacket flow that the upper edge of the screen has a radial distance from the gas outlet opening and the gas jacket flow only shortly before this upper edge puts on the inside of the screen. This can also be an undesirable Inflow of hot smoke gases along the inside of the screen, which are then prevented by the gas jacket flow would be mixed in at their point of exit.

This goal can be achieved both by making the screen cylindrical formed and arranged concentrically to the burner outlet. But it is also possible to give the screen itself a conical shape give, their inclination then to the expansion angle of the jacket flow is adjusted. In both cases, the Screen essentially parallel to the flame propagation direction, compared to the z. B. the extension of the conical screen in radial Direction is significantly smaller.

In principle, the screen can also be designed with two shells and are flowed through by the gas forming the gas jacket flow. The gas jacket can then, for example, completely or at least partially only emerge from the top of the screen. This Allows the gas to the screen, for example, from a high temperature resistant steel or a ceramic material exists, can still cool accordingly and thus that Prevention of thermal problems with the screen prevented.

A preferred place of use of the invention is gas turbines, in particular with several burners, preferably in ring combustion chambers, at which the inventive effect of reducing mutual Influence comes to bear.

Figur 1

einen Schnitt durch eine mit zylindrischem Schirm ausgerüstete Feuerung;

Figur 2

eine Aufsicht auf eine Feuerung gemäß Figur 1 mit mehreen Brennern;

Figur 3

einen Schnitt durch eine mit konischem Schirm ausgerüsteten Feuerung;

Figur 4

einen Schnitt durch eine Feuerung mit einem Schirm, der einen vorverlegten Brenneraustritt umfangt;

Figur 5

einen Schnitt durch eine Feuerung mit Zuführung für die Gasmantelströmung integriert in den Schirm.

Further advantages and features of the invention result from the following description of exemplary embodiments. It shows

Figure 1

a section through a furnace equipped with a cylindrical screen;

Figure 2

a top view of a furnace according to Figure 1 with multiple burners;

Figure 3

a section through a furnace equipped with a conical screen;

Figure 4

a section through a furnace with a screen that surrounds a forward burner outlet;

Figure 5

a section through a furnace with feed for the gas jacket flow integrated in the screen.

In Figure 1, a furnace equipped according to the invention is in the Section shown. It is a swirl burner, the one premixed fuel gas / air mixture 1 supplied via a burner tube 2 becomes. This burner tube 2 ends at a swirl cabinet 3, the is rotationally symmetrical and inclined guide vanes on its outer circumference 4 has. These vanes have a slope of about 30 °, whereby the outflowing fuel gas / air mixture Distraction and thus a swirl. Furthermore, there is something radial further inside than the guide vanes 4 distributed over the circumference several holes drilled through the swirl cabinet 3 5 attached, through which a partial flow of the fuel gas / air mixture can flow through and thus through pilot flame formation Flame stabilization contributes. On the outside 6 of the swirl cupboard 3 becomes the fuel gas / air mixture emerging from the burner ignites and forms a flame 7, which in a combustion chamber 8 occurs. This combustion chamber 8 is in the example shown here the annular combustion chamber of a gas turbine, the in FIG Combustion chamber downstream turbine sections not shown are.

The flame 7 is formed by the outer areas of the reacting Layers of fuel gas / air flow with an intense Flame color is the flame contour that can be recognized by an observer produce. This through a reacting fuel-air mixture A flame made of gas flows around the flame. This jacket is caused by a gas flow 9 through a Ring channel 10 passed parallel to the burner tube 2 through the burner is and exits the burner at gas outlet openings 11. A large number of these gas outlet openings is above the Circumference of the burner distributed. This multitude of openings is tight around the swirl cabinet 3 of the burner arranged around so that from the 11 corresponding to the number of gas outlet openings resulting multiple gas flows 9 complete the flame surrounding jacket flow forms.

So that the flow rate from the gas outlet openings 11 escaping gas jacket flows before they emerge the ring channel 10 is accelerated to the desired value in the embodiment shown here in the gas outlet openings 11 quarter-circle nozzles 12 built in, the strong acceleration especially the outer areas of the gas jacket flow in the axial direction (i.e. parallel to the axis 13 of the burner) cause.

The flow rate from the gas outlet openings 11 escaping gas jacket flow is due to the quarter circle nozzles 12 accelerated so far that the speed in the direction of the axis 13 is considerably higher than that of the outer areas of the flame 7 of the burning fuel gas / air mixture behind the swirl cabinet 3. This takes place in the area between the one burning in a flame Fuel gas / air mixture and the closely surrounding one Gas jacket flow partially accelerates the boundary layer burning, partially not yet ignited fuel gas / air mixture. This effectively prevents it in the edge area of the Flame for the formation of periodic, coherent ring vortex structures that comes through a quick reaction of the contained in them Flame / pressure vibrations due to in-phase energy supply can stimulate and reinforce.

Usually, the gas jacket flow is continuously from the Exit gas outlet openings 11. On the other hand, there are the ring vortex structures form periodically, there is also the possibility to operate the air flow periodically, that is, in discontinuous mode Wise. On the one hand, this means savings Air mass flow to reach, on the other hand, is a significantly higher Regulation effort necessary. In particular, the ones to be provided for this Control devices such as valves, controls etc. with associated with high costs and also have such additional Device parts an additional susceptibility to failure of the entire system result.

In the furnace shown, the combustion chamber is at the front side 14 8 a cylindrical screen 15 welded. That umbrella has a radial distance to the burner and also encompasses the Gas outlet openings 11. So outside of the screen 15 Flue gas recirculation area 16 separated from the gas flow 9. This prevents that in this area due to the flow conditions essentially radially inward flowing Flue gases, the flow path of which is indicated by the arrow lines 17 is also sucked into the gas flow 9 and thus in deteriorate their effect. Instead, the gas flow can In the initial area, expand unaffected like free jets.

This is particularly advantageous in the case of firing with several Burners, as shown in Figure 2. Figure 2 is a Section through an annular combustion chamber 8 of a gas turbine, in of which eight burners are distributed over the circumference. In supervision on these burners you can see the swirl cabinet 3 and the ring-shaped gas outlet openings 11, which on the burner generate a gas jacket flow. Around this gas jacket flow of the influence of neighboring burners or through them To shield flue gas recirculation caused by each burner surrounded by a corresponding screen 15.

With a cylindrical screen, as shown in Figure 1, is the radial distance between the screen 15 and the gas outlet opening 11 chosen so that the gas jacket flow 9, which their exit from the gas outlet openings 11 like free jets expands, only in the vicinity of the upper edge 18 of the screen 15 at its Inside. On the one hand, this can prevent the Gas flow is too early on the screen 15 and due to the friction with the wall formed by the screen 15 in unintentional Way is slowed down. On the other hand, it ensures that between the gas jacket flow and the upper edge 18 of the screen 15 Gap arises through the flue gases to the exit areas of the Gas jacket flow can flow, which is mixed in there undesired would.

The distance to be selected from these aspects is in a known, opening angle dependent on gas density and gas temperature the gas jacket flow as a function of the extension of the screen parallel to the flame propagation direction by simple to determine trigonometric relationships. For the sake of good order it should be mentioned that in the example described here the direction of flame propagation coincides with the axis of the burner 13.

Instead of a cylindrical screen as shown in Figure 1, can also be used a conical screen 19, the opening angle then roughly the opening angle from the gas outlet openings 11 emerging gas jacket flow 9 correspond should.

FIG. 4 also shows an embodiment, in which the burner within the cylindrical screen in the direction of flame propagation is brought forward. The effect achieved here is in essentially due to the fact that the recirculation of the Flue gas with a flow component directed radially towards the burner takes place in the flue gas recirculation area 16 and so in the plane in which in the example shown in FIG Gas outlet openings 11 are, the flue gas recirculation none noticeable radial flow component has more but essentially characterized by their axial flow.

Another alternative to this is shown in FIG. 5: Here is a double-walled screen 20 is provided by the gas for the Gas jacket flow is flowed through and corresponding at the upper edge Has provided gas outlet openings 21, from which then the gas jacket flow 22 emerges.

Here, too, is in the area in which the gas jacket flow 22 is off exits the gas outlet openings 21, the recirculation of the flue gases without essential radial flow component and the gas jacket flow 22 can prevent the ring vortex without going through here radially incoming smoke gases to be hindered. Here it is assumed that the areas in which ring vortices periodically attach to the Form the outer areas of the flame as described above, downstream of the gau outlet openings 21.

In the example shown in FIG. 5, this has the through double walled shield flowing gas still a cooling function for the umbrella.

Otherwise, the screens are each made of high temperature resistant Steel or from a corresponding ceramic material.

In summary, it can thus be stated that the inventive Use of an umbrella influencing the Gas jacket flow restricted by a flue gas circulation can be and therefore also with lower gas flows or Gas pulse currents adequately prevent ring vortex structures is achievable. Especially with gas turbines too Annular combustion chambers can thus be more problem-free with the invention Operation can be achieved.

Claims (11)

Device for suppressing flame / pressure vibrations in a furnace with at least one burner for generating a flame (7) and a combustion chamber (8) into which the flame (7) is directed, the furnace having at least one gas outlet opening (11, 21) , from which gas (9) flows, which surrounds the flame (7) in the form of a jacket and has a higher flow velocity in the flame propagation direction (13) than the outer regions of the flame,
characterized, that a screen (15, 19, 20) which surrounds the gas outlet opening (9, 21) and extends at a radial distance around the burner outlet is provided, through which a flue gas recirculation area (16) connected to the combustion chamber (8) from said gas ( 9) is separated. Device according to claim 1,
characterized, that the screen (15, 19) is single-shell. Device according to claim 1,
characterized, that the screen (20) has two shells and the gas (22) flows through it. Device according to claim 1,
characterized in that the screen (15, 19, 20) extends essentially parallel to the flame propagation direction (13). Device according to claim 1,
characterized, that the screen (15, 20) is cylindrical and concentric with the burner. Device according to claim 1,
characterized, that the screen (19) has a conical shape. Device according to claim 1,
characterized, that the upper edge (18) of the screen (15) is at a radial distance from the gas outlet opening (11) and that the gas jacket flow (9) only touches the inside of the screen at the end of the screen. Device according to claim 1,
characterized, that the screen is made of high temperature resistant steel. Device according to claim 1,
characterized, that the screen is made of ceramic material. Gas turbine with a device for suppressing flame / pressure vibrations according to claim 1,
the furnace has several burners. Gas turbine according to claim 10,
characterized, that the combustion chamber (8) into which the flame (7) is directed is an annular combustion chamber.

Images