EP3467383B1 - Boiler and method for the generation of heat through the combustion of at least one fuel - Google Patents

Description

The present invention relates to a boiler system and a method for generating heat by burning at least one fuel.

On heat generators such as boilers or boiler systems with tube-web-tube walls or fin walls as enclosing surfaces of the combustion chamber, generally referred to as water tube boilers, burner openings are made in the walls by bending tubes. These protruding tubes are also known as burner cages. The pipes are bent outwards and sealed and covered with refractory material. A burner box is welded gas-tight around the burner basket on the outside of the boiler wall, which covers and insulates the bent tubes. The burner is mounted on the burner box, the burner mouth of which leads into the furnace of the boiler.
The sum of the stretched tube length of all tubes in a burner basket depends on the required internal diameter of the burner. In the case of low-NOx burners with air and / or fuel staging, this installation diameter is larger than in the case of standard burners without staging.
In flame tube boilers, the burners are typically on the front wall
or front wall of the flame tube mounted. It is customary to provide the side of this front wall facing the combustion chamber with refractory material as insulation or, more rarely, as a smooth steel wall with water cooling.

It is known that the thermal formation of NOx during the combustion of gaseous, liquid and solid fuels can be effectively reduced by exhaust gas recirculation. A distinction is made between external and combustion chamber internal flue gas recirculation.
With the external exhaust gas recirculation, the exhaust gas flow follows
Leaving the furnace, a partial flow is removed and returned to the burner or into the furnace. This partial flow is often added to the combustion air in order to lower the oxygen partial pressure of the oxidizing agent.
In the case of flue gas recirculation inside the combustion chamber, on the other hand, the burner acts as an injector, which sucks in flue gas from the outer recirculation zone directly at the edge of the jet of the air outlet. In burners with supercritical swirl, exhaust gas is also recirculated on the flame axis or in the negative pressure area in the core of the flame root.

The efficiency of the flue gas recirculation inside the combustion chamber is influenced by several factors, such as the size of the propulsive impulse flow of the air flow emerging from the burner, the fuel flow or air-fuel mixture flow, possibly mixed with externally recirculated exhaust gas; the nozzle design of the burner and the intensity of the mixing of the propulsion jet and the internally drawn in exhaust gas flow. In terms of the nozzle design, it is particularly important whether the cross section of the nozzle has a cylindrical outlet, a conical widening or a conical taper.

The WO 2008/119753 A1 discloses a gasification reactor comprising a pressure jacket and a reaction zone which is partially delimited by a vertically oriented, tubular membrane wall. The gasification system also includes a burner basket for generating a flame and is set up to return exhaust gas to the flame by recirculating it. The exhaust gas passes through a cooling device.

The invention is based on the object of providing a boiler system and a method for generating thermal energy by burning at least one fuel by means of the boiler system according to the invention, with which a reduction in pollutant emissions, in particular NOx emissions, can be realized in an efficient and energy-saving manner .
This object is achieved by the boiler system according to the invention according to claim 1 and by the method for generating thermal energy with combustion of at least one fuel by means of the boiler system according to the invention according to claim 13. Advantageous embodiments of the boiler system are specified in subclaims 2-12. Advantageous embodiments of the method according to the invention for generating thermal energy are specified in subclaims 14 and 15.

The boiler system according to the invention is used to generate heat by burning at least one fuel and comprises a burner basket for receiving a burner with which a flame can be generated, the boiler system being set up to implement internal recirculation of exhaust gas generated during combustion into the flame , namely by returning exhaust gases recirculated in the combustion chamber directly to the burner outlet in the combustion process.
It is provided according to the invention that a cooling device is arranged in the region of the exhaust gas recirculation, with which heat from recirculated exhaust gas can be absorbed and dissipated, and that the cooling device has at least one cooling element in which a cooling medium can be absorbed or received, wherein the cooling element carrying the cooling medium protrudes so far into the combustion chamber or is positioned at such a distance from a boiler wall on which the burner is arranged that recirculated flue gas can flow around the cooling element.
This means that the cooling device is arranged where exhaust gases recirculated in the combustion chamber are returned, preferably directly to the burner outlet, into the combustion process, with a cooling element carrying coolant projecting so far into the combustion chamber or at such a distance from a boiler wall during operation of the boiler system, on which the burner is arranged, it is positioned that the cooling element can be flowed around by recirculated flue gas. This can be implemented in such a way that an intermediate space is formed between the cooling element and the relevant boiler wall, through which recirculating flue gas can flow and in this way can transfer heat to the cooling element, which is completely surrounded by flow.
With the cooling device, heat can be transported away from the point of heat absorption. The cooling device is not formed by the boiler wall itself, but in addition to the boiler wall there is an arrangement with which heat can be absorbed and dissipated from the recirculated exhaust gas. The orientation and shape of the burner mouth defines the orientation and position of the burner to be used, which generates the flame. The boiler system can also include the burner itself. By cooling the recirculated exhaust gas, an increase in the internally recirculated exhaust gas mass flow to the respective burner can be achieved.

This is essentially based on the fact that the temperature of the exhaust gas flow drawn in from the combustion chamber is reduced at the point of intake at the burner outlet. The burner works preferably as an injector and draws in an internally recirculated volume flow. The recirculated mass flow is directly dependent on the temperature of the recirculate.
Lower temperatures of the recirculate achieved by the cooling device lead to a higher mass of exhaust gas recirculated inside the combustion chamber.
In addition, the lower temperature of the recirculated exhaust gas - especially if it is sufficiently mixed with the combustion air - favors a lowering of the O2 partial pressure in the oxidizing agent with a reduction in the reaction rate. Further positive consequences of the temperature reduction are a lowering of the combustion temperature through so-called thermal ballast, namely inert components in the recirculate, which are heated to combustion temperature in the flame; as well as an equalization of the temperature profile and thus a reduction or elimination of temperature gradients in the combustion zone and corresponding avoidance of so-called "hot spots" in the flame.

The supply of cooled recirculate can also make a contribution to mixing.
The cooling device is preferably arranged so close to an intake point that the recirculated exhaust gas is cooled in the region of the intake point at a burner mouth of the burner. The burner outlet in the direction of the combustion chamber is arranged flush with the wall or preferably with a protrusion into the combustion chamber - referred to here as the immersion depth T. The burner has a characteristic diameter C in which the combustion air or the mixture of combustion air and externally recirculated exhaust gas and the fuel are introduced into the combustion chamber. It is irrelevant whether there is one or more air or fuel nozzles per burner. The burner diameter C encloses all the air and fuel outlets belonging to the burner. The characteristic diameter C of the burner determines the necessary bending of the tubes in the wall of the heat generator. The ratio of the immersion depth T to the characteristic burner diameter C is T / C 0.2 ... 1.0. A ratio T / C of 0.55 ... 0.75 is particularly advantageous.
The installation depth of the cooling device or the dimension of the projection "into the combustion chamber can also be set in relation to the characteristic burner diameter C and is X / C = 0.7 ... 1.4. A ratio of X / C is particularly advantageous = 1.1 ... 1.2.
The cooling element should be formed by at least one tube in which a cooling medium can be received or received. This cooling medium can be conducted away from the burner mouth through the pipe and can give off heat absorbed in the cooling medium at a certain distance from the burner mouth. To improve the convective heat transfer of the exhaust gas to the surface of the tubes of the cooling device, these can be equipped with additional cooling ribs or pins on the outside that is in contact with the exhaust gas.
In particular, it is provided that the boiler system has a combustion chamber wall which comprises at least one line element in which a cooling medium can be received or received, the pipe of the cooling device being fluidically connected to the line element. Preferably, several line elements, in particular also designed as tubes, are provided in a boiler wall, such as the end wall, on which several fluidically in the area of the Burner mouth extending pipes are each connected. In this way, heat is effectively dissipated from the area of the burner mouth into the medium in the boiler wall, from where the heat can be dissipated. The invention is not limited to this embodiment, but it can also be provided that the cooling medium is not provided from the medium present in the boiler wall, but is supplied to and removed from the cooling device separately.

Die Länge der Kühleinrichtung, welche um den Brenneraustritt angeordnet ist, kann sich vom Maß X bis zur Kesselwand erstrecken. In alternativer Ausgestaltung kann die Kesselanlage auch derart ausgebildet sein, dass der Brennermund im Wesentlichen mit einer Brennkammer-Wand abschließt und um den Brennermund herum die Kühleinrichtung zwecks Abkühlung des Rezirkulats angeordnet ist.In a preferred embodiment it is provided that the tube protrudes into a combustion chamber formed by the boiler system. This can be implemented in particular in that the pipe or several pipes that form the cooling device are turned into the furnace from a boiler wall. The tube bend in the boiler walls can thus be used to insert a burner or several burners for active cooling of the flue gas recirculation inside the combustion chamber. The cooling device extends into the furnace up to dimension X, with the dimension of the projection X in relation to the characteristic diameter of the burner C in the following ratio: $$\text{X}/\text{C.}>0.7...\mathrm{1.4.}$$

The length of the cooling device, which is arranged around the burner outlet, can extend from dimension X to the boiler wall. In an alternative embodiment, the boiler system can also be designed in such a way that the burner mouth essentially terminates with a combustion chamber wall and the cooling device is arranged around the burner mouth for the purpose of cooling the recirculate.

The cooling device preferably comprises a plurality of pipes as cooling elements in which a cooling medium can be or is received, the distance between adjacent pipes being at least large enough that the exhaust gas mass flow of the recirculated exhaust gas caused by the cooling effect of the pipes forming the cooling device, which is between the Pipes flowing through or around the circumference of the pipes is greater than in an embodiment of the boiler system that is identical except for the cooling device according to the invention. This means that the pipes must be spaced apart at least so far that they have a cooling effect on the recirculated exhaust gas, so that the exhaust gas mass flow of the recirculated exhaust gas is greater than in conventional embodiments that do not have a cooling device according to the invention on the burner mouth.
It should preferably be possible to reduce the temperature of the recirculated and sucked-in exhaust gas by at least 50 K through the pipes that form the cooling device and the cooling medium located therein.

In a special embodiment, the tubes have a minimum distance of 30 mm from one another.
These several tubes together form the cooling device in which the burner is to be inserted or inserted.
The cooling surface of the walls of the heat generator is increased by the sum
of all pipe surfaces of a burner basket, which in conventional embodiments could not take part in the heat exchange due to covering with insulating material. Compared to the conventional embodiments, no additional use of material is necessary, since only the conventionally outwardly designed protrusions of the tubes are now arranged according to the invention on the inside of the furnace so that the entire circumference of these tubes can absorb heat from the furnace. In contrast to the conventional embodiments, the entire circumference of the tubes is now available for heat absorption in the area of the protuberance. Depending on the number of burners and installation diameter as well as the existing wall surface, an increase in the available cooling surface of 5-9% compared to conventional designs can be expected. This leads, among other things, to the positive effect of the overall reduction in the furnace temperature, which also has a lowering effect on NOx emissions.

In a particular embodiment of the boiler system according to the invention, it is provided that the pipe or pipes through which the medium flows are arranged rotatably about an axis, the pipe or pipes being connected to a corresponding rotary leadthrough for supplying and discharging the cooling medium into the pipe or pipes Reservoir or is connected to tubes in the combustion chamber wall or are. This axis is preferably the longitudinal axis of the flame generated by the burner. When the cooling device is designed with a plurality of tubes, the plurality of tubes are accordingly also arranged to be rotatable about the longitudinal axis of the flame. In order to supply and discharge the cooling medium into the tube or tubes, the tube or tubes can be connected to a reservoir or tubes in the combustion chamber wall with corresponding rotary feedthroughs. This configuration brings about an additional increase in efficiency in the cooling effect of the recirculated exhaust gas.

Furthermore, the boiler system can have an injection device with which a fluid (eg feed water) can be injected into the area of the recirculation of exhaust gas into the combustion chamber. This can bring about a further cooling effect of the recirculate. In an advantageous embodiment, the spray device is designed in such a way that fluid discharged by it reaches the cooling device, so that, if necessary, that does not evaporate during the injection Fluid causes an additional cooling effect on the cooling device. A reservoir for the fluid to be injected can be fluidically coupled to the pipe or pipes of the cooling device.

The boiler system furthermore has at least one burner accommodated in a respective burner cage for generating a flame directed into the furnace of the boiler system along a longitudinal axis. The cooling device is preferably arranged such that it radially surrounds the longitudinal axis at least in sections.
The cooling device can be arranged in different, axial positions in relation to the burner or the burner mouth. For example, starting from the boiler wall in or on which the burner is arranged, the cooling device can end in front of the burner mouth in the axial direction along the longitudinal axis of a flame generated by the burner, or it can only begin behind the burner mouth or there can be an axial overlapping arrangement of cooling device and burner mouth can be realized.
In a first embodiment, the cooling device comprises a plurality of tubes as cooling elements, in which a cooling medium can be received or received, the boiler system having a combustion chamber wall from which the tubes extend into the interior of the furnace, and at least some of these tubes are two essentially parallel have mutually extending first sections which are arranged essentially parallel to the longitudinal axis and at an angle, in particular perpendicular to the combustion chamber wall.
Adjacent to this are two essentially angled, in particular perpendicular to the longitudinal axis and essentially parallel to the combustion chamber wall, second sections, and in turn at least one third section, which runs essentially parallel to the burner wall and at an angle, in particular perpendicular to the longitudinal axis and the second section . This results in a U-shaped course of such a tube, the U being bent over from the two-dimensional area in the direction of the third spatial coordinate. The distance between the pipes in the second and third section should be 30 ... 90 mm. A distance between the pipes of 45 ... 70 mm is particularly advantageous. The distance between the pipes to be selected depends, among other things, on the temperature of the recirculated exhaust gas in the outer recirculation zone before it passes through the cooling device.

In a second embodiment of the cooling device, it is provided that the cooling device comprises a plurality of tubes as cooling elements in which a cooling medium can be received or received, the boiler system having a combustion chamber wall from which the tubes extend into the interior of the combustion chamber, and at least some these tubes each have a first section which is arranged essentially parallel to the longitudinal axis and at an angle, in particular perpendicular to the combustion chamber wall. The first sections of the tubes are fluidically connected to an annular distributor which is arranged essentially parallel to the combustion chamber wall at an angle, in particular perpendicular, to the longitudinal axis. In particular, the annular distributor can have a circular shape and be arranged coaxially to the longitudinal axis. As a result, cooling medium can get into the distributor from a respective tube and be distributed by it or fed to other tubes. In a further advantageous embodiment, the first section of the tubes is not designed parallel to the burner axis, but rather has tubes on a larger pitch circle which are bent out of the combustion chamber wall in comparison with the annular distributor.
In a third embodiment of the cooling device it is provided that the cooling device comprises at least one tube as a cooling element which is arranged in a helical manner around the longitudinal axis. This helical tube can be fluidically coupled to line elements in the combustion chamber wall.
Furthermore, the helical tube can comprise a first winding region and a second winding region, the first winding region being arranged coaxially in relation to the second winding region and at least in sections radially inside the second winding region. The two winding areas are preferably formed by just one tube, so that this one tube merges in an axially end-side area from the first winding area into the second winding area. For this purpose, it is advisable for the first winding area and the second winding area to have opposite gradients, so that the transition between the first winding area and the second winding area can be implemented in a simple manner.

The cooling device can have a rotationally symmetrical, in particular a conical design, with an essentially parallel, in particular coaxial, alignment to the longitudinal axis. This means that the cooling element or several cooling elements of the cooling device are arranged in such a way that they form the lateral surface of a rotationally symmetrical body. In particular, the cooling device can in particular be designed such that the cone shape extends in the direction of the Firebox opens, that is, the smaller diameter is formed on the side of the arrangement of the burner on the boiler wall, and the larger diameter is formed on the opposite side. This embodiment has the advantage of partially shielding the boiler wall from radiant heat, so that it has a lower temperature in some areas and does not heat up exhaust gases that are recirculated close to it as much. However, a reverse orientation of the cone or a cylindrical shape of the cooling device should not be excluded.
This means that in an advantageous embodiment of the cooling device, the tubes extending into the combustion chamber have a different distance from the diameter C of the burner. The tubes that are placed closest to the combustion chamber wall should have the smallest distance from the burner outer diameter and the other tubes that extend deeper into the combustion chamber should be arranged with increasing distance from the burner diameter C. This results in a conical expansion of the cooling device, which has the smallest diameter at the beginning
the cooling device near the combustion chamber wall and at the end of the cooling device in the direction of the combustion chamber - at dimension X - has the largest diameter. The resulting angle of the conical expansion should be between 10 and 30 °. 15 ... 20 ° are particularly advantageous.
Furthermore, the boiler system can have a fluid supply device with which a fluid, such as fuel, air and / or recirculated exhaust gas, directed radially in the direction of the longitudinal axis, can be discharged through the cooling device. It is preferably an annular fluid supply device. With the fluid supply device it is achieved that by entrainment of flue gas by the discharged or flowing fluid, more flue gas is fed to the cooling device and consequently more flue gas can be cooled per unit of time.
It is provided that the flue gas or recirculated exhaust gas flows through between cooling elements or sections of a cooling element of the cooling device.

In the case of the boiler system as a flame tube boiler, the cooling system is preferably arranged on an end face of the flame tube on which the burner or burner mouth is also located. The end face can be lined with refractory material except for the cooling device, the tubes of the cooling device leading through the refractory material. By using the cooling device according to the invention, with the same fuel properties and the use of identical burners, a reduction in NOx emissions of around 10-15% can be expected.

Such a flame tube boiler can be supplemented by additional convective heating surfaces, preferably in tubes, around the burner head or the cooling device, which further increases the cooling effect of the exhaust gas recirculation. In flame tube boilers with a water-cooled front, the tubes of the cooling device can be fed from this water-cooled front and the heated fluid can be fed back to the water-cooled front.

To solve the problem, a method for generating thermal energy by burning at least one fuel by means of the boiler system according to the invention is also provided, in which a flame is generated in a furnace of the boiler system and the exhaust gas that is produced is returned to the flame, the cooling device being used for the Boiler system heat from the recirculated exhaust gas is absorbed and dissipated. As a result, in the manner described, the possibility of intensifying the flue gas recirculation inside the combustion chamber and a reduction in NOx emissions result.
In addition, the reduction in temperature of the recirculated exhaust gases promotes entrainment of this exhaust gas, since the density and viscosity of the exhaust gas produced in the combustion process in the same time window and the recirculated material returned in this time window are adjusted to one another.
The exhaust gas is preferably fed to the combustion process in the area of the burner mouth and cooled.
The cooling device of the boiler system can rotate when the recirculated exhaust gas is cooled, the pipe or pipes being connected to a reservoir or pipes in the combustion chamber wall with corresponding rotary feedthroughs for supplying and discharging the cooling medium into the pipe or pipes . are.
In addition to the cooling brought about by the cooling device, fluid can be injected into the area of the recirculation of exhaust gas into the combustion chamber by means of an injection device.

• Figur 1: eine Schnittansicht einer erfindungsgemäßen Kesselanlage einer ersten Ausführungsform im Bereich der Brenneraufnahme entlang des in Figur 2 angedeuteten Schnittes C-C,
• Figur 2: eine Schnittansicht einer erfindungsgemäßen Kesselanlage einer ersten Ausführungsform im Bereich der Brenneraufnahme entlang des in Figur 1 angedeuteten Schnittes A-A,
• Figur 3: eine Schnittansicht einer erfindungsgemäßen Kesselanlage einer ersten Ausführungsformim Bereich der Brenneraufnahme entlang des in Figur 1 angedeuteten Schnittes B-B,
• Figur 4: die in Figur 2 dargestellte Schnittansicht mit aufgenommenem Brenner und Flamme sowie Abgas-Rückführung,
• Figur 5: eine Schnittansicht einer erfindungsgemäßen Kesselanlage einer zweiten Ausführungsform im Bereich der Brenneraufnahme entlang des in Figur 6 angedeuteten Schnittes C-C,
• Figur 6: eine Schnittansicht einer erfindungsgemäßen Kesselanlage einer zweiten Ausführungsformim Bereich der Brenneraufnahme entlang des in Figur 5 angedeuteten Schnittes A-A,
• Figur 7: eine Schnittansicht einer erfindungsgemäßen Kesselanlage einer zweiten Ausführungsformim Bereich der Brenneraufnahme entlang des in Figur 5 angedeuteten Schnittes B-B,
• Figur 8: eine Schnittansicht einer erfindungsgemäßen Kesselanlage einer dritten Ausführungsform im Bereich der Brenneraufnahme entlang des in Figur 9 angedeuteten Schnittes C-C,
• Figur 9: eine Schnittansicht einer erfindungsgemäßen Kesselanlage einer dritten Ausführungsform im Bereich der Brenneraufnahme entlang des in Figur 8 angedeuteten Schnittes A-A,
• Figur 10: eine Schnittansicht einer erfindungsgemäßen Kesselanlage einer dritten Ausführungsform im Bereich der Brenneraufnahme entlang des in Figur 8 angedeuteten Schnittes B-B,
• Figur 11: ein den Zusammenhang zwischen der Temperatur und der NOx- Konzentration darstellendes Diagramm, und
• Fig. 12: eine Prinzip-Darstellung zwei unterschiedlicher Alternativen der Ausgestaltung der Kühleinrichtung im Schnitt.

The invention is explained below with reference to the exemplary embodiments shown in the accompanying drawings.
Show it

• Figure 1 : a sectional view of a boiler system according to the invention of a first embodiment in the area of the burner receptacle along the FIG Figure 2 indicated section CC,
• Figure 2 : a sectional view of a boiler system according to the invention of a first embodiment in the area of the burner receptacle along the FIG Figure 1 indicated section AA,
• Figure 3 : a sectional view of a boiler system according to the invention of a first embodiment in the area of the burner receptacle along the in Figure 1 indicated section BB,
• Figure 4 : in the Figure 2 shown sectional view with recorded burner and flame as well as exhaust gas recirculation,
• Figure 5 : a sectional view of a boiler system according to the invention of a second embodiment in the area of the burner receptacle along the in Figure 6 indicated section CC,
• Figure 6 : a sectional view of a boiler system according to the invention of a second embodiment in the area of the burner receptacle along the in Figure 5 indicated section AA,
• Figure 7 : a sectional view of a boiler system according to the invention of a second embodiment in the area of the burner receptacle along the in Figure 5 indicated section BB,
• Figure 8 : a sectional view of a boiler system according to the invention of a third embodiment in the area of the burner receptacle along the in Figure 9 indicated section CC,
• Figure 9 : a sectional view of a boiler system according to the invention of a third embodiment in the area of the burner receptacle along the in Figure 8 indicated section AA,
• Figure 10 : a sectional view of a boiler system according to the invention of a third embodiment in the area of the burner receptacle along the in Figure 8 indicated section BB,
• Figure 11 : a diagram showing the relationship between the temperature and the NOx concentration, and
• Fig. 12 : a schematic representation of two different alternatives for the design of the cooling device in section.

First, the boiler system according to the invention is based on the in the Figures 1-3 illustrated first embodiment explained.
The boiler system according to the invention comprises a combustion chamber wall 10, which is designed here as an end wall and consequently also as a boiler wall. It defines the end face 11 of the furnace of the boiler system. The combustion chamber wall 10 comprises several parallel Line elements 12 running towards one another, preferably in the form of a tube, which here form what is known as a fin wall.
These line elements 12 are connected to individual tubes 70 of a burner cage 20 via fluidic connections 13. This burner basket 20 forms a cooling device 60, namely by virtue of the fact that a cooling medium 61 can flow or flow through the tubes 70.
A burner 30 is arranged radially inside the burner cage 20 to form a flame in the combustion chamber.
As from the Figures 2 and 3 As can be seen, the tubes 70 of the cooling device 60 are shaped in a special way. They comprise 2 first sections 71 which run essentially parallel to one another and extend out of the plane of the combustion chamber wall 10. This is followed in each case by a second section which runs essentially perpendicular to the first section and is consequently arranged essentially parallel to the combustion chamber wall. A third section 73 connects the two second sections 72 with one another, so that the FIGS Figure 2 visible U-shape is realized.

To explain the functioning of the boiler system according to the invention in this embodiment, reference is made to Figure 4 . It is shown here that a burner 30 is located inside the burner cage 20. The flame 40 emerges from the burner mouth 31 or burner outlet along its longitudinal axis 41, which extends into the combustion chamber 1 of the boiler system. The boiler system is designed in such a way that the resulting exhaust gas 50 is returned to the combustion process or the flame in an exhaust gas recirculation 51 in a suction point 52, for example through a boiler wall (not shown here) opposite the burner 30, on which the flue gases deflected and directed back in the direction of the burner 30, as indicated by the flow arrows of the exhaust gas recirculation 51. The flue gas passes at least partially between the pipes 70 of the cooling device 60 and / or flows around them.

Due to the short distance between the cooling device 60 and the burner 30 or the suction point 52, the exhaust gas 50 is thus also fed into the cooling region of the cooling device 60 via the exhaust gas recirculation 51.

By cooling the recirculated exhaust gas 50 by means of the cooling device 60, the temperature of the exhaust gas 50 is reduced so that the exhaust gas mass flow can be increased and consequently more exhaust gas 50 can be recirculated into the combustion process per unit of time than with conventional devices. At the same time, the Lowered the temperature of the combustion process. As already described, these effects can significantly reduce NOx emissions.

A further reduction in the temperature can be brought about by using the injection device 80 shown, with which the injected fluid 81 can be discharged into the combustion process or in its vicinity.
The tubes 70 should have such a distance A, as in Figure 1 indicated, which enables sufficient heat transfer from exhaust gas 50 to cooling device 60.
Out Figure 4 it can also be seen that the maximum distance D of the cooling device 60 in relation to the burner mouth 31 is very small compared to the length L of the entire flow path of the exhaust gas 50 to be measured along the longitudinal axis 41 of the flame 40. It can be seen from this that the effect of the cooling device is generated essentially in the area in which the flame 40 also emerges from the burner 30 and in which the exhaust gas 50 is also fed back into the combustion process.
It can also be seen that the cooling device 60 protrudes into the furnace 1 by a dimension X. This essentially distinguishes the design of the boiler system according to the invention from that of conventional boiler systems, where a protuberance or projection of tubes arranged around the burner is usually led to the outside of the boiler system.

Further embodiments of the boiler system according to the invention are shown in Figures 5-7 and 8-10 evident.
In the in the Figures 5-7 In the embodiment shown, the cooling device 60 is also formed by a burner basket 20, which is implemented by a plurality of first sections 71 of tubes 70 running parallel to one another. Here, too, these tubes 70 are fluidically connected to line elements 12 of the combustion chamber wall 10.
These first sections 71 of the tubes 70 are all fluidically connected to an annular distributor 74, which makes it possible for the cooling medium 61 guided by the tubes to be distributed and passed on in the tubes 70.

In the in the Figures 8-10 In the illustrated embodiment, the cooling device 60 is also formed by a burner basket 20, which here, however, comprises a first winding area 75 of a tube 70 and a second winding area 76 of the tube 70, the first winding area 75 being arranged radially inside the second winding area 76.
This embodiment could also be implemented with just one turn area.

The two winding regions 75, 76 are technically connected to one another by means of a transition 77 flow. Furthermore, they are connected to the line elements 12 of the combustion chamber wall 10 via fluidic connections 13.

Figure 11 shows in a diagram the relationship between the temperature of the combustion process and the NOx concentration of the exhaust gas. It can be seen that when the temperature is reduced, a correspondingly significant reduction in the NOx concentration in the exhaust gas is recorded, which can be achieved with the cooling device according to the invention.

Figure 12 shows in section 2 different embodiments of the cooling device 60. Both variants are designed in such a way that the individual tubes 60 or sections of the tube 60 are arranged radially outside the burner 30 and axially overlap its burner mouth 31. In the variant embodiment shown above the longitudinal axis 41, the tubes 60 are arranged essentially in such a way that together they form a cylindrical shape.
In the variant embodiment shown below the longitudinal axis 41, the tubes 60 are arranged such that they define a conical shape, the region of the cooling device 60 facing the end face 11 having a smaller diameter than the side of the cooling device 60 facing away from it and is therefore arranged on the side of the burner mouth 31.
In this embodiment, it is also shown that the exhaust gas recirculation 51 runs between the tubes 60, so that heat can be transferred from the exhaust gas into the cooling medium in the tubes 60.
The conical design of the cooling device 60 has the particular advantage that it at least partially protects the frontal combustion chamber wall 10 from radiant heat, so that this area has a lower temperature and the cooling effect is thereby increased.

List of reference symbols

1

Firebox

10

Combustion chamber wall

11

Face

12th

Line element

13

Fluidic connection

20th

Burner basket

30th

burner

31

Burner mouth

40

flame

41

Longitudinal axis

50

Exhaust gas

51

Exhaust gas recirculation

52

Suction point

60

Cooling device

61

Cooling medium

70

Pipe, cooling element

71

first section

72

second part

73

third section

74

annular distributor

75

first turn area

76

second winding area

77

Transition between the first winding area and the second winding area

80

Injection device

81

Injected fluid

X

Dimension of the overhang

D.

maximum distance

L.

Length of the entire flow path

A.

distance

T

Immersion depth

C.

diameter

Claims (15)

1. A boiler plant for generating heat through combustion of at least one fuel, comprising a burner basket (20) for receiving a burner (30), with which a flame (40) can be generated, wherein the boiler plant is designed to realize an internal recycling of flue gas (50) generated during the combustion into the flame (40),
   namely by recycling flue gases recirculated in the incineration chamber directly to the burner outlet into the combustion process,
   wherein
   a cooling device (60) is arranged in the region of the flue gas recycling (51), with which heat can be received from the recycled flue gas (50) and conducted away,
   wherein
   the cooling device (60) has at least one cooling element, in which a cooling medium (61) can be received or is received,
   and wherein
   the cooling medium-carrying cooling element protrudes far enough into the combustion chamber or is positioned at such a distance from a boiler wall on which the burner is arranged that the cooling element can be flowed around by recycled flue gas (50).
2. The boiler plant according to Claim 1, wherein
   the cooling device (60) is arranged so closely to a suction point (52) that cooling down of the recycled flue gas (50) is realized in the region of the suction point (52) on a burner mouth (31) of the burner (30).
3. The boiler plant according to any one of Claims 1 and 2, wherein
   the cooling element is configured by at least one pipe (70).
4. The boiler plant according to Claim 3, wherein
   the boiler plant has a combustion chamber wall (10) which comprises at least one conducting element (12), in which a cooling medium (61) can be received or is received, wherein the pipe (70) of the cooling device (60) is fluidically connected to the conducting element (12).
5. The boiler plant according to any one of Claims 3 and 4, wherein
   the pipe (70) which is flowed through by the medium or the pipe (70) which can be flowed through by the medium is arranged rotatably about an axis, wherein in order to supply and conduct away the cooling medium into the pipe or the pipes, the pipe or the pipes is or are joined with corresponding rotary unions to a reservoir or to pipes in the combustion chamber wall.
6. The boiler plant according to any one of the preceding claims, wherein
   the boiler plant furthermore has an injection device (80), with which a fluid (81) can be injected into the region of the flue gas recycling (51) into the incineration chamber (1) in order to produce a cooling-down effect of the recirculated material.
7. The boiler plant according to any one of the preceding claims, wherein
   the boiler plant has at least one burner (30) which is received in each case in a burner basket (20) in order to generate a flame (40) directed into the incineration chamber (1) of the boiler plant along a longitudinal axis (41).
8. The boiler plant according to Claim 7, wherein
   the cooling device (60) comprises multiple pipes (70) as cooling elements, in which pipes a cooling medium (61) can be received or is received, wherein the boiler plant has a combustion chamber wall (10), starting from which the pipes (70) extend into the interior of the incineration chamber (1), and wherein at least some of these pipes (70) have two first portions (71) running substantially parallel to one another, which are arranged substantially parallel to the longitudinal axis (41) and angled to the combustion chamber wall (10), have joined thereto two second portions (72) running substantially angled to the longitudinal axis (41) and substantially parallel to the combustion chamber wall (10), and have arranged thereon at least one third portion (73) which runs substantially parallel to the burner wall (10) and angled to the longitudinal axis (41) and to the second portions (72).
9. The boiler plant according to Claim 7, wherein
   the cooling device (60) comprises multiple pipes (70) as cooling elements, in which pipes a cooling medium (61) can be received or is received, wherein the boiler plant has a combustion chamber wall (10), starting from which the pipes (70) extend into the interior of the incineration chamber (1), and wherein at least some of these pipes (70) each have a first portion (71), which are arranged substantially parallel to the longitudinal axis (41) and angled to the combustion chamber wall (10), and the first portions (71) of the pipes (70) are fluidically connected to an annular distributor (74), which is arranged substantially parallel to the combustion chamber wall (10) and angled to the longitudinal axis (41).
10. The boiler plant according to Claim 7, wherein
    the cooling device comprises at least one pipe (70) as a cooling element, which pipe is arranged in the form of a screw thread around the longitudinal axis (41).
11. The boiler plant according to any one of Claims 7-10, wherein
    the cooling device (60) has a rotationally symmetrical configuration, having a substantially parallel alignment to the longitudinal axis (41).
12. The boiler plant according to any one of Claims 7 to 11, wherein
    it has a fluid supply device, with which a fluid such as e.g. fuel, air and/or recycled flue gas (50), directed radially towards the longitudinal axis, can be dispensed through the cooling device.
13. A method for generating thermal energy involving combustion of at least one fuel by means of the boiler plant according to any one of Claims 1-12, in which a flame (40) is generated in an incineration chamber (1) of the boiler plant and flue gas (50) which is produced during this is recycled to the flame (40), wherein heat from the recycled flue gas (50) is received and conducted away by means of the cooling device (60) of the boiler plant.
14. The method for generating thermal energy according to Claim 13, wherein
    the cooling device (60) of the boiler plant rotates during cooling of the recycled flue gas (50); wherein in order to supply and conduct away the cooling medium into the pipe or the pipes, the pipe or the pipes is or are joined with corresponding rotary unions to a reservoir or to pipes in the combustion chamber wall.
15. The method generating thermal energy according to any one of Claims 13 and 14, wherein
    in addition to the cooling produced with the cooling device (60), fluid (81) is injected by means of an injection device (80) into the region of the flue gas recycling (51) into the incineration chamber (1).

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