Boiler plant and method for producing heat by combustion of at least one fuel

Abstract

The present invention relates to a boiler system and a method for generating heat by burning at least one fuel. The boiler system serves to generate heat by burning at least one fuel and comprises a burner (30) for generating a flame (40) directed along a longitudinal axis (41) into a combustion chamber (1) of the boiler system, wherein the boiler system is configured to implement an internal recirculation (51) of exhaust gas (50) generated during combustion into the flame (40), wherein a cooling device (60) is arranged in the area of ​​the exhaust gas recirculation (51), with which heat from the recirculated exhaust gas (50) can be absorbed and dissipated, wherein the cooling device (60) has at least one cooling element (70) in which a cooling medium (61) is absorbed or contained.and wherein the cooling element (70) carrying the cooling medium is surrounded by recirculated exhaust gas (50) and is displaceable by means of a positioning device (90) substantially along the longitudinal axis (41) of the flame (40) such that it can be positioned at different positions along the longitudinal axis (41) of the flame (40).

Description

[0001] The present invention relates to a boiler system and a method for generating heat by burning at least one fuel.

[0002] In heat generators such as boilers or boiler systems with tube-ribbed-tube walls or finned walls as the combustion chamber walls, generally referred to as water-tube boilers, burner openings in the walls are created by bending tubes. These projecting tubes are also called burner baskets. The tubes are bent outwards and sealed and covered with refractory material. A gas-tight burner box is welded around the burner basket on the outside of the boiler wall, covering and insulating the bent tubes. The burner is mounted on the burner box, with its burner nozzle leading into the boiler's combustion chamber.

[0003] The sum of the extended tube lengths of all tubes in a burner basket depends on the required clear installation diameter of the burner. For low-NOx burners with air and / or fuel staging, this installation diameter is larger than for standard burners without staging.

[0004] In fire-tube boilers, the burners are typically mounted on the end wall or front wall of the fire tube. The side of this front wall facing the combustion chamber is usually lined with refractory material for insulation, or, less commonly, with a smooth steel wall and water cooling.

[0005] It is known that NOx formation via thermal pathways 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 exhaust gas recirculation.

[0006] In external exhaust gas recirculation, a portion of the exhaust gas stream is extracted after it leaves the combustion chamber and returned to the burner or back into the combustion chamber. This portion is often mixed with the combustion air to lower the oxygen partial pressure of the oxidizer.

[0007] In contrast, with combustion chamber-internal exhaust gas recirculation, the burner acts as an injector, drawing exhaust gas from the outer recirculation zone directly at the edge of the air outlet. In burners with supercritical swirl, exhaust gas is also recirculated along the flame axis or in the low-pressure area at the core of the flame root.

[0008] The efficiency of internal combustion chamber exhaust gas recirculation is influenced by several factors, such as the magnitude of the motive impulse flow of the air stream exiting the burner, the fuel flow or air-fuel mixture flow, possibly mixed with externally recirculated exhaust gas; the burner nozzle design; and the intensity of the mixing of the motive jet and the internally drawn-in exhaust gas stream. Regarding the nozzle design, it is particularly important whether the nozzle cross-section has a cylindrical outlet, a conical widening, or a conical narrowing.

[0009] WO 2008 / 119753 A1 discloses a gasification reactor comprising a pressure jacket and a reaction zone partially bounded by a vertically oriented, tubular membrane wall. The gasification system further includes a burner basket for generating a flame and is designed to recirculate exhaust gas back to the flame. The exhaust gas passes through a cooling device.

[0010] EP 3 467 383 A1 discloses a boiler system according to the preamble of the first claim.

[0011] The invention is based on the objective of providing a boiler system and a method for generating heat by burning at least one fuel using the boiler system according to the invention, with which a reduction in pollutant emissions, in particular NOx emissions, can be achieved in an efficient and energy-saving manner.

[0012] This problem is solved by the boiler system according to claim 1 and by the method for generating heat energy by burning at least one fuel using the boiler system according to claim 15. Advantageous embodiments of the boiler system are specified in dependent claims 2-14.

[0013] The features of the claims can be combined in any technically meaningful way, taking into account the explanations from the following description as well as features from the figures, which include supplementary embodiments of the invention.

[0014] According to the invention, a boiler system for generating heat by combustion of at least one fuel is provided, which has a burner for generating a flame directed along a longitudinal axis into a combustion chamber of the boiler system, wherein the boiler system is configured to implement internal recirculation of exhaust gas generated during combustion into the flame. A cooling device is arranged in the area of ​​exhaust gas recirculation, with which heat from the recirculated exhaust gas can be absorbed and dissipated, wherein the cooling device has at least one cooling element in which a cooling medium is absorbed or contained. The cooling element carrying the cooling medium is surrounded by recirculated exhaust gas and can be displaced by means of a positioning device substantially along the longitudinal axis of the flame such that it can be positioned at different positions along the longitudinal axis of the flame.

[0015] The combustion chamber of the boiler system can also be called the combustion chamber. The cooling system allows heat to be transported away from the point of heat absorption. This cooling system is not formed by the boiler wall itself, but rather consists of an additional arrangement that captures and dissipates heat from the recirculated exhaust gas. The orientation and shape of the burner mouth define the orientation and position of the burner used to generate the flame. The boiler system can also include the burner itself.

[0016] Cooling the recirculated exhaust gas increases the internally recirculated exhaust gas mass flow rate to the respective burner. This is primarily due to the fact that the temperature of the exhaust gas drawn from the combustion chamber is reduced at the intake point near the burner outlet. The burner preferably operates as an injector, drawing in an internally recirculated volume flow. The recirculated mass flow rate is directly dependent on the temperature of the recirculated gas.

[0017] The lower temperatures of the recirculated fluid achieved by the cooling device result in a higher mass of exhaust gas recirculated within the combustion chamber.

[0018] Furthermore, the lower temperature of the recirculated exhaust gas—especially with sufficient mixing with the combustion air—favors a reduction in the O₂ partial pressure in the oxidizing agent, thus reducing the reaction rate. Further positive consequences of the temperature reduction include a lower combustion temperature due to so-called thermal ballast, namely inert components in the recirculated gas, which are heated to combustion temperature in the flame; as well as a more uniform temperature profile, thereby reducing or eliminating temperature gradients in the combustion zone and consequently preventing so-called "hot spots" in the flame. The introduction of cooled recirculated gas can also contribute to this mixing. The longitudinal axis of the flame is the so-called flame axis.The flame axis refers to an ideal line that runs from the burner mouth through the center of a flame and indicates its main direction of propagation.

[0019] Positioning the cooling element along the longitudinal axis of the flame allows for flexible positioning of the cooling element in different positions within the combustion chamber.

[0020] The length of the cooling element along the longitudinal axis of the flame can, for example, be up to one third of the flame length.

[0021] The boiler system can have a combustion chamber wall that includes at least one conduit element in which a cooling medium can be received or is contained, wherein the cooling element is fluidically connected to the conduit element. The cooling medium can, for example, be liquid.

[0022] The positioning device enables the cooling element carrying the cooling medium to be surrounded by recirculated exhaust gas in several of its possible positions along the longitudinal axis of the flame.

[0023] The positioning device may be designed such that, in at least one position, the cooling element can be positioned in front of or on the burner, thus preventing it from being in the immediate vicinity of the flame. It is also possible for the cooling element to be inserted into the combustion chamber from the outside.

[0024] The boiler system can be designed in such a way that it is set up to return exhaust gases recirculated in the combustion chamber directly to the burner outlet or in its vicinity.

[0025] The cooling element can be arranged in the combustion chamber using the positioning device in such a way that the cooling element carrying the cooling medium projects so far into the combustion chamber or is positioned at such a distance from a boiler wall on which the burner is located that the cooling element can be optimally surrounded by recirculated flue gas in order to achieve a low NOx value.

[0026] An advantageous embodiment of the boiler system provides that the cooling element is designed to radially surround the longitudinal axis of the flame, at least partially, in at least one position. This means that the cooling element has a defined axial position with respect to the longitudinal axis, in which it radially surrounds the longitudinal axis, at least in some areas.

[0027] The cooling element can have, at least in some areas, a substantially ring-shaped or hollow cylindrical geometry, whereby the flame can be generated or arranged inside the ring-shaped or hollow cylindrical geometry.

[0028] A geometry that is essentially ring-shaped or hollow cylindrical can, for example, be realized through a helical or meandering shape.

[0029] The shape of the cooling element can be essentially rotationally symmetrical, with the axis of rotation of the cooling element being essentially parallel to the longitudinal axis.

[0030] Furthermore, the boiler system can have a combustion chamber wall, and the positioning device can include at least one insertion sleeve in the combustion chamber wall, in which a duct element of the cooling device, which is fluidically connected to the cooling element, is received, so that the duct element can be guided through the insertion sleeve and thus the cooling device can be positioned at different positions along the longitudinal axis of the flame. A cooling medium is or may be received in the duct element.

[0031] The cooling element is mechanically connected to the conductor element in such a way that movement along the longitudinal axis between the conductor element and the cooling element can be transmitted.

[0032] If there are multiple cable elements, there are correspondingly multiple insertion sleeves.

[0033] The conductor element can be received in the insertion sleeve essentially parallel to the longitudinal axis.

[0034] The conductor element and the insertion sleeve can form a clearance fit.

[0035] In the case of a pipe as a conduit element, the inner diameter of the insertion sleeve is larger than the outer diameter of the pipe, so that guiding the conduit element is possible.

[0036] The insertion sleeve can be mechanically attached to the boiler wall, for example by welding. Alternatively, the mechanical attachment to the boiler wall can consist of an interference fit, a flange, and / or a bolted connection.

[0037] The positioning device can include a locking mechanism that allows individual positions of the cooling element to be fixed. The locking mechanism can, for example, be implemented using a clamping screw. During operation of the boiler system, a process-efficient position of the cooling element along the longitudinal axis of the flame can thus be determined and this position fixed using the clamping screw.

[0038] For example, during operation the position of the cooling device can be adjusted for different operating points of the boiler system, depending on, for example, the combustion power, the flame diameter and / or the concentration of individual substances or compounds, such as NOx, in the exhaust gas.

[0039] The cooling unit can be moved manually or by motor. In a motorized version, the positioning device can, for example, include an actuator and an exhaust gas sensor, such as a NOx sensor. The cooling unit can then be positioned along the longitudinal axis of the flame depending on the NOx concentration. The positioning device can also include a control unit that actuates the actuator and changes the position of the cooling unit based on the NOx concentration and / or predefined operating points.

[0040] In one embodiment, the cooling element can have a substantially rotationally symmetrical design. In an alternative embodiment, the cooling element is essentially shaped like a hollow cylinder. A specific embodiment of this cooling element provides that the cooling element essentially forms a hollow frustoconical shape. This design has the advantage of partially shielding the boiler wall from radiant heat, so that it has a lower temperature in certain areas and heats exhaust gases recirculated close to it less.

[0041] This means that the shape of the cooling element positioned in the combustion chamber can be expanded radially along the longitudinal axis of the flame in the direction of flame propagation.

[0042] Accordingly, the cooling element can be shaped in such a way that, along the longitudinal axis, at a position closer to the flame tip, it has a greater radial distance to the longitudinal axis of the flame than at a point further away from the flame tip and closer to the burner mouth.

[0043] The geometry of the cooling device can be modeled on a section-by-section contour of the flame, so that the cooling device can be positioned in a position where the flame contour is essentially parallel to the inner contour of the cooling element.

[0044] An additional reduction in NOx emissions can be achieved through radial expansion.

[0045] The cooling element can comprise at least one tube through which, or capable of being permeated by, a cooling medium flows. For example, the tube can have an outer diameter of 10 mm to 100 mm. Optionally, such a tube can be designed with a bulged structure. The cooling medium can be guided through the tube away from the burner mouth and release the heat absorbed in the cooling medium at a certain distance from the burner mouth. In a simpler, alternative embodiment, the cooling device is configured to transport heat from the recirculated exhaust gas away from the burner mouth by means of heat conduction and release it to the environment or another medium at a suitable location. To improve the convective heat transfer of the exhaust gas to the surface of the cooling device tubes, these can be equipped with additional cooling fins or pins on the outside that is in contact with the exhaust gas.

[0046] Optionally, the cooling device comprises several pipes as cooling elements in which a cooling medium is received or contained, wherein the distance between adjacent pipes is at least such that the exhaust gas mass flow rate of the recirculated exhaust gas, which flows between or around the circumference of the pipes and is caused by the cooling effect of the pipes forming the cooling device, is greater than in an embodiment of the boiler system identical to the one according to the invention except for the cooling device. This means that the pipes must be spaced at least far enough apart to produce a cooling effect on the recirculated exhaust gas, such that the exhaust gas mass flow rate of the recirculated exhaust gas is greater than in conventional embodiments that do not have a cooling device according to the invention at the burner mouth.

[0047] Preferably, the pipes forming the cooling device and the cooling medium contained therein should enable a temperature reduction of at least 50 K of the recirculated and drawn-in exhaust gas.

[0048] The pipes can, for example, have a minimum distance of 30 mm between them.

[0049] The cooling device can comprise several tubes as cooling elements in which a cooling medium can be received or is contained, wherein the boiler system has a combustion chamber wall from which the tubes extend into the interior of the combustion chamber, and wherein at least some of these tubes have two essentially parallel first sections, which are arranged essentially parallel to the longitudinal axis and at an angle, in particular perpendicular, to the combustion chamber wall. Adjoining these are two second sections, which are arranged essentially at an angle, in particular perpendicular to the longitudinal axis and essentially parallel to the combustion chamber wall, and in turn at least a third section is arranged thereafter, which is arranged essentially parallel to the burner wall and at an angle, in particular perpendicular, to the longitudinal axis and to the second sections.This results in a U-shaped profile for each such pipe, with the U being bent from the two-dimensional plane towards the third spatial coordinate. The distance between the pipes of the second and third sections should be 30 to 90 mm. A distance of 45 to 70 mm is particularly advantageous. The required pipe spacing depends, among other things, on the temperature of the recirculated exhaust gas in the outer recirculation zone before it passes through the cooling device.

[0050] In a further embodiment of the cooling device, the cooling device comprises several pipes as cooling elements, in which a cooling medium is received or contained. The boiler system has a combustion chamber wall from which the pipes extend into the interior of the combustion chamber. At least some of these pipes each have a first section that is arranged essentially parallel to the longitudinal axis and at an angle, particularly perpendicular, to the combustion chamber wall. The first sections of the pipes are fluidically connected to an annular distributor, which is arranged essentially parallel to the combustion chamber wall and at an angle, particularly perpendicular, to the longitudinal axis. The annular distributor can be circular and arranged coaxially to the longitudinal axis. This allows cooling medium to flow from a respective pipe into the distributor and be distributed by it or directed to other pipes.In another version, the first section of the pipes is not parallel to the burner axis, but instead features pipes bent out of the combustion chamber wall on a larger partial circle, compared to the ring-shaped distributor.

[0051] Another alternative design for the cooling device involves arranging the tube helically around the longitudinal axis. This helical tube can be fluidically coupled to duct elements in the combustion chamber wall. The helical shape can be formed in a spiral form. Furthermore, the helical tube can comprise a first winding section and a second winding section, the first winding section being coaxial with respect to the second winding section and at least partially radially within the second winding section. The two winding sections are preferably formed by a single tube, such that this single tube transitions from the first winding section to the second winding section at an axial end point.For this purpose, it is advantageous for the first winding area and the second winding area to have opposite slopes, so that the transition between the first winding area and the second winding area can be easily realized.

[0052] The helical shape can widen along the longitudinal axis of the flame. This means that the cooling element can be shaped in such a way that it has a larger radius at a point closer to the flame tip than at a point further away from the flame tip.

[0053] In an alternative embodiment, the tube meanders around the longitudinal axis of the flame. It is possible that the meandering shape has parallel sections, thus forming a hollow cylindrical shape. The meandering shape extends around the longitudinal axis of the flame. In one embodiment, the parallel sections can be arranged essentially parallel to the longitudinal axis of the flame.

[0054] The meandering shape can be essentially ring-shaped or hollow-cylindrical, with two parallel sections always connected by a curved end piece at one end of the sections. This ensures a fluid flow connection along the meandering shape of the cooling element. The curved end piece can also be called a loop and may be welded on.

[0055] It is not excluded that the cross-section of this cooling device deviates from a rotationally symmetrical shape, so that, for example, the meander shape forms the hollow truncated cone shape.

[0056] In the case of a meandering shape of the cooling device that essentially runs around the longitudinal axis, the widening can be achieved by bending a pair of parallel sections of the cooling element adjacent along the circumference radially outwards, so that the parallel sections curve radially outwards in a flower-like shape, or by running linearly and at an angle to the longitudinal axis.

[0057] Parallel sections can also include curved sections, which are so-called parallel curves, i.e., sections that have the same curvature and the same distance from each other.

[0058] In another embodiment, the parallel sections of the meandering cooling element are all aligned in one direction with at least one component perpendicular to the longitudinal axis. These can be parallel sections that are curved along a circumference, thus forming a ring-shaped or hollow cylindrical shape. For example, the parallel sections can be curved circumferentially around the longitudinal axis.

[0059] The distance between the parallel sections can be, for example, 30 mm or less. By closely arranging a large number of parallel sections, a large surface area can be provided for heat transfer from the exhaust gas to the cooling element.

[0060] In the case of a cooling element designed as a tube, its diameter can vary inside and / or outside along the meandering shape.

[0061] Alternatively, the cooling device can comprise several pipes with parallel first sections extending out of the plane of the combustion chamber wall. Each of these is followed by a second section, which runs essentially perpendicular to the first section and is therefore essentially parallel to the combustion chamber wall. A third section connects the two second sections, forming a U-shape. This means that the cooling element can comprise several sections that are essentially parallel to each other and / or parallel to the longitudinal axis.

[0062] The cooling element can comprise at least one flow guide element, which is arranged such that it guides recirculated exhaust gas from the radial outside into the flame. Such a flow guide element can facilitate the recirculated exhaust gas not flowing all the way to the burner, but rather being directed into the flame at the cooling device.

[0063] Here, the smoke or exhaust gases are drawn in due to negative pressure.

[0064] Furthermore, the flow guide element can also be designed in such a way that, despite its guiding function, it forms a low resistance for the recirculated exhaust gas and thus causes a low pressure loss in the recirculated exhaust gas, which ensures a large mass flow into the flame.

[0065] The flow guide element can have a heat transfer function, so that at least 80% of the heat introduced into a flow guide element can be transferred to the connected pipes and thus to the cooling medium transported in the pipes. Furthermore, each flow guide element increases the heat transfer surface area of ​​the cooling element.

[0066] The recirculated exhaust gas guided through the flow control element can potentially introduce turbulence into the flame. Turbulence in the flame can reduce the resistance of the flame contour and / or increase momentum transfer, thereby enhancing heat transfer with the cooling element and thus increasing the mass flow rate of the fluid drawn into the flame from the surroundings. This can lead to increased cooling of the recirculated exhaust gas and consequently a greater mass flow rate of recirculated exhaust gas into the flame.

[0067] In the case of a twisted flame, the flow guide element can be designed to direct the recirculated exhaust gas into the flame in such a way that the recirculated exhaust gas is directed into the flame in the direction of the twisting.

[0068] A twisted flame can indicate that there is a flow around the flame's longitudinal axis. This can be achieved, for example, by swirl elements in or at the burner mouth. These flow-guiding elements can, in some cases, enhance or even cause the twisting of the flame.

[0069] It is not excluded that the flow guide elements can also be used with a non-twisted flame, whereby the flow guide elements direct the exhaust gases in a movement with at least a rotational component towards the flame.

[0070] The flow guide element can be welded to one or more pipes of the cooling system, for example.

[0071] Several flow-guiding elements can be arranged along a circumference around the longitudinal axis of the flame. Flow-guiding elements adjacent to each other along the circumference can be arranged at the same distance from one another.

[0072] An embodiment of the cooling element designed with flow-guiding elements provides that the cooling element has at least one meandering pipe and at least one flow-guiding element arranged between pipe sections connecting loops of the meander. The flow-guiding element can be arranged between pipe sections connecting adjacent loops of the meander along the circumference of the cooling element. Such a flow-guiding element is thus designed as a so-called "fin" in the form of a web or sheet, which is arranged between two pipes of the cooling device connected to each other by a loop of the meander and is fixed to at least one of these pipes or pipe sections.

[0073] The cooling element can have the described hollow cylindrical shape or the hollow truncated cone shape.

[0074] Furthermore, pipes of the cooling device connected by a loop of the meander, between which a flow guide element is arranged, can be arranged in a plane that runs along a secant to direct flue gas towards a center of the cooling device.

[0075] The secant runs in a cross-section of the cooling device that is oriented perpendicular to the longitudinal axis of the flame. In a cooling device that essentially consists of an internal cavity, such as a hollow cylinder or a hollow frustocone, the center of the cooling device is located on the longitudinal axis of the flame.

[0076] Furthermore, an embodiment with a flow guide element can also be combined with the helical shape, such that the cooling element has at least one helically arranged tube around the longitudinal axis and at least one flow guide element which is arranged in at least one angular position on the circumference of the cooling element between the tube sections in this angular position.

[0077] This flow guide element can follow the slope of the helix formed by the pipe and extend partially or completely around the circumference.

[0078] The flow guide element can be fixed in an angular position on only one pipe section and form a guide surface that, in some areas, forms the lateral surface of an ideal hollow cone shape.

[0079] In this process, a flow guide element can be arranged on both sides of a pipe section of the helix, the guide surfaces of which are aligned along the same ideal hollow cone shape.

[0080] The flow guide element can be formed by a surface element following the helical shape, the surface of which runs at an angle of 20° to 70° in relation to the longitudinal axis of the flame.

[0081] The surface element can be arranged inside and / or outside the helical tube.

[0082] In the case of multiple pipes that form the cooling element and have a helical shape, multiple pipes with such flow guide elements can also be formed.

[0083] Furthermore, the cooling element can also be designed in such a way that the cooling element comprises at least one flow guide element through which a cooling medium flows or can flow through, wherein the flow guide element extends with at least one component of its longitudinal direction parallel to the longitudinal axis and is fluidically connected to a distribution device for distributing cooling medium onto the flow guide elements.

[0084] Several such flow guide elements can be encompassed by the cooling element. These flow guide elements are also arranged to guide recirculated exhaust gas from the radial outside into the flame. The longitudinal direction of these flow guide elements can be aligned parallel to the longitudinal axis.

[0085] In an alternative embodiment, the flow guide elements are radially expanded, so that they essentially form the shape of a hollow cone interrupted at the circumference. In this embodiment, the flow guide elements can widen with increasing distance from the burner mouth along the direction of flame propagation, so that in an area of ​​greater radial expansion they have a longer circumference than in an area of ​​lesser radial expansion.

[0086] The flow guide elements can have aerodynamically optimized inlet surfaces. For example, the flow guide elements can form a NACA airfoil in sections of their cross-section. The leading edge of the NACA airfoil can be flat. These airfoils ensure the aerodynamically optimized flow of exhaust gas into the cavity formed by the cooling element and thus to the flame or combustion process.

[0087] Flow guide elements arranged along the circumference can overlap each other radially and in certain areas along the circumference.

[0088] In this embodiment, unlike the embodiments mentioned above with at least one pipe which forms or is encompassed by the cooling element, no pipe is provided, except for the distribution device, on which the flow guide elements are arranged.

[0089] Furthermore, the boiler system may have a fluid supply device that allows a fluid, such as fuel, air, and / or recirculated exhaust gas, to be discharged radially along the longitudinal axis through the cooling unit. This may be an annular fluid supply device. The fluid supply device ensures that, by carrying flue gas along with the discharged fluid, more flue gas is drawn to the cooling unit, and consequently, more flue gas can be cooled per unit of time.

[0090] In one embodiment of the boiler system, the medium-flowing pipe(s) are arranged to rotate about an axis. This axis may be the longitudinal axis of the flame generated by the burner. Consequently, if the cooling system is configured with multiple pipes, these pipes are also arranged to rotate about the longitudinal axis of the flame. For supplying and discharging the cooling medium into and out of the pipe(s), the pipe(s) can be connected to a reservoir or to pipes in the combustion chamber wall via appropriate rotary unions. This configuration results in an additional increase in the efficiency of the cooling effect of the recirculated exhaust gas.

[0091] Furthermore, the boiler system can have a single-injection device with which a fluid, such as feedwater, can be injected into the area where exhaust gas is recirculated into the combustion chamber. This can cause a further cooling effect on the recirculated fluid. In an advantageous embodiment, the injection device is designed such that the fluid dispensed by it reaches the cooling device, so that any fluid that does not evaporate during injection provides an additional cooling effect on the cooling device. A reservoir for the injected fluid can be fluidically coupled to the pipe(s) of the cooling device.

[0092] In an embodiment of the boiler system according to the invention as a fire-tube boiler, the cooling system is preferably arranged on an end face of the fire tube, where the burner or burner mouth is also located. The end face can be lined with refractory material up to the cooling device, with the pipe(s) of the cooling device passing through the refractory material.

[0093] Such a flame-tube boiler can be supplemented by additional convective heating surfaces, preferably in tubes, around the burner head or the cooling unit, thereby further increasing the cooling effect of the exhaust gas recirculation. In flame-tube boilers with a water-cooled front, the tubes of the cooling unit can be supplied from this water-cooled front, and the heated fluid can be returned to the water-cooled front.

[0094] Another aspect of the present invention is a method for generating heat by combustion of at least one fuel using a described boiler system, in which a flame is generated along the longitudinal axis in the combustion chamber of the boiler system with the burner and the resulting exhaust gas is internally recirculated to the flame, wherein heat is absorbed and dissipated from the recirculated exhaust gas by means of the cooling device, and the cooling element of the cooling device, which carries the cooling medium, is moved substantially along the longitudinal axis of the flame generated by the burner before or during the exhaust gas recirculation and the position of the cooling element is adjusted substantially along the longitudinal axis.

[0095] The positioning device allows for readjustment of the axial position of the cooling element during operation of the boiler system in order to set a minimum NOx level in the exhaust gas.

[0096] This results, as described, in the possibility of intensifying the combustion chamber's internal exhaust gas recirculation and reducing NOx emissions.

[0097] Furthermore, the reduction in temperature of the recirculated exhaust gas promotes its entrainment, as the density and viscosity of the exhaust gas produced in the combustion process within the same time window and the recirculated gas within this time window are aligned.

[0098] Furthermore, the cooling system of the boiler may be designed to rotate while cooling the recirculated exhaust gas. In addition to the cooling effect of the cooling system, fluid can be injected into the combustion chamber via a single-injection device in the exhaust gas recirculation area.

[0099] The invention will be explained below with reference to the exemplary embodiments shown in the accompanying drawings.

[0100] They show Figure 1 : a sectional view of a section of the boiler system of a first embodiment, Figure 2 : a cooling device of a first embodiment in sectional view, Figure 3 : a cooling device of a second embodiment in sectional view, Figure 4 : a cooling device of a third embodiment in sectional view, Figure 5 : a diagram illustrating the relationship between temperature and NOx concentration, Figure 6 : a sectional view of a section of the boiler system of a second embodiment, Figure 7 : a cooling device of a fourth embodiment in side view, Figure 8 : the cooling device of the fourth embodiment in top view, Figure 9 : a cooling device of a fifth embodiment in top view, Figure 10 : the cooling device of the fifth embodiment in side view, Figure 11 : a cooling device of a sixth embodiment in side view, Figure 12: the cooling device of the sixth embodiment in top view, Figure 13 : the cooling device of the sixth embodiment in sectional view along the in Figure 12 indicated cutting line, Figure 14 : a cooling device of a seventh embodiment in side view, Figure 15 : the cooling device of the seventh embodiment in sectional view along the in Figure 14 indicated cutting line, Figure 16 : a cooling device of an eighth embodiment in side view, Figure 17 : the cooling device of the eighth embodiment in top view, Figure 18 : the cooling device of the eighth embodiment in sectional view along the in Figure 17 indicated cutting line, Figure 19 : a cooling device of a ninth embodiment in side view, and Figure 20 : the cooling device of the ninth embodiment in top view.

[0101] To explain the functioning of the boiler system according to the invention, reference is made to Figure 1 This figure shows a burner 30 located inside a burner basket 20. The flame 40 emerges from the burner mouth 31 along its longitudinal axis 41, which extends into the combustion chamber 1 of the boiler system. The boiler system is designed such that the resulting exhaust gas 50 is fed back into the combustion process or the flame via an exhaust gas recirculation system 51 at an intake point 52. This recirculation occurs, for example, through a boiler wall (not shown) opposite the burner 30, where the flue gases are deflected and directed back towards the burner 30, as indicated by the flow arrows of the exhaust gas recirculation system 51. The flue gas passes at least partially between and / or around the pipes 70 of the cooling device 60.

[0102] Due to the adjustable distance between the cooling unit 60 and the burner 30 or the intake point 52, exhaust gas 50 is supplied via the exhaust gas recirculation 51, thus also into the cooling area of ​​the cooling unit 60.

[0103] Cooling the recirculated exhaust gas 50 by means of the cooling device 60 reduces its temperature, thus increasing the exhaust gas mass flow and consequently allowing more exhaust gas 50 to be recirculated into the combustion process per unit of time than with conventional systems. Simultaneously, this lowers the temperature of the combustion process. As already described, these effects significantly reduce NOx emissions.

[0104] A further reduction in temperature can be achieved by using the illustrated single-nozzle device 80, with which injected fluid 81 can be applied to the combustion process or in its vicinity.

[0105] The pipes 70 should have a distance that allows sufficient heat transfer from the exhaust gas 50 to the cooling device 60.

[0106] It is evident that the effect of the cooling device is essentially generated in the area where the flame 40 exits the burner 30 and where the exhaust gas 50 is also fed back into the combustion process.

[0107] Furthermore, it can be seen that the cooling device 60 projects into the combustion chamber 1.

[0108] The extent of this projection, or the position of the tubes 70, which simultaneously form the cooling element 70, in relation to an end face 11 of the combustion chamber wall 10, can be adjusted by a positioning device 90, with which the cooling device 60 can be moved along the longitudinal axis 41 of the flame 40 in order to set an optimal, minimum value of NOx emissions.

[0109] In the embodiment shown here, two conduit elements 12 are fluidically connected to the cooling element 70 or its tubes. These conduits are oriented essentially parallel to the longitudinal axis 41 of the flame 40 and establish fluid connections 13 through the combustion chamber wall 10 to fluidically connect the cooling device 60 to a cooling medium reservoir (not shown). To allow relative movement of the conduit elements 12 to the combustion chamber wall 10, insertion sleeves 95 are provided in the wall, through which the conduit elements 12 pass.

[0110] In the Figures 2 and 3 In the illustrated embodiment, the cooling device 60 is also formed by a burner basket 20, which is realized by several parallel first sections 71 of tubes 70. These tubes 70 are also guided through the combustion chamber wall 10 by means of guide elements 12, as shown in the illustration. Fig. 1 described.

[0111] These first sections 71 of the pipes 70 are all fluidically connected to an annular distributor 74, which makes it possible to distribute and convey the cooling medium 61 carried by the pipes in the pipes 70.

[0112] In the Figure 4 In the illustrated embodiment, the cooling device 60 is also formed by a burner basket 20, which here, however, comprises a first coiled section 75 of a tube 70 and a second coiled section 76 of the tube 70, wherein the first coiled section 75 is arranged radially within the second coiled section 76. This embodiment could also be implemented with only one coiled section. The two coiled sections 75, 76 are fluidically connected to each other by means of a transition 77. Furthermore, they are connected to duct elements of the combustion chamber wall 10 via fluidic connections 13.

[0113] It is planned that the in the Figures 2-4 The cooling devices 60 shown also have a Figure 1 The described positioning device 90 interacts, but for the sake of clarity, it is shown in the Figures 2-4 not shown.

[0114] Figure 5 The diagram shows the relationship between the temperature of the combustion process and the NOx concentration in the exhaust gas. It is evident that a reduction in temperature leads to a correspondingly significant decrease in the NOx concentration in the exhaust gas, which can be achieved with the cooling device according to the invention.

[0115] Figure 6The cross-sectional view shows two different configurations of the cooling device 60. Both variants are designed such that the individual tubes 70 or sections of the tube 70 are arranged radially outside the burner 30 and axially overlap its burner mouth 31. In the configuration shown above the longitudinal axis 41, the tubes 70 are essentially arranged to form a hollow cylindrical shape. In the configuration shown below the longitudinal axis 41, the tubes 70 are arranged to define a conical shape, with the area 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 therefore located on the side of the burner mouth 31.In this embodiment, it is also shown that the exhaust gas recirculation 51 runs between the pipes 70, allowing heat to be transferred from the exhaust gas to the cooling medium in the pipes 70. The conical design of the cooling device 60 has the particular advantage that it at least partially protects the end wall of the combustion chamber 10 from radiant heat, so that this area has a lower temperature and thus enhances the cooling effect. Here, too, the positioning device 90 is provided, with which the cooling device 60 can be moved and flexibly positioned along the longitudinal axis 41 of the flame 40. The positioning devices 90 shown can have locking devices (not shown in detail here) with which the positions of the cooling devices 60 can be fixed.

[0116] The Figures 1-4 and 6show cooling devices 60 in rotationally symmetrical designs 100, wherein the Figures 1-4 Represent cooling elements, each essentially having a hollow cylindrical shape 101. Figure 6 As a variant, the cooling device 60, also in the form of a hollow cylinder 101, is shown above the longitudinal axis 41. Below the longitudinal axis 41, it shows Figure 6 the cooling device 60 in a hollow truncated cone shape 102 in which the axial side, which is away from the combustion chamber wall 10, has a larger radial width than the axial side, which is towards the combustion chamber wall 10.

[0117] The Figures 7-19 show further possible designs of the cooling device 60 or its cooling element 70.

[0118] Figure 7Figure 1 shows the cooling element 70 with connected conductor elements 12 in a meandering shape 110, which has parallel sections 111 of the tube 70 of the cooling element. These sections are fluidically connected to each other by loops 113, which are also formed by the tube 70 of the cooling element. The parallel sections 111 thus also form tube sections 112 connecting the loops 113. The cooling device shown here is also essentially designed in a hollow cylindrical shape and is designed to be aligned coaxially with the longitudinal axis of the flame. Figure 8 shows the top view of the in Figure 7 depicted meander shape. Figures 9 and 10 show a modification of the embodiment according to Figure 7in that the cooling device or cooling element 70 shown here no longer essentially forms a hollow cylindrical shape, but essentially a hollow truncated cone shape 102, which is also formed by a meander shape 110. However, the pipe sections 112 connecting the loops 113 are not aligned parallel to each other. This meander shape 110 is designed to be aligned coaxially with the longitudinal axis of the flame, with the radially wider open side against the combustion chamber wall 10, as shown in the Figure 1 and 6 It is shown that it should be arranged on the opposite side.

[0119] The Figures 11-13Figure 1 shows an alternative embodiment of the cooling device or its cooling element 60, which here is formed by a first coiled section 75 of the tube 70 of the cooling element, such that the cooling device has a helical shape. It is not excluded that such a cooling device could also have a second coiled section 76, as shown in Figure 2. Figure 4 The depicted image includes...

[0120] Figures 14 and 15 show an embodiment supplemented with flow-guiding elements 130 of the in the Figures 7 and 8 illustrated embodiment of the cooling device. Figures 16-18 show an embodiment supplemented with a flow guide element 130 of the Figures 11-13 illustrated embodiment of the cooling device.

[0121] In the Figures 14 and 15In the illustrated embodiment of the cooling device, it is also designed in a hollow cylindrical shape 101 with a meandering shape 110. However, here, flow-guiding elements 130 are located between adjacent parallel sections 111 of the tube 70 along its circumference. The adjacent parallel sections 111 of the tube 70 are aligned along secants 120, so that the flow-guiding elements 130 arranged thereon are also aligned according to these secants 120. The flow-guiding elements 130 ensure a flow-optimized supply of exhaust gases in the direction of the flame or its longitudinal axis.

[0122] In the Figures 16-18In the illustrated embodiment of the cooling device, two flow guide elements 130 are connected to its first coil section 75, following the helical shape of the first coil section 75. The two flow guide elements 130 are connected to opposite sides of the tube 70 and partially extend within ideal conical surfaces. Even with these flow guide elements 130, a flow-optimized supply of the exhaust gas to the flame is possible.

[0123] The Figures 19 and 20Figure 1 shows a modified embodiment of the cooling device in that, apart from the guide elements 12 in the area of ​​the exhaust gas flow, it has no pipes but is formed solely by flow guide elements 130, which are arranged along a circumference. These flow guide elements 130 comprise aerodynamically optimized inlet surfaces that facilitate the flow of exhaust gas into the interior of the cooling device and its deflection towards the longitudinal axis of the flame. Furthermore, these flow guide elements 130 can also be designed such that a cooling medium can flow through them for cooling the flow guide elements. This embodiment further includes a distribution device 140 for distributing the cooling medium to the flow guide elements 130. Reference symbol list

[0124] 1Combustion chamber 10Combustion chamber wall 11End face 12Conduit element 13Fluid connection 20Burner basket 30Burner 31Burner mouth 40Flame 41Longitudinal axis 50Exhaust gas 51Exhaust gas recirculation 52Intake point 60Cooling device 61Cooling medium 70Pipe, cooling element 71First section 74Annular distributor 75First coil section 76Second coil section 77Transition between the first coil section and the second coil section 80Injection device 81Injected fluid 90Positioning device 95Insertion sleeve 100Rotationally symmetrical design 101Hollow cylindrical shape 102Hollow truncated cone shape 110Meander shape 111Parallel section 112Connecting pipe section 113Loop 120Secant 130 Flow guide element 131 Inlet area 140 Distribution device

Claims

1. A boiler plant for generating heat by burning at least one fuel, comprising a burner (30) for generating a flame (40) which is oriented along a longitudinal axis (41) in a combustion chamber (1) of the boiler plant (40) , wherein the boiler plant is configured to perform an internal recirculation (51) of exhaust gas (50) generated during combustion back into the flame (40), wherein a cooling unit (60) is arranged in the region of the exhaust gas recirculation (51), with which heat from recirculated exhaust gas (50) can be absorbed and dissipated, wherein the cooling unit (60) comprises at least one cooling element (70) in which a cooling medium (61) can be accommodated or is accommodated, and wherein the cooling medium-carrying cooling element (70) can be flow-surrounded by recirculated exhaust gas (50), characterized in that the cooling medium-carrying cooling element (70) is displaceable by means of a positioning unit (90) substantially along the longitudinal axis (41) of the flame (40) such that it can be positioned at different positions along the longitudinal axis (41) of the flame (40).

2. The boiler plant according to claim 1, characterized in that the cooling element (70) at least partially surrounds the longitudinal axis (41) of the flame (40) radially, in at least one position.

3. The boiler plant according to one of the preceding claims, characterized in that the boiler plant comprises a combustion chamber wall (10) and the positioning unit (90) comprises at least one insertion sleeve (95) in the combustion chamber wall (10), in which a conduit element (12) of the cooling unit (60), which is fluidically connected to the cooling element (70), is received, such that the conduit element (12) can be guided through the insertion sleeve (95) and the cooling unit (60) can thus be positioned at different locations along the longitudinal axis (41) of the flame (40).

4. The boiler plant according to at least one of the preceding claims, characterized in that the cooling element (70) has a substantially rotationally symmetric configuration (100).

5. The boiler plant according to claim 4, characterized in that the cooling element (70) essentially has a hollow cylindrical shape (101).

6. The boiler plant according to claim 4, characterized in that the cooling element (70) essentially has a hollow truncated cone shape (102).

7. The boiler plant according to at least one of the preceding claims, characterized in that the cooling element (70) comprises at least one tube through which a cooling medium (61) flows or can flow through.

8. The boiler plant according to claim 7, characterized in that the tube (70) is arranged helically around the longitudinal axis (41).

9. The boiler plant according to claim 7, characterized in that the tube (70) extends in a meandering pattern around the longitudinal axis (41) of the flame (40).

10. The boiler plant according to at least one of the preceding claims, characterized in that the cooling element (70) comprises at least one flow-guiding element (130) arranged such that it has a guiding function for guiding recirculated exhaust gas (50) from the radial exterior into the flame (40).

11. The boiler plant according to claim 10, characterized in that the cooling element (70) comprises at least one meandering pipe and at least one flow-guiding element (130) arranged between pipe sections (112) connecting the loops (113) of the meander12. The boiler plant according to claim 10, characterized in that the cooling element comprises at least one tube (70) arranged helically around the longitudinal axis (41) and at least one flow guide element (130) arranged at at least one angular position at the circumference of the cooling element (70) between the tube sections at this angular position.

13. The boiler plant according to claim 10, characterized in that the cooling element 70 comprises at least one flow guide element 130 through which a cooling medium 61 flows or can flow through, wherein the flow guide element (130) extends with at least one component of its longitudinal direction parallel to the longitudinal axis (41) and is fluidically connected to a distribution unit (140) for distributing cooling medium (61) to the flow guide elements (130).

14. The boiler plant according to claim 13, characterized in that the flow guide elements (130) have flow-optimized inflow surfaces (131).

15. A method for generating heat by burning at least one fuel using a boiler plant according to any one of claims 1-14, in which a flame (40) is generated in the combustion chamber (1) of the boiler plant using the burner (30) along the longitudinal axis (41), and the resulting exhaust gas (50) is recirculated internally into the flame (40), wherein, by means of the cooling unit (60) heat is absorbed and dissipated from the recirculated exhaust gas (50), and by means of the positioning unit (90), the cooling medium-carrying cooling element (70) of the cooling unit (60) is displaced essentially along the longitudinal axis (41) of the flame (40) generated by the burner (30) and the position of the cooling element (70) is adjusted substantially along the longitudinal axis (41).

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