Recuperative burner
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-31
- Publication Date
- 2026-04-08
AI Technical Summary
Existing recuperator burners face challenges in efficiently reducing nitrogen oxide emissions and separately regulating fuel gas and combustion air volume flows, which limits their ability to burn different fuels like methane, hydrogen, and their mixtures effectively.
A recuperator burner with an exhaust gas recirculation device featuring a jet pump annular gap that converges before the combustion chamber, allowing for separate regulation of fuel gas and combustion air flows, and an integrated heat transfer body with counter-flowing fluid channels for enhanced heat exchange, enabling effective exhaust gas recirculation and reduced NOx formation.
The solution significantly reduces nitrogen oxide emissions and allows for adjustable fuel gas and combustion air flows, enabling efficient combustion of various fuels, including methane, hydrogen, and their mixtures, while maintaining a compact and efficient design.
Smart Images
Figure EP2024065070_05122024_PF_FP_ABST
Abstract
Description
[0001] Recuperator burner
[0002] The invention relates to a recuperator burner with the features of the preamble of claim 1.
[0003] DE 10 2014 224 086 A1 describes a burner with an exhaust gas recirculation device in which the exhaust gas is mixed with the combustion air within the burner, thus constantly circulating a portion of the exhaust gas within the burner. This increases the mass flow in the combustion chamber and simultaneously lowers the temperature; high peak temperatures in the combustion chamber are avoided. For this purpose, the air duct system is provided with a Venturi region with a reduced cross-section, forming a Venturi nozzle. The vacuum connection of the Venturi nozzle thus formed is connected to the exhaust gas duct system. This sucks in a portion of the exhaust gas flowing out of the combustion chamber and mixes it with the combustion air. The Venturi region is preferably located directly adjacent to the combustion chamber.However, such a burner provides exhaust gas recirculation directly from the combustion chamber outlet area and not from outside the burner, from the furnace chamber, so it cannot be combined with an upstream heat exchanger that draws in nitrogen oxides from the environment. US2018 / 0080647A1 discloses a method and combustion device for reducing nitrogen oxide formation. A Venturi nozzle positioned just upstream of the burner nozzle is used to draw in exhaust gas from outside the combustion chamber and feed it into the fuel gas mixture, thereby diluting it. Since the burner provides an open exhaust duct outside the combustion chamber tube and draws in the exhaust gas from the furnace chamber, a combination with an upstream recuperator is fundamentally possible.However, the exhaust gas intake capacity is already limited by the fact that only small openings in the wall can be provided in the area where the Venturi nozzle is constricted, so that the flow of the mixture of air and fuel gas is not excessively impeded. Nevertheless, the radial entry of the exhaust gas into the Venturi nozzle creates turbulence when it encounters the gas mixture flowing past at a right angle. A further disadvantage is that the mixture of fuel gas and combustion air must already be formed before entering the Venturi nozzle, and therefore the flow velocities of air and fuel gas can no longer be individually regulated.
[0004] DE 3041 177A1 shows a burner with an exhaust gas recirculation device. However, the mixture of exhaust gas from the furnace chamber and fresh air supplied from outside does not enter the burner tube, but rather along the outside of the burner tube to its end. Furthermore, no fresh air is supplied inside the burner tube. The mixing of all gases only occurs immediately upstream of the burner nozzle, which is positioned at the front edge of the burner tube. This creates turbulence in front of the burner tube, which complicates the optimization of the burner's efficiency and the reduction of nitrogen oxides.
[0005] WO2022117345A1 describes a burner with an exhaust gas recirculation device, in which the exhaust gas is mixed with the combustion air within the burner. Several jet nozzles cause the mixture to flow within the burner tube into the area of influence of the burner nozzle. Recuperator burners are also known, in which efficiency is increased by a heat exchange between the burner supply air and the burner's exhaust gas flow. The recuperator causes heat transfer between the two gas flows. For this purpose, the recuperator can be made of different materials, in particular metallic and ceramic materials. In particular, metallic materials are provided for low and medium temperature zones, and ceramic materials for high-temperature zones. By combining materials, the individual sections of the recuperator can be optimized for good heat transfer.
[0006] The object of the invention is therefore to improve a recuperative burner of the type mentioned above so that larger amounts of nitrogen oxides can be eliminated. Furthermore, the volume flows of the fuel gas and combustion air should be adjustable separately, in particular to enable the combustion of different fuel gases such as methane and hydrogen with the same recuperative burner or fuel gas mixtures thereof.
[0007] This object is achieved by a recuperator burner having the features of claim 1.
[0008] The recuperative burner according to the invention has an exhaust gas recirculation device with a jet pump driven by combustion air, which has a jet pump annular gap formed upstream of the mixing plane of the combustion gases flowing into the combustion chamber tube. As a result, the flow of the combustion gas itself remains completely unaffected. Instead, the combustion gas is directed directly to the burner nozzle, where the mixture of combustion air and the intake exhaust gas is added.
[0009] The jet pump annular gap is preferably annular, in particular circular, and converges in the flow direction.
[0010] "Annular" within the meaning of the invention also includes a meandering cross-section of the jet pump annular gap, especially when the jet pump is connected to an upstream heat transfer body with a linked arrangement of several outlet openings for the combustion air. A meandering shape adapts the jet pump annular gap to the shape of the outlet openings on the front side of the heat transfer body.
[0011] As a rule, the jet pump ring gap is designed to be endless, with at most a few support points being provided in the jet pump ring gap in order to keep an outer nozzle ring spaced from an inner pipe or the like.
[0012] Furthermore, it is possible to design the jet pump annular gap as an alternating sequence of closed and open cross-sectional areas along a circumferential line. Such a design of the jet pump annular gap is particularly feasible using an additive manufacturing process and serves the specific purpose of increasing the flow velocity of the combustion air by reducing the cross-section in the flow channel, thereby achieving a jet pump effect. In many cases, a converging shape of the jet pump annular gap is not required for this.
[0013] The jet pump, according to the invention, creates a recuperative burner for diluted combustion through exhaust gas intake. The recirculation of exhaust gas reduces nitrogen oxide formation, both with natural gas as fuel and with hydrogen or other fuels such as propane, butane, LPG, or ammonia. Because the invention provides a narrow annular gap at the jet pump nozzle, a thin, but large-diameter, propulsion jet is generated. The large outer surface of the annular air flow ensures effective intake of exhaust gas into the combustion chamber tube, with only the outer side of the air flow providing the intake.
[0014] A flow-free interior space is formed within the annular air flow. Lines for the gas supply and other elements such as a mixing unit, an ignition device, a burner nozzle, etc., can be routed within the interior space and thus do not represent any flow obstructions. Preferably, these elements are connected to form a burner insert, which can be removed as a whole from the combustion chamber tube. For such a burner design with a centrally feedable or removable burner insert, the exhaust gas recirculation device designed according to the invention thus represents neither a structural nor a functional flow obstruction.
[0015] In order to be able to operate the recuperator burner either with natural gas or hydrogen, two fuel gas lines are preferably provided, which are only brought together directly at the burner nozzle.
[0016] Preferably, an inner tube is provided adjoining the burner base, with an inner cavity having a continuous clear opening cross-section. The burner unit, in which the burner nozzle, fuel gas lines, etc. are connected to each other, can be pushed in from the burner base through the cavity of the inner tube or pulled out backwards, toward the burner base.
[0017] The invention provides a recuperator arranged upstream of the combustion chamber tube with a heat transfer body which has at least two separate flow channels provided for guiding counterflowing fluids, wherein the at least two fluids enter and exit the heat transfer body via inlet and outlet openings of the flow channels and of the fluids, one is formed by combustion air to be preheated and the other by the exhaust gas of the recuperator burner.
[0018] Alternatively, the flow-free interior space can also be filled with a heat exchanger element, with the fuel gas lines integrated into the heat exchanger element. A heat exchanger element arranged within the annular propulsion jet of the jet pump can be provided as a supplement to the heat exchanger of a larger recuperator. This allows additional heat exchanger surface area to be gained. However, a rear-removable burner insert can no longer be provided. In the preferred embodiment of a recuperator burner, the jet nozzle is formed on the outside of the inner tube of the heat transfer body. Outside the inner tube, one or more combustion air outlets are provided on the heat exchanger, at which the combustion air flow channel of the heat exchanger ends.
[0019] If a conical outer nozzle ring is provided, it is designed and arranged in such a way that it covers the combustion air outlets and guides the air flow to the outside of the inner tube, where it compresses it. A very narrow air ring gap is formed between the outer nozzle ring and the casing of the inner tube or another inner nozzle ring, thus achieving the function of a jet pump with an annular propulsion jet. At the same time, the outer nozzle ring leaves the exhaust gas inlets of the heat exchanger, located radially further outward, open for the exhaust gas flow channel, so that exhaust gases can be drawn in from there.
[0020] The preferred design of the exhaust gas recirculation device further provides that the inner tube opens into or at an inlet opening of an eductor that is larger in diameter than the combustion chamber tube, to which the combustion chamber tube is connected. An annular exhaust gas intake opening is formed between the outer side of the inner tube and the edge of the inlet opening. At the exhaust gas intake opening, the recuperator burner thus opens toward the furnace chamber, into which the recuperator burner extends, so that exhaust gas can be drawn in directly from there.
[0021] In a further positive design, the annular jet gap can be tapered inward. This ensures a more homogeneous mixing of combustion air and exhaust gas before this mixture reaches the axial position where the fuel gas is added.
[0022] To minimize flow resistance, it is preferable that the burner base or heat transfer body on one side and the eductor on the other side are connected to each other via several spacer elements distributed around the circumference. The very slim spacer elements hardly pose any flow obstruction, so that the exhaust gas intake opening functionally extends over almost 360°.
[0023] The eductor, the spacer elements, and the heat transfer body or burner base can be formed as a single piece using an additive manufacturing process. Preferably, the conical nozzle ring for forming the jet pump annular gap is also formed as a single piece with the heat transfer body.
[0024] It is also possible for the heat transfer body and the combustion chamber tube to be manufactured separately and then subsequently connected to each other using welded spacer elements.
[0025] The heat transfer body can thus be manufactured separately from the combustion chamber tube, particularly in an additive manufacturing process.
[0026] The jet pump integrated into the recuperative burner designed according to the invention recirculates the exhaust gas from the furnace combustion chamber into the combustion air. This changes the composition of the mixture of combustion air, fuel gas, and exhaust gas burning at the burner nozzle.
[0027] In combustion technology, the qualitative terms "rich" and "lean" are usually used to describe the ratio between oxidizer and fuel. This ratio remains unchanged during exhaust gas recirculation because only another gas (exhaust gas) is added. In order to nevertheless describe a change in the properties of the gas mixture in different operating stages, for example during start-up, a "lean" fuel gas-air mixture has a high exhaust gas content and a lower oxygen concentration within the meaning of the present invention. A "rich" fuel gas-air mixture, on the other hand, describes a state in which little to no exhaust gas is recirculated and the oxygen concentration is therefore higher. In this sense, a gas mixture of combustion air, fuel gas and exhaust gas is to be regarded as "lean", so that the ignitability of such a non-preheated mixture is reduced.Therefore, the recuperator burner goes out in the cold state as soon as exhaust gas is recirculated.
[0028] By delaying the air preheating of the recuperator, the ignitability of the air / exhaust gas / fuel mixture is gradually increased. To warm up the cold recuperator burner with the exhaust gas recirculation device, an additional control device for the exhaust gas recirculation device is preferably provided so that recirculation can be reduced for a few minutes during ignition until the system reaches operating temperature and warmed combustion air reaches the combustion chamber.
[0029] The control device is preferably formed by a bypass line inserted into the burner base. A portion of the air flow forming the jet pump's propulsion jet is guided via the bypass line through the supply opening or another channel past the exhaust gas recirculation device. This temporarily eliminates the intake power of the jet pump or reduces it to such an extent that the proportion of exhaust gas in the gas mixture in the combustion chamber is significantly reduced.
[0030] The bypass line should preferably be closable via a valve to cancel its effect once the start-up process is complete. This can be achieved by manually switching the valve if start-up processes are only required occasionally.
[0031] An automatic valve adjustment allows the start-up process to be integrated into the burner control system so that it can be carried out without user intervention.
[0032] Using a stepwise or continuously adjustable valve, the opening cross-section in the bypass line can be adjusted depending on the increasing temperature of the combustion air in the heat exchanger before the bypass line is completely closed. For further reduction of nitrogen oxides through even more intensive exhaust gas aftertreatment, it may be advantageous to connect the recuperative burner according to the invention in series with another exhaust gas recirculation unit, thereby forming a cascaded exhaust gas aftertreatment system. In this case, the flame or the mixture of combustion air and fuel gas serves as the driving force for a jet pump, which then draws exhaust gas into the flame downstream of the mixing level.
[0033] The additional exhaust gas recirculation device preferably comprises a Venturi nozzle module whose inlet opening is arranged behind the burner mouth cone. The efficiency of an exhaust gas recirculation device designed in this way depends significantly on the velocity of the propellant jet. In a conventional recuperative burner, this velocity results solely from the volume flow of the fuel gas and the volume flow of the supplied combustion air, with a slight increase in velocity resulting from the reaction that begins in the flame root. In conjunction with a recuperative burner designed according to the invention, with which so-called "diluted combustion" can be carried out, the velocity of the propellant jet for the downstream, second exhaust gas recirculation device increases significantly by the additional exhaust gas volume drawn in via the diluted combustion; a factor of 2 or more is conceivable in this case.In addition to the already reduced NOx load due to the first recirculation, the cascaded arrangement improves the effectiveness of the second recirculation device, as the velocity of the propellant jet increases accordingly. As a result, the NOx emissions of the recuperative burner are significantly improved compared to a burner with only one recirculation device.
[0034] It is also possible to design the recuperator burner to be particularly short, so that it is only slightly longer than the heat transfer body.
[0035] The heat transfer body has an internal cavity. Positioned within this cavity at the end of the heat transfer body facing the combustion chamber is a combustion chamber insert consisting of a conical combustion chamber tube and a trumpet-shaped burner nozzle element. The burner nozzle element adjoins the heat transfer body with its outer edge in such a way that it is positioned in front of the internal outlet openings of the air supply ducts, while at the same time, the external outlet openings of the exhaust gas intake ducts on the heat transfer body are exposed outside the closure element.
[0036] A flow reversal chamber is formed between the outlet openings of the air supply ducts and the burner mouth element. The burner mouth element has a curve to redirect the flow of combustion air guided through the air supply ducts by almost 180°.
[0037] Such an embodiment of the invention further provides that a nozzle ring gap is formed by a constriction between an inner wall of the heat transfer body and an outer wall of the combustion chamber tube. Adjoining this constriction is an annular space that widens in the flow direction with a cone angle of approximately 5° to 15° and ends at a deflection point at the rear end of the combustion chamber tube. The annular space is formed in particular by a cylindrical inner tube in the heat transfer body and the outer surface of a conical combustion chamber tube. Due to its convergent-divergent cross-sectional shape, it forms a jet nozzle that is driven by the supplied combustion air.
[0038] Through the thus formed annular jet nozzle, exhaust gas is drawn in from the combustion chamber via exhaust inlet openings on the heat transfer body. The exhaust intake channels on the heat transfer body branch out in such a way that a first flow path, starting from the exhaust inlet openings, leads directly into the jet nozzle, specifically directly behind the aforementioned nozzle ring gap, as seen in the direction of flow. A further path leads into the heat transfer body, where, in countercurrent operation, the combustion air is preheated.The mixture of combustion air and intake exhaust gas exits the annular jet nozzle formed between the heat transfer body and the combustion chamber tube at the rear end of the combustion chamber tube and reaches a trumpet-shaped deflection element that closes the inner free cross-section of the cavity in the heat transfer body and causes a flow deflection into the interior of the combustion chamber tube. There, it flows from the rear through the flow-permeable burner nozzle and burns together with the supplied fuel gas. Due to the doubly deflected flow, two sections of the jet pump's flow path run within the same length of the recuperator, thus achieving a particularly space-saving design for an exhaust gas recirculation device.In addition, despite the compact design, the exhaust gas recirculation device is arranged upstream of the mixing plane of the combustion gases flowing into the combustion chamber tube.
[0039] With this design, it is also possible to provide holes or other-shaped recesses, such as slots, on the burner orifice element in the area of the flow reversal chamber, particularly at the apex of the trumpet-shaped funnel. A portion of the primary air can be directed into the combustion chamber in front of the burner nozzle through these recesses. This creates an additional annular air flow around the flame, which stabilizes the flame and improves combustion efficiency and nitrogen oxide reduction.
[0040] The invention, with further advantageous embodiments, is explained in more detail below with reference to the exemplary embodiments shown in the drawings. The figures show in detail:
[0041] Fig. 1 shows a recuperator burner with exhaust gas recirculation device and recuperator in side view;
[0042] Fig. 2 shows a recuperator burner according to Fig. 1 in a perspective sectional view in longitudinal section; Fig. 3 shows an enlarged section from Fig. 2;
[0043] Fig. 4 Parts of the exhaust gas recirculation device on the recuperator burner in a partially sectioned perspective view, seen from the front;
[0044] Fig. 5 Parts of the exhaust gas recirculation device on the recuperator burner in a partially sectioned perspective view, seen from the rear;
[0045] Fig. 6 the recuperator burner with complete burner base in a perspective sectional view in longitudinal section;
[0046] Fig. 7 shows the recuperator burner in a perspective sectional view in longitudinal section in a sectional plane rotated by 90° compared to Figure 6;
[0047] Fig. 8 shows a recuperator for a recuperator burner according to a further embodiment of the invention;
[0048] Fig. 9 is a sectional view taken along the line XX in Fig. 8;
[0049] Fig. 10 shows a recuperator burner according to a further embodiment of the invention in a perspective sectional view;
[0050] Fig. 11 the recuperator burner according to Figure 10 with flow paths drawn and
[0051] Fig. 12 shows a burner with exhaust gas recirculation device according to a further embodiment in a perspective sectional view in longitudinal section;
[0052] Figure 1 shows a side view of a recuperative burner 100 according to the invention, designed as a recuperative burner. A burner base 10 with a combustion chamber flange 11 serves for attachment to a furnace wall of a furnace chamber. The parts located in the wall passage of the furnace chamber and those outside the furnace chamber, which adjoin the combustion chamber flange 11 on the right side of a recuperative burner installed in a furnace, are not shown here.
[0053] Adjacent to the burner base 10 is a recuperator 20 with an internal heat exchanger, in which incoming combustion air and outgoing exhaust gases are guided in opposite directions in separate flow channels, so that the incoming combustion air is preheated by the outgoing exhaust gas. The recuperator burner 100 opens into a combustion chamber in a combustion chamber tube 30, which tapers at the end at a burner mouth cone 31.
[0054] In the embodiment of the invention shown in Figure 1, the recuperator 20 and the combustion chamber tube 30 do not merge directly into one another. Rather, the combustion chamber tube 30 has an expanded diameter at its end facing the recuperator 20, which is caused by an eductor 32 inserted between them. The combustion chamber tube 30 is held at a distance from the recuperator 20 by inserted spacer elements 36. At the same time, the inner diameter of the eductor 32 is larger than the outer diameter of a nozzle ring 25 at the downstream end of the recuperator 20. The nozzle ring 25 separates the flow paths of the combustion air flowing into the combustion chamber tube 30 and the exhaust gas sucked in via an exhaust gas inlet opening 24 at the recuperator 20. Due to the axial distance between the eductor 32 and the recuperator 20 and the diameter difference therebetween, an opening extending over the entire circumference is formed therebetween.This serves as the exhaust gas intake opening 34 for the combustion chamber tube 30.
[0055] At a short axial distance from the exhaust gas intake opening 34, a jet pump annular gap 26 is formed, from which combustion air emerges from the corresponding flow channel in the recuperator 20 at high speed and with a largely laminar flow. As a result, a jet pump is formed in the opening between the eductor 32 and the recuperator 20, which leads to the intake of portions of the exhaust gas flowing in the opposite direction into the exhaust gas inlet opening 24. This partial flow of exhaust gas is guided, together with the combustion air, into the burner chamber in the combustion chamber tube 30, so that the recirculation of the exhaust gas and a reduction in the oxygen partial pressure in the burner chamber bring about a reduction in nitrogen oxides. Furthermore, the dilution of the combustion air can reduce the temperature in the combustion chamber, particularly during the combustion of hydrogen.
[0056] Figure 2 shows a perspective sectional view of the burner 100. To maximize the metallic surfaces of the flow channels usable for heat exchange, the heat transfer body 21 of the recuperator 20 has a very complex spatial geometry for the exhaust gas and combustion air and is shown here only in a simplified manner, with the dashed line indicating the internal separation of flow channels 101, 102. On the side of the heat transfer body facing the eductor 32, there is an annular combustion air outlet opening 23 on the inside and an annular exhaust gas inlet opening 24 on the outside, with the conical nozzle ring 25 in between.
[0057] The heat transfer body 21 has a continuous inner tube 22 at its center, with a cavity 27 that allows a burner insert 40 to be inserted from the side of the burner base 10 until the burner nozzle 41 is positioned in the combustion chamber tube 30. The burner nozzle 41 divides the combustion chamber tube 30 into a burner chamber 33 and an intermediate chamber 35.
[0058] In the illustrated embodiment, the nozzle insert 40 comprises a fuel gas pipe 42 for supplying methane and another fuel gas pipe 43 for supplying hydrogen. An inspection pipe 49 is also part of the burner insert 40, allowing the flame at the burner nozzle 41 to be observed visually and / or by sensor. Not visible in the sectional view of Figure 2 is a bypass pipe through which additional combustion air can be directed into the intermediate chamber 35, as will be described in more detail below.
[0059] In order to better illustrate the design of the jet pump provided according to the invention and the flow conditions in the area between the combustion chamber tube 30 and the recuperator 20, Figure 3 shows an enlarged section of the sectional view in Figure 2.
[0060] The hatched arrows indicate the exhaust gas flow. A major portion of the exhaust gas flow is drawn from the furnace chamber into the exhaust gas inlet opening 24 of the recuperator 20 by an external extraction device acting on an exhaust gas outlet opening at the base 10. A secondary flow is drawn laterally into the exhaust gas intake opening 34 by the jet pump formed at the transition between the combustion chamber tube 30 and the recuperator 20.
[0061] The unhatched arrows refer to the combustion air exiting the combustion air outlet openings 23 of the recuperator 20. The air flow is concentrated in a narrow jet pump annular gap 26 formed between the outer wall of the inner tube 22 and the inner wall of the conical, outer nozzle ring 25. The inner tube 22 extends axially further in the direction of the combustion chamber tube 30 than the conical nozzle ring 25, in particular at least to the axial position where the eductor 32 begins. The air jet exiting the jet pump annular gap 26 is supported by the extended inner tube 22 and guided into the combustion chamber tube 30 with little or no turbulence.The annular air flow, thus supported on the inner circumference, is exposed on its outer side exactly at the transition between the nozzle ring 25 and the eductor 32, so that exhaust gas is entrained from there and the combustion air diluted by the exhaust gas flows into the combustion chamber tube 30. The combustion air diluted by the exhaust gas is symbolized by the dot-hatched arrows.
[0062] Figure 4 shows the heat transfer body 21 with an eductor 32 cut in half. The combustion air outlet openings are covered by the conical nozzle ring 25 and are therefore not visible. An exhaust gas inlet opening 24 is formed by an annular arrangement of several individual exhaust gas inlet openings, which lies radially outside the nozzle ring 25. In a recuperative burner installed in a furnace, the exhaust gas inlet opening 24 is open toward the furnace chamber.
[0063] Figure 4 also clearly shows the very small radial width of the jet pump ring gap 26 and the axial offset between the nozzle ring 25 on the outside and the inner tube 22 on the inside.
[0064] Figure 5 is another perspective section, specifically a view obliquely from above and behind the transition between the heat transfer body 21 and the eductor 32. The radial width of the exhaust gas intake opening 34 is chosen to be large, so that from this perspective, a view into the interior of the combustion chamber tube 30 with a fuel gas tube 42 running therein is possible. The gap width is deliberately chosen to be large enough to minimize the flow resistance for the incoming exhaust gas, thus ensuring high efficiency of the jet pump.
[0065] In Figure 6, the recuperator burner 100 according to the invention is shown in a perspective sectional view, in full length, i.e. also with the sections of the burner base 10 located beyond the combustion chamber flange 11. The sectional plane is rotated by 90° compared to Figures 2 and 3, so that only one fuel gas pipe 42 is visible.
[0066] The normal path of the combustion air leads from an external fan via an air inlet nozzle 13 into a combustion air chamber 14 and from there into the radially inner flow path in the heat transfer body 21 of the recuperator 20. Exhaust gas enters the radially outer flow channels 101, 102 in the heat transfer body 21 at the exhaust gas inlet opening 24 and flows through them into an exhaust gas chamber 15, which surrounds the combustion air chamber 14. An external fan extracts the exhaust gas from the exhaust gas chamber 15. Due to the jet pump annular gap 26 provided according to the invention, a portion of the exhaust gas is sucked directly from the furnace chamber back into the combustion chamber tube 30 at the exhaust gas intake opening 34.
[0067] The flow conditions described above correspond to the normal operation of the recuperator burner 100. However, for start-up operation, the fuel gas-air mixture in the combustion chamber 33, which is diluted by exhaust gas, is too lean, so that an ignited flame quickly extinguishes again.
[0068] Since the high temperature load in the recuperator burner 100 makes it impossible to temporarily close the jet pump annular gap 26 using mechanically adjustable flaps or the like, a control device for carrying out a start-up process is designed in the form of a closable bypass line. The bypass line comprises a bypass line pipe 46, which also forms part of the burner insert 40 that can be inserted through the cavity 27 in the inner pipe 22. The bypass line pipe 46, like the inspection pipe 49, extends to a rear end flange 19 of the burner base 10. There, it is connected to the combustion air chamber 14 via a bypass pipe bend 17, wherein the flow path between the bypass line pipe 46 and the combustion air chamber 14 can be closed via a valve 18.
[0069] The fuel gas lines, the inspection pipe 49 and the bypass line pipe 46 run through the combustion air chamber 14. However, to prevent the combustion air from passing into the cavity 27 of the inner pipe 22, the various lines of the burner insert 40 are bundled by a common bulkhead plate 47, which creates an airtight barrier in the inner pipe 22, which can be bypassed by the bypass line pipe 46 guided through the bulkhead plate 47.
[0070] By opening valve 18, combustion air flows through the bypass pipe 46 into the intermediate chamber 35, and thus into the immediate vicinity of the burner nozzle 41. Since the flow resistance in the flow channel for the combustion air within the heat transfer body 21 is significantly higher than in the bypass line, the air flow flowing through the heat transfer body 21 is significantly weakened, which also reduces the effectiveness of the jet ring pump and consequently only a small amount of exhaust gas is drawn in. A rich gas-air mixture with only a small amount of exhaust gas is thus combusted, resulting in a stable flame in the burner chamber 33.
[0071] The recuperative burner 100 heats up with increasing combustion time solely through heat conduction and radiation. Since the air paths through the heat transfer body 21 are not completely interrupted even during start-up operation with the bypass line open, and air preheating also occurs in the combustion air chamber 14 surrounded by the exhaust gas chamber 15, the combustion air supplied through the bypass pipe 46 also heats up increasingly.
[0072] The valve 18 can be completely closed when a certain minimum temperature is reached in the combustion chamber 33. It is also possible to gradually reduce the air flow through the bypass line using a motor-driven valve adjustable via a control device, whereby the flow velocity at the jet pump annular gap 26 increases progressively and the exhaust gas content in the combustion chamber 33 increases until the start-up process is completed and the bypass line can be completely closed.
[0073] Figure 7 shows the recuperation burner 100 with the burner base 10 again in a sectional plane rotated by 90° compared to Figure 6, whereby this view is shortened by the combustion chamber tube adjoining the eductor 32.
[0074] The cutting plane intersects the bypass pipe 46 over its entire length. Also visible is the branch of the bypass pipe bend 17 on the underside of the combustion air chamber 14. In particular, the formation of an exhaust gas chamber 15 surrounding the combustion air chamber 14 can be seen, to which an exhaust gas outlet flange 16 with a large diameter is laterally connected, via which effective extraction of the exhaust gas is effected. Figure 8 shows parts of another embodiment of a recuperator burner with an exhaust gas recirculation device in a perspective longitudinal section. In a recuperator 220, an inner tube 222 with an inner cavity 227 passes through a heat transfer body 221. A combustion chamber tube 230, which has the same inner diameter, is arranged in alignment with the inner tube 222.
[0075] The special feature of this embodiment of a recuperative burner according to the invention is that an exhaust gas recirculation device with a jet pump that draws in exhaust gas is formed at the transition between the inner tube 222 and the combustion chamber tube 230, wherein this transition is located within the area surrounded by the heat transfer body 221. The jet pump is thus directly integrated into the heat transfer body 221. A jet pump annular gap 226 is formed between an inner conical nozzle ring 228 and an outer, likewise conical nozzle ring 225.
[0076] Two flow channels 201, 202 are formed in the heat transfer body 221, with combustion air being supplied to the inner flow channel 201 and flowing through the jet pump annular gap 226 into the combustion chamber tube 230. The exhaust gas enters the heat transfer body 221 at at least one exhaust gas inlet opening 224 and flows in the opposite flow direction to the combustion air in the outer flow channel 202 toward a burner base. A portion of the exhaust gas flow is sucked in at an annular exhaust gas intake opening 234 by means of the propulsion jet formed from fresh air at the jet pump annular gap 226 and guided into the combustion chamber tube 230.
[0077] In order to direct the flow from the expanded diameter region in the area of the jet pump annular gap 226 to the cross section of the combustion chamber tube 230, a conical eductor 232 is integrated into the heat transfer body 221. The complex shape of the heat transfer body 221, into which both the flow channels 201, 202 with maximized heat exchange surface as well as the exhaust gas recirculation device with the nozzle rings 225, 228 and the eductor 232 are integrated, and possibly also the inner tube 222 and the combustion chamber tube 230 as further integral components, is realized using an additive manufacturing process.
[0078] Figure 9 shows another perspective sectional view, with the sectional plane running transversely to the central axis, namely along section line XX in Figure 8. The view is directed into the jet pump ring gap 226. Only the inner nozzle ring 228 is visible. The outer nozzle ring is hidden in this viewing direction.
[0079] Figure 10 shows a recuperator burner 300 in a perspective, sectional view, in which, similar to the embodiment presented in Figure 8, a jet pump is formed in the interior of a recuperator 320.
[0080] A heat transfer body 321 of the recuperator 320 has an inner tube 322 with an internal cavity 327. Positioned therein at an end of the heat transfer body 321 facing a combustion chamber 333 is a combustion chamber insert consisting of a conical combustion chamber tube 330 and a trumpet-shaped burner mouth element 331. The burner mouth element 331 adjoins the heat transfer body 321 with its outer edge in such a way that it is positioned in front of the inner outlet openings 323 of the air supply ducts 301, and at the same time, the outer exhaust gas intake openings 334 on the heat transfer body 321 are exposed outside the burner mouth element 331.
[0081] A flow reversal chamber 328 is formed between the outlet openings 323 of the air supply ducts and the burner mouth element 331. The burner mouth element 331 has a concave curvature on the side facing the flow reversal chamber 323 in order to redirect the flow of the combustion air supplied via air supply ducts 301 by almost 180° to a constriction 325.
[0082] The constriction 325 is formed between an inner wall of the inner tube 322 in the heat transfer body 321 and an outer wall of the combustion chamber tube 330. Adjacent to the constriction 325 is an annular space widening in the flow direction with a cone angle of approximately 5° to 15°, forming a jet pump annular gap 326 and ending at a deflection point 351 at the rear end of the combustion chamber tube 330. The jet pump annular gap 326 is formed in particular by the cylindrical inner tube 322 in the heat transfer body 321 and the outer side of a conical combustion chamber tube 330, and due to its convergent-divergent cross-sectional shape, forms a jet nozzle driven by the supplied combustion air.
[0083] Exhaust gas is drawn in from the combustion chamber via the thus formed annular jet nozzle through intake openings 324 on the heat transfer body. The exhaust gas intake channels 302 on the heat transfer body 321 branch in such a way that, starting from the exhaust gas intake openings 334, a first flow path leads directly into the jet nozzle, specifically directly, as seen in the flow direction, behind the aforementioned constriction 325. A further path leads via an exhaust gas inlet opening 302 into an exhaust gas extraction channel 302 in the heat transfer body 321, where, in countercurrent operation, the combustion air supplied via the air supply channels 301 is preheated.
[0084] The mixture of combustion air and exhaust gas drawn from the combustion chamber via the exhaust gas intake openings 334 exits the annular jet nozzle formed between the heat transfer body 321 and the combustion chamber tube 330 at the rear end of the combustion chamber tube 330 and reaches a deflection element 350, also trumpet-shaped, which closes the inner free cross-section of the cavity 327 in the heat transfer body 321 and, with a concave curved section 351, causes a flow deflection into the interior of the combustion chamber tube 330. There, it flows from the rear through the flow-permeable burner nozzle 40 and burns there together with the supplied fuel gas. The section of the combustion chamber tube 330 located between the curved section 351 and the burner nozzle 41 has a diverging cross-section, so that there is a cross-sectional widening over the entire flow path, which begins at the constriction 325 and ends at the burner nozzle 41.This section is called intermediate chamber 335.
[0085] The concave curved section 351 tapers inwards and forms a burner tube guide 352 in which a central tube of the burner insert 40 is guided and sealed.
[0086] In the embodiment shown in Figure 10, primary air holes 332 are provided on the burner mouth element 331 in the region of the flow reversal chamber, specifically at the apex of the trumpet-shaped funnel forming the burner mouth element 331. A portion of the supplied primary air can be guided into the combustion chamber upstream of the burner nozzle 41 via the primary air holes 332. The resulting primary air flow forms an annular air flow that surrounds the combustion chamber 333 and the flame emerging from it, stabilizes the flame, and improves the efficiency of combustion and nitrogen oxide reduction.
[0087] Figure 11 is fundamentally identical to Figure 10, with the path of the supplied combustion air being indicated by a dotted line and the path of the exhaust gas being indicated by dashed lines.
[0088] Distributed around the circumference, all air and exhaust gas flow paths are present multiple times, so that air and exhaust gas flows are present next to each other at several locations. This results in the turbulence-free formation of an air-exhaust gas mixture in the area of the diverging annular gap 326, which is fed to the burner nozzle 41.
[0089] Figure 12 shows a recuperator burner 100' supplemented by a second exhaust gas recirculation device 400. The combustion chamber tube 30 and the second exhaust gas recirculation device 400 are arranged in a common jet tube 401. The exhaust gas recirculation device 400 comprises a Venturi nozzle module 402, which is arranged upstream of the burner mouth cone 31 of the recuperator burner 100 in the flow direction and whose inflow opening 406 is located behind the outflow opening of the burner mouth cone 31, with an annular gap remaining therebetween. Downstream of the Venturi nozzle module 402, several segmented flame tubes 403 are arranged in series one behind the other. The segmented flame tubes 403 are used to guide the hot flue gases in the jet tube 401.The exhaust gas recirculation device 400 is closed off by a cross-shaped spacer 405, which ensures optimal dimensioning of a recirculation gap between the segmented flame tube 403 and the jet tube 401.
[0090] Reference symbol:
[0091] 100; 100' recuperator burner
[0092] 101 ,102; 201 ,202 flow channels
[0093] 10 burner base
[0094] 11 Connection flange
[0095] 12 Fuel gas supply connection
[0096] 13 Air intake nozzle
[0097] 14 Combustion air chamber
[0098] 15 Exhaust chamber
[0099] 16 Exhaust outlet flange
[0100] 17 Bypass pipe bend
[0101] 18 Valve
[0102] 19 End flange
[0103] 20; 220 recuperator
[0104] 21 ; 221 heat transfer bodies
[0105] 22; 222 inner tube
[0106] 23 Combustion air outlet opening
[0107] 24; 224 exhaust inlet opening
[0108] 25; 225 outer nozzle ring
[0109] 26; 226 jet pump annular gap
[0110] 27; 227 inner cavity
[0111] 228 inner nozzle ring
[0112] 30; 230 combustion chamber tube
[0113] 31 Burner mouth cone
[0114] 32; 232 eductor
[0115] 33 Combustion chamber
[0116] 34; 234 exhaust intake opening
[0117] 35 Intermediate chamber
[0118] 36 spacer elements
[0119] 40 burner insert
[0120] 41 Burner nozzle
[0121] 42, 43 Fuel gas lines
[0122] 46 Bypass pipe
[0123] 47 bulkhead plate
[0124] 49 Inspection pipe
[0125] 300 recuperator burners
[0126] 301 Air supply duct
[0127] 302 Exhaust gas extraction duct 320 Recuperator
[0128] 321 Heat transfer bodies
[0129] 322 inner tube
[0130] 323 Combustion air outlet opening
[0131] 324 Exhaust inlet opening
[0132] 325 bottleneck
[0133] 326 jet pump annular gap
[0134] 327 inner cavity
[0135] 328 Flow reversal chamber
[0136] 329 diversion point
[0137] 330 combustion chamber tube
[0138] 331 burner mouth element
[0139] 332 primary air openings
[0140] 333 Combustion chamber
[0141] 334 Exhaust intake opening
[0142] 335 Intermediate chamber
[0143] 350 deflection element
[0144] 351 concave curved section
[0145] 352 burner tube guide
[0146] 400 second exhaust gas recirculation device
[0147] 401 jet pipe
[0148] 402 Venturi nozzle module
[0149] 403 segmented flame tubes
[0150] 405 spacers
Claims
AMENDED CLAIMS received by the International Bureau on 29 October 2024 (29.10.2024) 1. Recuperator burner (100; 100'; 300), comprising at least: a burner base (10) and a combustion chamber tube (30; 330), in which at least one burner nozzle (41) is positioned, at which at least one fuel gas line (42, 43) opens; an exhaust gas recirculation device with a jet pump operated with combustion air, which has a jet nozzle with a cross-section reducing in the flow direction and with a Jet pump annular gap (26; 226; 326) for sucking in exhaust gases from outside the combustion chamber tube (30; 230; 330) by means of an annular propulsion jet, wherein the exhaust gas recirculation device: upstream of the mixing plane of the combustion gases flowing into the combustion chamber tube (30; 230; 330), between the burner base (10) and the combustion chamber tube (30; 230; 330), is formed at least one endless exhaust gas intake opening (34; 234; 334) and / or a circumferential, self-contained arrangement of several exhaust gas intake openings, from which or from which at least one flow path leads into the interior of the combustion chamber tube (30; 330); characterized by an upstream of the combustion chamber tube (30; 330) arranged recuperator (20; 220; 320; 400) with a heat transfer body (21; 221; 321) which has at least two separate flow channels (101, 102; 201, 202; 301, 302) provided for guiding counterflowing fluids, wherein the at least two fluids enter / exit via inlet and outlet openings (23, 24; 323, 324) of the flow channels (101, 102; 201; 202; 301, 302) in the heat transfer body (21; 221; 321) and from the Fluids, one of which is formed by combustion air to be preheated and the other by the exhaust gas of the recuperator burner (100; 300), and wherein the jet nozzle is formed at a combustion air outlet opening (23) of the recuperator (20).
2. Recuperator burner (100) according to claim 1, characterized in that an inner tube (22) with an inner cavity (27) is connected to the base (10), which is guided through the combustion chamber tube (30) and / or through the heat transfer body (21); that the combustion air outlet opening (23) of the combustion air flow channel extends around the outside of the inner tube (22), that the nozzle of the jet pump is formed on the inside by the inner tube (22) and on the outside by the conical nozzle ring (25), which is guided with its tapered end to the outside of the inner tube (22), wherein the jet pump ring gap (26) is formed between the inner tube (22) and the nozzle ring (25), and that at least one exhaust gas inlet opening (24) for the exhaust gas flow channel of the combustion chamber tube (30) and / or the heat exchanger (21) is arranged outside the nozzle ring (25).
3. Recuperator burner (100) according to claim 1, characterized in that the inner tube (22) opens into or at an inlet opening of an eductor (32) which is wider in diameter than the combustion chamber tube (30), to which the combustion chamber tube (30) is connected, wherein the annular exhaust gas intake opening (34) is formed between the outside of the inner tube (22) and the edge of the inlet opening of the eductor (32).
4. Recuperator burner (300) according to claim 1, characterized in that an inner tube (222; 323) with an inner cavity (227; 327) is passed through the heat transfer body (221; 321); and that the jet pump annular gap (226; 326) and the exhaust gas intake opening (234; 334) are formed in a section of the inner tube (222) located within the heat transfer body (221).
5. Recuperator burner (300) according to claim 4, characterized in that a conical combustion chamber tube (330) with a trumpet-shaped burner mouth element (331) is arranged in the inner cavity (327), which extends up to the front side of the heat transfer body (321); that a flow reversal space (328) is formed between the mouth openings (323) of the flow channels (301) serving as air supply channels and the burner mouth element (331); that a nozzle ring gap (325) is formed between an inner wall of the heat transfer body (321) and an outer wall of the combustion chamber tube (330), to which a jet pump ring gap (326) widening in cross section in the flow direction is connected;that a first flow path, starting from the exhaust gas intake openings (334) on the outside of the heat transfer body (321), leads directly into the jet nozzle (326) and a further path leads into one of the flow channels (302) in the heat transfer body serving as an exhaust gas extraction channel, and that the jet pump annular gap (326) extends to a deflection point (351) at the rear, open end of the combustion chamber tube (330); 6. Recuperator burner (300) according to claim 5, characterized in that the burner mouth element (331) is connected to the heat transfer body (321) in such a way that it is positioned in front of internal outlet openings (323) of the air supply ducts (301) and the external exhaust gas intake openings (334) on the heat transfer body (321) are exposed outside the burner mouth element (331).
7. Recuperator burner (300) according to claim 5, characterized in that recesses are provided on the burner mouth element (331) in the region of the flow reversal space (328).
8. Recuperator burner (100; 300) according to one of the preceding claims, characterized in that the mouth of the jet pump annular gap (26; 326) is positioned within the cross section of the endless exhaust gas inlet opening (34; 324) or the closed arrangement of several exhaust gas intake openings.
9. Recuperator burner (100; 300) according to one of the preceding claims, characterized in that the jet pump annular gap (26; 226; 326) and / or the exhaust gas intake opening (34; 234; 334) each has a meandering course.
10. Recuperator burner (100) according to at least one of the preceding claims, characterized in that a further exhaust gas recirculation device (400) is provided with a jet pump which is operated with the mixture of fuel gas, combustion air and the recirculating exhaust gas obtained from the jet pump of the first exhaust gas recirculation device and which is formed downstream of the mixing plane of the fuel gases flowing into the combustion chamber in front of the mouth of the combustion chamber tube (30).
11. Recuperator burner (100) according to claim 10, characterized in that the further exhaust gas recirculation device (400) in Flow direction is arranged in front of a burner mouth cone (31) of the burner (100') and is arranged with the combustion chamber tube (30) in a common jet pipe (401).
12. Recuperator burner (100) according to claim 10 or 11, characterized in that the further exhaust gas recirculation device (400) comprises a Venturi nozzle module (402), the inflow opening of which is arranged behind the burner mouth cone (31).
13. Recuperator burner (100) according to one of claims 10 to 12, characterized by at least one segmented flame tube (403) arranged downstream of the Venturi nozzle module (402) in the jet tube (401).