RECUPERATIVE BURNER

Description

This nonprovisional application is a continuation of International Application No. PCT/EP2024/065070, which was filed on May 31, 2024, and which claims priority to German Patent Application No. 20 2023 103 002.5, which was filed in Germany on May 31, 2023, and German Patent Application No. 20 2023 104 586.3, which was filed in Germany on Aug. 11, 2023, and which are both herein incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention T

he invention relates to a recuperative burner having the features of the preamble of claim 1.

Description of the Background Art

DE 10 2014 224 086 A1 describes a burner with an exhaust gas recirculation device, in which the exhaust gas of the combustion air is mixed within the burner and thus a proportion of exhaust gas is constantly circulated within the burner. This increases the mass flow in the combustion chamber and, at the same time, lowers the temperature; high peak temperatures in the combustion chamber are avoided. For this purpose, it is provided that the air duct system has a venturi area with a decreased cross section, so that a Venturi nozzle is formed. The vacuum connection of the Venturi nozzle formed in this way is connected to the exhaust duct system. As a result, part of the exhaust gas flowing out of the combustion chamber is taken in and mixed with the combustion air. Preferably, the Venturi area is directly adjacent to the combustion chamber. However, such a burner provides for exhaust gas recirculation directly from the mouth area of the combustion chamber and not from outside the burner, from the furnace chamber, so that it cannot be combined with an upstream heat exchanger that draws in from the environment.

From US 2018/0080647A1, a method and a combustion device for the reduction of nitrogen oxide formation are known. A Venturi nozzle formed just upstream of the burner nozzle is used to draw in exhaust gas from outside the combustion chamber and direct it into the fuel gas mixture, which is diluted with it. Since the burner provides an open exhaust gas duct outside the combustion chamber tube and the exhaust gas is drawn in from the furnace chamber, a combination with an upstream recuperator is generally possible. However, the exhaust gas intake capacity is already limited by the fact that only small openings can be provided in the wall in the area of the constriction of the Venturi nozzle so that the flow of the mixture of air and fuel gas inside is not excessively obstructed. Nevertheless, the radial entry of the exhaust gas into the Venturi nozzle creates turbulence when it hits the gas mixture flowing past at right angles. A further disadvantage is that the mixture of fuel gas and combustion air must already be formed before it enters the Venturi nozzle and therefore the flow velocities of air and fuel gas can no longer be regulated individually.

DE 3041177A1, which corresponds to U.S. Pat. No. 4,380,429, shows a burner with an exhaust gas recirculation device. However, the mixture of exhaust gas from the furnace chamber and fresh air supplied from the outside does not enter the burner tube but rather flows along the outside of the burner tube to its end. Incidentally, no fresh air is carried in the burner tube, either. The mixing of all gases takes place directly in front of the burner nozzle, which is positioned at the front edge of the burner tube. This leads to turbulence in front of the burner tube, which makes it difficult to optimize the efficiency of the burner as well as the reduction of nitrogen oxides.

From WO2022117345A1, which corresponds to US 2024/0060638, a burner with an exhaust gas recirculation device is known, in which the exhaust gas is mixed with the combustion air inside the burner. A plurality of jet nozzles cause the mixture to flow within the burner tube into the area of influence of the burner nozzle.

Recuperative burners are also known, in which the efficiency is increased by an exchange of heat between the burner supply air and the exhaust gas flow of the burner. The recuperator causes heat transfer between the two gas flows. The recuperator can be made of different materials, especially metallic and ceramic materials. In particular, metallic materials are provided for low and medium temperature zones and ceramic materials for high temperature zones. A combination of materials can be used to optimize the individual sections of the recuperator for good heat transfer.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to improve a recuperative burner of the type mentioned above, in such a way that larger proportions of nitrogen oxides can be eliminated. Furthermore, the volume flows of fuel gas and combustion air should be separately adjustable, in particular in order to be able to burn different fuel gases such as methane and hydrogen with the same recuperative burner or fuel gas mixtures therefrom.

The recuperative burner according to an example of the invention has an exhaust gas recirculation device with a jet pump operated by combustion air, which has a jet pump annular gap, which is formed upstream of the mixing plane of the fuel gases flowing into the combustion chamber tube in front of the combustion chamber tube. As a result, the flow of the fuel gas itself remains completely unaffected. Rather, the fuel gas is directly routed to the burner nozzle, where the mixture of combustion air and the exhaust gas drawn in is added.

The jet pump annular gap can be annular, especially circular in shape, and converges in the flow direction.

“Annular” in the sense of the invention can also be a meandering cross section of the jet pump annular gap, in particular if the jet pump connects to an upstream heat transfer body with a chained arrangement of a plurality of outlet openings for the combustion air. By means of a meandering course, the jet pump annular gap is adapted to the course of the outlet openings on the front face of the heat transfer body.

As a rule, the jet pump annular gap is endless, with at most a few support points in the jet pump annular gap to keep an outer nozzle ring apart from an inner tube or the like.

Furthermore, it is possible to form the jet pump annular gap as an alternating sequence of closed and open cross-sectional surfaces along a circumferential line. Such a formation of the jet pump annular gap can be produced in particular in an additive manufacturing process and has the purpose of increasing the flow velocity of the combustion air by reducing the cross-sectional area in the throughflow channel of the combustion air to such an extent that a jet pump effect can be achieved. In many cases, this does not require a converging form of the jet pump annular gap.

According to the invention, the jet pump creates a recuperative burner for diluted combustion by exhaust gas intake. The recirculation of exhaust gas reduces the formation of nitrogen oxides, both with the fuel natural gas and with the fuel 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, due to its large diameter, large-area jet is generated. The large surface area of the annular air flow ensures effective intake of exhaust gas into the combustion chamber tube, wherein only the outside of the air flow has a suction effect.

Within the annular air flow, a flow-free interior is formed. Lines for gas supply and other elements such as a mixing unit, an ignition device, a burner nozzle, etc., can be routed within the interior and thus do not constitute flow obstacles.

Preferably, the elements mentioned are connected to form a burner insert, which can be removed as a whole from the combustion chamber tube. For such a design of the burner with a centrally fed or removable burner insert, the exhaust gas recirculation device designed according to the invention thus constitutes neither a structural obstacle nor a functional flow obstacle.

In order to be able to operate the recuperative burner optionally with natural gas or hydrogen, two fuel gas lines can be provided, which may only be joined right at the burner nozzle.

Preferably, an inner tube connected to the burner base with an inner cavity with a continuous clear opening cross section can be provided. 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 to the rear, towards the burner base.

The invention provides a recuperator arranged upstream of the combustion chamber tube, with a heat transfer body which has at least two separate throughflow channels to conduct counterflowing fluids, wherein the at least two fluids enter/exit via inlet and outlet openings of the throughflow channels in the heat transfer body, and, of the fluids, one is formed by combustion air to be preheated and the other is formed by the exhaust gas of the recuperative burner.

The flow-free interior can also be filled with a heat exchanger element, wherein the fuel gas lines are integrated into the heat exchanger element. A heat exchanger element arranged within the annular driving jet of the jet pump may be provided as a supplement to the heat exchanger of a larger recuperator. This can be used to gain additional heat exchanger space. However, it is no longer possible to provide a burner insert that can be removed from the rear.

In an example of a recuperative burner, the jet nozzle can be 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, where the combustion air throughflow channel of the heat exchanger ends.

If a conical, outer nozzle ring is provided, it can be designed and arranged in such a way that it covers the combustion air outlets and directs the air flow to the outside of the inner tube and compresses it there. A very narrow air ring gap is formed between the outer nozzle ring and the surface of the inner tube or another inner nozzle ring, which achieves the function of a jet pump with an annular driving jet. At the same time, the outer nozzle ring leaves the exhaust gas inlets of the heat exchanger, which are arranged radially further outwards, open for the exhaust gas throughflow channel, so that exhaust gases can be taken in from there.

The inner tube can open into or at an inlet opening of an eductor, which is enlarged in diameter relative to the combustion chamber tube, to which the combustion chamber tube is connected, with an annular exhaust gas intake opening formed between the outside of the inner tube and the edge of the inlet opening. At the exhaust gas intake opening, the recuperative burner thus opens towards the furnace chamber into which the recuperative burner protrudes, so that exhaust gas can be taken in directly from there.

The annular driving jet gap can be aligned inwards in a conical shape. This causes a more homogeneous mixing of combustion air and exhaust gas before this mixture reaches the axial position where the fuel gas is added.

In order to create as little flow resistance as possible, it is preferable that the burner base or the heat transfer body on one side and the eductor on the other side are connected to each other by a plurality of spacer elements distributed over the circumference. The very slim spacer elements hardly create any flow obstruction, so that the exhaust gas intake opening extends functionally over almost 360°.

The eductor, the spacer elements, and the heat transfer body or the burner base can be constructed in one piece using an additive manufacturing process. It is also preferable that the conical nozzle ring for the formation of the jet pump annular gap is formed in a single piece together with the heat transfer body.

It is also possible that the heat transfer body and the combustion chamber tube are each manufactured separately and then subsequently connected to each other via welded-on spacer elements.

The heat transfer body can thus be produced separately from the combustion chamber tube, especially in an additive manufacturing process.

The jet pump integrated into the recuperative burner designed according to the invention causes a recirculation of 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.

In combustion technology, the qualitative terms “rich” and “lean” can be generally used for the ratio between oxidizer and fuel. This ratio remains unchanged during exhaust gas recirculation, because only one more gas (exhaust gas) is added. However, in order to be able to describe a change in the properties of the gas mixture at different stages of operation, for example during start-up, a “lean” fuel gas-air mixture has a high exhaust gas content and a lower oxygen concentration in the sense 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 concentration of oxygen is therefore higher.

In this sense, a gas mixture of combustion air, fuel gas and exhaust gas can be regarded as “lean”, so that the ignitability of such a mixture that has not been preheated is reduced. Therefore, the recuperative burner goes out when cold as soon as exhaust gas is recirculated.

The delayed preheating of the air by the recuperator gradually increases the ignitability of the air/exhaust gas/fuel mixture again. In order to be able to heat up the cold recuperative burner with the exhaust gas recirculation device, preferably an additional control device for the exhaust gas recirculation device is provided, so that for ignition the recirculation can be reduced for a few minutes until the system is at operating temperature and heated combustion air reaches the combustion chamber.

The control device can be formed by means of a bypass line inserted in the burner base. Part of the air flow that forms the driving jet of the jet pump is routed past the exhaust gas recirculation device via the bypass line through the supply opening or another channel. This temporarily cancels the intake capacity 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 greatly reduced.

The bypass line can preferably be closed via a valve in order to cancel its effect as soon as the start-up process has been carried out. This can be done by manually switching the valve during start-up processes that are only occasionally necessary.

An automatic valve adjustment allows for the start-up process to be integrated into the burner control system, so that this process can be carried out without user intervention.

By means of a valve that can be adjusted in stages or infinitely variably, the opening cross section in the bypass line can be readjusted depending on the rising temperature of the combustion air in the heat exchanger before the bypass line is completely closed.

It can be advantageous, for the further reduction of nitrogen oxides through even more intensive exhaust gas aftertreatment, to connect the recuperative burner according to the invention in series with another exhaust gas recirculation unit and thus form a cascaded exhaust gas aftertreatment device. In this case, the flame or mixture of combustion air and fuel gas is the driving jet for a jet pump, which then draws exhaust gas into the flame downstream of the mixing plane.

Preferably, the other exhaust gas recirculation device can include a Venturi nozzle module, the inlet opening of which is located behind the burner mouth cone. The efficiency of an exhaust gas recirculation device designed in this way depends essentially on the speed of the driving jet. In a conventional recuperative burner, this speed results solely from the volume flow of the fuel gas and the volume flow of the combustion air supplied, with a slight increase in speed resulting from the reaction that begins in the flame root. In connection with a recuperative burner designed according to the invention, with which a so-called “diluted combustion” can be carried out, the speed of the driving jet for the downstream, second exhaust gas recirculation device is significantly increased by the additional exhaust gas volume drawn in via the diluted combustion; Factor 2 and above are conceivable here. In addition to the NOx load, which is already reduced by the first recirculation, the cascaded arrangement improves the effect of the second recirculation device, as the speed of the driving jet increases accordingly. As a result, the NOx emissions of the recuperative burner are significantly improved as compared to a burner with only one recirculation device.

It is also possible to make the recuperative burner particularly short, so that it is only slightly longer than the heat transfer body.

The heat transfer body can have an inner cavity. In it, a combustion chamber insert is positioned at the end of the heat transfer body facing the combustion chamber, which can be formed a conical combustion chamber tube and a trumpet-shaped burner mouth element. The burner mouth element connects to the heat transfer body with its outer edge in such a way that it is positioned in front of the inner openings of the air supply ducts, while at the same time the external outer openings of the exhaust gas intake channels on the heat transfer body are exposed outside the end element.

A flow reversal space can be formed between the mouth openings of the air supply ducts and the burner mouth element. The burner mouth element has a curvature to deflect the flow of combustion air through the air supply ducts by almost 180°.

Between an inner wall of the heat transfer body and an outer wall of the combustion chamber tube, a nozzle ring gap can be formed through a narrow space, to which an annular space extending in the flow direction with a cone angle of about 5° to 15° is connected, which 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 outside of a conical combustion chamber tube and, due to its convergent-divergent cross section, forms a jet nozzle that is driven by the supplied combustion air.

Exhaust gas is drawn in from the combustion chamber via the annular jet nozzle formed in this way via exhaust gas inlet openings on the heat transfer body. The exhaust gas intake channels on the heat transfer body branch in such a way that a first flow path is led directly into the jet nozzle from the exhaust gas intake openings, in particular directly behind the said nozzle annular gap in the flow direction. Another path leads into the heat transfer body, where the combustion air is preheated in counterflow.

The mixture of combustion air and drawn-in 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 deflection element, also trumpet-shaped, which 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 behind through the flow-permeable burner nozzle and burns there together with the supplied fuel gas. Due to the double-deflected flow, two sections of the flow path of the jet pump run within the same length of the recuperator, which results in a particularly space-saving design of an exhaust gas recirculation device. In addition, despite the compact design, it is ensured that the exhaust gas recirculation device is located upstream of the mixing plane of the fuel gases flowing into the combustion chamber tube.

Thus, it is also possible to provide holes or other recesses such as slots on the burner mouth element in the area of the flow reversal space, especially at the apex of the trumpet-shaped funnel. Part of the primary air in front of the burner nozzle can be directed into the combustion chamber via the recesses. An additional annular air flow forms around the flame, stabilizing the flame and improving the efficiency of combustion as well as nitrogen oxide reduction.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes, combinations, and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

FIG. 1 is a recuperative burner with exhaust gas recirculation device and recuperator in a side view;

FIG. 2 is a recuperative burner according to FIG. 1 in a longitudinal perspective sectional view;

FIG. 3 is an enlarged section of FIG. 2;

FIG. 4 is parts of the exhaust gas recirculation device on the recuperative burner in a partially cut perspective view, seen from the front;

FIG. 5 is parts of the exhaust gas recirculation device on the recuperative burner in a partially cut perspective view, seen from the rear;

FIG. 6 is the recuperative burner with a complete burner base in a perspective sectional view in a longitudinal section;

FIG. 7 is the recuperative burner in a perspective sectional view in a longitudinal section in a section plane rotated by 90° as compared to FIG. 6;

FIG. 8 is a recuperator for a recuperative burner according to an example of the invention;

FIG. 9 is a sectional view along the line X-X in FIG. 8;

FIG. 10 is a recuperative burner according to an example of the invention in perspective sectional view;

FIG. 11 is the recuperative burner according to FIG. 10 with flow paths drawn; and

FIG. 12 is a burner with an exhaust gas recirculation device according to an example in a perspective sectional view in a longitudinal section;

DETAILED DESCRIPTION

FIG. 1 shows a recuperative burner 100 according to the invention in a side view, which is designed as a recuperative burner. A burner base 10 with a combustion chamber flange 11 is used to attach to a furnace wall of a furnace chamber. The parts located in the wall feed-through of the furnace chamber, as well as the parts outside the furnace chamber, which connect to the combustion chamber flange 11 on the right of a recuperative burner installed in a furnace, are not shown here.

A recuperator 20 with an internal heat exchanger is connected to the burner base 10, in which the incoming combustion air and the outflowing exhaust gases are guided in opposite directions in separate throughflow channels, so that the incoming combustion air is preheated therein by the outflowing exhaust gas. The recuperative burner 100 flows into a combustion chamber in a combustion chamber tube 30, which tapers at the end at a burner mouth cone 31.

In the example of the invention shown in FIG. 1, the recuperator 20 and the combustion chamber tube 30 do not merge directly into each other. Rather, the combustion chamber tube 30 has an expansion of the diameter at its end facing the recuperator 20, which is effected by an eductor 32 inserted in between. The combustion chamber tube 30 is kept at a distance from the recuperator 20 by inserted spacer elements 36. At the same time, the inner diameter of the eductor 32 is greater 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 drawn in via an exhaust gas inlet opening 24 at the recuperator 20. Due to the axial distance of the eductor 32 and the recuperator 20 as well as the difference in diameter between them, an opening extending over the entire circumference is formed between them. This serves as the exhaust gas intake opening 34 for the combustion chamber tube 30.

At a short axial distance to the exhaust gas intake opening 34, a jet pump annular gap 26 is formed, from which combustion air escapes at high speed and with a largely laminar flow from the corresponding throughflow channel in the recuperator 20. 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 parts of the exhaust gas flowing in the opposite direction into the exhaust gas intake opening 24; this partial flow of the exhaust gas is directed together with the combustion air into the combustion chamber in the combustion chamber tube 30, so that a reduction in nitrogen oxides is caused by the recirculation of the exhaust gas and a reduction in the oxygen partial pressure in the combustion chamber. Furthermore, the temperature in the combustion chamber can be reduced by diluting the combustion air, especially when hydrogen is burned.

FIG. 2 shows a perspective cross sectional representation of the burner 100. In order to maximize the metallic surfaces of the throughflow channels that can be used for heat exchange, the heat transfer body 21 of the recuperator 20 has a very complex spatial geometry for exhaust gas and combustion air and is shown here only in a simplified form, wherein the dotted line indicates the internal separation of the throughflow 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 with the conical nozzle ring 25 in between on the outside.

In the center, the heat transfer body 21 has a continuous inner tube 22 with a cavity 27 over its length, which makes it possible to insert a burner insert 40 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.

In the example shown, the nozzle insert 40 comprises a fuel gas line 42 for the supply of methane and another fuel gas line 43 for the supply of hydrogen. An inspection tube 49 is also part of the burner insert 40 in order to be able to observe the flame visually and/or sensorially at the burner nozzle 41. Not visible in the cross-sectional representation of FIG. 2 is a bypass tube through which additional combustion air can be directed into the intermediate chamber 35, as will be described in detail below.

In order to better illustrate the formation 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, FIG. 3 shows an enlarged section of the cross-sectional representation in FIG. 2.

The hatched arrows indicate the exhaust gas flow. A major part of the exhaust gas flow is drawn out of the furnace chamber into the exhaust gas inlet opening 24 of the recuperator 20 by an external extraction device acting on an exhaust outlet opening at the base 10. A bypass flow is drawn into the side of the exhaust gas intake opening 34 by the jet pump formed at the junction between combustion chamber tube 30 and recuperator 20.

The arrows without hatching refer to the combustion air that comes out of the combustion air outlets 23 of the recuperator 20. The air flow is bundled in a narrow jet pump annular gap 26, which is 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 at which the eductor 32 begins. The air jet exiting from the jet pump annular gap 26 is supported by the extended inner tube 22 and fed into the combustion chamber tube 30 with little or no turbulence. The annular air flow supported in this way on the inner circumference is exposed exactly at the transition between the nozzle ring 25 and the eductor 32 on its outside, so that exhaust gas is carried along from there and the combustion air diluted by exhaust gas flows into the combustion chamber tube 30. The combustion air diluted by exhaust gas is symbolized by the arrows with point hatching.

FIG. 4 shows the heat transfer body 21 with an eductor 32 cut open in half. The combustion air outlet openings are covered by the conical nozzle ring 25 and are therefore not visible. An exhaust gas intake opening 24 is formed by an annular arrangement of a plurality of individual exhaust gas intake openings, which lies radially outside the nozzle ring 25. The exhaust gas inlet opening 24 is open to the furnace chamber in a recuperative burner installed in a furnace.

FIG. 4 also clearly shows the very small radial width of the jet pump annular gap 26 and the axial offset between the nozzle ring 25 on the outside and the inner tube 22 on the inside.

FIG. 5 is another perspective section, namely as a view from diagonally above at the rear of the transition between the heat transfer body 21 and the eductor 32. The radial width of the exhaust gas intake opening 34 is large, so that from the perspective it is even possible to look inside the combustion chamber tube 30 with a fuel gas line 42 running through it. The gap width is deliberately chosen so large that the flow resistance for the incoming exhaust gas is low and thus a high efficiency of the jet pump is given.

FIG. 6 shows the recuperative burner 100 according to the invention in a perspective sectional view, in its full length, i.e., including the sections of the burner base 10 beyond the combustion chamber flange 11. The cutting plane is rotated by 90° relative to FIGS. 2 and 3, so that only one fuel gas line 42 is visible.

The normal path of the combustion air leads from an external blower via an air inlet duct 13 into a combustion air chamber 14 and from there into the radial internal flow path in the heat transfer body 21 of the recuperator 20. Exhaust gas enters at the exhaust gas inlet opening 24 into the radial outer throughflow channels 101, 102 in the heat transfer body 21 and flows through them to an exhaust chamber 15, which surrounds the combustion air chamber 14. Extraction from the exhaust chamber 15 is carried out by an external blower. Due to the jet pump annular gap 26 provided for in the invention, part of the exhaust gas is taken in directly from the furnace chamber back into the combustion chamber tube 30 at the exhaust gas intake opening 34.

The flow conditions described above correspond to the normal operation of the recuperative burner 100. However, the fuel gas-air mixture diluted by exhaust gas in the combustion chamber 33 is too lean for start-up operation, so that an ignited flame is quickly extinguished again.

Since it is not possible to temporarily close the jet pump annular gap 26 by mechanically adjustable flaps or the like due to the high temperature load in the recuperative burner 100, a control device for carrying out a start-up process in the form of a lockable bypass line is provided. The bypass line comprises a bypass line tube 46, which also forms part of the burner insert 40, which can be inserted through the cavity 27 in the inner tube 22. The bypass line tube 46, as well as the inspection tube 49, is routed to a rear end flange 19 of the burner base 10. There, it is connected to the combustion air chamber 14 via a bypass line tube bend 17, wherein the flow path between the bypass line tube 46 and the combustion air chamber 14 can be closed via a valve 18.

The fuel gas lines, the inspection tube 49 and the bypass line tube 46 run through the combustion air chamber 14. However, to prevent the combustion air from entering the cavity 27 of the inner tube 22, the various lines of the burner insert 40 are bundled by a common bulkhead plate 47, through which an airtight barrier is created in the inner tube 22, which can be bypassed by the bypass line tube 46 running through the bulkhead plate 47.

By opening the valve 18, combustion air flows through the bypass line tube 46 to the intermediate chamber 35, and thus the immediate vicinity of the burner nozzle 41. Since the flow resistance in the throughflow channel for the combustion air within the heat transfer body 21 is much higher than in the bypass line, the air flow flowing through the heat transfer body 21 is significantly weakened, which also reduces the effect of the jet annular pump and consequently only a small amount of exhaust gas is sucked in. A rich gas-air mixture with only a small fraction of exhaust gas is burned, resulting in a stable flame in the burner chamber 33.

The recuperative burner 100 heats up as the burning time increases, if only 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 is also preheated in the combustion air chamber 14 surrounded by the exhaust chamber 15, the combustion air supplied by the bypass line tube 46 also heats up increasingly.

The valve 18 can be completely closed when a certain minimum temperature is reached in the combustion chamber 33. It is also possible to successively reduce the airflow through the bypass line by means of a motor-driven valve that can be adjusted via a control device, whereby the flow velocity at the jet pump annular gap 26 increases progressively and the fraction of exhaust gas in the combustion chamber 33 increases until the start-up process is completed and the bypass line can be completely closed.

FIG. 7 shows the recuperation burner 100 with the burner base 10 again in a cutting plane rotated by 90° relative to FIG. 6, wherein this view is shortened by the combustion chamber tube adjoining the eductor 32.

The cutting plane intersects the bypass line tube 46 over its entire length. The branch of the bypass line tube bend 17 on the underside of the combustion air chamber 14 is also visible. In particular, the formation of an exhaust chamber 15 surrounding the combustion air chamber 14 can be seen, to which an exhaust outlet flange 16 with a large diameter is connected to the side, through which effective extraction of the exhaust gas is caused.

FIG. 8 shows parts of another example of a recuperative 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. In alignment with the inner tube 222, a combustion chamber tube 230 is arranged, which has the same inner diameter.

The special feature of this example of a recuperative burner according to the invention lies in the fact that an exhaust gas recirculation device with an exhaust gas suction jet pump 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 therefore integrated directly into the heat transfer body 221. A jet pump annular gap 226 is formed between an inner conical nozzle ring 228 and an outer, also conical nozzle ring 225.

Two throughflow channels 201, 202 are formed in the heat transfer body 221, wherein combustion air is supplied in the inner throughflow channel 201, which flows 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 throughflow channel 202 towards a burner base. Part of the exhaust gas flow is sucked in by means of the driving jet formed from fresh air at the jet pump annular gap 226 at an annular exhaust gas intake opening 234 and fed into the combustion chamber tube 230.

In order to return the flow from the widened diameter area 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, in which both the throughflow channels 201, 202 with maximized heat exchange surface and the exhaust gas recirculation device with the nozzle rings 225, 228 and the eductor 232 are integrated, possibly also the inner tube 222 and the combustion chamber tube 230 as further integral components, is realized by means of an additive manufacturing process.

FIG. 9 shows another perspective sectional view, with the section plane running transversely to the center axis, namely along the X-X section line in FIG. 8. The view is directed into the jet pump annular gap 226. Only the inner nozzle ring 228 is visible. The outer nozzle ring is concealed in this line of sight.

FIG. 10 shows a recuperative burner 300 in a perspective, sectional view, in which, similar to the example presented in FIG. 8, a jet pump is formed in the interior of a recuperator 320.

A heat transfer body 321 of the recuperator 320 has an inner tube 322 with an inner cavity 327. In it, a combustion chamber insert is positioned at one end of the heat transfer body 321 facing a combustion chamber 333, which can be formed of a conical combustion chamber tube 330 and a trumpet-shaped burner mouth element 331. The outer rim of the burner mouth element 331 connects to the heat transfer body 321 in such a way that it is positioned in front of the internal outlet openings 323 of the air supply channels 301 and at the same time the external exhaust gas intake openings 334 on the heat transfer body 321 are exposed outside the burner mouth element 331.

A flow reversal space 328 is formed between the mouth 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 space 323 in order to divert the flow of the combustion air supplied via air supply channels 301 by almost 180° to a bottleneck 325.

The bottleneck 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. The bottleneck 325 is adjoined by an annular space widening in the flow direction with a cone angle of approx. 5° to 15°, which forms a jet pump annular gap 326 and ends 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 outside of a conical combustion chamber tube 330 and, due to its convergent-divergent cross-sectional course, forms a jet nozzle that is driven by the supplied combustion air.

Via the annular jet nozzle formed in this way, exhaust gas is sucked in from the combustion chamber via 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 a first flow path is led directly into the jet nozzle from the exhaust gas intake openings 334, and in particular directly, as viewed in the flow direction, behind the said bottleneck 325. A further path leads via an exhaust gas inlet opening 302 into an exhaust gas extraction duct 302 in the heat transfer body 321, where the combustion air supplied via the air supply channels 301 is preheated in countercurrent operation.

The mixture of combustion air and exhaust gas sucked in 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 that is also trumpet-shaped, which closes the inner free cross section of the cavity 327 in the heat transfer body 321 and which, with a concave curvature section 351, causes flow deflection into the interior of the combustion chamber tube 330. There, it flows from behind 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 curvature section 351 and the burner nozzle 41 has a divergent cross section, so that there is a widening of the cross section over the entire flow path, which begins at the bottleneck 325 and ends at the burner nozzle 41. This section is referred to as intermediate chamber 335.

The concave curvature 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.

In the example shown in FIG. 10, primary air holes 332 are provided on the burner mouth element 331 in the area of the flow reversal space, in particular at the apex of the trumpet-shaped funnel forming the burner mouth element 331. Via the primary air holes 332, part of the supplied primary air can be directed into the combustion chamber upstream of the burner nozzle 41. The primary air flow thus caused forms an annular air flow that encloses the combustion chamber 333 and the flame emerging from it, stabilizing the flame and improving the efficiency of combustion as well as nitrogen oxide reduction.

FIG. 11 is basically the same as FIG. 10, with the path of the combustion air supplied being indicated as a dotted line and the path of the exhaust gas being discharged with dotted lines.

Distributed around the circumference, all flow paths of air and exhaust gas occur a plurality of times, so that air and exhaust gas flows exist next to each other at a plurality of points. As a result, an air-exhaust gas mixture is formed in the area of the diverging annular gap 326 without turbulence, which is fed to the burner nozzle 41.

FIG. 12 shows a recuperative burner 100′, which is 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 in the flow direction in front of the burner mouth cone 31 of the recuperative burner 100 and whose inlet opening 406 is located behind the outlet opening of the burner mouth cone 31, leaving an annular gap between them. Downstream behind the Venturi nozzle module 402, a plurality of segment flame tubes 403 are arranged in series one after the other. The segment flame tubes 403 are used to guide the hot flue gases in the jet tube 401. The exhaust gas recirculation device 400 is terminated 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.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.