Burner with heat exchanger

Abstract

The invention relates to a heat exchanger (3) for a burner with a heat exchanger (1) having a circumferentially closed housing (31) surrounding an exhaust gas passage (32) with a hot side and a cold side and allowing longitudinal flow, and having a number of heat transfer pipes arranged in the exhaust gas passage, in which a first connection chamber (301) with a first supply connection end (37) for combustion air and a second connection chamber (302) with a second supply connection end (38) for combustion gas are connected on the cold side of the exhaust gas passage (32). The burner (1) is provided with a heat exchanger, in which the exhaust gas passage (32) is divided into at least a first segment (321) fluidly connected to the first connecting chamber (301) and a second segment (322) fluidly connected to the second connecting chamber (302), in which a part of the heat transfer pipe (33) is arranged in each segment, and in which the exhaust gas can flow in parallel in each segment, such that the ratio of the heat capacity flow on the low temperature side to the heat capacity flow on the high temperature side is between 0.9 and 1.1. The present invention further relates to a burner (1) with a heat exchanger.

Description

[Technical field]

[0001] The present invention relates to a heat exchanger for a burner with a heat exchanger and a burner with a heat exchanger. [Background technology]

[0002] In burners with heat exchangers, the incoming combustion air is preheated with the aid of the exhaust gases that are led out. Burners with heat exchangers are known, for example, from EP 1995516 A1. They are used in particular to generate process heat, for example for directly or indirectly heating industrial furnaces. In the case of direct heating, the combustion takes place in the furnace chamber. In the case of indirect heating, the combustion takes place in a chamber that is closed off relative to the furnace chamber, for example in a radiant pipe that projects into the furnace chamber but is closed off relative to it, in which case the chamber or radiant pipe is heated by the combustion and emits thermal radiation.

[0003] Modern burners with heat exchangers achieve a relative air preheat of more than 80% with respect to the exhaust gas intake temperature for fossil combustion gases with a heating value of more than about 5 kWh / m3, such as natural gas or propane. The combustion technical efficiency is therefore increased to more than 85%.

[0004] In the future, fossil combustion gases will increasingly be replaced by lean gases to generate process heat. Lean gases are gases or gas mixtures with low calorific value, such as gas mixtures in which high-energy alkanes are adulterated with non-combustible components, such as nitrogen, CO2 or water vapor. Lean gases include residual gases in the chemical and steel industries, residual gases from fuel cells, gases from wood gasification, cleaning gases from pressure change plants and landfill waste gases. Hydrogen and ammonia, which also have a much lower calorific value compared to natural gas or propane, are also referred to as lean gases in the context of this application.

[0005] For combustion gases with a lower heating value, the heat capacity flow of the exiting exhaust gases is much greater than that of the incoming combustion air, so that the exhaust gases are not cooled very much, despite the high air preheat. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] European Patent Application Publication No. 1995516(A1) Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to provide a heat exchanger for a burner with a heat exchanger and a burner with a heat exchanger, which enables a combustion technical efficiency of at least 80% by reducing the exhaust gas temperature to below 300°C even when lean gas is used. [Means for solving the problem]

[0008] This problem is solved by a heat exchanger having the features of claim 1 and by a burner with heat exchanger having the features of claim 12.

[0009] According to a first aspect, a heat exchanger for a burner with a heat exchanger is provided, which has a circumferentially closed housing surrounding an exhaust gas passage through which exhaust gas can flow longitudinally and a number of heat transfer pipes arranged in the exhaust gas passage, in which a first connection chamber with a first supply connection end for combustion air and a second connection chamber with a second supply connection end for combustion gas are provided on the low-temperature side of the exhaust gas passage, in which the exhaust gas passage is divided into at least a first segment fluidly connected to the first connection chamber and a second segment fluidly connected to the second connection chamber, in which parts of the heat transfer pipes are arranged in each segment such that the ratio of the heat capacity flow on the low-temperature side to the heat capacity flow on the high-temperature side is between 0.9 and 1.1, and in which the exhaust gas flows can flow in parallel.

[0010] In the context of this application, terms such as "one" and "one" are used merely as indefinite articles and should not be interpreted as numerical values. The concepts of "first" and "second" are merely used to distinguish elements and do not represent the order of elements.

[0011] The exhaust gas flows uniformly through two or more segments. As a result, both the combustion air and the combustion gas are heated by the exhaust gas in the heat exchanger segments. By feeding the combustion air and the combustion gas to the cold side, the heat capacity flow on the cold side is increased so that it is approximately equal to the heat capacity flow on the hot side. The heat capacity flow is the product of the mass flow and the heat capacity. With at least approximately equal heat capacity flows, the exhaust gas can be cooled approximately as much as the combustion air and the combustion gas are heated. For example, if the exhaust gas inlet temperature is 1000 °C and the combustion air and the combustion gas are preheated to 800 °C, the exhaust gas is cooled to the same extent, i.e. to less than 250 °C.

[0012] In one embodiment, the exhaust gas passage is divided into three segments, in which three gas streams, in particular primary air, secondary air and combustion gases, can flow in parallel through the heat transfer pipes arranged in the segments. The division of the combustion air into primary air and secondary air serves for staged combustion, which can reduce thermal NOx formation. In this case, in a preferred embodiment, separate connection chambers are provided for the three segments, each with its own supply connection.

[0013] In one embodiment, the three segments each have an equal flow cross-section, but different divisions are contemplated and may be made by one skilled in the art as appropriate for the particular application.

[0014] The division into segments is in one form only achieved by associating heat transfer pipes with connecting chambers, with the exhaust gases then flowing freely between the segments.

[0015] In another embodiment, filler elements are provided between the segments in order to reduce the flow cross-section, in particular the gap width, between the heat transfer pipes which are formed as flat pipes. In one embodiment, the filler elements are formed as perforated plates made of a heat-resistant material, in particular steel. In another embodiment, corrugated sheet inserts are provided as filler elements.

[0016] In one embodiment, the heat transfer pipe is accommodated on the cold side and / or on the hot side in a connecting plate arranged at a distance from the housing, with the outlet or inlet opening for the exhaust gas passage being formed between the connecting plate and the housing. The exhaust gas can then enter the exhaust gas passage from all sides. In a preferred embodiment, a collecting chamber is provided on the cold side, which surrounds the end of the heat transfer pipe and which is equipped with an exhaust gas pipe for the exhaust gas.

[0017] In one embodiment, a catalyst is arranged in the heat transfer pipe of the second segment, in particular a catalyst for ammonia decomposition. Due to the low flame speed, it is usually not possible to directly ignite ammonia. If the ammonia used as the combustion gas is preheated in the heat transfer pipe, the ammonia partially decomposes and hydrogen is formed, which promotes ignition. In one embodiment, this effect is increased by inserting a catalyst, for example a woven fabric made of nickel wire, into some or all of the heat transfer pipe of the second segment, i.e., into the heat transfer pipe where the combustion gas is heated.

[0018] Alternatively or additionally, in one embodiment, a catalyst, in particular a catalyst for oxidizing ammonia, is arranged in the exhaust gas passage, in the exhaust gas pipe and / or downstream of the exhaust gas pipe. If the combustion gas is ammonia, depending on the temperature and residence time in the heating chamber, respectively, traces of ammonia may remain in the exhaust gas. For this reason, in one embodiment, a catalyst is arranged downstream of the exhaust gas pipe, which oxidizes the remaining ammonia.

[0019] In one embodiment, a central pipe for start-up heating is arranged in the housing, with the exhaust gas passage surrounding the central pipe, and the heat transfer pipes are then arranged around the central pipe. The start-up heating is used for starting up the burner with a heat exchanger, especially when used with lean gases with very low calorific value, especially less than 1 kWh / m3. In one embodiment, the start-up heating has a gas lance and / or an electric heater for supplying gases with high calorific value.

[0020] In a preferred embodiment, the housing has a circular or polygonal cross section, in which case the exhaust gas passage is divided into coaxially arranged ring-shaped segments, which division allows a uniform flow through all segments. In some embodiments, a ring-shaped connecting chamber is provided on the cold side, which is coaxially arranged relative to the segments.

[0021] The heat transfer pipes are preferably formed as flat pipes, which are arranged in particular concentrically. Flat pipes are heat transfer pipes with a flattened gap cross section in the section used for heat transfer. In particular the ends of the flat pipes, which join the flat pipes to the connection plate, are rounded or polygonal in some embodiments. Heat exchangers with flat pipes are also called flat pipe heat exchangers. In one embodiment, corrugated sheet inserts are arranged between the flat pipes to increase the heat transfer area and reduce the gap width between the flat pipes.

[0022] According to a second aspect, a burner with a heat exchanger is provided having a heat exchanger, the heat exchanger having a circumferentially closed housing surrounding an exhaust gas passage through which exhaust gas can flow longitudinally, and a number of heat transfer pipes arranged in the exhaust gas passage, the exhaust gas passage being divided into at least two segments for preheating the combustion air and the combustion gas.

[0023] The heat transfer pipes of the first and second segments, in one embodiment, communicate on the hot side into a combustion chamber surrounded by a combustion chamber housing, also referred to as the combustion chamber and, similarly, the combustion chamber housing.

[0024] In one embodiment, a temperature sensor is provided at the inlet of the combustion chamber and a regulating device is provided at the first supply connection and / or at the second supply connection, the regulating device or devices being configured to adjust the amount of combustion air provided via the first supply connection in ratio to the amount of combustion gas provided via the second supply connection according to the temperature at the inlet of the combustion chamber detected by the temperature sensor. The burner with heat exchanger is driven in such a way that, in particular, as the temperature of the gas flow provided to the combustion chamber increases, the amount of combustion air provided to the combustion chamber is reduced relative to the amount of combustion gas provided to the combustion chamber, thereby making it possible to avoid an excessive temperature rise in the combustion chamber.

[0025] In one embodiment, the exhaust gas passage is divided into three segments, in which three gas streams, in particular primary air, secondary air and combustion gases, can flow in parallel through heat transfer pipes arranged in these segments, the heat transfer pipe of the third segment opening on the hot side into an air guide chamber surrounding the combustion chamber housing, which in a preferred embodiment surrounds the first and second segments.

[0026] This shape allows for staged combustion, where preheated primary air and preheated combustion gases are fed into the combustion chamber for the combustion process, the residual gases of which are combusted in the third segment with preheated secondary air, preferably in flameless oxidation, thereby preventing the formation of nitrogen oxides.

[0027] The combustion chamber housing and the air guide housing, in some configurations of burners with heat exchanger, have for this purpose an outlet nozzle into the furnace chamber.

[0028] Further advantages and aspects of the invention will become apparent from the claims and the following detailed description of the preferred embodiments of the invention, in which: [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 shows a longitudinal section of a burner with a heat exchanger, which is arranged in the furnace wall. [Diagram 2] FIG. 2 shows a section II-II of the connection head of the heat exchanger shown in FIG. [Diagram 3] FIG. 3 shows a bottom view of the burner with heat exchanger shown in FIG. [Figure 4] FIG. 4 shows a cross-sectional view of the heat exchanger shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Figures 1 to 3 show an embodiment of a heat exchanger burner 1, which has a heat exchanger 3 for preheating the combustion air and the fuel. Figure 4 shows a cross-section of the heat exchanger 3.

[0031] The illustrated burner with heat exchanger 1 can in particular be operated with so-called lean gas, in which case by means of the heat exchanger 3, both the supplied combustion air and also the supplied fuel gas are preheated using exhaust gas energy.

[0032] The illustrated burner with heat exchanger 1 is used, for example, to heat a furnace chamber 2 and is arranged in a furnace wall cutout within the furnace insulation 22 .

[0033] As can be seen particularly well in Figure 4, the illustrated heat exchanger 3 is a flat pipe heat exchanger having a housing 31 with a circular cross section. The housing 31 surrounds an exhaust gas passage 32 in which flat pipes 33 are accommodated. The flat pipes 33 are arranged in the housing 31 along a number of concentric circles, seven in the illustrated embodiment.

[0034] The flat pipes 33 are housed at their both ends in connecting plates 35. The flat pipes 33 are tightly connected to the connecting plates 35, for example by soldering thereto. The flat pipes 33 are longer than the housing 31 and the connecting plates 35 are each arranged displaced with respect to the ends of the housing 31, so that inlet and outlet openings 4 and 5 for the exhaust gases are formed between the ends and the connecting plates 35. A flange plate 36 is provided on the cold side of the heat exchanger 3 for mounting the heat exchanger 3 to the furnace wall.

[0035] In the illustrated embodiment, the exhaust gas passage 32 is divided into three segments 321, 322, 323 through which the exhaust gas can flow in parallel. Each of the segments 321, 322, 323 is assigned a portion of the flat pipe 33.

[0036] The heat exchanger 3 has a connection head 30 for supplying combustion air and fuel, which is arranged outside the furnace chamber 2, on the cold side of the heat exchanger 3. The connection head 30 is shown in cross section in FIG. 2. As is clear from FIG. 2, the illustrated connection head 30 has three separate supply connections 37, 38, 39 for materially separating the three gas streams and supplying them to the flat pipes 33 of the three segments 321, 322, 323. In the illustrated embodiment, a first supply connection 37 for the primary air supply, a second supply connection 38 for the fuel supply and a third supply connection 39 for the secondary air supply are provided. The supply connections 37, 38, 39 lead into the connecting chambers 301, 302, 303, respectively. The second supply connection 38 and the third supply connection 39 are arranged in the illustrated embodiment at a 90° offset with respect to the first supply connection 37, which is arranged between them. However, other arrangements are also conceivable. The connecting chambers 301, 302, 303 each have a circular cross section and are arranged concentrically with respect to the central axis of the heat exchanger 3. The first connecting chamber 301 is then located between the second connecting chamber 302 located on the inside and the third connecting chamber 303 located on the outside. These connecting chambers 301, 302, 303 are materially separated by webs.

[0037] In the illustrated embodiment, the segments 321, 322, 323 are each circular and arranged concentrically with respect to the central axis of the heat exchanger 3. The size and / or shape of the segments 321, 322, 323 can be appropriately selected by a person skilled in the art depending on the specific application. In the illustrated embodiment, the first centrally located segment 321 and the second inner segment 322 are selected such that they have the same number of flat pipes 33 and the flow cross sections around the flat pipes 33 are at least approximately equal, so that the gas flow guided in the flat pipes 33 during use is at least substantially equally heated by the exhaust gas flowing around the flat pipes 33.

[0038] Between the segments 321, 322, 323, filler elements 34 are arranged to reduce the gap width between the flat pipes. The filler elements 34 are preferably selected so as not to block the flow between the segments 321, 322, 323. For example, the filler elements are perforated plates made of heat-resistant steel, which provide swirling of the exhaust gas flow.

[0039] The illustrated burner with heat exchanger 1 is used for staged combustion.

[0040] For staged combustion, the burner with heat exchanger 1 has on the hot side a combustion chamber 11 (also called combustion chamber, primary combustion chamber or primary combustion chamber) surrounded by a combustion chamber housing 10, also called a combustion chamber housing 10, and an air guide housing 12 surrounding the combustion chamber housing 10. The combustion chamber housing 10 and the air guide housing 12 each have outlet nozzles 13, 14 into the furnace chamber 2.

[0041] In the embodiment shown, a temperature sensor 8, which is shown diagrammatically, is provided at the inlet of the combustion chamber 11. Furthermore, the first supply connection 37 and the second supply connection 38 are respectively provided with regulating devices 370, 380, by means of which the amount of primary air supplied via the first supply connection 37 or the amount of combustion gas supplied via the second supply connection 38 can be adjusted. In another embodiment, only one of the two supply connections 37, 38 is provided with a regulating device 370, 380.

[0042] 3 shows a bottom view of the burner with heat exchanger 1 with the outlet nozzles 13 in the combustion chamber housing 10 and the outlet nozzles 14 in the air guide housing 12. In the embodiment shown, the outlet nozzles 13, 14 are evenly distributed along circles concentric with the central axis of the heat exchanger. The arrangement and number of the outlet nozzles 13, 14 are merely schematic.

[0043] The combustion chamber 11 is supplied with primary air heated in a first segment 321 and fuel heated in a second segment 322 for oxidation. The reaction gas stream discharged from the combustion chamber 11 is fed via an outlet nozzle 13 to the furnace chamber 2 where it is fully oxidized, if necessary, by adding secondary air preheated in a third segment.

[0044] A pipe 6 is provided coaxially with respect to the central axis of the heat exchanger 3, and the pipe communicates with the inside of the combustion chamber 11. A baffle plate 60 is provided at the end of the pipe 6 that is disposed inside the combustion chamber.

[0045] In order to supply a fuel with a higher heating value to the combustion chamber 11, an additional device 7, for example in the form of a central gas lance, for starting the heat exchanger burner 1 is provided in the pipe 6. A fuel with a higher heating value, for example natural gas, is supplied via the additional device 7, for example to heat the furnace chamber 2. A flame is ignited in the combustion chamber 11, and the hot exhaust gases reach the furnace chamber 2 via the outlet nozzle 13, thereby heating the furnace chamber. Once the desired temperature has been reached, the heat exchanger burner 1 can be driven by lean gas.

[0046] After start-up, the oxidation process in the combustion chamber 11 and in the furnace chamber 2 is preferably carried out in such a way that flame formation is suppressed and thus thermal NOx formation is avoided.

[0047] The exhaust gas generated in the combustion is at least partially supplied to the exhaust gas passage 32 to heat both the combustion air and the supplied combustion gas in the segments 321, 322, 333. The heating of the combustion air and the combustion gas increases the heat capacity flow on the low temperature side, so that the heat capacity flow on the low temperature side is approximately equal to the heat capacity flow on the high temperature side.

[0048] In the illustrated embodiment, the regulating devices 370, 380 allow the amount of primary air supplied via the first supply connection 37 to be adjusted in ratio to the amount of combustion gas supplied via the second supply connection 38 in dependence on the temperature at the inlet to the combustion chamber 11, detected by the temperature sensor 8. The burner with heat exchanger can then be operated in such a way that, as the preheating of the gas flow supplied to the combustion chamber 11 increases, the amount of primary air supplied relative to the amount of combustion gas supplied is reduced. This makes it possible to avoid a significant temperature rise in the combustion chamber 11.

[0049] By simultaneously heating the combustion air and the combustion gases, the exhaust gas temperature can be reduced to below 300°C even in the lean gas case, so that a combustion technical efficiency of more than 80% can be achieved. At the same time, excessive air preheating, which can lead to thermal nitrogen oxide formation, can be avoided.

[0050] This makes it possible to increase the efficiency of the burner 1 with a heat exchanger without increasing the heat transfer area, as will be explained below using the example of a 50 kW burner with a flat-pipe heat exchanger for lean gas, hydrogen or ammonia, with a characteristic quantity kxA=50 W / K (A=heat exchanger area, k=heat transfer coefficient) at an exhaust gas inlet temperature of 1000°C.

[0051] [Table 1]

[0052] In one embodiment, the number of flat pipes 33 is evenly distributed among the three segments 321, 322, 323. In another embodiment, other distributions are made depending on the respective combustion gases.

Claims

1. A heat exchanger for a burner with a heat exchanger (1), comprising a circumferentially closed housing (31) surrounding an exhaust gas passage (32) having a hot side and a cold side and through which exhaust gas can flow in the longitudinal direction, and comprising a number of heat transfer pipes arranged in said exhaust gas passage, wherein at the cold side of the exhaust gas passage (32) there is provided a first connection chamber (301) having a first supply connection end (37) for combustion air and a second connection chamber (302) having a second supply connection end (38) for combustion gas, a heat exchanger, characterized in that the exhaust gas passage (32) is divided into at least a first segment (321) fluidly connected to the first connecting chamber (301) and a second segment (322) fluidly connected to the second connecting chamber (302), a part of the heat transfer pipe (33) is arranged in each segment so that the ratio of the heat capacity flow on the low temperature side to the heat capacity flow on the high temperature side is between 0.9 and 1.1, and the exhaust gas can flow in parallel in each segment.

2. 2. A heat exchanger according to claim 1, characterized in that the exhaust gas passage (32) is divided into three segments (321, 322, 323) and three gas streams, in particular a primary air stream, a secondary air stream and combustion gases, can flow in parallel through heat transfer pipes arranged in the three segments (321, 322, 323).

3. 3. A heat exchanger according to claim 2, characterized in that the three segments (321, 322, 323) have equal flow cross sections.

4. 4. A heat exchanger according to claim 1, 2 or 3, characterized in that between the segments (321, 322, 323) there are provided filling elements (34) for reducing the flow cross section, in particular the filling elements (34) being formed as perforated plates.

5. 5. A heat exchanger according to claim 1, characterized in that the heat transfer pipes are accommodated on the low temperature side and / or the high temperature side in a connecting plate (35) arranged at a distance from the housing (31), and an outlet or inlet opening for the exhaust gas passage (32) is formed between the connecting plate (35) and the housing (31).

6. 6. A heat exchanger according to claim 1, characterized in that in the heat transfer pipes of the second segment (322) a catalyst is arranged, in particular a catalyst for ammonia decomposition.

7. 7. A heat exchanger according to claim 1, characterized in that a catalyst, in particular a catalyst, is arranged in the exhaust gas passage (32), in the exhaust gas pipe (5) and / or downstream of the exhaust gas pipe (5).

8. 8. A heat exchanger according to claim 1, characterized in that in the housing (31) a central pipe (6) for start-up heating is arranged and the exhaust gas passage (32) surrounds the central pipe (6).

9. 9. A heat exchanger according to claim 1, characterized in that the housing (31) has a circular or polygonal cross section and the exhaust gas passage (32) is divided into coaxially arranged ring-shaped segments (321, 322, 323).

10. 10. A heat exchanger according to claim 9, characterized in that it is provided with a ring-shaped connecting chamber (301, 302, 303) arranged coaxially with respect to the segments (321, 322, 323).

11. 11. Heat exchanger according to claim 1, characterized in that the heat transfer pipes are designed as flat pipes (33), said flat pipes being arranged in particular concentrically.

12. A burner with a heat exchanger, comprising the heat exchanger according to any one of claims 1 to 11.

13. 13. The burner with heat exchanger according to claim 12, characterized in that the heat transfer pipes of the first segment (321) and the second segment (322) communicate at the hot side into a combustion chamber (11) surrounded by a combustion chamber housing (10).

14. 14. Burner with a heat exchanger according to claim 13, characterized in that a temperature sensor (8) is provided at the inlet of the combustion chamber (11) and an adjusting device (370, 380) is provided at the first supply connection (37) and / or the second supply connection (38), the adjusting device (370, 380) being configured to adjust the ratio of the amount of combustion air supplied via the first supply connection (37) to the amount of combustion gas supplied via the second supply connection (38) in accordance with the temperature at the inlet of the combustion chamber (11), detected by means of the temperature sensor (8).

15. 15. A burner with a heat exchanger according to claim 13 or 14, characterized in that the exhaust gas passage is divided into three segments and the heat transfer pipe of the third segment (323) is connected on the hot side into an air guide housing (12) surrounding the combustion chamber housing (10).

16. 16. Burner with heat exchanger according to claim 15, characterized in that the combustion chamber housing (10) and the air guide housing (12) have outlet nozzles (13, 14).

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