Background of the Invention
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The present invention relates to a burner assembly for combustion of an air-hydrogen mixture on a burner surface, comprising a burning unit with an air-hydrogen mixture flow-through section that comprises a plurality of slotted orifices for flow-through of air-hydrogen mixture. Furthermore, the present invention relates to an air-hydrogen mixture burning appliance comprising such a burner assembly.
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The document
DE 10 2019 216 769 A1 describes a burner assembly for combustion of an air-gas mixture on a burner surface. The burner assembly comprises a burning unit with a distributor plate and a thermal protection element that is embodied as a felted knitted fibre fabric with high-temperature resistant metallic fibres. The distributor plate forms an air-gas mixture flow-through section that comprises a plurality of orifices for flow-through of an air-gas mixture towards and through the thermal protection element, which therefore also comprises a plurality of orifices for flow-through of the air-gas mixture. The orifices of the plurality of orifices of the distributor plate are circular, but may also be slotted. The thermal protection element is connected to the distributor plate and forms a burning surface on which combustion of the air-gas mixture takes place. The air-gas mixture may be an air-hydrogen mixture.
Summary of the Invention
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The present invention relates to a burner assembly for combustion of an air-hydrogen mixture on a burner surface, comprising a burning unit with an air-hydrogen mixture flow-through section that comprises a plurality of slotted orifices for flow-through of air-hydrogen mixture. The air-hydrogen mixture flow-through section embodies the burner surface and comprises a first length and a first width that is smaller than the first length. Each slotted orifice of the plurality of slotted orifices comprises a second length and a second width that is smaller than the second length. The second width amounts at most to 0.6 mm, and the second length is at least essentially arranged in parallel to the first width.
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Combustion of an air-hydrogen mixture in a burner assembly of a burning appliance requires a number of features to be incorporated into the design of the burning unit of the burner assembly in order to reduce thermal loads induced onto the burning unit at a high turndown ratio, to sustain a stable flame that is free from flashbacks on the burning unit and, more particularly, on the burning surface, and to prevent unwanted flow noises or thermo acoustic noises preferably in a wide lambda range.
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More specifically, the nature of an air-hydrogen mixture flame results in the base of the flame being anchored very close to the burner surface of the burning unit due to the effects of preferential diffusion, which causes hydrogen molecules to travel to the base of the air-hydrogen mixture flame to combust and therefore increases the thermal load at the base of the flame, as well as an increased flame speed, e. g. with approximately 5 times of burning velocity compared to methane. This causes high thermo-mechanical stresses to be induced onto the burning unit and may drastically reduce the life expectancy of a conventional burning unit.
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Furthermore, air-hydrogen mixture flames are also known to be susceptible to flashbacks, performance and ignition issues due to minor changes to burner unit geometry or combustion settings, e. g. changes to air-hydrogen ratios. A flashback is an event where an air-hydrogen mixture flame propagates upstream of the burning unit, causing combustion of the air-hydrogen mixture in unintended locations upstream of the burning unit, which can be extremely damaging to the burner assembly and the burning appliance as a whole if the flame is allowed to accelerate into detonation, where large overpressures are witnessed.
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Unwanted thermo acoustic noises are considered to be any noise that might be heard during normal operation of a conventional burning appliance and that may result in a perception of poor quality or customer complaints. This includes excessively noisy operation of components of a conventional burning appliance.
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In contrast thereto, the inventive burner assembly advantageously comprises a burning unit with a plurality of slotted orifices having tightly controlled slot widths and port loading, i. e. controlling of the air-hydrogen mixture velocity through the slotted orifices. Thus, a respective air-hydrogen mixture flame may be stabilised and sustained reliably and securely on the burner surface of the burning unit, while limiting and equalizing thermo-mechanical stress induced onto the burning unit. This results in a longer lasting burning unit, which is also free from unwanted thermo acoustic noise during operation.
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More specifically, the inventive burner assembly advantageously enables a quick and reliable ignition of air-hydrogen mixture on the burner surface of the burning unit and an improved air-hydrogen mixture flame signal strength, as well as a reliable prevention of flashbacks. Furthermore, an easier detection of a respective burner assembly operation status is enabled and a reduction of emissions, in particular NOx emissions, is achieved. Moreover, a more equal distribution respectively a more stable flame over turndown ratio is obtained. These advantages may be obtained by using common and known material and production methods and an improved robustness and extended lifetime may be achieved through a reduction of thermomechanical stresses on the burning unit.
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According to one aspect, the burning unit is configured to enable stabilisation and sustainment of a flame of burning air-hydrogen mixture on the burner surface.
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Thus, a respective air-hydrogen mixture flame may reliably and securely be stabilised and sustained on the burner surface of the burning unit.
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Preferably, the plurality of slotted orifices in the air-hydrogen mixture flow-through section is arranged in at least one row in direction of the first length.
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Thus, a suitable pattern of slotted orifices may easily be formed.
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The plurality of slotted orifices in the air-hydrogen mixture flow-through section may be arranged in at least two rows, each one of the at least two rows being formed in direction of the first length, wherein the at least two rows are arranged at least essentially in parallel to each other in direction of the first width, and wherein at least two rows of the at least two rows which are adjacent in the direction of the first width are shifted relative to each other in the direction of the first length.
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Thus, a more equal distribution/more stable flame over turndown ratio may be obtained.
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According to one aspect, a predetermined distance between adjacent slotted orifices of the plurality of slotted orifices is greater than or equal to 1.1 mm.
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Thus, a secure and reliable burning unit may be provided.
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Preferably, the burning unit is embodied with a controlled pressure drop ρ for a given air flow rate V according to 0.00265V2 + 0.007V > p > 0.001V2 + 0.01V, wherein V defines the given air flow rate in L/min.
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Thus, suitable upper and lower limits of an allowable pressure drop may adequately be determined.
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According to one aspect, the burner assembly further comprises a diffuser unit for generating additional mixing of the air-hydrogen mixture.
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Thus, combustion of the burner assembly may easily be improved.
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Preferably, the diffuser unit is plate-shaped and arranged upstream of the burning unit, or the diffuser unit is integrated into the burning unit as an integral part thereof.
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Thus, a compact and robust burner assembly may be provided.
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Preferably, the burning unit is plate-shaped, and the air-hydrogen mixture flow-through section is flat, semi-cylindrical or cylindrical.
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Thus, different types of burning appliances may easily be equipped with the burner assembly.
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Furthermore, the present invention relates to an air-hydrogen mixture burning appliance comprising a burner assembly as described above.
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Thus, a reliable and secure air-hydrogen mixture burning appliance may be provided.
Brief Description of the Drawings
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Exemplary embodiments of the present invention are described in detail hereinafter with reference to the attached drawings. In these attached drawings, identical or identically functioning components and elements are labelled with identical reference signs and they are generally only described once in the following description.
- Fig. 1
- shows a schematic view of an air-hydrogen mixture burning appliance with a burning unit according to the present invention,
- Fig. 2
- shows a schematic view and an enlarged detail view of the burning unit of Fig. 1 with a flat air-hydrogen mixture flow-through section,
- Fig. 3
- shows the schematic view and the enlarged detail view of the burning unit of Fig. 2,
- Fig. 4
- shows an illustrative pressure drop diagram for the burning unit of Fig. 1 to Fig. 3,
- Fig. 5
- shows a schematic view of the burning unit of Fig. 2 and Fig. 3 with a diffuser unit,
- Fig. 6
- shows a perspective view of the burning unit of Fig. 1 with a semi-cylindrical air-hydrogen mixture flow-through section, together with the diffuser unit of Fig. 5,
- Fig. 7
- shows a perspective view of the burning unit of Fig. 1 with a cylindrical air-hydrogen mixture flow-through section, and
- Fig. 8
- shows a front view of the burning unit of Fig. 7 with the cylindrical air-hydrogen mixture flow-through section.
Detailed Description
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Fig. 1 shows an illustrative burner assembly 100 for combustion of an air-hydrogen mixture 115, with an air-hydrogen mixing unit 110 and a burning unit 120. The air-gas mixing unit 110 is preferably adapted for mixing of air and hydrogen to form the air-hydrogen mixture 115. Preferentially, the air-hydrogen mixture 115 is a homogenous mixture of air and hydrogen.
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By way of example, the burner assembly 100 may be used in an associated air-hydrogen mixture burning appliance. More particularly, the burner assembly 100 is preferably at least adapted for use in domestic appliances up to 70 kW.
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Preferably, the burning unit 120 is embodied with a controlled pressure drop for a given air flow rate. More specifically, a controlled pressure drop ρ for a given air flow rate V in L/min of the burning unit 120 may be determined according to the equation 0.00265V2 + 0.007V > p > 0.001V2 + 0.01V, wherein an upper allowable pressure drop should be smaller than 0.00265V2 + 0.007V, and wherein a lower allowable pressure drop should be greater than 0.001V2 + 0.01V.
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Fig. 2 shows the burning unit 120 of Fig. 1 with an air-hydrogen mixture flow-through section 230. The burning unit 120 is preferably plate-shaped, i. e. formed as a burner plate. Illustratively, the plate-shaped burning unit 120 comprises a frame portion 210 that may be provided to enable mounting of the burning unit 120 to the burner assembly 100 of Fig. 1.
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By way of example, the air-hydrogen mixture flow-through section 230 is flat. However, other realizations are readily available to the person skilled in the art and described by way of example below at Fig. 6 to Fig. 8.
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More specifically, the air-hydrogen mixture flow-through section 230 embodies a burner surface 235 for combustion of an air-hydrogen mixture and comprises a plurality of slotted orifices 250 for flow-through of the air-hydrogen mixture to the burner surface 235 in order to enable combustion of the air-hydrogen mixture on the burner surface 235. For simplicity and clarity, only three slotted orifices of the plurality of slotted orifices 250 are separately labelled with the reference signs 252, 255, 257.
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Illustratively, the air-hydrogen mixture flow-through section 230 comprises a length 232 and a width 234 that is smaller than the length 232. By way of example, the air-hydrogen mixture flow-through section 230 is rectangular.
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The plurality of slotted orifices 250 may be arranged in the air-hydrogen mixture flow-through section 230 in at least one row in direction of, i. e. running along the direction of the length 232. Illustratively, the plurality of slotted orifices 250 is arranged in four rows 262, 264, 266, 268. By way of example, the row 262 comprises the slotted orifices 252, 255, 257, which are illustratively arranged in series therein.
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Furthermore, at least two rows and, illustratively, all rows 262, 264, 266, 268 may be arranged at least essentially in parallel to each other in direction of the width 234. Moreover, at least two rows and, illustratively all rows 262, 264, 266, 268 which are adjacent in the direction of the width 234 may be shifted relative to each other in the direction of the length 232.
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Furthermore, each slotted orifice of the plurality of slotted orifices 250 illustratively comprises a length and a width that is smaller than its length. By way of example, the slotted orifice 255 is described in more detail hereinafter representative for all slotted orifices of the plurality of slotted orifices 250.
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Illustratively, the slotted orifice 255 has a length 259 and a width 258 that is smaller than the length 259. Preferably, the width 258 amounts at most to 0.6 mm. Furthermore, the length 259 is preferably at least essentially arranged in parallel to the width 234 of the air-hydrogen mixture flow-through section 230. In other words, a respective angle formed between the length 259 and the width 234 amounts preferably exactly to 0°, but the expression "at least essentially" contemplates also a possible angular deviation of at most 3° to 5°, which may e. g. occur due to manufacturing tolerances.
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Fig. 3 shows the burning unit 120 of Fig. 2 with the air-hydrogen mixture flow-through section 230 that comprises the plurality of slotted orifices 250 for flow-through of air-hydrogen mixture to the burner surface 235. As explained above at Fig. 2, the plurality of slotted orifices 250 is illustratively arranged in the four rows 262, 264, 266, 268 and comprises the slotted orifices 252, 257, 257, which are illustratively arranged in series in the row 262.
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Preferably, adjacent slotted orifices of the plurality of slotted orifices 250 in each one of the rows 262 ,264, 266, 268 are spaced apart from each other by a predetermined distance that is greater than or equal to 1.1 mm. Illustratively and representatively, the slotted orifices 252, 255 are spaced apart from each other by a predetermined distance 358 which is greater than or equal to 1.1 mm.
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Fig. 4 shows an illustrative pressure drop diagram 400 for the burning unit 120 of Fig. 1 to Fig. 3. The pressure drop diagram 400 has an abscissa 410 associated with air flow rates in L/min and an ordinate 420 associated with illustrative pressure drops in mbar.
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More specifically, the pressure drop diagram 400 shows an upper graph 430 that illustrates an upper pressure drop limit according to the expression 0.00265V2 + 0.007V, and a lower graph 440 that illustrates a lower pressure drop limit according to the expression 0.001V2 + 0.01V. The two graphs 430, 440 delimit an area 450 that defines allowable pressure drops which may be used as the controlled pressure drop ρ for an associated air flow rate V in L/min of the burning unit 120 of Fig. 1 to Fig. 3, as described above at Fig. 1, according to the equation 0.00265V2 + 0.007V > p > 0.001V2 + 0.01V.
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Fig. 5 shows the burning unit 120 of Fig. 2 and Fig. 3 with the air-hydrogen mixture flow-through section 230 that embodies the burner surface 235 for combustion of an air-hydrogen mixture. Preferably, the burning unit 120 is configured to enable stabilisation and sustainment of a flame 540 of burning air-hydrogen mixture on the burner surface 235.
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Furthermore, a diffuser unit 520 may be provided for generating additional mixing of an air-hydrogen mixture prior to combustion. For instance, an air-hydrogen mixture may be produced and guided towards the diffuser unit 520, as illustrated with arrows 510. The diffuser unit 520 may then diffuse and distribute the air-hydrogen mixture for combustion, as illustrated with arrows 530.
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By way of example, the diffuser unit 520 is plate-shaped, i. e. formed as a diffuser plate, and arranged upstream of the burning unit 120. Alternatively, the diffuser unit 520 may be integrated into the burning unit 120 as an integral part thereof.
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Fig. 6 shows the burning unit 120 of Fig. 2 and Fig. 3 with the air-hydrogen mixture flow-through section 230 and the plurality of slotted orifices 250. The burning unit 120 further comprises the frame portion 210 that may be provided to enable mounting of the burning unit 120 to the burner assembly 100 of Fig. 1.
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Similar to Fig. 2 and Fig. 3, the burning unit 120 is plate-shaped. However, in contrast to Fig. 2 and Fig. 3 the air-hydrogen mixture flow-through section 230 of the burning unit 120 is now semi-cylindrical.
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Illustratively, the semi-cylindrical air-hydrogen mixture flow-through section 230 is only provided with the single row 262 of slotted orifices. Thus, the plurality of orifices 250 is arranged in Fig. 6 in the single row 262.
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By way of example, the burning unit 120 is further illustrated with an inner mounting structure 620 and together with the diffuser unit 520 of Fig. 5. Similar to Fig. 5, the diffuser unit 520 is plate-shaped, but now comprises in contrast to Fig. 5 a semi-cylindrical diffusing section 525. Furthermore, two laterally arranged, strip-shaped frame members 610 are provided to enable mounting of the diffuser unit 520 onto the inner mounting frame 620 of the burning unit 620.
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It should be noted that the diffuser unit 520 is illustratively shown with circular diffusing orifices. However, as the diffusing orifices as such are not part of the present invention and may be provided in various different shapes, which are readily available to the person skilled in the art, they are not separately labelled.
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Fig. 7 shows the burning unit 120 of Fig. 2 and Fig. 3 with the air-hydrogen mixture flow-through section 230 and the plurality of slotted orifices 250, which are arranged in a plurality of rows comprising the rows 262, 264, 266, 268. The burning unit 120 further comprises the frame portion 210 that may be provided to enable mounting of the burning unit 120 to the burner assembly 100 of Fig. 1.
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Similar to Fig. 2 and Fig. 3, the burning unit 120 is plate-shaped. However, in contrast to Fig. 2 and Fig. 3 the air-hydrogen mixture flow-through section 230 of the burning unit 120 is now cylindrical such that the burning unit 120 is illustratively formed by a convoluted plate. Thus, in the burning unit 120 according to Fig. 7 the circumference of the cylindrical air-hydrogen mixture flow-through section 230 is considered to define the length 232 of the air-hydrogen mixture flow-through section 230 according to Fig. 2 and Fig. 3.
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Fig. 8 shows the burning unit 120 of Fig. 7 with the cylindrical air-hydrogen mixture flow-through section 230 and the plurality of slotted orifices 250, which are arranged in a plurality of rows comprising the rows 262, 264, 266, 268. Fig. 8 further illustrates the parallel and shifted arrangement of the rows 262, 264, 266, 268.
