Premix gas burner for combusting a hydrogen-containing premix gas having an insertion element

Abstract

The present invention relates to a premix gas burner for combusting a premix gas comprising a fuel gas, said fuel gas preferably comprising at least 98% hydrogen, comprising an apertured tubular burner deck having a gas distribution facing inner surface and opposite combustion chamber facing outer surface, the burner deck having an open first end for receiving the premix gas and an opposite second end. an unapertured tubular insertion element positioned spaced apart from the inner surface of the burner deck, the insertion element having a gas distribution facing surface, wherein the insertion element has a closed first end, wherein the gas distribution facing surface of the burner deck (2) and the gas distribution facing surface of the insertion element delimit a gas distribution chamber between them that is closed at the second end of the burner deck, and wherein noise-reduction elements are provided in the gas distribution chamber.

Description

[0001] Title: Premix gas burner for combusting a hydrogen-containing premix gas having an insertion element

[0002] FIELD OF THE INVENTION

[0003] The invention pertains to a premix gas burner for combusting a hydrogen-containing premix gas containing at least 98 vol% of hydrogen, and to a heater system comprising such a burner.

[0004] BACKGROUND OF THE INVENTION

[0005] The control of thermoacoustic instabilities in combustions systems is a difficult problem facing many challenges with great technological relevance. Most combustion systems are designed to operate in stable regimes. However, oscillations sometimes occur in practical combustion systems such as gas turbines, furnaces and heating systems. One major group of combustion instabilities are thermoacoustic instabilities, which are excited by a feedback loop between an oscillatory combustion process and, in general, one or more of the natural acoustic modes of the system. Thermoacoustic instabilities are a widely known problem in the manufacture and operation of premix gas burners. For natural gas burners, a multitude of solutions have been devised to prevent or eliminate thermoacoustic instabilities.

[0006] EP1538395 for example discloses the provision of partitions within a burner deck of a premix burner that divides the inner space of the burner deck in longitudinal sectors. Dividing the inner space into sectors produces chambers so sized as to absorb the resonance frequencies that are generated in the burner.

[0007] EP3431872 furthermore discloses a tube extending in a mixing chamber of a cylindrical premix gas burner. The tube is attached to an end cap of the premix burner, and an opposite end of the tube is open. The length of the tube is selected such that the length is approximately a quarter of the wavelength of the noise that would occur when the tube is not provided, thereby cancelling out the wave.

[0008] These solutions are known and widely used for the present natural gas burners, that usually have thermoacoustic issues at relatively low frequencies, e.g. 100-500 Hz. Today, however, a major transition toward hydrogen-based premix burners is underway. The thermoacoustic instabilities of hydrogen burners occur at much higher frequencies, e.g. in the range of 500-3000 Hz. The existing measures have therefore been shown to be ineffective against preventing or eliminating thermoacoustic instabilities in these novel hydrogen burners. Burners for combustion of hydrogen are difficult to develop, a well-known solution to solve the problems for combustion of hydrogen comprises by using clusters as laid down in EP2020087802, which is incorporated herein by reference.

[0009] DESCRIPTION OF THE INVENTION

[0010] The present invention aims to overcome those disadvantages at least partly or to provide a usable alternative. In particular the present invention aims to provide a premix burner for the combustion of a fuel gas consisting largely of hydrogen which has little to no thermos-acoustic instabilities.

[0011] This object is achieved by a premix gas burner for combusting a premix gas comprising a fuel gas, said fuel gas preferably comprising at least 98% hydrogen, comprising an apertured tubular burner deck having a gas distribution facing inner surface and opposite combustion chamber facing outer surface, the burner deck having an open first end for receiving the premix gas and an opposite second end, an unapertured tubular insertion element positioned spaced apart from the inner surface of the burner deck within the burner deck, the insertion element having a gas distribution facing surface, wherein the insertion element has a closed first end, wherein the gas distribution facing surface of the burner deck and the gas distribution facing surface of the insertion element delimit a gas distribution chamber between them that is closed at the second end of the burner deck, and wherein noise-reduction elements are provided in the gas distribution chamber.

[0012] The premix gas burner according to the invention is suitable for combusting a hydrogen-containing premix gas containing at least 98 vol% of hydrogen. The design of the burner allows a stable combustion of a hydrogen-containing premix gas containing at least 98 vol% of hydrogen.

[0013] The premix gas burner comprises an apertured tubular burner deck. The burner deck has a first end closest to the gas inlet and a second end extending into a combustion chamber. The burner deck provides the basis for the flame or flames when the premix gas burner is in use. The burner deck has a gas distribution facing inner surface and a combustion chamber facing outer surface, opposite of said inner surface of the burner deck. The combustion chamber facing outer surface faces the combustion chamber where the combustion of the hydrogen-containing premix gas that has passed through the apertured burner deck takes place.

[0014] A plurality of apertures is provided in the burner deck that extend through the burner deck from the gas distribution facing surface to the combustion chamber facing outer surface. These gas outflow apertures allow hydrogen-containing premix gas to flow from a gas supply to a combustion chamber adjacent the combustion chamber facing outer surface of the burner deck. The combustion chamber facing outer surface of the burner deck forms part of the outer surface of the premix gas burner.

[0015] The gas outflow apertures have a dimension, a total outflow surface (a.k.a. port) and mutual position to allow combustion of the hydrogen-containing premix gas in the combustion zone. Many, but not all, configurations of gas outflow apertures and the pattern or patterns in which they are arranged in the metal burner deck plate allow combustion of the hydrogencontaining premix gas in the combustion zone (in the combustion chamber) in a stable and safe manner. The skilled person is aware of combinations of dimensions and mutual positions that allow a safe and reliable combustion of hydrogen-containing premix gas in the combustion zone. Like for instance shown in W02021140036A1. The gas outflow apertures can be made in the metal burner deck plate in various ways, e.g. by punching, laser cutting, laser drilling, etching, (metal) die casting and / or mechanical drilling or deforming.

[0016] The metal burner deck plate is or comprises for example a flat plate, and / or made from a flat plate which has for example be pressed or rolled in the desired tubular shape (either cylindrical or non-cylindrical), and / or is made using moulding or casting techniques.

[0017] The premix burner furthermore comprises an insertion element that is positioned within the burner deck. The insertion element comprises a first end closest to the gas supply and a second end extending into the combustion chamber. The second end of the insertion element may be connected to the second end of the burner deck. The insertion element comprises a gas distribution facing outer surface that is spaced apart from the gas distribution facing inner surface of the burner deck. The gas distribution facing surface of the insertion element and the gas distribution facing inner surface of the burner deck delimit a gas distribution chamber between them. This gas distribution chamber is closed at the second end of the burner deck, preferably by connecting the second end of the burner deck with the second end of the insertion element. This may for example be achieved by welding the second end of the burner deck and the second end of insertion element, for example by using an annular connecting part. A gas tight connection between the second end of the burner deck and the second end of the insertion element is therewith obtained, such that leakage of uncombusted premix gas to the combustion chamber is prevented. Due to the insertion element the internal volume of the burner in the distribution chamber, containing the uncombusted premix gas is significantly reduced, which reduces the risk of flame flashback.

[0018] The first end of the tubular insertion element, said end being closest to the gas supply, may be closed by e.g. a closing element. This implies that the first end of the insertion element is gas tight, and no uncombusted hydrogen-containing premix gas may enter into the insertion element. This prevents uncombusted premix gas from mixing in with the combusted gasses in the combustion chamber. Moreover, this prevents any accumulation of premix gas within the premix burner, which is a potential problem for flame flashback or self-ignition at high temperatures.

[0019] The gas distribution chamber of the premix gas burner is adapted to receive the hydrogen-containing premix gas. For example, a gas supply system comprising for example an air supply duct, a gas valve, a fan, and a premix supply duct is provided to supply the premix gas containing at least 98 vol% of hydrogen to the gas distribution chamber of the premix gas burner. Due to the closed first end of the insertion element, supplied premix gas may only enter the gas distribution chamber, from where the premix gas flows through the gas-outflow apertures in the burner deck to the combustion chamber adjacent the combustion chamber facing surface of the burner deck.

[0020] It has been found by the inventors of the present invention that having an insertion element within the burner deck, provides an enormous reduction in noise levels. This may be the result of the insertion element preventing large temperature fluctuations in the inner space of the burner deck. These temperature fluctuations are very often the cause of thermoacoustic instabilities, and therefore cause a part of the noise of a burner. By having an insertion element within the burner deck these thermoacoustic instabilities are therefore reduced.

[0021] Another advantage of the insertion element is that the premix gas is more evenly distributed over the apertures of the burner deck. As the volume of the gas distribution chamber is significantly smaller with the insertion element, the flow rates in the gas distribution chamber, and thus near the apertures, of the premix gas will be much higher. Due to the higher flow rate and the resulting locally higher pressures, the chances of flame flashback are reduced. In addition, the total volume of premix gas in the burner is lower. So should impact occur, the effects are less severe.

[0022] In addition, the reduced volume of the burner provides advantages for the reduction of flashback and self-ignition. Flashback and self-ignition of the premix gas may be due to several reasons, e.g. too hot burner surface or a large shift of air excess. This applies to every burner but is especially the case for relatively large burners (e.g. with a diameter larger than 70 mm, preferably a diameter in the range of 70-500 mm, and more preferably in the range of 90-400 mm, such as 95-350 mm), that inherently have a high volume gas distribution chamber within the burner. A large shift of air excess factor (beyond the nominal adjustment) may occur as a result of a low pressure, high temperature, high relative humidity or high inlet pressure of the premix gas. The chance of a large shift in air excess, especially when the inlet air temperature is high, may be reduced by preheating the gas inlet, e.g. by passing the inlet air along the gas inlet tube. Consequently, because of the higher gas temperature, the amount of premix gas flowing in the gas distribution chamber will be reduced. This will slightly increase the total gas / air temperature, but the air excess factor will reduce significantly with a combined effect of significantly reducing the burning velocity, and thus reducing the chance of flashback.

[0023] The premix gas burner may optionally further comprise a gas distributor. The gas distributor may comprise a perforated metal plate which is arranged inside the gas distribution chamber with the aim of obtaining an even distribution of the premix gas to the gas outflow apertures of the burner deck. The design and use of such gas distributors is widely known in the field of premix gas burners.

[0024] The premix burner furthermore comprises noise-reduction elements that are provided within the gas distribution chamber. During operation of the burner, a standing wave may occur at the perimeter of the gas distribution chamber resulting in thermoacoustic instabilities. The likelihood thereof is particularly high for hydrogen burners, where the thermoacoustic instabilities have a frequency that strongly corresponds to the circumference of the gas distribution chamber. By having noise-reduction elements provided within the gas distribution chamber, the formation of the standing wave is prevented.

[0025] The noise-reduction elements are preferably provided at asymmetric positions within the gas distribution chamber as seen in the radial direction. Advantageously, the asymmetric positions of the noise-reduction elements prevent the occurrence of one large standing wave in the entire circumference of the gas distribution chamber, and simultaneously prevent the formation of two or more smaller waves that would occur when the elements would be positioned at symmetric positions.

[0026] In an embodiment of the invention, the noise-reduction elements are two or more separation walls provided in the gas distribution chamber. The separation walls may extend in the longitudinal direction of the burner deck. The separation walls may for example extend from the first end to the second end of the burner deck or from the first end to the second end of the insertion element. The separation walls preferably extend in a straight line in the longitudinal direction of the burner deck, but may also encompass another shape, such as a spiral shape. The separation walls furthermore preferably extend over the entire width of the gas distribution chamber, i.e. from the insertion element to the burner deck. Optionally, the separation walls are connected to the insertion element and / or the gas distribution chamber facing surface of the burner deck. Preferably the separation walls are only connected, e.g. by welding or clamping to the insertion element, and have only limited thermal contact to the inside of the burner deck or second end of the ring or endcap. This reduces the stress caused by temperature difference and prevents unwanted local cooling of the burner deck and thus additional heating of the premix gas.

[0027] It is preferred to provide two separation walls at asymmetric positions in the gas distribution chamber, but it is also possible to provide three or more separation walls, such as four or more. Preferably, all separation walls are provided at asymmetric positions as seen in the circumferential direction. However, when placing more than two separation walls, some separation walls may be positioned at symmetric positions, while some are placed asymmetrically, as seen in the circumferential direction.

[0028] The premix hydrogen burner mounted in a hydrogen boiler, according to the invention may replace an existing natural gas burner in a natural gas boiler. Typical residential burners of 24 kW using 1500m3 / year of natural gas, which are replaced by a hydrogen burner, using green H2, will each safe 2.6 ton CO2 emitted per year Every 1 million burners replaced will safe 2.6 Mton CO2 emissions per year. If gradually in Europe during 10 years’ time 30 million households are converted to hydrogen, an annual reduction of almost 80 Mton CO2 can be achieved.

[0029] Hydrogen burners emits far less NOx emission than conventional methane gas burners, or oil burners. With a typical saving of 41 mg / kWh for a methane burner, and even 69mgram for an oil burner. With only taking the natural gas boiler replacement into account a saving of 0.58 kg / year NOXper boiler may be achieved. Assume 50% of the houses in the Netherland convert to hydrogen combustion 2.32 Mkg NOXemission per year can be saved which is almost 4% of the yearly NOXemissions of the Netherlands.

[0030] In an embodiment of the invention, the insertion element comprises an open second end that faces the combustion chamber. An advantage thereof is that the combusted air may therefore enter into the inner space of the insertion element without mixing in with the supplied premix gas. The open second end has demonstrated many benefits for the functioning of hydrogen-containing premix gas burners. Because of the open second end, undesired heating of the insertion element is prevented, as will be the case for insertion elements that have a solid interior. These solid insertion elements retain too much heat which is transferred to the supplied premix gas in the gas distribution chamber. Such heated premix gas in the gas distribution chamber therefore would involve a higher risk of self-ignition before leaving the gas distribution chamber or flashback due to a higher temperature. Another advantage of the open second end is that due to the closed first end of the insertion element the internal volume of the burner in the distribution chamber, containing the gas / air mixture is significantly reduced.

[0031] Insertion elements with open second ends are only compatible with premix burners which combust fuels with a very high amount of hydrogen, such as a hydrogen-containing premix gas containing at least 98 vol% of hydrogen according to the present invention. These insertion elements when incorporated in prior art burners, that burn (partially) natural gas, will generate NOXand CO in large amounts during combustion. This is due to the combusted gasses in the combustion chamber accumulating in the open end of the insertion element, and the combustion taking place at low temperatures. Unfortunately, the conditions in the inner space of the insertion element, particularly the stagnant air and temperature, are such that exorbitant amounts of NOX, and CO will be formed. The use of such an insertion element with open top is therefore not suitable for burners which burn natural gas or a mixture of hydrogen and mainly natural gas.

[0032] In an embodiment of the invention, the wall of the insertion element is parallel with the wall of the burner deck. An advantage thereof is that the parallel walls of the insertion element and the burner deck form a gas distribution chamber which has a uniform thickness over the entire length and circumference of the gas distribution chamber. As a result, only a limited number of frequencies can form a standing wave in these areas, thereby reducing the undesired thermoacoustic noises.

[0033] Alternatively, the wall of the insertion element may be tapered. An advantage thereof is that the hydrogen-containing premix gas that enters the gas distribution chamber is more evenly distributed over the apertures in the burner deck. This is especially the case when having a uniform aperture pattern or a cluster pattern. Better mixing of the fuel gas prevents disproportionate distribution of the fuel gas and therefore decreases the probability of thermos-acoustic instabilities.

[0034] Alternatively, a part of the wall of the insertion element is parallel with the burner deck, while another part of the wall of the insertion element is tapered.

[0035] Optionally, the insertion element comprises a stepped second end. The stepped second end preferably comprises a circumference that corresponds to the diameter of the second end of the burner deck. This advantageously allows the insertion element to be connected to the burner deck, e.g. by welding. Alternatively, the second end of the burner deck may be crimped to correspond to the diameter of the second end of the insertion element, or the second end of the insertion element may be flared to correspond to the second end of the burner deck.

[0036] In an embodiment of the invention, the first end of the insertion element that is provided in the premix gas burner extends beyond the first end of the burner deck. The first end of the insertion element may thus extend into e.g. a gas supply duct that is connected to the burner deck.

[0037] An advantage thereof is that the first end of the insertion element improves the mixing of the hydrogen-containing premix gas that is supplied through the gas supply duct. This improved mixing has many advantages: as a result of the improved mixing, chances of the thermoacoustic instabilities arising are lowered, and undesired noises are therewith prevented. In addition, there is a better outflow distribution over the gas outflow apertures, which therefore results in a better proportional temperature distribution and thus a decrease in thermoacoustic instabilities. Moreover, the mixing reduces the likelihood of local fluctuations in the hydrogen concentration around some of the burner deck outflow apertures, which may increase the risk of flame flashback due to the locally higher flame velocity of the mixture.

[0038] The pressure drop within the gas distribution chamber may be optimized according to the shape of the part of the insertion element that protrudes beyond the first end of the burner deck. For example, a short distance between the protruding part of the insertion element and the walls of the gas inlet may result in a large increase in pressure drop. Optionally and preferably, at least the part of the insertion element that extends beyond the first end of the burner deck is tapered or conically shaped. Is has been found that such a shape provides the most advantages in relation to the pressure drop.

[0039] In an embodiment of the invention, the first end of the insertion element is closed by a closing element extending in the width direction beyond the circumference of the tubular insertion element. The closing element may extend beyond the entire circumference of the insertion element, or just a part thereof.

[0040] An advantage thereof is that, when the closing element extends in the width direction beyond the circumference of a part of the insertion element, it allows the closing element to function as a flash-back preventor in the case of flashbacks. During a flash back, ignited gas will shoot back into the burner at a high velocity and pressure. The closing element functions as a blockage for the flames, thereby slowing down the flame and reducing the damage sustained from the flash back.

[0041] Another advantage thereof is the thickness of the closing element during gas inlet may improve the mixing of the premix.

[0042] Optionally, the closing element is tapered or conically shaped. This advantageously improves the distribution of the hydrogen-containing premix gas into the gas distribution chamber.

[0043] In an embodiment of the invention, the diameter of the insertion element is 70-99%, preferably 60-95% of the diameter of the burner deck. The diameter of the insertion element and the burner deck determines the width of the circumference of the gas distribution chamber at the inlet of the gas distribution chamber.

[0044] An advantage thereof is that gas distribution chambers of such volumes result in an optimal reduction of thermoacoustic instabilities. At the same time, the volume reduction of the gas distribution chamber is beneficial in the prevention of flame flashback. Generally, for residential and small commercial heater systems, the width of the gas distribution chamber in the burner is 3-18mm, more preferably 6-15, and even more preferably 8-12mm. Having a gas distribution chamber that is too wide is undesirable, as this may cause recirculation of the gas within the gas distribution chamber. This may result in a pressure drop or unwanted heating of the premix gas.

[0045] An example of a premix gas burner comprises a burner deck with a diameter of 98 mm and a cross-sectional surface are of 7542 mm2. The insertion element may have a diameter of 78.8 mm such that the width of the gas distribution chamber is 9.6 mm. The insertion element therefore obstructs 65% of the cross-sectional surface area of the burner deck, allowing the premix gas to flow through the gas distribution chamber which has a cross- sectional surface of only 2666 mm2.

[0046] For larger commercial heater systems with burner diameters above 120mm the preferred width of the gas distribution zone is between 3% and 15% of the burner deck diameter, preferably between 5% and 13% of the burner deck diameter, and even more preferably between 7% and 12% of the burner deck diameter.

[0047] In an embodiment, the gas outflow apertures are arranged in clusters on the burner deck. The average of all adjacent heart-to-heart distances between adjacent gas outflow apertures in the same cluster is smaller than the smallest heart-to-heart distance between a first gas outflow aperture in a first cluster and a second gas outflow aperture in a second cluster, the second cluster being adjacent to the first cluster.

[0048] In an embodiment of the invention, insulation material is on a surface of the insertion element. The insulation material may for example be vermiculite a magnesium ferro aluminium silicate. The insulation material may be provided as a coating or as layers applied on the surface. It is preferred to have the insulation material to be placed on the combustion chamber facing of the insertion element. This prevents the insulation material from affecting conditions in the gas distribution chamber. Alternatively, however, the insulation material may also be provided on the gas distribution facing surface.

[0049] An advantage of the insulation material is that it prevents excessive heating of the insertion element, which may cause undesired heating of supplied hydrogen-containing premix gas in the gas distribution chamber. Heating of the premix gas before it has left the gas distribution chamber may cause self-ignition of the gas. Unequal heating of the walls may also induce thermoacoustic instabilities.

[0050] In an embodiment of the invention, the longitudinal axis of the insertion element and the longitudinal axis of the burner deck are positioned parallel and eccentrically. Consequently, the width of the gas distribution chamber is not equal over the entire circumference of the gas distribution chamber. Instead, the gas distribution chamber comprises a part of the circumference that has a larger width than the opposite circumferential side of the gas distribution chamber. The insertion element may for example, in a horizontally positioned burner, be positioned such that the gas distribution chamber has a larger width at the top of the gas distribution chamber than at the bottom of the gas distribution chamber. This is especially advantageous in a burner that is placed in non- symmetrically burner room of a heat exchanger: The volume of the gas distribution chamber at the top is larger than the volume of the gas distribution chamber at the bottom. As a result, the outflow velocity of the premix gas through the burner deck is slightly higher at the top of the gas distribution chamber, which decreases the chances of flame flashback. Surprisingly it was found that the overall pressure drop of a burner with an eccentrically placed insertion element, is lower than a symmetrically placed insertion element.

[0051] In the embodiment of the insertion element with a longitudinal axis which is parallel and eccentric to the longitudinal axis of the burner deck noise-reduction elements also prevents the circular gas flow around the insert, which cause unwanted recirculation and heating of the gas / air mixture, and with this reducing the risk of flash back or self-ignition. However, the eccentrically placed insertion element may be used without noise-reduction elements to obtain the reduction in pressure drop.

[0052] In an embodiment of the invention, the coefficient of expansion of the insertion element and the coefficient of expansion of the burner deck are similar, and preferably equal. The insertion element and the burner deck are for example made of substantially the same material. The material of the insertion element and the burner deck is for example stainless steel, such as 1.4509 or 1.4016 stainless steel or heat resistant stainless steel.

[0053] An advantage thereof is that, during operation of the burner, the stresses on the burner deck and insertion elements are at their lowest when the two have been manufactured from materials that have substantially the same coefficient of expansion.

[0054] Alternatively, the insertion element may consist of a ceramic material. An insertion element may also consist of a vermiculite or foam plate to reduce the volume of the gas distribution chamber and therewith reduce thermoacoustic instabilities.

[0055] In an embodiment of the invention, the insertion element has a wall thickness that is equal to or smaller than a wall thickness of the burner deck. An advantage thereof is that an equal or smaller, preferably smaller, wall thickness of the insertion element prevents that too much heat is stored in the wall of the insertion element during operation of the burner. Stored heat may be detrimental to function of the burner, as a high temperature insertion element may heat the hydrogen-containing premix gas when it enters the gas distribution chamber. As a result, the premix gas is already too warm before leaving the apertures and may therefore self-ignite or the premix gas is significantly heated up which causes that the flame velocity increases which may result in flashback.

[0056] In an embodiment of the invention, a textile fabric, comprising heat resistant fibers, is provided along the top part of the outer surface of the burner deck, not covering the burner deck apertures, wherein the textile fabric has a fabric section extending freely at the second end of the burner deck. Such a textile fabric section is disclosed in WO2019057483.

[0057] An advantage thereof is that the fabric section of the textile fabric is configured for providing a seal along the circumference of the burner deck between the second end of the burner and the end wall of the combustion chamber when the burner is in use, which prevents heating of the insertion element.

[0058] In an embodiment of the invention, a textile fabric is provided at the open first end of the burner deck. Optionally, the textile fabric covers the entire first end of the burner deck. Alternatively, the textile fabric is equal to the width of the gas distribution chamber.

[0059] The textile fabric at the open first end of the burner deck advantageously functions as a flame retarder and thus reduces any damages that may be the result of flame flashback.

[0060] The invention further pertains to a heater system comprising a premix gas burner according to the invention. The heater system for example is or forms part of a building heater system, a hot water system, e.g. a domestic hot water system or utility hot water system. Optionally, in this embodiment the heater system comprises a heat exchanger, which has a heat exchanger inlet, a heat exchanger outlet and a heat exchanger passage which extends from the heat exchanger inlet to the heat exchanger outlet.

[0061] In an embodiment of the heater system, the heater system comprises a heat exchanger with a heat load of up to 100 kW and a burner according to the invention with a diameter in the range of 50-120 mm. Heater systems with such a heat load are generally intended for domestic use or small commercial applications.

[0062] In an embodiment of the heater system, the heater system comprises a heat exchanger with a heat load of at least 100 kW and a burner according to the invention with a diameter in the range of 90-500 mm. Heater systems with such a heat load are generally intended for large commercial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The invention shall now be explained in more detail below by means of describing some exemplary embodiments in a non-limiting way with reference to the accompanying drawings, in which:

[0064] - Fig. 1 : schematically, a cross-sectional side view of a first embodiment of a premix gas burner according to the invention (including a flange);

[0065] - Fig. 2a: schematically, a bottom view of the premix gas burner of Fig. 1;

[0066] - Fig. 2b: schematically, a bottom view of a premix gas burner with an insertion element that is positioned parallel and eccentric to the burner deck;

[0067] - Fig. 3a: schematically, a cross-sectional side view of a further embodiment of a premix gas burner according to the invention, having an insertion element with a tapered tubular shape;

[0068] - Fig. 3b: schematically, a cross-sectional side view of a further embodiment of a premix gas burner according to the invention, having an insertion element that extends beyond the burner deck;

[0069] - Fig. 4: schematically, a cross-sectional side view of a further embodiment of a premix gas burner according to the invention with a closing element:

[0070] - Fig 5: schematically, a cross-sectional side view of a further embodiment of a premix gas burner according to the invention.

[0071] - Fig. 6 schematically, a cross-sectional side view of a further embodiment of a premix gas burner according to the invention having a a textile fabrics provided along the top of the outer surface of the burner deck;

[0072] - Fig. 7 schematically, a cross-sectional side view of an embodiment of a premix gas burner according to the invention arranged within a heat exchanger.

[0073] Throughout the figures, the same reference numerals are used to refer to corresponding components or to components that have a corresponding function.

[0074] DETAILED DESCRIPTION OF THE DRAWINGS

[0075] In fig. 1, a premix gas burner is shown that has been given the reference numeral 1. The premix gas burner 1 of fig. 1 comprises a tubular burner deck 2, having a cylindrical shape with a circular cross-section. In this embodiment a flange 4 is provided on a first end 6 of the burner deck 2. The flange 4 may be used for mounting the burner deck 2 in a heating appliance. The burner deck 2 extends with a second end 8 into a combustion chamber 10. The apertured burner deck 2 (apertures not shown) has a gas distribution inner surface 12, which faces a gas supply side, and a combustion chamber facing outer surface 14 on the opposite side. The combustion chamber facing outer surface 14 is facing a combustion chamber 10, where the combustion of the hydrogen-containing premix gas that has passed through the premix gas burner 1 takes place. The combustion chamber facing outer surface 14 of the burner deck 2 forms part of the outer surface of the premix gas burner 1.

[0076] Positioned within an inner space of the burner deck 2 is an unapertured tubular insertion element 16. The tubular insertion element 16 has a gas distribution facing surface 18 that is positioned spaced apart from the gas distribution facing inner surface 12 of the burner deck 2 to delimit a gas distribution chamber 20 between the two. The insertion element 16 has a first end 22 nearest the gas supply, and a second end 24 that extends into the combustion chamber 10. The insertion element 16 is with a second end 24 connected to the second end 8 of the burner deck 2, preferably by welding. This for example implies that any seals, welds or other connection elements are gas tight for this kind of premix gas. In this embodiment, the second end 24 of the insertion element 16 is flared. The flared second end 24 has an outer circumference that corresponds to the diameter of the burner deck 2, which facilitates easy welding.

[0077] Advantageously, the insertion element prevents high temperature gradients within the inner space of the burner deck 2. These temperature gradients are often the cause of thermos-acoustic instabilities in the premix burner 1. By placing an insertion element 16 within the burner deck 2 may thus prevent unwanted noises.

[0078] The second end 24 of the insertion element 16, which extends into the combustion chamber, is open. Combusted air from the combustion chamber 10 may therefore enter into the inner space of the insertion element 16 without mixing in with the supplied fuel. The open second end 24 has demonstrated many benefits for the functioning of hydrogen-containing premix gas burners. Because the second end 24 of the insertion element 16 is open, undesired heating of the insertion element 16 is prevented. This undesired heating would especially be the case with solid insertion elements whose interior space is completely filled, e.g. with a kind of metal. The material in the interior space would store and hold too much heat and therewith heat up the supplied hydrogen-containing premix gas before it leaves the gas distribution chamber. This results in a higher risk of self-ignition or flashback of the premix gas in the gas distribution chamber. Having a hollow insertion element 16 that is closed at the second end 24 would provide risks of explosions, as the pressure within the insertion element 16 may rise above a certain threshold limit. An open second end 24 prevents this pressure build up in the insertion element 16 and therefore eliminates risks of explosions.

[0079] The first end 22 of the tubular insertion element 16, said end being closest to the gas supply, is closed by a closing element 26. This implies that first end 22 of the insertion element 16 is gas tight, and no supplied hydrogen-containing premix gas flows into the insertion element 16. The closing element 26 is in this embodiment tapered to allow a better distribution of gas into the gas distribution chamber 20.

[0080] Hydrogen-containing premix gas is fed to the gas distribution chamber as shown by arrow F. The metal burner deck 2 further comprises a plurality of gas outflow apertures (not shown) that extend through the metal burner deck 2 from the gas distribution facing inner surface 12 to the combustion chamber facing outer surface 14. These gas outflow apertures allow the hydrogen-containing premix gas to flow to the combustion chamber 10, adjacent to the combustion chamber facing outer surface 14 of the metal burner deck 2. Because of the closed first end 22 of the insertion element 16, supplied gas can only move from the gas supply, into the gas distribution chamber 20, from where it flows through the apertures in the burner deck 2 into the combustion chamber 10.

[0081] In the embodiment shown in the figure the insertion element 16 has a circumferential wall that is substantially parallel to the circumferential wall of the burner deck 2. Advantageously, the parallel walls of the insertion element 16 and the burner deck 2 form a gas distribution chamber 20 which has a uniform thickness over the entire length and circumference of the gas distribution chamber 20. As a result, only a limited number of frequencies can form a standing wave in these areas, reducing the likelihood of undesired thermoacoustic noises. The burner furthermore comprises noise-reduction separation walls (see Fig. 2a) within the gas distribution chamber 10.

[0082] In the embodiment shown in the figure the closing element 26 of the insertion element 16 extends beyond the flange 4 of the burner deck 2. Advantageously, having the insertion element 16 extending into the gas supply duct improves the mixing of the premix before it enters the gas distribution chamber 20, thereby further reducing the risk of thermoacoustic instabilities.

[0083] In the embodiment shown in the figure, the insertion element and the burner deck have a substantially equal wall thickness. A wall thickness of the insertion element 16 that is equal to or smaller than the wall thickness of the burner deck 2 prevents an excessive amount of heat to be stored in the wall during operation of the burner. Stored heat may be detrimental to function of the burner 1, as a high temperature insertion element 16 may heat the hydrogen-containing premix gas when it enters the gas distribution chamber 20. As a result, the premix gas is already too warm before leaving the apertures and may therefore self-ignite or cause flashback. It is preferred that the insertion element 16 and the burner deck 2 are manufactured from materials having a similar or equal coefficient of expansion. This prevents an excessive amount of stress on the premix burner 1 when the premix burner 1 is in operation. The burner deck 2 and insertion element 16 are therefore preferably also manufactured from the same material, such as 1.4509 or 1.4016 or heat resistant stainless steel. In the embodiment of fig. 1 , the premix gas burner 1 optionally further comprises a gas distributor (not shown). The gas distributor may comprise a perforated metal plate which is arranged inside the gas distribution chamber with the aim of obtaining an even distribution of the premix gas to the gas outflow apertures (not shown) of the metal burner deck 2. The design and use of such gas distributors is widely known in the field of premix gas burners.

[0084] Fig. 2a shows, schematically, a bottom view of the burner of Fig. 1. In Fig. 2a the insertion element 16 and the burner deck 2 are positioned coaxially. An advantage thereof, especially when the circumference of the burner deck 2 and the insertion element 16 are substantially parallel over the entire length of the two, is that the width of the gas distribution chamber 20 is substantially even over the entire length and circumference of the gas distribution chamber 20. Consequently, a limited number of frequencies can stand in the longitudinal direction of the gas distribution chamber.

[0085] In fig. 2b the insertion element 16 and the burner deck 2 are positioned parallel and eccentrically. This arrangement may be beneficial for the distribution of the premix over the gas distribution chamber 20, especially if this burner room is not symmetric.

[0086] In both embodiments of fig. 2a and 2b, two separation walls 28, 30 are provided in the gas distribution chamber 20. Said separation walls 28, 30 extend in the longitudinal direction of the burner deck 2. The separation walls 28, 30 for example extend between the first 6 and the second end 8 of the burner deck 2, or from the first 22 to the second end 24 of the insertion element 16. The separation walls 28, 30 may furthermore extend over the entire width of the gas distribution chamber, i.e. from the insertion element 16 to the gas distribution facing surface 12 of the burner deck 2. The separation walls 28,30 and the burner deck 2 however preferably have only limited thermal contact. A small gap may for example be present between the separation walls and the burner deck 2. These separation walls are provided at asymmetric positions as seen in the radial direction in the gas distribution chamber 20. Advantageously, the separation walls 28, 30 prevent the formation of a standing wave in the circumferential direction of the burner deck 2, which would result in thermosacoustic noises. Although two separation walls 28, 30 are shown in this embodiment, three or more separation walls may also be provided, either extending over the entire length of the burner deck 2 or the insertion element 16 or extending over a part thereof. All separation walls 28, 30 are preferably positioned asymmetrically.

[0087] Fig. 3a and 3b both show, schematically, a cross-section of a side view of a premix burner 1 with an embodiment of an insertion element 16 according to the invention. In both figures, an insertion element 16 is shown having a tapered tubular shape. The tapered shape advantageously ensures that the hydrogen-containing premix gas in the gas distribution chamber 20 is evenly distributed over the apertures (not shown) in the burner deck 2. Better mixing of the fuel gas prevents disproportionate distribution of the fuel gas and therefore decreases the probability of thermoacoustic instabilities.

[0088] The insertion element 16 in these embodiments has a flat closing element 26 on the first side of the insertion element 16, but may also have other shapes, such as a tapered shape or conical shape. A tapered or conical shape advantageously further enhances the mixing and distribution of the hydrogen-containing premix gas, and might reduce the pressure drop.

[0089] In Fig. 3a, the insertion element 16 is in its entirety surrounded by the burner deck 2. In contrast, in fig. 3b, the insertion element 16 extends beyond the first end 4 of the burner deck 2, where generally a duct discharge for the supply of the hydrogen-containing premix gas is positioned. The insertion element 16 extending beyond the first end 4 of the burner deck 2 advantageously allows even better mixing of the premix gas, which, as mentioned before, advantageously reduces the chances of thermoacoustic instabilities.

[0090] Fig. 4 shows, schematically, a further embodiment of the premix burner 1 according to the invention. As in Fig. 3b, the insertion element 16 in this embodiment extends beyond the first end 4 of the burner deck 2, in the duct discharge of the premix gas. The insertion element 16 further comprises a closing element 26 on the first end 22 of the insertion element 16. The closing element 26 in this embodiment has a tapered shape, but may have other shapes as well, such as a conical shape. This advantageously allows the hydrogen-containing premix gas to easily pass the closing element 26, while also being properly mixed during passing of the closing element 26.

[0091] The closing element furthermore extends in the width direction beyond the circumference of the first end 22 of the insertion element 16. The closing element 26 may extend beyond the entire circumference of the insertion element 16, or just a part thereof. Such a configuration, wherein the closing element 26 extends in the width direction beyond the circumference of a part of the insertion element 16 allows the closing element 26 to function as a flash-back preventor in the case of flashbacks, during a flash back, ignited gas will shoot back into the burner at a high velocity and pressure, the closing element 26 causes the ignited gas to encounter a roadblock, slowing the flame, and reducing the damage sustained from the flash back. It is preferred that the closing element 26 is positioned in the premix gas inlet, but alternatively, the closing element 26 may also be positioned within the burner deck 2.

[0092] Fig. 5 shows, schematically, a further embodiment of the premix burner 1 according to the invention. The second end 24 of the insertion element 16 is stepped such that the diameter of the stepped second end 24 of the insertion element 16 corresponds to the diameter of the second end 8 of the burner deck 2. This advantageously allows easy connection of the insertion element 16 to the burner deck 2, e.g. by welding (shown as the dot).

[0093] Fig. 6 schematically shows a premix gas burner 1 with an insertion element 16 according to the invention having a textile fabric 32 comprising heat resistant fibers provided along the outer surface of the burner deck 2. The textile fabric 32 has a fabric section extending freely at the second end of the burner deck 2. An advantage thereof is that the fabric section of the textile fabric 32 is configured for providing a seal along the circumference of the burner deck 2 between the second end 8 of the burner deck 2 and a wall of the burner chamber 10 when the burner 1 is in use, which prevents heating of the insertion element 16.

[0094] Fig. 7 shows a premix gas burner 1 according to the invention in a heat exchanger 34. The premix gas burner 1 is arranged horizontally. The premix gas burner 1 comprises an insertion element 16 having a longitudinal axis that is parallel and eccentric to the longitudinal axis of the burner deck 2. The insertion element 16 is positioned such that the gas distribution chamber 20 has a larger width at the top of the gas distribution chamber 20 than at the bottom of the gas distribution chamber 20. As a result, the volume of the gas distribution chamber 20 at the top is larger than the volume of the gas distribution chamber 20 at the bottom. The outflow velocity of the premix gas through the burner deck is therefore slightly higher at the top of the gas distribution chamber 20, which decreases the chances of flame flashback. Alternatively, the insertion element may also be positioned relative to the burner deck such that the width of the gas distribution chamber at the bottom is larger than the width of the gas distribution chamber at the top.

Claims

CLAIMS1. Premix gas burner (1) for combusting a premix gas comprising a fuel gas, said fuel gas preferably comprising at least 98% hydrogen, comprising an apertured tubular burner deck (2) having a gas distribution facing inner surface and an opposite combustion chamber facing outer surface, the burner deck (2) having an open first end (6) for receiving the premix gas and an opposite second end (8), an unapertured tubular insertion element (16) positioned spaced apart from the inner surface of the burner deck (2) within the burner deck (2), the insertion element (16) having a gas distribution facing surface, wherein the insertion element (16) has a closed first end (22), wherein the gas distribution facing surface of the burner deck (2) and the gas distribution facing surface of the insertion element (16) delimit a gas distribution chamber (20) between them that is closed at the second end (8) of the burner deck (2), and wherein noise-reduction elements are provided in the gas distribution chamber (20).

2. Premix gas burner according to claim 1 , wherein the noise-reduction elements are provided at asymmetric positions in the gas distribution chamber (20) as seen in the radial direction.

3. Premix gas burner according to claim 1 or 2, wherein the noise-reduction elements are two or more separation walls (28, 30).

4. Premix gas burner according to claim 3, wherein said separation walls (28, 30) extend in a longitudinal direction of the burner deck (2), preferably from the first end (6) to the second end (8) of the burner deck (2) and / or from the first end (22) to the second end (24) of the insertion element (16).

5. Premix gas burner (1) according to claim 3 or 4 wherein the two or more separation walls (28, 30) are over their full length connected to the gas distribution facing surface of the insertion element (16) and / or to the gas distribution facing outer surface of the burner deck (2). .

6. Premix gas burner according to any one of the preceding claims, wherein the insertion element (16) comprises an open second end (25) opposite of the closed first end (22).

7. Premix gas burner (1) according to any one of the preceding claims, further comprising a closing element (26) provided at the first end (22) of the insertion element (16)for closing the first end of the insertion element (16), wherein the closing element (26) extends in the width direction beyond the circumference of the insertion element (16).

8. Premix gas burner (1) according to any one of the preceding claims, wherein the closing element (26) is tapered or conically shaped.

9. Premix gas burner (1) according to any one of the preceding claims, further comprising a textile fabric provided at the first end of the burner deck, wherein the textile fabric covers the width of the gas distribution chamber at the first end of the burner deck.

10. Premix gas burner (1) according to any one of the preceding claims, wherein a circumferential wall of the insertion element (16) is parallel to a circumferential wall of the burner deck (2) or wherein the circumferential wall of the insertion element (16) is tapered.

11. Premix gas burner (1) according to any one of the preceding claims, wherein the diameter of the gas distribution chamber (20) is in the range of 70-99% relative to the diameter of the burner deck (2).

12. Premix gas burner (1) according to one of the preceding claims, wherein a longitudinal axis of the insertion element (16) and the longitudinal axis of the burner deck (2) are parallel and eccentrically.

13. Premix gas burner (1) according to one of the preceding claims, wherein the insertion element (16) has a wall thickness that is substantially equal to or smaller than a wall thickness of the burner deck (2).

14. Premix gas burner (1) according to one of the preceding claims, wherein materials of the insertion element (16) and the burner deck (2) have a substantially equal coefficient of expansion.

15. Premix gas burner (1) according to one of the preceding claims, wherein the gas outflow apertures are arranged in clusters on the burner deck16. Premix gas burner (1) according to one of the preceding claims, wherein a textile fabric is provided along the outer surface of the burner deck (2), wherein the textile fabric has a fabric section extending freely at the second end of the burner deck (2).

17. Premix gas burner (1) according to one of the preceding claims, wherein a textile fabric is provided at the open first end (6) of the burner deck (2).

18. Heater system comprising heat exchanger and a premix gas burner (1) according to any one of the preceding claims.

19. Heater system according to claim 18, comprising a heat exchanger with a heat load up to 100 kW and a burner with a diameter in the range of 50-150 mm.

20. Heater system according to claim 18, comprising a heat exchanger with a heat load of at least 100 kW and a burner with a diameter in the range of 100-500 mm.

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