NL2029630B1

NL2029630B1 - Premix gas burner

Info

Publication number: NL2029630B1
Application number: NL2029630A
Authority: NL
Inventors: Hogenbirk Camillo; Bus Marc
Original assignee: Bekaert Combustion Tech Bv
Priority date: 2021-11-04
Filing date: 2021-11-04
Publication date: 2023-06-02
Also published as: WO2023078949A1

Abstract

The invention pertains to a premix gas burner for combusting a hydrogen-containing premix burner gas containing a fuel gas containing at least 80 vol% of hydrogen, comprising: - a gas supply chamber to receive the hydrogen-containing premix burner gas, - a burner deck, comprising a metal burner deck plate, having a chamber facing surface and a flame facing free surface, and a plurality of gas outflow apertures extending through the metal burner deck plate allowing hydrogen-containing premix burner gas to flow from the gas supply chamber to a combustion zone adjacent to the flame facing free surface of the metal burner deck plate, wherein the metal burner deck plate is made of a metal having a thermal conductivity coefficient at room temperature of at least 80 W/(mK) and having a Young’s modulus at room temperature of 150 GPa or less.

Description

P35100NLOO/NBL

Premix gas burner

The invention pertains to a premix gas burner for combusting a hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol®% of hydrogen, and to a heater system comprising such a burner.

Traditionally, in premix gas burners as are for example used in heater systems for buildings or domestic hot water systems, a premix burner gas is used that contains for example methane mixed with air. Currently, in order to reduce carbon dioxide emissions, developments are going on to add hydrogen to the premix burner gas, or even to replace the methane by hydrogen entirely.

However, the combustion process of hydrogen-containing premix burner gases is significantly different from the combustion of premix burner gases using only traditional fuel gases such as methane. When the fuel gas that is part of the premix burner gas contains 25 vol% of hydrogen or more, the influence of the presence of hydrogen on the combustion process is such that the design of the premix gas burner that is to be used has to be made suitable for combustion of the hydrogen-containing premix burner gas.

For example, if a premix burner gas that contains a fuel gas with a significant percentage of hydrogen, e.g. more than 30 vol%, is used in a premix gas burner, the flames will stabilise at a location which is closer to the burner deck of the premix gas burner than if pure methane or natural gas would have been used as a fuel gas. The combustion of hydrogen-containing fuel gas closer to the burner deck of the premix gas burner results in a high surface temperature, which in turn leads to high material stresses, large thermal expansion and large deformation of the burner deck.

In use, the burner deck of known premix gas burners often reach a high maximum temperature of at least 500°C, often even up to more than 800°C. The premix gas burners of the type to which the invention pertains are often used in modulating heater systems, in which the thermal load on the burner varies significantly during relatively short time spans. This causes changes in the burner deck temperature, and therewith the amount of thermal expansion and the magnitude of thermal stresses in the burner deck of the premix gas burner. These varying stresses are a major cause of thermal fatigue. Often, special designs are necessary to deal with the varying temperatures.

EP3187781 proposes to add a cooling fin to the burner at the entrance of the gas supply chamber, in order to cool this area of the burner by the incoming flow of fuel gas and/or air. While this is advantageous for the sealing in the entrance area, it has only a limited effect on the maximum burner deck temperature.

The invention aims to provide an improved premix gas burner, which has a good thermal fatigue resistance.

This object is obtained by a premix gas burner for combusting a hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol% of hydrogen, comprising: - a gas supply chamber which is adapted to receive the hydrogen-containing premix burner gas, - a burner deck, which burner deck comprises a metal burner deck plate, which metal burner deck plate has a chamber facing surface on one side and a flame facing free surface on the opposite side, and a plurality of gas outflow apertures that extend through the metal burner deck plate from the chamber facing surface to the flame facing free surface, the gas outflow apertures allowing hydrogen-containing premix burner gas to flow from the gas supply chamber to a combustion zone adjacent to the flame facing free surface of the metal burner deck plate, wherein the gas outflow apertures have a dimension and mutual position to allow combustion of the hydrogen-containing premix burner gas in the combustion zone, wherein the metal burner deck plate is made of a metal having a thermal conductivity coefficient at room temperature of at least 80 W/(mK) and having a Young's modulus at room temperature of 150GPa or less.

The premix gas burner according to the invention is suitable for combusting a hydrogen- containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol% of hydrogen. The premix burner gas contains at least an oxidiser gas and the hydrogen- containing fuel gas. The oxidiser gas is a gas which is or contains oxygen. The oxidiser gas is for example air. The hydrogen containing fuel gas contains at least 80 vol% hydrogen, for example at least 90 vol% hydrogen, e.g. at least 95 vol% of hydrogen, optionally at least 98 vol% hydrogen. The ratio between the oxidiser gas and the fuel gas in the premix burner gas is dependent on the operating conditions of the burner. In the art, the ration between the oxidiser gas portion and the fuel gas portion in the premix burner gas is commonly indicated in the art in the form of the air excess ratio. The air excess ratio reflects the amount of air or other oxidiser gas in the premix of air or other oxidiser gas and fuel gas, relative to the theoretically stoichiometrically required amount of air or other oxidiser gas for full combustion of the fuel gas. Suitable air excess ratios for this kind of premix burner gas are known in the art. The design of the burner allows a stable combustion of a hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol% of hydrogen.

The premix gas burner according to the invention is suitable for being arranged in a burner chamber, e.g. a burner chamber of a heater system, for example a burner chamber of a building heater system and/or a burner chamber of a hot water system.

The premix gas burner comprises a gas supply chamber which is adapted to receive the hydrogen-containing premix burner gas. For example, a gas supply system comprising for example an oxidiser gas supply duct, a fuel gas supply duct, an oxidiser gas supply fan, and a premix supply duct is provided to supply the premix burner gas containing at least 80 vol% of hydrogen to the gas supply chamber of the premix gas burner.

The premix gas burner further comprises a burner deck, which burner deck comprises a metal burner deck plate. Therewith, this premix gas burner is different from premix gas burners that have a burner deck made of fibre material, e.g. a metal fibre material, or of a woven wire mesh. The burner deck provides the basis for the flame or flames when the premix gas burner is in use. The metal burner deck plate optionally delimits at least one side of the gas supply chamber.

Optionally, the premix gas burner further comprises a gas distributor, a flange and/or elements for flash back prevention. The gas distributor is or comprises for example a perforated metal plate which is arranged in the gas supply chamber.

The metal burner deck plate has a chamber facing surface on one side and a flame facing free surface on the opposite side. The chamber facing surface faces the gas supply chamber and the flame facing free surface is facing a combustion zone, where the combustion of the hydrogen-containing premix burner gas that has passed through the premix gas burner takes place. The metal burner deck plate further comprises a plurality of gas outflow apertures that extend through the metal burner deck plate from the chamber facing surface to the flame facing free surface. These gas outflow apertures allow hydrogen- containing premix burner gas to flow from the gas supply chamber to a combustion zone adjacent to the flame facing free surface of the metal burner deck plate. The flame facing free surface of the metal burner deck plate forms part of the outer surface of the premix gas burner. No fibre material or woven wire mesh is present on the flame facing free surface of the metal burner deck plate.

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

The gas outflow apertures have a dimension and mutual position to allow combustion of the hydrogen-containing premix burner gas in the combustion zone. Many, but not all,

configurations of gas outflow apertures and the pattern or patterns in which that are arranged in the metal burner deck plate allow combustion of the hydrogen-containing premix burner gas in the combustion zone 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 burner gas in the combustion zone. 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, metal deformation and/or mechanical drilling.

The metal burner deck plate is made of a metal having a thermal conductivity coefficient at room temperature of at least 80 W/(mK). This is clearly higher than the thermal conductivity coefficient of steel which is generally used as the material for metal burner deck plates.

According to many sources, the thermal conductivity coefficient at room temperature of steel is in the order of 45 — 50 W/(mK), with stainless steel generally having an even lower thermal conductivity coefficient at room temperature. As a comparison, the thermal conductivity coefficient at room temperature of aluminium is about 240 W/mK), the thermal conductivity coefficient at room temperature of copper is about 400 W/(mK) and the thermal conductivity coefficient at room temperature of brass is about 100 W/(mK). Room temperature is defined as 20°C.

In addition, the metal of the metal burner deck plate has a Young's module at room temperature of 150 GPa or less. So, the Young's module at room temperature of the metal of the metal burner deck plate is lower than the Young's modulus of steel, which is about 190

GPa — 215 GPa. As a comparison, the Young’s modulus at room temperature of aluminium is about 68-70 GPa, the Young'’s modulus at room temperature of copper is about 120 GPa and the Young’s modulus at room temperature of brass is about 100 GPa.

Optionally, the metal of the metal burner deck plate has a Young’s module at room temperature of 125 GPa or less, for example 100 GPa or less. The lower the Young's module at room temperature, the lower the resulting thermal stresses at a certain amount of suppressed thermal expansion.

The relatively high thermal conductivity coefficient of the metal burner deck plate was found to be surprisingly effective in obtaining a relatively low maximum burner deck temperature. i.e. a maximum burner deck temperature that is lower than the maximum burner deck temperature of the same geometry under the same operating conditions but made of a regular steel burner deck material would be. In addition, the temperature is more evenly distributed over the burner deck, which reduces thermal stress in the burner deck. Heat is apparently distributed more easily and effectively transported away from burner deck at these values of the thermal conductivity coefficient at room temperature of the metal burner deck plate.

In use, the metal burner deck plate will thermally expand due to the increased temperature of the burner deck. If this thermal expansion is suppressed to at least some extent, this will cause thermal stresses in the metal burner deck plate. The magnitude of these thermal stresses is dependent on the amount of elongation that is suppresses and on the Young's module. A lower Young's module causes a lower thermal stress level for the same amount of suppressed elongation than a higher Young's module.

The metal that is used for the metal burner deck plate in the premix gas burner according to the invention is not a regular burner deck metal material such as heat resistant steel. Some materials that are suitable for use in the metal burner deck plate of the premix gas burner according to the invention may have a higher thermal expansion coefficient than the regular steel burner deck materials, but it was found that due to the lower temperature of the metal burner deck plate during use, the adverse effect that the higher thermal expansion coefficient might have on the thermal stresses (also in relation to the yield stress) in the metal burner deck plate was mitigated or even eliminated. So, even for materials with a higher thermal expansion coefficient, lower material stresses were found.

The reduction of the maximum burner deck temperature allows to use metal materials for the burner deck which are less heat resistant, which reduces the costs of manufacturing.

In addition, a reduced risk of flashback and a lower NOx production were observed in some cases.

Surprisingly, it was observed that when the premix gas burner according to the invention was applied in a modulating arrangement, i.e. with varying load, the burner deck temperature at the lower loads (optionally in combination with a higher air excess ratio) in the modulation spectrum decreased as compared to loads in the middle part of the modulation spectrum. Normally, the burner deck temperature at low loads is higher than at loads in the middle of the modulation spectrum, due to the lower gas velocity trough the gas outflow apertures of the burner deck at low loads. At lower gas velocities, the outwardly flowing premix burner gas has a lesser cooling effect on the burner deck. In addition, at a lower gas velocities, the flames are closer to the burner deck, which also leads to an increased burner deck temperature.

The relatively low burner deck temperature at low loads, as observed in the premix gas burner according to the invention, has several advantages. First, the lower the burner deck temperature, the lower the material stresses and thermal fatigue load on the burner deck. A low thermal fatigue load increases the expected life span of the premix gas burner, In known burners, often the fatigue loads at low loads have a significant influence on the expected life span because of the relatively high burner decks temperatures at low loads. For a premix gas burner according to the invention, it is expected that the relatively low burner deck temperatures at low loads have a positive effect on the overall expected life span of the premix gas burner.

A further advantage of the relatively low burner deck temperatures at low loads is that this reduces the risk of flashback. Flashback occurs when the flame velocity is higher than the outflow velocity of the premix burner gas. At low loads, the lowest outflow velocities occur, so the risk of flashback is highest at low loads. For hydrogen-containing premix burner gases, the flame velocity is dependent on the temperature of the premix burner gas: the higher the temperature, the higher the flame velocity. For hydrogen-containing premix burner gases, the temperature has a stronger influence on the flame velocity than for non-hydrogen-containing premix burner gases. A relatively cool burner deck will heat up the premix burner gas passing through the gas outflow apertures less than a hot burner deck. Therewith the relatively low temperature of the burner deck that is observed in the premix gas burner according to the invention contributes to a reduction of the risk of flashback.

In an embodiment, the thermal conductivity coefficient at room temperature of the metal burner deck plate is at least 100 W/(mK), optionally at least 120 W/{mK).

A higher thermal conductivity coefficient on the one hand allows a more effective heat transfer away from the metal burner deck plate, and therewith leads to an even more effective lowering of the temperature of the metal burner deck plate. On the other hand however, metals having such a high thermal conductivity generally have a rather low heat resistance, which makes them unlikely candidates for metal burner deck plate materials. However, surprisingly it was found that this type of metals allow to obtain such low temperatures of the metal burner deck to be obtained, that the lower heat resistance of the material is not a problem.

In an embodiment, the metal burner deck plate is at least partially made of a metal plate of aluminium or of an aluminium alloy or of copper or of a copper alloy, for example brass.

In an aluminium alloy, aluminium is the predominant metal in the alloy. In a copper alloy, copper is the predominant metal in the alloy.

Optionally, the metal burner deck plate is entirely made of a metal plate of aluminium or of an aluminium alloy or of copper or of a copper alloy, for example brass.

These materials are examples of metals that have a high thermal conductivity coefficient at room temperature, which allows to obtain a relatively low maximum burner deck temperature during use of the premix gas burner according to the invention, which maximum burner deck temperature is so low that these materials can be used despite their lesser heat resistance as compared to known burner deck materials. In addition, these materials have a relatively low Young's modulus at room temperature, in particular a Young's modulus at room temperature below 150GPa, (which is reduced further at elevated temperatures), which helps to prevent high thermal stresses.

For example, the metal burner deck plate is entirely or at least partially made of a metal plate of aluminium of the type AIMg3 (also known in the art as 5754 and/or 3.3535 and/or

A95754) or aluminium of the type 5454 also known in the art as 3.3537 and/or N51 and/or

AS95454), or aluminium of the type 5086.

In practice, of course the final selection of the material will depend on a variety of considerations, for example including the risk of galvanic corrosion.

In an embodiment, the premix gas burner further comprises a heat sink, which is thermally connected to the metal burner deck plate. The heat sink is arranged to extract heat from the metal burner deck plate and dissipate said extracted heat, e.g. dissipate the extracted heat to the environment.

Optionally, the heat sink is in direct contact with the metal burner deck plate, so the metal burner deck plate touches the heat sink to allow heat to be transferred from the metal burner deck plate to the heat sink. This allows to obtain a relatively low temperature of the metal burner deck plate during use of the premix gas burner.

Optionally, alternatively or in addition, the heat sink is in indirect contact with the metal burner deck plate, i.e. a heat transfer element is present between the metal burner deck plate and the heat sink to transfer heat from the metal burner deck plate to the heat sink.

Optionally, a plurality of heat transfer elements is present between the metal burner deck plate and the heat sink.

Optionally, the heat sink is provided with a cooling channel and/or a cooling fin. This may improve the dissipation rate of heat from the heat sink, allowing to obtain an even lower temperature of the metal burner deck plate.

In an embodiment, the metal burner deck plate is devoid of a cooling channel that extends in the plane of the metal burner deck plate.

Tests have shown that in many cases relatively low maximum burner deck temperatures can be obtained without additionally passing a cooling medium such as water or air through a cooling channel in the metal burner deck plate that extends in the plane of the metal burner deck plate.

In those cases, any cooling of the metal burner deck plate that is provided by the premix burner gas passing through the gas outflow apertures, and optionally additionally by the use of a heat sink, is sufficient to allow the use of metals having a thermal conductivity coefficient at room temperature of at least 80 W/mK) and having a Young's modulus at room temperature of 150 GPa or less for the metal burner deck plate of the premix gas burner according to the invention.

In an embodiment, the metal burner deck plate has a plate thickness of between 0.4 mm and 10 mm, preferably between 0.5 mm and 5.0 mm, optionally between 0.6 mm and 2.0 mm. As the skilled person knows, mm means millimetre(s).

Optionally, the metal burner deck plate is provided with one or more reinforcement ribs.

Tests with metal burner deck plates having a plate thickness in this range of plate thickness have shown good results. The larger the plate thickness, the better the heat is transferred through the metal burner deck plate, On the other hand, it is harder to make small outflow apertures, e.g. gas outflow apertures with a small diameter, e.g. a diameter of 0.4-0.8 mm, e.g. 0.5-0.7 mm, e.g. 0.6 mm, in a metal burner deck plate with a larger plate thickness.

In practice, therefore the selection of the plate thickness of the metal burner deck plate will be a balance between the efficiency of heat transfer and the ease of manufacturing.

For example, the metal burner deck plate is or comprises a plate of aluminium or of an aluminium alloy, which plate has a plate thickness of between 0.4 mm and 10 mm, preferably between 0.5 mm and 5.0 mm, optionally between 0.6 mm and 2.0 mm for example 1.5mm.

Optionally, the metal burner deck plate has a unform plate thickness. i.e. a plate thickness that varies only within normal manufacturing tolerances.

In an embodiment, a heat sink is provided which is thermally connected to the metal burner deck plate and the shortest distance between an edge of the metal burner deck plate and the heat sink is 60 mm or less, for example 40 mm or less, preferably 30 mm or less, optionally 20 mm or less. The connection of the heat sink to the metal burner deck plate can be either direct or indirect.

Optionally, the heat sink is arranged such that the shortest distance between any point of the metal burner deck plate and the heat sink is 80 mm or less, e.g. 60 mm or less, optionally 40 mm or less, preferably 30 mm or less, optionally 20 mm or less.

Optionally, in this embodiment, the metal burner deck plate has a plate thickness of between 0.4 mm and 10 mm, preferably between 0.5 mm and 5.0 mm, optionally between 0.6 mm and 2.0 mm, for example 1.5mm.

Optionally, in this embodiment, the metal burner deck plate is entirely or at least partially made of a metal plate of aluminium or of an aluminium alloy or of copper or of a copper alloy, for example brass.

Optionally, in this embodiment, the metal burner deck plate has a non-cylindrical shape.

For example, the metal burner deck plate has a flat or domed or curved shape. Optionally, the metal burner deck plate has a flat or domed or curved shape with an outer contour in the shape of a circle, an ellipse, a square, a rectangle, square or rectangle with rounded edges, a hexagon or an octagon. Optionally, the metal burner deck plate is provided with one or more reinforcement ribs. Optionally, the shape of the metal burner deck plate contains a feature (e.g. a ridge, a protrusion or a notch) which allows only one mounting position and/or mounting orientation of the metal burner deck plate in the premix gas burner.

Optionally, in this embodiment, the metal burner deck plate has a cylindrical shape. e.g. with a circular or elliptical cross section.

A short distance between the heat sink and the metal burner deck plate has a positive effect on the effectiveness on the heat sink.

In an embodiment, a heat sink is provided which is thermally connected to the metal burner deck plate and the shortest distance between the centre of the metal burner deck plate and the heat sink is 80 mm or less, e.g. 80 mm or less, optionally 40 mm or less, preferably 30 mm or less, optionally 20 mm or less. The connection of the heat sink to the metal burner deck plate can be either direct or indirect.

Optionally, in this embodiment, the gas outflow apertures have a diameter of 0.3 mm — 1.0 mm, for example 0.4 mm - 0.8 mm, e.g. 0.5mm - 0.7 mm, e.g. 0.6 mm.

Optionally, the gas outflow apertures have a circular shape, the shape of a slot, a star- like shape, an elliptical shape or another suitable shape.

A short distance between the heat sink and the metal burner deck plate and/or the use of a relatively narrow metal burner deck plate has a positive effect on the effectiveness on the heat sink.

In an embodiment, a heat sink is provided which is thermally connected to the metal burner deck plate and the shortest distance between an edge of the metal burner deck plate and the heat sink is 150 mm or less, e.g. 120 mm or less, for example 100 mm or less, optionally 80 mm or less, preferably 70 mm or less, optionally 60 mm or less. The connection of the heat sink to the metal burner deck plate can be either direct or indirect.

In this embodiment, the metal burner deck plate has a plate thickness of at least 1.5 mm, e.g. between 1.5 mm and 10 mm, preferably between 2.0 mm and 5.0 mm, optionally between 2.0 mm and 3.0 mm, for example 2.5mm.

Optionally, in this embodiment, the heat sink is arranged such that the shortest distance between any point of the metal burner deck plate and the heat sink is 150 mm or less, e.g. 120 mm or less, for example 100 mm or less, optionally 80 mm or less, preferably 70 mm or less, optionally 60 mm or less.

Optionally, in this embodiment, the gas outflow apertures have a diameter of 0.3 mm — 1.0 mm, for example 0.4 mm -0.8 mm, e.g. 0.5mm - 0.7 mm, e.g. 0.6 mm.

In an embodiment, the metal burner deck plate has a plate thickness of between 0.4 mm and 10 mm, preferably between 0.5 mm and 5.0 mm, optionally between 0.6 mm and 2.0 mm, for example 1.5mm.

In this embodiment, the metal burner deck plate is entirely or at least partially made of a metal plate of aluminium or of an aluminium alloy or of copper or of a copper alloy, for example brass.

In this embodiment, the metal burner deck plate has a non-cylindrical shape. For example, the metal burner deck plate has a flat or domed or curved shape. Optionally, the metal burner deck plate has a flat or domed or curved shape with an outer contour in the shape of a circle, an ellipse, a square, a rectangle, square or rectangle with rounded edges, a hexagon or an octagon. Optionally, the metal burner deck plate is provided with one or more reinforcement ribs. Optionally, the shape of the metal burner deck plate contains a feature (e.g. a ridge, a protrusion or a notch) which allows only one mounting position and/or mounting orientation of the metal burner deck plate in the premix gas burner.

In this embodiment, the metal burner deck plate has a cylindrical shape, for example with a circular or elliptical cross sectional shape.

Optionally, the burner deck has a first axial end which is connected to a flange, and a heat sink is thermally connected to the flange. Optionally, the burner deck is connected directly to the flange. Optionally, the heat sink is connected directly to the flange, or alternatively, the heat sink is connected indirectly, e.g. via a heat transfer element, to the flange.

In an embodiment, a heat sink is provided which is thermally connected to the metal burner deck plate. The premix gas burner further comprises a premix supply duct having a duct entrance and a duct discharge, and the gas supply chamber comprises a chamber entrance and a chamber inner volume. The duct discharge of the premix supply duct is connected to the chamber entrance of the gas supply chamber. A fuel gas flow path is present which extends from the duct entrance of the premix supply duct to the duct discharge of the premix supply duct, and further through the chamber entrance opening into chamber inner volume of the gas supply chamber. The heat sink is arranged outside the fuel gas flow path.

By arranging the heat sink outside the fuel gas flow path, the heat sink does not cause a pressure drop in the premix burner gas, which leads to less energy consumption for transporting the premix burner gas or the components of the premix burner gas to the metal burner deck plate.

In an embodiment, a burr and/or dross is present at a rim of at least one gas outflow aperture on the side of the chamber facing surface of the metal burner deck plate.

When the gas outflow apertures are made by for example mechanical drilling or punching, or other types of providing the gas outflow apertures by means of mechanically removing material, a burr may be formed on the edge of the gas outflow aperture on the side of the metal burner deck plate opposite to the side of the metal burner deck plate where the drill or punch or other tool enters the metal burner deck plate. When the gas outflow apertures are made by for example laser cutting, laser drilling, or other types of making the gas outflow apertures by means of removing material by melting, a dross may be formed on the edge of the gas outflow aperture on the side of the metal burner deck plate opposite to the side of the metal burner deck plate where the laser beam enters the metal burner deck plate.

In steel burner decks, positive effects on the susceptibility to flashback have been observed when the burr of dross is located on the flame facing free surface of the metal burner deck plate. Surprisingly, in premix gas burners according to the invention, tests show that a burr or dross on the chamber facing surface of the metal burner deck plate reduces the susceptibility to flashback.

In an embodiment, the combined surface area of the gas outflow apertures in the flame facing free surface of the metal burner deck plate is 10% or less of the total effective surface area of the flame facing free surface of the metal burner deck plate, optionally 7% or less, for example 5% or less.

The total effective surface area of the flame facing free surface of the metal burner deck plate is defined by the outermost gas outflow apertures of the metal burner deck plate: the shortest line or lines that can be drawn connecting the outermost edges of the outermost gas outflow apertures of the metal burner deck plate enclose or encloses the total effective surface area of the flame facing free surface of the metal burner deck plate.

The combined surface area of the gas outflow apertures is the sum of the surface areas of all gas outflow apertures on the flame facing free surface of the metal burner deck plate.

These ratios of the combined surface area of the gas outflow apertures to the total effective surface area of the flame facing free surface of the metal burner deck plate allow a design of a premix gas burner that is suitable for combustion of a hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol% of hydrogen

The relatively low burner deck temperature makes that the pressure drop over the metal burner deck plate is relatively low, even at al low percentage of combined surface area of the gas outflow apertures. This is most likely because the metal burner deck plate does not heat up the premix burner gas so much as a known metal burner deck plate, which gets much hotter during use.

In an embodiment, the gas outflow apertures are arranged in clusters on the metal burner deck plate. The smallest heart-to-heart distance 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.

This configuration allows a design of a premix gas burner that is suitable for combustion of a hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol% of hydrogen.

In an embodiment, the premix gas burner further comprises a burner hood, which is arranged facing the chamber facing side of the metal burner deck plate. The burner hood is made of a thermally conductive material and is in thermal contact with a portion of the metal burner deck plate. Therewith, the burner hood acts as a heat sink.

Optionally, the burner hood comprises at least one cooling channel which is adapted to allow a cooling medium, e.g. water, to flow through the burner hood.

Optionally, in this embodiment, the metal burner deck plate comprises a blind area in which no gas outflow apertures are present. For example, the blind area is located at an outer rim or a part of the outer rim of the metal burner deck plate and/or at a central portion of the metal burner deck plate, and/or between two areas of the metal burner deck plate which are provided with gas outflow apertures.

Optionally, the burner hood comprises a flange, which flange is in thermal contact with a blind area of the metal burner deck plate. Optionally, a cooling channel which is adapted to allow a cooling medium, e.g. water, to flow through the burner hood, extends through the flange.

Optionally, the burner hood comprises a rib, which rib is in thermal contact with the metal burner deck plate, e.g. with a non-perforated area of the metal burner deck plate.

Optionally, a cooling channel which is adapted to allow a cooling medium, e.g. water, to flow through the burner hood, extends through the rib.

Optionally, the metal burner deck plate and the burner hood are integral with each other and optionally are made of a cast aluminium or a cast aluminium alloy.

In an embodiment, the metal burner deck plate has a non-cylindrical shape.

For example, in this embodiment, the metal burner deck plate has a square, rectangular, elliptical or circular shape.

Optionally, the shape of the metal burner deck plate contains a feature (e.g. aridge, a protrusion or a notch) which allows only one mounting position and/or mounting orientation of the metal burner deck plate in the premix gas burner.

Optionally, the metal burner deck plate has a two dimensional shape, i.e. is a flat plate.

Optionally, the metal burner deck plate has a three dimensional shape. For example, the metal burner deck plate has a shape which extends on one or two sides beyond the mathematical plane that extends through the edge or edges of the metal burner deck plate.

For example, the metal burner deck plate has a curved or double curved shape.

For example, the metal burner deck plate has a flat or domed or curved shape. Optionally, the metal burner deck plate has a flat or domed or curved shape with an outer contour in the shape of a circle, an ellipse, a square, a rectangle, square or rectangle with rounded edges, a hexagon or an octagon.

In burners of this embodiment, the distance between an entrance of the gas supply and the flame facing free surface of the metal burner deck plate can be kept shorter than in cylindrical (or tubular) burners, which reduces the risk of detonation of the hydrogen in the premix burner gas.

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.

In an embodiment, the heater system according to the invention comprises a burner chamber and the premix gas burner is arranged in the burner chamber.

In an embodiment, the heater system further comprises a heat exchanger.

Optionally, at least a part of the heat exchanger is made of a cast metal, and wherein at least a part of the premix gas burner is made of a cast metal and the cast metal part of the premix gas burner is integral with the cast metal part of the heat exchanger.

Optionally, the heater system comprises a premix gas burner having a heat sink which is thermally connected to the metal burner deck plate, and the part of the premix gas burner which is made of a cast metal is or includes the heat sink.

Optionally, the cast metal is cast aluminium or a cast aluminium alloy.

In an embodiment, the heater system comprises an embodiment of a premix gas burner according to the invention which comprises a heat sink, which heat sink is provided with a cooling channel which is adapted to allow a cooling medium, e.g. water, to flow through the heat sink. The cooling channel of the heat sink has a cooling channel inlet and an cooling channel outlet.

In addition, in this embodiment the heater system comprises a water circulation circuit.

The cooling channel is connected to, in fluid communication with and optionally forms part of the of the water circulation circuit via the cooling channel inlet and the cooling channel outlet.

So, the cooling channel inlet receives water from the water circulation circuit and the cooling channel outlet discharges water to the water circulation circuit via the cooling channel outlet.

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. The heat exchanger passage forms part of the water circulation circuit. Optionally, the cooling channel inlet is connected to the water circulation circuit at or adjacent to the heat exchanger inlet and the cooling channel outlet is connected to the water circulation circuit at or adjacent to the heat exchanger outlet. Optionally, alternatively the cooling channel inlet is connected to the water circulation circuit at or adjacent to the heat exchanger outlet and the cooling channel outlet is connected to the water circulation circuit at or adjacent to the heat exchanger inlet

The invention will be described in more detail below under reference to the drawing, in which in a non-limiting manner exemplary embodiments of the invention will be shown. The drawing shows in:

Fig. 1: schematically, a first embodiment of a premix gas burner according to the invention, in side view,

Fig. 2: schematically, the embodiment of fig. 1, in cross section,

Fig. 3: schematically, an embodiment of metal burner deck plate 3 of a premix gas burner according to the invention, in top view,

Fig. 4: schematically, a second embodiment of a premix gas burner according to the invention, in isometric bottom view,

Fig. 5: schematically, an embodiment which contains the metal burner deck plate of fig. 3,

Fig. 6: schematically, a variant of the embodiment of fig. 5,

Fig. 7 :schematically, an embodiment of a gas outflow aperture,

Fig. 8: schematically, an example of a metal burner deck plate that can be used in premix gas burners according to the invention,

Fig. 9: schematically, a further embodiment of a premix gas burner according to the invention,

Fig. 10: schematically, an embodiment of heater system in which a premix gas burner according to the invention is applied,

Fig. 11 : schematically, a part of a further embodiment of a heater system comprising a premix gas burner according to the invention,

Fig. 12 : the Young's modulus at room temperature in GPa in relation to the thermal conductivity coefficient at room temperature in W/{mK) for a number of common metals.

Fig. 1 schematically illustrates a first embodiment of a premix gas burner according to the invention, in side view. Fig. 2. schematically illustrates the embodiment of fig. 1 in crass section.

The premix gas burner 1 of fig. 1 and fig. 2 is a cylindrical burner. The premix gas burner of fig. 1 and fig. 2 has burner deck 2, which has a cylindrical shape with a circular cross section. The burner deck 2 comprises a metal burner deck plate 3. In this example, the burner deck 2 is made of metal burner deck plate 3. The metal burner deck plate 3 has a cylindrical shape, with a circular cross section.

The premix gas burner of fig. 1 and fig. 2 further comprises a gas supply chamber 4.

The gas supply chamber 4 is adapted to receive the hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol% of hydrogen. This for example implies that any seals, welds or other connection elements are gas tight for this kind of premix burner gas.

For example, a gas supply system comprising for example an oxidiser gas supply duct, a fuel gas supply duct, an oxidiser gas supply fan, and a premix supply duct is provided to supply the hydrogen-containing premix burner gas to the gas supply chamber 4 of the premix gas burner 1. Optionally, in addition one or more gas valves are present.

In the embodiment of fig. 1 and fig 2, the metal burner deck plate 3 plate has a chamber facing surface 5 on one side and a flame facing free surface 6 on the opposite side. The chamber facing surface 5 faces the gas supply chamber 4 and the flame facing free surface 6 is facing a combustion zone, where the combustion of the hydrogen-containing premix burner gas that has passed through the premix gas burner 1 takes place. The flame facing free surface 6 of the metal burner deck plate 3 forms part of the outer surface of the premix gas burner 1. No fibre material, e.g. a metal fibre material, or woven wire mesh is present on the flame facing free surface 6 of the metal burner deck plate 3.

The metal burner deck plate 3 further comprises a plurality of gas outflow apertures 7 that extend through the metal burner deck plate 3 from the chamber facing surface 5 to the flame facing free surface 6. These gas outflow apertures 7 allow hydrogen-containing premix burner gas to flow from the gas supply chamber 4 to a combustion zone adjacent to the flame facing free surface 6 of the metal burner deck plate 3. For reasons of legibility of fig. 2, the gas outflow apertures 7 are only schematically indicated in fig. 2.

In the embodiment of fig. 1 and fig. 2, the metal burner deck plate 3 has a top portion 8 and a bottom portion 9 that extend beyond the burner deck 2. These portions are blind areas, without any gas outflow apertures 7. The burner deck 2 is defined by the outermost gas outflow apertures 7 of the metal burner deck plate 3: the shortest line or lines that can be drawn connecting the outermost edges of the outermost gas outflow apertures 7 of the metal burner deck plate 3 enclose or encloses the burner deck 2.

The gas outflow apertures 7 have a dimension and mutual position to allow combustion of the hydrogen-containing premix burner gas in the combustion zone. Many, but not all, configurations of gas outflow apertures and the pattern or patterns in which that are arranged in the metal burner deck plate 3 allow combustion of the hydrogen-containing premix burner gas in the combustion zone 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 burner gas in the combustion zone.

In the embodiment of fig. 1 and fig. 2, the gas outflow apertures are arranged in clusters 10, which are schematically represented in fig. 1 as squares. The areas of the burner deck 2 between the clusters 10 do not contain any gas outflow apertures 7 and are therefore non- perforated areas of the burner deck. Fig. 2 merely shows a highly schematic indication of the gas outflow apertures 7, without an explicit indication of the clusters 10. However, such clusters 10 should be considered to be present in the cross section of fig. 2 as well, in the same configuration as in fig. 1.

Detail A is an enlarged representation of a cluster 10, showing the individual gas outflow apertures 7. The smallest heart-to-heart distance between adjacent gas outflow apertures 7 in the same cluster 10 is smaller than the smallest heart-to-heart distance a first gas outflow aperture 7 in a first cluster 10 and a second gas outflow aperture 7 in a second cluster 10, the second cluster 10 being adjacent to the first cluster 10. The arrangement of gas outflow apertures 7 relative to each other within a cluster and the arrangement of clusters 10 relative to each other can be varied, for example as described in WO2021/140036. This configuration allows to design a premix gas burner that is suitable for combustion of hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol% of hydrogen. The skilled person will take into account normal design considerations when designing the burner deck, e.g. with respect to selecting the distance between adjacent clusters. Parameters like resulting temperature distribution, local thermal expansion and the level of thermal stresses will be taken into account.

The gas outflow apertures 7 can be made in the metal burner deck plate 3 in various ways, e.g. by punching, laser cutting, laser drilling, etching, {metal} die casting, metal deformation and/or mechanical drilling.

In the embodiment of fig. 1 and fig. 2, the premix gas burner 1 optionally further comprises a flange 12 and/or a gas distributor 11. The gas distributor 11 comprises a perforated metal plate which is arranged inside the gas supply chamber 4 with the aim of obtaining an even distribution of the premix burner gas to the gas outflow apertures 7 of the metal burner deck plate 3. The design and use of such gas distributors is widely known in the field of premix gas burners. Alternatively or in addition, optionally elements for prevention of thermal acoustic noise prevention and/or flame flashback are provided. Such elements are also well known in the art.

In the embodiment of fig. 1 and fig. 2, the metal burner deck plate 3 is made of a metal having a thermal conductivity coefficient at room temperature of at least 80 W/(mK). This is clearly higher than the thermal conductivity coefficient of steel. According to many sources, the thermal conductivity coefficient at room temperature of steel is in the order of 45 — 50

W/(mK), with stainless steel generally having an even lower thermal conductivity coefficient at room temperature. The types of stainless steel that are commonly used in known premix gas burners have a thermal conductivity coefficient at room temperature of about 10-30 W/mK.

As a comparison, the thermal conductivity coefficient at room temperature of aluminium is about 240 W/(mK), the thermal conductivity coefficient at room temperature of copper is about 400 W/(mK) and the thermal conductivity coefficient at room temperature of brass is about 100 W/(mK),

In addition, in the embodiment of fig. 1 and fig. 2, the metal of the metal burner deck plate 3 has a Young's module at room temperature of 150 GPa or less. So, the Young's module at room temperature of the metal of the metal burner deck plate is lower than the

Young's modulus of steel, which is about 190 GPa — 215 GPa. As a comparison, the Young's modulus at room temperature of aluminium is about 68-70 GPa, the Young’s modulus at room temperature of copper is about 120 GPa and the Young's modulus at room temperature of brass is about 100 GPa.

Optionally, the metal of the metal burner deck plate 3 has a Young's module at room temperature of 125 GPa or less, for example 100 GPa or less. The lower the Young's module at room temperature, the lower the resulting thermal stresses at a certain amount of suppressed thermal expansion.

Optionally, the thermal conductivity coefficient at room temperature of the metal burner deck plate 3 is at least 100 W/(mK), optionally at least 120 W/(mK).

In the embodiment of fig. 1 or fig. 2, the metal burner deck plate 3 is for example made of a metal plate of aluminium or of an aluminium alloy or of copper or of a copper alloy, for example brass.

These materials are examples of metals that have a high thermal conductivity coefficient at room temperature, which allows to obtain a relatively low maximum burner deck temperature during use of the premix gas burner according to the invention, which maximum burner deck temperature is so low that these materials can be used despite their lesser heat resistance as compared to known burner deck materials. In addition, these materials have a relatively low Young's modulus at room temperature, in particular a Young’s modulus at room temperature below 150GPa, (which is reduced further at elevated temperatures), which helps to prevent high thermal stresses.

A95454) or aluminium of the type 5086.

In the embodiment of fig. 1 and fig. 2, the premix gas burner further comprises a heat sink 20, which is thermally connected to the metal burner deck plate3, for example via the flange 12 as is shown in fig. 1 and fig. 2. The heat sink is arranged to extract heat from the metal burner deck plate 3 and dissipate said extracted heat, e.g. dissipate the extracted heat to the environment. Optionally, the heat sink comprises a cooling channel and/or a cooling fin, optionally multiple cooling channels and/or cooling fins.

In the embodiment of fig. 1 and fig. 2, the metal burner deck plate 3 does not contain a cooling channel that extends in the plane of the metal burner deck plate 3. The high thermal conductivity of the material of the metal burner deck plate is sufficient to keep the burner deck temperature sufficiently low, without having to pass a dedicated cooling medium {for example water) through the metal burner deck plate 3.

In the embodiment of fig. 1 and fig. 2, the metal burner deck plate 3 has a plate thickness of between 0.4 mm and 10 mm, preferably between 0.5 mm and 5.0 mm, optionally between 0.6 mm and 2.0 mm. The metal burner deck plate 3 has a unform plate thickness. i.e. a plate thickness that varies only within normal manufacturing tolerances

In this embodiment, the gas outflow apertures 7 have a diameter of 0.3 mm — 1.0 mm, for example 0.4 mm - 0.8 mm, e.g. 0.5 mm - 0.7 mm, e.g. 0.6 mm.

In the embodiment of fig. 1 and fig. 2, the heat sink 20 is thermally connected to the metal burner deck plate 3 and the shortest distance between the centre of the metal burner deck plate and the heat sink 20 is for example 80 mm or less, e.g. 60 mm or less, optionally 40 mm or less, preferably 30 mm or less, optionally 20 mm or less. The connection of the heat sink 20 to the metal burner deck plate can be either direct or indirect. Optionally, the heat sink is arranged such that the shortest distance between any point of the metal burner deck plate 3 and the heat sink is 80 mm or less, e.g. 80 mm or less, optionally 40 mm or less, preferably 30 mm or less, optionally 20 mm or less.

In case the metal burner deck plate 3 has a plate thickness of at least 1.5 mm, e.g. between 1.5 mm and 10 mm, preferably between 2.0 mm and 5.0 mm, optionally between 2.0 mm and 3.0 mm, for example 2.5 mm, the heat sink 20 is optionally arranged such that the shortest distance between any point of the metal burner deck plate 3 and the heat sink is 150 mm or less, e.g. 120 mm or less, e.g. 100 mm or less, optionally 80 mm or less, preferably 70 mm or less, optionally 60 mm or less.

In the embodiment of fig. 1 and fig. 2, optionally the combined surface area of the gas outflow apertures 7 in the flame facing free surface 6 of the metal burner deck plate 3 is 10% or less of the total effective surface area of the flame facing free surface 6 of the metal burner deck plate 3, optionally 7% or less, for example 5% or less.

The total effective surface area of the flame facing free surface 6 of the metal burner deck plate 3 is defined by the outermost gas outflow apertures 7 of the metal burner deck plate: the shortest line or lines that can be drawn connecting the outermost edges of the outermost gas outflow apertures 7 of the metal burner deck plate enclose or encloses the total effective surface area of the flame facing free surface 6 of the metal burner deck plate 3.

The combined surface area of the gas outflow apertures 7 is the sum of the surface areas of all gas outflow apertures 7 on the flame facing free surface 6 of the metal burner deck plate 3.

These ratios of the combined surface area of the gas outflow apertures 7 to the total effective surface area of the flame facing free surface 6 of the metal burner deck plate 6 allow a design of a premix gas burner that is suitable for combustion of a hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol®% of hydrogen.

The relatively low burner deck temperature makes that the pressure drop over the metal burner deck plate 3 is relatively low, even at al low percentage of combined surface area of the gas outflow apertures 7. This is most likely because the metal burner deck 3 plate does not heat up the premix burner gas so much as a known metal burner deck plate, which gets much hotter during use.

Fig. 3 shows, schematically, an embodiment of metal burner deck plate 3 of a premix gas burner according to the invention, in top view.

The metal burner deck plate 3 has a flat, predominantly two-dimensional, shape, with a rectangular outer contour with rounded corners. The metal burner deck plate of fig. 3 can for example be used in the premix gas burner as is shown in fig. 5, fig. 6, fig. 9 and/or fig. 10.

For example, the metal burner deck plate of fig. 3 can be used in a heater system that comprises a gas supply system comprising for example an oxidiser gas supply duct, a fuel gas supply duct, an oxidiser gas supply fan, and a premix supply duct is provided to supply the premix burner gas to the gas supply chamber 4 of the premix gas burner 1.

In the embodiment of fig. 3, the metal burner deck plate 3 plate has a chamber facing surface on one side and a flame facing free surface 6 on the opposite side. The chamber facing surface during use faces a gas supply chamber of the premix gas burner and the flame facing free surface 6 during use faces a combustion zone, where the combustion of the hydrogen-containing premix burner gas that has passed through the premix gas burner 1 takes place. The flame facing free surface 6 of the metal burner deck plate 3 forms (during use) part of the outer surface of the premix gas burner 1. No fibre material, e.g. a metal fibre material, or woven wire mesh is present on the flame facing free surface 6 of the metal burner deck plate 3 during use.

The metal burner deck plate 3 further comprises a plurality of gas outflow apertures 7 that extend through the metal burner deck plate 3 from the chamber facing surface to the flame facing free surface 6. These gas outflow apertures 7 allow hydrogen-containing premix burner gas to flow from the gas supply chamber 4 to a combustion zone adjacent to the flame facing free surface 6 of the metal burner deck plate 3.

In the embodiment of fig. 3, the metal burner deck plate 3 has an edge portion 13 which extends arounds the burner deck 2. This edge portion is a blind area, without any gas outflow apertures 7. The burner deck 2 is defined by the outermost gas outflow apertures 7 of the metal burner deck plate 3: the shortest line or lines that can be drawn connecting the outermost edges of the outermost gas outflow apertures 7 of the metal burner deck plate 3 enclose or encloses the burner deck 2.

In the embodiment of fig. 3, the gas outflow apertures 7 are arranged in clusters 10, which are schematically represented in fig. 3 as squares. The areas of the burner deck 2 between the clusters 10 do not contain any gas outflow apertures 7 and are therefore non- perforated areas of the burner deck.

Detail A is an enlarged representation of a cluster 10, showing the individual gas outflow apertures 7. The smallest heart-to-heart distance between adjacent gas outflow apertures 7 in the same cluster 10 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. The arrangement of gas outflow apertures 7 relative to each other within a cluster and the arrangement of clusters 10 relative to each other can be varied, for example as described in W02021/140036. This configuration allows to design a premix gas burner that is suitable for combustion of a hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol% of hydrogen.

The gas outflow apertures 7 can be made in the metal burner deck plate 3 in various ways, e.g. by punching, laser cutting, laser drilling, etching, (metal) die casting, metal deformation and/or mechanical drilling.

In the embodiment of fig. 3, the metal burner deck plate 3 is made of a metal having a thermal conductivity coefficient at room temperature of at least 80 W/(mK). This is clearly higher than the thermal conductivity coefficient of steel which is generally used as the material for metal burner deck plates. According to many sources, the thermal conductivity coefficient at room temperature of steel is in the order of 45 — 50 W/(mK), with stainless steel generally having an even lower thermal conductivity coefficient at room temperature. As a comparison, the thermal conductivity coefficient at room temperature of aluminium is about 240 W/(mK), the thermal conductivity coefficient at room temperature of copper is about 400

W/mK) and the thermal conductivity coefficient at room temperature of brass is about 100

WI(mK),

In addition, in the embodiment of fig. 3, the metal of the metal burner deck plate 3 has a

Young's module at room temperature of 150 GPa or less. So, the Young’s module at room temperature of the metal of the metal burner deck plate is lower than the Young'’s modulus of steel, which is about 190 GPa — 215 GPa. As a comparison, the Young's modulus at room temperature of aluminium is about 68-70 GPa, the Young's modulus at room temperature of copper is about 120 GPa and the Young's modulus at room temperature of brass is about 100 GPa.

Optionally, the metal of the metal burner deck plate 3 has a Young’s module at room temperature of 125 GPa or less, for example 100 GPa or less. The lower the Young's module at room temperature, the lower the resulting thermal stresses at a certain amount of suppressed thermal expansion.

In the embodiment of fig. 3, the metal burner deck plate 3 is for example made of a metal plate of aluminium or of an aluminium alloy or of copper or of a copper alloy, for example brass.

A95454).

In the embodiment of fig. 3, the metal burner deck plate 3 does not contain a cooling channel that extends in the plane of the metal burner deck plate 3. The high thermal conductivity of the material of the metal burner deck plate is sufficient to keep the burner deck temperature sufficiently low, without having to pass a dedicated cooling medium (for example water) through the metal burner deck plate 3.

In the embodiment of fig. 3, the metal burner deck plate 3 has a plate thickness of between 0.4 mm and 10 mm, preferably between 0.5 mm and 5.0 mm, optionally between 0.6 mm and 2.0 mm. The metal burner deck plate 3 has a unform plate thickness. i.e. a plate thickness that varies only within normal manufacturing tolerances

In the embodiment of fig. 3, the combined surface area of the gas outflow apertures 7 in the flame facing free surface 6 of the metal burner deck plate 3 is 10% or less of the total effective surface area of the flame facing free surface 6 of the metal burner deck 3 plate, optionally 7% or less, for example 5% or less.

The total effective surface area of the flame facing free surface 6 of the metal burner deck plate 3 is defined by the outermost gas outflow apertures? of the metal burner deck plate 3: the shortest line or lines that can be drawn connecting the outermost edges of the outermost gas outflow apertures 7 of the metal burner deck plate 3 enclose or encloses the total effective surface area of the flame facing free surface 6 of the metal burner deck plate 3.

These ratios of the combined surface area of the gas outflow apertures 7 to the total effective surface area of the flame facing free surface 6 of the metal burner deck plate 3 allow a design of a premix gas burner that is suitable for combustion of hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol% of hydrogen.

The relatively low burner deck temperature makes that the pressure drop over the metal burner deck plate 3 is relatively low, even at a low percentage of combined surface area of the gas outflow apertures. 7 This is most likely because the metal burner deck plate 3 does not heat up the premix burner gas so much as a known metal burner deck plate, which gets much hotter during use.

Fig. 4 shows, schematically, a second embodiment of a premix gas burner according to the invention, in isometric view.

The premix gas burner 1 of fig. 4 is a non-cylindrical burner. The premix gas burner of fig. 4 has burner deck 2, which has a curved, three-dimensional shape with a rectangular outer contour with rounded corners. The burner deck 2 comprises a metal burner deck plate 3. In this example, the burner deck 2 is made of metal burner deck plate 3. The metal burner deck plate 3 has a curved, three-dimensional shape, with a rectangular outer contour with rounded corners.

The premix gas burner of fig. 4 further comprises a gas supply chamber 4. The gas supply chamber 4 is present on the inside of the curved part of the metal burner deck plate 3, between the parts of the metal burner deck plate 3 that rise up relative to the outer circumference. The gas supply chamber 4 is adapted to receive the hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol% of hydrogen. This for example implies that any seals, welds or other connection elements are gas tight for this kind of premix burner gas.

For example, a gas supply system comprising for example an oxidiser gas supply duct, a fuel gas supply duct, an oxidiser gas supply fan, and a premix supply duct is provided to supply the premix burner gas to the gas supply chamber 4 of the premix gas burner 1.

In the embodiment of fig. 4, the metal burner deck plate 3 plate has a chamber facing surface 5 on one side and a flame facing free surface on the opposite side. The chamber facing surface 5 faces the gas supply chamber 4 and the flame facing free surface 6 faces a combustion zone, where the combustion of the hydrogen-containing premix burner gas that has passed through the premix gas burner 1 takes place. The flame facing free surface 6 of the metal burner deck plate 3 forms part of the outer surface of the premix gas burner 1. No fibre material, e.g. a metal fibre material, or woven wire mesh is present on the flame facing free surface 6 of the metal burner deck plate 3.

The metal burner deck plate 3 further comprises a plurality of gas outflow apertures 7 that extend through the metal burner deck plate 3 from the chamber facing surface 5 to the flame facing free surface 8. These gas outflow apertures 7 allow hydrogen-containing premix burner gas to flow from the gas supply chamber 4 to a combustion zone adjacent to the flame facing free surface 6 of the metal burner deck plate 3.

In the embodiment of fig. 4, the metal burner deck plate 3 has an edge portion 13 which extends arounds the burner deck 2. This edge portion is a blind area, without any gas outflow apertures 7. The burner deck 2 is defined by the outermost gas outflow apertures 7 of the metal burner deck plate 3: the shortest line or lines that can be drawn connecting the outermost edges of the outermost gas outflow apertures 7 of the metal burner deck plate 3 enclose or encloses the burner deck 2.

In the embodiment of fig. 4, the gas outflow apertures 7 are arranged in clusters 10, which are schematically represented in fig. 3 as squares. The areas of the burner deck 2 between the clusters 10 do not contain any gas outflow apertures 7 and are therefore non- perforated areas of the burner deck.

Detail A is an enlarged representation of a cluster 10, showing the individual gas outflow apertures 7. The smallest heart-to-heart distance between adjacent gas outflow apertures 7 in the same cluster 10 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. The arrangement of gas outflow apertures 7 relative to each other within a cluster and the arrangement of clusters 10 relative to each other can be varied, for example as described in WO2021/140036. This configuration allows to design a premix gas burner that is suitable for combustion of a hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol% of hydrogen.

In the embodiment of fig. 4, the premix gas burner 1 optionally further comprises a flange and/or a gas distributor (not shown). The gas distributor for example comprises a perforated metal plate with the aim of obtaining an even distribution of the premix burner gas to the gas outflow apertures 7 of the metal burner deck plate 3. The design and use of such gas distributors is widely known in the field of premix gas burners. Alternatively or in addition, optionally elements for prevention of flame flashback are provided. Such elements are also well known in the art.

In the embodiment of fig. 4, the metal burner deck plate 3 is made of a metal having a thermal conductivity coefficient at room temperature of at least 80 W/(mK). This is clearly higher than the thermal conductivity coefficient of steel which is generally used as the material for metal burner deck plates. According to many sources, the thermal conductivity coefficient at room temperature of steel is in the order of 45 — 50 W/(mK), with stainless steel generally having an even lower thermal conductivity coefficient at room temperature. As a comparison, the thermal conductivity coefficient at room temperature of aluminium is about 240 W/(mK), the thermal conductivity coefficient at room temperature of copper is about 400

W/(mK) and the thermal conductivity coefficient at room temperature of brass is about 100

W/(mK),

In addition, in the embodiment of fig. 4, the metal of the metal burner deck plate 3 has a

Young's module at room temperature of 150 GPa or less. So, the Young's module at room temperature of the metal of the metal burner deck plate is lower than the Young's modulus of steel, which is about 190 GPa — 215 GPa. As a comparison, the Young's modulus at room temperature of aluminium is about 68-70 GPa, the Young's modulus at room temperature of copper is about 120 GPa and the Young's modulus at room temperature of brass is about 100 GPa.

In the embodiment of fig. 4, the metal burner deck plate 3 is for example made of a metal plate of aluminium or of an aluminium alloy or of copper or of a copper alloy, for example brass.

A95454) or aluminium of the type 5086.

In the embodiment of fig. 4, the metal burner deck plate 3 does not contain a cooling channel that extends in the plane of the metal burner deck plate 3. The high thermal conductivity of the material of the metal burner deck plate is sufficient to keep the burner deck temperature sufficiently low, without having to pass a dedicated cooling medium (for example water) through the metal burner deck plate 3.

In the embodiment of fig. 4, the metal burner deck plate 3 has a plate thickness of between 0.4 mm and 10 mm, preferably between 0.5 mm and 5.0 mm, optionally between 0.6 mm and 2.0 mm. The metal burner deck plate 3 has a unform plate thickness. i.e. a plate thickness that varies only within normal manufacturing tolerances

In the embodiment of fig. 4, the combined surface area of the gas outflow apertures 7 in the flame facing free surface 6 of the metal burner deck plate 3 is 10% or less of the total effective surface area of the flame facing free surface 6 of the metal burner deck 3 plate, optionally 7% or less, for example 5% or less.

The relatively low burner deck temperature makes that the pressure drop over the metal burner deck plate 3 is relatively low, even at al low percentage of combined surface area of the gas outflow apertures. 7 This is most likely because the metal burner deck plate 3 does not heat up the premix burner gas so much as a known metal burner deck plate, which gets much hotter during use.

Fig. 5 schematically illustrates an embodiment which contains the metal burner deck plate of fig. 3. In this variant, the premix gas burner 1 is provided with a heat sink 20.

In the variant of fig. 5, the premix gas burner 1 further comprises a heat sink 20, which is thermally connected to the metal burner deck plate 3. The heat sink 20 is arranged to extract heat from the metal burner deck plate 3 and dissipate said extracted heat, e.g. dissipate the extracted heat to the environment.

In the variant of fig. 5, the heat sink 20 is in direct contact with the metal burner deck plate 3, so the metal burner deck plate 3 touches the heat sink 20 to allow heat to be transferred from the metal burner deck 3 plate to the heat sink 20 . This allows to obtain a relatively low temperature of the metal burner deck plate during use of the premix gas burner.

Alternatively or in addition, but not shown in fig. 5, the heat sink is in indirect contact with the metal burner deck plate, i.e. a heat transfer element is present between the metal burner deck plate and the heat sink to transfer heat from the metal burner deck plate to the heat sink. Optionally, a plurality of heat transfer elements is present between the metal burner deck plate and the heat sink.

In the variant of fig. 5, the heat sink 20 is provided with a cooling channel 21 and a plurality of cooling fins 24. The cooling channel 21 is adapted to allow a cooling medium, e.g. water, to flow through the heat sink 20. The cooling channel 21 of the heat sink has a cooling channel inlet 21 and an cooling channel outlet 23. In use, heat is transferred from the heat sink 20 to a cooling medium that flows through the cooling channel 21. The cooling medium removes the heat from the heat sink 20 when leaving the heat sink 20. The cooling fins 24 increase the outer surface of the heat sink 20, and therewith allow more heat to be dissipated from the heat sink.

The presence of the cooling channel 21 and the cooling fins 24 may improve the dissipation rate of heat from the heat sink 20, allowing to obtain an even lower temperature of the metal burner deck plate 3.

In the variant of fig. 5, preferably the shortest distance between an edge of the metal burner deck plate 3 and the heat sink is 60 mm or less, optionally 40 mm or less, preferably 30 mm or less, optionally 20 mm or less. The connection of the heat sink 20 to the metal burner deck plate 3 can be either direct or indirect.

Optionally, the heat sink 20 is arranged such that the shortest distance between any point of the metal burner deck plate 3 and the heat sink is 80 mm or less, optionally 80 mm or less, e.g. 40 mm or less, preferably 30 mm or less, optionally 20 mm or less.

Optionally, in this embodiment, the metal burner deck plate 3 has a plate thickness of between 0.4 mm and 10 mm, preferably between 0.5 mm and 5.0 mm, optionally between 0.6 mm and 2.0 mm, for example 1.5mm.

In case the metal burner deck plate 3 has a plate thickness of at least 1.5 mm, e.g. between 1.5 mm and 10 mm, preferably between 2.0 mm and 5.0 mm, optionally between 2.0 mm and 3.0 mm, for example 2.5mm, the heat sink 20 is optionally arranged such that the shortest distance between any point of the metal burner deck plate 3 and the heat sink is 150 mm or less, e.g. 120 mm or less, optionally 100 mm or less, for example 80 mm or less, preferably 70 mm or less, optionally 60 mm or less.

Fig. 6 shows schematically a variant of the embodiment of fig. 5.

In the variant of fig. 6, the heat sink 20 extends around the circumference of the metal burner deck plate 3.

Optionally, the heat sink 20 is provided with a cooling channel and/or a plurality of cooling fins. The cooling channel is adapted to allow a cooling medium, e.g. water, to flow through the heat sink.

Fig. 7 shows an embodiment of a gas outflow aperture 7. This embodiment of a gas outflow aperture 7 can be used in combination with all embodiments describes above and below.

In this embodiment, a burr 30 and/or dross 30* is present at a rim of at least one gas outflow aperture 7 on the side of the chamber facing surface 5 of the metal burner deck plate 3.

When the gas outflow apertures 7 are made by for example mechanical drilling or punching, or other types of providing the gas outflow apertures 7 by means of mechanically removing material, a burr 30 may be formed on the edge of the gas outflow aperture 7 on the side of the metal burner deck plate 3 opposite to the side of the metal burner deck plate 3 where the drill or punch or other tool enters the metal burner deck plate 3. When the gas outflow apertures 7 are made by for example laser cutting, laser drilling, or other types of making the gas outflow apertures 7 by means of removing material by melting, a dross 30* may be formed on the edge of the gas outflow aperture 7 on the side of the metal burner deck 3 plate opposite to the side of the metal burner deck plate 3 where the laser beam enters the metal burner deck plate 3.

In steel burner decks, positive effects on the susceptibility to flashback have been observed when the burr of dross is located on the flame facing free surface of the metal burner deck plate. Surprisingly, in premix gas burners according to the invention, tests show that a burr 30 or dross 30* on the chamber facing surface 5 of the metal burner deck plate 3 reduces the susceptibility to flashback.

Fig. 8 shows, schematically, an example of a metal burner deck plate 3 that can be used in premix gas burners according to the invention. It is noted that fig. 8 is not drawn to scale.

In this example, the gas outflow apertures 7 are arranged in clusters 10 with non- perforated areas 37 between the clusters 10. The smallest heart-to-heart distance between adjacent gas outflow apertures 7 in the same cluster 10 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.

The burner deck 2 is defined by the outermost gas outflow apertures 7 of the metal burner deck plate 3: the shortest line or lines 35 that can be drawn connecting the outermost edges of the outermost gas outflow apertures 7 of the metal burner deck plate 3 enclose or encloses the burner deck 2.

In fig. 8, the squares 36 are made up out of the shortest line or lines that can be drawn connecting the outermost edges of the outermost gas outflow apertures 7 of a single cluster 10. This defines the size and position of the clusters on the burner deck 2.

Optionally, in the example of fig. 8, the combined surface area of the gas outflow apertures 7 in the flame facing free surface 6 of the metal burner deck plate 3 is 10% or less of the total effective surface area of the flame facing free surface 6 of the metal burner deck 3 plate, optionally 7% or less, for example 5% or less.

The total effective surface area of the flame facing free surface 6 of the metal burner deck plate 3 is defined by the outermost gas outflow apertures 7 of the metal burner deck plate: the shortest line or lines35 that can be drawn connecting the outermost edges of the outermost gas outflow apertures 7 of the metal burner deck plate 3 enclose or encloses the total effective surface area of the flame facing free surface 6 of the metal burner deck plate 3.

These ratios of the combined surface area of the gas outflow apertures to the total effective surface area of the flame facing free surface of the metal burner deck plate allow a design of a premix gas burner that is suitable for combustion of a hydrogen-containing premix burner gas containing a fuel gas, which fuel gas contains at least 80 vol% of hydrogen.

Fig. 9 shows, schematically, a further embodiment of a premix gas burner according to the invention.

In this embodiment, the premix gas burner 1 for example comprises a metal burner deck plate 3 which has a two dimensional shape, i.e. is a flat plate.

Alternatively, the metal burner deck plate 3 has a non-cylindrical, three dimensional shape. For example, the metal burner deck plate 3 has a shape which extends on one or two sides beyond the mathematical plane that extends through the edge or edges of the metal burner deck plate 3. For example, the metal burner deck plate 3 has a curved or double curved shape. Optionally, the metal burner deck plate 3 has a non-cylindrical shape. For example, the metal burner deck plate 3 has a flat or domed or curved shape. Optionally, the metal burner deck plate 3 has a flat or domed or curved shape with an outer contour in the shape of a circle, an ellipse, a square, a rectangle, square or rectangle with rounded edges, a hexagon or an octagon. Optionally, the metal burner deck plate 3 in this embodiment is a metal burner deck plate in accordance with fig. 3 and fig. 4.

In this embodiment, the premix gas burner 1 further comprises a burner hood 51, which is arranged facing the chamber facing side 5 of the metal burner deck plate 3. The burner hood 51 is made of a thermally conductive material and is in thermal contact with a portion of the metal burner deck plate 3. Therewith, the burner hood acts as a heat sink.

In the example of fig. 9, the burner hood 51 comprises at least one cooling channel 52 which is adapted to allow a cooling medium, e.g. water, to flow through the burner hood 51.

Optionally, in this embodiment, the metal burner deck plate 3 comprises a non- perforated area 37 in which no gas outflow apertures 7 are present. In addition, in the embodiment shown in fig. 9, a blind area is located at an outer rim 38 or a part of the outer rim 38 of the metal burner deck plate 3.

Optionally, in the example of fig. 9, the burner hood 51 comprises a flange 54, which flange 54 is in thermal contact with the blind area 38 at the rim of the metal burner deck plate 3. In the example of fig. 9, the cooling channels 52 which is adapted to allow a cooling medium, e.g. water, to flow through the burner hood, extend through the flange 54.

In the example of fig. 9, the burner hood 51 comprises a rib 53, which rib 53 is in thermal contact with the non-perforated area 37 of the metal burner deck plate 3. Optionally, but not shown in fig. 9, a cooling channel which is adapted to allow a cooling medium, e.g. water, to flow through the burner hood, extends through the rib.

Fig. 10 shows, schematically, an embodiment of heater system in which a premix gas burner according to the invention is applied.

In the embodiment of fig. 10, a gas supply system 40 is provided, comprising for example an oxidiser gas supply duct 41, a fuel gas supply duct 42, an oxidiser gas supply fan 43, and a premix supply duct 44. The fuel gas and the oxidiser gas come together and are mixed to form the premix burner gas. The premix burner gas is supplied via the premix supply duct 44 to the gas supply chamber 4. The premix burner gas is combusted with the flames being stabilised onto the burner deck 2.

A heat exchanger 50 is provided, which comprises channels through which a medium, e.g. water or air, can pass that is heated by the flames on the burner deck 2. The medium absorbs heat that is generated by the flames, which heat is then used in the heater system, e.g. to heat a part of a building.

The heat exchanger is for example a cast metal heat exchanger or a stainless steel spiralled tube heat exchanger.

In the embodiment of fig. 10, a heat sink 20 is provided which is thermally connected to the metal burner deck plate of the burner deck 2.

The premix supply duct 44 has one or more duct entrances and a duct discharge, and the gas supply chamber 4 comprises a chamber entrance and a chamber inner volume. The duct discharge of the premix supply duct 44 is connected to the chamber entrance of the gas supply chamber. A fuel gas flow path is present which extends from the duct entrance of the premix supply duct 44 to the duct discharge of the premix supply duct 44, and further through the chamber entrance opening into chamber inner volume of the gas supply chamber 4. The heat sink 20 is arranged outside the fuel gas flow path.

In the embodiment of fig. 10, the heat sink 20 is in contact with the metal burner deck plate 3 as well as with the heat exchanger 50. This way, heat can be dissipated from the heat sink 20 via the heat exchanger.

Fig. 11 shows a part of a further embodiment of a heater system comprising a premix gas burner 1 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.

The heater system of fig. 11 further comprises a heat exchanger 50.

In this embodiment, at least a part of the heat exchanger 50 is made of a cast metal.

Optionally, in this embodiment, also at least a part 15 of the premix gas burner 1 is made of a cast metal. Optionally, but not shown in fig. 11, the cast metal part 15 of the premix gas burner 1 is integral with the cast metal part of the heat exchanger 50.

In the embodiment of fig. 11, the heater system comprises a premix gas burner 1 having a heat sink 20 which is thermally connected to the metal burner deck plate 3, and the part 15 of the premix gas burner which is made of a cast metal is or includes the heat sink 20.

Optionally, the cast metal is cast aluminium or a cast aluminium alloy.

Fig. 12 shows the Young's modulus at room temperature in GPa on the vertical axis and the thermal conductivity coefficient at room temperature in W/(mK) on the horizontal axis for a number of common metals. The references a — | represent: a: stainless steel b : cast iron c: iron d : nickel e : tungsten f: chromium g : brass h : platinum i © aluminium j: gold k : copper : silver

Claims

CONCLUSIONS

CLAIMS 1. Premix gas burner for burning a hydrogen-containing premix burner gas comprising a fuel gas, which fuel gas comprises at least 80 vol hydrogen, comprising - a gas supply chamber adapted to receive the hydrogen-containing premix burner gas, - a burner deck, which burner deck has a metal burner deck plate, said metal burner deck plate comprising a chamber-facing surface on one side and a flame-facing free surface on the opposite side, and a plurality of gas orifices extending through the metal burner deck plate from the chamber-facing surface to the flame-facing free surface surface, the gas orifices permitting the hydrogen-containing premix burner gas to flow from the gas supply chamber to a combustion zone adjacent the flame-facing free surface of the metal burner cover. wherein the gas orifices are sized and spaced to permit combustion of the hydrogen-containing premix burner gas in the combustion zone, wherein the metal burner cover plate is made of metal having a thermal conductivity coefficient at room temperature of at least 80 W/{mK) and a Young's modulus at room temperature of 150GPa or less.

The premix gas burner according to claim 1, wherein the premix gas burner further comprises a heat extractor, thermally connected to the metal burner cover, and adapted to extract heat from the metal burner cover and dissipate the extracted heat.

3. Premix gas burner according to one of the preceding claims, wherein the thermal conductivity coefficient at room temperature of the metal burner cover plate is at least 100 W/(mK), optionally at least 120 W/(mK).

4. Premix gas burner according to one of the preceding claims, wherein the metal burner cover plate has a plate thickness of between 0.4 mm and 10 mm, preferably between 0.5 mm and 5.0 mm, optionally between 0.6 mm and 2.0 mm.

5. Premix gas burner according to claim 2,

wherein the shortest distance between an edge of the metal burner cover plate and the heat extractor is 60 mm or less, for example 40 mm or less, preferably 30 mm or less, optionally 20 mm or less, and/or the shortest distance between the center of the metal burner cover plate and the heat sink 80 mm or less, e.g. 60 mm or less, optionally 40 mm or less, preferably 30 mm or less, optionally 20 mm or less.

A premix gas burner according to claim 2 or claim 5, wherein the premix gas burner comprises a premix supply channel having a channel entrance and a channel exit, and wherein the gas supply chamber comprises a chamber entrance and an internal chamber volume, the channel exit of the premix supply channel being connected with the chamber entrance of the gas supply chamber, and having a fuel gas flow path extending from the channel entrance of the premix supply channel to the channel exit of the premix supply channel and further through the chamber entrance opening to the interior chamber volume of the gas supply chamber, and wherein the heat extractor is located outside the fuel gas flow path.

7. Premix gas burner according to claim 2, claim 5 or claim 6, wherein the heat extractor is provided with a cooling channel and/or a cooling rib.

8. A premix gas burner according to any one of the preceding claims, wherein a burr or melting burr is present at an edge of at least one gas outlet opening on the side of the chamber-facing surface of the metal burner cover plate.

A premix gas burner according to any one of the preceding claims, wherein the combined area of the gas outlet openings in the flame-facing free surface of the metal burner cover plate is 10% or less of the total effective area of the flame-facing free surface of the metals. burner cover plate, e.g. 5% or less.

10. A premix gas burner according to any one of the preceding claims, wherein the gas outlet openings are arranged in clusters, wherein the smallest centre-to-centre distance between adjacent gas outlet openings in the same cluster is smaller than the smallest centre-to-centre distance between a first gas outflow opening in a first cluster and a second gas outflow opening in a second cluster, the second cluster being located adjacent to the first cluster.

A premix gas burner according to any one of the preceding claims, wherein the premix gas burner further comprises a burner cap extending around the periphery of the chamber-facing surface of the metal burner cover.

A premix gas burner according to claim 11, wherein the metal burner cover plate and the burner cap are integral with each other and are optionally made of cast aluminum or cast aluminum alloy.

A premix gas burner according to any one of the preceding claims, wherein the metal burner cover plate has a non-cylindrical shape.

A heating system comprising a premix gas burner according to any one of the preceding claims.

The heating system of claim 14, wherein the heating system further comprises a heat exchanger, and wherein at least part of the heat exchanger is made of cast metal, and wherein at least part of the premix gas burner is made of cast metal, and wherein the cast metal part of the premix gas burner is integral with the cast metal part of the heat exchanger.

A heating system according to claim 15, wherein the heating system comprises a premix gas burner according to claim 2, and wherein the part of the premix gas burner which was made of cast metal is or comprises the heat extractor.

A heating system according to any one of the preceding claims, wherein the heating system comprises a burner chamber and the premix gas burner is arranged in the burner chamber.