WO2023187215A1

WO2023187215A1 - Gas burner with low nox emission

Info

Publication number: WO2023187215A1
Application number: PCT/EP2023/058597
Authority: WO
Inventors: Willem Pieter Jacobus Pastoor; Marco Anton Frederik DERKSEN; Franciscus Adrianus Maria Knijnenburg; Marcus Theodorus van der Cruijsen
Original assignee: Combustion2 B.V.
Priority date: 2022-04-01
Filing date: 2023-04-01
Publication date: 2023-10-05
Also published as: EP4253838A1

Abstract

The invention provides a gas burner for burning a fuel gas using fuel staging, said gas burner having a center line A and comprising: - a primary fuel gas discharge opening (2) for introducing a first fraction of said fuel gas as primary fuel gas into a primary flame region (P) on said center line A for in operation fuelling a primary flame; - a series of main fuel gas discharge openings (3) for introducing a second fraction, larger than said first fraction, of said fuel gas as main fuel gas at a main flame region (M) downstream around said primary flame for in operation fuelling a main flame; - a series of exhaust gas return discharge openings (4) extending in said gas burner for introducing recirculated exhaust gas around said primary flame region (P) upstream of said primary flame for in operation introducing said exhaust gas into said main fuel before it ignites by said primary flame, and - an end plate at the end of the primary fuel gas discharge opening, wherein said exhaust gas discharge opening is upstream of said end plate.

Description

Gas burner with low NOx emission

Field of the invention

The invention relates to a gas burner, and a method for burning gas.

Background of the invention

JP2018076979 in its (translated) abstract states: “To provide a hydrogen gas combustion burner device capable of suppressing the generation of NOx without reducing the amount of combustion heat which can be taken out to the outside. [Means for solving] A hydrogen gas combustion burner device 1 has a return pipe 15 which has one end communicated with a combustion space I l a and which recirculates a part of a combustion exhaust gas generated by combustion by hydrogen gas and air in a combustion space 11 a. In a hydrogen gas combustion burner device 1, a hydrogen gas supply pipe 12 has an exhaust gas introduction port 12 b which is provided on an upstream side of an injection port 12 a and which is connected with the other end of a return pipe 15 opposite to the combustion space 11 a to introduce a combustion exhaust gas into the hydrogen gas supply pipe 12.”

This was found to increase the thermal efficiency (“stooktechnisch rendement”) and especially with hydrogen can lead to early combustion even to the place of introduction of the exhaust gas.

CN1 11121023 in its (translated) abstract states: “The invention discloses a fuelside flue gas recirculation low-nitrogen combustor and a combustion method thereof. The fuel-side flue gas recirculation low-nitrogen combustor comprises a pilot fuel pipe, an air flow channel, a main fuel mixing channel, a fuel distribution ring pipe and a recirculating flue gas distribution ring pipe. Fuel forms main fuel and pilot fuel through the fuel distribution ring pipe, and the main fuel and recirculating flue gas are rapidly mixed through the main fuel mixing channel to form mixed flue gas fuel which is then jetted into a combustion chamber. Meanwhile, the pilot fuel is pre-mixed with central air in a pilot fuel pre-mixing cavity to form a swirling lean fuel pre-mixed pilot flame in a swirling disc. The rest of air forms a high-speed jet through an annular air nozzle between the pilot fuel premixing cavity and the air flow channel and is quickly mixed with the mixed flue gas fuel, flameless combustion of the main fuel is achieved, and the generation of NOX is greatly reduced. The fuel-side flue gas recirculation low-nitrogen combustor and the combustion method thereof have the advantage of stable combustion, solve the contradiction between great reduction of the oxygen content in low-NOx combustion and combustion stability, and can achieve low-NOx emission.”

US2014/272736 in its abstract states: “ A low NOx combustion method includes steps of injecting reactants into a combustion chamber. A primary reactant stream, including fuel and combustion air premix, is injected from a premix burner port into the combustion chamber. A staged fuel stream is injected into the combustion chamber from a staged fuel injector port adjacent to the premix burner port. A stream of recirculated flue gas is injected into the combustion chamber from a flue gas injector port that is adjacent to the premix burner port and adjacent to the staged fuel injector port. In this manner, the stream of recirculated flue gas is injected into the combustion chamber unmixed with the primary reactant stream and unmixed with the staged fuel stream.”

US5284438 in its abstract states: “A multiple purpose burner process and apparatus in which a burner assembly having a burner member defining a burner throat bore extending therethrough and forming an ignition zone and at least one mixing zone in the burner throat bore, the total combustion air passing through the burner throat bore. A minor portion of fuel gas as ignition fuel produces a continuous ignition flame in the ignition zone, and plural meter channels extending through the burner member communicate with the mixing zone to pass an admixture of a diluent gas with the remainder portion of the fuel, as a primary fuel stream, to the mixing zone for forming with the remaining combustion air a primary fuel/diluent/combustion air mixture, and the primary fuel/diluent/combustion air mixture is ignited by the ignition flame in the mixing zone. Diluents can be internally recirculating flue gas or can be from an external source, and the flame envelope achieved by the burner assembly can be variously shaped for an industrial combustion application as required.”

Known gas burners produce a high amount of NOx, despite measures. The requirements regarding NOx emissions are getting ever tighter. Known gas burners with reduces NOx emission have reduced thermal efficiency, reduced reliability, condensation, and other drawbacks.

Summary of the invention A disadvantage of the prior art, as mentioned, is that measures to reduce NOx emission in gas burners have setbacks in view of condensation, reduced efficiencies, reduced reliability. For instance, when not in operation, channels are filled with air and these cause high local temperatures upon (re-)ignition.

Hence, it is an aspect of the invention to provide an alternative gas burner, which preferably further at least partly obviates one or more of above-described drawbacks.

There is provided a gas burner (1) for burning a fuel gas using fuel staging, said gas burner having a center line A and comprising:

- a primary fuel gas discharge opening (2) for introducing a first fraction of said fuel gas as primary fuel gas into a primary flame region (P) on said center line A for in operation fuelling a primary flame;

- a series of main fuel gas discharge openings (3) for introducing a second fraction, larger than said first fraction, of said fuel gas as main fuel gas at a main flame region (M) downstream around said primary flame for in operation fuelling a main flame;

- a series of exhaust gas return discharge openings (4) extending in said gas burner for introducing recirculated exhaust gas around said primary flame region (P) upstream of said primary flame for in operation introducing said exhaust gas into said main fuel before it ignites by said primary flame.

In particular the gas burner further comprises an end plate at the end of the primary fuel gas discharge opening, wherein said exhaust gas discharge opening is upstream of said end plate.

There is further provided a method for burning fuel gas comprising a combustion chamber and a gas burner extending into said combustion chamber, said method comprising providing a primary flame via said gas burner in said combustion chamber, introducing fuel gas around said primary flame, and introducing recirculated exhaust gas via said gas burner around said primary flame upstream of said primary flame for in operation mixing said exhaust gas into said main fuel before igniting into said main flame.

The presented design provides low NOx emission for hydrocarbon gas as fuel gas. The presented gas burner also provides a low NOx emission when using hydrogen as fuel gas. In fact, in both uses the resulting efficiencies and reliability are high. Furthermore, Condensation remains low. In combustion processes with air as oxidant, NOx usually forms at temperatures above 1500 degrees Celsius. The current gas burner design allows a low NOx emission while maintain a high efficiency.

Fuel gas comprises but is not limited to hydrogen, natural gas and other fuels that are in gaseous state when entering the burner and which have a lower heating value typically above 10 MJ/m3 at room temperature, or any mixtures thereof. Fuel gas can be a mixture of (these) gasses. In one embodiment, fuel gas mainly comprises natural gas. In another embodiment, fuel gas comprises mainly hydrogen. Hydrogen is mostly provided in a highly pure form.

Fuel gas can be a mixture of gasses. Such a mixture can comprise methane, hydrogen, and further lower hydrocarbon gas.

The current gas burner is for instance used in an assembly producing 2-50 MW of thermal heat input. More in particular, it is used in an assembly producing 3-50 MW. More in particular, the gas burner is used in an assembly producing 5-50 MW. More in particular, the gas burner is used in an assembly producing 5-35 MW. More in particular, the gas burner is used in an assembly producing 5-25 MW. Specifically, it is used in an assembly producing 5-15 MW. More than one of the current gas burners can be used in one hearth.

When properly operated, the current gas burner can be operated to result in a low NOx emission. In this respect, the gas burner can be operated with flue gasses still comprising oxygen but no unburnt fuel or combustion still taking place. In such conditions, NOx emission can be lower than 30 mg/m³ of flue gas (corrected to 3 vol.%02). The primary flame is maintained at the center line.

The current gar burner in an embodiment operated by a small overpressure of the various components. Often, the gaseous fuel is introduced at an overpressure of below 1 bar (10⁵ Pa). Often, the overpressure is more than 100 mbar (10 KPa). In most operating conditions, the overpressure is between 200 and 600 mbar (20-60 KPa). In other words and in particular, the air-sided overpressure over the gas burner is 15-20 mbar (1.5-2.0 Kpa). The other components like air and return exhaust gas are introduced at suitable pressures adapted to the fuel pressure and required gas burner conditions.

In the current gas burner, a distinction is made between the primary flame and the main flame. In this respect, the primary flame is a central flame that receives its fuel gas from the primary fuel gas discharge opening. The primary flame furthermore receives its oxygen mainly from the primary air discharge opening.

When operating the current gas burner, a primary flame is ignited and is set for proper burning. The main fuel gas is introduced with the exhaust gas from the installation recirculated and introduced functionally around the primary flame. In embodiments, a flame detector will be used to provide feedback for controlling the process of starting and operating the current gas burner.

In the current gas burner, there is provided an exhaust gas discharge opening. This discharge opening is provided for introducing exhaust gas. In an embodiment, at least a part of the exhaust gas is recirculated for an exhaust outlet from an installation in which the current gas burner is installed.

The current gas burner is suited for burning hydrogen, natural gas or mixtures thereof. The gas burner is also suitable for comparable high caloric gaseous fuels in an industrial Fire Tube Boiler, in particular having an output of more than 3MW. In an alternative embodiment, the gas burner is suitable for water-tube boilers. The current design enables an ultra-low NOx emission without compromising: o thermal efficiency of the installation (in other words, low O2 content in the exhaust gasses emitting from the exhaust pipe) o Stability and reliability of the installation o heat density (in other words, fire room/hearth/fumace/furnace room volume per MW introduced power, or typically 1.2 - 1.5 MW per m³ hearth space)

Unique features of the design o No external flue gas circulates directly into the central or primary flame, which provides a stable flame for the complete burner), keeping it stable, even in case of a high overall external exhaust gas recirculation o No risk of condensation of water vapor present in the exhaust gas on

□ flame supervision - preventing loss of view of the flame, causing ‘tripping’

□ the ignition burner, causing malfunctioning and preventing the installation to restart after downtime

□ Carbon steel internal parts, causing corrosion and failure in the long run o Resulting in extreme low NOx emission, even at high furnace heat loads, and even at high amounts of external exhaust gas recirculation.

Typical values relating to natural gas are o fire hearth load of 1 ,3MW/m³ of furnace room o NOx emission < 30mg/(m³ of furnace room) (corrected to 3 vol% O2

(BEMS), dry, in the flue gases exiting via the stack) o Turndown 1 : 10 or higher o O2 contents in the chimney <= 3% (vol, dry), aim is < 1% 02 (vol%, dry)

In an embodiment, the series of main fuel gas discharge openings are arranged around the gas burner center line (A).

In an embodiment, the series of exhaust gas return discharge openings are arranged around the gas burner center line (A).

In an embodiment, the series of exhaust gas discharge openings are provided upstream of a start of said primary flame (P).

In an embodiment, the first fraction is 1-35% of said fuel gas and said second fraction is 99-65 % of said fuel gas. In particular, the first fraction is 2-30% of said fuel gas and said second fraction is 98-70 % of said fuel gas. More in particular, the first fraction is 5-20% of said fuel gas and said second fraction is 95-80 % of said fuel gas.

In an embodiment, the gas burner further comprises a primary air discharge opening for introducing primary air into said primary flame region (P). In particular, the primary air discharge opening extends up to said primary flame region. More in particular the primary fuel gas inlet discharge opening has its central axis concentric with said center line (A).

In an embodiment, the gas burner further comprises a sleeve surrounding said series of main fuel gas inlet discharge openings and said series of exhaust gas return discharge openings. In particular the sleeve extends up at said main flame region (M).

In an embodiment, the sleeve at its downstream end continuing in a tapering ring extending up to said main flame region (M). More in particular said tapering ring has its upstream start at said primary flame region (P).

In an embodiment, the tapering ring comprises a downstream end, wherein at said downstream end parts of said tapering ring are taken out of said downstream end of said tapering ring. In particular, bites or indentions are taken out of the tapering ring. In particular these indentations are provided at, or are aligned with, each main fuel gas discharge opening. In an embodiment, the sleeve, the primary air discharge opening and the primary fuel gas discharge opening are functionally concentric. In particular, a spacing between said sleeve and said primary air discharge opening defines a main air discharge opening.

In an embodiment, the gas burner comprises an end plate at the end of the primary fuel gas discharge opening. In particular, the end plate is at said upstream start of said tapering ring.

In an embodiment, the end plate comprises a central opening on said center line (A). The primary fuel gas discharge opening is positioned upstream of said central opening.

In an embodiment, the end plate comprises radial slits. In particular these radial slits start at a distance from the central opening. In an embodiment they extend radially up to a distance from an edge of said end plate. These slits are positioned in such a way to provide the primary air discharge openings.

In an embodiment, the end plate closes off said primary air discharge opening. In this way the slits provide air discharge openings.

In an embodiment, an end opening of the tapering ring has a circumference that is larger than a circumference of said end plate.

In an embodiment, the main fuel gas discharge openings comprise a bent end which bends tangential with respect to a circle around said center line A.

In an embodiment, the main fuel gas discharge openings are grouped into pairs. In an embodiment the bent ends bend towards each other.

In an embodiment, the main fuel gas discharge opening is positioned downstream of the end plate.

In an embodiment, the main fuel gas discharge opening is upstream of an end of said tapered ring.

In an embodiment, the exhaust gas discharge opening is positioned at an upstream end of said tapered ring.

In an embodiment, the exhaust gas discharge opening is provided between a pair of main fuel gas discharge openings.

In an embodiment, the exhaust gas discharge opening is upstream of the end plate. In an embodiment, the gas burner is for burning hydrogen gas. In an embodiment, the end plate comprises 3-6 auxiliary passages around said main opening, and a series of primary fuel discharge openings at each auxiliary passage.

In an embodiment, the end plate comprises radial slits. In particular the auxiliary passages are provided between these radial slits.

In an embodiment, the primary fuel discharge openings are in substantially tangential direction with respect to a circle around the center line A. In particular, the primary fuel gas discharge openings are at bent ends of primary fuel conduits.

There is further provide the use of a gas burner as described for burning a fuel gas mainly comprising hydrogen (H2). In particular at least 90% wt. hydrogen. More in particular at least 95% wt. hydrogen. Specifically at least 99% wt. hydrogen.

There is further provide the use of a gas burner for burning a fuel gas mainly comprising methane (CH4). In particular at least 90% wt. methane. More in particular at least 95% wt. methane. Specifically at least 99% wt. methane.

Some of the embodiments described above may in particular be advantageous for using amounts of added hydrogen as a fuel. In particular using large additions of hydrogen. For instance at least 90% wt. hydrogen. More in particular at least 95% wt. hydrogen. Specifically at least 99% wt. hydrogen.

There is further provided a gas burner for burning a fuel gas using fuel staging, said gas burner having a center line A and comprising:

- a primary fuel gas discharge opening for introducing a first fraction of said fuel gas as primary fuel gas into a primary flame region on said center line A for in operation fuelling a primary flame;

- a series of main fuel gas discharge openings for introducing a second fraction, larger than said first fraction, of said fuel gas as main fuel gas at a main flame region downstream around said primary flame for in operation fuelling a main flame;

- a series of exhaust gas return discharge openings extending in said gas burner for introducing recirculated exhaust gas around said primary flame region upstream of said primary flame for in operation introducing said exhaust gas into said main fuel before it ignites by said primary flame.

In embodiments, features described above may in combination be included for solving the problems mentioned. The terms “upstream” and “downstream” relate to an arrangement of items or features relative to the flow of fuel gas, wherein relative to a first position within a gas burner, a second position in the gas burner closer fuel gas inlet “upstream”, and a third position within the gas burner further away from the gas inlet is “downstream”. In other words, relative to the main air flow direction through a gas burner, with respect to the gas burner head or exhaust nozzle, "upstream" means further into the gas burner and towards the air fan counter to the direction of the main air flow, and "downstream" means further away from the gas burner in the boiler, i.e. along the main flow direction of the gases.

The term “substantially” herein, such as in “substantially all emission” or in “substantially consists”, will be understood by the person skilled in the art. The term “substantially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term “substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” includes also embodiments wherein the term “comprises” means “consists of’.

The term "functionally" will be understood by, and be clear to, a person skilled in the art. The term “substantially” as well as “functionally” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective functionally may also be removed. When used, for instance in “functionally parallel”, a skilled person will understand that the adjective “functionally” includes the term substantially as explained above. Functionally in particular is to be understood to include a configuration of features that allows these features to function as if the adjective “functionally” was not present. The term “functionally” is intended to cover variations in the feature to which it refers, and which variations are such that in the functional use of the feature, possibly in combination with other features it relates to in the invention, that combination of features is able to operate or function. For instance, if an antenna is functionally coupled or functionally connected to a communication device, received electromagnetic signals that are receives by the antenna can be used by the communication device. The word “functionally” as for instance used in “functionally parallel” is used to cover exactly parallel, but also the embodiments that are covered by the word “substantially” explained above. For instance, “functionally parallel” relates to embodiments that in operation function as if the parts are for instance parallel. This covers embodiments for which it is clear to a skilled person that it operates within its intended field of use as if it were parallel.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices or apparatus herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The invention further applies to an apparatus or device comprising one or more of the characterising features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterising features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Furthermore, some of the features can form the basis for one or more divisional applications.

Brief description of the drawings Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Figure 1 schematically depicts a side view of a gas burner;

Figure 1A the gas burner of figure 1 with schematically the primary and main flame;

Figure 2 shows a perspective view of the gas burner of figure 1;

Figure 3 shows a frontal view of the gas burner of figures 1 and 2;

Figure 4 schematically depicts a perspective view of an alternative gas burner;

Figure 5 shows a front view of the gas burner of figure 4;

Figure 6 shows a side view of the gas burner of figures 4 and 5;

The drawings are not necessarily on scale

Description of preferred embodiments

In the description below, a first embodiment of a gas burner is illustrated in figures 1-3, and a second embodiment is illustrated in figures 4-6. Please note that for reason of readability, not all the features in the drawings comprise reference numbers, and in some drawings only one or more but not all of the similar or identical features are provided with reference numbers.

Figures 1-3 schematically depict various view of an embodiment a current gas burner 1. In particular, figure 1 schematically depicts a side view of a gas burner 1, figure 2 shows a perspective view of the gas burner 1 of figure 1, figure 3 shows a frontal view of the gas burner 1 of figures 1 and 2.

The gas burner 1 or burner head 1 has a center line A, a front end or downstream end where a flame is formed when the gas burner is in operation, and an upstream end where gasses (fuel, air/oxygen, exhaust return gas) are introduced. The gas burner 1 is usually mounted in a burner chamber or furnace room (not indicated).

Gas burner 1 in the depicted embodiment comprises various conduits for introducing gasses at well-defined regions of the gas burner 1. These conduits feed discharge openings that are positioned with respect to a gas burner center line A.

In the current gas burner 1, there are conduits to provide primary fuel gas and primary air/oxygen for a primary flame, as well as main fuel gas, main air/oxygen and recirculated exhaust gas for a main flame. In the current embodiment, it was found that the addition of recirculated exhaust gas in the way illustrated in the current embodiment lowers the amount of nitrogen oxides (NOx). It may be that the exhaust gas lowers the local flame temperature but does not lower the burning efficiency of the gasses.

In the embodiment illustrated in figures 1-3, there is provided a primary fuel gas discharge opening 2. The primary fuel gas discharge opening 2 may be functionally coaxially with the gas burner center line A. It can also be described or interpreted as that the center line of the primary fuel gas discharge opening 2 functionally defines the gas burner center line A. In the current embodiment, primary fuel gas discharge openings are provide around the center line A. The primary gas discharge opening 2 is fed by a primary fuel gas conduit 15. In order to provide a flow of primary gas along the gas burner center line A, the primary fuel gas conduit 15 can be provided substantially coaxially with respect to the gas burner center line A. In the current embodiment, each primary gas discharge opening 2 is fed by a primary fuel gas conduit 15. This allows introduction of fuel gas into a primary flame region P for in operation fuelling a primary flame.

The embodiment illustrated in figures 1-3 further comprises a series of main fuel gas discharge openings 3. These main fuel gas discharge openings 3 are provided for introducing fuel gas as main fuel at a main flame region M. In the current embodiment, this main flame region M is downstream around said primary flame P for in operation fuelling a main flame. The main fuel gas discharge openings 3 are fed by main fuel gas conduits 14. In the current embodiment, each main fuel gas discharge openings 3 is fed by a main fuel gas conduits 14. In the depicted embodiment, the main fuel gas conduits 14 run substantially parallel to the gas burner center line A. This provides a steady flow into the main flame region M. The primary flame region and main flame region are indicated in figure 1 A.

The amount of primary fuel gas and the amount of main fuel gas form respectively a first fraction and a second fraction. Usually, the second fraction is larger that the first fraction. In most applications, the first fraction is 5-20% of the fuel gas and the second fraction makes 95-80% of the fuel gas. In an embodiment, a cross sectional outlet opening of the primary fuel gas openings and a cross sectional outlet opening of the main fuel gas discharge openings are selected for realising the first and second fraction. The embodiment illustrated in figures 1-3 further comprises a series of exhaust gas discharge openings 4. These exhaust gas discharge openings 4 are positioned in said gas burner 1 for introducing recirculated exhaust gas around said primary flame region P upstream of said primary flame. Furthermore the exhaust gas discharge openings 4 are provided for in operation introducing the exhaust gas into the main fuel before it ignites by said primary flame. The exhaust gas is composed of recirculated exhaust gas. This was found to lower the NOx emission. This was possible for hydrocarbon fuel gas, but also and surprisingly for hydrogen fuel gas. There are many possible ways of providing discharge openings. In the current embodiment, each discharge opening is fed by an exhaust gas return conduit 16. For a steady flow, the exhaust gas return conduits 16 run substantially parallel to the gas burner center line A.

The specific introductions of fuel gas fractions, air/oxygen and exhaust gas is possible through the positioning of discharge openings at or near the (downstream) ends of the various, respective conduits.

In figures 1-3, the series of main fuel gas discharge openings 3 are arranged around the gas burner center line A. In the current embodiment shown, the series of main fuel gas discharge openings 3 are arranged on a circle around the gas burner center line A. In an alternative embodiment, a ring conduit around the gas burner center line A and provided with discharge openings may be provided. In the current embodiment, the main fuel gas discharge openings 3 are evenly divided on the circle around the gas burner center line A. This in operation allows providing a cylinder of main fuel gas around the gas burner center line A. Furthermore, this is downstream of the primary flame.

In the embodiment of figures 1-3, the series of exhaust gas discharge openings 4 are arranged around the gas burner center line A. In particular, these exhaust gas discharge openings 4 are here arranged on one circle around the gas burner center line A. In an alternative embodiment, again a circular ring with discharge openings may be provided.

In the current embodiment, the exhaust gas discharge openings 4 are provided near the main fuel gas discharge openings 3. The exhaust gas discharge openings 4 are in particular provided to emit (recirculated) exhaust gas near the main fuel gas discharge openings 3. In particular, the exhaust gas discharge openings 4 in particular are positioned to emit or inject exhaust gas downstream of a start of said primary flame P region for in operation introducing the exhaust gas into the main fuel before it ignites by said primary flame. In particular, by providing exhaust gas discharge openings 4 around the gas burner center line and around the primary flame, and mixing with the main fuel gas before it ignites, it allows lowering NOx formation.

In the current embodiment, actual main fuel gas discharge openings 3 are grouped. Here, each time two main fuel gas discharge openings 3 are grouped together or are paired. Each group provides a main gas flow of jet when in operation. They may be provided around the centre line in other configurations, or on more circles, for instance.

In the embodiment of figures 1-3, the series of main fuel gas discharge openings 3 emit their main fuel into said main flame region M.

The embodiment of figures 1-3 further comprise a primary air discharge opening 9 for introducing primary air into said primary flame region P. In particular, the primary air discharge opening 9 extends up to the primary flame region. The primary fuel gas discharge opening 2 may have its central axis concentric with said center line A. In the current embodiment, the primary fuel gas discharge openings 2 are positioned equidistantly around the center line A. In other words, on a circle having the center line as a circle center.

In the current embodiment, the various discharge openings are each fed by a conduit. These conduits here run substantially parallel to the gas burner center line A. The conduits described so far usually are rigid pipes, often made from steel. They have an open end that provide a discharge opening.

The depicted embodiment further comprises a sleeve 6 surrounding the series of main fuel gas discharge openings 3 and the series of exhaust gas discharge openings 4. In particular, the sleeve 6 extends up to the main flame region M. In an embodiment, the sleeve 6 is provided in such a way that the sleeve 6 extends up to a predetermined distance into a furnace, measured from the place the gas burner enters the furnace. Usually this is measured from the wall where in enters the furnace.

The inner surface of the sleeve 6 and the outer surface of the primary air conduit 17 provide the main air channel.

The illustrated sleeve 6 at its downstream end continues in, or comprises, a tapering ring 11. The tapering ring here extends up to the main flame region M. More in particular, the tapering ring 11 here has its upstream start at the primary flame region P. In most applications, the tapering ring 11 has an angle of between 40 and 50 degrees. In particular, the angle of the tapering ring will be between 42 and 47 degrees. In an embodiment, the angle is around 45 degrees.

In the depicted embodiment, the tapering ring 11 comprises a downstream end. At that downstream end, parts 13 of said tapering ring 11 are take out. In particular bites or indentions 13 are taken out of said downstream end of said tapering ring (11). In the embodiment, these indentations 13 are provided at, or are aligned with, each main fuel gas discharge opening 3.

In the illustrated embodiment, the sleeve 6, the primary air discharge opening 9, and the primary fuel discharge opening 2 are functionally concentric.

In the embodiment of figures 1-3, the gas burner 1 comprises an end plate 5 at or near the primary fuel gas discharge opening 2. In particular, the end plate 5 is provided at or near the upstream start of said tapering ring 11. The end plate 5 is provided at or near an end of the primary fuel gas conduit 2.

The end plate 5 here comprises a central opening 8 on said center line A. The primary fuel gas discharge opening 2 may be provided upstream of the central opening or passage 8. In the current embodiment, the gas burner 1 comprises an end plate attachment 10. Here, a pipe 10 is provided having an end attached to the end plate 5 for holding the end plate 5 in place. Alternatively, the pipe 10 ends at a distance upstream of the central opening. In an embodiment the end plate 5 is attached to and held in place by the primary air conduit 17. In such an embodiment, air flows out of the central opening 8 too.

In the current embodiment, the end plate 5 comprises radial slits 12 starting at a distance from the central opening 8. The radial slits 12 further extend radially up to a distance from an edge of end plate 5. An air discharge opening 9 is provided just upstream of the end plate. The air discharge opening 9 is here provided coaxially around the center line A. Thus, the end plate 5 and its radial slits are provided in such a manner that in operation the air from air discharge opening will flow through the radial slits. Downstream of the end plate 5, the air will start to mix with the primary fuel that flows out of the primary fuel discharge opening 2 and through the central opening 8 in the end plate 5. In the current embodiment, a primary air conduit 17 is provided. The primary air conduit 17 is here coaxial with the center line A. In particular, the primary air conduit 17 is coaxial around the primary fuel gas conduit 15. In the current embodiment, an end of primary air conduit 17 provides the primary air discharge opening 9. This primary air discharge opening is upstream just before the end plate central opening 8.

In the currently illustrated embodiment, an end opening of said tapering ring 11 has a circumference that is larger than a circumference of the end plate 5.

The configuration of the end plate 5, primary fuel gas discharge opening 2, tapering ring 11 and sleeve 6 define the primary flame region P. Furthermore, the main fuel gas discharge openings 3, exhaust gas discharge openings 4, the sleeve 6 and its tapering end 11 allow delivery of the respective recirculated exhaust gas and main fuel gas in a cylinder around the primary flame region P end define the main flame region M.

In the depicted embodiment, main fuel gas conduits 3 comprise a bent end 7. In the depicted embodiment, these bent ends 7 which bends in a tangential direction with reference to a circle having the center line A as its middle.

In the depicted embodiment, the main fuel gas conduits 3 are grouped into pairs or paired. In particular, the pairs of main gas conduits 3 have an exhaust gas conduit 4 between then. The bent ends 7 of the pairs of main fuel gas conduits 3 here bent in tangential direction towards each other. The bent ends 7 of the pairs are bent towards the exhaust gas conduit 4. This provides a proper mixing of fuel gas and exhaust gas before ignition by the primary flame. In some smaller gas burners, three pairs of main gas conduits are provided, and in larger type gas burners, four pairs are provided.

In the depicted embodiment, the main fuel gas discharge openings 3 are downstream of the end plate 5.

In the embodiment, the main fuel discharge openings 3 are in axial direction in the tapered ring 11. Furthermore, the exhaust gas discharge openings are upstream of the tapered ring 11. In an embodiment, the exhaust gas discharge openings are upstream of the end plate 5.

As explained before, the current gas burner is also very suitable for burning other gas, like for instance hydrogen. Hydrogen usually tends to bum fierce and at high temperatures, causing NOx formation. Furthermore in a gas burner, hydrogen tends to start burning at a much more broad range of mixtures of fuel and air than for instance methane or natural gas. Thus, it tends to start burning directly at the discharge openings. In figures 4-6, the current gas burner is provided with optimizations for making it more suitable for burning hydrogen. For this reason, there is no flame indicated in figures 4-6: the hydrogen starts burning directly at the discharge opening of fuel conduits.

In the embodiment of figures 4-6, the main parts are the same as presented in figures 1-3.

One of the differences is in the constellation of the introduction of the primary fuel gas for the primary flame. In the current embodiment, there are a series of primary fuel gas discharge openings 2 provided at the end plate 5. To that end, the end plate 5 is provided with end plate primary fuel gas openings 18. A series of primary fuel gas discharge openings 2 are provided. Here, these primary fuel gas discharge openings 2 are provided around the center line A. In particular, they can be provided on an imaginary circle. As already explains in the main fuel discharge opening 3 and exhaust gas return discharge opening 4, here also a circular ring can be provided, which circular ring van be provided with the discharge openings.

In the embodiment of figures 4-6, the primary fuel gas discharge openings 2 are provided by bent ends 18 of primary fuel gas conduits 15. These bent ends 18 are furthermore directed in a tangential direction with respect to a circle around the center line A. This allows proper mixing with primary air from the radial slits 12 and the central opening 8 of the end plate 5.

Another difference with respect to the embodiment of figures 1-3 is the end part of the main fuel gas conduits 14. In embodiment of figures 1-3, the ends of main fuel gas conduits 14 are bent. In the embodiment of figures 1-3, the main fuel gas conduits 14 have a bent part 7 that is designed to force a gaseous flow at an angle a away from the main fuel gas conduit’s axial direction, of with respect to the center line A. In this current embodiment, the bent part 7 is a tube end that is attached to the further main fuel gas conduit 14 at the angle a. In the depicted embodiment, it leaves an opening or slit at the start of the bent part 7 that allows a part of a fluid fuel flow to exit and leave the main fuel gas conduit 14 substantially in the axial direction A, or allows earlier mixing of some air.

In the embodiments shown, the tube end 7 that is set at an angle extends 1-4 cm.

In an embodiment, the angle is between 20° and 30°. In the embodiment shown, the angle is between 25° and 30°. The resulting bent part 7 is at an angle of about 10° - 15°. In particular, the angle is about 12°-14°. In the embodiment for burning hydrogen, i.e. the embodiment of figure 4-6, the end of the main fuel gas conduits 14 is bent, and tube end 7 is not present.

It will also be clear that the above description and drawings are included to illustrate some embodiments of the invention, and not to limit the scope of protection. Starting from this disclosure, many more embodiments will be evident to a skilled person. These embodiments are within the scope of protection and the essence of this invention and are obvious combinations of prior art techniques and the disclosure of this patent.

Reference numbers

1. Gas burner

2. Primary fuel gas discharge opening

3. Main fuel gas discharge opening

4. Exhaust gas return discharge opening

5. End plate

6. Sleeve

7. Bent end of main fuel gas inlet conduit

8. End plate central opening

9. Primary air discharge opening

10. End plate attachment

11. Tapered ring

12. End plate radial slits

13. Tapered ring indents

14. Main fuel gas conduit

15. Primary fuel gas conduit

16. Exhaust gas return conduit

17. Primary air conduit

18. End plate primary fuel gas opening

19. Bent end of primary fuel gas inlet conduit

A gas burner center line

P primairy flame region

M main flame region

Claims

1. A gas burner for burning a fuel gas using fuel staging, said gas burner having a center line and comprising:

- a primary fuel gas discharge opening for introducing a first fraction of said fuel gas as primary fuel gas into a primary flame region on said center line for in operation fuelling a primary flame;

- a series of exhaust gas return discharge openings extending in said gas burner for introducing recirculated exhaust gas around said primary flame region upstream of said primary flame for in operation introducing said exhaust gas into said main fuel before it ignites by said primary flame, and

- an end plate at the end of the primary fuel gas discharge opening, wherein said exhaust gas discharge opening is upstream of said end plate.

2. The gas burner according to claim 1, wherein said series of main fuel gas discharge openings are arranged around the gas burner center line.

3. The gas burner according to claim 1 or 2, wherein said series of exhaust gas return discharge openings are arranged around the gas burner center line.

4. The gas burner (1) according to any one of the preceding claims, wherein said series of exhaust gas discharge openings (4) are provided upstream of a start of said primary flame (P).

5. The gas burner according to any one of the preceding claims, wherein the first fraction is 5-20% of said fuel gas and said second fraction is 95-80 % of said fuel gas.

6. The gas burner according to any one of the preceding claims, further comprising a primary air discharge opening for introducing primary air into said primary flame region.

7. The gas burner according to claim 6, wherein said primary air discharge opening extends up to said primary flame region.

8. The gas burner according to any one of claims 6-7, wherein said primary fuel gas inlet discharge opening has its central axis concentric with said center line.

9. The gas burner according to any one of the preceding claims, further comprising a sleeve surrounding said series of main fuel gas inlet discharge openings and said series of exhaust gas return discharge openings.

10. The gas burner according to claim 9, wherein said sleeve extends up at said main flame region.

11. The gas burner according to any one of the preceding claims, wherein said sleeve at its downstream end continuous in a tapering ring extending up to said main flame region, more in particular said tapering ring has its upstream start at said primary flame region.

12. The gas burner of claim 11, wherein said tapering ring comprises a downstream end, wherein at said downstream end parts of said tapering ring, in particular bites or indentions, are taken out of said downstream end of said tapering ring, in particular said indentations are provided at, or are aligned with, each main fuel gas discharge opening.

13. The gas burner of one or more of claims 9-12, wherein said sleeve, said primary air discharge opening and said primary fuel gas discharge opening are functionally concentric, wherein a spacing between said sleeve and said primary air discharge opening defines a main air discharge opening.

14. The gas burner according to any one of the preceding claims, comprising the end plate at the end of the primary fuel gas discharge opening at said upstream start of said tapering ring.

15. The gas burner of claim 14, wherein said end plate comprises a central opening on said center line, and wherein said primary fuel gas discharge opening is positioned upstream of said central opening.

16. The gas burner of claim 15, wherein said end plate comprises radial slits, in particular said radial slits starting at a distance from said central opening and extending radially up to a distance from an edge of said end plate, the radial slits positioned for providing primary air discharge openings.

17. The gas burner of claims 15-16, wherein said end plate closes off said primary air discharge opening.

18. The gas burner according to any one of the preceding claims, wherein an end opening of said tapering ring has a circumference that is larger than a circumference of said end plate.

19. The gas burner according to any one of the preceding claims, wherein said main fuel gas discharge openings comprise a bent end which bent tangential with respect to a circle around said center line. 0. The gas burner of claim 19, wherein said main fuel gas discharge openings are grouped into pairs, wherein said bent ends bent towards each other. 1. The gas burner according to any one of the preceding claims, wherein said main fuel gas discharge opening is positioned downstream of said end plate. 2. The gas burner according to any one of the preceding claims, wherein said main fuel gas discharge opening is upstream of an end of said tapered ring.

23. The gas burner according to any one of the preceding claims, wherein said exhaust gas discharge opening is positioned at an upstream end of said tapered ring.

24. The gas burner according to any one of the preceding claims, wherein said exhaust gas discharge opening is provided between a pair of main fuel gas discharge openings.

25. The gas burner according to any one of the preceding claims for burning hydrogen gas, wherein said end plate comprises 3-6 auxiliary passages around said main opening, and a series of primary fuel discharge openings at each auxiliary passage.

26. The gas burner of claim 25, wherein said end plate comprises radial slits, and wherein said auxiliary passages are provided between said radial slits.

27. The gas burner of claim 25 or 26, wherein said primary fuel discharge openings are in substantially tangential direction with respect to a circle around the center line, in particular the primary fuel gas discharge openings are at bent ends of primary fuel conduits.

28. A method for burning fuel gas comprising a combustion chamber and a gas burner extending into said combustion chamber, said method comprising providing a primary flame via said gas burner in said combustion chamber, introducing fuel gas around said primary flame, and introducing recirculated exhaust gas via said gas burner around said primary flame upstream of said primary flame for in operation mixing said exhaust gas into said main fuel before igniting into said main flame, wherein said gas burner is provided with an end plate at the end of the primary fuel gas discharge opening, and said exhaust gas is provided by a discharge opening upstream of said end plate.

29. Use of a gas burner according to any one of the preceding claims 1-27 for burning a fuel gas mainly comprising hydrogen, in particular at least 90% by weight, more in particular at least 95% by weight, specifically at least 99% by weight. Use of a gas burner according to any one of the preceding claims 1-27 for burning a fuel gas mainly comprising methane, in particular at least 90% by weight, more in particular at least 95% by weight, specifically at least 99% by weight.

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