Surface-stabilized fully-premixed gas premix combustor for burning hydrogen and method for starting such a combustor

Abstract

A method for starting a burner, in which a premixed gas comprising a combustible gas and air is supplied, wherein the combustible gas comprises at least 50% by volume of hydrogen. The method comprises the following steps: During a start-up phase: supplying a premixed gas having a first λ value to the burner surface, wherein the first λ value is at least 1.85, and igniting the supplied premixed gas having the first λ value using an ignition source. During an operating phase after the premixed gas is ignited: supplying a premixed gas having a second λ value to the burner surface, wherein the first λ value is greater than the second λ value. Independent claims comprising a burner and a heating device.

Description

Technical Field

[0001] The present invention relates to the field of surface-stabilized fully premixed gas premix burners for combusting combustible gases including hydrogen, a method for starting such a burner, and an apparatus comprising such a burner. Background Art

[0002] It is well known that surface-stabilized premix burners are used to combust hydrocarbon gases, such as natural gas, methane, and propane gas, in heating appliances, particularly in gas heating appliances. They offer advantages in terms of size, emission, and the ability to modulate to different loads (also known as modulation).

[0003] In gas heating appliances with surface-stabilized premix burners, the most common way to control the mixture of combustible gas and air is to use a pneumatic gas valve. In such a system, the ratio of combustible gas to air is determined by the gas valve. For example, the gas valve can be biased to a closed position and can be opened due to aerodynamic forces. The force depends on the air flow, and the opening of the gas valve at a certain air flow rate is determined by the design of the gas valve. This is a master (air)-slave (combustible gas) solution. There are other available systems, such as control valves. Some systems use a feedback loop to control the gas-air ratio.

[0004] Most systems follow the following sequence to ignite the combustible gas. The fan is started, and in most cases, it is determined that air is flowing. Then, the ignition sequence is started by generating a spark or other ignition source on the burner surface of the burner. The next step is to open the gas valve. If the ratio of combustible gas to air is within a certain range, ignition will occur.

[0005] In recent years, the use of natural gas and propane gas has been criticized due to carbon dioxide emissions. Hydrogen has been proposed as an alternative fuel, particularly for domestic and industrial heating appliances. However, hydrogen or gaseous fuels with a high hydrogen content have different combustion behaviors compared to traditional hydrocarbon gases, such as a higher flame speed. Different combustion behaviors can lead to many problems, such as flashback. Flashback occurs when the upstream propagating part of the flame propagates back into the burner, which can be caused by a high flame speed.

[0006] International patent application WO2020 / 182902, which claims the priority of European patent application EP 19162278 of the present applicant, discloses a method for adjusting the ratio of air to combustible gas based on the load of the burner to mitigate risks such as flashback. EP 19162278 and WO2020 / 182902 are hereby incorporated by reference.

[0007] If a system using hydrogen as fuel is started in the above order and ignition is delayed for any reason, the mixture including hydrogen will fill the combustion chamber. Tests have shown that if ignition does occur with the combustion chamber at least partially filled with a hydrogen - air mixture, an explosion - like combustion may occur that can damage components of the heating system.

[0008] In addition, standards have been established to ensure the safe operation of burners. Among these standards, several tests are described as acceptance criteria. For example, the European standard EN 15502 - 1 Gas - fired heating boilers - Part 1: General requirements and tests describes several tests for natural gas and LPG. Although there is no standard for hydrogen as fuel at this time, it is expected that safety tests similar to those described in EN 15502 - 1 will apply to future gas - fired heating boilers using other gases than those described, for example, in EN 437. Similarly, outside Europe, there is a presence and / or expectation to develop similar standards for hydrogen as fuel.

[0009] One of the tests in current standards is the "delayed ignition test". During the delayed ignition test, combustible gas and air are first introduced into the combustion chamber for a short time before being ignited by an ignition source. This should not cause damage or other unwanted side - effects. However, tests have found that when a conventional burner uses hydrogen as fuel, flashback may occur during the test. Summary of the Invention

[0010] An object of the present invention is to mitigate one or more of the above - mentioned drawbacks, or at least to provide an alternative to existing methods and burners.

[0011] The above object is achieved by each of a method, a burner, and a hydrogen - combustion heating device according to the present invention as described herein.

[0012] The present invention relates to a method for starting a burner, in which a premixed gas including a combustible gas and air is supplied to a burner surface of the burner, where

[0013] · the combustible gas includes at least 50 vol% hydrogen,

[0014] · the λ value is defined as the ratio between the actually supplied amount of air and the amount of air required for stoichiometric combustion of the premixed gas,

[0015] · the burner is preferably a surface - stabilized fully - premixed gas premixed burner,

[0016] · the burner is preferably configured to be adjustable between a minimum load and a full load.

[0017] where the method includes the following steps

[0018] · During the start-up phase: A premixed gas having a first lambda value is supplied to the burner surface, where preferably, the first lambda value is at least 1.85, and the supplied premixed gas having the first lambda value is ignited using an ignition source.

[0019] · Preferably, during the operating phase after the premixed gas is ignited: A premixed gas having a second lambda value is supplied to the burner surface, where the first lambda value is greater than the second lambda value.

[0020] The present invention relates to a method for starting a burner. The burner is preferably a surface-stabilized fully premixed gas premixed burner, which can be used, for example, in heating devices for domestic and / or industrial applications. In such applications, it is desirable for the burner to be able to operate at a range of loads. For example, in domestic applications, the load required when a resident takes a hot shower may be much greater than the load required to maintain the temperature of the dwelling. Therefore, the burner is preferably configured to adjust between a minimum load and a full load. The modulation ratio, defined as the ratio of the full load to the minimum load, can be, for example, at least 3, preferably greater than 4, more preferably greater than 5, more preferably greater than 7, more preferably greater than 10. For example, the full load of the burner can be 24 kW, for example when the burner is used in a domestic heating device such as a boiler.

[0021] According to the present invention, a premixed gas comprising a combustible gas is supplied to the burner surface of the burner. The combustible gas comprises at least one gaseous fuel that can be burned to provide heat energy, and in the present invention, the gaseous fuel is hydrogen. It should be noted that some gases used in conventional heating devices may include small amounts of hydrogen; however, in these mixtures, the combustion behavior is actually still determined entirely by the hydrocarbons predominantly present. It has been found that when the combustible gas comprises a large amount of hydrogen, the combustion behavior changes significantly compared to conventional hydrocarbon gases. In particular, in the context of the present invention, the combustible gas comprises at least 50 vol% hydrogen. In addition to hydrogen, the combustible gas can, for example, include additives such as colorants and flavorants, or nitrogen. Carbon monoxide or carbon dioxide formed during the production of hydrogen may also be present. The combustible gas can also include small amounts of hydrocarbons such as methane or propane. These hydrocarbons can be intentionally added to reduce the price of the combustible gas, or they can be residual gases present in the pipeline used for distributing hydrogen, which was previously used for distributing the hydrocarbons. The combustible gas can also include small amounts of oxygen, which can thus affect the amount of oxygen or air required for combustion. It can depend on the required hydrogen purity at what concentration the additional chemicals are present therein.

[0022] The premixed gas further includes air. The air includes oxygen, which is required to ignite the combustible gas. Usually, the air is taken from the environment where the burner is located, such as the outside. Depending on the composition of the combustible gas on the one hand and the composition of the air on the other hand, a certain amount of air is required for the stoichiometric combustion of the premixed gas. However, in practice, the actual amount of air included in the premixed gas will be different from this. Traditionally, for hydrocarbon gases, a small amount of excess air is provided to avoid incomplete combustion that may lead to carbon monoxide. The λ value is defined as the ratio between the actually supplied amount of air and the amount of air required for the stoichiometric combustion of the premixed gas. Therefore, the λ value represents the excess air.

[0023] According to the present invention, the method includes a first step of supplying a premixed gas having a first λ value to the burner surface during a startup phase. During the startup phase, an ignition source is used to ignite the supplied premixed gas having the first λ value.

[0024] It should be noted that in some embodiments, the ignition source may have been activated, such as a spark, before supplying the premixed gas having the first λ value. Additionally, in some embodiments, air can be supplied to the burner surface first, then the ignition source is activated, then the combustible gas is supplied to the premixed gas, and then the premixed gas having the first λ value is supplied to the burner surface.

[0025] The method preferably further includes the step of supplying a premixed gas having a second λ value to the burner surface during an operation phase after the premixed gas has been ignited. According to the present invention, the first λ value is greater than the second λ value.

[0026] A difference is created between the startup phase and the operation phase. The startup phase includes supplying a premixed gas having a first λ value and igniting the supplied premixed gas. It should be noted that relative to the operation phase, the burner can be adjusted to a different load during the startup phase. Even during the startup phase and / or the operation phase itself, the burner can be adjusted to different loads. In this case, the first and / or second λ values may not be constant.

[0027] The present invention requires that initially, during the startup phase, the premixed gas supplied to the burner surface includes a relatively large amount of excess air. The inventors have found that when the premixed gas includes more air, the flame speed decreases, and correspondingly, the risk of flashback also decreases. Additionally, it has been found that after igniting the premixed gas having the first λ value present, a premixed gas having a lower λ value can be supplied during the operation phase. Since there is no longer or at least less accumulated premixed gas, the risk of flashback is reduced.

[0028] Another advantage of the present invention is to reduce the chance of flashback caused by recirculation. Recirculation occurs when the outlet gas is sucked into the inlet of the burner, for example, into the inlet of the fan. In fact, recirculation can occur, for example, when the outlet and inlet of the boiler system are arranged close to each other, such as on the roof of a building. Certain weather conditions such as strong winds can increase recirculation. When recirculation occurs, the air provided by the fan contains less oxygen. Additionally, during the startup phase before the combustible gas is ignited, unburned combustible gas can also be recirculated. As a result, the ratio of oxygen to combustible gas in the premixed gas supplied to the burner surface decreases, that is, the actual λ value decreases. By controlling the λ value during the startup phase to be higher, the chance of flashback is reduced.

[0029] Advantageously, the excess air can optionally be reduced, such that a second λ value during the operation phase can be selected, thereby improving other characteristics, such as efficiency. The first λ value is preferably at least 1.85. It has been found that this is the practical lower limit with satisfactory results. It should be noted that conventional hydrocarbons such as methane do not burn or burn poorly when the λ value is 1.85 or greater.

[0030] The λ value can be controlled during the startup phase and optionally during the operation phase. The λ value can be controlled, for example, by controlling the amount of air supplied by the air passage and / or the amount of combustible gas supplied by the combustible gas passage, for example, by using a controller. Several practical ways to control the λ value will be described in detail here.

[0031] In one embodiment, the burner includes a premixed gas supply circuit, the premixed gas supply circuit including: an air passage for supplying air; a combustible gas passage for supplying combustible gas; a mixing passage for mixing the air supplied by the air passage and the combustible gas supplied by the combustible gas passage into the premixed gas to be supplied to the burner surface; and at least one passage blocking element for partially blocking the combustible gas passage and / or the air passage. In this embodiment, the method further includes the following steps: during the startup phase: partially blocking the combustible gas passage with the at least one passage blocking element, so that less combustible gas is provided to the mixing passage during the startup phase relative to during the operation phase; and / or during the operation phase: partially blocking the air passage with the at least one passage blocking element, so that more air is provided to the mixing passage during the startup phase relative to during the operation phase.

[0032] In the described embodiment, the channel blocking element is used to block the combustible gas channel and / or the air channel, such that less combustible gas and / or air is supplied to the premixed gas respectively. Thus, the λ value can be adjusted, for example, from a first λ value to a second λ value. The channel blocking element can be implemented in various ways, and several of them will be explained in more detail below.

[0033] In one embodiment, the at least one channel blocking element is arranged in a rest position during the startup phase. In this embodiment, the method further includes the step of actuating the channel blocking element during the operation phase to arrange the channel blocking element in an actuated position.

[0034] Therefore, the rest position of the channel blocking element corresponds to the startup phase. The step of actively actuating the channel blocking element is required to achieve a reduction in the second λ value. In the case of a failure where the actuation step cannot be completed, the premixed gas will still have the first λ value during the operation phase, which may result in unsatisfactory efficiency. However, the failure will not affect the first λ value during the startup phase. The channel blocking element is also fail-safe.

[0035] In one embodiment, the first λ value is greater than 1.9, preferably greater than 2, for example between 2 and 5, preferably greater than 3, for example between 3 and 5, more preferably greater than 4, for example between 4 and 5. The larger the first λ value, the smaller the chance of flashback when igniting the premixed gas with the first λ value. However, if the first λ value is too large, incomplete combustion of the premixed gas may occur because there is too little combustible gas. In addition, the efficiency of the burner decreases as the first λ value increases. Tests have shown that a suitable upper limit is 7, preferably 6, more preferably 5. For example, the first λ value can be between 2 and 7, 2 and 6, 3 and 7, 3 and 6, 4 and 7, or 4 and 6.

[0036] In one embodiment, the second λ value is between 1 and 2, preferably between 1.05 and 1.5, more preferably between 1.05 and 1.3. Optionally, the second λ value is the λ value at full load. These have been shown to be suitable λ values for safe and efficient operation. Although theoretically the required amount of air corresponds to a λ value of 1, a small amount of excess air is preferably provided during the operation phase. This makes the flame speed slightly lower and also provides a buffer to avoid incomplete combustion in the case where the air contains less oxygen than normal, for example due to weather conditions or the burner being in a position with idle air, or when the combustible gas contains components different from the expected conditions. Incomplete combustion results in lower efficiency because less energy is used in the combustible gas. If the concentration of combustible gas in the exhaust gas is too high, incomplete combustion may also cause safety problems because it may cause an explosion or fire further downstream at an undesired location. In addition, reducing the λ value may also result in an increase in NOx in the exhaust gas.

[0037] In one embodiment, the first λ value is at least 1.5 times larger than the second λ value, preferably at least 2 times larger, for example at least 3 times larger. It has been found that these are the practical first λ values for which satisfactory results can be obtained.

[0038] In one embodiment, the combustible gas comprises at least 75 vol% hydrogen, preferably at least 80 vol% hydrogen, more preferably at least 95 vol% or at least 98 vol% hydrogen. Since the combustible gas comprises more hydrogen, the advantages associated with using hydrogen as a fuel increase. However, at the same time, the flame speed and the risk of flashback increase, making the present invention even more advantageous.

[0039] In one embodiment, the start-up phase lasts for at least 1 second, preferably at least 2 seconds, even more preferably at least 3 seconds, for example 3 - 6 seconds. Preferably, the start-up phase is long enough to ensure that the supplied premixed gas is ignited. Thus, after the ignition source has been activated, the start-up phase can last for at least a little while, for example 1 - 2 seconds. The start-up phase can also last for at least a little while, for example 1 - 2 seconds, after the flame detector has detected a flame. This ensures that the premixed gas with the first λ value is ignited before the start of the operation phase. In the case of using a flame detector, it may also take some time, for example 1 - 2 seconds, after the ignition source has been activated to detect a flame. In the case where the burner is started for a delayed ignition test, the standard EN15502-1 stipulates that the start-up phase can last up to 10 seconds. In the case where the premixed gas with the first λ value is not ignited, for example when no flame is detected, for example after a predetermined time, for example corresponding to the safety time according to EN 15502, the start-up of the burner can be interrupted. Optionally, after said interruption, the method according to the invention can be restarted.

[0040] In one embodiment, the method comprises the step of setting the fan to a high load during start-up, for example greater than 80% of the revolutions per minute RPM of full load, for example greater than 90% of the RPM of full load, for example greater than 95% of the RPM of full load, for example at full load.

[0041] The advantages of the described embodiment can be understood from the example where a resident wishes to take a hot shower when their boiler including a burner is turned off. To heat the water for the shower sufficiently, it is desirable for the burner to be at full load. However, in a conventional burner, the burner must start at a lower load, for example 25 - 40% of the load. Only after combustion has started can the burner be slowly increased to full load by adjusting the fan speed. However, this takes several seconds, for example because the safe and correct mixing of the premixed gas must be ensured as the flow rate of the fan increases. According to another aspect of the present invention, more air is provided during the startup phase. Thus, the fan can be set at a high load before adding the combustible gas to the premixed gas, which can be done more quickly. Once combustion has started, the amount of combustible gas can be adjusted during the operation phase, and the burner is faster at the desired high or full load. Thus, when the method according to this embodiment is applied, the resident obtains hot water more quickly in their shower.

[0042] In one embodiment, the second lambda value varies with the load. This is described in detail in international patent application WO2020 / 182902, which claims the priority of the European patent application with application number EP 19162278 by the present applicant. EP 19162278 and WO2020 / 182902 are hereby incorporated by reference. As explained in EP 19162278 and WO2020 / 182902, the lambda value at minimum load can be at least 20% higher than at full load, and optionally, the lambda value at average load can be less than 10% higher than at full load. Generally, the burner will start at a load within the adjustment range. According to the present invention, when the burner starts at said load, the first lambda value at any given load is higher than the second lambda value at said load. However, in some embodiments, the burner can start at a load below the minimum load, although this is limited by the reduced minimum load. Below said reduced minimum load, it is not possible to determine that ignition has occurred, or it is not possible to maintain stable combustion. On the other hand, above full load, it is also not possible to determine that ignition has occurred because the increased speed of the premixed gas passing through the burner surface may cause the flame to be further away from the burner surface compared to the flame detection sensor.

[0043] In one embodiment, the second lambda value is defined as the lambda value during operation at the same load at which the burner starts.

[0044] In one embodiment, the second lambda value is defined as the lambda value during full - load operation of the burner.

[0045] In one embodiment, the burner starts at a start-up load that is different from the desired load during the operation phase, and the method further includes a transition phase from the start-up phase to the operation phase after the premixed gas has been ignited, where the transition phase includes the step of changing the load to the desired load.

[0046] For example, in practice, a predetermined second λ value can be stored in a memory for each load during the operation phase. The second λ value can vary with the load. According to the present invention, if the burner starts at the start-up load, then if the load during the operation phase is equal to the start-up load, the first λ value will be greater than the second λ value corresponding to the start-up load. However, it is possible that the burner generally starts at the start-up load, which can be, for example, a relatively low load, regardless of the desired load actually required during the operation phase. In the case where the desired load during the operation phase is different from the start-up load at which the burner starts in the start-up phase, after the premixed gas has been ignited, there can be a transition phase from the start-up phase to the operation phase.

[0047] In a first embodiment, the transition phase includes: the step of changing the λ value of the supplied premixed gas to a second λ value associated with the start-up load if the load during the operation phase is equal to the start-up load; and subsequently the step of changing the load to the desired load and changing the λ value to a second λ value associated with the desired load.

[0048] In a second embodiment, the transition phase includes the steps of: changing the load to the desired load while maintaining the λ value of the supplied premixed gas at the first λ value, and then changing the λ value to a second λ value associated with the desired load.

[0049] In a third embodiment, the transition phase includes the step of simultaneously changing the load to the desired load and changing the λ value of the supplied premixed gas to a second λ value associated with the desired load.

[0050] In the case where the desired load is greater than the start-up load, the first and third embodiments during the transition phase can be preferred because in the second embodiment, the fan may not be able to provide the first λ value at the higher desired load.

[0051] It is noted that in the case where the desired load is less than the start-up load, the second λ value associated with the desired load can actually be greater than the first λ value when the burner starts at the start-up load. However, according to a preferred embodiment of the present invention, if the load during the operation phase is equal to the start-up load, the first λ value when the burner starts is greater than the second λ value associated with the start-up load.

[0052] In one embodiment, the first lambda value is below the blow-off value. The blow-off value is the lambda value at which, relative to the air in the premixed gas, there is so little combustible gas that any flame at the burner surface is blown out by the premixed gas because there is not enough combustible gas to sustain the flame.

[0053] In one embodiment, the first lambda value results in a concentration of combustible gas in the premixed gas that is below the upper flammability limit (also known as UFL), and / or above the lower flammability limit (also known as LFL). It should be noted that the lower and upper flammability limits are determined by the composition of the combustible gas, but also depend on factors such as temperature and pressure. Above the UFL, the premixed gas may be too rich to burn, and below the LFL, the premixed gas may be too lean to burn.

[0054] In one embodiment, when the fan is at full load, the first lambda value corresponds to an air volume that is lower than the air volume provided by the fan.

[0055] In one embodiment, the first lambda value results in a concentration of combustible gas in the premixed gas that is below the lower explosion limit (also known as LEL), which means that the first lambda value should be higher than the lambda value corresponding to the LEL. Preferably, the first lambda value is controlled to differ from the lower explosion limit by more than a predetermined safety margin, for example, the safety margin is 1.2 or 1.5 times. This ensures a safe start, even when the actual composition of the air or combustible gas is different from what is expected. It should be noted that for many gases, the LEL and LFL are corresponding, but for hydrogen-containing gases, this is not the same. For hydrogen-containing gases, there is a concentration range in which the premixed gas is combustible but will not explode, which is the preferred range for the startup phase. This range depends on temperature, pressure, possible other components in the combustible gas, and mixing. For pure hydrogen, when the premixed gas includes 4 - 17 vol% hydrogen, the concentration is between the LFL and LEL.

[0056] In one embodiment, the method further includes the step of maintaining the ignition source in an ignited state for up to an ignition period after it has been detected that the supplied premixed gas having a first λ value has been ignited. The ignited state corresponds to the action performed by the ignition source for igniting the premixed gas. For example, the ignition source may maintain a spark during the ignited state. For example, when the ignition source is a glow plug or a hot surface igniter, the current supplied to it may be maintained at a level that causes the ignition source to heat at a temperature at which the premixed gas is ignited. The ignition period may be, for example, a predetermined period, such as 1 second, 2 seconds, or 5 seconds. The ignition period may, for example, overlap with the end period of the startup phase, and / or the start period of the operation phase, and / or during the transition phase between the startup phase and the operation phase, where the λ value is adapted to be adjusted towards a second λ value, and / or the load is adapted to be adjusted from a startup load to a desired load. In various embodiments, the burner starts with a startup load that is different from the desired load of the operation phase, where the ignition source is maintained in the ignited state until the burner has been adjusted to the desired load and / or the second λ value associated with the desired load.

[0057] The described embodiment allows, for example, in the case where there is an accumulation of premixed gas inside the burner or in the combustion chamber, the accumulated premixed gas to be ignited by the ignition source. The accumulation of the premixed gas may occur, for example, when the flame has quickly moved away from the burner surface, for example, without burning all the gas present. For example, after the flame speed changes, the accumulated gas may cause unexpected and / or undesired flame behavior, which may occur, for example, when the burner is adjusted to a different load. By igniting and burning the accumulated gas, the described embodiment avoids the said unexpected and / or undesired behavior and thus further reduces the risk of, for example, flashback. Note that in the described embodiment, it may be advantageous if the ignition source is a glow plug or a hot surface igniter, especially when a flame detector that is adversely affected by the spark of a spark igniter is used. It is also possible to stop the ignition source, for example, spark ignition, in order to detect the flame, and start the ignition period after the flame has been detected.

[0058] The invention also relates to a burner configured to perform the method according to the invention. Preferably, the burner is a surface-stabilized fully premixed gas premixed burner. Optionally, the burner also conforms to the burner described below.

[0059] The invention also relates to a burner as described below. The method according to the invention can be performed with the burner; however, neither the method nor the burner is limited thereto. However, when referring to the burner, the features and definitions explained with reference to the method according to the invention can be similarly explained, and vice versa. In addition, features and / or embodiments explained with reference to the method according to the invention can be added to the burner according to the invention to achieve similar advantages, and vice versa.

[0060] The present invention relates to a burner for combusting a combustible gas comprising at least 50% by volume of hydrogen, wherein the burner is preferably a surface-stabilized fully-premixed gas premix burner, and wherein the burner is preferably configured to be adjusted between a minimum load and a full load,

[0061] The burner comprises

[0062] · a burner surface,

[0063] · a premixed gas supply circuit, comprising:

[0064] i. an air passage for supplying air,

[0065] ii. a combustible gas passage for supplying the combustible gas,

[0066] iii. a mixing passage for mixing the air supplied by the air passage and the combustible gas supplied by the combustible gas passage into a premixed gas to be supplied to the burner surface, wherein the λ value is defined as the ratio between the actually supplied amount of air and the amount of air required for the stoichiometric combustion of the premixed gas,

[0067] · an ignition source for igniting the premixed gas supplied to the burner surface,

[0068] · a controller configured to control the λ value of the supplied premixed gas by controlling the amount of air supplied by the air passage and / or the amount of combustible gas supplied by the combustible gas passage, wherein the controller is configured to:

[0069] i. supply a premixed gas having a first λ value during a start-up phase of the burner, wherein the ignition source is configured to ignite the supplied premixed gas having the first λ value, wherein the first λ value is preferably at least 1.85, and

[0070] ii. preferably, after the ignition source is configured to ignite the supplied premixed gas having the first λ value, supply a premixed gas having a second λ value during an operation phase of the burner, wherein the first λ value is greater than the second λ value.

[0071] The burner according to the invention is preferably a surface-stabilized fully premixed gas premixing burner. In this context, surface-stabilized should be interpreted as meaning that during normal operation, the flame is intended to be located on or close to the burner surface. In the present context, fully premixed gas should be interpreted as meaning that (substantially) all the air is added before the premixed gas reaches the burner surface. This is different from, for example, nozzle mixing systems in which the combustible gas and air meet at the burner surface, or partially premixed systems in which part of the air is added before the gas reaches the burner surface and part of the air is supplied directly to the burner surface.

[0072] The burner is adapted to burn a combustible gas comprising at least 50% by volume of hydrogen and is adjustable between a minimum load and a full load. The full load depends on the intended application, for example for a single household, multiple households such as an apartment building, or industry. Examples of full loads can be, for example, 20 kW, 24 kW, 30 - 40 kW, 90 - 150 kW, 200 - 300 kW, 2200 - 3000 kW.

[0073] The burner according to the invention comprises a premixed gas supply circuit, a burner surface and an ignition source. The premixed gas is supplied by the premixed gas supply circuit to the burner surface. The burner surface can, for example, comprise openings or perforations, for example circular or elongated, through which the premixed gas can flow into, for example, a combustion chamber. The ignition source is arranged near the burner, for example in the combustion chamber. The ignition source is configured to ignite the premixed gas such that the premixed gas burns and / or starts to burn. The ignition source can, for example, be a spark igniter, a glow plug or a hot surface igniter. Once the premixed gas is ignited, there is a flame. As long as there is a flame, the premixed gas supplied to the burner surface will generally ignite as soon as it reaches the flame. Ideally, during the operating phase, the flame is present on the burner surface. The burner surface can have any suitable shape, for example circular, curved or flat.

[0074] The premixed gas supply circuit includes an air passage, a combustible gas passage, and a mixing passage. In the mixing passage, the air supplied by the air passage and the combustible gas supplied by the combustible gas passage are mixed into the premixed gas. The mixing can be achieved naturally by the flow or, optionally, by means of a mixing element such as a fan. The air passage can be connected to ambient air, for example, through an intake port to provide air, and the air can be supplied to the mixing passage, for example, by a fan. The fan can be provided upstream or downstream of the mixing passage. Generally, the required volume of air is greater than the required volume of combustible gas. Therefore, the air passage can be larger than the combustible gas passage. Preferably, the combustible gas is supplied to the mixing passage at least partially by using the Venturi effect. This can be achieved, for example, by providing a narrowed or narrower portion of the air passage at the location where the combustible gas passage is connected to the air passage. The narrowed or narrower portion will result in a local increase in the air flow rate, thereby reducing the pressure and exerting a suction force on the combustible gas.

[0075] According to the invention, the burner further includes a controller. The controller is configured to control the λ value of the supplied premixed gas. The controller can be configured to achieve this in a variety of ways, and several of its embodiments will be described in further detail below. Generally, the controller is configured to control the λ value by controlling the amount of air supplied by the air passage and / or the amount of combustible gas supplied by the combustible gas passage.

[0076] According to the invention, the controller is configured such that during the startup phase, the premixed gas having a first λ value is supplied to the burner surface, and the supplied premixed gas is ignited by an ignition source. Only after the supplied premixed gas having the first λ value is ignited does the controller control the λ value such that the premixed gas having a second λ value is supplied during the operation phase. According to the invention, the first λ value is greater than the second λ value, and preferably, the first λ value is at least 1.85. In this way, the same advantages associated with the method according to the invention are achieved.

[0077] In one embodiment, the burner further includes at least one channel blocking element for partially blocking the combustible gas passage and / or the air passage. The controller is further configured to control the at least one channel blocking element to partially block the combustible gas passage during the startup phase and / or to partially block the air passage during the operation phase.

[0078] The channel blocking element can be implemented in various ways, and several of them will be explained in more detail below. By partially blocking the combustible gas passage or the air passage, less combustible gas or air will enter the mixing passage respectively. By blocking the gas passage during the startup phase and / or the air passage during the operation phase, the first λ value can be made greater than the second λ value.

[0079] Typically, the channel blocking element preferably has at least a first position in which the channel blocking element partially blocks the combustible gas channel or the air channel by being disposed in the corresponding channel. It also has a second position in which it is either not disposed in the corresponding channel or at least less blocks the corresponding channel. Optionally, in the second position or in an additional third position, the channel blocking element blocks the corresponding other channel.

[0080] In one embodiment, the at least one channel blocking element has an actuated position and a rest position, wherein the at least one channel blocking element is configured to be in the actuated position during the operation phase and in the rest position during the startup phase.

[0081] Thus, the rest position of the channel blocking element corresponds to the startup phase. Steps to actively actuate the channel blocking element are required to achieve a reduction in the second λ value. In the case of a failure where the actuation step cannot be completed, the premixed gas will still have the first λ value during the operation phase, which may result in unsatisfactory efficiency. However, the failure does not affect the first λ value during the startup phase. The channel blocking element is also fail-safe.

[0082] Whether the rest position corresponds to the first position or the second position depends on whether the channel blocking element is disposed in the combustible gas channel or the air channel.

[0083] In one embodiment, at least one channel blocking element is configured to be actuated by pneumatic, hydraulic, magnetic or mechanical forces to block the combustible gas channel and / or the air channel.

[0084] In one embodiment, the burner further includes a gas valve in addition to including at least one channel blocking element, wherein the gas valve is disposed in the combustible gas channel, and wherein the gas valve has a closed position and an open position. In the closed position, the combustible gas is prevented from flowing through the combustible gas channel, and in the open position, the combustible gas can flow through the combustible gas channel. It should be noted that in this embodiment, both the gas valve and the channel blocking element are present, i.e., as separate components. The gas valve is provided in the combustible gas channel, and the channel blocking element can be provided in the combustible gas channel or the air channel. Optionally, the controller is configured to control the gas valve.

[0085] The advantage of this embodiment is that the gas valve can be used to open or close the combustible gas channel regardless of the channel blocking element. Thus, the functions are decoupled. Additionally, the gas valve can be implemented with a simpler or cheaper structure, such as a pneumatic gas valve.

[0086] In some embodiments, the gas valve can be a control valve, such as an electronically actuated control valve, a pneumatically actuated control valve, or a hydraulically actuated control valve. In other embodiments, the gas valve is a pneumatic gas valve, preferably part of a master-slave relationship, where the air flow in the air passage is the master air flow. For example, the pneumatic gas valve can be biased to a closed position and opened due to aerodynamic forces, where the force depends on the air flow. The opening degree of the pneumatic gas valve at a certain air flow rate can be determined by the design of the pneumatic gas valve. In the system, the ratio of combustible gas to air is determined by the design of the pneumatic gas valve.

[0087] Optionally, the pneumatic gas valve is designed to have a negative offset, which means that a predetermined threshold of air flow or negative pressure must exist before the pneumatic gas valve can open. This avoids an undesired flow of combustible gas when there is no air flow, or when there is a negative pressure caused by other reasons, such as suction downstream, which may cause the air flow to be caused, for example, by the opening of the pneumatic gas valve. Such an undesired flow of combustible gas may cause the exhaust gas to be combustible, which is undesirable for safety reasons.

[0088] In one embodiment, at least one channel blocking element is a valve, such as an electronically actuated control valve, a pneumatically actuated control valve, or a hydraulically actuated control valve. This allows precise control of the volume of combustible gas and / or air supplied to the mixing channel and thus control of the λ value of the premixed gas.

[0089] In another embodiment, at least one of the at least one blocking element corresponds to a gas valve arranged in the combustible gas channel, where the gas valve has a closed position and an open position. In the closed position, the combustible gas is prevented from flowing through the combustible gas channel, and in the open position, the combustible gas can flow through the combustible gas channel.

[0090] In one embodiment, the burner further includes at least one oxygen sensor configured to measure a value representing the oxygen content of the flue gas generated by the burner or a value representing the oxygen content of the premixed gas supplied to the burner surface. The measured value can represent the λ value of the supplied premixed gas. The controller can be configured to control the λ value based on the measured value.

[0091] In one embodiment, the burner further comprises at least one flame detector configured to detect when the supplied premixed gas is ignited and / or burning and to generate a corresponding flame signal, wherein preferably the controller is further configured to control the premixed gas to have a second λ value after having received a flame signal from the detector. If the premixed gas having a second λ value is supplied when the premixed gas having a first λ value has not been ignited, the premixed gases having the first λ value and the second λ value will mix. This may result in the generation of a gas having a λ value that poses a risk of flashback. This embodiment mitigates this risk. In another embodiment, the controller may be configured to stop supplying the premixed gas if no ignition or burning of the premixed gas is detected after a predetermined time (e.g., 2, 5 or 10 seconds).

[0092] In one embodiment, the burner comprises a perforated metal plate for stabilizing the flame when the supplied premixed gas burns. The perforated metal plate may correspond to the burner surface, but the perforated metal plate may also be provided inside the burner surface, in which case the perforated metal plate is sometimes also referred to as a distributor or pressure distributor. In one embodiment, the perforated metal plate is implemented according to one or more embodiments shown in the following applications of the applicant, which are incorporated herein by reference: WO2011 / 069839, WO2009 / 077505 or WO02 / 44618.

[0093] In one embodiment, the burner comprises a second air passage having an air valve. The air valve has a first position and a second position. In the first position, air can be supplied to the premixed gas via the second air passage at a first flow rate. In the second position, air can be supplied to the premixed gas via the second air passage at a second flow rate. The second flow rate may be less than or greater than the first flow rate, and optionally the second flow rate is close to zero. The controller is further configured to control the air valve to be in the first position during the startup phase and to control the air valve to be in the second position during the operation phase. The air valve is preferably biased to the first position.

[0094] In one embodiment, the burner comprises a second combustible gas passage having a second combustible gas valve. The second combustible gas valve has a first position and a second position. In the first position, the combustible gas can be supplied to the premixed gas via the second combustible gas passage at a first flow rate. In the second position, the combustible gas can be supplied to the premixed gas via the second combustible gas passage at a second flow rate. The second flow rate may be less than or greater than the first flow rate, and optionally the second flow rate is zero. The controller is further configured to control the second combustible gas valve to be in the second position during the startup phase and to control the second combustible gas valve to be in the first position during the operation phase. The second combustible gas valve is preferably biased to the second position.

[0095] In one embodiment, the controller may further be configured to adjust the burner between a minimum load and a full load. To this end, the controller may control, for example, the fan, and / or the gas valve, and / or one or more channel blocking elements.

[0096] In one embodiment, the burner may further include a combustion chamber in which, for example, an ignition source, and / or an oxygen sensor, and / or a flame detector is arranged.

[0097] In one embodiment, the burner may further include a fan, and optionally, the controller is configured to control the fan.

[0098] The present invention also relates to a hydrogen combustion heating device including a burner according to the present invention. The heating device may be used, for example, for domestic or industrial applications, such as for a boiler.

[0099] The present invention will now be described by way of example with reference to the following drawings, in which the same reference numerals in different drawings denote the same features. However, it should be noted that the drawings are merely examples in which several alternative features are combined. The present invention is not limited to what is shown in the drawings. Description of the Drawings

[0100] Figure 1 A burner according to a first embodiment of the present invention is shown;

[0101] Figure 2 An example of the λ value as a function of time is shown;

[0102] Figure 3 Several factors that may be considered when determining a first λ value and / or a second λ value in an alternative embodiment are shown;

[0103] Figure 4 A second embodiment of the burner according to the present invention is shown;

[0104] Figure 5 A third embodiment of the burner according to the present invention is shown;

[0105] Figure 6 Steps of a method for starting a burner according to a possible embodiment of the present invention are schematically shown. Detailed Description of the Embodiments

[0106] Figure 1The burner 100 of the first embodiment of the present invention is schematically shown. The burner 100 is preferably a surface-stabilized fully premixed gas premix burner, which can be adjusted between a minimum load and a full load. The burner 100 includes a burner surface 123, and the premixed gas is supplied to the burner surface 123 through a premixed gas supply circuit. In the illustrated example, the burner surface 123 includes perforations, and the premixed gas flows into the combustion chamber 130 through the perforations. The combustion chamber 130 can be, for example, part of a heating device, where in particular water is heated. An ignition source 124 is also provided for igniting the supplied premixed gas. In the illustrated embodiment, the burner surface 123 is schematically shown as circular. However, in practice, the burner surface 123 can have any suitable shape, such as circular, curved or flat. The shape of the burner surface 123 can depend on the shape of the combustion chamber 130, and / or vice versa.

[0107] The premixed gas includes a combustible gas and air. Accordingly, the premixed gas supply circuit includes a combustible gas passage 111, and the combustible gas passage 111 is connected to a combustible gas supply 114. The combustible gas supply source 114 in the illustrated example is a tank, but other options include distribution networks similar to those known for distributing traditional hydrocarbon gases (such as methane) in municipal or industrial areas. In the context of the present invention, the combustible gas includes at least 50% by volume of hydrogen, and in some embodiments at least 80%, at least 95% or at least 98%.

[0108] A gas valve 112 is provided in the combustible gas passage 111, and the amount of combustible gas flowing through the combustible gas passage 111 can be adjusted by using the gas valve. In the illustrated example, the gas valve 112 is an electronically actuated control valve controlled by an electronic actuator 113. However, it is also known to design the gas valve 112 to open based on aerodynamic force. For example, the gas valve 112 can be biased to a closed position by a spring force, but when a negative pressure downstream of the gas valve 112 is generated by an air flow, the gas valve 112 automatically opens to allow the required amount of combustible gas to pass through.

[0109] In order to be able to ignite the combustible gas, oxygen is required. In the present invention, air is used to supply said oxygen. Accordingly, the premixed gas supply circuit includes an air passage 101 for providing air. Preferably, a fan 102 is provided to provide an air flow. Although in the illustrated example, the fan 102 is provided upstream of the position where the air passage 101 and the combustible gas passage 111 intersect, in some embodiments, the fan 102 may be provided downstream of said position. Optionally, multiple fans may also be arranged at multiple positions. The air passage 101 is also connected upstream to an air supply source (not shown). Generally, the air supply is only ambient air. For example, the air passage 101 may be connected to the outside air, for example, through a hole in the wall, and the fan 102 provides a suction force for sucking air into the air passage 101.

[0110] Figure 1 An optional air passage 101 is also shown to include a narrower portion 121, i.e., narrower than the more upstream portion of the air passage 101. The flow rate of the air increases in the narrower portion, and thus the pressure decreases, as described by the Bernoulli principle. The combustible gas passage 111 is connected to said narrower portion 121. Due to the pressure decrease of the air, a Venturi effect is produced, as a suction force is provided on the combustible gas, resulting in improved mixing of the combustible gas and air.

[0111] The premixed gas supply circuit further includes a mixing passage 122. In the mixing passage 122, the air supplied by the air passage 101 and the combustible gas supplied by the combustible gas passage 111 become a premixed gas to be supplied to the burner surface 123. Based on the composition of the combustible gas, a certain amount of oxygen is required for the complete combustion of the combustible gas. Based on the composition of the air, the amount of air required can be obtained from the amount of oxygen required. Since in practice, the amount of air will be different from this, the λ value is defined as the ratio between the actual amount of air supplied and the amount of air required for the stoichiometric combustion of the premixed gas.

[0112] Generally, the burner 100 is started according to the following process. First, the fan 102 is started so that air flows through the air passage 101. Then, the ignition source 124 is started, but since there is no combustible gas yet, there will be no combustion. Thereafter, the gas valve 112 is opened so that the combustible gas can flow in the combustible gas passage 111. The combustible gas and air are mixed in the mixing passage 122, and the premixed gas enters the combustion chamber 130 through the perforations of the burner surface 123. The still-activated ignition source 124 ignites the supplied premixed gas, and there is combustion and a flame in the combustion chamber 130.

[0113] However, if there is a malfunction or failure of, for example, the ignition source 124, immediate combustion of the supplied premixed gas may not occur. Thus, the premixed gas including the combustible gas will accumulate in the combustion chamber 130. The same situation will occur during the delayed ignition test. Tests have shown that in the case where the combustible gas includes a large amount of hydrogen, if the premixed gas accumulates after a certain amount of time of ignition, several problems will occur. These problems can lead to undesired damage and / or danger. For example, flashback can occur, i.e., the flame can propagate backward through the burner surface 123. An explosion may also occur in the combustion chamber 130.

[0114] Compared with during the operation phase, the present invention provides a solution by providing an additional excess of air during the startup phase. In Figure 2 an example of the λ value as a function of time is shown. It can be seen that the λ value is 4 between the first second and the sixth second. Note that initially only the fan is started to supply air, and the combustible gas is added after 1 second. After the eighth second, the λ value in the shown example is about 1.3, although the exact λ value may depend on the load. Tests have shown that the increased λ value during the startup phase reduces the above problems. Also note that the load during the startup phase can be different from the load during the operation phase. During the transition from the startup phase to the operation phase, which corresponds to the time period 6 - 8 seconds in Figure 2 the fan can also be adapted to provide a different flow rate.

[0115] Referring to Figure 1 , embodiments of the implementation of the present invention will be described in further detail. The burner 100 includes a controller 150. The controller 150 is configured to control the λ value of the supplied premixed gas. In the shown example, the controller 150 does this by controlling the gas valve 112. In particular, the controller 150 has an output 150.1 for sending a control signal 151 to an input 113.1 of an actuator 113 of the gas valve 112. By controlling the position of the gas valve 112, the amount of combustible gas entering the mixing channel 122 is controlled, and thus the ratio of air to combustible gas and the λ value are controlled. However, it should be noted that several other possibilities can be applied as an alternative or in combination to the electronically actuated control gas valve 112, some of which are elaborated here in detail.

[0116] According to the present invention, the controller 150 is configured to supply a premixed gas having a first λ value during a start-up phase of the burner 100. The time period before the ignition source 124 ignites the supplied premixed gas having the first λ value is part of the start-up phase. The ignition itself also occurs during the start-up phase. The controller 150 is further configured to supply a premixed gas having a second λ value during an operation phase of the burner. The operation phase begins after the ignition source 124 has ignited the supplied premixed gas having the first λ value. According to the present invention, the first λ value is greater than the second λ value.

[0117] In the case of a malfunction or during a delayed ignition test, the premixed gas having the first λ value can accumulate in the combustion chamber 130 until it is ignited. Since the initially ignited premixed gas has a lower first λ value, the flame speed is reduced. The risk of flashback and explosion is likewise reduced.

[0118] Preferably, the first λ value is at least 1.85. It has been found that this is the practical lower limit at which satisfactory results can be obtained.

[0119] The burner 100 preferably includes at least one channel blocking element 112, which is implemented as a gas valve 112 in the Figure 1 example shown. The channel blocking element 112 in this embodiment is arranged such that it can partially block the combustible gas channel 111. The controller 150 can control the channel blocking element 112 by outputting a control signal 151 via the output 150.1 to the input 113.1 of the actuator 113. During the start-up phase, the controller 150 controls the channel blocking element 112 such that the combustible gas channel 111 is partially blocked. In this way, less combustible gas is supplied to the premixed gas, resulting in a larger first λ value.

[0120] Preferably, the channel blocking element 112 is in a rest position during the start-up phase. Thus, the gas valve 112 can be biased, for example by one or more springs, to be partially closed. By applying a force with the actuator 113, the gas valve 112 can be further opened to an actuated position during the operation phase such that more combustible gas is supplied to the premixed gas. However, in the case of a malfunction, for example in the controller 150 or the actuator 113, the gas valve 112 will remain in the rest position even during the operation phase, and the premixed gas in the operation phase will have the first λ value. Although this may result in inefficient combustion, safety is ensured because too low a λ value during the start-up phase during such a malfunction is avoided.

[0121] When the transition from the startup phase to the operation phase can be completed, there are several possible implementation methods. Preferably, the startup phase lasts at least 1 second, preferably at least 2 seconds, and even more preferably at least 3 seconds, such as 3 - 6 seconds. In some embodiments, the controller 150 can be configured to automatically switch to the operation phase after a predetermined amount of time.

[0122] Figure 1 An optional flame detector 131 is shown disposed in the combustion chamber 130. The flame detector 131 is configured to generate a flame signal 153 when it detects a flame in the combustion chamber 130, and the flame signal 153 indicates that the supplied premixed gas is ignited and / or burning. The flame detector 131 can be implemented according to any known suitable principle for flame detection. The flame signal 153 is output to the controller 150 through the output terminal 131.1 and the input terminal 150.3. The controller 150 can use the information provided by the flame signal 153 in several ways. For example, the controller 150 can be configured to actuate the gas valve 112 to the actuated position only after detecting a flame, thereby preventing the premixed gas with the second λ value from reaching the combustion chamber 130 before the already existing premixed gas is ignited. This can be done as an alternative or addition to waiting for a predetermined amount of time as described above. The controller 150 can also control the ignition source 124, as Figure 1 shown, where the control signal 152 can be sent through the output terminal 150.2 and the input terminal 124.1. In this case, the controller 150 can be configured to stop the ignition source 124 from igniting the premixed gas if the flame detector 131 does not detect a flame after a certain amount of time. This will avoid a dangerous situation when a large amount of premixed gas accumulates in the combustion chamber 130 without being ignited. Note that some standards prescribe this as a mandatory measure. On the other hand, by controlling the ignition source 124, it can also be ensured that when the premixed gas has a satisfactory λ value, only the premixed gas supplied to the combustion chamber 130 is ignited. The controller 150 can also control the ignition source 124 to remain in the ignited state during the ignition cycle after detecting the initial ignition of the premixed gas. In this way, even when the flame has left the accumulated premixed gas, the accumulated premixed gas can burn.

[0123] Figure 3 Several factors that can be considered when determining the first λ value and / or the second λ value are shown in an alternative embodiment. These factors can be considered individually or in combination with each other. In Figure 3 the horizontal axis, the load of the burner is represented, and the λ value is represented on the vertical axis. Each line in the figure represents a different factor, which will be explained below. For each line, an arrow is provided indicating on which side of the corresponding line the λ value should preferably be.

[0124] The burner is configured to be adjustable between a minimum and a full load. For example, for a domestic heating device, the full load can be 24 kW. Traditionally, the modulation ratio (i.e., the ratio of the full load to the minimum load) is about 4:1 - 5:1, and recently modulation ratios of up to 10:1 have been proposed. In Figure 3 line 3.6 shows the lower limit of 20% when the modulation ratio is 5:1, while line 3.7 shows the lower limit of 10% when the modulation ratio is 10:1.

[0125] The second λ value is typically in the range of 1.05 - 1.3, especially at high or full load. In the case where the air and the combustible gas are not sufficiently mixed or the composition of the air and / or the combustible gas deviates, a small amount of excess air is provided to avoid incomplete combustion. Figure 3 Line 3.8 in Figure 3 shows an example of the second λ value as a function of the load. It has been found that when the combustible gas includes a significant amount of hydrogen, it may be optimal to adjust the λ value based on the load during the operating phase, and thus for example the second λ value. As explained in European patent application with application number 19162278, the λ value at the minimum load can be at least 20% higher than at the full load, and optionally, the λ value at the average load can be less than 10% higher than at the full load. Generally, the burner will start at a load within the adjustment range. According to the invention, when the burner starts at said load, the first λ value at any given load is higher than the second λ value at said load. This is represented by

[0126] line 3.10 in

[0127] which corresponds to line 3.8 multiplied by 1.5. However, in some embodiments, the burner can start at a load below the minimum load, although this is limited by a reduced minimum load, since below said minimum load it may not be possible to determine whether the flame or the burner is opened or closed within an acceptable time.

[0126] Preferably, the first λ value is below the blow - out value. The blow - out value is the λ value at which, relative to the air in the premixed gas, there is so little combustible gas that any flame at the burner surface is blown out by the premixed gas, because there is not enough combustible gas to maintain the flame burning.

[0127] Preferably, the first λ value is such that the concentration of the combustible gas in the premixed gas is below the upper flammability limit, also known as UFL, indicated by Figure 3 line 3.2 in Figure 3 . Preferably, the first λ value is such that the concentration of the combustible gas in the premixed gas is above the lower flammability limit, also known as LFL, indicated by Figure 3 line 3.1 in Figure 3 . Otherwise, it is not possible to ignite the premixed gas because the premixed gas is respectively too rich or too lean. It should be noted that a concentration of the combustible gas in the premixed gas above a certain threshold corresponds to a λ value below the λ value corresponding to said threshold. It should also be noted that the upper and lower flammability limits are determined by the composition of the combustible gas, but also depend on factors such as temperature and pressure.

[0128] In fact, the first lambda value can also be restricted by the fan, especially in embodiments where the lambda value is adjusted by partially blocking the air passage. The maximum capacity or power of the fan determines the maximum amount of air that can flow through the air passage, and this amount of air, together with a given amount of supplied combustible gas, determines the lambda value of the premixed gas. Of course, theoretically a larger fan could be provided, but in practice this may be undesirable due to cost considerations. Thus, when the fan is at full load, the first lambda value preferably corresponds to an amount of air lower than the amount of air provided by the fan. This is shown by line 3.3 in Figure 3 which. It should be noted that the amount of combustible gas can also be determined by the fan, especially when the fan is arranged downstream of the position where the combustible gas passage intersects the air passage.

[0129] Preferably, the first lambda value is such that the concentration of combustible gas in the premixed gas is lower than the lower explosion limit, also known as the LEL, which means that the first lambda value should be higher than the lambda value corresponding to the LEL, as shown by line 3.4 in Figure 3 which. It is best to control the first lambda value to differ from the lower explosion limit by more than a predetermined safety margin, for example the safety margin is 1.2 or 1.5 times, as shown by line 3.5 in Figure 3 which. This ensures a safe start, even when the actual composition of the air or combustible gas is different from what is expected.

[0130] Preferably, the first lambda value is lower than the lower temperature value, shown by line 3.9 in Figure 3 which. In this document, the lower temperature value is defined as the value at which the flame of the ignited premixed gas is at its extinguishing low temperature. In the case where the combustible gas consists only of hydrogen, the temperature is about 571 degrees Celsius.

[0131] As shown in Figure 3 when all the above-mentioned optional restrictions are followed, the ideal range of the first lambda value becomes apparent, which is indicated by reference numeral 3.50 in Figure 3 which. This can be used to determine the optimal first lambda value based on the composition of the combustible gas and air and environmental conditions such as temperature and pressure. Depending on how many of the above factors are considered, the range can be determined more precisely. However, in some cases, estimated or standard values can be used for one or more factors.

[0132] However, in practice, by determining Figure 3It may be troublesome to determine the first λ value and the second λ value based on all the lines shown in [the figure]. In testing and simulation, the applicant has found that generally the following rule of thumb gives satisfactory results. The first λ value is at least 1.85, preferably at least 1.9, preferably greater than 2, for example between 2 and 5, preferably greater than 3, for example between 3 and 5, more preferably greater than 4, for example between 4 and 5. The second λ value can be taken as 1 - 2, preferably 1.05 - 1.5, more preferably 1.05 - 1.3. Generally, the first λ value is preferably at least 1.5 times larger than the second λ value, preferably at least 2 times larger, for example at least 3 times larger.

[0133] Figure 4 Figure 4 shows a second embodiment of the burner 300 according to the present invention. Figure 4 The shown burner 300 differs from Figure 1 the shown burner 100 in terms of the channel blocking element and the gas valve. In Figure 4 , the channel blocking element 312 and the gas valve 212 are not the same element. Instead, there is a channel blocking element 312 in addition to the gas valve 212. Furthermore, in the shown embodiment, the gas valve 212 is not an electronically actuated control valve, but a mechanism that opens based on the aerodynamic balance upstream and downstream of the valve 212; however, this is not a requirement for the embodiment of the channel blocking element 312 as shown in Figure 4 .

[0134] The channel blocking element 312 is configured to be arranged in the combustible gas passage 111 in the static position, as shown in Figure 4 . In an actuated position (not shown), the channel blocking element 312 is not in the combustible gas passage 111, or at least the channel blocking element 312 blocks the combustible gas passage 111 less than in the static position. An actuator 313 is provided to move the channel blocking element 312 from the static position to the actuated position. The channel blocking element 312 is preferably biased to the static position so that a reverse movement back to the static position can be made using it, for example including spring force or gravity. The actuator 312 can be configured to move the channel blocking element 312 based on pneumatic, hydraulic, mechanical, and / or magnetic forces. The controller 150 is configured to control the actuator 313 with a control signal 351 via the output terminal 150.1 and the input terminal 313.1. The controller 150 is configured to arrange the channel blocking element 412 in the static position during the start-up phase and in the actuated position during the operation phase. The channel blocking element 312 itself can take any suitable shape and form.

[0135] Figure 5 Figure 5 shows a third embodiment of the burner 400 according to the present invention. Figure 5 The shown burner 400 differs from Figure 1The burner 100 shown is different in terms of the channel blocking element and the valve. In Figure 5 , the channel blocking element 412 is not the same element as the valve 212. Additionally, in the illustrated embodiment, the valve 212 is not an electronically actuated control valve, but a mechanism that opens based on the aerodynamic balance upstream and downstream of the valve 212; however, this is not a requirement for the embodiment of the channel blocking element 412 as shown in Figure 5 .

[0136] The channel blocking element 412 is configured to be arranged in the air channel 101 in the actuated position, as shown in Figure 5 . In a stationary position (not shown), the channel blocking element 412 is not in the air channel 101, or at least the channel blocking element 412 blocks the air channel 101 less compared to the actuated position. An actuator 413 is provided to move the channel blocking element 412 from the stationary position to the actuated position. The channel blocking element 412 is preferably biased to the stationary position so that the reverse movement back to the stationary position can be utilized, for example including spring force or gravity. The actuator 412 can be configured to move the channel blocking element 412 based on pneumatic, hydraulic, mechanical, and / or magnetic forces. The controller 150 is configured to control the actuator 413 with a control signal 451 via the output 150.1 and the input 413.1. The controller 150 is configured to arrange the channel blocking element 412 in the stationary position during the startup phase and in the actuated position during the operation phase. The channel blocking element 412 itself can take any suitable shape and form.

[0137] In the illustrated embodiment, different from the embodiments shown in Figure 1 and Figure 3 , the amount of air is reduced during the operation phase, rather than the amount of combustible gas during the startup phase.

[0138] In an embodiment (not shown), the channel blocking element 412 is configured to be arranged in the narrower portion 121. Since the narrower portion 212 is even narrower in this case, the velocity further increases and the pressure further decreases, and more combustible gas will be inhaled due to the reduced pressure.

[0139] Figure 6Schematically shows the steps of a method for starting a burner according to a possible embodiment of the present invention. In step 1001, there is a heat demand. The heat demand can be caused, for example, by heating in an open building or warm water required by a faucet or a shower. The heat demand may optionally trigger pre-purging in step 1002. Pre-purging requires blowing air through the burner to ensure that there is no combustible gas. After pre-purging, a premixed gas with a first λ value is supplied in step 1003, and an ignition source is controlled to be in an ignition state in step 1004. In the ignition state, the ignition source is suitable for igniting the premixed gas with the first λ value. Step 1004 can be performed before step 1003 or simultaneously with step 1003. Preferably, the first λ value is at least 1.85. Optionally, in step 1005, the ignition source is controlled to no longer be in the ignition state before performing flame detection in step 1006 using a flame detector. Step 1005 may be particularly beneficial if the ignition source is, for example, a spark igniter, as otherwise, flame detection will be adversely detected, which also depends on the type of sensor used as the flame detector. Steps 1001 - 1006 are part of 1100 during the start-up phase.

[0140] If no flame is detected in step 1006 after a safety time, step 1007 provides a restart, where the pre-purging in step 1002 ensures that there is no unburned premixed gas remaining in the burner. Optionally, step 1007 can be performed only a predetermined number of times, such that if the burner cannot be started after, for example, five attempts, the burner is completely shut down. The safety time can be according to EN 15502.

[0141] If a flame is detected in step 1006, the method can optionally include a transition phase 1200 after the start-up phase 1100. The transition phase 1200 is particularly advantageous if the burner starts with a start-up load different from the required load during the start-up phase 1100. In the illustrated embodiment, the transition phase 1200 includes step 1009 of changing the λ value of the supplied premixed gas to a second λ value associated with the start-up load if the load in the operating phase is equal to the start-up load. The transition phase 1200 then includes step 1010 of changing the load to the desired load and changing the λ value to a second λ value associated with the desired load. Other embodiments of the transition phase 1200 are possible, as explained herein.

[0142] After the transition phase, the method can include an operating phase 1400. The operating phase 1400 includes step 1012 of supplying a premixed gas with a second λ value to the burner surface. The first λ value is greater than the second λ value.

[0143] Figure 6An optional ignition period 1300 is also shown. The ignition period 1300 begins at step 1008, in which the ignition source is controlled to be in an ignition state, and at step 1011, the ignition source is controlled to not be in an ignition state. In the example shown, the ignition period 1300 corresponds to the end of the startup phase 1100, the transition phase 1200, and the beginning of the operation phase 1400.

[0144] Although shown herein as separate embodiments, it should be noted that one or more of the Figure 1 embodiments, namely the gas valve 112 serving as the channel blocking element 112; Figure 4 embodiments, namely the channel blocking element 312 provided in the combustible gas channel 111; and Figure 5 embodiments, namely the channel blocking element 111 arranged in the air channel 101.

[0145] As needed, detailed embodiments of the present invention are described herein. However, it must be understood that the disclosed embodiments are only examples, and the present invention can also be implemented in other forms. Therefore, the specific structural aspects disclosed herein should not be considered as limitations of the present invention, but only as the basis for the claims and as the basis for enabling the present invention to be implemented by those of ordinary skill in the art.

[0146] Furthermore, the various terms used in the specification should not be construed as restrictive, but should be construed as a comprehensive interpretation of the present invention.

[0147] Unless otherwise specified, the word "a" as used herein means one or more than one. The phrase "a plurality of" means two or more than two. The words "comprising" and "having" constitute open-ended language and do not exclude the presence of more elements.

[0148] The reference numerals in the claims should not be construed as limitations of the present invention. The specific embodiments do not need to achieve all the described purposes.

[0149] The fact that certain technical measures are specified in different dependent claims still allows the possibility of advantageously applying combinations of these technical measures.

Claims

1. A method for starting a burner, in which a premixed gas comprising a combustible gas and air is supplied to a burner surface of the burner, where ● the combustible gas comprises at least 50 vol% hydrogen, ● the λ value is defined as the ratio between the actually supplied amount of air and the amount of air required for stoichiometric combustion of the premixed gas, ● the burner is a surface-stabilized fully premixed gas premixed burner, ● the burner is configured to be adjustable between a minimum load and a full load, wherein the method comprises the following steps: ● During a start-up phase: supply a premixed gas having a first λ value to the burner surface, where the first λ value is at least 1.85, and ignite the supplied premixed gas having the first λ value using an ignition source, ● During an operation phase after the premixed gas is ignited: supply a premixed gas having a second λ value to the burner surface, where the first λ value is greater than the second λ value.

2. The method according to claim 1, wherein, the λ value is controlled during the start-up phase by controlling the amount of air supplied through the air passage and / or the amount of combustible gas supplied through the combustible gas passage.

3. The method according to claim 1 or claim 2, wherein, the burner comprises a premixed gas supply circuit, and the premixed gas supply circuit comprises: ● an air passage for supplying air, ● a combustible gas passage for supplying combustible gas, ● a mixing passage for mixing the air supplied through the air passage and the combustible gas supplied through the combustible gas passage into a premixed gas to be supplied to the burner surface, and ● at least one passage blocking element for partially blocking the combustible gas passage and / or the air passage, wherein the method further comprises the following steps: ● During the start-up phase: partially block the combustible gas passage with the at least one passage blocking element, so that less combustible gas is supplied to the mixing passage during the start-up phase compared to during the operation phase, and / or ● During the operation phase: partially block the air passage with the at least one passage blocking element, so that more air is supplied to the mixing passage during the start-up phase compared to during the operation phase.

4. The method according to claim 3, wherein, the at least one passage blocking element is arranged in a stationary position during the start-up phase, and the method further comprises the step of actuating the passage blocking element during the operation phase to arrange the passage blocking element in an actuated position.

5. The method according to claim 1 or 2, wherein, the first λ value is greater than 2.

6. The method according to claim 5, wherein, the first λ value is greater than 3.

7. The method according to claim 5, wherein, the first λ value is greater than 4.

8. The method according to claim 1 or 2, wherein, the second λ value is between 1 and 2.

9. The method according to claim 8, wherein, the second λ value is between 1.05 and 1.

5.

10. The method according to claim 8, wherein, The second λ value is between 1.05 and 1.

3.

11. The method according to claim 1 or 2, wherein, the first λ value is at least 1.5 times greater than the second λ value.

12. The method according to claim 11, wherein, the first λ value is at least 2 times greater than the second λ value.

13. The method according to claim 11, wherein, the first λ value is at least 3 times greater than the second λ value.

14. The method according to claim 1 or 2, wherein, the combustible gas comprises at least 95 vol% hydrogen.

15. The method according to claim 1 or 2, wherein, it lasts for at least 1 second during the start-up phase.

16. The method according to claim 15, wherein, it lasts for at least 2 seconds during the start-up phase.

17. The method according to claim 15, wherein, it lasts for at least 3 seconds during the start-up phase.

18. The method according to claim 1 or 2, wherein, the burner starts with a start-up load different from the desired load in the operation phase, wherein the method further comprises a transition phase from the start-up phase to the operation phase after the premixed gas is ignited, and wherein the transition phase comprises the step of changing the load to the desired load.

19. The method according to claim 1 or 2, wherein, the method further comprises the step of maintaining the ignition source in the ignited state for up to a continuous ignition period after it has been detected that the premixed gas supplied with the first λ value has been ignited.

20. A burner for burning a combustible gas comprising at least 50 vol% hydrogen, wherein the burner is a surface-stabilized fully premixed gas premixed burner, and wherein the burner is configured to adjust between a minimum load and a full load, the burner comprises: ● a burner surface, ● a premixed gas supply circuit, comprising i. an air passage for supplying air, ii. a combustible gas passage for supplying combustible gas, iii. a mixing passage for mixing the air supplied by the air passage and the combustible gas supplied by the combustible gas passage into a premixed gas to be supplied to the burner surface, wherein the λ value is defined as the ratio between the actually supplied amount of air and the amount of air required for the stoichiometric combustion of the premixed gas, ● an ignition source for igniting the premixed gas supplied to the burner surface, ● a controller configured to control the λ value of the supplied premixed gas by controlling the amount of air supplied by the air passage and / or the amount of combustible gas supplied by the combustible gas passage, wherein the controller is configured to: i. supply a premixed gas with a first λ value during the start-up phase of the burner, wherein the ignition source is configured to ignite the supplied premixed gas with the first λ value, and wherein the first λ value is at least 1.85, and ii. After the ignition source is configured to ignite the supplied premixed gas having a first λ value, a premixed gas having a second λ value is supplied during the operation phase of the burner, wherein the first λ value is greater than the second λ value.

21. The burner according to claim 20, further comprising at least one channel blocking element for partially blocking the combustible gas channel and / or the air channel, wherein, the controller is further configured to control the at least one channel blocking element to partially block the combustible gas channel during the startup phase and / or to partially block the air channel during the operation phase.

22. The burner according to claim 21, wherein, the at least one channel blocking element has an actuated position and a rest position, wherein the at least one channel blocking element is configured to be in the actuated position during the operation phase and in the rest position during the startup phase.

23. The burner according to claim 21, wherein, the burner further comprises a gas valve in addition to the at least one channel blocking element, wherein the gas valve is arranged in the combustible gas channel, wherein the gas valve has a closed position and an open position, in the closed position, the combustible gas is prevented from flowing through the combustible gas channel, and in the open position, the combustible gas can flow through the combustible gas channel.

24. The burner according to claim 21, wherein, the channel blocking element is a valve.

25. The burner according to claim 20 or 21, further comprising at least one oxygen sensor configured to measure a value representing the oxygen content of the flue gas generated by the burner or a value representing the oxygen content of the premixed gas supplied to the surface of the burner.

26. The burner according to claim 20 or 21, further comprising at least one flame detector configured to detect when the supplied premixed gas is ignited and / or burning and to generate a corresponding flame signal.

27. The burner according to claim 20 or 21, wherein, the burner includes a perforated metal plate for stabilizing the flame when the supplied premixed gas burns.

28. A heating device for burning hydrogen, comprising the burner according to claim 20 or 21.

29. The burner according to claim 24, wherein, the valve is an electronically actuated control valve.

30. The burner according to claim 26, wherein, the controller is further configured to control the premixed gas to have the second λ value after receiving the flame signal from the detector.

Images