EP4437274A1

EP4437274A1 - Flame acquisition system and method of retrofitting a combustion appliance with the system

Info

Publication number: EP4437274A1
Application number: EP22822423.4A
Authority: EP
Inventors: Job Rutgers; Chiel ter BRAAK; Ruud Boersen
Original assignee: BDR Thermea Group BV
Current assignee: BDR Thermea Group BV
Priority date: 2021-11-25
Filing date: 2022-11-25
Publication date: 2024-10-02
Also published as: EP4187151A1; WO2023094597A1

Abstract

Flame acquisition system (1) for a combustion appliance (2) for combusting a combustion gas, in particular for a gas boiler, the system (1) comprising at least a flame sensor (4) to acquire the presence of a flame and for generating a flame signal, the flame sensor (4) being connectable to a control system (3) of the combustion appliance (2) for controlling the combustion appliance (2), and a converter (5) connected or connectable to the flame sensor (4) to convert the flame signal generated by the flame sensor (4) into an electrical current used by the control system (3) for controlling the combustion appliance (2).

Description

FLAME ACQUISITION SYSTEM AND METHOD OF RETROFITTING A COMBUSTION APPLIANCE WITH THE SYSTEM

The invention relates to a flame acquisition system for a combustion appliance. Additionally, the invention relates to a combustion appliance comprising said flame acquisition system and the use of the flame acquisition system to convert a hydrocarbon gas boiler into a gas boiler for the combustion of combustion gas comprising more than 20 mol% hydrogen. Also, the invention relates to a method for retrofitting a combustion appliance.

The emission of carbon dioxide is one of the most relevant factors contributing to the pollution in environment. Since the contribution from the building sector is continuously increasing in the last decades, there is the need to reduce CO₂ emissions from this sector. Heating of spaces and heating of water are the two major causes of energy consumption and CO₂ emission from the building sector. Inefficient boilers and carbonintensive power can further worsen this problem.

Nowadays, the majority of boilers are gas boilers and are designed for natural gas, using hydrocarbons as fuel gas. Gas boilers combust gas fuel to heat water for domestic use and/or central heating systems in buildings. The market is looking into cleaner alternatives for combusting natural gas. One of these alternatives is combusting pure hydrogen. It is noted that gas boilers combusting pure hydrogen (i.e. hydrogen boiler) are boilers to which fuel gas is supplied that comprises at least 90 mol% hydrogen. Currently, there are natural gas (or propane) boilers on the market which are only suitable to combust up to 20% hydrogen into the gas blend (according to the specifications). In other words, current boilers on the market are not directly suitable for combustion of hydrogen and important modifications are needed to possibly convert a standard natural gas boiler into a hydrogen boiler. These modifications are in most cases expensive and time consuming.

For example, an ionization signal is used to acquire the flame in a hydrocarbon (i.e. natural gas) boiler. When combusting pure hydrogen, there is no (or really little) hydrocarbon and/or carbon content in the fresh gas mixture and/or the combustion gases. Therefore, the conventional applied ionization signal cannot be used anymore in hydrogen combusting boiler. In alternative, UV signal and/or temperature signal can be used to acquire the flame in a hydrogen boiler. Therefore, for converting a natural gas boiler into a hydrogen boiler, a control unit must be modified (e.g. reprogrammed and/or changed from the structural point of view) or a new control unit must be installed to acquire the flame signal (such as Uv or temperature). A hydrogen boiler is a boiler which can combust combustion gas comprising more than 20mol% hydrogen.

It is therefore desirable to obtain an easy and relatively low-cost conversion between a standard natural gas boiler and a hydrogen boiler for the flame acquisition. It is also desirable that the conversion is carried out reducing to the minimum the components to be added or modified.

Prior art fails to address the problem of converting a gas boiler combusting a type of fuel gas, such as natural gas, into a gas boiler combusting another type of fuel gas, such as pure hydrogen as regards the flame acquisition mechanism. Also, the prior art documents are not suitable to provide a solution that is cost effective and safe.

The object of the invention is therefore to provide a flame acquisition system that is effective in converting a natural gas combustion appliance into a hydrogen combustion appliance and still enables combustion of natural gas after conversion.

The object is solved by a flame acquisition system for a combustion appliance for combusting a combustion gas, in particular for a gas boiler, the system comprising at least a flame sensor to acquire the presence of a flame and for generating a flame signal, the flame sensor being connectable to a control system of the combustion appliance for controlling the combustion appliance, and a converter connected or connectable to the flame sensor to convert the flame signal generated by the flame sensor into an electrical current used by the control system for controlling the combustion appliance.

Thanks to the present flame acquisition system, it is possible to upgrade a combustion appliance such as a conventional hydrocarbon (i.e. natural gas) gas boiler into a hydrogen boiler in a very easy and safe way. Also, the conversion is cost effective since it can be realized without changing the measurement circuit of the controller of the starting gas boiler. Upgrading the combustion appliance can be intended that a conventional hydrocarbon gas boiler can be provided with an additional functionality of detecting the presence of a flame also in case the fuel gas does not comprise carbon containing compounds.

The converter may be connected or connectable to pass the electrical current to an ionization sensor for detecting a flame generated by the combustion of a combustion gas with (predominantly) carbon containing compounds (e.g. natural gas, methane) of the combustion appliance. Alternatively, the converter may be connected or connectable to pass the electrical current to the control system of the combustion appliance directly, optionally in parallel to an ionization sensor. Alternatively, the converter may be connected or connectable to pass the electrical current to the control system of the combustion appliance directly, in particular instead of the ionization sensor and/or by replacing the ionization sensor by the converter. In another embodiment the converter can disconnect the electrical connection between the flame sensor and the control system. In said case, an electrical current resulted in the convertor, in particular a current from a flame representation means, flows into the control system.

This provides for a flame acquisition system that allows upgrading a combustion appliance that is capable of determining physical properties of combustion which are used to determine whether a flame is present. The flame can be generated by the combustion of a carbon containing gas and flames generated by the combustion of combustion gas comprising at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen.

It is noted that the control system is configured to control the settings of the combustion appliance based on a determined current flowing in its circuit. Specifically, this is a control system for an appliance combusting hydrocarbon gas (i.e. natural gas or LPG (CxHy)) and the current is a so called ionization current that is usually generated by an ionization electrode. In particular, the present flame acquisition system is used to convert the flame signal coming from the flame sensor (adapted to acquire a flame generated by the combustion of a gas different form a hydrocarbon gas, for example pure hydrogen) into an electrical current or ionization signal that is an imitation of an ionization current that can be used by the control system to control the combustion appliance. In this way, the control system can maintain the functionality of controlling the settings of the appliance by receiving an electrical signal derived by the acquisition of a flame that is not necessarily generated by the combustion of hydrocarbon gas.

The combustion gas comprises air and fuel gas. A fan for supplying air to the air combustion can be controlled based on the electrical current or ionization signal. Alternatively or additionally, a gas valve for supplying the fuel gas to the combustion appliance can be controlled based on the electrical current or ionization signal. The control system can control the fan of the combustion appliance and/or the gas valve of the combustion appliance on the basis of the flame signal.

Examples of combustion appliances can include furnaces, water heaters, boilers, direct/in-direct make-up air heaters, power/jet burners and any other residential, commercial or industrial combustion appliance. In many cases, a combustion appliance can be modulated over a plurality of burner loads, with each burner load requiring a different flow rate of fuel gas resulting in a different heat output. At higher burner loads, more fuel gas and more air are typically provided to the burner, and at lower burner loads less fuel gas and less air are typically provided to the burner.

As explained below more in detail the flame sensor is a sensor by means of which at least the presence of a flame is detected. However, the flame sensor can be configured to acquire further information by means of which it is possible to determine the air to fuel gas ratio of a mixture supplied to a burner of the combustion appliance and/or the fuel gas flow rate supplied to the burner.

In one example, the converter can comprise a flame acquisition control unit and a switch element located between the control system and the flame sensor, wherein the flame acquisition control unit is connected to the flame sensor and the switch element and is configured to trigger the switch element based on the acquisition of the flame by the flame sensor, thereby causing an electrical current to flow from the flame sensor to the control system or from a flame representation means. In the latter case the switch element is triggered in such a position that the flame sensor is not electrically connected to the control system, in particular to the appliance control unit, but the flame representation means is electrically connected to the control system, in particular the appliance control unit.

The flame acquisition control unit can comprise one or more processor or be at least one processor for processing data. Additionally or alternatively, the flame acquisition control unit can comprise a printed circuit board.

The flame representation means is used to simulate a flame acquisition signal. For simulating the flame acquisition signal the flame representation means can comprise passive electrical components, in particular at least a diode and/or a resistor. The control system can apply a voltage, in particular an alternating voltage, on the flame representation means. In particular, the flame acquisitions system can be configured such that the flame representation means is applied with voltage from the control system, in particular the control unit, independent on the position of the switch element. Using of the flame representation means has the advantage that the control system can get the information that a flame, in particular a flame resulting from combustion of a combustion gas comprising more than 20 mol%, is present. This would not be possible by transmitting the signal of the flame sensor to the control system.

The flame acquisition control unit can monitor the flame sensor to determine the acquisition of a corresponding flame signal and can control the switch element based on the acquisition of the flame signal. In particular, the switch element connects the flame sensor to the control system of the combustion appliance In a first configuration, the switch element is in an open position, meaning that no electrical current flows into the control system coming from the flame sensor. In a second configuration, the switch element is in a close position, meaning that there is an electrical current flowing into the control system. Once a flame signal is detected, the flame acquisition control unit triggers the switch element to pass from the first to the second configuration and causing an electrical current to flow into the control system. The flowing current is interpreted by the control system as an ionization current and the combustion appliance can be controlled accordingly. As discussed above the current can result from the flame representation means. In particular, in the closed position of the switch element, the current flows from the flow representation means to the control system.

In examples, the flame sensor can be at least one of: an optical sensor, in particular a UV sensor or IR sensor; a temperature sensor, in particular a thermocouple, to be located in a burner of the gas boiler; a temperature sensor, in particular a thermocouple, to be located in a combustion chamber of the gas boiler; a dynamic pressure sensor; a sound or vibration sensor; and a catalytic sensor.

All these sensors, when properly located in the combustion appliance, can acquire the presence of the flame in the burner using different physical principles. Based on the characteristics of these sensors, it is possible to combine more of them for improving the performance of the flame acquisition system. In particular, it is possible by using for example the Uv sensor to determine the amount of fuel gas and/or the air to fuel gas ratio of the mixture supplied into the burner of the combustion appliance.

In another example, the flame acquisition control unit can be part of an appliance control unit to control the combustion appliance or the flame acquisition control unit can be separated from said appliance control unit. In other words, the flame acquisition control unit can be integrated in the control board or printed circuit board of the combustion appliance, in particular of the appliance control unit. Additionally or alternatively the appliance control unit can comprise one or more processors for processing data. This can be the appliance control unit present to manage and control the functionalities of the appliance. In this way, the control board already installed in the original combustion appliance can be also used to control the flame acquisition system in the upgraded appliance. Alternatively, the flame acquisition control unit is not integrated in the control board or printed circuit board of the combustion appliance and is separated from that. In particular, the flame acquisition control unit can be part of another printed circuit board.

In a further example, the flame sensor can be suitable for detecting a flame generated by the combustion of hydrogen gas. In this case, it is intended a fuel gas that comprises at least 20 mol%, in particular more than 20 mol% or at least 30mol% or at least 90 mol%, hydrogen.

In examples, the flame acquisition control unit can be configured to set an operating mode of the combustion appliance based on a flame acquisition signal acquired by the flame sensor. In this way, the appliance settings can be adapted to the presence of a combustion gas different from hydrocarbon gas, such as hydrogen gas. In many cases, a combustion appliance can be modulated over a plurality of burner loads, with each burner load requiring a different flow rate of fuel resulting in a different heat output. At higher burner loads, more fuel and more air are typically provided to the burner, and at lower burner loads less fuel and less air are typically provided to the burner. Accordingly, the acquisition of a flame generated by the combustion of a hydrogen gas can determine for example a reconfiguration of the modulation modes.

According to one aspect of the invention, a combustion appliance, in particular a gas boiler, is provided, the combustion appliance comprising an inventive flame acquisition system. Examples of combustion appliances can include furnaces, water heaters, boilers, direct/in-direct make-up air heaters, power/jet burners and any other residential, commercial or industrial combustion appliance. In addition to the inventive flame acquisition system, i.e. configured to detect flames fueled by a combustion gas without carbon containing compounds (e.g. hydrogen), the combustion appliance may comprise a further flame sensor, e.g. an ionization electrode, configured to detect flames fueled by a gas predominantly comprising carbon containing compounds (e.g. methane). This provides for a combustion appliance that can be used with carbon and non-carbon fuels, as well as mixtures thereof. Connecting the converter with the ionization electrode enables that the combustion appliance can combust natural gas, i.e. gas with less than 21 mol% hydrogen in the combustion gas, even after the flame acquisition system is connected with the combustion appliance, in particular the control system.

Therefore, in particular, the appliance can be selectively configured to combust a combustion gas comprising carbon containing compounds and/or a gas without carbon containing compounds and/or a combustion gas comprising more than 20mol% hydrogen or more than 30mol% hydrogen or more than 90mol% hydrogen. The present flame acquisition system can be used to acquire the flame generated by a combustion gas without carbon containing compounds, such as hydrogen.

In one example, the combustion appliance comprises a burner and a combustion chamber and the flame sensor can be located in the burner and/or the combustion chamber. In addition or alternatively, the combustion appliance can comprise a gas valve to control the inflow of the combustion gas, wherein the gas valve can be controlled electronically or pneumatically.

In case the gas valve is controlled electronically, a flame acquisition signal acquired by the flame sensor can be used to control an excess air factor. This is possible if the flame acquisition signal comprises information by means of which the fuel gas supplied to a burner of the combustion appliance can be determined. By adapting the gas valve position the air to fuel gas ratio of the mixture can be set.

As mentioned above, the combustion appliance can be originally designed for the combustion of hydrocarbons. However, in an example, the combustion appliance including the present flame acquisition system can be used also when the combustion gas comprises at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen. According to an embodiment, the converter can be connected or is connectable to the ionization electrode. In this case the converter can be connected or is connectable to the ionization electrode and the flame sensor. Thus, the further flame sensor, in particular ionization electrode, is part of the flame acquisition system in said embodiment.

The combustion appliance, in particular a gas boiler, for combusting a combustion gas comprising at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen, by using a flame acquisition system can be operated as follows: triggering the switch element to a first position for connecting the flame representation means to the control system when the flame sensor (4) detects a flame and/or triggering the switch element to a second position in which the flame representation means and the control system are not connected, when the flame sensor does not detect a flame.

The flame sensor and the further flame sensor, in particular ionization electrode, can be, in particular directly, connected to the flame acquisition control unit. As discussed above, the flame acquisition control unit can be connected to the switch element to trigger the position of the switch element. The flame acquisition control unit can be configured to trigger the switch element to a first position for connecting the flame representation means to the control system when a flame is acquired by the flame sensor and/or to trigger the switch element to a second position when no flame is acquired by the flame sensor. The control system can apply a voltage on the flame representation means, in particular independent on the position of the switch element. Thus, only current flows from the flame representation means to the control system when the switch element is in the first position. As mentioned above this is the case when the flame signal detects a flame acquisition signal.

Such a flame acquisition system has the advantage that a natural gas combustion appliance can be easily retrofitted to a hydrogen combustion appliance. Thereto, the flame acquisitions system has only to be electrically connected to the control system. In particular, it is only necessary to connect the converter such that it is electrically arranged between the control system and the ionization electrode and/or the flame sensor.

The flame acquisition control unit can be, in particular directly, connected to the control system, in particular the control unit of the control system. Thus, the flame acquisition control unit can monitor the flame sensor and the ionization electrode and transmits a signal to the control system when a flame acquisition signal is received from the flame sensor and an ionization signal is received from the ionization electrode. That means, the flame acquisition control unit does not only trigger the switch element but can communicate with the control system. For the case that the flame acquisition control unit acquires a flame signal from the flame sensor and the ionization electrode, the flame acquisition control unit communicates said information to the control system. The flame acquisition control unit can monitor the ionization electrode and can determine on the base of a received ionisation signal from the ionization electrode the presence and/or concentration of hydrocarbons in the combustion gas.

Acquiring the ionization signal or both signals by the flame acquisition control unit indicate impurities or the presence or concentration of hydrocarbons in the combustion gas comprising more than 20mol% hydrogen. Thus, communicating said information to the control system enables that the control system can initiate one or more measures to remove the impurities from the combustion gas.

The impurity refers to a combustion gas having 100 mol% hydrogen and the impurity can interfere with the proper functioning of the combustion appliance. Impurities can be defined in accordance with ISO 14687:2019 or can be predetermined value based on the respective combustion appliance.

In another aspect of the invention, the use of the inventive flame acquisition system for converting a hydrocarbon gas boiler into a gas boilerforthe combustion of pure hydrogen or of a combustion gas comprising at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen is provided. By using the present flame acquisition system, the gas boiler conversion can be easy to realize and can be safe and effective for the operation of a hydrogen boiler.

In a further aspect of the invention, a method for retrofitting a combustion appliance, in particular a gas boiler is provided. The combustion appliance is designed for combusting a gas mixture including hydrocarbons and the method comprises: installing the inventive flame acquisition system in the combustion appliance; and updating the setting parameters of the combustion appliance for the combustion of pure hydrogen or of a combustion gas comprising at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen. For retrofitting the ionization electrode can be disconnected from the control system. Afterwards, the ionization electrode can be connected to the flame acquisition control unit. In particular, the same, disconnected ionization electrode can be connected to the flame acquisition control unit. Alternatively, a new ionization electrode can be connected to the flame acquisition control unit.

In one example, installing the flame acquisition system comprises connecting the flame sensor and the converter to the control system of the combustion appliance Also, updating the setting parameters can occur automatically by detecting a flame acquisition signal acquired by the flame sensor.

In the figures, the subject-matter of the invention is schematically shown, wherein identical or similarly acting elements are usually provided with the same reference signs.

Figure 1 shows a schematic representation of a flame acquisition system connected to the control system of a combustion appliance according to an example.

Figure 2 shows a schematic representation of a control system of a combustion appliance combusting carbon containing compounds.

Figures 3A-B show a schematic representation of a flame acquisition system connected to the control system according to two different examples.

Figure 4 shows a schematic representation of a flame acquisition system connected to the control system of a combustion appliance according to another example.

Figure 5 shows a flow chart of a method for retrofitting a combustion appliance according to an example.

With reference to Figure 1 , a flame acquisition system 1 is shown. The system 1 basically comprises a flame sensor 4 and a converter 5 connected to the flame sensor 4. The flame sensor 4 can be a UV sensor or a thermic sensor configured to acquire the presence of a flame generated at the burner of a combustion appliance 2 for starting the ignition process. The flame acquisition system 1 is connected to a control system 3 of the combustion appliance 2. The control system 3 is configured to control the settings of the combustion appliance 2 based on a determined current (ionization current) flowing in its circuit. The flame sensor 4 generates a flame signal upon detecting the flame and the converter 5 converts the flame signal generated by the flame sensor 4 into an electrical current (i.e. the ionization current) used by the control system to control the appliance 2.

For example, the combustion appliance 2 is a conventional hydrocarbon (i.e. natural gas or LPG (CxHy)) gas boiler. Therefore, the control system 3 is an ionization circuit for receiving an ionization current generated by an ionization electrode. By using the flame acquisition system 1 , i.e. by connecting the system 1 to the control system 3 of the appliance 2, it is possible to convert the conventional combustion appliance 2 into an appliance using pure hydrogen as fuel gas. In fact, the flame sensor 4 is suitable to acquire a flame generated by the combustion of a fuel gas devoid of carbon containing compounds, such as pure hydrogen or of a combustion gas comprising at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen.

Figure 2 illustrates in detail the functioning of a control system 3 used in a conventional hydrocarbon gas boiler. The control system 3 comprise at least an ionization electrode

8 for detecting the flame generated by the combustion of a gas with carbon containing compounds. In particular, the ionization electrode 8 is used to acquire an ionization signal (ionization current) that the control system 3 can use to control the appliance 2. This current is present only if there is a flame and if the gas is a carbon one e.g. natural gas or LPG (CxHy). Carbon containing compounds present in the gas reduces the resistance of the flame allowing the passage of an electrical current so that by measuring the electrical current it is known whether there is a flame and whether the combustion gas comprises carbon containing compounds. The control system 3 comprises an amplifier

9 for amplifying the ionization current and an appliance control unit 7 for managing the received ionization current and controlling the appliance 2 settings.

Figures 3A and 3B describe the application of the flame acquisition system 1 according to two examples. The converter 5 of the flame acquisition system 1 comprises a flame acquisition control unit 6 and a switch element 10, whereas in one example the flame acquisition control unit 6 is separated by the appliance control unit 7 of the control system 3 (figure 3A) and in the other example, the flame acquisition control unit 6 is part of the appliance control unit 7 of the control system 3 (figure 3B). It is noted that the flame acquisition control unit 6 is connected (directly or indirectly) to the switch element 10 and to the flame sensor 4. The switch element 10 is electrically connected to the ionization electrode 8 and is configured to open or to close the electrical connection with said electrode 8. When a flame is detected by the flame sensor 4, the flame acquisition control unit 6 detects a flame signal and the switch element 10 is triggered in a close position to allow the flowing of an electrical current in the control system 3. In other words, by triggering the switch element 10 in a close position, the flame signal is used as an electrical current passing through the ionization electrode 8. This electrical current (flame signal) is interpreted by the control system 3 as an ionization current and is used to control the combustion appliance 2 as if the ionization electrode 8 would have been detected an ionization signal generated by the ionization of a fuel gas with carbon containing compounds.

Figure 4 shows a schematic representation of a flame acquisition system connected to the control system of a combustion appliance according to another example. The embodiment shown in figure 4 differs from the embodiment shown in figure 3A in that the converter 5 is electrically connected to the flame sensor 4 and to the ionization electrode 8. Additionally, the converter 5 is electrically connected to the control system 3.

The converter 5 comprises the flame acquisition control unit 6 and a flame representation means 11 . The flame representation means 11 is used for simulating a flame acquisition signal as it is explained below more in detail. It comprises passive components like a diode 12 and a resistor 13 that are electrically connected in series. A diode 12 is used to ensures that the flow of current can only be in one direction and a resistor 13 is used to limit the current to a specific value.

A voltage is applied by the control system 3, in particular by the appliance control unit 7 or the amplifier 9 of the control system 3, on the flame representation means 11. This is not shown in fig. 4. The voltage is applied independent on the position of the switch element 10. In case that the switch element 10 is in the first position the control system 3, in particular the appliance control unit 7, measures a current from the flame representation means 11. In particular, the control system 3 measures a current amplitude and direction. Thus, the control system 3 determines that a flame is present if the current is measured.

The flame acquisition control unit 6 is electrically, in particular directly, connected to the switch element 10 and to the flame sensor 4 and the ionization electrode 8. Additionally, the flame acquisition control unit 6 is electrically connected to the appliance control unit 7 of the control system 3.

The flame acquisition control unit 6 controls the switching element 10 based on the alternative flame sensor 4. That means, the flame acquisition control unit 6 triggers the switching element 10 to a first position in which the flame representing means 11 is electrically connected to the control system 3 when the flame sensor 4 detects a flame. In other words, the flame sensor 4 is not electrically connected to the control system 3 when a flame is acquired by the flame representing means 11 . As the flame representing means 11 simulates a flame acquisition signal, the control system 3 interprets the received signal that a flame is present and controls the combustion appliance using said signal. In particular, in said case the control system 3 receives the current as simulated flame acquisition signal from the flame representing means 11 and thus determines that a flame is present.

The flame acquisition control unit 6 can monitor the ionization electrode 8 and the flame sensor 4. If an ionization current resulted from the ionization electrode 8 is detected in addition to the acquired flame acquisition signal from the flame signal, the flame acquisition control unit 6 communicates said information to the appliance control unit 7. The appliance control unit 7 can adapt the operation of the combustion appliance on the basis of the determined impurities or concentration of hydrocarbons in the combustion gas.

Figure 5 schematically illustrates the steps of a method 100 for retrofitting a combustion appliance 2. In particular, the method 100 can be used to convert a combustion appliance such as a natural gas boiler into a hydrogen boiler.

At step S101 , the method 100 comprises the step of installing a flame acquisition system. For example, the flame sensor 4 and the converter 5 are connected to the control system 3. At step S102, the method 100 comprises updating the setting parameters of the combustion appliance 2 for the combustion of, in particular pure, hydrogen.

It is noted that to control the functioning of a gas boiler, a control unit comprising a printed circuit board (PCB) is provided. Hydrogen combustion requires at least different parameter settings compared to natural gas combustion. Accordingly, the setting parameters of the combustion appliance must be updated when installing the present flame acquisition system 1 , i.e. when converting the combustion appliance from a natural gas boiler to a hydrogen boiler. This can be done in different ways. In one example, the update can be performed by automatically detecting, in particular pure, hydrogen in the gas mixture, for example using a hydrogen detector suitably located in the combustion appliance 2. Alternatively, the updating of parameters (or software) can be carried out by the installer operator or by replacing the control board (PCB).

Reference Signs

1 . Flame acquisition system

2. Gas boiler

3. Control system

4. Flame sensor

5. Converter

6. Flame acquisition control unit

7. Appliance control unit

8. Ionization electrode

9. Amplifier

10. Switch element

11. Flame representation means

12. Diode

13. Resistor

Claims

PATENT CLAIMS

1 . Flame acquisition system (1) for a combustion appliance (2) for combusting a combustion gas, in particular for a gas boiler, the system (1) comprising: at least one flame sensor (4) to acquire the presence of a flame and for generating a flame signal, the flame sensor (4) being connectable to a control system (3) of the combustion appliance (2) for controlling the combustion appliance (2); and a converter (5) connected or connectable to the flame sensor (4) to convert the flame signal generated by the flame sensor (4) into an electrical current used by the control system (3) for controlling the combustion appliance (2).

2. Flame acquisition system (1) according to claim 1 , characterized in that the converter (5) comprises a flame acquisition control unit (6) and a switch element (10) located between the control system (3) and the flame sensor (4), wherein the flame acquisition control unit (6) is connected to the flame sensor (4) and the switch element (10) and is configured to trigger the switch element (10) based on the acquisition of the flame by the flame sensor (4), thereby causing an electrical current to flow from the flame sensor (4) to the control system (3) or from a flame representation means (11) of the flame acquisition system (1) to the control system (3).

3. Flame acquisition system (1) according to any one of claims 1 to 2, characterized in that the flame sensor (4) is at least one of: an optical sensor, in particular a UV sensor and/or IR sensor; a temperature sensor, in particular a thermocouple; a dynamic pressure sensor; a sound or vibration sensor; and a catalytic sensor.

4. Flame acquisition system (1) according to claim 2 or 3, characterized in that the flame acquisition control unit (6) is part of an appliance control unit (7) to control the combustion appliance (2) or the flame acquisition control unit (6) is separated from said appliance control unit (7).

5. Flame acquisition system (1) according to any one of claims 1 to 4, characterized in that a. the flame sensor (4) is suitable for detecting a flame generated by the combustion of comprising at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen and/or in that b. the converter (5) is connected or connectable to an ionization electrode (8).

6. Flame acquisition system (1) according to any one of claims 2 to 5, characterized in that a. the flame acquisition control unit (6) is configured to set an operating mode of the combustion appliance (2) based on a flame acquisition signal acquired by the flame sensor (4) and/or in that b. the flame acquisition control unit (6) is configured, in particular selectively, to trigger the switch element (10) to a first position for connecting the flame representation means (11) with the control system (7) when a flame is acquired by the flame sensor (4) and/or to trigger the switch element (10) to a second position when no flame is acquired by the flame sensor (4).

7. Combustion appliance (2) for combusting a combustion gas, in particular a gas boiler, comprising the flame acquisition system (1) of any one of claims 1 to 6.

8. Combustion appliance (2) according to claim 7, characterized in that a. the appliance (2) is selectively configured to combust a combustion gas comprising carbon containing compounds and/or a combustion gas without carbon containing compounds or a combustion gas comprising at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen and/or in that b. the appliance (2) comprises a control system (3), in particular an appliance control unit (7), and the flame acquisition system (7) is connected to the control system (3), in particular to the appliance control unit (7). 18

9. Combustion appliance (2) according to any one of claims 7 to 8, characterized in that the combustion appliance (2) comprises a burner and a combustion chamber and the flame sensor (4) is located in the burner and/or the combustion chamber; and/or the combustion appliance (2) comprises a gas valve to control the inflow of the combustion gas, wherein the gas valve can be controlled electronically or pneumatically.

10. Combustion appliance (2) according to claim 9, characterized in that in case the gas valve is controlled electronically, a flame acquisition signal acquired by the flame sensor (4) is used to control an excess air factor.

11 . Combustion appliance (2) according to any one of claims 7 to 10, characterized in that a. the combustion gas comprises at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen and/or in that b. the combustion appliance comprises an ionization electrode (8) for detecting a flame generated by the combustion of a combustion gas comprising at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen, and the flame acquisition system (1) is connected to the ionization electrode (8) to pass the electrical current generated by the convertor (5) through the ionization electrode (8).

12. Use of a flame acquisition system (1) according to any one of claims 1 to 6 for a. converting a hydrocarbon gas boiler into a gas boiler for the combustion of pure hydrogen or of a combustion gas comprising at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen and/or for b. determining impurities or a concentration of hydrocarbons in the combustion gas. 19

13. Method (100) for retrofitting a combustion appliance (2), in particular a gas boiler, for combusting a combustion gas including hydrocarbons, the method comprising: installing (S101) a flame acquisition system (1) according to any one of claims 1 to 6 in the combustion appliance (2); and updating (S102) the setting parameters of the combustion appliance (2) for the combustion of pure hydrogen or of a combustion gas comprising at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen.

14. Method according to claim 13, characterized in that the ionization electrode is disconnected from the control system (3) and/or in that the, in particular disconnected, ionization electrode is connected to the flame acquisition control unit (6).

15. Method for operating a combustion appliance (2), in particular a gas boiler, for combusting a combustion gas comprising at least 21 mol% hydrogen or at least 30 mol% hydrogen or at least 90 mol% hydrogen, by using a flame acquisition system (1) according to any one of claims 1 to 6, the method comprising triggering the switch element (10) to a first position for connecting the flame representation means to the control system (3) when the flame sensor (4) detects a flame and/or triggering the switch element (10) to a second position in which the flame representation means (11) and the control system are not connected, when the flame sensor (4) does not detect a flame.

16. Method according to claim 15, characterized in that a. the control system (3) applies a voltage on the flame representation means (11), in particular independent on the position of the switch element, and/or in that b. the flame acquisition control unit (6) monitors the flame sensor (4) and the ionization electrode (8) and transmits a signal to the control system (3) when a flame acquisition signal is received from the flame sensor (4) and an ionization signal is received from the ionization electrode (8) and/or in that c. the flame acquisition control unit (6) monitors the ionization electrode (8) and determines on the base of an received ionisation signal from the ionization electrode (8) the presence and/or concentration of hydrocarbons and/or on that 20 d. the control system applies a voltage, in particular an alternating voltage, on the flame representation means (11).