EP4102135A1

EP4102135A1 - Control mechanism for a gas boiler

Info

Publication number: EP4102135A1
Application number: EP21179112.4A
Authority: EP
Inventors: Andrea Pisoni; Job Rutgers; Sebastiano Temperato
Original assignee: BDR Thermea Group BV
Current assignee: BDR Thermea Group BV
Priority date: 2021-06-11
Filing date: 2021-06-11
Publication date: 2022-12-14
Also published as: EP4352415A1; EP4352416A1; WO2022258477A1; WO2022258479A1

Abstract

The invention relates to a control mechanism (1) for a gas boiler (2) for combusting combustion gas, the mechanism (1) comprising a flame sensor (3) for detecting the presence of a flame; a ionization electrode (4) for detecting a ionization current; and a control unit (5) to control the operation of the boiler (2), said control unit (5) being connected to the flame sensor (3) and the ionization electrode (4) to acquire a flame detection signal and ionization detection signal, respectively, wherein the control unit (5) is configured to set an operating mode of the boiler (2) based on at least one of the acquired flame detection signal and the acquired ionization detection signal.

Description

The invention relates to a control mechanism for a gas boiler and a method for operating a gas boiler. Additionally, the invention relates to a heating system and a use of said control mechanism. The invention also relates to a computer program product executing the method.
Gas boilers combust combustion gas to heat water for domestic use and/or central heating system facilities in buildings. The boilers can be used to operate in different modes during their functioning. However, the process steps of each operating mode can vary based on the characteristics of the gas boiler. In particular, the process steps of the operating mode can be adjusted or different control procedures can be taken into account, if a different combustion gas is used for the combustion. For example, some factors can count differently on the boiler's efficiency, if the combustion gas comprises pure hydrogen or pure hydrocarbons.
It is known that the control of gas mixture velocity is much more important when the boiler uses hydrogen as combustion gas rather than other combustion gasses comprising hydrocarbons (for example methane). Accordingly, flashback can occur more easily in hydrogen boilers since the flame speed of hydrogen air mixture is around seven times higher than the flame speed for methane air mixture. Therefore, hydrogen boilers are used to operate in a particular mode, in order to reduce the risk of flashback. On the other hand, methane boilers are not required to operate in such a particular mode since the issue of flashback is less relevant.
Another aspect influencing the operating modes of a gas boiler based on the composition of the combustion gas is the flame detection. Indeed, boilers using hydrocarbons as combustion gas usually rely on ionization electrodes for detecting a flame signal in the ignition phase since these electrodes are configured to detect the presence of carbon in the gas mixture, that is carbon containing compounds. On the other hand, gas boilers using pure hydrogen as fuel gas cannot employ such electrodes due to the absence of carbon containing compounds in the gas mixture. Accordingly, hydrogen boilers necessitate an alternative flame detection step, using for example an ultraviolet sensor.
It is therefore desirable to provide a mechanism for determining the conditions for a gas boiler to operate in a particular mode rather than another one, based on the combustion gas composition. It is also desirable that such mechanism can be used equally for gas boilers using different types of combustion gases, for example mainly containing hydrogen, mainly containing hydrocarbons or containing a mixture of both.
US 7,244,946 B2 is directed to provide flame detector systems that overcome one or more of challenges such as degradation of UV sensors overtime, difficulty to distinguish between UV radiation given off from a flame and other sources of UV radiation, so that the sensitivity of flame detector systems needs to be such that false alarms are minimized and to provide additional benefits over prior flame detector systems. In order to achieve this goal, US 7,244,946 B2 discloses a flame detector system including an ultraviolet sensor to detect ultraviolet radiation, and a microcontroller coupled to the ultraviolet sensor. The microcontroller processes output from the ultraviolet sensor to identify a flame. The system also includes an HV supply circuit to constantly refresh a drive voltage of the sensor, wherein the microcontroller can sense when the sensor discharges and thereupon immediately refresh the sensor. The microcontroller can also monitor a run time for the sensor and adjust a drive voltage for the sensor accordingly.
WO 2020/112333 A1 discloses that known flame detector systems comprising a UV sensor may erroneously output an alarm due to UV radiation from ambient light and furthermore, that known manufacturing methods of flame detection systems incorporating the UV sensing elements are fairly expensive. WO 2020/112333 A1 proposes a flame detector that includes a spacer, a UV transparent window, and a UV sensing elements. The spacer has a spacer wall that extends along a first axis between a first spacer end and a second spacer end. The UV transparent window is disposed at the first spacer end. The spacer wall and the UV transparent window define a gas space. The UV sensing elements is disposed within the gas space.
US 9,928,727 B2 is directed to flame detector solutions avoiding false alarms and discloses a flame detector including a UV sensor sensitive to solar UV radiation and a secondary sensor sensitive to non-UV radiation. A controller is operatively connected to the UV sensor and the secondary sensor to signal an alarm in response to receiving input from the UV sensor indicative of a strong UV source and input from the secondary sensor indicative of a weak non-UV radiation source. Also the controller is configured to suppress an alarm in response to receiving a signal from the UV sensor indicative of a strong UV source and a signal from the secondary sensor indicative of a strong non-UV radiation source.
GB 2037066 B is directed to providing an improved flame ionisation detector for use with a gas chromatograph and discloses a flame ionization detector comprising a burner having two coaxial tubes, one for conveying to the flame a mixture of a first gas, e.g. H₂, and the sample to be detected and the other for conveying to said flame a second gas, e.g. O₂ which combusts with said first gas.
EP 1 750 058 A2 relates to a combustion control method with guided set point search and discloses a system suitable for controlling combustion in heat-producing devices such as, for example, gas-powered boilers and water heaters, the system being based on the measurement of the ionisation current taken in proximity to the flame for the regulation of the quantity A which indicates the air/combustible ratio in a combustion process.
EP 2 385 300 A1 relates to a premixed burner, in particular a premixed burner for gas boiler provided with a ionisation sensor and is directed to overcoming drawbacks such as that for known premixed burners at low power values the combustion cannot be monitored effectively, overcoming drawback of introducing potential thermal unbalances caused by the localised differential load, with consequent potential risks of breakage. In addition, EP 2 385 300 A1 is directed to provide a premixed burner, associated with a ionisation sensor, with a high power modulation, while obviating the problems of local thermal unbalance and discloses a premixed burner for a gas boiler comprising a diffuser suitable for diffusing premixed combustion gases in a combustion chamber, and an ionisation sensor suitable for monitoring the ionisation current, wherein at least one portion of the diffuser, at the ionisation sensor, has a radius of curvature r and the ratio between the distance d of the ionisation sensor from the diffuser in the portion with radius of curvature r and the radius of curvature r is comprised between 0.015 and 0.6, the radius of curvature r being not greater than 30 mm.
GB 922910 A is directed to the field of flame ionisation detectors used as a detector for a gas chromatography column in which hydrogen is employed as the carrier gas, the gas from the column can be directly burned in the detector; if another gas, such as nitrogen, is used as the carrier gas, the gas from the column is first mixed with hydrogen and then supplied to the detector for burning therein. The magnitude of the output signal of the detector is found to increase almost linearly with the concentration of the organic components in the flame, as long as this concentration does not exceed a value in the range 100 to 1000 p.p.m. With higher concentrations, however, the sensitivity of the detector increases considerably; with a concentration of about 1% the sensitivity may even be double. When the detector is used for general gas analysis purposes, according to GB 922910 A it is very desirable that it should have a sensitivity which is constant over a greater concentration range than in known solutions. GB 922910 A discloses a method of detecting the presence of organic material in gases supplied to the flame of a flame ionization detector which burns hydrogen or a mixture of hydrogen and other gases such as nitrogen, argon or helium in the presence of a separately supplied combustion supporting gas, wherein the combustion supporting gas consists of a mixture containing carbon dioxide in addition to oxygen or a compound giving off oxygen.
WO 2010/094673 A1 is directed to providing an alternative premix burner with a control device and to provide a burner control system, which permits to verify the occurrence of combustion, show proof of clean combustion and permits an accurate signal evaluation. It is a further object WO 2010/094673 A1 to provide a burner control system which permits to control the air gas ratio of a burner. WO 2010/094673 A1 teaches a premix gas burner having a burner surface which exhibits a plurality of flow passages and at least two ionisation electrodes connected to a measuring device and preferably also to a control device. The ionization electrodes are arranged at different distances from the burner surface and the ionization electrodes are arranged electronically in parallel and electric currents are measured over each ionisation electrode and the burner surface, the burner thus serving as earth in the electrical circuit. The measured currents provide a more accurate verification of the occurrence of combustion and show proof of the combustion quality.
WO 2019/122976 A1 is directed to providing a device and method for control of the flame of a gas burner which is able to generate a flame signal with a reduced delay with respect to the variation of the flame and which is able to generate a flame signal with a greater resolution. For this purpose, WO 2019/122976 A1 proposes a control device for control and detection of the flame of a burner, comprising an ionization electrode arranged, in use, at a region in which a flame of the burner is present, and an electric circuit for generating a triangular voltage signal having a triangle wave form and connected to the ionisation electrode in such a way that on varying the ionisation current the average value of the triangular voltage signal also varies. The device also comprises an output circuit connected to the circuit for generating the triangular voltage signal and comprising an electronic group for generating a duty-cycle as a function of the average value of the triangular voltage signal.
EP3663648A1 is directed to providing a device and a method which, by means of non-invasive measurement, enable precise regulation of the mixing ratio of combustion air to fuel gas (lambda value), and also for different compositions of the fuel gas, in particular when hydrogen is added. EP3663648A1 discloses a device for influencing or regulating the mixing ratio (lambda) of combustion air and a gaseous fuel, which are supplied through a gas supply line and a combustion air supply line to a combustion chamber in a housing, with a pump arranged in front of or behind a junction with the gaseous fuel of the combustion air supply line and at least one first optical filter and at least one first optical sensor are provided on or in the housing, wherein the first optical sensor is arranged such that light from the combustion chamber can reach the first sensor via the first optical filter. EP3663648A1 further discloses a method for influencing or regulating the mixing ratio (lambda) of combustion air and a gaseous fuel which are burned together in a combustion chamber, the light produced during the combustion being selectively filtered and by at least a first optical sensor in one electrical sensor signal is converted, the strength of which is evaluated in an electronic module, the supply of combustion air and / or gaseous fuel to the combustion chamber being changed and the change in the sensor signal caused thereby being evaluated and the supply of combustion air and / or gaseous fuel is set or regulated depending on the result of the evaluation.
Prior art documents disclose devices, systems and methods that are not configured to determine the best operating mode of the boiler based on the composition of the combustion gas.
The object of the invention is therefore to provide a control mechanism for a gas boiler that is efficient in the determination of the best operating mode.
The object is solved by a control mechanism for a gas boiler for combusting combustion gas, the mechanism comprising:

a flame sensor for detecting the presence of a flame;
an ionization electrode for detecting an ionization current; and
a control unit to control the operation of the boiler, said control unit being connected to the flame sensor and the ionization electrode to acquire a flame detection signal and ionization detection signal, respectively, wherein
the control unit is configured to set an operating mode of the boiler based on at least one of the acquired flame detection signal or the acquired ionization detection signal.

A further object of the invention is to provide a method for operating a gas boiler by means of which different types of combustion gas combusted by the boiler can be used.
Method for operating a gas boiler that combusts combustion gas, the method comprising:

detecting whether the flame is present and acquiring a flame detection signal;
detecting whether an ionization current is present and acquiring an ionization detection signal; and
setting an operating mode of the boiler based on at least one of the acquired flame detection signal and the acquired ionization detection signal.

An advantage of the present mechanism is that it can be used equally with gas boilers employing different types of fuel gases, such as pure hydrogen fuel, pure carbon, in particular hydrocarbon, fuel (i.e. natural gas or LPG) or a combination of hydrogen fuel and carbon fuel. Based on the fact that the control unit detects a signal exclusively receiving from the flame sensor and the ionization electrode the information whether a flame is present and/or whether an ionization current is measured, it is possible to identify if the fuel gas is pure hydrogen or if carbons are present in the gas mixture. Consequently, the control unit can set a corresponding operating mode for the gas boiler dependent on the type of combustion gas.
A combustion gas is a gas that is combusted by a burner of the boiler. The combustion gas comprises air and fuel gas. The combustion gas can be premixed before it is supplied to the burner. The fuel gas can be a natural gas, methane, ethylene, propane, butane, coal gas, biogas etc., mixtures of the same, and mixtures of the same additionally comprising hydrogen or hydrogen, in particular pure hydrogen. Pure hydrogen is present if the fuel gas has a at least a value comprised between 95 mol% and 98 mol% of hydrogen.
The control unit is an electric control unit. Additionally, the control unit is adapted to receive electric sensor signals and to output electric control signals. The control unit can comprise at least one processor and/or a printed circuit board.
The ionization electrode is used to detect a ionization current that the burner control can measure. This current is present only if there is a flame and if the gas is a carbon one e.g. natural gas or LPG (C_xH_y). It is known that the 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 the combustion gas comprises carbon containing compounds.
The flame detection signal comprises the information whether a flame is present. Likewise the ionization detection signal comprises the information whether a ionization current is present.
According to an embodiment, the flame sensor is an ultraviolet (UV) sensor able to detect a UV radiation and accordingly the presence of a flame. Alternatively, the flame detector can be a temperature sensor, such as a thermocouple. A flame is present if the temperature sensor measures a temperature above a predetermined temperature. Compared to temperature sensors, UV sensors respond more quickly to changes in flame status since they are not subjected to black body radiation and lack of inertial memory of a thermocouple.
The control mechanism can set the operating mode of the boiler, in particular selectively, based on the acquired flame detection signal or the acquired flame detection signal and the acquired ionization detection signal. It depends on the type of combustion gas whether a flame detection signal and/or a ionization detection signal are detected. However, the capability to use both signals for the control enables that different types of combustion gas can be supplied to the boiler.
In a case that the flame sensor detects that a flame is present and the ionization electrode does not detect a ionization current, the control unit sets an operating mode by the control unit. However, if the flame sensor detects that a flame is present and the ionization electrode detects a ionization current, the control unit sets the operating mode dependent on the acquired ionization detection signal. As is explained later, by using the ionization detection signal, it is possible to further differentiate between different operating modes. In particular, the ionization detection signal is first checked. Based on the result, the type of gas is determined, and the corresponding operating parameters are set by a comparison with a map stored in the control unit.
If the fuel gas in the combustion gas comprises hydrogen with a concentration that is higher than a predetermined value, for example 95 mol%, a first operating mode is set by the control unit. In this case, only the first flame detection signal is acquired and/or the operating mode corresponds to a mode for operating a hydrogen boiler. It is noted that a hydrogen boiler is a boiler to which fuel gas is supplied that comprises at least 95 mol % hydrogen. In particular, pure hydrogen can be supplied to the hydrogen boiler. It is noted that the first device (i.e. flame sensor or ionization electrode) reacting is the device first detecting the flame, in particular for the detection of the flame after ignition. If the ionization electrode is not able to detect the flame, it means that there is only hydrogen and the system is set for pure hydrogen.
Under these circumstances, it can also be worth to carry out a plausibility check to exclude that the ionization electrode is not detecting any signal due to a malfunctioning issue, for example by a comparison with a map stored in the control unit.
If the fuel gas in the combustion gas comprises carbon containing compounds and hydrogen, wherein the concentration of hydrogen is lower than a predetermined value, in particular 95 mol %, the control unit sets a second operating mode. In this case both the flame detection signal and the ionization detection signal are acquired. The second operating mode corresponds to a mode for operating a boiler using a mixed fuel gas, for example hydrogen and natural gas.
If the fuel gas in the combustion gas comprises only carbon containing compounds, the control unit sets a third operation mode. This state is identified by considering the ionization detection signal. In this case both the flame sensor detects the presence of a flame and the ionization electrode detects a ionization current, a third operating mode is set by the control unit. The third operating mode corresponds to a mode for operating a carbon boiler using a pure hydrocarbon fuel gas.
To determine if the fuel gas comprises only carbon containing compounds or a combination of fuels gases, such as for example carbon containing compounds and hydrogen, the ionization electrode can be used. The flame sensor is used to determine whether the fuel gas comprises more than 95 mol % hydrogen.
The ionization detection signal varies based on the composition of fuel gas in the combustion gas, for example as a function of the presence or absence of carbons.
Also, the ionization detection signal varies based on an air to fuel gas ratio in the combustion gas, for example as a function of an air excess factor λ. This factor, defined as the ratio of the actual air to fuel ratio of the mixture relative to the stoichiometric air to fuel ratio, can influence the efficiency of the gas boiler. An air excess factor λ smaller than 1 means that there is not enough air for all of the fuel gas to combust, which means fuel gas is wasted and exits via a flue channel not combusted or partially combusted. This decreases the efficiency of the boiler. Also, the flame temperature may become too high. On the other hand, a high air excess factor λ means that there is too much air, which air is heated during the combustion, resulting in hot air and uncondensed water vapor due a lower dew point, leaving via the flue channel. This also decreases the efficiency of the boiler. Accordingly, the value of the air to fuel gas ratio and consequently the value of λ needs to be accurately selected to avoid efficiency issues.
In addition, the ionization detection signal varies based on a concentration of carbon containing compounds in the fuel gas in the combustion gas. In this way, it is possible to determine whether for example the fuel gas is pure carbon or whether hydrogen fuel is also present in the gas mixture.
Therefore, when determining which operating mode is the most appropriate for the gas boiler, the mechanism is not limited to the detection of the flame detection signal and/or the ionization detection signal but also to the analysis of the variation of the ionization detection signal in order to obtain information regarding for example the composition of fuel gas, the air excess factor λ and/or the concentration of carbon containing compounds in the fuel gas, as mentioned above.
The control mechanism can be used in an ignition sequence of the gas boiler. In an ignition sequence, after the spark is created and a fuel gas valve is open, a gas sensor measures the ignition ramp. In case the ignition ramp is correct, the control mechanism determines whether a flame signal is present. As mentioned above, this is carried out by combining the flame sensor and the ionization electrode. If the flame signal is correctly detected, before completing the ignition phase, an appropriate operating mode for the gas boiler is set by the control unit based on which signal is detected as flame signal, i.e. based on the composition of fuel gas.
According to an embodiment, the control unit is configured to adjust combustion settings of the boiler based on the ionization detection signal. In fact, based on the information derived from the ionization detection signal, i.e. the fuel gas composition, the value of the air excess factor and/or the concentration of carbon containing compounds, for example using internal setting curves, it is possible to adapt particular settings of the boiler, such as for example the fan speed, the fuel gas flow, etc.. In cases where the control unit sets the first operating mode, i.e. only flame detection signal is detected, the control unit adjusts the combustion settings of the boiler based on the flame detection signal.
In order to control the correct functioning of the gas boiler, the control unit can be configured to cause the interruption of the operation of the boiler when water or water condensate reaches the ionization electrode.
In an advantageous embodiment, the ionization electrode can also work as ignition electrode for creating a spark to ignite the fuel gas in the gas mixture. In this way, the same component can be used for more purposes, thereby leading to cost saving. In addition, a reduction in oxidation is obtained due to the fact that the spark "cleans" the oxidation.
According to an aspect of the present invention, a heating system with a gas boiler and an inventive control mechanism is provided. The control mechanism described above can be integrated in the boiler. The heating system can also comprise additional heating equipment, such as for example gas conduits, water conduits, and/or at least a radiator connected to the water conduits.
According to an embodiment, the flame sensor and the ionization electrode can be located in the boiler, in particular in the burner of the boiler. In this way, both the flame sensor and the ionization electrode can immediately detect the presence of a flame for combustion and at the same time inform the control unit regarding the fuel gas composition and/or concentration of carbon containing compounds. In particular, the flame sensor and the ionization electrode can be located at the location of the combustion flame of the burner. On the other hand, the flame sensor and the ionization electrode can be mounted outside the combustion chamber or burner and immediately at the exit of the burner.
In addition, the ionization electrode can detect a failure of a condensing trap. In fact, if a condensing trap is obstructed and does not discharge, water or water condense can rise on a pipe until reaching the ionization electrode. Accordingly, the water or water condensate can put in short circuit the system and block the boiler. Therefore, the ionization electrode can cause a short circuit in the boiler when a condensing trap is blocked.
An advantageous embodiment is a computer program product comprising instructions which, when the program is executed by a computer or by the control unit, cause the computer or the control unit to perform the inventive method. Furthermore, a data carrier is provide on which the computer program is stored and/or data carrier signal is provided which transmits the computer program.
Furthermore, an advantageous embodiment is the use of the inventive mechanism for setting a corresponding operating mode of a gas boiler, based on the acquisition of only a flame detection signal or based on the acquisition of both the flame detection signal and a ionization detection signal.
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 the control mechanism according to one embodiment.
Figure 2: shows a schematic representation of the heating system according to one embodiment.
Figure 3: shows a flow chart of an inventive method according to an embodiment.

Figure 1 illustrates a control mechanism 1 for a gas boiler 2 shown in fig. 2. The mechanism 1 comprises a UV flame sensor 3 and a ionization electrode 4, both electrically or electronically connected to a control unit 5. The connection between the control unit 5 and the UV flame sensor 3 and the ionization electrode 4 is shown by dotted lines.
The UV sensor 3 is a solid state electronic device for sensing the UV radiation emitted during combustion of the fuel gas. The UV sensor 3 is mounted outside the combustion chamber or burner 8 shown in fig. 2 and immediately at the exit of the burner 8, where it is possible to detect the presence of the flame. When a flame is detected, a flame detection signal is generated and sent to the control unit 5.
The ionization electrode 4 can comprise for example graphite and detect a ionization current when high temperature is generated by the presence of a flame. Alternatively, the ionization electrode 4 can comprise a particular fire-proof material such as kanthal (iron-chromium-aluminium, FeCrAI) alloy that is resistant to high temperatures and electrochemical corrosion. The carbon containing compounds present in the combusted gas reduces the resistance of the flame allowing the passage of the electrical current. The ionization electrode 4 is mounted downstream of the burner 8 so that it is exposed to the flame. A corresponding ionization detection signal is generated and sent to the control unit 5.
The control unit 5 receives the flame detection signal and the ionization detection signal generated by the flame sensor 3 and the ionization electrode 4, respectively. Based on the fact that the control unit 5 receives information whether a flame and/or a ionization current are detected, a particular operating mode of the boiler is set, for example by selecting among a first, a second, or a third operating mode.
Figure 2 illustrates a heating system 6 comprising a gas boiler 2 used for the combustion of carbons and/or hydrogen fuel. The fuel gas is mixed with air and is provided to the burner 8 through a gas mixture channel 9. The heating system 6 comprises a control mechanism 1 including a control unit 5, a UV sensor 3 and a ionization electrode 4. Both the UV sensor 3 and the ionization electrode 4 are located at the in the burner 8 to detect the presence of a flame. Also, the ionization electrode 4 serves as an ignition electrode to create a spark.
The UV sensor 3 and the ionization electrode 4 are connected to the control unit 5. Upon receiving the information from the acquired flame detection signal generated by the UV sensor 3 and the ionization detection signal generated by the ionization electrode 4 whether a flame and/or a ionization current is detected, the control unit 5 can set one of the operating modes that is the most appropriate.
It is noted that the ionization electrode 4 can also be used to detect a malfunction of a condensate trap 7. In fact, if the condensate trap 7 is obstructed or does not work correctly, water or the condensate rises on the pipe 10 (arrows) until it touches the ionization electrode 4. In this way, water/condensate puts in short circuit the system and blocks the boiler 2.
Figure 3 shows a flow chart of the method 100 for a gas boiler 2 and in particular for operating a gas boiler 2 using the control mechanism 1 as described above.
At step S101, the presence of a flame for the combustion of a fuel gas in a gas mixture is detected using the flame sensor 3. Accordingly, a corresponding flame detection signal is acquired. At step S102, a ionization current is measured using the ionization electrode 4. Accordingly, a corresponding ionization detection signal is acquired.
At step S103, a corresponding operating mode of the boiler 2 is set by the control unit 5 based on the acquisition of the two acquired signal. In particular, the control unit 5 sets the operating mode based on the information contained in the signals whether a flame is present and/or whether a ionization current is detected.
Within the step S103, three different setting steps can be considered. In particular, if only a flame is present and not ionization current is detected, the fuel gas in the combustion gas comprises hydrogen with a concentration that is higher than 95%. In said case the control unit 5 sets a first operating mode at step S104.
Optionally, before setting the operating mode of the boiler (2), in case only the flame detection signal is acquired, the method 100 can comprise a plausibility check step (S107) for controlling whether the ionization electrode 4 is correctly working. In fact, the absence of ionization current detection can result from a malfunctioning of the electrode 4. For example, the intensity of the ionization current can be checked by comparing this value with an intensity value of the ionization current of a previous heating cycle (stored in the control unit 5). If no relevant intensity difference is present (for example the intensity value is above a threshold value or within a predefined range), it is concluded that the ionization electrode 4 works correctly and the control unit 5 can set the first operating mode. If, on the other hand, a relevant intensity difference is present (for example the intensity value is below a threshold value or outside a predefined range), it is concluded that the ionization electrode 4 could be broken. In the latter case, the method may be arrested for maintenance and a corresponding alarm message can be generated (S108). Additionally, the intensity of the ionization current can be detected during a predefined range of time in order to check a possible intensity variation over time in order to perform a predictive maintenance step. If it is determined that the current signal is getting weaker, a corresponding alarm message can be generated for requesting maintenance.
If both the flame is present and a ionization current is detected, the fuel gas in the combustion gas comprises carbons and hydrogen, wherein the concentration of hydrogen is lower than 95%. In said case the control unit 5 sets a second operating mode at step S105.
If the fuel gas in the combustion gas comprises only carbons, a third operating mode is set at step S106.

Reference Signs

1: detection mechanism
2: gas boiler
3: flame sensor
4: ionization electrode
5: control unit
6: heating system
7: condensing trap
8: burner
9: gas mixture channel
10: pipe
100: detection method

Claims

Control mechanism (1) for a gas boiler (2) for combusting combustion gas, the mechanism (1) comprising:
a flame sensor (3) for detecting the presence of a flame;

an ionization electrode (4) for detecting an ionization current; and

a control unit (5) to control the operation of the boiler (2), said control unit (5) being connected to the flame sensor (3) and the ionization electrode (4) to acquire a flame detection signal and ionization detection signal, respectively, wherein

the control unit (5) is configured to set an operating mode of the boiler (2) based on at least one of the acquired flame detection signal or the acquired ionization detection signal.
Control mechanism (1) according to claim 1, characterized in that the control unit (5) sets the operating mode of the boiler (2), in particular selectively, based on the acquired flame detection signal or the acquired flame detection signal and the acquired ionization detection signal.
Control mechanism (1) according to claim 1 or 2, characterized in that
a. if the flame (3) sensor detects that a flame is present and the ionization electrode (4) does not detect a ionization current, an operating mode is set by the control unit (5); and/or

b. if the flame sensor (3) detects a flame and the ionization electrode (4) detects an ionization current, the control unit (5) sets the operating mode dependent on the acquired ionization detection signal.
Control mechanism (1) according to one of the claims 1 to 3, characterized in that
a. the ionization detection signal varies based on the composition of fuel gas in the combustion gas combusted by the boiler (2) and/or

b. the ionization detection signal varies based on an air to fuel gas ratio in the combustion gas combusted by the boiler (2) and/or

c. the ionization detection signal varies based on a concentration of carbon containing compounds in the combustion gas combusted by the boiler (2).
Control mechanism (1) according to claim 3 or 4, characterized in that
a. the control unit (5) sets a first operating mode if the combustion gas comprises hydrogen with a concentration that is higher than a predetermined value, in particular 95 mol%, and/or

b. the control unit (5) sets a second operating mode if the combustion gas comprises carbons and hydrogen, wherein the concentration of hydrogen is lower than a predetermined value, in particular 95 mol%; and/or in that

c. the control unit (5) sets a third operating mode if the combustion gas comprises only carbon containing compounds.
Control mechanism (1) according to one of the claims 1 to 5, characterized in that
a. the control unit (5) is configured to adjust combustion settings of the boiler (2) based on the ionization detection signal or flame detection signal; and/or

b. the control unit (5) is configured to cause the interruption of the operating of the boiler (2) when water or water condensate reaches the ionization electrode (4).
Control mechanism (1) according to one of the claims 1 to 6, characterized in that
a. the ionization electrode (4) in addition works as ignition electrode for creating a spark to ignite the fuel gas in the gas mixture; and/or in that

b. the flame detection signal is obtainable from a UV sensor and/or a ionization electrode (4).
Heating system (6) with a gas boiler (2) and a control mechanism (1) according to one of the claims 1 to 7.
Heating system (6) according to claim 8, characterized in that
a. the flame sensor (3) and the ionization electrode (4) are located in the boiler (2); and/or in that

b. the ionization electrode (4) detects a failure of a condensing trap (7); and/or in that

c. the ionization electrode (4) causes a short circuit in the boiler (2) when a condensing trap (7) is blocked.
Method (100) for operating a gas boiler (2) that combusts combustion gas, the method (100) comprising:
detecting (S101) whether the flame is present and acquiring a flame detection signal;

detecting (S102) whether an ionization current is present and acquiring an ionization detection signal; and

setting (S103) an operating mode of the boiler (2) based on at least one of the acquired flame detection signal and the acquired ionization detection signal.
Method (100) according to claim 10, characterized in that
a. the control unit (5) sets the operating mode of the boiler (2), in particular selectively, based on the acquired flame detection signal or based on the acquired the flame detection signal and the acquired ionization detection signal and/or in that

b. the control unit (5) sets an operating mode if only a flame is present; and/or

c. the control unit (5) sets the operating mode dependent on the acquired ionization detection signal if both the flame and the ionization current are detected.
Method (100) according to claim 10 or 11, characterized in that the method comprises:
a. setting a first operating mode (S104) if the combustion gas comprises hydrogen with a concentration that is higher than a predetermined value, in particular 95 mol%; and/or

b. setting a second operating mode (S105) if the combustion gas comprises carbon containing compounds and hydrogen fuel, wherein the concentration of hydrogen fuel is lower than 95 mol%, and/or

c. setting a third operating mode (S106) if the combustion gas comprises only carbon containing compounds.
Method (100) according to one of the claims 10 to 13, characterized in that the method (100) further comprises
a. adjusting combustion settings of the boiler (2) based on the ionization detection signal and/or

b. interrupting of the operation of the boiler (2) in case water or water condensate reaches the ionization electrode (4) and/or

c. controlling the fuel gas composition in the combustion gas based on the ionization detection signal and/or

d. controlling the air to fuel gas ratio in the combustion gas based on the ionization detection signal and/or

e. controlling the concentration of carbon containing compounds in combustion gas based on the ionization detection signal; and/or

f. before setting the operating mode (S103) of the boiler (2), controlling (S107) whether the ionization electrode (4) is correctly working, in case only the flame detection signal is acquired by comparing the intensity of the ionization current with an intensity value of the ionization current of a previous heating cycle stored in the control unit (5), wherein in particular the intensity of the ionization current is compared over time.
Computer program product comprising instructions which, when the program is executed by a computer or control unit (5), cause the computer or control unit (5) to perform the method according to one of the claims 10 to 15.
Use of a control mechanism (1) according to any one of claims 1 to 7 for setting an operating mode of a gas boiler (2).