Not Applicable
The present invention relates to the technical field of combustible gas burners. In particular, the present invention relates to the technical field of methods and apparatuses for monitoring and controlling combustion in combustible gas burners used, for example, in apparatuses, such as boilers, heaters, fireplaces and the like.
In the technical field of combustible gas burners, it is known that in order to maintain efficient combustion, it is necessary that, for all power supplied by the burner, the ratio between the amount of air and the amount of combustible gas introduced into the burner is kept at around a predetermined optimum value.
Efficient combustion allows obtaining and maintaining important benefits in time, such as reducing the dispersion of energy in flue gas and reducing the production of polluting gases, this latter parameter being required by regulations on emissions, which are in force in a growing number of countries.
In order to achieve the object of achieving and maintaining an optimum air/gas ratio, different methods and apparatuses have been developed in the technical field of combustible gas burners. Methods are known for monitoring and controlling combustion, and in particular, the ionization of gas in the combustion zone of the flame based on flame analyses, like the so-called SCOT method, an example of which is described in European patent EP770824.
The available state-of-the-art systems provide the use of an electrode arranged in the zone of the flame or close to the flame, connected to an electronic circuit, which applies, to the electrode, a fixed or varying electrical voltage and measures the current crossing said electrode when it is supplied by the aforesaid electrical voltage. Therefore, the estimate of one or more parameters correlated to the combustion is carried out by means of processing and analyzing the measured current signal measured. Various types of processing techniques are used, all of which are aimed at detecting an instability of the flame of the burner or sub-optimal combustion, so as to provide combustion process corrections adapted to bring it back to the required conditions (see, for example, the systems described in European patents EP1002997 and EP2901080).
The techniques in use have limitations and drawbacks related to different factors, including wear of the electrode, which is adapted to operate as a flame or ionization sensor, which can have repercussions on the precision and also reliability of the data analyzed by the current algorithms for processing the current signal detected.
Other drawbacks are linked to the fact that the current systems always work with a single closed control loop, and command of the gas valve and fan strictly depends on the feedback of the signal received by the ionization or flame sensor. This results in two problems:
The aforesaid limitations and drawbacks are more serious in so-called pneumatic systems, wherein the gas flow rate is directly determined by the air flow rate recalled by the system, but they can also still be found in the most recent control systems where the gas flow rate is directly regulated by an actuator regulating the degree of opening of an adjustment valve. In patent EP3751200, for example, a system is described for controlling a gas burner, wherein it is provided that a certain power value of the burner corresponds to a certain degree of opening of a valve for adjusting the flow rate of the combustible gas; the described adjustment occurs with the loop open at low powers and with the loop closed only for higher burner powers. Lastly, the following difficulties must be highlighted among the criticalities of the current systems, on the air side:
Furthermore, given that the power of the gas burner is determined by the amount of air introduced, the aforesaid difficulties make the estimate of actual power of the burner imprecise in a given step.
Therefore, it is an object of the present invention to introduce an apparatus and method for monitoring and controlling the combustion of a burner of combustible gas apparatus-through a precise adjustment of the gas mixture and air carried to the burner-which allow overcoming the limitations and drawbacks related to the prior art.
The present invention relates to an apparatus, and a related method for monitoring and controlling the combustion of a burner of combustible gas apparatuses by means of adjusting the gas mixture carried to the burner. Said burners are used in numerous applications, including, for example, common domestic boilers for producing domestic hot water and/or hot water for feeding hydraulic circuits for the heating of environments.
The apparatus and method according to the present invention are adapted to adjust, in a combustible gas burner, a mixture of gas formed by a first gas and a second combustible gas, wherein the gas mixture is provided through the appropriate mixing of an amount of said first gas by means of a first adjustment element and an amount of said combustible gas by means of a second adjustment element. Said first or second adjustment elements are managed, during operation, by a controller, which processes the data coming from at least two sensors.
In some embodiments of the invention, the first gas can be a gas for carrying the oxygen and the second gas can be a combustible gas to be mixed with the gas for carrying the oxygen. For example, the first gas can be air or a mixture of air and flue gas and the second gas can be a natural gas, such as methane or LPG.
Said combustible gas burners are characterized by the specific heat output range (e.g. from 3 kW to 30 kW) and in that said heat output is independent of the type of said second gas used.
Given that different combustible gases have different Wobbe indices
this means that, with the same power, the volumetric flow rate of gas will be different depending on the type of combustible gas used.
Furthermore, the Stoichiometric combustion of said second gas requires a supply of said first gas in an amount, which is, in the first approximation, independent of the type of said second gas used. Thus: with the same power, depending on which type of said second gas is used, the flow rate of the latter must be changed, but not the flow rate of said first gas (e.g., air).
Said burner must be able to operate with different types of said second gas and therefore, the control apparatus must be capable of manually (during the installation stage) or automatically adapting as said second gas changes.
In a preferred embodiment of the invention, said first adjustment element comprises a fan with a varying number of revs, which can be set by means of a first command and said second adjustment element comprises a valve, which is adjustable by means of a second command. For example, said valve can be provided with an actuator comprising a stepper motor, as described in international patent application WO2019116407A1 by the applicant.
Furthermore, in a preferred embodiment, said at least two sensors preferably comprise a first flame sensor arranged close to the flame of the burner and adapted to measure the electrical features of the flame of the burner including, for example, the resistance, Rel, or electrical conductivity, Gel, and a second sensor positioned in the fan and adapted to measure the number of revs of the fan, e.g. by means of a Hall sensor adapted to read the supply current of the fan or by means of another device or method adapted to read the number of revs of said fan.
In another preferred embodiment, said plurality of sensors preferably also comprises a third absolute pressure sensor, preferably placed at the entrance or exit of the fan. In a further preferred embodiment, said absolute pressure sensor is flanked by a sensor adapted to measure the temperature of the air, which is also preferably arranged at the entrance or exit of the fan. Advantageously, the temperature and pressure sensors can also be integrated into only one sensor.
Finally, the controller comprises a microprocessor, or an equivalent electronic processing element, and at least one associated memory unit. Said controller is adapted to carry out cyclic readings and process the signals coming from the aforesaid sensors and produce, based on said processing and, optionally, based on a comparison with values of reference stored in tables placed in the memory unit, appropriate drive signals for said fan and said adjustable valve.
For a correct combustion, the apparatus and method according to the present invention must supply the burner with an excess amount of air with respect to the stoichiometric amount.
The ratio between the amount of air provided for the combustion of a certain amount of combustible gas and the amount of air needed for the combustion of the same amount of gas in stoichiometric conditions is traditionally called “λ” (air number). The value of λ will be equal to 1 where the amount of air provided is equal to the amount of air for a stoichiometric combustion, while the combustion is usually considered optimal and safe where the λ is kept, in normal burner operating conditions, between 1.2 and 1.6.
The amount of air supplied to the burner varies proportionately as the revs “n” of the fan vary and it is influenced by the load losses of the fume discharge pipe, which may differ for each installation.
The amount of gas is determined by the degree of opening of the valve operated by an actuator, e.g., by a stepper motor, so that a certain opening section of the valve, and therefore a certain gas flow rate, will correspond to a certain number of steps “s” of the actuator.
At a certain Power “W”, while the number of revs “n” of the fan is substantially constant, the degree of opening of the valve depends on the type of combustible gas used. Therefore, different (at least two in number) different degrees of opening of the valve must be provided and thus, different numbers “s” of steps of the actuator of the valve, generally comprising a stepper motor.
During the development step of the apparatus according to the present invention, different “standard” tables are stored in the aforesaid controller, each of which, for each type of gas and for each power between the minimum power Wmin and the maximum power Wmax of the burner, indicates the “n” and “s” values, which are adapted to ensure the desired value of λ in installation conditions, which is, in fact, “standard”. At the site of installation, the person installing the burner can manually determine the type of gas and thus the table to be used among those stored or an automatic gas recognition method can be used based on the ionization sensor selected from the methods already known in the state-of-the-art. The controller needs these tables to generate the correct drives for the fan and actuator of the valve, which follow on from a certain request for power from the burner. Furthermore, said tables can be “dynamically” updated by the aforesaid controller with new values calculated according to the method of the invention, if these new values calculated are different to those stored in the aforesaid “standard” tables due to the fact that the installation conditions and/or contingent operating conditions, also after installation, are different to the “standard” ones considered during the factory testing of the boiler or burner.
According to the method of the invention, the drive signals and the measurements of the sensors, which determined them, may therefore be stored in the memory unit associated with the microprocessor, so as to update and cyclically complete said tables containing the optimum settings of the fan and of the valve of the apparatus, as a function of the changed operating boundary conditions. Thereby, the present invention allows obtaining an apparatus for monitoring and controlling the combustion of a burner, and a method related to said apparatus, which is capable of self-learning and self-adjustment so as to reach the optimum working conditions of the burner in terms of efficiency, stability and safety for the user.
On varying the thermal power requested of the burner, or if, with the same thermal power requested of the burner, a change is detected in the operating conditions, based on the reading of the signals coming from the signals of the apparatus, the controller varies the drive signals of the fan and/or the valve so as to restore the optimum combustion conditions corresponding to a desired excess air value, λ.
Advantageously, the controller, according to the invention, can be provided with a memory unit or with a plurality of memory units adapted to contain the drive signals for said fan and said adjustable valve and the corresponding measurements of the sensors, which determined them in known operating conditions. Thereby, a memory unit—and different corresponding setting value tables may be available, for use, for example, in different circumstances, such as the final testing or initial starting stage, or again a calibration or emergency operation stage to be set after a malfunctioning.
The operation of the controller according to the present description provides different control routines, based on the type of operation and conditions of use of the burner, succeeding in distinguishing between start-up, first installation, calibration and normal operation, allowing adapting the operation of the burner to changed conditions so as to optimize the working, and signal any potential alarm states. In a preferred embodiment, the control method applied by the controller according to the present description further provides using different feedbacked control loops, each based on the detections made by the aforesaid sensors and characterized by different speeds so as to appropriately react both to transients and the needs for rapid adjustment as in the case of a change in thermal power requested of the burner, and to slow deviations in the conditions and operating parameters as in the case of changes in the composition of the combustible gas mixture.
Further features and advantages of the invention will become apparent from the reading of the following detailed description, given by way of non-limiting example, with the aid of the figures shown in the accompanying tables, in which:
The following description of exemplary embodiments relates to the accompanying drawings. The same reference numbers in the various drawings identify the same elements or similar elements. The following detailed description does not limit the invention. The scope of the invention is defined by the appended claims.
[Adjustment of the Combustion with at Least Two Sensors]
With reference to the attached
Said adjustment element 5 can be placed upstream or downstream indifferently of the mixing point 11 between said first 3 and said second combustible gas 4.
Said first adjustment element 5 comprises a fan with a varying number of revs, which can be set by means of a first drive command and said second adjustment element 6 comprises a valve, which can be adjusted by means of a second drive command.
In a preferred embodiment of the invention, said at least two sensors comprise a first sensor 12 adapted to measure the number of revs of the fan 5 and a second flame sensor 8 associated with the flame of the burner 2, as shown in
In further detail, said second flame sensor 8 is preferably arranged close to the flame of the burner and is adapted to measure the resistance Rel, or the electrical conductivity, Gel, or other electrical parameters of the flame of the burner 2; said first sensor 12 is preferably placed inside the fan 5 and is adapted to measure the rotation speed of the electric motor of said fan 5, for example, expressed in number of revs per minute.
In another preferred embodiment of the invention, said adjustment element 5 is associated with a third absolute pressure sensor, or absolute pressure and temperature sensor 7. Said sensor 7 is preferably placed at the entrance or exit of the fan 5, which, in turn, may be placed both upstream and downstream of the mixing point 11.
Said controller 9 preferably comprises a microprocessor, or an equivalent electronic processing element, and at least one associated memory unit 13. Said controller 9 is adapted to carry out readings and cyclically process the signals coming from the aforesaid sensors 7, 8, 12 and produce, based on said processing and a comparison thereof with values of reference stored in tables allocated in the memory unit 13, appropriate drive signals for said fan 5 and said adjustable valve 6.
The drive signals and/or the measurements of the sensors, which determined them, and/or the various operating parameters, which are calculated to estimate the optimum operating point, may also be stored in the memory unit 13 associated with the microprocessor of the controller 9, so as to update and cyclically complete said tables containing the optimum settings of the fan 5 and of the valve 6 of the apparatus, as well as create and store new tables, as a function of the changed operating boundary conditions. Thereby, the present invention allows obtaining a method for monitoring and controlling the combustion of a burner, which is capable of self-learning and self-adjustment for achieving the optimum working conditions of the burner in terms of efficiency, stability and user safety.
The appended
With reference to the attached
With reference to the attached
By using the first flame sensor 8 arranged close to the flame of the burner 2 and a second sensor 12 of the number of revs n of the fan 5, it is possible to update the values of the column R and s, as described below: after fixing the value of the number of revs of the fan 5, n, corresponding to a certain thermal power W, the R value is traced, so that the desired excess air value, λ* is obtained, based on the following calibration sequence:
After constructing and updating table T2, as described in the calibration stage, this will be stored in the memory unit 13 and will be constantly updated during the operation of the burner, as described below.
The control sequence provides a first quick adjustment control loop and at least a second slow adjustment control loop.
With reference to the attached
Therefore, the fan 5 is driven 50 at a number of revs n1 corresponding to the amount of air needed for the required power W1 and, similarly, the actuator of the valve 6 will be brought 50 to the opening position s1. In table T2, in use, corresponding n and s values correspond to each thermal power value required of the burner in order to obtain, in the combustion λ, the desired, λ*.
With reference to the attached
According to this second adjustment control loop, a first monitoring of the combustion is carried out cyclically, exploiting the detections of said first flame sensor 8, verifying that the current R value does not deviate from the R1 value, provided in table T2 for W1 and corresponding to n1 and s1 and to the desired excess air value λ*.
If the measured R is equal, or sufficiently close to R1 in the table in use, for example, if the distance between the measured R and R1 is less than 10% of the original value of R1, further actions are not carried out; whereas, if the measured R is not sufficiently close to R1, for example, if the distance between the measured R and R1 is 10% greater than the original value of R1, then, while the n value is kept constant, the actuator of the valve 6 is moved into different positions until it reaches an s1n value whereby there is correspondence between the measured R and the R1 value provided for said power. Therefore, the s1n, value replaces the previous s1 value in the table.
With reference to the attached
With reference to the attached
In further detail, the corresponding change ΔR in the electrical flame resistance is detected and compared with the corresponding values listed in table T2, checking that the ΔR/Δs ratio corresponds to the value and the sign listed in table T2 for the current value of the number of revs n. In fact, if the value of the ratio ΔR/Δs detected were of a different sign to that shown in table T2 then the excess air λ would be <1 and the boiler might have to work in a potentially dangerous situation producing excess CO.
The procedure described above can also be useful for verifying any blockages, also partial, of the chimney and consequently producing adequate alarm signals for the user. This can happen simply by controlling the congruity of the value of the number of revs per minute of the fan 5: if the current number of revs is greater than the number required, the cause might be a reduced draught in the chimney. With reference to the attached
Should a recalibration be necessary:
Instead of the electrical flame resistance, R, other electrical parameters detected by said first sensor can be used, such as, the flame conductivity G or the flame capacity C, for example.
The method for monitoring and controlling the combustion of a burner for combustible gas apparatuses according to the invention allows continuously establishing the optimum working conditions of the burner, ensuring the thermal power required in a very wide range, from 100% of the nominal power value of the burner to about 5% of said nominal value. Furthermore, through the method according to the invention, it is possible to cause the burner to work with a desired excess air, λ, which can be set from a minimum value equal to 1 to a maximum value, also greater than 2 and, in particular, it can be set at an optimum value of just over 1, e.g., equal to 1.25.
Furthermore, the method and apparatus for monitoring and controlling the combustion of a combustible gas burner according to the invention allows verifying the safety of the apparatus and, in particular, of the λ, in particular, always ensuring that the λ is greater than 1 over the whole spectrum of operation, through a direct measurement and not through an estimate or a plausibility test.
[Realization with Third Sensor—Calibration Value n]
In the case of a preferred embodiment of the invention using a first sensor 12 adapted to measure the number of revs per minute of the fan 5, a second flame sensor 8 arranged close to the flame of the burner 2 and a third absolute pressure sensor 7 associated with the gas mixture, the calibration can also provide updating the value of the parameter n in table T2.
With reference to the attached
The correlation between thermal power W and number of revs n of the fan 5 must be precise otherwise there is the risk of having less air than necessary and therefore excess gas and combustion characterized by a sub-optimal air number A. Therefore, the product between the density p and the volumetric flow rate of the air Q must be kept constant so that if the density of the air decreases, the volume of air must be increased to ensure that the mass of air introduced into the burner 2 is always correct.
Again, with reference to the appended
In table T2, in order to control and update the value of the parameter n, it is possible, for example, to carry out a first reading of the pressure sensor 7 to measure the atmospheric pressure P0 and the ambient temperature TO with the fan at a standstill, and a second reading of the pressure sensor 7 to measure the pressure Pn1, after switching on the fan 5, at a constant speed n1 and thus, evaluate the change in pressure ΔP=Pn1−P0 representative of the initial boiler installation conditions. Thereby, the ratio between P and n, is stably fixed, starting from the assumption that an amount of air Qa1 (independently of the gas) will always correspond to a certain power W1, substantially tracing the correct load curve with boiler installed and thus the corresponding value n1.
If this procedure is repeated periodically, it may also be useful for verifying possible blockages, also partial, of the chimney and consequently producing adequate alarm signals for the user.
In summary, if the system possesses said pressure sensor 7, the air temperature and density are checked with every start-up, as well as any blockage of the chimney, updating, if necessary, in table T2 in use, the figure relative to the number of revs of the fan 5, n, thus also updating the trend of the curve binding the thermal power of the burner to the number of revs of the fan 5, W=f (Qa)=f (n).
If the system is provided with a flame sensor 8 and with a rotation speed sensor 12 of the fan 5, then, with every start-up and with every new request for thermal power W1, a number of revs of the fan 5, n1 is determined by means of a quick control loop referring to the current table T2 and a degree of opening of the valve 6, s1, to which both the requested thermal power should correspond and an electrical flame resistance value R1 corresponding to an optimum excess air value.
If a first slow control loop based on the measurement of the electrical flame resistance R=f(n) detects that, at the opening of the valve 6, s1, in table T2 an R1′ value is present, different to the one expected, then the degree of opening s of the valve 6 is modified until a value s1′, which allows reaching the desired value R1 and table T2 is updated, replacing the s1′ value with the previous one s1. If the difference between s1 and s1′ is greater than a certain threshold, a new calibration of the system can be provided, given that the operating conditions have probably changed, or the burner can be stopped, given that the current combustion conditions are deemed to be dangerous.
Furthermore, a second slow control loop, at predetermined intervals of time, further verifies that the combustion is proceeding optimally by controlling the ratio ΔR/Δs through the following sequence:
The method according to the present invention, in each of the embodiments thereof, can be used, with some possible variations, in each step of burner operation: in the initial calibration stage, in the first start-up stage after implementation, as well as during the normal operation stage.
The method according to the present invention in each of the embodiments thereof, is further adapted to be used for monitoring the current operating conditions and updating the tables containing the optimum settings of the fan 5 and the valve 6 of the apparatus as a function of the changed operating boundary conditions, so as to ensure the optimized working of the burner in an increasing number of situations, succeeding in preventing malfunctioning, which is potentially harmful both for the burner and the users.
Number | Date | Country | Kind |
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102021000032360 | Dec 2021 | IT | national |
This application claims priority to PCT International Application No. PCT/IB2022/062603 filed on Dec. 21, 2022, which applications claims priority to Italian Patent Application No. 102021000032360 filed on Dec. 23, 2021, the entire disclosures of which are expressly incorporated herein by reference.
Filing Document | Filing Date | Country | Kind |
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PCT/IB2022/062603 | 12/21/2022 | WO |