EP3904766B1 - Process for the plausibility check of a gaseous flow rate in a burner and gas boiler for carrying out the process - Google Patents

Description

The present invention relates to a method for checking the plausibility of a gas mixture volume flow in a burner. In the burner, a gas mixture comprising a gas and a fuel gas is burned in a combustion chamber by a combustion process, wherein the combustion process is monitored by evaluating a measured value V of at least one sensor. The measured value V is related to the combustion process in such a way that the quality of the combustion of the fuel gas can be detected.

Furthermore, the invention relates to a gas boiler with a burner in which a gas mixture comprising a gas and a fuel gas is burned in a combustion chamber by a combustion process.

Typically, such burners are defined in their performance parameters via previously known setpoints for gas and fuel gas supply.

It is from the WO 2012/004211 A2 It is known to use a transit time measurement in the volume flow to record a volume flow of gas and/or fuel gas supply. In this case, a pulse-like modulation is imposed on a volume flow of a fuel gas and a transit time of this modulation is measured until an effect attributable to it occurs in the burner.

The problem with the use of such methods is that rapidly changing environmental conditions, such as pressure fluctuations or abrupt deviations in the volume flow cannot be recognized as such by check valves located in front of the combustion chamber or in the exhaust system. but lead to falsified comparison values. To determine the volume flow more precisely, several consecutive series of measurements with subsequent averaging are therefore required. In addition, signal-response loops in microprocessors with comparatively high memory requirements and computing effort are required for the evaluation to process the measurement data.

The present invention is therefore based on the object of proposing a method for checking the plausibility of a gas mixture volume flow in a burner or a gas boiler with a burner, in which the effort for checking the plausibility of the gas mixture volume flow is reduced and the reliability of the plausibility is increased.

According to the invention, this object is achieved in conjunction with the preamble of patent claim 1 or 8 by the characterizing features of patent claim 1 or 8. Advantageous and expedient further developments are specified in the subclaims.

• a) zunächst wird eine impulsartige Modulation auf einen Volumenstrom des Brenngases, insbesondere einer Volumenstromänderung G auf einen Volumenstrom des Brenngases, zu einem ersten Zeitpunkt t_start gemäß einer Zeitreihe G(t) aufgeprägt, wobei hierdurch ein bekanntes Signal in das System des Brenners eingespeist wird, das später wiedererkannt werden kann und wobei die impulsartige Modulation beispielsweise ein Volumenstromsignal oder ein Steuersignal für einen Stellmotor, ein Ventil oder der Gleichen sein kann;
• b) ab einem zweiten Zeitpunkt t₂ wird ein Messwert V gemessen und eine Messwert-Zeitreihe V(t) erfasst, wobei sich hierdurch die Möglichkeit ergibt, die Auswirkung des Signals, beispielsweise ein Anstieg der Energieabgabe des Verbrenners, oder eine Erhöhung eines Ionisationssignals einer Ionisationselektrode innerhalb der Brennkammer in Abhängigkeit der Zeit zu messen;
• c) sodann wird jeweils ein Produkt P aus dem ersten Wert der Zeitreihe V(t) zum Zeitpunkt t_i und einem jeden Wert der Zeitreihe G(t) berechnet und nachfolgend eine Summe S_i aller berechneten Produkte gebildet;
• d) die erste Summe S_i wird in einem Zwischenspeicher gespeichert, wodurch eine spätere Nutzung dieser Daten ermöglicht wird;
• e) es wird jeweils ein Produkt P aus dem zweiten Wert aus der Zeitreihe V(t) zu einem Zeitpunkt t_i+i und einem jeden Wert der Zeitreihe G(t) berechnet und nachfolgend eine Summe S_i+1 aller berechneter Produkte gebildet;
• f) die Summe S_i+1 wird ebenfalls in einem Zwischenspeicher gespeichert und somit für eine darauf folgende Datenverarbeitung vorgehalten;
• g) es erfolgt ein Wiederholen der beiden Schritte e) und f) für die nachfolgenden Zeitpunkte t_i+n bis zu einem vorgegebenen Zeitpunkt t_stop;
• h) aus den gespeicherten Summen S_i bis S_i+n erfolgt eine Selektion der größten Summe, des Maximums S_max, der gespeicherten Summen S_i bis S_i+n und ein Ermitteln des Zeitpunktes t_i+x zu der Summe S_max;
• i) aus der Zeitdifferenz zwischen t_start und t_i+x wird die Laufzeit t_lauf der impulsartigen Modulation durch den Volumenstrom des Gasgemisches zur Brennkammer bestimmt;
• j.) die Laufzeit t_lauf wird mit einem Sollwert t_soll bei einem theoretischen Volumenstrom aus einem Speicher verglichen und darauf aufbauend ein Rückschluss auf den aktuell vorliegenden Volumenstrom des Brenners im aktuellen Zustand gezogen.

The method according to the invention for checking the plausibility of a gas mixture volume flow in a burner in which a gas mixture comprising a gas and a fuel gas is burned in a combustion chamber by a combustion process, wherein the combustion process is monitored by evaluating a measured value V of at least one sensor, wherein the measured value V is related to the combustion process in such a way that the quality of the combustion of the fuel gas can be detected, provides the following method steps:

• a) first, a pulse-like modulation is applied to a volume flow of the fuel gas, in particular a Volume flow change G is impressed on a volume flow of the combustion gas at a first time t _start according to a time series G(t), whereby a known signal is fed into the system of the burner which can be recognised later and whereby the pulse-like modulation can be, for example, a volume flow signal or a control signal for a servo motor, a valve or the like;
• b) starting from a second point in time t _{2 ,} a measured value V is measured and a measured value time series V(t) is recorded, whereby this makes it possible to measure the effect of the signal, for example an increase in the energy output of the combustor, or an increase in an ionisation signal of an ionisation electrode within the combustion chamber as a function of time;
• c) then a product P is calculated from the first value of the time series V(t) at time t _i and each value of the time series G(t) and subsequently a sum S _i of all calculated products is formed;
• d) the first sum S _i is stored in a buffer, allowing later use of this data;
• e) a product P is calculated from the second value from the time series V(t) at a time t _i+i and each value of the time series G(t) and subsequently a sum S _i+1 of all calculated products is formed;
• f) the sum S _i+1 is also stored in a buffer and thus kept available for subsequent data processing;
• g) the two steps e) and f) are repeated for the subsequent times t _i+n up to a predetermined time t _stop ;
• h) from the stored sums S _i to S _i+n, a selection is made of the largest sum, the maximum S _max , of the stored sums S _i to S _i+n and a determination of the time t _i+x for the sum S _max ;
• i) the running time t _run of the pulse-like modulation by the volume flow of the gas mixture to the combustion chamber is determined from the time difference between t _start and t _i+x ;
• j.) the running time t _run is compared with a setpoint t _set at a theoretical volume flow from a storage tank and, based on this, a conclusion is drawn about the current volume flow of the burner in the current state.

By applying this method, the actual volume flow is checked for plausibility and the entire response signal V(t) does not need to be stored, as the individual measured values are processed immediately and are no longer required for subsequent evaluation. This reduces the requirements for the control unit's electronics, as less data is required to be stored and less data needs to be evaluated.

In an advantageous embodiment, the time t _start (302) and the time t ₂ (301) are set at the same time. This ensures that all relevant information is included in the measured value time series V(t).

Furthermore, it is intended to delete and/or overwrite the measured value of the measured value time series V(t) at time t _i , i.e. V(t _i ), from a buffer after calculating the sum S _i . Because the measured values are not stored permanently, valuable storage space in the electronics can be saved.

It is also planned to design the pulse-like modulation in the form of a predefined, in particular stored, theoretical signal. The exact course of the pulse-like modulation is thus known and can be used for the calculation without any time delay, which means that the calculation can be carried out more quickly.

It is also intended that the pulse-like modulation is a measured signal, in particular an ionization signal from the burner. This ensures a signal that can be measured reliably.

It is also planned to record the entire time series V(t) in a memory. Recording the entire time series enables the flexible use of the data for further calculations.

In an advantageous embodiment, the time interval between a point in time t _i and a point in time t _i+i is set between 0.1 ms and 20 ms, in particular between 0.5 ms and 5 ms. By using short time intervals between the point in time t _i and a point in time t _i+i, the resolution of the measured value time series V(t) is increased, which allows a more precise evaluation of the data.

Finally, it is intended to carry out the method for checking the plausibility of a gas mixture volume flow according to the above-mentioned statements on a gas boiler with a burner in which a gas mixture comprising a gas and a fuel gas is burned in a combustion chamber by a combustion process. This monitors the operation of a gas boiler by checking the plausibility of the volume flow, which optimizes and reduces the requirements for the evaluation electronics.

For the purposes of the invention, a pulse-like modulation is understood to mean a time-limited signal change of any shape, comprising a triangular pulse, a rectangular pulse and a sinusoidal oscillation.

Furthermore, in the sense of the invention, the index "i" stands for a continuous number of measuring points that take place one after the other.

Additional details of the invention can be found in the drawings using schematic embodiments.

Figur 1

eine schematische Darstellung einer Gastherme, welche mittels des erfindungsgemäßen Verfahrens betreibbar ist und

Figur 2

ein schematisches Diagramm des erfindungsgemäßen Verfahrens.

This shows:

Figure 1

a schematic representation of a gas boiler which can be operated by means of the method according to the invention and

Figure 2

a schematic diagram of the process according to the invention.

In Figure 1 a gas boiler is shown which can be operated by means of the method according to the invention. According to an electronic combustion control method of a Control unit 10, a fuel gas 3 is let into a gas mixture blower 6 via a fuel gas control valve 2 and mixed there with a gas 4. The fuel gas control valve 2 is secured with a fuel gas safety valve 1 in order to prevent the inflow of fuel gas 3 in the event of an undesirable operating state and to ensure operational safety. The gas mixture blower 6 blows the fuel gas 3 with the gas 4 into the combustion chamber 11. This contains the burner 7, which burns the gas mixture 5 of gas 4 and fuel gas 3 in a combustion process. The combustion chamber 11 is closed on the exhaust side by means of a check valve 9, so that the combustion process is protected from external influences. The combustion process can now be monitored by means of a measured value from a sensor, for example an ionization electrode 8 shown in this design variant. The ionization electrode 8 provides measured values with the help of which the volume flow of the gas mixture 5, consisting of fuel gas 3 and gas 4, is checked for plausibility. As a result, the control unit 10 can be used to influence, for example, the gas mixture blower 6, the gas safety valve 1 and/or the gas control valve 2. In addition, the required burner output can be regulated according to a given heat requirement by changing a required amount of gas 4 with the speed-controlled gas mixture blower 6 of the control unit 10.

In Figure 2 a diagram is shown, based on which the method according to the invention is described. At a first time t _start 302, a pulse-like modulation in the form of a volume flow change G is impressed on the volume flow of the fuel gas 3. This takes place according to a time series G(t) 305, which is in particular a predefined and preferably a stored theoretical signal. The theoretical signal can now in particular a fuel gas volume flow signal or a control signal for a servomotor, a valve or the like. From a second time t ₂ 301, which is preferably the same time as t _start 302, at least one sensor, for example the one in Figure 1 shown ionization electrode 8 (not shown here), a measured value V is measured and a measured value time series V(t) 304 is recorded. As soon as the first value of the measured value time series V(t) 304 is available, suitable electronics form a product P from this value and each value of the known time series G(t) 305. A sum S _i is formed from the set of these products and stored in a buffer. Preferably, the respective value of the measured value time series V(t) 304 is deleted after the respective calculation and/or overwritten with the subsequent value of the measured value time series V(t) 304 in order to save storage space in the electronics. These steps now take place for each individual value of the measured value time series V(t) 304 up to a time t _stop 306. Preferably, the time intervals between a time t _i and a time t _i+i are between 0.1 ms and 20 ms, in particular between 0.5 ms and 5 ms. From all the sums S _i to S _i+n formed, the largest sum S _max is then selected and the corresponding time t _i+x is determined. From this, a time difference between t _start 302 and t _i+x can be determined as the running time t _run 303. This corresponds to the time that the pulse-like modulation by the volume flow of the gas mixture 5 (not shown here) takes. Figure 1 shown) to the combustion chamber 11 (not shown here) (in Figure 1 shown). This can be compared with a setpoint value t _setpoint of a theoretical volume flow from a storage tank. This comparison allows conclusions to be drawn about the combustion process and this can be monitored in order to make a gas mixture volume flow plausible.

List of reference symbols:

1

Fuel gas safety valve

2

Fuel gas control valve

3

Fuel gas

4

gas

5

Gas mixture

6

Gas mixture blower

7

burner

8th

Ionization electrode

9

Check valve

10

Control unit

11

Combustion chamber

301

Time t ₂

302

Start time t _start

303

Running time t _run

304

Measured value time series V(t)

305

Time series G(t)

306

Time t _stop

Claims (8)

1. Method for checking plausibility of a gas mixture volumetric flow rate in a burner in which a gas mixture (5) comprising a gas (4) and a fuel gas (3) is burned by a combustion process in a combustion chamber (11), wherein the combustion process is monitored by evaluation of a measured value V, from at least one sensor, wherein the measured value V is related to the combustion process in such a way that the quality of the combustion of the fuel gas is detectable, wherein the method comprises the following method steps:

   a. imposing a pulse-like modulation on a volumetric flow rate of the fuel gas (3), in particular a volumetric flow rate change G on a volumetric flow rate of the fuel gas (3), at a first point in time t_start (302) in accordance with a time series G(t) (305);

   b. measuring the measured value V starting from a second point in time t₂ (301) and capturing a measured value time series V(t) (304);

   c. calculating in each case a product P of the first value from the measured value time series V(t) (304) at a point in time t_i and each value of the time series G(t) (305) and subsequently forming a sum S_i of all the calculated products;

   d. storing the first sum S_i in a buffer memory;

   e. calculating in each case a product P of the second value from the measured value time series V(t) (304) at a point in time t_i+1 and each value of the time series G(t) (305) and subsequently forming a sum S_i+1 of all the calculated products;

   f. storing the first sum S_i+1 in a buffer memory;

   g. repeating the two steps e. and f. for the points in time t_i+n until a predefined point in time t_stop (306);

   h. selecting the maximum S_max of the stored sums S_i to S_i+n and ascertaining the point in time t_i+x with respect to the sum S_max;

   i. determining the time difference between t_start (302) and t_i+x as a delay time t_lauf (303) of the pulse-like modulation through the volumetric flow rate of the gas mixture to the combustion chamber;

   j. comparing the delay time t_lauf (303) with a target value t_soll for a theoretical volumetric flow rate from a memory and deducing the given volumetric flow rate.
2. Method according to Claim 1, characterized in that the point in time t_start (302) and the point in time t₂ (301) are a common point in time.
3. Method according to Claim 1 or 2, characterized in that, after the calculation of the sum S_i, the measured value of the measured value time series V(t) at the point in time t_i, i.e. V(t_i), is erased from a buffer memory and/or overwritten.
4. Method according to any of the preceding claims, characterized in that the pulse-like modulation is a predefined, in particular stored theoretical signal.
5. Method according to any of the preceding Claims 1 to 3, characterized in that the pulse-like modulation is a measured signal, in particular an ionization signal of the burner (7).
6. Method according to any of the preceding claims, characterized in that the measured value time series V(t) (304) is captured completely in a memory.
7. Method according to any of the preceding claims, characterized in that the time interval between a point in time t_i and a point in time t_i+i is between 0.1 ms and 20 ms, in particular between 0.5 ms and 5 ms.
8. Gas boiler with a burner, the gas boiler comprising a control device (10), the burner being designed to burn a gas mixture (5) comprising a gas (4) and a fuel gas (3) by a combustion process in a combustion chamber (11), characterized in that the control device (10) is designed to carry out a method for checking plausibility of a gas mixture volumetric flow rate according to any of the preceding claims.

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