DE102007053484A1 - Fuel gas air mixture regulating method for fuel gas operated burner e.g. thermal value equipment, involves comparing measured burner or flame temperature with calculated burner or flame temperature - Google Patents

Abstract

The method involves calculating a run of burner or flame temperature from an output temperature of a burner or a flame temperature. Fuel gas and combustion air stream are adjusted according to determined fuel gas volume or mass flow and combustion air volume or mass flow. Another burner or flame temperature is measured and is compared with the calculated burner or flame temperature, where the measured temperature at a preset point of time is larger or smaller than the calculated temperature at the point of time at a dynamic process, so that fuel gas flow or air mass is reduced or increased.

Description

The The invention relates to a method for controlling a fuel gas-air mixture over the on Burner, at the burner flame or in the vicinity of the burner flame a heater measured temperature.

to Control of a fuel gas-air mixture of heaters, in particular from condensing appliances, can the measurement of the burner or flame temperature can be used. Basis of such a scheme is the setting of a fuel gas-air mixture to a Target temperature, the z. B. is measured at the burner. It is too Note that larger deviations in a temperature difference (between a set and actual temperature) be avoided, otherwise due to the increase in the resulting CO emissions the combustion quality suffers.

The WO 2006/000366 A1 discloses a method for controlling a fuel gas-air mixture of a burner, in which the flame temperature is detected and regulated in dependence on the desired burner load and air ratio to a target temperature in the steady state. For this purpose, characteristic curves are used which assign the burner load to a specific setpoint temperature. Depending on the air mass flow, a target temperature to be controlled is determined. If, for example, the load is increased, on the one hand the current temperature is measured and the setpoint temperature is determined. If the setpoint temperature is greater than the outlet temperature, the fuel quantity is enriched until the deviation of the actual value from the setpoint value no longer exists. Since a certain inertia is to be expected during a load change due to the heat capacity of the burner system, the measured temperature changes even in the dynamic state, if the fuel quantity is not changed. So while the load in the dynamic state of a temperature rises continuously from an initial temperature to a higher setpoint temperature, the teaches WO 2006/000366 A1 to additionally grease the fuel quantity. As a result, the fuel gas-air mixture is first over-enriched; the temperature rises above the setpoint temperature, which is why the amount of fuel gas is emaciated, whereby it falls below the setpoint temperature. Ultimately, the temperature swings to the setpoint temperature.

Of the Invention is based on the object, a method of control a fuel gas-air mixture over the Burner or flame temperature to provide, in which Avoidance of pollutant emissions, the heating or cooling of the Burner components, especially during the starting phase and the Modulation phase is considered in the dynamic state.

• – mit dem Sensor wird eine Ausgangstemperatur gemessen,
• – bei Vorgabe einer Brennerbelastung werden der notwendige Brenngasvolumen- oder -massenstrom, unter Berücksichtigung der Verbrennungsluftzahl, des Verbrennungsluftvolumen- oder -massenstroms sowie aus einem Kennfeld oder einer Funktion die belastungsabhängige Brenner- oder Flammensolltemperatur bestimmt,
• – aus der Ausgangstemperatur und der Brenner- oder Flammensolltemperatur wird ein zeitlicher Verlauf der Brenner- oder Flammentemperatur errechnet,
• – gemäß des ermittelten Brenngasvolumen- oder -massenstroms und Verbrennungsluftvolumen- oder -massenstroms werden der Brenngas- und Verbrennungsluftstrom eingestellt,
• – die Brenner- oder Flammentemperatur wird gemessen und mit dem errechneten Verlauf der Brenner- oder Flammentemperatur verglichen,
• – ist die gemessene Brenner- oder Flammentemperatur zu einem bestimmten Zeitpunkt im dynamischen Verlauf ungleich der errechnete Brenner- oder Flammentemperatur zu diesem Zeitpunkt, so wird der Brenngasstrom oder die Luftmenge angepasst.

According to the invention this is realized according to the features of claim 1 with a method for controlling a fuel gas-air mixture of a fuel gas burner preferably a heater with the aid of a sensor for detecting the burner or flame temperature T and a control with the following method steps:

• With the sensor, a starting temperature is measured,
• When a burner load is specified, the required fuel gas volume or mass flow, taking into account the combustion air number, the combustion air volume or mass flow as well as from a characteristic field or a function, determines the load-dependent burner or flame target temperature,
• - a chronological progression of the burner or flame temperature is calculated from the starting temperature and the burner or flame set temperature,
• In accordance with the determined fuel gas volume or mass flow and combustion air volume or mass flow, the fuel gas and combustion air flow are adjusted,
• - The burner or flame temperature is measured and compared with the calculated course of the burner or flame temperature,
• - If the measured burner or flame temperature at a certain point in the dynamic course is not equal to the calculated burner or flame temperature at this time, the fuel gas flow or the air quantity is adjusted.

hereby the adjustment is significantly accelerated.

For smaller deviations applies: If the measured burner or flame temperature at a certain time in the dynamic course smaller than the calculated burner or flame temperature at this time, the fuel gas flow is increased or the amount of air reduced. If the measured burner or flame temperature at a certain time in the dynamic course greater than the calculated burner or flame temperature at this time, the fuel gas flow is reduced or the air increased amount. In the case of larger deviations, changing the mixture may result in a shift of the flame position, so that the measures mentioned above do not necessarily contribute to the regulation to the setpoint. In the majority of cases, however, due to the continuous control and the therefore relatively small expected deviations, it can be assumed that enrichment with too cold a flame leads to an increase in temperature and a decrease to a decrease in temperature.

For the scheme of the fuel gas-air mixture, a PI controller is preferred. With a PI controller is turned on Control value from a control deviation (difference between setpoint and Actual temperature) certainly. For A PI controller usually means that the P controller part has an occurring Rule difference quickly attempts to balance, with the I-regulator component subsequently eliminated the remaining control difference. Thus, a PI controller is working with appropriate setting fast and precise.

The Choosing an I-controller or P-controller, on the other hand, could be disadvantageous. Dependent from the system, the regulation can be applied to a very large integral share (I share) Although regulate very fast, but is a big jump in the temperature or a strong CO emissions too recorded. Choosing a very small I share is the jump very small, but the regulation time is very long.

For a reliable measurement result must be inertia a temperature measuring system are taken into account. This can be due to the sensors used as well as to the system behavior itself, be traced back.

The The invention will now be explained in detail with reference to FIGS. in this connection demonstrate

1 a profile of the burner temperature T as a function of the load Q. According to the state of the art,

2 a curve of the burner temperature T as a function of the time t during a modulation jump from 20 kW to 10 kW,

3 a course of the CO emission values as a function of the time t during a modulation jump from 20 kW to 10 kW,

4 a profile of the burner temperature T as a function of time t during a heating process via linear characteristics,

5 to 7 a modulation of the modulation at a higher power according to the inventive method and

8th to 10 a regulation of the modulation at a low power according to the inventive method.

Again 1 can be seen, the burner surface temperature T is low at a higher power and high at a low load, since the flame with increasing load Q. lifts off from the burner surface.

2 shows the system behavior during a load change (modulation jump) of the heater from 20 kW to 10 kW. The diagram illustrates that during operation, the difference between a burner or flame target temperature T ₂ , to which it is to be controlled, and an output temperature T _{0 can be} relatively large. Similarly, the system behaves during startup, because the heater (or the burner temperature) passes from the cold state in a modulation-dependent hot state.

Curve 3 in 2 represents the behavior of a heater at modulation jump from 20 kW to 10 kW under the condition that the air ratio lambda is kept constant.

The burner or flame temperature follows the curve 3 as a function of the time t, which can be reproduced by means of an exponential function, up to a stationary final value.

The heating or cooling processes taking place during modulation jumps during the modulation can be described by the following function:

T₀

– die Ausgangsbrenner- oder -flammentemperatur,

T₂

– die Brenner- oder Flammensolltemperatur,

T₁(t)

– der zeitliche Verlauf der Brenner- oder Flammensolltemperatur,

t

– die Zeit und

τ

– ein Regelungsparameter, der vorgegeben wird und Einfluss auf den Gradienten hat.

In the equation 1 mean

T ₀

The output burner or flame temperature,

T ₂

- the burner or flame set temperature,

T ₁ (t)

- the time course of the burner or flame set temperature,

t

- the time and

τ

- A control parameter that is specified and has an influence on the gradient.

The inventive method allows the modification of a stationary target temperature value T _{2 of} the control in a desired value T ₁ (t) as a function of time, wherein the time course of the burner or flame target temperature T _{1 of} an e-function (as curve 3 . 2 ) and depending on the output and burner or flame set temperature of the modulation or the load change is.

Indicators of a well-functioning control system are, in addition to the CO ₂ emissions that result from the excess air, especially under safety aspects, the CO emissions. 3 shows values of the CO emissions of the system at an exemplary modulation jump from 20 kW to 10 kW.

The curve 1 shows a CO course in the event that a control would dose the amount of gas so that would be controlled immediately after the burner start to the temperature target value. In this case, due to the large temperature difference, the gas valve would be opened so much that the combustion would no longer be standard or "clean." At the beginning, a markedly high CO emission is observed, which decreases with increasing time 2 shows a CO course, which takes into account the inventive approach at the same modulation jump (from 20 kW to 10 kW) sets.

The CO emissions according to the invention control, shown as a curve 2 in 3 , shows that CO emissions can be permanently kept at a low level. Thus, the excessive pollutant emissions which occur during combustion, in particular during the heating phase at startup or during modulation jumps, which would occur if the procedure according to the invention were regulated directly to the target temperature, are prevented.

During the Starting process itself, it usually comes to an incomplete combustion, in particular due to systemic mixture enrichment. This Effect has a for the device start characteristic, high CO emissions to Episode. This increase in CO is considered systemic in the control according to the invention provided and is from the CO courses shown to differentiate.

Another embodiment provides an approximation of the setpoint temperature T ₁ the heating behavior of the system (curve 6 . 4 ) via linear sections within a characteristic before, z. B. via an approach with two (curve 5 . 4 ) or with several sections (curve 4 . 4 ) such that always a sufficient quality of combustion is guaranteed.

First, the method for controlling the modulation on a higher burner power will be described. Here is an off burner and a heater, which is in a standby state to go out. With a temperature sensor, preferably with a PTC sensor, an output temperature T ₀ at the burner, z. B. T ₀ = 25 ° C measured.

For a heat request, eg Q. = 20 kW, a corresponding air mass flow (eg for lambda = 1.3 and Q = 20 kW) is set on the blower via a mass flow sensor. From a stored gas valve characteristic, as in 5 shown, the heat demand of 20 kW corresponding step number (eg 280) is determined and set. From a stored temperature characteristic, the heat-demand of 20 kW corresponding load-dependent burner or flame target temperature T _{2 is} determined, eg T ₂ = 350 ° C (s. 6 ).

The moment of a modulation jump or a heat load change is kept fixed by setting the time t to the value 0. At each subsequent time t ₁ to t _x , the time profile of the burner or flame temperature T _{1 is determined} according to Equation 1 ( 7 ). The burner or flame temperature is measured and compared with the calculated burner or flame temperature T ₁ (t).

The control only intervenes when a deviation of the measured burner or flame temperature (actual temperature) from the calculated burner or flame temperature T ₁ (t) (setpoint temperature) occurs. This deviation between the actual and desired temperature is controlled by the stepper motor of the gas valve, so that when the measured burner or flame temperature is greater than the calculated burner or flame temperature T ₁ (t), the fuel gas flow is reduced or the amount of air is increased or if the measured burner or flame temperature is greater than the calculated burner or flame temperature T ₁ (t), the fuel gas flow is reduced or the amount of air is increased.

The inventive method is terminated as soon as the measured burner or flame temperature of the burner or flame setpoint T ₂ corresponds.

A modulation of the modulation on a low load is similar to the scheme described above and is the 8th to 10 refer to. It is from the current load already mentioned above, eg Q. = 20 kW and from the measured at the burner output temperature T ₀ , eg T ₀ = 350 ° C assumed. After the modulation change of Q. = 20 kW on Q = 10 kW, the fan controls the corresponding air volume and the gas valve is set to the expected number of steps (in this case 150 steps) depending on the measured air mass flow. The necessary number of steps is determined from the stored gas valve characteristic.

The temperature increases with reduced load and the rise follows the curve shown. From the stored temperature characteristic is the for Q. = 10 kW corresponding burner or flame set temperature T ₂ , eg T ₂ = 550 ° C determined. The timing of the modulation jump is held fixed by setting the time t to the value 0. At each time t ₁ to t _{x of} the current time, the time profile of the burner or flame temperature T _{1 is determined} according to equation 1 and compared with the current, measured burner or flame temperature. Deviations between the measured and calculated temperature are also compensated by an adjustment of the stepper motor of the gas valve.

With the control method according to the invention should during combustion, especially at the start or at modulation jumps while the modulation, resulting pollutant emissions are prevented. It is not directly on a predetermined end-target temperature value regulated, but by the natural Heating behavior or cooling behavior of the system is integrated into the scheme. Thus, larger jumps in the Temperature difference between the setpoint and actual temperature avoided and a good combustion quality reached.

With Help of the method according to the invention Is it possible, a regulation aimed at measuring the burner or flame temperature to adapt for modulation jumps.

One unclean system behavior, eg. B. when heating the system after the burner start, is avoided, in which the control after the burner start always in operation and the quality of combustion is permanently checked and regulated becomes.

Claims (5)

Method for controlling a fuel gas-air mixture of a combustion gas-operated burner preferably a heater with the aid of a sensor for detecting the burner or flame temperature (T) and a control with the following steps: - With the sensor, an output temperature T _{0 is} measured, - at default a burner load (Q.) are the necessary Brenngasvolumen- (V. _B) or -massenstrom (m. _B), in consideration of the combustion air ratio (λ) of the Verbrennungsluftvolumen- (V. _L) or -massenstrom (m. _L) as well as from a characteristic map or a function, the load-dependent burner or flame target temperature T ₂ = f (Q.) Determined from the output temperature T ₀ and the burner or flame target temperature T ₂ is a time course of the burner or flame temperature T ₁ (t) = f (T ₀ , T ₂ , t) calculated according to the determined fuel gas volume (V _B ) or mass flow (m _B ) and combustion air volume (V _L ) or mass nstroms (. m _L) of the combustion gas and combustion air flow are adjusted, - the burner or flame temperature is measured and compared with the calculated burner or flame temperature T ₁ (t) are compared - is the measured burner or flame temperature at a certain time t in the dynamic course greater or smaller than the calculated burner or flame temperature T ₁ (t) at this time t, the fuel gas flow or the amount of air is reduced or increased. Method for controlling a fuel gas-air mixture according to claim 1, characterized in that the fuel gas stream is reduced or the amount of air is increased when the measured burner or flame temperature at a certain time t in the dynamic curve greater than the calculated burner or flame temperature T. ₁ (t) at this time t is, or the fuel gas flow is increased or the amount of air is reduced if the measured burner or flame temperature at a certain time t in the dynamic curve smaller than the calculated burner or flame temperature T ₁ (t) to this Time t is. Method for controlling a fuel gas-air mixture according to claim 1 or 2, characterized in that the determination of the time profile of the burner or flame temperature according to a formula

where τ is a control parameter. Method for controlling a fuel gas-air mixture according to one of claims 1 to 3, characterized in that the method is terminated when the measured burner or flame temperature of the burner or flame set temperature T ₂ corresponds. Method for controlling a fuel gas-air mixture according to claim 4, characterized in that the regulation of the fuel gas-air mixture after reaching the desired flame temperature T _{2 is carried out} according to a conventional PI control.