EP2092241B1 - Method for controlling an evaporator burner - Google Patents

Description

The invention relates to a method for controlling an evaporator burner referred to in the preamble of claim 1 Art.

Such burners are advantageously used in heating systems of residential and non-residential buildings. The heat generated by the burner when burning the fuel, for example, heats water in a boiler. In burners for liquid fuels such as heavy oil, extra light fuel oil or kerosene exist burners exist two basic types, namely on the one hand burners in which the liquid fuel is atomized by means of a nozzle, which are referred to as atomizer, and on the other hand burner in which the liquid fuel is evaporated under heat, which are referred to as evaporator burner.

A burner of the type mentioned in the preamble of claim 1 is known from WO-A1-00 / 12935 known. It is especially suitable for burning fuel oil. Arranged is such a burner in the lower part of the boiler.

In order to keep the losses during operation of the boiler as low as possible, so as to obtain an optimal energy yield, heating boilers have been designed as so-called condensing boiler, in which the exhaust gas is condensed, so that the heat of condensation of the exhaust gas can be used. The boiler temperature is only as high as absolutely necessary. If, for example due to the prevailing weather for the operation of the heating a flow temperature of 30 degrees Celsius is sufficient, the boiler has this temperature. Such a burner is off WO-A1-2004 / 109183 known.

In WO-A1-00 / 12935 It is described that the evaporator chamber is electrically heated at the start of the burner. As soon as the flame burns, the evaporator chamber is then heated by the hot combustion gases flowing past the evaporator chamber, which is achieved by means of a deflecting collar. Thus, then the electric heater can be turned off.

At the WO-A1-2004 / 109183 known burner does not need such Umlenkkragens because the flame burns below the evaporator chamber, so that the rising hot combustion gases heat up the evaporator chamber without additional aids. Shown here are but also embodiments of a specially designed shell, with which the heating of the evaporator chamber serving part of the hot combustion gases can be influenced.

Out JP-A-5-312 320 a burner is known which has a gasification chamber. From the fact that according to the figure, the fuel supply is surrounded by a jacket of combustion air, it may be concluded that it is a Zerstäuberbrenner. Due to the signal of a temperature sensor in the wall of the gasification chamber, the commissioning process is controlled, the object being to improve the ignition behavior for the gasified fuel.

The same applies to JP-A-8-42846 , which discloses a method according to the preamble of claim 1. Here, when the temperature measured at the gasification chamber is higher than a threshold, the amount of air is increased and at the same time the amount of fuel is reduced. This apparently serves the purpose of avoiding overheating of the gasification chamber, because such overheating could lead to a repulsion of the flame in the gasification chamber, which must be avoided.

In burners of this type, the evaporation of the fuel, for example, extra light fuel oil, extremely important. So the temperature of the evaporator chamber must be high enough for the fuel to evaporate completely. Practice has shown that in the course of the operation of such a burner by aging phenomena and by deposits in the boiler incidents can occur.

The invention has for its object to drastically reduce the frequency of such incidents to ensure trouble-free operation for a long time.

The above object is achieved by the features of claim 1. Advantageous developments emerge from the dependent claims.

An embodiment of the invention will be explained in more detail with reference to the drawing.

• Fig. 2 ein solches Diagramm, in dem eine Regelgröße eingetragen ist,
• Fig. 3 ein weiteres solches Diagramm für einen möglichen Betriebsfall,
• Fig. 4 ein Temperatur-Leistungs-Diagramm,
• Fig. 5 ein weiteres Temperatur-Zeit-Diagramm für ein vorteilhaftes Regelverfahren und
• Fig. 6 ein Temperatur-Zeit-Diagramm bei einer Leistungsänderung.

Show it: Fig. 1 a heating diagram for the evaporator chamber at the start of a burner,

• Fig. 2 such a diagram in which a controlled variable is entered,
• Fig. 3 another such diagram for a possible operating case,
• Fig. 4 a temperature-performance diagram,
• Fig. 5 another temperature-time diagram for a favorable control method and
• Fig. 6 a temperature-time diagram with a power change.

Burners to which the present invention is applied are as mentioned, for example WO-A1-00 / 12935 and WO-A1-2004 / 109183 known, so that the structure of such a burner does not need to be described here.

In the Fig. 1 is shown a heating diagram for the evaporator chamber at the start of a burner. On the abscissa axis, the time is shown on the ordinate axis, the temperature of the evaporator chamber. The course of an evaporator chamber temperature actual value T _VDKIst is shown by a solid line. At time t ₀ , the burner is started. This starts the commissioning process. This includes in known. Way switching on the electrical heating of the evaporator chamber and the pre-ventilation of the combustion chamber. As a result, the temperature of the evaporator chamber increases. As soon as the temperature of the evaporator chamber has reached a certain set value, the oil supply for the burner is started and the flame is then produced by the ignition on the burner. This temperature is referred to as evaporator _{chamber start} temperature T _VDKSt . This happens at time t ₁ .

As a result, the evaporator _chamber is now further heated by the heat generated by the flame, so that the evaporator _chamber temperature actual value T _VDKIst continues to increase. If this evaporator _chamber temperature actual value T _{VDKIst has reached} a switching _limit T _VDKSch , the electric heater of the evaporator _chamber is switched off. This happens at time t ₂ . From this time t ₂ , the further heating of the evaporator chamber is now carried out solely by the boiler produced in the boiler Warmth. The evaporator _chamber temperature actual value T _VDKIst continues to rise and asymptotically reaches a limit value T _{VDK limit} .

Field measurements have shown that the reached threshold T _{VDK limit is} not constant. It can be _assumed that fluctuations of the limit value _VDK limit are _related to the calorific value of the heating oil used, possibly also influenced by the temperature of the supply air for the combustion process. However, it has also been shown that the limit T _VDKGrenz changes over time, so it could have something to do with the condition of the boiler.

_According to the invention, it is now provided that, when the burner is in operation, the evaporator _chamber temperature actual value T _{VDKIst is controlled} to an evaporator _chamber temperature setpoint T _VDKSoll by varying the amount of air supplied to the burner, which is accomplished by controlling a speed D of the blower , If the evaporator ammertemperatur actual value T _VDKIst greater than the evaporator chamber temperature Sollwe T _VDKSoll , the speed D of the fan is increased. Because this increases the amount of air supplied to the burner, the evaporator _chamber temperature actual value T _{VDKIst decreases} because the excess of the supplied cold air cools the evaporator chamber. If the evaporator _chamber temperature actual value T _{VDKIst is} smaller than the evaporator _chamber temperature setpoint T _VDKSoll , then the rotational speed D of the blower is reduced. Because this reduces the amount of air supplied to the burner, the evaporator _chamber temperature actual value T _{VDKactual rises} because the smaller amount of cold air supplied _causes the evaporator chamber to be cooled less.

so, dass der Verdampferkammertemperatur-Istwert T_VDKIst einen Verdampferkammertemperatur-Sollwert T_VDKSoll erreicht.According to the invention thus takes place a regulation of the speed D of the blower of the burner by a function $$\mathrm{D}=f\left({\mathrm{T}}_{\mathrm{VDKIst}}\right)$$

such that the evaporator _chamber temperature actual value T _{VDKIst reaches} an evaporator _chamber temperature setpoint T _VDKSoll .

The evaporator _chamber temperature setpoint T _VDKsoll depends on the design of the boiler and the burner and is for example 480 ° C. In determining the optimum evaporator _chamber temperature setpoint T _VDKSoll for a particular burner design, it is necessary to ensure by measuring the exhaust gas flow that the emission limits are met. If this is done with the necessary care, then it is also ensured by controlling the evaporator chamber temperature actual value T _VDKIst to the evaporator _chamber temperature setpoint T _VDKSoll that the burner is operated low in pollutants.

In the Fig. 2 the same representation is chosen as in the Fig. 1 However, instead of the resulting without a control of the evaporator _chamber temperature limit T _VDKGrenz said evaporator _chamber temperature setpoint T _{VDKSoll is located} . As soon as the evaporator _chamber temperature actual value T _{VDKIst reaches} the evaporator _chamber temperature setpoint T _VDKSoll , which is the case at the time t ₃ , the aforementioned regulation of the evaporator _chamber temperature sets in.

In the Fig. 3 is a similar diagram as in the Fig. 2 shown, but here an operating case is shown, in which the evaporator _chamber temperature actual value T _VDKIst the evaporator _chamber temperature setpoint T _VDKSoll not reached. This can be an indication, for example, that the amount of air is too large. The event at time t ₃ does not occur. For such a case is provided in an advantageous manner that after a certain time, namely at time t ₄ , the control uses forcibly. In this case, the amount of air is thus reduced by a corresponding reduction in the speed of the fan, which then increases as a result of the evaporator _chamber temperature actual value T _VDKIst . Now, therefore, the inventive control of the evaporator chamber temperature takes place. The time t ₄ depends on the burner type. It can be defined, for example, by a time interval at time t ₂ .

abhängig zu machen. Für eine bestimmte Brennerbauart beträgt der optimale Verdampferkammertemperatur-Sollwert T_VDKSoll beim Kleinlastwert P_min beispielsweise 450 °C und bei Nennlast P_Nenn beispielsweise 500 °C. Bei Heizleistungen zwischen diesen beiden Grenzen wird der Verdampferkammertemperatur-Sollwert T_VDKSoll durch eine Interpolation festgelegt.If the burner is a modulatable burner, in which the heating power P between a _{low load} value P _min and a rated load P _nominal can be varied continuously or in stages, it is advantageous to set the evaporator _chamber temperature setpoint T _VDKSoll of the heating power P according to a function $${\mathrm{T}}_{\mathrm{VDKSoll}}=f\left(\mathrm{P}\right)$$

to make dependent. For a particular type of burner, the optimum evaporator _chamber temperature set point T _{VDKSoll is} for small load value P _min, for example 450 ° C and nominal load P _Nenn, for example, 500 ° C. For heat _outputs between these two limits, the evaporator _chamber temperature setpoint T _{VDKSoll is} determined by an interpolation.

This is in the Fig. 4 shown. On the abscissa axis, the burner output is shown, on the ordinate axis, the temperature of the evaporator chamber. The small load value P _min is assigned a vaporizing chamber temperature setpoint T _VDKSollmin, the rated load P _nominal an evaporator chamber temperature setpoint T _VDKSollNenn. In between is interpolated, which is represented by a straight line connecting these two endpoints.

Based on Fig. 2 and 3 had been described when the regulation of the evaporator chamber temperature begins, namely in the case of Fig. 2 at time t ₃ , in the case of Fig. 3 at time t ₄ . In the Fig. 5 is shown a further advantageous solution that is applicable to both cases. In this case, the control of the evaporator chamber temperature is switched on after a fixed period of time Δt from the time t ₂ . This is referred to as time t ₅ . Only from this point on is the evaporator _chamber temperature setpoint T _VDKSoll effective. In the Fig. 5 Two possible cases are shown. A solid line shows how during the period Δt the evaporator _chamber temperature actual value T _VDKIst rises so that at time t _{5 is} lower than the evaporator _chamber temperature setpoint T _VDKSoll -Folglich is now reduced by the controller, the speed D of the blower, so that the control difference is corrected.

A dotted line shows a second case in which during the period Δt the evaporator _chamber temperature actual value T _VDKIst increases more strongly, namely in such a way that at time t _{5 it is} higher than the evaporator _chamber temperature setpoint T _VDKSoll . Consequently, the speed D of the fan is now increased by the controller, so that the control difference is compensated.

In the Fig. 6 a temperature-time diagram is shown, which relates to an operating case in which at a time t _6, the burner power is changed due to a change in power requirements. Before the time t ₆ , the burner with a first Heating power P ₁ in operation. Associated with this heating power P ₁ is a certain evaporator chamber temperature setpoint T _VDKSoll1 - At time t _6, the heating power P is changed, namely, a second heating output P _2, which is greater in this case than the first heating output P. ₁ The second heating power P ₂ is in accordance with what is in the Fig. 4 is shown, another evaporator _chamber temperature setpoint T _VDKSoll assigned, namely a higher second evaporator _chamber temperature setpoint T _VDKSoll2 . At time t ₆ thus results in a setpoint jump.

The consequence of this setpoint jump would be that the speed D of the fan would have to be reduced immediately, because at time t ₆ the evaporator _chamber temperature actual value T _VDKIst still corresponds to the evaporator _chamber temperature setpoint T _VDKSoll1 , if the evaporator _chamber temperature before the time t _6, the control difference was corrected , The reduction would be greater, the greater the setpoint jump.

However, this could mean that the amount of air supplied to the burner becomes so small that combustion would no longer be complete, ie substoichiometric. Thus, the exhaust gas contained unburned hydrocarbons, which is not allowed.

Therefore, it is advantageous to change the evaporator _chamber temperature setpoint T _VDKSoll not abruptly, but steadily. This is done by slowly adjusting the evaporator _chamber temperature set point T _VDKSoll . The transition from the first evaporator _chamber temperature setpoint T _VDKSoll1 to the second evaporator _chamber temperature setpoint T _VDKSoll2 thus occurs continuously, for example, according to a linear transition function. The constant adaptation takes place during a transitional period tÜ, so that only after its expiry at a time t _7, the second evaporator _chamber temperature setpoint T _{VDKSoll2 is} reached. The adaptation can also be done according to an e-function.

This continuous adjustment of the evaporator _chamber temperature setpoint T _VDKSoll is also in the opposite case, in which the second evaporator _chamber temperature setpoint T _{VDKSoll2 is} lower than the first evaporator _chamber temperature setpoint T _VDKSoll1 , makes sense, because so that the operation with excess air, which in terms of efficiency of Heating is disadvantageous, is avoided.

The present control system is characterized by the fact that it is relatively sluggish, because the mass of the evaporator chamber is relatively large and the heat transfer of air or combustion gas must be made to the evaporator chamber. So there are similar conditions with respect to the inertia of the controlled system as in the control of a room temperature. As a result, it is advantageous to design the controller used as a PI or PID controller, so that when controlling the evaporator chamber temperature actual value T _{VDKIst is controlled} according to a PI or PID Regela rorithm.

The regulation according to the invention of the evaporator chamber temperature actual value T _{VDKIst achieves} optimum evaporation of the heating oil. The invention also achieves a trouble-free burner operation over a long period of use, in which the emission limit values are maintained.

Claims (10)

1. Method for controlling an evaporator burner, which has an electrically heatable evaporator chamber to which heating oil to be burned is supplied, and which has a fan for supplying the combustion air, characterized in that an actual evaporator chamber temperature value (T_VDKIst) is regulated to a setpoint evaporator chamber temperature value (T_VDKSoll) when the burner is in operation, namely by varying the amount of air supplied to the burner, which is carried out by means of controlling a rotational speed (D) of the fan according to a function dependent on the actual evaporator chamber temperature value (T_VDKIst) in that the rotational speed (D) of the fan is increased when the actual evaporator chamber temperature value (T_VDKIst) is higher than the setpoint evaporator chamber temperature value (T_VDKSoll), and the rotational speed (D) of the fan is reduced when the actual evaporator chamber temperature value (T_VDKIst) is lower than the setpoint evaporator chamber temperature value (T_VDKSoll).
2. Method according to claim 1, characterized in that the setpoint evaporator chamber temperature value (T_VDKSoll) is approximately 480 °C.
3. Method according to claim 1, characterized in that when the burner can be modulated with respect to its output (P) in which a heat output (P) can be varied between a low load value (P_min) and a nominal load (P_Nenn), the setpoint evaporator chamber temperature value (T_VDKSoll) is varied according to a function depending on the heat output (P).
4. Method according to claim 3, characterized in that the low load value (P_min) is assigned a setpoint evaporator chamber temperature value (T_VDKSollmin) and the nominal load (P_Nenn) is assigned a setpoint evaporator chamber temperature value (T_VDKSollNenn), and that during the operation of the burner with an output (P) between these limits the setpoint evaporator chamber temperature value (T_VDKSoll) assigned to the respective output (P) is determined by interpolation.
5. Method according to claim 4, characterized in that the setpoint evaporator chamber temperature value (T_VDKSollmin) assigned to the low load value (P_min) is approximately 450 °C and the setpoint evaporator chamber temperature value (T_VDKSollNenn) assigned to the nominal load (P_Nenn) is approximately 500 °C.
6. Method according to one of claims 1 to 5, characterized in that control is performed according to a closed-loop PI control algorithm.
7. Method according to one of claims 1 to 5, characterized in that control is performed according to a closed-loop PID control algorithm.
8. Method according to one of claims 1 to 7, characterized in that when after the start of the burner the actual evaporator chamber temperature value (T_VDKIst) does not reach the setpoint evaporator chamber temperature value (T_VDKSoll), the control of the actual evaporator chamber temperature value (T_VDKIst) is initiated at a point in time (t₄) by force in such a way that the rotational speed (D) of the fan and thus the air quantity is reduced until the actual evaporator chamber temperature value (T_VDKIst) has reached the setpoint evaporator chamber temperature value (T_VDKSoll).
9. Method according to one of claims 1 to 7, characterized in that the control of the actual evaporator chamber temperature value (T_VDKIst) commences after the expiration of a fixed time interval Δt from a point in time (t₂) at which the electric heating of the evaporator chamber is switched off.
10. Method according to one of claims 1 to 7, characterized in that at a change in the heating output (P) and the subsequently following change in the setpoint evaporator chamber temperature value (T_VDKSoll) the change from a first setpoint evaporator chamber temperature value (T_VDKSoll1) to a second setpoint evaporator chamber temperature value (T_VDKSoll2) occurs in such a manner that a continuous adjustment of the setpoint evaporator chamber temperature value (T_VDKSoll) during a transition period (t_Ü) is carried out.

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