EP0697564B1 - Method for controlling and monitoring the combustion in a furnace - Google Patents

Description

The invention relates to a method for regulation and Monitoring the combustion of a furnace according to the generic term of claim 1.

To save energy and avoid environmental damage Monitoring or regulation of combustion processes in combustion plants indispensable. The measurement of the oxygen content in Exhaust gases alone cannot indicate complete combustion deliver. It is therefore particularly important to determine the proportions of the Exhaust gas contained and unburned components to record and reduce. These unburned ingredients include Carbon monoxide and hydrogen. If there is an incomplete Combustion, hydrogen and carbon monoxide emissions occur in the exhaust gas always together. The exact ratio of hydrogen carbon monoxide, however, can vary depending on the burner setting Load factor, fuel load as well as air temperature and air pressure vary. As a benchmark by which it can be seen whether an incomplete Combustion begins, the occurrence of hydrogen as well as the occurrence of carbon monoxide in the exhaust gas will.

In the German patent application DE 43 40 534 A1 there is a method for controlling and monitoring an incineration plant, the operating point of the firing system then cyclically it is checked whether its setting the smallest possible excess of oxygen guaranteed in the exhaust gas. For the detection of the exhaust gas components two sensors are used, one for Determination of the oxygen content is used, and the second for detection of the hydrogen content in the exhaust gas. The signal input and Signal outputs of the two sensors are connected to the signal inputs and outputs of a processing unit connected, among other things all fault messages are output. The output signal of the Processing unit is fed to a control device. This can with its output signal, which is fed to an actuator the air supply to the incinerator using a Control air flap. With the probe used to capture the hydrogen is provided in the state of complete combustion the oxygen concentration in the exhaust gas can also be determined. In order to it is possible to use the two probes for mutual monitoring use, which increases the safety of the system. Disadvantageous however, this method requires two probes be, which increases the circuit complexity of the control doubled.

The invention has for its object a method for fail-safe To show monitoring and control of combustion plants, for that a minimum of probes as well as regulating and control devices is required.

This object is achieved by the features of the claim 1 solved.

A special feature of the method according to the invention is that only one sensor is required to monitor the furnace is. Its signal is monitored using a control and monitoring unit evaluated redundantly. The control and monitoring unit processes in addition to the stationary signal of the sensor, the signals from the actuators for the fuel and air supply and the dynamic signal from the sensor. She also investigates the differential change in the sensor signal with the change the position of the actuator for the air supply. Here is from made use of the fact that the goods to be monitored and regulated Firing system at least one adjustable air damper has, which is driven by a servomotor, and the respective Position of the air flap of the control and monitoring device is available as a measured value. For regulation and Monitoring of the firing system are carried out in addition to the stationary sensor signal U also the dynamic sensor behavior dU / dt as well the differential change in the sensor signal with the change in Actuator position dU / dS used. Another advantage of The procedure is that the functionality of the sensor is continuous is checked. This check is done once by registration the signal change of the sensor with a brief change the sensor temperature and secondly by registering one short signal rise when starting the furnace. Of the The sensor signal increases when the firing system is started through a brief increase in hydrogen / carbon monoxide emissions evoked. The sensor used is in DE-A-40 21,929. It has two measuring electrodes and one Reference electrode. One of the measuring electrodes is oxidation catalytic inactive and thus enables the hydrogen content to be recorded in the exhaust gas. The second measuring electrode is catalytically active. It can be used to determine the oxygen content in the exhaust gas. in the pollutant-free operation, without oxidizable flue gas components, the oxygen concentration of the exhaust gas can be determined from the sensor signal determine. If flammable gas components occur in the Exhaust gas, such as hydrogen or carbon monoxide, takes the sensor signal significantly higher values, from which the concentration of the oxidizable Gas components can be determined.

Fig. 1

eine Feuerungsanlage mit einer Regelungs- und Überwachungeinheit sowie einem Sensor,

Fig. 2

die Signalverläufe des Sensors,

Fig. 3, 4, und 5

die zeitlichen Verläufe des Sensorsignals,

Fig. 6

die Signalverläufe des Sensors bei Temperaturänderung,

Fig. 7

die Signalverläufe des Sensors nach dem Zünden des Brenners.

Further features essential to the invention are characterized in the claims. The invention is explained below with the aid of schematic drawings. Show it:

Fig. 1

a furnace with a control and monitoring unit and a sensor,

Fig. 2

the signal curves of the sensor,

3, 4 and 5

the time profiles of the sensor signal,

Fig. 6

the signal curves of the sensor when the temperature changes,

Fig. 7

the waveforms of the sensor after the burner has been ignited.

Fig. 1 shows a furnace 1, with a burner 2, one Furnace 3, an actuator 4 for the fuel supply Burner, an actuator 5 for the air supply to the burner, one Exhaust duct 6, a sensor 7 and a control and monitoring unit 8. The sensor 7 is at the exit of the furnace 3 installed in the exhaust duct 6. Its signal inputs and outputs 7A and 7B are connected to the signal inputs and outputs 8A and 8B Control and monitoring unit 8 in connection. The signal outputs 8V and 8W of the control and monitoring unit 8 are included the signal inputs of the actuators 4 and 5 for the supply of Fuel and the supply of air to the burner 2 connected.

2 shows various states of the furnace 1. Curve U shows the course of the stationary sensor signal, which can pass through areas A, B, C. In area A there is incomplete combustion due to lack of air, in area B there is incomplete combustion due to excess air and in area C there is complete combustion. As shown in Fig. 2, incomplete combustion can occur due to lack of air as well as excess air. If the excess of air is very high, the flame is cooled and the flame is incompletely burned due to the low temperature of the flame. In area C of complete combustion, the residual oxygen in the flue gas can be determined from the stationary sensor signal. In this area, a conventional lambda control can be carried out with the sensor 7. If the burner 2 moves into an area of incomplete combustion, the emission of unburned gas components such as hydrogen and carbon monoxide increases. The consequence of this is that the value of the stationary sensor signal U changes. Incomplete combustion is recognized by the control and monitoring unit 8 when the value of the stationary sensor signal U exceeds a defined limit value U _GM or U _GÜ . As can be seen from the course of the stationary sensor signal U, the limit value U _GM before the transition to area A with lack of air is greater than the limit value U _GÜ before the transition to area B with excess air. These limit values are stored once in the control and monitoring unit 8. If the combustion system moves from the state of complete combustion in the direction of incomplete combustion, the control and monitoring unit 8 recognizes when one of these limit values U _GM or U _{GÜ is reached} whether the combustion system 1 is moving towards the state of incomplete combustion, which is due to lack of air or excess air is caused.
In FIG. 2, the signal curve U of the sensor 7 is plotted over the respectively associated position S of the actuator 5. As can be seen from FIG. 2, the increase in hydrogen and carbon monoxide in the exhaust gas also increases the gradient α = dU / dS of the curve U. Incomplete combustion is additionally recognized by the control and monitoring unit 8 when the gradient α = dU / dS amounts to a limit value α _GM = | dU _M / dS _M | or. α _GÜ = | dU _Ü / dS _Ü | exceeds. These limit values are also stored once in the control and monitoring unit 8. Thus, the transition to incomplete combustion in the event of a lack of air as well as an excess of air can also be recognized by the control and monitoring unit 8 in this way. Countermeasures are initiated automatically by the control and monitoring unit 8. These can consist of an increase in the air supply when the combustion system moves into the area of lack of air, or a reduction in the air supply if the incomplete combustion takes place due to excess air. In the case of an already aged sensor, the sensor signal U _{A has} a smaller gradient α _A = dU _A / dS when an incomplete combustion is used than in the case of a new sensor. However, the slope α _AM or α _AÜ is now even greater than a fixed and stored limit value α _OM or α _OÜ . The limit values α _OM and α _OÜ are determined from the signal curve U _O plotted in FIG. This is plotted over the respectively associated position S of the actuator 5. The signal curve U _O corresponds to that of a sensor 7 if it works as a pure oxygen sensor or has lost its ability to detect hydrogen or carbon. A value α _{O is} assigned to each actuator position S. These values α _O correspond to the slope α _O = dU _O / dS of the sensor signal U _O at the respective actuator position S. When the limit values α _OM or α _{OÜ are reached} , the control and monitoring unit 8 recognizes that the combustion system is incomplete combustion during operation transforms. If the values α _O of the sensor signal U of the sensor 7 are reached or fallen below, the control and monitoring unit 8 recognizes that the sensor 7 must be replaced due to aging.

Another security check for monitoring the furnace can be derived from the dynamic course of the sensor signal dU / dt. This will be explained with reference to FIGS. 3, 4 and 5. In area C, when there is complete combustion, the oxygen content in the exhaust gas changes only slowly. Accordingly, the sensor voltage changes only slowly over time, ie dU / dt is small. If the combustion system 1 is in the state of incomplete combustion irrespective of whether there is a lack of air or excess air, hydrogen or carbon monoxide is emitted. These emissions do not occur uniformly, but more or less pulsating depending on the flame pattern. Sensor 7 follows these rapid changes in hydrogen and carbon monoxide emissions. The sensor signal becomes restless. As shown in FIG. 5, the dynamic signal curve dU / dt exceeds a limit value G _D. Regardless of the stationary sensor signal, the control and monitoring unit 8 can use the course of the dynamic signal to recognize whether the combustion system is in the state of incomplete combustion or not. Countermeasures are then automatically initiated by the control and monitoring unit 8.

All the above-described values α _O and limit values U _GM , U _GÜ , α _GM , α _GÜ , α _OM , α _OÜ , α _AM , α _AÜ , G _D , which are required for monitoring the furnace 1, are preferably used when commissioning the Firing system stored in the control and monitoring unit 8. For this purpose, the combustion system is brought into the states that can occur during its later operation.
The functionality of the sensor 7 itself can also be monitored by registering the sensor signal change when the sensor temperature changes briefly. A brief change in the sensor temperature will cause a brief change in the sensor signal in a functional sensor 7. This test can be performed either when the burner is shut down in air or when the burner is pre-vented, or while it is operating during a complete combustion condition. The temperature change is caused, for example, by a brief change in the heating voltage, as shown in FIG. 6. If no change in the sensor voltage dU is detected, the measuring electrode (not shown here) is faulty and the sensor 7 must be replaced.

Checking whether the measuring electrode (not shown here) of the sensor 7 is still able to detect hydrogen or carbon monoxide, can be made while the burner is starting up will. This test is explained with reference to FIG. 7. When igniting the burner inevitably produces a short-term hydrogen / carbon monoxide emission, which the sensor 7 detects when its sensitive function is OK. Sensor 7 detects briefly after the ignition process the increase in hydrogen and / or carbon monoxide not, it is defective and must be replaced. This is also displayed by the control and monitoring unit 8.

Claims (3)

1. Method for controlling and monitoring the combustion of a furnace (1) having a burner (2) for solid and liquid fuels, downstream of which furnace (1) a sensor (7) is connected, the actuators (4 and 5) for the supply of fuel and air for the burner (2) being controlled by a control and monitoring unit (8) to whose signal inputs the sensor (7) is connected, characterized in that in order to carry out the method a sensor (7) is used with which both the hydrogen content and the oxygen content in the exhaust gas of the furnace (1) can be determined, in that, before the furnace is commissioned, the limiting values U_GM and U_GÜ of the steady-state sensor voltage signal U is sensed in the case of upward transgression into the regions of incomplete combustion with excess air or a deficiency of air and stored, in that the limiting values α_GM = |dU_M/dS_M| and α_GÜ = |dU_Ü/dS_Ü| at which a change-over to incomplete combustion in the case of excess air or a deficiency of air takes place are determined from the profile of the voltage signal U of the sensor (7) by means of the respectively associated positions S of the actuator element (5) for the feeding in of air, and are stored, in that, in order to detect the malfunctioning of the sensor (7), the values of the increases α_O = dU_O/dS are determined from the profile of the voltage signal U of the sensor (7) by means of the respectively associated positions S of the actuator element (5) for the feeding in of air when the sensor (7) has exclusive sensitivity to oxygen, and are stored, in that these values α_O and the limit values α_OM and α_OÜ which are determined and at which complete combustion changes over into the state of incomplete combustion are stored, in that the profile of the voltage signal U of the sensor (7) is continuously monitored by the control and monitoring unit (8), and using the values α_O and limiting values U_GM and U_GÜ, α_GM and α_GÜ, α_OM and α_OÜ, respectively, which are stored in the control and monitoring unit 8, the change-overs to incomplete combustion in the case of a deficiency of air and excess air are detected and, when one of these limiting values U_GM and U_GÜ, α_GM and α_GÜ, α_OM and α_OÜ, respectively, is reached, counteracting measures in the form of an increase or a reduction in the supply of air are automatically initiated, in that the control and monitoring unit (8) additionally monitors the signal profile dU/dt of the sensor (7) and, when a limiting value (G_D) which relates to this and is also stored in the control and monitoring unit (8) is exceeded the furnace (1) is adjusted to complete combustion, and in that, in addition to checking the sensor (7), the heating voltage is changed and the brief emission of hydrogen/carbon monoxide when the burner is switched on is utilized.
2. Method according to Claim 1, characterized in that, in order to check the sensor (7) with the aid of the control and monitoring device (8) the heating voltage of the sensor (7) is changed and, when the sensor signal U is unchanged a malfunction of the sensor (7) is displayed by the control and monitoring unit (8).
3. Method according to one of Claims 1 or 2, characterized in that, in order to check the sensor (7), the brief emission of hydrogen/carbon monoxide when the burner is switched on is utilized, and when the sensor signal U is unchanged a malfunction of the sensor (7) is displayed by the control and monitoring unit (8).

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