EP0339135A1 - Composite controlling apparatus for a burner - Google Patents

Abstract

The composite controlling apparatus (1) receives "more" or "less" signals from a heating capacity control device (12), converts these into fuel adjustment pulses (BI) and integrates these and adds them up, so that a signal for the acute fuel flow (BS) is produced. This is supplied to a fuel flow valve setting module (25) and a fuel flow flap setting module (28). In these modules (25, 28), a few fixed points of a function are stored in each case; the other points are defined by third degree interpolations. In these modules (25, 28), there are also formed valve adjustment pulses (VI) and flap adjustment pulses (KI) respectively, with which a fuel servomotor (3) and an air servomotor (6) are driven and in this manner a fuel actuator (4) and an air actuator (7) are adjusted. For the correction of disturbances, interference signal modules (31) are possibly present. The apparatus serves for the regulation of the burner of heating systems and the like and is more simple than known composite controlling apparatuses. <IMAGE>

Description

The invention relates to a compound control device for a burner, primarily in a heating system.

In a heating system, but also in other combustion systems, a fuel flow flowing to a burner - oil, gas, also coal dust or wood chips - and an associated air flow have to be set and regulated in such a way that the fuel burns completely with the air on the one hand and only a small amount on the other Excess air occurs, which also absorbs combustion heat and dissipates a corresponding proportion of the combustion heat unused through the chimney, and that the lowest possible proportion of pollutants occurs.

The fuel flow is adjusted via a control valve, a gas flap, a speed-adjustable pump or - in the case of bulk goods - by a dosing system, the air flow via a speed-controlled blower or an air flap. These actuators are set according to the heating power required.

For some time now, compound control devices have become known which, depending on the heating power to be supplied by the heating system, bring both actuators for the fuel flow and those for the air flow into a position which enables complete combustion, with a single primary actuating device, for example an actuating motor. DE-OS 28 27 771 describes a purely mechanical device for this purpose.

US Pat. No. 4,545,009 describes an electrical compound control device for a burner of a steam boiler system, in which a required fuel flow is calculated on the basis of a measured steam pressure (by means of which the heating power can be determined). There are few in a memory of the compound control device Fixed points of a function between the position of the fuel valve and the fuel flow. The position of the fuel valve associated with the required fuel flow is determined by a linear interpolation between adjacent fixed points. At the same time, a linear interpolation is used to determine the required fuel flow and a function, also stored and containing a few fixed points, between the fuel flow and an air excess necessary for its complete combustion, and an air flow required for complete combustion is calculated therefrom. From a further stored function, which also contains only a few fixed points, between the air flow and the position of an air flap, the position of the air flap for the desired air flow is determined by linear interpolation between adjacent fixed points. It is now checked whether the fuel flow increases or decreases. If it rises, the air flow is set first, if it falls, the fuel flow is set first. The setting of the other flow is carried out in such a way that the current air flow is always greater than the air flow required by the fuel flow. In claim 1, US Pat. No. 4,545,009 is assumed to be the closest prior art.

In order to precisely determine the air flow at which the combustion takes place completely with the smallest excess of air, a point is determined with a CO probe in the combustion gas of the heating, going from high to low excess air, at which the CO content in the combustion gas increases. The air flow to be set is then set slightly larger than this point. However, since CO probes are relatively susceptible to wear, this method cannot be used continuously, but only for example during commissioning and maintenance. Therefore, for a given burner output, the O₂ content or the soot content, which can be measured with more robust probes, is determined as a function of the heating output for this point found with a CO probe and these values are used to adjust the Servomotor used for the air flap (DE-OS 35 26 384).

Types of fuel differ in their calorific value. If a different type of fuel is used, a different fuel flow must therefore be set for the same heating output, and the air flow at which the combustion takes place completely changes as well. The necessary measures are described for heating systems which do not work with compound control devices in US Pat. No. 4,576,570.

The invention has for its object to provide a composite control device with which the actuators for the fuel flow required by the heating power and the air flow required for a complete combustion of this fuel flow with a small excess of air can be set in a simpler manner than previously and can be adjusted without disturbance.

This object is achieved by the features of claim 1, the remaining claims contain advantageous embodiments and a method for setting such a compound control device.

• Fig. 1 ein Blockschaltbild einer elektrischen Einrichtung eines Brenners,
• Fig. 2a ein Diagramm für das Signal an einem Heizleistungseingang in Abhängigkeit von der Zeit in einer Regelphase,
• Fig. 2b ein Diagramm von Brennstoff-Verstellimpulsen in Abhängigkeit von der Zeit in einer Regelphase,
• Fig. 2c ein Diagramm über das Ausgangssignal am Eingangsmodul über die Zeit einer Regelphase,
• Fig. 2d ein Diagramm von Ventil-Verstellimpulsen in Abhängigkeit von der Zeit in einer Regelphase,
• Fig. 2e ein Diagramm von Klappen-Verstellimpulsen in Abhängigkeit von der Zeit in einer Regelphase,
• Fig. 3 die Stellung eines Brennstoffventils eines Brenners als Funktion des Brennstoffstroms und
• Fig. 4 die Stellung der Luftklappe des Brenners als Funktion des Brennstoffstroms.

The invention is explained in more detail by way of example with reference to the drawing, which show

• 1 is a block diagram of an electrical device of a burner,
• 2a shows a diagram for the signal at a heating power input as a function of time in a control phase,
• 2b shows a diagram of fuel adjustment pulses as a function of time in a control phase,
• 2c is a diagram of the output signal at the input module over the time of a control phase,
• 2d shows a diagram of valve adjustment pulses as a function of time in a control phase,
• 2e shows a diagram of flap adjustment pulses as a function of time in a control phase,
• Fig. 3 shows the position of a fuel valve of a burner as a function of the fuel flow and
• Fig. 4 shows the position of the air flap of the burner as a function of the fuel flow.

The electrical device of a burner shown in FIG. 1 consists of a compound control device 1 which has two electrical fuel setting outputs 2a and 2b to form a fuel servomotor 3 which is mechanically connected to a fuel actuator designed as a valve 4. Two electrical air adjustment outputs 5a and 5b continue from the composite control device 1, which lead to an air servomotor 6 which is mechanically connected to an air flap 7 serving as an air actuator. The fuel servomotor 3 and the air servomotor 6 are synchronous or stepper motors, the duration of their adjustment ranges is known and constant. A valve position sensor 8 is connected to a valve position input 9 and a flap position sensor 10 is connected to a flap position input 11 of the compound control device 1. The valve 4 controls the fuel flow BS (FIG. 3, FIG. 4) and the air flap 7 controls the air flow. However, it is also possible to use other actuators instead of the valve 4 and the air flap 7.

The composite control device 1 receives its input values from a heating power control device 12, for example from a universal controller described in the RWF 32,000 brochure from Landis & Gyr, which sends a signal "more heating power" to a heating power input 13a of the composite control device 1, to another heating power Input 13b a signal "less Heat output "can be output. Measurement sensors 14 are connected on the input side to the heating line control device 12. The heating power control device 12 can be integrated in the composite control device 1.

At least one interference signal generator 15 can be connected to the composite control device 1. At least one sensor 14 is also connected to it and it is electrically connected to an interference signal input 16 of the composite control device 1. The interference signal generator 15 can be integrated in the compound control device 1.

For programming the network control device 1, a hand terminal or a computer 17 with a display 18 and a keypad 19 can be connected to a computer input 20 of the network control device 1. Furthermore, control inputs 21a to 21n and monitoring outputs 22a, 22b can also be connected to it.

The composite control device 1 is constructed as a microcomputer and contains storage devices and functional modules, which partly consist of hardware and partly of software.

The signal input into the heating power input 13a, 13b is fed to an input module 23 and converted there, the signal to be processed further via a first switch 24 to a fuel flow valve position module 25 and from there via a second switch 26 and a valve setting time. Module 27 is given a connection for "more" and "less" to the fuel setting outputs 2a, 2b.

Between the first switch 24 and the fuel flow valve position module 25, the signal present there also goes to a fuel flow valve position module 28 and from there via a third switch 29 and a valve setting time module 30 via a connection for "more "and" less "to the air setting outputs 5a, 5b.

If interference signals are to be processed, each interference signal input 16 is connected to an interference signal input module 31 and from there a processed signal is transmitted via an interference signal adapter 32 either into the connection between the input module 23 and the fuel flow valve position module 25 or between the input module 23 and the fuel flow flap position module 28. In the example shown, the only interference signal adapter 32 is switched on in the connection to the fuel flow flap position module 28 and passes on its signal multiplicatively.

Connections lead from the computer input 20 to a program module 33, which can switch the switch 24 between the above-mentioned connection from the input module 23 and a connection from the program module 33, so that in the latter case, data from the computer, for example for programming, into the composite control device 1 , in particular into the fuel flow valve position module 25 and the fuel flow flap position module 29.

Connections from the heating power inputs 13a, 13b, from the program module 33 and from the control inputs 21a to 21n lead to a control module 34. The control module 34 switches the second switch 26 leading to the valve setting time module 27 between a connection to the fuel flow valve position module 25 and the third switch 29 leading to the flap setting time module 30 between a connection to the fuel flow valve setting module 28 and one connection to the control module 34.

A monitoring module 35 is connected to all modules of the composite control device 1; only the reciprocal connection to the control module 34 is shown in FIG. 1. Furthermore, the monitoring module 35 connects to the monitoring outputs 22a, 22b.

In the diagram shown in FIG. 2a, the course of the represented during a control phase at heating power input 13a, 13b as a function of time t. In this case, the heating power control unit 12 repeatedly sends signals “of the same time” or “less” at the same time, with a pause time that is long compared to the signal length, to the input module 23 of the composite control system 1 until the burner with its actual Heating power at a heating power setpoint time 36 has reached the desired target heating power. The rule phase is thus considered to have ended. The length of the signals "more" or the signals "less" can be, for example, a maximum of 20 seconds and becomes shorter as the target heating power is approached, the pause time can be 1 minute.

In the input module 23, brief, simultaneous fuel adjustment pulses BI (typical pulse length 0.1% of the entire adjustment range) are formed during each of these signals. These are shown in FIG. 2b as a function of the time t for the case in which the heating power control unit 12 emits the signal “more” and the fuel adjustment pulses BI are therefore positive. These fuel adjustment pulses BI are integrated and standardized so that their integral, added to a stored signal corresponding to the fuel flow BS (FIGS. 3 and 4) at the beginning of the control phase, at the end of the control phase at the output of the input module 23 is a setpoint the corresponding signal of the fuel flow BS. At the output of the input module 23, a signal is thus emitted which, increasing in steps with the fuel adjustment pulses BI, corresponds to the current fuel flow BS. This is shown in diagram 2c.

The values of the signal corresponding to the fuel flow BS formed by the integration of the fuel adjustment pulses BI are given to the fuel flow valve position module 25. In it are the point at the beginning of the control phase of a function shown in FIG. 3 between the fuel flow BS and the position BV of the valve 4 used as fuel actuator 4 temporarily and a few (for example 5 to 14) fuel fixed points BF1 to BFn of this function are stored permanently and with it the other points of this function can be interpolated by a higher than linear, for example third, degree four neighboring fuel fixed points BFi can be calculated. The third degree interpolation takes into account the shape of the function with an inflection point. Starting from the position BV of the valve 4 at the start of the control phase, the correspondingly required positions BV of the valve 4 are now successively calculated as a function of the change in the fuel flow BS to be caused by the fuel adjustment pulses BI. The associated valve (= fuel actuator) adjustment pulses VI, whose timing is shown in FIG. 2d because of the change in the slope of the function shown in FIG. 3, are sent to the valve setting time module via the second switch 26 27 passed on.

The second switch 26 establishes a connection between the fuel flow valve setting module 25 and the valve setting time module 27 as long as the signal "more" or "less" is connected to the heating power input 13a, 13b connected to it via the control module 34. is present. If the signal is not present, it can be switched.

The valve response time module 27 determines the position BV of the valve 4 via the valve position sensor 8. Due to the incoming valve adjustment pulses VI, it moves the position BV of the valve 4 via the fuel setting outputs 2a, 2b requiring "more fuel" or "less fuel" and the valve servomotor 3 until the heating output control device 12 has reached the heating power setpoint time 36. This tracking only takes place when the accumulated valve adjustment pulses VI have reached a certain period of time in order not to place excessive strain on the fuel servomotor 3.

With this control mode, changes in the calorific value of the fuel are also corrected, since the regulating phase lasts until the desired heating power required by the heating power control unit 12 is set independently of the calorific value of the fuel.

Each value of the fuel flow BS includes a value of an air flow in which the fuel is burned completely with a small excess of air. The air flow is set by the position LK of the air flap 7, which is shown as a function of the fuel flow BS in FIG. 4 and is set by the fuel flow air flap module 28. Few air fixed points LF1 to LFn for the same fixed fuel flow values as in the fuel flow valve position module 25 are permanently stored in an associated memory. The other points of this function are calculated by an interpolation of a higher than linear, for example third degree between each four adjacent fixed air points LFi. In addition, the point of this function for the value of the fuel flow BS is temporarily stored at the beginning of the control phase.

To determine the air fixed points LFi, the air flow corresponding to the fuel flow BS is set in each case during commissioning or when changing over. For this purpose, for example, a CO sensor is introduced into the combustion gas of the burner. It is used to change the air flow from large values to small values for each fuel flow BS corresponding to a fuel fixed point BFi by changing the position LK of the air flap 7 until the CO content increases. A position LK of the air flap 7 which is shifted slightly to larger values of the air flow is then the position LK of the air flap 7 which belongs to the fuel flow BS of the fuel fixed point BFi and is stored permanently in the fuel flow flap position module 28.

The fixed air points LFi thus represent those positions LK of the air flap 7 that for the fixed fuel points BFi corresponding fuel flows BS each generate an air flow which ensures complete combustion with a small excess of air. However, this only applies to a constant fuel composition.

During the control phase, the fuel adjustment pulses BI are fed to the fuel flow flap position module 28 and the positions LK of the air flap 7 and thus the flaps (= air actuator) - shown in FIG. 2e over time in the control phase - are calculated and adjusted given to the flap setting time module 30 via the switch 29.

If there is no normal burner operation in the heating system, position commands for the operating states "burner off", "preliminary ventilation", "ignition" etc. can be carried out via the switch 26 from the control module 34 via the valve setting time module 27 and the fuel Servomotor 3 to the fuel valve 4 or via the switch 29 and the flap setting time module 30 and the air servomotor 6 to the air flap 7.

The flap setting time module 30 determines the position LK of the air flap 7 via the flap position sensor 10. On the basis of the incoming flap adjustment pulses KI, it adjusts the position LK of the air flap 7 via the air setting outputs 5a, 5b and the air servomotor 6 which correspond to the two signs, so that the combustion always takes place completely with a small excess of air. If the valve adjustment pulses VI are too small for immediate tracking, the corresponding flap adjustment pulses KI are not yet carried out. A new fuel adjustment pulse BI can only begin when both the previous valve adjustment pulse VI and the previous flap adjustment pulse KI have been completed.

In order to avoid a lack of air during the control phase, when the fuel flow BS is adjusted to "more", a first flap adjustment pulse KI is carried out before the associated valve adjustment pulse VI is carried out synchronously with the second flap adjustment pulse KI at the earliest. When the fuel flow BS is adjusted to "less", a first valve adjustment pulse VI is first carried out before the associated flap adjustment pulse KI is carried out synchronously with the second valve actuation pulse VI at the earliest.

In order to avoid hysteresis when adjusting the valve 4 and the air flap 7, one of the adjustment directions, for example after "less", is adjusted beyond the positions BV of the valve 4 and KV of the air flap 7 corresponding to the heating output set point 36 and then both actuators 4, 7 are reset so that, regardless of the direction of adjustment, they always approach the point corresponding to the heating output set point 36 without hysteresis in the same direction.

Compared to known devices, the described composite control device 1 does not require any additional memory with an interpolation device for the excess air required for a fuel flow BS, since, to a greater extent, the interpolations are carried out, the avoidance of lack of air during the control phase is carried out in a simpler manner and it does not show any Hysteresis for control adjustments.

If the burner has a baffle plate, a flue gas recirculation or a similar assembly to be controlled depending on the fuel flow BS, these assemblies can be controlled by the same function groups as the air flap 7 depending on the fuel flow BS.

If the combustor is to be used to burn different fuels with a different chemical composition in particular, then a number of pairs of fuel flow valve position modules 25 and fuel flow flap position modules 28 with different first and second functions for each pair must be used in accordance with the number of fuels Compound control device 1 to be available. Each pair is then intended for one fuel, the pairs are selected via a switch.

As a disturbance variable, for example, the change in air temperature can occur, which generates a variable mass air flow from the delivered volume air flow via the high temperature expansion coefficient of the air - this should be kept constant in order to maintain the combustion conditions. In order to form the mass air flow from the volume air flow, the air temperature is measured at a suitable point in the air supply and converted into an electrical signal which indicates a temperature-related air density deviation from a desired value. This signal is input at the interference signal input 16 of the compound control device and the output of the input module 23, which corresponds to the fuel flow BS, is multiplied by the reciprocal of this signal immediately before the fuel flow flap position module 28. The resulting flap adjustment pulses KI then result in a change in the air flow, which ensures complete combustion with a small excess of air.

In certain cases, the burner is monitored by an oxygen monitoring system which specifies a specific target oxygen content in the combustion gas for each value of the fuel flow BS, in order to indicate that the combustion takes place completely with a small excess of air. The value of the oxygen content deviates from the target value when the air flow and fuel flow BS are initially set correctly, for example if the composition of the fuel changes. This deviation is entered as an electrical signal at the relevant interference signal input 16 of the compound control device 1. From the deviation, the air flow change required for correction is determined as a percentage of the air flow required for the fuel flow BS in question. By this percentage, the output of the input module 23, which corresponds to the fuel flow BS, is changed before the fuel flow flap position module 28 with the correct sign to get correct position LK of the air flap 7 for the fuel of the other composition.

Claims (10)

1. compound control device for a burner,
which receives signals "more" or signals "less" from a heating output control unit (12) at a heating output input (13a, 13b) and processes them until the burner has reached a desired heating target output,
- With which the positions (BV) of a fuel actuator (4) and associated positions (LK) of an air actuator (7) can be adjusted,
which contains a microcomputer which has memory,
- Which contains a fuel flow valve position module (25) in which a sequence of a few fuel fixed points (BFi) a first function between a fuel flow (BS) and the position (BV) of the fuel actuator (4) can be stored and with the further points of this first function can be calculated by interpolations, and
- which always regulates the position (LK) of the air actuator (7) as a function of the fuel flow (BS) in such a way that combustion takes place completely in the burner with a small excess of air,
characterized,
- That in a fuel flap position module (28) a sequence of a few airflow fixed points (LFi) a second function between the fuel flow (BS) and the position (LK) of the air actuator (7) can be stored and other points of this second Function can be calculated by interpolations,
- that the interpolations are of a higher than linear degree,
- That the signals output by the heating power control unit (12) "more" or signals "less" with the same sign are subdivided into short-term, simultaneous fuel adjustment pulses (BI), these are integrated into a signal corresponding to the current fuel flow (BS) and from this fuel actuator. Adjustment impulses (VI) and Air actuator adjustment pulses (AI) of different durations are formed. 2. Compound control device according to claim 1, characterized in that it has a computer input (20) to which a computer (17) or a hand terminal can be connected for programming. 3. Compound control device according to claim 1 or 2, characterized in that when adjusting the heating power after "more" first an air actuator adjusting pulse (KI) is carried out before the associated fuel actuator adjusting pulse (VI) at the earliest synchronously with the second air actuator adjustment pulse (KI) is executed, and when the heating power is adjusted to "less", a first fuel actuator adjustment pulse (VI) is carried out before an air actuator adjustment pulse (KI) at the earliest synchronously with a second Fuel actuator adjustment pulse (VI) is executed. 4. Compound control device according to one of claims 1 to 3, characterized in that when adjusting the fuel actuator (4) and the air actuator (7) in one direction of adjustment first of the position corresponding to the heating target power (BV) of the fuel -Actuator (4) and and the corresponding position (LK) of the air actuator (7) is extended so that these positions (BV, LK) corresponding to the heating set power can always be approached from the same direction regardless of the direction of adjustment. 5. Compound control device according to one of claims 1 to 4, characterized in that for the combustion of fuels of different composition, a number of pairs of fuel flow valve position modules (25) for storing fuel fixed points (BF1 to BFn) corresponding to the number of fuel types. and fuel flow flap position modules (28) for storing air fixed points (LF1 to LFn) are present and for each Type of fuel that the corresponding one of these pairs can be used. 6. Compound control device according to one of claims 1 to 5, characterized in that disturbance variables, which are measured with sensors (14) and can be given via an interference signal transmitter (15) to an interference signal input (16) of the composite control device (1) and for correcting the positions ( BV, LK) of the fuel actuator (4) and / or the air actuator (7) can be processed. 7. Compound control device according to claim 6, characterized in that the disturbance variable is the temperature of the air flow, this is convertible into an electrical signal that indicates the temperature-related change in air density from a setpoint, this signal is entered at the interference signal input (16) of the compound control device (1) and the fuel adjustment pulses (BI) immediately before the fuel flow flap position module (28) are multiplied by the reciprocal of this signal. 8. Compound control device according to claim 6, characterized in that the disturbance variable is the oxygen content of the combustion gas, which can be converted into an electrical signal which indicates the deviation from the setpoint, this signal can be input at the interference signal input (16) into the compound control device (1) this deviation, an air flow change can be formed as a percentage of the set air flow and the fuel adjustment pulses (BI) in front of the fuel flow flap position module (30) can be changed by this percentage with the correct sign. 9. Compound control device according to one of the preceding claims, in which the burner contains a baffle plate and / or a flue gas recirculation or / and similar components to be controlled as a function of the fuel flow (BS) and in which these components each have the same functional group as the air flap (7 ) is controlled depending on the fuel flow (BS). 10. The method for setting a compound control device according to one of claims 1 to 8, characterized in that a CO probe is introduced into the combustion gas of the burner, for determining the air fixed points (LFi) of the fuel flow (BS) for a fuel fixed point ( BFi) and the air flow is changed by changing the position (LK) of the air actuator (7) from large values to small values until the CO content increases, the position belonging to the air fixed point (LFi) (LK ) of the air actuator (7) is then shifted slightly towards larger values of the air flow.

Images