JP2551411B2 - Multistage control type air-fuel ratio control method and apparatus in combustion apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control method and device in a combustion device for performing appropriate combustion control in a combustion device such as a boiler or various industrial furnaces.

(Prior Art) The ratio between the theoretical air amount and the actual air amount required to burn a fixed fuel is called the air-fuel ratio and is represented by the following equation.

When the air-fuel ratio is brought close to 1, that is, the excess air amount is reduced, the combustion efficiency is improved, but the smoke generation amount is increased.

On the other hand, if the amount of excess air is too large, the combustion efficiency will deteriorate and the amount of NO _x and SO _x will increase. Therefore, combustion with an extremely small amount of excess air is desired from the viewpoint of pollution prevention.

FIG. 2 shows an air-fuel ratio control device in a conventional combustion device disclosed in JP-A-57-150728 (1).
Is a package boiler, (2) is a brackish water drum, (3) is a water supply pipe, (4) is a steam pipe, (5) is a burner, (6) is a fuel supply pipe, (7) is a blower, and (8) is exhaust gas. duct,
(10) is an automatic combustion control device (ACC) (12) is a control motor, (14) is a link mechanism, (15) is a fuel valve,
(16) is an air damper, (19) is an oxygen gas concentration analyzer (O ₂ sensor), and (20) is an O ₂ controller.

In the figure, the fuel supplied from the fuel supply pipe (6) and the air supplied by the blower (7) are blown into the combustion chamber of the package boiler (1) by the burner (5) and burned.

Steam generated from the brackish water drum (2) to the steam pipe (4)
To the load.

The steam pressure is guided from the steam pipe (4) of the package boiler to the automatic combustion control device (ACC) (10), and the level of this pressure causes the (ACC) (10) to send a signal to the control motor (12). The levers linked from the control motor (12) by the link (14) move together. A fuel valve (15) and an air damper (16) are jointed to the link (14) through a lever. If the characteristics of these valves and dampers are adjusted in advance, the fuel injection control to the boiler is mechanically performed by the movement of the control motor (12).

Further, O ₂ (oxygen concentration) is measured by the O ₂ sensor (19) inserted inside the exhaust gas duct (8).

Then, the signal is guided to the O ₂ controller (20), and acts so as to correct the air flow rate by controlling the rotation of the air blower (7) using a value that is predetermined based on the value of the opening signal as a set value. It is supposed to do.

Further, Japanese Patent Laid-Open No. 57-198920 discloses data indicating the relationship between the fuel valve opening and the fuel flow rate, the data indicating the relationship between the air damper opening and the air flow rate, and the excess air ratio to the fuel flow rate. By adjusting the fuel valve opening degree and the air damper opening degree based on the data representing the relationship so as to automatically have an appropriate relationship, and by inputting the detection data of the oxygen concentration in the exhaust gas of the combustion device, The data which shows the relationship of the air flow rate with respect to the air damper opening and which can be changed is shown.

(Problems to be Solved by the Invention) In the former conventional case as described above, the pressure adjustment in the boiler passes through the automatic combustion control device (ACC), the set pressure and the load at that time, that is, the steam usage amount, And a pressure signal (a signal detected by PID control) that takes into consideration process usage conditions such as can water temperature, water supply amount, and oil amount, and the difference is compared by the link (14) to the fuel valve (AC one that is adapted to adjust the opening degree of the valve) and push air damper (FDF), the O ₂ control the axis of the control motor with a pressure adjusting function is said master control motor when performing O ₂ trimming provided in advance is set to the sequencer oxygen concentration is set based on the amount of fuel as a target value for an alternative to the load, the value measured by the zirconia O ₂ concentration installed in the exhaust gas duct (8) Serial comparison operation with the target value, the deviation and PID operation, and rotates controlling the blower.

That is, the damper opening at each load point is determined in advance by the link mechanism, and the difference between the target value and the actually measured value is obtained to control the rotation of the motor to operate at an appropriate O ₂ amount.

The above-mentioned method is not proportional control but three-position control, but the set target value of O ₂ , that is, the oxygen concentration set based on the fuel amount for the load is set as a substitute target value in the sequencer. Is set according to the opening degree of the oil amount control valve, and therefore the oil amount changes due to wear of the valve seat due to changes over time, and it is necessary to correct the set target value. Since the correction is performed by changing the length of the link and the joint position, it is difficult to make the desired adjustment, and the damper adjustment is prone to gradual deviation due to the play of the joint due to the wear of the link itself, and detailed management is required. Further, the occurrence of wear and play causes hysteresis due to an increase and decrease in load, which causes a deviation between the set value and the actually measured value, which makes fine adjustment more difficult. Hysteresis here refers to the error in the air volume relative to the oil volume controlled by the control motor, and the relationship with other control items.Because it is a link connection, there is rattling due to wear of the joint and the damper. Adjustment is easy to get out of order.

On the other hand, in the case of proportional control, the fuel injection pump is operated at constant rotation and constant pressure regardless of the load, and because the oil amount is adjusted by the bypass circuit, the spray pressure becomes unstable and this causes the oil amount to become unstable. In addition to the above, in the case of heavy oil, the fluctuation of the oil temperature causes a viscosity change, and the spray pressure and the spray amount change, so that it is difficult to control the oxygen concentration, and it is unavoidable to control the excess air amount. Also, as a problem of the O ₂ sensor, the zirconia type or the magnetic type is used as the sensor, but for industrial use, the zirconia type is often used and it is necessary to periodically adjust the sensor with standard gas. high.
The magnetic method is not common here because it utilizes the property that O ₂ is magnetized, because continuous measurement cannot be performed and cleaning is required after use.

In addition, the control using the O ₂ sensor as described above controls only by comparing the signal of the sensor and the set signal, and because there is a sensor in the exhaust gas duct, it can be detected only after 2 to 3 seconds after combustion. , Therefore, there is a delay in response.

Further, in the latter case, the valve opening degree according to the fuel flow rate indicated by the output of the fuel flow rate calculation means is determined from the stored data indicating the relationship between the fuel flow rate and the fuel flow rate, and the excess air ratio with respect to the fuel flow rate is determined. From the data representing the relationship, the excess air ratio corresponding to the fuel flow rate indicated by the output of the fuel flow rate calculation means is determined, the air flow rate is determined based on this excess air ratio, and the data representing the relationship between the air flow rate and the opening degree of the air damper is determined. , The damper opening degree is determined according to the air flow rate indicated by the output of the air flow rate calculating means, the valve opening degree calculated value is applied to the fuel operating means according to the increase or decrease of the output of the fuel flow rate calculating means, and the damper opening degree value is set. The excess air ratio calculated from the opening of the fuel valve and air damper, which is applied to the air operation means and changes accordingly, is compared with the excess air ratio in the previous period and is within the allowable range. And controls each output to be maintained. That is, the stored data is the basic value of the calculating means for each output, and the data is not directly output as an output value to each control device.

The data is calculated and becomes an output value, and each output calculated value is finally output while being compared with the target value calculated from the data with the excess air ratio to determine whether it is within the allowable range.

This means that the stored data does not match the output value, and the stored data is not the output value.

It is clear that the thing with such a calculation function and the function to compare with the target value is so unresponsive that it cannot be adjusted immediately in the event of smoke, and smoke is a major pollution factor in combustion control. This is a problem, and the ease of adjustment is an important point for combustion management for combustion operators.
I can't do this. Furthermore, the latter one is mainly for controlling the damper from the combustion amount and the air amount, and although the combustion element must be considered by the burner type,
There is no consideration on this point.

Generally, it is expected that the combustion amount and the air amount will increase as the load increases. Therefore, it is often considered that these two should be mainly used as the control means, but the combustion device is a burner type or Actually, there are various control items due to the problem of the balance between the primary damper and the secondary damper and the control of various auxiliary dampers and valves that are performed to reduce NO _x. Optimal control cannot be achieved only by controlling the damper opening based on the value (target excess air ratio).

In the latter, the combustion amount and air amount, which are the control values to be controlled next, are calculated and predicted from the fuel valve and air damper opening, which causes problems of responsiveness and mechanical accuracy and is expensive. It becomes equipment.

Further, the use of an oxygen concentration meter or the like poses a problem of maintenance from the viewpoint of preventing influence on the control due to contamination during use, and in general, it is rarely used as a combustion control management device. The reason is that the detector is exposed to smoke, and it is easy to get dirty, and it takes time to clean, and the cost of the equipment increases the maintenance cost.

Also, in the latter, because the load followability is emphasized
Since each output value is calculated and output as a stepless value by PID calculation, it is impossible to adjust the combustion data by adjusting the stored data and the calculation means is adjusted, but this is an inconvenient combustion It makes it difficult to deal with the occurrence of.

(Means for Solving Problems) The technical problem of the present invention is to solve the above problems and to provide a fuel amount, an air amount, and a fuel atomizing gas as necessary without using an oximeter. Another object of the present invention is to provide a combustion method and apparatus that facilitates combustion control by controlling the amount of gas or fluid for combustion assistance in multiple stages and in stages, and performing appropriate combustion for each load.

The technical means of the present invention for solving this technical problem is to detect a fluctuating load as an analog value, convert it into an input signal, and use a PID calculator that judges whether the load is increased or decreased from the input signal. State and the displacement state of the load that is the difference between the target combustion state obtained by the PID calculator, and the load position determination calculator from the load displacement state that is the obtained analog value, calculation with hysteresis characteristics Due to
The load position is determined, and this is output as a digital value, and various output data for combustion control such as oil amount, air flow rate, etc. corresponding to the load position are output in advance by various output data determined for each load position. It is a multi-stage control type air-fuel ratio control method in a combustion system that reads out from the stored memory and outputs it to correlate the varying load and output data to perform multi-stage combustion control. As a device to do, a load meter that detects fluctuating load,
The converter that converts the detected load into an input signal, and the PID calculator that determines whether the load increases or decreases from the input signal from the converter, the difference between the current combustion state and the target combustion state obtained by the PID calculator. Then, the load position is determined by the operation of the load position determining calculator from the load displacement state and the load variation state representing the amount of variation per unit time from the load meter. Output as a value, and various output data for oil control, air flow rate and other combustion control corresponding to the load position are read out from the memory storing various output data previously determined for each load position and output. In this way, there are a control device that determines the multi-stage by correlating the fluctuating load and the output data, and a motor such as a blower, an oil amount pump, or a water supply pump that is controlled by the output signal. It is given by the frequency converter of the motor, also the damper, what is reciprocated like a valve, a multi-controlled air-fuel ratio control system in the combustion apparatus constituted by a positioner.

In the control device, the displacement state of the load is obtained by the PID calculator that compares the input signal with the previous signal and judges the increase or decrease of the load, and then the control amount of each controller output by the load position determination calculator is used. Data to be output from each memory that determines the load position for determining output data such as certain frequency data and position data, and stores various output data in advance in the output data selection calculator for each load position. Is read out and part or all of the output data is displayed, and an output signal corresponding to the displacement state of the load is output to each adjustment position.

It should be noted that each memory here is a sliding resistance type that converts a mechanical quantity into an electric signal because it uses a memory that is a storage device of a microcomputer as a memory and can read an analog signal as data. This is because the analog-type control device such as the displacement-voltage converter, which is a potentiometer, can be understood as a kind of memory.

As a function of other control devices, as a measure against inverter failure, a switching mechanism that bypasses the inverter and supplies commercial power directly to the motor is provided, and the output at each load position for the commercial power is also stored in the memory. It is desirable to store it as data so that the control method at the time of inverter failure can be performed only by electrical switching.

(Effects of the Invention) In the combustion method and apparatus of the present invention, the output value is not directly calculated, but the output value is directly stored, and this output facilitates combustion adjustment. The one equipped with a comparison function with is so unresponsive, and the one that cannot be adjusted immediately in the event of smoking, the present invention, when an inconvenience such as smoking occurs, the output data at the stage where the inconvenience occurs It can be dealt with by direct adjustment, and the driver can respond immediately by sight.

That is, output data setting changes and fine adjustments at each load position can be made by changing the data in each memory.
The operation method can also be performed by increasing or decreasing the set data value,
It is easy to manage and allows fine adjustments while driving.

Further, according to the present invention, it is possible to perform proper combustion in proportion to load fluctuations without using an oxygen concentration meter, and to properly maintain the oxygen concentration in the exhaust gas, so that the combustion efficiency is improved. This is because, as a result of conducting an experiment using the boiler equipment, the oxygen concentration in the exhaust gas in the conventional equipment is feedback controlled using an oxygen sensor as shown in FIG. Although it is difficult to narrow down the oxygen concentration in the equipment equipped with the combustion control device of the present invention, the oxygen concentration can be suppressed to near the smoke limit, so that the oxygen concentration can be set as low as about 20 to 50% as compared with the conventional equipment.

In addition, the use of a control device that does not require an oximeter eliminates the need for feedback in combustion control, and as a combustion control method, a prompt response can be taken in order to perform proper combustion in the change of combustion with respect to load fluctuation. You can do it.

Further, as in the conventional control, the occurrence of hysteresis in the increase / decrease of various outputs corresponding to the load fluctuation caused by the abrasion of the constituent equipment is eliminated, and stable combustion can be obtained.

Further, since the control device of the present invention does not have a mechanical adjustment part such as a link, the output value and the execution result are consistent,
Highly reliable control.

Looking at the power of the blower, because of the rapid combustion control by stepwise control, compared with the conventional control method, the power consumption is lower by the lower oxygen concentration in the exhaust gas, especially at low combustion. Since it requires only power, it is possible to save a great deal of labor, and it does not burn under conditions other than preset combustion conditions, so smoke and inconvenience in combustion do not occur, and in the unlikely event of smoke or combustion failure, that It is easy to adjust because it can be adjusted in points.

If other inverter failure countermeasures are taken, the reliability of this system equipped with a variable speed control device can be met without stopping the equipment from the time of failure until the operation is restored, and by only electrical switching. Will be increased.

Further, in the present invention, the number of burners is one, and it can be controlled by a single device such as air amount, fuel amount, load detector, etc. Unlike the positioning detector, no measuring device is required.

(Example) In FIG. 1, (1) is a package boiler, (2) is a brackish water drum, (3) is a water supply pipe, (4) is a steam pipe, (5)
Is a burner, (6) is a fuel supply pipe, (7) is a blower,
(8) is an exhaust gas duct, (33) is a gas line for fuel spray, and (9) is a pressure gauge, that is, a load gauge. In addition to the pressure gauge, the load gauge may be a thermometer, a flowmeter, or the like.

The load fluctuation is detected by the pressure gauge (9) which is one of the load gauges, becomes a signal by the pressure regulator (17), and is supplied as an input signal to the control device (21) at regular intervals.

In the controller (21), the signal from the pressure regulator (17) is compared with the previous signal by the PID calculator (23) shown in FIG. Know the condition. Next, after determining the load position that determines the output data to be output by the load position determination calculator (25), various output data determined in advance for each load position are output to the output data selection calculator (24). The data to be output is read out from the stored memory (26), the output data is displayed (27) (28) (29) (34), and the output signal corresponding to the load fluctuation state is given to each adjusting device. It is designed to output. The output data may be displayed as needed, and it is not necessary to display all the various output data.

Here, the PID calculator detects a fluctuating load as an analog value, and "determines whether the load increases or decreases" based on the deviation from a preset target value, that is, the load displacement state and the fluctuation per unit time. Based on the size and direction of
The "load fluctuation state" is detected.

In addition, the load position determination calculator calculates the load position by adding a hysteresis characteristic from the obtained displacement value or fluctuation state of the load, which is an analog value, and outputs the load position to be selected next as a digital value. It has a function to determine.

In other words, the load position determination calculator receives pressure value data and load change state data, and is given a hysteresis characteristic, and a function to calculate the next selectable load position as a digital value. Have.

Due to the hysteresis characteristic, even if the detected pressure value is the same, the output value may differ depending on the state.

As described above, the load position determination calculator converts an input value, which is an analog value, into a digital value in accordance with the combustion stage while having a hysteresis characteristic.

The PID computing unit and the load position determining computing unit according to the present invention are configured as described above, and the specific configuration can be freely selected by the designer.

Further, the control device is provided with a setting change function for facilitating the setting change of the output data and a proportional band setting function for freely controlling the control range.

This makes it possible to measure the oxygen concentration of the exhaust gas while operating the combustion equipment and easily make fine adjustments while observing the measured value.

The detection of the fluctuating load differs depending on the type of the boiler. The steam boiler has a steam pressure, the hot water boiler has a temperature, and the like, but depending on the situation, the steam amount, the hot water amount, etc. may be detected as input values. In this case, another type of detector (not shown) is used as the load meter.

The fuel injection pump (11) and the blower (7) are controlled by the output signals from the control device controlling the rotation of the respective motors via the frequency converters (18) and (22).

The blower damper (16) and the fuel spray gas valve (31) control the servomotors (27) (32), which are examples of positioners, by the output signals from the control device, and adjust the opening of each.

In general equipment, the control of the injection pump, blower, and blower damper is the main control, and it is necessary to adjust the opening degree of the secondary blower damper, the gas valve for fuel spraying, and the control valve for combustion-assisting gas or fluid. It may be carried out according to the above, and it may not be carried out.

Further, in this embodiment, the heater current control device (13) and the fuel heater (30) are arranged in front of the fuel injection pump in order to keep the fuel temperature constant in order to stabilize the combustion.

This is to avoid instability of combustion due to change in fuel viscosity due to change in fuel temperature, change in atomization pressure and change in fuel amount, and it may not be necessary depending on the selected fuel oil. is there.

Fig. 3 shows the blower from the blower (7) divided into the primary and the secondary. (16 ') and (27') are the secondary damper and servomotor, and (39) is the service tank. ,
(40) indicates an oil feed pump.

As described above, the control device (21) is configured as shown in FIG. 4, and the load position determining calculator (25) determines the load position for determining the output data. As described above, when the load P is in a stepwise manner with respect to the target load curve, for example, when the load P is in the curve of A and B, that is, the amount of steam used is increasing, and the load P, that is, pressure is decreasing. When the load fluctuation state is small and the load displacement state is small, point F is selected, and when the load fluctuation state and / or the load displacement state is large, an appropriate point from G to I is selected. That is, even if the load fluctuation state or the load displacement state changes while the F point is selected, if the change is small, the F point remains selected.
This phenomenon is an error between the input value and the output value, that is, the hysteresis characteristic of the present invention has an error in the relationship between the pressure and the load position that determines all control items including the oil amount. It refers to the state of doing.

In the past, the main control item called the oil amount was determined by detecting the pressure, and other control items were also physically synchronized so that the error caused by physical factors is not I said.

When the load position is determined, the output data selection calculator (2
4) reads various output data at the selected load position from the memory (26) and outputs it to each device.

At this time, a part of the data may be obtained by a control device such as a potentiometer which is represented in analog.

In the method of the present invention as described above, pressure is detected as an analog value, point P (PID control output, analog value) is obtained from the difference from the target pressure value, and hysteresis characteristics are provided in accordance with the step control. However, it means that the digitization element that selects each stage is necessary.

In addition, FIG. 5 shows another example in which fuel and water, a combustion auxiliary agent, etc. are mixed. For example, in the case of an emulsion of water, from the water supply pipe (37) through the service tank (36), The water supply pump (35) is rotationally controlled by the inverter (38) and is appropriately supplied to the mixer (34) in the fuel pipe in accordance with the combustion state and the fuel amount.

FIG. 8 is an example of using the control device in a control method for controlling a plurality of facilities by using the present control device. Here, load detection and extraction are performed at an integrated position of a plurality of facilities, output data for each facility can be set according to the load state, and the data can be stored in a memory. Although an example of a type of equipment is given, it is possible to simultaneously control different kinds of equipment such as equipment that requires fuel spray gas and equipment that does not. In this case, a more flexible control method can be achieved by adding functions such as the number designation and priority instruction to the output function of the data selection calculator.

Further, the number of positions of the load position is freely decided in the case of the load control of the single combustion equipment, which is the original purpose, and the load control of the plurality of combustion equipment, and in the control in the plurality of combustion equipment, It is also possible to simultaneously store the load positions corresponding to the respective facilities in the plurality of combustion facilities, or to store the load positions of the control device separately for the number of the plurality of combustion facilities and to control them. .

At this time, the greatest advantage of this control method is that the output data of each equipment can be changed while operating a plurality of equipment with one control device.

Therefore, each oxygen concentration can be easily managed, and when operating multiple equipment in combination,
It is also possible to manage the number of units in operation (the number of units that are actually burning) in proportion to the load condition.

In short, the present invention performs simplified control without measuring the oxygen concentration of the exhaust gas, and makes the fuel amount, the air amount, and other combustion control amounts stored in advance according to the load change, follow the memory. The amount of fuel, the corresponding amount of air, and other combustion control amounts are stored in multiple stages for each load stage, and the output data and the load fluctuation are made to follow in a correlative manner to perform multiple stages of combustion control. It is a thing.

Generally, the two-position control is a two-step control of stop and combustion, and refers to ON-OFF control, not positioning control or flow rate control. Although it is a three-position control system, it has three stages of combustion: stop, low-combustion and high-combustion. There are two stages of combustion, and in the case of a small boiler that uses a simple switch control method. It is performed by 2-position / 3-position control, which is different from the multi-step control method of the present invention.

While the control method up to the three-position control is a mechanism that cannot perform linear control at all, in the present invention, the control method and devices are all capable of linear control while realizing multi-step control.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a first embodiment of the present invention device. FIG. 2 is a schematic diagram of a conventional device. FIG. 3 is a schematic diagram of a second embodiment of the present invention device. FIG. 4 is a schematic diagram of a control device. FIG. 5 is a schematic diagram according to a third embodiment of the present invention device. FIG. 6 is a load curve diagram. FIG. 7 is a curve diagram showing the relationship between load and oxygen concentration. FIG. 8 is a fourth embodiment of the present invention device. It is a schematic diagram concerning. (1) …… Package boiler (2) …… Brackish water drum (3) …… Water supply pipe (4) …… Steam pipe (5) …… Burner (6) …… Fuel supply pipe (7) …… Blower (8) ) …… Exhaust gas duct (9) …… Pressure gauge (11) …… Fuel injection pump (13) …… Heater current control device (16) …… Air damper (17) …… Pressure regulator (18) (22) …… Frequency converter (21) …… Control device (27) (32) …… Servo motor (30) …… Fuel heater (31) …… Fuel atomizing gas valve (33) …… Fuel atomizing gas conduit

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shinichi Sekiguchi 1-6-24 Sengoku, Bunkyo-ku, Tokyo (56) References JP-A-57-198920 (JP, A)

Claims (2)

(57) [Claims] 1. A variable load is detected as an analog value,
Convert to an input signal, determine the load displacement state by the PID calculator that determines the increase or decrease of the load from the input signal, and determine the hysteresis characteristic by the load position determination calculator from the load displacement state that is the obtained analog value. The load position is determined by the calculation that is carried out, this is output as a digital value, and various output data for oil control, air flow rate and other combustion control corresponding to the load position are determined in advance for each load position. A multi-stage control type air-fuel ratio control method in a combustion device in which various types of output data are read out from a memory and output to output the output data in a correlative manner so that combustion control is performed in multiple stages. 2. A load meter for detecting a fluctuating load, a converter for converting the detected load into an input signal, and a PID calculator for judging an increase / decrease of the load from the input signal from the converter to detect the load displacement state. The load position is determined from the displacement state of the load and the load fluctuation state from the load meter by the calculation of the load position determination calculator, and this is output as a digital value, and the oil amount and the air flow rate corresponding to the load position are determined. Various other output data for combustion control are read out from the memory that stores various output data determined in advance for each load position, and output to output the data to correlate the varying load and output data. And a multi-stage determination control device, and a motor such as a blower, an oil amount pump, and a water supply pump, which is controlled by the output signal, has a motor, a frequency converter, and a motor. Bar, which reciprocated such valves, multi-controlled air-fuel ratio control system in the combustion apparatus constituted by a positioner.