JPS6040566B2 - Method for controlling combustion conditions in a combustion furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for controlling the combustion state by moving the burner position in a combustion furnace. The present invention relates to a control method for automatically adjusting the position of the tip of a burner in a burner tile based on a detected value of a vibration pattern of minute pressure superimposed on the furnace pressure.

Current combustion management involves the problems of N*x and smoke for energy conservation and pollution prevention, and requires extremely strict control. To deal with these issues, important control factors include air ratio, atomization amount (liquid fuel), furnace pressure, burner position, air flow rate, and fuel flow rate. There is a shift to precise control using the so-called cascade method, which adjusts the ratio according to the amount of combustion. However, in most actual reactors, control factors are still simply set at constant values, and in actual reactors with many variable factors, there are many problems in combustion management. When managing combustion, it is basically a very important issue to accurately determine the combustion state that changes from moment to moment and to maintain combustion under appropriate conditions.

The details of the factors that affect the combustion state vary widely, such as furnace characteristics, burner characteristics, operational factors, etc., but the burner tile structure, which directly affects the mixing action of fuel and combustion air, and the burner tip, which is the fuel injection position. Location has become an important factor. For example, by displacing the burner position in the burner tile from its normal position and installing it closer to the inside of the furnace, fuel and combustion air are mixed slowly, and combustion proceeds slowly.

Conversely, it is generally known that the closer the burner is located within the burner tile, the more rapid the combustion state becomes. However, even if the burners are initially placed in the correct position to obtain the optimum combustion conditions, fluctuations in combustion conditions during actual furnace operation, especially the fuel flow rate and the actual air ratio (such as intrusion air and measurement at low flow rates) (Due to errors, equipment characteristics, etc.)

Combustion conditions vary significantly as a result of fluctuations in For example, the combustion flow rate in a soaking furnace is approximately 2 to 1 between the maximum and minimum.
There is a large difference of up to 0 times, and for this reason, even if the air ratio is controlled to be constant, the combustion state deviates from the optimum state. The present invention has been made to overcome the above-mentioned problems, and is based on the fact that the combustion state varies greatly depending on the burner position. The aim is to control the burner position so that the combustion state can be maintained.

In other words, under the conditions of the highest furnace load and maximum combustion rate where smoke is likely to occur, the burner position that provides the optimal combustion state is determined in advance based on the smoke generation situation, the amount of flame radiation, or visual observation. At the same time, the in-furnace pressure vibration, preferably the pressure vibration superimposed on the in-furnace pressure, is measured,
By determining the vibration pattern in advance, detecting the pressure vibration in the furnace during combustion, preferably the pressure vibration, and automatically moving the burner position to the optimum position based on the vibration pattern, the fuel flow rate and The combustion condition is optimally stabilized despite other temporal fluctuations.

The design and dimensions of conventional combustion equipment are uniquely designed based on the purpose of use and specifications such as combustion amount, combustion air flow path diameter (air throat diameter), and burner type. No consideration is given to controlling the combustion conditions against physical changes.

However, in actual furnace operation, as mentioned above, there is always a change in the combustion flow rate over time and a fluctuation in the combustion air flow rate due to this. This causes an unexpected change in the mixing state of fuel and air, causing the combustion state to deviate significantly from the optimal state.
In the present invention, the combustion pressure vibration pattern in the optimum combustion state is determined in advance, and based on this, the burner tip position is automatically controlled in accordance with changes in the vibration pattern, so that fuel and air are This is to maintain the optimum mixing condition at all times and to achieve optimum combustion.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

In Fig. 1 showing the control system for the burner position, 1 is a combustion furnace, 2 is a burner tile hole of the combustion furnace 1, and 3 is arranged coaxially with the center axis 1 of the burner tile hole 2. 4 is a well-known suitable electrical and mechanical structure in which the burner 3 is moved along the central axis 1 by the guide of a guide roller 5. This burner drive device 4 has an in-furnace pressure sampling probe 6 with a detection unit facing inside the furnace chamber, and converts in-furnace pressure vibrations picked up by the in-furnace pressure sampling probe 6 into electrical signals. An amplifier 8 separates the detection signal of the detector 7 into the absolute value of the furnace pressure and the combustion pressure vibration component superimposed thereon, and amplifies the combustion pressure vibration component.
, a frequency analyzer 9 that analyzes the waveform of the combustion pressure vibration amplified by the amplifier 81 using an analysis method such as Fourier analysis, and calculates a necessary control index value from the power spectrum obtained by the frequency analyzer 9 using the method described below. Arithmetic unit 10
, the control index value obtained by the arithmetic unit 10' is compared with a preset control target value, and a necessary control signal is outputted via the controller 12 according to the difference signal to control the burner drive device. 4, and a vibration energy setting regulator 11 that controls the operation of the burner drive device.
The position of the burner tip is automatically adjusted to an appropriate position between the position of the end face inside the burner tile furnace and the rear inside the tile hole (on the left side in the figure) in response to changes in the pressure vibration pattern.

Below, we will first describe the relationship between the combustion state and pressure vibration when the burner tip position is changed in a combustion test furnace (1◇×4 skin L, fireproof wall structure).

In Figure 2 A, 1 to V, butane gas is used as the fuel and a commercially available normal type burner is used, and the exhaust gas 02 concentration is 3.0.
In addition to adjusting the air ratio to be ±0.2%, the combustion amount was set to a constant value of 400,000 Kcal/day, and the pressure vibration patterns are shown when the burner tip position is varied.

The position of each burner tip corresponds to point a (furnace wall surface or 7th rib) on the center axis 1 in Fig. 1 in Fig. 1, 0 corresponds to point b (on the 270 side), and m corresponds to point b (on the 270 side). Point c (370 ribs),
W corresponds to point d (470 yen) and V corresponds to point e (57 yen), respectively. Also, according to the observation results of the combustion conditions when each of the vibration patterns 1 to V in Figure 2 was obtained, the closer the burner tip position is to the inside of the furnace, the slower the combustion, and the larger the flame shape is, the longer the flame is. However, as the burner position was moved away from the inside of the furnace, it was observed that the flame became short and eventually became a transparent flame, transitioning to a rapid combustion state similar to a so-called mixed flame. (Figure V). Looking at the vibration waveform shown in Figure 2A in response to the transition of this combustion situation, when combustion is slow (when the burner position is close to the inside of the furnace), a large and gentle waveform is drawn (the same The waveform changes from large waves to small waves as the state of rapid combustion progresses, and the frequency becomes extremely high in the state of transparent flame (V in the same figure). Looking at the change in the above waveform from the power spectrum density analysis results shown in Figure 2B, in the state of slow combustion, it is approximately 2-4H.
The Z frequency component is the main component (Figure 1, D, etc.)
On the other hand, it is observed that as the combustion becomes more rapid, the temperature shifts to about 12 to 13 HZ (such as m in the figure), and further to about 20 to 25 HZ (V in the figure).

In this way, as the combustion changes from a slow state to a rapid state similar to a premixed flame, the frequency components of the slow vibration in the furnace tend to gradually increase, indicating that the combustion state and the vibration pattern correspond. is recognized.

Although actual vibrations include components from about 0 to 500 Hz, here, as a representative example, analysis results from 0 to 45 Hz, which allow determination of the combustion state, are shown.

Based on the fact that the combustion state can be determined based on the pattern of combustion pressure vibration as described above, a method of controlling the burner position using this as a control signal will be described.

First, when using a vibration pattern as a control signal, it is necessary to express it uniquely, but in this method, for example, as shown in Figure 2B above, when the combustibility goes to a rapid state, the high frequency component increases. (Conversely, it is also possible to focus on the characteristic that low frequency components decrease.

), a specific frequency band is set in which the vibration component changes in response to the combustion state. In the example of Fig. 2B, 15Hz or more is set as the specific frequency band S, and the integral value EH of the vibration energy of the specific frequency band S with respect to the total vibration energy BT.
Let us express the ratio EH//ET by the vibration energy ratio R. An increase in this vibrational energy ratio R indicates that the combustibility is heading in a sharp direction, and can be an indicator of the combustion state (even if the specific frequency band is set to 15Hz or less, the trend will be reversed, and the same will occur) (This is an indicator of combustion status.) Fig. 3 is a graph schematically showing an example of changing the burner tip position in comparison with the combustion flow rate over one heat cycle of a soaking furnace. The relative positions of a to f in FIG. 1 are shown (the actual distance in an actual furnace is equivalent to about 1.5 tones).

In the figure, the curve F shows the change in fuel flow rate, and the curve m shows the change in the burner tip position according to the method of the present invention. Note that the '2 female burner is in the conventional burner position and is fixed in the burner tile hole f. '
This is an example in which the burner is fixed at a position (near d in Fig. 1) that provides the optimum combustion state under the maximum combustion condition. Same figure 0
is a graph schematically showing the change in vibration energy ratio R when the burner tip is installed as described above, and curves 1, 2, and 3 indicate the positions of the burner tip shown in curves 1, 2, and 3, respectively. It shows the change in the vibration energy ratio R when adjusted to . Note that T indicates a change in the temperature inside the furnace. As shown in the figure, when using the conventional method, the vibration energy ratio R
The level of is high, and the vibration energy ratio R increases as the fuel flow rate changes (curve 2). Furthermore, when the burner tip position is fixed at the optimal position (near d in Figure 1) under maximum combustion conditions, the initial level of vibration energy ratio R is at the set level, but as the fuel flow rate changes, it increases. The trend is shown (curve 3). In contrast, according to the method of the present invention, the vibration energy ratio R remains stable at a low level regardless of fluctuations in the fuel flow rate (curve 1). This means that optimal combustion conditions can be maintained. In addition, in FIG. 1, the burner tip is at position f before ignition to protect the burner, and during combustion is controlled to be at any position from a to f.
After extinguishing the fire, it is automatically fixed at position f. The control of the burner tip position in the present invention is performed based on the optimal combustion state determined in advance (smoke generation situation, flame flare, temperature distribution, zero exhaust gas, etc.).
(2) pressure vibration energy ratio R (determined from the concentration, flame shape, etc.).

This is done on the basis of FIG. 4 is an example of a graph in which the vibration energy ratio R was determined under the maximum combustion condition by changing the burner position to create various combustion states.

The burner position (rib) on the horizontal axis is shown as a distance toward the inside of the furnace from the conventional burner tip position as a base point.

Note that the inner end surface of the burner tile furnace in the same example is located at a position of 700 ribs. In the figure, curve 1 shows the change in vibration energy ratio obtained by moving the burner position and measuring vibrations at the air throat section under the condition of maximum combustion amount (heavy oil flow rate, 4001/H).

Curve 2 shows the change in the vibrational energy ratio when the combustion rate is reduced to approximately 1'3. It can be seen that at the same burner position, curve 2 has a higher vibration energy level and a sharp increase in combustibility. Furthermore, in any case, by moving the burner position toward the inside of the furnace, the vibration energy ratio R tends to decrease, indicating that the combustibility tends to be gentler. Now, if the vibration energy ratio R that can be judged to be the optimum combustion state under the maximum combustion condition (curve 1) is 0.2, then using this as the set value Ro, the burner tip position will be at the 12th edge position at maximum combustion, and the fuel When the flow rate gradually decreases to 1'3, the burner position 620 will be controlled, which corresponds to the vibration energy ratio of curve 2 of 0.2.

Note that the shaded area A in the figure indicates the smoke generation area. That is, if the burner tip position is adjusted so that the vibration energy ratio R is approximately 0.15 or less, smoke will occur regardless of the fuel flow rate. Therefore, in order to reduce the occurrence of smoke, it is necessary to avoid combustion control in which the vibration energy ratio is set to 0.15 or less. Note that this vibrational energy ratio R generally varies depending on the type of fuel, type of furnace, type of burner, and operating conditions, so in order to perform appropriate combustion control in actual operation, it is necessary to It is desirable to adjust the burner position based on the vibration energy ratio R.The burner position can be controlled, for example, as shown in FIG. is guided to the detector 7, separated and amplified by the intensifier 8 into the absolute value of the reactor pressure and the pressure vibration component superimposed on it, and then sent to the frequency analyzer 9.
sent to.

The frequency analyzer 9 calculates the energy density distribution of the vibration frequency, and the result is input to the calculator 10. The arithmetic unit 10 outputs the ratio R of the integral value of vibration energy in a preset specific frequency band to the total energy of vibration as an output signal. This signal enters the vibration energy setting regulator 11, compares it with a preset value of vibration energy ratio Ro (for example, 0.2), and transmits it to the burner drive device via the limiter 12 according to the deviation signal. 4 (e.g., motor-driven, pneumatic/hydraulic-driven) and drives the device 4, the burner body 3 is moved forward or backward on the guide rollers 5.

Incidentally, as shown in FIG. 5, a burner position adjuster 13 is provided between the limiter 12 and the burner drive device 4, and the burner position corresponding to the signal is set, and the burner displacement device provided in the burner disturbance device 4 is set. Practically speaking, it is preferable for the burner drive device 4 to compare the position measurement value from the meter with the burner position set value and provide the burner drive device 4 with a control signal in accordance with the deviation.

Here, the limiter 12 is a device for minimizing the disturbance given to the control system even when an abnormal value is detected in the vibration energy ratio R or the detection system, and when a signal with a large fluctuation is received. This is to temporarily stop burner position control (maximum and minimum limit values can be set here).

As mentioned above, in the above method, the combustion pressure vibration can be measured anywhere within the vibration propagation range, such as inside the air throat, inside the burner tile, inside the combustion furnace, or in the flue. Measurement within the range is most preferred.

The pressure vibration detector 7 is one that can sufficiently detect pressures in the water column of -50 to 16 meters, and preferably can detect frequencies from 0 to 500 days, and is a pressure transducer using a strain gauge. Alternatively, it is preferable to use a crystal converter or the like to convert the pressure vibration into an analog signal into an electric signal.

When using vibration as a control signal, it may be used in the form of furnace pressure + pressure vibration, including the absolute value of the furnace pressure, but if the combustion amount fluctuates significantly in an actual furnace, there may be problems with the vibration measurement position. Alternatively, in consideration of detector drift and the like, it is better to isolate and extract only the pressure vibration component superimposed on the in-furnace pressure as a more stable control signal.

In addition, the frequency band of vibration used as a control signal is 0 to 500Hz.
However, a low-pass filter or a band-pass filter may be incorporated into the multiplier 8 or the frequency analyzer 9 to limit the frequency to a specific frequency or frequency band. The frequency analyzer 9 is
Although it is possible to use a vibration analyzer, it is desirable to be able to analyze it in real time.
F vibration analyzer, FFT (FAST FOU
An octave band type digital vibration analyzer, an octave band type analyzer, or the like can be employed.

In order to concretely use a vibration pattern as a control signal, it is necessary to express it uniquely, and the following method can be considered as a method for this.

The vague diagram is shown in Fig. 6, and after obtaining the power spectrum with the frequency analyzer 9, (a) a method of simply using a specific frequency or the maximum energy level Q of Obijo S as an index (Fig. a〉.

tb' A method in which the ratio Q/8 between the maximum energy level Q of a specific frequency or band S and the maximum energy level P of frequencies in other regions is used as an index (FIG. 6b).

'c} A method using the integral value EH of the energy of a specific frequency band S (Fig. 6c).

{d} A method based on the ratio R of the energy integral value EH of the specific frequency band S to the integral value ET of the total energy of vibration (FIG. 6d, this is as explained above).

)and so on.

The specific frequency band S here refers to the vibration band that changes in response to the combustion state, and can be an index representing the combustion state in any of the above (chapters a to [d), but in reality In cases where the combustion amount and other conditions are likely to fluctuate, such as in a furnace, or in consideration of detector drift, the W-based method is considered to be optimal.

Vibration patterns can be expressed uniquely by these methods. Methods {a] to {c- are also clear from FIG. 2, but a supplementary explanation is as follows.

Figure 2 shows the vibration pattern and its spectrum when the combustion conditions were all the same and only the burner position was changed. Method WLO. (c) Power
d q nok 8th day spectrum a position (
1] one [B] o. 2xlo-2 o. lo 4.5x
lo-2b〃Blood-[B]o. 4xlo-2 0.
20 9.9xlo-2c 〃 D-[B]0.7
xlo-2 0.4413.5xlo-2d 〃 side]-[B]18xlo-2 1.29 428xlo-
2e 〃 N〕-[B]2.2xlo-2 2.2o
45. As in OXLO-2 and above, also in the methods [a} to {c}, changes in the combustion state due to differences in burner position can be indexed.

As long as it can be indexed, it can be controlled in exactly the same way as {d}. It goes without saying that the method (d) can be treated as a dimensionless number, clearly shows the bias, and is easy to use as a control signal.

Figure 7 shows the vibration energy ratio R for fluctuations in fuel flow rate.
1 is a graph showing a specific example of a change in . In the figure, '1} indicates {2} when the burner position is automatically adjusted based on the deviation between the vibration energy ratio R and the set value Ro using the method of the present invention. } is based on the conventional method, and {3} is the case where the burner tip is fixed at a position closer to the inside of the furnace than in the conventional method.

Note that S indicates a smoke generation danger line, and when the vibration energy ratio R becomes below this line, smoke will occur. As shown in the figure, in the conventional method (■ in the figure), the vibration energy ratio R is high regardless of the fuel flow rate.
This becomes especially noticeable when the fuel flow rate decreases. Also, when the burner position is fixed close to the inside of the furnace ('3 in the figure)
) is low when the fuel flow rate is high, but becomes high when the fuel flow rate is low, which poses a problem. (2) is a case where the burner tip position is changed and fixed based on the low fuel flow rate in order to deal with the problem of the vibration energy ratio R increasing in the low fuel flow rate region at t3'. In this case, although the above problem is solved, when the fuel flow rate increases, the combustion state enters the smoke generation region, which is not preferable. On the other hand, according to the method of the present invention, there is no such problem, and the vibration energy ratio R is always maintained at a stable setting state, and the initially set optimal combustion state is maintained. As described above, according to the method of the present invention, a stable and optimal combustion state can be maintained at all times by controlling the burner tip position by changing the pressure vibration pattern that reflects the combustion state.

The combustion state is kept constant by controlling the position of the burner tip because the mixing state of fuel and air is thereby adjusted. In other words, when the burner tip is moved toward the inside of the furnace, the mixing of fuel and air within the burner tile is suppressed, resulting in slower combustion; conversely, as the burner tip is moved away from the furnace side, rapid mixing occurs within the burner tile. At this point, rapid mixed combustion occurs, so the combustion state can be controlled by the burner position. In addition, in soaking furnaces, etc., when the burner position is fixed at a constant position and the combustion rate fluctuates, the mixing ratio in the burner tile increases as the burner position decreases, and the burner position appears to be lower than when the burner is at maximum combustion rate. As it moves away from the furnace side, the combustibility changes rapidly.

In such a case, the combustion state can be returned to its original state by moving the burner position to the inside of the furnace. The method of the present invention is not limited by the type/model of the furnace, the type of fuel, etc., and can be appropriately adopted in various industrial combustion furnaces when combustion is performed using various gaseous and liquid fuels. can.

Next, the method of the present invention will be specifically explained with reference to Examples.

EXAMPLE Combustion was carried out in a scorching furnace having the following specifications using Minas heavy oil as fuel.

At that time, based on the vibration energy ratio of the optimum combustion state under the maximum combustion condition determined in advance, the position of the burner tip is automatically controlled in response to the change in vibration energy ratio over time, thereby reducing the vibration energy ratio to 0. The combustion condition was controlled to maintain the temperature at 2. Specifications of soaking furnace Furnace type: Upper 2-way firing, Furnace type: 660 x 2650 W x 387
5th, Fuel consumption 0-400 (1/ratio) Combustion conditions Burner: High pressure steam mist type, Atomization: Steam, Exhaust gas 02:3
~4%, secondary air temperature: 750°C, vibration measurement location: air throat The results of the above combustion test are shown in FIG.

Figure 1 is a graph showing fuel flow rate changes, melon vibration energy ratio, and countersunk burner position control, where W is NOK for reference.
This shows the changes in Note that in FIGS. 1, 0, m, and W, {11 is a result of the method of the present invention, and {11 is a result of the conventional method. In addition, the burner position movement distance in Figure m indicates the movement distance in the direction of the furnace, and in the conventional method {2}, it is fixed,
In the method of the present invention, the burner position is moved within a range of about 62 m in response to the change in the vibration energy ratio shown in FIG. As is clear from FIG. 0, in the conventional method, the vibration energy ratio increases as the fuel flow rate changes over time, and has already reached 0.4 at a fuel flow rate of 3001/day.
On the other hand, according to the method of the present invention, the vibration energy ratio hardly changed and remained at the set value of 0.2, indicating that the optimum combustion state initially set was maintained. There is. The amount of fuel used in this case is shown in Figure 1.
As can be seen from the figure, there was a fuel saving effect of approximately 8%.

In addition, the amount of N○× produced as shown in W in the figure is also constant at about 8 pm, which is also effective in preventing pollution. As described above, according to the present invention, the mixture of fuel and air is always maintained in a suitable state by controlling the position of the burner tip, so the combustion state is stabilized, and the burner is moved forward toward the inside of the furnace. In this case, a slow combustion state occurs even at a low fuel flow rate, and an effect of increasing the luminous flame thermal efficiency can be obtained, as well as an effect of suppressing N○k in terms of pollution prevention.

In addition, since the combustion state is basically controlled using a signal that directly reflects the combustion state, even if operating factors other than the combustion amount fluctuate, the combustion state is controlled to be optimal even if operating factors other than the combustion amount change. There are big benefits.

[Brief explanation of the drawing]

Figure 1 is a schematic side view showing the burner section of the combustion furnace, Figure 2A
is the combustion pressure oscillation waveform when the burner position is moved in the combustion test, Figure B is a graph showing the power spectrum as a result of waveform analysis, and Figure 3 1 schematically shows the change in fuel flow rate and burner position over time. Graph, 4th rough diagram schematically showing the change in vibration energy ratio and furnace temperature over time.
The figure is a graph showing the relationship between vibration energy ratio and burner position for each combustion amount, Figure 5 is a concrete configuration diagram of burner position control using vibration, Figure 6 is a schematic analysis diagram of vibration patterns, and Figure 7 is a concrete diagram. Figure 8 is a graph showing the relationship between heavy oil flow rate and vibration energy ratio, Figure 8 1 is a graph showing changes over time in heavy oil flow rate in a soaking furnace, Figure 8 is a graph showing changes in vibration energy ratio, and m in Figure 8 is a graph showing the change in vibration energy ratio. Figure W is a graph showing changes in NOx discharge concentration over time. 1: Combustion furnace, 2: Burner tile, 3: Burner, 4: Burner drive device, 6: Furnace pressure sampling probe, 7:
Detector, 8: Amplifier, 9: Frequency analyzer, 10: Arithmetic unit, 11: Vibration energy setting regulator. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Completed Figure 8

Claims (1)

[Scope of Claims] 1. In various industrial combustion furnaces, in order to perform combustion by mixing the fuel flow injected from the burner in the burner tile hole and the air flow injected from the combustion air supply port, the furnace The internal pressure vibration is detected and the vibration waveform is subjected to Fourier analysis, and the vibration waveform corresponding to the desired combustion state is determined.
Either a predetermined frequency distribution, frequency energy distribution, or vibration energy in a specific frequency band is used as a set value, and a value corresponding to the set value obtained based on this set value and the vibration waveform of each combustion state is set. and, based on the comparison results, change the position of the burner tip in the burner tile hole in each combustion state in order to maintain the combustion state at the target combustion state. How to control the state. 2. In various industrial combustion furnaces, when the fuel flow injected from the burner in the burner tile hole and the air flow injected from the combustion air supply port are mixed to perform combustion, the pressure in the furnace is This is a method of detecting minute pressure vibrations and controlling the combustion state based on the signal, in which the frequency band in which the vibration pattern changes in response to at least a change in the combustion state of the pressure vibration in the furnace is determined in advance. Detect and perform Fourier analysis of the vibration waveform in the desired combustion state in one heat cycle of the combustion furnace, and from the obtained power spectrum, calculate the integral value of the energy in the specific frequency band with respect to the integral value of the entire vibration energy. Using the ratio of
The burner in the burner tile hole in each combustion state is determined according to the deviation between the set value and the ratio of the integral value of the specific frequency band to the integral value of the entire vibration energy in each combustion state obtained thereby. A method for controlling the combustion state in a combustion furnace, characterized by changing the position of the tip.