JPH01150716A - Method for controlling combustion of side combustion multi-zone type heating furnace - Google Patents

Abstract

PURPOSE:To enable a stable uniform heating to be performed when a high turn down operation is carried out by a method wherein some detected values of a plurality of thermometers installed within each of the zones are weighted to obtain their means value, and an amount of fuel and air in respect to all the burners in the zones are totally controlled with a zone representative temperature calculated in reference to a corrected value corresponding to an ignition distributing pattern. CONSTITUTION:A representative furnace temperature for use in controlling a cyclic combustion is accurately determined, controlled in response to this representative furnace temperature and a cyclic uniform heating when a high turn down operation is carried out stably. That is, in a combustion control system in which a plurality of burners within each of the zones of a side combustion multi-zone type heating furnace are ignited in sequence in a periodic manner and diminished to performed a controlling of combustion for carrying out a high turn down control, values of a plurality of thermometers installed within each of the zones are weighted by an arrangement of the thermometers so as to obtain their mean values and then an amount of fuel-air in respect to an zone representative temperature Tpv expressed by an equation (I) calculated by the corrected values corresponding to a fire diminishing and ignition distribution pattern of the burners in the zone.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a side-fired multi-zone heating furnace. Multiple burners installed in a zone are ignited in sequence and periodically in order to perform combustion control that allows for wide-range combustion load changes, that is, high turndown combustion control.

This relates to a combustion control method for extinguishing a fire.

[Conventional technology]

Conventionally, combustion control for side-fired multi-zone heating furnaces is based on the difference between the temperature inside the furnace and the target temperature, which is measured using thermocouples installed at one or more locations inside the furnace. The fuel and air control valves are operated to control the temperature inside the furnace to match the target temperature, and generally each zone of the heating furnace has a

A plurality of burners are installed, and the amount of fuel and air used for burner combustion in each zone is collectively controlled.

The range of the amount of fuel and air in each zone is such that the maximum flow rate is the flow rate required at the maximum load to avoid insufficient burning of the steel in the furnace. At that time, the minimum flow rate is naturally restricted due to hardware constraints of flowmeters and control valves, and in order to uniformly heat the zone in the width direction of the furnace, the flame length must be constant so that the heat reaches the center of the furnace width direction. There is also a minimum flow rate required to ensure the minimum flow rate, and the minimum flow rate cannot be arbitrarily selected.

During furnace operation, low-load combustion operations such as holding down due to trouble or low-load combustion by charging hot pieces are also required, and high turndown combustion control is essential for furnace operation.

With current technology, the flow rate ratio for ensuring the required flame length is smaller than the flow rate ratio determined by the flow rate control system, and a high turndown ratio, i.e., based on the minimum flow rate constraint for ensuring the required flame length, is lower than the flow rate ratio determined by the flow control system. The maximum/minimum flow ratio is determined.

When performing low-load combustion as described above, part of the burner in the zone is extinguished in order to ensure a turndown ratio that is higher than the turndown ratio determined by the minimum flow rate constraint to ensure the required flame length. , a method has been considered in which thinning combustion is performed to increase the combustion load on the lit burner and to allow heat to reach the center in the width direction of the furnace (Japanese Patent Application Laid-Open No. 60-50).
No. 113).

In this case, if the steel remains in the furnace length direction (steel material movement direction) for a long time, a temperature difference will occur between the position near the ignition burner and the position near the extinguishing burner, which will prevent uniform heating in the furnace length direction. A method of sequentially and periodically changing the extinguishing burner position (hereinafter referred to as cyclic combustion) has been proposed (Japanese Patent Application No. 61-164350).

For example, in the case of side-firing multi-zone heating f as shown in Figures 1 and 2, a thermometer is installed at one location on the ceiling or hearth of the zone as shown in Figures 3 and 4. Combustion control is performed by a control system as shown in FIG. Using the difference between the furnace temperature obtained by the thermometer 9 and the target temperature, the furnace temperature regulator 14 determines whether the furnace temperature is within the permissible range. If it is outside the permissible range, the fuel flow rate is reduced to bring the temperature within the permissible range. If the fuel flow rate has not been reached, the fuel flow rate control valve 10 is operated by the fuel flow rate regulator 15 to increase the fuel flow rate. Further, like the fuel flow rate, the air flow rate control valve 17 is operated by the air flow rate regulator 16 so that the ratio of fuel and air is constant.

On the other hand, in order to achieve uniform heating in the width direction of the furnace during low load combustion (low T/D), it is necessary to increase the T per zone as shown in Figure 6.
As the /D ratio (combustion load factor) decreases, it is necessary to reduce the number of combustion burners, reduce the number of ignition burners per burner, and increase the T/D ratio (combustion load factor) per burner, as shown in Figure 7. In addition, in order to eliminate the temperature difference between the ignition burner and the extinguishing burner that occurs in the furnace length direction, and to achieve uniform heating in the furnace length direction, the burner ignition position is switched at certain predetermined intervals as shown in Figure 8. The fuel cutoff valves 11 to 13. are operated by the cutoff valve operation control device 18. This is done by operating the air cutoff valves 19 to 21, that is, selecting the mode (all burner combustion, 1 row thinning or 2 row thinning) shown in FIG. 8 corresponding to the T/D ratio per zone, and When in between-column mode or between-two-column mode.

Pattern shown in FIG. 8 11t 21y 31* 11+
...or pattern 12*22*3□, 12.・
...and switches the ignition and extinguishing burner.

[Problem to be solved by the invention]

However, in the burner combustion control method described above,
Although the deviation is within the tolerance, rapid changes in the temperature distribution within the zone occur over time due to the ignition and extinguishing of the burners in the zone, so it is necessary to use the conventional thermometer at one location or several locations along the width of the furnace. When the furnace temperature in the zone is controlled by (for example, Japanese Patent Application Laid-Open No. 11018/1982), hunting occurs in the detected value of the thermometer as shown in Figure 9, making normal control impossible or causing burner failure. The furnace temperature will be different than when ignition and extinguishing are not performed, making it difficult to determine the representative furnace temperature of the control zone.

Therefore, an object of the present invention is to rationally determine the representative furnace temperature and stably perform cyclic uniform heating during high turndown operation of a side burner-fired heating furnace.

[Means for solving problems]

In order to achieve the above object, the present invention accurately determines a representative furnace temperature for control in cyclic combustion, and controls based on the representative furnace temperature to stabilize cyclic uniform heating during high turndown operation. In other words, in a combustion control method in which multiple burners in each zone of a side-fired multi-zone heating furnace are sequentially and periodically ignited and extinguished to achieve high turndown control, multiple burners are arbitrarily installed in each zone. The zone representative temperature Tpv is calculated by weighting and averaging the values of the thermometers according to the arrangement of the thermometers, and using the correction value corresponding to the extinguishing and 2 ignition distribution pattern of the burners in the zone, n: number of thermometers in the width direction of the furnace, m : Number of thermometers in the furnace length direction.

Tij: Thermometer reading at the i-th position in the furnace width direction and the j-th position in the furnace length direction.

αi: Weighting coefficient of the i-th thermometer in the furnace width direction.

βj: Weighting coefficient of the jth thermometer in the furnace length direction, K:
The amount of fuel and air for all burners in the zone is collectively controlled based on the correction value corresponding to the extinguishing 1 ignition distribution pattern of the burners in the zone.

[Effect]

According to this, since it is possible to evaluate the average furnace temperature in the same manner as when cyclic combustion is not performed, taking into account the temperature distribution within the zone, it is possible to control the case when transitioning to cyclic combustion in the same way as when it is not performed.

Normal control is possible without falling into an uncontrollable state such as hunting.

The features of the present invention include the indicated value at the installation position of the thermometer and its weighting coefficients αi, βj↓; calculating a more average furnace temperature; The effect on the thermometer, that is, the deviation from the case where one burner is fixed to extinguish and the other burner is fixed to ignition (when there is no cyclic combustion), is determined by a correction value of 1. This corrects the temperature and gives the same furnace temperature as without cyclic combustion.

In the embodiment of the present invention, thermometers were arranged in a row at three locations in the width direction of the oven, and were installed in two rows in the oven length direction.

【Example〕

FIG. 10 shows an example of a continuous heating furnace in which the side burner combustion control method of the present invention is implemented, and FIG.
The cross section of the continuous heating furnace shown in the figure is shown in Figure 12.
FIG. 10 shows a plan view of one zone of the continuous heating furnace shown in FIG. 10, looking down from the line ■-■. In these figures, 1 is a pass line, 2 is a material to be heated, 3 is a furnace body, 4 is a heating space, and 5 is a heating space.
is a burner (side burner) installed on the side of the furnace body 3,
6 is the flame emitted from the burner 5, 7 is the partition wall, 8 is the side wall,
80 is an extraction port for extracting the material to be heated from the furnace. 27~
32 is a thermometer for the upper zone, and 33 to 35 are thermometers for the lower zone.

The material to be heated 2 placed on a skid (not shown) passes through the pass line 1 and is transported inside the furnace toward the extraction port 80 . The furnace body 3 is divided into a plurality of zones by a partition wall 7, and combustion control of the burner 5 within the zone is performed for each zone. That is, the temperature inside the furnace is controlled for each zone.

Referring to FIG. 12, there are three pairs of side burners 5 (A-F) in one zone, and combustion of these is controlled in burner pair units.

FIG. 13 is a block diagram of the three pairs of burners and valve arrangement in one zone of the furnace and the system for controlling the combustion of the three pairs of burners.

In FIG. 13, 10 is a fuel flow control valve, 11 to 13
17 is an air flow control valve, and 19 to 21 are cutoff valves. 1st pair A: B, 2nd pair C9D and 3rd pair E
, F, each pair of burners 5 is controlled as one unit.

In the side burner combustion control method for a continuous heating furnace of this embodiment, combustion control is performed in units of 1,000 (3 pairs in each unit) above one zone, so for example, 3 pairs (total number N = 6. Heat input Q per burner with total logarithm Nl = 3)
When c1 (instruction value) is given, the maximum logarithm n1 of the burner is calculated from this and the heat input amount 9o of one side burner as follows.

2(nt + 1)・q o >Qct≧2nt・+
IaIn addition, if this is expressed as a -conversion, the total number of burners N, the number of combustion burners n, and the required amount of human heat Qc.

(n+1)・qo>Qc≧n’+t.

N≧n, and the opening degree of the fuel control valve 10 is set to the opening degree that supplies fuel corresponding to Qcx, and the n1 pair of burners is turned on (combustion: fuel supply) by opening and closing the shutoff valves 11 to 13. ),
N1 (=3)-nt pairs of burners are turned off (non-combustion: fuel cutoff), and each pair is Burner on/off pattern (in all burner combustion mode, all burners are ignited continuously; in 1 row thinning mode, patterns 11 to 31.2
Patterns 12 to 32) in column thinning mode.

In FIG. 8, the circle mark indicates on (ignition) and the x mark indicates off (extinguishing), and in this embodiment, switching is performed at a cycle of 2 minutes. These judgments are made by the shutoff valve operation control device 18 shown in FIG.

In this example, the burners A-F are all of the same construction and dimensions, the isolation valves 11-13 are also all of the same construction and dimensions, and through one flow control valve 10, all burners in the on (combustion) setting are , the total amount of heat input Q c
1 corresponding fuel is supplied, so each burner that is set to on has the same amount of Qe1/2n1 (heat input unit)
Corresponding fuel is supplied.

FIGS. 6 and 7 show characteristic diagrams when such combustion control is performed. That is, FIG. 6 shows the relationship between the T/D ratio (combustion load factor) and the number of combustion burners per upper section of one zone of the heating furnace, and FIG.
It shows the relationship between the T/D ratio (combustion load factor) per upper section of the zone and the T/D ratio (combustion load factor) per burner. In each zone of the heating furnace, the number of combustion burners (full combustion mode, inter-row mode, or 2-row thinning mode shown in FIG. 8) changes depending on the combustion load rate, and As a result, the combustion load rate per burner changes, so the combustion load rate per low zone is 10 to 30.
%, without reducing the combustion load rate per burner.
It shows that it can be driven.

At this time, in the zone representative temperature equation, the number of thermometers in the oven width direction is n=3. The number of thermometers in the furnace length direction is m = = 2, and the zone representative temperature 'l'pv is, where the thermometers T11゜''β21, 'ra in the first row in the furnace width direction are
1 and 2nd row thermometer 'rt 2 , T22.

Ta2 is thermometers 27 to 29 and 30 to 32 in FIG.
, and their weighting coefficients are the coefficients α1 . α2. α3 and column arrangement coefficient β1. The product with β2 is αi·βj. These weighting coefficients are determined by the area in the furnace that the thermometer represents, and in the case of this embodiment, as shown by the dotted line in FIG.
The furnace length direction plane is divided into 3 parts in the furnace width direction and 2 parts in the furnace length direction, divided into 6 equal areas, and a thermometer is installed in the center of each of them to evenly distribute the furnace temperature to the 6 thermometers. By dividing α1=1. α2=1. α3=1, β1=1.
β2=1. The weighted average value using this weighting coefficient is calculated as an average furnace temperature in consideration of the furnace temperature distribution within the zone.

During cyclic combustion, the readings on each thermometer repeatedly fluctuate up and down as shown in Figure 9 each time the burner is lit and extinguished. The indicated value will fluctuate.

Focusing on all the thermometers, these fluctuation cycles are the same, but one phase is shifted from each other. The above-mentioned "average furnace temperature", which is the average of the temperatures indicated by each thermometer, is obtained by smoothing out the fluctuations. The correction value that makes the furnace temperature smoothed in this way (the weighting of the indicated value of each thermometer is an average value) to the same value as the average temperature when cyclic combustion is not performed is K.

K is a constant determined by the heating furnace, such as the furnace type, refractory composition, and burner ignition characteristics, and is determined by which pattern (Figure 8) is being executed in cyclic combustion. .

For example, in the all-burner combustion shown in FIG. 8, since all burners are continuous combustion, Km is set to O or a required value. 8th
In the three patterns 11 to 13 of the one-row thinning mode shown in the figure and the three patterns 12 to 3a of the two-row thinning mode shown in the figure, for example, pattern 11 of the one-row thinning mode (burner A, B
For example, when this pattern is continuous and when this pattern is included in cyclic combustion, even if the pattern is the same, when cyclic combustion Since there is a switch to ignition, at the same time (for example, 2 minutes, which is the switching period of the cyclic combustion switching pattern), the influence of the furnace temperature is different from that during continuous combustion, and the detected value by the thermometer is different. To correct this, the correction value is 11 (pattern 11
In the case of the 3-mode 7 pattern (all-burner combustion mode is one pattern) in Fig. 8, which is the correction value assigned to during execution), 1 is therefore Koo (assigned in all-burner combustion mode) * Kt t~Kig (assigned to patterns 11~31) and 21~2
3 (assigned to patterns 12 to 32).

FIG. 14 shows patterns 11 to 1. in the one-row thinning mode shown in FIG. Average furnace temperature TPV'' during cyclic combustion in which the period is changed over every 2 minutes (solid line: TPV not including the term
pv calculation formula) and the average furnace temperature Tpv' for each 2-minute period of each pattern when each of patterns 11 to 13 are continuous (dotted line: calculated using the Tpν calculation formula that does not include the term As shown in Figure 14, even with the same pattern, the calculated furnace temperature when cyclic combustion is used is the same as when cyclic combustion is not performed. Since the calculated furnace temperature deviates, the amount of deviation (deviation) is determined in advance and used as a correction value.

In this example, the correction value Kll when burners A and B in FIG. 8 are extinguished (pattern 11) is as shown in FIG. 14.
The difference between pattern 11 when cyclic combustion is performed and when it is not performed is set to 11=10.

Similarly, when burners C and D are extinguished (pattern 2
The correction value of 1) is set to 12 = 5 according to FIG. Also, when burners E and F are extinguished (pattern 31
) is set to 111 and 13=0 according to FIG.

Correction values 21 to 23 are similarly determined to be assigned to patterns 12 to 32 in the two-column thinning mode.

The above coefficient α1. α2. αa, β1. β2 and correction value K
Calculate the representative temperature Tpv of the zone using l 1 "" K18 e K21 ~ 2 a using the temperature calculation device 2 in Fig. 13.
6, the zone representative temperature Tpv is obtained by the temperature calculation device 26, and the target furnace temperature Ts is obtained by the temperature adjustment 1114.
v and determine the required amount of fuel and air. The flow control device 15 operates and controls the flow regulating valves 10.17 so that the required amount of fuel and air flows.

As a result of the above control, as shown in No. 151, when conventional cyclic combustion was performed, the furnace temperature fluctuated greatly and was difficult to control, but the furnace temperature changed smoothly and combustion controllability was improved. .

〔Effect of the invention〕

As explained above, according to the combustion control method of the present invention, furnace temperature controllability in the case of cyclic combustion is improved, and controllability equivalent to that in the case of no cyclic combustion can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of a side-fired continuous heating furnace, Fig. 2 is a sectional view taken along line I-1 of the continuous heating furnace shown in Fig. 1, and Fig. 3 is a longitudinal sectional view of a side-fired continuous heating furnace.
FIG. 2 is a sectional view taken along the line n-■ of the continuous heating furnace shown in FIG. 1. FIG. FIG. 4 is a plan view of one zone of the continuous heating furnace shown in FIG. 1, looking down from above the line 1-m, and FIG. 5 is a block diagram showing a conventional control system. Figure 6 shows the load factor per zone (horizontal axis) when cyclic combustion is performed.
Figure 7 is a graph showing the relationship between the load factor per zone (horizontal axis) and the load factor of one burner being burned (vertical axis). 8
The figure is a plan view showing the control pattern for one zone shown in Fig. 2, and Fig. 9 is a graph showing the transition of the detected furnace temperature under normal combustion control (without cyclic combustion) and during cyclic combustion. be. FIG. 10 is a longitudinal sectional view of a side-fired continuous heating furnace to which an embodiment of the present invention is applied, FIG. 11 is a sectional view taken along the line IV-mV of the continuous heating furnace shown in FIG. 10, and FIG. Fig. 10 is a plan view of one zone of the continuous heating furnace looking down from above the ■-v line, Fig. 13 is a block diagram showing a control system implementing one embodiment of the present invention, and Fig. 14 is a FIG. 15 is a graph showing the difference in weighted average furnace temperature between when cyclic combustion is performed and when cyclic combustion is not performed in an embodiment of the present invention, and FIG. 15 is a graph showing detected furnace temperatures between the embodiment of the present invention and the conventional example. . 1: Pass line 2: Heated material 3: Furnace body
4: Heating space 5: Burner (side burner) 6: Flame 7: Partition wall 8:
Side wall 9: Thermometer 10: Combustion control valve 1
1.12, 13: Fuel cutoff valve 14: Temperature regulator 15: Fuel regulator 16: Air regulator 1
7: Air control valve 18: Shutoff valve control device 19.
20, 21: Air cutoff valve 22: Fuel pipe 23
: Orifice 24: Air piping 25: Orifice 26; Zone representative temperature calculator 27, 28, 2
9, 30, 31, 32, 33, 34.35: Thermometer 8
0: Extraction port 90: Thermocouple hole 51 Figure 9 figure Ginma (min) Voice 10 figure Voice 11 figure 12 figure

Claims (1)

[Claims] In a combustion control method that performs high turndown control by sequentially and periodically igniting and extinguishing a plurality of burners in each zone of a side-fired multi-zone heating furnace, a plurality of burners installed in each zone are provided. The zone representative temperature Tpv is calculated by weighting and averaging the detection values of each thermometer according to the arrangement of the thermometers, and using correction values corresponding to the extinguishing and ignition distribution pattern of the burners in the zone. ▲Mathematical formulas, chemical formulas, tables, etc. are available▼ n: number of thermometers in the furnace width direction, m: number of thermometers in the furnace length direction, Tij: thermometer reading at the i-th position in the furnace width direction and j-th position in the furnace length direction, αi: i-th position in the furnace width direction The weighting factor of the thermometer, βj:
The weighting coefficient of the j-th thermometer in the furnace length direction, K_l: Correction value corresponding to the extinguishing and ignition distribution pattern of the burner in the zone when reading the detected value of the thermometer, and calculates the amount of fuel and air for all burners in the zone. A combustion control method for a side-fired multi-zone heating furnace characterized by collective control.