JP2010060156A - NOx SUPPRESSION CONTROLLING DEVICE OF HEATING FURNACE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce NOx concentration in a heating furnace comprising a continuous combustion burner at low costs without badly affecting a combustion state in the continuous combustion burner and slab charged into the furnace. <P>SOLUTION: This NOx suppression controlling device includes: an exhausting means 9a for discharging a part of the preheated combustion air preheated by a heat exchanging means 5 to the external; a supplying means 14 for supplying the unpreheated cold air to the preheated combustion air supplied to the continuous combustion burner 2; an NOx measuring means 11 for measuring NOx concentration in a combustion exhaust gas discharged from the heating furnace 1; and a control means 12 for allowing the exhausting means 9a to discharge a part of the preheated combustion air to lower a temperature of the combustion air supplied to the continuous combustion burner 2 when the NOx concentration measured by the NOx measuring means 11 is over a predetermined set value, and supplies the cold air of the amount corresponding to the preheated combustion air discharged to the external, to the preheated combustion air supplied to the continuous combustion burner 2 by the supplying means 14. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a NOx suppression control device for a heating furnace provided with a continuous combustion burner.

  In recent years, in a continuous heating furnace of a hot rolling facility, an energy saving effect is improved by recovering exhaust heat of combustion exhaust gas and preheating combustion air. In this case, as the exhaust heat recovery from the combustion exhaust gas is increased, the combustion air can be preheated at a higher temperature, and a higher heat exchange rate can be obtained. However, when the preheating temperature of the combustion air becomes high, the flame temperature of the burner installed in the heating furnace rises locally, and there is a problem that the concentration of nitrogen oxide (NOx), which is an air pollutant, rapidly increases. .

  In addition, in the case where the burner provided in the heating furnace is of a type that gives a strong swirling flow in a burner tile such as a roof burner and causes abrupt combustion in the burner tile or in the vicinity of the ceiling, the NOx concentration is Become very expensive.

In such a case, as a method for reducing the NOx concentration, for example, water or steam is supplied to the combustion air preheated by heat exchange with the combustion exhaust gas, the combustion air is humidified, and the combustion temperature in the burner is lowered. Thus, a method for reducing the generation of NOx has been proposed (see, for example, Patent Document 1). As another method for reducing the NOx concentration, a method of providing a denitration device in the exhaust equipment of a heating furnace has been proposed (see, for example, Patent Documents 2 and 3).
JP-A-2005-241184 JP 2001-79394 A JP-A-9-141363

  However, since the method described in Patent Document 1 requires a humidifier for supplying water or water vapor, the equipment becomes complicated, equipment costs increase, and the humidity in the furnace is high. As a result, there is a problem that scale is likely to occur in the slab in the heating furnace. In addition, the methods described in Patent Documents 2 and 3 have many problems such as the high cost of the denitration apparatus and the need for attention in handling ammonia.

  The present invention has been proposed in view of such conventional circumstances, and is capable of reducing NOx concentration in a heating furnace equipped with a continuous combustion burner at low cost and in the combustion state in the continuous combustion burner, It is an object of the present invention to provide a NOx suppression control device that can be performed without adversely affecting the slab charged in the furnace.

The gist of the present invention aimed at solving the above problems is as follows.
(1) A heating furnace provided with a continuous combustion burner that continuously burns in the furnace, and combustion air supplied to the continuous combustion burner after recovering exhaust heat of combustion exhaust gas discharged from the bottom of the furnace In a heating furnace having a chimney for preheating the heat exchange means, and a chimney for dissipating the combustion exhaust gas after the exhaust heat is recovered by the heat exchange means into the atmosphere,
Exhaust means for discharging a part of the preheated combustion air preheated by the heat exchange means to the outside;
Supply means for supplying cold air that is not preheated into preheated combustion air supplied to the continuous combustion burner;
NOx measuring means for measuring NOx concentration in the combustion exhaust gas discharged from the heating furnace;
When the NOx concentration measured by the NOx measuring means exceeds a preset value, the exhaust means is used to reduce the temperature of the combustion air supplied to the continuous combustion burner. And a control means for controlling the supply of the cold air in an amount corresponding to the preheated combustion air discharged to the outside into the preheated combustion air supplied to the continuous combustion burner by the supply means A NOx suppression control device for a heating furnace, characterized by comprising:
(2) The NOx of the heating furnace according to (1), wherein the exhaust amount of the preheated combustion air is determined according to a difference between the NOx concentration measured by the NOx measuring means and a preset set value. Suppression control device.

  As described above, according to the present invention, since it has a simple equipment configuration, it can be easily applied to an existing heating furnace, and at a low cost, the amount of combustion air and the amount of moisture to be supplied into the heating furnace. Because there is almost no fluctuation in the temperature, combustion in the burner can be continued stably, and exhaust heat in the exhaust gas discharged from the furnace bottom of the heating furnace can be recovered without adversely affecting the slab charged in the furnace. In addition, the NOx concentration in the exhaust gas can be reduced to a preset value or less, and the effect in this field is great.

Hereinafter, a NOx suppression control device for a heating furnace to which the present invention is applied will be described in detail with reference to the drawings.
(First embodiment)
First, as a first embodiment, a case where the present invention is applied to a continuous heating furnace 1 of a hot rolling facility as shown in FIG. 1 will be described as an example.

  A continuous heating furnace (hereinafter referred to as a heating furnace) 1 of this hot rolling facility is a walking beam that is a conveying means for transferring a slab (slab) that is a material to be heated, which is charged into the furnace from the charging port 1a. (Not shown). While passing through the pre-tropical zone, heating zone, and soaking zone in the furnace in sequence, the burner is heated to a predetermined temperature. The slab heated to a predetermined temperature is extracted from the extraction port 1b of the heating furnace 1 and then sent to a rolling line (not shown) in the next step.

  The heating furnace 1 is provided with a plurality of continuous combustion burners 2 for continuously heating the inside of the furnace. For example, the continuous combustion burner 2 is arranged in the upper part of the heating furnace 1 so as to be aligned in the furnace width and furnace length directions. In addition to the roof burner, the continuous combustion burner 2 includes a side burner arranged at the side of the heating furnace 1, an axial flow burner arranged along the furnace length direction at the upper or lower part of the heating furnace 1, and the like. These continuous combustion burners 2 can be used singly or in combination of two or more.

  The heating furnace 1 has, as its exhaust heat recovery equipment, an exhaust system 3 that exhausts combustion exhaust gas in the furnace from the furnace bottom side, and a single chimney 4 that exhausts combustion exhaust gas discharged from the exhaust system 3 into the atmosphere. And a recuperator 5 which is a heat exchange means for recovering the exhaust heat of the exhaust gas discharged from the exhaust system 3 and preheating the combustion air.

  The recuperator 5 collects exhaust heat of the combustion exhaust gas discharged from the exhaust system 3, preheats the combustion air introduced through the cold air pipe 7 by the combustion air fan (blower) 6, and then preheats the combustion air pipe 8. To the continuous combustion burner 2.

  In the exhaust heat recovery facility of the heating furnace 1 having the above structure, the recuperator 5 recovers exhaust heat of the combustion exhaust gas discharged from the exhaust system 3 and preheats the combustion air supplied to the continuous combustion burner 2. Thus, exhaust heat recovery from the combustion exhaust gas discharged from the furnace bottom of the heating furnace 1 can be performed.

  By the way, in such an exhaust heat recovery facility of the heating furnace 1, it is necessary to suppress the generation of NOx as an environmental measure so that the NOx concentration does not exceed a set value (for example, a regulation value according to legal regulations). That is, as a background of such low NOx, there is a strict regulation of NOx concentration by regulations or the like, a total amount control of exhausted NOx, and the like.

  Therefore, in the present invention, when it is difficult for the NOx concentration to fall below such a set value, continuous combustion is prioritized over the recovery of exhaust heat from the combustion exhaust gas discharged from the furnace bottom of the heating furnace 1 described above. It was decided to reduce NOx by lowering the temperature of the combustion air supplied to the burner 2.

  Specifically, the present invention is preheated by exhaust pipe 9a (exhaust means) provided with an exhaust valve 9 for discharging preheated combustion air preheated by the recuperator 5 to the outside, and preheated combustion air from the recuperator 5. A bypass pipe (supply means) 14 provided with a supply valve 10 for supplying non-air (outside air) and a NOx meter for measuring the NOx concentration in the combustion exhaust gas discharged from the furnace bottom of the heating furnace 1 (Measuring means) 11 and a controller (control means) 12 for controlling the temperature of the combustion air supplied to the continuous combustion burner 2 are provided.

  The exhaust pipe 9 a is provided in the middle part of the preheating combustion air pipe 8. Further, the exhaust valve 9 is a flow rate adjusting valve, and is connected to the control unit 12 via the flow rate indicating controller 13. Further, the bypass pipe 14 bypasses the recuperator 5 and is connected to the preheated combustion air pipe 8 at a position subsequent to the connection portion of the exhaust pipe 9a, and the unpreheated air introduced by the combustion air fan 6 ( Part of the outside air) can be supplied into the preheated combustion air pipe 8. The supply valve 10 provided in the bypass pipe 14 is a flow rate adjusting valve, and is connected to the control unit 12 via a flow rate indicating controller 15. The NOx meter 11 is arranged at a position subsequent to the recuperator 5 of the exhaust system 3, measures the NOx concentration in the combustion exhaust gas flowing through the exhaust system 3, and outputs the measurement data to the sequential control unit 12.

  The control unit 12 includes a main computer that controls each part of the heating furnace 1, or a computer connected to or independent from the main computer. When measurement data is input from the NOx meter 11, the control unit 12 records therein. In accordance with the program, it is determined whether or not the NOx concentration exceeds a preset set value, and when the NOx concentration exceeds the set value, control for lowering the temperature of combustion air supplied to the continuous combustion burner 2 described later. I do.

  In the heating furnace 1 having the above structure, when the NOx concentration measured by the NOx meter 11 exceeds the set value, the flow rate indicating controller 13 controls the opening degree of the exhaust valve 9 in accordance with an instruction from the control unit 12. By controlling, a part of the preheated combustion air is discharged from the exhaust pipe 9a to adjust the flow rate of the preheated combustion air flowing through the preheated combustion air pipe 8. On the other hand, when the flow rate indicating controller 15 controls the opening degree of the supply valve 10 in accordance with the instruction from the control unit 12, the amount corresponding to the preheated combustion air discharged to the outside from the exhaust valve 9, that is, the same amount of preheat. The flow rate of the cold air flowing through the bypass pipe 14 is adjusted so that cold air (outside air supplied from the combustion air fan 6) that has not been supplied is supplied from the bypass pipe 14 to the preheated combustion air pipe 8. As a result, the preheated combustion air from the recuperator 5 is diluted with cold air, so that the temperature of the combustion air supplied to the continuous combustion burner 2 can be lowered, for example, as shown in FIG. Generation can be suppressed.

Next, the control of the preheated combustion air amount from the exhaust pipe 9a and the cold air amount from the bypass pipe 14 in the control unit 12 will be described in more detail.
In the control unit 12, first, when the measured value of the NOx meter 11 is inputted, an average value within a preset time (for example, 1 hour) is calculated, and when this average value exceeds the set value, this difference (ΔNOx) Next, from this difference (ΔNOx), the cold air mixing rate is calculated based on FIG. 4 (a diagram showing the relationship between the NOx reduction amount and the cold air mixing rate determined in advance). Then, the amount of cold air mixed is obtained by multiplying the total amount of combustion air used in the continuous combustion burner 2 by the calculated cold air mixing ratio.

  Then, an opening degree command for the exhaust valve 9 is output to the flow rate indicating controller 13 so that the preheated combustion air corresponding to the cold air mixing amount is discharged from the exhaust pipe 9a to the outside, and the cold air mixing amount is supplied from the bypass pipe 14. An opening degree command is output to the flow rate indicating controller 15 so that the cold air is supplied to the preheated combustion air pipe 8. As a result, the exhaust valve 9 is opened by its opening, and preheated combustion air is discharged from the exhaust pipe 9 a to the outside, and cold air is supplied to the preheated combustion air pipe 8 through the bypass pipe 14. As described above, since the preheated combustion air and the cold air that are discharged are the same amount, the amount of air necessary for combustion is ensured.

  Moreover, it is preferable that the air flow control of the combustion air fan 6 is performed by an instruction from the control unit 12. That is, a command for increasing the rotational speed of the combustion air fan 6 is sent to the drive unit (not shown) of the combustion air fan 6 so that the amount of air blown from the combustion air fan 6 is increased by the calculated amount of cold air mixed. Output to. That is, the amount of air discharged from the combustion air fan is increased by the amount of air discharged to the outside from the exhaust pipe 9a, and the discharge pressure of the fan is decreased, so that the air amount and pressure required for combustion are maintained so that the air amount and pressure required for combustion are maintained. Control is in progress.

  As described above, in the present invention, NOx is generated by lowering the temperature of the combustion air supplied to the continuous combustion burner 2 when the NOx concentration in the combustion exhaust gas discharged from the furnace bottom of the heating furnace 1 exceeds the set value. Can be suppressed.

(Second Embodiment)
Next, as a second embodiment, a case where the present invention is applied to a continuous heating furnace 21 of a hot rolling facility as shown in FIG. 2 will be described as an example.

  As in the first embodiment, the heating furnace 21 includes a continuous combustion burner 22 that continuously heats the inside of the furnace, and combustion and exhaust in the furnace alternately. There is installed a regenerative burner (regenerative burner) 23 that regenerates heat with a heat storage body and preheats combustion air with heat stored in the heat storage body during combustion.

  Since the continuous combustion burner 22 is the same as that of the first embodiment, the description is omitted here. The regenerative burner 23 includes a pair of burners provided with heat accumulators arranged opposite to the side of the heating furnace 21, and the pair of burners alternately repeat combustion and exhaust, while burning one of the burners. By passing the combustion exhaust gas generated by the above to the heat storage body of the other burner, the sensible heat in the combustion exhaust gas is stored in the heat storage body, and when the other burner burns, the combustion air is passed through this heat storage body In this way, the combustion air is preheated. The regenerative burner 23 is installed on the upper side and the lower side of the heating furnace 21 on both sides of the pre-tropical zone and the heating zone, with the slab conveying path interposed therebetween. The regenerative burner 23 is not limited to the above-described arrangement, and can be arbitrarily installed on any side of the pre-tropical zone, heating zone, and soaking zone.

  The heating furnace 21 includes an induction fan 27 as an exhaust heat recovery facility, and a first exhaust system for introducing the combustion exhaust gas of the heat storage burner 23 into a second exhaust system 25 described later in the vicinity of the chimney 26. 24 and a second exhaust system 25 for introducing the combustion exhaust gas in the furnace from the furnace bottom side to the chimney 26, and the second exhaust system 25 is a furnace pressure control means as described above. A furnace pressure damper 28 and a recuperator 29 as heat exchange means are provided.

  Further, since the combustion air supply system supplied to the continuous combustion burner 22 of the present embodiment is the same as that of the first embodiment, description thereof will be omitted here. Further, the combustion air supply system of the regenerative burner 23 is configured to pipe a part of the combustion air from the combustion air fan 30 before the combustion air from the combustion air fan 30 is supplied to the regulator 29 ( (It is not shown in the figure.) Is branched and supplied to each regenerative burner 23. At this time, this pipe is controlled by a flow rate adjusting valve (not shown) so that the amount of air for branch combustion becomes a target value.

  The NOx meter 35 is disposed in the second exhaust system 25 between the joining position of the first exhaust system 24 and the chimney 26, measures the NOx concentration in the combustion exhaust gas flowing into the chimney 26, and the measurement data Is input to the control unit 36.

  As in the first embodiment, the control unit 36 includes a main computer that controls each part of the heating furnace 21, or a computer connected to or independent of the main computer. When the set value is exceeded, the difference (ΔNOx) is obtained, and the NOx reduction amount of the continuous combustion burner 22 is obtained from the amount gradually reduced by the combustion amount ratio of the continuous combustion burner 22 with respect to the combustion amount of the entire furnace. The same control as in the embodiment is performed.

  When the measured value of the NOx meter 35 is input, an average value within a preset time (for example, 1 hour) is calculated, and when this average value exceeds the reference value, this difference (ΔNOx) is obtained, and this difference (ΔNOx ) To calculate the temperature drop amount (ΔT) of the combustion air supplied to the continuous combustion burner 22, and the amount of preheated combustion air discharged from the exhaust pipe 33a to the atmosphere and the bypass pipe 38 so as to be the temperature drop amount (ΔT). The amount of cold air (outside air) supplied to the preheated combustion air piping 32 is calculated, and the calculated amounts of both air are output to the flow rate indicating controllers 37 and 39 to control the opening degree of the exhaust valve 33 and the supply valve 34. To do.

  Then, the preheated combustion air is discharged from the exhaust pipe a33 to the outside air, and the amount of preheated cold air (outside air) equivalent to the discharged amount of preheated combustion air is supplied from the bypass pipe 38 to the preheated combustion air pipe 32. The Thereby, the temperature of the combustion air supplied to the continuous combustion burner 22 can be lowered, and the generation of NOx can be suppressed.

  The present invention can be applied not only to the above-described continuous heating furnaces 1 and 21 of the hot rolling equipment, but also to a heating furnace having at least a continuous combustion burner. The control units 12 and 36 obtain the difference (ΔNOx) between the NOx concentration measured by the NOx meter 35 and the set value, and the exhaust valves 9 and 33 and the supply valves 10 and 34 are based on this difference (ΔNOx). However, the present invention is not limited to this, and it is not limited to this, but in advance at predetermined intervals (preferably about 10% of the rated air volume of the combustion air fan) step by step with a pitch of 5 to 10 minutes. In addition, the opening control of the exhaust valves 9 and 33 and the supply valves 10 and 34 may be repeated until the measured NOX concentration becomes a set value or less.

These are the schematic diagrams of the waste heat recovery equipment of the heating furnace shown as 1st Embodiment. These are the schematic diagrams of the waste heat recovery equipment of the heating furnace shown as 2nd Embodiment. These are the graphs which show the relationship between the dilution rate which dilutes preheating combustion air with cold air, and the temperature of the preheating combustion air supplied to a continuous combustion burner. These are graphs showing the relationship between the dilution rate and the NOx reduction amount.

Explanation of symbols

1, 2: Heating furnace
2, 22: Continuous combustion burner
3, 25: Exhaust system
4, 26: Chimney
5, 29: Recuperator (heat exchange means)
6, 30: Combustion air fan
8, 32: Preheated combustion air piping
9, 33: Exhaust valve
9a, 33a: Exhaust piping (exhaust means)
10, 34: Supply valve
11, 35: NOx meter (NOx measuring means)
12, 36: Control unit (control means)
14, 31: Bypass piping (supply means)
23: Regenerative burner

Claims (2)

A heating furnace having a continuous combustion burner that continuously burns in the furnace, and recovering exhaust heat of combustion exhaust gas discharged from the bottom of the heating furnace to preheat the combustion air supplied to the continuous combustion burner In a heating furnace having a heat exchange means and a chimney for dissipating the combustion exhaust gas after the exhaust heat is recovered by the heat exchange means into the atmosphere,
Exhaust means for discharging a part of the preheated combustion air preheated by the heat exchange means to the outside;
Supply means for supplying cold air that is not preheated into preheated combustion air supplied to the continuous combustion burner;
NOx measuring means for measuring NOx concentration in the combustion exhaust gas discharged from the heating furnace;
When the NOx concentration measured by the NOx measuring means exceeds a preset value, the exhaust means is used to reduce the temperature of the combustion air supplied to the continuous combustion burner. And a control means for controlling the supply of the cold air in an amount corresponding to the preheated combustion air discharged to the outside into the preheated combustion air supplied to the continuous combustion burner by the supply means A NOx suppression control device for a heating furnace, characterized by comprising:   2. The NOx suppression control device for a heating furnace according to claim 1, wherein the exhaust amount of the preheated combustion air is determined in accordance with a difference between the NOx concentration measured by the NOx measuring means and a preset set value.

Images