JP2005213586A - Method for controlling afterburn in direct-flame anti-oxidation heater, and apparatus therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controlling method for preheating a steel sheet while completely combusting flue gases in a preheating furnace for preheating the steel sheet, in a direct-flame anti-oxidation heater of a continuous annealing facility, and to provide an apparatus therefor. <P>SOLUTION: This apparatus has the preheating furnace 3 arranged so as to adjoin the direct-flame anti-oxidation heater 2, into which the flue gases of the direct-flame anti-oxidation heater 2 are introduced, and a slit burner 4 arranged in a portion of connecting the preheating furnace 3 with the direct-flame anti-oxidation heater 2. The method for reliably combusting the flue gases includes feeding fuel and air to the slit burner 4, while controlling the amount of fuel to the minimally necessary amount for heating the unburned gases in the flue gases to the ignition temperatures, and the amount of air to the necessary amount for completely combusting the fuel and the unburned fuel gas. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an afterburn control method and apparatus for a direct flame heating type non-oxidation furnace for continuously annealing a steel sheet.

  A direct flame heating type non-oxidation furnace (hereinafter referred to as “NOF”) with high heating efficiency is used for continuous heat treatment of the steel sheet. This NOF has an air-fuel ratio to avoid the formation of an oxide film on the steel sheet surface. Since combustion is performed at 1 or less, unburned fuel gas remains in the combustion exhaust gas. Therefore, various methods have been proposed for the treatment of unburned fuel gas of NOF.

  3 and 4 are schematic views showing a conventional method for treating unburned fuel gas. For example, in Patent Document 1, as shown in FIG. 3, when heating the steel sheet 1, a preheating furnace 3 is provided in front of the NOF 2 heated by the burner 11, and unburned fuel gas generated in the heating zone is provided. A method is disclosed in which air is ejected from the air nozzle 12 to the preheating furnace 3 and the unburned fuel gas is burned at the same time as being introduced into the preheating furnace 3.

In Patent Document 2, as shown in FIG. 4, an afterburning chamber 14 and a heat exchanger 15 are installed in the middle of the exhaust duct 13, and a burner 16 is attached to the afterburning chamber 14. A technology that injects the minimum fuel required to maintain the temperature at the ignition point temperature of the unburned fuel gas in the combustion exhaust gas and the air required to completely burn both the fuel to be injected and the unburned fuel gas. It is disclosed.
Japanese Patent Publication No.53-39848 Japanese Patent Laid-Open No. 55-110725

  However, the method described in Patent Document 1 has a problem that unburned fuel gas cannot be burned even when air is injected because the temperature of the preheating furnace is low at the start of operation or during low production. Further, the method described in Patent Document 2 has a problem that the installation of the afterburning chamber has to be provided with a separate facility for that purpose, and the thermal efficiency is not good.

  Therefore, in the present invention, in the NOF, without providing an afterburning chamber in the middle of the exhaust duct, the unburned fuel gas in the combustion exhaust gas is burned even when the temperature of the preheating furnace is low at the start of operation or low production. An afterburn control method and apparatus for a direct flame heating type non-oxidation furnace capable of preheating a steel sheet are provided.

  An afterburn control method for a direct flame heating type non-oxidation furnace according to the present invention is a continuous annealing method for a steel sheet, wherein a preheating furnace is provided adjacent to the direct flame heating type non-oxidation furnace, and the combustion exhaust gas of the direct flame heating type non-oxidation furnace Is necessary to raise the temperature of the unburned fuel gas in the combustion exhaust gas to the ignition point by installing a slit burner at the joint between the direct flame heating type non-oxidation furnace and the preheating furnace. It is characterized by controlling the supply of a minimum amount of fuel and the amount of air necessary for complete combustion of this fuel and unburned fuel gas.

  Further, the afterburn control device for a direct flame heating type non-oxidation furnace of the present invention is provided with a preheating furnace adjacent to the direct flame heating type non-oxidation furnace in a continuous annealing equipment for steel sheets, Combustion exhaust gas is introduced into the preheating furnace, and a slit burner is provided at the joint between the direct flame heating type non-oxidation furnace and the preheating furnace, and the temperature of the unburned fuel gas in the combustion exhaust gas is raised to the ignition point in this slit burner. And a control means for controlling the supply of the minimum amount of fuel necessary for this and the amount of air necessary for complete combustion of this fuel and unburned fuel gas.

    If the combustion control method for a direct flame heating type non-oxidation furnace according to the present invention is used, it is not necessary to provide an afterburning chamber in the middle of the exhaust duct, so there is no need for capital investment for installing the afterburning chamber, and a slit burner is used. Since the flame is injected from the vertical direction of the steel plate to the entire cross section in the width direction of the steel plate, unburned fuel gas in the NOF combustion exhaust gas can be reliably burned even when the temperature of the preheating furnace at the start of operation or low production is low. In addition, since the steel sheet is preheated directly by combustion of unburned fuel gas, it is more efficient than providing an afterburning chamber in the middle of the exhaust duct and recovering heat with a heat exchanger.

  FIG. 1 is a block diagram showing an embodiment of a control apparatus for carrying out the control method of the present invention, and FIG. 2 is a cross-sectional view taken along the line AA of FIG. In FIG. 1, a preheating furnace 3 for preheating the steel strip 1 is integrally provided at the front part of the NOF 2, and the preheating furnace 3 is provided with a combustion gas discharge port 3a, and the combustion gas in the furnace is attracted to exhaust the combustion gas. It is discharged from the outlet 3a.

  Slit burners 4 are installed on the upper and lower sides of the steel plate 1 between the NOF 2 and the preheating furnace 3. As shown in FIG. 2, the slit burner 4 is formed with a curtain of flame 4 a in the furnace width direction, and completely burns unburned fuel gas attracted from the NOF 2 to the preheating furnace 3.

  A combustion air supply pipe 5 and a fuel gas supply pipe 6 for supplying fuel air are connected to the slit burner 4, and flow rate adjusting valves 5a and 6a and flow rate adjusting orifices 5a and 6b are provided in the supply pipes 5 and 6, respectively. Yes. The flow rate adjusting valves 5a and 6a and the flow rate adjusting orifices 5a and 6b of the supply pipes 5 and 6 are adjusted in flow rate by flow rate indicating controllers (FIC) 5c and 6c, respectively. The preheating furnace 3 is provided with a temperature detector 17 for measuring the temperature in the furnace.

  As control means for controlling the amount of combustion air and fuel gas supplied to the slit burner 4, unburned fuel gas combustion air amount calculation means 8, hydrogen combustion air amount calculation means 9, and cross limit control means 10 in NOF 2 are provided. Is provided.

  In the unburned fuel gas combustion air amount calculation means 8 in the NOF 2, the actual air flow rate value and fuel actual value of the NOF 2 are inputted to calculate the unburned fuel gas combustion air amount, and the hydrogen combustion air amount In the calculation means 9, the actual hydrogen flow rate value of NOF 2 is input to calculate the hydrogen combustion air amount, and in the cross limit control means 10, the actual air flow rate and fuel flow rate value, the control output of the temperature indicating controller 7, The unburned fuel gas combustion air amount calculated by the unburned fuel gas combustion air amount calculation means 8 and the hydrogen combustion air amount calculated by the hydrogen combustion air amount calculation means 9 are input, and the fuel gas A flow rate set value and an air flow rate set value are set. This cross-limit control limits the flow rate command values of both fuel and combustion air from the actual flow rate values of fuel and combustion air to save energy, prevent pollution, and control the atmosphere in an industrial combustion furnace. It is a method to control.

  Based on the fuel gas flow rate calculated by the cross limit control means, the respective flow rates are set in the combustion air flow rate controller 5c and the fuel gas flow rate indicating controller 6c.

 The control of the slit burner 4 can be realized by an instrumentation controller such as DCS (Distributed Control System) described below. Calculation is performed for each control cycle, and the air flow rate setting value of the slit burner 4 and the fuel gas flow rate setting value are set in the respective flow rate controllers 5c and 6c. The procedure for controlling the slit burner 4 is as follows.

(1) A target air-fuel ratio for final combustion in the slit burner 4 is set in advance (usually about 1.05).

(2) The amount of unburned air for completely burning the hydrogen charged into the furnace is calculated by the hydrogen burning air amount calculating means 9 and the amount of air for completely burning the unburned gas in NOF2 is calculated. It is calculated by the unburned fuel gas combustion air amount calculation means 8. At the time of calculation, the target air-fuel ratio at the time of burning with the slit burner 4 set in the above (1) is set.

(3) In the combustion control of the slit burner 4 itself, the fuel gas flow rate is set according to the furnace temperature, the air flow rate is calculated so as to be the target air-fuel ratio set in (1), and the flow rate controller 5c. And combustion control is performed accordingly. Since the air flow rate and the fuel gas flow rate are adjusted by the cross limit control 10, they are automatically controlled so as to achieve the set air-fuel ratio.

  Combustion control is performed at a stable air-fuel ratio by the above control method, and the flame covers the entire cross-section in the width direction of the steel plate 1 by the slit burner 4, so that unburned gas and hydrogen can be reliably burned. Furthermore, since the steel plate 1 can be burned evenly in the width direction and the preheating of the steel plate 1 can be performed uniformly in the width direction, an efficient operation is possible.

  In the embodiment of the present invention, the installation position of the slit burner is a pair of upper and lower sides across the steel plate of the connecting portion between the preheating furnace and the NOF, but in consideration of the capacity and installation space of the slit burner, a plurality of installation positions are provided in the steel plate traveling direction. You may arrange in parallel. Alternatively, when the width of the slit burner is narrow, it may be arranged in a plurality of rows in a staggered manner in the steel plate traveling direction. Moreover, you may arrange | position the installation position of a slit burner in the both sides of the furnace of the connection part of a preheating furnace and NOF. Furthermore, you may arrange | position on the four surfaces of the furnace of the connection part of a preheating furnace and NOF.

  Moreover, although the horizontal furnace was illustrated in the Example of this invention, it cannot be overemphasized that it is applicable also to a vertical furnace.

The block diagram which shows one Example of the control apparatus for implementing the control method of this invention. AA sectional drawing of FIG. The block diagram which shows a prior art (injection of only air to a preheating furnace). The block diagram which shows a prior art (afterburner room separate installation).

Explanation of symbols

1: Steel strip 2: Direct flame heating type non-oxidation furnace (NOF)
3: Preheating furnace 4: Slit burner 5: Combustion air supply pipe 5a: Flow rate adjusting valve 5b: Flow rate adjusting orifice 5c: Flow rate indicating controller (FIC)
6: Fuel gas supply pipe 6a: Flow rate adjusting valve 6b: Flow rate adjusting orifice 6c: Flow rate indicating controller (FIC)
7: Temperature indicating controller 8: Unburned fuel gas combustion air amount calculation means in NOF2
9: Air amount calculation means for hydrogen combustion 10: Cross limit control means
11: Burner 12: Air nozzle 13: Duct 14: Afterburning chamber
15: Heat exchanger
16: Burner
17: Temperature detector

Claims (2)

  In the continuous annealing method for steel sheets, a preheating furnace is provided adjacent to the direct flame heating type non-oxidation furnace, the combustion exhaust gas of the direct flame heating type non-oxidation furnace is introduced into the preheating furnace, and the direct flame heating type non-oxidation furnace and preheating furnace A slit burner is provided at the connection with the fuel, and a minimum amount of fuel necessary for raising the temperature of the unburned fuel gas in the combustion exhaust gas to the ignition point, and the fuel and the unburned fuel gas. Afterburn control method of direct flame heating type non-oxidation furnace characterized by controlling supply with air of quantity required for complete combustion of coal.   In the continuous annealing equipment for steel plates, a preheating furnace is installed adjacent to the direct flame heating type non-oxidation furnace, the combustion exhaust gas of the direct flame heating type non-oxidation furnace is introduced into the preheating furnace, the direct flame heating type non-oxidation furnace and the preheating furnace A slit burner is provided at the connection with the fuel, and a minimum amount of fuel required to raise the temperature of the unburned fuel gas in the combustion exhaust gas to the ignition point and the fuel and unburned fuel gas are provided in the slit burner. And a control means for controlling the supply of air in an amount necessary for complete combustion of the afterburning control apparatus for a direct flame heating non-oxidation furnace.

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