JP2009299153A - Nonoxidation heating method and nonoxidation heating furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonoxidation heating method where, when performing nonoxidation heating for heating a material such as a steel in a nonoxidizing state, equipment cost is made low and a labor load is not imposed on a furnace operator, and to provide a nonoxidation heating furnace. <P>SOLUTION: When performing direct fire type nonoxidation heating where the combustion gas of a radiant burner 4B burnt at an air ratio of ≤1.0 is applied to the surface of a steel strip S, and heating is performed, fuel and air used in the radiant burner 4B are premixed, and the premixed gas is preheated to a prescribed temperature (e.g., to 600°C), and is supplied to the radiant burner 4B. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-oxidation heating method and a non-oxidation heating furnace for heating a material such as a steel material in a non-oxidation state.

Conventionally, as a non-oxidative heating technique in a continuous annealing furnace for steel strips, a continuous galvanizing facility or the like, there is a direct flame type non-oxidative heating method described in Patent Document 1 or Patent Document 2. In this direct-fire type non-oxidation heating method, the combustion gas of the burner burned at an air ratio of 1.0 or less is applied to the surface of the material and heated.
Japanese Patent Publication No. 62-21051 Japanese Patent Publication No. 3-68932

  However, in the non-oxidation heating methods described in Patent Document 1 and Patent Document 2, fuel and preheated air are supplied to the burner to realize nonoxidation heating. However, fuel and preheat air are respectively supplied to a plurality of burners. Since the fuel and air supply ratio (air ratio) must be adjusted individually for each burner, the fuel pipe and air pipe are concentrated around the furnace where the burners are installed. In addition, a large number of devices such as a regulating valve for regulating the fuel and air of each burner and an orifice for controlling the flow rate are required, resulting in an increase in equipment costs.

  Further, in the non-oxidation heating methods described in Patent Document 1 and Patent Document 2, if the air ratio management of each burner is not properly performed, the air ratio varies from burner to burner, and the combustion gas of the burner that has excessive air is oxidized. As a result, the quality of the steel strip surface deteriorates, and the burner with excessive fuel has a problem of generating soot and degrading the quality of the steel strip surface. However, automatic air ratio control is applied to each burner. Attempts to do so increase equipment costs. Instead, periodic air ratio management (combustion management) is required by the operator, and there is a problem that the operator is burdened with labor.

  The present invention has been made in view of the circumstances as described above, and when performing non-oxidative heating in which a material such as steel is heated in a non-oxidized state, the equipment cost is low and no burden is imposed on the operator. An object of the present invention is to provide a stable non-oxidation heating method and a non-oxidation heating furnace.

  In order to solve the above problems, the present invention has the following features.

  [1] In a non-oxidation heating method in which a combustion gas of a burner burned at an air ratio of 1.0 or less is applied to the material surface and heated, the fuel and air of the burner are mixed in advance, and the premixed gas is heated to a predetermined temperature. A non-oxidative heating method characterized by pre-heating.

  [2] The non-oxidizing heating method according to [1], wherein the premixed gas is preheated to a temperature of 600 ° C. or lower.

  [3] The non-oxidative heating method according to [1] or [2], wherein the premixed gas is preheated using combustion exhaust gas from a furnace in which the burner is installed.

  [4] In a non-oxidation heating furnace in which the combustion gas of the burner burned at an air ratio of 1.0 or less is heated against the material surface, the fuel and air of the burner are mixed in advance, and the premixed gas is heated to a predetermined temperature. A non-oxidizing heating furnace characterized in that it is preheated.

  [5] The non-oxidizing heating furnace according to [4], wherein the premixed gas is preheated to a temperature of 600 ° C. or lower.

  [6] The nonoxidizing heating furnace according to [4] or [5], wherein the premixed gas is preheated using the combustion exhaust gas of the nonoxidizing heating furnace.

  In the present invention, when performing direct flame type non-oxidation heating in which the combustion gas of a burner burned at an air ratio of 1.0 or less is applied to the material surface and heated, the fuel and air of the burner are premixed and premixed By preheating the gas to a predetermined temperature, a high-temperature combustion gas is obtained from the burner, thereby achieving stable non-oxidative heating. And when fuel and air are premixed, the fuel amount and air amount are adjusted and supplied to the burner, so the piping to each burner is only the piping that distributes the premixed air, and individually It is not necessary to install a large number of regulating valves to regulate the fuel and air of the burner, and the equipment cost is reduced. Moreover, since it is sufficient to adjust the air ratio when premixing fuel and air, it becomes easy to perform automatic air ratio control, and the labor load on the operator is reduced by performing the automatic air ratio control. be able to.

  An embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a steel strip non-oxidation heating furnace showing an embodiment of the present invention. The non-oxidizing heating furnace F is a direct-fired non-oxidizing heating furnace that heats a burner combustion gas burned at an air ratio of 1.0 or less against the surface of the steel strip S. In a three-zone non-oxidation heating furnace consisting of three zones, zone 6 and third zone 4, a steel strip S that is an object to be heated passes through the furnace from the top to the bottom. Here, coke oven gas (COG) is used as the fuel to be used, but any gas fuel such as city gas or LPG may be used.

  And in this 3 zone type direct fire type non-oxidation heating furnace F, in the 1st zone 5 and the 2nd zone 6, since the temperature of steel strip S is relatively low and the oxidation rate of steel strip S is slow, comparison The diffusion flame burners 5B and 6B mainly using convection heat transfer that can obtain a high heat flow rate in a low temperature range are used.

At that time, the combustion air supplied to the diffusion flame burners 5B and 6B is preheated by the air preheater 8 using the exhaust gas sensible heat of the non-oxidation heating furnace F as a heat source. That is, the furnace exit flue gas in the non-oxidizing heating furnace F, CO for incompletely combusted in a non-oxidizing heating furnace F, there is a unburned H _2, the latent heat of the unburned In order to use it effectively, it is mixed with air in the secondary combustion chamber 7 and subjected to secondary combustion, leading to a combustion air preheater 8 for energy saving.

  Further, in the first zone 5 and the second zone 6, the combustion air and the fuel gas are adjusted to the required amounts by the combustion air regulating valves 5a and 6a and the fuel regulating valves 5g and 6g in the respective zones. Yes.

  On the other hand, in the third zone 4, the surface of the steel strip S that is heated and enters in a weakly oxidized state is reduced, and at the same time, a radiant burner 4B mainly composed of radiant heat transfer that can obtain a high heat flow rate in a high temperature region. Is used.

  As for the air and fuel used in the radiant burner 4B, the air that has passed through the third zone combustion air regulating valve 4a and the fuel gas that has passed through the third zone fuel regulating valve 4g are preliminarily mixed in the mixer (premixer) 2. The premixed gas (premixed gas) is preheated to a predetermined temperature (for example, 600 ° C.) by the preheater 1, and then supplied to the radiant burner (premixed burner) 4B through the backfire preventer 3. Yes.

  Incidentally, when preheating the fuel / air premixed gas, Patent Document 1 describes that it is dangerous to mix the fuel and preheated air. However, the inventors preheat the premixed gas. However, the conditions under which stable combustion is possible were derived through experiments. That is, when coke oven gas (COG) is used as fuel, the temperature at which the premixed gas burns is found to be 650 to 670 ° C., and further experiments with variable burner combustion load and furnace temperature are continued. As a result, it was confirmed that the preheating limit temperature of the premixed gas that enables stable non-oxidation heating was 600 ° C. Therefore, in this case, the preheating temperature of the premixed gas supplied to the radiant burner 4B may be set to an appropriate temperature of 600 ° C. or lower.

  The heat source of the above-mentioned premixed gas preheater 1 may be a preheater that uses the combustion heat of an electric heater or fuel. However, the sensible heat of the combustion exhaust gas of the non-oxidizing heating furnace F is used to save energy. Yes. As the exhaust gas, whether the exhaust gas before the secondary combustion chamber 7 or the exhaust gas after the secondary combustion chamber 7 is used does not change the effect, but here, the exhaust gas after the secondary combustion chamber 7 is used. Since this is higher temperature exhaust gas than the exhaust gas before the secondary combustion chamber 7, the premixed gas preheater 1 can be made smaller, so the exhaust gas after the secondary combustion chamber 7 is used as a heat source.

  Thus, in this embodiment, when performing direct flame type non-oxidation heating in which the combustion gas of the radiant burner 4B burned at an air ratio of 1.0 or less is applied to the surface of the steel strip S and heated, the radiant burner is used. The fuel and air used in 4B are premixed and the premixed gas is preheated to a predetermined temperature (for example, 600 ° C.) to obtain a high-temperature combustion gas from the radiant burner 4B, so that stable non-oxidative heating is achieved. Achieved. And when fuel and air are premixed, the fuel amount and the air amount are adjusted and supplied to the radiant burner 4B, so that the pipes to each radiant burner 4B are only pipes that distribute the premixed gas, In order to adjust the fuel and air of the individual radiant burner 4B, it is not necessary to install a large number of regulating valves, and the equipment cost is reduced. Moreover, since it is sufficient to adjust the air ratio when premixing fuel and air, it becomes easy to perform automatic air ratio control, and the labor load on the operator is reduced by performing the automatic air ratio control. be able to.

It is a figure which shows one Embodiment of this invention.

Explanation of symbols

1 Premixed gas preheater 2 Mixer (premixer)
3 Backfire prevention device 4 Non-oxidation heating furnace 3rd zone 4B Non-oxidation heating furnace 3rd zone burner (premix burner)
4a 3rd zone combustion air regulating valve 4g 3rd zone fuel regulating valve 5 Non-oxidation heating furnace 1st zone 5B Non-oxidation heating furnace 1st zone burner (diffusion flame burner)
5a First zone combustion air regulating valve 5g First zone fuel regulating valve 6 Non-oxidation heating furnace second zone 6B Non-oxidation heating furnace second zone burner (diffusion flame burner)
6a Second zone combustion air regulating valve 6g Second zone fuel regulating valve 7 Secondary combustion chamber 8 Combustion air preheater

Claims (6)

  In a non-oxidative heating method in which a combustion gas of a burner burned at an air ratio of 1.0 or less is applied to a material surface and heated, the fuel and air of the burner are premixed, and the premixed gas is preheated to a predetermined temperature. A non-oxidative heating method.   The non-oxidizing heating method according to claim 1, wherein the premixed gas is preheated to a temperature of 600 ° C or lower.   The non-oxidative heating method according to claim 1 or 2, wherein the premixed gas is preheated using combustion exhaust gas from a furnace in which the burner is installed.   In a non-oxidation heating furnace in which the combustion gas of a burner burned at an air ratio of 1.0 or less is applied to the material surface and heated, the fuel and air of the burner are premixed and the premixed gas is preheated to a predetermined temperature. A non-oxidizing heating furnace characterized by that.   The non-oxidizing heating furnace according to claim 4, wherein the premixed gas is preheated to a temperature of 600 ° C or lower.   6. The non-oxidizing heating furnace according to claim 4, wherein the pre-mixed gas is pre-heated using the combustion exhaust gas of the non-oxidizing heating furnace.

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