JP2013096628A - Control method and control device for radiant tube furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress variation in RT (Radiant Tube) surface temperature.SOLUTION: A control part measures a temperature of a combustion chamber 3c in which fuel gas is combusted and controls a flow rate of combustion air supplied to the combustion chamber 3c based upon the measured temperature of the combustion chamber 3c. Consequently, a variation in RT surface temperature can be suppressed. Further, the control part 103 measures a surface temperature of a recuperator 4 and controls the flow rate of combustion air supplied to the combustion chamber 3c based upon the measured surface temperature of the recuperator 4. Consequently, the variation in RT surface temperature can be further suppressed.

Description

  The present invention relates to a control method and control device for a radiant tube furnace that heats an object to be heated such as a steel plate using combustion exhaust gas generated by burning fuel gas.

  In steelworks, a by-product gas called a by-product gas is generated from facilities such as a coke oven, a blast furnace, and a converter. This by-product gas contains impurities such as sulfur and dust in addition to combustible components that can be used as fuel such as hydrogen, carbon monoxide, and methane. For this reason, by-product gas is utilized as a fuel of the burner installed in the heating furnace, after removing impurities and dust in the purification process.

  In general, in the by-product gas purification step, dust contained in the by-product gas is removed by injecting cleaning water into the by-product gas. For this reason, the by-product gas after a refinement | purification process contains much moisture. When the by-product gas containing moisture is supplied to the burner of the heating furnace, the actual fuel gas flow rate decreases due to the amount of moisture contained in the by-product gas, so the amount of combustion air supplied to the burner becomes excessive, and the burner The combustion efficiency of is deteriorated.

  From such a background, Patent Document 1 describes a technique for suppressing deterioration in combustion efficiency by controlling the amount of combustion air in accordance with the amount of water contained in the fuel gas. Specifically, the technology described in Patent Document 1 is a direct-fired heating furnace that heats a steel sheet with a flame generated by a burner, and the amount of moisture contained in the fuel gas in the concentration of oxygen gas or carbon monoxide gas in the combustion exhaust gas. The amount of combustion air supplied to the burner is controlled based on the measured gas concentration.

  On the other hand, a radiant tube (RT) furnace that heats steel sheets using combustion exhaust gas generated by burning fuel gas has more burners than a direct-fired heating furnace, and the fuel gas flow rate between the burners The variation of is large. Further, when the radiant tube has a crack, the concentration of the combustion exhaust gas changes as the atmospheric gas in the furnace is sucked into the radiant tube. For this reason, generally, in a radiant tube furnace, control of the combustion air quantity based on the density | concentration of oxygen gas or carbon monoxide gas is not performed, but the control described in patent documents 2-4 is performed.

  Specifically, Patent Document 2 describes a technique for controlling the furnace temperature in order to ensure a target steel plate temperature. Patent Document 3 describes a technique for controlling the fuel gas flow rate in each zone based on the surface temperature of a radiant tube (hereinafter referred to as RT surface temperature). Patent Document 4 describes a technique for calculating the theoretical combustion air amount by predicting the saturated water vapor amount in the fuel gas from the temperature of the fuel gas and the atmosphere, and calculating the actual fuel gas flow rate from the predicted saturated water vapor amount. ing.

Japanese Patent Publication No. 2-8213 Japanese Patent No. 2823645 JP-A-8-35015 JP 2009-68774 A

  However, since the technique described in Patent Document 2 does not measure the variation of the RT surface temperature that governs the furnace temperature, the change in the furnace temperature is detected after the RT surface temperature has changed. For this reason, according to the technique of patent document 2, since the delay generate | occur | produces in control of furnace temperature, the fluctuation | variation of RT surface temperature cannot be suppressed.

  Further, the technique described in Patent Document 3 cannot instantaneously measure the flame temperature of the burner that greatly affects the change in the RT surface temperature. For this reason, according to the technique described in Patent Document 3, since the change in the RT surface temperature is detected after the flame temperature has changed, a delay occurs in the control of the fuel gas flow rate, and the fluctuation in the RT surface temperature is suppressed. Can not do it.

  According to the technique described in Patent Document 4, since the influence of moisture in the air supplied to the burner is not considered, when the moisture content in the air varies, the flame temperature varies, and the RT surface temperature It is impossible to suppress fluctuations in

  In summary, according to the techniques described in Patent Documents 2 to 4, fluctuations in the RT surface temperature cannot be suppressed, and as a result, the temperature of the steel sheet cannot be accurately heated to the target temperature. For this reason, provision of the technique which can suppress the fluctuation | variation of RT surface temperature was anticipated.

  This invention is made | formed in view of the said subject, The objective is to provide the control method and control apparatus of a radiant tube furnace which can suppress the fluctuation | variation of RT surface temperature.

  In order to solve the above-mentioned problems and achieve the object, a method for controlling a radiant tube furnace according to the present invention includes a radiant tube furnace that heats an object to be heated using combustion exhaust gas generated by burning fuel gas. A control method comprising: a combustion cylinder temperature measuring step for measuring a temperature of a combustion cylinder in which the fuel gas burns; and a combustion cylinder temperature supplied to the combustion cylinder based on the temperature of the combustion cylinder measured in the combustion cylinder temperature measuring step And a control step for controlling the flow rate of air.

  In the control method for a radiant tube furnace according to the present invention, in the above invention, the control step includes a step of reducing a flow rate of air supplied to the combustion cylinder when the temperature of the combustion cylinder is lower than a target temperature. It is characterized by.

  In the control method for a radiant tube furnace according to the present invention, in the above invention, the control step includes a step of increasing a flow rate of air supplied to the combustion cylinder when the temperature of the combustion cylinder is higher than a target temperature. It is characterized by.

  The method of controlling a radiant tube furnace according to the present invention is the recuperator surface for measuring the surface temperature of the recuperator that preheats the air supplied into the combustion cylinder using the exhaust heat of the combustion exhaust gas. A temperature measurement step, wherein the control step includes a step of controlling a flow rate of air supplied to the combustion cylinder based on the surface temperature of the recuperator measured in the recuperator surface temperature measurement step. And

  In order to solve the above-described problems and achieve the object, a control apparatus for a radiant tube furnace according to the present invention uses a combustion exhaust gas generated by burning a fuel gas to heat the object to be heated. A control device for measuring a temperature of a combustion cylinder in which the fuel gas burns; and a flow rate of air supplied to the combustion cylinder based on the temperature of the combustion cylinder measured by the measurement means. Control means.

  According to the control method and control apparatus for a radiant tube furnace according to the present invention, fluctuations in the RT surface temperature can be suppressed.

FIG. 1 is a diagram showing the relationship between flame temperature, combustion cylinder temperature, RT surface temperature, furnace temperature, and steel plate temperature. FIG. 2 is a schematic diagram showing a configuration of a radiant tube furnace to which a control device according to an embodiment of the present invention is applied. FIG. 3 is a block diagram showing the configuration of the control apparatus according to the first embodiment of the present invention. FIG. 4 is a flowchart showing the flow of the combustion control process according to the first embodiment of the present invention. FIG. 5 is a block diagram showing a configuration of a control apparatus according to the second embodiment of the present invention. FIG. 6 is a diagram showing a result of evaluating the deviation of the RT surface temperature when the combustion control process of the first and second embodiments is executed and when it is not executed.

[Concept of the present invention]
First, the concept of the present invention will be described with reference to FIG.

  FIG. 1 is a diagram showing the relationship between flame temperature, combustion cylinder temperature, RT surface temperature, furnace temperature, and steel plate temperature. As shown in FIG. 1, the inventors of the present invention have found that the flame temperature that affects the RT surface temperature also affects the combustion cylinder temperature. Specifically, when moisture is contained in the fuel gas or combustion air, the flame temperature is lowered due to the influence of the moisture, and at that time, it has been found that the combustion cylinder temperature is also lowered. In addition, although the combustion cylinder temperature changes with the change in flame temperature, a response delay occurs in the RT surface temperature and the furnace temperature, and eventually the response delay also occurs in the steel plate temperature due to the delay. did. From the above, the inventor of the present invention considered that the fluctuation of the RT surface temperature is suppressed by controlling the amount of combustion air based on the combustion cylinder temperature. The reason for controlling the amount of air based not on the flame temperature but on the combustion cylinder temperature is that an expensive measuring device is required to measure the flame temperature, but the combustion cylinder temperature can be measured with an inexpensive thermocouple. Because.

  Hereinafter, the configuration and operation of a control apparatus according to an embodiment of the present invention conceived based on this idea will be described.

[Configuration of Radiant Tube Furnace]
First, a configuration of a radiant tube furnace to which a control device according to an embodiment of the present invention is applied will be described with reference to FIG.

  FIG. 2 is a schematic diagram showing a configuration of a radiant tube furnace to which a control device according to an embodiment of the present invention is applied. As shown in FIG. 2, the radiant tube furnace to which the control device according to one embodiment of the present invention is applied includes a plurality of radiant tubes 1 arranged along the length direction of the steel sheet S. However, in FIG. 2, only one of the plurality of radiant tubes is illustrated. The radiant tube 1 is constituted by a pipe curved in a substantially W shape, and both ends thereof are fixed so as to be located outside the furnace wall 2 a of the heating furnace 2.

  A burner 3 and a recuperator 4 are attached to the end 1a and the end 1b of the radiant tube 1, respectively. The burner 3 includes a pilot burner 3a, a main burner 3b, and a combustion cylinder 3c. The pilot burner 3a includes a fuel gas pipe (not shown) for supplying fuel gas, a combustion air pipe (not shown) for supplying combustion air, a fuel gas supplied from the fuel gas pipe, and a combustion air supplied from the combustion air pipe. And an ignition device (not shown) that ignites the mixed gas to generate an ignition seed.

  The main burner 3b includes a fuel gas pipe (not shown) that supplies fuel gas into the combustion cylinder 3c. A mixed gas of the fuel gas supplied into the combustion cylinder 3c and the combustion air in the combustion cylinder 3c is burned by the seed fire generated by the pilot burner 3a to form a flame. The inside of the radiant tube 1 is heated by luminous flame radiation from the flame in the combustion cylinder 3c and forced convection by the combustion exhaust gas, and the inside of the heating furnace 2 and the steel sheet S are heated by the radiant heat radiated from the outer surface of the radiant tube 1. The

  The flow rate of the fuel gas supplied to the main burner 3b is that of the flow rate adjusting valve 7, the shutoff valve 8 and the on-off valve 9 provided in the pipe 6 connecting the main burner 3b and the fuel gas main pipe 5 through which the fuel gas flows. It is controlled by controlling the opening. The pipe 6 is provided with an orifice flow meter 10 for measuring the flow rate of the fuel gas.

  The recuperator 4 collects the exhaust heat of the combustion exhaust gas discharged from the combustion cylinder 3c through the flue 11, and supplies the exhaust gas to the combustion cylinder 3c through the inside of the radiant tube 1 using the recovered exhaust heat. Preheated air. The heat efficiency of the radiant tube furnace can be improved by using the exhaust heat of the combustion exhaust gas for preheating the air supplied into the combustion cylinder 3c. The combustion exhaust gas flowing through the flue 11 is discharged to the outside of the furnace through the chimney 13 after adjusting its pressure by the exhaust pressure adjusting valve 12.

  The flow rate of the air supplied to the recuperator 4 includes a flow rate adjusting valve 16, a shutoff valve 17, and an on-off valve 18 provided in a pipe 15 that connects the recuperator 4 and the combustion air main pipe 14 through which the combustion air flows. It is controlled by controlling the opening degree. The pipe 15 is provided with an orifice flow meter 19 for measuring the flow rate of the combustion air.

[First Embodiment]
Next, with reference to FIGS. 3 and 4, the configuration and operation of the control apparatus according to the first embodiment of the present invention will be described.

[Configuration of control device]
FIG. 3 is a block diagram showing the configuration of the control apparatus according to the first embodiment of the present invention. As shown in FIG. 3, the control device according to the first embodiment of the present invention includes a furnace temperature measurement unit 101, a combustion cylinder temperature measurement unit 102, and a control unit 103. The combustion cylinder temperature measurement unit 102 and the control unit 103 function as a measurement unit and a control unit according to the present invention, respectively.

  The furnace temperature measuring unit 101 measures the temperature in the heating furnace 2 shown in FIG. 2 as the furnace temperature, and inputs the measured furnace temperature data to the control unit 103. The combustion cylinder temperature measuring unit 102 is constituted by a thermocouple. The combustion cylinder temperature measurement unit 102 measures the temperature of the combustion cylinder 3 c shown in FIG. 2 and inputs the measured combustion cylinder temperature data to the control unit 103.

  The control unit 103 is configured by an information processing device such as a computer. The control unit 103 sets the opening degree of the flow rate adjusting valves 7 and 16 shown in FIG. 2 based on the data input from the furnace temperature measuring unit 101 and the combustion cylinder temperature measuring unit 102 and the measured values of the orifice flow meters 10 and 19. By controlling, the flow rate of fuel gas and combustion air is controlled.

  The control device having such a configuration suppresses fluctuations in the RT surface temperature by executing the combustion control process described below. Hereinafter, with reference to the flowchart shown in FIG. 4, operation | movement of the control apparatus at the time of performing a combustion control process is demonstrated.

[Combustion control processing]
FIG. 4 is a flowchart showing the flow of the combustion control process according to the first embodiment of the present invention. The flowchart shown in FIG. 4 starts at the timing when the operation of the radiant tube furnace is started, and the combustion control process proceeds to the process of step S1. This combustion control process is repeatedly executed every predetermined control period while the radiant tube furnace is operating.

  In the process of step S1, the control unit 103 measures the combustion cylinder temperature Tbc using the combustion cylinder temperature measurement unit 102. Thereby, the process of step S1 is completed and a combustion control process progresses to the process of step S2.

  In the process of step S2, the control unit 103 compares the magnitude relationship between the combustion cylinder temperature Tbc measured by the process of step S1 and the target combustion cylinder temperature Tbm obtained from the target temperature of the steel sheet S. As a result of the comparison, when the combustion cylinder temperature Tbc is lower than the target combustion cylinder temperature Tbm, the control unit 103 advances the combustion control process to the process of step S3. On the other hand, when the combustion cylinder temperature Tbc is higher than the target combustion cylinder temperature Tbm, the control unit 103 advances the combustion control process to the process of step S4. If the combustion cylinder temperature Tbc and the target combustion cylinder temperature Tbm are equal, the control unit 103 ends the combustion control process.

  In the process of step S3, the control unit 103 determines that the combustion cylinder temperature Tbc has decreased due to an increase in the amount of water in the fuel gas or combustion air, and decreases the amount of combustion air supplied to the combustion cylinder 3c. By reducing the amount of combustion air, excess air and moisture in the combustion cylinder 3c are reduced, and the flame temperature rises. As a result, the difference between the flame temperature and the target flame temperature is reduced, and fluctuations in the RT surface temperature can be suppressed. Thereby, the process of step S3 is completed and a series of combustion control processes are complete | finished.

  In the process of step S4, the control unit 103 determines that the combustion cylinder temperature Tbc has increased due to a decrease in the amount of water in the fuel gas or combustion air, and increases the amount of combustion air supplied to the combustion cylinder 3c. By increasing the amount of combustion air, excess air and moisture in the combustion cylinder 3c increase and the flame temperature decreases. As a result, the difference between the flame temperature and the target flame temperature is reduced, and fluctuations in the RT surface temperature can be suppressed. Thereby, the process of step S4 is completed and a series of combustion control processes are complete | finished.

  In the above-described combustion control process, the control unit 103 controls only the combustion air amount, but also controls the fuel gas flow rate Fg using the following formula (1). In Equation (1), parameters Tam and Tac indicate the target furnace temperature and the actual furnace temperature, respectively, and parameters Wa and Wb indicate weighting factors. The weighting factor can be obtained statistically (correlation analysis, etc.) according to the operation data (temperature, flow rate).

  As is apparent from the above description, in the control device according to the first embodiment of the present invention, the control unit 103 measures the temperature Tbc of the combustion cylinder 3c where the fuel gas burns, and the measured combustion cylinder 3c is measured. Since the flow rate of the combustion air supplied to the combustion cylinder 3c is controlled based on the temperature Tbc, fluctuations in the RT surface temperature can be suppressed.

[Second Embodiment]
Next, the configuration and operation of the control device according to the second embodiment of the present invention will be described with reference to FIG.

[Configuration of control device]
FIG. 5 is a block diagram showing a configuration of a control apparatus according to the second embodiment of the present invention. As shown in FIG. 5, the control device according to the second embodiment of the present invention includes a recuperator surface temperature measurement unit 104 in addition to the configuration of the control device according to the first embodiment. The recuperator surface temperature measuring unit 104 measures the surface temperature of the recuperator 4 shown in FIG. 2 and inputs the measured surface temperature data to the control unit 103. The control unit 103 is shown in FIG. 2 based on data input from the furnace temperature measuring unit 101, the combustion cylinder temperature measuring unit 102, and the recuperator surface temperature measuring unit 104 and the measured values of the orifice flowmeters 10 and 19. The flow rate of the fuel gas and the combustion air is controlled by controlling the opening degree of the flow rate adjusting valves 7 and 16.

[Combustion control processing]
In the radiant tube furnace, slow combustion is performed to suppress the amount of NOx generated. For this reason, the fuel gas that has not burned in the vicinity of the combustion cylinder may burn until it passes through the recuperator 4. For this reason, the temperature distribution in the axial direction of the radiant tube differs depending on the flow rate of the fuel gas that has not been burned, and the RT surface temperature may vary. Therefore, in the present embodiment, the control unit 103 estimates the flow rate of the fuel gas that has not been burned near the combustion tube by measuring the surface temperature of the recuperator 4, and the combustion tube is based on the estimated fuel gas flow rate. The amount of combustion air supplied to 3c is controlled.

At this time, the control unit 103 also executes the combustion control process described in the first embodiment. In the present embodiment, the control unit 103 controls the combustion gas flow rate Fg by using the following formula (2). In Equation (2), parameters Trm and Trc indicate the target recuperator surface temperature and the actual recuperator surface temperature, respectively, and parameter Wc indicates a weighting factor. The weighting factor can be obtained statistically (correlation analysis, etc.) according to the operation data (temperature, flow rate).

  As is clear from the above description, in the control device according to the second embodiment of the present invention, the control unit 103 measures the surface temperature Trc of the recuperator 4 and the measured surface temperature of the recuperator 4. Since the flow rate of the combustion air supplied to the combustion cylinder 3c is controlled based on Trc, fluctuations in the RT surface temperature can be suppressed.

〔Example〕
Finally, FIG. 6 shows the result of evaluating the deviation of the RT surface temperature when the combustion control process of the first and second embodiments is executed and when it is not executed (prior art). As shown in FIG. 6, in the prior art, the deviation of the RT surface temperature was ± 10 ° C., whereas when the combustion control process of the first and second embodiments was executed, the RT surface temperature Deviations of ± 7 ° C. and ± 5 ° C., respectively. From the above, it was confirmed that the fluctuation of the RT surface temperature can be suppressed by executing the combustion control processing of the first and second embodiments.

  Although the embodiment to which the invention made by the present inventor is applied has been described above, the present invention is not limited by the description and the drawings that form a part of the disclosure of the present invention according to this embodiment. That is, other embodiments, examples, operational techniques, and the like made by those skilled in the art based on the present embodiment are all included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Radiant tube 2 Heating furnace 2a Furnace wall 3 Burner 3a Pilot burner 3b Main burner 3c Combustion cylinder 4 Recuperator 5 Fuel gas main pipe 6, 15 Piping 7, 16 Flow control valve 8, 17 Shut-off valve 9, 18 On-off valve 10 , 19 Orifice flow meter 11 Chimney 12 Exhaust pressure regulating valve 13 Chimney 14 Combustion air main pipe 101 Furnace temperature measurement unit 102 Combustion cylinder temperature measurement unit 103 Control unit 104 Recuperator surface temperature measurement unit S Steel plate

Claims (5)

A control method for a radiant tube furnace that heats an object to be heated using combustion exhaust gas generated by burning fuel gas,
A combustion cylinder temperature measuring step for measuring a temperature of a combustion cylinder in which the fuel gas burns;
And a control step of controlling a flow rate of air supplied to the combustion cylinder based on the temperature of the combustion cylinder measured in the combustion cylinder temperature measuring step.   The method of controlling a radiant tube furnace according to claim 1, wherein the control step includes a step of reducing a flow rate of air supplied to the combustion cylinder when the temperature of the combustion cylinder is lower than a target temperature. .   The radiant tube furnace according to claim 1 or 2, wherein the control step includes a step of increasing a flow rate of air supplied to the combustion cylinder when the temperature of the combustion cylinder is higher than a target temperature. Control method.   A recuperator surface temperature measuring step for measuring a surface temperature of a recuperator that preheats air supplied into the combustion cylinder using exhaust heat of the combustion exhaust gas, and the control step includes a recuperator surface temperature 4. The method according to claim 1, further comprising a step of controlling a flow rate of air supplied to the combustion cylinder based on a surface temperature of the recuperator measured in the measuring step. 5. Radiant tube furnace control method. A control device for a radiant tube furnace that heats an object to be heated using combustion exhaust gas generated by burning fuel gas,
Measuring means for measuring the temperature of a combustion cylinder in which the fuel gas burns;
A control device for a radiant tube furnace, comprising: control means for controlling a flow rate of air supplied to the combustion cylinder based on the temperature of the combustion cylinder measured by the measuring means.

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