JP4899583B2 - heating furnace - Google Patents

Description

  The present invention relates to a heating furnace using various fuel gases such as coke oven gas.

  Conventionally, as a heating furnace for heating steel materials at steelworks, the furnace body is divided into a plurality of combustion zones, and a burner is provided for each combustion zone to supply fuel gas such as coke oven gas and combustion air to the burner. There is known a technique in which a flame generated by burning fuel gas is blown into a furnace (for example, Patent Document 1).

FIG. 11 is a diagram showing a schematic configuration of a general steel heating furnace to which such a technique is applied. This heating furnace has a furnace body 32 for continuously heating the steel material 31. A plurality of burners 33 are installed in the furnace body 32 as heating devices, and fuel gas and combustion air are supplied to the burners. Combustion control consists of all four zones of 1 to 4 zones. Coke oven gas generated from a coke oven at a steel mill is used as fuel. The calorific value of the coke oven gas is 4350 kcal / Nm ³ . The fuel is supplied at a pressure of 700 mmAq at point A in FIG. 11 which is a supply source of coke oven gas. Then, it branches to each combustion zone (1-4 zones) via piping 34. The pipe 34 before branching is provided with a flow meter 35 and an emergency shut-off valve 36. After branching, the coke oven gas is supplied to the burner 33. The pipe after branching is provided with a fuel flow meter 37 and a fuel flow control valve 38 for each zone (only one zone is shown) in each zone. Combustion air is supplied by a combustion air blower 39, and an air flow meter 40 and an air flow control valve 41 are individually installed in each combustion zone. The fuel flow rate signal and the air flow rate signal are input to the regulator 42, and control signals are output from the regulator 42 to the fuel flow rate control valve 38 and the air flow rate control valve 41 so that the air ratio in each zone is constant. Automatically controlled.

  Further, a thermometer 43 is individually arranged in each zone of the heating furnace, and if the combustion control in each zone is given a set furnace temperature, the measured value of the thermometer 43 is ± 5 of the set furnace temperature. This is a system in which the opening degree of the fuel flow rate adjustment valve 38 and the air flow rate adjustment valve 41 is automatically controlled so as to keep the air ratio constant so that it is within the temperature.

Now, in order to increase the amount of heat treatment per hour of the steel material 31 in the furnace main body 32, it is desired to increase the amount of heat input to the furnace by 10% to 3830 Mcal / h. However, the opening of the fuel flow control valve 38 is already fully open, and the supply amount of coke oven gas, which is fuel gas, cannot be increased any more. That is, the supply pressure of the coke oven gas is supplied at 700 mmAq at point A in FIG. 11. At this pressure, the flow rate of the coke oven gas that can be supplied to the burner 33 is when the fuel gas flow control valve 38 is fully open. The maximum is 800 Nm ³ / h. Accordingly, the maximum amount of heat input to the heating furnace 32 is 3480 Mcal / h.

If the amount of heat is increased by increasing the amount of coke oven gas, 880 Nm ³ / h is required. To achieve this, a method of increasing the coke oven gas supply pressure at point A to 850 mmAq can be considered. However, in order to increase the heat treatment capacity, it is necessary to increase the pressure of the coke oven gas. The booster blower, the power supply for the blower, the blower and the blower power supply explosion-proof device, the pressure adjustment mechanism after the pressure increase, the pressure of each flow meter Correction is required. Therefore, there is a problem that a large-scale structure is required due to installation work of the booster, remodeling work of the coke oven gas piping before and after the booster, and cost increases.

Further, the flow rate of the coke oven gas supplied to the furnace body 32 may fluctuate, and it may be difficult to ensure a certain amount of heat generation in the furnace body.
JP-A-6-2003328

  This invention is made | formed in view of this situation, Comprising: It aims at providing the heating furnace which can heat-process with desired heat quantity and can be operated stably.

To solve the above problems, the present invention includes a furnace body and a front Symbol furnace first fuel gas feeding the Kyusuru first fuel gas piping toward the body, different from the second and the first fuel gas And the second fuel gas from the second fuel gas pipe provided in the first fuel gas pipe is converted into the first fuel gas. a fuel gas mixing portion is fully mixed, before Symbol wherein the first fuel gas the second fuel gas is burned completely mixed fuel gas and a burner for heating the furnace body, A heating furnace that performs heat treatment by supplementing or stabilizing the amount of heat generated by the first fuel gas with the second fuel gas, wherein the fuel gas mixing unit is continuous with the first fuel gas pipe, A main pipe having a circular or substantially circular cross section, and an injection port opening on the inner surface of the main pipe And a gas blowing nozzle that is continuous with the second fuel gas pipe and blows the second fuel gas into the main pipe, and the gas blowing nozzle has an injection direction of the second fuel gas as described above. The outer peripheral portion of the main pipe is provided so as to be tangential or substantially tangential, and the injection speed of the second fuel gas from the gas blowing nozzle is at least twice the gas flow speed after mixing, and the burner There is provided a heating furnace characterized in that combustion air is supplied separately from a fuel gas in which the first fuel gas and the second fuel gas are completely mixed .

The fuel gas mixing unit comprises at least two nozzles for blowing the gas, it said at least two gas blow nozzles can be used which is provided to swivel direction are the same. The first fuel gas pipe further includes a shut-off valve capable of shutting off the supply of the first fuel gas, and the shut-off valve is provided in the first fuel gas supply source rather than the mixing unit. It is preferable that it is provided on the side.

  According to the present invention, in the heating furnace that performs the heat treatment using the first fuel gas, the second fuel gas having a calorific value different from that of the first fuel gas is mixed and supplied to the heating furnace. Even when the first fuel gas has a shortage of heat due to the amount restriction or the supply of the first fuel gas is not stable, it is possible to stably operate with a desired amount of heat. Specifically, in a steel plant using a coke oven gas as the first fuel gas, even if the supply stability of the coke oven gas is insufficient, the second fuel gas is usually used as the second fuel gas. By controlling the amount of input heat using the city gas supplied to the steelworks, it is possible to more easily and stably operate with a desired amount of heat.

  Also, a heating furnace provided with a heating device that mixes the first fuel gas and the second fuel gas in the mixing section, burns the mixed first fuel gas and the second fuel gas, and heats the inside of the furnace body. In the above, the first fuel gas and the second fuel gas can be more reliably mixed by attaching the main pipe and the mixing portion including one or more gas blowing nozzles. It can be simply and stably operated with a desired amount of heat. Furthermore, since the gas mixing distance is shorter, a smaller space can be achieved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing a schematic configuration of a heating furnace according to an embodiment of the present invention in which coke oven gas and city gas are mixed and supplied.
As shown in FIG. 1, this heating furnace has a heating furnace 2 for continuously heating the steel material 1. The furnace body 2 is provided with a plurality of burners 3 as heating devices, and fuel gas and combustion air are supplied to the burners. Combustion control consists of all four zones of 1 to 4 zones. Here, coke oven gas generated from a coke oven at a steel mill is used as the first fuel gas which is the main fuel gas. The coke oven gas is supplied to the pipe 4 at a predetermined pressure at a point A in FIG. On the downstream side of the point A, the pipe 4 branches to each combustion zone (1 to 4 zones). The pipe 4 before branching is provided with a flow meter 5 and a shut-off valve 6.

  In this embodiment, the city gas supplied to the vicinity of the heating furnace is used as the second fuel gas for assisting the coke oven gas that is the main fuel gas. A mixer 14 for mixing city gas and coke oven gas is installed immediately downstream of the shutoff valve 6. This is to prevent the city gas from flowing back to the supply side on the coke oven gas side when the shutoff valve 6 is closed in an emergency. The city gas is supplied at a predetermined pressure at point B in FIG. 1, passes through the pipe 15, is introduced into the mixer 14, and is mixed with the coke oven gas. The pipe 15 is provided with a city gas flow meter 16, a city gas flow rate adjustment valve 17, and a city gas cutoff valve 18 from the upstream side. The flow rate of the city gas is measured by the city gas flow meter 16 and is controlled by the city gas flow rate adjustment valve 17 so as to be a predetermined ratio with respect to the measured value of the coke oven gas flow meter 5. Thereby, even if the fuel flow rate supplied to the heating furnace 2 changes, it is possible to always maintain a constant calorific value.

  The coke oven gas flow rate and city gas flow rate signals are input to the regulator 19, and a control signal is output from the regulator 19 to the city gas flow rate control valve 17 to automatically control the mixing ratio of the coke oven gas and the city gas. Is done. The mixed gas is supplied to the burner 3 through the pipe 4 after branching to each combustion zone. The pipe 4 after branching is provided with a fuel flow meter 7 and a fuel flow control valve 8 for each zone in each zone. Combustion air is supplied by a combustion air blower 9, and an air flow meter 10 and an air flow control valve 11 are individually installed in each combustion zone. The fuel flow rate and air flow rate signals are input to the regulator 12 so that the air ratio of each zone (the ratio of air expressed as air required for combustion as 1) is a predetermined value, for example, 1.2. Control signals are output from the regulator 12 to the fuel flow rate adjustment valve 8 and the air flow rate adjustment valve 11 to be automatically controlled.

  Further, thermometers 13 are individually arranged in each zone of the heating furnace, and when the set furnace temperature is given for the combustion control in each zone, the measured value of the thermometer 13 is ± 5 of the set furnace temperature. The fuel flow control valve 8 and the air flow control valve 11 are automatically controlled so as to keep the air ratio constant so that the temperature is within the temperature range.

  In the heating furnace configured as described above, coke oven gas is supplied to the pipe 4 at point A and flows through the pipe 4 while the flow rate is measured by the flow meter 5. The coke oven gas flowing through the pipe 4 is branched and supplied to the combustion zones 1 to 4. The coke oven gas supplied to each zone flows through the piping of each combustion zone while the flow rate is measured by the fuel flow meter 7 installed for each zone. The measured flow rate signal is input to the regulator 12. On the other hand, the combustion air supplied from the combustion air blower 9 is measured by the air flow meter 10 for the flow rate of the combustion air. This measured signal is input to the regulator 12. The fuel flow rate control valve 8 and the air flow rate from the regulator 12 so that the air ratio of each zone becomes a predetermined value, for example, 1.2, based on the flow rate signals of the coke oven gas and the combustion air input to the regulator 12. Control signals are respectively output to the control valves 11. The coke oven gas is supplied to the burner 3 of each combustion zone while the flow rate is adjusted by the fuel flow rate control valve 8 according to the output signal, and the combustion air is adjusted to each combustion zone while the flow rate is adjusted by the air flow rate control valve 11. To the burner 3. The coke oven gas supplied to the burner 3 is combusted, and a flame generated by the combustion is blown into the furnace body 2 from the burner 3 to heat the steel material 1.

  In addition, when the measured value of the thermometer 13 arranged in each zone exceeds the range of ± 5 ° C. of the preset furnace temperature set in advance, it is within ± 5 ° C. of the set furnace temperature. The fuel flow rate control valve 8 automatically controls the flow rate of the coke oven gas, and the air flow rate control valve 11 automatically controls the flow rate of the combustion air while maintaining a constant air ratio. Supplied to the burner 3.

  However, if only the coke oven gas is used as the fuel gas, the amount of heat of the coke oven gas may be insufficient, or the supply flow rate may not be stable, and it may be difficult to obtain a constant calorific value even if the above control is performed.

  In this embodiment, in such a case, city gas is mixed with the coke oven gas as the second fuel gas. Since city gas is supplied to the vicinity of such a heating furnace and itself has a high calorific value, it is suitable as a fuel gas for such purposes.

  The city gas is supplied at point B of the pipe 15, flows through the pipe 15 while the flow rate is measured by the flow meter 16, and is mixed with the coke oven gas by the mixer 14. At this time, signals of the coke oven gas flow rate measured by the flow meter 5 and the city gas flow rate measured by the flow meter 16 are input to the regulator 19. Based on this input signal, a control signal is output from the regulator 19 to the city gas flow rate control valve 17 so that the city gas flow rate becomes a predetermined ratio with respect to the coke oven gas flow rate. According to the output control signal, the city gas flows through the pipe 15 while the flow rate is adjusted by the flow control valve 17, and is mixed with the coke oven gas flowing through the pipe 4 by the mixer 14. The mixed gas mixed in the mixer 14 is supplied to the burner 3 in each combustion zone while the flow rate is adjusted in the same manner as in the case of the above-described coke oven gas alone, and the flow rate is adjusted in the same manner so that the combustion air is burned. , The mixed gas is combusted, and a flame generated by the combustion is blown into the furnace body 2 from the burner 3 to heat the steel material 1.

  Similarly to the case of the coke oven gas alone, when the measured value of the thermometer 13 arranged in each zone exceeds the preset furnace temperature range of ± 5 ° C., the set furnace temperature So that the air ratio between the flow rate of the mixed gas and the flow rate of the combustion air is kept constant so that the gas flow rate is within ± 5 ° C. Supplied.

  Thus, by mixing the city gas as the second combustion gas with the coke oven gas, even if the calorific value of the coke oven gas is insufficient, the city gas can compensate for the shortage, and the desired amount can be obtained. Combustion energy can be obtained. Moreover, even when the supply of coke oven gas is not stable, it can be heated with a stable calorific value by mixing city gas. Furthermore, it only mixes coke oven gas and city gas, and it is not necessary to introduce special equipment such as pressure-resistant equipment to mix the gas, and it is a simple and small-scale structure, so it is low cost and small space. be able to.

  By the way, when city gas is mixed immediately downstream of the shutoff valve 6, in order to prevent unfavorable combustion control such as supply of fuel having a different calorific value between zones to disturb the air ratio, the It is preferable to mix thoroughly at a distance during which branching into each zone begins. Further, it is preferable that the mixing can be performed completely even when the part from the shutoff valve 6 to the part where the branching starts is short.

  Hereinafter, the structure of the preferable mixer 14 which can implement | achieve such a thing is demonstrated. FIG. 2 is a side view showing a mixer having such a preferred structure, FIG. 3 is a transverse sectional view thereof, and FIG. 4 is a longitudinal sectional view thereof. 3 is a cross-sectional view taken along line AA in FIG.

  As shown in FIG. 2, a gas blowing nozzle 21 that blows city gas is connected to a main pipe 20 that forms a part of the pipe 4 so as to blow city gas in the tangential direction of the outer peripheral portion of the main pipe 20. .

  As shown in FIG. 3, the gas mixer 14 has a circular cross section and forms a part of the pipe 4. The main pipe 20 through which coke oven gas flows and the injection port 21 a are the inner surfaces of the main pipe 20. And a gas blowing nozzle 21 for blowing city gas into the main pipe 20. The city gas injection direction from the gas blowing nozzle 21 is the tangential direction of the outer periphery of the main pipe 20, and the city gas injection flow rate from the gas blowing nozzle 21 is more than twice the mixed gas flow rate.

  With such a configuration, the coke oven gas flows inside the main pipe 20 from the direction of the arrow in FIG. When the city gas is blown from the gas blowing nozzle 21, the city gas swirls along the inner peripheral surface of the main pipe 20 as indicated by the arrow 22, and mixes with the coke oven gas in the traveling direction of the coke oven gas. It flows in the direction of an arrow. Then, when it reaches a certain distance, it mixes completely.

The description has been given of the case where the number of gas blowing nozzles 21 is one. Next, the configuration of the mixer when the gas blowing nozzles 21 of the mixer 14 are two will be described below.
FIG. 5 is a transverse sectional view showing a mixer in the case of two gas blowing nozzles, and FIG. 6 is a longitudinal sectional view. 5 is a cross-sectional view taken along the line BB in FIG.

  As shown in FIG. 5, the two gas blowing nozzles 21 with respect to the main pipe 20 are arranged such that the city gas injection direction with respect to the main pipe 20 is the tangential direction of the outer peripheral portion of the main pipe 20, and the turning direction is the same. It is installed to become.

  Due to the configuration of the mixer when there are two gas blowing nozzles 21 of the mixer 14, the city gas is blown so that the gas blowing nozzle 21 blows in the tangential direction of the outer peripheral portion and the swirl direction is the same, and coke Coke oven gas and city gas can be mixed thoroughly with the furnace gas, more reliably and efficiently, and with a shorter mixing distance. For this reason, since there is no dispersion | variation in the combustion at the time of the mixed gas combusting, a heating furnace can be more stably operated with a desired calorie | heat amount. And since it mixes with a shorter mixing distance, a heating furnace can be made smaller space.

  Note that when a mixer having a complicated structure is used, the coke oven gas contains dust tar and easily accumulates dust, so that the frequency of cleaning increases and the productivity of the furnace decreases. However, the mixer in the above embodiment has a simple structure, hardly accumulates dust, and requires less cleaning frequency, so that the productivity of the furnace is improved.

Next, an example in which city gas is mixed by a heating furnace using a mixer having such a structure to improve the processing capacity of the heating furnace will be described.
Now, in order to increase the heat treatment amount per hour of the steel material 1 by 10%, it is desired to increase the heat input to the furnace by 10% to 3830 Mcal / h. To that end, the coke oven gas calorific value 4350kcal / Nm ³ of, since the calorific value of city gas is 9500kcal / Nm ^3, coke oven gas 730 nm ³ / h, 70 Nm city gas ³ / h mixture was heat value A total of 800 Nm ³ / h of 4800 kcal / Nm ³ of gas may be supplied.

First, the first embodiment will be described.
In this embodiment, the coke oven gas is supplied to the pipe 4 having a pipe diameter of 150 A (inner diameter: 155.2 mm) at a point A in FIG. On the other hand, the city gas is supplied to the pipe 15 having a pipe diameter of 65 A (inner diameter: 70.2 mm) at a point B in FIG.

  By the way, the distance from immediately after the shut-off valve to the start of branching of each zone (symbol Y in FIG. 1) is 1200 mm, and it is necessary to uniformly mix the city gas with the coke oven gas under this condition. Therefore, it is desirable to use a mixer in order to shorten the mixing distance. Note that if the coke oven gas pressure is lowered by using a mixer, the gas supply flow rate will decrease, which will be disadvantageous for increasing the input heat amount, so the coke oven gas pressure loss is minimized. A mixer is desirable. Moreover, when not using a mixer, in order to mix city gas and coke oven gas uniformly, the distance (symbol Y in FIG. 1) from a mixing part to the start of branching of each zone is set to 3.1 to 4.7 m. It is necessary to do it above. Therefore, in this embodiment, it is desirable to use a mixer.

In the present embodiment, the city gas blowing nozzle 21 of the mixer 14 is formed by restricting the 65A pipe 15 to 20A (inner diameter 21.6 mm). Under this condition, signals of the coke oven gas flow rate measured by the flow meter 5 and the city gas flow rate measured by the flow meter 16 are input to the regulator 19. Now, the flow rate of the coke oven gas is 730 Nm ³ / h, and a signal of 730 Nm ³ / h is input from the flow meter 5 to the regulator 19. From this input signal, the regulator 19 controls the city gas flow rate control valve so that the flow rate of the city gas becomes 9.6% of the measured value of the coke oven gas flow rate, that is, 70 Nm ³ / h. A control signal is output to 17. By this output control signal, the city gas flows through the pipe 15 while the flow rate is adjusted to 70 Nm ³ / h by the flow control valve 17, and is mixed with the coke oven gas flowing through the pipe 4 by the mixer 14. Is done. After mixing, the flow rate of the gas is 800 Nm ³ / h and flows through the pipe 4. In this case, the flow velocity of the city gas is 57 m / s at a temperature of 20 ° C., the flow velocity in the pipe of the mixed gas is 12.6 m / s at a temperature of 20 ° C., and the speed ratio is 4.5. Note that the speed ratio is obtained by dividing the gas flow rate (in this case, the flow rate at which city gas is blown) from the tangential direction in the mixer by the gas flow rate after mixing (in this case, the flow rate of the mixed gas of coke oven gas and city gas). It is the value.

  The pressure loss before and after the mixer 14 on the coke oven gas side is Δ2 mmAq, which is sufficiently large in comparison with the supply pressure 700 mmAq, and a decrease in the flow rate can be ignored. The city gas side blowing pressure loss is Δ120 mmAq, but the city gas pressure required immediately before the city gas blowing is 820 mmAq. The city gas flow meter 16, the city gas flow control valve 17, and the supply of the city gas supply system Even if the pressure loss such as the distribution (pressure immediately before blowing from the point B) is estimated to be approximately 500 mmAq, it is sufficient because the pressure required at the point B is 1320 mmAq and the actual pressure at the point B is 2000 mmAq.

About the mixability of coke oven gas and city gas, the calorific value for each zone after mixing was determined by measuring the sample heat in the piping for each zone. As a result, all were 4800 kcal / Nm ³ . That is, it was confirmed that uniform mixing was sufficiently completed within a distance of 1200 mm from the start of mixing.

  Next, Example 2 which can cope with the case where the city gas supply pressure is as low as 1250 mmAq using the heating furnace according to the present embodiment will be described.

In this case, if the pressure loss of the city gas supply system pipe 15, city gas flow meter 16, and city gas flow rate control valve 17 is Δ500 mmAq, the city gas pressure immediately before blowing is 750 mmAq. Since the pressure on the coke oven side is 700 mmAq, the city gas cannot be mixed to a predetermined flow rate unless the pressure loss of the city gas is set to Δ50 mmAq or less. Therefore, with a 20A nozzle, the city gas side blowing pressure loss is Δ120 mmAq, which is not realized. Therefore, here, the nozzle for blowing city gas was set to 40A (inner diameter 41.6 mm), and further two nozzles were used. In this case, the blowing speed of the city gas blowing nozzle is 7.7 m / s at a temperature of 20 ° C., the pressure loss is Δ2 mmAq, and the speed ratio at this time is 0.6. About mixing property, as a result of measuring the gas calorific value for each zone after mixing with piping for each zone, all were 4800 kcal / Nm ³ . That is, it was confirmed that uniform mixing was sufficiently completed within a distance of 1200 mm from the start of mixing.

Therefore, according to Examples 1 and 2, as in Example 2, even when the city gas supply pressure is low, the coke oven gas with a calorific value of 4350 kcal / Nm ³ is 730 Nm ³ / h, city gas heating value is 9820kcal / Nm ³ were mixed 70 Nm ³ / h, to obtain a large combustion force by burning with 800 Nm ³ / h feed the heating value 4800kcal / Nm ³ of gas in total, Rohe The purpose of increasing the amount of heat input by 10% can be achieved.

  In addition, when the city gas supply pressure is even lower, for example, 1050 mmAq, the city gas pressure before mixing is designed to reduce the pressure loss of the city gas pipe 15, the city gas flow meter 16, and the regulating valve 17 to Δ300 mmAq. It can be 750 mmAq, and the object can be achieved.

It is preferable to use a mixer having such a structure. However, if the mixing of the gas is performed reliably and the heating furnace can operate stably, such as when there is a sufficient mixing distance, the mixer as described above is not necessarily used. You do not need to use it. Further, in the first and second embodiments, the city gas and the coke oven gas are used. However, as long as the desired amount of heat can be obtained, not only the mixture of the city gas and the coke oven gas but also other fuel gases may be combined. I do not care. Furthermore, although two kinds of city gas and coke oven gas are mixed and used, three or more kinds of gases may be mixed as long as a desired amount of heat can be obtained. Furthermore, in Examples 1 and 2, the density of coke oven gas is 0.6 kg / Nm ³ , the density of city gas is 0.8 kg / Nm ³ , and the density of mixed gas is 0.62 kg / Nm ^3. Since the increase in pressure loss due to the increase in density until the mixed gas mixed in the mixer reaches the burner is in a negligible range, there is no problem since the decrease in the mixed gas flow rate is negligible. However, when the density is not city gas but the density is high, for example, when propane gas (density 2 kg / Nm ³ ) is mixed with the coke oven gas, the density of the mixed gas increases, and the mixed gas mixed in the mixer is supplied to the burner. The increase in pressure loss until it reaches is large. For this reason, if the decrease in flow rate cannot be ignored, there is no problem if the mixing ratio is adjusted in advance so that the amount of heat input to the furnace can be increased to the target value, that is, the amount of heat generated by the gas after mixing increases. .

  Next, the examination results up to the mixer having the preferable structure used in the heating furnace according to the present embodiment will be described. Here, in confirming the performance of the mixer, the gas to be mixed is referred to as gas A (air) and gas B (oxygen) for convenience.

  When evaluating the performance of a gas mixer, one of the performances is the mixing distance, but it mixes gas A and gas B from where they begin to mix to a certain degree of mixing. If the pipe diameter of the mixing section is the same, the shorter the distance, the better the mixing efficiency, and the size of the mixer main body can be reduced. The mixing distance is a distance in the symbol X direction required for mixing the gas A and the gas B to a predetermined degree of mixing from the line AA where the gas A and the gas B start to be mixed as shown in FIG.

  Further, the dimensionless mixing distance is obtained by dividing the mixing distance by the pipe inner diameter after mixing. That is, in general, if the gas flow rate is large, the pipe diameter for transporting the gas will inevitably increase. Therefore, it is not sufficient to discuss only the absolute mixing distance when comparing the performance of the mixer. . Therefore, when discussed in terms of dimensionless mixing distance, the influence of the pipe diameter is eliminated, and the performance can be compared according to the mixer type.

  However, simply blowing the gas B from the gas blowing nozzle 21 increases the mixing distance and the mixing efficiency is not sufficient.

  According to the examination results of the present inventors, in order to increase the mixing efficiency, the value obtained by dividing the nozzle blowing flow rate by the flow rate of the mixed gas rather than simply blowing the gas B from the gas blowing nozzle 21 (this is calculated as follows). Increasing the speed ratio) proved to be effective.

  Based on the above examination results, first, the results of testing the performance when the gas blowing nozzle of the mixer is one will be described in detail below.

  As a test condition when the gas blowing nozzle of the mixer is one, the number of gas blowing nozzles 21 for blowing oxygen is one, and the nozzle diameter is 20A (inner diameter 21.6 mm) and 10A (nozzle inner diameter 12.7 mm). Two types of cases were used. The speed ratio at this time is 1.1 for 20A nozzles and 3.3 for 10A nozzles.

FIG. 7 shows the test results of the mixing degree when the speed ratio is 1.1 and 3.3.
Here, for convenience, air 193 Nm ³ / h and oxygen gas 17 Nm ³ / h were mixed. Since the oxygen in the air is 20.9%, the oxygen concentration when completely mixed at the above flow rate ratio is 27.4%. In the test, air was allowed to flow through a 80A (inner diameter 80.7 mm) straight tube, and oxygen gas was injected and mixed from a 20A (inner diameter 21.6 mm) blowing nozzle ejected in a tangential direction in the straight tube. 200 mm downstream from the mixing location (dimensionalless mixing distance = 2.5), 400 mm (dimensionalless mixing distance = 5), 600 mm (dimensionalless mixing distance = 7.5), 800 mm (dimensionalless mixing distance = 10), At each distance of 1000 mm (dimensionless mixing distance = 12.5), the oxygen concentration at 9 points in the cross section of the flow path in the pipe was measured. The absolute value of the difference between the maximum value and the minimum value of oxygen concentration (%) measured in each cross section was defined as oxygen concentration deviation (%). Since mixing progresses as it goes downstream, the oxygen concentration deviation becomes smaller. However, a distance where the oxygen concentration deviation Δ is less than 2.5% is obtained from experiments, and the smaller the distance, the higher the degree of mixing.

  According to the graph shown in FIG. 7, the oxygen concentration deviation Δ is 2.5% when the speed ratio is 1.1 and is about 900 mm (dimensionalless mixing distance = 11), and when the speed ratio is 3.3. Is about 450 mm (dimensionless mixing distance = 5.6), and it is confirmed that the oxygen concentration deviation becomes smaller at a shorter mixing distance when the speed ratio is larger than when the speed ratio is small. It was found that the degree was obviously higher when the speed ratio was larger.

  Next, the dimensionless mixing distance at which the oxygen concentration deviation Δ was 2.5% was determined by the same experiment with various speed ratios changed. The result is shown in FIG. From this figure, in the range where the speed ratio is smaller than 2, the mixing distance does not increase even if the speed ratio increases, but when the speed ratio becomes 2 or more, the degree of mixing increases rapidly (the dimensionless mixing distance decreases). ) Was confirmed. From this, the speed ratio is set to 2 or more, that is, the injection flow rate of the gas B from the gas blowing nozzle is set to be twice or more the gas flow rate after mixing, and the mixing distance can be shortened to perform efficient gas mixing. It turned out to be preferable.

  Tables 1 and 2 show the main results obtained in a series of tests when the speed ratio is 1.1 and 3.3. For comparison, Table 3 shows the results of a similar test performed with a conventional swirl vane mixer. As shown in these tables, when the speed ratio is 3.3, it can be seen that the mixing ratio (mixing distance at which the oxygen concentration deviation becomes 2.5%) is inferior to that of the conventional swirl vane mixer. . In addition to the mixing distance, the pressure loss is also important as a characteristic of the mixer, and in particular, it is important that the pressure loss on the gas A side is low. The pressure loss was as low as 3 mmAq. On the other hand, in the swirl vane type mixer, it was confirmed that the pressure loss on the gas A side was 77 mmAq and the pressure loss was clearly large.

  In addition, the cross-sectional shape of the main pipe 20 is not limited to a circle, and may be a substantially circle. For example, a hexagon or more polygon is exemplified. Further, the cross-sectional shape of the gas blowing nozzle 21 is not limited to a circle, and may be any shape such as a flat shape or a rectangular shape.

  Further, the size of the gas blowing nozzle 21 is not particularly limited. However, as shown in FIG. 9, the size h of the gas blowing nozzle 21 when viewed in a cross section of the main tube 20 is ¼ or less of the inner diameter d of the main tube 20. It is preferable that By doing so, a preferable swirl flow can be easily formed. This effect can be obtained regardless of the cross-sectional shape of the gas blowing nozzle 21 as long as these dimensions are satisfied.

  Furthermore, although the example in which the gas blowing nozzle 21 is provided so that the gas injection direction is the tangential direction of the main pipe 20 is shown, it may not be completely tangential, and the main pipe 20 has a cross-sectional shape. Even if it is not a circle, it may be a tangential direction or a substantially tangential direction of a circumscribed circle.

  Next, the result of having tested the performance about the case where the gas blowing nozzle of a mixer is two is demonstrated in detail below.

FIG. 10 shows the test results obtained by comparing the mixing degrees when the number of nozzles is one and two. Here, air 193 Nm ³ / h and oxygen gas 17 Nm ³ / h were mixed as in the case of a single gas blowing nozzle. In the test, air was allowed to flow through a 80A (inner diameter 80.7 mm) straight tube, and oxygen gas was injected and mixed from a 20A (inner diameter 21.6 mm) blowing nozzle ejected in a tangential direction in the straight tube. 200 mm downstream from the mixing location (dimensionalless mixing distance = 2.5), 400 mm (dimensionalless mixing distance = 5), 600 mm (dimensionalless mixing distance = 7.5), 800 mm (dimensionalless mixing distance = 10), At each distance of 1000 mm (dimensionless mixing distance = 12.5), the oxygen concentration at 9 points in the cross section of the flow path in the pipe was measured. The absolute value of the difference between the maximum value and the minimum value of oxygen concentration (%) measured in each cross section is defined as oxygen concentration deviation (%), and the distance by which the oxygen concentration deviation Δ is less than 2.5% is obtained from experiments. The smaller the distance, the higher the degree of mixing. The above was performed in the case of one blowing nozzle and in the case of two blowing nozzles, and the degree of mixing was compared. Table 4 shows main results obtained in a series of tests in the case of two gas blowing nozzles.

  According to the graph of FIG. 10, the oxygen concentration deviation Δ becomes 2.5% when the number of nozzles is one, about 900 mm (dimensionless mixing distance = 11), and when the number of nozzles is two, it is about 400 mm (dimensionless). It was confirmed that the mixing distance = 5) and the oxygen concentration deviation becomes smaller at a shorter mixing distance by using two blowing nozzles. That is, it was confirmed that the mixing efficiency is extremely improved by using two gas blowing nozzles. The speed ratio is 1.1 for one nozzle and 0.55 for two nozzles (two nozzles have the same flow rate). By using two nozzles, the speed ratio is smaller than 2. Also, the mixing distance can be shortened.

  As shown in Table 4, when there are two gas blowing nozzles, not only the pressure loss on the gas A side is as low as 3 mmAq, but also the speed of the gas B may be small. 4 mmAq was confirmed to be extremely low.

  By providing two nozzles for blowing gas in this way, the mixing distance can be shortened and the two gases can be mixed efficiently.

  In addition, when there are two gas blowing nozzles, the cross-sectional shape of the main pipe, the cross-sectional shape of the gas blowing nozzle, the cross-sectional area ratio thereof, the direction of the gas blowing nozzle, etc., is one gas blowing nozzle. It is the same as the case of. Furthermore, although two examples of the gas blowing nozzles have been shown, three or more nozzles may be used. Furthermore, although an example in which two gas blowing nozzles are arranged at the same cross-sectional position of the main pipe has been shown, two or more gas blowing nozzles may be arranged at intervals in the longitudinal direction of the main pipe. Furthermore, although the gas blown from the two gas blowing nozzles is the same gas, different gases may be blown, and in that case, three kinds of gases are mixed. When three or more gas blowing nozzles are used, four or more kinds of gases can be mixed. However, as for the gas to be blown from one gas blowing nozzle, the gas injection flow rate from the gas blowing nozzle is at least twice the mixed gas flow rate as in the case of one gas blowing nozzle. It is necessary to.

  According to the present invention, the processing capacity of steel materials can be improved with a simple and small-scale structure, which is optimal for increasing the processing capacity of the heating furnace and has high industrial utility value.

The schematic block diagram which shows the structure of the heating furnace which concerns on one Embodiment of this invention. The figure which shows the gas mixer applicable to the heating furnace of FIG. The cross-sectional view which shows the gas mixer with one nozzle for gas blowing. The longitudinal cross-sectional view which shows the gas mixer with one nozzle for gas blowing. The cross-sectional view which shows the gas mixer with two nozzles for gas blowing. The longitudinal cross-sectional view which shows the gas mixer with two nozzles for gas blowing. The figure which shows the relationship between the distance from the mixing start and oxygen concentration deviation in speed ratio 1.1 and 3.3. The figure which shows the relationship between a speed ratio and the dimensionless mixing distance used as oxygen concentration deviation 2.5%. The figure for demonstrating the preferable dimension of the nozzle for gas blowing. The figure which shows the relationship between the distance from the mixing start in the case of 1 and 2 blowing nozzles, and oxygen concentration deviation. The schematic block diagram which shows the structure of the conventional heating furnace.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Heating furnace 3 Burner 4,15 Piping 5 Flow meter 6 Shut-off valve 14 Mixer 20 Main pipe 21 Gas blowing nozzle 22 Turning direction

Claims (3)

A furnace body;
The first and the fuel gas piping for feeding the first fuel gas toward Previous Symbol furnace body,
A second fuel gas pipe through which a second fuel gas different from the first fuel gas flows;
A fuel gas mixing section provided in the first fuel gas pipe, wherein the second fuel gas from the second fuel gas pipe is completely mixed with the first fuel gas ;
Before Symbol wherein the first fuel gas the second fuel gas is burned completely mixed fuel gas and a burner for heating the furnace body,
A heating furnace for performing heat treatment by supplementing or stabilizing the calorific value of the first fuel gas with the second fuel gas,
The fuel gas mixing part
A main pipe that is continuous with the first fuel gas pipe and has a circular or substantially circular cross section;
A gas blowing nozzle that opens to the inner surface of the main pipe and is continuous with the second fuel gas pipe, and blows the second fuel gas into the main pipe;
The gas blowing nozzle is provided such that the injection direction of the second fuel gas is the tangential direction or substantially tangential direction of the outer peripheral portion of the main pipe, and the second fuel from the gas blowing nozzle The gas injection flow rate is more than twice the gas flow rate after mixing,
A heating furnace , wherein combustion air is supplied to the burner separately from the fuel gas in which the first fuel gas and the second fuel gas are completely mixed . The fuel gas mixing unit, said provided at least two nozzles for blowing a gas, said at least two gas blow nozzles is claimed in claim 1, characterized in that provided as swivel direction are the same Heating furnace. A shut-off valve provided in the first fuel gas pipe and capable of shutting off the supply of the first fuel gas;
The heating furnace according to claim 1 or 2 , wherein the shutoff valve is provided closer to the first fuel gas supply source than the mixing unit.

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