JP5966352B2 - Radiant tube heating device - Google Patents

Description

  The present invention relates to a radiant tube heating device that heats a steel plate or a steel material by radiant heat from the radiant tube.

  Conventionally, a radiant tube heating device including a regenerative heat exchanger that repeatedly performs a heat storage cycle and a heat release cycle is known (see Patent Documents 1 to 3). According to such a radiant tube type heating device, the stored heat of the exhaust gas is accumulated in the heat storage cycle, and the combustion air is preheated by the heat accumulated in the heat storage cycle in the heat release cycle, thereby improving the fuel combustion efficiency. Can be made.

JP-A-10-132222 JP-A-11-257611 Japanese Patent Laid-Open No. 11-351520

  In recent years, there has been proposed a radiant tube heating device including a continuous heat exchanger that continuously preheats combustion air by simultaneously performing a heat storage cycle and a heat release cycle. According to the radiant tube heating device provided with such a continuous heat exchanger, higher efficiency can be realized than the radiant tube heating device provided with the regenerative heat exchanger. However, in a radiant tube type heating device including a continuous heat exchanger, the side on which the fuel burns is always one end side of the radiant tube, and is maintained at a higher temperature than the exhaust side. For this reason, in a radiant tube type heating device equipped with a continuous heat exchanger, the flame temperature becomes higher than that of a radiant tube type heating device equipped with a regenerative heat exchanger, and therefore the temperature dependency is high. The NO generation reaction is promoted, and the amount of NOx emission increases.

  This invention is made | formed in view of the said subject, The objective is to provide the radiant tube type heating apparatus which can suppress the discharge | emission amount of NOx increasing.

  In order to solve the above problems and achieve the object, the radiant tube heating device according to the present invention includes a radiant tube having a cylindrical structure in which one end is open and the other end is closed, A continuous heat exchanger provided on the open end side of the radiant tube for preheating air supplied from the outside by heat exchange with the exhaust gas after heating the radiant tube, and the continuous heat exchange The fuel is burned using the air preheated by the continuous heat exchanger, which is disposed adjacent to the heater, so that a central axis is provided with a gap between the burner that discharges the flame and the burner. And a mixing cylinder, which is disposed in the radiant tube so as to be substantially coaxial with the central axis of the gas, and into which the flame discharged by the burner flows.

  In the radiant tube heating device according to the present invention, in the above invention, the heat is transferred from the combustion gas to the mixing cylinder, which is disposed from the inlet of the mixing cylinder to a position at least three times the inner diameter of the mixing cylinder. It is characterized by comprising a thermal radiation promoting body for promoting the above.

  The radiant tube heating device according to the present invention is characterized in that, in the above invention, the thermal radiation promoting body is made of a ceramic material.

  The radiant tube heating device according to the present invention is characterized in that, in the above invention, the inner diameter of the flame discharge port of the burner is smaller than the inner diameter of the mixing cylinder.

  In the radiant tube heating device according to the present invention, in the above invention, the burner includes a fuel supply port for supplying fuel and an air supply port for supplying a part of the air preheated by the continuous heat exchanger. And the air supply port has an air amount such that the amount of air supplied into the flame holding tube is insufficient for complete combustion of the fuel supplied from the fuel supply port at least in a steady combustion state. It is characterized by limiting the amount of.

  The radiant tube heating device according to the present invention is the radiant tube heating device according to the second aspect, wherein the burner supplies the other part of the air heated by the continuous heat exchanger provided on the outlet side of the flame holding cylinder. The second air supply port has an amount sufficient for the complete combustion of the fuel supplied from the fuel supply port in the steady combustion state at least in the sum of the amount of air supplied from the air supply port. The amount of air is adjusted so that

  In the radiant tube heating device according to the present invention, in the above invention, the burner is provided with a discharge port that is disposed downstream of the second air supply port in the air flow direction and is smaller than the inner diameter of the flame holding tube. And a discharge nozzle for discharging a flame formed in the flame holding cylinder.

  The radiant tube heating device according to the present invention is characterized in that, in the above invention, the discharge nozzle is made of a ceramic material.

  According to the radiant tube heating device according to the present invention, it is possible to suppress an increase in NOx emission.

FIG. 1 is a cross-sectional view showing a configuration of a radiant tube heating device according to an embodiment of the present invention. FIG. 2 is a view showing a modification of the cross-sectional shape of the radiant tube. FIG. 3 is an enlarged cross-sectional view showing the configuration of the heat exchanger and the burner shown in FIG. FIG. 4 is a diagram illustrating a configuration example of a flame distributor.

  Hereinafter, a configuration of a radiant tube heating device according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a configuration of a radiant tube heating device according to an embodiment of the present invention. FIG. 2 is a view showing a modification of the cross-sectional shape of the radiant tube. FIG. 3 is an enlarged cross-sectional view showing the configuration of the heat exchanger and the burner shown in FIG. FIG. 4 is a diagram illustrating a configuration example of a flame distributor.

  As shown in FIG. 1, a radiant tube heating apparatus 1 according to an embodiment of the present invention is disposed on a furnace wall W of a heating furnace that heats steel sheets and steel materials for annealing, quenching, normalizing, tempering, and the like. It is installed. The radiant tube heating device 1 includes a radiant tube 2. The radiant tube 2 has a flat cylindrical structure in which one end 2a in the length direction is open and the other end 2b is closed, and is disposed so as to protrude from the furnace wall W in the furnace direction. The cross-sectional shape of the radiant tube 2 on the end 2a side is a rounded rectangular shape composed of two straight lines parallel to each other and a semicircle whose both ends are in contact with the two straight lines.

  The sectional shape of the end portion 2b of the radiant tube 2 is such that the absolute value of the curvature of the straight portion of the rounded rectangle is smaller than the absolute value of the curvature of the semicircles at both ends, and the sign of the curvature of the straight portion of the rounded rectangle is It has a negative shape, in other words, a saddle-shaped shape in which the center of the side surface is recessed inward. The radiant tube 2 is manufactured by a cold isostatic pressing (CIP) method in which silicon carbide powder is compressed at a high pressure and then sintered in a high temperature furnace. In this molding method, an undercut portion cannot be formed on the inner surface because the sintered body is removed from the mold.

  For this reason, when the cross-sectional shape on the end portion 2a side is a rounded rectangular shape and the short side radius is the same even in the central portion in the length direction of the radiant tube 2, in order to configure the entire cross section with a curve, As described above, the cross-sectional shape on the end portion 2b side may be a saddle shape. The cross-sectional shape of the radiant tube 2 is not limited to the cross-sectional shape of the present embodiment, and a cross-sectional shape as shown in FIG. 2 can be adopted. Specifically, the cross-sectional shape shown in FIG. 2A shows an elliptical shape in which the length of the major axis is different from the length of the minor axis. In the cross-sectional shape shown in FIG. 2B, the absolute value of the curvature of the straight part of the rounded rectangle is smaller than the absolute value of the curvature of the semicircles at both ends, and the sign of the curvature of the straight part of the rounded rectangle is positive. A certain shape is shown.

  According to such a cross-sectional shape, since the radiant tube 2 has no flat portion, the thermal stress generated by the temperature difference between the end 2a and the end 2b is released as a change in curvature, and the radiant tube 2 is caused by the thermal stress. It can suppress that a crack generate | occur | produces. In addition, although mentioned later in detail, since the combustion air does not contact the radiant tube 2 directly on the end 2a side, the temperature of the end 2a is kept low. For this reason, even if there is a plane portion on the component surface of the end 2a, the magnitude of the thermal stress applied to the end 2a is small, so that the radiant tube 2 is not cracked.

  On the end 2a side of the radiant tube 2, a heat exchanger 3 and a burner 4 are disposed adjacent to each other. The heat exchanger 3 is constituted by a heat exchanger element formed by processing a ceramic honeycomb member mainly composed of silicon carbide, and exchanges heat with the exhaust gas after heating the radiant tube 2. Thus, the air supplied from the outside through the cold air supply box 3a is preheated. By arranging the heat exchanger 3 and the burner 4 adjacent to each other, the structure of the radiant tube 2 can be simplified, and high-temperature preheated air can be supplied from the heat exchanger 3 to the burner 4 over a short distance. The thermal expansion length of the connecting member can be reduced by reducing the amount. By configuring the heat exchanger 3 with a ceramic member, it is possible to realize high heat resistance and high efficiency of the heat exchanger.

  A ceramic foam 5 is disposed in the vicinity of the exhaust gas inlet to the heat exchanger 3. The semi-ramic foam 5 absorbs the radiant heat from the radiant tube 2 before reaching the heat exchanger 3 and recirculates the absorbed radiant heat into the radiant tube 2. By disposing the ceramic foam 5, it is possible to prevent the radiant heat from the radiant tube 2 from going directly to the heat exchanger 3 and increase the effective heat into the furnace.

  As shown in FIG. 3, the burner 4 is connected to the heat exchanger 3 via a hot air supply box 6. The hot air supply box 6 includes a burner air inlet 6a and a primary air supply 6b, and high-temperature air generated by the heat exchanger 3 is supplied into the burner air inlet 6a. A portion of the high-temperature air supplied into the burner air inlet 6 a has an air ratio of 0.2 due to the primary air restriction hole 6 c provided outside the plate integral with the bottom plate of the flame holding cylinder 4 b constituting the burner 4. The flow rate is limited so as to be approximately, and the distribution in the circumferential direction is made uniform, and the air is supplied into the primary air supply unit 6b.

  The high temperature air supplied into the primary air supply unit 6b is supplied while swirling into the flame holding cylinder 4b from the primary air supply port 6d opened by cutting and raising the bottom plate of the flame holding cylinder 4b. Another part of the high-temperature air supplied into the burner air inlet 6a has an air ratio of about 0.3 from the secondary air supply port 6e opened in the outer peripheral portion of the flame holding cylinder 4b inward in the radial direction. The flow rate is restricted so as to be supplied into the flame holding cylinder 4b. As a result, the amount of air that contributes to the combustion of the fuel inside the flame holding cylinder 4b becomes an amount that is insufficient for the complete combustion of the fuel at least in the steady combustion state. Therefore, residual oxygen at the outlet side of the flame holding cylinder 4b is eliminated, and NOx Generation can be suppressed.

  The remaining part of the high-temperature air supplied into the burner air inlet 6a has an air ratio from a tertiary air supply port 6f opened at the tip of the flame-holding cylinder 4b parallel to the central axis L of the flame-holding cylinder 4b. It is supplied into the discharge nozzle 4c while the flow rate is limited to about 0.7. The total opening area of the tertiary air supply port 6f is designed to be larger than the total opening area of the primary air restriction hole 6c and the secondary air supply port 6e. Thereby, the air supply amount from the tertiary air supply port 6f becomes larger than the air supply amounts from the primary air restriction hole 6c and the secondary air supply port 6e. Further, since the air that is deficient inside the flame holding cylinder 4b is supplied as the tertiary air, the fuel discharged in an unburned state can be eliminated and energy saving can be realized. Further, since the tertiary air is supplied substantially parallel to the central axis of the flame-holding cylinder 4b, it diffuses slowly with the unburned components in the flame, and it is possible to reduce the number of oxygen-excess locations locally at high temperatures. Generation can be suppressed.

  Although not shown, ceramic fibers are filled between the outer peripheral portion of the heat exchanger 3, the cold air supply box 3 a, and the cold air supply box 6 and the inner peripheral portion of the radiant tube 2. By filling the ceramic fiber, it is possible to prevent leakage of exhaust gas and air, and to absorb a change in dimensions caused by a temperature difference of each part.

  The burner 4 includes an ignition unit 4a, a flame holding cylinder 4b, and a discharge nozzle 4c. The ignition part 4a includes an outer cylindrical part 4d and an inner cylindrical part 4e having an outer diameter smaller than the inner diameter of the outer cylindrical part 4d, and the inner cylindrical part 4e contacts the outer cylindrical part 4d in the outer cylindrical part 4d. It is arranged without. One end of the outer cylindrical portion 4d and the inner cylindrical portion 4e is connected to an external device (not shown), and the other end is connected to the flame holding cylinder 4b. The central axes of the outer cylindrical part 4d and the inner cylindrical part 4e are arranged on the same axis as the central axis L of the flame holding cylinder 4b.

  The gap between the inner peripheral portion of the outer cylindrical portion 4d and the outer peripheral portion of the inner cylindrical portion 4e functions as a fuel gas flow path 4f, and the fuel gas supplied from an external device (not shown) to the fuel gas flow path 4f is fuel swirled. The valve 4g is supplied into the flame holding cylinder 4b while being swung in the same rotational direction as the primary air. The inside of the inner cylindrical portion 4e functions as an ignition auxiliary air flow path 4h, and the ignition auxiliary air supplied from an external device (not shown) to the ignition auxiliary air flow path 4h is supplied into the flame holding cylinder 4b. The ignition auxiliary air functions as a combustion aid when initially forming a flame.

  An ignition electrode 4j is disposed on the central axis of the inner cylindrical portion 4e in a state of being supported by a support insulator 4i. The ignition electrode 4j is made of a steel material whose tip is bent at a right angle. When an external device (not shown) first forms a flame, a voltage is applied between the ignition electrode 4j and the inner cylindrical portion 4e functioning as a ground electrode, whereby the tip of the ignition electrode 4j and the inner cylindrical portion 4e Generate electric sparks between.

  The flame holding cylinder 4b is constituted by a cylindrical member. Inside the flame holding cylinder 4b, the fuel gas supplied from the fuel gas passage 4g and the primary air supplied from the primary air supply port 6d are mixed while swirling to hold the flame. The secondary air supplied from the secondary air supply port 6e into the flame holding cylinder 4b reaches the center of the partial combustion gas to assist combustion, and stops the swirling flow of the fuel gas and the primary air. The discharge nozzle 4c is composed of a ceramic member having high heat resistance, and the inner diameter on the outlet side is smaller than the inner diameter of the flame holding cylinder 4b. According to such a configuration, since the flow of the combustion air from the flame holding cylinder 4b is narrowed toward the outlet of the discharge nozzle 4c, a pseudo laminar flow in which the turbulence in the radial direction of the combustion air is attenuated Become. As a result, the tertiary air supplied into the discharge nozzle 4c and the unburned components in the flame diffuse slowly, and the number of locations where oxygen is excessive at high temperatures can be reduced. Therefore, the generation of NOx can be suppressed.

  As shown in FIG. 1, the mixing tube 7 is arranged in the radiant tube 2 with a gap between the discharge nozzle 4c so that the central axis thereof is on the same axis as the central axis L of the discharge nozzle 4c. It is installed. The mixing cylinder 7 has an inner diameter of about 1.5 times the inner diameter of the discharge nozzle 4c on the outlet side, and is formed by molding silicon carbide by the CIP method. The inlet side of the mixing cylinder 7 has a smooth circular cross-sectional shape so as not to hinder the flow of flame and exhaust flowing into the mixing cylinder 7. On the outer periphery of the mixing cylinder 7, a protrusion 7a formed of silicon carbide is joined with metal silicon. The protrusion 7 a supports the mixing cylinder 7 so that the mixing cylinder 7 is arranged in parallel with the central portion in the length direction of the radiant tube 2.

  By providing the mixing cylinder 7 inside the radiant tube 2, the flame discharged from the burner 4 burns while being dissipated, so the maximum temperature of the flame can be kept low and the generation of NOx can be suppressed. Further, by making the inner diameter of the outlet side of the discharge nozzle 4c smaller than the inner diameter of the mixing cylinder 7, the flame discharged from the discharge nozzle 4c is decelerated in the mixing cylinder 7 from the speed at the outlet of the discharge nozzle 4c, and the pressure is recovered. As a result, an action of sucking the atmosphere in the radiant tube 2 into the mixing cylinder 7 occurs. As a result, the exhaust gas circulates in the mixing cylinder 7 due to the ejector effect, so that the maximum temperature of the flame can be kept low and the generation of NOx can be further suppressed.

  A cylindrical ceramic heat radiation promoting body 7b is disposed at a position at least three times the inner diameter of the mixing cylinder 7 from the inlet of the mixing cylinder 7. The heat radiation promoting body 7b promotes heat transfer from the flame to the mixing cylinder 7. By promoting the transfer of heat from the flame to the mixing cylinder 7, it is possible to promote the cooling of the flame and suppress the discharge of NOx, and to enhance the efficiency by promoting the heat transfer to the radiant tube 2. In addition, since the momentum diffusion between the flame and the tertiary air or the suction atmosphere is completed at a position about three times as long as the inner diameter of the mixing cylinder 7 from the inlet of the mixing cylinder 7, it should be on the downstream side of this length position. For example, even if an obstacle is inserted, the influence on the flow is small. In the present embodiment, the heat radiation promoting body 7b is constituted by a cylindrical member. However, as shown in FIG. 4, a flame distributor 8 such as a core buster having a cross-sectional shape is used instead of the heat radiation promoting body 7b. It may be arranged.

  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 this embodiment are all included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Radiant tube type heating apparatus 2 Radiant tube 3 Heat exchanger 3a Cold air supply box 4 Burner 4a Ignition part 4b Flame holding cylinder 4c Discharge nozzle 4d Outer cylindrical part 4e Inner cylindrical part 4f Fuel gas flow path 4h Ignition auxiliary air flow path 4i Support Insulating electrode 5j Ignition electrode 5 Ceramic foam 6 Hot air supply box 6a Burner air inlet 6b Primary air supply 6c Primary air restriction hole 6d Primary air supply 6e Secondary air supply 6f Tertiary air supply 7 Mixing cylinder 7a Protrusion 7b Heat Radiator 8 Flame Disperser

Claims (7)

A radiant tube having a cylindrical structure with one end open and the other end closed;
A continuous heat exchanger provided on the open end side of the radiant tube for preheating air supplied from the outside by heat exchange with the exhaust gas after heating the radiant tube;
A burner disposed adjacent to the continuous heat exchanger and configured to burn the fuel by using the air preheated by the continuous heat exchanger to discharge a flame;
A mixing cylinder for introducing the flame discharged by the burner, disposed in the radiant tube so that a central axis is substantially coaxial with the central axis of the burner with a gap between the burner and the burner;
A heat radiation promoting body for promoting the transfer of heat from the flame to the mixing cylinder, which is disposed in the mixing cylinder at a position at least three times the inner diameter of the mixing cylinder from the inlet of the mixing cylinder; ,
A radiant tube type heating device comprising: The radiant tube heating device according to claim 1 , wherein the heat radiation promoting body is made of a ceramic material. 3. The radiant tube heating device according to claim 1, wherein an inner diameter of a flame discharge port of the burner is smaller than an inner diameter of the mixing cylinder. The burner includes a flame holding tube having a fuel supply port for supplying fuel and an air supply port for supplying a part of the air preheated by the continuous heat exchanger, and the air supply port has a flame holding port. claim 1-3 the amount of air supplied into the cylinder, characterized in that to limit the amount of air so that the amount is insufficient for complete combustion of the fuel supplied from the fuel supply port at least a steady combustion state Among these, The radiant tube type heating apparatus of any one. The burner includes a second air supply port that is provided on the outlet side of the flame-holding cylinder and supplies the other part of the air heated by the continuous heat exchanger, and the second air supply port is The amount of air is adjusted so that the sum of the amount of air supplied from the air supply port becomes a sufficient amount for complete combustion of the fuel supplied from the fuel supply port at least in a steady combustion state. The radiant tube heating device according to claim 4 . The burner has a discharge port that is disposed downstream of the second air supply port in the air flow direction and is smaller than the inner diameter of the flame holding tube, and discharges a flame formed in the flame holding tube. The radiant tube heating apparatus according to claim 5 , further comprising a discharge nozzle that performs the discharge nozzle. The radiant tube heating device according to claim 6 , wherein the discharge nozzle is made of a ceramic material.

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