JP2011257014A - Melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simply-constituted melting furnace saving energy and making NOx low.SOLUTION: The melting furnace 1 includes: a furnace body 2 for housing a material As to be melted; a burner 3 which can mix and burn fuel and main combustion air, so as to form a concentrated flame colliding with the material to be melted, and which can only partially burn the fuel by reducing a flow rate of the main combustion air; an auxiliary air nozzle 4 which supplies the inside of the furnace body 2 with supplemental combustion air for self-burning the fuel remaining in combustion gas after the fuel has been partially burnt by the burner 3; and a control means 10 which decreases the flow rate of the main combustion air of the burner 3 and increases the flow rate of the supplemental combustion air of the auxiliary air nozzle 4 when the material As to be melted is melted down.

Description

  The present invention relates to a melting furnace.

  From the viewpoint of environmental protection, NOx reduction in exhaust gas is also required for melting furnaces for melting scraps (melting materials) such as aluminum and copper. For example, Patent Document 1 discloses a melting furnace in which NOx is reduced by providing a burner that supplies fuel and air from a remote location in the furnace and slowly burns (diffusion combustion). Further, in Patent Document 1, a pair of burners having a heat storage body are alternately operated in a melting furnace, exhaust gas is exhausted through a burner that is not combusted, and heat is recovered from the combustion exhaust gas by the heat storage body, It is described that a regenerative burner that preheats combustion air with a heat-recovered heat storage body and performs combustion operation is described.

  However, in the melting furnace, for example, as described in Non-Patent Document 1, a melting rate can be improved by causing a flame to collide with a material to be melted and efficiently transferring heat. For this reason, from the standpoint of energy saving, the melting furnace is supplied with a mixture of fuel and air and intensively burned to create a highly directional concentrated flame that collides with the material to be melted with high kinetic energy. The burner that is formed is considered preferred.

  Further, as described in Patent Document 2, when a diffusion combustion type burner is used in a melting furnace, low-temperature material to be melted is deposited in front of the burner at the initial stage of operation. There is also a problem that incomplete combustion occurs when hitting a low-temperature material to be melted and soot is generated. For this reason, Patent Document 2 proposes a melting furnace provided with a main burner that performs diffusion combustion and an auxiliary burner that forms a concentrated flame that collides with a material to be melted. If a plurality of burners are provided in this way, the configuration becomes complicated and the melting furnace becomes expensive.

JP-A-8-94253 JP-A-11-325734

Kamitsugami, “Current status of energy saving in aluminum melting furnaces using regenerative burners”, AL-Aru, Light Metal Communications Co., Ltd., July 2009, P17-20

  In view of the above problems, an object of the present invention is to provide a melting furnace that is energy saving, low NOx, and simple in configuration.

  In order to solve the above problems, a melting furnace according to the present invention forms a concentrated flame that collides with a material to be melted by mixing a furnace body containing the material to be melted and fuel and main combustion air to be burned. A burner capable of burning only a part of the fuel by reducing the flow rate of the main combustion air, and auxiliary combustion air for self-combusting the fuel remaining in the combustion gas after being burned by the burner When the material to be melted is dissolved, the flow rate of the main combustion air in the burner is decreased and the flow rate of the auxiliary combustion air in the auxiliary air nozzle is increased. And control means.

  According to this structure, until the material to be melted is melted, the melting of the material to be melted can be promoted by efficiently applying heat by directly applying the concentrated flame of the burner to the material to be melted. In addition, after the material to be melted is melted, the main combustion air is reduced so that only a part of the fuel can be burned in the concentrated flame, and the fuel remaining in the combustion gas is fed into the furnace by the air supplied from the auxiliary air nozzle. By diffusing and burning in a dispersive manner in these places, the entire surface of the molten metal in which the material to be melted is radiantly heated, and the rise in the molten metal temperature can be promoted. Also, NOx generation can be suppressed by diffusing and burning the fuel.

  Further, in the melting furnace of the present invention, if the flow rate of the main combustion air after the material to be melted is reduced to an air ratio of 0.2 or less, generation of NOx can be sufficiently suppressed.

  In the melting furnace of the present invention, the air ratio of the total flow rate of the main combustion air and the auxiliary combustion air to the fuel flow rate of the burner is after the material to be melted is melted than before the material to be melted is melted. If it is made lower, incomplete combustion of the concentrated flame in the initial stage of operation can be prevented, and NOx in diffusion combustion for increasing the temperature of the molten metal can be reduced.

  In addition, in the melting furnace of the present invention, the material to be melted that is not melted blocks the concentrated flame, so that the radiant heat of the flame does not reach the portion behind it and the temperature is lowered. Therefore, the melting state of the material to be melted can be detected by the temperature distribution in the furnace.

  Further, in the melting furnace of the present invention in which the state of the flame and the position where the flame is formed are changed, if a temperature sensor is provided in the furnace, an error in the detected temperature increases due to the influence of the radiant heat of the flame. Therefore, the temperature of the exhaust gas may be detected as an index of the temperature in the furnace by detecting the temperature of the exhaust gas in the flue not receiving the flame radiation. Furthermore, since the furnace temperature rises as the melting of the material to be melted progresses, the melting state of the material to be melted can be estimated from the exhaust gas temperature in the flue.

  As described above, according to the present invention, it is possible to cause the concentrated flame to collide with the material to be melted and efficiently melt it with one burner, or to efficiently radiate and heat the entire molten metal with the diffusion flame. Thereby, the melting furnace of the present invention can save fuel consumption and achieve energy saving, and can maintain the NOx concentration in the exhaust gas low.

It is a block diagram of the melting furnace of 1st Embodiment of this invention. It is a figure which shows the separate air flow rate in the melting furnace of FIG. It is a figure which shows the total air flow rate in the melting furnace of FIG. It is a block diagram of the melting furnace of 2nd Embodiment of this invention. It is a figure which shows the air flow rate in the melting furnace of FIG. It is a block diagram of the melting furnace of 3rd Embodiment of this invention.

  Embodiments of the present invention will now be described with reference to the drawings. First, in FIG. 1, the structure of the melting furnace 1 of 1st Embodiment of this invention is shown. A melting furnace 1 includes a furnace body 2 that can store a material to be melted (aluminum scrap) As as illustrated by a two-dot chain line, and can store a melt Am in which the material to be melted is melted as indicated by a solid line; Fuel (for example, LNG) and air (main combustion air) are mixed and injected into the furnace body 2 and burned so as to form a concentrated flame, and from the vicinity of the burner 3 to the interior of the furnace body 2 And an auxiliary air nozzle 4 capable of introducing auxiliary combustion air.

  The combustion gas in the furnace body 2 is exhausted from the flue 5 through the recuperator 6. The recuperator 6 performs heat recovery by exchanging heat between the exhaust gas and the auxiliary combustion air supplied to the auxiliary air nozzle 4. Both the main combustion air and the auxiliary combustion air are supplied by the air supply fan 7. The flow rate of the main combustion air is adjusted by the main adjustment valve 8, and the flow rate of the auxiliary combustion air is adjusted by the auxiliary adjustment valve 9. The opening degree of the main regulating valve 8 and the auxiliary regulating valve 9 is adjusted according to the exhaust gas temperature detected by the temperature sensor 11 provided in the flue 5 by a control device (control means) 10 comprising a computer.

  FIG. 2 shows the flow rates of the main combustion air and the auxiliary combustion air in the melting furnace 1 as a ratio (air ratio) to the theoretical air amount of fuel supplied to the burner 3. In the melting furnace 1, the fuel with the maximum combustion amount of the burner 3 is supplied until the exhaust gas temperature reaches, for example, 1200 ° C., and thereafter the fuel flow rate is adjusted so that the exhaust gas temperature is maintained at 1200 ° C. The The melting furnace 1 continues the combustion operation until the temperature of the molten metal reaches a predetermined temperature while maintaining the exhaust gas temperature at 1200 ° C.

  As shown in the figure, in the melting furnace 1, no auxiliary combustion air is supplied until the exhaust gas temperature reaches 500 ° C., main combustion air having an air ratio of 1.2 is supplied to the burner 3, and the burner 3 is completely burned. Let At this time, all of the supplied fuel burns inside the concentrated flame. The concentrated flame formed by the burner 3 has high straightness (directivity), collides with the stacked materials to be melted As, and effectively transfers heat to the materials to be melted with the high kinetic energy.

  Since the melting temperature of aluminum is 660 ° C., when the exhaust gas temperature reaches 500 ° C., the material to be melted As that is directly exposed to the concentrated flame becomes higher and melts at least partially. It is thought that it is Am. Therefore, in the melting furnace 1, when the exhaust gas temperature becomes 500 ° C. or higher, the flow rate of the main combustion air in the burner 3 is reduced and the auxiliary combustion air is supplied from the auxiliary air nozzle 4 into the furnace body 2.

  By reducing the flow rate of the main combustion air, in the concentrated flame of the burner 3, some fuel remains without being burned, and combustion gas containing unburned fuel diffuses into the furnace body 2. Since this combustion gas has a temperature equal to or higher than the ignition point of the fuel, the unburned fuel self-combusts when it encounters oxygen contained in the auxiliary combustion air supplied from the auxiliary air nozzle 4. That is, a part of the fuel supplied to the burner 3 is desorbed from the concentrated flame and burned while diffusing inside the furnace body 2 to form a diffusion flame at various places.

  Such a diffusion flame is also formed in a portion where the concentrated flame does not reach, and heats the solid material As or the molten metal Am by radiant heat. When melting of the material to be melted advances and the amount of molten metal Am increases, heat can be transferred more efficiently by radiant heating as a whole by diffusion flame than by local heating by concentrated flame. For this reason, in the melting furnace 1, as shown in FIG. 2, as the exhaust gas temperature rises, the flow rate of the main combustion air is gradually decreased, and at the same time, the flow rate of the auxiliary combustion air is increased.

  In the melting furnace 1, when the exhaust gas temperature reaches 800 ° C., it is considered that almost all of the material As to be melted is melted to become a molten metal Am. Therefore, in the melting furnace 1, when the exhaust gas temperature reaches 800 ° C., the air ratio of the main combustion air is set to 0.1, and the air ratio of the auxiliary combustion air is set to 1.0. Here, as shown in FIG. 3, it is noted that the air ratio of the total amount of the main combustion air and the auxiliary combustion air is 1.1. This is because, in the melting furnace 1, the fuel is diffused and burnt slowly at high temperatures, so that the fuel can be burned without leaving any fuel even at a low air ratio as compared to the case of forming a concentrated flame at low temperatures.

  The melting furnace 1 can suppress the generation of NOx by lowering the air ratio in this way. In order to obtain the NOx reduction effect, the air ratio of the main combustion air is preferably 0.2 or less. Although the air ratio of the main combustion air may be further reduced, it is necessary to leave a concentrated flame for holding the flame. Therefore, the air ratio of the main combustion air must be at least about 0.01.

  The temperature of the exhaust gas in the flue 5 is substantially the same as the temperature of the combustion gas inside the furnace body 2, but if the temperature sensor 11 is provided inside the furnace body 2, the temperature sensor 11 itself is caused by the radiant heat of the flame. It is directly heated and detects a temperature higher than the temperature of the combustion gas. In the melting furnace 1, since the flame state and the position where the flame is formed change, the detection error due to the radiant heat of the flame is not constant, and it is difficult to empirically correct the detection temperature. For this reason, in the melting furnace 1, the temperature sensor 11 is provided in the flue 5 which is not influenced by the flame radiation.

  Subsequently, FIG. 4 shows a melting furnace 1a according to a second embodiment of the present invention. In the following description, the same components as those of the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted. The melting furnace 1a has two burners 3 and two auxiliary air nozzles 4 as a pair. Each of the auxiliary air nozzles 4 has a heat storage body 12 and can supply auxiliary combustion air through the heat storage body 12.

  The main combustion air whose flow rate is adjusted by the main regulating valve 8 is supplied only to one burner 3 selected by the main supply valve 13, and only one burner 3 is in a combustion operation. The auxiliary combustion air whose flow rate is adjusted by the auxiliary regulating valve 9 is supplied into the furnace body 2 from the auxiliary air nozzle 4 on the same side as the burning burner 3 selected by the auxiliary supply valve 14. The

  In addition, the auxiliary air nozzle 4 is connected to an exhaust passage including an exhaust adjustment valve 16 and an exhaust fan 17 via an exhaust valve 15, and the combustion gas in the furnace body 2 can be exhausted through the heat storage body 12. It is like that.

  That is, in the melting furnace 1a, when performing diffusion combustion, auxiliary combustion air is supplied from one of the auxiliary air nozzles 4 and the combustion gas in the furnace body 2 is exhausted through the other auxiliary air nozzle 4 to alternate them. By operating, a so-called regenerative burner effect that preheats auxiliary combustion air by recovering heat from the exhaust gas by the heat storage body 12 can be obtained.

  In addition, the melting furnace 1 a has a total amount of main combustion air supplied to the furnace body 2 through the burner 3 and a furnace body 2 through the auxiliary air nozzle 4 in order to keep a balance between heating and cooling of the heat storage body 12. The opening degree of the exhaust adjustment valve 16 is adjusted so that an amount of combustion gas corresponding to about 20% of the auxiliary combustion air supplied to the exhaust gas is exhausted through the flue 5.

  FIG. 5 shows the flow rates of main combustion air and auxiliary combustion air in the melting furnace 1a of the present embodiment. In this embodiment, since the exhaust gas temperature in the flue 5 is low, the air ratio of the main combustion air of the burner 3 is suppressed to 0.5, and auxiliary combustion air with an air ratio of 0.7 is introduced from the auxiliary air nozzle 4. is doing. Further, in the present embodiment, the main combustion air does not gradually change the flow rates of the main combustion air and the auxiliary combustion air, but when the exhaust gas temperature reaches 800 ° C. and all the materials to be dissolved are dissolved. The air ratio is changed to 0.1 and the air ratio of the auxiliary combustion air is changed to 1.0, so that the ratio between the concentrated combustion and the diffusion combustion is changed discontinuously.

  In the melting furnace 1a of the present embodiment, the melted material As is supplied immediately after discharging the molten metal Am that has reached a predetermined temperature, and the next combustion operation is started in a state where the furnace body 2 is somewhat hot. Assumes that. However, if the exhaust gas temperature is even lower than 300 ° C., such as at the start of the first operation after a holiday, the main combustion air ratio is set to 1.2 and the auxiliary combustion air is not introduced. The operation may be started only by concentrated combustion.

  Of course, in the melting furnace 1a of the apparatus configuration of the present embodiment having the heat storage body 12, as shown in FIG. 2, the main combustion air is decreased and the auxiliary combustion air is increased as the exhaust gas temperature rises. The ratio between the concentrated flame and the diffusion flame may be continuously changed.

  Furthermore, FIG. 6 shows a melting furnace 1b according to a third embodiment of the present invention. In the present embodiment, a plurality of temperature sensors 18 are arranged on the ceiling of the furnace body 2 along the flame forming direction of the burner 3. As described above, each temperature sensor 18 exposed inside the furnace body 2 detects not only the temperature of the combustion gas inside the furnace body 2 but also the radiant heat of the flame formed by the burner 3.

  As shown in the figure, when there is a solid material to be melted As, the concentrated flame formed by the burner 3 is interrupted by the material to be melted As. Therefore, only the temperature sensor 18 provided at a position close to the burner 3 during the combustion operation detects the radiant heat of the concentrated flame, and detects a temperature higher than the temperature sensor 18 on the side far from the burner 3 during the combustion operation. That is, it is considered that the material to be dissolved As is dissolved immediately below the temperature sensor 18 having a high detection temperature.

  When the material to be melted is melted as a whole to become the molten metal Am, the concentrated flame traverses the inside of the furnace body 2, and all temperature sensors detect the radiant heat of the concentrated flame in substantially the same manner. Therefore, in the melting furnace 1b, when the difference in the temperature detected by the temperature sensor 18 is equal to or lower than a certain temperature, it is determined that the material As to be melted has melted into the molten metal Am, and the flow rate of the main combustion air is determined. Reduce the flow of auxiliary combustion air, reduce the concentrated flame, and diffusely burn the remaining fuel.

  In the present invention, in addition to the method of the above embodiment, for example, a video camera for photographing the inside of the furnace body 2 may be provided, and the degree of dissolution of the material As to be dissolved may be determined by image processing.

  In addition, the terms main combustion air and auxiliary combustion air in the present invention refer to a gas that supplies oxygen necessary for combustion, and it should be understood that any gas that serves as an oxygen supply source can be included in these terms. .

DESCRIPTION OF SYMBOLS 1,1a, 1b ... Melting furnace 2 ... Furnace body 3 ... Burner 4 ... Auxiliary air nozzle 5 ... Flue 7 ... Air supply fan 8 ... Main adjustment valve 9 ... Auxiliary adjustment valve 10 ... Control apparatus 11 ... Temperature sensor 12 ... Thermal storage Body 18 ... Temperature sensor

Claims (5)

A furnace body containing the material to be melted;
A burner capable of forming a concentrated flame that collides with the material to be dissolved by mixing and burning fuel and main combustion air, and burning only a part of the fuel by reducing the flow rate of the main combustion air When,
An auxiliary air nozzle for supplying auxiliary combustion air into the furnace body for self-combustion of fuel remaining in the combustion gas after being burned by the burner;
And a control means for reducing the flow rate of the main combustion air of the burner and increasing the flow rate of the auxiliary combustion air of the auxiliary air nozzle when the material to be melted is melted. .   The melting furnace according to claim 1, wherein a flow rate of the main combustion air after the material to be melted is melted is an air ratio of 0.2 or less.   The air ratio of the total flow rate of the main combustion air and the auxiliary combustion air to the fuel flow rate of the burner is lower after the material to be dissolved is lower than before the material to be dissolved is dissolved. The melting furnace according to claim 1 or 2.   4. The melting furnace according to claim 1, wherein the control means detects a melting state of the material to be melted by a temperature distribution in the furnace. 5.   The melting furnace according to any one of claims 1 to 4, wherein the control means estimates a melting state of the material to be melted based on an exhaust gas temperature in the flue.

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