TWI429872B - Melting furnace - Google Patents

Description

Melting furnace Field of invention

The present invention relates to a melting furnace.

Background of the invention

From the viewpoint of environmental protection, the melting furnace for melting waste materials (melted materials) such as aluminum or copper is also required to have low NOx emission. For example, Patent Document 1 describes a melting furnace provided with a burner that supplies fuel and air from an isolated position to a furnace and slowly burns (diffusion combustion) to reduce NOx. Further, Patent Document 1 discloses that a pair of burners having a heat storage body are alternately operated in a melting furnace, and combustion exhaust gas is discharged through an unburned burner, and heat is recovered from the combustion exhaust gas by the heat storage body, and the heat is recovered. The recovered regenerator heats the combustion air to perform a combustion operation of a Regenerative Burner.

However, in the melting furnace, for example, as disclosed in Non-Patent Document 1, the melting rate can be increased by allowing the flame to be sprayed toward the material to be melted for efficient heat transfer. Therefore, from the viewpoint of energy saving, a burner which is concentrated and burned by mixing fuel and air and then supplied to a melting furnace to form a concentrated flame having high kinetic energy and being sprayed toward the melted material is suitable.

Further, as disclosed in Patent Document 2, when a burner of a diffusion combustion type is used in a melting furnace, since the low-temperature melted material accumulates in front of the burner at the initial stage of operation, the unburned fuel hits a low-temperature melted material. Incomplete combustion occurs, and there is also the problem of generating soot. Therefore, in Patent Document 2, a main burner for performing diffusion combustion and a melting furnace for forming a supplementary burner for spraying a concentrated flame of a material to be melted are proposed. If a plurality of burners are provided like this, the construction becomes complicated and the melting furnace becomes expensive.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Publication No. 8-94253

Patent Document 2: Japanese Laid-Open Patent Publication No. Hei 11-325734

Non-patent literature

Non-Patent Document 1: In the past, "the energy-saving status of the aluminum melting furnace using a regenerative burner", AL- (monthly), 軽metal communication KEIKINZOKO TSUSHIN AL CO, LTD), July 2009 issue, P17-20

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

In order to solve the above problems, a melting furnace according to the present invention is a furnace body having a material for containing a molten material, and a concentrated flame which is sprayed toward the melted material can be formed by mixing and burning the fuel and the main combustion air, and A burner capable of reducing the flow rate of the main combustion air and allowing only a part of the fuel to be burned, and a supplementary combustion air supply for self-ignition of the fuel remaining in the combustion gas after combustion by the burner The auxiliary air nozzle to the furnace body and the control device for increasing 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 molten material is melted.

If this configuration is utilized, it is possible to more efficiently transfer heat by directly aligning the concentrated flame of the burner with the molten material until the molten material is melted, thereby facilitating melting of the molten material. In addition, after being melted by the molten material, only a part of the fuel in the concentrated flame can be burned by reducing the main combustion air, and the fuel remaining in the combustion gas is dispersed throughout the furnace by the air supplied from the auxiliary air nozzle. In the manner of diffusion combustion, the entire surface of the molten metal melted by the molten material is radiantly heated to promote the temperature of the molten metal. In addition, since the fuel is diffused and burned, the occurrence of NOx can also be suppressed.

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

Further, in the melting furnace of the present invention, the air ratio of the fuel flow rate of the burner with respect to the total flow rate of the main combustion air and the auxiliary combustion air is reduced to be melted after the melted material is melted. When the material is low before melting, it is possible to prevent incomplete combustion of the concentrated flame at the initial stage of operation, and to reduce NOx during diffusion combustion for raising the temperature of the molten metal.

Further, in the melting furnace of the present invention, since the unmelted molten material blocks the concentrated flame, the radiant heat of the flame cannot reach the portion behind it, and the temperature becomes low. Therefore, the melted state of the melted material can be detected by the temperature distribution in the furnace.

Further, in the melting furnace of the present invention in which the flame state and the flame forming position are changed, if a temperature sensor is provided in the furnace, the error in the detected temperature is increased by the influence of the flame of the flame. Therefore, it is preferable to detect the temperature of the exhaust gas in the flue which is not subjected to flame radiation, thereby serving as an index of the temperature in the furnace. Further, since the temperature in the furnace rises as the melting of the molten material proceeds, the melting state of the molten material can be evaluated by using the temperature of the exhaust gas in the flue.

As described above, according to the present invention, it is possible to efficiently melt the concentrated flame by spraying the concentrated flame toward the material to be melted by one burner, or to efficiently heat the entire molten metal by the diffusion flame. Accordingly, the melting furnace of the present invention can save energy by saving fuel consumption, and can maintain NOx in the exhaust gas at a low concentration.

Simple illustration

Fig. 1 is a configuration diagram of a melting furnace according to a first embodiment of the present invention.

Figure 2 is a schematic illustration of the individual air flow rates in the melting furnace of Figure 1.

Fig. 3 is a schematic view showing the total amount of air flow in the melting furnace of Fig. 1.

Fig. 4 is a view showing the configuration of a melting furnace according to a second embodiment of the present invention.

Fig. 5 is a schematic view showing the flow rate of air in the melting furnace of Fig. 4.

Fig. 6 is a view showing the configuration of a melting furnace according to a third embodiment of the present invention.

Form for implementing the invention

Starting from this point, an embodiment of the present invention will be described with reference to the accompanying drawings. First, Fig. 1 shows the configuration of a melting furnace 1 according to a first embodiment of the present invention. The melting furnace 1 has a furnace body 2 which can accommodate a mountain of molten material (a waste material of aluminum) As as shown by a double-dotted line as shown, and stores a molten metal melted by the molten material as indicated by a solid line. Am, and, in the furnace body 2, a fuel (for example, LNG) and air (main combustion air) are mixed and injected to burn to form a concentrated flame burner 3, and auxiliary combustion can be performed from the vicinity of the burner 3. The air is introduced into the auxiliary air nozzle 4 inside the furnace body 2.

The combustion gas in the furnace body 2 is discharged from the flue 5 through a recuperator 6. The recuperator 6 performs heat exchange between the exhaust gas and the auxiliary combustion air supplied to the auxiliary air nozzle 4 to perform heat recovery. The main combustion air and the auxiliary combustion air are supplied together by the air supply fan 7. The flow of the main combustion air is regulated by the main regulator valve 8, and the flow of the auxiliary combustion air is regulated by the auxiliary adjustment valve 9. The opening degree of the main adjustment valve 8 and the auxiliary adjustment valve 9 is adjusted by the temperature of the exhaust gas detected by the temperature sensor 11 provided on the flue 5 by a control device (control means) 10 composed of a computer.

In the second drawing, the flow rate of the main combustion air and the auxiliary combustion air in the melting furnace 1 is expressed as a ratio (air ratio) to the theoretical air amount of the fuel supplied to the burner 3. Further, in the melting furnace 1, until the exhaust gas temperature reaches, for example, 1200 ° C, the fuel of the maximum combustion amount of the burner 3 is supplied, and thereafter the fuel is adjusted so that the exhaust gas temperature is maintained at 1200 °C. Then, the exhaust gas temperature is maintained at 1200 ° C, and the melting furnace 1 is continuously burned until the temperature of the molten metal reaches a predetermined temperature.

As shown in the figure, in the melting furnace 1, until the exhaust gas temperature reaches 500 ° C, the auxiliary combustion air is not supplied, but the main combustion air of the air ratio of 1.2 is supplied to the burner 3 to completely burn the burner 3. At this time, all of the supplied fuel is burned inside the concentrated flame. The concentrated flame formed by the burner 3 has a high straightness (directivity), and is sprayed toward the deposited material As, which is deposited as a mountain, and efficiently transfers heat to the material A to be melted due to its high kinetic energy.

Since the melting temperature of aluminum is 660 ° C, and if the temperature of the exhaust gas reaches 500 ° C, the temperature of the molten material As directly exposed to the concentrated flame will be higher, and we believe that at least some of it will melt into molten metal Am. Therefore, in the melting furnace 1, if the exhaust gas temperature reaches 500 ° C or higher, the main combustion air flow rate of the burner 3 is reduced, and the auxiliary combustion air is supplied from the auxiliary air nozzle 4 to the inside of the furnace body 2.

Since the flow rate of the main combustion air is reduced, a part of the fuel in the concentrated flame of the burner 3 is not burned, and the combustion gas containing the unburned fuel is diffused in the furnace body 2. Since the combustion gas has a temperature higher than the fuel ignition point, the unburned fuel spontaneously ignites upon encountering the 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 separated from the concentrated flame, and is burned while being diffused inside the furnace body 2 to form a diffusion flame everywhere.

Such a diffusion flame is also formed in a portion where the concentrated flame cannot reach, whereby the solid melted material As or the molten metal Am is heated by radiant heat. When the melting of the molten material As continues, and the molten metal Am increases, the heat can be more efficiently radiated by the radiant heating by the diffusion flame as compared with the partial heating by the concentrated flame. Therefore, in the melting furnace 1, as shown in Fig. 2, as the temperature of the exhaust gas 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, if the temperature of the exhaust gas reaches 800 ° C, it is considered that the melting of the molten material As is almost completely melted to become the molten metal Am. Therefore, in the melting furnace 1, when the exhaust gas temperature becomes 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, the air ratio of the main combustion air to the total amount of the auxiliary combustion air is 1.1. In the melting furnace 1, since the fuel is diffused at a high temperature and then slowly burned, it can be burned without remaining fuel even if the air ratio is low as compared with the case where a concentrated flame is formed at a low temperature.

By reducing the air ratio like this, the melting furnace 1 can suppress the generation of NOx. In order to obtain the effect of reducing NOx, it is preferable to set the air ratio of the main combustion air to 0.2 or less. Although it is also possible to further reduce the air ratio of the main combustion air, it is necessary to retain the concentrated flame in order to stabilize the flame, so the air ratio of the main combustion air must be ensured to be at least about 0.01.

Further, although the temperature of the exhaust gas in the flue 5 is approximately the same as the temperature of the combustion gas inside the furnace body 2, if the temperature sensor 11 is disposed inside the furnace body 2, the temperature sensor 11 itself It is directly heated by the radiant heat of the flame, resulting in the detection of a temperature higher than the temperature of the combustion gas. In the melting furnace 1, since the state of the flame and the position at which the flame is formed are changed, the detection error due to the radiant heat of the flame is not fixed, and it is difficult to correct the detected temperature by experience. Therefore, in the melting furnace 1, the temperature sensor 11 is placed in the flue 5 which is not affected by the radiation of the flame.

Next, a melting furnace 1a according to a second embodiment of the present invention is shown in Fig. 4. In the following description, structural elements that are the same as those in the embodiment described above are denoted by the same reference numerals, and the description thereof will not be repeated. The melting furnace 1a has two burners 3 and a supplementary air nozzle 4 which are two pairs. Each of the auxiliary air nozzles 4 has a heat storage body 12, and a state in which the combustion air can be supplied by the heat storage body 12 is formed.

The main combustion air whose flow rate is regulated by the main regulator valve 8 is supplied only to the one-side burner 3 selected by the main supply valve 13, and the other burner 3 is subjected to the combustion operation. Further, the auxiliary combustion air adjusted by the flow rate assist adjustment valve 9 is supplied to the inside of the furnace body 2 from the auxiliary air nozzle 4 which is selected on the same side as the combustion burner 3, which is selected depending on the auxiliary supply valve 14.

Further, the auxiliary air nozzle 4 is connected to the exhaust flow path equipped with the exhaust gas adjustment valve 16 and the exhaust fan 17 through the exhaust valve 15, and the combustion gas in the furnace body 2 can be exhausted by the heat storage body 12.

In other words, when the diffusion combustion is performed in the melting furnace 1a, the combustion air is supplied from one of the auxiliary air nozzles 4, and the combustion gas in the furnace body 2 is discharged through the other auxiliary air nozzle 4, and the like. By alternately operating, it is possible to obtain the effect of a so-called regenerative burner that uses the regenerator 12 to recover heat from the exhaust gas and preheat the auxiliary combustion air.

Further, in order to maintain the balance between heating and cooling of the heat storage body 12, the degree of opening of the exhaust gas regulating valve 16 is adjusted to the total amount of the main combustion air supplied to the furnace body 2 through the burner 3 via the flue 5. And, the combustion gas supplied to the furnace body 2 by the auxiliary air nozzle 4 in an amount corresponding to about 20% of the auxiliary combustion air is exhausted.

The flow rate of the main combustion air and the auxiliary combustion air in the melting furnace 1a of the present embodiment is shown in Fig. 5. In the present embodiment, when the temperature of the exhaust gas in the flue 5 is low, the air ratio of the main combustion air of the burner 3 is suppressed to 0.5, and the auxiliary combustion air having an air ratio of 0.7 is introduced from the auxiliary air nozzle 4. In addition, in this embodiment, the flow rate of the main combustion air and the auxiliary combustion air is not gradually changed, but the exhaust gas temperature reaches 800 ° C. When we think that the molten material has been completely melted, the air ratio of the main combustion air is changed. 0.1. The air ratio of the auxiliary combustion air is 1.0, and the state in which the ratio of the concentrated combustion to the diffusion combustion is discontinuously changed is formed.

Further, in the melting furnace 1a of the present embodiment, it is assumed that the molten material As is supplied immediately after the molten metal Am having reached a predetermined temperature is discharged, and the furnace body 2 starts the next combustion in a state of a certain high temperature. Running. However, at the beginning of the initial operation after the shutdown, etc., when the exhaust gas temperature is lower than 300 °C, the air ratio of the main combustion air can be set to 1.2, no auxiliary combustion air is introduced, and only concentrated combustion is used. Start running.

Needless to say, in the melting furnace 1a having the apparatus of the present embodiment having the heat storage body 12, as shown in Fig. 2, it is also possible to increase the amount of the combustion air by reducing the main combustion air by increasing the temperature of the exhaust gas. Let the ratio of concentrated flame to diffuse flame continuously change.

Further, a melting furnace 1b according to a third embodiment of the present invention is shown in Fig. 6. In the present embodiment, a plurality of temperature sensors 18 are arranged side by side in the flame forming direction of the burner 3 at the top of the furnace body 2. As described above, each of the temperature sensors 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, when there is a solid melted material As, the concentrated flame formed by the burner 3 is blocked by the molten material As on the way. Thus, only the temperature sensor 18 disposed at a position close to the burner 3 in the combustion operation is detected by the temperature sensor 18 that detects the radiant heat of the concentrated flame and away from the burner 3 side in the combustion operation. A higher temperature. That is, the molten material As is being melted directly under the temperature sensor 18 where the detection temperature is high.

If the molten material As is completely melted into the molten metal Am, the concentrated flame will traverse the inside of the furnace body 2, and all the temperature sensors will detect the radiant heat of the concentrated flame approximately the same. Therefore, in the melting furnace 1b, when the difference in the detected temperature of the temperature sensor 18 falls below a certain temperature, it is judged that the molten material As is melted into the molten metal Am, thereby reducing the flow rate of the main combustion air, increasing The flow of combustion air is subsidized to reduce the concentrated flame and allow the remaining fuel to spread and burn.

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

In addition, the term "main combustion air" as used in the present invention, which is used to supplement combustion air, refers to a gas which supplies oxygen necessary for combustion, and any gas which is an oxygen supply source must also be understood as being included in these terms.

1,1a, 1b. . . Melting furnace

2. . . Furnace body

3. . . burner

4. . . Subsidized air nozzle

5. . . Flue

7. . . Air supply fan

6. . . Reheater

8. . . Main adjustment valve

9. . . Subsidy adjustment valve

10. . . Control device

11. . . Temperature sensor

12. . . Heat accumulator

18. . . Temperature sensor

Am. . . Molten metal

As. . . Melting material

Fig. 1 is a configuration diagram of a melting furnace according to a first embodiment of the present invention.

Figure 2 is a schematic illustration of the individual air flow rates in the melting furnace of Figure 1.

Fig. 3 is a schematic view showing the total amount of air flow in the melting furnace of Fig. 1.

Fig. 4 is a view showing the configuration of a melting furnace according to a second embodiment of the present invention.

Fig. 5 is a schematic view showing the flow rate of air in the melting furnace of Fig. 4.

Fig. 6 is a view showing the configuration of a melting furnace according to a third embodiment of the present invention.

1. . . Melting furnace

2. . . Furnace body

3. . . burner

4. . . Subsidized air nozzle

5. . . Flue

6. . Reheater

7. . . Air supply fan

8. . . Main adjustment valve

9. . . Subsidy adjustment valve

10. . . Control device

11. . . Temperature sensor

Am. . . Molten metal

As. . . Melting material

Claims (5)

A melting furnace characterized by having a furnace body for accommodating a material to be melted, and combusting by mixing fuel and main combustion air to form a concentrated flame sprayed onto said melted material, and reducing said main combustion air a fuel for which only a part of the fuel is burned, and a subsidy for supplying the combustion air which is self-igniting the fuel in the combustion gas after burning by the burner to the furnace body An air nozzle, and a melting flame is formed in the burner to directly heat the melted material before the melted material is melted, and when the melted material is melted, the flow rate of the main combustion air of the burner is reduced, and The diffusion flame is formed by increasing the flow rate of the auxiliary combustion air of the auxiliary air nozzle, and the control device for melting the material is heated by the radiant heat of the diffusion flame. The melting furnace according to claim 1, wherein the flow rate of the main combustion air is equal to or less than 0.2 in air ratio after the molten material is melted. The melting furnace according to the first or second aspect of the invention is characterized in that, in the air ratio of the fuel flow rate of the burner with respect to the total flow rate of the main combustion air and the auxiliary combustion air, the melted material is melted. It is lower than before the melted material is melted. The melting furnace described in the first or second aspect of the patent application is characterized in that The control device detects the melting state of the melted material by using the temperature distribution in the furnace. The melting furnace according to claim 1 or 2, wherein the control device estimates the melting state of the molten material by using the temperature of the exhaust gas in the flue.