JPH1038248A - Melting furnace for incineration residue including salts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the problem that fugacity restriction effect of a low boiling point substance is small. SOLUTION: There are provided an electrode rod 13 inserted into a furnace, a furnace bottom electrode 14 provided on the furnace bottom, and a incineration residue insertion cylinder 15 inserted into a furnace upper part. A furnace body 10 is divided into a slug retaining part 11 for retaining and heating melted slug and a salt retaining part 12 extended onto the slug retaining part for retaining salts. A cooling apparatus 16 is provided on an outer periphery of the salt retaining part 12. The incineration residue insertion cylinder 15 is inserted so as to be located in its lower end at a position lower than a melt surface level upon a melted salt layer 51 being formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a melting furnace for melting incineration residues containing salts such as municipal waste incineration residues.

[0002]

2. Description of the Related Art Most of the incineration residues generated when municipal solid waste and industrial waste are incinerated are disposed of in landfills. However, as it becomes difficult to secure landfill sites, it is required to reduce the volume. Was. Also, of the incineration residues, the ash (fly ash) scattered with the combustion exhaust gas and collected by the dust collector contains heavy metals such as lead and cadmium, and is designated as a specially controlled general waste. At the time of its disposal, it must be treated to detoxify heavy metals.
Therefore, there is a need to reduce the volume of incineration residues directly taken out of the incinerator and to render fly ash harmless.

[0003] As a technique capable of simultaneously reducing the volume of incineration residues and insolubilizing and detoxifying heavy metals in response to such problems, a treatment method for melting and solidifying incineration residues has been developed. As one method of the melt-solidification treatment, there is a method of sequentially melting the charged incineration residues while keeping the incineration residue melt in the furnace. In the method of melting the incineration residue in this way, while the generated melt stays in the furnace, the components in the melt are separated by a difference in specific gravity, and separated into a molten slag layer and a molten salt layer. In addition, the molten material can be separated and discharged into a molten slag and a molten salt.

However, in the above melt processing method,
The generated molten salt always remains in the furnace, and since the molten salt contains a large amount of chlorides of alkali metals such as NaCl and KCl having a low boiling point, these low-boiling substances volatilize in large amounts. Then a problem arises. When low-boiling substances evaporate, the evaporated alkali metal salts condense and adhere in the exhaust system equipment, and these deposits can cause clogging of the exhaust system or corrode the equipment. Therefore, stable operation of the melting furnace is hindered.

As a technique for solving such a problem, Japanese Patent Application Laid-Open No. 7-42924 discloses a melting furnace in which the evaporation of low-boiling substances is suppressed. This melting furnace is of an electric resistance heating type, and in the melting treatment by this furnace, electricity is passed between the electrodes immersed in the melt of the incineration residue staying in the furnace, and the electric power of the melting furnace itself is reduced. The melt is heated by resistance heat, and the charged incineration residues are sequentially melted.

FIG. 6 is a longitudinal sectional view showing the melting furnace.
30 is a furnace main body, 31 is an electrode, 50 is an incineration residue charged, 52 is a molten slag layer formed by melting the incineration residue,
Reference numeral 51 denotes a molten salt layer formed by melting salts in the incineration residue. Reference numeral 32 denotes an incineration residue input port, 33 denotes an exhaust gas discharge port, and 34 denotes a melt discharge port. In this melting furnace, the molten salt layer 51 inside the partition wall 35 provided between the ceiling wall of the furnace main body 30 and the melting region is covered with the incineration residue 50 injected, and the outside of the partition wall 35 is covered. The molten salt layer 51 is covered with a powder material 38 such as carbon having a melting point higher than the furnace temperature and a specific gravity smaller than that of the molten salt, so that the volatilization of low-boiling substances from the molten salt layer 51 can be suppressed. It is planned.

[0007]

The incineration residue containing salts is a mixture of oxides having a melting point of 1400 ° C. to 1600 ° C. and salts having a melting point of 700 ° C. to 800 ° C. Since the melting process is a process that melts all the components in the incineration residue, in the operation of the melting furnace, heating is performed until the temperature reaches the high-temperature region where all the components melt, that is, the temperature equal to or higher than the melting point of the oxide. You. For this reason, the salts having a low melting point are heated as they are and become high-temperature molten salts. The salts have a boiling point of about 1400 ° C. to 1600 ° C. and a vapor pressure of 11
Since the temperature rises sharply from above about 00 ° C., low-boiling substances are very easily volatilized in the furnace.

In this regard, in the above-mentioned prior art, the molten salt is covered with a powdered material such as incineration residue or carbon, but the vapor pressure of the molten salt, which is a volatile source of low-boiling substances, can be suppressed. Rather, it is a treatment that only aims at the trapping effect of incineration residues, carbon, and the like, so that the effect of suppressing volatilization of low-boiling substances cannot be expected much.

It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a melting furnace for incineration residues containing salts which can greatly suppress the volatilization of low-boiling substances.

[0010]

In order to achieve the above object, a melting furnace according to the first aspect of the present invention melts an incineration residue containing salts, and the molten material is retained in the melting furnace to be melted. In the electric resistance heating type melting furnace that separates the molten slag and the molten salt separately into a slag layer and a molten salt layer,
A slag that has an electrode rod inserted into the furnace, a bottom electrode provided on the bottom of the furnace, and an incineration residue charging pipe provided on the top of the furnace, and the furnace body is configured to retain and heat the molten slag. Means for adjusting the temperature of the molten salt layer at the outer peripheral portion of the slag retaining portion, which is divided into a stagnant portion and a portion extending above the slag retaining portion and retaining the molten salt. It is characterized by being provided.

In the melting furnace according to the second aspect of the present invention, the incineration residue containing salts is melted, and the melt is retained in the melting furnace to be separated into a molten slag layer and a molten salt layer. In an electric resistance heating type melting furnace for separately discharging, an electrode rod inserted into the furnace, a furnace bottom electrode provided at the furnace bottom, and an incineration residue charging pipe provided at the furnace upper part The furnace body is divided into a slag retaining section for retaining and heating the molten slag, and a salt retaining section for reducing the cross-sectional area inside the furnace body and extending over the slag retaining section to retain the molten salt. It is characterized by having.

According to a third aspect of the present invention, there is provided a melting furnace.
In the melting furnace according to the invention, a means for cooling the molten salt layer is provided on an outer peripheral portion of the salt retaining section.

According to a fourth aspect of the present invention, there is provided a melting furnace.
In the melting furnace according to the third aspect of the present invention, the incineration residue charging pipe provided in the salt accumulation section is inserted such that the lower end thereof is located below the level of the molten metal when the molten salt layer is formed. It is characterized by being.

In the present invention, the incineration residue containing salts is dust ash (fly ash) generated when municipal solid waste is incinerated. It refers to both of those where dust ash is mixed.

In each of the above inventions, the basic requirement is to lower the temperature of the molten salt layer to lower the vapor pressure of the low-boiling substances, thereby suppressing the volatilization of the low-boiling substances.

Therefore, in the melting treatment method according to the present invention, the temperature of the molten salt layer is adjusted so as to fall within a predetermined range. The low-boiling substances contained in the incineration residue are mainly chlorides of alkali metals such as NaCl and KCl.
Since the temperature is around 0 ° C., in order to suppress the volatilization, the temperature of the molten salt layer must be controlled so as to be 1000 ° C. or less. However, if the temperature of the molten salt layer is lower than about 700 ° C., the melt may be solidified. Therefore, when controlling the temperature of the molten salt layer, it is appropriate to set the range of 700 ° C. to 1000 ° C. as the predetermined control temperature.

The molten salt layer generated when the incineration residue is melted is heated by heat transfer from a high-temperature molten slag layer that is in contact therewith. Then, in order to prevent the temperature of the molten salt layer from increasing, the amount of heat transfer from the molten slag layer is reduced, or the amount of heat radiation from the molten salt layer is increased, or the molten salt layer is It is necessary to take measures such as artificial cooling. For this reason, it is desirable that the melting furnace used for melting the incineration residue containing salts has a structure in which consideration is given to maintain the temperature of the molten salt layer in an appropriate range.

First, in the present invention, as one of means for lowering the temperature of the molten slag layer, means for cooling the molten salt layer at the outer peripheral portion of the salt stagnating portion is provided, and the molten salt layer is forcibly cooled.

There are several measures to reduce the amount of heat transfer from the molten slag layer to the molten salt layer. However, the reduction of the amount of heat transfer requires charging the incineration residue into the molten salt layer. Is also achieved by For this reason, in the melting furnace of the present invention, the incineration residue charging pipe is disposed such that the lower end thereof is lower than the molten metal level when the molten salt layer is formed,
The lower part of the incineration residue charging pipe is immersed in the molten salt layer. When the incineration residue is charged in such a state, the incineration residue is gradually settled and dispersed in the molten salt layer, and a portion where the incineration residue and the molten salt are mixed at the lower portion of the molten salt layer (hereinafter, a mixed layer). You can say). This mixed layer is in a state where the particles of the incineration residue are suspended or in a slurry state, and a solid component having poor thermal conductivity is mixed. Lower than. For this reason, the mixed layer becomes a region that hinders heat transfer, and an excessive rise in temperature of the molten salt layer is suppressed.

Another method for reducing the amount of heat transfer from the molten slag layer is to reduce the area of the interface between the molten salt layer and the molten slag layer.
In this regard, in the melting furnace according to the present invention, the upper part of the furnace body has a reduced shape, the molten salt is retained in the reduced portion, and the molten slag is stored in the unreduced portion thereunder. Can be retained. Therefore, the area of the interface between the two layers is reduced, the amount of heat transferred from the molten slag layer to the molten salt layer is reduced, and an excessive rise in the temperature of the molten salt layer is suppressed.

When the molten salt is retained in the reduced portion, the ratio of the furnace wall area to the retained amount of the molten salt increases, and the amount of heat released from the molten salt layer increases, and the excessive amount of the molten salt layer increases. Temperature rise is suppressed.

Further, when the molten salt is retained in the reduced portion, the ratio of the area of the outer periphery of the furnace wall to the retained amount of the molten salt becomes large, and only a small amount of the molten salt is retained.
Since the height of the molten salt layer can be increased, it is easy to provide cooling means outside the furnace wall to forcibly cool the molten salt layer.

[0023]

FIG. 1 is a plan view showing an embodiment of a melting furnace according to the present invention, and FIG.
It is sectional drawing of a part. The melting furnace is an electric resistance heating furnace using a direct current method, and includes a melting furnace body 10, an electrode rod 13,
A main part is constituted by the furnace bottom electrode 14 and the plurality of incineration residue charging tubes 15. In the figure, reference numeral 50 denotes an incineration residue containing the charged salts, 51 denotes a molten salt layer, and 52 denotes a molten slag layer.

The melting furnace main body 10 is divided into a part for storing molten slag and a part for storing molten salt. The lower part of the melting furnace main body 10 has a slag storing part 11, and the upper part has a salt storing part 12. Has become.

The slag retaining section 11 retains the molten slag therein, energizes and heats the electrode rod 13 immersed in the molten slag layer 52 and the furnace bottom electrode 14, and heats the molten slag layer 52. While maintaining the temperature in a high temperature state, it serves to melt the incineration residue sent through the incineration residue charging pipe 15.

The incineration residue charging section 12 is provided with three incineration residue charging pipes 15.
Numeral 5 penetrates the furnace lid of the salt retaining section 12 and is inserted so that its lower end is located below the level of the molten metal when the molten salt layer 51 is formed. Therefore, the charged incineration residue is charged into the molten salt layer 51. The shape of the incineration residue charging pipe 14 is limited to a cylindrical shape because the incineration residue charging pipe 14 has only to have a function of lowering the charged incineration residue into the molten salt layer 51. Instead, it may be square or another shape.

Further, the salt retaining section 12 is provided with a cooling device 16 on its outer peripheral portion. The cooling device 16 is provided for forcibly cooling the molten salt layer 51,
The water cooling tube has a structure embedded in the refractory, and is provided from near the level of the interface between the molten salt layer 51 and the molten slag layer 52 from the level of the molten salt layer 51. On the contrary, the surface portion of the molten salt layer 51 is easily cooled, and if the temperature is excessively lowered, the fluidity of the molten salt is reduced and its discharge becomes difficult. It is desirable that a heating device including an induction heating coil or the like be provided at or around the outer peripheral portion so that heating can be performed as necessary.

The operation for melting the incineration residue containing salts by the melting furnace having the above configuration is performed as follows.

After the incineration residue is weighed, the molten salt layer 51
It is thrown into the incineration residue charging pipe 15 immersed inside,
The lower part is filled. This incineration residue gradually descends in the incineration residue charging pipe 15 by its own load while being preheated, and is charged into the molten salt layer 51 formed in the salt accumulation section 12. The incineration residue 50 charged into the molten salt layer 51 is dispersed while gradually settling to form a portion where the incineration residue is suspended, that is, a mixed layer 51a. As described above, the mixed layer 51a has a function of preventing heat transfer from the molten slag layer 52 to the molten salt layer 51 and suppressing an excessive rise in temperature of the molten salt layer 51.

The incineration residue 50 charged in the molten salt layer 51
Is partially melted in the molten salt layer 51, but the rest drops to the interface with the molten slag layer 51 maintained at a high temperature and melts there. When the incineration residue is melted, its components are separated by a difference in specific gravity, and a molten salt layer 51,
Three layers of the molten slag layer 52 and the molten metal layer 53 are formed.

The molten slag layer 52 in the slag retaining section 11
Is heated by its own electric resistance heat by energization between the electrodes. The temperature of the molten slag layer 52 is maintained in the range of 1400 ° C to 1600 ° C by adjusting the input power.

On the other hand, the temperature of the molten salt layer 51 formed in the salt accumulating portion 12 is based on the measurement value of the thermometer 22 for measuring the intermediate portion in which the detecting portion is disposed at the intermediate portion of the molten salt layer 51. Adjustment of the cooling device 16 is maintained in an appropriate range. That is, the cooling device 1 is set so that the temperature of the intermediate portion of the molten salt layer 51 measured by the thermometer 22 is in a range (700 ° C. to 1000 ° C.) in which low-boiling substances do not volatilize.
Adjust the water flow to 6.

Then, each of the above-mentioned melts is separately extracted. First, the molten salt is extracted from a salt discharge port 17 provided on a side wall above the salt stagnation section 12 (a position above the lower end of the incineration residue charging pipe 15). Since almost no solid content is contained, fluidity is maintained. Therefore, the salt outlet 1
7, the molten salt can be extracted at a small flow rate, and an overflow method can be adopted for the extraction.

The molten salt is discharged in the desired state as described above because the incineration residue charging pipe 15 is immersed in the molten salt layer 51 and the salt discharge port 17 is connected to the incineration residue charging pipe 15. Is disposed above the level at which the mixed layer 51a in which the incineration residue is suspended is formed above the lower end of the incineration residue. This is because the mixing phenomenon does not occur.

If the incineration residue charging pipe 15 is the molten salt layer 5
1 and the incineration residue is charged on the molten salt layer 51, the incineration residue is suspended in the entire molten salt layer,
The molten salt is extracted with the incineration residue mixed therein. When the powder of the incineration residue is mixed with the molten salt, the viscosity of the powder is greatly increased, the fluidity is reduced, and the problem that the discharge of the molten salt becomes difficult is caused.

The molten slag is continuously or intermittently extracted from a slag discharge port 18 provided on the upper side wall of the slag retaining section 11. The furnace body 10 is divided into a slag retaining section 11 and a salt retaining section 12. Configuration
At the time of extraction, the level of the interface between the molten salt layer 51 and the molten slag layer 52 must be located below the salt stagnation section 12 and the level must not be fluctuated.

Therefore, the molten salt layer 51 and the molten slag layer 5
It is necessary to extract the molten slag while grasping the level of the interface of No. 2. By the way, since the temperature in the height direction of the molten salt layer 51 rises as it approaches the interface with the molten slag layer 52 from the molten metal surface, if the temperature near the level of the interface is continuously measured, The position of the interface can be grasped. Therefore, if the detection unit adjusts the amount of molten slag withdrawn so that the measurement value of the lower measurement thermometer 23 disposed below the molten salt layer 51 is maintained at a predetermined value, the molten salt layer 51 and The interface of the molten slag layer 52 is maintained at a predetermined level.

Then, the molten metal is intermittently extracted from a metal discharge port 19 provided on a side wall below the slag retaining section 11. In addition, gas generated during melting is extracted from the exhaust gas outlet 20 and is separately processed.

FIG. 3 is a plan view showing another embodiment of the melting furnace according to the present invention, and FIG. 4 is a cross-sectional view taken along the line BB in FIG. 3 and FIG. 4, FIG. 1 and FIG.
The same reference numerals are given to the portions having the same configuration as the melting furnace according to the above, and the description is omitted. In this example, the salt retaining portion 12 has its inner diameter (cross-sectional area inside the furnace body) greatly reduced with respect to the inner diameter of the slag retaining portion 11, and is extended to a central portion on the slag retaining portion 11. I have. For this reason,
The side surface shape of the melting furnace body 10 is convex. Further, the salt accumulation section 12 is provided with an incineration residue charging pipe 15, and the lower end of the incineration residue charging pipe 15 is located below the molten metal level when the molten salt layer 51 is formed. Has been inserted to be.

In the operation using this melting furnace, the interface between the molten salt layer 51 and the molten slag layer 52 can be formed at an appropriate level, but different effects can be obtained depending on where the interface is formed. .

First, as shown in FIG. 4, if the interface between the molten salt layer 51 and the molten slag layer 52 is formed at a place where the inner diameter of the furnace body is reduced, the interface is reduced as described above. As a result, the amount of heat transferred from the molten slag layer 52 to the molten salt layer 51 decreases, and the amount of heat released from the furnace wall also increases.
The temperature rise of the molten salt layer is further suppressed. For this reason, according to this operation method, the required amount of cooling heat of the molten salt layer becomes very small, and the load on the cooling device 16 is greatly reduced. In a small melting furnace in which the required amount of cooling heat is further reduced, it may not be necessary to equip the cooling device 16.

Further, as shown in FIG. 5, when the interface between the molten salt layer 51 and the molten slag layer 52 is formed at a location where the inner diameter of the furnace body is small or at a location where it is not reduced, the area of the interface is small. 4, the amount of heat transfer from the molten slag layer 52 to the molten salt layer 51 increases, and the load on the cooling device 16 increases accordingly. However, melting of the incineration residue mainly occurs near the interface. As a result, the melting capacity of the incineration residue is increased.

[0043]

According to the present invention, the furnace body is divided into a slag retaining portion for retaining and heating molten slag and a salt retaining portion which is a portion extended thereon and retains molten salt. Since means for adjusting the temperature of the molten salt layer is provided on the outer peripheral portion of the salt retaining section, it is possible to lower the temperature of the molten salt layer and lower the vapor pressure of the low boiling point substance, thereby Volatilization of low-boiling substances can be suppressed.

When the salt accumulation portion is smaller than the slag accumulation portion, the area of the interface between the molten salt layer and the molten slag layer can be reduced, so that the salt is moved from the molten slag layer to the molten salt layer. The amount of heat decreases, and the amount of heat released from the furnace wall also increases. For this reason, the temperature rise of the molten salt layer is further suppressed, and the volatilization of low-boiling substances is suppressed.

In the case where the incineration residue charging pipe provided in the salt accumulation section is inserted so that the lower end thereof is located below the level of the molten metal when the molten salt layer is formed,
Since the incineration residue is charged into the molten salt layer and a mixed layer in which the molten salt and the incineration residue are mixed is formed below the molten salt layer, heat transfer from the molten slag layer to the molten salt layer is prevented. . For this reason, the temperature rise of the molten salt layer is suppressed, and the volatilization of low-boiling substances is suppressed.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of an embodiment according to a melting furnace of the present invention.

FIG. 2 is a cross-sectional view taken along the line AA in FIG.

FIG. 3 is a plan view showing another example of the embodiment of the melting furnace of the present invention.

FIG. 4 is a sectional view taken along the line BB in FIG. 3;

FIG. 5 is a diagram showing a state when the level of the interface between the molten salt layer and the molten slag layer is changed.

FIG. 6 is a schematic longitudinal sectional view showing an example of a conventional melting furnace in which a low-boiling substance is prevented from volatilizing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Melting furnace main body 11 Slag accumulation part 12 Salt accumulation part 13 Electrode 14 Furnace bottom electrode 15 Incineration residue charging pipe 16 Cooling device 17 Molten salt discharge port 18 Slag discharge port 19 Metal discharge port 20 Exhaust gas discharge port 21, 22, 23 Temperature Total 50 Incineration residues containing salts 51 Molten salt layer 51a Mixed layer 52 Molten slag layer 53 Molten metal layer

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Tsuyoshi Nakao 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd.

Claims (4)

[Claims] 1. An electric resistance heating method for melting an incineration residue containing salts, retaining the melt in a melting furnace to separate it into a molten slag layer and a molten salt layer, and discharging the molten slag and the molten salt separately. In the melting furnace, there is an electrode rod inserted into the furnace, a furnace bottom electrode provided on the furnace bottom, and an incineration residue charging pipe provided on the furnace upper part, the furnace body stays molten slag The slag retention portion to be heated and heated, and a portion extending above the slag retention portion, which is divided into a salt retention portion for retaining the molten salt, the temperature of the molten salt layer at the outer peripheral portion of the salt retention portion A melting furnace for incineration residues containing salts, characterized in that the furnace is provided with a means for adjusting the temperature. 2. An electric resistance heating method in which the incineration residue containing salts is melted, the melt is retained in a melting furnace to be separated into a molten slag layer and a molten salt layer, and the molten slag and the molten salt are separately discharged. In the melting furnace, an electrode rod inserted into the furnace, a furnace bottom electrode provided on the furnace bottom, and an incineration residue charging pipe provided on the furnace upper part, the furnace body stays molten slag The slag retention portion to be heated and heated, and the salt is characterized in that the cross-sectional area inside the furnace body is reduced and is extended on the slag retention portion and is divided into a salt retention portion for retaining the molten salt. Melting furnace for incineration residues including. 3. The furnace for melting incineration residues containing salts according to claim 2, wherein a means for adjusting the temperature of the molten salt layer is provided on an outer peripheral portion of the salt accumulation section. 4. The method according to claim 1, wherein the lower end of the incineration residue charging pipe is inserted so as to be located below the level of the molten metal when the molten salt layer is formed. A melting furnace for an incineration residue containing the salt according to any one of the above.