JP2000107724A - Melting treatment of incineration residue containing salts and melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of dust of alkali metal salts by keep the temperature of a gas phase in a melting furnace. SOLUTION: In a melting furnace body 10, molten salts on a molten slag layer 42 are heated by high-temperature molten slag during a melting treatment of a incineration residue, thereby many of the salts are gasified to move into a gas phase. The amount of the gas generated at the melting is very small, so that the resultant gas moves toward a gas discharge pipe 13 at an extremely slow speed. In such a condition, the gas phase is heated by a heater 14 so as to keep its temperature at a set temperature between 700 and 1,000 deg.C. Thereby, heavy metal salts in the gasified molten salts together with exhaust gas are drawn to the outside of the furnace as gas. However, alkali metal salts are condensed to become particles of the molten salts, and, while staying in the furnace, they are flocculated with newly condensed salts to grow and to drop down. The alkali metal salts, which have dropped down, are returned to a molten salt layer 41, then drawn out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for melt-treating incineration residues containing salts such as municipal waste incineration residues and a melting furnace for carrying out the method.

[0002]

2. Description of the Related Art In recent years, it has become necessary to insolubilize heavy metals in incineration residues and reduce the volume of incineration residues themselves when disposing of incineration residues generated when incineration of municipal solid waste and industrial wastes is performed. It has become. For this reason, some incineration residues are treated by a melting method in which volume reduction and heavy metal insolubilization are performed simultaneously. Melting treatment of incineration residues is performed by various methods. Among these methods, in the method using an electric resistance type melting furnace or the method using an induction heating type melting furnace, the incineration residue A process is performed in which the molten material is heated and held while being retained, and the incineration residue is charged and sequentially melted. For example, operation by a method using an electric resistance melting furnace is performed as follows.

An electrode is immersed in a melt of the incineration residue retained in a furnace, and the incineration residue is charged while energizing between the electrodes and heating the melt by its own electric resistance heat.

[0004] The incineration residue is charged so that there is always unmelted material in the furnace and the molten material is covered with the incineration residue. The incineration residue charged in the furnace is heated by the melt and melts sequentially from the lower part in contact with the melt. At this time, if the incineration residue contains salts, the generated melt is separated by the difference in specific gravity while staying in the furnace, and is separated into molten slag and molten salt. Therefore, a molten salt layer having a low specific gravity is formed on the upper portion of the melt, and a molten slag layer is formed therebelow. The separated molten salt and molten slag are separately extracted.

[0005] Since the extracted molten slag has been subjected to the insolubilization treatment of heavy metals, it is cooled and solidified.
It is landfilled or partly used for roadbed materials. The molten salt is disposed after being subjected to a heavy metal insolubilization treatment by a method of mixing a liquid chelating agent or the like.

[0006] On the other hand, the gas generated when the incineration residue is heated and melted is sent to an exhaust gas treatment device for purification treatment.

[0007]

However, in the operation of the prior art, the melting slag in the melting furnace has a melting point of 13 ° C.
Since the molten salt layer is present on the high-temperature molten slag layer mainly composed of an oxide of 00 ° C to 1500 ° C, the molten salt layer is heated as it is and becomes high temperature. And when the molten salt layer becomes high temperature, what is contained in the molten salt layer is an alkali metal salt such as sodium chloride or potassium chloride and zinc, lead,
Since it is a chloride of a heavy metal such as cadmium and a substance having a relatively low boiling point, vaporization of these low-boiling substances occurs.

At this time, the melt in the furnace is covered with unmelted incineration residues, and the incineration residues serve as a heat insulating layer and hinder upward heat transfer from the high-temperature melt. The temperature of the gas phase in the furnace is much lower than the temperature of the melt.
For this reason, the vaporized low-boiling substance is cooled in the gas phase, condensed and solidified, becomes dust, and is discharged together with the exhaust gas.

As described above, when low-boiling substances are vaporized, a large amount of dust mainly composed of alkali metal chlorides is generated, causing various obstacles to the exhaust gas treatment system.
That is, among the low-boiling substances, the alkali metal salt has an adhesive property, so that the alkali metal salt adheres to the exhaust gas duct and causes clogging, or the clogging of the dust collector is promoted and the processing ability is reduced. Occurs and hinders the continuous operation of the melting furnace.

According to the present invention, even if the incineration residue containing salts is melted, the generation of alkali metal salt dust can be suppressed, and the operation of the exhaust gas treatment device does not suffer.
An object of the present invention is to provide a method for melting incineration residues and a melting furnace for performing the method.

[0011]

According to a first aspect of the present invention, there is provided a melt processing method for maintaining the temperature of a gas phase in a melting furnace at 700 ° C. to 1000 ° C. And

[0012] A melting treatment method according to a second invention is characterized in that, in the first invention, the gas phase in the melting furnace is heated and the temperature of the gas phase is maintained at 700 ° C to 1000 ° C. .

[0013] A melting furnace according to a third aspect of the invention is characterized in that a heating device is provided in a gas phase portion in the furnace.

In the melting furnace according to a fourth aspect of the present invention, in the third aspect, the furnace body is divided into two sections through which the gas phase communicates. It is characterized by comprising a molten processing section for retaining and separating the components by components, and a molten salt discharging section for receiving and discharging the molten salt overflowing from the molten processing section.

In the melting furnace according to a fifth aspect of the present invention, in the third or fourth aspect, a molten salt layer is formed at an upper end of the furnace body on the side where the molten salt discharge port is provided. A submerged weir for discharging molten salt is provided below the height corresponding to the molten metal level at the time, and the upper part of the submerged weir is formed in an open shape.

In the operation of a melting furnace in which the incineration residue is charged and melted while the molten material is retained in the furnace, since molten salts are present on the high-temperature molten slag, alkali metal salts, heavy metals, etc. It cannot prevent the phenomenon that the low-boiling substance vaporizes itself. However, the present inventors have conducted various studies on a method for suppressing generation of dust caused by vaporization of an alkali metal salt. as a result,
Once the vaporized alkali metal salt and heavy metal salt are separated in the furnace, the alkali metal salt remains in the furnace, and a method capable of mainly discharging the heavy metal salt together with the exhaust gas to the outside of the furnace has been found.

This study started by examining the difference between the vapor pressure characteristics of the alkali metal salt and the heavy metal salt, and examining the vapor pressure of both. First, according to the table described in the Chemical Handbook, the vapor pressures of the two are generally shown as follows. NaCl and KCl as alkali metal salts
Has almost the same vapor pressure characteristics, and the vapor pressure increases from about 1000 ° C. or higher. On the other hand, heavy metals such as zinc, lead and cadmium are mainly ZnCl ₂ , PbC
l ₂ , present in the form of CdCl ₂ , which compounds generate vapors in excess of 760 mmHg in the temperature range below 1000 ° C. For this reason, the heavy metal salt vaporizes in a temperature range considerably lower than the vaporization temperature of the alkali metal salt. Particularly, among the heavy metal salts in the dust discharged together with the exhaust gas, ZnCl _{2, which} has the highest content, has a vapor pressure of 760 mmHg near 700 ° C., and is much lower than the vaporization start temperature of the alkali metal salt. To vaporize.

As described above, since the vapor pressure characteristics of the alkali metal salt and the heavy metal salt are different from each other as described above, what is the state when the mixture of the alkali metal salt and the heavy metal salt is gradually heated. As a result, first, the heavy metal salt vaporizes, and the alkali metal salt remains in a solid or liquid state. Next, on the contrary, assuming a state where the mixed vapor of the alkali metal salt and the heavy metal salt is gradually cooled, first, the alkali metal salt condenses,
At that time, the heavy metal salt exists as a gaseous state.

Therefore, if the temperature of the gas phase in the melting furnace is maintained at a temperature higher than the temperature at which the heavy metal salt vaporizes and within a temperature range in which the vaporization of the alkali metal salt does not occur, of the molten metal vaporized, The salt vapor is discharged together with the exhaust gas, and is condensed and solidified outside the furnace to become dust. On the other hand, the vapor of the alkali metal salt condenses in the furnace to form molten salt particles. These particles aggregate and grow while staying in the furnace,
Fall. The dropped molten salt is extracted.

Since the alkali metal salt is condensed as described above, in order to discharge the heavy metal salt together with the exhaust gas, it is necessary to maintain the temperature of the gas phase in the furnace in the range of 700 ° C. to 1000 ° C. It costs. Lower limit of this temperature range 700 ° C
Is ZnC, which has the highest content in heavy metal salts, especially dust.
l ₂ is kept in a gaseous state and an alkali metal salt (N
aCl, KCl, etc.). The upper limit of 1000 ° C. is a temperature at which the alkali metal salt exists in a molten state.

The lower limit of the temperature of the gas phase in the furnace is 700 ° C.
However, this temperature was adjusted to the alkali metal salt (N
aCl, KCl) are in the temperature range where they exist in a molten state. Originally, the melting point of NaCl and KCl is 750 ° C. to 800
Although the melting point of these mixtures falls to the range of 700 ° C. or less, the molten salt generated when the incineration residue containing a plurality of salts is melted does not solidify at 700 ° C.

The temperature of the gas phase in the furnace is set at 700 ° C. to 1000 ° C.
When the temperature is maintained at, the temperature of the gas phase can be maintained in an appropriate range by heating the gas phase in the furnace with a heater. Also, as described above, in the operation of a melting furnace in which the incineration residue is charged while the molten material is retained in the furnace and melted, the molten material in the furnace is covered with unmelted incineration residue. Since the incineration residue acts as a heat insulating layer and hinders heat transfer from the high-temperature melt to the gas phase, changing the thickness of the incineration residue allows the gas phase to be at an appropriate temperature. .

[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 an arrow view part. The melting furnace shown in FIGS. 1 and 2 is of an electric resistance type, and 10 is a melting furnace main body, 41 is a molten salt layer, 42 is a molten slag layer, 43 is a molten metal layer, 40
Indicates the incineration residue that is charged and covers the melt. 1 and 2, reference numeral 11 denotes a charging pipe for incineration residues, 12 denotes an electrode that is immersed in a melt to generate electric resistance heat, 13 denotes a gas discharge pipe, and 14 heats a gas phase in the furnace. Is a dive weir for discharging molten salt. Reference numeral 30 denotes an outlet for molten salt, 31 denotes an outlet for molten slag, and 32 denotes an outlet for molten metal. The dive weir 15 is for preventing the incineration residue from being mixed when the molten salt is discharged, and the molten salt discharge port 30 of the furnace body is provided so as to surround the inside of the molten salt discharge port 30. It is provided on the upper part of the side. The lower end is located below the height corresponding to the molten metal level when the molten salt layer is formed and above the upper surface level when the molten slag layer is formed. or,
The upper part of the dive weir 15 is open so that the gas phase inside the furnace body 10 is not partitioned.

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

[0025] The incineration residue is charged into a furnace in which the melt heated by energization between the electrodes 12 stays, and is melted. The incineration residue is introduced into the furnace from the incineration residue charging pipe 11, and is in a state of covering the melt. The incineration residue 40 covering the melt is sequentially melted from the lower portion while being preheated by the heat transfer from the melt. When the incineration residue is melted, its components are separated into a molten salt, a molten slag, and a molten metal due to a difference in specific gravity.
1. Three layers of a molten slag layer 42 and a molten metal layer 43 are formed. Then, the molten salt, the molten slag, and the molten metal are continuously or intermittently extracted from the molten salt outlet 30, the molten slag outlet 31, and the molten metal outlet 32, respectively. Further, the exhaust gas is extracted from the gas discharge pipe 13 and sent to an exhaust gas treatment device.

During the melting treatment of the incineration residue, the molten salt present on the molten slag layer 42 is heated by the high-temperature molten slag, and most of it is vaporized and transferred to the gas phase. However, the amount of gas generated during melting is generated by the decomposition of a small amount of unburned matter contained in the incineration residue or the evaporation of water, so the amount is very small, When the incineration residue taken out by the dry method when the material is incinerated is melted, usually only about 50 to 100 Nm ³ per ton of the incineration residue is generated. Therefore, the generated gas flows toward the gas discharge pipe 13 at a very slow speed.

In this state, the gas phase is heated by the heater 14 and maintained at a set temperature between 700 ° C. and 1000 ° C.
The heavy metal salt is extracted out of the furnace together with the exhaust gas as a gas. However, the alkali metal salt condenses into particles of a molten salt, grows while coagulating with newly condensed salts while staying in the furnace, and falls. The dropped alkali metal salt returns to the molten salt layer 41 and is extracted from the molten salt outlet 30.

FIG. 3 is a plan view showing another embodiment of the melting furnace according to the present invention, and FIG. 4 is a sectional view taken along the line BB in FIG. 3 and FIG. 4, FIG. 1 and FIG.
The same parts as those described above are denoted by the same reference numerals and description thereof will be omitted. In this embodiment, a protruding portion through which the gas phase portion passes is provided in the furnace main body 10. The furnace body 10 is partitioned at its upper end by an overflow weir 20 located at the level of the upper surface level of the melt to be retained. And a molten salt layer 41, a molten slag layer 42, and a molten metal layer 43, which are separated into three components: a molten salt layer 41, a molten slag layer 42, and a molten metal layer 43. The discharge section 10b is divided into two sections. A gas discharge pipe 1 is connected to the molten salt discharge section 10b.
3 are provided. In the melting furnace having the above configuration, the molten salt in the melting section 10a overflows and the molten discharge section 1
0b, and is discharged from the molten salt discharge port 30.

By providing the molten salt discharge section 10b, the volume of the gas phase section is increased, and the gas discharge pipe 13 is further provided in the molten salt discharge section 10b. The time required to reach the discharge pipe 13 increases, and the residence time of the molten salt particles in the furnace increases. For this reason, the aggregation of the alkali metal salt further progresses, and the molten particles thereof become larger, which makes it easier to settle. As a result, the amount of the alkali metal salt discharged out of the furnace accompanying the exhaust gas is further reduced.

Not all of the heavy metal salts in the molten salt generated in the molten processing section 10a are vaporized and disappear, but part of the heavy metal salts remains in the molten salt and overflows to discharge the molten salt discharge section 10b. to go into. For this reason, the heater 22 is provided through the side wall of the molten salt discharge portion 10b so that the molten salt 44 accumulated in the molten salt discharge portion 10b can be heated. By this heating, the temperature of the molten salt 44 is reduced to 7
The molten salt can be maintained at 00 ° C. to 1000 ° C. so that the molten salt is not solidified, and the heavy metal salt in the molten salt is vaporized to further reduce the content of the heavy metal in the extracted molten salt.

FIG. 5 is a sectional view showing still another embodiment of the melting furnace according to the present invention. In FIG. 5, FIG.
4 and the same parts as those in FIG. In this embodiment, the furnace body 10 is
The upper end is partitioned by a partition wall 21 located at a position higher than the upper surface level of the molten material to be retained, and
a and a molten salt discharge section 10b.

In the melting furnace having the above-described structure, the molten salt in the molten salt layer 41 formed in the melting section 10a is condensed after being entirely vaporized and collected in the molten salt discharge section 10b, and is discharged to the molten salt discharge section 10b. The air is discharged from the outlet 30. For this reason, in the operation of the melting furnace, the level control of the melt is facilitated. That is, when the separated discharge of the molten salt is based on the overflow method, the molten salt overflows from the upper part of the furnace, and the molten slag is extracted from the lower part of the furnace.
When withdrawing the molten slag, adjust the amount of molten slag withdrawn so that the level of the interface between the molten salt layer and the molten slag layer is appropriately lowered from the upper end of the overflow weir,
Molten slag must not be discharged with the molten salt. However, in the melting furnace of FIG. 5, there is nothing that overflows and is discharged from the melting processing section 10a.
There is no need for strict control over the melt level. Note that the partition wall 21 also serves to prevent incineration residues from being mixed into the molten salt in the molten salt discharge section 10b.

Next, the operation results when the incineration residue containing salts is melted will be described. First, the results obtained when a furnace having the same configuration as that of FIGS. 3 and 4 showing the melting furnace of the present invention were used are as follows. Incineration ash and fly ash (composition shown in Table 1) mixed in a ratio of 7: 3 in an electric resistance type melting furnace with a processing capacity of 200 kg / h are continuously charged at a supply rate of 200 kg / h. And melted. At this time, the gas phase was heated by a heater having a silicon carbide heating element, and the temperature was maintained at about 800 ° C. The molten salt collected in the molten salt discharge section was heated by a heater and maintained at about 850 ° C.

The gas emission during this operation is about 30 Nm ³ / h
(Water content 30%, temperature 800 ° C.). The dust concentration of the exhaust gas was about 40 g / Nm ³ (dry basis). Table 2 shows the composition of the dust collected by the exhaust gas treatment device.
Table 3 shows the composition of the extracted molten salt.

When the above operation was continued, 12
Even after the elapse of 0 hours, no trouble occurred due to blockage of the exhaust gas duct or the like. Further, the molten salt collected in the molten salt discharging section was low in viscosity and could be discharged smoothly.

On the other hand, the results obtained when a conventional melting furnace having no heater in the gas phase were used were as follows.

After the elapse of 60 hours, the exhaust gas duct began to clog, and the state of exhaust gas suction deteriorated. The composition of the molten salt extracted during this operation was as shown in Table 3.

According to the operation results under the above two conditions, it has been clarified that no trouble occurs in the exhaust gas treatment system if the gas phase in the furnace is heated and maintained in a predetermined temperature range.

Comparing the compositions of the two types of molten salts shown in Table 3, the molten salt according to the present invention has a very low heavy metal content of Zn and Pb as compared with the prior art. This is due to an increase in the amount of heavy metal salt vaporized in the molten salt and an increase in the rate of recovery of the vaporized alkali metal salt as a molten salt.

When the heavy metal content of the molten salt is reduced as described above, the amount of expensive chemicals such as a liquid chelating agent added in the heavy metal insolubilization treatment at the time of disposing the molten salt is greatly reduced, thereby reducing the processing cost. Is achieved.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

According to the present invention, the temperature of the gas phase in the melting furnace is maintained at a temperature at which the heavy metal salt is present in a gaseous state and within a temperature range in which the alkali metal salt is maintained in a molten state. Therefore, the vapor of the alkali metal salt in the gas phase is condensed and most of the vapor falls, and the heavy metal salt is discharged out of the furnace together with the exhaust gas as a gas. For this reason, generation | occurrence | production of an alkali metal salt dust can be suppressed, the operation | movement of an exhaust gas processing apparatus does not interfere, and the molten salt with very little heavy metal content is discharged.

[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 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 sectional view showing still another example of the embodiment of the melting furnace of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Melting furnace main body 10a Melt processing part 10b Molten salt discharge part 11 Incineration residue charging pipe 12 Electrode 13 Exhaust gas discharge pipe 14 Heater 15 Submerged weir 20 Flood weir 21 Partition wall 30 Molten salt discharge port 31 Molten slag discharge port 32 Melt Metal outlet 40 Incineration residue 41 Molten salt layer 42 Molten slag layer 43 Molten metal layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takuya Shinagawa 1-2-1 Marunouchi, Chiyoda-ku, Tokyo F-term in Nihon Kokan Co., Ltd. (reference) 3K061 AA18 AA23 AB03 AC03 BA05 BA08 CA12 NB02 NB21 NB27

Claims (5)

[Claims] 1. A melting method in which an incineration residue is charged and melted while a melt is retained in a melting furnace, wherein the temperature of a gas phase in the melting furnace is maintained at 700 ° C. to 1000 ° C. For melting incineration residues containing salts. 2. The method according to claim 1, wherein the gas phase in the melting furnace is heated and the temperature of the gas phase is maintained at 700 ° C. to 1000 ° C. . 3. A melting furnace for incineration residues containing salts, wherein a heating device is provided in a gas phase portion in the furnace, wherein the incineration residue is charged while retaining the molten material. 4. A furnace body is divided into two sections through which a gas phase portion passes, and a melting processing section for charging and melting the incineration residue, retaining the melt, and separating the melt into components. 4. The melting furnace for incineration residues containing salts according to claim 3, further comprising a molten salt discharging section for receiving and discharging the molten salt overflowing from the processing section. 5. A molten salt discharge, wherein the lower end of the molten salt discharge is located at an upper portion of the furnace body on the side where the molten salt discharge port is provided, below a height corresponding to a molten metal level when a molten salt layer is formed. 5. The melting furnace for incineration residues containing salts according to claim 3, wherein a submerging weir is provided, and the upper part of the submerging weir is formed in an open shape.