JPH10323645A - Method for melting fly ash containing calcium chloride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent formation of molten salt layer even in the case fly ash containing calcium chloride is treated in an electric resistance type melting furnace by adding alkali metal compounds to the fly ash, adjusting the composition as to produce chlorides of alkali metals and eliminate calcium chloride in high temperature region, and then melting the resultant fly ash. SOLUTION: In a method for melting fly ash containing calcium chloride, salts of alkali metals such as sodium, potassium, etc., which produce salts with relatively lower melting point at the time of reacting with calcium chloride are added to the fly ash. Practically, ores containing alkali metal salts such as carbonates, silicates of alkali metals, etc., glass compositions containing alkali metals may be added. The ratio (mole ratio) of the alkali metals to the chlorine in the fly ash is adjusted to be 1.0 or higher. Moreover, alkali metal compounds are added to the fly ash or a mixture of the fly ash and incinerator ash to adjust the components and the resultant mixture is granulated and after that the granulated mixture is added to a melting furnace to further quickly carry out melting process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of melting fly ash containing calcium chloride in an electric resistance melting furnace.

[0002]

2. Description of the Related Art In a refuse incineration plant, a treatment for removing hydrogen chloride contained in exhaust gas generated from an incinerator is performed. One of the hydrogen chloride removal methods is hydrogen chloride in combustion exhaust gas. There is a method of reacting with calcium-containing substances such as slaked lime and calcium carbonate to trap.
In the removal of hydrogen chloride by this method, when incineration is performed in a stoker furnace, a kiln furnace, or the like, an operation of blowing the powder of the calcium-containing substance into a flue of combustion exhaust gas is performed, and incineration is performed in a fluidized bed furnace. In such a case, an operation of charging the calcium-containing substance into the incinerator is performed. When these operations are performed, the reaction product of hydrogen chloride and the calcium compound is collected by the dust collector. For this reason, in the dust collector, fly ash containing a large amount of calcium chloride or its double salt, which is a reaction product, is collected in addition to the medium dust scattered from the incinerator.

[0003] On the other hand, of the incineration residues (incineration ash and fly ash) generated when municipal waste is incinerated, fly ash contains harmful heavy metals and is designated as a specially managed municipal waste. At the time of final disposal, it must be treated to render the heavy metals harmless. The method of this detoxification treatment is specified by the law as a treatment method such as melt-solidification treatment.One of the melt-solidification treatment methods is a method of melting the incineration residue in an electric resistance melting furnace. is there. This method has advantages such as easy exhaust gas treatment due to a small amount of generated gas and high thermal efficiency, and is a processing method that has attracted attention. In a processing method using an electric resistance melting furnace, a current is applied between electrodes inserted into the melt in the melting furnace to generate Joule heat in the melt, and the heat is used to heat the melt, thereby causing a temperature of 1400 ° C. ~ 1500
High temperature of up to ° C. Then, the incineration residue charged on the melt is heated and melted by heat transfer from the melt.

[0004]

[0007] By the way, calcium chloride
Fly ash containing indium is incineration residue containing a large amount of salts,
Are shown in Tables 1 to 5. Such a flight
When the ash is melted, SiO _Two, CaO, Al_TwoO_ThreeEtc.
Molten slag consisting mainly of oxides and sodium chloride
And molten salt mainly composed of potassium chloride and calcium chloride
Two types of melts are formed, and these two types of melts
Separates into two layers.

At this time, since sodium chloride and potassium chloride have relatively low boiling points, most of them are volatilized in the furnace maintained in the high temperature region as described above, but the boiling point is high (1600 ° C.). Above) Calcium chloride remains in the furnace as it is and is accumulated. When the thickness of the molten salt layer becomes thicker, the electric resistance of the molten salt is much smaller than that of the molten slag. , And the operation of the melting furnace becomes impossible.

Therefore, when an electric resistance melting furnace is used, fly ash containing a large amount of calcium chloride cannot be melted.

[0007] It is an object of the present invention to provide a melting method in which a molten salt layer is not formed even when fly ash containing calcium chloride is melted in an electric resistance melting furnace.

[0008]

According to a first aspect of the present invention, a fly ash containing calcium chloride contains a substance containing an alkali metal compound having a reactivity with calcium chloride in a high temperature region. It is added and adjusted to a component composition in which calcium chloride disappears and an alkali metal chloride is formed in a high temperature range, and then melts.

In the second invention, a fly ash containing calcium chloride is added with a substance containing an alkali metal compound having a reactivity with calcium chloride in a high temperature region and incineration ash, and the calcium chloride disappears in a high temperature region. Then, the composition is adjusted to a component composition that produces an alkali metal chloride, and the mixture is melted.

In a third aspect of the present invention, a mixture of the fly ash containing calcium chloride and a substance containing an alkali metal compound in the first aspect is made into a granular material, and the granular material is melted.

In a fourth aspect, the mixture of the fly ash containing calcium chloride and the substance containing the alkali metal compound and the incineration ash according to the second aspect is made into granules, and the granules are melted.

In a fifth aspect, the granular material according to the third aspect or the fourth aspect is subjected to a firing treatment.

In the present invention, fly ash refers to scattered matter discharged from a furnace when incinerated in a stoker furnace, kiln furnace, or the like in which incineration residues are separated into incinerated ash and fly ash, and It refers to the scattered matter discharged from the furnace when incinerated in a fluidized bed furnace. In addition, the incineration ash refers to incineration ash when incineration is performed in a furnace in which incineration residues are discharged separately into incineration ash and fly ash.

As described above, the melting furnace cannot be operated when the fly ash that is collected when the calcium-containing substance is injected into the flue of the exhaust gas or the incinerator and contains a large amount of salts is melted. The substance that falls into the state is calcium chloride, and the same salts, sodium chloride and potassium chloride, do not cause any problems.

Therefore, in the present invention, a certain substance is added to react with calcium chloride, and calcium chloride is converted into another compound to eliminate it. The additive substance reacts with calcium chloride when heated to a high temperature range, and a newly generated compound is a slag composed of an oxide mainly composed of SiO ₂ , CaO, Al ₂ O ₃ or the like. It is selected from those having a high vapor pressure even in a temperature range lower than the melting point. A specific form that meets this condition is a compound of an alkali metal such as sodium or potassium that generates salts having a relatively low boiling point when reacted with calcium chloride, such as carbonate, silicate, and borate. Alkali metals, minerals containing alkali metals such as lazolite (main component: Na ₂ B ₄ O ₇ ), glass compositions containing alkali metals, and the like.
For example, when a sodium compound is added, a reaction shown in the following formulas (1) and (2) occurs, calcium chloride disappears, and sodium chloride is generated. CaCl ₂ + Na ₂ CO ₃ = 2NaCl + CaO + CO ₂ (1) CaCl ₂ + Na ₂ SiO ₃ = 2NaCl + CaSiO ₃ (2)

Therefore, in the present invention, an alkali metal compound-containing substance is added to increase the amount of alkali metal that reacts with calcium chloride, and the ratio (molar ratio) of alkali metal to chlorine in fly ash is one. 0.0 or more.

As described above, even for fly ash containing a large amount of calcium chloride, a substance containing an alkali metal compound that reacts with calcium chloride is added to balance the chlorine content and the alkali metal content in the fly ash. If the components are adjusted as described above, calcium chloride will not be present in the high-temperature region, so that operation inhibition due to calcium chloride will not occur.

The reaction between the calcium chloride and the alkali metal compound proceeds in a temperature range lower than the melting temperature of the fly ash, and if the two are sufficiently mixed, the fly ash charged into the melting furnace will not melt. The reaction is carried out at a stage before the reaction. If calcium chloride has disappeared at this stage, a newly generated alkali metal chloride will also be volatilized at the same time, so that the molten salt layer hardly exists in the melting furnace.

By the way, examples of the composition of incineration ash among the incineration residues are as shown in Tables 2 to 4. According to these tables, the total molar ratio of Na and K to Cl is 2 or more, and Na and K are in excess.

Therefore, in the present invention, the components of fly ash are adjusted using the alkali metals Na and K in the incineration ash. In this case, the addition amount of the alkali metal compound-containing substance is reduced, and incineration ash is added so that the molar ratio of the alkali metal component to the chlorine content is adjusted to 1.0 or more.

In the present invention, the fly ash or a mixture of fly ash and incinerated ash, to which an alkali metal compound-containing substance is added and whose components are adjusted, is granulated and charged into a melting furnace. Is performed more quickly, and the reaction between calcium chloride and the alkali metal compound is further promoted. When powder such as fly ash is molded and charged as a granular material, the calcium chloride particles and the particles of the alkali metal compound-containing substance are in a densely aggregated state. And the reaction starts immediately. In addition, when the charge is granulated, the charge put on the melt tends to sink in the melt, and the heating is performed in the high-temperature melt, so that the heating efficiency is extremely high. Get better.

Further, in the present invention, after the alkali metal compound-containing substance is added to the fly ash or the mixture of the fly ash and the incinerated ash to adjust the components, before the granulated granules are charged into the melting furnace, A high-temperature heat treatment for baking is performed so that calcium chloride reacts with the alkali metal compound outside the furnace. Since there is no unreacted calcium chloride in the melting furnace in which the reacted granules are charged, the operation abnormality due to the current drift is reliably avoided.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a process diagram showing an example of an embodiment of a melting treatment method according to the present invention. In this method, an alkali metal compound-containing substance is added to fly ash containing calcium chloride to increase the content of alkali metal, and the molar ratio of alkali metal to chlorine is 1.
A mixture whose components are adjusted to be 0 or more is prepared.
Next, this mixture is charged into an electric resistance melting furnace and melted.

FIG. 5 shows an example of the configuration of the electric resistance melting furnace used in the present invention. In FIG.
10 is a hopper for charging fly ash with adjusted components, 11 is a screw feeder, 12 is an electrode, 13 is a slag outlet, 1
Reference numeral 4 denotes a gas outlet, 50 denotes fly ash whose components have been adjusted, and 51 denotes molten slag. When the fly ash whose components are adjusted is charged into the melting furnace, the fly ash 50 is put on the molten slag 51, and is heated by the heat transfer from the molten slag to be melted.
It becomes molten slag. The molten slag is extracted from a slag discharge port 13 provided at a lower part of the furnace.

While the fly ash whose components are adjusted as described above is melted, a reaction between calcium chloride and an alkali metal compound as shown in the formula (1) occurs, and calcium chloride disappears, and sodium chloride NaCl or An alkali metal chloride such as potassium chloride KCl is formed. When the alkali metal chloride is heated to around 1000 ° C., it is mostly volatilized and scattered together with the molten exhaust gas, and is collected during dust collection. For this reason, a layer of the molten salt is not formed in the melting furnace, and the operation can be continued for a long time without causing an abnormality due to the current drift.

The alkali metal compound-containing substance added to the fly ash may be in the form of a powder or a solution. When added in a solution state,
In particular, when mixing with a large amount of particles belonging to coarse particles such as fly ash generated from a fluidized bed furnace, the mixing becomes uniform.

When powder additives are mixed with fly ash having a lot of coarse particles, the particle diameters of the two are different. Therefore, when transported or withdrawn from the hopper, both are separated and segregation occurs, resulting in insufficient mixing. Is charged to the melting furnace. When calcium chloride and an alkali metal compound are not sufficiently mixed and charged into a melting furnace, excess or deficiency of the alkali metal compound occurs in each part of the furnace, and a part remains unreacted. Become like In a melting furnace at a high temperature of 1400 ° C. to 1500 ° C., a part of the alkali metal compound added to react with calcium chloride volatilizes, and some calcium chloride remains unreacted. As a result, a molten salt layer is formed.

On the other hand, when the alkali metal compound-containing substance is added in the form of a solution, the solution adheres to the fly ash particles when added and is dispersed, so that a uniform mixture is prepared.

The component adjustment for adding the alkali metal compound-containing substance to the fly ash can also be performed in the process of transporting the fly ash or charging the fly ash into the melting furnace. In this case, a component adjustment may be performed to add the required amount of the alkali metal compound-containing substance, or a secondary adjustment of the fly ash whose components have been adjusted in advance, or an additional component as shown in FIG. 6 may be added. Adjustment may be used.

In FIG. 6, the same parts as those in FIG. 5 are denoted by the same reference numerals, and the description is omitted. In this method, an alkali metal compound-containing substance is added to the screw feeder 11 at a stage where the fly ash whose components have been adjusted is extracted from the charging hopper 10. The added alkali metal compound-containing substance is well mixed while being conveyed by the screw feeder 11, and is charged into a melting furnace.

If the alkali metal compound-containing substance is added as described above, the amount of addition can be appropriately increased or decreased according to the conditions of the melting furnace, and the fly ash whose component is adjusted by the increase or decrease can be immediately melted. Since it is charged into the furnace, the operation can be continued with the chlorine content and the alkali metal content in the fly ash present in the melting furnace being balanced.

FIG. 2 is a process chart showing another embodiment of the melting treatment method of the present invention. In FIG. 2, FIG.
The description of the items already described in is omitted. In this method, an alkali metal compound-containing substance and incineration ash are mixed with fly ash containing calcium chloride to increase the alkali metal content, and the components are adjusted so that the molar ratio of the alkali metal content to the chlorine content becomes 1.0 or more. Prepare a conditioned mixture of fly ash. Next, this mixture is charged into an electric resistance melting furnace and melted.

As in the case of FIG. 1, the mixture of fly ash charged in the melting furnace causes a reaction between calcium chloride and an alkali metal compound, so that calcium chloride disappears and an alkali metal chloride is generated. Most of the alkali metal chloride is volatilized. For this reason, a layer of the molten salt is not formed in the melting furnace, and the operation can be continued for a long time without causing an abnormality due to the current drift.

According to the method shown in FIG. 2, since the amount of the alkali metal compound-containing substance added is reduced, the cost of adjusting the components is reduced, and the viscosity when the fly ash is melted by adding the incinerated ash is reduced. This also has the effect of lowering the melt and facilitating the discharge of the melt.

When adding the incinerated ash, it is preferable that the incinerated ash discharged from the incinerator is sieved and the finest possible ash is added. Even for incineration ash, the finer the content, the higher the content of heavy metals. Therefore, if the incineration ash is made finer and melted, an additional effect of insolubilizing the heavy metals in the incineration ash is obtained. It is also preferable to pulverize the fine incineration ash and add more fine incineration ash. If fine incineration ash is added, the reaction between calcium chloride and the alkali metal compound in the melting furnace proceeds rapidly.

FIG. 3 is a process chart showing still another embodiment of the melting treatment method of the present invention. In FIG. 3, the description of the items already described in FIGS. 1 and 2 is omitted. In this method, by mixing a fly ash containing calcium chloride with an alkali metal compound-containing substance and incineration ash, a mixture whose components are adjusted such that the molar ratio of the alkali metal component to the chlorine component is 1.0 or more is obtained. After preparation, this mixture is granulated, and the granules are charged into an electric resistance melting furnace and melted.

FIG. 4 is a process chart showing still another embodiment of the melting treatment method according to the present invention. In FIG. 4, the description of the items already described in FIGS. In this method, by mixing a fly ash containing calcium chloride with an alkali metal compound-containing substance and incineration ash, a mixture whose components are adjusted such that the molar ratio of the alkali metal component to the chlorine component is 1.0 or more is obtained. After granulation, the granules are fired at a temperature of 500C to 1200C. Then, the fired product is charged into an electric resistance melting furnace and melted.

The calcined granules are in a state where the reaction between the calcium chloride and the alkali metal compound is almost completed.
Even if this calcined product is charged into a melting furnace, a molten salt layer of calcium chloride is not formed. Therefore, the operation can be continued for a long time without causing an abnormality due to the current drift.

[0039]

【Example】

(Example 1) 15 parts by weight of a 20 wt% sodium carbonate solution was added to 100 parts by weight of fly ash collected when municipal waste was incinerated in a fluidized bed furnace, and mixed. Table 1 shows the analysis values of the fly ash and the fly ash whose components were adjusted. In this table, the molar ratio of the alkali metal to the chlorine is also shown. As shown in this table, the fly ash whose components have been adjusted has a molar ratio of Cl / (Na + K) of about 1.2, and is adjusted so that the alkali metal component that reacts with the chlorine component is more than the theoretical value. Was.

Then, this component-adjusted fly ash was charged into an electric resistance type test melting furnace having the same configuration as that shown in FIG. 5 and melted, but a molten salt layer was not formed in the furnace. ,
No anomaly due to current drift occurred.

[0041]

[Table 1]

(Example 2) Fly ash collected when municipal waste was incinerated in a stoker furnace, incinerated ash, and sodium carbonate powder were mixed at a ratio of 10: 30: 1 (weight ratio).
The incinerated ash was sieved with a 5 mm sieve and further ground and mixed to a particle size of 2 mm or less. Table 2 shows the analysis values of the fly ash, incineration ash and the mixture whose components were adjusted.
Shown in As shown in this table, the fly ash whose components have been adjusted is Cl
The molar ratio of / (Na + K) was about 1.2, and the alkali metal content reacting with the chlorine content was adjusted to be more than the theoretical value.

Then, this mixture was charged into a test melting furnace of the same electric resistance type as in Example 1 and melted.
No molten salt layer was formed in the furnace, and no abnormalities due to current drift occurred.

[0044]

[Table 2]

Example 3 By the same operation as in Example 2, fly ash and incinerated ash collected when municipal solid waste was incinerated in a stoker furnace were mixed at a ratio (weight ratio) of 100: 250. Then, 16 parts by weight of 20% by weight sodium carbonate was added to 100 parts by weight of this mixture and mixed. Table 3 shows the analysis values of the fly ash, the incineration ash, and the mixture whose components were adjusted. As shown in this table, the mixture whose components have been adjusted is C
The molar ratio of 1 / (Na + K) was adjusted to about 1.2.

Then, this mixture was charged into a test melting furnace of the same electric resistance type as in Example 1 and melted.
No molten salt layer was formed in the furnace, and no abnormalities due to current drift occurred.

[0047]

[Table 3]

(Example 4) First, fly ash, incinerated ash, and sodium carbonate powder collected when municipal solid waste was incinerated in a stoker furnace were subjected to the same operation as in Example 2 to obtain 10: They were mixed in a ratio of 25: 2 (weight ratio). Table 4 shows the analysis values of the fly ash, the incineration ash, and the mixture whose components were adjusted. The adjusted mixture is Cl /
The molar ratio of (Na + K) was adjusted to about 1.2.

Next, this mixture was charged into a granulator and sprayed with water to granulate. What is discharged from the granulator includes:
Some of the granules were not granulated, but all of the granulated ones were dried and then charged into the same electric resistance type test melting furnace as in Example 1 for melting. On this occasion,
No molten salt layer was formed in the furnace, and no abnormalities due to current drift occurred.

[0050]

[Table 4]

(Embodiment 5) By the same operation as in Embodiment 4, 10 pieces of fly ash, incinerated ash, and sodium carbonate powder collected when municipal solid waste was incinerated in a stoker furnace were used.
The mixture was mixed at a ratio of 0: 250: 16 (weight ratio), and the mixture was granulated. Then, the granules were fired at 900 ° C. for 60 minutes. Table 5 shows the analysis values of the fly ash, the incinerated ash, and the baked granules treated at this time. As shown in this table, the content of Cl in the fired granules was very small, and most of the Cl contained in fly ash was volatilized. Therefore, it was confirmed that most of the calcium chloride had disappeared.

Then, the fired product was charged into a test melting furnace of the same electric resistance type as in Example 1 and subjected to a melting treatment, but no abnormalities due to current drift occurred.

[0053]

[Table 5]

In conducting the baking treatment of the granular material, a test was conducted in advance to determine the temperature at which the baking treatment was performed. In this firing test, first, a mixture of fly ash containing calcium chloride and sodium carbonate was subjected to differential thermal analysis. As a result, at 490 ° C., an exothermic peak, which indicates that the reaction between calcium chloride and sodium carbonate had progressed, appeared. From this, if the firing temperature is set to 500 ° C. or higher,
It was found that the above reaction proceeded and sodium chloride was produced.

Next, incineration ash and sodium carbonate were added to the fly ash of the stoker furnace, and the molar ratio of Cl / (Na + K) was about 1.2.
The mixture whose components had been adjusted as described above was calcined at various temperatures of 500 ° C. or higher, and the temperature range was determined based on the results. The firing time was 60 minutes each. Then, the chlorine content in the fired product was analyzed, and the behavior of sodium chloride generated by the above reaction was examined. Table 6 shows the results. According to Table 6, when the calcination temperature was between 500 ° C and 700 ° C, the chlorine content did not decrease, indicating that the sodium chloride generated by the above reaction remained in the calcination product. Have been. However, when the calcination temperature was set to 800 ° C. or higher, it was recognized that the chlorine content was reduced and that sodium chloride was volatilized.

As is clear from the above results, the behavior of sodium chloride as a reaction product changes depending on the temperature range in which the calcination of the granular material is performed. If baking is performed at a temperature in the range of 500 ° C. or more and less than 800 ° C., calcium chloride and sodium carbonate react to form sodium chloride, and the sodium chloride remains in the fired product. And this sodium chloride volatilizes at the stage of being charged into a melting furnace.

If the firing is performed at a temperature in the range of 800 ° C. or more, the sodium chloride produced by the above reaction volatilizes during the firing, and the fired product charged into the melting furnace does not contain sodium chloride. When firing at 800 ° C. or higher, energy consumption increases, but almost no sodium chloride is brought into the melting furnace, so that salts are not mixed into the molten slag, and the slag can be effectively used in various fields. I can do it. However, even if the firing temperature is excessively increased in an attempt to reduce sodium chloride in the fired product charged into the melting furnace, the volatilization rate of sodium chloride does not increase so much. Therefore, the upper limit of the firing temperature is preferably set to about 1200 ° C.

[0058]

[Table 6]

[0059]

According to the present invention, a substance containing an alkali metal compound having a reactivity with calcium chloride in a high-temperature region is added to fly ash containing calcium chloride. After adjusting to a component composition that produces chloride, it is melted. Therefore, in a high-temperature melting furnace, newly produced alkali metal chloride is also volatilized and disappears, and no molten salt is present. For this reason,
No abnormal operation of the melting furnace occurs due to the presence of the molten salt.

[Brief description of the drawings]

FIG. 1 is a process chart showing an example of an embodiment according to a melting treatment method of the present invention.

FIG. 2 is a process chart showing another embodiment of the melting treatment method of the present invention.

FIG. 3 is a process chart showing still another embodiment according to the melting treatment method of the present invention.

FIG. 4 is a process chart showing still another embodiment of the melting treatment method of the present invention.

FIG. 5 is a schematic sectional view showing an example of an electric resistance melting furnace used in the present invention.

FIG. 6 is an explanatory view relating to an example of a method for adjusting a component by adding an alkali metal compound-containing substance at a stage of charging fly ash.

[Description of Signs] 10 Feed ash charging hopper 11 with component adjusted 11 Screw feeder 12 Electrode 13 Slag outlet 50 Component adjusted fly ash 51 Melted slag

Claims (5)

[Claims] 1. A method for melting a fly ash containing calcium chloride in an electric resistance melting furnace, wherein a substance containing an alkali metal compound having reactivity with calcium chloride in a high temperature region is added to the fly ash containing calcium chloride. A method for melting fly ash containing calcium chloride, wherein the composition is adjusted to a composition in which calcium chloride disappears in a high-temperature region to generate an alkali metal chloride, followed by melting. 2. A method for melting a fly ash containing calcium chloride in an electric resistance melting furnace, wherein the fly ash containing calcium chloride contains a substance containing an alkali metal compound having reactivity with calcium chloride in a high temperature region and incineration. A method for melting fly ash containing calcium chloride, comprising adding ash to adjust the component composition so that calcium chloride disappears in a high temperature region to generate an alkali metal chloride, and the mixture is melted. 3. The fly ash containing calcium chloride according to claim 1, wherein a mixture obtained by adding a substance containing an alkali metal compound to fly ash containing calcium chloride is granulated, and the granulated substance is melted. Melt processing method. 4. The method according to claim 2, wherein a mixture of a fly ash containing calcium chloride and a substance containing an alkali metal compound and incineration ash is granulated, and the granulated material is melted. Method for melting fly ash. 5. The method for melting fly ash containing calcium chloride according to claim 3, wherein the granular material to be melted has been calcined.