JPH11325425A - Method and apparatus for treating waste material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely and economically remove hazardous substances in exhaust gas by activating char with wastage treatment while itself not being affected at all by the char. SOLUTION: Wastage A containing organic substances is pyrolyzed by a pyrolysis furnace 1 to generate pyrolysis gas and char. The char is cleaned by cleaning means 3 and then dewatered by dewatering means 4 and heated to be activated by an activating means 5. Activated char is filled into an adsorption means 6, for adsorbing hazardous substances in combustion exhaust gas caused through the combustion of the pyrolysis gas in a secondary combustion furnace 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waste treatment method and a waste treatment device capable of removing harmful substances such as dioxins discharged together with combustion exhaust gas when the waste is incinerated. .

[0002]

2. Description of the Related Art Recently, when incinerating waste, dioxins discharged together with the combustion exhaust gas have become a major social problem. Attempts have been made to decompose dioxins by producing char and burning them at an appropriate excess air ratio to obtain high-temperature flue gas. However, with such a method alone, it is difficult to constantly reduce the content of dioxins in exhaust gas to a sufficiently low value.In order to more reliably remove harmful substances such as dioxins, For example, in order to stably obtain high-temperature exhaust gas, it is necessary to burn the auxiliary fuel to heat the exhaust gas, or to adsorb harmful substances by activated carbon, activated coke, a catalyst, or the like. Activated coke, catalyst, etc. must be consumed, which is not economical.

In order to solve such a problem,
For example, in Japanese Patent Application Laid-Open No. 9-53815, as a method of treating combustion exhaust gas when waste is incinerated by a fluidized bed incinerator, a fluid medium containing char and incombustibles is extracted from a fluidized bed of the fluidized bed incinerator. Separate the char,
It has been proposed to use this char instead of activated carbon to adsorb harmful substances such as dioxins in exhaust gas. Therefore, such a treatment method does not require expensive activated carbon, activated coke, a catalyst or the like, and can effectively utilize the char generated in the process of incineration of waste, which is economical.

[0004]

By the way, in such a treatment method, the above-mentioned char is produced by carbonizing the organic matter in the waste in the fluidized bed, and is made porous, that is, activation (activation). It is brought into a state where it can be used for adsorption of dioxins and the like. Here, in the exhaust gas treatment method described in the above publication, the amount of char activated in the fluidized bed can be controlled by the temperature of the fluidized bed and the amount of fluidized gas (primary air) supplied to the fluidized bed. It is said that the adsorption capacity can be controlled by the bed temperature and the amount of flowing gas.

[0005] However, in the treatment method described in the above publication in which char is activated in a fluidized bed incinerator, the operating conditions of the fluidized bed incinerator are controlled in order to control the amount of activated char and the adsorption capacity thereof. Is adjusted, there is a possibility that the original performance of the incinerator may not be obtained depending on the amount of waste and the calorific value of the waste supplied to the fluidized bed incinerator. On the other hand, if the operating conditions of the fluidized bed incinerator are set so as to be adapted to the incineration of waste, it is not possible to produce a char with sufficient adsorption capacity in an appropriate amount, that is, these wastes themselves It has been considered difficult to operate the incinerator under conditions that are optimal for both the treatment of activated carbon and the production of activated char.

The present invention has been made under such a background, and activates the char without any influence on the waste treatment itself, thereby reliably and economically removing harmful substances in the exhaust gas. It is an object of the present invention to provide a method and an apparatus for treating waste that can be removed.

[0007]

Means for Solving the Problems To solve the above problems and achieve such an object, a method for treating waste according to the present invention comprises the steps of: And char, and after the char is washed, dehydrated, further heated and activated, and the activated char adsorbs harmful substances in the combustion exhaust gas obtained by burning the pyrolysis gas. Features. However, in such a waste treatment method, by thermally decomposing the waste containing the organic matter, the organic matter is decomposed into the pyrolysis gas and the char as described above. Since high combustion exhaust gas temperature is obtained by burning at an excess air ratio, harmful substances such as dioxins in the exhaust gas can be suppressed to some extent. On the other hand, the amount of char generated at this time varies depending on the type of organic matter, the thermal decomposition temperature, and the like, but is generally about 10% to 60% by weight of the organic matter to be thermally decomposed. A sufficient char can be ensured regardless of the processing amount and the processing temperature.

[0008] However, the thermal decomposition temperature at this time is usually 3
Since the temperature is from 00 ° C. to 600 ° C., the generated char is only obtained by carbonizing the organic matter, and does not have a sufficient adsorption ability. Therefore, the char is washed and then dehydrated, and further heated and activated to give the char a sufficient adsorption capacity, so that the harmful substances remaining in the exhaust gas can be adsorbed and removed.
That is, the char and the ash content such as calcium chloride are mixed in the char generated by thermally decomposing the waste, and by washing this, the salt is dissolved in the washing water and separated. By heating the dehydrated cake obtained by dehydrating the washed char under conditions in which no oxygen is present, the water in the cake evaporates as water vapor and the char reduces the water vapor by the reducing action of the water vapor. It is activated to be porous, and its specific surface area is increased, so that adsorption capacity is generated.

[0009] Here, it is desirable that the char adsorbing the harmful substances in the exhaust gas is burned and treated, whereby the adsorbed harmful substances such as dioxins are decomposed and made harmless. Further, as a heat source for heating and activating the washed and dehydrated char, combustion heat generated when the pyrolysis gas is burned, or when burning the char which adsorbs harmful substances as described above By using the combustion heat generated in the above or both of them together, it is possible to promote more economical exhaust gas treatment.

[0010] On the other hand, the waste treatment apparatus of the present invention comprises a pyrolysis furnace for pyrolyzing waste containing organic matter, and separation means for separating pyrolysis gas generated in the pyrolysis furnace from char. A washing unit for washing the char separated by the separating unit, a dehydrating unit for dehydrating the washed char, an activating unit for heating and activating the dehydrated char, and the separating unit. It comprises a combustion furnace for burning the pyrolysis gas, and adsorption means for adsorbing harmful substances in the exhaust gas generated in the combustion furnace by the char activated by the activation means, based on the processing method described above. As a result, harmful substances in the exhaust gas can be economically and reliably removed.

[0011]

FIG. 1 shows an embodiment of a waste treatment apparatus according to the present invention. The waste treatment method according to the present invention will be described below with reference to FIG.
In FIG. 1, reference numeral 1 denotes a fluidized bed type pyrolysis furnace. Slaked lime B is added to waste A containing organic matter and supplied to the pyrolysis furnace 1, and the pyrolysis is performed. From the pressurized chamber 1A formed at the lower part of the furnace 1, a flowing gas C whose oxygen concentration is adjusted so as to keep the temperature of the fluidized bed in the pyrolysis furnace 1 constant at about 300 ° C. to 600 ° C. Supplied. In the pyrolysis furnace 1, the organic matter in the waste A is partially burned, and the remaining most is pyrolyzed to generate pyrolysis gas and char. The chlorine contained in the waste A is thermally decomposed in the pyrolysis furnace 1 to temporarily produce hydrogen chloride, and then neutralized by slaked lime B to produce calcium chloride.

The pyrolysis gas and char generated by pyrolysis of the organic matter in the waste A in the pyrolysis furnace 1 as described above, the flowing gas partially burned in the pyrolysis furnace 1, salts such as calcium chloride, and waste The ash contained in A is discharged from the top of the pyrolysis furnace 1 and separated by the separation means 2 into a solid content and a gas content. As the separating means 2, a dust collector such as a cyclone or a high temperature bag filter can be used, but a cheaper cyclone is sufficient.

Next, the solid component collected by the separating means 2 and separated from the gas component, ie, the char,
The salts and ash are supplied to the washing means 3 and washed with washing water to form a slurry. In the present embodiment, a repulp tank is used as the cleaning means 3,
In this washing means 3, water-soluble salts such as calcium chloride in solids are dissolved in washing water.

Further, the solids thus washed and slurried are dehydrated while being further supplied with washing water D by a dehydrating means 4, and solidified into a filtrate in which the salts are dissolved and a dehydrated cake composed of char and ash. The liquid is separated.
Here, a general filter type dehydrator such as a belt filter or a filter press can be used as the dehydrating means 4. However, the filtrate in which salts in the dehydrated cake are dissolved can be quickly washed and removed. A countercurrent multistage washing type dehydrator which requires a small amount of washing water in the dehydrating means 4 is suitable. The water content of the dewatered cake solid-liquid separated by the dewatering means 4 is such that the amount of steam required in the steam activation described below is substantially the same as that of the char, and
In addition, since the parts by weight of the char and the ash in the solid content are substantially the same, it is desirable that the content be about 20 wt% to 40 wt%, and if it is less than this, there is a possibility that sufficient steam for activating the char may not be obtained. On the other hand, if it is too much, unnecessary water must be evaporated, which is uneconomical.
A part of the filtrate generated during the dehydration is returned to the washing means 3 and reused as washing water, and the remaining is treated as wastewater E.

The dewatered cake thus solid-liquid separated is supplied to the activation means 5 and heated, whereby water in the dewatered cake evaporates to form steam, which acts at a high temperature to produce a char. Is activated by steam, the char becomes porous and its specific surface area is increased. The heating method in the activation means 5 includes a direct heating method such as a fluidized bed method, an internal heat rotary kiln method and a multi-stage furnace method, and an indirect heating method such as an external heat rotary kiln method and a multi-tube method. In consideration of the amount of scattering and the yield, the indirect heating method is preferable.In the present embodiment, the dehydration cake is supplied inside the tube and a high-temperature gas is supplied outside the tube. A multi-tube indirect heating activation device that evaporates water and raises the temperature of the char to a temperature required for activation is employed.

Further, the heating temperature in the activation means 5,
That is, the higher the activation temperature, the shorter the char can be activated in a shorter time. However, considering the durability and the like of the device material in the activation means 5 and the temperature and the temperature sufficient for the activation,
About 700 ° C to 900 ° C is sufficient. That is, if the activation temperature is lower than 700 ° C., the char may not be activated enough to adsorb dioxins or the like, or the activation may take a long time.
If the temperature exceeds 00 ° C., the time required for activation is reduced, but the activation means 5 is required to have high heat resistance and durability in accordance with this, which is rather uneconomical. further,
The time required to activate this char, that is, the activation time,
As described above, the higher the activation temperature is, the shorter the time is. However, when the activation temperature is set in the above range, about 1 to 5 hours is sufficient.

The specific surface area of the char activated in the activating means 5 is increased to 100 m ² / g or more, and the char can be used for adsorbing harmful substances such as dioxins. Then, the activated char is supplied to the adsorbing means 6 and is filled in a filling layer, a moving layer and the like formed in the adsorbing means 6.

On the other hand, the gas separated from the solid in the separation means 2, that is, the pyrolysis gas and the flowing gas, are supplied from the separation means 2 to the secondary combustion furnace 7 and burned. Then, the combustion exhaust gas is heat-recovered and cooled by waste heat recovery means 8 such as a boiler, an air preheater, and a hot water recovery device, and then is removed by a dust removal means 9 such as a bag filter. The harmful substances such as dioxins are supplied and adsorbed, and are discharged as exhaust gas F. The exhaust gas F thus adsorbed with the harmful substances is partially mixed with air to adjust the oxygen concentration, and supplied to the pressurizing chamber 1A of the pyrolysis furnace 1 as the flowing gas C. The rest is released to the atmosphere.

Further, in the present embodiment, the char having thus adsorbed the harmful substance in the exhaust gas by the adsorbing means 6 is extracted from the packed bed or the moving bed of the adsorbing means 6 and then supplied to the melting furnace 10 as fuel. The supplied ash is burned at a high temperature of 1300 ° C. or more, and is supplied to the ash supplied to the melting furnace 10 via the activation means 5 and the adsorption means 6 together with the char to reduce the volume of the ash. By burning at a high temperature, harmful substances such as dioxins adsorbed on the char are decomposed and rendered harmless in the melting furnace 10. Here, as the melting furnace 10, a general melting furnace such as a swirling melting furnace and a pulverized coal burner can be used. After the molten ash is cooled, it is reused as a stone substitute G or the like.

Further, in the present embodiment, the melting furnace 10
The high-temperature combustion exhaust gas discharged from the furnace is supplied to the activation means 5 and used as a heat source when the dewatered cake is heated to activate the char by steam. That is, in the present embodiment, the combustion exhaust gas discharged from the melting furnace 10 is used as a high-temperature gas supplied outside the tube of the multi-tube indirect heating activation device employed as the activation means 5. . Further, the exhaust gas thus provided for activating the char in the activation means 5 is sent to the waste heat recovery means 8 together with the exhaust gas discharged from the secondary combustion furnace 7 and the dust removal means 9 is provided.
Then, the exhaust gas F is passed through the adsorption means 6.

As described above, in the waste treatment apparatus having the above-described structure and the waste treatment method according to the present embodiment using the treatment apparatus, first, the waste A containing an organic substance is thermally decomposed to form a pyrolysis gas. Since chars are generated and the pyrolysis gas is burned to treat waste A, harmful substances such as dioxins contained in the combustion exhaust gas are small, and harmful substances in the exhaust gas are removed by heat. Since the adsorption and removal are performed using the char generated by the decomposition, it is possible to more economically reduce harmful substances in the exhaust gas F.
In the present embodiment, the char that adsorbs this harmful substance is generated in the pyrolysis furnace 1 and separated from the pyrolysis gas by the separation means 2, washed by the cleaning means 3 and then dewatered by the dehydration means 4. It is activated by dehydration and further heating by the activation means 5, regardless of the operating conditions of the pyrolysis furnace 1 and the secondary combustion furnace 7.
A predetermined amount of char can be activated. Therefore, according to the waste treatment method and the waste treatment apparatus having the above configuration, the waste A itself can be surely treated under the optimal operating conditions for the treatment, while the waste A can be treated under the optimal conditions for the char. It can be activated to give a high adsorption capacity, and it is possible to reliably adsorb harmful substances.

In the present embodiment, the char having absorbed the harmful substance is supplied from the adsorption means 6 to the melting furnace 10 and burned as a fuel at a high temperature of 1300 ° C. or more, thereby being adsorbed by the char. Harmful substances such as dioxins are decomposed and made harmless. Therefore,
According to the present embodiment, it is possible to prevent a situation in which the harmful substance adsorbed on the char is released in a subsequent process and adversely affects the surrounding environment. It is possible to ensure safety. Moreover, in the present embodiment, the heat generated by burning the char in the melting furnace 10 melts the ash generated when the organic matter of the waste A is thermally decomposed to reduce the volume of the ash. In addition, since the melt is cooled and can be reused as the stone substitute G, it is possible to provide a treatment method suitable for the recent tightness of landfill for waste incineration ash.

Further, in the present embodiment, the melting furnace 10
In the above, the high-temperature combustion exhaust gas generated by burning the char is supplied to the activating means 5 so as to be used as a heating source for heating and activating the washed and dehydrated char. The heat generated in the process of A can be effectively used without waste, and more economical and efficient waste disposal can be achieved. In the present embodiment, the combustion exhaust gas generated in the melting furnace 10 is used as a heating source of the activation unit 5. For example, the combustion exhaust gas generated in the secondary combustion furnace 7 is supplied to the waste heat recovery unit 8. The heating means may be supplied to the activating means 5 without performing the heat treatment. Further, both of the melting furnace 10 and the combustion exhaust gas generated in the secondary combustion furnace 7 may be used as the heating source of the activating means 5. You may.

Furthermore, in this embodiment, dioxins are listed as harmful substances that are adsorbed and removed by the activated char. However, chars having a specific surface area of 100 m ² / g or more activated under the above-described conditions. According to this, in addition to dioxins, it is also possible to adsorb and remove other harmful substances such as sulfur oxides and nitrogen oxides contained in exhaust gas.
In particular, regarding the adsorption and removal of nitrogen oxides, the efficiency of adsorption and removal of nitrogen oxides is further improved by adding ammonia and urea to the exhaust gas at the inlet of the exhaust gas in the adsorption means 6. be able to.

[0025]

EXAMPLES The effects of the present invention will be specifically described below with reference to examples of the present invention. In this example, 100% of waste A having a composition of 44 wt% of water, 9 wt% of non-combustible material, and 47 wt% of combustible material was used using the treatment apparatus of the embodiment shown in FIG.
Slaked lime B was added at 2 kg / h with respect to kg / h, and supplied to the pyrolysis furnace 1;
m ³ / h, pre-filled average particle size 330 μm
Of the waste A was thermally decomposed at 570 ° C. while partially burning the waste.
Next, the solid component and the gas component discharged from the pyrolysis furnace 1 were separated by a cyclone of the separating means 2 to collect a solid component having a composition and a calorific value as shown in Table 1 of 43 kg / h.

[0026]

[Table 1]

Further, the solid matter thus collected is washed and washed with 850 kg / h of washing water in a repulping tank of the washing means 3 and repulped. After the salts contained in the solid matter are dissolved, the solid matter is dehydrated. The dehydration was performed by the countercurrent multistage washing dehydrator of the means 4 while performing three-stage countercurrent washing with 100 kg / h of initial washing water to obtain a dewatered cake of 96 kg / h. A part of the filtrate generated during the dehydration was returned to the repulp tank and reused for solid repulp. Table 2 shows the composition and calorific value of the dehydrated cake thus obtained.

[0028]

[Table 2]

Then, the dehydrated cake thus obtained is
The char was supplied to the inside of the tube of the multi-tube indirect heating activation device of the activation means 5 and heated by supplying the combustion exhaust gas discharged from the melting furnace 10 outside the tube to activate the char in the dewatered cake. At this time, in this example, the activation time and the activation temperature in the activation means 5 were changed, and the specific surface area of the char activated at that time was measured. FIG. 2 shows the measurement results obtained when the activation temperature was changed with the activation time being 1 hour, and FIG. 3 shows the results obtained when the activation time was changed with the activation temperature set at 850 ° C.

Further, the char thus activated is filled into the packed bed of the adsorbing means 6 together with the ash of the waste, and the gas separated by the separating means 2 is burned in the adsorbing means 6 in the secondary combustion furnace 7. Then, the combustion exhaust gas passed through the waste heat recovery means 8 and the dust removal means 9 was passed, and harmful substances such as dioxins, sulfur oxides, and nitrogen oxides contained in the combustion exhaust gas were adsorbed and removed. FIG. 4 shows the relationship between the specific surface area of the activated char at this time and the removal efficiency of dioxins, sulfur oxides, and nitrogen oxides.

However, from the results shown in FIG. 4, the specific surface area of the dioxins is particularly 100 m ² / g.
It can be seen that a removal efficiency of 90% or more was obtained in the case of. Incidentally, in the present embodiment, the temperature of the flue gas burned in the secondary combustion furnace 7 was 1020 ° C. and the concentration of dioxins was 0.4 ng / Nm ³ (TEQ). After cooling to 220 ° C. in the heat recovery means 8, the specific surface area 100
The concentration of dioxins in the exhaust gas F discharged from the adsorption means 6 is reduced to 0.01 ng / Nm ³ (TEQ) by passing through the adsorption means 6 filled with char activated to m ² / g. It was confirmed that dioxins could be sufficiently adsorbed and removed by the char activated to have a specific surface area of 100 m ² / g or more. Also,
In particular, as shown in FIG. 2, even when the activation time required for activation is one hour, if the activation temperature in the activation means 5 is 700 ° C. or higher, the specific surface area of the char can be activated to 100 m ² / g or more. It can be seen that a char having the above-described removal efficiency can be obtained.

In this embodiment, the char and the ash of the waste A thus adsorbing the harmful substances are withdrawn from the packed bed of the adsorbing means and supplied to the melting furnace 10. 1 for each harmful substance adsorbed as
It was burned at a high temperature of 400 ° C., whereby harmful substances were decomposed and made harmless. By the way, this melting furnace 10
The concentration of dioxins in the combustion exhaust gas generated in the above was as low as 0.04 ng / Nm ³ (TEQ). The high-temperature combustion exhaust gas generated in the melting furnace 10 is supplied to the activation means 5 as a heating source as described above, and is used for heating and activating the dehydrated char. The gas is supplied to the waste heat recovery means 8 together with the combustion exhaust gas of the above-mentioned gas, and the dust removal means 9 and the adsorption means 6
Processed through. On the other hand, the ash of the waste A supplied to the melting furnace 10 together with the char is melted by the heat of combustion in the melting furnace 10, then extracted from the melting furnace 10 and cooled, and is again converted into a harmless stone substitute G. Used.

[0033]

As described above, according to the present invention,
The char generated by pyrolysis of waste containing organic matter is separated from pyrolysis gas, washed and dehydrated, and the dewatered cake is heated and activated to operate the pyrolysis furnace and incinerator. Regardless of the waste treatment process itself, this char can be provided with a sufficient specific surface area. Therefore, it becomes possible to efficiently adsorb and remove harmful substances generated when the pyrolysis gas is burned by the activated char, thereby more reliably and economically suppressing the emission of harmful substances. Can be planned.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a waste treatment apparatus of the present invention.

FIG. 2 is a view showing a relationship between a char activation temperature and a specific surface area in the activation means 5 in the example of the present invention.

FIG. 3 is a diagram showing the relationship between the activation time of char in the activation means 5 and the specific surface area in the example of the present invention.

FIG. 4 is a diagram showing the relationship between the specific surface area of activated char and the removal efficiency of harmful substances in the example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pyrolysis furnace 2 Separation means 3 Cleaning means 4 Dehydration means 5 Activation means 6 Adsorption means 7 Secondary combustion furnace 8 Waste heat recovery means 9 Dust removal means 10 Melting furnace

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B09B 3/00 F23G 7/00 ZABZ F23G 5/14 ZAB B01D 53/34 A 5/44 ZAB B09B 3/00 302G 7/00 ZAB F23J 15/00 J F23J 15/00

Claims (4)

[Claims] 1. A waste containing organic matter is thermally decomposed to generate a pyrolysis gas and char, and the char is washed, dehydrated, heated and activated, and activated by the activated char. A method for treating waste, comprising adsorbing harmful substances in combustion exhaust gas obtained by burning pyrolysis gas. 2. The method for treating waste according to claim 1, wherein the char which adsorbs harmful substances is burned and treated. 3. The cleaning and dehydrating char is heated and activated by at least one of combustion heat of burning the pyrolysis gas and combustion heat of the char adsorbing harmful substances. The method for treating waste according to claim 1 or claim 2. 4. A pyrolysis furnace for pyrolyzing waste containing organic matter, separation means for separating pyrolysis gas generated in the pyrolysis furnace from char, and char separated by the separation means. Washing means for washing, dehydrating means for dehydrating the washed char, activation means for heating and activating the dehydrated char, and a combustion furnace for burning the pyrolysis gas separated by the separating means, A waste treatment apparatus, comprising: an adsorbing means for adsorbing harmful substances in exhaust gas generated in the combustion furnace by char activated by the activating means.