JP2005246280A - Method for thermally decomposing dioxins contained in flying ash and its apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for thermally decomposing dioxins contained in flying ash capable of preventing a low melting point substance from melting and adhering to a thermal decomposition apparatus at a low cost and simply, and further without adversely affecting to mixing treatment in cement solidification after thermal decomposition is completed; and its apparatus. <P>SOLUTION: In the thermal decomposition apparatus having a heating drum 24 provided with heating means 41 and agitating means (stirrer 25), heating the flying ash collected by a dust collector from an exhaust gas in a thermal treatment furnace while agitating in an oxygen deficient atmosphere by the thermal decomposition apparatus, and thermally decomposing and removing dioxins contained in the flying ash, a means for adding the collected flying ash with slaked limes is provided on the thermal decomposition apparatus or on the upper stream side of the thermal decomposition apparatus and an amount of addition of slaked limes is preferably made about 25 wt% or more of the flying ash, thereby increasing the melting point of the flying ash. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for thermally decomposing and removing dioxins contained in fly ash collected from an exhaust gas from a heat treatment furnace such as an incinerator or a melting furnace.

The fly ash contained in the exhaust gas from heat treatment furnaces such as incinerators and melting furnaces contains harmful substances such as dioxins and heavy metals. The fly ash is collected by a dust collector such as a bag filter or an electrostatic precipitator provided at the latter stage of the heat treatment furnace, and subjected to treatment such as melt solidification, cement solidification, and stabilization by chelate to make it harmless.
However, since dioxins are likely to elute after cement solidification and stabilization with chelate, it is desirable to heat fly ash to thermally decompose and remove dioxins.
In general, dioxins are considered that dioxins precursors such as chlorinated aromatic compounds contained in exhaust gas form dioxins by the catalytic action of fly ash. For the thermal decomposition treatment of dioxins, a Hagenmeier process, that is, a treatment method in which fly ash containing dioxins is kept at about 300 to 400 ° C. for about 1 to 2 hours in a reducing atmosphere such as nitrogen gas has been effective. There are various devices proposed in accordance with this processing method.

For example, according to Patent Document 1 (Japanese Patent No. 2953889), Patent Document 2 (Japanese Patent No. 2645799), etc., fly ash is kept at a high temperature state of 400 ° C. or higher for 30 minutes or more under lack of oxygen by an ash heating means. An apparatus is provided that thermally decomposes dioxins, vaporizes low boiling point heavy metals such as mercury, separates and cools the hot gas containing heavy metals, and condenses and separates heavy metals in the hot gas.
With these devices, it becomes possible to separate and remove harmful substances such as dioxins and heavy metals contained in the fly ash to make the fly ash harmless.

However, there are some problems in operating these devices smoothly. One of the problems is that the low melting point substance contained in the fly ash melts and adheres to the apparatus and solidifies, thereby hindering the operation of the apparatus and damaging the apparatus.
Therefore, in Patent Document 1, in order to prevent the trouble of fixing fly ash to the ash cooling device provided at the subsequent stage of the ash heating means, the gas generated by the ash heating means is sucked to separate the low melting point heavy metals. After that, the gas is circulated by feeding back to the ash heating means.
Moreover, in patent document 2, the means to heat fly ash supply means, such as an ash hopper and a supply rotary valve, is provided, and it prevents that fly ash adheres to a fly ash supply means.

Japanese Patent No. 2953889 Japanese Patent No. 2645799

Thus, when dioxins in fly ash are thermally decomposed, there is a problem that the low melting point substance contained in the fly ash adheres and solidifies, thereby hindering operation and causing damage to the apparatus. It was. By using the devices disclosed in Patent Documents 1 and 2, adhesion and solidification to the fly ash cooling device and ash supply device can be prevented, but adhesion and solidification of low melting point substances to the pyrolysis device itself can be prevented. The actual situation was not completed.
When a low-melting-point substance adheres to the inner wall of the thermal decomposition apparatus and solidifies, it rubs the melt with the stirrer such as a stirrer attached to the apparatus, causing abnormal noise and abnormal vibration, making it impossible to operate. End up.

Therefore, in order to prevent the low melting point material from melting and adhering to the thermal decomposition equipment, a filter cloth protective agent with a high melting point mainly composed of Al ₂ O ₃ or SiO ₂ used in filtration dust collectors is fly ash. In this method, the melting point of fly ash is increased.
However, such a filter cloth protective agent is very expensive, and there is a problem that processing costs increase. Furthermore, when a filter cloth protective agent was mixed, fly ash was kneaded with cement after thermal decomposition, and when solidified, the filter cloth protective agent with high water repellency had an adverse effect and could not be uniformly mixed. .
Therefore, in view of the above-mentioned problems of the prior art, the present invention can easily prevent the fly ash from adhering to the pyrolysis apparatus at low cost, and further adversely affect the kneading process in cement solidification after the pyrolysis process. An object of the present invention is to provide a thermal decomposition method and apparatus for dioxins contained in fly ash.

Therefore, in order to solve this problem, the present invention provides:
The fly ash collected from the exhaust gas of the heat treatment furnace by the dust collector is introduced into the thermal decomposition apparatus, and the fly ash is heated in the thermal decomposition apparatus in an oxygen-deficient atmosphere while being stirred and contained in the fly ash. In the method of pyrolytic removal of dioxins,
The powder containing slaked lime (hereinafter referred to as slaked lime) is added to the fly ash collected by the dust collector directly or upstream of the pyrolyzer to add the melting point of the fly ash. It is characterized by being raised.

According to the present invention, the melting point of the fly ash is increased by adding slaked limes to the fly ash, it is possible to prevent melting and fixing of the low melting point substance in the thermal decomposition apparatus, abnormal noise due to friction with the stirring means, Abnormal vibration can be avoided, and further damage to the apparatus can be prevented, and stable operation can be performed. Moreover, in this invention, since cheap slaked lime is used, processing cost can be reduced. Furthermore, even when the cement is mixed and kneaded in the subsequent stage, uniform kneading is possible without adverse effects.
Furthermore, in the present invention, it is preferable that the amount of slaked lime added is about 25 wt% or more of the fly ash, whereby the melting start temperature of the fly ash can be raised to about 400 ° C. or more.

As another invention, the fly ash collected from the exhaust gas of the heat treatment furnace by a dust collector is introduced into a thermal decomposition apparatus, and the fly ash is heated with stirring in an oxygen-deficient atmosphere in the thermal decomposition apparatus. In the method for thermally decomposing and removing dioxins contained in the fly ash,
When fly ash is collected by the dust collector, slaked lime of about 25 wt% or more of the fly ash is added to the fly ash to increase the melting point of the fly ash.
According to the present invention, the same effect as the above-described invention can be achieved, and slaked lime has been added in the dust collector for the purpose of removing hydrogen chloride and sulfur oxide, but this slaked lime addition means is utilized. Because it is possible, it can be handled with existing facilities, and the equipment cost can be reduced.

In the dust collector, slaked lime may be blown for the purpose of removing hydrogen chloride and sulfur oxide as described above. The slaked lime added at this time was suppressed to about 2 to 8% by weight of fly ash, and at most about 10% by weight. This is an amount in consideration of dust collection efficiency in the dust collector, and is determined based on, for example, clogging of the bag filter or current efficiency in the electric dust collector.
However, in the present invention, slaked limes are added mainly for the purpose of raising the melting point of fly ash, and therefore, the amount of slaked limes added is about 25 wt% or more, and a larger amount of slaked limes is mixed than before. . By adding this amount of slaked lime, the melting point of fly ash can be reliably raised to 400 ° C. or higher, and problems in the thermal decomposition apparatus disposed downstream of the dust collector can be prevented.

Moreover, in these inventions, the temperature in the said thermal decomposition apparatus was about 350-380 degreeC, It is characterized by the above-mentioned.
In general, it has been found that dioxins are thermally decomposed when heated to about 350 to 500 ° C. in an oxygen-deficient atmosphere or burned at 800 ° C. or higher. Accordingly, in the present invention, dioxins are thermally decomposed by heating fly ash at about 350 to 380 ° C., and further, the thermal efficiency is improved by setting it to about 380 ° C. or less, and the melting point is increased to about 400 ° C. or more by slaked limes. It is possible to thermally decompose the fly ash that has risen without melting, and it is possible to achieve removal of dioxins without melting and fixing the fly ash.

Furthermore, the slaked lime is transported to an inert gas introduced into the thermal decomposition apparatus and added to the fly ash. An inert gas such as N ₂ gas is introduced into the thermal decomposition apparatus in order to maintain an oxygen-deficient atmosphere. By introducing the slaked limes into the apparatus by transporting them to this inert gas, it is not necessary to provide new slaked lime addition means, and slaked limes are uniformly added to the fly ash without hardening by the inert gas flow Can be mixed.

In addition, as an invention of a device capable of suitably thermally decomposing dioxins in fly ash,
A pyrolysis apparatus having a heating means and a stirring means, wherein fly ash collected from a waste gas from a heat treatment furnace by a dust collector is heated with stirring in an oxygen-deficient atmosphere in the thermal decomposition apparatus, In a device for pyrolytic removal of dioxins contained in fly ash,
Means for adding slaked lime to the collected fly ash on the upstream side of the pyrolyzer or the pyrolyzer, and increasing the melting point of the fly ash in the pyrolyzer And
At this time, the slaked lime addition means is preferably a means for adding slaked lime of about 25 wt% or more of the fly ash.

Furthermore, a pyrolysis apparatus having a heating means and a stirring means, wherein fly ash collected from exhaust gas from a heat treatment furnace by a dust collector is heated with stirring in an oxygen-deficient atmosphere in the thermal decomposition apparatus. In the apparatus for thermally decomposing and removing dioxins contained in the fly ash,
Means for adding slaked lime of about 25 wt% or more of the fly ash to the fly ash is provided in the dust collector, and the melting point of the fly ash in the thermal decomposition apparatus is increased.
In these inventions, the amount of slaked lime added is most preferably in the range of 25 wt% to 40 wt% of the fly ash.
In these inventions, the temperature in the thermal decomposition apparatus is preferably about 350 to 380 ° C.

Furthermore, the slaked lime addition means is an inert gas inlet provided in the thermal decomposition apparatus, and the slaked lime is added to the fly ash by being conveyed to an inert gas.
Further, a kneader for solidifying cement of fly ash discharged from the thermal decomposition apparatus is provided on the downstream side of the thermal decomposition apparatus. Conventionally, a filter cloth protective agent mainly composed of Al ₂ O ₃ or SiO ₂ has been mixed into the fly ash to prevent the fly ash from being melted and fixed in the thermal decomposition equipment. Although difficult, in the present invention, since slaked lime having low water repellency is used, uniform kneading is possible.

  As described above, in the present invention, the melting point of the fly ash is increased by adding slaked limes to the fly ash, so that the low melting point substance can be prevented from being melted and fixed in the thermal decomposition apparatus, and abnormal noise due to friction with the stirring means. Abnormal vibrations can be avoided, and as a result, damage to the apparatus can be prevented and stable operation can be achieved. Moreover, in this invention, since cheap slaked lime is used, processing cost can be reduced. Furthermore, even when cement is mixed and kneaded in the subsequent stage, uniform kneading is possible without adversely affecting the kneading.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.
1 is an overall configuration diagram of an ash treatment system equipped with a thermal decomposition apparatus according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a dioxin thermal decomposition apparatus according to Embodiment 1 of the present invention, and FIG. Enlarged view of the heating drum, FIG. 4 is a table showing actual measurement data of the fly ash melting point with respect to the slaked lime addition rate, and FIGS. 5 to 7 are temperature curves and differential heat curves of the fly ash when the slaked lime addition rate is varied. It is a graph which shows.

FIG. 1 shows an example of an ash treatment system to which the thermal decomposition apparatus according to this embodiment is applied. The ash treatment system includes a main ash storage tank 11 and a fly ash storage tank 12 for storing main ash and fly ash collected after incineration of general waste and industrial waste, respectively. The ash charged from the storage tank 12 is melted in the melting furnace 13, and the exhaust gas generated in the melting furnace 13 is burned at a high temperature in the secondary combustion chamber 14, and then recovered and cooled by the cooling device 14. It introduces into the filter 16 to collect fly ash in the exhaust gas.
The collected fly ash is once accumulated in the ash storage tank 21 and introduced into the heating drum 24 by a predetermined amount. The fly ash is heated in the heating drum 24 while stirring in an oxygen-deficient atmosphere, and after dioxins are removed by thermal decomposition, the fly ash is introduced into the cooling drum 27 and cooled.

  The fly ash cooled by the cooling drum 27 is introduced into the kneader 32 via the ash discharge device 29. The kneading machine 32 is charged with a predetermined amount of cement from the cement storage tank 30 via the cement supply device 31, kneaded with the fly ash by the kneading machine 32, and then molded and solidified by the molding machine 33. The Thereby, harmful heavy metals contained in the fly ash are fixed in the cement. An effective method for detoxifying fly ash is to add an agent such as a liquid chelating agent before kneading to change the heavy metal into a heavy metal compound having low solubility and insolubilize it.

FIG. 2 shows an outline of the dioxin pyrolysis apparatus in this example. Such a dioxin pyrolysis apparatus 20 includes an ash storage tank 21 that stores fly ash, an ash supply apparatus 22 that includes ash feeding means such as a screw feeder, and heating that heats fly ash while stirring in an oxygen-deficient atmosphere. The drum 24, the dust filter 26 that sucks the heated gas in the heating drum 24 while filtering it, the cooling drum 27 that cools the fly ash discharged from the heating drum 24, and the cooled fly ash are kneaded. The ash discharge device 29 sent out to the machine 33 is a main component.
The fly ash stored in the ash storage tank 21 is, for example, fly ash collected from the exhaust gas of the melting furnace 13 by a dust collector as shown in FIG. This molten fly ash contains a lot of chlorides, has the characteristics that it tends to generate dioxins and has a low melting start temperature, but it can be easily rendered harmless by using the thermal decomposition apparatus shown in this embodiment. it can. However, the present invention is not limited to molten fly ash, but can be applied to fly ash generated in various incinerators, for example.

Further, since the heating drum 24 and the cooling drum 27 need to be in an oxygen-deficient atmosphere, between the ash supply device 22 and the heating drum 24 and between the cooling drum 27 and the ash discharge device 29. Are provided with rotary valves 23 and 28, which are configured so that the inside of these drums has an oxygen-deficient atmosphere and can quantitatively cut out fly ash.
The heating drum 24 has a stirring means such as a stirrer 25 and a heating means for indirectly heating the inside, and the charged fly ash is heated while stirring, and dioxins contained in the fly ash Is pyrolyzed, and low-boiling heavy metals such as mercury are volatilized. At this time, in the heating means, the inside of the drum is preferably heated to about 350 to 380 ° C., preferably 350 to 360 ° C.

The heated gas containing the volatilized low-boiling heavy metals is sucked by a circulation fan (not shown) and removed through the dust filter 26, and then cooled by a gas cooling means (not shown). The heavy metals are condensed and removed by cooling. The separated heavy metals are stabilized by chelate treatment or the like. On the other hand, the gas from which the heavy metals have been separated may be introduced again into the heating drum 24 and recycled.
Here, an example of a specific configuration of the heating drum 24 will be described with reference to FIG. 3A is a side sectional view of the heating drum 24, and FIG. 3B is a sectional view taken along line XX of FIG. The heating drum 24 has a horizontal cylindrical outer shell, and a rotating shaft 42 is inserted on the central axis of the outer shell, and a plurality of stirrers 25 are provided in the circumferential direction of the rotating shaft. Has been. The stirring bar 25 is configured to slidably contact the inner wall of the outer shell and to stir the inside of the outer shell.
The heating drum 24 has a heating means 41 for indirectly heating the inside of the drum from the outer peripheral portion. This may be heated using the exhaust heat of the melting furnace 13, or an electric heater or a gas heater may be used.

Further, the main feature of the present embodiment is that means for adding slaked limes to the fly ash to be put into the heating drum 24 is provided. The slaked lime addition means is provided directly on the heating drum 24 or on the upstream side of the heating drum 24. For example, as shown in FIG. 2, the slaked lime addition means uses an N ₂ gas introduction port that is introduced to make the inside of the heating drum 24 into an oxygen-deficient atmosphere, and is conveyed to the N ₂ gas to be drums. It can also be introduced directly into. Further, slaked lime addition means may be provided on the upstream side of the heating drum 24, that is, on the ash storage tank 21, the ash supply device 22, the dust collector 21, and the like.
The slaked lime may be a commercially available slaked lime (Ca (OH) ₂ ) alone, or cement or cement mixed with slaked lime may be used as a powder, and it is a non-water-repellent powder containing a high melting point inorganic compound. Any body can be used.

  As described above, the melting point of fly ash is increased by adding slaked limes to the fly ash, and when the fly ash is heated in the heating drum 24, the fly ash is melted and fixed to the inner wall of the drum. Thus, abnormal noise and abnormal vibration due to friction of the stirrer 25 can be avoided. Furthermore, since slaked limes are inexpensive, the operation cost can be reduced, and since they are not water-repellent, they do not adversely affect the kneading and cement solidification processing in the kneader 32 provided on the downstream side.

  The amount of slaked lime added is about 25 wt% or more of fly ash, preferably about 25 wt% to 40 wt%. This is the case where the inventors measured the fly ash melting start temperature by varying the amount of slaked lime added to the fly ash, and as a result, the actual measurement data shown in FIG. 4 was obtained. It was revealed that the melting point of fly ash rose to about 400 ° C or higher. FIG. 4 presents a part of the measured data, which is obtained from a temperature-differential thermothermal curve as shown in FIGS. FIG. 7 is a graph showing a temperature curve and a differential heat curve in this example (mixed with 26% slaked lime), FIG. 5 is a graph showing a temperature curve and a differential heat curve in Comparative Example 1 (no slaked lime added), and FIG. 6 is a comparative example. It is a graph which shows the temperature curve and differential heat curve in 2 (mixing 10% of slaked lime).

  The differential thermal curve is obtained by differential thermal analysis (DTA). Differential thermal analysis is a method of measuring the temperature difference between a sample and a reference material as a function of temperature while changing the temperature of the sample and the reference material according to a fixed program. It is an effective way to do. From the differential thermal curves shown in FIGS. 5 to 7, the fly ash transition temperature is obtained, and it can be seen that the melting start temperature is 327.6 ° C. in Comparative Example 1 in FIG. 5 where slaked lime is not added to the fly ash. 6 has a melting start temperature of 357.6 ° C., and in Example 1 of FIG. 7 in which the amount of slaked lime added to fly ash is 26%, the melting start temperature is 408.5. It turns out that it is ° C.

Further, based on other data actually measured by the present inventors, the fly ash melting start temperature is about 400 ° C. or higher from the temperature curve and differential heat curve graph (not shown) when the slaked lime addition amount is around 26%. It was found that the amount of slaked lime added was about 25 wt% or more.
Since the heating drum 24 operates at about 350 to 380 ° C., the melting point of the fly ash can be set to about 400 ° C. or more by using the slaked lime addition amount as described above. Therefore, stable operation of the thermal decomposition apparatus is possible.

It is a whole block diagram of the ash processing system provided with the thermal decomposition apparatus which concerns on the Example of this invention. It is a block diagram of the dioxin pyrolysis apparatus which concerns on Example 1 of this invention. FIG. 3 is a side sectional view (a) of the heating drum of FIG. It is a table | surface which shows the actual measurement data of the fly ash melting point with respect to the amount of slaked lime addition. It is a graph which shows the temperature curve and differential heat curve in the comparative example 1 (no slaked lime addition). It is a graph which shows the temperature curve and differential heat curve in the comparative example 2 (10% of slaked lime mixing). It is a graph which shows the temperature curve and differential thermal curve in a present Example (26% of slaked lime mixing).

Explanation of symbols

DESCRIPTION OF SYMBOLS 13 Melting furnace 16 Bag filter 21 Ash storage tank 22 Ash supply machine 24 Heating drum 25 Stirrer 26 Dust filter 27 Cooling drum 32 Kneading machine 33 Molding machine 41 Heating means 42 Rotating shaft

Claims (11)

The fly ash collected from the exhaust gas of the heat treatment furnace by the dust collector is introduced into the thermal decomposition apparatus, and the fly ash is heated in the thermal decomposition apparatus in an oxygen-deficient atmosphere while being stirred and contained in the fly ash. In the method of pyrolytic removal of dioxins,
The powder containing slaked lime (hereinafter referred to as slaked lime) is added to the fly ash collected by the dust collector directly or upstream of the pyrolyzer to add the melting point of the fly ash. A method for thermally decomposing dioxins contained in fly ash, characterized in that it is raised.   The method for thermally decomposing dioxins contained in fly ash according to claim 1, wherein the amount of slaked lime added is about 25 wt% or more of the fly ash. The fly ash collected from the exhaust gas of the heat treatment furnace by the dust collector is introduced into the thermal decomposition apparatus, and the fly ash is heated in the thermal decomposition apparatus in an oxygen-deficient atmosphere while being stirred and contained in the fly ash. In the method of pyrolytic removal of dioxins,
Contained in fly ash, which is characterized in that when fly ash is collected by the dust collector, slaked lime of about 25 wt% or more of the fly ash is added to the fly ash to increase the melting point of the fly ash. Thermal decomposition method of dioxins.   The temperature in the said thermal decomposition apparatus was about 350-380 degreeC, The thermal decomposition method of the dioxins contained in the fly ash in any one of the Claims 1 thru | or 3 characterized by the above-mentioned.   The method for thermally decomposing dioxins contained in fly ash according to claim 1 or 3, wherein the slaked lime is conveyed to an inert gas introduced into the thermal decomposition apparatus and added to the fly ash. . A pyrolysis apparatus having a heating means and a stirring means, wherein fly ash collected from a waste gas from a heat treatment furnace by a dust collector is heated with stirring in an oxygen-deficient atmosphere in the thermal decomposition apparatus, In a device for pyrolytic removal of dioxins contained in fly ash,
A means for adding slaked lime to the collected fly ash is provided upstream of the pyrolyzer or the pyrolyzer, and the melting point of fly ash in the pyrolyzer is increased. Thermal decomposition equipment for dioxins contained in flying ash.   The thermal decomposition apparatus for dioxins contained in fly ash according to claim 6, wherein the slaked lime addition means is means for adding slaked lime of about 25 wt% or more of the fly ash. A pyrolysis apparatus having a heating means and a stirring means, wherein fly ash collected from a waste gas from a heat treatment furnace by a dust collector is heated with stirring in an oxygen-deficient atmosphere in the thermal decomposition apparatus, In a device for pyrolytic removal of dioxins contained in fly ash,
In the fly ash, the means for adding slaked lime of about 25 wt% or more of the fly ash to the fly ash is provided in the dust collector, and the melting point of the fly ash in the thermal decomposition apparatus is increased. Equipment for thermal decomposition of dioxins contained.   The temperature in the said thermal decomposition apparatus was about 350-380 degreeC, The thermal decomposition apparatus of the dioxins contained in the fly ash in any one of Claim 6 thru | or 8 characterized by the above-mentioned.   The slaked lime addition means is an inert gas inlet provided in the thermal decomposition apparatus, and the slaked lime is added to the fly ash by being conveyed to an inert gas. A thermal decomposition apparatus for dioxins contained in the fly ash according to 8.   The heat of dioxins contained in fly ash according to claim 6 or 8, wherein a kneader for solidifying cement of fly ash discharged from the pyrolyzer is provided downstream of the pyrolyzer. Disassembly equipment.

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