JP4833093B2 - Waste incineration fly ash treatment method - Google Patents

Description

  The present invention relates to a method for treating waste incineration fly ash, and more particularly to a method for treating waste incineration fly ash for reducing the content of hexavalent chromium, dioxin and the like that are harmful substances in waste incineration fly ash.

  As is well known, fly ash generated when incinerating industrial waste and municipal waste is collected by a dust collector such as a bag filter disposed in an incinerator or the like.

  The collected fly ash contains harmful substances such as dioxins and heavy metals. The diffusion of these fly ash to the external environment causes environmental pollution. As a technology to suppress the diffusion of fly ash to the external environment, a technology (cement solidification method) that prevents fly ash from diffusing to the external environment by pelletizing fly ash with a binder such as cement or bentonite is known. It has been.

For example, in Patent Document 1, a municipal pellet incineration fly ash is added and kneaded with a binder such as carbon and cement and water to form a raw pellet, and then the raw pellet is heated at a high temperature of 900 to 1300 ° C. A municipal waste incineration fly ash sintering method characterized in that dioxins in raw pellets are thermally decomposed by sintering for more than a minute is described.
JP-A-6-39363

  By the way, municipal waste incineration fly ash contains harmful hexavalent chromium. When fly ash is pelletized by the cement solidification method, usually hexavalent chromium still remains in the pellet. Such pellets are usually landfilled in the soil or reused for applications such as concrete aggregates, roadbed materials, backfill materials, flower bed watering promoters, and the like. In any case, when hexavalent chromium remains in the pellet, the hexavalent chromium may diffuse into the soil due to the collapse of the pellet. The diffusion of hexavalent chromium has a problem of adversely affecting the environment.

  The present invention solves the above-mentioned problems, reduces the content of hexavalent chromium, dioxin, etc., which are harmful substances contained in waste incineration fly ash, and can form pellets that are not easily disintegrated. It is an object to provide a method for treating ash.

  The waste incineration fly ash treatment method of the present invention comprises a pellet granulation step of obtaining waste incineration fly ash pellets by blending and granulating powdered aluminum with waste incineration fly ash containing hexavalent chromium, and the waste incineration fly A reduction treatment step of reducing the hexavalent chromium to trivalent chromium by heat-treating the ash pellets at a temperature of 800 ° C. or higher and 1500 ° C. or lower. Thus, by mixing aluminum powder with the waste incineration fly ash containing hexavalent chromium and pelletizing it, and performing the heat treatment as described above, the hexavalent chromium contained in the waste incineration fly ash pellet is aluminum. It is reduced to harmless trivalent chromium by the reducing action. In addition, by heat treating the waste incineration fly ash pellets at the above temperature, harmful dioxins contained in the waste incineration fly ash are also thermally decomposed. Furthermore, since the compressive strength of the pellets obtained by using aluminum as a binder during firing is increased, it is possible to suppress the generation of dust due to the collapse of the pellets. For this reason, soil contamination due to the components contained in the pellets Reduce the possibility of

  Moreover, in the said processing method, it is preferable to provide the water solution process which collects the gas component which generate | occur | produces at the said reduction process process, and dissolves the collected gas component in water. By such a process, since lead chloride containing lead, which is a harmful heavy metal generated in the reduction treatment process, can be collected as an aqueous solution, lead chloride and the like can be easily separated.

  Moreover, in the said processing method, the mercury which evaporates mercury by further heat-processing the said waste incineration fly ash pellet at the temperature of 350 degreeC or more and less than 800 degreeC between the said pellet granulation process and the said reduction process process. It is preferable to provide a separation step. By such a process, mercury can be easily separated.

  The treatment method preferably includes a mercury recovery step of collecting mercury vapor generated in the mercury separation step and recovering mercury by liquefying the collected mercury vapor by cooling. By such a process, mercury can be easily recovered.

  According to the waste incineration fly ash treatment method of the present invention, harmful hexavalent chromium contained in waste incineration fly ash can be reduced to harmless trivalent chromium. At the same time, harmful dioxins are also thermally decomposed. Furthermore, since aluminum functions as a binder during firing, the resulting pellets have high compressive strength, and the generation of dust due to the collapse of the pellets is suppressed. Therefore, the contents of hexavalent chromium, dioxin, etc., which are harmful substances contained in the waste incineration fly ash, can be easily reduced, and the possibility of soil contamination can be reduced.

  Hereinafter, a preferred embodiment of the waste incineration fly ash treatment method of the present invention will be specifically described with reference to the schematic explanatory view of FIG.

  In FIG. 1, the kneading means 1, the granulator 2, and the waste incineration fly ash treatment apparatus 3 are disposed from the upstream side toward the downstream side, for carrying out the waste incineration fly ash treatment method of the present invention. An example of the process configuration is shown.

  In the pellet granulation step in the present invention, powder incineration fly ash discharged from a waste incineration facility is mixed with powdered aluminum, kneaded with a kneader and then granulated to a predetermined size by a granulator. This is a step of obtaining fly ash pellets, and is specifically performed as follows.

  In FIG. 1, a kneading means 1 is a means used for producing a waste incineration fly ash pellet, and a kneader 1a and a waste incineration fly ash silo 1b for supplying the waste incineration fly ash to the kneader 1a, It comprises a powder aluminum silo 1c for supplying powdered aluminum powder and a water supply tank 1d for supplying water.

  The silos 1b and 1c are each provided with an unillustrated quantitative feeder for controlling the supply amount at the bottom, and the supply amount of each component is controlled by the quantitative feeder. The water supply tank 1d is also provided with a control valve (not shown) for quantitatively supplying water.

  And each component of refuse incineration fly ash, powdered aluminum, and water is supplied to the kneader 1a from the silos 1b and 1c and the water supply tank 1d, and various components are kneaded by the kneader 1a and kneaded from the discharge port of the kneader 1a. The product M is discharged, and the discharged kneaded material M is supplied to the granulator 2 disposed on the downstream side of the kneading means 1. And it pelletizes to a desired shape with the granulator 2, and the waste incineration fly ash pellet P is obtained. As the kneader 1a, a single screw extruder, a twin screw extruder or the like is used. As the granulator 2, a known granulator such as various pelletizers or a vibration granulator is used.

  Waste incineration fly ash containing hexavalent chromium used in the present invention is waste incineration fly ash discharged from municipal waste incineration facilities, etc., and usually heavy metals such as hexavalent chromium, mercury, lead, dioxins, etc. Contains harmful substances.

  Moreover, the powder aluminum used for this invention is a component aiming at the reduction | restoration of the hexavalent chromium contained in a waste incineration fly ash to a trivalent chromium, when heat-treating a waste incineration fly ash pellet. Moreover, when a refuse incineration fly ash pellet is baked, it also has a function as a binder for maintaining the shape of a pellet.

  Powdered aluminum is considered to reduce hexavalent chromium to trivalent chromium by a so-called thermite reaction, which is known as a high-temperature reduction method for metal oxides. Therefore, by holding pellets obtained by granulating powdered aluminum and waste incineration fly ash at a temperature of 800 ° C. or higher at which the thermite reaction is activated, hexavalent chromium in the waste incineration fly ash is 3 It is thought that it is reduced to chromium. In addition, since the reduction reaction at this time is an exothermic reaction, the amount of heat given by the electric heating element or the like in the heat treatment step described later can be reduced by this amount of heat generation.

  Any powder aluminum can be used without particular limitation as long as it is commercially available as powder aluminum having a median particle diameter measured by a particle size distribution meter of about 0.2 to 100 μm. Moreover, it is preferable from the viewpoint of effective utilization of the aluminum waste material when the cutting waste (Dalai powder) produced when cutting an aluminum ingot or the like is preferably pulverized.

  The compounding quantity of powder aluminum will not be specifically limited if it is the range which can reduce | restore hexavalent chromium contained in refuse incineration fly ash to trivalent chromium. Specifically, since it depends on the content ratio of hexavalent chromium contained in the waste incineration fly ash, it cannot be specified unconditionally, but usually 0.5 parts by mass or more with respect to 100 parts by mass of the waste incineration fly ash It is preferable that In the case of the blending amount, it is considered that hexavalent chromium contained in the waste incineration fly ash is sufficiently reduced. Moreover, although the upper limit of the compounding quantity of powder aluminum is not specifically limited, From a viewpoint of economical efficiency, it is preferable that it is 10 mass parts or less, Furthermore, it is preferable that it is 5 mass parts or less.

  Furthermore, it is preferable to mix water in the waste incineration fly ash pellet in order to enhance the binding property of the pellet. In general, the amount of water to be blended is preferably 10 to 30 parts by mass with respect to 100 parts by mass of the waste incineration fly ash from the viewpoint of the binding property of the pellets.

  As the shape of the waste incineration fly ash pellet, when granulating using a pelletizer, a spherical shape having a diameter of about 10 to 20 mm, a cylindrical shape having a diameter of about 20 mm and a length of about 20 to 30 mm, and a vibration granulator In the case of granulating using, a massive shape having a diameter of about 5 to 50 mm can be mentioned.

  By subjecting the waste incineration fly ash pellets thus obtained to the heat treatment described below, the amount of hexavalent chromium contained in the pellets is reduced, and dioxins are also thermally decomposed.

  Based on FIG. 1, each heat treatment process in the present invention will be described.

  The waste incineration fly ash pellets P are supplied to a waste incineration fly ash treatment device 3 disposed on the downstream side of the granulator 2.

  The waste incineration fly ash treatment apparatus 3 is provided with a pellet rectification chamber 3a, a low temperature heat treatment chamber 3b, and a high temperature heat treatment chamber 3c that are independently temperature controlled from the upstream side to the downstream side. A grate 3e that circulates in the horizontal direction is provided as a basic configuration. The pellet rectifying chamber 3a has a pellet receiving port 3i, the low temperature heat treatment chamber 3b has a first duct 4a for collecting gas generated in the low temperature heat treatment chamber 3b, and the high temperature heat treatment chamber 3c has a high temperature heat treatment chamber. A second duct 4b for collecting the gas generated in 3c is provided. In addition, the waste incineration fly ash treatment apparatus includes a pre-heat treatment chamber controlled at a temperature of less than 350 ° C. for the purpose of removing moisture in the pellets further upstream from the low-temperature heat treatment chamber 3b, etc. The configuration may be added.

  The grate 3e is hung on a pair of left and right sprockets 3f and 3h, and is driven to circulate through the sprockets 3f and 3h by rotational driving of a driving means (not shown). The waste incineration fly ash pellet P supplied from the pellet receiving port 3i is loaded, and the waste incineration fly ash pellet P is transferred in the order of the pellet rectification chamber 3a, the low temperature heat treatment chamber 3b, and the high temperature heat treatment chamber 3c. Yes.

  Each of the pellet rectifying chamber 3a, the low temperature heat treatment chamber 3b, and the high temperature heat treatment chamber 3c has a refractory construction on the inner surface of the chamber, and a heat source such as an electric heating element (not shown) is disposed in each chamber. Be controlled. Further, as necessary, an inert gas may be blown into each room to reduce the oxidation of the powdered aluminum to create a reducing atmosphere.

  The pellet rectification chamber 3a is a chamber for adjusting the layer thickness of the pellets loaded on the grate 3e, the low temperature heat treatment chamber 3b is a chamber controlled at a temperature of 350 ° C. or higher and lower than 800 ° C., and the high temperature heat treatment chamber is The chamber is controlled at a temperature of 800 ° C. or higher and 1400 ° C. or lower.

  The layer thickness of the pellet P adjusted in the pellet rectifying chamber 3a is appropriately adjusted from the viewpoint of processing efficiency, but it is usually preferable to adjust the thickness to about 5 to 100 mm.

  The pellet rectifying chamber is preferably controlled at a temperature of 100 ° C. or lower, particularly 80 ° C. or lower, and further at a temperature near room temperature.

  The pellet P whose thickness is adjusted in the pellet rectifying chamber 3a is preferably treated in a mercury separation process described below in order to separate only the mercury contained in the waste incineration fly ash in advance.

  The mercury separation process is a treatment process provided as needed for the purpose of evaporating the mercury contained in the pellets P to separate and recover the mercury, and the boiling point of mercury (356 ° C.) at which mercury vaporization becomes intense. This is a step of heat treatment at a slightly lower temperature of 350 ° C. or higher, preferably 400 ° C. or higher and lower than 800 ° C.

  The treatment time for the mercury separation step is preferably about 10 to 120 minutes, and more preferably about 10 to 60 minutes. By performing heat treatment under the above conditions for the treatment time, mercury vapor can be recovered sufficiently with high treatment efficiency.

  In FIG. 1, the mercury separation step is performed in the low temperature heat treatment chamber 3b. The temperature control in the low temperature processing chamber 3b is, for example, provided with a temperature sensor in the low temperature heat processing chamber 3b and controlled to a preset temperature based on the temperature measured by the temperature sensor. In the temperature control, when the measured temperature is lower than a preset temperature, the amount of heat necessary for setting the preset temperature from a heat source such as an electric heating element is supplied to the low temperature heat treatment chamber 3b. Means such as reducing the amount of heat supplied from a heat source such as an electric heating element, or providing an intake / exhaust duct in the low-temperature heat treatment chamber 3b to lower the temperature to approach the set temperature by sucking air or the like from the outside Can be controlled.

  The low temperature heat treatment chamber 3b is provided with a first duct 4a for collecting a gas containing mercury vapor generated in the low temperature heat treatment chamber 3b, and the first duct 4a is provided with an induction fan through a cooling capacitor 6. 7 is communicated. The gas sucked and collected by the first duct 4a by the induction blower 7 is liquefied by the cooling condenser 6 provided in the middle of the path, and liquid mercury is recovered. The cooling condenser 6 is usually connected to a drain facility such as a drain tank 8 for removing water collected together with mercury.

  In this mercury separation process, since heat treatment is performed in a temperature range where mercury evaporates, mercury can be easily separated and recovered.

  And the waste incineration fly ash pellet from which mercury was separated in the mercury separation step in the low temperature heat treatment chamber 3b is transferred to the high temperature heat treatment chamber 3c and processed in the reduction treatment step.

  The reduction treatment step is a treatment step aimed at reducing hexavalent chromium to trivalent chromium by the reducing action of powder aluminum contained in the waste incineration fly ash pellets P, and thermally decomposing dioxin, Moreover, in this process, the compressive strength of a pellet is raised because aluminum functions as a binder.

  The reduction treatment step is a step controlled at a temperature of 800 ° C. or higher and 1500 ° C. or lower, preferably 1000 ° C. or higher and 1400 ° C. or lower. Moreover, in this process, lead chloride contained in the waste incineration fly ash evaporates.

  Here, since the powder aluminum in the pellet is confined in the pellet, the powder aluminum in the waste incineration fly ash pellet exists in a state where it is difficult to come into contact with oxygen. Therefore, most of the powdered aluminum contained in the waste incineration fly ash pellets is not oxidized and exists as a simple substance. And by heating the said pellet to 800 degreeC or more, the hexavalent chromium in a garbage incineration fly ash pellet is reduce | restored to trivalent chromium by the reduction | restoration effect | action of powder aluminum. Moreover, the dioxin contained in fly ash is also thermally decomposed by heat processing at 800 degreeC or more in this way.

  The treatment time in the reduction treatment step is preferably about 5 to 30 minutes, and more preferably about 5 to 20 minutes from the efficiency of the reduction reaction of hexavalent chromium to trivalent chromium.

  Note that the temperature control in the reduction process is performed in the same manner as the temperature control in the low temperature process described above.

  In this step, it is preferable that the gas of heavy metal compound such as lead chloride contained in the pellet is collected by the second duct 4b provided in the high temperature heat treatment chamber 3c.

  The second duct 4 b communicates with the induction blower 7 through the wet processing means 9. And the gas such as lead chloride sucked and collected by the second duct 4b by the induction fan 7 is dissolved in water by the wet processing means 9 provided in the middle of the path. Then, for example, by dissolving the dissolved lead chloride in an aqueous solution, the lead chloride is reduced to lead and can be recovered as metallic lead. Examples of the wet processing means 9 include various wet processing apparatuses such as a means for bubbling a gas component in water to make an aqueous solution, and a means for spraying water to make a gas component an aqueous solution. Since the suctioned and collected gas is at a high temperature, an air inlet may be provided for the purpose of cooling the high temperature gas.

  Next, the pellet P2 treated by the reduction treatment step suppresses the combustion reaction of the remaining powdered aluminum that has not contributed to the reduction reaction, and suppresses heat generation due to the combustion reaction, as a subsequent step of the high temperature heat treatment step, It is preferable to cool until it becomes about 30-200 degreeC. The cooling is performed, for example, in a cooling zone 3d provided on the downstream side of the high temperature heat treatment chamber 3c. The cooling is preferably performed by means of forced cooling by ventilation or water cooling. Moreover, in order to suppress that trivalent chromium is oxidized again and returns to hexavalent chromium, it is preferable to cool in a reducing atmosphere.

  Then, the cooled pellet P2 is sent to the storage silo 10.

  The heat-treated pellet P2 obtained by such a process is one in which harmful substances such as dioxin and hexavalent chromium are greatly reduced as compared with the pellet P before the treatment. In addition, since aluminum functions as a binder during firing, the heat-treated pellet P2 has a higher compressive strength than the pellet P before processing, and is a pellet in which generation of dust that is difficult to collapse is suppressed. Therefore, when it is landfilled, the environmental impact is low, and because harmful substances are greatly reduced, it can be safely used as a concrete aggregate, roadbed material, backfill material, flower bed watering promoter, etc. It can also be used.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited at all by the Example.

(Examples 1-12)
Based on the process shown in FIG. 2, waste incineration fly ash pellets were manufactured and heat-treated. Specifically, 100 parts of waste incineration fly ash collected from the bag filter of municipal waste incineration equipment (mass part, the same applies hereinafter), 0-5 parts of powdered aluminum with a median particle diameter of 18-41 μm shown in Table 1, water After adding 10-30 parts and knead | mixing with the uniaxial kneader 1a and obtaining the kneaded material M, it granulates to the spherical pellet of about 30 mm in diameter with the vibration granulator 2, and the waste incineration fly ash pellet P is made into Obtained.

  And the waste incineration fly ash pellet P was continuously supplied to the pellet receiving port 3i of the incineration fly ash pellet processing apparatus 3.

  The supplied waste incineration fly ash pellets P were loaded on the grate 3e and transferred from the pellet rectification chamber 3a to the high temperature heat treatment chamber 3c. In the pellet rectification chamber 3a, the thickness of the loaded waste incineration fly ash pellets P was adjusted to about 5 to 100 mm. Note that the temperature of the pellet rectification chamber 3a is not controlled and is around room temperature.

  The waste incineration fly ash pellets P loaded on the grate 3e that passed through the pellet rectifying chamber 3a were transferred to the adjacent high temperature heat treatment chamber 3c for processing in the reduction process. The pellets were passed through the high temperature heat treatment chamber 3c controlled at 1200 ° C. for 2 minutes or 5 minutes.

  The heat-treated waste incineration fly ash pellets P2 loaded on the grate 3e that passed through the high-temperature heat treatment chamber 3c were cooled in the cooling zone 3d, and then sent to the storage silo 10 and stored.

The pellet P2 stored in the storage silo 10 was evaluated by the following method.
[Measurement of hexavalent chromium and total chromium content]
According to T-Cr: 12.1.0 of the method described in the Circular Environment Pipe No. 127 “Revision of Bottom Sediment Survey Method”, the total chromium content is changed to Cr (VI ): The hexavalent chromium content was measured according to 12.3.1.
[Compressive strength]
Using a pellet tester (manufactured by Showa Keiki Co., Ltd.), which is a pellet compressive strength measuring device, the pellet was compressed under a compression speed of 10 mm / min, and the stress when the pellet collapsed was measured. The unit of Kg / p in Table 1 indicates the compressive strength per pellet.

(Comparative Example 1)
The above evaluation was performed by heat treatment in the same manner as in Example 1 except that the waste incineration fly ash pellets containing no aluminum powder were used.

(Comparative Example 2)
The said evaluation was performed about the waste incineration fly ash pellet P which has not performed the said heat processing.

  The evaluation results are shown in Table 1.

  From the results of Table 1, 11.6 ppm of hexavalent chromium content converted to the amount in the waste incineration fly ash was detected from the waste incineration fly ash pellet P which was not heat-treated in Comparative Example 2. On the other hand, the content of hexavalent chromium in the waste incineration fly ash pellets containing the aluminum powders of Examples 1 to 12 and heat-treated was 2 ppm or less.

  The compressive strength of Example 1 is 72.3 kg / p, whereas in Comparative Example 1 heat-treated under the same conditions except that it does not contain aluminum powder, it is 1.3 kg / p. It can be seen that the inclusion of aluminum powder significantly increases the compressive strength of the pellet and makes it difficult to collapse.

  From the above results, the waste incineration fly ash pellets obtained by the treatment method of the present invention are those in which the content of hexavalent chromium is greatly reduced, and the pellets have high compressive strength, so that they are difficult to disintegrate and dust. Occurrence can also be suppressed. Therefore, it turns out that it can use safely for uses, such as a concrete aggregate, a roadbed material, a backfilling material, and a flower bed watering promoter.

It is typical explanatory drawing which illustrates the process of the waste incineration fly ash pellet processing method of this invention. It is typical explanatory drawing which illustrates the process of the waste incineration fly ash pellet processing method used in the Example.

Explanation of symbols

M Kneaded material P Waste incineration fly ash pellet P2 Heat-treated waste incineration fly ash pellet Hg Mercury W1, W2 Water D1, D2 Damper 1 Kneading means 1a Kneading machine 1b Incineration fly ash silo 1c Powder aluminum silo 1d Water supply tank 2 Granulation Machine 3 Incineration fly ash treatment device 3a Pellet rectification chamber 3b Low temperature heat treatment chamber 3c High temperature heat treatment chamber 3e Grate 3f, 3h Sprocket 3i Pellet inlet 4a First duct 4b Second duct 6 Cooling capacitor 7 Induction blower 8 Drain tank 9 Wet treatment means 10 Storage silo

Claims (4)

A method for treating garbage incineration fly ash,
Waste incineration fly ash by mixing 0.5 to 10 parts by mass of powdered aluminum having a median particle diameter of about 0.2 to 100 μm with 100 parts by mass of waste incineration fly ash containing hexavalent chromium. Pellet granulating step to obtain pellets;
A waste incineration fly ash treatment method comprising: a reduction treatment step of reducing the hexavalent chromium to trivalent chromium by heat-treating the waste incineration fly ash pellets at a temperature of 800 ° C. to 1500 ° C. In the waste incineration fly ash treatment method according to claim 1,
A waste incineration fly ash treatment method comprising a water-soluble step of collecting a gas component generated in the reduction treatment step and dissolving the collected gas component in water. In the waste incineration fly ash treatment method according to claim 1 or claim 2,
The method further comprises a mercury separation step for evaporating mercury by heat-treating the waste incineration fly ash pellet at a temperature of 350 ° C. or higher and lower than 800 ° C. between the pellet granulation step and the reduction treatment step. Waste incineration fly ash treatment method. In the waste incineration fly ash treatment method according to claim 3,
A waste incineration fly ash treatment method comprising: a mercury recovery step of collecting mercury vapor generated in the mercury separation step, and recovering mercury by liquefying the collected mercury vapor by cooling.

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