JP2016019947A - Waste treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste treatment method for enabling long-term stable treatment of waste including heavy metal on a commercial scale to enable efficient recycling of heavy metal.SOLUTION: In performing thermal decomposition treatment of waste 2 including heavy metal, the waste 2 is supplied to a thermal decomposition furnace 1, and at least one treatment selected from combustion, gasification, melting is performed in the presence of chlorine or a chlorine compound under reduction atmosphere so as to generate chloride of heavy metal. Treatment processes from a thermal decomposition process in the thermal decomposition furnace 1 to a dust removal process in a dust collector 11 are performed under reduction atmosphere so as to trap the chloride of the heavy metal by the dust collector 11.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating waste containing heavy metals.

  In recent years, many waste treatment furnaces that thermally decompose general waste, industrial waste, etc. by combustion, gasification, or melting have been used. However, in these treatment furnaces, depending on the type of waste, fly ash dust adheres and accumulates on the inner wall of the duct through which the exhaust gas generated during the treatment passes, and the duct may be blocked. For example, waste paint (coating waste) generated when a bridge is repainted contains a large amount of lead and sometimes contains PCB. If such a waste or its pyrolyzate contains a large amount of low melting point substances (for example, lead dioxide has a melting point of 290 ° C.), these will evaporate in the furnace, and the evaporated part will be cooled. There is a problem that it adheres to the inner wall surface of the duct and then grows up to block the duct. In such a case, the operation of the processing furnace is forced to stop, and stable operation cannot be performed over a long period of time.

  In order to prevent such a problem, the low-boiling gaseous substance in the exhaust gas is cooled and solidified by blowing a coolant such as water or mist into the duct to prevent the duct from being blocked. It has been proposed to prevent (see, for example, Patent Documents 1 to 4) and scrape off deposits on the duct by a mechanical method (for example, Patent Document 5).

  However, in the method in which the refrigerant is blown into the inside of the duct, a sufficient blocking suppression effect may not be obtained depending on the type of waste and the blowing position of the refrigerant. For example, even if refrigerant is blown into the duct, the exhaust gas temperature is high in the vicinity of the duct entrance, so low-boiling substances in the exhaust gas may adhere to the duct entrance and eventually block the duct. There is. Similarly, in the method of blowing mist inside the duct, if the spreading angle of the mist to be blown is not properly set with respect to the inner diameter of the duct, refrigerant such as mist collides with and adheres to the inner wall of the duct and becomes non-evaporated water. It may be difficult to control the gas cooling device installed downstream of the furnace.

  On the other hand, when a low boiling point gaseous substance (metal fume) adheres to the inner wall of the duct and the duct is blocked, it is removed using a mechanical removing means. For example, Patent Document 5 discloses a duct cleaning device including a drive shaft having scraping blades inserted into a duct and drive means for rotating the drive shaft and reciprocating in the axial direction. Yes.

  In this method, since the drive shaft reciprocates while rotating, there is a possibility that the gas generated in the furnace leaks from the gas seal part or the outside air is sucked into the duct. In particular, in a furnace that generates CO gas during operation, there is a risk of leakage of CO gas to the outside. Further, when CO gas is to be reused as energy, inhaling external air leads to a reduction in energy of the obtained gas. Further, in this method, air for cooling the drive shaft is made to flow near the central axis of the drive shaft. However, when the inside of the duct is hot, the outer surface of the drive shaft may be thermally damaged. Conceivable. In particular, when the inside of the duct is significantly blocked, the load on the drive shaft must be increased, which increases the time required to remove the blocked object and further increases thermal damage. , Both device damage and gas leaks are significant

  In addition to this, when using a normal incinerator, combustion is performed using combustion air in the combustion process, but in order to prevent the adhesion of fly ash, discard so that the heavy metal concentration of fly ash dust is reduced. Adhesion clogging prevention is performed by adjusting operation such as the amount of objects. However, since it is in an oxidizing atmosphere, elution of heavy metals in fly ash dust occurs, and there is a problem that the amount of auxiliary agent needs to be increased to prevent this elution.

  In addition, as described above, in order to prevent adhesion clogging, the concentration of heavy metal in the fly ash dust must be lowered, so the concentration of heavy metal in the collected fly ash dust is low and is not suitable for recycled metal recycling. There is a problem that it must be disposed of in landfills.

JP 2001-033027 A JP 2002-349841 A JP-A-7-197046 JP-A-8-219436 JP 2002-168433 A

  An object of the present invention is to provide a waste treatment method for stably treating waste containing heavy metals on a long-term scale on a commercial scale and enabling efficient recycling of heavy metals. .

  The waste treatment method of the present invention that achieves the above object is a method for thermally decomposing waste containing heavy metals, supplying the waste to a pyrolysis furnace, in the presence of chlorine or a chlorine compound, and At least one treatment selected from combustion, gasification, and melting is performed in a reducing atmosphere to generate the heavy metal chloride, and the treatment steps from the pyrolysis step in the pyrolysis furnace to the dust removal step in the dust collector are performed. It is carried out in a reducing atmosphere, and the heavy metal chloride is captured by the dust collector.

  In the waste treatment method of the present invention, waste containing heavy metal is pyrolyzed in the presence of chlorine or a chlorine compound in a reducing atmosphere pyrolysis furnace, so that heavy metal (eg lead) is chloride (eg dichloride). Lead) is fixed in a stable form, and the steps from the pyrolysis step to the dust removal step are performed in a reducing atmosphere, so that heavy metal oxide is not generated and is recovered as fly ash dust. Since the heavy metal chloride contained in the fly ash dust has a high melting point, the heavy metal chloride does not adhere to the duct and can prevent the duct from being blocked, thereby enabling a long-term stable operation. Furthermore, since this fly ash dust has a higher concentration of heavy metals than before, it is sent to a smelting factory and can be reused as a metal recycling material for effective use.

  As a waste containing the heavy metal, a waste containing chlorine can be treated. By thermally decomposing waste containing heavy metal and chlorine, the generated hydrogen chloride and heavy metal can be reacted in a reducing atmosphere to obtain a heavy metal chloride. As a result, the amount of chlorine and chlorine compounds supplied to the pyrolysis furnace can be reduced or eliminated.

  Further, other waste containing chlorine can be supplied as the chlorine compound. Other waste containing chlorine can be added, and chlorine or hydrogen chloride derived from the other waste can be reacted with the heavy metal derived from the waste under a reducing atmosphere to obtain a heavy metal chloride. Thereby, it is possible to prevent shortage of chlorine or a chlorine compound that reacts with the heavy metal, and the heavy metal can be reliably chlorinated and stabilized in the pyrolysis furnace.

  Examples of heavy metals include lead. By treating the waste containing lead with the method of the present invention, the obtained effect can be further increased. Examples of such waste include waste paint, and waste paint containing PCB can also be treated.

  In the present invention, the concentration of heavy metals in the waste is not limited, and it can be processed up to 100% by weight. In addition, the waste itself can be treated instead of the ash obtained by incinerating the waste.

  In the present invention, since the heavy metal chloride supplemented in the dust removal step has a high content of heavy metal, it can be reused for metal recycling.

It is explanatory drawing which shows the system flow (with no waste heat recovery boiler equipment) for collect | recovering fly ash dust which illustrates embodiment of the waste processing method of this invention. It is explanatory drawing which shows the system flow (with waste heat recovery boiler equipment) for collect | recovering fly ash dust by the waste processing method which consists of another embodiment.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, the waste treatment system used in the treatment method of the present invention includes a pyrolysis furnace 1, a gas cooling device 7, and a dust removal device 11. The waste 2 containing heavy metal charged into the pyrolysis furnace 1 is treated with at least one selected from combustion, gasification, and melting to generate molten slag 3, molten metal 4, and exhaust gas 5. At this time, the organic matter contained in the waste 2 is gasified to produce a high calorie gas that can be used as fuel, and the formation of a pyrolysis zone is promoted. Ash and valuable metals in the waste 2 are converted into molten slag 3 and molten metal 4 and taken out of the pyrolysis furnace 1.

  The pyrolysis furnace 1 is maintained in a reducing atmosphere by supplying waste and coke and adjusting the supply amount of oxygen to be in an oxygen deficient state. Evaporated metals gasified at 850 ° C. or more in the furnace through this reducing atmosphere zone are transferred from the furnace outlet to the gas cooling device 7 through the duct 6 and cooled by the mist 9 supplied from the nozzle 8. The fly ash dust 12 cooled and solidified is taken out from the gas cooling device 7 and transferred to a metal recycling material. On the other hand, the cooled exhaust gas is transferred to the dust removing device 11 through the duct 10 and fine fly ash dust 12 is collected. The exhaust gas that has exited the dust removing device is guided to the halogen recovery device 14 and treated with the exhaust gas 15.

  In the present invention, the waste 2 is a waste such as a general waste or an industrial waste containing a high concentration of heavy metal. Specifically, waste paint (coating waste), shredder dust from discarded automobiles and home appliances, PCB contaminants, municipal waste represented by garbage, and plastic waste, iron scrap, incineration ash, earth and sand Including digging trash, sludge, sludge, steelmaking dust, medical waste, and even waste wood. Examples of the heavy metal include Pb, Zn, Cr and the like, and among them, waste containing Pb can be more efficiently treated. The heavy metal concentration in the waste is not particularly limited, but from the industrial value of fly ash, for example, if the zinc content is 35% or more, it becomes a valuable resource, and by making it 55% by weight or more, The industrial value is greatly increased, and an effect that cannot be obtained by the conventional processing method can be achieved. Moreover, the waste containing a heavy metal may contain chlorine with a heavy metal. For example, waste such as coating waste containing lead and PCB may be used. Note that PCB is pyrolyzed into hydrocarbons and chlorine in the pyrolysis zone of the pyrolysis furnace 1 preferably in a reducing atmosphere of 800 to 1600 ° C., and reacts with hydrogen to become hydrogen chloride.

  In the present invention, in the pyrolysis furnace 1, chlorine is reacted with heavy metal in a reducing atmosphere to be stabilized as chloride. As for the supply of chlorine to the pyrolysis furnace 1, the waste containing heavy metal may supply chlorine, chlorine or a chlorine compound, or other waste containing chlorine. Moreover, when the chlorine in the waste containing a heavy metal and other wastes is insufficient with respect to the heavy metal in a waste, chlorine or a chlorine compound can also be supplementarily added. Chlorine contained in these chlorine compounds and other wastes becomes hydrogen chloride gas or the like in the pyrolysis furnace 1 and reacts with heavy metals to produce heavy metal chlorides. The surplus of chlorine and hydrogen chloride is separated and removed from the exhaust gas by blowing an auxiliary such as slaked lime into the dust removal equipment 11 installed at the rear stage of the gas cooling device 7.

At this time, heavy metal (for example, Pb) and chlorine (Cl) are stabilized in the form of lead dichloride (PbCl ₂ ) through the following reaction. First, heavy metal (for example, PbS contained in coating film waste) in the waste once becomes lead oxide by combustion (for example, 2PbS + 3O ₂ → 2PbO + 2SO ₂ ). After this oxidation reaction, O is separated from Pb by the action of C and CO in a reducing atmosphere in which coke and the like existed (for example, PbO + C → Pb + CO, PbO + CO → Pb + CO ₂ ). Further, Cl in the waste or additionally added Cl promotes the chlorination reaction to stabilize Pb in the form of stabilized PbCl ₂ (for example, Pb + HCl → PbCl ₂ + 2H).

In a conventional furnace in an oxidizing atmosphere, Pb in the waste does not react with chlorine, but generates a simple oxide (for example, PbO ₂ ). For this reason, the melting point of PbO ₂ was as low as 290 ° C., and adhesion and elution into the duct occurred. On the other hand, stable PbCl ₂ is obtained by the method of the present invention, and its melting point is 501 ° C. (difference from the oxide PbO ₂ is about 200 ° C.), which prevents adhesion and elution in the duct. can do.

Since a normal furnace is an oxidation furnace in an oxygen atmosphere, heavy metal (for example, Pb) once becomes an oxide of PbO, and then becomes a Pb-containing oxide (PbO ₂ ). This Pb-containing oxide has a low melting point and adhesion, and there is a concern that the duct may be blocked. Furthermore, oxides of other heavy metals are easy to dissolve in water, and in many cases, it is difficult to pass the landfill standard, so it has been necessary to devise contrivances such as kneading with an elution inhibitor and increasing the amount. On the other hand, the furnace of the present invention is a furnace in a reducing atmosphere, and even the dust collector is in a reducing atmosphere. Further, as described above, chlorine coexists with lead. For this reason, lead is fixed in a stable form of chloride (for example, PbCl ₂ ), and is recovered as fly ash dust without adhering to the duct. Furthermore, this fly ash dust has a high lead concentration and is effectively used as a metal recycling material.

As described above, in the treatment method of the present invention, it is necessary to place a heavy metal (for example, Pb) in a reducing atmosphere and to make a coexistence atmosphere with chlorine. As a method for placing a heavy metal (for example, Pb) in a reducing atmosphere, for example, coke or charcoal is used as a waste auxiliary material in the furnace, combustion air is shut off, and the furnace is heated at a high temperature (for example, 2300 ° C.). The reduction reaction can be maintained in a so-called reduction furnace maintained in an oxygen deficient state. Further, for example, N ₂ is used as a gas used for the mist spray in the gas cooling device 7 so that there is no oxygen source, and the gas cooling device 7 to the dust collector 11 (bag filter) are maintained in a reducing atmosphere. I can do it.

  In the pyrolysis furnace 1, as a method for forming a coexistence atmosphere with chlorine, hydrogen chloride produced by pyrolysis can be used when chlorine is contained in the waste. Also, it is ideal if the equivalent of chlorine is adjusted according to the amount of heavy metal in the waste and the relationship of heavy metal: chlorine = 1: 1 is maintained in the equivalent ratio, but in reality the amount of heavy metal in the waste is Since it is only an estimate, after adding salt materials (chlorine, chlorinated products, chlorine-containing waste) excessively, after halogen reaction with heavy metals, after removing the reaction product with a dust removal device, surplus in the halogen recovery device It is also possible to employ a method of recovering the hydrogen chloride in the minute.

  The processing method of the present invention is not limited to the system flow shown in FIG. 1, and for example, the system flow illustrated in FIG. 2 can be used. In the example of FIG. 2, in addition to the embodiment of FIG. 1, a waste heat boiler 16 is installed between the pyrolysis furnace 1 and the gas cooling device 7. The configuration after the gas cooling device 7 is the same as that of the embodiment of FIG. In this example, it is possible to recover and use the waste heat in the exhaust gas 5 as the recovered steam 18 by the waste heat boiler 16.

  In a conventional waste processing method, when processing Pb-rich waste such as coating waste, lead becomes an oxide (lead dioxide) because of the oxidizing atmosphere. Since lead dioxide has a low melting point, it is scattered as liquid fly ash dust, and when the temperature drops, it adheres to the inner wall surface of the duct and solidifies, which may block the duct. For this reason, the operating conditions must be limited so that the heavy metal content in the fly ash dust is extremely low, and the fly ash dust collected by the dust collector is subjected to metal recycling to refine and recycle the heavy metals. It was difficult. On the other hand, as described above, the present invention can process high-concentration heavy metals (for example, lead), and can reliably recover heavy metals as chlorides with high contamination concentration. It is easy to recycle metal.

  By adopting the method of the present invention, it becomes possible to detoxify medical wastes, contaminated soil, and hazardous wastes such as polychlorinated biphenyls (PCB). Furthermore, it is also effective for the treatment of lead-containing waste (for example, coating film waste).

As waste, lead-containing waste paint (coating waste) containing PCB having the composition shown in Table 1 is treated using a smelting reduction pyrolysis furnace. This waste paint has a lead content of 30% by weight and further contains 300 ppm of PCB. The conditions of the smelting reduction pyrolysis furnace were as follows: pre-oxygen lance temperature 2300 ° C., charging point temperature 1600 ° C., negative pressure control CO ₂ / CO = 25% The concentration (ppm) of heavy metals in the obtained molten slag and the heavy metal components (ppm) in the fly ash dust were analyzed and are shown in Table 2.

As a result of continuously treating 10000 kg of the above-described coating film scraps under the operating conditions of 2000 kg / day, the fly ash dust captured by the dust collector was 460 kg / ton of coating film. In this fly ash dust, lead dichloride (PbCl ₂ ) was 402.65 kg / ton of coating film, and the ratio was 87.5 wt%. Furthermore, although the coating waste contained 300 ppm of PCB, the PCB concentration in the fly ash dust was 0.000067 ppm, and the decomposition rate of PCB was 99.99999%.

As can be seen from Tables 1 and 2, when the waste paint containing lead containing PCB is treated by the treatment method of the present invention, the heavy metal (lead) in the waste reacts with chlorine and can be recovered as stable PbCl _2. Therefore, blockage of the duct can be prevented. In addition, since the lead concentration is higher than in the past, it can be reused as a recycled metal material.

  On the other hand, when a waste paint containing lead containing the same PCB as described above is continuously incinerated under an oxidizing atmosphere and operating conditions of 2000 kg / day using an ordinary combustion furnace of approximately the same scale, approximately 30 hours. There is a concern that the duct with an inner diameter of 300 mm will be closed later and the operation must be stopped.

DESCRIPTION OF SYMBOLS 1 Pyrolysis furnace 2 Waste 3 Molten slag 4 Molten metal 5 Exhaust gas 6 Duct 7 Gas cooling device 8 Nozzle 9 Mist 10 Duct 11 Dust collector 12 Fly ash dust 13 Fly ash dust (metal recycling material)
14 Halogen recovery device 15 Exhaust 16 Waste heat boiler 17 Duct 18 Recovery steam

Claims (7)

  A method for thermally decomposing waste containing heavy metal, wherein the waste is supplied to a pyrolysis furnace, and at least one selected from combustion, gasification, and melting in the presence of chlorine or a chlorine compound and in a reducing atmosphere The heavy metal chloride is generated, and the treatment process from the pyrolysis process in the pyrolysis furnace to the dust removal process in the dust collector is performed in a reducing atmosphere, and the heavy metal chloride is collected in the dust collection process. A waste disposal method characterized by being captured by an apparatus.   The waste treatment method according to claim 1, wherein the waste contains chlorine.   The waste treatment method according to claim 1, wherein the chlorine compound is another waste containing chlorine.   The waste treatment method according to claim 1, wherein the heavy metal is lead.   The method for treating waste according to any one of claims 1 to 4, wherein a single heavy metal concentration in the waste is 35 wt% or more.   The waste treatment method according to claim 1, wherein the waste is waste paint and further contains PCB.   The waste processing method according to claim 1, wherein the heavy metal chloride supplemented in the dust removal step is reused for metal recycling.

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