JP2003269710A - Waste treatment device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress elution of harmful matter by improving treatment of fly ash collected by a heat recovering means of a waste treatment device. <P>SOLUTION: The waste treatment device is provided with a thermal decomposition furnace 1 for cracking waste, a combustion melting furnace 5 for burning cracked gas exhausted from the thermal decomposition furnace and melting at least noncombustible solid matter entrained in the cracked gas, and heat recovering means 9 and 11 for recovering heat of exhaust gas exhausted from the combustion melting furnace. The device is also provided with a sieve 31 classifying the fly ash that have settled in the heat recovering means, a fly ash returning means for melting the settled fly ash on the sieve by inputting it into the combustion melting furnace, and a chemical treatment means 33 for treating harmful matter by adding a chemical under the sieve. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waste treatment device, and more specifically, it stabilizes harmful substances in fly ash obtained by treating combustion exhaust gas produced by burning pyrolysis gas of waste. Related to conversion processing.

[0002]

2. Description of the Related Art As a waste treatment apparatus, a pyrolysis furnace thermally decomposes waste, a combustion melting furnace burns pyrolysis gas, and a non-combustible solid substance entrained in the pyrolysis gas is melted and treated. It is known that the heat of combustion exhaust gas discharged from the combustion melting furnace is recovered by a heat recovery means such as a waste heat boiler. Fly ash entrained in the combustion exhaust gas discharged from such a combustion melting furnace is collected by heat recovery means such as a waste heat boiler by gravity settling or inertial dust collection.
Since the fly ash thus collected contains harmful metals such as lead contained in the waste, it is necessary to carry out stabilization treatment to prevent elution of these harmful metals when, for example, landfill disposal. is there.

Therefore, conventionally, the desalination residue discharged from the bag filter type desalination apparatus for removing chlorine gas in the combustion exhaust gas provided on the downstream side of the heat recovery means is collected by the heat recovery means. It has been proposed to mix fly ash and treat with a chelating agent.

[0004]

However, when the fly ash collected by the heat recovery means is mixed with the desalting residue and stabilized by a chelating agent, the pH of the eluate becomes high (for example, 12 or more), There is a problem that lead (Pb) is easily eluted.

In particular, it has been found that among the fly ash collected by the heat recovery means, fly ash having a particle size of 1 mm or more has a high Pb concentration and Pb is easily eluted.

It was also found that if cement is added to the fly ash collected by the heat recovery means without mixing with the desalination residue, the pH of the eluate becomes 12 or more and Pb easily elutes. did.

[0007] Therefore, it is an object of the present invention to improve the treatment of fly ash collected by the heat recovery means of the waste treatment device to suppress the elution of harmful substances.

[0008]

In order to solve the above problems, the waste treatment apparatus of the present invention combusts a pyrolysis furnace for pyrolyzing waste and a pyrolysis gas discharged from the pyrolysis furnace. In addition, it comprises at least a combustion melting furnace for melting the incombustible solid matter entrained in the pyrolysis gas, and a heat recovery means for recovering the heat of the combustion exhaust gas discharged from the combustion melting furnace. A means for classifying the fly ash that has settled in the means, a fly ash reflux means for charging the settled fly ash on the sieve of the sieve and melting it in the combustion melting furnace, and a harmful agent by adding a chemical under the sieve of the sieve. It is characterized in that a medicine processing means for processing an object is provided.

That is, according to the present invention, since the fly ash captured by the heat recovery means contains particles having a large particle size, it may be difficult to suppress the elution of harmful metals such as Pb even if the chemical treatment is performed. It was made with a focus on many things. Therefore, the fly ash captured by the heat recovery means is classified by a sieve, and only the particles having a small particle size that can be stabilized by the chemical treatment are subjected to the chemical treatment to be stabilized and used as final waste such as landfill. On the other hand, the screen is characterized by being returned to the combustion melting furnace and being circulated, so that it is melted or finely pulverized in the process, so that it is easy to perform a treatment that does not require treatment or a chemical treatment. This also reduces the amount of drug used. The chemical treatment is generally a chelate treatment using a chelating agent, and the chelate treatment forms a complex to suppress the outflow of harmful metals such as Pb.

Here, the mesh opening of the sieve, that is, the mesh width is 1 m.
It is preferably m to 7 mm, more preferably 5 mm. In addition, a switching damper for switching the fly ash to either the fly ash recirculation means or the sieve is provided in the fly ash conveying path that has settled in the heat recovery means, and sulfur oxidation in the combustion exhaust gas discharged from the heat recovery means is provided. When the concentration of the substance or hydrogen chloride is higher than the set value, it is preferable to switch the switching damper to the sieve side. In other words, the concentration of Pb, etc. in the fly ash has a certain correlation with the concentrations of sulfur oxides and hydrogen chloride in the exhaust gas, so by analyzing the concentrations of sulfur oxides and hydrogen chloride in the exhaust gas, It is possible to estimate the concentration of Pb or the like in the ash. Therefore, when the concentration of Pb or the like in the fly ash is low, the concentration of Pb or the like in the fly ash is concentrated in order to circulate the collected fly ash in the combustion melting furnace to form molten slag. , Stop circulation and discharge to the outside of the system.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall system configuration diagram of the waste treatment device of the present invention. As shown in the figure, the pyrolysis drum 1 is a tubular container having a double structure with both ends closed, and is provided to be inclined by making one end slightly higher than the other end. An input port for appropriately crushed waste 3 is provided at one end side thereof, and an outlet port for a thermal decomposition gas generated by thermal decomposition of the waste substance 3 and an outlet port for a thermal decomposition residue are provided at the other end side. ing. A screw feeder that conveys waste is provided in the inner cylinder of the pyrolysis drum 1, and a large number of pipes that are parallel to the axis are arranged between the inner cylinder and the outer cylinder, and the inside of the pipe is a heat source for pyrolysis. The high temperature air flows from the other end side toward the one end side.

The pyrolysis gas discharged from the pyrolysis drum 1 is supplied to the combustion melting furnace 5, where it is combusted, and the incombustible solid matter contained in the gas is melted and discharged as slag 7. It is like this.

The high temperature air heater 9 is located in the downstream of the combustion melting furnace 5 and exchanges heat between the combustion exhaust gas discharged from the combustion melting furnace 5 and air, recovers the heat of the combustion exhaust gas and converts the high temperature air. It is designed to generate. The high temperature air is circulated and supplied to the thermal decomposition drum 1 as a heat source for thermal decomposition in the thermal decomposition drum 1. The high temperature air sent to the thermal decomposition drum 1 heats the waste material to thermally decompose it, and then returns to the high temperature air heater 9 to be heated again.

The waste heat boiler 11 is located downstream of the high temperature air heater 9, and the combustion exhaust gas discharged from the high temperature air heater 9 flows therethrough. A heat transfer tube through which water flows is arranged in the waste heat boiler 11, and heat of the combustion exhaust gas is recovered to generate steam 13, which is sent to a power generator (not shown).

The temperature reducing tower 15 sprays water on the combustion exhaust gas discharged from the waste heat boiler 11 to lower the temperature. The combustion exhaust gas whose temperature has been lowered in the temperature reducing tower 15 is guided to the dust removing bag filter 17 and fly ash is collected. The combustion exhaust gas dedusted by the dust removal bag filter 17 is guided to the desalination bag filter 19,
Hydrogen chloride contained in the combustion exhaust gas is removed by the reaction with the desalting agent. The combustion exhaust gas discharged from the desalination bag filter 19 is discharged from the chimney 23 to the atmosphere 25 via the induced air blower 21.

The fly ash captured by the heat recovery means of the high temperature air heater 9 and the waste heat boiler 11 passes through the pipe line and the switching damper 27.
Be transported to. The switching damper 27 is for switching the destination of the fly ash to be transported, one destination being the combustion melting furnace 5 and the other destination being the sieve 31. This switching is performed by a control signal from a control device (not shown) according to an analysis value of an analyzer 29 that analyzes sulfur oxides in the combustion exhaust gas flowing between the dust removing bag filter 17 and the desalting bag filter 19. Done.

The sieve 31 classifies the fly ash sent through the switching damper 27, and the upper portion of the sieve is conveyed to the combustion melting furnace 5, and the lower portion of the sieve is to a chemical treatment means 33 for performing chemical treatment with a chelating agent. Be transported. The sieve 31 is used for classification according to the particle size of fly ash, and a rod-shaped sieve formed in a comb shape, a wire net, a punch net, or the like is appropriately used. The openings of the sieve 31 are selected so as to remove fly ash that has a large particle size and cannot prevent the elution of lead even if the chemical treatment with a chelating agent is performed. For example, the opening of the sieve 31 is 1 mm or more and 7
The range is preferably not more than mm, and more preferably 5 mm.
Further, the sieve 31 is preferably provided so as to be inclined with respect to the horizontal direction so that the fly ash is not clogged with the sieve 31. In addition, for screening, either a fixed type, a vibration type, or a rotary type is used depending on the shape and properties of the fly ash.

The desalination residue discharged from the desalination bag filter 19 is conveyed to the ash processing device 35 and treated with chemicals. Further, the pyrolysis residue discharged from the pyrolysis drum 1 is sent to a separation facility 37, is transported to the outside of the system to reuse the metal 39 such as iron and aluminum, and the char that is unburned carbon is burned in a combustion melting furnace. It is designed to be transported to 5.

Next, the operation and features of the waste treatment apparatus thus constructed will be described. Combustible gas is generated from the waste material 3 that is pyrolyzed by the pyrolysis drum 1 and is sent to the downstream combustion-melting furnace 5. In the combustion melting furnace 5, the combustible gas and the char sent from the separation equipment 37 are burned, and the ash contained in the gas and the char is melted to generate the slag 7
Discharge as. The combustible gas burned in the combustion melting furnace 5 is a high temperature air heater 9 in the downstream as combustion exhaust gas,
The heat is recovered by the waste heat boiler 11. The temperature of the combustion exhaust gas from which the heat has been recovered is lowered in the temperature reducing tower 15, and is sent to the dust removing bag filter 17 to be removed of dust, and then sent to the desalting bag filter 19 for removing hydrogen chloride in the combustion exhaust gas to be oxidized. A desalting agent such as calcium is added for desalting treatment. The combustion exhaust gas after desalting is discharged from the chimney 23 to the atmosphere 25 by the induced blower 21.

Fly ash containing sulfur oxides, lead compounds and the like is mixed in the combustion exhaust gas discharged from the combustion melting furnace 5, and the high temperature air heater 9 and the waste heat boiler 11 which are the downstream of the combustion melting furnace 5. It is captured by gravity settling or the action of inertia. At this time, solids such as lead compounds are captured by the high temperature air heater 9 and the waste heat boiler 11. On the other hand, some of the sulfur oxides are attached to the fly ash and captured by the high temperature air heater 9 and the waste heat boiler 11, but the sulfur oxides in the form of gas such as sulfur dioxide are reduced in the downstream temperature. The ash treatment device 35 flows out to the tower 15, the dust removal bag filter 17, and the desalination bag filter 19 and is processed by the desalination bag filter 19 together with the desalination residue.
To be processed into medicine.

The fly ash thus captured by the high temperature air heater 9, the waste heat boiler 11, the temperature reducing tower 15, and the dust removing bag filter 17 is returned to the combustion melting furnace 5 without being discharged to the outside of the system. . However, since it is circulated without being discharged to the outside of the system, the concentrations of lead compounds and sulfur oxides in the fly ash circulating in the system become high.

Therefore, an analyzer 29 for analyzing the kind and amount of sulfur oxide in the combustion exhaust gas flowing into the desalting bag filter 19 is provided, and when the concentration of the predetermined sulfur oxide is equal to or higher than the set value, The sulfur oxides and lead compounds are discharged out of the system. In the present embodiment, the switching damper 27 is switched so that a part of the fly ash captured by the high temperature air heater 9 and the waste heat boiler 11 is extracted to the outside of the system. That is, when the amounts of sulfur oxides and lead compounds in the system increase, the amount of sulfur oxides analyzed by the analyzer 29 also increases. Therefore, when the analysis value of the analyzer 29 exceeds a predetermined value, the fly ash captured by the high temperature air heater 9 and the waste heat boiler 11 is switched by the control of the switching damper 27 by the control device (not shown), and the sieve. 31 and the chemical treatment means 33 to treat the chemicals and dispose of them in landfill. In this way, only the fly ash captured by the high temperature air heater 9 and the waste heat boiler 11 is taken out of the system because the fly ash contains a large amount of lead compounds, sulfur oxides, and the like.

The chemical treatment in the chemical treatment means 33 is for fixing metals such as lead contained in fly ash so that there is no risk of elution even if they are disposed of by landfill. For example, a chelate is added by adding a chelating agent. The reaction forms a complex to suppress the elution of lead and the like. However, among the fly ash captured, the one with a large particle size contains a lot of lead compounds,
There is a problem that the amount of the chelating agent used increases because it is easily eluted.

Therefore, in this embodiment, the sieve 31 is provided,
Fly ash having a particle diameter that is difficult to be treated with a chemical agent is separated and returned to the combustion melting furnace 5, and fly ash having a small particle diameter is supplied to the chemical treatment means 33. The size of the sieve 31 is 1 mm depending on the shape and properties of the fly ash discharged depending on the type of waste.
The range is preferably 7 mm or less and more preferably 5 mm.

Table 1 shows the high temperature air heater 5 and the waste heat boiler 1
1 shows the results of a Pb (lead) dissolution test based on the dissolution test of Notification 13 of the Environmental Agency for the fly ash captured in 1.

[0026]

[Table 1] Fly ash A in Table 1 is obtained by crushing the captured fly ash as it is without sieving, B is a ash having a mesh size of 5 mm and a ash having a particle size on the sieve of more than 5 mm, and C is a mesh size of 5 mm. Of the fly ash having a particle size of 5 mm or less under the sieve and subjected to chelation treatment with a chelating agent, and subjected to an elution test. The drug used was dithiocarbamic acid, and A, B and C were added in the same amount. Result is,
Only fly ash with a particle size of 5 mm or less is the standard value for landfill.
The value was 3 mg / L (liter).

As described above, if fly ash captured in a high temperature portion such as the high temperature air heater 9 and the waste heat boiler 11 is sieved and classified, and fly ash having a small particle size is treated with a chemical, it can be disposed of in landfill. The elution of Pb (lead) does not exceed the landfill standard value. Further, as for the amount of chemicals used, if classification is not carried out with a sieve, it is necessary to use a large amount in order to reduce the reference value, whereas fly ash classified with a sieve having a small particle size can reduce the amount of chemicals used.

In this embodiment, the sulfur oxide analyzer is used, but the present invention is not limited to this, and a hydrogen chloride concentration analyzer may be used. Experiments have confirmed that there is a correlation between the increase of lead compounds and sulfur oxides in the system and the increase of hydrogen chloride.

[0029]

According to the present invention, it is possible to improve the treatment of fly ash collected by the heat recovery means of the waste treatment device and suppress the elution of harmful substances.

[Brief description of drawings]

FIG. 1 is an overall system configuration diagram of a waste treatment device to which the present invention is applied.

[Explanation of symbols]

1 Pyrolysis drum 3 waste 5 Combustion melting furnace 7 slag 9 High temperature air heater 11 Waste heat boiler 13 steam 15 Temperature reducing tower 17 Dust removal bag filter 19 Desalination bag filter 21 Induction fan 27 switching damper 29 Analyzer 31 sieve 33 Medication processing means

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F23G 5/00 115 F23G 5/44 Z 5/14 5/50 F 5/44 F23J 1/00 A 5 / 50 B09B 5/00 N F23J 1/00 3/00 303L 304G F term (reference) 3K061 AA24 AB02 AB03 AC01 AC03 BA05 CA07 DA03 DA18 DA19 FA10 FA21 NA01 NA14 3K062 AA24 AB02 AB03 AC01 AC03 BA02 CA00 CB08 DA26 DA40 DB17 3K02 AB03 AC01 AC03 BA05 HA02 HA03 4D004 AA37 AA46 AB03 BA03 BA05 CA08 CA27 CA29 CA34 CB36 CC06 CC12 DA01 DA02 DA10 DA20 4D021 AA03 AB02 CA01 CA03 CA11 EA10

Claims (2)

[Claims] 1. A thermal decomposition furnace for thermally decomposing waste, and a combustion melting furnace for combusting the thermal decomposition gas discharged from the thermal decomposition furnace and melting at least the non-combustible solid matter entrained in the thermal decomposition gas. And a heat recovery means for recovering heat of combustion exhaust gas discharged from the combustion melting furnace, wherein a sieve for classifying fly ash settled in the heat recovery means, and a sieve of the sieve It is characterized in that a fly ash reflux means for charging the above settled fly ash into the combustion melting furnace for melting and a chemical treatment means for treating harmful substances by adding chemicals under the sieve are provided. Waste treatment equipment. 2. The fly ash that has settled in the heat recovery means is provided with a switching damper for switching the fly ash to either one of the fly ash recirculation means and the screen, and the fly ash is discharged from the heat recovery means. The waste treatment device according to claim 1, wherein the switching damper is switched to the sieve side when the concentration of sulfur oxides or hydrogen chloride in the combustion exhaust gas to be generated is equal to or higher than a set value.