JP2011156501A - Method for thermally treating contaminated soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new method for thermally treating contaminated soil which enables stable treatment to be performed by rationally carrying out the treatment of dust separated from an exhaust gas and minimizing the load variation of a heater, when cleaning the contaminated soil containing a volatile organic compound such as benzene or the contaminated soil containing tar or a cyanide etc. <P>SOLUTION: This method for removing a harmful substance contained in the contaminated soil S0 by thermal treatment involves the following procedures: first, the moisture content value of the material to be treated is measured prior to introducing it into a heater for performing the heating treatment, then a dust D contained in the exhaust gas of the heater is recovered. Further, the dust D is included in the material to be treated before introducing the dust D into the heater, and after the moisture content value of the material is thereby adjusted to a specified value, the material to be treated is introduced into the heater. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for purifying contaminated soil containing low-boiling volatile organic compounds such as benzene and high-boiling compounds such as tar and cyanide, and particularly for treating contaminated soil having a variation in moisture value. The present invention relates to a heat treatment method for contaminated soil that can be implemented rationally.

In the former site of a chemical factory, contaminated soil due to residual chemical substances immersed during operation may be found.
If such contaminated soil is left unattended, harmful substances will ooze out into the groundwater or be released into the air.
In order to remove the harmful substances, the contaminated soil is heat-treated.

At that time, the dust contained in the hot air exhausted from the heating device may still contain harmful substances that could not be removed by the heat treatment. Since the property of the to-be-processed object and dust after heat processing differs, the process using the apparatus only for dust processing is performed (for example, refer patent document 1).
In addition, as other treatment forms of the dust, cement solidification, chemical treatment, washing, etc. are also performed, and in order to perform such treatment, initial cost for construction of treatment equipment, for transportation There is a problem that not only the cost is increased but the entire processing flow becomes complicated.

By the way, the contaminated soil that is the object to be treated often has different moisture values, for example, in the ground surface layer portion and in the deep ground portion portion, so that the load of the heating device fluctuates and the operation control is performed. Sometimes it became difficult.
Therefore, in order to avoid such load fluctuations, lime and the like are mixed as a moisture adjusting agent in the contaminated soil before being charged into the heating device, and the moisture value is made uniform before being charged into the heating device. There are also attempts.
However, in this case, lime may be fixed in the heating device, and further, lime is mixed into the exhaust gas of the heating device, so that the load of the dust treatment facility increases or becomes complicated. There was a problem.

JP2002-219444

  The present invention has been made in view of such a background, and in purifying contaminated soil containing volatile organic compounds such as tar and benzene, cyanide compounds, etc., dust separated from exhaust gas is used. The technical problem is to develop a new method for heat treatment of contaminated soil, which can be performed stably by suppressing the load fluctuation of the heating device while rationally performing the above treatment.

  That is, the heat treatment method for contaminated soil according to claim 1 is put into a heating device for performing the heat treatment in a method for removing harmful substances contained in the soil by heat treating the contaminated soil. Measuring the moisture value of the previous object to be processed, collecting dust contained in the exhaust of the heating device, and mixing this dust into the object to be processed before being put into the heating device. The moisture value of the object is adjusted to a predetermined value and then put into the heating device.

In addition to the above requirements, the heat treatment method for contaminated soil according to claim 2 is configured to remove the dust from the heating device when the moisture content of the material to be treated before being put into the heating device is low. It is characterized by being mixed in the processed material.
The above problems can be solved by using the configuration of the invention described in each of the claims as a means.

First, according to the first aspect of the present invention, the load of the heating device can be reduced by setting the moisture value of the workpiece to be low, and the moisture fluctuation of the workpiece can be suppressed. A stable operation can be performed by reducing the load fluctuation of the heating device.
In addition, a dust-dedicated processing process or processing equipment is not required, and initial costs and running costs can be reduced.

  According to the second aspect of the present invention, in particular, in the case of an object to be processed having a low moisture value, if dust is mixed into the object to be processed, the object to be processed put into the heating device has a lower moisture value and is heated. Since the amount of dust generated from the apparatus increases and the dust collection system cannot be operated, this can be avoided. Moreover, the load fluctuation | variation of a heating apparatus can be reduced and the stable driving | operation can be performed.

It is a skeleton figure which shows a contaminated soil processing apparatus. It is a block diagram which shows a contaminated soil processing apparatus.

  The best mode of the heat treatment method for contaminated soil of the present invention is as shown in the following examples. However, it is possible to appropriately modify this example within the scope of the technical idea of the present invention. .

Hereinafter, the apparatus for implementing the heat treatment method of the contaminated soil of this invention is demonstrated based on drawing, and this invention is demonstrated with the operating state of this apparatus.
In the figure, what is indicated by a symbol M is a contaminated soil treatment device, and this is a classifier 1, a supply hopper 2, a first heating furnace 3, a conveyor device 4, a water addition device 5, and a second in the order in which the objects to be treated flow. A heating furnace 6, a cooling device 7, and a water supply device 8 are provided.
A dust collector 9 for removing dust D from the exhaust of the first heating furnace 3 is provided.
Such a contaminated soil treatment apparatus M is installed on or near a land contaminated with a low boiling point volatile organic compound such as benzene and a high boiling point compound such as cyanide or tar, and is excavated from the land. By treating the contaminated soil S0 with heat, the treated soil S3 from which the organic compound or inorganic compound has been removed is obtained, and the modified soil S4 is returned to the same moisture value as the contaminated soil S0 before the treatment. It is a device used when land is reformed by being backfilled.
In the present specification, the low boiling point volatile organic compound means a volatile organic compound having a boiling point temperature equal to or lower than that of water, and examples thereof include trichloroethylene and benzene.
The high boiling point compound means a compound having a boiling point higher than that of water, and examples include components or tars contained in heavy oil or light oil, and cyanide compounds such as potassium cyanide that cause hydrolysis in the presence of moisture. It is done.

Hereinafter, various members constituting the contaminated soil treatment apparatus M will be described in detail.
First, the classifier 1 will be described. This is a device for sieving the contaminated soil S0 as an object to be processed and sending the contaminated soil S0 having a predetermined particle size or less to the next step. Note that a soil mass having a predetermined particle size or more is sent to an appropriate pulverizer 10 and finely pulverized, and then supplied to the classifier 1 again.
In addition, a moisture meter 11 (infrared moisture meter or the like) is provided at an appropriate position on the transport path of the contaminated soil S0 discharged from the classifier 1.

  Next, the supply hopper 2 will be described. The supply hopper 2 comprises a screw conveyor 21 driven by a suitable motor at the bottom of the hopper 20, and the object to be processed accommodated in the hopper 20 is transferred to the screw conveyor. It is a device that discharges an appropriate amount according to the number of rotations of 21. A belt conveyor can be used instead of the screw conveyor 21.

Next, the first heating furnace 3 will be described. This is a device for vaporizing a low-boiling volatile organic compound and moisture. By supplying hot air from the combustion furnace 30 to the rotating cylinder 35, the rotating cylinder 35 is provided. It is the apparatus comprised so that the to-be-processed object might be heat-processed inside.
The combustion furnace 30 is lined with an appropriate refractory material, and the burner 31 burns fuel to heat the exhaust gas of the second heating furnace 6 sucked by the blower 32 to generate hot air at a desired temperature. It is a device to do.
Further, as an example, the rotary drum 35 is mounted on four support rollers 35a and is driven to rotate by a variable speed motor. Both ends of the rotary drum 35 are appropriately sealed at the boundary by lid members. It is blocked by the state.
In this embodiment, a rotary shaft 36 that is driven to rotate by a variable speed motor is provided so as to pass through the vicinity of the center of the rotary drum 35, and the rotary shaft 36 is provided with a stirring blade 37. .
The lid that closes both ends of the rotating drum 35 is formed with an inlet 33, an exhaust outlet 38 and an outlet 39, and a hopper 34 is provided so as to face the inlet 33.
Further, a temperature sensor 38a is provided in the vicinity of the exhaust port 38, and the burnup of the burner 31 is appropriately adjusted according to the detected value of the temperature sensor 38a.

Next, the conveyor device 4 will be described. As an example, a screw conveyor is applied. In this embodiment, the conveyor 41 that receives the dust D supplied from the dust collector 9 and is discharged from the conveyor 41. A conveyor 42 for receiving the dust D and the contaminated soil S1 discharged from the first heating furnace 3 is provided.
A feedback path 43 of dust D is formed between the discharge port 41a of the conveyor 41 and the supply hopper 2. The feedback path 43 supplies the dust D to the hopper 20 in a fixed amount. It is comprised by the appropriate conveying apparatus so that it can do.

Moreover, the said water addition apparatus 5 is an apparatus for adding a water | moisture content to the contaminated soil S1, provided with the screw conveyor 51 driven by a suitable motor in the bottom part of the hopper 50 as an example, and the contaminated soil S1 accommodated in the hopper 50 Is discharged according to the number of rotations of the screw conveyor 51.
A water supply port 52 is formed in the screw conveyor 51, and is configured such that water can be appropriately added to the contaminated soil S1 located in the screw conveyor 51.
The screw conveyor 51 is provided with a moisture meter 53 (infrared moisture meter or the like), and hydration is performed by the hydration device 5 in accordance with the moisture value of the contaminated soil S1 detected by the moisture meter 53.
Further, as will be described in detail later, the water supply device 5 is provided with two screw conveyors 51 independently, a water supply port 52 is formed for each, and a moisture meter 53 is provided.

Next, the dust collector 9 will be described. This is a device for collecting the dust D contained in the exhaust gas of the first heating furnace 3, and includes a cyclone 91 and a bag filter 92 as an example. The cyclone 91 is provided in the next stage of the exhaust port 38 in the first heating furnace 3, and the bag filter 92 is further provided in the next stage.
The gas that has passed through the bag filter 91 is rendered harmless by an appropriate exhaust gas processing device (not shown).
Depending on the properties of the object to be processed, either the cyclone 91 or the bag filter 92 may be used, or another dust collector may be applied.

Next, the second heating furnace 6 will be described. This apparatus is an apparatus for decomposing and / or vaporizing a high boiling point compound.
Specifically, by supplying the contaminated soil S2 discharged from the water adding device 5 into the rotary drum 61, and supplying the hot air generated by the burner 67b into the jacket body 62 surrounding the rotary drum 61. It is the apparatus comprised so that the contaminated soil S2 could be heated indirectly. The rotating drum 61 is placed on four support rollers 61a and is driven to rotate by a variable speed motor. Both ends of the rotating drum 61 are closed with the boundary portion appropriately sealed by a lid member. It is peeling off.
In this embodiment, a lifter is provided on the inner peripheral surface of the rotating drum 61, and the contaminated soil S2 is stirred and fed as the rotating drum 61 rotates.
An inlet 63, an outlet 64, and an outlet 65 are formed in the lid that closes both ends of the rotating drum 61.
Further, the inside of the jacket body 62 is partitioned into a plurality of spaces by a partition plate 66, and an air supply port 67 and an exhaust port 68 are formed for each space, and a burner 67b is provided inside the air supply port 67. Is provided.
A burner fan 67 a is connected to the air supply port 67.
Further, a circulation blower 69 is connected to the exhaust port 68 through an appropriate pipe line, and the hot air exhausted from the exhaust port 68 is supplied from the input port 63 into the rotary drum 61 by the circulation blower 69. ing.
And by adopting such a configuration, the hot air sent into the rotary drum 61 by the circulation blower 69 directly heats the contaminated soil S2 in the rotary drum 61, and also decomposes vaporized substances that have been decomposed and vaporized by heating. Accompanying, exiting the exhaust port 64 and sent to the blower 32.

Next, the cooling device 7 will be described. This device is for cooling the treated soil S3 discharged from the second heating furnace 6, and as an example, a drum cooling device 70 and a screw cooling device. It is comprised with 75.
First, the drum-type cooling device 70 is one in which the treated soil S3 is supplied into the rotary drum 71, and a cooling medium such as water supplied from the water supply port 72a in the jacket body 72 surrounding the rotary drum 71. This is an apparatus configured to be able to indirectly cool the workpiece.
The rotating drum 71 is mounted on four support rollers 71a and is driven to rotate by a variable speed motor. Both ends of the rotating drum 71 are appropriately sealed at the boundary by lid members. These lids are formed with an inlet 73 and an outlet 74.
In addition, the jacket body 72 is divided into two parts along the longitudinal direction of the rotary drum 71, and a water supply port 72a and a drain port 72b are formed in each divided part.
In this embodiment, a lifter is provided on the inner peripheral surface of the rotating drum 71, and the treated soil S3 is stirred and fed as the rotating drum 71 rotates.

  The screw-type cooling device 75 is configured by surrounding a screw conveyor 76 with a jacket body 79, and before the treated soil S3 charged into the charging port 77 is discharged from the discharging port 78. The apparatus is configured to be indirectly cooled by a cooling medium such as water. The cooling medium (water W) is supplied from a water supply port 79a formed in the jacket body 79, and is discharged to the outside through a discharge port 79b.

Next, the water supply device 8 will be described. In this device, a water supply port 81 is formed on the side periphery of the screw conveyor 80, and the treated soil S3 charged into the input port 82 is discharged from the discharge port 83. In the meantime, the water content of the treated soil S3 can be increased.
It should be noted that a moisture meter 85 for measuring the moisture value of the treated soil S <b> 3 to be input to the input port 82 is provided at an appropriate location near the input port 82.

And in this embodiment, due to the difference in processing capacity per unit time between the first heating furnace 3 and the second heating furnace 6, between the water adding device 5 and the water supply device 8 as shown in FIG. Two devices were arranged in parallel.
Specifically, two second heating furnaces 6 and two cooling devices 7 are provided side by side (second heating furnace 6B, cooling device 7B (drum-type cooling device 70B, screw-type cooling device 75B)). In addition to providing two screw conveyors 51 in the hydration apparatus 5, the output destinations are distributed to the second heating furnace 6 and the second heating furnace 6B. The screw conveyor 80 in the water supply device 8 is supplied with treated soil S3 from both the screw cooling device 75 and the screw cooling device 75B.

The contaminated soil treatment apparatus M provided for carrying out the present invention has the above-described configuration as an example, and while explaining the operating state of this apparatus, the contaminated soil heat treatment of the present invention is also described below. A method will be described.
[Classification process and moisture adjustment]
First, the classifier 1 performs sieving of the contaminated soil S0, which is an object to be treated, and the contaminated soil S0 having a predetermined particle size or less is sent to the supply hopper 2. A soil mass having a predetermined particle size or more is appropriately sent to the pulverizer 10, pulverized, and then supplied to the classifier 1 again.
The contaminated soil S0 discharged from the classifier 1 has a moisture value measured by the moisture meter 11, and when this value is equal to or greater than a predetermined value (25% WB as an example). The dust D discharged from the dust collector 9 is mixed into the contaminated soil S0 before being put into the first heating furnace 3, and is sent from the classifier 1 to the supply hopper 2 using a control device (not shown). According to the amount of the contaminated soil S0, an appropriate amount of dust D is supplied to the hopper 20 through the feedback path 43. By such an operation, the moisture value of the contaminated soil S0 is adjusted to be a predetermined value or less. Further, the dust D that has not been distributed to the feedback path 43 is supplied to the water adding device 5 via the conveyor 42.
On the other hand, when the moisture value of the contaminated soil S0 discharged from the classifier 1 is equal to or less than a predetermined value (for example, 25% WB), the feedback of the dust D is not performed. In this case, especially in the case of the contaminated soil S0 having a low moisture value, it is possible to avoid further lowering the moisture value, and the load fluctuation of the first heating furnace 3 can be reduced and a stable operation can be performed. Further, stable operation can be performed without causing troubles such as blockage due to an increase in the amount of dust D scattered to the dust collector 9.

[Water and low boiling point volatile organic compound removal step]
Next, the contaminated soil S0 is supplied from the supply hopper 2 to the first heating furnace 3 and comes into contact with hot air of about 800 ° C. supplied from the combustion furnace 30 in the rotary drum 35. Further, the rotation of the rotary drum 35 and the stirring blade 37 are contacted. The heat treatment is performed while being crushed and stirred by the action.
At this time, low-boiling volatile organic compounds such as benzene and moisture are volatilized (vaporized) and removed from the soil components.
As described above, in the low boiling point volatile organic compound removing step, the load on the first heating furnace 3 is reduced by setting the moisture value of the contaminated soil S0 to a low moisture value, and the moisture fluctuation of the contaminated soil S0 is also reduced. Is suppressed, load fluctuation of the first heating furnace 3 is reduced, and stable operation is performed.
Thereafter, the moisture value is 5% W.V. as an example. B. The contaminated soil S <b> 1 set as follows is discharged from the discharge port 39 and sent to the conveyor 42.
Note that the moisture value of the contaminated soil S1 at this time is close to a value suitable for treatment in the high boiling point compound removal step described later, and does not exceed this suitable value (for example, 5% WB). In addition, the contaminated soil S0 is dried by the first heating furnace 3.

[Separation process]
On the other hand, the exhaust gas (about 200 ° C.) discharged from the exhaust port 38 is sent to the cyclone 91 to separate the dust D, and the separated dust D is sent to the conveyor 41.
The exhaust gas is sent from the cyclone 91 to the bag filter 92 to further separate fine dust D. The separated dust D is sent to the conveyor 41. A part of the dust D discharged from the discharge port 41a in the conveyor 41 is fed back as described above. The exhaust gas discharged from the bag filter 92 is subjected to deodorization processing and harmful component combustion processing by an appropriate device (not shown) and then exhausted to the atmosphere.

[Mixing and water addition process]
Next, the dust D and the contaminated soil S <b> 1 are mixed on the conveyor 42 and are put into the hopper 50 of the water adding device 5. The moisture value of the contaminated soil S1 in the hopper 50 is measured by the moisture meter 53 while being sent by the screw conveyor 51.
If the measured moisture value is lower than a value suitable for processing in the high boiling point compound removing step (for example, 5% WB), water W is supplied to the water supply port 52 to contaminate soil S1. Is adjusted to a value suitable for the treatment in the high boiling point compound removing step.
Then, the contaminated soil S2 having a desired moisture value is sent to the second heating furnace 6.
The contaminated soil S1 and dust D discharged from the first heating furnace 3 are temporarily stored in the hopper 50 of the hydration apparatus 5 and then hydrated while being quantitatively cut out (conveyed) by the screw conveyor 51. Thus, contaminated soil S2 having a constant moisture value can be obtained. This also makes it possible to perform processing in the second heating furnace 6 stably and efficiently.

[High boiling point compound removal process]
For example, hot air of 450 ° C. is supplied to the second heating furnace 6 by the burner 67b, and the temperature of the contaminated soil S2 charged into the rotary drum 61 is raised to 400 ° C.
For this reason, the cyanide compound which is an example of the high boiling point compound contained in the contaminated soil S2 has a moisture value of 5% W.W. B. In this state, heat at 400 ° C. is applied, causing hydrolysis and decomposition, and further vaporization.
Further, when the contaminated soil S2 contains a high boiling point compound such as tar, this is thermally decomposed and further vaporized.
At this time, the hot air exhausted from the exhaust port 64 is sent to the blower 32 in the first heating furnace 3, and the temperature of the exhaust is increased by the combustion of fuel in the burner 31. Compared to the case, fuel consumption can be greatly reduced.
Further, the hot air exhausted from the exhaust port 68 is supplied to the input port 63 by the circulation blower 69 to directly heat the contaminated soil S2 and function as a carrier gas, and then to the blower 32 in the first heating furnace 3 from the exhaust port 64. Sent.
Thus, the to-be-processed object from which the high boiling point compound was removed in the 2nd heating furnace 6 becomes processed soil S3, is discharged | emitted from the discharge port 65, and is sent to the cooling device 7 (at this time of processed soil S3) As an example, the temperature is 350 ° C.).

[Cooling process]
The treated soil S3 is initially charged into the drum-type cooling device 70, and water W is supplied to the water supply port 72a in this device, and the treated soil S3 is charged into the rotary drum 71. The soil S3 is cooled, and finally discharged from the discharge port 74 in a state of 80 ° C. as an example.
Next, the treated soil S3 is put into a screw type cooling device 75, and water W is supplied to the water supply port 79a in this device, and the treated soil S3 is cooled and finally at room temperature ( It is discharged from the discharge port 78 in a state of about 30 ° C.).
In this way, by indirectly cooling the object discharged from the high boiling point compound removing step (second heating furnace 6), water evaporation that occurs when water W is added is prevented, and the object to be processed is The treated soil S3 can be set to a desired moisture value. For this reason, since evaporation of moisture in the cooling process can be suppressed, an exhaust process for the evaporated moisture becomes unnecessary.
Moreover, while being able to utilize the cooling water used for indirect cooling in another process, the cooling water heated up after cooling can also utilize the heat effectively.

[Water supply process]
Next, the treated soil S3 is sent to the water supply device 8, where the moisture value is measured by the moisture meter 85, and water is supplied according to this value, before the treatment by the first heating furnace 3 is performed. Moisture value of contaminated soil S0 of 25% W. B. An appropriate amount of water W is supplied to the water supply port 81 so as to have the same value.
In addition, when the moisture value of the contaminated soil S0 supplied to the contaminated soil treatment device M changes, the contaminated soil S0 uses the classifier 1 to cool the moisture value of the contaminated soil S0 measured by the moisture meter 11 as a cooling device. After the passage time until the water is discharged from 7, the modified soil having the same moisture value as the moisture value at the time of supply can be obtained by reflecting the amount of water added to the treated soil S3 by the water supply device 8.

  Thus, the modified soil S4 obtained by decomposing and removing the low-boiling volatile organic compounds and the high-boiling compounds from the contaminated soil S0 can be obtained, and the modified soil S4 can be sprinkled appropriately to prevent drying. Soil modification will be carried out by backfilling the soil in the original place.

In the above-described embodiment, the moisture value of the dust D discharged from the dust collector 9 is 0 to 5% W.W. B. However, since the moisture measurement on the conveyor 41 is omitted, the accuracy of moisture adjustment of the contaminated soil S0 can be improved by providing the conveyor 41 with a moisture measuring unit as appropriate.
In the above-described embodiment, only the dust D discharged from the conveyor 41 is fed back to the supply hopper 2, but a mixture of the contaminated soil S1 and dust D discharged from the conveyor 42 may be fed back.

M Contaminated Soil Treatment Equipment 1 Classifier 10 Crusher 11 Moisture Meter 2 Supply Hopper 20 Hopper 21 Screw Conveyor 3 First Heating Furnace 30 Combustion Furnace 31 Burner 32 Blower 33 Input Port 34 Hopper 35 Rotating Body 35a Support Roller 36 Rotating Shaft 37 Agitation Wing 38 Exhaust port 38a Temperature sensor 39 Discharge port 4 Conveyor device 41 Conveyor 41a Discharge port 42 Conveyor 43 Feedback path 5 Hydrating device 50 Hopper 51 Screw conveyor 52 Water supply port 53 Moisture meter 6 Second heating furnace 6B Second heating furnace 61 Rotating drum 61a Support roller 62 Jacket body 63 Input port 64 Exhaust port 65 Discharge port 66 Partition plate 67 Air supply port 67a Burner fan 67b Burner 68 Exhaust port 69 Circulating blower 7 Cooling device 7B Cooling device 70 Drum type cooling device 70B Drum type cooling device 71 Rotating body 71a Support roller 72 Jacket body 72a Water supply port 72b Drain port 73 Input port 74 Discharge port 75 Screw type cooling device 75B Screw type cooling device 76 Screw conveyor 77 Input port 78 Discharge port 79 Jacket body 79a Water supply port 79b Drain port 8 Water supply device 80 Screw conveyor 81 Water supply port 82 Input port 83 Discharge port 85 Moisture meter 9 Dust collector 91 Cyclone 92 Bag filter D Dust S0 Contaminated soil S1 Contaminated soil S2 Contaminated soil S3 Treated soil S4 Modified soil W Water

Claims (2)

  In the method of removing harmful substances contained in the soil by heating the contaminated soil, the moisture value of the object to be treated before being put into the heating device for performing the heat treatment is measured, and After collecting the dust contained in the exhaust of the heating device and mixing this dust into the workpiece before being put into the heating device, the moisture value of the workpiece is adjusted to a predetermined value, A method for heat treatment of contaminated soil, characterized in that the method is put into the heating device.   2. The heating of contaminated soil according to claim 1, wherein the dust is mixed into the workpiece discharged from the heating device when the moisture value of the workpiece before being put into the heating device is low. Processing method.

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