JP2013100203A - Solid-liquid separation method for silicon slurry and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-liquid separation method for silicon slurry which is capable of recycling silicon slurry with a simple structure and to provide an apparatus therefor.SOLUTION: The solid-liquid separation apparatus 10 includes a silicon slurry stock solution tank 12, a reaction tank 20, an acidic solution tank 22, a neutralization tank 30, a neutralizing agent solution tank 32, a thermal decomposition machine 40, and a hot blast generating furnace 50. The silicon slurry containing a solid component and a liquid component is sufficiently reacted with the acidic solution in the reaction tank 20, then neutralized in the neutralization tank 30 by the neutralizing agent and subsequently the liquid component is vaporized by the thermal decomposition machine 40. Thus the silicon slurry is separated into solid and liquid. The solid component that is obtained by the solid-liquid separation is a powder material and includes silicon powder as a main ingredient. Therefore, the silicon powder can be recycled from the silicon slurry. Also when the vaporized liquid component is distilled, oil can be recovered and recycled as a resource.

Description

  The present invention relates to a solid-liquid separation method and apparatus for reusing silicon slurry as a resource.

When manufacturing a solar panel used for photovoltaic power generation from a silicon ingot or manufacturing a large-scale integrated circuit from a silicon wafer, the silicon ingot is thinly cut using a wire saw and the silicon wafer is polished. At this time, the cutting operation is performed while supplying cutting oil, and the polishing operation is performed while supplying abrasive grains and a water-soluble or oil-based dispersant, so that these waste liquids are collected as by-products such as silicon powder and abrasive grains. A silicon slurry containing a solid component made of a solid material and a liquid component made of a liquid such as a cutting oil or a dispersant is discharged.
Most of the silicon slurry is disposed of. However, since the silicon slurry contains many organic and inorganic substances such as silicon powder, abrasive grains, cutting oil, and dispersant, the environmental impact due to disposal is a problem. Further, even if it is attempted to render the silicon slurry harmless in consideration of environmental problems, the processing requires a great deal of cost and equipment.
Therefore, in order to make this silicon slurry reusable as a resource, a method for recovering silicon powder from the silicon slurry has been proposed, and examples thereof include the following. In the present specification, the term “silicon slurry” includes silicon sludge in which the components contained in the silicon slurry are coagulated and settled.

JP 2001-278612 A JP 2004-174300 A JP2007-246366 JP2008-162813

Patent Document 1 discloses an organic solvent cleaning step in which a solid content obtained by solid-liquid separation of a silicon slurry is used to wash the solid content with an organic solvent, and a dispersant contained in the solid content is removed. A silicon recovery method is disclosed that includes a separation step of removing silicon oxide and abrasive grains from the solid content after the step is performed to obtain a powder mainly composed of silicon.
Patent Document 2 discloses a method of obtaining a dried silicon slurry having a low oxygen concentration by maintaining a silicon slurry excluding moisture in a vacuum state at a temperature of 1500 K or higher.
Patent Document 3 discloses a method for reliably removing water-soluble coolant in order to recover a silicon-containing material that is a solid content from a silicon slurry.
According to Patent Document 4, if the liquid component is not removed from the silicon slurry, it is put into the oven of the dryer as it is, and if the rotation speed during stirring is controlled according to the heating temperature, the metal silicon particles contained in the silicon slurry It is said that silicon oxide grains can be generated by oxidizing the above.

  As shown in Patent Documents 1 to 3, conventionally, when collecting silicon powder from silicon slurry, first, the liquid component was removed, and the remaining solid component cake was washed and dried. It is not easy to remove the liquid component from the silicon slurry, and a number of processes such as filtration and centrifugation are required. Therefore, there is a problem that large-scale equipment, cost, and time are required.

  Therefore, a silicon slurry drying method as disclosed in Patent Document 4 has been devised. However, since the number of rotations must be controlled according to the heating temperature, there is a problem that the management is difficult. This method can be applied only when the silicon slurry does not contain oil. This is because if the silicon slurry containing the oil is dried, the oil and oxygen react and burn, and in the worst case, there is a risk of a fire or explosion of the dryer. .

Here, all petrochemical product wastes such as waste oil and used plastic packaging containers invented by the applicant can be pulverized and put into the furnace as they are, and can be pyrolyzed, refined oil, gas, And an apparatus capable of producing a carbonized product (Japanese Patent Laid-Open No. 2011-6528).
However, when the silicon slurry is put into the furnace of this apparatus as it is and processed, the solid component and the liquid component can be separated, but in the process of thermal decomposition, the solid mainly composed of silicon powder remaining in the furnace. There arises a problem that the components cause some chemical reaction and solidify firmly in a state where they are stuck in the furnace, and the solid components cannot be taken out.

  As described above, it is difficult to recycle silicon slurry, and many facilities are required. In addition, since a recycling technology with a simple configuration has not yet been established, there is a reality that a large amount of silicon slurry is still disposed of and has an adverse effect on the natural environment.

  In view of the above-described problems of the prior art, an object of the present invention is to provide a silicon slurry solid-liquid separation method and apparatus capable of recycling the silicon slurry with a simple configuration.

  In the present invention, an acidic solution is added to a silicon slurry containing a solid component containing silicon powder and a liquid component containing cutting oil or a dispersant, and then neutralized by adding a neutralizer solution, and then thermally decomposed. The above-mentioned problems have been solved by a solid-liquid separation method for silicon slurry, characterized in that the liquid component is vaporized to separate the solid component and the liquid component. The reaction vessel for adding an acidic solution to a silicon slurry containing a solid component containing silicon powder and a liquid component containing a cutting oil or a dispersant according to claim 2, and neutralizing the silicon slurry to which the acidic solution is added A neutralization tank for adding the agent solution, and a cylindrical heating tank having a heat transfer surface on the inner peripheral surface for thermally decomposing the silicon slurry to which the neutralizer solution is added, and provided at the center of the heating tank. A plurality of base blades are attached to the rotating shaft, and when the base blades rotate, the silicon slurry to which the neutralizer solution is added is scooped up and pressed against the heat transfer surface on the inner periphery of the heating tank by centrifugal force. It is preferable that the solid-liquid separation method is carried out by a solid-liquid separation device including a pyrolyzer having a structure.

  Moreover, it is preferable to set it as the solid-liquid separator provided with the distillation apparatus which distills the thermally decomposed and vaporized liquid component like Claim 3, Furthermore, it collects with a distillation apparatus like Claim 4. The non-condensable gas may be used as a fuel for a hot air generating furnace that generates hot air that heats the heat transfer surface of the pyrolyzer.

  Further, as in claim 5, there is provided a cylindrical cooling tank having a cooling surface on the inner peripheral surface for cooling the separated solid component, and a plurality of base blades on a rotating shaft provided at the center of the cooling tank. It is preferable that the solid-liquid separation device is provided with a cooler that is attached to the base blade and thermally decomposed by rotating the base blade, and is pressed against the cooling surface of the inner periphery of the cooling tank by centrifugal force. .

  According to the present invention, the solid component and the liquid component of the silicon slurry can be separated without undergoing a treatment such as filtration or centrifugation, and the silicon powder remaining in the furnace of the pyrolyzer is the main component. Since the solid component after the thermal decomposition treatment is as hard as a cookie, a powdery substance containing silicon powder as a main component can be easily obtained. As described above, when the silicon slurry is pyrolyzed without any treatment, the solid components remaining in the furnace of the pyrolyzer harden. This is caused by aggregation of solid component particles when the liquid component is vaporized during thermal decomposition, and is not due to thermal fusion of silicon carbide contained in the silicon slurry. This is because the melting point of silicon carbide is 2,730 ° C., so that silicon carbide does not melt at the temperature of the pyrolyzer. On the other hand, when an acid solution is added to the silicon slurry, a neutralizer solution is added and then pyrolyzed, the solid component of the silicon slurry after the pyrolysis treatment can be made as hard as a cookie. This is because, after adding an acidic solution to the silicon slurry, neutralization is performed by adding a neutralizer solution to inhibit aggregation between particles during thermal decomposition, or some chemical reaction occurs in the silicon slurry, or particles It is thought that this is because fine bubbles were generated between them to reduce the cohesive strength of the solid components. Thus, since it can process without passing through the process of separating silicon slurry into a solid component and a liquid component by filtration or centrifugation, it has been necessary to separate the silicon slurry into a solid component and a liquid component. No equipment or cost is required. Moreover, since it heat-decomposes, ie, heats in an oxygen-free state, even if it processes the silicon slurry containing an oil component, there is no danger of an oil component burning and an explosion, and it can process safely. Furthermore, in the process of pyrolysis, it is not necessary to control the apparatus, for example, the rotational speed.

  Moreover, if the solid-liquid separator of Claim 2 is used, the silicon slurry to which the neutralizing agent solution is added is lifted up by the base blade and pressed against the heat transfer surface on the inner periphery of the heating tank by centrifugal force. As a result, the high moisture content is preferentially pressed against the heat transfer surface, and the silicon slurry becomes a thin film and comes into contact with the heat transfer surface. It can be carried out.

  Moreover, if the distillation apparatus which distills the thermally decomposed and vaporized liquid component is provided like Claim 3, the oil component contained in the vaporized liquid component can be collect | recovered. In addition, when water is mixed in the vaporized liquid component, the oil is recovered through an oil-water separation process. This oil component is neutral because it is obtained by thermally decomposing a neutralized solution obtained by adding an acidic solution to a silicon slurry and then neutralizing it. If the oil thus obtained is fractionally distilled using another distillation apparatus, it is possible to collect heavy oil and light oil separately. In addition, if the non-condensable gas such as propane gas generated in the distillation apparatus is used as a fuel for a hot air generating furnace for generating hot air for heating the heat transfer surface of the pyrolyzer, the distillation process Thus, the condensable gas recovered in step (3) can be used effectively, and the running cost such as the fuel cost of the solid-liquid separator can be reduced.

  Moreover, it has a cylindrical cooling tank having a cooling surface on the inner peripheral surface for cooling the separated solid component, that is, a powdery substance mainly composed of silicon powder, as in claim 5. A plurality of base blades are attached to a rotating shaft provided at the center of the slab, and the solid components decomposed by the rotation of the base blades are scooped up and cooled against the cooling surface of the inner periphery of the cooling tank by centrifugal force. If the solid-liquid separation device is equipped with a machine, the powdery substance mainly composed of silicon powder which has been pyrolyzed and heated to a high temperature can be cooled in a short time and recovered safely.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic of the solid-liquid separator of 1st Embodiment of this invention. Schematic of the solid-liquid separator of 2nd Embodiment of this invention. Schematic of the solid-liquid separator of 3rd Embodiment of this invention. Schematic of embodiment of the thermal decomposition machine of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. However, the present invention is not limited to this embodiment.

  1 includes a silicon slurry stock solution tank 12, a reaction tank 20, an acidic solution tank 22, a neutralization tank 30, a neutralizing agent solution tank 32, a thermal decomposer 40, and a hot air generator 50. Yes. Since the valve V is provided at the connection part of the piping of each device, the flow rate of the silicon slurry as a raw material can be adjusted and controlled, and air can be prevented from entering the pyrolyzer 40. Therefore, the sealing structure of the pyrolyzer 40 can be ensured.

  First, the silicon slurry is put into the silicon slurry stock solution tank 12 in the state of the waste liquid discharged from the factory. Here, in the present invention, the steps such as filtration and centrifugal separation for separating the solid component and the liquid component of the silicon slurry, which are conventionally required for many processing methods, are not necessary. The silicon slurry charged into the silicon slurry stock solution tank 12 is then charged into the reaction tank 20 and the acid solution prepared in the acid solution tank 22 is added. After the acidic solution is added, the silicon slurry and the acidic solution are preferably stirred by a stirring device (not shown) to promote the reaction. The type and concentration of the optimum acidic solution to be used may vary depending on the concentration of the silicon slurry and the components contained, but it is preferable to use a strong acid such as hydrochloric acid or sulfuric acid. It has been found that if the slurry is sufficiently reacted and neutralized and then thermally decomposed, the remaining solid components will not harden. Next, the silicon slurry is put into the neutralization tank 30 and the neutralizer solution prepared in the neutralizer solution tank 32 is added. Also in this neutralization tank 30, it is preferable that the silicon slurry and the neutralizing agent solution are stirred by a stirrer (not shown) to promote the neutralization reaction. Moreover, although the caustic soda liquid is mentioned as a neutralizing agent solution to be used, in short, what kind of thing may be used if it can neutralize.

  Next, the neutralized silicon slurry is put into the pyrolyzer 40. The inside of the pyrolyzer 40 is kept in an oxygen-free state (1% or less). The oxygen-free state (1% or less) is preferably ensured by nitrogen replacement in which the pyrolyzer 40 is filled with nitrogen and the air inside is released to the outside of the pyrolyzer 40. Moreover, since air is prevented from being mixed in from the outside by the valve V provided in the piping of the pyrolyzer 40, the pyrolyzer 40 has a sealed structure.

  As such a pyrolyzer 40, for example, the one disclosed in JP-A-10-18513 is used. FIG. 4 is a schematic diagram of the state during operation of the pyrolyzer 40. As shown in FIG. 4, the pyrolyzer 40 includes a motor M and a cylindrical heating tank 42, and an outer peripheral jacket 44 into which hot air from the hot air generating furnace 50 shown in FIG. The base 41 includes a plurality of base blades 48 attached to a rotating shaft 46 at the center of the heating tank 42 for rotating the silicon slurry S against the heat transfer surface 41 by centrifugal force. When the base blade 48 rotates, the silicon slurry S is scooped up as shown in FIG. 4, that is, along the heat transfer surface 41, and becomes a thin film by the action of centrifugal force. Pressed against. As a result, the heating area is widened, the heating efficiency is increased, and the one having a high water content is preferentially in contact with the heat transfer surface 41, so that heating and vaporization can be performed simultaneously. In addition, the hot air sent from the hot air generator 50 shown in FIG. 1 is about 500-600 degree | times, and the silicon slurry S at the time of the operation | movement of the pyrolyzer 40 is heated to about 300-400 degree | times. Further, since the silicon slurry S is exposed not only to the portion in contact with the heat transfer surface 41 but also to the inner surface S1, it can be efficiently decomposed in a short time. In this way, the liquid component of the silicon slurry S is vaporized and gas is generated, and a solid component that becomes a powdery substance mainly composed of silicon powder remains in the heating tank 42. As described above, the pyrolyzer 40 has a hermetically sealed structure, and the inside is maintained in an oxygen-free state (1% or less), so that the oil content of the silicon slurry S reacts with oxygen in the pyrolysis process. The process can be performed safely.

  Thus, as shown in FIG. 1, the gas from which the liquid component of the silicon slurry is vaporized can be recovered from the arrow A, and the powdered material mainly composed of the silicon powder as the solid component can be recovered from the arrow B. .

  Next, FIG. 2 shows a solid-liquid separator 10a according to a second embodiment of the present invention. The solid-liquid separator 10a includes a silicon slurry stock solution tank 12, a reaction tank 20, an acidic solution tank 22, a neutralization tank 30, a neutralizer solution tank 32, a thermal decomposition machine 40, and a hot air generator 50, as well as a cooling machine. 60, a single distillation apparatus 70 which is a distillation apparatus, and an oil / water separation tank 80. In addition, since the process from putting silicon slurry into the silicon slurry stock solution tank 12 until it is thermally decomposed by the pyrolyzer 40 is the same as the described solid-liquid separation apparatus 10, the description thereof is omitted.

  The powdery substance mainly containing silicon powder, which is a solid component of the silicon slurry, collected from the pyrolyzer 40 is sent to the cooler 60. The cooler 60 includes a cylindrical cooling tank 62 having a cooling surface 61 on the inner peripheral surface, and includes a plurality of base blades 68 on a rotating shaft 66 provided at the center of the cooling tank 62. The basic operation is the same as that of the pyrolyzer 40, and cooling water or the like is circulated through the outer jacket 64, whereby the cooling surface 61 is cooled, and the charged object can be cooled efficiently. By providing this cooler 60, it is possible to cool in a short time the powdery substance mainly composed of silicon powder that has become high temperature by the thermal decomposition treatment of the pyrolyzer 40, and to safely recover it from the arrow C. it can. The powdery substance mainly composed of the silicon powder collected in this way can be reused as cement material or horticultural sand.

  On the other hand, the gas in which the liquid component is vaporized is sent to the single distillation apparatus 70 and condensed by passing through the cooling unit 72. The non-condensable gas that has not been condensed at this time is sent to the hot air generating furnace 50 and reused as fuel for the hot air generating furnace 50. By doing so, the fuel cost of the solid-liquid separator 10a can be reduced. On the other hand, the condensed liquid is sent to the oil / water separation tank 80, and moisture is recovered from the arrow D and oil is recovered from the arrow E. If solid content etc. are removed from this oil component, it will become refined oil and can be utilized as a raw material or fuel of cutting oil.

  Further, a solid-liquid separation device 10b shown in FIG. 3 includes a fractionation device 110 which is a second distillation device for fractionating the oil component distilled by the single distillation device 70 and recovered from the oil / water separation tank 80. It is. The oil recovered from the oil / water separation tank 80 of the solid-liquid separator 10 b is sent to the heating furnace 100 and then sent to the fractionator 110. Then, fractionation is performed by the fractionator 110, and heavy oil is recovered from the arrow F and light oil is recovered from the arrow G. The gas not condensed here is sent to the capacitor 120. The oil component cooled and condensed by the cooling unit 122 of the condenser 120 is recovered from the arrow H as light oil. The non-condensable gas that has not been condensed even after passing through the condenser 120 is sent to the hot air generating furnace 50 and reused as fuel. The recovered heavy oil is at least A heavy oil class and can be used for diesel engines. Light oil can be reused as cutting oil.

  Further, if the intermediate tank 90 is provided as in the solid-liquid separator 10b, the silicon slurry that has been subjected to the neutralization reaction in the neutralization tank 30 can be stored in the intermediate tank 90. The treatment can be continued in the reaction tank 20 and the neutralization tank 30 even while 40 is in operation. That is, since the standby time of the apparatus is eliminated and a series of processes can be performed continuously, the processing efficiency can be increased.

  As described above, according to the present invention, silicon slurry, which has been difficult to recycle in the past, is simply put into a solid-liquid separator without passing through a process such as filtration or centrifugation. The solid component and the liquid component contained in the slurry can be separated, and can be recovered as a powdery substance mainly composed of silicon powder, heavy oil, light oil, or non-condensable gas. Therefore, the silicon slurry can be solid-liquid separated and reused as a resource by a method and apparatus with a simple configuration.

DESCRIPTION OF SYMBOLS 10, 10a, 10b Solid-liquid separation apparatus 20 Reaction tank 30 Neutralization tank 40 Thermal decomposition machine 41 Heat transfer surface 42 Heating tank 46 Rotating shaft 48 Base blade 50 Hot-air generating furnace 60 Cooler 61 Cooling surface 62 Cooling tank 66 Rotating shaft 68 Base blade 70, 110 Distillation equipment

Claims (5)

After adding an acidic solution to a silicon slurry containing a solid component containing silicon powder and a liquid component containing cutting oil or a dispersant, the solution is neutralized by adding a neutralizer solution, and then thermally decomposed to form the liquid. Vaporizing components, separating the solid component and liquid component,
Solid-liquid separation method of silicon slurry. A reaction vessel for adding an acidic solution to a silicon slurry containing a solid component containing silicon powder and a liquid component containing cutting oil or dispersant;
A neutralization tank for adding a neutralizer solution to the silicon slurry to which the acidic solution has been added;
A cylindrical heating tank having a heat transfer surface on an inner peripheral surface for thermally decomposing the silicon slurry to which the neutralizing agent solution is added, and a plurality of base blades on a rotating shaft provided at the center of the heating tank Is attached, and when the base blade rotates, the silicon slurry to which the neutralizing agent solution has been added is scooped up and pressed against the heat transfer surface on the inner periphery of the heating tank by centrifugal force. It is characterized by having a machine,
Silicon slurry solid-liquid separator.   3. The silicon slurry solid-liquid separator according to claim 2, further comprising a distillation apparatus for distilling the thermally decomposed and vaporized liquid component.   The solid-liquid separator for silicon slurry according to claim 3, wherein the non-condensable gas recovered by the distillation apparatus is used as a fuel for a hot air generating furnace for generating hot air for heating a heat transfer surface of the pyrolyzer.   A cylindrical cooling tank having a cooling surface on the inner peripheral surface for cooling the separated solid component, and a plurality of base blades are attached to a rotating shaft provided at the center of the cooling tank. The solid component of the silicon slurry according to any one of claims 2 to 4, further comprising a cooler that scoops up the solid component thermally decomposed by rotation of the substrate and is pressed against a cooling surface of the inner periphery of the cooling tank by centrifugal force. Liquid separation device.

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