JP2005231984A - Thermal decomposition recycling method of fluorine-containing solid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the thermal decomposition recycling method of a fluorine-containing solid, by which a large amount of fluorine-containing solid can be efficiently decomposed and the decomposed product can be recovered as a valuable substance without producing harmful reaction products. <P>SOLUTION: The thermal decomposition recycling method includes a first thermal decomposition process for gasifying the fluorine-containing solid in a rotary kiln whose inside is kept at a reducing atmosphere and hydrolyzing gasified products, a second thermal decomposition process for introducing the thermally decomposed gas generated in the first thermal decomposition process into a secondary combustion furnace having an oxidizing atmosphere and being kept at a temperature of ≥1,100°C and thermally decomposing the gas into a gas containing main components composed of carbon dioxide, steam and hydrogen fluoride, and a thermal decomposition gas cooling process for rapidly cooling the thermally decomposed gas generated in the second thermal decomposition process with water so as to absorb hydrogen fluoride and recover it as hydrofluoric acid. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

Fluorine-containing solids are synthetic polymers containing fluorine atoms in their molecules, that is, fluorine resins, elastic fluororubbers, and fluorine-based thermoplastic elastomers. There are many types of fluororesins, all of which are heat resistant. Excellent in corrosion resistance and corrosion resistance. There are many types of fluorine rubber, and it is known that they are excellent in heat resistance, chemical resistance and the like, as in the case of fluorine resin. For this reason, it is used in a wide range of industries.
The present invention collects fluorine-containing solids as separated products of general waste and industrial waste, or as yield-removed products produced from production processes in factories, and decomposes them by high-temperature pyrolysis, and then removes the fluorine content. The present invention relates to a recycling method for recovering as hydrofluoric acid.

Fluorine-containing solids are one of the most stable materials among synthetic polymers, and from the viewpoint that waste plastics are stable materials for landfill disposal, they have conventionally been used as landfill disposal as waste.
However, fluorine-containing solids are often mixed in incinerators for general waste and industrial waste. When incinerating them, the heat of fluorine-containing solids in the exhaust gas treatment equipment of conventional incineration equipment is used. Since hydrogen fluoride generated by decomposition is a strong corrosive gas, if the fluorine content is high, steel structures and refractories are corroded in a short time, and it is difficult to take measures against them. Mixing of contained solids has been a problem.

  In addition, when planning a dedicated incinerator for processing fluorine resin, etc., it is difficult from the viewpoint of decomposition efficiency and corrosion resistance of the equipment simply by applying conventional incinerator technology for general waste and industrial waste. In many cases, no examples have been put to practical use.

For example, Patent Documents 1 to 3 specifically describe methods for treating a fluorine resin, which is known to be difficult to incinerate.
Patent Document 1 discloses a method in which a fluorine resin is burned in the presence of a calcium inorganic compound, and an example discloses an example in which a fluorine resin is buried in slaked lime and burned by fire.
Patent Document 2 states that “when a fluorine-containing organic compound is reacted, an oxygen-containing gas is supplied so that the oxygen concentration after the reaction is about 10 vol% or more, and the reaction product gas after the reaction is fixed as fluoride. "A method for treating a fluorine-containing organic compound characterized by the above" is disclosed. Specifically, a fluorinated resin sheet or the like cut into pieces is charged into a nickel reactor, heated while flowing air or oxygen, converted into carbonyl fluoride, this reaction product gas is hydrolyzed, And fixed as a fluoride such as calcium fluoride.
Patent Document 3 discloses a method in which a fluorine-containing resin is subjected to floating combustion in a swirling air flow at a combustion temperature of 1000 to 1600 ° C. in a state where the ratio of hydrogen atoms to fluorine atoms is in a specific range.
JP-A-48-54180 JP-A-3-26384 Japanese Patent No. 3438174

Requirements required when pyrolyzing a fluorine-containing solid and recycling it as hydrogen fluoride are as follows.
1. The equipment has good corrosion resistance and has a sufficient life against substances generated in the pyrolysis process of fluorine-containing solids.
2. Substances generated in the pyrolysis process of fluorine-containing solids should not leak from the processing equipment.
3. Fluorine-containing solids that are synthetic polymers must be decomposed into hydrogen fluoride, water, and carbon dioxide at a sufficient decomposition rate when decomposition is completed.
4). When hydrogen fluoride is used separately, it can be converted into a form that can be easily used as a chemical raw material.

  These requirements are difficult to solve by conventional incineration techniques. The reason why it is difficult to solve the above problems in the conventional rotary kiln incinerator, stoker incinerator, and fluidized bed incinerator will be specifically described below.

FIG. 2 shows an example of incineration equipment using a conventional incinerator. In FIG. 2, 21 is an incinerator such as a rotary kiln, a stoker furnace or a fluidized bed furnace, followed by a recombustion furnace 22, a temperature reducing tower 23, a dust collector 24, a wet scrubber 25, an induction fan 26, a chimney. 27 etc. In the conventional technique, a combustible element mainly composed of carbon content of a fluorine-containing solid is combusted by combustion air in a state in which the fluorine-containing solid charged into the incinerator 21 is burned in the auxiliary burner. In the process, hydrogen fluoride decomposed and released is generated in the incinerator 21.
Most of the fluorine-containing solids decompose at a normal incineration temperature (800 to 900 ° C.) to produce a large amount of fixed carbon. However, even in the presence of oxygen, combustion cannot proceed sufficiently, and A large amount of fuel remains. On the other hand, hydrogen fluoride as a decomposition product reacts with silicon dioxide (SiO ₂ ) and calcium oxide (CaO) constituting the refractory of the incinerator, and extremely deteriorates the life of the refractory.
In addition, in flue and wet cleaning towers where the exhaust gas temperature of exhaust gas treatment equipment decreases, the temperature of the steel plate that forms the shell is below the dew point of hydrogen fluoride and is subject to acid corrosion by hydrofluoric acid, which significantly reduces the life of the equipment. Let Since the above states are caused, the conventional incineration technique is difficult to apply practically.

The present invention has been developed to achieve the functions required for pyrolyzing and recycling the above fluorine-containing solid.
The first aspect of the present invention is a first pyrolysis step in which a fluorine-containing solid is gasified in a rotary kiln maintained in a reducing atmosphere and maintained at 700 ° C. or higher to hydrolyze a gasification product, and the first heat The pyrolysis gas generated from the decomposition process is introduced into a secondary combustion furnace maintained at 1100 ° C. or higher in an oxidizing atmosphere, and the main components gas of carbon dioxide (CO ₂ ), water, and hydrogen fluoride (HF) are heated. It comprises a second pyrolysis step for decomposing, and a pyrolysis gas cooling step in which the pyrolysis gas generated from the second pyrolysis step is quenched with water, concentrated to a required concentration, and recovered as hydrofluoric acid. This is a method for thermally decomposing and recycling fluorine-containing solids.

According to the method for pyrolyzing and recycling a fluorine-containing solid described in claim 1, steam is added in the front space in the rotary kiln furnace into which the fluorine-containing solid is charged, and the gas temperature inside the rotary kiln is increased. However, a small amount of combustion air necessary for burning a part of the fluorine-containing solid is introduced into the rotary kiln in a state where the combustion air ratio is maintained at 700 to 900 ° C. by the combustion of the auxiliary burner whose combustion air ratio is set to less than 1. By doing so, the internal atmosphere of the rotary kiln is maintained in a high-temperature reduced state.
Under this reaction condition, the fluorine-containing solid partially sublimates without producing a large amount of free fixed carbon, and part of the fluorine-containing solid reacts with the added water vapor to be reformed to carbon monoxide and hydrogen by a water gas reaction. The reaction product together with free fixed carbon is introduced into the second pyrolysis step. In the secondary combustion furnace of the second pyrolysis step, heat introduced from the first pyrolysis step is formed by introducing combustion air or burning an auxiliary combustion burner as necessary to form a high-temperature oxidation state of 1100 ° C. or higher. The cracked gas is oxidatively decomposed at high temperature.

Since the product gas generated in the first pyrolysis process is reformed into an easily decomposable gas, the combustible substance is easily decomposed into carbon dioxide, water, and hydrogen fluoride with high efficiency in a high-temperature oxidation state. can do. Furthermore, the high-temperature combustion exhaust gas is introduced into a directly-cooled water quenching section (cooling function section of the cooling can) that is installed directly connected to the secondary combustion space while maintaining a high temperature, and is only below the boiling point of water. It cools in a short time and prevents the recombination of harmful substances such as dioxin-related substances that are usually generated in the slow cooling of combustion exhaust gas.
At the same time, hydrogen fluoride is very water-soluble, so most of it is absorbed in the cooling water as hydrofluoric acid, and the unabsorbed gas is absorbed in the absorption tower installed next to the cooling can, Almost all of the hydrogen fluoride is recovered as hydrofluoric acid.
In the pyrolysis gas cooling step, hydrogen fluoride is absorbed and then concentrated to a desired concentration to recover hydrofluoric acid. This is because it can be easily used when separately used as a chemical raw material.

In the invention according to claim 2, the rotary kiln to be used has a corrosion-resistant and heat-resistant metal lift pin inserted therein, and the amount of air leaked into the furnace of the rotary kiln rotating sliding portion is suppressed to 30 Nm ³ / h or less per 1 m of seal length. The inside of the furnace is made of a hard refractory material containing 98% or more of Al ₂ O ₃ . As the corrosion-resistant and heat-resistant metal used for the lift pins, it is preferable to use a corrosion-resistant and heat-resistant cast steel or Hastelloy.

The rotary kiln used for the thermal decomposition in the present invention stirs the bulk bulk solid charged in the kiln so that the individual solids constituting the fluorine-containing solid are uniformly heated and heated. A corrosion-resistant and heat-resistant metal lift pin is inserted so as to generate a sliding surface inside the bulk solid layer. This lift pin suppresses the sliding of the fluorine-containing solid in the rotary kiln, and the lifted bulk solid slides and stirs inside the solid as the rotary kiln rotates. As an apparatus for performing this stirring, for example, an apparatus described in JP-A-10-267239 is preferably used.
Further, generally, a minute gap is formed in the rotary sliding part of the rotary kiln, and the internal pressure is set to a negative pressure during the operation of the rotary kiln, so that air leaks into the furnace from the outside. If this leakage amount becomes large, the internal atmosphere of the rotary kiln cannot be maintained in a reducing atmosphere, so the amount of leakage air in the rotating sliding portion must be suppressed to 30 Nm ³ / h or less per 1 m of seal length. is there. For this purpose, it is preferable to use, for example, a device disclosed in Japanese Patent Application Laid-Open No. 2001-21046 as a sealing device for the rotary sliding portion.
A large amount of hydrogen fluoride accompanying the decomposition of the fluorine-containing solid exists in the pyrolysis product gas in the rotary kiln. By this hydrogen fluoride, silicon dioxide and calcium oxide constituting the refractory are depleted, and the strength of the refractory is reduced. It is preferable that the content of the order Al ₂ O ₃ constitutes a gas contacting portion in the surface layer in the refractory of 98% or more.

In order to make the refractory in the rotary kiln described above into a hard refractory surface layer containing 98% or more of Al ₂ O ₃ , 85% or more of Al ₂ O is used as the refractory of the rotary kiln. A high alumina refractory containing ₃ is lined, and hydrogen fluoride is reacted with calcium oxide (CaO) and silicon dioxide (SiO ₂ ) present in the surface layer at the initial stage of operation in the lining layer to react CaF ₂ and SiF ₄ . The product is volatilized in the gas, and the surface layer is reformed to a hard alumina layer having an Al ₂ O ₃ content of 98% or more so as to be corrosion-resistant and passivated against hydrogen fluoride.
The reaction in the 800 ° C. region between CaO, SiO ₂ and hydrogen fluoride can be represented by the formulas (1) and (2).

1

CaO (s) + 2HF (g) → CaF ₂ (g) + H ₂ O (g) (1)

2

SiO ₂ (s) + 4HF (g) → SiF ₄ (g) + 2H ₂ O (g) (2)

According to the formula (1), CaO reacts immediately with HF in the gas in chemical equilibrium. According to the equation (2), the amount of corrosion loss due to the acid of SiO ₂ is 15 kg / h when the exhaust gas amount of the kiln is 760 Nm ³ / h, the exhaust gas composition is H ₂ O 20%, HF 10%, and the dimensions of the rotary kiln Is 1.6 mφ and length L is 3.6 m, the bulk specific gravity is γ = 2.5 t / m ³ , the amount of wear from the chemical equilibrium is 0.33 mm / h, and SiO ₂ in the surface layer is volatilized early. It can be seen that.

On the other hand, the reaction of Al ₂ O ₃ and hydrogen fluoride in the 800 ° C. region is as shown in formula (3).

Chemical 3

γ-Al ₂ O ₃ (s) + 6HF (g) → 2AlF ₃ (g) + 3H ₂ O (g) (3)
According to the equation (3), the corrosion depletion amount due to the acid of Al ₂ O ₃ is 0.017 kg / h, assuming that the kiln exhaust gas amount is 760 Nm ³ / h, the exhaust gas composition is H ₂ O 20%, and HF 10%. Assuming that the kiln size is 1.6 mφ and the length L is 3.6 m, γ = 2.5, and the amount of wear as viewed from the chemical equilibrium is 3 mm / 8000 h.
This property difference makes it possible to modify the surface refractory to a dense and hard pure alumina layer at the beginning of operation.

The invention according to claim 4 is that the refractory of the rotary kiln used in the present invention is provided with an alumina heat insulating board or heat insulating wool on the shell side, and contains 98% or more of Al ₂ O ₃ on the inside of the furnace. It is equipped with.
As a structure of the refractory of the rotary kiln, a two-layer structure of heat insulating castable + fireproof castable or heat insulating brick + refractory brick is generally used. Since construction is performed on the rotating body, a heat insulating board is not used to strengthen the holding force. However, the heat-insulating castable has a high content of SiO ₂ and CaO in order to maintain the heat-insulating function, and when processing fluorine-containing solids, hydrogen fluoride enters the refractory through brick joints or castable spalling gaps. Erosion of heat-insulated castable or heat-insulated bricks installed on the iron skin side. As a result, the holding power of the refractory castable or the refractory brick is damaged, and the refractory is dropped off. In the present invention, a heat insulating board or heat insulating wool is used in place of a normal heat insulating castable or heat insulating brick. As a result, if the hook metal fitting is properly disposed and the strength is increased by the reduced holding force, it has a function equivalent to a general heat-insulating castable + fire-resistant castable.

In the method for pyrolyzing and recycling fluorine-containing solids according to claim 5, the rotary kiln is in contact with the fluorine-containing solid input part before the furnace where unreacted fluorine-containing solids are introduced on the surface of the refractory material inside the furnace. It is characterized in that a corrosion-resistant special steel is lined on the surface of the refractory material on the inner wall of the furnace.
The fluorine-containing solid charging portion is supplied with water vapor for water gas reaction, combustion exhaust gas from a reduction combustion auxiliary burner for maintaining the furnace temperature, and a small amount of combustion air as required.
The fluorine gas liberated from the fluorine-containing solid instantly changes to hydrogen fluoride by the reaction (4) due to the presence of water vapor.

4

2H ₂ O (g) + 2F ₂ → 4HF (g) + O ₂ (g) (4)
Considering from chemical equilibrium, fluorine gas exists almost as hydrogen fluoride regardless of the oxygen concentration. Assuming that H ₂ O is 20% and the hydrogen fluoride concentration is 10%, the molar concentration of fluorine gas is 1.75 × 10 ⁻²¹ (reducing atmosphere) to 3.03 × 10 ⁻²⁰ (oxidizing atmosphere) at 800 ° C. In terms of chemical equilibrium, it is not necessary to consider the presence of fluorine gas. However, it is also true that fluorine gas exists as a reaction precursor in a space where a fluorine-containing solid exists. The reaction between the fluorine gas and Al ₂ O ₃ can be represented by the formula (5).

5

6F ₂ (g) + 2γ-Al ₂ O ₃ (s) → 4AlF ₃ (g) + 3O ₂ (g) (5)
If the molar concentration of the fluorine gas coexisting with hydrogen fluoride in chemical equilibrium is 21.75 × 10 ⁻²¹ , the depletion rate is 0.001 times slower than the reaction between hydrogen fluoride and Al ₂ O _3. Considering the fluorine gas as the reaction precursor, there is a possibility that Al ₂ O ₃ depletion that cannot be ignored depending on the operating conditions occurs.
It is possible to further extend the life of the refractory by lining the refractory surface layer where there is a possibility that the Al ₂ O ₃ is depleted to protect the Al ₂ O ₃ by lining a corrosion-resistant special steel such as Hastelloy. it can.

  The method for pyrolyzing and recycling fluorine-containing solid according to claim 6, wherein the combustion air ratio of the auxiliary combustion burner attached to the fixed hood in front of the kiln furnace is reduced and burned in the range of 0.5 to 0.9 as means for forming a reducing atmosphere. It is characterized by doing. The main component elements constituting the fluorine-containing solid are carbon and fluorine, and generally the hydrogen content is small. Therefore, since the residue from which fluorine is detached from the solid by high-temperature pyrolysis is mainly composed of carbon, it is difficult to generate a reducing gas only by pyrolysis of the fluorine-containing solid. Accordingly, a reducing atmosphere is formed by reducing and burning the auxiliary burner attached to the fixed hood in front of the kiln furnace as described above.

The method of pyrolyzing and recycling a fluorine-containing solid according to claim 7, wherein water necessary for hydrolysis is blown as water vapor in the supply chute of the fluorine-containing solid, and the film gas in contact with the fluorine-containing solid is replaced with water vapor Thus, a fluorine-containing solid is supplied to the rotary kiln.
The fluorine-containing solid is heated at a high temperature, and immediately after the fluorine is desorbed from the fluorine-containing solid by thermal decomposition, a short period of time from the reaction (4) until it reacts with water vapor to produce hydrogen fluoride exists as fluorine gas. . Reaction (4) is an instantaneous reaction, but its reaction rate depends on the diffusion rate of water vapor.
Accordingly, when the fluorine-containing solid is supplied in advance and the boundary film in contact with the fluorine-containing solid is replaced with water vapor, or if the atmosphere around the fluorine-containing solid has a sufficient water vapor partial pressure, the water vapor can be easily and quickly added. The gas is replaced with hydrogen fluoride. As a result, erosion of the refractory by the fluorine gas can be suppressed.

The invention's effect

  According to the method for pyrolytic recycling of a fluorine-containing solid according to claim 1, the apparatus is constructed without leaving unburned carbon in the pyrolysis gas and leaving no harmful substances such as dioxin-related compounds in the pyrolysis gas. By extending the life of the steel structure and refractory, the operating rate of the equipment can be increased, and high-purity hydrofluoric acid containing no impurities can be recovered.

The fluorine-containing solid is uniformly heated by the corrosion-resistant and heat-resistant metal lift pins 11a and 11b inserted in the rotary kiln according to claim 2 by the thermal decomposition and recycling method of the fluorine-containing solid according to claim 2, and the unreacted solid Can be quickly extinguished, and the inside of the furnace can be kept in a reducing atmosphere by applying the sealing device 10a that can suppress the leakage air into the furnace of the rotary kiln rotary sliding part to 30 Nm ³ / h or less per 1 m of seal length, The life of the refractory can be extended by forming a hard refractory surface layer that comprises 98% or more of Al ₂ O ₃ as the refractory surface layer.

According to the method for thermally decomposing and recycling a fluorine-containing solid according to claim 3, an Al ₂ O ₃ content of 98 is obtained from a normal high alumina refractory containing 85% or more of Al ₂ O ₃ by a refractory reforming operation at the initial stage of operation. % Hard alumina layer can extend the life of the refractory.

According to the pyrolytic recycling method for fluorine-containing solid according to claim 4, the heat insulation function cannot be achieved with 98% dense Al ₂ O ₃ by Al ₂ O ₃ heat insulation board 12b or heat insulation wool provided on the shell side. Refractory support hook metal fittings were properly placed and support strength was strengthened to prevent refractories from falling off.

The rotary containing a non-reacted fluorine-containing solid placed on the surface of the refractory material inside the furnace in the fluorine-containing solid charging portion in front of the furnace according to the method for pyrolyzing and recycling fluorine-containing solid according to claim 5. In the kiln furnace, the corrosion-resistant special steel 31 lined on the surface of the alumina refractory completely protected Al ₂ O ₃ and extended the life of the refractory.

  According to the method for pyrolyzing and recycling fluorine-containing solid according to claim 6, the atmosphere in the rotary kiln furnace can be stably maintained in a reducing atmosphere, and the auxiliary fuel is burned to provide a heating source necessary for high-temperature pyrolysis. .

  According to the pyrolytic recycling method for fluorine-containing solids according to claim 7, the fluorine gas generated by pyrolysis of the fluorine-containing solids can be instantaneously converted to hydrogen fluoride, and refractory erosion by fluorine can be suppressed.

  FIG. 1 is a process flow diagram of a pyrolytic recycling facility for fluorine-containing solids. Moreover, FIG. 3 is an enlarged view of the rotary kiln furnace front charging part. A facility for carrying out the present invention will be described with reference to FIGS.

The fluorine-containing solid to be processed is received by the charging hopper 1 shown in FIG. 1 and charged into the rotary kiln 5 via the charging chute 4 by the cutting conveyor 2. The charging chute 4 is provided with a shut-off valve 3 for shutting off from the furnace space when stopped.
The fluorine-containing solid charged into the rotary kiln 5 is maintained at an elevated temperature before the furnace (TE1) of 700 to 900 ° C. by the auxiliary burner 5a, and the auxiliary combustion is burned when the air-fuel ratio of the auxiliary burner 5a is less than 1. Thermally decomposed in an atmosphere consisting of a mixture of exhaust gas, water vapor blown into the furnace, and a small amount of combustion air supplied as necessary, CO ₂ , H ₂ O, HF, CO, H ₂ , floating carbon, Then, it is converted to a sublimation gas of fluorine-containing solid, and the atmosphere of these mixed gases is maintained in a reduced state. In order to prevent a large amount of air from leaking into the furnace, high-performance kiln seal devices 10a and 10b capable of maintaining a leakage amount of 30 Nm ³ / h or less per 1 m of seal length are provided.

Since the fluorine-containing solid charged in the kiln furnace can be sufficiently brought into contact with the high-temperature furnace atmosphere gas in a short time, a plurality of rows of stirring devices 11a and 11b using corrosion-resistant and heat-resistant metal lift pins are provided in the furnace. The fluorine-containing solid is interpolated by the stirring device, and is sufficiently stirred by the corrosion-resistant and heat-resistant metal lift pins 11a and 11b that are driven as the rotary kiln is rotated.
The outlet temperature (TE2) of the first pyrolysis step is maintained at 700 to 900 ° C.

The pyrolysis gas discharged from the first pyrolysis step is introduced into the secondary combustion furnace 7, and the unburned content contained in the exhaust gas is maintained at a secondary combustion furnace outlet temperature of 1100 ° C. or higher by the auxiliary burner 7a. In the secondary combustion space, the entire amount is converted to CO ₂ , H ₂ O, and HF by being subjected to high temperature oxidative decomposition.

The outlet pyrolysis gas in the second pyrolysis step is introduced from the water injection nozzle 14 into the gas flow path of the secondary combustion furnace outlet water-cooled flue 13 that is introduced into the water quenching device 8 for the pyrolysis gas and indirectly cooled. Water quenching is directly performed by the cooled cooling water. As a second method of water quenching directly, the open end of the inlet pyrolysis gas introduction pipe is immersed in the can water accumulated in the cooling can 15 so that the pyrolysis gas is jetted into the can water and directly into the water. A method of rapid cooling can also be selected. In this case, the water injection nozzle 14 becomes unnecessary.
Hydrogen fluoride contained in the pyrolysis gas comes into contact with and is absorbed by water in the pyrolysis gas water quenching device 8, and most of it becomes hydrofluoric acid. Exhaust gas containing a small amount of hydrogen fluoride that is not absorbed by water is introduced into the exhaust gas absorption tower 9 through the cooling can 15, and the small amount of hydrogen fluoride is almost eliminated by the absorption tower circulating liquid to which makeup water is added in the packed bed 19. Fully absorbed. Absorption tower circulating liquid blow water which becomes surplus with the addition of makeup water flows down from the liquid reservoir at the lower part of the absorption tower 9 through the absorption tower overflow pipe 18 as overflow water and is supplied to the cooling can. As a result, surplus cooling pipe circulating water in the cooling can circulation system is withdrawn from the discharge side of the cooling can circulation pump 16 as recovered acid. The concentration of hydrofluoric acid in the recovered acid can be adjusted to a required concentration by setting the amount of makeup water.

The form for implementing this invention in the front part of an above described rotary kiln furnace is demonstrated based on FIG.
In the rotary kiln pre-sealing device 10a, a presser plate 34 is fixed to the roller chain 33, and a flexible joint seal material 37 is attached to the sliding seal seat 36 by a presser bolt attached through the fixed plate. Press against. Grease the sliding seat if necessary. One end of the joint seal material is fixed to the rotary kiln front fixed hood, and the other end is fixed to the roller chain pressing plate 34. The roller chain is wound around the rotary kiln fuselage so that it does not synchronize with the rotation of the kiln so that the rotation is constrained at the joint of the roller chain for one week and all rollers are in contact with the rotary kiln fuselage. Clog up.

The Al ₂ O ₃ insulation board 12b according to claim 4, placed inscribed in a rotary kiln furnace shell steel shell, to suppress excessive heat transfer to the furnace shell. Even if corrosive components of pyrolysis gas containing hydrogen fluoride enter through the spalling gap generated in the rotary kiln refractory 12, the heat insulating function is not hindered by Al ₂ O ₃ having sufficient corrosion resistance, and the corrosion is reduced. Therefore, the retention of the refractory 12 can be maintained for a long time.

  The corrosion-resistant special steel lining 31 according to claim 5 is used for a corrosion-resistant special steel lining fixed to the rotary kiln shell 30 in the range where the injected fluorine-containing solid exists and contacts the refractory of the rotary kiln. A necessary quantity for simultaneously holding the lining 31 is arranged in a plane on the surface of the refractory so that the mounting hook 32 penetrates the refractory and protrudes to the surface of the refractory. The lining 31 is fixed by a mounting hook 32. About the stirrer 11a, a corrosion-resistant metal, for example, a steel bar made of Hastelloy, is attached to the rotary kiln shell so that it can be replaced by a mounting flange.

  The fluorine-containing solid to be treated in the present invention is a synthetic polymer containing fluorine atoms in the molecule, that is, a fluorine resin, an elastic fluorine rubber, a fluorine-based thermoplastic elastomer, or the like. Fluororesin includes polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polychlorotrifluoroethylene (PCTFE), ethylenetetrafluoro. There are ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), ethylene-chlorotrifluoroethylene copolymer (ECTFE), etc., all of which are excellent in heat resistance, corrosion resistance and the like. Fluoro rubber includes vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, tetrafluoroethylene-propylene-vinylidene fluoride copolymer, etc. Like the fluororesin, it has excellent heat resistance and chemical resistance.

Using the fluorine-containing solid pyrolysis recycling demonstration facility with the same configuration as the process flow shown in FIG. 1, the demonstration operation was conducted for the four types of fluorine-containing solids shown in Table 1. The amount of air leaked into the furnace of the rotary kiln rotary sliding part during the demonstration operation was maintained at 30 Nm ³ / h or less per 1 m of seal length.

  The results of the demonstration operation are shown in Table 2. As a result of investigating the concentration of CO and organic fluorine compounds as representative substances as unreacted gas remaining in the pyrolysis gas at the outlet of the secondary combustion furnace, all are undetected and good decomposition performance It was confirmed.

Three types of high-alumina refractories were adopted as the refractories of the rotary kiln by changing the alumina content, and three types of high-alumina refractories were constructed at appropriate locations in the rotary kiln.
The composition change of the refractory before and after the operation and the composition of the residue accumulated in the residue accumulation box at the rotary kiln outlet as the refractory exfoliation were investigated.

  Table 3 shows changes in properties before and after operation for three types of high alumina refractories. From this result and the result of inspection in the furnace after operation, the following results were obtained.

The high-alumina refractory A shown as a comparative example turns red, and the range of about 500 mm from the furnace front is particularly remarkable. In addition, peeling of the surface and local pitting are also observed. Furthermore, the exposure of the tip of the anchor hook for fixing the castable was confirmed at two places. The refractory is brittle enough to be easily peeled off. It has been found that this is because SiO ₂ is eroded by hydrogen fluoride and Al ₂ O ₃ whose bond strength is damaged is peeled off.
It was confirmed from Table 3 that the Al ₂ O ₃ peeled off as described above was the main component of the residue from the property investigation of the residue.

  The surface of the high-alumina refractory B shown as a comparative example was rough, and although not as high as the high-alumina refractory A, the surface was peeled off. Moreover, although the exposure of the tip of the anchor hook for castable fixation was confirmed at one place, the refractory had a hardness that could not be easily peeled off.

The high alumina refractory C had a smooth surface and was slightly reddish. The surface layer of the refractory was very hard. See that the content of Al ₂ O ₃ as described above has a significant effect on consumption of refractories, when the content of Al ₂ O ₃ is 85%, the SiO ₂ contained a small amount in the beginning of operation It was confirmed that the Al ₂ O ₃ content could be modified to a hard and dense surface layer close to 100% by reacting with hydrogen fluoride and desorbing.

The range of 500 mm from the front of the furnace is a range where the pyrolysis of the fluorine-containing solid is actively performed. When the consumption rate of Al ₂ O ₃ becomes a practical problem, the surface of the refractory is made of a corrosion-resistant special steel, for example, By constructing the lining made in, the life of the refractory can be extended.

An object of the present invention is to effectively recycle fluorine, which is a main component of a fluorine-containing solid, as an industrial raw material by desorbing raw material or raw material waste by means of thermal decomposition.
Residues from the production process in the fluorine resin manufacturing industry, defective products that deviate from product specifications, or products that have lost yield during product processing, etc., are subjected to the fluorine desorption treatment of the present invention as one step in the production process, It can be used as a resource recycling facility without being treated as waste.
Furthermore, when many fluorine-containing solids distributed in the market are disposed of as waste, the fluorine desorption treatment of the present invention is performed to reduce the volume of waste and recover fluorine. Can be used to prolong the life and recycle resources, and its usage is very wide for industrial benefits.

1 is a process flow sheet constituting the present invention. It is a block block diagram of the general waste incineration equipment which concerns on a prior art. It is sectional drawing which shows the outline | summary of the front part of the rotary kiln in the 1st thermal decomposition process of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fluorine containing solid injection hopper 2 Fluorine containing solid cutting conveyor 3 Shut-off valve 4 Input chute 5 Rotary kiln 5a Rotary kiln auxiliary burner 6 Residual box 7 Secondary combustion furnace 7a Secondary combustion furnace auxiliary burner 8 Water quenching device of pyrolysis gas 9 Exhaust gas absorption tower 10a Rotary kiln furnace front seal device 10b Rotary kiln furnace bottom seal device 11a First row furnace anti-corrosion heat resistant metal lift pin 11b Second row furnace anti-corrosion heat resistant metal lift pin 12 Rotary kiln refractory 12a In front of rotary kiln furnace Refractory weir 12b Rotary kiln insulation board 13 Secondary combustion furnace outlet water cooling flue 14 Pyrolysis gas water injection nozzle 15 Cooling can 16 Cooling can circulation pump 17 Absorption tower circulation pump 18 Absorption tower overflow pipe 19 Packed bed 21 Incinerator 22 Recombustion furnace 23 Decreasing tower 24 Dust collector 25 Wet scrubber 26 Induction fan 2 7 Chimney 30 Rotary kiln shell shell 31 Corrosion resistant special steel lining 32 Hook for mounting 33 Roller chain 34 Presser plate 35 Presser bolt 36 Seal sliding seat 37 Joint sealant

Claims (7)

  A first pyrolysis step in which a fluorine-containing solid is gasified in a rotary kiln maintained at 700 ° C. or higher in a reducing atmosphere in the furnace, and the gasification product is hydrolyzed, and thermal decomposition generated from the first pyrolysis step A second pyrolysis step in which the gas is introduced into a secondary combustion furnace maintained at 1100 ° C. or higher in an oxidizing atmosphere and pyrolyzed into main components gas of carbon dioxide, water and hydrogen fluoride, and the second pyrolysis A method for pyrolyzing and recycling fluorine-containing solids, comprising a pyrolysis gas cooling step in which pyrolysis gas generated in the process is quenched with water, concentrated to a required concentration and then recovered as hydrofluoric acid. The rotary kiln has a corrosion-resistant and heat-resistant metal lift pin inserted therein, the amount of air leaked into the furnace of the rotary kiln rotary sliding part is suppressed to 30 Nm ³ / h or less per 1 m of seal length, and 98% or more of Al is placed inside the furnace. pyrolysis recycling method of the fluorine-containing solid according to claim 1, wherein is composed of a hard refractory material comprising ₂ O _3. A hard refractory containing 98% or more of Al ₂ O ₃ in a rotary kiln is lined with a high alumina refractory containing 85% or more of Al ₂ O ₃ and is present in the surface layer in the initial stage of operation in the lining layer. Calcium oxide, silicon dioxide and fluorine compound to be reacted are volatilized in a gas as a reaction product, and the surface layer is modified to a hard alumina layer having an Al ₂ O ₃ content of 98% or more to form a fluorine compound. 3. The method for pyrolyzing and recycling a fluorine-containing solid according to claim 1 or 2, wherein the fluorine-containing solid is subjected to corrosion resistance passivation. The rotary kiln is provided with a hard refractory containing an alumina-based heat insulation board or heat insulation wool on the shell side and containing 98% or more of Al ₂ O ₃ on the inner side of the furnace. The method for thermally decomposing and recycling fluorine-containing solids as described.   5. The rotary kiln is provided with a corrosion-resistant special steel lining on the surface of the refractory material on the inner wall surface of the furnace in contact with the charged unreacted fluorine-containing solid at the fluorine-containing solid charging portion before the furnace. The method for thermal decomposition and recycling of a fluorine-containing solid according to any one of the above.   The reducing atmosphere in the first pyrolysis step is formed by reducing and burning the combustion air ratio of the auxiliary combustion burner installed in the fixed hood before the furnace of the rotary kiln in the range of 0.5 to 0.9. 6. The method for pyrolyzing and recycling a fluorine-containing solid according to any one of 5 above.   Moisture required for hydrolysis in the first pyrolysis step is blown into the supply chute of the fluorine-containing solid as water vapor, and the fluorine gas is contained in the rotary kiln in a state where the film gas contacting the fluorine-containing solid is replaced with water vapor. The method for pyrolyzing and recycling a fluorine-containing solid according to any one of claims 1 to 6, wherein the solid is supplied.

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