JP3492104B2 - Method and apparatus for liquefying plastic waste - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method and an apparatus for decomposing plastic waste into oil by a reaction using water in the supercritical range as a reaction medium. More specifically, the present invention relates to a method and an apparatus for decomposing plastic waste into oil by the above reaction using high-pressure steam such as a power generation boiler.

[0002]

2. Description of the Related Art Conventionally, most of various plastic wastes are subjected to landfill disposal or incineration treatment and are not effectively used as resources. Further, landfill disposal causes problems such as difficulty in securing landfill site and destabilization of ground after landfill, and incineration causes problems such as damage to furnace and generation of harmful gas and odor. For this reason, the Containers and Packaging Waste Law was enacted in 1995, and it has become mandatory to collect and reuse plastic. In response to these circumstances, it has been attempted in recent years to recycle plastic waste, one of which is a reaction using supercritical water (called supercritical water) as a reaction medium (supercritical water). A method of decomposing plastic waste into oil and recovering a useful oily substance (referred to as supercritical water method) is proposed (Japanese Patent Publication No. 56-501205, JP-A-57).
-4225, JP-A-5-31000, JP-A-6-2
79762 (see publication)).

Supercritical water or supercritical steam has a temperature above the critical temperature (374 ° C.) and a pressure above the critical pressure (22.1 ° C.).
It is water or steam in a state of (MPa) or higher.
Since supercritical water easily penetrates into molten plastic oil droplets, the supercritical water method has a faster reaction than thermal decomposition under atmospheric pressure, produces less gas and less residues, and achieves a high oil conversion rate. can do.

However, the technology for the treatment of plastic wastes by the supercritical water method is currently not well established, and in particular, problems such as speeding up of reaction, large-scale treatment of wastes, and heating equipment have been considered. There is an urgent need to overcome and industrialize.
That is, in the conventional treatment of plastic waste by the supercritical water method, a small cell is used for batch treatment at a temperature of about 400 ° C.
It took a long time of 0 minutes or more, and it was difficult to perform a large amount of treatment, and the melting of plastics, the reaction equipment and the heat treatment therefor hindered the industrialization of plastic waste treatment.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in the processing of plastic waste by the supercritical water method, a method of decomposing and oilifying the plastic waste at a high speed and treating it in a large amount. The purpose of this invention is to provide a technology for economically performing the process and to industrialize the treatment of plastic waste by the supercritical water method.

[0006]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the inventors of the present invention can decompose plastic waste by supercritical water reaction and oilize it at high speed, in large quantities, continuously, and economically. As a result of studying the means that can be carried out, the reaction was carried out under the conditions of supercritical water at a temperature of 420 ° C. or higher in the case of polystyrene and 500 ° C. or higher in the case of polyethylene, polypropylene, polyvinyl chloride or the like. In this case, for example, it was found that the plastic was decomposed and oiled in a short time of 2 minutes or less. Regarding the means for treating plastic waste by the supercritical water method, we found that a large amount can be treated by using a tubular continuous reactor, and further, in order to obtain supercritical water, high pressure steam such as a power generation boiler is used. In particular, it is economically advantageous to use a vapor having a critical temperature or pressure and to melt the plastic waste by utilizing the heat of the reaction product. By using combustible gas and oil as fuel, it has been found that steam more than the used steam can be generated, and the present invention has been completed.

That is, the present invention uses a thermoplastic waste containing at least one of polyethylene, polypropylene, polyvinyl chloride, and polystyrene as a raw material, melts the plastic, and then supplies the molten plastic with a critical temperature supplied from a boiler. The above steam is added, and the decomposition reaction of the plastic is performed at a temperature of 400 to 600 ° C., a pressure of 22.1 to 50 MPa, and a reaction time of 10 minutes or less using water in the supercritical region as a reaction medium, and the reaction product is converted into oil or oil. Oil recovery method and apparatus for recovering a mixture of methane and flammable gas, and further oil waste obtained by oilification of plastic waste or plastic waste using oil and flammable gas as fuel for the boiler The present invention provides a method for liquefying a product and an apparatus therefor.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
The types of plastics that can be treated by the present invention are primarily thermoplastics, including partially cured resins, whether single types, mixtures or composite materials such as alloys. May be. As the thermoplastic resin, polyethylene, polypropylene, poly-4-methylpentene-1, ionomer, polystyrene, AS resin, AB
Examples thereof include S resin, polyvinyl chloride, polyvinylidene chloride, methacrylic resin, polyvinyl alcohol, EVA, and cellulosic plastics. Preferably, it is a plastic waste containing at least one general-purpose plastic such as polyethylene, polypropylene, polystyrene, or polyvinyl chloride.

Plastic waste may be crushed, if necessary,
After pretreatment such as separation and fractionation, it is heated and melted. When a gas such as hydrogen chloride is generated during heat melting, the gas can be separated and removed, washed and recovered, or neutralized. The plastic waste may be supplied to a vertical or horizontal melting tank using a feeder or the like. Melting of plastic waste is 200-400 ° C, preferably 250-3
It is carried out at 50 ° C. The heating and melting are performed in a melting tank, and may be melted by the plastic alone, may be melted in a dispersed state in heated water, or may be in a state of being dissolved in the oil obtained by the reaction, or in the oil. The dissolved product may be in a state of being dispersed in heated water.

When the plastics alone are melted or dissolved in the oil obtained in the reaction, they may be mixed with water after leaving the melting tank and dispersed in heated water. . For transporting molten plastic alone,
It is possible to use a press-fitting device equipped with a single or twin screw. Chlorine-containing plastics such as polyvinyl chloride generate hydrogen chloride gas at the time of heating and melting and reaction, or generate hydrochloric acid in the state of generating condensed water, resulting in significant material corrosion. Therefore, it is desirable to separate and remove the produced hydrogen chloride in the gas phase. Furthermore, equipment using an acid resistant material such as Hastelloy C or Carbate is required. Alternatively, during melting or reaction, an amount of a basic substance, such as ammonia, caustic soda, sodium carbonate, etc., which is commensurate with the generated acidic substance or more, can be added.

The advantage of dissolving the plastic waste in the obtained oil is that the pretreatment such as cutting of the plastic waste is unnecessary or reduced, the dissolution is easy and the treatment is possible in a short time, and the obtained liquid is obtained. Since it has a reduced viscosity, it is easy to transport. In addition, high melting point resin in plastic waste,
Easily remove non-melting materials such as thermosetting resins, inorganic fillers, especially glass, short fibers such as carbon, long fibers or whiskers, or mixed metal pieces from the plastic to be melted by filtration means, centrifugal separation means, etc. can do. These oils naturally do not interfere with the cracking reaction.

The temperature of the reaction using water in the supercritical region as a reaction medium is 400 ° C. or higher, preferably 500 ° C. or higher, and the upper limit of the reaction temperature is that of steam that is industrially obtained on a large scale. It is about 600 ° C from the point. The reaction temperature varies depending on the type of plastic and the processing time, but for example,
In the case of polystyrene, the temperature is 420 ° C or higher, polyethylene,
In the case of polypropylene, polyvinyl chloride, etc., the plastic is decomposed and liquefied at a temperature of 500 ° C. or higher and in a short time of 2 minutes or less when the reaction is performed. Reaction pressure is 22.1
˜50 MPa, preferably 23-30 MPa,
It depends on the type of plastic and processing time.

The amount of water added is such that the weight ratio of plastic waste / water is too low, and it is economically unfavorable if it is 0.1 or less. Since a highly viscous product is produced, it is preferably 0.15.
The range is from 0.5 to 0.5. The treatment time (reaction time with supercritical water) is 0.1 to 10 minutes, preferably 2 minutes or less.
What is supplied to the reaction zone may be the above-mentioned molten plastic alone, may be dispersed in high temperature water, may be dissolved in oil, or may be dissolved in oil and dispersed in heated water. It may be in the state of being crushed. The decomposition conditions are
It is selected according to the temperature, pressure and amount of steam that can be used, the type and amount of plastic waste, the time to be treated, etc., and the flammable gas / oil ratio and the heavy oil / light oil ratio of oil can be widely varied.

As the reactor, various types such as a tubular type, a tower type, a tank type and a multi-stage tank type can be used. The reaction operation can be performed in a continuous system, a semi-batch system, or a quasi-continuous batch system such as a tank type switching. By using a tubular continuous reactor as the reactor, it is possible to speed up the reaction, process a large amount, and downsize the reactor. The material of the reactor is metal,
Examples include ceramics, carbates, glass, and lining-treated products of these. As a metal material,
Examples include special steels such as Ni, Cr, V, and Mo, austenitic stainless steels, and the like.

The flammable gas and oil obtained by the above decomposition treatment differ depending on the type of raw material and the processing conditions. In the case of polystyrene, the combustible gas content is small and most of the decomposition product oil is polyethylene, polypropylene. In case of 1
Combustible gas mainly composed of 5 to 20% of hydrocarbons and the remaining cracked oil are produced. The total yield of these fuels is 90 to 100%, and none of them contains sulfur and heavy metals, and the total combustion heat of these fuels shows a calorific value similar to that of heavy oil. Therefore, for example, if fuel is obtained by processing at a plastic waste / water weight ratio of 1/3, about 300 kg of fuel will be obtained from 1/3 t of plastic waste and 1 t of steam, which is a supercritical value. This corresponds to the fuel required to generate about 3 t of steam in the state.

The steam used is a large-scale private power generation boiler,
It is possible to use the one from the boiler for the electric power business. Even if the temperature and pressure of these vapors are both above the critical point, the pressure is below the critical pressure, but the temperature is superheated above the critical temperature, and when added to the molten plastic or the mixture of molten plastic and water, Any vapor can be used as long as it can decompose plastics using water in the critical region as a reaction medium. Specifically, such steam has a temperature of 500 ° C. or higher, a pressure of 8 MPa, a temperature of 570 ° C.,
For a pressure of 17.4 MPa and a boiler for a higher power utility, a temperature of 542 to 567 ° C and a pressure of 2
5.1 MPa, especially most of the recent boilers for thermal power generation are above the critical point, and the supercritical state from the supercritical pressure transformer operation once-through boiler or the supercritical pressure combined circulation type transformer operation once-through boiler. What is preferable can be used.

Therefore, the device of the present invention can be used economically by using steam by attaching it to an existing boiler or by constructing and using the device and the boiler at the same time, and effectively using the obtained fuel such as oil. Can be used for. Since the reaction mass after the decomposition reaction has a high temperature, it is used for heating the melted plastic and further used for melting the plastic waste. Large private power generation boiler,
In boilers for electric power business, the amount of steam generated is several hundred t / hr.
.About.several thousand t / hr, while the throughput of plastic waste is several hundred kg / hr to several thousand kg / hr. As mentioned above, since the plastic waste / water weight ratio is practically in the range of 0.15 to 0.5, it is suitable for large-scale private power generation boilers, power utility boilers, etc. as steam for power generation. Although there is a small reduction in the amount, it is possible to allocate steam for the plastic waste treatment in view of the importance of the plastic waste treatment and the effective utilization of the obtained fuel.

An example of the method and apparatus of the present invention will be described below with reference to FIG.
Will be explained. The plastic waste 1 which has been pretreated as necessary is supplied to a melting tank 2 having a stirrer (not shown). In the melting tank 2, for example, 250 ℃
Water containing high temperature and pressure, and the molten plastic and water are stirred to form the dispersion 3. The melting tank 2 is internally provided with a heat exchange pipe 4 such as a coil and a flexible pipe, and the dispersion is heated by a plastic decomposition product of supercritical water flowing in the heat exchange pipe 4. The dispersion (molten plastic) 3 discharged from the melting tank 2 is heated via a preheater 5 if necessary, and supplied to the reactor 6. On the other hand, high temperature steam 8 is supplied from the boiler 7 to the reactor 6, and a decomposition reaction by supercritical water occurs to generate a reaction product 9.

The reaction product 9 discharged from the reactor 6 is cooled by the preheater 5, supplied to the melting tank 2 and used for melting the plastic waste 1, and further cooled by the heat exchanger 10 if necessary. Is supplied to the gas-liquid separator 11 and separated into a gas component 13 and a liquid component. The liquid component is further separated in the separator 12 into an oil layer 14 and an aqueous layer 15. The water layer 15 is reused for melting the plastic waste 1. The oil layer 14 may be directly used as fuel for the boiler 7,
You may fractionate and divide into various boiling point components. The gas component 13 can be generated by the fuel of the boiler 7. When hydrogen gas or the like is contained, the gas component 13 may be passed through the aftertreatment device 16 or the like for removal. As another method, after the reaction product 9 is supplied to the melting tank 2 and used for melting the plastic waste 1, the high boiling residual oil, the gas, the low boiling fraction oil and the water are subjected to flash distillation or the like. The high-boiling point residual oil may be used for dissolving the plastic waste 1 by dividing it into the fractions. The obtained gas and oil, when used as a fuel, has less sulfur and heavy metals that cause pollution compared to heavy oil and coal, and
The calorific value during combustion is also high. Further, the oil component can be used as a hydrocarbon solvent and the like.

[0020]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited thereto. Examples 1 to 4 Using the apparatus shown in FIG. 1, the plastic waste 1 having the composition shown in Table 1 and steam were used for melting and decomposition. In addition, as for the oil component added at the time of dissolution in Example 3, the flash distillation residue was collected and used.

The results are shown in Table 1. As can be seen from Table 1, when the supercritical water reaction is performed, it is possible to continuously melt and decompose a large amount of plastic waste in a short time as compared with thermal decomposition, and to increase the fuel gas and oil. The yield could be obtained. The amounts of fuel gas and oil obtained were, in terms of heat quantity, at least the heat quantity of steam used for dispersion. Further, by dissolving the raw material plastic waste in the recovered oil, the pretreatment such as shredding of the raw material is alleviated, the dissolution time is shortened, and the foreign matter and the inorganic filler in the raw material are easily removed, The equipment can be operated continuously for a long time.

[Table 1]

[0022]

EFFECTS OF THE INVENTION It becomes possible to decompose plastic waste, turn it into oil, and reuse the obtained fuel in a boiler.
A technique for processing a large amount of plastic waste at a high speed and economically has been obtained.

[Brief description of drawings]

FIG. 1 is a system flow diagram illustrating an example of the method and apparatus of the present invention.

[Explanation of symbols]

1 plastic waste 2 melting tank 3 molten plastic 4 heat exchange pipes 5 Preheater 6 reactor 7 boiler 8 water vapor 9 Reaction products 10 heat exchanger 11 gas-liquid separator 12 separator 13 gas components 14 oil layer 15 water layer 16 Post-processor

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-184555 (JP, A) JP-A-9-501458 (JP, A) International Publication 94/022979 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C10G 1/10 C08J 11/14-11/28 B09B 3/00

Claims (11)

(57) [Claims] 1. Thermoplastic waste is used as a raw material to melt plastic, and then steam having a critical temperature or pressure supplied from a boiler is added to the melted plastic to add water in a supercritical region as a reaction medium. As a temperature of 400-6
An oilification method for plastic waste, comprising decomposing a plastic at 00 ° C, a pressure of 2.1 to 50 MPa, and a reaction time of 10 minutes or less to recover oil or a mixture of oil and a flammable gas from a reaction product. 2. The thermoplastic is polyethylene,
The method for oilizing plastic waste according to claim 1, comprising at least one of polypropylene, polyvinyl chloride, and polystyrene. 3. A decomposition reaction at 500 to 600 ° C., 22.1
The method for liquefying plastic waste according to claim 1 or 2, wherein water in a supercritical region of -40 MPa is used as a reaction medium. 4. The method for liquefying plastic waste according to claim 1, 2 or 3, wherein the decomposition reaction time is 2 minutes or less. 5. The method for liquefying plastic waste according to claim 1, wherein the added steam is steam having a supercritical point or higher. 6. The method for liquefying plastic waste according to claim 1, wherein the boiler is a thermal power generation boiler. 7. The method for liquefying plastic waste according to claim 1, wherein the raw plastic waste is melted by exchanging heat with the reaction product. 8. The method of oilizing plastic waste according to claim 1, wherein the raw plastic waste is melted by adding oil obtained by oilification of the plastic waste. 9. The method for oiling plastic waste according to claim 1, wherein water is added to the molten plastic to prepare a mixed dispersion of water and the plastic, which is preheated and then steam is added. 10. The method for oilizing plastic waste according to claim 1, wherein oil or oil and combustible gas obtained by oiling plastic waste is used as fuel for the boiler. 11. Melting with an agitator and a heat exchange pipe
An oil liquefier consisting of a tank, a reactor, and a separator is installed in a thermal power generation boiler.
Attached to the rack and is used as a source of thermoplastic waste.
After melting the plastic in the melting tank as a raw material,
To the reactor and at the same time to the reactor from the thermal power boiler.
Of steam above the critical temperature and pressure
Using water as a reaction medium
After obtaining the reaction product, the reaction product is mixed with the heat exchange pipe in the melting tank.
And melt the raw plastic waste by the heat
The water and oil or water and oil and flammable gas with a separator.
Separate and collect the obtained oil or oil and flammable gas
Liquefaction equipment for plastic waste used for fuel.