JP2002167466A - Method and apparatus for thermally decomposing waste plastic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently producing medium molecular weight materials having a molecular weight distribution of petroleum asphalt range by thermally decomposing waste plastics and recovering the materials. SOLUTION: By at least either a reflux method in which a cracked gas discharged from a thermal decomposition vessel 1 is condensed in a cooling device 7a and is flown back into the thermal decomposition vessel 1 or a pressurization method in which the cracked gas is thermally decomposed in a pressurization condition, the medium molecular weight materials are efficiently produced by thermal decomposing in the condition where low molecular weight materials are retained in high concentrations in the thermal decomposition vessel 1, and then the medium molecular weight materials are taken out by a transportation pump 9 and are recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for thermally decomposing waste plastics, and more particularly to a method for efficiently recovering medium-molecular-weight substances having properties and medium-molecular weights different from those of the original waste plastics from the pyrolysis tank efficiently. And a device for performing the method.

[0002]

2. Description of the Related Art There are various types of waste plastics, and in many cases, waste plastics are discharged in a state of being mixed or dirty so that recycling is difficult. In order to utilize these as resources, a material cycle can be performed if thorough sorting and pretreatment such as washing are performed.However, separation is difficult due to the fact that it is difficult to distinguish them and the morality at the time of disposal is low. It is not performed sufficiently, and pre-processing is not feasible in terms of cost. For this reason, such waste plastics have been put to practical use in oil processing, which can be collectively processed, as aggregates of building materials that do not need to be separated, or processed as solid fuel. Other than that, as a method of solving those problems, for example, Japanese Patent Laid-Open No. 2000-16
There is a technique for reusing synthetic asphalt by thermally decomposing plastics as disclosed in Japanese Patent No. 9856.

[0003] As a method for recovering useful resources from waste plastics, a thermal decomposition method is widely adopted. In the general pyrolysis method, waste plastic is heated and pyrolyzed in the absence of oxygen in a pyrolysis tank, and the low-molecular-weight decomposed gas generated is taken out, condensed in a condenser, and collected as oil. Is the way. In general, a pyrolysis tank is operated under normal pressure or reduced pressure, and the generated decomposition gas is mainly composed of waste plastic monomer as a raw material and a low molecular weight substance containing a dimer or trimer thereof. , A mixture containing other slight impurities.

However, in the case of this method, particularly when the object to be treated is a plastic mainly composed of polystyrene (PS) and acrylonitrile butadiene styrene (ABS),
Since the thermal decomposition reaction is not random and the depolymerization reaction to the monomer is dominant, a lot of light styrene monomers are generated, medium-molecular weight substances equivalent to petroleum asphalt are not sufficiently generated, and high molecular weight plastics It has been found that there is a possibility that the target proceeds directly to low-molecular-weight substances from the starting material and the yield of the target synthetic asphalt decreases. To prevent this, the thermal decomposition temperature may be lowered (350 ° C. or less), but in that case, the processing time becomes longer and the practicality is poor.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a new treatment method for solving the problems, and more specifically, to distill a pyrolysis product without lowering the temperature during pyrolysis. The thermal decomposition method that suppresses the low molecular weight pyrolysis reaction by suppressing it and efficiently generates waste plastics, which are high molecular weight substances, into highly functional, medium molecular weight substances with excellent viscosity and extensibility, and implemented the method It is an object of the present invention to provide a suitable thermal decomposition apparatus for performing the above.

[0006]

Means for Solving the Problems The first invention of the present invention is a pyrolysis method for pyrolyzing waste plastic in a pyrolysis tank and directly recovering the obtained medium molecular weight substance from the pyrolysis tank. Medium-molecular-weight substances generated in the thermal decomposition tank by thermal decomposition by at least one of the reflux method in which the decomposition gas flowing out of the thermal decomposition tank is agglomerated in the cooling device and refluxed to the thermal decomposition tank, and the pressurization method in which thermal decomposition is performed under pressure. And recovering it (claim 1).

In the above-mentioned pyrolysis method, the decomposition gas in the pyrolysis tank is discharged by stopping reflux to the pyrolysis tank at the end of the operation of the pyrolysis tank or by returning the pressure of the pyrolysis tank to normal pressure. The medium molecular weight substance can be taken out and recovered from the decomposition tank (claim 2). Further, in any of the above pyrolysis methods, when a pressurization method is employed, the pressure of the pyrolysis tank can be increased to a range of 0.020 MPa to 0.51 MPa.

A second invention of the present invention is an apparatus for thermally decomposing waste plastic in a pyrolysis tank and directly recovering the obtained medium molecular weight substance from the pyrolysis tank. This pyrolysis device
The pyrolysis tank includes a waste plastic introduction section, a decomposition gas discharge section, and a medium molecular weight substance discharge section, and a reflux device that cools the decomposition gas discharged from the decomposition gas discharge section and returns it to the pyrolysis layer. Switching means for stopping and discharging the decomposition gas to the condenser is provided (claim 4).

Further, a third invention of the present invention is an apparatus for thermally decomposing waste plastic in a pyrolysis tank and recovering the obtained medium molecular weight substance directly from the pyrolysis tank. In this pyrolysis apparatus, the pyrolysis tank is provided with a waste plastic introduction section, a decomposition gas discharge section, and a medium molecular weight substance discharge section, and a pressurizing means for pressurizing the pyrolysis tank and stopping the pressurization to normal pressure. A return switching means is provided (claim 5).

[0010] The medium molecular weight substance obtained by the pyrolysis method of the present invention has an average molecular weight of several hundreds to several thousands, and is suitable for low molecular substances such as petroleum products and high molecular substances such as resins. Medium molecular weight substances obtained from polystyrene and acrylonitrile-butadiene styrene resin (ABS) have properties like petroleum asphalt with excellent adhesiveness and elongation, and are suitable for road paving materials and waterproofing. It can be used for raw materials such as binders, adhesives and fillers for materials. Medium molecular weight substances obtained from polyethylene, polypropylene and the like can be used as raw materials for car wax and the like.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a process flow diagram of a pyrolysis apparatus for performing the pyrolysis method of the present invention by a reflux method. 1 is a pyrolysis tank, 2 is a heating device, 3 is a stirring device, 3a is a rotating blade, 4
Is a drive unit, 4a is a drive shaft, 5 is a waste plastic introduction unit, 6 is a decomposition gas discharge unit, 7 is a reflux device, 7a is a cooling device constituting the reflux device 7, 8 is a medium molecular weight material discharge unit, 9
Is a transfer pump, 10 is a heating gas generator, 11 is a combustion burner, 12 is a waste plastic supply device, 13 is a condenser, 14 is a recovery tank, 15 is a gas treatment device, 16 is a regulating valve, 17 is a control device, Reference numeral 18 denotes a switching unit, 19 denotes a heating / melting unit, 20 denotes an extruding unit, a to j denote pipes, and D1 to D3 denote ducts.

The tank-type pyrolysis tank 1 has a cylindrical shape, and has a conical bottom. A waste plastic introduction part 5 and a decomposition gas discharge part 6 are provided in the upper part of the thermal decomposition tank 1, and the waste plastic introduction part 5 is connected to the discharge side of the extruding part 20 in the supply device 12 by a pipe b covered with heat. The gas discharge part 6 is provided with a cooling device 7a by a vertically rising pipe c.
And a recirculation device 7 is constituted by a pipe c perpendicular to the cooling device 7a. The cooling device 7a has a cooling pipe extending in a bellows shape in the vertical direction in the container, and the decomposition gas moves in the cooling pipe. Cooling water from a pipe J is supplied into the container.

A heating device 2 is arranged around the pyrolysis tank 1, and a heating gas is supplied from the heating gas generator 10 to the heating device 2 through a duct D1 to heat the pyrolysis tank 1 from the outside. The heating gas generator 10 generates a heating gas by burning a liquid or gaseous fuel supplied through a pipe i with a combustion burner 11. The heating gas discharged from the heating device 2 is supplied to the extruding section 20 of the supply device 12 through the duct D2, and heats and keeps the temperature. The heating device 2 may be of an electric heating type.

The stirring device 3 provided in the pyrolysis tank 1 includes:
The driving device 4 includes a driving device 4 such as a motor having a speed reduction mechanism, a driving shaft 4a extending from the driving device 4, and a rotating blade 3a connected to a tip of the driving shaft 4a. This rotor 3
a rotates slowly during the thermal decomposition operation to stir the molten plastic inside. As the supply device 12, for example, a melt extrusion device generally used for a plastic injection molding machine or the like can be used. The supply device 12 heats and melts the crushed waste plastic supplied to a receiving unit such as a hopper (not shown) in a melting unit 19 and continuously extrudes the molten plastic from an extrusion unit 20 having a screw. Further, a mere plunger can be used as the supply device 12, and the crushed waste plastic can be directly supplied to the pyrolysis tank 1. The condenser 13 cools and condenses the decomposed gas flowing out of the reflux device 7. The condensed component is discharged to the recovery tank 14 via the pipes e and g, and the non-condensed gas is discharged to the gas treatment device 15 via the pipes e and f. Is discharged to The gas treatment device 15 performs non-condensation processing such as deodorization of the non-condensed gas and discharges the non-condensed gas from the duct D3.

Next, a method for recovering medium molecular weight substances from waste plastics by a reflux method using the thermal decomposition apparatus shown in FIG. 1 will be described. The waste plastic is finely pulverized and supplied from the pipe a to the supply device 12, where it is heated and melted to become molten plastic. The molten plastic is extruded batchwise into the pipe b from the extruder 20 and supplied to the pyrolysis tank 1. As described above, the pulverized solid waste plastic can be directly supplied to the pyrolysis tank 1 in batches without providing the supply device 12.

At the start of operation, the inside of the pyrolysis tank 1 is replaced with an inert gas such as nitrogen to make it a normal pressure state in which no oxygen is present, and the temperature is raised to the pyrolysis temperature by the heating gas from the heating gas generator 10. deep. The pyrolysis temperature varies depending on the properties of the waste plastic to be supplied.
The temperature is in the range of 50 ° C., and in the case of a styrene-based polymer such as an ABS resin, the temperature is preferably in the range of 300 to 400 ° C.

The waste plastic is heated and decomposed in the pyrolysis tank 1. The generated low molecular weight decomposed gas is discharged from the vertically rising pipe c and supplied to the cooling device 7a where it is cooled and condensed. When performing the reflux operation of the decomposition gas, the cooling capacity is maintained so that all the decomposition gas supplied to the cooling device 7a can be condensed. The cooling capacity of the cooling device 7a can be changed by adjusting the flow rate of the cooling water supplied from the pipe j by the adjusting valve 16. The control device 17 includes a setting section for setting the flow rate of the cooling water and a control section for outputting a control signal to the regulating valve 16 so that the flow rate is set at the setting section, and can be constituted by a personal computer or the like.

The cracked gas is cooled and condensed by the cooling device 7a, becomes a liquid component, flows backward (drops) through the vertical pipe b, and returns to the pyrolysis tank 1 from the cracked gas discharge unit 6. As described above, the low molecular weight decomposed gas discharged from the pyrolysis tank 1 flows back as a liquid component, so that a low molecular weight component having a higher concentration than the conventional method stays in the pyrolysis tank 1. Then, the transition from the plastic to the low molecular weight substance is suppressed in chemical equilibrium, and as a result, a large amount of the medium molecular weight substance is recovered. Therefore, a large amount of intermediate molecular weight, that is, a medium molecular weight substance, is generated between the high molecular weight substance at the raw material stage and the low molecular weight substance which is the main component of the decomposition gas.

The medium molecular weight substance thus produced is not simply a structure in which the chain of the polymer substance as the raw material is cut, but has a different structure and function. In order to increase the concentration of the low-molecular substance as much as possible from the beginning of the thermal decomposition, a gaseous (or liquid) low-molecular substance is introduced into the thermal decomposition tank 1 in advance. However, if the identity of the waste plastic, which is the raw material to be thermally decomposed, is not clear, such means should be avoided.

When a predetermined amount of a medium molecular weight substance is generated in the thermal decomposition tank 1, the operation of the thermal decomposition reaction is terminated. At the end of the operation, the reflux of the reflux device 7 is stopped, and the decomposition gas remaining in the pyrolysis tank 1 and the cooling device 7a is discharged to the condenser 13,
The condensed component is collected in the collection tank 14, and the non-condensed gas is processed by the gas processing device and discharged. Further transfer pump 9
Is operated to take out the medium-molecular-weight substance from the middle-molecular-weight substance discharge section 8 at the bottom of the decomposition tank 1 via a pipe h and collect it in a storage tank (not shown). The low molecular weight substance collected in the collection tank 14 can be used as fuel for the heating gas generator 10. To end the operation of the pyrolysis, the supply of the waste plastic from the supply device 12 is stopped, and
The amount of the heating gas supplied from the heating gas generator 10 to the heating device 2 is stopped.

In order to stop the reflux of the reflux device 7 and to switch so as to discharge the decomposition gas to the condenser 13, for example, the cooling water flow rate set value set in the setting section of the control device 17 constituting the switching means 18 is changed. The control valve 16 is closed by lowering or zeroing, whereby the cooling device 7a
The condensing action is stopped by stopping the cooling water supplied to the tank.
As another method for stopping the coagulation action, a method of increasing the cooling temperature or extracting the cooling water from the condenser 13 can be adopted. On the other hand, the medium-molecular-weight substance remaining in the pyrolysis tank 1 is taken out from the pipe h to reduce the amount retained. Therefore, the transfer pump 9 is stopped at an appropriate time to terminate the recovery operation. Then, thermal decomposition is started again.

FIG. 2 is a process flow chart of a pyrolysis apparatus for performing the pyrolysis method of the present invention by a pressurization method, and the same parts as those in FIG. 1 are denoted by the same reference numerals. In this example, the reflux device 7 is not provided as shown in FIG. 1, but instead the pyrolysis tank 1 is operated in a pressurized state to efficiently generate and recover medium molecular weight substances. Be composed. Therefore, the description of the same parts as in the example of FIG. 1 will be omitted. If the operation is performed such that the decomposition gas generated in the thermal decomposition tank 1 is confined in the tank without discharging, the pressure of the thermal decomposition tank 1 gradually increases, and accordingly, the concentration of the retained low molecular weight substance also increases. Then, similarly to the reflux method of FIG. 1, the chemical equilibrium shifts to a region where medium molecular weight substances are efficiently generated.

According to the experiment, the pressure of the pyrolysis tank 1 was set to 0.0
20 MPa to 0.51 MPa, desirably 0.020 M
It has been found that medium-molecular-weight substances can be efficiently produced when pyrolysis is performed under pressure in the range of about Pa to 0.20 MPa.
When the pressure is lower than 0.020 MPa, the generation rate of the medium molecular weight substance tends to decrease, and when the pressure exceeds 0.51 MPa, the chemical equilibrium tends to shift to the low molecular weight substance due to the temperature rise.

In FIG. 2, a regulating valve 21 and a safety valve are provided in parallel on a pipe c extending from the cracked gas discharge part 6, and a buffer tank 25 is connected to the outlet side thereof via a pipe d. Further, the condenser 13 is connected to the buffer tank 25 via a pipe k. The regulating valve 21 is provided to regulate the flow rate of the decomposition gas discharged from the thermal decomposition tank 1 and increase the internal pressure thereof, and is controlled by a control signal from a control device 22 constituted by a personal computer or the like.

The pressure in the pyrolysis tank 1 or the pipe c is measured by a pressure measuring device (not shown), and the measurement signal is sent to the control device 22.
Is input to The control device 22 includes a pressure setting unit and a control unit that outputs a control signal to the adjustment valve 21 so that the measured pressure matches the set pressure. Control pressure. The control device 22 and the regulating valve 21 constitute a pressurizing unit 23. The adjusting valve 21 may be a self-powered adjusting valve using a spring. In that case, the control device 22
Can be omitted.
Constituting No. 3.

When the pyrolysis is started by setting the pressure of the pyrolysis tank 1 within the above range, the regulating valve 21 is controlled to be closed since the pyrolysis tank 1 is initially at normal pressure. When the thermal decomposition is continued, the pressure in the thermal decomposition tank 1 gradually increases, and when the pressure exceeds the set pressure, the regulating valve 21 opens accordingly, and the excess decomposition gas is released to the buffer tank 25. However, if the pressure set value is set near the upper limit of the pressure range, it takes a considerable time to reach the upper limit pressure, so that a considerable amount of low-molecular-weight substance is retained in the pyrolysis tank 1 during that time. Can be.

If the pressure in the pyrolysis tank 1 rises suddenly for some reason, the opening of the regulating valve 21 alone may not be enough. At that time, the safety valve 24 operates to quickly release the decomposition gas to the buffer tank 25. Therefore, the buffer tank 25 is designed to have such a capacity as to receive the decomposition gas discharged rapidly as described above. The decomposed gas discharged to the buffer tank 25 is cooled and cooled by the condenser 13.
Condensed.

When a predetermined amount of the medium molecular weight substance has accumulated in the thermal decomposition tank 1, the operation of the thermal decomposition reaction is terminated. To do so, the supply of the waste plastic from the supply device 12 is stopped, the pressure setting of the control device 22 is reduced, the pyrolysis tank 1 is returned to normal pressure, and the supply of the heating gas to the heating device 2 is further reduced.

The operation of switching the pressurized pyrolysis tank 1 to normal pressure can be automatically performed by the controller 22. That is, the pressure set value is gradually changed to the normal pressure direction, whereby the regulating valve 21 is gradually opened to gradually lower the pressure. The control device 22 is the pyrolysis tank 1 according to the present invention.
The function of the switching means 26 for stopping the pressurization and returning to the normal pressure is constituted. When the control valve 21 is opened by a control signal from the control device 22, the decomposition gas remaining in the thermal decomposition tank 1 is discharged to the buffer tank 25, and further introduced into the condenser 13 via the pipe k to be cooled and condensed. . The condensed low molecular weight substance is collected in the collection tank 14, and the non-condensed gas is processed by a gas processing device and discharged.

The discharge of the liquid medium-molecular substance retained at the bottom of the thermal decomposition tank 1 is performed by operating the transfer pump 9 in accordance with a control signal from the control device 22. When the transfer pump 9 is operated, the medium molecular substance is discharged from the medium molecular substance discharge section 8 to the pipe h.
And collected in a storage tank (not shown). By removing the medium molecular weight substance retained in the pyrolysis tank 1, the retained amount is reduced. Therefore, at an appropriate time, the transfer pump 9 is stopped to end the recovery operation. Then, thermal decomposition is started again. These series of batch operations are the same as in the example of FIG.

[0031]

Embodiment 1 Next, an embodiment of the thermal decomposition method of the present invention will be described.
A pyrolysis tank was constituted by a flask vessel equipped with a thermometer, and then a pipe was vertically set up as shown in FIG. 1 to connect a water-cooled cooler to form a reflux device. 200 g of ABS pellets are charged into a flask container, and the surroundings are 35
Heated to about 0 ° C. When the internal temperature rose to about 300 degrees, the ABS was almost dissolved, and thermal decomposition proceeded. The decomposed gas generated by the thermal decomposition is a low molecular weight substance mainly composed of styrene, acetonitrile, etc., which flows out of the flask container, is cooled by a reflux device, and is refluxed again by dropping it into the flask container.

The temperature of the reflux apparatus was adjusted by adjusting the flow rate of the cooling water, and was set to about 50 ° C., which is the temperature at which the decomposition gas was sufficiently condensed. After maintaining this state for about 1 hour, the set temperature of the reflux device was lowered to about 150 ° C., the condensation was stopped, and the decomposition gas was discharged to another condenser. The amount of the low molecular weight substance recovered as a liquid from the condenser after flowing out for about 20 minutes is 7
It was 5 g.

The amount remaining in the flask container after the effluent operation was about 120 g. As a result of analysis, it was found that the minimum molecular weight was about 200, the maximum molecular weight was about 10,000, and the average molecular weight was about 4,000. there were. This medium molecular weight substance is rich in adhesiveness and elongation, and has a softening point and a penetration of 55 ° C. and 48 (1/10), respectively, which are petroleum asphalt test methods.
mm, 25 ° C.). This property is suitable as a raw material for road pavement.

[0034]

Embodiment 2 A thermometer and a pressure gauge are attached to a pressure-resistant container having a capacity of 500 mml, and a pipe connected to the pressure-resistant container is provided with a pressure regulating valve and a manual on-off valve set so that the internal pressure is opened at 0.3 MPa in parallel. Their outlets were connected by pipes to a water-cooled condenser. 2 ABS pellets in a pressure vessel
Then, 00 g was charged and heated from the outside with a mantle heater. When the internal temperature reaches 200 to 300 ° C, the internal pressure increases,
Pyrolysis started. The internal pressure further increased due to the generation of the decomposition gas containing styrene or acetonitrile as a main component and the increase in the concentration thereof, and the reaction was continued at a temperature of about 350 ° C. until the internal pressure reached 0.3 MPa. It is presumed that a part of the polymer substance in the pressure vessel is converted into a medium molecular weight substance while dissolving and thermally decomposing during that time.

When about 23 minutes have passed, the internal pressure becomes 0.3MP.
a, and the outflow of the decomposition gas from the pressure regulating valve started.
When the effluent was continued for 30 minutes, about 50 g of the low molecular weight substance was collected by condensation. Thereafter, the heating was stopped, and when the internal pressure dropped to 0.1 MPa, the manual on-off valve was opened to return the pressure-resistant container to normal pressure. At this time, about 30 g of a low-molecular substance obtained by condensing the decomposed gas flowing out by releasing the pressure is used, and about 1 g of the substance remains in the pressure-resistant container.
It was 10 g. As a result of analyzing the residual components, it was a medium molecular weight substance having a minimum molecular weight of about 200, a maximum molecular weight of about 9,500, and an average molecular weight of about 4,200. This medium molecular weight substance is rich in tackiness and ductility, and has a softening point and a penetration of 58 ° C. and 43
(1/10 mm, 25 ° C.).

[0036]

As described above, the pyrolysis method according to the first invention of the present invention comprises a reflux method in which cracked gas flowing out of a pyrolysis tank is aggregated by a cooling device and refluxed to the pyrolysis tank, and a pressurized state. The waste plastic is pyrolyzed in a state where the concentration of the low molecular weight substance is increased by at least one of the pressurization methods in which thermal decomposition is performed.The medium molecular weight substance generated and retained in the pyrolysis tank is taken out and collected. And According to the above-mentioned pyrolysis method, the medium molecular weight substance can be efficiently taken out of the pyrolysis tank directly from the waste plastic and recovered.

In the above-mentioned pyrolysis method, when a predetermined amount of the medium-molecular-weight substance accumulates in the pyrolysis tank, the reflux to the pyrolysis tank is stopped, or the pressure in the pyrolysis tank is returned to normal pressure, whereby And the oil component can be removed from the pyrolysis tank and recovered. By doing so, the medium molecular weight substance can be easily taken out from the pyrolysis tank and recovered. Further, in any of the above pyrolysis methods,
When the pressurization method is adopted, the pressure of the pyrolysis tank is set to 0.020.
Pressurization can be performed in the range of MPa to 0.51 MPa. By performing the thermal decomposition operation in this range, a medium molecular weight substance can be generated and recovered with higher efficiency.

In the thermal decomposition apparatus according to the second aspect of the present invention, the thermal decomposition tank has a waste plastic introduction section, a decomposition gas discharge section, and a medium molecular weight substance discharge section, and the decomposition gas discharged from the decomposition gas discharge section. It is characterized in that a reflux device for cooling the gas and returning it to the pyrolysis tank and a switching means for stopping the reflux and discharging the cracked gas to the condenser are provided. Therefore, by using this apparatus, the thermal decomposition method of the present invention having the above-described excellent effects can be suitably performed.

Further, in the pyrolysis apparatus according to the third aspect of the present invention, the pyrolysis tank has a waste plastic introduction section, a decomposition gas discharge section and a medium molecular weight substance discharge section, and a pressurizing means for pressurizing the pyrolysis tank. Switching means for stopping the pressurization and returning to normal pressure is provided. Therefore, by using this apparatus, the thermal decomposition method of the present invention having the above-described excellent effects can be suitably performed.

[Brief description of the drawings]

FIG. 1 is a process flow diagram of a pyrolysis apparatus that performs a pyrolysis method of the present invention by a reflux method.

FIG. 2 is a process flow diagram of a pyrolysis apparatus that performs the pyrolysis method of the present invention by a pressurization method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pyrolysis tank 2 Heating device 3 Stirring device 3a Rotating blade 4 Drive device 4a Drive shaft 5 Waste plastic introduction part 6 Decomposed gas discharge part 7 Reflux device 7a Cooling device 8 Medium molecular weight substance discharge part 9 Transfer pump 10 Heated gas generation device 11 Combustion burner 12 Supply device 13 Condenser 14 Recovery tank 15 Gas treatment device 16 Adjusting valve 17 Control device 18 Switching means 19 Heating and melting unit 20 Extruding unit 21 Adjusting valve 22 Control device 23 Pressurizing means 24 Safety valve 25 Buffer tank 26 Switching means a ~ K piping D1 ~ D3 duct

Claims (5)

[Claims] 1. A pyrolysis method in which waste plastic is pyrolyzed in a pyrolysis tank 1 and the obtained medium molecular weight substance is directly recovered from the pyrolysis tank 1, wherein a decomposition gas flowing out of the pyrolysis tank 1 is cooled. It is thermally decomposed by at least one of the reflux method of aggregating and refluxing the thermal decomposition tank 1 in the apparatus 7a and the pressurizing method of thermally decomposing under pressure, and the medium molecular weight substance generated in the thermal decomposition tank 1 is taken out and collected. A method for thermally decomposing waste plastic, characterized in that: 2. Decomposition gas in the thermal decomposition tank 1 is discharged by stopping reflux to the thermal decomposition tank 1 at the end of the operation of the thermal decomposition tank 1 or by returning the pressure of the thermal decomposition tank 1 to normal pressure. The method for thermally decomposing waste plastic according to claim 1, wherein the medium molecular weight substance is taken out from the tank 1 and recovered. 3. The method for thermally decomposing waste plastic according to claim 1, wherein the pressure in the pyrolysis tank 1 is increased to a range of 0.020 MPa to 0.51 MPa when the pressure method is employed. 4. An apparatus for thermally decomposing waste plastics in a pyrolysis tank 1 and directly recovering the obtained medium molecular weight substance from the pyrolysis tank 1. The pyrolysis tank 1 comprises a waste plastic introduction section 5, a decomposition gas A recirculation device 7 having a discharge part 6 and a medium molecular weight substance discharge part 8 for cooling the decomposed gas discharged from the decomposed gas discharge part 6 and returning the decomposed gas to the pyrolysis tank 1; A waste plastic pyrolysis device, comprising a switching means 18 for discharging the waste plastic into the vessel 13. 5. An apparatus for thermally decomposing waste plastic in a pyrolysis tank 1 and recovering the obtained medium molecular weight substance directly from the pyrolysis tank 1, wherein the pyrolysis tank 1 comprises a waste plastic introduction section 5, a decomposition gas A waste plastic provided with a discharge section 6 and a medium molecular weight substance discharge section 8 and provided with a pressurizing means 23 for pressurizing the pyrolysis tank 1 and a switching means 26 for stopping the pressurization and returning to normal pressure. Pyrolysis equipment.