JPH09104874A - Pyrolysis of plastic and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pyrolyzing apparatus for a plastic having high pyrolying ratio of a thermosetting plastic and high energy efficiency. SOLUTION: This pyrolyzing apparatus contains a weighing means 200a and 200b for respectively weighing a thermosetting plastic 10a and a thermoplastic 10b so as to become prescribed weights, a plastic-feeding means capable of independently feeding these two kinds of plastics, a melting tank 310 for melting these termoplastics by heating and a means for feeding them from the melting tank to a pyrolyzing tank 320.

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 plastic to reduce its volume or to make it into fuel.

[0002]

2. Description of the Related Art Prior art relating to a method and an apparatus for thermally decomposing plastics by thermally decomposing plastics to reduce the volume or make them into fuel is described in "Research Report on Waste Plastics Thermal Decomposition / Oilization Technology", Promotion of Plastics Processing It is described in the association (March 1993).

Although many methods have been described in the prior art, most target thermoplastics such as polyethylene, polypropylene and polystyrene for processing. There is a system of USS Co., Ltd. that can process thermosetting plastics. This is composed of a waste plastic injection part, a thermal decomposition furnace, a reaction tower, a condenser, an oil recovery part, and a gas cleaning tower, and the batch operation is performed in one thermal decomposition tank having a stirring function.

[0004]

Plastic has excellent properties such as being lightweight, resistant to corrosion, and easy to mold. While the production volume is increasing year by year, the proportion of plastics in waste is also increasing rapidly. Conventionally, plastic is collected as combustible waste like paper waste and kitchen waste, and incinerated at a waste disposal site.

However, in the incineration process due to the property of plastic, (1) the calorific value is very large as compared with other combustible waste, and the incinerator wall is damaged. (2) Hydrogen chloride gas is generated, which causes corrosion. (3) Problems such as generation of harmful substances such as dioxins are occurring.

[0006] Therefore, although plastics are inherently flammable, some local governments have also sorted and collected landfill waste as waste unsuitable for combustion. Even so, securing landfill sites is not easy.

Therefore, there is a demand for a technique for reducing the volume of plastic or converting it into fuel for reuse.

Plastics are generally classified into two types. One is a thermoplastic that is easily decomposed by heat and melts into gas when heated, and the other is a thermosetting plastic that decomposes only slightly when heated and hardens as a solid.

Thermosetting plastics have high heat resistance, which is a weak point of plastics as materials, and have high industrial utility value. However, from the standpoint of waste treatment, it is difficult to reduce the volume and to make it into fuel, so a technology for promoting the decomposition of thermosetting plastics is necessary.

The conventional technology of USS Co., Ltd. can process thermosetting plastics, but no measures have been taken to accelerate its decomposition.

[0011]

SUMMARY OF THE INVENTION The present invention comprises heating a mixture of a thermosetting plastic and a thermoplastic,
In a method of thermally decomposing a plastic to be melted or gasified, the thermal decomposition of the mixture is characterized in that it is thermally decomposed while adding a thermoplastic.

A thermal decomposition apparatus for carrying out the present invention comprises at least a weighing means for weighing thermosetting plastics and thermoplastics so that each has a predetermined weight, and the two types of plastics are independently supplied. It comprises a possible plastic supply means, a melting tank for heating and melting the thermoplastic, and a means for supplying the thermoplastic to the thermal decomposition tank for heating and thermally decomposing the plastic from the melting tank.

The rate of decomposition of the thermosetting plastic is improved when the thermosetting plastic is thermally decomposed by mixing with the thermoplastic rather than by thermally decomposing the thermosetting plastic alone. This is considered to be due to the interaction of the decomposition products generated in the thermal decomposition process of both, the type of plastic to be mixed,
The effect changes depending on the amount.

The thermoplastic is polyethylene,
There are types such as polypropylene and polystyrene, but since the decomposition temperature and speed differ depending on the type, their proportions change as the decomposition process progresses.

According to the present invention, since the thermoplastic resin having a low decomposition temperature is additionally supplied as the decomposition progresses, it is possible to consistently maintain the weight ratio suitable for improving the decomposition rate of the thermosetting plastic. it can.

Therefore, it is possible to improve the decomposition rate of the thermosetting plastic which is difficult to thermally decompose.

Further, in the thermal decomposition of the thermosetting plastic, a high temperature is required and the decomposition time is long. The present invention also has an effect of saving energy required for decomposition by efficiently performing thermal decomposition.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of the present invention.

The present embodiment is an apparatus for thermally decomposing plastic collected as waste and converting it into fuel.
00, measuring devices 200a and 200b, melting tank 31
0, decomposition tank 320, residue drying furnace 330, chlorine fixing tank 37
0a and 370b, a reflux lightening tank 380, a catalyst reforming tank 400, a condenser 430, and the like.

The thermosetting plastics 10a and the thermoplastics 10b are once stored in the storage tanks 100a and 100b, respectively, and sent to the crusher 300 by a predetermined weight by the measuring devices 200a and 200b for individually weighing the respective plastics. , A few mm to a few cm
It is crushed and mixed into corners and sent to the melting tank 310.

The weights 550a and 550b detected by the measuring devices 200a and 200b are fed back to the control device 500.

In the melting tank 310, the thermoplastic is heated and melted at about 250.degree. Here, 90% or more of the chlorine component contained in the polyvinyl chloride is generated as hydrogen chloride gas, so that the first chlorine fixing tank 370a.
The chlorine component is removed by reacting with the calcium hydroxide charged in.

The mixed plastic from which the chlorine component has been removed is
It is sent to the decomposition tank 320 by opening a butterfly valve between the melting tank 310 and the decomposition tank 320. Decomposition tank 320
Undergoes thermal decomposition at about 500 ° C. to generate decomposition gas 570.

After the mixed plastic of the thermosetting plastic 10a and the thermoplastic plastic 10b is sent to the decomposition tank 320, only the thermoplastic plastic 10b is weighed and crushed in a predetermined amount, and the chlorine component is melted in the melting tank 310. To remove.

When the decomposition of the thermosetting plastic is completed in the decomposition tank 320, the thermoplastic plastic remaining in the decomposition tank 320 in a molten state is sent to the upper melting tank 310 and decomposed next. It is mixed with the crushed material of the plastic 10a and the thermoplastic 10b.

The undecomposed residue remaining in the decomposition tank 320 is transferred to the residue drying furnace 330 in the lower stage by opening the butterfly valve, and is discharged as a dry residue 355 to the residue tray 350.

Conventionally, when the residue is discharged, there is a problem that the viscosity becomes large when the residue is exposed to a low temperature atmosphere outside the decomposition tank and the discharge port is blocked. In the present embodiment, the residue drying furnace 330 dries until the heavy oil is exhausted, so the above problem does not occur. Further, since the residue drying furnace is installed separately from the decomposition tank, it is possible to perform the drying of the residue and the thermal decomposition of the plastic for the next time in parallel, which improves the utilization efficiency of the apparatus.

The decomposition gas 570 generated in the decomposition tank 320 and the residue drying furnace 330 is introduced into the reflux lightening tank 380 kept at 300 ° C., and the heavy components having a boiling point of 300 ° C. or higher are condensed and decomposed again. Return to 320. Reflux lightening tank 38
After passing 0, the remaining chlorine component is removed through the gas flow meter 390 and in the second chlorine fixing tank 370b. Then, in the catalyst reforming tank 400, the catalyst is brought into contact with the zeolite-based catalyst at about 350 ° C. to be further lightened. Next, it is cooled by heat exchange with the heat transfer oil 490 in the cooler 410, and further cooled by the condenser 4
At 30 it is cooled to room temperature. The cooled decomposition gas is separated into a gas 540 that does not condense even at room temperature and a liquid fuel oil 530, and the fuel oil 530 is stored in the recovered oil tank 440.
The cooling water of the condenser 430 is cooled in the cooling tower 420 and circulates as cooling water again.

The obtained fuel oil 530 can be used as various fuels. Part of the gas 540 burns as the heating fuel 545 in the gas burners 340a and 340b, and heats the decomposition tank 320 and the residue drying furnace 330. The residue drying furnace 330 is usually heated by heat exchange with the combustion combustion gas 510 in the decomposition tank 320, but can be heated by the gas burner 340b when combustion gas in the decomposition tank is unavailable, such as when the apparatus is stopped. It is like this.

The combustion gas 510 after heating the residue drying furnace 330 is heated by the heat medium heating heat exchanger 360.
The temperature of 90 is raised, and further, the catalytic reforming tank 400 and the air preheater 450 are sequentially heated, and finally, the gas is discharged to the outside of the system through the exhaust gas treatment device 460.

The heat medium oil heated by the heat medium heating heat exchanger 360 is used for heating the melting tank 310, and is cooled by the cooler 41.
It is preheated to 0 and circulates.

The thermoplastic 10b is easily melted by heating and decomposes into gas, but the thermosetting plastic 10a is difficult to thermally decompose and does not melt even when heated, and a part of it decomposes into gas. However, most of it remains as a solid and remains as a residue.

Plastic is generally a material that melts by heating and is easy to mold, but on the other hand,
This property indicates that heat resistance is weak, which was also a weak point of plastics. Thermosetting plastics have a high industrial utility value to compensate for this weakness.

On the other hand, in processing plastics as waste, in order to reduce the volume of thermosetting plastics or to make it into fuel,
Conventionally, a high temperature requires a long decomposition time, the treatment is difficult, and the energy required therefor is large.

In order to increase the decomposition rate of thermosetting plastics, the method of mixing with thermoplastics and pyrolyzing is effective. "Study on reduction of thermal decomposition residue of waste plastics" The 68th Chemical Society of Japan It is described in the Proceedings of Autumn Annual Lectures. According to this, the decomposition rate of the thermosetting plastic is improved because both decomposition products generated in the decomposition process interact with each other. Fig. 2 shows the effect of improving the decomposition rate of thermosetting plastics described in "Study on reduction of thermal decomposition residue of waste plastics".

It has been shown that, when the thermosetting plastic is pyrolyzed alone, the residue is reduced to 1/4 or less when the thermosetting plastic is mixed with the thermoplastic and pyrolyzed. It is also stated that the effect varies depending on the ratio of the thermosetting plastic and the thermoplastic to be mixed and the type of the thermoplastic. However, even if thermosetting plastics and thermoplastics are mixed and pyrolyzed, the thermoplastics volatilize first because they are easily gasified at a relatively low temperature. Therefore, in the process of progressing the thermal decomposition, the decomposition products of the thermoplastic required for improving the decomposition rate are reduced.

In the present invention, since the thermoplastic resin is additionally supplied in the process of thermal decomposition, it is possible to always secure the amount of the decomposition product suitable for increasing the decomposition rate of the thermosetting plastic.

In this embodiment, such a problem is solved as follows.

The gas flow meter 390 measures the amount of decomposed gas, and the measured value is sent to the control device 500.

The control device 500 detects a decrease in the amount of decomposition gas, and in order to additionally supply the thermoplastic resin in a molten state in the melting tank 310 to the decomposition tank 320 in accordance with the decrease amount and the decrease rate, the melting tank 320 The opening degree of the valve connecting the 310 and the decomposition tank 320 is controlled to a predetermined position. When the amount of thermoplastics supplied from the melting tank 310 to the decomposition tank 320 exceeds the set value, the thermoplastics are taken out from the storage tank 100b, and the weight 550b detected by the measuring device 200b reaches the set value. Up to the melting tank 310 to replenish.

In the present embodiment, the temperature of the melting tank 310, the decomposition tank 320, the residue drying furnace 330, the temperature of the decomposition gas, the temperature of the reflux lightening tank 380, and the temperature of the catalyst reforming tank 400 are measured by temperature sensors 470a and 470b, respectively. 470c, 470d, 4
It is measured by 70e and 470f. The liquid level sensor 480 measures the fuel oil level in the recovered oil tank 440. The measurement information of the temperature and the liquid level is sent to the control device 500 and utilized for operation control.

In the present embodiment, the additional supply amount of the thermoplastic is determined by the measured value of the cracked gas flow rate, but it may be carried out based on the temperature of the cracked gas or the change of the liquid level in the recovered oil tank. Good. Further, the relationship between the passage of time and the volatilization amount of the thermoplastic in the decomposition tank may be obtained in advance, and the additional supply amount of the thermoplastic may be determined according to the passage of time from the start of decomposition.

FIG. 3 shows the melting tank 310 and the decomposition tank 3 of this embodiment.
20. Regarding the residue drying furnace 330, a more detailed structure is shown.

The plastic crushed by the crusher 300 is supplied to a melting tank 310 separated by two ball valves 302 and 303. Crusher 300
Since sheet-shaped or film-shaped plastic is difficult to crush, the molten plastic is pumped up from the melting tank 310 by the pump 313 and sprayed from the nozzle 301 onto the raw material plastic to cause thermal contraction.

In the melting tank 310, a heat transfer tube 314 for heating is arranged along the tank wall, and a mesh fence 316 is arranged inside in order to prevent the solid matter from directly contacting the heat transfer tube. The stirring motor 311 rotates the stirring blade 312 to keep the temperature in the tank uniform.

The melting tank 310 and the decomposition tank 320, and the decomposition tank 320 and the residue drying furnace 330 are separated by butterfly valves 315 and 324 whose opening can be adjusted. The decomposition tank 320 and the residue drying furnace 330 also stir inside the tank by stirring blades 322 and 333 rotated by stirring motors 321 and 331, respectively.

When moving the residue from the decomposition tank 320 to the residue drying furnace 330, the molten thermoplastic resin remaining in the decomposition tank 320 is extracted from the bottom of the tank and the pump 32 is used.
At 3, it is transferred to the decomposition tank 320. At that time, the solid residue is pump 3
A mesh fence 325 is provided so as not to flow into 23. The mesh fence 325 also prevents direct contact of solid residue with the hot walls of the gas burner, causing caulking.

After the heavy oil is dried in the residue drying furnace 330, the butterfly valve 332 is opened and the residue 355 is discharged.

A modification of the present invention is shown in FIG. This figure constitutes a system for generating electricity using the fuel oil obtained by the thermal decomposition apparatus shown in FIG.

Fuel oil 530 can be obtained by the plastic thermal decomposition apparatus of the present invention, and this fuel oil 530 is used as fuel for the diesel engine generator 600 to generate electric power.
You can also get 620. A part of the electric power obtained here can also be used as a power source for the crusher 300, the agitation motors 311 and 321 and 331, the pumps 313 and 323, and the like.

Further, the amount of heat held in the exhaust gas 610 of the diesel engine generator 600 is recovered and used in the air preheater 4
It can also be part of a heating source of 50.

FIG. 5 shows an example in which the plastic thermal decomposition apparatus of the present invention is applied to a waste power generation system.

The waste power generation system uses combustible waste 77
0 is incinerated in an incinerator 760, and the incineration heat is used to generate electricity. The combustion gas of the incinerator sequentially gives heat to the steam superheater 820 and the heat recovery boiler 790, and the exhaust gas treatment device 80
It is discharged from the chimney 810 to the atmosphere through 0.

The steam generated from the heat recovery boiler 790 is heated in the steam superheater 820 to become superheated steam 830 at about 300 ° C. and 30 ata, which drives the steam turbine 840 to obtain electric power from the generator 850. The steam that has exited the steam turbine is condensed in the condenser 860 and is sent to the heat recovery boiler 790 again by the water supply pump 870.

Among the combustible wastes, the plastics are separately collected and used as fuel in the thermal decomposition apparatus 700 of the present invention. In this embodiment, the combustion exhaust gas 720 finally discharged from the thermal decomposition apparatus 700 and the water supply 750 to the heat recovery boiler 790.
Are heat-exchanged with the heat exchanger 740 to heat the feed water.
Further, of the gases generated by the thermal decomposition apparatus 700, the remaining gas 710 excluding the fuel gas 545 for self-heating is used as fuel for the feed water heater 730 to further raise the feed water temperature.

Normally, the heat of the heat recovery boiler is raised by using the retained heat of the combustion exhaust gas which is not used in the thermal decomposition apparatus 700 itself or the surplus generated gas, so that the power generation amount of the waste power generation system can be increased. it can.

As described above, according to this embodiment, the decomposition rate of the thermosetting plastic, which has been difficult to thermally decompose, can be improved, and the energy required for decomposition can be saved.

[0058]

According to the present invention, since thermoplastics are additionally supplied as the decomposition progresses, it is possible to consistently maintain a weight ratio suitable for improving the decomposition rate of thermosetting plastics. Therefore, it is possible to improve the decomposition rate of the thermosetting plastic that is hard to thermally decompose.

According to the present invention, the energy required for decomposition can be reduced by efficiently performing thermal decomposition.

[Brief description of the drawings]

FIG. 1 is a system diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory view showing the effect of mixed pyrolysis.

FIG. 3 is a system diagram showing the structure of the device.

FIG. 4 is a system diagram showing an application example of the present invention to a power generation system.

FIG. 5 is a system diagram showing an application example of the present invention to a waste power generation system.

[Explanation of symbols]

10a ... Thermosetting plastic, 10b ... Thermoplastic, 100a, 100b ... Storage tank, 200a, 2
00b ... measuring device, 300 ... crusher, 310 ... melting tank,
320 ... Decomposition tank, 330 ... Residue drying furnace, 340a, 34
0b ... gas burner, 350 ... residue tray, 360 ... heat medium oil heating heat exchanger, 370a, 370b ... chlorine fixing tank,
380 ... reflux lightening tank, 390 ... decomposition gas flow meter, 40
0 ... Catalyst reforming tank, 410 ... Cooler, 420 ... Cooling tower,
430 ... Condenser, 440 ... Collected oil tank, 450 ... Air preheater, 460 ... Exhaust gas treatment device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yoshinari Hori Inventor, Yoshinari, Ibaraki Prefecture, 7-1, 1-1 Omika-cho, Hitachi City Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Yoshikichi Yamada 7, 1-chome, Omika-cho, Hitachi, Ibaraki No. 1 Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Tomoko Kaneko 7-1, Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Hitachi Research Laboratory

Claims (9)

[Claims] 1. A method for thermally decomposing a plastic by heating a mixture of a thermosetting plastic and a thermoplastic to melt or vaporize it, while adding the thermoplastic as the thermal decomposition of the mixture progresses. A method for thermally decomposing a plastic, characterized by thermally decomposing. 2. The plastic according to claim 1, wherein the thermoplastic resin is pyrolyzed while adding the thermoplastic resin in the thermal decomposition process of the mixture so as to maintain the weight ratio of the thermosetting plastic and the thermoplastic resin. Pyrolysis method. 3. The mixture according to claim 1 or 2, wherein the weight ratio of the thermosetting plastic to the thermoplastic is 0.1 or more, and preferably 1.0.
A method for pyrolyzing plastics that mixes as described above. 4. A heating means capable of controlling the temperature of an object to be heated,
In a plastic thermal decomposition apparatus equipped with a thermal decomposition tank that is heated by the heating means, means for weighing thermosetting plastics and thermoplastics so that each has a predetermined weight, and the two types of plastics are independent. And a time elapsed after the plastic is supplied to the thermal decomposition tank that heats and thermally decomposes the plastic, the temperature in the thermal decomposition tank, or the decomposition gas generated from the thermal decomposition tank. Quantity or cracked gas temperature or at least one of cracked oil amounts obtained by cooling and condensing the cracked gas, and based on the measured value, the weight of the thermoplastic to be additionally supplied to the thermal cracking tank is measured. An apparatus for pyrolyzing plastics, characterized by comprising means for determining. 5. A heating means capable of controlling the temperature of an object to be heated,
In a plastic thermal decomposition apparatus equipped with a thermal decomposition tank that is heated by the heating means, a measuring means for measuring the thermosetting plastic and the thermoplastic plastic so that each has a predetermined weight, and the two types of plastics A plastic supply means that can be independently supplied, a melting tank that heats and melts the thermoplastic, and a means that supplies the thermoplastic to the thermal decomposition tank that heats and decomposes the plastic from the melting tank. A thermal decomposition device for plastics, characterized by being provided. 6. The reforming means for adjusting the decomposition gas generated from the thermal decomposition tank to a component suitable as a fuel according to claim 4 or 5, and the decomposition gas after being reformed by the reforming means. A pyrolysis device for plastics, comprising means for cooling and condensing to obtain fuel oil. 7. A plastic oilification power generation system for generating the fuel oil produced by the plastic thermal decomposition apparatus according to claim 6 as a fuel for a diesel engine generator. 8. The method according to claim 5, wherein, in addition to the thermal decomposition tank,
A plastic thermal decomposition apparatus equipped with a residue drying furnace for heating and drying undecomposed residues. 9. The heat of plastic according to claim 5, comprising means for bringing a part of the molten plastic in the melting tank into contact with plastic as a raw material, and means for crushing the raw plastic after the treatment by the means. Decomposing device.