JP4485621B2 - Thermal decomposition of waste plastic - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a thermal decomposition method for waste plastics containing vinyl chloride. In particular, the waste plastics containing vinyl chloride can be efficiently oiled by melting, dehydrochlorination, and thermal decomposition in a single pyrolysis tank. Relates to the thermal decomposition method.
[0002]
[Prior art]
When converting plastic waste containing vinyl chloride into oil, it is processed through pretreatment including crushing and foreign matter separation, melting, dehydrochlorination, pyrolysis and reformed distillation, but these are continuously processed. It is common. The heat necessary for such melting, dehydrochlorination and thermal decomposition was supplied by the following method.
1. The heat required for melting and dehydrochlorination is set by an extruder and a heating medium heating section, introduced by heating medium oil and supplied by indirect heating.
2. The heat required for melting and pyrolysis is supplied by directly heating the outer wall of the tank with an electric heater or combustion gas.
3. The heat required for pyrolysis is obtained by extracting a certain amount of residual oil from the pyrolysis tank with a pump, circulating it through the heating section to the pyrolysis tank, and giving the heat necessary for pyrolysis in the heating section. Supply.
4). Heat is supplied by directly heating the fraction containing the pyrolysis product oil to a pyrolysis tank after heating at a high temperature in a heating furnace.
[0003]
Moreover, the following two methods were employ | adopted when extracting the thermal decomposition residue.
1. The pyrolysis residual oil is introduced into the gravity separation tank at a high temperature, periodically dropped into a cylindrical cylindrical tank with a jacket provided at the bottom, and cooled and discharged out of the system.
2. A screw conveyor is provided at the bottom of the pyrolysis tank via a ball valve, a ball valve is also installed at the outlet of the screw conveyor, and the outside is discharged out of the system while being cooled by the screw conveyor.
[0004]
Moreover, in order to discharge the coke precursor produced at the time of thermal decomposition to the outside of the system, gravity sedimentation separation or centrifugal separation has been adopted.
[0005]
By the way, when thermally decomposing mixed waste plastics, the thermal decomposition rate of each plastic differs depending on the temperature. Especially, vinyl chloride, polystyrene and polypropylene are thermally decomposed at a lower temperature than polyethylene, but the processing speed of the entire mixed waste plastic is increased. Therefore, the treatment temperature is set to a temperature corresponding to the thermal decomposition rate of polyethylene, which takes the longest time for decomposition.
[0006]
[Problems to be solved by the invention]
However, the conventional thermal decomposition method of waste plastic has the following problems.
1. In the method of heating with heat transfer oil, the limit temperature of commercially available heat transfer oil is as low as about 300 ° C and can only be used for melting waste plastic, while the temperature of dehydrochlorination is 300 ° C to 320 ° C. Since the temperature difference ΔT is small, it cannot be heated efficiently, and if the temperature of the heat transfer oil is raised to a temperature higher than the limit temperature, the heat deteriorates and the life is shortened.
2. In-pipe coking occurs when the pyrolysis residue is circulated and heated.
3. When heat is supplied only by heating the pyrolysis product oil at a high temperature and blowing it into the tank, the heating furnace becomes large.
4). In the method of directly heating the outer wall of the tank with an electric heater or high-temperature combustion gas, coking is likely to be generated on the inner wall of the tank.
5). In particular, if heat is retained in each tank or each device with a heat medium device or the like during batch processing, the cost increases.
[0007]
In addition, when the waste plastic to be pyrolyzed is only polyethylene, polypropylene and polystyrene in the conventional waste plastic pyrolysis method, the residue can be discharged out of the system relatively easily, but the waste collected separately from general waste is collected. Plastics contain vinyl chloride, thermosetting resin, wood chips, rubber, metal, earth and stone, etc. When waste plastic containing these is pyrolyzed, the residual fluidity is poor, and the conventional method is stable outside the system. It cannot be discharged.
[0008]
Furthermore, in the conventional waste plastic pyrolysis method, the pyrolysis temperature is set high in order to improve the processing speed, especially when pyrolyzing mixed waste plastic, it is set to the pyrolysis temperature and reaction time of polyethylene which is most difficult to decompose. Therefore, plastics that are more easily decomposed than polyethylene are decomposed and vaporized earlier, and the resulting residue is exposed to a high-temperature atmosphere within the reaction time of polyethylene, so that it is transformed into asphalt, pitch, and even coke.
[0009]
Here, FIG. 5 shows thermal decomposition characteristics of various plastics when the temperature is raised by 300 ° C. per hour in an N ₂ atmosphere. In the figure, PVC is vinyl chloride resin, UF is urea resin, UR is polyurethane resin, PF is phenol resin, PMMA is methacrylic resin, PS is polystyrene resin, ABS is ABS resin, PP is polypropylene resin, PE is polyethylene resin, PET Is a PET resin.
[0010]
In addition, it is desirable that the coke precursor produced by the pyrolysis reaction is concentrated early and discharged out of the system, but in reality, many foreign substances may be entangled and fluidity may be reduced, making it difficult to discharge. Maybe there. Therefore, in the conventional thermal decomposition method of waste plastic, discharging is performed in a state before concentration, and since the amount of thermal decomposition is small, the oil yield is reduced.
[0011]
Further, in the conventional thermal decomposition method of waste plastic, there are the following problems when continuously converting the mixed waste plastic containing vinyl chloride into oil.
1. Since the dehydrochlorination treatment is carried out continuously with an extruder, pretreatment facilities such as crushing, fractionation and drying are expensive.
2. Since the raw material is waste, clogging of each device or piping is likely to occur. In the continuous method, it is difficult to cope with the occurrence of a blockage, and the number of devices is increased and complicated, and advanced operation techniques are required.
3. Since dehydrochlorination is performed continuously, short paths are likely to occur, the dehydrochlorination rate is not stable, and as a result, the physical properties of the product are adversely affected.
[0012]
In view of such conventional problems, the present invention is a waste plastic in which waste plastic containing vinyl chloride can be efficiently liquefied by performing batch, melting, dehydrochlorination, and thermal decomposition in one pyrolysis tank. It is an object of the present invention to provide a thermal decomposition method.
[0013]
[Means for Solving the Problems]
Therefore, in the method for pyrolyzing waste plastic according to the present invention, the waste plastic containing vinyl chloride is melted in a batch in a thermal decomposition tank, dehydrochlorinated, and then thermally decomposed. The waste plastic is pyrolyzed at a temperature as low as 400 ° C within the decomposable temperature range, and half of the waste plastic is liquefied. The residue is extracted from the pyrolysis tank, and the waste plastic is pyrolyzed. The residue is pyrolyzed at a high temperature within the temperature range, and the residue is converted to oil. On the other hand, of the semi-pyrolytic oil at low temperature, the semi-pyrolytic oil is twice as heavy as the amount of waste plastic input. It is made to remain in a cracking tank, and the amount of heat required for melting and dehydrochlorination of the next input waste plastic is supplied by the retained heat of the remaining semi-pyrolytic oil.
[0014]
One of the features of the present invention is that the amount of heat required for melting and dehydrochlorination of the next input waste plastic is left in the pyrolysis tank with semi-pyrolytic oil twice the weight of the amount of waste plastic input. However, if the amount of heat is simply supplied by the retained heat of the semi-pyrolytic oil, the amount of heat necessary for melting and dehydrochlorination may be insufficient. In this case, as shown in FIG. 3, among the pyrolysis product oil extracted from the pyrolysis tank, the light oil fraction is heated to form high-temperature steam V, and the high-temperature steam V1, V2 is converted into the pyrolysis tank 100. By flowing through the jacket and the serpentine tube, it is possible to supply a shortage of heat necessary for melting and dehydrochlorination of the next input waste plastic.
[0015]
In addition, the high temperature steam of the light oil fraction is circulated through the jacket and serpentine of the pyrolysis tank to supply the shortage of heat necessary for melting and dehydrochlorination. Of the pyrolysis product oil extracted from the tank, the light oil fraction is heated to form high-temperature steam, part V1, V2 of which is circulated through the jacket and serpentine of the pyrolysis tank 100, and the remaining part V3 is the pyrolysis tank. The amount of heat necessary for thermal decomposition can be supplied by blowing directly into 100.
[0016]
As mentioned above, waste plastic is mildly pyrolyzed at a low temperature in a pyrolysis tank, and the amount of heat required for melting and dehydrochlorination is supplied with the semi-pyrolytic oil, but when mild pyrolysis is adopted, Oil conversion efficiency decreases. Therefore, if the residue after mild pyrolysis is extracted from the pyrolysis tank and subjected to high-temperature hard pyrolysis, the oil conversion efficiency can be improved. That is, according to the present invention, it is possible to provide a method for pyrolyzing waste plastic in which the waste plastic is pyrolyzed in two stages, mild pyrolysis and hard pyrolysis.
[0017]
The method for pyrolyzing waste plastics according to the present invention is a method in which waste plastics containing vinyl chloride are melted and dehydrochlorinated in batches in a pyrolysis tank, and then thermally decomposed to oily waste plastics. The waste plastic is mildly pyrolyzed at a low temperature within the temperature range in which the waste plastic can be pyrolyzed, and half of the waste plastic is liquefied, and the residue is extracted from the melting, dehydrochlorination, and pyrolysis tank. In addition, the residue is hard pyrolyzed at a high temperature within a temperature range in which the waste plastic can be pyrolyzed, thereby converting the residue into oil.
[0018]
Since the hard pyrolysis is performed by extracting the residue from the pyrolysis tank, it is necessary to perform it with the equipment for hard pyrolysis. That is, hard pyrolysis is performed by introducing the residue together with sand or ceramic balls into a kiln furnace or a tank equipped with a stirrer. The conditions for hard pyrolysis are appropriately selected according to the type of waste plastic to be input. However, considering the type of waste plastic to be actually recovered, hard pyrolysis is performed by reacting at a temperature of about 475 ° C. for about 1 hour. Can be.
[0019]
According to the tank-type batch experiment conducted by the present inventors, the waste plastic was melted at 300 ° C, and the vinyl chloride was heated at 300 ° C for about 3 hours to obtain a dehydrochlorination rate of 95%. It was confirmed that the pyrolysis of major plastics except polyethylene was completed in about 4 hours.
[0020]
In the present invention, heat necessary for melting, dehydrochlorination and thermal decomposition is supplied by the following method. That is, the heat twice the weight of about 380 ° C thermal decomposition residue oil of the required heat amount to the molten-dehydrochlorination of (semi pyrolysis oil) waste plastics charged amount leaving the pyrolysis chamber, leaving the By mixing the cracked residue and waste plastic, the necessary heat is supplied by the retained heat of the pyrolyzed residue. The waste plastic melts in a short time due to the retained heat of the pyrolysis residual oil and reaches a dehydrochlorination temperature of 300 ° C. When the amount of heat is insufficient, out of the pyrolysis product oil from the jacket of the pyrolysis tank and the tub tube in the tank, light oil is converted into high-temperature steam at the heating section, and this is used as a heat medium to supply the shortage of heat. it can. At that time, vaporized hydrogen chloride, moisture, light hydrocarbons, phthalic acid and the like are treated in a neutralization or hydrochloric acid recovery step. Further, the waste plastic is charged with a slide damper 120 as shown in FIG.
[0021]
Moreover, the heat required for thermal decomposition is supplied by the following method. That is, of the pyrolysis product oil obtained by pyrolysis, light oil is used as high-temperature steam, a part is given from the jacket of the tank and the serpentine in the tank, and the other can be given by blowing directly into the tank. . Each step of melting, dehydrochlorination, and thermal decomposition is performed according to the time schedule shown in FIG.
[0022]
It is important not to carry out pyrolysis at once, but to divide it into two stages: mild pyrolysis at low temperature and hard pyrolysis at high temperature (thermal decomposition temperature of about 475 ° C., reaction time of 1 hour). That is, as shown in FIG. 4, mild pyrolysis is performed in the pyrolysis tank 100, and hard pyrolysis is performed using a special device for the residue obtained from mild pyrolysis. The special equipment is an external heat type small kiln furnace 140 or a tank with a stirrer, and it is necessary to heat while mixing with sand or ceramic balls in order to peel off the coke. A small kiln furnace 140 or a tank with a stirrer is provided with a low-pressure steam or warm water jacket 141 and heated, while the residue is discharged out of the system via a ball valve 142.
[0023]
When waste plastic containing vinyl chloride and foreign matter (metal, wood scrap, thermosetting resin, rubber, etc.) is pyrolyzed, the pyrolysis residue will be less fluid and difficult to discharge out of the system. Discharge mechanically by the method.
1. As shown in FIG. 3, no valve is provided between the bottom of the pyrolysis tank 100 and the screw conveyor 110, the nozzle diameter of the tank bottom is 6B or more, and the pyrolysis tank 100 and the screw conveyor 110 are integrated. And
2. The pitch and depth of the screw conveyor 110 are determined in consideration of the size of the foreign matter, and the screw outlet side is free to absorb thermal expansion. The screw body is provided with a jacket 113 and heated using a high temperature steam of light oil as a heat medium.
3. A ball valve 112 having a diameter of 6B or more is provided at the outlet of the screw conveyor 110, and a pusher 111 driven by an air cylinder is attached to prevent the ball valve 112 from being blocked.
4). The pyrolysis residue receiving tank 130 is provided with a low pressure steam or hot water jacket 131, and a ball valve 132 having a diameter of 6B or more is attached to the bottom of the tank. In order to prevent the ball valve 132 from being blocked, it is driven by an air cylinder. A machine 133 is provided and discharged outside the system at a temperature of 150 ° C. or lower.
[0024]
[Operation and effect of the invention]
According to the present invention, the following effects can be obtained.
1. Batch effect
(1). The specifications of the pretreatment (crushing, dividing of foreign matter, drying) equipment will be relaxed.
(2). Raw material conditions (type, shape, etc.) are relaxed.
(3) A high removal rate of hydrogen chloride can be stably obtained in the dehydrochlorination treatment.
(4) The equipment is simple and operation is particularly easy.
(5). Reliability is ensured for product properties.
(6) The equipment capacity is larger than the continuous type, but the number of equipment is small and the equipment cost can be made almost the same.
(7) Heat and product loss can be minimized by creating a time schedule.
[0025]
2. Effect of heat supply method
(1). The melting, dehydrochlorination, and thermal decomposition times per batch can be greatly reduced. According to the experiments by the present inventors, it was confirmed that the conventional heat supply method required 9.5 hours instead of 12 hours per operation.
(2). High temperature semi-pyrolysis oil twice the weight of waste plastic input is mixed, so the viscosity of the melt quickly decreases and there is no short path in the pyrolysis tank. A stable dehydrochlorination rate can be obtained.
(3) Since heat is supplied to the pyrolysis tank in a mild manner, coking is unlikely to occur.
(4). Expensive heat transfer oil and equipment can be eliminated.
[0026]
3. Effect of residue extraction method
(1). It can sufficiently deal with waste plastics separated from general waste with the most severe foreign matters.
(2). Pretreatment equipment specifications and raw material conditions can be relaxed.
[0027]
4). Effects of mild and hard pyrolysis
(1) Even if undecomposed oil is present in the residue, since the residual oil is hard pyrolyzed in a later step, the oil yield is improved.
(2) Since only pyrolysis is performed in the pyrolysis tank, coking can be greatly suppressed.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on specific examples shown in the drawings. FIG. 1 shows a preferred embodiment of the waste plastic pyrolysis method according to the present invention. The processing raw material is a waste plastic separately collected from general waste, and foreign substances include sand, pebbles, metal, wood scrap, thermosetting resin, synthetic rubber and the like. The waste plastic is subjected to bag breaking, foreign matter separation, drying, and compression packaging in a known pretreatment device 10.
[0029]
Before the waste plastic is charged, about 380 ° C residual thermal cracking residue for dilution is left in the pyrolysis tank 12 twice as much as the amount of raw material input, and the jacket and the serpentine tube of the pyrolysis tank 12 are about 460 ° C. High-temperature steam of pyrolysis light oil is circulated as a heat transfer oil.
[0030]
Most of the heat required for melting and dehydrochlorination of the input material is provided by the retained heat of the pyrolysis residual oil of about 380 ° C. left in the pyrolysis tank 12, and the insufficient heat is the jacket of the pyrolysis tank 12. And given from the serpentine.
[0031]
The raw material is charged into the thermal decomposition tank 12 by the slide damper 11, and the valve 31 is opened and the valve 32 is closed from the time of loading. In this state, the input raw material is dissolved in the thermal decomposition tank 12, and dehydrochlorination is performed at about 300 ° C. After the raw material is charged, if it is held for about 3 hours, the raw material is melted and dehydrochlorinated.
[0032]
The mixed gas containing hydrogen chloride is incinerated while suppressing dioxins by a waste gas treatment device such as submerged combustion. After 3 hours, the valve 32 and the valve 33 are opened, and the valve 31 is closed.
[0033]
The amount of heat required for the pyrolysis reaction is that the pyrolysis light oil is heated to about 460 ° C. in the heating furnace 28, and a part thereof is directly blown into the pyrolysis tank 12 and distributed to the jacket and the serpentine of the pyrolysis tank 12 And the temperature of the pyrolysis tank 12 is controlled to be about 400 ° C.
[0034]
When the internal temperature of the pyrolysis tank 12 reaches 400 ° C., when the reaction time is about 1.5 hours and the tank level of the pyrolysis tank 12 decreases to a certain value, the first stage of pyrolysis (mild heat) It is determined that (disassembly) has been completed, and the valve 33 is closed.
[0035]
Next, residual oil having poor fluidity including foreign matters remaining in the pyrolysis tank 12 is transferred to the residue receiving tank 15 while the valve 42 provided at the outlet of the screw conveyor 13 is opened and the pusher 14 is driven. After the residual oil is cooled to about 150 ° C. in the residue receiving tank 15, the valve 43 is opened and the pusher 16 is driven to discharge the residue out of the system.
[0036]
In order to improve the oil yield of waste plastic, instead of the residue receiving tank 16, a small external heat kiln furnace or a tank with a stirrer is used, mixed with sand or ceramic balls for peeling off the coke growing on the inner wall, and the temperature Hard pyrolysis is performed under conditions of about 475 ° C. and a residence time of about 1 hour. The vaporized pyrolysis vapor is sent to the distillation column 18.
[0037]
When the transfer to the residue receiving tank 15 is completed, the next raw material is charged into the pyrolysis tank 12.
[0038]
The pyrolysis product oil pyrolyzed in the pyrolysis tank 12 is extracted and blown into the distillation tower 18. The distillation column 18 is provided with a cooler 21 at the top and a heating serpentine 19 at the bottom.
[0039]
The tower top temperature of the distillation tower 18 is normally controlled to about 150 ° C. by the tower top cooler 21, and only the pyrolysis light oil is condensed and cooled via the heat exchanger 20 and the cooler 22, and is sent to the light oil receiving tank 23. Can be stored. Of the pyrolysis product oil, medium oil and heavy oil are stored as they are at the bottom of the distillation column 18.
[0040]
Light oil in the pyrolysis light oil receiving tank 23 is sent to the heating furnace 28 via the heat exchanger 20 and the heat exchanger 26 by the pump 39, and is heated to about 460 ° C. As described above, this high-temperature steam is used as the amount of heat necessary for melting / dehydrochlorination and thermal decomposition.
[0041]
When the thermal decomposition in the thermal decomposition tank 12 or the external heat type small kiln furnace is completed, the valve 35 is opened, high temperature steam of about 460 ° C. is allowed to flow through the bottom tube of the distillation column 18, and The distillation operation of medium heavy oil accumulated at the bottom begins. By changing the temperature at the top of the distillation column 18, the medium oil is extracted and condensed and cooled by the heat exchanger 20 and the cooler 22, then the valve 36 is closed and the valve 37 is opened so that the activated clay is attached. It is sent to the medium oil tank 24 and collected. Although the distillation system is batch-wise as described above, the distillation system can be continuous.
[0042]
The heavy oil remaining at the bottom of the distillation tower 18 is sent by a pump 38 to a heavy oil receiving tank 30 with activated clay through a cooler 29.
[0043]
Raw materials in the slide damper 11 when projected input to the thermal decomposition tank 1 2, after cooling to below 380 ° C if the liquid temperature of the thermal decomposition tank 12 is not less than 380 ° C, placing the raw material Is desirable.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a preferred embodiment of a method for pyrolyzing waste plastic according to the present invention.
FIG. 2 is a diagram illustrating a timing chart of operations according to the embodiment.
FIG. 3 is a diagram for explaining means for solving the problem.
FIG. 4 is a diagram for explaining means for solving the problem.
FIG. 5 is a diagram for explaining a problem to be solved by the invention.
[Explanation of symbols]
12 Pyrolysis tank 13 Screw conveyor 14 Pusher 42 Valve at the screw conveyor outlet

Claims (3)

Waste plastic containing vinyl chloride is melted in batches in a thermal decomposition tank, dehydrochlorinated, and then thermally decomposed.
Waste plastic is pyrolyzed at a temperature as low as 400 ° C of the temperature range in which the waste plastic can be pyrolyzed in the pyrolysis tank, and half of the waste plastic is converted to oil, and the residue is extracted from the pyrolysis tank. And the residue is pyrolyzed at a high temperature within the temperature range in which the waste plastic can be pyrolyzed,
Of the semi-pyrolytic oil at low temperature, the semi-pyrolytic oil having a weight twice as much as the amount of waste plastic to be charged next is left in the pyrolysis tank, and the following heat is retained by the retained heat of the remaining semi-pyrolytic oil. A method for thermal decomposition of waste plastic, characterized in that the amount of heat required for melting and dehydrochlorination of the input waste plastic is supplied.   Of the pyrolysis product oil extracted from the pyrolysis tank, the light oil fraction is heated to form high-temperature steam, and the high-temperature steam is circulated through the jacket and the serpentine of the pyrolysis tank to melt the next input waste plastic. 2. The method for pyrolyzing waste plastics according to claim 1, wherein a shortage of heat necessary for dehydrochlorination is supplied.   Among the pyrolysis product oil extracted from the pyrolysis tank, the light oil fraction is heated to form high-temperature steam, a part of which is circulated through the jacket and serpentine of the pyrolysis tank, and the remainder is directly in the pyrolysis tank. The waste plastic thermal decomposition method according to claim 1, wherein the amount of heat necessary for thermal decomposition is supplied by blowing.

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