JP2002179837A - Method of treating waste plastic and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for processing waste plastics that can subject waste plastics to the thermal cracking whereby the cracked distillate is formed and the pH of the distillate can be neutralized simultaneously. SOLUTION: Alkaline substance is added from the alkaline additive feeder 20 to waste plastics including PET. The waste plastics 1 is subjected to pyrolytic dechlorination in the pyrolytic dechlorinator 3, then to thermal cracking in the thermal cracker 4 to form the cracked gas. The acidic gas occurring in the thermal cracker 4 is neutralized with an alkaline substance. The cracked gas from the thermal cracker 4 is recovered in the cracked oil recovery equipment 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating waste plastic, and more particularly, to a method and an apparatus for treating waste plastic for generating cracked oil from waste plastic discharged from homes.

[0002]

2. Description of the Related Art FIG.
This will be described below. In FIG. 15, waste plastic 1 discharged from home is pre-treated (removal of foreign matter and crushed) by a pre-treatment device 2, and is decomposed through a heating dechlorination treatment device 3, a thermal decomposition treatment device 4 and a decomposition gas cooling device 5. The cracked oil is recovered by the oil recovery device 6. The gas (hydrogen chloride, steam, combustible gas) generated in the heating dechlorination apparatus 3 is processed in the desalination gas processing apparatus 7 as a desalination gas. Ashes, carbides, and the like remaining in the thermal decomposition treatment device 4 are discharged as residues 8.

[0003]

The waste plastic discharged from the home contains about 5 to 15% of PVC, and hydrogen chloride gas is generated at the time of thermal decomposition in the thermal decomposition processing apparatus 4, and the Therefore, dechlorination is performed in the dechlorination apparatus 3 before thermal decomposition in order to reduce the amount of organic chlorine in the decomposed oil in order to cause corrosion of the decomposed oil and acidification of the decomposed oil. However, in recent waste plastics, even after dechlorination, the cracked oil shows an acidity of 2 to 4 and is neutralized (neutral range in petroleum refining: 4.
4 or more and less than 8.2). For this reason, corrosion of the distillation column 9 provided on the downstream side of the cracked oil recovery device 6 and the storage tank 10 of the refined oil has become apparent.

[0004] The present invention has been made in view of the above points, and a method and a method for treating waste plastic capable of producing cracked oil from waste plastic and neutralizing the cracked oil. It is intended to provide a device.

[0005]

Means for Solving the Problems The present inventors diligently studied the acidification of cracked oil, and found that, in addition to 5 to 15% of PVC which has been conventionally mixed, recently waste plastics have 2 to 15%. 15% (about 8% on average) of PET is mixed in, and when PET undergoes thermal decomposition treatment at 400 ° C. or higher, organic acids containing benzoic acid as a main component are generated, and these organic acids are gaseous. Therefore, it was found that the acidification of the cracked oil was caused despite the desalting operation, because the cracked oil was mixed with the cracked oil together with other cracked gas.

The present invention achieves neutralization of cracked oil by neutralizing and fixing benzoic acid generated during the thermal decomposition treatment with an alkali substance and separating it from a cracked gas.

That is, the present invention provides a method for treating waste plastic containing PET, the step of adding an alkaline substance to the waste plastic, the step of thermally decomposing the waste plastic in a thermal decomposition apparatus, A process for generating cracked oil in a cracked oil recovery device using cracked gas generated from the processing device, wherein the acidic gas generated in the pyrolysis process is neutralized with an alkaline substance. It is.

[0008] The present invention relates to an apparatus for treating waste plastic containing PET, an apparatus for adding an alkaline substance to waste plastic, a pyrolysis apparatus for thermally decomposing waste plastic, and a thermal decomposition apparatus. And a cracked oil recovery unit that generates cracked oil from cracked gas generated from the waste gas.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment An embodiment of the present invention will be described below with reference to the drawings. 1 to 6 are views showing a first embodiment of the present invention.

As shown in FIGS. 1 to 6, a waste plastic processing apparatus includes a waste plastic 1 pre-processing apparatus 2;
The apparatus includes a heat dechlorination apparatus 3 for thermally dechlorinating the waste plastic 1 and a thermal decomposition apparatus 4 for thermally decomposing the waste plastic 1.

A pretreatment device 2 and a heat dechlorination device 3
Between them, an alkaline substance addition device 20 for adding an alkaline substance to the waste plastic 1 is provided. Further, a desalination gas treatment device 7 including an incinerator and the like is connected to the heat dechlorination treatment device 3.

A cracking oil recovery device 6 is connected to the thermal cracking treatment device 4 via a cooling device 5. The cracking oil recovery device 6 has a distillation column 9 and refined oil storage tanks 10a, 10a.
0b and 10c are sequentially connected.

Further, a residue hopper 8a for receiving the residue 8 is connected to the thermal decomposition processing apparatus 4.

Next, the operation of the present embodiment having the above configuration will be described. As shown in FIG. 1, the waste plastic 1 is pre-processed (for removing foreign matters,
Then, an alkaline substance (eg, slaked lime, quick lime) is added to the waste plastic 1 from the alkaline substance addition device 20. The waste plastic 1 is then subjected to a heat dechlorination treatment by the heat dechlorination treatment device 3, and gas (hydrogen chloride, steam,
The combustible gas) is dechlorinated in the dechlorination unit 7 as desalination gas.

Here, the thermal dechlorination in the thermal dechlorination apparatus 3 is a known technique, and has a desalination characteristic as shown in FIG. As shown in FIG. 2, the desalination reaction starts at about 250 ° C., but at 250 ° C., the reaction takes a long time, so it is set to a slightly higher temperature (300 to 350 ° C.) and
(Residence time of 00 to 300 seconds) to perform dechlorination of about 90%.

Thereafter, the waste plastic 1 is thermally decomposed in the thermal decomposition treatment device 4, and the decomposed gas is cooled in the cooling device 5 and then recovered in the decomposed oil recovery device 6.

The cracked oil in the cracked oil recovery device 6 is distilled in the distillation column 9 and the refined oil storage tanks 10a, 10b, 1
It is stored in 0c.

The thermal decomposition treatment in the thermal decomposition treatment device 4 is also a known technique, and the molten waste plastic 3 after the dechlorination treatment is used.
1 is thermally decomposed while maintaining a high temperature to obtain a decomposed gas. The main components in waste plastic 1 are PE, PP, PS,
PET and PVC, which have thermal decomposition characteristics as shown in FIG. FIG. 3 shows a relatively large heating rate (3
(00 ° C./h), which indicates that the decomposition rate is small. However, when the heating rate is reduced, the graph shifts to the left and decomposes at a lower temperature. In FIG. 3, when each temperature is maintained for about one hour, PS becomes 350
° C, PP decomposes at 400 ° C, PE decomposes at 420 ° C
And PET decomposes at 90% or more at 430 ° C. From such knowledge, usually, in the thermal decomposition processing apparatus 4, 35
Hold at 0-450 ° C for several hours.

During this time, the PV contained in the waste plastic 1
FIG. 4 shows the reaction between C and PET and the alkaline substance (slaked lime) added from the alkaline substance addition device 20. The reaction is performed in the following order.

(1) Generation of hydrogen chloride gas by dechlorination of PVC First, PVC is decomposed in the thermal dechlorination apparatus 3 to generate hydrogen chloride gas.

(2) Partial neutralization of hydrogen chloride with alkali Alkaline substance (slaked lime) in the heating dechlorination apparatus 3
Particles are masked by a plastic melt (molten waste plastic) 31 such as PP or PE, so that only a part (about 50%) of the hydrogen chloride gas is neutralized on the surface of the slaked lime particles to form calcium chloride. Generate. Unreacted hydrogen chloride gas is discharged to the desalination gas treatment device 7. Unreacted slaked lime becomes residual slaked lime, which accompanies the calcium chloride and the molten waste plastic 31 in the thermal decomposition treatment apparatus 4.
Move to

(3) Generation of Benzoic Acid by Decomposition of PET Next, in the thermal decomposition treatment device 4, the molten waste plastic 31 is thermally decomposed. At this time, since the thermal decomposition reaction is an endothermic reaction, thermal decomposition is performed in ascending order of thermal decomposition temperature, that is, PS and PP, and finally PE and PET are thermally decomposed. PE
The pyrolysis of T produces benzoic acid gas at approximately 40% by weight of PET.

(4) Immobilization of benzoic acid by alkali During this time, in the thermal decomposition treatment device 4, PET is concentrated around the remaining calcium particles when PS and PP are decomposed, and the generated benzoic acid gas Is efficiently captured and immobilized on the surface of calcium particles to produce calcium benzoate. Calcium benzoate is a very stable solid at high temperatures. For example, the efflorescence and decomposition temperature of calcium benzoate are 600 ° C. or higher, and are retained in the thermal decomposition treatment device 4 and do not mix into the cracked oil in the cracked oil recovery device 6.

(5) Discharge of calcium benzoate Calcium chloride, unreacted calcium, calcium benzoate and the like in the thermal decomposition treatment device 4 are discharged as residue 8 to a residue hopper 8a.

The effect of removing benzoic acid and P
H is shown in FIG. 5, and a list of the effects is shown in FIG. According to the present invention, in order to add an alkaline substance into the waste plastic 1 before the heating dechlorination treatment apparatus 3,
The pH of the cracked oil is improved from 2.5 to 3.5 to around 5.0 to 7.5. For this reason, corrosion of the distillation column 9 can be prevented, and benzoic acid (and benzoate) can be reduced to 0.05%.
% Of benzoic acid (and benzoate)
Blockage of the pipe due to precipitation of the water can be prevented.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIGS.

(Basic configuration) In the thermal decomposition treatment apparatus 4, the molten waste plastic 31 is heated to 350 to 400 ° C. by appropriately setting the holding time or catalyzing by a trace amount of metal contained in the waste plastic 1. Then PE
It was found that components other than T and PE were almost decomposed.

The present embodiment is based on this finding.
In the thermal decomposition treatment apparatus 4, the concentration of PET and PE is promoted to increase the reaction efficiency between the alkaline substance and the acidic gas generated by the decomposition of PET. Depending on the type of the thermal decomposition processing apparatus 4, two types of constitutions, continuous decomposition and intermittent (batch) decomposition, are possible. Each is described below.

(Construction of Continuous Decomposition) FIG. 7 shows the structure of the thermal decomposition apparatus 4 for continuous decomposition. As shown in FIG. 7, the thermal decomposition processing apparatus 4 has a horizontal kiln type thermal decomposition tank 30,
The molten waste plastic 31 is supplied to the pyrolysis tank 3 by the input device 32.
It is designed to be continuously charged into 0. Pyrolysis tank 3
The molten waste plastic 31 charged into the chamber 0 is gradually decomposed by heat and becomes the residue 8 and moves to the discharge port 33 side. During this time, the pyrolysis tank 30 is rotated by a roller 34 driven by a motor 34.

As shown by the solid line in FIG. 8, the inside of the pyrolysis tank 30 has a temperature gradient such that the temperature gradually increases from the charging side A to the discharging side C. For example, the temperature of the input side A of the pyrolysis tank 30 is 350 ° C., the temperature of the center B is 400 ° C., and the temperature of the discharge side C is 500 ° C. At this time, PE between 350 and 400 ° C.
Since components other than T and PE are almost decomposed, PET, PE, and alkali powder are concentrated in the molten waste plastic 31. The concentration of the alkaline substance increases toward the discharge side C as indicated by the dashed line in FIG. For this reason, the acidic gas generated when PET is decomposed at around 430 ° C. efficiently reacts with the alkaline substance powder and is neutralized and fixed. Therefore, the amount of powder of the alkaline substance added can be reduced.

Configuration of Intermittent (Batch) Decomposition FIG. 9 shows the structure of the thermal decomposition processing apparatus 4 at the time of intermittent (batch) decomposition. As shown in FIG. 9, the thermal decomposition processing apparatus 4 has a vertical stirring type thermal decomposition tank 40 and a molten waste plastic 31.
Into the thermal decomposition tank 40 intermittently. Molten waste plastic 3 charged in pyrolysis tank 40
1 is gradually decomposed with time, and is discharged from the discharge valve 41 as the residue 8 after the completion of the pyrolysis. In FIG. 9, reference numeral 43 denotes a stirring blade.

As shown by the solid line in FIG. 10, the temperature in the pyrolysis tank 40 gradually increases from the charging side to the residue discharging side. For example, 350-
If the temperature is gradually increased from the end of charging and the temperature is set to 500 ° C. when the residue is discharged, the P
Components other than ET and PE decompose. For this reason,
In the molten waste plastic 31, concentration of PET, PE, and alkali powder occurs. As shown by the one-dot chain line in FIG. 10, the concentration of the alkali powder gradually increases from the start of charging to the end of charging. For this reason, the acidic gas generated when PET is decomposed at around 430 ° C. efficiently reacts with the alkaline substance powder to be neutralized and fixed, whereby the amount of the alkaline substance powder added can be reduced.

As described above, according to the present embodiment, the concentration of the powder of PET, PE, and the alkaline substance is promoted by the thermal decomposition treatment apparatus 4, and the reaction between the alkaline substance and the acidic gas generated by the PET decomposition is performed. Increases efficiency. Therefore, the amount of the alkali powder added can be reduced.

Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIGS. As shown in FIGS. 11 to 14,
The alkaline substance may be added from the alkaline substance adding device 20 by an addition amount determined based on the content of PET and PVC in the waste plastic.

The addition rate (%) of an alkaline substance (eg, slaked lime powder, quick lime powder) is determined in advance by experiments based on the mixing rate of PVC and PET contained in the waste plastic 1. FIG. 13 shows the results of this experiment. In FIG. 13, the addition rate (%) of the alkaline substance is set in a range from the lower limit addition rate to the upper limit addition rate (preferably, an appropriate addition rate).
The specific range of the addition rate is as shown in the quick reference table shown in FIG. The addition rates shown in FIGS. 13 and 14 are for the case where the alkaline substance is slaked lime powder, and when the alkaline substance is the quick lime powder, the respective addition rates are multiplied by 0.78.

Referring to FIG. 13 and FIG.
The case where the mixing amount = 0.56 × the PET mixing amount is used as a boundary. The pH of petroleum is specified in JIS-K2252 (petroleum products and reaction test method) to be in the range of 4.4 to 8.2, and the lower limit addition rate shown in FIGS. 13 and 14 is for preventing acidification of cracked oil. , And the upper limit addition rate indicates an addition rate determined for the purpose of preventing alkalinization of the cracked oil.

By the way, a part of the alkaline substance (eg, slaked lime powder, quick lime powder) added to the waste plastic 1 is consumed in the heat dechlorination apparatus 3 as shown in FIG. The remaining alkaline substance undergoes a reaction as shown in FIG. 12 in the thermal decomposition treatment apparatus 4 to fix benzoic acid, prevent benzoic acid from being mixed into the decomposed oil, and suppress the acidification of the decomposed oil.

FIGS. 11 and 12 show waste plastic 1
PVC mixing rate of 10%, PET mixing rate of 10%,
In addition, it is an experimental result showing a relationship between slaked lime addition rate and hydrochloric acid recovery rate (A) when slaked lime is used as the alkaline substance powder, and a relationship between slaked lime addition rate and benzoic acid recovery rate in cracked oil (B). . In this case, the slaked lime addition rate was determined based on FIG.
The appropriate addition rate becomes 5.9%.

In FIG. 11, a represents a reaction efficiency of 0%.
B shows the case where the reaction efficiency is 100%, and c shows the case
Indicates an experimental value (average reaction efficiency 60%).

[0040] In FIG. 11, for example, when HCl recovery rate of the _{A 1,} Based on the experimental value C, the unreacted slaked lime _X 1 -X ₂ is generated in the heating dechlorination unit 3.

The unreacted slaked lime of X ₁ -X ₂ is then sent to the thermal decomposition treatment unit 4.

In FIG. 12, d indicates the case where the reaction efficiency is 0%, e indicates the case where the reaction efficiency is 100%, and c indicates the experimental value (average reaction rate 50%).

In FIGS. 11 to 14, the addition ratio of the alkaline substance is as follows.

(Equation 1) Say.

As described above, according to the present embodiment, an appropriate alkali substance addition rate according to the PVC mixing rate and the PET mixing rate in the waste plastic 1 is obtained.
Even if the PVC mixing ratio and the PET mixing ratio change, the pH of the cracked oil can be maintained at neutral.

Another Embodiment Next, another embodiment of the present invention will be described. In FIG. 1, the heat dechlorination apparatus 3 may be omitted. In this case, since hydrogen chloride gas is not generated from the heat dechlorination apparatus 3, no alkaline substance is consumed by the hydrogen chloride gas. Therefore, the added alkaline substance firstly undergoes a neutralization reaction with an acid gas such as benzoic acid generated by the decomposition of PET in the thermal decomposition treatment device 4. In this case, the descriptive formula for the case (2) is used in FIG. 13 for the necessary alkali addition rate. In FIG. 14, the case where PVC is 0% is used, and an alkaline substance is added based on the addition rate of the alkaline substance corresponding to the content (%) of PET.

In FIG. 1, the decomposition gas of the molten waste plastic 31 generated in the thermal decomposition processing device 4 is cooled by a cooling device 5.
May be sent directly to the cracked oil recovery device 6 without cooling.

Organic acids such as terephthalic acid and benzoic acid mixed in the decomposition gas precipitate at a temperature in the range of 200 to 300 ° C., and cause clogging of piping and corrosion of equipment. By sending the cracked gas to the cracked oil recovery device 6 without cooling, the addition of an alkaline substance removes the organic acid gas such as terephthalic acid and benzoic acid, and further prevents the precipitation of these organic acids. Prevention of pipe blockage and corrosion of equipment can be prevented.

The waste plastic 1 may contain PVC or may not contain PCV.

Although the alkaline substance used, alkaline substance powder, slaked lime powder and quick lime powder have been described, they are not necessarily limited to powder. For example, it is possible to use alkaline substance pellets, alkaline substance lumps, and shaped alkaline substances.

Further, FIG. 1 shows an example in which the alkaline substance adding device 20 is provided in front of the thermal dechlorination device 3, but the present invention is not limited to this. It is also possible to add directly to the thermal decomposition apparatus 4.

In this case, the consumption of alkali in the heating dechlorination apparatus 3 used for fixing and removing the organic acid gas such as terephthalic acid and benzoic acid generated in the thermal decomposition processing apparatus 4 is reduced by the total amount of the added alkaline substance. Since it does not occur, the amount of alkali added can be reduced.

[0052]

As described above, according to the present invention, PH in cracked oil obtained by subjecting waste plastic to thermal decomposition is neutralized, and corrosion of equipment can be prevented. In addition, because benzoic acid and benzoate can be removed to a high degree,
Pipe clogging caused by precipitation of benzoic acid and benzoate can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a waste plastic processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram in a heating dechlorination apparatus.

FIG. 3 is a diagram showing thermal decomposition characteristics of various plastics.

FIG. 4 is an explanatory view showing a calcium balance model.

FIG. 5 is a characteristic diagram showing the effect of the present invention.

FIG. 6 is a table showing effects of the present invention.

FIG. 7 is a configuration diagram of a thermal decomposition processing apparatus according to a second embodiment of the present invention.

FIG. 8 is a characteristic diagram showing an operation of the thermal decomposition processing apparatus according to the second embodiment of the present invention.

FIG. 9 is a configuration diagram of another thermal decomposition processing apparatus according to the second embodiment of the present invention.

FIG. 10 is a characteristic diagram showing the operation of another thermal decomposition processing apparatus according to the second embodiment of the present invention.

FIG. 11 is a diagram showing a relationship between slaked lime addition rate and hydrochloric acid recovery rate in the third embodiment of the present invention.

FIG. 12 is a graph showing the relationship between slaked lime addition rate and benzoic acid recovery rate in cracked oil in the third embodiment of the present invention.

FIG. 13 is a graph showing an alkali addition rate.

FIG. 14 is a chart showing a quick reference table of an alkali addition rate.

FIG. 15 is a view showing a conventional waste plastic processing apparatus.

[Explanation of symbols]

 DESCRIPTION OF REFERENCE NUMERALS 1 Waste plastic 2 Pretreatment device 3 Heat dechlorination treatment device 4 Thermal decomposition treatment device 5 Cooling device 6 Cracked oil recovery device 7 Desalination gas treatment device 20 Alkaline substance addition device

Claims (10)

[Claims] 1. A method for treating a waste plastic containing PET, comprising: a step of adding an alkaline substance to the waste plastic; a step of thermally decomposing the waste plastic in a pyrolysis apparatus; A step of generating cracked oil in a cracked oil recovery device using a cracked gas, wherein the acidic gas generated in the thermal cracking process is neutralized with an alkaline substance. 2. The waste plastic further contains PVC, and after adding an alkaline substance to the waste plastic,
The method for treating waste plastic according to claim 1, further comprising a step of subjecting the waste plastic to heat dechlorination in a heat dechlorination apparatus. 3. The heating dechlorination treatment step comprises the steps of:
The thermal dechlorination treatment is performed in a short time at a temperature of 300 ° C., and in the thermal decomposition treatment step, the temperature is sequentially raised from a low temperature to a high temperature at a temperature of 300 to 500 ° C. to perform thermal decomposition. How to treat plastic. 4. The method for treating waste plastic according to claim 2, wherein the alkaline substance is added in an amount previously determined based on the contents of PET and PVC in the waste plastic. 5. The waste plastic according to claim 1, wherein the waste plastic does not contain PVC, and in the thermal decomposition treatment step, the thermal decomposition is performed by sequentially increasing the temperature from a low temperature to a high temperature at a temperature of 300 to 500 ° C. Waste plastic treatment method. 6. The method for treating waste plastic according to claim 5, wherein the alkaline substance is added in an amount determined in advance based on the content of PVC in the waste plastic. 7. The method for treating waste plastic according to claim 1, wherein when generating the cracked oil from the cracked gas, the cracked gas is cooled by a cooling device. 8. An apparatus for treating waste plastic containing PET, wherein the apparatus comprises an alkaline substance addition apparatus for adding an alkaline substance to the waste plastic, a thermal decomposition apparatus for thermally decomposing the waste plastic, and a thermal decomposition apparatus. A waste plastic processing apparatus, comprising: a cracked oil recovery device that generates cracked oil from cracked gas. 9. The waste plastic processing apparatus according to claim 8, further comprising a heating dechlorination apparatus for heating and dechlorinating the waste plastic between the alkaline substance adding apparatus and the thermal decomposition processing apparatus. 10. The waste plastic processing apparatus according to claim 8, wherein a cooling apparatus is provided between the thermal decomposition processing apparatus and the cracked oil recovery apparatus.