JP6984455B2 - Pyrolysis and recycling method of waste plastic - Google Patents

Description

The present invention relates to a method of thermally decomposing and recycling waste plastic using a coke oven.

Conventionally, waste plastic has been landfilled as it is, or crushed or incinerated. However, these disposal methods have problems such as lack of landfill and environmental pollution by dioxins generated at the time of incineration. Therefore, in recent years, various waste plastic recycling technologies have been put into practical use. Among them, the method of carbonizing waste plastic in a coke oven is known as an effective recycling means because a large amount of waste plastic can be recycled and almost 100% of the waste plastic can be recycled.

For example, Patent Document 1 describes a method of reusing waste plastic by mixing plastic granules molded at 100 to 160 ° C. with coal and carbonizing the plastic in a coke oven. However, in this method, the coke strength decreases when a large amount of plastic is mixed, so that the mass ratio of plastic is 5% or less with respect to coal. According to the findings of the present inventors, in order to keep the decrease in coke strength to about several percent, the mass ratio of plastic must be 1% or less with respect to coal, depending on the target coke strength level. Is limited in the amount that can be reused.

On the other hand, in Patent Document 2, the coke strength is lowered by charging the charged coal for coke production into the coke oven and then charging the waste plastic from the charging inlet into the furnace top space on the charged coal. It describes how to dispose of large amounts of waste plastic without.

Japanese Unexamined Patent Publication No. 2001-49261 Japanese Unexamined Patent Publication No. 8-157834

The method described in Patent Document 2 can treat a large amount of waste plastic without lowering the coke strength, but the raw material charging lid is opened and the waste plastic is loaded while the coal is carbonized in the carbonization chamber of the coke oven. Therefore, it is necessary to prevent the amount of gas generated in the carbonization chamber from exceeding the gas recovery capacity of the riser pipe.

On the other hand, high-strength coke can be obtained by using highly caking coal, but non-slightly caking coal is depleted in terms of resources and the price is soaring. Is required to be used in large quantities. Therefore, the present inventors have verified the effect of the method described in Patent Document 2 when a coke raw material having a high proportion of non-slightly caking coal is used. As a result, when a coke raw material having a high content of non-slightly caking coal is used in the method described in Patent Document 2, for example, the amount of gas generated from the carbonization chamber depends on the specific surface area of the molded product of the waste plastic and the charging timing. Due to the increase in the amount of waste, the negative pressure in the carbonization chamber could not be maintained, and a large amount of waste plastic could not be charged.
This is because waste plastic generates a large amount of gas from a low temperature compared to ordinary coke-making coal, and in addition, the amount of gas generated per unit mass of non-slightly caking coal is larger than that of caking coal. It is caused. It is also due to the fact that a large amount of water is released from the raw material and the amount of gas generated increases for about 1 hour after the coke raw material is charged.

The present invention has been made in view of such circumstances, and in the operation of a coke oven using a coke raw material having a high content of non-slightly caking coal, a large amount of waste plastic is charged into the coke oven and pyrolyzed and recycled. The purpose is to provide a possible method.

In order to achieve the above object, in the present invention, a coke raw material having a non-slightly caking coal content of 30% by mass or more is charged into the carbonization chamber of the coke oven and then disposed of in the furnace top space on the coke raw material. It is a method of charging plastic and thermally decomposing and recycling it.
Waste plastic having a mesh size of 10 mm under ratio of 20% by mass or less and a specific surface area of 500 mm ² / g or less, which has been formed into granules by extruding into a columnar shape in advance, is placed at least 1 hour after charging the coke raw material. It is characterized in that it is charged into the furnace top space after a lapse of time (however, the charging of the waste plastic into the furnace top space excludes 4 hours until the coke is taken out) .

By charging the waste plastic into the furnace top space on the coke raw material charged in the carbonization chamber, a large amount of waste plastic can be treated without lowering the coke strength. However, in the case of coke raw materials with a high proportion of non-slightly caking coal, the amount of gas generated per unit mass of non-slightly caking coal is larger than that of caking coal, so gas is rapidly generated and waste plastic is recycled. The amount is limited.

The present inventors have discovered that when the heat receiving area per unit mass of the waste plastic charged into the furnace top space is large, the amount of gas generated increases sharply. Therefore, in the present invention, the particle size and specific surface area of the waste plastic charged into the furnace top space are specified to reduce the heat receiving area per unit mass of the waste plastic, thereby reducing the amount of gas generated per unit time from the waste plastic. Suppress. Specifically, the furnace top space is made of granular waste plastic with a mesh size of 10 mm under ratio of 20% by mass or less and a specific surface area of 500 mm ^{2 / g or less with respect to the total waste plastic to be charged by pre-molding.} Charge to.
In addition, since a large amount of raw material moisture is released for about 1 hour after charging the coke raw material, avoid charging waste plastic during this period, and wait at least 1 hour after charging the coke raw material for the furnace top space. Fill with waste plastic.

Further, in the method for thermally decomposing and recycling waste plastic according to the present invention, ^{it is preferable that the specific surface area of the waste plastic as granules is 200 mm 2} / g or less.
According to this configuration, the heat receiving area per unit mass of the waste plastic is further reduced, so that the amount of gas generated per unit time from the waste plastic is further suppressed.

In the method for thermally decomposing and recycling waste plastic according to the present invention, the particle size and specific surface area of the waste plastic charged into the furnace top space are specified to reduce the heat receiving area per unit mass of the waste plastic, and the raw material moisture is large. Since the waste plastic is charged while avoiding the time when it is released into the air, rapid gas generation is suppressed in the operation of the coke oven using coke raw material with a high proportion of non-slightly caking coal, and a large amount of waste plastic is recycled. can do.

It is a schematic diagram which showed the state which the waste plastic was charged in the coke oven carbonization chamber in the pyrolysis recycling method of the waste plastic which concerns on one Embodiment of this invention. It is a cross-sectional view of a main part of an extruder. It is a front view of the die plate which constitutes the same extruder. It is a schematic diagram of a double roll type molding machine.

Subsequently, an embodiment embodying the present invention will be described with reference to the attached drawings, and the present invention will be understood.

The procedure of the thermal decomposition and recycling method of the waste plastic according to the embodiment of the present invention will be described with reference to FIG.
In the present embodiment, the coke raw material C having a high mixing ratio of non-slightly caking coal is charged into the carbonization chamber 11 of the coke oven 10. The blending ratio of the non-slightly caking coal is 30% by mass or more with respect to the total coke raw material C to be charged. The upper limit of the blending ratio of the non-slightly caking coal is not particularly set, but is usually about 60% by mass.

After at least one hour has passed after charging the coke raw material C, the waste plastic P is charged into the furnace top space 12 on the coke raw material C from the charging inlet 13. At that time, the whole amount of the waste plastic P may be charged at one time, but it may be charged in a plurality of times.
Since it takes about 1 hour for the charged waste plastic P to be thermally decomposed, assuming that the carbonization time of the coke raw material C is 20 hours, the upper limit of the waste plastic P charging time is 19 hours after the coke raw material C is charged.

The amount of waste plastic P charged is such that the amount of gas generated in the carbonization chamber 11 does not exceed the gas recovery capacity of the riser pipe 14. Before charging the waste plastic P, it is preferable to perform a negative pressure operation in the carbonization chamber 11 by increasing the pressure at the time of spraying ammonia water in the curved pipe portion 14a of the rising pipe 14.

Waste plastics are plastic products that are discarded after use and waste plastics generated in the manufacturing process. General waste plastics from homes, stores, offices, etc., and industries from the manufacturing, processing, and distribution processes of plastic products. It is divided into waste plastics.
The waste plastic P used in the present embodiment corresponds to a synthetic resin having a large amount of volatile matter and generating a large amount of gas. Specifically, polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) and the like.

In the present embodiment, the granules having a sieve mesh of 10 mm under ratio of 20% by mass or less and a specific surface area of 500 mm ² / g (preferably 200 mm ² / g) or less with respect to the total waste plastic P to be charged by the molding machine. Use pre-molded waste plastic P on the object.

Granules with a mesh under 10 mm have a significantly large heat-receiving area per unit mass, and waste plastic P, which is a granule with a mesh under 10 mm, is contained in an amount of more than 20% by mass with respect to the total waste plastic P. The amount of gas generated increases sharply. On the other hand, if the amount of waste plastic P in the form of granules under 10 mm is 20% by mass or less, a relatively low amount of gas generated tends to continue for a long time.

Further, when the specific surface area of the waste plastic P as a granular material ^{exceeds 500 mm 2} / g, the heat receiving area per unit mass increases, so that the amount of gas generated increases sharply. On the other hand, when the specific surface area of the waste plastic P as a granular material is 500 mm ² / g or less, a relatively low amount of gas generated tends to continue for a long time.
Although the lower limit of the specific surface area of the waste plastic P is not particularly defined, the specific surface area of the granular material that can be generally produced ^{is about 50 mm 2} / g.

An extrusion molding machine, a double roll type molding machine, or the like can be used for pre-molding the waste plastic P.
2 and 3 show an example of the extruder 20. The extruder 20 is roughly composed of a pair of screw feeders 22 arranged in parallel, a die plate 23 arranged at the front end of the pair of screw feeders 22, and a casing 21 covering the pair of screw feeders 22.
The die plate 23 is formed with an annular extrusion region 24 centered on the axis of each screw feeder 22, and each extrusion region 24 is composed of a plurality of through holes 25 and 26. A rod-shaped heater 27 is embedded and sealed in the through hole 26 indicated by the mark, and a rod-shaped heater 28 is inserted in the peripheral portion of the die plate 23. Further, the casing 21 portion close to the die plate 23 is covered with the panel heater 29.

When the waste plastic is thrown into the casing 21 from the opening 21a provided on the rear side of the casing 21, the waste plastic in the casing 21 is pumped to the die plate 23 by the pair of screw feeders 22. The waste plastic pumped to the front side of the screw feeder 22 is heated and melted by the panel heater 29 and the rod-shaped heaters 27 and 28, and is extruded as a molded product from the through hole 25. The molded product extruded from the through hole 25 is cut to a predetermined length by a cutting machine (not shown).

On the other hand, as shown in FIG. 4, the double roll type molding machine 30 is installed in a hopper 31 into which waste plastic is charged, a pair of rolls 33 for compression molding the waste plastic, and a pair of rolls 33. It is roughly configured with a screw feeder 32 that supplies waste plastic between them. A plurality of recesses 34 are formed on the roll surface of each roll 33, and the recesses 34 formed in one roll 33 and the recesses 34 formed in the other roll 33 are configured to be aligned in the circumferential direction.

When the waste plastic in the hopper 31 is charged, the waste plastic in the hopper 31 is sent between the pair of rolls 33 by the screw feeder 32. The pair of rolls 33 arranged side by side rotate in opposite directions to each other, and the waste plastic inserted between the pair of rolls 33 passes through the pair of rolls 33, and the recess 34 formed in the one roll 33. And the recess 34 formed in the other roll 33 is compression molded.

The specific surface area of the preformed waste plastic P is determined by the following procedure.
(1) When pre-molded by the extrusion molding machine 20, the molded product (granular substance) of the waste plastic P becomes a columnar shape. The inner diameter of the through hole 25 formed in the die plate 23 is obtained from the drawing as the outer diameter of the molded product, and the length is measured by actually measuring the molded product and the surface area of the molded product is calculated. On the other hand, in the case of pre-molding with the double roll type molding machine 30, the size of the recess 34 formed on the surface of the roll 33 is obtained from the drawing, and the surface area of the molded product is calculated based on the obtained size. However, in calculating these surface areas, the amount of expansion due to gas generation is not taken into consideration.
(2) Select five actual molded products that are close to the dimensions of the molded product calculated based on the drawings, measure their masses to calculate the average value, and calculate the surface area in (1) as the average mass. Divide by the value to obtain the specific surface area of the waste plastic P.
The actual molded product, which is determined not to have the dimensions of the molded product calculated based on the drawings, is mainly a collapsed portion of the molded product, and most of the actual molded products have a sieve mesh of 10 mm or less.

Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and is within the scope of the matters described in the claims. It also includes other possible embodiments and variations. For example, in the above embodiment, an extrusion molding machine and a double roll type molding machine are taken as examples as molding machines, but the molding machine is not limited to these, and it goes without saying that other types of molding machines may be used.

The verification test carried out for verifying the effect of the present invention will be described.
Non-slightly caking coal has a maximum fluidity index of 10 ddpm or less in the fluidity test by the Giesellerplastometer method specified in JIS M8801 "Coal-Test Method", or JIS M8816 "Coal microstructure components and Coal having a Vitrinit average reflectance of 1.0 or less measured by the method specified in "Reflectance Measuring Method" was used.
As the waste plastic, the waste plastic collected based on the Containers and Packaging Recycling Law (Act on Promotion of Separate Collection and Recycling of Containers and Packaging) was used.

The above-mentioned extrusion molding machine was used for pre-molding the waste plastic.
The specific surface area of the waste plastic was adjusted by changing the particle size and molding load at the time of molding. The water content of the waste plastic before molding was 5 to 7% by mass.
Further, the temperature of the waste plastic at the time of pre-molding was adjusted to the maximum temperature in the extruded region, and the temperature of the extruded molded product was measured by a radiation thermometer. The maximum temperature of the waste plastic at the time of premolding was about 160 ° C.

The waste plastic was charged into the carbonization chamber using a charging vehicle used for normal coal charging, and the total amount was charged once.
Before charging the waste plastic, the pressure at the time of spraying with cheap water was increased to make the pressure in the carbonization chamber negative.

A list of test results is shown in Table 1. In the table, the ratio of non-slightly caking coal is the ratio to the total amount of coke charged, the ratio of waste plastic under 10 mm is the ratio to the total amount of waste plastic to be charged, and the charging time is the elapsed time from the charging of coke raw material.

The amount of waste plastic that can be charged is set in increments of 1% by mass, and the cases in which the amount of waste plastic is the largest in the range where the static pressure of the rising pipe is -49.03 Pa (-5 mmAq) or less are shown in the same table.
Although it was possible that the static pressure of the riser pipe would be -5 mmAq or less even if 5% by mass or more of waste plastic was charged, the geometrical conditions of the carbonization chamber (space where waste plastic can be stored, generated gas) In consideration of (securing a space that can be passed through), etc., the upper limit is 5% by mass, and 5% by mass or more is described in the table.

The test results were evaluated based on the amount of waste plastic that can be charged and the ratio of non-slightly caking coal. Specifically, the case where the waste plastic chargeable amount is less than 2% by mass is × (impossible), and the case where the waste plastic chargeable amount is 2% by mass or more and the non-slightly caking coal compounding ratio is less than 30% by mass. △ (possible), the case where the amount of waste plastic that can be charged is 2% by mass or more and the non-slightly caking coal compounding ratio is 30% by mass or more is ○ (good), and the amount of waste plastic that can be charged is 5% by mass or more. Cases in which the non-slightly caking coal content was 30% by mass or more were designated as ⊚ (excellent).

The following can be seen from the table.
・ Waste plastic with a mesh under 10 mm ratio of 20% by mass or less and a specific surface area of 500 mm ² / g or less is placed in the furnace top space at least 1 hour after the coke raw material is charged. If it is added, a large amount of waste plastic can be recycled even if the compounding ratio of the non-slightly caking coal is 30% by mass or more (comparison between Example 1 and Comparative Examples 1 to 3, and Example 2 and Comparative Example). Comparison of 4).
-When the waste plastic, which is a granular material with a sieve mesh under 10 mm ratio of 20% by mass or less, is charged into the furnace top space at least 1 hour after the coke raw material is charged, the specific surface area of the waste plastic is charged. The smaller the value, the larger the amount of waste plastic that can be recycled (comparison between Example 1 and Example 3, comparison between Example 2 and Example 4).
-When the waste plastic, which is a granular material with a sieve mesh under 10 mm ratio of 20% by mass or less, is charged into the furnace top space at least 1 hour after the coke raw material is charged, the specific surface area of the waste plastic is charged. By reducing the amount of waste plastic, a large amount of waste plastic can be recycled even if the compounding ratio of the non-slightly caking coal is extremely high (comparison between Example 2 and Example 4).
-With the conventional non-slightly caking coal compounding ratio, a large amount of waste plastic is recycled even if the particle size of the waste plastic, the specific surface area, or the charging time of the waste plastic does not meet the requirements of the present invention. (Comparison of Conventional Example 1 and Comparative Example 1, Comparison of Conventional Example 2 and Comparative Example 2, Comparison of Conventional Example 3 and Comparative Example 3).

10: coke oven, 11: carbonization chamber, 12: furnace top space, 13: inlet, 14: rising pipe, 14a: curved pipe, 20: extrusion molding machine, 21: casing, 21a: opening, 22, 32: Screw feeder, 23: Die plate, 24: Extrusion area, 25, 26: Through hole, 27, 28: Rod heater, 29: Panel heater, 30: Double roll type molding machine, 31: Hopper, 33: Roll, 34: Recess, C: Coke raw material, P: Waste plastic

Claims (2)

A method in which a coke raw material having a non-slightly caking coal content of 30% by mass or more is charged into a carbonization chamber of a coke oven, and then waste plastic is charged into the furnace top space on the coke raw material for thermal decomposition recycling. And,
Waste plastic, which has been extruded into a columnar shape in advance to form granules with a sieve mesh under 10 mm ratio of 20% by mass or less and a specific surface area of 500 mm ² / g or less, is charged at least 1 hour after charging the coke raw material. A method for thermally decomposing and recycling waste plastic, which is characterized in that the waste plastic is charged into the furnace top space after a lapse of time (however, the waste plastic is charged into the furnace top space until the coke is taken out. (Excluding 4 hours) . The method for thermally decomposing and recycling waste plastic according to claim 1, wherein the specific surface area of the waste plastic as granules is 200 mm ² / g or less.

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