CONTINUOUS PYROLYSIS METHOD OF WASTE PLASTIC AND PYROLYSIS SYSTEM OF WASTE PLASTIC

Provided is a continuous pyrolysis method of waste plastic, including the following steps: crushing and drying the waste plastic, and then carrying out pyrolysis reaction under an oxygen-free condition to obtain pyrolysis products, where the obtained pyrolysis products include pyrolysis oil and gas, and a pyrolysis solid. A temperature of the pyrolysis reaction remains stable in the range of 450-500° C. for more than 7 days, pyrolysis reaction time is controlled at 30-40 min, and a proportion of the pyrolysis solid in the pyrolysis products is less than 20% by weight. According to the continuous pyrolysis method of the waste plastic and a pyrolysis system of waste plastic, a continuous and stable operation can be kept for a long period of time, the temperature of pyrolysis reaction can be kept stable for a period of up to 28 days, the amplitude of temperature fluctuation is lower than 100° C.

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Description
TECHNICAL FIELD

The present disclosure relates to the field of resource utilization of waste plastic, in particular to a continuous pyrolysis method of waste plastic, and a pyrolysis system of waste plastic.

BACKGROUND

Plastic products have become the necessities in daily life of humans, including packaging boxes, plastic bags, electronic protective cases and so on. With the increasing number and variety of plastic products, the treatment of waste plastic products, especially resource treatment, has gradually become the focus of environmental governance. At present, most of the waste plastic is treated by incineration, landfilling, or ocean dumping. However, these methods will eventually lead to new pollution problems.

In order to turn waste plastic into valuable things, high temperature cracking/pyrolysis of waste plastic has gradually attracted attention. It has been reported that there are various problems in the pyrolysis of plastic due to its light weight and low melting point. For example, the melt is adhered to and accumulated on the pyrolysis device during pyrolysis, which leads to frequent failures of the pyrolysis device and makes the pyrolysis device difficult to operate continuously for a long time. Due to the defects of structural design, the pyrolysis device is prone to coking, which leads to the decrease of heat transfer efficiency of pyrolysis, and insufficient pyrolysis leads to low yield of pyrolysis oil and gas, and poor quality of pyrolysis products.

SUMMARY

For the disadvantages in the prior art, a first aspect of the present disclosure provides a continuous pyrolysis method of waste plastic, including the following steps:

    • crushing and drying the waste plastic, and then carrying out pyrolysis reaction under an oxygen-free condition to obtain pyrolysis products, where the pyrolysis products include pyrolysis oil and gas, and a pyrolysis solid; a temperature of the pyrolysis reaction remains stable in the range of 450-500° C. for more than 60 days, pyrolysis reaction time is controlled at 30-40 min, and a proportion of the pyrolysis solid in the pyrolysis products is less than 20% by weight.

In an embodiment, the temperature of the pyrolysis reaction remains stable in the range of 450-500° C. for more than 20 days. Preferably, the temperature of the pyrolysis reaction remains unchanged for more than 10 days. Preferably, a moisture content of the waste plastic after drying is less than 5% by weight.

In another aspect, the present disclosure provides a pyrolysis system of waste plastic, which is used for implementing the continuous pyrolysis method of waste plastic, including a feeding unit, a pyrolysis unit for pyrolysis reaction, and a separation unit for pyrolysis product separation. The feeding unit, the pyrolysis unit and the separation unit are connected in turn. A discharge port of the feeding unit is hermetically connected to a feed port of the pyrolysis unit, a pyrolysis product outlet of the pyrolysis unit communicates with the separation unit, and the separation unit is used to separate pyrolysis oil and gas from a pyrolysis solid.

The pyrolysis unit includes a pyrolysis reactor, and a flue gas channel arranged around an outer wall of the pyrolysis reactor. The flue gas channel is used for circulating a hot flue gas, thus providing a heat source for the pyrolysis reactor.

The flue gas channel is provided with a flue gas inlet, and a flue gas outlet. The flue gas inlet is arranged on a feed port side of the pyrolysis reactor, and the flue gas outlet is arranged on a pyrolysis product outlet side of the pyrolysis reactor.

A stirring assembly is arranged in an inner cavity of the pyrolysis reactor, and the stirring assembly is in tangential contact with an inner wall of the pyrolysis reactor when rotating.

In an embodiment, the stirring assembly includes a rotating shaft, and multiple stirring rods arranged on the rotating shaft. The rotating shaft is arranged on a central line of the pyrolysis reactor along a length of the pyrolysis reactor.

One end of the stirring rod is fixedly connected to the rotating shaft, the other end of the stirring rod is connected to a scraping plate, and the scraping plate can rotate at an end of the stirring rod. The shape of the scraping plate is a long-strip plate, and both ends of the scraping plate have different weights.

In an embodiment, an included angle between the stirring rod and the rotating shaft is 30-90 degrees.

In an embodiment, on the rotating shaft, a vertical distance between two adjacent stirring rods on the rotating shaft is 1.5-3 times a length of the scraping plate.

In an embodiment, the pyrolysis system includes two or more stages of pyrolysis units, two adjacent stages of pyrolysis units are in closed communication, and the separation unit communicates with the last stage of pyrolysis unit.

In an embodiment, each stage of pyrolysis unit is provided with an independent flue gas channel, and the flue gas channels of two adjacent stages of pyrolysis units are in communication.

According to the continuous pyrolysis method of the waste plastic and a pyrolysis system of waste plastic provided by the present disclosure, a continuous and stable operation can be kept for a long period of time, the temperature of pyrolysis reaction can be kept stable for a period of up to 60 days, and the amplitude of temperature fluctuation is lower than 100° C. Therefore, the quality of the pyrolysis product is greatly improved, and the cost of equipment maintenance and frequent maintenance and debugging is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings:

FIG. 1 is a front view of a pyrolysis reactor;

FIG. 2 is a sectional view of a pyrolysis reactor;

FIGS. 3A-3C are schematic sectional diagram of stirring rods arranged on a rotating shaft in a pyrolysis reactor, where FIG. 3A is a schematic sectional diagram showing that an included angle between the stirring rods is 180 degrees; FIG. 3B is a schematic sectional diagram showing that an included angle between the stirring rods is 120 degrees; and FIG. 3C is a schematic sectional diagram showing that an included angle between the stirring rods is 90 degrees.

FIG. 4 is a schematic sectional diagram of an exemplary pyrolysis reactor;

FIG. 5 is a structural diagram of a spiral reactor;

 IN THE DRAWINGS

    • 1—pyrolysis reactor; 11—feed port; 12—pyrolysis solid outlet; 2—rotating shaft; 3—stirring rod; 4—scraping plate; 5—counterweight.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Also, all conjunctions used are to be understood in the most inclusive sense possible. Thus, the word “or” should be understood as having the definition of a logical “or” rather than that of a logical “exclusive or” unless the context clearly necessitates otherwise. Further, the singular forms and the articles “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms: includes, comprises, including and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Further, it will be understood that when an element, including component or subsystem, is referred to and/or shown as being connected or coupled to another element, it can be directly connected or coupled to the other element or intervening elements may be present.

It will be understood that although terms such as “first” and “second” are used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, an element discussed below could be termed a second element, and similarly, a second element may be termed a first element without departing from the teachings of the present invention.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The present disclosure is further described below with reference to accompanying drawings.

A continuous pyrolysis method of waste plastic provided by the present disclosure includes the following steps:

the waste plastic is crushed and dried, and then subjected to pyrolysis reaction under an oxygen-free condition to obtain pyrolysis products, where the obtained pyrolysis products include pyrolysis oil and gas, and a pyrolysis solid. According to the continuous pyrolysis method of the waste plastic, in the operation process, a temperature of the pyrolysis reaction can be kept stable in the range of 450-500° C. within the operation time of more than 60 days, and even the temperature of the pyrolysis reaction can be kept stable in the range of 450-500° C. within the operation time of 20 days.

According to the present disclosure, pyrolysis reaction time of the waste plastic ranges from 30 min to 40 min.

According to the continuous pyrolysis method of waste plastic, the waste plastic can be uniformly and sufficiently pyrolyzed since the pyrolysis reaction temperature is relatively stable, and small in amplitude of fluctuation, and a proportion of obtained pyrolysis solid in the pyrolysis products is greatly reduced, thereby improving the quality of the pyrolysis product. In some embodiments, the proportion of the pyrolysis solid in the pyrolysis products is less than 20% by weight, even less than 19% by weight, more preferably less than 16% by weight, and even more preferably less than 15% by weight.

In the present disclosure, before the pyrolysis process, the waste plastic is preferably dried to make the moisture content of the waste plastic less than 5% by weight. High moisture content in the waste plastic will affect the energy consumption of the pyrolysis unit, and the higher the moisture content, the higher the energy consumption. In order to avoid the high energy consumption of the reactor, it is preferable to dry the waste plastic to make the moisture content thereof less than 3% by weight.

The continuous pyrolysis method provided by the present disclosure is suitable for various types of waste plastic, for example, the waste plastic may be gift packaging boxes, soft packaging of electronic products, and plastic containers; the waste plastic may be thermoplastic or thermosetting plastic. The types of plastic in the waste plastic may be polyolefin, polystyrene, polyamide, polyether, polyester and polyacrylic acid, etc. The plastic content may be greater than 60% by weight. If the plastic content in the waste plastic is less than 60% by weight, a front-end sorting unit needs to be added.

Pyrolysis System

A continuous pyrolysis method of waste plastic provided by the present disclosure is implemented through the following pyrolysis system. The pyrolysis system includes a feeding unit, a pyrolysis unit for pyrolysis reaction, and a separation unit for pyrolysis product separation. The feeding unit, the pyrolysis unit and the separation unit are connected in turn. A discharge port of the feeding unit is hermetically connected to a feed port of the pyrolysis unit, a pyrolysis product outlet of the pyrolysis unit communicates with the separation unit, and the separation unit is used to separate pyrolysis oil and gas from a pyrolysis solid.

The pyrolysis unit includes a pyrolysis reactor, and a flue gas channel arranged around an outer wall of the pyrolysis reactor. The flue gas channel is used for circulating a hot flue gas, thus providing a heat source for the pyrolysis reactor.

The flue gas channel is provided with a flue gas inlet, and a flue gas outlet. The flue gas inlet is arranged on a feed port side of the pyrolysis reactor, and the flue gas outlet is arranged on a pyrolysis product outlet side of the pyrolysis reactor.

A stirring assembly is arranged in an inner cavity of the pyrolysis reactor, and the stirring assembly is in tangential contact with an inner wall of the pyrolysis reactor when rotating.

In the present disclosure, the tangential contact refers to that the stirring assembly is in linear contact, or even surface contact, with an inner wall of the pyrolysis reactor when rotating and stirring, thus scrapping attachments on the inner wall of the pyrolysis reactor.

In an embodiment, the degree of tangential contact is at least as follows: the stirring assembly continues to make contact with the inner wall of the pyrolysis reactor within a rotation angle of 360 degrees, at least within 30 degrees, at least within 60 degrees, at least within 180 degrees, or even within 360 degrees.

In an embodiment, as shown in FIG. 1 and FIG. 2, FIG. 1 is a front view of a pyrolysis reactor, and FIG. 2 is a sectional view of a pyrolysis reactor.

As shown in FIG. 1, the pyrolysis reactor 1 is provided with a feed port 11 for inputting the waste plastic, a pyrolysis solid outlet 12, a pyrolysis gas outlet (not shown). The stirring assembly includes a rotating shaft 2, and multiple stirring rods 3 arranged on the rotating shaft. The rotating shaft is arranged on a central line of the pyrolysis reactor along a length of the pyrolysis rector 1. One end of the stirring rod 3 is fixedly connected to the rotating shaft 2, and the other end of the stirring rod is connected to a scraping plate 4. The scraping plate 4 may rotate at an end of the stirring rod 3 to achieve tangential contact with the inner wall of the pyrolysis reactor.

In an embodiment of the present disclosure, an included angle between the stirring rod and the rotating shaft is 45-90 degrees, preferably 75-85 degrees.

In an embodiment of the present disclosure, multiple stirring rods are equidistantly and uniformly arranged on the rotating shaft, and included angles between the stirring rods and the rotating shaft are the same. Alternatively, as shown in FIGS. 3A-3C, in a circumferential direction of the rotating shaft 1, an included angle between the stirring rods 3 may be 60 degrees and more, e.g., 180 degrees (FIG. 3A), 120 degrees (FIG. 3B), and 90 degrees (FIG. 3C).

In an embodiment of the present disclosure, in order to effectively remove attachments on the inner wall, especially a coking material, a vertical distance between two adjacent stirring rods on the rotating shaft is 0.5-1 times a length of the scraping plate.

The scraping plate can rotate at the end of the stirring rod. In addition, “rotating at the end of the stirring rod” refers to that the scraping plate rotates at the end of the stirring rod when subjected to a friction force or resistance, rather than displacing in the length direction of the stirring rod.

In an embodiment, the stirring rod is connected to the scraping plate by a conventional sleeve. As an example, a movable inner tube is perpendicularly fixed to one end, away from the rotating shaft, of the stirring rod, a movable outer tube is sleeved outside and rotatably connected both ends of the movable inner tube, and the scraping plate is fixed to the outside of the movable outer tube. The scraping plate can rotate at the end of the stirring rod under the mechanism action of the movable outer tube and the movable inner tube.

In order to achieve the tangential contact between the scraping plate and the inner wall of the pyrolysis reactor, as an example, one end, in contact with the pyrolysis reactor, of the scraping plate is an arc, the arc can be in fit with the inner wall of the pyrolysis reactor, thus making linear contact, even surface contact, with the pyrolysis reactor.

The shape of the scraping plate is a long-strip plate, and both ends of the scraping plate have different weights. The length of the scraping plate can be adjusted according to the length of the pyrolysis reactor. In an embodiment, the length of the scraping plate is that an arc end of the scraping plate is at an angle of 45-60 degrees when making tangential contact with the inner wall of the pyrolysis reactor.

The scraping plate may have a width, and the width of the scraping plate should not be too large or too small. Excessive width of the scraping plate will increase the rotation resistance of the scraping plate, which is conducive to the smooth rotation of the scraping plate for a long time. Small width of the scraping plate will make the contact area with the pyrolysis reactor smaller, which will affect the scraping efficiency. In the present disclosure, the width of the scraping plate may be 2-15 cm, preferably 8-15 cm. In addition, in order to achieve better scraping effect, the total width of the scraping plates in the length direction of the pyrolysis reactor is 0.6-0.9 times the length of the pyrolysis reactor, more preferably 0.7-0.8 times.

As an example, a counterweight is fixed to a panel of the scraping plate, which makes both ends of the scraping plate have different weights and is used for controlling the rotation opportunity of the scraping plate. The counterweight can be fixed to a panel, facing the inner wall of the pyrolysis reactor, of the scraping plate, or a panel facing the stirring rod. A fixation position of the counterweight on a single scraping plate can be arranged independently, thus controlling the rotation opportunity of the single scraping plate. The sufficient scrapping of the attachments on the inner wall of the pyrolysis reactor can be achieved through the rotating scraping behavior of multiple scraping plates.

As an example of the stirring assembly, in the pyrolysis reactor 1 shown in FIG. 4, an included angle between the stirring rods 3 in a circumferential direction of the rotating shaft 2 is 180 degrees, the counterweight 5 is arranged on each scraping plate 4, and an arc sharp end in the arc end of the scraping plate faces a rotating direction of the rotating shaft 2. A position of the counterweight 5 is that all stirring rods 3 are located on a same horizontal line in the circumferential direction of the rotating shaft 2, the counterweight blocks 5 are at the same side of the horizontal line. Therefore, when the scraping plates 4 are in contact with the inner wall of the pyrolysis reactor for scraping, the counterweights 5 can play a synergistic unbalanced role, making the scraping plates 4 achieve a synergistic scraping effect.

As a preferred embodiment of the stirring assembly, two stirring rods are arranged on the same circumferential section of the rotating shaft, and the two stirring rods are at an angle of 180 degrees, a tail end of each stirring rod is provided with one scraping plate, and the scraping plates have the same width. When the waste plastic undergoes the pyrolysis reaction, most of the waste plastic is located at the bottom of the pyrolysis reactor, and the attachments on the inner wall are basically located at the bottom of the pyrolysis reactor. When the stirring assembly operates, two horizontally arranged scraping plates can couple with each other to scrape the bottom of the pyrolysis reactor alternately, thus achieving a more sufficient scraping effect.

The volume of the counterweight should not be too large or too small. If the volume of the counterweight is too large, the space between the scraping plate and the connecting rod will be occupied, which will affect the rotation angle of the scraping plate. If the volume of the counterweight is too small, it is difficult to control the rotation angle of the scraping plate in a suitable range. In the present disclosure, the height that the counterweight is higher than the panel of the scraping plate may be 1-3 cm, such as 2 cm.

As the waste plastic of the present disclosure is light in weight, in a molten state after pyrolysis, and viscous. When waste plastic undergoes pyrolysis reaction in the pyrolysis reactor, molten materials are easy to adhere to the stirring assembly, and the pyrolysis products are easy to adhere to and accumulate on the inner wall of the pyrolysis reactor when the pyrolysis products cannot be removed in time, leading to influence on the stability of the pyrolysis temperature. In the present disclosure, a thickness of the scraping plate needs to be controlled within 6-10 mm. Excessive thickness of the scraping plate will lead to large rotation resistance of the rotating shaft, and small thickness of the scraping plate will affect scraping strength.

In an embodiment of the present disclosure, a weight w1 of the scraping plate, a weight w2 of the counterweight, a width m of the scraping plate and a distance L from the counterweight to the axis of rotation of the scraping plate satisfy the following relationship: (w2×L+0.5w1×0.5 m)/(0.5w1×0.5 m)=2-3.

In an embodiment, the weight w1 of the scraping plate is equal to 7612 g, the weight w2 of the counterweight is equal to 3806 g, the width m of the scraping plate is equal to 8 cm, and the distance L from counterweight to the axis of rotation of the scraping plate is equal to 8 cm.

According to the continuous pyrolysis method of waste plastic provided by the present disclosure, the pyrolysis efficiency of the waste plastic may reach 0.1-1 t/h.

In an embodiment, the heat required for the pyrolysis reaction in the present disclosure comes from indirect heating of a hot flue gas. In this embodiment, an outer wall of the pyrolysis reactor is provided with a flue gas channel for conveying the hot flue gas. A flow direction of the hot flue gas is opposite to a conveying direction of the waste plastic in the pyrolysis reactor. The flue gas channel is provided with a flue gas inlet, and a flue gas outlet. In order to ensure that the temperature of the pyrolysis reaction reaches 450-500° C., a temperature at the flue gas inlet can be controlled at 700-800° C., and a temperature at a flue gas outlet can be controlled at 300-400° C., for example, the temperature at the flue gas outlet can be controlled at 350-400° C. A temperature sensor is arranged at the flue gas outlet for monitoring the temperature at the flue gas outlet. When the temperature fluctuation at the flue gas outlet reaches 100° C. and above, the pyrolysis reaction is stopped. Generally, the hot flue gas is generated by gas combustion. In an embodiment, the flow rate of the flue gas can be controlled at 2000-3200 Nm3/h.

The pyrolysis system provided by the present disclosure is used for continuous pyrolysis of the waste plastic, and the temperature fluctuation at the flue gas outlet is kept below 100° C., even below 50° C., below 30° C. and below 25° C. during the continuous operation for more than 30 days, 40 days, 50 days and 60 days, and the temperature at the flue gas outlet remains unchanged during the continuous operation for more than 10 days. The proportion of the pyrolysis solid in pyrolysis products is less than 20% by weight, even less than 19% by weight, more preferably less than 16% by weight, and even more preferably less than 15% by weight, thus acquiring the pyrolysis products with excellent quality.

In a specific embodiment, the specification of the pyrolysis reactor may be any size, for example, an inner diameter is 1.2 m, and a length is 9 m.

In an embodiment, at least two stirring rods are arranged on the same circumferential section of the rotating shaft as a group, each stirring rod is provided with a scraping plate, and the width of each scraping plate is 15-20 cm. 40-60 groups of stirring rods can be arranged on the rotating shaft.

In an embodiment, the pyrolysis treatment capacity of the pyrolysis system for the waste plastic can reach 0.8-1.5 t/h, for example, 1 t/h.

The pyrolysis method and system provided by the present disclosure are used to continuously pyrolyze the waste plastic, the proportion of the obtained pyrolytic solid in the pyrolysis products may be less than 25% by weight, even less than 22% by weight, and even less than 20% by weight.

The pyrolysis system is used to continuously pyrolyze the waste plastic, the filling degree of materials in the pyrolysis reactor can reach 20%-60% by volume, and the inner wall of the pyrolysis reactor can be kept basically free of attachments at the rotating speed of 2-5 r/min, and the thickness of the attachment is less than 1 mm.

In an embodiment, the filling degree of materials in the pyrolysis reactor is 20% by volume, such as 40% by volume, 60% by volume, and 80% by volume.

In an embodiment, the rotating speed of the rotating shaft may be 2-5 r/min.

The waste plastic is pyrolyzed by the pyrolysis system provided by the present disclosure, and the thickness of the attachment on the inner wall of the pyrolysis reactor may be below 0.5 mm, or below 0.8 mm.

The pyrolysis system may include two or more stages of pyrolysis units, two adjacent stages of pyrolysis units are in closed communication, and the separation unit communicates with the last stage of pyrolysis unit.

In some embodiments, each stage of pyrolysis unit is provided with an independent flue gas channel, and the flue gas channels of two adjacent stages of pyrolysis units are in communication.

The present disclosure is described below in detail with reference to embodiments.

The waste plastic treated in the following embodiments and comparative examples is a waste agricultural film, with a PE content of 90% by weight, and a moisture content of the waste agricultural film is 5% by weight after crushing and drying.

EMBODIMENT

The waste plastic is continuously fed into the pyrolysis reactor by a closed screw conveyor, and the feeding rate is controlled at 0.1 t/h.

The hot flue gas is used to heat the pyrolysis reactor indirectly, that is, the flue gas is isolated from the waste plastic in the pyrolysis reactor. The flue gas quantity is 3200 Nm3/h, the temperature at the flue gas inlet is controlled at 700-800° C., it is observed that the temperature at the flue gas outlet is controlled at 350-450° C., and the temperature of pyrolysis reaction is 450-500° C. The residence time of the waste plastic in the pyrolysis reactor is 40 min.

When the temperature fluctuation at the flue gas outlet reaches 100° C., the operation of the pyrolysis system is stopped, and the pyrolysis reactor is checked.

The pyrolysis reactor is horizontal, with a length of 9 m and an inner diameter of 1.2 m. Two stirring rods are arranged on the same section of the rotating shaft as a group, and an included angle between the stirring rod and the rotating shaft is 90 degrees. A total of 90 groups of stirring rods are arranged on the rotating shaft, and the rotating speed of the rotating shaft is 2 r/min.

Parameters of the scraping plate and counterweight on the stirring rod are as follows:

The weight w1 of the scraping plate is equal to 7612 g, the weight w2 of the counterweight is equal to 3806 g, the width m of the scraping plate is equal to 8 cm, and the distance L from the counterweight to the axis of rotation of the scraping plate is equal to 8 cm (satisfying the following relationship: (w2×L+0.5w1×0.5 m)/(0.5w1×0.5 m)=2-3).

The pyrolysis reactor generates a high-temperature pyrolysis gas and a pyrolysis solid, and the high-temperature pyrolysis gas is condensed and separated to obtain plastic pyrolysis oil and plastic pyrolysis gas, and the pyrolysis solid generated by pyrolysis reaction is discharged by a cooling screw conveyor.

After the pyrolysis system continuously operates for 28 days, and the fluctuation of the temperature at the flue gas outlet is summarized in the following Table 1.

TABLE 1 1th 5th 10th 15th 20th 25th 30th 40th 50th 55th 60th 65th Days day day day day day day day day day day day day Temperature at 350° C. 350° C. 350° C. 353° C. 366° C. 369° C. 375° C. 385° C. 400° C. 416° C. 435° C. 455° C. flue gas outlet

As can be seen from Table 1, when the pyrolysis system operates continuously for 10 days, the temperature at the flue gas outlet is always kept stable at 350° C., and no temperature fluctuation has been found. On the 15th to 30th day of operation, the temperature at the flue gas outlet fluctuates obviously, but the amplitude of fluctuation is within 30° C., and the temperature rises particularly slowly. On the 40th day of operation, there is obvious temperature fluctuation. After continuous observation for 25 days, it is found that the temperature rises significantly. On the 65th day, the temperature reaches 455° C., so the pyrolysis system is stopped in time to check the pyrolysis reactor. It is found that an average thickness of the attachments on the inner wall pyrolysis reactor is 1 mm.

The pyrolysis products (yield, weight %) obtained during the operation of the pyrolysis system are recorded and summarized in the following table 2.

TABLE 2 Yield of Yield of Yield of Pyrolysis pyrolysis pyrolysis pyrolysis Yield of product oil gas solid water 5th day 65% 15% 15% 5% 10th day 65% 15% 15% 5% 15th day 63% 15% 16% 5% 30th day 63% 14% 18% 5% 40th day 62% 14% 19% 5% 50th day 62% 13% 20% 5% 60th day 60% 12% 23% 5% 65th day 58% 11% 26% 5%

COMPARATIVE EXAMPLE

The pyrolysis reactor of Embodiment 1 is replaced with a spiral reactor with the same size (as shown in FIG. 5), in which the materials in the reactor are stirred and propelled by a spiral stirring mechanism, the reactor has a length of 9 m, an inner diameter of 1.2 m, and a pitch of 15 cm. According to the process parameters the same as those in Embodiment 1, the pyrolysis system of the comparative example is in continuous operation. The temperature fluctuation at the flue gas outlet during operation is observed and summarized in the following table 5.

TABLE 5 1st 3rd 5th 7th 10th 15th 20th Days day day day day day day day Temperature at 350° C. 365° C. 385° C. 430° C. 457° C. 487° C. 522° C. flue gas outlet

On the 5th day of operation, the temperature at the flue gas outlet of the pyrolysis system of the comparative example increases obviously, and reaches 457° C. on the 10th day and 522° C. on the 20th day. The pyrolysis system is stopped, and the spiral reactor is inspected, it is found that there is a thick black substance attached to the inner wall of the spiral reactor, and an average thickness of the attachment reaches 5 mm, mainly a coking material.

The pyrolysis products obtained during the operation are recorded and summarized in the following table 6.

TABLE 6 Pyrolysis product Yield of Yield of Yield of pyrolytic pyrolysis pyrolysis Yield of Days oil gas solid water 1st day 65% 15% 15% 5% 3rd day 63% 14% 18% 5% 7th day 61% 13% 21% 5% 10th day 58% 10% 27% 5% 15th day 53% 10% 35% 5% 20th day 43%  9% 45% 5%

The above are the preferred embodiments of the present disclosure, and the scope of protection of the present disclosure is not limited accordingly. Therefore, all equivalent changes made according to the structure, shape and principle of the present disclosure should be included in the scope of protection of the present disclosure.

While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims

1. A continuous pyrolysis method of waste plastic, comprising the following steps:

crushing and drying the waste plastic, and then carrying out pyrolysis reaction under an oxygen-free condition to obtain pyrolysis products, wherein the pyrolysis products comprise pyrolysis oil and gas, and a pyrolysis solid; a temperature of the pyrolysis reaction remains stable in the range of 450-500° C. for more than 60 days, pyrolysis reaction time is controlled at 30-40 min, and a proportion of the pyrolysis solid in the pyrolysis products is less than 20% by weight.

2. The continuous pyrolysis method of waste plastic according to claim 1, wherein the temperature of the pyrolysis reaction remains stable in the range of 450-500° C. for more than 20 days.

3. The continuous pyrolysis method of waste plastic according to claim 1, wherein the temperature of the pyrolysis reaction remains unchanged for more than 10 days.

4. The continuous pyrolysis method of waste plastic according to claim 1, wherein a moisture content of the waste plastic after drying is less than 5% by weight.

5. A pyrolysis system of waste plastic, which is used for the continuous pyrolysis method of waste plastic according to claim 1, wherein the system comprises a feeding unit, a pyrolysis unit for pyrolysis reaction, and a separation unit for pyrolysis product separation; the feeding unit, the pyrolysis unit and the separation unit are connected in turn; a discharge port of the feeding unit is hermetically connected to a feed port of the pyrolysis unit, a pyrolysis product outlet of the pyrolysis unit communicates with the separation unit, and the separation unit is used to separate pyrolysis oil and gas from a pyrolysis solid;

the pyrolysis unit comprises a pyrolysis reactor, and a flue gas channel arranged around an outer wall of the pyrolysis reactor, and the flue gas channel is used for circulating a hot flue gas, thus providing a heat source for the pyrolysis reactor;
the flue gas channel is provided with a flue gas inlet, and a flue gas outlet; the flue gas inlet is arranged on a feed port side of the pyrolysis reactor, and the flue gas outlet is arranged on a pyrolysis product outlet side of the pyrolysis reactor; and
a stirring assembly is arranged in an inner cavity of the pyrolysis reactor, and the stirring assembly is in tangential contact with an inner wall of the pyrolysis reactor when rotating.

6. The pyrolysis system of waste plastic according to claim 5, wherein the stirring assembly comprises a rotating shaft, and a plurality of stirring rods arranged on the rotating shaft, and the rotating shaft is arranged on a central line of the pyrolysis reactor along a length of the pyrolysis reactor;

one end of the stirring rod is fixedly connected to the rotating shaft, the other end of the stirring rod is connected to a scraping plate, and the scraping plate is able to rotate at an end of the stirring rod; and
a shape of the scraping plate is a long-strip plate, and both ends of the scraping plate have different weights.

7. The pyrolysis system according to claim 5, wherein an included angle between the stirring rod and the rotating shaft is 30-90 degrees.

8. The pyrolysis system according to claim 5, wherein on the rotating shaft, a vertical distance between two adjacent stirring rods on the rotating shaft is 1.5-3 times a length of the scraping plate.

9. The pyrolysis system according to claim 5, wherein the pyrolysis system comprises two or more stages of pyrolysis units, two adjacent stages of pyrolysis units are in closed communication, and the separation unit communicates with the last stage of pyrolysis unit.

10. The pyrolysis system according to claim 9, wherein each stage of pyrolysis unit is provided with an independent flue gas channel, and the flue gas channels of two adjacent stages of pyrolysis units are in communication.

11. The pyrolysis system of waste plastic according to claim 5, wherein the temperature of the pyrolysis reaction remains stable in the range of 450-500° C. for more than 20 days.

12. The pyrolysis system of waste plastic according to claim 5, wherein the temperature of the pyrolysis reaction remains unchanged for more than 10 days.

13. The pyrolysis system of waste plastic according to claim 5, wherein a moisture content of the waste plastic after drying is less than 5% by weight.

Patent History
Publication number: 20260201253
Type: Application
Filed: Jan 15, 2025
Publication Date: Jul 16, 2026
Inventors: Yinghan JIANG (Beijing), Baolin SUN (Beijing), Hongmin QI (Beijing), Shuimiao CHEN (Beijing), Yanbing ZHAO (Beijing), Dongfang WANG (Beijing)
Application Number: 19/021,718
Classifications
International Classification: C10B 47/36 (20060101); C10B 53/07 (20060101); C10B 57/10 (20060101); C10B 57/14 (20060101); C10G 1/02 (20060101);