Cascade countercurrent fluidized bed reaction system for producing oil by cracking waste plastics

Abstract

The invention discloses a cascade countercurrent fluidized bed reaction system for producing oil by cracking waste plastics, and relates to the technical field of waste plastic treatment. According to the invention, the material returning pipe is combined with high-rate circulating catalyst particles and the inclined air distribution plate, and the air speed at two sides is regulated and controlled, so that the transverse diffusion capability of molten plastic is enhanced, the risks of local flow loss and wall adhesion are effectively reduced, and the operation stability of the cracking furnace is obviously improved; easily-cracked hydrocarbons are moderately converted in a low-temperature area, and difficultly-cracked components and oil gas intermediates are deeply reacted in a high-temperature area, so that light components are accurately inhibited from being excessively cracked into non-condensable gas, and the yield of target oil products is remarkably improved; a three-stage series rectifying tower is innovatively adopted, and a precise temperature zone is formed by utilizing countercurrent flow heat exchange to separate gasoline and diesel oil; and heavy oil with poor flowability at the tower bottom is driven by high-temperature catalyst particle flow to enter a high-temperature cracking furnace for cyclic cracking, so that high-value-added products are efficiently collected, and the economical efficiency is remarkably improved while the equipment compactness is improved.

Description

Technical Field

[0001] This invention relates to the field of waste plastic treatment technology, specifically to a cascade countercurrent fluidized bed reaction system for pyrolysis of waste plastics to produce oil. Background Technology

[0002] Plastics are widely used in all walks of life due to their low production cost and ease of processing. While bringing great convenience to people's lives, they have also generated a large amount of white pollution. The world's total annual production of plastic waste has reached 50 million tons. For the past few decades, waste plastics have been part of municipal solid waste (MSW). According to surveys, in industrialized countries, waste plastics account for 4%-10% (wt) or 10%-20% (v%) of MSW, mainly from packaging waste, automobile waste, and processing waste. The percentages of various types of waste plastics are as follows: low-density polyethylene (LDPE) 27%; high-density polyethylene (HDPE) 21%; polypropylene (PP) 18%; polystyrene (PS) 16%; and polyvinyl chloride (PVC) 7%.

[0003] Due to the lack of efficient, clean, and large-scale technologies, waste plastics have become a pressing environmental problem worldwide. In the treatment of urban plastic solid waste, traditional methods such as incineration, landfill, physical recycling, and modified regeneration have gradually faded from view due to stringent environmental requirements and economic constraints. Currently, rapid pyrolysis / catalytic pyrolysis of waste plastics for liquefaction or chemical production has become a hot topic both domestically and internationally, and represents the most promising waste plastic treatment technology for industrialization. Rapid pyrolysis / catalytic pyrolysis of waste plastics involves heating waste plastics at high temperatures under anaerobic or low-oxygen conditions to decompose them and produce valuable products, such as gasoline, diesel, petroleum wax, and other chemical raw materials. However, due to the characteristics of waste plastics such as large size, light weight, easy expansion, easy melting and adhesion, and poor thermal conductivity, it is difficult to solve the problems of continuous feeding and rapid heating. At present, most waste plastic pyrolysis liquefaction adopts batch reaction in reactor type and horizontal rotary reaction. The heating rate is slow, the feed adhesion and coking are serious, the yield and added value of liquid products are low, the processing capacity is difficult to improve, and the scale-up of pyrolysis equipment is difficult, which restricts the efficient, clean and large-scale utilization of waste plastics.

[0004] The plastic pyrolysis system disclosed in CN114989846A uses a rotary reactor, but it does not address the mass transfer difficulties caused by the high viscosity of molten plastic, nor does it propose specific solutions to improve product yield / selectivity.

[0005] The apparatus and method disclosed in CN116254127A achieve continuous feeding by using paraxylene to liquefy waste plastics, thus improving processing efficiency and capacity. It features rapid pyrolysis, low energy consumption, and a product containing over 50 wt% gasoline and diesel fractions. However, the product is still a mixed fuel oil containing multiple components such as gasoline, diesel, and heavy oil, lacking effective component separation methods and failing to achieve high-value-added graded utilization of the product.

[0006] CN205024166U discloses a method for producing gasoline and diesel fuel from waste polyethylene plastic in a fluidized bed, achieving continuous feeding and catalyst particle recycling, thus improving raw material utilization and product productivity. However, in fluidized bed pyrolysis reactions, both easily and difficult-to-pyrolyze hydrocarbons come into contact with the high-temperature catalyst, which can easily cause excessive decomposition of hydrocarbons into non-condensable gases.

[0007] In summary, existing waste plastic pyrolysis technologies generally suffer from difficulties in continuous feeding, relying on traditional screw feeders for individual feeding. Molten plastic is prone to sticking to the walls and clogging, leading to unstable operation and affecting the long-term operation of the unit. In fluidized beds, both easily pyrolyzable light components and difficult-to-pyrolyzable heavy components are exposed to high-temperature catalysts, causing excessive pyrolysis of light components to generate non-condensable gases, significantly reducing the yield of the target product. Traditional condensation and collection rely on multiple distillation columns arranged in series, resulting in a large and non-compact system that only produces low-value-added mixed fuel oil, failing to achieve high-value-added graded utilization. Therefore, a new solution is needed to address the above problems. Summary of the Invention

[0008] The purpose of this invention is to provide a cascade countercurrent fluidized bed reaction system for pyrolysis of waste plastics to produce oil, so as to solve the technical problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a cascade countercurrent fluidized bed reaction system for pyrolysis of waste plastics to produce oil, comprising a feed inlet, a low-temperature pyrolysis furnace, a first cyclone separator, a regeneration combustion chamber, a second cyclone separator, a first-stage distillation chamber, a first heat exchanger, and a high-temperature pyrolysis furnace. The feed inlet is connected to the low-temperature pyrolysis furnace. A partition wall is provided at the bottom of the low-temperature pyrolysis furnace, dividing the interior of the low-temperature pyrolysis furnace into left and right sides. A second induced draft fan and a third induced draft fan are respectively connected to the bottom of the left and right sides. The second and third induced draft fans are used to blow in pyrolysis gas at different flow rates. The air distribution plate on the left side is arranged at an angle. A first cyclone separator is connected to one side of the low-temperature pyrolysis furnace. The first cyclone separator is used for gas-solid separation. The gas separation port of the first cyclone separator is connected to the first-stage distillation chamber. The solids separated in the first cyclone separator are returned to the low-temperature pyrolysis furnace for recycling reaction. During the recycling reaction, plastic melting is performed through low-temperature catalyst particles. A regeneration combustion chamber is provided on the other side of the low-temperature pyrolysis furnace. The regeneration combustion chamber is used to roast regenerated carbon deposit catalyst particles. Both the primary distillation chamber and the second cyclone separator are connected to the first heat exchanger. A high-temperature pyrolysis furnace is located on the side of the primary distillation chamber away from the low-temperature pyrolysis furnace.

[0010] Furthermore, the primary distillation chamber is connected in sequence to the secondary and tertiary distillation chambers, which form three different temperature zones. The high-temperature gas is cooled into liquid as it passes through the three distillation chambers in sequence. Due to the different specific gravities of the liquids, different products can be collected and separated.

[0011] Furthermore, a second heat exchanger is connected to one side of the first heat exchanger, and the high-temperature flue gas exiting the first heat exchanger re-enters the second heat exchanger to preheat the cracked gas from the tertiary distillation chamber.

[0012] Furthermore, a fourth induced draft fan is provided at the bottom of the regenerative combustion chamber, which is used to input preheated air into the regenerative combustion chamber.

[0013] Furthermore, a third cyclone separator is provided on the side of the high-temperature pyrolysis furnace away from the primary distillation chamber.

[0014] Furthermore, a blower is provided at the third-stage distillation chamber, and the blower is used to exchange heat with the incoming air.

[0015] Furthermore, a first induced draft fan is provided at the bottom of the high-temperature pyrolysis furnace.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention abandons the traditional screw feeder and uses a return pipe combined with high-ratio circulating catalyst particles and inclined air distribution plate to enhance the lateral diffusion capacity of molten plastic by controlling the wind speed on both sides, effectively reducing the risk of local flow loss and wall adhesion, and significantly improving the operational stability of the pyrolysis furnace.

[0017] 2. This invention utilizes the synergistic effect of a low-temperature cracking zone (low-temperature catalyst) and a high-temperature cracking zone (high-temperature catalyst) to enable easily crackable hydrocarbons to undergo moderate conversion in the low-temperature zone, while difficult-to-crack components and oil and gas intermediates undergo deep reaction in the high-temperature zone. This precisely inhibits the excessive cracking of light components into non-condensable gases, significantly improving the yield of target oil products (gasoline and diesel). 3. This invention innovatively adopts a three-stage series distillation column, which uses countercurrent heat exchange to form a precise temperature zone separation of gasoline and diesel; and uses high-temperature catalyst particle flow to carry the heavy oil with poor flowability at the bottom of the column into the high-temperature cracking furnace for circulating cracking, so as to achieve efficient collection of high value-added products, improve equipment compactness and significantly improve economy. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the entire invention.

[0020] The components are: 1. Waste plastic feed inlet; 2. Low-temperature pyrolysis furnace; 3. First cyclone separator; 4. Combustion regeneration chamber; 5. Second cyclone separator; 6. First-stage distillation chamber; 7. High-temperature pyrolysis furnace; 8. Third cyclone separator; 9. Second-stage distillation chamber; 10. Third-stage distillation chamber; 11. First heat exchanger; 12. Second heat exchanger; 13. Blower; 14. First induced draft fan; 15. Second induced draft fan; 16. Third induced draft fan; 17. Fourth induced draft fan. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] Please see Figure 1 A cascade countercurrent fluidized bed reaction system for pyrolysis of waste plastics to produce oil includes a feed inlet 1, a low-temperature pyrolysis furnace 2, a first cyclone separator 3, a regeneration combustion chamber 4, a second cyclone separator 5, a first-stage distillation chamber 6, a first heat exchanger 11, and a high-temperature pyrolysis furnace 7. The feed inlet 1 is connected to the low-temperature pyrolysis furnace 2. The bottom of the low-temperature pyrolysis furnace 2 is equipped with a partition wall, which divides the interior of the low-temperature pyrolysis furnace 2 into left and right sides. The bottom of the left and right sides is respectively connected to a second induced draft fan 15 and a third induced draft fan 16. The second induced draft fan 15 and the third induced draft fan 16 are used to blow in pyrolysis gas at different flow rates. The air distribution plate on the left side is arranged at an angle. Waste plastics and catalyst are added from feed inlet 1 and enter the low-temperature pyrolysis furnace 2. Pyrolysis gas with different flow rates is blown in by the second induced draft fan 15 and the third induced draft fan 16 respectively. The fluidization air velocity on the left is 3-5 m / s and the fluidization air velocity on the right is 1-3 m / s.

[0023] A first cyclone separator 3 is connected to one side of the low-temperature pyrolysis furnace 2. The first cyclone separator 3 is used for gas-solid separation. The gas separation port of the first cyclone separator 3 is connected to the first-stage distillation chamber 6. The solid separated in the first cyclone separator 3 is returned to the low-temperature pyrolysis furnace 2 for recycling reaction. During the recycling reaction, plastic melting is carried out through low-temperature catalyst particles. A regeneration combustion chamber 4 is set on the other side of the low-temperature pyrolysis furnace 2. The regeneration combustion chamber 4 is used to roast the regenerated carbon deposit catalyst particles. When waste plastic and low-temperature catalyst particles enter the left side of the low-temperature pyrolysis furnace 2 through the feed inlet 1 for reaction, a portion of the gas-solid mixture enters the first cyclone separator 3 on the left side of the low-temperature pyrolysis furnace 2 for gas-solid separation. The gas is discharged from the top and enters the first-stage distillation chamber 6. The unreacted plastic melt and catalyst particles re-enter the low-temperature pyrolysis furnace 2 for recycling reaction. Under the combined action of the high recycling rate of the low-temperature catalyst particles and the inclined air distribution plate, the lateral diffusion ability of the molten plastic is enhanced. When the plastic melt adhering to the surface of the low-temperature catalyst particles has completed the reaction, its surface viscosity will decrease. Due to the different wind speeds on both sides, the catalyst will roll over the partition wall and enter the right side, falling into the bottom of the regeneration combustion chamber 4.

[0024] Both the primary distillation chamber 6 and the second cyclone separator 5 are connected to the first heat exchanger 11; A high-temperature cracking furnace 7 is installed on the side of the primary distillation chamber 6 away from the low-temperature cracking furnace 2.

[0025] A second heat exchanger 12 is connected to one side of the first heat exchanger 11. The high-temperature flue gas that comes out of the first heat exchanger 11 re-enters the second heat exchanger 12 to preheat the cracked gas from the tertiary distillation chamber 10.

[0026] A fourth induced draft fan 17 is provided at the bottom of the regeneration combustion chamber 4. The fourth induced draft fan 17 is used to input preheated air into the regeneration combustion chamber 4.

[0027] The preheated pyrolysis gas is sent into the combustion regeneration chamber 4 by the fourth induced draft fan 17, and reacts with the catalyst with carbon attached to the bottom surface of the combustion regeneration chamber 4. The preheated pyrolysis gas, as a heat source, enables the combustion regeneration chamber to heat up rapidly to remove the carbon on the surface of the catalyst particles.

[0028] A third cyclone separator 8 is installed on the side of the high-temperature cracking furnace 7 away from the primary distillation chamber 6.

[0029] The primary distillation chamber 6 is connected in sequence to the secondary distillation chamber 9 and the tertiary distillation chamber 10. The primary distillation chamber 6, the secondary distillation chamber 9 and the tertiary distillation chamber 10 form three different temperature zones. The high-temperature gas is cooled into liquid as it passes through the three distillation chambers in sequence. Due to the different specific gravities of the liquids, different products can be collected and separated.

[0030] Blowers 13 are installed at 10 locations in the three-stage distillation chamber. Blowers 13 are used to exchange heat from the incoming air.

[0031] The bottom of the high-temperature pyrolysis furnace 7 is equipped with a first induced draft fan 14.

[0032] In the first-stage distillation chamber 6, the high-temperature oil-gas mixture from the first cyclone separator 3 and the third cyclone separator 8 exchanges heat with the air supplied from the third-stage distillation chamber 10 via the blower 13, forming three different temperature zones. The high-temperature gas is cooled into a liquid as it passes through the three distillation chambers sequentially. Due to the different specific gravities of the liquids, different products are collected and separated: gasoline in the third-stage distillation chamber 10, diesel in the second-stage distillation chamber 9, and heavy oil in the first-stage distillation chamber 6. Liquid outlets are provided at the bottom of the third-stage distillation chamber 10 and the second-stage distillation chamber 9 to facilitate the collection of the cooling liquid. The heavy oil at the bottom of the tower condenses. Subsequently, its fluidity slows down. When the high-temperature catalyst particles separated by the second cyclone separator 5 pass through the first-stage distillation chamber 6, the condensed heavy oil falls downwards due to gravity and flows into the high-temperature cracking furnace 7 under the influence of the high-temperature catalyst particle flow. The cracked gas preheated by the second heat exchanger 12 is sent into the high-temperature cracking furnace 7 as a fluidizing gas by the first induced draft fan for reaction. The gas-solid mixture after reaction undergoes gas-solid separation in the third cyclone separator 8. The solid catalyst particles are sent back into the high-temperature cracking furnace 7, while a portion of the catalyst particles are sent from the bottom into the low-temperature cracking furnace 2.

[0033] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A stepped countercurrent fluidized bed reaction system for oil production from waste plastic pyrolysis, characterized in that: The system includes a feed inlet (1), a low-temperature pyrolysis furnace (2), a first cyclone separator (3), a regeneration combustion chamber (4), a second cyclone separator (5), a first-stage distillation chamber (6), a first heat exchanger (11), and a high-temperature pyrolysis furnace (7). The feed inlet (1) is connected to the low-temperature pyrolysis furnace (2). The bottom of the low-temperature pyrolysis furnace (2) is equipped with a partition wall, which divides the interior of the low-temperature pyrolysis furnace (2) into left and right sides. The bottom of the left and right sides is connected to a second induced draft fan (15) and a third induced draft fan (16), respectively. The second induced draft fan (15) and the third induced draft fan (16) are used to blow in pyrolysis gas with different flow rates. The air distribution plate on the left side is arranged at an angle. A first cyclone separator (3) is connected to one side of the low-temperature pyrolysis furnace (2). The first cyclone separator (3) is used for gas-solid separation. The gas separation port of the first cyclone separator (3) is connected to the first-stage distillation chamber (6). The solid separated in the first cyclone separator (3) is returned to the low-temperature pyrolysis furnace (2) for recycling reaction. During the recycling reaction, plastic melting is carried out through low-temperature catalyst particles. A regeneration combustion chamber (4) is provided on the other side of the low-temperature pyrolysis furnace (2). The regeneration combustion chamber (4) is used for roasting regenerated carbon deposit catalyst particles. The primary distillation chamber (6) and the second cyclone separator (5) are both connected to the first heat exchanger (11); A high-temperature pyrolysis furnace (7) is installed on the side of the primary distillation chamber (6) away from the low-temperature pyrolysis furnace (2).

2. The stepped countercurrent fluidized bed reaction system for pyrolysis of waste plastics to produce oil according to claim 1, characterized in that: The primary distillation chamber (6) is connected in sequence to the secondary distillation chamber (9) and the tertiary distillation chamber (10). The primary distillation chamber (6), the secondary distillation chamber (9) and the tertiary distillation chamber (10) form three different temperature zones. The high-temperature gas is cooled into liquid as it passes through the three distillation chambers in sequence. Due to the different specific gravities of the liquids, different products can be collected and separated.

3. The cascade countercurrent fluidized bed reaction system for pyrolysis of waste plastics to produce oil according to claim 2, characterized in that: A second heat exchanger (12) is connected to one side of the first heat exchanger (11). The high-temperature flue gas after exiting the first heat exchanger (11) re-enters the second heat exchanger (12) to preheat the cracked gas from the third-stage distillation chamber (10).

4. A stepped countercurrent fluidized bed reaction system for pyrolysis of waste plastics to produce oil, as described in claim 3, is characterized in that: The bottom of the regenerative combustion chamber (4) is provided with a fourth induced draft fan (17), which is used to input preheated air into the regenerative combustion chamber (4).

5. A stepped countercurrent fluidized bed reaction system for pyrolysis of waste plastics to produce oil, as described in claim 4, characterized in that: A third cyclone separator (8) is provided on the side of the high-temperature cracking furnace (7) away from the primary distillation chamber (6).

6. A stepped countercurrent fluidized bed reaction system for pyrolysis of waste plastics to produce oil, as described in claim 5, characterized in that: A blower (13) is provided at the third-stage distillation chamber (10), and the blower (13) is used to exchange heat with the incoming air.

7. A stepped countercurrent fluidized bed reaction system for pyrolysis of waste plastics to produce oil according to claim 6, characterized in that: The high-temperature pyrolysis furnace (7) is equipped with a first induced draft fan (14) at its bottom end.

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