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CN-119060754-B - Processing method and processing system for pyrolysis and cracking of waste plastics

CN119060754BCN 119060754 BCN119060754 BCN 119060754BCN-119060754-B

Abstract

A processing method and a processing system for pyrolysis cracking of waste plastics comprise the steps of S1, enabling waste plastics to be processed to enter a waste plastics liquefying unit for liquefying treatment to obtain liquefied waste plastics, S2, enabling the liquefied waste plastics to enter a plastic reduction and viscosity reduction unit for treating to obtain liquefied waste plastics oil, S3, extracting low-ash materials from the upper portion of a reactor of the plastic reduction and viscosity reduction unit for heating to obtain high-temperature low-ash materials, extracting high-ash materials from the lower portion of the reactor, S4, enabling the high-temperature low-ash materials or the high-temperature low-ash materials and the high-ash materials to be mixed to enter a pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke, and S5, further separating to obtain dry gas, liquefied gas, gasoline fractions, diesel fractions and wax oil fractions. The method and the system provided by the invention effectively realize the recycling, large-scale and continuous utilization of waste plastics, prolong the operation period of the device and reduce the generation of coke.

Inventors

  • REN LEI
  • LI ZIFENG
  • WANG YONG
  • DONG MING
  • SHEN HAIPING
  • MA SHOUYI

Assignees

  • 中国石油化工股份有限公司
  • 中石化石油化工科学研究院有限公司

Dates

Publication Date
20260512
Application Date
20230531

Claims (20)

  1. 1. A processing method for pyrolysis cracking of waste plastics, which is characterized by comprising the following steps: S1, enabling waste plastics to be treated to enter a waste plastic liquefying unit for liquefying treatment to obtain liquefied waste plastics, wherein the technological conditions of the liquefying treatment comprise outlet temperature of 370-500 ℃, and residence time of 5-20 min; S2, enabling the liquefied waste plastics to enter a plastic-reducing and visbreaking unit for plastic-reducing and visbreaking treatment to obtain plastic-reducing and visbreaking liquefied waste plastic oil, wherein the technological conditions of the plastic-reducing and visbreaking treatment comprise a reaction temperature of 370-450 ℃, a residence time of 2-120 min; S3, extracting low ash materials from the upper part of the reactor of the plastic reduction and viscosity reduction unit, and heating the low ash materials in a heating furnace to obtain high temperature low ash materials; s4, the high-temperature low-ash material and the high-ash material enter a pyrolysis reaction unit to carry out pyrolysis reaction to obtain pyrolysis products and coke; S5, the pyrolysis product enters a separation unit to be separated to obtain dry gas, liquefied gas, gasoline fraction, diesel fraction and wax oil fraction.
  2. 2. The method for processing pyrolytic cracking of waste plastics according to claim 1, wherein in step S1, the waste plastics liquefying unit performs the liquefying treatment using a first screw type heating and conveying apparatus selected from a twin screw type or a single screw type heating and conveying apparatus with heating.
  3. 3. The method for processing waste plastic by pyrolysis cracking according to claim 1 or 2, wherein in the step S1, the liquefying process is performed under the process conditions that the outlet temperature is 380-450 ℃ and the residence time is 5-15 min.
  4. 4. The method for processing waste plastics by pyrolysis cracking according to claim 1 or 2, wherein in step S2, the plastic-reducing and visbreaking unit performs the plastic-reducing and visbreaking treatment by using an adiabatic plastic-reducing and visbreaking reactor.
  5. 5. The method for processing pyrolytic cracking of waste plastics according to claim 4, wherein in the step S2, the technological conditions of the plastic-reducing visbreaking treatment comprise a reaction temperature of 380-420 ℃ and a residence time of 30-70 min.
  6. 6. The process for pyrolytic cracking of waste plastics according to claim 1 or 2, wherein in step S3, the extraction weight ratio of the low ash material to the high ash material is 1-20:1.
  7. 7. The method for processing pyrolytic cracking of waste plastics according to claim 1 or 2, wherein in step S3, a vertical baffle is arranged in the reactor of the plastic reduction and viscosity reduction unit, the top of the baffle is closed, the bottom of the baffle is opened, wherein the middle part of one side of the baffle is fed, the upper part of the other side of the baffle is used for extracting low ash materials, and the lower part of the other side of the baffle is used for extracting high ash materials.
  8. 8. The method for processing waste plastic by pyrolysis and cracking according to claim 1 or 2, wherein in the step S3, the process conditions of the heating furnace comprise that the outlet temperature of the heating furnace is 480-600 ℃, water vapor is injected into the heating furnace, and the steam injection amount is 0.5-5 wt%.
  9. 9. The method for processing pyrolytic cracking of waste plastics according to claim 8, wherein in step S3, the outlet temperature of the heating furnace is 500-580 ℃, and the steam injection amount of the heating furnace is 0.5-3 wt%.
  10. 10. The method for processing waste plastics by pyrolysis cracking according to claim 1 or 2, wherein in step S4, the high-temperature low-ash material and the high-ash material are mixed and then enter a pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke.
  11. 11. The process for the pyrolytic cracking of waste plastics according to claim 10, characterized in that in step S4, the high temperature low ash material is mixed with the high ash material in a mixer in a weight ratio of 1-20:1.
  12. 12. The method for processing waste plastic by pyrolysis cracking according to claim 1 or 2, wherein in the step S4, the process conditions of the pyrolysis reaction comprise that the pressure of a top of the pyrolysis tower is 0.05-0.6 MPa, the temperature of the pyrolysis reaction is 450-580 ℃ and the operation period is 1-500 h.
  13. 13. The method for processing waste plastic by pyrolysis cracking according to claim 12, wherein in the step S4, the pressure of the top of the pyrolysis tower of the pyrolysis reaction is 0.1-0.3 Mpa, the temperature of the pyrolysis reaction is 480-550 ℃, and the operation period is 10-240 h.
  14. 14. The process for the pyrolytic cracking of waste plastics according to any one of claims 1, 2, 5, 9, 11, 13, characterized in that, before step S1, the process further comprises: s0, enabling the chlorine-containing waste plastic raw material to enter a waste plastic melting and dechlorinating unit for hot melting and dechlorinating treatment to obtain hydrogen chloride-containing gas and dechlorinated waste plastic materials; the dechlorinated waste plastic material enters the waste plastic liquefying unit or And cooling and crushing the dechlorinated waste plastic material in sequence to obtain dechlorinated waste plastic particles, and enabling the dechlorinated waste plastic particles to enter the waste plastic liquefying unit.
  15. 15. The process for the pyrolytic cracking of waste plastics according to claim 14, further comprising: The chlorine-containing gas enters a hydrogen chloride absorption unit and is contacted with a hydrogen chloride absorbent to be subjected to hydrogen chloride absorption treatment to obtain the chlorine-containing absorbent and dechlorinated dry gas, wherein the hydrogen chloride absorbent is water or alkali liquor with pH value of more than 7.
  16. 16. The processing method of pyrolysis cracking of waste plastics according to claim 14, wherein the waste plastics melting dechlorination unit comprises a second screw type heating and conveying device and a vacuum device communicated with the second screw type heating and conveying device, wherein the second screw type heating and conveying device is selected from a double screw type conveying device or a single screw type conveying device; The technological conditions of the hot melting dechlorination treatment comprise a feeding rate of 5-5000 kg/h, an outlet temperature of 150-370 ℃, a reaction time of 0.1-0.5 h and a vacuum degree of 50-300 mmHg; The particle size of the dechlorinated waste plastic particles obtained by crushing treatment is 100-2000 mu m.
  17. 17. The method for processing the pyrolysis cracking of the waste plastics, which is characterized in that the process conditions of the hot melting dechlorination treatment comprise a feeding rate of 100-4000 kg/h, an outlet temperature of 300-330 ℃, a reaction time of 0.1-0.3 h and a vacuum degree of 50-150 mmHg.
  18. 18. The process for the pyrolytic cracking of waste plastics according to any one of claims 1, 2, 5, 9, 11, 13, further comprising returning at least a portion of the wax oil fraction from said separation unit to said plastics reduction and visbreaking unit for recycling.
  19. 19. The method for processing waste plastics by pyrolysis and cracking according to claim 18, wherein the weight ratio of the recycled wax oil fraction to the waste plastics to be processed is 0.2-5.0:1, and the fraction with the distillation range of more than 350 ℃ obtained by separation of the separation unit is used as the wax oil fraction.
  20. 20. The method for processing waste plastics by pyrolysis cracking according to any one of claims 1,2, 5, 9, 11 and 13, wherein the waste plastics to be processed comprise one or more of LDPE, HDPE, PS, PP, PET and PVC, the content of PVC in the waste plastics to be processed is less than 10 wt%, and the ash content in the waste plastics to be processed is 1-40 wt%.

Description

Processing method and processing system for pyrolysis and cracking of waste plastics Technical Field The invention relates to the field of recycling of waste plastic resources, in particular to a processing method and a processing system for viscosity reduction, classification, pyrolysis and cracking of waste plastic. Background At present, with technological progress and industrial development, plastic is used as a packaging material in daily life of human beings, used waste plastic cannot be automatically decomposed in nature, only a few kinds of waste plastic can be reprocessed and utilized through a specific recycling channel, and a large amount of waste plastic enters a landfill in a form of household garbage, and a large amount of space is occupied because the waste plastic is not easy to decompose. In particular, in recent years, the amount of waste plastics generated has been increased, and the waste plastics have been rapidly recycled in a green manner, which has become an urgent task. The simplest chemical method for treating waste plastics is direct incineration, but the direct incineration can generate toxic gas harmful to human bodies, thereby causing secondary environmental pollution. The waste plastic oil-treatment technology is to crack the waste plastic under the condition of no oxygen or oxygen deficiency by heating or under the condition of catalyst, so that the high polymer is cracked into low molecular substances to obtain gasoline, kerosene, diesel oil fraction, partial pyrolysis gas and the like, on one hand, the pollution problem caused by the waste plastic is relieved, on the other hand, the recycling of the waste plastic is realized, and the waste plastic oil-treatment technology is an important direction of waste plastic recycling treatment. At present, the waste plastic oiling recovery technology mainly comprises waste plastic thermal cracking, catalytic thermal cracking, thermal cracking catalytic modification technology and the like. The thermal cracking method has the advantages of simple process, relatively less equipment investment, no catalyst, short reaction flow and the like, and compared with the other two technical units, the thermal cracking method has the lowest oiling cost. The general waste plastics in the household garbage are subjected to high-temperature pyrolysis reaction at 380-500 ℃, the pyrolysis speed is high, and the product components are relatively single and can be used as oil products or chemical raw materials. CN109401774a discloses a continuous thermal cracking system for waste plastics and a thermal cracking method thereof, the system comprises a feeding device, a thermal cracking reaction kettle and a slag discharging device which are connected in sequence, and because plastics are macromolecular polymers, non-newton fluid is formed in the heating process, and a screw propeller is used. The plastic liquefying process is heated unevenly, and is easy to produce coking and scale deposition. CN10461030a discloses a coking method for producing fuel oil from waste plastics, which is to preheat the high aromatic component and the waste plastics or plastic oil by a raw material buffer tank, then enter a tubular heating furnace to raise the temperature, and spray into a delayed coking tower to carry out coking reaction. CN112538363a discloses a process for co-converting waste plastics, selected from polyethylene, polypropylene and, polystyrene, PET and metal-added multilayer plastics, also excluding polyvinyl chloride, together with petroleum residuum raw materials, in a delayed coker unit. The waste plastics have the problem of density difference between the high-viscosity polymer melt formed in the melting process and hydrocarbon raw materials, so that the mixed fluid of hydrocarbon and polymer melt can cause the problems of blockage, coking and the like of a delayed coking heating furnace tube. Disclosure of Invention The invention aims to solve the technical problem of providing a processing method and a processing system for viscosity-reducing graded pyrolysis cracking of waste plastics, which can effectively realize recycling, large-scale and continuous utilization of the waste plastics, prolong the working period and reduce coke generation. In order to achieve the aim, the invention provides a processing method of pyrolysis cracking of waste plastics, which comprises the following steps of S1, enabling waste plastics to be processed to enter a waste plastics liquefying unit for liquefying treatment to obtain liquefied waste plastics, S2, enabling the liquefied waste plastics to enter a plastic reduction viscosity breaking unit for carrying out plastic reduction viscosity breaking treatment to obtain plastic reduction viscosity breaking liquefied waste plastics oil, S3, extracting low ash materials from the upper part of a reactor of the plastic reduction viscosity breaking unit for heating treatment to obtain high-temperature low ash materials, extrac