Processing method and system of waste polyolefin

Abstract

The invention relates to the technical field of waste plastic pyrolysis, in particular to a waste polyolefin processing method and system. The method comprises the steps that 1, waste polyolefin makes contact with a product guiding agent, a pyrolysis reaction is conducted, and pyrolysis oil gas and residues are obtained; wherein the product guiding agent is naphthenic oil; the feeding temperature of the waste polyolefin is 80-120 DEG C, and the feeding temperature of the product guiding agent is 250-400 DEG C; the pyrolytic reaction at least comprises a first stage and a second stage; the temperature of the first stage is 250-400 DEG C, and the retention time of the first stage is 0.5-5.5 s; the temperature of the second stage is 450-650 DEG C, and the retention time of the second stage is 1-10 minutes; 2, the pyrolysis oil gas is separated, and pyrolysis oil I with the boiling point larger than or equal to 40 DEG C to 60 DEG C and pyrolysis gas I with the boiling point smaller than 40 DEG C to 60 DEG C are obtained; according to the processing method of the waste polyolefin, provided by the invention, the content of gasoline fraction in pyrolysis oil gas can be remarkably increased.

Description

Technical Field

[0001] The invention relates to the technical field of waste plastic pyrolysis, and in particular to a method and system for processing waste polyolefins. Background Art

[0002] According to statistics, my country produces about 60 million tons of waste plastics every year, of which about 1 / 3 is recycled, mainly PET; and 2 / 3 of the waste plastics are incinerated or landfilled, which includes a considerable portion of waste polyolefin plastic products.

[0003] As we all know, the atomic composition of polyolefins is C and H, and theoretically does not contain other heteroatoms. If this part of waste plastics is not effectively utilized, it will not only cause serious environmental pollution, but also affect the ecological balance in the natural environment; on the other hand, it will also cause serious waste of petrochemical resources.

[0004] Existing methods of disposing of waste plastics mainly include physical recycling, incineration power generation, landfill and other methods. Physical recycling refers to the physical treatment of relatively single, high-value waste plastics, such as PET mineral water bottles, which are recycled into plastic products for downgrading. They cannot be recycled again after 2-3 cycles; incineration power generation can maximize the reduction of waste plastics, but this causes a large amount of carbon emissions; since the degradation cycle of waste plastics is as long as 200-500 years, landfill cannot fundamentally solve the problem of white pollution, and it also occupies a large amount of land resources. Therefore, the international community no longer recommends landfilling of waste plastics.

[0005] Domestically, most high-value waste plastics are physically recycled, while the most used polyolefin packaging films are often discarded and incinerated in power plants due to their high recycling costs and low recycling value. Based on literature and field research, polyolefin chemical recycling is considered to be the only process that can achieve sustainable development. Among them, the pyrolysis process has attracted the attention of researchers and companies from various countries due to its environmental protection and high yield. Major international refining and chemical companies all have polyolefin pyrolysis processes with independent intellectual property rights.

[0006] However, as far as the existing technology is concerned, there are two problems with polyolefin pyrolysis technology. On the one hand, due to its low thermal conductivity, local overheating during the pyrolysis process leads to low pyrolysis oil yield. On the other hand, since polyolefin cracking conforms to the random chain breaking mechanism, while ensuring oil yield, the distribution range of pyrolysis products is relatively wide, covering all fractions from naphtha to heavy oil, and further distillation treatment is required during subsequent processing. Summary of the invention

[0007] The purpose of the present invention is to solve the problems of low pyrolysis oil yield and wide distribution range of pyrolysis products in polyolefin pyrolysis, and to provide a processing method and system for waste polyolefin.

[0008] In order to achieve the above object, the first aspect of the present invention provides a method for processing waste polyolefins, wherein the method comprises the following steps:

[0009] (1) contacting waste polyolefin with a product directing agent to perform a pyrolysis reaction to obtain pyrolysis oil gas and residue; wherein the product directing agent is cycloalkane oil; the feed temperature of the waste polyolefin is 80-120° C., and the feed temperature of the product directing agent is 250-400° C.;

[0010] The pyrolysis reaction includes at least a first stage and a second stage; wherein the temperature of the first stage is 250-400°C, and the residence time of the first stage is 0.5-5.5s; the temperature of the second stage is 450-650°C, and the residence time of the second stage is 1-10mins;

[0011] (2) Separating the pyrolysis products to obtain pyrolysis oil I with a boiling point of ≥40-60° C. and pyrolysis gas I with a boiling point of <40-60° C.

[0012] The second aspect of the present invention provides a processing system for waste polyolefins, wherein the system comprises: a feeder 1, a lock hopper 2, a feed dragon 3, a pyrolysis reaction device 4, a first heat exchanger 5, a second heat exchanger 6, a first gas-liquid separator 7, a third heat exchanger 8, a second gas-liquid separator 9 and a boiler 10;

[0013] Wherein, the feeder 1 is provided with an external heating jacket 1; the locking hopper 2 is arranged between the feeder 1 and the feeding dragon 3;

[0014] The pyrolysis reaction device 4 is a vertical pyrolysis reactor, comprising a first feed inlet, a second feed inlet, a pyrolysis product outlet, a slag outlet, a built-in heating coil and an external heating jacket II; the first feed inlet is connected to the feed dragon 3; the heat medium outlet of the built-in heating coil is connected to the heat medium inlet of the external heating jacket II;

[0015] The cold medium inlet of the primary heat exchanger 5 is the product directing agent inlet, and the cold medium outlet of the primary heat exchanger 5 is connected to the second feed inlet of the pyrolysis reaction device 4; the hot medium inlet of the primary heat exchanger 5 is connected to the pyrolysis product outlet of the pyrolysis reaction device 4, and the hot medium outlet of the primary heat exchanger 5 is connected to the hot medium inlet of the secondary heat exchanger 6;

[0016] The cold medium inlet of the secondary heat exchanger 6 is connected to the heating medium outlet of the external heating jacket II, and the cold medium outlet of the secondary heat exchanger 6 is connected to the heating medium inlet of the external heating jacket I; the hot medium outlet of the secondary heat exchanger 6 is connected to the first gas-liquid separator 7;

[0017] The gas phase outlet of the first gas-liquid separator 7 is connected to the cooling medium inlet of the first heat exchanger 5 and the hot medium inlet of the third heat exchanger 8, respectively, and the hot medium outlet of the third heat exchanger 8 is connected to the second gas-liquid separator 9; the cold medium inlet of the third heat exchanger 8 is connected to the hot medium outlet of the external heating jacket 1, and the cold medium outlet of the third heat exchanger 8 is connected to the boiler 10;

[0018] The gas phase outlet of the second gas-liquid separator 9 is connected to the boiler 10 , and the boiler 10 is connected to the heat medium inlet of the built-in heating coil.

[0019] Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

[0020] 1) The processing method of waste polyolefin provided in the present invention can, on the one hand, improve the thermal conductivity of waste polyolefin during pyrolysis, and prevent the waste polyolefin from forming large pieces or large clumps of materials during the pyrolysis reaction; on the other hand, it can cause the polymer chain to be cracked into stable products with smaller molecular weights, thereby preventing secondary reactions from occurring and preventing repolymerization into products with larger molecular weights, and significantly increasing the content of gasoline fractions;

[0021] 2) The waste polyolefin processing system provided in the present invention can efficiently utilize the heat in the pyrolysis reaction process and realize the optimization of heat supply and energy of the whole system by arranging an external heating jacket I, a built-in heating coil, an external heating jacket II, a first heat exchanger, a second heat exchanger, a first gas-liquid separator, a third heat exchanger, a second gas-liquid separator and a boiler. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of a waste polyolefin processing system provided in the present invention.

[0023] Description of reference numerals:

[0024] 1. Loading machine 2. Locking hopper 3. Feeding dragon

[0025] 4, pyrolysis reaction device 5, first heat exchanger 6, second heat exchanger

[0026] 7, first gas-liquid separator 8, third heat exchanger 9, second gas-liquid separator

[0027] 10. Boiler 11. Steam cooler 12. Water-gas separator

[0028] 13, sediment tank 14, fourth heat exchanger 15, fifth heat exchanger DETAILED DESCRIPTION

[0029] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0030] A first aspect of the present invention provides a method for processing waste polyolefins, wherein the method comprises the following steps:

[0031] (1) contacting waste polyolefin with a product directing agent to perform a pyrolysis reaction to obtain pyrolysis oil gas and residue; wherein the product directing agent is cycloalkane oil; the feed temperature of the waste polyolefin is 80-120° C., and the feed temperature of the product directing agent is 250-400° C.;

[0032] The pyrolysis reaction includes at least a first stage and a second stage; wherein the temperature of the first stage is 250-400°C, and the residence time of the first stage is 0.5-5.5s; the temperature of the second stage is 450-650°C, and the residence time of the second stage is 1-10mins;

[0033] (2) Separating the pyrolysis products to obtain pyrolysis oil I with a boiling point of ≥40-60° C. and pyrolysis gas I with a boiling point of <40-60° C.

[0034] In step (1):

[0035] In a preferred embodiment of the present invention, the waste polyolefin contains waste polyethylene and / or waste polypropylene; wherein the content of the waste polyethylene and / or waste polypropylene is ≥80wt%, preferably ≥90wt%.

[0036] The waste polyolefins in the present invention are mainly waste polyethylene and / or waste polypropylene. In addition, they may also contain water, mechanical impurities (such as bricks, bamboo, paper and a small amount of metal) and a small amount of other types of waste plastics (such as waste polystyrene, polyethylene terephthalate, polyvinyl chloride, etc.). Preferably, the water content is ≤5wt%, the mechanical impurities content is ≤3wt%, and the other types of waste plastics content is ≤2wt%.

[0037] In a preferred embodiment of the present invention, the length of the waste polyolefin is ≤100 mm, preferably ≤50 mm, and more preferably ≤20 mm. The length of the waste polyolefin is the maximum length between any two points of the irregular film.

[0038] In the present invention, the shape of the waste polyolefin is not particularly limited, and it can be a film or a shell of various shapes. In order to further improve the processing effect of the waste polyolefin, it is preferred to crush the waste polyolefin.

[0039] In a preferred embodiment of the present invention, the waste polyolefin is dried before being contacted with the product directing agent; wherein the drying temperature is 80-120°C, preferably 90-105°C.

[0040] Among them, in the present invention, after drying treatment, the moisture content in waste polyolefin can be reduced, the pyrolysis energy consumption can be reduced, and the water content in pyrolysis oil can be reduced. The water vapor discharged during the drying process can be sent to a sewage treatment plant after cooling and discharged after being treated to meet the requirements.

[0041] In a preferred embodiment of the present invention, the content of cycloalkane in the cycloalkane oil is ≥ 60 wt%, preferably ≥ 80 wt%.

[0042] Wherein, in the present invention, the cycloalkane in the cycloalkane oil can provide hydrogen and alkyl for the pyrolysis reaction, can significantly improve the alkane and cycloalkane content in the pyrolysis oil I, and then increase the productivity of the gasoline fraction. In the present invention, cycloalkane refers to a saturated hydrocarbon comprising one or more rings, and each ring of the cycloalkane optionally has one or more paraffin side chains. For example, include but are not limited to cyclopentane, cyclohexane, hydrogenated indene, decahydronaphthalene, decahydroanthracene, and the alkyl substituent of the above-mentioned cycloalkane.

[0043] In a preferred embodiment of the present invention, the distillation range of the cycloalkane oil is 40-350°C, preferably 150-350°C.

[0044] In a preferred embodiment of the present invention, the cycloalkyl oil is selected from one or more of cycloalkyl crude oil, cycloalkyl lubricating oil, cycloalkyl transformer oil, refrigeration oil and cycloalkyl rubber oil.

[0045] Among them, in the present invention, the cycloalkyl lubricating oil, cycloalkyl transformer oil, refrigeration oil, and cycloalkyl rubber oil can be synthesized according to a known method or sold on the market, or can be a fraction with a boiling point of ≤350° C. recovered from waste cycloalkyl lubricating oil, waste cycloalkyl transformer oil, waste refrigeration oil, and waste cycloalkyl rubber oil.

[0046] In a preferred embodiment of the present invention, the mass ratio of the waste polyolefin to the product directing agent is 1:0.01-0.5, preferably 1:0.1-0.2.

[0047] In a preferred embodiment of the present invention, the feed temperature of the waste polyolefin is 95-110°C, and the feed temperature of the product directing agent is 330-370°C.

[0048] Among them, in the present invention, the inventors have found through research that contacting a product directing agent at high temperature with waste polyolefin at low temperature can make the two mixed more evenly, and it is also beneficial for the high-temperature product directing agent to transfer heat to the low-temperature waste polyolefin.

[0049] In a preferred embodiment of the present invention, the product directing agent is fed by spraying. In the present invention, the high-temperature product directing agent is sprayed into the waste polyolefin. When the high-temperature product directing agent contacts the low-temperature waste polyolefin, the high-temperature product directing agent transfers the heat it carries to the waste polyolefin. The waste polyolefin melts and shrinks due to the heat, wraps the high-temperature product directing agent, and then liquefies to form droplets. The formed droplets can better mix the product directing agent and the waste polyolefin, providing space for the interaction between the product directing agent and the waste polyolefin.

[0050] In a preferred embodiment of the present invention, the temperature of the first stage is 300-340°C, and the residence time of the first pyrolysis stage is 1-3 s; the temperature of the second stage is 500-550°C, and the residence time of the second stage is 3-7 min.

[0051] Among them, in the present invention, after the waste polyolefin is mixed with the product directing agent, it falls from top to bottom into the pyrolysis reaction zone, and the pyrolysis reaction zone is divided into an upper area and a lower area. The first stage is carried out in the upper area, and the waste polyolefin is heated and agglomerated to form droplets coated with the product directing agent. The formed droplets continue to fall into the lower area, and the second stage, that is, the pyrolysis reaction, is carried out in the lower area to obtain pyrolysis oil and gas. Compared with the pyrolysis reaction without setting the first stage, the setting of the first stage can provide sufficient time conditions for the formation of droplets, which can significantly improve the pyrolysis effect, increase the generation of alkanes and cycloalkanes in the pyrolysis oil I, and at the same time increase the content of gasoline fraction in the pyrolysis oil I.

[0052] In a preferred embodiment of the present invention, the residue includes mechanical impurities and / or semi-coke generated by pyrolysis.

[0053] In step (2):

[0054] In a preferred embodiment of the present invention, the present invention does not specifically limit the separation of pyrolysis oil and gas, and conventional separation methods in the art can be used in the present invention.

[0055] In a preferred embodiment of the present invention, in the pyrolysis oil I, the content of gasoline (IBP-180°C) is 15-30wt%, the content of diesel (180-350°C) is 30-60wt%, and the content of distillate oil (350-500°C) is 10-25wt%.

[0056] In the present invention, the petroleum fraction boiling range distribution determination method (gas chromatography, GC-D2887) is used to analyze the distillation range of the pyrolysis oil I. From the analysis results, it can be seen that the pyrolysis oil I does not contain a fraction greater than 500° C. The pyrolysis oil I can be further separated according to actual needs to obtain gasoline, diesel and distillate oil.

[0057] In a preferred embodiment of the present invention, the separation comprises the following sub-steps:

[0058] (2-1), performing a first separation on the pyrolysis oil and gas to obtain pyrolysis oil II with a boiling point of ≥150-350°C and pyrolysis gas II with a boiling point of <150-350°C;

[0059] (2-2), dividing the pyrolysis gas II into at least part A and part B; wherein the part A is returned to step (1) and added to the product directing agent; and the part B is subjected to a second separation to obtain pyrolysis oil III with a boiling point ≥40-60°C and pyrolysis gas I with a boiling point <40-60°C;

[0060] (2-3) The pyrolysis oil II and the pyrolysis oil III are mixed to obtain pyrolysis oil I.

[0061] In a preferred embodiment of the present invention, the present invention does not specifically limit the first separation and the second separation, and conventional separation methods in the art can be used in the present invention.

[0062] In a preferred embodiment of the present invention, the A portion accounts for 1-50% of the total mass of the pyrolysis gas II, preferably 5-15%; the B portion accounts for 99-50% of the total volume of the pyrolysis gas II, preferably 85-95%.

[0063] In a preferred embodiment of the present invention, after the part A is returned to step (1) and added to the product directing agent, the amount of the product directing agent is reduced by 25-50%, preferably 30-45%; the mass ratio of the part A to the reduced product directing agent is 1:0.2-1.2, preferably 1:0.4-0.8.

[0064] Among them, in the present invention, the pyrolysis gas II contains a large amount of cycloalkanes generated during the pyrolysis process, and part of the pyrolysis gas II can be returned to the pyrolysis reaction for recycling. When part of the pyrolysis gas II is returned to the pyrolysis reaction, the amount of the product directing agent can be reduced accordingly according to the amount of the pyrolysis gas II returned, so as to ensure that the content of cycloalkanes after the A part is mixed with the product directing agent is still ≥60wt%, preferably ≥80wt%.

[0065] In a preferred embodiment of the present invention, the method further includes step (3): burning the pyrolysis gas I, and the heat generated by the combustion provides a heat exchange medium for the pyrolysis reaction, the first separation, the second separation, the drying of the waste polyolefin, the pyrolysis oil II and the pyrolysis oil III.

[0066] The second aspect of the present invention provides a processing system for waste polyolefins, wherein the system comprises: a feeder 1, a lock hopper 2, a feed dragon 3, a pyrolysis reaction device 4, a first heat exchanger 5, a second heat exchanger 6, a first gas-liquid separator 7, a third heat exchanger 8, a second gas-liquid separator 9 and a boiler 10;

[0067] Wherein, the feeder 1 is provided with an external heating jacket 1; the locking hopper 2 is arranged between the feeder 1 and the feeding dragon 3;

[0068] The pyrolysis reaction device 4 is a vertical pyrolysis reactor, comprising a first feed inlet, a second feed inlet, a pyrolysis product outlet, a slag outlet, a built-in heating coil and an external heating jacket II; the first feed inlet is connected to the feed dragon 3; the heat medium outlet of the built-in heating coil is connected to the heat medium inlet of the external heating jacket II;

[0069] The cold medium inlet of the primary heat exchanger 5 is the product directing agent inlet, and the cold medium outlet of the primary heat exchanger 5 is connected to the second feed inlet of the pyrolysis reaction device 4; the hot medium inlet of the primary heat exchanger 5 is connected to the pyrolysis product outlet of the pyrolysis reaction device 4, and the hot medium outlet of the primary heat exchanger 5 is connected to the hot medium inlet of the secondary heat exchanger 6;

[0070] The cold medium inlet of the secondary heat exchanger 6 is connected to the heating medium outlet of the external heating jacket II, and the cold medium outlet of the secondary heat exchanger 6 is connected to the heating medium inlet of the external heating jacket I; the hot medium outlet of the secondary heat exchanger 6 is connected to the first gas-liquid separator 7;

[0071] The gas phase outlet of the first gas-liquid separator 7 is connected to the cooling medium inlet of the first heat exchanger 5 and the hot medium inlet of the third heat exchanger 8, respectively, and the hot medium outlet of the third heat exchanger 8 is connected to the second gas-liquid separator 9; the cold medium inlet of the third heat exchanger 8 is connected to the hot medium outlet of the external heating jacket 1, and the cold medium outlet of the third heat exchanger 8 is connected to the boiler 10;

[0072] The gas phase outlet of the second gas-liquid separator 9 is connected to the boiler 10, and the boiler 10 is connected to the heat medium inlet of the built-in heating coil. Figure 1 shown.

[0073] Among them, in the present invention, by arranging an external heating jacket I, a built-in heating coil, an external heating jacket II, a first heat exchanger, a second heat exchanger, a first gas-liquid separator, a third heat exchanger, a second gas-liquid separator and a boiler, the heat in the pyrolysis reaction process can be efficiently utilized to achieve optimization of heating and energy of the entire system.

[0074] In a preferred embodiment of the present invention, the feeder 1 is selected from a bucket elevator and / or a pneumatic conveying machine. In the present invention, the external heating jacket 1 provided in the feeder dries the waste polyolefin using flue gas or steam waste heat from a boiler. One end of the feeder is connected to a material pit storing waste polyolefin, and the other end is connected to a feeding dragon, so that the waste polyolefin in the material pit can be transported to the locking hopper.

[0075] In a preferred embodiment of the present invention, when the loading machine is a bucket elevator, the system further includes a water vapor cooler 11 ; wherein the water vapor cooler is connected to the gas outlet of the lock hopper 2 .

[0076] Among them, in the present invention, the waste polyolefin from the feeder can realize water vapor separation in the lock hopper, and the separated water vapor can be cooled by the water vapor cooler to collect the water evaporated from the waste polyolefin during the drying process.

[0077] In a preferred embodiment of the present invention, when the feeder is a pneumatic conveying machine, the system further comprises a water vapor cooler 11 and a water vapor separator 12; wherein the water vapor cooler 11 is connected to the gas outlet of the lock hopper 2, and the water vapor separator 12 is connected to the water vapor cooler 11. The water vapor separator is used to separate the transport gas from the pneumatic conveying machine.

[0078] In a preferred embodiment of the present invention, a stirring device is provided in the lock hopper 2. The present invention does not specifically limit the stirring device, and the stirring device may be one or more of a screw belt type, an anchor type, a paddle type, a turbine type, a propulsion type, a frame type, etc. Preferably, a heating jacket is provided outside the lock hopper 2.

[0079] In a preferred embodiment of the present invention, the lower end of the locking hopper 2 is a conical head; the locking hopper 2 is equipped with a stirring device, and the outermost edge of the stirring blade of the stirring device is parallel to the inner wall of the hopper; wherein the stirring device is immersed in the conical head, and the distance between the stirring device and the inner wall of the conical head is less than 10 cm, preferably less than 5 cm.

[0080] In a preferred embodiment of the present invention, a cooling coil and / or cooling jacket is provided in the feed dragon 3. The cooling medium in the cooling coil and / or cooling jacket is cooling water, which is used to prevent the temperature of the feed dragon from rising due to long-term operation.

[0081] In a preferred embodiment of the present invention, the feeding auger 3 includes a horizontal conveying auger and a feeding auger. In the present invention, the horizontal conveying auger is used to convey waste polyolefins, and the feeding auger is used to feed waste polyolefins into the pyrolysis reaction device.

[0082] In a preferred embodiment of the present invention, both the horizontal conveying auger and the unloading auger are provided with bulking spirals, and the spiral pitch of the bulking spirals is ≥ 4 times the length of the waste polyolefin, preferably 8-12 times.

[0083] In a preferred embodiment of the present invention, the bulk material screws in the horizontal conveying auger and the unloading auger are selected from shafted screws or shaftless screws, preferably shaftless screws.

[0084] In a preferred embodiment of the present invention, the outlet of the unloading auger is conical, and the cone angle of the longitudinal section of the cone is 15-60°.

[0085] In a preferred embodiment of the present invention, in the pyrolysis reaction device 4, the first feed port and the second feed port are arranged at the upper part of the pyrolysis reaction device 4, the built-in heating coil and the pyrolysis product outlet are arranged at the lower half of the pyrolysis reaction device 4, and the slag outlet is arranged at the bottom of the pyrolysis reaction device 4.

[0086] In a preferred embodiment of the present invention, the second feed port is an aerosol nozzle, which is inclined downward, with an angle α with the horizontal direction, 0<α≤5°.

[0087] In a preferred embodiment of the present invention, the second feed inlet is provided in plurality, wherein the plurality of second feed inlets are arranged opposite to each other (ie symmetrically).

[0088] In a preferred embodiment of the present invention, the pyrolysis reaction device 4 further comprises a slag tank 13, wherein the slag tank 13 is arranged at the bottom of the pyrolysis reaction device 4 and is connected to the slag outlet through a valve.

[0089] In the present invention, the valve between the sludge tank and the sludge outlet can withstand a temperature of up to 550° C. The sludge tank is provided with a rake-type coke cleaner to regularly clean the residue generated inside the reactor; the sludge tank is also provided with a cooling device for cooling the residue, including but not limited to a cooling water coil or an external cooling jacket.

[0090] In a preferred embodiment of the present invention, the system further comprises a fourth heat exchanger 14, wherein the hot medium inlet of the fourth heat exchanger 14 is connected to the liquid phase outlet of the first gas-liquid separator 7, the cold medium inlet of the fourth heat exchanger 14 is connected to the hot medium outlet of the external heating jacket I, and the cold medium outlet of the fourth heat exchanger 14 is connected to the boiler 10.

[0091] In a preferred embodiment of the present invention, the system further comprises a fifth heat exchanger 15, wherein the heat medium inlet of the fifth heat exchanger 15 is connected to the heat medium outlet of the external heating jacket 1, and the heat medium outlet of the fifth heat exchanger 15 is respectively connected to the cooling medium inlets of the third heat exchanger 7 and the fourth heat exchanger 14. The cooling medium of the fifth heat exchanger 15 is selected from cooling water or air. The various devices in the processing system of the present invention are not particularly limited and can be selected according to common knowledge.

[0092] The present invention will be described in detail below by way of examples. Figure 1 The processing system shown in the figure is carried out. Among them, the feeder is a pneumatic conveying machine, and a stirring device is arranged in the conical head at the lower end of the locking hopper. The stirring device is immersed in the conical head. The stirring blade of the stirring device is a conical plate matching the conical head. The outermost edge of the conical plate is parallel to the inner wall of the hopper, and the distance between the two is 3cm;

[0093] The feeding dragon is a shaftless spiral, including a horizontal conveying auger and a feeding auger. Both the horizontal conveying auger and the feeding auger are provided with cooling coils, and the cooling coils use cooling water as the cooling medium; the spiral pitch of the bulk material spirals provided in the horizontal conveying auger and the feeding auger is 5 times the length of the waste polyolefin; the outlet of the feeding auger is conical, and the cone angle of the longitudinal section of the cone is 30°;

[0094] The second feed inlet of the pyrolysis reaction device is an aerosol nozzle, 4 of which are arranged opposite to each other, and the angle α with the horizontal direction is 2.5°.

[0095] The waste polyethylene is crushed into pieces, wherein the polyethylene content is 93.0wt%, the water content is 3wt%, the mechanical impurity content is 2wt%, the other plastic content is 2wt%, and the length is ≤20mm.

[0096] The waste polypropylene is crushed into pieces, wherein the polypropylene content is 90.0wt%, the water content is 5wt%, the mechanical impurity content is 2wt%, the other plastic content is 3wt%, and the length is ≤20mm.

[0097] Example 1

[0098] (1) The waste polyethylene is transported by pneumatic conveying machinery, a lock hopper, and a feeding dragon in sequence and then enters the pyrolysis reaction device; wherein, the waste polyethylene is heated by the pneumatic conveying outer heat jacket and the lock hopper outer heat jacket during transportation, and the waste polyethylene is dried at 100°C to generate water vapor; the generated water vapor is separated in the lock hopper, and the separated water vapor is cooled by a water vapor cooler and treated by a water vapor separator to obtain waste water, which is then sent to a wastewater treatment plant for treatment; the temperature of the waste polyethylene entering the pyrolysis reaction device is 105°C;

[0099] The product directing agent is preheated to 350°C by the first heat exchanger and then atomized and sprayed into the pyrolysis reaction device. Under the action of the built-in heating coil and the external heating jacket II, the upper temperature of the pyrolysis reaction device is 320°C and the lower temperature is 525°C. The first stage is carried out at the upper part of the pyrolysis reaction device, and the second stage is carried out at the lower part of the pyrolysis reaction device to obtain pyrolysis oil and gas. The product directing agent is a fraction with a distillation range of 150-350°C recovered from waste cycloalkane lubricating oil, containing 91.2wt% of cycloalkanes and 8.8wt% of aromatic hydrocarbons. The mass ratio of waste polyethylene to product directing agent is 1:0.1, the residence time of the first stage is 2s, and the residence time of the second stage is 5min.

[0100] (2) The obtained pyrolysis oil and gas are cooled and then transported to a gas-liquid separator for gas-liquid separation to obtain pyrolysis oil I with a boiling point ≥50°C and pyrolysis gas I with a boiling point <50°C.

[0101] Example 2

[0102] The waste polyethylene is transported by pneumatic conveying machinery, lock hopper and feeding dragon in sequence and then enters the pyrolysis reaction device; the waste polyethylene is heated by the pneumatic conveying outer heat jacket and the lock hopper outer heat jacket during transportation, and the waste polyethylene is dried at 100°C to generate water vapor; the generated water vapor is separated in the lock hopper, and the separated water vapor is cooled by a water vapor cooler and treated by a water vapor separator to obtain waste water, which is sent to a wastewater treatment plant for treatment; the temperature of the waste polyethylene entering the pyrolysis reaction device is 100°C;

[0103] The product directing agent is preheated to 330°C by the first heat exchanger and then atomized and sprayed into the pyrolysis reaction device. Under the action of the built-in heating coil and the external heating jacket II, the upper temperature of the pyrolysis reaction device is 310°C and the lower temperature is 510°C. The first stage is carried out at the upper part of the pyrolysis reaction device, and the second stage is carried out at the lower part of the pyrolysis reaction device to obtain pyrolysis oil gas at 510°C. Among them, the product directing agent is a fraction with a boiling point range of 150-350°C recovered from waste cycloalkane lubricating oil, containing 91.2wt% of cycloalkanes and 8.8wt% of aromatic hydrocarbons. The mass ratio of waste polyethylene to product directing agent is 1:0.2, the residence time of the first stage is 3s, and the residence time of the second stage is 6min.

[0104] The obtained pyrolysis oil and gas are cooled to 380°C in the first heat exchanger, and then enter the second heat exchanger to exchange heat with the heating medium from the external heating jacket II, and further cooled to 280°C, and then enter the first gas-liquid separator to perform gas-liquid separation at 280°C and 0.1MPa to obtain pyrolysis oil II with a boiling point ≥280°C and pyrolysis gas II with a boiling point <280°C;

[0105] The obtained pyrolysis gas II is divided into part A and part B, wherein part A accounts for 10% of the total mass of pyrolysis gas II and part B accounts for 90% of the total volume of pyrolysis gas II; part A is introduced into the first heat exchanger and added to the product directing agent, and the amount of the product directing agent is reduced by 30%, and the mass ratio of part A to the reduced product directing agent is 1:0.4; part B is introduced into the third heat exchanger and heat-exchanged with the pyrolysis device from the external heating jacket I, and then sent to the second gas-liquid separator, and gas-liquid separation is performed at 28°C and 0.1MPa, and the pyrolysis oil III with a boiling point ≥50°C separated from the second gas-liquid separator is cooled to room temperature and sent to the pyrolysis oil storage tank; the pyrolysis gas I with a boiling point <50°C separated from the second gas-liquid separator is sent to the boiler;

[0106] The obtained pyrolysis oil II is introduced into the fourth heat exchanger to exchange heat with the heating medium from the external heating jacket I, and after cooling to room temperature, it is sent to the pyrolysis oil storage tank to mix with the pyrolysis oil III; the heating medium from the external heating jacket I is sent to the boiler; the steam generated by the boiler is introduced into the built-in heating coil.

[0107] Example 3

[0108] Waste polypropylene is transported by pneumatic conveying machinery, lock hopper and feeding dragon in sequence and then enters the pyrolysis reaction device; the waste polypropylene is heated by the pneumatic conveying outer heat jacket and the lock hopper outer heat jacket during transportation, and the waste polypropylene is dried at 100°C to generate water vapor; the generated water vapor is separated in the lock hopper, and the separated water vapor is cooled by a water vapor cooler and treated by a water vapor separator to obtain waste water, which is sent to a wastewater treatment plant for treatment; the temperature of the waste polypropylene entering the pyrolysis reaction device is 110°C;

[0109] The product directing agent is preheated to 350°C by the first heat exchanger and then sprayed into the pyrolysis reaction device. Under the action of the built-in heating coil and the external heating jacket II, the upper temperature of the pyrolysis reaction device is 350°C and the lower temperature is 550°C. The first stage is carried out at the upper part of the pyrolysis reaction device, and the second stage is carried out at the lower part of the pyrolysis reaction device to obtain pyrolysis oil gas at 550°C. The product directing agent is a fraction with a distillation range of 150-350°C recovered from waste cycloalkane lubricating oil, containing 91.2wt% of cycloalkanes and 8.8wt% of aromatic hydrocarbons. The mass ratio of waste polypropylene to the product directing agent is 1:0.15. The residence time of the first stage is 1s, and the residence time of the second stage is 4min.

[0110] The obtained pyrolysis oil and gas are cooled to 380°C in the first heat exchanger, and then enter the second heat exchanger to exchange heat with the heating medium from the external heating jacket II, and further cooled to 280°C, and then enter the first gas-liquid separator to perform gas-liquid separation at 280°C and 0.1MPa to obtain pyrolysis oil II with a boiling point ≥280°C and pyrolysis gas II with a boiling point <280°C;

[0111] The obtained pyrolysis gas II is divided into part A and part B, wherein part A accounts for 5% of the total mass of pyrolysis gas II and part B accounts for 95% of the total volume of pyrolysis gas II; part A is introduced into the first heat exchanger and added to the product directing agent, and the amount of the product directing agent is reduced by 45%, and the mass ratio of part A to the reduced product directing agent is 1:0.8; part B is introduced into the third heat exchanger and heat-exchanged with the pyrolysis device from the external heating jacket I, and then sent to the second gas-liquid separator, and gas-liquid separation is performed at 28°C and 0.1MPa, and the pyrolysis oil III with a boiling point ≥50°C separated from the second gas-liquid separator is cooled to room temperature and sent to the pyrolysis oil storage tank; the pyrolysis gas I with a boiling point <50°C separated from the second gas-liquid separator is sent to the boiler;

[0112] The obtained pyrolysis oil II is introduced into the fourth heat exchanger to exchange heat with the heating medium from the external heating jacket I, and after cooling to room temperature, it is sent to the pyrolysis oil storage tank to mix with the pyrolysis oil III; the heating medium from the external heating jacket I is sent to the boiler; the steam generated by the boiler is introduced into the built-in heating coil.

[0113] Example 4

[0114] Compared with Example 1, the difference is that the product directing agent is a cycloalkane lubricating oil with added paraffin and aromatic hydrocarbons, the distillation range is 180-350° C., the content of cycloalkane is 64.1wt%, the content of paraffin is 23.3wt%, and the content of aromatic hydrocarbon is 12.6wt%;

[0115] The temperature of waste polyethylene entering the pyrolysis reaction device is 95°C. The product directing agent is preheated to 300°C through the first heat exchanger and then atomized and sprayed into the pyrolysis reaction device. The temperature of the first stage is 280°C, and the residence time of the first stage is 4s; the temperature of the second stage is 480°C, and the residence time of the second stage is 7min.

[0116] Example 5

[0117] Compared with Example 1, the difference is that the product directing agent is a cycloalkane lubricating oil with added paraffin and aromatic hydrocarbons, the distillation range is 180-350° C., the content of cycloalkane is 64.1wt%, the content of paraffin is 23.3wt%, and the content of aromatic hydrocarbon is 12.6wt%;

[0118] The temperature of waste polyethylene entering the pyrolysis reaction device is 115°C. The product directing agent is preheated to 390°C through the first heat exchanger and then atomized and sprayed into the pyrolysis reaction device. The temperature of the first stage is 360°C, and the residence time of the first stage is 0.5s; the temperature of the second stage is 570°C, and the residence time of the second stage is 3min.

[0119] Comparative Example 1

[0120] The same as Example 1, except that the product directing agent is omitted.

[0121] Comparative Example 2

[0122] The same as Example 1, except that the product directing agent and waste polyethylene are fed from the lower part of the pyrolysis reaction device (i.e., the part where the second stage reaction is carried out) and stay at 525° C. for 5 minutes.

[0123] Comparative Example 3

[0124] The same as Example 1, except that the feed temperature of the product directing agent is 150°C, and the feed temperature of the waste polyolefin is 60°C.

[0125] Dry ash-free three-phase yield of waste plastics:

[0126] The pyrolysis raw materials of the present invention include waste plastics and a product-directing agent. Under the same conditions, the product-directing agent is subjected to pyrolysis reaction alone, and the generated amounts of pyrolysis oil, pyrolysis gas and pyrolysis semi-coke are analyzed; and then the dry ash-free three-phase yield of the waste plastic itself can be calculated by combining the generated amounts of residue, pyrolysis oil I and pyrolysis gas I in Examples 1-5 and Comparative Examples 1-3. The dry ash-free three-phase yields of the pyrolysis semi-coke, pyrolysis oil and pyrolysis gas of the waste plastic itself in Examples 1-5 and Comparative Examples 1-3 are shown in Table 1.

[0127] The moisture and ash contents of the waste polyolefins were determined by referring to the industrial analysis method for coal (GB / T212-2008). The masses of the residue and pyrolysis oil I were obtained by weighing, and the mass of the pyrolysis semi-coke was equal to the mass of the residue minus the mass of the ash.

[0128] The composition of the pyrolysis gas is analyzed by gas chromatography. The volume flow rate is obtained by reading the gas meter before the pyrolysis gas is sent to the boiler. The mass flow rate is then calculated based on the composition of the pyrolysis gas, and the mass of the pyrolysis gas is obtained by integration. The calculation method is as follows:

[0129]

[0130] In the formula, m gas is the mass of pyrolysis gas, g; t is the product calculation cycle time, s; V i is the volume flow rate of pyrolysis gas component i, L / s; V i is the molar mass of pyrolysis gas component i, g / mol.

[0131] According to the mass of the three-phase products, the dry ash-free three-phase yield of the pyrolysis semi-coke, pyrolysis oil and pyrolysis gas of the waste plastics itself is calculated according to the following formula:

[0132]

[0133]

[0134]

[0135] Where y oil ,y gas ,y char are the dry ash-free yields of pyrolysis oil, pyrolysis gas and pyrolysis semi-coke of waste plastics, %; m, m oil 、m gas 、m char are the masses of waste polyolefins, pyrolysis oil, pyrolysis gas and pyrolysis semi-coke during the pyrolysis of waste plastics and product-directing agents, g; M ad and A ad are respectively the moisture and ash contents in waste polyolefins, %; m oil-agent 、mgas-agent 、m char-agent They are the masses of pyrolysis oil, pyrolysis gas and pyrolysis semi-coke generated when the product directing agent added in the pyrolysis process reacts alone under the same reaction conditions, g.

[0136] Table 1

[0137]

[0138] Distillation range and hydrocarbon composition of pyrolysis oil generated from waste plastics themselves:

[0139] The pyrolysis oil I in the present invention is partially derived from the pyrolysis of waste plastics, and partially derived from the product directing agent. Under the same conditions, the product directing agent is subjected to pyrolysis reaction alone, and the distillation range and hydrocarbon composition of the pyrolysis oil generated thereby are analyzed; and then the distillation range and hydrocarbon composition of the pyrolysis oil I in Examples 1-5 and Comparative Examples 1-3 are combined to calculate the distillation range and hydrocarbons of the pyrolysis oil generated by the waste plastics themselves.

[0140] Among them, the distillation range of the pyrolysis oil I obtained in Examples 1-5 and Comparative Examples 1-3 was analyzed by petroleum fraction boiling range distribution determination method (gas chromatography, GC-D2887), and the hydrocarbon composition in the pyrolysis oil I obtained in Examples 1-5 and Comparative Examples 1-3 was analyzed by GC-MS.

[0141] Taking waste polyethylene as an example, the distillation range and hydrocarbon composition of the pyrolysis oil generated by waste plastics themselves can be calculated according to the following formula:

[0142]

[0143] In the formula, y i-PE is the content of product component i based on waste polyethylene, %; m total is the total mass of PE and product directing agent during pyrolysis, g; y i-total is the content of a certain component i in the product obtained by pyrolysis of waste polyethylene and product directing agent, %; m agent is the mass of product directing agent added during pyrolysis, g; y i-agent is the content of component i when the product directing agent is pyrolyzed alone, %; m PE is the mass of waste polyethylene used in the co-pyrolysis process, g.

[0144] Table 2

[0145]

[0146]

[0147] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for processing waste polyolefins, characterized in that: The processing method comprises the following steps: (1) contacting waste polyolefin with a product directing agent to perform a pyrolysis reaction to obtain pyrolysis oil gas and residue; wherein the product directing agent is cycloalkane oil; the feed temperature of the waste polyolefin is 80-120° C., and the feed temperature of the product directing agent is 250-400° C.; The pyrolysis reaction includes at least a first stage and a second stage; wherein the temperature of the first stage is 250-400°C, and the residence time of the first stage is 0.5-5.5s; the temperature of the second stage is 450-650°C, and the residence time of the second stage is 1-10mins; (2) Separating the pyrolysis oil and gas to obtain pyrolysis oil I with a boiling point of ≥40-60° C. and pyrolysis gas I with a boiling point of <40-60° C.

2. The processing method according to claim 1, wherein: The waste polyolefin contains waste polyethylene and / or waste polypropylene; Preferably, the content of the waste polyethylene and / or waste polypropylene is ≥80wt%, preferably ≥90wt%; Preferably, the content of cycloalkanes in the cycloalkane oil is ≥60wt%, preferably ≥80wt%; Preferably, the distillation range of the naphthenic oil is 40-350°C, preferably 150-350°C; Preferably, the cycloalkyl oil is selected from one or more of cycloalkyl crude oil, cycloalkyl lubricating oil, cycloalkyl transformer oil, refrigeration oil, and cycloalkyl rubber oil.

3. The processing method according to claim 1 or 2, wherein: The mass ratio of the waste polyolefin to the product directing agent is 1:0.01-0.5, preferably 1:0.1-0.2; Preferably, the feed temperature of the waste polyolefin is 95-110°C, and the feed temperature of the product directing agent is 330-370°C; Preferably, the product directing agent is fed by injection.

4. The processing method according to any one of claims 1 to 3, wherein: The temperature of the first stage is 300-340°C, and the residence time of the first pyrolysis stage is 1-3s; the temperature of the second stage is 500-550°C, and the residence time of the second stage is 3-7min.

5. The processing method according to any one of claims 1 to 4, wherein: The separation comprises the following sub-steps: (2-1), performing a first separation on the pyrolysis oil and gas to obtain pyrolysis oil II with a boiling point ≥150-300°C and pyrolysis gas II with a boiling point <150-300°C; (2-2), dividing the pyrolysis gas II into at least part A and part B; wherein the part A is returned to step (1) and added to the product directing agent; and the part B is subjected to a second separation to obtain pyrolysis oil III with a boiling point ≥40-60°C and pyrolysis gas I with a boiling point <40-60°C; (2-3) The pyrolysis oil II and the pyrolysis oil III are mixed to obtain pyrolysis oil I.

6. The processing method according to claim 5, wherein: The A portion accounts for 1-50% of the total mass of the pyrolysis gas II, preferably 5-15%; the B portion accounts for 99-50% of the total volume of the pyrolysis gas II, preferably 85-95%; Preferably, after the A portion is returned to step (1) and added to the product directing agent, the amount of the product directing agent is reduced by 25-50%, preferably by 30-45%; the mass ratio of the A portion to the reduced product directing agent is 1:0.2-1.2, preferably 1:0.4-0.

8.

7. The processing method according to any one of claims 1 to 6, wherein: The method further comprises step (3): burning the pyrolysis gas I, and the heat generated by the combustion is used to provide heat exchange medium for pyrolysis reaction, first separation, second separation, waste polyolefin drying, pyrolysis oil II and pyrolysis oil III in sequence.

8. A system for processing waste polyolefins, characterized in that: The system comprises: a feeder (1), a lock hopper (2), a feed dragon (3), a pyrolysis reaction device (4), a first heat exchanger (5), a second heat exchanger (6), a first gas-liquid separator (7), a third heat exchanger (8), a second gas-liquid separator (9) and a boiler (10); Wherein, the feeder (1) is provided with an external heating jacket I; the locking hopper (2) is arranged between the feeder (1) and the feeding dragon (3); The pyrolysis reaction device (4) is a vertical pyrolysis reactor, comprising a first feed inlet, a second feed inlet, a pyrolysis product outlet, a slag outlet, a built-in heating coil and an external heating jacket II; the first feed inlet is connected to the feed dragon (3); the heat medium outlet of the built-in heating coil is connected to the heat medium inlet of the external heating jacket II; The cold medium inlet of the primary heat exchanger (5) is the product directing agent inlet, and the cold medium outlet of the primary heat exchanger (5) is connected to the second feed inlet of the pyrolysis reaction device (4); the hot medium inlet of the primary heat exchanger (5) is connected to the pyrolysis product outlet of the pyrolysis reaction device (4), and the hot medium outlet of the primary heat exchanger (5) is connected to the hot medium inlet of the secondary heat exchanger (6); The cold medium inlet of the secondary heat exchanger (6) is connected to the heating medium outlet of the external heating jacket II, and the cold medium outlet of the secondary heat exchanger (6) is connected to the heating medium inlet of the external heating jacket I; the hot medium outlet of the secondary heat exchanger (6) is connected to the first gas-liquid separator (7); The gas phase outlet of the first gas-liquid separator (7) is respectively connected to the cooling medium inlet of the first heat exchanger (5) and the hot medium inlet of the third heat exchanger (8), and the hot medium outlet of the third heat exchanger (8) is connected to the second gas-liquid separator (9); the cold medium inlet of the third heat exchanger (8) is connected to the hot medium outlet of the external heating jacket I, and the cold medium outlet of the third heat exchanger (8) is connected to the boiler (10); The gas phase outlet of the second gas-liquid separator (9) is connected to the boiler (10), and the boiler (10) is connected to the heat medium inlet of the built-in heating coil.

9. The processing system according to claim 8, wherein: The loading machine (1) is selected from a bucket elevator and / or a pneumatic conveying machine; Preferably, the feeder (1) is a bucket elevator, and the system further comprises a water vapor cooler (11); Preferably, when the feeder (1) is a pneumatic conveying machine, the system further comprises a water vapor cooler (11) and a water vapor separator (12).

10. The processing system according to claim 8 or 9, wherein: The system further comprises a fourth heat exchanger (14), wherein a hot medium inlet of the fourth heat exchanger (14) is connected to a liquid phase outlet of the first gas-liquid separator (7), a cold medium inlet of the fourth heat exchanger (14) is connected to a hot medium outlet of an external heating jacket I, and a cold medium outlet of the fourth heat exchanger (14) is connected to a boiler (10); Preferably, the system further comprises a fifth heat exchanger (15), wherein the heat medium inlet of the fifth heat exchanger (15) is connected to the heat medium outlet of the external heating jacket I, and the heat medium outlet of the fifth heat exchanger (15) is respectively connected to the cooling medium inlets of the third heat exchanger (8) and the fourth heat exchanger (14).

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