CN111778046A - Method and system for efficiently recycling plastic waste - Google Patents
Method and system for efficiently recycling plastic waste Download PDFInfo
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- CN111778046A CN111778046A CN202010456205.6A CN202010456205A CN111778046A CN 111778046 A CN111778046 A CN 111778046A CN 202010456205 A CN202010456205 A CN 202010456205A CN 111778046 A CN111778046 A CN 111778046A
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
- C10B53/00—Destructive distillation, specially adapted for particular solid raw materials or solid raw materials in special form
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
- C10B57/00—Other carbonising or coking processes; Features of destructive distillation processes in general
Abstract
The invention provides a method and a system for efficiently recycling plastic wastes, which comprises the following steps: drying the plastic waste until the moisture content is lower than 10 wt%, and crushing the plastic waste until the particle size is smaller than 50 mm; heating and melting the broken plastic waste under the oxygen-free or oxygen-deficient condition, wherein the heating and melting temperature is within the range of 120-180 ℃; pyrolyzing the molten plastic waste under the oxygen-free or oxygen-deficient condition, wherein the pyrolysis temperature is in the range of 500-800 ℃ to generate pyrolysis steam and pyrolysis carbon; fractionating the pyrolysis steam in a heat exchanger assembly with a temperature gradient to obtain a pyrolysis oil graded product, wherein the heat exchanger assembly comprises at least 3 heat exchangers sequentially arranged according to the process trend of the pyrolysis steam, and the temperature of the heat exchangers decreases progressively according to the process trend of the pyrolysis steam. The method and the system realize the gradient grading of the pyrolysis oil.
Description
Technical Field
The invention relates to the field of solid waste treatment, in particular to a method and a system for efficiently recycling plastic waste.
Background
The discarded plastics are light and bulky, and are not easy to decompose after being discarded, so that soil hardening can be caused, and the breathing and absorption of crops are preventedUnder the action of ultraviolet rays or during combustion, CO, vinyl chloride monomer, HCl, methane, NOx and SO are emitted2Aromatic hydrocarbons, etc., which cause pollution to water and air. Particularly, chlorine-containing plastics can generate harmful substances such as dioxin and the like after being burnt, and the pollution to the environment is more serious. Therefore, the search for a technology for efficiently making plastic wastes harmless, reducing and recycling is urgent.
The oil produced by plastic pyrolysis is the most industrially applicable method in the plastic waste recovery method. The pyrolysis oil can be processed into high-quality gasoline, diesel oil, liquefied gas, chemical raw materials or furnace fuels and the like, so that a large amount of imported crude oil can be replaced, and remarkable social benefits and economic benefits are created. However, the process for preparing oil by plastic pyrolysis still has many technical difficulties, such as poor heat conductivity of plastic wastes, extremely uneven temperature in a cracking furnace, high pyrolysis energy consumption, difficulty in grading pyrolysis oil products, difficulty in scale enlargement, low heat transfer efficiency of a reaction kettle, poor slag discharge continuity, easy occurrence of coking phenomenon in the pyrolysis process due to uneven pyrolysis heating, poor quality of produced oil products and difficulty in recovery due to uneven heating, and the like.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a method and a system for efficiently recycling plastic wastes.
The method for efficiently recycling the plastic waste comprises the following steps:
drying the plastic waste until the moisture content is lower than 10 wt%, and crushing the plastic waste until the particle size is smaller than 50 mm;
heating and melting the broken plastic waste under the condition of no oxygen or oxygen deficiency, wherein the heating and melting temperature is within the range of 120-180 ℃. Melting tends to occur in a physical change process, and if the temperature for melting by heating is higher than 180 ℃, chemical bonds may be broken, etc., and chemical reactions may occur. If the temperature for melting by heating is less than 120 ℃, the melting effect may be poor.
Pyrolyzing the molten plastic waste under the condition of no oxygen or oxygen deficiency, wherein the pyrolysis temperature is in the range of 500-800 ℃ to generate pyrolysis steam and pyrolysis carbon. This temperature range is a more suitable pyrolysis temperature range, and if the pyrolysis temperature is lower than 500 ℃, the pyrolysis degree is low, and if the pyrolysis temperature is higher than 800 ℃, the energy consumption is more from the process point of view.
Fractionating the pyrolysis vapor in a heat exchanger assembly having a temperature gradient to obtain a pyrolysis oil fraction product, wherein,
the heat exchanger assembly comprises at least 3 heat exchangers which are sequentially arranged according to the process trend of the pyrolysis steam, and the temperature of the heat exchangers is gradually decreased according to the process trend of the pyrolysis steam.
In some embodiments, the temperature gradient ranges from 50 to 500 ℃.
In some embodiments, the temperature gradient is from 350-.
In some embodiments, the heat transfer medium in the heat exchanger is a heat transfer oil.
In some embodiments, the plastic waste after drying has a moisture content in the range of less than 10% by weight during said drying. For example 5-10 wt%.
In some embodiments, the temperature of the oven drying is in the range of 80-110 ℃, such as in the range of 100-105 ℃. If the drying temperature is too low, the drying efficiency is low, and if the drying temperature is too high, the physical and chemical states of the materials are changed or reacted.
The system for efficiently recycling the plastic waste comprises a drying device, a crushing device, a heating and melting device, a pyrolysis device, a heat exchanger assembly and a flue gas furnace which are sequentially connected, wherein the heat exchanger assembly comprises a heat exchanger I, a heat exchanger II and a heat exchanger III which are sequentially connected.
In some embodiments, the heating and melting device has a sleeve structure, and includes an outer ring body and an inner ring body, the inner ring body is arranged in the outer ring body, and a flue gas chamber is formed between the inner ring body and the inner ring body, the outer ring body is provided with a flue gas inlet and a flue gas outlet, an inner cavity of the inner ring body forms the heating and melting chamber, the inner ring body is provided with a material inlet and a melting material outlet, and a spiral feeder is arranged on a central shaft of the inner ring body.
In some embodiments, the pyrolysis device comprises a flue gas inlet and a flue gas outlet, the flue gas inlet of the heating and melting device is connected with the flue gas outlet of the flue gas furnace, and the flue gas inlet of the pyrolysis device is connected with the flue gas outlet of the heating and melting device.
In the research on the method and the system for efficiently recycling the plastic wastes, the inventor obtains a method capable of gradiently grading pyrolysis oil through a large amount of experimental research, reasonably designs the system, obtains a system with low energy consumption, high efficiency and high yield of pyrolysis oil, and finally obtains pyrolysis oil products comprising gasoline with the yield of more than 9.8 wt%, diesel oil with the yield of more than 35.7 wt% and lubricating oil heavy oil with the yield of more than 25.2 wt%. Wherein the yield of cracked gas is more than 13.1 wt%.
Drawings
FIG. 1 is a schematic structural diagram of a system for implementing the method for efficient recycling of plastic waste according to the present application;
FIG. 2 is a schematic diagram of a heating and fusing apparatus of the system of the present application;
FIG. 3 is a schematic diagram of a pyrolysis unit of the system of the present application;
FIG. 4 is a schematic view of the stirring blade structure of the pyrolysis apparatus of the present application;
FIG. 5 is a schematic diagram of the heat exchange process of pyrolysis steam in the method for recycling plastic waste efficiently;
FIG. 6 is a schematic diagram of the heat exchange process of the high-temperature flue gas in the method for efficiently recycling the plastic waste.
Description of reference numerals:
a drying device-1; a crushing device-2; a heating and melting device-3; a pyrolysis unit-4; a heat exchanger I-5; a heat exchanger II-6; a heat exchanger III-7; a heat exchanger IV-8; flue gas furnace-9; waste plastic-101; pyrolytic carbon-102; lube oil and heavy oil fractions-103; diesel fraction-104; gasoline fraction-105; air-106; flue gas-107;
a material inlet-31; a molten material outlet-32; a flue gas inlet-33; a flue gas outlet-34; a screw feeder-35; a flue gas chamber-36; a heating and melting chamber-37; a motor-38;
a pyrolysis chamber-41; feed inlet-42; a flue gas outlet-43; a first pyrolysis vapor outlet-44; a second pyrolysis vapor outlet-45; flue gas inlet-46; a charcoal outlet-47; helix-48; a stirring scraper-49; a flue gas chamber-410; a heat-insulating layer-411; a heat transfer layer-412; variable frequency motor-413; a scraper-491; connecting rod-492; securing slots-493; spring-494.
Detailed Description
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The present invention will be described in detail below to make the above objects, features and advantages of the present invention more comprehensible.
The invention provides a safe, reliable and efficient plastic pyrolysis method and system. The technical scheme of the invention is that according to the characteristics of the plastic waste, the plastic waste with high water content is firstly dried by the drying device, and the drying aims to reduce the water content in the plastic waste, thereby reducing the energy consumption of a subsequent pyrolysis device, and reducing the amount of water mixed into pyrolysis oil, thereby reducing the cost of sewage treatment. The plastic in the plastic waste may include polyethylene plastic, polyvinyl chloride plastic, polypropylene plastic, polystyrene plastic, and the like.
The dried materials are crushed by the crushing device, and the materials crushed to small particle size are more favorable for subsequent feeding and uniform heating of plastic wastes. The particle size of the broken plastic waste is less than 50mm, preferably less than 30 mm.
And heating the crushed materials in a pyrolysis melting device so that the materials are heated to a molten state. It is particularly important to control the temperature of the heating melt. In the present invention, the temperature of the heat-melting is in the range of 120 ℃ to 180 ℃ in consideration of the complexity of the plastic waste material. If the temperature is too low, the materials cannot be ensured to be completely in a molten state, and the subsequent pyrolysis step is influenced; if the temperature is too high, the material is easy to generate thermal cracking reaction, so that the subsequent process is difficult to control.
The waste plastic in the molten state is pumped into the pyrolysis device through the extruding pump, the thermal cracking reaction is generated in the pyrolysis device, and the molten-state thermoplastic enters the pyrolysis device, so that the rapid heating can be realized, and the heating is uniform. The residence time of the material in the pyrolysis device is, for example, 10 to 60 min. The pyrolysis is carried out in the absence of oxygen or oxygen at a temperature in the range of 500-800 deg.C, such as 600 deg.C, 650 deg.C, 700 deg.C, 750 deg.C. The material can be completely and effectively pyrolyzed in a very short time.
High-temperature pyrolysis steam is generated through pyrolysis reaction in a pyrolysis device, the pyrolysis steam passes through a specially designed heat exchanger assembly, and pyrolysis oil products can be separated by controlling the temperature of the heat exchanger to obtain lubricating oil, heavy oil fraction, diesel oil fraction and gasoline fraction. In the present invention, the temperature gradient of the heat exchanger assembly is generally in the range of 50 ℃ to 500 ℃. In one embodiment, the heat exchanger assembly comprises a heat exchanger I, a heat exchanger II and a heat exchanger III which are connected in sequence. And the pyrolysis oil gas discharged from the pyrolysis device sequentially enters a heat exchanger I, a heat exchanger II and a heat exchanger III, the temperatures of different heat exchangers are controlled at different temperatures, pyrolysis oil sections with different distillation ranges are condensed, and lubricating oil, heavy oil fractions, diesel oil fractions and gasoline fractions are obtained. The non-condensable pyrolysis gas discharged from the last heat exchanger is rich in H2、 CH4CO and hydrocarbon gas can be recycled, and can also be used as fuel gas to be sent to a flue gas furnace for combustion, and high-temperature flue gas is generated to provide heat for the pyrolysis device, the heating and melting device and the drying device in sequence. The heat exchanger adopts heat conduction oil as a heat exchange medium, and the heat conduction oil is heated to a certain temperature while the pyrolysis steam is cooled in sections. Heat conduction oil led out by the heat exchange assembly can exchange heat with air through the heat exchanger to heat the air, and the heated air can be used as combustion-supporting air for fuel gas in the flue gas furnaceAnd the energy consumption can be efficiently utilized and saved by combustion. The heat transfer oil is adopted as the heat exchange medium, and the advantages are that: the heat conducting oil has large specific heat capacity, the heat exchanger has small volume and low investment. And the safety risk brought by the heat exchange of the pyrolysis gas and the air is avoided. A useful heat transfer oil is, for example, biphenyl heat transfer oil.
In one embodiment, the heat exchange process for the pyrolysis vapor is as shown in FIG. 5.
In one embodiment, the high temperature flue gas produced by the flue gas furnace flows from the high temperature unit to the low temperature unit throughout the system, enabling the recycling of heat energy. For example, high-temperature flue gas (temperature of 800-. The heat exchange process of the high-temperature flue gas is shown in figure 6.
In one embodiment, the method for efficiently recycling the plastic waste comprises the following specific steps:
(1) drying the plastic waste in a drying device under the heating condition of flue gas, wherein the drying temperature is controlled at 100 ℃ and 105 ℃, and drying is carried out until the moisture content is 5-10 wt%. If the water content of the waste plastic is less than 10 percent, drying is not needed;
(2) crushing the dried plastic waste in a crushing device, wherein the particle size of the crushed plastic waste is less than 50mm, heating and melting the crushed plastic waste in a heating and melting device, adjusting the heating temperature according to the type of the plastic, controlling the temperature range to be 120-180 ℃, and keeping the retention time for 10-60 min;
(3) the heated and melted plastic is subjected to thermal cracking reaction in a pyrolysis device under the condition of no oxygen or oxygen deficiency, the pyrolysis temperature is 500-800 ℃, the generated high-temperature pyrolysis steam is led out from a pyrolysis steam outlet, and the pyrolysis carbon is discharged from a carbon outlet;
(4) high-temperature pyrolysis steam is led out from the pyrolysis device and then sequentially passes through the heat exchanger I, the heat exchanger II and the heat exchanger III, pyrolysis oil separation of different distillation ranges is realized under different temperature conditions, and fractions obtained through the heat exchanger I, the heat exchanger II and the heat exchanger III are respectively lubricating oil and heavy oil fractions, diesel oil fractions and gasoline fractions; and a medium for exchanging heat with pyrolysis steam in the heat exchanger I, the heat exchanger II and the heat exchanger III is heat conduction oil, and the heat conduction oil sequentially passes through the heat exchanger III, the heat exchanger II and the heat exchanger I. The temperature of the heat exchanger I is controlled to be 350-500 ℃, the temperature of the heat exchanger II is controlled to be 200-350 ℃, and the temperature of the heat exchanger III is controlled to be 50-200 ℃;
(5) the temperature of the heat-conducting oil led out from the heat exchanger I is within the range of 300-;
(6) the non-condensable gas led out from the heat exchanger III is rich in H2、CH4CO and hydrocarbon gas, wherein a part of the pyrolysis gas is used as fuel gas and is sent into the flue gas furnace, and the temperature of the discharged flue gas is 800-;
(7) leading out high-temperature flue gas from the flue gas furnace, sequentially passing through a pyrolysis device, a heating and melting device and a drying device, wherein the flow direction of the flue gas is in counter flow with the conveying direction of the waste plastics, and heating the plastics; during the operation of the whole system, the hot flue gas and the pyrolysis material are in counter-current.
In one embodiment, a system for implementing the method for efficient resource utilization of plastic waste is shown in fig. 1, and the system comprises a drying device 1, a crushing device 2, a heating and melting device 3, a pyrolysis device 4, a heat exchange assembly, a heat exchanger iv 8 and a flue gas furnace 9 which are connected in sequence. The heat exchange assembly comprises a heat exchanger I5, a heat exchanger II 6 and a heat exchanger III 7 which are connected in sequence.
The material outlet of the drying device 1 is connected with the material inlet of the crushing device 2; the material outlet of the crushing device 2 is connected with the material inlet of the heating and melting device 3; the material outlet of the heating and melting device 3 is connected with the material inlet of the pyrolysis device 4; a pyrolysis steam outlet of the pyrolysis device 4 is connected with a gas inlet of the heat exchanger I5; a gas outlet of the heat exchanger I5 is connected with a gas inlet of the heat exchanger II 6, and a gas outlet of the heat exchanger II 6 is connected with a gas inlet of the heat exchanger III 7; a gas outlet of the heat exchanger III 7 is connected with a gas inlet of a flue gas furnace 9; a heat conduction oil outlet of the heat exchanger IV 8 is connected with a heat conduction oil inlet of the heat exchanger III 7; a heat conduction oil outlet of the heat exchanger III 7 is connected with a heat conduction oil inlet of the heat exchanger II 6; a heat conduction oil outlet of the heat exchanger II 6 is connected with a heat conduction oil inlet of the heat exchanger I5; a heat conduction oil outlet of the heat exchanger I5 is connected with a heat conduction oil inlet of the heat exchanger IV 8; an air outlet of the heater IV 8 is connected with a combustion air inlet of the flue gas furnace 9; a smoke outlet of the smoke furnace 9 is connected with a smoke inlet of the pyrolysis device 4; the flue gas outlet of the pyrolysis device 4 is connected with the flue gas inlet of the heating and melting device 3; and the smoke outlet of the heating and melting device 3 is connected with the smoke inlet of the drying device 1.
The drying device can adopt a chain plate type dryer which is conventional equipment and can be obtained commercially.
The crushing device can adopt a crusher for quickly crushing materials by a rotary knife, and can be a plastic crusher produced by Rongxin machinery in Guangdong Dongguan city.
The heat exchanger can adopt a tube type heat exchanger.
In the present application, a schematic view of the structure of the heating and melting apparatus 3 is shown in fig. 2. As shown in fig. 2, the heating and melting apparatus 3 includes: the device comprises a material inlet 31, a molten material outlet 32, a spiral feeder 35, a flue gas chamber 36, a heating and melting chamber 37, a flue gas inlet 33, a flue gas outlet 34 and a motor 38. The material inlet 31 is communicated with the heating melting chamber 37; the molten material outlet 32 is arranged at the tail end of the heating and melting device 3 body and is communicated with the heating and melting chamber 3; the flue gas inlet 33 and the flue gas outlet 34 are communicated with a flue gas chamber 36 and are respectively arranged at two ends of the heating and melting device 3; a screw feeder 35 is provided on the central shaft in the heating and melting chamber 37; the outer wall of the flue gas chamber 36 is provided with heat insulation materials, and the heat insulation materials can be rock wool. The materials enter the heating and melting chamber 37 from the material inlet 31, are melted under the heating condition of flue gas in the conveying and stirring process under the pushing of the spiral feeder 35 and are discharged through the melted material outlet 32; the flue gas is fed into the flue gas chamber 36 from the flue gas inlet 33 and discharged from the flue gas outlet 34, and the flow direction of the flue gas is countercurrent to the flow direction of the materials.
In the present application, the pyrolysis device 4 comprises a pyrolysis chamber 41 and a flue gas chamber 410, the pyrolysis chamber 41 comprises a feed port 42, a first pyrolysis steam outlet 44, a first pyrolysis steam outlet 45 and a char outlet 47, and the flue gas chamber 410 comprises a flue gas inlet 46 and a flue gas outlet 43; the pyrolysis reaction in the pyrolysis chamber 41 is heated using the hot flue gas in the flue gas chamber 410, so that the pyrolysis reaction is performed under oxygen-free or oxygen-deficient conditions.
The pyrolysis apparatus is shown in fig. 3, and comprises: the device comprises a pyrolysis chamber 41, a feed inlet 42, a flue gas outlet 43, a first pyrolysis steam outlet 44, a second pyrolysis steam outlet 45, a flue gas inlet 46, a charcoal outlet 47, a spiral 48, a stirring scraper 49, a flue gas chamber 410, a heat insulation layer 411, a heat transfer layer 412 and a variable frequency motor 413.
The pyrolysis chamber 41 is used for pyrolysis reaction, and the outer wall of the pyrolysis chamber 41 is wrapped with a heat transfer layer 412 which is corrugated to increase the heat transfer area between the hot flue gas and the pyrolysis chamber, so as to achieve the purpose of enhancing heat transfer.
A first pyrolysis vapor outlet 44 is provided at the middle of the pyrolysis chamber 41 and communicates with the pyrolysis chamber 41, and a second pyrolysis vapor outlet 45 is provided at the end of the pyrolysis chamber 41 and communicates with the pyrolysis chamber 41.
A rotating shaft is arranged on the central shaft of the pyrolysis chamber 41, penetrates through the pyrolysis chamber 41, and is driven by an external variable frequency motor. The inside of the pyrolysis chamber 41 is provided with a spiral 48, a central axis of the spiral 48 coincides with an axial center of the rotation shaft, and the spiral 48 is disposed at a front stage of the pyrolysis chamber 41. The length of the spiral 48 is 1/3-1/2 of the length of the pyrolysis chamber 41. The present application makes use of the spiral 48 to achieve a uniform distribution of material within the pyrolysis chamber 41.
A stirring blade 49 is provided in the pyrolysis chamber 41, and the stirring blade 49 is fixedly arranged on the central shaft and can rotate along with the rotation of the central shaft. Stirring blades 49 are distributed throughout the rear section of the pyrolysis chamber 41. The stirring blades 49 are distributed over 1/2-2/3 of the length of the pyrolysis chamber. This application adopts the stirring scraper blade can realize the stirring of pyrolysis material to can constantly clear away owing to be heated and the coking material that produces on the inner wall of pyrolysis chamber 41, effectively prevent the thermal stagnation phenomenon that the coking produced from this.
Wherein the distance between the spiral and the outer wall of the pyrolysis chamber 41 is 2-5 mm; the stirring blade may contact the inner wall of the pyrolysis chamber.
The flue gas chamber 410 is an interlayer space formed between a heat transfer layer 412 and an insulating layer 411. The hot flue gas is in the circulation of flue gas indoor, passes through indirect heat transfer mode with heat transfer to pyrolysis chamber 41, heats pyrolysis chamber 41, provides the energy for the pyrolytic reaction.
The outer wall of the pyrolysis chamber 41 is provided with a feed inlet 42, which is located at the front section of the pyrolysis chamber 41 and is communicated with the pyrolysis chamber 41.
The outer wall of the pyrolysis chamber 41 is provided with a charcoal outlet 47, which is located at the bottom of the tail end of the pyrolysis chamber and is communicated with the pyrolysis chamber 41. The pyrolysis material is added into the pyrolysis device through the feed inlet 42, and the pyrolysis carbon generated by pyrolysis is discharged out of the pyrolysis device through the carbon outlet 47.
The outer wall of the flue gas chamber 410 is provided with a flue gas outlet 43 and a flue gas inlet 46. The flue gas outlet 43 is located at the front section of the flue gas chamber 410 near the feed port 42 and communicates with the flue gas chamber 410. The flue gas inlet 46 is disposed at an end of the flue gas chamber 410 in communication with the flue gas chamber 410. The flow direction of the hot flue gas and the conveying direction of the materials in the pyrolysis chamber are in a counter-current mode.
The outer part of the pyrolysis device is provided with a variable frequency motor 413 which is in driving connection with a rotating shaft in the pyrolysis chamber 41 and used for driving the rotating shaft.
The insulating layer 411 can be made of rock wool, the thickness of the insulating layer is within the range of 50-80mm, and the insulating layer has a good insulating effect.
The heat transfer layer 412 is wrapped on the outer wall of the pyrolysis chamber, the material of the heat transfer layer 412 is stainless steel and is the same as that of the outer wall of the pyrolysis chamber 41, and the surface of the heat transfer layer 412 is provided with corrugations to enhance the heat transfer effect.
In another embodiment, the stirring blade 49 in the pyrolysis apparatus is as shown in FIG. 4 herein.
The stirring scraper 49 includes a scraper 491, a connecting rod 492, a fixing groove 493, and a spring 494 embedded in the fixing groove, the scraper 491 is fixed at the end of the connecting rod 492, the other end of the connecting rod 492 is fixedly connected to the spring 494, and the fixing groove 493 is fixedly connected to the central shaft of the pyrolysis apparatus.
The scraper 491 is made of stainless steel plate and has a thickness of 30-50 mm. The connecting rod 492 is a stainless steel cylinder having a diameter of 30-50 mm. The fixing groove 493 is a stainless steel cylinder with a diameter of 100 mm and 200 mm. The spring 494 is a telescopic spring and is made of stainless steel; the diameter is 30-50 mm. The blade 491 is connected to the connecting rod 492 by welding. The connecting rod 492 is connected to a spring 494. The spring 494 is connected with the bottom of the fixing groove 493; the fixing groove 493 is welded to the central shaft of the pyrolysis apparatus.
The center of the cylinder of the fixing groove 493 is provided with a cylindrical groove, and the spring 494 and the connecting rod 492 are arranged in the groove.
The scraper 491 forms an angle of 10-20 degrees with the central axis of the pyrolysis device.
In practice, the material in the pyrolysis chamber is continuously stirred and scraped by the scraper blades during the conveying process. The spring can solve the problem that the device cannot operate due to thermal deformation at different temperatures.
With reference to fig. 1, the general process of the system of the present application during operation is described as follows:
(1) conveying the high-moisture waste plastic 101 to a drying device 1 for drying, discharging after drying to a certain degree, conveying the waste plastic into a crushing device 2 for crushing, and discharging after crushing to a specified particle size;
(2) the material discharged by the crushing device 2 is conveyed to a heating and melting device 3 for heating and melting, and the heating temperature is adjusted according to the type of the plastic;
(3) the heated and melted material is sent into the pyrolysis device 4, the pyrolysis reaction is generated in the pyrolysis device 4, the generated high-temperature pyrolysis steam is led out from a pyrolysis steam outlet, and the pyrolysis carbon 102 is discharged from a carbon outlet;
(4) high-temperature pyrolysis steam is led out from the pyrolysis device 4 and then sequentially passes through the heat exchanger I5, the heat exchanger II 6 and the heat exchanger III 7, and pyrolysis oil separation of different distillation ranges is realized under different temperature conditions; the heat transfer oil is selected as a medium for exchanging heat with pyrolysis steam in the heat exchanger I5, the heat exchanger II 6 and the heat exchanger III 7, and the heat transfer oil sequentially passes through the heat exchanger III 7, the heat exchanger II 6 and the heat exchanger I5; fractions obtained from the heat exchanger I5, the heat exchanger II 6 and the heat exchanger III 7 are respectively a lubricating oil and heavy oil fraction 103, a diesel oil fraction 104 and a gasoline fraction 105;
(5) heat conducting oil led out from the heat exchanger I5 is conveyed to a heat exchanger IV 8 through a circulating pump, heat exchange is carried out between the heat conducting oil and air 106 in the heat exchanger IV 8, and the heated air is taken as combustion-supporting air and introduced into the flue gas furnace 9;
(6) the non-condensable gas led out from the heat exchanger III 7 is rich in H2、CH4CO and hydrocarbon gas, wherein a part of the pyrolysis gas is used as fuel gas and is sent into the flue gas furnace 9;
(7) high-temperature flue gas passes through pyrolysis device 4, heating melting device 3, drying device 1 in proper order after 9 are derived from the flue gas stove, and in drying device 1, the flow direction of flue gas is the adverse current with material direction of delivery to the realization heats the material.
The method and the system provided by the application comprise plastic drying, crushing, heating and melting, pyrolysis, a high-efficiency heat exchange system, high-efficiency utilization of hot smoke and the like. The whole set of method and system has simple equipment, easy operation and high thermal efficiency. Pyrolysis oil produced by pyrolysis of plastic waste is separated according to a distillation range to obtain lubricating oil, heavy oil fraction, diesel oil fraction and gasoline fraction, so that the utilization value of the pyrolysis oil is higher; the method and the system are provided with the heating and melting process, so that the problems of slow plastic pyrolysis process and easy coking caused by poor plastic thermal conductivity in the pyrolysis process of the plastic waste are solved; by integrating the drying, crushing, heating and melting, pyrolysis and heat exchange systems, the problems of slow heating of the plastic, serious secondary cracking degree and low yield of pyrolysis oil in the prior pyrolysis technology are solved; and through the heating circulation of the high-temperature flue gas in the whole system, the efficient energy grading utilization is realized, and the problem of low energy utilization in the plastic pyrolysis process is solved.
Example 1
The results of the analysis of polyethylene-rich plastic waste obtained from a certain paper mill are shown in table 1:
TABLE 1
Conveying the plastic waste rich in polyethylene into a drying device, drying under the heating condition of flue gas, controlling the drying temperature at 105 ℃, and drying the plastic until the moisture content is about 8 wt%. And (4) conveying the dried plastic waste to a crushing device for crushing, wherein the particle size of the crushed plastic waste is less than 50 mm. Conveying the crushed plastic waste into a heating and melting device to be heated and melted, and controlling the temperature range to be 140 ℃. Then the molten plastic is conveyed into a pyrolysis device, thermal cracking is carried out in the pyrolysis device, the pyrolysis temperature is 600 ℃, the generated high-temperature pyrolysis steam is led out from a pyrolysis steam outlet, and the pyrolysis carbon is discharged from a carbon outlet; high-temperature pyrolysis steam is led out from the pyrolysis device and then sequentially passes through the heat exchanger I, the heat exchanger II and the heat exchanger III, the temperature of the heat exchanger I is controlled to be 400 ℃, the temperature of the heat exchanger II is controlled to be 300 ℃, and the temperature of the heat exchanger III is controlled to be 150 ℃. The medium for exchanging heat with pyrolysis steam in the heat exchanger I, the heat exchanger II and the heat exchanger III is biphenyl heat conduction oil (commercially available), and the biphenyl heat conduction oil sequentially passes through the heat exchanger III, the heat exchanger II and the heat exchanger I. The temperature of heat conducting oil led out from the heat exchanger I is 300 ℃, the heat conducting oil is conveyed to a heat exchanger IV through a circulating pump, heat exchange is carried out between the heat exchanger IV and air, the temperature of the heated air is 120 ℃, and the heated air is used as combustion-supporting air and introduced into the flue gas furnace; the non-condensable gas led out from the heat exchanger III is rich in H2、CH4CO and hydrocarbon gas, wherein part of the pyrolysis gas is used as fuel gas and is sent into the flue gas furnace, and the temperature of the discharged flue gas is 900 ℃; high-temperature flue gas is led out from the flue gas furnace and then sequentially passes through the pyrolysis device, the heating and melting device and the drying device, and the flow direction of the flue gas and the conveying direction of the waste plastics are in a countercurrent mode to heat the waste plastics. The product analysis is shown in table 2.
TABLE 2
In the operation process of the embodiment, the pyrolysis retention time is 20min, no obvious coking phenomenon exists, and the pyrolysis energy consumption is 2.1 GJ/t.
Comparative example
The plastic waste in example 1 was directly pyrolyzed, and the specific process is described as follows:
the waste plastics are directly pyrolyzed by adopting a spiral pyrolysis reactor, the pyrolysis temperature is controlled at 600 ℃, the pyrolysis retention time is 40min, a serious coking phenomenon occurs, and the pyrolysis energy consumption is 2.5 GJ/t. Pyrolysis oil can not be separated according to the distillation range, and because the plastic materials are heated unevenly and the heat transfer efficiency is low, the pyrolysis time is long, secondary cracking is easy to occur, the oil yield is reduced, and the energy consumption is overhigh. The product analysis is shown in table 3.
TABLE 3
Although the present disclosure has been described above, the scope of the present disclosure is not limited thereto. Various changes and modifications may be effected therein by one of ordinary skill in the pertinent art without departing from the spirit and scope of the present disclosure, and these changes and modifications are intended to be within the scope of the present disclosure.
Claims (9)
1. A method for efficiently recycling plastic wastes is characterized by comprising the following steps:
drying the plastic waste until the moisture content is lower than 10 wt%, and crushing the plastic waste until the particle size is smaller than 50 mm;
heating and melting the broken plastic waste under the oxygen-free or oxygen-deficient condition, wherein the heating and melting temperature is within the range of 120-180 ℃;
pyrolyzing the molten plastic waste under the oxygen-free or oxygen-deficient condition, wherein the pyrolysis temperature is in the range of 500-800 ℃ to generate pyrolysis steam and pyrolysis carbon;
fractionating the pyrolysis vapor in a heat exchanger assembly having a temperature gradient to obtain a pyrolysis oil fraction product, wherein,
the heat exchanger assembly comprises at least 3 heat exchangers which are sequentially arranged according to the process trend of the pyrolysis steam, and the temperature of the heat exchangers is gradually decreased according to the process trend of the pyrolysis steam.
2. The method for efficiently recycling plastic waste according to claim 1, wherein the temperature gradient is in the range of 50-500 ℃.
3. The method as claimed in claim 2, wherein the temperature gradient is in the order of 350-500 ℃, 200-350 ℃ and 50-200 ℃ according to the process trend of the pyrolysis steam.
4. The method for efficiently recycling plastic wastes according to claim 1, wherein the moisture content of the dried plastic wastes is in the range of 5 to 10% by weight during the drying.
5. The method as claimed in claim 1, wherein the drying temperature is within the range of 100-105 ℃.
6. The method for efficiently recycling plastic wastes according to any one of claims 1 to 5, wherein the heat-conducting medium in the heat exchanger is heat-conducting oil.
7. The utility model provides a system with high-efficient resource utilization of plastic waste which characterized in that, includes drying device, breaker, heating melting device, pyrolysis device, heat exchanger subassembly and the flue gas stove that links to each other in proper order, and wherein the heat exchanger subassembly includes heat exchanger I, heat exchanger II, heat exchanger III that link to each other in proper order.
8. The system for high-efficiency resource utilization of plastic wastes according to claim 7, wherein the heating and melting device has a sleeve structure and comprises an outer ring body and an inner ring body, the inner ring body is arranged in the outer ring body, a flue gas chamber is formed between the inner ring body and the inner ring body, the outer ring body is provided with a flue gas inlet and a flue gas outlet, the inner cavity of the inner ring body forms the heating and melting chamber, the inner ring body is provided with a material inlet and a molten material outlet, and a spiral feeder is arranged on a central shaft of the inner ring body.
9. The system for efficiently recycling plastic waste as claimed in claim 7, wherein the pyrolysis device comprises a flue gas inlet and a flue gas outlet, the flue gas inlet of the heating and melting device is connected with the flue gas outlet of the flue gas furnace, and the flue gas inlet of the pyrolysis device is connected with the flue gas outlet of the heating and melting device.
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