A waste plastic radiation pyrolysis process and system

Abstract

The present disclosure relates to the technical field of plastic cracking, and specifically provides a waste plastic radiation heat cracking process and system. The process includes first-stage cracking and second-stage cracking. Waste plastics are melted in the first-stage cracking, and are cracked into light oil, cracking gas and residue in the second-stage cracking. The residue enters the first-stage cracking as a waste plastic melting medium and melts together with the waste plastic. The cracking gas produced in the second-stage cracking is stored as a fuel reserve, and the light oil is extracted and recovered. In this aspect, cracking of high-quality combustible gas is the principle, and the cracking equipment mainly uses radiation cracking. The heating pipe radiates and heats the waste plastic for decomposition. At the same time, high-molecular-weight organic matter is further decomposed into high-calorific-value combustible gas after passing through the 800 DEG C high-temperature pipe, and the gas production rate is high. The present disclosure solves the problems of high cost and environmental pollution in the prior art, such as physical recycling, landfilling, incineration and power generation.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of plastic pyrolysis, and specifically provides a waste plastic radiation pyrolysis process and system. BACKGROUND

[0002] The statements herein merely provide background information related to the present disclosure and do not necessarily constitute the prior art.

[0003] At present, with the development of industry, plastics are used more and more, and therefore the recycling of waste plastics has become a big problem. At present, the recycling of waste plastics mainly includes physical recycling, landfill, incineration power generation and the like.

[0004] However, the physical recycling method has a high requirement on the quality of the plastic, cannot have impurities, and needs a large amount of pretreatment work such as sorting, and therefore its application range is limited. As for landfill, it has the problems of occupying limited arable land and seriously wasting land resources, and will cause the landfill site to become a soft foundation, which is difficult to reuse in the future. Incineration treatment utilizes the characteristics of high calorific value and large heat output of macromolecular materials such as plastics. However, incineration of waste plastics is easy to coke, and has high requirements on the incinerator and other devices, and a complete set of related supporting devices need to be established, which has a very high cost.

[0005] Therefore, the inventors have observed and analyzed the waste plastic treatment methods in the prior art and found that the physical recycling, landfill and incineration power generation methods cannot well solve the problem of recycling waste plastics, and specifically have the problems of high cost and environmental pollution. SUMMARY

[0006] In view of the problems of high cost and environmental pollution and the like of the physical recycling, landfill and incineration power generation methods for treating waste plastics in the prior art, the present disclosure uses a new way of radiation pyrolysis to perform harmless treatment of waste plastics. The waste plastics are radiation pyrolyzed at an appropriate temperature to form low-pollution and high-calorific-value combustible gas for use in a factory boiler. This treatment method of resource recycling is an important development direction of waste plastic treatment.

[0007] In one or some embodiments of the present disclosure, a waste plastic radiation pyrolysis process is provided, which includes first-stage pyrolysis and second-stage pyrolysis. The waste plastics are melted in the first-stage pyrolysis and are pyrolyzed into light oil, pyrolysis gas and slag in the second-stage pyrolysis. The slag enters the first-stage pyrolysis as a waste plastic melting medium and cooperates with the waste plastics to melt. The oil-gas mixture produced in the second-stage pyrolysis is separated. The separated pyrolysis gas is stored as fuel for standby use, and the separated light oil is extracted and recovered after separating a small amount of water.

[0008] The amorphous radiation cracking process design of the application mainly takes cracking high-quality combustible gas as the principle, and the cracking equipment mainly takes radiation cracking as the principle. The waste plastics are radiated and heated by the heating pipe for decomposition. At the same time, the high-molecular-weight organic matter is further decomposed into high-calorific-value combustible gas after passing through the 800 DEG C high-temperature pipe, and the gas production rate is high.

[0009] In one or some embodiments of the present disclosure, a system for realizing the above-mentioned waste plastic radiation thermal cracking method is provided, which comprises a crusher, a mixer, a waste plastic thermal cracking machine and a dry bin connected in sequence.

[0010] One or some of the above technical solutions have the following advantages or beneficial effects:

[0011] 1) The existing technology has high requirements for processing plastics, and can only process single type of plastics. The plastics must be strictly classified before processing, which cannot meet the needs of various occasions, has high use cost, and is difficult to popularize. The waste plastics are directly cracked into gas in the present application, which has no selectivity for waste plastics and high applicability. The required supporting equipment is less, and the investment is relatively small.

[0012] 2) The existing technology mainly adopts a batch feeding mode. The waste plastics can only be added one by one during processing. The plastics must be cooled and reheated after the previous reaction is completed, which greatly wastes energy. In addition, part of the cracking gas will escape from the reactor during each addition, which pollutes the environment. Therefore, the reaction efficiency is very low, the processing capacity is not high, and the practicality is not strong. The present disclosure uses slag as a medium to improve the heat absorption capacity of plastics during radiation, and uses the high-temperature flue gas generated during cracking to preliminarily heat the plastics. The plastics can be continuously fed, and the reaction slag can be continuously used as a medium, so that the plastics can be completely utilized. There is no problem of incomplete reaction and low utilization rate of plastics.

[0013] 3) In the existing technology, the plastics are directly placed in the reactor for heating without using a carrier. The waste plastics are not uniformly heated, which can easily cause the plastics to melt and directly stick to the reactor wall, directly coking, reduce the cracking efficiency, change the product, and reduce the oil yield. At the same time, the reactor is also damaged. The present disclosure uses high-temperature slag as a medium to prevent the plastics from forming a molten state in the waste plastic thermal cracking machine.

[0014] 4) Based on the basic principles of pyrolysis and the practical application of radiation pyrolysis of waste plastics, this disclosure presents a process and system designed for this purpose. This system can recycle various types of waste plastics without prior sorting. The main recycled products are combustible gases, followed by liquid hydrocarbons and solid products. The combustible gases can be used directly as fuel. The composition of waste plastics generated by paper mills is: polyethylene (PE) 42%, polyolefins 35%, polystyrene 18%, chlorides 2%, and other components 5%. Due to the absence of oxidative pyrolysis, no dioxins are produced, and the combustible gases, after purification, are considered clean energy.

[0015] 5) This disclosure employs a thermal cracking method, eliminating the need for a catalyst, thus reducing processing costs and facilitating widespread adoption. Using catalysts has several drawbacks: 1. Catalysts are often rare metals or metal compounds, resulting in high costs; 2. Catalysts are prone to deactivation. During the reaction, due to high temperature, high pressure, and the formation of certain solid products, catalysts often rapidly lose their activity. This is a characteristic of the coke deposition process, requiring continuous addition of catalyst to maintain catalysis. However, some catalysts are very expensive, leading to excessively high costs for thermal cracking; 3. During use, the catalyst mixes with the reaction products (e.g., coke, ash, slag). Therefore, it is difficult to separate the catalyst from the products, preventing catalyst recycling. Furthermore, the mixing of catalysts hinders the utilization of the remaining solid phase. Therefore, catalytic cracking results in excessively high costs, hindering its widespread adoption. Compared to catalytic cracking, thermal cracking reduces costs and facilitates wider adoption. Attached Figure Description

[0016] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute an undue limitation of this disclosure.

[0017] Figure 1 This is a diagram of the waste plastic radiation pyrolysis system described in Example 2.

[0018] Among them: 1. Crusher; 2. Mixer; 3. Waste plastic pyrolysis machine; 31. High temperature flue gas; 32. High temperature slag; 33. Standardized slag; 34. Mixed oil and gas; 4. Dry material bin; 5. Oil and gas separation device; 51. Oil and water separation device. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The existing technology mainly uses physical recycling, landfill and incineration to treat waste plastics, which has a series of problems such as high cost and environmental pollution.

[0021] In one or some embodiments of the present disclosure, a waste plastic radiation thermal cracking process is provided, which includes a first-stage cracking and a second-stage cracking. The waste plastics are melted in the first-stage cracking, and are cracked into light oil, cracking gas and residue in the second-stage cracking. The residue enters the first-stage cracking as a waste plastic melting medium and melts together with the waste plastics. The oil-gas mixture generated in the second-stage cracking is separated. The separated cracking gas is stored as fuel for standby, and the separated light oil is extracted and recovered after separating a small amount of water.

[0022] Preferably, before the two-stage cracking, the waste plastics are preliminarily sorted: iron wires and stones are sorted out, and the waste plastics are crushed into small particles.

[0023] Preferably, the waste plastic small particles and the residue are mixed and preheated before the first-stage cracking.

[0024] Preferably, part of the cracking gas generated in the cracking is used for preheating the mixture of the waste plastic small particles and the residue.

[0025] Preferably, the specific steps of the first-stage cracking are as follows: the mixture of the waste plastics and the residue with residual heat is continuously rotated, part of the easy-to-crack plastics is directly thermally cracked into gas, and the other part of the waste plastics is melted,

[0026] Preferably, the gas generated in the first-stage cracking is used for preheating the mixture of the waste plastic small particles and the residue.

[0027] Preferably, the specific steps of the second-stage cracking are as follows: the melted plastics after the first-stage cracking are radiantly combusted, the high-molecular components in the waste plastics are cracked into light oil and combustible gas, and the remaining waste plastics are carbonized to form residue, and the residue is introduced into the first-stage cracking.

[0028] Preferably, the process is a continuous feeding process.

[0029] Preferably, the process further includes a step of water-oil separation of the cracking gas and the light oil.

[0030] In one or some embodiments of the present disclosure, a system for realizing the above-mentioned waste plastic radiation thermal cracking method is provided, which includes a crusher, a mixer, a waste plastic thermal cracking machine and a dry material bin connected in sequence.

[0031] Preferably, there is a high-temperature flue gas conveying pipeline between the waste plastic thermal cracking machine and the mixer.

[0032] Preferably, there is a high-temperature residue conveying pipeline between the waste plastic thermal cracking machine and the mixer.

[0033] Preferably, the waste plastic thermal cracking machine is further connected to a separation and recovery device.

[0034] Preferably, the light oil and the cracking gas are separated in the separation and recovery device, and specifically, the separation and recovery device comprises an oil-gas separation device and an oil-water separation device, the light oil and the cracking gas are separated in the oil-gas separation device, however, the separated light oil contains a small amount of water, thus, the oil-water separation device is needed to separate the light oil and the water, the light oil is recycled and reused, and the water is discharged.

[0035] Preferably, the crusher is a two-stage crushing and tearing machine.

[0036] Preferably, the waste plastic to be treated is filled in the entire mixer, so that the mixer is sealed.

[0037] Preferably, the mixer is a jacket structure, and the high-temperature flue gas passes through the interlayer to heat the waste plastic.

[0038] Embodiment 1

[0039] The embodiment provides a waste plastic radiation thermal cracking process, which comprises the following steps,

[0040] 1) Preparation: preliminary sorting of waste plastic: sorting out iron wires and particles of stone blocks larger than 100 mm and storing separately; after removing iron by strong magnet, the waste plastic is sent to a crusher 1 to be torn and crushed into materials smaller than 30 mm, and then sent to a mixer 2 by a conveyor, in the mixer 2, the waste plastic is mixed with high-temperature residue 32 provided by a waste plastic thermal cracking machine 3, and the mixture carries the residual heat of high-temperature flue gas 31. The high-temperature flue gas 31 is flue gas generated in the waste plastic thermal cracking machine 3, i.e. flue gas generated in the waste plastic thermal cracking process, which has high temperature and is suitable as a preheating heat source. Specifically, the waste plastic thermal cracking machine 3 can add the high-temperature residue 32 into the mixer 2 by a quantitative feeding device, and the amount of the high-temperature residue 32 is controlled at the same time of feeding, and specifically, the amount of the high-temperature residue 32 is adjusted according to the amount of different waste plastics.

[0041] 2) First stage cracking: the mixture of waste plastics with residual heat and high-temperature slag 32 is sent into the waste plastic thermal cracking machine 3, the waste plastics are melted, and part of the easy-to-crack plastics is directly cracked into gas. The other part of the waste plastics is continuously updated on the surface under the action of rotation and gradually heated under the action of heat radiation, so that the melting is more complete, and the high-temperature slag 32 and the crushed waste plastics are fully contacted in the waste plastic thermal cracking machine 3. And because the waste plastics are mixed with the high-temperature slag 32 in the first stage cracking, the high-temperature slag 32 is used as a medium to prevent the waste plastics from forming a molten state in the waste plastic thermal cracking machine 3, and the waste plastics are heated by the residual heat in the second stage cracking to shrink and reduce the volume and temperature, evaporate the water in the plastics, and provide a basic temperature for the second stage cracking reaction. Oxygen is isolated during the entire first stage cracking process, and the exhaust gas is purified before the second stage cracking begins.

[0042] Specifically, the first stage cracking and the second stage cracking can be separated by using a device, that is, the waste plastic thermal cracking machine 3 is divided into a first stage cracking unit and a second stage cracking unit, and the two units are separated from each other to realize the separation of the two cracking stages. The two cracking stages can also not be separated, but only the reaction conditions are controlled to control the understanding, that is, the first stage cracking temperature is low, and the air is isolated, and the second stage cracking temperature is correspondingly increased.

[0043] In the first stage cracking, the temperature in the furnace is maintained above 550°C, and the waste plastics rapidly heat up and crack in the furnace. Experimental operation proves that the plastic cracking gas production is positively correlated with the heating speed.

[0044] 3) Second stage cracking: the waste plastics melted in the first stage cracking begin the second stage cracking, in which the high-molecular components in the waste plastics are cracked into light oil and combustible gas, and the remaining waste plastics are carbonized. That is, under the action of continuous rotation, the surface of the waste plastics is continuously updated, gradually heated, and mixed oil gas 34 and qualified slag 33 (mainly carbonized plastics) are generated.

[0045] The second stage cracking device can be arranged in multiple layers of heat pipes. The cracking oil and macromolecular organic matter evaporate through the high-temperature radiation cracking pipe at 800-900°C, are further cracked into low-molecular-weight, high-fuel-value combustible gas, and the gas production is further improved.

[0046] The mixed oil gas 34 enters the oil gas separation device 5 to realize separation and recovery, that is, the mixed oil gas 34 is separated into light oil and cracking gas in the oil gas separation device 5. The light oil contains a small amount of water, and the quality of the light oil is low. The light oil and a small amount of water are separated in the oil-water separation device 51, the light oil is recycled and reused, and the water is discharged.

[0047] 4) The separated cracking gas is introduced into the gas-fired boiler of the paper mill to provide fuel for papermaking.

[0048] Example 2

[0049] The embodiment provides a waste plastic radiation thermal cracking system, which can realize the waste plastic radiation thermal cracking process in the embodiment 1.

[0050] The waste plastic radiation thermal cracking system comprises a crusher 1, a mixer 2, a waste plastic thermal cracking machine 3 and a dry bin 4 connected in sequence. The connection mode is in the process order, that is, the waste plastic is first crushed, then mixed with medium high-temperature slag 32 in the mixer and preheated, then enters the waste plastic cracking machine for two-stage cracking, and finally the remaining qualified slag 33 enters the dry bin 4. Specifically, the crusher 1 is a two-stage crushing and tearing machine. The mixer 2 is a jacket structure, and high-temperature flue gas heats the waste plastic through the interlayer.

[0051] The waste plastic thermal cracking machine 3 is connected with the mixer 2 through a high-temperature slag conveying pipeline. The high-temperature slag can be used as the medium of the first-stage cracking. The waste plastic thermal cracking machine 3 is connected with the mixer 2 through a high-temperature flue gas conveying pipeline, and the high-temperature flue gas heats the waste plastic and the high-temperature slag 32, so that the two have a certain heat.

[0052] The waste plastic thermal cracking machine 3 is further connected with an oil-gas separation device 5. The obtained cracking gas and light oil are stored.

[0053] The light oil and the cracking gas are separated in the oil-gas separation device 5. The light oil and water are separated in an oil-water separation device 51.

[0054] The above only discloses the preferred embodiments of the present application, and of course cannot limit the scope of the present application. Therefore, the equivalent changes made in the patent application scope of the present application still belong to the scope covered by the present application.

Claims

1. A process for the radiative thermal cracking of waste plastics, characterized in that, The process comprises a first stage of cracking and a second stage of cracking, in which the waste plastics are melted in the first stage of cracking and cracked into light oil, cracking gas and slag in the second stage of cracking, the slag being used as a melting medium for the waste plastics in the first stage of cracking and melted together with the waste plastics; The oil and gas mixture produced in the second stage of cracking is separated, the cracking gas separated is stored as fuel for standby, and the light oil separated is extracted and recovered after being separated from a small amount of water; Before the two stages of cracking, the waste plastics are preliminarily sorted: iron wires and stones are sorted out, and the waste plastics are crushed into small particles, specifically, the waste plastics are crushed into materials smaller than 30 mm; The waste plastic small particles and the slag are mixed and preheated before the first stage of cracking; The amount of the slag is adjusted according to the amount of the waste plastics; Oxygen is isolated during the whole process of the first stage of cracking; The specific steps of the first stage of cracking are as follows: the mixture of the waste plastics and the slag with residual heat is continuously rotated, part of the easily cracked plastics is directly thermally cracked into gas, and the other part of the waste plastics is melted; The gas generated in the first stage of cracking is used for preheating the mixture of the waste plastic small particles and the slag; The specific steps of the second stage of cracking are as follows: the melted plastics after the first stage of cracking are radiantly combusted, the high molecular components in the waste plastics are cracked into light oil and combustible gas, and the remaining waste plastics are carbonized to form slag, and the slag is fed into the first stage of cracking; Part of the cracking gas generated is used for preheating the mixture of the waste plastic small particles and the slag.

2. The waste plastic radiation thermal pyrolysis process of claim 1, wherein, The process is a continuous feeding process.

3. The waste plastic radiation thermal pyrolysis process of claim 1, wherein, The process further comprises a step of water-oil separation of the cracking gas and the light oil.

4. A system for carrying out the method of waste plastic radiation pyrolysis according to any one of claims 1 to 3, characterized in that, The process comprises a crusher, a mixer, a waste plastic thermal cracking machine and a dry material bin connected in sequence.

5. The system for the waste plastic radiation thermal pyrolysis method according to claim 4, characterized by, There is a high-temperature flue gas conveying pipeline between the waste plastic thermal cracking machine and the mixer.

6. The system for the waste plastic radiation thermal pyrolysis method according to claim 5, characterized by, There is a high-temperature slag conveying pipeline between the waste plastic thermal cracking machine and the mixer.

7. The system for the waste plastic radiation thermal pyrolysis method according to claim 4, wherein The waste plastic thermal cracking machine is further connected to a separation and recovery device.

8. The system for the method of waste plastic radiation thermal pyrolysis according to claim 7, characterized in that, The light oil and the cracking gas are separated in the separation and recovery device. The process further comprises a step of water-oil separation of the cracking gas and the light oil.

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