Method for processing waste material and use thereof

Abstract

This invention relates to the field of plastic and rubber recycling and discloses a method for treating waste materials and its application. The method includes: (1) thermally or catalytically cracking the waste materials to obtain degraded oil; (2) steam cracking the degraded oil in a steam cracking furnace to obtain low-carbon olefins; wherein the steam cracking furnace includes a convection section and a radiation section, and the degraded oil is mixed with dilution steam and heated to a transverse temperature in the convection section before entering the radiation section for steam cracking; wherein the transverse temperature is 280-500°C lower than the temperature of the steam cracking reaction; the waste materials are waste plastics and / or waste rubber. The waste material treatment method provided by this invention has high production efficiency, the equipment is not prone to coking, it is conducive to the resource utilization of waste plastics and waste rubber, and provides a new approach for the preparation of low-carbon olefins.

Description

Technical Field

[0001] This invention relates to the field of plastic and rubber recycling, specifically to a method for treating waste materials and its application. Background Technology

[0002] Low-carbon olefins such as ethylene, propylene, and butadiene are important basic raw materials for the petrochemical industry. Currently, the main method for producing low-carbon olefins is the tubular furnace petroleum hydrocarbon steam cracking process. The core equipment of the tubular furnace petroleum hydrocarbon steam cracking process is the tubular cracking furnace (hereinafter referred to as "cracking furnace"). When the cracking feedstocks such as ethane, propane, naphtha, and hydrotreated tail oil are heated to high temperatures in the cracking furnace, carbon chain breaking chemical reactions occur, generating low-carbon olefins such as ethylene, propylene, and butadiene.

[0003] Waste plastics and waste tires contain approximately 13.5% hydrogen, making them a valuable resource given the current scarcity of fossil fuels. However, current methods for treating waste plastics include landfilling or discharge into the natural environment (72%), incineration (14%), and recycling (14%). These crude recycling methods still lead to soil and air pollution. The degradation oil produced during the chemical recycling of waste plastics or waste tires is prone to coking, often occurring in the convection section of the pyrolysis furnace, a relatively low-temperature region. Once coking occurs in the convection section, it cannot be removed by online burning and often requires shutdown for manual decoking, significantly impacting the pyrolysis furnace's online time and reducing production efficiency and output. Therefore, although existing technologies have developed a series of pyrolysis technologies for waste plastics or waste tires to generate degradation oil, most of this degradation oil is directly burned as raw material, leaving a large amount of resources unutilized.

[0004] Therefore, the process of recycling waste plastics into high-value-added products has a very broad application prospect. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of low resource utilization rate of waste plastics or waste rubber in the existing technology, easy coking in pyrolysis furnaces and low production efficiency in conventional chemical recycling, and to provide a method for treating waste materials and its application. This method can realize the production of low-carbon olefins from waste plastics or waste rubber, with high production efficiency and the equipment is not prone to coking.

[0006] To achieve the above objectives, the present invention provides a method for processing waste materials, comprising the following steps:

[0007] (1) The waste materials are subjected to thermal or catalytic cracking to obtain degraded oil;

[0008] (2) The degradation oil is subjected to a steam cracking reaction in a steam cracking furnace to obtain low-carbon olefins;

[0009] The steam cracking furnace includes a convection section and a radiation section. The degradation oil is mixed with dilution steam and heated to the cross temperature in the convection section before entering the radiation section for steam cracking reaction.

[0010] The cross temperature is 280-500°C lower than the temperature of the steam cracking reaction;

[0011] The waste materials are waste plastics and / or waste rubber.

[0012] A second aspect of the present invention provides the application of the above method in the preparation of olefins.

[0013] The present invention provides a method for treating waste materials, which degrades waste plastics or non-rubber materials through chemical recycling to obtain degraded oil. This degraded oil can be used directly as a pyrolysis feedstock or, after being treated by a hydrogenation process, as a pyrolysis feedstock for steam cracking to produce low-carbon olefins. At the same time, it overcomes the problem of coking in the pyrolysis furnace (especially the convection section) when using waste plastics or waste tire degraded oil as pyrolysis feedstock to produce olefins in existing steam cracking processes, resulting in low online rate, thus improving production efficiency.

[0014] The waste material treatment method provided by this invention is beneficial to the resource utilization of waste plastics and waste rubber, and provides a new approach for the preparation of low-carbon olefins. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the steam pyrolysis furnace used in Embodiment 1 of the present invention;

[0016] Figure 2 This is a schematic diagram of the convection section in the steam cracking furnace used in Embodiment 1 of the present invention;

[0017] Figure 3 This is a schematic diagram of the sidewall burner's installation position in Embodiment 3 of the present invention.

[0018] Explanation of reference numerals in the attached figures

[0019] 1. Fan 2. Convection section 3. Radiant furnace tube

[0020] 4 Combustion system 5 Radiant section 6 Quenching boiler

[0021] 7. Degradable oil 8. Boiler feedwater 9. Dilution steam

[0022] 10 High-pressure steam; 11 Raw material preheating section; 12 Boiler feedwater preheating section

[0023] 13 Dilution Steam Superheating Section 14 Ultra-High Pressure Steam Superheating Section 15 Mixing Heating Section

[0024] 16 Flue gas transverse section 17 Gasification separation unit 18 Radiant section furnace tubes

[0025] 19 Sidewall Burners Detailed Implementation

[0026] The endpoints and any values ​​of the ranges disclosed herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0027] The first aspect of this invention provides a method for processing waste materials, comprising the following steps:

[0028] (1) The waste materials are subjected to thermal or catalytic cracking to obtain degraded oil;

[0029] (2) The degradation oil is subjected to a steam cracking reaction in a steam cracking furnace to obtain low-carbon olefins;

[0030] The steam cracking furnace includes a convection section and a radiation section. The degradation oil is mixed with dilution steam and heated to the cross temperature in the convection section before entering the radiation section for steam cracking reaction.

[0031] The cross temperature is 280-500°C lower than the temperature of the steam cracking reaction;

[0032] The waste materials are waste plastics and / or waste rubber.

[0033] Currently, chemical recycling and chemical cycle methods are considered the only sustainable way to recycle waste plastics or rubber. However, existing pyrolysis technologies for waste plastics or rubber produce degradation oils, most of which are burned directly as raw materials, lacking effective resource utilization. If waste materials could be utilized to produce high-value-added low-carbon olefins, it would not only benefit the resource utilization of waste plastics and rubber but also provide a new pathway for the preparation of low-carbon olefins.

[0034] However, the degradation oil obtained from the chemical recycling process of waste materials, such as waste rubber or waste plastic, is prone to coking during steam cracking. Therefore, when the above-mentioned oil is used as the raw material for steam cracking, it is often necessary to shut down the steam cracking furnace to clean the coking section, resulting in a low online rate when using the above-mentioned oil for olefin production.

[0035] Generally, the main function of the convection section of a steam pyrolysis furnace is to preheat, gasify, and superheat the feedstock to the cross temperature before it enters the radiant section for pyrolysis; and to recover waste heat from the flue gas in the radiant section. Under normal circumstances, the convection section has different tube arrangements depending on the process requirements, generally including the following heat exchange sections: feedstock preheating section, boiler feedwater preheating section, steam superheating section, and mixing heating section. The feedstock and dilution steam mixture is heated to the cross temperature at the outlet of the mixing heating section before entering the radiant section. For steam pyrolysis furnaces, once coking reaches a certain level in the radiant section, the coke layer adhering to the tube wall must be cleaned online before continued feeding and operation. However, if coking is severe in the convection section, the cleaning operation must be performed manually after the furnace is shut down and cooled, which takes up a significant amount of time and reduces the online rate of the steam pyrolysis furnace. In addition to maintenance costs, the shutdown and startup of the steam pyrolysis furnace increase energy consumption and operating costs.

[0036] During the research process, the inventors of this invention cleverly discovered that by appropriately lowering the temperature of the convection section, coking in the convection section can be reduced, thereby increasing the online rate of the processing system.

[0037] In this invention, the "cross temperature" refers to the inlet temperature of the radiation section (XOT), and the "temperature of the steam cracking reaction" refers to the outlet temperature of the radiation section (COT).

[0038] According to the present invention, preferably, the spanning temperature is 350-600°C, more preferably 430-550°C.

[0039] The outlet temperature of the radiant section will vary depending on the feedstock for pyrolysis. To obtain higher pyrolysis product yields, the temperature of the steam pyrolysis reaction is preferably 750-850℃, and more preferably 790-820℃.

[0040] According to the present invention, there are no special requirements regarding the source of the waste plastics or waste rubber, which can come from waste plastics and waste tires, etc. Preferably, the waste plastics include, but are not limited to, one or more of polyethylene, polypropylene, and polystyrene. The waste rubber can come from rubber products such as waste tires, waste gloves, and waste sponges.

[0041] In this invention, the waste material is subjected to thermal or catalytic cracking to break down complex macromolecules into smaller molecules, yielding gaseous small molecules and degraded oil. The specific methods and conditions for the thermal or catalytic cracking are not particularly limited in this invention, and conventional methods known in the art can be used. Preferably, the conditions for the catalytic cracking include: a reaction temperature of 100-500℃, a reaction pressure of 0.1-3 MPa, and a mass hourly space velocity (HHSV) of 500-2000 h⁻¹ for the waste material. -1 .

[0042] The present invention does not impose any particular limitation on the catalytic cracking catalyst, and any catalyst well known to those skilled in the art that can be used for catalytic cracking reactions can be used. For example, alumina-supported Cr and / or Ni catalysts.

[0043] Preferably, the conditions for the thermal pyrolysis include: a reaction temperature of 300-700℃ and a reaction pressure of 0.1-5MPa.

[0044] Using the above-mentioned preferred embodiments to perform steam cracking on the degraded oil is beneficial to obtaining a higher oil yield from waste materials and improving the overall profitability of steam cracking.

[0045] In this invention, there are no special limitations on the apparatus for catalytic cracking or thermal cracking, and conventional reactors in the art can be used, such as fixed-bed reactors or fluidized-bed reactors, preferably fixed-bed reactors.

[0046] To further reduce coking in the convection section of a steam pyrolysis furnace and improve its online operation rate, according to a preferred embodiment of the present invention, the degradation oil can have unvaporized heavy components removed during the heating and gasification process in the convection section of the steam pyrolysis furnace (via a gasification separation device installed in the convection section). The remaining light components are then heated to a cross-temperature range after gasification before entering the radiation section. The present invention does not impose any particular limitations on the gasification separation device, as long as it can remove the unvaporized heavy components from the degradation oil during the heating and gasification process in the convection section, allowing the light components to be heated to a cross-temperature range before entering the radiation section.

[0047] In this invention, the heavy components refer to components in the degradation oil with a vaporization temperature > 400°C, and the light components refer to components in the degradation oil with an initial boiling point of around 400°C.

[0048] In this invention, there are no special limitations on the mixing method of the degradation oil and the dilution vapor, which can be adjusted according to actual production needs. For example, the dilution vapor can be introduced into the convection section in one go to mix with the degradation oil; or it can be introduced into the convection section in stages to mix with the degradation oil step by step.

[0049] According to a preferred embodiment of the present invention, the dilution steam is mixed with the degradation oil by a single injection method, and the temperature of the dilution steam is 400-700°C, preferably 450-650°C.

[0050] According to the present invention, preferably, the weight ratio of the degradation oil to the dilution steam is 1-4:1, more preferably 1.5-2.5:1. In the above preferred embodiment, it is beneficial to reduce coking of the degradation oil during steam cracking and increase the yield of low-carbon olefins.

[0051] According to the present invention, preferably, the method further includes: preheating the degradation oil in a convection section before mixing the dilution steam with the degradation oil to obtain preheated degradation oil.

[0052] Preferably, the temperature of the preheated degradation oil is 200-400℃, more preferably 250-350℃.

[0053] To further reduce coking in the convection section during the steam cracking of waste material degradation oil, a two-stage injection method can preferably be used to mix the dilution steam with the degradation oil in the convection section. This two-stage injection method involves injecting dilution steam into the convection section twice to mix with the degradation oil: first, a high-temperature dilution steam injection is performed to dilute and preheat the degradation oil; then, the diluted degradation oil is mixed with ultra-high-temperature steam, heated to the required temperature, and then sent to the radiation section.

[0054] Preferably, the two-stage injection method includes:

[0055] (1-1) Mix high-temperature steam with the degradation oil to dilute and preheat the degradation oil;

[0056] (1-2) Mix the ultra-high temperature steam with the product of step (1-1).

[0057] According to the present invention, preferably, the temperature of the high-temperature steam is 150-450°C, more preferably 180-350°C.

[0058] According to the present invention, preferably, the temperature of the ultra-high temperature steam is 400-700℃, more preferably 450-650℃.

[0059] Preferably, the weight ratio of the high-temperature steam to the degradation oil is 0.3-1:1.

[0060] Preferably, the weight ratio of the ultra-high temperature steam to the product of step (1-1) based on the mass of the degraded oil is 0.2-0.6:1.

[0061] According to the present invention, the degradation oil obtained from waste plastics or waste rubber exhibits significant differences in properties due to variations in raw material composition. Some lower-quality raw materials cannot be directly used as steam cracking feedstocks and require hydrogenation treatment. Preferably, the method further includes: contacting the degradation oil with a hydrogenation catalyst to perform a hydrogenation reaction, obtaining a hydrogenated fraction of the degradation oil, which is then fed into a steam cracking furnace.

[0062] In this invention, the hydrogenation reaction can be carried out using conventional methods in the art. The selection range of the hydrogenation catalyst is wide, and any catalyst capable of catalyzing the hydrogenation reaction can be applied to this invention. Those skilled in the art can select according to actual needs. The hydrogenation catalyst can be a noble metal catalyst, for example, a platinum and / or palladium catalyst supported on an alumina support.

[0063] The present invention offers a wide range of options for the specific conditions of the hydrogenation reaction, which can be selected by those skilled in the art according to actual needs. Preferably, the conditions for the hydrogenation reaction include: a reaction temperature of 200-400℃, more preferably 250-350℃; a reaction pressure of 2-4 MPa, more preferably 2.5-3.5 MPa; and a hydrogen-to-oil ratio of 100-400:1, more preferably 150-350:1. Adopting the above preferred embodiments helps to reduce coking of the degradation oil during steam cracking and improves the yield of low-carbon olefins.

[0064] According to a preferred embodiment of the present invention, the method further includes: cooling and separating the products after steam cracking to obtain low-carbon olefins.

[0065] Preferably, the reacted materials are cooled and separated in a quench boiler.

[0066] In this invention, the method may further include: the material obtained after steam cracking in the radiation section first enters a quenching device for cooling and separation into cracked gas and steam. The separated steam enters a steam drum for gas-liquid separation; the separated high-pressure steam can enter a convection section for heating to obtain ultra-high-pressure steam; the separated water can be used as cooling water for the quenching heat exchanger; the cracked gas enters a subsequent separation device through a cracked gas main to separate the target product. The high-temperature flue gas generated by combustion in the radiation section enters the convection section through a flue gas traversing section.

[0067] According to a preferred embodiment of the present invention, the method further includes: increasing the heating supply to a portion of the furnace tubes in the radiant section. The method of increasing the heating supply may include (in the radiant section) providing enhanced heat transfer elements and / or (in the portion of the furnace tubes in the radiant section) providing enhanced heating devices. If the radiant section already has a certain number of enhanced heat transfer elements, the heating supply can be increased by increasing the number of elements or by replacing them with heat transfer elements that have better enhanced heat transfer performance.

[0068] Preferably, the enhanced heat transfer element increases the heat transfer coefficient of the furnace tube at the location where it is installed by 50-800% compared to a bare tube. The "bare tube" refers to a furnace tube without the enhanced heat transfer element installed. That is, after installing the enhanced heat transfer element, the heat transfer coefficient at the installation location on the furnace tube is 1.5-9 times that before installation.

[0069] In this invention, there are no particular limitations on the enhanced heat transfer element, as long as it facilitates heat transfer in the radiant section. For example, the enhanced heat transfer element can be an inner insert of a spiral plate, an inner insert of a twisted ribbon, an inner insert of a cross-serrated shape, an inner insert of a coil core, a porous body with a twisted wire, an inner insert of a spherical matrix, etc. The same enhanced heat transfer element can be set at different positions in the radiant section furnace tube, or different enhanced heat transfer elements can be set in different parts of the furnace tube.

[0070] In this invention, the enhanced heating device is used to improve the heat transfer efficiency of the first-pass furnace tube, and any enhanced heating device that can achieve this purpose can be applied to this invention.

[0071] Preferably, the enhanced heating device strengthens the heating after the raw material enters the first pass of the radiant section furnace tubes. More preferably, the enhanced heating device increases the heating at the corresponding position of the first pass tube by 1-50% compared to when the enhanced heating device is not installed.

[0072] In this invention, to enhance the heating of the first-pass furnace tube, an enhanced heating device can be added to the furnace sidewall of the first-pass furnace tube. Alternatively, the furnace wall of the first-pass furnace tube can be modified and designed to enhance its heating. For example, a reflection enhancement element can be installed on the furnace wall, or the reflection angle of the furnace wall can be changed to increase the radiant heating of the first-pass furnace tube.

[0073] Preferably, the enhanced heating device includes a burner and / or a reflective enhancement element disposed on the side wall of the furnace chamber above the first pass furnace tube.

[0074] On the other hand, the steam pyrolysis furnace used in the above method also falls within the scope of protection of this invention. This steam pyrolysis furnace includes: a convection section and a radiation section connected in series;

[0075] In this invention, the decrease in cross-sectional temperature results in a lower outlet temperature for the material in the convection section. Upon entering the radiation section, the material requires a longer heating period to reach the reaction temperature. During their research, the inventors also discovered that to reduce the impact of the low outlet temperature of the convection section on the reaction process, an enhanced heating device can be installed in the radiation section of the steam cracking furnace to improve the heating efficiency of the radiation section, thereby increasing the heating rate of the material in the radiation section and enabling it to reach the reaction temperature more quickly.

[0076] According to a preferred embodiment of the present invention, the radiant section includes 2-6 passes of furnace tubes, wherein one pass of furnace tubes is provided with an enhanced heating device. The features of the enhanced heating device are as described above and will not be repeated here.

[0077] According to a preferred embodiment of the present invention, the radiant section employs a two-pass furnace tube.

[0078] Preferably, the two-pass furnace tube is a 2-1 type radiant furnace tube or a 4-1 type radiant furnace tube. That is, in the two-pass furnace tube, the first pass consists of two parallel vertical inlet tubes, and the second pass consists of one vertical outlet tube, forming a 2-1 type radiant furnace tube. Alternatively, the first pass consists of four parallel vertical inlet tubes, and the second pass consists of one vertical outlet tube, forming a 4-1 type radiant furnace tube.

[0079] According to a preferred embodiment of the present invention, the ratio of the inner diameter of the outlet pipe of the radiant section furnace tube to the inner diameter of the inlet pipe is greater than 1 and less than or equal to 2.5.

[0080] Preferably, the inner diameter of the inlet pipe is 25-70 mm, more preferably 40-65 mm.

[0081] Preferably, the inner diameter of the outlet pipe is 45-120 mm, more preferably 60-95 mm.

[0082] To further improve heat transfer in the radiant section, according to a preferred embodiment of the present invention, the radiant section further includes an enhanced heat transfer element installed in the furnace tube of the radiant section. The features of the enhanced heat transfer element are as described above and will not be repeated here.

[0083] To further reduce coking in the convection section, especially when using heavy pyrolysis feedstocks (such as degradation oil generated from the chemical recycling of waste plastics or waste tires) for steam pyrolysis, according to a preferred embodiment of the present invention, the pyrolysis furnace is further equipped with a gasification separation device in the convection section. This gasification separation device is used to remove unvaporized heavy components from the degradation oil in the convection section. The present invention does not impose any particular limitations on the gasification separation device, as long as it can remove the unvaporized heavy components from the degradation oil during the heating and gasification process in the convection section, allowing the lighter components to be heated to a cross-temperature range before entering the radiation section.

[0084] According to a preferred embodiment of the present invention, the steam pyrolysis furnace further includes a high-pressure steam drum, a combustion system, and a quench boiler. The material obtained after pyrolysis in the radiant section can first enter the quench boiler for cooling and separation into pyrolysis gas and steam. The separated steam enters the steam drum for gas-liquid separation; the separated high-pressure steam can enter the convection section for heating to obtain ultra-high-pressure steam, and the separated water can be used as cooling water for the quench heat exchanger. The pyrolysis gas enters the subsequent separation device through the pyrolysis gas main to separate the desired target product. The high-temperature flue gas generated by combustion in the radiant section enters the convection section through the flue gas traversing section.

[0085] In this invention, to fully utilize the heat from the high-temperature flue gas in the radiant section, the convection section of the pyrolysis furnace can be equipped with multiple sections for heat recovery. Typically, the convection section can include a feedstock preheating section, a boiler feedwater preheating section, a dilution steam superheating section, an ultra-high pressure steam superheating section, and a mixing heating section. The feedstock preheating section is typically used to preheat the pyrolysis feedstock. The boiler feedwater preheating section is typically used to preheat the boiler feedwater supplied to the steam drum. The dilution steam superheating section is typically used to preheat the dilution steam (e.g., water vapor). The ultra-high pressure steam superheating section is typically used to heat the high-pressure steam from the steam drum to obtain ultra-high pressure steam. The mixing heating section is typically used to heat the degradation oil to a temperature range. In this preferred embodiment, in the convection section, along the flow direction of the high-temperature flue gas, the mixing heating section, ultra-high pressure steam superheating section, dilution steam superheating section, boiler feedwater preheating section, and feedstock preheating section are preferably arranged sequentially.

[0086] The convection section preferably includes a first convection section tube group (including a raw material preheating section, a boiler feedwater preheating section, a dilution steam superheating section, an ultra-high pressure steam superheating section, and a mixing heating section) and a second convection section tube group (including a mixing heating section). The degradation oil is fully vaporized in the first convection section tube group, effectively improving the steam cracking effect.

[0087] To further improve the heat transfer efficiency of the radiant section (single-pass tubes), the radiant section tubes of the steam cracking furnace can be divided into several large groups, each group containing several multi-pass tubes. During the arrangement of the radiant section tubes, the single-pass tubes within the same large group are arranged together. Radiant heat transfer to the single-pass tubes is increased within the radiant section from the inlet to the upper third of its height.

[0088] Preferably, the radiant furnace tubes are arranged vertically in the radiant section.

[0089] A second aspect of the present invention provides the application of the above method in the preparation of olefins.

[0090] The present invention will be described in detail below through embodiments.

[0091] The gas composition of the product in the examples was determined by gas chromatography.

[0092] The structure of the steam pyrolysis furnace used in the embodiment is as follows: Figure 1 As shown, the steam pyrolysis furnace includes: a blower 1, a convection section 2, a radiant furnace tube 3, a combustion system 4, a radiant section 5, and a quench boiler 6. The material outlet of the convection section 2 is connected to the material inlet of the radiant section 5. The convection section of the steam pyrolysis furnace includes a raw material preheating section, a boiler feedwater preheating section, a dilution steam superheating section, an ultra-high pressure steam superheating section, and a mixing heating section. (Combined with...) Figure 2In the pyrolysis furnace, high-pressure steam from the steam drum is heated by the ultra-high-pressure steam superheating section 14 to generate high-pressure steam 10. The separated high-pressure steam can enter the convection section for heating. Degradation oil 7 (i.e., pyrolysis feedstock) enters the convection section, is preheated in the feedstock preheating section 11, and then enters the mixing heating section 15 for preheating before entering the radiation section. Boiler feedwater 8 enters the boiler feedwater preheating section 12 for preheating before entering the steam drum. Dilution steam 9 is preheated by the dilution steam superheating section 13 and then mixed with the preheated degradation oil. The degradation oil is gasified and passes through the gasification separation device 17. The light fraction in the gas phase enters the mixing heating section 15 together with the dilution steam, while the heavy fraction in the liquid phase goes to other units. Figure 2 (Not shown in the image). In the mixing and heating section 15, the preheated degradation oil is heated to a temperature spanning the specified range. The radiant section is connected to the quench boiler via piping to transport the cracking products to the quench boiler for cooling and separation to obtain low-carbon olefins.

[0093] Example 1

[0094] (1) Waste plastic degradation oil was obtained by thermal pyrolysis of waste plastics using a tubular fixed bed reactor. The waste plastics consisted of a mixture of polypropylene, polystyrene, and polyvinyl chloride as the main components, with the three main components accounting for 30 wt%, 30 wt%, and 30 wt%, respectively, and the remaining plastics accounting for 10 wt%. The thermal pyrolysis reaction temperature was 520℃, the reaction pressure was 2 MPa, and the oil yield was 78%. The obtained degradation oil was then hydrogenated to obtain the hydrogenated fraction of waste plastic degradation oil, with a hydrogen-to-oil ratio of 300:1, a reaction pressure of 3.5 MPa, a reaction temperature of 330℃, and a 3 wt% Pt / Al2O3 hydrogenation catalyst. The basic properties of the waste plastic degradation oil and the hydrogenated fraction of waste plastic degradation oil are compared in Table 1.

[0095] (2) In such Figure 1 In the steam cracking furnace shown, the hydrogenated fraction of the degradation oil undergoes a steam cracking reaction. The radiant furnace tube 3 is a two-pass 2-1 type furnace tube, with an inlet diameter of 51 mm and a tube length of 13.3 m; the outlet diameter of the furnace tube is 73 mm and the tube length is 13.3 m.

[0096] In convection section 2, the hydrogenated fraction of the degradation oil at 60°C is mixed with high-temperature steam at 400°C for dilution and preheating, with a weight ratio of high-temperature steam to degradation oil of 0.6:1. The preheated degradation oil is at 180°C. Then, ultra-high temperature steam at 600°C is injected, with a weight ratio of ultra-high temperature steam to degradation oil of 0.3:1. After heating to the cross temperature (XOT), it enters the radiant furnace tube 3 for steam cracking reaction. The cross temperature (XOT) is 450°C. The outlet temperature (COT) of the radiant section of the steam cracking furnace is 790°C, meaning the cross temperature is 340°C lower than the steam cracking reaction temperature. The degradation oil feed rate is 58,000 kg / h, and the dilution steam rate (total of high-temperature steam + ultra-high temperature steam) is 52,200 kg / h. The main components of the cracking products are shown in Table 2.

[0097] Following the operation of Example 1, the pyrolysis furnace operates on a 60-day cycle, with online coking occurring 5 times per year, each coking session lasting 2 days. In this example, the cross-temperature of the material was reduced, which effectively reduced the pyrolysis reaction in the convection section, decreased coking, and eliminated the need for decoking in the convection section, thereby extending the online time.

[0098] Table 1

[0099] project Waste plastic degradation oil Hydrogenation products for waste plastic degradation oil <![CDATA[Density (20 °C), kg / m 3 > 833.6 824.0 Distillation range, °C 140-600 84-530 S, μg / g 360 108 N, μg / g 630 192 Si, μg / g 46 ＜1 Cl, μg / g 284 ＜0.5 Metal content, μg / g Fe 1.0 ＜1 Ca 1.0 ＜1 Mass composition Alkane wt% 28.4 38.8 Total cycloalkanes / olefins wt% 55.3 38.9 Total aromatics wt% 26.3 22.3

[0100] Table 2

[0101]

[0102]

[0103] Comparative Example 1

[0104] Following the same method as in Example 1, except that the radiant furnace tube 3 adopts a two-pass 2-1 type furnace tube, with an inlet diameter of 51 mm and a tube length of 12.8 m; the outlet diameter of the furnace tube is 73 mm, and the tube length is 12.8 m. The cross temperature (XOT) is 520°C, and the radiant section outlet temperature (COT) of the steam cracking furnace is 790°C. The cross temperature is 270°C lower than the cracking temperature of the radiant section.

[0105] Following the operation of Comparative Example 1, the cracking furnace operates on a 60-day cycle, with one coking cleaning of the convection section per year (7 days, plus one shutdown and one start-up), and five online coking cycles.

[0106] A comparison of Example 1 and Comparative Example 1 shows that Example 1 reduced the material cross-section temperature. Compared to Comparative Example 1 (520℃), the reduction in cross-section temperature effectively reduced coking in the convection section. To ensure that the raw material receives sufficient heat in the radiation section, the lengths of the inlet and outlet pipes of the radiant furnace tube 3 were increased by 0.5 meters each.

[0107] Compared to Comparative Example 1, Example 1 showed that the cracking furnace's online time increased by 7 days within a year, resulting in a significant increase in product output, with an increase of 3,696 tons in triene products alone (ethylene, propylene, and butadiene). Based on an average product price of RMB 7,000 per ton, this translates to an increase in revenue of RMB 25.87 million from triene products alone. Furthermore, compared to Comparative Example 1, Example 1 also saved substantial start-up, shutdown, and maintenance costs.

[0108] Example 2

[0109] The method is the same as in Example 1, except that the pyrolysis feedstock used in step (2) is the degradation oil of waste plastics that has not undergone hydrogenation treatment. The main components of the pyrolysis products are shown in Table 2.

[0110] Example 3

[0111] The same processing system as in Example 1 is used, except that a sidewall burner 19 is arranged 3 meters from the top of the radiant section (see reference for arrangement). Figure 3 The burner position corresponds to the first pass of the furnace tube bank in the radiant section furnace tube 18. The radiant furnace tube 3 adopts a two-pass 2-1 type furnace tube, with an inlet tube diameter of 49mm and a tube length of 13.5m; the outlet tube diameter is 71mm and the tube length is 13.5m. The ratio of the inner diameter of the outlet tube to the inner diameter of the inlet tube in the radiant section furnace tube is 1.45.

[0112] Specific handling methods:

[0113] (1) Perform the procedure as described in Example 1.

[0114] (2) In convection section 2, the 60°C degradation oil fraction is diluted and preheated by mixing with 400°C high-temperature steam. The weight ratio of high-temperature steam to degradation oil is 0.6:1. The preheated degradation oil is at 180°C. Then, 600°C ultra-high-temperature steam is injected, with a weight ratio of ultra-high-temperature steam to degradation oil of 0.3:1. After heating to the cross temperature (XOT), it enters the radiant furnace tube 3 for steam cracking reaction. The cross temperature (XOT) is 430°C. The outlet temperature (COT) of the radiant section of the steam cracking furnace is 790°C. Enhanced heat transfer elements are added to the radiant furnace tube 3, increasing the heat transfer coefficient at the installation location by 500% compared to the bare tube. The main components of the cracking products are shown in Table 2.

[0115] The comparison shows that by enhancing the heating device, the radiative heat transfer in the upper part of the first-pass tube is strengthened (resulting in a 20% increase in heating at the corresponding position of the first-pass furnace tube compared to when no burner is installed), allowing the material to heat up rapidly after entering the radiant section. With the same tube length as Comparative Example 1 and a lower temperature in the cross section, the same residence time in the high-temperature zone is achieved, resulting in comparable product yields and charring cycles in the radiant section.

[0116] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for treating waste materials, comprising the following steps: (1) The waste materials are subjected to thermal cracking or catalytic cracking to obtain degraded oil; (2) The degradation oil is subjected to steam cracking reaction in a steam cracking furnace to obtain low-carbon olefins; The steam cracking furnace includes a convection section and a radiation section. The degradation oil is mixed with dilution steam and heated to the cross temperature in the convection section before entering the radiation section for steam cracking reaction. Wherein, the spanning temperature is 340-500°C lower than the temperature of the steam cracking reaction; the spanning temperature is 350-430°C; The waste materials are waste plastics and / or waste rubber.

2. The method of claim 1, wherein, The temperature of the steam cracking reaction is 750-850℃.

3. The method according to claim 2, wherein, The temperature of the steam cracking reaction is 790-820℃.

4. The method according to claim 1, wherein, The waste plastic is selected from at least one of polyethylene, polypropylene and polystyrene; And / or, the catalytic cracking includes: contacting waste materials with a catalytic cracking catalyst under catalytic cracking reaction conditions to obtain degraded oil; And / or, the catalytic cracking conditions include: the reaction temperature is 100-500℃, the reaction pressure is 0.1-3MPa, the mass space velocity of the waste material is 500-2000h -1 ; And / or, the conditions for the thermal pyrolysis include: a reaction temperature of 300-700°C and a reaction pressure of 0.1-5 MPa.

5. The method according to claim 1, wherein, The dilution steam is mixed with the degradation oil in a single injection manner, and the temperature of the dilution steam is 400-700℃.

6. The method according to claim 5, wherein, The dilution steam is mixed with the degradation oil in a single injection manner, and the temperature of the dilution steam is 450-650℃.

7. The method according to claim 5, wherein, The weight ratio of the degradation oil to the dilution steam is 1-4:

1.

8. The method according to claim 7, wherein, The weight ratio of the degradation oil to the dilution steam is 1.2-2.5:

1.

9. The method according to claim 5, wherein, The method further includes: preheating the degradation oil in a convection section before mixing the dilution steam with the degradation oil to obtain preheated degradation oil.

10. The method according to claim 9, wherein, The temperature of the preheated degradation oil is 180-400℃.

11. The method according to claim 10, wherein, The temperature of the preheated degradation oil is 180-350℃.

12. The method according to claim 1, wherein, The dilution vapor is mixed with the degradation oil in a two-stage injection process.

13. The method according to claim 12, wherein, The two-stage injection methods include: (1-1) Mix high-temperature steam with the degradation oil to dilute and preheat the degradation oil; (1-2) Further heat the mixture of ultra-high temperature steam and step (1-1); The temperature of the high-temperature steam is 150-450℃; The temperature of the ultra-high temperature steam is 400-700℃.

14. The method according to claim 13, wherein, The weight ratio of the high-temperature steam to the degradation oil is 0.3-1:1; And / or, the weight ratio of the ultra-high temperature steam to the degradation oil is 0.2-0.6:1; And / or, the temperature of the high-temperature steam is 180-400°C; And / or, the temperature of the ultra-high temperature steam is 450-650°C.

15. The method according to claim 13, wherein, The method further includes: contacting the degradation oil with a hydrogenation catalyst to carry out a hydrogenation reaction, obtaining a hydrogenated fraction of the degradation oil, and then sending it into a steam cracking furnace.

16. The method according to claim 15, wherein, The conditions for the hydrogenation reaction include: a reaction temperature of 200-400℃; a reaction pressure of 2-4MPa; and a hydrogen-to-oil ratio of 100-400:

1.

17. The method according to claim 16, wherein, The conditions for the hydrogenation reaction include: a reaction temperature of 250-350℃; a reaction pressure of 2.5-3.5MPa; and a hydrogen-to-oil ratio of 150-350:

1.

18. The method according to any one of claims 1-17, wherein, The method also includes separating the products after steam cracking to obtain low-carbon olefins.

19. The application of the method according to any one of claims 1-18 in the preparation of olefins.

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