Treatment system and application of waste materials

Abstract

The application relates to the field of plastic and rubber recycling, and discloses a waste material processing system and application, wherein the processing system comprises a pyrolysis reactor and a steam cracking furnace which are sequentially connected in a material flow direction; the waste material comprises waste plastics and / or waste rubber; the steam cracking furnace comprises a convection section and a radiation section which are connected in series; the pyrolysis reactor is used for pyrolysis or catalytic cracking of the waste material to obtain degradation oil; the convection section is used for contact of the degradation oil with steam and heating to a transverse temperature, and the convection section can make the transverse temperature be 280-500 DEG C lower than the cracking temperature of the radiation section. The processing system can realize degradation of the waste material through a chemical recycling method, the degradation oil is used as a cracking raw material or is treated through a hydrogenation process and then used as a cracking raw material to prepare low-carbon olefins through steam cracking, meanwhile, the steam cracking process is not prone to coking, and the production efficiency is high.

Description

Technical Field

[0001] This invention relates to the field of waste material recycling, and specifically to a waste material processing system and its application. Background Technology

[0002] Due to its excellent properties, plastic products have gradually become one of the most important and widely used materials in the world since their invention. According to statistics, from 1950 to 2018, the global total production of plastics was approximately 8.3 billion tons, and it increased at an annual growth rate of 5%. However, about 76% of the total plastic production eventually became waste. The accumulation of large amounts of waste plastics in landfills and even the natural environment has caused serious white pollution and even ecological disasters.

[0003] Currently, the main methods for treating waste plastics include landfilling or discharge into the natural environment (72%), incineration (14%), and recycling (14%). However, these crude recycling methods still cause problems such as land and air pollution. Chemical recycling and chemical cycle methods are currently considered the only sustainable method for recycling waste plastics. This method refers to the technology of converting waste plastics into smaller molecules (usually gases or liquids), which can be further used to produce petrochemical products or plastic raw materials. Domestic and foreign companies have developed a series of pyrolysis technologies for waste plastics or waste tires, generating degradation oils from waste plastics / waste tires. However, most of these degradation oils are directly burned as raw materials. CN113502174A discloses a method for directly preparing aviation gasoline and aviation kerosene from waste polyolefin plastics. This method employs a bifunctional catalyst composed of a precious metal and an inorganic solid acid, achieving a coupling of hydrogenation degradation and isomerization reactions of high-molecular-weight polyolefin plastics. This one-step continuous process produces high-value oil products from polyolefin plastics with a conversion rate of approximately 99%, of which aviation fuel accounts for as much as 80%. CN1613972A discloses a method for degrading polypropylene waste plastics to produce fuel oil. The method involves using a water filling rate of 20-40%, with water and polypropylene... Waste polypropylene plastics are added to a reactor at a weight ratio of 1-10:1. Under a nitrogen atmosphere, the reaction temperature is increased to 380-450℃ at a heating rate of 10-15℃ / min, and the reaction pressure is increased to 30-48MPa. The reaction is carried out for 1-60 minutes, cooled to room temperature, and the gas-liquid products are separated. The liquid-phase oil-water emulsion is extracted with tetrahydrofuran for oil-water separation. The separated tetrahydrofuran-soluble matter is added to anhydrous Na2SO4 to remove trace amounts of water. The tetrahydrofuran-extracted oil is then subjected to rotary evaporation at atmospheric pressure and 0-70℃ to obtain fuel oil.

[0004] Waste plastics and waste tires contain approximately 13.5% hydrogen, making them a very valuable resource given the current scarcity of fossil fuels. Therefore, the recycling of 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 existing technologies, such as the lack of effective chemical recycling methods for waste plastics and waste rubber, and the low added value of by-products after recycling. This invention provides a waste material treatment system and its application. This system can efficiently and greenly recycle waste plastics or waste rubber to obtain low-carbon olefins. The system has a high online rate and high production efficiency.

[0006] To achieve the above objectives, the present invention provides a waste material treatment system, the system comprising a pyrolysis reactor and a steam cracking furnace connected sequentially along the material flow direction;

[0007] The waste materials include waste plastics and / or waste rubber;

[0008] The steam pyrolysis furnace includes a convection section and a radiation section connected in series.

[0009] The pyrolysis reactor is used to thermally or catalytically crack waste materials to obtain degraded oil.

[0010] The convection section is used to contact the degradation oil with steam and heat it to a cross temperature, which allows the cross temperature to be 280-500°C lower than the pyrolysis temperature of the radiation section.

[0011] A second aspect of the present invention provides the application of a processing system in the recycling and processing of waste materials.

[0012] Effective chemical recycling methods for waste plastics and rubber are lacking. Currently, most common chemical recycling processes for waste plastics and tires focus on single-product recycling, such as the degradation of PE and PP, and the hydrolysis or alcoholysis of PET. However, in reality, waste polymer products are difficult to sort and screen, making single-product processing impossible. The materials typically requiring processing include mixtures of plastics, rubber, and fibers. While thermal degradation of waste polymer materials can treat mixed materials, the resulting degradation oil is mostly used as fuel oil, resulting in low added value. The inventors of this invention have creatively proposed a scheme for the chemical recycling of waste plastics or rubber to prepare low-carbon olefins, achieving efficient and green recycling of waste plastics or rubber with a high online rate and high production efficiency.

[0013] When the degradation oil obtained from waste plastics and / or waste rubber through thermal cracking or catalytic cracking is used as a cracking feedstock for steam cracking to produce olefins, the steam cracking furnace (especially the convection section) is prone to coking. The waste material treatment system provided by this invention effectively reduces the amount of coking in the convection section and effectively improves production efficiency and output.

[0014] By using chemical recycling methods to degrade waste plastics or waste rubber to obtain degradation oil, this degradation oil can be used directly as a pyrolysis feedstock or processed through hydrogenation to be used as a pyrolysis feedstock for steam cracking to produce low-carbon olefins. This method has high production efficiency and high online rate, providing a brand-new way to recycle and process waste plastics or waste rubber, and realizing the resource reuse of waste plastics or waste rubber. 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. 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 the present invention provides a waste material treatment system, the treatment system comprising a pyrolysis reactor and a steam cracking furnace connected sequentially along the material flow direction;

[0028] The waste materials include waste plastics and / or waste rubber;

[0029] The steam pyrolysis furnace includes a convection section and a radiation section connected in series.

[0030] The pyrolysis reactor is used to thermally or catalytically crack waste materials to obtain degraded oil.

[0031] The convection section is used to contact the degradation oil with steam and heat it to a cross temperature, which allows the cross temperature to be 280-500°C lower than the pyrolysis temperature of the radiation section.

[0032] 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.

[0033] Meanwhile, chemical recycling and chemical cycle methods are currently considered the only sustainable way to recycle waste plastics. However, existing pyrolysis technologies for waste plastics or waste tires produce degradation oils from these waste plastics / tires, but most of these degradation oils are burned directly as raw materials, lacking effective recycling and treatment.

[0034] Degraded oils obtained from the chemical recycling of waste materials, such as waste rubber or waste plastics, are prone to coking during steam cracking. Therefore, when using these oils as feedstock for steam cracking, it is often necessary to shut down the steam cracking furnace to clean the convection section, resulting in low online efficiency when using these oils for olefin production. The inventors of this invention ingeniously discovered during their research that appropriately lowering the temperature of the convection section can reduce coking in the convection section and improve the online efficiency of the processing system.

[0035] 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, including but not limited to at least one of polyethylene, polypropylene, and polystyrene. The waste rubber can come from rubber products such as waste tires, waste gloves, and waste sponges.

[0036] In this invention, there are no special requirements for the pyrolysis reactor, as long as it can pyrolyze the waste material, breaking down the complex plastic macromolecules into smaller molecules to obtain gaseous small molecules and degraded oil. Preferably, the pyrolysis reactor is a fluidized bed reactor or a fixed bed reactor.

[0037] According to the present invention, preferably, the processing system further includes a hydrogenation reactor disposed between the pyrolysis reactor and the steam cracking furnace, for hydrogenating the degradation oil obtained from the pyrolysis reactor before feeding it into the steam cracking furnace. The degradation oil obtained from waste materials exhibits significant differences in properties due to variations in raw material composition; some lower-quality raw materials cannot be directly used as steam cracking feedstock, thus requiring hydrogenation treatment. The above-described preferred embodiment is beneficial for improving the yield of low-carbon olefins when the degradation oil is used as a steam cracking feedstock, while simultaneously mitigating the coking process of the degradation oil in the radiant section of the cracking furnace.

[0038] According to the present invention, preferably, the convection section enables the transverse temperature to be 300-450°C lower than the pyrolysis temperature of the radiation section.

[0039] According to the present invention, preferably, the convection section enables the cross temperature to be 350-500°C, more preferably 430-480°C.

[0040] In this invention, the transverse temperature refers to the radiation section inlet temperature (XOT), and the radiation section pyrolysis temperature refers to the radiation section outlet temperature (COT).

[0041] In this invention, the decrease in cross-temperature results in a lower temperature at the outlet of the convection section. Upon entering the radiation section, the material requires a longer heating time 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.

[0042] According to the present invention, preferably, the radiant section includes 2-6 passes of furnace tubes, wherein one pass of furnace tubes is provided with an enhanced heating device.

[0043] According to the present invention, preferably, the radiant section adopts a two-pass furnace tube, more 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.

[0044] According to the present invention, the enhanced heating device is used to improve the heat transfer efficiency of the first-pass furnace tubes, and any enhanced heating device capable of achieving this purpose is applicable to the present invention. According to a preferred embodiment of the present invention, the enhanced heating device strengthens the heating after the degraded oil enters the first-pass furnace tubes in the radiant section. Preferably, the enhanced heating device increases the heating at the corresponding position of the first-pass furnace tubes by 1-50% compared to when the enhanced heating device is not installed.

[0045] In this invention, to enhance the heating of the first-pass furnace tube, a heating enhancement 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 reflective 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. Preferably, the heating enhancement device includes a burner and / or a reflective enhancement element installed on the upper furnace sidewall of the first-pass furnace tube.

[0046] According to the present invention, preferably, the ratio of the inner diameter of the outlet pipe to the inner diameter of the inlet pipe of the furnace tube in the radiant section is greater than 1 and less than or equal to 2.5.

[0047] Preferably, the inner diameter of the inlet pipe is 25-70 mm, and more preferably 40-65 mm.

[0048] Preferably, the inner diameter of the outlet pipe is 45-120 mm, and more preferably 60-95 mm.

[0049] To further improve heat transfer in the radiant section, according to a preferred embodiment of the present invention, the radiant section further includes enhanced heat transfer elements installed in the furnace tube. If the radiant section already has a certain number of enhanced heat transfer elements, the heat transfer in the radiant section can be improved by increasing the number of elements or replacing them with heat transfer elements that have better enhanced heat transfer effects.

[0050] 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.

[0051] 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.

[0052] To further reduce coking in the convection section during steam pyrolysis of biodegradable oil made from waste plastics or waste rubber, according to a preferred embodiment of the present invention, the steam 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 biodegradable oil in the convection section. The present invention does not impose any particular limitations on the gasification device, as long as it can remove the unvaporized heavy components from the biodegradable 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.

[0053] In this invention, the heavy component refers to the component with a vaporization temperature > 400°C, and the light component refers to the component with an initial boiling point of around 400°C.

[0054] 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 transverse section.

[0055] In this invention, to fully utilize the heat from the high-temperature flue gas in the radiant section, the convection section of the steam pyrolysis furnace can be equipped with multiple sections for heat recovery. Preferably, the convection section can be equipped with 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. The raw material preheating section is typically used to preheat the degradation oil. 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 (such as 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, the ultra-high pressure steam superheating section, the dilution steam superheating section, the boiler feedwater preheating section, and the raw material preheating section are preferably arranged sequentially.

[0056] According to the present invention, preferably, the convection section comprises 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.

[0057] In this invention, the mixing heating section includes several sets of heating section pipe arrays for heating the degradation oil to a cross-temperature range in the convection section. There are no special requirements for the number of heating section pipe arrays, as long as the aforementioned cross-temperature range requirement can be achieved.

[0058] To further improve heat transfer in the first-pass section of the radiant section, the radiant section tubes of the steam cracking furnace can be divided into several large groups, each group comprising several multi-pass tubes. During the arrangement of the radiant section tubes, the first-pass tubes within the same large group are arranged together. Radiant heat transfer to the first-pass tubes is increased within the radiant section from the inlet to the upper third of its height.

[0059] Preferably, the radiant furnace tubes are arranged vertically in the radiant section.

[0060] A second aspect of the present invention provides the application of the above-described processing system in the recycling and processing of waste materials.

[0061] Preferably, the application includes: in the treatment system, pyrolyzing or catalytically degrading waste materials to obtain degraded oil, the degraded oil being hydrogenated in a hydrogenation reactor, and the resulting hydrogenated degraded oil being mixed with steam in the convection section and heated to the cross temperature, and then entering the radiation section for steam cracking reaction to obtain low-carbon olefins.

[0062] The waste materials include waste plastics and / or waste rubber; there are no special requirements for the source of the waste plastics or waste rubber, which can come from any polymer-synthesized waste plastics or waste rubber.

[0063] The processing system is the aforementioned waste material processing system, comprising a pyrolysis reactor and a steam cracking furnace connected sequentially along the material flow direction.

[0064] Preferably, the processing system further includes a hydrogenation reactor disposed between the pyrolysis reactor and the steam cracking furnace, for hydrogenating the degradation oil obtained from the pyrolysis reactor before feeding it into the steam cracking furnace.

[0065] According to the present invention, applying the above-described processing system to waste material recycling can recycle waste plastics and / or waste rubber to prepare low-carbon olefins, which is beneficial to the resource utilization of waste materials.

[0066] 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, including but not limited to at least one of polyethylene, polypropylene, and polystyrene. The waste rubber can come from rubber products such as waste tires, waste gloves, and waste sponges.

[0067] Preferably, the catalytic cracking includes: contacting waste materials with a catalytic cracking catalyst under catalytic cracking reaction conditions to obtain degraded oil.

[0068] In this invention, the waste material is subjected to thermal or catalytic cracking to break down complex plastic macromolecules into smaller molecules, yielding gaseous small molecules and degraded oil. There are no particular limitations on the specific methods and conditions for the thermal or catalytic cracking; conventional methods known in the art can be used. Preferably, the waste material is subjected to catalytic cracking. Preferably, the conditions for catalytic cracking include: a reaction temperature of 100-500℃, more preferably 200-450℃; a reaction pressure of 0.1-10 MPa, more preferably 0.1-5 MPa; and a mass hourly space velocity (HHSV) of 100-2000 h⁻¹ for the waste material. -1 Preferably 300-2000h -1 Catalytic cracking catalysts in catalytic cracking processes are generally noble metal catalysts, such as noble metal-supported molecular sieve catalysts.

[0069] Preferably, the conditions for the thermal pyrolysis include: a reaction temperature of 300-700℃ and a reaction pressure of 0.1-5MPa.

[0070] According to the present invention, preferably, the application further includes: increasing the heating supply to a portion of the furnace tube in the radiant section; the method of increasing the heating supply may include setting up a heat transfer enhancement element in the radiant section and / or setting up a heat supply enhancement device in the radiant section, the specific heat transfer enhancement element and / or heat supply enhancement device being as described above, and will not be repeated here.

[0071] According to the present invention, the enhanced heating device is used to improve the heat transfer efficiency of the first-pass furnace tubes, and any enhanced heating device capable of achieving this purpose is applicable to the present invention. According to a preferred embodiment of the present invention, the enhanced heating device strengthens the heating after the degraded oil enters the first-pass furnace tubes in the radiant section. Preferably, the enhanced heating device increases the heating at the corresponding position of the first-pass furnace tubes by 1-50% compared to when the enhanced heating device is not installed.

[0072] More preferably, the enhanced heating device includes a burner and / or a reflection enhancement element disposed on the side wall of the furnace chamber above the furnace tube.

[0073] 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 application 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 the convection section.

[0074] In this invention, the hydrogenation reaction can be carried out using methods conventional in the art.

[0075] The selection range of the hydrogenation catalyst is relatively wide, and any conventional catalyst capable of catalyzing hydrogenation reactions in the art can be used. The present invention does not have any particular limitation in this regard. Preferably, the hydrogenation catalyst is a noble metal catalyst, such as a Pt catalyst supported on an alumina support.

[0076] In this invention, preferably, the conditions for the hydrogenation reaction include: a reaction temperature of 200-400℃, more preferably 250-350℃; a hydrogen pressure of 1-5MPa, more preferably 2-4MPa; and a hydrogen-to-oil ratio of 100-1000:1, more preferably 100-500:1.

[0077] In this invention, there are no special limitations on the mixing method of the degradation oil and water vapor, which can be adjusted according to actual production needs. For example, the water vapor can be introduced into the convection section in one stage 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.

[0078] According to a preferred embodiment of the present invention, the water vapor is mixed with the degradation oil by a single-stage injection method, and the temperature of the water vapor is 400-600°C, preferably 450-550°C.

[0079] According to a preferred embodiment of the present invention, the weight ratio of the degradation oil to water vapor is 1-4:1, preferably 1.2-2.5:1.

[0080] 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 water vapor with the degradation oil in the convection section. This two-stage injection method involves injecting water vapor into the convection section twice to mix with the degradation oil: first, a water vapor injection is performed to dilute and preheat the degradation oil; then, a second water vapor injection is performed to mix the diluted degradation oil with high-temperature steam, which is then heated to a suitable temperature before being sent to the radiation section.

[0081] Preferably, the two-stage injection method includes:

[0082] (1) Mix high-temperature steam with the degradation oil to dilute and preheat the degradation oil;

[0083] (2) Mix the ultra-high temperature steam with the product of step (1).

[0084] More preferably, the temperature of the high-temperature steam is 300-500℃, more preferably 350-450℃, and even more preferably 380-420℃.

[0085] More preferably, the temperature of the ultra-high temperature steam is 500-700℃, and more preferably 550-600℃.

[0086] According to a preferred embodiment of the present invention, the method further includes: preheating the degradation oil in a convection section before mixing the water vapor with the degradation oil to obtain the preheated raw material.

[0087] Preferably, the temperature of the preheated raw material is 150-350℃, more preferably 200-300℃.

[0088] Preferably, the weight ratio of the degradation oil to the high-temperature steam is 1.2-2:1.

[0089] Preferably, the weight ratio of the product of step (1) to the amount of ultra-high temperature steam used is 4-10:1, based on the mass of the degraded oil.

[0090] According to a preferred embodiment of the present invention, the conditions for the steam cracking reaction include: the outlet temperature of the radiation section is 750-850°C, preferably 790-840°C.

[0091] 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.

[0092] Preferably, the reacted materials are cooled and separated in a quench boiler.

[0093] In this invention, the application 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 the 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 the 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 the flue gas traversing section.

[0094] The present invention will be described in detail below through embodiments.

[0095] Example 1

[0096] The processing system used includes a pyrolysis reactor and a steam cracking furnace connected sequentially along the material flow direction.

[0097] The pyrolysis reactor is a tubular fixed-bed reactor; the steam pyrolysis furnace is as follows: Figure 1 As shown, it 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 cracking 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 2 In the steam cracking furnace, high-pressure steam from the steam drum is heated by the ultra-high-pressure steam superheating section 14 to produce high-pressure steam 10. The separated high-pressure steam can enter the convection section for heating. Degradable oil 7 enters the convection section, is preheated in the raw material 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. Steam 9 is preheated by the dilution steam superheating section 13 and then mixed with the preheated degradable oil. The degradable 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 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 steam cracking products to the quench boiler for cooling and separation to obtain low-carbon olefins.

[0098] Among them, the radiant furnace tube 3 adopts a two-pass 2-1 type furnace tube, the inner diameter of the furnace tube inlet pipe is 49mm, the length of the inlet pipe is 13.5m; the inner diameter of the furnace tube outlet pipe is 71mm, the length of the outlet pipe is 13.5m, and the ratio of the inner diameter of the outlet pipe to the inner diameter of the inlet pipe of the radiant section furnace tube is 1.45.

[0099] The specific processing method is as follows:

[0100] (1) Waste plastic degradation oil was obtained by catalytic degradation of waste plastics using a tubular fixed-bed reactor. The waste plastics consisted of a mixture of polyethylene, polypropylene, and polystyrene as the main components, with a mass ratio of 40:30:20, and the remaining waste plastics accounted for 10 wt%. The waste plastic degradation oil was obtained by catalytic cracking using ZSM-5 catalyst supported on 0.3 wt% Pt. The reaction temperature was 430℃, the reaction pressure was 0.6 MPa, and the mass hourly space velocity (MSV) was 300 h⁻¹. -1 The oil yield was 82%. The properties of the degradation oil obtained under these conditions are shown in Table 1.

[0101] (2) The degradation oil is introduced into the pyrolysis furnace by a secondary gas injection method. In the convection section 2, the degradation oil at 60°C is mixed with high-temperature steam at 400°C for dilution and preheating. The weight ratio of degradation oil to high-temperature steam is 1.8:1. The preheated degradation oil is at 180°C. Then, ultra-high temperature steam at 600°C is injected. The weight ratio of degradation oil to ultra-high temperature steam is 4.5:1. After being heated to the cross temperature, it enters the radiant furnace tube 3 for steam pyrolysis reaction.

[0102] The preheating temperature of the raw material in the convection section, i.e., the cross temperature (XOT) of the steam pyrolysis furnace, is 450℃. The outlet temperature (COT) of the radiant section of the steam pyrolysis furnace is 790℃. That is, the cross temperature is 340℃ lower than the pyrolysis temperature of the radiant section. Other process parameters of the steam pyrolysis furnace are shown in Table 2 (where XOT is the inlet temperature of the radiant section, COT is the outlet temperature of the radiant section, XOP is the inlet pressure of the radiant section, and COP is the outlet pressure of the radiant section). The main components of the steam pyrolysis products are shown in Table 3.

[0103] As shown in Table 2, in this embodiment, the processing system operates on a 65-day cycle, with online coking occurring four times a year, each coking session lasting two days. In this embodiment, the material's cross-temperature was reduced, which effectively decreased the pyrolysis reaction within the convection section and reduced coking, eliminating the need for convection section decoking and thus extending the online time.

[0104] Comparative Example 1

[0105] The same processing system as in Example 1 is used, except that the radiant furnace tube 3 is a two-pass 2-1 type furnace tube. The inner diameter of the inlet tube is 51 mm and the length of the inlet tube is 12.8 m; the inner diameter of the outlet tube is 73 mm and the length of the outlet tube is 12.8 m. The ratio of the inner diameter of the outlet tube to the inner diameter of the inlet tube in the radiant section is 1.43.

[0106] (1) Perform the same operation as in Example 1.

[0107] (2) In the convection section 2, the degradation oil at 60°C is mixed with high-temperature steam at 400°C for dilution and preheating. The weight ratio of degradation oil to high-temperature steam is 1.8:1. The preheated degradation oil is at 180°C. Then, ultra-high temperature steam at 600°C is injected. The weight ratio of degradation oil to ultra-high temperature steam is 4.5:1. After heating to the cross temperature, it enters the radiant furnace tube 3 for steam cracking reaction. The preheating temperature of the raw material in the convection section, i.e., the cross temperature (XOT) of the steam cracking furnace, is 520°C. The outlet temperature (COT) of the radiant section of the steam cracking furnace is 790°C. That is, the cross temperature is 270°C lower than the cracking temperature of the radiant section. Other process parameters of the steam cracking furnace are shown in Table 1, and the main components of the cracking products are shown in Table 2.

[0108] As can be seen from Table 1, the processing system 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.

[0109] A comparison of Example 1 and Comparative Example 1 shows that Example 1 reduces the heat exchange between the raw material and steam mixture and the flue gas in the mixing heating section, thereby lowering the material cross temperature. The cross temperature is 340°C lower than the pyrolysis temperature, effectively reducing coking in the convection section compared to Comparative Example 1. To ensure that the raw material receives sufficient heat in the radiation section, the lengths of the inlet and outlet pipes of the radiation furnace tube 3 were increased by 0.7 meters each.

[0110] The comparison shows that, compared to Comparative Example 1, Example 1's processing system had 9 more days of online time and significantly increased product output within one year, with an increase of 3,796 tons in triene products alone. Based on a product price of 7,000 RMB / ton, this translates to an increase in revenue of 26.57 million RMB from triene products alone. Furthermore, compared to Comparative Example 1, Example 1 also saved substantial start-up, shutdown, and maintenance costs.

[0111] Example 2

[0112] 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 3The 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 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.

[0113] Specific handling methods:

[0114] (1) Perform the procedure as described in Example 1.

[0115] (2) In convection section 2, 60°C degradation oil is mixed with 400°C high-temperature steam for dilution and preheating. The weight ratio of degradation oil to high-temperature steam is 2:1, and the preheated degradation oil temperature is 220°C. Then, 550°C high-temperature steam is injected, with a weight ratio of degradation oil to high-temperature steam of 4.5:1. After heating to the cross temperature, it enters the radiant furnace tube 3 for steam cracking reaction. The degradation oil is preheated in the convection section and then heated to the cross temperature (XOT) of 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, which increases the heat transfer coefficient of the installation part by 500% compared to the bare tube. Other process parameters of the steam cracking furnace are shown in Table 2, and the main components of the cracking products are shown in Table 3.

[0116] 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 in 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 yield and charring cycle in the radiant section.

[0117] Example 3

[0118] The processing system includes a pyrolysis reactor, a hydrogenation reactor, and a steam cracking furnace connected sequentially along the material flow direction.

[0119] (1) The degradation oil obtained in Example 1 was hydrogenated in a hydrogenation reactor and then entered a steam cracking furnace. The hydrogen-to-oil ratio was 300:1, the reaction pressure was 3.5 MPa, the reaction temperature was 330 °C, and the hydrogenation catalyst used was 3 wt% Pt-Al2O3. The basic properties of the degradation oil of waste plastic and the fraction after hydrogenation of the degradation oil are compared in Table 1.

[0120] (2) The main components of the pyrolysis product obtained according to step (2) in Example 1 are shown in Table 3.

[0121] Table 1

[0122]

[0123]

[0124] Table 2

[0125] Operation period Example 1 Comparative Example 1 Example 2 Example 3 Feed rate (kg / h) 58000 58000 58000 58000 Dilution steam volume (kg / h) 40600 40600 40600 40600 XOT(°C) 450 520 430 450 COT(°C) 790 790 790 790 XOP(MPa, G) 0.12 0.12 0.12 0.12 COP(MPa, G) 0.08 0.08 0.08 0.08 Coking cycle of the radiant section (days) 65 60 65 65

[0126] Table 3

[0127] product Example 1 Comparative Example 1 Example 2 Example 3 Hydrogen (wt%) 0.49％ 0.48％ 0.48％ 0.52％ Ethylene (wt%) 21.42％ 21.40％ 21.41％ 22.63％ Propylene (wt%) 12.16％ 12.15％ 12.16％ 12.45％ Butadiene (wt%) 4.40％ 4.38％ 4.40％ 4.56％

[0128] 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. An application of a waste material processing system in the recycling and treatment of waste materials, characterized in that, The processing system includes a pyrolysis reactor and a steam pyrolysis furnace connected sequentially along the material flow direction; The waste materials include waste plastics and / or waste rubber; The steam pyrolysis furnace includes a convection section and a radiation section connected in series. The pyrolysis reactor is used to thermally or catalytically crack waste materials to obtain degraded oil. The convection section is used to contact the degradation oil with steam and heat it to a cross temperature, which is 340-500°C lower than the pyrolysis temperature of the radiation section; the convection section is also used to make the cross temperature 350-430°C.

2. The application according to claim 1, wherein, The pyrolysis reactor is a fluidized bed reactor or a fixed bed reactor; And / or, the processing system further includes a hydrogenation reactor disposed between the pyrolysis reactor and the steam cracking furnace, for hydrogenating the degradation oil obtained from the pyrolysis reactor before feeding it into the steam cracking furnace.

3. The application according to claim 1, wherein, The radiant section includes 2-6 passes of furnace tubes, one of which is equipped with an enhanced heating device. The enhanced heating device strengthens the heating after the degraded oil enters the radiant section furnace tube; And / or, the enhanced heating device includes a burner and / or a reflective enhancement element disposed on the furnace sidewall above a pass furnace tube.

4. The application according to claim 3, wherein, The radiant section uses two-pass furnace tubes.

5. The application according to claim 4, wherein, The two-stage furnace tubes are either type 2-1 radiant furnace tubes or type 4-1 radiant furnace tubes.

6. The application according to claim 3, wherein, The enhanced heating device increases the heating supply to the corresponding position of the furnace tube by 1-50% compared to when the enhanced heating device is not installed.

7. The application according to claim 3, wherein, The ratio of the inner diameter of the outlet pipe to the inner diameter of the inlet pipe of the furnace tube in the radiant section is greater than 1 and less than or equal to 2.

5.

8. The application according to claim 7, wherein, The inner diameter of the inlet pipe is 25-70mm; And / or, the inner diameter of the outlet pipe is 45-120 mm.

9. The application according to claim 8, wherein, The inner diameter of the inlet pipe is 40-65mm; And / or, the inner diameter of the outlet pipe is 60-95mm.

10. The application according to claim 1, wherein, The radiant section also includes enhanced heat transfer elements installed in the furnace tubes.

11. The application according to claim 10, wherein, The enhanced heat transfer element increases the heat transfer coefficient of the part of the furnace tube where the enhanced heat transfer element is installed by 50-800% compared to the bare tube.

12. The application according to claim 1, wherein, The convection section is also equipped with a gasification separation device, which is used to remove unvaporized heavy components from the degradation oil in the convection section.

13. The application according to claim 1, wherein, The steam pyrolysis furnace also includes a high-pressure steam drum, a combustion system, and a quench boiler.

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