Apparatus and method for producing low carbon olefins by coupling hydrocarbon oil and steam cracking

Abstract

The application provides a device for coupling steam cracking of hydrocarbon oil to produce low-carbon olefins, which is characterized in that two radiation sections are arranged, and two-stage steam cracking is performed on heavy hydrocarbon oil and one-stage steam cracking is performed on light hydrocarbon oil, so that the coupling steam cracking of light and heavy hydrocarbon oils can be realized, the cracking capacity for heavy hydrocarbon oil can be effectively improved, the consumption of dilution steam for cracking light hydrocarbon oil is reduced, the total low-carbon olefin yield of the raw materials is improved, and the device is flexible and convenient to operate, has low investment cost and occupies less land.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steam cracking in petrochemical industry, and in particular to a device and method for producing low-carbon olefins by coupling hydrocarbon oil with steam cracking. BACKGROUND

[0002] Low-carbon olefins, represented by ethylene, are important chemical raw materials and play an important role in the national economy. With the continuous expansion of the production capacity of ethylene cracking units, the supply of ethylene cracking raw materials is showing a trend of shortage. In order to make up for this problem, the ethylene cracking raw materials are gradually developing towards heavy and diversified. In addition, in view of the serious overcapacity of oil refining, the unreasonable oil product structure, and the insufficient high-end production capacity to meet market demand, the transformation of oil refining enterprises from "fuel type" to "chemical type" has become a general trend. Among them, the technology of producing low-carbon olefins from diesel and other middle distillate oils as raw materials has become an important measure to promote the transformation and upgrading of refining structure, increase chemical production and reduce oil production in the refining industry, and promote the green, low-carbon and sustainable development of the industry.

[0003] At present, about 98% of the world's ethylene production process adopts tubular furnace steam cracking process. As a traditional technology for producing ethylene, steam cracking uses ethane, C3, C4, light hydrocarbon, naphtha, hydrogenated tail oil and other hydrocarbons as raw materials, has a high ethylene yield, and produces basic chemical raw materials such as propylene, butadiene, benzene, toluene, xylene, C5 and C9, which plays an important role in petrochemical industry. Using steam cracking technology to process excess diesel and other intermediate distillate oil products from oil refining will solve the problems of excess diesel and shortage of ethylene raw materials, and promote the transformation of fuel diesel to high-value chemical products. However, due to the coking tendency of diesel and other heavier hydrocarbon oils at high temperatures, catalytic cracking or special treatment followed by steam cracking is often used to realize the production of low-carbon olefins, which cannot be cracked simultaneously in the same device, resulting in a long and complicated process, and even the need for other special devices and catalysts, increasing the device occupation, and increasing the operating cost and investment.

[0004] For example, Chinese patent document CN201510710907.1 discloses a combined process of catalytic cracking of heavy petroleum hydrocarbons and steam cracking of light petroleum hydrocarbons, which utilizes the advantage of strong adaptability of catalytic cracking device to raw materials to preferentially process heavy petroleum hydrocarbons, and then uses a steam cracking device to further convert the light petroleum hydrocarbons generated in the catalytic cracking process into low-carbon olefins and other products. This method takes advantage of the respective advantages of the two sets of devices, and can maximize the conversion of heavy petroleum hydrocarbons to low-carbon olefins, improving the utilization rate of raw materials. However, due to the coking tendency of diesel and other heavier hydrocarbon oils at high temperatures, catalytic cracking or special treatment followed by steam cracking is often used to realize the production of low-carbon olefins, which requires other device investment.

[0005] CN201811508969.4 discloses a treatment method for straight-run diesel oil. To improve the utilization rate of straight-run diesel oil, the method first performs solvent extraction or adsorption separation de-aromatization treatment on the straight-run diesel oil, performs steam cracking treatment on the obtained de-aromatization component to obtain an olefin product, and performs hydro-upgrading or aromatic hydrogenation lightening treatment on the obtained aromatic-rich component to obtain a modified product. The method can more effectively improve the cracking capacity and cracking efficiency of the steam cracking device, and realizes comprehensive optimization and utilization of the aromatic-rich component and the de-aromatization component. However, the processing process in the method is long and complicated, and even requires other special devices and their matching catalysts, increasing the operation cost and investment.

[0006] CN202011136718.5 discloses a production method for ethylene steam cracking raw material. The method is aimed at gasoline-diesel mixed oil raw material, and separates the gasoline-diesel mixed oil into naphtha fraction and diesel fraction by flash separation. The naphtha fraction is used as ethylene cracking raw material after hydrogenation desulfurization, denitrification and olefin saturation reaction. The diesel fraction is used as ethylene cracking raw material after deep hydrogenation desulfurization, denitrification reaction, selective hydrogenation saturation and ring-opening reaction of polycyclic aromatic hydrocarbons. However, the processing process in the method is long and complicated, and even requires other special devices and their matching catalysts, increasing the operation cost and investment.

[0007] CN202110668660.7 discloses a method for producing low-carbon olefins by steam cracking of coal-based Fischer-Tropsch synthetic oil. To solve the problem of future ethylene raw material sources, the method performs hydrofining and hydrocracking treatment on coal-based Fischer-Tropsch synthetic oil to obtain high-quality naphtha or straight-run diesel oil, and then performs steam cracking on the naphtha or straight-run diesel oil. The cracking product has high ethylene and propylene yield. Although the method can expand the source of cracking raw material, the content of straight-chain hydrocarbons in Fischer-Tropsch synthetic oil is high, and the added value of Fischer-Tropsch synthetic oil itself is high. In addition, when Fischer-Tropsch synthetic oil is used as steam cracking raw material, naphtha and straight-run diesel oil need special cracking conditions, and cannot be cracked in the same device at the same time, increasing the device occupation.

[0008] In view of the above problems, the Chinese patent document CN202010556727.3 discloses a steam cracking simulation test device for producing olefins, which adopts a three-stage cracking reaction system. Water is introduced into the convection section, and the heat of the cracking reaction system is used for heating and vaporization, thereby saving energy. The cracking raw material is introduced into the cross section and the radiation section, and the mixing and preheating process and the reaction process of the cracking raw material and water vapor are carried out in stages, so that the process conditions of the cracking reaction process can be flexibly controlled, different types of cracking raw material feed can be met, different ethylene steam cracking furnace types can be truly simulated, and raw material cracking evaluation data can be provided for steam cracking industrial furnaces. However, this method can only evaluate one kind of raw material at a time, and cannot realize simultaneous feeding and evaluation of light and heavy raw materials, and improve the low-carbon olefin yield of heavy raw materials. SUMMARY

[0009] Therefore, the present application provides a device for producing low-carbon olefins by coupling steam cracking of hydrocarbon oils, which can realize coupling steam cracking of light and heavy hydrocarbon oils in the same cracking reaction furnace tube, improve the cracking capacity of heavy raw material hydrocarbon oils, reduce the consumption of light raw material cracking dilution steam, and improve the overall low-carbon olefin yield of the raw materials.

[0010] To this end, the present application provides the following technical solutions:

[0011] A device for producing low-carbon olefins by coupling steam cracking of hydrocarbon oils, comprising a feeding system, a cracking reaction system and a cooling and separation system connected in sequence;

[0012] The feeding system comprises at least one light raw material pipeline and at least one heavy raw material pipeline, each light raw material pipeline is connected with a water pipeline, and each heavy raw material pipeline is connected with a water pipeline; preferably, each light raw material pipeline is connected in parallel with the corresponding water pipeline, and each heavy raw material pipeline is connected in parallel with the corresponding water pipeline;

[0013] The cracking reaction system comprises a first convection section and a second convection section, and a first cross section, a first radiation section, a second cross section and a second radiation section connected in sequence;

[0014] The inlet of the first convection section is connected with the outlet of the first water pipeline, and the outlet of the first convection section and the outlet of the heavy raw material pipeline are respectively connected with the inlet of the first cross section; the inlet of the second convection section is connected with the outlet of the second water pipeline, and the outlet of the second convection section and the outlet of the light raw material pipeline are respectively connected with the inlet of the second cross section;

[0015] The outlet of the second radiation section is connected with the cooling and separation system.

[0016] Optionally, in the device for producing low-carbon olefins by hydrocarbon oil coupled steam cracking provided by the present application, the first convection section and the second convection section are arranged in parallel or arranged in an up-down manner.

[0017] The first convection section and the second convection section are respectively composed of a plurality of U-shaped tubes arranged in a transverse series connection. The number of U-shaped tubes in the first convection section and the second convection section can be adjusted according to actual conditions.

[0018] Optionally, in the device for producing low-carbon olefins by hydrocarbon oil coupled steam cracking provided by the present application, the first cross section and the second cross section are respectively one U-shaped tube arranged in a longitudinal manner; preferably, the length ratio of the U-shaped tube in the first cross section to the U-shaped tube in the second cross section is 1:0.8-1.2.

[0019] Optionally, in the device for producing low-carbon olefins by hydrocarbon oil coupled steam cracking provided by the present application, the first radiation section and the second radiation section are respectively composed of U-shaped tubes arranged in a longitudinal series connection; preferably, the number of U-shaped tubes in the first radiation section is 1-3, and the number of U-shaped tubes in the second radiation section is 3-7.

[0020] In the device for producing low-carbon olefins by hydrocarbon oil coupled steam cracking provided by the present application, the length of each U-shaped tube in the first radiation section and / or the second radiation section is not specifically limited. Since the purpose of the cross section is to mix water and oil products, cooling will be generated in the mixing process. In order to promote the mixing and preheating effect of the cracking raw material and water vapor, the length of the U-shaped tube in the first cross section and / or the second cross section can be appropriately lengthened. However, if the device can ensure the heating efficiency, the length of the U-shaped tube in the first cross section and / or the second cross section can be appropriately shortened. Preferably, the length of each U-shaped tube in the first radiation section and / or the second radiation section is 0.7-0.9 times the length of the U-shaped tube in the first cross section and / or the second cross section.

[0021] Optionally, in the device for producing low-carbon olefins by hydrocarbon oil coupled steam cracking provided by the present application, at least one inlet for introducing gas is further arranged on the heavy raw material pipeline. The gas is introduced from the inlet and enters the cracking reaction system through the inlet of the first cross section, so as to purge the residual steam cracking raw material in the pipeline of the cracking reaction system and perform decoking.

[0022] Optionally, in the device for producing low-carbon olefins by hydrocarbon oil coupled steam cracking provided by the present application, in the feeding system, the light raw material pipeline is connected with a light raw material tank; the heavy raw material pipeline is connected with a heavy raw material tank; in the water pipeline, a first water pipeline is connected with a heavy raw material dilution water tank, and a second water pipeline is connected with a light raw material dilution water tank. The materials in the heavy raw material dilution water tank and the light raw material dilution water tank are both conveyed by a metering pump, and the conveying quality is calculated by a tank bottom metering scale.

[0023] Optionally, in the device for producing low-carbon olefins by coupling hydrocarbon oil with steam cracking provided by the present application, the cooling and separating system can adopt conventional cooling and separating devices in the industry, for example, the following cooling and separating system can be selected: a first quenching pipe, a second quenching pipe, a cooling collection tank, a cooling backflow pipe, a cryogenic collection tank, a cryogenic backflow pipe, a system pressure regulating device, a buffer tank and a wet gas flow meter are sequentially connected through pipelines.

[0024] Optionally, in the above cooling and separating system, the first quenching pipe, the second quenching pipe, the cooling collection tank, the cooling backflow pipe, the cryogenic collection tank and the cryogenic backflow pipe are all shell coolers; the front end of the first quenching pipe is communicated with the U-shaped pipe of the second radiation section, and the temperature of the high-temperature cracking product output from the U-shaped pipe of the second radiation section can be rapidly reduced to 40-70°C after being cooled by the first quenching pipe and the second quenching pipe; the temperature of the cracking product from the second quenching pipe can be reduced to 20-40°C after being cooled by the cooling collection tank and the cooling backflow pipe; the temperature of the cracking product can be further reduced to 0-5°C by the cryogenic collection tank and the cryogenic backflow pipe.

[0025] Optionally, in the above cooling and separating system, the buffer tank contains water, and the gas-phase cracking product is buffered and humidified in the buffer tank before entering the wet gas flow meter for gas flow metering.

[0026] The present application also provides a method for producing low-carbon olefins by coupling hydrocarbon oil with steam cracking, which adopts the device for producing low-carbon olefins by coupling hydrocarbon oil with steam cracking described above, and comprises the following steps:

[0027] Preheating: when the temperature of the entire cracking reaction system is raised to 290-310°C, water is input into the first convection section and the second convection section of the cracking reaction system through the water pipeline in the feeding system;

[0028] Cracking: after the cracking reaction system is heated to a predetermined temperature, the light feedstock output through the outlet of the light feedstock pipeline is mixed with the water vapor discharged from the outlet of the second convection section in the second cross section and then enters the second radiation section for cracking; and / or, the heavy feedstock output through the outlet of the heavy feedstock pipeline is mixed with the water vapor discharged from the outlet of the first convection section in the first cross section and then enters the first radiation section for preliminary cracking, and the preliminarily cracked material enters the second cross section and the second radiation section for cracking;

[0029] Cooling and separating: the mixture after cracking enters the cooling and separating system which reaches a predetermined temperature for cooling and separating to obtain products.

[0030] Optionally, in the preparation method of low carbon olefins by hydrocarbon oil coupled steam cracking provided by the present application, the mass flow ratio of the light feedstock output from the outlet of the light feedstock pipeline to the water output from the outlet of the second water pipeline is 1:0.45-0.55.

[0031] The mass flow ratio of the heavy feedstock output from the outlet of the heavy feedstock pipeline to the water output from the outlet of the first water pipeline is 1:0.65-0.85.

[0032] Optionally, in the preparation method of low carbon olefins by hydrocarbon oil coupled steam cracking provided by the present application, the mass flow ratio of the light feedstock output from the outlet of the light feedstock pipeline to the heavy feedstock output from the outlet of the heavy feedstock pipeline is 1:0.1-1. The light feedstock is selected from naphtha, aromatic raffinate and similar or mixed oil products, etc. The heavy feedstock is selected from normal two-line oil, normal three-line oil, reduced one-line oil and similar or mixed oil products, etc.

[0033] Optionally, in the cracking step of the preparation method of low carbon olefins by hydrocarbon oil coupled steam cracking provided by the present application, the predetermined temperature of the first convection section and the second convection section in the cracking reaction system is 500-550℃.

[0034] In the cracking step, the predetermined temperature of the first transverse section in the cracking reaction system is 480-560℃, and the predetermined temperature of the second transverse section is 560-630℃.

[0035] In the cracking step, the predetermined temperature of the first radiation section in the cracking reaction system is 700-800℃, and the predetermined temperature of the second radiation section is 810-850℃.

[0036] Optionally, in the cracking step of the preparation method of low carbon olefins by hydrocarbon oil coupled steam cracking provided by the present application, after the overall temperature of the cracking reaction system reaches the predetermined temperature of the first convection section or the second convection section, the first transverse section, the second transverse section, the first radiation section and the second radiation section are programmed to be heated, and the rate of the programmed heating is controlled to be within 10℃ / min.

[0037] Optionally, in the preparation method of low carbon olefins by hydrocarbon oil coupled steam cracking provided by the present application, the cooling separation step is divided into three steps, preferably, the first step is cooled to 40-70℃, the second step is cooled to 20-40℃, and the third step is cooled to 0-5℃.

[0038] Optionally, the preparation method of low carbon olefins by hydrocarbon oil coupled steam cracking provided by the present application comprises the following steps:

[0039] (a-1) start all cooling devices in the cooling separation system, and adjust the cooling temperature of each cooling device;

[0040] (a-2) start the cracking reaction system to directly heat the whole cracking reaction system, when the temperature of each convection section, each cross section and each radiation section in the cracking reaction system reaches about 290-310℃, start the heavy feedstock dilution water feed connected with the first water pipeline and / or the light feedstock dilution water feed connected with the second water pipeline in the feed system, and adjust the water feed flow rate to the set flow rate (which can be adjusted according to the actual situation);

[0041] (a-3) continue to heat the cracking reaction system, when the temperature of each convection section, each cross section and each radiation section in the cracking reaction system reaches the set temperature of the convection section, maintain the temperature of each convection section unchanged, and program the temperature of each cross section and each radiation section, and the programming rate is controlled to be less than or equal to 10℃ / min;

[0042] (a-4) when each cross section and each radiation section in the cracking reaction system reaches the corresponding set temperature, open the heavy feedstock pipeline connected with the heavy feedstock tank and / or the light feedstock tank connected with the light feedstock tank in the feed system to feed;

[0043] (a-5) when the pressure of each cross section and each radiation section is stable (the pressure value does not fluctuate obviously), the temperature of each cross section and each radiation section, the feed of light feedstock and heavy feedstock and water all reaches the set value, and the whole cracking reaction system can be kept stable for 5-10 min, open the drain valve at the bottom of the cooling collection tank and the cryogenic collection tank in the cooling separation system to drain the liquid phase cracking product. If it is in the experimental stage, after the liquid phase cracking product is drained, the drain valve is closed, the wet gas flow meter value is recorded, the test is started, and the gas phase cracking product discharged from the wet gas flow meter is collected and analyzed by gas chromatography;

[0044] (a-6) after the test is completed, the heavy feedstock feed and the light feedstock feed in the feed system are closed, the cumulative reading of the wet flow meter is recorded, the mass of the liquid phase cracking product in the cooling collection tank and the cryogenic collection tank in the cooling separation system is collected and measured, and the heating of the cracking reaction system is stopped;

[0045] (a-7) when the temperature of each section (convection section, cross section and radiation section) in the cracking reaction system is lower than 300℃, the heavy feedstock dilution water feed and the light feedstock dilution water feed in the feed system are closed, and all the cooling devices in the cooling separation system are stopped.

[0046] Optionally, the preparation method of low-carbon olefin by coupling hydrocarbon oil and steam cracking provided by the present application further comprises a coking step, and the coking comprises the following steps:

[0047] Under the condition of keeping all cooling devices in the cooling separation system running and the overall temperature of the cracking reaction system not lower than 300℃, the light feedstock pipeline and the heavy feedstock pipeline are closed, and nitrogen is input into the cracking reaction system and the cooling separation system through the gas inlet on the heavy feedstock pipeline for purging, so as to remove the residual steam cracking feedstock in the cracking reaction system and the cooling separation system and the carbon powder in the pipelines of the cracking reaction system and the cooling separation system, prevent the pipelines from being blocked by aggregation, then nitrogen is switched to air, and decoking is performed on the cracking reaction system.

[0048] Optionally, in the decoking step of the method for preparing low-carbon olefins by coupling hydrocarbon oil with steam cracking provided by the present application, the purging time of nitrogen is 5-20 min.

[0049] Optionally, in the decoking step of the method for preparing low-carbon olefins by coupling hydrocarbon oil with steam cracking provided by the present application, the first cross section, the second cross section, the first radiation section and the second radiation section are subjected to synchronous temperature rising decoking, and the temperature rising program is not limited, and a conventional temperature rising program in the industry can be used, for example, an experience type temperature rising program commonly used in the industry, and the specific temperature rising program can be selected as 810℃-820℃-830℃-840℃-850℃ for the first section, the second section, the third section, the fourth section and the fifth section, and the temperature rising condition of each section is determined according to the temperature drop of the last section, and after the carbon dioxide volume concentration in the decoking tail gas is lower than 0.1% under the temperature condition of the last section, the decoking is stopped.

[0050] Optionally, the decoking step (for cleaning the U-shaped furnace tube in each cross section and each radiation section in the cracking reaction system) of the method for preparing low-carbon olefins by coupling hydrocarbon oil with steam cracking provided by the present application comprises the following steps:

[0051] (b-1) under the condition of keeping all cooling devices in the cooling separation system running and keeping the temperature of each section of the cracking reaction system not lower than 300℃, closing the feeding of the heavy feedstock and the light feedstock in the feeding system, and keeping the feeding of the heavy feedstock dilution water and the light feedstock dilution water in the feeding system, and the water feeding flow rate meets the decoking requirement (can be consistent with the experimental condition, and is not lower than the design parameter of the device for decoking);

[0052] (b-2) opening the gas inlet on the heavy feedstock pipeline, inputting nitrogen, purging for 5-20 min, and removing the residual feedstock in the pipeline;

[0053] (b-3) switching the gas inlet pipeline to air, performing synchronous temperature rising program decoking on the U-shaped tube of each cross section and each radiation section, and analyzing CO and CO2 in the decoking tail gas discharged from the wet gas flow meter;

[0054] (b-4) After the charring is completed, stop heating the cracking reaction system, and after the temperature of the entire cracking reaction system is lower than 300 DEG C, close the heavy feedstock dilution water feed and the light feedstock dilution water feed in the feed system, stop all cooling devices in the cooling and separation system, and close the gas inlet pipeline on the heavy feedstock pipeline.

[0055] The device for coupling steam cracking of hydrocarbon oil to produce low-carbon olefins provided by the present application can realize coupling steam cracking of light and heavy hydrocarbon oils, has the characteristics of high yield of low-carbon olefins and convenient operation.

[0056] 1. The device for coupling steam cracking of hydrocarbon oil to produce low-carbon olefins provided by the present application can realize coupling steam cracking of light and heavy hydrocarbon oils in the cracking reaction system of the device, and has the advantages of flexible and convenient operation, low investment cost and small land occupation.

[0057] 2. The device for coupling steam cracking of hydrocarbon oil to produce low-carbon olefins provided by the present application can effectively improve the cracking capacity of heavy feedstock hydrocarbon oil, reduce the consumption of light feedstock cracking dilution steam, and improve the overall low-carbon olefin yield of the feedstock by setting two radiation sections and combining two-stage steam cracking of heavy feedstock hydrocarbon oil and one-stage steam cracking of light feedstock hydrocarbon oil. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 The device for coupling steam cracking of hydrocarbon oil to produce low-carbon olefins provided by the present application;

[0059] Figure 2 The device for coupling steam cracking of hydrocarbon oil to produce low-carbon olefins provided by the present application;

[0060] Figure 3 The device for coupling steam cracking of hydrocarbon oil to produce low-carbon olefins provided by the present application;

[0061] BRIEF DESCRIPTION OF DRAWINGS: 1, feed system; 2, cracking reaction system; 3, cooling and separation system; 11, metering scale; 12, heavy feedstock dilution water tank; 13, light feedstock dilution water tank; 14, heavy feedstock tank; 15, light feedstock tank; 16, metering pump; 17, light feedstock pipeline; 18, heavy feedstock pipeline; 19(1), first water pipeline; 19(2), second water pipeline; 4, gas pipeline; 21, second convection section; 22, first convection section; 23, first cross section; 24, first radiation section; 25, second cross section; 26, second radiation section; 31, first quenching pipe; 32, second quenching pipe; 33, cooling collection tank; 34, cooling reflux pipe; 35, cryogenic collection tank; 36, cryogenic reflux pipe; 37, system pressure regulating device; 38, buffer tank; 39, wet gas flowmeter. DETAILED DESCRIPTION

[0062] The following detailed description of the embodiments of the present application is made on the premise of the technical solutions of the present application, and detailed implementation manners and processes are given, but the protection scope of the present application is not limited to the following embodiments. The experimental methods not specified in the following embodiments are usually performed according to the conventional conditions.

[0063] The present application provides a device for producing low-carbon olefins by coupling steam cracking of hydrocarbon oil, as shown in the figure, comprising a feed system 1, a cracking reaction system 2 and a cooling and separation system 3 connected in sequence through pipelines. Figure 1

[0064] Specifically, the light feedstock pipeline 17 is in communication with the light feedstock tank 15, the heavy feedstock pipeline 18 is in communication with the heavy feedstock tank 14, and the water pipeline is in communication with the dilution water tank.

[0065] The cracking reaction system 2 comprises a first convection section 22 and a second convection section 21, and a first cross section 23, a first radiation section 24, a second cross section 25 and a second radiation section 26 connected in sequence through pipelines.

[0066] The inlet of the first convection section 22 is in communication with the outlet of the first water pipeline 19(1), and the outlet of the first convection section 22 and the outlet of the heavy feedstock pipeline 18 are respectively in communication with the inlet of the first cross section 23 (the outlet of the first convection section 22 and the outlet of the heavy feedstock pipeline 18 are combined and then communicated with the inlet of the first cross section 23, or the outlet of the first convection section 22 and the outlet of the heavy feedstock pipeline 18 are directly communicated with the inlet of the first cross section 23 respectively); the inlet of the second convection section 21 is in communication with the outlet of the second water pipeline 19(2), and the outlet of the second convection section 21 and the outlet of the light feedstock pipeline 17 are respectively in communication with the inlet of the second cross section 25.

[0067] The outlet of the second radiation section 26 is in communication with the cooling and separation system.

[0068] In an embodiment, the first convection section 22 and the second convection section 21 are arranged in parallel or arranged vertically.

[0069] In an embodiment, the first convection section 22 and the second convection section 21 are respectively composed of a plurality of U-shaped tubes connected in series transversely. Specifically, the number of U-shaped tubes in the first convection section 22 and the second convection section 21 can be adjusted according to actual conditions.

[0070] ​In an embodiment, the first cross section 23 and the second cross section 25 are both a U-shaped tube arranged longitudinally; preferably, the length ratio of the U-shaped tube of the first cross section 23 to the U-shaped tube of the second cross section 25 is 1:0.8-1.2. The first cross section 23 and the second cross section 25 are arranged to make the water vapor and the raw material mix uniformly.

[0071] In an embodiment, the first radiation section 24 and the second radiation section 26 are both composed of U-shaped tubes arranged longitudinally in series; the number of the U-shaped tubes arranged in series in each radiation section can be adjusted according to actual conditions, and the length of the U-shaped tubes arranged in series in each radiation section is the same or similar, for example, the U-shaped tubes of the first radiation section 24 can be selected as 1-3, and the U-shaped tubes of the second radiation section 26 can be selected as 3-7.

[0072] In an embodiment, the length of each U-shaped tube in the first radiation section 24 and / or the second radiation section 26 is 0.7-0.9 times the length of the U-shaped tube of the first cross section 23 and / or the second cross section 25. The material is mixed in the cross section, and there is a certain temperature drop. By arranging the U-shaped tube of the cross section to be longer than the U-shaped tube of the radiation section, slightly extending the pipe length can ensure the temperature of the material entering the radiation section.

[0073] In an embodiment, at least one gas inlet for introducing gas is further arranged on the heavy raw material pipeline 18, the gas inlet is communicated with the gas pipeline 4, the gas is introduced from the inlet and enters the cracking reaction system 2 through the inlet of the first cross section 23, for purging the residual steam cracking raw material in the pipeline of the cracking reaction system 2 and carrying out decoking.

[0074] In an embodiment, the first water pipeline 19(1) is connected with the heavy raw material dilution water tank 12, the second water pipeline 19(2) is connected with the light raw material dilution water tank 13, the materials in the heavy raw material tank 14, the light raw material tank 15, the heavy raw material dilution water tank 12 and the light raw material dilution water tank 13 are all transported by the metering pump 16, and the transported quality is calculated by the tank bottom metering scale 11.

[0075] Specifically, the device for coupling hydrocarbon oil and steam cracking to produce low-carbon olefins provided by the present application adopts a conventional cooling and separating device in the industry, and in an embodiment, the following cooling and separating system can be selected: a first quenching pipe 31, a second quenching pipe 32, a cooling and collecting tank 33, a cooling reflux pipe 34, a cryogenic collecting tank 35, a cryogenic reflux pipe 36, a system pressure adjusting device 37 (which can be a conventional pressure adjusting valve in the industry), a buffer tank 38 and a wet gas flow meter 39 connected in sequence through pipelines.

[0076] In an embodiment, the first quenching pipe 31, the second quenching pipe 32, the cooling collection tank 33, the cooling backflow pipe 34, the deep cooling collection tank 35 and the deep cooling backflow pipe 36 in the cooling separation system are all shell coolers; the front end of the first quenching pipe 31 is communicated with the U-shaped pipe of the second radiation section 26, and the cooling temperature of each cooling device can be adjusted according to actual conditions, for example, the temperature of the high-temperature pyrolysis product output from the U-shaped pipe of the second radiation section 26 is rapidly reduced to 40-70 DEG C after being cooled by the first quenching pipe 31 and the second quenching pipe 32; the temperature of the pyrolysis product from the second quenching pipe 32 can be reduced to 20-40 DEG C after being cooled by the cooling collection tank 33 and the cooling backflow pipe 34; the temperature of the pyrolysis product can be further reduced to 0-5 DEG C by the deep cooling collection tank 35 and the deep cooling backflow pipe 36.

[0077] In an embodiment, the cooling separation system, the buffer tank 37 contains water, and the gas-phase pyrolysis product is buffered and humidified in the buffer tank, and then enters the wet gas flow meter 38 for gas flow metering.

[0078] The device for coupling steam cracking of hydrocarbon oil to produce low-carbon olefins can be used for steam cracking of heavy oil alone, steam cracking of light oil alone, or steam cracking of heavy oil and light oil simultaneously, and when used for steam cracking of heavy oil alone or steam cracking of light oil alone, all water pipelines are in an open state.

[0079] When the device is used for coupling steam cracking of heavy oil, light oil, or light oil and heavy oil to produce low-carbon olefins, the reaction parameters of the devices involved in each system can be conventional in the industry, and can be adjusted and set according to actual conditions, for example:

[0080] The mass flow ratio of the light raw material output from the outlet of the light raw material pipeline to the water output from the outlet of the second water pipeline is 1:0.45-0.55;

[0081] The mass flow ratio of the heavy raw material output from the outlet of the heavy raw material pipeline to the water output from the outlet of the first water pipeline is 1:0.65-0.85;

[0082] The mass flow ratio of the light raw material output from the outlet of the light raw material pipeline to the heavy raw material output from the outlet of the heavy raw material pipeline is 1:0.1-1.

[0083] The set temperature of the first convection section and the second convection section is 500-550 DEG C;

[0084] The set temperature of the first transverse section in the pyrolysis reaction system is 480-560 DEG C, and the set temperature of the second transverse section is 560-630 DEG C;

[0085] The first radiation section of the cracking reaction system is set at a temperature of 700-800°C, and the second radiation section is set at a temperature of 810-850°C.

[0086] Specifically, the low-carbon olefin is prepared by using the above-mentioned device for preparing low-carbon olefin by coupling steam cracking of hydrocarbon oil, which comprises the following steps:

[0087] Preheating: when the temperature of the entire cracking reaction system is raised to 290-310°C, water is input into the first and second convection sections of the cracking reaction system through the water pipelines in the feeding system;

[0088] Cracking: after the cracking reaction system is raised to the predetermined temperature, the light feedstock output through the outlet of the light feedstock pipeline is mixed with the water vapor discharged from the outlet of the second convection section in the second cross section and then enters the second radiation section for cracking; and / or, the heavy feedstock output through the outlet of the heavy feedstock pipeline is mixed with the water vapor discharged from the outlet of the first convection section in the first cross section and then enters the first radiation section for preliminary cracking, and the preliminarily cracked material enters the second cross section and the second radiation section for cracking;

[0089] Cooling and separation: the cracked mixture enters the cooling and separation system which reaches the predetermined temperature for cooling and separation to obtain the product.

[0090] In one embodiment, the mass flow ratio of the light feedstock output through the outlet of the light feedstock pipeline to the water output through the outlet of the second water pipeline is 1:0.45-0.55, such as 1:0.48, 1:0.50, 1:0.52, etc.

[0091] The mass flow ratio of the heavy feedstock output through the outlet of the heavy feedstock pipeline to the water output through the outlet of the first water pipeline is 1:0.65-0.85, such as 1:0.68, 1:0.70, 1:0.75, 1:0.80, etc.

[0092] In one embodiment, the mass flow ratio of the light feedstock output through the outlet of the light feedstock pipeline to the heavy feedstock output through the outlet of the heavy feedstock pipeline is 1:0.1-1, such as 1:0.3, 1:0.2, 1:0.5, 1:0.8, 1:0.9, etc.

[0093] The light feedstock and the heavy feedstock can be any conventional light oil or heavy oil, for example, the light feedstock can be selected from naphtha, aromatic raffinate and similar or mixed oil products thereof, etc.; and the heavy feedstock can be selected from normal two-line oil, normal three-line oil, reduced one-line oil and similar or mixed oil products thereof, etc.

[0094] In one embodiment, the predetermined temperature of the first and second convection sections in the cracking reaction system can be selected from 500-550°C; the predetermined temperature of the first cross section can be selected from 600-750°C, and the predetermined temperature of the second cross section can be selected from 700-800°C; the predetermined temperature of the first radiation section can be selected from 700-800°C, and the predetermined temperature of the second radiation section can be selected from 810-850°C.

[0095] Alternatively, in the cracking step of the method for preparing low-carbon olefins by hydrocarbon oil coupled steam cracking, after the overall temperature of the cracking reaction system reaches the predetermined temperature of the first or second convection section, the first cross section, the second cross section, the first radiation section and the second radiation section are subjected to programmed temperature rising, and the programmed temperature rising rate is controlled within 10°C / min.

[0096] In one embodiment, the cooling separation step is performed in three steps, preferably, the first step is cooled to 40-70°C, the second step is cooled to 20-40°C, and the third step is cooled to 0-5°C.

[0097] In one embodiment, the method for preparing low-carbon olefins by using the above-mentioned device for preparing low-carbon olefins by hydrocarbon oil coupled steam cracking comprises the following steps:

[0098] (a-1) starting all cooling devices in the cooling separation system and adjusting the cooling temperature of each cooling device;

[0099] (a-2) starting the cracking reaction system to directly heat the entire cracking reaction system, and when the temperature of each convection section, each cross section and each radiation section in the cracking reaction system reaches about 300°C, starting the heavy feedstock dilution water feed connected with the first water pipeline and / or the light feedstock dilution water feed connected with the second water pipeline in the feed system, and adjusting the water feed flow rate to the set flow rate (which can be adjusted according to the actual situation);

[0100] (a-3) continuing to heat the cracking reaction system, and when the temperature of each convection section, each cross section and each radiation section in the cracking reaction system reaches the set temperature of the convection section, maintaining the temperature of each convection section unchanged, and subjecting each cross section and each radiation section to programmed temperature rising, and the programmed temperature rising rate is controlled within 10°C / min;

[0101] (a-4) after each cross section and each radiation section in the cracking reaction system reaches the corresponding set temperature, starting the heavy feedstock pipeline connected with the heavy feedstock tank and / or the light feedstock tank connected with the light feedstock tank in the feed system to perform feeding;

[0102] (a-5) When the pressure of each cross section and each radiation section is stable, the temperature of each cross section and each radiation section, the feed of light feedstock and heavy feedstock and water all reach the set value, and the whole cracking reaction system can be kept stable for 5-10 minutes, open the drain valve at the bottom of the cooling collection tank and the cryogenic collection tank in the cooling separation system to drain. If it is in the experimental stage, after the cracking liquid phase product is drained, close the drain valve, record the value of the wet gas flow meter, start the test, collect and measure the mass of the cracking liquid phase product in the cooling collection tank and the cryogenic collection tank in the cooling separation system, and stop heating the cracking reaction system;

[0103] (a-6) After the test is completed, close the heavy feedstock feed and the light feedstock feed in the feed system, record the cumulative reading of the wet flow meter, collect and measure the mass of the cracking liquid phase product in the cooling collection tank and the cryogenic collection tank in the cooling separation system, and stop heating the cracking reaction system;

[0104] (a-7) When the temperature of each section (convection section, cross section and radiation section) in the cracking reaction system is lower than 300℃, close the heavy feedstock dilution water feed and the light feedstock dilution water feed in the feed system, and stop all cooling equipment in the cooling separation system.

[0105] In an embodiment, the process for preparing low carbon olefins using the above device further comprises a decoking step, which comprises the following steps:

[0106] Under the condition that the overall temperature of the cracking reaction system is kept not lower than 300℃, close the light feedstock pipeline and the heavy feedstock pipeline, and input nitrogen gas through the inlet for gas input in the heavy feedstock pipeline to purge the cracking reaction system and the cooling separation system to remove the residual steam cracking raw material in the cracking reaction system and the cooling separation system, then switch the nitrogen gas to air, and decoking the cracking reaction system.

[0107] In an embodiment, the nitrogen gas purging time during decoking is 5-20 minutes.

[0108] In the decoking step of an embodiment, the first cross section, the second cross section, the first radiation section and the second radiation section are heated to decoking, and an experience-based temperature rising program commonly used in the industry can be used, for example, the temperature rising program can be selected as 810℃-820℃-830℃-840℃-850℃ for the first section, the second section, the third section, the fourth section and the fifth section, and the temperature rising condition of each section is that the temperature of the last section of furnace tube falls back, and after the carbon dioxide concentration in the decoking tail gas is lower than 0.1% under the temperature condition of the last section, the decoking is stopped.

[0109] In an embodiment, the specific decoking (for decoking the U-shaped furnace tube in each cross section and each radiation section of the cracking reaction system) comprises the following steps:

[0110] (b-1) keep all cooling equipments in the cooling separation system running, keep the temperature of each furnace tube in the cracking reaction system not lower than 300℃, close the feed of heavy feedstock and light feedstock in the feed system, keep the feed of heavy feedstock dilution water and light feedstock dilution water in the feed system, and the feed flow of water should meet the requirement of decoking (it can be consistent with the experimental condition, not lower than the design parameter of the device decoking) ;

[0111] (b-2) open the inlet for gas in the heavy feedstock pipeline, blow nitrogen for 5-20 min, and clean the residual feedstock in the pipeline;

[0112] (b-3) switch the gas inlet pipeline to air, and perform programmed temperature decoking on the U-shaped tube of each cross section and each radiation section, and analyze the decoking tail gas discharged from the wet gas flow meter for CO and CO2;

[0113] (b-4) after the decoking is completed, stop heating the cracking reaction system, after the temperature of the entire cracking reaction system is lower than 300℃, close the feed of heavy feedstock dilution water and light feedstock dilution water in the feed system, stop all cooling equipments in the cooling separation system, and close the gas inlet pipeline in the heavy feedstock pipeline.

[0114] The technical scheme of the present application and the effects achieved thereby will be further described below through specific examples.

[0115] Any light hydrocarbon oil and heavy hydrocarbon oil feedstock formed in the prior art can meet the implementation of the technical scheme of the present application, for the convenience of comparison, the light hydrocarbon oil and heavy hydrocarbon oil with the following properties are used in the following examples and comparative examples:

[0116] Table 1 main physical property data of heavy feedstock

[0117]

[0118]

[0119] Table 2 naphtha composition (ω%)

[0120] Carbon number Naphthene Isoalkane n-Alkane Aromatic hydrocarbon Total 5 0.15 0.24 0.45 - 0.84 6 5.78 8.4 2.62 0.21 17.01 7 13.54 10.58 2.17 0.61 26.9 8 16.13 9.53 1.53 0.81 28 9 12.2 7.73 0.93 0.37 21.23 10 2.8 2.57 0.35 - 5.72 11 - 0.11 - - 0.11 Poly 0.19 - - - 0.19 Total 50.79 39.16 8.05 2 100

[0121] Table 3 aromatic hydrocarbon raffinate composition (ω%)

[0122] Carbon number Naphthene Isoalkane n-Alkane Cyclalkene Alkene Aromatic hydrocarbon Total 4 - 0.06 0.11 - - - 0.17 5 1.91 5.25 5.47 - 0.05 - 12.68 6 3.83 33.08 13.34 0.09 0.85 0.1 51.29 7 3.3 14.33 4.81 0.11 1.79 0.41 24.75 8 3.09 2.31 1.79 - 0.14 0.46 7.79 9 1.34 0.77 1.12 - - 0.02 3.25 10 - - 0.03 - - - 0.03 12+ - 0.04 - - - - 0.04 Figure 1 13.47 55.84 26.67 0.2 2.83 0.99 100

[0123] Examples 1-3

[0124] Examples 1-3 all use Figure 1The device shown carries out different light, heavy hydrocarbon oil coupling feed steam cracking to produce low carbon olefins, and determines the low carbon olefin yield under different cracking conditions to show the advantages and performance of the present application. The reaction parameters and results of each embodiment are shown in Table 4 below.

[0125] Figure 1 The specific settings in the device are as follows: the first convection section and the second convection section are arranged vertically, there are 3 U-shaped tubes in the first convection section and 3 U-shaped tubes in the second convection section, the lengths of the U-shaped tubes are equal, and the temperature settings of the two convection sections are also the same.

[0126] The U-shaped tubes in the first cross section and the U-shaped tubes in the second cross section have the same length, there are 2 U-shaped tubes in the first radiation section, and there are 5 U-shaped tubes in the second radiation section; the lengths of the U-shaped tubes in the first radiation section and the second radiation section are the same, and the lengths are 0.8 times the length of the U-shaped tubes in the first cross section.

[0127] Table 4: Cracking conditions and product yields of different raw materials

[0128]

[0129]

[0130] From the data in the above table, it can be seen that the device for producing low carbon olefins by coupling steam cracking of hydrocarbon oil provided by the present application can realize coupling steam cracking of light and heavy hydrocarbon oils, and has the advantages of flexible and convenient operation, low investment cost, and small land occupation. By setting two radiation sections and combining two-stage steam cracking of heavy raw material hydrocarbon oil and one-stage steam cracking of light raw material hydrocarbon oil, the cracking capacity for heavy raw material hydrocarbon oil can be effectively improved, the consumption of dilution steam for cracking light raw materials can be reduced, and the overall low carbon olefin yield of the raw materials can be improved. The total yield of ethylene, propylene and butadiene can reach more than 48.8%.

[0131] Example 4

[0132] This embodiment is similar to Example 1, and the only differences are as follows:

[0133] In this embodiment, the mass ratio of normal two-line oil to aromatic residue oil feed is 0.15, the feed ratio (dilution mass ratio) of normal two-line oil raw material dilution water to normal two-line oil raw material is 0.7, the feed ratio (dilution mass ratio) of aromatic residue oil raw material dilution water to aromatic residue oil raw material is 0.45, the temperatures of the first convection section and the second convection section are both 500℃, the temperature of the first cross section is 500℃, the temperature of the second cross section is 610℃, the temperature of the first radiation section is 780℃, and the temperature of the second radiation section is 850℃.

[0134] In this embodiment, the final yield of ethylene was 31.54%, the yield of propylene was 13.66%, the yield of butadiene was 4.31%, and the total yield of the trienes reached 49.51%.

[0135] Example 5

[0136] This embodiment is similar to Embodiment 2, with the only differences being the following:

[0137] In this embodiment, the feed mass ratio of conventional third-line oil to naphtha is 1, the feed ratio (dilution mass ratio) of conventional third-line oil feedstock dilution water to conventional third-line oil feedstock is 0.7, the feed ratio (dilution mass ratio) of naphtha feedstock dilution water to naphtha feedstock is 0.48, the temperature of the first convection section and the second convection section is 550°C, the temperature of the first transverse section is 510°C, the temperature of the second transverse section is 620°C, the temperature of the first radiation section is 800°C, and the temperature of the second radiation section is 810°C.

[0138] In this embodiment, the final yield of ethylene was 28.14%, the yield of propylene was 14.59%, the yield of butadiene was 5.34%, and the total yield of the trienes reached 48.07%.

[0139] Comparative Examples 1-3

[0140] The apparatus used in Comparative Examples 1-3 is the same as that used in Example 1. Figure 1 Similar to (as shown), the only difference is that the apparatus used in Comparative Examples 1-3 does not have a first convection section, a first transverse section, and a first radiation section, and does not have a heavy raw material feed pipeline connected to the first transverse section. Figure 1 The gas inlet on the heavy feed pipeline is located on the light feed pipeline, and the rest are connected to it. Figure 2 Same, specifically as Figure 1 As shown.

[0141] Specifically, in Comparative Examples 1-3, the mixed oil obtained by mixing light and heavy hydrocarbon oils was mixed with water from the second convection section via a light feed pipeline and entered the second transverse section, where it underwent steam cracking in the second radiation section. The water-to-oil ratio in the tests was calculated based on the average of the corresponding heavy hydrocarbon oil water-to-oil ratio and light hydrocarbon oil feed ratio in Examples 1-3, ensuring that the feed rates of Comparative Examples 1-3 were consistent with those of Examples 1-3. The cracking process conditions were correspondingly selected from the more advantageous second transverse section temperature and second radiation section temperature in Examples 1-3, to demonstrate the optimal cracking performance of the light and heavy hydrocarbon oil mixture in a conventional steam cracking test apparatus. The evaluation test conditions and results are shown in Table 5.

[0142] Table 5. Pyrolysis conditions and product yields of different feedstocks

[0143]

[0144] From the data in the above table, it can be seen that the overall yield of ethylene, propylene and butadiene obtained by using the mixed light and heavy hydrocarbon oil feed is lower, and the triene yield is reduced compared with the corresponding example, and the overall yield is reduced by 2.3%.

[0145] Comparative Examples 4-6

[0146] The device used in Comparative Examples 4-6 is the same as the device used in Example 1 (as shown in the figure) and is similar to the device used in Example 1 (as shown in the figure), except that the device used in Comparative Examples 4-6 does not have a second convection section, and there is no light feedstock feed line connected to the second cross section, and the rest are the same as Figure 1 , as shown in the figure. Figure 3 ​

[0147] Specifically, the mixed oil obtained by mixing the light hydrocarbon oil and the heavy hydrocarbon oil is mixed with water from the first convection section through the heavy feedstock feed line into the first cross section, and then into the subsequent first radiation section, second cross section and second radiation section for steam cracking. The water / oil ratio is calculated according to the average of the water / oil ratio of the heavy hydrocarbon oil and the light hydrocarbon oil feed ratio in Example 1 to ensure that the feed amount of Comparative Example 1 is consistent with Example 1, and the furnace tube temperature is set the same as in Example 1. The evaluation test conditions and results are shown in Table 6.

[0148] Table 6 Cracking conditions and product yields of different feedstocks

[0149]

[0150] From the data in the above table, it can be seen that the overall yield of ethylene, propylene and butadiene obtained by using the mixed light and heavy hydrocarbon oil feed is lower, and the triene yield is reduced compared with the corresponding example, and the overall yield is reduced by 2.6%.

[0151] Of course, the present application can have other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application, but these corresponding changes and modifications should all belong to the protection scope of the present application.​​

Claims

1. An apparatus for producing low-carbon olefins via hydrocarbon-oil coupled steam cracking, characterized in that, It includes a feeding system, a pyrolysis reaction system, and a cooling and separation system connected in sequence; The feeding system includes at least one light raw material pipeline and at least one heavy raw material pipeline, each of the light raw material pipelines being connected to a corresponding water pipeline, and each of the heavy raw material pipelines being connected to a corresponding water pipeline. The pyrolysis reaction system includes a first convection section and a second convection section, as well as a first transverse section, a first radiation section, a second transverse section, and a second radiation section connected in sequence. The inlet of the first convection section is connected to the outlet of the first water pipeline, and the outlet of the first convection section and the outlet of the heavy raw material pipeline are respectively connected to the inlet of the first cross section; the inlet of the second convection section is connected to the outlet of the second water pipeline, and the outlet of the second convection section and the outlet of the light raw material pipeline are respectively connected to the inlet of the second cross section. The outlet of the second radiation section is connected to the cooling separation system; The first convection section and the second convection section are each composed of multiple transversely connected U-shaped tubes.

2. The apparatus for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 1, characterized in that, The first convection section is arranged parallel to or vertically above the second convection section.

3. The apparatus for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 1, characterized in that, The first span and the second span are each a longitudinally arranged U-shaped pipe.

4. The apparatus for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 1, characterized in that, The first radiation section and the second radiation section are each composed of U-shaped tubes connected in series longitudinally.

5. The apparatus for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 1, characterized in that, The heavy feedstock pipeline is also provided with at least one inlet for introducing gas, which enters through this inlet and then enters the pyrolysis reaction system through the inlet of the first cross section.

6. The apparatus for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 3, characterized in that, The length ratio of the U-shaped tube in the first span to the U-shaped tube in the second span is 1:0.8-1.

2.

7. The apparatus for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 4, characterized in that, The first radiating section has 1 to 3 U-shaped tubes, and the second radiating section has 3 to 7 U-shaped tubes.

8. A method for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking, characterized in that, The apparatus for producing low-carbon olefins using hydrocarbon oil coupled steam cracking according to any one of claims 1-7 comprises the following steps: Preheating: When the pyrolysis reaction system is started and the temperature of the entire pyrolysis reaction system is raised to 290~310°C, water is introduced into the first convection section and the second convection section of the pyrolysis reaction system through the water pipeline in the feed system. Cracking: After the cracking reaction system is heated to a predetermined temperature, the light raw material output from the outlet of the light raw material pipeline is mixed with the water vapor discharged from the outlet of the second convection section in the second cross section and then enters the second radiation section for cracking; and / or, the heavy raw material output from the outlet of the heavy raw material pipeline is mixed with the water vapor discharged from the outlet of the first convection section in the first cross section and then enters the first radiation section for preliminary cracking, and the material after preliminary cracking enters the second cross section and the second radiation section for further cracking; Cooling and separation: The pyrolysis mixture enters a cooling and separation system that reaches a predetermined temperature for cooling and separation to obtain the product.

9. The method for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 8, characterized in that, The mass flow ratio of the light feedstock output from the outlet of the light feedstock pipeline to the water output from the outlet of the second water pipeline is 1:0.45~0.55; and / or The mass flow ratio of the heavy raw material output from the outlet of the heavy raw material pipeline to the water output from the outlet of the first water pipeline is 1:0.65~0.

85.

10. The method for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 8, characterized in that, The mass flow ratio of the light raw material output from the outlet of the light raw material pipeline to the heavy raw material output from the outlet of the heavy raw material pipeline is 1:0.1~1.

11. The method for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 8, characterized in that, In the pyrolysis step, the predetermined temperature of the first convection section and the second convection section in the pyrolysis reaction system is 500~550℃; and / or In the pyrolysis step, the predetermined temperature of the first transverse section in the pyrolysis reaction system is 480~560℃, and the predetermined temperature of the second transverse section is 560~630℃; and / or In the pyrolysis step, the predetermined temperature of the first radiation section in the pyrolysis reaction system is 700~800℃, and the predetermined temperature of the second radiation section is 810~850℃.

12. The method for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 8, characterized in that, In the pyrolysis step, after the overall temperature of the pyrolysis reaction system reaches the predetermined temperature of the first convection section or the second convection section, the first cross section, the second cross section, the first radiation section and the second radiation section undergo programmed temperature increase, and the rate of programmed temperature increase is controlled within 10℃ / min.

13. The method for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 8, characterized in that, The cooling process in the cooling separation step is carried out in stages.

14. The method for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 8, characterized in that, It also includes a charring step, which includes the following steps: The light feedstock pipeline and the heavy feedstock pipeline are shut down, and nitrogen is introduced into the pyrolysis reaction system and the cooling separation system through the gas inlet on the heavy feedstock pipeline for purging. Then, the nitrogen is switched to air and the pyrolysis reaction system is charred.

15. The method for producing low-carbon olefins by coupled hydrocarbon-oil steam cracking as described in claim 13, characterized in that, The cooling separation step consists of three steps: the first step is to cool to 40~70℃, the second step is to cool to 20~40℃, and the third step is to cool to 0~5℃.

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