CN116143579A

CN116143579A - Method and system for producing low-carbon olefin by crude oil steam cracking

Info

Publication number: CN116143579A
Application number: CN202211338615.6A
Authority: CN
Inventors: 何细藕; 白飞; 孙丽丽; 王子宗; 吴德飞; 袁晴棠; 林江峰; 邵晨; 赵永华
Original assignee: China Petroleum and Chemical Corp; Sinopec Engineering Inc
Current assignee: China Petroleum and Chemical Corp; Sinopec Engineering Inc
Priority date: 2021-10-29
Filing date: 2022-10-28
Publication date: 2023-05-23

Abstract

The present disclosure relates to a method and system for producing light olefins by crude oil steam cracking. The method comprises the steps of performing first flash evaporation on crude oil to obtain a first gas phase fraction and a first liquid phase fraction, mixing the first liquid phase fraction with steam, preheating, and performing second flash evaporation to obtain a second gas phase fraction and a second liquid phase fraction; then, mixing the second liquid phase fraction with steam and then carrying out third flash evaporation to obtain a third gas phase fraction and a third liquid phase fraction, so that effective gas-liquid separation can be realized, and coking can be prevented in the crude oil gasification process; for crude oil with different groups, the high-efficiency cracking of different fractions obtained by flash evaporation can be realized, the olefin yield is high, the energy consumption is reduced, or the proper fractions enter an oil refining device for continuous processing; the existing steam cracking technology can be furthest applied, the technology is mature, and the operation is simple; aromatic hydrocarbon can be produced from the separated fraction which is not suitable for steam cracking or can be sold as oil, so that olefine can be realized, aromatic hydrocarbon can be realized, and oil can be realized.

Description

Method and system for producing low-carbon olefin by crude oil steam cracking

Technical Field

The present disclosure relates to the field of hydrocarbon processing, and in particular, to a method and system for producing low-carbon olefins by crude oil steam cracking.

Background

In order to cope with the impact of market competition, the raw material source of the ethylene cracking device is expanded, the processing flow of the oil refining device is shortened, crude oil is used as the raw material of steam cracking, the cost of the raw material is reduced, and the restriction of raw material varieties is eliminated; meanwhile, the investment of oil refining devices is reduced, and the method is an effective means for reducing the cost and enhancing the efficiency of the traditional ethylene enterprises for improving the production flexibility.

However, when crude oil is used as the raw material of the steam cracking furnace, the problems of high final boiling point (higher than 520 ℃), high colloid content, difficult vaporization, easy coking and the like exist, so that corresponding treatment and improvement are required in the design and production process flow of the cracking furnace to be suitable for the characteristics of the crude oil. At present, the Extra-abroad mainly comprises ExxonMobil company, satex America company, IQ Stokes chemical company, lummes company and the like, which are conducted in deep research on crude oil cracking technology, and the domestic mainly comprises Shanghai completion chemical engineering design Limited company and the like.

The company of lumes technology, limited liability, discloses a process for thermally cracking crude oil and heavy feeds in a pyrolysis reactor to produce olefins (CN 107001955B). The method describes the combination scheme of a convection section of a cracking furnace, a multi-stage (3 stages at most) separator and a fractionating tower, and can carry out multiple gas-liquid separation on a mixture of crude oil and steam and send the mixture with different severity into different radiant section furnace tubes for cracking. The method mentions that crude oil is preheated in an external heat exchanger prior to entering the convection section of the pyrolysis furnace, but does not account for the heat source. The method carries out gas-liquid separation on the mixture through a multistage separator and a fractionating tower and cracks different fractions through different radiation furnace tubes, and the cracking selectivity is improved, but the equipment is complicated, the investment is large, and the method is not suitable for light crude oil.

The history of the Exxon Mobil company in developing ethylene by cracking crude oil has also been long known. As early as 1970, ikesen Mobil proposed the use of crude oil steam cracking to produce low-carbon raw materials. It should be noted that, the technique of cracking the crude oil by exxonmobil does not directly use the purchased crude oil in the steam cracker, but performs pretreatment first. The treatment process mainly comprises the following steps: raw material preparation, hydrotreating and flash evaporation/separation. 2 month 2005, the chinese patent CN100564484C, a method for steam cracking heavy hydrocarbon feedstock, was filed by the elkesen chemical patent company, and the above process is described in detail, wherein the heavy hydrocarbon feedstock mainly comprises: crude oil, naphtha, gas oil, fuel oil, natural gasoline (condensate oil), oil residue and the like, the flash vaporization separation process is described in the method, but the gas-liquid components are difficult to separate well only by simple flash vaporization, and particularly, heavy components are difficult to avoid being entrained in the gas phase, so that coking in a convection section is easy to cause and further coking in a radiant section furnace tube is serious.

The process for the preparation of ethylene by cracking crude oil/condensate is described by the company ilex in the patents CN101528894a and CN101778929 a. CN101528894a describes that after the crude oil/condensate is preheated in the convection section, the separated light component enters the pyrolysis furnace to enter the convection section to be superheated, then enters the radiation section to be cracked, and then is recombined and sent to the atmospheric tower, and then is further separated by the vacuum tower, CN101778929a describes that the heavy raw material mixed with 30% of the raw material, such as crude oil or condensate, enters the upper part of the separation device to separate out the protection naphtha and lighter component after being preheated in the convection section, the separated liquid phase enters the lower packing tower to be further separated, how the separated heavy component is treated is not described, the two patent evaporation units adopt a stripper tower containing packing or trays, wherein the upper evaporation zone contains a gas-liquid separator, and gas-liquid separation can be realized, but the liquid phase after flash evaporation is relatively heavy and viscous; packing and tray openings are also prone to plugging.

The Shanghai Ming chemical engineering design Co., ltd discloses a combined processing method and device (CN 111196936A) for producing low-carbon olefin by directly steam cracking crude oil, which adopts pretreatment such as desalting, dewatering and the like to remove impurities, then sends the impurities into an ethylene cracking convection section for heating, and sends the heated feed into a gas-liquid separator to separate lighter hydrocarbon gas, and sends the lighter hydrocarbon gas into the convection section and a radiation section for steam cracking reaction to produce olefin. The liquid from the gas-liquid separator contains components such as atmospheric residuum, etc., and returns to the convection section and the radiation section after being sent to the hydrogenation unit for further treatment. In the method, overheated crude oil is directly sent to a gas-liquid separator, and the expected gas-liquid separation effect is difficult to achieve.

Crude oil is a mixture of various distillate oils, which has light hydrocarbon, light naphtha fraction, heavy naphtha fraction, kerosene fraction, diesel fraction, wax oil fraction, and the like. Different distillate oils contain different components, the content of aromatic hydrocarbon unsuitable for cracking is also different, and the conditions for cracking crude oil from different sources are also different. When the crude oil mixed by various fractions is cracked, the cracking of heavy components needs to be considered in order to avoid the too short operation period of the radiant section furnace tube, and the cracking temperature needs to be avoided to be too high, however, the cracking of light components is difficult to occur, and the finally obtained olefin yield is lower. At present, a method for realizing efficient pyrolysis of crude oil from different sources in the same system through a simple process is not available.

Disclosure of Invention

The invention aims to provide a method and a system for producing low-carbon olefin by crude oil steam cracking, which can effectively adapt to taking crude oil as a steam cracking raw material, prevent coking in the crude oil gasification process, realize high-efficiency gas-liquid separation and enable the crude oil to be cracked efficiently.

To achieve the above object, a first aspect of the present disclosure provides a method for producing light olefins by steam cracking of crude oil, the method comprising the steps of: s1, enabling crude oil to enter a first flash tank for first flash separation to obtain a first gas phase fraction and a first liquid phase fraction; s2, mixing the first liquid phase fraction with a first part of steam, preheating, and then entering a second flash tank for second flash separation to obtain a second gas phase fraction and a second liquid phase fraction; s3, mixing the second liquid phase fraction with a second part of steam, preheating, and then entering a third flash tank for third flash separation to obtain a third gas phase fraction and a third liquid phase fraction; s4, mixing the first gas phase fraction with the third part of steam to obtain a first gas phase fraction mixed material; and respectively enabling the first gas phase fraction mixture material, the optional second gas phase fraction and the optional third gas phase fraction to enter a convection section of a steam cracking device for superheating, and then enter a radiation section of the steam cracking device for steam cracking.

Optionally, the final distillation point of the distillation range of the first gas phase fraction is 80-160 ℃; the initial distillation point of the first liquid phase fraction is not higher than the final distillation point of the first gas phase fraction distillation range; the final distillation point of the second gas phase fraction is 160-250 ℃, and the initial distillation point of the second liquid phase fraction is not higher than the final distillation point of the second gas phase fraction distillation range;

the final distillation point of the third gas phase fraction is 250-350 ℃; the initial point of the third liquid phase fraction is not higher than the final point of the third gas phase fraction.

Optionally, the method further comprises: all the second gas phase fraction enters a convection section of a steam cracking device to be overheated, and then enters a radiation section of the steam cracking device to be subjected to steam cracking; or passing all of said second vapor fraction to a refinery for further processing; or a part of the second gas phase fraction enters a convection section of a steam cracking device to be overheated, then enters a radiation section of the steam cracking device to be subjected to steam cracking, and the other part of the second gas phase fraction enters an oil refining device to be continuously processed; optionally, the method further comprises: all the third gas phase fraction enters a convection section of a steam cracking device to be overheated, and then enters a radiation section of the steam cracking device to be subjected to steam cracking; or passing all of said third vapor fraction to a refinery unit for further processing; or a part of the third gas phase fraction enters a convection section of the steam cracking device to be overheated, then enters a radiation section of the steam cracking device to be subjected to steam cracking, and the other part of the third gas phase fraction enters an oil refining device to be continuously processed.

Optionally, along the height direction of the steam cracking device, the convection section is sequentially provided with a first mixed superheating section, a second mixed superheating section, a third mixed superheating section, a fourth steam superheating section, a fifth mixed superheating section, a sixth mixed superheating section and a seventh mixed superheating section which are mutually independent from top to bottom; the method further comprises the steps of: mixing the first liquid phase fraction with a first part of steam, and then feeding the mixture into the first mixing superheating section for heating; feeding the heated first liquid fraction mixture into the second flash tank for the second flash separation; preferably, the temperature of the heated first liquid fraction mixture is 200-350 ℃; mixing the second liquid phase fraction with a second portion of steam and then entering the third mixing superheating section for heating; then mixing the heated second liquid phase fraction mixture with a fourth part of steam, and then entering the third flash tank for third flash separation; preferably, the temperature of the heated second liquid fraction mixture is 250-400 ℃; optionally, the fourth part of steam is the steam heated by the fourth steam superheating section, and preferably, the temperature of the heated fourth part of steam is 400-575 ℃; optionally, the weight ratio of the third portion of steam to the first gas phase fraction is from 0.35 to 1, preferably from 0.4 to 0.6; the weight ratio of the first part of steam to the second gas phase fraction is 0.4-1, preferably 0.5-0.7; the weight ratio of the total amount of the second part of steam and the fourth part of steam to the third gas phase fraction is 0.5 to 1, preferably 0.7 to 0.9.

Optionally, the method further comprises: mixing the first gas phase fraction with a third part of steam, then entering the second mixing superheating section for heating, and then entering the fifth mixing superheating section for heating to 550-720 ℃ to obtain a first stream to be cracked; optionally, the second gas phase fraction enters the sixth mixing superheating section and is heated to 500-680 ℃ to obtain a second stream to be cracked; optionally, the third gas phase fraction enters the seventh mixing superheating section and is heated to 400-650 ℃ to obtain a third stream to be cracked; respectively enabling the first stream to be cracked, the optional second stream to be cracked and the optional third stream to be cracked to enter a radiation section of the steam cracking device for steam cracking; optionally, when the BMCI value in the second cracking stream is above 30, the second cracking stream does not enter the steam cracking device for cracking, and the second cracking stream is sent to an oil refining device; when the BMCI value in the third cracking material flow is more than 30, the third cracking material flow does not enter a steam cracking device for cracking, and the second cracking material flow is sent to an oil refining device; optionally, the method further comprises: enabling the first to-be-cracked material flow, the second to-be-cracked material flow and the third to-be-cracked material flow to enter different cracking furnace tubes of the same steam cracking device respectively for cracking; or the first stream to be cracked, the second stream to be cracked and the third stream to be cracked respectively enter different cracking furnace tubes of different steam cracking devices for cracking.

Optionally, the convection section of the steam cracking device further comprises a raw material preheating section, and the raw material preheating section is arranged above the first mixing superheating section along the height direction of the steam cracking device; the method further comprises the steps of: leading crude oil from a storage tank to undergo first heat exchange through a quenching water preheater and then to be introduced into a convection section of a steam cracking device for continuous heating, so as to obtain first preheated crude oil; enabling the first preheated crude oil to enter a desalting pretreatment device for desalting pretreatment to obtain desalted crude oil; heating the desalted crude oil in a raw material preheating section of the steam cracking device to obtain second preheated crude oil; then passing the second preheated crude oil into the first flash tank for the first flash separation; optionally, the temperature of the second preheated crude oil is 180-350 ℃; optionally, the method further comprises: buffering the third liquid phase fraction from the third flash tank in a buffer tank and leading out; preferably, the third liquid phase fraction from the buffer tank is divided into three parts, the first part of the third liquid phase fraction enters a hydrogenation device for hydrogenation treatment, and the second part of the third liquid phase fraction enters a catalytic cracking device for catalytic cracking treatment; refluxing a third portion of the third liquid fraction into the buffer tank; optionally, the crude oil is at least one of paraffin-based crude oil, intermediate-based crude oil and cycloalkyl crude oil; optionally, the method further comprises: controlling the pressure of the material before entering the first flash tank by arranging a pressure regulating valve on a feeding line of the first flash tank for introducing the second preheated crude oil from the raw material preheating section; optionally, the method further comprises: controlling the pressure of the second flash tank by arranging a pressure regulating valve at a gas phase outlet of the second gas phase fraction of the second flash tank; optionally, the method further comprises: a water injection mixer is arranged on an introduction pipeline of a liquid phase outlet of the second liquid phase fraction of the second flash tank, a thermometer is arranged on a feed pipeline of the third flash tank for introducing the heated second liquid phase fraction and steam mixture from the first mixing superheating section, and the temperature of the heated second liquid phase fraction and steam mixture is controlled through the water injection amount of the water injection mixer; optionally, the method further comprises: a water injection inlet is arranged on a feed line of the third flash tank for introducing the heated second liquid phase fraction and steam mixture from the first mixed superheating section to control the gasification rate of the third flash tank.

Optionally, the method further comprises: at least part of the third liquid phase fraction enters a dilution steam generator for treatment to obtain dilution steam; dividing at least part of the dilution steam into four parts, which are respectively the first part steam, the second part steam, the third part steam and the fourth part steam.

Optionally, the method further comprises: before the second gas phase fraction enters the oil refining device, the part of the second gas phase fraction and crude oil to be preheated respectively enter a gas phase fraction first cooler for heat exchange to obtain liquid phase second gas phase fraction and crude oil after preheating; allowing the second gas phase fraction of the liquid phase to enter a refining device for continuous processing; optionally, the method further comprises: before the third gas phase fraction enters the oil refining device, the part of the third gas phase fraction and crude oil to be preheated respectively enter a gas phase fraction second cooler for heat exchange to obtain a liquid phase third gas phase fraction and preheated crude oil; allowing the third gas phase fraction of the liquid phase to enter a refining device for continuous processing; optionally, the method further comprises: performing a first external pre-heat treatment on a second pre-heated crude oil from the feedstock pre-heat section before the second pre-heated crude oil enters the first flash tank; performing a second external pre-heat treatment on the first liquid fraction from the first flash tank before the first liquid fraction enters the second flash tank; subjecting the second liquid fraction from the second flash tank to a third external pre-heat treatment before it enters the third flash tank; wherein the first external preheating treatment, the second external preheating treatment and the third external preheating treatment are respectively carried out outside the steam cracking device, and the heat sources of the first external preheating treatment, the second external preheating treatment and the third external preheating treatment are waste heat materials from any device.

A second aspect of the present disclosure provides a system for producing light olefins by steam cracking of crude oil, the system comprising a first flash tank, a second flash tank, a third flash tank, and a steam cracking device, the steam cracking device comprising a convection section and a radiation section, the convection section being disposed above the radiation section along a height direction of the steam cracking device; wherein the first flash tank is provided with a crude oil inlet, a first gas phase fraction outlet and a first liquid phase fraction outlet; the second flash tank is provided with a first gas phase fraction inlet, a second gas phase fraction outlet and a second liquid phase fraction outlet; the third flash tank is provided with a second liquid phase fraction inlet, a third gas phase fraction outlet and a third liquid phase fraction outlet; the first liquid phase fraction outlet is communicated with the first liquid phase fraction inlet, and the second liquid phase fraction outlet is communicated with the second liquid phase fraction outlet; the radiation section of the steam cracking device is provided with a first raw material inlet to be cracked, an optional second raw material inlet to be cracked and an optional third raw material inlet to be cracked; the first raw material inlet to be cracked is communicated with the first gas phase fraction outlet, the second raw material inlet to be cracked is communicated with the second gas phase fraction outlet, and the third raw material inlet to be cracked is communicated with the third gas phase fraction outlet.

Optionally, along the height direction of the steam cracking device, the convection section is sequentially provided with a raw material preheating section, a first mixed superheating section, a second mixed superheating section, a third mixed superheating section, a fifth mixed superheating section, a sixth mixed superheating section and a seventh mixed superheating section which are mutually independent from top to bottom; the raw material preheating section is provided with a crude oil preheating inlet and a crude oil preheating outlet, and the crude oil preheating outlet is communicated with the crude oil inlet of the first flash tank; the first mixing superheating section is provided with a first superheating inlet and a first superheating outlet, and the first superheating inlet is communicated with a first liquid fraction outlet of the first flash tank through a first pipeline; said first superheat outlet being in communication with a first liquid fraction inlet of said second flash tank; the third mixing superheating section is provided with a third superheating inlet and a third superheating outlet, and the third superheating inlet is communicated with a second liquid fraction outlet of the second flash tank through a second pipeline; the third superheating outlet is communicated with a second liquid fraction inlet of the third flash tank through a fourth pipeline; the second mixing superheating section is provided with a second superheating inlet and a second superheating outlet, and the second superheating inlet is communicated with the first gas phase fraction outlet of the first flash tank through a third pipeline; the fifth mixed superheating section is provided with a fifth superheating inlet and a fifth superheating outlet, the fifth superheating inlet is communicated with the second superheating outlet of the second mixed superheating section, and the fifth superheating outlet is communicated with the first raw material to be cracked inlet of the radiation section; the sixth mixing superheating section is provided with a sixth superheating inlet and a sixth superheating outlet, and the sixth superheating inlet is communicated with the second gas phase fraction outlet of the second flash tank; the sixth overheating outlet is communicated with a second raw material inlet to be cracked of the radiation section; the seventh mixed superheating section is provided with a seventh superheating inlet and a seventh superheating outlet, and the seventh superheating inlet is communicated with a third gas phase fraction outlet of the third flash tank; the seventh overheating outlet is communicated with a third raw material inlet to be cracked of the radiation section; optionally, a first part of steam inlet is further formed in the first pipeline; a second part of steam inlet is also arranged on the second pipeline; a third part of steam inlet is also formed in the third pipeline; a fourth part of steam inlet is also arranged on the fourth pipeline; optionally, the convection section of the steam cracking device further comprises a fourth steam superheating section; the fourth steam superheating section is provided with a steam superheating inlet and a steam superheating outlet, and the steam superheating outlet is communicated with a fourth part of steam inlet on the fourth pipeline; preferably, the first flash tank, the second flash tank and the third flash tank are sequentially arranged along the same central axis in the vertical direction; optionally, the system further comprises a buffer tank, a pump, a desalination pre-processor and a chilled water pre-heater; the buffer tank is at least provided with a liquid-phase heavy component buffer inlet, a liquid-phase heavy component buffer outlet, a steam purging port and a nitrogen purging port; the pump includes an input port and an output port; the desalting pretreatment device is provided with a crude oil desalting inlet and a crude oil desalting outlet; the quenching water preheater is provided with a quenching water heat exchange inlet, a quenching water heat exchange outlet, a crude oil heat exchange first inlet and a crude oil heat exchange first outlet; the crude oil heat exchange first outlet of the quenching water preheater is communicated with the crude oil desalting inlet of the desalting pretreatment device, and the crude oil desalting outlet is communicated with the crude oil preheating inlet of the raw material preheating section; optionally, the outlet of the pump is used for communicating with the raw material inlet of the catalytic cracking device and/or the raw material inlet of the hydrotreater; optionally, the system further comprises a flow control unit, wherein the flow control unit comprises a liquid level transmitter, a pump reflux control valve and a liquid level control valve; the buffer tank is also provided with a heavy component reflux inlet which is communicated with the outlet of the pump; the liquid level transmitter is communicated with the inner space of the buffer tank and used for controlling the liquid level in the buffer tank.

Through the technical scheme, the disclosure provides a method for producing low-carbon olefin by crude oil steam cracking, which at least comprises the following beneficial effects:

(1) Compared with the technical scheme that crude oil in the conventional method is treated by an atmospheric and vacuum tower of a oil refining device, and part of crude oil enters the oil refining device and enters a cracking furnace as a cracking raw material for cracking, the method has the advantages that the atmospheric and vacuum device and other secondary processing devices are omitted, the process flow is simplified, the investment and the operation cost are saved, the conventional steam cracking technology can be furthest applied, the technology is mature, and the operation is simple;

(2) The present disclosure facilitates control of relevant parameters such as temperature, pressure, and the amount of steam introduced into the process in the various steps; the method can flexibly separate and process crude oil raw materials with different bases, for example, for paraffin-based crude oil, can realize high-efficiency pyrolysis of different fractions obtained by flash evaporation, has high olefin yield, reduces energy consumption, can maximally apply the existing steam pyrolysis technology, has mature technology and is simple to operate; for intermediate base crude oil or cycloalkyl crude oil with higher aromatic hydrocarbon content, proper fractions can be flexibly selected for steam cracking, and the proper fractions are selected for introduction into an oil refining device, so that resource utilization is realized to a greater extent;

(3) Compared with other crude oil cracking technologies, the process flow disclosed by the invention has high energy utilization rate, fully utilizes the abundant capability of the ethylene device and the heat demand of the system to be fully combined, further reduces the energy consumption of the ethylene device and correspondingly saves the investment;

(4) The method is suitable for crude oil with various bases, has wide application range on the crude oil, can be practically used for upgrading and enhancing the efficiency of the existing refining integrated device, can also be used for producing low-carbon olefin, especially ethylene, by using the novel refining integrated device, and can be used for constructing less refining devices such as atmospheric and vacuum pressure, reforming and the like; and the three gas phase fractions obtained by separation can be subjected to steam cracking on the light paraffin-based crude oil, so that an oil refining device can be omitted, and the device investment is reduced.

Additional features and advantages of the present disclosure will be set forth in the detailed description which follows.

Drawings

The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification, illustrate the disclosure and together with the description serve to explain, but do not limit the disclosure. In the drawings:

FIG. 1 is a schematic flow diagram of a method for producing light olefins by steam cracking of crude oil provided by the present disclosure;

Fig. 2 is a schematic flow chart of a method for producing light olefins by steam cracking of crude oil provided by the present disclosure.

Description of the reference numerals

1-a raw material preheating section, 2-a first flash tank, 3-a first mixed superheating section, 4-a second flash tank, 5-a third flash tank, 6-a second mixed superheating section, 7-a third mixed superheating section, 8-a fourth steam superheating section, 9-a fifth mixed superheating section, 10-a sixth mixed superheating section, 11-a seventh mixed superheating section, 12-a buffer tank, 13-a pump, 15-a desalination preprocessor, 16-a quenching water preheater, b and a pump reflux control valve; c. level control valve d, pump outlet flow meter, 101-crude oil, H1-quench water, 103-desalted crude oil, 104-second preheated crude oil, 105-first gas phase fraction, 106-first liquid phase fraction, 107-first liquid phase fraction and primary dilution steam mixture, 108-second gas phase fraction, 109-second liquid phase fraction, 110-primary dilution steam, 111-heated second liquid phase fraction and steam mixture, 112-secondary dilution steam, 113-third gas phase fraction, 114-third liquid phase fraction, 115-third liquid phase fraction from buffer tank, 118-primary dilution steam, 119-primary dilution steam, 120-first gas phase fraction and primary dilution steam mixture, 121-first stream to be cracked, 122-second stream to be cracked, 123-third stream to be cracked, 124-superheated secondary dilution steam

Detailed Description

Specific embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating and illustrating the disclosure, are not intended to limit the disclosure.

In the present disclosure, unless otherwise indicated, the terms "first," "second," "third," and the like are used merely to distinguish between different components and do not have the actual meaning of a tandem connection sequence. In this disclosure, terms such as "upper and lower, top and bottom" are used to generally refer to the upper and lower, top and bottom, of the device in its normal use. "inner and outer" are for the device profile.

In this disclosure, the words "primary dilution steam", "secondary dilution steam", "first portion steam", "second portion steam", and the like are used only to distinguish introduced steam in different steps, and do not contain actual meanings of the nature of the steam itself.

The method comprises the steps of performing first flash evaporation on crude oil to obtain a first gas phase fraction and a first liquid phase fraction, mixing the first liquid phase fraction with steam, and performing second flash evaporation to obtain a second gas phase fraction and a second liquid phase fraction; then mixing the first liquid phase fraction with steam and then carrying out third flash evaporation to obtain a third gas phase fraction and a third liquid phase fraction, so that effective gas-liquid separation can be realized; the inventor of the present disclosure found that materials suitable for producing low-carbon olefins by steam cracking of a cracking furnace, such as a first gas phase fraction, a second gas phase fraction and a third gas phase fraction, can be obtained through the above steps, and the separated fractions unsuitable for steam cracking can be used for producing aromatic hydrocarbons or selling as oil products, namely, alkene, aromatic hydrocarbon and oil can be realized; further, as the steam is introduced in the processes of the second flash evaporation and the third flash evaporation respectively, the separated second gas phase fraction and third gas phase fraction can be directly used for cracking in a cracking furnace as the steam is carried in the second gas phase fraction and the third gas phase fraction, the steam is not required to be additionally introduced, and the steam is only required to be introduced into the cracking furnace for steam cracking after the steam is introduced into the first gas phase fraction, so that the introduced amount of the steam in the whole process is easy to control.

A first aspect of the present disclosure provides a method for producing light olefins by steam cracking of crude oil, as shown in fig. 1, the method comprising the steps of:

s1, enabling crude oil to enter a first flash tank 2 for first flash separation to obtain a first gas phase fraction and a first liquid phase fraction;

s2, mixing the first liquid phase fraction with a first part of steam, preheating, and then entering a second flash tank 4 for second flash separation to obtain a second gas phase fraction and a second liquid phase fraction;

s3, mixing the second liquid phase fraction with a second part of steam, preheating, and then entering a third flash tank 5 for third flash separation to obtain a third gas phase fraction and a third liquid phase fraction;

s4, mixing the first gas phase fraction with the third part of steam to obtain a first gas phase fraction mixed material; the first gas phase fraction mixture, the optional second gas phase fraction and the optional third gas phase fraction are respectively sent to a convection section of a steam cracking device for superheating, and then sent to a radiation section 17 of the steam cracking device for steam cracking.

The present disclosure provides a method for producing low-carbon olefins by crude oil steam cracking, which omits an atmospheric and vacuum device and other secondary processing devices, simplifies the process flow and saves the investment; the present disclosure facilitates controlling the amount of steam introduced into the appropriate steam in the various steps; the process can be flexibly configured for the crude oil raw materials with different bases, for example, for paraffin-based crude oil, the high-efficiency pyrolysis of different fractions obtained by flash evaporation can be realized, the olefin yield is high, the energy consumption is reduced, the existing steam pyrolysis technology can be furthest applied, the technology is mature, and the operation is simple; for intermediate base crude oil or cycloalkyl crude oil with higher aromatic hydrocarbon content, proper fractions can be flexibly selected for steam cracking, and the proper fractions are selected for introducing into an oil refining device to more extent for resource utilization; the method has wide application range on crude oil, can be practically used for upgrading and enhancing the efficiency of the existing refining integrated device, can also be used for producing low-carbon olefin, especially ethylene, by using the novel refining integrated device, can be used for constructing few refining devices such as atmospheric and vacuum pressure, reforming and the like, can be used for constructing light paraffin-based crude oil without constructing the refining devices, and can reduce the device investment.

In a preferred embodiment, the end point of the first gas phase distillation range is 80 to 160 ℃; the initial distillation point of the first liquid phase fraction is not higher than the final distillation point of the first gas phase fraction distillation range;

the final distillation point of the second gas phase fraction is 160-250 ℃, and the initial distillation point of the second liquid phase fraction is not higher than the final distillation point of the second gas phase fraction distillation range;

In a specific embodiment, the first gas phase fraction comprises naphtha and a lighter gas phase fraction, and the first liquid phase fraction comprises a heavier liquid phase fraction than naphtha; the second gas phase fraction comprising kerosene and lighter fractions and a diesel gas phase fraction heavier than kerosene to below heavy diesel, the second liquid phase fraction comprising a liquid phase fraction above heavy diesel; the third gas phase fraction comprises a diesel gas phase fraction below the heavy diesel and the third liquid phase fraction comprises a liquid phase fraction above the heavy diesel.

It should be understood that the final distillation point of the vapor phase fraction and the final distillation point of the liquid phase fraction obtained by flash separation in the present disclosure are both in the range values, and may be any temperature within the range values in actual practice. And the present disclosure may select the separated fractions according to actual production needs, for example, in the first flash separation, a light naphtha fraction and a lighter fraction may be selected as the first gas phase fraction as needed, and then the final distillation point of the first gas phase fraction may be 80 ℃ or less, 90 ℃ or less, 100 ℃ or less, or the like; or selecting the whole fraction naphtha fraction as the first gas phase fraction, the final distillation point of the first gas phase fraction may be 160 ℃ or less, 150 ℃ or less, 140 ℃ or less, or the like. And in a practical process, the first liquid phase component may also contain light components, for example, a light fraction which may have an initial boiling point of 60 ℃ is also contained in the first liquid phase fraction.

In the present disclosure, steam is carried in each fraction separated in the first flash tank, the second flash tank, and the third flash tank, and the distillation range temperature of each fraction in the present disclosure is the crude oil component separated in the fraction except for the steam.

In this disclosure, the first flash tank and the second flash tank and the third flash tank are conventionally selected devices in the art; wherein the third flash tank has a flash hydrocyclone structure for effecting gas-liquid separation in a third flash process, and the gas (vapor) phase outlet may be one or more. According to the embodiment, the third flash tank with the flash evaporation hydrocyclone structure is adopted, so that the third liquid phase fraction can be more thoroughly separated through third separation, namely, heavy components which cannot be used for steam cracking in crude oil are more thoroughly separated, and the phenomenon that the third gas phase fraction carries the heavy components and the radiant tube is coked in the cracking process is prevented.

In one embodiment, the feedstock crude oil is at least one of a paraffinic, an intermediate, or a naphthenic crude oil.

In one embodiment, the method further comprises: all the second gas phase fraction enters a convection section of a steam cracking device to be overheated, and then enters a radiation section 17 of the steam cracking device to be subjected to steam cracking; or alternatively

Passing all of said second vapor fraction to a refinery unit for further processing; or alternatively

And (3) allowing one part of the second gas phase fraction to enter a convection section of the steam cracking device for superheating, then entering a radiation section 17 of the steam cracking device for steam cracking, and allowing the other part of the second gas phase fraction to enter an oil refining device for continuous processing.

In one embodiment, as shown in fig. 1 or fig. 2, the method further comprises: all the third gas phase fraction enters a convection section of a steam cracking device to be overheated, and then enters a radiation section 17 of the steam cracking device to be subjected to steam cracking; or alternatively

Feeding all the third gas phase fraction into a refinery device for further processing; or alternatively

And (3) allowing one part of the third gas phase fraction to enter a convection section of the steam cracking device for superheating, then entering a radiation section 17 of the steam cracking device for steam cracking, and allowing the other part of the third gas phase fraction to enter an oil refining device for continuous processing.

In the present disclosure, the treatment modes of the second gas phase fraction and the third gas phase fraction are independent from each other, and may be arbitrarily selected according to actual requirements. For example, the following four ways may be included: mode 1, subjecting the second gas phase fraction to subsequent steam cracking, and subjecting the third gas phase fraction to oil refining; mode 2, carrying out subsequent steam cracking on the third gas phase fraction, and refining oil on the second gas phase fraction; mode 3, subjecting the second gas phase fraction and the third gas phase fraction to subsequent steam cracking; and 4, refining the second gas phase fraction and the third gas phase fraction.

In the disclosure, the obtained second gas phase fraction or third gas phase fraction and third liquid phase fraction may be treated differently according to the weight of crude oil and the source and composition of crude oil, for example, according to whether the crude oil is paraffinic crude oil or naphthenic crude oil, the third gas phase fraction is introduced into a steam cracking device as a raw material to be cracked or directly introduced into a oil refining device, or a part of the third gas phase fraction is introduced into the steam cracking device as a raw material to be cracked, and the rest of the third gas phase fraction is introduced into the oil refining device for secondary processing, so as to improve the overall utilization efficiency of the process.

In one embodiment, as shown in fig. 1, the present disclosure further includes the following steps: when the crude oil is paraffin-based crude oil, introducing at least part of the third gas phase fraction into a refinery device for treatment. In the embodiment, the third gas phase fraction distilled from the paraffin-based crude oil is introduced into the oil refining device for treatment, so that the fraction unsuitable for being used as the steam cracking raw material can be used for producing aromatic hydrocarbon oil products, namely, olefine and olefine can be realized, aromatic hydrocarbon and oil can be realized, and the flexible utilization of the fractions separated from different types of raw material crude oil can be realized.

In another embodiment, as shown in FIG. 2, when the feedstock crude is a naphthenic crude, the entire third vapor phase fraction is introduced into the radiant section of the steam cracker without introduction into the refinery to further increase olefin yield.

According to the two specific embodiments, the third gas phase fraction (the mixed material of the diesel gas phase fraction below heavy diesel and steam) obtained by the third flash evaporation separation can be treated differently according to different raw crude oil types, the raw crude oil application range is wide, the separated fraction can be flexibly utilized, and the quality improvement and the synergy with the existing refining integrated device are realized.

In an alternative embodiment, the method further comprises: all the first gas phase fraction enters a convection section of another steam cracking device to be overheated, and then enters a corresponding radiation section to be steam cracked; or all the second gas phase fraction enters a convection section of another steam cracking device to be overheated, and then enters a corresponding radiation section to be steam cracked; the third gas phase fraction enters a convection section of the steam cracking device to be overheated, and then enters a radiation section of the steam cracking device to be subjected to steam cracking. In a word, three parts of gas phase fractions can enter different cracking furnaces for cracking in principle, one part of the gas phase fractions can enter the cracking furnace, the other two parts of the gas phase fractions enter other cracking furnaces for cracking, various combinations can be adopted, each part of the gas phase fractions enter different cracking furnaces respectively, or the two parts of the gas phase fractions enter the same cracking furnace, and only the conditions that the cracking furnaces are easy to operate and control are met, so that the cracking furnaces can be operated at full load or can be utilized with high efficiency to the greatest extent.

In one embodiment, as shown in fig. 1, along the height direction of the steam cracking apparatus, the convection section is sequentially provided with a first mixed superheating section 3, a second mixed superheating section 6, a third mixed superheating section 7, a fourth steam superheating section 8, a fifth mixed superheating section 9, a sixth mixed superheating section 10 and a seventh mixed superheating section 11, which are independent from each other, from top to bottom; the method further comprises the steps of:

mixing the first liquid phase fraction with a first part of steam, and then feeding the mixture into the first mixing superheating section 3 for heating; then the heated first liquid fraction mixture enters the second flash tank 4 for the second flash separation; preferably, the temperature of the heated first liquid fraction mixture is 200-350 ℃; mixing the second liquid phase fraction with a second part of steam, and then feeding the mixture into the third mixing superheating section 7 for heating; then mixing the heated second liquid phase fraction mixture with a fourth part of steam, and then entering the third flash tank 5 for third flash separation; preferably, the temperature of the heated second liquid fraction mixture is between 250 and 400 ℃. Further preferably, the present disclosure may provide a boiler feedwater injection port at an inlet of the third mixing superheater section 7 to control a temperature of the heated second liquid fraction mixed material, thereby controlling a liquid film temperature to be less than 500 ℃, preventing decomposition, coking, etc. of the material in the third flash tank.

In the method, the mixed material of the first liquid phase fraction and the first part of steam is introduced into the first mixed superheating section of the convection section for heating, and the mixed material of the second liquid phase fraction and the second part of steam is introduced into the third mixed superheating section for heating, so that the heat utilization efficiency of the whole process can be improved; the second liquid phase fraction is firstly mixed with primary dilution steam (second part steam), heated and then mixed with heated secondary dilution steam (fourth part steam), and the secondary dilution steam (fourth part steam) is independently introduced afterwards, so that the effect of steam stripping of the mixed flow can be achieved, and the third flash separation effect of the second liquid phase fraction is further improved.

In an alternative embodiment, the fourth part of steam is the steam heated by the fourth steam superheating section 8, and preferably, the temperature of the heated fourth part of steam is 400-575 ℃.

In one embodiment, the weight ratio of the third portion of steam to the first gas phase fraction is from 0.35 to 1, preferably from 0.4 to 0.6;

the weight ratio of the first part of steam to the second gas phase fraction is 0.4-1, preferably 0.5-0.7;

the weight ratio of the total amount of the second part of steam and the fourth part of steam to the third gas phase fraction is 0.5 to 1, preferably 0.7 to 0.9. The flash separation device is beneficial to controlling the flash separation effect in different flash tanks, and realizes that different gas phase components are separated to the greatest extent for cracking. In the present disclosure, since the separated first, second and third gas phase fractions are each mixed with steam, the present disclosure is based on the mass of components from crude oil remaining after removal of steam in the first, second and third gas phase fractions when controlling the amount of introduced steam.

In one embodiment, as shown in fig. 1, the method further comprises: mixing the first gas phase fraction with a third part of steam, then entering the second mixing superheating section 6 for heating, and then entering the fifth mixing superheating section 9 for heating to 550-720 ℃ to obtain a first stream to be cracked;

optionally, the second gas phase fraction enters the sixth mixing superheating section 10 and is heated to 500-680 ℃ to obtain a second stream to be cracked;

optionally, the third gas phase fraction enters the seventh mixing superheating section 11 and is heated to 400-650 ℃ to obtain a third stream to be cracked;

the first stream to be cracked, the optional second stream to be cracked and the optional third stream to be cracked are respectively introduced into the radiant section 17 of the steam cracker for the steam cracking.

Different fractions obtained by different flash evaporation separation are introduced into different superheating sections to be heated respectively, and the different fractions can be heated to a proper cracking initial temperature (crossing temperature) respectively; the first stream to be cracked, the second stream to be cracked and the third stream to be cracked are respectively introduced into a radiation section (such as a cracking furnace) of the steam cracking device for cracking, which is beneficial to controlling the cracking conditions of different streams to be cracked, so that each stream to be cracked can be cracked under proper conditions, and the final olefin yield is improved.

Specifically, the conditions for steam cracking the first stream to be cracked, the second stream to be cracked, and the third stream to be cracked in the radiant section of the present disclosure may be conventional in the art, and the cracking catalyst may be selected from the types of catalysts known in the art.

In a specific embodiment, when the BMCI value in the second cracking stream is more than 30, the second cracking stream does not enter the steam cracking device for cracking, and the second cracking stream is sent to an oil refining device;

and when the BMCI value in the third cracking material flow is more than 30, the third cracking material flow does not enter the steam cracking device for cracking, and the second cracking material flow is sent to an oil refining device. "BMCI" (U.S. Bureau of Mines Correlation Index) refers to the aromatic index, which represents the aromaticity index of an oil.

In a specific embodiment, the method further comprises: enabling the first to-be-cracked material flow, the second to-be-cracked material flow and the third to-be-cracked material flow to enter different cracking furnace tubes of the same steam cracking device respectively for cracking; or the first stream to be cracked, the second stream to be cracked and the third stream to be cracked respectively enter different cracking furnace tubes of different steam cracking devices for cracking. The selection can be made according to the actual situation.

In the disclosure, the first mixed superheating section 3, the second mixed superheating section 6, the third mixed superheating section 7 and the fourth steam superheating section 8 may be different heat exchange tubes at the upper part of the convection section of the same pyrolysis furnace or heat exchange tubes at the upper part of the convection section of different pyrolysis furnaces; the fifth mixed superheating section 9, the sixth mixed superheating section 10 and the seventh mixed superheating section 11 can be different heat exchange tubes at the lower part of the convection section of the same pyrolysis furnace or heat exchange tubes at the lower part of the convection section of different pyrolysis furnaces.

In one embodiment, as shown in fig. 1, the convection section of the steam cracking device further comprises a raw material preheating section 1, and the raw material preheating section 1 is arranged above the first mixing superheating section 3 along the height direction of the steam cracking device; the method further comprises the steps of: introducing crude oil from a storage tank into a convection section of a steam cracking device for continuous heating after carrying out first heat exchange by a quenching water preheater 16, and taking the obtained preheated crude oil as the first preheated crude oil;

feeding the first preheated crude oil into a desalting preprocessor 15 for desalting pretreatment to obtain desalted crude oil;

heating the desalted crude oil in a raw material preheating section 1 of the steam cracking device to obtain second preheated crude oil; then passing the second preheated crude oil into the first flash tank 2 for the first flash separation; optionally, the temperature of the second preheated crude oil is 180-350 ℃;

Optionally, the method further comprises: the third liquid phase fraction from the third flash tank 5 is led out after being buffered by a buffer tank 12; preferably, the third liquid phase fraction from the buffer tank 12 is divided into three parts, the first part of the third liquid phase fraction is sent to a hydrogenation device for hydrogenation treatment, and the second part of the third liquid phase fraction is sent to a catalytic cracking device for catalytic cracking treatment; a third portion of the third liquid fraction is refluxed into the buffer tank 12.

In a specific implementation mode, the flow sequence of crude oil preheating can also adopt the heat exchange of the waste heat of an ethylene device to replace the heat exchange of quenching water, and then the quenching water is subjected to heat exchange and preheating with high-temperature heavy oil obtained in the crude oil cracking flow; the crude oil can also exchange heat with the waste heat of the ethylene device, then desalt, and exchange heat with the high-temperature heavy oil obtained by the crude oil cracking device flow. Therefore, heat energy exchange among various devices is realized, particularly, the energy consumption of an ethylene device is reduced, the heat energy recycling is realized, and the investment is saved.

In one embodiment, the method further comprises: dividing at least part of the dilution steam into four parts, which are respectively the first part steam, the second part steam, the third part steam and the fourth part steam.

In one embodiment, the method further comprises: before the second gas phase fraction enters the oil refining device, the part of the second gas phase fraction and crude oil to be preheated respectively enter a gas phase fraction first cooler for heat exchange to obtain liquid phase second gas phase fraction and crude oil after preheating; and allowing the second gas phase fraction of the liquid phase to enter a refining device for continuous processing.

In one embodiment, the method further comprises: before the third gas phase fraction enters the oil refining device, the part of the third gas phase fraction and crude oil to be preheated respectively enter a gas phase fraction second cooler for heat exchange to obtain a liquid phase third gas phase fraction and preheated crude oil; allowing the third gas phase fraction of the liquid phase to enter a refining device for continuous processing; wherein the crude oil to be preheated is crude oil in any step prior to entering the first flash tank 2. The vapor fraction first cooler and the vapor fraction second cooler may be used in series with other devices in the disclosed system that treat the feed oil prior to entering the separation column. In the disclosure, when the second gas phase fraction or the third gas phase fraction is introduced into the oil refining device, the cooler is required to cool the gas phase fraction into a liquid phase and then refining the oil, and the gas phase fraction and the crude oil to be preheated can exchange heat in the cooler, so that the heat utilization effect is further improved.

In one embodiment, the method further comprises: the first external preheating treatment is carried out on the second preheated crude oil from the raw material preheating section 1 before the second preheated crude oil enters the first flash tank 2; the first liquid fraction from the first flash tank 2 is subjected to a second external pre-heat treatment before it enters the second flash tank 4; subjecting the second liquid fraction from the second flash tank 4 to a third external pre-heat treatment before it enters the third flash tank 5;

the first external preheating treatment, the second external preheating treatment and the third external preheating treatment are respectively carried out outside the steam cracking device, and heat sources of the first external preheating treatment, the second external preheating treatment and the third external preheating treatment are waste heat materials from any device, so that the heat utilization effect is further improved, and particularly, the utilization effect of the waste heat materials obtained by other devices in a factory is improved. The first external preheating treatment, the second external preheating treatment and the third external preheating treatment are independent of the heating steps in the superheating section of the steam cracking apparatus, and can be selected according to practical situations and can be used simultaneously.

The methods provided by the present disclosure may also control the temperature or pressure of the material in several ways.

In a specific embodiment, the method further comprises: the feed pressure before entering the first flash tank 2 is controlled by setting a pressure regulating valve on the feed line of the first flash tank 2 for introducing the second preheated crude oil 104 from the feed preheating section 1 so as to control the temperature and vaporization rate required for the primary flash.

In a specific embodiment, the method further comprises: the flash vaporization rate is controlled by controlling the pressure of the flash tank by providing a pressure regulating valve at the gas phase outlet of the second gas phase fraction 108 of the second flash tank 4 to control the pressure of the second flash tank 4.

In a specific embodiment, the method further comprises: a water injection mixer is provided on the introduction line of the liquid phase outlet of the second liquid phase fraction 109 of the second flash tank 4, a thermometer is provided on the feed line of the third flash tank 5 for introducing the heated second liquid phase fraction from the first mixing superheat section 3 and the steam mixture 111, and the temperature of the heated second liquid phase fraction and the steam mixture 111 is controlled by the water injection amount of the water injection mixer to prevent coking during the preheating.

Optionally, the method further comprises: a water injection inlet is provided in the feed line of the third flash tank 5 for introducing the heated second liquid fraction and vapor mixture 111 from the first mixing superheat section 3 to control the vaporization rate of the third flash tank 5.

The control scheme of the present disclosure may be any one of the above control schemes, or a control scheme of any combination.

The operating temperature adopted by the method is the temperature after pressure balance in the normal operating range under the normal operating condition of the cracking furnace, and optionally, the pressure related to gasification can be adjusted by adding pressure control measures according to the properties of crude oil and the actual cutting needs, so that the related operating temperature is correspondingly controlled.

A second aspect of the present disclosure provides a system for producing light olefins by steam cracking of crude oil, as shown in fig. 1, the system includes a first flash tank 2, a second flash tank 4, a third flash tank 5, and a steam cracking device, the steam cracking device includes a convection section and a radiation section 17, and the convection section is disposed above the radiation section 17 along a height direction of the steam cracking device; wherein, the liquid crystal display device comprises a liquid crystal display device,

the first flash tank 2 is provided with a crude oil inlet, a first gas phase fraction outlet and a first liquid phase fraction outlet; the second flash tank 4 is provided with a first gas phase fraction inlet, a second gas phase fraction outlet and a second liquid phase fraction outlet; the third flash tank 5 has a second liquid fraction inlet, a third vapor fraction outlet, and a third liquid fraction outlet;

the first liquid phase fraction outlet is communicated with the first liquid phase fraction inlet, and the second liquid phase fraction outlet is communicated with the second liquid phase fraction outlet;

The radiant section 17 of the steam cracker is provided with a first feed inlet to be cracked, an optional second feed inlet to be cracked and an optional third feed inlet to be cracked; the first raw material inlet to be cracked is communicated with the first gas phase fraction outlet, the second raw material inlet to be cracked is communicated with the second gas phase fraction outlet, and the third raw material inlet to be cracked is communicated with the third gas phase fraction outlet.

In one embodiment, as shown in fig. 1, along the height direction of the steam cracking device, a raw material preheating section 1, a first mixed superheating section 3, a second mixed superheating section 6, a third mixed superheating section 7, a fifth mixed superheating section 9, a sixth mixed superheating section 10 and a seventh mixed superheating section 11 which are mutually independent are sequentially arranged in the convection section from top to bottom;

the raw material preheating section 1 is provided with a crude oil preheating inlet and a crude oil preheating outlet, and the crude oil preheating outlet is communicated with a crude oil inlet of the first flash tank 2;

the first mixed superheating section 3 is provided with a first superheating inlet and a first superheating outlet, and the first superheating inlet is communicated with the first liquid fraction outlet of the first flash tank 2 through a first pipeline; the first superheating outlet is in communication with the first liquid fraction inlet of the second flash tank 4;

the third mixed superheating section 7 is provided with a third superheating inlet and a third superheating outlet, and the third superheating inlet is communicated with the second liquid fraction outlet of the second flash tank 4 through a second pipeline; the third superheating outlet is communicated with the second liquid fraction inlet of the third flash tank 5 through a fourth pipeline;

The second mixed superheating section 6 is provided with a second superheating inlet and a second superheating outlet, and the second superheating inlet is communicated with the first gas phase fraction outlet of the first flash tank 2 through a third pipeline; the fifth mixed superheating section 9 is provided with a fifth superheating inlet and a fifth superheating outlet, the fifth superheating inlet is communicated with the second superheating outlet of the second mixed superheating section 6, and the fifth superheating outlet is communicated with the first raw material to be cracked inlet of the radiation section 17;

the sixth mixing superheat section 10 is provided with a sixth superheat inlet and a sixth superheat outlet, wherein the sixth superheat inlet is communicated with the second gas phase fraction outlet of the second flash tank 4; the sixth superheating outlet is communicated with the second raw material inlet to be cracked of the radiant section 17;

the seventh mixed superheating section 11 is provided with a seventh superheating inlet and a seventh superheating outlet, and the seventh superheating inlet is communicated with the third gas phase fraction outlet of the third flash tank 5; the seventh superheating outlet communicates with the third feed inlet to be cracked of the radiant section 17.

Specifically, the radiant section of the steam cracking device (cracking furnace) includes a first cracking furnace tube, a second cracking furnace tube and a third cracking furnace tube which are arranged independently of each other, the first cracking furnace tube is provided with a raw material inlet formed as a first raw material inlet to be cracked, the second cracking furnace tube is provided with a raw material inlet formed as a second raw material inlet to be cracked, and the third cracking furnace tube is provided with a raw material inlet formed as a third raw material inlet to be cracked. Optionally, the first cracking furnace tube, the second cracking furnace tube and the third cracking furnace tube may be different radiant section furnace tubes entering the same furnace chamber of the same cracking furnace; or the radiation furnace tubes in the hearths of different radiation sections of the same cracking furnace; or the radiation furnace tubes of different cracking furnaces can be arranged according to actual conditions.

In a preferred embodiment, the first flash tank 2, the second flash tank 4 and the third flash tank 5 are sequentially arranged in the vertical direction along the same central axis, so that space is saved and arrangement is facilitated.

In one embodiment, the first pipeline is further provided with a first part of steam inlet; a second part of steam inlet is also arranged on the second pipeline; a third part of steam inlet is also formed in the third pipeline; a fourth part of steam inlet is also arranged on the fourth pipeline;

the convection section of the steam cracking device also comprises a fourth steam superheating section 8; the fourth steam superheating section 8 is provided with a steam superheating inlet and a steam superheating outlet, and the steam superheating outlet is communicated with a fourth part of steam inlet on the fourth pipeline.

In a specific embodiment, a first mixer is further provided at the first portion of the vapor inlet of the first line for mixing the first liquid fraction from the first flash tank with the first portion of the vapor; a second mixer is further arranged at the inlet of the second part of steam of the second pipeline and is used for mixing the second liquid phase fraction from the second flash tank with the second part of steam; a third mixer is further arranged at the steam inlet of the third part of the third pipeline and is used for mixing the first liquid phase fraction from the first flash tank with the steam of the third part; a fourth mixer is also provided at the fourth portion of the steam inlet of the fourth line for mixing the stream from the third mixing superheat section with the fourth portion of the steam. The first mixer, the second mixer, the third mixer and the fourth mixer can enable the materials and the steam to be mixed more uniformly, and coking is prevented. Any mixer of the kind known in the art that satisfies the above mixing effect may be employed.

In one embodiment, the system further comprises a buffer tank 12, a pump 13, a desalination pre-processor 15, and a quench water preheater 16;

the buffer tank 12 is provided with at least a liquid-phase heavy component buffer inlet, a liquid-phase heavy component buffer outlet, a heavy component return inlet, a steam purge port and a nitrogen purge port; the pump 13 includes an input port and an output port; the desalting preprocessor 15 is provided with a crude oil desalting inlet and a crude oil desalting outlet; the quenching water preheater 16 is provided with a quenching water heat exchange inlet, a quenching water heat exchange outlet, a crude oil heat exchange first inlet and a crude oil heat exchange first outlet;

wherein the crude oil heat exchange first outlet of the quenching water preheater 16 is communicated with the crude oil desalting inlet of the desalting pretreatment device 15, and the crude oil desalting outlet is communicated with the crude oil preheating inlet of the raw material preheating section 1;

the liquid-phase heavy component buffer inlet of the buffer tank 12 is communicated with the third liquid-phase fraction outlet of the third flash tank 5, and the liquid-phase heavy component buffer outlet is communicated with the input port of the pump 13; optionally, the output of the pump 13 is used for communicating with the feedstock inlet of the catalytic cracking unit and/or the feedstock inlet of the hydrotreater;

optionally, the system further comprises a flow control unit, wherein the flow control unit comprises a liquid level transmitter, a pump reflux control valve b, a liquid level control valve c, a pump outlet flowmeter d, a heavy component delivery flowmeter e and a crude oil feeding flowmeter f; the top of the buffer tank 12 is also provided with a heavy component reflux inlet;

Wherein, the liquid level transmitter is communicated with the inner space of the buffer tank 12 and used for controlling the liquid level in the buffer tank 12; a heavy component reflux outlet is arranged on a pipeline between the pump outlet flowmeter d and the liquid level control valve c, and is communicated with a heavy component reflux inlet of the buffer tank 12 through a return pipeline; the pump reflux control valve b is arranged on the return pipeline, and the liquid level control valve c is in signal connection with the liquid level transmitter; in the present disclosure, the liquid level of the liquid phase material in the buffer tank 12 is controlled by the liquid level control valve c, and the temperature of the liquid phase material in the buffer tank 12 is controlled to 200 to 270 ℃ by the pump back flow control valve b.

The present disclosure will be further described with reference to specific examples.

Example 1

According to the process flow shown in FIG. 1, crude oil (Tahe ShunBei heavy oil) of API (38-46) is selected, and components with boiling point below 430 ℃ in the crude oil are introduced into a cracking furnace as much as possible for cracking reaction. The method specifically comprises the following steps:

s1, enabling crude oil 101 and waste heat material H1 (such as quench water) to respectively enter a quench water preheater 16 and then to be subjected to primary preheating (first heat exchange, heating to a desalting treatment temperature of 70-120 ℃), and then enabling the obtained first preheated crude oil to be subjected to desalting and impurity removal through a desalting preprocessor 15 to obtain desalted crude oil 103. The desalted crude oil 103 enters a raw material preheating section 1 of a convection zone of a steam cracking device to be heated, and a second preheated crude oil 104 (180-350 ℃) is obtained.

S2, feeding the second preheated crude oil 104 into a first flash tank 2, and separating by first flash to obtain naphtha and lighter gas phase fraction 105 (first gas phase fraction, final distillation point is 80-160 ℃) and liquid phase fraction 106 heavier than naphtha. The first vapor fraction 105 obtained through the first flash tank 2 is mixed with primary dilution steam 119 (third portion steam) according to the steam: the weight ratio of the fractions is 0.40-0.6: 1, mixing the first liquid fraction 106 with primary dilution steam 118 (first partial steam) to obtain two mixed materials (wherein the weight ratio of the primary dilution steam 118 to the weight of the second gas fraction 108 obtained by subsequent separation is 0.45-0.7); then the mixture of the first gas phase fraction and the steam enters a second mixing superheating section 6 for heating, and the mixture of the first liquid phase fraction and the steam enters a first mixing superheating section 3 for heating; the temperature of the heated first liquid fraction mixture is 200-350 ℃.

S3, enabling the heated first liquid phase fraction obtained in the step to enter a second flash tank 4 with the primary dilution steam mixture 107 for second flash separation, and obtaining the following fractions: kerosene and lighter fractions and a diesel gas phase fraction 108 (second gas phase fraction, end point 160-250 ℃) heavier than kerosene to below heavy diesel and a second liquid phase fraction 109 above heavy diesel, the secondary dilution steam 112 being superheated to 400-575 ℃ in the fourth part of the steam of the fourth steam superheating section 8). Mixing the second liquid phase fraction 109 obtained in the above step with primary dilution steam 110 (second part steam), heating the obtained second liquid phase fraction and steam mixture in a third mixing superheating section 7, mixing the heated second liquid phase fraction and steam mixture 111 with superheated fourth part steam 124 (wherein the weight ratio of the total weight of the primary dilution steam 110 and the secondary dilution steam 124 to the third gas phase fraction 113 obtained by subsequent separation is 0.7-0.9), and then entering a third flash tank 5 for third flash separation to obtain the following fractions: a diesel gas phase fraction 113 (third gas phase fraction, end point 250 to 350 ℃) of heavy diesel or a liquid phase fraction 114 of heavy diesel or more.

S4, the heated first gas phase fraction obtained in the step and the primary dilution steam mixture 120 enter a fifth mixing superheating section 9 to be heated to 550-720 ℃ to obtain a first stream 121 to be cracked; the second gas phase fraction 108 obtained from the second flash tank enters a sixth mixed superheating section 10 and is heated to 500-680 ℃ to obtain a second stream 122 to be cracked; the third gas phase fraction 113 obtained from the third flash tank enters a seventh mixed superheating section 11 to be heated to 400-650 ℃ to obtain a third stream 123 to be cracked;

s5, respectively enabling the first stream to be cracked 121, the second stream to be cracked 122 and the third stream to be cracked 123 to enter a radiation section 17 of the steam cracking device for steam cracking; the three streams to be cracked can respectively enter into different radiant section furnace tubes of the same furnace chamber of the same cracking furnace or the radiant furnace tubes in the different radiant section furnace chambers of the same cracking furnace or the radiant furnace tubes of different cracking furnaces for cracking;

and S6, enabling the third liquid phase fraction 114 subjected to flash vapor-liquid separation in the third flash tank 5 to enter the buffer tank 12, and controlling the liquid level of the buffer tank through a liquid level regulating valve c.

Example 2

According to the process flow shown in FIG. 2, crude oil (heavy oil in the North of Tahe) of API (38-46) is selected, and light components with the boiling point below 260 ℃ in the crude oil are introduced into a cracking furnace as much as possible for cracking reaction. The method specifically comprises the following steps:

S1, enabling crude oil 101 and waste heat materials H1 (such as quench water) to respectively enter a quench water preheater 16 and then to be subjected to primary preheating (first heat exchange, heating to a desalting treatment temperature of 70-120 ℃), then enabling the obtained first preheated crude oil to pass through a desalting preprocessor 15 for desalting and removing impurities to obtain desalted crude oil 103, and enabling the desalted crude oil 103 to enter a raw material preheating section 1 of a convection zone of a steam cracking device for heating to obtain second preheated crude oil 104 (180-350 ℃).

S3, enabling the heated first liquid phase fraction obtained in the step to enter a second flash tank 4 with the primary dilution steam mixture 107 for second flash separation, and obtaining the following fractions: kerosene and lighter fractions and a diesel gas phase fraction 108 (second gas phase fraction, end point 160-250 ℃) heavier than kerosene to below heavy diesel and a second liquid phase fraction 109 above heavy diesel, the secondary dilution steam 112 (fourth partial steam) is superheated in the fourth steam superheating section 8 to 400-575 ℃. Mixing the second liquid phase fraction 109 obtained in the above step with primary dilution steam 110, heating the obtained second liquid phase fraction and steam mixture in a third mixing superheating section 7, mixing the heated second liquid phase fraction and steam mixture 111 with superheated secondary dilution steam 124 (wherein the weight ratio of the total weight of the primary dilution steam 110 and the secondary dilution steam 124 to the third gas phase fraction 113 obtained by subsequent separation is 0.7-0.9), and then entering a third flash tank 5 for third flash separation to obtain the following fractions: a diesel gas phase fraction 113 (third gas phase fraction, end point 250 to 350 ℃) of heavy diesel or a liquid phase fraction 114 of heavy diesel or more.

S4, the heated first gas phase fraction obtained in the step and the primary dilution steam mixture 120 enter a fifth mixing superheating section 9 to be heated to 550-720 ℃ to obtain a first stream 121 to be cracked; the second gas phase fraction 108 obtained from the second flash tank enters a sixth mixed superheating section 10 and is heated to 500-680 ℃ to obtain a second stream 122 to be cracked;

the third gas phase fraction 113 obtained from the third flash tank 5 is sent to a second cooler for cooling the gas phase fraction, and then the liquid phase fraction obtained by cooling is sent to a refinery (not shown);

s5, respectively enabling the first stream 121 to be cracked and the second stream 122 to be cracked to enter a radiation section 17 of the steam cracking device for steam cracking; the two streams to be cracked can respectively enter into different radiant section furnace tubes of the same furnace chamber of the same cracking furnace or the radiant furnace tubes in the different radiant section furnace chambers of the same cracking furnace or the radiant furnace tubes of different cracking furnaces for cracking;

and S6, enabling the third liquid phase fraction 114 subjected to flash vapor-liquid separation in the third flash tank 5 to enter the buffer tank 12, controlling the liquid level of the buffer tank 12 through a liquid level regulating valve c, and regulating the amount of the returned third liquid phase material 117 through a pump return flow regulating valve b. The temperature of the liquid phase material in the buffer tank 12 is controlled to be 150-300 ℃, the ratio of the third liquid phase fraction to the crude oil can be measured and calculated (e/f) through a flowmeter e and a flowmeter f, and the water injection amount is controlled through a regulating valve a.

The preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, but the present disclosure is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solutions of the present disclosure within the scope of the technical concept of the present disclosure, and all the simple modifications belong to the protection scope of the present disclosure.

In addition, the specific features described in the above embodiments may be combined in any suitable manner without contradiction. The various possible combinations are not described further in this disclosure in order to avoid unnecessary repetition.

Moreover, any combination between the various embodiments of the present disclosure is possible as long as it does not depart from the spirit of the present disclosure, which should also be construed as the disclosure of the present disclosure.

Claims

1. A method for producing low-carbon olefin by crude oil steam cracking, which is characterized by comprising the following steps:

s1, enabling crude oil to enter a first flash tank (2) for first flash separation to obtain a first gas phase fraction and a first liquid phase fraction;

s2, mixing the first liquid phase fraction with a first part of steam, preheating, and then entering a second flash tank (4) for second flash separation to obtain a second gas phase fraction and a second liquid phase fraction;

S3, mixing the second liquid phase fraction with a second part of steam, preheating, and then entering a third flash tank (5) for third flash separation to obtain a third gas phase fraction and a third liquid phase fraction;

s4, mixing the first gas phase fraction with the third part of steam to obtain a first gas phase fraction mixed material; the first gas phase fraction mixture, the optional second gas phase fraction and the optional third gas phase fraction are respectively sent to a convection section of a steam cracking device for superheating, and then sent to a radiation section (17) of the steam cracking device for steam cracking.

2. The process of claim 1, wherein the first vapor phase fraction has a final boiling point of from 80 ℃ to 160 ℃; the initial distillation point of the first liquid phase fraction is not higher than the final distillation point of the first gas phase fraction distillation range;

3. The method according to claim 1, characterized in that the method further comprises: all the second gas phase fraction enters a convection section of a steam cracking device to be overheated, and then enters a radiation section (17) of the steam cracking device to be subjected to steam cracking; or alternatively

A part of the second gas phase fraction enters a convection section of a steam cracking device to be overheated, then enters a radiation section (17) of the steam cracking device to be subjected to steam cracking, and the other part of the second gas phase fraction enters an oil refining device to be continuously processed;

optionally, the method further comprises: all the third gas phase fraction enters a convection section of a steam cracking device to be overheated, and then enters a radiation section (17) of the steam cracking device to be subjected to steam cracking; or alternatively

And (3) enabling one part of the third gas phase fraction to enter a convection section of the steam cracking device for overheating, then enter a radiation section (17) of the steam cracking device for steam cracking, and enabling the other part of the third gas phase fraction to enter an oil refining device for continuous processing.

4. A method according to claim 3, wherein the convection section is provided with a first mixing superheat section (3), a second mixing superheat section (6), a third mixing superheat section (7), a fourth steam superheat section (8), a fifth mixing superheat section (9), a sixth mixing superheat section (10) and a seventh mixing superheat section (11) which are independent from each other in sequence from top to bottom along the height direction of the steam cracking device; the method further comprises the steps of:

Mixing the first liquid phase fraction with a first part of steam and then heating the mixture in the first mixing superheating section (3); feeding the heated first liquid fraction mixture into the second flash tank (4) for the second flash separation; preferably, the temperature of the heated first liquid fraction mixture is 200-350 ℃;

mixing the second liquid phase fraction with a second part of steam and then heating the mixture in the third mixing superheating section (7); then mixing the heated second liquid phase fraction mixture with a fourth part of steam, and then entering a third flash tank (5) for third flash separation; preferably, the temperature of the heated second liquid fraction mixture is 250-400 ℃;

optionally, the fourth part of steam is the steam heated by the fourth steam superheating section (8), and preferably, the temperature of the heated fourth part of steam is 400-575 ℃;

optionally, the weight ratio of the third portion of steam to the first gas phase fraction is from 0.35 to 1, preferably from 0.4 to 0.6;

the weight ratio of the total amount of the second part of steam and the fourth part of steam to the third gas phase fraction is 0.5 to 1, preferably 0.7 to 0.9.

5. The method of claim 4, further comprising:

mixing the first gas phase fraction with a third part of steam, then entering the second mixing superheating section (6) for heating, and then entering the fifth mixing superheating section (9) for heating to 550-720 ℃ to obtain a first stream to be cracked;

optionally, the second gas phase fraction enters the sixth mixing superheating section (10) and is heated to 500-680 ℃ to obtain a second stream to be cracked;

optionally, the third gas phase fraction enters the seventh mixing superheating section (11) and is heated to 400-650 ℃ to obtain a third stream to be cracked;

subjecting the first stream to be cracked, the optional second stream to be cracked and the optional third stream to be cracked to a radiant section (17) of the steam cracker for steam cracking, respectively;

optionally, when the BMCI value in the second cracking stream is above 30, the second cracking stream does not enter the steam cracking device for cracking, and the second cracking stream is sent to an oil refining device;

when the BMCI value in the third cracking material flow is more than 30, the third cracking material flow does not enter a steam cracking device for cracking, and the second cracking material flow is sent to an oil refining device;

Optionally, the method further comprises: enabling the first to-be-cracked material flow, the second to-be-cracked material flow and the third to-be-cracked material flow to enter different cracking furnace tubes of the same steam cracking device respectively for cracking; or the first stream to be cracked, the second stream to be cracked and the third stream to be cracked respectively enter different cracking furnace tubes of different steam cracking devices for cracking.

6. The method according to claim 4, characterized in that the convection section of the steam cracker further comprises a feed preheating section (1), and that the feed preheating section (1) is arranged above the first mixing superheating section (3) in the height direction of the steam cracker; the method further comprises the steps of:

leading crude oil from a storage tank to undergo first heat exchange through a quenching water preheater (16) and then introducing the crude oil into a convection section of a steam cracking device for continuous heating to obtain first preheated crude oil;

enabling the first preheated crude oil to enter a desalting pretreatment device (15) for desalting pretreatment to obtain desalted crude oil;

heating the desalted crude oil in a raw material preheating section (1) of the steam cracking device to obtain second preheated crude oil; then passing the second preheated crude oil into the first flash tank (2) for the first flash separation; optionally, the temperature of the second preheated crude oil is 180-350 ℃;

Optionally, the method further comprises: buffering a third liquid phase fraction from the third flash tank (5) by a buffer tank (12) and leading the third liquid phase fraction out; preferably, the third liquid phase fraction from the buffer tank (12) is divided into three parts, the first part of the third liquid phase fraction is sent to a hydrogenation device for hydrogenation treatment, and the second part of the third liquid phase fraction is sent to a catalytic cracking device for catalytic cracking treatment; reflux a third portion of the third liquid fraction into the buffer tank (12);

optionally, the crude oil is at least one of paraffin-based crude oil, intermediate-based crude oil and cycloalkyl crude oil;

optionally, the method further comprises: controlling the material pressure before entering the first flash tank (2) by arranging a pressure regulating valve on a feeding line of the first flash tank (2) for introducing second preheated crude oil (104) from the raw material preheating section (1);

optionally, the method further comprises: controlling the pressure of the second flash tank (4) by setting a pressure regulating valve at a gas phase outlet of the second gas phase fraction (108) of the second flash tank (4);

optionally, the method further comprises: a water injection mixer is arranged on an introduction pipeline of a liquid phase outlet of a second liquid phase fraction (109) of the second flash tank (4), a thermometer is arranged on a feed pipeline of a third flash tank (5) for introducing a heated second liquid phase fraction and steam mixture (111) from the first mixing superheat section (3), and the temperature of the heated second liquid phase fraction and steam mixture (111) is controlled through the water injection amount of the water injection mixer;

Optionally, the method further comprises: a water injection inlet is arranged on a feed line of the third flash tank (5) for introducing the heated second liquid phase fraction and steam mixture (111) from the first mixed superheating section (3) to control the gasification rate of the third flash tank (5).

7. The method of claim 6, wherein the method further comprises:

at least part of the third liquid phase fraction enters a dilution steam generator for treatment to obtain dilution steam; dividing at least part of the dilution steam into four parts, which are respectively the first part steam, the second part steam, the third part steam and the fourth part steam.

8. The method of claim 6, wherein the method further comprises:

before the second gas phase fraction enters the oil refining device, the part of the second gas phase fraction and crude oil to be preheated respectively enter a gas phase fraction first cooler for heat exchange to obtain liquid phase second gas phase fraction and crude oil after preheating; allowing the second gas phase fraction of the liquid phase to enter a refining device for continuous processing;

optionally, the method further comprises:

before the third gas phase fraction enters the oil refining device, the part of the third gas phase fraction and crude oil to be preheated respectively enter a gas phase fraction second cooler for heat exchange to obtain a liquid phase third gas phase fraction and preheated crude oil; allowing the third gas phase fraction of the liquid phase to enter a refining device for continuous processing;

Optionally, the method further comprises: carrying out first external preheating treatment on the second preheated crude oil from the raw material preheating section (1) before the second preheated crude oil enters the first flash tank (2); subjecting the first liquid fraction from the first flash tank (2) to a second external pre-heat treatment before it enters the second flash tank (4); subjecting the second liquid fraction from the second flash tank (4) to a third external pre-heat treatment before it enters the third flash tank (5);

wherein the first external preheating treatment, the second external preheating treatment and the third external preheating treatment are respectively carried out outside the steam cracking device, and the heat sources of the first external preheating treatment, the second external preheating treatment and the third external preheating treatment are waste heat materials from any device.

9. A system for producing low-carbon olefin by crude oil steam cracking, which is characterized by comprising a first flash tank (2), a second flash tank (4), a third flash tank (5) and a steam cracking device, wherein the steam cracking device comprises a convection section and a radiation section (17), and the convection section is arranged above the radiation section (17) along the height direction of the steam cracking device; wherein, the liquid crystal display device comprises a liquid crystal display device,

the first flash tank (2) is provided with a crude oil inlet, a first gas phase fraction outlet and a first liquid phase fraction outlet; the second flash tank (4) is provided with a first gas phase fraction inlet, a second gas phase fraction outlet and a second liquid phase fraction outlet; the third flash tank (5) is provided with a second liquid phase fraction inlet, a third gas phase fraction outlet and a third liquid phase fraction outlet;

the radiation section (17) of the steam cracking device is provided with a first raw material inlet to be cracked, an optional second raw material inlet to be cracked and an optional third raw material inlet to be cracked; the first raw material inlet to be cracked is communicated with the first gas phase fraction outlet, the second raw material inlet to be cracked is communicated with the second gas phase fraction outlet, and the third raw material inlet to be cracked is communicated with the third gas phase fraction outlet.

10. The system according to claim 9, wherein the convection section is provided with a raw material preheating section (1), a first mixed superheating section (3), a second mixed superheating section (6), a third mixed superheating section (7), a fifth mixed superheating section (9), a sixth mixed superheating section (10) and a seventh mixed superheating section (11) which are independent from each other from top to bottom in sequence along the height direction of the steam cracking apparatus;

the raw material preheating section (1) is provided with a crude oil preheating inlet and a crude oil preheating outlet, and the crude oil preheating outlet is communicated with the crude oil inlet of the first flash tank (2);

the first mixing superheating section (3) is provided with a first superheating inlet and a first superheating outlet, and the first superheating inlet is communicated with a first liquid fraction outlet of the first flash tank (2) through a first pipeline; said first superheating outlet being in communication with a first liquid fraction inlet of said second flash tank (4);

The third mixing superheating section (7) is provided with a third superheating inlet and a third superheating outlet, and the third superheating inlet is communicated with a second liquid phase fraction outlet of the second flash tank (4) through a second pipeline; the third superheating outlet is communicated with a second liquid fraction inlet of the third flash tank (5) through a fourth pipeline;

the second mixing superheating section (6) is provided with a second superheating inlet and a second superheating outlet, and the second superheating inlet is communicated with the first gas phase fraction outlet of the first flash tank (2) through a third pipeline; the fifth mixing superheating section (9) is provided with a fifth superheating inlet and a fifth superheating outlet, the fifth superheating inlet is communicated with the second superheating outlet of the second mixing superheating section (6), and the fifth superheating outlet is communicated with the first raw material to be cracked inlet of the radiation section (17);

the sixth mixing superheating section (10) is provided with a sixth superheating inlet and a sixth superheating outlet, and the sixth superheating inlet is communicated with a second gas phase fraction outlet of the second flash tank (4); the sixth superheating outlet is communicated with a second raw material inlet to be cracked of the radiant section (17);

the seventh mixed superheating section (11) is provided with a seventh superheating inlet and a seventh superheating outlet, and the seventh superheating inlet is communicated with a third gas phase fraction outlet of the third flash tank (5); the seventh overheating outlet is communicated with a third raw material inlet to be cracked of the radiation section (17);

Optionally, a first part of steam inlet is further formed in the first pipeline; a second part of steam inlet is also arranged on the second pipeline; a third part of steam inlet is also formed in the third pipeline; a fourth steam inlet is also formed in the fourth pipeline;

preferably, the first flash tank (2), the second flash tank (4) and the third flash tank (5) are sequentially arranged along the same central axis in the vertical direction;

optionally, the convection section of the steam cracking device further comprises a fourth steam superheating section (8); the fourth steam superheating section (8) is provided with a steam superheating inlet and a steam superheating outlet, and the steam superheating outlet is communicated with a fourth steam inlet on the fourth pipeline;

optionally, the system further comprises a buffer tank (12), a pump (13), a desalination pre-processor (15) and a chilled water preheater (16);

the buffer tank (12) is at least provided with a liquid phase heavy component buffer inlet, a liquid phase heavy component buffer outlet, a steam purging port and a nitrogen purging port; the pump (13) comprises an input and an output; the desalting preprocessor (15) is provided with a crude oil desalting inlet and a crude oil desalting outlet; the quenching water preheater (16) is provided with a quenching water heat exchange inlet, a quenching water heat exchange outlet, a crude oil heat exchange first inlet and a crude oil heat exchange first outlet;

Wherein the crude oil heat exchange first outlet of the quenching water preheater (16) is communicated with the crude oil desalting inlet of the desalting pretreatment device (15), and the crude oil desalting outlet is communicated with the crude oil preheating inlet of the raw material preheating section (1);

the liquid-phase heavy component buffer inlet of the buffer tank (12) is communicated with the third liquid-phase fraction outlet of the third flash tank (5), and the liquid-phase heavy component buffer outlet is communicated with the input port of the pump (13); optionally, the output port of the pump (13) is used for communicating with the raw material inlet of the catalytic cracking device and/or the raw material inlet of the hydrotreater;

optionally, the system further comprises a flow control unit, wherein the flow control unit comprises a liquid level transmitter, a pump back flow control valve (b) and a liquid level control valve (c); the buffer tank (12) is also provided with a heavy component reflux inlet which is communicated with the outlet of the pump (13); the liquid level transmitter is communicated with the inner space of the buffer tank (12) and used for controlling the liquid level in the buffer tank (12).