A method and system for steam cracking of crude oil to produce light olefins

Abstract

The present disclosure relates to a method and system for producing low-carbon olefins by steam cracking of crude oil. The present disclosure first flash distills the crude oil to obtain a first gas phase fraction and a first liquid phase fraction, then preheats the first liquid phase fraction mixed with steam and performs a second flash distillation to obtain a second gas phase fraction and a second liquid phase fraction; then performs a third flash distillation on the second liquid phase fraction mixed with steam to obtain a third gas phase fraction and a third liquid phase fraction, which can effectively separate gas and liquid and prevent coking during the gasification of crude oil; for different base crude oils, different fractions obtained by flash distillation can be efficiently cracked, the yield of olefins is high, the energy consumption is reduced, or suitable fractions can enter a refinery device for further processing; the existing steam cracking technology can be applied to the maximum extent, the technology is mature and the operation is simple; the fractions obtained by separation that are not suitable for steam cracking can be used to produce aromatic hydrocarbons or sold as oil products, that is, olefins are used for olefins, aromatics are used for aromatics, and oil is used for oil.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of hydrocarbon processing, in particular, to a method and system for steam cracking of crude oil to produce low carbon olefins. BACKGROUND

[0002] In order to cope with the impact of market competition, expand the raw material sources of ethylene cracking device, shorten the processing flow of oil refining device, use crude oil as the raw material of steam cracking, reduce the cost of raw material, and get rid of the restriction of raw material variety; At the same time, reduce the investment of oil refining device, and improve the production flexibility, which becomes an effective means for traditional ethylene enterprises to reduce cost and increase benefit.

[0003] However, when using crude oil as the raw material of steam cracking furnace, there are problems such as high final boiling point (greater than 520℃), high gum content, difficult to vaporize and easy to cause coking, etc., so the design of cracking furnace and production process need to be handled and improved accordingly to adapt to the characteristics of crude oil. At present, foreign companies such as Exxon Mobil Company, Saudi Aramco Company, Iqiestra Chemical Company and Lummus Company have carried out in-depth research on crude oil cracking technology, and domestic companies such as Shanghai Junming Chemical Engineering Design Co., Ltd. have carried out research on crude oil cracking technology.

[0004] Lummus Technology Limited Liability Company discloses a method for thermal cracking of crude oil and heavy feedstock in a pyrolysis reactor to generate olefins (CN107001955B). The method describes the combination of the convection section of the cracking furnace and the multi-stage (up to 3 stages) separator and fractionating column. The method can carry out gas-liquid separation of the mixture of crude oil and steam for multiple times, and send the mixtures with different gravities into different radiant section furnace tubes for cracking. The method mentions that the crude oil is preheated in an external heat exchanger before entering the convection section of the cracking furnace, but does not mention the heat source. The method carries out gas-liquid separation of the mixture through the multi-stage separator and fractionating column, and cracks different fractions through different radiant furnace tubes, which improves the cracking selectivity, but the equipment is redundant, the investment is large, and it is not suitable for light crude oil.

[0005] ExxonMobil has a long history of developing ethylene from crude oil cracking. As early as January 1970, ExxonMobil proposed to produce low-carbon chemical raw materials by steam cracking of crude oil. It is worth noting that ExxonMobil's crude oil cracking technology is not directly used for steam cracking of purchased crude oil, but first undergoes pretreatment. Its treatment process mainly includes: raw material blending, hydrotreating and flash / vaporization separation. In February 2005, ExxonMobil Chemical Patents Inc. applied for a Chinese patent CN100564484C - Method for steam cracking of heavy hydrocarbon feedstock, which detailed the above process. In this method, heavy hydrocarbon feedstock mainly includes: crude oil, naphtha, gas oil, fuel oil, natural gasoline (condensate oil), residual oil, etc. The method describes the flash vaporization separation process, but it is difficult to separate gas and liquid components well through simple flashing, especially it is difficult to avoid entraining heavy components in the gas phase, which can easily cause coking in the convection section and further coking in the radiant section.

[0006] In patents CN101528894A and CN101778929A, Igus Chemical Company introduced the process technology of cracking ethylene from crude oil / condensate oil. CN101528894A introduced that the light components separated from the crude oil / condensate oil after preheating in the convection section enter the convection section of the cracking furnace for superheating and then enter the radiant section for cracking, and the heavy components are sent to the atmospheric column for further separation. CN101778929A introduced that the heavy feedstock such as crude oil or condensate oil mixed with 30% in the feedstock is preheated in the convection section and then enters the upper separation device to separate the protective naphtha and lighter components, and the heavy components separated are not introduced. The evaporation unit of the two patents uses a stripping column containing packing or trays, and the upper evaporation zone contains a gas-liquid separator, which can achieve gas-liquid separation, but the liquid phase after flashing is relatively heavy and viscous; the packing and tray openings are also easy to block.

[0007] Shanghai Junming Chemical Engineering Design Co., Ltd. disclosed a combined processing method and device for producing low-carbon olefins by direct steam cracking of crude oil (CN111196936A). First, impurities are removed by pretreatment such as desalting and dewatering, then the feed is sent to the convection section of the ethylene cracking furnace for heating, the heated feed is sent to the gas-liquid separator, the lighter hydrocarbon gas is separated and sent to the convection section and the radiant section for steam cracking reaction to produce olefins. The liquid from the gas-liquid separator contains atmospheric residue and other components, which is sent to the hydrogenation unit for further treatment and then returned to the convection section and the radiant section. In this method, the superheated crude oil is directly sent to the gas-liquid separator, which is difficult to achieve the expected gas-liquid separation effect.

[0008] Crude oil is a mixture of various distillate oils, which has light hydrocarbon, light naphtha fraction, heavy naphtha fraction, kerosene fraction, diesel fraction and wax oil fraction, etc. Different distillate oils contain different components, and the content of unsuitable cracking aromatic hydrocarbons is also different. The cracking conditions of crude oil from different sources are also different. When the crude oil mixed with various distillate oils is cracked, in order to avoid the short operation cycle of the radiant section furnace tube, the cracking of heavy components needs to be considered, and the cracking temperature needs to be avoided to be too high, which will lead to the difficulty of cracking of light components, and finally the yield of olefins is low. At present, there is no method for efficient cracking of crude oil from different sources in the same system by simple process. SUMMARY

[0009] The purpose of the present disclosure is to provide a method and system for producing low-carbon olefins by steam cracking of crude oil, which can effectively adapt to the use of crude oil as the steam cracking raw material, prevent coking during the gasification of crude oil, realize efficient gas-liquid separation, and enable efficient cracking of crude oil.

[0010] In order to achieve the above-mentioned purpose, the first aspect of the present disclosure provides a method for producing low-carbon olefins by steam cracking of crude oil, which comprises the following steps: S1, making crude oil 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, then preheating and 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, then preheating and 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 a third part of steam to obtain a first gas phase fraction mixture; making the first gas phase fraction mixture, optionally the second gas phase fraction and optionally the third gas phase fraction enter the convection section of a steam cracking device for superheating, and then enter the radiant section of the steam cracking device for steam cracking.

[0011] Optionally, the end boiling point of the first gas phase fraction is 80-160℃; the initial boiling point of the first liquid phase fraction is not higher than the end boiling point of the first gas phase fraction; the end boiling point of the second gas phase fraction is 160-250℃, and the initial boiling point of the second liquid phase fraction is not higher than the end boiling point of the second gas phase fraction;

[0012] The end boiling point of the third gas phase fraction is 250-350℃; and the initial boiling point of the third liquid phase fraction is not higher than the end boiling point of the third gas phase fraction.

[0013] Optionally, the method further comprises: passing all of the second gas phase fraction into a convection section of a steam cracking device for superheating, and then into a radiation section of the steam cracking device for steam cracking; or passing all of the second gas phase fraction into a refinery for further processing; or passing a portion of the second gas phase fraction into the convection section of the steam cracking device for superheating, and then into the radiation section of the steam cracking device for steam cracking, and passing another portion of the second gas phase fraction into the refinery for further processing; optionally, the method further comprises: passing all of the third gas phase fraction into the convection section of the steam cracking device for superheating, and then into the radiation section of the steam cracking device for steam cracking; or passing all of the third gas phase fraction into the refinery for further processing; or passing a portion of the third gas phase fraction into the convection section of the steam cracking device for superheating, and then into the radiation section of the steam cracking device for steam cracking, and passing another portion of the third gas phase fraction into the refinery for further processing.

[0014] 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 from top to bottom; the method further comprises: mixing the first liquid phase fraction with a first portion of steam and then passing the mixture into the first mixed superheating section for heating; passing the mixture of the heated first liquid phase fraction into the second flash tank for the second flash separation; preferably, the temperature of the mixture of the heated first liquid phase fraction is 200-350℃; mixing the second liquid phase fraction with a second portion of steam and then passing the mixture into the third mixed superheating section for heating; and then mixing the mixture of the heated second liquid phase fraction with a fourth portion of steam and then passing the mixture into the third flash tank for the third flash separation; preferably, the temperature of the mixture of the heated second liquid phase fraction is 250-400℃; optionally, the fourth portion of steam is steam heated by the fourth steam superheating section, and preferably, the temperature of the heated fourth portion of steam is 400-575℃; optionally, the weight ratio of the third portion of steam to the first gas phase fraction is 0.35-1, preferably 0.4-0.6; the weight ratio of the first portion of steam to the second gas phase fraction is 0.4-1, preferably 0.5-0.7; and the weight ratio of the total amount of the second portion of steam and the fourth portion of steam to the third gas phase fraction is 0.5-1, preferably 0.7-0.9.

[0015] Optionally, the method further comprises: mixing the first gas phase fraction with a third portion of steam and then entering the second mixed superheating section for heating, and then entering the fifth mixed superheating section for heating to 550-720°C to obtain a first to-be-cracked stream; optionally, entering the second gas phase fraction into the sixth mixed superheating section for heating to 500-680°C to obtain a second to-be-cracked stream; optionally, entering the third gas phase fraction into the seventh mixed superheating section for heating to 400-650°C to obtain a third to-be-cracked stream; entering the first to-be-cracked stream, the optional second to-be-cracked stream and the optional third to-be-cracked stream into the radiant section of the steam cracking device respectively for the steam cracking; optionally, when the BMCI value of the second cracking stream is 30 or more, the second cracking stream does not enter the steam cracking device for cracking, and the second cracking stream is sent to a refinery device; when the BMCI value of the third cracking stream is 30 or more, the third cracking stream does not enter the steam cracking device for cracking, and the second cracking stream is sent to a refinery device; optionally, the method further comprises: entering the first to-be-cracked stream, the second to-be-cracked stream and the third to-be-cracked stream into different cracking furnace tubes of the same steam cracking device respectively for cracking; or entering the first to-be-cracked stream, the second to-be-cracked stream and the third to-be-cracked stream into different cracking furnace tubes of different steam cracking devices respectively for cracking.

[0016] 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 mixed superheating section along the height direction of the steam cracking device; the method further comprises: introducing the crude oil from the storage tank into the convection section of the steam cracking device for further heating after first heat exchange by the quenching water preheater to obtain first preheated crude oil; introducing the first preheated crude oil into the desalination pre-treater for desalination pre-treatment to obtain desalinated crude oil; introducing the desalinated crude oil into the raw material preheating section of the steam cracking device for heating to obtain second preheated crude oil; and then introducing 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: introducing the third liquid phase fraction from the third flash tank into the buffer tank for buffering; preferably, the third liquid phase fraction from the buffer tank is divided into three parts, the first part of the third liquid phase fraction is introduced into the hydrogenation device for hydrogenation treatment, and the second part of the third liquid phase fraction is introduced into the catalytic cracking device for catalytic cracking treatment; and the third part of the third liquid phase fraction is introduced into the buffer tank in reflux; optionally, the crude oil is at least one of paraffin-based crude oil, intermediate-based crude oil and naphthenic-based 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 the feed pipeline 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 on the gas phase outlet of the second gas phase fraction of the second flash tank; optionally, the method further comprises: arranging a water injection mixer on the introduction pipeline of the liquid phase outlet of the second liquid phase fraction of the second flash tank, and arranging a thermometer on the feed pipeline of the third flash tank for introducing the heated second liquid phase fraction and the steam mixture from the first mixed superheating section, so as to control the temperature of the heated second liquid phase fraction and the steam mixture by the water injection amount of the water injection mixer; optionally, the method further comprises: arranging a water injection inlet on the feed pipeline of the third flash tank for introducing the heated second liquid phase fraction and the steam mixture from the first mixed superheating section to control the vaporization rate of the third flash tank.

[0017] Optionally, the method further comprises: introducing at least part of the third liquid phase fraction into the dilution steam generator for treatment to obtain dilution steam; and dividing at least part of the dilution steam into four parts as the first part of steam, the second part of steam, the third part of steam and the fourth part of steam respectively.

[0018] 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 the crude oil to be preheated enter a gas phase fraction first cooler respectively for heat exchange, to obtain a liquid phase second gas phase fraction and preheated crude oil; the liquid phase second gas phase fraction enters the oil refining device for further 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 the crude oil to be preheated enter a gas phase fraction second cooler respectively for heat exchange, to obtain a liquid phase third gas phase fraction and preheated crude oil; the liquid phase third gas phase fraction enters the oil refining device for further processing; optionally, the method further comprises: before the second preheated crude oil from the crude preheating section enters the first flash tank, the second preheated crude oil is subjected to a first external preheating treatment; before the first liquid phase fraction from the first flash tank enters the second flash tank, the first liquid phase fraction is subjected to a second external preheating treatment; before the second liquid phase fraction from the second flash tank enters the third flash tank, the second liquid phase fraction is subjected to a third external preheating treatment; wherein the first external preheating treatment, the second external preheating treatment and the third external preheating treatment are respectively performed externally to the steam cracking device, and the heat source for the first external preheating treatment, the second external preheating treatment and the third external preheating treatment is waste heat material from any device.

[0019] The second aspect of the present disclosure provides a system for producing low-carbon olefins from crude oil by steam cracking, comprising a first flash tank, a second flash tank, a third flash tank and a steam cracking device, wherein the steam cracking device comprises a convection section and a radiation section, and the convection section is arranged above the radiation section along the height direction of the steam cracking device; 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 in communication with the first liquid phase fraction inlet, and the second liquid phase fraction outlet is in communication with the second liquid phase fraction outlet; the radiation section of the steam cracking device is provided with a first to-be-cracked raw material inlet, an optional second to-be-cracked raw material inlet and an optional third to-be-cracked raw material inlet; the first to-be-cracked raw material inlet is in communication with the first gas phase fraction outlet, the second to-be-cracked raw material inlet is in communication with the second gas phase fraction outlet, and the third to-be-cracked raw material inlet is in communication with the third gas phase fraction outlet.

[0020] Optionally, along the height direction of the steam cracking device, the convection section is sequentially provided with raw material preheating section, first mixed superheating section, second mixed superheating section, third mixed superheating section, fifth mixed superheating section, sixth mixed superheating section and seventh mixed superheating section from top to bottom, which are independent of each other; the raw material preheating section is provided with crude oil preheating inlet and crude oil preheating outlet, and the crude oil preheating outlet is communicated with the crude oil inlet of the first flash tank; the first mixed superheating section is provided with first superheating inlet and first superheating outlet, and the first superheating inlet is communicated with the first liquid phase fraction outlet of the first flash tank through the first pipeline; the first superheating outlet is communicated with the first liquid phase fraction inlet of the second flash tank; the third mixed superheating section is provided with third superheating inlet and third superheating outlet, and the third superheating inlet is communicated with the second liquid phase fraction outlet of the second flash tank through the second pipeline; the third superheating outlet is communicated with the second liquid phase fraction inlet of the third flash tank through the fourth pipeline; the second mixed superheating section is provided with second superheating inlet and second superheating outlet, and the second superheating inlet is communicated with the first gas phase fraction outlet of the first flash tank through the third pipeline; the fifth mixed superheating section is provided with fifth superheating inlet and 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 to-be-cracked raw material inlet of the radiation section; the sixth mixed superheating section is provided with sixth superheating inlet and sixth superheating outlet, and the sixth superheating inlet is communicated with the second gas phase fraction outlet of the second flash tank; the sixth superheating outlet is communicated with the second to-be-cracked raw material inlet of the radiation section; the seventh mixed superheating section is provided with seventh superheating inlet and seventh superheating outlet, and the seventh superheating inlet is communicated with the third gas phase fraction outlet of the third flash tank; the seventh superheating outlet is communicated with the third to-be-cracked raw material inlet of the radiation section; optionally, the first pipeline is further provided with first part steam inlet; the second pipeline is further provided with second part steam inlet; the third pipeline is further provided with third part steam inlet; the fourth pipeline is further provided with fourth part steam inlet; optionally, the convection section of the steam cracking device further comprises fourth steam superheating section; the fourth steam superheating section is provided with steam superheating inlet and steam superheating outlet, and the steam superheating outlet is communicated with the fourth part steam inlet on the fourth pipeline; preferably, the first flash tank, the second flash tank and the third flash tank are sequentially arranged in the vertical direction along the same central axis; optionally, the system further comprises a buffer tank, a pump, a desalination pretreater and a quenching water preheater; the buffer tank is provided with at least liquid phase heavy component buffer inlet, liquid phase heavy component buffer outlet, steam purging port and nitrogen purging port; the pump comprises input port and output port; the desalination pretreater is provided with crude oil desalination inlet and crude oil desalination outlet; the quenching water preheater is provided with quenching water heat exchange inlet, quenching water heat exchange outlet, crude oil heat exchange first inlet and crude oil heat exchange first outlet;The first outlet of the crude oil heat exchange of the quenching water preheater is communicated with the crude oil desalting inlet of the desalting preprocessor, 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 being communicated with the raw material inlet of the catalytic cracking device and / or the raw material inlet of the hydrogenation treatment device; optionally, the system further comprises a flow control unit, the flow control unit comprises a liquid level transmitter, a pump backflow control valve and a liquid level control valve; the buffer tank is further provided with a heavy component backflow inlet, and the heavy component backflow inlet is communicated with the outlet of the pump; wherein the liquid level transmitter is communicated with the internal space of the buffer tank to control the liquid level in the buffer tank.

[0021] Through the technical scheme, the method for producing low-carbon olefins by steam cracking of crude oil is provided, and the beneficial effects at least include:

[0022] (1) Compared with the technical scheme in the conventional method, in which the crude oil is treated by the atmospheric and vacuum tower of the oil refining device, and then a part of the crude oil enters the oil refining device and a part of the crude oil is used as a cracking raw material to enter the cracking furnace for cracking, the atmospheric and vacuum device and other secondary processing devices are cancelled in the present disclosure, the process flow is simplified, the investment and operation cost are saved, and the existing steam cracking technology can be maximally applied, the technology is mature, and the operation is simple.

[0023] (2) The present disclosure is easy to control the related parameters such as temperature, pressure and the amount of introduced steam in different steps; different base crude oil raw materials can be flexibly separated and treated, for example, for paraffin-based crude oil, different fractions obtained by flash distillation can be efficiently cracked, the olefin yield is high, the energy consumption is reduced, and the existing steam cracking technology can be maximally applied, the technology is mature, and the operation is simple; for intermediate base crude oil or naphthenic base crude oil with high aromatic content, appropriate fractions can be flexibly selected for steam cracking, and appropriate fractions can be introduced into the oil refining device, so that the resource utilization is realized to a greater extent.

[0024] (3) Compared with other crude oil cracking technologies, the process flow of the present disclosure has high energy utilization rate, the abundant capacity of the ethylene device and the heat demand of the system itself are fully combined, and the energy consumption of the ethylene device is further reduced, and the corresponding investment is saved.

[0025] (4) The present disclosure is suitable for various base crude oils, has a wide range of crude oil adaptation, can be used for upgrading and efficiency improvement of the existing refining and chemical integrated device, and can also be used for producing low-carbon olefins in a new refining and chemical integrated device, especially ethylene; for a newly built refining and chemical integrated device, the oil refining device such as atmospheric and vacuum tower and reformer can be less constructed; and for light paraffin base crude oil, three gas phase fractions obtained by separation can all be subjected to steam cracking, so that the oil refining device can not be constructed, and the device investment is reduced.

[0026] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of the specification, illustrate embodiments of the present disclosure and serve to explain the principles of the present disclosure, but are not intended to limit the present disclosure. In the drawings:

[0028] Figure 1 is a flow diagram of a method for producing low-carbon olefins by steam cracking of crude oil provided by the present disclosure;

[0029] Figure 2 is a flow diagram of a method for producing low-carbon olefins by steam cracking of crude oil provided by the present disclosure.

[0030] BRIEF DESCRIPTION OF DRAWINGS

[0031] 1 - feedstock preheating section, 2 - first flash tank, 3 - first mixed superheating section, 4 - second flash tank, 5 - third flash tank, 6 - second mixed superheating section, 7 - third mixed superheating section, 8 - fourth steam superheating section, 9 - fifth mixed superheating section, 10 - sixth mixed superheating section, 11 - seventh mixed superheating section, 12 - buffer tank, 13 - pump, 15 - desalting pre-treater, 16 - quench water preheater, b, pump backflow control valve; c, liquid level control valve, d, pump outlet flow meter, 101 - crude oil, H1 - quench water, 103 - desalted crude oil, 103 - desalted crude oil, 104 - second preheated crude oil, 105 - first gas phase fraction, 106 - first liquid phase fraction, 107 - mixture of first liquid phase fraction and primary dilution steam, 108 - second gas phase fraction, 109 - second liquid phase fraction, 110 - primary dilution steam, 111 - mixture of heated second liquid phase fraction and steam, 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 - mixture of first gas phase fraction and primary dilution steam, 121 - first to-be-cracked stream, 122 - second to-be-cracked stream, 123 - third to-be-cracked stream, 124 - superheated secondary dilution steam DETAILED DESCRIPTION

[0032] The specific embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the present disclosure, and are not intended to limit the present disclosure.

[0033] In the present disclosure, the words "first", "second", "third" and the like used herein are merely used to distinguish different components and do not contain actual meanings such as sequence of connection and the like, unless otherwise specified. In the present disclosure, the orientation words such as "upper", "lower", "top" and "bottom" generally refer to the upper and lower, top and bottom in the normal use state of the device. "Inner" and "outer" are relative to the outline of the device.

[0034] In the present disclosure, the words "once diluted steam", "secondary diluted steam", "first part steam", "second part steam" and the like used herein are merely used to distinguish the introduced steam in different steps and do not contain actual meanings such as the nature of the steam itself.

[0035] The present disclosure first flashes the crude oil to obtain a first gas phase fraction and a first liquid phase fraction, then mixes the first liquid phase fraction with steam to perform a second flash to obtain a second gas phase fraction and a second liquid phase fraction, and then mixes the first liquid phase fraction with steam to perform a third flash to obtain a third gas phase fraction and a third liquid phase fraction, so as to realize effective gas-liquid separation. The present disclosure discloses that the above steps can obtain materials suitable for steam cracking in a cracking furnace to produce low-carbon olefins, such as the first gas phase fraction, the second gas phase fraction and the third gas phase fraction, and the separated fractions which are not suitable for steam cracking are used to produce aromatic hydrocarbons or sold as oil products, that is, olefins are used when appropriate, and aromatic hydrocarbons and oil products are used when appropriate. Further, since steam has been introduced in the second flash and the third flash, the second gas phase fraction and the third gas phase fraction obtained by separation carry steam themselves and can be directly used for cracking in the cracking furnace, without the need to additionally introduce steam. Only steam needs to be introduced into the first gas phase fraction before being introduced into the cracking furnace for steam cracking, and the amount of steam introduced in the whole process is easy to control.

[0036] The first aspect of the present disclosure provides a method for producing low-carbon olefins by steam cracking of crude oil, as shown in the formula: Figure 1 The method comprises the following steps:

[0037] S1, introducing the crude oil into a first flash tank 2 to perform a first flash separation to obtain a first gas phase fraction and a first liquid phase fraction;

[0038] S2, mixing the first liquid phase fraction with a first part of steam, then preheating and introducing into a second flash tank 4 to perform a second flash separation to obtain a second gas phase fraction and a second liquid phase fraction;

[0039] S3, mixing the second liquid phase fraction with a second part of steam, then preheating and introducing into a third flash tank 5 to perform a third flash separation to obtain a third gas phase fraction and a third liquid phase fraction;

[0040] S4, mixing the first gas phase fraction with a third portion of steam to obtain a first gas phase fraction mixture; feeding the first gas phase fraction mixture, optionally the second gas phase fraction and optionally the third gas phase fraction into a convection section of a steam cracking device respectively to be superheated, and then into a radiant section 17 of the steam cracking device to be steam cracked.

[0041] The present disclosure provides a method for producing low-carbon olefins by steam cracking of crude oil, which cancels the atmospheric and vacuum distillation device and other secondary processing devices, simplifies the process flow, and saves investment. The present disclosure is easy to control the amount of steam introduced in different steps. The process can be flexibly configured for different base crude oil feedstocks. For example, for paraffin-based crude oil, different fractions obtained by flashing can be efficiently cracked, the olefin yield is high, the energy consumption is reduced, and the existing steam cracking technology can be maximally applied, which is mature and easy to operate. For intermediate base crude oil or naphthenic base crude oil with high aromatic content, appropriate fractions can be flexibly selected for steam cracking, and appropriate fractions can be introduced into a refinery device to maximize resource utilization. The present disclosure has a wide range of crude oil adaptability, can be used with existing refining and chemical integrated devices to improve quality and efficiency, and can also be used for new refining and chemical integrated devices to produce low-carbon olefins, especially ethylene. For newly built refining and chemical integrated devices, the refinery device such as atmospheric and vacuum distillation and reforming can be built less, and for light paraffin-based crude oil, the refinery device can also not be built, thereby reducing device investment.

[0042] In a preferred embodiment, the end boiling point of the first gas phase fraction is 80-160℃; the initial boiling point of the first liquid phase fraction is not higher than the end boiling point of the first gas phase fraction;

[0043] The end boiling point of the second gas phase fraction is 160-250℃, and the initial boiling point of the second liquid phase fraction is not higher than the end boiling point of the second gas phase fraction;

[0044] The end boiling point of the third gas phase fraction is 250-350℃; and the initial boiling point of the third liquid phase fraction is not higher than the end boiling point of the third gas phase fraction.

[0045] In a specific embodiment, the first gas phase fraction includes naphtha and lighter gas phase fractions, and the first liquid phase fraction includes liquid phase fractions heavier than naphtha; the second gas phase fraction includes kerosene and lighter fractions and diesel gas phase fractions heavier than kerosene to heavy diesel, and the second liquid phase fraction includes liquid phase fractions heavier than heavy diesel; the third gas phase fraction includes diesel gas phase fractions lighter than heavy diesel, and the third liquid phase fraction includes liquid phase fractions heavier than heavy diesel.

[0046] It should be understood that the end boiling point of the gas phase fraction and the end boiling point of the liquid phase fraction obtained by flash separation in the present disclosure are both range values, and in actual operation, can be any temperature within the range. And the present disclosure can select the separated fractions according to actual production needs, for example, in the first flash separation, the light naphtha fraction and a lighter fraction can be selected as the first gas phase fraction according to needs, and the end boiling point of the first gas phase fraction can be 80°C or lower, 90°C or lower, 100°C or lower, etc. Or the full-range naphtha fraction is selected as the first gas phase fraction, and the end boiling point of the first gas phase fraction can be 160°C or lower, 150°C or lower, 140°C or lower, etc. And in the actual process, the first liquid phase component obtained by separation may also contain light components, for example, a light fraction with an initial boiling point of 60°C can also be contained in the first liquid phase fraction.

[0047] In the present disclosure, each fraction obtained by separation in the first flash tank, the second flash tank and the third flash tank carries steam, and the distillation temperature of each fraction in the present disclosure is the separated crude oil component in the fraction excluding steam.

[0048] In the present disclosure, the first flash tank, the second flash tank and the third flash tank are devices conventionally selected in the art; wherein the third flash tank has a flash rotating liquid separation structure for gas-liquid separation in the third flash process, and the gas (steam) phase outlet can be one or more. The third flash tank with a flash rotating liquid separation structure in the present embodiment can more completely separate the third liquid phase fraction by the third separation, that is, more completely separate the heavy components in the crude oil that cannot be used for steam cracking, to prevent the phenomenon that the heavy components carried in the third gas phase fraction cause coking of the radiant tube in the cracking process.

[0049] In an embodiment, the raw material crude oil is at least one of a paraffin-based crude oil, an intermediate-based crude oil or a naphthenic-based crude oil.

[0050] In an embodiment, the method further comprises: passing all of the second gas phase fraction into a convection section of a steam cracking device to be superheated, and then into a radiant section 17 of the steam cracking device to be steam cracked; or

[0051] passing all of the second gas phase fraction into a refinery device for further processing; or

[0052] passing a part of the second gas phase fraction into a convection section of a steam cracking device to be superheated, and then into a radiant section 17 of the steam cracking device to be steam cracked, and passing another part of the second gas phase fraction into a refinery device for further processing.

[0053] In an embodiment, as Figure 1 or Figure 2As shown, the method further comprises: passing all of the third gas phase fraction into a convection section of a steam cracking device for superheating, and then into a radiation section 17 of the steam cracking device for steam cracking; or

[0054] passing all of the third gas phase fraction into a refinery device for further processing; or

[0055] passing part of the third gas phase fraction into a convection section of a steam cracking device for superheating, and then into a radiation section 17 of the steam cracking device for steam cracking, and passing another part of the third gas phase fraction into a refinery device for further processing.

[0056] In the present disclosure, the processing modes of the second gas phase fraction and the third gas phase fraction are independent of each other, and can be selected arbitrarily according to actual needs. For example, the following four modes can be included: mode 1, performing subsequent steam cracking on the second gas phase fraction and performing refining on the third gas phase fraction; mode 2, performing subsequent steam cracking on the third gas phase fraction and performing refining on the second gas phase fraction; mode 3, performing subsequent steam cracking on both the second gas phase fraction and the third gas phase fraction; and mode 4, performing refining on both the second gas phase fraction and the third gas phase fraction.

[0057] In the present disclosure, the second gas phase fraction or the third gas phase fraction and the third liquid phase fraction obtained can be processed differently according to the lightness or heaviness of the crude oil and the source and composition of the crude oil. For example, whether the crude oil is a paraffin-based crude oil or a naphthenic-based crude oil can be used to determine whether the third gas phase fraction is introduced into a steam cracking device as a cracking raw material or directly introduced into a refinery device, or part of the third gas phase fraction is introduced into a steam cracking device as a cracking raw material and the remaining part of the third gas phase fraction is introduced into a refinery device for secondary processing, so as to improve the overall utilization efficiency of the process.

[0058] In one specific embodiment, as shown in Figure 1 the present disclosure further comprises the following step: when the crude oil is a paraffin-based crude oil, introducing at least part of the third gas phase fraction into a refinery device for processing. In this embodiment, introducing the third gas phase fraction obtained by fractionating the paraffin-based crude oil into a refinery device for processing can use the fraction that is not suitable as a steam cracking raw material to produce aromatic oil, that is, the principle of “suitable for cracking, suitable for cracking, suitable for oil” can be realized, and the fractions separated from different types of raw material crude oil can be flexibly utilized.

[0059] In another specific embodiment, as shown in Figure 2 when the raw material crude oil is a naphthenic-based crude oil, introducing all of the third gas phase fraction into a radiation section of a steam cracking device and not introducing it into a refinery device, so as to further improve the yield of olefins.

[0060] As can be seen from the above two specific implementation methods, the third gas phase fraction (a mixture of diesel gas phase fraction below heavy diesel and steam) obtained by the third flash separation can be processed differently depending on the type of crude oil. It has a wide range of adaptability to crude oil and the separated fraction can be used flexibly to achieve quality improvement and efficiency enhancement with existing integrated refining and chemical units.

[0061] In one optional embodiment, the method further includes: superheating all of the first vapor fraction in the convection section of another steam cracking unit, and then subjecting it to steam cracking in its corresponding radiative section; or superheating all of the second vapor fraction in the convection section of another steam cracking unit, and then subjecting it to steam cracking in its corresponding radiative section; the third vapor fraction is superheated in the convection section of the steam cracking unit, and then subjecting it to steam cracking in the radiative section of the steam cracking unit. In principle, the three vapor fractions can be fed into different cracking furnaces for cracking. One portion can be fed into the same cracking furnace, while the other two portions can be fed into other cracking furnaces. Various combinations are possible, including each vapor fraction being fed into a different cracking furnace, or two vapor fractions being fed into the same cracking furnace. The goal is to ensure that the cracking furnace is easy to operate and control, and that it operates at full load or achieves maximum efficiency.

[0062] In one implementation, such as Figure 1 As shown, along the height direction of the steam cracking device, the convection section is provided with, from top to bottom, an independent first mixing superheating section 3, a second mixing superheating section 6, a third mixing superheating section 7, a fourth steam superheating section 8, a fifth mixing superheating section 9, a sixth mixing superheating section 10, and a seventh mixing superheating section 11; the method further includes:

[0063] The first liquid phase fraction is mixed with a first portion of steam and then enters the first mixing superheating section 3 for heating; then the heated first liquid phase fraction mixture enters the second flash tank 4 for the second flash separation; preferably, the temperature of the heated first liquid phase fraction mixture is 200-350°C; the second liquid phase fraction is mixed with a second portion of steam and then enters the third mixing superheating section 7 for heating; then the heated second liquid phase fraction mixture is mixed with a fourth portion of steam and then enters the third flash tank 5 for the third flash separation; preferably, the temperature of the heated second liquid phase fraction mixture is 250-400°C. More preferably, this disclosure allows for the installation of a boiler feedwater inlet at the inlet of the third mixing superheating section 7 to control the temperature of the heated second liquid phase fraction mixture, thereby controlling the liquid film temperature to be less than 500°C and preventing decomposition, coking, etc., of the material in the third flash tank.

[0064] The mixture 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 mixture of the second liquid phase fraction and the second part of steam is introduced into the third mixed superheating section for heating, which can improve the overall heat utilization efficiency of the process; in the present disclosure, the second liquid phase fraction is first mixed with the primary dilution steam (the second part of steam), heated, and then mixed with the heated secondary dilution steam (the fourth part of steam), and the separate introduction of the secondary dilution steam (the fourth part of steam) can have the effect of stripping the mixed stream, thereby further improving the third flash separation effect of the second liquid phase fraction.

[0065] In an optional embodiment, the fourth part of steam is steam heated by the fourth steam superheating section 8, and preferably, the temperature of the heated fourth part of steam is 400-575°C.

[0066] In an embodiment, the weight ratio of the third part of steam to the first gas phase fraction is 0.35-1, preferably 0.4-0.6.

[0067] The weight ratio of the first part of steam to the second gas phase fraction is 0.4-1, preferably 0.5-0.7.

[0068] 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 0.5-1, preferably 0.7-0.9. This is beneficial for controlling the flash separation effect in different flash tanks to achieve maximum separation of different gas phase components for cracking. In the present disclosure, since the first gas phase fraction, the second gas phase fraction and the third gas phase fraction obtained by separation all contain steam, the mass of the components remaining in the first gas phase fraction, the second gas phase fraction and the third gas phase fraction after removal of steam is used as the basis for controlling the amount of steam introduced.

[0069] In an embodiment, as shown in Figure 1 The method further comprises: mixing the first gas phase fraction with the third part of steam and then introducing the mixture into the second mixed superheating section 6 for heating, and then introducing the mixture into the fifth mixed superheating section 9 for heating to 550-720°C to obtain a first to-be-cracked stream;

[0070] Optionally, the second gas phase fraction is introduced into the sixth mixed superheating section 10 for heating to 500-680°C to obtain a second to-be-cracked stream;

[0071] Optionally, the third gas phase fraction is introduced into the seventh mixed superheating section 11 for heating to 400-650°C to obtain a third to-be-cracked stream;

[0072] The first to-be-cracked stream, the optional second to-be-cracked stream, and the optional third to-be-cracked stream are respectively introduced into the radiant section 17 of the steam cracking device to perform the steam cracking.

[0073] The present disclosure introduces different fractions obtained by different flash separations into different superheating sections for heating respectively, and the different fractions can be heated to appropriate initial cracking temperatures (crossing temperatures) respectively. The first to-be-cracked stream, the second to-be-cracked stream, and the third to-be-cracked stream are respectively introduced into the radiant section (for example, a cracking furnace) of the steam cracking device for cracking, which is beneficial to controlling the cracking conditions of different to-be-cracked streams, so that each to-be-cracked stream can be cracked under appropriate conditions to improve the final olefin yield.

[0074] Specifically, the conditions for the steam cracking of the first to-be-cracked stream, the second to-be-cracked stream, and the third to-be-cracked stream in the radiant section in the present disclosure can adopt conventional conditions in the art, and the cracking catalyst can be selected from catalysts known in the art.

[0075] In a specific embodiment, when the BMCI value of the second cracking stream is 30 or more, the second cracking stream is not introduced into the steam cracking device for cracking, and the second cracking stream is sent to a refinery device.

[0076] When the BMCI value of the third cracking stream is 30 or more, the third cracking stream is not introduced into the steam cracking device for cracking, and the second cracking stream is sent to a refinery device. The "BMCI value" (U.S. Bureau of Mines Correlation Index) refers to an aromatic index, which represents an aromaticity index of an oil product.

[0077] In a specific embodiment, the method further comprises: introducing the first to-be-cracked stream, the second to-be-cracked stream, and the third to-be-cracked stream into different cracking furnace tubes of the same steam cracking device for cracking; or introducing the first to-be-cracked stream, the second to-be-cracked stream, and the third to-be-cracked stream into different cracking furnace tubes of different steam cracking devices for cracking. The selection can be made according to actual conditions.

[0078] In the present 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 can be different heat exchange tubes at the upper part of the convection section of the same cracking furnace, or heat exchange tubes at the upper part of the convection section of different cracking 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 cracking furnace, or heat exchange tubes at the lower part of the convection section of different cracking furnaces.

[0079] In an embodiment, as Figure 1As shown, the convection section of the steam cracking device further comprises a raw material preheating section 1, and along the height direction of the steam cracking device, the raw material preheating section 1 is arranged above the first mixed superheating section 3; the method further comprises: introducing the crude oil from the storage tank into the steam cracking device convection section for further heating after first heat exchange by the quenching water preheater 16, and taking the obtained preheated crude oil as the first preheated crude oil.

[0080] The first preheated crude oil is introduced into the desalination pretreater 15 for desalination pretreatment, and desalinated crude oil is obtained.

[0081] The desalinated crude oil is introduced into the raw material preheating section 1 of the steam cracking device for heating, and the second preheated crude oil is obtained; then the second preheated crude oil is introduced into the first flash tank 2 for the first flash separation; optionally, the temperature of the second preheated crude oil is 180-350℃.

[0082] Optionally, the method further comprises: introducing the third liquid phase fraction from the third flash tank 5 into the buffer tank 12 for buffering, and then leading 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 introduced into the hydrogenation device for hydrogenation treatment, the second part of the third liquid phase fraction is introduced into the catalytic cracking device for catalytic cracking treatment, and the third part of the third liquid phase fraction is introduced into the buffer tank 12 for reflux.

[0083] In a specific embodiment, the flow sequence of crude oil preheating can also use the heat exchange of the waste heat of the ethylene device instead of the quenching water heat exchange, and then the heat exchange preheating with the high-temperature heavy oil obtained in the ethylene cracking process; the crude oil can also be first heat exchanged with the waste heat of the ethylene device, then desalted, and then heat exchanged with the high-temperature heavy oil obtained in the ethylene cracking process. In this way, the exchange of thermal energy between multiple devices is realized, especially the energy consumption of the ethylene device is reduced, the thermal energy is recycled and utilized, and the investment is saved.

[0084] In an embodiment, the method further comprises: dividing at least part of the dilution steam into four parts, respectively as the first part of the steam, the second part of the steam, the third part of the steam, and the fourth part of the steam.

[0085] In an embodiment, the method further comprises: before introducing the second gas phase fraction into the oil refining device, introducing the second gas phase fraction and the to-be-preheated crude oil into a gas phase fraction first cooler respectively for heat exchange, to obtain a liquid-phase second gas phase fraction and preheated crude oil; and introducing the liquid-phase second gas phase fraction into the oil refining device for further processing.

[0086] 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 the crude oil to be preheated enter a gas phase fraction second cooler respectively for heat exchange, to obtain the third gas phase fraction in liquid phase and the preheated crude oil; the third gas phase fraction in liquid phase enters the oil refining device for further processing; wherein the crude oil to be preheated is the crude oil in any step before entering the first flash tank 2. The gas phase fraction first cooler and the gas phase fraction second cooler can be used in series with other devices in the system of the present disclosure for processing the raw oil before entering the separation tower. In the present disclosure, when the second gas phase fraction or the third gas phase fraction is introduced into the oil refining device, a cooler is needed to cool the gas phase fraction into liquid phase before oil refining, and in the cooler, the gas phase fraction can be used for heat exchange with the crude oil to be preheated, further improving the heat utilization effect.

[0087] In one embodiment, the method further comprises: before the second preheated crude oil from the raw material preheating section 1 enters the first flash tank 2, the second preheated crude oil is subjected to first external preheating treatment; before the first liquid phase fraction from the first flash tank 2 enters the second flash tank 4, the first liquid phase fraction is subjected to second external preheating treatment; before the second liquid phase fraction from the second flash tank 4 enters the third flash tank 5, the second liquid phase fraction is subjected to third external preheating treatment.

[0088] 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 source of the first external preheating treatment, the second external preheating treatment and the third external preheating treatment is waste heat material from any device, further improving the heat utilization effect, especially the utilization effect of waste heat material obtained from other devices in the plant. 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 device, and can be selected according to actual conditions, and can be used simultaneously.

[0089] The method provided by the present disclosure can also control the temperature or pressure of the material in the following ways.

[0090] In one specific embodiment, the method further comprises: on the feed line of the first flash tank 2 for introducing the second preheated crude oil 104 from the raw material preheating section 1, a pressure regulating valve is arranged to control the pressure of the material before entering the first flash tank 2, so as to control the temperature and gasification rate required for the first stage flash evaporation.

[0091] In one specific embodiment, the method further comprises: on the gas phase outlet of the second gas phase fraction 108 of the second flash tank 4, a pressure regulating valve is arranged to control the pressure of the second flash tank 4, and the flash evaporation rate is controlled by controlling the pressure of the flash tank.

[0092] In one embodiment, the method further comprises: providing a water injection mixer on the introduction pipeline of the liquid phase outlet of the second liquid phase fraction 109 of the second flash tank 4, and providing a thermometer on the feed pipeline 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, and controlling the temperature of the heated second liquid phase fraction and steam mixture 111 by the water injection amount of the water injection mixer to prevent coking in the preheating process.

[0093] Optionally, the method further comprises: providing a water injection inlet on the feed pipeline 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 vaporization rate of the third flash tank 5.

[0094] The control scheme of the present disclosure can be any one of the above control schemes, or any combination of control schemes.

[0095] The operating temperatures adopted by the present disclosure are all pressure-balanced temperatures within the normal operating range under conventional operating conditions of the cracking furnace. Optionally, pressure control measures can be added to adjust the pressure related to vaporization according to the properties of the crude oil and the actual needs of cutting, and the related operating temperatures are correspondingly controlled.

[0096] The second aspect of the present disclosure provides a system for producing low-carbon olefins from crude oil by steam cracking, as shown in Figure 1 The system comprises 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 radiant section 17, and the convection section is arranged above the radiant section 17 along the height direction of the steam cracking device; wherein,

[0097] 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; and 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.

[0098] The first liquid phase fraction outlet is in communication with the first liquid phase fraction inlet, and the second liquid phase fraction outlet is in communication with the second liquid phase fraction outlet.

[0099] The radiant section 17 of the steam cracking device is provided with a first to-be-cracked raw material inlet, an optional second to-be-cracked raw material inlet, and an optional third to-be-cracked raw material inlet; the first to-be-cracked raw material inlet is in communication with the first gas phase fraction outlet, the second to-be-cracked raw material inlet is in communication with the second gas phase fraction outlet, and the third to-be-cracked raw material inlet is in communication with the third gas phase fraction outlet.

[0100] In one embodiment, as shown in Figure 1As shown, along the height direction of the steam cracking device, the convection section is sequentially provided with the raw material preheating section 1, the first mixed superheating section 3, the second mixed superheating section 6, the third mixed superheating section 7, the fifth mixed superheating section 9, the sixth mixed superheating section 10 and the seventh mixed superheating section 11 which are independent of each other.

[0101] 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.

[0102] 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 phase fraction outlet of the first flash tank 2 through a first pipeline; the first superheating outlet is communicated with the first liquid phase fraction inlet of the second flash tank 4.

[0103] 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 phase fraction outlet of the second flash tank 4 through a second pipeline; the third superheating outlet is communicated with the second liquid phase fraction inlet of the third flash tank 5 through a fourth pipeline.

[0104] 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, and 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 to-be-cracked raw material inlet of the radiation section 17.

[0105] The sixth mixed superheating section 10 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 4; the sixth superheating outlet is communicated with the second to-be-cracked raw material inlet of the radiation section 17.

[0106] 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 is communicated with the third to-be-cracked raw material inlet of the radiation section 17.

[0107] Specifically, the radiation section of the steam cracking device (cracking furnace) includes the first cracking furnace tube, the second cracking furnace tube and the third cracking furnace tube which are independently arranged, the first cracking furnace tube is provided with a raw material inlet which forms the first to-be-cracked raw material inlet, the second cracking furnace tube is provided with a raw material inlet which forms the second to-be-cracked raw material inlet, and the third cracking furnace tube is provided with a raw material inlet which forms the third to-be-cracked raw material inlet. Optionally, the first cracking furnace tube, the second cracking furnace tube and the third cracking furnace tube can be different radiation section furnace tubes in the same furnace chamber of the same cracking furnace; or radiation furnace tubes in different radiation section furnace chambers of the same cracking furnace; or radiation furnace tubes of different cracking furnaces, which can be arranged according to actual conditions.

[0108] In a preferred embodiment, the first flash tank 2, the second flash tank 4 and the third flash tank 5 are arranged in sequence along the same central axis in the vertical direction, saving space and facilitating arrangement.

[0109] In an embodiment, the first pipeline is further provided with a first partial steam inlet; the second pipeline is further provided with a second partial steam inlet; the third pipeline is further provided with a third partial steam inlet; the fourth pipeline is further provided with a fourth partial steam inlet;

[0110] 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 in communication with the fourth partial steam inlet on the fourth pipeline.

[0111] In a specific embodiment, a first mixer is further provided at the first partial steam inlet of the first pipeline for mixing the first liquid phase fraction from the first flash tank with the first partial steam; a second mixer is further provided at the second partial steam inlet of the second pipeline for mixing the second liquid phase fraction from the second flash tank with the second partial steam; a third mixer is further provided at the third partial steam inlet of the third pipeline for mixing the first liquid phase fraction from the first flash tank with the third partial steam; and a fourth mixer is further provided at the fourth partial steam inlet of the fourth pipeline for mixing the stream from the third mixed superheating section with the fourth partial steam. The first mixer, the second mixer, the third mixer and the fourth mixer can make the mixing of the material and steam more uniform, preventing coking. Any mixer known in the art that meets the above mixing effect can be used.

[0112] In an embodiment, the system further comprises a buffer tank 12, a pump 13, a desalting pretreater 15 and a quench water preheater 16;

[0113] 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 reflux inlet, a steam purge port and a nitrogen purge port; the pump 13 comprises an input port and an output port; the desalting pretreater 15 is provided with a crude oil desalting inlet and a crude oil desalting outlet; and the quench water preheater 16 is provided with a quench water heat exchange inlet, a quench water heat exchange outlet, a crude oil heat exchange first inlet and a crude oil heat exchange first outlet;

[0114] The crude oil heat exchange first outlet of the quench water preheater 16 is in communication with the crude oil desalting inlet of the desalting pretreater 15, and the crude oil desalting outlet is in communication with the crude oil preheating inlet of the raw material preheating section 1;

[0115] The liquid phase heavy component buffer inlet of buffer tank 12 is connected to the third liquid phase distillate outlet of third flash tank 5, and the liquid phase heavy component buffer outlet is connected to the inlet of pump 13; optionally, the outlet of pump 13 is used to connect to the feed inlet of catalytic cracking unit and / or the feed inlet of hydrotreating unit.

[0116] Optionally, the system also includes a flow control unit, which includes a level transmitter, a pump reflux control valve b, a level control valve c, a pump outlet flow meter d, a heavy component outflow flow meter e, and a crude oil feed flow meter f; the top of the buffer tank 12 is also provided with a heavy component reflux inlet.

[0117] The level transmitter is connected to the internal space of the buffer tank 12 to control the liquid level inside the buffer tank 12; a heavy component return outlet is provided on the pipeline between the pump outlet flow meter d and the level control valve c, and the heavy component return outlet is connected to the heavy component return inlet of the buffer tank 12 through a return pipeline; the pump return control valve b is located on the return pipeline, and the level control valve c is signal-connected to the level transmitter; in this disclosure, the liquid level of the liquid phase material in the buffer tank 12 is controlled by the level control valve c, and the temperature of the liquid phase material in the buffer tank 12 is controlled to be 200-270℃ by the pump return control valve b.

[0118] The present disclosure will be further described below with reference to specific embodiments.

[0119] Example 1

[0120] This embodiment follows Figure 1 The process flow shown selects crude oil with an API grade of 38-46 (Tarim Basin Shunbei Heavy Oil). In this embodiment, components with a boiling point below 430°C are introduced into the cracking furnace for cracking reaction as much as possible. Specifically, the process includes the following steps:

[0121] S1. Crude oil 101 and waste heat material H1 (such as quench water) are respectively introduced into quench water preheater 16 for preliminary preheating (first heat exchange, heating to desalination temperature 70-120℃). Then, the first preheated crude oil is desalted and impurities are removed by desalting preprocessor 15 to obtain desalted crude oil 103. Desalted crude oil 103 is then introduced into the feedstock preheating section 1 of the convection zone of the steam cracking unit for heating to obtain second preheated crude oil 104 (180-350℃).

[0122] S2, the second preheated crude oil 104 into the first flash tank 2, through the first flash separation of naphtha and lighter gas phase fraction 105 (the first gas phase fraction, the final boiling point is 80-160 ℃) and heavier than naphtha liquid phase fraction 106. The first gas phase fraction 105 obtained by the first flash tank 2 and the first dilution steam 119 (the third part of the steam) is mixed according to the steam: fraction weight ratio of 0.40-0.6:1, the first liquid phase fraction 106 and the first dilution steam 118 (the first part of the steam) is mixed, to obtain two kinds of mixture (in which the weight of the first dilution steam 118 introduced and the weight of the second gas phase fraction 108 obtained by subsequent separation is 0.45-0.7); then the first gas phase fraction and the steam mixture into the second mixed superheating section 6 for heating, the first liquid phase fraction and the steam mixture into the first mixed superheating section 3 for heating; the temperature of the first liquid phase fraction after heating is 200-350 ℃.

[0123] S3, the first liquid phase fraction after heating obtained by the above step and the first dilution steam mixture 107 into the second flash tank 4 for second flash separation, to obtain the following fraction: kerosene and lighter fraction and diesel gas phase fraction 108 (second gas phase fraction, the final boiling point is 160-250 ℃) and heavier than kerosene to heavy diesel below diesel and second liquid phase fraction 109, secondary dilution steam 112 in the fourth steam superheating section 8 fourth part of the steam) is superheated to 400-575 ℃. The second liquid phase fraction 109 obtained by the above step and the first dilution steam 110 (the second part of the steam) is mixed, and the second liquid phase fraction and steam mixture obtained is heated in the third mixed superheating section 7, and the second liquid phase fraction and steam mixture 111 is then mixed with the superheated fourth part of the steam 124 (in which the total weight of the first dilution steam 110 and the second dilution steam 124 and the weight of the third gas phase fraction 113 obtained by subsequent separation is 0.7-0.9), and then enters the third flash tank 5 for third flash separation, to obtain the following fraction: heavy diesel below diesel gas phase fraction 113 (third gas phase fraction, the final boiling point is 250-350 ℃) and heavy diesel above liquid phase fraction 114.

[0124] S4, the first gas phase fraction after heating obtained by the above step and the first dilution steam mixture 120 into the fifth mixed superheating section 9 to 550-720 ℃, to obtain the first cracking feed stream 121; the second gas phase fraction 108 obtained by the second flash tank enters the sixth mixed superheating section 10 to 500-680 ℃, to obtain the second cracking feed stream 122; the third gas phase fraction 113 obtained by the third flash tank enters the seventh mixed superheating section 11 to 400-650 ℃, to obtain the third cracking feed stream 123;

[0125] S5. The first pyrolysis stream 121, the second pyrolysis stream 122, and the third pyrolysis stream 123 are respectively introduced into the radiant section 17 of the steam pyrolysis device for steam pyrolysis; wherein the above three pyrolysis streams can be introduced into different radiant section furnace tubes in the same furnace chamber of the same pyrolysis furnace, or into radiant furnace tubes in different radiant section furnace chambers of the same pyrolysis furnace, or into radiant furnace tubes of different pyrolysis furnaces for pyrolysis.

[0126] S6. The third liquid fraction 114 after the flash vapor-liquid separation in the third flash tank 5 enters the buffer tank 12. The liquid level in the buffer tank is controlled by the liquid level regulating valve c.

[0127] Example 2

[0128] This embodiment follows Figure 2 The process flow shown selects crude oil with an API grade of 38-46 (Tarim Basin Shunbei Heavy Oil). In this embodiment, the light components with a boiling point below 260°C are introduced into the cracking furnace for cracking reaction as much as possible. Specifically, the process includes the following steps:

[0129] S1. Crude oil 101 and waste heat material H1 (such as quench water) are respectively introduced into quench water preheater 16 for preliminary preheating (first heat exchange, heating to desalination temperature 70-120℃). Then, the first preheated crude oil is desalted and impurities are removed by desalting preprocessor 15 to obtain desalted crude oil 103. Desalted crude oil 103 is then introduced into the raw material preheating section 1 of the convection zone of the steam cracking unit for heating to obtain second preheated crude oil 104 (180-350℃).

[0130] S2. The second preheated crude oil 104 is introduced into the first flash tank 2, and after the first flash separation, naphtha and a lighter gas phase fraction 105 (first gas phase fraction, with a final boiling point of 80-160℃) and a heavier liquid phase fraction 106 than naphtha are obtained. The first vapor fraction 105 obtained from the first flash tank 2 is mixed with primary dilution steam 119 (third part of the steam) at a steam:fraction weight ratio of 0.40 to 0.6:1. The first liquid fraction 106 is mixed with primary dilution steam 118 (first part of the steam) to obtain two mixtures (the weight ratio of the primary dilution steam 118 to the weight of the second vapor fraction 108 obtained after subsequent separation is 0.45 to 0.7). Then, the mixture of the first vapor fraction and the steam enters the second mixing superheating section 6 for heating, and the mixture of the first liquid fraction and the steam enters the first mixing superheating section 3 for heating. The temperature of the first liquid fraction mixture after heating is 200 to 350°C.

[0131] S3, the heated first liquid phase fraction obtained in the above step is mixed with the first dilution steam mixture 107 to enter the second flash tank 4 to perform second flash separation, to obtain the following fractions: kerosene and lighter fraction, diesel gas phase fraction 108 (second gas phase fraction, final boiling point 160-250°C) heavier than kerosene to below heavy diesel, and second liquid phase fraction 109 heavier than heavy diesel, and the second dilution steam 112 (fourth part of steam) is superheated to 400-575°C in the fourth steam superheating section 8. The second liquid phase fraction obtained in the above step is mixed with the first dilution steam 110, and the second liquid phase fraction and steam mixture enters the third mixing superheating section 7 to be heated, and the heated second liquid phase fraction and steam mixture 111 is then mixed with the superheated second dilution steam 124 (the total weight of the first dilution steam 110 and the second dilution steam 124 is 0.7-0.9 times the weight of the third gas phase fraction 113 obtained by subsequent separation), and then enters the third flash tank 5 to perform third flash separation, to obtain the following fractions: diesel gas phase fraction 113 (third gas phase fraction, final boiling point 250-350°C) below heavy diesel, and liquid phase fraction 114 heavier than heavy diesel.

[0132] S4, the heated first gas phase fraction obtained in the above step is mixed with the first dilution steam mixture 120 to enter the fifth mixing superheating section 9 to be heated to 550-720°C, to obtain the first to-be-cracked stream 121; the second gas phase fraction 108 obtained by the second flash tank enters the sixth mixing superheating section 10 to be heated to 500-680°C, to obtain the second to-be-cracked stream 122;

[0133] The third gas phase fraction 113 obtained by the third flash tank 5 enters the gas phase fraction second cooler to be cooled, and then the cooled liquid phase fraction is sent to the oil refining device (the oil refining device is not shown);

[0134] S5, the first to-be-cracked stream 121 and the second to-be-cracked stream 122 enter the radiant section 17 of the steam cracking device respectively to perform steam cracking; wherein the above two to-be-cracked streams can enter different radiant section furnace tubes in the same furnace chamber of the same cracking furnace, or radiant furnace tubes in different radiant section furnace chambers of the same cracking furnace, or radiant furnace tubes of different cracking furnaces;

[0135] S6, the third liquid phase fraction 114 after the gas-liquid separation by the third flash tank 5 enters the buffer tank 12, the liquid level of the buffer tank 12 is controlled by the liquid level regulating valve c, and the amount of the backflow of the third liquid phase material 117 is adjusted by the pump backflow regulating valve b. The temperature of the liquid phase material in the buffer tank 12 is controlled to be 150-300°C, the ratio of the third liquid phase fraction to the crude oil can be measured and calculated by the flow meter e and the flow meter f (e / f), and the amount of water injection is controlled by the regulating valve a for control.

[0136] The preferred embodiments of the present disclosure are described in detail above with reference to the drawings, but the present disclosure is not limited to the specific details in the above-described embodiments. Various simple modifications can be made to the technical solutions of the present disclosure within the technical concept of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0137] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, various possible combinations are not described again in the present disclosure.

[0138] In addition, various different embodiments of the present disclosure can also be combined in any appropriate manner, as long as they do not deviate from the idea of the present disclosure, and they should also be considered as disclosed by the present disclosure.

Claims

1. A process for the steam cracking of crude oil to produce lower olefins, characterized in that, The method comprises the following steps: S1, crude oil is introduced into a first flash tank (2) for first flash separation to obtain a first gas phase fraction and a first liquid phase fraction; S2, the first liquid phase fraction is mixed with a first portion of steam, and then after preheating, is introduced into a second flash tank (4) for second flash separation to obtain a second gas phase fraction and a second liquid phase fraction; S3, the second liquid phase fraction is mixed with a second portion of steam, and then after preheating, is introduced into a third flash tank (5) for third flash separation to obtain a third gas phase fraction and a third liquid phase fraction; S4, the first gas phase fraction is mixed with a third portion of steam to obtain a first gas phase fraction mixed material; the first gas phase fraction mixed material, optionally the second gas phase fraction and optionally the third gas phase fraction are introduced into a convection section of a steam cracking device for superheating, and then are introduced into a radiant section (17) of the steam cracking device for steam cracking; Along the height direction of the steam cracking device, the convection section is sequentially provided with first, second, third, fourth, fifth, sixth and seventh mixed superheating sections (3, 6, 7, 8, 9, 10 and 11) which are independent of each other from top to bottom; the method further comprises: The first liquid phase fraction is mixed with the first portion of steam and then is introduced into the first mixed superheating section (3) for heating; the heated first liquid phase fraction mixed material is introduced into the second flash tank (4) for the second flash separation; The second liquid phase fraction is mixed with the second portion of steam and then is introduced into the third mixed superheating section (7) for heating; then the heated second liquid phase fraction mixed material is mixed with a fourth portion of steam and then is introduced into the third flash tank (5) for the third flash separation; The weight ratio of the third portion of steam to the first gas phase fraction is 0.35-1; The weight ratio of the first portion of steam to the second gas phase fraction is 0.4-1; The total amount of the second portion of steam and the fourth portion of steam to the weight ratio of the third gas phase fraction is 0.5-1.

2. The method of claim 1, wherein, The end boiling point of the first gas phase fraction is 80-160℃; the initial boiling point of the first liquid phase fraction is not higher than the end boiling point of the first gas phase fraction; The end boiling point of the second gas phase fraction is 160-250℃, and the initial boiling point of the second liquid phase fraction is not higher than the end boiling point of the second gas phase fraction; The end boiling point of the third gas phase fraction is 250-350℃; and the initial boiling point of the third liquid phase fraction is not higher than the end boiling point of the third gas phase fraction.

3. The method of claim 1, wherein, The method further comprises: all of the second gas phase fraction is introduced into the convection section of the steam cracking device for superheating, and then is introduced into the radiant section (17) of the steam cracking device for steam cracking; or All of the second gas phase fraction is introduced into a refinery device for further processing; or part of the second gas phase fraction is heated to superheat in a convection section of a steam cracking unit and then enters a radiant section (17) of the steam cracking unit for steam cracking, and another part of the second gas phase fraction is sent to a refinery for further processing.

4. The method of claim 3, wherein, The method further comprises: heating all of the third gas phase fraction to superheat in a convection section of a steam cracking unit and then entering a radiant section (17) of the steam cracking unit for steam cracking; or heating all of the third gas phase fraction to superheat in a convection section of a steam cracking unit and then entering a radiant section (17) of the steam cracking unit for steam cracking; or part of the third gas phase fraction is heated to superheat in a convection section of a steam cracking unit and then enters a radiant section (17) of the steam cracking unit for steam cracking, and another part of the third gas phase fraction is sent to a refinery for further processing.

5. The method of claim 1, wherein, The temperature of the heated first liquid phase fraction mixture is 200-350℃. The temperature of the heated second liquid phase fraction mixture is 250-400℃.

6. The method of claim 1, wherein, The fourth part of steam is steam heated by the fourth steam superheating section (8).

7. The method of claim 6, wherein, The temperature of the heated fourth part of steam is 400-575℃.

8. The method of claim 1, wherein, The weight ratio of the third part of steam to the first gas phase fraction is 0.4-0.

6. The weight ratio of the first part of steam to the second gas phase fraction is 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 0.7-0.

9.

9. The method of claim 1, wherein, The method further comprises: mixing the first gas phase fraction with the third part of steam and then entering the second mixed superheating section (6) for heating, and then entering the fifth mixed superheating section (9) for heating to 550-720℃ to obtain a first cracking feed stream; entering the second gas phase fraction into the sixth mixed superheating section (10) for heating to 500-680℃ to obtain a second cracking feed stream; entering the third gas phase fraction into the seventh mixed superheating section (11) for heating to 400-650℃ to obtain a third cracking feed stream; entering the first cracking feed stream, optionally the second cracking feed stream, and optionally the third cracking feed stream into the radiant section (17) of the steam cracking unit for steam cracking.

10. The method of claim 9, wherein, The method further comprises: when the BMCI value of the second cracking feed stream is 30 or more, the second cracking feed stream does not enter the steam cracking unit for cracking, and the second cracking feed stream is sent to a refinery; when the BMCI value of the third cracking feed stream is 30 or more, the third cracking feed stream does not enter the steam cracking unit for cracking, and the third cracking feed stream is sent to a refinery.

11. The method of claim 10, wherein, The method further comprises: entering the first cracking feed stream, the second cracking feed stream, and the third cracking feed stream into different cracking furnace tubes of the same steam cracking unit for cracking; or entering the first cracking feed stream, the second cracking feed stream, and the third cracking feed stream into different cracking furnace tubes of different steam cracking units for cracking.

12. The method of claim 1, wherein, 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 mixed superheating section (3) along the height direction of the steam cracking device; the method further comprises: The crude oil from the storage tank is introduced into the convection section of the steam cracking device after first heat exchange through the quenching water preheater (16) to continue heating, and first preheated crude oil is obtained; The first preheated crude oil is introduced into the desalting pretreater (15) to perform desalting pretreatment, and desalted crude oil is obtained; The desalted crude oil is introduced into the raw material preheating section (1) of the steam cracking device to perform heating, and second preheated crude oil is obtained; then the second preheated crude oil is introduced into the first flash tank (2) to perform the first flash separation.

13. The method of claim 12, wherein, The temperature of the second preheated crude oil is 180-350 ℃.

14. The method of claim 12, wherein, The method further comprises: the third liquid phase fraction from the third flash tank (5) is buffered through the buffer tank (12) and then introduced out.

15. The method of claim 14, wherein, The method further comprises: 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 introduced into a hydrogenation device to perform hydrogenation treatment, and the second part of the third liquid phase fraction is introduced into a catalytic cracking device to perform catalytic cracking treatment; the third part of the third liquid phase fraction is introduced into the buffer tank (12) in reflux.

16. The method of claim 1, wherein, The crude oil is at least one of paraffin-based crude oil, intermediate-based crude oil, and naphthenic-based crude oil.

17. The method of claim 1, wherein, The method further comprises: a pressure regulating valve is arranged on a feed pipeline of the first flash tank (2) for introducing the second preheated crude oil (104) from the raw material preheating section (1) to control the pressure of the material before being introduced into the first flash tank (2).

18. The method of claim 1, wherein, The method further comprises: a pressure regulating valve is arranged at a 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).

19. The method of claim 1, wherein, 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 (109) of the second flash tank (4), and a thermometer is arranged on a feed pipeline 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), so that the temperature of the heated second liquid phase fraction and steam mixture (111) is controlled by the water injection amount of the water injection mixer.

20. The method of claim 1, wherein, The method further comprises: a water injection inlet is arranged on the feed pipeline 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 vaporization rate of the third flash tank (5).

21. The method of claim 12, wherein, The method further comprises: At least part of the third liquid phase fraction is introduced into a dilution steam generator to perform treatment, and dilution steam is obtained; at least part of the dilution steam is divided into four parts, which are respectively used as the first part of steam, the second part of steam, the third part of steam, and the fourth part of steam.

22. The method of claim 12, wherein, The method further comprises: Before the second gas phase fraction is introduced into the oil refining device, the part of the second gas phase fraction and the to-be-preheated crude oil are introduced into a gas phase fraction first cooler respectively to perform heat exchange, and the second gas phase fraction in liquid phase and preheated crude oil are obtained; the second gas phase fraction in liquid phase is introduced into the oil refining device to continue processing; Before the third gas phase fraction enters the oil refinery, the third gas phase fraction and the crude oil to be preheated are respectively introduced into a second gas phase fraction cooler to exchange heat, so as to obtain a liquid phase third gas phase fraction and preheated crude oil; the liquid phase third gas phase fraction enters the oil refinery for further processing; Before the second preheated crude oil from the raw material preheating section (1) enters the first flash tank (2), the second preheated crude oil is subjected to first external preheating treatment; before the first liquid phase fraction from the first flash tank (2) enters the second flash tank (4), the first liquid phase fraction is subjected to second external preheating treatment; before the second liquid phase fraction from the second flash tank (4) enters the third flash tank (5), the second liquid phase fraction is subjected to third external preheating treatment; The first external preheating treatment, the second external preheating treatment and the third external preheating treatment are respectively performed outside the steam cracking device, and the heat source of the first external preheating treatment, the second external preheating treatment and the third external preheating treatment is waste heat material from any device.

23. A system for the production of low carbon olefins by steam cracking of crude oil according to the process of claim 1, characterized in that, The system comprises the first flash tank (2), the second flash tank (4), the third flash tank (5) and the steam cracking device, the steam cracking device comprises a convection section and a radiation section (17), and the convection section is arranged above the radiation section (17) in the height direction of the steam cracking device; wherein, 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; and 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 first liquid phase fraction outlet is in communication with the first liquid phase fraction inlet, and the second liquid phase fraction outlet is in communication with the second liquid phase fraction inlet; The radiation section (17) of the steam cracking device is provided with a first to-be-cracked raw material inlet, an optional second to-be-cracked raw material inlet and an optional third to-be-cracked raw material inlet; the first to-be-cracked raw material inlet is in communication with the first gas phase fraction outlet, the second to-be-cracked raw material inlet is in communication with the second gas phase fraction outlet, and the third to-be-cracked raw material inlet is in communication with the third gas phase fraction outlet.

24. The system of claim 23, wherein, In the height direction of the steam cracking device, the convection section is sequentially provided with the raw material preheating section (1), the first mixed superheating section (3), the second mixed superheating section (6), the third mixed superheating section (7), the fifth mixed superheating section (9), the sixth mixed superheating section (10) and the seventh mixed superheating section (11) 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 in communication with the 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, the first superheating inlet is in communication with the first liquid phase fraction outlet of the first flash tank (2) through a first pipeline, and the first superheating outlet is in communication with the first liquid phase fraction inlet of the second flash tank (4); The second mixed superheating section (6) is provided with a second superheating inlet and a second superheating outlet, the second superheating inlet is in communication with the second liquid phase fraction outlet of the second flash tank (4) through a second pipeline, and the second superheating outlet is in communication with the second liquid phase fraction inlet of the third flash tank (5); The third mixed superheating section (7) is provided with a third superheating inlet and a third superheating outlet, the third superheating inlet is communicated with the second liquid phase fraction outlet of the second flash tank (4) through a second pipeline; the third superheating outlet is communicated with the second liquid phase 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, 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 to-be-cracked raw material inlet of the radiation section (17); The sixth mixed superheating section (10) is provided with a sixth superheating inlet and a sixth superheating outlet, the sixth superheating 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 to-be-cracked raw material inlet of the radiation section (17); The seventh mixed superheating section (11) is provided with a seventh superheating inlet and a seventh superheating outlet, the seventh superheating inlet is communicated with the third gas phase fraction outlet of the third flash tank (5); the seventh superheating outlet is communicated with the third to-be-cracked raw material inlet of the radiation section (17).

25. The system of claim 24, wherein, The first pipeline is further provided with a first partial steam inlet; the second pipeline is further provided with a second partial steam inlet; the third pipeline is further provided with a third partial steam inlet; and the fourth pipeline is further provided with a fourth steam inlet.

26. The system of claim 24, wherein, The first flash tank (2), the second flash tank (4) and the third flash tank (5) are arranged in sequence along the same central axis in the vertical direction.

27. The system of claim 25, wherein, 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 the fourth steam inlet on the fourth pipeline.

28. The system of claim 24, wherein, The system further comprises a buffer tank (12), a pump (13), a desalination pretreater (15) and a quenching 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 steam purging port and a nitrogen purging port; the pump (13) comprises an input port and an output port; the desalination pretreater (15) is provided with a crude oil desalination inlet and a crude oil desalination outlet; and 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; The crude oil heat exchange first outlet of the quenching water preheater (16) is communicated with the crude oil desalination inlet of the desalination pretreater (15), and the crude oil desalination 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).

29. The system of claim 28, wherein, The output of the pump (13) is configured to communicate with a feedstock inlet of a catalytic cracking device and / or a feedstock inlet of a hydroprocessing device.

30. The system of claim 25, wherein, The system further comprises a flow control unit comprising a level transmitter, a pump return control valve (b), a level control valve (c); the buffer tank (12) is further provided with a heavy component return inlet, which communicates with the outlet of the pump (13); wherein the level transmitter communicates with the internal space of the buffer tank (12) to control the liquid level in the buffer tank (12).

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