A process and system for producing olefins from a heavy feedstock

Abstract

The present disclosure relates to a method and system for producing olefins by cracking heavy feedstock. The heavy feedstock (crude oil and / or heavy hydrocarbon) is mixed with steam and then subjected to first flash separation, then the first liquid phase fraction is mixed with steam and subjected to second flash separation, and then the second liquid phase fraction is mixed with steam and subjected to third flash separation; at least one of the three gas phase fractions obtained by the three flash separations is heated and introduced into a cracking furnace for cracking. The process is simpler, has strong adaptability to crude oil and heavy hydrocarbon, is conducive to cutting different components of different crude oil and heavy hydrocarbon by optimizing process operation, realizes efficient cracking of different fractions, and has high olefin yield. According to the composition of the heavy feedstock and the processing requirements, the fraction suitable for producing olefins can be selected as the cracking feedstock, and the fraction not suitable for being the cracking feedstock can be used to produce aromatic hydrocarbon or be sold as oil products, that is, olefins can be produced when appropriate, aromatics can be produced when appropriate, and oil can be produced when appropriate.

Description

Technical Field

[0001] This disclosure relates to the field of hydrocarbon processing, and more specifically, to a method and system for producing olefins by cracking heavy feedstocks. Background Technology

[0002] In 2019, my country's ethylene production capacity reached 30.66 million tons, an increase of 5.34 million tons compared to 2018. However, my country's equivalent demand for ethylene in 2019 reached 47.2 million tons, still unable to meet market demand. Currently, my country still relies heavily on imports for a large amount of ethylene and its derivatives annually. Therefore, expanding the feedstock sources for ethylene cracking units, shortening the processing flow of oil refining units, using crude oil as feedstock for steam cracking, reducing feedstock costs, breaking free from the constraints of feedstock varieties, and simultaneously reducing investment in oil refining units have become effective means for traditional ethylene enterprises to reduce costs and increase efficiency to cope with the impact of market competition, thereby improving production flexibility.

[0003] Compared to traditional cracking feedstocks, using crude oil as feedstock in steam cracking furnaces presents challenges such as a high final boiling point (above 540℃), high gum content, difficulty in vaporization, and a tendency to coke. Therefore, corresponding modifications and treatments are needed in the design of the cracking furnace and the production process to accommodate the characteristics of crude oil.

[0004] CN111196936A discloses a combined processing method and apparatus for direct crude oil cracking to produce olefins. The method first employs pretreatment processes such as desalting and dehydration to remove impurities, then feeds the crude oil into an ethylene cracking convection section for heating. The heated feed is then sent to a gas-liquid separator, where lighter hydrocarbon gases are separated and sent to the convection and radiant sections for steam cracking to produce olefins. The liquid exiting the gas-liquid separator contains components such as atmospheric residue and needs to be further processed in a hydrotreating unit before being returned to the convection and radiant sections. This method directly feeds superheated crude oil into the gas-liquid separator, making it difficult to achieve the desired gas-liquid separation effect.

[0005] CN107001955B discloses a method for thermally cracking crude oil and heavy feedstock in a pyrolysis reactor to produce olefins. This method describes a scheme combining a cracking furnace convection section with multi-stage (up to three stages) separators and fractionation towers. This method can perform multiple gas-liquid separations on a mixture of crude oil and steam, and feed mixtures of different densities into different radiant furnace tubes for cracking. However, this method does not specify the specific heat source for preheating the crude oil in an external heat exchanger. Furthermore, while this method improves cracking selectivity to some extent by using multi-stage separators, fractionation towers, and different radiant furnace tubes to crack different fractions, it is cumbersome, requires significant investment, and is unsuitable for light crude oils, limiting its applicability to a narrow range of crude oils.

[0006] CN100564484C discloses a method for steam cracking of heavy hydrocarbon feedstocks, wherein the heavy hydrocarbon feedstocks mainly include: crude oil, naphtha, gas oil, fuel oil, natural gasoline (condensate oil), residue oil, etc. The method describes a flash steaming separation process, but it is difficult to separate the gas and liquid components well by simply flashing, especially since the gas phase component carries some heavy components, which can easily cause coking in the convection section and then lead to severe coking in the radiant section furnace tubes.

[0007] Ignesta Chemicals describes a process technology for producing ethylene from crude oil / condensate through cracking in patents CN101528894A and CN101778929A. CN101528894A describes a process where, after preheating the crude oil / condensate in the convection section, the separated light components enter the cracking furnace's convection section for superheating before entering the radiant section for cracking. The heavier components are sent to an atmospheric distillation tower and a vacuum distillation tower for further separation. CN101778929A describes a process where, after preheating the feedstock (containing 30% heavy feedstock such as crude oil or condensate) in the convection section, the feedstock enters the upper part of a separation unit, separating out the protective naphtha and lighter components. The separated liquid phase enters a packed tower below for further separation. The treatment of the separated heavy components is not described. Both patents use stripping towers with packed or trayed sections in their evaporation units. The upper evaporation zone contains a gas-liquid separator, enabling gas-liquid separation. However, the liquid phase after flash evaporation is relatively heavy and viscous; the packing and tray openings are also prone to clogging. Summary of the Invention

[0008] The purpose of this disclosure is to provide a method and system for producing low-carbon olefins by steam cracking of heavy feedstocks, which can prevent coking during the gasification process of heavy feedstocks such as crude oil and heavy hydrocarbons and achieve efficient gas-liquid separation.

[0009] To achieve the above objectives, the first aspect of this disclosure provides a method for producing olefins by cracking heavy feedstock. The method includes the following steps: S1, mixing the heavy feedstock with a first portion of steam, and then entering 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 second portion of steam, and then entering a second flash tank for second flash separation to obtain a second gas phase fraction and a second liquid phase fraction; S3, mixing the second liquid phase fraction with a third portion of steam, and then mixing it with a fourth portion of steam, and then entering a third flash tank for third flash separation to obtain a third gas phase fraction and a third liquid phase fraction; S4, heating the first gas phase fraction in the convection section of a steam cracking device, and then cracking it in the radiation section of the steam cracking device.

[0010] Optionally, the first vapor-phase fraction comprises a mixture of a first light component from the heavy feedstock and carried vapor, and the first liquid-phase fraction comprises a first heavy component from the heavy feedstock; wherein the final boiling point of the first light component is 80–180°C, and the initial boiling point of the first heavy component is not higher than the final boiling point of the first light component; the second vapor-phase fraction comprises a mixture of a second light component from the heavy feedstock and carried vapor, and the second liquid-phase fraction comprises a second heavy component from the heavy feedstock, wherein the final boiling point of the second light component is 250–350°C, and the initial boiling point of the second heavy component is not higher than the final boiling point of the second light component; the third vapor-phase fraction comprises a mixture of a third light component from the heavy feedstock and carried vapor, and the third liquid-phase fraction comprises a third heavy component from the heavy feedstock, wherein the final boiling point of the third light component is 350–460°C, and the initial boiling point of the third heavy component is not higher than the final boiling point of the third light component.

[0011] Optionally, the method further includes: heating all of the second vapor fraction in the convection section of a steam cracking unit, and then pyrolyzing it in the radiant section of the steam cracking unit; or heating all of the second vapor fraction in a refining unit for further processing; or heating a portion of the second vapor fraction in the convection section of a steam cracking unit, and then pyrolyzing it in the radiant section of the steam cracking unit; and pyrolyzing another portion of the second vapor fraction in a refining unit for further processing; preferably, the method further includes: exchanging heat between the second vapor fraction and the crude oil to be preheated in a vapor fraction first cooler to obtain a cooled liquid second vapor fraction and preheated crude oil; and pyrolyzing the cooled liquid second vapor fraction in a refining unit for further processing; wherein the crude oil to be preheated is crude oil from any step before entering the first flash tank; optionally, the method further includes: heating all of the third vapor fraction in the convection section of a steam cracking unit. The third vapor fraction is heated and then enters the radiant section of the steam cracking unit for cracking; or all of the third vapor fraction is sent to the refining unit for further processing; or a portion of the third vapor fraction is sent to the convection section of the steam cracking unit for heating and then to the radiant section of the steam cracking unit for cracking; another portion of the third vapor fraction is sent to the refining unit for further processing; preferably, when the BMCI value of the crude oil component of the third vapor fraction is above 30, the third vapor fraction is sent to the refining unit for hydrotreating and then returned to the steam cracking unit for cracking; preferably, the method further includes: sending the third vapor fraction and the crude oil to be preheated to the second vapor fraction cooler for heat exchange to obtain a cooled liquid third vapor fraction and preheated crude oil; sending the cooled liquid third vapor fraction to the refining unit for further processing; wherein the crude oil to be preheated is crude oil from any step before entering the first flash tank.

[0012] Optionally, along the height direction of the steam cracking device, the convection section is sequentially provided with a first feedstock preheating section, a fourth mixing superheating section, a fifth mixing superheating section, a sixth steam superheating section, a seventh mixing superheating section, an eighth mixing superheating section, and a ninth mixing superheating section, which are independent of each other from top to bottom; the method further includes: mixing the heavy feedstock with the unsuperheated first portion of steam, and then entering the first flash tank for the first flash separation; mixing the first liquid phase fraction from the first flash tank with the superheated second portion of steam, and then entering the second flash tank. The second flash separation is performed in the tank, wherein the temperature of the superheated second portion of steam is 250–450°C; the mixture of the second liquid fraction and the third portion of steam is then introduced into the fifth mixing superheating section and heated to 290–430°C to obtain a second liquid fraction mixture stream; the superheated fourth portion of steam is then mixed with the second liquid fraction mixture stream and introduced into the third flash tank, wherein the temperature of the superheated fourth portion of steam is 400–575°C; preferably, the method further includes: introducing steam into the sixth steam superheating section. After being superheated, the vapor phase is divided into two parts. One part is used as the second part of the superheated steam and mixed with the first liquid phase fraction from the first flash tank. The other part is used as the fourth part of the superheated steam and mixed with the second liquid phase fraction from the fifth mixing superheating section. Optionally, the method further includes: heating the first vapor phase fraction in the fourth mixing superheating section and then further heating it to 550-720°C in the seventh mixing superheating section to obtain the first material to be cracked; optionally, heating the second vapor phase fraction in the eighth mixing superheating section to 450-685°C to obtain the second material to be cracked; optionally, heating the third vapor phase fraction in the ninth mixing superheating section to 400-645°C to obtain the third material to be cracked; the first material to be cracked, the optional second material to be cracked, and the optional third material to be cracked are respectively introduced into the radiant section of the steam cracking device for cracking; optionally, the first material to be cracked, the second material to be cracked, and the third material to be cracked can be introduced into different radiant furnace tubes of the same cracking furnace for cracking, or introduced into different cracking furnaces for cracking.

[0013] Optionally, the method further includes: buffering the third liquid phase fraction in a buffer tank before sending it out; allowing the heavy feedstock and waste heat material from the storage tank to enter a quench water preheater for a first heat exchange, respectively, to obtain a first preheated heavy feedstock and a cooled material; optionally, the temperature of the first preheated heavy feedstock is 70–120°C; or allowing the crude oil from the storage tank to undergo a first heat exchange in the quench water preheater before being introduced into the convection section of a steam cracking unit for further heating, to obtain a first preheated heavy feedstock; allowing the first preheated heavy feedstock to enter a desalination preprocessor for desalination pretreatment, to obtain a desalted heavy feedstock; and allowing the desalted heavy feedstock to enter the steam cracking unit. The feedstock is heated in a first preheating section to obtain a third preheated heavy feedstock; then the third preheated heavy feedstock is mixed with a first portion of steam and enters the first flash tank; optionally, the temperature of the third preheated heavy feedstock is 180-330°C; optionally, the method further includes: dividing the third liquid phase fraction from the buffer tank into three parts, allowing the first part of the third liquid phase fraction to enter a hydrogenation unit for hydrogenation treatment, allowing the second part of the third liquid phase fraction to enter a catalytic cracking unit for catalytic cracking treatment; and allowing the third part of the third liquid phase fraction to reflux back into the buffer tank; optionally, the heavy feedstock is crude oil and / or heavy hydrocarbons.

[0014] Optionally, the method further includes: using at least a portion of the third liquid fraction as a heat source to enter a dilution steam generator to obtain dilution steam; dividing a portion of the dilution steam into four parts, which are respectively used as the first part steam, the second part steam, the third part steam, and the fourth part steam; optionally, the method further includes: performing a first external preheating treatment on the heavy feedstock outside the convection section before introducing the heavy feedstock into the first flash tank; the first external preheating treatment is independent of the preheating in the first feedstock preheating section; and before allowing the first liquid fraction from the first flash tank to enter the second flash tank, performing a first external preheating treatment outside the convection section. The first liquid phase fraction undergoes a second external preheating treatment; the second external preheating treatment is independent of the heating in the third mixing superheating section; and before the second liquid phase fraction from the second flash tank enters the third flash tank, the second liquid phase fraction undergoes a third external preheating treatment outside the convection section; the third external preheating treatment is independent of the heating in the fifth mixing superheating section; optionally, the heat source for the first, second, and third external preheating treatments is waste heat material from any device, preferably the heat source for the second and third external preheating treatments is selected from at least one of low-pressure steam, medium-pressure steam, and high-pressure steam.

[0015] Optionally, the method further includes: controlling the weight ratio of steam to heavy feedstock in the first stream to be pyrolyzed to be 0.35 to 1, preferably 0.40 to 0.7; controlling the weight ratio of steam to heavy feedstock in the second stream to be pyrolyzed to be 0.4 to 1, preferably 0.6 to 0.8; and controlling the weight ratio of steam to heavy feedstock in the third stream to be pyrolyzed to be 0.5 to 1, preferably 0.7 to 0.9.

[0016] This disclosure provides a system for producing olefins by cracking heavy feedstock. The system includes a first flash tank, a second flash tank, a third flash tank, and a steam cracking device. The steam cracking device includes a convection section and a radiation section, with the convection section positioned above the radiation section along the height direction of the steam cracking device. The first flash tank has a heavy feedstock inlet, a first vapor phase outlet, and a first liquid phase outlet. The second flash tank has a first vapor phase inlet, a second vapor phase outlet, and a second liquid phase outlet. The third flash tank has a second liquid phase inlet, a third vapor phase outlet, and a third liquid phase outlet. The heavy feedstock inlet of the first flash tank is connected to a heavy feedstock input pipeline, and a first steam inlet is provided on the heavy feedstock input pipeline. The first liquid phase outlet of the first flash tank is connected to the first vapor phase outlet of the second flash tank. The liquid phase fraction inlet is connected, and a second steam inlet is provided on the connecting pipeline between the first liquid phase fraction outlet and the first liquid phase fraction inlet; the second liquid phase fraction outlet of the second flash tank is connected to the second liquid phase fraction inlet of the third flash tank, and a second steam inlet and a third steam inlet are provided on the connecting pipeline between the second liquid phase fraction outlet and the second liquid phase fraction inlet, and the second steam inlet is located upstream of the third steam inlet along the material flow direction; the radiation section of the steam cracking device is provided with a first material to be cracked inlet, an optional second material to be cracked inlet, and an optional third material to be cracked inlet; the first material to be cracked inlet is connected to the first gas phase fraction outlet, the second material to be cracked inlet is connected to the second gas phase fraction outlet, and the third material to be cracked inlet is connected to the third gas phase fraction outlet.

[0017] Optionally, the convection section is provided from top to bottom with independent first raw material preheating section, fourth mixing superheating section, fifth mixing superheating section, sixth steam superheating section, seventh mixing superheating section, eighth mixing superheating section, and ninth mixing superheating section; the first raw material preheating section has a first superheating inlet and a first superheating outlet, the first superheating outlet being connected to a first pipeline for the heavy raw material inlet of the first flash tank, and the first steam inlet being located on the first pipeline; the first liquid phase fraction outlet of the first flash tank is connected to the first liquid phase fraction inlet of the second flash tank via a second pipeline. The second steam inlet is located on the second pipeline; the fourth mixing superheating section has a second superheating inlet and a second superheating outlet, the second superheating inlet being connected to the first vapor phase distillate outlet of the first flash tank; the fifth mixing superheating section has a third superheating inlet and a third superheating outlet, the third superheating inlet being connected to the second liquid phase distillate outlet of the second flash tank via a third pipeline, the third steam inlet being located on the third pipeline; the third superheating outlet being connected to the second liquid phase distillate inlet of the third flash tank via a fourth pipeline, the fourth steam inlet being located on the fourth pipeline; The second steam superheating section is provided with a steam superheating inlet and a steam superheating outlet; the steam superheating outlet is connected to the second steam inlet of the second pipeline and the fourth steam inlet of the fourth pipeline, respectively; the seventh mixing superheating section is provided with a fourth superheating inlet and a fourth superheating outlet, the fourth superheating inlet being connected to the second superheating outlet of the fourth mixing superheating section, and the fourth superheating outlet being connected to the first inlet of the material to be cracked in the radiation section; the eighth mixing superheating section is provided with a fifth superheating inlet and a fifth superheating outlet, the fifth superheating inlet being connected to the second vapor fraction outlet of the second flash tank, and the fifth superheating outlet being connected to... The second inlet of the material to be pyrolyzed in the radiation section is connected; the ninth mixing superheating section is provided with a sixth superheating inlet and a sixth superheating outlet; optionally, the sixth superheating inlet is connected to the third vapor fraction outlet of the third flash tank, and the sixth superheating outlet is connected to the third inlet of the material to be pyrolyzed in the radiation section; optionally, each of the second steam inlet, the third steam inlet, and the fourth steam inlet is independently provided with a material mixer for mixing the material and steam introduced into the mixer; preferably, the first flash tank, the second flash tank, and the third flash tank are arranged sequentially in the vertical direction along the same central axis.

[0018] Optionally, the system further includes a buffer tank, a pump, a desalination preprocessor, and a quench water preheater; the buffer tank is provided with a liquid-phase heavy component buffer inlet, a liquid-phase heavy component buffer outlet, and a heavy component reflux inlet; the pump includes an inlet and an outlet; the desalination preprocessor is provided with a heavy feed desalination inlet and a heavy feed desalination outlet; the quench water preheater is provided with a quench water heat exchange inlet, a quench water heat exchange outlet, a heavy feed heat exchange first inlet, and a heavy feed heat exchange first outlet; wherein the heavy feed heat exchange first outlet of the quench water preheater is connected to the... The heavy feed desalination inlet of the desalination preprocessor is connected to the heavy feed desalination outlet of the desalination preprocessor, which is connected to the heavy feed preheating inlet of the first feed preheating section. The liquid phase heavy component buffer inlet of the buffer tank is connected to the third liquid phase fraction outlet of the third flash tank, and the liquid phase heavy component buffer outlet is connected to the input port of the pump. The output port of the pump is either externally supplied or connected to the heavy component reflux inlet of the buffer tank. The level transmitter is connected to the inside of the buffer tank to control the liquid level inside the buffer tank.

[0019] Through the above technical solution, this disclosure provides a method and system for producing olefins from cracked heavy feedstocks, with beneficial effects including at least the following:

[0020] (1) In this disclosure, heavy feedstock (crude oil and / or heavy hydrocarbons) is mixed with steam and then subjected to a first flash separation. Then, the first liquid phase fraction is mixed with steam and subjected to a second flash separation. The second liquid phase fraction is mixed with steam and subjected to a third flash separation. Then, at least one of the three gas phase fractions obtained from the three flash separations is heated and introduced into a cracking furnace for cracking. Compared with other crude oil or heavy hydrocarbon cracking technologies, the process flow of this disclosure has strong adaptability to crude oil and heavy hydrocarbons (the API range of crude oil is wider, and the API can be between 30 and 50).

[0021] (2) By performing multi-stage flash distillation on heavy feedstock to obtain multiple gas phase fractions, it is beneficial to optimize process operations (such as the dilution ratio of heavy feedstock to steam, cracking temperature, etc.) to separate different crude oil and heavy hydrocarbon components, achieve efficient cracking of different fractions, high olefin yield, and maximize the application of existing steam cracking technology. The technology is mature and the operation is simple.

[0022] (3) The present disclosure introduces steam into each flash material before it enters the flash tank, which can reduce the hydrocarbon partial pressure and reduce the required flash temperature.

[0023] (4) This disclosure subdivides the components of heavy feedstock, and can select the fraction suitable for producing olefins as cracking feedstock according to the composition and processing requirements of heavy feedstock, and use the fraction unsuitable as cracking feedstock to produce aromatics or sell as oil products. In other words, it can achieve the goal of producing olefins where appropriate, aromatics where appropriate, and oil where appropriate. Furthermore, due to the subdivision of the fractions, it is beneficial to crack the fractions used as cracking feedstock under the most suitable conditions to obtain a high olefin yield.

[0024] (5) Compared with conventional crude oil cracking processes (e.g., crude oil is processed by the atmospheric and vacuum distillation tower of the refining unit, and part of it enters the refining unit and part of it is used as cracking feedstock to enter the cracking furnace for cracking), this disclosure simplifies the process of crude oil and heavy hydrocarbon to olefins, eliminates the atmospheric and vacuum distillation unit, and saves investment; at the same time, this disclosure has a wide range of applicability to crude oil, can be used to improve the quality and efficiency of existing integrated refining and chemical units, and can also be used to produce ethylene in new integrated refining and chemical units. For newly built integrated refining and chemical units, fewer refining units such as atmospheric and vacuum distillation and reforming units can be built, and for light paraffin-based crude oil, no refining unit needs to be built. Attached Figure Description

[0025] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0026] Figure 1 This is a schematic diagram of a process flow diagram for producing olefins from pyrolysis of heavy feedstocks provided in this disclosure;

[0027] Figure 2 This is a schematic diagram of a process flow diagram for producing olefins from pyrolysis of heavy feedstocks provided in this disclosure.

[0028] Explanation of reference numerals in the attached figures

[0029] 1-First raw material preheating section; 3-First flash tank; 5-Second flash tank; 6-Fourth mixing superheating section; 7-Fifth mixing superheating section; 8-Third flash tank; 9-Fifth mixing superheating section; 10-Seventh mixing superheating section; 11-Eighth mixing superheating section; 12-Ninth mixing superheating section; 13-Buffer tank; 14-Pump; 16-Desalination pre-processor; 17-Quick coolant preheater

[0030] 101-Crude oil, 102-Waste heat material, 104-Desalted crude oil, 105-First portion of steam, 106-Mixture of crude oil and steam, 107-First vapor fraction, 108-First liquid fraction, 109-Second portion of steam, 111-Second vapor fraction, 112-Second liquid fraction, 113-Third portion of steam, 114-Mixture of second liquid fraction, 115-Fourth portion of steam, 116-Third vapor fraction, 117-Third liquid fraction, 118-Externally delivered third liquid fraction, 119-First material to be cracked, 120-Second material to be cracked, 121-Third material to be cracked, 123-Recirculated third liquid fraction Detailed Implementation

[0031] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0032] In this disclosure, unless otherwise stated, the terms "first," "second," and "third" are used only to distinguish different components and do not imply any actual connection order. In this disclosure, directional terms such as "upper," "lower," "top," and "bottom" generally refer to the upper and lower, top and bottom, of the device in its normal operating state. "Inner" and "outer" refer to the outline of the device.

[0033] In this disclosure, the terms "primary dilution steam," "secondary dilution steam," "first part steam," and "second part steam" are used only to distinguish the steam introduced in different steps and do not contain any actual meaning such as the properties of the steam itself.

[0034] The first aspect of this disclosure provides a method for producing olefins by cracking heavy feedstock. The method includes the following steps: S1, mixing the heavy feedstock with a first portion of steam, and then entering a first flash tank 3 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 second portion of steam, and then entering a second flash tank 5 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 third portion of steam, and then with a fourth portion of steam, and then entering a third flash tank 8 for third flash separation to obtain a third gas phase fraction and a third liquid phase fraction; S4, heating the first gas phase fraction in the convection section of a steam cracking device, and then cracking it in the radiation section 18 of the steam cracking device.

[0035] This disclosure provides a method and system for producing olefins from heavy feedstocks through pyrolysis. The method involves mixing heavy feedstocks (crude oil and / or heavy hydrocarbons) with steam and performing a first flash separation. Then, the first liquid fraction is mixed with steam and subjected to a second flash separation. The second liquid fraction is then mixed with steam and subjected to a third flash separation. At least two of the three gaseous fractions obtained from the three flash separations are then heated and introduced into a pyrolysis furnace for further pyrolysis. Compared to other crude oil or heavy hydrocarbon pyrolysis technologies, this disclosure offers a simpler process flow, strong adaptability to crude oil and heavy hydrocarbons, and the multi-stage flash separation of heavy feedstocks to obtain multiple gaseous fractions facilitates the segmentation of different crude oil and heavy hydrocarbon components through optimized process operations (such as the dilution ratio of heavy feedstock to steam), achieving efficient pyrolysis of different fractions, high olefin yield, and maximizing the application of existing steam pyrolysis technologies. The technology is mature and easy to operate. Furthermore, this disclosure introduces steam into each flash material before it enters the flash tank, which reduces the hydrocarbon partial pressure and lowers the required flash temperature. This disclosure, by subdividing the heavy feedstock components, allows for the selection of fractions suitable for olefin production as cracking feedstocks based on the composition and processing requirements of the heavy feedstock. Fractions unsuitable for cracking can be used to produce aromatics or sold as oil products. This achieves the goal of selecting the appropriate fraction for olefins, aromatics, or oil. Furthermore, the subdivision of fractions ensures that the feedstock fractions are cracked under optimal conditions, resulting in high olefin yields. Compared to conventional crude oil cracking processes (where crude oil is processed in the atmospheric and vacuum distillation unit of a refinery, with a portion going to the refinery and a portion serving as cracking feedstock), this disclosure simplifies the process for producing olefins from crude oil and heavy hydrocarbons, eliminating the need for atmospheric and vacuum distillation units and saving investment. Moreover, this disclosure has a wide range of applicability to crude oil, suitable for upgrading and improving the efficiency of existing integrated refining and chemical plants, and can also be used in new integrated refining and chemical plants for ethylene production. New integrated refining and chemical plants may require fewer refining units such as atmospheric and vacuum distillation units and reforming units, and for light paraffinic crude oil, refining units may not be necessary.

[0036] In this disclosure, the "first light component in the first gas phase fraction" includes kerosene, naphtha, and lighter gas phase fractions; the "first heavy component in the first liquid phase fraction" includes liquid phase fractions heavier than kerosene; the "second light component in the second gas phase fraction" includes light diesel oil and lighter gas phase fractions; the "second heavy component in the second liquid phase fraction" includes liquid phase fractions heavier than light diesel oil; the "third light component in the third gas phase fraction" includes heavy diesel oil and lighter gas phase fractions; and the "third heavy component in the third liquid phase fraction" includes liquid phase fractions heavier than heavy diesel oil.

[0037] In a preferred embodiment, the first vapor fraction is a mixture of a first light component from the heavy feedstock and the carried vapor, and the first liquid fraction contains a first heavy component from the heavy feedstock; wherein the final boiling point of the first light component is 80–180°C, and the initial boiling point of the first heavy component is not higher than the final boiling point of the first light component.

[0038] The second vapor fraction is a mixture of a second light component in the heavy feedstock and the carried vapor, and the second liquid fraction contains a second heavy component in the heavy feedstock, wherein the final boiling point of the second light component is 250-350°C, and the initial boiling point of the second heavy component is not higher than the final boiling point of the second light component.

[0039] The third vapor fraction is a mixture of a third light component from the heavy feedstock and the carried vapor. The third liquid fraction contains a third heavy component from the heavy feedstock. The final boiling point of the third light component is 350–460°C, and the initial boiling point of the third heavy component is not higher than the final boiling point of the third light component.

[0040] It should be understood that the initial or final boiling point of each fraction in this disclosure is a range value, and in actual operation, it can be any temperature within the range. Furthermore, this disclosure allows for the selection of the separated fractions according to actual production needs.

[0041] The first flash tank, second flash tank, and third flash tank used in this disclosure are conventionally selected devices in the art. The third flash tank is a flash cyclone separator, wherein there can be one or more gas (vapor) phase outlets. This embodiment uses a third flash tank with a flash cyclone separation structure, which can more thoroughly separate the third liquid phase fraction, that is, more thoroughly separate the heavy components in the heavy feedstock that cannot be used for steam cracking, preventing the phenomenon of heavy components being carried in the third gas phase fraction and causing coking in the radiant tubes during the cracking process.

[0042] In one specific embodiment, the heavy feedstock used in this disclosure is crude oil and / or heavy hydrocarbons; the crude oil is at least one of paraffin-based crude oil, intermediate-based crude oil, or naphthenic crude oil; the heavy hydrocarbons are hydrocarbon materials containing heavy components, for example, containing heavy components with a boiling point of 500°C or higher.

[0043] In this disclosure, the obtained second vapor fraction can be processed differently depending on the weight and source and composition of the crude oil. For example, depending on whether the crude oil is paraffinic or naphthenic, the second vapor fraction can be introduced into the steam cracking unit as feedstock or directly into the refining unit. Alternatively, a portion of the second vapor fraction can be introduced into the steam cracking unit as feedstock, while the remaining portion can be introduced into the refining unit for secondary processing, thereby improving the overall process efficiency. The subsequent processing of the third vapor fraction is similar to that of the second vapor fraction.

[0044] In one specific embodiment, the method further includes: heating all of the second gaseous fraction in the convection section of a steam cracking unit, and then allowing it to undergo cracking in the radiation section 18 of the steam cracking unit; or

[0045] The entire second vapor fraction is fed into the refining unit for further processing; or

[0046] A portion of the second vapor fraction is heated in the convection section of the steam cracking unit and then cracked in the radiation section 18 of the steam cracking unit; another portion of the second vapor fraction is further processed in the refining unit.

[0047] Another preferred embodiment is as follows Figure 1 or Figure 2 As shown, the method further includes: heating all of the third gaseous fraction in the convection section of the steam cracking unit, and then allowing it to enter the radiation section 18 of the steam cracking unit for cracking; or

[0048] The entire third vapor fraction is fed into the refining unit for further processing; or

[0049] A portion of the third vapor fraction is heated in the convection section of a steam cracking unit and then cracked in the radiation section 18 of the steam cracking unit; another portion of the third vapor fraction is processed in a refining unit. Preferably, when the BMCI value of the crude oil components in the third vapor fraction is 30 or higher, the third vapor fraction is hydrotreated in the refining unit and then returned to the steam cracking unit for cracking. The "BMCI value" (USBureau of Mines Correlation Index) refers to the aromaticity index, representing the aromatization index of a petroleum product.

[0050] For example, in one specific embodiment, this disclosure further includes the following step: when the crude oil is paraffinic crude oil, at least a portion of the third vapor-phase fraction is introduced into a refining unit for processing. In this embodiment, introducing the third vapor-phase fraction from paraffinic crude oil into a refining unit allows fractions unsuitable as steam cracking feedstock to be used for the production of aromatic oils, thus enabling flexible utilization of fractions separated from different types of crude oil feedstocks. In another specific embodiment, when the crude oil feedstock is naphthenic crude oil, all of the third vapor-phase fraction is introduced into the radiant section of the steam cracking unit, without being introduced into the refining unit, to further improve the olefin yield.

[0051] As can be seen from the above two specific implementation methods, the second and third gas phase fractions obtained from the third flash separation can be processed differently depending on the type of crude oil. This method has a wide range of applicability to raw crude oil, and the separated fractions can be used flexibly to achieve quality improvement and efficiency enhancement with existing integrated refining and chemical units.

[0052] In this disclosure, the processing methods for the second and third gas phase fractions are independent of each other and can be arbitrarily selected according to actual needs. For example, it can include the following four methods: Method 1, subjecting the second gas phase fraction to subsequent steam cracking and the third gas phase fraction to oil refining; Method 2, subjecting the third gas phase fraction to subsequent steam cracking and the second gas phase fraction to oil refining; Method 3, subjecting both the second and third gas phase fractions to subsequent steam cracking; Method 4, subjecting both the second and third gas phase fractions to oil refining.

[0053] In a further preferred embodiment, the method further includes: allowing the second vapor fraction and the crude oil to be preheated to enter the first vapor fraction cooler for heat exchange, to obtain a cooled liquid second vapor fraction and preheated crude oil; allowing the cooled liquid second vapor fraction to enter the refining unit for further processing; wherein the crude oil to be preheated is crude oil from any step before entering the first flash tank 2;

[0054] The third vapor fraction and the crude oil to be preheated are respectively fed into the second vapor fraction cooler for heat exchange to obtain the cooled liquid third vapor fraction and the preheated crude oil; the cooled liquid third vapor fraction is fed into the refining unit for further processing; wherein the crude oil to be preheated is the crude oil in any step before entering the first flash tank 2.

[0055] The first and second vapor phase coolers can be connected in series with other devices in this system that process the feedstock before it enters the first flash tank. In this disclosure, when the second or third vapor phase fraction is introduced into the refining unit, a cooler is needed to cool the vapor phase fraction into a liquid phase before refining. This disclosure allows the vapor phase fraction to exchange heat with the crude oil to be preheated in the cooler, further improving heat utilization.

[0056] In one implementation, such as Figure 1 As shown, along the height direction of the steam cracking device, the convection section is sequentially arranged from top to bottom with an independent first raw material preheating section 1, a fourth mixing superheating section 6, a fifth mixing superheating section 7, a sixth steam superheating section 9, a seventh mixing superheating section 10, an eighth mixing superheating section 11, and a ninth mixing superheating section 12; the method further includes:

[0057] The heavy raw material is mixed with the first portion of unheated steam and then enters the first flash tank 3 for the first flash separation.

[0058] The first liquid fraction from the first flash tank 3 is mixed with the superheated second part of the steam, and then enters the second flash tank 5 for the second flash separation, wherein the temperature of the superheated second part of the steam is 250-450°C.

[0059] The mixture of the second liquid fraction and the third part of the steam is then introduced into the fifth mixing and superheating section 7 and heated to 290-430°C to obtain the second liquid fraction mixture stream; the superheated fourth part of the steam is then mixed with the second liquid fraction mixture stream and introduced into the third flash tank 8, wherein the temperature of the superheated fourth part of the steam is 400-575°C;

[0060] Preferably, the method further includes: after the steam enters the sixth steam superheating section 9 for superheating, it is divided into two parts, one part of which is used as the second part of superheated steam and mixed with the first liquid phase fraction from the first flash tank 3, and the other part of which is used as the fourth part of superheated steam and mixed with the second liquid phase fraction mixture from the fifth mixing superheating section 7.

[0061] More preferably, this disclosure may provide a boiler feedwater inlet at the inlet of the third mixing superheating section 7 to control the temperature of the heated second liquid phase distillate mixture, thereby controlling the liquid film temperature to be less than 500°C and preventing the material in the third flash tank from decomposing or coking.

[0062] In this disclosure, heavy feedstock is mixed with unsuperheated primary dilution steam (the first portion of unsuperheated steam) for first flash separation, which is beneficial for controlling the steam dilution ratio in the first flash separation process, thereby further improving the overall fine fractionation of the process and the subsequent cracking effect of different fractions. In this disclosure, the first liquid phase fraction is mixed with superheated primary dilution steam (the second portion of superheated steam, which may come from the sixth steam superheating section 9 in the convection section) for second flash separation. The second liquid phase fraction is mixed with unsuperheated primary dilution steam (the third portion of unsuperheated steam) and heated, and then mixed with superheated secondary dilution steam (the fourth portion of superheated steam, which may come from the sixth steam superheating section 9 in the convection section) for secondary dilution before third flash separation. This not only utilizes the heat of the convection section to heat the steam and make full use of thermal energy, but also allows for different levels of steam dilution for different fractions. This not only helps to heat different fractions to the most suitable temperature in different superheating sections, making it easier to control the fraction temperature and further improve the flash separation effect, but also makes it easier to control the temperature and steam dilution ratio of the dilution steam introduced for different fractions.

[0063] In a further embodiment, such as Figure 1 As shown, the method further includes: heating the first gaseous fraction to 230-450°C in the fourth mixing superheating section 6; and then further heating it to 550-720°C in the seventh mixing superheating section 10 to obtain the first material to be cracked;

[0064] Optionally, the second gaseous fraction is introduced into the eighth mixing and superheating section 11 and heated to 450-685°C to obtain the second material to be cracked;

[0065] Optionally, the third gaseous fraction is introduced into the ninth mixing superheating section 12 and heated to 400-645°C to obtain the third material to be cracked;

[0066] The first material to be cracked, the optional second material to be cracked, and the optional third material to be cracked are respectively introduced into the radiation section 18 of the steam cracking device for cracking.

[0067] In this disclosure, different fractions obtained from different flash tanks are introduced into different superheating sections for heating, which can heat the different fractions to a suitable initial cracking temperature (across different temperatures); the first material to be cracked, the second material to be cracked, and the optional third material to be cracked are introduced into the radiation section (e.g., cracking furnace) of the steam cracking unit for cracking, which is beneficial to control the cracking conditions of different material streams to be cracked, so that each material stream to be cracked can be cracked under suitable conditions, thereby improving the final olefin yield.

[0068] Specifically, the conditions under which the first material to be cracked, the optional second material to be cracked, and the optional third material to be cracked undergo steam cracking in the radiation section in this disclosure can be conventional conditions in the art, and the catalyst can be selected from catalysts known in the art.

[0069] In this disclosure, different materials to be pyrolyzed can be introduced into different radiant furnace tubes in the same furnace chamber of the same pyrolysis furnace; or into radiant furnace tubes in different radiant furnace chambers of the same pyrolysis furnace; or into radiant furnace tubes of different pyrolysis furnaces, which can be set according to the actual situation.

[0070] Specifically, in this disclosure, the first raw material preheating section 1, the fourth mixing superheating section 6, and the fifth mixing superheating section 7 can be different heat exchange tubes in the upper part of the convection section of the same cracking furnace, or heat exchange tubes in the upper part of the convection section of different cracking furnaces; the sixth steam superheating section 9, the seventh mixing superheating section 10, the eighth mixing superheating section 11, and the ninth mixing superheating section 12 can be different heat exchange tubes in the lower part of the convection section of the same cracking furnace, or heat exchange tubes in the lower part of the convection section of different cracking furnaces.

[0071] In one embodiment, the method further includes: controlling the weight ratio of steam to heavy feedstock in the first stream to be pyrolyzed to be 0.35 to 1, preferably in the range of 0.40 to 0.7;

[0072] The weight ratio of steam to heavy feedstock in the second stream to be pyrolyzed is controlled to be 0.4 to 1, preferably in the range of 0.6 to 0.8;

[0073] The weight ratio of steam to heavy feedstock in the third pyrolysis stream is controlled to be 0.5 to 1, preferably within the range of 0.7 to 0.9. In this disclosure, the amount of steam introduced in each step is adjusted by the final weight ratio of steam to heavy feedstock in the pyrolysis stream.

[0074] In one implementation, such as Figure 1 As shown, the method further includes: buffering the third liquid phase fraction in a buffer tank 13 and then pumping it out through a pump 14;

[0075] The heavy raw material and waste heat material from the storage tank are respectively introduced into the quench water preheater 17 for the first heat exchange to obtain the first preheated heavy raw material and the cooled material; optionally, the temperature of the first preheated heavy raw material is 70-120°C; or the crude oil from the storage tank is introduced into the convection section of the steam cracking unit after the first heat exchange in the quench water preheater 17 to continue heating to obtain the first preheated heavy raw material.

[0076] The first preheated heavy raw material is fed into the desalination preprocessor 16 for desalination pretreatment to obtain desalinated heavy raw material;

[0077] The desalted heavy raw material is heated in the first raw material preheating section 1 to obtain the third preheated heavy raw material; then the third preheated heavy raw material is mixed with the first part of steam and then enters the first flash tank 3; optionally, the temperature of the third preheated heavy raw material is 180-330°C.

[0078] Optionally, the method further includes: dividing the third liquid phase fraction from the buffer tank 13 into three parts, allowing the first part of the third liquid phase fraction to enter the hydrogenation unit for hydrogenation treatment, allowing the second part of the third liquid phase fraction to enter the catalytic cracking unit for catalytic cracking treatment, and allowing the third part of the third liquid phase fraction to be refluxed back into the buffer tank 13.

[0079] In this disclosure, the heavy raw material from the storage tank is first exchanged with the waste heat material, and the desalted heavy raw material is exchanged with the third liquid phase fraction in a second heat exchange, realizing heat exchange between multiple materials. This not only increases the temperature of the heavy raw material to be processed, but also cools the liquid phase heavy components of the output system. The second preheated heavy raw material is introduced into the raw material preheating section for heating, further improving the overall heat utilization rate of the process.

[0080] In one specific embodiment, the preheating process for heavy feedstock can also utilize waste heat from the ethylene unit instead of quench water for heat exchange, followed by heat exchange with high-temperature heavy oil obtained from the crude oil cracking process. Alternatively, the heavy feedstock can first exchange heat with waste heat from the ethylene unit, then undergo desalting treatment, and finally exchange heat with high-temperature heavy oil obtained from the crude oil cracking process. This achieves heat exchange between multiple units, particularly reducing the energy consumption of the ethylene unit, realizing heat recovery and utilization, and saving investment.

[0081] In one embodiment, the method further includes: using at least a portion of the third liquid phase fraction as a heat source to enter a dilution steam generator to obtain dilution steam; and dividing a portion of the dilution steam 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.

[0082] Optionally, the method further includes: detecting the temperature of the liquid phase material in the buffer tank 13 and obtaining a temperature signal; adjusting the reflux flow rate of the third part cooling the third liquid phase fraction according to the temperature signal, so that the temperature of the liquid phase material in the buffer tank 12 is controlled at 150-300°C; preferably, when the third liquid phase fraction is used to generate dilution steam, the temperature of the liquid phase material is controlled at 190-300°C.

[0083] In one embodiment, the method further includes: subjecting the heavy raw material to a first external preheating treatment outside the convection section before introducing the heavy raw material into the first flash tank 3; the first external preheating treatment is independent of the preheating in the first raw material preheating section 1; and

[0084] Before the first liquid fraction from the first flash tank 3 enters the second flash tank 5, it undergoes a second external preheating treatment outside the convection section; this second external preheating treatment is independent of the heating in the third mixing superheating section 4; and

[0085] Before the second liquid fraction from the second flash tank 5 enters the third flash tank 8, it undergoes a third external preheating treatment outside the convection section. This third external preheating treatment is independent of the heating in the fifth mixing superheating section 7. Optionally, the heat source for the first, second, and third external preheating treatments can be waste heat material from any unit; preferably, the heat source for the second and third external preheating treatments is selected from at least one of low-pressure steam, medium-pressure steam, and high-pressure steam. This further improves the heat utilization effect, especially the utilization effect of waste heat material obtained from other units within the plant area. The first, second, and third external preheating treatments are independent of the heating steps in the superheating section of the steam cracking unit and can be selected according to actual conditions.

[0086] The operating temperatures used in this disclosure are all within the normal operating range under conventional operating conditions of the pyrolysis furnace after pressure equilibrium.

[0087] A second aspect of this disclosure provides a system for producing olefins by cracking heavy feedstocks, such as... Figure 1 As shown, the system includes a first flash tank 3, a second flash tank 5, a third flash tank 6, and a steam pyrolysis unit. The steam pyrolysis unit includes a convection section and a radiation section 18. Along the height direction of the steam pyrolysis unit, the convection section is located above the radiation section 18.

[0088] The first flash tank 3 is provided with a heavy feed inlet, a first vapor phase distillate outlet and a first liquid phase distillate outlet; the second flash tank 5 is provided with a first vapor phase distillate inlet, a second vapor phase distillate outlet and a second liquid phase distillate outlet; the third flash tank 6 is provided with a second liquid phase distillate inlet, a third vapor phase distillate outlet and a third liquid phase distillate outlet.

[0089] The heavy material inlet of the first flash tank 3 is connected to a heavy material input pipeline, and a first steam inlet is provided on the heavy material input pipeline;

[0090] The first liquid phase fraction outlet of the first flash tank 3 is connected to the first liquid phase fraction inlet of the second flash tank 5, and a second steam inlet is provided on the connecting pipeline between the first liquid phase fraction outlet and the first liquid phase fraction inlet; the second liquid phase fraction outlet of the second flash tank 5 is connected to the second liquid phase fraction inlet of the third flash tank 6, and a second steam inlet and a third steam inlet are provided on the connecting pipeline between the second liquid phase fraction outlet and the second liquid phase fraction inlet, and the second steam inlet is located upstream of the third steam inlet along the material flow direction;

[0091] The radiation section 18 of the steam cracking unit is provided with a first material inlet to be cracked, an optional second material inlet to be cracked, and an optional third material inlet to be cracked; the first material inlet to be cracked is connected to the first gas phase distillate outlet, the second material inlet to be cracked is connected to the second gas phase distillate outlet, and the third material inlet to be cracked is connected to the third gas phase distillate outlet.

[0092] In a preferred embodiment, the first flash tank 3, the second flash tank 5, and the third flash tank 6 are arranged sequentially in the vertical direction along the same central axis, which saves space and facilitates the arrangement.

[0093] In one implementation, such as Figure 1 As shown, the convection section is provided with the following independent sections from top to bottom: first raw material preheating section 1, fourth mixing superheating section 6, fifth mixing superheating section 7, sixth steam superheating section 9, seventh mixing superheating section 10, eighth mixing superheating section 11 and ninth mixing superheating section 12.

[0094] The first raw material preheating section 1 is provided with a first superheat inlet and a first superheat outlet. The first superheat outlet is connected to the first pipeline of the heavy raw material inlet of the first flash tank 3, and the first steam inlet is set on the first pipeline.

[0095] The first liquid phase distillate outlet of the first flash tank 3 and the first liquid phase distillate inlet of the second flash tank 5 are connected through a second pipeline, and the second steam inlet is provided on the second pipeline.

[0096] The fourth mixing superheating section 6 is provided with a second superheating inlet and a second superheating outlet. The second superheating inlet is connected to the first vapor fraction outlet of the first flash tank 3.

[0097] The fifth mixing superheating section 7 is provided with a third superheating inlet and a third superheating outlet. The third superheating inlet is connected to the second liquid phase fraction outlet of the second flash tank 5 through a third pipeline, and the third steam inlet is provided on the third pipeline. The third superheating outlet is connected to the second liquid phase fraction inlet of the third flash tank 6 through a fourth pipeline, and the fourth steam inlet is provided on the fourth pipeline.

[0098] The second steam superheating section 9 is provided with a steam superheating inlet and a steam superheating outlet; the steam superheating outlet is connected to the second steam inlet of the second pipeline and the fourth steam inlet of the fourth pipeline, respectively.

[0099] The seventh mixing superheating section 10 is provided with a fourth superheating inlet and a fourth superheating outlet. The fourth superheating inlet is connected to the second superheating outlet of the fourth mixing superheating section 6, and the fourth superheating outlet is connected to the first inlet of the material to be cracked in the radiation section 18.

[0100] The eighth mixing superheating section 11 is provided with a fifth superheating inlet and a fifth superheating outlet. The fifth superheating inlet is connected to the second vapor fraction outlet of the second flash tank 5, and the fifth superheating outlet is connected to the second inlet of the material to be cracked in the radiation section 18.

[0101] The ninth mixing superheating section 12 is provided with a sixth superheating inlet and a sixth superheating outlet; optionally, the sixth superheating inlet is connected to the third vapor fraction outlet of the third flash tank 8, and the sixth superheating outlet is connected to the third inlet of the material to be cracked in the radiation section 18.

[0102] Specifically, the radiant section of the steam cracking unit (cracking furnace) includes three independently arranged cracking furnace tubes: a first cracking furnace tube, a second cracking furnace tube, and a third cracking furnace tube. The first cracking furnace tube has a raw material inlet, forming the first inlet for the material to be cracked; the second cracking furnace tube has a raw material inlet, forming the second inlet for the material to be cracked; and the third cracking furnace tube has a raw material inlet, forming the third inlet for the material to be cracked. Optionally, the first, second, and third cracking furnace tubes can be different radiant section furnace tubes in the same furnace chamber of the same cracking furnace; or radiant furnace tubes in different radiant sections of the same cracking furnace; or radiant furnace tubes from different cracking furnaces, which can be arranged according to the actual situation.

[0103] In a preferred embodiment, such as Figure 1 As shown, each of the second, third, and fourth steam inlets is independently equipped with a material mixer for mixing the material and steam introduced into the mixer. In this embodiment, installing a mixer at the steam inlet allows for more uniform mixing of the material and steam, preventing coking. Any mixer of a type known in the art that achieves the aforementioned mixing effect can be used.

[0104] In one implementation, such as Figure 1 As shown, the system also includes a buffer tank 13, a pump 14, a desalination pre-processor 16, and a quench water preheater 17;

[0105] Buffer tank 13 is provided with a liquid phase heavy component buffer inlet, a liquid phase heavy component buffer outlet and a heavy component reflux inlet; pump 14 includes an inlet and an outlet; desalination preprocessor 16 is provided with a heavy raw material desalination inlet and a heavy raw material desalination outlet; quench water preheater 17 is provided with a quench water heat exchange inlet and a quench water heat exchange outlet, a heavy raw material heat exchange first inlet and a heavy raw material heat exchange first outlet;

[0106] The first outlet of the heavy raw material heat exchanger of the quench water preheater 17 is connected to the heavy raw material desalination inlet of the desalination preprocessor 16, and the heavy raw material desalination outlet of the desalination preprocessor 16 is connected to the heavy raw material preheating inlet of the first raw material preheating section 1.

[0107] The liquid phase heavy component buffer inlet of buffer tank 13 is connected to the third liquid phase distillate outlet of third flash tank 6, the liquid phase heavy component buffer outlet is connected to the inlet of pump 14, the outlet of pump 14 is sent out, or the outlet of pump 14 is connected to the heavy component reflux inlet of buffer tank 13.

[0108] The level transmitter is connected to the inside of the buffer tank 13 to control the liquid level inside the buffer tank 13.

[0109] Optionally, in this disclosure, the heat source of the third liquid phase fraction from the third flash tank can be used to heat the low-pressure boiler feedwater into dilution steam, which is then used as the primary dilution steam in the entire cracking process system, further improving the heat recovery rate in the process system and the integration of different devices.

[0110] The present disclosure will be further described below with reference to specific embodiments.

[0111] Example 1

[0112] See Figure 1 The process flow shown, taking crude oil from the Shunbei Oilfield with an API value of 41 as an example, involves introducing as many light components with a boiling point below 430℃ as possible into the cracking furnace for cracking reaction. Specifically, it includes the following steps:

[0113] S1. The crude oil 101 from the storage tank and the waste heat material 102 are first heat exchanged in the quench water preheater 17. The temperature range of the first preheated heavy raw material after heat exchange is 70-120℃. Then, the heated crude oil is desalted in 16 to remove impurities such as metals and non-metals to obtain desalted crude oil 104.

[0114] S2. The desalted crude oil 104 is heated to 180-330°C in the first feedstock preheating section 1 of the convection section, and then mixed with unsuperheated first-stage dilution steam (first part steam) 105. The mixture of crude oil and steam 106 is then fed into the first flash tank 3 for first flash evaporation to obtain the first gas phase fraction 107 (containing kerosene, naphtha and below, and the carried steam, the final boiling point of the first light component is 80-180°C) and the first liquid phase fraction 108 (the first heavy component heavier than kerosene).

[0115] S3. The first liquid phase fraction 108 separated from the mixture is mixed with the superheated first-stage dilution steam (second part steam, 250-450°C) 109 from the sixth steam superheating section 9 (the temperature of the mixed material is 230-370°C) and then enters the second flash tank 5 for second flash separation to obtain the second gas phase fraction 111 (the second light component of light diesel oil and below and the steam it carries, the final boiling point of the second light component is 250-350°C) and the second liquid phase fraction 112 (the second heavy component that is heavier than light diesel oil).

[0116] S4. The second liquid phase fraction 112, heated in the above steps, is mixed with the unsuperheated primary dilution steam (third part steam) 113 and fed into the fifth mixing superheating section 7 of the convection section, where it is heated to 290-430°C. The resulting second liquid phase fraction mixture stream 114 is mixed with the superheated secondary dilution steam 115 (fourth part steam, heated to 400-575°C via the sixth steam superheating section 9) from the sixth steam superheating section 9 and fed into the third flash tank 8 for third flash separation, yielding the third gas phase fraction 116 (the third light component of heavy diesel oil and below, and the carried steam, with the final boiling point of the third light component being 350-460°C) and the third liquid phase fraction 117 (the third heavy component heavier than heavy diesel oil).

[0117] S5. The first gas phase fraction 107 separated by the above steps is further preheated in the fourth mixing superheating section 6 of the convection section. Then the heated first gas phase fraction 118 is heated to 550-720°C in the seventh mixing superheating section 10 to obtain the first material to be cracked 119. The weight ratio of steam to heavy raw material in the first material to be cracked is 0.40-0.7.

[0118] The second vapor fraction 111 is introduced into the eighth mixing and superheating section 11 and heated to 450-685°C to obtain the second material to be cracked 120. The weight ratio of steam to heavy feed in the second material to be cracked is 0.6-0.8.

[0119] The third vapor fraction 116 is introduced into the ninth mixing and superheating section 12 and heated to 400-645°C to obtain the third material to be cracked 121. The weight ratio of steam to heavy feed in the third material to be cracked is 0.7-0.9.

[0120] S6. The first material to be cracked 119, the second material to be cracked 120, and the third material to be cracked 121 are respectively introduced into the radiant section 18 of the steam cracking device for steam cracking; wherein the above three materials to be cracked can be introduced into different radiant section furnace tubes in the same furnace chamber of the same cracking furnace, or into radiant furnace tubes in different radiant section furnace chambers of the same cracking furnace, or into radiant furnace tubes of different cracking furnaces for cracking; wherein the cracking temperature of the first material to be cracked is 820-850℃; the cracking temperature of the second material to be cracked is 800-830℃; and the cracking temperature of the third material to be cracked is 790-820℃;

[0121] S7. The third liquid fraction 117 after flash vapor-liquid separation in the third flash tank 8 enters the buffer tank 13. The liquid level in the buffer tank is controlled by a level transmitter. Depending on actual needs, the third liquid fraction from the buffer tank 13 can also be introduced into the refining unit for secondary processing, or introduced into the hydrogenation unit for hydrogenation treatment and then entered into the heavy feedstock cracking furnace as cracking feedstock to further produce olefins and other products, or introduced into the dilution steam generator for treatment to obtain dilution steam.

[0122] Example 2

[0123] See Figure 2 The process flow shown, taking DSW crude oil (API 41.2) as an example, involves introducing as many light components with a boiling point below 350°C as possible into the cracking furnace for cracking reaction. Specifically, it includes the following steps:

[0124] S1. The crude oil 101 from the storage tank and the waste heat material 102 are first heat exchanged in the quench water preheater 17. The temperature range of the first preheated heavy raw material after heat exchange is 70-120℃. Then, the heated crude oil is desalted in 16 to remove impurities such as metals and non-metals to obtain desalted crude oil 104.

[0125] S2. The desalted crude oil 104 is heated to 180-330°C in the first feedstock preheating section 1 of the convection section, and then mixed with unsuperheated first-stage dilution steam (first part steam) 105. The mixture of crude oil and steam 106 is then fed into the first flash tank 3 for first flash evaporation to obtain the first gas phase fraction 107 (containing kerosene, naphtha and below, and the carried steam, the final boiling point of the first light component is 80-180°C) and the first liquid phase fraction 108 (the first heavy component heavier than kerosene).

[0126] S3. The first liquid phase fraction 108 separated from the mixture is mixed with the superheated first-stage dilution steam (second part steam, 250-450°C) 109 from the sixth steam superheating section 9 (the temperature of the mixed material is 230-370°C) and then enters the second flash tank 5 for second flash separation to obtain the second gas phase fraction 111 (the second light component of light diesel oil and below and the steam it carries, the final boiling point of the second light component is 250-350°C) and the second liquid phase fraction 112 (the second heavy component that is heavier than light diesel oil).

[0127] S4. The second liquid phase fraction 112, heated in the above steps, is mixed with the unsuperheated primary dilution steam (third part steam) 113 and fed into the fifth mixing superheating section 7 of the convection section, where it is heated to 290-430°C. The resulting second liquid phase fraction mixture stream 114 is mixed with the superheated secondary dilution steam 115 (fourth part steam, heated to 400-575°C via the sixth steam superheating section 9) from the sixth steam superheating section 9 and fed into the third flash tank 8 for third flash separation, yielding the third gas phase fraction 116 (the third light component of heavy diesel oil and below, and the carried steam, with the final boiling point of the third light component being 350-460°C) and the third liquid phase fraction 117 (the third heavy component heavier than heavy diesel oil).

[0128] S5. The first gas phase fraction 107 separated by the above steps is further preheated in the fourth mixing superheating section 6 of the convection section. Then the heated first gas phase fraction 118 is heated to 550-720°C in the seventh mixing superheating section 10 to obtain the first material to be cracked 119. The weight ratio of steam to heavy raw material in the first material to be cracked is 0.40-0.7.

[0129] The second vapor fraction 111 is introduced into the eighth mixing and superheating section 11 and heated to 450-685°C to obtain the second material to be cracked 120. The weight ratio of steam to heavy feed in the second material to be cracked is 0.6-0.8.

[0130] The third vapor fraction 121 is cooled in the second vapor fraction cooler, and then the resulting liquid fraction is sent to the refining unit (the refining unit is not shown).

[0131] S6. The first material to be cracked 119 and the second material to be cracked 120 are respectively introduced into the radiant section 18 of the steam cracking device for steam cracking; wherein the two materials to be cracked can be introduced into different radiant section furnace tubes in the same furnace chamber of the same cracking furnace, or into radiant furnace tubes in different radiant section furnace chambers of the same cracking furnace, or into radiant furnace tubes of different cracking furnaces for cracking; wherein the cracking temperature of the first material to be cracked is 810-840℃; and the cracking temperature of the second material to be cracked is 790-820℃.

[0132] S7. The third liquid fraction 117, after flash vapor-liquid separation in the third flash tank 8, enters the buffer tank 13. The liquid level in the buffer tank 13 is controlled by a level transmitter. Depending on actual needs, the third liquid fraction from the buffer tank 13 can also be introduced into a refining unit for secondary processing, or into a hydrogenation unit for hydrogenation treatment before entering a heavy feedstock cracking furnace as cracking feedstock to further produce olefins and other products, or into a steam generator for processing to obtain steam.

[0133] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0134] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0135] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for producing olefins by cracking heavy feedstock, characterized in that, The method includes the following steps: S1. Mix the heavy raw material with the first part of steam, and then enter the first flash tank (3) for the first flash separation to obtain the first gas phase fraction and the first liquid phase fraction; S2. Mix the first liquid phase fraction with the second part of the vapor, and then enter the second flash tank (5) for second flash separation to obtain the second gas phase fraction and the second liquid phase fraction; S3. Mix the second liquid phase fraction with the third part of steam, then mix with the fourth part of steam, and then enter the third flash tank (8) for third flash separation to obtain the third gas phase fraction and the third liquid phase fraction. S4. The first gaseous fraction is heated in the convection section of the steam cracking device and then enters the radiation section (18) of the steam cracking device for cracking. The method also includes: The heavy raw material is mixed with the unheated first portion of steam and then enters the first flash tank (3) for the first flash separation; The first liquid fraction from the first flash tank (3) is mixed with the superheated second part of the steam and then enters the second flash tank (5) for the second flash separation, wherein the temperature of the superheated second part of the steam is 250~450℃; The mixture of the second liquid fraction and the unsuperheated third part of the steam is then fed into the fifth mixing superheating section (7) and heated to 290~430°C to obtain the second liquid fraction mixture stream; the superheated fourth part of the steam is then mixed with the second liquid fraction mixture stream and fed into the third flash tank (8), wherein the temperature of the superheated fourth part of the steam is 400~575°C.

2. The method according to claim 1, characterized in that, The first vapor fraction is a mixture of a first light component in the heavy feedstock and the carried vapor, and the first liquid fraction contains a first heavy component in the heavy feedstock; wherein the final boiling point of the first light component is 80~180°C, and the initial boiling point of the first heavy component is not higher than the final boiling point of the first light component. The second vapor fraction is a mixture of a second light component in the heavy feedstock and the carried vapor, and the second liquid fraction contains a second heavy component in the heavy feedstock, wherein the final boiling point of the second light component is 250~350°C, and the initial boiling point of the second heavy component is not higher than the final boiling point of the second light component. The third vapor fraction is a mixture of a third light component from the heavy feedstock and the carried vapor. The third liquid fraction contains a third heavy component from the heavy feedstock. The final boiling point of the third light component is 350-460°C, and the initial boiling point of the third heavy component is not higher than the final boiling point of the third light component.

3. The method according to claim 1, characterized in that, The method further includes: heating all of the second vapor fraction in the convection section of the steam cracking unit, and then allowing it to enter the radiation section (18) of the steam cracking unit for cracking; or The entire second vapor fraction is fed into the refining unit for further processing; or A portion of the second vapor fraction is heated in the convection section of the steam cracking unit and then cracked in the radiation section (18) of the steam cracking unit; another portion of the second vapor fraction is further processed in the refining unit.

4. The method according to claim 3, characterized in that, The method further includes: allowing the second gas phase fraction and the crude oil to be preheated to enter the first gas phase fraction cooler for heat exchange, to obtain the cooled liquid second gas phase fraction and the preheated crude oil; allowing the cooled liquid second gas phase fraction to enter the refining unit for further processing; wherein the crude oil to be preheated is the crude oil in any step before entering the first flash tank (3).

5. The method according to claim 3, characterized in that, The method further includes: heating all of the third vapor fraction in the convection section of the steam cracking unit, and then allowing it to enter the radiation section (18) of the steam cracking unit for cracking; or The entire third vapor fraction is fed into the refining unit for further processing; or A portion of the third gaseous fraction is heated in the convection section of the steam cracking unit and then cracked in the radiation section (18) of the steam cracking unit; another portion of the third gaseous fraction is further processed in the refining unit.

6. The method according to claim 5, characterized in that, When the BMCI value of the crude oil component in the third gas phase fraction is above 30, the third gas phase fraction is fed into the refining unit for hydrotreating and then returned to the steam cracking unit for cracking.

7. The method according to claim 3, characterized in that, The method further includes: allowing the third gas phase fraction and the crude oil to be preheated to enter the second gas phase fraction cooler for heat exchange, to obtain the cooled liquid third gas phase fraction and the preheated crude oil; allowing the cooled liquid third gas phase fraction to enter the refining unit for further processing; wherein the crude oil to be preheated is any crude oil in any step before entering the first flash tank (3).

8. The method according to claim 1, characterized in that, Along the height direction of the steam cracking device, the convection section is provided with a first raw material preheating section (1), a fourth mixing superheating section (6), a fifth mixing superheating section (7), a sixth steam superheating section (9), a seventh mixing superheating section (10), an eighth mixing superheating section (11), and a ninth mixing superheating section (12) that are independent of each other from top to bottom. The method further includes: after the steam enters the sixth steam superheating section (9) for superheating, it is divided into two parts, one part of which is used as the second part of superheated steam and mixed with the first liquid phase fraction from the first flash tank (3), and the other part is used as the fourth part of superheated steam and mixed with the second liquid phase fraction mixture from the fifth mixing superheating section (7).

9. The method according to claim 8, characterized in that, The method further includes: allowing the first gaseous fraction to enter the fourth mixing superheating section (6) for heating and then entering the seventh mixing superheating section (10) for further heating to 550~720°C to obtain the first material to be cracked; The second gaseous fraction is introduced into the eighth mixing superheating section (11) and heated to 450~685°C to obtain the second material to be cracked; The third gas phase fraction is introduced into the ninth mixing superheating section (12) and heated to 400~645°C to obtain the third material to be cracked; The first material to be cracked, the optional second material to be cracked, and the optional third material to be cracked are respectively introduced into the radiation section (18) of the steam cracking device for cracking; The first, second, and third materials to be cracked can be introduced into different radiant furnace tubes of the same cracking furnace for cracking, or introduced into different cracking furnaces for cracking.

10. The method according to claim 8, characterized in that, The method also includes: The heavy raw materials and waste heat materials from the storage tank are respectively fed into the quench water preheater (17) for the first heat exchange, so as to obtain the first preheated heavy raw materials and cooled materials; The first preheated heavy raw material is fed into the desalination preprocessor (16) for desalination pretreatment to obtain desalinated heavy raw material; The desalted heavy raw material is heated in the first raw material preheating section (1) of the steam cracking device to obtain the third preheated heavy raw material; then the third preheated heavy raw material is mixed with the first part of steam and then enters the first flash tank (3).

11. The method according to claim 1, characterized in that, The method also includes: The third liquid fraction is buffered in a buffer tank (13) before being sent out.

12. The method according to claim 11, characterized in that, The method further includes: dividing the third liquid phase fraction from the buffer tank (13) into three parts, allowing the first part of the third liquid phase fraction to enter the hydrogenation unit for hydrogenation treatment, allowing the second part of the third liquid phase fraction to enter the catalytic cracking unit for catalytic cracking treatment, and allowing the third part of the third liquid phase fraction to be refluxed into the buffer tank (13).

13. The method according to claim 10, characterized in that, The heavy feedstock is crude oil and / or heavy hydrocarbons.

14. The method according to claim 10, characterized in that, The temperature of the first preheated heavy feedstock is 70~120℃; or the crude oil from the storage tank is introduced into the convection section of the steam cracking unit after undergoing the first heat exchange through the quench water preheater (17) to obtain the first preheated heavy feedstock.

15. The method according to claim 10, characterized in that, The temperature of the third preheated heavy raw material is 180~330℃.

16. The method according to claim 11, characterized in that, The method further includes: using at least a portion of the third liquid phase fraction as a heat source to enter a dilution steam generator to obtain dilution steam; and dividing a portion of the dilution steam into four parts, which are respectively used as the first part steam, the second part steam, the third part steam, and the fourth part steam.

17. The method according to claim 10, characterized in that, The method further includes: subjecting the heavy raw material to a first external preheating treatment outside the convection section before introducing the heavy raw material into the first flash tank (3); the first external preheating treatment is independent of the preheating in the first raw material preheating section (1); and Before the first liquid fraction from the first flash tank (3) enters the second flash tank (5), the first liquid fraction undergoes a second external preheating treatment outside the convection section; the second external preheating treatment is independent of the heating in the third mixing superheating section (4); and Before the second liquid fraction from the second flash tank (5) enters the third flash tank (8), the second liquid fraction is subjected to a third external preheating treatment outside the convection section; the third external preheating treatment is independent of the heating in the fifth mixing superheating section (7).

18. The method according to claim 17, characterized in that, The heat source for the first, second, and third external preheating treatments is waste heat material from any device.

19. The method according to claim 17, characterized in that, The heat sources for the second and third external preheating treatments are selected from at least one of low-pressure steam, medium-pressure steam, and high-pressure steam.

20. The method according to claim 9, characterized in that, The method also includes: The weight ratio of steam to heavy feedstock in the first stream to be pyrolyzed is controlled to be 0.35~1; The weight ratio of steam to heavy feedstock in the second pyrolysis stream is controlled to be 0.4~1; The weight ratio of steam to heavy feedstock in the third pyrolysis stream is controlled to be 0.5~1.

21. The method according to claim 20, characterized in that, The method also includes: The weight ratio of steam to heavy feedstock in the first stream to be pyrolyzed is controlled to be 0.40~0.7; The weight ratio of steam to heavy feedstock in the second stream to be pyrolyzed is controlled to be 0.6~0.8; The weight ratio of steam to heavy feedstock in the third pyrolysis stream is controlled to be 0.7~0.

9.

22. A system for producing olefins by cracking heavy feedstock, characterized in that, The system includes a first flash tank (3), a second flash tank (5), a third flash tank (8), and a steam cracking device. The steam cracking device includes a convection section and a radiation section (18). Along the height direction of the steam cracking device, the convection section is located above the radiation section (18). The first flash tank (3) is provided with a heavy raw material inlet, a first vapor phase distillate outlet and a first liquid phase distillate outlet; the second flash tank (5) is provided with a first vapor phase distillate inlet, a second vapor phase distillate outlet and a second liquid phase distillate outlet; the third flash tank (8) is provided with a second liquid phase distillate inlet, a third vapor phase distillate outlet and a third liquid phase distillate outlet; The heavy raw material inlet of the first flash tank (3) is connected to a heavy raw material input pipeline, and a first steam inlet is provided on the heavy raw material input pipeline; The first liquid phase fraction outlet of the first flash tank (3) is connected to the first liquid phase fraction inlet of the second flash tank (5), and a second steam inlet is provided on the connecting pipeline between the first liquid phase fraction outlet and the first liquid phase fraction inlet; the second liquid phase fraction outlet of the second flash tank (5) is connected to the second liquid phase fraction inlet of the third flash tank (8), and a second steam inlet and a third steam inlet are provided on the connecting pipeline between the second liquid phase fraction outlet and the second liquid phase fraction inlet, and the second steam inlet is located upstream of the third steam inlet along the material flow direction; The radiation section (18) of the steam cracking device is provided with a first material inlet to be cracked, an optional second material inlet to be cracked, and an optional third material inlet to be cracked; the first material inlet to be cracked is connected to the first gas phase distillate outlet, the second material inlet to be cracked is connected to the second gas phase distillate outlet, and the third material inlet to be cracked is connected to the third gas phase distillate outlet.

23. The system according to claim 22, characterized in that, The convection section is provided with, from top to bottom, a first raw material preheating section (1), a fourth mixing superheating section (6), a fifth mixing superheating section (7), a sixth steam superheating section (9), a seventh mixing superheating section (10), an eighth mixing superheating section (11), and a ninth mixing superheating section (12), which are independent of each other. The first raw material preheating section (1) is provided with a first superheating inlet and a first superheating outlet. The first superheating outlet is connected to the first heavy raw material inlet pipeline of the first flash tank (3). The first steam inlet is located on the first pipeline. The first liquid phase distillation outlet of the first flash tank (3) is connected to the first liquid phase distillation inlet of the second flash tank (5) through a second pipeline, and the second steam inlet is provided on the second pipeline; The fourth mixing superheating section (6) is provided with a second superheating inlet and a second superheating outlet. The second superheating inlet is connected to the first vapor fraction outlet of the first flash tank (3). The fifth mixing superheating section (7) is provided with a third superheating inlet and a third superheating outlet. The third superheating inlet is connected to the second liquid phase distillate outlet of the second flash tank (5) through a third pipeline. The third steam inlet is located on the third pipeline. The third superheating outlet is connected to the second liquid phase distillate inlet of the third flash tank (8) through a fourth pipeline. The fourth steam inlet is located on the fourth pipeline. The sixth steam superheating section (9) is provided with a steam superheating inlet and a steam superheating outlet; the steam superheating outlet is connected to the second steam inlet of the second pipeline and the fourth steam inlet of the fourth pipeline respectively; The seventh mixing superheating section (10) is provided with a fourth superheating inlet and a fourth superheating outlet. The fourth superheating inlet is connected to the second superheating outlet of the fourth mixing superheating section (6), and the fourth superheating outlet is connected to the first inlet of the material to be cracked in the radiation section (18). The eighth mixing superheating section (11) is provided with a fifth superheating inlet and a fifth superheating outlet. The fifth superheating inlet is connected to the second vapor fraction outlet of the second flash tank (5), and the fifth superheating outlet is connected to the second inlet of the material to be cracked in the radiation section (18). The ninth mixing superheating section (12) is provided with a sixth superheating inlet and a sixth superheating outlet; optionally, the sixth superheating inlet is connected to the third gas phase distillate outlet of the third flash tank (8), and the sixth superheating outlet is connected to the third pyrolysis material inlet of the radiation section (18).

24. The system according to claim 23, characterized in that, Each of the second steam inlet, the third steam inlet, and the fourth steam inlet is independently equipped with a material mixer for mixing the materials and steam introduced into the mixer.

25. The system according to claim 23, characterized in that, The first flash tank (3), the second flash tank (5) and the third flash tank (8) are arranged in sequence in the vertical direction along the same central axis.

26. The system according to claim 23, characterized in that, The system also includes a buffer tank (13), a pump (14), a desalination pre-processor (16), and a quench water preheater (17). The buffer tank (13) is provided with a liquid phase heavy component buffer inlet, a liquid phase heavy component buffer outlet and a heavy component reflux inlet; the pump (14) includes an inlet and an outlet; the desalination preprocessor (16) is provided with a heavy raw material desalination inlet and a heavy raw material desalination outlet; the quench water preheater (17) is provided with a quench water heat exchange inlet, a quench water heat exchange outlet, a heavy raw material heat exchange first inlet and a heavy raw material heat exchange first outlet; The first outlet of the heavy raw material heat exchanger of the quench water preheater (17) is connected to the heavy raw material desalination inlet of the desalination preprocessor (16), and the heavy raw material desalination outlet of the desalination preprocessor (16) is connected to the heavy raw material preheating inlet of the first raw material preheating section (1). The liquid phase heavy component buffer inlet of the buffer tank (13) is connected to the third liquid phase distillate outlet of the third flash tank (8), the liquid phase heavy component buffer outlet is connected to the input port of the pump (14), the output port of the pump (14) is sent out, or the output port of the pump (14) is connected to the heavy component reflux inlet of the buffer tank (13). The level transmitter is connected to the inside of the buffer tank (13) to control the level inside the buffer tank (13).

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