Method and system for producing low-carbon olefin through steam cracking

Abstract

The invention relates to a method and a system for producing low-carbon olefin by steam cracking, which are characterized in that raffinate naphtha and raffinate normal-pressure diesel oil which are obtained by an oil product extraction device are used as cracking raw materials and are fed into a cracking furnace of an ethylene device for steam thermal cracking reaction, so that a thermal coupling synergistic effect is exerted; the lean aromatic raffinate oil flowing out of the top of the extraction tower is directly sent to the convection section of the ethylene cracking furnace for preheating, and correspondingly, the excess heat on the flue gas side of the convection section is used for heating the self-produced methane fuel gas of the separation unit of the ethylene cracking device, so that the fuel consumption of the ethylene cracking furnace is saved by 0.90-1.66%, the thermal load of the ethylene cracking furnace is reduced by 0.91-1.69%, and the energy consumption of the ethylene cracking furnace is reduced. The yield of ethylene is increased by 0.06-0.68 wt%, the yield of ethylene is increased by 69-25840 t / a, and the method can be applied to large-scale commercial industrial production of ethylene products.

Description

Technical Field

[0001] The present invention relates to the field of light olefin production, and in particular to a method and system for producing light olefins through steam cracking. Background Art

[0002] The steam pyrolysis process is a petrochemical process that uses a catalyst-free cracking chemical reaction to produce "triene" products such as ethylene, propylene, and butadiene, and "triphenylene" products such as benzene, toluene, and xylene. These products are then further refined into three major product categories: synthetic resins, synthetic rubber, and synthetic fibers. The steam pyrolysis process can use liquid distillate oils such as naphtha, atmospheric diesel, vacuum diesel, and hydrogenated tail oil as cracking feedstocks. Currently, the production capacity of domestic ethylene plants is increasing. The oil extraction process, which uses solvent extraction to separate aromatic and non-aromatic components from petroleum fractions such as gasoline and diesel, can effectively improve the quality of the cracking feedstock.

[0003] In order to advance the technology of oil extraction process and steam thermal cracking process, there are continuous reports on the optimization of cracking raw materials, especially naphtha, atmospheric diesel and hydrogenated tail oil.

[0004] Patent application number CN200910204253.X in the prior art discloses a method for the comprehensive utilization of hydrocracking tail oil, which includes the following specific steps: first, subjecting the hydrocracking tail oil to vacuum fractionation; the resulting light fraction of the hydrocracking tail oil is used as a feedstock for steam cracking to produce ethylene, and the heavy fraction of the hydrocracking tail oil is used as a feedstock for producing lubricant base oil. The heavy fraction of the hydrocracking tail oil can be processed through processes including isodewaxing and supplementary refining to produce high-quality lubricant base oil. Compared to the prior art, the method of the present invention not only produces high-quality lubricant base oil but also provides a feedstock for ethylene cracking. It also improves the yield of olefins and lubricant base oil, reduces product costs, effectively addresses the problem of raw material shortages for lubricant base oil production, and increases product flexibility. Patent application number CN201210333626.5 in the prior art discloses a method for increasing the production of light olefins and aromatics by steam cracking naphtha with an aromatics content of 9% or more. The method adds a backwash-free polar solvent aromatics extraction system before the steam cracking unit, thereby reducing the aromatics content in the naphtha cracking feedstock; improving the selectivity of olefins in the cracking process, directly increasing the yield of light olefins, while reducing the coking rate of the equipment and the temperature of the cracking reaction, and extending the decoking cycle. The method of the present invention effectively recovers aromatic components while pretreating the cracking feedstock, thereby increasing the total aromatics yield by more than 40% compared to the case without pretreatment. The method of the present invention uses a backwash-free solvent extraction process, optimizes the cracking feedstock, expands the source of raw materials, increases the yield of light olefins and aromatics, and effectively reduces the energy consumption of the device and equipment investment. Patent application number CN201910901193.0, filed in the prior art, discloses an ethylene cracking furnace and ethylene cracking method. The ethylene cracking furnace comprises a high-pressure steam drum, a convection section, a radiant section, a quench boiler, and a burner. The radiant section is arranged with multiple radiant tube groups, each including multiple radiant tubes. The convection section is arranged with convection section heat exchange tubes, each comprising multiple horizontally arranged heat exchange tube bundles. The multiple heat exchange tube bundles are arranged such that the convection section includes an upper feed preheater, a boiler feedwater preheater, a lower feed preheater, a primary dilution steam superheater, a secondary dilution steam superheater, an upper mixing preheater, an ultra-high-pressure steam superheater, and a lower mixing preheater. Different convection section layout schemes are proposed to address the potential coking problem in the convection section for feedstocks of varying properties, particularly heavy feedstocks. The scheme also more effectively utilizes flue gas waste heat, reduces heat exchange area, and saves investment. Patent application number CN202010682905.7 in the prior art discloses a high-yield device and method for low-carbon olefins and aromatics, which includes two riser reactors, two settlers, two fractionating towers, a gasoline hydrodesulfurization device, a gasoline cutting distillation device and an aromatics extraction device.The first riser reactor, the first settler, the catalytic gasoline outlet of the first fractionator, the feed inlet of the second riser reactor, the second settler, the second fractionator, the catalytic gasoline outlet of the second fractionator, the gasoline hydrodesulfurization unit, the gasoline cutting distillation unit, and the gasoline heavy fraction outlet of the gasoline cutting distillation unit are sequentially connected to the aromatics extraction unit. This multi-product unit has a simple structure and utilizes a combined catalytic cracking-aromatics extraction process to process low-quality heavy oil, producing light olefins and aromatics while avoiding low-quality catalytic gasoline and catalytic diesel. This enables the transformation of an oil refining unit into a chemical plant, with significant economic and social benefits. Patent No. CN115725327A in the prior art discloses a system and method for producing ethylene through steam pyrolysis, belonging to the field of ethylene production technology. This steam pyrolysis ethylene production system includes an aromatics extraction unit and an ethylene cracking unit. By setting up parallel extraction towers, naphtha and atmospheric diesel are extracted and separated through the oil extraction unit to obtain raffinate naphtha and raffinate atmospheric diesel, which are then fed into the cracking furnace as cracking feedstock for steam pyrolysis. This invention increases ethylene production while maintaining the same feedstock. It can be applied to commercial, large-scale industrial production of ethylene products. Prior art patent number CN112538366A discloses an ethylene cracking furnace and ethylene cracking method. The ethylene cracking furnace comprises a high-pressure steam drum, a convection section, a radiant section, a quench boiler, and a burner. The radiant section is equipped with multiple radiant tube groups, each including multiple radiant tubes. The convection section is equipped with convection section heat exchange tubes, each comprising multiple horizontally arranged heat exchange tube bundles. The multiple heat exchange tube bundles are arranged such that the convection section includes an upper feed preheater, a boiler feedwater preheater, a lower feed preheater, a primary dilution steam superheater, a secondary dilution steam superheater, an upper mixing preheater, an ultra-high-pressure steam superheater, and a lower mixing preheater. Prior art patent number CN110184086A discloses a cracking furnace for the thermal cracking of light hydrocarbons, including a method for heating the cracking feedstock in the convection section.

[0005] Prior art patent application number CN200910204253.X only discloses a technical solution for using light fractions from hydrocracking tail oil as a feedstock for steam cracking to produce ethylene. Prior art patent application number CN201210333626.5 only discloses a technical solution for reducing the aromatics content in naphtha cracking feedstock, improving olefin selectivity during the cracking process, and increasing the yield of light olefins. Prior art patent application number CN201910901193.0 only discloses an ethylene cracking furnace and ethylene cracking method. Prior art patent application number CN202010682905.7 only discloses a method for increasing the yield of liquefied gas and aromatics using a combined catalytic cracking and aromatics extraction process. Prior art patent No. CN115725327A fails to consider the thermal coupling between the extraction unit and the ethylene plant. Instead, the 90-120°C aromatic-poor raffinate flowing from the extraction tower overhead is first cooled to room temperature using circulating cooling water in a heat exchanger before being delivered to the extraction unit boundary. The room-temperature aromatic-poor raffinate then enters the ethylene unit boundary where it is preheated to 90-120°C using methane fuel gas combustion flue gas in the convection section of the ethylene cracking furnace. Further heating is then performed before the cracking reaction. Prior art patents No. CN112538366A and CN110184086A merely disclose methods in which the cracking feedstock is heated using the flue gas in the convection section.

[0006] In summary, while the aforementioned prior art has partially optimized steam cracking for ethylene production, none of them addresses how to improve ethylene yield while reducing energy consumption. In reality, high temperature and short residence time are crucial elements of the ethylene cracking reaction. As is well known, these conditions often lead to increased equipment investment, utility costs, and equipment energy consumption, making it difficult to achieve both low energy consumption and high ethylene yield. As described in the aforementioned prior art, steam cracking for ethylene production involves the acquisition of cracking feedstock, the cracking process, and subsequent separation and processing steps. This complex system, characterized by complex processes and lengthy procedures, often requires significant changes. Modifying a single step often results in changes to multiple equipment steps, changes to process pipeline reconfigurations, and so on. Therefore, how to improve existing complex production systems or processes to achieve improved ethylene yield while reducing energy consumption is a relatively difficult technical problem. Summary of the Invention

[0007] Through research, the inventors of the present invention unexpectedly discovered that by thermally coupling the extraction device with the ethylene cracking device, after naphtha and atmospheric diesel are extracted and separated in a large-scale industrial-scale oil extraction device to obtain residual naphtha and residual atmospheric diesel, they are not cooled as cracking raw materials, but are further heated using the waste heat from the convection section of the ethylene cracking furnace before entering the cracking furnace of the ethylene device for steam thermal cracking reaction. At the same time, the excess waste heat on the flue gas side of the convection section is used to heat the methane fuel gas produced by the separation unit of the ethylene cracking device. This not only reduces the energy consumption of the process system but also can improve the ethylene yield, and has extremely high promotion and application value.

[0008] In order to achieve the above-mentioned purpose of the invention, the first aspect of the present invention is to provide a method for producing light olefins by steam cracking, comprising: extracting and separating an aromatic oil product to obtain an aromatic-poor raffinate oil, preheating the aromatic-poor raffinate oil as a cracking feed in the convection section of a cracking furnace and then conveying it to the radiant section of the cracking furnace for cracking to obtain a mixed gas containing light olefins; separating the mixed gas to obtain cracking products, wherein all or part of the obtained methane is preheated on the flue gas side of the convection section of the cracking furnace and then conveyed to the cracking furnace as fuel.

[0009] According to some preferred embodiments of the present invention, the residence time of the cracking raw material in the radiation section is 0.22-0.28 s, and the outlet temperature of the cracking furnace is 805-875°C.

[0010] According to some preferred embodiments of the present invention, the flue gas side of the convection section of the cracking furnace is divided into the uppermost end, the second uppermost end and the uppermost end from top to bottom; wherein the operating temperature of the uppermost end is 94-114°C, the operating temperature of the second uppermost end is 141-161°C, and the operating temperature of the uppermost end is 343-363°C.

[0011] According to some preferred embodiments of the present invention, the aromatic oil product is naphtha and / or atmospheric diesel.

[0012] According to some more preferred embodiments of the present invention, when the aromatic oil product is atmospheric pressure diesel, the preferred process parameters are: the operating temperature of the uppermost end of the flue gas side of the convection section of the ethylene cracking furnace (C1) is 94-114°C, the operating temperature of the second upper end is 141-161°C, and the operating temperature of the upper end is 343-363°C; the residence time of the radiation section of the ethylene cracking furnace (C1) is 0.25-0.27s, and the COT at the furnace outlet is 805-815°C; or,

[0013] According to some more preferred embodiments of the present invention, when the aromatic oil product is naphtha, the preferred process parameters are: an operating temperature of 94-114°C at the top end of the flue gas side of the convection section of the ethylene cracking furnace (C1), 141-161°C at the next top end, and 343-363°C at the next top end. The residence time in the radiant section of the ethylene cracking furnace (C1) is 0.22-0.28 seconds, and the COT at the furnace outlet is 835-875°C.

[0014] The inventors of the present invention have found that under the operating process conditions of the above-mentioned preferred and more preferred embodiments, combined with the coupling method of the present invention, both the preheating of the methane fuel gas and the preheating of the poor aromatic raffinate oil are achieved, further saving energy consumption. Combined with the above-mentioned process parameters, the ethylene yield is further improved.

[0015] According to some preferred embodiments of the present invention, the methane fuel gas is operated at an inlet temperature of 25-55°C and an outlet temperature of 65-95°C at the flue gas side of the convection section of the cracking furnace; and / or the aromatic-poor raffinate is operated at an inlet temperature of 90-120°C and an outlet temperature of 286-316°C at the convection section of the cracking furnace. In this preferred embodiment, the present invention further reduces energy consumption and further improves ethylene yield.

[0016] According to some preferred embodiments of the present invention, the aromatic oil product is extracted through N extraction towers connected in series to obtain an aromatic-lean raffinate and an aromatic-rich solvent; preferably, the aromatic oil product and the extraction solvent flow in countercurrent within the N extraction towers connected in series; and / or, the aromatic-lean solvent obtained by stripping the aromatic-rich solvent through a stripping tower is recycled back to the extraction tower as an extraction solvent.

[0017] According to some preferred embodiments of the present invention, the aromatic oil product enters the bottom of the first extraction tower, the extraction solvent enters from the top of the extraction tower, the purified oil product after extraction is discharged from the top of the extraction tower, and the aromatic solvent is discharged from the bottom of the extraction tower; the purified oil product discharged from the top of the previous extraction tower enters the bottom of the next extraction tower; the extraction solvent of the previous extraction tower comes from the aromatic solvent discharged from the bottom of the next extraction tower, and so on; the aromatic solvent discharged from the bottom of the first extraction tower enters the stripping tower, the poor aromatic solvent flowing out of the bottom of the stripping tower returns to the last extraction tower, the aromatic-rich raffinate oil flowing out of the top of the stripping tower is sent out of the boundary, and the poor aromatic raffinate oil is obtained at the top of the last extraction tower and enters the cracking furnace as a cracking feedstock.

[0018] According to some preferred embodiments of the present invention, the operating pressure of the extraction tower is 0.19-0.39 MPaA, and / or the operating temperature is 90-120° C.; and / or the operating pressure of the stripping tower is 0.19-0.39 MPaA, and / or the operating temperature is 140-170° C.; and / or the number of extraction towers connected in series is N=1-6, where N is an integer; and / or the extraction solvent is one of sulfolane and N-methylpyrrolidone; and / or,

[0019] The mass ratio of the extraction solvent to the aromatic oil product is 1.2 to 1.8.

[0020] According to the present invention, the mixed gas containing light olefins includes ethylene, propylene, butadiene, benzene, toluene, xylene, and methane.

[0021] According to some preferred embodiments of the present invention, during the process of feeding methane as fuel into the cracking furnace, the flow rate and / or pressure of methane in the pipeline is detected and adjusted, and preferably the methane pressure is overridden.

[0022] According to some preferred embodiments of the present invention, the mixed gas containing light olefins is subjected to rapid cooling and terminating the steam thermal cracking reaction, and then separated. The separation step includes: first entering a rapid cooling oil tower for cooling and distillation separation, and then the top material enters a rapid cooling water tower, is cooled and separated by water washing, and the obtained top material enters a compression unit and a separation unit in sequence for separation treatment, at least part of the methane flowing out of the separation unit is fed into a cracking furnace as fuel, and the separation unit obtains hydrogen, ethylene, propylene, and cracked carbon four and sends them out of the boundary;

[0023] Preferably, the heavy pyrolysis gasoline flowing out of the kettle of the quenching water tower and the light pyrolysis gasoline flowing out of the separation unit are combined into one pyrolysis gasoline and sent out of the boundary;

[0024] Preferably, the cracked heavy oil flowing out of the kettle of the quench oil tower is sent out of the boundary.

[0025] Other process parameters of the cracking and separation stages in the present invention may refer to the process conditions of Ethylene Process and Technology (Essence Edition) (edited by Wang Songhan, published by China Petrochemical Press in September 2012), and will not be repeated here.

[0026] The second aspect of the present invention is to provide a system for producing light olefins through steam cracking, preferably used in the method described in the first aspect, wherein the system comprises an aromatics extraction unit, a light olefin cracking furnace, and a cracking gas separation unit connected in sequence; the cracking furnace comprises a convection section and a radiation section from top to bottom;

[0027] The aromatic-poor raffinate oil obtained from the aromatic extraction unit enters the radiant section of the cracking furnace through a feed pipeline for cracking, and part of the feed pipeline of the aromatic-poor raffinate oil is arranged in the convection section of the cracking furnace;

[0028] All or part of the methane obtained by the cracking gas separation unit is connected to the fuel feed port of the cracking furnace through a fuel feed pipeline, and part of the fuel feed pipeline is arranged on the flue gas side of the convection section of the cracking furnace.

[0029] According to some preferred embodiments of the present invention, the feed line of the aromatic-poor raffinate oil is directly connected to the convection section of the cracking furnace without a cooling unit; and / or

[0030] The outer side of the feed pipeline of the aromatic-poor raffinate oil is provided with a thermal insulation layer; and / or,

[0031] In the convection section of the cracking furnace, a heat exchange mechanism containing external finned coils is provided at the location where the feed pipeline of the aromatic-poor raffinate oil is arranged for preheating.

[0032] According to some preferred embodiments of the present invention, on the flue gas side of the convection section of the cracking furnace, a plate-fin heat exchange junction is provided at the location where the fuel feed pipeline is arranged for preheating; and / or,

[0033] The fuel feed pipeline is provided with a flow detector and a flow regulator, a pressure detector and an override control valve; preferably, the override control valve divides the methane fuel gas from the separation subunit into two branches, one of which is connected to the fuel feed port of the cracking furnace.

[0034] According to some preferred embodiments of the present invention, the aromatics extraction device includes a stripping tower and N extraction towers connected in series; wherein each extraction tower is provided with a tower bottom feed port, a tower top feed port, a tower top discharge port and a tower bottom discharge port, wherein, according to the logistics direction, the aromatic oil product raw material source is connected to the tower bottom feed port of the first extraction tower; the tower top discharge port of the previous extraction tower is connected to the tower bottom feed port of the next extraction tower; the tower top feed port of the previous extraction tower is connected to the tower bottom discharge port of the next extraction tower; the tower bottom discharge port of the first extraction tower is connected to the feed port of the stripping tower, and the tower bottom discharge port of the stripping tower is connected to the tower top feed port of the last extraction tower; the tower top discharge port of the last extraction tower is connected to the aromatic-poor raffinate oil feed pipeline;

[0035] Preferably, N is an integer of 1-6.

[0036] According to some preferred embodiments of the present invention, the cracking gas separation unit includes a quenching subunit, a compression subunit, and a separation subunit connected in sequence; preferably, the quenching subunit includes a quenching oil tower and a quenching water tower connected in sequence;

[0037] More preferably, the top discharge port of the quenching oil tower is connected to the feed port of the quenching water tower, and the top discharge port of the quenching water tower is connected to the feed port of the compression unit; and / or, the bottom discharge port of the quenching oil tower and the bottom discharge port of the quenching water tower are each connected to the outside through a pipeline.

[0038] Compared with the prior art, the advantages of the present invention are:

[0039] The extraction unit is thermally coupled with the ethylene cracking unit. After naphtha and atmospheric diesel are extracted and separated in a large-scale industrial-scale oil extraction unit to obtain residual naphtha and residual atmospheric diesel, they are used as cracking raw materials without cooling. Instead, they are further heated by the waste heat from the convection section of the ethylene cracking furnace and then enter the radiation section of the cracking furnace of the ethylene unit for steam thermal cracking reaction. At the same time, the excess heat from the flue gas side of the convection section is used to heat the methane fuel gas produced by the separation unit of the ethylene cracking unit. This can reduce the energy consumption of the process system while increasing the ethylene yield, and has extremely high promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the process flow of thermally coupling the extraction device and the ethylene device of the present invention;

[0041] Figure 2 The temperature distribution diagram of part of the material and part of the flue gas in the convection section of the ethylene cracking furnace (C1).

[0042] In the figure: the extraction tower is A, the number after A is the sequence number of the extraction tower, A1 is the first extraction tower, A2 is the second extraction tower; B1 is the solvent stripping tower; C1 is the ethylene cracking furnace; C2 is the quench boiler; C3 is the quench oil tower; C4 is the quench water tower; C5 is the compression unit; C6 is the separation unit;

[0043] 101 Aromatic oil products; 102 Aromatic-rich extracted oil; 201 Aromatic raffinate oil; 202 Aromatic solvent; 203 Aromatic-rich solvent; 204 Aromatic-poor solvent; 205 Aromatic-poor raffinate oil; 301 High-temperature cracking gas; 302 Methane fuel gas; 303 Medium-temperature cracking gas from the top of the quench oil tower; 304 Low-temperature cracking gas from the top of the quench water tower; 305 Heavy cracking gasoline from the bottom of the quench water tower; 306 Light cracking gasoline from the separation unit; 401 Hydrogen; 402 Remaining methane; 403 Ethylene; 404 Propylene; 405 Cracking C4; 406 Cracking gasoline; 407 Cracking heavy oil DETAILED DESCRIPTION

[0044] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art to the present invention based on the contents of the present invention still fall within the scope of protection of the present invention.

[0045] As mentioned above, the present invention relates to a method and system for producing light olefins by steam cracking. In the present invention, after naphtha and atmospheric diesel are extracted and separated by a large-scale industrial-scale oil extraction device to obtain raffinate naphtha and raffinate atmospheric diesel, the raffinate naphtha and raffinate atmospheric diesel are used as high-quality cracking raw materials to enter the cracking furnace of an ethylene device with a production scale of 115,000 to 3.8 million tons / year for steam thermal cracking reaction. The synergistic effect of thermal coupling between the oil extraction device and the ethylene cracking device is fully utilized, and the poor aromatic raffinate oil flowing out of the extraction device is not cooled to room temperature through a heat exchanger, but is directly sent to the convection section of the ethylene cracking furnace for further preheating treatment. Correspondingly, the excess heat on the flue gas side of the convection section is used to heat the separation of the ethylene cracking device. The methane fuel gas produced by the unit is used to thermally couple the extraction unit with the ethylene cracking unit. After the naphtha and atmospheric diesel are extracted and separated in a large-scale industrial-scale oil extraction unit to obtain residual naphtha and residual atmospheric diesel, they are used as cracking raw materials without cooling. Instead, they are further heated using the waste heat from the convection section of the ethylene cracking furnace and then enter the cracking furnace of the ethylene unit for steam thermal cracking reaction. At the same time, the excess waste heat from the flue gas side of the convection section is used to heat the methane fuel gas produced by the separation unit of the ethylene cracking unit. This reduces the energy consumption of the process system while increasing the ethylene yield, and has extremely high promotion and application value.

[0046] The process flow is as follows: Figure 1 As shown, in the system and method for producing light olefins by steam cracking:

[0047] Taking the number of extraction towers connected in series as N=2 as an example, the aromatic oil product (101) from outside the boundary enters the bottom of the extraction tower (A1), and the aromatic solvent (202) enters the top of the extraction tower (A1). In the extraction tower (A1), the density of the oil product is less than the density of the solvent. The oil product flows from bottom to top, and the solvent flows from top to bottom. The oil product and the solvent flow in counter-current. After sufficient liquid-liquid contact of the "oil phase-solvent phase", a two-phase mass transfer process occurs, and the aromatic hydrocarbons entrained in the aromatic oil product are extracted into the solvent by the solvent. The aromatic raffinate (201) flowing out of the top of the extraction tower (A1) enters the bottom of the extraction tower (A2), and the poor aromatic solvent (204) enters the top of the extraction tower (A2). In the extraction tower (A2), the density of the oil product is less than that of the solvent. The oil product flows from bottom to top, while the solvent flows from top to bottom. The oil product and the solvent flow in counter-currents. Through sufficient liquid-liquid contact between the "oil phase and the solvent phase," a two-phase mass transfer process occurs, and the aromatic hydrocarbons entrained in the aromatic oil product are extracted into the solvent by the solvent. The aromatic-rich solvent (203) flowing out of the bottom of the extraction tower (A1) enters the solvent stripping tower (B1). In the solvent stripping tower (B1), the aromatic hydrocarbons are separated from the solvent by steam stripping. The aromatic-poor solvent (204) flowing out of the bottom of the solvent stripping tower (B1) returns to the top of the extraction tower (A2), and the aromatic-rich extracted oil (102) flowing out of the top of the solvent stripping tower (B1) is sent out of the boundary. The aromatic-poor raffinate (205) flowing out of the top of the extraction tower (A2) directly enters the convection section of the ethylene cracking furnace (C1) for further heating and then enters the radiation section of the ethylene cracking furnace (C1) for steam thermal cracking reaction of the oil product to generate cracked gas of basic organic chemical products such as ethylene, propylene, butadiene, benzene, toluene, and xylene. The cracked gas is then cooled by the quenching boiler (C2) and the steam thermal cracking reaction is terminated to become high-temperature cracked gas (301) and enter the quenching oil tower (C3). After the cracked gas is cooled and distilled in the quenching oil tower (C3), the medium-temperature cracked gas (303) flowing out of the top of the tower enters the quenching water tower (C4). After the cracked gas is cooled and washed and separated in the quenching water tower (C4), the low-temperature cracked gas (304) flowing out of the top of the tower enters the compression unit (C5) and the separation unit (C6) in sequence for separation and treatment to obtain hydrogen (401), ethylene (403), propylene (404), and cracked carbon four (405) and send out of the boundary. The heavy pyrolysis gasoline (305) flowing out of the bottom of the quench water tower (C4) and the light pyrolysis gasoline (306) flowing out of the separation unit (C6) are combined to form pyrolysis gasoline (406) and sent out of the reactor. The pyrolysis heavy oil (407) flowing out of the bottom of the quench oil tower (C3) is sent out of the reactor. The methane flowing out of the separation unit (C6) is split into two parts, one portion of which is returned to the ethylene cracking furnace (C1) as methane fuel gas (302), and the remaining portion of methane (402) is sent out of the reactor.

[0048] Since the waste heat of 90-120°C of the aromatic-poor raffinate oil (205) flowing out of the top of the extraction tower (A2) is fully utilized, the excess waste heat on the flue gas side of the convection section of the ethylene cracking furnace (C1) can be used to heat the methane fuel gas (302) flowing out of the separation unit (C6).

[0049] In order to ensure the stable operation of the waste heat recovered by the thermal coupling between the oil extraction unit and the ethylene cracking unit, it is preferred to set up a flow detection and regulation (FC) system on each fuel gas branch pipe, and at the same time set up a pressure detection and separation unit (C6) on each fuel gas branch pipe and a regulation (PC) system on the methane main pipe.

[0050] The pressure of the methane fuel gas (302) is over-controlled to prevent external fluctuations under conventional control conditions from affecting the normal and stable combustion of the fuel in the fuel gas system of the ethylene cracking furnace, thus playing a protective role.

[0051] Furthermore, the present invention has made the following improvements:

[0052] (1) In order to realize the technical means of heating the methane fuel gas (302) produced by the separation unit (C6) of the ethylene cracking unit to 65-95°C by the excess waste heat on the flue gas side of the convection section, it is preferred to add a methane fuel gas pipeline system, set flow (FC) detection and regulation, pressure (PC) detection and overspeed control. The methane pipeline flowing out of the separation unit (C6) is provided with an overspeed control regulating valve to split the methane fuel gas into two parts, one part of which is returned to the ethylene cracking furnace (C1) as methane fuel gas (302). In order to ensure that the waste heat recovered by the thermal coupling of the oil extraction unit and the ethylene cracking unit can operate stably, it is necessary to set a flow detection and regulation (FC) system on each fuel gas branch pipe, and set a pressure detection system on each fuel gas branch pipe and a regulation (PC) system on the methane main pipe flowing out of the separation unit (C6). The pressure of the methane fuel gas (302) is overspeed controlled to avoid external fluctuations under conventional control conditions affecting the normal and stable combustion of the fuel in the fuel gas system of the ethylene cracking furnace body.

[0053] (2) In order to realize the technical means of directly sending the 90-120°C poor aromatic raffinate oil (205) flowing out of the top of the extraction tower (A2) to the convection section of the ethylene cracking furnace (C1) for further preheating treatment without cooling it to room temperature through a heat exchanger, the poor aromatic raffinate oil (205) material pipeline from the top of the extraction tower (A2) to the convection section of the ethylene cracking furnace (C1) needs to be insulated to reduce heat loss and prevent burns to operators.

[0054] (3) In order to heat the methane fuel gas (302) produced by the separation unit (C6) of the ethylene cracking device to 65-95°C, the convection section equipment of the ethylene cracking furnace (C1) needs to be equipped with a methane fuel gas heat exchange device or the existing convection section coil needs to be modified or other technical means of modifying the equipment need to be adopted to achieve thermal coupling between the extraction device and the ethylene device. It is not possible to simply heat the methane fuel gas pipeline on the flue gas side of the convection section of the cracking furnace. For example, the space on the flue gas side of the convection section of the cracking furnace is small and the equipment weight cannot be large. The inventor of the present invention creatively applies a plate-fin heat exchange mechanism to the heat exchange between the methane fuel gas (302) and the convection section flue gas. This is the first time that a plate-fin heat exchange mechanism has been applied to a cracking furnace. The plate-fin heat exchange mechanism has the characteristics of compact structure, low equipment weight, and less steel structure support. It creatively solves the problem of preheating the methane fuel gas on the flue gas side of the convection section of the cracking furnace. Preferably, the methane fuel gas (302) and the convection section flue gas are heat exchanged through the equipment of the plate-fin heat exchange mechanism.

[0055] Preferably, the aromatic-poor raffinate oil (205) and the convection section flue gas are heat exchanged through a device containing an external finned coil heat exchange mechanism, which has the characteristics of high heat transfer efficiency, low equipment investment, and easy maintenance.

[0056] (4) Optimizing process parameters include:

[0057] The residence time of the cracking raw material in the radiation section is 0.22-0.28s, and the cracking furnace outlet temperature is 805-875°C;

[0058] The operating temperature of the top end of the flue gas side of the convection section of the ethylene cracking furnace (C1) is 94-114°C, the operating temperature of the second top end is 141-161°C, and the operating temperature of the top end is 343-363°C. Figure 2 : Distribution diagram of partial material temperature and partial flue gas temperature in the convection section of the ethylene cracking furnace (C1).

[0059] Improving the COT of the ethylene cracking furnace increases the ethylene yield and maximizes the use of heat to achieve the goal of thermal coupling between the extraction unit and the ethylene unit.

[0060] More preferably, the operating pressure / operating temperature of the extraction tower (A1); the operating pressure / operating temperature of the solvent stripping tower (B1), the operating temperature of the methane fuel gas (302) side inlet of the convection section of the ethylene cracking furnace (C1), the operating temperature of the methane fuel gas (302) side outlet, the operating temperature of the poor aromatic raffinate oil (205) side inlet, and the operating temperature of the poor aromatic raffinate oil (205) side outlet can improve the quality of the poor aromatic raffinate oil (205) cracking feedstock, improve the COT of the ethylene cracking furnace, increase the ethylene yield, and maximize the use of heat to achieve the goal of thermal coupling between the extraction unit and the ethylene unit.

[0061] (5) High temperature, short residence time, and low hydrocarbon partial pressure are the three key elements of the ethylene cracking reaction. The 90-120°C poor aromatic raffinate oil (205) flowing out of the top of the extraction tower (A2) is directly sent to the convection section of the ethylene cracking furnace (C1) for further preheating without cooling through a heat exchanger, thereby reducing the residence time of the poor aromatic raffinate oil (205) in the ethylene cracking furnace (C1). Optimizing process parameters such as the operating pressure / operating temperature of the extraction tower (A1) and the operating pressure / operating temperature of the solvent stripping tower (B1) can improve the quality of the poor aromatic raffinate oil (205) cracking feedstock, increase the COT of the ethylene cracking furnace, and increase the ethylene yield.

[0062] The cracking furnace in the present invention is a conventional ethylene cracking furnace comprising a convection section, a radiant section, a quench boiler, a high-pressure steam drum, and a burner. Specifically, the cracking furnace can be described in patent document CN201910901193.0 (CN112538366A). The mixed gas containing light olefins is rapidly cooled by the quench boiler to terminate the steam thermal cracking reaction.

[0063] As an example, more preferably, the process parameters are as follows:

[0064] The operating pressure of the extraction tower (A1) is 0.19-0.39 MPaA, and the operating temperature is 90-120° C.; the operating pressure of the extraction tower (A2) is 0.19-0.39 MPaA, and the operating temperature is 90-120° C.; the operating pressure of the solvent stripping tower (B1) is 0.19-0.39 MPaA, and the operating temperature is 140-170° C.; the number of extraction towers connected in series is N=1-6, the solvent is one of sulfolane and N-methylpyrrolidone, and the mass ratio of the solvent to the aromatic oil product is 1.2-1.8.

[0065] The operating temperature of the methane fuel gas (302) side inlet of the convection section of the ethylene cracking furnace (C1) is 25-55°C, and the operating temperature of the outlet is 65-95°C; the operating temperature of the aromatic-poor raffinate oil (205) side inlet of the convection section of the ethylene cracking furnace (C1) is 90-120°C, and the operating temperature of the outlet is 286-316°C.

[0066] The operating temperature at the top of the flue gas side of the convection section of the ethylene cracking furnace (C1) is 94-114°C, the next top is 141-161°C, and the next top is 343-363°C. The residence time in the radiant section of the ethylene cracking furnace (C1) is 0.22-0.28 seconds, and the COT at the furnace outlet is 805-875°C.

[0067] The methane fuel gas (302) and the flue gas of the convection section are heat exchanged through a device with a plate-fin heat exchange mechanism, and the lean aromatic raffinate oil (205) and the flue gas of the convection section are heat exchanged through a device with an external fin coil heat exchange mechanism.

[0068] When the aromatic oil product is atmospheric diesel, the preferred process parameters are: an operating temperature of 94-114°C at the top of the flue gas side of the convection section of the ethylene cracking furnace (C1), 141-161°C at the next top, and 343-363°C at the next top. The residence time in the radiant section of the ethylene cracking furnace (C1) is 0.25-0.27 seconds, and the COT at the furnace outlet is 805-815°C.

[0069] When the aromatic oil product is naphtha, the preferred process parameters are: an operating temperature of 94-114°C at the top end of the flue gas side of the convection section of the ethylene cracking furnace (C1), 141-161°C at the next top end, and 343-363°C at the next top end. The residence time in the radiant section of the ethylene cracking furnace (C1) is 0.22-0.28 seconds, and the COT at the furnace outlet is 835-875°C.

[0070] In the following examples and comparative examples, the ethylene yield was calculated using the method described in Ethylene Process and Technology (Essence Edition) (edited by Wang Songhan, published by China Petrochemical Press in September 2012, pages 93-111).

[0071] Unless otherwise specified in the present invention, the process parameters not described in detail in the embodiments and comparative examples are the process parameters of the prior art, and preferably, the process methods and process conditions in "Ethylene Process and Technology (Essence Edition)" (edited by Wang Songhan, published by China Petrochemical Press in September 2012) can be used as reference.

[0072] Related raw materials:

[0073] Imported Middle Eastern crude oil is delivered to refineries by large transport vessels. The crude oil is distilled and separated through the refinery's atmospheric and vacuum units to produce naphtha and atmospheric diesel. These naphtha and atmospheric diesel are then sent to the oil extraction unit via the raw material tank farm. The properties of typical Middle Eastern high-sulfur intermediate-base light crude oil are as follows:

[0074] Crude oil classification High sulfur intermediate Initial distillation point / ℃ 91 <![CDATA[Density (20 °C) / kg·m -3 > 859.8 Distillation rate (V) / % API 32.35 100℃ 3.11 Freezing point / ℃ -17 150℃ 13.02 Wax content / % 3.48 200℃ 22.64 Residual carbon / % 4.25 250℃ 32.07 Elemental analysis 300℃ 40.99 sulfur / % 2.30 350℃ 48.83 nitrogen / % 0.05 400℃ 58.03 <![CDATA[Nickel / μg·g -1 > 5.40 450℃ 64.79 <![CDATA[Vanadium / μg·g -1 > 18.30 500℃ 72.55

[0075] Domestically produced crude oil is extracted and sent to a refinery. The crude oil is then distilled and separated through the refinery's atmospheric and vacuum units to produce naphtha and atmospheric diesel. These naphtha and atmospheric diesel are then sent to the oil extraction unit via the raw material tank farm. The properties of a typical sulfur-containing paraffinic broad-cut crude oil from the Zhongyuan Oilfield are as follows:

[0076]

[0077]

[0078] Domestically produced crude oil is extracted and sent to a refinery. The crude oil is then distilled and separated through the refinery's atmospheric and vacuum units to produce naphtha and atmospheric diesel. These naphtha and atmospheric diesel are then sent to the oil extraction unit via the raw material tank farm. The properties of a typical wide-cut, low-sulfur paraffinic crude oil from the Daqing Oilfield are as follows:

[0079] Crude oil classification Low sulfur paraffin base Initial distillation point / ℃ 113 <![CDATA[Density (20 °C) / kg·m -3 > 861.7 Distillation rate (V) / % API 32.0 100℃ 0.2 Freezing point / ℃ 33 120℃ 1.3 <![CDATA[H2O content / %]]> 0.01 140℃ 2.5 Wax content / % 26.3 160℃ 3.8 Asphaltene / % 0.0 180℃ 5.6 Gum / % 8.36 200℃ 7.8 Residual carbon / % 3.10 220℃ 10.0 Ash / % 0.012 240℃ 12.6 Elemental analysis 260℃ 15.6 sulfur / % 0.11 280℃ 17.6 nitrogen / % 0.16 300℃ 20.6 <![CDATA[Nickel / μg·g -1 > 3.06 400℃ 30.5 <![CDATA[Vanadium / μg·g -1 > 0.04 500℃ 53.7

[0080] Domestically produced crude oil is extracted and sent to a refinery. The crude oil is then distilled and separated through the refinery's atmospheric and vacuum units to produce naphtha and atmospheric diesel. These naphtha and atmospheric diesel are then sent to the oil extraction unit via the raw material tank farm. The properties of a typical sulfur-containing intermediate base broad-cut crude oil from Shengli Oilfield are as follows:

[0081]

[0082]

[0083] Naphtha is obtained by distillation and separation of crude oil in the above-mentioned vacuum unit. The main properties of typical naphthas such as Middle East naphtha, Zhongyuan naphtha, Daqing naphtha and Shengli naphtha are as follows:

[0084]

[0085] Atmospheric diesel is obtained by distillation and separation of the crude oil through the above-mentioned atmospheric pressure reduction unit. The main properties of typical atmospheric diesel such as Middle East atmospheric diesel, Zhongyuan atmospheric diesel, Daqing atmospheric diesel and Shengli atmospheric diesel are as follows:

[0086]

[0087]

[0088] [Example 1]

[0089] like Figure 1The process flow shown in this embodiment relates to a method for thermally coupling an extraction unit with an ethylene unit. The ethylene unit has a nominal capacity of 115,000 tons / year and uses Middle Eastern naphtha as the cracking feedstock. The process parameters for the oil extraction unit are as follows: 1 extraction column, N = 1; extraction column (A1) operating pressure of 0.19 MPaA, operating temperature of 90°C; solvent stripping column (B1) operating pressure of 0.19 MPaA, operating temperature of 140°C; solvent is sulfolane; and the mass ratio of solvent to aromatic oil is 1.2. The oil then enters the radiation section of the ethylene cracking furnace (C1) for steam thermal cracking of the oil product. The operating temperature of the methane fuel gas (302) side inlet of the ethylene cracking furnace (C1) convection section is 25°C, the operating temperature of the methane fuel gas (302) side outlet is 65°C, the operating temperature of the poor aromatic raffinate oil (205) side inlet is 90°C, the operating temperature of the poor aromatic raffinate oil (205) side outlet is 286°C, the operating temperature of the top end of the flue gas side is 94°C, the operating temperature of the second top end of the flue gas side is 141°C, and the operating temperature of the top end of the flue gas side is 343°C. The cracked gas of basic organic chemical products such as ethylene, propylene, butadiene, benzene, toluene, and xylene is generated. After cracking, a mixed gas containing light olefins is obtained, which is separated by a separation unit to obtain hydrogen (401), methane fuel gas (302), methane (402), ethylene (403), propylene (404), cracked C4 (405), cracked gasoline (406), and cracked heavy oil (407). As a result, the fuel consumption of the ethylene cracking furnace (C1) is 6.63 t / hr, and the total heat load of the ethylene cracking furnace (C1) is 95.82 MW. The fuel consumption of the ethylene cracking furnace (C1) is saved by 60.31 kg / hr, a relative saving of 0.90%. The total heat load of the ethylene cracking furnace (C1) is reduced by 0.87 MW, a relative reduction of 0.91%. The residence time of the radiation section of the ethylene cracking furnace (C1) is 0.28 s, the COT at the furnace outlet is 835°C, the ethylene yield is 30.88 wt%, the ethylene yield is increased by 0.06 wt%, and the ethylene production is increased by 69 t / a, achieving good technical results.

[0090] [Comparative Example 1]

[0091] The extraction unit process parameters were the same as in Example 1, except that there was no thermal coupling between the extraction unit and the ethylene cracking unit. Because the oil extraction unit and the ethylene cracking unit were not thermally coupled, the aromatic-poor raffinate oil exiting the oil extraction unit was cooled from 90°C to 25°C and sent to an intermediate tank farm for storage. From there, it was sent to the convection section of the cracking furnace in the ethylene cracking unit. After being preheated from 25°C to 90°C, it was further preheated to the cracking reaction temperature.

[0092] Therefore, the fuel consumption of the ethylene cracking furnace (C1) is 6.69 t / hr, the total heat load of the ethylene cracking furnace (C1) is 96.69 MW, and the ethylene yield is 30.82 wt%, and the technical effect is not ideal.

[0093] [Example 2]

[0094] Similar to Example 1, this embodiment relates to a method for thermally coupling an extraction unit and an ethylene unit. The nominal scale of the ethylene unit is 300,000 tons / year, the cracking feedstock is Middle Eastern atmospheric diesel, and the process parameters of the extraction unit are as follows: the number of extraction towers is N = 1, the operating pressure of the extraction tower (A1) is 0.23 MPaA, the operating temperature of the extraction tower (A1) is 96°C, the operating pressure of the solvent stripping tower (B1) is 0.23 MPaA, the operating temperature of the solvent stripping tower (B1) is 146°C, the solvent is N-methylpyrrolidone, and the mass ratio of the solvent to the aromatic oil product is 1.3. The operating temperature of the methane fuel gas (302) side inlet of the convection section of the ethylene cracking furnace (C1) is 31°C, the operating temperature of the methane fuel gas (302) side outlet is 71°C, the operating temperature of the poor aromatic raffinate oil (205) side inlet is 96°C, the operating temperature of the poor aromatic raffinate oil (205) side outlet is 292°C, the operating temperature of the uppermost end of the flue gas side is 98°C, the operating temperature of the second uppermost end of the flue gas side is 145°C, and the operating temperature of the uppermost end of the flue gas side is 347°C. As a result, the fuel consumption of the ethylene cracking furnace (C1) is 19.60 t / hr, and the total heat load of the ethylene cracking furnace (C1) is 283.35 MW. The fuel consumption of the ethylene cracking furnace (C1) is saved by 219.53 kg / hr, a relative saving of 1.11%. The total heat load of the ethylene cracking furnace (C1) is reduced by 3.17 MW, a relative reduction of 1.12%. The residence time of the radiation section of the ethylene cracking furnace (C1) is 0.27 s, the COT at the furnace outlet is 805°C, the ethylene yield is 27.18 wt%, the ethylene yield is increased by 0.15 wt%, and the ethylene production is increased by 450 t / a, achieving good technical results.

[0095] [Comparative Example 2]

[0096] The extraction unit process parameters were the same as in Example 2, except that there was no thermal coupling between the extraction unit and the ethylene cracking unit. Because the oil extraction unit and the ethylene cracking unit were not thermally coupled, the aromatic-poor raffinate oil exiting the oil extraction unit was first sent to an intermediate tank farm for storage, and then from there to the convection section of the cracking furnace in the ethylene cracking unit. After preheating, the aromatic-poor raffinate oil was further preheated to the cracking reaction temperature. Consequently, the fuel consumption of the ethylene cracking furnace (C1) was 19.82 t / hr, the total heat load of the ethylene cracking furnace (C1) was 286.53 MW, and the ethylene yield was 27.03 wt%, resulting in unsatisfactory technical results.

[0097] [Example 3]

[0098] Similar to Example 1, this example relates to a method for thermally coupling an extraction unit with an ethylene unit. The ethylene unit has a nominal capacity of 1 million tons / year, and the cracking feedstock is Daqing atmospheric diesel. The extraction unit process parameters are as follows: the number of extraction towers N = 3, the operating pressure of extraction tower (A1) is 0.27 MPaA, and the operating temperature of extraction tower (A1) is 102°C; the operating pressure of solvent stripping tower (B1) is 0.27 MPaA, and the operating temperature of solvent stripping tower (B1) is 152°C; the solvent is sulfolane, and the mass ratio of solvent to aromatic oil is 1.4. The operating temperature of the methane fuel gas (302) side inlet of the convection section of the ethylene cracking furnace (C1) is 37°C, the operating temperature of the methane fuel gas (302) side outlet is 77°C, the operating temperature of the poor aromatic raffinate oil (205) side inlet is 102°C, the operating temperature of the poor aromatic raffinate oil (205) side outlet is 298°C, the operating temperature of the uppermost end of the flue gas side is 102°C, the operating temperature of the second uppermost end of the flue gas side is 149°C, and the operating temperature of the uppermost end of the flue gas side is 351°C. As a result, the fuel consumption of the ethylene cracking furnace (C1) is 64.52 t / hr, and the total heat load of the ethylene cracking furnace (C1) is 932.72 MW. The fuel consumption of the ethylene cracking furnace (C1) is saved by 1045.21 kg / hr, a relative saving of 1.59%. The total heat load of the ethylene cracking furnace (C1) is reduced by 15.11 MW, a relative reduction of 1.62%. The residence time of the radiation section of the ethylene cracking furnace (C1) is 0.26 s, the COT at the furnace outlet is 810°C, the ethylene yield is 27.47 wt%, the ethylene yield is increased by 0.24 wt%, and the ethylene production is increased by 2400 t / a, achieving good technical results.

[0099] [Comparative Example 3]

[0100] The extraction unit process parameters were the same as in Example 3, except that there was no thermal coupling between the extraction unit and the ethylene cracking unit. Because the oil extraction unit and the ethylene cracking unit were not thermally coupled, the aromatic-poor raffinate oil exiting the oil extraction unit was first sent to an intermediate tank farm for storage, and then from there to the convection section of the cracking furnace in the ethylene cracking unit. After preheating, the aromatic-poor raffinate oil was further preheated to the cracking reaction temperature. Consequently, the fuel consumption of the ethylene cracking furnace (C1) was 65.56 t / hr, the total heat load of the ethylene cracking furnace (C1) was 947.83 MW, and the ethylene yield was 27.23 wt%, resulting in unsatisfactory technical results.

[0101] [Example 4]

[0102] Similar to Example 1, this embodiment relates to a method for thermally coupling an extraction unit and an ethylene unit. The nominal scale of the ethylene unit is 1.2 million tons / year, the cracking feedstock is Shengli atmospheric diesel, and the process parameters of the oil extraction unit are as follows: the number of extraction towers is N = 4, the operating pressure of the extraction tower (A1) is 0.31 MPaA, the operating temperature of the extraction tower (A1) is 108°C, the operating pressure of the solvent stripping tower (B1) is 0.31 MPaA, the operating temperature of the solvent stripping tower (B1) is 158°C, the solvent is N-methylpyrrolidone, and the mass ratio of the solvent to the aromatic oil is 1.6. The operating temperature of the methane fuel gas (302) side inlet of the convection section of the ethylene cracking furnace (C1) is 43°C, the operating temperature of the methane fuel gas (302) side outlet is 83°C, the operating temperature of the poor aromatic raffinate oil (205) side inlet is 108°C, the operating temperature of the poor aromatic raffinate oil (205) side outlet is 304°C, the operating temperature of the uppermost end of the flue gas side is 106°C, the operating temperature of the second uppermost end of the flue gas side is 153°C, and the operating temperature of the uppermost end of the flue gas side is 355°C. As a result, the fuel consumption of the ethylene cracking furnace (C1) is 77.10 t / hr, and the total heat load of the ethylene cracking furnace (C1) is 1114.59 MW. The fuel consumption of the ethylene cracking furnace (C1) is saved by 1279.85 kg / hr, a relative saving of 1.63%. The total heat load of the ethylene cracking furnace (C1) is reduced by 18.50 MW, a relative reduction of 1.66%. The residence time of the radiation section of the ethylene cracking furnace (C1) is 0.25 s, the COT at the furnace outlet is 815°C, the ethylene yield is 27.77 wt%, the ethylene yield is increased by 0.33 wt%, and the ethylene production is increased by 3960 t / a, achieving good technical results.

[0103] [Comparative Example 4]

[0104] The extraction unit process parameters were the same as in Example 4, except that there was no thermal coupling between the extraction unit and the ethylene cracking unit. Because the oil extraction unit and the ethylene cracking unit were not thermally coupled, the aromatic-poor raffinate oil exiting the oil extraction unit was first sent to an intermediate tank farm for storage, and then from there to the convection section of the cracking furnace in the ethylene cracking unit. After preheating, the aromatic-poor raffinate oil was further preheated to the cracking reaction temperature. Consequently, the fuel consumption of the ethylene cracking furnace (C1) was 78.38 t / hr, the total heat load of the ethylene cracking furnace (C1) was 1133.09 MW, and the ethylene yield was 27.44 wt%, resulting in unsatisfactory technical results.

[0105] [Example 5]

[0106] Similar to Example 1, this embodiment relates to a method for thermally coupling an extraction device and an ethylene device. The nominal scale of the ethylene device is 1.4 million tons / year, the cracking feedstock is Central Plains naphtha, and the process parameters of the oil extraction device are as follows: the number of extraction towers is N = 5, the operating pressure of the extraction tower (A1) is 0.35 MPaA, the operating temperature of the extraction tower (A1) is 114°C, the operating pressure of the solvent stripping tower (B1) is 0.35 MPaA, the operating temperature of the solvent stripping tower (B1) is 164°C, the solvent is sulfolane, and the mass ratio of the solvent to the aromatic oil is 1.7. The operating temperature of the methane fuel gas (302) side inlet of the convection section of the ethylene cracking furnace (C1) is 49°C, the operating temperature of the methane fuel gas (302) side outlet is 89°C, the operating temperature of the poor aromatic raffinate oil (205) side inlet is 114°C, the operating temperature of the poor aromatic raffinate oil (205) side outlet is 310°C, the operating temperature of the uppermost end of the flue gas side is 110°C, the operating temperature of the second uppermost end of the flue gas side is 157°C, and the operating temperature of the uppermost end of the flue gas side is 359°C. As a result, the fuel consumption of the ethylene cracking furnace (C1) is 78.23 t / hr, and the total heat load of the ethylene cracking furnace (C1) is 1130.95 MW. The fuel consumption of the ethylene cracking furnace (C1) is saved by 1314.28 kg / hr, a relative saving of 1.65%. The total heat load of the ethylene cracking furnace (C1) is reduced by 19.00 MW, a relative reduction of 1.68%. The residence time of the radiation section of the ethylene cracking furnace (C1) is 0.25 s, the COT at the furnace outlet is 860°C, the ethylene yield is 32.05 wt%, the ethylene yield is increased by 0.41 wt%, and the ethylene production is increased by 5740 t / a, achieving good technical results.

[0107] [Comparative Example 5]

[0108] The extraction unit process parameters were the same as in Example 5, except that there was no thermal coupling between the extraction unit and the ethylene cracking unit. Because the oil extraction unit and the ethylene cracking unit were not thermally coupled, the aromatic-poor raffinate oil exiting the oil extraction unit was first sent to an intermediate tank farm for storage before being sent from the intermediate tank farm to the convection section of the cracking furnace in the ethylene cracking unit. After preheating, the aromatic-poor raffinate oil was further preheated to the cracking reaction temperature. Consequently, the fuel consumption of the ethylene cracking furnace (C1) was 79.55 t / hr, the total heat load of the ethylene cracking furnace (C1) was 1149.95 MW, and the ethylene yield was 31.64 wt%, resulting in unsatisfactory technical results.

[0109] [Example 6]

[0110] Similar to Example 1, this embodiment relates to a method for thermally coupling an extraction device and an ethylene device. The nominal scale of the ethylene device is 1.5 million tons / year, the cracking raw material is Daqing naphtha, and the process parameters of the oil extraction device are as follows: the number of extraction towers is N = 5, the operating pressure of the extraction tower (A1) is 0.39 MPaA, the operating temperature of the extraction tower (A1) is 120°C, the operating pressure of the solvent stripping tower (B1) is 0.39 MPaA, the operating temperature of the solvent stripping tower (B1) is 170°C, the solvent is N-methylpyrrolidone, and the mass ratio of the solvent to the aromatic oil is 1.8. The operating temperature of the methane fuel gas (302) side inlet of the convection section of the ethylene cracking furnace (C1) is 55°C, the operating temperature of the methane fuel gas (302) side outlet is 95°C, the operating temperature of the poor aromatic raffinate oil (205) side inlet is 120°C, the operating temperature of the poor aromatic raffinate oil (205) side outlet is 316°C, the operating temperature of the uppermost end of the flue gas side is 114°C, the operating temperature of the second uppermost end of the flue gas side is 161°C, and the operating temperature of the uppermost end of the flue gas side is 363°C. As a result, the fuel consumption of the ethylene cracking furnace (C1) is 83.26 t / hr, and the total heat load of the ethylene cracking furnace (C1) is 1203.68 MW. The fuel consumption of the ethylene cracking furnace (C1) is saved by 1407.13 kg / hr, a relative saving of 1.66%. The total heat load of the ethylene cracking furnace (C1) is reduced by 20.34 MW, a relative reduction of 1.69%. The residence time of the radiation section of the ethylene cracking furnace (C1) is 0.24 s, the COT at the furnace outlet is 865°C, the ethylene yield is 32.35 wt%, the ethylene yield is increased by 0.50 wt%, and the ethylene production is increased by 7,500 t / a, achieving good technical results.

[0111] [Comparative Example 6]

[0112] The extraction unit process parameters were the same as in Example 6, except that there was no thermal coupling between the extraction unit and the ethylene cracking unit. Because the oil extraction unit and the ethylene cracking unit were not thermally coupled, the aromatic-poor raffinate oil exiting the oil extraction unit was first sent to an intermediate tank farm for storage, and then from there to the convection section of the cracking furnace in the ethylene cracking unit. After preheating, the aromatic-poor raffinate oil was further preheated to the cracking reaction temperature. Consequently, the fuel consumption of the ethylene cracking furnace (C1) was 84.67 t / hr, the total heat load of the ethylene cracking furnace (C1) was 1224.03 MW, and the ethylene yield was 31.85 wt%, resulting in unsatisfactory technical results.

[0113] [Example 7]

[0114] Similar to Example 1, this embodiment relates to a method for thermally coupling an extraction device and an ethylene device. The ethylene cracking device has a nominal capacity of 3 million tons / year, and two independent production lines are provided, each with a nominal capacity of 1.5 million tons / year. The cracking feedstock is Shengli naphtha. The process parameters of the oil extraction device are as follows: the number of extraction towers is N = 5, the operating pressure of the extraction tower (A1) is 0.35 MPaA, the operating temperature of the extraction tower (A1) is 114°C, the operating pressure of the solvent stripping tower (B1) is 0.35 MPaA, the operating temperature of the solvent stripping tower (B1) is 164°C, the solvent is sulfolane, and the mass ratio of the solvent to the aromatic oil is 1.7. The operating temperature of the methane fuel gas (302) side inlet of the convection section of the ethylene cracking furnace (C1) is 49°C, the operating temperature of the methane fuel gas (302) side outlet is 89°C, the operating temperature of the poor aromatic raffinate oil (205) side inlet is 114°C, the operating temperature of the poor aromatic raffinate oil (205) side outlet is 310°C, the operating temperature of the uppermost end of the flue gas side is 110°C, the operating temperature of the second uppermost end of the flue gas side is 157°C, and the operating temperature of the uppermost end of the flue gas side is 359°C. As a result, the fuel consumption of the ethylene cracking furnace (C1) is 166.52 t / hr, and the total heat load of the ethylene cracking furnace (C1) is 2407.37 MW. The fuel consumption of the ethylene cracking furnace (C1) is saved by 2814.27 kg / hr, a relative saving of 1.66%. The total heat load of the ethylene cracking furnace (C1) is reduced by 40.68 MW, a relative reduction of 1.69%. The residence time of the radiation section of the ethylene cracking furnace (C1) is 0.23 s, the COT at the furnace outlet is 870°C, the ethylene yield is 32.64 wt%, the ethylene yield is increased by 0.59 wt%, and the ethylene production is increased by 17,700 t / a, achieving good technical results.

[0115] [Comparative Example 7]

[0116] The extraction unit process parameters were the same as in Example 7, except that there was no thermal coupling between the extraction unit and the ethylene cracking unit. Because the oil extraction unit and the ethylene cracking unit were not thermally coupled, the aromatic-poor raffinate oil exiting the oil extraction unit was first sent to an intermediate tank farm for storage, and then from there to the convection section of the cracking furnace in the ethylene cracking unit. After preheating, the aromatic-poor raffinate oil was further preheated to the cracking reaction temperature. Consequently, the fuel consumption of the ethylene cracking furnace (C1) was 169.34 t / hr, the total heat load of the ethylene cracking furnace (C1) was 2448.05 MW, and the ethylene yield was 32.05 wt%, resulting in unsatisfactory technical results.

[0117] [Example 8]

[0118] Similar to Example 1, this embodiment relates to a method for thermally coupling an extraction device and an ethylene device. The nominal scale of the ethylene device is 3.8 million tons / year, and three independent production lines are provided. The nominal scales of each production line are 1 million tons / year, 1.2 million tons / year, and 1.6 million tons / year, respectively. The cracking raw material is Shengli naphtha. The process parameters of the oil extraction device are as follows: the number of extraction towers is N=6, the operating pressure of the extraction tower (A1) is 0.39 MPaA, the operating temperature of the extraction tower (A1) is 120°C, the operating pressure of the solvent stripping tower (B1) is 0.39 MPaA, the operating temperature of the solvent stripping tower (B1) is 170°C, the solvent is N-methylpyrrolidone, and the mass ratio of the solvent to the aromatic oil is 1.8. The operating temperature of the methane fuel gas (302) side inlet of the convection section of the ethylene cracking furnace (C1) is 55°C, the operating temperature of the methane fuel gas (302) side outlet is 95°C, the operating temperature of the poor aromatic raffinate oil (205) side inlet is 120°C, the operating temperature of the poor aromatic raffinate oil (205) side outlet is 316°C, the operating temperature of the uppermost end of the flue gas side is 114°C, the operating temperature of the second uppermost end of the flue gas side is 161°C, and the operating temperature of the uppermost end of the flue gas side is 363°C. As a result, the fuel consumption of the ethylene cracking furnace (C1) is 213.06 t / hr, and the total heat load of the ethylene cracking furnace (C1) is 3080.17 MW. The fuel consumption of the ethylene cracking furnace (C1) is saved by 3558.18 kg / hr, a relative saving of 1.64%. The total heat load of the ethylene cracking furnace (C1) is reduced by 51.44 MW, a relative reduction of 1.67%. The residence time of the radiation section of the ethylene cracking furnace (C1) is 0.22 s, the COT at the furnace outlet is 875°C, the ethylene yield is 32.94 wt%, the ethylene yield is increased by 0.68 wt%, and the ethylene production is increased by 25,840 t / a, achieving good technical results.

[0119] [Comparative Example 8]

[0120] The extraction unit process parameters were the same as in Example 8, except that there was no thermal coupling between the extraction unit and the ethylene cracking unit. Because the oil extraction unit and the ethylene cracking unit were not thermally coupled, the aromatic-poor raffinate oil exiting the oil extraction unit was first sent to an intermediate tank farm for storage, and then from there to the convection section of the cracking furnace in the ethylene cracking unit. After preheating, the aromatic-poor raffinate oil was further preheated to the cracking reaction temperature. Consequently, the fuel consumption of the ethylene cracking furnace (C1) was 216.62 t / hr, the total heat load of the ethylene cracking furnace (C1) was 3131.61 MW, and the ethylene yield was 32.26 wt%, resulting in unsatisfactory technical results.

[0121] In summary, the present invention uses the raffinate naphtha and raffinate normal pressure diesel obtained by extraction and separation of the oil product extraction device as high-quality cracking raw materials and feeds them into the cracking furnace of the ethylene cracking device with a production scale of 115,000 to 3.8 million tons / year for steam thermal cracking reaction. The synergistic effect of the thermal coupling between the oil product extraction device and the ethylene cracking device is fully utilized, and the 90-120°C poor aromatic raffinate oil (205) flowing out of the top of the extraction tower (A2) is directly fed into the convection section of the ethylene cracking furnace (C1) for preheating treatment. Accordingly, the excess heat on the flue gas side of the convection section is used to heat the methane fuel gas (302) produced by the separation unit (C6) of the ethylene cracking device to 65-95°C. Preferably, the residence time of the cracking raw materials in the radiation section, the outlet temperature of the cracking furnace, the convection section flue gas of the cracking furnace, and the temperature of the cracking furnace are optimized. The uppermost operating temperature, the second-upper operating temperature and the third-upper operating temperature are adjusted to reduce the fuel consumption of the ethylene cracking furnace (C1) by 60.31 to 3558.18 kg / hr, a relative saving of 0.90 to 1.66%, and the heat load of the ethylene cracking furnace (C1) is reduced by 0.87 to 51.44 MW, a relative reduction of 0.91 to 1.69%. At the same time, the ethylene yield is increased by 0.06 to 0.68 wt%, and the ethylene production is increased by 69 to 25,840 t / a, achieving good technical results.

[0122] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation of the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for producing light olefins by steam cracking, comprising: Aromatic oil products are extracted and separated to obtain aromatic-poor raffinate oil, which is used as a cracking feedstock and then preheated in the convection section of a cracking furnace before being transported to the radiation section of the cracking furnace for cracking to obtain a mixed gas containing light olefins; the mixed gas is separated to obtain cracking products, wherein all or part of the obtained methane is preheated on the flue gas side of the convection section of the cracking furnace before being transported to the cracking furnace as fuel.

2. The method according to claim 1, wherein: The residence time of the cracking raw material in the radiation section is 0.22 to 0.28 seconds, and the cracking furnace outlet temperature is 805 to 875°C; and / or, The operating temperature of the top end of the convection section of the cracking furnace on the flue gas side is 94-114°C, the operating temperature of the next top end is 141-161°C, and the operating temperature of the next top end is 343-363°C; and / or, The aromatic oil product is naphtha and / or normal pressure diesel; Preferably, when the aromatic oil product is atmospheric pressure diesel, the preferred process parameters are: the operating temperature of the uppermost end of the flue gas side of the convection section of the ethylene cracking furnace is 94-114°C, the operating temperature of the second upper end is 141-161°C, and the operating temperature of the uppermost end is 343-363°C; the residence time of the radiation section of the ethylene cracking furnace is 0.25-0.27s, and the furnace outlet temperature is 805-815°C; or, Preferably, when the aromatic oil product is naphtha, the preferred process parameters are: an operating temperature of 94-114°C at the top end of the flue gas side of the convection section of the ethylene cracking furnace, 141-161°C at the next top end, and 343-363°C at the next top end. The residence time in the radiant section of the ethylene cracking furnace is 0.22-0.28 seconds, and the furnace outlet temperature is 835-875°C.

3. The method according to claim 2, wherein: The methane fuel gas has an inlet operating temperature of 25-55° C. and an outlet operating temperature of 65-95° C. on the flue gas side of the convection section of the cracking furnace; and / or The inlet operating temperature of the aromatic-poor raffinate oil at the convection section of the cracking furnace is 90-120° C., and the outlet operating temperature is 286-316° C.

4. The method according to claim 1, wherein: The aromatic oil product is extracted through N extraction towers connected in series to obtain an aromatic-poor raffinate and an aromatic-rich solvent; preferably, the aromatic oil product and the extraction solvent flow in countercurrent in the N extraction towers connected in series; and / or, the aromatic-rich solvent is stripped through a stripping tower to obtain an aromatic-poor solvent which is recycled back to the extraction tower as an extraction solvent; preferably, The operating pressure of each extraction tower is 0.19-0.39 MPaA, and / or the operating temperature is 90-120°C; and / or the operating pressure of the stripping tower is 0.19-0.39 MPaA, and / or the operating temperature is 140-170°C; and / or the number of extraction towers connected in series is N=1-6, where N is an integer; and / or, The extraction solvent is one of sulfolane and N-methylpyrrolidone; and / or, The mass ratio of the extraction solvent to the aromatic oil product is 1.2 to 1.

8.

5. The method according to any one of claims 1 to 4, characterized in that: The mixed gas containing light olefins includes ethylene, propylene, butadiene, benzene, toluene, xylene, and methane; and / or, During the process of feeding methane as fuel into the cracking furnace, the flow rate and / or pressure of methane in the pipeline is detected and adjusted, preferably the methane pressure is overridden; and / or, The mixed gas containing light olefins is rapidly cooled and the steam thermal cracking reaction is terminated, and then separated. The separation steps include: first entering a quenching oil tower for cooling and distillation separation, and then the top material enters a quenching water tower for cooling and water washing separation. The obtained top material enters a compression unit and a separation unit in sequence for separation treatment. At least part of the methane flowing out of the separation unit is sent to a cracking furnace as fuel. The separation unit obtains hydrogen, ethylene, propylene, and cracked carbon four and sends them out of the boundary.

6. A system for producing light olefins by steam cracking, preferably used in the method according to any one of claims 1 to 5, the system comprising an aromatics extraction unit, a light olefin cracking furnace, and a cracking gas separation unit connected in sequence; the cracking furnace comprising, from top to bottom, a convection section and a radiant section; in, The aromatic-poor raffinate oil obtained from the aromatics extraction unit enters the radiant section of the cracking furnace through a feed pipeline for cracking, and part of the feed pipeline of the aromatic-poor raffinate oil is arranged in the convection section of the cracking furnace; All or part of the methane obtained by the cracking gas separation unit is connected to the fuel feed port of the cracking furnace through a fuel feed pipeline, and part of the fuel feed pipeline is arranged on the flue gas side of the convection section of the cracking furnace.

7. The system according to claim 6, characterized in that: The feed pipeline of the aromatic-poor raffinate oil is directly connected to the convection section of the cracking furnace without a cooling unit; and / or The outer side of the feed pipeline of the aromatic-poor raffinate oil is provided with a thermal insulation layer; and / or, In the convection section of the cracking furnace, a heat exchange mechanism containing external finned coils is provided at the location where the feed pipeline of the aromatic-poor raffinate oil is arranged for preheating.

8. The system according to claim 6, characterized in that: On the flue gas side of the convection section of the cracking furnace, a plate-fin heat exchange junction is provided at the location where the fuel feed pipeline is arranged for preheating; and / or, The fuel feed pipeline is provided with a flow detector and a flow regulator, a pressure detector and an override control valve; preferably, the override control valve divides the methane fuel gas from the separation subunit into two branches, one of which is connected to the fuel feed port of the cracking furnace.

9. The system according to any one of claims 6 to 8, characterized in that: The aromatics extraction device includes a stripping tower and N extraction towers connected in series; wherein each extraction tower is provided with a bottom feed port, a top feed port, a top discharge port and a bottom discharge port, wherein, according to the logistics direction, the aromatic oil raw material source is connected to the bottom feed port of the first extraction tower; the top discharge port of the previous extraction tower is connected to the bottom feed port of the next extraction tower; the top feed port of the previous extraction tower is connected to the bottom discharge port of the next extraction tower; the bottom discharge port of the first extraction tower is connected to the feed port of the stripping tower, and the bottom discharge port of the stripping tower is connected to the top feed port of the last extraction tower; the top discharge port of the last extraction tower is connected to the aromatic-poor raffinate oil feed pipeline; preferably, N is an integer of 1-6.

10. The system according to any one of claims 6 to 8, characterized in that: The cracking gas separation unit includes a quenching subunit, a compression subunit, and a separation subunit connected in sequence; preferably, the quenching subunit includes a quenching oil tower and a quenching water tower connected in sequence; More preferably, the top discharge port of the quenching oil tower is connected to the feed port of the quenching water tower, and the top discharge port of the quenching water tower is connected to the feed port of the compression unit; and / or, the bottom discharge port of the quenching oil tower and the bottom discharge port of the quenching water tower are each connected to the outside through a pipeline.

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