Method and system for preparing needle coke, and needle coke prepared by the method

Abstract

The present invention relates to the technical field of hydrocarbon oil processing, and in particular to a method and system for preparing needle coke, and a needle coke prepared by the method. The method comprises the following steps: (1) distilling a mixed diesel fraction to obtain a heavy fraction with a distillation range of 235-400°C; (2) optionally, subjecting the heavy fraction and an extractant to solvent extraction, and separating the obtained extracted heavy oil phase through a first solvent to obtain a heavy fraction rich in ideal components; (3) subjecting the heavy fraction or the heavy fraction rich in ideal components to high-pressure delayed coking as a coking raw material to obtain needle coke; the mixed diesel fraction contains a diesel fraction I extracted online from a catalytic cracking unit and a diesel fraction II from a tank farm; the conditions for the high-pressure delayed coking include: the top pressure of the coke tower is 1-3MPa(A). The method realizes a raw material route for producing needle coke from a catalytic diesel fraction by precisely controlling the ideal components in the mixed diesel fraction.

Description

Technical Field

[0001] The invention relates to the technical field of hydrocarbon oil processing, and in particular to a method and system for preparing needle coke, and needle coke prepared by the method. Background Art

[0002] The raw material for needle coke production is mainly the slurry oil from the catalytic cracking series of devices. As a byproduct of catalytic cracking, the annual output of slurry oil is estimated to be about 7.5 million tons according to the current catalytic cracking series process technology. Without considering the use of other products such as road asphalt, ship fuel and other blending components, the crude slurry oil is used to produce needle coke. According to the existing technology, only two-thirds of the crude slurry oil can be used as the raw material for needle coke, which is less than 5 million tons. At a needle coke (green coke) yield of 40%, the maximum production capacity is less than 2 million tons of needle coke (green coke). It can be seen that one of the outstanding problems facing my country's needle coke industry is the shortage of raw materials.

[0003] In recent years, with the development of domestic electric furnace steelmaking, electric vehicles and lithium battery industries, needle coke products and related projects have attracted the attention of market players, and a number of needle coke production facilities and enterprises have been built. At present, the production capacity of needle coke (green coke, coal-containing) facilities in my country has reached more than 1.5 million tons / year, but the actual annual output is about 500,000 tons, and some enterprises are planning, designing or building needle coke projects.

[0004] As we all know, high-quality needle coke products require special process conditions and preferred raw materials, and the corresponding process technology and raw material pretreatment technology are indispensable. Although the basic principle of needle coke production is well known, most of the needle coke produced has problems such as uneven quality and poor stability, low strength and high powder coke content, and parameters such as thermal expansion coefficient and true density are not ideal enough, which makes it difficult to reach the quality level of imported products. The reason may be that some process details, the understanding of ideal components in raw materials and the removal of non-ideal components are still rough and insufficient. As far as raw material pretreatment is concerned, everyone knows that sulfur, nitrogen, ash, colloid and asphaltene in crude oil slurry are harmful impurities, and the oil slurry is required to have a certain aromatic content and density, forming a clear limit index, that is, the sulfur content of needle coke raw material is required to be less than 0.5wt%, the nitrogen content is less than 0.4wt%, the ash is less than 100ppm, the colloid is less than 5wt%, the asphaltene is less than 1wt%, and the density is greater than 1030kg / m at 20℃. 3 , the aromatic content is greater than 45wt%. However, based on experimental research, there is a lack of in-depth analysis and quantitative description or correlation of the raw material components and the corresponding process conditions and product quality indicators. For example, which are the ideal components and which are non-ideal components in the raw materials, at what level the corresponding concentrations need to be controlled, how to constrain and control them, etc.

[0005] CN107987875A discloses a method and apparatus for preparing needle coke raw materials, comprising: subjecting a mixed raw material containing catalytic cracking oil slurry and coking raw materials to cracking reaction; fractionating the generated oil-gas mixture to obtain a wax oil component; further separating the wax oil component into a wax oil light component rich in one-ring and two-ring aromatic hydrocarbons and a wax oil heavy component rich in three-ring and four-ring aromatic hydrocarbons; further subjecting the wax oil light component to condensation reaction to obtain a liquid phase component rich in three-ring and four-ring aromatic hydrocarbons. However, this method has the following problems: the catalytic cracking oil slurry is subjected to a cracking reaction with a conventional After the coking raw materials are mixed, they are heated to 490-515°C and cracked in the coke tower. The three-ring and four-ring aromatic hydrocarbons originally contained in the oil slurry also undergo partial condensation reaction under this condition to form ordinary petroleum coke or coke precursors, resulting in a decrease in the content of three-ring and four-ring aromatic hydrocarbons in the oil-gas mixed product; in addition, the coking wax oil generated by the cracking reaction of ordinary atmospheric residue oil, vacuum residue oil and other coking raw materials under the above conditions has a lower content of three-ring and four-ring aromatic hydrocarbons than that in the oil slurry. Therefore, the wax oil fractionated from the oil-gas mixed product generated by the cracking reaction of the mixed raw materials, and the wax oil heavy component obtained by further separation, in which the content of three-ring and four-ring aromatic hydrocarbons should be significantly reduced compared with the same fraction of the oil slurry, and at a lower level. Therefore, it is difficult to improve the quality of needle coke by producing needle coke with such wax oil heavy component raw materials, and correspondingly, it is impossible to achieve the purpose of increasing the raw materials of needle coke.

[0006] CN110283612A discloses a method for producing oil-based needle coke, wherein the catalytic oil slurry is sequentially passed through an oil slurry filtering unit, a vacuum distillation device, an aromatic oil hydrogenation unit, a vacuum cutting unit, a furfural extraction unit, a coking unit, and a calcination unit to obtain needle coke. Although the method proposes a relatively complete catalytic oil slurry treatment process unit, the treatment process is not sophisticated enough, and the control of the ideal components of the high-quality needle coke raw material is not accurate enough.

[0007] CN106147835A discloses a combined method for separating catalytic cracking oil slurry and preparing oil-based needle coke. The method adopts C 3 -C 5 The light hydrocarbon fraction is used as the extraction solvent to perform subcritical or supercritical extraction on the catalytic cracking oil slurry, and the obtained extracted oil phase is subjected to supercritical recovery solvent to prepare extraction components, which are used as the raw materials for preparing mesophase asphalt, and the mesophase asphalt is prepared by thermal polycondensation reaction, and then the mesophase asphalt is subjected to delayed coking reaction to prepare high-quality oil-based needle coke; when the sulfur content of the catalytic cracking oil slurry is high, the extracted light components can be first subjected to hydrodesulfurization treatment, and the hydrogenated oil can be fractionated to collect the hydrogenated tail oil, and the hydrogenated tail oil can be used as the raw material for preparing mesophase asphalt, and then the needle coke can be prepared. However, due to the C 3 -C 5The solvent has low selectivity for slurry oil extraction treatment, and the control over the ideal components of high-quality needle coke raw materials is not precise enough. It is difficult to generate high-quality mesophase asphalt and obtain high-quality needle coke products using such light components.

[0008] Therefore, a new method for preparing needle coke is urgently needed. Summary of the invention

[0009] The purpose of the present invention is to overcome the problems existing in the existing needle coke preparation method, such as insufficient raw materials, imprecise control of ideal components of needle coke raw materials, complicated process flow, and low quality of the obtained needle coke, and to provide a method and device for preparing needle coke raw materials, and a needle coke prepared by the method. The method uses a mixed diesel fraction as a raw material and combines the technical means of distillation, optional solvent extraction and high-pressure delayed coking to achieve precise control of the ideal components in the needle coke raw materials, thereby improving the product quality of the needle coke; at the same time, the method also expands the source of needle coke raw materials.

[0010] In order to achieve the above object, the first aspect of the present invention provides a method for preparing needle coke, the method comprising the following steps:

[0011] (1) distilling the mixed diesel fraction to obtain a heavy fraction with a distillation range of 235-400° C.;

[0012] (2) Optionally, the heavy fraction and the extractant are subjected to solvent extraction, and the obtained extracted heavy oil phase is separated by a first solvent to obtain a heavy fraction rich in the desired component;

[0013] (3) using the heavy fraction or the heavy fraction rich in the desired component as a coking feedstock to perform high pressure delayed coking to obtain needle coke;

[0014] The mixed diesel fraction contains diesel fraction I extracted online from the catalytic cracking unit and diesel fraction II from the tank farm;

[0015] Wherein, the conditions of the high-pressure delayed coking include: the top pressure of the coke tower is 1-3 MPa (A).

[0016] The second aspect of the present invention provides needle coke produced by the method provided by the first aspect.

[0017] A third aspect of the present invention provides a system for preparing needle coke, comprising a catalytic cracking unit, a mixing unit, a distillation unit, an optional solvent extraction unit and a high-pressure delayed coking unit connected in sequence;

[0018] Wherein, the catalytic cracking unit is used to extract diesel fraction I online;

[0019] The mixing device is used to mix the diesel fraction I with the diesel fraction II from the tank area to obtain a mixed diesel fraction;

[0020] The distillation device is used to distill the mixed diesel fraction to obtain a heavy fraction with a distillation range of 235-400° C.

[0021] The solvent extraction device is used to perform solvent extraction on the heavy fraction and the extractant, and the obtained extracted heavy oil phase is separated by a first solvent to obtain a heavy fraction rich in desired components;

[0022] The high-pressure delayed coking unit is used to carry out high-pressure delayed coking using the heavy fraction or the heavy fraction rich in ideal components as a coking raw material to obtain needle coke.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The method provided by the present invention uses a mixed diesel fraction as a raw material, and in particular, by adjusting the weight ratio of diesel fraction I and diesel fraction II in the mixed diesel fraction, the source of needle coke raw materials is expanded;

[0025] (2) The method provided by the present invention uses a mixed diesel fraction containing diesel fraction I extracted online from a catalytic cracking unit and diesel fraction II from a tank farm as a raw material, and combines distillation, optional solvent extraction and high-pressure delayed coking techniques to achieve a raw material route for producing needle coke from catalytic diesel fractions by precisely controlling the ideal components in the mixed diesel fractions; in particular, by combining hydrodesulfurization and solvent extraction, the ideal components in the heavy fraction are further purified, which is more conducive to improving the performance parameters of needle coke produced from catalytic diesel;

[0026] (3) The method provided by the present invention simplifies the process flow and is convenient for industrial large-scale production; in particular, the non-ideal components (i.e., light fractions and heavy fractions rich in non-ideal components) are returned and subjected to catalytic cracking reactions, thereby increasing the raw material amount of needle coke. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of a system for preparing needle coke provided by the present invention.

[0028] Description of Reference Numerals

[0029] 1. Diesel fraction I 2. Diesel fraction II 3. Mixed diesel fraction

[0030] 4. Heavy fraction 5. Top oil and gas 6. Light fraction

[0031] 7. Extraction agent 8. Heavy fraction rich in desirable components

[0032] 9. Heavy fractions rich in non-ideal components 10. Hydrodesulfurization products

[0033] 11. Needle coke 12. Oil and gas

[0034] I. Catalytic cracking unit I-1, reactor I-2, fractionation tower

[0035] II, mixing device III, distillation device IV, high pressure delayed coking unit

[0036] IV-1, Heating furnace IV-2, Coke tower V, Condensation device

[0037] VI. Solvent extraction unit VII. Hydrodesulfurization unit

[0038] S1, valve-1 S2, valve-2 S3, valve-3

[0039] S4, valve-4 S5, valve-5 S6, valve-6

[0040] S7, valve-7 S7', valve-7' DETAILED DESCRIPTION

[0041] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0042] In the present invention, unless otherwise specified, "first" and "second" do not indicate a sequence or limit the materials or steps, but are only used to distinguish that they are not the same materials or steps. For example, "first" and "second" in "first reaction" and "second reaction" are only used to indicate that they are not the same reaction.

[0043] A first aspect of the present invention provides a method for preparing needle coke, the method comprising the following steps:

[0044] (1) distilling the mixed diesel fraction to obtain a heavy fraction with a distillation range of 235-400° C.;

[0045] (2) Optionally, the heavy fraction and the extractant are subjected to solvent extraction, and the obtained extracted heavy oil phase is separated by a first solvent to obtain a heavy fraction rich in the desired component;

[0046] (3) using the heavy fraction or the heavy fraction rich in the desired component as a coking feedstock to perform high pressure delayed coking to obtain needle coke;

[0047] The mixed diesel fraction contains diesel fraction I extracted online from the catalytic cracking unit and diesel fraction II from the tank farm;

[0048] Wherein, the conditions of the high-pressure delayed coking include: the top pressure of the coke tower is 1-3 MPa (A).

[0049] In the present invention, unless otherwise specified, (A) represents absolute pressure; (G) represents gauge pressure; the difference between absolute pressure (A) and gauge pressure (G) is 0.1 MPa, for example, 1-3 MPa (A) is equivalent to 0.9-2.9 MPa (G).

[0050] The inventors of the present invention have found that compared with the conventional use of catalytic oil slurry as a needle coke raw material, the distillation range of the catalytic diesel fraction (165-400°C) is generally very light; and the output of the catalytic diesel fraction in a set of catalytic cracking units accounts for only 10-25% of the raw material or the scale of the device. For an industrial-scale needle coke device, if the heavy fraction of the catalytic diesel fraction is used as a raw material, the scale of the upstream series catalytic cracking units generally does not match the scale of the existing needle coke device. In other words, the amount of fresh catalytic diesel fraction continuously produced by the upstream series catalytic cracking units is relatively small, and the heavy fraction is even less, which cannot meet the production capacity requirements of an existing set of process devices, and an additional part of the catalytic diesel fraction needs to be purchased. This part of the catalytic diesel fraction from other tank farms or other enterprises may be oxidized due to long-distance transportation by various means of transportation and various long-term storage, and the content of colloid and asphalt increases, and the quality is worse than that of fresh catalytic diesel fraction. Therefore, the present invention uses a mixed diesel fraction of a diesel fraction I extracted online from a catalytic cracking unit and a diesel fraction II from a tank area in a specific weight ratio as a needle coke raw material, and combines specific technical means to solve the problem that the prior art cannot use catalytic diesel fractions to produce needle coke, thereby expanding the source of needle coke raw materials; in particular, the heavy fraction is subjected to solvent extraction with a specific extractant, thereby further improving the quality parameters of the needle coke; at the same time, non-ideal components (light fractions and heavy fractions rich in non-ideal components) are recycled (i.e., the first reaction and the second reaction), thereby increasing the amount of needle coke raw material used, and further solving the problem of insufficient needle coke raw material.

[0051] In some embodiments of the present invention, preferably, in step (1), the weight ratio of diesel fraction I to diesel fraction II in the mixed diesel fraction is 99-1:1-99, preferably 80-20:20-80, to meet the material ratio of industrial reality.

[0052] In a preferred embodiment of the present invention, the mixed diesel fraction is composed of a diesel fraction I extracted online from a catalytic cracking unit and a diesel fraction II from a tank farm, wherein, relative to 100 parts by weight of the mixed diesel fraction, the amount of the diesel fraction I is 1-99 parts by weight, preferably 20-80 parts by weight, and the amount of the diesel fraction II is 99-1 parts by weight, preferably 80-20 parts by weight.

[0053] In the present invention, the physical property parameters of the mixed diesel fraction are common performance indicators. Preferably, the physical property parameters of the mixed diesel fraction meet the following requirements: sulfur content is 0.3-1wt%; density is 0.86-1.03g / cm 3 ; The colloid content is 0.1-3wt%, the asphaltene content is 0.01-0.3wt%; the saturated hydrocarbon content is 25-65wt%; the aromatic hydrocarbon content is 35-75wt%; and the aromatic carbon number CA value is 25-55%.

[0054] In the present invention, unless otherwise specified, the diesel fraction I extracted online from the catalytic cracking unit is used as the fresh catalytic diesel fraction, that is, the diesel fraction I continuously produced by the catalytic cracking unit is directly supplied to the distillation device of the present invention through a pipeline without buffering or storage in a tank area.

[0055] In some embodiments of the present invention, preferably, based on the total weight of the diesel fraction I, the colloid content in the diesel fraction I is less than 0.1 wt%, and the asphaltene content in the diesel fraction I is less than 0.01 wt%.

[0056] In the present invention, unless otherwise specified, the diesel fraction II from the tank area is used as the aged catalytic diesel fraction, that is, the diesel fraction may come from the upstream catalytic cracking unit, but due to being buffered or stored in the tank area and exposed to more air, water, etc., aromatic hydrocarbons dissolve more oxygen than saturated hydrocarbons and are more easily combined with oxygen to be oxidized, thereby resulting in an increase in the content of gum and asphaltene; it may also be the diesel fraction from other catalytic devices or other tank areas other than the upstream catalytic cracking unit, which is oxidized during long-distance transportation or long-term storage, and the oxygen content increases, thereby resulting in an increase in the content of gum and asphaltene in the diesel fraction II; it also affects the quality of the needle coke product.

[0057] In the present invention, the content of gum and asphaltene in the diesel fraction II is higher than that in the diesel fraction I. Preferably, based on the total weight of the diesel II, the content of gum in the diesel fraction II is 0.1-5wt%, and the content of asphaltene is 0.01-0.5wt%.

[0058] In some embodiments of the present invention, preferably, the physical properties of the diesel fraction I and the diesel fraction II independently satisfy the following: density at 20°C is 0.86-1.03 g / cm 3; Ash content ≤0.1wt%; Sulfur content ≤1.0wt%; Nitrogen content ≤0.3wt%; Saturated hydrocarbon content is 15-75wt%; Aromatic hydrocarbon content is 25-85wt%; Aromatic carbon number CA value is 25-55%; Distillation range is 150-400℃.

[0059] In the present invention, the sources of the diesel fraction I and the diesel fraction II have a wide selection range, as long as the above physical property parameters are met. Preferably, the diesel fraction I and the diesel fraction II are each independently selected from at least one of catalytic light cycle oil (abbreviated as LCO), catalytic heavy cycle oil (abbreviated as HCO) and catalytic middle distillate oil.

[0060] In the present invention, the distillation is intended to cut the light fraction and the heavy fraction in the mixed diesel fraction according to the boiling point, thereby removing the non-ideal components in the mixed diesel fraction, i.e., the light fraction. Preferably, in step (1), the distillation conditions include: the tower top pressure is 2-600 kPa (A), for example, 2 kPa (A), 10 kPa (A), 50 kPa (A), 100 kPa (A), 150 kPa (A), 200 kPa (A), 300 kPa (A), 400 kPa (A), 500 kPa (A), 600 kPa (A), and any value in the range of any two values, preferably 10-200 kPa (A).

[0061] In some embodiments of the present invention, preferably, the physical property parameters of the heavy fraction meet the following requirements: density ≥ 0.9 g / cm at 20°C 3 , preferably ≥0.93g / cm 3 ; Aromatic content is 40-80wt%; Aromatic carbon number CA value is 30-60%. Adopting the optimal conditions is more conducive to improving the product quality of needle coke.

[0062] According to the present invention, preferably, the overhead oil gas obtained by the distillation is condensed to obtain a light fraction.

[0063] In the present invention, the light fraction is used as a non-ideal component of the needle coke raw material. The light fraction is returned to the catalytic cracking unit for the first reaction, thereby increasing the raw material amount of needle coke and further solving the problem of insufficient raw material of needle coke.

[0064] In the present invention, unless otherwise specified, the process of the first reaction includes: subjecting the light fraction and the acidic molecular sieve catalyst to a first reaction (i.e., cracking, condensation), and obtaining the diesel fraction I after fractionation of the obtained first reaction product; wherein the temperature of the first reaction is 500-700°C, and the time is 1-10s. In the present invention, the acidic molecular sieve catalyst includes but is not limited to a Y-shaped molecular sieve catalyst and a shape-selective molecular sieve catalyst.

[0065] In the present invention, the solvent extraction is intended to further remove non-ideal components in the heavy fraction to obtain a concentrated heavy fraction rich in ideal components. Preferably, in step (2), the weight ratio of the heavy fraction to the extractant is 1:1-5, for example, 1:1, 1:2, 1:2.5, 1:3, 1:3.5, 1:5, and any value in the range of any two values, preferably 1:2-3.5. The preferred weight ratio is used to further concentrate the ideal components in the heavy fraction, that is, to obtain a high-concentration heavy fraction rich in ideal components.

[0066] In the present invention, the extractant can further purify and concentrate the desired components in the heavy fraction. Preferably, the extractant is selected from organic hydrocarbons and optional water, wherein the organic hydrocarbon is selected from at least one of furfural, tetrahydrofuran, 2-butanone and n-heptane, preferably selected from furfural and / or n-heptane.

[0067] In some embodiments of the present invention, preferably, the extractant contains furfural, n-heptane and water, wherein the weight ratio of furfural, n-heptane and water is 40-99:1-50:0-10, preferably 50-69:30-45:1-5.

[0068] In some embodiments of the present invention, the physical property parameters of the heavy fraction rich in the desired component meet the following requirements: density ≥ 0.93 g / cm at 20°C. 3 , preferably ≥0.96g / cm 3 ; Aromatic hydrocarbon content is 45-85wt%; aromatic carbon number CA value is 35-65%.

[0069] According to the present invention, preferably, the extracted light oil phase obtained by the solvent extraction is separated by a second solvent to obtain a heavy fraction rich in non-ideal components; further preferably, the heavy fraction rich in non-ideal components is returned to the reactor in the catalytic cracking unit for a second reaction. This arrangement further solves the problem of insufficient needle coke raw materials and increases the amount of needle coke raw materials.

[0070] In the present invention, unless otherwise specified, the process of the second reaction includes: subjecting the heavy fraction rich in non-ideal components to a second reaction (i.e., cracking, condensation) with an acidic molecular sieve catalyst, and obtaining the diesel fraction I after fractionation of the obtained second reaction product; wherein the temperature of the second reaction is 500-700°C, and the time is 1-10s. In the present invention, the acidic molecular sieve catalyst includes but is not limited to a Y-shaped molecular sieve catalyst and a shape-selective molecular sieve catalyst.

[0071] In some embodiments of the present invention, preferably, in step (3), the conditions of the high-pressure delayed coking include: the top pressure of the coke drum is 1.6-2.6 MPa (A); the operation cycle of the coke drum is 16-72 hours, preferably 24-60 hours; the outlet temperature of the heating furnace is 430-600° C., preferably 430-560° C. The use of the preferred conditions is more conducive to improving the product quality of needle coke.

[0072] According to the present invention, preferably, the method further comprises: when the sulfur content in the mixed diesel fraction is ≥0.5wt%, before the heavy fraction is subjected to the solvent extraction or the high-pressure delayed coking, hydrodesulfurizing the heavy fraction.

[0073] In a specific embodiment of the present invention, when the sulfur content in the mixed diesel fraction is ≥0.5wt%, the heavy fraction is first subjected to hydrodesulfurization and then subjected to the high-pressure delayed coking to obtain needle coke.

[0074] In another specific embodiment of the present invention, when the sulfur content in the mixed diesel fraction is ≥0.5wt%, the heavy fraction is first subjected to hydrodesulfurization, and then subjected to solvent extraction and high-pressure delayed coking in sequence to obtain needle coke.

[0075] In some embodiments of the present invention, preferably, the conditions for hydrodesulfurization include: a reaction temperature of 260-400°C, preferably 260-360°C; and a pressure of 3-6 MPa(G), preferably 3-5 MPa(G).

[0076] The second aspect of the present invention provides needle coke produced by the method provided in the first aspect.

[0077] The needle coke prepared by the method provided by the present invention has a higher true density and a lower thermal expansion coefficient. Preferably, the true density of the needle coke is 2.1-2.2 g / cm 3 , preferably 2.12-2.16 g / cm 3 ;The thermal expansion coefficient is (1-1.6)×10 -6 ℃ -1 , preferably (1-1.4)×10 -6 ℃ -1 .

[0078] In the present invention, unless otherwise specified, the true density parameter is measured using GB / T 24533-2019 or GB / T32158-2015; the thermal expansion coefficient is measured using GB / T 3074.4-2016.

[0079] A third aspect of the present invention provides a system for preparing needle coke, the system comprising: a catalytic cracking unit, a mixing device, a distillation device, an optional solvent extraction device and a high-pressure delayed coking unit connected in sequence;

[0080] Wherein, the catalytic cracking unit is used to extract diesel fraction I online;

[0081] The mixing device is used to mix the diesel fraction I with the diesel fraction II from the tank area to obtain a mixed diesel fraction;

[0082] The distillation device is used to distill the mixed diesel fraction to obtain a heavy fraction with a distillation range of 235-400° C.

[0083] The solvent extraction device is used to perform solvent extraction on the heavy fraction and the extractant, and the obtained extracted heavy oil phase is separated by a first solvent to obtain a heavy fraction rich in desired components;

[0084] The high-pressure delayed coking unit is used to carry out high-pressure delayed coking using the heavy fraction or the heavy fraction rich in ideal components as a coking raw material to obtain needle coke.

[0085] The present invention provides a coefficient schematic diagram for preparing needle coke, such as Figure 1 As shown, the system comprises: a catalytic cracking unit I, a mixing device II, a distillation device III, an optional solvent extraction device VI and a high-pressure delayed coking device IV which are connected in sequence; wherein the catalytic cracking unit I is used to extract a diesel fraction I1 online; the mixing device II is used to mix the diesel fraction I1 with the diesel fraction II2 from the tank area to obtain a mixed diesel fraction 3; the distillation device III is used to distill the mixed diesel fraction 3 to obtain a heavy fraction 4 with a distillation range of 235-400°C; the solvent extraction device VI is used to perform solvent extraction on the heavy fraction 4 and an extractant 7, and the obtained extracted heavy oil phase is separated by a first solvent to obtain a heavy fraction 8 rich in ideal components; the high-pressure delayed coking unit IV is used to perform high-pressure delayed coking on the heavy fraction 4 or the heavy fraction 8 rich in ideal components as a coking feedstock to obtain needle coke 11.

[0086] In some embodiments of the present invention, preferably, Figure 1 As shown, the catalytic cracking unit I includes: at least one reactor I-1 and a fractionation tower I-2. In the present invention, the reactor I-1 includes but is not limited to a riser reactor, which is used to crack and condense the raw material and the acid molecular sieve catalyst to obtain oil and gas 12; the fractionation tower I-2 is used to fractionate the oil and gas 12 to obtain the diesel fraction I1.

[0087] In the present invention, the type of the mixing device II is not limited, as long as the mixing device can mix the diesel fraction I and the diesel fraction II uniformly.

[0088] In the present invention, the distillation device III includes but is not limited to at least one distillation column.

[0089] In the present invention, the high-pressure delayed coking unit is a semi-continuous operation, and is provided with more than two coke drums, wherein the coke drums adopt periodic intermittent switching operation of online coking and online decoking, or one coke drum is online coking and the other is offline decoking, and the operation is periodically reciprocated.

[0090] In some embodiments of the present invention, preferably, Figure 1 As shown, the high-pressure delayed coking unit IV includes: at least one heating furnace IV-1 and at least two coke towers IV-2; the heating furnace IV-1 is used to heat the coking raw materials; the coke tower IV-2 is used to perform the high-pressure delayed coking on the heated coking raw materials to obtain needle coke 11.

[0091] In some embodiments of the present invention, preferably, Figure 1 As shown, the system also includes: a condensing device V connected to the top of the distillation device III, for condensing the top oil gas 5 obtained by the distillation to obtain a light fraction 6.

[0092] In some embodiments of the present invention, preferably, Figure 1 As shown, the outlet of the condensing device V is connected to the catalytic cracking unit I for returning the light fraction 6 and performing a first reaction.

[0093] In some embodiments of the present invention, preferably, Figure 1 As shown, valve-1S1 and valve-2S2 are provided on the pipeline connecting the condensing device and the catalytic cracking unit.

[0094] In some specific embodiments of the present invention, when valve-1S1 is opened and valve-2S2 is closed, the light fraction 6 is returned and undergoes the first reaction; when valve-1S1 is closed and valve-2S2 is opened, the light fraction 6 is discharged.

[0095] In a specific embodiment of the present invention, the condensing device is connected to the riser reactor in the catalytic cracking unit, and valve 1 and valve 2 are provided on the pipeline connecting the condensing device and the riser reactor. When valve 1 and valve 2 are opened, the light fraction is returned and the first reaction is carried out; when valve 1 is closed and valve 2 is opened, the light fraction is discharged.

[0096] In some embodiments of the present invention, preferably, Figure 1As shown, the solvent extraction device VI is connected to the catalytic cracking unit I, and is used to separate the extracted light oil phase obtained by the solvent extraction through a second solvent, and the obtained heavy fraction 9 rich in non-ideal components is returned and subjected to a second reaction.

[0097] In some embodiments of the present invention, preferably, Figure 1 As shown, the system also includes: a hydrodesulfurization device VII arranged after the distillation device III and before the solvent extraction device VI and the high-pressure delayed coking unit IV, which is used to hydrodesulfurize the heavy fraction 4 before the heavy fraction 4 is subjected to the solvent extraction or the high-pressure delayed coking when the sulfur content in the mixed diesel fraction 3 is ≥0.5wt%.

[0098] In some embodiments of the present invention, preferably, Figure 1 As shown, a valve-3S3 is provided on the pipeline connecting the distillation device III and the high-pressure delayed coking unit IV, and a valve-4S4 is provided on the pipeline connecting the distillation device III and the solvent extraction device VI.

[0099] In some embodiments of the present invention, preferably, when valve-3S3 is opened and valve-4S4 is closed, the heavy fraction 4 is subjected to the high-pressure delayed coking; when valve-3S3 is closed and valve-4S4 is opened, the heavy fraction 4 is subjected to the solvent extraction.

[0100] In some embodiments of the present invention, preferably, Figure 1 As shown, valve-5S5 and valve-6S6 connect the solvent extraction unit VI and the catalytic cracking unit I.

[0101] In some embodiments of the present invention, preferably, when valve-5S5 is opened and valve-6S6 is closed, the heavy fraction 9 rich in non-ideal components is returned and subjected to the second reaction; when valve-5S5 is closed and valve-6S6 is opened, the heavy fraction 9 rich in non-ideal components is discharged.

[0102] In some embodiments of the present invention, preferably, Figure 1 As shown, valve-7S7 connects the distillation unit III and the hydrodesulfurization unit VII, and valve-7'S7' connects the hydrodesulfurization unit VII and the solvent extraction unit VI.

[0103] In some embodiments of the present invention, preferably, when valve-3S3 and valve-4S4 are closed, and valve-7S7 and valve-7'S7' are opened, the heavy fraction 4 is subjected to the hydrodesulfurization; when valve-3S3, valve-7S7 and valve-7'S7' are closed, and valve-4S4 is opened, the heavy fraction 4 is subjected to the solvent extraction; when valve-4S4, valve-7S7 and valve-7'S7' are closed, and valve-3S3 is opened, the heavy fraction 4 is subjected to the high-pressure delayed coking.

[0104] In a specific embodiment of the present invention, a valve-3 is provided on the pipeline connecting the distillation apparatus and the high-pressure delayed coking unit, a valve-4 is provided on the pipeline connecting the distillation apparatus and the solvent extraction apparatus, a valve-7 is connected to the distillation apparatus and the hydrodesulfurization apparatus, and a valve-7' is connected to the hydrodesulfurization apparatus and the solvent extraction apparatus VI. When valve-3 and valve-4 are closed, and valve-7 and valve-7' are opened, the heavy fraction is subjected to hydrodesulfurization; when valve-3, valve-7 and valve-7' are closed, and valve-4 is opened, the heavy fraction is subjected to solvent extraction; when valve-4, valve-7 and valve-7' are closed, and valve-3 is opened, the heavy fraction is subjected to high-pressure delayed coking.

[0105] According to a particularly preferred embodiment of the present invention, a method for preparing needle coke comprises the following steps:

[0106] (1) distilling the mixed diesel fraction to obtain a heavy fraction with a distillation range of 235-400° C.;

[0107] (2) subjecting the heavy fraction and the extractant to solvent extraction, separating the obtained extracted heavy oil phase with a first solvent to obtain a heavy fraction rich in desired components, and separating the obtained extracted light oil phase with a second solvent to obtain a heavy fraction rich in non-desirable components;

[0108] (3) using the heavy fraction rich in the desired components as a coking feedstock for high-pressure delayed coking to obtain needle coke;

[0109] The mixed diesel fraction contains diesel fraction I extracted online from the catalytic cracking unit and diesel fraction II from the tank area; the weight ratio of diesel fraction I to diesel fraction II in the mixed diesel fraction is 80-20:20-80;

[0110] The overhead oil gas obtained by the distillation is condensed to obtain a light fraction;

[0111] The conditions of the high-pressure delayed coking include: the top pressure of the coke tower is 1.6-2.6 MPa (A), the operation cycle of the coke tower is 24-60 hours, and the outlet temperature of the heating furnace is 430-560° C.;

[0112] The light fraction and the heavy fraction rich in non-ideal components are returned to the catalytic cracking unit for the first reaction and the second reaction respectively.

[0113] The present invention will be described in detail below through examples.

[0114] True density parameters are measured using GB / T 24533-2019 or GB / T 32158-2015;

[0115] The thermal expansion coefficient is measured using GB / T 3074.4-2016.

[0116] The physical properties of diesel fraction A1, diesel fraction A2 and diesel fraction A3 are listed in Table 1; among them, diesel fraction I extracted online from the catalytic cracking unit, i.e., diesel fraction A1; light fraction recycling + heavy fraction recycling rich in non-ideal components + diesel fraction I extracted online from the catalytic cracking unit, i.e., diesel fraction A2; diesel fraction II from the tank farm, i.e., diesel fraction A3.

[0117] Table 1

[0118]

[0119] Example 1

[0120] Systems for preparing needle coke, such as Figure 1 As shown, the system comprises: a catalytic cracking unit I, a mixing unit II, a distillation unit III and a high-pressure delayed coking unit IV connected in sequence; and a condensing unit V connected to the top of the distillation unit III;

[0121] Among them, valve-1S1 and valve-2S2 are provided on the pipeline connecting the condensing device V and the catalytic cracking unit I; valve-3S3 is provided on the pipeline connecting the distillation device III and the high-pressure delayed coking unit IV;

[0122] When valve-1S1 is closed and valve-2S2 is opened, the light fraction 6 is discharged;

[0123] When valve-3S3 is opened, the heavy fraction 4 is directly subjected to high pressure delayed coking.

[0124] A method for preparing needle coke, the method comprising:

[0125] (1) Diesel fraction A1 and diesel fraction A3 are mixed in a weight ratio of 50:50, and the obtained mixed diesel fraction is distilled, wherein the distillation conditions include: the tower top pressure is 150 kPa (A), and a heavy fraction is obtained;

[0126] (2) The heavy fraction is used as coking feedstock P1 for high pressure delayed coking to obtain needle coke S1, wherein the physical properties of the coking feedstock P1 are listed in Table 2; the conditions for high pressure delayed coking and the physical properties of needle coke S1 are listed in Table 3.

[0127] Example 2

[0128] Systems for preparing needle coke, such as Figure 1 As shown, the system comprises: a catalytic cracking unit I, a mixing unit II, a distillation unit III, a solvent extraction unit VII and a high-pressure delayed coking unit IV connected in sequence; and a condensing unit V connected to the top of the distillation unit III;

[0129] Among them, valve-1S1 and valve-2S2 are provided on the pipeline connecting the condensing device V and the catalytic cracking unit I; valve-3S3 is provided on the pipeline connecting the distillation device III and the high-pressure delayed coking unit IV, valve-4S4 is provided on the pipeline connecting the distillation device III and the solvent extraction device VI; valve-5S5 and valve-6S6 are provided for connecting the solvent extraction device VI and the catalytic cracking unit I;

[0130] When valve-1S1 is closed and valve-2S2 is opened, the light fraction 6 is discharged;

[0131] When valve-3S3 is closed and valve-4S4 is opened, heavy fraction 4 is directly subjected to solvent extraction, and the obtained heavy fraction 8 rich in the desired components is subjected to high-pressure delayed coking;

[0132] When the valve 5S5 is closed and the valve 6S6 is opened, the heavy fraction 9 rich in non-desirable components is discharged.

[0133] A method for preparing needle coke, the method comprising:

[0134] (1) Diesel fraction A1 and diesel fraction A3 are mixed in a weight ratio of 50:50, and the obtained mixed diesel fraction is distilled, wherein the distillation conditions include: the tower top pressure is 150 kPa (A), and a heavy fraction is obtained;

[0135] (2) subjecting the heavy fraction and the extractant to solvent extraction in a weight ratio of 1:3, and separating the obtained extracted heavy oil phase with a first solvent to obtain a heavy fraction rich in the desired components; wherein the extractant is furfural, n-heptane and water, and the weight ratio of furfural, n-heptane and water is 72:25:3;

[0136] (3) The above-mentioned heavy fraction rich in ideal components is used as a coking feedstock P2 for high-pressure delayed coking to obtain needle coke S2, wherein the physical properties of the coking feedstock P2 are listed in Table 2; the conditions for high-pressure delayed coking and the physical properties of the needle coke S2 ​​are listed in Table 3.

[0137] Example 3

[0138] Systems for preparing needle coke, such as Figure 1 As shown, the system comprises: a catalytic cracking unit I, a mixing unit II, a distillation unit III, a solvent extraction unit VII and a high-pressure delayed coking unit IV connected in sequence; and a condensing unit V connected to the top of the distillation unit III;

[0139] Among them, valve-1S1 and valve-2S2 are provided on the pipeline connecting the condensing device V and the catalytic cracking unit I; valve-3S3 is provided on the pipeline connecting the distillation device III and the high-pressure delayed coking unit IV, valve-4S4 is provided on the pipeline connecting the distillation device III and the solvent extraction device VI; valve-5S5 and valve-6S6 are provided for connecting the solvent extraction device VI and the catalytic cracking unit I;

[0140] When valve-1S1 is opened and valve-2S2 is closed, the light fraction 6 is returned and subjected to the first reaction;

[0141] When valve-3S3 is closed and valve-4S4 is opened, heavy fraction 4 is subjected to solvent extraction, and the obtained heavy fraction 8 enriched in the desired components is subjected to high pressure delayed coking;

[0142] When valve-5S5 is opened and valve-6S6 is closed, the obtained heavy fraction 9 rich in non-desirable components is returned and subjected to the second reaction.

[0143] A method for preparing needle coke, the method comprising:

[0144] (1) Diesel fraction A2 and diesel fraction A3 are mixed in a weight ratio of 55:45, and the obtained mixed diesel fraction is distilled, wherein the distillation conditions include: the tower top pressure is 150 kPa (A), and a heavy fraction and tower top oil gas are obtained, wherein the tower top oil gas is condensed, and the obtained light fraction is returned to the catalytic cracking unit for reaction;

[0145] (2) subjecting the heavy fraction and the extractant to solvent extraction at a weight ratio of 1:3, and separating the obtained extracted heavy oil phase and the extracted light oil phase by a first solvent and a second solvent, respectively, to obtain a heavy fraction rich in desired components and a heavy fraction rich in undesirable components; wherein the extractant is furfural, n-heptane and water, and the weight ratio of furfural, n-heptane and water is 72:25:3; wherein the heavy fraction rich in undesirable components is returned to the catalytic cracking unit for reaction;

[0146] (3) The above-mentioned heavy fraction rich in ideal components is used as a coking feedstock P3 for high-pressure delayed coking to obtain needle coke S3, wherein the physical properties of the coking feedstock P3 are listed in Table 2; the conditions for high-pressure delayed coking and the physical properties of the needle coke S3 are listed in Table 3.

[0147] Comparative Example 1

[0148] The mixed crude oil slurry raw material comes from the online slurry oil of the catalytic cracking unit and the purchased slurry oil. The heavy oil slurry and a small amount of light components are cut by a 500,000 tons (raw material) / year vacuum distillation unit. The operating conditions of the vacuum tower are a top pressure of 5 kPa (A) and an outlet temperature of 390°C. The distilled slurry oil is then hydrodesulfurized by a 300,000 tons / year hydrodesulfurization unit. The properties of the obtained hydrogenated tail oil are shown in Table 2. The hydrogenated tail oil is used as the coking feedstock DP1, and a two-furnace four-tower process is used for delayed coking to obtain needle coke DS1.

[0149] The physical properties of the coking raw material DP1 are listed in Table 2; the conditions for delayed coking and the physical properties of the needle coke DS1 are listed in Table 3.

[0150] Table 2

[0151]

[0152] Note: * refers to the recycling of non-ideal components, that is, the recycling of light fractions and the recycling of heavy fractions rich in non-ideal components.

[0153] From the data in Table 2, it can be seen that through distillation cutting, the density and aromatic content of the heavy fraction in the mixed diesel fraction are improved, the saturated hydrocarbon content is reduced, and the distillation range is narrowed, which is conducive to the production of needle coke products.

[0154] Compared with Example 1, Example 2 uses an extractant to extract the heavy fraction to further separate the non-ideal components in the heavy fraction. Although the amount of raw materials is reduced, its density, aromatic content and aromatic number CA value are significantly improved, which is more conducive to the production of high-quality needle coke products; other parameters such as distillation range, ash content and sulfur and nitrogen content are slightly different, but the difference is not large.

[0155] Compared with Example 2, Example 3 recycles the non-ideal components, that is, the light fraction and the heavy fraction rich in non-ideal components are recycled separately, and the raw material amount, density, aromatic content and aromatic number CA value are slightly improved, which is more conducive to the production of high-quality needle coke products; although other parameters such as distillation range, ash content and sulfur and nitrogen content are slightly different, the difference is not large.

[0156] Table 3

[0157]

[0158] Note: * refers to the recycling of non-ideal components, that is, the light fraction and the heavy fraction rich in non-ideal components are recycled independently.

[0159] It can be seen from the data in Table 3 that the use of heavy fractions concentrated with ideal components as coking raw materials and high-pressure delayed coking process can produce needle coke products equivalent to those in Comparative Example 1.

[0160] Compared with Example 1, Example 2 adopts the technical means of distillation+solvent extraction+high-pressure delayed coking to obtain a needle coke product with better quality.

[0161] Compared with Example 1, Example 3 adopts the technical means of non-ideal component recycling + distillation + solvent extraction + high-pressure delayed coking to obtain a needle coke product with better quality.

[0162] Example 4 and Comparative Example 2

[0163] (1) Based on the expanded needle coke feedstock, both Example 4 and Comparative Example 2 used mixed diesel fraction FCC-LCO as the coking feedstock, and the physical property parameters are listed in Table 4;

[0164] (2) Based on the needle coke process, the raw materials need to be heated in a tubular heating furnace before entering the coke drum. In order to avoid adverse phenomena such as coking in the furnace tube, 1-3wt% of water or steam needs to be injected into the furnace tube;

[0165] (3) Based on the formation mechanism of needle coke, the coking raw materials must meet a temperature of more than 435°C in the coke tower to allow aromatic polymerization and fusion reactions to occur until the intermediate phase is generated and grows;

[0166] (4) The coking raw materials must be in a liquid phase environment for a long time in the early stage of a cycle in the coke tower to facilitate the formation and growth of the intermediate phase.

[0167] The test conditions are to flash the catalytic diesel fraction mixed with 1wt% water vapor at 435℃ and different pressures, and compare the flash tank liquid yield or retention rate at different pressures. Since "the raw material is in a liquid phase reaction environment at a temperature above 435℃ for a long time" is the key condition of needle coke production technology, if the flash tank liquid yield or retention rate of the catalytic diesel fraction under one pressure condition is significantly lower or less than 30%, it means that the catalytic diesel fraction cannot meet the "key conditions of needle coke production technology" under this pressure condition, or cannot meet the conditions for producing needle coke.

[0168] The calculation results of the two coke towers of Example 4 (numbered: T3-PAT, T4-PAT) and the two coke towers of Comparative Example 2 (numbered: T1-CTRST, T2-CTRST) are listed in Table 5.

[0169] Table 4

[0170]

[0171]

[0172] Table 5

[0173]

[0174] According to Table 5, using the same catalytic diesel as the coking raw material, the same material temperature of 435°C in the coke drum, and 1wt% water is injected into the furnace tubes, the coke drum pressure of Comparative Example 2 adopts one of the larger values ​​of 0.8MPa(A) in the prior art, and the corresponding liquid phase retention rate in the coke drum is 0wt%; the other adopts 1.1MPa(A) slightly higher than the prior art, and the corresponding liquid phase retention rate in the coke drum is only 3wt%. In both cases, more liquid raw materials available for reaction cannot be formed or are difficult to form in the coke drum, that is, at an operating pressure below 1.1MPa(A), the catalytic diesel fraction cannot be used to produce needle coke.

[0175] Compared with the coke drum pressure of Example 4, which is 1.5MPa(A) and 2.1MPa(A), the corresponding liquid phase retention rates in the coke drum are 48wt% and 86wt%, respectively, which effectively guarantees the formation of more liquid phase raw materials for reaction in the coke drum. That is, the use of a high-pressure coke drum different from conventional technology creates conditions for producing needle coke using catalytic diesel as a lighter raw material.

[0176] Therefore, the use of catalytic diesel refining and high-pressure delayed coking technology can achieve the production of needle coke using catalytic diesel fraction as raw material.

[0177] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing needle coke, characterized in that: The method comprises the following steps: (1) Distilling the mixed diesel fraction to obtain a heavy fraction with a distillation range of 235-400°C; wherein the physical property parameters of the heavy fraction meet the following requirements: density ≥ 0.9 g / cm at 20°C; 3 ; Aromatic content is 40-80wt%; Aromatic carbon number CA value is 30-60%; (2) subjecting the heavy fraction and the extractant to solvent extraction, and separating the obtained extracted heavy oil phase with a first solvent to obtain a heavy fraction rich in the desired component; (3) using the heavy fraction or the heavy fraction rich in the desired component as a coking feedstock to perform high pressure delayed coking to obtain needle coke; The mixed diesel fraction contains diesel fraction I extracted online from the catalytic cracking unit and diesel fraction II from the tank farm; Wherein, the conditions of the high-pressure delayed coking include: the top pressure of the coke tower is 1.6-3MPa(A).

2. The method according to claim 1, wherein: In step (1), the weight ratio of diesel fraction I to diesel fraction II in the mixed diesel fraction is 99-1:1-99.

3. The method according to claim 2, wherein: The weight ratio of the diesel fraction I to the diesel fraction II in the mixed diesel fraction is 80-20:20-80.

4. The method according to claim 1, wherein: Based on the total weight of the diesel fraction I, the colloid content in the diesel fraction I is less than 0.1wt%, and the asphaltene content is less than 0.01wt%; Based on the total weight of the diesel fraction II, the colloid content in the diesel fraction II is 0.1-5wt%, and the asphaltene content is 0.01-0.5wt%; The physical properties of the diesel fraction I and the diesel fraction II independently satisfy the following conditions: density at 20°C is 0.86-1.03 g / cm 3 ; Ash content ≤0.1wt%; Sulfur content ≤1wt%; Nitrogen content ≤0.3wt%; Saturated hydrocarbon content is 15-75wt%; Aromatic hydrocarbon content is 25-85wt%; Aromatic carbon number CA value is 25-55%; Distillation range is 150-400℃.

5. The method according to claim 1, wherein: In step (1), the distillation conditions include: the tower top pressure is 2-600 kPa (A); The physical properties of the heavy fraction meet the following requirements: density ≥ 0.93 g / cm at 20°C 3 ; The overhead oil gas obtained by the distillation is condensed to obtain a light fraction.

6. The method according to claim 5, wherein: The distillation conditions include: the tower top pressure is 10-200 kPa (A); The light fraction is returned to the catalytic cracking unit for a first reaction.

7. The method according to claim 1, wherein: In step (2), the weight ratio of the heavy fraction to the extractant is 1:1-5; The extractant is selected from organic hydrocarbons and water, wherein the organic hydrocarbon is selected from at least one of furfural, tetrahydrofuran, 2-butanone and n-heptane.

8. The method according to claim 7, wherein: The weight ratio of the heavy fraction to the extractant is 1:2-3.5; The organic hydrocarbon is selected from furfural and / or n-heptane.

9. The method according to claim 8, wherein: The extractant contains furfural, n-heptane and water, wherein the weight ratio of furfural, n-heptane and water is 40-99:1-50:0-10.

10. The method according to claim 9, wherein: The extractant contains furfural, n-heptane and water, wherein the weight ratio of furfural, n-heptane and water is 50-69:30-45:1-5.

11. The method according to claim 1, wherein: The physical property parameters of the heavy fraction rich in ideal components meet the following requirements: density ≥ 0.93 g / cm at 20°C 3 ; Aromatic content is 45-85wt%; aromatic carbon number CA value is 35-65%.

12. The method according to claim 11, wherein: The physical property parameters of the heavy fraction rich in ideal components meet the following requirements: density ≥ 0.96 g / cm at 20°C 3 .

13. The method according to claim 1, wherein: In step (3), the conditions of the high-pressure delayed coking include: the top pressure of the coke drum is 1.6-2.6 MPa(A); the operation cycle of the coke drum is 16-72 hours; and the outlet temperature of the heating furnace is 430-600°C.

14. The method according to claim 13, wherein: In step (3), the conditions of the high-pressure delayed coking include: the operation cycle of the coke drum is 24-60 hours; the outlet temperature of the heating furnace is 430-560°C.

15. The method according to any one of claims 1 to 14, wherein: The method further comprises: when the sulfur content in the mixed diesel fraction is ≥0.5wt%, before the heavy fraction is subjected to the solvent extraction or the high-pressure delayed coking, hydrodesulfurizing the heavy fraction.

16. The method according to claim 15, wherein: The conditions for the hydrodesulfurization include: a reaction temperature of 260-400° C.; and a pressure of 3-6 MPa(G).

17. The method according to claim 16, wherein: The conditions of the hydrodesulfurization include: reaction temperature of 260-360° C.; pressure of 3-5 MPa(G).

18. A system for preparing needle coke, characterized in that: The method described in any one of claims 1 to 17 is carried out in the system, which comprises: a catalytic cracking unit, a mixing unit, a distillation unit, a solvent extraction unit and a high-pressure delayed coking unit connected in sequence; Wherein, the catalytic cracking unit is used to extract diesel fraction I online; The mixing device is used to mix the diesel fraction I with the diesel fraction II from the tank area to obtain a mixed diesel fraction; The distillation device is used to distill the mixed diesel fraction to obtain a heavy fraction with a distillation range of 235-400° C. The solvent extraction device is used to perform solvent extraction on the heavy fraction and the extractant, and the obtained extracted heavy oil phase is separated by a first solvent to obtain a heavy fraction rich in desired components; The high-pressure delayed coking unit is used to carry out high-pressure delayed coking using the heavy fraction or the heavy fraction rich in ideal components as a coking raw material to obtain needle coke.

19. The system of claim 18, wherein: The system also includes: a condensing device connected to the top of the distillation device, which is used to condense the top oil gas obtained by the distillation to obtain a light fraction.

20. The system of claim 19, wherein: The outlet of the condensing device is connected to the catalytic cracking unit for returning the light fraction to the catalytic cracking unit for a first reaction.

21. The system of claim 20, wherein: The pipeline connecting the condensing device and the catalytic cracking unit is provided with valve-1 and valve-2; When valve-1 is opened and valve-2 is closed, the light fraction is returned to the catalytic cracking unit for the first reaction; when valve-1 is closed and valve-2 is opened, the light fraction is discharged.

22. The system of claim 18, wherein: The system also includes: a hydrodesulfurization device arranged after the distillation device and before the solvent extraction device and the high-pressure delayed coking unit, which is used to hydrodesulfurize the heavy fraction before the heavy fraction is subjected to the solvent extraction or the high-pressure delayed coking when the sulfur content in the mixed diesel fraction is ≥0.5wt%.

23. The system of claim 22, wherein: A valve-3 is provided on the pipeline connecting the distillation device and the high-pressure delayed coking unit, and a valve-4 is provided on the pipeline connecting the distillation device and the solvent extraction device; Wherein, when valve-3 is opened and valve-4 is closed, the heavy fraction is subjected to the high-pressure delayed coking; when valve-3 is closed and valve-4 is opened, the heavy fraction is subjected to the solvent extraction.

24. The system of claim 23, wherein: A valve-7 is provided on the pipeline connecting the distillation device and the hydrodesulfurization device, and a valve-7' is provided on the pipeline connecting the hydrodesulfurization device and the solvent extraction device; Wherein, when valve-3 and valve-4 are closed, and valve-7 and valve-7' are opened, the heavy fraction is subjected to the hydrodesulfurization; when valve-3, valve-7 and valve-7' are closed, and valve-4 is opened, the heavy fraction is subjected to the solvent extraction; when valve-4, valve-7 and valve-7' are closed, and valve-3 is opened, the heavy fraction is subjected to the high-pressure delayed coking.

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