A system for producing light aromatics from heavy oil raw materials

Abstract

The invention discloses a system for preparing light aromatics from heavy oil raw materials, which belongs to the reprocessing of inferior diesel in the field of petroleum refining. The system comprises a double riser catalytic cracking device, a main fractionating tower, a sub-fractionating tower, a main cutting fractionating tower and a sub-cutting fractionating tower. The heavy oil raw materials are sequentially subjected to primary catalytic cracking in the heavy oil riser, fractionation in the main fractionating tower and cutting in the main cutting fractionating tower to form light fractions and heavy fractions. The heavy fractions are mixed with the light fractions after primary hydrogenation in a main hydrogenation reactor and sent to a second riser for secondary catalytic cracking. The gasoline components generated by the secondary cracking are subjected to secondary hydrogenation in the sub-hydrogenation reactor and are cut in the sub-cutting fractionating tower to separate the light components and the heavy fractions. The heavy fractions are finally sent to an aromatics joint device to separate three products. In the whole system, the inferior diesel needs to be subjected to secondary catalytic cracking and secondary hydrogenation, which not only reduces the pressure of hydrogenation and significantly reduces the hydrogen consumption, but also the yield of C6-C9 aromatics in the final product can reach more than 50wt%.

Description

Technical Field

[0001] The present invention relates to the reprocessing of heavy oil raw materials in the field of petroleum refining, and in particular to a system for preparing light aromatics from heavy oil raw materials. Background Art

[0002] Heavy oil raw materials refer to oil with a distillation range greater than 350°C. The existing processing method generally involves catalytic cracking in a catalytic cracking unit to produce diesel. However, the market share of diesel has not changed much in recent years, resulting in a structural surplus of diesel. Correspondingly, benzene, toluene, and xylene BTX in aromatics are basic organic chemical raw materials for the petrochemical industry, which can be used to produce a variety of chemical products such as synthetic rubber, synthetic fibers and synthetic resins, and can also be used to produce a variety of fine chemical products. The market demand for BTX is increasing.

[0003] my country's annual output of low-cetane diesel LCO exceeds 10Mt. It is becoming increasingly difficult to use it as a blending component for automotive diesel. Even after hydrotreating, it is difficult to meet the needs of refineries for blending and producing automotive diesel. The investment in building a diesel hydrotreating unit is quite huge. How to use LCO to produce high-value-added light aromatics and gasoline has certain development significance.

[0004] At present, domestic and foreign research institutions mainly process low-quality diesel through hydrocracking, solvent extraction, hydrogenation-reforming and hydrogenation-catalysis to produce aromatics or gasoline:

[0005] CN 103214332 discloses a method for producing light aromatics and high-quality oil products from catalytic cracking diesel. The method extracts catalytic cracking diesel with a solvent to obtain extracted oil rich in polycyclic aromatics and raffinate oil rich in alkanes, and the extracted oil is subjected to hydrorefining and hydrocracking under hydrogenation reaction conditions to produce light aromatics and high-octane gasoline fractions. While obtaining light aromatics, the method can produce diesel with a high cetane number and high-octane gasoline as by-products, but the diesel utilization rate of the method is low and the value of the by-products is low.

[0006] CN 105542849 discloses a method for producing clean diesel and light aromatics from inferior diesel. The method removes sulfur and nitrogen compounds, olefins and colloids from inferior diesel after medium-low pressure hydrogenation to obtain hydrogenated refined diesel. The refined diesel is subjected to simulated moving bed adsorption separation to remove aromatics and sulfides to obtain clean diesel and heavy aromatics. The heavy aromatics enter a light-weighting reactor and are hydrogenated at medium-low pressure to generate BTX light aromatics, gasoline components and a small amount of light hydrocarbons. The process for producing clean diesel and light aromatics from inferior diesel provided by the method can process catalytic cracking diesel and coking diesel, and the generated clean diesel and gasoline components can meet the National V standard, while BTX light aromatics are produced as a by-product. However, the process flow is relatively long and the conversion depth is relatively low.

[0007] CN106753551A discloses a method for producing high-octane gasoline from catalytic cracking diesel. In this method, catalytic diesel is hydrotreated and then cut into a fraction below 280°C and a fraction above 280°C. The fraction above 280°C is subjected to aromatic extraction to obtain a raffinate oil, which is fed into a catalytic cracking unit together with the fraction below 280°C to produce high-octane gasoline, while the extracted oil rich in aromatics is utilized for aromatics. In this method, a large amount of dicyclic and tricyclic aromatics in HLCO are not utilized and are directly discharged from the unit, resulting in poor overall economic benefits.

[0008] In summary, among the existing methods for processing low-quality diesel to obtain aromatics or gasoline, the hydrocracking process can produce high-quality catalytic reforming raw materials and improve the quality of diesel, but the investment is obviously larger; the solvent extraction process can improve the properties of low-quality diesel, but the utilization of extracted aromatics needs further research and discussion; the hydrogenation-reforming LCO-XTM combination process can only process a small amount of LCO light fractions and is not suitable for large-scale processing; the hydrogenation-catalysis combination MGHC technology works well when processing hydrofining LCO alone, but if hydrofining LCO is blended when processing catalytic raw oil, it will obviously affect the cracking and processing capacity of the raw oil, and this operation mode cannot produce BTX products. Summary of the invention

[0009] In order to solve the problem of high processing cost in the existing technology of producing light aromatics from diesel, the present invention provides a system for preparing light aromatics from heavy oil raw materials, which directly utilizes the existing catalytic cracking unit to directly produce light aromatics from heavy oil raw materials, maximizes the use of existing equipment, reduces production costs, greatly reduces hydrogen consumption, and also increases the yield of C6-C9 light aromatics and reduces the yield of diesel.

[0010] The technical solution adopted by the present invention to solve the above technical problems is as follows: a system for preparing light aromatics from heavy oil raw materials, comprising a double-riser catalytic cracking unit, a main fractionation tower, a sub-fractionation tower, a main cutting fractionation tower and a sub-cutting fractionation tower, wherein the reaction oil gas generated by the heavy oil riser of the double-riser catalytic cracking unit is sent to the main fractionation tower for fractionation through a reaction oil gas pipeline I, the catalytic cracking diesel generated by the fractionation of the main fractionation tower is sent to the main cutting fractionation tower for cutting through a catalytic cracking diesel pipeline, the generated light fraction I is sent to the reflux pipeline through the light fraction main pipeline, the generated heavy fraction I is sent to the main hydrogenation reactor through the heavy fraction main pipeline for primary hydrogenation, and the generated hydrogenated catalytic diesel is also sent to the reflux pipeline and mixed with the light fraction I and sent to the second riser of the double-riser catalytic cracking unit for secondary cracking reaction;

[0011] The reaction oil and gas produced by the secondary cracking reaction is sent to the secondary distillation tower for secondary distillation through the reaction oil and gas pipeline II. The generated gasoline components enter the main gasoline pipeline, and are sent to the secondary hydrogenation reactor for secondary hydrogenation after being separated from the rich gas and sewage by the oil and gas separator I. Thereafter, they are sent to the secondary cutting distillation tower for cutting. The generated light fraction II is discharged to the tank area through the light aromatics pipeline for blending with gasoline, and the generated heavy fraction II is sent to the aromatics joint unit through the heavy fraction secondary pipeline to produce C6~C9 light aromatics products, raffinate gasoline products and heavy aromatics products respectively.

[0012] As an optimization scheme for the above-mentioned system of producing light aromatics from heavy oil raw materials, the gasoline component produced by distillation in the main distillation tower is introduced into the oil-gas separator II, after the rich gas and sewage are separated, it is sent to the absorption tower through the auxiliary gasoline pipeline.

[0013] As another optimization scheme for the above-mentioned system for producing light aromatics from heavy oil feedstock, the diesel fraction produced by secondary fractionation in the secondary fractionation tower is combined with the catalytic cracking diesel pipeline and then sent to the main cutting fractionation tower.

[0014] As another optimization scheme for the above-mentioned system for producing light aromatics from heavy oil raw materials, the heavy oil slurry produced by distillation in the main distillation tower is divided into two paths through a circulation pipeline, one path is refluxed to the main distillation tower, and the other path is sent to the secondary distillation tower through the heavy oil pipeline I.

[0015] As another optimization scheme for the above-mentioned system for producing light aromatics from heavy oil feedstock, the heavy oil produced by secondary distillation in the secondary distillation tower is sent back to the circulation pipeline of the main distillation tower via the heavy oil pipeline II.

[0016] As another optimization scheme for the above-mentioned system for producing light aromatics from heavy oil raw materials, the reaction temperature in the heavy oil riser is 480-530°C, the catalyst-oil ratio is 4-8, the reaction pressure is 0.12-0.38MPa, the reaction time is 2.2-4.5s, and the atomized water vapor is 4-8wt% of the feed amount.

[0017] As another optimization scheme for the above-mentioned system for producing light aromatics from heavy oil raw materials, the feed temperature of the main distillation tower is 480-530°C, the bottom temperature is 350-420°C, the top temperature is 80-150°C, and the top pressure is 0.01-0.3MPa.

[0018] As another optimization scheme for the system of producing light aromatics from the above-mentioned heavy oil raw materials, in the main cutting distillation tower, the feed temperature is 220-320°C, the bottom temperature is 100-350°C, the top temperature is 90-150°C, and the top pressure is 0.01-1MPa. Light fraction I is obtained from the top of the tower, and heavy fraction I is obtained from the bottom of the tower.

[0019] As another optimization scheme for the above-mentioned system for producing light aromatics from heavy oil raw materials, in the main hydrogenation reactor, the reaction temperature of the primary hydrogenation is 320-390°C, the hydrogen partial pressure is 5.0-10.0 MPa, the volume space velocity is 0.5-1.5 h-1, and the hydrogen / oil volume ratio is 300-800:1.

[0020] As another optimization scheme for the above-mentioned system for producing light aromatics from heavy oil raw materials, the reaction temperature of the secondary cracking reaction in the second riser is 560-630°C, the catalyst-oil ratio is 9-13, the reaction pressure is 0.12-0.38MPa, the reaction time is 2.2-4.5s, and the atomized water vapor accounts for 1.2-3.5wt% of the feed amount.

[0021] As another optimization scheme for the above-mentioned system for producing light aromatics from heavy oil raw materials, the feed temperature of the secondary distillation tower is 450-530°C, the bottom temperature is 250-350°C, the top temperature is 80-150°C, and the top pressure is 0.01-0.3MPa.

[0022] As another optimization scheme for the above-mentioned system for producing light aromatics from heavy oil raw materials, in the secondary hydrogenation reactor, the reaction temperature of the secondary hydrogenation is 300-420°C, the hydrogen partial pressure is 2.5-3.5MPa, the hydrogen / oil volume ratio is 500-800:1, and the volume space velocity is 1.5-4h-1.

[0023] As another optimization scheme for the above-mentioned system for producing light aromatics from heavy oil raw materials, the feed temperature of the secondary cutting distillation tower is 50-90°C, the bottom temperature is 100-150°C, the top temperature is 40-80°C, and the top pressure is 0.01-0.3MPa.

[0024] As another optimization scheme for the above-mentioned system for producing light aromatics from heavy oil feedstock, in the aromatics complex, the top temperature of the extraction tower used for aromatics extraction is 130-190° C. and the pressure is 1.0-2.0 MPa.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) The present invention makes the most of the existing hydrogenation equipment and catalytic cracking device, reducing the investment and operation cost of the equipment. The heavy oil raw material is first catalytically cracked in the heavy oil riser, and then the gasoline fraction and the catalytic cracking diesel fraction are fractionated in the main fractionation tower. The catalytic cracking diesel is cut in the main cutting fractionation tower to form a light fraction and a heavy fraction. The heavy fraction is hydrogenated in the main hydrogenation reactor and then mixed with the light fraction and sent to the second riser for secondary catalytic cracking. At this time, the reaction oil and gas are fractionated in the secondary fractionation tower to form gasoline and diesel. The diesel component is refluxed to the main cutting fractionation tower for continuous reaction, and the gasoline component is hydrogenated for a second time in the secondary hydrogenation reactor. After the reaction, it enters the secondary cutting fractionation tower for cutting to separate the light fraction and the heavy fraction. The heavy fraction is finally sent to the aromatics complex to separate three products: light aromatics, raffinate gasoline and heavy aromatics. In the whole system, the diesel produced by the catalytic cracking of heavy oil needs to be subjected to secondary catalytic cracking and secondary hydrogenation, which not only reduces the pressure of hydrogenation, but also significantly reduces the hydrogen consumption (relative to the technology of producing BTX raw materials by hydrocracking, the hydrogen consumption of this process can be reduced from more than 4wt% to less than 2.0wt%, and the hydrogenation pressure can be reduced from 12MPa to about 7MPa), and the yield of C6-C9 aromatics in the final product can reach more than 50wt%;

[0027] 2) In the present invention, the inferior diesel produced by catalytic cracking of heavy oil is separated into two parts: "saturated hydrocarbons + monocyclic aromatic hydrocarbons" and dicyclic and higher aromatic hydrocarbons. The dicyclic and higher aromatic hydrocarbons are hydrogenated to produce monocyclic aromatic hydrocarbons. On the one hand, the circulation of saturated hydrocarbons and monocyclic aromatic hydrocarbons in the hydrogenation device is avoided, which leads to an increase in the hydrogen consumption of the device. On the other hand, the dicyclic aromatic hydrocarbons in the inferior diesel are hydrogenated and saturated into monocyclic aromatic hydrocarbons, which improves the hydrogenation efficiency and further reduces the hydrogen consumption.

[0028] 3) The present invention utilizes the second riser of the double riser catalytic cracking unit to crack the hydrocatalytic diesel and light fractions, thereby significantly reducing the operating cost of producing aromatics from diesel and improving the process economy;

[0029] 4) The present invention uses the existing diesel hydrogenation-catalytic cracking process as a basis, and carries out process transformation on the basis of the process, first cutting and then secondary hydrogenation, and uses low-quality diesel to produce high-value-added light aromatic products. While improving economic benefits, it can solve the problem of the outlet of low-quality diesel in refineries, and has significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0031] Figure 2 It is a schematic diagram of the process flow of Comparative Example 1;

[0032] Figure 3 It is a schematic diagram of the process flow of Comparative Example 2;

[0033] Figure numerals: 1. heavy oil riser, 2. second riser, 3. reaction oil and gas pipeline I, 4. main fractionator, 5. catalytic cracking diesel pipeline, 6. main cutting fractionator, 7. heavy fraction main pipeline, 8. light fraction main pipeline, 9. main hydrogenation reactor, 10. reflux pipeline, 11. reaction oil and gas pipeline II, 12. secondary fractionator, 13. oil and gas separator I, 14. main gasoline pipeline, 15. secondary hydrogenation reactor, 16. secondary cutting fractionator, 17. heavy fraction secondary pipeline, 18. aromatics complex, 19. light fraction secondary pipeline, 20. diesel pipeline, 21. oil and gas separator II, 22. secondary gasoline pipeline, 23. heavy oil pipeline I, 24. circulation pipeline, 25. heavy oil pipeline II. DETAILED DESCRIPTION

[0034] The technical scheme of the present invention is further elaborated in detail below in conjunction with specific embodiments. The parts of the present invention not elaborated in the following embodiments are all prior arts, such as the selection of catalysts used in catalytic cracking, the structure of the oil-gas separator, the structure of the aromatics complex, the structure of the hydrogenation reactor, the structure of the cutting and splitting tower, and the structure of the fractionation tower.

[0035] Example 1

[0036] A system for producing light aromatics from low-quality diesel, such as Figure 1As shown, it includes a double riser catalytic cracking unit, a main fractionator 4, a secondary fractionator 12, a main cutting fractionator 6 and a secondary cutting fractionator 16. The low-quality diesel raw material enters the heavy oil riser 1 of the double riser catalytic cracking unit to perform a primary catalytic cracking reaction. The reaction temperature of the primary catalytic cracking is 480-530°C, the catalyst-oil ratio is 4-8, the reaction pressure is 0.12-0.38MPa, the reaction time is 2.2-4.5s, the atomized water vapor accounts for 4-8wt% of the feed amount, and the reaction generated by the reaction is 1.5wt% of the feed amount. After the oil and gas are settled in the main settler, they are sent to the main fractionation tower 4 through the reaction oil and gas pipeline Ⅰ3 for fractionation. The feed temperature during fractionation is 480-530°C, the tower bottom temperature is 350-420°C, the tower top temperature is 80-150°C, and the tower top pressure is 0.01-0.3MPa. The fractionation produces three parts, namely, gasoline component, catalytic cracking diesel and heavy oil slurry. Among them, the catalytic cracking diesel produced by the fractionation of the main fractionation tower 4 is sent to the main cutting fractionation tower 6 through the catalytic cracking diesel pipeline 5 for cutting. In the main cutting fractionation tower 6, The material temperature is 220-320°C, the tower bottom temperature is 100-350°C, the tower top temperature is 90-150°C, and the tower top pressure is 0.01-1MPa. A light fraction I is obtained from the tower top, and a heavy fraction I is obtained from the tower bottom. The light fraction I is sent to the reflux pipeline 10 through the light fraction main line 8, and the heavy fraction I is sent to the main hydrogenation reactor 9 through the heavy fraction main line 7 for primary hydrogenation. The reaction temperature of the primary hydrogenation is 320-390°C, the hydrogen partial pressure is 5.0-10.0MPa, and the volume space velocity is 0.5 ~1.5h-1, the hydrogen / oil volume ratio is 300~800:1; the hydrogenated catalytic diesel generated by the primary hydrogenation is also sent to the reflux pipeline 10 and mixed with the light fraction I, and then sent to the second riser 2 of the double riser catalytic cracking unit for secondary cracking reaction. The reaction temperature of the secondary cracking reaction is 560~630℃, the catalyst-oil ratio is 9~13, the reaction pressure is 0.12~0.38MPa, the reaction time is 2.2~4.5s, and the atomized water vapor accounts for 1.2~3.5wt% of the feed amount;

[0037] The reaction oil and gas produced by the secondary cracking reaction are settled in the secondary settler and then sent to the secondary distillation tower 12 through the reaction oil and gas pipeline II 11 for secondary distillation. The feed temperature of the secondary distillation is 450-530°C, the tower bottom temperature is 250-350°C, the tower top temperature is 80-150°C, and the tower top pressure is 0.01-0.3MPa. The distillation produces three parts, namely, gasoline component, diesel component and heavy oil slurry. Among them, the generated gasoline component enters the main gasoline pipeline 14, is separated from the rich gas and sewage by the oil-gas separator I 13, and then sent to the secondary hydrogenation reactor 15 for secondary hydrogenation. The reaction temperature of the secondary hydrogenation is 300-420°C, the hydrogen partial pressure is 2.5-3.5MPa, the hydrogen / oil volume ratio is 500-800:1, and the volume space velocity is 1.5-4h-1; after the secondary hydrogenation, it is sent to The waste is then fed into the secondary cutting distillation tower 16 for cutting. The feed temperature in the secondary cutting distillation tower 16 is 50-90°C, the tower bottom temperature is 100-150°C, the tower top temperature is 40-80°C, and the tower top pressure is 0.01-0.3MPa. The cutting produces light fraction II and heavy fraction II. The produced light fraction II is mainly C5C6 alkane, which is discharged to the tank area through the light fraction secondary pipeline 19 for blending gasoline. The produced heavy fraction II is sent to the aromatics joint unit 18 through the heavy fraction secondary pipeline 17. In the aromatics joint unit 18, the tower top temperature of the extraction tower used for aromatics extraction is 130-190°C, and the pressure is 1.0-2.0MPa, respectively producing C6-C9 light aromatics products, raffinate gasoline products and heavy aromatics products. The raffinate gasoline and heavy aromatics are sent to the gasoline pool for blending gasoline.

[0038] The process route of this embodiment is that the raw material undergoes a catalytic cracking reaction in the heavy oil riser 1 of the double riser catalytic cracking unit, and the generated product reaction oil and gas enters the main distillation tower 4 through the first reaction oil and gas pipeline 3 for fractionation, and the catalytic cracking diesel produced by the fractionation enters the main cutting distillation tower 6 through the catalytic cracking diesel pipeline 5. After being cut and fractionated by the main cutting distillation tower 6, the light fraction is sent to the reflux pipeline 10 through the light fraction main pipeline 8, and returns to the second riser 2 of the double riser catalytic cracking unit through the reflux pipeline 10, and the heavy fraction is sent to the main hydrogenation reactor 9 through the heavy fraction main pipeline 7 for primary hydrogenation, and the generated hydrogenated catalytic diesel is returned to the second riser 2 of the double riser catalytic cracking unit through the reflux pipeline 10 for secondary cracking reaction;

[0039] The reaction oil and gas produced in the second riser 2 enters the secondary fractionation tower 12 through the second reaction oil and gas pipeline 11 for fractionation. The gasoline component produced after fractionation enters the secondary hydrogenation reactor 15 through the main gasoline pipeline 14 for secondary hydrogenation, and then is sent to the secondary cutting fractionation tower 16 for cutting and fractionation. The light fraction produced is discharged to the tank area through the light fraction secondary pipeline 19 for blending gasoline, and the heavy fraction is sent to the aromatics complex 18 through the heavy fraction secondary pipeline 17 to produce three products (C6-C9 light aromatics, raffinate gasoline and heavy aromatics).

[0040] The diesel produced by fractionation in the secondary fractionation tower 12 enters the primary cutting fractionation tower 6 through the diesel pipeline 20;

[0041] The light fraction produced by the distillation in the main distillation tower 4 is a gasoline component and is sent to the absorption tower through the auxiliary gasoline pipeline 22.

[0042] Example 2

[0043] This embodiment is a limited scheme for Example 1, and its main structure is the same as that of Example 1, and the limited part is that the gasoline component produced by the distillation of the main distillation tower 4 is introduced into the oil-gas separator II 21, and after the rich gas and sewage are separated, they are sent to the absorption tower through the auxiliary gasoline pipeline 22.

[0044] Example 3

[0045] This embodiment is another limitation of the embodiment 1, and its main structure is the same as that of the embodiment 1, except that the diesel fraction produced by the secondary fractionation in the secondary fractionation tower 12 is combined with the catalytic cracking diesel pipeline 5 through the diesel pipeline 20 and then sent to the main cutting fractionation tower 6.

[0046] Example 4

[0047] This embodiment is another limitation of the embodiment 1, and its main structure is the same as that of the embodiment 1, except that the heavy oil slurry produced by the distillation of the main distillation tower 4 is divided into two paths through the circulation pipeline 24, one path is refluxed to the main distillation tower 4, and the other path is sent to the auxiliary distillation tower 12 through the heavy oil pipeline Ⅰ23.

[0048] Example 5

[0049] This embodiment is another limitation of the embodiment 1, and its main structure is the same as that of the embodiment 1, except that the heavy oil produced by the secondary distillation in the secondary distillation tower 12 is sent back to the circulation pipeline 24 of the main distillation tower 4 via the heavy oil pipeline II 25.

[0050] In order to verify the advantages of the present invention compared with the prior art, the process equipment of the present invention was used to carry out the following detection tests and comparative experiments.

[0051] Detection experiment

[0052] The test experiment used Figure 1 The specific process flow of the equipment is as follows:

[0053] 1) The heavy oil raw material is introduced into the heavy oil riser 1 for catalytic cracking reaction, and the reaction oil gas is sent to the main fractionation tower 4 for fractionation, and the gasoline component is directly sent to the absorption tower, and the catalytic cracking diesel component (its composition properties are shown in Table 1) is sent to the main cutting fractionation tower 6, the feed temperature is 220°C, the tower bottom temperature is 300°C, the tower top temperature is 240°C, and the tower top pressure is 0.01MPa. A light fraction is obtained from the tower top and a heavy fraction is obtained from the tower bottom;

[0054] 2) sending the heavy fraction obtained in step 1) into the main hydrogenation reactor 9 for a primary hydrogenation reaction to saturate the polycyclic aromatic hydrocarbons in the heavy fraction into monocyclic aromatic hydrocarbons to obtain hydrogenated catalytic diesel;

[0055] The reaction temperature of the primary hydrogenation reaction is 390°C, the hydrogen partial pressure is 10.0 MPa, the volume space velocity is 2.5 h-1, the hydrogen / oil volume ratio is 800:1, the active metal in the catalyst used is nickel, and the mass of the active metal accounts for 12% of the total mass of the catalyst;

[0056] 3) The hydrogenated catalytic diesel from step 2) and the light fraction obtained from step 1) are combined and sent together to the second riser 2 for secondary cracking, and the reaction oil and gas produced by the secondary cracking are sent to the secondary fractionation tower 12 to fractionate cracked gasoline and cracked diesel, and the cracked diesel is sent back to the main cutting fractionation tower 6;

[0057] The reaction temperature of the secondary cracking in the second riser 2 is 600°C, the catalyst-oil ratio is 14, the reaction pressure is 0.3Mpa, the reaction time is 4s, and the atomized water vapor accounts for 1wt% of the feed amount;

[0058] 4) The cracked gasoline fractionated in step 3) is sent to the secondary hydrogenation reactor 15 for secondary hydrogenation reaction to obtain refined gasoline, and is cut and fractionated at 75° C. as a cut point in the secondary cutting fractionation tower 16 to obtain a heavy fraction greater than the cut point and light aromatics less than the cut point, and the light fraction is used as a gasoline blending product;

[0059] In this step, the reaction temperature of the secondary hydrogenation reaction is 420°C, the hydrogen partial pressure is 3.5 MPa, the hydrogen / oil volume ratio is 500:1, the volume space velocity is 4h-1, and the catalyst is a cobalt-molybdenum catalyst, and the addition amount thereof is 6wt%;

[0060] 5) sending the heavy fraction in step 4) to the aromatics complex 18, which extracts and fractionates the heavy fraction to obtain C6-C9 light aromatics products, raffinate gasoline and heavy aromatic components, and the raffinate gasoline and heavy aromatic components are used as gasoline blending products;

[0061] In this step, when the aromatics are extracted, the extraction solvent is cyclopentane sulfone, and the mass ratio of the extraction solvent to the heavy fraction is 8:1; the top temperature of the extraction tower used for the aromatics extraction is 190°C and the pressure is 2.0 MPa.

[0062] The hydrogen consumption and product distribution of the entire process in this test experiment are shown in Table 2.

[0063] Table 1 Properties of catalytic cracking diesel

[0064]

[0065] Table 2 Hydrogen consumption of the whole process and product distribution

[0066]

[0067] Comparative Example 1

[0068] The catalytic cracking diesel used in this comparative example was taken from the diesel produced by catalytic cracking of heavy oil feedstock in the test experiment, see Table 1, and the Figure 2 The process flow shown in the figure is different from the detection experiment in that the catalytic diesel after catalytic cracking in the heavy oil riser 1 is not fractionated in the main fractionator 4 and cut in the main cutting fractionator 6, but is all sent to the main hydrogenation reactor 9 for hydrogenation refining and then to the second riser 2 for secondary cracking. The reaction oil and gas are not fractionated in the secondary fractionator 12, but are directly sent to the secondary hydrogenation reactor 15 for secondary hydrogenation, and then cut and fractionated in the secondary cutting fractionator 16, and extracted and fractionated in the aromatics combined unit 18 to obtain the product.

[0069] The reaction conditions of the main hydrogenation reactor 9 are the same as those in the test experiment, the reaction parameters during cracking of the second riser 2 are also the same as those in the test experiment, the reaction parameters of the auxiliary hydrogenation reactor 15 are also the same as those in the test experiment, the parameters of the auxiliary cutting distillation tower 16 and the aromatics combined unit 18 are also the same as those in the test experiment, and the obtained hydrogen consumption of the whole process and the product distribution are shown in Table 2.

[0070] Comparative Example 2

[0071] The catalytic cracking diesel used in this comparative example was taken from the diesel produced by catalytic cracking of heavy oil feedstock in the test experiment, see Table 1, and the Figure 3 The process flow shown in FIG. 1 is different from the detection experiment in that the catalytic diesel after catalytic cracking in the heavy oil riser 1 is directly introduced into the secondary hydrogenation reactor 15 for hydrogenation, and then cut and fractionated in the secondary cutting fractionation tower 16, and aromatics are extracted and fractionated in the aromatics combined unit 18 to obtain products, wherein the reaction parameters of the secondary hydrogenation reactor 15, the secondary cutting fractionation tower 16 and the aromatics combined unit 18 are the same as those in the detection experiment, and the obtained full process hydrogen consumption and product distribution are shown in Table 2.

[0072] From the data comparison in Table 2, it can be seen that the hydrogen consumption in the test experiment can be reduced to below 2wt%, and the total yield of benzene, toluene, xylene and trimethylbenzene can reach more than 50wt%. The hydrogen consumption of Comparative Example 1 is 4.16wt%, and the hydrogen consumption of Comparative Example 2 is 4.20wt%. That is to say, the process of the present invention not only reduces the pressure of hydrogenation, but also significantly reduces the hydrogen consumption.

[0073] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes and modifications may be made to the embodiments without departing from the principles and essence of the invention. The scope of protection of the present invention is limited only by the appended claims.

Claims

1. A system for producing light aromatics from heavy oil raw materials, comprising a double riser catalytic cracking unit, a main fractionator (4), a secondary fractionator (12), a main cutting fractionator (6) and a secondary cutting fractionator (16), characterized in that: The reaction oil gas produced by the heavy oil riser (1) of the double riser catalytic cracking unit is sent to the main fractionation tower (4) through the reaction oil gas pipeline I (3) for fractionation. The catalytic cracking diesel produced by the fractionation in the main fractionation tower (4) is sent to the main cutting fractionation tower (6) through the catalytic cracking diesel pipeline (5) for cutting. The light fraction I produced is sent to the reflux pipeline (10) through the light fraction main pipeline (8). The heavy fraction I produced is sent to the main hydrogenation reactor (9) through the heavy fraction main pipeline (7) for primary hydrogenation. The generated hydrogenated catalytic diesel is also sent to the reflux pipeline (10) and mixed with the light fraction I to be sent to the second riser (2) of the double riser catalytic cracking unit for secondary cracking reaction. The reaction oil and gas produced by the secondary cracking reaction is sent to the secondary fractionation tower (12) through the reaction oil and gas pipeline II (11) for secondary fractionation. The generated gasoline component enters the main gasoline pipeline (14), is separated into rich gas and sewage by the oil and gas separator I (13), and is sent to the secondary hydrogenation reactor (15) for secondary hydrogenation. Thereafter, it is sent to the secondary cutting fractionation tower (16) for cutting. The generated light fraction II is discharged to the tank area through the light fraction secondary pipeline (19) for blending with gasoline. The generated heavy fraction II is sent to the aromatics complex (18) through the heavy fraction secondary pipeline (17) to produce C6-C9 light aromatics products, raffinate gasoline products and heavy aromatics products respectively. The diesel fraction produced by the secondary fractionation in the secondary fractionation tower (12) is combined with the catalytic cracking diesel pipeline (5) through the diesel pipeline (20) and then sent to the main cutting fractionation tower (6); In the main cutting fractionation tower (6), the feed temperature is 220-320°C, the tower bottom temperature is 100-350°C, the tower top temperature is 90-150°C, and the tower top pressure is 0.01-1 MPa. A light fraction I is obtained from the tower top, and a heavy fraction I is obtained from the tower bottom.

2. A system for producing light aromatics from heavy oil raw materials according to claim 1, characterized in that: The gasoline components produced by the distillation in the main distillation tower (4) are introduced into the oil-gas separator II (21), where the rich gas and the waste water are separated and then sent to the absorption tower through the auxiliary gasoline pipeline (22).

3. A system for producing light aromatics from heavy oil raw materials according to claim 1, characterized in that: The heavy oil slurry produced by the distillation in the main distillation tower (4) is divided into two paths through a circulation pipeline (24), one path is refluxed to the main distillation tower (4), and the other path is sent to the auxiliary distillation tower (12) through a heavy oil pipeline I (23).

4. A system for producing light aromatics from heavy oil raw materials according to claim 1, characterized in that: The heavy oil produced by the secondary fractionation in the secondary fractionation tower (12) is sent back to the circulation pipeline (24) of the main fractionation tower (4) via the heavy oil pipeline II (25).

5. A system for producing light aromatics from heavy oil raw materials according to claim 1, characterized in that: The reaction temperature in the heavy oil lifting pipe (1) is 480-530° C., the catalyst-oil ratio is 4-8, the reaction pressure is 0.12-0.38 MPa, the reaction time is 2.2-4.5 s, and the atomized water vapor is 4-8 wt% of the feed amount.

6. A system for producing light aromatics from heavy oil raw materials according to claim 1, characterized in that: The main fractionation tower (4) has a feed temperature of 480-530°C, a tower bottom temperature of 350-420°C, a tower top temperature of 80-150°C, and a tower top pressure of 0.01-0.3 MPa.

7. A system for producing light aromatics from heavy oil raw materials according to claim 1, characterized in that: In the main hydrogenation reactor (9), the reaction temperature of the primary hydrogenation is 320-390°C, the hydrogen partial pressure is 5.0-10.0 MPa, and the volume space velocity is 0.5-1.5 h -1 , the hydrogen / oil volume ratio is 300~800:

1.

8. The system for producing light aromatics from heavy oil raw materials according to claim 1, characterized in that: The reaction temperature of the secondary cracking reaction in the second riser (2) is 560-630°C, the catalyst-oil ratio is 9-13, the reaction pressure is 0.12-0.38 MPa, the reaction time is 2.2-4.5 s, and the atomized water vapor accounts for 1.2-3.5 wt% of the feed amount.

9. A system for producing light aromatics from heavy oil raw materials according to claim 1, characterized in that: The feed temperature of the secondary fractionation tower (12) is 450-530°C, the tower bottom temperature is 250-350°C, the tower top temperature is 80-150°C, and the tower top pressure is 0.01-0.3 MPa.

10. A system for producing light aromatics from heavy oil raw materials according to claim 1, characterized in that: In the secondary hydrogenation reactor (15), the reaction temperature of the secondary hydrogenation is 300-420°C, the hydrogen partial pressure is 2.5-3.5 MPa, the hydrogen / oil volume ratio is 500-800:1, and the volume space velocity is 1.5-4 h -1 .

11. A system for producing light aromatics from heavy oil raw materials according to claim 1, characterized in that: The feed temperature of the secondary cutting fractionation tower (16) is 50-90°C, the tower bottom temperature is 100-150°C, the tower top temperature is 40-80°C, and the tower top pressure is 0.01-0.3 MPa.

12. A system for producing light aromatics from heavy oil raw materials according to claim 1, characterized in that: In the aromatics complex (18), the top temperature of the extraction tower used for aromatics extraction is 130-190° C., and the pressure is 1.0-2.0 MPa.

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