Method for producing clean fuel oil by processing coal tar

Abstract

The present invention discloses a method for producing clean fuel oil from coal tar. The method comprises the following steps: mixing a coal tar feedstock with an alkali metal and entering an alkali metal treatment reaction zone. Preferably, the coal tar feedstock is fractionated and cut to obtain a heavy fraction, which is then mixed with the alkali metal and entered into the alkali metal treatment reaction zone. More preferably, the coal tar feedstock is fractionated and cut to obtain a light fraction, which is then treated with an alkali metal and then mixed with the heavy fraction and the alkali metal and entered into the alkali metal treatment reaction zone; the effluent from the alkali metal treatment reaction zone is separated and treated to obtain an oil phase material, which is fractionated to obtain naphtha, diesel, and tail oil; the tail oil enters a fixed-bed hydrogenation reaction zone, contacts a catalyst, and undergoes a hydrogenation reaction. The effluent from the fixed-bed hydrogenation reaction zone is recycled back to the alkali metal treatment reaction zone. The method can improve the quality and yield of light oil products and achieve efficient utilization of coal tar resources.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal tar processing and utilization, and in particular relates to a method for producing clean fuel oil by processing coal tar. Background Art

[0002] Coal tar is a black or dark brown, viscous liquid with a pungent odor produced during the dry distillation of coal. It can be categorized by the distillation temperature as low-temperature, medium-temperature, and high-temperature coal tar. Faced with the increasing shortage of conventional petroleum resources and the growing demand for light oil products, the hydrogenation of coal tar to produce light oil products has attracted widespread attention.

[0003] CN103059973A discloses a slurry bed and fixed bed coupling method for hydrogenating a full fraction of coal tar. The full fraction of coal tar is pretreated by dehydration, dust removal, etc., and is mixed with a hydrocracking catalyst and preheated before entering a slurry bed reactor for a hydrocracking reaction. The primary hydrogenated product after the reaction is fractionated to obtain a light component that enters a fixed bed hydrorefining unit. The middle fraction and catalyst are recycled back to the slurry bed hydrogenation reactor. The heavy component is filtered to remove part of the catalyst and the coke produced by cracking and returned to the tar pretreatment unit for cyclic hydrogenation. The light component is subjected to conventional hydrorefining and then distilled to obtain gasoline and diesel products. This method uses slurry bed hydrogenation technology to pretreat the coal tar raw material. The amount of catalyst added in the slurry bed hydrogenation technology is small and unevenly distributed, resulting in poor catalytic hydrogenation effect. At the same time, the coke yield is high, and coal tar resources are not fully and effectively utilized.

[0004] CN111378490 A discloses a combined ebullated-bed and fixed-bed treatment process for a full-fraction coal tar fraction. The combined process comprises mixing the full-fraction coal tar feedstock and an additive in a pretreatment tank. After mixing, liquid-solid separation is performed. The resulting liquid phase enters an ebullated-bed hydrogenation reaction unit for hydrogenation. The resulting reaction effluent enters a separation tank for gas-liquid separation, yielding a gas phase and a liquid phase. The liquid phase is divided into two streams, a first liquid phase and a second liquid phase, with the first liquid phase recycled to the pretreatment tank. The second liquid phase enters a fixed-bed hydrogenation reaction unit for hydrogenation. The reaction effluent is fractionated to yield naphtha, diesel, and hydrogenated tail oil. The ebullated-bed hydrogenation unit in this patent performs feedstock pretreatment, but the full-fraction coal tar has a relatively high oxygen content, and the water generated during hydrogenation can easily break the catalyst, placing extremely high demands on the catalyst's water resistance. Summary of the Invention

[0005] To address the challenges of existing technologies, the present invention proposes a method for producing clean fuel oil from coal tar. This method utilizes a combination of alkali metal treatment and fixed-bed hydrogenation technology to treat the coal tar feedstock. This method can improve the quality and yield of light oil products, achieving efficient utilization of coal tar resources.

[0006] The invention provides a method for producing clean fuel oil by processing coal tar. The method comprises the following steps: coal tar raw material is mixed with alkali metal and enters into an alkali metal treatment reaction zone. Preferably, the coal tar raw material is fractionated and cut to obtain a heavy fraction, which is mixed with the alkali metal and enters into the alkali metal treatment reaction zone. More preferably, the coal tar raw material is fractionated and cut to obtain a light fraction, which is treated with alkali metal and then mixed with the heavy fraction and alkali metal and enters into the alkali metal treatment reaction zone. Effluent from the alkali metal treatment reaction zone is separated and treated to obtain an oil phase material. The oil phase material is fractionated to obtain naphtha, diesel and tail oil. The tail oil enters into a fixed-bed hydrogenation reaction zone to contact with a catalyst for hydrogenation reaction. The effluent from the fixed-bed hydrogenation reaction zone is circulated back to the alkali metal treatment reaction zone. Preferably, the coal tar raw material and the effluent from the fixed-bed hydrogenation reaction zone are mixed with alkali metal and enter into the alkali metal treatment reaction zone.

[0007] A specific method for producing clean fuel oil by processing coal tar comprises the following steps:

[0008] (1) The coal tar raw material is fractionated and cut to obtain a light fraction and a heavy fraction, wherein the cutting point is 230-300°C, preferably 240-280°C;

[0009] (2) In the presence of hydrogen, the light fraction in step (1) is mixed with an alkali metal and then enters a first alkali metal treatment reaction zone;

[0010] (3) The effluent from the first alkali metal treatment reaction zone in step (2) is mixed with the heavy fraction and the alkali metal and then enters the second alkali metal treatment reaction zone for reaction;

[0011] (4) The effluent from the second alkali metal treatment reaction zone in step (3) is separated to obtain an oil phase material, and the oil phase material is fractionated to obtain naphtha, diesel and tail oil;

[0012] (5) The tail oil in step (4) enters the fixed bed hydrogenation reaction zone to contact with the catalyst for hydrogenation reaction to obtain a reaction effluent. The effluent of the fixed bed hydrogenation reaction zone is circulated to the second alkali metal treatment reaction zone. Preferably, the effluent of the first alkali metal treatment reaction zone is mixed with the heavy fraction, the fixed bed hydrogenation reaction effluent and the alkali metal again and then enters the second alkali metal treatment reaction zone.

[0013] In step (1) of the method of the present invention, the coal tar raw material is at least one of low-temperature coal tar, medium-temperature coal tar and high-temperature coal tar; the low-temperature coal tar has a distillation range of 50-450°C, the medium-temperature coal tar has a distillation range of 50-600°C, and the high-temperature coal tar has a distillation range of 50-650°C.

[0014] In step (1) of the method of the present invention, the coal tar raw material is preferably first subjected to dehydration and desolidification treatment; the dehydration treatment can adopt any method for dehydrating coal tar that can be achieved in the art, such as centrifugal dehydration and coalescence dehydration; the desolidification treatment can adopt any method for desolidifying coal tar that can be achieved in the art, such as centrifugal desolidification and filtration desolidification. The coal tar obtained after the dehydration and desolidification treatment has a water content of 0.5wt%-3.0wt% and a solid content of 0.05wt%-0.35wt%, preferably a water content of 1.0wt%-2.5wt% and a solid content of 0.10wt%-0.20wt%.

[0015] In step (2) of the method of the present invention, the alkali metal belongs to Group IA of the periodic table and is at least one of lithium, sodium, potassium, rubidium, cesium, and francium, preferably sodium or potassium. The mass ratio of the light fraction to the alkali metal in the first alkali metal treatment reaction zone is (2.0-15.0):100, preferably (5.0-12.0):100.

[0016] In step (2) of the method of the present invention, the first alkali metal treatment reaction zone is provided with at least one alkali metal treatment reactor, and the reactor is at least one of a tubular reactor, a kettle reactor and a jet reactor, preferably a tubular reactor.

[0017] In step (2) of the method of the present invention, the process conditions of the first alkali metal treatment reaction zone are as follows: reaction temperature 150-300°C, reaction pressure 2.0-10.0 MPa, residence time 0.5-2.5h, hydrogen to oil volume ratio 300-1500 Nm 3 / m 3 Preferably, the reaction temperature is 200-280 ° C, the hydrogen partial pressure is 5.0-10.0 MPa, the residence time is 0.5-1.5h, and the hydrogen-oil volume ratio is 500-1000Nm 3 / m 3 .

[0018] In step (3) of the method of the present invention, the alkali metal belongs to Group IA elements in the periodic table and is at least one of lithium, sodium, potassium, rubidium, cesium and francium, preferably sodium or potassium; the mass ratio of the alkali metal in the second alkali metal treatment reaction zone to the first alkali metal treatment reaction zone is (30-80):100, preferably (40-60):100.

[0019] In step (3) of the method of the present invention, the second alkali metal treatment reaction zone is provided with at least one alkali metal treatment reactor, and the reactor is at least one of a tubular reactor, a kettle reactor and a jet reactor, preferably a tubular reactor.

[0020] In step (3) of the method of the present invention, compared with the first alkali metal treatment reaction zone, the reaction temperature of the second alkali metal treatment reaction zone is controlled to be 80-200°C higher, the reaction pressure is 2.0-10.0 MPa higher, the residence time is 0.5-2.0 h longer, and the hydrogen-to-oil volume ratio is 300-800 Nm 3 / m 3 Preferably, the reaction temperature is 100-150 ° C, the reaction pressure is 2.0-5.0 MPa, the residence time is 1.5-1.5h, and the hydrogen-to-oil volume ratio is 300-500Nm 3 / m 3 .

[0021] In step (4) of the method of the present invention, the separation treatment may adopt any method capable of achieving solid-liquid two-phase separation in the prior art, such as decantation separation, centrifugal separation, filtration separation, and sedimentation separation.

[0022] In step (4) of the method of the present invention, the solid content of the liquid phase material obtained by the separation treatment is controlled to be 10-200 ppm, and the acid value is less than 1.0 mgKOH / g; preferably, the solid content is 20-100 ppm, and the acid value is less than 0.5 mgKOH / g.

[0023] Furthermore, in step (4) of the method of the present invention, the separation treatment includes a primary separation treatment and a secondary separation treatment; first, the effluent of the second alkali metal treatment reaction zone in step (3) is subjected to a primary separation treatment to obtain an oil phase material A; the solid content of the oil phase material A is controlled to be 100-1000 ppm, and the alkali value is 15-30 mgKOH / g, preferably the solid content is 300-800 ppm, and the alkali value is 11-20 mgKOH / g; an acidic additive is added to the oil phase material A, and then a secondary separation treatment is performed to obtain an oil phase material B, wherein the acidic additive includes one or more of formic acid, hydrochloric acid, trichloroacetic acid, sulfuric acid and phosphoric acid solution; the solid content of the oil phase material B obtained after the secondary separation treatment is controlled to be 10-200 ppm, preferably 20-100 ppm; and the acid value is less than 1.0 mgKOH / g, preferably less than 0.5 mgKOH / g.

[0024] In step (5) of the method of the present invention, the fixed-bed hydrogenation reaction zone is provided with at least one fixed-bed hydrogenation reactor, and the reactor is filled with at least one hydrocracking catalyst.

[0025] In step (5) of the method of the present invention, the hydrocracking catalyst comprises a hydrogenation-active metal component and a carrier; the carrier comprises a Y or β-type molecular sieve and amorphous silica-alumina, and the hydrogenation-active metal component comprises molybdenum and / or tungsten, a Group VIB metal, and cobalt and / or nickel, a Group VIII metal; and the content of the hydrogenation-active metal component, calculated as oxide, is 10-30 wt.% based on the mass of the catalyst. The hydrocracking catalyst may be a commercial catalyst, such as one or more of the hydrocracking catalysts with trade names 3824, 3903, 3971, 3976, FC-12, FC-32, FC-36, FC-46, and FC-76 developed by the Dalian Research Institute of Petrochemicals of Sinopec, or a hydrocracking catalyst prepared independently according to the prior art in the art.

[0026] In step (5) of the method of the present invention, the process conditions of the fixed bed hydrogenation reaction zone are as follows: reaction temperature is 350-450°C, total reaction pressure is 10.0-20.0 MPa, liquid hourly volume space velocity is 0.1-0.5h -1 , the hydrogen-oil volume ratio is 1000:1-2000:1; preferably, the reaction temperature is 370-420°C, the total reaction pressure is 12.0-18.0 MPa, and the liquid hourly volume space velocity is 0.15-0.4h -1 , the volume ratio of hydrogen to oil is 1200:1-1800:1.

[0027] The method of the present invention combines alkali metal treatment technology with fixed-bed hydrogenation technology to process coal tar feedstock. Alkali metal treatment technology eliminates the catalyst bed, eliminating the bed clogging caused by mechanical impurities and heavy metals that can occur during fixed-bed hydrorefining. Leveraging the high impurity tolerance and high metal removal capacity of the alkali metal treatment reaction zone, the combined technology significantly improves feedstock adaptability, enabling the processing of low-quality feedstocks such as full-fraction low-temperature coal tar, full-fraction medium-temperature coal tar, and even full-fraction high-temperature coal tar.

[0028] The present invention proposes a reverse-series combination of an alkali metal treatment unit and a fixed-bed hydrogenation unit. The effluent from the fixed-bed hydrogenation reaction zone is mixed with the coal tar feedstock to serve as feed to the alkali metal treatment unit, and the tail oil from the alkali metal treatment unit enters the fixed-bed hydrogenation reaction zone for treatment. This combined technology prevents excessive cracking of light fractions and improves the yield of light oil products. Furthermore, the oil generated from the fixed-bed hydrogenation reaction zone is rich in monocyclic and dicyclic aromatics. This, when mixed with the coal tar feedstock, increases the solubility of three- and higher-ring aromatics in the coal tar, thereby improving the colloidal stability of the coal tar system.

[0029] During the research process, it was found that in the coal tar system, asphaltenes and heavy colloids are the dispersed phases, while light colloids, aromatic fractions, and saturated fractions are the dispersed medium. The stability of the coal tar system is closely related to the peptization ability of the dispersed medium. In the method of the present invention, the alkali metal treatment reaction zone includes a first alkali metal treatment reaction zone and a second alkali metal treatment reaction zone. By regulating the operating conditions of the first and second alkali metal treatment reaction zones, the dispersion medium contained in the light fraction is suppressed from converting into small molecules with poorer peptization ability, which slows down the decline in the peptization ability of the dispersion medium, thereby suppressing the precipitation of asphaltenes during the reaction of the coal tar raw material and alleviating problems such as coking and increased bed pressure drop.

[0030] During the research, analysis of the composition and properties of the coal tar feedstock revealed that oxygenated compounds—phenol and its derivatives—are concentrated in the fraction below 230°C. Furthermore, phenol and its derivatives are highly polar molecules. Therefore, the present method cuts the coal tar feedstock to produce a light fraction rich in phenol and its derivatives. This fraction possesses strong polarity, and upon entering the first alkali metal treatment reaction zone and reacting with the alkali metal, it increases the dispersion of the molten alkali metal in the reaction system, thereby significantly accelerating the reaction rate. Furthermore, the light fraction contacts the alkali metal to form alkali metal alkoxides. The resulting oil, containing these alkali metal alkoxides, enters the second alkali metal treatment reaction zone, where it acts as a surfactant, further achieving a high degree of dispersion of the alkali metal.

[0031] Compared with the prior art, the advantages of the method of the present invention are:

[0032] 1. The present method combines alkali metal treatment technology with fixed-bed hydrogenation technology to process coal tar feedstock. Leveraging the high impurity resistance and high demetallization capabilities of the alkali metal treatment reaction zone, the combined technology significantly improves feedstock adaptability, enabling the processing of low-quality feedstocks such as full-fraction low-temperature coal tar, full-fraction medium-temperature coal tar, and even full-fraction high-temperature coal tar.

[0033] 2. In the method of the present invention, the alkali metal treatment reaction zone includes a first alkali metal treatment reaction zone and a second alkali metal treatment reaction zone. By regulating the operating conditions of the first and second alkali metal treatment reaction zones, the dispersion medium contained in the light fraction is inhibited from converting into small molecular substances with poorer peptizing ability, thereby slowing down the decline in the peptizing ability of the dispersion medium, thereby inhibiting the precipitation of asphaltenes during the reaction of the coal tar raw material, and alleviating problems such as coking and increased bed pressure drop.

[0034] 3. The present method cuts the coal tar feedstock to produce a light fraction rich in phenol and its derivatives. This fraction has strong polarity and, when entering the first alkali metal treatment reaction zone and reacting with the alkali metal, increases the dispersion of the molten alkali metal in the reaction system, thereby significantly accelerating the reaction rate. Furthermore, the light fraction contacts the alkali metal to form alkali metal alkoxides. The resulting oil containing these alkali metal alkoxides enters the second alkali metal treatment reaction zone, where it acts as a surfactant, further achieving a high degree of dispersion of the alkali metal. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Attachment Figure 1 This is a process flow chart of a method for producing clean fuel oil by processing coal tar provided by the present invention.

[0036] Among them, 1-new hydrogen, 2-coal tar raw material, 3-heating furnace, 4-alkali metal treatment device feed, 5-alkali metal, 6-alkali metal treatment device, 7-alkali metal treatment device reaction effluent, 8-hot high-purity separator, 9-circulating hydrogen, 10-circulating hydrogen compressor, 11-hot high-purity separator effluent, 12-separation device, 13-impurities removed by the separation device, 14-separation device effluent, 15-fractionation tower, 16-gas, 17-gasoline, 18-diesel, 19-tail oil, 20-fixed bed hydrogenation device, and 21 is the effluent material of the fixed bed hydrogenation device. Implementation Method

[0037] The method provided by the present invention is described below with reference to the accompanying drawings.

[0038] The coal tar raw material 2 is mixed with the new hydrogen 1 and the circulating hydrogen 9 compressed by the circulating hydrogen compressor 10 and then enters the heating furnace 3. The obtained alkali metal treatment device feed 4 is mixed with the alkali metal 5 and the fixed bed hydrogenation device effluent material 21 and enters the alkali metal treatment device 6 for reaction. The obtained reaction effluent 7 enters the hot high-separation tank 8, and the hot high-separation tank effluent 11 enters the separation device, wherein the removed impurities 13 are drawn out of the device, and the separation device effluent 14 enters the distillation tower 15 for fractionation to obtain gas 16, gasoline 17, diesel 18 and tail oil 19, wherein the tail oil 19 enters the fixed bed hydrogenation device 20 for hydrogenation reaction.

[0039] The following examples will further illustrate the method provided by the present invention, but are not intended to limit the present invention.

[0040] In the examples, each alkali metal treatment reaction zone is equipped with an alkali metal treatment reactor, and the reactor used is a tubular reactor. The fixed-bed hydrogenation reaction zone is equipped with a fixed-bed hydrogenation reactor, and the catalysts used are the commercial brands FF-36 and FC-12 hydrogenation catalysts developed by Sinopec Fushun Petrochemical Research Institute. The FF-36 and FC-12 hydrogenation catalysts are loaded in a volume ratio of 30:70.

[0041] The raw material used in the examples and comparative examples is medium and low temperature coal tar, and its properties are shown in Table 1.

[0042] Example 1

[0043] (1) Coal tar feedstock and fixed bed hydrogenation reaction effluent are mixed with alkali metals and enter the alkali metal treatment reactor;

[0044] (2) The reaction effluent obtained in step (1) is subjected to separation treatment to obtain an oil phase material, and the oil phase material is fractionated to obtain naphtha, diesel and tail oil; the separation treatment includes a primary separation treatment and a secondary separation treatment; first, the reaction material obtained in step (1) is subjected to a primary separation treatment to obtain an oil phase material A; an acidic additive is added to the oil phase material A, and then a secondary separation treatment is performed to obtain an oil phase material B; the acidic additive used is a mixture of formic acid and acetic acid, and the mass ratio of formic acid to acetic acid is 2:1.

[0045] (3) The tail oil enters a fixed bed hydrogenation reactor and contacts with a catalyst for hydrogenation reaction.

[0046] Example 2

[0047] The process flow of this embodiment is the same as that of embodiment 1.

[0048] Example 3

[0049] The process flow of this embodiment is the same as that of embodiment 1.

[0050] Example 4

[0051] (1) Coal tar raw materials are fractionated and cut into light fractions and heavy fractions;

[0052] (2) In the presence of hydrogen, the light fraction in step (1) is mixed with the alkali metal and then enters the first alkali metal treatment reactor;

[0053] (3) The effluent from the first alkali metal treatment reactor in step (2) is mixed with the heavy fraction, the effluent from the fixed bed hydrogenation reactor and the alkali metal and then enters the second alkali metal treatment reactor for reaction;

[0054] (4) The effluent from the second alkali metal treatment reactor in step (3) is separated to obtain an oil phase material; the oil phase material is fractionated to obtain naphtha, diesel and tail oil; the separation treatment includes a primary separation treatment and a secondary separation treatment; first, the reaction material obtained in step (1) is subjected to a primary separation treatment to obtain an oil phase material A; an acidic additive is added to the oil phase material A, and then a secondary separation treatment is performed to obtain an oil phase material B; the acidic additive used is a mixture of formic acid and acetic acid, and the mass ratio of formic acid to acetic acid is 2:1;

[0055] (5) The tail oil in step (4) enters the fixed bed hydrogenation reactor and contacts with the catalyst for hydrogenation reaction to obtain a reaction effluent. The effluent of the fixed bed hydrogenation reaction zone repeats the process of step (3).

[0056] Example 5

[0057] The process flow of this embodiment is the same as that of Example 4.

[0058] Example 6

[0059] The process flow of this embodiment is the same as that of Example 4.

[0060] The process conditions of the above examples are shown in Table 2, and the product properties are shown in Table 3.

[0061] Table 1 Coal tar raw material properties

[0062]

[0063] Table 2 Process conditions of the embodiment

[0064]

[0065] Table 3 Product properties

[0066]

[0067] Comparative Example 1

[0068] The coal tar feedstock first enters the hydrotreating reaction zone for reaction. The resulting reaction effluent enters the hydrocracking reaction zone for hydrocracking, where it is separated into gas, gasoline, diesel, and tail oil. The catalyst used in the hydrotreating reaction zone is the commercially available 3936 hydrotreating catalyst developed by the Sinopec Fushun Research Institute of Petrochemicals. The catalyst used in the hydrocracking reaction zone is the commercially available FF-36 and FC-12 hydrogenation catalysts developed by the Sinopec Fushun Research Institute of Petrochemicals. The volume ratio of FF-36 to FC-12 is 30:70. Operating conditions and product properties are shown in Table 4.

[0069] Table 4 Operating conditions and product properties of Comparative Example 1

[0070]

Claims

1. A method for producing clean fuel oil by processing coal tar, characterized in that: The method specifically comprises the following steps: (1) Coal tar raw materials are fractionated and cut into light fraction and heavy fraction, with the cutting point being 230-300℃; (2) In the presence of hydrogen, the light fraction in step (1) is mixed with an alkali metal and then enters a first alkali metal treatment reaction zone; (3) The effluent from the first alkali metal treatment reaction zone in step (2) is mixed with the heavy fraction and the alkali metal and then enters the second alkali metal treatment reaction zone for reaction; (4) The effluent from the second alkali metal treatment reaction zone in step (3) is separated to obtain an oil phase material, and the oil phase material is fractionated to obtain naphtha, diesel and tail oil; (5) The tail oil in step (4) enters the fixed bed hydrogenation reaction zone to contact with the catalyst for hydrogenation reaction to obtain a fixed bed hydrogenation reaction effluent, and the fixed bed hydrogenation reaction zone effluent is circulated to the second alkali metal treatment reaction zone; In step (2), the alkali metal is at least one of lithium, sodium, potassium, rubidium, cesium and francium; the mass ratio of the light fraction to the alkali metal in the first alkali metal treatment reaction zone is (2.0-15.0):100; In step (2), the process conditions of the first alkali metal treatment reaction zone are as follows: reaction temperature 150-300°C, reaction pressure 2.0-10.0 MPa, residence time 0.5-2.5 h, hydrogen to oil volume ratio 300-1500 Nm 3 / m 3 ; In step (3), the mass ratio of the alkali metal in the second alkali metal treatment reaction zone to the mass ratio of the alkali metal in the first alkali metal treatment reaction zone is (30-80):100; In step (3), compared with the first alkali metal treatment reaction zone, the reaction temperature of the second alkali metal treatment reaction zone is controlled to be 80-200°C higher, the reaction pressure is 2.0-10.0 MPa higher, the residence time is 0.5-2.0 h longer, and the hydrogen-to-oil volume ratio is 300-800 Nm 3 / m 3 .

2. The method according to claim 1, wherein: The coal tar raw material is fractionated and cut into light fraction and heavy fraction, and the cutting point is 240-280℃.

3. The method according to claim 1, wherein: The effluent from the first alkali metal treatment reaction zone is mixed with the heavy fraction, the fixed bed hydrogenation reaction effluent and the alkali metal again and then enters the second alkali metal treatment reaction zone.

4. The method according to claim 1, wherein: In step (1), the coal tar raw material is at least one of low-temperature coal tar, medium-temperature coal tar and high-temperature coal tar; the low-temperature coal tar has a distillation range of 50-450°C, the medium-temperature coal tar has a distillation range of 50-600°C, and the high-temperature coal tar has a distillation range of 50-650°C.

5. The method according to claim 1, wherein: In step (2), the alkali metal is at least one of sodium and potassium; the mass ratio of the light fraction to the alkali metal in the first alkali metal treatment reaction zone is (5.0-12.0):

100.

6. The method according to claim 1, wherein: In step (2), the first alkali metal treatment reaction zone is provided with at least one alkali metal treatment reactor, and the reactor is at least one of a tubular reactor, a kettle reactor and a jet reactor.

7. The method according to claim 6, characterized in that: The reactor is a tubular reactor.

8. The method according to claim 1, wherein: In step (2), the process conditions of the first alkali metal treatment reaction zone are as follows: reaction temperature 200-280°C, hydrogen partial pressure 5.0-10.0 MPa, residence time 0.5-1.5 h, hydrogen to oil volume ratio 500-1000 Nm 3 / m 3 .

9. The method according to claim 1, wherein: In step (3), the mass ratio of the alkali metal in the second alkali metal treatment reaction zone to that in the first alkali metal treatment reaction zone is (40-60):

100.

10. The method according to claim 1, wherein: In step (3), compared with the first alkali metal treatment reaction zone, the reaction temperature of the second alkali metal treatment reaction zone is controlled to be 100-150°C higher, the reaction pressure is 2.0-5.0 MPa higher, the residence time is 1.5-1.5 hours longer, and the hydrogen-to-oil volume ratio is 300-500 Nm 3 / m 3 .

11. The method according to claim 1, wherein: In step (4), the separation treatment is one or more of decantation separation, centrifugal separation, filtration separation and sedimentation separation.

12. The method according to claim 1, wherein: In step (5), the fixed bed hydrogenation reaction zone is provided with at least one fixed bed hydrogenation reactor, and the fixed bed hydrogenation reactor is filled with at least one hydrocracking catalyst.

13. The method according to claim 12, wherein: In step (5), the hydrocracking catalyst comprises a hydrogenation active metal component and a carrier; the carrier comprises Y or β-type molecular sieve and amorphous silica-alumina, and the hydrogenation active metal component comprises Group VIB metals molybdenum and / or tungsten and Group VIII metals cobalt and / or nickel; the content of the hydrogenation active metal component in terms of oxide is 10-30 wt.% based on the mass of the catalyst.

14. The method according to claim 1, wherein: In step (5), the process conditions of the fixed bed hydrogenation reaction zone are as follows: reaction temperature is 350-450°C, total reaction pressure is 10.0-20.0 MPa, liquid hourly volume space velocity is 0.1-0.5h -1 , the volume ratio of hydrogen to oil is 1000:1-2000:

1.

15. The method according to claim 14, characterized in that: In step (5), the process conditions of the fixed bed hydrogenation reaction zone are as follows: reaction temperature is 370-420 ° C, total reaction pressure is 12.0-18.0 MPa, liquid hourly volume space velocity is 0.15-0.4h -1 , the volume ratio of hydrogen to oil is 1200:1-1800:1.

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