A method and system for pretreatment and purification of coal tar

Abstract

The present invention provides a method and system for pre-treatment and purification of coal tar, the method comprising: adding a purifier to the coal tar and performing dehydration and desolidification treatment on the coal tar, performing solid-liquid separation on the dehydrated and desolidified coal tar and then performing fractionation and cutting to obtain tower top oil, side line oil and tower bottom coal tar; performing solvent extraction on the obtained tower bottom coal tar, performing solvent recovery treatment on the extraction phase to obtain solvent and deasphalted oil, the solvent is circulated to perform the solvent extraction, the deasphalted oil is mixed with the tower top oil and side line oil for hydrogenation treatment; performing asphalt stripping on the raffinate phase obtained by the solvent extraction, performing the solvent recovery on the obtained solvent and oil products, and extracting the deoiled asphalt obtained by the asphalt stripping as a product. The method can maximize the utilization rate of coal tar, and the purified coal tar directly enters the fixed bed hydrogenation reaction system, which is mature and stable, and the process and investment are much lower than those of hydrogenation reaction systems such as ebullating bed and slurry bed.

Description

Technical Field

[0001] The invention belongs to the field of coal tar processing and relates to a method and system for pre-processing and purifying coal tar. Background Art

[0002] Coal tar is a liquid product produced during the pyrolysis, dry distillation and gasification of coal. It is a dark brown viscous liquid at room temperature. The estimated components of coal tar are about 10,000, of which only about 500 have been separated and identified. They are mainly aromatic compounds, and most of them are polycyclic aromatic compounds with more than two rings. According to the production method and pyrolysis temperature, the following types of coal tar can be obtained: low-temperature coal tar (450-600℃), medium-low-temperature coal tar (600-800℃), medium-temperature coal tar (700-900℃), and high-temperature coal tar (900-1000℃).

[0003] Traditional coal tar hydrogenation is done by fixed bed hydrogenation. Since coal tar contains impurities such as water, metals, and asphaltene that affect the long-term operation of fixed bed hydrogenation catalysts, vacuum distillation is usually used to remove about 15-20% of coal tar pitch rich in metals and other impurities, and the remaining components enter the hydrogenation system, resulting in a low oil yield. Therefore, the core of coal tar hydrogenation is pretreatment, and after removing the impurities that affect fixed bed hydrogenation, as much of the fraction as possible enters the fixed bed reactor for hydrogenation reaction.

[0004] CN 110093176A discloses a method for purifying coal tar. The method comprises: extracting a de-powdering agent, the mass of which is 0.05% to 0.1% of the mass of the coal tar to be purified; mixing the de-powdering agent with the coal tar to be purified to form a coal tar mixture; conveying the coal tar mixture to a sedimentation tank; wherein the de-powdering agent is a compound that can accelerate the agglomeration, sedimentation and separation of solid impurities in the coal tar. The method of the present invention can be used to sediment and separate solid impurities in the coal tar. After 48h to 120h of sedimentation, the mechanical impurities in the coal tar can be reduced to 0.05%, and the removal rate of solid impurities can reach 90%. In the process of sedimentation and separation, a large amount of washing oil and dilution of the coal tar are not required.

[0005] CN 206646066 U discloses a coal tar purification system, comprising a first heater, an electric desalting device, a second heater, a fractionating tower, a cooler and a separation tank, wherein the first heater is used for heating the coal tar and then outputting it, the electric desalting device is connected to the first heater and is used for performing electric desalting treatment on the coal tar to obtain desalted coal tar and output it, the second heater is connected to the electric desalting device and is used for heating the desalted coal tar and then outputting it, the fractionating tower is connected to the second heater and is used for flash evaporation and dehydration treatment on the desalted coal tar to obtain desalted and dehydrated coal tar and oily wastewater and output them, the cooler is connected to the fractionating tower and is used for cooling the oily wastewater and then outputting it, and the separation tank is connected to the cooler and is used for separating the oily wastewater to obtain light oil and output it. Summary of the invention

[0006] In view of the technical problems existing in the prior art, the present invention provides a method and system for pretreatment and purification of coal tar, which can maximize the utilization rate of coal tar. The purified coal tar directly enters the fixed bed hydrogenation reaction system, which is mature and stable, and the process and investment are much lower than those of hydrogenation reaction systems such as boiling bed and slurry bed.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] One of the purposes of the present invention is to provide a method for pre-treatment and purification of coal tar, the method comprising the following steps:

[0009] (1) adding a purifier to coal tar and performing a dehydration and desolidification treatment on the coal tar, performing solid-liquid separation on the dehydrated and desolidified coal tar and then performing fractionation and cutting to obtain tower top oil, side line oil and tower bottom coal tar pitch;

[0010] (2) subjecting the bottom coal tar pitch obtained in step (1) to solvent extraction, subjecting the extract phase to solvent recovery treatment to obtain a solvent and deasphalted oil, wherein the solvent is circulated to perform the solvent extraction, and the deasphalted oil is mixed with the top oil and the sideline oil in step (1) to hydrogenation treatment;

[0011] (3) The raffinate phase obtained from the solvent extraction in step (2) is subjected to asphalt stripping, and the obtained solvent and oil product are subjected to the solvent recovery in step (2), and the deoiled asphalt obtained from the asphalt stripping is produced as a product.

[0012] In the present invention, the coal tar is desolidified and dehydrated, and then distilled and cut into tower top oil, side line oil and tower bottom coal tar. After the impurities such as metals in the coal tar that affect the fixed bed hydrogenation are removed by solvent extraction, the coal tar enters the fixed bed hydrogenation system together with the tower top oil and the side line oil. The metal content of the coal tar after pretreatment and purification is less than 20 ppm, and the yield reaches 95-97%, which meets the feed requirements of the fixed bed hydrogenation system and greatly improves the oil product yield.

[0013] In the present invention, the fractionation cutting is a common process in the art, and the specific fractionation conditions can be adjusted according to the ratio of each component to be cut, so they are no longer described in detail in the specification.

[0014] As a preferred technical solution of the present invention, the coal tar in step (1) includes any one of low-temperature coal tar, medium-low-temperature coal tar, medium-temperature coal tar, high-temperature coal tar, coal-based gasification oil or heavy oil, or a combination of at least two of them. Typical but non-limiting examples of the combination include: a combination of low-temperature coal tar and medium-low-temperature coal tar, a combination of medium-low-temperature coal tar and medium-temperature coal tar, a combination of medium-temperature coal tar and high-temperature coal tar, a combination of high-temperature coal tar and coal-based gasification oil, a combination of coal-based gasification oil and heavy oil, or a combination of low-temperature coal tar, medium-low-temperature coal tar, medium-temperature coal tar and high-temperature coal tar, etc.

[0015] Preferably, the amount of the purifier added in step (1) is 0.2-1wt% of the coal tar, such as 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt% or 0.9wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] Preferably, the purifier in step (1) comprises any one of ammonium sulfate, phosphate, polyphosphate or organic phosphoric acid, or a combination of at least two thereof, such as a combination of ammonium sulfate and phosphate, a combination of phosphate and polyphosphate, a combination of polyphosphate and organic phosphoric acid, a combination of organic phosphoric acid and ammonium sulfate, a combination of ammonium sulfate and polyphosphate, or a combination of ammonium sulfate, phosphate and polyphosphate, etc.

[0017] As a preferred technical solution of the present invention, the dehydration and desolidification method in step (1) comprises: removing water from the coal tar by flash evaporation, and removing solid impurities from the dehydrated coal tar by filtering.

[0018] Preferably, the flash evaporation temperature is 120-180°C, such as 130°C, 140°C, 150°C, 160°C or 170°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0019] As a preferred technical solution of the present invention, the coal tar pitch at the bottom of the tower in step (1) accounts for 10 to 25 wt% of the total distillation and cutting products, such as 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt% or 24 wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] As a preferred technical solution of the present invention, the solvent used for the solvent extraction in step (2) includes any one of cyclohexane, pentane, benzene, toluene, light oil fractions or mixed aromatics, or a combination of at least two of them. Typical but non-limiting examples of the combination include: a combination of cyclohexane and pentane, a combination of benzene and toluene, and a combination of toluene and light oil fractions.

[0021] Preferably, the volume ratio of the solvent to the coal tar pitch at the bottom of the tower in the solvent extraction of step (2) is (1-10):1, such as 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or 9:1, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably (2-4):1.

[0022] Preferably, the temperature of the solvent extraction in step (2) is 100-200° C. and the pressure is 0.1-2.0 MPaG.

[0023] Wherein, the temperature may be 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C or 190°C, etc., and the pressure may be 0.2MpaG, 0.5MpaG, 0.8MpaG, 1.0MpaG, 1.2MpaG, 1.5MpaG or 1.8MpaG, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical ranges are equally applicable.

[0024] Preferably, the temperature of the solvent extraction in step (2) is 150° C. and the pressure is 1.0 MPaG.

[0025] As a preferred technical solution of the present invention, the extraction rate of the solvent extraction in step (2) is 50-90%, such as 55%, 60%, 65%, 70%, 75%, 80% or 85%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] As a preferred technical solution of the present invention, the conditions for asphalt stripping in step (3) are a temperature of 250-280°C, such as 255°C, 260°C, 265°C, 270°C or 275°C, and a pressure of 0.1-0.3MpaG, such as 0.12MpaG, 0.15MpaG, 0.18MpaG, 0.20MpaG, 0.22MpaG, 0.25MpaG or 0.28MpaG, but are not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0027] As a preferred technical solution of the present invention, the method for pretreatment and purification of coal tar comprises the following steps:

[0028] (1) adding a purifier to coal tar and performing dehydration and desolidification treatment on the coal tar, wherein the amount of the purifier added is 0.2 to 1 wt% of the amount of coal tar, and the dehydrated and desolidified coal tar is subjected to solid-liquid separation and then fractionated and cut to obtain top oil, side line oil and bottom coal tar, wherein the bottom coal tar accounts for 10 to 25 wt% of the total product of the fractionation and cutting;

[0029] The dehydration and desolidification treatment method in step (1) comprises: flash evaporation to remove water from the coal tar, filtering the dehydrated coal tar to remove solid impurities, and the flash evaporation temperature is 120-180° C.

[0030] (2) subjecting the bottom coal tar pitch obtained in step (1) to solvent extraction, wherein the volume ratio of the solvent to the bottom coal tar pitch is (1-10):1, the temperature is 100-200° C., the pressure is 0.1-2.0 MPaG, the extraction phase is subjected to solvent recovery treatment to obtain solvent and deasphalted oil, the solvent is circulated to perform the solvent extraction, and the deasphalted oil is mixed with the top oil and the sideline oil in step (1) for hydrogenation treatment;

[0031] (3) The raffinate phase obtained from the solvent extraction in step (2) is subjected to asphalt stripping at a temperature of 250-280° C. and a pressure of 0.1-0.3 MPaG. The obtained solvent and oil product are subjected to the solvent recovery in step (2), and the deoiled asphalt obtained from the asphalt stripping is produced as a product.

[0032] The second object of the present invention is to provide a coal tar pretreatment purification system for use as described above, the system comprising a dehydration and desolidification device, a fractionation device, an extraction device and a stripping device connected in sequence, the extraction phase outlet of the extraction device and the light component outlet of the stripping device are independently connected to the raw material inlet of a solvent recovery device, and the solvent outlet of the solvent recovery device is connected to the extractant inlet of the extraction device.

[0033] Preferably, the dehydration and desolidification device comprises a flash evaporation device and a filtering device which are connected in sequence.

[0034] As a preferred technical solution of the present invention, the fractionation device is a fractionation tower, and the fractionation tower includes a top oil outlet, a side oil outlet, and a coal tar outlet, and the coal tar outlet is connected to the coal tar inlet of the extraction device;

[0035] Preferably, the raffinate phase outlet of the extraction device is connected to the raw material inlet of the stripping device;

[0036] Preferably, the injection pipeline of the purifier is connected to the pipeline between the fractionation device and the extraction device.

[0037] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0038] (1) The present invention provides a method for pre-treatment and purification of coal tar, wherein the metal content of the coal tar after pre-treatment and purification is less than 20 ppm, and the yield reaches 93-97%, which meets the feed requirements of the fixed bed hydrogenation system and greatly improves the oil yield;

[0039] (2) The present invention provides a method for pretreatment and purification of coal tar, which can maximize the utilization rate of coal tar. After purification, the coal tar directly enters the fixed bed hydrogenation reaction system, which is mature and stable, and the process and investment are much lower than those of hydrogenation reaction systems such as boiling bed and slurry bed. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a schematic structural diagram of a coal tar pretreatment purification system provided in Example 6 of the present invention;

[0041] In the figure: 1-dehydration and desolidification device, 11-flash evaporation device, 12-filtration device, 2-tar fractionation tower, 3-extraction tower, 4-asphalt stripping tower, 5-solvent recovery device.

[0042] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0044] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0045] Example 1

[0046] This embodiment provides a method for pre-treatment and purification of coal tar, and its process is as follows: Figure 1 As shown, the method comprises the following steps:

[0047] (1) adding 0.2 wt% of the total amount of coal tar to low-temperature coal tar as a purifier ammonium sulfate, flash distilling the low-temperature coal tar to remove moisture by 120° C., filtering the low-temperature coal tar after moisture removal to remove solid impurities, and fractionating and cutting the dehydrated and desolidified coal tar to obtain top oil, side line oil and bottom coal tar, wherein the bottom coal tar accounts for 10 wt% of the total product of the fractionation and cutting;

[0048] (2) subjecting the bottom coal tar pitch obtained in step (1) to solvent extraction, wherein the solvent is pentane, the volume ratio of the solvent to the bottom coal tar pitch is 1:1, the temperature is 200° C., the pressure is 2.0 MPaG, the extraction rate is 50%, the extraction phase is subjected to solvent recovery treatment to obtain solvent and deasphalted oil, the solvent is circulated to perform the solvent extraction, and the deasphalted oil is mixed with the top oil and the sideline oil in step (1) for hydrogenation treatment;

[0049] (3) The raffinate phase obtained from the solvent extraction in step (2) is subjected to asphalt stripping at a temperature of 250° C. and a pressure of 0.1 MPaG. The obtained solvent and oil product are subjected to the solvent recovery in step (2), and the deoiled asphalt obtained from the asphalt stripping is produced as a product.

[0050] The metal content of the coal tar after the above pretreatment and purification is 19.8 ppm, and the yield reaches 94.1%.

[0051] Example 2

[0052] This embodiment provides a method for pre-treatment and purification of coal tar, and its process is as follows: Figure 1 As shown, the method comprises the following steps:

[0053] (1) adding 1.0 wt% of the total amount of coal tar to the medium-low temperature coal tar as a purifier ammonium phosphate, flash distilling the coal tar to remove water by 180° C., filtering the dehydrated medium-low temperature coal tar to remove solid impurities, fractionating and cutting the dehydrated and desolidified coal tar to obtain top oil, side line oil and bottom coal tar, wherein the bottom coal tar accounts for 20 wt% of the total product of the fractionation and cutting;

[0054] (2) subjecting the bottom coal tar pitch obtained in step (1) to solvent extraction, wherein the solvent is cyclohexane, the volume ratio of the solvent to the bottom coal tar pitch is 5:1, the temperature is 120° C., the pressure is 1.5 MPaG, the extraction rate is 80%, the extraction phase is subjected to solvent recovery treatment to obtain solvent and deasphalted oil, the solvent is circulated to perform the solvent extraction, and the deasphalted oil is mixed with the top oil and the sideline oil in step (1) for hydrogenation treatment;

[0055] (3) The raffinate phase obtained from the solvent extraction in step (2) is subjected to asphalt stripping at a temperature of 280° C. and a pressure of 0.3 MPaG. The obtained solvent and oil product are subjected to solvent recovery in step (2), and the deoiled asphalt obtained from the asphalt stripping is produced as a product.

[0056] The metal content of the coal tar after the above pretreatment and purification is 18.2 ppm, and the yield reaches 94.5%.

[0057] Example 3

[0058] This embodiment provides a method for pre-treatment and purification of coal tar, and its process is as follows: Figure 1 As shown, the method comprises the following steps:

[0059] (1) adding 0.5 wt% of the total amount of coal tar into medium-temperature coal tar as a purifier ammonium polyphosphate, flash distilling the coal tar at 150° C. to remove water, filtering the dehydrated medium-temperature coal tar to remove solid impurities, fractionating and cutting the dehydrated and desolidified coal tar to obtain top oil, side line oil and bottom coal tar, wherein the bottom coal tar accounts for 15 wt% of the total product of the fractionation and cutting;

[0060] (2) subjecting the bottom coal tar pitch obtained in step (1) to solvent extraction, wherein the solvent is toluene, the volume ratio of the solvent to the bottom coal tar pitch is 5:1, the temperature is 150° C., the pressure is 1.0 MPaG, the extraction rate is 90%, and the extraction phase is subjected to solvent recovery treatment to obtain a solvent and deasphalted oil, the solvent is circulated to perform the solvent extraction, and the deasphalted oil is mixed with the top oil and the sideline oil in step (1) for hydrogenation treatment;

[0061] (3) The raffinate phase obtained from the solvent extraction in step (2) is subjected to asphalt stripping at a temperature of 260° C. and a pressure of 0.2 MPaG. The obtained solvent and oil product are subjected to solvent recovery in step (2), and the deoiled asphalt obtained from the asphalt stripping is produced as a product.

[0062] The metal content of the coal tar after the above pretreatment and purification is 18.0 ppm, and the yield reaches 95.2%.

[0063] Example 4

[0064] This embodiment provides a method for pre-treatment and purification of coal tar, and its process is as follows: Figure 1 As shown, the method comprises the following steps:

[0065] (1) adding 0.5 wt% of the total amount of coal tar to high-temperature coal tar as a purifier ammonium sulfate, flash distilling the coal tar at 150° C. to remove water, filtering the dehydrated high-temperature coal tar to remove solid impurities, fractionating and cutting the dehydrated coal tar to obtain top oil, side line oil and bottom coal tar, wherein the bottom coal tar accounts for 25 wt% of the total product of the fractionation and cutting;

[0066] (2) subjecting the bottom coal tar pitch obtained in step (1) to solvent extraction, wherein the solvent is benzene, the volume ratio of the solvent to the bottom coal tar pitch is 10:1, the temperature is 100° C., the pressure is 0.1 MPaG, the extraction rate is 75%, the extraction phase is subjected to solvent recovery treatment to obtain solvent and deasphalted oil, the solvent is circulated to perform the solvent extraction, and the deasphalted oil is mixed with the top oil and the sideline oil in step (1) for hydrogenation treatment;

[0067] (3) The raffinate phase obtained from the solvent extraction in step (2) is subjected to asphalt stripping at a temperature of 270° C. and a pressure of 0.25 MPaG. The obtained solvent and oil product are subjected to the solvent recovery in step (2), and the deoiled asphalt obtained from the asphalt stripping is produced as a product.

[0068] The metal content of the coal tar after the above pretreatment and purification is 17.0 ppm, and the yield reaches 94.8%.

[0069] Example 5

[0070] This embodiment provides a method for pre-treatment and purification of coal tar, and its process is as follows: Figure 1 As shown, the method comprises the following steps:

[0071] (1) adding 0.5 wt% of the total amount of heavy oil to the purifier ammonium sulfate, and flash distilling the heavy oil to remove water by 150° C., filtering the dehydrated heavy oil to remove solid impurities, and fractionating and cutting the dehydrated and desolidified heavy oil to obtain top oil, side line oil and bottom coal tar pitch, wherein the bottom coal tar pitch accounts for 20 wt% of the total products of the fractionation and cutting;

[0072] (2) adding ammonium sulfate, a purifying agent, which accounts for 0.5 wt% of the total amount of coal tar, to the bottom coal tar obtained in step (1), and performing solvent extraction after mixing, wherein the solvent is benzene, the volume ratio of the solvent to the bottom coal tar is 8:1, the temperature is 180° C., the pressure is 1.8 MPaG, the extraction rate is 80%, and the extraction phase is subjected to solvent recovery treatment to obtain a solvent and deasphalted oil, the solvent is circulated for the solvent extraction, and the deasphalted oil is mixed with the top oil and the sideline oil in step (1) for hydrogenation treatment;

[0073] (3) The raffinate phase obtained from the solvent extraction in step (2) is subjected to asphalt stripping at a temperature of 250° C. and a pressure of 0.2 MPaG. The obtained solvent and oil product are subjected to the solvent recovery in step (2), and the deoiled asphalt obtained from the asphalt stripping is produced as a product.

[0074] The metal content of the coal tar after the above pretreatment and purification is 20.0 ppm, and the yield reaches 94.5%.

[0075] Example 6

[0076] This embodiment provides a coal tar pretreatment purification system used in the methods described in embodiments 1-5, and its structure is as follows: Figure 1 As shown, the system comprises:

[0077] A dehydration and desolidification device 1, a tar fractionation tower 2, an extraction tower 3 and an asphalt stripping tower 4 are connected in sequence, the extraction phase outlet of the extraction tower 3 and the light component outlet of the asphalt stripping tower 4 are independently connected to the raw material inlet of the solvent recovery device 5, and the solvent outlet of the solvent recovery device 5 is connected to the extractant inlet of the extraction tower 3;

[0078] The dehydration and desolidification device 1 comprises a flash evaporation device 11 and a filtering device 12 connected in sequence;

[0079] The tar fractionation tower 2 includes a top oil outlet, a side oil outlet and a coal tar outlet, and the coal tar outlet is connected to the coal tar inlet of the extraction tower 3; the raffinate phase outlet of the extraction tower 3 is connected to the raw material inlet of the asphalt stripping tower 4; the injection pipeline of the purifier is connected to the pipeline between the tar fractionation tower 2 and the extraction tower 3.

[0080] The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0081] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0082] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0083] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for pretreatment and purification of coal tar, characterized in that: The method comprises the following steps: (1) adding a purifier to coal tar and performing dehydration and desolidification treatment on the coal tar, performing solid-liquid separation on the dehydrated and desolidified coal tar and then performing fractionation and cutting to obtain tower top oil, side line oil and tower bottom coal tar pitch; (2) subjecting the bottom coal tar pitch obtained in step (1) to solvent extraction, subjecting the extract phase to solvent recovery treatment to obtain solvent and deasphalted oil, wherein the solvent is circulated to perform the solvent extraction, and the deasphalted oil is mixed with the top oil and sideline oil in step (1) to hydrogenation treatment; (3) The raffinate phase obtained by the solvent extraction in step (2) is subjected to asphalt stripping, the obtained solvent and oil product are subjected to the solvent recovery in step (2), and the deoiled asphalt obtained by the asphalt stripping is produced as a product; The dehydration and desolidification treatment method in step (1) comprises: removing water from the coal tar by flash evaporation, and removing solid impurities from the dehydrated coal tar by filtering; the temperature of the solvent extraction in step (2) is 100-200°C and the pressure is 0.1-2.0 MpaG; The purifier in step (1) includes any one of ammonium sulfate, phosphate or organic phosphoric acid, or a combination of at least two thereof; The flash evaporation temperature is 120-180°C.

2. The method according to claim 1, characterized in that The coal tar in step (1) includes any one of low-temperature coal tar, medium-low-temperature coal tar, medium-temperature coal tar, or high-temperature coal tar, or a combination of at least two of them.

3. The method according to claim 1, characterized in that The amount of the purifier added in step (1) is 0.2-1 wt% of the coal tar.

4. The method according to claim 1, characterized in that: The phosphates include polyphosphates.

5. The method according to claim 1, characterized in that: The coal tar pitch at the bottom of the tower in step (1) accounts for 10-25 wt% of the total fractionation and cutting products.

6. The method according to claim 1, characterized in that The solvent used for the solvent extraction in step (2) includes any one of cyclohexane, pentane, benzene, toluene, light oil fractions or mixed aromatics, or a combination of at least two of them.

7. The method according to claim 1, characterized in that The volume ratio of the solvent in the solvent extraction of step (2) to the coal tar pitch at the bottom of the tower is (1-10):

1.

8. The method according to claim 1, characterized in that The volume ratio of the solvent in the solvent extraction of step (2) to the coal tar pitch at the bottom of the tower is (2-4):

1.

9. The method according to claim 1, characterized in that: The temperature of the solvent extraction in step (2) is 150° C. and the pressure is 1.0 MpaG.

10. The method according to claim 1, characterized in that The extraction rate of the solvent extraction in step (2) is 50-90%.

11. The method according to claim 1, characterized in that: The temperature of the asphalt stripping in step (3) is 250-280°C and the pressure is 0.1-0.3 MPaG.

12. The method according to claim 1, characterized in that The method comprises the following steps: (1) adding a purifier to coal tar and performing dehydration and desolidification treatment on the coal tar, wherein the amount of the purifier added is 0.2-1 wt% of the amount of coal tar, and the coal tar after dehydration and desolidification is subjected to solid-liquid separation and then fractionated and cut to obtain top oil, side line oil and bottom coal tar, wherein the bottom coal tar accounts for 10-25 wt% of the total product of the fractionation and cutting; The dehydration and desolidification treatment method in step (1) comprises: flash evaporating the coal tar to remove water, filtering the dehydrated coal tar to remove solid impurities, and the flash evaporation temperature is 120-180°C; (2) subjecting the bottom coal tar pitch obtained in step (1) to solvent extraction, wherein the volume ratio of the solvent to the bottom coal tar pitch is (1-10):1, the temperature is 100-200° C., the pressure is 0.1-2.0 MPaG, the extraction phase is subjected to solvent recovery treatment to obtain solvent and deasphalted oil, the solvent is circulated to perform the solvent extraction, and the deasphalted oil is mixed with the top oil and the sideline oil in step (1) for hydrogenation treatment; (3) The raffinate phase obtained by the solvent extraction in step (2) is subjected to asphalt stripping, the temperature of the asphalt stripping is 250-280°C, and the pressure is 0.1-0.3 MPaG. The obtained solvent and oil product are subjected to the solvent recovery in step (2), and the deoiled asphalt obtained by the asphalt stripping is produced as a product.

13. The method according to any one of claims 1 to 12, characterized in that: The method is carried out by using a coal tar pretreatment purification system, which includes a dehydration and desolidification device, a fractionation device, an extraction device and a stripping device connected in sequence, wherein the extraction phase outlet of the extraction device and the light component outlet of the stripping device are independently connected to the raw material inlet of a solvent recovery device, and the solvent outlet of the solvent recovery device is connected to the extractant inlet of the extraction device.

14. The method according to claim 13, characterized in that The dehydration and desolidification device comprises a flash evaporation device and a filtering device which are connected in sequence.

15. The method according to claim 13, characterized in that The fractionation device is a fractionation tower, which comprises a top oil outlet, a side oil outlet and a coal tar outlet, and the coal tar outlet is connected to the coal tar inlet of the extraction device.

16. The method according to claim 13, characterized in that The raffinate phase outlet of the extraction device is connected to the raw material inlet of the stripping device.

17. The method according to claim 13, characterized in that The injection pipeline of the purifier is connected to the pipeline between the fractionation device and the extraction device.

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