Coal tar deep processing technology of anthracene oil premixing back blending coupled with double-column negative pressure rectification

Abstract

The application discloses a coal tar deep processing technology of anthracene oil premixing back blending coupled with double-tower negative pressure rectification, which comprises the following steps: mixing coal tar and anthracene oil according to a proportion, heating and feeding into a dehydration tower for treatment, collecting anhydrous coal tar at the bottom of the dehydration tower, heating and feeding into a fraction tower for treatment, feeding soft pitch at the bottom of the fraction tower into an anthracene tower for negative pressure distillation, heating and feeding the distillate at the top of the anthracene tower into a heat exchanger to obtain anthracene oil, using part of the anthracene oil to mix with the coal tar, and first exchanging heat between the medium-temperature pitch at the bottom of the anthracene tower and the soft pitch at the bottom of the fraction tower, and then feeding the medium-temperature pitch into a heating furnace for heating and returning to the bottom of the anthracene tower. The anthracene oil homologues are premixed back to realize modification at the molecular level of raw materials, anthracene and carbazole are precisely enriched in stages by combining with double-tower gradient negative pressure rectification, and finally high-quality anthracene oil products are stably produced. Meanwhile, the gasification endothermic effect of the anthracene oil is used to reduce the outlet temperature of the heating furnace, coking of the furnace tube is inhibited from the root, and energy saving and consumption reduction are realized by connecting multiple levels of waste heat gradient recovery.

Description

Technical Field

[0001] This invention belongs to the field of coal tar deep processing technology, specifically relating to a coal tar deep processing process using anthracene oil premixing and remixing coupled with dual-tower negative pressure distillation. Background Technology

[0002] High-temperature coal tar is an important byproduct of the coking industry and a core source for the industrial extraction of high-value-added fine chemical raw materials such as anthracene and carbazole. The component purity and quality stability of anthracene oil directly determine the resource utilization rate and industrial economic benefits of deep coal tar processing. Existing traditional coal tar distillation processes for anthracene oil production have long suffered from problems such as easy coking of furnace tubes, high energy consumption, low enrichment efficiency of target components, and large fluctuations in product quality, severely restricting the long-term stable operation of production facilities and the mass production of high-end products.

[0003] In conventional coal tar distillation processes, to meet the heating requirements of the entire system, the outlet temperature of the process heater must be continuously maintained above 360℃. However, the heavy asphaltenes and gums in the tar system are prone to thermal condensation and polymerization reactions within the high-temperature furnace tubes, continuously forming a dense coking layer on the inner wall of the furnace tubes. Coking reduces the cross-sectional area of ​​the furnace tubes and causes a continuous increase in the system's operating pressure differential. Industrial plants typically require shutdown for coking removal every 3-4 months, severely disrupting production continuity. Furthermore, the coking layer leads to uneven heat conduction and localized overheating in the furnace body, easily causing safety accidents such as furnace tube burn-through and media leakage, resulting in high equipment maintenance costs and safety risks. To suppress coking, existing technologies mainly employ two approaches: one is to reduce the outlet temperature of the heating furnace. However, limited by the rigid requirements of the entire system's distillation heat load, simply lowering the temperature leads to insufficient heating at the bottom of the column and a decrease in fraction cutting accuracy, making it difficult to achieve both simultaneously. The other approach is to inject steam or softened water into the furnace tubes to increase the flow rate and dilute heavy components. However, this method introduces additional moisture and gas phase load, significantly increasing the energy consumption of subsequent dehydration and condensation systems, and has no substantial destructive effect on the already formed molecular association structure, resulting in limited anti-coking effectiveness. Therefore, how to reduce the thermal intensity of the furnace tubes by addressing the heating method itself without sacrificing distillation separation accuracy remains a long-standing and unresolved technical challenge in this field.

[0004] In raw coal tar, anthracene and carbazole naturally exhibit low concentrations and dispersed components. Furthermore, the presence of numerous heavy asphaltic and pectin macromolecules within the system creates a strong molecular association and encapsulation effect on anthracene and carbazole aromatic molecules. Traditional distillation processes lack effective means to break this molecular bondage. During distillation, anthracene and carbazole are easily carried away with lighter components such as naphthalene and wash oil, or remain trapped with heavy asphaltic components, resulting in extremely low enrichment rates of the target components and significant waste of refined resources. Simultaneously, traditional processes employ a single centralized heating furnace without a multi-stage waste heat recovery system, resulting in an overall waste heat recovery rate of less than 30%. Fuel costs account for over 40% of the total processing cost per ton of product, leading to substantial energy consumption. Moreover, due to fluctuations in raw material composition, severe component loss, and insufficient fraction cutting precision, the batch purity of anthracene oil produced by traditional processes varies significantly, failing to consistently meet the quality standards of high-tech products. Summary of the Invention

[0005] To address the aforementioned shortcomings, this invention discloses a coal tar deep processing technology based on anthracene oil premixing and remixing coupled with dual-tower negative pressure distillation. This process achieves molecular-level modification of the raw materials through anthracene oil homologue premixing and remixing, and combines this with dual-tower gradient negative pressure distillation to achieve precise enrichment of anthracene and carbazole at each stage, ultimately producing a stable high-quality anthracene oil product. Simultaneously, it utilizes the gasification endothermic effect of the remixed anthracene oil in the heating furnace to construct an in-furnace self-cooling mechanism. While ensuring heating at the bottom of the tower, the furnace outlet temperature is reduced to 345–355°C, fundamentally inhibiting coking in the furnace tubes. Furthermore, a multi-stage waste heat recovery system throughout the entire process achieves energy conservation and consumption reduction.

[0006] This invention is achieved using the following technical solution: A deep processing technology for coal tar using anthracene oil premixing and coupled dual-tower negative pressure distillation includes the following steps: (1) Coal tar and anthracene oil are fed into a pipeline static mixer and mixed evenly to obtain a mixture. The mass ratio of coal tar to anthracene oil is 20:(1-5). The mixture is heated to 160-180°C and then sent to a dehydration tower for treatment. (2) A portion of the anhydrous tar from the bottom of the dehydration tower is heated to 200-220°C by an anthracene oil tar heat exchanger and then sent to the distillation tower for processing. At the same time, a portion of the anhydrous tar is heated to 190-210°C by a vapor phase heat exchanger at the top of the anthracene tower and then returned to the bottom of the dehydration tower. (3) The absolute pressure inside the distillation tower is controlled at 20-30 kPa, and the temperature at the bottom of the distillation tower is controlled at 315-330℃. The distillate produced at the top of the distillation tower is heated by the gas phase heat exchanger at the top of the distillation tower and the mixture in step (1) to obtain a three-mixed oil containing naphthalene oil, wash oil and phenol oil. A portion of the soft asphalt at the bottom of the distillation tower is heated to 320-340℃ by the medium temperature asphalt heat exchanger and then refluxed to the bottom of the distillation tower. At the same time, a portion of the soft asphalt is sent to the anthracene tower for negative pressure distillation. (4) The absolute pressure inside the anthracene tower is controlled at 10-20 kPa, and the temperature at the top of the anthracene tower is controlled at 260-280℃. The distillate produced at the top of the anthracene tower is heated by the gas phase heat exchanger at the top of the anthracene tower, and then heated by the anthracene oil tar heat exchanger to obtain liquid anthracene oil. The anthracene oil is divided into two paths. The first path is cooled by the anthracene oil finished product cooler and then sent to the finished product storage tank for storage. The second path is sent to the pipeline static mixer in step (1) to mix with coal tar. The medium-temperature asphalt extracted from the bottom of the anthracene tower is divided into two paths. The first path is sent to the modified asphalt production process. The second path is heated by the medium-temperature asphalt heat exchanger and the soft asphalt in step (3), and then returned to the bottom of the anthracene tower after being heated by the heating furnace. The outlet temperature of the heating furnace is 345-355℃.

[0007] This invention constructs a self-cooling mechanism in the heating furnace by reprocessing anthracene oil, thereby inhibiting coking in the furnace tubes from the source. The specific mechanism is as follows: First, this invention reprocesses anthracene oil into the raw coal tar in a certain proportion, so that 8% to 12% of the excess anthracene oil component is stably retained in the medium-temperature pitch discharged from the bottom of the anthracene tower. This is equivalent to continuously introducing a batch of low-boiling-point components that can undergo phase change in the furnace into the circulating heating medium, providing a material basis for subsequent gasification endothermic reaction. This portion of anthracene oil is not an external diluent or inert medium, but rather the target product of this process itself. It does not introduce any additional impurities and will not increase the subsequent separation load.

[0008] Secondly, the circulating medium-temperature asphalt is cooled by exchanging heat with the soft asphalt at the bottom of the distillation tower through a medium-temperature asphalt heat exchanger before entering the heating furnace. This allows the material to enter the furnace tube at a lower temperature, extending its heating journey in the furnace. This ensures that the vaporization zone of the low-boiling-point components in the surplus anthracene oil fully overlaps with the overall heating zone of the material, and the heat absorption process and heating process are well matched, preventing the material from contacting the high-temperature wall surface and overheating instantly in the early stage of entering the furnace.

[0009] Thirdly, within the heating section of the furnace tube, the low-boiling-point components in the surplus anthracene oil preferentially undergo phase change vaporization, absorbing a large amount of latent heat of vaporization. This forms a continuous internal heat absorption buffer inside the furnace tube. Compared to the traditional process that relies solely on external adjustment of combustion intensity to control temperature, the heat absorption of this invention occurs inside the heated material. This directly suppresses the rate of temperature rise of the furnace tube wall and eliminates local hot spots, keeping the wall temperature always below the critical coking temperature. This fundamentally inhibits the thermal condensation, polymerization, and coking reactions of asphaltene and resin from the perspective of heat transfer.

[0010] Fourth, supported by the aforementioned internal heat absorption buffer, the heating furnace can meet the heat load requirements of the anthracene tower bottom without increasing the combustion intensity, and the outlet temperature can be stably controlled within the range of 345-355℃, which is 5-15℃ lower than the outlet temperature of over 360℃ in traditional processes. Since the thermal condensation rate of asphaltene increases exponentially with increasing temperature, the downward shift of this temperature range significantly reduces the coking reaction rate, completely avoiding the critical temperature range of thermal condensation coking of heavy components, eliminating coking in the furnace tubes from the root, greatly extending the continuous operation cycle of the unit, reducing the frequency of shutdown for coking and the resulting operation and maintenance costs and safety risks.

[0011] Fifth, the mild, low-temperature heating environment can effectively prevent the anthracene and carbazole aromatic components from undergoing high-temperature cracking and polymerization, and retain the effective components after enrichment by the double tower to the greatest extent. While preventing coking, it can simultaneously ensure the purity of anthracene oil products, so that the two goals of preventing coking and improving quality can be achieved synergistically under the same process.

[0012] Furthermore, the temperature at the top of the dehydration tower in step (2) is controlled at 85-95°C.

[0013] Furthermore, the distillate produced at the top of the dehydration tower in step (2) is condensed and cooled to extract light oil and phenol water.

[0014] Furthermore, the temperature at the top of the distillation column in step (3) is controlled at 185–195°C.

[0015] Furthermore, in step (4), the bottom of the anthracene tower produces medium-temperature pitch with an anthracene oil mass fraction of 8% to 12%.

[0016] Compared with existing technologies, this technical solution has the following advantages: 1. This invention utilizes the compatibility and permeability characteristics of anthracene oil homologues to effectively disrupt the binding and association of heavy gums and asphaltenes in primary tar with anthracene and carbazole molecules, significantly improving the activity and relative volatility of anthracene and carbazole components, reducing the mass transfer resistance of distillation, and solving the problem of easy loss and difficulty in enrichment of target components from the source, which is conducive to subsequent efficient distillation enrichment.

[0017] 2. This invention sets up a dehydration tower to thoroughly remove free water, light oil and gas and other low-boiling impurities from the raw materials through distillation, eliminating the adverse effects of impurities on distillation accuracy and furnace operation. At the same time, a closed-loop heat exchange circuit is set up in the dehydration tower. The anhydrous tar circulating at the bottom of the tower is heated by recovering the latent heat of vaporization of an anthracene oil vapor phase through the vapor phase heat exchanger at the top of the anthracene tower and then returned to the bottom of the dehydration tower, accurately replenishing the heat load in the tower and reducing the input of external heat sources.

[0018] 3. The distillation column of this invention adopts a negative pressure distillation mode to achieve precise fractionation. The top of the distillation column yields a three-phase mixture containing naphthalene oil, wash oil, and phenol oil. All of its latent heat of vaporization is recovered and used for preheating the coal tar and anthracene oil mixture, achieving closed-loop utilization of waste heat. Simultaneously, due to the better separation characteristics of the coal tar and anthracene oil mixture, it precisely separates light and heavy fractions within the distillation column, effectively retaining the target components of anthracene and carbazole, avoiding component loss caused by light component entrainment and heavy component sedimentation, and achieving preliminary and efficient enrichment of anthracene and carbazole components.

[0019] 4. The anthracene column of this invention employs a lower internal pressure than the fractionation column, forming a gradient negative pressure distillation system that matches the fractionation column, further reducing the distillation temperature and improving the accuracy of component separation. High-purity anthracene oil vapor is collected from the top of the anthracene column, and its latent heat can be recovered for heat exchange in the dehydration column system. The anthracene tower consistently produces medium-temperature pitch with an anthracene oil content of 8%–12% at the bottom. A portion of this pitch is first cooled through heat exchange before being fed into a heating furnace. Utilizing the endothermic properties of the abundant anthracene oil components in the pitch as they rapidly vaporize within the furnace, the pitch continuously absorbs heat, ensuring a stable temperature rise and facilitating control of the furnace outlet temperature within the range of 345–355°C. This temperature range completely avoids the critical temperature for thermal condensation and coking of heavy components, preventing coking in the furnace tubes at its source. Finally, the vaporized material is returned to the anthracene tower along with the medium-temperature pitch. Simultaneously, the mild, low-temperature heating environment effectively prevents high-temperature cracking, polymerization, and deterioration of anthracene and carbazole aromatic components, maximizing the retention of the enriched effective components and ensuring product purity. Furthermore, the heated medium-temperature pitch is recycled back to the bottom of the anthracene tower, providing a stable heat source for deep distillation.

[0020] 5. This invention simultaneously couples the latent heat of the three-phase mixed oil vapor phase, the sensible heat of the anthracene oil product, and the waste heat of medium-temperature asphalt, achieving multi-stage cascade recovery. This completely changes the traditional single-furnace heating mode, significantly improving the system's waste heat utilization rate, drastically reducing fuel energy costs, and making the process suitable for large-scale industrial continuous production conditions. It is both economical and environmentally friendly. The resulting anthracene oil product has a total mass content of anthracene and carbazole ≥25.5%, with small batch-to-batch quality fluctuations and stable purity meeting standards. This completely solves the defects of traditional processes, such as low effective component content and large batch-to-batch differences, significantly improving the added value of fine chemical products and the resource utilization rate of coal tar. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the coal tar deep processing technology of anthracene oil premixing and coupling dual-tower negative pressure distillation as described in this invention. Detailed Implementation

[0022] The present invention is further illustrated by the following examples, but these are not intended to limit the invention. Specific experimental conditions and methods not specified in the following examples are generally conventional methods well known to those skilled in the art.

[0023] Example 1: A deep processing technology for coal tar using anthracene oil premixed remixing coupled with dual-tower negative pressure distillation, comprising the following steps: (1) Coal tar and anthracene oil are fed into a pipeline static mixer and mixed evenly to obtain a mixture. The mass ratio of coal tar to anthracene oil is 20:4. The mixture is heated to 170°C and then sent to a dehydration tower for treatment. (2) A portion of the anhydrous tar collected from the bottom of the dehydration tower is heated to 210°C by an anthracene oil tar heat exchanger and then sent to the distillation tower for processing. At the same time, a portion of the anhydrous tar collected is heated to 205°C by a vapor phase heat exchanger at the top of the anthracene tower and then returned to the bottom of the dehydration tower. The temperature at the top of the dehydration tower is controlled at 88°C. The distillate produced at the top of the dehydration tower is condensed and cooled to extract light oil and phenol water. (3) The absolute pressure inside the distillation tower is controlled at 25 kPa, and the bottom temperature of the distillation tower is controlled at 318°C and the top temperature of the distillation tower is controlled at 190°C. The distillate produced at the top of the distillation tower is heated by the gas phase heat exchanger at the top of the distillation tower and the mixture in step (1) to obtain a three-mixed oil containing naphthalene oil, wash oil and phenol oil. A portion of the soft asphalt at the bottom of the distillation tower is heated to 325°C by the medium temperature asphalt heat exchanger and then refluxed to the bottom of the distillation tower. At the same time, a portion of the soft asphalt is sent to the anthracene tower for negative pressure distillation. (4) The absolute pressure inside the anthracene tower is controlled at 15 kPa, and the temperature at the top of the anthracene tower is controlled at 270°C. The distillate produced at the top of the anthracene tower is heated by the gas phase heat exchanger at the top of the anthracene tower, and then heated by the anthracene oil tar heat exchanger to obtain liquid anthracene oil. The anthracene oil is divided into two paths. The first path is cooled by the anthracene oil finished product cooler and then sent to the finished product storage tank for storage. The second path is sent to the pipeline static mixer in step (1) to be mixed with coal tar. The medium-temperature asphalt extracted from the bottom of the anthracene tower is divided into two paths. The first path is sent to the modified asphalt production process. The second path is heated by the medium-temperature asphalt heat exchanger and the soft asphalt in step (3), and then returned to the bottom of the anthracene tower after being heated by the heating furnace. The outlet temperature of the heating furnace is 350°C. The mass fraction of anthracene oil in the medium-temperature asphalt is 10.2%.

[0024] Example 2: A deep processing technology for coal tar using anthracene oil premixed remixing coupled with dual-tower negative pressure distillation, comprising the following steps: (1) Coal tar and anthracene oil are fed into a pipeline static mixer and mixed evenly to obtain a mixture. The mass ratio of coal tar to anthracene oil is 20:1. The mixture is heated to 160°C and then sent to a dehydration tower for treatment. (2) A portion of the anhydrous tar collected from the bottom of the dehydration tower is heated to 200°C by an anthracene oil tar heat exchanger and then sent to the distillation tower for processing. At the same time, a portion of the anhydrous tar collected is heated to 190°C by a vapor phase heat exchanger at the top of the anthracene tower and then returned to the bottom of the dehydration tower. The temperature at the top of the dehydration tower is controlled at 85°C. The distillate produced at the top of the dehydration tower is condensed and cooled to extract light oil and phenol water. (3) The absolute pressure inside the distillation tower is controlled at 20 kPa, and the bottom temperature of the distillation tower is controlled at 315°C and the top temperature of the distillation tower is controlled at 185°C. The distillate produced at the top of the distillation tower is heated by the gas phase heat exchanger at the top of the distillation tower and the mixture in step (1) to obtain a three-mixed oil containing naphthalene oil, wash oil and phenol oil. A portion of the soft asphalt at the bottom of the distillation tower is heated to 320°C by the medium temperature asphalt heat exchanger and then refluxed to the bottom of the distillation tower. At the same time, a portion of the soft asphalt is sent to the anthracene tower for negative pressure distillation. (4) The absolute pressure inside the anthracene tower is controlled at 10 kPa, and the temperature at the top of the anthracene tower is controlled at 260°C. The distillate produced at the top of the anthracene tower is heated by the gas phase heat exchanger at the top of the anthracene tower to obtain anthracene oil, and then heated by the anthracene oil tar heat exchanger to obtain liquid anthracene oil. The anthracene oil is divided into two paths. The first path is cooled by the anthracene oil finished product cooler and then sent to the finished product storage tank for storage. The second path is sent to the pipeline static mixer in step (1) to mix with coal tar. The medium-temperature asphalt extracted from the bottom of the anthracene tower is divided into two paths. The first path is sent to the modified asphalt production process. The second path is heated by the medium-temperature asphalt heat exchanger and then returned to the bottom of the anthracene tower after being heated by the heating furnace. The outlet temperature of the heating furnace is 345°C. The mass fraction of anthracene oil in the medium-temperature asphalt is 8.4%.

[0025] Example 3: A deep processing technology for coal tar using anthracene oil premixed remixing coupled with dual-tower negative pressure distillation, comprising the following steps: (1) Coal tar and anthracene oil are fed into a pipeline static mixer and mixed evenly to obtain a mixture. The mass ratio of coal tar to anthracene oil is 20:3. The mixture is heated to 175°C and then sent to a dehydration tower for treatment. (2) A portion of the anhydrous tar collected from the bottom of the dehydration tower is heated to 215°C by an anthracene oil tar heat exchanger and then sent to the distillation tower for processing. At the same time, a portion of the anhydrous tar collected is heated to 205°C by a vapor phase heat exchanger at the top of the anthracene tower and then returned to the bottom of the dehydration tower. The temperature at the top of the dehydration tower is controlled at 86°C. The distillate produced at the top of the dehydration tower is condensed and cooled to extract light oil and phenol water. (3) The absolute pressure inside the distillation tower is controlled at 28 kPa, and the bottom temperature of the distillation tower is controlled at 325°C and the top temperature of the distillation tower is controlled at 193°C. The distillate produced at the top of the distillation tower is heated by the gas phase heat exchanger at the top of the distillation tower and the mixture in step (1) to obtain a three-mixed oil containing naphthalene oil, wash oil and phenol oil. A portion of the soft asphalt at the bottom of the distillation tower is heated to 335°C by the medium temperature asphalt heat exchanger and then refluxed to the bottom of the distillation tower. At the same time, a portion of the soft asphalt is sent to the anthracene tower for negative pressure distillation. (4) The absolute pressure inside the anthracene tower is controlled at 12 kPa, and the temperature at the top of the anthracene tower is controlled at 275°C. The distillate produced at the top of the anthracene tower is heated by the gas phase heat exchanger at the top of the anthracene tower to obtain anthracene oil, and then heated by the anthracene oil tar heat exchanger to obtain liquid anthracene oil. The anthracene oil is divided into two paths. The first path is cooled by the anthracene oil finished product cooler and then sent to the finished product storage tank for storage. The second path is sent to the pipeline static mixer in step (1) to mix with coal tar. The medium-temperature asphalt extracted from the bottom of the anthracene tower is divided into two paths. The first path is sent to the modified asphalt production process. The second path is heated by the medium-temperature asphalt heat exchanger and then returned to the bottom of the anthracene tower after being heated by the heating furnace. The outlet temperature of the heating furnace is 350°C. The mass fraction of anthracene oil in the medium-temperature asphalt is 10.8%.

[0026] Example 4: A deep processing technology for coal tar using anthracene oil premixed remixing coupled with dual-tower negative pressure distillation, comprising the following steps: (1) Coal tar and anthracene oil are fed into a pipeline static mixer and mixed evenly to obtain a mixture. The mass ratio of coal tar to anthracene oil is 20:5. The mixture is heated to 180°C and then sent to a dehydration tower for treatment. (2) A portion of the anhydrous tar collected from the bottom of the dehydration tower is heated to 220°C by an anthracene oil tar heat exchanger and then sent to the distillation tower for processing. At the same time, a portion of the anhydrous tar collected from the bottom of the dehydration tower is heated to 210°C by a vapor phase heat exchanger at the top of the anthracene tower and then returned to the bottom of the dehydration tower. The temperature at the top of the dehydration tower is controlled at 95°C. The distillate produced at the top of the dehydration tower is condensed and cooled to extract light oil and phenol water. (3) The absolute pressure inside the distillation tower is controlled at 30 kPa, and the bottom temperature of the distillation tower is controlled at 330°C and the top temperature of the distillation tower is controlled at 195°C. The distillate produced at the top of the distillation tower is heated by the gas phase heat exchanger at the top of the distillation tower and the mixture in step (1) to obtain a three-mixed oil containing naphthalene oil, wash oil and phenol oil. A portion of the soft asphalt at the bottom of the distillation tower is heated to 340°C by the medium temperature asphalt heat exchanger and then refluxed to the bottom of the distillation tower. At the same time, a portion of the soft asphalt is sent to the anthracene tower for negative pressure distillation. (4) The absolute pressure inside the anthracene tower is controlled at 20 kPa, and the temperature at the top of the anthracene tower is controlled at 280°C. The distillate produced at the top of the anthracene tower is heated by the gas phase heat exchanger at the top of the anthracene tower to obtain anthracene oil, and then heated by the anthracene oil tar heat exchanger to obtain liquid anthracene oil. The anthracene oil is divided into two paths. The first path is cooled by the anthracene oil finished product cooler and then sent to the finished product storage tank for storage. The second path is sent to the pipeline static mixer in step (1) to mix with coal tar. The medium-temperature asphalt extracted from the bottom of the anthracene tower is divided into two paths. The first path is sent to the modified asphalt production process. The second path is heated by the medium-temperature asphalt heat exchanger and then returned to the bottom of the anthracene tower after being heated by the heating furnace. The outlet temperature of the heating furnace is 355°C. The mass fraction of anthracene oil in the medium-temperature asphalt is 9.2%.

[0027] Comparative Example 1: The difference between the coal tar deep processing technology described in this comparative example and the process described in Example 1 is that in step (1), no anthracene oil is added to the coal tar, but the coal tar is directly heated and sent to the dehydration tower for processing.

[0028] Experimental Example: The anthracene oil was processed according to the process described in Examples 1-4 and Comparative Example 1. The content of anthracene and carbazole in the anthracene oil was detected, and the standard coal consumption per ton of product was calculated. The specific results are shown in Table 1. The anthracene oil product obtained by deep processing coal tar according to the method of the present invention (Examples 1-4) has high purity and stable quality, and the standard coal consumption per ton of product is low, with obvious energy-saving effect.

[0029] Table 1. Test results of anthracene oil products obtained by different processes and statistics of standard coal consumption per ton of product.

[0030] As shown in Table 1, Comparative Example 1 did not re-introduce anthracene oil into the coal tar, and the anthracene oil obtained contained only 16.0% anthracene and carbazole, with a standard coal consumption of 27.0 kg per ton of product. In contrast, the anthracene oil obtained in Examples 1-4 contained 25.8%-26.1% anthracene and carbazole, an increase of 9.8-10.1 percentage points compared to Comparative Example 1, representing a relative increase of approximately 61%-63%. The standard coal consumption per ton of product in Examples 1-4 was 14.0-14.9 kg, a decrease of 12.1-13.0 kg compared to Comparative Example 1, representing a decrease of approximately 45%-48%. Furthermore, the range of anthracene and carbazole content in the anthracene oil among Examples 1-4 was only 0.3 percentage points, indicating that the product quality of the process described in this invention has good batch stability. In Comparative Example 1, due to the lack of premixed anthracene oil homologues, the association and encapsulation of anthracene and carbazole molecules by heavy gums and asphaltenes could not be broken. The target components were either carried away with the light components or settled and retained with the heavy components, resulting in a significant deterioration in enrichment efficiency and product quality. Furthermore, due to the lack of gasification endothermic effect and waste heat recovery brought about by the lack of anthracene oil remixing, the heating furnace needed to operate at a higher temperature, resulting in a significant increase in energy consumption.

[0031] Meanwhile, the effect of this invention on inhibiting coking in furnace tubes was examined by observing the operating conditions of the heating furnace. In Examples 1-4, the circulating asphalt at the bottom of the anthracene tower was cooled by a medium-temperature asphalt heat exchanger before entering the furnace. The low-boiling-point components in the excess anthracene oil in the furnace preferentially vaporized and absorbed the latent heat of vaporization during the heating section. The outlet temperature of the heating furnace was stably controlled at 345-355℃, which is 5-15℃ lower than the outlet temperature of over 360℃ in the traditional process. At the same time, the standard coal consumption per ton of product in Examples 1-4 was only 14.0-14.9 kg, which is 45%-48% lower than the 27.0 kg in Comparative Example 1. This indicates that under the condition of comparable heat load at the bottom of the anthracene tower, the external heat supply required to maintain this outlet temperature is significantly reduced, and the heat supply intensity in the furnace is substantially weakened.

[0032] It is important to note that the furnace outlet temperature represents the body temperature of the heated material, while the coking rate is determined by the metal wall temperature of the furnace tubes; a heat transfer temperature difference exists between the two. Although Comparative Example 1 uses the same outlet temperature setting as Example 1, because its circulating asphalt lacks the vaporizable excess anthracene oil component, there is no internal heat-absorbing buffer within the furnace tubes. To transfer the same amount of heat to the material, a larger heat transfer temperature difference must be maintained; that is, the furnace tube wall temperature must be significantly higher than the material temperature, thus the wall temperature is closer to or even exceeds the critical temperature for asphaltene thermal condensation and coking. Conversely, in Examples 1-4, the vaporization and heat absorption process of the excess anthracene oil occurs precisely in the boundary layer region near the tube wall, directly consuming heat and stabilizing the wall temperature near the wall, thus narrowing the temperature difference between the wall and the material. Therefore, this invention does not simply lower the outlet temperature setting, but rather, by changing the heat absorption method within the furnace, simultaneously lowers the furnace tube wall temperature while achieving the same distillation heating, thereby inhibiting coking from the essence of heat transfer. Furthermore, Comparative Example 1 requires operation at a higher combustion intensity due to the aforementioned reasons. The increased thermal intensity of the furnace tubes will further accelerate coking, creating a vicious cycle. This is consistent with the measured result that Comparative Example 1 consumes as much as 27.0 kg of standard coal.

[0033] In summary, the anthracene oil product obtained by deep processing of coal tar according to the method described in this invention has high purity and stable quality, low standard coal consumption per ton of product, and significantly reduced furnace outlet temperature and furnace tube thermal intensity. This can fundamentally inhibit coking of furnace tubes, which is conducive to long-term stable operation of the equipment. The energy-saving effect and operational reliability are significantly better than traditional processes.

[0034] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A deep processing technology for coal tar using anthracene oil premixing and coupled dual-tower negative pressure distillation, characterized in that: Includes the following steps: (1) Coal tar and anthracene oil are fed into a pipeline static mixer and mixed evenly to obtain a mixture. The mass ratio of coal tar to anthracene oil is 20:(1-5). The mixture is heated to 160-180°C and then sent to a dehydration tower for treatment. (2) A portion of the anhydrous tar from the bottom of the dehydration tower is heated to 200-220°C by an anthracene oil tar heat exchanger and then sent to the distillation tower for processing. At the same time, a portion of the anhydrous tar is heated to 190-210°C by a vapor phase heat exchanger at the top of the anthracene tower and then returned to the bottom of the dehydration tower. (3) The absolute pressure inside the distillation tower is controlled at 20-30 kPa, and the temperature at the bottom of the distillation tower is controlled at 315-330℃. The distillate produced at the top of the distillation tower is heated by the gas phase heat exchanger at the top of the distillation tower and the mixture in step (1) to obtain a three-mixed oil containing naphthalene oil, wash oil and phenol oil. A portion of the soft asphalt at the bottom of the distillation tower is heated to 320-340℃ by the medium temperature asphalt heat exchanger and then refluxed to the bottom of the distillation tower. At the same time, a portion of the soft asphalt is sent to the anthracene tower for negative pressure distillation. (4) The absolute pressure inside the anthracene tower is controlled at 10-20 kPa, and the temperature at the top of the anthracene tower is controlled at 260-280℃. The distillate produced at the top of the anthracene tower is heated by the gas phase heat exchanger at the top of the anthracene tower, and then heated by the anthracene oil tar heat exchanger to obtain liquid anthracene oil. The anthracene oil is divided into two paths. The first path is cooled by the anthracene oil finished product cooler and then sent to the finished product storage tank for storage. The second path is sent to the pipeline static mixer in step (1) to mix with coal tar. The medium-temperature asphalt extracted from the bottom of the anthracene tower is divided into two paths. The first path is sent to the modified asphalt production process. The second path is heated by the medium-temperature asphalt heat exchanger and the soft asphalt in step (3), and then returned to the bottom of the anthracene tower after being heated by the heating furnace. The outlet temperature of the heating furnace is 345-355℃.

2. The coal tar deep processing technology according to claim 1, characterized in that: The temperature at the top of the dehydration tower in step (2) is controlled at 85-95℃.

3. The coal tar deep processing technology according to claim 1, characterized in that: The distillate produced at the top of the dehydration tower in step (2) is condensed and cooled to extract light oil and phenol water.

4. The coal tar deep processing technology according to claim 1, characterized in that: The temperature at the top of the distillation column in step (3) is controlled at 185-195℃.

5. The coal tar deep processing technology according to claim 1, characterized in that: In step (4), the bottom of the anthracene tower produces medium-temperature pitch with an anthracene oil mass fraction of 8% to 12%.

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