A tar distillation process for improving wash oil quality

Abstract

The application discloses a tar distillation process for improving oil quality, and relates to the technical field of deep processing of coal tar. The process is a coal tar atmospheric and vacuum distillation process for full distillation of unwashed three-mixed oil on the top of a tar distillation column. The core of the process is that, without changing the main structure of the original distillation equipment, four core process parameters, including backflow, vacuum degree at the top of the column, temperature at the bottom of the column and temperature at the top of the column, are simultaneously and cooperatively controlled in the vacuum distillation process of the tar distillation column, and the distillation quality control thresholds of unwashed three-mixed oil and carbon black oil are matched and set. The application solves the problems of wide process parameter control, low and unstable product quality of the existing tar distillation process, and can make the downstream washed oil product reach the first-grade product requirement in the GB / T24217-2025 standard, while not affecting the raw material adaptability of carbon black oil to the downstream modified pitch device. The application has the advantages of low modification cost, easy industrialization, stable product quality and remarkable economic benefits.

Description

Technical Field

[0001] This invention relates to the field of coal tar deep processing technology, specifically a tar distillation process for improving the quality of washed oil. Background Technology

[0002] Coal tar is a core byproduct of the coking industry. Its processed products are widely used in chemical, carbon materials, pharmaceutical, and new energy fields. Major products include phenols, naphthalene, wash oil, crude anthracene, and pitch. Wash oil, as one of the core products of coal tar distillation, is mainly used for the absorption of benzene hydrocarbons in coke oven gas and the extraction of raw materials for organic synthesis. Its quality directly determines the downstream application effect and product added value. Currently, the tar distillation processes of domestic coal tar processing enterprises are mainly divided into two categories: one is the process of using a side stream from the distillation tower to obtain three-mixed fractions, and the other is the process of using the top distillate of unwashed three-mixed oil. The latter is widely used in small and medium-sized coking and tar processing enterprises due to its simple equipment structure and convenient operation. In the existing tar distillation process that yields unwashed mixed oil from the top of the column, the quality of the wash oil depends entirely on the fractionation precision of the upstream tar distillation stage. The core flaw of the existing process is that the process control indicators of the tar distillation column are broad and the parameter adjustment range is large. During the production process, the core control objective is only to ensure the quality of carbon black oil products. A collaborative control system for distillation parameters, unwashed mixed oil components, and downstream wash oil quality has not been established. This results in large fluctuations in the composition of the unwashed mixed oil produced. Ultimately, the quality of the downstream wash oil products can only meet the qualified product standard and cannot consistently meet the requirements of first-class products (Grade 1 products). Among the existing technologies related to wash oil quality improvement, Chinese patent CN109355083B discloses a process for collecting three-mixed fractions in tar vacuum distillation. Its core is to collect the three-mixed fractions via a side stream from the distillation tower to increase naphthalene concentration. However, this process is designed for side stream collection and cannot be adapted to existing equipment where the unwashed three-mixed oil is fully distilled from the top of the tower. Furthermore, it lacks a corresponding parameter control system for improving wash oil quality. Chinese patent CN111334324A discloses a method for producing high-quality wash oil, which achieves quality improvement through secondary distillation after wash oil production. This requires two additional distillation units, resulting in high investment and operating costs, and cannot solve the problem of low wash oil quality at the source of tar distillation. In summary, the existing technologies lack a solution that can simultaneously improve carbon black oil quality and downstream wash oil quality in tar distillation processes where the unwashed three-mixed oil is fully distilled from the top of the tower, without modifying existing equipment, simply by optimizing process parameters. This is a common pain point faced by small and medium-sized tar processing enterprises in China. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to solve the problems of low quality and poor stability of wash oil products in existing tar distillation processes, high cost of upgrading schemes, and incompatibility with existing top-distillation unwashed three-blended oil units. The invention provides a tar distillation process that can stably improve the quality of wash oil products without modifying the main structure of the original distillation equipment, solely through collaborative closed-loop control of core process parameters. This process ensures that wash oil consistently meets first-grade standards while guaranteeing the compatibility of carbon black oil as feedstock for downstream modified asphalt units.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A tar distillation process for improving the quality of washed oil, wherein the process is a coal tar atmospheric and vacuum distillation process in which all unwashed mixed oil is distilled from the top of a tar distillation column, and includes the following steps: S1: The raw material tar is sent to the tar dehydration tower for dehydration treatment. Light oil and water are separated from the top of the tar dehydration tower, and anhydrous tar is obtained from the bottom of the tower. S2: After heating the anhydrous tar, it is fed into a tar distillation column under reduced pressure. During the distillation and separation process, four process parameters of the tar distillation column, namely the column reflux flow rate, column top vacuum degree, column bottom temperature, and column top temperature, are simultaneously controlled in a coordinated manner. S3: The vapor phase distilled from the top of the tar distillation tower is cooled and enters the reflux tank. Part of the resulting liquid phase is returned to the top of the tar distillation tower as reflux liquid, and the other part is collected as unwashed mixed oil and transported to the downstream fraction washing unit for phenol removal and the industrial naphthalene distillation unit for the production of wash oil. At the same time, carbon black oil is collected from the bottom of the tar distillation tower. S4: Improve the quality of downstream wash oil products by matching and setting the fraction quality control thresholds for unwashed mixed oil and carbon black oil.

[0005] Furthermore, in step S1, the raw material tar is first heated to 160~180℃ through heat exchange before being sent to a tar dehydration tower operating at atmospheric pressure; the top temperature of the tar dehydration tower is controlled at 95~110℃ and the bottom temperature is controlled at 200~220℃.

[0006] Furthermore, in step S2, the anhydrous tar is heated to 320~330°C in a heating furnace and then fed into the tar distillation tower; the reduced pressure environment of the tar distillation tower is maintained by a vacuum pump unit.

[0007] Furthermore, the coordinated control range of the four process parameters of the tar distillation column in step S2 is as follows: column reflux flow rate 3.5~3.7t / h, column top vacuum degree -58~-57KPa, column bottom temperature 280~283℃, and column top temperature 194~197℃.

[0008] Furthermore, in step S2, the reflux flow rate of the tar distillation column is stably controlled at 3.6 t / h.

[0009] Furthermore, in step S2, the vacuum at the top of the tar distillation column is stably controlled at -57.5 kPa.

[0010] Furthermore, in step S2, the bottom temperature of the tar distillation column is stably controlled at 281~282℃.

[0011] Furthermore, in step S2, the top temperature of the tar distillation column is stably controlled at 195~196℃.

[0012] Furthermore, the fractional mass control threshold for the unwashed three-mixed oil mentioned in step S4 is: naphthalene mass fraction 65~70%, and subsequent unknown component mass fraction ≤10%.

[0013] Furthermore, the fractional quality control threshold for the carbon black oil described in step S4 is: softening point 25~33℃.

[0014] This invention addresses the characteristics of atmospheric and vacuum distillation of coal tar, specifically the unwashed mixed oil from the top of a coal tar distillation column. Based on the gas-liquid equilibrium separation principle of vacuum distillation of coal tar, it achieves precise fraction cutting from the distillation source through coordinated closed-loop control of core process parameters and matching control of fraction quality thresholds. This ultimately leads to a stable improvement in the quality of downstream wash oil products. The underlying working mechanism is as follows: The core essence of vacuum distillation of coal tar is to utilize the differences in boiling points of different hydrocarbon components to lower the boiling points of each component under negative pressure, preventing tar components from cracking and coking at high temperatures. Through countercurrent contact and mass and heat transfer between the gas and liquid phases within the column, the light and heavy components are separated by distillation. For the process of obtaining unwashed mixed oil from the top of the column, the component stability of the unwashed mixed oil directly determines the final quality of the downstream wash oil. However, existing technologies, due to their wide range of process parameter control and large fluctuations in the gas-liquid equilibrium conditions within the column, cannot achieve precise fractionation, ultimately resulting in inconsistent wash oil quality.

[0015] This invention precisely locks the overall distillation conditions of a tar distillation column through the coordinated closed-loop control of four core process parameters, fundamentally solving the problem of operating condition fluctuations: First, by using a column top vacuum of -58 to -57 kPa (corresponding to an internal column absolute pressure of 43 to 44 kPa) as the benchmark for distillation conditions, a narrow range is locked between the overall column pressure field and the boiling point range of each component, eliminating the offset of the fraction cut-off point caused by vacuum fluctuations and laying a stable pressure foundation for precise component separation; Second, by controlling the heat input of the distillation process with a column bottom temperature of 280 to 283°C, this ensures that the light components corresponding to the unwashed three-component blend are fully vaporized and rise, preventing light components from being lost to the carbon black oil at the bottom of the column, while controlling the degree of vaporization of heavy components through the upper temperature limit, reducing the entry of heavy impurities into the top fraction. Simultaneously, it directly locks in the softening point range of the carbon black oil at the bottom of the tower, taking into account the quality of the carbon black oil product; thirdly, it directly and precisely matches the distillation range of the unwashed three-component blended oil with a tower top temperature of 194~197℃. This temperature range precisely locks in the vaporization range of the core effective components of the wash oil, such as naphthalene and methylnaphthalene, controlling the naphthalene content distribution of the unwashed three-component blended oil from the source; fourthly, it regulates the gas-liquid balance in the tower with a tower reflux flow rate of 3.5~3.7t / h, and enhances the distillation separation efficiency of the tower plates through stable liquid phase reflux, further refining the cutting precision of light and heavy components, while offsetting the small fluctuations in vacuum and temperature, stabilizing the component stability of the top fraction. The four parameters form a closed-loop control system that is interconnected and mutually compensating, completely solving the core defects of the existing process parameters being too broad and the operating conditions fluctuating greatly.

[0016] Based on this, the present invention achieves source control of wash oil quality by matching and setting the distillate quality control thresholds for unwashed three-component blended oil and carbon black oil: the naphthalene mass fraction of unwashed three-component blended oil is stably controlled at 65~70%, and the mass fraction of unknown components is ≤10%. This provides a stable feed for downstream distillate washing processes, fixes the operating window of the phenol and naphthalene removal processes, and can stably control the residual naphthalene content of the wash oil product to within 10%, meeting the requirements of first-grade product standards. At the same time, by limiting the unknown heavy components, the distillation range index of the wash oil product is guaranteed to meet the standards. Meanwhile, the softening point of carbon black oil is controlled at 25~33℃, which fully matches the feedstock requirements of downstream modified asphalt units, achieving a synergistic balance between wash oil quality improvement and carbon black oil quality stability.

[0017] In summary, the core mechanism of this invention is to target the rectification characteristics of the unwashed three-blended oil process at the top of the tower. Based on the principle of vacuum distillation gas-liquid balance, it replaces the extensive parameter adjustment of the existing technology with narrow-range, closed-loop collaborative control of process parameters. This locks in the component distribution of the unwashed three-blended oil from the source of tar distillation, eliminates the impact of raw material fluctuations and operational fluctuations on product quality, and ultimately achieves a stable improvement in the quality of downstream wash oil products to the first-class standard without modifying the original equipment or affecting the original product system.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. Zero modification cost and extremely strong adaptability: This invention does not require any modification to the equipment, pipelines, or main structure of the original tar distillation unit. It can achieve the upgrading of wash oil simply by controlling the core process parameters in a coordinated closed loop. It is fully compatible with most existing tar processing units in China that use the top-distillation unwashed three-mixed oil process. No additional investment is required, and the difficulty of industrialization is extremely low.

[0019] 2. Precise fraction cutting and stable washing oil quality: This invention establishes a four-parameter collaborative control system of "tower reflux flow rate - tower top vacuum degree - tower bottom temperature - tower top temperature", which locks the core boundary of fraction cutting in the tar distillation process and solves the problems of wide process parameters and large component fluctuations in the existing process. It can stably control the naphthalene content of unwashed mixed oil at 65~70%, and the downstream washing oil product ultimately meets the first-class requirements of GB / T24217-2025 standard 100% stably, completely solving the industry pain point of large fluctuations in washing oil quality and inability to consistently meet standards.

[0020] 3. Coordinated Quality of Multiple Products Without Affecting the Original Production System: While improving the quality of wash oil, this invention sets a matching softening point control threshold for carbon black oil. Under the premise of ensuring the quality of wash oil, the carbon black oil fully meets the raw material feeding requirements of the downstream modified asphalt unit without adjusting the production process of the downstream unit. This achieves the dual goals of "improving the quality of wash oil + stabilizing the quality of carbon black oil" without affecting the company's original product system and production plan.

[0021] 4. Significant Economic Benefits and Application Value: By improving the quality grade of the oil washing product, this invention significantly increases the added value of the product and the market competitiveness of the enterprise. At the same time, it reduces the risk of pipeline blockage and equipment failure for downstream users caused by poor oil washing quality, reduces quality disputes and sales risks, and can directly create significant economic benefits for tar processing enterprises. Attached Figure Description

[0022] Figure 1 This is a diagram of a tar distillation process for improving the quality of wash oil according to the present invention; Figure 2 A table showing the quality control indicators for a tar distillation tower; Figure 3 This is a table of the GB / T24217-2025 quality standard for wash oil products. Detailed Implementation

[0023] The technical solutions of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] like Figure 1-3As shown, a tar distillation process for improving the quality of washed oil is described. The process involves atmospheric and vacuum distillation of coal tar to obtain unwashed mixed oil from the top of a tar distillation column, and includes the following steps: S1: The raw material tar is sent to the tar dehydration tower for dehydration treatment. Light oil and water are separated from the top of the tar dehydration tower, and anhydrous tar is obtained from the bottom of the tower. S2: After heating the anhydrous tar, it is fed into a tar distillation column under reduced pressure. During the distillation and separation process, four process parameters of the tar distillation column, namely the column reflux flow rate, column top vacuum degree, column bottom temperature, and column top temperature, are simultaneously controlled in a coordinated manner. S3: The vapor phase distilled from the top of the tar distillation tower is cooled and enters the reflux tank. Part of the resulting liquid phase is returned to the top of the tar distillation tower as reflux liquid, and the other part is collected as unwashed mixed oil and transported to the downstream fraction washing unit for phenol removal and the industrial naphthalene distillation unit for the production of wash oil. At the same time, carbon black oil is collected from the bottom of the tar distillation tower. S4: Improve the quality of downstream wash oil products by matching and setting the fraction quality control thresholds for unwashed mixed oil and carbon black oil.

[0025] Furthermore, in step S1, the raw material tar is first heated to 160~180℃ through heat exchange before being sent to a tar dehydration tower operating at atmospheric pressure; the top temperature of the tar dehydration tower is controlled at 95~110℃ and the bottom temperature is controlled at 200~220℃.

[0026] Furthermore, in step S2, the anhydrous tar is heated to 320~330°C in a heating furnace and then fed into the tar distillation tower; the reduced pressure environment of the tar distillation tower is maintained by a vacuum pump unit.

[0027] Furthermore, the coordinated control range of the four process parameters of the tar distillation column in step S2 is as follows: column reflux flow rate 3.5~3.7t / h, column top vacuum degree -58~-57KPa, column bottom temperature 280~283℃, and column top temperature 194~197℃.

[0028] Furthermore, in step S2, the reflux flow rate of the tar distillation column is stably controlled at 3.6 t / h.

[0029] Furthermore, in step S2, the vacuum at the top of the tar distillation column is stably controlled at -57.5 kPa.

[0030] Furthermore, in step S2, the bottom temperature of the tar distillation column is stably controlled at 281~282℃.

[0031] Furthermore, in step S2, the top temperature of the tar distillation column is stably controlled at 195~196℃.

[0032] Furthermore, the fractional mass control threshold for the unwashed three-mixed oil mentioned in step S4 is: naphthalene mass fraction 65~70%, and subsequent unknown component mass fraction ≤10%.

[0033] Furthermore, the fractional quality control threshold for the carbon black oil described in step S4 is: softening point 25~33℃.

[0034] The raw material tar used in the examples has the following basic indicators: density at 20℃ 1.18 g / cm³, toluene insoluble content 3.5%, moisture content 1.5%, and naphthalene content 10.2%. All product testing was carried out in accordance with national and industry standards, and the quality testing of wash oil products was based on GB / T24217-2025.

[0035] The specific process steps are as follows: 1. Raw material tar dehydration pretreatment: The raw material tar is pumped from the raw material tar tank 1 and heated to 170°C before being fed into the tar dehydration tower 2, which operates at atmospheric pressure. The top temperature of the tar dehydration tower 2 is controlled at 100°C and the bottom temperature at 205°C. The light oil and water vapor separated at the top of the tower are cooled and then enter the oil-water separator to complete the oil-water separation. Anhydrous tar is collected from the bottom of the tower. After testing, the water content of the anhydrous tar is 0.05%, which meets the requirements for subsequent distillation.

[0036] 2. Anhydrous tar heating and distillation feed: Anhydrous tar is pumped from the bottom of tar dehydration tower 2 and fed into tubular heater 3 to be heated to 325°C. Then it is continuously fed into the middle of tar distillation tower 4 which is under reduced pressure. The reduced pressure environment of tar distillation tower 4 is maintained by a vacuum pump group.

[0037] 3. Collaborative Closed-Loop Control of Core Process Parameters: During the distillation and separation process, the four core process parameters of tar distillation column 4 are simultaneously controlled in a collaborative closed-loop manner. The specific control values ​​are: the column reflux flow rate is stably controlled at 3.6 t / h, the column top vacuum degree is stably controlled at -57.4 kPa (corresponding to an absolute pressure of 43.925 kPa inside the column), the column bottom temperature is stably controlled at 281.0 ℃, and the column top temperature is stably controlled at 195.4 ℃.

[0038] 4. Product Extraction and Quality Control: The vapor phase distilled from the top of tar distillation tower 4 is cooled and enters reflux tank 5. A portion of the resulting liquid phase is returned to the top of tar distillation tower 4 at a reflux rate of 3.6 t / h, while the other portion is extracted as unwashed mixed oil and sent to unwashed mixed oil storage tank 6. It is then transported to the downstream fraction washing unit for phenol removal and the industrial naphthalene distillation unit for washing oil production. Simultaneously, carbon black oil is extracted from the bottom of tar distillation tower 4 and sent to carbon black oil storage tank 7, which is then transported to the downstream modified asphalt unit. Testing in this embodiment showed the following parameters for the unwashed mixed oil: naphthalene mass fraction 65.9%, and unidentified component mass fraction 7.3%; the carbon black oil parameters were: softening point 28.1℃, fully meeting the raw material requirements of the downstream modified asphalt unit.

[0039] 5. Quality Inspection of Wash Oil Products The unwashed mixed oil produced in this embodiment is processed through downstream conventional phenol removal and distillation to remove naphthalene, yielding the wash oil product. The indicators of the wash oil product are as follows: The unwashed mixed oil produced in this embodiment, after undergoing conventional downstream processes for phenol removal and distillation to remove naphthalene, yielded washed oil. Testing revealed the following specific indicators: Density at 20℃ was 1.05 g / ml, meeting the first-grade standard requirement of 1.03~1.06 g / ml; Distillate volume fraction before 230℃ was 0%, meeting the first-grade standard requirement of no more than 3%; Distillate volume fraction before 270℃ was 74.0%, meeting the first-grade standard requirement of no less than 70%; Distillate volume fraction before 300℃... The product exhibits the following properties: 98.0% purity (volume fraction), meeting the first-class product standard requirement of no less than 90%; 0.1% phenol content (volume fraction), meeting the first-class product standard requirement of no more than 0.5%; 4.1% naphthalene content (mass fraction), meeting the first-class product standard requirement of no more than 10%; 0.02% moisture content, meeting the first-class product standard requirement of no more than 1%; 1.2 E50 viscosity, meeting the first-class product standard requirement of no more than 1.5; and no crystals at 15℃, meeting the first-class product standard requirement. In summary, all indicators of the wash oil product produced in this embodiment meet the first-class product requirements of GB / T24217-2025 standard.

[0040] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. These embodiments are merely descriptions of preferred embodiments and are not intended to limit the scope or concept of the invention. The specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. Such combinations, as long as they do not violate the spirit of the present invention, should also be considered as part of this disclosure. To avoid unnecessary repetition, the present invention will not further describe the various possible combinations.

[0041] This invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this invention and without departing from the design idea of ​​this invention, all modifications and improvements made by those skilled in the art to the technical solutions of this invention should fall within the protection scope of this invention. The technical content for which protection is sought in this invention has been fully described in the claims.

Claims

1. A tar distillation process for improving the quality of wash oil, characterized in that, Includes the following steps: S1: The raw material tar is sent to the tar dehydration tower for dehydration treatment. Light oil and water are separated from the top of the tar dehydration tower, and anhydrous tar is obtained from the bottom of the tower. S2: After heating the anhydrous tar, it is fed into a tar distillation column under reduced pressure. During the distillation and separation process, four process parameters of the tar distillation column, namely the column reflux flow rate, column top vacuum degree, column bottom temperature, and column top temperature, are simultaneously controlled in a coordinated manner. S3: The vapor phase distilled from the top of the tar distillation tower is cooled and enters the reflux tank. Part of the resulting liquid phase is returned to the top of the tar distillation tower as reflux liquid, and the other part is collected as unwashed mixed oil and transported to the downstream fraction washing unit for phenol removal and the industrial naphthalene distillation unit for the production of wash oil. At the same time, carbon black oil is collected from the bottom of the tar distillation tower. S4: Improve the quality of downstream wash oil products by matching and setting the fraction quality control thresholds for unwashed mixed oil and carbon black oil.

2. The tar distillation process for improving wash oil quality according to claim 1, characterized in that, In step S1, the raw material tar is first heated to 160~180℃ through heat exchange, and then sent to a tar dehydration tower operating at atmospheric pressure; the top temperature of the tar dehydration tower is controlled at 95~110℃, and the bottom temperature is controlled at 200~220℃.

3. The tar distillation process for improving the quality of wash oil according to claim 1, characterized in that, In step S2, the anhydrous tar is heated to 320~330℃ in a heating furnace and then fed into the tar distillation tower; the reduced pressure environment of the tar distillation tower is maintained by a vacuum pump group.

4. The tar distillation process for improving the quality of wash oil according to claim 1, characterized in that, The coordinated control range of the four process parameters of the tar distillation column in step S2 is as follows: column reflux flow rate 3.5~3.7t / h, column top vacuum degree -58~-57KPa, column bottom temperature 280~283℃, and column top temperature 194~197℃.

5. The tar distillation process for improving the quality of wash oil according to claim 4, characterized in that, In step S2, the reflux flow rate of the tar distillation column is stably controlled at 3.6 t / h.

6. The tar distillation process for improving wash oil quality according to claim 4, characterized in that, In step S2, the vacuum at the top of the tar distillation column is stably controlled at -57.5 kPa.

7. The tar distillation process for improving the quality of wash oil according to claim 4, characterized in that, In step S2, the bottom temperature of the tar distillation column is stably controlled at 281~282℃.

8. The tar distillation process for improving the quality of wash oil according to claim 4, characterized in that, In step S2, the top temperature of the tar distillation column is stably controlled at 195~196℃.

9. The tar distillation process for improving the quality of wash oil according to claim 1, characterized in that, The fractional mass control threshold for the unwashed three-mixed oil mentioned in step S4 is: naphthalene mass fraction 65~70%, and mass fraction of unknown components ≤10%.

10. A tar distillation process for improving the quality of wash oil according to claim 1, characterized in that, The fractional quality control threshold for the carbon black oil described in step S4 is: softening point 25~33℃.

Images