A method for increasing the recovery of crude benzol

Abstract

This invention discloses a method for improving crude benzene yield, belonging to the field of coke oven gas purification and crude benzene recovery technology. The method includes: S1, gas pretreatment: after primary cooling, the coke oven gas enters the final cooler, where it is cleaned by circulating ammonia water spraying, controlling the gas temperature after final cooling to 20℃~25℃; S2, dual-tower series deep absorption: the pretreated gas sequentially enters a primary benzene washing tower and a secondary benzene washing tower for series absorption; the wash oil adopts a reverse cascade utilization method, i.e., lean oil is first finely absorbed by the secondary benzene washing tower, and then enters the primary benzene washing tower for main absorption; S3, pressure and flow control: a pressure balancing pipe and an electric regulating valve are installed between the primary and secondary benzene washing towers to maintain a stable pressure difference between the two towers; a flow stabilizing orifice plate is installed on the pipeline from the outlet of the primary tower to the inlet of the secondary tower to ensure gas-liquid contact balance. This invention employs a dual-tower series deep benzene washing process, which can significantly reduce benzene series emissions and improve crude benzene yield.

Description

Technical Field

[0001] This invention belongs to the field of coke oven gas purification and crude benzene recovery technology, and in particular relates to a method for improving crude benzene yield. Background Technology

[0002] Crude benzene, a crucial chemical product in coke oven gas, significantly impacts its purification level and directly determines the economic benefits of enterprises. Currently, coking plants commonly employ wash oil absorption to recover crude benzene, with the traditional process primarily using a single-tower wash oil absorption method. This method involves countercurrent contact between coke oven gas and wash oil within a single benzene washing tower, utilizing the selective absorption of benzene compounds by the wash oil to achieve separation.

[0003] However, single-tower processes have a series of obvious shortcomings in practical applications:

[0004] Maintaining absorption equilibrium is difficult: Due to the limited mass transfer area and residence time within the tower, the absorption process often fails to reach an ideal equilibrium, resulting in persistently high benzene content in the downstream gas. This not only causes a significant loss of benzene compounds but also leads to generally low crude benzene recovery rates, typically only reaching a low level.

[0005] High energy consumption: To compensate for the insufficient absorption efficiency of a single tower, a large amount of wash oil circulation must be maintained during operation, which significantly increases the energy consumption of pumping, cooling and regeneration, thereby driving up the overall operating cost.

[0006] Wash oil is prone to deterioration: During long-term cyclic use, wash oil is susceptible to the effects of high temperatures, oxygen, and impurities, undergoing chemical reactions such as oxidation and polymerization, leading to increased viscosity and decreased absorption capacity. This deterioration further weakens the system's absorption efficiency and may cause problems such as equipment blockage.

[0007] Difficulty in deep absorption: The single-tower structural design limits the maximization of the concentration gradient, resulting in insufficient absorption driving force. Therefore, benzene compounds in coal gas are difficult to remove completely, which not only increases resource loss but also leads to excessive benzene compounds in exhaust gas, exacerbating environmental compliance pressures and environmental risks. Summary of the Invention

[0008] This invention provides a method for improving the yield of crude benzene by employing a dual-tower series deep benzene washing process, which overcomes the shortcomings of the existing single-tower process, achieving the goals of low retrofit investment, high absorption efficiency, stable operation, significant reduction of benzene series emissions, improved crude benzene yield, and reduced operating costs.

[0009] To achieve the above-mentioned technical objectives, the present invention is implemented through the following technical solution: A method for improving the yield of crude benzene includes: S1. Gas pretreatment: After primary cooling, coke oven gas enters the final cooler, where it is cleaned by circulating ammonia water spraying, and the gas temperature after final cooling is controlled to be 20℃~25℃. S2, Dual-tower series deep absorption: The pretreated coal gas enters the primary benzene washing tower and the secondary benzene washing tower in series for absorption; the wash oil adopts a reverse cascade utilization method, that is, the lean oil is first finely absorbed by the secondary benzene washing tower, and then enters the primary benzene washing tower for main absorption. S3. Pressure and flow control: A pressure balancing pipe and an electric regulating valve are installed between the primary and secondary benzene washing towers to maintain a stable pressure difference between the two towers; a flow stabilizing orifice plate is installed on the pipeline from the outlet of the primary tower to the inlet of the secondary tower to ensure gas-liquid contact balance.

[0010] Preferably, in S2, the primary benzene washing tower serves as the main absorption section, using stainless steel perforated corrugated packing with a specific surface area of ​​not less than 250 m² / m³, a total packing height of 18 m, and divided into 3 to 4 independent packing layers.

[0011] Preferably, a liquid redistributor is installed between sections, a grid plate is installed at the bottom of the packing layer, and a packing pressure ring is installed at the top.

[0012] Preferably, a baffle plate demister is installed at the top of the primary benzene washing tower to prevent the washing oil droplets from being entrained by the gas.

[0013] Preferably, the top of the primary benzene washing tower is equipped with 2 to 3 trough-type liquid distributors with a liquid distribution point of not less than 30 points / m². The liquid flows from top to bottom through uniform distribution and forms a liquid film on the surface of the packing with the high-concentration benzene series gas flowing from bottom to top, thus completing the mass transfer and absorption of benzene series compounds.

[0014] Preferably, in S2, the secondary benzene washing tower serves as the fine absorption section, using structured metal wire mesh packing with a specific surface area of ​​not less than 350 m² / m³, a total packing height of 12 m, and divided into 2 to 3 independent packing layers.

[0015] Preferably, in S2, the coal gas adopts a bottom-up flow path in both the primary and secondary benzene washing towers, while the washing oil is sprayed from top to bottom, forming a completely countercurrent gas-liquid contact state.

[0016] Preferably, in S2, a double demister liquid eliminator layer is provided at the top of the secondary benzene washing tower, with a wire mesh demister at the bottom and a baffle plate demister at the top.

[0017] Preferably, in S2, the bottom of the secondary benzene washing tower is equipped with a dual anti-cross-gas device consisting of a U-shaped liquid seal and a check valve.

[0018] Preferably, the top of the secondary benzene washing tower is equipped with a dual liquid distribution system consisting of a trough-type liquid distributor and a tubular liquid distributor, with a liquid distribution point of not less than 40 / m². The new lean oil first enters the secondary benzene washing tower, and the high absorption activity of the lean oil with its extremely low benzene content is used to deeply and efficiently absorb trace amounts of benzene compounds in the coal gas.

[0019] The advantages and technical effects of this invention are: This invention achieves a significant increase in crude benzene yield by employing a dual-tower staged positioning technology, resulting in substantial production gains. Specifically, the primary benzene washing tower performs initial collection, while the secondary benzene washing tower utilizes the high activity of lean oil for deep collection. This dual-tower staged approach significantly reduces the benzene content in the downstream gas, ensuring the cleanliness of the emitted gas. Simultaneously, by optimizing the utilization of the wash oil, such as recycling and precise proportioning, the utilization rate of the absorbent is effectively improved, and the unit consumption of wash oil is significantly reduced, further lowering operating costs. Furthermore, this invention is based on the modification of existing single-tower units, requiring only the addition of one benzene washing tower and optimization of the piping system. Therefore, it has the advantages of low investment and short modification cycle, facilitating rapid deployment and application on existing production lines. Detailed Implementation

[0020] To make the above-mentioned objectives, control system design, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0021] This invention aims to solve the problems of high benzene content, low recovery rate, and high energy consumption in the existing single-tower benzene washing process. It provides a deep benzene washing process that adopts a dual-tower series design to achieve secondary fine absorption, so as to significantly reduce benzene series emissions, increase crude benzene yield, and reduce operating costs.

[0022] This process addresses the problems of incomplete benzene absorption, high benzene content at the post-tower level, and low recovery rate associated with traditional single-tower benzene washing. It provides a dual-tower series countercurrent absorption technology. The process uses a primary benzene washing tower (main absorber) and a secondary benzene washing tower (fine absorber) as the main equipment. After pretreatment by a final cooler, the coal gas sequentially enters the primary and secondary benzene washing towers for two-stage series countercurrent absorption. It innovatively employs a reverse cascade utilization method, where lean oil undergoes fine absorption in the secondary benzene washing tower before entering the primary benzene washing tower for main absorption. Combined with strict temperature and pressure stabilization control, this achieves deep capture of benzene compounds in the coal gas.

[0023] A method for improving the yield of crude benzene includes: S1. Gas pretreatment: After primary cooling, coke oven gas enters the final cooler, where it is cleaned by circulating ammonia water spraying, and the gas temperature after final cooling is controlled to be 20℃~25℃. The coke oven gas first undergoes preliminary cooling in a primary cooler to lower its temperature and remove some heavy tar and impurities. Then, the gas enters the final cooler, where it is sprayed and cleaned with circulating ammonia water. The ammonia water effectively removes tar droplets and fine particulate matter from the gas. After the final cooling process, the gas temperature is precisely controlled between 20°C and 25°C.

[0024] S2, Dual-tower series deep absorption: The pretreated coal gas enters the primary benzene washing tower and the secondary benzene washing tower in series for absorption; the wash oil adopts a reverse cascade utilization method, that is, the lean oil is first finely absorbed by the secondary benzene washing tower, and then enters the primary benzene washing tower for main absorption. Pretreated coke oven gas enters the primary and secondary benzene washing towers sequentially in a co-current, counter-current contact manner. The gas flows upwards in both towers, while the wash oil is sprayed downwards, creating a completely counter-current gas-liquid contact state with the gas, achieving cascaded absorption and deep capture of benzene compounds. The core innovation of this method lies in the dual-tower staged positioning and the counter-current cascaded utilization of the wash oil.

[0025] Pretreated coke oven gas is sequentially fed into a primary benzene washing tower and a secondary benzene washing tower in a co-current, counter-current contact configuration. The gas flows upwards in both towers, while the wash oil is evenly sprayed downwards from the top via a top spray device, creating a completely counter-current gas-liquid contact with the gas. This flow design improves mass transfer efficiency, ensuring sufficient contact between the gas and wash oil within the towers, thereby achieving cascaded absorption and deep capture of benzene compounds. The primary benzene washing tower focuses on the initial absorption of a large amount of benzene compounds, while the secondary benzene washing tower performs subsequent fine capture, ensuring the complete removal of residual components. The core innovation of this invention is the dual-tower staged positioning and the counter-current cascaded utilization of wash oil. By optimizing the flow rate and concentration distribution of wash oil through staged optimization, not only is the recovery rate of benzene compounds improved, but energy consumption and wash oil consumption are also reduced, making it suitable for gas purification processes in the coking industry.

[0026] Primary benzene washing tower: main absorption section (coarse absorption); The primary benzene scrubbing tower is the main absorption unit, responsible for absorbing most of the benzene series compounds in the coal gas. Its core function is to rapidly reduce the concentration of benzene series compounds in the coal gas, creating low-concentration conditions for deep absorption in the secondary benzene scrubbing tower.

[0027] Tower internal structure and packing selection: The tower uses stainless steel perforated corrugated packing with a specific surface area ≥250 m² / m³. The total height of the packing layer is approximately 18 m, and it can be divided into 3-4 independent packing layers. Liquid redistributors are installed between the layers to prevent liquid from flowing off the tower wall and to ensure uniform gas-liquid contact. A grid plate support is installed at the bottom of the packing layer, and a packing pressure ring is installed at the top to prevent the packing from loosening or overturning. A baffle demister is installed at the top of the first-stage tower to prevent wash oil droplets from being entrained by the gas.

[0028] Spraying and liquid distribution system: Two to three trough-type liquid distributors are installed at the top of the tower, with a liquid distribution point count of ≥30 / m², ensuring uniform distribution of the wash oil across the tower cross-section. The uniformly distributed liquid flows from top to bottom and forms a liquid film on the packing surface with the high-concentration benzene series gas flowing from bottom to top, completing the mass transfer and absorption of the benzene series compounds.

[0029] Liquid level and anti-gas cross-flow control: An automatic regulating valve-based liquid level control system is installed at the bottom of the tower to maintain and regulate the liquid level. Simultaneously, an anti-gas-crossing device with a certain liquid seal height is installed to prevent coal gas from entering the oil pipeline.

[0030] Operating parameter control: The benzene content in the rich oil at the outlet of the first-stage tower is precisely controlled by adjusting the rich oil circulation rate; the empty tower gas velocity in the first-stage benzene washing tower is adjusted to ensure mass transfer efficiency while avoiding droplet entrainment; a certain pressure difference is formed between the operating pressure inside the tower and the second-stage benzene washing tower to ensure that the gas flows smoothly through the two towers without backflow or deviation.

[0031] Secondary benzene washing tower: fine absorption section; The secondary benzene scrubbing tower is a deep benzene removal unit specifically designed to capture residual trace amounts of benzene compounds in the gas exiting the primary benzene scrubbing tower. It is the core step in achieving benzene content downstream of the tower, and its key function is to utilize the high absorption activity of the fresh lean oil to complete the deep equilibrium absorption of benzene compounds.

[0032] Tower internal structure and packing selection: The tower uses high-efficiency structured metal wire mesh packing with a specific surface area ≥350m² / m³. The total height of the packing layer is approximately 12m, divided into 2-3 independent packing layers. Liquid redistributors are installed between the layers to further improve the uniformity of gas-liquid contact and separate entrained droplets. A two-stage demister and liquid trapping layer is installed at the top of the tower: a wire mesh demister at the bottom and a baffle plate demister at the top, to completely prevent the washing oil droplets from being carried away by the gas.

[0033] Spraying and liquid distribution system: The tower top is equipped with a dual liquid distribution system consisting of a trough-type liquid distributor and a tubular liquid distributor, with a distribution point count of ≥40 / m², ensuring uniform distribution of lean oil across the tower cross-section. New lean oil first enters the secondary benzene washing tower, where its extremely low benzene content and high absorption activity enable deep and efficient absorption of trace amounts of benzene compounds in the coal gas.

[0034] Liquid level and anti-gas cross-flow control: An automatic regulating valve is installed at the bottom of the tower to maintain and regulate the liquid level. A dual anti-gas-crossing and anti-backflow device, consisting of a U-shaped liquid seal and a check valve, is installed to prevent coal gas from entering.

[0035] Operating parameter control: The benzene content in the rich oil at the outlet of the secondary benzene washing tower is precisely controlled by adjusting the lean oil feed rate; the gas velocity in the empty tower of the secondary benzene washing tower is controlled to be lower than that in the primary benzene washing tower, extending the gas-liquid contact time and improving the deep absorption efficiency; the operating pressure inside the tower is controlled to form a stable pressure difference with the primary tower, ensuring smooth gas flow.

[0036] S3. Pressure and flow control: A pressure balancing pipe and an electric regulating valve are installed between the primary and secondary benzene washing towers to maintain a stable pressure difference between the two towers; a flow stabilizing orifice plate is installed on the pipeline from the outlet of the primary tower to the inlet of the secondary tower to ensure gas-liquid contact balance.

[0037] The pressure balancing system is a dual-tower linkage control system with a pressure balancing pipe between the primary and secondary benzene washing towers. The pipe is equipped with an electric regulating valve and a differential pressure transmitter. The system monitors the pressure difference between the two towers in real time to ensure stable control of the pressure difference. Its core function is to ensure uniform airflow in the two towers and achieve stable linkage operation of the two towers.

[0038] The flow stabilization system is equipped with a flow stabilization orifice plate and flow meter on the gas pipeline from the outlet of the primary benzene washing tower to the inlet of the secondary tower. The orifice plate diameter is precisely designed according to the gas processing capacity to avoid gas-liquid contact imbalance and insufficient absorption caused by sudden changes in gas flow.

[0039] The system employs pressure stabilization control, with the entire benzene washing system operating under a slightly positive pressure. Automatic pressure stabilizing valves and venting valves are installed on the clean gas pipeline at the outlet of the secondary benzene washing tower to maintain stable system pressure.

[0040] The two towers are connected in series, ensuring a unified flow of gas and wash oil. Gas flow direction (co-current series): Final cooler, bottom of primary benzene washing tower, countercurrent contact of packing layer inside the tower (main absorption), top of primary benzene washing tower, bottom of secondary benzene washing tower, deep absorption of packing layer inside the tower (fine absorption), top of secondary benzene washing tower, clean gas pipeline; Wash oil flow direction (reverse cascade utilization): Lean oil cooler, top spray of secondary benzene washing tower (fine absorption), bottom of secondary benzene washing tower, top spray of primary benzene washing tower (main absorption), bottom of primary benzene washing tower, benzene removal system.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the yield of crude benzene, characterized in that, include: S1. Gas pretreatment: After primary cooling, coke oven gas enters the final cooler, where it is cleaned by circulating ammonia water spraying, and the gas temperature after final cooling is controlled to be 20℃~25℃. S2, Dual-tower series deep absorption: The pretreated coal gas enters the primary benzene washing tower and the secondary benzene washing tower in series for absorption; the wash oil adopts a reverse cascade utilization method, that is, the lean oil is first finely absorbed by the secondary benzene washing tower, and then enters the primary benzene washing tower for main absorption. S3. Pressure and flow control: A pressure balancing pipe and an electric regulating valve are installed between the primary and secondary benzene washing towers to maintain a stable pressure difference between the two towers; a flow stabilizing orifice plate is installed on the pipeline from the outlet of the primary tower to the inlet of the secondary tower to ensure gas-liquid contact balance.

2. The method for improving crude benzene yield according to claim 1, characterized in that: In S2, the primary benzene washing tower serves as the main absorption section, employing stainless steel perforated corrugated packing with a specific surface area of ​​not less than 250 m² / m³. The total height of the packing layer is 18 m, divided into 3 to 4 independent packing layers.

3. The method for improving crude benzene yield according to claim 2, characterized in that: Liquid redistributors are installed between sections, grid supports are installed at the bottom of the packing layer, and packing pressure rings are installed at the top.

4. The method for improving crude benzene yield according to claim 2, characterized in that: A baffle plate demister is installed at the top of the primary benzene washing tower to prevent wash oil droplets from being entrained by the gas.

5. The method for improving crude benzene yield according to claim 2, characterized in that: The top of the primary benzene washing tower is equipped with 2 to 3 trough-type liquid distributors, with a liquid distribution point of not less than 30 points / m². The liquid flows from top to bottom through uniform distribution and forms a liquid film on the surface of the packing with the high-concentration benzene series gas flowing from bottom to top, thus completing the mass transfer and absorption of benzene series compounds.

6. The method for improving crude benzene yield according to claim 1, characterized in that: In S2, the secondary benzene washing tower serves as the fine absorption section, employing structured metal wire mesh packing with a specific surface area of ​​not less than 350 m² / m³. The total height of the packing layer is 12 m, divided into 2 to 3 independent packing layers.

7. The method for improving crude benzene yield according to claim 1, characterized in that: In S2, the coal gas flows from bottom to top in both the primary and secondary benzene washing towers, while the wash oil is sprayed from top to bottom, forming a completely countercurrent gas-liquid contact state.

8. The method for improving crude benzene yield according to claim 1, characterized in that: In S2, a dual demister liquid trap is installed at the top of the secondary benzene washing tower, with a wire mesh demister at the bottom and a baffle plate demister at the top.

9. The method for improving crude benzene yield according to claim 1, characterized in that: In S2, the bottom of the secondary benzene washing tower is equipped with a dual anti-cross-gas device consisting of a U-shaped liquid seal and a check valve.

10. The method for improving crude benzene yield according to claim 1, characterized in that: The top of the secondary benzene washing tower is equipped with a dual liquid distribution system consisting of a trough-type liquid distributor and a tubular liquid distributor, with a liquid distribution point of not less than 40 / m². The new lean oil first enters the secondary benzene washing tower, and takes advantage of the high absorption activity of the lean oil with its extremely low benzene content to deeply and efficiently absorb trace amounts of benzene series compounds in the coal gas.