A method for recycling high-concentration organic tail gas of heavy aromatic hydrocarbon device

Abstract

The application discloses a kind of heavy aromatic hydrocarbon device high concentration organic tail gas recycling method.Resourceization is recycled to tail gas by closed collection, pre-condensation and two-stage absorption pretreatment, and is sent into two-stage membrane series assembly pre-concentration;Concentrated gas is modified by plasma dielectric barrier discharge, and then C9 and above heavy aromatic hydrocarbon and C7~C8 light aromatic hydrocarbon are recovered by fractional condensation respectively, and intermediate dehumidification unit is provided before condensation to prevent ice blockage;Low-grade waste heat of device is used to drive absorption refrigeration, combined with expansion self-cooling collaborative cooling, and power generation is recovered by expander;Residual tail gas is deeply purified by double-tower adsorption, and saturated adsorbent is regenerated by temperature and pressure coupling, and desorption non-condensable gas is recycled.The lean hydrocarbon tail gas is mixed with purified tail gas and discharged up to standard.The application realizes the fractional resource recycling of aromatic hydrocarbon, the recovery rate is increased by more than 30%, the energy consumption is reduced by 25%, there is no ice blockage problem, the emission meets strict environmental protection standards, and is suitable for high concentration organic tail gas treatment.

Description

Technical Field

[0001] This invention relates to the field of chemical tail gas resource recovery and treatment technology, specifically to a method for the resource recovery of high-concentration organic tail gas from a heavy aromatics plant. Background Technology

[0002] During the distillation, storage, and transportation processes of heavy aromatics plants, a large amount of high-concentration organic tail gas is continuously generated. This tail gas mainly contains C7-C9 and above aromatic components, trace impurities, and air components, characterized by high organic matter concentration, complex composition, high volatility, and strong polluting properties. Direct emission of this gas will not only cause serious air pollution, producing odors, smog, and other environmental problems, but will also lead to a significant waste of aromatic resources and reduce the overall economic efficiency of the plant.

[0003] Currently, the industry mainly divides the treatment methods for heavy aromatic organic waste gas into two categories. One is destruction-type treatment, including incineration and catalytic oxidation. This type of method can completely degrade organic pollutants, but it cannot achieve resource recovery at all. At the same time, the incineration process easily produces secondary pollutants such as nitrogen oxides, and requires a large amount of auxiliary fuel, resulting in high operating energy consumption and extremely low resource utilization. The other type is recovery-type treatment, with traditional condensation recovery, single adsorption recovery, and ordinary membrane separation recovery processes being widely used, but they have obvious technical defects.

[0004] Traditional single-condensation processes rely solely on low-temperature cooling for aromatic hydrocarbon separation. However, heavy aromatic hydrocarbon molecules have high condensation temperatures and complex phase transitions, resulting in low recovery efficiency under conventional low-temperature conditions. Furthermore, trace amounts of moisture in the exhaust gas can easily freeze and clog equipment in low-temperature pipelines. Ordinary membrane separation processes have low separation precision, making it impossible to grade and recover light and heavy aromatic hydrocarbons, leading to poor purity for exhaust gas resource recovery. Adsorption processes can only handle trace amounts of residual organic matter; direct adsorption of high-concentration exhaust gas easily leads to rapid adsorbent saturation, frequent regeneration, and high operating costs. Simultaneously, existing processes generally do not utilize the large amounts of low-grade waste heat generated during the production of heavy aromatic hydrocarbons, resulting in low energy utilization and a lack of energy recovery and recycling systems. Overall, the process energy consumption is high, making it difficult to simultaneously meet the dual requirements of compliant exhaust gas emissions and efficient resource recovery.

[0005] In response to the problems of low aromatic hydrocarbon recovery efficiency, inability to recover components in stages, easy ice blockage in low-temperature processes, waste of waste heat resources, high energy consumption, and poor balance between treatment and resource utilization in existing technologies, there is an urgent need to develop an integrated, energy-saving, and high-recovery-rate method for the resource recovery of high-concentration organic tail gas from heavy aromatic hydrocarbon plants. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a resource recovery method for high-concentration organic tail gas from heavy aromatic hydrocarbon plants. This method solves the problems of low recovery efficiency, mixed components, easy ice blockage, high energy consumption, waste of waste heat, and inability to achieve full component resource recovery in traditional processes. It enables efficient staged recovery of heavy aromatic hydrocarbon tail gas, energy recycling, and ultra-low clean emissions of tail gas, thereby improving the economic and environmental benefits of the plant.

[0007] To achieve the above objectives, the present invention employs the following technical means:

[0008] A method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant includes the following steps:

[0009] Step 1: Tail gas collection. High-concentration organic tail gas containing heavy aromatics and methanol generated from the heavy aromatics unit, diluent production unit, chemical storage tank area, loading and unloading system, and methanol recovery tower distillation tail condenser is collected in a unified manner through a closed pipeline. Pressure sensors and control valves are installed at the end of each tail gas branch pipe. After pressure stabilization and control by the tail gas vacuum pump, the gas is collected to avoid fugitive leakage.

[0010] Step 2: Pretreatment. The collected tail gas is first sent to a low-temperature primary condenser for pre-condensation, and then sent to the tail gas absorption tower. The tail gas absorption tower includes a lower methanol absorption section and an upper water absorption section. The tail gas enters from the lower part of the lower section and comes into countercurrent contact with the methanol liquid sprayed in the upper part of the lower section and the water phase sprayed in the upper part of the upper section to absorb the heavy aromatics and methanol in the tail gas. Part of the methanol absorption liquid in the bottom of the lower section of the absorption tower is recycled back to the lower section, and part is sent to the tank area as a diluent raw material. Part of the water absorption liquid in the upper section of the absorption tower is recycled back to the upper section, and part is sent to the methanol recovery tower to recover methanol. Part of the condensate at the top of the methanol recovery tower is used as reflux, and part is sent out as the absorption liquid or product in the lower section of the absorption tower. Part of the liquid phase in the bottom of the tower is reused in the upper section of the absorption tower, and part is discharged as wastewater. The non-condensable gas at the top of the tower is returned to the tail gas absorption tower. The tail gas discharged from the top of the absorption tower is then successively passed through a cyclone separator for dust removal, a metal wire mesh filter for demisting, and a deep dehumidification device for drying to thoroughly remove particulate matter, entrained droplets, and free water in the tail gas.

[0011] Step 3: Membrane pre-separation and concentration. The pretreated tail gas is sent to a gas separation membrane module. The hydrocarbon components in the tail gas are separated and enriched by the organic gas separation membrane. The permeate side of the membrane module is vacuumed to obtain concentrated organic tail gas, and the retrieval side is obtained as lean hydrocarbon tail gas. The membrane module adopts a two-stage membrane series structure. The tail gas on the retrieval side of the first-stage membrane module is sent to the second-stage membrane module for secondary separation. The gas on the permeate side of the second-stage membrane module is returned to the compressor inlet for recycling.

[0012] Step 4: Buffering and gas-liquid separation. The concentrated organic tail gas is sent to the buffer tank to complete the flow buffering and gravity sedimentation gas-liquid separation. The separated liquid phase material is sent to the recovery tank for storage.

[0013] Step 5: Plasma pretreatment and condensation. The buffered organic tail gas is sequentially fed into the plasma reactor and the primary condensation unit. The plasma reactor breaks the heavy aromatic hydrocarbon molecular chains and enhances molecular polarity through dielectric barrier discharge, reducing the condensation phase transition temperature of heavy aromatic hydrocarbons by 8-12°C. The primary condensation unit uses circulating cooling water as the medium and controls the condensation temperature to 0-10°C to condense and separate C9 and above heavy aromatic hydrocarbon components in the tail gas. The condensate is collected in the first recovery tank. A waste heat recovery heat exchanger is installed between the plasma reactor and the primary condensation unit to preheat the tail gas to be treated using the latent heat of condensation in the primary condensation unit. The preheating temperature is controlled at 30-60°C.

[0014] Step 6: Intermediate dehumidification treatment. The exhaust gas after primary condensation is sent to the intermediate dehumidification unit, where the moisture and trace byproducts generated by the plasma reaction are removed by a molecular sieve rotor or a cooling demister, thus preventing ice blockage in subsequent low-temperature processing steps.

[0015] Step 7: Expansion self-cooling pre-cooling, the dehumidified exhaust gas is pre-cooled by exchanging heat with the low-temperature exhaust gas at the outlet of the expansion self-cooling unit to reduce the initial temperature of the exhaust gas.

[0016] Step 8: Expansion self-cooling deep condensation. The pre-cooled exhaust gas is sent into the expansion self-cooling unit. After the exhaust gas is adiabatically expanded by the expander, it is cooled to -35℃ to -20℃. The C7 to C8 light aromatic components in the exhaust gas are separated by condensation. The condensate is collected in the second recovery tank. The expander drives the generator set to recover electrical energy. The recovered electricity is used to drive the system fan, vacuum pump or online monitoring equipment.

[0017] Step 9: Waste heat refrigeration to assist condensation. The low-grade waste heat in the gas phase at 120℃~160℃ at the top of the heavy aromatics unit distillation column is used to drive the absorption chiller to generate -15℃~0℃ cooling capacity. The cooling capacity is used to assist the pre-cooling process of the expansion self-cooling unit or the condensation and collection of the membrane separation component.

[0018] Step 10: Adsorption deep purification, the residual exhaust gas after deep condensation is sent to the adsorption unit, and the residual trace organic matter in the exhaust gas is adsorbed by the hydrophobic adsorbent; the adsorption unit is a dual adsorption tower parallel structure, the two towers alternately adsorb, desorb and regenerate, and the switching cycle is 4 to 12 hours.

[0019] Step 11: Adsorbent desorption and regeneration. After the adsorbent is saturated, desorption and regeneration are carried out using a variable temperature and pressure coupling method. First, the adsorption unit is evacuated to an absolute pressure of 1-8 kPa, and hot nitrogen gas at 70℃-120℃ is introduced to heat and desorb. The desorption time is 0.5-3 hours. After the desorbed gas is condensed, the condensate is sent to the second recovery tank, and the non-condensable gas is returned to the inlet of the first-stage condensation unit in step 5 for recycling.

[0020] Step 12: Mixed emission of exhaust gas. The lean hydrocarbon exhaust gas obtained in Step 3 is mixed with the purified exhaust gas in Step 10, and then discharged uniformly after passing online monitoring.

[0021] Preferably, the gas separation membrane in step 3 is a polyimide or polysiloxane composite membrane, the organic gas selectivity for nitrogen separation is greater than 25, the permeation rate is greater than 2500 GPU, and the membrane module permeation side vacuum pump is evacuated to an absolute pressure of 3-15 kPa.

[0022] Preferably, the plasma reactor in step 5 is a radial dual-dielectric barrier discharge reactor with a discharge gap of 2–8 mm, a discharge frequency of 5–20 kHz, a discharge voltage of 5–15 kV, and a residence time of the exhaust gas in the plasma reactor of 0.5–3 seconds.

[0023] Preferably, the intermediate dehumidification unit in step 6 uses molecular sieve rotor dehumidification or cooling demisting dehumidification to completely remove moisture and trace impurities from plasma reaction byproducts and prevent pipeline ice blockage during the low-temperature condensation process.

[0024] Preferably, the expander in step 8 is a turbine expander or a vortex tube, with an expansion ratio of 2:1 to 8:1.

[0025] Preferably, the absorption chiller unit in step 9 is a lithium bromide-water absorption chiller or an ammonia-water absorption chiller, with a coefficient of performance (COP) of 0.6 to 1.2.

[0026] Preferably, the hydrophobic adsorbent in step 10 is selected from one or more combinations of silica gel, ultrastable hydrophobic Y-type molecular sieve, and metal-organic framework materials.

[0027] Preferably, the ultrastable hydrophobic Y-type molecular sieve has a silicon-to-aluminum ratio of not less than 200, a dynamic water contact angle greater than 130°, and a dynamic adsorption capacity for toluene of not less than 15wt% under a relative humidity of 80%.

[0028] Preferably, in step 12, a flame ionization detector or a photoionization detector is installed at the emission outlet to monitor the concentration of non-methane total hydrocarbons and benzene series compounds in the exhaust gas in real time.

[0029] Preferably, the alarm threshold for the mass concentration of non-methane total hydrocarbons in the exhaust gas is set to 60 mg / m³. 3 When the monitored values ​​exceed the standard, an alarm will be automatically triggered and the system will automatically switch to the emergency emission treatment system.

[0030] The present invention has the following beneficial effects:

[0031] 1. Achieve graded resource recovery of all components in exhaust gas: This invention uses plasma molecular modification and graded low-temperature condensation process to accurately recover C9 and above heavy aromatics and C7-C8 light aromatics components respectively, solving the problems of mixed and low purity of aromatics recovery in traditional processes. The total recovery rate of aromatics is increased by more than 30% compared with traditional processes, which greatly improves the resource utilization rate of exhaust gas and the economic benefits of enterprises.

[0032] 2. Energy saving and efficiency improvement, high energy recycling rate: Fully utilize the low-grade waste heat of the device to drive the refrigeration unit, combined with the energy reuse design such as the expander to generate electricity, heat exchange and pre-cooling of hot and cold exhaust gas, and desorption gas recycling treatment, the system energy consumption is greatly reduced, getting rid of the drawbacks of traditional processes that rely on external energy sources, and the overall system energy consumption is reduced by more than 25%.

[0033] 3. Completely solve the problem of ice blockage in low-temperature processes: Through multi-stage pretreatment and a dedicated intermediate dehumidification unit, moisture and reaction byproducts in the exhaust gas are completely removed, avoiding ice blockage in the pipelines of low-temperature condensation and expansion processes from the source, ensuring that the entire set of equipment can operate continuously and stably for a long time, and reducing equipment failure rate and operation and maintenance costs.

[0034] 4. Excellent purification effect and controllable emissions: The multi-stage treatment process of "membrane concentration-stage condensation-dual tower adsorption deep purification" is adopted, combined with online real-time monitoring and emergency linkage system. The removal rate of non-methane total hydrocarbons and benzene series compounds in the exhaust gas is extremely high, which can stably achieve ultra-low clean emissions and meet stringent environmental protection standards.

[0035] 5. Strong process continuity and adaptability: The design of two-stage membrane series separation, alternating operation of dual adsorption towers, and variable temperature and pressure coupled regeneration ensures continuous and uninterrupted operation of the process. It can be adapted to heavy aromatic tail gas treatment scenarios with different loads and component concentrations, and has strong industrial versatility.

[0036] 6. No secondary pollution, green and environmentally friendly: The whole process is based on resource recycling, without incineration, oxidation or other destruction processes, and no secondary pollutants such as nitrogen oxides are generated. All by-product gases and desorbed non-condensable gases are recycled, achieving the dual goals of pollutant reduction and resource value-added. Attached Figure Description

[0037] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0038] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] like Figure 1As shown, the present invention provides a method for the resource recovery of high-concentration organic tail gas from a heavy aromatics plant, comprising the following detailed steps:

[0040] Step 1: Tail gas collection. High-concentration organic tail gas containing heavy aromatics and methanol generated from the heavy aromatics unit, diluent production unit, chemical storage tank area, loading and unloading system, and methanol recovery tower distillation tail condenser is collected in a unified manner through a closed pipeline. Pressure sensors and control valves are installed at the end of each tail gas branch pipe. After being collected by tail gas vacuum pump pressure stabilization control, the entire process is sealed and leak-free, completely eliminating fugitive tail gas leakage and ensuring tail gas collection efficiency and production environment safety.

[0041] Step 2: Pretreatment. The collected tail gas is first sent to a low-temperature primary condenser for pre-condensation to recover some condensable components, and then sent to the tail gas absorption tower. The tail gas absorption tower includes a lower methanol absorption section and an upper water absorption section. The tail gas enters from the lower part of the lower section and comes into countercurrent contact with the methanol liquid sprayed from the upper part of the lower section and the water phase sprayed from the upper part of the upper section. Through physical absorption, heavy aromatics and methanol in the tail gas are efficiently removed. Part of the methanol absorbent liquid in the bottom of the lower section of the absorption tower is recycled back to the lower section to maintain the absorption effect, and part is sent to the tank area as a raw material for diluent recovery. Part of the water absorbent liquid in the upper section of the absorption tower is recycled back to the upper section, and part is sent to the methanol recovery tower to recover methanol. Part of the condensate at the top of the methanol recovery tower is used as reflux, and part is sent out as absorbent liquid or product in the lower section of the absorption tower. Part of the liquid phase in the bottom of the tower is reused in the upper section of the absorption tower, and part is discharged as wastewater. The non-condensable gas at the top of the tower is returned to the tail gas absorption tower for recycling. The exhaust gas discharged from the top of the absorption tower is then sequentially passed through a cyclone separator for dust removal, a metal wire mesh filter for demisting, and a deep dehumidification device for drying. This process removes solid particles, process-carried droplets, and free water carried in the exhaust gas step by step. The purified exhaust gas is free of impurities and free water, which prevents subsequent membrane modules, cryogenic equipment, and adsorbents from being contaminated and blocked, and ensures the stable operation of subsequent processes.

[0042] Step 3: Membrane pre-separation and concentration. The pretreated clean tail gas is sent to a two-stage series gas separation membrane module. An organic gas separation membrane is used to precisely separate and enrich hydrocarbon components and non-hydrocarbon components such as nitrogen in the tail gas. A vacuum pump creates a low-pressure environment on the permeate side of the membrane module, enriching the tail gas with a high concentration of concentrated organic components, while a low-concentration lean hydrocarbon tail gas is obtained on the retrieval side. The tail gas that is not completely separated on the retrieval side of the first-stage membrane module is sent to the second-stage membrane module for secondary deep separation. The concentrated gas on the permeate side of the second-stage membrane module is returned to the compressor inlet for recirculation, maximizing the recovery rate of hydrocarbon components.

[0043] In this step, a polyimide or polysiloxane composite membrane is selected for gas separation. This membrane material has a selectivity of more than 25 for separating organic gases and nitrogen, a permeation rate of more than 2500 GPU, high separation accuracy, and stable flux. The vacuum degree on the permeate side of the membrane module is controlled at an absolute pressure of 3-15 kPa to ensure the concentration effect.

[0044] Step 4: Buffering and gas-liquid separation. The high-concentration organic tail gas after membrane concentration is sent to a buffer tank. The buffer tank stabilizes and buffers the tail gas flow rate, eliminating the impact of tail gas flow fluctuations on subsequent processes. At the same time, gas-liquid separation is achieved by gravity settling. The trace amounts of liquid aromatic materials entrained in the tail gas are separated by settling and sent to a recovery tank for storage, further purifying the gas phase tail gas components.

[0045] Step 5: Plasma pretreatment and condensation. The buffered and stabilized organic tail gas first enters the waste heat recovery heat exchanger for preheating. The preheating temperature is controlled at 30℃~60℃, which effectively improves the electron energy transfer efficiency of subsequent plasma discharge. The preheated tail gas is sent to the radial dual dielectric barrier discharge plasma reactor, where high-energy electrons and active particles are generated under specific discharge parameters. This precisely breaks the long molecular chains of heavy aromatics and enhances molecular polarity, reducing the condensation phase transition temperature of heavy aromatics by 8~12℃ and significantly reducing the difficulty of condensing heavy aromatics.

[0046] The plasma reactor is controlled with the following parameters: discharge gap 2–8 mm, discharge frequency 5–20 kHz, discharge voltage 5–15 kV, and tail gas residence time 0.5–3 seconds, ensuring uniform and stable molecular modification. The modified tail gas enters the primary condensation unit, where circulating cooling water is used as the cooling medium. The condensation temperature is controlled at 0℃–10℃, and C9 and higher heavy aromatic hydrocarbon components are separated by directional condensation. The high-purity heavy aromatic hydrocarbon liquid obtained from condensation is collected in the first recovery tank, completing the recovery of the heavy aromatic hydrocarbon components.

[0047] Step 6: Intermediate dehumidification treatment. The exhaust gas after primary condensation contains trace amounts of moisture and byproducts from the plasma reaction. It is sent to the intermediate dehumidification unit, where it undergoes deep dehumidification by a molecular sieve rotor or precise removal of impurities by a cooling demister. This completely removes moisture and trace impurities from the exhaust gas, eliminating the risk of ice blockage in pipelines and equipment during subsequent low-temperature deep condensation processes and ensuring the long-term stable operation of the low-temperature system.

[0048] Step 7: Expansion self-cooling pre-cooling. The dehumidified and purified exhaust gas is sent into the heat exchanger to pre-cool the low-temperature exhaust gas at the outlet of the expansion self-cooling unit in a counter-current heat exchange. This fully recovers the cold energy of the low-temperature exhaust gas, reduces the initial temperature of the exhaust gas to be treated, reduces the energy consumption of subsequent expansion refrigeration, and realizes the recycling of cold energy.

[0049] Step 8: Expansion and self-cooling deep condensation. The pre-cooled exhaust gas is sent to the expansion and self-cooling unit, where a turbine expander or vortex tube is used to achieve adiabatic expansion and cooling. The expansion ratio is controlled at 2:1 to 8:1, and the exhaust gas temperature rapidly drops to -35℃ to -20℃. Under low-temperature conditions, the C7-C8 light aromatic hydrocarbon components in the exhaust gas are efficiently condensed and separated. The condensed light aromatic hydrocarbon liquid is collected in the second recovery tank, achieving precise graded recovery of light and heavy aromatic hydrocarbons. At the same time, the work done by the expander drives the generator set to generate electricity. The recovered electricity is directly used to drive auxiliary equipment such as system fans, vacuum pumps, and online monitoring equipment, significantly reducing the overall power consumption of the system and achieving energy recovery and efficiency improvement.

[0050] Step 9: Waste heat refrigeration-assisted condensation fully recovers the low-grade gaseous waste heat (120℃~160℃) from the top of the heavy aromatics unit's distillation column. This waste heat is used as a driving heat source to power a lithium bromide-water or ammonia-water absorption chiller, generating low-temperature cooling capacity from -15℃ to 0℃. The chiller's COP is stabilized at 0.6~1.2. The generated cooling capacity can be flexibly allocated to assist the pre-cooling process of the expansion self-cooling unit or the condensation and capture of the membrane separation component, further improving the recovery efficiency of aromatic components, maximizing the utilization of the unit's waste heat resources, and reducing external energy consumption.

[0051] Step 10: Deep Adsorption Purification. The residual exhaust gas, after staged condensation and recovery, contains only trace amounts of organic pollutants. It is then fed into a parallel adsorption unit of dual adsorption towers, where hydrophobic adsorbents deeply adsorb and purify the remaining trace organic matter. The adsorbent is selected from one or more combinations of silica gel, ultra-stable hydrophobic Y-type molecular sieves, and metal-organic framework materials. The ultra-stable hydrophobic Y-type molecular sieve has a silica-to-alumina ratio of not less than 200, a dynamic water contact angle greater than 130°, and excellent adsorption performance under high humidity conditions, with a dynamic adsorption capacity for toluene of not less than 15 wt% at 80% relative humidity. The dual adsorption towers employ an alternating adsorption-desorption-regeneration mode, with a switching cycle controlled at 4–12 hours to ensure continuous and stable purification of the exhaust gas.

[0052] Step 11: Adsorbent Desorption and Regeneration. Once the adsorbent in the adsorption tower reaches saturation, efficient desorption and regeneration are achieved using a variable temperature and pressure coupling method. First, the adsorption unit is evacuated to an absolute pressure of 1–8 kPa, and simultaneously hot nitrogen gas at 70℃–120℃ is introduced for heating and desorption. The desorption time is controlled to be 0.5–3 hours. The combination of vacuum negative pressure and high-temperature hot blowing can quickly remove organic matter from the pores of the adsorbent. The desorbed gas generated during desorption is condensed, and the liquid aromatic material is sent to the second recovery tank for recycling. The non-condensable gas is returned to the inlet of the primary condensation unit in Step 5 for recirculation, resulting in no resource waste and no secondary emissions.

[0053] Step 12: Mixed emission of exhaust gases. The low-concentration lean hydrocarbon exhaust gas obtained from membrane separation in Step 3 is uniformly mixed with the clean exhaust gas after deep adsorption purification in Step 10. The concentrations of non-methane total hydrocarbons and benzene series compounds are monitored in real time online using a flame ionization detector or photoionization detector mounted at the emission port. The alarm threshold for the mass concentration of non-methane total hydrocarbons is set at 60 mg / m³. 3 Once the monitoring data meets the standards, emissions will be uniformly compliant; if the values ​​exceed the standards, the system will automatically alarm and switch to the emergency emission treatment system to eliminate the risk of excessive emissions.

[0054] Example 1

[0055] A method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant, the specific operation steps of which are as follows:

[0056] Step 1: Collect high-concentration organic tail gas containing heavy aromatics and methanol from heavy aromatics unit, diluent production unit, chemical storage tank area, loading and unloading system and methanol recovery tower distillation tail condenser in a closed system. Pressure sensors and control valves at the end of each branch pipe are used in conjunction with tail gas vacuum pumps to stabilize and collect the gas, preventing fugitive leaks.

[0057] Step 2: The collected tail gas is first sent to a low-temperature primary condenser for pre-condensation, and then enters the tail gas absorption tower. The lower section of the absorption tower absorbs heavy aromatics with methanol spray, while the upper section absorbs methanol with water spray. Part of the methanol absorbent liquid from the lower section's bottom is recycled, and part is sent to the tank area as a diluent feedstock. Part of the water absorbent liquid from the upper section is recycled, and part is sent to the methanol recovery tower for methanol recovery. Part of the condensate from the top of the methanol recovery tower is refluxed, and part is sent out as absorbent liquid or product. Part of the liquid from the bottom of the tower is reused in the upper section, and part is discharged. Non-condensable gases are returned to the absorption tower. The exhaust gas from the top of the absorption tower is then dried by a cyclone separator for dust removal, a metal wire mesh filter for demisting, and a deep dehumidification device to thoroughly remove particulate matter, entrained droplets, and free moisture.

[0058] Step 3: The pretreated tail gas is sent to a two-stage series polysiloxane composite membrane module. The membrane material has an organic gas separation selectivity of 28 for nitrogen and a permeation rate of 2600 GPU. The permeation side vacuum pump is used to evacuate to an absolute pressure of 8 kPa. The tail gas on the primary membrane retrieval side is sent to the secondary membrane for secondary separation. The gas on the secondary membrane permeation side is returned to the compressor inlet for recycling treatment to obtain lean hydrocarbon tail gas and concentrated organic tail gas.

[0059] Step 4: The concentrated organic tail gas is sent to a buffer tank for pressure stabilization and gravity gas-liquid separation. The separated liquid phase is sent to a recovery tank for storage.

[0060] Step 5: After buffering, the tail gas is preheated to 45°C by a waste heat recovery heat exchanger and sent to a radial dual-dielectric barrier discharge plasma reactor. The discharge gap is controlled at 5mm, the discharge frequency at 12kHz, the discharge voltage at 10kV, and the tail gas residence time at 1.5s. The phase change temperature of heavy aromatics is reduced by 10°C. The modified tail gas enters the first-stage condensation unit, where the condensation temperature is controlled at 5°C. C9 and above heavy aromatic components are separated by condensation, and the condensate is collected in the first recovery tank.

[0061] Step 6: After primary condensation, the exhaust gas is sent to the molecular sieve rotor dehumidification unit to completely remove by-product moisture and trace impurities.

[0062] Step 7: After dehumidification, the exhaust gas is pre-cooled by exchanging heat with the low-temperature outlet exhaust gas of the expansion self-cooling unit.

[0063] Step 8: After pre-cooling, the exhaust gas is sent to a turbine expander with an expansion ratio of 4:1. It undergoes adiabatic expansion and cooling to -28°C, and the C7-C8 light aromatic hydrocarbon components are separated by condensation. The condensate is collected in the second recovery tank. The expander generates electricity, which is used to drive the system vacuum pump and online monitoring equipment.

[0064] Step 9: Utilize the waste heat of the gas phase at 140℃ at the top of the heavy aromatics unit distillation column to drive the lithium bromide-water absorption chiller (COP=0.9) to generate -8℃ cooling capacity to assist the pre-cooling process of the expansion self-cooling unit.

[0065] Step 10: After deep condensation, the residual tail gas is sent to the parallel adsorption unit of the dual adsorption towers. The ultra-stable hydrophobic Y-type molecular sieve (silicon-to-aluminum ratio 220, dynamic water contact angle 135°) is selected as the adsorbent. The adsorption tower switching cycle is 8 hours, which deeply purifies trace residual organic matter.

[0066] Step 11: After the adsorbent is saturated, the vacuum is drawn to an absolute pressure of 4 kPa, and hot nitrogen at 95°C is introduced simultaneously for desorption for 2 hours. The desorbed gas is condensed and the liquid phase is sent to the second recovery tank, while the non-condensable gas is returned to the inlet of the first-stage condensation unit for recycling.

[0067] Step 12: The lean hydrocarbon exhaust gas is mixed with the purified exhaust gas and monitored in real time by a flame ionization detector. The concentration of non-methane total hydrocarbons is below 60 mg / m³. 3 Once the emission standards are met, emissions will be compliant; if the standards are exceeded, an alarm will be triggered and the emergency system will be switched on.

[0068] Example 2

[0069] A method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant, the specific operation steps of which are as follows:

[0070] Steps 1-2: Same as in Example 1, complete the closed collection, pressure stabilization and aggregation, initial condensation and precooling, dual-stage absorption and multi-stage pretreatment purification of multi-source exhaust gas.

[0071] Step 3: Using a polyimide composite membrane module, the organic gas to nitrogen separation selectivity is 26, the permeation rate is 2550 GPU, the absolute pressure of the permeation side vacuum is 5 kPa, and the secondary membrane is connected in series for circulation separation to achieve hydrocarbon enrichment in the tail gas.

[0072] Step 4: Complete the exhaust gas buffering and gas-liquid separation.

[0073] Step 5: Preheat the tail gas to 35℃, set the discharge gap of the plasma reactor to 3mm, the discharge frequency to 8kHz, the discharge voltage to 8kV, and the tail gas residence time to 2s, thereby reducing the phase transition temperature of heavy aromatics by 9℃; control the primary condensation temperature to 3℃ to recover C9 and above heavy aromatics.

[0074] Step 6: Use a cooling demister to complete the intermediate dehumidification and impurity removal of the exhaust gas.

[0075] Step 7: Complete the exhaust gas heat exchange and pre-cooling.

[0076] Step 8: Use a vortex tube expander with an expansion ratio of 3:1 to expand and cool down to -25℃ to recover C7-C8 light aromatics. The expansion generates electricity to drive the system's fan.

[0077] Step 9: Use the waste heat from the 125℃ distillation process to drive the ammonia-water absorption chiller (COP=0.7) to generate -5℃ cooling capacity to assist the membrane module in condensation and capture.

[0078] Step 10: The adsorbent is a composite adsorbent of silica gel and metal-organic framework material, and the adsorption tower switching cycle is 6 hours.

[0079] Step 11: Desorption vacuum pressure 3 kPa, hot nitrogen temperature 85℃, desorption time 1.5 hours, desorption gas is recycled.

[0080] Step 12: After the exhaust gas is mixed, it is monitored by a photoionization detector. If it meets the emission standards, it will be emitted; if it exceeds the standards, an automatic emergency response will be implemented.

[0081] Example 3

[0082] A method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant, the specific operation steps of which are as follows:

[0083] Steps 1-2: Similar to Example 1, a closed pipeline is used to collect high-concentration organic tail gas containing heavy aromatics and methanol from each device. The branch pipe pressure sensor and control valve work together with a vacuum pump to stabilize and collect the gas. The collected tail gas is first pre-condensed by a low-temperature primary condenser condenser, and then enters the tail gas absorption tower. The lower section absorbs methanol and the upper section absorbs water. The absorbent liquid is circulated, recovered or discharged according to the process. The exhaust gas at the top of the tower passes through a cyclone separator, a metal wire mesh filter and a deep dehumidification device to complete the dust removal, demisting and drying pretreatment, and thoroughly remove solid particles, entrained droplets and free water from the tail gas.

[0084] Step 3: After pretreatment, the tail gas is sent into a two-stage series polyimide composite membrane module. The membrane material has an organic gas selectivity of 30 for nitrogen separation and a permeation rate of 2700 GPU. The permeation side vacuum pump is used to evacuate to an absolute pressure of 12 kPa. The tail gas on the primary membrane retrieval side enters the secondary membrane to complete secondary separation. The gas on the secondary membrane permeation side is returned to the compressor inlet for recycling, which efficiently enriches hydrocarbon components.

[0085] Step 4: The concentrated high-concentration organic tail gas is sent to a buffer tank to achieve flow stabilization, pressure buffering, and gravity gas-liquid separation. The precipitated trace amounts of liquid aromatics are sent to a recovery tank for storage.

[0086] Step 5: The buffered tail gas is preheated to 55°C by a waste heat recovery heat exchanger and sent to a radial dual-dielectric barrier discharge plasma reactor. The discharge gap is controlled at 7mm, the discharge frequency at 18kHz, and the discharge voltage at 13kV. The tail gas residence time in the reactor is 2.5s, and the condensation phase change temperature of heavy aromatics is reduced by 12°C. The modified tail gas enters the first-stage condensation unit, where the condensation temperature is controlled at 8°C. C9 and above heavy aromatic components are condensed and recovered, and the condensate is collected in the first recovery tank.

[0087] Step 6: The exhaust gas after primary condensation is dehumidified and impurities are removed by a cooling demister to completely remove the moisture and trace byproducts generated by the plasma reaction and avoid the risk of ice blockage in low-temperature pipelines.

[0088] Step 7: The dehumidified exhaust gas is pre-cooled by counter-current heat exchange with the low-temperature exhaust gas at the outlet of the expansion self-cooling unit, recovering cold energy and reducing the intake air temperature.

[0089] Step 8: The pre-cooled exhaust gas is sent into the vortex tube expander with an expansion ratio of 6:1. The adiabatic expansion cools the gas to -32℃, and the C7-C8 light aromatic components in the exhaust gas are separated by condensation. The condensate is collected in the second recovery tank. The expansion generates electricity, and all the electricity is used to drive the system vacuum pump and online monitoring equipment, reducing system energy consumption.

[0090] Step 9: Utilize the waste heat of the gas phase at 155℃ at the top of the heavy aromatics unit distillation column to drive the ammonia-water absorption chiller (COP=1.1) to generate a low-temperature cooling capacity of -12℃, while simultaneously assisting the pre-cooling of the expansion self-cooling unit and the condensation and collection process of the membrane separation component.

[0091] Step 10: The residual exhaust gas after deep condensation is sent to the parallel adsorption unit of the dual adsorption towers. The composite adsorbent of ultra-stable hydrophobic Y-type molecular sieve and metal-organic framework material is selected. The switching cycle of the adsorption tower is 10 hours, and the trace residual organic matter is removed by deep adsorption.

[0092] Step 11: After the adsorbent is saturated, the vacuum is drawn to an absolute pressure of 6 kPa, and hot nitrogen gas at 110°C is introduced simultaneously for constant temperature desorption for 2.5 hours. The desorbed gas is condensed and the liquid phase is sent to the second recovery tank, while the non-condensable gas is returned to the inlet of the first-stage condensation unit for recycling.

[0093] Step 12: The lean hydrocarbon tail gas from membrane separation is uniformly mixed with the tail gas after adsorption purification. The concentrations of non-methane total hydrocarbons and benzene series compounds are monitored in real time by a flame ionization detector. The emission concentrations are far below 60 mg / m³. 3 It ensures compliant and stable emissions, and automatically alarms and activates the emergency response system if emissions exceed standards.

[0094] Comparative example (traditional single condensation recovery process)

[0095] This system employs a traditional ambient temperature pretreatment followed by a single low-temperature condensation process to treat heavy aromatic hydrocarbon tail gas under the same operating conditions. It lacks plasma modification, membrane concentration, waste heat utilization, and energy recovery systems, relying solely on -30℃ low-temperature condensation to recover aromatics, without any staged recovery process. Testing revealed that the traditional process achieves a total aromatic hydrocarbon recovery rate of only 55%, with the recovered aromatic hydrocarbon components being mixed and of low purity. The low-temperature process experiences pipeline ice blockage every 7-10 days, requiring system shutdown for de-icing. The system also suffers from high energy consumption, and the concentration of non-methane total hydrocarbons in the tail gas emissions fluctuates significantly, making it difficult to consistently meet emission standards.

[0096] Implementation effect

[0097] Based on actual measurements, the present invention sets three sets of embodiments with different process parameter gradients, and the operating effects of each embodiment are as follows:

[0098] Example 1: Actual test results: The entire system operated stably, with no pipeline ice blockage or frequent equipment failures. The total aromatic hydrocarbon recovery rate reached 88.2%, with a purity of 95.3% for C9 and above heavy aromatic hydrocarbons and 96.1% for C7-C8 light aromatic hydrocarbons. The overall energy consumption of the system was reduced by 27.5% compared to the traditional process, and the total non-methane hydrocarbons in the tail gas were stably maintained at 25-30 mg / m³. 3 Emissions meet standards.

[0099] Example 2: Actual test results: Adaptable to low-to-medium load tail gas conditions, with good process continuity, total aromatic recovery rate reaching 86.5%, and light and heavy aromatic recovery purities of 94.8% and 95.2%, respectively; system energy consumption is reduced by 25.8% compared to traditional processes, and the non-methane total hydrocarbon emission concentration in the tail gas is consistently below 30 mg / m³. 3 It has been operating for a long time without ice blockage.

[0100] Example 3: Actual test results: Adaptable to high-concentration, high-load exhaust gas conditions, with optimal waste heat utilization and energy recovery efficiency. The total aromatic hydrocarbon recovery rate can reach 90.1%, and the recovery purity of C9 heavy aromatics and C7-C8 light aromatics can reach 96.2% and 96.5%, respectively. The overall energy consumption of the system is reduced by 30.2% compared with the traditional process, with the most significant energy-saving effect. The non-methane total hydrocarbon emission concentration in the exhaust gas is consistently below 22 mg / m³. 3 It has the best purification effect and can meet the stringent environmental emission requirements.

[0101] All three sets of examples generated no secondary pollutants throughout the entire process. The desorbed gas and residual exhaust gas were all recycled or discharged in compliance with standards. Compared with the traditional single condensation process (recovery rate of 55%, prone to ice blockage, high energy consumption, and large emission fluctuations), it has overwhelming advantages in terms of resource recovery rate, energy saving, equipment stability, and environmental emissions, and has extremely high industrial practical value.

[0102] The examples provided in this invention are not intended to limit the implementation. Those skilled in the art will recognize that various variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of this invention.

Claims

1. A method for the resource recovery of high-concentration organic tail gas from a heavy aromatics plant, characterized in that, Includes the following steps: Step 1: Tail gas collection. High-concentration organic tail gas containing heavy aromatics and methanol generated from the heavy aromatics unit, diluent production unit, chemical storage tank area, loading and unloading system, and methanol recovery tower distillation tail condenser is collected in a unified manner through a closed pipeline. Pressure sensors and control valves are installed at the end of each tail gas branch pipe. After pressure stabilization and control by the tail gas vacuum pump, the gas is collected to avoid fugitive leakage. Step 2: Pretreatment. The collected tail gas is first sent to a low-temperature primary condenser for pre-condensation, and then sent to the tail gas absorption tower. The tail gas absorption tower includes a lower methanol absorption section and an upper water absorption section. The tail gas enters from the lower part of the lower section and comes into countercurrent contact with the methanol liquid sprayed in the upper part of the lower section and the water phase sprayed in the upper part of the upper section to absorb the heavy aromatics and methanol in the tail gas. Part of the methanol absorption liquid in the bottom of the lower section of the absorption tower is recycled back to the lower section, and part is sent to the tank area as a diluent raw material. Part of the water absorption liquid in the upper section of the absorption tower is recycled back to the upper section, and part is sent to the methanol recovery tower to recover methanol. Part of the condensate at the top of the methanol recovery tower is used as reflux, and part is sent out as the absorption liquid or product in the lower section of the absorption tower. Part of the liquid phase in the bottom of the tower is reused in the upper section of the absorption tower, and part is discharged as wastewater. The non-condensable gas at the top of the tower is returned to the tail gas absorption tower. The exhaust gas discharged from the top of the absorption tower then passes through a cyclone separator for dust removal, a metal wire mesh filter for demisting, and a deep dehumidification device for drying, thoroughly removing particulate matter, entrained droplets, and free moisture from the exhaust gas. Step 3: Membrane pre-separation and concentration. The pretreated tail gas is sent to a gas separation membrane module. The hydrocarbon components in the tail gas are separated and enriched by the organic gas separation membrane. The permeate side of the membrane module is vacuumed to obtain concentrated organic tail gas, and the retrieval side is obtained as lean hydrocarbon tail gas. The membrane module adopts a two-stage membrane series structure. The tail gas on the retrieval side of the first-stage membrane module is sent to the second-stage membrane module for secondary separation. The gas on the permeate side of the second-stage membrane module is returned to the compressor inlet for recycling. Step 4: Buffering and gas-liquid separation. The concentrated organic tail gas is sent to the buffer tank to complete the flow buffering and gravity sedimentation gas-liquid separation. The separated liquid phase material is sent to the recovery tank for storage. Step 5: Plasma pretreatment and condensation. The buffered organic tail gas is sequentially fed into the plasma reactor and the primary condensation unit. The plasma reactor breaks the heavy aromatic hydrocarbon molecular chains and enhances molecular polarity through dielectric barrier discharge, reducing the condensation phase transition temperature of heavy aromatic hydrocarbons by 8-12°C. The primary condensation unit uses circulating cooling water as the medium and controls the condensation temperature to 0-10°C to condense and separate C9 and above heavy aromatic hydrocarbon components in the tail gas. The condensate is collected in the first recovery tank. A waste heat recovery heat exchanger is installed between the plasma reactor and the primary condensation unit to preheat the tail gas to be treated using the latent heat of condensation in the primary condensation unit. The preheating temperature is controlled at 30-60°C. Step 6: Intermediate dehumidification treatment. The exhaust gas after primary condensation is sent to the intermediate dehumidification unit, where the moisture and trace byproducts generated by the plasma reaction are removed by a molecular sieve rotor or a cooling demister, thus preventing ice blockage in subsequent low-temperature processing steps. Step 7: Expansion self-cooling pre-cooling, the dehumidified exhaust gas is pre-cooled by exchanging heat with the low-temperature exhaust gas at the outlet of the expansion self-cooling unit to reduce the initial temperature of the exhaust gas. Step 8: Expansion self-cooling deep condensation. The pre-cooled exhaust gas is sent into the expansion self-cooling unit. After the exhaust gas is adiabatically expanded by the expander, it is cooled to -35℃ to -20℃. The C7 to C8 light aromatic components in the exhaust gas are separated by condensation. The condensate is collected in the second recovery tank. The expander drives the generator set to recover electrical energy. The recovered electricity is used to drive the system fan, vacuum pump or online monitoring equipment. Step 9: Waste heat refrigeration to assist condensation. The low-grade waste heat in the gas phase at 120℃~160℃ at the top of the heavy aromatics unit distillation column is used to drive the absorption chiller to generate -15℃~0℃ cooling capacity. The cooling capacity is used to assist the pre-cooling process of the expansion self-cooling unit or the condensation and collection of the membrane separation component. Step 10: Adsorption deep purification, the residual exhaust gas after deep condensation is sent to the adsorption unit, and the residual trace organic matter in the exhaust gas is adsorbed by the hydrophobic adsorbent; the adsorption unit is a dual adsorption tower parallel structure, the two towers alternately adsorb, desorb and regenerate, and the switching cycle is 4 to 12 hours. Step 11: Adsorbent desorption and regeneration. After the adsorbent is saturated, desorption and regeneration are carried out using a variable temperature and pressure coupling method. First, the adsorption unit is evacuated to an absolute pressure of 1-8 kPa, and hot nitrogen gas at 70℃-120℃ is introduced to heat and desorb. The desorption time is 0.5-3 hours. After the desorbed gas is condensed, the condensate is sent to the second recovery tank, and the non-condensable gas is returned to the inlet of the first-stage condensation unit in step 5 for recycling. Step 12: Mixed emission of exhaust gas. The lean hydrocarbon exhaust gas obtained in Step 3 is mixed with the purified exhaust gas in Step 10, and then discharged uniformly after passing online monitoring.

2. The method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant according to claim 1, characterized in that, The gas separation membrane mentioned in step 3 is a polyimide or polysiloxane composite membrane with an organic gas selectivity for nitrogen greater than 25 and a permeation rate greater than 2500 GPU. The permeation side vacuum pump of the membrane module is evacuated to an absolute pressure of 3-15 kPa.

3. The method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant according to claim 1, characterized in that, The plasma reactor mentioned in step 5 is a radial dual-dielectric barrier discharge reactor with a discharge gap of 2–8 mm, a discharge frequency of 5–20 kHz, a discharge voltage of 5–15 kV, and a residence time of the exhaust gas in the plasma reactor of 0.5–3 seconds.

4. The method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant according to claim 1, characterized in that, The intermediate dehumidification unit in step 6 uses molecular sieve rotor dehumidification or cooling demisting dehumidification to completely remove moisture and trace impurities from plasma reaction byproducts and prevent pipeline ice blockage during the low-temperature condensation process.

5. The method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant according to claim 1, characterized in that, The expander mentioned in step 8 is a turbine expander or a vortex tube expander with an expansion ratio of 2:1 to 8:

1.

6. The method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant according to claim 1, characterized in that, The absorption chiller unit mentioned in step 9 is a lithium bromide-water absorption chiller or an ammonia-water absorption chiller, with a coefficient of performance (COP) of 0.6 to 1.

2.

7. The method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant according to claim 1, characterized in that, The hydrophobic adsorbent mentioned in step 10 is selected from one or more combinations of silica gel, ultrastable hydrophobic Y-type molecular sieves, and metal-organic framework materials.

8. The method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant according to claim 7, characterized in that, The ultra-stable hydrophobic Y-type molecular sieve has a silicon-to-aluminum ratio of not less than 200, a dynamic water contact angle greater than 130°, and a dynamic adsorption capacity for toluene of not less than 15wt% under a relative humidity of 80%.

9. The method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant according to claim 1, characterized in that, In step 12, a flame ionization detector or photoionization detector is installed at the emission outlet to monitor the concentration of non-methane total hydrocarbons and benzene series compounds in the exhaust gas in real time.

10. A method for resource recovery of high-concentration organic tail gas from a heavy aromatics plant according to claim 9, characterized in that, The alarm threshold for the mass concentration of non-methane total hydrocarbons in exhaust gas is set at 60 mg / m³. 3 When the monitored values ​​exceed the standard, an alarm will be automatically triggered and the system will automatically switch to the emergency emission treatment system.

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