Method for recycling styrene from exhaust gas of artificial-stone production line on basis of synergy of adsorption and absorption

Abstract

The present invention relates to VOC tail gas treatment in the field of environmental protection, and specifically discloses a method for recycling styrene from exhaust gas of an artificial-stone production line on the basis of the synergy of adsorption and absorption. The method comprises: under the suction action of a fan, feeding exhaust gas of an artificial-stone production line into an absorption tower from an exhaust gas inlet at the lower part of the absorption tower and bringing same into successive countercurrent contact with an absorbent that is sprayed in from top toward bottom, which enables most of styrene to be absorbed; and feeding the semi-purified exhaust gas that is discharged from the top of the absorption tower into an adsorption tower, further adsorbing the residual styrene component, directly discharging, via a chimney, the purified exhaust gas from an adsorption tower group, and feeding a rich liquid having absorbed the styrene component into a flash kettle for distillation to recover styrene, wherein the rich liquid is divided into two streams, the first stream is heated to 60-65°C and then sent to the flash kettle for desorption to recover the styrene component, and the second stream is sent to a rich-liquid refluxing and washing tower to capture fine fog-drops in flash vapor from the flash kettle. The present invention has the characteristics of low investment and operation costs, a good exhaust gas purification effect, effective coupling of absorption with adsorption, a high styrene recovery rate, and environmental friendliness.

Description

A method for styrene resource recovery from waste gas in artificial stone production lines based on adsorption-absorption synergy Technical Field

[0001] This invention belongs to the field of environmental protection and relates to a resource recovery and utilization method for pollutants in VOC exhaust gas. Specifically, it is a method for resource recovery of styrene from waste gas in artificial stone production lines based on adsorption-absorption synergy. Background Technology

[0002] Styrene, an important raw material in the chemical industry, is a crucial monomer in the production of synthetic resins, ion exchange resins, and synthetic rubber, and has a wide range of applications. In the production of artificial stone, resin is one of the key raw materials. During the stirring, mixing, molding, and curing processes, a large amount of styrene waste gas is generated, causing serious pollution to the surrounding environment and posing a serious threat to human health.

[0003] To control styrene exhaust pollution, the current end-of-pipe control technologies are all traditional VOCs waste gas treatment technologies, which are divided into two types: destruction technology and recycling technology.

[0004] Destruction technologies typically employ chemical or biochemical methods, including thermal destruction, plasma methods, photodegradation, and biological methods. Recycling technologies typically employ physical methods, including membrane separation, condensation, adsorption, and absorption [Ling Fan et al. Comparison of CO2 / CH4 separation by membrane separation, chemical absorption, and combined methods. Journal of Power Engineering, 2015, 35(03):245-250; Liu Yingshu et al. Study on the influence of process parameters on SO2 in flue gas adsorption desulfurization and desorption gas by condensation method. Journal of Chemical Industry and Engineering, 2020, 71(12):5620-5627; Guo Yuchen et al. Research progress on VOCs waste gas treatment technology. Chemical Industry Management, 2019, (07):114-116].

[0005] In addition, due to the influence of the types and properties of VOCs, it is often difficult to achieve the emission standards of VOCs by using a single technology. Therefore, physical and chemical or physical-chemical and biological methods are often used to treat VOCs, which are more economical and efficient than single technologies.

[0006] Almost all organic pollutants can be converted into CO2 and H2O when burned at a certain temperature. The thermal destruction method is to take advantage of the flammability of VOCs and convert them into harmless substances by fully burning them with the help of fuel or auxiliary materials. It mainly includes direct combustion, regenerative combustion and catalytic combustion [Zhang Ruibo, Yang Yumin. Experimental study on combustion treatment of VOCs in petrochemical enterprises. Energy and Environmental Protection, 2020, 34(02):53-56]. Direct combustion is to treat VOCs directly by burning them as fuel. It is suitable for high concentration VOCs. For industries with low concentration and large flow of VOCs, auxiliary fuels need to be added, and the operating cost is high [Khan FI, Ghoshal A K. Removal of volatile organic compounds from polluted air[J]. Journal of loss prevention in the process industries, 2000, 13(6):527-545]. Catalytic combustion involves lowering the activation temperature with the help of a catalyst, causing VOCs to be catalytically oxidized into CO2 and H2O at low temperatures. It boasts high purification efficiency but suffers from catalyst poisoning and is suitable for low concentrations and low air volumes. Regenerative thermal combustion, on the other hand, uses heat exchange technology and regenerative materials to convert VOCs into CO2 and H2O, making it suitable for large air volumes and high concentrations of organic waste gas.

[0007] Because the concentration of pollutants in styrene tail gas is greatly affected by the climate of the production environment, and the concentration of styrene in tail gas varies greatly in different seasons, traditional VOC tail gas treatment processes and equipment have poor adaptability, are difficult to control, and have poor production stability, which in turn greatly increases equipment investment and operating costs. Summary of the Invention

[0008] The purpose of this invention is to solve the above-mentioned technical problems and provide a styrene component recovery process for artificial stone tail gas based on absorption-coupling adsorption, which is simple in system, low in investment and operating costs, has good tail gas purification effect, effectively couples absorption and adsorption, saves energy and reduces consumption, and has a high styrene recovery rate.

[0009] This invention relates to a method for the resource recovery of styrene from waste gas in an artificial stone production line based on adsorption-absorption synergy. The method includes: waste gas from the artificial stone production line enters an absorption-adsorption unit under the suction of a fan; the gas enters the absorption tower from the bottom inlet and comes into countercurrent contact with absorbent sprayed from top to bottom, resulting in the absorption of most of the styrene; semi-purified waste gas discharged from the top of the absorption tower enters an adsorption tower, where residual styrene components are further adsorbed; the purified waste gas exiting the adsorption tower group is directly discharged through a chimney; the rich liquid containing styrene components enters a flash evaporation unit for distillation and recovery of styrene. The flash evaporation unit includes a flash kettle and a rich liquid reflux scrubbing tower. The rich liquid is divided into two streams: the first stream is heated to 60-65°C and sent to the flash kettle for desorption and recovery of styrene components; the second stream is sent to the rich liquid reflux scrubbing tower for washing and heat exchange with flash steam and stripping gas from the flash kettle, and for capturing fine droplets; the rich liquid exiting the rich liquid reflux scrubbing tower is sent back to the flash kettle for desorption and recovery of styrene components.

[0010] The absorbent is sprayed in at least three stages from the middle of the absorption tower downwards into the corresponding at least three packing layers. The absorbent in each spray stage is sprayed independently and circulated. Fresh lean liquid and fresh absorbent are replenished from the upper layer into the absorption tower. The spray liquid from the previous stage flows into the next stage when it is fully loaded.

[0011] The absorption-adsorption unit includes an absorption tower and an adsorption tower group. The adsorption tower group includes at least two adsorption towers connected in parallel. The parallel adsorption towers alternately perform adsorption, desorption, and cooling processes.

[0012] The adsorption, desorption, and cooling processes performed alternately by the parallel adsorption towers are as follows:

[0013] The semi-purified tail gas from the absorption tower is continuously fed into the adsorption tower in the adsorption stage and then purified tail gas is discharged. When the adsorption tower in any adsorption stage is saturated, it switches to the desorption and cooling stage, and the semi-purified tail gas exiting the absorption tower is simultaneously switched to the adsorption tower in the adsorption stage.

[0014] The adsorption process of the adsorption tower in the desorption and cooling stages is completed by spraying hot lean liquor onto the packing layer from the top of the adsorption tower.

[0015] After the adsorption tower in the desorption and cooling stage has completed desorption, it enters the cooling stage. The purified tail gas discharged from other adsorption towers in the adsorption stage is introduced from the exhaust port at the top of the adsorption tower in the cooling stage and enters the adsorption tower in the cooling stage. The cooling gas is discharged from the bottom of the tower. After cooling is completed, it enters the adsorption stage. Multiple adsorption towers alternately carry out the adsorption, desorption and cooling process.

[0016] In the desorption stage, the absorbent used to wash the packing layer in the adsorption tower comes from the hot lean liquor desorbed from the flash evaporator. During one desorption cycle, the temperature of the rich washing / desorption liquor exiting the adsorption tower after spray washing is monitored in real time. Based on the temperature change of the rich washing / desorption liquor, the desorption process is divided into three stages: Stage 1 is when the temperature of the rich washing / desorption liquor rises to within 11-15°C below the temperature of the hot lean liquor entering the tower; Stage 2 is when the temperature of the rich washing / desorption liquor rises to within 5-10°C below the temperature of the hot lean liquor entering the tower; and Stage 3 is when the temperature of the rich washing / desorption liquor rises to within 5°C below the temperature of the hot lean liquor entering the tower. After entering Stage 3, the spray washing time is controlled, and spray washing continues until the temperature of the rich washing / desorption liquor is within 2°C below the temperature of the hot lean liquor entering the tower, thus completing the desorption process.

[0017] The temperature of the cooling gas in the tower is detected in real time. When the temperature difference between the cooling gas and the temperature of the cooling gas entering the tower is 10-15℃, the cooling process of the adsorption tower is completed.

[0018] In the first phase, the washing and desorption rich liquid after washing the packing layer is sent back to the flash evaporator along with the rich liquid at the bottom of the absorber for flash evaporation and recovery of styrene components. In the second phase, the absorbent after washing the packing layer is introduced into the bottom spray layer of the absorber to participate in the absorption of styrene components in the original tail gas. In the third phase, the absorbent after washing the packing layer is introduced into the middle spray layer of the absorber to participate in the absorption of styrene components in the original tail gas.

[0019] In the first stage of the desorption process, the rich washing and desorption liquid after washing the packing layer is sent to a flash evaporator for flash evaporation and recovery of styrene components. In the second stage of the desorption process, the rich washing and desorption liquid after washing the packing layer is sent to the lower section of the absorption tower for spray washing of the artificial stone exhaust gas. In the third stage of the desorption process, the rich washing and desorption liquid after washing the packing layer is sent to the middle section of the absorption tower for spray washing of the artificial stone exhaust gas.

[0020] The lean liquid exiting the flash evaporator is divided into two streams by the liquid holding column. The first stream is returned to the absorption tower for circulating spraying to absorb styrene in the tail gas of the artificial stone production line. The second stream is sent to the adsorption tower group to spray and wash the packing layer in the adsorption tower that is saturated with adsorption for desorption.

[0021] The first rich liquid drawn from the bottom of the absorption tower exchanges heat with the first lean liquid from the liquid holding column, and then mixes with the washing and desorption rich liquid from the first time period of the adsorption tower group after washing the packing layer. After being heated to 60-65°C, it is sent to the flash evaporator.

[0022] The flash evaporator is provided with at least two flash chambers from top to bottom, and a liquid storage tank is provided at the bottom.

[0023] The upper section of the flash evaporator is a primary flash chamber, and the lower section is a secondary flash chamber. The bottom liquid storage tank is divided into a lean liquid tank and a semi-lean liquid tank by at least one overflow plate. The upper part of the primary flash chamber is equipped with a primary flash atomizer and a reflux rich liquid atomizer, and the bottom is a primary flash guide plate. The upper part of the secondary flash chamber is equipped with a secondary flash atomizer, and a portion of the lower part of the secondary flash chamber, located above the semi-lean liquid tank, is equipped with a secondary flash guide plate, while the remaining area is connected to the lean liquid tank. The front end of the secondary flash guide plate is inserted into the lean liquid tank. The secondary flash guide plate and the overflow plate separate the semi-lean liquid tank from the secondary flash chamber. The gas phase space above the semi-lean liquid tank is connected to the primary flash chamber via a gas lift gas guide pipe. The semi-lean liquid tank is connected to the secondary flash atomizer via a semi-lean liquid heater, and the primary flash chamber is connected to the semi-lean liquid tank via a primary flash guide pipe.

[0024] The rich liquid at the bottom of the absorption tower, together with the absorbent after washing the packing layer, is sent to the primary flash atomizer in the primary flash chamber for flash evaporation. The semi-lean liquid after primary flash evaporation falls into the semi-lean liquid tank, is then extracted, heated to 65-70°C, and sent to the secondary flash atomizer in the secondary flash chamber for secondary flash evaporation. The resulting lean liquid falls into the lean liquid tank and is then led out of the flash chamber. The flash vapor from the secondary flash chamber and the flash vapor from the primary flash chamber exit the flash reactor under negative pressure and are sent to the flash vapor condenser to recover styrene products.

[0025] The rich liquid from the reflux washing tower is divided into two streams. The first stream is sent to the reflux rich liquid atomizer in the flash evaporator for flash evaporation. The second stream is mixed with the first stream of rich liquid at the bottom of the absorption tower and the washing and desorption rich liquid after washing the packing layer in the first phase. The mixture is then heated to 60-65°C and sent to the first-stage flash evaporator in the first-stage flash evaporator for flash evaporation.

[0026] Inert gas components with boiling points lower than styrene and insoluble in the absorbent are introduced into the lean and semi-lean liquid tanks in the flash evaporator to further strip the styrene components remaining in the lean and semi-lean liquids. These inert gas components are water vapor, or a mixture of water vapor and nitrogen or carbon dioxide.

[0027] The gas escaped from the semi-lean liquid tank is introduced into the first-stage flash chamber through the gas lift pipe and demister; the gas escaped from the lean liquid tank directly enters the second-stage flash chamber, and the gas phase in the first-stage and second-stage flash chambers is drawn out of the flash reactor under the suction of the vacuum pump.

[0028] The gas phase exiting the flash evaporator is washed by a rich liquid reflux scrubbing tower and then sent to a flash steam condenser to separate condensate and non-condensable gases. The condensate is then separated into styrene components and condensate by an oil-water separator before the pump. The separated condensate is heated and vaporized, and then used as steam to be fed into the lean liquid tank and semi-lean liquid tank in the flash evaporator to remove styrene components from the lean and semi-lean liquids, thus realizing the circulation of condensate.

[0029] The non-condensable gas separated by the flash condenser is extracted by a vacuum pump and divided into two streams. The first stream, together with the tail gas of the artificial stone production line, is sent into the absorption tower, and the second stream, together with the water vapor, is sent into the lean liquid tank and the semi-lean liquid tank in the flash evaporator for gas stripping.

[0030] The negative pressure of the flash evaporator, flash condenser, and oil-water separator before the pump is controlled below 4 kPa absolute pressure. Addressing the problems in the background technology, the inventors, by setting up an absorption-adsorption unit, coupled absorption and adsorption, and combining it with the flash evaporation unit, achieve the purification and emission standards of the exhaust gas from the artificial stone production line, as well as the recovery of styrene components from the exhaust gas. Specific improvements are as follows:

[0031] (1) The flash evaporation unit is equipped with a rich liquid reflux scrubbing tower to achieve rich liquid reflux. The flash evaporation unit includes a flash evaporator and a rich liquid reflux scrubbing tower. The rich liquid reflux scrubbing tower is located downstream of the gas phase outlet of the flash evaporator. Under the suction of the vacuum pump, the flash steam after atomization and flash evaporation in the flash evaporator enters the rich liquid reflux scrubbing tower through the gas phase outlet of the flash evaporator. It comes into countercurrent contact with the rich liquid from the absorption tower sprayed in from the top of the tower through the packing layer, and exchanges heat and captures fine droplets.

[0032] Cold rich liquid is sprayed into the rich liquid reflux scrubbing tower, allowing it to come into direct contact with the flash steam. This captures the fine droplets in the flash steam, reducing absorbent loss. Simultaneously, the direct contact between the cold rich liquid and the flash steam cools the flash steam, recovering the cold energy from the rich liquid and reducing the cooling energy required for flash steam condensation.

[0033] On the other hand, within the operating temperature range (30-60℃), the saturated vapor pressure of water is significantly affected by temperature (4.245 kPa at 30℃; 7.381 kPa at 40℃; 19.932 kPa at 60℃). The incoming rich liquor comes into direct contact with the flash steam, which cools the liquor, causing a large amount of water vapor to condense and enter the rich liquor. The rich liquor then passes through a primary flash atomizer and enters the flash evaporator for primary flash evaporation. Almost all the water in the rich liquor vaporizes and enters the flash steam. After passing through the rich liquor reflux scrubbing tower, most of the water is condensed again. This cycle of water accumulation leads to an increasingly higher concentration of water vapor in the primary flash steam, resulting in more and more water being absorbed by the reflux rich liquor until an equilibrium state is reached. When the rich liquor, in this water equilibrium state, returns to the flash evaporator for atomization and flash evaporation, it intensifies the water vapor stripping effect, significantly improving the distillation efficiency.

[0034] (2) Set up one absorption tower corresponding to at least two adsorption towers connected in parallel. The parallel adsorption towers alternately perform adsorption, desorption, and cooling processes. Specifically, the semi-purified tail gas from the absorption tower is sent to the adsorption tower in the adsorption stage and is then adsorbed to obtain purified tail gas before being discharged. When the adsorption tower is saturated, it enters the desorption and cooling stage. At the same time, the semi-purified tail gas is switched to the adsorption tower that has completed desorption and cooling. This alternation achieves continuous and efficient purification of tail gas from the artificial stone production line.

[0035] (3) Hot lean liquor desorption. A hot lean liquor is used to wash and desorb the adsorption tower before desorption and cooling. The hot lean liquor is sprayed from the top of the tower to wash and desorb the adsorption packing layer. After desorption, purified tail gas is introduced from the purified tail gas outlet at the top of the tower to cool the packing layer. The cooling gas is discharged from the semi-purified tail gas inlet at the bottom of the adsorption tower and introduced into the absorption tower for further absorption. During the cooling process of the purified tail gas, the packing layer also has a deep desorption effect. The adsorption tower after the purified tail gas is cooled enters the desorption stage, and this process is repeated to achieve efficient recovery of styrene components in the tail gas of the artificial stone production line.

[0036] The adsorption tower stage packing layer used for desorption and cooling uses lean absorbent solution for washing and desorption, as well as gas used for cooling, which comes from the system itself. Except for replenishing the adsorbent, no new adsorbent needs to be introduced from outside, thus realizing the recycling of the adsorbent.

[0037] (4) The flash evaporator has a multi-layer structure for multi-stage flash evaporation, making the equipment compact and safe. The flash evaporator is equipped with multi-stage flash chambers and a stripping section at the bottom, which organically combines multi-stage flash evaporation with stripping to improve the rich liquid distillation effect, save space, improve the vacuuming effect of the vacuum pump, and save the operating cost of the vacuum pump.

[0038] The flash evaporation unit has at least two flash chambers, with corresponding connected lean and semi-lean liquid tanks. The rich liquid is first introduced into the upper primary flash chamber and flashed by a primary flash atomizer. The semi-lean liquid after flashing falls into the semi-lean liquid tank through the primary flash guide pipe. It is then extracted, heated by a semi-lean liquid heater, and sent to the lower secondary flash chamber for secondary flashing by a secondary flash atomizer. The lean liquid falls into the lean liquid tank through a secondary flash guide plate. The front end of the secondary flash guide plate is inserted below the liquid surface of the lean liquid tank, forming a liquid seal that separates the secondary flash chamber from the gas lift zone above the semi-lean liquid tank. On one hand, by setting two stages of flash evaporation within a single flash evaporator, the desorption effect is enhanced; on the other hand, the primary and secondary flash chambers are not interconnected, ensuring the optimal flash evaporation effect.

[0039] Aeration heads are installed in the lean and semi-lean liquid tanks. The condensate, from which non-condensable gases and styrene components are separated after flash evaporation, is heated and vaporized by a heater and then introduced into the aeration heads as steam. This allows for gas stripping of the lean and semi-lean liquid tanks, truly realizing the reuse of condensate. At the same time, the non-condensable gases separated by the flash condenser are also divided into two streams and sent back to the absorption tower and aeration heads respectively, also realizing the reuse of non-condensable gases, saving energy and reducing consumption, and being environmentally friendly.

[0040] (5) The hot lean liquid after flash evaporation is used to desorb the adsorption-saturated packing layer in the adsorption tower. The rich liquid for washing and desorption is introduced into different operating units according to different stages of the washing and desorption cycle. The rich liquid for washing and desorption in the first stage is returned to the flash evaporator together with the rich liquid at the bottom of the absorption tower for flash evaporation to recover styrene components (the styrene concentration in the rich liquid for washing and desorption in the first stage is relatively high); the rich liquid for washing and desorption in the second stage is introduced into the bottom spray layer of the absorption tower to participate in the absorption of styrene components in the original tail gas (the styrene concentration in the rich liquid for washing and desorption in the second stage is lower than that in the initial rich liquid for washing and desorption); the rich liquid for washing and desorption in the third stage is introduced into the middle spray layer of the absorption tower to participate in the absorption of styrene components in the original tail gas (the styrene concentration in the rich liquid for washing and desorption in the third stage is the lowest), so as to realize the cascade utilization of the rich liquid and reduce the flash evaporation cost.

[0041] (6) Install a liquid-holding column to eliminate cavitation. Considering the cavitation problem at the bottom of the flash reactor, a liquid-holding column is installed to increase the pump pressure for extracting the lean liquid. Since the working pressure of the flash reactor is maintained below 4 kPa (absolute pressure), which is much lower than atmospheric pressure, when the lean liquid is directly pumped from the bottom of the flash reactor into the atmospheric pressure absorption-adsorption unit, the pressure difference before and after the pump is large. The residual styrene components and dissolved water in the lean liquid will cause cavitation, which will affect the stability of pump operation and cause the pump blades to be impacted and corroded. Installing a liquid-holding column and drawing the lean liquid from the bottom of the liquid-holding column into the absorption tower increases the liquid phase pressure at the pump inlet, effectively overcoming the cavitation phenomenon.

[0042] (7) Control the negative pressure of the flash chamber, flash condenser, and oil-water separator before the pump to below 4 kPa absolute pressure. The reason for choosing a flash pressure below 4 kPa is due to the following factors: First, it reduces the polymerization of the recovered styrene component. Styrene polymerization accelerates at 60°C; below 4 kPa, the boiling point of styrene is below 55°C, at which point polymerization is negligible. Second, at an absolute pressure of 4 kPa, the rich liquid temperature only needs to be controlled at around 60°C to achieve a high desorption effect, reducing the temperature resistance requirements of the equipment and its sealing materials, thus lowering equipment investment. Third, an operating pressure of 4 kPa saves on investment and operating costs. If the operating pressure is too low, the load on the vacuum pump increases, and the equipment strength and sealing requirements of the vacuum system are also higher. Operating pressures higher than 4 kPa are detrimental to styrene desorption.

[0043] (8) Maintain a constant flow of condensate from the oil-water separator before the pump to the condensate tank, and increase the oil-water interface level in the oil-water separator before the pump to discharge excess condensate. Since some of the water vapor carried by the tail gas during absorption is absorbed by the absorbent, during flash evaporation, the boiling point of water is lower than that of styrene, so the water preferentially vaporizes and enters the flash steam along with the introduced steam. After condensation, it enters the condensate, disrupting the system's water balance, and excess water needs to be discharged. Maintaining a constant flow of condensate from the oil-water separator before the pump to the condensate tank and increasing the oil-water interface level facilitates the discharge of water absorbed from the tail gas along with the oil phase, thereby reducing the styrene concentration in the aqueous phase and improving the styrene recovery rate. Because the higher the oil-water interface level, the more thorough the oil phase separation at the aqueous phase outlet, thus reducing the styrene concentration in the circulating steam entering the flash evaporator.

[0044] (9) Maintaining a balance of water vapor and water volume in the flash evaporator is beneficial to improving the styrene recovery rate. Controlling the amount of aeration water vapor entering the flash evaporator to 0.5-0.7% (mass ratio) of the rich liquor volume is beneficial. Excess water carried in by the rich liquor is discharged along with the condensate oil phase through the increased oil-water interface in the pre-pump oil-water separator, thus maintaining a balance of water vapor and water volume in the flash evaporator and improving the styrene recovery rate. Experiments show that when the rich liquor contains a certain amount of water, the styrene desorption rate increases significantly. Since the partial pressure of water vapor in the flash steam is much higher than the partial pressure of styrene, and the saturated vapor pressure of water is greatly affected by temperature within the operating temperature range (7.381 kPa at 40℃; 19.932 kPa at 60℃), rotary evaporation experiments show that the maximum desorption rate is reached when all the water in the rich liquor is evaporated (i.e., when the water phase disappears). This technical solution involves continuous aeration of lean and semi-lean liquor with steam (approximately 75 kg / h, 3000 m3), resulting in a high gas-liquid ratio of approximately 200-300:1, which helps to further reduce the concentration of residual styrene in the lean liquor. Beneficial effects:

[0045] This process system is simple and easy to operate, with low investment and operating costs, good exhaust gas purification effect, effective coupling of absorption and adsorption, energy saving and consumption reduction, high styrene recovery rate, and environmental friendliness. Attached Figure Description

[0046] Figure 1 is a process flow diagram of the present invention.

[0047] Figure 2 shows the fitting curve of the Henry's constant determined in the experiment of this invention. 1a: Fan; 2: Absorption tower; 3a: Adsorption tower A; 3b: Adsorption tower B; 3c: Adsorption tower C; 4a: Third-stage spray pump; 4b: Second-stage spray pump; 4c: First-stage spray pump; 4d: Absorption tower rich liquid pump; 4e: Adsorption tower rich liquid pump; 4f: Absorption tower lean liquid pump; 4g: Adsorption tower lean liquid pump; 4h: Lean liquid circulation pump; 4j: Lean liquid discharge pump; 4r: First-stage flash pump; 4s: Second-stage flash pump; 4t: Rich liquid reflux pump; 4u: Condensate pump; 5a-1: First desorption rich liquid intermediate tank; 5a-2: First desorption rich liquid intermediate tank; 5a-3: First desorption rich liquid intermediate tank; 5b: First-stage flash rich liquid tank; 6: Absorption liquid intermediate tank 7a: Lean liquor cooler for tower inlet; 7b: Lean-rich liquor heat exchanger; 8: Lean liquor tank for tower inlet; 9: Flash vapor condenser; 10a: Rich liquor heater; 10b: Semi-lean liquor heater; 10c: Condensate vaporization heater; 11: Vacuum pump; 12a: Primary flash demister; 12b: Secondary flash demister; 12c: Stripping demister; 13: Flash evaporator; 13-1: Reflux rich liquor atomizer; 13-2: Primary flash atomizer; 13-3: Secondary flash atomizer; 13-4: Primary flash baffle; 13-5: Primary... 13-6: Secondary flash evaporation guide pipe; 13-7: Air stripping guide pipe; 13-8: Secondary flash evaporation guide pipe; 13-9: Overflow plate; 13-10: Lean liquor tank; 13-11: Semi-lean liquor tank; 13-12: Semi-lean liquor aeration head; 13-13: Lean liquor aeration head; 14: Rich liquor reflux scrubbing tower; 15: Liquid holding column; 15-1: Lean liquor overflow pipe; 16: Vacuum discharge valve; 17: Oil-water separator before pump; 18a: A tower inlet valve; 18b: B tower inlet valve; 18c: C tower inlet valve; 18e 18f: Tower A inlet valve; 18g: Tower B inlet valve; 18h: Tower A exhaust valve; 18p: Tower B exhaust valve; 18q: Tower C exhaust valve; 18r: Tower A drain valve; 18s: Tower B drain valve; 18t: Tower C drain valve; 18u: Tower A cooling gas outlet valve; 18v: Tower B cooling gas outlet valve; 18w: Tower C cooling gas outlet valve; 18x: Tower A cooling gas inlet valve; 18y: Tower B cooling gas inlet valve; 18z: Tower C cooling gas inlet valve; 19: Intermediate oil tank; 20: Condensate tank. Detailed Implementation

[0048] The system of the present invention will be further explained below with reference to the accompanying drawings:

[0049] Referring to Figure 1, the system of the present invention includes an absorption-adsorption unit and a flash evaporation unit. The absorption-adsorption unit includes an absorption tower 2 and an adsorption tower group 3. The tail gas outlet at the top of the absorption tower 2 is connected to the tail gas inlet of the adsorption tower group 3. In this embodiment, the adsorption tower group 3 consists of three adsorption towers A 3a, B 3b and C 3c connected in parallel. The three adsorption towers connected in parallel take turns to perform adsorption, desorption and cooling processes.

[0050] The purified exhaust gas outlet at the top of the adsorption tower group 3 is connected to a chimney for external discharge. The rich liquid outlet at the bottom of the tower is connected to three parallel rich liquid intermediate tanks (first desorption rich liquid intermediate tank 5a-1, second desorption rich liquid intermediate tank 5a-3, and first desorption rich liquid intermediate tank 5a-3), and then divided into three paths by the adsorption tower rich liquid pump 4e. The first path is connected to the flash evaporator 13 via a primary flash pump 4r, a lean-rich liquid heat exchanger 7b, and a rich liquid heater 10a; the second path is connected to the middle spray layer of the absorption tower 2; and the third path is connected to the bottom spray layer of the absorption tower 2.

[0051] The lean liquid outlet at the bottom of the flash evaporator 13 is connected to the absorbent inlet of the adsorption tower group 3 via the liquid holding column 15 and the lean liquid pump 4g of the adsorption tower. At the same time, the bottom outlet of the liquid holding column 15 is also connected to the absorbent inlet of the adsorption tower 2 via the lean liquid circulation pump 4h, the lean-rich liquid heat exchanger 7b, the lean liquid cooler 7a, the lean liquid tank 8, the lean liquid pump 4f of the adsorption tower, and the primary spray pump 4c.

[0052] The liquid holding column 15 is provided with an overflow port, a lean liquid inlet and a lean liquid outlet at its upper, middle and lower parts, respectively. The overflow port is connected to the lean liquid tank 13 via the lean liquid overflow pipe 15-1, the lean liquid inlet is connected to the lean liquid outlet at the bottom of the flash evaporator 13, and the lean liquid outlet of the liquid holding column 15 is connected to the absorption tower 2.

[0053] The flash evaporation unit includes a flash evaporator 13 and a rich-liquid reflux scrubbing tower 14. The flash evaporator 13 has at least two flash chambers. Specifically, the upper section of the flash evaporator is a primary flash chamber, and the lower section is a secondary flash chamber. The bottom is divided by an overflow plate 13-9 (or an overflow pipe) into a lean liquid tank 13-10 and a semi-lean liquid tank 13-11. The upper part of the primary flash chamber is equipped with a primary flash atomizer 13-2, and the bottom is equipped with a primary flash guide plate 13-4. The upper part of the secondary flash chamber is equipped with a secondary flash atomizer 13-3, and the lower part is equipped with a secondary flash guide plate 13-5. The front end of the secondary flash guide plate 13-5 is inserted into the lean liquid tank 13-10. The primary flash chamber is connected to the semi-lean liquid tank 13-11 via the primary flash guide pipe 13-5. The secondary flash chamber is connected to the lean liquid tank 13-10 via the secondary flash guide plate 13-5. The air-lift zone above the semi-lean liquid tank 13-11 and the primary flash chamber are also connected via the air-lift gas guide pipe 13-7. A steam-lift demister 12-7 is installed on the pipe. The air-lift gas pipe 13-7 can be installed inside or outside the flash reactor 13, preferably outside the reactor, which can save space inside the reactor, reduce the upward flow velocity of flash steam, and facilitate the settling of fine droplets generated by atomization flash evaporation. The semi-lean liquid tank 13-11 is connected to the secondary flash atomizer 13-3 via the secondary flash pump 4s and the semi-lean liquid heater 10b.

[0054] The vapor phase outlets of the primary and secondary flash chambers are connected to the lower vapor phase (flash steam) inlet of the rich liquid reflux scrubbing tower 14 via the corresponding primary flash demister 12a and secondary flash demister 12b, respectively. The top vapor phase outlet of the rich liquid reflux scrubbing tower 14 is connected to the flash steam condenser 9. The condensate outlet of the flash steam condenser 9 is connected to the pre-pump oil-water separator 17. The condensate outlet of the pre-pump oil-water separator 17 is connected via the condensate tank 20, the condensate pump 4u, and the condensate vaporization heater 10c to the aeration heads 13-13 and 13-12 in the lean liquid tank 13-10 and semi-lean liquid tank 13-11 inside the flash reactor 13. The oil phase outlet of the pre-pump oil-water separator 17 is connected sequentially to the vacuum discharge valve 16 and the intermediate oil tank 18. The non-condensable gas outlet of the flash condenser 9 is connected to the aeration heads 13-13 and 13-12 in the lean liquid tank 13-10 and semi-lean liquid tank 13-11 of the absorption tower 2 and flash evaporator 13, respectively.

[0055] The rich liquid outlet at the bottom of the absorption tower 2 is divided into two paths by the rich liquid pump 4d. One path is connected to the first-stage flash atomizer 13-2 of the first-stage flash chamber of the flash reactor 13 via the first-stage flash rich liquid tank 5b, the first-stage flash pump 4r, the lean and rich liquid heat exchanger 7b, and the rich liquid heater 10a. The other path is connected via the reflux rich liquid atomizer 13-1 connected to the first-stage flash chamber.

[0056] The negative pressure of the flash chamber 13, flash steam condenser 9, oil-water separator 17 before the pump, and condensate vaporization heater 10c is controlled to be below 4 kPa absolute pressure.

[0057] Process:

[0058] Under the suction of the blower 1a, the exhaust gas from the artificial stone production line enters the absorption tower 2 from the exhaust gas inlet at the bottom of the absorption tower 2 and comes into countercurrent contact with the absorbent. Most of the semi-purified exhaust gas containing styrene is absorbed and discharged from the top of the absorption tower 2 into the adsorption tower group 3, where the remaining styrene components are further adsorbed. The purified exhaust gas from the adsorption tower group 3 is then directly discharged through the chimney.

[0059] In this embodiment, the adsorption tower group 3 consists of three parallel adsorption towers: adsorption tower A 3a, adsorption tower B 3b, and adsorption tower C 3c. The tail gas inlet, purified tail gas outlet, absorbent inlet, and absorbent outlet of each adsorption tower are connected in parallel. Each tower has a cooling gas inlet and outlet; the cooling gas inlet is connected to the purified tail gas outlet at the top of the adsorption tower, and the cooling gas outlet is connected to the fan inlet. Specifically, the tail gas outlet of adsorption tower 2 is connected to the tail gas inlets of adsorption tower A 3a, adsorption tower B 3b, and adsorption tower C 3c, respectively. The purified tail gas outlets of adsorption tower A 3a, adsorption tower B 3b, and adsorption tower C 3c are all connected to chimneys. The absorbent inlets of adsorption tower A 3a, adsorption tower B 3b, and adsorption tower C 3c are all connected to liquid holding columns 15. The rich liquid outlets of the three towers each have three desorption rich liquid intermediate tanks (first desorption rich liquid intermediate tank 5a-1, second desorption rich liquid intermediate tank 5a-3, and first desorption rich liquid intermediate tank 5a-3). The three adsorption towers alternately perform adsorption, desorption, and cooling processes. Specifically, the adsorption and desorption processes of adsorption tower group 3 are as follows:

[0060] The semi-purified tail gas from the absorption tower is fed into the adsorption towers (such as adsorption tower A 3a, adsorption tower B 3b, and adsorption tower C 3c) in the adsorption stage through the tail gas inlet. After adsorption, the purified tail gas is discharged from the tail gas outlet. When any adsorption tower in the adsorption stage (such as adsorption tower A 3c) becomes saturated, the feeding of semi-purified tail gas into that tower is stopped, and the desorption stage is switched. At this time, the semi-purified tail gas is continuously fed into either of the other two towers (adsorption tower B 3b or adsorption tower C 3c) that has completed desorption and cooling. At this time, the hot lean liquid from the liquid holding column 15 enters the adsorbent inlet and enters the desorption stage. The adsorption tower (adsorption tower A 3c) in the first stage washes the packing layer. The circulating washing liquid is sampled and analyzed periodically. When the styrene concentration in the washing liquid exceeds the set value, washing and desorption are stopped, and the adsorption tower (adsorption tower A 3c) enters the cooling stage. Purified tail gas from the other two towers (adsorption tower B 3b and adsorption tower C 3c) is introduced to cool the adsorption tower (adsorption tower A 3c), completing one adsorption-desorption-cooling cycle. After cooling, the tower enters the adsorption tower in the adsorption stage. With the switching of valves on the pipeline, multiple adsorption towers alternately perform adsorption, desorption, and cooling processes.

[0061] The washing and desorption rich solution after washing the packing layer enters the rich solution intermediate tank 5a-1, 5a-2, or 5a-3 according to different stages of the washing and desorption process of adsorption tower group 3. It is then extracted by the adsorption tower rich solution pump 4e and, together with the rich solution from the bottom of the absorption tower, is heated to 60-65℃ by the rich solution heater 10a. It is then sent to the flash evaporation kettle 13 via the primary flash evaporation rich solution tank 5b and the primary flash evaporation pump 4r, or enters the bottom spray layer of absorption tower 2, or the middle spray layer of absorption tower 2. Specifically:

[0062] The hot lean liquid from the liquid-holding column 15 enters the adsorption tower (adsorption tower A 3a) in the desorption stage through the adsorbent inlet to wash the packing layer. The temperature of the absorbent (i.e., the rich liquid for washing and desorption) exiting the adsorption tower after spray washing is monitored in real time. Based on the temperature of the rich liquid for washing and desorption, the desorption process is divided into three stages: Stage 1 is when the temperature of the rich liquid for washing and desorption rises to within 11-15°C below the temperature of the hot lean liquid entering the tower; Stage 2 is when the temperature of the rich liquid for washing and desorption rises to within 5-10°C below the temperature of the hot lean liquid entering the tower; and Stage 3 is when the temperature of the rich liquid for washing and desorption rises to within 5°C below the temperature of the hot lean liquid entering the tower. After the spray washing enters Stage 3, the spray washing time is controlled, and spray washing continues until the temperature of the rich liquid for washing and desorption is within 2°C below the temperature of the hot lean liquid entering the tower, thus completing the desorption process.

[0063] Based on the temperature of the washing and desorption rich liquid exiting the adsorption tower (adsorption tower A 3a), the washing and desorption rich liquid is introduced into the desorption rich liquid intermediate tank 5a. The washing and desorption rich liquid of the first stage is introduced into the desorption rich liquid intermediate tank 5a-1, the washing and desorption rich liquid of the second stage is introduced into the desorption rich liquid intermediate tank 5a-2, and the washing and desorption rich liquid of the third stage is introduced into the desorption rich liquid intermediate tank 5a-3.

[0064] The washing and desorption rich solutions from the intermediate desorption rich solution tanks 5a-1, 5a-2, and 5a-3 are introduced into the rich solution heater 10a and heated to 60-65℃ via the rich solution pump 4e in the absorption tower. Then, they are sent to the flash evaporation kettle 13 via the primary flash evaporation rich solution tank 5b and the primary flash evaporation pump 4r. The bottom spray layer of the absorption tower 2 participates in the absorption of styrene components in the original tail gas, as do the middle spray layers. This achieves cascade utilization of the rich solution, reduces flash evaporation desorption costs, and saves energy.

[0065] The rich liquid pump 4d at the bottom of the absorption tower 2 divides the liquid into two streams. One stream is pressurized by the first-stage flash evaporation rich liquid tank 5b and the first-stage flash pump 4r, and then sent together with the absorbent from the adsorption tower group 3 into the lean-rich liquid heat exchanger 7b to exchange heat with the lean liquid from the bottom of the flash kettle 13. After exiting the lean-rich liquid heat exchanger 7b, it is sent together with the rich liquid from the rich liquid reflux washing tower 14 into the rich liquid heater 10a for heating, and then sent into the first-stage flash atomizer 13-2 of the flash kettle 13 for spraying. The other stream is sent into the rich liquid reflux washing tower 14 to exchange heat with the gas phase washing of the flash kettle 13. The rich liquid flowing out from the bottom of the rich liquid reflux washing tower 14 is divided into two streams. One stream is sent into the reflux rich liquid atomizer 13-1 of the flash kettle 13, and the other stream is sent into the rich liquid heater 10a.

[0066] In the flash evaporator 13: the hot rich liquid from the rich liquid heater 10a is first sprayed into the first flash chamber through the first flash atomizer 13-2 for flash evaporation. The decomposed flash vapor rises and exchanges heat with the cold rich liquid sprayed from the rich liquid return washing tower 14 by the return rich liquid atomizer 13-1. After the droplets are removed by the first flash demister 12a at the top, it is led out. The decomposed semi-lean liquid flows into the first flash guide pipe 13-5 through the first flash guide plate 13-4 and into the semi-lean liquid tank 13-11 at the bottom.

[0067] The semi-lean liquid in the semi-lean liquid tank 13-11 is then extracted by the secondary flash pump for 4 seconds, heated to 65-70℃ by the semi-lean liquid heater 10b, and then sent to the secondary flash atomizer 13-3 for secondary flash evaporation. The gas phase in the secondary flash evaporation chamber is led out through the secondary flash evaporation gas pipe 13-8 and the droplets are removed by the secondary flash evaporation demister 12b. Together with the gas phase exiting the primary flash evaporation chamber, it enters the tower from the bottom of the rich liquid reflux scrubbing tower 14 and comes into countercurrent contact with the cold rich liquid sprayed in from the top of the tower. Based on the principle of "particle diameter matching", the sprayed rich liquid can effectively wash and capture the fine droplets in the flash steam. The flash steam after being washed and captured by the cold rich liquid is led out by the suction of the suction pump 11 and sent to the flash steam condenser 9. The decomposed lean liquid falls into the lean liquid tank 13-10 along the secondary flash evaporation guide plate 13-5 and is then led out of the flash evaporation kettle 13.

[0068] Due to the presence of the overflow plate 13-9, the lean liquid in the lean liquid tank 13-10 can overflow unidirectionally into the semi-lean liquid tank 13-11. Water vapor is introduced into the lean liquid tank 13-10 and the semi-lean liquid tank 13-11 through the corresponding aeration heads 13-13 and 13-12 to further strip the residual styrene components in the lean and semi-lean liquids. The stripped gas in the lean liquid tank 13-10 directly enters the secondary flash chamber, while the stripped gas in the semi-lean liquid tank 13-11 is collected by the stripping zone above and led out by the stripping guide pipe 13-7. After being demisted by the stripping demister 12-7, it is sent into the primary flash chamber.

[0069] After being pressurized, the lean liquid holding column from the flash evaporator 13 is divided into two streams. The first stream, as the absorbent, is pumped by the lean liquid circulation pump 4h and exchanges heat with the rich liquid from the absorption tower 2 in the lean-rich liquid heat exchanger 7b. After being further cooled by the tower lean liquid cooler 7a, it is sent to the tower lean liquid tank 8. Finally, it is sent to the absorption tower 2 by the absorption tower lean liquid pump 4f and the first-stage spray pump 4c to spray and wash the tail gas of the artificial stone production line. The second stream is sent to the adsorption tower group 3 by the adsorption tower lean liquid pump 4g to wash the packing layer.

[0070] The gas phase from the rich liquid reflux scrubbing tower 14 is sent to the flash condenser 9 to separate condensate and non-condensable gas. The condensate is separated into styrene component and water by the pre-pump oil-water separator 17. The separated styrene component is sent to the intermediate oil tank 19 for collection via the vacuum discharge valve 16. A polymerization inhibitor is added to the intermediate oil tank and mixed with the recovered styrene product. The amount of condensate discharged from the pre-pump oil-water separator 17 to the condensate tank 20 is kept constant, raising the oil-water interface to a higher position. Excess water absorbed by the absorbent from the tail gas is discharged, and this water is discharged with the oil phase, thereby reducing the styrene concentration in the aqueous phase. This is beneficial to improving the styrene recovery rate (because the higher the liquid level at the oil-water interface, the more thorough the oil phase separation at the aqueous phase discharge outlet, thereby reducing the styrene concentration in the water vapor circulating into the flash reactor). Maintaining the balance of water vapor and water volume in the flash reactor 13 is also beneficial to improving the styrene recovery rate.

[0071] The separated condensate is collected in condensate tank 20 and then heated and vaporized by condensate vaporization heater 10c. The vapor is then introduced into aeration heads 13-13 and 13-12 in the lean liquid tank 13-10 and semi-lean liquid tank 13-11 of flash evaporator 13, where it is sprayed out to remove styrene components from the lean and semi-lean liquids, thus achieving condensate recycling and reducing wastewater discharge. Carbon dioxide or nitrogen can be added to the vapor introduced into aeration heads 13-13 and 13-12 as needed.

[0072] The non-condensable gas separated from the flash steam condenser 9 is divided into two streams by the air pump 11. One stream, together with the tail gas of the artificial stone production line, is sent into the absorption tower 2. The other stream, together with the water vapor used for air stripping in the flash evaporator 13, is sent into the aeration heads 13-13 and 13-12 in the lean liquid tank 13-10 and the semi-lean liquid tank 13-11 and sprayed out.

[0073] The absorbent used in this invention is a high-boiling-point organic solvent with a boiling point more than 100°C higher than that of styrene, preferably diethyl phthalate.

[0074] Referring to Figure 2, the Henry's constant of the solution after diethyl phthalate absorbs styrene is 23.04 kg / (mol·kPa).

[0075] The system of this invention can recover more than 98% of the styrene components in styrene tail gas, purify the tail gas to meet emission standards, and consume less than 0.1 kg / t-styrene absorbent. Compared with the distillation process, it saves more than 50% of energy consumption and reduces the recovery cost by more than 50%.

Claims

1. A method for the resource recovery of styrene from waste gas in an artificial stone production line based on adsorption-absorption synergy, comprising: exhaust gas from the artificial stone production line enters an absorption-adsorption unit under the suction of a fan; the exhaust gas enters the absorption tower from the lower exhaust gas inlet and sequentially contacts the absorbent injected from top to bottom in a countercurrent manner, where most of the styrene is absorbed; the semi-purified exhaust gas discharged from the top of the absorption tower enters an adsorption tower group, where the remaining styrene components are further adsorbed; the purified exhaust gas exiting the adsorption tower group is directly discharged through a chimney; the rich liquid at the bottom of the absorption tower, having absorbed the styrene components, enters a flash evaporation unit for distillation to recover styrene, characterized in that… The flash evaporation unit includes a flash evaporator and a rich liquor reflux scrubbing tower. The rich liquor is divided into two streams. The first stream is heated to 60-65°C and sent to the flash evaporator for desorption and recovery of styrene components. The second stream is sent to the rich liquor reflux scrubbing tower for washing and heat exchange with flash steam and stripping gas from the flash evaporator, and for capturing fine droplets. The rich liquor exiting the rich liquor reflux scrubbing tower is sent back to the flash evaporator for desorption and recovery of styrene components.

2. The method for resource recovery of styrene from waste gas in artificial stone production lines based on adsorption-absorption synergy as described in claim 1, characterized in that, The absorbent is sprayed in at least three stages from the middle of the absorption tower downwards into the corresponding at least three packing layers. The absorbent in each spray stage is sprayed independently and circulated. Fresh lean liquid and fresh absorbent are replenished from the upper layer into the absorption tower. The spray liquid from the previous stage flows into the next stage when it is fully loaded.

3. The method for resource recovery of styrene from waste gas in artificial stone production lines based on adsorption-absorption synergy as described in claim 1, characterized in that, The absorption-adsorption unit includes an absorption tower and an adsorption tower group. The adsorption tower group includes at least two adsorption towers connected in parallel. The parallel adsorption towers alternately perform adsorption, desorption, and cooling processes.

4. The method for styrene resource recovery from waste gas in artificial stone production lines based on adsorption-absorption synergy as described in claim 3, characterized in that, The adsorption, desorption, and cooling processes performed alternately by the parallel adsorption towers are as follows: The semi-purified tail gas from the absorption tower is continuously fed into the adsorption tower in the adsorption stage and then purified tail gas is discharged. When the adsorption tower in any adsorption stage is saturated, it switches to the desorption and cooling stage, and the semi-purified tail gas exiting the absorption tower is simultaneously switched to the adsorption tower in the adsorption stage. The adsorption process of the adsorption tower in the desorption and cooling stages is completed by spraying hot lean liquor onto the packing layer from the top of the adsorption tower. After the adsorption tower in the desorption and cooling stage is desorbed, it enters the cooling stage. The purified tail gas discharged from other adsorption towers in the adsorption stage is introduced from the exhaust port at the top of the adsorption tower in the cooling stage and enters the adsorption tower in the cooling stage. The cooling gas is discharged from the bottom of the tower and sent to the absorption tower. After cooling is completed, it enters the adsorption stage. Multiple adsorption towers alternately carry out the adsorption, desorption and cooling process. In the desorption stage, the absorbent used to wash the packing layer in the adsorption tower comes from the hot lean liquor desorbed from the flash reactor. During one desorption cycle, the temperature of the rich washing / desorption liquor exiting the adsorption tower after spray washing is monitored in real time. Based on the temperature change of the rich washing / desorption liquor, the desorption stage is divided into three phases: Phase 1 is when the temperature of the rich washing / desorption liquor rises to within 11-15°C below the temperature of the hot lean liquor entering the tower; Phase 2 is when the temperature of the rich washing / desorption liquor rises to within 5-10°C below the temperature of the hot lean liquor entering the tower; and Phase 3 is when the temperature of the rich washing / desorption liquor rises to within 5°C below the temperature of the hot lean liquor entering the tower. After entering Phase 3, the spray washing time is controlled, and spray washing continues until the temperature of the rich washing / desorption liquor is within 2°C below the temperature of the hot lean liquor entering the tower, thus completing the desorption process. The temperature of the cooling gas in the tower is detected in real time. When the temperature difference between the cooling gas and the temperature of the cooling gas entering the tower is 10-15℃, the cooling process of the adsorption tower is completed. In the first stage of the desorption process, the rich washing and desorption liquid after washing the packing layer is sent to a flash evaporator for flash evaporation and recovery of styrene components. In the second stage of the desorption process, the rich washing and desorption liquid after washing the packing layer is sent to the lower section of the absorption tower for spray washing of the artificial stone exhaust gas. In the third stage of the desorption process, the rich washing and desorption liquid after washing the packing layer is sent to the middle section of the absorption tower for spray washing of the artificial stone exhaust gas.

5. The method for styrene resource recovery from waste gas in artificial stone production lines based on adsorption-absorption synergy as described in claim 2, characterized in that, The lean liquid exiting the flash evaporator is divided into two streams by the liquid holding column. The first stream is returned to the absorption tower for circulating spraying to absorb styrene in the tail gas of the artificial stone production line. The second stream is sent to the adsorption tower group to spray and wash the packing layer in the adsorption tower that is saturated with adsorption for desorption.

6. The method for resource recovery of styrene from waste gas in artificial stone production lines based on adsorption-absorption synergy as described in claim 5, characterized in that, The first rich liquid drawn from the bottom of the absorption tower exchanges heat with the first lean liquid from the liquid holding column, and then mixes with the washing and desorption rich liquid from the first time period of the adsorption tower group after washing the packing layer. After being heated to 60-65°C, it is sent to the flash evaporator.

7. The method for resource recovery of styrene from waste gas in artificial stone production lines based on adsorption-absorption synergy as described in claim 1, characterized in that, The flash evaporator is provided with at least two flash chambers from top to bottom, and a liquid storage tank is provided at the bottom.

8. The method for resource recovery of styrene from waste gas in artificial stone production lines based on adsorption-absorption synergy as described in claim 7, characterized in that, The upper section of the flash evaporator is a primary flash chamber, and the lower section is a secondary flash chamber. The bottom liquid storage tank is divided into a lean liquid tank and a semi-lean liquid tank by at least one overflow plate. The upper part of the primary flash chamber is equipped with a primary flash atomizer and a reflux rich liquid atomizer, and the bottom is a primary flash guide plate. The upper part of the secondary flash chamber is equipped with a secondary flash atomizer, and a portion of the lower part of the secondary flash chamber, located above the semi-lean liquid tank, is equipped with a secondary flash guide plate, while the remaining area is connected to the lean liquid tank. The front end of the secondary flash guide plate is inserted into the lean liquid tank. The secondary flash guide plate and the overflow plate separate the semi-lean liquid tank from the secondary flash chamber. The gas phase space above the semi-lean liquid tank is connected to the primary flash chamber via a gas lift gas guide pipe. The semi-lean liquid tank is connected to the secondary flash atomizer via a semi-lean liquid heater, and the primary flash chamber is connected to the semi-lean liquid tank via a primary flash guide pipe.

9. The method for resource recovery of styrene from waste gas in artificial stone production lines based on adsorption-absorption synergy as described in claim 8, characterized in that, The rich liquid at the bottom of the absorption tower, together with the absorbent after washing the packing layer, is sent to the primary flash atomizer in the primary flash chamber for flash evaporation. The semi-lean liquid after primary flash evaporation falls into the semi-lean liquid tank, is then extracted, heated to 65-70°C, and sent to the secondary flash atomizer in the secondary flash chamber for secondary flash evaporation. The resulting lean liquid falls into the lean liquid tank and is then led out of the flash chamber. The flash vapor from the secondary flash chamber and the flash vapor from the primary flash chamber exit the flash reactor under negative pressure and are sent to the flash vapor condenser to recover styrene products.

10. The method for resource recovery of styrene from waste gas in artificial stone production lines based on adsorption-absorption synergy as described in claim 9, characterized in that, The rich liquid from the reflux washing tower is divided into two streams. The first stream is sent to the reflux rich liquid atomizer in the flash evaporator for flash evaporation. The second stream is mixed with the first stream of rich liquid at the bottom of the absorption tower and the washing and desorption rich liquid after washing the packing layer in the first phase. The mixture is then heated to 60-65°C and sent to the first-stage flash evaporator in the first-stage flash evaporator for flash evaporation.

11. The method for resource recovery of styrene from waste gas in artificial stone production lines based on adsorption-absorption synergy as described in claim 9, characterized in that, Inert gas components with boiling points lower than styrene and insoluble in the absorbent are introduced into the lean and semi-lean liquid tanks in the flash evaporator to further strip the styrene components remaining in the lean and semi-lean liquids. These inert gas components are water vapor, or a mixture of water vapor and nitrogen or carbon dioxide.

12. The method for resource recovery of styrene from waste gas in artificial stone production lines based on adsorption-absorption synergy as described in claim 11, characterized in that, The gas escaped from the semi-lean liquid tank is introduced into the first-stage flash chamber through the gas lift pipe and demister; the gas escaped from the lean liquid tank directly enters the second-stage flash chamber, and the gas phase in the first-stage and second-stage flash chambers is drawn out of the flash reactor under the suction of the vacuum pump.

13. The method for resource recovery of styrene from waste gas in artificial stone production lines based on adsorption-absorption synergy as described in claim 11, characterized in that, The gas phase exiting the flash evaporator is washed by a rich-liquid reflux scrubbing tower and then sent to a flash condenser to separate condensate and non-condensable gases. The condensate is separated into styrene components and condensate water by an oil-water separator before the pump. The separated condensate water is heated and vaporized, and then used as steam to be fed into the lean and semi-lean liquid tanks in the flash evaporator to strip the styrene components from the lean and semi-lean liquids, thus realizing condensate water circulation. The non-condensable gases separated by the flash condenser are extracted by a vacuum pump and divided into two streams. The first stream is sent to an absorption tower along with the tail gas from the artificial stone production line, and the second stream is sent to the lean and semi-lean liquid tanks in the flash evaporator along with the steam for stripping.

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