Flash evaporation-stripping method of styrene absorption liquid

Abstract

The invention relates to a mixed liquor distillation process for chemical separation, in particular to a flash evaporation-stripping method of styrene absorption liquid, which comprises the following steps: sending rich liquor which is from the bottom of an absorption tower and absorbs styrene into a flash evaporation kettle for flash evaporation analysis to form a gas phase product and a liquid phase product, and is characterized in that the rich liquor is divided into two streams, the first part is heated and then sent into a flash kettle to analyze and recover styrene components; the second stream is fed into a pregnant solution reflux washing tower to be in countercurrent contact with the gas phase from the flash evaporation kettle for washing, and pregnant solution discharged from the pregnant solution reflux washing tower is fed into the flash evaporation kettle for flash evaporation analysis; introducing water vapor or other low-boiling-point component gas insoluble in an absorbent into the liquid-phase product in the flash evaporation kettle, and further carrying out gas stripping on the residual styrene component in the liquid-phase product; and feeding a gas phase discharged from the flash kettle into a rich liquid reflux washing tower for washing. The method is simple in process control, low in equipment investment, high in flash evaporation efficiency, low in operation cost, energy-saving, consumption-reducing, free of waste gas and waste water discharge and environment-friendly.

Description

Technical Field

[0001] The invention belongs to the field of chemical separation and relates to a distillation method for absorbing rich liquid, in particular to a flash evaporation-stripping method for styrene absorbing liquid. Background Art

[0002] Distillation is a thermodynamic separation process. It uses the different boiling points of the components in a mixed liquid or liquid-solid system to evaporate the low-boiling-point component and then condense it to separate the entire component. It is a unit operation process that combines the two unit operations of evaporation and condensation. The principle is to use the different boiling points of different component liquids, heat the mixed liquid to a certain temperature, and vaporize the low-boiling-point component to achieve the separation of different components.

[0003] According to the different equipment used in the distillation process, distillation can be divided into rotary distillation, flash distillation, super gravity distillation, etc. According to the different operating pressures, distillation can be divided into atmospheric distillation and vacuum distillation; according to the different distillation methods, distillation can be divided into simple distillation, rectification, special distillation, special distillation includes steam distillation, azeotropic distillation, molecular distillation, etc.

[0004] Rotary evaporation is based on the principle that the rotary distillation kettle drives the liquid phase in the kettle to transfer under reduced pressure to increase the evaporation area to achieve the separation of the mixture. It is mainly used for continuous distillation of volatile solvents under reduced pressure, and is applied to the fields of chemistry, chemical industry, biomedicine, etc. Since the rotary evaporation process requires the liquid phase to rotate under reduced pressure, it is not suitable for the separation of large flow mixed liquids, and has high requirements for the sealing of the rotating parts.

[0005] Flash evaporation is based on the principle that the solubility of gaseous solutes in liquid solvents is different at different temperatures and partial pressures. The high-pressure saturated liquid is sent into a relatively low-pressure container, and the low-boiling point components are vaporized to achieve the separation process of the saturated liquid. Flash evaporation is the process in which a saturated liquid changes from one thermodynamic equilibrium state to the next thermodynamic equilibrium state. The energy for flash evaporation is provided by the solvent itself, so the temperature of the solvent decreases during the flash evaporation process. From a higher certain pressure to a lower certain pressure, the amount of solute desorbed when the desorption equilibrium is reached is certain, and the amount of solute remaining in the corresponding solvent is also certain, so there is only one control target for flash evaporation, which is the pressure of the flash evaporation.

[0006] Atmospheric distillation, also known as simple distillation or ordinary distillation, refers to the distillation process operated under normal pressure conditions. The solution is heated under normal pressure, and the light components with lower boiling points are vaporized and condensed to separate. The operation of vaporizing and condensing the light components with lower boiling points to roughly separate them is called distillation; the operation of repeatedly using partial vaporization and partial condensation to achieve accurate separation of the components is called rectification.

[0007] Vacuum distillation, also known as vacuum distillation, is based on the principle that the boiling point of a liquid changes with the change of external pressure. The pressure in the system is reduced with the help of a vacuum pump, thereby reducing the boiling point of the liquid. Vacuum distillation is one of the common methods for separating and purifying organic compounds.

[0008] In addition to atmospheric distillation and reduced pressure distillation, pressure distillation can be performed under pressure when the light component and the heavy component in a two-component mixture are relatively easy to separate.

[0009] Simple distillation, also known as differential distillation, is also a unipolar distillation operation, often carried out in an intermittent manner. Simple distillation is a non-steady-state process. Although the vapor and liquid formed instantly can be considered to be in equilibrium with each other, all the vapor formed is not in equilibrium with the remaining liquid. For example, making distilled water to remove dissolved solid impurities; making distilled wine to concentrate alcohol and remove part of the water, all belong to simple distillation. Due to the limitation of the phase equilibrium ratio, the separation degree of simple distillation is not high.

[0010] Rectification is also called fractionation. Rectification is usually carried out in a distillation tower. The gas and liquid phases are in countercurrent contact to conduct interphase heat and mass transfer. The volatile components in the liquid phase enter the gas phase, and the non-volatile components in the gas phase are transferred to the liquid phase, so that almost pure volatile components can be obtained at the top of the tower, and almost pure non-volatile components can be obtained at the bottom of the tower. The feed liquid is added from the middle of the tower. The tower section above the feed port further concentrates the volatile components in the rising vapor, which is called the distillation section; the tower section below the feed port extracts the volatile components from the descending liquid, which is called the stripping section. The vapor drawn from the top of the tower is condensed, and a part of the condensate is returned to the distillation tower from the top of the tower as reflux liquid, and the remaining distillate is the top product. The liquid drawn from the bottom of the tower is partially vaporized by the reboiler, and the vapor rises along the tower, and the remaining liquid is the bottom product. The ratio of the amount of liquid refluxed into the tower from the top of the tower to the amount of the top product is called the reflux ratio, and its size will affect the separation effect and energy consumption of the distillation operation.

[0011] Steam distillation is based on Dalton's law. The total vapor pressure corresponding to the liquid of an immiscible mixture is equal to the sum of the partial pressures of each component gas. The total vapor pressure of the mixture at any temperature is always greater than the vapor pressure of any component. Under the same external pressure, the boiling point of a mixture of immiscible substances is lower than the boiling temperature of the component with the lowest boiling point.

[0012] Steam distillation is only suitable for the extraction of volatile components that can be distilled with steam without being destroyed, do not react with water, and are poorly soluble or insoluble in water.

[0013] Azeotropic distillation is a method of separating a mixture by distillation, utilizing the property that the boiling point of the azeotrope formed by the components in the mixture is lower than the boiling point of any component.

[0014] During the azeotropic distillation process, the added entrainer forms new azeotropes with one or more components in the original solution. These azeotropes usually have lower boiling points, so they are preferentially distilled out of the mixture during distillation. In this way, mixtures that are difficult to separate can be effectively separated and purified. The selection of the entrainer is crucial, and it needs to meet certain conditions, such as forming azeotropes with the components of the original solution, having a suitable boiling point, and being easy to separate and recycle. Azeotropic distillation is widely used in various separation processes in the chemical industry.

[0015] Molecular distillation is a liquid-liquid separation technology developed along with vacuum technology and vacuum distillation technology. Its principle is to use the difference in the free motion path of different substances to achieve the separation of substances, and can achieve operations far away from the boiling point. Molecular distillation has the characteristics of low distillation pressure, short heating time, and high degree of separation. It can greatly reduce the separation cost of high-boiling point materials and extremely protect the quality of heat-sensitive substances.

[0016] As a highly efficient, new green separation technology, molecular distillation technology has incomparable advantages over conventional vacuum distillation technology. It is currently widely used in various fields such as fine chemicals, medicine, food, oils, papermaking, etc.

[0017] However, due to the unique structure of the molecular distillation device, there are some obvious constraints in its promotion and application:

[0018] (1) The distance between the evaporation surface and the condensation surface must be smaller than the mean free path of light molecules, resulting in large equipment investment;

[0019] (2) At the same time, the mean free paths of light and heavy molecules in the liquid phase must be different, and the larger the difference, the better. In fact, if the distance between the evaporator surface and the condenser surface is less than the mean free path of the molecules, it is often very uneconomical. Therefore, the distance is usually slightly larger than the mean free path of the molecules and is controlled within the same order of magnitude.

[0020] (3) The operating pressure of molecular distillation is low, usually controlled at 0.4-40Pa, which requires high sealing performance of the equipment and consumes a lot of power for vacuuming, especially in chemical production units with large flow gas absorption and analysis, which consumes a lot of energy.

[0021] As two important separation technologies, distillation and flash evaporation are widely used in chemical, petroleum, pharmaceutical and other fields. Distillation has high separation accuracy and wide adaptability, but high energy consumption; flash evaporation has the advantages of simple equipment, low energy consumption, and large processing capacity, but limited separation accuracy. In practical applications, appropriate separation technology should be selected according to specific process requirements and material properties. At the same time, with the continuous development of technology, distillation and flash evaporation technologies need to be continuously improved and innovated to improve separation efficiency and reduce energy consumption to better meet the needs of industrial production. Summary of the invention

[0022] The purpose of the present invention is to solve the above technical problems and provide a flash evaporation-stripping method for styrene absorption liquid which has simple process, good flash evaporation effect, energy saving and consumption reduction and is environmentally friendly.

[0023] The present invention comprises sending the rich liquid absorbed by styrene from the bottom of the absorption tower into a flash kettle for flash evaporation and analysis to form gas phase products and liquid phase products, characterized in that the rich liquid is divided into two streams, the first stream is heated and sent to the flash kettle for analysis and recovery of styrene components; the second stream is sent to a rich liquid reflux washing tower for countercurrent contact and washing with the gas phase from the flash kettle, and the rich liquid from the rich liquid reflux washing tower is sent to the flash kettle for flash evaporation and analysis;

[0024] Water vapor or other low-boiling-point component gas insoluble in the absorbent is introduced into the liquid phase product in the flash kettle to further strip the residual styrene component in the liquid phase product; the gas phase out of the flash kettle is sent to the rich liquid reflux washing tower for washing.

[0025] The flash kettle is provided with at least two stages of flash chambers from top to bottom, and a liquid storage tank is provided at the bottom.

[0026] The upper section of the flash still is a primary flash chamber, 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 provided with a reflux rich liquid atomizer and a primary flash atomizer, and the bottom is a primary flash guide plate; the upper part of the secondary flash chamber is provided with a secondary flash atomizer, and the bottom is a secondary flash guide plate, the front end of the secondary flash guide plate is inserted into the lean liquid tank; the primary flash chamber is connected to the semi-lean liquid tank via a guide pipe, The secondary flash chamber is connected to the lean liquid tank via the secondary flash guide plate, and 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 the gas stripping gas air guide pipe, the semi-lean liquid tank is connected to the secondary flash atomizer via the semi-lean liquid heater, the gas phase outlet of the secondary flash chamber is connected to the primary flash chamber via the second-layer air guide pipe, and the gas phase outlet of the primary flash chamber is connected to the rich liquid reflux washing tower via the upper-layer air guide pipe.

[0027] The first rich liquid from the absorption tower is heated to 60-65°C and sprayed into the first-level flash chamber through atomization by a first-level flash atomizer for flash evaporation; the semi-lean liquid after the first-level flash evaporation is introduced into the semi-lean liquid tank through the first-level flash guide plate and the first-level flash through the guide pipe, and then drawn out from the semi-lean liquid tank, heated to 65-70°C, and then sprayed into the second-level flash chamber through atomization by a second-level flash atomizer for further atomization and flash evaporation. The obtained lean liquid enters the lean liquid tank and is then drawn out of the flash chamber; the flash steam in the second-level flash chamber is merged into the first-level flash chamber through the second-layer air guide pipe and is drawn out of the flash kettle together with the flash steam in the first-level flash chamber through the upper-layer air guide pipe.

[0028] The lean liquid exiting the flash kettle is sent back to the absorption tower via the liquid holding column and recycled as an absorbent.

[0029] The rich liquid from the rich liquid reflux washing tower is sprayed into the primary flash chamber through the rich liquid reflux atomizer in the flash kettle for atomization and flash evaporation. The stripping gas overflowing from the semi-lean liquid tank is introduced into the primary flash chamber through the air guide pipe; the stripping gas overflowing from the lean liquid tank directly enters the secondary flash chamber.

[0030] The gas phase leaving the flash kettle is washed and demisted in the rich liquid reflux washing tower to capture some fine droplets, and then further demisted by the electronic demister. It is then drawn out from the top of the tower and sent to the flash steam condenser for condensation to separate the condensate and non-condensable gases.

[0031] The separated condensate is separated into styrene components and condensed water through a pre-pump oil-water separator. The separated condensed water is heated and vaporized and then introduced into the lean liquid tank and semi-lean liquid tank in the flash kettle as water vapor to strip the styrene components in the lean liquid and semi-lean liquid, thereby realizing the condensed water circulation. The separated non-condensable gas is returned to the absorption tower through a vacuum pump.

[0032] Control the operating pressure of the flash kettle, rich liquid reflux washing tower, flash steam condenser and pre-pump oil-water separator below 4kPa absolute pressure.

[0033] The electronic defogger emits electrons through the field electron emission material after being energized to charge the fine mist droplets, and then intercepts the fine mist droplets through the cathode porous plate after being energized. In view of the problems existing in the background technology, the inventor has made the following improvements:

[0034] (1) Use cold rich liquid from the absorption tower to reflux and wash the flash steam. Set up a rich liquid reflux washing tower downstream of the flash kettle gas phase outlet to achieve rich liquid reflux. The flash steam after atomization flash in the flash kettle enters the rich liquid reflux washing tower through the flash kettle gas phase outlet, and contacts with the rich liquid from the absorption tower sprayed in from the top of the tower through the packing layer in countercurrent, exchanges heat and captures fine droplets; spray cold rich liquid into the rich liquid reflux washing tower, the rich liquid directly contacts the flash steam, the fine droplets in the flash steam are captured, and the absorbent loss is reduced. At the same time, the cold rich liquid directly contacts the flash steam, directly cools the flash steam, recovers the coldness of the rich liquid, and reduces the coldness required for the condensation of the flash steam.

[0035] In the operating temperature range (30-60℃), the saturated vapor pressure of water is greatly affected by temperature (4.245kPa at 30℃, 7.381kPa at 40℃, and 19.932kPa at 60℃). The incoming rich liquid is in direct contact with the flash steam, and the flash steam is cooled down. A large amount of water vapor condenses and enters the rich liquid. The rich liquid enters the flash kettle through the first-stage flash atomizer for first-stage flash evaporation. Almost all the water in the rich liquid is vaporized and enters the flash steam. After the rich liquid refluxes to the washing tower, most of it is condensed again. The water circulates in this way, and the water vapor concentration in the first-stage flash steam becomes higher and higher. The reflux rich liquid condenses and absorbs more and more water until a balance state of reflux rich liquid absorbing water is formed. When the rich liquid in the water balance state returns to the flash kettle for atomization and flash evaporation, the gas lift effect of water vapor is intensified, which can significantly improve the distillation effect.

[0036] (2) Multi-stage flash evaporation. A multi-stage flash evaporation chamber is set in the flash evaporation kettle, and a gas stripping section is set at the bottom of the kettle. The multi-stage flash evaporation and gas stripping are organically combined to improve the rich liquid distillation effect, save space, improve the vacuum pump effect, and save the operating cost of the vacuum pump; a multi-layer structure is set in the flash evaporation kettle, and the equipment structure is compact and safe.

[0037] The flash evaporation kettle of the flash evaporation analysis unit has at least two flash evaporation chambers, and correspondingly connected lean liquid tanks and semi-lean liquid tanks are arranged. The rich liquid is first introduced into the upper first-stage flash evaporation chamber and sprayed out by the first-stage flash evaporation atomizer for flash evaporation. The semi-lean liquid after flash evaporation falls into the semi-lean liquid tank through the first-stage flash evaporation guide pipe, and then is drawn out and heated by the semi-lean liquid heater and sent to the second-stage flash evaporation chamber of the lower stage for spraying by the second-stage flash evaporation atomizer for secondary flash evaporation. The lean liquid falls into the lean liquid tank through the second-stage flash evaporation guide plate. The front end of the second-stage flash evaporation guide plate is inserted below the liquid level of the lean liquid tank to form a liquid seal, which separates the second-stage flash evaporation chamber from the gas stripping area above the semi-lean liquid tank. On the one hand, by arranging two-stage flash evaporation in one flash evaporation kettle, the analysis effect is enhanced. On the other hand, the first-stage flash evaporation chamber and the second-stage flash evaporation chamber are not connected to each other, so as to ensure the flash evaporation effect.

[0038] In the multi-stage flash evaporation process, the temperature and circulation volume of the absorption liquid for flash evaporation are gradually increased to improve the flash evaporation efficiency.

[0039] (3) An aeration head is set in the lean liquid tank and the semi-lean liquid tank. The condensed water separated by the flash steam condenser and the pre-pump oil-water separator is heated and vaporized by the condensed water vaporization heater and then introduced into the aeration head in the form of water vapor. The lean liquid tank and the semi-lean liquid tank can be gas-lifted, which truly realizes the reuse of the condensed liquid, saves energy and reduces consumption, and is environmentally friendly.

[0040] (4) Setting a liquid holding column to eliminate "cavitation". Considering the problem of "cavitation" when the lean liquid is drawn out from the bottom of the flash kettle, a liquid holding column is set to increase the pressure before the pump to extract the lean liquid. Since the working pressure of the flash kettle is maintained below 4 kPa (absolute pressure), which is much lower than the atmospheric pressure, when the lean liquid is directly drawn out from the bottom of the flash kettle through a pump and enters the absorption-adsorption unit at normal pressure, the pressure difference before and after the pump is large, and the residual styrene components and dissolved water in the lean liquid will produce "cavitation", which not only affects the stability of the pump operation, but also causes the pump blades to be impacted and corroded. Setting a liquid holding column to draw 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.

[0041] (5) Control the negative pressure of the flash chamber, flash steam condenser and pre-pump oil-water separator below an absolute pressure of 4 kPa. First, reduce the polymerization of the recovered styrene component. When the styrene temperature reaches 60°C, the polymerization rate intensifies. When it is below 4 kPa, the boiling point of styrene is lower than 55°C, and the polymerization of styrene at this temperature can be ignored; second, under an absolute pressure of 4 kPa, the rich liquid temperature only needs to be controlled at around 60°C to achieve a high decomposition effect, and the temperature resistance requirements for the equipment and its sealing materials are not high, reducing equipment investment; third, the operating pressure of 4 kPa can save investment and operating costs. When the operating pressure is too low, the load of the vacuum pump used increases, and at the same time, the equipment strength and sealing requirements of the vacuum system are higher. When the operating pressure is higher than 4 kPa, it is not conducive to the decomposition of styrene.

[0042] (4) Control the amount of condensed water discharged from the oil-water separator before the pump to the condensate tank, increase the oil-water interface level in the oil-water separator before the pump, and discharge excess condensate. Since part of the water vapor brought in by the tail gas during the absorption process is absorbed by the absorbent, the boiling point of water is lower than that of styrene during flash evaporation analysis, and the water vaporizes first and enters the flash steam together with the water vapor introduced. After condensation, it enters the condensate, which breaks the water balance of the system and the excess water needs to be discharged. Keeping the amount of condensed water discharged from the oil-water separator before the pump to the condensate tank constant and raising the oil-water interface to a higher position is conducive to discharging the water absorbed by the absorbent from the tail gas together with the oil phase, thereby reducing the styrene concentration in the water phase; it is conducive to improving the styrene recovery rate. Because the higher the level of the oil-water interface, the more thorough the separation of the oil phase at the water phase outlet level, thereby reducing the styrene concentration in the water vapor circulating into the flash kettle.

[0043] (5) Maintaining the balance of water vapor and water in the flash kettle is beneficial to improving the recovery rate of styrene. The amount of aerated water vapor entering the flash kettle is controlled to be 0.5-0.7% (mass ratio) of the amount of rich liquid entering the kettle. The excess water brought into the rich liquid is discharged together with the condensate oil phase through the increase of the oil-water interface in the oil-water separator before the pump to maintain the balance of water vapor and water in the flash kettle, which is beneficial to improving the recovery rate of styrene. Experiments show that when the rich liquid contains a certain amount of water, the desorption rate of styrene increases significantly. Since the water vapor partial pressure in the flash steam is much higher than the styrene partial pressure, and the saturated vapor pressure of water is greatly affected by temperature within the operating temperature range (7.381 kPa at 40°C; 19.932 kPa at 60°C), the rotary evaporation experiment shows that the maximum desorption rate is achieved when all the water in the rich liquid is evaporated (that is, when the water phase disappears). This technical solution aerates the lean liquid and semi-lean liquid with water vapor (about 75kg / h, 3000m3) for a long time, with a high gas-liquid ratio of about 200-300:1, which is beneficial to further reduce the residual styrene concentration in the lean liquid.

[0044] (6) An electronic demister is arranged below the top gas phase outlet of the rich liquid reflux washing tower, and adopts a structure in which an anode tube is arranged in the center, multiple cathode arc plates are arranged on the periphery, and a cathode porous plate is arranged on the top surface. After the flash steam in the rich liquid reflux washing tower is cooled by rich liquid washing and fine droplets are captured, it enters the electronic demister upward; after the cathode porous plate, anode tube, and cathode arc plate of the electronic demister are powered on, the field electron emission material embedded on the inner surface of the cathode arc plate emits electrons, and moves toward the center under the action of the electric field force between the anode tube and the cathode arc plate installed at the central axis position of the electronic demister; during the movement of the electrons, they collide with the flash steam, and the particle size of the fine droplets in the flash steam is much larger than the diameter of the gas molecules, The probability of colliding with electrons is much greater than the probability of gas molecules colliding with electrons; after the fine mist droplets collide and capture electrons, the mist droplets are negatively charged, and under the action of the electric field force and the drag force of the upward flowing airflow, the mist droplets move upward along the center, and when they move to the area below the cathode porous plate, under the action of the electric field force of the cathode porous plate, the charged fine mist droplets are blocked from continuing to move upward, and are forced to move toward the central anode tube; the fine mist droplets are captured after moving to the surface of the anode tube, and the droplets not captured by the surface continue to move upward, and are intercepted by the cathode porous plate due to their negative charge, thereby achieving the purpose of effective demisting, greatly improving the demisting effect and efficiency. Compared with traditional demisters, the electronic demister in the present invention can capture more than 99.9% of fine mist droplets.

[0045] The invention has simple process control, low equipment investment, high flash evaporation efficiency, low operating cost, energy saving and consumption reduction, no waste gas and wastewater discharge, and is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Process flow chart of the present invention.

[0047] Figure 2 This is the front view of the electronic defogger.

[0048] Figure 3 for Figure 1 Middle AA section view.

[0049] Figure 4 for Figure 1 Middle BB section view.

[0050] Figure 5 for Figure 1 Middle CC section view.

[0051] Figure 6 This is a fitting curve diagram of the Henry constant determined experimentally in the present invention.

[0052] Wherein: 1: flash kettle; 1-1a: reflux rich liquid atomizer; 1-1b: primary flash atomizer; 1-1c: secondary flash atomizer; 1-2a: primary flash guide plate; 1-2b: secondary flash guide plate; 1-3: guide pipe; 1-4a: upper air guide pipe; 1-4b: second air guide pipe; 1-4c: air stripping air guide pipe; 1-5: lean liquid overflow pipe; 1-6a: lean liquid tank; 1-6b: semi-lean liquid tank; 1-7a: semi-lean liquid aeration head; 1-7b: lean liquid aeration head; 1-8: overflow plate;

[0053] 2: Rich liquid reflux washing tower; 2-1: Reflux rich liquid nozzle; 2-2: Washing filler; 2-3: Storage tank under the tower;

[0054] 3: Electronic defogger;

[0055] 3-1, insulated hot wire column; 3-2, cathode porous plate; 3-3, insulating gasket; 3-4, cathode arc plate; 3-5, anode tube; 3-6, anode tube bracket; 3-7, porous plate insulating seat; 3-8, field electron emission material;

[0056] 4: Flash steam condenser; 5: Vacuum pump; 6: Oil-water separator; 7: Condensate tank; 8a: Condensate vaporization heater; 8b: Rich liquid heater; 8c: Semi-lean liquid heater; 9: Oil tank; 10a: Rich liquid reflux pump; 10b: Condensate pump; 10c: Primary flash pump; 10d: Secondary flash pump; 10e: Lean liquid discharge pump; 10f: Lean liquid circulation pump; 11: Vacuum unloading valve; 12: Liquid holding column; 13: Rich liquid tank of absorption tower. DETAILED DESCRIPTION

[0057] The system of the present invention is further explained below in conjunction with the accompanying drawings:

[0058] The system of the present invention comprises an absorption tower rich liquid tank 13, a flash kettle 1 and a rich liquid reflux washing tower 2, wherein the liquid phase outlet of the absorption tower rich liquid tank 13 is divided into two paths, one of which is connected to the first-stage flash atomizer 1-1b of the flash kettle 1 through a rich liquid heater, and the other is connected to the reflux rich liquid nozzle 2-1 of the upper section of the rich liquid reflux washing tower 2, and the rich liquid outlet at the bottom of the rich liquid reflux washing tower 2 is connected to the reflux rich liquid atomizer 1-1a of the flash kettle 1; the gas phase outlet of the flash kettle 1 is connected to the lower section of the rich liquid reflux washing tower 2, and the lean liquid outlet at the bottom of the flash kettle 1 is connected to the lean liquid nozzle 2-1 of the upper section of the rich liquid reflux washing tower 2 through a continuous The liquid column 12 is connected to the absorption tower; the gas phase outlet at the top of the rich liquid reflux washing tower 2 is connected to the flash steam condenser 4, the condensate outlet of the flash steam condenser 4 is connected to the pre-pump oil-water separator 6, and the non-condensable gas outlet is connected to the absorption tower via the vacuum pump 5; the condensate outlet of the pre-pump oil-water separator 6 is connected to the semi-lean liquid aeration head 1-7a and the lean liquid aeration head 1-7b in the lean liquid tank 1-6a and the semi-lean liquid tank 1-6b in the flash kettle 1 via the condensate tank 7 and the condensate vaporization heater 8a, and the oil phase outlet is connected to the vacuum unloading valve 11 and the intermediate oil tank 9 in sequence.

[0059] The upper section of the flash kettle is a primary flash chamber, and the lower section is a secondary flash chamber. The lower storage tank is divided into a lean liquid tank 1-6a and a semi-lean liquid tank 1-6b by an overflow plate 1-8; a reflux rich liquid atomizer 1-1a and a primary flash atomizer 1-1b are arranged at the upper part of the primary flash chamber (the reflux rich liquid atomizer 1-1a is located above the primary flash atomizer 1-1b), and a primary flash guide plate 1-2a is arranged at the bottom; a secondary flash atomizer 1-1c is arranged at the upper part of the secondary flash chamber, and a secondary flash guide plate 1-2b is arranged at the bottom. The rear end of the flash guide plate 1-2b is fixed on the wall of the flash kettle 1, and the front end passes over the overflow plate 1-8 and is inserted into the lean liquid tank 1-6a; the secondary flash guide plate 1-2b and the overflow plate 1-5 separate the semi-lean liquid tank 1-6b from the secondary flash chamber; the primary flash chamber is connected to the semi-lean liquid tank 1-6b via the guide pipe 1-3, and the gas stripping area above the semi-lean liquid tank 1-6b is also connected to the primary flash chamber via the gas guide pipe 1-4c; the semi-lean liquid tank 1-6b is connected to the secondary flash atomizer 1-1c via the semi-lean liquid heater 8c. Lean liquid aeration heads 1-7b and semi-lean liquid aeration heads 1-7a are provided in the lean liquid tank 1-6a and the semi-lean liquid tank 1-6b respectively.

[0060] The upper, middle and lower parts of the liquid holding column 12 are respectively provided with an overflow port, a lean liquid inlet and a lean liquid outlet. The overflow port is connected to the lean liquid tank 1-6a through a lean liquid overflow pipe 1-5, the lean liquid inlet is connected to the lean liquid outlet at the bottom of the lean liquid tank 1-6a, and the lean liquid outlet of the liquid holding column 12 is connected to the absorption tower.

[0061] The rich liquid reflux washing tower 2 is provided with a demister, a reflux rich liquid nozzle 2-1, a washing filler 2-2 and a storage tank 2-3 under the tower in sequence from top to bottom. The demister can use an existing conventional demister, or an electronic demister 3. The electronic demister 3 includes a plurality of cathode arc plates 3-4 located at the periphery of the inner wall of the tower, an anode tube 3-5 and a cathode porous plate 3-2 located at the center correspondingly. The cathode arc plates 3-4 are provided with insulating gaskets 3-3 through the inner wall of the tower, and field electron emission materials 3-8 are uniformly embedded in the inner surface; the anode tube 3-5 is fixed in the tower through an anode tube bracket 3-6, and the cathode porous plate 3-2 is fixed in the tower through a porous plate insulating seat 3-7. The anode tube 3-5, the plurality of cathode arc plates 3-4 and the cathode porous plate 3-2 are all connected to the outside of the tower through an insulating hot wire column 3-1.

[0062] Process:

[0063] Take a certain artificial stone production plant as an example. The plant has two artificial stone production lines. The VOC production units mainly come from mixing, feeding, unloading, laying, vacuuming, pressing, film lifting, and drying. The main pollutants are styrene, non-methane total hydrocarbons, etc. During the collection process, the tail gas rich in styrene is 20,000-25,000 Nm 3 / h, styrene concentration in tail gas in summer

[0064] 1500-2000mg / Nm 3 , 300-500mg / Nm in winter 3 .

[0065] The rich liquid tank 13 of the absorption tower collects the rich liquid (temperature 20-30°C) that absorbs styrene from the bottom of the absorption tower. The rich liquid exiting the rich liquid tank 13 of the absorption tower is divided into two streams. The first stream, at a rate of 10-11 tons / hour, is heated to 60-65°C and sent to the first-stage flash atomizer 1-1b of the flash kettle for atomization, spraying, and analyzing to recover the styrene component. The second stream, at a rate of 4-5 tons / hour, is sent to the reflux rich liquid nozzle 2-1 of the rich liquid reflux washing tower 2 for spraying, countercurrent contact, washing, and heat exchange with the flash steam from the flash kettle 13. The rich liquid (temperature 25-35°C) exiting the rich liquid reflux washing tower 2 is sent to the reflux rich liquid atomizer 1-1a of the flash kettle 1 for atomization, spraying, and analyzing to recover the styrene component.

[0066] In the flash evaporator 1: gradually increase the temperature and circulation volume of the absorption liquid for flash evaporation to improve the flash evaporation efficiency. The temperature of the rich liquid entering the first flash evaporation chamber is controlled at 60-65°C, and the rich liquid flow rate is controlled at 10-15 tons / hour; the temperature of the rich liquid entering the second flash evaporation chamber is controlled at 65-70°C, and the rich liquid flow rate is controlled at 20-25 tons / hour. The semi-lean liquid after rich liquid flash analysis is sprayed out by the reflux rich liquid nozzle 2-1 and the primary flash atomizer 1-1b and falls into the semi-lean liquid tank 1-6a through the guide pipe 1-4c, and then is extracted, heated to 65-70°C and sent to the secondary flash chamber by the secondary flash atomizer 1-1c for spraying for secondary flash evaporation. The obtained lean liquid falls into the lean liquid tank 1-6b along the secondary flash guide plate 1-2b and then is led out of the flash kettle 1; the flash gas in the secondary flash chamber is merged into the primary flash chamber through the second-layer air guide pipe 1-4b, and then is led out of the flash kettle 1 together with the flash gas in the primary flash chamber through the top upper air guide pipe 1-4a.

[0067] Water vapor or other low-boiling-point component gas (such as carbon dioxide, nitrogen, etc.) insoluble in absorbent is introduced into the lean liquid tank 1-6a and the semi-lean liquid tank 1-6b in the flash kettle to further strip the residual styrene component in the lean liquid and the semi-lean liquid. The stripping gas overflowing from the semi-lean liquid tank 1-6b is introduced into the primary flash chamber through the stripping gas guide pipe 1-4c to merge with the flash gas; the stripping gas overflowing from the lean liquid tank 1-6a directly enters the secondary flash chamber to merge with the flash gas; the lean liquid in the lean liquid tank 1-6a is drawn out through the lean liquid outlet and then returned to the absorption tower through the liquid holding column 12 as a circulating absorbent to wash the tail gas containing styrene, and the overflow liquid at the top of the liquid holding column 12 is returned to the lean liquid tank 1-6a through the lean liquid overflow pipe 1-5.

[0068] The gas phase from the flash kettle 1 is sent to the rich liquid reflux washing tower 2 through the upper gas guide pipe 1-4a. In the rich liquid reflux tower: the flash gas passes through the packing layer 2-2 from bottom to top, and is countercurrently contacted and washed by the rich liquid sprayed from the reflux rich liquid nozzle 2-1 from top to bottom, and is finally defogged by the electronic demister 3 and then led out from the top of the tower. When the washed flash gas passes through the electronic demister 3 in the energized state, the anode tube 3-5 provides a strong electric field, and the field electron emission material 3-8 emits electrons. The mist particles passing through the field capture the electrons and move to the surface of the anode tube 3-5 (electric field force). The mist droplets not captured by the surface continue to move upward. Due to the negative charge, they are intercepted by the cathode porous plate 3-2, thereby achieving the purpose of efficient demisting.

[0069] The gas phase after washing and demisting at the top of the rich liquid reflux washing tower 2 is sent to the flash steam condenser 4 to separate the condensate and non-condensable gas. The separated condensate is separated into styrene components and condensed water by the pre-pump oil-water separator 6. The separated condensed water is collected by the condensate tank 7, and then heated and vaporized by the condensate vaporization heater 8a. It is passed as water vapor into the semi-lean liquid aeration head 1-7a and the lean liquid aeration head 1-7b in the lean liquid tank 1-6a and the semi-lean liquid tank 1-6b in the flash kettle 1, which is used for gas stripping the styrene components in the lean liquid and semi-lean liquid to realize the condensate circulation; the separated non-condensable gas is returned to the absorption tower after the vacuum pump group. It is preferred to control the operating pressure of the flash kettle 1, the flash steam condenser 4 and the pre-pump oil-water separator 6 to be below the absolute pressure of 4kPa.

[0070] In this embodiment, the rich liquid from the absorption tower refers to the absorbent that has absorbed styrene. The absorbent is a high-boiling point organic solvent whose boiling point is 150° C. or more higher than that of styrene, and is preferably diethyl phthalate.

[0071] See also Figure 6 The Henry constant of the solution after diethyl phthalate absorbs styrene is: 23.04kg / (moL·kPa).

[0072] More than 98% of the styrene components in styrene tail gas are recovered, and the tail gas is purified to meet emission standards. The absorbent consumption is less than 0.1kg / t-styrene. 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 flash distillation-stripping method for styrene absorption liquid, comprising sending the rich liquid absorbed by styrene from the bottom of an absorption tower into a flash kettle for flash distillation and analysis to form a gas phase product and a liquid phase product, characterized in that: The rich liquid is divided into two streams, the first stream is heated and sent to a flash kettle for analysis and recovery of styrene components; The second stream is sent to the rich liquid reflux washing tower for countercurrent contact and washing with the gas phase from the flash kettle, and the rich liquid from the rich liquid reflux washing tower is sent to the flash kettle for flash evaporation and analysis; Water vapor or other low-boiling-point component gas insoluble in the absorbent is introduced into the liquid phase product in the flash reactor to further strip the residual styrene component in the liquid phase product; The gas phase leaving the flash kettle is sent to the rich liquid reflux washing tower for washing.

2. The flash distillation-stripping method of styrene absorption liquid according to claim 1, characterized in that: The flash kettle is provided with at least two stages of flash chambers from top to bottom, and a liquid storage tank is provided at the bottom.

3. The flash distillation-stripping method of styrene absorption liquid according to claim 1, characterized in that: The upper section of the flash kettle is a primary flash chamber, 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 provided with a reflux rich liquid atomizer and a primary flash atomizer, and the bottom is a primary flash guide plate; the upper part of the secondary flash chamber is provided with a secondary flash atomizer, and the bottom is a secondary flash guide plate, and the front end of the secondary flash guide plate is inserted into the lean liquid tank; The first-stage flash chamber is connected to the semi-lean liquid tank via a guide pipe, and the second-stage flash chamber is connected to the lean liquid tank via a second-stage flash guide plate, and the second-stage flash guide plate and the overflow plate separate the semi-lean liquid tank from the second-stage flash chamber; The gas phase space at the upper part of the semi-lean liquid tank is connected to the primary flash chamber through a gas stripping gas air guide pipe, the semi-lean liquid tank is connected to the secondary flash atomizer through a semi-lean liquid heater, the gas phase outlet of the secondary flash chamber is connected to the primary flash chamber through a second-layer air guide pipe, and the gas phase outlet of the primary flash chamber is connected to the rich liquid reflux washing tower through an upper-layer air guide pipe.

4. The flash distillation-stripping method of styrene absorption liquid as claimed in claim 3, characterized in that: The first rich liquid from the absorption tower is heated to 60-65°C and then sprayed into the first flash chamber by a first-level flash atomizer for flash evaporation; the semi-lean liquid after the first flash evaporation is introduced into the semi-lean liquid tank through the first-level flash guide plate and the first flash through the guide pipe, and then drawn out from the semi-lean liquid tank, heated to 65-70°C, and then sprayed into the second flash chamber by a second-level flash atomizer for further atomization and flash evaporation. The obtained lean liquid enters the lean liquid tank and is then drawn out of the flash chamber; the flash steam in the second-level flash chamber is merged into the first flash chamber through the second-layer air guide pipe and is drawn out of the flash kettle together with the flash steam in the first flash chamber through the upper-layer air guide pipe.

5. The flash distillation-stripping method of styrene absorption liquid according to claim 1, characterized in that: The lean liquid exiting the flash kettle is sent back to the absorption tower via the liquid holding column and recycled as an absorbent.

6. The flash distillation-stripping method of styrene absorption liquid according to claim 1, characterized in that: The rich liquid from the rich liquid reflux washing tower is atomized by the reflux rich liquid atomizer in the flash kettle and sprayed into the primary flash chamber for atomization flash evaporation.

7. The flash distillation-stripping method of styrene absorption liquid according to claim 4, characterized in that: The stripping gas overflowing from the semi-lean liquid tank is introduced into the primary flash chamber through the air guide pipe; the stripping gas overflowing from the lean liquid tank directly enters the secondary flash chamber.

8. The flash evaporation-stripping method of styrene absorption liquid according to any one of claims 3 to 5, characterized in that: The gas phase leaving the flash kettle is washed and demisted in the rich liquid reflux washing tower to capture some fine droplets, and then further demisted by the electronic demister. It is then drawn out from the top of the tower and sent to the flash steam condenser for condensation to separate the condensate and non-condensable gases.

9. The flash distillation-stripping method of styrene absorption liquid according to claim 8, characterized in that: The separated condensate is separated into styrene components and condensed water through a pre-pump oil-water separator. The separated condensed water is heated and vaporized and then introduced into the lean liquid tank and semi-lean liquid tank in the flash kettle as water vapor to strip the styrene components in the lean liquid and semi-lean liquid, thereby realizing the condensed water circulation. The separated non-condensable gas is returned to the absorption tower through a vacuum pump.

10. The flash evaporation-stripping method of styrene absorption liquid according to claim 9, characterized in that: Control the operating pressure of the flash kettle, rich liquid reflux washing tower, flash steam condenser and pre-pump oil-water separator below 4kPa absolute pressure.

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