Waste gas solvent recovery method

Abstract

The invention provides a waste gas solvent recovery method. The invention relates to a waste gas solvent recovery method, and aims to improve the recovery efficiency of an organic solvent in waste gas and reduce environmental pollution. The method comprises the following steps: pretreating waste gas to remove impurities and adjust temperature and humidity; a solvent is adsorbed in the first-stage adsorption tank through an electric field enhanced adsorption technology; the waste gas enters a secondary adsorption tank, the low-polarity solvent is separated through a separation membrane, and the waste gas is discharged; desorption and solvent recovery are performed through steam heating, pressure reduction and electric field inversion; and condensing the mixed gas and improving the purity of the solvent through supergravity separation. By comprehensively applying technologies such as electric field enhanced adsorption, hot steam desorption, condensation and supergravity separation, efficient recovery of the organic solvent in the waste gas is achieved, the solvent recovery rate is increased, resource waste is reduced, waste gas emission is reduced, and remarkable economic benefits and environmental protection value are achieved.

Description

Technical Field

[0001] The invention relates to the field of environmental protection, and in particular to a waste gas solvent recovery method. Background Art

[0002] In the process of industrial production, especially in the fields of chemical industry, coating, printing, solvent recovery, etc., the waste gas often contains a large amount of organic solvent components. These organic solvents not only cause serious pollution to the environment, but may also pose a threat to human health. Therefore, how to effectively recover and treat organic solvents in waste gas has become an important issue in environmental protection and resource recycling. Traditional methods for recovering waste gas solvents mainly include adsorption, condensation, washing, etc. The adsorption method usually uses adsorption materials such as activated carbon and molecular sieves to remove solvent components in waste gas by physical adsorption, but because the solvent recovery efficiency is low and it is easy to cause adsorbent saturation, it needs to be replaced or regenerated regularly. The condensation method condenses the solvent vapor into liquid by lowering the temperature and separates the solvent from the gas phase. It is suitable for situations where the solvent is highly volatile, but the condensation efficiency is closely related to conditions such as temperature and pressure changes, and the processing capacity is limited.

[0003] In view of these problems, the prior art has proposed some improvement plans, but there are still certain limitations. For example, the patent with publication number CN220257590U discloses an organic waste gas solvent recovery device, but it still has the following shortcomings: for some mixed solvents with complex components, the existing recovery device may not be able to achieve efficient separation and recovery. Different solvents have different physical properties such as boiling point and volatility. It is difficult to accurately control parameters such as temperature and pressure during the recovery process, resulting in some solvents being unable to be completely recovered, or the purity after recovery is not high. Summary of the invention

[0004] 1. Technical issues to be resolved In view of the deficiencies of the prior art, the present invention aims to provide a method for recovering waste gas solvents, which solves the problems existing in the prior art. First, by utilizing electric field enhanced adsorption technology, the adsorption effect between solvent molecules and activated carbon is enhanced according to the polarity differences of different solvents, thereby ensuring efficient separation. Secondly, by precisely controlling the temperature, pressure and electric field direction during the desorption process, the recovery difficulties caused by the differences in the physical properties of the solvents are effectively overcome, ensuring that more solvents can be desorbed. For low-polarity and small-molecule solvents, secondary adsorption and separation membrane technology are used to further optimize the separation process to ensure that the recovered solvent is purer. Finally, ultra-gravity separation technology further improves the purity of the solvent and ensures efficient recovery. Through these innovations, the present invention can solve the problems of separation difficulties and low purity in the complex solvent recovery process, and achieve efficient and accurate solvent recovery.

[0005] (II) Technical solution To achieve the above object, the present invention provides the following technical solution: a method for recovering waste gas solvent, comprising the following steps: S1 pretreatment: the waste gas containing solvent is passed into the pretreatment mechanism for filtration and temperature and humidity adjustment; S2 primary adsorption: the pretreated exhaust gas is passed into the primary adsorption tank and adsorbed by activated carbon plates and electric field enhancement; S3 secondary adsorption: the waste gas enters the secondary adsorption tank, and the low-grade and small-molecule solvents are separated by the separation membrane, and the waste gas is discharged through the chimney; S4: Desorption: Steam is introduced into the primary adsorption tank for 15-30 minutes to perform decompression desorption while adjusting the direction and intensity of the electric field; S5 condensation: condensing the desorbed mixed gas in a condensation mechanism; S6 separation: separating the condensed mixed liquid in an ultra-gravity separation mechanism; S7 Solvent Recovery: The separated high-purity solvent is transported to the solvent recovery tank for storage and subsequent use.

[0006] Preferably, in the S1 pretreatment step, the temperature of the exhaust gas is controlled at 25-30°C and the humidity is controlled at 60%-80%.

[0007] Preferably, in the S2 primary adsorption step, the activated carbon plate is spiral-shaped, a central electrode is fixed to the central axis of the activated carbon plate, an interlayer electrode is embedded in the activated carbon plate, and both ends of the central electrode are connected to a reversible power supply.

[0008] Preferably, in the S2 primary adsorption step, the exhaust gas flow rate is controlled at 2000 m³ / h, the specific surface area of ​​the activated carbon plate is controlled at 1500 m2 / g, the porosity is greater than 80%, and the intensity of the electric field is controlled at 5-10 kV / m.

[0009] Preferably, in the S4 desorption step, the steam temperature is controlled at 120-150°C.

[0010] Preferably, in the S4 desorption step, the pressure of the adsorption tank during the reduced pressure desorption is controlled at 50-80 mbar.

[0011] Preferably, in the S4 desorption step, the intensity of the electric field is controlled to be 3-5 kV / m, and the direction of the electric field is opposite to that of the electric field in the S2 primary adsorption step.

[0012] Preferably, in step S5 condensation, the condensation temperature is controlled at 5-10°C.

[0013] Preferably, in the separation step S6, the centrifugal force of the ultra-gravity separation device is 500-1000G.

[0014] (III) Beneficial effects The purpose of the present invention is to provide a method for recovering waste gas solvents, which adopts advanced multi-step technology, significantly improves the recovery efficiency of organic solvents in waste gas, and effectively reduces environmental pollution. The key innovation of the present invention is to combine electric field enhanced adsorption, steam desorption, condensation, ultra-gravity separation and other technologies to form a set of efficient waste gas solvent recovery system.

[0015] First, through the electric field enhanced adsorption technology, the activated carbon plate is combined with the electric field to enhance the interaction between the solvent molecules and the adsorbent, significantly improving the adsorption efficiency of organic solvents in the exhaust gas. The electric field can not only improve the directional adsorption of the solvent, but also enhance the binding force between the solvent and the adsorbent, making it easier for the solvent molecules to be adsorbed on the activated carbon plate. Secondly, the desorption process combines high-temperature steam and vacuum decompression technology. By adjusting the direction and intensity of the electric field, the desorption efficiency of the solvent is further improved, ensuring that the adsorption saturated activated carbon can quickly restore its adsorption capacity and efficiently recover the organic solvent.

[0016] In the condensation stage, the present invention uses a low-temperature cooling medium to condense the mixed gas after desorption, effectively separating the solvent and other components in the waste gas, and further improving the purity of the solvent recovery. Subsequently, the ultra-gravity separation technology is used to finely separate the condensate through centrifugal force to remove impurities and moisture in the solvent, ensuring the high purity of the recovered solvent, which is suitable for reuse in the production process and reducing resource consumption.

[0017] Through the combination of this series of technologies, the present invention realizes the efficient recovery and separation of organic solvents in waste gas, which not only improves the solvent recovery rate and reduces the emission of harmful waste gas, but also effectively saves resources and reduces industrial production costs. It has significant economic benefits and environmental value and is suitable for multiple industrial fields, especially in waste gas treatment in the coatings, printing, chemical and other industries, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings: Figure 1 It is a schematic diagram of the whole waste gas solvent recovery method of the present invention; Figure 2 It is a schematic diagram of a primary adsorption tank in a waste gas solvent recovery method of the present invention; Figure 3 A schematic diagram of an activated carbon plate in a waste gas solvent recovery method of the present invention; Figure 4 for Figure 3An enlarged view of point A in the schematic diagram of an activated carbon plate in a waste gas solvent recovery method of the present invention; Figure 5 A schematic diagram of overall adsorption and emission in a waste gas solvent recovery method of the present invention; Figure 6 A schematic diagram of overall desorption and solvent recovery in a waste gas solvent recovery method of the present invention; In the figure: 1-fixed frame, 2-pretreatment mechanism, 3-primary adsorption tank, 4-secondary adsorption tank, 5-condensation mechanism, 6-supergravity separation mechanism, 7-solvent recovery tank, 8-steam furnace, 9-vacuum adsorption pump, 10-chimney, 31-tank body, 32-activated carbon plate, 33-internal reinforcement column, 34-center electrode, 35-interlayer electrode, 36-wiring pipe, 37-reversible power supply. DETAILED DESCRIPTION

[0019] The following will be combined with the attached examples of the present invention Figure 1 to Figure 6 A clear and complete description is given to the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] The device of the waste gas solvent recovery method comprises: a fixed frame 1, a pretreatment mechanism 2 is arranged on the right side of the fixed frame 1, a primary adsorption tank 3 is fixed at the lower end of the fixed frame 1, a secondary adsorption tank 4 is arranged on the left side of the primary adsorption tank 3, a condensation mechanism 5 is arranged at the front of the fixed frame 1, a super gravity separation mechanism 6 is connected to the rear end of the condensation mechanism 5, a solvent recovery tank 7 is connected to the left side of the super gravity separation mechanism 6, a steam furnace 8 is arranged at the rear end of the fixed frame 1, and a vacuum adsorption pump 9 is arranged at the upper end of the fixed frame 1. A chimney 10 is arranged at the rear end of the fixed frame 1.

[0021] The pretreatment mechanism 2 is used for preliminary treatment of the waste gas containing organic solvents. The primary adsorption tank 3 is used for adsorption treatment of the pretreated waste gas to remove most of the organic solvents. The secondary adsorption tank 4 is used as a supplement to the primary adsorption tank to supplement the adsorption of the solvent that is difficult to adsorb in the primary adsorption tank. The condensation mechanism 5 is used to cool the desorbed organic solvent vapor into a liquid state. The supergravity separation mechanism 6 further separates the condensed liquid mixture. The solvent recovery tank 7 is used to collect the high-purity organic solvent obtained after supergravity separation. The steam furnace 8 is used to provide steam for the desorption of activated carbon in the adsorption tank. After the activated carbon is saturated with adsorption, the steam generated by the steam furnace enters the adsorption tank, and the high temperature and high energy of the steam are used to promote the desorption of organic solvent molecules from the surface of the activated carbon. At the same time, the steam can also clean the pores of the activated carbon, restore the adsorption performance of the activated carbon, extend the service life of the activated carbon, and ensure the long-term stable operation of the adsorption tank. The vacuum adsorption pump 9 is used to reduce the pressure in the adsorption tank during the desorption process, promote the desorption of organic solvents from the surface of the activated carbon, and also prevent abnormal pressure in the system to ensure the safe operation of the system. The chimney 10 serves to provide a safe exhaust gas discharge channel for the entire organic solvent recovery system.

[0022] The primary adsorption tank 3 includes a tank body 31, an activated carbon plate 32 is fixed inside the tank body 31, an internal reinforcement column 33 is arranged in the middle of the activated carbon plate 32, a central electrode 34 is arranged in the middle of the internal reinforcement column 33, and an interlayer electrode 35 is arranged inside the activated carbon plate 32. The activated carbon plate 32 has a huge specific surface area and a rich pore structure, and can adsorb organic solvent molecules in the exhaust gas on its surface and in the pores through physical adsorption. The internal reinforcement column 33 mainly plays a role in enhancing the structural strength of the activated carbon plate. The central electrode 34 is located in the internal reinforcement column in the middle of the activated carbon plate. When the power is turned on, the central electrode can generate an electric field around the activated carbon plate. For polar organic solvent molecules in the exhaust gas, the electric field can cause them to be oriented and arranged, making them easier to be adsorbed on the surface of the activated carbon plate; for non-polar molecules, it can also induce them to produce polarization, thereby enhancing the adsorption effect with the activated carbon plate. In addition, the electric field can also change the charge distribution on the surface of the activated carbon plate, increase the adsorption sites, and further improve the adsorption efficiency of the activated carbon plate for organic solvents.

[0023] The activated carbon plate 32 is spiral-shaped, and the central electrode 34 is arranged on the central axis of the spiral activated carbon plate 32. The spiral activated carbon plate 32 and the central electrode 34 arranged on the central axis. The spiral design of the spiral activated carbon plate 32 makes the flow path of the exhaust gas no longer a simple straight line when it flows through the activated carbon plate in the tank body, but it moves along the spiral channel in a circuitous way. This greatly prolongs the contact time between the exhaust gas and the activated carbon plate, allowing the organic solvent molecules in the exhaust gas to have more opportunities to fully contact with the surface and pores of the activated carbon plate, thereby increasing the probability of the organic solvent being adsorbed and enhancing the adsorption effect.

[0024] The central electrode 34 is arranged on the central axis of the spiral activated carbon plate 32, and the electric field generated after power is turned on can radiate in a relatively uniform manner. Since the activated carbon plate is spirally wrapped around the electrode, this layout allows the electric field to penetrate the entire activated carbon plate more evenly, ensuring that each part can be affected by the electric field, so that the organic solvent molecules at different positions of the activated carbon plate can be subjected to a relatively consistent adsorption force enhancement effect, thereby improving the uniformity and overall efficiency of adsorption. The position of the central axis allows the electric field force to act effectively along the radial direction of the spiral activated carbon plate. For polar organic solvent molecules in the exhaust gas, they will move radially toward the surface of the activated carbon plate under the action of the electric field force, making them easier to be adsorbed; for non-polar molecules, they can also be better adsorbed by the polarization induced by the electric field, giving full play to the strengthening effect of the electric field on the adsorption process.

[0025] The interlayer electrode 35 is a metal sheet, which is spirally embedded in the activated carbon plate 32. The interlayer electrode 35 is made of metal sheet, which can effectively conduct current and ensure that the expected electric field effect can be generated after power is turned on or induced charging. At the same time, the relatively thin nature of the metal sheet makes it easier to bend into a shape that matches the spiral activated carbon plate, which is convenient for embedded installation inside the activated carbon plate. The interlayer electrode 35, which is spirally embedded in the activated carbon plate, further optimizes the electric field distribution inside the activated carbon plate by cooperating with the central electrode 34 of the central axis. When the central electrode is energized to generate an electric field, the interlayer electrode will be charged due to electrostatic induction, forming a more complex and detailed electric field network inside the activated carbon plate. This electric field network can penetrate into each fine pore area of ​​the activated carbon plate, so that the adsorption process of organic solvent molecules inside the activated carbon plate is subject to more comprehensive and accurate electric field regulation, further improving the adsorption efficiency.

[0026] The electric field formed by the interlayer electrode 35 can cooperate with the electric field of the central electrode 34 to provide a stronger adsorption driving force for the organic solvent molecules in the exhaust gas, whether polar or non-polar. For example, polar molecules will be more firmly adsorbed on the activated carbon plate due to the combined effect of electric field forces from different directions; non-polar molecules can also be further enhanced under the influence of this synergistic electric field, thereby improving the adsorption capacity of the entire activated carbon plate for organic solvents.

[0027] Example 1: Waste gas containing alkane solvents Process flow: Source of waste gas: The waste gas mainly comes from the solvent use section of a chemical plant. The waste gas mainly contains alkane solvents (such as n-hexane, n-heptane, etc.), and the solvent concentration is about 1500-2000 mg / m³.

[0028] S1: Pretreatment: The exhaust gas is filtered through a high-efficiency filter to remove particulate matter, ensuring that the particulate matter content is less than 5 mg / m³. The exhaust gas temperature is then adjusted to 28°C and the humidity is adjusted to 65% through a temperature and humidity control device.

[0029] S2 primary adsorption: The waste gas enters the primary adsorption tank and is physically adsorbed by contacting the spiral activated carbon plate. Alkane solvent molecules are effectively adsorbed by physical adsorption. Other waste gases after adsorption are directly discharged through the chimney.

[0030] Electric field-assisted adsorption: An electric field (with an intensity of 7 kV / m) was applied inside the activated carbon plate to enhance the adsorption of alkane solvents.

[0031] S3 desorption: Steam desorption: When the activated carbon plate is saturated with adsorption, the hot steam (120°C) generated by the steam furnace enters the primary adsorption tank, exchanges heat with the solvent molecules, and promotes the desorption of the solvent from the activated carbon surface.

[0032] Vacuum desorption: The pressure in the adsorption tank is reduced to 80 mbar by a vacuum adsorption pump to accelerate the desorption of the solvent.

[0033] Electric field adjustment: The direction of the electric field was reversed and the intensity was reduced to 3 kV / m, which further reduced the adsorption force between the solvent and activated carbon and promoted desorption.

[0034] S4 Condensation: The temperature inside the condenser is controlled at 8°C. Cold water acts as a cooling medium to take away the heat of the solvent vapor, turning the toluene, acetone and ethanol vapors into liquid.

[0035] S5 Ultra-gravity separation: The liquid mixture enters the ultra-gravity separation equipment, and under the action of 800G centrifugal force, a small amount of impurities and water in the solvent are effectively separated.

[0036] S6 Solvent Recovery: After ultra-gravity separation, the purity of toluene, acetone and ethanol solvents reaches 98.5% and is transported to the solvent recovery tank for storage and can be reused in production.

[0037] Example 2: Waste gas containing aromatic hydrocarbon solvents Process flow: Source of waste gas: The waste gas comes from a printing factory, which uses aromatic hydrocarbon solvents (such as benzene, toluene, xylene, etc.) in the production process. The solvent concentration in the waste gas is about 3000-5000 mg / m³.

[0038] S1 pretreatment: filtration and temperature and humidity adjustment: the waste gas passes through a high-efficiency filter to remove particulate matter, and the particulate matter content is less than 5mg / m³. The temperature and humidity adjustment device controls the temperature of the waste gas at 30℃ and the humidity at 60%.

[0039] S2 primary adsorption: The exhaust gas enters the primary adsorption tank and comes into contact with the spiral activated carbon plate. The aromatic hydrocarbon solvent molecules are adsorbed on the surface of the activated carbon through physical adsorption.

[0040] Electric field-assisted adsorption: An electric field (with a strength of 9 kV / m) is applied inside the activated carbon plate to enhance the adsorption of aromatic hydrocarbon solvents, especially for solvent molecules with strong polarity (such as benzene and toluene).

[0041] S3 secondary adsorption: Solvent characteristics: Since the waste gas contains some smaller molecular weight, low polarity alkane solvents (such as alkanes, cycloalkanes, etc.) in addition to aromatic hydrocarbon solvents, secondary adsorption is required for further treatment.

[0042] Waste gas enters the secondary adsorption tank: the waste gas enters the secondary adsorption tank through the outlet of the primary adsorption tank and contacts the separation membrane. The pore size and properties of the separation membrane can be screened according to the size and polarity of the solvent molecules, so that aromatic hydrocarbon solvents (such as benzene and toluene) are intercepted, while other small molecule solvents (such as alkanes) can be separated through the membrane. The separated waste gas is discharged through the chimney.

[0043] S4 desorption stage: Steam desorption: When the adsorption capacity of the activated carbon plate reaches saturation, the steam furnace (120°C) releases hot steam into the primary adsorption tank to desorb the solvent.

[0044] Vacuum desorption: The pressure in the adsorption tank is reduced to 50-80 mbar by a vacuum adsorption pump to promote the desorption of the solvent.

[0045] Electric field adjustment: Adjust the direction and intensity of the electric field to further promote the desorption of the solvent from the activated carbon surface and the separation membrane.

[0046] S5 Condensation: The temperature inside the condenser is controlled at 7°C, and the refrigerant takes away the heat of the solvent vapor, turning the solvent vapor into liquid.

[0047] S6 Super Gravity Separation: The liquid mixture enters the ultra-gravity separation equipment, where the impurities and water in the solvent are separated under the action of 700G centrifugal force, with a separation purity of 93%.

[0048] S7 Solvent Recovery: After ultra-gravity separation, the purity of toluene, n-hexane, acetone, cyclohexane and ethyl acetate solvents reaches 99% and is transported to the solvent recovery tank for storage and can be reused in production. At the same time, the waste gas treated by the secondary adsorption tank meets the emission standards and is discharged through the chimney.

[0049] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for recovering a waste gas solvent, comprising the following steps: S1 pretreatment: the waste gas containing solvent is passed into the pretreatment mechanism for filtration and temperature and humidity adjustment; S2 primary adsorption: the pretreated exhaust gas is passed into the primary adsorption tank and adsorbed by activated carbon plates and electric field enhancement; S3 secondary adsorption: the waste gas enters the secondary adsorption tank, and the low-grade and small-molecule solvents are separated by the separation membrane, and the waste gas is discharged through the chimney; S4: Desorption: Steam is introduced into the primary adsorption tank for 15-30 minutes to perform decompression desorption while adjusting the direction and intensity of the electric field; S5 condensation: condensing the desorbed mixed gas in a condensation mechanism; S6 separation: separating the condensed mixed liquid in an ultra-gravity separation mechanism; S7 Solvent Recovery: The separated high-purity solvent is transported to the solvent recovery tank for storage and subsequent use.

2. A method for recovering waste gas solvent according to claim 1, characterized in that: In the S1 pretreatment step, the temperature of the exhaust gas is controlled at 25-30° C., and the humidity is controlled at 60%-80%.

3. The method for recovering waste gas solvent according to claim 1, characterized in that: In the S2 primary adsorption step, the activated carbon plate is spiral-shaped, a central electrode is fixed to the central axis of the activated carbon plate, an interlayer electrode is embedded in the activated carbon plate, and both ends of the central electrode are connected to a reversible power supply.

4. The method for recovering waste gas solvent according to claim 1, characterized in that: In the S2 primary adsorption step, the exhaust gas flow rate is controlled at 2000m³ / h, the specific surface area of ​​the activated carbon plate is controlled at 1500㎡ / g, the porosity is greater than 80%, and the intensity of the electric field is controlled at 5-10kV / m.

5. The method for recovering waste gas solvent according to claim 1, characterized in that: In the S4 desorption step, the steam temperature is controlled at 120-150°C.

6. The method for recovering waste gas solvent according to claim 1, characterized in that: In the S4 desorption step, the pressure of the adsorption tank is controlled at 50-80 mbar during the reduced pressure desorption.

7. The method for recovering waste gas solvent according to claim 1, characterized in that: In the S4 desorption step, the intensity of the electric field is controlled to be 3-5 kV / m, and the direction of the electric field is opposite to that in the S2 primary adsorption step.

8. The method for recovering waste gas solvent according to claim 1, characterized in that: In the S5 condensation step, the condensation temperature is controlled to be 5-10°C.

9. The method for recovering solvent from waste gas according to claim 1, characterized in that: In the separation step S6, the centrifugal force of the ultra-gravity separation device is 500-1000G.

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