A method and system for treating waste gas containing volatile organic compounds

Abstract

The present invention provides a method and system for treating waste gas containing volatile organic compounds. After the waste gas containing volatile organic compounds is pretreated, the pretreatment includes, for example, filtering, heat exchange cooling, water washing, alkali washing and cooling, and then contacting with a metal salt solution, and the waste gas is absorbed and treated with an organic solvent capable of absorbing volatile organic compounds to obtain waste gas containing very low volatile organic compounds. The waste gas containing very low volatile organic compounds is optionally sent to an adsorption tower or a thermal incinerator or a catalytic oxidation furnace equipped with an adsorption material for treatment, and the volatile organic compounds therein are further removed, and the volatile organic content of the treated waste gas is further reduced. Since the use of metal salts can control the moisture in the waste gas at a reasonable level, the removal of VOCs by the organic solvent is stabilized; since the volatile organic compounds in the waste gas are treated by solvent absorption, the load of treating volatile organic compounds is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of waste gas treatment, and in particular relates to a method and system for treating waste gas containing volatile organic compounds. Background Art

[0002] The emission of industrial volatile organic compounds (VOCs) is one of the main sources of air pollution. For example, various polymers that are currently widely used, such as butyl rubber, halogenated butyl rubber, butadiene rubber, solution-polymerized styrene-butadiene rubber, ethylene-propylene rubber, silicone rubber, polyisoprene rubber, chloroprene rubber, hydrogenated nitrile rubber, styrene-butadiene-styrene block copolymer (SBS), acrylonitrile-butadiene-styrene (ABS), hydrogenated styrene-butadiene block copolymer (SEBS), styrene-isoprene-styrene copolymer (SIS), hydrogenated styrene-isoprene-styrene copolymer (SEPS), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, polybutene, polyacrylonitrile, polystyrene and other polymer preparation processes, the polymerization product treatment steps from the reactor all include the recovery of the polymer, the recovery of the solvent (such as n-hexane) and the unreacted monomer, and the drying process of the aqueous polymer. The waste gas generated during the drying process of aqueous polymers usually contains industrial volatile organic compounds (VOCs) (such as organic matter such as hydrocarbons), polymer particles, etc., and usually needs to be further treated before being discharged. However, the treatment of this waste gas is relatively difficult.

[0003] For the treatment of the above-mentioned waste gas, the current industrial technologies mainly include activated carbon adsorption treatment process, thermal incineration treatment process, and catalytic oxidation tail gas treatment process. Among them, the thermal incineration treatment process is simple and has low one-time investment, but it requires a large amount of fuel for combustion and has high operating costs. The catalytic oxidation tail gas treatment process uses precious metal platinum and palladium series catalysts to catalytically oxidize organic matter in the tail gas at 250-600°C to convert the organic matter into carbon dioxide and water; it has the advantages of low reaction temperature and high organic matter removal rate, but because a large amount of precious metals are used as catalysts, the treatment cost is greatly increased. Compared with the two waste gas treatment processes of thermal incineration and catalytic oxidation tail gas, the activated carbon adsorption method is a physical method with the advantages of simple operation, thorough adsorption of organic matter such as hydrocarbons, and organic matter such as hydrocarbons can be recovered during the regeneration process of activated carbon. However, when activated carbon adsorption is used in industry to treat this type of tail gas, there are problems such as low activated carbon adsorption rate, frequent regeneration, frequent blockage of activated carbon bed, severe corrosion of activated carbon adsorption equipment, high operating cost of tail gas treatment device, and sometimes failure to meet emission standards. Summary of the invention

[0004] The inventors of this application have proposed in previous studies to reduce VOCs by organic solvent adsorption (see the inventors' prior application No. 201910182080.X). Based on this, after further research, the inventors found that the moisture content in the exhaust gas will affect the treatment effect of the organic solvent on VOCs. Specifically, if the moisture content is high (specifically, if it is higher than 15g / m 3 ), it will directly reduce the treatment effect of organic solvent adsorption to remove VOCs, and even cause the VOCs treatment system to collapse, such as causing the adsorption effect of the organic solvent adsorbent that adsorbs VOCs to drop sharply, and also causing the activity of the VOCs treatment catalyst to drop sharply; therefore, it is necessary to control the moisture content, but the existing water absorbents are usually expensive, difficult to recycle and regenerate, and have defects such as being uneconomical and unsuitable for industrialization. Therefore, under the premise of ensuring the effect of organic solvent adsorbents in removing VOCs from waste gas, choosing a cheaper moisture absorbent to treat waste gas, controlling the moisture at a lower level, reducing the difficulty of operation, and reducing the treatment cost are the key research directions of this application.

[0005] The methods for removing moisture known in the industry at present include: (1) cooling and cooling to precipitate saturated water. However, research has found that the moisture content in the waste gas treated by this method is still relatively high, which is not suitable for the conditions of the present invention; (2) using molecular sieve dehydration or glycol dehydration. Research has found that although this method has a high moisture removal rate, it has the disadvantages of complex regeneration equipment and high treatment costs.

[0006] The present invention proposes for the first time such a method for treating waste gas containing volatile organic compounds, specifically, the waste gas containing at least volatile organic compounds is subjected to pretreatment (including one of the processes of filtration, heat exchange and cooling, water washing, alkali washing, cooling and cooling, or a combination thereof), contacted with a metal salt solution to control the moisture content, solvent absorption to remove volatile organic compounds, and optionally solid adsorbent adsorption or thermal incineration or catalytic oxidation treatment steps to further remove volatile organic compounds, so that the content of volatile organic compounds in the discharged waste gas is less than or equal to the emission standard specified in the "Comprehensive Emission Standard of Air Pollutants" (GB16297-1996). The treatment method has a simple process, requires less treatment equipment, has low treatment costs, and can also achieve efficient removal of volatile organic compounds contained in the waste gas, so that the waste gas treatment device can operate stably for a long time, and the treated waste gas can meet the emission standards. At the same time, the treatment method controls the moisture content in the exhaust gas to avoid reducing the emulsification of the organic solvent that absorbs volatile organic compounds due to excessive moisture content, and further avoids affecting the adsorption efficiency of volatile organic compounds, thereby achieving improved stability of VOCs treatment efficiency.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] A method for treating waste gas containing volatile organic compounds, the method comprising the following steps:

[0009] 1) Pre-treating the waste gas containing volatile organic compounds; the pre-treatment includes filtering, heat exchange and cooling, water washing, alkali washing, cooling and cooling, or a combination thereof;

[0010] 2) contacting the waste gas obtained in step 1) with a metal salt solution;

[0011] 3) contacting the waste gas obtained in step 2) with an organic solvent that has an absorption effect on volatile organic matter;

[0012] 4) optionally contacting the waste gas obtained in at least one of step 2) and step 3) with a solid adsorbent having an adsorption effect on volatile organic compounds, or subjecting the waste gas to thermal incineration treatment or catalytic oxidation treatment;

[0013] 5) Discharging the waste gas obtained in at least one of step 3) and optionally step 4) into the atmosphere.

[0014] According to the present invention, the method further comprises:

[0015] 6) The part of the waste gas obtained by the treatment in step 2) is returned to step 1) after being heated, and is contacted with the waste gas containing volatile organic compounds again.

[0016] Preferably, the method further comprises the steps of:

[0017] 7) Part or all of the waste gas obtained by treatment in step 3) and optionally in at least one of step 4) is returned to step 1) after heat exchange, and is contacted with the waste gas containing volatile organic compounds again.

[0018] The volatile organic matter content in the waste gas treated by the method of the present invention meets the following emission standards: "Integrated Emission Standards for Air Pollutants" (GB16297-1996), and can be directly discharged.

[0019] According to the present invention, in step 2), the metal salt in the metal salt solution is selected from halides, hydroxides, sulfates or nitrates of Group I, Group II or transition metals, preferably one or a mixture of calcium chloride, lithium chloride, lithium bromide and zinc chloride.

[0020] Preferably, the concentration of the metal salt solution is 25-70wt%, for example 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt% or 70wt%.

[0021] Preferably, the metal salt solution is an aqueous metal salt solution.

[0022] According to the present invention, in step 2), the waste gas obtained in step 1) is 4 Nm 3 The volume of the metal salt solution used is 0.5 to 50 ml 3 .

[0023] According to the present invention, the water content in the waste gas obtained in step 2) is less than or equal to 10 g / m 3 .

[0024] According to the present invention, the purpose of setting step 3) is to remove most of the volatile organic compounds in the exhaust gas.

[0025] According to the present invention, in step 3), the organic solvent having an absorption effect on volatile organic compounds is selected from an organic solvent having a boiling point or an initial boiling point greater than or equal to 100°C and at the same time, the boiling point or the initial boiling point of the organic solvent is higher than the boiling point of the volatile organic compounds by more than 30°C. Exemplarily, the organic solvent having an absorption effect on volatile organic compounds is selected from paraffin oil, and in particular, the paraffin oil has a good absorption effect on hydrocarbon volatile organic compounds.

[0026] According to the present invention, in step 3), the waste gas obtained in step 2) is 4 Nm 3 The organic solvent used has an absorption effect on volatile organic compounds and the concentration is 0.5 to 50 m 3 .

[0027] According to the present invention, the content of volatile organic matter in the waste gas obtained in step 3) is 5 to 500 mg / m 3 .

[0028] The present invention also provides a system for realizing the above-mentioned method for treating waste gas containing volatile organic compounds, the system comprising a pretreatment device, a metal salt solution absorption tower and an organic solvent de-volatile organic compound absorption tower; the pretreatment device is connected to the metal salt solution absorption tower, and the metal salt solution absorption tower is connected to the organic solvent de-volatile organic compound absorption tower;

[0029] The pretreatment equipment includes one or more combinations of a filter, a heat exchanger, a water washing tower, an alkali washing tower, and a cooler.

[0030] According to the present invention, the system comprises a pretreatment device, a metal salt solution absorption tower, an organic solvent devolatilization absorption tower, and further comprises a solid devolatilization adsorption tower or a thermal incinerator or a catalytic oxidation furnace; the pretreatment device, the metal salt solution absorption tower, the organic solvent devolatilization absorption tower, and optionally the solid devolatilization adsorption tower or the thermal incinerator or the catalytic oxidation furnace are sequentially connected along the exhaust gas direction;

[0031] The pretreatment equipment includes one or more combinations of filters, heat exchangers, water washers, alkali washers, and coolers. The waste gas is preferably pretreated in the following order: filtration, heat exchange and cooling, water washing, alkali washing, and cooling, that is, the corresponding pretreatment equipment is a filter, a heat exchanger, a water washer, an alkali washer, and a cooler.

[0032] Beneficial effects of the present invention:

[0033] The present invention provides a method and system for treating waste gas containing volatile organic compounds. After the waste gas containing volatile organic compounds is pretreated, the pretreatment includes, for example, filtering, heat exchange cooling, water washing, alkali washing and cooling, and then contacting with a metal salt solution, and the waste gas is subjected to absorption treatment with an organic solvent capable of absorbing volatile organic compounds to obtain waste gas containing very low volatile organic compounds, and the waste gas containing very low volatile organic compounds is optionally sent to an adsorption tower or a thermal incinerator or a catalytic oxidation furnace equipped with an adsorption material for treatment, and the volatile organic compounds therein are further removed, and the volatile organic compound content of the treated waste gas is further reduced. The use of metal salts can control the moisture in the waste gas at a reasonable level, stabilizing the removal of VOCs by organic solvents. Specifically, by controlling the moisture content in the waste gas, the emulsification of the organic solvent that absorbs volatile organic compounds can be avoided due to excessive moisture content, and the effect on the adsorption efficiency of volatile organic compounds can be avoided, thereby achieving the improvement of the stability of VOCs treatment efficiency; the use of solvents to absorb and treat volatile organic compounds in the waste gas reduces the load of treating volatile organic compounds. The volatile organic compounds absorbed by the solvent are regenerated and recovered, and most of the volatile organic components are recovered, thereby improving the economic benefits of waste gas treatment. The waste gas after the organic solvent absorbs the volatile organic compounds is returned to the drying unit for recycling, which can achieve zero emission of waste gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The present invention is a flowchart of a method and system for treating waste gas according to a preferred embodiment of the present invention.

[0035] Figure symbols: 1. Air or nitrogen; 2. Gas heater; 3. Dryer; 4. Waste gas containing VOCs and water; 5. Filter; 6. Cooler; 7. Metal salt solution feed; 8. Metal salt solution absorption tower; 9. Metal salt solution discharge; 11. Waste gas from solvent removal and VOCs removal tower; 12. DeVOCs solvent feed; 13. Solvent deVOCs tower; 14. DeVOCs solvent discharge; 15. Waste gas applied after solvent deVOCs; 16. Waste gas from solid deVOCs tower after solvent deVOCs; 17. Solid deVOCs tower; 18. Standard exhaust gas after solid deVOCs; 19. Waste gas applied after solid deVOCs. DETAILED DESCRIPTION

[0036] In a specific embodiment of the method, the content of volatile organic matter in the waste gas of step 1) is 40-80 g / m 3 , such as about 50g / m 3 .

[0037] In a specific embodiment, the water content in the waste gas of step 1) is greater than or equal to 20 g / m 3 .

[0038] In a specific embodiment, in step 1), the waste gas containing volatile organic compounds comes from the waste gas of a spraying workshop, the waste gas of a paper mill workshop, the waste gas of a printing and dyeing factory workshop, and can also come from the waste gas generated by drying printed materials, printed and dyed products, furniture, and tobacco. It can also come from the dry waste gas of polymers such as butyl rubber, halogenated butyl rubber, butadiene rubber, solution-polymerized styrene-butadiene rubber, ethylene-propylene rubber, silicone rubber, polyisoprene rubber, chloroprene rubber, hydrogenated nitrile rubber, styrene-butadiene-styrene block copolymer (SBS), acrylonitrile-butadiene-styrene (ABS), hydrogenated styrene-butadiene block copolymer (SEBS), styrene-isoprene-styrene copolymer (SIS), hydrogenated styrene-isoprene-styrene copolymer (SEPS), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, polybutylene, polyacrylonitrile, polystyrene, etc.

[0039] In a specific embodiment, in step 1), the waste gas containing volatile organic compounds also contains solid particles. Specifically, the content of the solid particles is 10 to 5000 mg / m 3 .

[0040] In a specific scheme, in step 1), the waste gas containing volatile organic compounds is pretreated, and the pretreatment includes one of the following processes: filtration, heat exchange and cooling, water washing, alkali washing, cooling and cooling, or a combination thereof. The purpose of filtering the waste gas is to remove most of the solid particles in the waste gas; the purpose of heat exchange and cooling the waste gas is to recover part of the energy and reduce the temperature of the waste gas; the purpose of water washing the waste gas is to further remove the solid particles in the waste gas and further reduce the temperature of the waste gas; the purpose of alkali washing the waste gas is to remove the acidic components in the gas and reduce the moisture content in the waste gas; the purpose of cooling the waste gas is to further reduce the moisture in the waste gas; one of the above-mentioned treatment processes or a combination thereof can be used to form the pretreatment process of the waste gas, and the waste gas is preferably pretreated in the following order: filtration, heat exchange and cooling, water washing, alkali washing, cooling and cooling.

[0041] In a specific embodiment, in step 1), the filtration in the pretreatment process can be performed in a filter, for example, which is a conventional filter known in the art, such as a bag filter, a membrane filter, or an activated carbon filter; the heat exchange and cooling in the pretreatment process adopts conventional methods known in the art to heat the waste gas with a relatively high temperature. The purpose of heat exchange is to cool the waste gas and improve the energy utilization efficiency; illustratively, the cold medium is air or nitrogen, and circulating water or other refrigerants can also be used; if it is waste gas generated during the drying process, the temperature of the dryer intake air can also be increased by preheating the dryer intake air to improve the energy utilization efficiency.

[0042] The water washing in the pretreatment process is completed in a water washing tower, for example, and the temperature of the water washing is 20-80°C; the alkali washing in the pretreatment process is completed in an alkali washing tower, for example, and the temperature of the alkali washing is 15-80°C.

[0043] The cooling in the pretreatment process can be performed by conventional cooling methods, and can be cooled by a heat exchanger with a cold medium, and the cold medium can be cold water.

[0044] In a specific embodiment, in step 1), the volatile organic matter is selected from organic chemicals having a boiling point or an initial boiling point lower than or equal to 250°C. Exemplarily, it is selected from aliphatic hydrocarbons having a carbon number less than or equal to 12, cyclic hydrocarbons having a carbon number less than or equal to 14, aromatic hydrocarbons having a carbon number less than or equal to 14, halogenated hydrocarbons having a carbon number less than or equal to 6, ester compounds having a carbon number less than or equal to 12, ether compounds having a carbon number less than or equal to 12, nitrogen- or sulfur-containing organic matter having a carbon number less than or equal to 10, or a mixture thereof. Exemplarily, the volatile organic matter is selected from at least one of hexane, heptane, cyclohexane, benzene, toluene, xylene, ethyl acetate, methyl tert-butyl ether, and acetonitrile.

[0045] In a specific embodiment, in step 1), the temperature of the waste gas before pretreatment is 50-150° C., preferably 70-95° C. The temperature of the waste gas after pretreatment is below 60° C., preferably below 30° C.

[0046] In the present invention, the purpose of setting step 4) is to further remove volatile organic compounds in the exhaust gas.

[0047] In a specific embodiment, in step 4), the solid adsorbent having an adsorption effect on volatile organic compounds is selected from activated carbon.

[0048] In a specific embodiment, in step 4), the waste gas obtained in step 3) is 4 Nm 3 The solid adsorbent used has an adsorption effect on volatile organic compounds and is 0.5 to 50 m3 .

[0049] In a specific embodiment, in step 4), the thermal incineration treatment is to send the waste gas into a thermal incinerator for incineration. The incineration treatment process is a conventional process step for treating volatile organic compounds known in the art.

[0050] In a specific embodiment, in step 4), the catalytic oxidation treatment is to send the waste gas into a catalytic oxidation furnace for treatment. The catalytic oxidation treatment process is a conventional process step for treating volatile organic compounds known in the art.

[0051] In a specific embodiment, the content of volatile organic matter in the waste gas obtained in step 4) is 0.1 to 120 mg / m 3 .

[0052] In a specific embodiment, if the content of volatile organic matter in the waste gas obtained in step 3) is greater than 100 mg / m 3 , then you can consider implementing step 4).

[0053] In a specific embodiment, the method further comprises at least one of the following steps 8) to 10):

[0054] 8) regenerating the metal salt solution after contacting the exhaust gas in step 2);

[0055] 9) regenerating the organic solvent that has an absorbing effect on the volatile organic matter after absorbing the volatile organic matter components;

[0056] 10) Regenerating the solid adsorbent having adsorption effect on volatile organic components after adsorbing the volatile organic components.

[0057] In a specific embodiment, in steps 8) to 10), the regeneration treatment is carried out by a method known in the art. For example, the regeneration treatment includes distilling the metal salt solution whose concentration has become diluted after contact with the exhaust gas to regenerate the concentration; using distillation regeneration to remove the organic solvent that has an absorption effect on volatile organic compounds; regenerating the solid absorbent by hot nitrogen or water vapor, etc.

[0058] In a specific solution of the system, a fan or a compressor may be configured in the system as required.

[0059] In a specific embodiment, the metal salt solution absorption tower is directly connected to the organic solvent devolatilization organic matter absorption tower.

[0060] In a specific embodiment, the organic solvent devolatilization organic matter absorption tower is directly connected to the discharge end, or is connected to the discharge end through a solid devolatilization organic matter absorption tower or a thermal incinerator or a catalytic oxidation furnace.

[0061] In a specific embodiment, the system further comprises at least one of a metal salt solution regeneration unit, a devolatilization organic solvent regeneration unit, and a solid adsorption devolatilization organic tower regeneration unit.

[0062] In a specific embodiment, the metal salt solution absorption tower is connected to the metal salt solution regeneration unit; the organic solvent devolatilization absorption tower is connected to the devolatilization organic solvent regeneration unit; and the solid devolatilization adsorption tower is connected to the solid adsorption devolatilization tower regeneration unit.

[0063] The present invention will be described in further detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0064] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0065] The term "optional" means that the feature may or may not exist, and also means that the feature must exist, but the specific selection can be arbitrary. The devices in the schematic diagram do not represent the actual number or size of the devices.

[0066] Example 1

[0067] like Figure 1 As shown, this embodiment provides a system for treating waste gas containing volatile organic compounds, the system comprising a filter 5, a cooler 6, a metal salt solution absorption tower 8, an organic solvent devolatilization organic compound absorption tower 13, a solid devolatilization organic compound adsorption tower 17, and a fan or compressor configured as needed.

[0068] The filter 5, the cooler 6, the metal salt solution absorption tower 8, the organic solvent devolatilization absorption tower 13, and the solid devolatilization absorption tower 17 are sequentially connected along the exhaust gas direction.

[0069] Example 2

[0070] This embodiment provides a method for treating waste gas containing volatile organic compounds, the method comprising the following steps:

[0071] The waste gas 4 containing volatile organic compounds contains polymer particles (such as butadiene particles), volatile organic compounds and other substances, wherein the volatile organic compounds are aliphatic hydrocarbons (alkanes or alkenes or alkynes) with a carbon number less than or equal to 12, cyclic hydrocarbons with a carbon number less than or equal to 14, aromatic hydrocarbons with a carbon number less than or equal to 14, halogenated hydrocarbons with a carbon number less than or equal to 6, ester compounds with a carbon number less than or equal to 12, ether compounds with a carbon number less than or equal to 12, nitrogen-containing or sulfur-containing organic compounds with a carbon number less than or equal to 10, or mixtures thereof. Exemplarily, the volatile organic compounds are selected from hexane, heptane, cyclohexane, benzene, toluene, xylene, ethyl acetate, methyl tert-butyl ether, acetonitrile, and the like.

[0072] The waste gas 4 is filtered through a filter 5 to remove most of the polymer particles. The filtration can be carried out by bag filtration, membrane filtration or activated carbon filtration; the filtered waste gas enters the cooler 6 to be cooled to 10-30°C, and then enters the metal salt solution absorption tower 8. The metal salt solution enters from the top of the metal salt solution absorption tower 8 (i.e., metal salt solution feed 7), and the metal salt solution that has contacted with the waste gas is discharged from the bottom of the metal salt solution absorption tower 8 (i.e., metal salt solution discharge 9), or it can enter from the top of the metal salt solution absorption tower 8 for recycling (recycled metal salt solution feed 7); the waste gas 11 from the desolventizing and de-VOCs tower that has contacted with the metal salt solution enters the solvent de-VOCs tower 13. The solvent de-VOCs tower absorbs volatile organic compounds in the waste gas with an organic solvent that is compatible with the volatile organic compound components. For hydrocarbon volatile organic compounds, paraffin oil is preferred. The organic solvent for removing volatile organic compounds enters from the top of the solvent de-VOCs tower 13 (i.e., the de-VOCs solvent feed 12), and is discharged from the bottom of the solvent de-VOCs tower 13 (i.e., the de-VOCs solvent discharge 14) for recycling or for reuse after distillation and recovery. The waste gas after the above treatment contains a small amount of volatile organic compounds and can further enter the solid de-VOCs tower 17.

[0073] The waste gas is further subjected to the removal of volatile organic matter by the solid VOCs removal tower 17. After the solid VOCs removal by the solid VOCs removal tower 17, the volatile organic matter content in the exhaust gas 18 that meets the emission standard "Integrated Emission Standard of Air Pollutants" (GB16297-1996) meets the emission standard and can be directly discharged.

[0074] As needed, Figure 1 In the process shown, the solid VOCs removal tower 17 is omitted, and the waste gas passes through the solvent VOCs removal tower 13. The volatile organic matter content in the treated waste gas meets the emission standard "Integrated Emission Standard of Air Pollutants" (GB16297-1996) and can be discharged directly.

[0075] As needed, Figure 1In the process shown, the waste gas 15 is applied after the solvent VOCs is removed through the solvent VOCs removal tower 13, and is returned to the inlet of the gas heater 2 to be recycled as a drying gas; the waste gas 19 is applied after the solid VOCs is removed through the solid VOCs removal tower 17, and is returned to the inlet of the gas heater 2 to be recycled as a drying gas.

[0076] Example 3

[0077] This embodiment provides a method for treating waste gas containing volatile organic compounds based on the system of the above-mentioned embodiment 1 and the process of the embodiment 2. The method comprises the following steps:

[0078] The exhaust gas flow rate from the bromobutyl rubber drying equipment through the cyclone separator is 39000m 3 / hr, temperature is about 85℃. After filtration and heat exchange, the temperature is about 25℃, and the flow rate is about 32100m 3 / hr, water content 15g / m 3 , containing about 2500mg / m 3 Then it enters the CaCl2 aqueous solution absorption tower, and the flow rate of 50% calcium chloride solution is 224t / h (about 160m 3 / h), the operating temperature of the CaCl2 aqueous solution absorption tower is about 10°C, and the exhaust gas after contact with 50% CaCl2 aqueous solution contains 8g / m 3 The exhaust gas is sent to the paraffin oil absorption tower to remove VOCs. The absorption tower operates at 20-30°C and the amount of paraffin oil is 120m 3 (about 101t / h), the hexane content in the waste gas treated by the paraffin oil absorption tower is about 250mg / m 3 , water content 7.5g / m 3 The waste gas is then sent to an activated carbon adsorption tower for treatment. The operating temperature of the activated carbon adsorption tower is about 30°C, and the hexane content in the waste gas discharged from the adsorption tower is less than 20 mg / m 3 The emission requirements are met and the waste gas is directly discharged into the atmosphere, indicating that the solution of this embodiment can achieve the treatment of waste gas containing volatile organic compounds in the present application.

[0079] The paraffin oil (rich liquid) after contacting with the waste gas is sent to the paraffin oil recovery tower, where the absorbed hexane is removed by distillation, and the obtained paraffin oil (lean liquid) is returned to the paraffin oil absorption tower for reuse. The paraffin oil regeneration recovery rate is 99.9%.

[0080] Example 4

[0081] The process route of this embodiment is different from that of embodiment 3 in that the waste gas (containing 250 mg / m 3 , water content 7.5g / m 3 , flow rate 32100m3 / hr) returns to the inlet of the drying unit gas heater 2, mixes with part of the fresh air, and enters the dryer 3 after being heated to dry the brominated butyl rubber particles.

[0082] The exhaust gas flow rate from the bromobutyl rubber drying equipment through the cyclone separator is 40000m 3 / hr, temperature is about 85℃. After filtration and heat exchange, the temperature is about 25℃, and the flow rate is about 32100m 3 / hr, water content about 15g / m 3 , containing about 2840 mg / m 3 Then it enters the CaCl2 aqueous solution absorption tower, and the flow rate of 50% calcium chloride solution is 224t / h (about 160m 3 / h), the operating temperature of the CaCl2 aqueous solution absorption tower is about 10°C, and the exhaust gas after contact with 50% CaCl2 aqueous solution contains 8g / m 3 The exhaust gas is sent to the paraffin oil absorber to remove VOCs. The operating temperature of the absorber is 20-30°C. The hexane content in the exhaust gas treated by the paraffin oil absorber is about 240 mg / m 3 , water content 7.5g / m 3 The exhaust gas is returned to the inlet of the drying unit gas heater 2 for recycling.

[0083] The hexane content in the exhaust gas discharged from the system is about 19 mg / m 3 , meeting the emission requirements, indicating that the scheme of this embodiment can realize the treatment of waste gas containing volatile organic compounds in this application.

[0084] Comparative Example 1

[0085] The exhaust gas flow rate from the bromobutyl rubber drying equipment through the cyclone separator is 39000m 3 / hr, temperature is about 85℃. After filtration and heat exchange, the temperature is about 25℃, and the flow rate is about 32100m 3 / hr, water content 15g / m 3 , containing about 2500mg / m 3 ; The waste gas is directly sent to the paraffin oil absorption tower to remove VOCs. The absorption tower operates at 25°C and the amount of paraffin oil is 120m 3 (about 101t / h), the hexane content in the waste gas treated by the paraffin oil absorption tower is about 270mg / m 3 The waste gas is then sent to an activated carbon adsorption tower for treatment. The operating temperature of the activated carbon adsorption tower is about 30°C, and the hexane content in the waste gas discharged from the adsorption tower is less than 20 mg / m 3 . Meet emission requirements and discharge directly into the atmosphere.

[0086] After contacting with the waste gas, the paraffin oil (rich liquid) emulsifies. A liquid separation tank is set up to allow the layers to stand. The upper layer is sent to the paraffin oil recovery tower to remove the absorbed hexane by distillation. The obtained paraffin oil (lean liquid) is returned to the paraffin oil absorption tower for reuse. However, due to the serious emulsification of the paraffin oil and the poor stratification effect, the recovery rate of the paraffin oil regeneration is reduced, the regeneration treatment system collapses, and the equipment has to be stopped.

[0087] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for treating waste gas containing volatile organic compounds, characterized in that: The method comprises the following steps: 1) Pre-treating the waste gas containing volatile organic compounds; the pre-treatment includes filtering, heat exchange and cooling, water washing, alkali washing, cooling and cooling, or a combination thereof; 2) The waste gas obtained in step 1) is contacted with a metal salt solution, and the contact is carried out in an absorption tower. The operating temperature of the absorption tower is 10°C. The water content in the waste gas obtained is greater than or equal to 8g / m 3 And less than or equal to 10g / m 3 The metal salt in the metal salt solution is selected from calcium chloride; the concentration of the metal salt solution is 40 to 60 wt%, and the metal salt solution is a metal salt aqueous solution; the exhaust gas obtained in step 1) is 10 4 Nm 3 The volume of the metal salt solution used is 0.5~50 m 3 ; 3) contacting the waste gas obtained in step 2) with an organic solvent that has an absorbing effect on volatile organic matter; 4) contacting the waste gas obtained in step 3) with a solid adsorbent having an adsorption effect on volatile organic compounds or subjecting the waste gas to thermal incineration treatment or catalytic oxidation treatment; 5) discharging the waste gas obtained in at least one of step 3) and step 4) into the atmosphere; 6) returning part of the waste gas obtained through the treatment in step 2) to step 1) after heating, and contacting it again with the waste gas containing volatile organic compounds; 7) returning part or all of the waste gas obtained by at least one of step 3) and step 4) to step 1) after heat exchange to contact with the waste gas containing volatile organic compounds again; The exhaust gas obtained in step 2) is 4 Nm 3 The organic solvent used has an absorption effect on volatile organic compounds and the concentration is 0.5~50m 3 ; Step 3) The content of volatile organic matter in the exhaust gas obtained is 5~500mg / m 3 .

2. The processing method according to claim 1, characterized in that: In step 3), the organic solvent having an absorption effect on volatile organic compounds is selected from organic solvents having a boiling point or an initial distillation point greater than or equal to 100° C. and the boiling point or the initial distillation point of the organic solvent is at least 30° C. higher than the boiling point of the volatile organic compounds.

3. The processing method according to claim 2, characterized in that: The organic solvent capable of absorbing volatile organic compounds is selected from paraffin oil.

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