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This article introduces the VOC waste gas treatment process
.
It is the following: thermal destruction method, activated carbon adsorption, condensation, membrane separation, adsorption technology reform, a thermal oxidation method, a catalytic combustion method, liquid absorption, biological method and the like
.
VOC gas is used as a solvent in petrochemical, printing, artificial leather and electronic components, baking varnishes, medicine and other chemical fields.
Volatile organic compounds, referred to as VOC (Volatile Organic Compounds) for short, are usually used as solvents
.
If these organic solvents volatilize into the atmospheric environment, they will not only cause serious pollution to the atmospheric environment, but also cause harm to human health after the human body breathes in the polluted gas
.
For example, as a solvent, benzene volatilizes into the atmosphere.
It can not only be absorbed by the skin of the human body, but also enter the human body through the respiratory system, causing chronic or acute poisoning
.
Benzene compounds not only cause certain damage to the central nervous system of the human body, but also may cause obstacles to the nervous system.
After entering the human body, they will also harm the blood and hematopoietic organs, and even have bleeding symptoms or suffer from sepsis
.
Under the action of oxidation, benzene can be oxidized into phenol in the organism, which causes abnormal liver function, which is very unfavorable to the growth and development of bones, and induces aplastic anemia
.
Therefore, ACGIH lists benzene as a potential carcinogen
.
Halogenated hydrocarbon compounds can cause neurosis, platelet reduction, hepatosplenomegaly and other adverse conditions, and are likely to cause cancer
.
Therefore, VOC emissions must be controlled, which is not only responsible for the environment, but also for our lives and health
.
VOC waste gas treatment process At present, VOC waste gas treatment technology mainly includes thermal destruction method, pressure swing adsorption separation and purification technology, adsorption method and oxidation treatment method
.
Thermal destruction method Thermal destruction method refers to the direct and auxiliary combustion of VOC gas, or the use of a suitable catalyst to accelerate the chemical reaction of VOC, and ultimately reduce the concentration of organic matter to make it no longer harmful
.
The thermal destruction method has a better effect on the treatment of low-concentration organic waste gas.
Therefore, it has been widely used in the treatment of low-concentration waste gas
.
This method is mainly divided into two types, namely direct flame combustion and catalytic combustion
.
The heat treatment efficiency of direct flame combustion for organic waste gas is relatively high, and can reach 99% under normal circumstances
.
Catalytic combustion refers to accelerating the chemical reaction rate of organic waste gas under the action of the catalytic bed
.
This method takes less time than direct combustion and is the preferred technology for purification of high-concentration, low-flow organic waste gas
.
The activated carbon adsorption method uses the porous structure of adsorbents (granular activated carbon and activated carbon fibers) to capture VOCs in the exhaust gas
.
The VOC-containing organic waste gas is passed through the activated carbon bed, and the VOC therein is adsorbed by the adsorbent, and the waste gas is purified and discharged into the atmosphere
.
The carbon adsorption method is mainly used for the recovery of fatty and aromatic hydrocarbons, most chlorinated solvents, commonly used alcohols, some ketones and esters
.
When the carbon adsorption reaches saturation, the saturated carbon bed is desorbed and regenerated; steam is introduced to heat the carbon layer, VOC is blown off, and forms a steam mixture with water vapor, leaving the carbon adsorption bed together, and the steam mixture is cooled by a condenser , Make the steam condense into liquid
.
For water-soluble VOC gas, the liquid mixture is purified by distillation; for water-insoluble VOC gas, VOC is directly recovered with a precipitator
.
For example, the "triphenyl" used in coatings is immiscible with water, so it can be directly recycled
.
Carbon adsorption technology is mainly used in situations where the components in the exhaust gas are relatively simple and the recycling value of organic matter is high.
It is suitable for painting, printing and adhesives where the temperature is not high, the humidity is low, and the exhaust volume is large, especially for Purification and recovery of halogenated compounds is more effective
.
It is separated from the exhaust gas of the condensation method and directly recycled
.
However, in this case, the exhaust gas leaving the condenser still contains a very high concentration of VOC, which cannot meet the environmental emission standards
.
To obtain a high recovery rate, the system requires high pressure and low temperature, and the equipment cost increases significantly
.
This treatment method is mainly suitable for the treatment of organic waste gas with high concentration and relatively low temperature
.
It is usually suitable for the recovery and treatment of organic waste gas with high VOC content (a few percent) and small gas volume.
Since most VOCs are flammable and explosive gases, they are limited by the explosion limit, and the VOC content in the gas will not be too high.
Therefore, to achieve a higher recovery rate, it is necessary to adopt a very low temperature condensing medium or high pressure measures, which will inevitably increase equipment investment and processing costs.
Therefore, this technology is generally used as a primary processing technology and combined with other technologies
.
Membrane separation technology The basis of membrane separation technology is to use a polymer membrane with selective permeability to organics, which is 10-100 times easier to permeate organic vapors than air, so as to realize the separation of organics
.
It is suitable for the recovery of high-concentration, high-value organic matter, and its equipment cost is relatively high
.
The simplest membrane separation is a single-stage membrane separation system, which directly allows compressed gas to pass through the membrane surface to achieve VOC separation
.
Because of the low degree of separation of single-stage membranes, it is difficult to meet the separation requirements, while multi-stage membrane separation systems will greatly increase equipment investment, so there is still a lot of room for research in this area of technology
.
The adsorbent of swing adsorption technology adsorbs organic matter under a certain pressure; when the adsorbent is saturated, the desorbed organic matter is "released" through pressure change
.
It is characterized by no pollutants, high recovery efficiency, and reactive organic matter can be recovered
.
However, the operation cost of this technology is relatively high, the adsorption needs to be pressurized, and the desorption needs to be decompressed, and it is less used in environmental protection
.
The thermal oxidation method eliminates organic matter through combustion, and its operating temperature is as high as 700℃-1,000℃, which inevitably has high fuel costs; in order to reduce fuel costs, heat needs to be recovered, there are two ways: traditional partition heat exchange , A new type of non-steady state heat storage and heat exchange technology
.
Dividing wall thermal oxidation uses tube or plate partition heat exchangers to capture the heat of the purified exhaust gas.
It can recover 40% -70% of the heat energy and use the recovered heat to preheat the organic waste gas entering the oxidation system
.
The preheated exhaust gas is then passed through the flame to reach the oxidation temperature for purification.
The disadvantage of the heat exchange between the partition walls is that the heat recovery efficiency is not high
.
Regenerative thermal oxidation (RTO for short) uses a new non-steady state heat transfer method to recover heat
.
The main principle is: the organic waste gas and the purified exhaust gas alternately circulate, and the flow direction is continuously changed many times to maximize the capture of heat.
The heat storage system provides extremely high heat recovery
.
Catalytic combustion method paint exhaust gas enters the catalytic purification device through the flame arrestor, and exchanges heat with the high-temperature exhaust gas in the plate heat exchanger.
The preheated exhaust gas enters the heating chamber (with electric heating tube) to further increase the temperature, reaching the ignition temperature.
The exhaust gas continues to enter the catalytic bed, and under the action of the precious metal Pt and Pd catalysts, the organic solvent is completely oxidized and decomposed into H2O and CO2, and a large amount of reaction heat is released, which can maintain the ignition temperature required for catalytic combustion and achieve thermal equilibrium
.
The plate heat exchanger exchanges heat between the high-temperature exhaust gas and the imported low-temperature exhaust gas, part of the heat is recovered, and the preheating energy consumption is reduced
.
The high-temperature tail gas that has recovered part of the heat is discharged through the exhaust tube under the suction force of the induced draft fan
.
After the system reaches thermal equilibrium, the electric heating device is automatically turned off.
After that, the catalytic combustion system relies on the thermal energy generated when the organic solvent in the exhaust gas burns, and the catalytic combustion continues until the end without additional energy
.
Considering that the purification device needs to be repaired, a bypass pipe and a bypass valve are set before the filter flame arrestor
.
In industries that use organic solvents, such as automotive coating and printing industries, where the concentration of organic solvents is low and the air volume is large, if the above methods are used, huge equipment will be used and a lot of money will be consumed
.
At present, the following methods are mainly used to treat such low-concentration and large-volume organic waste gas
.
Honeycomb wheel type concentration system This system uses honeycomb wheels to continuously adsorb and separate organic solvents in the exhaust with low concentration and high air volume; then, use small air volume hot air to desorb to obtain high concentration, small air volume containing organic solvents.
Solvent gas
.
The concentrated gas is combined with a small catalytic combustion or activated carbon recovery device to form an economical treatment system
.
The exhaust after desorption can be processed with a device that absorbs one-tenth of the air volume
.
The system is small in size and low in cost.
It has become the first choice for the treatment of low-concentration and large-volume organic waste gas in foreign countries, and has been widely used
.
In the liquid absorption method, the organic waste gas is contacted with the liquid absorbent, so that the organic solvent is absorbed by the absorbent, and then the organic solvent is removed or recovered after desorption, so that the absorbent is regenerated and reused
.
Biological biological deodorization uses microorganisms to decompose organic solvents
.
People pay attention to it because of its very low energy consumption and low operating costs.
Especially in Europe, technology development is centered on Germany, and application examples are gradually increasing
.
.
It is the following: thermal destruction method, activated carbon adsorption, condensation, membrane separation, adsorption technology reform, a thermal oxidation method, a catalytic combustion method, liquid absorption, biological method and the like
.
VOC gas is used as a solvent in petrochemical, printing, artificial leather and electronic components, baking varnishes, medicine and other chemical fields.
Volatile organic compounds, referred to as VOC (Volatile Organic Compounds) for short, are usually used as solvents
.
If these organic solvents volatilize into the atmospheric environment, they will not only cause serious pollution to the atmospheric environment, but also cause harm to human health after the human body breathes in the polluted gas
.
For example, as a solvent, benzene volatilizes into the atmosphere.
It can not only be absorbed by the skin of the human body, but also enter the human body through the respiratory system, causing chronic or acute poisoning
.
Benzene compounds not only cause certain damage to the central nervous system of the human body, but also may cause obstacles to the nervous system.
After entering the human body, they will also harm the blood and hematopoietic organs, and even have bleeding symptoms or suffer from sepsis
.
Under the action of oxidation, benzene can be oxidized into phenol in the organism, which causes abnormal liver function, which is very unfavorable to the growth and development of bones, and induces aplastic anemia
.
Therefore, ACGIH lists benzene as a potential carcinogen
.
Halogenated hydrocarbon compounds can cause neurosis, platelet reduction, hepatosplenomegaly and other adverse conditions, and are likely to cause cancer
.
Therefore, VOC emissions must be controlled, which is not only responsible for the environment, but also for our lives and health
.
VOC waste gas treatment process At present, VOC waste gas treatment technology mainly includes thermal destruction method, pressure swing adsorption separation and purification technology, adsorption method and oxidation treatment method
.
Thermal destruction method Thermal destruction method refers to the direct and auxiliary combustion of VOC gas, or the use of a suitable catalyst to accelerate the chemical reaction of VOC, and ultimately reduce the concentration of organic matter to make it no longer harmful
.
The thermal destruction method has a better effect on the treatment of low-concentration organic waste gas.
Therefore, it has been widely used in the treatment of low-concentration waste gas
.
This method is mainly divided into two types, namely direct flame combustion and catalytic combustion
.
The heat treatment efficiency of direct flame combustion for organic waste gas is relatively high, and can reach 99% under normal circumstances
.
Catalytic combustion refers to accelerating the chemical reaction rate of organic waste gas under the action of the catalytic bed
.
This method takes less time than direct combustion and is the preferred technology for purification of high-concentration, low-flow organic waste gas
.
The activated carbon adsorption method uses the porous structure of adsorbents (granular activated carbon and activated carbon fibers) to capture VOCs in the exhaust gas
.
The VOC-containing organic waste gas is passed through the activated carbon bed, and the VOC therein is adsorbed by the adsorbent, and the waste gas is purified and discharged into the atmosphere
.
The carbon adsorption method is mainly used for the recovery of fatty and aromatic hydrocarbons, most chlorinated solvents, commonly used alcohols, some ketones and esters
.
When the carbon adsorption reaches saturation, the saturated carbon bed is desorbed and regenerated; steam is introduced to heat the carbon layer, VOC is blown off, and forms a steam mixture with water vapor, leaving the carbon adsorption bed together, and the steam mixture is cooled by a condenser , Make the steam condense into liquid
.
For water-soluble VOC gas, the liquid mixture is purified by distillation; for water-insoluble VOC gas, VOC is directly recovered with a precipitator
.
For example, the "triphenyl" used in coatings is immiscible with water, so it can be directly recycled
.
Carbon adsorption technology is mainly used in situations where the components in the exhaust gas are relatively simple and the recycling value of organic matter is high.
It is suitable for painting, printing and adhesives where the temperature is not high, the humidity is low, and the exhaust volume is large, especially for Purification and recovery of halogenated compounds is more effective
.
It is separated from the exhaust gas of the condensation method and directly recycled
.
However, in this case, the exhaust gas leaving the condenser still contains a very high concentration of VOC, which cannot meet the environmental emission standards
.
To obtain a high recovery rate, the system requires high pressure and low temperature, and the equipment cost increases significantly
.
This treatment method is mainly suitable for the treatment of organic waste gas with high concentration and relatively low temperature
.
It is usually suitable for the recovery and treatment of organic waste gas with high VOC content (a few percent) and small gas volume.
Since most VOCs are flammable and explosive gases, they are limited by the explosion limit, and the VOC content in the gas will not be too high.
Therefore, to achieve a higher recovery rate, it is necessary to adopt a very low temperature condensing medium or high pressure measures, which will inevitably increase equipment investment and processing costs.
Therefore, this technology is generally used as a primary processing technology and combined with other technologies
.
Membrane separation technology The basis of membrane separation technology is to use a polymer membrane with selective permeability to organics, which is 10-100 times easier to permeate organic vapors than air, so as to realize the separation of organics
.
It is suitable for the recovery of high-concentration, high-value organic matter, and its equipment cost is relatively high
.
The simplest membrane separation is a single-stage membrane separation system, which directly allows compressed gas to pass through the membrane surface to achieve VOC separation
.
Because of the low degree of separation of single-stage membranes, it is difficult to meet the separation requirements, while multi-stage membrane separation systems will greatly increase equipment investment, so there is still a lot of room for research in this area of technology
.
The adsorbent of swing adsorption technology adsorbs organic matter under a certain pressure; when the adsorbent is saturated, the desorbed organic matter is "released" through pressure change
.
It is characterized by no pollutants, high recovery efficiency, and reactive organic matter can be recovered
.
However, the operation cost of this technology is relatively high, the adsorption needs to be pressurized, and the desorption needs to be decompressed, and it is less used in environmental protection
.
The thermal oxidation method eliminates organic matter through combustion, and its operating temperature is as high as 700℃-1,000℃, which inevitably has high fuel costs; in order to reduce fuel costs, heat needs to be recovered, there are two ways: traditional partition heat exchange , A new type of non-steady state heat storage and heat exchange technology
.
Dividing wall thermal oxidation uses tube or plate partition heat exchangers to capture the heat of the purified exhaust gas.
It can recover 40% -70% of the heat energy and use the recovered heat to preheat the organic waste gas entering the oxidation system
.
The preheated exhaust gas is then passed through the flame to reach the oxidation temperature for purification.
The disadvantage of the heat exchange between the partition walls is that the heat recovery efficiency is not high
.
Regenerative thermal oxidation (RTO for short) uses a new non-steady state heat transfer method to recover heat
.
The main principle is: the organic waste gas and the purified exhaust gas alternately circulate, and the flow direction is continuously changed many times to maximize the capture of heat.
The heat storage system provides extremely high heat recovery
.
Catalytic combustion method paint exhaust gas enters the catalytic purification device through the flame arrestor, and exchanges heat with the high-temperature exhaust gas in the plate heat exchanger.
The preheated exhaust gas enters the heating chamber (with electric heating tube) to further increase the temperature, reaching the ignition temperature.
The exhaust gas continues to enter the catalytic bed, and under the action of the precious metal Pt and Pd catalysts, the organic solvent is completely oxidized and decomposed into H2O and CO2, and a large amount of reaction heat is released, which can maintain the ignition temperature required for catalytic combustion and achieve thermal equilibrium
.
The plate heat exchanger exchanges heat between the high-temperature exhaust gas and the imported low-temperature exhaust gas, part of the heat is recovered, and the preheating energy consumption is reduced
.
The high-temperature tail gas that has recovered part of the heat is discharged through the exhaust tube under the suction force of the induced draft fan
.
After the system reaches thermal equilibrium, the electric heating device is automatically turned off.
After that, the catalytic combustion system relies on the thermal energy generated when the organic solvent in the exhaust gas burns, and the catalytic combustion continues until the end without additional energy
.
Considering that the purification device needs to be repaired, a bypass pipe and a bypass valve are set before the filter flame arrestor
.
In industries that use organic solvents, such as automotive coating and printing industries, where the concentration of organic solvents is low and the air volume is large, if the above methods are used, huge equipment will be used and a lot of money will be consumed
.
At present, the following methods are mainly used to treat such low-concentration and large-volume organic waste gas
.
Honeycomb wheel type concentration system This system uses honeycomb wheels to continuously adsorb and separate organic solvents in the exhaust with low concentration and high air volume; then, use small air volume hot air to desorb to obtain high concentration, small air volume containing organic solvents.
Solvent gas
.
The concentrated gas is combined with a small catalytic combustion or activated carbon recovery device to form an economical treatment system
.
The exhaust after desorption can be processed with a device that absorbs one-tenth of the air volume
.
The system is small in size and low in cost.
It has become the first choice for the treatment of low-concentration and large-volume organic waste gas in foreign countries, and has been widely used
.
In the liquid absorption method, the organic waste gas is contacted with the liquid absorbent, so that the organic solvent is absorbed by the absorbent, and then the organic solvent is removed or recovered after desorption, so that the absorbent is regenerated and reused
.
Biological biological deodorization uses microorganisms to decompose organic solvents
.
People pay attention to it because of its very low energy consumption and low operating costs.
Especially in Europe, technology development is centered on Germany, and application examples are gradually increasing
.
