The activated carbon adsorption method is one of the most commonly used and mature technologies in industrial waste gas treatment. It is particularly suitable for dealing with low-concentration, high-volume organic waste gases (VOCs) and malodorous gases. The key lies in the unique adsorption properties of activated carbon.
I. Working Principle and Characteristics of Activated Carbon
1. Adsorption Principle
1.1 Physical adsorption: Mainly relies on the huge specific surface area of activated carbon (typically 500-1500 m²/g) and the abundant microporous structure. Through intermolecular forces (van der Waals forces), pollutants in the exhaust gas are captured and fixed on the surface of the pores. This is its main mechanism of action.
1.2 Chemical adsorption: Some activated carbon that has undergone special chemical treatment (such as impregnated carbon) will have surface functional groups that react with specific pollutants (such as H₂S, SO₂, mercury vapor, etc.) to remove them.
2. Characteristics of Activated Carbon
2.1 High specific surface area: Provides a large amount of adsorption space.
2.2 Rich pore structure: Includes micropores, mesopores, and macropores, which are responsible for adsorbing substances of different molecular sizes.
2.3 Adjustable surface chemical properties: Through activation or impregnation treatment, specific pollutants can be targeted for treatment.
2.4 Hydrophobicity: Strongly adsorbs organic gases and is relatively less affected by humidity.
II. Main Application Scenarios
The activated carbon adsorption system is widely used for waste gas treatment in the following industries.
1. Spray and painting industries: Handling benzene, toluene, xylene and other VOCs generated during painting and drying processes.
2. Petrochemical industry: Treating low-concentration organic waste gas from tank breathing, leakage points, etc.
3. Printing and packaging industries: Dealing with organic waste gas from ink and thinner evaporation.
4. Electronic and semiconductor industries: Handling solvent waste gas used in cleaning, lithography and other processes.
5. Food processing industry: Removing odors and volatile organic compounds generated during production.
6. Sewage treatment plants and garbage stations: As an odor removal unit, effectively removing H₂S, ammonia, mercaptans and other foul gases.
III. Design and Selection of Exhaust Gas Treatment System
A typical activated carbon adsorption system mainly consists of pre-treatment unit, adsorption unit, desorption and regeneration unit, and post-treatment unit.
1. System Flow
1.1 Pre-treatment: The exhaust gas first passes through filters (such as bag filters, dehumidifiers) to remove dust, water mist, and oil mist, to prevent these substances from blocking the pores of the activated carbon and causing its failure.
1.2 Adsorption Unit: The pre-treated exhaust gas enters the adsorption tank (column), passes through the activated carbon bed, and the pollutants are adsorbed. The purified gas is discharged into the atmosphere by the blower.
1.3 Desorption and regeneration (applicable to large continuous systems)
1.3.1 Steam desorption: Use low-pressure steam to heat the activated carbon bed to desorb the adsorbed organic substances, forming high-concentration exhaust gas.
1.3.2 Hot air desorption: Use hot nitrogen or hot air for desorption, suitable for organic substances with poor water solubility or prone to hydrolysis.
1.3.3 Pressure reduction desorption: Mainly used for gas separation, less common in exhaust gas treatment.
1.4 Post-treatment: The high-concentration exhaust gas produced during desorption needs to be introduced to subsequent treatment facilities, such as:
1.4.1 Condensation recovery: Condense the high-concentration exhaust gas to recover organic solvents.
1.4.2 Catalytic combustion, regenerative combustion.
2. Key Design and Selection Parameters
2.1 Exhaust gas volume (m³/h): Determines the size of the adsorption tank.
2.2 Exhaust gas concentration (mg/m³): Determines the adsorption cycle and filling amount of the activated carbon.
2.3 Exhaust gas composition and properties: Determine the type of activated carbon (coal-based, wood-based, coconut shell-based, impregnated carbon).
2.4 Residence time: The residence time of the exhaust gas in the activated carbon bed, usually designed to be between 0.5 and 2 seconds, is a core design parameter.
2.5 Adsorption temperature: Generally should be below 40°C. The higher the temperature, the lower the adsorption efficiency.
2.6 Humidity: Relative humidity should be controlled below 60%, as high humidity will compete for adsorption sites.
IV. Activated Carbon Materials and Technical Specifications
1. Main Materials
Waste gas treatment activated carbon usually refers to coal-based granular activated carbon, but it can be classified based on raw materials and forms as follows.
1.1 Coal-based Activated Carbon
1.1.1 Raw materials: Anthracite, bituminous coal, lignite.
1.1.2 Characteristics: This is the most commonly used activated carbon for waste gas treatment. Its advantages are high mechanical strength, relatively low price, and wide raw material sources. It is particularly suitable for large volume, medium-low concentration organic waste gas treatment.
1.1.3 Form: Mostly in cylindrical particles (such as diameter 4mm/3mm, length variable).
1.2. Wood-based Activated Carbon
1.2.1 Raw materials: Wood chips, coconut shells, fruit shells, etc.
1.2.2 Characteristics: Usually has a more developed microporous structure, excellent adsorption performance, especially strong adsorption capacity for low molecular weight VOCs (volatile organic compounds). However, its mechanical strength is usually lower than coal-based carbon and the price is also higher.
1.2.3 Application: Often used in scenarios where the outlet gas quality is extremely high or where organic solvents need to be recovered.
1.3 Honeycomb Activated Carbon
1.3.1. Raw materials: Based on coal or wood powder carbon, mixed with adhesives and then compressed and activated.
1.3.2 Characteristics: The shape is honeycomb-shaped cuboids, with a high open porosity, so the pressure loss is very small. This is its greatest advantage, especially suitable for large volume, low concentration waste gas treatment, and can directly replace the traditional granular carbon adsorption bed.
1.3.3 Disadvantages: The iodine value/tetrachloromethane adsorption rate is usually lower than high-quality granular carbon, and the strength is also lower, prone to breakage.
1.4 Selection of activated carbon: In most industrial waste gas treatment, coal-based cylindrical activated carbon is the most widely used choice due to its cost-effectiveness and strength advantages. Honeycomb activated carbon is favored in scenarios where the need to reduce fan energy consumption or handle extremely large volumes of gas is required.
2. Technical Indicators
When selecting activated carbon for treating exhaust gas, one should not merely consider the price. Instead, one must pay attention to the following key technical indicators, as they directly determine the adsorption efficiency and service life.
| Serial Number | Sub – item Name | Meaning and Function | Regular Technical Indicators (Coal – based Columnar Activated Carbon) | Testing Standard |
| 1 | Iodine Adsorption Value (mg/g) | Evaluates the adsorption capacity of activated carbon for low-molecular-weight substances (pore diameter ≈ 1.0nm). It is a key indicator of the total specific surface area and the development degree of micropores. The higher the value, the stronger the adsorption capacity. | ≥800 mg/g | GB/T 7702.7 – 2008 |
| 2 | Carbon Tetrachloride Adsorption Rate (%) | Evaluates the adsorption capacity of activated carbon for medium-molecular-weight organic substances (such as VOCs), which is closer to the actual waste gas treatment working condition. It is a core performance indicator. | ≥50% | GB/T 7702.13 – 1997 |
| 3 | Apparent Density (g/cm³) | The mass of activated carbon per unit volume. If the density is too high, the porosity may be low; if the density is too low, the mechanical strength is easy to be low. It affects the filling amount and pressure drop of the adsorption tank. | 0.45 – 0.6g/cm³ | GB/T 7702.4 – 1997 |
| 4 | Strength/Abrasion Loss (%) | Measures the resistance of activated carbon particles to crushing and abrasion. Low strength will lead to a large amount of dust generated during operation, blocking pores and increasing system resistance. | ≥90% | GB/T 7702.3 – 2008 |
| 5 | Moisture Content (%) | The mass percentage of water contained in activated carbon. Water will occupy pores and reduce the effective adsorption capacity. | ≤5% | GB/T 7702.1 – 1997 |
| 6 | Ash Content (%) | The residue of activated carbon after combustion. A high ash content means a low component of effective carbon and poor adsorption capacity. | ≤15% | GB/T 7702.15 – 2008 |
| 7 | Benzene Adsorption Value (mg/g) | Specially tests the adsorption capacity for benzene – series substances. It is of great reference value for treating waste gas containing benzene. | ≥300 mg/g (Common Requirement) | GB/T 7702.8 – 2008 |
| 8 | Ignition Point (℃) | The temperature at which activated carbon is ignited in the air. It is an important safety indicator to prevent self – ignition under conditions such as adsorption heat or external conditions. | ≥350 ℃ | GB/T 7702.9 – 2008 |
3. Selection and Usage Tips
3.1 Ranking of key indicators: For VOCs waste gas treatment, the adsorption rate of carbon tetrachloride > iodine value > strength > packing density. Do not only pursue high iodine value while neglecting the adsorption rate of carbon tetrachloride.
3.2 Speciality of honeycomb carbon: When purchasing honeycomb carbon, in addition to paying attention to iodine value and adsorption rate of carbon tetrachloride, one must also pay attention to wall thickness and bulk density. The thinner the wall (commonly 0.4mm, 0.5mm), the higher the opening rate, the lower the wind resistance, but the strength will decrease.
3.3 Safety First
3.3.1, Ensure that the ignition point of activated carbon meets the requirements.
3.3.2 When dealing with high-temperature and high-concentration waste gas, a pre-cooling and pre-treatment device must be installed to prevent the temperature of the activated carbon bed from being too high and causing a fire.
3.3.3 Unsaturated activated carbon is also prone to spontaneous combustion during unloading, and proper handling is required.
3.4 Timely replacement: Activated carbon has a saturation life. It needs to be replaced regularly based on the designed air volume, concentration and actual emission monitoring results. Otherwise, it will not only lose its effectiveness but also become a pollution source.
3.5 Comply with Standards: Activated carbon should meet the requirements of international environmental protection standards and other relevant standards.
V. Operation Management and Maintenance
Effective management is the key to ensuring the long-term stable operation of the system.
1. Replacement and Regeneration of Activated Carbon
1.1 One-time use: For intermittent operation with low wind volume and low concentration, when the activated carbon becomes saturated, it should be directly replaced with new carbon, and the waste carbon should be entrusted to a qualified unit for disposal as hazardous waste.
1.2 Regeneration and Recycling: For continuous operation with high wind volume, a desorption regeneration system should be designed. The activated carbon should be regularly regenerated to extend its service life (usually up to 3-5 times).
2. Key Monitoring Points
2.1 Pressure drop monitoring: Regularly check the pressure difference before and after the adsorption tank. A significant increase in pressure drop indicates that the carbon bed may be clogged with dust or undergoes moisture condensation.
2.2 Temperature monitoring: Monitor the adsorption temperature to ensure it is within the design range.
2.3 Outlet concentration monitoring: Install an online monitoring instrument (PID/FID) to monitor the purification efficiency in real time, ensuring compliance with emission standards. This is a mandatory requirement for environmental protection supervision.
3. Safety Risk Management
3.1 Fire prevention and explosion protection: When activated carbon adsorbs organic substances, it releases heat (adsorption heat). When dealing with high-concentration, ketone-type, etc., highly reactive substances, there is a risk of accumulated heat and spontaneous combustion. Strict control of the inlet concentration and temperature must be implemented, and temperature alarms and fire-fighting facilities (such as nitrogen protection, spray system) should be set up.
3.2 Corrosion prevention: When treating exhaust gases containing chlorine, sulfur, etc., select corrosion-resistant materials or impregnate the carbon to prevent equipment corrosion.
4. Records and Ledgers
Establish a complete operation and maintenance record, including the purchase/ replacement date of activated carbon, filling volume, reasons for each replacement/regeneration, transfer forms of waste carbon, etc. This is an important part of the enterprise’s environmental protection management, to be prepared for inspection by environmental protection departments.
VI. Advantages and Limitations
1. Advantages
1.1 Mature technology and high treatment efficiency (usually > 90%).
1.2 Relatively low investment cost (one-time system).
1.3 Wide application range, effective for various VOCs and malodors.
1.4 Simple operation, convenient maintenance.
2. Limitations
2.1 High cost of activated carbon consumption and waste carbon disposal (for one-time system).
2.2 Not suitable for handling high-concentration, high-temperature, high-humidity exhaust gases.
2.3 There is a fire risk (for specific organic substances).
2.4 It is a “transfer” treatment rather than “destruction” treatment. Waste carbon as hazardous waste needs to be properly disposed of.
VII. Future Development Trends
1. Innovation in activated carbon materials: Develop new activated carbon materials with higher adsorption capacity, stronger selectivity, easier regeneration, and better flame retardancy.
2. Combined processes: Adopt more “adsorption concentration + catalytic combustion” combined technologies to balance economic efficiency and treatment efficiency, achieving resource recovery or complete destruction of VOCs.
3. Intelligent management: Utilize Internet of Things (IoT) technology to monitor parameters such as carbon bed saturation, temperature, and pressure drop in real time, enabling predictive replacement and energy-saving operation.
4. Waste carbon resource utilization: Explore waste activated carbon regeneration technologies and resource utilization pathways to reduce environmental risks and disposal costs.
VIII. Summary and Brand, Performance
Activated carbon adsorption is an indispensable technology in the field of waste gas treatment. Its successful application relies on precise design selection, standardized operation and maintenance, and strict safety management. Enterprises should fully understand the characteristics of their own waste gas, select appropriate activated carbon and process routes, and establish complete operation records and safety plans to ensure that the treatment facilities operate stably, stably, up to standard, and safely for a long time, achieving the unity of environmental benefits and economic benefits.
Based in China, Chengde Jibei Yanshan Activated Carbon Co., Ltd. is a professional manufacturer specializing in activated carbon for water treatment systems. It supplies clients with high-quality activated carbon, marketed under the brand “Yanshan”.
“Chengde Cankeshi Import and Export Trading Co., Ltd.”, responsible for the service of the foreign market, provides excellent pre-sale, in-sale and after-sale services for users.
The “Yanshan” brand’s activated carbon lineup comprises coconut shell activated carbon, fruit shell activated carbon, coal-based activated carbon, powdered activated carbon, honeycomb activated carbon, and silver-loaded activated carbon, among other variants.
Our clients: Intel, Tesla, Samsung Electronics, BASF, Yangtze Memory Technologies, Guangzhou Cansemi Semiconductor, BOE Optoelectronics Technology, BYD, Capital Iron and Steel Company, China National Nuclear Corporation, Coca-Cola, Yunnan Baiyao Group, Tsumura Pharmaceuticals.