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Adsorption-Desorption-Catalytic Combustion combined process is an efficient composite technology for treating organic waste gas with medium and low concentration and large air volume. It integrates the concentration capability of adsorption technology and the degradation capability of catalytic combustion technology. Featuring high purification efficiency, low operating cost and no secondary pollution, this process is widely applied in organic waste gas treatment for chemical, coating, printing, rubber and plastic industries.
Ⅰ. Process Principle and Flow
The core technical logic is concentration first, degradation later. The overall process consists of three key stages, matched with complete pretreatment and auxiliary systems.
1. Pretreatment Stage
Raw organic waste gas passes through pretreatment units such as bag filters, activated carbon filters and demisters to remove impurities including dust, particulate matter, ink mist and moisture. This procedure prevents adsorbent pore blockage and catalyst poisoning, ensuring stable operation of subsequent treatment units.
2. Adsorption and Concentration Stage
The pretreated low-concentration and large-air-volume organic waste gas enters adsorption towers filled with adsorbents such as activated carbon, molecular sieve and activated carbon fiber. Organic pollutant molecules are physically or chemically adsorbed by the microporous structure on the adsorbent surface, and VOCs in the waste gas are intercepted. The purified gas can be discharged up to standard. When the adsorbent reaches saturation, the system switches to a standby adsorption tower to ensure continuous gas treatment, while the saturated tower enters the desorption process.
3. Desorption Stage
Hot airflow (hot air or inert gas at 120-180℃) is delivered into the saturated adsorption tower. Organic pollutants attached to the adsorbent are thermally desorbed to form high-concentration waste gas with small air volume. This concentration process significantly reduces the air volume and energy consumption required for subsequent combustion treatment. After desorption, the adsorbent recovers its adsorption capacity and can be reused.
4. Catalytic Combustion Stage
The concentrated high-concentration organic waste gas is sent into the catalytic combustion reactor. Under the action of catalysts (precious metals such as Pt and Pd, or non-precious metal oxides such as Mn and Cu), organic pollutants are completely oxidized into harmless CO₂ and H₂O at a low temperature of 200-400℃. A large amount of heat released during the catalytic reaction is recovered by heat exchangers to heat the airflow required for desorption, realizing thermal self-sufficiency and reducing system operating costs.
Ⅱ. Core Process Advantages
1. High Purification Efficiency
The VOCs removal rate in the adsorption stage exceeds 90%, and the degradation rate of catalytic combustion reaches 95%-99%. The final emission concentration can steadily meet national standard requirements.
2. Low Energy Consumption
Only a small amount of energy is consumed for initial heating during desorption. The heat generated by catalytic combustion can be recycled. This process is particularly suitable for long-term treatment of medium and low-concentration waste gas.
3. Wide Application Range
It can treat most types of organic waste gas including benzene, ketone, ester, alcohol and alkane substances, adapting to inlet VOCs concentration ranging from 100mg/m³ to 1000mg/m³.
4. No Secondary Pollution
The final decomposition products are CO₂ and H₂O without generating nitrogen oxides and other secondary pollutants. In addition, adsorbents can be regenerated and reused for multiple times.
Ⅲ. Key Equipment and Parameter Control
1. Core Equipment
Adsorption Tower: Fixed bed or fluidized bed structure is commonly adopted, made of anti-corrosion carbon steel or stainless steel. The adsorbent filling quantity is calculated according to actual waste gas air volume and concentration.
Desorption Heating System: Equipped with electric heater or gas heater to keep the desorption temperature within a reasonable range and avoid adsorbent carbonization caused by overheating.
Catalytic Combustion Reactor: Built-in modular catalyst with thermal insulation layer to ensure uniform reaction temperature and prevent local overheating.
Heat Exchanger: Plate-type or tube-type heat exchanger is applied to recover combustion heat, with a heat recovery efficiency of 60%-80%.
2. Key Control Parameters
Adsorption wind speed: Controlled at 0.5-1.5m/s. Excessively high wind speed reduces adsorption efficiency, while excessively low wind speed increases equipment investment.
Desorption temperature: Adjusted according to adsorbent types. The desorption temperature of activated carbon is 120-150℃, and that of molecular sieve is 150-180℃.
Catalytic combustion temperature: Higher than the light-off temperature of pollutants and lower than the maximum endurance temperature of catalysts (generally not exceeding 400℃).
Ⅳ. Application Precautions
Strict Waste Gas Pretreatment: Dust, ink mist and moisture must be thoroughly removed to prevent adsorbent deactivation and irreversible catalyst poisoning.
Catalyst Maintenance: Regularly inspect catalyst activity. Purge or replace aging catalysts in time to avoid excessive pollutant emission caused by decreased catalytic efficiency.
Safety Protection Measures: High-concentration organic waste gas is flammable and explosive. The system shall be equipped with explosion-proof valves, flame arresters, temperature monitoring and alarm devices to ensure operational safety.
Ⅴ. Process Limitations
It is not applicable for organic waste gas with excessive concentration (>5000mg/m³), as excessive combustion heat may cause potential safety hazards.
Poor purification performance for waste gas containing chlorine, sulfur and phosphorus, which will lead to permanent catalyst poisoning.
Adsorbents have a limited service life. Repeated regeneration will gradually reduce adsorption performance, and regular replacement is required.
