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Catalytic Oxidation (CO) is an efficient treatment technology for volatile organic compounds (VOCs). With the assistance of catalysts, organic pollutants in printing waste gas are oxidized and decomposed at relatively low temperature into harmless carbon dioxide and water. This technology is widely applicable to volatile organic compounds generated during printing production, including benzene series, esters, alcohols and ketones.
Ⅰ. Core Technical Principle
VOCs molecules in printing waste gas are adsorbed on the catalyst surface, and then undergo oxidation reaction with oxygen at a low temperature of 200℃~400℃. Compared with direct thermal combustion (requiring 800℃~1200℃), catalytic combustion reduces the activation energy of chemical reaction by utilizing catalysts, which greatly cuts down energy consumption and inhibits the generation of nitrogen oxides (NOₓ).
Ⅱ. Process Composition (Adapted to Printing Waste Gas Characteristics)
Printing waste gas features complex components and fluctuating concentration. A complete catalytic oxidation system consists of the following core units:
1. Pretreatment Unit
Printing waste gas usually contains ink mist, dust, colloids and other impurities, which will cover the active sites of catalysts and cause irreversible catalyst poisoning. The pretreatment system generally adopts multi-stage filter cotton, activated carbon filter or spray tower to remove particulate matter and viscous contaminants, ensuring stable operation of the catalytic reaction unit.
2. Heating Unit
The temperature of raw printing waste gas is normally between room temperature and 60℃. Electric heaters or gas heaters are equipped to heat the flue gas to the catalyst light-off temperature (200℃~300℃). If the VOCs concentration is relatively high, the heat released by oxidation reaction can maintain self-heating circulation without external supplementary heating.
3. Catalytic Reaction Unit
As the core of the whole system, the reactor is filled with dedicated catalysts. Two types of catalysts are commonly used for printing waste gas treatment:
Precious Metal Catalysts: Platinum (Pt) and Palladium (Pd). They possess high activity and low light-off temperature, but are expensive and vulnerable to poisoning caused by sulfur and chlorine impurities.
Non-precious Metal Catalysts: Oxides or composite oxides of manganese, cobalt and copper. With low cost and good poisoning resistance, they are suitable for printing waste gas containing a small amount of impurities.
4. Heat Recovery Unit
A large amount of heat is released during catalytic oxidation. The heat exchanger transfers the residual heat of high-temperature purified flue gas to the low-temperature raw waste gas for preheating, realizing internal heat recycling. This energy-saving design is particularly important for printing enterprises to reduce operating costs.
5. Exhaust Discharge Unit
The purified gas (mainly CO₂, H₂O and unreacted oxygen) is discharged through the chimney up to standard, complying with the Emission Standard of Air Pollutants for Printing Industry (GB 41616-2022) and other local environmental regulations.
Ⅲ. Technical Advantages for Printing Industry
High Purification Efficiency: The VOCs removal efficiency of printing waste gas can reach more than 95% with stable purification performance.
Low Energy Consumption: Low light-off temperature. When the VOCs concentration is ≥2000mg/m³, the system can realize self-heating operation without additional heat supply.
Less Secondary Pollution: Low-temperature reaction avoids massive NOₓ generation, with no black smoke or peculiar smell emission.
Simple Operation: Fast startup and shutdown, high automation degree, which can adapt to the intermittent production mode of printing lines.
Ⅳ. Important Operation Precautions
Catalyst Poisoning Prevention: Substances such as sulfur-containing compounds (mercaptan), chlorine-containing solvents and heavy metals will cause permanent catalyst deactivation. It is necessary to strictly control raw material impurities or adopt anti-poisoning catalysts.
Concentration Control: The VOCs concentration must be kept below 25% of the lower explosion limit to avoid explosion risks. Fresh air shall be introduced for dilution under excessive concentration conditions.
Catalyst Maintenance: Regularly inspect catalyst activity. Purge, regenerate or replace aging catalysts once purification efficiency declines.
Strict Pretreatment Requirements: Dust, oil mist and viscous substances must be thoroughly removed to prevent pore blockage and performance degradation of catalysts.
