+86 15853145085
Printing waste gas is mainly composed of volatile organic compounds (VOCs), including benzene series, esters, alcohols and other organic substances volatilized from ink and solvents. The treatment scheme shall be selected according to waste gas concentration, air volume, composition and emission standards. Common treatment technologies are divided into two major categories: recovery type and destruction type. The detailed introduction is as follows:
Ⅰ. Recovery Treatment Technology
The core principle of recovery technology is to separate and recycle organic solvents from waste gas. It is suitable for printing waste gas with high concentration and single composition, such as benzene and ester solvents produced in gravure printing and flexographic printing processes.
1. Activated Carbon Adsorption Method
(1) Technical Principle
Relying on the porous structure of activated carbon to adsorb organic molecules in waste gas. After saturation, the adsorbent is regenerated by steam desorption to realize solvent recovery.
(2) Advantages
Simple equipment, convenient operation and low cost. Suitable for pretreatment of low-concentration waste gas with medium and small air volume.
(3) Disadvantages
Activated carbon is easily saturated and requires regular regeneration or replacement. It has poor adsorption performance for high-boiling solvents, and the adsorption efficiency decreases under high humidity conditions.
2. Zeolite Rotor Adsorption and Concentration Technology
(1) Technical Principle
Zeolite molecular sieve has strong selective adsorption capacity for VOCs. When waste gas passes through the rotor, VOCs are adsorbed and purified gas is discharged. When the rotor rotates to the desorption area, high-temperature air is used to desorb and concentrate VOCs with a concentration ratio of 10~20 times. The concentrated waste gas is sent to subsequent destruction equipment for further treatment.
(2) Advantages
High treatment efficiency for low-concentration and large-air-volume waste gas, small floor area, and the zeolite can be regenerated for long-term use. It is highly suitable for concentration pretreatment of large-air-volume and low-concentration waste gas in the printing industry.
(3) Disadvantages
High initial equipment investment. Regular maintenance is required to prevent zeolite blockage.
3. Condensation Recovery Method
(1) Technical Principle
Based on the difference in saturated vapor pressure of organic substances at different temperatures, VOCs are condensed into liquid for separation and recovery by cooling and pressurizing.
(2) Advantages
The recovered solvent has high purity and can be directly reused in production without secondary pollution.
(3) Disadvantages
It is only applicable for high-concentration and high-boiling VOCs. The energy consumption is extremely high under low concentration conditions, and it is usually combined with adsorption technology.
Ⅱ. Destruction Treatment Technology
This type of technology decomposes organic pollutants in waste gas into harmless CO₂ and H₂O. It is the core end-of-pipe treatment technology and suitable for medium-low concentration printing waste gas with complex components.
1. Catalytic Oxidation (CO)
(1) Technical Principle
Under the action of catalyst, organic pollutants are oxidized and decomposed into CO₂ and H₂O at a low temperature of 200~400℃.
(2) Advantages
Low light-off temperature, low energy consumption, high treatment efficiency (over 95%), suitable for medium and high-concentration VOCs. No open flame ensures high operational safety.
(3) Disadvantages
Catalysts are easily poisoned by impurities such as sulfur and chlorine and need regular replacement. The waste gas must be pretreated to remove dust and particulate matter.
2. Regenerative Thermal Oxidizer (RTO)
(1) Technical Principle
Waste gas is heated above 760℃ by ceramic regenerators for oxidative decomposition. The purified high-temperature flue gas releases heat through another regenerator to preheat the incoming waste gas and reduce energy consumption.
(2) Advantages
High purification efficiency (≥99%), suitable for large-air-volume and medium-high concentration VOCs. Waste heat can be recycled to reduce operating costs.
(3) Disadvantages
Large equipment volume and high initial investment. High energy consumption during startup, suitable for continuous and stable waste gas emission conditions.
3. Regenerative Catalytic Oxidation (RCO)
(1) Technical Principle
Combining the heat storage advantage of RTO and the low-temperature catalysis advantage of CO, the waste gas is preheated by regenerators and then oxidized and decomposed at 300~400℃ under catalytic action.
(2) Advantages
Lower energy consumption than RTO, high purification efficiency, suitable for medium and low-concentration VOCs. Higher safety without high-temperature flame.
(3) Disadvantages
High catalyst cost with poisoning risk. Impurity removal pretreatment is mandatory.
4. Photocatalytic Oxidation Method
(1) Technical Principle
Ultraviolet rays excite catalysts such as TiO₂ to generate hydroxyl radicals for oxidative decomposition of VOCs.
(2) Advantages
Simple equipment, small floor area and low operating cost, suitable for auxiliary treatment of low-concentration waste gas.
(3) Disadvantages
The treatment efficiency is greatly affected by humidity and gas composition. It is difficult to meet emission standards when used alone, usually applied as pretreatment or advanced treatment unit.
Ⅲ. Combined Treatment Process
Due to the complex composition and fluctuating concentration of printing waste gas, single treatment technology is difficult to meet emission standards. Combined processes are widely adopted in practical engineering applications.
1. Pretreatment + Main Treatment
Typical process: Spray tower for defogging and dedusting + Zeolite rotor concentration + RCO/RTO. Suitable for large-air-volume and low-concentration waste gas generated in gravure printing and flexographic printing industries.
2. Recovery + Destruction
Typical process:Activated carbon adsorption + Condensation recovery + Catalytic combustion. Suitable for high-concentration solvent-based ink waste gas to realize dual goals of resource recovery and compliant discharge.
Ⅳ. Auxiliary Emission Reduction Measures
In addition to end-of-pipe treatment, pollutant generation can be reduced from the source and production process.
1. Source Control
Adopt environmentally friendly ink such as water-based ink and UV curing ink to replace solvent-based ink, fundamentally reducing VOCs emissions.
2. Process Optimization
Optimize printing process parameters to improve ink utilization rate. Enclose printing machines to collect unorganized exhaust gas and reduce gas escape.
