Application of Regenerative Thermal Oxidizer in Printing Industry
Application of Regenerative Thermal Oxidizer in Waste Gas Treatment in the Printing Industry
1. Industry and Waste Gas Characteristics
The flexible packaging printing industry is one of the major sources of VOC emissions (waste gas) in the light industry. During the production process, a large amount of organic solvents is used, especially in the drying stage, where waste gas containing Volatile Organic Compounds is continuously generated. With increasingly stringent environmental regulations, this industry has placed higher requirements on efficient and stable waste gas treatment technologies.
Industry Characteristics:
(1) The printing industry features large air volume and high concentration of VOC emissions, requiring RTO purification efficiency to reach over 99.5%;
(2) There is a widespread demand for waste heat recovery, and the “Regenerative Thermal Oxidizer + waste heat recovery (hot water, hot air, steam, thermal oil, etc.)” technology has been widely adopted;
(3) Waste gas sources: organized emissions from printing ovens and laminating machine ovens, as well as unorganized emissions from printing workshops and ink mixing rooms;
(4) Waste gas components: ethyl acetate, n-propyl acetate, butanone (MEK), isopropanol, ethanol, propylene glycol methyl ether acetate (PGMEA);
(5) Process route: unorganized gas collection + rotary concentrators + organized air volume reduction and concentration + rotary valve RTO + waste heat recovery.
2. Efficient Treatment Route
1) Unorganized Waste Gas Control and Collection Technology
The core of unorganized waste gas control lies in effective collection, achieved through proper airflow organization design:
① Ensure supply air volume ≤ unorganized exhaust air volume (maintain slight negative pressure in the workshop);
② Ensure air supply at the printing machine operation side ≤ exhaust volume of each machine (maintain slight negative pressure at equipment level);
③ Install enclosures for each printing machine and magnetic curtain partitions between color units;
④ Set up top and side exhaust systems to capture unorganized waste gas at key points such as oven discharge outlets.
2) Air Volume Reduction, Concentration, and Energy-Saving Technology
The “box-type internal circulation” LEL parallel air volume reduction and concentration heating device is a hot air system designed for flexible packaging printing machines. It can significantly reduce exhaust air volume and increase waste gas concentration.
Main technical features:
① All hot air components are arranged within an insulated box (50 mm insulation thickness), with built-in return air channels to reduce heat loss;
② Secondary return air internal circulation with short flow paths to significantly reduce airflow resistance;
③ Dual fans for active air supply and exhaust, with variable frequency control, allowing linear adjustment of the reduction and concentration ratio;
④ Large-diameter floor exhaust system to reduce unorganized emissions in the workshop;
⑤ Patented technology with independent parallel air reduction and concentration for each color unit, without mutual interference;
⑥ Real-time LEL monitoring to ensure safe and reliable operation.
3) Rotary Concentrators
Low-concentration waste gas can be concentrated by 8–30 times using a rotary concentrator, while reducing the air volume to 1/8–1/30, and then sent to the RTO for treatment. When waste gas passes through the rotary concentrators, VOCs are adsorbed by the rotary concentrators, and the purified air is discharged through the chimney. Then, a small volume of high-temperature air is used to desorb the VOCs from the rotor, which are subsequently sent to the RTO for final treatment.
Applicable range:
- Flow rate: 10,000–200,000 m³/h
- Temperature: ≤35°C
- Relative humidity: ≤80% RH
- Concentration: <1000 mg/m³
- (Treatment efficiency: 95%)
4) Waste Heat Recovery Methods
RTO is not only an efficient purification device but also an important energy recovery unit. When the waste gas concentration reaches ≥1.5–2 g/m³, the system can achieve self-sustaining combustion and generate recoverable excess heat.
Common waste heat recovery methods include:
- Hot air reuse
- Hot water systems
- Thermal oil systems
- Steam systems
Enterprises can select appropriate recovery methods according to the heating requirements of printing equipment, enabling cascade energy utilization and significantly reducing overall energy consumption.
3. Selection and Comparison of Core RTO Equipment
In the printing industry, RTO technology has evolved from two-bed and three-bed systems to rotary systems. The following comparison is based on a treatment capacity of 30,000 Nm³/h:
| Performance | Indicator | 2-Chamber RTO | 3-Chamber RTO | Rotary RTO | Remarks |
|---|---|---|---|---|---|
| Advanced | Technology generation | 1st generation | 2nd generation | 3rd generation | |
| Number of chambers | 2 | 3 | 12 | ||
| Reliability | Number of valves | 4 | 9 | 1 | |
| Annual valve switching times | 350,000 | 520,000 | / | Rotary valve operates continuously without switching | |
| Pipeline pressure fluctuation | ±500 Pa | ±250 Pa | ±25 Pa | ||
| Compliance | Overall purification efficiency | 95% | 99% | 99.5% | |
| Maximum concentration range | <1 g | <5 g | <10 g | 50 mg/m³ emission standard | |
| Energy efficiency | Heat transfer area | 100 m² | 145 m² | 95 m² | |
| Thermal efficiency | 90% | 95% | 96% | ||
| Start-up heating time | 2.5 h | 3 h | 2 h | Cold start | |
| Self-sustaining concentration | 2.5 g/m³ | 2.2 g/m³ | 1.8 g/m³ | Ethyl acetate | |
| Economics | Ceramic media volume | 18 m³ | 26 m³ | 17 m³ | |
| Weight | 65 t | 102 t | 62 t | ||
| Practicality | Footprint | L12×W7 | L16×W7 | L12×W7 | m |
The third-generation rotary RTO demonstrates superior overall performance in treatment efficiency, thermal efficiency, and operational reliability, and has become the preferred choice for many enterprises.
4. Summary
For the flexible packaging printing industry, characterized by large air volume, high concentration, and energy-sensitive VOCs waste gas, the integrated solution of “precise unorganized collection + air volume reduction and concentration + zeolite rotor concentration + RTO + waste heat recovery” has become the mainstream approach.
This solution not only ensures stable compliance with emission standards but also significantly reduces operating costs through energy recovery and system optimization, delivering both environmental and economic benefits.
Under increasingly stringent environmental regulations, selecting more efficient, reliable, and energy-saving RTO technology will be a key driver for the green transformation of printing enterprises.