Application of Regenerative Thermal Oxidizer in the Ink and Coating Industry

 With increasingly stringent environmental regulations, industries such as ink, coatings, and adhesives are facing higher requirements for VOCs (Volatile Organic Compounds) emission control. Since large amounts of organic solvents are used during ink production, the generated waste gas is characterized by large air volume, complex compositions, and fluctuating concentrations. Therefore, selecting a stable, efficient, and energy-saving Waste Gas Treatment Technology is particularly important.

RTO (Regenerative Thermal Oxidizer), as one of the most widely used thermal oxidation technologies in industrial Vocs Treatment, has been extensively applied in industries such as inks, coating, chemicals, packaging and printing, and new materials due to its high heat recovery efficiency, stable operation, and strong adaptability to complex working conditions. RTO systems decompose VOCs in organic waste gas through high-temperature oxidation, converting them into CO₂ and H₂O, while ceramic heat storage media are used to recover thermal energy. The heat recovery efficiency can generally exceed 95%, making RTO highly advantageous for medium- and low-concentration, large-air-volume VOCs treatment conditions. Particularly in the ink industry, where exhaust gas often contains esters, alcohols, and other organic solvents, rotary RTO systems can not only improve purification efficiency but also effectively reduce natural gas consumption and operating costs.

I. Introduction to Ink Production

Ink and similar product manufacturing refers to the production activities of colored paste-like substances used for printing, computer printing, and copier ink, which are produced by mixing and grinding pigments, binders (vegetable oils, mineral oils, resins, solvents), and fillers.

During production, solvents are used for material dispersion and dissolution. These solvents mainly include ethyl acetate, propyl acetate, n-propanol, isopropanol, anhydrous ethanol, toluene, xylene, and propylene glycol monomethyl ether acetate.

The main production processes of ink include mixing, stirring, grinding, dispersion, filling, and cleaning. Among them, mixing, stirring, and grinding are the primary stages generating VOCs emissions. Since large quantities of organic solvents volatilize during production, the waste gas treatment system is generally required to have strong resistance to impact loads, adaptability to concentration fluctuations, and continuous stable operation capability. This is also an important reason why RTO systems are widely used in the ink industry.

Figure 1 Production Process Flow and VOCs Emission Points

II. Overall Technical Solution for VOCs Treatment in the Ink and Coating Industry
1. Selection of Treatment Technology Route

The ink industry emits a large amount of VOCs, but the emissions are relatively dispersed. Due to differences in production processes and raw materials, the generated waste gas compositions also vary, resulting in certain treatment difficulties. Therefore, suitable treatment technologies should be selected according to the actual conditions of the enterprise.

Generally, the VOCs concentration of waste gas from ink production lines is 900–1500 mg/m³, with an exhaust air volume of 10,000–20,000 m³/h, which belongs to the typical working condition of large air volume and medium VOCs concentration. Under such conditions, RTO incineration technology has obvious advantages in treatment efficiency, system stability, and thermal energy utilization.

Considering both environmental compliance and operating cost reduction, the technical route of “front-end filtration + RTO” is proposed for treating VOCs emissions from ink production lines. The specific process is as follows:

Collect VOCs emitted from each production process section;
The organic mixed waste gas to be treated passes through a front-end filtration device to remove dust and particulate matter from the exhaust gas, preventing blockage of the ceramic heat storage media inside the RTO;
The pretreated waste gas enters the rotary RTO system through pipelines and is discharged after high-temperature combustion treatment.

Figure 2 VOCs Waste Gas Treatment Process Flow

2. Factors for Selecting Treatment Equipment
1) Selection of Filtration Equipment

Dry filters are generally selected for waste gas filtration systems. Commonly used primary filters are G3/G4, while medium-efficiency filters include F5/F6. These filters feature high dust holding capacity, good air permeability, modular design, convenient assembly, and long service life.

G3 efficiency: For particles ≥5.0 μm, filtration efficiency 70＞E≥50% (corresponding to U.S. standard L5);

G4 efficiency: For particles ≥5.0 μm, filtration efficiency 90＞E≥70% (corresponding to U.S. standard L6);

F5 efficiency: For particles ≥1.0 μm, filtration efficiency 50＞E≥30% (corresponding to U.S. standards M9 and M10);

F6 efficiency: For particles ≥1.0 μm, filtration efficiency 80＞E≥50% (corresponding to U.S. standards M11 and M12).

2) Selection of Incineration Equipment

Currently, the mainstream backend incineration technologies are RCO and RTO. Due to the complex solvent compositions used in ink production, catalyst poisoning and deactivation are likely to occur in RCO systems. In addition, the investment cost of large-air-volume RCO systems is relatively high, and the catalyst service life is generally only about 8,000 hours, resulting in excessive replacement costs. Therefore, RTO is selected as the backend treatment method.

RTO systems adopt the principle of high-temperature thermal oxidation to treat VOCs waste gas and achieve high removal efficiency for esters, alcohols, and other organic compounds. The system also offers stronger operational stability and better adaptability to fluctuations in waste gas concentration.

Since the VOCs concentration of this project is about 900–1500 mg/m³, which belongs to a typical medium- and low-concentration working condition, a rotary RTO system with higher thermal efficiency and lower operating energy consumption is selected.

3. Equipment Selection

The VOCs waste gas generated by a certain ink enterprise mainly comes from processes such as mixing, stirring, and grinding. After organized collection, the exhaust air volume is approximately 20,000 m³/h.

It should be noted that the waste gas collection efficiency varies among enterprises, and the actual collected concentration fluctuates significantly. Therefore, before designing the RTO system, on-site measurements and analysis should be conducted according to actual operating conditions. If waste gas containing halogen components such as chlorine or fluorine is present, separate collection and treatment are recommended to reduce equipment corrosion risks and ensure long-term stable operation of the RTO system.

The main exhaust gas parameters are as follows:

Selected dry filtration equipment: 20,000 m³/h, two-stage filtration with G4 and F6;

Selected RTO equipment: 20,000 m³/h.

4. Emission Treatment Targets

After treatment, the VOCs emission concentration is ≤30 mg/m³, meeting local environmental protection standards.

III. Social Benefits

The application of rotary RTO equipment for treating VOCs waste gas generated during ink production can achieve the following effects:

VOCs emission concentration ≤30 mg/m³, meeting national and local environmental protection emission standards;
The RTO system adopts thermal oxidation decomposition technology and does not generate secondary pollution such as wastewater;
The RTO heat storage system can effectively recover combustion heat energy, reducing natural gas consumption and enterprise operating costs;
Rotary RTO equipment features a high degree of automation and can realize long-term continuous and stable operation, reducing environmental management pressure for enterprises;
It helps enterprises achieve green production and energy-saving/emission-reduction goals while enhancing environmental compliance capability and industry competitiveness.