The treatment of VOCs (Volatile Organic Compounds) in the offset printing industry has gradually evolved from simple collection and treatment to a development direction that emphasizes both deep purification and energy conservation. As one of the most widely applied and highly efficient technologies in industrial VOCs control, theRTO (Regenerative Thermal Oxidizer) has become a key solution for achieving ultra-low emissions in offset printing, packaging printing, and publication printing industries due to its VOC removal efficiency of over 99%, thermal recovery efficiency exceeding 95%, and stable, reliable operating performance.

For the offset printing industry's characteristic large air volume and low VOC concentration exhaust gas, the combined process of Rotary Concentrator + Rotary RTO can effectively increase VOC concentration, reduce natural gas consumption, and achieve both high-efficiency VOC treatment and optimized operating costs.

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I. Overall Technical Solution for Offset Printing VOCs Treatment

1. Selection of Treatment Technology Route

At present, VOC emissions in the offset paper printing industry mainly originate from the volatilization of varnish, blanket wash, fountain solution, hot-melt adhesives used in bookbinding, and other materials.

According to material balance calculations and actual testing data:

• VOC concentration in exhaust gas from paper printing workshops: 80–120 mg/m³
• Exhaust air volume of each offset printing production line: 15,000–20,000 m³/h

This operating condition belongs to a large-air-volume, low-concentration VOC emission source.

Considering both environmental compliance and operating cost reduction, the following treatment route is proposed:

Partition Enclosure → Bag Filtration → Zeolite Rotary Concentration → Rotary RTO Thermal Oxidation

This process is designed to effectively control VOC emissions from offset printing operations.

Specific Process Description

1) Partitioned containment structures enclose the offset printing production line to prevent uncontrolled airflow from dispersing into the open workshop space. This facilitates the attainment of higher VOC concentrations at lower exhaust air volumes and improves collection efficiency.

2) Workshop exhaust gas is introduced into a bag filter system equipped with F7 secondary deep filtration, removing large particulate matter from the exhaust stream and preventing blockage of the downstream zeolite modules.

3) After filtration, the exhaust gas enters the zeolite rotary concentrator. VOCs are adsorbed by activated zeolite and subsequently desorbed by high-temperature hot air.

The purified air after adsorption is discharged directly in compliance with emission standards.

After desorption with a 1:10 concentration ratio, the exhaust airflow is reduced to one-tenth of the original volume, while the VOC concentration increases to 800–1,200 mg/m³.

4) The concentrated gas stream, characterized by low airflow and high VOC concentration, is then directed to the rotary RTO for thermal oxidation treatment and discharged after meeting emission standards.

5) A small amount of UV exhaust gas and hot-melt adhesive exhaust gas containing high-boiling-point polymers is sent directly to the RTO for combustion treatment and compliant discharge.

VOC Exhaust Gas Collection and Treatment Flow Diagram

2. Factors for Treatment Equipment Selection

1) Selection of Filtration Equipment

Large particulate matter in printing workshop exhaust gas has a significant impact on the zeolite rotor.

Therefore, F5 + F9 bag filters are selected. After filtration, the purification efficiency for 1 μm dust particles reaches 99%.

2) Selection of Adsorption Equipment

Since the main VOC components in offset paper printing exhaust gas are alcohols and esters, a zeolite rotary concentrator capable of high-temperature desorption and high desorption efficiency is selected.

3) Selection of Thermal Oxidation Equipment

A rotary RTO is adopted for the downstream thermal oxidation process.

The rotary RTO features:

• Compact structure
• Small footprint
• VOC destruction efficiency exceeding 99%

In addition, high-temperature air is extracted from the top combustion chamber and sent through a heat exchanger to heat ambient air, providing the desorption heat required by the zeolite rotor.

3. Equipment Sizing and Selection

The VOC emissions generated during offset paper printing mainly originate from:

• Printing inks
• Varnish
• Blanket wash
• Fountain solution
• Hot-melt adhesives

Taking three 4-color offset printing presses as an example:

• Exhaust airflow per printing unit: approximately 2,000 m³/h
• Total airflow per press: 8,000 m³/h
• Enclosed-area fugitive exhaust airflow: 8,000 m³/h

Therefore:

• Total airflow per printing press: 16,000 m³/h
• Total airflow for three presses: 48,000 m³/h

Selected Bag Filter System

• Capacity: 50,000 m³/h
• Filtration grade: F5 + F9

Dimensions: 2500 mm × 2500 mm × 2500 mm

Selected Rotary Concentrator

• Capacity: 50,000 m³/h
• Concentration ratio: 1:10
• Purification efficiency: 90%

Dimensions: 4000 mm × 3000 mm × 3480 mm

Selected RTO System

• Capacity: 5,000 m³/h
• Configuration: 8-Chamber Rotary RTO

Dimensions: 6800 mm × 2200 mm × 15000 mm

Overall System Dimensions：16400 mm × 5300 mm × 15000 mm

4. Emission Control Targets

VOC Emission Concentration After Treatment< 30 mg/m³, complying with local environmental regulations.

Odor Removal Efficiency: 95%

No obvious odor shall be detected in the treated exhaust gas.

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5. Energy Consumption Targets

Assuming the workshop exhaust concentration is 100 mg/m³, after a 1:10 concentration ratio, the VOC concentration becomes 1 g/m³, and the concentrated airflow is 5,000 m³/h.

When all three production lines are operating simultaneously, the natural gas consumption is only 1.02 m³/h.

Assuming a natural gas price of RMB 3/m³, the operating cost is approximately RMB 3 per hour, achieving complete VOC oxidation.

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RTO Cold Start (2 Hours)

Total Cost: RMB 92 per start-up

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RTO Hot Start (1 Hour)

Total Cost: RMB 46 per start-up

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Normal System Operation (Full Load)

Total Operating Cost: RMB 84 per hour

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III. Social Benefits

The application of rotary RTO technology for treating exhaust gas generated during offset printing production can achieve the following benefits:

1. VOC emissions below 30 mg/m³, meeting national and local emission standards;
2. Comprehensive elimination of exhaust gas odors;
3. No secondary pollution, such as wastewater or solid waste generation, is produced by the process.