1. Project Overview

2. Pollutant Analysis and Hazards

2.1 Main Pollutants

2.2 Formation and Hazards of Pollutants

2.2.1 Hazards to Human Health

2.2.2 Production Safety Risks

2.2.3 Ecological Environmental Impacts

As the core precursors of ozone (O₃) and fine particulate matter (PM2.5), VOCs participate in photochemical reactions after being discharged into the atmosphere, aggravating regional haze and photochemical smog pollution and deteriorating air quality. Paint mist particles settle with rainwater and pollute soil and water bodies. The internal resin components are difficult to degrade and will damage the ecological balance for a long time. The strong pungent odor will also affect the quality of life of surrounding residents, trigger environmental complaints, and damage the brand image and market reputation of listed enterprises.

3. Design Basis and Principles

3.1 Design Basis

• Environmental Protection Law of the People's Republic of China (Revised in 2015)

• Atmospheric Pollution Prevention and Control Law of the People's Republic of China (Revised in 2018)

• GB 16297-1996 Comprehensive Emission Standard of Air Pollutants

• GBZ 2.1-2019 Occupational Exposure Limits for Hazardous Factors in Workplace Part 1: Chemical Hazardous Factors

• GB 3095-2012 Ambient Air Quality Standards

• HJ 1093-2021 Technical Specification for Performance Evaluation of Regenerative Thermal Oxidizer (RTO)

• HJ 2027-2013 Technical Specification for Industrial Organic Waste Gas Treatment Engineering by Catalytic Combustion Method (Auxiliary Reference)

• GB 37822-2019 Emission Control Standard for Volatile Organic Compounds Without Organization

• GB 50160-2008 Fire Protection Standard for Petrochemical Enterprises (2018 Edition)

• GB 50243-2016 Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Engineering

• GB 50235-2010 Code for Construction and Acceptance of Industrial Pipeline Engineering

• National electrical industry standards: GB 50054-2011 Code for Design of Low Voltage Power Distribution

• GB 50034-2013 Standard for Lighting Design of Buildings

• Mature cases and technical data of spray paint waste gas treatment in domestic and foreign precision manufacturing enterprises

3.2 Design Principles

• Accurate Compliance Principle: The discharged spray paint waste gas shall strictly comply with GB 16297-1996 and GB 37822-2019 standards, in which VOCs emission concentration ≤30mg/m³, toluene + xylene ≤10mg/m³, particulate matter ≤5mg/m³. It shall also meet the relevant requirements of the VOCs governance campaign and the environmental disclosure standards for listed enterprises.

• High-efficiency Purification Principle: The combined process of "pretreatment defogging + RTO thermal oxidation" is adopted. The high-efficiency defogging device removes paint mist particles first, and then the RTO equipment thermally oxidizes and decomposes VOCs into CO₂ and H₂O at high temperature, ensuring the total purification efficiency ≥99% for deep waste gas purification.

• Safety and Energy-saving Principle: The RTO equipment adopts a three-chamber heat storage structure with a heat recovery efficiency ≥95%. The combustion heat of VOCs is used to preheat inlet gas to reduce energy consumption. The system is equipped with safety devices such as explosion-proof, explosion venting and nitrogen purging devices, combined with online VOCs concentration monitoring and automatic interlock control to completely eliminate potential safety hazards.

• Production Adaptation Principle: The system air volume accurately matches the production capacity of the spray painting line to meet the demands of multi-shift production and intermittent emission. The equipment is convenient for operation and maintenance with a long regenerator replacement cycle. The service life of the main RTO equipment is ≥15 years, which is in line with the enterprise's long-term stable production plan.

4. Design Objectives

1. The purification efficiency of spray paint waste gas is ≥99%. After treatment, VOCs ≤30mg/m³, toluene + xylene ≤10mg/m³, particulate matter ≤5mg/m³, and oxygen content ≤10%, which fully meets national and local environmental protection standards to ensure stable compliant discharge and satisfy environmental information disclosure requirements.

2. A special exhaust funnel with a height of no less than 18 meters shall be constructed, equipped with sampling platform, monitoring holes and online monitoring equipment in accordance with specifications. Rainproof caps and flow measuring devices shall be installed at the exhaust funnel outlet to ensure high-altitude compliant discharge of waste gas.

3. The unorganized emission concentration of VOCs in the spray workshop is controlled within the limit of GB 37822-2019 (non-methane total hydrocarbons ≤6mg/m³). The pungent odor is completely eliminated to improve the workshop operating environment, reduce the risk of employee occupational diseases, and meet the requirements of safety production standardization.

4. The system realizes fully automatic operation and intelligent monitoring with functions such as VOCs concentration over-limit alarm, equipment fault self-diagnosis and emergency shutdown protection. The heat recovery efficiency is ≥95%, the annual energy consumption cost is reduced by more than 40%, and the annual stable operation time is ≥8500 hours, adapting to the enterprise's continuous production demand.

5. Spray Paint Waste Gas Treatment Process Design and Description

5.1 Process Selection Basis

• Top-tier purification efficiency: RTO equipment oxidizes and decomposes VOCs into harmless CO₂ and H₂O at 800-850℃. The degradation efficiency of benzene series, esters and other VOCs is ≥99%, which is much higher than traditional processes such as activated carbon adsorption and catalytic combustion, ensuring the emission concentration is steadily lower than strict standards.

• Remarkable energy-saving benefit: The three-chamber heat storage structure recovers more than 95% of combustion heat to preheat raw waste gas. Only a small amount of auxiliary fuel needs to be supplemented during normal operation, and even the combustion heat of VOCs can maintain the furnace temperature, greatly reducing operating costs.

• Comprehensive safety performance: The system is equipped with online VOCs concentration monitor (0-100%LEL). Fresh air dilution is automatically started when the concentration exceeds the limit. The equipment is provided with explosion-proof membranes, explosion venting ports and nitrogen purging system. The regenerator is made of high-temperature and corrosion-resistant materials to completely avoid explosion and equipment damage risks.

• Enterprise development adaptation: The equipment processing air volume can be flexibly adjusted to adapt to future capacity expansion. It operates stably with a long maintenance cycle. A small amount of waste residue generated can be disposed of centrally, meeting the environmental compliance and sustainable development requirements of listed enterprises.

5.2 Process Flow Chart

5.3 Detailed Process Description

1. Efficient source collection: Separate gas collection devices are set for spray booth and drying chamber. The spray booth adopts fully enclosed negative pressure gas collection with side suction air curtain to prevent waste gas overflow, and the wind speed is controlled at 0.8-1.0m/s. The drying chamber adopts top gas collecting hood to ensure full collection of high-temperature waste gas. Waste gas is summarized through FRPP anti-corrosion pipelines with the internal wind speed maintained at 15-18m/s to avoid deposition and blockage of paint mist particles.

2. Pretreatment impurity removal: The waste gas firstly enters the water curtain cabinet to capture more than 60% of large-diameter paint mist particles through high-pressure water mist. Then, primary filter cotton (filtration accuracy: 5μm) is used to remove residual paint mist, and medium-efficiency filter cotton (filtration accuracy: 1μm) is applied for deep defogging with a defogging efficiency ≥99%. Finally, the activated carbon pre-adsorption layer removes part of viscous components that easily block the regenerator to protect the core RTO equipment.

3. RTO core oxidation: The pretreated waste gas enters the three-chamber RTO equipment for efficient treatment through periodic switching of heat storage chambers and oxidation chambers. In the first stage, the waste gas enters heat storage chamber A and is preheated to above 700℃ by high-temperature regenerators. In the second stage, the preheated waste gas flows into the oxidation chamber, and VOCs are completely oxidized and decomposed into CO₂ and H₂O at 800-850℃ with the assistance of auxiliary burners. In the third stage, the purified high-temperature gas enters heat storage chamber B to release heat and heat the regenerator, then is discharged by the induced draft fan. Heat storage chamber C performs purging and regeneration. The three-chamber circulation ensures the heat recovery efficiency ≥95%.

4. Safety monitoring and control: The system is equipped with 2 sets of online VOCs concentration monitors (one set at the inlet and one at the outlet) to monitor concentration changes in real time. When the inlet concentration ≥25%LEL, the fresh air dilution device is automatically started. The RTO equipment is built-in with temperature sensors and pressure sensors. Once the temperature or pressure exceeds the standard, an alarm is triggered immediately, and measures such as nitrogen purging and emergency shutdown are activated. All electrical equipment adopts explosion-proof design to ensure operational safety.

5. Waste heat recovery and operation maintenance: The high-temperature waste heat generated by RTO equipment is recovered through heat exchangers for drying chamber heating or workshop heating, reducing natural gas consumption by more than 40% annually. System operation data is uploaded to the enterprise central control platform and environmental protection monitoring system in real time for remote monitoring. The regenerator is inspected and maintained every 2 years. Activated carbon and filter cotton are replaced regularly according to operating load. Waste activated carbon is disposed of by qualified institutions to form a closed environmental protection loop.