How to treat solvent exhaust gas in ship painting workshops? Collection and treatment configuration for segmented painting

Ship painting is one of the industry scenarios where solvent usage is concentrated: after segmented sandblasting, primer and topcoat are applied, and operations are carried out in cabins, decks, and segment workshops in rotation. Solvent evaporation points constantly move according to production plans. Unlike fixed-station painting lines, the governance challenges of ship painting lie in its "large" and "dispersed" nature - the operation space is large, points are dispersed, and batch fluctuations are severe. Governance configuration should focus on these two characteristics, with the collection end following the operation surface and the processing end capable of handling pulses. Only when the configurations at both ends are complementary can there be an overall effect.

What are the characteristics of painting exhaust gas

Firstly, the volume fluctuates dramatically: during the segmented spraying periods, both air volume and concentration surge, while during non-operating periods, they almost return to zero, resulting in a pulsed load curve. Secondly, the point locations follow the plan: the spraying equipment continuously rotates within the workshop in segments, and the fixed collection hoods cannot keep up with the working surface. Thirdly, the components change with the type of paint: alternating between primer and topcoat, solvent-based and water-based paints, the components and concentration levels of the exhaust gas vary significantly. These characteristics determine the configuration approach: the collection end must "move with the people", while the processing end must "withstand the pulse". Only when the two are matched can an overall effect be achieved.

How to organize collection

The enclosed segmented booth is the main force in collection: spraying is carried out in the segmented booth, and the directional airflow inside the booth collects organic waste gases as a whole. The concentration and air volume are controllable, making it an effective organizational method at present. For large-scale segmented and cabin operations that cannot be carried out in the booth, local enclosures and mobile negative pressure units are used for supplementary collection. The exhaust gas from operations in confined spaces such as cabins is led out through temporary air ducts to avoid diffusion within the hull. The collection system is scheduled according to the operation plan: the equipment is turned on centrally during the painting period, and the branches are shut down during non-operation periods, which not only saves energy but also stabilizes the inlet conditions of the treatment section. The door curtains, air vents, and seals of the segmented booth wear out with operation, and are included in weekly inspections. Most of the decrease in collection efficiency is first seen in these small parts.

How to configure for processing

Pulse loads are absorbed through pre-positioned buffers and multi-channel regulation: The combination of rotary concentration and condensation is suitable for high air volume and low to medium concentration scenarios. After the rotary device concentrates the air volume by more than ten times, the condensation section is configured for low air volume and high concentration, significantly reducing the deep cooling load. For paint types with high recovery value, the condensed recovery liquid is stored by type. The capacity of the processing section is configured based on the pulse peak value of a typical working day, with buffer volume used to trim peaks during short-term excess. Instead of focusing on extreme single points, it is more cost-effective to invest in common operating conditions.

Configuration key points reference

How to implement operation management

1. Integrate production scheduling with governance, and submit the spraying plan to the processing system in advance;
2. Regular testing of directional airflow in segmented rooms, with collection efficiency data available for reference;
3. The branch air valve is opened and closed according to the operation plan, and is shut down during non-operation periods;
4. For regular review of rotary concentration, first check the collection end if the concentration decreases;
5. The recovered liquid is stored and tested by paint type, with records corresponding to each batch;
6. Record the pressure difference and energy consumption of the processing section on a daily basis, and investigate any abnormal trends immediately.

Frequently Asked Questions

The old factory area lacks segmented rooms. How can we commence the treatment?

Let's start with concentration: consolidate scattered spray painting operations into fixed areas, equip with mobile enclosures and negative pressure units, and gradually upgrade and modify the segmented rooms. Governance investment can be carried out in stages, controlling the large areas first and then addressing the details, which is easier to implement than a one-step solution.

Do we still need to take measures after replacing with water-based paint?

Yes, but the load structure has changed: the volatile solvents in water-based paints have been significantly reduced, and the configuration of the collection and treatment sections can be correspondingly downgraded. After the alternative plan is determined, the load should be recalculated, and the treatment facilities should be adjusted accordingly, rather than simply carrying on with the original infrastructure.

Can the recycled solvent still be used after mixing with several paint types?

The components of mixed recycling liquid are complex, leading to a significant reduction in reuse value. Collecting and storing by paint type is crucial to preserve value. For those that are indeed mixed, they should be downgraded for cleaning and dilution purposes, with records kept of their whereabouts.

This article is compiled by Luoyang Wohong Petrochemical Equipment Co., Ltd., which provides design, manufacturing, and operation and maintenance services for condensation recovery, membrane separation recovery, and complete solvent recovery equipment to chemical and pharmaceutical enterprises. If you need process evaluation or scheme configuration, please feel free to contact us for discussion.