Retrofitting from wet
to dry separation
Overspray cannot be entirely avoided in the classic wet painting process. Separating these particles from the recirculated or exhaust air is essential for stable painting processes and environmental compliance.
Many paint shops in the automotive and supplier industries, as well as in mechanical and plant engineering, still operate with classic wet separation systems such as Venturi scrubbers or water curtain systems. While this technology is proven, it is associated with high energy consumption, complex system technology, the use of chemicals, and corresponding maintenance and disposal requirements.
Rising operating costs, stricter environmental regulations, and the desire for lean, low-maintenance processes are prompting a rethink of existing plant concepts.
Switching to dry separation offers an economical and sustainable alternative. Benefits include reduced energy and operating costs, simplified system technology, and significantly improved operational clarity. The robustness against new paint systems, which eliminates the need for system adjustments, also makes a strong case for dry separation.
Initial situation with wet separation
In wet separation, paint overspray is separated from the process air using water and chemical additives and bound in the form of paint foam or sludge. Stable operation requires various auxiliary units, including:
- Water tanks and pump systems
- Dosing technology for detackifiers, flocculants, and biocides
- Foam/sludge removal, drying, and disposal
- Continuous monitoring of water quality and chemical dosing
In addition to the high equipment requirements, energy consumption is also significant. This is due in no small part to the fact that conventional wet scrubbing typically operates with dedicated supply and exhaust air systems. In this supply/exhaust air mode, the entire supply air is extensively conditioned—meaning heated, cooled, and humidified—before being completely discharged via the exhaust system and thus removed from the process. In large paint shops in particular, this continuous air exchange is one of the largest energy consumers in the entire production process.
Basic principle of dry separation
Note: For the sake of completeness, please note that this analysis excludes dry separation using stone powder and focuses exclusively on dry separation using cardboard filters such as the PaintBlock.
Dry separation systems mechanically capture paint overspray, usually via multi-stage filter systems, and do not require water or chemically active process media. The system design is significantly simpler and focuses on:
- defined airflow
- adequately dimensioned filter surfaces
- controlled pressure drops
- predictable filter service life
A key advantage of dry separation is the ability to recirculate the cleaned booth air, either partially or completely, without the need for dehumidification or humidification. This significantly reduces the demand for elaborately conditioned fresh air, leading to a noticeable decrease in energy consumption.
Energy and resource efficiency
In practice, dry separation proves its strengths particularly with high air volume flows and long operating times. Due to the high recirculation rate, the energy required for the following can be significantly reduced:
- Heating in winter
- Cooling in summer
- Significantly reducing the humidification and dehumidification of supply air.
At the same time, water- and chemical-intensive process steps are eliminated, such as:
- Water consumption
- Use of chemicals
- Disposal of paint sludge as liquid hazardous waste (overspray + chemicals + water)
Dry separation produces filter-bound waste that is often cured or dried, which is generally easier to handle and dispose of.
Retrofitting instead of new construction
For operators of existing systems, the crucial point is: a retrofit does not necessarily require building a new paint booth. In many cases, existing components can continue to be used, such as: booth enclosures, air ducts, fans, and, above all, the existing production layout.
Wet separation under the booth floor is replaced by dry modules. The same applies to the water curtain in the booth. This reduces investment costs, shortens conversion times, and minimizes downtime risks. Especially for paint shops with service lives of 20 to 30 years, modernizing the separation technology can make a significant contribution to long-term economic efficiency, which is why more and more companies are choosing to take this step.
Classification
Dry separation is now a proven industrial process for every paint shop. While it was primarily used for special applications over a decade ago, the technology has evolved significantly and is now established in almost all sectors – from the automotive industry and mechanical engineering to wood finishing.
At the same time, no two systems are alike, and every retrofit must be considered individually and holistically. Key factors include:
- paint type/paint system and application method
- overspray ratio and particle sizes
- recirculated air ratio
- structural and process-related framework conditions
A well-founded decision therefore always requires an application-specific analysis of the existing system.
FAQs
Which paint materials and applications is dry separation suitable for?
Modern dry separation systems are suitable for a wide range of paint materials and paint systems. These include solvent-based, water-based, and 2K paint systems, as well as primers, basecoats, clearcoats, and industrial coatings. As a result, they are fundamentally suitable for all wet paint systems.
The decisive factor is not so much the specific type of paint, but rather the amount of overspray generated, the particle characteristics, and the professional design of the filter stages. With correctly dimensioned systems, stable service lives and consistently high separation efficiencies can be reliably achieved.
How does the maintenance and servicing effort change?
Compared to wet separation, a large portion of traditional maintenance work is eliminated, such as:
- Cleaning of water tanks
- Maintenance of pumps and piping
- Monitoring and dosing of chemicals
Instead, the effort shifts to monitoring and the scheduled replacement of filters. In practice, this is perceived as much more structured and easier to plan. Maintenance intervals can be precisely defined, and downtime can be easily integrated into existing maintenance windows. To avoid downtime for filter changes, dry separation systems such as E-Cube systems, trolley systems, or switching walls are available, which allow for filter changes even during ongoing operation.
Is it realistic to convert from wet to dry separation during ongoing operations?
No. In many cases, the conversion takes place during scheduled shutdowns or in clearly defined construction phases. Thanks to the modular design of dry separation systems, disruptions to ongoing operations can be kept to a minimum.
The specific procedure, however, depends on the existing plant structure, available space, and production requirements. Individual planning is therefore crucial for a smooth implementation.
What are the technical limitations of dry separation?
Dry separation is now a high-performance, established process that is successfully replacing wet separation.
Limitations can arise primarily with very high overspray volumes or extremely fine or dry particles. In such cases, careful dimensioning of the filter stages, sufficiently large filter surfaces, and, if necessary, multi-stage pre-separation become even more critical. For these requirements, the experts at NeuFilter are often involved as early as the planning and design phase.
Planning requirements can also increase in cases of highly fluctuating process conditions or confined installation spaces. In practice, however, these challenges can be reliably managed through customized system concepts, modular and flexible solutions, and application-specific design of the dry separation filters.
Conclusion: The technical limitations lie less in the process itself and more in the system design. With proper planning, dry separation offers an efficient, economical, and future-proof solution for most applications.
How is dry separation classified in terms of fire protection?
Dry separation is now considered state-of-the-art and is fully integrated into the relevant standards and regulations for paint shops. Fire safety requirements are not an additional add-on, but an integral part of the application-specific design of the overall system concept.
Binding overspray within the filter unit creates a defined fire load that is specifically accounted for during the planning and design phase. With standard-compliant design, proper operation, and regular maintenance, fire protection is clearly structured, verifiable, and permanently manageable.
What regulatory requirements apply to dry separation?
When retrofitting paint shops to dry separation, the same fundamental environmental, occupational, and fire safety requirements apply as with wet separation. Dry separation systems are clearly defined in the relevant regulations. Proper design, correct operation, and regular maintenance are always required.
Key regulations include:
- TA Luft (Technical Instructions on Air Quality Control), limiting particle and solvent emissions; properly designed dry separation systems achieve very low emission levels.
- DIN EN 16985 (spray booth standard), the central safety standard for paint booths, including fire protection, explosion protection, airflow, and filter technology
- DGUV Information 209-087, guidelines for fire protection in paint shops
- DGUV Information 209-046, detailed specifications for fire and explosion protection,
- Occupational health and safety: requirements for ventilation, equipment, filter replacement, cleaning, and personal protective equipment.
- ATEX / explosion protection (if applicable), depending on the paint, solvents, and application process.
- Waste and disposal regulations: dry separation systems generate solid, filter-bound waste, eliminating the need for liquid paint sludge disposal.
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