Why It's Worth Switching from Wet Scrubbing to a Dry Separation System
Dry separation is now a well-established industrial process for paint shops. However, no two systems are alike, so every conversion must be evaluated on a case-by-case basis and from a holistic perspective. Dry separation offers significant potential for improving energy and resource efficiency.
Key Factors
for a Retrofit
Where Do We Stand Today?
The Current State of Paint Separation
Overspray cannot be completely avoided in traditional wet painting processes. Separating these particles from process or exhaust air is essential for stable painting processes and environmental protection. Many paint systems in the automotive and supplier industries, as well as in mechanical and plant engineering, still rely on traditional wet scrubbing systems, such as Venturi scrubbers or water curtain systems. While this technology is reliable, it is associated with high energy consumption, complex system engineering, chemical use, and the resulting maintenance and disposal costs.
Rising operating costs, stricter environmental regulations, and the demand for lean, low-maintenance processes are prompting manufacturers to rethink existing system designs. Dry separation is a particularly cost-effective and sustainable alternative, especially for retrofit applications. The primary advantages are reduced energy and operating costs, simplified system engineering, and significantly improved operational transparency. In addition, the ability of dry separation systems to handle new paint systems without requiring system modifications is another key benefit.
The Wet Scrubbing Process
In this process, paint overspray is separated from the air using water and chemical additives and is then captured in the form of foam or sludge.
This process requires:
- Water tanks and pump systems
- Dosing systems for detackifiers, flocculants, and biocides
- Foam/sludge transport, drying, and disposal systems
- Continuous monitoring of water quality and chemical dosing
In addition to the high equipment and chemical costs, energy consumption is considerable. Conventional wet washing typically operates with supply and exhaust air. In a supply/exhaust air configuration, all supply air is conditioned - that is, its temperature is controlled and its humidity is regulated - before being fully exhausted through the exhaust air system and removed from the process. This continuous air exchange is one of the largest sources of energy consumption in the entire production process.
The Basic Principle of Dry Separation
Filter-based dry separation systems use mechanical processes to capture paint overspray, typically using multi-stage filter systems. They operate without water or chemically active process media. The system design is simple and focuses on:
- Properly sized filter surfaces
- Controlled pressure drops
- Predictable filter service life
Although some dry separation systems use pre-coating agents, these systems are significantly more complex in terms of system engineering and process control. They will therefore not be discussed further here.
A key advantage of dry separation is the ability to recirculate a large proportion of purified booth air without the need for additional humidity control. This significantly reduces the amount of conditioned fresh air required, resulting in substantial energy savings. However, because toxic substances or explosive media, such as solvents, can become concentrated during recirculation, a supply of fresh air is required. These hazardous substances typically also require exhaust air treatment, which can be scaled down in proportion to the reduced fresh air volume.
Today, dry separation is a high-performance, proven, and well-established process that can successfully replace wet separation.
For clean and simple dry separation, Eisenmann offers the reliable E-Cube system.
Energy and Resource Efficiency of Dry Separation
In practice, dry separation is particularly effective with high airflow rates and long operating times. The high proportion of recirculated air, combined with a significant reduction in additional moisture entering the system, substantially reduces energy consumption.
This has a positive effect on:
- Heating in winter
- Cooling in summer
- Humidification and dehumidification of process air
- Exhaust air treatment
Water- and chemical-intensive process steps, as well as the disposal of process by-products in the form of sludge (overspray + chemicals + water), are eliminated. Dry separation produces filter-bound waste that is often hardened or dried and is generally easy to handle and dispose of.
Retrofit Instead of New Construction
Converting from a wet to a dry system does not necessarily mean building a new paint booth. In many cases, existing components can continue to be used. These include the booth enclosure, air ducts, fresh air systems, fans, and, most importantly, the existing production layout.
During the conversion process, the wet separation system located beneath the booth floor is replaced with dry separation modules. The same applies to the water wall inside the booth. This reduces investment costs, shortens conversion times, and minimizes the risk of downtime. In addition to replacing the filtration technology, the process airflow and its optimization potential should also be evaluated.
Frequently Asked Questions
Which Coating Materials and Applications Are Suitable for Dry Separation?
All wet coating systems.
The type of coating is less important than the overspray percentage, particle characteristics, and proper design of the filter stages. With properly sized systems, a stable service life and consistently high separation efficiency can be reliably achieved.
How Does the Maintenance and Servicing Workload Change?
Compared with wet separation, many traditional maintenance tasks are eliminated, including:
- Cleaning water tanks
- Maintaining pumps and piping
- Monitoring and dosing chemicals
The workload is reduced primarily to inspecting and replacing filters according to a scheduled maintenance plan. In practice, this is perceived as significantly more structured and easier to plan. Maintenance intervals can be clearly defined, and downtime can easily be integrated into existing maintenance windows.
Is It Realistic to Switch from Wet to Dry Separation While Operations Are Ongoing?
No. Conversion and system modifications should be carried out during scheduled shutdowns or in clearly defined construction phases. Thanks to the modular design of dry separation systems, disruption to ongoing operations can be minimized.
However, the specific conversion process depends on the existing system structure, available space, and production requirements. Customized planning is crucial for smooth implementation.
What Are the Technical Limitations of Dry Separation?
Technical limitations lie more in the design than in the process itself. With proper planning, dry separation is an efficient, economical, and future-proof solution for most applications.
However, limitations may arise with very high overspray volumes or extremely fine or dry particles. In such cases, it is advisable to carefully size the filter stages, ensure sufficiently large filter areas, and, if necessary, implement multi-stage pre-separation. Planning efforts may also increase with highly fluctuating process conditions or confined installation spaces.
What Fire Safety Measures Must Be Observed When Using Dry Separation?
Dry separation is a state-of-the-art process that is addressed in the relevant standards and regulations for paint shops. The overspray captured in the filter unit creates a fire load that must be considered from the outset of the planning and design phases. Fire suppression systems must be appropriately sized and positioned to reliably reach potential fire sources.
How Should Dry Separation Be Classified in Terms of Explosion Protection?
When considering dry separation, it must be taken into account that contaminated filters must be treated as "paint reservoirs." As with the entire paint shop, explosive vapors must not be allowed to accumulate. Adequate air exchange must always be ensured.
What Rules and Standards Apply to Dry Separation?
The same basic environmental, occupational safety, and fire safety requirements apply when converting paint booths to dry separation as they do to wet scrubbing. Dry separation systems are clearly addressed in the relevant regulations. Proper design, operation, and maintenance are always required.
Key regulatory frameworks include:
- TA Luft (Technical Instructions on Air Quality Control): Limits on particulate matter and solvent emissions. When properly designed, dry separation systems can achieve very low emission levels.
- DIN EN 16985 (Spray Booth Standard): A central safety standard for paint booths, including fire protection, explosion protection, airflow, and filtration technology.
- DGUV Information 209-087: Guidelines for fire protection in paint booths.
- DGUV Information 209-046: Detailed specifications for fire and explosion protection.
- Occupational health and safety requirements: Requirements for ventilation, equipment, filter replacement, cleaning, and personal protective equipment.
- ATEX/explosion protection (if applicable): Depending on the paint, solvents, and application method.
- Waste and disposal regulations (e.g., ADR): Dry separators primarily generate solid, filter-bound waste and do not produce liquid paint sludge.