We present a case study showing the operation of an electrostatic separation system for a renowned vehicle manufacturer.
by Doris Schulz*
The painting process represents up to 70% of the energy consumed in the manufacture of trolleys. A 75% reduction in energy consumption not only significantly reduces operating costs, but also reduces carbon emissions.
Eisenmann's painting workshop at Volkswagen's Bratislava plant proves that it is possible to achieve this. The electrostatic separation system of excess spraying known commercially as E-Scrub makes a fundamental contribution to efficient resource management.
In their efforts to make the production process more environmentally friendly, automotive manufacturers have prioritized reducing emissions and conserving resources. This was made clear in Volkswagen's tenders for an additional paint line at its Bratislava (Slovakia) plant, which would be used in the manufacturing process of the new Volkswagen up! and other compact models.
Eisenmann was selected as the paint shop's prime contractor, thanks to the strength of his resource preservation solution. Compared to conventional painting installations, Eisenmann's technology allows savings of up to 75%. Additionally, it reduces water consumption by approximately 87%. This is mainly due to the electrostatic separation system of excess spraying.
This solution not only generates substantial savings, but also creates ideal conditions for the vehicle finishing process. The raw bodies are transported by the pre-treatment and electro-immersion coating lines by the E-Shuttle transport system.
Efficient air recirculation
The new paint shop is designed to process 150,000 bodies per year. In line with Volkswagen's "Process 2010", a coating without primer is applied there. The exhaust air loaded with paint particles generated in the painting process is sucked out and directed to the separation system, located under a spray booth grille. E-Scrub combines maximum separation efficiency with minimal pressure loss, allowing the solution to operate on 95% recirculated air.
High voltages instead of filters
The operation of the system is due to its operating principle. The excess spray generated throughout the paint area is transported to the E-Scrub separation unit. The air loaded with paint particles passes through an alternative system of active and passive elements. The high-voltage cables of the active elements give the paint particles a negative charge. Consequently, they are attracted to and retained by the grounded passive separation plates, which are coated with a separating agent.
Once the paint particles have been removed by a special discharge system, most of the separating agent is pumped back into the separator modules.
By eliminating mechanical filter systems, the E-Scrub provides constant airflow in the spray booths, without pressure fluctuations. This creates the ideal conditions to produce high-quality coatings. Additionally, the separation system does not significantly alter the air condition, which means that a large proportion of the separated air can be sucked out and returned to the spray booth using a recirculation fan.
Substantial savings
Bratislava's new paint line works with approximately 80 recirculated air and 20% fresh air. Fresh air is pre-conditioned, because it comes from other areas of the plant, such as quality control. This plays an important role in the significant reduction in the energy consumption of the air supply, compared to supply/exhaust air systems (from an average of 50,000 MWh to only 11,000 MWh per year).
Consequently, a reduction in CO2 emissions is achieved. The E-Scrub also reduces water consumption, from approximately 60,000 cubic meters, in wet scrubbers, to an annual average of 7,500 cubic meters. In addition, fewer chemicals are required.
Drastic reduction in particulate emissions
The electrostatic separation system can remove the smallest paint particles from the air. In combination with air recirculation, particulate emissions at Volkswagen's Bratislava plant are below 0.3 mg per cubic meter of air, for both the base coating and transparent coating lines.
The above figure is well below the threshold of 3 mg per cubic metre supported by Germany's Technical Guidelines on Air Quality Control (TA-Luft).
Low waste level
Except for the separating agent, which is recycled, E-Scrub does not require any other chemicals to remove paint particles from the air. This means that little waste is generated. Depending on the solids content in the paint, the electrostatic separation of one kilo of excess spray produces less than a kilo of paint residue, while a dry scrubber generates several kilos of waste that must be disposed of. This feature also contributes to protecting the environment and reducing carbon emissions as well as operating costs.
In light of these benefits, the European automotive manufacturer also implements in its new paint shops in Brazil and China the electrostatic separation system of the paint particles in the air from Eisenmann.
Optimized pretreatment process
The E-Shuttle conveyor system, which is used to transport raw bodies through pre-treatment and electro-coating stations, also plays an important role in conserving resources and maximizing coating quality.
Thanks to the fact that each transport system has three axes of free programming (horizontal, vertical and rotation) and that it is equipped with its own controller, the immersion curves and processing times can be programmed individually, with little effort, for any type of body.
The flexibility of the E-Shuttle, compared to conventional rigid pendulum conveyors, allows for faster immersion and drainage. Additionally, with the transport system of the German manufacturer it is possible to reach the cavities and indentations of difficult access. And the movement sequences adapted to each particular body ensure a perfectly even coating with less fouling and the need to exert less force on the adhered surfaces.
The bathing time of the process can be reduced, compared to other methods that use pendulum transport systems, which decreases the consumption of the process fluid. This is also good for the environment and reduces operating costs, as less water, chemicals and energy are required.
* Doris Schulz is a specialist in the field of surface treatment, has her own public relations consultant who currently leads the Paint Expo 2013 fair in Istanbul, Turkey, which will take place from September 12 to 14 and Paint Expo 2014 that will take place from April 8 to 11 at Messe Karlsruhe, Germany. [email protected].
Photo: Courtesy of Eisenmann
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