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Filter technology during wet painting processes saves energy and the environment

The regenerative dry separation system RECLAIM offers a reliable, cost and energy efficient separation of wet paint overspray. Air recirculation reduces the energy consumption by 50 % and auxiliary materials within the process can be reused recycled even as "waste" material

The challenge in terms of sustainability:

Energy and material efficient processes are demanded. On the one side by the customer for economical reasons to reduce operating costs and on the other hand by society for ecological aspects to safe our environment. Also operators of wet paint systems are struggling with challenges concerning the resource efficiency. Especially the extremely high energy demand for conditioning the supply air in painting systems may not meet today's basic standards. So the electricity requirement and material consumption had to be analyzed and optimized.

The initial situation:

So far, wet scrubbers had been used to separate adhesive materials. However, high operating costs resulting from power and water consumption as well as the consumption of chemical auxiliary material and the corresponding waste disposal more and more initiate operators to switch to dry separation. With this proceeding, operating costs are considerably lower although an exchange of the filters is necessary. But also here exists potential for optimization especially with regard to the energy requirement because for the conditioning, which is the warming and moisturizing of the supply air which is necessary to maintain air quality within the painting booth, a lot of energy is needed.

The solution:

The new ProBran filters – reusable and efficient

The filters are cleaned online while the system is operating. "We optimized the dimensions, surface structure and the material composition for our new ProBran filters", explains Joachim Haußmann, Sales Manager at Keller Lufttechnik. The woven fabric filter material with a rigid structure is equipped with a membrane consisting of a smooth surface which prevents the overspray from accumulating inside the filter pores," which would interfere with compressed air cleaning of the filters. This usually occurs with other types of filters with various coating types and materials. By contrast, the coating of the ProBran filters reliably ensures a pure surface filtration.

Filters can be cleaned with a lower pressure of only 3.5 bar

"The filter resistance is reduced by 40 – 50 percent due to the large surface and its optimized structure. At the same time, considerably less compressed air is required for the cleaning process because of the reduced supply pressure as compared to its ancestor SINBRAN", says Haußmann. "Instead of six bar, it is only 3.5 bar. This optimization means a great improvement in the system's energy consumption." At the same time, these types of filters are sturdier and can handle constant temperatures of up to 110 degrees Celsius instead of 60 degrees Celsius. For utilizing the system in painting systems, it is necessary that the filters be free of paint-wetting impairment substances (PWIS) such as, for example, silicone. "We inspect each filter element with regard to this capability and document our inspections with retained samples", explains Haußmann.

The sustainable strengths:

Energy-saving air recirculation

RECLAIM cleanses the air so thoroughly, that air recirculation in automatic coating plants is possible and useful. Because of the high separation efficiency of our ProBran filters, up to 95 % of the separated dirty air is recirculated into the paint booth as preconditioned clean air. This results in considerable energy-savings. The energy costs for the paint booths can be reduced by up to 50 %. To illustrate, 1000 cubic meters of fresh air per hour which has to be ducted from the outdoors and heated can consume 60 megawatts of energy. Energy savings of up to 60.000 € per year can be achieved because only five percent of air is required from outdoors and subsequently heated as opposed to 100 percent. The RECLAIM system pays for itself within 1.5 to 3 years.

Energy-savings in after-treatment of the exhaust air

Air recirculation leads to an accumulation of solvents (Volatile Organic Compounds, VOCs) which pass through the filters as gaseous materials. This requires the addition of approximately 5 percent of fresh air. The system required to treat the solvent fumes for these considerably smaller exhaust air flows that are concentrated with VOCs, , becomes substantially reduced. Due to the higher solvent concentration, the thermal after treatment can be operated without requiring any additional energy supply. This is another advantage of the air recirculation which contributes to the reduction in the energy consumption of the exhaust air after treatment system, as well as in investment and operating costs.

Recyclable precoating material

Limestone powder coats the filter with an auxiliary layer. "When selecting this precoating material, it was important to consider occupational safety, to choose a material which does not react with other substances in the separator - that means it should be inert", explains Haußmann.  "Moreover, the global availability of the material also plays a role." Another important consideration: the limestone powder which bonds to adhesive aerosols can be used several times. After filter cleaning, it falls into a collection tank, the silo, below the separator. A so-called fluidization process performs the blending, so that the adhesive particles are encased in limestone powder and the mixture of limestone powder and paint overspray can be blown upwards onto the cleaned filter elements to create a new auxiliary layer.

Even „waste" can be recycled

Depending on the composition of the paint overspray, the online filter cleaning is either controlled by the differential pressure or interval-controlled, or a combination of both. Should the filter resistance reach a maximum value, the compressed air pulse cleans as many filter plates sequentially as possible until a defined value – adjusted as lower filter resistance – is reached. Once the limestone powder is fully saturated, it is automatically discharged from the system and new limestone powder is added. Depending on the size of the paint booths and the RECLAIM system, the supply and disposal containers can differ: 25 kg bags, Big-Bags or silos are all available. The mixture of the waste paint overspray and limestone powder is dry and can therefore be recycled without any further treatment. An application example is in the cement industry, or thermal reutilization is another possibility. This is an additional advantage of the RECLAIM process.

The inventors:

RECLAIM was developed and advanced by our development team in close collaboration with well-known customers according to the requirements of the painting industry.

Company information:

Name: Keller Lufttechnik GmbH + Co. KG
Headquaters: Kirchheim unter Teck/Jesingen
Year established: 1903
Employees: 280
Solutions: Development, production and sales of our air pollution control systems, filters and components to keep the air clean
Internationality: 3 subsidiaries as well as 16 representative offices and licence holders in the most important markets in Europe, Asia and America
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