A 100-kW fine dust filter in the field trial
© CCA – Carola Clean Air GmbH

Left: Precipitator prototypes in test operation Top right: Corona discharge at the high voltage electrode Bottom right: Precipitator in the model with the ionizer and brush for the collector
© links: KIT, rechts: CCA – Carola Clean Air GmbH
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Alternative precipitator technologies

Precipitators are already particularly used for larger plants. These operate according to different principles. A simple, inexpensive form of flue gas filtration is offered by cyclone precipitators. With these the flue gas is tangentially fed into a pipe, the cyclone, which causes the gas flow to rotate. The cyclone tapers toward the outlet side. Because the angular momentum is maintained, the rotational speed increases as the pipe cross-section decreases. The centrifugal forces push the dust particles outwards towards the casing where they are separated. This technique is used in bagless vacuum cleaners. Cyclones, however, only achieve low separation rates with the very fine particles produced by optimised wood chip boilers. Another disadvantage in terms of the energy consumption is the high pressure loss.

With fabric filters, clean gas values ranging from 2 to 20 mg/m³ dust can be achieved depending on the filter material. Sticky soot particles cause, however, unstable filter operation, which requires elaborate and additional technical measures. Necessary fire protection measures increase the investment costs and the pressure loss that is inherent to the principle increases the operating costs.

The first electrostatic precipitators for small firing systems have now appeared on the market. These are dry electrostatic precipitators that come with and without integrated cleaning systems. In particular these differ from the system presented here in terms of the type of cleaning. This is where the researchers see an advantage: „The self-cleaning ensures a longer service life and good separation rates in the long term,“ confirms Paur.

From research project to product

The research was funded as part of the „Energy Efficient Utilisation of Biomass“ programme run by the German Federal Ministry for Economic Affairs and Energy. In 2012 this led to the founding of a company that further developed the separation technology to market maturity. Following numerous tests, the German Institute for Building Technology (DIBt) granted national technical approval for the patented precipitator in the summer of 2015. The testing was also monitored by the Technischer Überwachungsverein (German Technical Inspectorate (TÜV)). Among other things this confirmed the high separation efficiency, electrical safety and soot fire resistance. The precipitator is the first dry particle precipitator with fully automatic cleaning to be approved for the German market for wood-fired boiler systems in the 50-200 kW thermal output range. The newly founded company, CCA – Carola Clean Air GmbH, is now producing electrostatic particle precipitators for domestic and industrial systems with thermal outputs between 25 and 1,000 kW.

The market is growing

Thanks to modern combustion technology, manufacturers of biomass heating systems have already significantly reduced the particulate emissions. However, in order to permanently meet the second limit level of the 1st Ordinance on the Implementation of the Federal Immission Control Act, these primary-side optimisations are not sufficient. Secondary measures are required. Therefore the market for separation systems is growing in Germany. For the thermal output range covered by the 1st Ordinance on the Implementation of the Federal Immission Control Actbetween 4 and 1,000 kW, a market volume of approximately 40,000 boiler systems per year is expected, which will need to be partly equipped with precipitators. In terms of the export possibilities within Europe, the researchers believe that Italy and Austria have considerable potential because relevant boiler manufacturers are located there.

Projektinfo 06/2016:
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Biomass boiler manufacturer – adaptation of the precipitator for HDG wood chip boilers
HDG Bavaria GmbH

Development of the Carola particle precipitator


BINE-Projektinfo 06/2016
(PDF, 4 pages, 771 kB)

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Deutsches Biomasseforschungszentrum gemeinnützige GmbH (DBFZ)