Representation of the addition of CF-containing waste in the cement rotary kiln process Copyright: © TEER

In cooperation with the project partner VDZ Technology gGmbH of the Verein Deutscher Zementwerke e.V., the AiF project EVCAZ - Procedural investigation of the energetic-material utilisation of waste containing carbon fibres in cement plants examines the treatment of non-recyclable waste materials containing CF as substitute fuel in the rotary kiln process.

Due to their mechanical properties, carbon fibres are increasingly used in composite materials. Mechanical and pyrolytic recycling processes produce low-grade fillers, staple fibre yarns and random fibre fleeces from carbon fibre-reinforced polymers. The process-immanent fibre shortening with increasing number of cycles leads to the formation of non-recyclable residues and the release of WHO fibres harmful to health and environment.

Currently, there is no thermal treatment or disposal option for end-of-life waste. Studies for the German Federal Environmental Agency (FKZ 3716 34 3180) have shown that conventional thermal waste treatment plants are not suitable for the conversion of carbon fibres (CF) due to their process conditions. However, the high temperatures and dwell times in the cement rotary kiln process have proven promising for complete conversion of the fibres in short-term tests.

The aim of the EVCAZ project is the development of a sustainable energetic-material utilisation path for non-recyclable CF-containing waste in the cement plant. Based on extensive laboratory tests on the combustion behaviour, three test campaigns are carried out in industrial rotary cement kilns. These include the dosing of CF-containing waste fractions via different feed points (main firing, shaft, calciner, etc.) and the subsequent post-testing to record long-term effects. The tests are supported by comprehensive gas analysis, dust, and solids sampling. Thus the conversion of the CF, possible accumulation effects and emissions of respirable WHO fibres are examined.

In addition, a safety concept for the handling of corresponding waste fractions in the cement plant is being developed. Based on the results, an evaluation of the process success and the influences on process engineering, product quality, occupational health and safety and emissions is carried out. The final technology evaluation serves operators of cement plants, waste processors, CF-processing companies and licensing authorities as a well-founded basis for decisions on the future utilisation of CF-containing waste.

The project is being funded for two and a half years by the BMWK via the research association VDZ Technology gGmbH as part of the IGF programme of the AiF under project no. 23009 N.