Evaluation of the temperature-dependent adhesion characteristics of fly ashes with a HT-rheometer

In high temperature processes like incineration, gasification or pyrolysis of biomass and waste, the long-term stable filtration performance is drastically reduced due to a significant fraction of sticky particulates. Especially in these processes, the fly ashes can already soften at temperatures below 400 °C. In consequence, filter clogging is enhanced and regeneration is hindered. For the evaluation of the filtration performance and for the adjustment of the recleaning parameters, the analysis of the temperature-dependent adhesion characteristics of fly ashes and dusts is essential. Conventional shear cells, however, usually require precompressing of the samples and will be operated intermittent at one temperature per sample. A continuous measurement of highly porous dusts is not possible. Therefore, a rotational rheometer was developed, which permits – in a temperature range up to 1300 °C – conclusions on the height of the effective adhesive forces. Continuously measured variable is the torque of a slowly rotating stirrer, which results from the relocation and displacement of particles and/or agglomerates in a non-compacted powder and correlates directly with the current adhesion characteristics. On the basis of model dusts the advantages and possibilities of the measuring method are pointed out and apparatus- as well as material-related relevant parameters will be discussed.