Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Physical/mechanical tests - ash melting behaviour

The determination of biofuels ash melting behaviour is of high importance for all thermal conversion processes. The temperature range of sintering, softening and melting can vary broadly, depending primarily on ash composition.

Although biofuels ashes were tested by seven methods, only from improved DIN ("German industry norm"), MAF ("melt area fraction") and CFBA ("controlled fluidised bed agglomeration") temperature information can be derived that can be compared directly. For synthetic samples it was revealed that only the DIN and the MAF method are able to quantify melting temperatures. However, DIN and MAF are ash-testing methods suitable for standardisation whereas CFBA may be used as reference for agglomeration/sintering.

The recently developed MAF method shows large potential to become reproducible and repeatable. The MAF method has been proven to determine the temperature of 10% and 50% melt in the ash samples tested. Though, some modifications are needed for problematic ashes, e.g. straw ash, which tends to form "cakes" (agglomerates) during handling. Moreover, further improvement is required concerning melt viscosity and the possible sample shrinking.

The technologies of TGA/SDTA ("thermogravimetric analysis"/"simultaneous differential thermal analysis") cannot be standardised at present, but they have the potential to confirm various phenomena associated with ash melting behaviour. SEM-EDS ("scanning electron microscope" combined with an "energy dispersive x-ray analyser") is predestined for providing valuable information on the ash compositions and species. Testing the XRD ("X-ray diffraction") method revealed that the amount of amorphous phase is valuable if the connection between amorphous phase and melt phase is clarified before.

Besides the suitability of test methods, issues such as really required information to forecast ash melting and the relation of acceptable analysis cost. It is generally accepted that testing of initial melt temperature as well as the rate of melt formation is essential. With regard to the costs, bed sintering methods and methods as TGA/SDTA that produce results that have to be evaluated by specialists can be eliminated. The improved DIN method is an attempt to get around with comparatively simple and low-cost manner in the standards. This is also true for the MAF method.

However, there certainly are some problems about the identification of the characteristic temperatures for biomass ashes. This is also true for variations (not studied within BioNorm) in the density of the test specimen that is produced by compression. Furthermore, the reproducibility has to be improved.

Reported by

TFZ - Technologie- und Förderzentrum Nachwachsende Rohstoffe
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