Application of Novel and Advanced Fuel Characterization Tools for the Combustion Related Characterization of Different Wood/Kaolin and Straw/Kaolin Mixtures

The increased demand for energy from biomass enforces the utilization
of new biomass fuels (e.g., energy crops, short-rotation coppices,
as well as wastes and residues from agriculture and the food industry).
Compared to conventional wood fuels, these new biomass fuels usually
show considerably higher ash contents and lower ash sintering temperatures,
which leads to increased problems concerning slagging, ash deposit
formation, and particulate matter emissions. One possibility to combat
these problematic behaviors is the application of fuel additives such
as kaolin. In contrast to the usual approach for the application of
additives based on an experimental determination of an appropriate
additive ratio, this study applies novel and advanced fuel characterization
tools for the characterization of biomass/kaolin mixtures. In the
first step the pure biomass fuels (softwood from spruce and straw)
and the additive were chemically analyzed. On the basis of the analysis
theoretical mixing calculations of promising kaolin ratios were conducted.
These theoretical mixtures were evaluated with fuel indexes and thermodynamic
equilibrium calculations (TEC). Fuel indexes provide the first information
regarding high temperature corrosion (2S/Cl) and ash melting tendency
(Si + P + K)/(Ca + Mg + Al). TEC can be used for a qualitative prediction
of the release of volatile and semivolatile elements (K, Na, S, Cl,
Zn, Pb) and the ash melting behavior. Moreover, selected mixtures
of spruce and straw with kaolin were prepared for an evaluation and
validation of the release behavior of volatile and semivolatile ash
forming elements with lab-scale reactor experiments. The validation
of the ash melting behavior was conducted by applying the standard
ash melting test. It could be shown that the new approach to apply
novel and advanced fuel characterization tools to determine the optimum
kaolin ratio for a certain biomass fuel works well and thus opens
a new and targeted method for additive evaluation and application.
In addition, it helps to significantly reduce time-consuming and expensive
testing campaigns.