Ash-induced Agglomeration of bubbling fluidized beds during gasification of biofuels with low melting ashes

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Ash-induced agglomeration of bed particles due to low melting ashes is the key problem of the thermal conversion of particularly alkali-rich biofuels in fluidized bed systems. The mechanism of the formation of agglomeration in gasifiers is still not clear in detail, especially the underlying effect of altered agglomeration temperature in presence of residual char particles.The main objective of the proposed project is, therefore, the identification of agglomeration mechanism during thermal gasification and the clarification of influential plant and fuel/ash parameters plus high char contents. To achieve this goal, we propose a combination of experimental and numeric approaches:On the experimental side, the analysis of time-resolved pressure fluctuations in lab-scale fluidized bed gasifiers shall allow the detection of ash-induced changes of the fluidized beds fluid dynamics at an early stage. We will perform experiments with different feedstock, plant parameters and residual char content.In addition, numerical Lattice-Boltzmann simulations will predict the formation of agglomerates of individual bed material particles covered with liquid melt films and coke particles. The simulation of particle collisions on single particle scales will provide the agglomeration tendency with respect to the temperature and ash properties. Eventually, a large-scale, close to reality model will be developed and compared to experimental findings in order to review the agglomeration criteria and formulate a plausible and verified agglomeration mechanism for thermal fluidized-bed gasification.