Hydrodynamic behaviour of coal and bottom ash mixtures in a fluidized bed gasifier

Conference Dates

May 22-27, 2016


systems. One of the principal applications of such systems are in combustion and gasification of solid fuels (coal, pet coke, and biomass), wherein the fuel and the inorganic residue (“ash”) form a system of binary fluidization. Even though the fluid bed gasification of coal per se is a relatively well-known operation, however the technology for high ash coal (>30% ash in the native coal) is still in its nascent stage. Existing knowhow on such operations cannot predict interactions of a constantly depleting coal inventory and constantly evolving ash inventory.

With this backdrop we attempt here to study the dynamic behavior of coal and ash in a fluidized bed. In order to simulate a realistic bed composition of a gasifier, hydrodynamic characteristics were studied under various proportions of coal and ash on laboratory scale cold flow setup. A three-dimensional transient CFD model was set up to predict the dynamic and time-averaged profiles of coal and ash concentrations. The same were validated against chordal averaged solids holdup (coal and ash) characteristics measured using γ-ray densitometry, with a single collimated source (Cs-137) aligned with a scintillation NaI detector. The other part of the validation, involving the comparison of measured solids velocity profiles and CFD-predicted ones, is accomplished by implementing the Radioactive Particle Tracking (RPT) technique. In the latter technique, a single radioactive particle designed to mimic a single typical coal particle is tracked for a long time in the vessel using strategically placed scintillation detectors, and its position-time history is processed to yield the solids velocity field.

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