Fluidized Bed Combustion of Liquid Biofuels: Application of Integrated Diagnostics FOR Micro-explosions Characterization

A novel integrated diagnostic technique has been developed for the analysis of the "regime with micro-explosions" that may be established during the low-temperature (T < 800 degrees C) fluidized bed combustion of liquid fuels. It consists of the comparison among three analogue data series: (i) pressure signals measured in the freeboard and high-pass filtered, (ii) oxygen molar fractions measured by zirconia-based probes at two elevations in the bed and in the splash region, and (iii) video frames of the bed surface recorded and purposely worked out. The integrated technique has been applied to the combustion of biodiesel at minimum fluidization and has proven to be a valid tool to provide the fingerprints of the mechanism of the low-temperature fluidized combustion of liquid fuels. The time series generated from the measured data sets have been analyzed with the aid of the Hurst's rescaled range analysis, the V-statistic, and the Lyapunov exponents' evaluation. The issue of localizing micro-explosions throughout bed, bubbles, and splash zone has been tackled by the V-statistic analysis, which has proven that the location of micro-explosions is just at the bed surface when T = 650 degrees C and moves deeper and deeper into the bed when its temperature increased to about 800 degrees C. The values found for the largest Lyapunov exponent in the time series demonstrate that the investigated system is not only dynamic but also chaotic in its nature.