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

Abstract

A novel integrated diagnostic technique has been developed for the analysis of the "regime with microexplosions" that may be established during the low-temperature (T < 800 °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 °C and moves deeper and deeper into the bed when its temperature increased to about 800 °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.

Characterization on hydrodynamic behavior in liquid‐containing gas‐solid fluidized bed reactor

“…Hurst analysis, also called R/S analysis, is a method to quantify persistence of time series and has been successfully applied in many multiphase systems . The related specific mathematical algorithm and the implementation details of this analysis can be found in this reference .…”

Conversion of liquid and gaseous fuels in fluidized bed combustion and gasification

“…The discontinuous eruption of bubbles at the bed surface causes the establishment of a turbulent region (Horio et al, 1980;Pemberton and Davidson, 1984;Van der Honing, 1991;Solimene et al, 2007), which makes the gas mixing more effective than in the bulk of the bed. Ferrante et al (2008) carried out detailed measurements in the splash zone of a pre-pilot combustor burning biodiesel under minimum fluidization conditions with a fixed excess air factor. In particular, they obtained timeresolved profiles of the O 2 concentration by means of a zirconia probe and video recordings of the hot bed surface taken from the top, like those reported in Fig.…”

“…Figure 8.9 displays the experimental results of DT versus T b for two different sizes of the fuel nozzle, d 0 . All other conditions being equal, DT decreases as the 8.8 Sequence of frames representing the bed surface recorded from the top during a combustion test at pre-pilot scale, with biodiesel as fuel, the bed at minimum fluidization and T b = 800°C (courtesy of Ferrante et al, 2008). bed temperature increases due to the faster kinetics of hydrocarbon oxidation.…”

Experimental Demonstration of Deterministic Chaos in a Waste Oil Biodiesel Semi-Industrial Furnace Combustion System

“…Jeon et al (2018) used a visualization system to analyze spatial combustion flame and investigated B20 combustion and soot emission processes under different injection pressure conditions [14].By determining whether the combustion process of biodiesel is random, regular, or chaotic, useful strategies and short-term predictions can be provided for combustion in industrial production. Nonlinear deterministic and chaotic characteristics in the combustion process have been shown in many studies [15][16][17][18][19][20]. Currently, chaotic features can be identified by different methods and standards, such as Lorenz map [21], Poincare map [22], Grassberger-Procaccia algorithm [23], power spectrum and strange attractor [24], and Lyapunov stabilization [25,26].…”