M.A. Bergougnou

Fast pyrolysis of biomass

Abstract The development of viable fast pyrolysis processes for biomass and other carbonaceous feedstocks will offer significant advantages over conventional pyrolysis, flash pyrolysis and gasification processes with respect to product yield quality and flexibility. Fast pyrolysis is defined and related to other biomass thermochemical conversion processes in some detail. Brief references are made to corresponding coal, hydrocarbon and oil conversion research and development. Proposed mechanisms and chemical pathways are reviewed, potential products. product upgrading and product applications are identified. Fast pyrolysis research is reviewed on both the fundamental bench-scale level and the applied process development level.

A novel calibration procedure for a fiber optic solids concentration probe

Optical fiber probes for the measurement of local solids concentration must be accurately calibrated with defined limits and, in such a way, optimized for the flow densities to be measured. In this study, a multi-fiber optical reflection probe was uniquely calibrated in a downer to obtain quantitatively precise solids holdup. An iteration procedure was utilized to modify the initial calibration curves, which was verified both theoretically and practically. Calibrations using two different batches of FCC particles, with different carbon contents, indicate that these probes are sensitive to minor variations of particle colour and reflective properties; however, the characteristic shape of the calibration curves remains unchanged and a simple linear relationship exists between the curves from different batches of FCC particles.

Hydrodynamic behavior of slurry bubble column at high solids concentrations

Abstract Hydrodynamics of a slurry bubble column have been investigated up to slurry concentrations of 40 vol.% and gas velocities of 0.26 m/s. High slurry concentrations represent high catalyst loading to increase reactor productivity, while high gas velocities would be required to increase reactor throughputs. The solid particles used are 35 μm glass beads representing typical particle size for catalytic slurry reactors. The two important hydrodynamic parameters investigated are gas holdup and solids concentration profiles. The average gas holdups decreased with increasing slurry concentration but the rate of decrease slowed down for higher slurry concentrations. The analysis of axial gas holdup profiles indicated that decrease in gas holdup due to solids addition could be attributed to a decrease in bubble breakup rates. The experimental gas holdups are compared with literature correlations and models. The axial distribution of slurry concentration followed the classical sedimentation–dispersion model. Effects of gas velocity on axial solids distribution are found to be minimal over the range of gas velocities investigated.

Application of fiber optic reflection probes to the measurement of local particle velocity and concentration in gas—solid flow

Abstract New, technically sophisticated measurement techniques must not be used blindly. In order to ensure accurate measurements, the limits of such devices must be well known. In this study a single-fiber optic reflection probe was thoroughly tested in two-phase gas—solid flows for the measurement of particle velocity and concentration. A novel, dynamic calibration procedure for particle concentration measurements has been proposed and tested in the downflow reactor section of a pilot-scale circulating fluidized bed. The results show that, as a particle concentration measuring device, the probe is very sensitive to electrostatic effects in the flow medium. The velocity measurements are relatively unaffected and were shown to be reproducible with errors of between 10 and 15% for particle velocities of up to 8 m/s.

The calculation of the characteristics of a chaotic attractor in a gas-solid fluidized bed

Abstract This paper presents an application of “chaos” or “deterministic chaos” analysis to the performance of a gas-solid fluidized bed. From the point of view of the still developing field of chaos the significance of this analysis is the constancy of the correlation dimension and the Lyapunov exponent over a range of operating conditions. From the point of view of fluidized bed theory these quantitative numbers provide a method of characterizing performance. In addition, in the latter case, the presence of the chaotic attractor indicates several general properties of this dynamical system.

Bubble characteristic in three phase fluidized beds

Abstract Bubble size and rising velocity in freely bubbling liquid-gas and three phase fluidized beds have been measured by means of movie photography. Three solids (1–6 mm), a variety of liquids, and air were employed as the three phases. Both bubble size and rising velocity were found to increase with gas velocity but were relatively insensitive to the liquid velocity, viscosity, and surface tension. At the high gas rates employed, the bubble characteristics were independent of particle size. Correlations are presented for calculating bubble size and rising velocity.

Size distribution of particles entrained from fluidized beds: Electrostatic effects

Abstract Experimental results obtained with solids ranging from 69 μm cracking catalyst to 400 μm polyethylene showed that the smallest particles were not the most easily elutriated from fluidized beds of mixed size particles. This is in contradiction with the assumption made by existing models for the prediction of the flux and size distribution of particles elutriated from a fluidized bed. The smallest particles cannot be removed by elutriation from a mixture of particles of various sizes. The smallest particles may be agglomerated with larger particles. Reducing or eliminating particle electrostatic charges by injecting counteracting charges or increasing the gas humidity did not greatly affect the size distribution of the elutriated particles. Electrostatic forces were, thus, not responsible for particle agglomeration. Electrostatic effects, on the other hand, greatly reduced the flux of elutriated particles by creating an extra electrostatic pressure drop in the fluidized bed freeboard. They also changed the fluidization quality of the bed of polyethylene particles.

The kinetics of vapour-phase cellulose fast pyrolysis reactions

Abstract Biomass fast pyrolysis reactions consist of primary activation and fragmentation reactions, followed by secondary vapour-phase cracking reactions. Kinetic data derived from in-house experiments and published literature have clearly indicated that under true fast pyrolysis conditions, the primary reaction rates exceed those of the secondary reactions by several orders of magnitude. Therefore, since the cracking reactions are rate-limiting, an estimation of the rate of conversion of biomass to secondary products is in fact an estimation of the secondary reaction rate. This paper focuses on the determination of the key kinetic parameters (rate constants, pre-exponential constant and activation energy) for the vapour-phase cracking reactions which occur during cellulose pyrolysis. The parameters were determined using a first-order kinetic model and a non-linear regression routine. The experimental work was conducted in the Ultrapyrolysis equipment at the University of Western Ontario in London, Canada.

Biodiesel Production from Jatropha curcas Oil Using Potassium Carbonate as an Unsupported Catalyst

Jatropha curcas (JTC) oil, an inedible vegetable oil, can be a substitute feedstock for traditional food crops in the production of environment friendly and renewable fuel (biodiesel). In the present study, unsupported potassium carbonate was used as a catalyst to provide an understanding of the catalytic activity in the transesterification reaction. Researching the potential and the behavior of potassium carbonate is very important because every biomass ash contains this compound in a significant amount. It can be extracted by using classical extraction or leaching technologies. During the biodiesel production reaction, the formation of soap as a byproduct was also monitored using the FTIR-ATR method. From this study it was observed that the transesterification of JTC oil to JTC biodiesel appeared to be complete within 15 minutes when a 5 wt% (based on the wt. of the oil) potassium carbonate, 6:1 methanol to oil molar ratio, 60°C or a 4 wt% potassium carbonate, 9:1 methanol to oil molar ratio and 60°C reaction temperature were used.

Effects of micron-sized particles on hydrodynamics and local heat transfer in a slurry bubble column

Abstract Hydrodynamics and heat transfer in an air–water–glass bead system are investigated to study the effects of particle size (11–93 μm) and slurry concentration (up to 40 vol.%). The effect of particle size on gas holdup is only slight over the range of particle size investigated. This can be attributed to differences in rise velocities of different bubble fractions. Small bubble rise velocities are systematically lower for a particle size of 93 μm compared to 11- and 35-μm particles. Larger bubble rise velocities decreased with increasing particle size. Heat transfer coefficients decreased with increasing particle size at the column center, but no significant difference is observed at the column wall. At the column bottom, the heat transfer behaviour of the 11-μm particles is distinctly different from the 35- and 93-μm particles. With the 11-μm particles, there is a smaller effect of slurry concentration on local heat transfer coefficient. Estimated interfacial area results show a sharp decrease due to addition of fine particles into the liquid. The decrease is more dramatic as the slurry concentration is increased.