Cedric Briens

Biomass Valorization for Fuel and Chemicals Production - A Review

The transformation of biomass into fuel and chemicals is becoming increasingly popular as a way to mitigate global warming and diversify energy sources. Biomass is a renewable, carbon-neutral resource, and fuels derived from biomass usually burn more cleanly than fossil fuels. It has been estimated that biomass could provide about 25% of global energy requirements. In addition, biomass can also be a source of valuable chemicals, pharmaceuticals and food additives. Several kinds of biomass can be converted to fuel and chemicals. Examples are wood and wood waste, agricultural crops, agricultural waste, litter from animal feedlots, waste from food processing operations and sludge from water treatment plants.Various processes can be used to convert biomass to energy. The biomass can be burned, transformed into a fuel gas through partial combustion, into a biogas through fermentation, into bioalcohol through biochemical processes, into biodiesel, into a bio-oil or into a syngas from which chemicals and fuels can be synthesized. Wood combustion, bioethanol production from either sugarcane or corn, and biodiesel production from oilseeds are currently the most economically significant processes but still need significant improvements. A detailed review of the many processes that can convert biomass into fuels and chemicals shows that no individual process is without drawbacks. As a result, it is recommended that a biorefinery is the best solution to combine and integrate various processes to maximize economic and environmental benefits, while minimizing waste and pollution.

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.

Carbon Nanotube Synthesis: A Review

Discovered in 1991, carbon nanotubes (CNTs) have reached the forefront of many industrial research projects. Carbon nanotubes are tubular carbon molecules with remarkable mechanical, chemical, thermal and electrical properties, which make them useful in various applications. This paper reviews three methods of synthesizing the nanomaterial, namely arc-discharge, laser-ablation and fixed bed/fluidized bed catalytic. These methods have generated a large interest in many industrial companies to date. At the moment, the most critical issue faced by industrial companies is determining the best synthesis method, which will give the most economical large-scale production of CNTs. Compared to the other two methods, the catalytic technique to synthesize CNTs is simple, inexpensive, energy-efficient and can produce large CNTs quantities of high yield and purity.

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.

Digital X-ray Imaging Technique to Study the Horizontal Injection of Gas-Liquid Jets into Fluidized Beds

Gas-liquid jets injected into fluidized beds of particles/catalyst find applications in many industrial processes. The effective distribution and mixing of the feed droplets with the entrained bed particles is vital in improving the process efficiency. The present study utilizes a sophisticated digital X-ray imaging system to study the internal flow structure of jets injected into fluidized beds. The system is equipped with an X-ray image intensifier (XRII) and optical detectors, which convert the transmitted X-ray photons into digital images of up to 60 frames s-1. The imaging technique provides useful information such as the jet expansion angle and the penetration distance. These are functional quantities in optimizing the performance of feed nozzles, and in modeling the jet-fluidized bed interactions.In this work, the horizontal injection of gas, gas-liquid, and liquid jets into fluidized beds is investigated. The results indicate that the jet expansion (half-angle) is considerably reduced for a gas-liquid jet (5-7 degrees) when compared to that of a gas jet (10-15 degrees). The gas-liquid jet also appears to penetrate more than a gas jet with the same momentum. When a liquid feed is introduced into a fluidized bed of particles, the particles may agglomerate if they are wet-enough to form liquid bridges. Improper feed distribution may be a direct contributor to enhanced agglomeration. In this regard, radio-opaque tracers mixed with the feed liquid are injected to track the formation and the movement of agglomerates. The tracer experiments show that the agglomerates are generated at the end of the jet region, close to its maximum penetration distance. A brief discussion on the modifications required to achieve improved contrast for the acquired images, and the effect of some important X-ray parameters are also included in the present study.

The design of flights in rotary dryers

Abstract Rotary dryers for particulate solids commonly use flights along the length of the shell to lift solids and make them rain across the dryer section. These flights are critical to dryer performance. Previous models for the prediction of the solids holdup in rotary drums have assumed that the angle of the solids level in a flight is independent of the flight geometry. They have considered only the case of extended circular flights and angular flights with two segments. New equations were derived to predict the solids holdup in flights with three segments. Their predictions were compared to measurements performed with a pilot plant rotary dryer. Theoretical equations provided estimates of the flight holdup that were accurate enough to predict the power required to lift the solids. On the other hand, the model is not accurate enough to predict the variations in the flux of solids over the drum cross-section. This shows that the angle of the solids level in a flight can be affected by the flight geometry.

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.

Horizontal Penetration of Gas-Liquid Spray Jets in Gas-Solid Fluidized Beds

A new method has been developed to predict the horizontal jet penetration of gas-liquid sprays injected into gas-solid fluidized beds. The technique involves combining a theoretical model to predict the momentum flux of two-phase sprays with the Benjelloun et al. (1995) correlation for gas jets. Following this treatment, a generalized version of the jet penetration correlation has been developed, which includes the effect of nozzle geometry. The correlation predictions are in very good agreement with the experimental data for a wide range of nozzle geometries, nozzle scales, and jet fluids.

Hydrodynamics, gas-liquid mass transfer and particle-liquid heat and mass transfer in a three-phase fluidized bed for biochemical process applications.

Abstract Particle-liquid heat and mass transfer, hydrodynamics and gas-liquid mass transfer were simultaneously measured in three-phase fluidized beds of light particles under conditions typical of biochemical applications. Although there was no analogy between particle-liquid heat and mass transfer, the effect of the particle density could be, in both cases, modelled through its effect on the liquid holdup. The effect of the particle density on gas-liquid mass transfer could not be modelled through its effect on the liquid holdup. Decreasing the particle density enhanced gas-liquid mass transfer in the three-phase fluidized bed.

Detection of local fluidization characteristics using the V statistic

Abstract Defluidized zones degrade the performance of fluidized beds. Triboelectric currents at the distributor were measured in a variety of gas–solid fluidized beds. A V statistic below 1.5 ms −0.5 indicated a defluidized zone. This criterion allowed detection of defluidized zones in an industrial bed within 100 ms and is thus suitable for process control.