INFLUENCE OF PROCESS PARAMETERS ON FLUIDISED BED DRYING OF POWDERED MATERIALS

The present study reports preliminary characterization about the fluidised bed drying of powdered materials. Tests were carried out in a Lexan® lab-scale fluidised bed with solids selected to effectively surrogate powders of interest in the manufacture of pharmaceuticals. The process was monitored to correlate the temperature and the flow rate of the fluidising gas, the temperature and the moisture level in the bed, the qualitative fluidisation patterns. Bed material was characterized to assess the modifications of the population of agglomerates as a function of the operating conditions

ASSESSMENT OF KINETICS FOR BUTANOL PRODUCTION BY CLOSTRIDIUM ACETOBUTYLICUM

The economic scenario established at the beginning of the third millennium has revived the interest in Acetone-Butanol-Ethanol (ABE) fermentations. Recent developments in molecular techniques applied to solventogenic microrganisms in combination with recent advances in fermentation systems and downstream processing have contributed to improve ABE fermentation processes feasibility and competitiveness. The challenges raised over the last years as regards ABE production may be synthesized in: i) use of renewable resources as substrate; ii) selection of strains characterized by high ABE productivity; iii) development of new fermentation systems; iv) development of new downstream strategies for enhanced solvent recovery. The selection of unconventional substrates is favoured by the ability of clostridia strains to metabolize a wide range of carbohydrates like glucose, lactose, etc...., typically present in wastewater streams e.g. from food industries. Even though clostridia have been proven successful to produce ABE, information about kinetics of substrate conversion, cell growth and butanol production is still lacking. Studies available in literature most typically regard batch tests whose results do not apply easily to continuous processes. The strong interaction between the growth/acidogenesis phase and the solventogenesis phase should be taken into account. The reactor systems investigated for the ABE fermentation belong to the batch and fed-batch typologies. Some attempts are reported in literature regarding continuous fermentation by means of clostridia strains confined in the reactor by immobilization or cell-recycling. The present study reports the preliminary results of a research activity aiming at investigating the feasibility of the ABE production by Clostridium acetobutylicum ATCC824 in a continuous biofilm reactor adopting cheese whey as feedstock. The contribution regards the characterization of the kinetics related to the ABE production process by free C. acetobutylicum ATCC824 adopting as medium lactose solutions, in order to emulate the cheese whey. The conversion process is characterized in terms of cells, acids, solvents, pH, gas composition and total organic compounds as a function of time. Results are worked out to assess the kinetics of the cells growth and of the ABE production. The yields of the carbon source in cells, acids and solvents are also assessed. The investigation is carried out adopting both batch reactors and two continuous reactors. In particular, the continuous reactors are equipped to operate under controlled conversion regimes, acidogenesis or solventogenesis. Tests carried out under batch conditions show that: i) cells growth follows the Monod kinetics for lactose concentration (CL) smaller than 100 g/L; ii) the butanol specific production rate increases linearly with CL; iii) the lactose conversion - measured at the end of the solventogenesis phase - decreases with CL; iv) the selectivity of butanol with respect to total solvents increases with CL and stabilizes at about 72%W for CL larger than 30 g/L. Preliminary tests carried out with the continuous reactor operated under solventogenesis regime show that steady state establishes with respect to cells and metabolites concentration at dilution rate of about 0.04 h-1

Laser Diagnostics of Hydrodynamics and Gas-Mixing in the Splash Zone of Gas-Fluidized Beds

The hydrodynamic patterns of gas flow associated with bubbles bursting at the surface of gas-fluidized beds have been investigated by means of planar laser induced fluorescence using acetone as diffusive gas tracer. The flow structures generated by the eruption of an isolated bubble have been characterized as a function of bed material size and of bubble injection level

A CFD-VOF based model to address intensive photobioreactor design

The design and optimization of photobioreactors for intensive microalgal cultures are key issues to increase process performance. A model to assess the photosynthetic performance of tubular, bubble column and flat photobioreactors is presented. The model has coupled microalgal light distribution, photosynthesis kinetics and gas-liquid hydrodynamics. A lumped kinetic parameter model of photosynthetic unit (PSU) has been adopted for photosynthetic reactions. The dynamics of a microalgal cell has been described according to the gas-liquid flow of a bubble column. The flow field induced by liquid turbulence and bubbles uprising throughout the photobioreactor have been simulated with ANSYS-FLUENT. A representative domain of the flat photobioreactor has been selected by adopting proper periodic boundary conditions. Turbulence dispersion fields have been assessed by numerical simulations for several bubble size. A random-walk model developed in MATLAB has been adopted to microalgal cells to assess the irradiance experienced by the PSU-cell in the photobioreactors. The photobioreactor performances - expressed in terms of global photosynthesis rate – have been assessed. Irradiance level and biomass concentration have been changed in the range of operating conditions typically adopted for known processes

Bioreactor and bioprocess design issues in enzymatic hydrolysis of lignocellulosic biomass

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Self-Fluidization of Fastly-Moving Granular Gravity Currents with Implication on Pyroclastic Flows

The fast motion of gravity currents of group A granular solids is studied with a focus on the dynamical structure of the frontal zone. The frontal zone of the current is “immobilized” and observed in a fixed frame of reference by letting the current flow inside a rotary drum, big enough to make curvature effects negligible. The establishment of a variety of flow regimes, including intermittent avalanching, periodic “plunging breaking” and permanent fluidization of the granular solids in the frontal zone, can be related to flow conditions and to the nature of the granular solids

Hydrodynamic Characterization of GULF STREAM Circulation in a Pilot Scale Fluidized Bed Combustor

The present study addresses the hydrodynamics of a pilot-scale fluidized bed combustor with a focus on the establishment of "Gulf Stream" circulation patterns as a solids mixing promoter. Time-resolved pressure signals measured at different locations in the bed and in the plenum were analyzed in the time, frequency and phase-space domains. Results were matched against qualitative characterization of fluidization patterns by visual observation of the bed surface

CFD Simulation of Binary Fluidized Mixtures: Effects of Restitution Coefficient and Spatial Discretization Methods

The work focuses on the CFD simulation of fluidized bidisperse solid particles with same density and different size. We successfully predicted the minimum superficial gas velocity required to steadily fluidize the particles by employing a second-order upwind spatial discretization method and a non-ideal value of the restitution coefficient

Butanol production by clostridium acetobutylicum in a series of packed biofilm bed reactors

The reactor design plays a key role in the fermentative production of biobutanol. The high cell concentration that may be reached in confined – biofilm, membrane, recycling - cell reactors offers high conversion rates. To the authors knowledge, the concentration of solvents in the broth from biofilm reactors reported in literature is not particularly high and it negatively affects the successive stages for butanol recovery. The low concentration of solvents in the produced stream is typically due to the inhibitory effect of solvents on the fermentation. Therefore, the butanol bioreactor productivity is as low as the bioreactor behaviour approaches the CSTR limit. The aim of this contribution is to report recent results on the design of a continuous biofilm reactor to optimize the process performances. Clostridium acetobutylicum DSM 792 was adopted for the fermentation process. The conversion was carried out in 4 packed bed reactors (PBRs) connected in series: the first reactor of the series was kept under acidogenesis and the successive reactors were kept under solventogenesis. Tests were carried out feeding the reactor system with solutions bearing glucose. Please click Additional Files below to see the full abstract

Preliminary assessments of microalgae direct transesterification for biodiesel production

Biodiesel is a renewable fuel which can be produced from a wide range of biomasses. In recent years, the possibility to produce it from non-food feedstock such as microalgae has been proposed. It is well known that: i) microalgae may accumulate significant quantities of triglycerides; ii) they are fast-growing photosynthetic organisms capable of sequestering CO2; iii) they can be cultivated in fresh and sea water. Nevertheless the potential of biodiesel production from microalgae, the industrial development still asks investigation. The present contribution reports about recent results of a research program in Napoli on the biodiesel production from microalgae. The study carried out so far have highlighted the success with Stichococcus strains as microalgal feedstocks to produce fatty acid methyl esters (FAMEs) according to traditional processes: lipid extraction coupled with alkaline catalyzed transesterification of lipids (Olivieri et al., 2011, 2013). Results of the direct alkaline transesterification process of Stichococcus bacillaris algal strains are here presented. Tests were carried out under wide intervals of operating conditions: pre-contact time (time of contact of biomass with alkaline methanol at room temperature), catalyst concentration, methanol/biomass weight ratio, reaction temperature, reaction time, biomass water concentration. Effects of operating conditions on FAME yield were assessed