High Solids Concentrations (high + solid_concentration)

Distribution by Scientific Domains

Selected Abstracts

Hydrodynamic behaviour of a full-scale anaerobic contact reactor using residence time distribution technique

Isabel Capela
Abstract BACKGROUND: The knowledge of the fluid pattern of full-scale anaerobic reactors is of fundamental importance for the optimisation of biological processes. High solids concentrations often lead to inefficient mixing conditions, which may reduce treatment capacity due to heterogeneity within the biomass. RESULTS: The hydrodynamic characteristics of a full-scale anaerobic contact reactor treating evaporator condensate from a sulphite pulp mill were investigated. The methodology applied was based on the residence time distribution (RTD) technique using lithium as a tracer. Different non-ideal hydraulic flow models were tested and the best model fitting RTD data was the Gamma distribution model with by-pass. It was concluded that the full-scale bioreactor presents a good degree of mixing with about 22% of non-effective volume due to the presence of high amounts of inorganic materials. CONCLUSION: As a result of this study it was possible to both improve the full-scale bioreactor performance and decrease the running costs by changes in the plant operation strategies which allowed reduction of the huge amount of inorganic materials contributing to the non-effective volume. The methodology is simple and results from a unique RTD experiment and confirms the importance of considering mixing characteristics when assessing complex full-scale treatment processes. Copyright © 2009 Society of Chemical Industry [source]

Simultaneous saccharification and co-fermentation of paper sludge to ethanol by Saccharomyces cerevisiae RWB222.

Part II: Investigation of discrepancies between predicted, observed performance at high solids concentration
Abstract The simultaneous saccharification and co-fermentation (SSCF) kinetic model described in the companion paper can predict batch and fed batch fermentations well at solids concentrations up to 62.4,g/L cellulose paper sludge but not in batch fermentation at 82.0,g/L cellulose paper sludge. Four hypotheses for the discrepancy between observation and model prediction at high solids concentration were examined: ethanol inhibition, enzyme deactivation, inhibition by non-metabolizable compounds present in paper sludge, and mass transfer limitation. The results show that mass transfer limitation was responsible for the discrepancy between model and experimental data. The model can predict the value of high paper sludge SSCF in the fermentation period with no mass transfer limitation. The model predicted that maximum ethanol production of fed-batch fermentation was achieved when it was run as close to batch mode as possible with the initial solids loading below the mass transfer limitation threshold. A method for measuring final enzyme activity at the end of fermentation was also developed in this study. Biotechnol. Bioeng. 2009; 104: 932,938. © 2009 Wiley Periodicals, Inc. [source]

The effect of particle shape on pipeline friction for newtonian slurries of fine particles

Jason Schaan
Abstract Experiments have been conducted to assess the effect of particle shape on pipeline friction in turbulent flow, using laboratory pipelines of nominal diameter 50 mm and 150 mm. The experiments were intended to examine the extent to which a fluid model is appropriate for slurries of this type, especially at high solids concentrations. The experiments confirm that fluid friction at low and moderate solids concentrations is proportional to slurry density, with particle shape being of minor importance. At high solids concentrations, additional increases in friction are observed and these depend upon the ratio of the solids concentration to the maximum settled concentration. Although this friction increase is qualitatively similar to that which would result from increased slurry viscosity, the evidence suggests that particle-wall contact is the mechanism. However, the transition from turbulent to laminar flow indicates that an effective viscosity should be used in calculating critical Reynolds numbers. Afin d'évaluer l'effet de la forme des particules sur le frottement dans les pipelines en régime turbulent, des expériences ont été menées avec des pipelines de laboratoire d'un diamétre nominal de 50 mm et de 150 mm. Le but de ces expériences était de voir jusqu'à quel point un fluide modèle est approprié pour ce type de suspensions, en particulier à de fortes concentrations de solides. Les expériences confirment que le frottement du fluide à des concentrations de solides faibles ou moyennes est proportionnel à la masse volumique des suspensions, la forme des particules étant de peu d'importance. À de fortes concentrations de solides, on observe un accroissement supplémentaire du frottement qui est lié au rapport entre la concentration de solides et la concentration sédimentée maximum. Bien que cette augmentation du frottement soit d'un point de vue qualitatif semblable à ce qu'il réulterait d'une viscosité accrue des suspensions, selon toutes les apparences le mécanisme réside dans le contact particules-paroi. Cependant, la transition de l'écoulement turbulent à l'écoulement laminaire indique qu'une viscosité effective devrait ##etre utilisée dans le calcul des nombres de Reynolds critiques. [source]

Nanoparticle Production with Stirred-Media Mills: Opportunities and Limits

C. Knieke
Abstract Nanoparticles can be produced by wet grinding in stirred-media mills. In the lower nanometer range a true grinding limit exists, where the transferred energy from the grinding media is no longer sufficient to induce further breakage of the particles even after stressing events with high stress energies. Variations in process conditions lead to the conclusion that the grinding limit is hardly affected by most of the investigated process parameters. However, at high solids concentrations and/or small particle sizes, a drastic increase in suspension viscosity occurs, which leads to a dampening of the grinding media motion and to a reduction in the transferred stress energy. Hence, the rheological behavior can limit the grinding process, and a viscous dampening-related grinding limit can be reached prior to the true grinding limit. [source]