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AbstractThe aim of this work is to investigate and model the simultaneous adsorption of Cu(II), Cd(II), and Pb(II) in the presence and absence of humic acid on kaolinite‐based clays. The preliminary capacity estimation of clays for metal was made with the use of a modified Langmuir approach, and adsorption data collected at various pH were processed using the FITEQL 3.2 computer program to establish the model. The three types of surface sites responsible for adsorption were considered to be the permanent charge sites X, and variable charge sites comprised of S1OH silanol groups and S2OH aluminol groups of kaolinite‐based clays. Heavy metal cations were assumed to bind to the surface in the form of outer sphere and inner sphere monodentate complexes. When humic acid was added, divalent metal ion adsorption was modeled using a multisite binding model by the aid of FITEQL 3.2. Since the stability of the ternary surface complexes in the presence of humic acid was higher than that of the corresponding binary heavy metal cation complexes, the adsorption versus pH curves were steeper (and distinctly S‐shaped) compared with the tailed curves observed in binary clay‐metal ion systems, probably due to the fact that humic acid‐coated kaolinite essentially constituted the active surface for metal sorption. Although competitive metal adsorption from (metal ions mixture+humate) solutions was generally lower than those from individual metal ion solutions, Cd2+, being the metal ion with the highest affinity toward permanent charge sites, was the least affected ion at relatively low pH from competitive adsorption. © 2008 American Institute of Chemical Engineers Environ Prog, 2009

The present article deals with an exergy analysis of a process under development for the gasification of biomass in supercritical water (supercritical water gasification, SCWG). This process is aimed at generating hydrogen out of the biogenic feedstock sewage sludge. The principle of the process is based on making use of the modifications of specific physical and chemical properties of water above the critical point (T=374°C, p=221 bar). These properties allow for a nearly complete conversion of the organic substance contained in the feed material into energy-rich fuel gases, containing hydrogen, carbon dioxide and methane. Based on a steady-state model of the process, exergy flow rates are calculated for all components and a detailed exergy analysis is performed. From the exergetic variables, options to improve the individual plant components as well as the overall plant are derived. The components with the highest proportion of exergy destruction in the complete process are identified and possibilities of improving them and the complete system in order to increase the overall efficiency are demonstrated. The combustion chamber necessary for heat supply is found to be the component with the highest proportion of exergy destruction of the complete plant. Moreover, the components of air preheater, reactor contribute significantly to the exergy destruction of the complete system. Copyright © 2006 John Wiley & Sons, Ltd.

Abstract Biomass and low rank fuel gasification is a very promising process for conversion of fuels to a high quality fuel (Syngas). In the present paper research work on the design of a high pressure entrained flow gasifier for biomass based fuels is shown. Atomization quality of twin fluid nozzles as a function of gas velocity and reactor pressure is analyzed. The developed and characterized atomizers are used in an atmospheric entrained flow gasifier, to detect the influence of spray quality on gasification process. Furthermore, a CFD model of a high pressure entrained flow gasifier was developed. A significant influence of gas velocity and reactor pressure on Sauter Mean Diameter (SMD) of the produced spray was detected. Increasing gas velocity decreases the SMD, whereas increasing reactor pressure leads to the increase in drop diameter. An influence of SMD on gasification process was observed from organic carbon and methane concentration measurements as well as from the radial temperature profiles at various positions along the reactor centerline. Finally the CFD model of high pressure entrained flow gasification of biomass based slurries shows a very pronounced influence of drop size distribution on gasification quality.

Abstract Biomass is a sustainable alternative to fossil energy carriers which are used to produce fuels, electricity, chemicals, and other goods. At the moment, the main biobased products are obtained by the conversion of biomass to basic products like starch, oil, and cellulose. In addition, some single chemicals and fuels are produced. Presently, concepts of biorefineries which will produce a multitude of biomass-derived products are discussed. Biorefineries are supposed to contribute to a more sustainable resource supply and to a reduction in greenhouse gas emissions. However, biobased products and fuels may also be associated with environmental disadvantages due to, e.g. land use or eutrophication of water. We performed a Life Cycle Assessment of a lignocellulose feedstock biorefinery system and compared it to conventional product alternatives. The biorefinery was found to have the greatest environmental impacts in the three categories: fossil fuel use, respiratory effects, and carcinogenics. The environmental impacts predominantly result from the provision of hydrochloric acid and to a smaller extent also from the provision of process heat. As the final configuration of the biorefinery cannot be determined yet, various variants of the biorefinery system were analysed. The optimum variant (acid and heat recoveries) yields better results than the fossil alternatives, with the total environmental impacts being approx. 41% lower than those of the fossil counterparts. For most biorefinery variants analysed, the environmental performance in some impact categories is better than that of the fossil counterparts while disadvantages can be seen in other categories.

This research investigates the flight behavior of refuse-derived fuel (RDF) in a drop shaft using Computer Vision to obtain statistical data on the aerodynamic properties of the particles. Methods to determine 3D geometry models of complex-shaped particles by photogrammetry and to obtain time resolved particle positions and velocities are described. Furthermore, an approach to obtain the frequency distribution of drag and lift coefficients from photogrammetric analysis and drop shaft experiments is presented. The image evaluation is based on algorithms of the open-source libraries OpenCV, COLMAP as well as MeshLab and Open3D. The precision of the system is validated employing model particles with known geometry. The 3D particle models overestimate the particle surface area by 4.58 %, the position detection works with a mean deviation of 2.73 %. The average sink rate is calculated with an accuracy of 4.87 % and the drag coefficient with an accuracy of 2.08 %. Finally, the frequency distribution of four RDF fractions, namely, textiles, cardboard, 3D plastic particles and 2D plastic foils are presented.

The sandwich-like nickel/palladium/carbon electrodes exhibiting ability to absorb hydrogen in alkaline solution are presented. Electrodes were prepared by successive deposition of palladium and polyaniline layers on nickel foam substrate followed by heat treatment to give Ni/Pd/C electrode. It was shown that thermal conversion of polymer into carbon layer and subsequent thermal activation of carbon component bring about the modification of the mechanism of reversible hydrogen sorption. It was proven that carbon layer, interacting with Pd catalyst, plays a considerable role in the process of hydrogen storage. In the other series of experiments, Pd particles were dispersed electrochemically on carbon coating leading to Ni/C/Pd system. The adding of the next carbon layer resulted in Ni/C/Pd/C electrodes. Electrochemical properties of the electrodes depend on both the sequence of Pd and C layers and the preparation/activation of carbon coating. Electrochemical behavior of sandwich-like electrodes in the reaction of hydrogen sorption/desorption was characterized in 6 M KOH using the cyclic voltammetry method and the results obtained were compared to those for Ni/Pd electrode. The anodic desorption of hydrogen from electrodes free and containing carbon layer was considered after the potentiodynamic as well as potentiostatic sorption of hydrogen. The influence of the sorption potential and the time of rest of electrodes at a cut-off circuit on the kinetics of hydrogen recovery were examined. The results obtained for Ni/Pd/C electrodes indicate that the displacement of hydrogen between C and Pd phase takes place during the rest at a cut-off circuit. Electrodes containing carbon layer require longer time for hydrogen electrosorption. On the other hand, the presence of carbon layer in electrodes is advantageous because a considerable longer retention of hydrogen is possible, as compared to Pd/Ni electrode. Hydrogen stored in sandwich-like electrodes can instantly be recovered upon starting the anodic process.

Abstract The objective of this study was to gain further insight into the characteristic behavior of reaction systems for establishment of intrinsic and effective particle gasification kinetics. A wood-derived char was subjected to the carbon dioxide-containing atmospheres of four different reaction systems: a thermogravimetric analyzer (TGA), a fluidized-bed reactor (FBR), a fixed-bed reactor (FFB) and a drop-tube reactor (DTR). All systems contained the same CO2 partial pressure of 800 mbar at atmospheric pressure. A temperature span from 700 to 1600 °C and residence times from 200 ms to over 8 h were investigated. Reactivities spanning five orders of magnitude were observed. The gasification experiments resulted in the identification of four fundamentally different reaction domains; two were classified as true particle behavior, while the observed reaction rates of the other two domains are mainly dominated by the characteristics of the reaction system applied. The domains were referred to as: chemical control, particle diffusion control, bed diffusion control, and system response control. Within the present work, the occurrence of these reaction domains is discussed in regard to the physical nature of the experiments, and implications towards the measurement of reliable particle kinetics are formulated.

The hydrothermal gasification is a promising process to produce hydrogen from biomass with high water content. In a lot of cases, this biomass may contain proteins, for example, in residues from the food industry or sewage sludge. In Part I of this serial, experiments on hydrothermal gasification of protein containing biomass (zoo mass) have been reported. This biomass produces lower gas yields than biomass originating exclusively from plants (phyto mass). To understand these findings, experiments with model compounds are necessary. Here, such experiments with model compounds in a tubular and a batch reactor are described. The model system for the phyto mass is glucose with a potassium salt, and the model system for the zoo mass is glucose, potassium salt, and the amino acid alanine. The model systems show a lower gas yield in the presence of alanine. So the presence of alanine in the model system has a similar effect to the presence of proteins in biomass. Additionally, the gas composition and the concentration of selected key compounds are slightly changed by alanine addition. Likely, consecutive products of carbohydrate and protein degradation react with each other. In such Maillard reactions, free radical scavengers might be formed, reducing the reaction rate of free radical chain reactions that are highly relevant for gas formation. Therefore, the gas yield is lower in the presence of proteins or amino acids compared with systems without these compounds. In addition, experiments with real biomass in a batch reactor were reported to verify the assumption of Maillard products reducing free radical reactions. As an example, the addition of urea to phyto mass leads to a decrease of the gas yield to a value similar to that found for zoo mass.