oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Biochemical Engineering Parameters for Hydrometallurgical Processes: Steps towards a Deeper Understanding  [PDF]
K. Kundu,A. Kumar
Journal of Mining , 2014, DOI: 10.1155/2014/290275
Abstract: Increasing interest in biomining process and the demand for better performance of the process has led to a new insight toward the mining technologies. From an engineering point of view, the complex network of biochemical reactions encompassed in biomining would best be performed in reactors which allow a good control of the significant variables, resulting in a better performance. The subprocesses are in equilibrium when the rate of particular metal ion; for example, iron turnover between the mineral and the bacteria, is balanced. The primary focus is directed towards improved bioprocess kinetics of the first two subprocesses of chemical reaction of the metal ion with the mineral and later bacterial oxidation. These subprocesses are linked by the redox potential and controlled by maintenance of an adequate solids suspension, dilution rate, and uniform mixing which are optimised in bioreactors during mining operations. Rate equations based on redox potential such as ferric/ferrous-iron ratio have been used to describe the kinetics of these subprocesses. This paper reviews the basis of process design for biomining process with emphasis on engineering parameters. It is concluded that the better understanding of these engineering parameters will make biomining processes more robust and further help in establishing it as a promising and economically feasible option over other hydrometallurgical processes worldwide. 1. Introduction Biomining is gaining importance as a unit process which involves biological organisms in mineral extraction industries worldwide. With the decreasing high grade ore reserves and increased concern regarding the effect of mining on the environment, biomining technology, which was nevertheless age old deserted technique, is now being developed as a main process in the mining industry to meet the demand [1]. Another important aspect is the feasibility of biomining technologies to treat ores deposits with complex mineralogy, which could be difficult to treat by conventional methods [2]. Besides, the most attractive feature of biomining is economic feasibility compared to other competitive techniques [2]. Gahan et al. [2] comparatively analysed how gold and copper biomining operations played a role with the increase or decrease in metal pricing over time. Their analysis indicated that most biohydrometallurgical innovations have been commercially implemented during leaner times [3]. Economic factors such as eliminations of net Smelter Royalties associated with smelting and refining and possibility of the use bioleaching for on-site acid
Biofilm reactors for industrial bioconversion processes: employing potential of enhanced reaction rates
Nasib Qureshi, Bassam A Annous, Thaddeus C Ezeji, Patrick Karcher, Ian S Maddox
Microbial Cell Factories , 2005, DOI: 10.1186/1475-2859-4-24
Abstract: Biochemical reactors play an important role in the biochemical industry as the rate of reaction, ease, and length of reactor operation affect reactor productivities and hence process economics [1,2]. In order to employ a most appropriate reactor for an industrial operation, reaction rate should be high and the reactor configuration should be simple. Under optimized parameters such as pH, temperature, substrate, and medium components, reaction rate can be increased by increasing cell mass concentration in the reactor. There are two methods commonly used for increasing cell mass concentration inside the reactor; first, use of a permeable membrane to retain cells; and the other, use of immobilized cell technique. Membrane reactors allow passing of liquid, substrate, and product out of the reactor while retaining the cells. In these reactors, high cell concentrations can be achieved [3]. Unfortunately, for some processes such as waste water treatment, these reactors are not preferred due to their high cost and problems with fouling. Other processes where the relatively high cost of these reactors does not allow their use include production of large volume, low cost chemicals such as vinegar or acetic acid.Other types of reactors that offer high reaction rates are immobilized cell reactors [4]. In these reactors, high cell concentrations are achieved by fixing them on various supports. Cells can be immobilized by three different techniques; namely, adsorption, entrapment, and covalent bond formation. Entrapment and covalent bond formation require use of chemicals that add to the cost of production and perhaps restrict further propagation or increase in cell concentration inside the reactor. The third technique is of natural origin as cells "adsorb/and adhere" to the support naturally and firmly [4-6]. This technique is called "adsorption" and has been used extensively in the literature to adsorb microbial cells. Table 1 shows a comparison of these techniques with the mem
Nuclear processes in magnetic fusion reactors with polarized fuel  [PDF]
Michail P. Rekalo,Egle Tomasi-Gustafsson
Physics , 2000,
Abstract: We consider the processes $d +d \to n +{^3He}$, $d +{^3He} \to p +{^4He}$, $d +{^3H} \to n +{^4He}$, ${^3He} +{^3He}\to p+p +{^4He}$, ${^3H} +{^3He}\to d +{^4He}$, with particular attention for applications in fusion reactors. After a model independent parametrization of the spin structure of the matrix elements for these processes at thermal colliding energies, in terms of partial amplitudes, we study polarization phenomena in the framework of a formalism of helicity amplitudes. The strong angular dependence of the final nuclei and of the polarization observables on the polarizations of the fuel components can be helpful in the design of the reactor shielding, blanket arrangement etc..We analyze also the angular dependence of the neutron polarization for the processes $\vec d +\vec d \to n +{^3He}$ and $\vec d +\vec {^3H} \to n +{^4He}$.
OPTIMAL ESTIMATION OF SOME OF THE SPACE-TIME PROCESSES IN NUCLEAR REACTORS  [cached]
Andrzej Mas?owski
Bulletin of the Institute of Heat Engineering , 1971,
Abstract: Problem of optimal state function estimation of some of the space-time processes in nuclear reactors - particularly in power reactors - has been considered.General mathematical model of dynamics and observations of these processes, useful for the problem being under consideration has been given-as well as the concise description of proper formulation of this problem.General quadratic estimation performance index of some nuclear processes has been propesed and discussed.Basing on the above mentioned mathematical model and proposed quadratic estimation performance index the problem of optimal state function estimation has been formulated.
Biomining: an Established and Dynamic Biotechnology  [cached]
DAVID BARRIE JOHNSON
Microbiology Indonesia , 2012, DOI: 10.5454/mi.6.4.7
Abstract: “Biomining” is generic term to describe the application of living organisms to extract and recover metals from mineral ores and waste materials. Since its inception as a crude technology (“dump leaching”) for treating “run of mine” rocks and boulders that contained too little copper to be processed by conventional processing, engineering options used in biomining have become increasingly refined and diverse. Currently, microbiological processing is used to extract both base metals (copper, and to lesser extents nickel and zinc) and precious metals (mostly gold) from ores and mineral concentrates in heaps and stirred-tank bioreactors, as well as in dumps. Recent developments include the demonstration, at pilot-scale, of indrect leaching of zinc sulfide concentrates, in which the biological step (regeneration of ferric iron) is carried out independently of abiotic mineral oxidation, and using microbiologically-mediated reductive dissolution of ferric iron minerals to liberate nickel from lateritic ores.
Process Modelling of Chemical Reactors: Zero- versus Multi-dimensional Models
Bj?rn H. Hjertager
Modeling, Identification and Control , 1997, DOI: 10.4173/mic.1997.1.2
Abstract: Trends in modelling of flow processes in the chemical reactors are presented. Particular emphasis is given to models that use the multi-dimensional multi-fluid techniques. Examples are given for both gas/liquid as well as gas/particle reators.
Use of tower reactors for continuous ethanol production
Viegas, M.C.;Andrietta, S.R.;Andrietta, M.G.S.;
Brazilian Journal of Chemical Engineering , 2002, DOI: 10.1590/S0104-66322002000200012
Abstract: the purpose of this work was to develop a continuous fermentation system operating with a tower reactor using some flocculent yeast strains isolated from an industrial process. the strain was an used in the trial of the proposed system, composed of two serial glass tower reactor. the effects of the following variables were studied on the yield and productivity of the system: total reducing sugar (trs), concentration in feeding, recycle flow in the second reactor, residence time and diameter/height ratio of the reactors. it was observed that the trs concentration in feeding and residence time is the variables that interfere most with the productivity of the system. yield was not affected by any of the variables within the range of values studied. all trials were performed according to a factorial experimental design (making up a total of 19 trials) and the results were evaluated by response surface.
Use of tower reactors for continuous ethanol production  [cached]
Viegas M.C.,Andrietta S.R.,Andrietta M.G.S.
Brazilian Journal of Chemical Engineering , 2002,
Abstract: The purpose of this work was to develop a continuous fermentation system operating with a tower reactor using some flocculent yeast strains isolated from an industrial process. The strain was an used in the trial of the proposed system, composed of two serial glass tower reactor. The effects of the following variables were studied on the yield and productivity of the system: total reducing sugar (TRS), concentration in feeding, recycle flow in the second reactor, residence time and diameter/height ratio of the reactors. It was observed that the TRS concentration in feeding and residence time is the variables that interfere most with the productivity of the system. Yield was not affected by any of the variables within the range of values studied. All trials were performed according to a factorial experimental design (making up a total of 19 trials) and the results were evaluated by response surface.
THREE-DIMENSIONAL MATHEMATICAL MODELING OF TRANSPORT PROCESSES IN CVD REACTORS
HE Youduo,Baotou Institute of Iron,Steel Technology,Baotou,ChinaYSAHAI,The Ohio State University,USA,
Y.
,SAHAI

金属学报(英文版) , 1989,
Abstract: A mathematical model to represent the fluid flow, temperature distribution and mass transfer in CVD reactors has been developed. The model is used to predict the velocity, temperature, and molar concentration profiles in the tapered annulus of a reactor for silicon deposition from SiCl_4 in H_2. Results of the investigation contribute to the understanding of the transport pro- cesses involved in such a system. The model can also be used for optimizing the design parameters, such as inlet flow rate, susceptor tilt angle, etc.
Dynamic modelling of catalytic three-phase reactors for hydrogenation and oxidation processes  [cached]
Salmi T.,W?rn? J.,Toppinen S.,R?nnholm M.
Brazilian Journal of Chemical Engineering , 2000,
Abstract: The dynamic modelling principles for typical catalytic three-phase reactors, batch autoclaves and fixed (trickle) beds were described. The models consist of balance equations for the catalyst particles as well as for the bulk phases of gas and liquid. Rate equations, transport models and mass balances were coupled to generalized heterogeneous models which were solved with respect to time and space with algorithms suitable for stiff differential equations. The aspects of numerical solution strategies were discussed and the procedure was illustrated with three case studies: hydrogenation of aromatics, hydrogenation of aldehydes and oxidation of ferrosulphate. The case studies revealed the importance of mass transfer resistance inside the catalyst pallets as well as the dynamics of the different phases being present in the reactor. Reliable three-phase reactor simulation and scale-up should be based on dynamic heterogeneous models.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.