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21.
Analysis of growth models for batch kefir grain biomass production in RC1 reaction system
Marko Tramšek, Andreja Goršek, 2008, izvirni znanstveni članek

Opis: This work describes the statistical analysis of three mathematical models, modified for describing the kefir grain biomass growth curve. Experimental data of time-dependent kefir grain mass increase were used. The propagation was performed in RC1 batch reaction system under optimal bioprocess parameters (temperature, rotational frequency of stirrer, glucose mass concentration) using traditional cultivation in fresh, high-temperature, pasteurized whole fat cow's milk. We compared values of biological parameters obtained by applying the nonlinear regression of experimental data in logistic, Gompertz and Richards models. The most statistically appropriate model was determined using the seven statistical indicators. We established that the kefir grain biomass growth curve during batch propagation under optimal bioprocess conditions can be most successfully described using the Gompertz growth model.
Ključne besede: chemical processing, milk products, kefir grain growth, process parameters, design of experiments, modeling, mathematical models, Gompertz growth model, RC1
Objavljeno: 31.05.2012; Ogledov: 1830; Prenosov: 69
URL Povezava na celotno besedilo

22.
Kefir grains production - An approach for volume optimization of two stage bioreactor system
Andreja Goršek, Marko Tramšek, 2008, izvirni znanstveni članek

Opis: The main objective of the present study was to design a continuous two-stage bioreactor system for kefir grains production. Based on the experimental data of time-depended kefir grain mass increase and average pH profile during kefir grains batch propagation, parameters of predictive growth and exponential pH models were initially estimated. Afterwards, the non-linear programming (NLP) optimization problem for estimating the optimal volumes of two unequal in series connected continuously stirred tank bioreactors (CSTB) has been developed. The NLP problem is based on criterion of minimal total holding time (MTHT), kefir grain mass balances in CSTB and parameters of the growth and pH models. The results showed that novel kefir grains production plant with two-stage continuous operation, at capacity, qm,KG,pr=3 kgh-1 and conversion, Xo,2=0.980, would primarily require investment in two CSTB with V1=5.93 m3 and V2=5.62 m3, respectively. Technological and economical authorization for a two-stage continuous bioreactor system was mainly confirmed with a more than five times lower total bioreactor volume compared to one-stage plant.
Ključne besede: chemical processing, bioprocesses, milk products, kefir grains production, bioreactor design, modeling, optimization
Objavljeno: 31.05.2012; Ogledov: 1891; Prenosov: 76
URL Povezava na celotno besedilo

23.
In-situ investigation of sucrose hydrolysis - successful link between design of experiment, RC1 and reactIR system
Katja Zajšek, Andreja Goršek, 2008, izvirni znanstveni članek

Opis: The main purpose of this work was combining the modern laboratory equipment (RC1 reaction calorimeter and ReactIRTMiC10 reaction analysis system) and the concept of the Taguchi fs design of experiment to determine the relative influence of important process parameters affecting the sucrose hydrolysis. The reaction was catalyzed by strong acidic cation-exchange resin Amberlite IR-120 in H+ form. Four process parameters, including reaction temperature (.), sucrose mass concentration (fÁS), catalyst mass concentration (fÁC) and the rotational frequency of the stirrer (fm) at four levels were considered in this study. Relative contributions of the proposed influencing process parameters on hydrolysis time were estimated by analysis of the variance (ANOVA). The results showed that . had a substantial effect on the reaction time (78,3 %), the fm and fÁC had a smaller ones (7,9 % and 6,4 %, respectively), meanwhile the remain fraction to 100 % represents error (7,4 %). The optimum conditions, where the time required for complete sucrose hydrolysis would be the shortest, are: .= 79 Ključne besede: sucrose hydrolysis, catalyst, Taguchi method, in-situ FTIR, reaction calorimeter RC1
Objavljeno: 31.05.2012; Ogledov: 1309; Prenosov: 20
URL Povezava na celotno besedilo

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Production of unique naturally immobilized starter : a fractional factorial design approach towards the bioprocess parameters evaluation
Andreja Goršek, Marko Tramšek, 2011, samostojni znanstveni sestavek ali poglavje v monografski publikaciji

Objavljeno: 01.06.2012; Ogledov: 1633; Prenosov: 63
URL Povezava na celotno besedilo

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Experimental design of crystallization processes using Taguchi method
Miran Hvalec, Andreja Goršek, Peter Glavič, 2004, izvirni znanstveni članek

Opis: Crystallization has become one of the most important unit operation in the chemical industries. The need to reduce the time from product discovery to market introduction is an inherent concern. In order to achieve the prescribedproduct quality characteristics, the process of engineering experimentation has to be optimized. Therefore, an experimental design method for crystallization processes is presented in this paper. Initially, the standardized Taguchi method was used to plan a minimum number of experiments. After identifying the working levels of the design factors and the main performance characteristics of the product under study, the method can be successfully applied to the crystallization processes. The simultaneous variations of the main crystallization parameters and their interactions were investigated using orthogonal array technique. A statistical analysis of 'signal-to-noise' ratio was followed by performing a variance analysis. After developing some special criteria, which depend on performance objectives, the optimal levels of the design factors were determined. Crystallization of $KNO_3$ with desirable particle size as a performance characteristic was used to illustrate the design procedure. The effects of rotational frequency of the stirrer, linear cooling rate and added admixture on final particle size were studied. In order to keep the selected parameters constant during the experiment and to ensure reproduction of entire experiment the automated reaction calorimeter RC1 was used.
Ključne besede: crystallization, particle size, Taguchi method
Objavljeno: 01.06.2012; Ogledov: 1427; Prenosov: 52
.pdf Celotno besedilo (701,22 KB)
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29.
Process integration of a steam turbine
Andreja Goršek, Peter Glavič, 2003, izvirni znanstveni članek

Opis: Cogeneration consists of combined production of electricity and heat using only one fuel which allows remarkable energy savings in comparison with a system producing electricity and heat separately. The possibilities for integrating a cogeneration system with chemical processes has been studied in this paper. Improvement in the systems where high temperature streams exist can be achieved by direct integration of steam turbine with them. Hot reactor utility was used instead of fuel to produce electricity and steam for further process heat requirements. A thermodinamics oriented approach to identify and preliminary design a cogeneration plant that completely satisfies process heat and power demand is highlighted. Pinch analysis with extended grand composite curve enables rational choice of utilities. The acrylic acid process was used to illustrate the procedure proposed. Economic attractiveness based on payback time and net present worth indicated that the steam turbine based cogeneration system would yield return period of less than 3 months, showing that the investment in cogeneration could be of interest for this plant.
Ključne besede: process energetics, efficient energy use, process industry, cogeneration systems, acrylic acid, technological processes
Objavljeno: 01.06.2012; Ogledov: 1036; Prenosov: 61
URL Povezava na celotno besedilo

30.
Equilibrium limited reactions
Darja Pečar, Andreja Goršek, 2012, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: estrification, limited reactions, kinetic studies
Objavljeno: 10.07.2015; Ogledov: 653; Prenosov: 19
URL Povezava na celotno besedilo

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