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1.
Direct enthalpy exchange between process utilities
Zorka Novak-Pintarič, Peter Glavič, 2002, professional article

Abstract: This paper presents an application of the improved pinch methodology by performing a simplified exergy analysis in a real-size ammonia plant. Besides the well known pinch technics like composite curves and grand composite curve, the improved approach with the extended grand composite curve was implemented. The latter presents the most energy intensive units in the process separated from the process background as well as the direct transfer of enthalpy from hot utilities to cold utilities. Based on this presentation the synthesis of modified heat exchanger network was performed which results in considerable decrease of utilities demand.
Keywords: chemical engineering, process design, exergy analysis, ammonia plant, pinch methodology, extended hrand composite curve method, enthalpy exchange, distillation column, heat exchanger network
Published in DKUM: 10.07.2015; Views: 1185; Downloads: 81
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Identification of critical points for the design and synthesis of flexible processes
Zorka Novak-Pintarič, Zdravko Kravanja, 2008, original scientific article

Abstract: Optimization problems for the design and synthesis of flexible chemical processes are often associated with highly discretized models. The ultimate goal of this work is to significantly reduce the set of uncertain parameter points used in these problems. To accomplish the task, an approach was developed for identifying the minimum set of critical points needed for flexible design. Critical points in this work represent those values of uncertain parameters that determine optimal overdesign of process, so that feasible operation is assured within the specified domain of uncertain parameters. The proposed approach identifies critical values of uncertain parameters a-priori by the separate maximization of each design variable, together with simultaneous optimization of the economic objective function. During this procedure, uncertain parameters are transformed into continuous variables. Three alternative methods are proposed within this approach: the formulation based on Karush-Kuhn-Tucker (KKT) optimality conditions, the iterative two-level method, and the approximate one-level method. The identified critical points are then used for the discretization of infinite uncertain problems, in order to obtain the design with the optimum objective function and flexibility index at unity. All three methods can identify vertex or even nonvertex critical points, whose total number is less than or equal to the number of design variables, which represents a significant reduction in the problem's dimensionality. Some examples are presented illustrating the applicability and efficiency of the proposed approach, as well as the role of the critical points in the optimization of design problems under uncertainty.
Keywords: chemical processing, process synthesis, flexibility, design, critical point, vertex, nonvertex
Published in DKUM: 01.06.2012; Views: 1499; Downloads: 81
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4.
Synthesis of non-isothermal heat integrated water networks in chemical processes
Miloš Bogataj, Miguel J. Bagajewicz, 2008, original scientific article

Abstract: This paper presents a new approach for the simultaneous synthesis and optimization of heat integrated water networks. A new superstructure for heat exchanger network (HEN) synthesis is proposed. The procedure is based on mixed integer non-linear mathematical programming (MINLP). Four relevant examples are presented to illustrate various aspects of the proposed approach.
Keywords: chemical processing, chemical process design, process water networks, water networks, wastewater minimization, heat integration, MINLP, HEN synthesis, superstructures, process synthesis
Published in DKUM: 31.05.2012; Views: 1708; Downloads: 82
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5.
Analysis of growth models for batch kefir grain biomass production in RC1 reaction system
Marko Tramšek, Andreja Goršek, 2008, original scientific article

Abstract: 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.
Keywords: chemical processing, milk products, kefir grain growth, process parameters, design of experiments, modeling, mathematical models, Gompertz growth model, RC1
Published in DKUM: 31.05.2012; Views: 2344; Downloads: 118
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6.
Multiperiod investment models for the gradual reconstruction of chemical processes
Zorka Novak-Pintarič, Zdravko Kravanja, 2007, original scientific article

Abstract: A multiperiod mixed-integer nonlinear programming (MINLP) model is presented for planning an optimal investment policy for the gradual retrofit of chemical plants over a specified time frame. This approach can be applied when the available funds are insufficient to perform the optimal reconstruction at once. Through gradual improvements, the process progressively approaches its optimum with considerably lower requirements for new capital whilst still exhibiting an attractive increase in economic performance. In the proposed multiperiod problem for gradual retrofit, certain amounts of capital enter into the periods for the gradual increase of equipment, in order to improve the performance of the process, e.g. increase in conversion or energy recovery. This capital may arise from internal sources of the company or can be borrowed. The financial benefits resulting from the improvements at the end of the periods can be reinvested for additional reconstruction over the next periods. In this way, self-sustained capital generation for future reconstruction is achieved, and any additional funds required minimized. The objective function of the proposed problem is formulated as the net present worth of the gradually retrofitted system. This enables several techno-economic analyses to be performed. The proposed multiperiod investment strategies are illustrated by an investment planning example for the retrofit of a heat-exchanger network.
Keywords: chemical processing, process design, process retrofit, investment, modeling, processing, techno-economic criteria
Published in DKUM: 31.05.2012; Views: 1335; Downloads: 117
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7.
Quantitative examination of process parameters during kefir grain biomass production
Andreja Goršek, Marko Tramšek, 2007, short scientific article

Abstract: This article examines the propagation of kefir grains in fresh HTP whole fat cows' milk, with some additions (glucose and bakers yeast). The objective of our work was an experimental determination of the various process parameters relative influence on the propagation and daily kefir grain increase mass, using the Taguchi method for experimental design. The effects of medium temperature, glucose mass concentration, bakers yeast mass concentration and the rotational frequency of the stirrer at four levels were studied. Orthogonal array layout of L16 was selected for the proposed experimental design. All experiments were performed in an automated laboratory reaction calorimeter RC1 (Mettler-Toledo) with the same milk (3.5 % fat). The gravimetric method was used to determine daily kefir grain mass increases. Relative contributions of the proposed influencing process parameters on the daily kefir grains increase mass were estimated by analysis of the variance (ANOVA). The highest increase (51.5 %) was found at the rotational frequency of the stirrer 90 (1/min), at glucose mass concentration 20 g/L, and at mediumtemperature 24 °C. Within the observed range of yeast mass concentrationthis process parameter was found to be insignificant compared to others. The rotational frequency of the stirrer has the highest relative influence on the daily kefir grains increase mass (37.3 %) while glucose mass concentration and medium temperature have lower ones, 18.8 % and 9.9 %, respectively. The remaining fraction represents error influence. The main reason for its relatively high value (34.0 %) is that kefir grains are bulky and awkward to handle. This fact confirms the importance of optimal kefir grains production management.
Keywords: chemical processing, milk products, kefir, kefir grain growth, process parameters, design of experiments, Taguchi method, RC1
Published in DKUM: 31.05.2012; Views: 2202; Downloads: 42
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8.
Review of sustainability terms and their definitions
Peter Glavič, Rebeka Kovačič Lukman, 2007, original scientific article

Abstract: Terminology in the field of sustainable development is becoming increasingly important because the number of terms continues to increase along with the rapid increase in awareness of the importance of sustainability. Various definitions of terms are used by different authors and organizations, for example, green chemistry, cleaner production, pollution prevention, etc. The importance of this topic has stimulated research into the problems of clarifying ambiguity and classifying terms used in the sustainability field. This paper provides results of the literature survey and summarizes the definitions of the terms, focusing on the environmental engineering field. In some cases, it proposes an improved definition. A hierarchical classification of the terms and their relationships has been based on a layer format that is presented graphically.
Keywords: chemical process design, sustainability, environmental protection, cleaner production, terminology, definitions, classification
Published in DKUM: 31.05.2012; Views: 1796; Downloads: 103
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9.
Design of the optimal total site heat recovery system using SSSP approach
Andreja Goršek, Peter Glavič, Miloš Bogataj, 2006, original scientific article

Abstract: Site expansions or changes in production capacities are usually related with changes of utilities demands andžor utility system design. Despite several available and well established techniques for process synthesis and integration, very often, changes in process designs are made on the basis of intuition and experiences of engineers. In this paper possibilities of rational energy consumption and energy integration in an existing site for production of specialty chemicals were studied. On the basis of real process parameters and computer simulation results energy integration was re-examined.Total site analysis using modified Site Sink Source Profiles, which gives a profound insight into the site utility system configuration, heating-cooling demands and cogeneration design was performed. The existing site was found to be very well designed. With only few modifications additional 9% of hot utilities and 5% of cold utilities savings are possible.
Keywords: chemical engineering, process design, optimization, heat integration, cogeneration, pinch method, energy retrofit
Published in DKUM: 30.05.2012; Views: 2299; Downloads: 83
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10.
Heat integration in a speciality product process
Majda Krajnc, Anita Kovač Kralj, Peter Glavič, 2006, original scientific article

Abstract: The essence of effective process designing is to use methods which are efficient to engineers in practice and not only to scientists. The proposed design procedure is composed of two steps: conceptual one and optimization one. At the conceptual step, pinch design analysis is used. In the optimization step pinch analysis and mixed-integer nonlinear programming method are applied. In the case study analysed, a speciality product is to beproduced in continuous chemical process with a capacity which causes smallerheat flow rates and needs smaller heat exchanger areas than usual. Therefore, an equation for cost estimation of heat exchangers with areas smaller than 7 m2 was developed and used in the optimization procedure. Using thermodynamic pinch analysis and mathematical programming method, the heat integrated structures were synthesized and compared with the base process flowsheet. Finally, the optimal structure was determined.
Keywords: načrtovanje procesov, načrtovanje procesov, ekonomska analiza, prenos toplote, optimizacija, chemical process design, economic analysis, heat integration, optimization
Published in DKUM: 30.05.2012; Views: 1997; Downloads: 64
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