Heat integration in a speciality product processMajda Krajnc
, Anita Kovač Kralj
, Peter Glavič
, 2006, izvirni znanstveni članek
Opis: 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.
Ključne besede: načrtovanje procesov, načrtovanje procesov, ekonomska analiza, prenos toplote, optimizacija, chemical process design, economic analysis, heat integration, optimization
Objavljeno: 30.05.2012; Ogledov: 1066; Prenosov: 4
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The contents of Cu, Mn, Zn, Cd, Cr, and Pb at different stages of the winemaking processMetka Slekovec
, Marjan Veber
, Janja Kristl
, 2003, izvirni znanstveni članek
Opis: In samples taken during different stages of winemaking process (from grapes, crushed grapes, pressed pomace, must deposit, deposit of lees, must before and after clarification and wine) the Cu, Mn and Zn contents were determined by flame atomic absorption spectrometry (FAAS) and the Cd, Pb and Cr contents were determined by electrothermal atomic absorption spectrometry (ETAAS). Grapes, crushed grapes, pressed pomace, must deposit and deposit of lees were microwave digested with nitric acid, hydrofluoric acid and hydrogen peroxide solution, while for must and wine no special treatments were necessary. The highest contents of Cu, Mn, Zn, Pb, Cd and Cr were determined in the pressed pomace, lees, and in white grape varieties also in must deposit. Mean values obtained of dry weight (pressed pomace, lees, must deposit) were 63 mg/kg, 300 mg/kg, 184 mg/kg for Cu, 11 mg/kg, 15 mg/kg, 134 mg/kg for Mn, 14 mg/kg, 35 mg/kg, 17 mg/kg for Zn, 0.3 mg/kg, 0.5 mg/kg, 0.6 mg/kg for Pb, 0.5 mg/kg, 1.0 mg/kg, 1.8 mg/kg for Cr, 15.4 µg/kg, 24.4 µg/kg, 13.0 µg/kg for Cd. The Cu content was decreasing from the grapes to the bottled wine, whereas the Mn, Zn, Cd, Cr and Pb contents in the bottled wine were higher than in musts in all investigated white and red grape varieties. In ten wine samples the following contents were determined: Cu; mean 0.12 mg/L (range: 0.06-0.30 mg/L), Mn; mean 1.04 mg/L (range: 0.60-1.78 mg/L), Zn; mean 0.50 mg/L (range: 0.13-1.03 mg/L), Cd; mean 0.34 µg/L (range: 0.08-1.04 µg/L), Cr; mean 17.0µg/L (range: 5.2-25.1 µg/L) and Pb; mean 25.3 µg/L (range: 16.4-37.8 µg/L).
Ključne besede: viticulture, chemical processes, chemical elements, chemical analysis
Objavljeno: 10.07.2015; Ogledov: 456; Prenosov: 18
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Direct enthalpy exchange between process utilitiesZorka Novak-Pintarič
, Peter Glavič
, 2002, strokovni članek
Opis: 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.
Ključne besede: chemical engineering, process design, exergy analysis, ammonia plant, pinch methodology, extended hrand composite curve method, enthalpy exchange, distillation column, heat exchanger network
Objavljeno: 10.07.2015; Ogledov: 474; Prenosov: 10
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Chemical and fruit skin colour markers for simple quality control of tomato fruitsVesna Bukovac
, Tatjana Unuk
, 2015, izvirni znanstveni članek
Opis: The orientation of this research was to evaluate the classic parameters regarding the external and internal quality of tomato fruits cv. ‘Brilliant‘ at different stages of maturity and to define the dynamics of their changes during the ripening in storage at 18 °C. Principal component analysis (PCA) and multivariate canonical discriminant analysis (DA) were used to classify tomato samples according to quality (internal and external) and nutritional value based on fruit mass, fruit skin colour, contents of soluble solids (SS), total titratable acids (TTA), ascorbic acid (AA), and total antioxidant potential (TAP). Several methods are usedfor determining AA content and TAP in plant samples. A simple routine method, direct redox titration with iodate solution and spectrophotometric determination of TAPSP, as described by Singleton and Rossi, also called total phenols, were used respectively. The results show that the stage of maturity (based on fruit skin colour) strongly determines the quality and nutritional value of the tomato fruit. Tomatoes harvested at table maturity (red colour, index a*/b* ≥ 0.85) have a significantly higher nutritional value (in terms of antioxidants – TAPSP and AA content) and overall quality than those harvested at an earlier maturity stage and then ripened in storage. This brings out the importance of short food supply chains and, from the viewpoint of overall fruit quality, it raises doubt about harvesting before reaching table maturity. On the other hand, it is necessary to be extremely attentive when determining optimal maturity, because when the plant becomes over-ripe or when stored, the nutritional value and overall quality decrease drastically. Besides the colour parameters, AA content is the most important chemical marker for a simple quality control. By using a simple and reliable analytical method for determining AA content, such as direct redox titratiation, the monitoring of tomato fruit quality could also be easily performed in situ.
Ključne besede: chemical markers, quality control, antioxidant, tomato, discriminant analysis
Objavljeno: 24.10.2017; Ogledov: 89; Prenosov: 10
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An evaluation of marine sediments in terms of their usability in the brick industryPatrik Baksa
, Franka Cepak
, Rebeka Lukman
, Vilma Ducman
, 2018, izvirni znanstveni članek
Opis: A dredging process is essential for the development of harbours and ports, allowing the functional daily operation of the port. The management of dredged material represents a worldwide challenge, especially considering unwanted deposition of material. Because of their chemical, petrographic, mineralogical and homogeneity composition, marine sediments could represent an appropriate raw material for the brick industry, particularly for the production of clay blocks, roofing and ceramic tiles. In this study dredged material from Port of Koper was tested for such use, thus various analyses were carried out in order to determine if the dredged material is environmentally friendly and suitable for use in the brick industry. These included: chemical analysis, mineralogical analysis, particle size analysis, chloride content analysis and tests of firing in a gradient furnace. Furthermore, tests of mechanical properties, as well as tests of the frost-resistance of the samples were carried out. On the basis of the primary analyses and samples prepared in a laboratory, it was confirmed that marine sediments from the Port of Koper, without any additives are only conditionally suitable as a source material for producing brick products, because without additives they exhibit too much shrinkage on drying and firing, as well as high water absorption, this can be improved by the incorporation of suitable additives, for example, virgin clay or other suitable waste material. The approach described herewith can also be followed to assess sediments from other ports and rivers regarding its potential use in clay brick sector.
Ključne besede: dredge marine sediment, recycling, clay bricks, mechanical properties, chemical analysis
Objavljeno: 21.12.2017; Ogledov: 220; Prenosov: 12
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