1. Maximizing the power output and net present value of organic rankine cycle: application to aluminium industryMonika Dokl, Rok Gomilšek, Lidija Čuček, Ben Abikoye, Zdravko Kravanja, 2022, izvirni znanstveni članek Opis: This study presents an integrated design and optimization of an Organic Rankine Cycle (ORC) for the recovery of waste heat from aluminium production. Non-Linear Programming (NLP) models were developed, with the objectives of maximizing electricity production and the Net Present Value (NPV) of the system. The models account for optimizing the operating conditions and changes in thermodynamic features of the system. The developed models are applied to a case study of Slovenian aluminium company where the performance of three different working fluids (R245fa, R1234yf and R1234ze) are compared. The optimization is performed considering different temperatures and prices of produced hot water and electricity, minimum approach temperature (DTmin), concentration of CO2 in flue gas and temperature and flowrate of flue gas. Results show that the selected working fluids for the proposed waste heat-based ORC system have the potential to substitute up to about 830 kW of electricity in a sustainable and economic manner. Out of the three working fluids considered, R245fa showed up to 7.9% efficiency of the ORC cycle and was identified as the best performing working fluid considering both economic viability and the amount of electricity produced by the system, however the refrigerant inherently has higher GHG footprint.
Ključne besede: waste heat, waste heat utilization, aluminium industry, organic rankine cycle, power generation, optimization
Objavljeno v DKUM: 10.04.2025; Ogledov: 0; Prenosov: 1
 Celotno besedilo (2,73 MB)
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2. Synthesis of Rankine cycle systems with cascade and separate configurations utilising multiple heat sources at different temperature levelsMonika Dokl, Rok Gomilšek, Petar Varbanov, Yee Van Fan, Zdravko Kravanja, Lidija Čuček, 2023, izvirni znanstveni članek Ključne besede: multiple heat sources, Organic Rankine cycle, separate and cascade designs, Steam Rankine cycle, thermodynamic optimisation
Objavljeno v DKUM: 28.02.2025; Ogledov: 0; Prenosov: 2
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3. Integrated optimization framework for a biomass supply network and steam Rankine cycleMonika Dokl, Zdravko Kravanja, Lidija Čuček, 2024, izvirni znanstveni članek Opis: The optimization of biomass supply chains is becoming increasingly important, especially for low-density biomass feedstocks that have limited market value and require efficient handling and logistics. This study addresses this issue by proposing an integrated approach to optimize biomass supply chain networks for energy production with the steam Rankine cycle. The approach takes into account the inherent variability of feedstock availability and energy market values, to ensure adaptability to fluctuating conditions. The biomass supply network is formulated as a mixed-integer nonlinear programming problem, where the optimization objective is to maximize the economic viability of the system. The optimal configuration of the supply network includes the selection of biomass supply zones and storage facilities, the transportation links, and the optimization of the process variables within the conversion plants, taking into account the variable heat demand. The optimization approach is applied to a hypothetical case study of a relatively small region in Slovenia. The results show the economic viability of biomass utilization with a net present value of almost 300 MEUR, generating about 4 MW of electricity and 65 MW of heat. The uncertainties of the biomass supply, the fluctuations in product prices and the spatial scope of the case study are evaluated in addition. This analysis highlights and discusses the impact of these factors on the economic performance of the biomass supply chain network.
Ključne besede: copper(II) coordination compounds, methylamines, crystal structure, magnetic properties, thermogravimetric analysis
Objavljeno v DKUM: 31.01.2025; Ogledov: 0; Prenosov: 3
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4. Global projections of plastic use, end-of-life fate and potential changes in consumption, reduction, recycling and replacement with bioplastics to 2050Monika Dokl, Anja Copot, Damjan Krajnc, Yee Van Fan, Annamaria Vujanović, Kathleen B. Aviso, Raymond R. Tan, Zdravko Kravanja, Lidija Čuček, 2024, izvirni znanstveni članek Opis: Excessive production, indiscriminate consumption, and improper disposal of plastics have led to plastic pollution and its hazardous environmental effects. Various approaches to tackle the challenges of reducing the plastic footprint have been developed and applied, such as the production of alternative materials (design for recycling), the production and use of biodegradable plastic and plastics from power-to-X, and the development of recycling approaches. This study proposes an optimisation strategy based on regression to evaluate and predict plastic use and end-of-life fate in the future based on historical trends. The mathematical model is formulated and correlations based on functions of time are developed and optimised by minimising the sum of squared residuals. The plastic quantities up to the year 2050 are projected based on historical trends analysis, and for improved sustainability, projections are additionally based on intervention analyses. The results show that the global use of plastics is expected to increase from 464 Mt in 2020 up to 884 Mt in 2050, with up to 4725 Mt of plastics accumulated in stock in 2050 (from the year 2000). Compared to other available forecasts, a slightly lower level of plastic use and stock are obtained. The intervention analysis estimates a range of global plastics' consumption between 594 Mt and 1018 Mt in 2050 by taking into account its different increment rates (between −1 % and 2.65 %). In the packaging sector, the implementation of reduction targets (15 % reduction in 2040 compared to 2018) could lead to a 27.3 % decrease in plastic use in 2050 as compared to 2018, while achieving recycling targets (55 % in 2030) would recycle >75 % of plastic packaging in 2050. The partial substitution of fossil-based plastics with bioplastics (polyethylene) will require significant land area, between 0.2 × 106 km2 for obtaining switchgrass and up to around 1.0 × 106 km2 for obtaining forest residue (annual yields of 58.15 t/ha and 3.5 t/ha) in 2050. The intervention analysis shows that proactive policies can mitigate sustainability challenges, however achieving broader sustainability goals also requires reduction of footprints related to energy production and virgin plastic production, the production of bio-based plastics, and the full implementation of recycling initiatives.
Ključne besede: plastic use, plastic waste, end-of-life fate, forecasting, hostorical trends, regression analysis, least square method, intervention analysis
Objavljeno v DKUM: 31.01.2025; Ogledov: 0; Prenosov: 2
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5. Isolation and characterization of nanocellulose from Polypodiophyta fern using chemo-mechanical methodKatja Vasić, Monika Dokl, Željko Knez, Maja Leitgeb, 2024, izvirni znanstveni članek Opis: Nanocellulose is considered a promising and sustainable biomaterial, with excellent properties of biorenewability with improved mechanical properties. As a unique natural biopolymer, it has been applied to many different industries, where efficient and environmentally friendly productions are in demand. For the first time, ferns from the class Polypodiopsida were used for the isolation of cellulose fibers, which was performed using a chemo-mechanical method. As chemical treatment plays a crucial role in the isolation of nanocellulose, it affects the efficiency of the extraction process, as well as the properties of the resulting nanocellulose. Therefore, mechanical fibrillation was performed via grinding, while the chemical process consisted of three different treatments: alkali treatment, bleaching, and acid hydrolysis. In three different experiments, each treatment was separately prolonged to investigate the differing properties of isolated nanocellulose. Structural analysis and morphological analysis were investigated by SEM, EDS, FT-IR, and DLS. The thermal stability of cellulose fibers was investigated by TGA/DSC. The morphology of obtained nanocellulose was confirmed via SEM analysis for all samples, with particles ranging from 20 nm up to 600 nm, while the most consistent sizes were observed for NC3, ranging from 20 to 60 nm. FT-IR spectra showed prominent absorption peaks corresponding to cellulose, as well as the absence of absorption peaks, corresponding to lignin and hemicellulose. The EDS confirmed the elemental purity of nanocellulose, while TGA/DSC indicated higher thermal stability of nanocellulose, compared to untreated fern, which started to degrade earlier than nanocellulose. Such characteristics with unique properties make nanocellulose a versatile biomaterial for the industrial production of cellulosic materials.
Ključne besede: nanocellulose, isolation, Polypodiophyta fern, chemo-mechanical method, biomaterial, biopolymers
Objavljeno v DKUM: 31.01.2025; Ogledov: 0; Prenosov: 3
Celotno besedilo (3,75 MB) |
6. A waste separation system based on sensor technology and deep learning: a simple approach applied to a case study of plastic packaging wasteRok Pučnik, Monika Dokl, Yee Van Fan, Annamaria Vujanović, Zorka Novak-Pintarič, Kathleen B. Aviso, Raymond R. Tan, Bojan Pahor, Zdravko Kravanja, Lidija Čuček, 2024, izvirni znanstveni članek Ključne besede: waste management, smart waste bin system, central post-sorting, sensor technology, deep learning, convolutional neural networks
Objavljeno v DKUM: 23.08.2024; Ogledov: 51; Prenosov: 9
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7. A game theoretic approach for plastic life cycle assessmentChunyan Si, Yee Van Fan, Lidija Čuček, Monika Dokl, Petar Varbanov, 2023, izvirni znanstveni članek Opis: Plastic production and its end-of-life management pose a significant environmental footprint. The mitigation strategies of the plastic industry are comparatively attainable than the other hard-to-abate sector. However, the involvement of different stakeholders is needed. The life cycle analysis proposed in this study allocated the environmental footprint to stakeholders based on the game theory concept. It addresses the limitation of previous approaches that do not guarantee the stakeholders from different stages will participate in the initiatives with the lowest net environmental footprint due to the dissatisfaction or imbalance in the allocated unburdening footprint (benefit) and burdening footprint. The applicability of the proposed approach is demonstrated through a plastic recycling case study. An allocation of 82 % of environmental benefit to the producer, 14 % to the manufacturer, and 4 % to the user are suggested to achieve efficiency (lowest external interference) and stable cooperation (participation in recycling). This work serves as an initial assessment in demonstrating the integration of the game theory concept in environmental footprint allocation or Life Cycle Assessment.
Ključne besede: plastic production, environmental footprint, life cycle
Objavljeno v DKUM: 18.04.2024; Ogledov: 155; Prenosov: 6
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8. Optimizacija geotermalne elektrarne v El Salvadorju z ozirom na termodinamiko in rudarjenje Bitcoina : magistrsko deloAndrej Zidarič, 2023, magistrsko delo Opis: V okviru magistrske naloge smo analizirali delovanje geotermalne elektrarne, natančneje uporabo organskega Rankinovega cikla za izkoriščenje geotermalne energije. Magistrska naloga je osnovana na realnem primeru geotermalne elektrarne v El Salvadorju. V magistrski nalogi smo zasnovali ORC sistem iz vidika termodinamike in s programom Matlab optimizirali maksimalni in minimalni tlak sistema ter njegovo maksimalno temperaturo. Poskušali smo najti najučinkovitejšo delovno tekočino, ki bo omogočila maksimalno učinkovitost sistema. Rezultate pridobljene s pomočjo Matlaba smo validirali s programoma Aspen Plus in DWSIM.
Kot rezultat optimizacije in validacije smo ugotovili, da so najučinkovitejše delovne tekočine za zasnovo ORC sistema n-butan, R245fa in izobutan. Vse tri delovne tekočine so varne, imajo nizek potencial globalnega segrevanja in ničen potencial tanjšanja ozona. Povprečna učinkovitost ORC sistema, dobljena z njihovo uporabo, je znašala malo več kot 12 %.
Hipotetični primer uporabe geotermalne elektrarne v El Salvadorju smo predpostavili z namenom rudarjenja kriptovalute Bitcoin. Za izračune smo ustvarili matematične funkcije predvidevanja cene in težavnosti rudarjenja do leta 2050. Ugotovili smo, da bi bil tovrsten projekt izvedljiv in profitabilen.
Ključne besede: Organski Rankinov cikel, Geotermalna energija, Optimizacija, Matlab, Bitcoin, rudarjenje Bitcoina
Objavljeno v DKUM: 16.02.2023; Ogledov: 728; Prenosov: 116
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9. Okoljska analiza organskega rankinovega cikla za proizvodnjo električne energije iz industrijske odpadne toplote : diplomsko delo visokošolskega strokovnega študijskega programa I. stopnjeGaja Strajnar, 2022, diplomsko delo Opis: V diplomskem delu smo ocenili okoljski vpliv ORC elektrarne, ki uporablja odpadno toploto iz proizvodnje aluminija in predlaga različne scenarije, v smislu trajnostne in konvencionalne proizvodnje električne energije. Za analizo smo podatke o energijskih bilancah ter učinkovitosti sistema glede na termodinamične in ekonomske cilje pridobili iz simulacij v programski opremi Aspen Plus in optimizirani v programu GAMS za tri delovne tekočine (R245fa, R1234yf in R1234ze) po članku [1]. Ob upoštevanju vseh ustreznih vhodov in izhodov procesa, same proizvodnje komponent in vpliv delovnih tekočin, v njegovi življenjski dobi, se okoljski vpliv sistema analizira s programsko opremo OpenLCA z integriranimi zbirkami podatkov. Primerjali smo med tremi električnimi mešanicami (Slovenski električni mix, Evropski povprečni električni mix in COP26 mešanica obnovljivih virov električne energije). Dobljeni rezultati primerjalno kažejo, kateri predlagani scenariji bi bolj razbremenili okolje. Uporaba ORC namesto mešanice električne energije v EU bo imela največji vpliv na okoljsko razbremenitev, sledita ji Slovenska in nato mešanica COP26, kar je pričakovano.
Ključne besede: Okoljska analiza, organski Rankinov cikel, odpadna toplota, obnovljivi viri energije, proizvodnja aluminija
Objavljeno v DKUM: 11.10.2022; Ogledov: 802; Prenosov: 96
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