1. Advancing energy recovery: evaluating torrefaction temperature effects on food waste properties from fruit and vegetable processingAndreja Škorjanc, Sven Gruber, Klemen Rola, Darko Goričanec, Danijela Urbancl, 2025, izvirni znanstveni članek Opis: Most organic waste from food production is still not used for energy production. From the perspective of energy production, one option is to valorise the properties of organic waste. The fruit juice industry is growing rapidly and generates large amounts of waste. One of the main wastes in food and fruit juice processing is peach pits and apple peels. The aim of this study was to analyse the influence of torrefaction temperature on the properties of food waste, namely apple peels, peach pits and pea shells, in order to improve their energy value and determine their potential for further use and valorisation as a renewable energy source. The aim was to analyse the influence of different torrefaction temperatures on the heating value (HHV), mass yield (MY) and energy yield (EY) in order to better understand the behavior of the thermal properties of individual selected samples. The torrefaction process was carried out at temperatures of 250 ◦C, 350 ◦C and 450 ◦C. The obtained biomass was compared with dried biomass. For apple peels, HHV after torrefaction was (28 kJ/kg), MY decreased by (66–34%), while EY fell by (97–83%). Peach pits, despite a higher HHV after torrefaction (18 kJ/kg), achieved low MY (38–89%) and EY (59–99%), which reduces their efficiency in biochar production. Pea peels had EY (82–97%) and a lower HHV after torrefaction (11 kJ/kg), but their high ash content limits their wider use. The results confirm that, with increasing temperature, MY and EY for all selected biomasses decrease, which is a consequence of the degradation of hemicellulose and cellulose and the loss of volatile compounds. In most cases, increasing the torrefaction temperature improved the resistance to moisture adsorption, as this is related to the thermal process that causes structural changes. The results showed that the torrefaction process improved the hydrophobic properties of the biomass samples. Temperature was seen to have a great impact on mass energy efficiency. Apple peels generally had the highest mass and energy yield. Ključne besede: torrefaction, food waste, energy from waste, higher heating value, energy potential Objavljeno v DKUM: 07.02.2025; Ogledov: 0; Prenosov: 3
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2. Recent advances in ejector-enhanced vapor compression heat pump and refrigeration systems : a reviewSven Gruber, Klemen Rola, Danijela Urbancl, Darko Goričanec, 2024, izvirni znanstveni članek Opis: The incorporation of ejectors into heat pump and refrigeration cycles has been the subject
of growing interest, largely due to their simple structure, high reliability, and cost-effectiveness. This
paper investigates the recent advancements in novel design concepts of ejector-enhanced vapor
compression heat pump and refrigeration cycles. An overview of novel single-stage and twostage compression cycles utilizing a single or multiple ejectors is provided. First, the system setup,
operational principles, description, and figures of the existing schemes are provided. Second, the
main results, such as the coefficient of performance (COP), volumetric heating capacity and exergy
destruction, are discussed. In conclusion, the paper presents a coherent summary of the current
developments, future prospects, and the current knowledge gap. A plethora of research is present
in developing theoretical systems with high efficiency. However, experimental tests for real-life
implementations are limited. This review aims to provide the reader with an overview of recent
theoretical and experimental studies.
Ključne besede: ejector, heat pump, refrigeration, vapor compression system, review Objavljeno v DKUM: 03.09.2024; Ogledov: 51; Prenosov: 17
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3. Waste Lignocellulosic Biomass as a Source for Bioethanol ProductionKlemen Rola, Sven Gruber, Danijela Urbancl, Darko Goričanec, 2024, izvirni znanstveni članek Opis: Synthetically produced biofuels play a critical role in the energy transition away from fossil fuels. Biofuels could effectively lower greenhouse gas (GHG) emissions and contribute to better air quality. One of these biofuels is bioethanol, which could act as a gasoline replacement. For this purpose, a simulation of bioethanol production through lignocellulosic biomass fermentation, focused on distillation, was carried out in simulation software Aspen Plus. Since the possibility of absolute ethanol production through distillation is limited by the ethanol–water azeotrope, pressure swing distillation (PSD) was used to obtain fuel-grade ethanol (EtOH) with a fraction of 99.60 wt.%. The flowsheet was optimised with NQ analysis, which is a simple optimisation method for distillation columns. We found that the PSD has the potential to concentrate the EtOH to a desired value, while simultaneously removing other unwanted impurities whose presence is a consequence of pretreatment and fermentation processes. Ključne besede: bioethanol, distillation, lignocellulosic biomass, azeotrope, Aspen Plus Objavljeno v DKUM: 14.08.2024; Ogledov: 99; Prenosov: 5
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4. Carbon-free heat production for high-temperature heating systemsSven Gruber, Klemen Rola, Danijela Urbancl, Darko Goričanec, 2023, izvirni znanstveni članek Opis: The article presents a new carbon-free heat production technology for district heating, which consists of a combined heat and power generation fuel cell (FC CHP) with CO2 capture and a two-stage cascade high-temperature heat pump (TCHHP). The FC generates heat and electricity, the latter being used to drive the compressors of the TCHHP. During the winter period, the water temperature achieved can occasionally be too low, so it would be heated up with hydrogen gas boilers. The hydrogen would be produced by reforming natural gas, synthetic methane, or biogas. The results are presented with natural gas utilization—the ratio between the obtained heat flow transferred directly to the water for district heating and the input heat flow of natural gas. In the case of a return water temperature of 60 °C and district heating temperature of 85 °C, the TCHHP, whose heat source is groundwater, achieves plant efficiency of 270.04% in relation to the higher heating value (HHV) and 241.74% in relation to the lower heating value (LHV) of natural gas. A case with a TCHHP whose heat source is low-temperature geothermal water achieves a plant efficiency of 361.36% in relation to the HHV and 323.49% in relation to the LHV. Ključne besede: carbon-free, decarbonization of district heating systems, fuell cell, high-temperature district heating, high-temperature heat pump Objavljeno v DKUM: 10.05.2024; Ogledov: 233; Prenosov: 17
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5. Utilisation of renewable electricity to produce synthetic methaneKlemen Rola, Sven Gruber, Danijela Urbancl, Darko Goričanec, 2023, izvirni znanstveni članek Ključne besede: power-to-methane, P2M, synthetic methane, CO2 methanation, Aspen Plus, Aspen Adsorption Objavljeno v DKUM: 18.04.2024; Ogledov: 203; Prenosov: 13
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6. Izraba obnovljivih virov energije za proizvodnjo sintetičnega metana : magistrsko deloKlemen Rola, 2023, magistrsko delo Opis: Magistrsko delo predstavlja proizvodnjo sintetičnega metana, ki bi lahko nadomestil zemeljski plin. Za reakcijo metanacije je potreben vodik. Ta se v delu proizvede z elektrolizo, ki jo poganja elektrika obnovljivih virov. Proces je namenjen sezonskemu shranjevanju energije, kjer se viški elektrike poletnega časa shranijo v obliki metana za obdobja primanjkljajev energije. V ta namen, smo s programom Aspen Plus najprej izvedli poenostavljeno enostopenjsko simulacijo metanacije CO2. Pretok CO2 je baziral na ocenjeni sestavi in pretoku bioplina iz realne bioplinarne. Upoštevali smo, da se tudi celoten bioplin lahko uporabi kot reaktant. Enostopenjska metanacija je služila predvsem za razumevanje obnašanja reakcije. Ker z eno reakcijsko stopnjo v produktu nismo dosegali dovolj visokega deleža metana, smo izvedli še poenostavljeno dvostopenjsko metanacijo. Določili smo pogoje, pri katerih bi dosegali dovolj visoko vsebnost metana, da bi produkt bil primeren za injiciranje v plinovode. Za primer, ko se bioplin ne uporabi v metanaciji, smo v programu Aspen Adsorption izvedli dinamični simulaciji nadgradnje bioplina z adsorpcijskimi tehnikami. Mešanico bioplina smo z nizkimi izgubami metana uspešno nadgradili do biometana, s sestavo, ki je primerna za injiciranje v plinovode. S pomočjo rezultatov začetne dvostopenjske simulacije smo razvili delno integrirano shemo s sočasno proizvodnjo elektrike, ki je sposobna proizvesti od 1 t/h do 1,3 t/h sintetičnega metana. Pri tem je v procesu možna uporaba čistega CO2, ali pa celo mešanice bioplina in CO2. Proizveden sintetični metan je vseboval več kot 97 mol.% CH4, po dehidraciji s silikagelom, pa smo zagotovili sestavo, ki je primerna za injiciranje v plinovode mnogih Evropskih držav. Ključne besede: Sintetični metan, bioplin, metanacija CO2, adsorpcija, Aspen Plus, Aspen Adsorption Objavljeno v DKUM: 14.09.2023; Ogledov: 631; Prenosov: 0
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7. Proizvodnja bioetanola iz lignocelulozne biomase : diplomsko delo univerzitetnega študijskega programa I. stopnjeKlemen Rola, 2021, diplomsko delo Opis: V diplomskem delu je predstavljen proces proizvodnje bioetanola iz lignocelulozne biomase, skupaj s problematiko s katero se v procesu srečujemo. Poudarek je predvsem na destilaciji in dehidraciji bioetanola. V ta namen je bila v programu Aspen Plus izvedena simulacija za pridobivanje bioetanola blizu azeotropne sestave. Destilacija je sestavljena iz dveh zaporedno vezanih rektifikacijskih kolon, ki sta bili vsaka zase modelirani in optimizirani z NQ analizo. Na vsaki koloni je bila izvedena občutljivostna analiza za namen proučevanja vpliva različnih parametrov na porabo toplotne energije. Za pridobivanje čistega etanola smo izvedli azeotropno destilacijo s cikloheksanom in destilacijo s spreminjajočim tlakom. Cilj dehidracije je pridobiti 99,60 ut.% etanola. Azeotropna destilacija je bila modelirana z dvema kolonama: glavno kolono, kjer se pridobi bioetanol visoke čistoče in regeneracijsko kolono, kjer se na dnu kolone pridobi čista voda. Destilacija s spreminjajočim tlakom je bila modelirana z dvema zaporedno vezanima kolonama, ki obratujeta pri različnih tlakih. To omogoči pridobivanje čistega bioetanola. Na sistemu se je izvedla občutljivostna analiza, za namen proučevanja interakcij med obema kolonama. Ugotovljeno je bilo, da ima spreminjanje deleža destilata obeh kolon največji vpliv na porabo energije v obeh kolonah. Za namen primerjanja porabe toplotne energije smo izračunali neto porabo toplotne energije na enoto proizvedenega brezvodnega bioetanola. Vrednosti so bile primerljive z literaturo. Ugotovljeno je bilo da se dodatno znižanje v porabi energije lahko doseže z rekuperacijo energije, ali z uporabo drugih tehnik za dehidracijo. Kombinacija rekuperacije in uporabe manj energijsko intenzivnih postopkov lahko močno zmanjša porabo energije v procesu. Zaključili smo, da je za zmanjšanje porabe energije v proizvodnji bioetanola iz lignocelulozne biomase smiselno razmišljati tudi o kogeneraciji energije iz drugih stranskih produktov. Ključne besede: Bioetanol, Destilacija, Lignocelulozna biomasa, Azeotrop, Aspen Plus Objavljeno v DKUM: 22.09.2021; Ogledov: 1254; Prenosov: 155
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