Production of expanded perlite microspheres- Process development and mathematical modeling

391 σ.Ο περλίτης είναι ηφαιστειακό πέτρωµα ρυολιθικής σύστασης µε χαρακτηριστική υαλώδη δοµή, αποτελείται κυρίως από πυρίτιο ενώ στην µάζα του περιλαµβάνει χηµικά δεσµευµένο νερό σε περιεκτικότητα 2-6%. Όταν ο περλίτης θερμαίνεται γρήγορα σε θερμοκρασία που ξεπερνά το σημείο μαλάκυνσης του διογκώνεται και αποκτά φαινόμενη πυκνότητα συνήθως μικρότερη από 150 kg∙m-3 και σημαντικές θέρμο- και ήχο-μονωτικές ιδιότητες. Σε βιομηχανική κλίμακα, η διόγκωση του περλίτη λαμβάνει χώρα σε κάθετες έμφλογες καμίνους, ενώ τα μειωνεκτήματα της μεθόδου επηρεάζουν τόσο τις ιδιότητες των προϊόντων όσο και την οικονομικότητα και αποδοτικότητα της διεργασίας. Σκοπός του παρόντος διδακτορικού είναι η ανάπτυξη µιας εξολοκλήρου νέας τεχνολογίας για την παραγωγή τεµαχιδίων διογκωµένου περλίτη υψηλής ποιότητας. Συγκεκριμένα, επιδιώκεται η παραγωγή ελαφροβαρών μικροσφαιριδίων διογκωμένου περλίτη, µε ικανοποιητική αντοχή και περιορισµένη απορροφητική ικανότητα. Τα ανωτέρω χαρακτηριστικά πληρούνται όταν ο διογκωµένος περλίτης έχει σφαιρικό σχήµα και περιορισµένο εξωτερικό ανοιχτό πορώδες. Για να επιτευχθεί αυτό, απαιτείται ο ακριβής έλεγχος της διεργασίας. Στη νέα µέθοδο διόγκωσης περλίτη που αναπτύχθηκε στα πλαίσια της παρούσας διδακτορικής διατριβής εφαρµόστηκε η Τεχνολογία Έµµεσης Θέρµανσης για την κατασκευή µίας νέου τύπου καµίνου για τη διόγκωση του περλίτη. Ο σχεδιασµός της νέας καµίνου διόγκωσης επιτρέπει την ακριβή ρύθµιση των συνθηκών που επικρατούν εντός του θαλάµου διόγκωσης και µέσω αυτού, του χρόνου παραµονής και της θερµοκρασίας των τεμαχιδίων. Σκοπεύοντας στη µελέτη της επίδρασης των παραµέτρων λειτουργίας της καµίνου στο πεδίο ροής εντός του θαλάµου διόγκωσης, πραγματοποιήθηκε αριθµητική προσοµοίωση της λειτουργίας της καµίνου µε τη μέθοδο πεπερασµένων στοιχείων στο πρόγραµµα FLUENT® µε στόχο τη µελέτη της κατανομής της θερμοκρασίας και της ταχύτητας του αέρα κατά μήκος του θαλάµου για διαφορετικά σενάρια λειτουργίας της καµίνου. Διενεργήθηκε σηµαντικός αριθµός πειραµάτων διόγκωσης στη νέα κάθετη ηλεκτρική κάµινο και σε συμβατική έµφλογη κάµινο διόγκωσης µε σκοπό την ανάλυση της διεργασίας στις δύο μεθόδους και τη σύγκριση των ιδιοτήτων των προϊόντων που προέκυψαν. Τα νέα προϊόντα παρουσιάζουν σημαντικά βελτιωμένη αντοχή σε συμπίεση που σε ορισμένες περιπτώσεις ξεπερνά το 500% και παρόμοια ή μειωμένη ύδρο- και έλαιο-απορροφητικότητα. Επιπλέον, χαρακτηρίζονται από στενότερη κοκκοµετρική κατανοµή, μικρότερο ποσοστό παραµένοντος νερού, μεγαλύτερο ποσοστό επαρκώς διογκωμένων κόκκων και σφαιρικό σχήμα με μειωμένο ανοικτό επιφανειακό πορώδες. Σκοπεύοντας στην εις βάθος κατανόηση της διεργασίας στη νέου τύπου κάμινο, αναπτύχθηκε ένα νέο µαθηµατικό µοντέλο που περιγράφει την διόγκωση ενός κόκκου περλίτη εντός της καµίνου. Για την προσομοίωση της διόγκωσης του κόκκου αναπτύχθηκε ένα νέο μοντέλο, στο οποίο θεωρείται ότι στο κέντρο του κόκκου υπάρχει φυσαλίδα εντός της οποίας περιέχεται το επιδρών στην διόγκωση νερό. Το μαθηματικό μοντέλο προσφέρει την δυνατότητα διαμόρφωσης διαφορετικών σεναρίων μεταβάλλοντας τα φυσικοχημικά χαρακτηριστικά της πρώτης ύλης αλλά και τις συνθήκες λειτουργίας της καμίνου διόγκωσης με τελικό σκοπό τη προσομοίωση της διεργασίας για διάφορες συνθήκες διόγκωσης και για περλίτη διαφορετικής χημικής σύστασης και υπολογίζει τη χρονική μεταβολή της ταχύτητας, θερμοκρασίας και διαμέτρου του κόκκου κατά μήκος της τροχιάς που διαγράφει εντός της καμίνου.Perlite is a naturally occurring volcanic siliceous rock which has the potential to expand between 4 and 20 times when heated beyond its softening point, due to the presence of 2-6% chemically bound water in its structure. During expansion, perlite acquires outstanding physical properties like low density, low thermal conductivity and high sound reduction index. In the industry, perlite expansion is performed in cylindrical vertical furnaces and the technique drawbacks affect product quality as well as process productivity and efficiency. The scope of the doctoral study has been the development of a new expansion method for the production of high quality expanded perlite microspheres. The main specifications of the new products are low loose bulk density, increased durability, and low water and oil absorption. As far as the grain morphology is concerned, spherical particle with closed structure and low specific surface area is required. In order to produce expanded perlite microspheres with the aforementioned characteristics, the precise control of the expansion process is necessary. In the framework of this study, a new expansion method has been developed and a new pilot-scale vertical electrical furnace for perlite expansion has been designed and constructed aiming to overcome the drawbacks of the conventional expansion method. The new perlite expansion method allows the milder, gradual heating of perlite grains, as well as the variation of perlite grain residence time in the heating chamber. In order to study the effect of furnace operating parameters on the chamber internal flow field, a mathematic model has been developed by the implementation of finite volumes method in commercial software (FLUENT®, ANSYS). The mathematical model enlightens the conditions that prevail in the heating chamber, especially air temperature and velocity and enables the investigation of the effect of operating conditions on them. A significant number of perlite expansion experiments have been performed in both vertical electrical and in conventional expansion furnace, in order to investigate the effect of expansion process in products quality. Perlite particles that had been expanded in the vertical electrical furnace are of high quality having significantly improved compression strength (in some cases exceeds 500%). Additionally, the particles water and oil absorption is the same and in some cases reduced by 20%, with narrower particle size distribution, lower resident water content. Aiming at better understanding of the perlite expansion process in the new vertical electrical furnace, a mathematical model has been developed for the simulation of the process evolution in the new vertical electrical furnace. The dynamic model consists of ordinary differential equations for both air and particle heat and momentum balances, as well as nonlinear algebraic equations for both air and perlite melt thermophysical and transport properties. The expansion phenomenon has been simulated by a new steam bubble growth model that has been developed. The mathematical model probes the air temperature and velocity distribution within the vertical electrical furnace as well as the particle velocity, temperature and size along its trajectory inside the heating chamber.Παναγιώτης Μ. Αγγελόπουλο

Carbon Capture Utilisation and Storage in Extractive Industries for Methanol Production

The elevated increase of CO2 emissions related to activities of the extractive industry is becoming a challenging issue gradually affecting climate change and global warming. In this frame, the effective utilisation of CO2 through the techniques of Carbon Capture and Storage (CCS) as well as Carbon Capture and Utilisation (CCU) can alleviate the greenhouse effect. Converting CO2 into a value-added chemical or liquid fuel (e.g., methanol, hydrocarbons, propylene, dimethyl ether, ethylene, etc.) is a promising approach in this regard. Methanol (MeOH) synthesis offers a key feedstock for industries, being both an industrial commodity for several chemical products and an efficient transportation fuel. This article presents a review of the CCS and CCU technologies for the production of MeOH in extractive industries. The CCS technologies investigated in this framework are the amine-based absorption and the WGS-enhanced CCS. The CCU technologies are CO2 hydrogenation and enhanced CO2 transformation by the Fischer-Tropsch reaction. Incorporating these systems for the processing of the flue-gases of the extractive industries significantly reduces the CO2 emissions, while creating new revenues by the production of valuable MeOH

Modelling the Thermal Treatment and Expansion of Mineral Microspheres (Perlite) in Electric Furnace Through Computational Fluid Dynamics (CFD): Effect of Process Conditions and Feed Characteristics

A model-based investigation of the interplay between furnace setup and spatio-temporal evolution of particles’ state variables is also presented. The effect of feed size distribution and processing of ultrafine ore are discussed. The process is controlled primarily by the wall temperature and secondarily the air feeding rate; an increase of furnace wall temperature from 900 to 1200°C reduced the final density to 484, 979, and 1262 kg/m3 for feed size of 150 μm, 250 μm, and 350 μm. Model predictions are in good agreement with the experimental measurements possessing differences below 10% in most cases.</p

Thermal decomposition of volcanic glass (rhyolite): Kinetic deconvolution of dehydration and dehydroxylation process

Thermal decomposition of hydrous volcanic glass occurs through the release of different water species under overlapping processes over wide temperature range. Its investigation is of practical interest since it constitutes integral processing part towards its valorization as source for the production of high-quality porous material for various applications. The study presents investigation of thermal decomposition of hydrous rhyolite through the non-isothermal solid-state kinetics approach. Rhyolite decomposition occurs through three partially overlapping processes, where loosely held and chemically bound water, as well as hydroxyl release at different temperature regions and through different mechanisms. The separation of overlapped thermal curves was done through peak deconvolution method using Frazier-Suzuki equation. Subsequently, the isoconversional (model-free) Friedman, generalized master-plots and Kissinger methods were applied for the determination of apparent activation energy (Ea), reaction model (f(a)) and pre-exponential factor (A) for each individual reaction step considered. Using the kinetic triplet values of each process, the kinetic rate equations were combined allowing precise simulation of the dehydration and dihydroxylation processes. A comparison of model results with thermogravimetric (TG) data, as well as data from the literature, showed the satisfactory accuracy of the model in the simulation of the process and the successful prediction of each water type fraction, during the process evolution. Spectroscopy techniques in UV―VIS and NIR (near infra-red) spectral ranges were applied to raw rhyolite and sample with different water content allowed calculation of color coordinates and its correlation with dehydration and dehydroxylation degrees, and also identification of water species

Dehydration of rhyolite: activation energy, water speciation and morphological investigation

Rhyolite is an extrusive, igneous rock of aluminosilicate composition that upon rapid cooling forms obsidian. Obsidian is amorphous and contains limited water portions ( lt 2 mass%); however, secondary hydration turns it either to perlite (H2O approximate to 2-5 mass%) or pitchstone (> 5 mass%). In the current study, kinetics of hydrous rhyolite dehydration were investigated by thermogravimetry up to 1000 degrees C, at heating rates of 2.5, 5, 10 and 20 degrees C min(-1)and under inert atmosphere. The mass loss is approx. 7.6 mass%, occurs along wide temperature range (100-800 degrees C) and is solely attributed to the release of molecular water ((H2O)(m)) and hydroxyl groups (OH). Rhyolite dehydration was considered as a solid-state reaction, and the apparent activation energy (E-a) of dehydration was calculated throughout the whole conversion range (a) by applying the isoconversional Friedman and advanced Vyazovkin methods. Both methods revealed inverse sigmoid trend in E(a)values versus conversion degree, possessing almost stable value of 61 +/- 5 kJ mol(-1)for Friedman method and 59.44 kJ mol(-1)for Vyazovkin method on conversion range between 0.25 and 0.75, and sharp increase at higher conversion degree. The intensive change inE(a)during dehydration progression is attributed to the change in releasing species (from (H2O)(m)to OH). Raman and FT-IR spectroscopy analyses of raw and partially dehydrated samples at different stages revealed that up to 300 degrees C mainly (H2O)(m)is diffused out of the material causing sample enrichment in OH groups. OH release, which occurs at relatively higher temperature, is accompanied by increase in apparent E(a)value of dehydration. Concerning microstructure of raw rhyolite, it exhibits a network of micro-fractures which serve as water release routes. Upon heating, more and wider fractures are created. At 600 degrees C, fractures merging occurs creating voids, which constitute forerunners of the expansion phenomenon. Further temperature increase causes material softening allowing local plastic deformation, which under the high pressure that is exerted by the releasing water species incites the formation of large cavities and fractures, initiating expansion

Multi-Model Assessment for Secondary Smelting Decarbonisation: The Role of Hydrogen in the Clean Energy Transition

Extensive decarbonisation efforts result in major changes in energy demand for the extractive industry. In 2021, the extraction and primary processing of metals and minerals accounted for 4.5 Gt of CO2 eq. per year. The aluminium industry was responsible for 1.1 Gt CO2 eq. direct and indirect emissions. To reach the European milestone of zero emissions by 2050, a reduction of 3% annually is essential. To this end, the industry needs to take a turn towards less impactful production practices, coupling secondary production with green energy sources. The present work aims to comprehensively compare the lifecycle energy consumption and environmental performance of a secondary aluminium smelter employing alternative thermal and electricity sources. In this frame, a comparative analysis of the environmental impact of different thermal energy sources, namely natural gas, light fuel oil, liquified petroleum gas, hydrogen and electricity, for a secondary aluminium smelter is presented. The results show that H2 produced by renewables (green H2) is the most environmentally beneficial option, accounting for &minus;84.156 kg CO2 eq. By producing thermal energy as well as electricity on site, H2 technologies also serve as a decentralized power station for green energy production. These technologies account for a reduction of 118% compared to conventionally used natural gas. The results offer a comprehensive overview to aid decision-makers in comparing environmental impacts caused by different energy sources

Dehydration of rhyolite: activation energy, water speciation and morphological investigation

Rhyolite is an extrusive, igneous rock of aluminosilicate composition that upon rapid cooling forms obsidian. Obsidian is amorphous and contains limited water portions ( 5 mass%). In the current study, kinetics of hydrous rhyolite dehydration were investigated by thermogravimetry up to 1000 °C, at heating rates of 2.5, 5, 10 and 20 °C min−1 and under inert atmosphere. The mass loss is approx. 7.6 mass%, occurs along wide temperature range (100–800 °C) and is solely attributed to the release of molecular water ((H2O)m) and hydroxyl groups (OH). Rhyolite dehydration was considered as a solid-state reaction, and the apparent activation energy (Ea) of dehydration was calculated throughout the whole conversion range (a) by applying the isoconversional Friedman and advanced Vyazovkin methods. Both methods revealed inverse sigmoid trend in Ea values versus conversion degree, possessing almost stable value of 61 ± 5 kJ mol−1 for Friedman method and 59.44 kJ mol−1 for Vyazovkin method on conversion range between 0.25 and 0.75, and sharp increase at higher conversion degree. The intensive change in Ea during dehydration progression is attributed to the change in releasing species (from (H2O)m to OH). Raman and FT-IR spectroscopy analyses of raw and partially dehydrated samples at different stages revealed that up to 300 °C mainly (H2O)m is diffused out of the material causing sample enrichment in OH groups. OH release, which occurs at relatively higher temperature, is accompanied by increase in apparent Ea value of dehydration. Concerning microstructure of raw rhyolite, it exhibits a network of micro-fractures which serve as water release routes. Upon heating, more and wider fractures are created. At 600 °C, fractures merging occurs creating voids, which constitute forerunners of the expansion phenomenon. Further temperature increase causes material softening allowing local plastic deformation, which under the high pressure that is exerted by the releasing water species incites the formation of large cavities and fractures, initiating expansion

Ureteral stent related symptoms: A comparative study

Background: In urology, ureteral stents are used to treat obstructive diseases. Hematuria (54%), fever, discomfort, and lower urinary system symptoms are the predominant symptoms related to ureteral stent. Aim: This article links stent symptoms to double-j width and length, as well as patient’s height, weight, and body mass index (BMI). Ureteric Stent Symptoms Questionnaire (USSQ) was used to measure ureteral stent symptoms at 1st and 4th week of stent in situ as well as the 4th week after pigtail removal. Methods: A 200-patient prospective study, where patients were allocated into four groups following ureteral stent insertion depending on the stent characteristics. Those groups were: 4.8 Fr./26 cm (Group A), 4.8 Fr./28 cm (Group B), 6 Fr/26 cm (Group C), and 6 Fr/28 cm (Group D). Results: Men comprised 53.5% of 200 patients. Participants had an average age of 49 ± 15.5 years, height of 175 ± 8.94 cm, and BMI of 23.8 ± 7.6 cm. The laboratory results were identical between groups. At the first and fourth week, groups had similar urine symptoms, pain severity, health status and occupational activities. The difference in pain location was statistically significant. Group A had 82.4% renal back pain in the first week, whereas Group B had 68.8%, Group C 31.3% and Group D 62.5 (p = 0.04). At the fourth week, 64.7% of Group A patients reported kidney front pain, compared to 100% of Group B, 93.3% of Group C, and 100% of Group D (p = 0.04). There was statistical significance in the sexual activity of the patients. 24.4% of Group C patients stopped sexual activity before stent installation, compared to 10.6%, 8.3%, and 6.4% of the other groups (p = 0.03). A moderate percentage of patients had active sexual activity at week 4 (Group A: 7.8%, Group B: 5.8%, Group C: 8.2%, Group D: 4.1%), p = 0.83. In multivariate analysis, urinary catheter group, age, weight, height, and BMI did not significantly affect urine index score (UIS), pain index score (PIS), general health (GH), quality of work (QW), and quality of sex (QS). Conclusions: Despite various attempts to establish the best ureteral stent, the effect of double-j stent physical features on stent-related symptoms remained unknown. No verdict is conceivable without adequate empirical data

Episodic Visual Learning/Memory and Attentional Flexibility in Patients With Major Depressive Disorder After Clinically Effective Electroconvulsive Therapy

Objectives This study is a follow-up of a previous one reporting that the neuropsychological profile of pharmacoresistant patients with major depressive disorder referred for electroconvulsive therapy (ECT, ECT group) contrasted with that of their pharmacorespondent counterparts (NECT group). The NECT group exhibited severe visuospatial memory and minor executive deficits; the ECT group presented the reverse pattern. In that same ECT group, the current follow-up study examined the effects of clinically effective ECT on both cognitive domains 2 months later. Methods Fifteen ECT patients were administered Hamilton Depression (HAMD-24), Hamilton Anxiety (HAMA), Mini-Mental State Examination Scales and 5 tests of Cambridge Neuropsychological Test Automated Battery at intake (pre-ECT), end of ECT course (post-ECT), and 2 months thereafter (follow-up). Results Electroconvulsive therapy was effective in relieving clinical depression. After a post-ECT decline, the patients exhibited significant improvement in both Cambridge Neuropsychological Test Automated Battery, paired associate learning, and Stockings of Cambridge. By contrast, their major pre-ECT deficit in intra/extradimensional set shifting remained virtually unaffected. Conclusions Our findings suggest that attentional flexibility deficits may constitute a neuropsychological trait-like feature of pharmacoresistant, ECT-referred major depressive disorder patients. However, this deficit does not seem generalized, given patient improvement in episodic visual learning/memory and some indication of improvement in spatial planning after ECT