Production of versatile char via lignite coal and leonardite pyrolysis
Notice bibliographique
Résumé
The effects of climate change due to anthropogenic activities have generated discussions on controlling greenhouse gas emissions. As a result, coal is predicted to lose prominence in power generation due to the greenhouse gas emissions associated with its combustion. Therefore, this research investigates char production from coal to provide alternate applications for coal postcombustion. Lignite coal and leonardite from the Poplar River mine in Saskatchewan, Canada, were characterized using proximate and ultimate analyses, pore structural analyses, X-Ray Fluorescence (XRF), Scanning Electron Microscope (SEM), and Fourier Transform Infrared (FTIR) spectroscopy to establish their physical and chemical properties. They were then used as feedstocks in the pyrolysis experiments to produce versatile char for different applications. Temperature and time were varied from 450 °C to 850 °C, and 30 minutes to 120 minutes, respectively, and their effects on the products’ distribution and characteristics were investigated. The results were subjected to statistical analysis using a two-way analysis of variance and pairwise multiple comparison tests to validate the observed trends. The catalytic effects of potassium, calcium, and iron on lignite and leonardite pyrolysis and their product characteristics were also investigated. The investigations were capped off with a kinetic study using the Coats-Redfern model-fitting approach. The ultimate and XRF analyses showed that lignite and leonardite possess similar elemental compositions. However, their proximate results revealed significant differences between them. Lignite possessed higher fixed carbon, 29.32 wt%, than leonardite, 16.65 wt% (air-dry basis), while leonardite had a higher volatile matter, 40.12 wt%, than lignite, 32.26 wt% (air-dry basis), which was attributed to the oxidation process leading to leonardite formation. The structures of lignite and leonardite were similar under the scanning electron microscope, while the FTIR and pore analysis also revealed similar identities. The product distribution showed that the chars produced from lignite and leonardite maximized at 450 °C and decreased as the temperatures increased due to higher thermal energies, allowing the various pyrolysis reactions to initiate and intensify. Consequently, the gas yields increased with temperature and maximized at 850 °C. The liquid yields peaked at 650 °C and decreased thereafter when the temperatures were increased due to the predominance of depolymerization reactions at lower temperatures, and cracking reactions at higher temperatures, respectively. The effect of time on the products’ yields was not very significant, especially at higher temperatures, because the reactions were faster. The analysis of variance (ANOVA) and multiple comparison test revealed that char properties, including pore volume, surface area, volatile matter, fixed carbon, H/C, and O/C ratios, significantly depended on temperature and time. Additionally, the structure of the chars, analyzed with Raman spectroscopy, revealed the evolution of the char’s structure into a more aromatic structure with temperature and time. Preliminary catalytic studies conducted using K, Ca, and Fe catalysts showed that K increased char yields in both lignite and leonardite, while Ca and Fe increased gas yields in leonardite and lignite, respectively. However, the Ca and Fe catalysts reduced the activation energies at high temperatures, while the K catalyst increased the activation energy, thereby acting as an inhibitor. The kinetic studies on the non-catalytic pyrolysis showed that the activation energy increased with the order of reaction. However, the first-order approximation best predicted the devolatilization rates in both lignite and leonardite, with absolute average deviations (AADs) less than 2%.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».