- Title
- Fundamental studies of the coal to metallurgical coke transformation
- Creator
- Isah, Umar Abdullahi
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2023
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The ever-increasing concerns of the community about the impact of coal use on the environment have led to the adoption of more efficient and cleaner technologies for coal utilisation [1]. In coal utilisation processes, the fundamental understanding of the coal’s chemical, physical, and structural properties remain vital and often challenging to coal experts [2, 3]. However, understanding coal's structural properties are essential in identifying the chemical and physical interactions with other reactants [2]. The coke-making industry is interested in predicting the strength of coke and coal blends based on the parent coal. The accurate coke quality prediction for blending is essential in relation to coal blends. Furthermore, the chemistry of coal transformation to coke during the coking process is still not well known and clearly understood. The technical risk of obtaining high-resolution spectra and results interpretation is still a major concern. It impedes the technical marketing capability of providing reliable recommendations to customers and marketers alike. Moreso, lost time due to unpredicted and unexpected changes in coal quality, resulting in production losses leading to a decrease in revenue and turnover, is not desirable. Therefore, developing proper and applicable analytical tools that can be used online to produce accurate real-time data is of great importance to the economic and viable sustainability of the coal industry [4]. In addition, the intricate nature of the coal structure makes it complicated to use a single analytical technique. A particular technique chosen by an analyst depends on the task at hand. However, multiple techniques are often used to complement each other in providing more information or confirmation of the presence of a particular specie [5, 6]. FTIR has been extensively used to investigate the changes in coal structure during carbonisation and provides valuable information on coals' chemical composition and structure. The spectral analyses of real-time changes have seldom been conducted. Few prior studies measured spectra at specific temperatures using different pellets prepared from individual coal. This method had a substantial possibility of experimental error due to the heterogenous nature of coal. Also, mixing the pellets with KBr, as mostly done by researchers, will not provide actual information on the behaviour of these coals during their transformation to coke in the coke oven because of reactions with the binder during heat treatment. A novel contribution to the field of coal transformation to coke has been developed in this study. The most significant contribution is the development and demonstration of a novel analytical system (in-situ FTIR/MS technique) which facilitates in-situ evaluation (under reaction conditions) of the coal to coke transformation by FTIR (of the solid), coupled with MS for real-time evolved gas analysis using pelleted samples comprised of only coal, rather than pellets containing KBr as have been applied in most prior work. This provides for a potentially very powerful analytical system with the capability of providing new understanding about chemical changes that occur during the thermal transformation of coal to coke. Other state-of-the-art techniques, namely solid-state 13C-NMR and Raman spectroscopy, but these latter studies used thermally transformed samples that were analysed at ambient conditions (ex-situ). A thermogravimetric analysis (TGA) and computer-aided thermal analysis (CATA) methods were also utilised to characterise and study the devolatilisation and kinetics of the Australian coals. The complementary application of the aforementioned state-of-the-art techniques can provide new understandings about the chemical changes that occur during the coking process and thereby help inform coal blending strategies of commercial importance. The concentration of several functional groups based on the FTIR spectra of the analysed samples was determined. These parameters provide quantifiable and measurable evidence of increased aromaticity and the loss of aliphatics with increasing coking temperature. This study also revealed that coal aromaticity and the degree of substitution of aromatic rings (DOS) are rank dependent. However, as observed for coal C, maximum fluidity has some contributing effects. Thus, coal rank and vitrinite composition in coal influence coal-to-semi-coke transformation and higher maximum fluidity in mid-ranked coals. Results obtained from the solid-state 13C-NMR technique revealed that coal rank and vitrinite content are the dominant factors responsible for the increased aromaticity and aromatic bridgehead carbon in coal. However, the maximum fluidity also showed some contributing effects. In addition, results from the Raman analysis revealed that coal rank, vitrinite composition and maximum fluidity influence the crystallite size and, thus, the carbon structure in coals. Results from the TGA analysis also revealed that coal with higher vitrinite content and lower fluidity devolatilises at a lower maximum rate of weight loss, while coal with lower vitrinite content and higher fluidity devolatilises at a higher maximum rate of weight loss. By increasing the heating rate, the devolatilisation rate shifted to higher temperatures, and both Tmax and Rmax increased. In addition, the second-order reactions in both the primary and secondary devolatilisation stages fit better representations of the non-isothermal pyrolysis processes of the studied coal samples, with the activation energy ranging from 43 to 59 kJ/mol. The total activation energy ranges from 99 to 106 kJ/mol based on increasing coal rank. These values depend on each coal's chemical structure, determining pyrolysis reactivity. For the Australian coals studied in this work, the coal rank based on the mean maximum reflectance impacted more on the chemical–structural changes during the coal-to-semi-coke transformation. Its influences on hydrogen and carbon monoxide evolution were demonstrated. In addition, for C2 – C5 evolution, coal rank has an effect within the plastic region (350 - 450 °C), while maximum fluidity has an impact after resolidification (>500 °C). Finally, results obtained from the aforementioned state-of-the-art techniques employed in this study have provided new understandings about the chemical changes that occur during coal coking and thereby help inform coal blending strategies of commercial importance.
- Subject
- coal; coke; coking; FTIR; spectroscopy; TGA; raman; 13C NMR
- Identifier
- http://hdl.handle.net/1959.13/1479692
- Identifier
- uon:50350
- Rights
- Copyright 2023 Umar Abdullahi Isah
- Language
- eng
- Full Text
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