- Title
- Physical, chemical and thermal changes of coals and coal maceral concentrates during coke formation
- Creator
- Xie, Wei
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2013
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The measured coke reactivity index (CRI) and coke strength after reaction (CSR) determined in experiments based on coke formed in pilot-scale coke ovens are the two main parameters that are employed to evaluate coke for its potential utilization in the blast furnace. Thermoplasticity, such as swelling, permeability and fluidity, chemical reactions, such as the evolution of gases and tars, and thermal changes, such as heat of devolatilisation and thermal conductivity, on coal heating are known to dominate the transformation of coal to coke in the coke oven, and determine the CRI and CSR of coke. Coal properties, such as vitrinite and inertinite components, and coking conditions, such as heating rate and particle size, have also been found to influence the physical, chemical and thermal properties during coking. Many studies have previously investigated the swelling of different coals and coal maceral concentrates as well as the influence of heating rate and particle size on swelling during coking. The literature has highlighted the correlations between swelling, mass loss and the properties of the released tars and gases for a range of coals and coal maceral concentrates using a number of techniques. However, the correlations between swelling and the dynamic evolution of total volatiles (gases and tars), and the physical and chemical properties of the evolved tars, are made from data collected from independent experiments and therefore the interpretations are not very clear. Previous work compared heat of devolatilisation between thermal coals and coking coals. For coking coals only, the differences in heat of devolatilisation and thermal conductivities between high fluidity and low fluidity coking coals also were studied. However, reasons for the differences in the thermal properties of different coals are still unclear. In particular, the effects of coal maceral components on heat of coal devolatilisation and thermal conductivity are still unknown. The potential associations of swelling and thermal changes with the properties of tars for coals and coal maceral concentrates are scarcely studied. The main objectives of this study are therefore to identify the sequence of physical, chemical and thermal changes of heating coal and coal maceral concentrates to provide insights into the fundamental mechanisms in the transformation of coal to coke. This work in particular is focused on (a) separation of coal maceral concentrates without using chemicals; (b) simultaneous measurements of swelling and thermal changes of heating coal and coal maceral concentrates from a single experimental run; (c) characterising the dynamic evolution of gases and tars for difference coal maceral concentrates; (d) revealing the mechanisms in the transformation of coal to coke thereby correlating the physical, chemical and thermal changes of coal and coal maceral concentrates. To achieve the objectives, three novel techniques were employed. A water based device called the Reflux Classifier was employed to separate coal maceral concentrates on the basis of varying settling rates of different density particles. The existing Computer Aided Thermal Analysis (CATA) technique was modified to simultaneously estimate swelling and shrinkage, permeability, apparent volumetric specific heat and thermal conductivity of heating coal and coal maceral concentrates. Swelling and shrinkage of the heating coal and coal maceral concentrates were measured by the contraction and expansion of a compressible spring. The permeability of heating coal pellet was estimated based on Darcy’s law by the measurements of swelling of coal sample bed and the pressure drop of gas flowing through the coal sample bed. The pressure drop of gas flowing through the coal sample bed was measured using a pressure sensor. Endothermic and exothermic behaviour of heating samples was evaluated based on the estimated apparent volumetric specific heat. The apparent volumetric specific heat and thermal conductivity were estimated by the measurements of the control, surface and centre temperatures of the heating sample. A new technique, Dynamic Elemental Thermal Analysis (DETA), was used to measure the evolution of total volatiles, gases and tars from different coal maceral components. The released tars of maceral concentrates during devolatilisation were condensed using a tar condenser, while the residual tars in char were extracted using solvents of acetone and toluene. The physical properties, such as boiling point, and chemical properties, such as elemental compositions, for condensable and extracted tars also were evaluated using the DETA technique.
- Subject
- coals; macerals; coke; blast furnace
- Identifier
- http://hdl.handle.net/1959.13/1037772
- Identifier
- uon:13484
- Rights
- Copyright 2013 Wei Xie
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT02 | Thesis | 3 MB | Adobe Acrobat PDF | View Details Download |