http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:503 Measurements of the intrinsic reactivity of chars to oxygen are increasingly being sought as an indicator of the combustion potential of fuels. The coal reflectogram has been used to characterize the chemical properties of coal and its resultant char structure. In this study, six Australian coals varying in rank were separated using density separation technique to obtain vitrinite and inertinite rich fractions. Chars were obtained from these density fraction samples in a Drop Tube Furnace (DTF) at 1673 K. The reactivity of the chars was measured non-isothermally in a Thermal Gravimetric Analysis (TGA) in the temperature range of 573-1073 K. The results suggested that with the increase in the coal rank, the maximum reactivity of chars derived from vitrinite rich fractions decreases, while the reactivity of chars derived from inertinite rich fractions decreases with the increase in the inertinite content in samples and has no obvious relationship with rank. The kinetic parameters were derived using data from non-isothermal TGA after accounting for changing in surface area with conversion. The frequency factor is found to decrease with increasing coal FMR, defined as the summation of each reflectance value multiplied by its frequency, for a constant activation energy (E = 146 kJ/mol). This suggests that the behavior of a maceral is characterized primarily by its reflectance distribution instead of the type of its parent coal. 2010-04-27T05:40:54.858Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:543 Coal is a heterogeneous substance and its heterogeneity is identified and characterized by variation in reflectance. The main objective of this paper is to characterize the heterogeneity of char and to correlate it with the coal reflectogram, which accounts for both rank and maceral composition effects. Chars from two density fractions in a set of coals were obtained in a Drop Tube Furnace (DTF) at 1400 degrees C in N-2 environment. The chars were examined under a Scanning Electron Microscope (SEM) and the morphology information was obtained from the image-processing technique. The average porosity of char changes systematically with the FMR of its parent coals (defined as the summation of each reflectance multiplied with its frequency). The char porosity increased with an increase in FMR up to a critical value around 98. With further increase in FMR, the corresponding char becomes dense. The char macro porosity distribution was found to be related to the coal reflectogram. In general, the char porosity distribution shows two peaks, which corresponds to the inertinite and vitrinite peaks in reflectogram. The intensity depends on the maceral content. The relationship between the char porosity and coal reflectance for this set of sample has been found, which is strongly dependent on the coal rank. However. these findings cannot be applied to coals with a strong maceral association (microlithotype). 2010-04-27T05:40:33.078Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:527 Proximate and ultimate analyses of a coal are regarded as sufficient to describe its chemical composition, and they have been widely used for practical applications. However, coal is actually a heterogeneous substance and is composed of different materials (macerals); therefore, the corresponding chemical compositions are average values of the individual composition of the macerals present in the coal. The reflectance distribution of a coal (the reflectogram), which shows the heterogeneity of the coal, can be represented by several reflectance bins. In this paper, the variation of chemical properties of a coal is differentiated by the difference in reflectance. The main focus of this paper is to establish correlations between chemical properties of a single reflectance bin and its reflectance from a maceral-independent approach and maceral-dependent approach. The bulk chemical properties (volatile matter (VM) content, ratio of hydrogen to carbon (H/C), etc.) of a coal then can be obtained by adding the properties of each individual reflectance bin together. Proximate and ultimate analyses with reflectogram analyses were conducted for 29 coal samples. A least-squares fit strategy was applied to derive the correlations, which were then used to predict the bulk properties of another eight samples. The relative error of the estimated VM from the maceral-dependent approach is 3.9%, whereas the relative error from the maceral-independent approach is 7.9%. No single reflectance bin data are available in the literature; therefore, comparisons between the properties of single reflectance bin from maceral-dependent approach and bulk properties of maceral-rich fractions (bulk VM content versus mean maceral reflectance) in the literature have been made, and both show similar qualitative trends. 2010-04-27T05:39:06.090Z ]]>