Advanced coal characterization: A review

Coal is highly heterogeneous in nature, and for this reason, several analytical techniques are needed for its characterization so as to accurately predict its behavior during conversion processes such as combustion, gasification, or liquefaction. Conventional analyses such as proximate analysis, ash analysis, and ash fusion temperatures assume coal as a homogeneous material and provide only bulk properties. The performance correlations based on these analyses are unable to describe adequately the impact of coal quality on conversion efficiencies and plant performance. A number of advanced bulk analytical techniques, such as FTIR and C-13 NMR, provide information on the organic structure of coal. Chemical fractionation technique provides information on the inorganic matter present in coal in a form other than mineral grains. Bulk analysis techniques such as XRD and SIROQUANT provide information on the types of minerals present in coal. Thermomechanical analysis (TMA)an advanced bulk analytical techniqueprovides detailed thermal behavior of ash relevant to power-plant operations. Several advanced characterization techniques have emerged recently which consider pulverized coal as a heterogeneous material made up of individual particles and are able to examine these coal particles in much greater detail. An automated reflectogram (AR) technique provides a variation of reflectivitya measure of heterogeneity in the organic part. A computer-controlled scanning electron microscopy (CCSEM) analysis technique has been developed over the last 25 years to provide much more detailed information on mineral matter in coal and mineral-coal associations in pulverized coal. The paper discusses the details of these techniques and how the analysis from these techniques is used in modeling procedures to provide a better understanding of coal conversion behavior.