Advanced coal characterization with micro-focus X-ray tomography

J. Hoffmana, G. Naudeb, F. de Beera

aNecsa, Pelindaba, Pretoria (0001), South Africa

bExxaro, Roger Dyason Ave, Pretoria (0001), South Africa

Abstract

Coal remains one of the largest energy sources in the world and numerous industrially important chemicals are produced from coal. This is especially true in a developing country like South Africa where coal is abundant but of low quality. The aim of many coal researchers is therefore to maximize the amount of energy and chemicals that can be obtained from natural reserves through processes like gasification. Characterization of the physical properties of coal is an important and major field in coal research and gasification optimization and numerous methods are applied that include also micro-focus X-ray tomography. Porosity is a property of coal that is of crucial importance since this is the reaction surface area where the chemical conversion occurs during gasification. Porosity quantification is usually performed by destructive methods that are mostly an indication of only the connected pores and not the unconnected pores inside the sample. Therefore, micro-focus X-ray tomography as non-destructive testing method is especially important since the inside unconnected porosity can be isolated and calculated independently from the outside connected pores. Organic constituents (maceral) of coal directly determine the quality and reaction behavior of coal, and therefore are invaluable in predicting coal behavior and calorific values in gasification. Micro-focus X-ray tomography is a powerful technique to study the maceral and mineral distribution since the technique itself indicates different density regions and therefore could predict regions of different macerals and catalytic or inhibiting minerals. The relationship of these macerals and minerals with the reactive surface area (that is deduced from the porosity) is therefore directly observed and numerous modeling parameters can be concluded and also optimized. This paper therefore highlights how process tomography is used as a powerful and invaluable non-destructive research method in coal sciences and contributes to the intelligent beneficiation of this limited energy source.

Keywords: Coal Science; Micro-focus X-ray Tomography; Pyrolysis