Coal Petrography & Fuel Chemistry
Report of the project:
In two sub-projects BGR investigates chemical and petrographical properties of exclusively selected coal probes in three distinctive test areas affected by coal fire zones: Wuda, Gulaben and Rujigou. During the summer - campagne 2004 and 2005 and in collaboration with Deutsche Montan Technologie GmbH (DMT) round 150 coal channel samples were collected mainly from coal seams at the respective coal fire zones within the particular test areas.
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For the purpose of maturity determination via measurement of vitrinite reflectance, the coal sample mate-rial was gently crushed at BGR to a grain size of 0-1 mm. Wendt Scientific Preparation Labor, Lehrte prepared high gloss polished block samples from the coal channel samples collected during the summer-campagne 2004. These polished block samples were examined by Reinhardt Geological Consulting International, Hannover by applying reflected light fluorescence microscopy in the determination of vitrinite reflectance and the analysis of maceral group composition.
All micropetrographic results attained were secluding verified in the coal petrography laboratory at BGR and the combustion- and oxidation relevant appearances and phenomena as well as prominent features of the examined coals and specific micropetrographic characteristics were complemented. Recapitulating, in all examined polished blocks fluorescent macerals of the liptinite group are only sporadically observed.
Shrinkage cracks in the macerals of the vitrinite group
Source: BGR
The perm-carboniferous coals from the Wuda test area are considered to be of low coalification as the vitrinite reflectance ranges between 0.91 and 1.01 % Rr. In the coal fire zone 8 within the Wuda test area the temperature increase related coalification grade rises from 0 ,91 % Rr to 1.01 % Rr and is comparable with the values of the high reflecting macerals of the inertinite group (oxidised cell tissue). With regard to the micropetrographic features, the perm-carboniferous coals exhibit over and over again thermal encroachment, in particular in form of shrinkage crack, “melt-out” pores and in few cases the be-ginning of coke formation.
The jurassic coals of the remaining test areas are considered to be of high coalification stage with the overall vitrinite reflectance from 1,6 to 2,2 % Rr. These display a much more significant effect of the thermal and tectonic impact giving rise to the formation of “melt-out” pores cokes and mylonite.