MACERAL COMPOSITION STUDY FOR VARIOUS COAL FRACTION SIZES, SEAM A1, WEST BANKO PIT, PT BUKIT ASAM TBK

• Main Author: Dian Rifaldi, Mirza
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/64024
• Institution: Institut Teknologi Bandung

The coal fraction size in mining activities changes along with the coal handling process; the process of extracting, loading, transporting, and crushing changes the size of the coal fraction at each stage of the activity. PT Bukit Asam Tbk. (PTBA) is experiencing problems with changes in coal quality in its mining activities. Based on the results of previous studies, this is thought to be caused by several factors, namely the heterogeneity of the PTBA coal seam, poor sampling conditions and techniques, the relatively increased percentage of refined coal, the analytical database used, and the distribution of minerals in the coal. Coal quality is closely related to the maceral composition of the coal, and differences in the maceral composition affect the heterogeneity of the coal. A sampling at each stage of coal handling without considering the physical properties of the maceral as well as the fraction size of the samples taken can result in unrepresentative samples that seem to cause changes in coal quality. Changes in the fraction's size and the coal handling process are related to the distribution and composition of the maceral group at a certain size fraction. Each maceral group has different physical properties; the huminite/vitrinite maceral group has relatively brittle properties, the inertinite maceral group has relatively hard properties, and the liptinite maceral group has relatively toughness and high tensile strength properties. This difference can cause the concentration of a group maceral at a specific grain size. This study aims to determine the relationship between the size of the fraction to the composition of PTBA coal maceral. A total of 6 samples were taken using the channel sampling technique ply-by-ply with an interval of 2 meters. Of the 6 samples, 3 were selected to represent the top, middle, and bottom of the Seam A1 coal seam. Each sample was then crushed and classified into 6 size fractions (+5 mesh, -5 to +35 mesh, -35 to +60 mesh, -60 to +120 mesh, -120 to + 230 mesh, and -230 mesh) to obtain a total of 18 samples. Samples from each fraction were then analyzed using the sieve analysis method and coal petrography. The petrographic analysis shows that Seam A1 coal is composed mainly of huminite, with huminite content ranging from 85.03 – 88.68% vol. (mmf); the inertinite content ranged from 8.07 to 10.96% vol. (mmf); and liptinite content ranged from 3.25 to 4.87% vol. (mmf). In addition, only small amounts of minerals are found in Seam A1 coal (upper:0.45%, middle: 0.17%, and lower 4.28% vol.). The composition of the huminite group maceral (vitrinite) relatively increases with decreasing size of the fraction, the composition of inertinite group maceral decreases with decreasing size of the fraction, while the composition of liptinite maceral has a random distribution/does not have a tendency towards coal fraction size. These results indicate that coal is a heterogeneous material, with changes in the maceral composition at each size fraction. Therefore, the size of the fraction and the composition of the coal maceral need to be a concern in the sampling process both at the mining front, stockpile, train loading station, and port. Sampling must be carried out on the overall size of the existing fraction to obtain a more representative sample and represent the actual condition.