Afrah, Bazlina Dawami, Boonrood Sajjakulnukit, and Muhammad Djoni Bustan. 2017. “Product Competitiveness of Upgrading Brown Coal (UBC) Process in Indonesia”. International Journal on Advanced Science, Engineering and Information Technology 7 (4):1289-95. https://doi.org/10.18517/ijaseit.7.4.2488.