Ombilin coal low rank coal maceral rank type upgraded brown coal utilization Additive Asem-Asem coal BCL technology Bayah Bukit Asam CBM Coal Coal liquefaction Dispersing additive LSWR South Sumatera Spontaneous combustion Tertiary coal UBC UCG apparent viscosity calorific value coal liquefaction coal quality coal sedimentation coal water mixture comparative petrography crossing point temperature differential thermal analysis exploration financial analysis geology inherent moisture intrusion effect investors kerosene moisture content oils for UBC and oils substitute organic petrology petrographic analysis petrographic characteristics petrography presidential decree presidential instruction rheology spray oil stabilizing additive