Residual fuel

Residual fuel is the heavy fraction left at the bottom of the refinery distillation and conversion train, blended into marine grades RMA through RMK under ISO 8217. It is dense and viscous, carrying asphaltenes, sediment, sulfur, vanadium, and sodium, so it needs heating to about 130 to 150 degrees C and centrifugal cleaning before injection. The named grades scale by maximum viscosity at 50 degrees C, from RMA 10 up to RMK 700, with RMG 380 the common heavy grade; combustion of residual fuel falls under the MARPOL Annex VI sulfur limits and the scrubber or low-sulfur-blend choice.