The vacuum distillation (VD) unit in the petroleum refinery separates the heavier
fraction of crude oil from the atmospheric distillation unit (ADU) into light
vacuum gasoil (LVGO) and heavy VGO (HVGO) under a vacuum to
avoid thermal cracking of the heavier hydrocarbons. The
two-phase mixture of the reduced crude oil (RCO) liquid and
vapor from the ADU enters the VD column flash zone and flashes
further under low pressure.