Abstract: A large amount of dirty oil is produced in the preheating and cooling processes of coke drum, among which the light dirty oil during the preheating and cooling stages cannot be directly recycled due to its high water content. In traditional processes, this part of the dirty oil is mainly treated through long-term sedimentation and dehydration in the dirty oil tank before being recycled, resulting in the problems of prolonged treatment cycles, heat loss, and environmental pollution. In order to realize the direct recovery of the dirty oil, CNOOC Ningbo Daxie (Zhoushan) Petrochemical Co., Ltd. modified the venting system and the recovery process of the 2.4 Mt/a delayed coking unit, adding hot VGO feed, injection agent, waste heat recovery and direct refining process of light and heavy dirty oil. The goal that dirty oil could be directly refined without settling into dirty oil tank was realized, the process of dirty oil recovery was shortened, the energy consumption of the unit was decreased, and the environmental pollution was reduced. After modification, the amount of dirty oil thrown outside the unit decreased from 67 t/d to 0, which has achieved good energy-saving and emission reduction effects.

Key words: delayed coking, dirty oil, recycling, demulsifier