Authors:Li Shuangxi, Li Guang(PetroChina Sichuan Petrochemical Co., Ltd.)

Abstract: In the storage and transportation system of a refining and chemical integration enterprise in Southwest China, when the crude oil storage tanks, refinery intermediate feedstock storage tanks and heavy and light waste oil storage tanks in the tank farm perform dehydration operations, the hydrogen sulfide concentration near the dehydration outlet often exceeds the alarm threshold, causing severe on-site odor and major harm to the environment and personnel health;

the discharged oily wastewater contains a lot of oil and carries oil sludge, which easily causes blockage of drainage pipes. In order to ensure odor-free tank dehydration and long-term stable compliance of the oily wastewater tank, the original underground dehydration system of the above-mentioned tank farm storage tanks was transformed into an above-ground visualized closed drainage system; in order to better meet environmental protection requirements, reduce the pressure of oily wastewater on the downstream sewage treatment plant, a set of high-efficiency coalescing pressure oil remover plus cyclone dissolved-air flotation unit was added.

The oil content of the externally discharged oily wastewater from the storage and transportation system was reduced from less than 100,000 mg/L to below 100 mg/L, effectively reducing the oil concentration of the wastewater discharged from the tank farm, and effectively recovering and separating the separated waste oil, reducing the loss of the unit during operation.

Keywords: oily wastewater; closed drainage; odor; high-efficiency coalescing pressure oil remover; cyclone dissolved-air flotation