Abstract: This paper analyzed the operation problems of 1.2Mt/a delayed coking unit in PetroChina Lanzhou Petrochemical Company and introduced the results after technical transformation. The problems in existing unit included: (i) high content of oil, COD and suspended matter in coke quench sewage, which was unable to reuse as a cold coke cutting water; (ii) coke fines in the sour water from fractionator overhead, and in coking gasoline and diesel, which influence long period operation of the downstream unit; (iii) design defects in process interlock of heating furnace, leading to an invalid use. To solve these problems, a cold coke sewage treatment system and a coke powder removing system were added. Then the treated cold coke sewage can be reused and the influence of coke fines on the operation for downstream unit is reduced; the interlocking mode of heater furnace was changed from“one-out-of-one”to “two-out-of-three”, and is successfully applied after transformation.

Key words: delayed coking, coke quench sewage, sour water, coke fine, process interlock