Abstract: A model for 4.0 Mt/a wax oil hydrocracking unit fractionation system of CNOOC Huizhou Petrochemical Company Limited is established by process simulation software. A comprehensive systematic analysis and diagnosis for the fractionation system was conducted to find out the unreasonable or operation parameter optimization space. Optimization measures are proposed and implemented such as reducing the pressure of the main fractionator, minimizing the flow of the recirculated tail oil to the furnace, and optimizing the stripping steam volume, resulting in improved the clarity of cutting, the separation of products, and the yield of high-value products such as heavy naphtha and aviation kerosene. The economic benefit of the unit is increased. At the same time, the energy of the fractionation system is comprehensively optimized. The load of the heating furnace is vacated through the reduction of operation pressure of the fractionation tower and the optimization of the heat distribution, which solves the bottleneck of insufficient heating furnace load and increases the production flexibility of the unit.

Key words: hydrocracking, fractionation optimization, product separation, comprehensive energy optimization