The crack gas compressors are the core equipment of the ethylene plant

whose smooth start plays an important role in the whole plant's start-up process. In traditional start-up process

the crack gas compressors start with the crack gas

which is replaced by other working mediums in recent years

such as nitrogen

natural gas or mixed hydrocarbon. Due to the impossibility to test on the equipment

the chemical engineering simulation technology has become the important tool to solve these problems. In this paper

according to the "steady-state/dynamic/start-up" method

a steady-state simulation model of crack gas compressors is built

and the steady-state operation parameters of the crack gas

nitrogen and mixed hydrocarbon were determined. Then

the steady-state model was converted to the dynamic model. At last

the safety and feasibility of transformation process between various working conditions were verified.