(29e) Dynamic Simulation of CGC System Under Ethylene Plant Turnarounds

CGC system (Cracked Gas Compression system), or Multistage compression system, is a vital section during ethylene production. It is located after the cracking furnaces and quench towers, and ahead of the distillation section, which is considered as the "heart" of an ethylene plant because its reliability, stability and sustainability determines the production capacity of that plant.  Thus, the CGC system needs to be strictly controlled and operated, especially during plant turnarounds.  Generally, plant planned turnarounds include startup and shutdown operations, which have two levels of requirements: i) A feasible and safe startup/shutdown strategy needs to be well developed.  Many past turnaround cases failed due to compressor surge, which caused severe equipment damages and unnecessary flaring.  ii) An optimal startup/shutdown strategy is better to be pursued if possible in order to minimize startup/shutdown time and reduce flaring emission, raw material usage and energy consumption.

Based on the above consideration, this paper employs rigorous dynamic simulations to help plant turnaround operations, i.e., examine and improve operation strategies of a CGC system for ethylene plant startup and shutdown. For safety consideration, anti-surge process design and control strategies are dynamically evaluated along with alternative turnaround procedures. Dynamic operating trajectories for every stage of CGC are also identified.  Assisted by the dynamic simulation, the improvement of plant startup and shutdown performance are demonstrated.