Simulation and optimization of an ethylene plant

The objective of this project is to develop a simplified ethylene plant model, which includes a thermal cracking section, a separation system and an integrated refrigeration system, and use it to study plant-wide time-domain optimization.

The mixture of ethane and propane is feedstock for the cracking furnace while free radical mechanism is a basis for the decomposition of hydrocarbons, A one dimensional plug flow model, integrated by LSODE package, is employed to describe the species profile, temperature profile, pressure profile, and coke thickness profile, and benchmarked by the industrial data. The pyrolysis gas is sent to a series of distillation for separations into the final products. An approximate model with lumping technology is used to predict the top and bottom product impurity and the required refrigerant, which are also benchmarked by plant data.

NPSOL is used to search the optimal operation points for the processes. Because of the simplification in the modeling work, preliminary optimization results are obtained. The optimization results show that the furnace part is the heart of the ethylene plant while the separation system and refrigeration system limits the maximum furnace effluent. By adjusting the feedstock flow rate and the dilution steam to hydrocarbon ratio, the gross profit of the plant is increased by 6%, comparing to the base case data.