(249q) Study on Advanced Plant-Wide Control Strategies of an Ethylene Plant

The production of ethylene is an important index to evaluate the strength and economy of a country, since ethylene is the raw material to synthesize other chemicals. Normally, ethylene is produced via the thermal cracking method. With this method, various feedstock will be firstly cracked into small molecular hydrocarbons, mainly ethylene and propylene in the furnace section. Then, the cracked gas will be compressed and dehydrated. After that, a series of chilling and separation processing will be conducted, so that main products such as ethylene, propylene, hydrogen, and methane will be recovered. The whole ethylene plant is highly material and energy integrated, which is susceptible to many external and inherent disturbances, which could upset a part of manufacturing process or even the entire plant. If these disturbances are not well adopted, significant utility or/and process losses could be induced. Therefore, an appropriate and optimal plant-wide control strategy is very important for ethylene plants to absorb these disturbances and accomplish the smooth production.

In this paper, we have studied possible best plant-wide control strategies for an ethylene plant via virtual dynamic simulations. First, we developed a plant-wide dynamic model for the studied ethylene plant. Next, the plant-wide dynamic model has been validated via real plant upset data to ensure its operability. After that, the model is employed to study the control performance of an inherent disturbance caused by a furnace shutdown for decoking operations. Several plant-wide advanced control strategies have been setup, simulated and compared to shorten the upset time period under such disturbances. Through this virtual study, it demonstrates that only small additional control efforts could effectively adopt such significant inherent disturbances with all productions still on specifications during the transitional time period. The best plant-wide advanced control strategy need not to stabilize every process responses; it should better utilize process dynamics of each operating sections to accomplish the disturbance adoptions.