(130d) Startup Optimization and Flexibility Analysis for Ethylene Procedures

Authors: 
Zhang, J., Lamar University
Ge, S., Lamar University
Xu, Q., Lamar University
Ho, T., Lamar University
Startup procedures of ethylene plants normally take several days, consume million pounds of materials, and generate a lot of flare emissions. Startup procedures also face many uncertainties. A single facility failure may lengthen the whole startup and dramatically increase flare emissions.

In our previous works, startup procedures have been simulated by dynamic simulation, and several improvement procedures have been proposed to reduce the startup time and flare emissions. Based on previous works, we build a MIP (Mixed-Integer Programming) model to optimize the schedule of the whole startup procedure. In this model, the startup procedure is divided into many steps of facilities, which can be re-scheduled by the MIP model to get optimized startup time and flare emissions.

The MIP model can also handle flexibility issues during startup. Possible delays of key steps are listed in the model, and mathematical programming can re-schedule subsequent steps to keep overall startup time minimal.

A case study is also presented. Comparing to base case, the optimized case reduces startup time by 20%, and reduced overall flare emissions by 50%. Moreover, even with delays of several key facilities, the total startup time and flare emissions are still less than the base case.