Site-modeling and Its Applications

A large-scale chemical production site consists of multiple production and utility plants that are interconnected with utility and material-flow networks. The idea of having an integrated mathematical model (site-model) to assist in site-wide operations and development is gradually being accepted by the industry. This paper presents some experiences in constructing a site-model based upon simple linear plant models that can be generated directly from historical plant data. To handle discrete conditions such as equipment selection, a site-model is normally built as a mixed integer linear programming (MILP) model that consists of the main energy and material balances of each plant unit and their interconnections. With discrete variables, the model is able to handle problems with multiple time periods and/or scenarios, making it suitable for various types of applications. A modeling environment has been tailored for site modeling that integrates a graphical user interface for model generation, the Access database for model management, and an Excel spreadsheet for customizing data input/output. This paper will present a few industrial applications of applying the site-model for production planning, assisting in investment decisions, maintenance planning and scheduling, and optimizing long-term material and utility supply contracts. Modeling, solution techniques and analytical methods regarding these applications will also be presented in this paper.