ABSTRACT
This chapter focuses on optimization from an economic point of view. It presents several optimization techniques but just to provide an introduction to the subject. Dynamic optimization requires complicated and lengthy calculations which have to be carried out offline. In static optimization the process is described by an algebraic set of equations and an economic objective function, indicating how the profit of the process depends on process conditions, values of raw materials and products, and so forth. In optimization an objective function and constraints have to be added to the process model. A step of optimization involves the process operators. Ethylene plants are particularly suitable for optimization because of the large volume of feed stocks processed. The variables for plant optimization are the furnace feed rates and severity targets for different plant feeds. Constraints considered in the optimization include projected furnace load and maximum severity limits for each feed type as well as ethane recycle limits.
