(302f) Profit Control: A Paradigm Shift in Control System Design

Since the inception of feedback control, there has always been a strong, but vague, relationship between control system performance (in a disturbance rejection or regulatory sense) and the time-averaged profit of the plant (which is a function the nominal or steady-state operating conditions). The transformative concept underlying Profit Control is the simple notion of quantifying this relationship, which will enable control system design while simultaneously maximizing plant profit. Such an approach represents a paradigm shift in controller design, in that the controller can be tailored not only to the dynamics of the plant but also to the specific economic situation.

The notions of Profit Control will be illustrated through application to a Fluidized Catalytic Cracking (FCC) unit. The FCC process converts heavy oils into lighter more valuable hydrocarbons, and thus is a key unit in the overall profitability of a refinery. While maximum conversion is an element of process profitability, operation must take place in the context of other process constraints. For example, regenerator and cyclone temperatures must stay below 1000 K due to metallurgical limits. Similarly the manipulated variables (the catalyst recycle rate and air feed rate) are bounded by upper and lower limits. During plant operation a number of disturbances are expected to push the process away from the optimal steady state operating point. In this study we will consider the inlet temperature of the heavy oil and the coking characteristics of the catalyst. For a given control system and disturbance characterization one can easily determine the Expected Dynamic Operating Region (EDOR) of the process. Then to accommodate for FCC dynamics, one should re-optimize the steady-state operating point so as to ensuring the EDOR is contained in the constraint set. Within the Profit Control framework this re-optimization of the steady-state operating point is performed simultaneous to controller design and thus will achieve profit improvements.