Incorporating Integrating Variables into Steady-State Models for Plantwide Control Analysis and Design

Abstract

In many processes level loops are important in terms of the operability of plantwide control schemes. Arkun and Downs have presented an approach from which a steady-state gain matrix which includes the rate of change of levels can be calculated. Their approach makes use of a dynamic process model, which is often not available in practice. Steady-state process simulators assume that levels are perfectly controlled. Thus, these simulators cannot be used directly to obtain gain matrices that include level variables. This paper presents an approach to using steady-state simulators to obtain approximately the same gain matrix as that in the Arkun and Downs approach. Once this matrix is calculated, it can be used to assess the operability of plantwide control schemes. The methodology is developed using a distillation tower system, and then it is applied to analyze the “snowball effect” in a three reactor/three distillation tower plant. The methodology is also applied to the Tennessee Eastman process where level...