Dynamic Operability Analysis of Nonlinear Processes Based on a Network View

The increase of raw material and energy costs has caused a shift in process design philosophy such that engineers are forced to design complex plants utilising heat integration and material recycles. The process design which is based only on steady-state economic considerations often leads to processes that are difficult to operate. The dynamic operability analysis on nonlinear multivariable chemical processes is often difficult to perform. Thus, the study of process dynamic operability on the earlier stages of process development is rarely considered. In this work, an approach based on a network perspective and the concept of dissipative systems is developed. This approach views a large-scale nonlinear process as an interconnected system of individual mass and energy balances (treated as subsystems) and as such can be represented by the simple nonlinear models of individual subsystems and the interconnections between them. The dissipativity of these simple subsystems can often be easily determined based on dissipation inequalities. The dissipativity property (in terms of supply rate) of the entire nonlinear process can be parameterised by the dissipativity of individual subsystems, leading to a cluster of supply rates. The operability of the nonlinear process (e.g., stability and stabilizability) can then be determined based on the above parameterised dissipativity which is much less conservative than existing nonlinear analysis. The effects of interactions caused by the interconnections are considered explicitly in this network perspective. The stability and stabilizability analysis problem is then converted into a feasibility problem with linear matrix inequalities and can be solved numerically.