Flowsheet Level Steady-State Multiplicities

Among many others, Giittinger (1998) and Sneesby et al. (1998a) study the occurrence of multiple steady states in columns with reactive core i.e. hybrid RD column). Their research work suggests that two types of multiplicities may occur in RD, 

Prom a mathematical point of view, the sufficient and necessary conditions for output multiplicity are given by the following inequalities. 

In the previous subsection multiplicity in RD has been described and possible causes have been discussed. This subsection addresses the consequences of multiplicity from an industrial point of view. Undesired situations can be encountered in RD processing due to multiplicity, namely, 

Implications for process control. Avoiding multiplicity is certainly an important consideration for process control and its interactions with design (Chen et al., 2002). An appropriate control configuration is an effective tool to avoid multiplicity. Giittinger and Morari (1997) show, for the MTBE column studied by Jacobs and Krishna (1993), that 

3 Additional Modeling Implications for Multiple Steady States 

---