EVALUATION OF OPERATING PROCEDURES BASED ON STATIONARY-STATE STABILITY

The safe and reliable operation of chemical plants depends on high-integrity operating procedures. Such procedures often involve process transition through stationary states. The stability of these states is an important part of the integrity evaluation. The methodology presented in this paper qualitatively identifies families of inherently stable chemical operations and establishes design rules for the synthesis of stable stationary states. These rules have been developed using the Routh-Hurwitz conditions for three qualitative levels of dynamic system models. These levels represent the gains of the dynamic system by the signs of the gains (+, 0, -), the signs and their equality (+, 0, -, =), and finally the gains represented by their order of magnitude values (+, 0, -, =, <, <<, >, >>). Example design rules have been developed during the synthesis of operating procedures for a series of vessels with composition control and temperature control of an exothermic chemical reaction. The most robust design rules apply to systems that can be proven stable by the sign level of gain representation. Less robust rules with a wider range of applicability to dynamic systems have been developed using the equality and order of magnitude representations.