State-based modelling in hazard identification

Abstract

The signed directed graph (SDG) is the most commonly used type of model for automated hazard identification in chemical plants. Although SDG models are efficient in simulating the plant, they have some weaknesses, which are discussed here in relation to typical process industry examples. Ways to tackle these problems are suggested, and the view is taken that a state-based formalism is needed, to take account of the discrete components in the system, their connection together, and their behaviour over time. A strong representation for operations and actions is also needed, to make the models appropriate for modelling batch processes. A research prototype for HAZOP studies on batch plants (CHECKOP) is also presented, as an illustration of the suggested approach to modelling.

Functional Modeling View on Product and Process Engineering in Design and Operations

“…Model-based methods for fault diagnosis have been reviewed by Venkatasubramanian et al , To support qualitative model-based monitoring and emergency planning, a modeling methodology that can support causal and consequential reasoning is needed. Several such systems have been suggested; one particularly popular form is the signed directed graph, which is qualitative; however, often the knowledge representation used is structure-centered rather than functionality-centered. Another class of graphsbond graphsconstitute an interesting originally quantitative graphical representation of a physical dynamic system that covers multiple energy domains seamlessly.…”

An automated system for batch hazard and operability studies

“…However, they do not allow a flexible enough representation of the alternative operating sequences which arise from deviations from intended operations, or where some part of the plant is modified. McCoy et al [28] have considered the use of Petri nets in hazard identification systems. They found that if the order of two operating instructions is exchanged, or if a new equipment item is added to the plant, it is very difficult to modify the Petri net to take account of this.…”