Creating Signed Directed Graph Models for Process Plants

Abstract

The concept of qualitative modeling is briefly described. This paper focuses on the use of signed directed graphs to model fault propagation in process plants. It is common to use a unit-based approach for modeling. Two kinds of problems, which arise when constructing unit-based qualitative models, are identified: (1) The models are difficult to construct. (2) Ambiguities due to multiple causal paths may occur when the models are combined. A method that allows models to be built simply and correctly is proposed. The method incorporates features from the knowledge acquisition field, and a computer-aided modeling tool, Equipment Model Builder, has been built to support this method. A new modular approach is presented which overcomes the problem of ambiguous inference when qualitative models are combined. Two case studies were used to evaluate the method developed and the support tool.

Signed directed graph based modeling and its validation from process knowledge and process data

“…This plant topology information can be expressed by a text file that can be automatically generated by CAD tools (such as the DXF format developed by AutoCAD for enabling data interoperability). The program should extract related information from it to identify process units and flowsheets (Palmer and Chung, 2000). For a standard and uniform extraction of connectivity information, XML (eXtensible Markup Language) is one possible source of information.…”

“…Maurya et al (2003b) analyzed model description in detail by distinguishing an initial response and a steady-state response and modified the SDG by adding redundant equations. Palmer and Chung (2000) developed the modular approach to remove redundant paths. Neither of these efforts can solve the problem perfectly or efficiently without investigating real data, especially for large processes.…”

“…While detailed information can also be obtained to exclude the inexistent arcs or choose the dominant path, the effort would be multiplied because quantitative process knowledge is needed in addition to qualitative information. In the modular approach (Palmer and Chung, 2000), this task is left to the user, although semi-automated; it still highly relies on experience. Thus we limit the process knowledge of concern to P&IDs, that is to say, qualitative connectivity information.…”

“…Under this circumstance, complex structures, such as dividers, headers, or recycle loops, often make the qualitative algebra provide ambiguous results that are difficult to improve according to qualitative information because the intensity of each arc is unknown. This is an intrinsic problem of the SDG model, although a few researchers have made some improvements (Palmer and Chung, 2000;Maurya et al, 2003b).…”

An automated system for batch hazard and operability studies

“…The search continues in this manner until a given equipment item is located. For descriptions of more detailed algorithms which allow paths to be identified in plants containing equipment items with multiple connections see Palmer [31] and Drath et al [32].…”