VDE : an expert system for evaluation of vapor-liquid equilibrium data

Abstract

Evaluated data, more specifically vapor-liquid equilibrium (VLE) data, for designing equipment and improving models are critical to the chemical process industry. Because designs based on poor data often lead to inefficient or unsafe processes, with significant capital and human costs, there is an increasing concern and need for good data. Evaluation is a lengthy, strenuous, and costly task which requires considerable expertise. Therefore, the expertise for evaluating data is not readily available to small or middle-size corporations. The evaluation procedure includes error estimations, consistency tests, fitting to models, and eventual comparisons of data sets. In particular, the assessment of the errors requires a knowledge derived from years of experience with the experimental procedures. The need for numerical methods (including simulation and optimization) and for symbolic methods (including logical and heuristic reasoning) is characteristic of engineering and science. Hybrid expert systems, which couple numeric and symbolic computing, offer the best available technology to capture these fundamental aspects of scientific activities. They offer the best tools to capture the reasoning and the knowledge of data evaluators. VLE-DATA-EXPERT (VDE), a user-friendly hybrid expert system for the evaluation of vapor-liquid equilibrium data from published data, has been developed on a SUN-3/80 workstation using the Automated Reasoning Tool (ART). An architecture somewhat similar to the so-called blackboard offers sufficient modularity for incremental growth and maintenance. Ample use of menus and graphics improves the friendliness of the system. VDE reduces experts' evaluation time and helps novices to estimate imprecisions and inaccuracies of temperature, pressure, and composition from the relevant information provided in the publications, and to perform the statistical analysis of the data. These estimations are very challenging because the necessary information often is not present. VDE deals with missing information by using default values and default procedures. It knows about the thermometers, the pressure instruments, the methods for measuring the composition, sampling procedures and apparatus commonly used in vapor-liquid equilibrium experiments. In addition to providing a menu of classical models for mathematical representations of the excess Gibbs energy, VDE is capable of accepting other models given by the user.