PIP--PROCESS INVENTION PROCEDURE: A PROTOTYPE EXPERT SYSTEM FOR SYNTHESIZING CHEMICAL PROCESS FLOWSHEETS

Most of the recent design research has been focused on the development of more rigorous procedures for the design or the synthesis of subsystems of chemical plants. At the preliminary stage of design, however, less than 1% of ideas ever prove to be successful, so that the emphasis at this stage of a design should be placed on the quick screening of numerous process alternatives. The computer program described in this research is used to develop conceptual designs. PIP (Process Invention Procedure) is an hierarchical based expert system for the synthesis of chemical process flowsheets. It uses a combination of qualitative knowledge, i.e. heuristics, and quantitative knowledge, i.e. design and cost calculations, to identify the unit operations involved in a flowsheet and the interconnections between those units. A hybrid, expert system control architecture was developed for PIP that allows these two types of knowledge-bases to interact at each decision level while inventing the flowsheet. In addition, at each decision level, where finer details of the process structure are added, the significant design variables are identified, and the processing costs (both annualized capital and operating) are calculated in terms of these design variables so that a decision may be made on whether to terminate the project or to continue on to the next level. PIP has the advantage of very rapid response times (short-cut models are used so that the calculation for a complete plant takes only a few seconds) and ease of changing the structure of a flowsheet. The design of the user interface for PIP took into account three very important considerations: (1) the structure and characteristics of the system\u27s decision strategy and the way it is presented to the user; (2) the state of the problem at any point in time as it is perceived by the user; and (3) the physical representation of the data and results. Thus, PIP allows a design engineer to invent and to evaluate initial chemical flowsheet structures rapidly, to identify possible process alternatives, and to obtain an estimate of the optimum values of the design variables