1999

Heikkilä, Anna-Mari

An inherently safer design is one that avoids hazards instead of controlling them, particularly by reducing the amount of hazardous material and the number of hazardous operations in the plant. Methods developed to date have largely been for the evaluating the safety of a proposed design. In the future the emphasis will be more and more on the synthesis of an inherently safer plant. At the moment it seems that the best practice is not adopted quickly enough by the potential practitioners. The aim of this work is to try to reduce this hinder by presenting an improved method for inherently safer design. In this thesis an Inherent Safety Index for conceptual chemical process design is presented. This is required, since inherent safety should be considered in the early phases of design when the major decisions on the chemical process are made. The presented methodology allows such a consideration since the index is based on the knowledge available in the preliminary process design stage. The total index is divided into Chemical and Process Inherent Safety Index. The previous is formed of subindices for reaction heats, flammability, explosiveness, toxicity, corrosiveness and chemical interaction. The latter is formed of subindices for inventory, process temperature, pressure and the safety of equipment and process structure. The equipment safety subindex was developed based on accident statistics and layout data separately for isbl and osbl areas. The subindex for process structure describes the safety from the system engineering's point of view. It is evaluated by case-based reasoning on a database of good and bad design cases i.e. experience based information on recommended process configurations and accident data. This allows the reuse of existing design experience for the design of new plants, which is often neglected. A new approach for computerized Inherent Safety Index is also presented. The index is used for the synthesis of inherently safer processes by using the index as a fitness function in the optimization of the process structure by an algorithm that is based on the combination of an genetic algorithm and case-based reasoning. Two case studies on the synthesis of inherently safer processes are given in the end.