Including Inherent Safety in the Design of Chemical Processes

Past industrial accidents have raised major concern for the inclusion of safety as part of the design of a chemical process, an item typically carried out after the process design has been completed. In this work, a procedure for the inclusion of inherent safety that can be used to compare different technologies at the design stage is presented. The combination of two indices, one that rates the process routes and a second one that rates the process streams, provides the basis for a safety metric. Results from simulations of process flowsheets can be conveniently used to obtain the data needed for the application of the safety indices. The procedure was applied to two technologies for the production of ethylene and four alternatives for the production of methanol. In addition to the ranking of technologies from safety considerations, economic and environmental measures were also applied. The results provided the options with the best inherent safety properties, but conflicts with the other metrics were observed. It is shown how a given design can then be revised to improve one of the three properties under consideration. In particular, process modifications aiming to improve safety, guided from the values of the inherent safety indices, were explored. From the methodology, a selection of alternatives with suitable safety, economic, and environmental indicators can be identified.