(346b) Integrated Environmental, health and safety index (IEHS): An index’s evolution into a flowsheet design tool

Authors: 
Jairam, S., Texas A&M University
El-Halwagi, M., Texas A&M University

A great wealth of knowledge about environmental impacts, employee health and process safety is available from databases, simple formulas, or first principle knowledge. A designer charged with developing the process flowsheet for a new plant often cannot access this information due to time restraints, market pressures or difficult interpretation. This is heightened in operations that are small, produce specialty chemicals or use novel processes. Ruling the design decisions during this stage are quick economic analyses and rules of thumb. This stage is often overlooked by many who want to focus on the initial reaction selection or the general input output structure of the plant. In terms of design decisions, EHS mistakes are often made in this stage or can only start being examined here due to lack of specificity.

The proposed index will adapt the EHS index developed by Koller et. al. [1] specifically for this process flowsheet development phase. It will add information to design decisions that is easy to compute and interpret, while replacing rules of thumb for safety. From start to finish, the procedure will be built around the lack of information from new chemicals and novel units. This will work for designs ranging from an incomplete flowsheet to a rigorous technoeconomic study. The index will provide information on the effects of design decisions on the entire plant, as well as their environment, health and safety consequences.

The main addition to the index will be a set of factors quantifying different interaction effects. These factors can be seen as a different perspective on the same design. The chemical mixing interactions will be assessed using first principle equations and predicative variables. The perspective of the maintenance engineer changes the potential failure rate of the unit through unit-process interactions. A simplified and automated HAZOP team will look at the unit-unit interactions to understand the operability of the design. These new variables will be available for optimization and gives the designer a sense of how well the pieces “fit” together. The inclusion of EHS aspects in design choices will better represent the decision to management as well as the designer. This is in addition to preventing unsafe plants from advancing past this phase by working with the designer to pinpoint the problem in a transparent manner.

References

[1] Koller, G., Fischer, U., and Hungerbühler, K. (2000) Assessing Safety, Health, and Environmental Impact Early during Process Development. Ind. Eng. Chem. Res. 39, 960–972.

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