Process thermal safety - Assessment of runaway risks

Reaction runaways are not uncommon and have a definite destructive potential, which has led to a strengthening of regulatory systems, of which the Seveso Directive is probably the most representative. Assessing the thermal risks inherent in chemical reactions is often difficult because it calls on a number of different disciplines.

• Process design: the operating mode is a key risk factor. Obviously, a batch reaction will be more difficult to control than a semi-batch reaction, where one of the reagents is added as the reaction progresses.

• Chemical engineering: the design and construction of the technical equipment, and the control and regulation elements implemented, play a decisive role in controlling an exothermic reaction. The power of the heating and cooling system is particularly important in this context.

• Chemistry: the nature of the reaction and the properties of the compounds present must be known, not only under the planned operating conditions, but also in the event of deviations from these conditions (e.g. possible secondary reactions, instability of certain compounds, tendency to decompose).

• Physical chemistry and chemical kinetics: the dynamics of a chemical reaction and the physical and chemical properties of reaction mixtures are of paramount importance in any risk assessment.

Understanding and interpreting thermal data is not always easy. This document is intended to guide the reader through the interpretation of thermal data and the assessment of thermal risks by providing a systematic and structured approach – i.e. asking the right questions, giving the right answers derived from thermal analysis data.

To achieve this, we use a selective approach which ensures that all the necessary data has been determined and interpreted correctly. The systematic approach, developed in the safety research laboratory of a major industrial group, is based on a powerful tool: the elaboration of a failure scenario and the determination of criticality classes. It has proved its worth in many industrial companies.