Thermal Methods Used in Chemical Process Safety

While thermal safety is a major concern for operators of industrial chemical processes, it also plays an important role in the development of safe processes. Indeed, a safe process, i.e. one that is under control, is also one that delivers products of consistent quality. Thermal process safety has a long tradition, marred by industrial accidents which have led to the development of a risk assessment methodology and specific instrumental methods.

The methodology followed for safety studies must enable an efficient assessment of thermal risks, i.e. it proceeds in stages from the numerous thermodynamic, kinetic and technical data used in thermal risk assessment, so as to determine only the data required, but all the data required. The approach presented in this article is based on a failure scenario, which provides the key questions guiding the design of experiments and consequently the choice of instrumental techniques to be used. The techniques presented are illustrated by examples of solved problems, based on industrial cases.

The recommended approach is based on an industrial question or problem, from which an experimental plan is drawn up. The measurements obtained are then evaluated, often using original techniques. The results must then be interpreted in terms of risk, in order to define a risk reduction strategy. Thermal methods are at the heart of this approach. The first paragraph describes a systematic procedure for thermal risk assessment.

If the data required is very diverse, so are the devices on the market. It is therefore important to find the most appropriate measurement method for solving a given safety problem. The second section is devoted to the principles of thermal methods, and more specifically to their specificity in the context of safety studies. These methods can be divided into two main categories: thermal analysis and calorimetric methods.

Thermal analysis instruments operate mainly in temperature scanning mode, and are dedicated to determining energy potentials (temperature and pressure). These are generally microcalorimetric methods, working on small sample masses. These methods are ideally suited to the study of secondary reactions and thermal stability. Thermal stability also requires kinetic data: the notion of runaway time (tmr _ad ) under adiabatic conditions. Methods for determining energy potentials and runaway times are described in the third paragraph.

The fourth section deals with reaction calorimeters which, as their name suggests, are designed to study chemical reactions from a safety angle, but often also from an optimization angle. After a description of the various calorimeters available on the market,...