Thermal process safety

Thermal Process Safety , Expert Commission for Safety in the Swiss Chemical Industry, Basle, Switzerland, 1993. 

ESCIS 1993. Thermal Process Safety Data, Assessment Criteria, Measures. Safety Series, Booklet 8. Basel, Switzerland Expert Commission for Safety in the Swiss Chemical Industry. April. Order online at www.escis.ch/seiten/englrsh/ publication.htm. 

Hoffmann, W. (2000). "The Basic Principles of Thermal Process Safety Towards a Better Communication Between Safety Experts and Process Chemists." Process Chem. Pharm. Ind., 389-408. 

The kinetic and thermodynamic characterisation of chemical reactions is a crucial task in the context of thermal process safety as well as process development, and involves considering objectives as diverse as profit and environmental impact. As most chemical and physical processes are accompanied by heat effects, calorimetry represents a unique technique to gather information about both aspects, thermodynamics and kinetics. As the heat-flow rate during a chemical reaction is proportional to the rate of conversion (expressed in mol s 1), calorimetry represents a differential kinetic analysis method [ 1 ]. For a simple reaction, this can be expressed in terms of the mathematical relationship in Equation 8.1 ... 

The introduction of this knowledge and a presentation of these methods are the objective of this book. In the present chapter, the essential theoretical aspects of thermal process safety are reviewed. Often-used fundamental concepts of thermodynamics are presented in the first section with a strong focus on process safety. In the second section, important aspects of chemical kinetics are briefly reviewed. The third section is devoted to the heat balance, which also governs chemical... 

When considering thermal process safety, the key of mastering the reaction course lays in governing the reaction rate, which is the driving force of a mnaway reaction. This is because the heat release rate of a reaction is proportional to the reaction rate. Thus, reaction kinetics plays a fundamental role in the thermal behavior of a reacting system. In the present section, some specific considerations on reaction kinetics with regard to process safety consider the dynamic aspects of reactions. 

Understanding the heat balance is essential when considering thermal process safety. This also applies to the industrial scale for reactors or storage units, as well as at laboratory scale for understanding the results of calorimetric experiments. In fact, the same heat balance terms will serve in both situations. For this reason, we first present the different terms of the heat balance of a reactor with a reacting system. This is followed by an often-used and simplified heat balance and finally we will study how reaction rate is affected by adiabatic conditions. 

Gygax, R. (1993) Thermal Process Safety, Data Assessment, Criteria, Measures,... 

Presently there is no direct quantitative measure of the probability of occurrence of an incident, or in the case of thermal process safety, of the occurrence of a runaway reaction. Nevertheless, if we consider the runaway curves presented in Figure 3.3, the two cases presented are very different. In case 1, after the temperature increase due to the main reaction, there is enough time left to take measures to regain control or recover a safe situation. If we compare the probability of runaway in both cases, it becomes clear that the probability of triggering the runaway is higher in case 2 than in case 1. Thus, while we cannot easily quantify probabilities, we can at least compare them on a semi-quantitative scale. 

Like most rules of thumb, this one, too, may lead to dangerous misjudgments with respect to the thermal process safety, if not applied correctly. The following shall demonstrate this. One of the fundamental theories used for the safety assessment of exothermic chemical reactions is explained in detail in Chapter 4.2 the thermal or heat explosion theory by Semenov [18], The central statement of this theory is that an explosion-like runaway of an exothermic chemical reaction will always occur... 

Gygax R (1993) Thermal process safety, data assessment, criteria, measures. In ESCIS (ed) ESCIS booklets, vol 8. SUVA, Luzern... 

Even if polymerization reactions are critical from the point of view of thermal process safety, there are means to systematically identify the risks and to design the... 

---