Thermal safety assessment

Fierz, H. (1994). "Assessment of Thermal Safety During Distillation of DMSO."... 

Several methods have been developed over the years for the thermochemical characterisation of compounds and reactions, and the assessment of thermal safety, e.g. differential scanning calorimetry (DSC) and differential thermal analysis (DTA), as well as reaction calorimetry. Of these, reaction calorimetry is the most directly applicable to reaction characterisation and, as the heat-flow rate during a chemical reaction is proportional to the rate of conversion, it represents a differential kinetic analysis technique. Consequently, calorimetry is uniquely able to provide kinetics as well as thermodynamics information to be exploited in mechanism studies as well as process development and optimisation [21]. 

For the determination of reaction parameters, as well as for the assessment of thermal safety, several thermokinetic methods have been developed such as differential scanning calorimetry (DSC), differential thermal analysis (DTA), accelerating rate calorimetry (ARC) and reaction calorimetry. Here, the discussion will be restricted to reaction calorimeters which resemble the later production-scale reactors of the corresponding industrial processes (batch or semi-batch reactors). We shall not discuss thermal analysis devices such as DSC or other micro-calorimetric devices which differ significantly from the production-scale reactor. 

Thermal Safety of Chemical Processes Risk Assessment and Process Design. Francis Stoessel Copyright 2008 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31712-7... 

The six key questions presented above ensure that the essential knowledge about the thermal safety of a process is addressed. In this sense, they represent a systematic way of analysing the thermal safety of a process and building the cooling failure scenario. Once the scenario is defined, the next step is the actual assessment of the thermal risks, which requires assessment criteria. The criteria used for the assessment of severity and probability are presented below. 

Wiss, J. (1993) A systematic procedure for the assessment of the thermal safety and for the design of chemical processes at the boiling point. Chimia, 47 (11), 417-23. 

These points are explained in detail in this chapter. In a first section, the general aspects of reaction engineering for batch reactors are briefly presented. The mass and heat balances are analysed and it is shown that a reliable temperature control is central to the safety of batch reactors. The different strategies of temperature control and their consequences on reactor safety are explained in the following sections. For each strategy, the design criteria and the safety assessment procedure are introduced. The chapter is closed by recommendations for the design of thermally safe batch reactions. 

The safety assessment for isoperibolic reactions is essentially the same as for isothermal reactions. Since the initial temperature of the reaction mass is often equal to the temperature of the cooling system, the MTSR may be calculated in the same way by using Equation 6.12. The thermal stability of the reaction mass must be ensured at this temperature (MTSR). 

Using the thermogram represented in Figure 7.7, assess the thermal safety of the substitution reaction example A + B —> P (see Section 5.3.1) performed as an isothermal semi-batch reaction at 80 °C with a feed time of 4 hours. At industrial scale, the reaction is to be in a 4 m3 stainless steel reactor with an initial charge of 2000kg of reactant A (initial concentration 3molkg 1). The reactant B (1000kg) is fed with a stoichiometric excess of 25%. 

Stoessel, F. and Ubrich, O. (2001) Safety assessment and optimization of semibatch reactions by calorimetry. Journal of Thermal Analysis and Calorimetry, 64, 61-74. 

Assess the thermal safety of the intended storage. Propose technical solutions to improve the safety. 

Gygax, R. (1993) Thermal Process Safety, Assessment, Criteria, Measures, Vol. 8 (ed. ESCIS), ESCIS, Lucerne. 

The objective of the book is not to turn the reader into a specialist in thermal safety. It is to guide those who perform risk analysis of chemical processes, develop new processes, or are responsible for chemical production, to understand the thermal aspects of processes and to perform a scientifically founded-but practically oriented-assessment of chemical process safety. This assessment may serve as a basis for the optimization or the development of thermally safe processes. The methods presented are based on the author s long years of experience in the practice of safety assessment in industry and teaching students and professionals... 

Part I gives a general introduction and presents the theoretical, methodological and experimental aspects of thermal risk assessment. The first chapter gives a general introduction on the risks linked to the industrial practice of chemical reactions. The second chapter reviews the theoretical background required for a fundamental understanding of mnaway reactions and reviews the thermodynamic and kinetic aspects of chemical reactions. An important part of Chapter 2 is dedicated to the heat balance of reactors. In Chapter 3, a systematic evaluation procedure developed for the evaluation of thermal risks is presented. Since such evaluations are based on data, Chapter 4 is devoted to the most common calorimetric methods used in safety laboratories. 

The dinitration process posed thermal hazards requiring thorough safety assessment. 

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... 

The flow chart showing the iterative safety assessment procedure for a chemical process under normal operating conditions (c.f. Section 2.1) has its central step in the evaluation of an adequate thermal design of the process. This is shown in a simplified form as the comparison of the chemically produced heat and the heat removal capacity of the system. A necessary prerequisite to this assessment of the suitability of the design is the knowledge of the time course of the heat production rate, which itself is directly proportional to the chemical reaction rate. This explains the pivotal significance of the identification of a reaction rate law that describes the investigated process with sufficient accuracy, and its parameters. 

The complete procedure of assessment of the thermal safety of cooled semibatch processes shall be demonstrated with the help of an example ... 

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