General Aspects of Reactor Safety

A pharmaceutical intermediate was initially produced at a scale of 500 kg (product) per batch in a 2.5 m3 reactor. The reaction was the condensation of an amino-aromatic compound with an aromatic chloride to form a di-phenyl amine by elimination of hydrochloric acid. This acid was neutralized in situ by sodium carbonate, forming water, sodium chloride, and carbon dioxide. The manufacturing procedure was very simple The reactants were mixed at 80 °C, a temperature above the melting point of the reaction mass. Then the reactor was heated with steam in the jacket to a temperature of 150 °C. At this temperature, the steam valve had to be closed and the reaction left to proceed for a further 16 hours. During this time, the temperature increased to a maximum of 165 °C. Several years later, the batch size was increased to 1000 kg per batch in a 4 m3 reactor. Two years after this a further increase to 1100 kg was decided. 

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 consequences were an interruption of the whole plant for two months. For the particular process involved in the incident the interruption was over six months. The material damage was several millions of US dollars. 

The inquiry showed that the process was operated in the parametric sensitive range. As the batch size was increased to 1100 kg, the maximum temperature during the holding phase increased to 170 °C. Moreover, the thermometer had a range of 200 °C from -30 °C to +170 °C, because the reactor was multi-purpose equipment also equipped with a brine cooling system. Thus, the technical equipment was not adapted to the process conditions. 

Neither the process conditions nor the technical equipment of the reactor were adapted to the nature of the reaction. Moreover the effect of the increase in batch sized was overlooked. The process had to be changed to semi-batch operation in order to ensure a safe control of the reaction. 

---

General Aspects of Reactor Safety Table 5.3 Reactor characteristics. 

In the following chapters, an example reaction system will be used for illustrating purposes. In order to focus on thermal aspects of reactor safety, no explicit chemistry will be used, but a general reaction scheme is used instead ... 

In Section 11.2, general principles of reactor safety and heat balance of reactors are presented, with an emphasis on specific aspects of polymerizations. Section 11.3 is devoted to safety-related thermodynamics and reaction engineering aspects of polymerization reactions. In Section 11.4, cooling of polymerization reactors is reviewed. The chapter is concluded by a section describing safety aspects of industrial processes, together with technical risk-reducing solutions. 

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. 

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 notion that methods of statistical analysis should be applied to reactor safety standards was first put forward by Siddall of Atomic Energy of Canada Ltd., Chalk River, Ontario in 1959 (57). This early paper is of interest because it invokes the notion of a balance between increased wealth of the community that may be expected to accrue from the advent of nuclear power on the credit side, and risks of injuries and deaths because of the hazards of the nuclear process on the other it goes on to suggest money costs (economic criteria) as the avenue through which to achieve such a balance. The details given in the paper are only generally relevant today, but some of the introductory sentences have a modern sound to them and are worth quoting as an introduction to the basic philosophy of the probability approach to reactor safety. The study of nuclear-reactor safety (i.e., in 1959, some 15 years ago in the life of an industry now only 20 years of age) is in an unsatisfactory state. Some aspects of the problem have received... 

Section 2 introduces the general safety objectives, concepts and principles for the safety of nuclear installations with emphasis on the radiation safety and nuclear safety aspects of research reactors. This section draws on Ref. [1]. 

---