200
8 Thermal Process Safety
vessels, they can be initiated, for example, by external heat sources or through
contamination within the tank itself. During a production process in a reactor,
runaway reactions can arise from the heat produced by the desired reaction or by
undesired decomposition reactions set off by the accumulation of reactants, lack of
a cooling medium, loss of agitation, etc.
Applying thermal process safety within process risk assessment involves identifying and managing the thermal risks that are present, which includes a characterization of (1) the energy potential of the chemicals involved in the process,
(2) their potential reaction and decomposition rates, and (3) the implications for
the process equipment. This normally requires the review of substance data (e.g.,
physicochemical properties), the use of estimation methods (e.g., QSARs based
on the molecular structure), thermodynamic and kinetic calculations (e.g., heat
balances), and experimental measurements (e.g., testing of thermal stability).
In this chapter, Sect. 8.2 introduces some of the fundamental concepts of thermodynamics and kinetics related to reactor stability. Then, Sect. 8.3 (1) introduces
important thermokinetic concepts, (2) presents the scenario of a thermal runaway
as result of a cooling failure during an exothermic batch reaction, 1 and (3) analyzes
thermal risks in terms of impact and probability and evaluates the level of risk.
Finally, Sect. 8.4 applies these concepts within the process risk assessment of the
grinding of cyanuric chloride, which was first introduced in Chap. 7. For further,
in-depth explanations of these concepts and additional examples, see the textbook
developed by Stoessel (2008).
8.2
Heat Balance and Reactor Stability
Ensuring safe process conditions for a chemical process is based on a good
understanding of its heat balance. Some of the fundamental characteristics that
define a chemical process and directly affect the generation and management of
its heat include:
• the mode of the reaction (e.g., batch, semi-batch, continuous)
• the type of mechanism used for heat removal (e.g., external cooling via reactor
wall, melt, or evaporative cooling, etc.)
• the choice of operating parameters (e.g., temperature, concentration, dosing time,
stirring intensity, etc.)
• the design of the reactor (e.g., specific cooling surface, stirrer, reactor material,
etc.)
1 Most of the chemical reactions performed in the fine chemical industry are exothermic.
8 Thermal Process Safety
vessels, they can be initiated, for example, by external heat sources or through
contamination within the tank itself. During a production process in a reactor,
runaway reactions can arise from the heat produced by the desired reaction or by
undesired decomposition reactions set off by the accumulation of reactants, lack of
a cooling medium, loss of agitation, etc.
Applying thermal process safety within process risk assessment involves identifying and managing the thermal risks that are present, which includes a characterization of (1) the energy potential of the chemicals involved in the process,
(2) their potential reaction and decomposition rates, and (3) the implications for
the process equipment. This normally requires the review of substance data (e.g.,
physicochemical properties), the use of estimation methods (e.g., QSARs based
on the molecular structure), thermodynamic and kinetic calculations (e.g., heat
balances), and experimental measurements (e.g., testing of thermal stability).
In this chapter, Sect. 8.2 introduces some of the fundamental concepts of thermodynamics and kinetics related to reactor stability. Then, Sect. 8.3 (1) introduces
important thermokinetic concepts, (2) presents the scenario of a thermal runaway
as result of a cooling failure during an exothermic batch reaction, 1 and (3) analyzes
thermal risks in terms of impact and probability and evaluates the level of risk.
Finally, Sect. 8.4 applies these concepts within the process risk assessment of the
grinding of cyanuric chloride, which was first introduced in Chap. 7. For further,
in-depth explanations of these concepts and additional examples, see the textbook
developed by Stoessel (2008).
8.2
Heat Balance and Reactor Stability
Ensuring safe process conditions for a chemical process is based on a good
understanding of its heat balance. Some of the fundamental characteristics that
define a chemical process and directly affect the generation and management of
its heat include:
• the mode of the reaction (e.g., batch, semi-batch, continuous)
• the type of mechanism used for heat removal (e.g., external cooling via reactor
wall, melt, or evaporative cooling, etc.)
• the choice of operating parameters (e.g., temperature, concentration, dosing time,
stirring intensity, etc.)
• the design of the reactor (e.g., specific cooling surface, stirrer, reactor material,
etc.)
1 Most of the chemical reactions performed in the fine chemical industry are exothermic.