Many chemical processes are exotherm and release a defined amount of energy. If the energy released can't be removed instantaneously, the temperature will rise. Even those processes that are intended to be run isothermally show a small deviation from the target temperature. This temperature deviation may have important implications on reaction kinetics and safety of the process. Temporary temperature changes are due to physical effects, and vary with the reactant addition rate, the heat release rate, the process dynamics, and the reactor vessel. Such behavior may also be caused by limitations of the temperature control or heating and cooling capacity. This occurs when reactions are fast and strong and the heat release is larger than the heat removal capacity. When this happens, a defined amount of heat is accumulated temporarily, and released again over time. Consequently, the temperature changes initially, but returns to the defined target temperature at the end of the reaction.
In chemical process scale-up, understanding temperature change and the associated heat that is accumulated by the reaction are critical to understand process safety. This white paper discusses how to assess the implications of changing temperature regimes in chemical reactions. Examples from both lab and pilot plant are used to answer the following questions:
- Why and when does thermal accumulation occur?
- Is accumulation important to consider, and how big is it?
- What is the impact of an incorrect calculation of accumulation?