A new approach for the early runaway detection in chemical reactors by coupling UV-visible and temperature sensors was developed. Measurable variables such as i) conversion and ii) temperature were used as input to our model based on the divergence calculation. The runaway criterion was defined when the divergence of the reactor becomes positive on a segment of the reaction path. We used a lab-scale chemical reactor (0.5 L) working under batch isoperibolic conditions, equipped with two kinds of sensors: i) a set of three Pt thermo-resistances for measuring the temperatures both within the reactor and in the cooling jacket and ii) an UV-visible probe for the indirect evaluation of the conversion through measurements of light absorbance. The early warning detection system (EWDS) was tested for the sulphuric acid catalyzed esterification of acetic anhydride and methanol, a very simple reaction but releasing ~ 70 kJ per mole of anhydride consumed. The responses given by EWDS were examined during the simulation of runaway reactions Different chemical heat flows were generated by varying the concentration of the sulphuric acid and adding at once the acetic anhydride into the reactor. The behaviour of the detection criterion was evaluated comparing the EWDS signals using both temperature and conversion as input variables, with the responses obtained from only temperature measurements. A detailed kinetic model was also developed to solve the differential energy and mass balance equations and define the runaway boundaries. Results showed the importance of an input variable indirectly related to conversion in such kinds of processes where other enthalpy variations (i.e. due to an endothermic mixing of the reagents) may hide a thermal runaway.
An Integrated Approach for the Early Detection of Runaway Reactions by Using UV-Visible and Temperature Sensors
AMPELLI, Claudio;
2013-01-01
Abstract
A new approach for the early runaway detection in chemical reactors by coupling UV-visible and temperature sensors was developed. Measurable variables such as i) conversion and ii) temperature were used as input to our model based on the divergence calculation. The runaway criterion was defined when the divergence of the reactor becomes positive on a segment of the reaction path. We used a lab-scale chemical reactor (0.5 L) working under batch isoperibolic conditions, equipped with two kinds of sensors: i) a set of three Pt thermo-resistances for measuring the temperatures both within the reactor and in the cooling jacket and ii) an UV-visible probe for the indirect evaluation of the conversion through measurements of light absorbance. The early warning detection system (EWDS) was tested for the sulphuric acid catalyzed esterification of acetic anhydride and methanol, a very simple reaction but releasing ~ 70 kJ per mole of anhydride consumed. The responses given by EWDS were examined during the simulation of runaway reactions Different chemical heat flows were generated by varying the concentration of the sulphuric acid and adding at once the acetic anhydride into the reactor. The behaviour of the detection criterion was evaluated comparing the EWDS signals using both temperature and conversion as input variables, with the responses obtained from only temperature measurements. A detailed kinetic model was also developed to solve the differential energy and mass balance equations and define the runaway boundaries. Results showed the importance of an input variable indirectly related to conversion in such kinds of processes where other enthalpy variations (i.e. due to an endothermic mixing of the reagents) may hide a thermal runaway.Pubblicazioni consigliate
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