Chemical Reaction Hazards (CRH)

What are the main reasons explosions take place in Chemical plants?

All exothermic reactions generate heat which together with solvents or other volatile liquids may generate very high pressures. This can also happen when the reaction temperature rises above the boiling point of the solvent.

A reaction may be exothermic even if it is necessary to heat the reaction mass initially to get the reaction started. As the temperature of a reaction increases it can lead to a thermal runaway created by a linear loss of temperature but also because of an exponential rise in temperature due to the exothermic reaction. In such a case the control of vessel will be lost and there is little time for correcting the situation. Consequently, the reaction vessel may be at risk either from over-pressurisation due to violent boiling or rapid gas generation. Moreover, the elevated temperatures may initiate secondary, more hazardous runaways or decompositions. If either of these scenarios generates enough pressure and the vessel relief systems are inadequately designed, there is a risk of vessel rupture or uncontrolled release of flammable or toxic gas. Seveso in Italy and Bhopal are two major incidents caused by runaway reactions.

How can GVS Cibatech help?

For thermal instability hazards, published data may be adequate for common materials. However, for proprietary materials or mixtures, laboratory testing will be required. For thermally unstable substances or mixtures, tests must be conducted. The test may be small scale screening tests such as Differential Scanning Calorimetry (DSC). This quick test may provide data of onset conditions and the magnitude of the decomposition.

If the DSC test result indicate that instability occurs at close to the operating conditions, then more accurate testing techniques such as Accelerating Rate Calorimetry (ARC) may be required. Interpretation of the data from such tests requires a good understanding of the test results so that appropriate safety margins can be applied.

For exothermic chemical reaction processes, which have the potential to runaway, a good understanding of the thermodynamics, kinetics and gas generation / vapour pressure of the process is needed to evaluate the consequences of deviation from the specified process conditions. GVS Cibatech can conduct thermal safety studies using various tools like DSC, ARC, RC1. Results from these investigations are used in combination with any thermal stability data to allow an understanding of the behavioural limits during foreseen deviations in the normal process and designing your processes to ensure safe operation.

There can be no ‘one-size-fits-all’ solution when consultancy service on Chemical Reaction Hazards are needed. The best place would be to start with a discussion of how we can tailor our services to meet your requirement, please contact us.