Calculating vents: DIERS methods - Gassy Reactions

In the first folder , we presented the vent sizing methods developed by DIERS, for controlling runaway reactions in chemical industry reactors and equipment. In the same text, we gave a detailed presentation of the methods applicable to reaction systems with high vapor pressure ("High Vapor Systems").

This second issue concerns "Gassy Reactions". In the DIERS methodology , "Gassy Reactions" are condensed-phase reactions that produce incondensable gases such as CO, CO ₂ , N ₂ , NO, N ₂ O, O ₂ , H ₂ , HCl.... These are often decomposition reactions. When one of these reactions runs riot in an enclosure, the pressure in the enclosure is solely or essentially related to the accumulation of incondensable gases; there is no vapor pressure, or this contribution is negligible or not essential.

As a result, the system temperature is not controllable. Even if we manage to limit the pressure in the enclosure by operating a vent, there is no vaporization heat sink, the temperature rise is unaffected and chemical reactions accelerate with increasing temperature. These reaction systems are said to be untempered, meaning that the temperature of the reaction mixture is not linked to pressure by the relationship P = f(T), which would be imposed by a liquid equilibrium – vapor.

For these reactions, the pressure in the vessel depends on the filling ratio. The higher the filling ratio, the greater the pressure increase and the higher the rate of pressure rise. In laboratory tests designed to reproduce industrial conditions, such as Vent Sizing Package tests using closed measuring cells, the filling ratio frequently has to be limited to avoid bursting the measuring cell. As a result, experimental conditions may be far from adiabatic or industrial conditions, and it may be preferable in such cases to use open-cell tests to avoid this drawback. The sizing of vents to control runaway reactions producing non-condensable gases is based on the maximum gas production rate measured under adiabatic conditions or under conditions representative of the industrial situation. It is indeed conservative to assume that...