Closed Gassy Systems

Closed gassy system gas release in a closed reactor. 

Closed tempered system vapor pressure in a closed system. 

Open tempered system vapor release in an open system. 

The volume of gas potentially released by a reaction (including secondary reactions in criticality classes 4 and 5) can be known from the chemistry or measured experimentally by appropriate calorimetric methods, as for example, Calvet calorimetry, mini-autoclave, Radex, or Reaction Calorimetry (as V at T k. and /Jmes). It must be corrected for the temperature to be considered, MTSR (class 2), MTT (class 3 or 4), or Tf (class 5). Where the gas stems from the main reaction, only the accumulated fraction (X) will be released  

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For gassy systems, this will depend on the rate of pressure rise in a closed system (rate of gas generation). Since gassy systems are untempered, the rate of interest is the maximum rate. This is likely to be at close to the maximum temperature reached by the runaway. 

The information required for relief sizing for gassy systems is the rate of gas evolution, Qg, (for the full-scale vessel), as a function of temperature. This can be calculated from the rate of pressure rise in the small-scale test by means of one of the following equations111,121. Equation (A2.3) is the more general equation and is best used for data from closed tests ... 

In an open test, the pressure measured will be,the pressure in the containment vessel. If the test is done with the containment vessel closed and the nitrogen pressure control system off, then any permanent gas produced by the reaction will cause the containment vessel pressure to rise. Thus a constant containment vessel pressure indicates a vapour pressure system and a rising containment vessel pressure indicates a gassy or hybrid system. 

Huff, J. E., Emergency Venting Requirements for Gassy Reactions from Closed System Tests, Plant/Operations Progress, 3(1), 50-59 (Jan. 1984). 

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