Alternative relief system sizing methods for tempered hybrid systems

2 Alternative relief system sizing methods for tempered hybrid systems 

Leung[341 has proposed an alternative sizing method for tempered hybrid systems (see A5.11). This method makes the same assumptions as that above, except that the conservative assumption that the allowable temperature rise is the same as that in a closed vessel does not need to be made. The method is therefore likely to yield smaller relief sizes than the method above. However, the method is more time-consuming to evaluate as it requires a trial and error procedure.  

Computer simulation can also be used for relief sizing (see Annex 4). This may be the only safe alternative in cases where physical properties are non-ideal, multiple reactions occur or there are significant continuing.feed streams or external heating. It will be necessary to choose a computer simulation package which can handle multi-component mixtures comprising both volatile and permanent gas components. 

It may also be possible to use computer simulation in cases where the reaction is initially tempered but stops tempering later in the runaway when a volatile solvent has boiled off. However, a good understanding of the reacting system would be required in order to have confidence in the results of such a simulation. Alternatively, the reaction could be treated as an untempered hybrid (see 8.4). 

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