Alternative methods to reduce the relief system size

1 Alternative methods to reduce the relief system size 

If an expensive downstream disposal system is to be provided, it is likely to be cost effective to seek the minimum safe relief size. Also, if the relief system size on a multipurpose plant is being checked for a new duty, there will be an incentive to demonstrate, if possible, that the existing relief system is adequate. 

If it is still desired to reduce the calculated size of the relief system, then more accurate calculation methods may give rise to a smaller relief size. 

Significant reduction in relief system size may be possible if the reacting system can be shown not to be inherently foamy (see 4.3 and Annex 2) so that account can be taken of vapour/ liquid disengagement within the reactor. There are two types of method which take advantage of this  

Type (b) methods above, are likely to yield smaller relief sizes than type (a). However, great care is needed when using type (b) methods to ensure that they do not undersize, e.g. through the inadvertent choice of a flow regime which does not occur in practice. Consequently, a higher safety factor might be expected for type (b) methods than type (a) methods. See Annex 7. 

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