Wildays method including disengagement for vapour pressure systems

5 WILDAY S METHOD INCLUDING DISENGAGEMENT FOR VAPOUR PRESSURE SYSTEMS 

This method131 is a modification of Leung s method for vapour pressure systems (see 

3) and shares the same conditions of applicability. It allows some account to be taken of vapour/ liquid disengagement for systems which are not inherently foamy. However, this method assumes that homogeneous two-phase relief from the reactor occurs, whereas actually the two-phase mixture would contain a higher fraction of vapour than this. This assumption should increase the conservatism of the method in that more latent heat than assumed is lost via the relief system. However, this is balanced by considerable uncertainty in estimating the reactor void fraction at which total vapour/ liquid disengagement would occur. 

Before using the method, the void fraction at disengagement must be evaluated at conditions corresponding to the maximum accumulated pressure during relief. This can be done by level swell calculation (see A3.3) or possibly by a small-scale experiment that uses depressurisation to achieve the same vapour superficial velocity as in the full-scale reactor during relief (see Annex 2). The required relief rate can then be calculated fromt31  

The method is only valid if disengagement occurs before the pressure would have turned over due to sufficient emptying during two-phase relief. The following applicability criterion131 needs to be applied (at conditions corresponding to the maximum accumulated pressure) to the result obtained from equation (A5.14)  

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