Pressure relief values application

Appendix 0 Guideline for Application of Pressure Relief Values (PRVs)... 

Uncertainty is introduced at many stages in the sizing of pressure relief systems for runaway chemical reactions, and the application of a safety factor to offset this uncertainty may be appropriate. This Annex gives some guidance on the selection of an appropriate value for any safety factor. 

This is one of the simplest applications of the flow of a compressible fluid and it can be used to illustrate many of the features of the process. In practical terms, it is highly relevant to the design of relief valves or bursting discs which are often incorporated into pressurised systems in order to protect the equipment and personnel from dangers which may arise if the equipment is subjected to pressures in excess of design values. In many cases it is necessary to vent gases evolved in a chemical reaction. 

The difference between the two methods may be due to deviations from the applicability of the Clausius-Cjapeyron equation (for the alternative method). Therefore, G has been taken from equation (9.3) (the average value of G of 2738 kg/m2s between the relief pressure and maximum accumulated pressure) for sizing purposes. However, this must be,multiplied by the discharge coefficient of the safety... 

This method14 is for vapour pressure systems. It solves the material and energy balance equations, on which Leung s method (see 6.3) is based, in a step-wise manner. The method shares most of the conditions of applicability of Leung s method (see 6.3.1) but does not require values of parameters to be constant over the pressure range from the relief pressure to the maximum pressure. Indeed, systems in which there is a discontinuity in rate of reaction or physical properties can be handled by this method, provided that the step boundaries are chosen such that any discontinuity coincides with a boundary (see, for example, Figure A5.1).. 

Safety Relief Valves These valves become activated by upstream pressures that exceed some value. The valves serve as safety valves or relief valves. They are used in liquid or in gas, steam, or vapor applications. 

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