Practice-Oriented Approach to the Design of Safety Valves and Their Blow-Off Pipes for Flow of Gas/Vapour-Liquid Mixtures, Part 1

Abstract

The design of an integral safety valv-eblow-off pipe system embraces the following essential steps: 1. An incident scenario must first be defined. All reasonable deviations from proper operation of plant must be considered. 2. The flow state at the entry to the safety valve must then be ascertained (one-phase or binary flow); and 3. the minimal mass flow from the plant component to be protected must be calculated. Independently thereof, it is necessary 4. to determine the mass flow density in the blow-off pipe system; it is usually related to the cross-sectional area of the valve seat. The ratio of the two quantities gives the minimum necessary blow-off cross-sectional area. 5. In the final step, the pressure drop in the feed line and the counter-pressure at the valve exit must be examined in order to assure reliable functioning of the valve also in conjunction with the pipe system. Steps 1. to 3. are considered in this article, and steps 4. and 5. will be addressed in Part 2 to be published in this journal. Appropriate recommendations and the necessary equations are given for each step. The main emphasis is placed on applicability of the calculations.