MOMENTUM CHANGE IN DIGESTION RELIEF HEADERS

This paper discusses and demonstrates a method developed in engineering design for sizing of the relief header, and stress analysis of the header. The Leung’s Omega calculation is used to size the header. An in-house, two-phase flashing flow, slip model predicts the force arising for a change in momentum with respect to time.

Stresses within the header pipework is analysed by use of available commercial software (e.g. CAESAR II and AutoPIPE). The analysis shows that the transmitted reaction force is up to 22% higher than the steady state load. This result is based on a relief header size that provides a relief flow rate of 1000 kg/s with a backpressure at the relief valve discharge of 30% of the set pressure. The contribution from momentum forces on the overall piping system can cause a multiplied effect of up to 2 times in comparison with the static case (without considering momentum forces).