Dear all,

Recently we were checking the adequacy of existing Flare network and Flare KODs in some of our oil and gas production stations for increased flowrates. The design flow rate was 1400 ksm3/day

We found that the flare headers are adequately sized based on header back pressure calculations. However the Flare KOD nozzles (16" nozzles) failed the momentum criteria based on the Shell DEP guidelines. The KOD diameter and length were found to be adequate. We were ending up with 20" KOD inlet (with half cut pipe) and outlet nozzles. The existing piping diameter of 16" was adequate. Replacing the KOD came out to be the only option as changing the nozzles alone is not practical considering the shutdown time limitations.

The current DEP specifies an inlet momentum of maximum 5000 kg/ms2 at inlet nozzles with halfcut pipes. With shoepentator the limit goes up to 10,000.

Please share your experience on the momentum criteria. What are the implications in case of a deviation? Do we expect lower seperation efficiencies ? Or liquid carryover to flare tip? How important is this criteria? Can it be relaxed considering the fact that maximum flowrates in Flare header are expected rarely? Do we have simillar guidelines in other company engineering guides?

Regards
Benoy

The way i view the momentum criteria is it link to the separation efficiency. Exceeding recommended momemtum criteria will lead to lower separation efficiency as compare to benchmarked separation efficiency.

There is another DEP for Gas-Liquid Separator. This document is used for normal gas liquid separation. It has lower momemtum criteria. The figure that you have quoted, has been adopted for Flare KOD which is intermittent in service (as far as i interprete these two DEP).

As far as i aware, only SHELL DEP requiring lower inlet momemtum to ensure / enhance separation efficiency. Other company guideline adopt in different way.