2 replies to this topic

[HKk]

Dear Friends

I would like to know the governing case for flare height calculation in NG based Ammonia Plant. What could be the point from where flow is to be considered for this. If flow from different points ( eg LTS o/l Absorber i/l , o/l NG line) are to be considered concurrently or only one point of flaring is to be considered for calculation.

regards

[kkala]

I would like to know the governing case for flare height calculation in NG based Ammonia Plant. What could be the point from where flow is to be considered for this. If flow from different points ( eg LTS o/l Absorber i/l , o/l NG line) are to be considered concurrently or only one point of flaring is to be considered for calculation.

I can only say that once (1990) we specified flare header size based on hydrocarbon gas discharge, given by the foreign company elaborating basic engineering (mainly for cost estimation) for an ethylene revamp/propylene plant in a Refinery. There were quite a lot of discharges to flare, not all of them occurring simultaneously. As informed, there were some 12 discreet cases and 8 or 9 of them were accepted to occur simultaneously, giving the max load to flare. The whole treatment was by computer in USA and understood to be rather complex, but we had no participation in it.
For a fertilizer plant producing NH3 from NG, case may be simpler. It may be easier to estimate discharges to flare in case of fire, power failure, cooling water failure, etc, starting from each individual PSV (or other discharge to flare). Not only good knowledge of the plant, but also of the local regulations and practices is necessary, as I had understood at that time. Usually not all is clear (at least in the case of Refinery), so sound assumptions are necessary to proceed.
One final note: In another refinery a very conservative flare design was realized some 25 years ago. It has now been recognized as useful, since it covered so many new units or revamps. Not being expert, I feel that "max load" to flare (for what frequency? and how this related to discharges?)can be subjective and should be clearly documented.
Hopefully someone expert can contribute to the subject.

Edited by kkala, 06 March 2011 - 06:27 AM.

[Erwin APRIANDI]

Hi HHk

for generic and standard calculation of flare stack you can follow the calculation which is given in API STD 521