3 replies to this topic

[nabeelsp1036]

Hi,

 

I'm experiencing a case where there are two BDVs installed in a closed volume. The second BDV came into picture while modification of existing plant (addition of new vessel in red color in attached picture). All of the system (green + red) is built and operational. There is an expected change in composition in the process fluid due to which client wants us to check the adequacy of the whole system including the installed BDVs. As marked in attached rough PFD, BDV-2 starts with a time delay of 2 min than BDV-1.

 

I want to know the strategy how should i proceed with adequacy check for these BDVs.

 

Strategy 1:

Use all volume (green+red), use existing orifice size of BDV-1 and lets check the time to depressurize. Then open the BDV-2 after 2 min time delay with existing orifice size and check whether this whole system can still depressurize within 15 min. If yes, then both BDVs' orifice are OK. If not, then we need to increase BDV-2 size and fix it to get 15 min depressurization time for the whole system. I don't know if this solution is simulatable or not, but in reality this is what BDVs will be operating actually.

 

Strategy 2: 

Use volume of green part system for BDV-1 adequacy check by fixing the depressurization time of 15 min and calculate the required orifice size. If larger than existing, then inadequate; if smaller or equal to the existing orifice size, then adequate. Same procedure 'separately' for the red part for BDV-2. This procedure i see separates the two volumes which in reality will not be the case.

 

I hope i'm not missing any technical information to decide about the strategy. Please put up questions in case i missed anything critical.

Attached Files

•  BDVs Adequacy Check.pdf   26.74KB   14 downloads

Edited by nabeelsp1036, 22 January 2025 - 04:41 AM.

[Pilesar]

Check if first valve by itself is adequate. If not, check if both valves together are adequate. The time delay for the second valve opening seems arbitrary. For me, I would use the volume of the first vessel with the first valve and the volume of the second vessel with the second valve and treat them as independent systems. Why not?

[Dacs]

Unless you can isolate both green and red vessels (not present in the schematic), Strategy 2 won't work. Also, treating them separately may impact on the backpressure on both BDV, in which might affect the performance of both BDVs.

[nabeelsp1036]

Check if first valve by itself is adequate. If not, check if both valves together are adequate. The time delay for the second valve opening seems arbitrary. For me, I would use the volume of the first vessel with the first valve and the volume of the second vessel with the second valve and treat them as independent systems. Why not?

Time delay i believe in previous project was done due to limited capacity of flare package. 

"why not" -- i'll say, because this can never be the reality. In actual when the BDV-1 will be in action it will be facing all the volume (red+green).