Wetted area, Pool Fire Scenario, Packed Column, Bed, Chromatography Column

[rocketscientist]

I have an interesting problem for you. I am reviewing a rupture disc sizing of a chromatography column. Typically, these are packed beds with media or beads. There is a mobile phase that contains a solvent and a stationary phase. Solvents used in this column include ethanol and amyl acetate. By volume, they are typically 70-80% solid and 20-30% solvent slurry. The column is fed a slurry of solvent and product.

Recent calculations assumed two-phase flow which resulting in a 3-time increase in the diameter of the rupture disc. The feed line to the column is only 2". Digging into the calculations I found a few suspicious things: 1) the engineer assumed 100% of the column was the wetted area; 2) yet, he use an NFPA-30 deduction (Changing a 1 factor to 0.3) for the sprinkler system that looks inadequate even if it could reach the column from the rats nest of piping overhead.

I contacted a few manufacturers for chromatography columns and dug deep into literature on calculating the wetted area for a packed bed but could only find a reference to Table 4, API Std. 521, 4.4.13.2.3, 6th edition, 2014.

So, does anyone have any insight into calculating a wetted area for a packed bed containing only a fraction of flammable solvent or better yet, a chromatography column?

 

[Latexman]

How big is this column? Gas or liquid chromatography?

For a "column", whether packed or trayed, my company uses wetted area = 50% of the column wall area, as default. A detailed engineering analysis can over ride this. The heads are treated separately, the top head is usually not wetted, and the bottom head is usually wetted.

We take no NFPA 30 reduction of heat input from fire for "general sprinklers" (per NFPA 13), but we do (0.3 factor) for "direct, automatic water spray protection if provided at a rate of 0.25 gpm/ft2 or greater (per NFPA 15)".

Good Luck,
Latexman