3 replies to this topic

[stacgre]

Good morning all,

I am working on a project that has a CO2 and H2S process gas stream that will need a relief system designed to scrub the H2S. so far the only thing that we have come up with is a packed bed liquid/vapor contactor that has been garunteed to scrubb out the the H2S before reliving into the atmosphere.

there is a lot of push back from the engineering group based on reliving through a packed bed and the potential fro plugging.

my question is two fold:
1. What is the API regulation that clearly identifies the design mentality that should be used when designing proper relieving paths for gas streams? I have looked into it, but i have been not able to find a specific passage of code that strictly identifies the design requirements for relieving systems.

2. if there have been systems used through packed beds in the past, that are currently in industrial process operation, can you please provide me with some exaples. One that I was informed of recently is the Alky Relief Neutralizer...please comment.

thank you all in advance.
GS

[Technical Bard]

In many plants, such a relief is routed to the flare, where assist gas (natural gas) is added to bring the heating value above some regulated level (say 12 MJ/m³) to ensure combustion of the H2S, and then burned. I have also done something similar using an enclosed incinerator instead of a flare.

[S.AHMAD]

1. What is the differenc between your packed bed tower with others such is for absorbtion or distillation?
2. Is it worst than a fixed-bed reactor?
3. My view is that your case is not a special case - it is the same as an existing similar cases.

[Dacs]

I've seen systems where the outlet going to PSV is located on top of the vessel downstream of the trays/bed.

Thing is, the people who are thinking of placing the outlet upstream of the bed/trays are considering the failure of the vessel because of severe plugging of the internals in such way that the upstream of the internals is experiencing pressure above the PSV set pressure.

However (IMHO) I find this not credible due to these points:
1. In H2S scrubbing, you are more likely to have pressure delta because of foaming, and even so, the pressure drop will be at the magnitude below 1 bar.
2. Fouling is a long term process (in this kind of system), something which will not happen instantly. In this case, a properly designed system will place a PDAH to detect excessive pressure drop.
3. Beds/trays are designed to handle a certain pressure delta across the internal. Even if we consider total fouling which constricts the flow that may result to overpressure, I believe you'd break apart the internals first (due to failure of tray/bed support), which I believe is very unlikely as well.

My 2 cents