4 replies to this topic

[Helme75]

Dear all,

 

My name is Norhelme and this is my first post to this forum.

 

I have a request from our customer to change their acetic acid relief valve and rupture disc used to relief to atmospheric to closed system.

 

Previously, the relief is vent to atmospheric, however due to incident that cause chemical burnt to  people, the plant management has decide not to allow that anymore.

 

Though, it will go to closed system, it is not to thermal destruction (flare) system. As Acetic acid is easily mix with water, the idea of water scrubber looks credible as it will strips acetic acid and left gas to atmosphere with acetic acid free.

 

Water scrubbing system normally design with continuous feed gas, and not intermittent or once in a blue moon of PSV that will pop up.

 

Therefore, I am looking for any idea, practical and proven solution to address this specific issue that may be been implemented else where.

 

Many thanks in advance for your kind attention.

 

Norhelme

Process Engineering

[fallah]

 

I have a request from our customer to change their acetic acid relief valve and rupture disc used to relief to atmospheric to closed system.

 

Previously, the relief is vent to atmospheric, however due to incident that cause chemical burnt to  people, the plant management has decide not to allow that anymore.

 

Though, it will go to closed system, it is not to thermal destruction (flare) system. As Acetic acid is easily mix with water, the idea of water scrubber looks credible as it will strips acetic acid and left gas to atmosphere with acetic acid free.

 

Water scrubbing system normally design with continuous feed gas, and not intermittent or once in a blue moon of PSV that will pop up.

 

Therefore, I am looking for any idea, practical and proven solution to address this specific issue that may be been implemented else where.

 

 

Norhelme,

 

Lack of adequate info...type of PSV?...relief composition?....

 

Anyway, you can use a static water column in PSV discharge line to absorb the acid from each relief with a drain at low point to replace with fresh and new water after relief. Of course the relevant vessel design pressure and PSV set pressure should be such that you can increase the PSV set pressure, within allowable range, equal to the additional back pressure due to considering such water column...

[Helme75]

Dear Naser Fallah,

 

Thanks for chip in!

 

It has all three type of PSV, however majority is conventional type.

 

One example :

 

Type :Conventional

Set pressure : 1.8 kg/cm8g

Overpresure : 10%

Composition :  Acetic Acid       8%

                        Water                1%

                        Methyl Acetate  5%

                        Gas N2             86%

 

 

I like your idea to have water column at discharge piping PSV. I have 2 concerns :

 

1) Would piping arrangement with water column against codes i.e. API if it get audited?  Or...would be nicer if we have all piping out let PSV to common before it goes to KO drum with water seal before discharge to atmosphere?

 

2) How to estimate water column to balance with the limitation of backpressure PSV and contact time to ensure acetic acid really wash out?

 

Many thanks!

 

Norhelme

[fallah]

 

Type :Conventional

Set pressure : 1.8 kg/cm8g

Overpresure : 10%

Composition :  Acetic Acid       8%

                        Water                1%

                        Methyl Acetate  5%

                        Gas N2             86%

 

 

I like your idea to have water column at discharge piping PSV. I have 2 concerns :

 

1) Would piping arrangement with water column against codes i.e. API if it get audited?  Or...would be nicer if we have all piping out let PSV to common before it goes to KO drum with water seal before discharge to atmosphere?

 

2) How to estimate water column to balance with the limitation of backpressure PSV and contact time to ensure acetic acid really wash out?

 

 

Norhelme,

 

1) If there are several PSV's with the same conditions, yes it would be better having common PSV discharge header terminated to a KOD equipped with water seal before discharge to the atmosphere.

 

2) You can calculate maximum allowable back pressure from allowable PSVs setting range (manufacturer specified) and set the corresponding water column/path inside the KOD. If total acid content wouldn't be removed it might getting help of the other facilities, say by adjusting the water temperature for more solubility of acid in water.

[Helme75]

Dear Naser Fallah,

 

Many thanks on your additional input. Appreciate very much.

 

I will talk to client to seek their operational experience on solubility issue of acid acetic and water.