8 replies to this topic

[Ade24]

My blowdown system collects the PSV discharge and the depressurisation valve. The two discharges are not simultaneous; in the case of the PSV I have a mixed phase (fluid is water), in the case of the depressurisation fluid is methane. We have installed a ko drum and the gas is discharged into the atmosphere. What should I do to avoid air ingress? N2 flushing.
I have also thought about the possibility of installing a PV on the line going to the safe location and in parallel another line where a rupture disc is placed.
The PV will work until it can, and if the pressure rises too much, the rupture disc is our protection.


Thank you for your support

[fallah]

My blowdown system collects the PSV discharge and the depressurisation valve. The two discharges are not simultaneous; in the case of the PSV I have a mixed phase (fluid is water), in the case of the depressurisation fluid is methane. We have installed a ko drum and the gas is discharged into the atmosphere. What should I do to avoid air ingress? N2 flushing.
I have also thought about the possibility of installing a PV on the line going to the safe location and in parallel another line where a rupture disc is placed.
The PV will work until it can, and if the pressure rises too much, the rupture disc is our protection.


Thank you for your support

 

Hi,

 

The system operability should be discussed and analyzed in detail and also in risk assessment standpoint.

 

Anyway, in general yes, the KOD should be kept at a positive pressure, say, by N2 blanketing. Also using PV and a RD in parallel seems to be a good idea to disperse the Methane in a safe manner against overpressure but it should also be dispersed per the acceptable and safe models such that not to be the cause of a pool fire or an explosion at nearby. 

[Ade24]

I totally agree with you! 

I made a calculation of the LEL of the stream leaving the KO Drum. It is 13%; it is well below the LFL of 50% which I understand is the limit that cannot be exceeded.

I have also evaluated the diameter of the vent stack.

The standard indicates that in order to avoid the formation of flammable mixtures and to provide excellent dispersion, the vent size should be selected to provide a discharge velocity of at least 500 ft/s (152 m/s). In addition, the vent size should be checked to ensure that sonic flow does not occur.

 

Do you think all these assessments are sufficient?

 

Thank you very much

[fallah]

 

I totally agree with you! 

I made a calculation of the LEL of the stream leaving the KO Drum. It is 13%; it is well below the LFL of 50% which I understand is the limit that cannot be exceeded.

I have also evaluated the diameter of the vent stack.

The standard indicates that in order to avoid the formation of flammable mixtures and to provide excellent dispersion, the vent size should be selected to provide a discharge velocity of at least 500 ft/s (152 m/s). In addition, the vent size should be checked to ensure that sonic flow does not occur.

 

Do you think all these assessments are sufficient?

 

Thank you very much

 

 

What is the standard you are referring to?

 

If it's acceptable, such as API 521, it might be sufficeinet... 

[breizh]

Hi,

Would not be better to route the methane stream to a flare, meaning 2 separate KO drums?

I don't see the point to bring the methane to a shared KO drum and then to dispose it to atmosphere.

Check regulations in your area.

My 2 cents.

Breizh 

Attached Files

•  FlareSel.pdf   750.33KB   7 downloads

[Ade24]

Thank you Breizh!

Unfortunately the flare is not always in operation and for this vent they have not taken into account that the flare is in operation.

Furthermore, it appears that they are not even going to use nitrogen for purging to avoid air intake, so I think the only possible alternative is to install a PV on the line going to the safe location and in parallel another line where a rupture disc is installed.

The PV will work until it can, and if the pressure rises too much, the burst disc is our protection.

I am not really sure about this configuration, I would prefer to have a flare system.

[Pilesar]

Why would not a flame arrestor on the vent line be sufficient for depressuring safely?

[Ade24]

Thank you Pilesar for your reply!

I had never thought about it. In your experience, is it enough to prevent air intake in the KO Drum blowdown and can it replace nitrogen purging?

 

Regards

[breizh]

Hi,

FYI this link : 

End-of-Line Deflagration Flame Arresters | Protectoseal

this technology is to prevent flame to reach the sky of the vessel or storage tank. It will not prevent fire outside if you have a combination (flammable material, oxygen and sparks)

Breizh