14 replies to this topic

[shahzaib]

plz tell me that, is it neccessary to install PSV at FKO drum?
thanks

[Majid-Process]

Hi there,
Flare KO drum is the only vessel in your plant containig hydrocarbons, may got a back pressure as high as 15 barg and doen not need any PSV. As it is connected to atmosphere via stack and flare tip and is designed to meet design pressure at worst reliefing scenario, there is no need for PSV.

[fallah]

plz tell me that, is it neccessary to install PSV at FKO drum?
thanks

Because there is no cause to overpressure the KOD beyond its design pressure (isolation valve(s) between KOD outlet and flare tip would be in CSO/LO position),there is no need the KOD to be protected against overpressure by PSV.

On the other hand,if we imagine the PSV would be considered for overpressure protection,PSV inlet and outlet lines became connected because KOD space and flare header already connected to each other.

[JoeWong]

plz tell me that, is it neccessary to install PSV at FKO drum?
thanks

You may start to asking yourself what is the purpose of PSV and what is the potential of overpressure of Flare KOD.

Any equipment or system potentially experience overpressure, a pressure relief device i.e. PSV, RD, etc is required. Now you have asked yourself, should the Flare KOD experience credible overpressure ?

Majid-Process and Fallah have given you opinion where commonly no PSV is required for a Flare KOD. They have the opinion that there is no possibility of credible overpressure based on "common" practice and normal flare system they have seen/used to. Nevertheless, they have not actually seen your system design. I believe only yourself can answer this question.

[kkala]

plz tell me that, is it neccessary to install PSV at FKO drum?

Having read the interesting opinions on the subject, I would like to add another:
1. High pressures on the knock out drum are results of explosion from air back flow into flare tip. We can suppose that these pressures are considered non credible events by usual codes. Design pressures of flare header, knock out drum, water seal drum, in refineries are usually about 3.5 barg. I have heard that only in nuclear applications this design pressure goes to about 12 barg.
2. If such an explosion occurs, a PSV will not open quickly enough to relieve pressure. Even a huge bursting disk may not manage it. All flare stack downstream of drum makes an open pipe. If bursting pressure were developed slowly enough, relief could be done through this "pipe".
3. So PSV does not seem to be useful for the majority of cases.

[fallah]

Design pressures of flare header, knock out drum, water seal drum, in refineries are usually about 3.5 barg. I have heard that only in nuclear applications this design pressure goes to about 12 barg.

Just for your information:

In some gas refinery plants there are HP flare systems including header,KOD,water seal drum,...with desigh pressure up to 14 barg.

[kkala]

Design pressures of flare header, knock out drum, water seal drum, in refineries are usually about 3.5 barg. I have heard that only in nuclear applications this design pressure goes to about 12 barg.

In some gas refinery plants there are HP flare systems including header,KOD,water seal drum,...with desigh pressure up to 14 barg.

----------------------------
Interesting to know of so high design pressures.
As a young engineer I made a specification for flare, water seal drum, KO drum, etc. Accidental pressures due to explosion could reportedly be up to 12 (or 15?) barg, so I set a design pressure covering this. Then a flare supplier advised that this specification was excessive, proper for nuclear applications and not for common plants.
Later on, a refinery flare system design I was involved in had 3.5 Barg design pressure and so have existing refinery flare headers and drums.
As I try to imagine the case, design pressure as high as 14 Barg means care for Protection against accidental explosion (not considered, say, 20 years ago). ΔP of 14 Bar along flare header is quite unlike - High pressure release needs header isolation to result in 14 Barg, not permissible. Both cases lastly mentioned concern header only, not tip or water seal drum, being close to atmosphere.
It would be encouraging to consider Protection against explosion, but is it so? Can members advise whether this really happens?

[Qalander (Chem)]

Design pressures of flare header, knock out drum, water seal drum, in refineries are usually about 3.5 barg. I have heard that only in nuclear applications this design pressure goes to about 12 barg.

In some gas refinery plants there are HP flare systems including header,KOD,water seal drum,...with desigh pressure up to 14 barg.

----------------------------
Interesting to know of so high design pressures.
As a young engineer I made a specification for flare, water seal drum, KO drum, etc. Accidental pressures due to explosion could reportedly be up to 12 (or 15?) barg, so I set a design pressure covering this. Then a flare supplier advised that this specification was excessive, proper for nuclear applications and not for common plants.
Later on, a refinery flare system design I was involved in had 3.5 Barg design pressure and so have existing refinery flare headers and drums.
As I try to imagine the case, design pressure as high as 14 Barg means care for Protection against accidental explosion (not considered, say, 20 years ago). ΔP of 14 Bar along flare header is quite unlike - High pressure release needs header isolation to result in 14 Barg, not permissible. Both cases lastly mentioned concern header only, not tip or water seal drum, being close to atmosphere.
It would be encouraging to consider Protection against explosion, but is it so? Can members advise whether this really happens?

Dear kkala,
Most Probably here in fallah's post "design" pressure implied "MAWP"and not normal operating pressure(s)

[kkala]

Dear Qalander
Certainly it concerns MAWP / design pressure. My question is whether this design pressure of up to 14 Barg is set to cover an internal explosion incident. If so, this is a safety enhancement over past design practices.

[Qalander (Chem)]

Dear Qalander
Certainly it concerns MAWP / design pressure. My question is whether this design pressure of up to 14 Barg is set to cover an internal explosion incident. If so, this is a safety enhancement over past design practices.

Dear

I do endorse your opinion if 14 Bar is accurately reffered/ quoted, this might be a specially fabricated KOD.

However only the OP may comment.

Edited by Qalander (Chem), 26 December 2009 - 04:03 PM.

[fallah]

Design pressures of flare header, knock out drum, water seal drum, in refineries are usually about 3.5 barg. I have heard that only in nuclear applications this design pressure goes to about 12 barg.

In some gas refinery plants there are HP flare systems including header,KOD,water seal drum,...with desigh pressure up to 14 barg.

----------------------------
Interesting to know of so high design pressures.
As a young engineer I made a specification for flare, water seal drum, KO drum, etc. Accidental pressures due to explosion could reportedly be up to 12 (or 15?) barg, so I set a design pressure covering this. Then a flare supplier advised that this specification was excessive, proper for nuclear applications and not for common plants.
Later on, a refinery flare system design I was involved in had 3.5 Barg design pressure and so have existing refinery flare headers and drums.
As I try to imagine the case, design pressure as high as 14 Barg means care for Protection against accidental explosion (not considered, say, 20 years ago). ΔP of 14 Bar along flare header is quite unlike - High pressure release needs header isolation to result in 14 Barg, not permissible. Both cases lastly mentioned concern header only, not tip or water seal drum, being close to atmosphere.
It would be encouraging to consider Protection against explosion, but is it so? Can members advise whether this really happens?

As far as i know design pressure of 14 barg is not considered for protection against explosion (because i think,but not sure, with liquis seal or other type of seals it is supposed not to have any burnback from tip to upstream header) and covers all possible upstream pressures.
Indeed,i think potential of vacuum condition in flare system could be more than explosion,because any liquid seal in flare system will operate in reverse to break vacuum (due to condensation,....) and usually there is positive fuel gas injection to cope with this issue.

Edited by fallah, 29 December 2009 - 02:24 AM.

[S.AHMAD]

plz tell me that, is it neccessary to install PSV at FKO drum?
thanks

Hi Shah

Consider fire case since the drum mainly contains hydrocarbon. However, if the drum bottom is higher than 25 ft above ground then fire case is not valid case.

[Vijay77]

plz tell me that, is it neccessary to install PSV at FKO drum?
thanks

You may start to asking yourself what is the purpose of PSV and what is the potential of overpressure of Flare KOD.

Any equipment or system potentially experience overpressure, a pressure relief device i.e. PSV, RD, etc is required. Now you have asked yourself, should the Flare KOD experience credible overpressure ?

Majid-Process and Fallah have given you opinion where commonly no PSV is required for a Flare KOD. They have the opinion that there is no possibility of credible overpressure based on "common" practice and normal flare system they have seen/used to. Nevertheless, they have not actually seen your system design. I believe only yourself can answer this question.

[aju_1807]

Design pressures of flare header, knock out drum, water seal drum, in refineries are usually about 3.5 barg. I have heard that only in nuclear applications this design pressure goes to about 12 barg.

In some gas refinery plants there are HP flare systems including header,KOD,water seal drum,...with desigh pressure up to 14 barg.

----------------------------
Interesting to know of so high design pressures.
As a young engineer I made a specification for flare, water seal drum, KO drum, etc. Accidental pressures due to explosion could reportedly be up to 12 (or 15?) barg, so I set a design pressure covering this. Then a flare supplier advised that this specification was excessive, proper for nuclear applications and not for common plants.
Later on, a refinery flare system design I was involved in had 3.5 Barg design pressure and so have existing refinery flare headers and drums.
As I try to imagine the case, design pressure as high as 14 Barg means care for Protection against accidental explosion (not considered, say, 20 years ago). ΔP of 14 Bar along flare header is quite unlike - High pressure release needs header isolation to result in 14 Barg, not permissible. Both cases lastly mentioned concern header only, not tip or water seal drum, being close to atmosphere.
It would be encouraging to consider Protection against explosion, but is it so? Can members advise whether this really happens?

We have a HP flare system where we have considered sonic flare tip with DP across stack of 4.0 bar and the design pressure of the flare is 17.7 bar g and 100 c. The maximum back pressure expected in the system is almost in teh range of 15 bar during sequential depressurization.

Technically, nothing wrong in having higher back pressure system, any concerns??
Regards,

Ajau

[fallah]

plz tell me that, is it neccessary to install PSV at FKO drum?
thanks

Hi Shah

Consider fire case since the drum mainly contains hydrocarbon. However, if the drum bottom is higher than 25 ft above ground then fire case is not valid case.

Criteria of 25 ft above ground is a height limitation for considering wetted wall in fire relief load calculation not for determination of fire case validity!

Actually,at first fire case validity is recognized and then height evaluation for wetted wall would be done.