7 replies to this topic

[shahzaib]

hi to all,
plz dears tell me that, in our plant, our FKO drum is designed at 163psi & operating pressure is 5psi at which it can handle 15mm gas having no safty device, But here we handle 27mm gas if any incident or ESD happend all 27mm gas goes into FKO drum & than flare, can it handle this or need any safty device or modification?
THANKS FOR YOUR TIME.

[JoeWong]

What do you mean by "...15mm gas..." ?

Higher the flow passing flare system in particular exceeded it capacity , results higher velocity, noise, vibration, backpressure, choking possibility, etc which possibly lead to catastrophe. A simple "safety device" may not sufficient from this aspect. A proper and detail analysis is required.

[shahzaib]

thanks for reply,
dear 15mm means 15million square cubic feet gas .

[JoeWong]

thanks for reply,
dear 15mm means 15million square cubic feet gas .

For flow,
should be "cubic". "Square" should NOT present.

The unit may be for volume not for flow. Gas flow should have time unit i.e. sec, min, hrs, day, etc.

Proper communication is key to success.

Edited by JoeWong, 17 December 2009 - 12:49 PM.

[Shahnawaz Makroo]

Dear Shazaiab,

Drum volume is not important at all for absolute volume.KOD is sort of gravity separator ,its size determines the knoking efficieny rather than gas handling capacity.Let me explain,

If your KOD upstream and down stream lines are not designed for Emergency flow loads,then system as a whole is not adequate not Drum.If system can handle huge specified loads(flows) through upstream and down tream piping of KOD there will be no problem in KOD safety,only knocking efficiency of kod will decrease.


Regards
Shahnawaz

[fallah]

If system can handle huge specified loads(flows) through upstream and down tream piping of KOD there will be no problem in KOD safety,only knocking efficiency of kod will decrease.

The volume of the KOD should be so enough to handle collected knocking liquid.In many plants there is unit shut down signal on HHLL of relevant flare KOD.

[kkala]

plz dears tell me that, in our plant, our FKO drum is designed at 163psi & operating pressure is 5psi at which it can handle 15mm gas having no safty device, But here we handle 27mm gas if any incident or ESD happend all 27mm gas goes into FKO drum & than flare, can it handle this or need any safety device or modification?

Chances are that droplets will not be totally retained in the knock out drum at max discharge (flow increases 1.8x), which is dangerous seeing that liquid droplets being burnt will be dispersed out of flare tip to the air *. So knock out drum size should be checked (e.g. per API 521 - Sizing a knockout drum) and drum modified / changed if inadequate.
This activity includes two main steps for the given drum and the new max flow:
(1) Find max drum level assuring liquid dropout (this has to be above drum HLL = high liquid level)
(2) Liquid volume between above max dropout level and HLL should represent 20-30 min liquid hold up. For instance, suppose the 27 MM ft3/h carry over 15 m3/h of liquid, said liquid volume should be 5-7.5 m3, so that operator has time to correct situation in such case.
API 521 explains well these two sizing criteria. If they are not satisfied, a bigger drum should be examined.
After this procedure, noise - vibration has to be checked (noted by JoeWong), if existing drum is OK.
Above supposes that all other flare components and header have been previously checked OK.

* note: a flare can handle small-sized liquid droplets, with diameter less than 300 μm, as API 521 let us understand. Formula of dropout velocity holds for droplet sizes between 300 and 600 μm.

Edited by kkala, 22 December 2009 - 01:23 PM.

[Qalander (Chem)]

plz dears tell me that, in our plant, our FKO drum is designed at 163psi & operating pressure is 5psi at which it can handle 15mm gas having no safty device, But here we handle 27mm gas if any incident or ESD happend all 27mm gas goes into FKO drum & than flare, can it handle this or need any safety device or modification?

Chances are that droplets will not be totally retained in the knock out drum at max discharge (flow increases 1.8x), which is dangerous seeing that liquid droplets being burnt will be dispersed out of flare tip to the air *. So knock out drum size should be checked (e.g. per API 521 - Sizing a knockout drum) and drum modified / changed if inadequate.
This activity includes two main steps for the given drum and the new max flow:
(1) Find max drum level assuring liquid dropout (this has to be above drum HLL = high liquid level)
(2) Liquid volume between above max dropout level and HLL should represent 20-30 min liquid hold up. For instance, suppose the 27 MM ft3/h carry over 15 m3/h of liquid, said liquid volume should be 5-7.5 m3, so that operator has time to correct situation in such case.
API 521 explains well these two sizing criteria. If they are not satisfied, a bigger drum should be examined.
After this procedure, noise - vibration has to be checked (noted by JoeWong), if existing drum is OK.
Above supposes that all other flare components and header have been previously checked OK.

* note: a flare can handle small-sized liquid droplets, with diameter less than 300 μm, as API 521 let us understand. Formula of dropout velocity holds for droplet sizes between 300 and 600 μm.

Dear Shahzaib,

Although you already got fairly satisfying guidance from the forum colleagues.However consider two more points for any decrease in degree/extent of exposure.
(All subject to mechanical works possibility and permissibility:as otherwise another 'KOD in parallel' might be be your solution indeed.)

1 Provision of impingement plate(s) right in front of the incoming pipeline delivery point inside the subject vessel (if does not exist already) 45 degrees so inclined to help knock down liquid droplets entrained from carry over to flare tip

2) Increase/Gear up liquid draw-off & pump out capabilities from the Flare KOD vessel.

Definitely a proper hazop of whole scheme involving the operating, mechanical maintenance/design, instruments and advisory people should be of great help.

Best of luck,hope this in some way proves helpful!