8 replies to this topic

[umeshCHE]

This question is related to an Air Assisted Flare system. Our Client has been experiencing issues at one of flare stacks with liquid hydrocarbon carry-over from the knock-out drum to the flare stack, which backflows to the corresponding air blower system. This exposes the facilities to an unacceptable risk of hydrocarbon release and fire.

Possible cause of liquid carryover could be inadequate KOD.

However, the client is interested in a solution which may avoid the resizing of KOD.

1. Has anybody experienced this problem in operating plants?
2. What were the solutions employed (other than KOD upgrade)?

 

Thanks

 

Apurv

[umeshCHE]

^{Would appreciate, If anyone can share relevant documents / flare vendor feedback.}

[Zauberberg]

Reduce flare load (examine which scenarios lead to liquid carryover and try to mitigate them by using IPF) would be an interesting option to look at.

[shan]

Install a piece of U section between KOD and flare stack to allow liquid droplets accumulation in it.

[Bobby Strain]

How can we possibly help you solve this problem with no information? How much gas? How much liquid? Size and orientation of drum? Drum internals? etc. Including piping details from KO drum to the flare. And the flare riser and tip.

 

Bobby

[fallah]

Apurv,

 

IMO, the main problem in the mentioned flare system is liquid HC carry over into the flare stack, hence backflowing toward corresponding air blower system shoud be considered as subsequent problem. Then, you have to upgrade the KOD or, as Zauberberg mentioned, try to mitigate the flare load toward the situation with no/minimum liquid carry over.

 

However, there are some not specified issues regarding the system you described:

 

1-Suppose the air blower would be operated continuously (usually two-speed motor to cover all relief rates with energy saving), how can the HC liquid backflow toward air blower?

2-If part of liquid droplets is contributing to backflow, would the remain go away the flare tip and then would fall on the ground?

[umeshCHE]

All,

 

Thanks for the response.

 

As rightly picked up by most of you, the KOD is  main source of problem (inadequate separation of liquid).

However, replacing KOD would take longer. Hence, as a first step, it is desired to address the issues downstream the KOD. This may include minor piping modifications (like the suggestion from Shan "Install a piece of U section between KOD and flare stack to allow liquid droplets accumulation in it.").  or else, modifications in flare stack/tip area in consulation with vendors.

 

More comments and any specific documents for similar issue are welcome.

 

Apurv.

[umeshCHE]

Apurv,

 

IMO, the main problem in the mentioned flare system is liquid HC carry over into the flare stack, hence backflowing toward corresponding air blower system shoud be considered as subsequent problem. Then, you have to upgrade the KOD or, as Zauberberg mentioned, try to mitigate the flare load toward the situation with no/minimum liquid carry over.

 

However, there are some not specified issues regarding the system you described:

 

1-Suppose the air blower would be operated continuously (usually two-speed motor to cover all relief rates with energy saving), how can the HC liquid backflow toward air blower?

2-If part of liquid droplets is contributing to backflow, would the remain go away the flare tip and then would fall on the ground?

Fallah,

 

1. Could be because the droples from KOD to stack are larger in size  and / or the blower is inefficient due to old age.

2. Yes, part of droplets fall on ground (as fireballs !!!!!). Real risk.

 

Further, possible damage to flare tip/ stack/ air duct might  be causing the backflow to blowers.

 

Thanks.

Apurve.

[fallah]

 

Hence, as a first step, it is desired to address the issues downstream the KOD. This may include minor piping modifications (like the suggestion from Shan "Install a piece of U section between KOD and flare stack to allow liquid droplets accumulation in it."). 

 

Hi,

 

It might cause the pressure at the stack base, which shouldn't be lower than a specified value, would be decreased leading to reduction in flare relieving capacity...