5 replies to this topic

[bernath]

Dear All,

As we all know, the purpose of flare is to act as a safety device to protect vessels or pipes from over-pressuring due to unplanned upsets. But in order to keep the flare system functional, a small amount of gas is continuously burned, like a pilot light, so that the system is always ready for its primary purpose as an over-pressure safety system.

My question is how to determine the load of this continuous gas? Is there any ruled of thumb or formula to calculate this continuous load? Please kindly advise.

More over, how to keep the flare continuously burns? Do the gas we employ to ignite the combustion use the same line that we use to de-pressuring (blow down valves) or relieving (PSVs) our system? Once my senior told me that we use small line size that transport the gas to the stack so that the system is always ready to burn the gas. I'm not so sure about that and perhaps someone could clarify it to me.

thank you
regards,
bernath

[Erwin APRIANDI]

Dear Bernath,

A pilot burner which is a small, continuously operating burner that provides ignition energy to light the flared gases is provided in the Flare system. The flow rate of pilot gas will vary depend on the type of ignition which is used, you can consult with the preferred vendor. I have also attach one of the vendor data sheet.

The pilot gas, is supplied to the flare system thruu different distribution line, mostly this gas will be your fuel gas. Please also find the enclosed P&ID

Attached Files

•  Flare Pilots Datasheet.pdf   328.41KB   106 downloads
•  Flare System PID.pdf   53.44KB   121 downloads

[ankur2061]

Bernath,

All flares require a minimum purge gas as well as pilot gas (very small quantity) for continuous and reliable operation of the flare as well as to prevent flashback and detonation due to ingress of air (oxygen) in the system. If fuel gas (hydrocarbon gas) is used as purge gas then it needs to be burned continuously and is also sometimes called as sweeping gas. Pilot ignition systems such as a "Flame Front Generator" may be used to ignite the pilots in case of any failure of the system.

Due to environmental emission norms getting stricter newer methods for ignition which do not require continuous pilot ignition have been developed specially in the North Sea. The small amount of leak / purge gas in the main flare header is recovered using Flare Gas Recovery systems and flare is ignited only when emergency flaring is required using a special Ballistic Ignition (Pellet Type) which is considered very reliable. Refer the link below for the various types of ignition systems:

http://www.argoflare...ion-systems.htm

Also refer the link below where we had a very enlightening discussion on Purge or Sweeping gas for flares:

http://www.cheresour...5258#entry25258

Regards,
Ankur.

[bernath]

Dear Erwin and Ankur,

Thank you for the kind explanation.

A pilot burner which is a small, continuously operating burner that provides ignition energy to light the flared gases is provided in the Flare system. The flow rate of pilot gas will vary depend on the type of ignition which is used, you can consult with the preferred vendor. I have also attach one of the vendor data sheet.

The pilot gas, is supplied to the flare system thruu different distribution line, mostly this gas will be your fuel gas. Please also find the enclosed P&ID

According to your P&ID, the pilot gas (or purge gas) was supplied from fuel gas distribution header which means that the pilot gas was supplied by a dedicated fuel gas line. I have seen that the fuel gas line is split into two lines. The first was sent directly to the flare tip for pilot gas while the other line was combine with gas downstream of flare KO drum before being sent to flare tip. I suppose that these gases are combined in order to increase gas flammability. If anyone can confirm it. Please advise.

thank you
regards,
bernath

[Erwin APRIANDI]

Hi bernarth,

what you have seen is a purge gas, this is a fuel gas or non-condensable inert gas added to the flare header to mitigate air ingress and burnback. this is to ensure that no air entering the flare header, which will lead to safety hazard as what Ankur has explain before.

I will recommend you to read API STD 521 first, before you design any flare system and also to consult with HSE engineer regarding to the environmental regulation in your area. Where Ankur has mentioned also, in some country it is forbidden to have an continous flaring.

Edited by erwin.apriandi, 13 March 2011 - 09:43 PM.

[bernath]

Hi bernarth,

what you have seen is a purge gas, this is a fuel gas or non-condensable inert gas added to the flare header to mitigate air ingress and burnback. this is to ensure that no air entering the flare header, which will lead to safety hazard as what Ankur has explain before.

I will recommend you to read API STD 521 first, before you design any flare system and also to consult with HSE engineer regarding to the environmental regulation in your area. Where Ankur has mentioned also, in some country it is forbidden to have an continous flaring.

thanks erwin for the confirmation..