8 replies to this topic

[areads]

Hi, I’ve started working on a project involving oil extraction offshore. When the oil is flashed, some gas will be released (mainly C1 to C3 compounds). The issue is whether to flare or vent this gas. Based on some environmental knowledge, I believe flaring is more advisable. Is this right? Are there any regulations that confirm whether to vent or flare?
Thanks!

[Shubhasis]

Hi,

For all the hydrocarbon service vents should be located to Flare. There are different type of flares viz. LP, HP, Acid Gas flare etc. The overpressure line should be vented out to suitable type of flare on the basis of system pressure. Mainly Process units like CDU/VDU/NHT/KHDS are under LP flare system and DHDT,RFCC,RHDS,HGO Hydrotreater,HGO hydrotreater, DCU etc.For upstream processes you have to make the decision on the operating pressure of the system. It will be dangerous to route the hydrocarbon vapour line (flash vapour)into atmosphere and can create fire hazards. For the vapour lines
pursuing adequate H2S and other toxic gases should be routed to acid gas flare. Only water service and LP steam service could be routed to atmosphere and should be at safe location. For high pressure steam service discharging to atmosphere should be vented to atmosphere at safe location via suitable silencer.

Hope this helps. For further query you can free to contact with me @ subhasis_chakraborty@fwuk.fwc.com

With thanks and regards,
Shubhasis

[areads]

Thanks for the reply Shubhasis

[shan]

You have to indicate the volume of gas to determine the way of handling it. If the volume is large enough, you may consider installation of compressor to send it onshore or deliver it to fuel gas system. Also, you need to indicate if there is a flare system available or a venting system available. There is no such thing as one answer that fits all in the chemical engineering business. Otherwise, all of us or most of us have lost job many, many years ago. Right?

[areads]

You're quite right Shan!

There is no design of a flare or vent yet, waiting for the decision of whether to flare this gas or not.
The venting/flaring of this gas would normally be 50kg/h (continuously), but it could reach 400kg/h in peak conditions.
It's all hydrocarbons and there is no hydrogen sulfide.

[amirentezari.k]

hi

• if the deign pressure of offshore facility is equal to well shut in tube pressure then a cold vent is adequate otherwise you should design a flare system as a secondary safety factor

[Narayanan.u]

Hi,

The link below might be usefull for getting answers.

http://www.cheresour...tor-downstream/


Narayanan

[Himanshu Sharma]

Dear Sir

I'll be really happy if in case economics works out to allow an option of vapor recovery.

Since you have not disclosed location of your platform ,environment norms applicable are not known at hand.In case you opt for flare please take following into consideration

• smokeless flare
• Sonic Limit/Sound Limit in surroundings
• Radiation Intensity
• Flare design only for gas or for certain ratio of Gas/Liquid

Its not uncommon for Offshore platforms to have a suitable vent to atmosphere comprising of a suitable vent tip with anti-static rings,steam or air dispersion ring,noise shroud, heat tracing & insulation( to prevent freezing in cold climate) and fire snuffing with steam, carbon dioxide or dry chemical.

​@Shubhasis ,Sir your quote makes perfect sense for a refinery system in general but as per my understanding things work different in case of an offshore platform.Have you ever seen a marketing terminal(Light naphtha/Gasoline Huge Inventory) with a flare system operating ?

Adding more to it , the decision for two pressure level flare system depends on refinery configuration.It's typically viable if you have a refinery towards diesel maximization with high pressure units like HCU/DHDT/LC Fining etc.Cutting fine,you have to counter Bigger PSV Sizes vs Bigger flare headers and choose what makes economic sense.

[kkala]

In addition to above posts, please note following previous threads that could be helpful, although concerning plants on land (onshore).
1. http://www.cheresou...ansfer-system/ , from post No 11 on.
2. http://www.cheresou...bined-with-psv , from post No 11 on.
In brief, 1st source indicates that policy of local refineries (Greece) is not to release hydrocarbons to atmosphere. But PSVs of a local LNG terminal discharge to atmosphere (if they ever open).
Continuous discharge of 50 - 400 kg/h of hydrocarbon gas (C1 to C3) to atmosphere does have risks. C3H8 is heavier than air, even gases lighter than air can behave as heavy gases if their discharge temperature is quite low.
I am not aware of API 2510, local regulations, practices specifically related to offshore installations (on sea), which may give further insight and clarify whether venting to atmosphere is acceptable and under what conditions (to minimize risks).
Of course not discharging hydrocarbons to atmosphere is safer.

Edited by kkala, 29 February 2012 - 04:11 AM.