5 replies to this topic

[T Rustagi]

Hi,

 

I am currently working on engineering of natural gas compressor station which has a requirement of Cold Flare System. I was wondering which Code is used to design the same. Is it API 521, if yes then to design a cold flare system we just need to take heat radiation as 0 and design the rest of the system as in case of hot flare?

 

Could you please let me know if my understanding is correct.

 

Also, any literature on design of the same would be really helpful.

 

Thanks and Regards,

 

Tanmay

Edited by T Rustagi, 02 May 2014 - 06:02 AM.

[ankur2061]

Tanmay,

 

The usual term for what you call as 'cold flare' is 'cold vent'. What you are mentioning as 'hot flare' is basically burning of waste gases usually from an elevated flare emanating from various sources such as relief devices and vents from vessels / tanks in a plant or unit.

 

Cold vents require an elevated stack with the elevation being decided based on a combintaion of pressure drop (back pressure) in the vent system and the dispersion of waste gases to the atmosphere with minimum adverse impact on the surroundings.

 

Cold vent systems are no longer acceptable in many countries where environmental regulations prevent discharge of natural gas to the atmosphere because natural gas contains trace amounts of highly toxic compounds (mercury and aromatic cyclic compunds). Cold vents should be used only in remote and unpopulated areas subject to the local emission regulations. New installations for long distance natural gas pipelines envisages a mobile flare for remote loactions when planned pipeline depressurization operations are to be carried out.

 

Even flaring where burning is done to break up the natural gas to CO2 and water vapor is highly regulated these days due to uncontrolled release of greenhouse gases such as CO2 and nitrous oxides. The international community has introduced a new commodity called "Carbon Credits" which is to encourage reduction of emission of CO2 or other greeenhouse gases. Refer the link below to understand what "Carbon Credit" means:

 

http://en.wikipedia....i/Carbon_credit

 

To conclude, design of gaseous emission systems either cold (without burning) or with burning (flare) require careful consideration of environmental regulations related to where the system has to be installed.

 

Regards,

Ankur

Edited by ankur2061, 02 May 2014 - 09:48 AM.

[fallah]

Tanmay,

 

When you use the term "Flare" you should expect to have "Combustion" and following that "Radiation". Then the cold flare is a flare network receives the relieving vapors/liquids from low temperature sources. Of course, it might connected to common header with hot flare after outgoing from relevant knock out drum finally would terminate to a common flare stack...

[mgamil24]

Tanmay,
Heat Radiation shall be taken into consideration according to API 537 as it may ignite and snuffing system is corrupted. That is the reason the cold vent is normally designed to be inclined tips to overcome the long length required.

[T Rustagi]

ankur2061

 

Thank you for your help. I agree by 'cold flare' i mean cold vent and that venting NG in straight into atmosphere requires lot of considerations concerning environmental impact. We have done all those.

 

fallah

 

Thank you for your help. The vent stack I am talking about is referred to as cold because there is no combustion of blowdown or waste gas.

 

mgamil24

 

Thank you for your help. API 537 gives Hot Flare details but my query is regarding design of cold vent.

 

 

 

The question remains - how to design the vent stack. At present we are designing the vent stack as per API 521, as stated before taking heat radiation as 0. I feel applying API 521 for design cold vent gives a very conservative design. Hence, I request you all if you could provide guidance in how to design the cold vent. 

 

Would it be sufficient to design the vent stack based on backpressure only? 

 

Thanks and Regards,

 

Tanmay

[Bobby Strain]

Surely you know that methane is a much worse greenhouse gas than carbon dioxide. Venting is not the proper disposal means by a long shot.

 

Bobby