Smokeless Flaring Possible without Air Blower or Steam Supply

[Patel85]

Dear All,

First of all, I would like to tell you that I am Beginner in Flare Field. So you Might think that the question is stupid.
I apologize for the same. but I want to know whether Smokeless Flaring is possible without supplying additional air or Addition Steam.

I am handling a project where in Feed Document, I can see that Smokeless flaring is specified and they have specified Air and Steam Assistant as "Nil".

Thanks in advance.

Regards,

VK (Mechanical)

 

[georgeverghese]

Though I'm not a flare expert, my limited experience with LP and HP flares tells me that unassisted smokeless operation becomes a challenge with one or more of the following

a) Gas mol wt is high (maybe more than 25)
b) High turndown requirement
c) Allocated flare tip dp is low at design rate

Smokeless flaring is even more difficult if you have H2S.

Tell us a bit more about the design case requirements for this flare tip

 

[EmmanuelTop]

If you are burning light Hydrocarbon gases, there is no need to consider steam or air in order to ensure smokeless flaring.
What are the design cases and compositions for the Flare?

Dejan IVANOVIC
Process Engineer, MSChE

 

[EmmanuelTop]

Here is some interesting stuff to read:

http://people.clarkson.edu/~wwilcox/Design/FlareSel.pdf

http://www.gasflare.org/pdf/Flare_Type.pdf

http://www.epa.gov/ttnchie1/ap42/ch13/final/c13s05.pdf

http://repository.tamu.edu/bitstream/handle/1969.1/93877/ESL-IE-79-04-91.pdf?sequence=1

Dejan IVANOVIC
Process Engineer, MSChE

 

[georgeverghese]

In general, would agree that all refinery flares, HP, LP , LLP cannot be smokeless without assist air or steam.

 

[Patel85]

Dear All,

Thanks for your reply.

Content of flare Gas are as following : H2O, H2S, N2, Methane, ethane, propane, I-Butane, n-Butane, i and n-pentane, n-hexane, n-octane, n-nonane, n-decane, Benzene, p-xylene, COS, Methyl Mercaptan and Ethyl Mercaptan. Molecular weight of Flare gas is 19.97.

This is HP Flare. Pressure Drop allowed for Tip and seal is 4.5 Bar.

One note is written " Flare shall be provided with a smokeless flaring capacity equivalent to at least 15% of design load.

Please correct if I am wrong. I understand from above note that Smokeless flaring is required on and above 15% Design Load.

For above content whether smokeless flaring is possible without Blower or not. Please guide me.



Regards,

VK (Mechanical)

 

[EmmanuelTop]

Considering 19.97 Molecular Weight you are burning mostly Methane and (some) Ethane. Concentrations of other components seem to be negligible. It is hard to imagine that you would need any kind of assist fluid to ensure smokeless flaring.

Dejan IVANOVIC
Process Engineer, MSChE

 

[Patel85]

Please below the Content Analysis.

Regards,

VK (Mechanical)

 

[georgeverghese]

Is this flare gas composition relevant to all flaring cases, or only to the peak flow case?

What about max intermittent continous loads that may be due to a compressor shutdown etc?

Assuming this flare gas composition is relevant to continous intermittent case also, at 15% flow, tip dp would have dropped to 0.15^2 * 4.5 = 0.1bar = 1.5psi, which isnt much at all.

Maybe ask a flare tip vendor about this turndown limit with this flare gas composition.

But at peak flow, dont see a problem with smokelss operation.

At 2% H2S, the other question to ask the flare tip vendor is destruction efficiency for H2S - you may need to ask the plant owner what turndown is applicable to H2S.

 

[Patel85]

Dear Sir,

I have checked datasheet as you have told. As you have rightly said that There are some other Design cases also which has to be considered.

One more Question came in My mind. Flare Tip (Sonic) Designed for High Pressure Drop like 4.5 Bar can also work with lower allowable pressure drop like 0.15 bar???

Here in one of the case, Other flare package gas (i.e. LP Flare) is by passed in this flare package.

Will this flare tip work with this much lower Pressure drop????????..........

Regards,

VK (Mechanical)

 

[georgeverghese]

Usually LP flare gas is much richer than HP flare gas.

So, smokeless flaring is most likely not possible for this mode.

But is the LP flare package shutdown case flow below or above the turndown limit of 15% for the HP flare?

At the outset, must say I have not come across a case where the HP flare takes on the load from an LP flare outage - there may be overpressure concerns for equipment tied into the LP flare collection header - but this is not the topic of this posting.

These days, there are many concerns with BTX emissions, even when concentration in the air is of the order of a few ppm. We should also ask the flare tip vendor for destruction eff values for these (benzene, toluene, xylene ) components over the 15-100% flow range also.

 

[MortenA]

IMO your reference composition is fairly close to natural gas pipeline spec and i think it would be close to smokeless even at a fairly high flow rate (purging)

Best regards, Morten