×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Creating a Flammable Mixture

Creating a Flammable Mixture

Creating a Flammable Mixture

(OP)
Hi

A post from the UK.

I've been asked to calculate the amount of Fuel Gas that would nee to be added to an acid gas stream to create a flammable mixture.  I have a full Hysys simulation to hand so physical properties are readily available.

Any suggestions??
 

RE: Creating a Flammable Mixture

Acid gas been laden with fuel gas?
Dangerous association...

RE: Creating a Flammable Mixture

(OP)
The "acid gas" stream mostly consists of the reject streams from Glycol and Amine units.  This will be sent to a dedicated Acid Gas Flare.

I'm interested in making a very rough estimate of the amount of fuel gas need to be blended into the stream without having to go to flare tip vendors.
 

RE: Creating a Flammable Mixture

As a first pass, le Chatalier's rule can be used to estimate the LFL of a mixture.

1/LFL_mix = y_1/LFL_1 + y_2/LFL_2 ...

y's are mole fraction, LFL the lower flammability limit.  Same equation applies for UFL.

As an aside, is flaring the acid gas BAT?  I don't know the answer, but am curious.

Matt

RE: Creating a Flammable Mixture

In the US, we have rules that state the acid gas must be at least 300 BTU/ft if going to a flare.

If you assume the acid gas has 0 BTU's and natural gas has 1000 BTU's, then 1/3 natural gas, 2/3 acid gas.

RE: Creating a Flammable Mixture

When you flare a gas, you want it outside the flammable range until it gets to the flare tip, i.e. above the UFL or below the MOCC.  Generally a flare tip does not have any flash back protection, until you get to a liquid seal near the base of the flare stack. In your case (from what I understand of it) you want to use the fuel gas to take the concentration of the mixture above the UFL.  Otherwise the pilot will ignite the mixture at the flare tip and flash back through the flare stack and possibly into the flare header.  Ideally, the waste gas mixes with the air at the flare tip, the air brings the waste gas back into the flammable range and it burns outside the flare tip to prevent damage to the flaring system.

Without knowing what the composition is of the acid gas or which fuel gas you are using, I can't tell you what concentration to enrich the acid gas too.  However normally depending on how you plan to control the fuel gas rate, you would take the concentration to at least 25-50% above the UFL of the mixture before you get anywhere near the flare tip.

I hope that helps.

RE: Creating a Flammable Mixture

(OP)
Thanks for all your answers.  I'll run a few calc's later today

RE: Creating a Flammable Mixture

dcasto,

The 300 BTU/cu.ft that you mention seems to agree well with the practical experience of landfill gas flaring and power generation.

In many US landfills, when the gas vented from the landfill is flared or sent to an internal combustion engine, the BTU content must be about 300 BTU/Cu.ft or higher.

Typical landfill gas consituents are methane, CO2, N2, O2 and traces of others

-MJC

   

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources