4 replies to this topic

[Amardeep]

Can we use flue gases of heater as an inert gas (Nitrogen)? This is for the operation of Pig launchers.

 

Thanks

Amardeep

[Mahdi1980]

What are the constituents of the flue gas?

In general, it cannot be used since there are some undesirable materials sent to the heater or furnaces to be burnt as the flue gas.

So, it might be poisonous.

Anyhow, let us know the composition to recommend you.

 

Mahdi

[manojkaila]

Dear Amerdeep,

 

I did not see by my self but I heard from my senior that in India One of old FCC in vadodara old russian design used flue gas as a inert as after filtering. Though later on it was changed in Nitrogen after many years of successful operation.

 

Regards,

 

Manoj

[Saml]

I used to work in a plant built in the late 60's where they used an "inert gas generator" by burning a hydrogen rich gas from a platformer or natural gas if the unit was down. I don't remember all the details, but if my menory does not fail, after the burner they sent it to a water scrubber to cool it down. It was humid, acidic (because of C02). It was anything but "inert".  Today, you can get nitrogen from membranes using less energy than that unit did.

 

So, back to your anser, yes. You may blanket a tank with flue gas provided excess oxygen is low.  But you will get into the following issues:

- It will be corrosive

- The O2 content in the flue gas will change from "combustion optimization" to "safety critical" probably requiring more instrumentation and protections.

- You will need to install condensate collection points in the distribution system

- Then you have the installation: it means the duct from the stack to your unit, a cooler/scruber and a compressor. I have not made any numbers, but probably that custom built unit is more expensive than a packaged N2 one.

[Art Montemayor]

I would normally not use any flue gas as an "inert" source of gas because:

• Even though I have generated a lot of flue gas for the expressed intention of CO₂ recovery and the flue gas always was analyzed as having only fractions of a percentage of oxygen content, the detailed total composition of flue gas always includes a water content.  It is this water content that ultimately condenses once the flue gas is cooled, and this water may contaminate your product.
• If the fuel being burned to produce the flue gas contains any sulfur compounds, the sulfur will exit as part of the flue gas composition as oxides of sulfur, producing a corrosive liquid fluid when the water in the flue condenses.  This is what causes flue gas ducts to corrode when operated at reduced temperatures.

I don't know what you mean by "filtering".  Please explain in detail.  There is nothing wrong with applying CO₂, nitrogen, or flue gas composed ONLY of  CO₂ + nitrogen - but this is rarely the case and it costs money to clean up any contaminated flue gas.  There is an old saying in Spanish: "El lavado cuesta mas que la camisa" - the laundry costs more than the shirt.