Oxygen in Air

If there is no flammable material to consume the O₂ the concentration will remain the same as in room temperature (21% by volume). That temperature range is too low to form NOx gases.

Thanks for your reply,

Let me explain the application.

I am using a heat exchanger to recover the thermal energy from the flue gas of a furnace.

The combustion air of the burner is heated through this exchanger. This is a common application to recover the spare heat energy.

There is a set point in the temperature range where this operation is no more viable because there is too little oxygen in the air. In this situation the fuel does not burn due to lack of oxygen.

Many years back I had seen a graphic giving the density of the oxygen on one scale and the temperature on the other. This is what I am searching for or any information that can help.

Thanks

What I do not get is that if he is using a heat exchanger to preheat air using hot flue gas, there is a separation between the two streams and there should be no change in oxygen concentration. Bioramani

Quite.

It sounds to me as though you are using some thermal energy in your flue gas to pre-heat your primary combustion gas. If this is the case, then there is no change in the composition of your combustion gas due to the pre-heat. As others have stated, heating a gas doesn't change its composition because no chemical reaction is involved.

Thank you for your clarifications and good information. You got me on the right track. I am using a constant volume blower so all I need to know is the coefficient of thermal expansion of air (will search on the net) and I can calculate the rest.

Thanks again

I have awarded the cantankerous alien a GA. So should you.

So have I.

I don't have much time to look into the CR4 although I find it interesting. This time it was useful.

"I have awarded the cantankerous alien a GA."

Excuse my ignorance but if you can enlighten me on "cantankerous alien and GA" I will be happy to do so. I owe "Dvander1000" a favour.

Thanks

Hi Angelo,

It's just the humor around here leaking.

I think it dates from the autograph signing incident.

I didn't follow the "autograph signing incident" but my question calls for a good laugh.

Have a nice day

Thanks for the GA guys, and I owe you an explanation for the cellphone incident. That schoolgirl told me that someone had rigged her phone to be used as a radio detonator for a bomb in the convention center, so I had to disarm the system to prevent the bomb from going off.

Hey, I might be evil but I'm still a soldier and an engineer you know.

Although the other posters have given you technically correct information, I believe they have missed your point. It is true that the oxygen concentration (volume/volume) remains constant regardless of temperature, the oxygen density (mass/volume) changes.

At constant pressure, T1/T2 = V1/V2, where V is volume and T is in Kelvin.

If your consider 25C to be "standard", at 50C the volume increases by a factor of 323/293 = 1.08. At 400C 673/293 = 2.3. The relative oxygen density is the inverse of this number.

So, if a burner requires 1 l/min. of air at 25C to properly burn, you must supply 2.3 l/min. at 400C to supply the same amount of oxygen.

Thank you Tad, I've already worked out that formulation and presumably solved the problem. I will be trying the furnace with the new settings one of these days.