Dew Point of Flue Gas

[Deleted]

The dew point of flue gas with no excess air is about 132°F, 56°C.
With 100% excess air it will be about 113°F, 45°C.

At 212 °F, 100°C one cubic meter of air can carry bout 590g water steam.
www.engineeringtoolbox.com/water-vapor-saturation-pressure-air-d_689.html

1 kg wood with 20% moisture contains about 400g chemicaly bound water,
which results in a total of about 600g of water.

1 kg wood will produce about 5 cubic meter flue gas with no excess air (at 32 °F, 0°C).
With 100% excess air it will be about 9 cubic meter.
The real volume of the flue gas will be significantly higher,
but the air will contain some water steam to.
Omitting the additional volume compensates the air moisture.
donkey32.proboards.com/thread/759/resulting-gas-volume-kilo-wood

To further enhance thermal efficiency of a stove time, effort and money would be well invested
in more thermal mass and a chimney fan powered by a thermal electricity generator (TEG).


Power plants which want to regain phase change energy by condensation are firing extremely wet biomass
or even add water for other fuel, to make it technicaly feasible.

If the chimney can resist some acid the TEG could also power a water sprayer,
to "wash out" some steam and fine particles, regaining some energy in this way too.
The first aircon used this to cool and dry air.

[alezgroe]

The dew point of flue gas with no excess air is acerca 132 ° F, 56 ° C.

With 100% excess air acerca it will be 113 ° F, 45 ° C.

 

hi karl
in relation to the previous paragraph

How do you determine if there is excess air in the combustion?

[Deleted]

Jul 14, 2014 8:49:33 GMT -8 alezgroe said:

How do you determine if there is excess air in the combustion?

Can be calculated from remaining oxygen and created carbon oxides.
I think I have posted the formulas somewhere.

Excess Air = Excess Oxygen
www.departments.bucknell.edu/chem_eng/cheg200/CinChE_Manual/Ch05/examples/excess_air.pdf

Excess air in combustion - Energy Manager Training
www.energymanagertraining.com/Documents/lecture9.doc

[alezgroe]

HI Karl.
thanks for your answer, I'm reading the material and suddenly I realize that my previous question was more related to this: I'm sitting on a warm bench in my greenhouse heated by a rocket adapted to an iron stove (the circuit is not affected by cooking the oven will only fail) and I realize that my gas output at the end of the bank between 30 and 50 degrees normally and never condensacion.Tampoco tube problems in the course of the bank.

  This fact is stronger than a thousand theories, but I wonder if there is an explanation for this.

Besides abusing your generosity I wonder where temperatures are measured in the flue gas, the external duct temperature is taken?

Thank you very much.

Alex

[Deleted]

Water condensation is an adsorption of water to a surface.
Under normal conditions virtualy any surface is covered by a thin layer of water,
thus with respect to condensation virtualy any surface can be be considered to be a water surface.
The conditions in flues are no normal conditions.

The amount of adsorption/condensation is influenced by:
Temperature
Temperature gradient
Size of the surface and the surface itself.
Turbulence
Pressure
composition of gas mixture

Any gas movement lowers the the pressure towards the surface.
Gas movement makes evaporation more likely than condensation, if both where equaly likely otherwise.
Flue gas is not air, thus the dew point from flue gas will differ from the dew point from air.
Particles or small droplets of combustion residues will catch some of the water.

Aerosols can be hygroscopic.
From Wikipedia:
An aerosol is a colloid of fine solid particles or liquid droplets, in air or another gas.
Examples of aerosols include haze, dust, particulate air pollutants and smoke ...

The internal duct temperature is taken.

[Daryl]

Correct me if I am wrong but the condensation point of creosote is under 250F degrees. It is recommended that flue/chimney temps stay above 250F.

I am posting this because I am seeing an alarming number of stoves being built off this site that in the future will be a b word to fix because of the mass and design. I'm not seeing anyone on youtube or sites promoting keeping the temps hot the whole way through the build. Not that I know everything but I know enough about science to think "Danger Will Robinson!"

[peterberg]

Jan 11, 2015 6:57:49 GMT -8 Daryl said:

Correct me if I am wrong but the condensation point of creosote is under 250F degrees. It is recommended that flue/chimney temps stay above 250F.

Condensation range of creosote is 170 F and lower. Boiling point on the other hand is about 400 F and higher. Whether or not this dangerous substance will accumulate in a chimney depends for the best part on the quality of the combustion.

[Deleted]

Rockets do not produce creosote as they are burning far to hot,
if properly built and maintained.

If a fool stuffs a rocket full with green wood and uses kerosene to get it burning,
some creosote may escape unburnt before the rocket reaches sufficient temperature.