[Stoves] benefits from reduced indoor air pollution.

[Andrew Heggie]

On 16 October 2017 at 11:59, Crispin Pemberton-Pigott
<crispinpigott at outlook.com> wrote:
> Dear Andrew
>
> I need a further explanation please:
>
>>The oxygen in the wood is already bonded to hydrogen and carbon, true it is not in it's lowest energy state but it's close. So the oxygen in wood does not significantly contribute at all.
>
> Contribute significantly to what? I don't follow. I presume you meant for heat generation (?), but I was talking about the chemistry of combustion.

Sorry Crispin, I was at cross purposes and thought you meant energy,
Yes all the Oxygen in the wood ends up in steam AND/OR CO2.
>
> For this reason the air demand of any fuel containing oxygen is lower than any otherwise similar fuel that does not.

Agreed


> Wood doesn't contain nearly enough oxygen to burn the carbon (which can remain behind), but does contain nearly enough to burn all the hydrogen (which can't). When it is heated to a low temperature the O and H disassociate to make water vapour, leaving the char (carbon) behind.

Yes  but I don't agree with your use of the term "burn", the oxygen in
the wood has already oxidised the elements it is bonded to, any oxygen
 necessary to "burn" the fuel, i.e. oxidise it completely comes from
the air supplied.
>
> You are quite correct about the energy released, net, being low. That is why it is important to determine the ultimate analysis of what just burned in real time, so that the energy available can be calculated and the true efficiency determined in real time. The determination of what just burned requires separating the water vapour originating as fuel moisture from water vapour that results from combusting hydrogen - something heretofore not possible using carbon balance or chemical mass balance analysis methods. The presentation was on a method of doing exactly that: solving the water vapour split.

One can make a fair stab at this from the other angle; burn a kg of
oven dry wood, using the formula C5H7O3 as the approximation for wood
that Tom Reed suggested all those years ago, to give its Higher
Heating value, 20.5MJ. Burn an amount of carbon with the same mass as
the carbon content of the wood, 0.52kg @33MJ/kg =>17.16MJ. You will
see the "spare" hydrogen atom in the wood only contributes a little
more than the energy changing the H and O in the wood solid to a
vapour.
>
> By the way that group is modeling combustion of fuels and particle formation using a very nice computer: 2.5 peta-flops; $100m. The simulation takes three days to run. I think I need a new laptop.

I only used a calculator ;-)
Andrew