[Stoves] benefits from reduced indoor air pollution.

[tmiles at trmiles.com]

" 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."

Wow. That beats doing the stoichiometry long hand. At least long hand
reminds you of the chemistry involved. 

Tom 

-----Original Message-----
From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
Crispin Pemberton-Pigott
Sent: Monday, October 16, 2017 3:59 AM
To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] benefits from reduced indoor air pollution.

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.
We know the O in fuel ends up in the exhaust gases. The thermal
decomposition of biomass releases H and O and N and S approximately in the
same ratio as they occur in the fuel (with some exception made for S which
sometimes clings to C.) 

For this reason the air demand of any fuel containing oxygen is lower than
any otherwise similar fuel that does not. It happens that I gave a
presentation on this to the CFD modeling group at the Chinese Academy of
Sciences today. Lambda (total air demand) for a fuel containing oxygen is
not Excess Air Factor +1, because the "1" is not correct for any fuel that
contains oxygen. For wood it is about 0.76 if it is burned homogeneously and
varies from about 0.2 to 0.99 in a real fire depending on what fraction of
the fuel happens to be burning at the time (i.e. ignition volatiles v.s.
char burning).

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. 

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.

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.

Regards
Crispin


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