[Stoves] Understanding TLUDs, MPF and more. (was Re: Bangladesh TLUD )

[Paul Anderson]

Crispin,

Your key sentence is this:
>  Whether one can do it [with only the oxygen atoms in the biomass] in 
> tin cans on a small scale is a different matter. 
You conveniently glide past the fact that what we are really interested 
in on this Stoves Listserv IS about stoves that are of small scale.

What you provide below is quite idealized, in perfect condition, shown 
in theory and a chemical formula.  Maybe that way it might be confirmed 
by a chemist as being true, but it certainly is of minimal relevance to 
solving the cookstove problems of impoverished people.

The term "splitting hairs" comes to mind.   I looked at what you wrote, 
but I certainly did not seriously study it.  You comments might be 
rignt, but your comments are of minimal or no relevance.

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype:   paultlud    Phone: +1-309-452-7072
Website:  www.drtlud.com

On 12/12/2017 8:27 PM, Crispin Pemberton-Pigott wrote:
>
> Dear Andrew and All
>
> Now that everyone is or is not a chemist, it is time to end the fun.
>
> This is the major point made by you and Paul.
>
> *>*My point remaining that to release heat from wood you need to add 
> oxygen and the fact the wood already has oxygen containing molecules 
> within it is irrelevant.
>
> I am suggesting that this is incorrect. Whether one can do it in tin 
> cans on a small scale is a different matter.
>
> There are two possible processes that can take place without oxygen 
> (heating fuel without the addition of any air at all). They are
>
> Auto-catalysis
>
> Auto-pyrolysis
>
> The first is what I described using a chemically balanced equation to 
> demonstrate that there is enough oxygen in biomass to combust 93.6% of 
> the hydrogen. This is true, but auto-catalysis (the reformation of all 
> the bonds to provide a re-ordering in a new form to provide H2O and 
> CO2 as the only outputs) does not take place in biomass. It is true 
> that /in a fire/ this could happen, and does, but it is not true that 
> it can happen without a fire, even though all the elements are present 
> to do so.
>
> Correction:
>
> The calculated energy available was using Tom Reed’s formula is for 
> the energy released upon the complete combustion of the fuel. I 
> pointed to the 93.6% of hydrogen combustion which is not the same as 
> 100% combustion. So the actual energy available for the re-ordering of 
> the chemistry of biomass without adding air is 0.5 MJ less than for 
> the full oxidation of the hydrogen. The heat available using only the 
> internal O is 1.7 MJ/kg for dry biomass. That is theoretical and based 
> on the chemical mass balance that would result from auto-catalysis of 
> the elements. As I said, auto-catalysis does not happen below 1000 
> degrees. It is very likely to happen above 2700 C which would require 
> a reactor beyond our common materials.
>
> On the matter of auto-pyrolysis of biomass, this /does/ happen in the 
> complete absence of air, and this is the key point of the conversation.
>
> Here is a plot of the energy released by the heating of biomass in an 
> inert environment:
>
> Please note the spike in heat released at 360-400 C. That is the 
> cellulose (etc) breaking down. There is a net release of energy. The 
> charts come from here 
> <http://onlinelibrary.wiley.com/doi/10.1002/pol.1968.150061202/full>. 
> (H/T Philip Lloyd)
>
> “An application of TGA technique to elucidate the chain reaction 
> mechanism of cellulose pyrolysis is discussed.”
>
> The reference to a chain reaction is the way they describe the 
> self-sustaining, auto-pyrolysis of cellulose. There is an investment 
> of energy at 320 C and strong release of energy at 360. The TGA charts 
> above show what happens with other fuel components.
>
> Once it starts, it can continue until there is no raw biomass left to 
> react, provided it is not cooled at a rate greater than the net gain 
> in energy. In an ideal container there would be thermal runaway: the 
> rate of heat release would increase. This reaction (shown above) takes 
> place in the absence of air.
>
> This second phenomenon is not dependent on the chemical balance (which 
> while theoretically possible, does not happen in biomass at a 
> realisable temperature). Auto-pyrolysis actually happens. Additional 
> studies investigating the energy needed/released are here 
> <http://onlinelibrary.wiley.com/doi/10.1002/app.1970.070140518/full> 
> and here 
> <http://onlinelibrary.wiley.com/doi/10.1002/app.1989.070371203/full>.
>
> If readers can accept the results of these experiments (showing the 
> auto-pyrolysis taking place and validation of the theoretical 
> exothermic reactions proven) there are implications for the stove 
> makers. One is that as biomass can pyrolyse without any air at all (as 
> demonstrated) we can drop the claim that it doesn’t.
>
> >…if I am wrong I admit it, I am also not a chemist nor ever claimed 
> to be.
>
> I am wrong several times a day. I don’t see why you shouldn’t be 
> affected by those same experiences. We have on this list a chemist in 
> the shape and likeness of Prof Philip Lloyd, I believe the past 
> president of the South African Institute of Chemical Engineers (I hope 
> I have the name correct).
>
> Regards
>
> Crispin
>
>
>
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