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

Tue Dec 12 23:43:19 CST 2017

This is an interesting topic and one i have wondered about. When packing 
hard a pipe with biomass then flushing with N2 then placing in an oven 
to heat from the outside to a temperature to 550c a lot of gases come 
out the small hole at the end.  That will ignite if the door is opened 
and O2 contact. I have wondered if any heat is being produced in the 
pipe itself? or all from external heat? If there is it can't be much 
because the temperature advances at a continuous rate. Should you see 
the temperature jump well above 550c its because air leaked in to the 
furnace and there is a flame.

Frank

On 12/12/17 9:07 PM, Paul Anderson wrote:
> 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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>
>
>
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-- 
Frank Shields
444 Main Street Apt. 4205
Watsonville, CA  95076

(831) 246-0417 cell
franke at cruzio.com

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