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

Paul Anderson psanders at ilstu.edu
Mon Dec 11 19:07:11 MST 2017


Gordon and Crispin,       (First of 3 replies to about a dozen messages 
on this topic.  Not in any special order.  I thank everyone for their 
comments.)

There is O in the carbohydrates.   And during pyrolysis / carbonization, 
carbon is left behind.   Chemical compositions have changed.   But that 
does not mean that the O is "freed" to combust.   Pyrolytic gases are 
essentially "smoke" that is with lots of tars and long-chain 
hydrocarbons.  Note, long-chain hydROcarbons that will take oxygen atoms 
with them up into the combustion zone where the secondary air is present.

I do not know how much O of biomass hydrocarbons becomes freed, but 
certainly not all of it, and maybe not much it.  I hope that some 
combustion chemist can clarify about this.

I appreciate Crispin's reply statement in a differnent recent message 
(copied below) and I hope for some chemist to be able to reply.
>
> For those who want to look further into the chemistry of this process, 
> there is a calculation made in the HTP analysis spreadsheet that 
> calculates the air demand of the fuel based on the elemental 
> composition of the fuel and the char remaining at the end. From an 
> assumed need for all oxygen to come from air, the actual requirement 
> for a TLUD making a lot of char is only 20% of the theoretical need 
> for the whole fuel, because 80% is provided from the biomass itself.
>
> EA+1 = λ
>
> where λ is the total air demand. This calculation is incorrect. The 
> real values for a TLUD are
>
> EA+0.2 = λ
>
> You only need to provide 1/6^th of the theoretical oxygen requirement 
> of the fuel, provided it is biomass and you want to make char.
>

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 12/10/2017 12:05 PM, Crispin Pemberton-Pigott wrote:
>
> Dear Gordon
>
> To be technical about it, the thermal decomposition of biomass 
> releases O (not O2) as well as N and H in approximately the same ratio 
> as they occur in the material.
>
> All that is required is to heat the fuel. If it is heated with 
> inadequate oxygen available, some of the fuel will remain unburned. 
> That naturally is the carbon, which is the most difficult to 
> evaporate. The surface burns.
>
> As explained earlier, if the fuel is heated enough, a TLUD burning 
> wood pellets would continue burning (pyrolysing) without any added 
> air. As the H burned, it would release 120 MJ/kg and the carbon burned 
> to CO would release about 8 MJ/kg. There is enough to keep the fire 
> going if it is large enough and insulated.
>
> Regards
>
> Crispin
>
> *From:*Stoves [mailto:stoves-bounces at lists.bioenergylists.org] *On 
> Behalf Of *Gordon West
> *Sent:* 10-Dec-17 22:42
> *To:* Discussion of biomass cooking stoves 
> <stoves at lists.bioenergylists.org>
> *Subject:* Re: [Stoves] Understanding TLUDs, MPF and more. (was Re: 
> Bangladesh TLUD )
>
> Is there a report on monitoring an Adams retort MPF using 
> thermocouples? I am still not successfully visualizing the process.
>
> I did a bit of a search of technical reports on the chemistry of woody 
> biomass pyrolysis and have not yet found a reference to the release of 
> O2 from heating the feedstock and its subsequent recombination with 
> other elements resulting in an MPF. Several analyses of syngas that I 
> saw show plenty of oxygen but it is bound in various fuel molecules.
>
> Gordon
>
>

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