[Stoves] Char from TLUDs and retorts

[AJH]

On Tue, 10 Apr 2007 07:39:44 -0500, Paul S. Anderson wrote:

>
>About the carbon conversion efficiency of the TLUD:
>>
>> I've not managed better than 25% of the dry weight, whereas with a low
>> temperature retort I've achieved 45% albeit with a <80% fixed carbon,
>> at a guess.
>
>In the TLUD the heat for pyrolysis came from the fuel.  But in the retort, was
>the heat from an outside source? 

No I used the pyrolysis offgas burning in the way Yuri described but
the wood was very dry and there was need for support fuel at the
beginning, Yuri described a means of rotating the retorts through the
process so that the process could become self sustaining but these
sort of retorts do have limitations for controlling temperature and as
has been noted the containment suffers the full secondary combustion
temperatures, so doesn't last well. Again there's this scalability
problem when the surface area of the retort is also the only means of
heat transfer, which is why overall the re  circulating kiln should
work better.

> If so, how much heat, and how does that
>amount of outside heat relate to the heat used by the TLUD?

Sorry Paul I have no way of measuring such things, interesting
experiments though they would be, we can only make deductions from the
amount of input fuel and the amount (and quality) of char produced.
>
>Also, if the TLUD's 25% char was nearly 100% fixed carbon, 

But I doubt it could be, we are only experiencing temperatures around
500-700C. IIRC if you cook wood to 900C the char yield drops to about
15% of the dry matter weight and the fixed carbon reaches about 99%,
so there's a gradation from high volatiles char with <70% fixed carbon
and made at ~350C up to pure carbon at 900C. You also need to consider
how the temperature varies through the particle, the perceived wisdom
was also that the process only became exothermic in the range 350C to
440C.


>and the 
>retort's 45%
>char was less than 80% fixed carbon, a full 20% of 45% (which is 9%) should be
>reduced from the retort's output, meaning at best only 36% fixed carbon output
>from the retort (with outside heat source) should be compared with the 
>25% from
>the TLUD that had to supply its own heat.
>
>Are we seeing that TLUD production of char could be about as productive as
>retort production of char?

I doubt the tlud would ever compete for fixed carbon output as I
believe it runs off a proportion of its fixed carbon, whereas in a
dedicated kiln or retort it is possible to use the heat from oxidation
of the offgas to drive the process.
>
>Andrew, I am pushing the limits of my knowledge here.  Please be gentle as you
>teach me!!!!    :-))

I've never been a teacher and e-mail always seems a bit terse, I know
what you mean and apologies for any un intended offence.

AJH