[Stoves] TLUD theory -- Fuel Bed Temperatures

[Josh Kearns]

Sorry - realized I didn't answer the original question:

We measure temperature in the fuel bed.

JK


On Mon, Jun 17, 2013 at 12:44 PM, Josh Kearns
<yeah.yeah.right.on at gmail.com>wrote:

> Using a 1-gal TLUD "Toucan" model in natural and forced air modes, we have
> seen, pretty consistently, ND peak temps. 600-650 C, and FD peak temps
> 900-950 C. This has been across feedstocks - wood pellets, sugarcane
> bagasse pellets, bamboo chips, jatropha presscake pellets, pecan shells,
> cherry pits.
>
> Temperature is controlled by draft, and we were lucky to achieve high
> draft conditions in our 55-gal drum TLUD without applying a fan. Feedstock
> granularity, density, and bed density had to be within an optimal range
> however. High draft 55-gal TLUD chars from dense, uniform feedstocks (e.g.
> eucalyptus branches 1-2-" dia cut into 4-6" segments) seem to offer
> equivalent sorption performance as 1-gal FD chars made from wood pellets.
>
> Interestingly, temperatures have been more or less independent of
> feedstock, but burn duration is longer with denser feedstocks. If
> feedstocks are insufficiently dense, e.g. the bagasse pellets I made with
> our crappy benchtop pelletizer, then they tend to burn up and the char
> yield is very low if draft is high.
>
> Also, interestingly, feedstock did not seem to matter much for sorption of
> our probe compounds (e.g herbicide), where peak temperatures were
> consistent. This agrees with other work that finds peak temperature, and to
> a lesser extent heating duration, to be controlling factors in product char
> properties, with feedstock identity exerting less of an influence (except
> insofar as feedstock identity exerts intrinsic effects on the pyrolysis
> regime).
>
> JK
>
>
>
> On Mon, Jun 17, 2013 at 8:56 AM, Alex English <english at kingston.net>wrote:
>
>>
>>
>> Julien,
>> Josh Kearns has posted graphs of bed temperatures.
>>
>> I data logged a T-LUD on wood pellets
>> http://www.bioenergylists.org/stovesdoc/English/bigtop2.htm
>>
>> Switching units I have choked primary air as low as possible while
>> maintaining a flame. That corresponded to a peak fuel bed temperature of
>> 480 C.
>> My impression, though unmeasured, that the gas composition was different
>> than at high temperatures. I hav also pushed the TLUD with a high pressure
>> blower and at no time did it fail to produce combustible gasses.
>>
>> Alex
>>
>>
>>
>> On 16/06/2013 10:57 PM, Julien Winter wrote:
>>
>> Dear stovers;
>>
>> What do we know about the temperature in the fuel bed of top-lit
>> updraft gasifier stoves (TLUDs)?
>>
>> Almost all features of TLUD function are affected by the temperature
>> of the fuel bed.  This includes the combustion quality of the effluent
>> gases, the stability and momentum of the reaction, water boiling rate,
>> the quality of biochar, the yield of biochar, the nature of effluent
>> particles, production of crystobalites, production of polynuclear
>> aromatic hydrocarbons, etc.
>>
>> In the last 30 years, temperature data has been published for
>> laboratory bench-top reactors that were, ostensibly, forced-air TLUDs.
>>  Most of this work was done to understand the function of moving grate
>> gasifiers for urban waste and biomass fuels (and even earlier research
>> on coal).  Along with other measurements, temperature observations
>> were used to calibrate computer simulations.
>>
>> An example of bench-top TLUD data is attached as a pdf.
>>
>> These bench-top TLUDs do not cover the range of conditions experienced
>> in the real world of feral TLUD cookstoves.
>>
>> What observations are there on fuel bed temperatures in TLUD cookstoves?
>>
>> What range of temperatures are possible for a functional stove?  If
>> the reaction is too cool, we just get incombustible shouldering smoke.
>>  Will the stove function poorly if the temperature is too high and
>> most of the gases oxidized to CO2 within the bed?  Is there a sweet
>> spot temperature range, and does it vary between fuels (e.g., grass,
>> chips, pellets, briquettes)?
>>
>>
>> Just as an aside, someone should make virtual TLUD stove for testing
>> theories and teaching.  That shouldn't be too hard for pellets.
>>
>> Cheers,
>> Julien-the-eyebrowless
>>
>>
>>
>>
>>
>>
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>
>
> --
> Josh Kearns
> PhD Candidate, Environmental Engineering
> University of Colorado-Boulder
> Visiting Researcher, North Carolina State University
>
> Director of Science
> Aqueous Solutions
> www.aqsolutions.org
>
> Mobile: 720 989 3959
> Skype: joshkearns
>
>
>
>


-- 
Josh Kearns
PhD Candidate, Environmental Engineering
University of Colorado-Boulder
Visiting Researcher, North Carolina State University

Director of Science
Aqueous Solutions
www.aqsolutions.org

Mobile: 720 989 3959
Skype: joshkearns
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