[Stoves] Increasing ND-TLUD riser height accelerates gasification and increases bed temperature

[Dean Still]

Hi Julien and All,

Any serious researcher is welcome to come to  the Aprovecho lab and pursue
the open source description of natural draft TLUD operation. We have a nice
dorm room, hot lunches, good coffee and offer a stipend of $500/month. I
think a minimum of three months would result in some good data but six
months (or more) would be better. Scientific investigation can be tedious
but, as you say, it's very much needed.

We're doing an Open House the week after ETHOS again (January 27-29) and it
would be a good time to look at our lab and talk to the staff.

All Best,

Dean



On Sun, Dec 14, 2014 at 3:17 PM, Julien Winter <winter.julien at gmail.com>
wrote:
>
> Dear Crispin et al;
>
> It would be nice if I had some good gear for my experiments, but what I
> used was sufficient for my purpose.  I need to get some very basic
> performance characteristics for a natural draft, top-lit updraft gasifier
> (ND-TLUD).
>
> The take-home message from my graphs is just how sensitive the reaction is
> to small alterations of primary air at low rates.  Anybody designing a
> ND-TLUD will see that the knob that adjusts primary air should move a
> manageable distance to regulate primary air at low to nil rates.  As for
> people who want to make biochar, or use the reactor as manufacturing
> furnace, for the first time there is publically available observations on
> what temperatures to expect when gasifying softwood pellets.
>
> What I used for this research is (1) a scale to measure fuel and char, (2)
> an overhead scale to measure mass loss during gasification, (3) a four
> channel thermocouple data logger, and (4) an oven I can hold to 105°C to
> measure fuel moisture content.  For unfunded, recreational research, that
> is not bad.
>
> What would have been the biggest improvement for my experiment would be to
> set-up a more sophisticated method of feeding primary air, and measuring
> the primary air superficial velocity (SV).  Expressing my results in terms
> of grate aperture is very useful for TLUD design, but SV would have allowed
> me to  compare directly my results to published papers on FD-TLUDs.  If I
> had SV, for the first time, we would have known exactly were ND-TLUDs lie
> on the range of primary air flow rates for top lit gasifiers and
> combustors.  For research on gas burners, the flow rate of secondary air
> and monitoring emissions are important.  Gear like that needs a full-time
> laboratory.
>
> As for trying to explain my observations, just about all explanations for
> ND-TLUDs are speculative, because ND-TLUD SCIENCE DOES NOT EXIST.  There
> are at least 50 peer-reviewed papers on 'FD-TLUDs' dating back to 1947.  No
> all of them are appropriate to cookstoves, but a lot of them are.  For
> ND-TLUDs there is nothing.
>
> For the moment, that means that my graph showing the regression of
> temperature on specific gasification rate is there mostly for "gee-wiz,
> that is a high R²."  If someone was burning softwood pellets, and knew
> their gasification rate, they could estimate the temperature.   If this
> kind of regression is common across fuels, then it will beg an
> explanation.
>
> For now what we need are some very basic empirical studies on ND-TLUD
> performance, so that builders of stoves can make more deliberate decisions,
> so that rural extension workers can have confidence that their advise is
> well-grounded, and so that both can respond effectively to unexpected
> situations.
>
> We need to start building ND-TLUD science at a very basic
> empirical level.  Nobody has actually measured primary and secondary air
> flow, so nobody really knows the their optimum proportions for low
> emissions and how that changes with gasification temperature, types of
> burner and fuel.  Nobody has actually proven that preheating secondary air
> is effective; it is just assumed to work, even though we are taking heat
> from the reactor to create more viscous and less dense air.  If preheating
> makes no difference, then it becomes easier to design the gas burner and
> the gasification reactor as separate modules, that are mixed and matched
> according to need.  Nobody has shown that TLUD biochar has safe levels of
> polycyclic aromatic hydrocarbon and dioxins.  All this, and more, needs
> clarification in replicated, controlled experiments ... and open access
> publication.
>
> Cheers,
> Julien.
> --
> Julien Winter
> Cobourg, ON, CANADA
>
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