[Stoves] stoves and credits again

[Andrew Heggie]

On 22 September 2017 at 03:54, Ronal W. Larson
<rongretlarson at comcast.net> wrote:

>Andrew wrote
> There might be a slight case for saying a
> gasifier stove can achieve  a lower massflow (particularly lower N2)
> because the primary combustion doesn't go to completion so less
> primary air is used,  the corollary may be that the secondary flame
> also can be burned with less excess air because the offgas has a
> higher calorific value but not enough to make up for using 50% less
> energy..
>
>
> [RWL2:  Given my response in “1” - I need to address the term “50”

Ronal I clarified this in my reply to Paul, obviously it is subject to
experimental measurements but from a desk study given that the char is
reacted at 600C AND 20% of the original biomass dry weight remains as
char then it looks like the energy remaining in the char is closer to
1/3 than 1/2 of the original energy in the dry wood.

> Andrew:  I am not understanding your last 15 words.


Partially dealt with above but also what I was meaning was that  the
offgas from a TLUD, with just sufficient primary are to maintain the
descending pyrolysis front, will be largely the pyrolysis offgas plus
the small amount of gases from the combustion that provides the heat
to drive the process. So it will be little diluted by CO2 and nitrogen
than from a traditional fire which supplies enough under grate
(primary) air to completely burn out the char. Hence the offgas from
TLUD is of a higher calorific value and as such needs less  excess air
to maintain a clean flame. On a larger scale with lower heat losses in
the primary region this may not be the case.


>
> Disagree with Crispin’s statement that a case with 25% char retention
> involves “50% of the original energy” (as did Paul Anderson).

Also dealt with but we need corroboration from analysis of TLUD char.


> Agree with most by Andrew - but think the last sentence needs amplification.
> That is  - lower temperature char can be a better economic choice, even if
> “fixed carbon retention” is less.  This is better discussed on the biochar
> list.  pH value is one criterion that could point toward lower T’s.

...and of course lower fuel input cost would make it more economic
even if the carbon credit paid to the producer were based solely on
the fixed carbon.

>
> [RWL7:   I have seen NO data to show that LPG stoves do not
> have lower emissions than any solid fuel stove.

It seems unlikely to me that simple stoves could have lower emissions
than a LPG flame but Crispin did say as near as makes no difference
and good enough works for me.


>Andrew
>The trouble is I have a
> parochial view and not a good worldview of what types of persons
> depend on biomass fuelled stoves. Are they also predominantly growers?
>
>
> [RWL9:  Yes to Andrew’s last question.  I disagree with Andrew calling
> himself “parochial” - when he supports (as do I) the ethics of “a subsidy
> funded by the developed world”.

I was referring more to my lack of experience of stoves in the real
developing world compared with yourself, Crispin, Nikhil and many
others.
>
>
> So my contention is that apart from the carbon credit there is a value
> to the land in not having to export a cash crop.
>
>
> [RWL10:   Agree totally.

It still means the grower needs to recognise that exporting a
conventional cash crop is removing mineral wealth from the holding, in
many soils with high initial fertility this may not be significant. So
whilst the cash that the grower/stove user might receive will be
linked  to the carbon credit paid for using the resultant char as a
soil amendment he might also value not having to use the land for a
cash crop and possibly growing stove fuel.
>
> `Andrew - thanks for your above rebuttal to Crispin.

Ronal I don't see it in those terms. Crispin has a different viewpoint
but his goal is the same in promoting clean cookstoves.

Andrew