[Stoves] stoves and credits again

[Ronal W. Larson]

Andrew and list:

	Thanks for the new thread name.  A few comments below.


> On Sep 21, 2017, at 9:47 AM, Andrew Heggie <aj.heggie at gmail.com> wrote:
> 
> I've changed the title to move back to the idea of what value can be
> added to TLUD use:
> 
> On 18 September 2017 at 20:21, Crispin Pemberton-Pigott
> <crispinpigott at outlook.com> wrote:
> 
>> As pointed out here years ago, the challenge for pyrolytic stoves to have a
>> heat transfer efficiency that more than makes up for the additional fuel
>> requirement. If you look back far enough I provided a formula for
>> calculating the requirement.

	[RWL1:  I’d sure like to see that formula.    The “requirement” one that is being used by Jim Jetter and his ISO panel is 

e3 = e1/(1-e2), 

where e1 is the energy transferred to the cookpot, e2 is the energy remaining in the char, (1-e2) is the energy that is available for being transferred to the cookpot (any disagreement on this meaning of (1-e2)?), and the overall efficiency, according to this part of the ISO process, is e3.

	Example:   If e1 and e2 are both 1/3, then the inefficiency (energy not doing anything valuable) is obviously also 1/3 and the energy available to go to the cookpot is (1-e2 =2/3).   As an individual interested in getting char in the ground for climate reasons,  i’d like to say that the overall efficiency is e3’ = e1+e2 = 2/3.  But I can agree that is too high from a cooking perspective - so I support the lower number e3 = (1/3)/(2/3) = 1/2.

	I think Crispin believes that the right answer here from a cooking perspective is e3” =  e1 = 1/3.  He apparently believes the e2 in char was simply lost forever (even though it could be later converted at the above presumed/predicted stove efficiency e3 = 1/2, so 1/2 * 1/3 = 1/6. This later cooking value when added to the measured e1 = 1/3 gives 1/3 + 1/6 = 1/2 (amazingly - the same e3 as when the char energy e2 is placed in soil).

	Crispin’s formula is unknown to me, if not this last e3 example.
> 
> Which to me is an impossible challenge so not worthy of discussion,
> the simple fact is that if 50% of the energy remains bound up in the
> char then it is not available for cooking. The heat exchange
> efficiency will not differ much between a TLUD flame and any other
> stove using a flame. 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” (as I am claiming in my example e2 = 1/3).  Paul Anderson has expressed concern about an e2 number as large as 1/2, and I agree.  But another way of looking at the 50% number is to note that e2/(e1+e2) is 1/2 = 50% in my hypothetical example.  Perhaps some of the commenters are (correctly) using 50% in this context.
	Andrew:  I am not understanding your last 15 words.   I agree with Paul’s comment that we need to applaud the fact that cookstoves love H2 and biochar proposers mostly hate it.   I think we are finding that TLUDs DO generally offset the “loss” to soil placement.
>> 
>> As whole-wood burning cooking stoves have reached the 33-35% efficiency
>> range, the efficiency of a gasifier has to be high enough to compensate for
>> the additional fuel, if the fuel savings matters to the project, which in
>> the case of CDM and GS it does. If the char retention is 25% of dry mass,
>> and that fraction contains 50% of the original energy in the fuel (at
>> least), then the stove will have to be twice as efficient as the wood
>> burner, i.e. 66-70% heat transfer efficiency. In theory it is possible, in
>> practice I haven’t seen it. All pyrolytic gasifiers consume more fuel than
>> the best wood burner available at the time.
> 
> I agree all that but cannot see why the heat transfer efficiency
> between the two types should differ.

	[RWL3:   Agree with Andrew.  The above e3 formula is in accord with this “fact”.   

	Disagree with Crispin’s statement that a case with 25% char retention involves “50% of the original energy” (as did Paul Anderson).
> 
>> Your stoves might compare favourably with an open fire or a declared 10 or
>> 15% efficient baseline, but they will not be as fuel efficient as a stove
>> that burns wood completely.
> 
> In my view this is only true if you are going to argue that the
> remaining char is a heat loss to the system, I argue that it is a co
> product  which contains unused potential chemical energy. If Kevin and
> Paul get their spreadsheet terms right the value of carbon credit can
> be calculated. Apart from being put off examining Kevin's spreadsheet,
> because it uses imperial units and thus not checking the calculation,
> he is entirely right that the carbon credit payable to the stove user
> must exceed the fuel value remaining in the char.

	RWL4   Of course disagree with the Crispin sentence.   Check the data.

	I think Kevin is forgetting that people for thousands of years have placed char in soil without ever being concerned about its energy value (nor anything about climate benefits.   Not only does the value of the land immediately go up, but there is increased yield for hundreds if not thousands of years.  To limit char’s value to potential carbon credits is missing everything about biochar.
>> 
>> 
>> A stove that burns wood completely paralleled with a small charcoal making
>> operation in the same community might use less total wood and produce more
>> total char because both technologies can be optimised to their function.
> 
> I really cannot see this, see above. To make charcoal in a dedicated
> device still requires that the offgas is used for it to be efficient
> as there is an excess over that necessary to raise the raw material to
> pyrolysis temperature, unless it is exceptionally wet.

	[RWL5:  Like Kevin,  Crispin doesn’t understand either the soil or atmospheric values of biochar.  The biochar world is bigger than cooking - and even bigger than both cooking and climate.  That is - farmers are beginning to see the values of improved yield, and reduced irrigation and fertilizer expenses - just to start with a few other biochar benefits.

	Agree with Andrew.
> 
>> If
>> the purpose is to create the most char and the most cooking from a given
>> source of biomass, so at least, a pyrolytic gasifier is not the best option.
> 
> 
> ...and this depends on what sort of char you require. For smoke free
> cooking it needs to be made at sufficiently high a temperature that it
> burns without evolving a tarry offgas. As a soil amendment the lower
> temperature char will contain the same minerals plus some
> hydrocarbons which bugs will feed on for a while but it won't have the
> higher cation exchange capacity which growers want nor the level of
> adsorptivity to hold organic compounds (in order to prevent leaching
> or oxidation of soil organic matter) which growers desire. As a result
> the fixed carbon retention is also less than char made above 600C.

	[RWL6:  I’m looking forward to Crispin’s identification of stoves better than TLUDs.

	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.
> 
> 
>> It is an option but it is not yet out-competing other technology
>> combinations. The cleanest wood burning stoves are as clean-burning as an
>> LPG stove, or there is not enough between them to find a meaningful
>> difference.
> 
> Good it's nice to see that reiterated, it means it remains a goal, to
> aim for the dissemination of better solid fuel cook stoves.

	[RWL7:  Crispin is claiming that “pyrolytic gasifiers” (i.e. TLUDs) are being “out-competed [by] other technology combinations.  Could be true but I haven’t seen that - and so ask for the names of these other supposedly superior approaches.  I have seen NO data to show that LPG stoves do not have lower emissions than any solid fuel stove.  Where do I go to find the converse?
>> 
>> 
>> 
>> If one can sift through a biomass source and take out everything ideal for a
>> wood burner, and pyrolyse the rest into char, that is a reasonable thing to
>> do if the char has a use or value.
> 
> Of course that is what we did in UK but in that instance the logs and
> firewood were luxury goods and not necessities.

	[RWL8:   I contend that biochar has already amply proven that “char has a use or value”.  Watch what happens when credits are available to the extent they deserve.
>> 
>> 
>> 
>> I proposed two years ago that in Hebei, which has a serious problem with air
>> pollution caused by the in-field burning of crop residue, that they put a
>> small price on the material making it worth collecting it to a central
>> point. This could be charred while making wood gas that can be piped into
>> the local distribution network. The remaining char would go into the input
>> line of local fertiliser factories that are making organic fertiliser, of
>> which char is one component. There are multiple factories making these
>> products, almost of all of which is sold outside the province to others
>> which subsidise organic fertiliser products (Hebei doesn’t).
> 
> There appears to be a win win situation here and I gather there is
> still a vast part of equatorial Africa where annual burning  takes
> place. However it brings me to another reason I like the idea, though
> not the practicalities, of a householder-subsistance farmer being paid
> a subsidy funded by the developed world. 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”.

	Re Crispin’s report on Hebei, thank goodness the Chinese have apparently recently understood the idiocy of burning straw in the field.  On both this the biochar list,  I have recently commented on northern China (bigger than Hebei) having established a biochar goal  (I think official) in which the biochar amount will grow by a factor of 50  (fifty!!) in the five year period 2016-2020 (an annual growth rate of about 120%).  Most assumptions I see about biochar growth rates are a factor of ten smaller.  See  http://www.biochar-international.org/node/8858 <http://www.biochar-international.org/node/8858> .   I mention this to emphasize both that burning straw is a horrible practice and that biochar is a high priority solution.  No proof that TLUDs pyrolizing this same straw are likely to benefit - but I guess they will,

> 
> Please bear with this preamble:
> 
> When biomass burning  came to the fore in UK it was largely from
> forestry residues which typically had mineral ash of about 1% of the
> dry matter, less if left to lose their needles prior to harvesting.
> Then a firm had a simple  steam turbine design , taken from a naval
> design, and their raw material was agricultural waste including the
> litter from chicken houses. The chicken litter was for free, apart
> from haulage, but straw from OSR, wheat, barley and oats had to be
> bought and it wasn't long before farmers realised the price being
> offered was less than the cost of the mineral fertilisers that had to
> be replaced before another cereal crop could be grown. Combine
> harvesters were modified to chop the straw rather than bale it for
> sale, so the straw could be incorporated into the soil for the next
> season's growth.
> 
> Nothing is ever black or white so there remain both baling and carting
> and straw chopping and incorporation depending on local variations in
> costs and returns.
> 
> A bit long-winded but to my point: we are, on this list, addressing
> relative poverty. If it were not so everyone could have gas and
> electricity for cooking. So I am happy to see these carbon credits and
> CDM?? neither of which I am familiar with, used to subsidise improved
> stoves. I like the idea of paying a near subsistence farmer to put a
> char  soil amendment in the soil because it becomes a cash crop that
> she/he does not have to go to the trouble of exporting away from the
> locality with the aforesaid loss of mineral fertility which I suspect
> in many cases is not being replaced.
> 
> Here in UK we have a very benign, if cold and occasionally miserable,
> climate but we do have a history of soil deterioration from
> overgrazing and export of minerals on the hoof in some lighter soils
> which were the ones initially cleared from the wild-wood that covered
> much of southern Britain. We also know when European farming practises
> were exported to the American midwest that the climate there was less
> forgiving of old world practices.
> 
> 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.  And I think this is what will eventually kill the geoengineering technology that is often placed ahead of biochar - BECCS.  In BECCS, as with “clean coal”, the CO2 from combustion (never pyrolysis) is placed, as  liquid, deep underground.   Major expenses needed to protect the world’s soil are not needed for biochar.  Soil quality is closely linked to carbon content - and biochar does this with no penalty - while apparently being the cleanest and most efficient of all possible solid-fuel stoves.

`Andrew - thanks for your above rebuttal to Crispin.

Ron
> 
> 
> Andrew
> 
> _______________________________________________
> Stoves mailing list
> 
> to Send a Message to the list, use the email address
> stoves at lists.bioenergylists.org
> 
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
> 
> for more Biomass Cooking Stoves,  News and Information see our web site:
> http://stoves.bioenergylists.org/
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20170921/d53111a4/attachment.html>