Thanks for bringing the Subject back to the TLUD issue about charcoal. Therefore, this is NOT about making charcoal by other means, whether by stove or not. This is only about TLUD charcoal.
A. The realities (presented as generalities) about TLUD energy release and char include:
1. Pyrolysis is around the 550 to 650 C range (unless burning very hot with much forced air)
2. The char yield is about 20% of the dry weight of the biomass fuel (mainly think of wood).
3. That char contains about 30% (NOT 50%) of the ENERGY of the biomass.
4. And that char contains almost 50% of the carbon atoms. (The “extra” energy came from the hydrogen in the carbohydrates.)
If writers wish to continue to say 50% of the ENERGY remains in TLUD-type charcoal, then let’s resolve that here and now. Otherwise there can be no true discussion about the value of the TLUD char.
B. Fuel effeciencies ARE compared with the baseline fuel consumption figures of the 3-stone fire and other horribly inefficient very simple stoves. TLUD stoves in the carbon credit program in India save about 60% of the fuel, but basically I say “more than half”. That can be compared with the “Save 80” stove which is named for saving 80%. And well made Rocket stoves generally claim to save 75 to 85% of the fuel compared to the baseline stoves. (Correct me if I am wrong about any of this.)
C. So, compared with Rocket stoves, TLUDs have inputs of more fuel. How much? Not well studied because so few of the well funded research studies have bothered to include TLUD stoves. But in general, the raw fuel differences (compared to baseline stoves) are:
about 55% for TLUD and about 80% for Rocket, being a difference of 25%. Plus or minus how much? 5% difference would give a difference between 20% or 30% of the FUEL usage, with the advantage for Rocket stoves.
D. Well, if there is 30% of the original energy still in the created TLUD charcoal, that means TLUDs could be equated with Rockets about ENERGY efficiency (not talking about FUEL efficiency), OR that the TLUDs are actually 10% BETTER about energy efficiency than are the Rocket stoves. Maybe just call it “even”. But stop implying inferiority of TLUD stoves regarding ENERGY.
E. I do not have the time, funds or equipment to quantify or verify what is stated (“claimed”) in the above paragraphs. But unless someone does that measurement (and then it is subject to laboratory error and human factors such as micro-control of the placement of the Rocket wood pieces), the issues of char production and energy efficiency and fuel effeciency are as is stated above.
F. Note that this discussion is NOT about heat transfer efficiency. Simply placing a pot too high above the combustion configuration can make major shifts in heat captured by the pot. There is nothing inherently better or worse about TLUD-ND heat transfer compared with Rocket stove heat transfer. Correct position, shielding, etc. for both types. [[ Note: I do expect to show someday within 6 months that TLUD-FA (Fan Assisted) will have an improvement of the heat transfer, but leave that for later.]]
G. And the financial value of the charcoal from TLUDs can then be discussed, with all of the cultural and environmental factors that raise or lower the dollar values. Of note:
1. where fuel (wood or other accepted biomass fuel) is plentify (or even needs to be “removed” because of space or fire hazzard or cropland issues), there are reasons to FAVOR the TLUD stoves to consume more fuel (not more energy) over Rocket and other ICS stoves which have measurably higher harmful emissions.
2. Where there are established (or strongly potential) needs and uses of charcoal of the type from TLUD stoves, the financial value of the char can far exceed what an additional release of 30% of the raw-fuel energy could bring. Charcoal has many uses.
3. The value of carbon credits is VARIABLE, even at the same moment in time. Cookstove carbon credits have consistently been purchased at higher values than carbon credits from wind turbines, etc, But that is IF the carbon credits have been identified (and verified) as having come from cookstove projects. If they are simply lumped in with all the other carbon credits, their value will have been “averaged” lower. [[ I will be saying more about this in coming weeks..]]
Paul
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@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.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..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.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.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.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.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.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.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? 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. Andrew _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address stoves@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/