[Stoves] Is there a role for combining torrefaction and char-making stoves?

[rongretlarson at comcast.net]

AD and stove list (and please say hello to Priya) 

See inserts below. I just mentioned in a separate note today that I am working on a response (that you initiated) on the economics of combining torrefaction and stoves. This is still not that response, but it contains some of the flavor . 

Apologies in advance for breaking up your 8-sentence single paragraph to make my response easier 
----- Original Message -----
From: "Anand Karve" <adkarve at gmail.com> 
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org> 
Sent: Monday, February 27, 2012 8:26:29 PM 
Subject: Re: [Stoves] Is there a role for combining torrefaction and char-making stoves? 


Dear Ron, 
the work by Kirk Smith exposed all of us to the problem of indoor air pollution. 
[RWL1: I have the greatest admiration for Kirk's work. For a time, I put this aspect high on the list of advantages for char-making stoves. Now I think other advantages are equally important - AND have more obvious dollar streams of revenue. I think Kirk is wrong to conclude (I think this is still his position) that all forms of cooking with biomass are doomed to failure and that fossil fuels for cooking in developing countries is the best solution health-wise. I see test results for some char-making stoves that are better than typical LPG stoves. I think there are many health aspects to excess atmospheric carbon that his proposed cookstove solutions will not help - especially as we add taxes. ] 

Even the Government of India stopped insisting on biomass burning stoves with high efficiency and started to recommend stoves that burned the fuel more cleanly. 
[RWL2: One can achieve both simultaneously with char-making stoves. Health and efficiency need not be at odds. I believe the present spurt in stove research will confirm this - and you/ARTI have some excellent char-making contenders that should be in that mix. ] 

>From the point of view of clean burning, charcoal and biogas stand at the top of the scale. 
[RWL3: I think that char-making stoves are inherently much (repeat much) cleaner than char-using stoves. Do we differ on this point? 
I have no problem with biogas - and hope we can follow up on the possibility that char makes biogas production more efficient (which some of your fellow biogas experts seemed to deny a few months ago). As you surely know, I am favoring Biochar for atmospheric and soil improvement (carbon-negative) reasons where biogas can play no (?) role - but we should also be doing a lot more with biogas which can (like biochar) back up wind and solar. 

Irrespective of whether you burn these fuels in the open, or in a well designed stove, they burn cleanly. 
[RWL4: Again I am not sure of your meaning above on "clean burning, charcoal". I disagree strongly that char-consuming stoves are cleaner than char-making stoves . ] 

I know that you are against using charcoal as cooking fuel, but I want to state that charcoal is a very convenient, cleanly burning and high energy fuel. 
[RWL5: All true. But there are excellent reasons, that I know you know well, for it to be outlawed in many countries. I see no way char-using stoves can be considered at all competitive with stoves that make char.] 

Making it is relatively easy, and we have shown that it is not necessary to cut trees for making charcoal. 
[RWL6: No disagreement on making char without cutting trees. My point is that making char in the field is sub-optimal . I am not yet sure of it, but I am tending to believe that torrefaction (the name of this thread) will be found to be an essential part of char-making stoves replacing char-consuming (and Rockets, etc) stoves. This will be especially true for urban users - as TBD will be found to be superior to char, when the former may travel a shorter distance - and the legality of the product is not at question (and may carry a subsidy rather than a tax). 
My reading of forestry is that there are excellent reasons for owners to be trimming trees (excellent for both your approach and mine) - but that is off-topic. 

One can make it from dry agricultural waste or even from the fallen leaves from underneath the trees. 
[RWL7: No disagreement. However, torrefaction (and/or pelletizing) can also do the same. And pelletizing ag wastes and leaves for char-making stoves (and therefor/thereby Biochar) is being done today (notably with ALL World Stove operations) - Note also that Nat Mulcahy is asserting that his (I think all) char-making stoves are sufficiently more efficient that the total fuel use in MJ/GJ terms need not go up at all - even as half the carbon is placed in the ground. 
I would greatly value your opinion on the cost you would feel comfortable charging if torrefied biomass material (TBM) became commonplace. I guesstimate that one should charge in the range of 1/2 the price of char per kilo from the same field - as one is bringing roughly three times as much energy back (albeit heavier, of course). I think the extra transportation cost will be covered in any free-market competitive exchange between factors of 2 (price) and 3 (energy content) and differences in transportation costs. Torrefaction not only means one is only transporting energy (and not water), but the user need not use as much TBD for the cooking task (a characteristic shared with charcoal; this being a statement comparing to "raw" biomass). 
To me the best feature of char-making stoves is the dollar savings/earnings for cooks - as they produce a commodity (Biochar) with economic value measured in lifetimes. 

We are currently helping some forest officials in our state in popularising our leaf based charcoal among the inhabitants of our forests, so that they don't fell the trees for making charcoal illegally. 
[RWL8: I thank you for that popularization effort. But I still want to convince you that there is an opportunity even better with the exact same resource. Roughly three times as much cooking can be done with torrefied pellets (or maybe even small suitable shaped/sized pellet like material) than with char. To perhaps repeat once too often: your form of char-production does not capture the exceedingly valuable and scarce available pyrolysis gas energy in the targeted resource. 
Of course I am weighting the atmospheric and soil improvement aspects of Biochar at least as high as the energy aspects. Your char could be placed directly in the ground - but that is not a permissible discussion option on a stove list 
We should continue any AGW discussion over on "Biochar-policy". My arguments for torrefaction are independent of that topic. 

Apologies again for my verbosity - but I value your opinion highly. I just believe you are defending a sub-optimum (from every perspective) solution - when you flare these valuable pyrolysis gases. 

Ron ] 

Yours 
A.D.Karve 

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