[Stoves] More on briquettes and pellets

[rongretlarson at comcast.net]

Richard and 2 lists: 

Thanks for the complete response. I conclude that pellets and briquettes are possibly able to act similarly in char-making stoves, but briquettes look better in traditional stoves. Apparently not much comparative work done yet for advantages of production of one vs the other. 

Just a few more responses/questions. 

1. You asked below : "long time, eh" . 
RWL: Yup. We met maybe ten or more years ago at a Boulder conference. I was impressed then and still am. 

2. At your recent African Briquette conference (or anywhere anytime), was anyone talking about removal of briquettes part way through the combustion cycle, when one might have essentially only char? I do this in a home heating stove - and we see increasing mention of "pit" char-making on the biochar lists. The advantage of doing this with a cookstove is the productive use of all the pyrolysis gases for cooking. The hole in the briquette could facilitate its removal (for dunking in a pail of water perhaps). I am asking if briquettes act like wood in terms of exhausting all the pyrolysis gases before the outer layer of (newly formed) char can start to be consumed? Also, whether there is enough structural integrity to the briquette at that point? 

3. You said (2a): "Forgive me if I am off here but from what I have seen in practice, the dampening of the stove if not carefully implemented, can generate a sudden burst of CO. Pellets would seem to be far harder to regulate in this regard because to be burned optimally, it would seem that --as with the ordinary mechanised pellet stove sold in the states and Europe at least-- only a few at a time are fed into the combustion chamber...Now how this could be made into a continuous feed process with continuous production of char as the product ---while regulating air flow (as that seems to be essential to the process)--- could be a real challenge.. " 
[RWL3: This doesn't sound like any of the char-making stoves - which usually (only?) start with a full starting load of pellets (or similar) and is top-lit. The pyrolysis zone moves downward slowly, producing pyrolysis gases (CO, Hq, CH4, etc) which travel upward through the char layers above which cannot combust because all the primary air oxygen is consumed at the pyrolysis front. I know of no char-making cook stove that operates a few pellets at a time. I have been told by Nat Mulcahy of World Stove that he is working with pellet stove companies to convert to one with char-making capability. I have no idea how to do that "real challenge" - but hope others can offer ideas. I think you have to have a pretty large supply of fuel and move it out at the right time, probably with separate primary and secondary air supplies. Nat's Lucia stove doesn't exactly do that, but there, but air supply is still critical. 
It is true that the most critical times are during damping - shutting down as the pyrolysis front reaches the bottom. I wish it were not so and more work needs to be done on making that a smoother operation. 

4. You said (2a): " Ratios of net non wood biomass energy values of 10 to 50--- to net wood biomass energy values of 1, would not be unreasonable." 
[RWL4: I am not understanding this statistic. Is this a statement that wood is in short supply in many places? 

5. Also 2a: "... .20% of the total of the charcoal being produced winds up on the seller's floor as such waste ." 
[RWL5: I believe we will find in many cases that this char should be put in the ground to improve crop productivity. It is not clear to me why this "waste char" helps so much in making a superior briquette. Certainly one will get more energy per unit weight of briquette - but that assumes a low price for this char dust - which it shouldn't have when its ag and sequestration value is understood . But I am not urging getting Biochar material this way. All char should be ideally made with productive use of the pyrolysis gases. 

6. Also not understanding this statement near the end: ".. Thats the reality you have to reach its the so called boondocks where the 90% of the rest of us live. " 
[RWL: Do you mean that 90% of those making char and/or briquettes are living in the boondocks? I can believe that. I am pretty sure that the global average is over 50% urban for "rest" (and rapidly increasing in the urban direction.) 

I couldn't find much on your site about the conference. Can you give a specific link or stillcoming? 

Again - thanks. 

Ron 

----- Original Message ----- 
From: "Richard Stanley" <rstanley at legacyfound.org> 
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>, "biochar-policy" <biochar-policy at yahoogroups.com> 
Sent: Wednesday, December 1, 2010 8:29:21 PM 
Subject: Re: [Stoves] K Smith Article in Energy for Sustainable Development 

Hi Ron, long time eh? 
Let me respond in kind, as much as I can at least... 


On Nov 29, 2010, at 7:55 PM, rongretlarson at comcast.net wrote: 




See some questions/notes below on your message today. You said: 


" I would buy the one that burned some form of densified non wood biomass "cleanly" ...... 

[RWL1: Those of us who are promoting char-producing stoves believe that they are much cleaner than those that only combust. The usual low-cost stoves in developing countries almost universally use only wood (with some still-minor use of your briquettes of course). For those new to the subject, the difference is whether there is a single air supply or two. Does anyone reading this think that char-making stoves are not inherently cleaner? 
First I wish I could take full credit for the briquette idea but if you were to enter the word fuel briquette on a google search or a you tube survey, you would need a very tall cuppa java to get through it all these days. The briquette producer conference we just hosted in east Africa well proves the point that the adaptations of the process and blends and stoves being tested are well beyond anything we cooked up through Ben Bryant's initial ideas... 
As to cleaner burn the question is two pronged the front end particulate and aromatics issue / "smoke" and the end burn with the risk of CO which is not so obvious...Many in the conference and globally now favor higher concentrations of charcoal dust. Some of these are charring ag residues beforehand because most see smoke as equivalent to all pollution... The CO awareness issue is still much in need of greater public awareness and it is at this end of the combustion cycle that where the char can be produced. I'll return to this issue subsequently... 





But I especially want to support your use of the term "densified non-wood" - which I think is also much needed in char-making stoves. Nat Mulcahy of World Stoves always emphasizes the use of "densified non-wood" as one of the main advantage of his Lucia stove (which could combust or gasify - but he chooses to operate in only a pyrolysis mode). See his website for his rationales - which are (in part) similar to yours. 
Several questions to you (as the person who probably knows the most on this densified non-wood cooking issue): 
1a. What are the relative advantages of making (not using) pellets vs briquettes? 
I am not claiming that pellets are 'less better'. In fact they may be far better given the high surface to volume ratio they present relative to the briquette. But what is better technically, is only part of the story. Issues like produce-ability and ease of use in the typical stove with its large grate for example...these are as or more important tht sheer technical advantages at eas tin the eyes of the consumers and producers we spoke with.. 





It would seem that it should be much easier to "press" (I like your closing below) pellets than briquettes (especially the "holey" type). Do you have any data on the relative power or energy and/ or cost requirements for production of pellets vs briquettes? 
There are about 25 generically different briquette presses out on the internet as we speak. I know of at least two more deisgns in the offing. I have seen several pellet type presses mostly of the modified meat mincer type. To make money in the typical rural market across Africa and much of Latin America, one producer with their hand press of whatever design, has to crank (or press or screw, or ratchet or lever for that matter) out about 16 to 20 kgs per day. I do not know what the hand operated pellet presses are capable of but I would be surprised if it is much different--again pe individual worker, using some form of hand press. 
In either case however, it is not the pressing which limits production of pettets or briquettes at the hand process level, at least where ag residues are concerned. It is the sorting and chopping fermenting mashing and blending of the residues which consumes the greater part of the energy required for briquette making at the hand /micro scale level. There is a very interesting technical innovation which will soon make it far more efficient. The guy doing the work on this is not ready to break the surface 'til he has something to brag about but a the rate he is moving it will probably be ready in a month or so...Its really his call to bring it out into the daylight when he's ready. We're just adding our two cents in here and there.. 






1b. For those wanting char and not ash, the charred pellet is already in a wonderful form for application to soils. Pellets mean some extra costs for the fuel supply in the front end of cooking - but could be a wonderful boon both in burning more cleanly and evenly and in later application of Biochar to the soil. The same is possibly/probably true for briquettes - which I presume break up easily after being pyrolyzed. Do you have any reason to think briquettes would be better than pellets in either pyrolysis or char-application terms? 
Intersting issue this 'clean burning' idea. Smoke was a big issue amongs the the participants in the workshop. What seemed to come out of it was the fact that one does not want to be attempting to try to ignite the whole mass to flash point in order to get a fire started..The idea is evolving that you only want to burn the immediate surface to start with.. Pellets can be ignited quickly becasue of their high surface area to volume ratio. Briquettes like most larger chunky fuels, have to be either top lit or side lit or as Robert Williams of the gorila conservati0on project in the DRC has demonstrated, diagonally lit. The idea is in all cases, to heat only the surface to ignite it , then progress to succesfully larger mass of fuel. Side fed stoves, off the Approvecho rocket stove idea, is now well actualised by Rok Oblak's side fed briquette stove design which is producing remarkable results (see rokstoves.org---I think its already long archived in the Stoves list) 


Forgive me if I am off here but from what I have seen in practice, the dampening of the stove if not carefully implemented, can generate a sudden burst of CO. Pellets would seem to be far harder to regulate in this regard because to be burned optimally, it would seem that --as with the ordinary mechanised pellet stove sold in the states and Europe at least-- only a few at a time are fed into the combustion chamber...Now how this could be made into a continuous feed process with continuous production of char as the product ---while regulating air flow (as that seems to be essential to the process)--- could be a real challange.. 


Char making therefore seems--again, for at least the intended small cookstove user, to therefore be best handled in a batch process, with larger batches of fuel being pyrolised at any one time... 
In short, I think that for the intended user and stove the briquette would probably be easier to manage for pyrolsis in a batch process...Frankly though, I have not ever focused any real effort to make char (on purpose at least) so anybody's insights more than welcome. 







You concluded:] 

".... and would avoid both the wood supply and the char producing problems in one go ." 

[RWL: 2a. Re the first issue of supply (with which I agree), I have recently read an article (author's name forgotten - I will try to find it) that showed a breakdown of the well known global net primary productivity (NPP) number of about 60 Gt C/yr. They had about half going into wood and half into leaves - a ratio I had not previously seen. Since you are promoting thformer (leaves) over the latter (wood) - and because almost all rural stove users are now using only wood (and even many briquettes and pellets seem to be made up of ground-up or chipped wood), have you seen this relative photosynthesis production ratio - which would seem to imply a huge wasted resource all over the world? I have not seen this figure before but would be curious as to how it as derived. In more immediately recogniseable terms however, the fuel value of the leaves off any one species compared to the fuel value off its wood would offer an interesting if not more direclty applicable comparison for any one project site. Ratios of net non wood biomass energy values of 10 to 50--- to net wood biomass energy values of 1, would not be unreasonable. 
On the one hand you have a far lower volume of a less dense energy supply per year throughout the tree's life (eg., leaves) being offset by the tree's greater wood energy supply albeit afforded only once during its lifetime... In our Theory and Applications manual we did lots of analysis in concert with a japanese agricultural research organisation working in Uganda with then, already several years experience, to derive fuel carrying capacities from non wood biomass residue per unit area. We did this over various land forms and land uses including of course normal offtake for soil tilth, as well as for feed and fodder here appropriate . And we have not begun to consider of course processing waste: paper, cardboard, sawdust, rice husks, charcoal dust and crumbs ( some 20% of the total of the charoal being produced winds up on the seller's floor as such waste).. Such processed biomass residues can easily constitute 50% or more of the whole briquette. Its a huge amount of waste in tems of available non wood biomass but outrageously hugewhenyou combine that with the commercially processed residues. 







2b. But I don't understand your term "char producing problems". To me there are only benefits and advantages (at least with kitchen stoves). If you meant the horrible production of most charcoal out in the boondocks - with global warming and carcinogenic gases much worse than CO2 being produced - then I agree. To prove that it is better for society to promote household production of Biochar (char placed in the ground) will be the subject of my next message. Briefly it is that we need to make the economic argument that Biochar's two main advantages (carbon sequestration and soil improvements) outweigh the further combustion of the char for its energy value. Two main reasons that I think we can make this argument (which I do not contend has already been proven). First is the 2:1 advantage in the three-flows of money (which seem in the same ballpark). But more important is that the first two monetary flows (climate and soils) are both investments - with good payback over long time periods. The energy application of the char is only a single use - no out-year advantages at all. More coming on the many out-year advantages of Biochar. 

This is not to suggest that you do not believe in all this already - but others could interpret your sentence to favor burning of "densified non-woody biomass" rather than pyrolysis of the same. 

Ron, the argument is not whether or not it is justified on economic terms. I am sure the numbers prove its viability, especially with all teh intellectual horesopower working on the issue: 
But like much of development work, its not purely an intellectual issue: Its about the cultural ease and the real cost of embedding the concept ...Thats the reality you have to reach its the so called boondocks where the 90% of the rest of us live. 


The notion of promoting a longer term reward in a subsistence level economy at the cost of an immediate efficiency (viz., shortening the length of cooking by dampening it for production of biochar which may generate some income down the line, is a hard sell... 


It matters not whether I personally favor burning biomass over controlled pyrolsis but what the actual user actually favors. They do what you and I would do under their own circumstances--They use what they have for that day as optimally as they can use it. Unless they can be charring for making charcoal, I do not see them investing the char in the soil for returns over the next several years--- Not at least without some form of very intensive, sustained awareness promotion augmented by long term assistance to offset their immediate added fuel costs. 


Lest we scoff at that notion, one need only ask how many of us with our onw fuller stomachs, better education greate raccess to resources and far greater global awareness, are using biofuels or electric vehicles as we rant on about global warming..Look athe proposed subsidies tax rebates etc offered to incentivise the change look at teh politics and hte lobbying to maintain the status quo and look a the results. Its all abit relative, eh. When you can say that you are prepared to offset the user's losses and are prepared to really invest in the policy and public awareness promotion of Biochar then its time to talk about implementing it...And I say this as a technical convert to the idea... 


Cheers, 


Richard Stanley 
www.legacyfound.org 


ps., If anybody is interested we put up a summary of the conference in te news seciton of or website..Great stuff is happening in the briquetting world. 









Ron] 


pressing on, 


Richard Stanley 
www.legacyfound.org 





On Nov 29, 2010, at 4:12 PM, Crispin Pemberton-Pigott wrote: 
[RWL: I have snipped this to keep the responses separate - being different issues.] 





Dear Friends 

I agree with Ron that $10 is a believable figure for an improved stove with a dramatic (90%) reduction in emissions of PM. For the +$50 stove 

<snipped> 




_______________________________________________ 
Stoves mailing list 

to Send a Message to the list, use the email address 
Stoves mailing list 

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://www.bioenergylists.org/ 
Stoves at lists.bioenergylists.org 
http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20101205/357fa8ce/attachment.html>