Dear Andrew, Julian and Paul, Andrew, thanks for the compliment but wet process briquetting is no more my 'bag' than it is the thousands of others producing and training in production of briquettes in 65 nations that we know of…. by now. Lots has crossed the screen about briquettes over the pas week or so , so let me ramble on a bit my two cents, hopefully contributing something useful to the main points;
Char, ash or nothing-- as residue from combustion: What we hear back and can confirm ourselves is that the briquette varies considerably in terms of performance viz., char-producing versus ash-producing versus nothing-producing depending upon ingredient and skill at blending and of course the combustion appliance itself. One can pretty much control char output from the hollow core briquette, as one would with wood. Others say no charcoal is necessary in an agro-residue briquette for combustion; in fact they say that charcoal indeed retards combustion of some of the better agro- residues blends I have seen combusted. That aside, charcoal may or may not be desired anyway, as it all depends upon what the cook is cooking! Briquette size .. The size can vary from 2.5" to 6" square to round octagonal hexagonal..and everything in between. Some have managed to create 4 to 6 wedges of ~ 1" on a side ( as viewed on the end face) as Paul will attest but I do not know the outcome of that effort. Adding charcoal to the center hole, Like adding wood sticks tends to sustain an otherwise poorly or barely burning briquette, poor being determined by again, moisture content and/or blend and/or combustion appliance. The best bet is to super dry the briquette nest to the stove BEFOR putting it into the combustion chamber. Especially effective is you have aromatics which you want driven off into the room without smoke…And once the aromatics are driven off, the briquette is now bone dry and pre heated (at around 150 degrees F maximum, you can usually still hold it though) , and the briquette ignites almost immediately, with almost no smoke. Win Win. Sticks and charcoal can actually retard burning, if they block air flow thru the center hole too much. Blending process; It sounds simple but the bit about" the fibers separate then , mesh together" could contain a PhD dissertation.. On the ground, its right at this point that knowing how to make the fibers flexible but still with retained strength (at least in tension) and know how to bend in other residues, which will infill the matrix of such fibers --and how to create this blend on a continuous basis efficiently, that separates the hobbyist from the sincere producer.. Pressing issues; Starting saturated volumes of such blends are typically reduced by a factor to two to three in a typical hand actuated press in a production setting. Typical working pressures in such presses are between 14 and 18 bars/kg/cc ( ~200 to ~ 250 psi). But it's not so much the pressure that determines the quality and density of the final briquette but rather the quality of the attention to the kind of residues used, their blending and the infilling process. There are more than 25 generically different presses up on-line now but most will fall in-between the mentioned working pressure range- if they have been optimised to a sustained production operation in the various local market environments. More recently colleagues in Haiti, Hungary, and Uganda have been developing multi-cylinder batch fed hydraulic jack actuated presses producing in excess of 20 briquettes per minute (as co-venters in that process, we will be returning to Guatemala this fall with to work with various artisanas there in adapting selected design elements of these presses, as a practical Guatemalan version this fall. With all that though, the pressing is only effective if the material selection processing and blending bits are gotten right in the first place… Use of grass or other ag residue green versus non green. Our own experience and observations tell us that attempting to burn a green material, is fraught with difficulties. The compounds resulting from combustion are very likely carcinogenic but more importantly to the typical user, "smokey". We recommend processing, blending then burning pre browned material only. Some will make up the briquette with green--particularly--grass as such, are more temptingly enough, pliable and sticky in that state. They will then wait for the compressed green briquette to naturally brown-out in the finished briquette. That takes a lot longer to happen than simple drying of a pre-browned briquette, but so be it. More sophisticated special air drying units have proven able to burn green grass with minimal smoke but that's not generally a technology that the rest of the 90% of us can access- much less use practically. Combustion, Rok Oblak dove into the adaptation of side-fed rocket stoves of the Approvecho sort, several years ago and he has managed to produce some fairly good results as you can see on his site. Josh Guinto has managed the same effect in the Philippines, as has Isaac Owor in Uganda. But appropo of this group's ongong passion for perfection in nomenclature, a bit of clarification of terminology is needed when it comes to side fed stoves. To say "top lit" is to bend the rules as it is lit from the outside horizontal feed end of the stove and is combusted from there into the center of the stove. "Side lit, interior-trending draft" is probably a bit closer to the mark . Kobus Venter and I managed to gassify top lit coal blend versions with a near-perfect gas stove burner-like output for several minutes, and as long as the wind was not blowing. But those were the heady days in Paushoft. Kobus has since taken it way beyond this point. These are just two of probably the hundreds of examples of good combustion that we have seen by now: We are nothing compared to the real scale of on-going production activities. As to cost, The hollow core briquette product is (at least as produced by the more successful self sustaining producers who are generally working in response to their respective local markets) will typically sell for between 1.5 and 2.5% of one worker's daily wage (it's relatively easy to assume this range, as the production cost –in the micro entreprenur level at least– is over 90% labor cost-dependent); Generally costs will fall between 2.5 and 6 US cents per each 4" /10cm dia x 3"/ 7.5cm tall briquette. Cost increases generally with more charcoal content, built in aromatic qualities (for such as hotel ambience, religious ceremony, or health). Their value goes up, if produced then sold during the rainy season (in like proportion to wood and charcoal). Generally, 2 ½ such briquettes (roughly 350 to 400 grams of briquetted biomass in total) is needed per person, per day in the typical rural pr urban poor household in the third world. Agh but how we need these things called words and numbers to describe it all and do we ever have a hey day with that, eh ? The simple fact is that most of the real masters of the craft have little knowledge of all these numbers and terminology. They rather, have this kind of "feel" and a sence for it. Their hands are moisture meters compression and density instruments far more fine tuned that our own tech dependent appendages And beyond that, this battery free "sense for it all" seems to quite naturally resonate with most other trainees who are similarly close to the land, despite near impossible language and cultural barriers .. A kind of (Rupert) Sheldrakian twist to our notion of science, as it were.. The fun part is discovering what you can learn from others you have taught…better still, to learn how to learn from them is the thing… Hasta badaye, Richard Stanley www.Legacyfound.org On Apr 28, 2013, at 8:43 AM, [email protected] wrote: [Default] On Sun, 28 Apr 2013 08:08:40 -0400,Julien Winter <[email protected]> wrote: > Of course, the preferred choice is to use pellets in stoves, but for > some people, pellets could be a bit expensive. Briquettes look like a > good compromise between uncompressed crop residues and pellets, if > they can be made using low-cost equipment that doesn't require > electricity. > > What is the experience of stove researchers with briquettes? Do they > burn cleanly and efficiency in TLUD stoves? Are they a bit bulky for > cookstoves? Do they make biochar, or do they turn to ash as they burn > in from the outside? The briquetting is Richard's bag and I expect he will reply. To say that pellets "could be a bit expensive" is an understatement for those people that the Legacy Foundation teaches how to utilise crop residues as a cooking fuel. Essentially the process is a bit like making papiere mache from residues that has started to decompose, the fibres separate and then mesh together in a simple wet press. Other wastes like sawdust and charcoal fines can be entrained in the mesh of fibres to bulk the briquette and often in crease the energy content. They then dry in the sun. Yes they do burn TLUD http://stoves.bioenergylists.org/node/185 Have a search on Kobus Ventner and Rok Oblak at this site as they have a wealth of experience making briquette burning stoves. AJH _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] 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/ _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] 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/
