Stoves Archive for September 2002

Stovers: an interesting response re the charcoaling and Terra Petra from Richard Stanley, who said:

Stanley: You have just posted this heavy weight coverage of pyrolosis versus charcoal making etc, with rather convincing arguements for the former. You proceeded to nicely compliment me on the use of biomass briquettes as a pyrolsis primarily heat source.

Interestingly enough, I was about to post up an idea or more an observation, about how many of those whom we have trained in briqueting, seem to learn quite quickly, how to load their simple jikos so that it automatically encourages increased secondary air and reduced primary air flow as pyrolsis is completed and gassification potentially begins! They simply stuff a traditional jiko to capacity (in the case of briquettes, using whole and broken off pieces, or in the case of wood fuel, various lengths of sticks ) . During the flare up stage, the mass of course draws "primarily' upon bottom fed "primary" air. As the ashes build up and the mass of the fuel subsides, the ashes clog off primary air inlets as the secondary air holes (positioned about midway up the sides of the stove) become exposed with the subsiding fuel mass, for gassification to proceed quite naturally , This simple modification is not new nor is it reported widely it seems. Nor could those who use this technique describe gassification or pyrolsis but they well recognise it and utilise the principles in their daily cooking. Admittedly, however, few have benefit of the stoves group's knowledge of insulation and clean burning and exit temperature control, and carbon sequestering etc. It does tend to make me wonder about the need for observation with/ inclusion of those who are there actually living with the problem.

[Ron Larson]: re the first part of this paragraph, I am guessing that they don't worry about top-lighting and that there is not enough draft to get pyrolysis prior to mixing with secondary air and then combustion of the pyrolysis gases. But after hearing about the results of Crispin's firings (bottom lighting - but still getting pyrolysis first) I am not sure what is going on in either yours or his work. it will be great when we can finally get some detailed test results.

With you back in Kampala, I hope you will send us continued observations on what is going on in the real world - like that below.

As to your comments about charcoal use, I abhor the notion of charcoal making, whether as done in Niarobi or elsewhere, as most of the heat is lost to the atmosphere before anything useful can come of it. I would add that there is tremendous waste associated with its distribution at least as done by the masses of national users.
[Ron Larson] We mostly agree on this list about the terrible waste in rural making of charcoal - but also there is (as I know you know) usually in rural areas much worse contribution to GW than if the pyrolysis gases were flared rather than vented. Fortunately I believe that all charcoal makers on this list do flaring,

[Ron Larson] But I am not sure what you mean by waste in the distribution process. Is this the fines that accumulate? I wonder how we could encourage getting those into the ground and the ground where the fines are stored returned back to productive use?

In Kampala for example, with its 1 million plus population, and its more or less typical energy consumption pattern for an East and Central African city, some 30,000 tons of charcoal dust fines (wasted charocal accumilated around most local charcoal seller's sites) are generated each year. This might be a source of the "tierra preta" in the Amazon too but for us it potentially provides (@ a consumption rate of about 120 g per person per day in the form of two briquettes of 40% charcoal fines composition each) a cooking and basic hot water sanitation supply in the briquetted form for just about that same 1 million population ! A wet process charcoal briquette is a higly sought-after commodity. It is far easier to store, cleaner to use than charcoal or wood, and has a far greater energy output that normal agroresidue blends, particularly and not suprisingly, in the later 'post pyrolsis' stages of the burn. I wonder how this factors into global warming ?

(RWL): I gather that the anthropologists and archaeologists have not yet determined the production means for the charcoal in the terra petra. As to your use of charcoal fines and GW - I think its productive use is positive when you either avoid cutting trees or prevent the anaerobic digestion (and unwanted production of methane) of ag waste. The key question is whether the fines would possibly do better in improving someone's garden soil (with a subsequent greater annual removal of CO2 from the atmosphere from that particular plot of land. With the fines just sitting on the ground, they are not being productive in any way). I don't know the overall answer yet - but still think it is an interesting question - and I am pretty sure that it is best to get the fines away from where they are.

FW: Richard Stanley related to Terra petra