[Stoves] Looking for stove designþ

[Lloyd Helferty]

Crispin,

   I was looking up the topic of Zambia (part of a task I have been 
doing recently looking at what countries might be seeking out 
biochar-producing stoves), and I came across this old email, where right 
at the end (bottom) you write, "The soils of Zambia are already 
/*famously productive*/".
   This was _not_ the impression that I had been given about Zambia:

http://en.wikipedia.org/wiki/Ecoregions_of_Zambia#Soils

  * Red sandveld soils *cover _most of the country_*, and are generally
    *not very fertile* due to weathering and leaching; the top soil is
    *sandy*


  * Grey dambo soils contain more nutrients but are waterlogged in the
    rainy season and often *very acidic*, restricting the plants which
    can grow there to sedges and wiry grasses tolerant of marshy conditions.

  * Kalahari Sands in the south-west of the country are *infertile and
    do not retain moisture*

ONLY:

  * *Black soils of floodplains* are fertile, grasses grow on them as
    soon as the annual flood recedes and provide a rich resource for
    herbivores.*If the annual flood is _disrupted by dams_, woody shrubs
    of lower nutritional value tend to replace grasses and so reduce the
    number of herbivores and biodiversity.*


Are you referring (only) to the "Black soils of floodplains"? What about 
the rest of the country?

Regards,

   Lloyd Helferty, Engineering Technologist
   Principal, Biochar Consulting (Canada)
   www.biochar-consulting.ca
   48 Suncrest Blvd, Thornhill, ON, Canada
   905-707-8754
   CELL: 647-886-8754
      Skype: lloyd.helferty
   Steering Committee coordinator
   Canadian Biochar Initiative (CBI)
   CURRENTS, A working group of Science for Peace
   http://www.scienceforpeace.ca/currents/
   President, Co-founder & CBI Liaison, Biochar-Ontario
   National Office, Canadian Carbon Farming Initiative (CCFI)
   Organizing team member, 2013 N/A Biochar Symposium:
     www.carbon-negative.us/symposium
   Member of the Don Watershed Regeneration Council (DWRC)
   Manager, Biochar Offsets Group:
            http://www.linkedin.com/groups?home=&gid=2446475
    Advisory Committee Member, IBI
   http://www.linkedin.com/groups?gid=1404717
   http://www.facebook.com/group.php?gid=42237506675
   http://groups.google.com/group/biochar-ontario
   http://www.meetup.com/biocharontario/
   http://www.biocharontario.ca
    www.biochar.ca

"Producing twice as much food with diminishing resources, without further loss of natural habitats and biodiversity and in a changing climate may be the greatest challenge facing humanity."
    - Lloyd Helferty

On 2011-11-14 3:35 PM, Crispin Pemberton-Pigott wrote:
>
> Dear Vetle
>
> This is exactly the sort of information that builds the case for a new 
> stove or a new approach to fuelling and operation.
>
> Use acceptance is a major issue and the follow-up is important -- 
> meaning do the new stoves remain in use. When they do, it is often for 
> reasons that have to do with fuel availability in my limited 
> experience. Not have to go as far or spend as much for fuel is a 
> strong incentive. The only thing that mitigates hard against it is if 
> the stove is inconvenient to use or won't cook properly. African women 
> tend to like a high heat (high firepower) to 'cook fast' so speed to 
> boil is important.
>
> >The 6 liter Peko Pe stove can be filled with 600 grams of Maize cobs, 
> with
> the sizes of 40-60 mm, it will burn for about 30 minutes and boil one
> liter of water within 9 minutes after ignition (6,5 minutes after the pot
> is put on the "flame").
>
> Is 1 litre large enough to interest a family? How much to people cook 
> at a time? The answer might be 'a little in the morning and a lot in 
> the evening'. It is quite reasonable for there to be two stove sizes 
> or for one to be used only for certain tasks. If the fit is good, 
> people will adopt them.
>
> If I estimate 600 g @ 15% moisture (air dry in summer) I get about 7.8 
> MJ of potential energy. Subtracting for 20% char (125 g) I get 4.1 MJ 
> of heat over that 30 minutes. That is 2.3 kW average (with perhaps a 
> peak of 3 kW?).  Does that sound reasonable? Is the heat fairly 
> constant during that time? If so, it is going to have a pretty 
> constant thermal efficiency.
>
> If the fire is low for 2.5 minutes then the pot goes on, and the 
> boiling is 6.5 minutes per litre, that is an overall efficiency of 
> about (0.335 MJ heat absorbed / 0.975 MJ heat applied) = 34%.  If the 
> power is not up to that 2.5 kW average at the time, perhaps it is 
> higher. If the fire is really large at that time, perhaps the 
> efficiency is In the high 20's. Does any of this sound like what you 
> are seeing?
>
> 30% is pretty good.
>
> So the information I will be looking for relates to the cooking power 
> in the first phase (pyrolysis), the duration of the burn and the 
> heating power that is available if one wanted to continue to simmer on 
> the remaining char.
>
> There is a test which would be very valuable and it is a water heating 
> (not boiling) test.
>
> Put on a large pot with a lot of water, large enough that it will not 
> boil for at least 40 minutes. Record the temperature every 20 seconds 
> or so (be regular to make it easier to analyse) using a thermometer 
> that gives 0.1 Degrees.
>
> As the thermal efficiency will probably not change a great deal during 
> the cooking session, the temperature rise /rate/ is an indicator of 
> power output. It can be calculated for various intervals based on time 
> or temperature. I have attached a typical result of such a test for an 
> old Panda paraffin stove using a heterogeneous test protocol. The top 
> blue line is the mass of water remaining. You can see when the stove 
> was changed from High to Medium power as the boiling rate (water mass 
> loss) changes. The thermal efficiency line (green) detects a change in 
> efficiency with the turn-down.
>
> If the power level changes the slope of the water heating line will 
> change. This can tell you what the power change is as the stove goes 
> from ignition to a fully developed fire to a late-pyrolysis burn. This 
> information is very valuable for you. It would be very helpful if you 
> share the result. Using this approach, you can tune the performance to 
> a cooking task in a given community.
>
> If the pot boils during this type of test the result is harder to get 
> because it has to be done on a scale but it can be done if you have to.
>
> >For normal cooking of Nshima and similar food
> preparing, 30 minutes would be enough for each meal in everyday use.
>
> For South Africa and vicinity it would take 45 minutes after boiling 
> to cook 'pap' which is much longer.
>
> >Cooking Nshima need less than 10 minutes so usually they can prepare 
> most of their additional food with one filling.
>
> That is a very good fit then, especially if adding some chopped wood 
> will extend it by a few minutes if needed. Do people object to 
> chipping/chopping the wood? Zimbabwe (rural) had difficult with 
> splitting wood for cooking because the trees are so hard. That problem 
> is avoided it no wood or little wood is involved. As the maize cobs 
> collect around the house it should be used first I guess. Hopefully.
>
>
> >We do feel that 6 liter Peko Pe stove is a suitable size for unprocessed
> BIOmass wich are most available around the farms.
>
> Agreed, by the sound of it. You have a good match between the stove, 
> fuel and the cooking task.
>
> >Since they already are cooking with one pot at the time, we don't think
> they need to have more than one stove,.
>
> Good point. How do they prepare the 'relish' to go with the nshima? I 
> have seen it prepared in a smaller separate pot.
>
> >This is off course an investment cost up for discussion for every 
> household. When less cooking time are needed they can
> just use less fuel.
>
> Exactly.
>
> >With beans, the farmers will spend more time for cooking. This can either
> be done by empty the stove and refilling it with maize or use smaller 
> cobs
> (>10 - 20mm) to get more mass into the stove (800g = <40 min "flame 
> time") or also by
> using other kind of denser BIOmass. Chopped wood will burn for more 
> than 1
> hour.
>
> Is the burn rate (mass per minute) the same with all the fuels or do 
> see a noticeable difference?
>
> So far it seems that the farmers are satisfied with both the size and 
> cooking time. Time will show if adjustment of stove size are required.
>
> Agreed.
>
> >Since the farmers in this project are targeted to collect BIOchar from 
> maize cobs used for household energy purpose, they will refill the 
> stove when needed to get sufficient cooking/energy time.
>
> They will probably do that until they run low on fuel and there is 
> nothing wrong with that.
>
> >The BIOchar will be stored for later to be used as soil improvement 
> instead of using it as glowing charcoal.
>
> I understand that process. *The soils of Zambia are already famously 
> productive* so any effect will be important to document.
>
> I really appreciate you taking the time to provide hard data for us 
> who are disconnected from the work on the ground. I would have shown 
> one to the Chinese rural energy delegation Roger Samson is bring 
> around this week if I had a working sample. We are going to 
> demonstrate several stoves that can burn pelletized (and chunked) 
> switchgrass to try to generate interest in TLUD technologies.
>
> Thanks
>
> Crispin
>
>
> _______________________________________________
> Stoves mailing list

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20140313/ea45b378/attachment.html>