[Stoves] K Smith Article in Energy for Sustainable Development

[rongretlarson at comcast.net]

Otto (cc "stoves" and "biochar-policy") 

1. Thanks for the reminder to look at the three You Tube videos, which were given by you on the 7th as: 

http://www.youtube.com/watch?v=amaUDK6VyRg 
http://www.youtube.com/watch?v=gi3Xx7NtTGw&feature=related 
http://www.youtube.com/watch?v=dsfuVGBi4fc&feature=related 

2. I had seen the first two - but not the third. They all emphasized the use of grass - and I think this is wonderful. I have never tried grass in these stoves - although I have mostly used thin twigs and the same fuel orientation and shape. I have to say I am dubious of a general proposition that 1 kg of grass can replace 5 kg of wood. This must be comparing with a very inefficient wood stove. 
None of the videos mention charcoal production . Is this guaranteed or an option? 

3. I find I still do not know the geometry and especially the hole sizes and placements. So I have these questions (need a cross-section diagram, optimally, as well): 

a. Is there any attempt to control (during cooking, so as to be able to control flame height and power output) the size of the lower holes? If not, I suggest that would be an important added feature for the convenience of the cooks, and justifiable economically in fuel savings.. 

b. It is not clear whether the space between the inner and outer cans is used to preheat secondary air. Can you clarify the air flow pattern in that space? Regardless, I think two concentric cans probably pays quickly for that extra metal in (possibly important) captured and otherwise wasted radial heat loss. It might even pay to have three concentric cans. But these cans are not needed for TLUD operation. They are needed for Nat Mulcahy's TLOD design - which I am pretty sure is not going on with Paal's design. 

c. In my development of something similar in the mid 90's, I found it important to have a much taller secondary gas-combustion chamber above the fuel supply than I see in these videos - for two reasons. First was to get complete combustion before the flame hits the cookpot. But also to get more air flow (to get a lower pressure above the fuel). Has Paal or yourself investigated the impact of greater height above the secondary air holes (assuming there is separation of primary and secondary air)? 

d. The use of three stoves in parallel was interesting, and should/could have some advantages. But I wonder if there has been any work on a larger single stove insert - which should be cheaper. I was able (sort of) to cook enjira in Ethiopia on a 60 cm ceramic griddle (magogo) with a pretty large single stove diameter of maybe 30 cm. 

Again, thanks for the reminder. Few more questions below. Ron 

----- Original Message ----- 
From: "Otto Formo" <formo-o at online.no> 
To: rongretlarson at comcast.net, "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>, "biochar-policy" <biochar-policy at yahoogroups.com> 
Sent: Monday, November 29, 2010 10:30:28 AM 
Subject: SV: [Stoves] K Smith Article in Energy for Sustainable Development 

Dear Ron and all, 
I hope you have had the chance to look at the videos linked to you from You Tube and then you will see that Paal was introducing the "GrassBurner" in 1994 in Uganda. 
[RWL: See above.] 

About biochar, we have found it more easy to handle after the residue are made into pellets, not "only" because it burns so cleanly in the TLUD ND Gaisifier Unit. 
[RWL1 This implies that Paal is always obtaining char. Is the ratio of char weight out to grass weight in about 25%? Wood char can be pretty tough stuff to break up. Are you saying that the grass-char breaks up too much? ] 

Pellets made out of pinewood also gives a compact and clear surface of the char with a minimum of waste and dust. 
[RWL2: Would there be a preference for either grass or wood pellets - forgetting cost? Can you explain "waste"? ] 

This will make it easier to transport and spread in the field thinking about coaldust and silicosis. 
[RWL3: Are you expressing concern for the small size of char dust made from grasses? 

One type of fuel (pellets), preferable made out of agri-residue, for one type of stove (TLUD`s), can it be more easy? 
[RWL4: Until this question, I was pretty excited about the use of grass as a fuel (which I repeat I have never used - as grass in Colorado is not like that shown in the videos). As big grass is abundant in many places, in surplus often, easy to grow, etc. , help me understand your emphasis on pellets here.] 

According to scientist working on biochar, the agriwaste gives the best or most suitable biochar for cornfields, but also smaller quantities than wood. 
[RWL5: Can you give a cite? I don't recall any conclusion like this before. Also, not sure the meaning of the last clause - is that referring to Paal's ratio of 1 grass to 5 wood? (I need more convincing - I think both will give about 15-17 MJ/kg) - and maybe more for the wood.] 

We still prefer to use the forest and agri-residue as Household Energy, until further notice............ 
[RWL6 : Otto - This worries me a good bit. I hope you are not on the side of those saying it is better to combust the char (assuming the Peko Pe makes a lot of good char) rather than to get the many advantages of placing char in the ground . My hope is that you are only saying here that "forest and agri-residue" is a better choice than fossil fuels. That I can agree with. ] 

Ron ] 

Otto 

> From: rongretlarson at comcast.net 
> Sent: 2010-11-29 17:55:42 MET 
> To: Discussion of biomass cooking stoves [stoves at lists.bioenergylists.org], biochar-policy [biochar-policy at yahoogroups.com] 
> Subject: Re: [Stoves] K Smith Article in Energy for Sustainable Development 
> 
> Richard (cc two lists) 
> 
<snip remainder> 
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