[Stoves] More on the Alternatives to Charcoal.

Sat Apr 13 23:37:55 CDT 2013

List : 

1. This is to keep alive this dialog between a few of us on the question of char and sustainability for a bit longer - until Paul's full (25MB??) PPt is placed up on the stoves site by Tom MIles. Paul was kind enough to independently send me a copy (and I can send to others - but think that the full PPt will soon be up.) 

2. Paul's Slide # 5 has this sentence which sets the tone for his reason for preparing the PPt : 
" In Kenya 2006, biomass demand was estimated at 38.1 million tonnes against a sustainable supply of 15.4 million tonnes, creating a demand-supply deficit of 60 percent. " 
Whew - the most damning statistic I have seen. 

3. Slide 20: This is to ask Paul to help explain this slide. The obvious decrease in forest size is his (and my) main criterion. But I am not sure how to get numerical estimates here as the ordinate is in relative distance, not forest area units. Paul - Your help?? 

4. Paul is consuming the char, not using it as biochar. The latter will obviously initially require more land (probably almost twice as much) - but this disparity rapidly disappears if soil productivity improves. That discussion is beyond the scope of this message, but the Terra Preta soils in Brazil are now 2 and 3 times more annually productive. It will not take many years for the average response to make up for the placement of char in soil to overcome the apparent (but I believe incorrect) preference of some for combustion over pyrolysis alone. 

5. Slide 21 shows pellets having a transport cost only slightly more for pellets over improved charcoal, but only 60% as much for traditional char production (Paul's distance assumed not known by me for this slide). This is the slide I said disproved Crispin's assertions on the relative cost of transport. To understand when this is true we need Paul's distance assumption. 

6. Slide 22: charcoal about 120 kg/m3 and 3.3 GJ/m3 (ratio meaning PM is using 3300 MJ/120 kg = 27.5 MJ/kg ) 
pellets about 600 kg/m3 and 10 GJ/m3 (similarly, 10,000/600 = 16.7 MJ/kg) 

These (my reading from graphs - not Paul's) are very close to Crispin's values. 
Paul's emphasis is on volumes - with a factor of three in favor of pellet energy and five in terms of pellet weight. I hope Crispin can respond further on the importance of volumes rather than weights - using ratios like these.. 

7. A few inserts below: 
----- Original Message -----
From: "Crispin Pemberton-Pigott" <crispinpigott at gmail.com> 
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org> 
Sent: Friday, April 12, 2013 9:08:42 PM 
Subject: Re: [Stoves] More on the Alternatives to Charcoal. 

Dear Paul M 

Thanks for taking the time to consider this systematically, meaning as a systems problem. 

I will add one consideration that I did not see which is that the thermal efficiency (raw fuel to hot pot efficiency) of the stove is usually quite different between wood stoves and charcoal stoves. 

[RWL: Paul puts the eff ic ienc ies as almo st the same (for improved charcoal-using stoves - not th ose mostly in use today ). Crispin is NOT reporting anywhere in this post on the effic ienc i es of char-making stoves (or even Rockets) - or about standard char-using stoves. 

I have just been testing a charcoal stove (Anglo Supra and Anglo Supra Nova) which are widely used in this area for party cooking and commerce. They have an efficiency of about 50%. There is nothing like that available for wood. The Keren wood stoves, basically a sheltered fire made from terracotta, are about 18-22% efficient. Maybe 15%. 

[RWL: Paul's assumptions on the efficiency of the char-making stove is vastly different (40 + %). 

The difference is large and when the numbers you correctly considered for the available energy in the forest delivered to the pot are factored for stove performance, the result is a surprise to many people, meaning a surprise for those who consider charcoal to be an ‘inefficient’ fuel overall. Not only is it not nearly as bad as they have assumed, it has easily be improved (all elements of the system). 

[RWL: But not using Paul's numbers.] 

The jury is thus still out on which way to go with charcoal, even if it has a large crowd hissing at it. Charcoal is a major employer, it is a preferred fuel (mostly because it is clean burning and doesn’t make pots dirty) and the system is ripe for improvement. 

[RWL: Note Crispin is not talking at all about required forest area (or the volume computat ions I have quoted above) . But also much of the recent discussion today (Dr. Nurhuda, etc) has been on the advanta ge of not using forests at all - but rather ag wastes. For many of us, the issue is as in Paul 's 5th slide for Kenya - sustainability. 

But, I go further and say we have to start practicing CDR = carbon dioxide remova l; by not consuming the char. If anyone has a better way to reach the 350 ppm CO2 recommended by J im Hansen - I have yet to see it . If you aren't already convinced that climate change is real, then you are not likely to be following this argument. 

A bit more still below. ] 

Regards 

Crispin 

[RWL: This is Paul Means talk ing to the l ist shortly before Crispin's above response. I have bolded & underlined for emphasis.] 

Dale, thank you for getting this discussion going. I think we all would agree that the traditional charcoal production & use systems around the world have much to be improved upon. 

Some comments - many in response to Chrispen's comments: 

1. I could not agree more about the social (& market) aspects of substituting dried woody biomass for charcoal. That is a big issue which has yet to be tackled. It could be a show stopper for some of the alternatives. 

2. In terms of transport economics, no doubt that charcoal has a substantially higher net (LHV) energy density than dry wood, not to mention wet wood. Consequently for the same amount of energy shipping the same distance charcoal wins hands down. 

For my analysis I used 10% moisture which assumes either aggressive solar drying or that some of the biomass is being burned to dry the remaining fuel. Even with this much drying, the hauling cost penalty of biomass over charcoal is about 67%. Where the analysis becomes interesting, at least to me, is when the whole system is considered. In this case we need to factor in the efficiency of the charcoal production vs. the woody biomass production and this effect on forest area required. Bottom line is that the charcoal must be hauled in from a much larger land area just because of the gross inefficiency of the charcoal making process. This has the potential to make the hauling cost on a per MJ basis actually 40% LESS for dried biomass. I say potential because it will all be specific to the forest area, it's density (tons of biomass / hectare) and it's distance from the point of fuel use. This collection hauling penalty for traditional charcoal, has not been discussed much from what I have seen. 

The other interesting point is that dried biomass is actually equivalent to charcoal on a MJ / m3 basis. Consequently, the truck will need to haul more weight per MJ with dried biomass, but not more volume . 

3. On the stove side, there is much work to do, from what I can tell, to make a TLUD burning dried biomass as attractive to the user as a charcoal stove burning charcoal. In fact it may never be. However, it seems to me that there is the potential . Given that this fuel is consumed in the city there should be an easy & efficient way to burn the residual charcoal. Also perhaps turn-down needs improvement in the gasification phase. And of course it needs to be simple to operate. Each one of these issues may represent substantial work to develop solutions for. 

4. Speaking of development, a low capital method for distributed drying of woody biomass is another area that will need substantial appropriate technological development for this to be successful. 

5. Final comment on Pellets: I am most familiar with pellets, and many know they are now a major energy commodity in the developed world. The downside is that they take much higher electrical or diesel energy input than simply chipping or splitting biomass. Also, they require more capital, and the plants are more complex to operate and maintain. Consequently they are less suited for a widely distributed system - like the existing charcoal production - especially in developing countries. If the pellet plants are large then the wet wood is hauled further to get to the plant and the benefit in comparison to charcoal is reduced. Still they are the most uniform, transportable, and appealing of the dried woody biomass options. It just remains to be seen which of these different approaches - pellets, chipped, crumbled, or split dry biomass will develop more over time. 

RWL: End. Ron 

- Paul 

-- 

Paul M. Means 

Research & Testing Manager 

Burn Design Lab 

(253) 569-2976 (mobile) 

http://www.burndesignlab.org/ 

“In the whole of world history there is always only one really significant hour – the present…If you want to find eternity, you must serve the times.” - Dietrich Bonhoeffer 
_ 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20130414/773dc8f4/attachment.html>