[Stoves] More on the Alternatives to Charcoal.

Fri Apr 12 22:08:42 CDT 2013

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.

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%. 

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).

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.

Regards

Crispin

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. 

- Paul

-- 

Paul M. Means

Research & Testing Manager

Burn Design Lab 

(253) 569-2976 <tel:%28253%29%20569-2976>  (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/20130413/a2d6210e/attachment.html>