[Stoves] Last? Alternative to Charcoal

Sat Apr 20 16:03:01 CDT 2013

Charcoal will burn at a very slow rate and wood has to burn at a larger rate to 
maintain flaming combustion.
So for low and slow like for simmering, charcoal could be more efficient even 
considering all the energy wasted making the charcoal from wood.

Using wood for the high power phase of cooking like bringing a pot to boil and 
then using the charcoal made from the wood for low power cooking like for 
simmering or holding food hot just seems to fall into place.
I believe it was Crispin that said that a lot of efficiency is lost because the 
fuel wood is a size that required a too large a fire to maintain flaming 
combustion. A fire too large to be most efficient at capturing the heat with a 
pot.

________________________________
From: Crispin Pemberton-Pigott <crispinpigott at gmail.com>
To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org>
Sent: Sat, April 20, 2013 4:34:23 PM
Subject: Re: [Stoves] Last? Alternative to Charcoal

Dear Mike

>Great conversations on Charcoal verses everything else.  I can't understand how 
>percentages can be the same for all and less than charcoal?  What no one seems 
>to be speaking about is the inefficiency of making charcoal in the 1st place?  

To cut straight to the heart of the matter, the fact that charcoal ‘is 
inefficient’ is not a simple a statement as it first appears.

Turning any biomass (it does not have to be a tree) into charcoal changes its 
properties a great deal. It first of all becomes dried completely which takes a 
great deal of energy and it why the energy of fresh char is about double (or 
more) the energy per kg of the biomass that was put into the process. The ‘total 
loss’ is not a simple as trying to match the potential fry fuel energy with some 
‘loss’. That is an overly simplistic view so the get somewhere with the 
conversation it is important to view entire system from the sources (a field or 
plantation of forest) to the heat inside the pot at the far end.

Paul M mentioned that the transport for the equation he is putting together he 
set at 3 times that of wood fuel because of the area needed to produce the fuel. 
Well, that might be true in certain circumstances but it is not generally true 
and not for agrifuels turned into charcoal. The value of an agriwaste turned 
into char is greatly enhanced and as the transport is a variable, I prefer not 
to fix an expense for transport until the local circumstances.

Paul, thanks for replying to my queries. I am holding open the issue of the 
transport value because as it is significant, I wouldn’t like to see a final 
outcome that was strongly affected by an assumption like triple the 
transportation cost. 

Urban area produce a great deal of tree cuttings that is not exactly prized 
cooking fuel. The value of a processed fuel is high for a reason, not just 
production costs. Predictable fuels like char briquettes (especially little ones 
that can be hopper fed) give much better performance than random tree cuttings.

As it is true that a pelletized fuel (made from the same raw material as the 
char) has more total energy, it is fair to compare them in terms of their ‘as 
produced’ energy per unit mass, however the cost of making pellets is a heck of 
a lot higher per MJ than char. That matters in the overall energy equation.

Although people routinely suggest that pellets are a great fuel, the energy 
intensity is high. The Chinese machine that was mentioned recently on this list 
has 2 x 60 kW electric motors. Consider the  GEK Power Pallet. It runs on wood 
pellets. There is a positive return on the system, meaning the Power Pallet can 
produce enough electricity to operate a machine that will make enough pellets to 
run the gasifier and the Power Pallet. However it might not also be able to 
produce the gasifier, the engine and the generator that produces the electricity 
and the wood pelleting machine with its components and motor. Do you see what I 
am getting at? Something has to power the system. We can’t take part of the 
system assuming that the energy needed to run it comes free from somewhere else.

Char making (from biomass in general) is a low tech energy non-intensive process 
that provides a net gain in energy, taking only biomass to begin with and 
produce net energy for cooking. At present the use of diesel trucks to move it 
has turned what used to be a biomass (draft animals) into an extended supply 
chain that probably, ultimately, runs on oil. That could be improved by using 
non-woody biomass as an input like the Sarai Stove fuel from sugar cane leaves, 
but only applies to certain areas where the distances are ‘right’. 

To look for real, bankable alternatives, we have to keep an open mind think of 
all the possible technologies that we could apply to the problems in the 
production and consumption chain. Innovative changes to the charcoal market, as 
were tried very successfully in Chad, can dramatically change the entire market 
into a sustainable, profitable and effective system for provision of non-fossil 
cooking fuels.

Regards
Crispin
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