[Stoves] Traditonal Charcola Making Process / retort

[Kevin Chisholm]

Dear Crispin

Crispin Pemberton-Pigott wrote:
> Dear Kevin
> 
> We are on the right track - except that I have no intention of gasifying the
> charcoal.
> 
> I want to make charcoal for sale, to burn later in the stove being fired.

OK!! So it looks like what you want to do is make charcoal and burn any 
residual gas to operate a kiln making Mandelo Ceramic Stoves.
1: Do you want to make charcoal using an externally heated retort?
or
2: Do you want to have a gasifier system where you air blow the ignited 
biomass, to produce a partially combusted pyrolysis gas and charcoal?
> 
> I want to work it out 'per stove' so as I need a total of 3.5 KWHe to fire a
> stove (over 18 hrs) the answer would be in kg per stove, not kg per hour.

You will need to feed your system with "X" kG per hour of biomass/wood 
"Y" hours. Is the 18 hours you refer to above the "time when the 
electric switch is turned on", or is it the "time at the required firing 
temperature?"
> 
> Then based on the capacity of the kiln, I can work out the gasifier size.
> Tom reported on a large, modern gasifier in BC Canada which was over 100 KW
> so this is heading in the right direction.

What does the "100 KW" actually mean? Is this the energy content of the 
input biomass, or the energy content of the gas output? Is it a "full 
gasifier" or does it produce char?

The assumption that you will need twice the gas energy as you will need 
in electrical energy is critically important to system sizing.
> 
> That portion of the wood left as charcoal, being perhaps 25-35% will be
> sold.  The gas yielded will fire the stoves. 

My feeling is that you could perhaps get the 25% to 35% charcoal weight 
yield with an externally fired retort system, but that you would 
probably get in the range of 20% charcoal weight yield on an air blown 
gasifier/charcoaler system.

  We can tinker with this later:
> for example there is a large resource of kernel-less cashew nuts which have
> a high oil content and might make a great fuel and yield charcoal nuggets
> perfect for cooking in an MCS.

I have no experience with gasifying or charring cashew biomass.
> 
> But stick with wood for the moment: How many Kg of 15% MC wood is needed to
> gas-fire a stove needing 3.5 KWHe, using what is basically a charcoal making
> operation to generate the gas.  I guess we can optimise the economic by
> giving the wood and the charcoal a commercial value, as well as the gas
> generated.

Assuming that wood has a heat content of 8,500 BTU per bone dry pound, 
ie, 3863 BTU/kG =  1.13 kw-hr per bone dry kG, with 15% moisture, this 
would tend to increase the wood requirement to about 1.33 kG of wood per 
kW-hr of total contained energy. With total gasification with an air 
blown gasifier, we assume that 70% of the contained energy ends up as a 
cooled fuel gas suitable for combustion elsewhere. With this system, you 
would require about 1.9 kG of wood per kw-hr of Fuel Gas.
I cannot answer your specific question "How many Kg of 15% MC wood is 
needed to gas-fire a stove needing 3.5 KWHe?" because of the unknowns 
relating to the "2:1 Gas/Electric substitution ratio" and the required 
burn time, but if it was 2:1 for 18 hours, then it would be about 
1.9x2x18 = 68 kG of wood.

The above is a "base case example" assuming char consumption. This is 
not what you want... you want to save the charcoal.

If you have an air blown gasifier where you save the charcoal, charcoal 
weight yield will be about 20%, but that char will contain about 30% of 
the incoming energy. In this case, you would probably need about 68/.7 
or 97 kG using the above assumptions.

If you had a conventional charcoal retort system that was externally 
heated with pyrolysis gases, the questions that would arise is what 
percentage of pyrolysis gas energy yield was required to heat the 
retorts, and what percentage of incoming Cashew Biomass energy remained 
in the outgoing charcoal? Would you have any suggestions or insights here?
> 
> Christa Roth did a similar calculation when she looked at how long it took
> people in Malawi to save the fuel wood it took to fire a Mandeleo clay
> stove.  This is a reasonable, holistic approach to the intervention.

Would her experience be transferrable to your situation?

Sorry I can't be more helpful... there are a lot of "loose ends" and 
ways to proceed that could change the wood requirements significantly.

Best wishes,

Kevin


> 
> Regards
> Crispin looking for Pandas...
>