[Stoves] Calculating th LHV for Biomass and Coal

[Thomas Reed]

Dear Crispin and All:

I mis-spoke below.  I should have said the LHV is 18.5 kJ/g, 425 
kJ/mole.  I must have been breathing too much "smoke". 
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While I usually write the formula for dry biomass as CH1.4O0.6. When 
considering its conversion to "charcoal" (a term of 1000 meanings) think 
of it as C(H2O)0.6H0.2 and the process as one of dehydration.  As one 
heats charcoal it first converts to the torrefied wood stage (250-275 
C); then to the "Sea Sweep" stage, 350C; then to the "cooking charcoal" 
stage, 450 C; then to metalurgical charcoal stage; 600 C?; then to 
activated charcoal, 800C; and finally to CH0.2 above 1000C as it 
steadily loses more and more of its 0.6(H2O). 

Check out the FUEL C-H-O diagram that I am sending to Tom Miles and will 
mount on our website this week. 

Yours truly,

TOM REED
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Crispin Pemberton-Pigott wrote:
>
> Dear Dr Tom and Kevin
>
>  
>
> Thank you both for responding.  I am working on the remaining charcoal 
> in a fire so the issue of its moisture content doe not arise.  It is 
> presumed that charcoal that is either presently burning or was 
> recently formed in the fire has zero moisture content.  In fact that 
> water loss has to be accounted for in the calculation of the net heat 
> yielded by burning the wood and volatile portion.
>
>  
>
> If there is no visible method for assessing what 'average charcoal 
> remaining in a fire' contains in terms of volatiles, then I will have 
> to use 'ordinary' charcoal (which is not consistent) and announce that 
> the subject is not closed, or perhaps even closeable.
>
>  
>
> *Dr TR>*The LHV of biomass is then ~ 21-2.5 = 18.5 kJ/mole or 1.03 
> kJ/g, ~ 12% less than the HHV. good enough for a general rule and warning.
>
>  
>
> Actually when I tried that it did not work out so well as will be seen 
> in a forthcoming message.  The HHV of our fuels ranges from about 12 
> to 21 MJ/Kg while the water energy demand remains constant per gm.  
> The charcoal heat content is probably pretty constant for our stove 
> conditions, exacerbating the problem because if the wood heat energy 
> for a certain species is low, and the charcoal heat content is 
> constant, there is an ever-increasing gap between the calculated value 
> (using that method) and the real value.
>
>  
>
> Can I take the Hydrogen content of charcoal to be 2%?
>
>  
>
> Regards
>
> Crispin
>

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