4 replies to this topic

[TreeHuggingTreeCutter]

If wood is about 50% carbon by dry weight.  

What percentage of the carbon in the wood can be sequestered in biochar?

[jimmason]

yield rates in pyrolysis vary signficantly depending on the type of pyrolysis reactor.  types that burn a bit of the charcoal to generate heat will yield less than retort types that burn the gas to generate heat.    on average each will do about 20% and 25% resepctively.

these numbers correspond to the amount of fixed carbon in the biomass.  the rest of the carbon is in the volatiles.  with pressure and/or passing the gas back over the charcoal and lowered temp you can get secondary reactions and deposition that will increase the carbon yield in the charcoal.  however, this may/might/possibly change the character of the charcoal in ways which are non-good for biochar purposes, though fine for charcoal as fuel purposes.

if i remember correctly, the absolute carbon amount in biomass by weight is 42%.   biomass is chemically on average C H1.4 O.06.  anyone want to multiply that out by the atomic weights of C, H and O to see what the real number is?

jim

[TreeHuggingTreeCutter]

Lets see if I can extend this math out a bit.  If fresh cut wood is 50% water weight when cut and then 50% of the dry weight is Carbon and a retort can yield about 20% of that as biochar....  

100 x .5 x .5 x .2 = 5

That means 100lbs of fresh cut wood turns into about 5lbs of char.  

I just looked this fact up on the internet so it must be true....charcoal has about 12,800btu per pound.  

And wood at 0% MC has 8,600btu per pound.  

So using our approximate numbers from above.

50lbs of bone dry wood has 430,000btu

50 x 8,600 = 430,000btu

5 lbs of charcoal has 64,000btu

5 x 12,800 =64,000btu

so...430,000-64,000=366,000btu from volatiles or about 85% of the energy

The charcoal represents about 15% of the energy of the wood
64,000/430,000=14.88%

If the charcoal represents 20% of the mass of the carbon but only about 15% of the energy than charcoal has less energy per pound than the volatiles?    

So on a per pound basis, a pound of wood has 8600btu with about 7300btu from the volatiles and about 1300btu in the biochar.  

Am I missing anything here or is this about right?

If you can then subtract out the energy used to boil off the water in the wood based on MC% feedstock and (I'm not sure I totally understand this part) the energy needed in the pyrolization process, from the quantified energy yielded from the volatiles, you have the Net yield in heat.   Which is the number I'm looking for...cool!!!

[TreeHuggingTreeCutter]

For the application I am considering I want to be able to use the biochar as a soil amendment and utilize the "waste heat".  Am I limited to batch systems or are there currently continuous feed systems?

[TreeHuggingTreeCutter]

Carbon 1 x 12.0107=12,0107
Hydrogen 1.4 x 1=1.4
Oxygen .06 x 15.9994=.959964

12.0107 + 1.4 + .959964=14.370664

Carbon 12.0107/14.370664=83.6%
Hydrogen 1.4/14.370664=9.7%
Oxygen .959964/14.370664=6.7%