We know that carbonization and spontaneous decomposition process only ends when the carbonization residue is called charcoal under low oxygen combustion in the carbonization furnace. Unless more external heat can be provided, the process will stop when the temperature reaches its larger value of 800°C.
However, this charcoal still contains appreciable amounts of asphalt residues and ashes of native wood. The ash content of charcoal is about 3% to 5%; the weight of asphalt residues is about 30%, and the rest is solid carbon-about 65% to 70%. The carbonization process is a better process, which is good for the entire carbonization effect. The use and sealing of the carbonization furnace is very important.
Further heating can increase the solid carbon content by removing and decomposing more tar. When the temperature reaches 50°C, a typical solid carbon content of 85% and a volatile content of about 10% can be obtained. The output of charcoal at this temperature is about 33% of the weight of the absolute dry wood being charred-neglecting the wood that is burned to char other wood.
Therefore, due to the change in the content of volatile asphalt, the theoretical output of charcoal varies with the temperature of the carbonization in the carbonization furnace. Although the lower carbonization temperature of the carbonization furnace can obtain a higher charcoal output, because the charcoal has low quality and corrosiveness, and contains acid tar, the charcoal produced cannot be burned with a clean smokeless flame. The carbon content of commercial carbon should be about 75% or more, which requires that the carbonization temperature in the carbonization furnace is always around 500°C.