Hello Giorgio,
yes, that’s right. If you use only dry charcoal, there is excess heat in the gasifier. If you don’t want to waste it, there are some possibilities:
- EGR:
Pro: Cooling the reaction and longer life of the nozzle, saving of charcoal (the CO2 from the exhaus tis reduced to CO, so you recycle parts of the exhaust).
Quite easy to make and adjust, no problem in freezing conditions.
Con: No extra power. - Water or steam addition:
Pro: Give extra power due to more hydrogen in the gas
Con: Probably more difficult, problems with freezing in winter.
Easiest way is to use moist charcoal. However, this only works in a downdraft. - Mixture of wood an charcoal (Kristijan uses this method)
Pro: Easy, just mix raw wood in. Also gives extra power due to more hydrogen
Con: Gasifier must be able to split the tar of the wood.
Never mix too much of exhaust gas or water. Then it could not be reduced and just steal heat from the reduction. For EGR and water, a reaction temperature of 900 degree Celsius is for best heat economy ans equilibrium of the reaction: Hotter and you don’t use all excess heat, lower and you can’t reduce all and get weak gas with CO2 and/or just hot steam.
Some theory:
Library / Gengas | Drive On Wood! from page 16 onwards
Library / Pegasus Gasifier | Drive On Wood! from page 36 onwards
Both are in English
page 205 onwards for exhaust, page 266 onwards for water. In German.
Kind Regards,
Til