A Charring Fire

1. A Charring Fire A Little Understanding of Heat and Fire to Help You Make Good Biochar Biochar

2. Three Things Every Fire Needs heat fuel air (oxygen)

3. Three Ways That Heat Moves Inside a solid material Conduction Radiation heat flows out to fill the volume Convection In a gas or liquid heat glows outward in all directions In anything clear hot fluid moves upwards For certain temperatures, we see this radiation glow as light.

4. Glow Color Tells the Fire’s Temperature Visible Colors orange or red least hot yellow or white hot blue orviolet very hot Invisible colors Infrared very warm Ultraviolet hottest yellow white A fire is hottest at the bottom and coolest at the top.

5. How a Fire Burns Hot spark starts the flame Flame move down to find fresh fuel Radiation heats the nearby air Convection moves hot air upward Upwelling air pulls fresh air in behind it Upwelling air won’t let fresh air reach the flame from the side Hot air loses heat by radiation as it rises: we see flame color! air air air air air Burning Zone air air

6. Good Burning and Poor Burning • Body of the Flame – Poor Burning: • Less oxygen – flames below used it and no new oxygen gets in • Cooler flame: white, yellow, orange, red • Base of the Flame – Good Burning: • Lots of oxygen because it keeps getting pulled in • Fresh fuel available • Hottest flame: blue or ultraviolet • Just Below the Flame – Charring: • No oxygen – air gets sucked into the flame • Heat from radiation and conduction boils off any water and gases in the fuel to make char

7. Which Way the Fire Burns Bottom-burning fire Top-burning fire burns faster burns hotter invisible, very hot, ultraviolet flames Most of the fuel is in the flame (poor burning) Burning zone moves down into fuel (good burning) burns longer charring from high heat Top-burning fire is better for making char.

8. Heating Without Burning • carbon dioxide • water vapor • soot • ash • lots of HEAT oxygen Combustion • no heat • no carbon dioxide • water vapor • volatile gases • char heat fuel Pyrolysis no oxygen (pie-RAWL-i-sis) For pyrolysis, you have to ADD heat

9. Pyrolyzer (PIE-ro-lize-er) Nested – Barrel Pyrolyzer Biomass for burning (combustion) Combustion provides heat for pyrolysis Biomass for charring (pyrolysis) Air can’t get into the smaller barrel. chimney lid Smaller Barrel Holes let air into the larger barrel from the bottom. Larger Barrel

10. A Good Fire for Making Biochar A top-burning fire is the best fire for making biochar. It burns hot and clean, and leaves very little ash.

11. Making Biochar Temperature inside inner barrel Fahrenheit Centigrade Smoke turns a little dark Smoke is clear or a little white Smoke is clear 1000° 500° brakes down wood into char and gives off combustible gases 800° 400° 600° 300° bakes water out of wood molecules 400° 200° boils off any free water 100° 200° outer barrel kills anything alive 50° 100° Biomass for Charring inner barrel Combustible gases leak out and feed the flame.

12. Why are the air holes at the bottom of the barrel? Good Question! Convection makes hot air rise Rising air pulls fresh air behind it Holes at the bottom let airflow work with convection, not against it. air air air air air air air

13. Why does the barrel need a lid? Good Question! Making good biochar takes high heat Convection also lets heat escape. A lid stops radiation and slows convection, trapping more heat inside the barrel. Radiation lets heat escape from the barrel.

14. What does the chimney do? Good Question! Without a chimney… With a chimney… The rising hot air spreads out and slows down as soon as it goes through the lid. The rising hot air speeds up in the chimney. This pulls fresh air in faster, helping the fire burn cleaner and hotter.

15. Why does the barrel need insulation? Good Question! Making good biochar takes high heat Without insulation… With insulation… air air air barrel wall heat from fire barrel wall heat from fire insulation Conduction moves fire heat through barrel wall. Wall gets hot. Insulation has very low conduction. Fire heat is trapped in the barrel. Inside gets very hot. air air air Convection lets heat escape from barrel, making inside cooler.

16. What’s the difference between heat and temperature? Really Good Question! Temperature – how fast the atoms in the material are vibrating. hotter cooler When making biochar… Temperature determines how well-charred the biomass will be. Heat – how much total vibration energy something has. more heat less heat Heat determines how much biomass you can char. same temperature Something with more temperature can have less heat,if it’s small less heat more heat