Your beautiful and well maintained lawn can be one of the best carbon sequestration devices in existance. Lawn grass, because of its abundance, captures more ambient CO2 than any existing or proposed technology. The plants in home landscaping are well watered, well fed and well cared for (generally) and grow at optimum rates, which means optimum carbon dioxide uptake. If this captured carbon dioxide can be diverted and sequestered the power of this resource can be realized. Well now it can.
How? By converting your weekly yard waste into biochar using your backyard BBQ. Once your yard waste has been reduced to its native carbon it can be bagged and disposed of ease with the trash, added to your compost heap or buried in that old family Cold War era bomb shelter.
Now that summer is here most of will be mowing the grass and firing up the BBQ. For those of us with a charcoal BBQ the leftover coals can be put to good use. I haven't tried with a gas grill yet, but I will. What we're going to do is make a simple biochar reactor and use the BBQ, some charcoal and a small fan to turn it into biochar.
Here's some helpful hints:
hint #1: Don't be an idiot. Make sure you produce more charcoal than you burn.
hint #2: Check your local burning regulations
hint #3: This stuff is hot, really hot, be careful
Step 1: Bill of Materials
Biochar is produced by combustion of organic material, normally plant material, in the abscence of oxygen. To do that we going to take a steel can and drill some holes in the side. Then we're going to fill the can up with grass trimmings and seal it up. Then we're going to heat it up and see what happens....
Okay, you're going to need a lawn...or yard waste from a lawn...
Also you'll need a backyard charcoal BBQ with a cover. I'm using a small Weber brand for the proof concept. The cover may be optional, I remember a traditional style BBQ with a wind shield. That could work as well since the wind shield will capture the fan breeze.
A method for lighting the charcoal. I'm using petroleum based charcoal lighter fluid. I've seen the starters cans that use newspaper and they work pretty well. I may get one....
A small fan. I'm using a standard electric fan but I recommend a small battery powered fan with a solar recharger.
A steel can with a lid. I'm using a 1 gallon paint can I picked up at my local paint store for $2. It will do for this purpose and fits inside the small Weber. The can must have a lid which can be secured in a way that will withstand heat. I've got an idea for another reactor design I got from homedistillers.org I will update this if that works out. To scale up use a full size Weber kettle and a 5 gallon paint can from the paint store.
A drill and drill bit for drilling ventilation holes in the steel can. This will vent the methane and other gasses produced into the fire where it will be consumed.
Okay with all of that we're ready to start....
Step 2: Assemble the Biochar Reactor
That's a fancy way to say drill some holes in the side of the can, fill it with grass and hammer down the lid. Make sure it's secure.
I picked a drill bit at random and started drilling. Not the best plan as it turned out. You want to make a reasonable vent for gasses that develop during the creation of the biochar. The metal walls aren't that thick and if one goes drilling around at random the grid becomes too weak. Drill from the center out and don't go crazy.
I drilled on the opposite side from the seam for no particular reason at all...
Once you've drilled the vent remove the lid and fill it with grass clippings. I have no good advice on how to fill it, I'm new here myself. I didn't pack it down tightly and have no idea what the yields will be, I will update this as I progress.
Now put the lid back on and press it down tightly. I originally pressed mine in by hand after a little bit in the fire the metal expanded and the lid fell off. I hammered it back down ( lightly ) and it seems to be secure.
Step 3: We Didn't Start the Fire...
It was always burning since the world was turning...Sorry these Billy Joel moments come and go. Okay with the lid securely on the can we're ready to start making our biochar.
At this point I'm not sure how much charcoal to use or what the yield will be. Your mileage may vary so experiment.
If you've started the coals in the metal gizmos with newspaper arrange them on the fire grill in circle with enough room in the center for the can. Otherwise just put some charcoal briquets in a circle with enough room for the can.
If you want to be really, really, really clever you've prepared your biochar reactor in advance. Once you've finished the hamburgers for dinner you can carefully remove the food grill, push the hot coals around with a spatula and place the biochar reactor into the coal bed.
Place the can on its side in the center of the circle. Push the coals as close to the edge of the can as you can.
Place additional coals so you've got two levels. If your using the leftover coals make sure you've got a solid coal bed against the sides and ends of the cans.
If you're charcoal lighter spray it liberally on the charcoal and light.
Once the coals have begun to show some gray ash position the fan so that it blows air onto the coals.
Once the coals are firmly established place the lid partially over the grill to bank the heat. Leave a gap turned towards the fan and place the hood vent holes opposite for smooth air flow.
NOTE: You have now turned your BBQ into a mini-blast furnace for making biochar. It will get hotter than you think. Use a pair of heavy garden gloves once things heat up.
Step 4: Cooking - the Final Frontier
Once you've got things underway there's not much too it. Periodically it needs to be checked the coals pressed close into the can. Don't be an idiot use a firestick.
I stirred the coals twice pushing increasingly smaller chunks of coal against the sides and ends of the can.
I also added briquets at key point to create hot spots that looked weak. They burn nicely if well placed and will ignite from a small contact with a burning (gray area) coal.
Due to the forced air feed the fire burns much hotter and faster than normal. Experimentation will determine the correct placement and number of coals.
My fire has burned for just over two hours and seems about burned out. Remember that the contents of the can are also combusting (in the abscence of oxygen).
TO AVOID RISK OF SPONTANEOUS COMBUSTION INTO FLAME ALLOW THE CAN TO COOL COMPLETELY BEFORE OPENING.
Step 5: Disposal and Sequestration
Obviously some of the biochar you've created can be preserved and used in the next round.
Otherwise, if you've done it right, you've created an extremely high quality carbon suitable for long term sequestration. Pour it into a plastic bottle and throw it into the regular trash where it will be buried in a landfill for thousands of years. If you put it in the recycle bin the carbon will get recycled into mulch and re-released.
Now you've got something to talk about over the water cooler on Monday morning. "What did you do this weekend" "Oh, I sequestered 10 lbs of CO2 from my lawn...and you?"
To increase the carbon recovery from this process there are two very simple steps you can.
Dump your power mower and get a reel mower. Yes, they still make them. They're quiet, clean and you get exercise while you use them. Simply by switching from fuel powered to human power maintenance you have substantially increased your carbon recovery and improved your health.
Instead of the electric fan pictured use a battery powered fan with solar recharged batteries.
That's it. I hope you find this useful. I am starting work on a follow up instructable for a biochar burner.