[Terrapreta] charcoal making

[Sean K. Barry]

Hi Richard,

I noticed a couple of things you said.

"The upper vent was cycling this morning between steam and white smoke."

"I am very interested that this technique did not make excessive smoke, which is a big plus in my neighborhood. We should look at a version of this burn where we scrub the outlet gasses to make wood vinegar. Any ideas?"

White smoke and steam means the carbonization is not done yet.  The wet hay (and wet cardboard?) could also have been steaming off the water in it, I suppose.  The smoke will turn bluish to clear when no more charcoal can be made from the biomass (and it gets hotter).  Then is when you want to STOP ALL AIR going into the pile; close all vents, bury the stacks.  You don't really want to keep the fire cool with water when charcoal is being made.  Just control the air.  Use side/bottom vents and vents with stacks, alternating along the side, under the edge of the pile and into it a good foot or so.  The air will suck into a vent, go up into the inside of the pile, then back down and out a vent with a stack on it.

Below is a drawing of a "stack vent".  Make about a dozen of them.  Use heavy gauge steel U-channel and steel pipe, welded.

Don't dig a pit, use flat ground, maybe even up on a small rise, so as not to gather water.  Stack the wood in a close pile, ellipse or circle shaped, on top of kindling in the center.  Leave the center open so you can get at the kindling to light it.  That was a good idea to put the wood pile on top of pallets.  Light the kindling down at the bottom center.  Slide the vents in, evenly space all around the pile, right into the pallets and under the wood.  Once the fire is going good in the kindling, take four to six "stacks" (4" sheet metal tubes, maybe 6 feet long) and stand them around the fire into the pile, a couple feet back or so.  Then bury the pile around the "stacks".

The wood will begin to burn from the center of the pile out, sucking air in through the vents and under the pallets and exhausting through the "stacks".  The "stacks" and air under the pallets are needed to form a strong draft.  Done right, the "stacks" will be billowing smoke and getting very hot.  Keep them a couple/few feet back of the flames as it spreads out.  Finish burying the pile, leaving the edges of the pallets open and the twelve "stack vents" sticking out around the sides.  After its burned for an hour, then bury the pallet openings around the sides in soil or sand, leaving the all of the "stack vents" open.

Pull the "stacks" out of the pile and slide six of them, alternating every other one, onto the cylinders at the top outer ends of the "stack vents", which are sticking out from under the pile.  Then bury in soil the bottom U-channel end of each "stack vent" that has a "stack" pushed onto it.  Leave the other six "stack vents" unburied and open.  Every 3 or 4 hours, switch the "stacks" over to the alternate "stack vents" and unbury or bury the ends as required.  You should be able to do several tons of wood, two or three cords this way.  It will take maybe 24-36 hours to burn, depending on the size of the pile and/or rain.  As I said before, when no more charcoal can be made from the pile, the smoke will go from white to bluish/clear.

When you see the bluish/clear smoke, than you must totally suffocate that pile of charcoal; pull all the "stacks" off, bury or pull the "stack vents" out and bury any openings left.  Make double sure there are no air in or smoke out openings!  You can put a very light water spray onto the pile (without washing the dirt away) if you want to, but be careful.  You want NO SMOKE, so putting water on can be a problem, because it will steam when it dribbles down to the hot charcoal, the exiting steam can make openings, and you can't tell smoke for the steam.  I think it better to just bury the pile, so there is no air going in, and no smoke coming out.  It will take at least 24-36 hours to cool (probably as long as it took to char everything).

When you do open it, be very careful to quench any flare ups in dirt or water or both.  If there are a lot of flare ups or the opening feels uncomfortably warm as you open the pile, its not cool enough yet, so bury it again and wait some more.  Make sure there are no openings again.  If it seems cooled, then pull the charcoal apart into separate piles, so if any flares up, it won't burn up the whole pile.  You can douse as much water as you want onto the charcoal when you are taking it out of the pile.  It is not usual to put water onto charcoal.  I say you can do this only because the charcoal you make is intended for soil (not for combustion), so you do not care about moisture content being low.

As for gathering wood vinegar and or producer gases, pits and piles are no good.  The best thing I think to do to accomplish this is to use an air-blown, "down-draft" gasifier/pyrolysis reactor.  There needs to be a drain at the bottom for the liquids and way to capture them.  The charcoal and the gas also both exit out the bottom.  When the pyrolysis reactor is producing a higher yield of charcoal, its produces a lower BTU gas stream (and vice versa).  So, if you want high charcoal yield, the gas will probably be useless for power conversion for instance.  It should be flared (burned) though, because carbon monoxide (CO) and methane (CH4) are much more potent greenhouse gases than the exhaust gases from combustion.  The combustion products from the fuel gases in the producer gas (H2, CO, CH4) are carbon dioxide (CO2) and water vapor (H2O), which are ecologically better than releasing the fuel gases.  The faster you pull charred biomass out of the bottom of the down-draft reactor, the lower the temperatures inside will be, and consequently, the more volatile matter (tars, wood vinegar, ligno-cellulosic acid, etc.) will be in the charcoal, and condensing and draining out of the reactor.  It's hot and corrosive (acidic), so it needs to be gathered up in stainless steel barrels (very expensive).  It gets gooey fast as it cools and then gets hard as it get cooler (like room temperature), so cleaning the barrels is tough and dirty business.  You would almost want to process it immediately, while its hot and before you would need to store it and or ship it.  Some have found ways to run boilers or low-temp heaters (greenhouses?) for instance.

Let me know if you have any question and/or how it goes if you try any of my suggestions.

Regards,

Sean K. Barry
Principal Engineer/Owner
Troposphere Energy, LLC
11170 142nd St. N.
Stillwater, MN 55082
(651) 351-0711 (Home/Fax)
(651) 285-0904 (Cell)
sean.barry at juno.com<mailto:sean.barry at juno.com>






  ----- Original Message ----- 
  From: Richard Haard<mailto:richrd at nas.com> 
  To: terrapreta at bioenergylists.org<mailto:terrapreta at bioenergylists.org> 
  Cc: Larry Williams<mailto:lwilliams at nas.com> ; Biorefiner at aol.com<mailto:Biorefiner at aol.com> ; veronica<mailto:veronicacanoe at yahoo.com> ; Todd Jones<mailto:tjones at nas.com> ; Sean K. Barry<mailto:sean.barry at juno.com> ; John Flottvik<mailto:jflottvik at yahoo.ca> 
  Sent: Sunday, April 01, 2007 10:53 PM
  Subject: Re: [Terrapreta] charcoal making




  On Apr 1, 2007, at 5:49 PM, Sean K. Barry wrote:


    Hi Richard,

    You do live in an area of some beauty.  How long after you started the kindling under the split logs was it when you bury the burning pile? 



  No kindling, just split cordwood that has been drying for 2 years. Larry was late coming out and I started the fire with those paraffin impregnated fireplace logs. By the time he arrived 15 minutes later it was blazing in 2 places and we worked for about an hour finishing the stack with another 1/2 cord of half dry alder, etc and holding the fire back with a open garden hose. I think stacking on the pallets helped feed the fire with lots of air.


  Larry thinks it almost got away from us as the tractor was late arriving and the neighbor who came by with some wet hay for us was recruited to help with his mini loader bucket.


  Larry by the way should be posting here soon as he has been having difficulty with signing in. He should have more to say on this.




    Did you leave any small air intake vents/ output stacks at the bottom or stacks out the top?  



  The first day we had  2 vents in the lower front about 6 inches across and the  single vent on the upper end. The deck of the fire bed did slope uphill. On the upper end we had buried a standing pallet and we allowed a single vent to stay open. There was much discussion during the day as i was worried the fire did not have enough air and is the reason we opened the lower end at end of day. It was really hot and when we covered up for the night we only left a vent at the top


  This morning I checked and the cardboard and wet hay was still intact on the middle and the temp 6 inches into this layer with my 6" probe was 160-166 F. Roughly the same as when we left. The upper vent was cycling this morning between steam and white smoke. We had planned originally to open the pile today but after much neighborhood discussions we decided to leave till next weekend. If it seems to be cooling we will open the lower vent again and Larry will blow in some air with his lawn blower.


  Our local friends told us stories about a burn pile with buried hot coals that lasted all winter and another told us about forest fire burns at  that stayed hot all winter at loading dock piles under many feet of snow. 


  I am very interested that this technique did not make excessive smoke, which is a big plus in my neighborhood. We should look at a version of this burn where we scrub the outlet gasses to make wood vinegar. Any ideas?


  I am impressed with the Indonesian flat kiln Tom put the pdf into files section. It would fit well with my willow coppice work 



    Who is the John you refer to? 



  John is John Flottvik, our neighbor just across the border in Canada who manufactures a pyrolyser and has been keeping me well supplied with charcoal powder during the 2-3  years of my farm experiments. I think his current company name is JF Waste Bioenergy. He reads this list.





    Are you the two pictured?  



  Yup That's us. I had emailed Tom during our burn and told him he could call in to kibbitz, which he did and we had a great conversation. Later he commented to us we should have been in costume so i suppose next time we should wear our SCA (Society for Creative Anachonism) outfits. 


    Did you measure or estimate the weight of the wood you put into the pit?


  Three pretty full loads in my (old) Nissan pickup about 1 and 1/2 cords.


    Will you measure the weight of the resulting charcoal?  Will you be doing a proximate analysis of the charcoal?


  Probably not, since we quench in water and my experiments will be set up by volume. I am looking for about 80 gallons of charcoal pieces for this treatment set. We also hope to save an equal amount until next year by composting in forest litter in the active root zone of a mixed conifer/hardwood forest. Larry will also be taking the small bits and dust for his garden.


  Proximate analysis will be done and  also all treatments and additives will be subjected to:  pH, Buffer pH, Extractable Nutrients, Extractable Heavy Metals (e.g. Lead), Cation Exchange Capacity, and Percent Base Saturation. 


  And of course OM. Pretty much standard farmer stuff.


  As we had covered the burn pit with wet hay and farm soil the char we harvested yesterday was contaminated with these materials but as this is going to be mixed in with the same soil i am only going to separate the big pieces of soil and hay and not worry about washing the charcoal. Larry is thinking about burning the hay pieces with his propane weed burner but I think I want to preserve those volatiles. What do you think?



    Good luck with your "Terra Preta" making adventure.  I hope you have some interesting results with the pot tests also.

  re "Terra Preta" Larry and I have had much discussion on this and we have decided to separate the use of this term from charcoal in agricultural soils. 


  Me too, this is a big effort and I want to get it set up right. An advisor with more experience than I with pot experiments (and charcoal!) commented to cut back on treatment sets and increase the number of replications. I am in the last step of deciding this now and will be focusing primarily on depleted farm soil that has just finished a 2 year rotation and focus closely on our current fertilizer and OM amendment protocols. Even irrigation is a worry and I have decided to place the pots in our field and give them the same irrigation sets as our seedbeds.  


  Best


  Rich Haard, Bellingham, Washington
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