Biochar Kiln Operation: Update 12 - Freed pipe and 3rd Burn

Starting the day at the welder's shop.  Human error in construction in Lima welded a pipe that was supposed to be free. The extremely high temperatures in the pyrolysis chamber (800+ ºC at times) causes the air ductwork to expand.  It's not much, but over three meters of stainless steel pipe, it's enough to blow a lot of rivets and allow enough air to enter to make ash instead of biochar.  

We didn't have a plasma cutter, and the way the locating plate on the pipe is oriented, you can't quite get in with an angle grinder.  An oxy-acetylene torch would punch a hole in the metal, but since it reaches 3,000º it would punch a hole through everything, our ceramic insulation included.  The town welder had a very clever idea: crank up the amperage on an arc welder, run the polarity so the current passes through the electrode and that is enough to burn a hole in meter.  Above is our test on some 309s stainless steel scrap.

Yuri at work.

The result, a free pipe

Finishing the second pipe

Back in business! Charring at 722ºC above the biomass

The temperature above the stainless steel heatshield.  The heatshield blocks the fire from burning the biomass but allows the heat to pass to perpetuate the pyrolysis reaction, liberating syngas from the biomass and further feeding the combustion above the heatshield.  By manipulating where atmospheric air (namely, its oxygen fraction) we can control where combustion is happening.  When things get toasty, the stainless steel waterjet nozzles can drop the temperature 100º C in 15 seconds.  Quenching from 800 to below 100 takes around 10-15 minutes.

A great mix of technology and tradition.  We used automotive silicon on the thinner seams, but ultimately, the easiest material to use to seal the door is good old fashioned clay, mined a hundred meters from the work site.  The dried clay will be mixed into subsequent batches prior to pyrolysis to mineralize the biochar.

Side view of the reactor with some condensed pyrolysis bio-liquids leaking out the bottom.   In a more advanced system, or with some retrofits on this design, we could condense and capture these liquids and see if they hold potential to be converted into biofuels.

While we're making biochar at the oven site, the municipality's 130 HP tractor is prepping our parcel sites.  We have two particularly tenacious occupants, exotic Brachiaria grass and native Psidium (guava) trees.

Another view of the sealed door

Cooling the door handle to open

Opened door and commencing the quench.

Yanking out the first crate with the assistance of a bent piece of rebar that is the crate hook: part # 91263

Dousing the first crate.  Though we engage the sprinklers and reduce the ambient temperature in the chamber to ~93ºC, the center of the feedstock crates continues to pyrolyze.  Once exposed to oxygen, it begins to combust, and we lose biochar.  Though, the ash from that combustion will enrich the biochar from a agronomic standpoint.

Another view inside, glowing embers in background

The cooled crates.  

Still quenching.  A small ember left overnight could leave us with a pile of ash in the morning.  This, our 3rd run left us with more than 500 pounds of biochar, our best yield yet.  There was a small amount of torrified wood on the bottom, btu we're tweaking the process boost our yield.  To come, a double header biochar day with two cycles in a day, thermal images of the machine in operation and the door opening, and experimenting with chipped biomass.