[Terrapreta] Some more trial data

[MFH]

>From this weekend:

 

Assume that the drum is set up in the brick kiln

Equipment: chainsaw, axe and wheelbarrow

Old and dry fallen timber is available 30 metres from trial site.

Chainsaw and split 110 kg hardwood for drum load

Ditto 40kg for fuelwood

Load drum

Gather twigs and small dry branches, load fireplace with these and the 40kg
wood

Seal drum and light fire.

Time = 45 minutes

Char output = 29kg.

 

Rough cost, including chainsaw fuel and some provision for wear and tear,
and (say) $A20/hr for labour, then maybe $18 for 29kg char. If I could get
$1/kg for char chunks for BBQ's, and keep the fines for the soil, I'd be
about square. Packaged charcoal (in briquettes with sawdust and other stuff
added) retails in Oz for around $2/kg.

 

I still maintain and will get around to proving it some time, that if
surplus gas could be withdrawn and stored, and then used for the fire, the
40kg of firewood would not be necessary. The level of the flames from the
gas escaping through the poor drum seal demonstrates this, plus there are
opportunities to improve on my rudimentary house brick insulation.

 

An observation is that smaller pieces of wood are more efficient. And the
smaller the pieces the more mass that can be loaded into the drum. I've had
successful chars with hardwood up to 20cm diameter, but I've also had some
cases where the centres weren't fully charred. A compromise is maximum
thicknesses around 8-10cm.

 

I have to admit that I remain in awe of the whole process. Normally I start
the fire around 17:00. It's autumn here and dark and increasingly chilly by
18:00, which is around when the gas starts to flow. There's a gentle whistle
to start with, and within 15 or 20 minutes this becomes a muted roar, the
flames creep around the gap between the drum and the bricks and filter
through the bricks on top of the drum, the top bricks begin to glow red, and
I sit (with glass in hand) and ponder on the vast amount of energy being
released from 110kg of wood, and which lasts for several hours.

 

My latest garden trial includes basil, broad beans, corn, capsicum, egg
plant and parsley in the trial plots. The beds were made on top of untilled
soil, which is compacted and so hard that in another bed I had to use a
mattock to break it up. The mix in the main bed includes mulch, cocopeat,
some worm compost and char. This has now been established for 6 weeks, and
not only is it easy to dig down to the base by hand, the first inch or so of
soil under the bed is friable. The bed without the worm compost and char is
also friable but the soil layer underneath is still rock-hard. The colour,
vigour and size of the plants in the bed with char are substantially ahead
of the control bed. Also, we've had no rain for 2 months and all plants are
only watered once/week. There's something going on here that I don't fully
understand, but I'm not complaining.

 

Max H

 

 

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