[Terrapreta] Farm Produced Biochar

[Tom Miles]

Gerrit,

The field presents some formidable challenges even for direct combustion as
we discovered building mobile field sanitizers. Our largest machines were 35
ft wide by 35 ft long (10.7 m x 10.7 m). They   travelled at about 1.5 mph
(2.4 km/hr) which was determined by the time that it takes to convert a damp
solid to a dry solid, solid to gas, and burn the gas, then burnout the char.
We used the straw itself as fuel and used no auxiliary fuel. We consumed
about 12 tons/hr of straw stubble at 2 t/acre (4.5 mt/ha). Travel time over
a single spot was about 10-12 seconds. Due to the moisture in the ground and
the insulating properties of the soil the ground temperature was typically
not more than 200 F (93C) even though we consumed all the straw and burned
it completely at 1500-1800F (815-980C). At 6 acres/hr it took 17 hours to
sanitize a 100 acre field. The small machines covered 3 acres per hour. Each
machine required a tractor to pull it and a separate tractor pulling a tank
of water for fire control. There is a wide variation in field conditions
even when you have removed the excess straw. You have occupied two people,
and two machines to process 12 tons of straw per hour. And you have the
weather.  

Now think of doing the same work picking up the straw from with an 8 ft (2.5
m) swath or a 35 ft row (10.7 m). To partially burn the straw and char it
you will need heavier equipment by possibly three times what we used due to
the air control, refractory insulation, etc. And you will need to re-inject
the biochar across a 35 ft path unless the injection is a secondary
operation. It is likely that you would reinject the 2 t/a (4.5 mt/ha) in
concentrated rows as they did in Australia in the Oil Mallee project so it
probably would be a separate operation.

Compare this with high speed field collection and packaging into uniform
bales with low average moisture content; processing in a stationary device
where you have automated fuel and char handling and control of the process;
you can capture the gaseous effluents like nitrogen; and have a concentrated
dense char  product that can be injected in the field in whatever
concentration you need. If I'm running the plant I'll take the stationary
process any day.

The value of the biochar will drive what can be done on the farm. We have
not established that value yet and that should be our priority. For the time
being we can assume that the biochar comes from heaven. We must ask how much
do we use on what crops and with what expected results?

Tom                 


   

  
> -----Original Message-----
> From: Gerald Van Koeverden [mailto:vnkvrdn at yahoo.ca]
> Sent: Thursday, August 16, 2007 3:53 PM
> To: Tom Miles
> Cc: 'terra preta'
> Subject: Re: [Terrapreta] Farm Produced Biochar
> 
> Just a wild idea...this sounds crazy...in fact the whole idea is
> ridiculous...
> 
> I keep thinking about the difference between a mobile pyrolysis unit
> vs. a fixed one in terms of making char out of field residues.
> Actually, both require field biomass, eg. corn stover, to be baled
> and brought to a point, and then later picked up again and re-
> distributed on the field.  It would be much neater, if we could
> justify a simple charring unit solely for char production, but only
> if there is a flow through process such that one could drive through
> the field towing this unit, continually processing crop residues as
> one is driving, and spreading the char as it goes....Now that would
> be a real "mobile" charring unit!
> 
> But I would have no idea how to make this actually work!  Even if it
> is possible, it probably be much too expensive of an idea!
> 
> Just dreaming,
> Gerrit