[Terrapreta] Farm Produced Biochar

[Tom Miles]

Richard,

Agreed. Production and use of the charcoal on the farm is not trivial. It's
at a different scale than commercial charcoal production but it is done with
a purpose. That purpose is clearly defined in your case. It is not yet clear
in many cases.    

The actual cost may exceed the current returns on the investment of labor
and capital but the value (cost/benefit) may not be calculated in strictly
current economic terms. That's not uncommon when developing new technologies
or applications, so I jokingly say that it must be amortized on its
entertainment value. The point is that there must be a purpose, a product
and a value.

Serious farm production of biochar in our area will be regulated in a
similar manner as outdoor wood boilers: systems will have to comply with
air, soil and water quality regulations. The amount of regulation will
depend on the scale of the charcoal production. Let's look at scale.

In your plots you have used 30 gallons (4 ft3) or 60 lbs (4 ft3 x 15 lb/ft3)
of charcoal in 85 ft2 plots (5 x 17ft= 4). 60 lb/85 ft2 = 0.7 lbs/ft2 equal
to about 14 tons of charcoal per acre. If your planted area is 50% of the
total area you would use 7 tons of charcoal per acre.

If you used a kiln the size of Robert Flanagan's (1.5 tonnes [1.65 t]
biomass per charge) you would produce about 0.66 tons per day (at two
charges/day) or 20 tons of charcoal in 30 days
http://terrapreta.bioenergylists.org/flanaganvinegar
So if you ran Flanagan's kiln for 30 days at two charges per day you could
treat about 3 acres per year (20 tons/7 tons per acre). In 15 years you'll
cover the whole 45 acre nursery. 1.65 tons/8 hours with wood vinegar
recovery would exhaust about 3 MMBtuh which is large enough to be regulated
in some states.  

If you treat 5 acres per year that's 35 tons of charcoal per year
representing 175 tons of biomass (35 tons charcoal/20%) per year. If you
make your own charcoal at 5 tons of charcoal per day (175 tons/30 days = 5.8
t/day) each kiln charge would be about 25 tons of biomass/24 hours or 1 ton
per hour (2 big bales). Your kiln will be rated at about 12 million Btuh
(80% biomass x 15 MM Btu/ton x 1 ton/hour) if no oil is recovered, or 5
million Btuh if just the offgas is burned to drive the process of making oil
and char. Either way you have an system is large enough that it will be
regulated for particulate, CO and NOx emissions. 

A system of this size is likely to be operated as a stationary production
facility operating 250 days per year (6250 tons biomass or 1250 tpy
charcoal). Large bale combustors of the 1980s (Agrifurnaces, IA) were rarely
moved. Most systems included debalers like the farm scale straw burning
gasifiers and boilers or today. 

A farm scale charcoal system might include the same amount of equipment as
Vidir's Greenhouse Gas Displacement system which gasifies straw to replace
natural gas for heating heat poultry houses.
http://www.vidir.biz/index-biomass.htm Vidir's smallest system consumes 500
lb/hr (3 Million Btuh) of wheat straw. If built as a pyrolyzer it would
produce 100 lb charcoal and 1-2 million Btuh heat. The system cost is
$200,000. Annual operating cost with straw at $10/bale is estimated at
$16,000. Labor is figured at 3 hours per day $15/hr. Economics are based on
6 months operating time (in Manitoba) or 375 tonnes (752 x 500 kg
bales/year). At 20% yield that would produce 82 tons (75 tonnes) of charcoal
which could treat about 12 acres (at 7 tons/acre). In four years you would
produce enough charcoal for a 40 acre farm. At $200/ton the charcoal would
be worth about $16,400/year whch would just offset the operating costs but
not capital. If you had a use for the heat (2 million btuh x 70% to hot
water = 1.4 MMBtuh, 33.6 MMBtu/day) in 30 days you would recover more than
$12,800 additional revenue to help pay for the plant. In six months you
would recover $16,400 in charcoal value and $76,800 in heat savings. So the
payback could be 4 years with heat recovery.

To a see a system like that in operation would be entertaining. 

Regards,

Tom             
    
 

 



> Entertainment is something like chasing a ball with a stick - what we
> are doing is a bit more than that.
> 
> Rich H