[Terrapreta] Charcoal in Compost? 4USA?

[Tom Miles]

Sean,

 

Another look at costs from "Canada: From bark to bio-oil" on the Advanced
Biorefinery (ABRI) demonstration project.

http://www.timberbuysell.com/Community/DisplayNews.asp?id=1083

 

 "Pyrolysis is essentially the process of converting a solid biomass such as
wood fiber or peat moss into a liquid by using high heat in a carefully
controlled, oxygen deprived environment where the internal temperature in
the reactor can reach 1,000 degrees Fahrenheit. The process itself is
extremely quick, partially to prevent secondary chemical reactions. It takes
biomass entering the ABRI pyrolysis system about one minute to separate into
solid, liquid, and gas streams. The biomass produces about 60 percent
bio-oil, and 40 percent charcoal and synthetic gas. The charcoal and
synthetic gas are used to dry the biomass prior to conversion and to produce
the heat needed for the conversion process, leaving behind only ash as a
byproduct."

 

"So, just how cost competitive is bio-oil and how does its energy output
compare to conventional fossil fuels?

The straight conversion cost taking into consideration such issues as labor,
equipment, amortization of capital, and standard fixed and operating
expenses, but without taking the cost of the feedstock into consideration,
is about $2 per gigajoule. In terms of feedstock costs, ABRI says every $10
per dry tonne of material adds about $1 per gigajoule. It estimates its
feedstock costs at $20 per dry tonne, meaning that the company's break-even
cost for producing a gigajoule of energy is between $4 and $5. This is as
compared to the $8 to $10 per gigajoule cost of natural gas or $15 to $20
per gigajoule of #2 fuel oil."

 

ABRI assumes a gross heating value for biomass of about 16.7 GJ/tonne dry
(1.055 GJ/MMBtu) so that the heating value of the product oil is 10 GJ/tonne
feedstock (16.7 GJ x 60% = 10 GJ). At 10 GJ/tonne a process cost of $2/GJ is
equal to $20/tonne feedstock. 

 

Assume the same plant is making charcoal as a primary product and uses the
oil and gas to heat the system. It still costs $20 to process a tonne of
biomass. Charcoal yield is 20%. If no oil is sold and the gas is used to
heat the process the processing cost is  $100/tonne charcoal ($20/20% yield)
with no biomass cost.  Add the biomass cost of $20/ton at 20% yield and you
get ($20/20%) = $100. So your total cost is $200/ton charcoal if no heat or
oil is recovered and sold as co-products. At $50/tonne biomass the charcoal
cost goes up to $350/ton ($50+$20=$70/20%)  

 

If you burn two thirds of the oil (6.7 GJ/tonne biomass) in a combustion
turbine (26.3% net efficiency) you can generate 511 kWh. My best electricity
price is $0.06/kWh. If it costs $0.03/kW to run the turbine-generator (or
engine) then I can apply $0.03/kWh toward process. 511 kWh x 0.03 =
$15/tonne biomass. That will pay for part of the processing leaving a cost
of $5/tonne ($20-$15) biomass plus the cost of the biomass. If biomass costs
$20/ton then the charcoal will cost $25/tonne of biomass or $125/tonne
charcoal ($25/20%).  Power has reduced the cost of the charcoal from
$200/ton to $125/ton.

 

These costs will change with yields and circumstances but I do not think
that the costs of delivering charcoal from a modular pyrolysis plant is
going to be far from $100-$200/ton. Making charcoal as a co-product of
bio-oil or power is clearly a benefit. I would expect the costs-benefit
analysis for BEST, Dynamotive and others to be similar. 

 

Tom

  

 

 

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