Energy Cost of Charcoal

Tom Miles

Energy Cost of Charcoal
Bryce Nordgren, (Rev) March 26, 2009

Because I really had no idea about how much energy it takes to make
charcoal, I made a table from the specs of the Chinese equipment posted by
gordon eliot. Then I calculated the "Energy Cost" of each component in
(MJ/kg). Finally I aggregated the energy costs from the "suggested
charcoal plants" to get an idea of the energy cost of the entire system.
Note that all of their plants use the new high efficiency coal bar
machine. This should represent a best case scenario: maximum rated
charcoal production at rated power. If you make less charcoal and consume
the same power, the energy cost goes up.

Consider this a first step in understanding the energy efficiency of the
entire process. To complete the analysis, we would have to know the energy
content (MJ/kg) of the produced charcoal. The big question is: can you
power a 30kW generator with the syngas in order to take the small charcoal
plant off the grid?

I hope this comes thru. I'm pasting the tables as html into the mail
message. I'm also attaching the spreadsheet from whence these tables came
in OpenDocument format. I exported the OpenDocument spreadsheet into excel
(attached). This retains the equations so people can plug in their own numbers?
The "source" of the numbers is the Gongyi Sanjin Charcoal Machines Factory:

Charcoal Plant Proposals
# Description Components (MJ/kg) Total
Crusher Drier Coal-bar
1 25-30MT per month 0.00 0.05 0.17 0.22
2 80-100MT per month 0.09 0.03 0.17 0.29
3 180-200MT per month 0.14 0.02 0.17 0.32

Note that the bigger crushers have a higher energy cost than the small
crushers. I would have expected the reverse. Also, the high-efficiency
energy saving coal bar machine is less efficient than the multi-function
coal bar machine. The net result is that larger charcoal plants appear to
be less efficient (have a higher energy cost) than smaller plants. As the
table shows, inefficiencies in the crusher overpower the efficiency gains
by the drier. The most efficient small scale plant would include the 11kW
coal bar machine instead of the "high efficiency" 15kW one.

This message is intended to give ballpark figures for the energy cost of
producing biochar using a sample of COTS equipment specifications. It
does not represent an endorsement or criticism of the vendor by any
agency, department, or program of the United States Government.

Bryce Nordgren