Production of
biochar could
theoretically
reduce world
greenhouse
gas emissions
by … about
12 percent.
directly to produce electric power, as assumed by Woolf
et al., that biomass could instead be used in an integrated
gasification/combined-cycle plant, in which carbon diox-
ide is captured during the biomass gasification process
and geologically sequestered.
Such a design could potentially produce highly efficient
electricity and reduce overall greenhouse gases consider-
ably more than either of the two approaches discussed by
Woolf et al. While geologic sequestration of CO2 presents
challenges to avoid leakage, numerous reputable, peer-
reviewed studies and field experiments have concluded
that it is feasible and economic, although it will require
long-term development to be proven on a large scale. Some
who oppose geologic sequestration of carbon dioxide from
coal plants argue that even a leakage rate of only a few per-
cent per century would be unacceptable. But Woolf et al.
assumed a baseline half-life of 300 years for biochar in
the soil. This means that 20 percent of it would enter the
atmosphere in 100 years. Half-life would be reduced if the
biochar-enhanced soil were subjected to conventional till-
ing, which would expose the biochar to air.
Slow pyrolysis for the production of a combination of
biochar and biofuel is clearly not a panacea and will not by
itself solve the greenhouse gas problem. But neither will
any other single energy technology. How much of a role
biochar can play will depend on its long-term effects on soil
productivity and carbon storage and the extent to which
direct energy production (especially including carbon cap-
ture and storage) proves more practical. We need to better
understand the long-term effects of different formulations
of biochar in different soils. We also need a comprehensive
economic and carbon accounting analysis that considers
the transportation and sale of biochar, as well as added prof-
itability resulting from stimulated crop production, and
compares the overall cost-effectiveness of biochar to that
of bioenergy production. Such an analysis should include
sensitivity to future carbon prices.
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