Image via Wikipedia
The growing
concerns about climate change have brought biochar, a charcoal produced from
biomass combustion, into limelight. Biochar is a carbon-rich, fine-grained
residue which can be produced either by ancient techniques (such as covering
burning biomass with
soil and allowing it to smoulder) or
state-of-the-art modern pyrolysis
processes. Combustion and decomposition of woody biomass and agricultural residues
results in the emission of a large amount of carbon dioxide. Biochar can store
this CO2 in the soil leading to reduction in GHGs emission and
enhancement of soil fertility. Biochar holds the promise to tackle
chronic human development issues like hunger and food insecurity, low
agricultural productivity and soil depletion, deforestation and biodiversity
loss, energy poverty, air pollution and
climate change. Thus, biochar could make a difference in the energy-starved
countries of Asia, Africa and Latin America as well as the industrialized world
with its vast array of benefits.
The two main methods
for biochar production are fast pyrolysis and slow pyrolysis. The biochar yield
is more than 50% in slow pyrolysis but it takes hours to complete. On the other
hand, fast pyrolysis yields 20% biochar
and takes seconds for complete pyrolysis. In addition, fast pyrolysis gives 60%
bio-oil and 20% syngas.
Bio-oil is a dark brown liquid and has a similar
composition to biomass. It is composed of a complex mixture of oxygenated
hydrocarbons with an Bio-oil has a much higher density than woody materials
(three to six times, depending on form), which reduces storage and transport
costs. Bio-oil is not suitable for direct use in standard internal combustion
engines. Alternatively, the oil can be upgraded to either a special engine fuel
or through gasification processes to a syngas and then bio-diesel.
Bio-oil is
particularly attractive for co-firing because it can be more readily handled
and burned than solid fuel and is cheaper to transport and store. Since the oil has a density of about 1200 kg m-3, it
can be conveniently transported over long distances. Current end-use
possibilities are as a boiler fuel for stand-alone heat or in combined heat and
power (CHP) using the steam cycle after either diesel or gas turbine
electricity generation. The majority of these options have been found to be
technically feasible. In addition, bio-oil is also a vital source for a wide
range of organic compounds and speciality chemicals.
