Pyrolysis
What is Pyrolysis?
Pyrolysis of woody biomass is an
endothermic thermo-chemical process, which
needs heat to occur. Similar to gasification,
pyrolysis causes heat and chemical reactions
to take place, simultaneously changing the
chemical composition and physical phase of
the fuel. Pyrolysis actually takes place during
the gasification process. However, pyrolysis
is different from gasification and other hightemperature processes because it does not
involve reactions with other reagents such as
oxygen or steam, and the products formed
are different.
The process of pyrolysis is commonly used
in the chemical industry to produce charcoal,
activated carbon, methanol, and other
chemicals from wood and to convert biomass
into syngas and bio-char.
How Pyrolysis Works?
Pyrolysis takes place under various controlled
conditions within different pyrolysis reactors
(e.g., bubbling fluidized bed, circulating
fluidized beds, rotating cone pyrolyzer
etc.). The methods and feedstocks used in
pyrolysis depend on the desired products.
The process can be made quite efficient as a
portion of the fuels produced can be used to
provide all of the necessary energy to drive
the reaction. There are two main types of
pyrolysis:
Fast Pyrolysis: Utilizes woody feedstocks,
which have been ground to relatively small
particles >3mm and dried to a low moisture
content of 10% or less. Fuel is then subjected
to temperatures of 400-500°C or higher
for a very short time of between 0.5 to 2
seconds. The high temperature and oxygen
starved environment within the pyrolysis
chamber cause the organic matter to
thermally decompose. The chemical bonds
of the material break down at a very fast
rate changing the physical state of the fuel.
Separation occurs as the solids, liquids, and
gases produced separate and by-products
are formed. Typical product yields from fast
pyrolysis are about 60-70% bio-oil, 12-15%
char, and 13-25% gas.
Slow Pyrolysis: Also known as carbonization
begins between 200-400°C. Woody fuel is
placed into the pyrolysis chamber where
it stays for minutes, hours, or even days.
Depending on the system, feedstocks
used may be larger than those used in fast
pyrolysis. Size, moisture content, feedstock
type and length of time the fuel is left in the
reactor will all depend on the desired yields.
Products of slow pyrolysis differ from fast
pyrolysis because the lower temperature and
longer exposure time favor the formation of
solids. This method creates larger quantities
of bio-char (activated carbon), although gas
and bio-oil are also produced.
Pyrolysis
Benefits of Pyrolysis
• Pyrolysis uses biomass
to produce bio fuels, which
help to mitigate the effects
of global warming by
reducing use of fossil fuels.
• Promoting good forestry
practices by building up
new forest industry and
technologies benefits
communities and the
environment.
• Pyrolysis facilities can
achieve high efficiency
rates by generating heat
and power from their own
processes.
• Pyrolysis plants are made up of units,
which can be changed to deal with available
waste streams or feedstocks (e.g., wood
chips or farm waste). This flexibility allows
for advantageous adaptation to industry
changes.
• The pyrolysis process produces multiple
useful products, much like the petroleum
industry. This value added product stream
maximizes the benefits of biomass use.
• Char, oil and gas are comparable to
naturally occurring fossil fuels in terms of
composition and formation process, and can
be excellent substitutes for fossil fuels.
• Bio-char produced from pyrolysis improves
soil health by increasing its ability to retain
fertilizers and release them slowly. It also
contains many micronutrients needed by
plants. It is safer than manure and sewage
since it has been disinfected at high
temperatures. When used as fertilizer biochar acts as a carbon sink, sequestering
carbon in the ground and helping to mitigate
climate change.
• Bio-char releases nutrients at a slow rate
and greatly reduces the risk of water table
contamination when used as a fertilizer.
• Liquid bio-oil produced from pyrolysis is
similar to synthetic diesel fuel and can be
used as a fuel.
• Bio-oil has a fuel value that is 50-70% that
of petroleum based fuels making it more cost
effective to transport than raw biomass. Biooil can also be used in boilers or upgraded to
a transportation fuel.
Information Sources:
US Department of Agriculture (2010) Biomass
pyrolysis research: what is pyrolysis? Retrieved May
24, 2012, from http://www.ars.usda.gov/Main/docs.
htm?docid=19898
Kansas State University (2011) Sustainable Energy
Research Experience for Undergraduates. Retrieved
May 25, 2012, from http://sustainable-energy.ksu.edu/
REU/S11/jmarkham/index_background_info.html
Wise Geek.com (n.d) What is pyrolysis? Retrieved
May 25, 2012, from http://www.wisegeek.com/what-ispyrolysis.htm
Friends of the Earth (2009) Pyrolysis, gasification and
plasma. Retrieved May 25, 2012, from http://www.foe.
co.uk/resource/briefings/gasification_pyrolysis.pdf