Biomass Pyrolysis

Introduction- Carefully controlled reaction temperature of around
Pyrolysis is the thermal decomposition of biomass500oC in the vapour phase
occurring in the absence of oxygen. It is the- Residence time of pyrolysis vapours in the reactor
fundamental chemical reaction that is the precursorless than 1 sec
of both the combustion and gasification processes- Quenching (rapid cooling) of the pyrolysis vapours
and occurs naturally in the first two seconds. Theto give the bio-oil product.
products of biomass pyrolysis include biochar, bio-oilUses of Bio-Oil
and gases including methane, hydrogen, carbonBio-oil is a dark brown liquid and has a similar
monoxide, and carbon dioxide.  Depending on thecomposition to biomass. It has a much higher density
thermal environment and the final temperature,than woody materials which reduces storage and
pyrolysis will yield mainly biochar at low temperatures,transport costs. Bio-oil is not suitable for direct use in
less than 450 0C, when the heating rate is quitestandard internal combustion engines. Alternatively,
slow, and mainly gases at high temperatures, greaterthe oil can be upgraded to either a special engine fuel
than 800 0C, with rapid heating rates. At anor through gasification processes to a syngas and
intermediate temperature and under relatively highthen bio-diesel. Bio-oil is particularly attractive for
heating rates, the main product is bio-oil.co-firing because it can be more readily handled and
Pyrolysis can be performed at relatively small scaleburned than solid fuel and is cheaper to transport and
and at remote locations which enhance energystore.  Co-firing of bio-oil has been demonstrated in
density of the biomass resource and reduce350 MW gas fired power station in Holland, when 1%
transport and handling costs.  Heat transfer is aof the boiler output was successfully replaced. It is in
critical area in pyrolysis as the pyrolysis process issuch applications that bio-oil can offer major
endothermic and sufficient heat transfer surface hasadvantages over solid biomass and gasification due to
to be provided to meet process heat needs.the ease of handling, storage and combustion in an
Pyrolysis offers a flexible and attractive way ofexisting power station when special start-up
converting solid biomass into an easily stored andprocedures are not necessary. In addition, bio-oil is
transported liquid, which can be successfully used foralso a vital source for a wide range of organic
the production of heat, power and chemicals.compounds and speciality chemicals.
Feedstock for PyrolysisImportance of Biochar
A wide range of biomass feedstocks can be used inThe growing concerns about climate change have
pyrolysis processes. The pyrolysis process is verybrought biochar into limelight. Combustion and
dependent on the moisture content of thedecomposition of woody biomass and agricultural
feedstock, which should be around 10%. At higherresidues results in the emission of a large amount of
moisture contents, high levels of water are producedcarbon dioxide. Biochar can store this CO2 in the soil
and at lower levels there is a risk that the processleading to reduction in GHGs emission and
only produces dust instead of oil. High-moisture wasteenhancement of soil fertility. In addition to its
streams, such as sludge and meat processing wastes,potential for carbon sequestration, biochar has
require drying before subjecting to pyrolysis.several other advantages.
The efficiency and nature of the pyrolysis process is- Biochar can increase the available nutrients for plant
dependent on the particle size of feedstocks. Mostgrowth, water retention and reduce the amount of
of the pyrolysis technologies can only process smallfertilizer by preventing the leaching of nutrients out
particles to a maximum of 2 mm keeping in view theof the soil.
need for rapid heat transfer through the particle. The- Biochar reduces methane and nitrous oxide
demand for small particle size means that theemissions from soil, thus further reducing GHGs
feedstock has to be size-reduced before being usedemissions.
for pyrolysis.- Biochar can be utilized in many applications as a
Types of Pyrolysisreplacement for other biomass energy systems.
Pyrolysisprocesses can be categorized as slow- Biochar can be used as a soil amendment to
pyrolysis or fast pyrolysis. Fast pyrolysis is currentlyincrease plant growth yield.
the most widely used pyrolysis system. SlowConclusions
pyrolysis takes several hours to complete and resultsBiomass pyrolysis has been attracting much attention
in biochar as the main product. On the other hand,due to its high efficiency and good environmental
fast pyrolysis yields 60% bio-oil and takes secondsperformance characteristics. It also provides an
for complete pyrolysis. In addition, it gives 20%opportunity for the processing of agricultural residues,
biochar and 20% syngas.  Fast pyrolysis processeswood wastes and municipal solid waste into clean
include open-core fixed bed pyrolysis, ablative fastenergy. In addition, biochar sequestration could make
pyrolysis, cyclonic fast pyrolysis, and rotating corea big difference in the fossil fuel emissions worldwide
fast pyrolysis systems. The essential features of aand act as a major player in the global carbon market
fast pyrolysis process are:with its robust, clean and simple production
- Very high heating and heat transfer rates, whichtechnology.
require a finely ground feed.