14
[76]. The feedstock composition and the process parameters influence the type of
pyrolysis chemical mechanisms in the reactor, but the reactions taking place are a
combination of depolymerization, rearrangement, breaking and dehydration [78].
Bio-oil production through fast pyrolysis has some benefits such as high thermal
efficiency, atmospheric pressure conditions and the simplicity of the operation [79].
This pyrolytic liquid can be applied as an energy vector or for production of chemical compounds [80]. The secondary products of fast pyrolysis (solid residue and gas
fraction) are also considered to be valuable materials for heat and power generation [80].
5.1 Comparison Between Slow, Intermediate
and Fast Pyrolysis
Products from the intermediate process present different properties compared to the
slow and fast pyrolyses. Intermediate and slow pyrolyses are the most appropriate
methods to produce biochar, while intermediate pyrolysis provides shorter solid
residence times [73]. Additionally, slow pyrolysis is a restricted method mainly
applied for the formation of char, and it is hardly seen to produce bio- oil [75].
The main difference between intermediate and fast pyrolysis technologies is the
solid residence times which produce a dissimilar heat transfer to the materials.
Intermediate pyrolysis enhances the components’ thermal cracking and conducts a
superior control of the chemical reactions, thus improving the physicochemical
properties of biofuel [81]. Intermediate pyrolysis bio-oil showed a low level of tars,
ashes and viscosity, and it led to a more natural separation between the aqueous
phase and organic phase, which is in contrast with fast pyrolysis bio-oil [75, 82].
Another limitation of fast pyrolysis is the processing of different feedstocks,
which need to have low water contents and fine particle sizes when processed by a
fluidized bed reactor [83]. This process requires extra filters and post-cyclones to
extract the dust and char present in the pyrolysis gases. Furthermore, fast pyrolysis
is only well succeeded in converting woody feedstocks, and normally the bio-oil
produced is rich in ashes, water, tars and acids [54, 84].
The benefits of mixing biochar with fresh biomass were proven via intermediate
pyrolysis. The extended residence time of the solid residue has a catalytic effect in
the bio-oil quality, increasing the calorific value, producing lighter organic compounds (mostly aromatics such as toluene, benzene and ethylbenzene and olefins)
and reducing the moisture content and viscosity [74, 83]. Intermediate pyrolysis
biochar, bio-oil and gas have suitable physical and chemical properties which can
be applied as energy vectors.
The biochar can be applied as a solid fuel in combustion and gasification plants
to produce power and heat [75]. It can also be an optimum soil fertilizer/conditioner
(depending on feedstock), which can sequester carbon from the soil [85]. The biooil showed a low level of water, oxygen, viscosity and tar, hence a suitable fuel to
H. Jahangiri et al.
[76]. The feedstock composition and the process parameters influence the type of
pyrolysis chemical mechanisms in the reactor, but the reactions taking place are a
combination of depolymerization, rearrangement, breaking and dehydration [78].
Bio-oil production through fast pyrolysis has some benefits such as high thermal
efficiency, atmospheric pressure conditions and the simplicity of the operation [79].
This pyrolytic liquid can be applied as an energy vector or for production of chemical compounds [80]. The secondary products of fast pyrolysis (solid residue and gas
fraction) are also considered to be valuable materials for heat and power generation [80].
5.1 Comparison Between Slow, Intermediate
and Fast Pyrolysis
Products from the intermediate process present different properties compared to the
slow and fast pyrolyses. Intermediate and slow pyrolyses are the most appropriate
methods to produce biochar, while intermediate pyrolysis provides shorter solid
residence times [73]. Additionally, slow pyrolysis is a restricted method mainly
applied for the formation of char, and it is hardly seen to produce bio- oil [75].
The main difference between intermediate and fast pyrolysis technologies is the
solid residence times which produce a dissimilar heat transfer to the materials.
Intermediate pyrolysis enhances the components’ thermal cracking and conducts a
superior control of the chemical reactions, thus improving the physicochemical
properties of biofuel [81]. Intermediate pyrolysis bio-oil showed a low level of tars,
ashes and viscosity, and it led to a more natural separation between the aqueous
phase and organic phase, which is in contrast with fast pyrolysis bio-oil [75, 82].
Another limitation of fast pyrolysis is the processing of different feedstocks,
which need to have low water contents and fine particle sizes when processed by a
fluidized bed reactor [83]. This process requires extra filters and post-cyclones to
extract the dust and char present in the pyrolysis gases. Furthermore, fast pyrolysis
is only well succeeded in converting woody feedstocks, and normally the bio-oil
produced is rich in ashes, water, tars and acids [54, 84].
The benefits of mixing biochar with fresh biomass were proven via intermediate
pyrolysis. The extended residence time of the solid residue has a catalytic effect in
the bio-oil quality, increasing the calorific value, producing lighter organic compounds (mostly aromatics such as toluene, benzene and ethylbenzene and olefins)
and reducing the moisture content and viscosity [74, 83]. Intermediate pyrolysis
biochar, bio-oil and gas have suitable physical and chemical properties which can
be applied as energy vectors.
The biochar can be applied as a solid fuel in combustion and gasification plants
to produce power and heat [75]. It can also be an optimum soil fertilizer/conditioner
(depending on feedstock), which can sequester carbon from the soil [85]. The biooil showed a low level of water, oxygen, viscosity and tar, hence a suitable fuel to
H. Jahangiri et al.