Environmental Engineering Reference
In-Depth Information
Apart from syngas, significant amount of pollutants such as tar and polycyclic
aromatic hydrocarbons (PAHs) are also generated from the gasification process.
This is one of the most significant technical barriers to its commercialization [60].
3.3.4
Pyrolysis
Pyrolysis is a thermal treatment that decomposes organic biomass into low-
molecular-weight liquid, solid, and gaseous products in the absence of air or
oxygen. The process is conducted in the absence of air to prevent the combustion
of biomass into carbon dioxide. The liquid fraction obtained at the end of pyrolysis
refers to pyrolysis oil or bio-oil. It is a mixture of hydrophilic organics, water, and
tars [61]. Bio-oil can be used directly as fuel to generate heat or electricity through
a turbine or a boiler. However, due to its poor purity, low heating value, incompat-
ibility with conventional fuels, high viscosity, incomplete volatility, and chemical
instability [62, 63], its direct application as engine fuel is restricted. With further
upgrading processes to purify, condition, and deoxygenate, bio-oil could poten-
tially be used as transportation fuel, generating much interest from industry.
FigureĀ 3.10 shows the potential applications of bio-oil as raw materials for fuels
and chemicals production. The remaining solid of pyrolysis refers to as bio-char
orĀ charcoal consists of around 85% carbon [65]. Bio-char is usually returned to
the ground for soil remediation. The gas fraction consists mainly of CO, CO 2 , H 2
and CH 4 . Forestry residues and agricultural by-products such as wood residue,
plant stalks, rice shells, or corn stovers are the commonly used renewable feed-
stock in pyrolysis [66].
Extraction
Chemicals
Furnace
Heat
Electricity/
CHP
Bio-oil
Boiler
Steam turbine
Gas turbine
Engine
Upgrading
Tr ansport fuel
Figure 3.10 Potential applications of bio-oil after further upgrading. Reproduced from [64],
with permission from Elsevier.
 
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