By Hamza Zahid
(19-CHE-18)
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The term “conversion technology”
encompasses a broad range of technologies
used to convert solid waste into useful
products, chemicals and fuels. Conversion
technology facilities represent the next
evolutionary step of solid waste material
recovery systems, diverting organic (carboncontaining) solid wastes from the traditional
disposal activities of landfilling and Municipal
Solid Waste combustion.
Conversion technology facilities can use a
number of process technologies, including:
anaerobic digestion, gasification, pyrolysis,
thermal depolymerization and
transesterification. These technologies can
be defined by three types of conversion
pathways or processes:
1) Biochemical
2) Thermochemical
3) Physiochemical.
All three pathways use or demonstrate
using separated organic solid wastes
(sometimes in combinations with industrial
or petroleum refining residues).
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Types of Conversion Pathways:
 1)
Biochemical
 2) Thermochemical
 3) Physiochemical
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This Process involves high-temperature
chemical reformation process which requires
bond breaking and reforming of organic
matter into biochar (solid), synthesis gas and
highly oxygenated bio-oil (liquid).
Within thermochemical conversion, there are
three main process alternatives available that
are gasification, pyrolysis, and liquefaction.
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Gasification is basically a thermochemical
process which converts biomass materials
such as forest and agriculture waste into
gaseous components that can be used in
various applications.
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Pyrolysis is thermal decomposition of
biomass that takes place in the absence of
oxygen with operating temperature ranges
from 350 to 550 °C that could reach up to
700 °C. Pyrolysis process decomposes
organic materials into solid,liquid and gas
mistures
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Thermochemical liquefaction process involves
the production of bio-oil at low temperature
and elevated pressure with or without catalyst
in the presence of hydrogen.
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Biochemical conversion encompasses the
utilization of the yeast and or specialized
bacteria yeast to convert biomass or waste
into useful energy. The classical process
options are:
Anaerobic digestion
Alcoholic fermentation and
Photobiological techniques which lead to
different biofuels produced.
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Anaerobic digestion is a sequence of
processes by which microorganisms break
down biodegradable material in the absence
of oxygen. The process is used for industrial
or domestic purposes to manage waste or to
produce fuels
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Gasification:
Gasification is done in
the presence of air
The advantageous of
the gasification
are: high carbon
conversion, higher
calorific value than the
combustible gases
derived from pyrolysis
of the syngas
Advantageous Method
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Pyrolysis:
Pyrolysis is done in the
absence of air
Low carbon conversion
Low calorifc value
Syngas Produced
Less Advantageous
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Pyrolysis:
At low pressure and high
temprature
Conversion yields up to
60% were obtained for
pyrolysis at 550 °C.
The best energy
conversion rates were
83% for pyrolysis.
Product ; Pyrolysis oil
Less Advantageous
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Hydrothermal
Liquifaction:
At low temprature and
high pressure
Conversion yields up to
67% were obtained for
HTL at 220 °C.
The best energy
conversion rates were
90% for HTL
Product; Bio-oil
More Advantageous