4. Conversion technology
These technologies can be defined by three types
of conversion processes:
1) Biochemical
2) Physiochemical
3) Thermochemical
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5. Biochemical conversion
It include …
Anaerobic digestion (occurs in controlled reactors or
digesters and also in a less controlled environment in
landfills)
Anaerobic fermentation (for example, the conversion
of sugars from cellulose to ethanol)
Biochemical conversion proceeds at lower temperatures
and lower reaction rates than other conversion
processes.
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6. Physiochemical conversion
It include …
Transesterification (biodiesel production)
Physical and chemical synthesis of products from
feedstock
It is primarily associated with the transformation of
fresh or used vegetable oils, animal fats, greases, tallow
and other suitable feedstocks into liquid fuels or
biodiesel.
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8. Gasification
Partial oxidation process using air, pure
oxygen, oxygen enriched air, hydrogen, or
steam.
Produces electricity, fuels (methane, hydrogen, ethanol,
synthetic diesel), and chemical products
Temperature > 700oC
More flexible than incineration, more technologically
complex than incineration or pyrolysis, more public
acceptance
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9. Pyrolysis
Thermal degradation of carbonaceous materials.
Lower temperature than gasification (400 – 700oC)
Absence or limited oxygen
Products are pyrolitic oils and gas, solid char
Distribution of products depends on temperature
Pyrolysis oil used for (after appropriate post-treatment)
liquid fuels, chemicals, adhesives, and other products
A number of processes directly combust pyrolysis gases,
oils, and char
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10. Waste Incineration
Energy recovery through complete oxidation
• Volume and weight reduced (approx. 90% vol. and 75%
wt reduction)
• Waste reduction is immediate, no long term residency
required
• Destruction in seconds where LF requires 100s of years
• Incineration can be done at generation site
• Air discharges can be controlled
• Ash residue is usually non-putrescible, sterile, inert
• Small disposal area required
• Cost can be offset by heat recovery/ sale of energy
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11. Thermochemical conversion
It is characterized by higher temperatures and
faster conversion rates.
Best suited for lower moisture feedstock.
Thermochemical routes can convert the entire
organic (carbon) portion of suitable feedstocks.
Inorganic fraction (ash) of a feedstock does not
contribute to the energy products but may
increased nutrient loading in wastewater
treatment and disposal facilities.
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12. Environmental and Other Benefits
Products and benefits from conversion
technologies will differ based on the
technology used and the feedstock
converted.
The following discusses products and
benefits derived by type of conversion
process.
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13. Environmental and Other
Benefits
Thermochemical conversion processes such as
gasification, pyrolysis and incineration can
remove materials from the solid waste stream
and can also create:
1) liquid fuels such as biodiesel, ethanol and oil
2) electricity, heat and steam from combustible
gases such as methane
3) chemicals and consumer products from oils and
syngas
4) activated carbon for the food processing
industry
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14. Carbon and Energy Considerations
Tonne of waste creates 3.5 MW of energy
during incineration (eq. to 300 kg of fuel oil)
powers 70 homes.
Biogenic portion of waste is considered CO2
neutral (tree uses more CO2 during its lifecycle
than released during combustion).
Unlike biochemical conversion processes,
nonbiogenic CO2 is generated Should not
displace recycling.
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