(best examples and good practices) on household organic waste ...

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below pyrolysis temperatures where the bulk of the hydrocarbon gases are
formed. It is therefore possible to cleave most of the chlorine from PVC at a
temperature just above 300°C <strong>and</strong> collect it separately. As not all the chlorine
will be removed in this way, further treatment is needed.
Ammonia can be added as an alternative to lime <strong>and</strong> this forms ammonium
chloride. Ammonium chloride is less of a problem in a fluidized bed. Pyrolysis
of mixed plastics produces oils that typically contain between 50 <strong>and</strong> 500 ppm
organic-bound chlorine. Fortunately no chlorinated dibenzodioxins can be
detected in the organochlorides.8 If the feed stock initially contains dioxins
then fluidized bed pyrolysis at 700°C will reduce levels by about 75%. For the
produced oils to be acceptable for use by a petrochemical plant, the levels of
organ chlorides would need to be less than 10 ppm. This can be achieved by
introducing sodium vapor to the syngas at 500°C.
3.2.6. Gasification
Gasification involves heating carbon rich waste in an atmosphere with slightly
reduced oxygen concentration. The majority of carbon is converted to a
gaseous form leaving an inert residue from break down of organic molecules.
Gasification is a thermo chemical process involving several steps. First,
carbonaceous material is dried to evaporate moisture. Depending on the
process, pyrolysis then takes place in a controlled, low air environment in a
primary chamber, at around 45 0 C, converting the feedstock into gas, vaporized
liquids <strong>and</strong> a solid char residue. Finally gasification occurs, in a secondary
chamber at between 700-1000 o C (dependent on gasification reactor type). Here
the pyrolysis gases <strong>and</strong> liquids <strong>and</strong> solid char undergo partial oxidation into a
gaseous fuel, comprising a variety of gases (dependent on reactor configuration
<strong>and</strong> oxidant used). These gases include carbon monoxide, carbon dioxide,
hydrogen, water, <strong>and</strong> methane (<strong>and</strong> much smaller concentrations of larger
hydrocarbon molecules, such as ethane/ethane). Oils, ash tars <strong>and</strong> small char
particles are also formed in the reaction, acting as contaminants. The heat
source for the gasification process can be heated coke. Superheated steam can
also be injected at this point to facilitate the conversion into gaseous fuel.
Process description varies for different specific technologies <strong>and</strong> is generally
patented. The conversion process can utilize air, oxygen, steam or a
combination of these gases. Gasification using air the most widely used
technique produces a fuel gas suitable for boiler/engine use, but it is difficult
to transport in pipelines. Nitrogen is evolved since air is used in the oxidation
process.