Environmental Engineering Reference
In-Depth Information
9.2.3.2 Plasma Arc Gasification
A recent development is the plasma-assisted gasification that volatilizes
the waste at very high temperatures in an oxygen-deficient environment
yielding syngas efficiently (Hrabovsky, 2011; Zhang et al., 2012). Plasma
torches that produce arcs (>7000°F are reached in the plasma) are used as
the heat source, and the temperature can usually be controlled regardless
of variations in the feed stream. Because of the higher temperatures, even
waste with high levels of moisture can be used as feedstock. It is an efficient
and environmentally-benign gasification technology as only syngas and a
vitreous slag residue (sometimes used as aggregate in concrete) are
produced. Slag temperatures are around 3000°F and therefore no
potentially toxic organic residues are present in the slag. Both air emissions
(Zhang et al., 2013) as well as slag toxicity (Lapa et al., 2002) are minimal.
However, the capital cost for plasma-arc gasifiers is relatively high and
explainswhynocommercialfacilitiesareinoperationintheUnitedStatesat
this time. The need to shred the waste feedstock and high operational costs
are the other disadvantages of the process.
Table 9.5
summarizes the main
features of the thermal treatment methods applicable to plastics waste.
