Environmental Engineering Reference
In-Depth Information
9.2.3 Gasification
9.2.3.1 Thermal Gasification
Pyrolysis of mixed waste at a temperature higher than about 600°C in
a controlled atmosphere of air, O
2
, or steam yields a mix of gaseous
oxygenated products (CO, H
2
, and CH
4
) (Aznar et al., 2006; Zia et al.,
2007). As with pyrolysis proper, this process leaves behind a char residue
and yields fuel gas. Plastics are often co-gasified with biomass (Pinto et al.,
2002), coal (Aznar et al., 2006), or wood (van Kasteren, 2006) in mixed
waste streams. The composition of products obtained depends on the mix
of waste used, temperature, and atmosphere as well as the residence time
in the reactor (He et al., 2009). The variability in composition of input
waste streams does not allow gasification or other advanced thermolytic
techniques to deliver a product stream of consistent composition or quality.
Gasification of PE (He et al., 2009), PP (Xiao et al., 2007), and
PET-containing waste streams (Pohorely et al., 2006) has been studied in
some detail. The products include some char, liquid fuel, and fuel gases;
at higher temperatures and longer residence times more of the gaseous
products are obtained.
reactions are also involved in gasification (see for instance de Souza-Santos,
2010), but a detailed discussion of their chemistry is beyond the scope of
this chapter.
