TITLE:
Gasification of plastic waste as waste-to-energy or waste-to-syngas recovery route
AUTHORS:
Anke Brems, Raf Dewil, Jan Baeyens, Rui Zhang
KEYWORDS:
Plastic Waste; Re-Use; Gasification; Syngas; Char; Sustainability; Reaction Rate
JOURNAL NAME:
Natural Science,
Vol.5 No.6,
June
13,
2013
ABSTRACT: The disposal of plastic solid waste (PSW) has become
a major worldwide environmental problem. New sustainable processes have
emerged, i.e. either advanced
mechanical recycling of PSW as virgin or
second grade plastic feedstock, or thermal treatments to recycle the waste as
virgin monomer, as synthetic fuel gas, or as heat source (incineration
with energy recovery). These processes avoid
land filling, where the non-biodegradable plastics remain a lasting
environmental burden. Within the
thermal treatments, gasification and pyrolysis gain increased interest. Gasification
has been widely studied and applied for biomass and coal, with results reported
and published in literature. The application to the treatment of PSW is less
documented. Gasification is commonly
operated at high temperatures (> 600℃ to 800℃) in an air-lean environment
(or oxygen-deficient in some applications): the air factor is generally between
20% and 40% of the amount of air needed for the combustion of the PSW.
Gasification produces mostly a gas phase and a solid residue (char and ashes). The
use of air introduces N2 in the product gases, thus considerably reducing
the calorific value of the syngas, because of the dilution. The paper will
review the existing literature data on PSW gasification, both as the result
of laboratory and pilot-scale research. Processes developed in the past will
be illustrated. Recently, the use of a sequential gasification and combustion
system (at very high temperatures) has been applied to various plastic-containing
wastes, with atmospheric emissions shown to be invariably below the legal
limits. Operating results and
conditions will be reviewed in the paper, and completed with recent own
lab-scale experimental results. These results demonstrate that gasification
of PSW can be considered as a first order reaction, with values of the
activation energy in the order of 187 to 289 kJ/mol as a function of the PSW
nature.