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TOLEDO (SPAIN)GASIFICATION: AN INNOVATIVE APPROACH FOR THE THERMAL TREATMENTOF PLASTIC RESIDUES
V. Wilk1 and H. Hofbauer2
1 Bioenergy2020+ GmbH, Wienerstraße 49, 7540 Güssing, Austria
2 Institute of Chemical Engineering, Vienna University of Technology, Getreidemarkt 9/166, 1060 Vienna, Austria

e-mail: veronika.wilk@bioenergy2020.eu

Abstract
The dual fluidized bed gasification system yields high quality producer gas and reaches high conversion efficiency on smallscale (10-20 MW). In contrast to conventional combustion processes, not only heat and power production is possible, butalso polygeneration by means of chemical synthesis or selective removal of valuable gases. Test runs in the gasification pilot
plant demonstrate that gasification of different plastic residues (plastic from shredder light fraction and polyethylene) isfeasible. The producer gas has high hydrogen, methane and ethylene contents, but also high tar loads have been assessed.
Selective removal of valuable gases is a promising application.

Keywords: steam gasification, dual fluidized bed gasifier, shredder light fraction, polyethylene, polygeneration

1. Introduction
Modern societies generate more and more plastic
residues every year, as the quantity of disposablecommodities increases. The European Union aims toenhance recycling of waste streams and has establisheda waste hierarchy, which gives priority to prevention andrecycling over recovery and disposal [1]. 35% of plastic
residues have been recycled in a material-sensitive way
in Austria in 2008. In the countries of EU27 the share ofmaterial-sensitive recycling of plastics amounts to 30%
owing to initiatives for selective collection [2]. However,plastic residues are most commonly recovered thermallyin waste incineration plants as a part of municipal solidwaste.

2. Materials and Methods
Dual fluidized bed gasification
The dual fluidized bed gasifier has been developed at
Vienna University of Technology. Since 2001 thedemonstration plant of this technology is in operation
successfully in Güssing (Austria). Now the dual fluidized
bed gasifier is commercially available and several
gasifiers at industrial scale are in operation or underconstruction in Europe.
producer gas(CH4, CO, H2, CO2, H2O)

flue gas

heatgasification

combustion

feedstockauxiliaryfuelGasification is an innovative approach for thermal
treatment of plastic residues. The gasification process
has been originally designed for woody biomass andreaches high conversion efficiency on small scale(10-20 MW) [3].
In Figure 1 the principle of the gasification process isillustrated. The main characteristic of this gasification
process is that gasification and combustion take place inspatially divided reactors. Bed material is circulating
between the two reactors. The feedstock is inserted into
the bubbling fluidized bed of the gasification reactor and
it is gasified with steam. Residual ungasified char istransported into the combustion reactor together with thecirculating bed material. There it is combusted with air.
The hot bed material returns to the gasifier and provides
the heat for the endothermic gasification reactions. Thus,
high quality producer gas is yielded, which is rich inhydrogen and virtually free of nitrogen.
100 kW gasification pilot plant
At Vienna University of Technology, a gasification pilot
plant is operated for scientific purposes. It is similar indesign to the Güssing gasifier. Extensive gas analysis
equipment is installed at the pilot plant for measurementof producer gas and flue gas properties.
In order to evaluate the suitability of the gasification
process for the treatment of plastic residues, gasification
experiments are conducted in the pilot plant. Two typesof plastics are investigated: plastics from shredder lightfraction (SLF) and polyethylene.

circulation
steam (bed material, char) air

Fig. 1. Basic principle of the dual fluidized bed gasifierinteriores libro.indd 111

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6th International Symposium on Feedstock Recycling of Polymeric Materials

3. Results and Discussion
Gasification experimentsSLF-plastics is produced in a mechanical sorting plant,
where shredder light fraction from end-of-life vehicles,
plastics from commercial waste and electrical equipment
are processed. It is selected for the experiments,
because it is waste plastics, which also contains
inorganic pollutants and cannot be used in materialsensitive way anymore. Polyethylene is selected,
because it is used very frequently for the production offoils, plastic bags, food packages and other disposable
products. Table 1 summarizes the properties of bothsamples.
Table 1. Properties of SLF-plastics and polyethylene

LCV, kJ/kg
water, wt.-%
ash, wt.-%, dry
volatiles, wt.-%, dry
C, wt.-%, dry
H, wt.-%, dryO, wt.-%, dryN, wt.-%, dry
S, wt.-%, dry
Cl, wt.-%, dry

SLF-plastics
31946
0.87
10.67
79.72
65.00
7.95
13.48
0.93
0.31
1.67

polyethylene
43379
0.00
0.00
>99
85.90
14.08
0.00
0.09
0.00
0.00

During the experiments, the main operational conditions
are kept constant, so that the results are comparable.
The gasification temperature amounts to 850°C and thefuel input is 90 kW. In Table 2 the average producer gas
composition is compiled.
Table 2. Producer gas composition, vol.-% (dry gas)

H2COCO2CH4C2H4
C2H6
C3H8
others

SLF-plastics
45.0
8.1
16.6
21.9
4.8
0.3
0.5
1.7

polyethylene
36.5
7.0
7.8
29.1
14.4
0.7
0.6
3.9

Other gas compounds are light hydrocarbons, such as
C3H6, that are gaseous, but cannot be measured with theinstalled analyzers. The producer gas is rich in H2 andCH4 and has an average lower calorific value of17 MJ/m³ (SLF) and 25 MJ/m³ (PE). As there is nooxygen in polyethylene, the oxygen containing
compounds CO and CO2 are only formed by reaction ofhydrocarbons with steam. C1- to C3-hydrocarbons aredecomposition products of the polymers. Gasification ofpolyethylene yields a considerable amount of its
monomer C2H4. As SLF-plastics contains nitrogen, sulfurand chlorine, also NH3, H2S and HCl are present in theproducer gas. More details on that are available in [4].

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The dual fluidized bed gasifier generates very low
amounts of tars (condensable higher hydrocarbons),
when biomass is gasified (~ 2 g/m³ gravimetric tar, 6 g/m³GC/MS tars). Gasification of plastics yields markedly
higher tar loads (SLF: 38 g/m³ grav. tar, 70g/m³ GC/MStar, PE: 40 g/m³ grav. tar, 121 g/m³ GC/MS tars).
Producer gas application
In the dual fluidized bed gasification plants the producer
gas is combusted in gas engines for heat and power
production. Therefore, two stage-producer gas cleaning
is implemented, which consists of a bag filter and anorganic solvent for tar removal. If plastic residues aregasified, the tar scrubber has to be adapted to the hightar loads. According to the concentration of nitrogen in
the fuel and the emission limit values, removal of NH 3
may be mandatory.
In contrast to conventional combustion processes, where
only heat and electricity is produced, steam gasification
allows polygeneration. Chemical synthesis converts theproducer gas into synthetic fuels, such as FischerTropsch diesel, methanol, etc. [6] By means ofmembrane separation processes, gas compounds suchas hydrogen or methane can be separated selectively. [7]The producer gas from gasification of plastic residues
appears to be well-suited for selective separation of CH4
because of the high methane yield. In consequence ofthe low CO and CO2 concentration, steam reforming of
the producer gas would be necessary to adjust theH2/CO ratio for other syntheses processes.

4. Conclusions
Test runs in the dual fluidized bed gasification pilot plantdemonstrate that gasification of different plastic residues
is feasible. The producer gas cannot only be used forheat and power production, but also in polygeneration
processes. With appropriate gas cleaning (tar removal),
the selective separation of valuable gas compounds is apromising application.

References[1] Directive 2008/98/EC of the European Parliament andof the Council of 19 November 2008.
[2] Eurostat Database on Environment (09/01/2011)[3] H. Hofbauer, R. Rauch, G. Loeffler, S. Kaiser, E.
Fercher, H. Tremmel; In: Proc.12th European Biomass
Conference, pp.982-985, Amsterdam, (2002).
[4] V. Wilk, S. Kern, H. Kitzler, S. Koppatz, J. C. Schmid,
H. Hofbauer: In: Proc. Internat. Conf. PolygenerationStrategies, Vienna (2011).
[6] M. Kaltschmitt, H. Hartmann, H. Hofbauer eds:
Energie aus Biomasse. Berlin, Springer (2009).
[7] T. Mayer, A. Makaruk, N. Diaz, K. Bosch, M. Miltner,M. Harasek, H. Hofbauer, In: Proc. Intern. Conf.
Polygeneration Strategies, Leipzig (2010).

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