5-7 OCTOBERISFR2011

99

TOLEDO (SPAIN)

AIR GASIFICATION OF MIXED PLASTIC WASTES USING A TWO-STAGE GASIFIERFOR THE PRODUCTION OF A PRODUCER GAS WITH LOW TAR AND A HIGHCALORIC VALUE
Joo-Sik Kim, Jin-Won Kim and Tae-Young Mun
Faculty of Energy and Enviromental System Engineering., Univ. of Seoul, 90 JeonnongǦDong,
DongdaemunǦGu, Seoul 130Ǧ743, Republic of KoreaEǦmail: joosik@uos.ac.kr

Abstract
Air gasification was conducted with a fraction of mixed plastic wastes in a newly developed two-stage gasifier. In this work,
the influence of equivalence ratio on the producer gas composition and tar removal were investigated. In addition, the effectsof activated carbon and dolomite were also examined. At an equivalence ratio of 0.21, a very clean producer gas wasobtained with a LHV of 13.44MJ/Nm3. Activated carbon showed a better tar removal efficiency than dolomite. The amount ofadditive had significant effects on the tar removal efficiency and hydrogen production. When 640 g of activated carbon wasapplied, the total tar production was about 2.5 times less and H2 production 2 times higher than without activated carbon.

Keywords: Air Gasification; Mixed plastic wastes; Tar; Two-stage gasifier; Activated carbon

1. Introduction
The traditional ways of plastic wastes disposal have been
to either bury or burn them in landfills and incinerators,
respectively. Landfills and incineration, however, areassociated with serious environmental problems.[1].
Plastics recycling can be divided into three methods:
mechanical recycling, feedstock (or chemical) recycling
and energy recovery [2]. Feedstock recycling, whichconverts plastic materials into useful basic chemicals,has been recognized as an advanced technology
process. Gasification is one example of these feedstock
recycling technologies, which converts carbonaceous
materials into a combustible gas, referred to as producergas. Producer gas can be applied for heating and power
generation. One main obstacle that needs to overcome
with gasification is the problem associated with theproduction of tar. In particular, plastic gasification
generates a huge amount of tar [3], which can cause
environmental and operational problems. Fundamentally,
there are two methods for the removal of tar: primarymethods, where measurements are taken from thegasifier itself, and secondary methods, wheremeasurements are taken downstream [4]. In the present
study, a fraction of post-consumed mixed plastic wastes
was gasified in a newly developed two-stage gasification
process. This study aimed to create a producer gas with
low tar and high LHV by applying additives in a newly
developed two-stage gasifier.

2. Materials and Methods
Material. A recycling center in Korea provided a fractionof pellet-type post-consumed mixed plastic wastes. Thefeed material was firstly ground and successively sieved

interiores libro.indd 99

to obtain materials with diameters between 0.85-2 μm
and 2-3.35 μm, respectively. In each experiment, 300 gof the feed material was applied.
Gasfier and experimental procedure Fig. 1 shows thegasification plant.

Figure 1. Schematic diagram of the two-stage
gasification plant
The gasifier is divided into two parts; namely, the bottom
reactor and the upper reactor, which are heatedseparately using electricity furnaces. The bottom reactor
is filled with silica sand, which serves as a fluidized bed
material. The upper reactor is filled with activated carbon
or dolomite, which is used for tar cracking. The tworeactors
Reaction conditions. Table 1 shows the reaction
parameters. Experimental Runs 1–4 were performed toinvestigate the effect of the ER. The results of Runs 1and 5-9 were conducted to observe the effects of theamount of activated carbon or dolomite on the producer
gas composition and tar removal. The results of Runs 8

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6th International Symposium on Feedstock Recycling of Polymeric Materials

and 9 were compared with Runs 1 and 6, respectively, tocompare the effects of activated carbon or dolomite on
the producer gas properties.

cracking can be enhanced by the presence of activatedcarbon.

Table 1. Reaction conditions
Parameter Run1 Run2
Upper
806
800
reactor (˚C)
Bottom
798824
reactor (˚C)
Feed rate
7.14
5.77(g/min)
ER
0.21
0.26
430a
Additive(g) 430a
Parameter Run6 Run7Upper
802798reactor (˚C)
Bottom804
819
reactor (˚C)
Feed rate
7.5
7.31(g/min)
ER
0.2
0.21
0Additive(g) 640aa: activated carbon d:dolomite

Run3803

Run4804

Run5797825827795

4.84

2.4

7.31

0.31430a
Run88000.62430a
Run9794

0.21500a

819

817

7.31

7.31

0.21
430d

0.21640d

Fig. 3. Total tar yield at various ERs andwith activated carbon (AC) and dolomite (D).
In Fig. 3, the following facts can be observed: 1) the total
amount of tar rapidly decreases at higher ERs, especiallyat an ER of 0.62 (Run4), due to the strengthenedoxidization reactions. 2) When the amount of activatedcarbon increases, the total amount of tar decreases
steeply from 50.99 g (Run7) to 19.95 g (Run6), due tothe strengthened tar adsorption followed by tar cracking.
3) The total amount of tar generated, when activatedcarbon is applied (Runs 1 and 6), is smaller than when
dolomite is applied (Runs 8 and 9). Therefore, activatedcarbon seems to be more effective for tar removal thandolomite.

3. Results and Discussion
20
H2

Gas composition (vol.%)

CO
CO2
CH415

C2H6

4. Conclusions

C2H4
C3+C4+C5
Benzene10500.210.26

0.310.61a)

ER25
H2COCO2

Gas composition (vol.%)

20

CH4C2H6C2H415C3+C4+C5Air gasification of a fraction of mixed plastic wastes wasconducted to yield a clean and high caloric producer gas.
The maximum LHV of the producer gas was about 14.5
MJ/Nm3. At higher ERs, an increase in the CO2
concentration, and decreases in the concentrations of H2,
CO, CH4 and hydrocarbons were observed. It wasrevealed that activated carbon was superior to dolomite
for tar removal. The amount of additive was also animportant factor for efficient tar removal. In addition to thereduction of tar, the use of activated carbon realized ahigh production of H2.

BenzeneReferences

10500430500

Activated carbon(g)640b)

Fig. 2. Effects of (a) ER and (b) the amount of activatedcarbon on the producer gas composition.
In Fig. 2(a), with increasing ER, the variation in the H2concentration is not significant. The CO concentration
decreases from 6.56 to 5.01 vol.% and that of CH4
decreases steeply from 15.7 to 3.64 vol.%. In Fig. 2 (b),the most notable result is the increased H2 production.
The tar-cracking reactions produce hydrogen, and tarinteriores libro.indd 100[1] Pohorely M, Vosecky M, Hejdova P. Gasification ofcoal and PET in fluidized bed reactor. Fuel 2006; 85:2458-2468.
[2] Siddique R, Khatib J, Kaur I. Use of recycled plastic in
concrete: A review. Waste Manage 2008; 28: 1835-1852.
[3] Arena U, Zaccariello L, Mastellone ML. Tar removal
during the fluidized bed gasification of plastic waste.
Waste Manage 2009; 29: 783-791.
[4] Devi L, Ptasinski KJ, Janssen FJJG. A review of theprimary measures for tar elimination in biomass
gasification processes. Biomass Bioenergy 2003; 24:125-140.

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