Steam Plasma Gasification of Pyrolytic Oil from Used Tires
M. Hrabovsky, M. Konrad, V. Kopecky, M. Hlina, T. Kavka, O. Chumak and A. Maslani
Institute of Plasma Physics ASCR, Praha, Czech Republic
Abstract: Production of syngas by gasification of pyrolysis oil was studied in
plasma reactor with hybrid water/gas plasma torch. High enthalpy steam plasma
was generated in dc arc torch with water stabilized (Gerdien) arc. Reactions of
steam, oxygen and carbon dioxide with oil produced by pyrolysis of used tires
were studied for arc power 110 kW. Syngas with high content of hydrogen and
carbon monoxide and very low content of carbon dioxide and other components
was produced. Very low content of complex hydrocarbons and tar was detected.
For steam gasification, water was added into the reactor together with treated
material, in other experiments CO2 and O2 were supplied as oxidation medium.
Keywords: thermal plasma, plasma gasification, waste treatment, syngas
1. Introduction
Sustainable development in transport includes
proper handling of used tires. The amount of waste
tires in EU, USA and Japan is around 6 million tones
per year and will increase in the future [1]. In EU
countries landfill directive imposes a ban on the
landfilling of tires from the year 2006. Retreading is
environmentally positive solution but not widely
used as the costs of new tires are the same as of
retreaded tires. Recycling by mechanical shredding
and subsequent grinding produces rubber granules.
The process consumes lot of energy and has very
limited market for application. Recovery of energy
by incineration is another possibility (tire derived
fuel), but the process brings problems with
hazardous emissions and subsequent flue gas
cleaning at high capital costs. Also some methods
for rubber reclaiming were developed, but the
products are of poor quality and the costs are similar
to the costs of new rubber.
The mentioned drawbacks of these technologies
have led to research on other possibilities of
recycling. One of the methods is pyrolysis of rubber
from waste tires [2, 3]. The products of pyrolysis are
solid char, liquid pyrolytic oil and synthetic gas. The
pyrolytic products are of poor quality and therefore
investigations on upgrading of properties of these
products are taking place. In this study we have
investigated the possibilities of pyrolytic oil
upgrading by gasification in thermal plasma reactor.
The pyrolytic oil as low grade fuel should be
converted to synthesis gas comprising mainly
hydrogen and carbon monoxide as high grade fuel.
Thermal plasma offers possibility of decomposition
of organic materials by pure pyrolysis in the absence
of oxygen, or with stoichiometric amount of oxygen
added for complete gasification of carbon present in
treated material. Oxygen needed for complete
gasification of materials can be supplied either by
addition of oxygen, air, steam or CO2. Utilization of
air is the cheapest option but it results in dilution of
produced syngas by nitrogen.
In experiments presented in this paper we studied
pyrolytic oil gasification in steam thermal plasma
generated in dc arc torch with water stabilized
(Gerdien) arc. The composition of plasma gas is
suitable for plasma gasification as plasma gas does
not contain gas components which would dilute
produced syngas (mixture of H2 and CO), with the
exception of small amount of argon. Water, carbon
dioxide and oxygen were used as oxidizing media.
2. Experimental system
The plasma gasification reactor (Fig.1) was designed
for operation up to 1700°C wall temperature [4, 5].
The reactor has ceramic lining, the inner volume is
0.206 m3, and the outer steel walls of the reactor are
water cooled with possibility of calorimetric
measurements on cooling circuits. The pyrolytic oil
was fed into the reactor through a nozzle 0.5 mm in
diameter. The oil from a pump with the manual
control of oil flowrate was fed through a hose into
feeding nozzle. Oxygen and carbon monoxide were
supplied directly into the reactor by inputs at the
reactor side, water was injected into the same nozzle
as oil. The output of gas is positioned close to the
plasma input and thus outgoing gas passes high
temperature region with high level of uv radiation.
Gaseous reaction products are fed into the quenching
chamber where their temperature is reduced to 300
0
C in water spray with automatically controlled flow
rate. The gas then flows into the combustion
chamber at the output of the system.
Oil input
nozzle. The produced synthetic gas (syngas) was
quenched in a chamber with water spray.
Table 1. Operation parameters of plasma torch.
Arc current [A]
Arc power [kW]
Steam plasma flow rate [g/s]
Argon plasma flow rate [slm]
Torch efficiency [%]
Mean plasma enthalpy [MJ/kg]
Bulk plasma temperature [K]
400
110
0.3
7
59
129
14 200
The composition of the syngas was measured online
by mass spectrometer Omnistar (Pfeiffer Vacuum)
with mass range 0-100 amu. The selected gases for
monitoring were hydrogen, carbon monoxide,
carbon dioxide, methane, oxygen, and argon.
2. Results and Discussion
Figure 1. Scheme of plasma gasification reactor.
Plasma torch with hybrid gas/water stabilization of
arc [6, 7] was attached at the top of the reactor. The
torch generates an oxygen-hydrogen-argon plasma
jet with extremely high plasma enthalpy and
temperature. Plasma gas is a mixture of steam with
small amount of argon. The values of basic
parameters of plasma torch used in presented
experiments are given in Tab. 1. Due to the principle
of arc stabilization by a water vortex the flow rate of
plasma gas is very low, plasma enthalpy and plasma
temperature is very high. This is the main difference
from gas plasma torches using steam as plasma gas
with temperatures below 8 000 K. The utilization of
high enthalpy, high temperature plasma is
advantageous for the adjustment of a high reaction
temperature and easy control of syngas composition.
The flow rates of oxidizing gases were controlled by
thermal mass flow controllers (Brooks Instrument,
Aalborg). The stream of pyrolytic oil crosses the
plasma jet about 30 cm downstream of the torch
The results of analysis of elemental composition
of the studied pyrolytic oil, made on two samples in
two laboratories, are presented in Tab. 2. The oil
contained more than 21 wt.% of water, the density
was 0.9 kg/l, and the heating value based on Dulong
equation was 42.1 MJ/kg for oil without water and
39.5 MJ/kg for oil with water. From the elemental
composition of the oil follows its molecular formula
C5H8O.
Table 2. Elemental composition of pyrolytic oil.
C [wt.%]
H [wt.%]
S [wt.%]
N [wt.%]
Cl [wt.%]
85.8
10.2
0.72
0.62
8.2 x 10-4
88.18
9.39
1.18
0.85
≤ 5 x 10-3
For the gasification an oxidizing medium was fed
into the reactor in stoichiometric ratio to oxidize the
surplus of carbon to carbon monoxide. Water,
oxygen or carbon dioxide were used, separately, or
in a mixture, according to equations
C5 H 8 O + 4H 2 O → 5CO + 8H 2
(1)
C5 H8O + 4CO2 → 9CO + 4H2
(2)
C 5 H 8 O + 2O 2 → 5CO + 4H 2
(3)
The arc current and power as well as feeding rates of
material and flow rates of oxidizing gases are given
in Tab. 3. The table also shows average temperatures
Tr of inner reactor wall, which was measured at five
positions, and temperature of syngas Tg, measured at
the output tube from the reactor before quenching.
Before each measurement of produced syngas
composition, the reactor was run at least 5 min to
reach steady state output of gas composition
monitoring. Results of measurement of composition
of produced syngas are shown in Tab. 4. The table
does not include concemtrations of argon from the
torch, that were in all cases below 1%. Several
results for same conditions, taken in different times,
are given in Tab. 4 to illustrate stability of the
output. The table presents also low heating values of
produced syngas and yields of carbon gasification,
defined as ratio of carbon content in syngas to total
carbon supplied in treated material and added gases.
In Fig. 2 average values of syngas components
concentrations are shown for cases of gasification
with addition of water, oxygen, carbon dioxide and
mixture of CO2 and O2.
100
90
19
27
80
70
48
58
Vol %
60
H2
CO
54
50
CO2
CH4
53
40
30
O2
47
32
20
10
4
5
0
water
25
16
0.5
3
CO2
0.5
1.5
3
O2
0.2
1.5
0.3
CO2+O2
Oxidation medium
Figure 2. Composition of syngas for various oxidizing media
It can be seen that efficiency of carbon gasification
varied between 0.58 and 0.67 for gasification with
water, the value 0.58 was obtained for gasification
with CO2. The highest efficiency of gasification 0.85
was obtained if oxygen was used as gasification
medium; values 0.68 and 0.77 were obtained for
mixture of CO2 with O2. The heating values of
syngas are high due to high content of hydrogen and
carbon monoxide. Higher content of CO2 and
consequently lower syngas heating values were
obtained in case of gasification with CO2 as
oxidizing gas. The reactor temperatures as well as
syngas temperatures in runs with feeding of O2 were
higher compared to CO2 and water feeding, as in
latter cases part of the input plasma energy is spent
for dissociation of water and CO2. In all cases, no tar
production was detected. This fact was confirmed by
the analyses made in our previous experiments with
steam plasma gasification of organic materials [4, 5].
3. Conclusions
Management of waste tires represents important
environmental issue. The both usual methods of tire
treatment, grinding or combustion have many
drawbacks. The pyrolysis is promising technology
for treatment of waste tires, but techniques for the
upgrade of products of pyrolysis have to be
developed. The plasma gasification of pyrolytic oil
is one of the possibilities as it produces high quality
syngas with high heating value up to 12 MJ/Nm3.
Plasma gasification of pyrolytic oil was studied in
plasma reactor with hybrid water/gas dc arc torch.
High enthalpy, high temperature steam plasma was
generated in the torch with very low plasma flow
rate. Plasma produced from steam does not dilute
produced syngas by other plasma gases. Synthesis
gas with high content of hydrogen and carbon
monoxide, low content of carbon dioxide and
methane, and high heating value was produced when
water or oxygen were used as oxidizing medium. If
carbon dioxide was used for oxidation of surplus of
carbon in the oil, the content of CO2 in produced
syngas was higher. The efficiency of carbon
gasification was 0.6 to 0.7 for gasification with
water and CO2 and 0.9 in case of gasification with
oxygen.
Acknowledgement
The work was supported by the Grant Agency of the
Czech Republic under the project P 205/11/2070.
References
[1] M. Juma et al., Petroleum & Coal 48 (2006), pp.
15-26.
[2] I.M. Rodriguez et al.,
Technology, 72(2001), pp. 9-2.
Fuel
Processing
[3] M.F. Laresgoiti et al., J. Anal. Appl. Pyrolysis
71(2004), pp. 917–934.
[6] M. Hrabovsky et al., IEEE Trans. Plasma
Science, 34 (2006), pp. 1566-1575.
[4] M. Hrabovsky et al., High Temp. Mat. Process.
10 (2006), pp. 557-570.
[7] M. Hrabovsky, Pure and Appl. Chem. 74 (2002),
pp. 429-433.
[5] M. Hlina et al., Czechoslovak J. of Physics, Vol.
56 (2006), Suppl. B, B1179-1184.
Table 3. Torch parameters, reactor and syngas temperatures, and input flow rates.
No. I [A] P[kW] Tr [oC] Tg [oC] oil [kg/h] H2 O [kg/h] CO2 [slm] O2 [slm]
1
400
110
1074
877
8.8
10.6
0
0
2
3
400
400
110
110
1072
1066
876
878
8.8
8.8
10.6
10.6
0
0
0
0
4
400
110
1199
1048
10.6
0
0
92
5
6
400
400
110
110
1194
1208
1042
1059
10.6
10.6
0
0
0
0
92
92
7
8
400
400
110
110
1202
1057
1054
958
10.6
10.6
0
0
0
182
92
92
9
10
400
400
110
110
1087
1056
968
991
10.6
10.6
0
0
182
182
92
0
Table 4. Syngas composition,low heating value and carbon gasification efficiency.
No. % H2 % CO
1
56.6
33.4
% CO2 %CH4
4.5
5.5
% O2
0.1
Cout /Cin LHV [MJ/Nm 3]
0.58
12.3
2
3
57.7
58.5
32.7
31.6
4.1
4.7
4.9
5.0
0.7
0.4
0.67
0.67
12.1
12.1
4
5
6
50.0
47.9
45.5
46.0
47.0
48.8
2.3
2.9
4.1
1.5
2.0
1.5
0.0
0.0
0.1
0.74
0.77
11.7
11.8
11.6
7
8
49.1
19.0
46.8
53.2
2.5
25.4
1.5
1.8
0.1
0.2
0.68
0.84
11.7
9.4
9
10
19.2
26.9
53.7
53.2
25.1
16.4
1.6
1.9
0.0
0.3
0.85
0.58
9.4
10.7