5-7 OCTOBERISFR2011

41

TOLEDO (SPAIN)CONICAL SPOUTED BEDS TECHNOLOGY FOR RECYCLING OF POLYETHYLENE
WASTES
M.J. San José1, S. Alvarez1, A. Mouriz1, L. Ahedo1 and J. Fernandez de Mendiola2
1Departamento de Ingeniería Química. Facultad de Ciencia y Tecnología. Universidad del País Vasco. Aptdo 644. 48080

Bilbao. Spain
2CTL-TH Engineering (Tuboplast Hispania S.A.) company. Vitoria-Gasteiz. Spaine-mail:mariajose.sanjose@ehu.esAbstract
Conical spouted beds for recycling of polyethylene wastes have been used in order to tune up and determine theoperating conditions for the thermal treatment. Hydrodynamic study has been carried with beds consisting of polyethylene
wastes, of polyethylene pellets and of their mixtures at different operating conditions. Operation maps to operate intransition regime have been determined, as well as, the evolution of bed expansion with gas velocity to design conicalcontactor height.

Keywords: Spouted Beds, conical spouted beds, polyethylene wastes, polyethylene recycling, thermal recycling

1. Introduction
The increasing in consumption of plastic materials indeveloped countries has become in an environmental,
therefore recycling is the viable option at the moment,
thermal decomposition or pyrolysis is one of theprocedures for recycling plastic with best perspectives for
obtaining feedstock and fuel.
Spouted beds technology has been used in the design
and in the pyrolysis of virgin plastics [1-4], which great
advantages over other gas-solid contact techniques,particularly over the bubbling fluidized-bed reactor, whichis the more developed technology for this process.
However, bubbling fluidized-bed reactor has the greatinconvenience of defluidization caused by the stickinessof sand particles coated with fused plastic [4]. The
conical spouted bed has a vigorous movement of thesolid which avoids the agglomeration of particles, so, theconical spouted bed requires a lower sand/plastic ratio,
and so it has a greater production capacity by volumeunit.
In a previous paper, the contactor has been designed
and operating conditions has been determined with beds
consisting of virgin raw polyethylene. In this paper,
operating conditions to operate in transition regime andthe evolution of bed expansion with gas velocity havebeen determined for thermal treatment of polyethylene
wastes in conical spouted beds.

2. Materials and Methods
The experimental unit used has been described in detailin previous papers [5] and allows for operating withcontactors of different geometry. The blower supplies amaximum air flow-rate of 300 Nm 3 h-1 at a pressure of 15
kPa. The flow rate is measured by means of two massinteriores libro.indd 41

flowmeters controlled by a computer and by tworotameters up to 300 Nm3 h-1 The accuracy of this control
is 0.5% of the measured flow rate [6].
A differential pressure transducer (Siemens Teleperm)
registers bed pressure drop signal. AMR-Control
software registers and processes the air velocity data,
which allows the acquisition of continuous curves ofpressure drop vs. air velocity.
A conical contactor, Figure 1, made of polymethyl
methacrylate has been used, whose dimensions are:column diameter, Dc, 0.36 m; bed bottom diameter, Db,0.06 m; contactor angle, , 36º; gas inlet diameter, Do,
0.03, 0,04, and 0.05 m.

Fig. 1. Geometric factors of the conical contactor andoutline of the particles.
The solids used are pellets of high density polyethylene(HDPE) and low density polyethylene (LDPE) and plastic
wastes supplied by company Tuboplast Hispania S.A.
Material properties and recycling symbols of plastic
wastes are shown in Table 1. Melting point of HDPE andLDPE are 137 and 115ºC respectively and glasstransition temperature -90ºC and of LDPE -110ºC. Both26/9/11 13:12:46

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6th International Symposium on Feedstock Recycling of Polymeric Materials

plastic materials are chemically resistant against acids,basics and alcohols. Mixtures, Table 2, have beenobtained mixing polyethylene pellets and wastes of thesame material with 25, 50 and 75 wt%. The stagnant bed
heights studied are in the range 0.05 - 0.35 m.
Table 1. Properties of the materials.

(kg/m3)size range
(mm)

923

2.7-5

3.5

0.95 0.34

940

2.7-5

3.5

0.92 0.36923

10x12x0.514x18x0.5

5.3

0.24 0.35

MaterialsLDPEpellets
HDPE
pellets
LDPE
wastes940

LDPE
wastesdoS(mm)

10x12x0.514x18x0.5

5.3

0.24 0.35

Table 2. Properties of the mixtures.
Material

LDPEmixturesHDPE
mixturessweight percent(kg/m3)

(wt%)

923

25, 50, 75

3.8 4.2 4.7

940

25, 50, 75

3.8 4.2 4.7

dS

mixture(mm)

3. Results and Discussion
The stable operating conditions of beds of polyethylene
wastes in spouted beds have been delimited in diagramsof stagnant bed height, Ho, against gas velocity, u.
0,25Ho (m)

Fixed
bed

0,20

Spouted bed

0,15Transition

Classic

0,100,05

Instablespouting

Dilutespouted bed

0,000481216u (m/s)

Fig. 2. Operating regimes in conical contactors.
Experimental conditions: = 36°; Do = 0.04 m and HDPEof d = 5.3 mm.
Sinteriores libro.indd 42

In Figure 2, the results plotted as an example correspondto a spouted bed contactor geometry ( = 36º; Do= 0.04m) and for a bed consisting of HDPE of 3.5 mm ofparticle diameter and for different values of the stagnant
bed height. The borders between the regimes, drawn
with solid lines, have been obtained experimentally foreach stagnant bed height. As it is observed, as gas
velocity is increased bed passes from fixed bed tospouted bed regime. It is noteworthy that the HDPE has
an instability region for low stagnant bed heights.
The experimental value of minimum spouting velocity isdetermined from the values of pressure drop by
decreasing slowly gas flow as the point when thepressure drop levels off and it increases as stagnant bed
height is increased and.

4. Conclusions
Gas inlet diameter and height of conical spouted bed
reactor have been obtained for thermal treatment ofpolyethylene pellets, wastes and their mixtures, in a wide
range of gas flow rate. Furthermore, it is determined thatmixtures improve bed performance in the transition
regime between conventional spouted bed and dilute
spouted bed regimes.
These results predict good perspectives for polyethylene
wastes recycling by this technology.

References[1] M. Olazar, M.J. San José, S. Alvarez, A. Morales andJ. Bilbao. Design in Conical Spouted Beds for theHandling of Low-Density Solids. Ind. Eng. Chem. Res.,
43(2004) 655-661.
[2] R. Aguado, M. Olazar, B. Gaisán, R. Prieto, and J.
Bilbao. Kinetic Study of Polyolefin Pyrolysis in a ConicalSpouted Bed Reactor. Ind. Eng. Chem. Res., 41(2002)
4559-4566.
[3] R. Aguado, M. Olazar, M.J. San José, B. Gaisán, andJ. Bilbao. Wax Formation in the Pyrolysis of Polyolefins
in a Conical Spouted Bed Reactor. Energy & Fuels,
16(2002) 1429-1437.
[4] G. Elordi, M. Olazar, G. Lopez, M. Amutio, M. Artetxe,R. Aguado and J. Bilbao. Catalytic pyrolysis of HDPE incontinuous mode over zeolite catalysts in a conicalspouted bed reactor. J Anal Appl Pyrol. 85(2009) 345351.
[5] R. Aguado, R. Prieto, M.J. San José, S. Alvarez, M.
Olazar, and J. Bilbao. Defluidization modelling ofpyrolysis of plastics in a conical spouted bed reactor.
Chem. Eng. Process 44(2005) 231-235.
[6] M. Olazar, M.J. San José, A.T. Aguayo, J.M. Arandes
and J. Bilbao. Stable Operation Conditions for Gas-SolidContact Regimes in Conical Spouted Beds. Ind. Eng.
Chem. Res. 31(1992) 1784-1792.

Acknowledgements
This work was carried out with the financial support of theSpanish Ministry of Science and Innovation (ProjectTRA2009-0318 and Project CTQ2010-18697) and of theMinistry of the Basque Country (Project SA-2010/00097).

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