Development of fluidized-bed pyrolysis of waste tires

vo.. 3,

Conservoriori

d Wecycimg.

GPergamon

Press Ltd.. 1979 Printed in Great Britain.

DEVELOPMENT T. ARAKI,

0361.3658/79/09-Ji5S

pp. 155 - 164.

OF FLLXDIZED-BED K. NIIKAWA,

Governmenl

H. HOSODA,

PYROLYSIS

OF WASTE

H. NISHIZAKI

and S. MITSUI”

Industrial Deveiopment Laborato
:42.W/O

TIRES

Sapporo-Shi 061-01, Japan.

and K. ENDOH Process Chemical Engineering

Department,

Hokkaido

University. Sapporo-Shi 060, Japan

and K. YOSHIDA Engineering

Research Instuure,

Universify of Tokyo, Bunkyo-Ku,

Tokyo

113,Japan

4bstraet - The problem of waste Tire disposal has become crirical in all industrialized nations and will -worsen in the future. A fluidized-bed process has been developed to treat these waste tires, wherein :he rires were mostly pyrolyzed by the heat of oxidation of the tires themselves. Experiments using both tire ‘chips and whole tires are described. All the products, such as oi’, char and gas, were found to be capable of reutilization as important resources.

NOMENCLATURE D 6 G, KO M, Tb T,, UO W * P’

= = = = = = = = = = =

bed Uiameter, mm mass-flow rate of waste rire, kg/m’ h mass-flow rate of air, kg/m2 h F,/G, molecular weight of oil, kg/kg-mol bed temperature, “C boiling temperature, “C superficial air velocity, cm/s initial weight of sample, kg defined by equation (1) defined by equation (4)

“,. INTRODUCTIOIL; The development of a satisfactory disposal method fo; waste car ilres is a common problem in all industrialized countries, where motorized vehicles play an essential role in daily living. Japan is no exception. As shown in Table 1 [l], about 34 million tires were generated in 1972 and the amoun: has been increasing every year. Only about 35% of these, however, are recovered by reclaiming, splitting etc. and the rest is buried in landfills, as summarized in Table 2[1]. Landfill is very simple, but the available area is limited in a small country like Japan. Furthermore, there is then no recovery of resources, though car tires are composed mostly of rubber and carbon black.

* At present, with Waste Engineering Laboratory, Sapporo-Shi. Manuscript received: 16 September 1978; revised manuscript received:

I February

1979.

T. ARAKI et ai.

156 Table YCZlr

1. Waste tire generation

in Japanjl]

1972

1973

1974

1975

1976

75 641.1 450 561

86 205.7 517 655

92 656.9 555 057

98 400.9 589 670

104 373.7 624 922’

26 402.4 343 710

32 499.7 429 636

36 221 .O 471 670

39 710.0 514 178

43 058.0 556 680

7 474.7 89 696.4

11 271.2 135 494.4

13 367.4 160 408.8

15 144.0 181 728.0

16 614.0 199 368.0

33 877.1 433 406.4

43 790.7 565 130.4

49 588.4 632 078.8

54 854.0 675 906.0

59 672.0 756 098.0’

Classification Production of new tires numbers (x 10’) weight (tons) Generation of waste tires by tire change numbers (x 10”) weight (tons) by car scrapping numbers (x 10’) weight (tons) Total numbers (X lOJ) weight (tons) * Tubes are included.

Table 2. Waste tire processing

by various

methods[l]

A. Reutilization in original form (I) export as old tire (i) (ii) reclaimed tire (iii) fish reef sand guard (iv) shelter for afforestation (v) (vi) frost shelter (vii) others (playing tool, road mats etc.) sub total (Ii) by physical or chemical treatment reclaimed rubber (i) (ii) others (for investigation of pyrolysis etc.) sub total Total B. Final disposal Total

(in 1972)

39 923 44 853 120 3600 300 7 800 720 97 316

tons

75 000 180 75 180 175 496 433 406

In the Government Industrial Development Laboratory, Hokkaido, the application of various solid wastes has been studied to resolve process problems and improve overall process design. One of the applications involved work on fluidized-bed pyrolysis of waste tires, and a semi-commercial plant has been developed. Pyrolysis of waste tires was first attempted by the U.S. Bureau of Mines in collaboration with the Firestone Company in the United States[2]. The operation, a batch process is still on a small scale. In Japan, Kobe Steel Company has developed a pyrolysis process by means of a rotary kiln averaging 2.4 tons/day[3], and experimentation has been intensively carried out. In this paper the history of the development of the Hokkaido process will be traced. This process facilitates the recovery of oil and char from waste.

2. BASIC

EXPERIMENTS

Pyrolysis is simply described as the thermal decomposition of carbonaceous materia! in the absence of oxygen. Figure 1 shows TG curves of tire chips for various heating rates in a nitrogen atmosphere. The sample used throughout the studies was of tires produced by the Bridgestone

FLUIDIZED-BED

40i

150

I 200

250

300

PYP.OLYSIS

I 350

I 300

Temperature,

450

5c10

I 550

c 0

7‘_

Fig. 1. TG curves of tire chips in N, stream

of 10 cm/s.

Company whose trade makes are B.S. 4.50-10, 5.60-10, 5.60-13 and 7.00-15. The firsi number represents the width of tire (in inches) and the second number represents the diameter of the rim (inches). The material of the tire was a copolymer of styrene and butadiene; the butadiene is decomposed at lower temperatures than is styrene. This may cause the inflection of TG curves at about 3OO”C, when the heating rate is relatively slow.

,s OS

hopper crew feeder

3

Blower

s

Fluidized

:s

hopper

@

Dust co1 ector

3

Sample

xqe

bed

Fig. 2. Fluidized

bed used for basic experiment

The same sample was hung in a fluidized-bed and the weight loss measured. The apparatus used in this experiment is shown in Fig. 2. The reactor was a 150 mm i.d. stainless steel tube and the quartz sand was fluidized by air. After the bed was heated up to the desired temperature by an external heater, tire chips in a cage were dipped into the bed. Pyrolysis caused the change in weight of sample. In addition, the crumbling of tire chips was found to be an important -factor in weight loss.

T. ARAKI el al.

158

The weight measured given by initial

at regular

weight

@=

[kg] initial

intervals

weight measured

weight

0

is plotted,

[kg]

IO

I2

e DO I

Defining obtained,

is

[kg]

2468

Fig. 3. Relationship

as shown in Fig. 3, where the ordinate

between

the time of complete conversion &,, can be expressed as

14

16

I8

20

22

min

weight change

of sample

and time.

as 0 ,00, which is given by extrapolation

0 ,00 = 2 (weight loss) + Oar

of the line

(2)

where O0 represents the time necessary for preheating Experiments at 450°C gave the relations

of the sample.

0 100 = 4.4 + 7.2 [min],

for B.S. 4.50-10: and

(3) for B.S. 7.00-15:

The effects respectively.

3 100 = 4.9 f 14.0[min].

of bed temperatures

and air velocities

3. FLUIDIZED-BED

PYROLYSIS

on B,,, are shown

OF TIRE

in Digs 4 (a) and jb),

CHIPS

Fluidized-bed pyroiysis was conducted to find the optimum conditions and procedures of operation. A flow diagram of the experimental apparatus, comprising the reactor and auxiliary equipment, is shown in Fig. 5. Two different sizes of fluidized bed, i.e. 150 mm and 300 mm i.d. were used in this study. The gas distributors for both reactors were a stainless steel perforated plate with 2 mm holes and 1.0% opening ratio. Quartz sand was first used as fluidizing particles but was finally replaced by tire char particies produced in this experiment, because sand particles tend to become agglomerates with char

FLUIDIZED-BED

PYROLYSIS

-59

Tire=BS. 450-10 U,= IO cm/set W=O.3 kg

2

I 0 .g)

5

I I5

IO

21

cm/set

uo,

Fig. 4. Effects of bed temperature

3

Strop

@

Tire

@

Magnetic

@

Hopper

0

Screw

5

tire breaker seporotor

feeder

and air velocity

@

Stirred

on time for complete

fluidized

bed

(@

Hopper

@

Dust

collccto

‘@

Char

@

lieot

EXChaWJer

@

Burner

09 0IO

Blower

314

Stock

Fig. 5. Flow diagram

conversion.

of char take

off

valve

Preheater

of fluidized-bed

pyrolysis.

particles and, in addition, require recycling; the tire char solved all these problems. Air was heated to 250°C by a preheater and introduced into the bed filled with the tire char particles previously produced. The bed temperatures were sustained by the heat of partial .oxidation of char in the range 350 to 600°C and controlled by adjusting the feed rate of tire chips with an accuracy off 2°C. A stirrer was installed in the bed and revolved slowly; it was quite effective in preventing the danger of hot spot formation due to the accumulation of tire chips on the distributor. For the 150 mm bed waste tires were completely crushed into fine particles, while in the 300 mm bed smail pieces of 20-50 mm diameter were introduced by a screw feeder. In the iatter case it was necessary to equip a breaker in the hopper and to arrange an appropriate gap

160

T. ARAXI et al.

between the tube wall and the screw. Tables 3 and 4 give the size distribution of feed material used by 150 mm bed and data on technical analysis of material fed in both beds, respectively. Table 3. Sieve analysis

of feed material (wt 070)

(mm) +2.38 -2.38 -1.41 - 1.00 -0.71 PO.50 -0.35

+ + + + +

4.2 21.3 19.5 16.1 12.1 11.2 9.6

1.41 1.00 0.71 0.50 0.35

Table 4. Technical Moisture

Volatile

matter

71.41

analysis

of feed material

Ash

Fixed carbon

4.31

24.23

Sulfur 1.91 [wt qlo]

Char particles produced in the bed were continuously recovered through an overflow pipe from the reactor, and on the other hand, both gas and oil were introduced through a dust collector into a condenser so as to recover the oil. The remaining gas was discharged through a stack after combustion in a burner. The main operating conditions are summarized in Table 5. Table 5. Operating Operating temperature Fluidized-bed height Superficial air velocity Particle size of char Minimum fluidization velocity Feed rate of tire chips Rotation

speed of stirrer

conditions

350-600°C 300 mm 6- 12 cm/s at 20°C average 0.63 mm 1.1 cm/s at 20°C 9.0 - 28 kg/hr for 150 mm bed 28.0-68.5 kg/hr for 300 mm bed 60 r.p.m. for 150 mm bed t0 r.p.m. for 300 mm bed

Figure 6 shows the relationship between the yield of products and the bed temperature. A bed temperature of about 450°C was found to be optimum per oil yield. The amount of char remained almost constant over the whole range and corresponded to that of carbon black

Fig. 6. Relationship

between

product

yield and bed temperature.

PLUIDIZED-BED

161

PYROLYSIS

included in the feed material. In both fluidized beds it was found that the mass flow rates of tire chips F, are related to [hat of air Go for various bed temperatures as a parameter, as shown in Fig. 7. Therefore, the relationship between the value of K. = FJG, and bed temperature is given by a straight line; This is useful in scaling-up the process. 600

1400

I200

IO00 k 800 7 s 600 c 400

200

0

200 I

0

200 Go 1

Fig. 7. Relationship

4. FLUIDIZED-BED

between

403

600

kg/m’ hr

mass-flow

rates of tire and air.

PYROLYSIS OF ORIGINAL TIRES

In the processes mentioned above the tire was shorn and broken into small pieces of about 20 - 50 mm using a breaker. In this process bead wires and steel cords contained in the tire were shorn and almost all of them were stripped. Therefore, about 99.0% of the wire could be removed though a magnetic separator. Nevertheless, The breaking-up of tires is a laborintensive process and the accumulation of wire chips in fluidized beds may cause trouble in the operation after many hours. Thus, an experiment for processing tires keeping their original form was carried out. The whole arrangement is shown schematically in Fig. 8. The fluidized bed was 80 cm in diameter and 1 m in bed height. Char particles made from tire were fluidized by air and steam, and partly burned to maintain the bed temperature for pyrolysis. The temperature was controlled by adjusting the feed-rate of steam. After the bed temperature reached the desired level, tires were hung one after another on the hooks of a chain and transported downwards from the freeboard of the fluidized bed into the bed. After dipping for a certain time in the bed only bead wires remained on the hook and were removed by winding up the chain. Above the bed a specially designed automatic driving device for the chain was installed.

!62

T. ARAKI

et ai.

&JChor

receiver

S P

Stirrer

Fig. 8. .Apparatus

i’or pyrolysis

of origina;

* 0

2

4

I 6

8

IO

Residence time, Fig. 9. Relationship

Figure

between

9 shows the several experimental initial

weight

[kg] -

weight

results,

wire weight

[kg] -

shaped

tire.

Preheating for 12 min I I 1 12 14 16 min change

of tin-c and time.

where rhe ordinate weight measured

@’ =

Cp’ is given by [kg] x !oo.

initial

weight

[kg] -

wire weight [kg]

Two kinds of experiments were conducted for both new and waste tires; one was without preheating of tires and the other was with preheating in the freeboard for 12 min. As expected, the effect of preheating was remarkably large. This led to the conclusion that the processing capacity is rather small in comparison with the process using small tire chips.

SLUIDIZED-BED

5. YIILIZATION

P?-KO LYSIS

163

OF PRODUCTS

Analytical results of oil produced from fluidized-bed pyrolysis using tire chips are summarized in Table 6. The sulfur content ranged from 1.35 to 1.46%. Therefore, it can be used as a substitute for B-grade fuel oil with calorific value of about 10 000 kcal/kg. Table 6. Analysis _-._-i-b, (“C) M,

-150 114

C,”H >“I+> r, {“C)

400 f 450 500 \ 550

of oil produced

m200 142

~250 180

(300 .xun bed at r/, = IO cm/s)

-300 215

m,350 267

GO0 310

Ca

C,,

C,,

CM

CM

C,,

20.1 23.5 22.8 23.3

14.5 17.0 17.0 17.0

9.7 10.4 10.8 12.3

a.4 8.6 9.1 10.0

6.2 7.5 a.5 9.1

10.5 10.0 11.4 9.2

-450 368 Cl8

Spec. gravity

Sulfur [%I

30.5 23.1 20.6 19.0

0.918 0.934 0.926 0.927

1.35 1.38 1.46 1.36

Data on the technical analysis and the size distribution of char produced are given respectively in Tables 7 and 8. Sulfur, to an extent of more than 2%, is contained in the form of zinc sulfide, formed by the reaction of zinc oxide with sulfur in the tire. Table 7. Technical

Tb 400°C .500”C

analysis

of char produced

{wt.%)

Water

Ash

Volatile matter

Fixed carbon

Sulfur

0.39 0.51

14.2 15.05

15.07 6.3

70.43 80.01

2.16 2.46

Table 8. Sieve analysis

of char (300 mm bed)

(mm)

(wt.%)

+ 2.00 --2.00 + 1.68 - 1,68 + 1.19 - 1.19 + 1.10

5.42 1.75 11.62 L5.52

(mm) -1.10 -0.71 -0.50 -0.25

+ 0.71 + 0.50 + 0.25

(wt. o/o) 17.05 11.62 18.62 12.40

Tests conducted by another group showed that this char can be recycled as a high-quality carbon black for the rubber industry, when the char particles are ground into fine powders. -41~0, it was shown that activation of char by steam in a fluidized bed is a promising way for reutilization of char particles. The composition of gas remaining to be uncondensed is shown in Table 9. The gas contains mainly nitrogen in the air used for fluidization and some amounts of Con, CO, CH, etc. All the sulfur is included in the form of H,S whose removal is possible by use of iron oxide. Heat, therefore, can be recovered from the combustion of the gas.

Table 9. Analysis

N2

1.OO* trace 0.050 0.051 0.125 0.008 0.025

0, Hz CO CH, GHs GH, *N, gas was taken

as unity.

of gas produced at 450°C C,H, C,H. CO, KS C,H, 0 C,Hs CsHa

0.002 0.010 0.235 0.017 0.006 0.020 0.056

T. ARAKI et al.

164

6. FINAL REMARKS

Various experiments on waste tire pyrolysis in fluidized beds are described by following their development stages. At present, based on these results, the process has been scaled up to a precommercial plant having a capacity of 1 ton/hr (6 600 tons/yr) by Nippon Zeon Company in collaboration with Japan Gasoline Company Limited. The results obtained in this plant show that this process is practically promising in reutilizing waste tires. The final commercialization of this process is dependent on the establishment of a social ‘system facilitating the collection of waste tires and the recycling of the products obtained from pyrolysis. Acknowledgements

- The authors wish to express :heir deep appreciation to the staff of both the Process Development Department of Nippon Zeon Co. Ltd. and Japan Gasoline Co. Ltd. for their efforts extended in this work and for their kind consideration

with respect to publication.

REFERENCES 1. Ministry for Int. Trade and Industry Ed., Reufilizotion c$ Wosre, Chapter 3 (1974). 2. Bureau of Mines Report, No. 7302, Sept. (1969). 3. S. Kawakami and K. Inoue, Thermal decomposition of waste tires, PPM 4, (4), 20 (1977). 4. K. Niikawa, H. Hosoda, T. Araki, M. Mitsui and K. Endoh, Disposal of scrap tire by stirred fluidized bed, Kugoku Kogaku (Chem. eng. Japan) 38, 385 (1974).

5. Y. Saeki and G. Suzuki, Fluidized thermal cracking process for waste tires, Rubber Age, 180, (2), 33 (1976).