Pyrolysis of Plastic Waste and Scrap Tires Using a Fluidized-Bed

31 Pyrolysis of Plastic Waste and Scrap Tires Using a Fluidized-Bed Process WALTER KAMINSKY and HANSJÖRG SINN

Downloaded by UNIV OF PITTSBURGH on May 16, 2016 | http://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch031

Universität Hamburg, Institut für Anorganische und Angewandte Chemie, Martin-Luther-King-Platz 6, 2 Hamburg 13, West Germany

Increasing numbers of old tyres and waste plastics are creating problems regarding their disposal. Alternatively, there is a continuing search for new sources of hydrocarbons as a result of increasing energy and raw material needs. Old tyres and waste plastic can be converted by pyrolysis into almost residue free organic raw materials, to meet this need (1, 2, 3, 4, 5). About 340.000 t.a. of scrap tyres arise out of Western Germany's total production of 6.4 million tons p.a. of plastic and rubber which are dealt with in the following ways (6). Table I Removal or Reuse of O l d Tyres. Scrap Tyres t/a.

Methods o f Removal or Reuse Regeneration o f Rubber Recycling Pyrolysis Burning Remoulding C o n t r o l l e d Dumping Uncontrolled Dumping (whereabouts unknown) Others (e.g. boat-fenders) Total

7.000 90.000 85.000

-

100.000 6.000

30 1

338.OOO

lOO

20.000 30.000

circa

% 6 9 0 2 27 25

About 180.000 t/a. of scrap tyres remain to be processed, for instance by pyrolysis. In comparison the amount of plastic waste is about 1.4.106 t/a which is significantly higher. The main part (about 1.1.106 t/a) is mixed up with household waste (7), and therefore only a few hundred thousand tons are easily available from the producing and processing industries. Two different procedures exist for dealing with the latter 0-8412-0565-5/80/47-130-423$05.00/0 © 1980 American Chemical Society Jones and Radding; Thermal Conversion of Solid Wastes and Biomass ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

THERMAL CONVERSION OF SOLID WASTES AND BIOMASS


424

waste. Through Re-use the macro-molecular s t r u c t u r e stays i n t a c t i n c o n t r a s t to other methods ( P y r o l y s i s , H y d r o l y s i s , Burning) which change the chemical s t r u c t u r e to produce raw m a t e r i a l s or energy. F i f t y percent of the t o t a l energy needed t o produce p l a s t i c m a t e r i a l s i s used i n the p o l y m e r i z a t i o n process. Thus at f i r s t s i g h t , i t seems s e n s i b l e to re-use p l a s t i c and rubber waste mat e r i a l s (J3) . But Re-use processes have a negative i n f l u e n c e on the macro-molecular s t r u c t u r e which i s mainly a chain depolymerisation e f f e c t (9_) . Therefore Re-use by i t s e l f i s not a s a t i s f a c t o r y process. In a d d i t i o n , a l a r g e p r o p o r t i o n o f the p l a s t i c waste i s p o l l u t e d and mixed with other types o f waste so t h a t Re-use i s impossible . Therefore, the way i s open f o r p y r o l y s i s processes. These take place e i t h e r i n the t o t a l absence o f oxygen or with a lack of a s t o c h i o m e t r i c a l l y needed amount of oxygen. These processes aim to maintain the valuable C-H-bonding of the macro-molecules t o obt a i n smaller molecules, which can be used as energy recources or chemical raw m a t e r i a l s . These processes take place i n r o t a r y k i l n s , screw-kilns, melting v e s s e l s , or f l u i d i z e d bed r e a c t o r s . The problem l i e s i n t r a n s f e r r i n g the heat to s o l i d m a t e r i a l s i n such a way that the c o n d i t i o n s of p y r o l y s i s are evenly d i s t r i b u t e d t o produce the d e s i r e d product spectrum. Using r o t a r y or other i n d i r e c t l y heated k i l n s with t h e i r v a r y i n g temperature zone r e s u l t s i n an uneven decomposition of the m a t e r i a l . However by using a quartz sand or carbon black f l u i d i z e d bed with i t s even heat t r a n s f e r propert i e s , uniform c o n d i t i o n s f o r decomposition can be reached (_10, 11 ) . At the U n i v e r s i t y of Hamburg we have been developing a f l u i d i z e d bed process f o r the p y r o l y s i s of p l a s t i c waste and scrap t y r e s since 1970. We used three stages of u p - s c a l i n g - 0.1 kg/h; 10 kg/h; 100 kg/h. Laboratory s c a l e

experiments

Figure 1 shows a flow diagram of the p l a n t f o r l a b o r a t o r y e x p e r i ments with a continuous throughput o f O.l kg/h (12): A screw conveyor feeds through a cooled downpipe the e l e c t r i c a l l y heated q u a r t z - r e a c t o r which has a diameter of 5 cm and a f l u i d i z i n g zone o f up to 8 cm. The f l u i d i z i n g gas i s about 500 1/h of e i t h e r n i t r o g e n or c i r c u l a t e d cracker gas. A cyclone separates s o l i d s from the hot p y r o l y s i s gas stream; an e l e c t r o s t a t i c p r e c i p i t a t o r and a system o f i n t e n s i v e c o o l e r s and hydrocyclones condense the l i q u i d p o r t i o n s o f the cracked products, The non-condensable p y r o l y s i s - g a s e s are measured. The f i r s t column i n Table II shows the composition of the pyr o l y s i s products from an input o f p o l y e t h y l e n e . Beside the gaseous products, i . e . mainly methane, ethane, ethylene and propene, the l i q u i d products c o n s i s t o f up to 95 % benzene, toluene, styrene and naphthalene. Only a small amount (1.0 wt-%) of carbon black i s produced. The product spectrum can be i n f l u e n c e d to a c e r t a i n degree by changes i n temperature, Figure 2 shows the p y r o l y s i s of granulated

Jones and Radding; Thermal Conversion of Solid Wastes and Biomass ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


KAMiNSKY AND SINN

Figure 1.

Pyrolysis of Plastic Waste and Scrap Tires

425

Flow diagram of the laboratory test plant offluidized-bedpyrolysis.

(1) plastic feed hopper; (2) screw conveyor; (3) downpipe with cooling jacket; (4) fluidized-bed reactor; (5) heater; (6) cyclone; (7) cooler; (8) electrostatic precipitator; (9) intensive cooler; (10) cyclone; (11) gas sampler; (12) gas meter; (13) throttle; (14) compressor; (15) rotameter.



426

Table I I . Products o f f l u i d i z e d bed p y r o l y s i s o f p l a s t i c waste and scrap t y r e s (wt-%) TWS-1

TWS-1

TWS-1

TWS-2

PE

PE

used Syringes

tyre pieces

whole tyres

740

780

720

7 50

700

Hydrogen Methane Ethane Ethylene Propane Propene Butene Butadiene Isoprene Cyclopentadiene Other a l i p h a t i c compounds Benzene Toluene Xylene Styrene Indan, Indene Naphthalene Methylnaphthalene Diphenyl Fluorene Phenanthrene Pyrene Other aromatic compounds Carbon monoxide Carbon dioxide Water Hydrogen S u l f i d e Thiophene Carbon soot, f i l l e r s S t e e l cord

0,5 16,1 5,3 25,4 + 9,3 0,5 2,8 + 1,0

1,17 20,27 4,33 16,89 0,80 5,35 0,08 1,28 0,09 2,63

0,49 19,09 6,64 15,44 0,12 9,93 3,03 1,38 0,31 2,08

1,30 15,13 2,95 3,99 0,29 2,50 1,31 0,92 0,34 0,39

0,42 6,06 2,34 1,65 0,43 1,53 1,41 0,25 0,35 0,25

13,3 12,2 3,6 1,1 If 1 0,3 0,7 0,15 0,02 0,01 0,02 +

0,69 24,75 5,94 + 1,46 1,27 3,73 0,84 0,34 0,29 0,59 0,22

3,13 13,62 4,20 + 0,45 0,46 2,48 0,92 0,33 0,15 0,47 +

0,36 4,75 3,62 + 0,17 0,31 0,85 0,83 0,49 0,16 0,29 0,21

1,07 2,42 2,65 + 0,35 0,48 0,42 0,67 0,39 + 0,19 0,06

5,1

5,40

8,24

0,9

1,50

5,80

8,50 3,80 1,95 0,10 0,23 0,15 40,59 1,62

13,67 1,48 1,74 5,11 0,02 0,25 40 11,30

Balance

99,4

99,91

98,76

98,10

96,96

Reactor

LWS

Feed m a t e r i a l


Temperatur

ο C

LWS: l a b o r a t o r y s c a l e d r e a c t o r , TWS-1: p i l o t p l a n t , TWS-2: p i l o t p l a n t f o r whole t y r e s , PE: polyethylene, + : t r a c e d e t e c t i o n


KAMiNSKY AND SINN

Pyrolysis of Plastic Waste and

Scrap Tires

All


31.

Figure 2.

Product composition from fluidized-bed pyrolysis of granulated rubber tires, plotted as weight percent vs. temperature



428

THERMAL

CONVERSION

OF SOLID WASTES AND

BIOMASS

scrap t y r e s . By i n c r e a s i n g the temperature, the y i e l d of carbon b l a c k , hydrogen, methane and benzene r i s e s , and the y i e l d o f o i l f a l l s . Because a high percentage (about 35 wt-%) o f the o r i g i n a l feed m a t e r i a l i s carbon black, i t i s evident that, i t w i l l form a l a r g e p a r t o f the p y r o l y s i s products (over 38 wt-%). The l i q u i d f r a c t i o n has a l s o a high aromatic content. The bound c h l o r i d e i n p l a s t i c s c o n t a i n i n g PVC i s recovered as hydrogen c h l o r i d e gas from p y r o l y s i s . Considerable amounts o f carbon soot are produced i n t h i s r e a c t i o n . By adding superheated steam and hydrogen, the amount of carbon black produced can be r e duced from 8.8 to 2.1 wt-% (13). For the p y r o l y s i s of p l a s t i c waste with a high PVC content, i t i s probably b e t t e r to f i r s t dehydrohalogenize i t i n a r e a c t o r with added sand. Tests have shown that hydrogen c h l o r i d e gas can be produced from PVC at temperatures o f between 350 and 400°C, which i s up to 99 % pure and, a f t e r adsorption of the r e s i d u a l hydrocarbons, may be used to make very pure h y d r o c h l o r i c a c i d . A f t e r t r e a t i n g PVC f o r 20 minutes at a temperature of 350°C, more than 90 % of the bound c h l o r i d e has s p l i t o f f . This time i s reduced to l e s s than 10 minutes i f the temperature i s i n c r e a s e d to 400°C

(12) . I f the PVC content of the p l a s t i c waste i s low, the hydrogen c h l o r i d e produced can be absorbed e i t h e r d i r e c t l y i n the f l u i d i z e d bed to which calcium oxide or magnesium oxide i s added, or i n a separately connected f l u i d i z e d bed. This method has proved s a t i s f a c t o r y , at l e a s t f o r the absorption of hydrogen f l u o r i d e i n the p y r o l y s i s o f PTFE-containing p l a s t i c wastes and f o r hydrogen s u l fide i n the p y r o l y s i s of rubber. P i l o t p l a n t experiments These r e s u l t s l e d to the design o f a p i l o t p l a n t with a throughput o f 10 kg/h whose o v e r a l l layout i s shown i n Figure 3. The p r o j e c t was financed by the A s s o c i a t i o n of the P l a s t i c Produc i n g Industry (Verband Kunststofferzeugende I n d u s t r i e , VKE) and the F e d e r a l M i n i s t r y o f Research and Technology (BMFT). P l a s t i c m a t e r i a l i s p y r o l y z e d i n a f l u i d i z e d bed r e a c t o r u t i l i z i n g quartz sand heated to about 800°C. The f l u i d i z i n g medium i s preheated p y r o l y s i s gas. To observe the p r i n c i p l e o f i n d i r e c t heating and to avoid any p o l l u t i o n of the products, we used f i r e tubes i n s i d e the sand bed, i n which e i t h e r propane (for the s t a r t i n g period) or p y r o l y s i s gas can be burned. The feed enters the sand bed e i t h e r at the top of the r e a c t o r through an a i r lock (ZR 1) or through a water-cooled screw feeder ( ZR 2 with S 1) a t the s i d e . A water-cooled screw conveyer (S 2) i s i n s t a l l e d as an o u t l e t f o r the quartz sand. At the top of the r e a c t o r i s a safety b u r s t i n g d i s c . The lower h a l f of the r e a c t o r i s b r i c k e d with f i r e - p r o o f mortar. The r e a c t o r i s b u i l t up with three p a r t s , each o f a diameter of 0.5 m and d i f f e r e n t lengths of



Flow diagram of the pilot plant for the pyrolysis of plastic waste and scrap tires.

(PI) Pressure indication device; (PIC) automatic pressure control; (TI) temperature indicating device; (TIC) automatic temperature control; (FI) flow-meter; (LC) level indicator; (R) reactor; (M) motor; (WT) heat exchanger; (ZR) bucket wheel lock; (KM) membrane compressor; (KR) cryostat; (Κ) cooler; (S) screw feeder; (G) container; (F) flare; (TG) dip pipe; (Z) cyclone; (P) pump; (EF) electric separator; (DK) packed distillation column

Figure 3.

Pla sties



430

THERMAL CONVERSION OF SOLID WASTES AND

BIOMASS

1.0 m, 0.5 m and 0.3 m. The upper p a r t c a r r i e s the feeding tunnel f o r coarse m a t e r i a l (e.g. rubber pieces) and sand, the s a f e t y d i s c and the connection flange f o r the gas o u t l e t . The feed screw con veyor and the four P-shaped burners - two of each are r e s p e c t i v e l y above and below the conveyor l e v e l - are i n s t a l l e d i n the middle p a r t . The power output of the four burners i s r e g u l a t e d by varying the pressure of the burning gas. The bottom of the f l u i d i z e d bed has an i n c l i n e of about 15° and c a r r i e s the bent gas i n l e t tubes. These tubes are movable ver t i c a l l y so that t h e i r distance from the bottom of the f l u i d i z e d bed can be v a r i e d . With t h i s arrangement there i s a v a r i a b l e s e t t l i n g zone f o r small metal p i e c e s such as w i l l be deposited on pyr o l y t i c s t r i p p i n g of copper-cored w i r i n g . A flanged i n s p e c t i o n cover i s f i t t e d to the bottom of the gas d i s t r i b u t i o n zone. A p i c t u r e of t h i s p y r o l y s i s r e a c t o r i s shown i n Figure 4. The p y r o l y s i s gas produced i s cleaned together with the f l u i d i z i n g gas i n a cyclone (Z 1); i f the feed contains scrap t y r e m a t e r i a l , char and z i n c oxide w i l l be p r e c i p i t a t e d . The cleaned gas i s l e d to the condenser (Κ 1) which i s a c t u a l l y a v e r t i c a l t u b u l a r heat exchan ger. In the case o f condenser f a i l u r e , a three way cock allows the gas to be fed d i r e c t l y to the f l a r e . The gas leaves the condenser (Κ 1) a t 20 to 50°C, or at 100°C i f the c o o l i n g c a p a c i t y i s r e duced to avoid clogging by p a r a f f i n waxes* Condensed products are c o l l e c t e d i n a r e c e i v e r (G l ) . I n a counter-current packed washer (K 2) the gas i s then cooled to -20 C. The condensed products are d i s s o l v e d i n a scrubber o i l pump. For c o o l i n g the scrubber o i l to -20°C a counter-current t u b u l a r heat exchanger (WT 1) i s used. The l i q u i d products c o l l e c t e d are processed together with the scrubber o i l f i r s t i n a 0.1 m diam packed g l a s s r e c t i f i c a t i o n column, i n which high b o i l i n g (b»p. above 150°C) and low b o i l i n g products are separated. Gaseous products are r e c i r c u l a t e d to become the p y r o l y s i s gas. The low b o i l i n g f r a c t i o n i s r e f i n e d again i n a second 8 cm diameter packed column to give four f r a c t i o n s : a low b o i l i n g , a high b o i l i n g , a benzene, and a toluene f r a c t i o n . The high b o i l i n g f r a c t i o n ( i . e . xylene) i s pumped back continuously i n t o the washing tower, any excess being taken o f f . A l l products are drawn o f f and s e p a r a t e l y analyzed. The non-condensable components of the p y r o l y s i s gas are com pressed to 2 to 3 bar and s t o r e d i n a gasometer. F l u i d i z i n g gas as w e l l as f u e l gas f o r the r a d i a t i n g f i r e tubes i s drawn o f f as r e q u i r e d . The f l u i d i z i n g gas i s preheated to 400°C i n a countercurr e n t heat exchanger (WT 2) by the exhaust gas of the four f i r e tubes. Because o f s a f e t y reasons i t i s necessary to avoid any a i r or oxygen w i t h i n the whole product cycle- Therefore i n case of a drop below atmospheric pressure,a by-pass f o r the compressor allows product gas to flow back from the gasometer i n t o the system. The p l a n t i s equipped with numerous d a t a - c o l l e c t i n g i n s t r u ments. Because we have d e l i b e r a t e l y separated the hot and c o l d p a r t s o f the p l a n t , the l a t t e r , together with the p r o c e s s i n g of


KAMiNSKY AND SINN

Pyrolysis of Plastic Waste and

Scrap Tires

431


31.

Figure 4.

Pyrolysis reactor with a feed screw for plastic, a withdrawal screw for solid materials, and a cyclone


432

THERMAL

CONVERSION OF SOLID WASTES AND BIOMASS


the p y r o l y s i s o i l , are s i t u a t e d i n an explosion proof room. Sur v e i l l a n c e i s c a r r i e d out by continuous a n a l y s i s of the room a i r as w e l l as by e x p l o s i o n l i m i t c o n t r o l s . The p y r o l y s i s gas i s analyzed a u t o m a t i c a l l y by a gas chromatograph. A l l data c o l l e c t e d are graphed to achieve energy- and massbalances . Some b a s i c components are continuously monitored by i n f r a r e d spectroscopy, i . e . ethylene i n the p y r o l y s i s gas, sulphur d i o x i d e and oxygen i n the exhaust gas. The d e s c r i b e d p i l o t p l a n t has been operating f o r more than 700 running hours. Within these runs, i t has been proved t h a t the process i s s e l f - s u f f i c i e n t i n i t s energy needs (Table I I I ) . Table I I I Energy balance f o r the p y r o l y s i s o f 19,1 kg/h Polyethylene/Polypropylene ( r a t i o 1:1) a t 71^°C . P y r o l y s i s gas (produced): 8,0 m /h 3

Heat s u p p l i e d (burning of 4,6 m /n D i s s i p a t e d heat Burner gases P y r o l y s i s gases Crack energy Cooler (Κ 1) Water c o o l i n g I n s u l a t i o n l o s s e s (remainder)

Gas)

6

209,8·10 J 6. 77,0·10^J 2,1· 47,3*10 J 46 9-10 J 14,7-10 J 21,8*10 J f

Almost h a l f the amount o f p y r o l y s i s gas produced was burnt i n the exhaust gas f l a r e ; the other p a r t was s u f f i c i e n t to support the energy demands o f the process, being burnt i n the r a d i a t i o n f i r e tubes. Waste heat from the r e a c t o r heating (cooler) was s u f f i c i e n t to heat the d i s t i l l a t i o n column. A n a l y s i s o f the product spectrum shows t h a t between 40 and 60 wt-% o f the feed i s gained as worthwhile l i q u i d products (Table ID · Table IV shows the p a r t i c u l a r f r a c t i o n s which are obtained from the process, In the p y r o l y s i s of polyethylene at 810°C, the low b o i l i n g f r a c t i o n contains, apart from benzene, more than 10 wt-% of c y c l o pentadiene. I f benzene-rich f i r s t runnings and l a s t runnings (to luene-rich) are removed, one can o b t a i n a f r a c t i o n c o n t a i n i n g about 98 wt-% o f benzene. The main c o n s t i t u e n t s o f the high b o i l i n g f r a c t i o n s are naphthalene, methylnaphthalene and indene, as w e l l as h i g h l y condensed aromatics. As a general example f o r contaminated p l a s t i c scrap we pyrol y z e d shreddered syringe m a t e r i a l s - c o n t a i n i n g p o l y e t h y l e n e , p o l y propylene and rubber (Table I I ) . The p y r o l y s i s of these syringes i s without doubt h y g i e n i c and gives n e a r l y the same products as


31.

KAMiNSKY AND SINN


433

Table IV Composition o f v a r i o u s product f r a c t i o n s obtained through the p y r o l y s i s o f p o l y ethylene a t 810°C

vol %

low boiling wt-%

benzenerich wt-%

20,7 40,8 7,1 22,2 5,9 0,2 1,0 0,2

10,6 76,9 2,0

0,1 97,9 0,9

1,9

10,5

1,1

gas


Substance

Hydrogen Methane Ethane Ethylene Propene Cyclopentadiene Benzene Toluene Styrene Naphthalene Others 1

50-70

B o i l i n g r a n g e ( °C)

high boiling wt-%

toluenerich wt-%

47,6 51,9 0,2

0,1 2,3 24,5 73,1

0,3 80-100

70- 80

above 150

f r o m a n i n p u t o f p o l y e t h y l e n e . The p r o d u c t s show o n l y t r a c e s o f w a t e r , c a r b o n d i o x i d e and m o n o x i d e , and a c e t o n i t r i l e ; t h e p e r c e n t a g e o f c a r b o n s o o t can b e up t o 5.8 wt-% b e c a u s e o f t h e r u b b e r content. These r e s u l t s p r o v e t h a t p y r o l y s i s i s an a d e q u a t e p r o c e s s t o reprocess pure p l a s t i c m a t e r i a l s as w e l l as contaminated p l a s t i c f r a c t i o n s o f household waste. P r e v a i l i n g c o n d i t i o n s i n West Germany mean t h a t a r o m a t i c s a r e t o be f a v o u r e d as p r o d u c t s . We have now o p t i m i z e d t h e p r o c e s s t o a c h i e v e t h e maximum y i e l d o f benzene p o s s i b l e , b y v a r y i n g t h e temperature o f the f l u i d b e d , t h e f e e d and t h e f l o w o f t h e f l u i d i z i n g g a s . S t a t i s t i c a l p l a n n i n g o f t e s t r u n s l e d t o t h e f o l l o w i n g e f f e c t s and r e g r e s s i o n e q u a t i o n s . The y i e l d s o f b e n z e n e and e t h y l e n e can be c a l c u l a t e d from the f o l l o w i n g e q u a t i o n , u s i n g percentage w e i g h t i n r e l a t i o n to the feed. wt-% b e n z e n e

= 21.095 + 2.323 t - 1.381 d + 0.731 w - 0.680 t d + 0.581 dw + 0.104 t w - 0.377 t - 0.910 d 0.457 w 2

2

2

wt-% e t h y l e n e = 18.733 - 1.195 t - 0.132 d - 1.785 w - 2.436 t d + 2.643 dw - 0.341 tw - 1.618 t + 3.240 d + 1.263 w 2

2

2


THERMAL

434 in

CONVERSION

OF SOLID WASTES AND

BIOMASS

which t

temperature - 750°C 30°C

d

throughput - 14,18 5,03 kg/h

kg/h 3

w

f l u i d i z i n g gas/h - 32,85 m /h


365

3

m /h

Figure 5 shows the graphing of the flow of f l u i d i z i n g gas against the feed; i t w i l l be n o t i c e d that a maximum i n the y i e l d of benzene almost corresponds to a minimum i n the y i e l d o f e t h y l e ne. From these r e s u l t s and from experiments with s i n g l e p a r t i c l e s , i t can be concluded that aromatics are produced from o l e f i n s such as ethylene, propene and butadiene. The s l i g h t d i f f e r e n c e between the above maximum and minimum y i e l d s , and the d i f f e r e n t gradients of the y i e l d curves i n d i c a t e the existence of successive and parallel r e a c t i o n s : the p y r o l y s i s r e a c t i o n has a two-stage mechanism. In the f i r s t stage, macromolecules are decomposed i n t o small, mostly o l e f i n i c compounds. During the second stage, aromatics are produced from the i n t e r - r e a c t i o n of these compounds, and hydrogen and methane are given o f f . By r a i s i n g the temperature, the flow of f l u i d i z i n g gas and the residence time, the y i e l d of aromatics i n creases. Larger amounts of benzene were produced by the p i l o t p l a n t than by the l a b o r a t o r y s c a l e p l a n t , as a r e s u l t of a longer residence time i n the r e a c t o r . Prototype f o r Whole-Tyre

Pyrolysis

F l u i d i z e d sand beds are s u r p r i s i n g l y i n s e n s i t i v e to the u n i t s i z e of the feed m a t e r i a l . P i e c e s of scrap t i r e s up to a weight of 2.7 kg/each were fed and q u a n t i t a t i v e l y pyrolyzed. These r e s u l t s proved the f e a s i b i l i t y o f p y r o l y t i c processing of scrap tyres without p r i o r s i z e r e d u c t i o n . Most p y r o l y s i s processes use crushed feed down to between 200 and 20 mm i n s i z e which causes considerable expense (_10, 14, 15) . The f o l l o w i n g companies have c a r r i e d out p y r o l y s i s e x p e r i ments i n i n d i r e c t l y heated r o t a r y k i l n s using such feed m a t e r i a l : Kobe S t e e l (_16) i n Japan Goodyear and TOSCO (_17) i n the U.S.A. GMU (_18) n d Herko-Kiener (19) i n West Germany. a

In cooperation with the Hamburg company C.R.Eckelmann and promoted by the F e d e r a l M i n i s t r y of Research and Technology a p i l o t p l a n t f l u i d bed r e a c t o r f o r a 1.5 to 2.5 t / d throughput of scrap tyres




KAMiNSKY AND SINN


435


436


was b u i l t at the Hamburg i n s t i t u t e (20_, 21) . The f l u i d bed has i n t e r n a l dimensions of 900 χ 900 M.M. so that i n d i v i d u a l unshredded t y r e s of up to 20 kg i n weight can be processed. The high cost of shredding can t h e r e f o r e be dispensed with ( F i g . 6). The p y r o l y s i s zone, a f l u i d i z e d sand bed or carbon black bed i s i n d i r e c t l y heated up t o between 650 t o 850°C by seven r a d i a t i n g f i r e - t u b e s , arranged i n 2 l a y e r s . One p a r t of the product gas i s used t o f l u i d i z e the bed, the other being burnt to heat the pro cess . The whole t y r e s r o l l through a g a s t i g h t lock i n t o the r e a c t o r (Fig. 7). Observable events can be d e s c r i b e d as f o l l o w s . The t y r e / landing on the f l u i d bed g r a d u a l l y s i n k s i n t o the sand. The mate r i a l heats up and s o f t e n s , i t s surface becoming covered with hot sand g r a i n s . Through the shearing f o r c e s of the f l u i d bed - increased be cause of the r e d u c t i o n of the f r e e cross s e c t i o n of the bed - an "exchange" o f sand g r a i n s takes p l a c e at the surface of the softened m a t e r i a l ; the abrasion o f small p a r t i c l e s and t h e i r de composition begins. A methane and ethylene r i c h gas as w e l l as a condensable l i q u i d p a r t with a high percentage o f aromatics are produced (see Table I I ) , The main p a r t o f the f i l l e r m a t e r i a l s - carbon soot and z i n c o x i d e - i s blown out of the f l u i d bed and can be separated i n a cyclone. The carbon soot i s dry and t r i c k l e s out of the cyclone. A f t e r 2 or 3 minutes, the t y r e i s completely p y r o l y z e d . What remains i n the sand bed i s a mass o f t w i s t e d s t e e l wires, which are removed by a t i l t a b l e grate extended i n t o the f l u i d bed. The p y r o l y s i s products together with the f l u i d i z i n g gas ( i . e . the non-condensable p y r o l y s i s gases) leave the r e a c t o r v i a a cyclone, where dry carbon soot and f i l l e r m a t e r i a l s are p r e c i p i t a ted. The hot gases are cooled t o room temperature by an o i l scrub ber and then r e f i n e d i n the washer and r e c t i f i c a t i o n u n i t used i n the smaller p i l o t p l a n t d e s c r i b e d above. The p i l o t p l a n t has been running since l a t e 1978. I t was proved i n a t e s t run with a feed o f more than 150 car t y r e s , that the process i s s e l f - s u f f i c i e n t i n i t s energy needs, producing a t a temperature o f 720°C, even excess p y r o l y s i s gas t o supply other heat necessary. Waste heat from the r e a c t o r heating i s s u f f i c i e n t to heat the d i s t i l l a t i o n column. The balance o f the products i s as f o l l o w s (compare with Table I I ) : 22 27 39 12

wt-% wt-% wt-% wt-%

gas liquids carbon soot s t e e l cord

The sulphur content of the aromatic f r a c t i o n i s l e s s than 0.4 wt-% and that of the gas l e s s than 0.1 wt-%. Carbon b l a c k con t a i n i n g z i n c oxide and sulphides can be separated i n t o re-usable



437


KAMINSKY AND SÎNN

Figure 6. Flow diagram of the prototype reactor for whole-tire pyrolysis. (1) steel wall with fireproof bricking; (2) fluidized bed; (3) tillable grate; (4) radiation fire tubes; (5) nozzles to remove sand and metal; (6, 8, and 9) flange for observation and repairs; (7) gastide lock; (10) shaft for steel cord.



438


Figure 7. Placement of whole tires into the lock of the prototype reactor



31.

KAMiNSKY AND SINN

Pyrolysis of Plastic Waste and Scrap Tires 439

Η.A.T.-quality and waste carbon black by an air classifier. The waste carbon black is an interesting source of zinc (4-5 wt-%). If the price we can obtain for pyrolysis o i l stays above 580 DM/t (this corresponds to a benzene price level of llOO DM/t) and that of carbon black over 300 DM/t, then operating costs and capital costs of a plant with a capacity of 7500 t/a will show a profit of 7 % p.a. At present, the price of benzene amounts to 900 - 1000 DM/t, and prices of up to 600 DM/t for carbon black are possible. As a result of our work, the firm C.R. Eckelmann are planning to build a commercial plant with a capacity of 6.OOO to lO.OOO t/a of unshredded scrap tyres and hydrocarbon-containing waste. In addition, we have succeeded recently in treating aliphatic waste o i l and the liquid extracts of oil-sands to produce aromatic compounds. In conclusion,it may be possible to gain aromatic liquids from oil-sands in a one-stage process, using the sand in the feed as the medium for the fluid bed. Literature Cited 1. Sanner, W.S. Bureau of Mines TN 23. U7 No. 742862206173 2. Kaminsky, W.; Menzel, J.; Sinn, H. Int. J. Conservation & Re cycling 1976, 1, 91 3. Tsutsumi, S. CRE Conference Paper, Montreux 1976, 567 4. Beckmann, J.A.; Crane, G.; Kay, E.L.; Laman, J.R. Rubber Chem. Technol., 1974, 47, 597 5. Spendlove, M.J. Umschau, 1973, 73, 364 6. Umweltbundesamt der BRD, Materialien zum Abfallwirtschaftspro gramm '75, Materialien 2/76, Berlin 1976 7. Glenz, W. Kunststoffe, 1977, 67, 165 8. Data received from Stanford Research Institute, April 1973 9. Ranby, B. Kunststoffe German Plastics, 1978, 68, 10 10. Sinn, H.; Kaminsky, W.; Janning, J. Angew. Chem. Ed. Engl., 1976, 15, 660 11. Kaminsky, W.; Menzel, J.; Sinn, H.; Plastic and Rubber, Pro cessing June 1976, 69 12. Menzel, J. Chem.-Ing.-Techn., 1974, 46, 607 13. Kaminsky, W.; Sinn, H. Kunststoffe German Plastics, 1978, 68, 14 14. Schnecko, H.W. Chem.-Ing.-Tech. 1976, 48, 443 15. Luers, W. Gummi-Asbest-Kunstst., 1975, 28, 770 16. Takamura, Α.; Inone, K.; Sakai, T. CRE Conference Paper, Montreux 1976, 532 17. Ricci, L.J. Chem. Eng. (Aug. 1976) 52 18. Collin, G.; Grigoleit, G.; Bracker, G.-P. Chem.-Ing.-Tech., 1978, 50, 836 19. Tabasaran, O.; Besemer, G.; Thomanetz, E. Müll Abfall, 1977, 9, 293 20. Kaminsky, W.; Sinn, H.; Janning, J. European Rubber J., 1979 161, 15 21. Kaminsky, W.; Sinn, H.; Janning, J. Chem.-Ing.-Tech., 1979, 51, 419 RECEIVED November 16, 1979. Jones and Radding; Thermal Conversion of Solid Wastes and Biomass ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

Pyrolysis of Plastic Waste and Scrap Tires Using a Fluidized-Bed

Recommend Documents