**Waste Tire Pyrolysis Recycling with Steaming: Heat-Mass Balances & Engineering Solutions for By-Products Quality**

Uladzimir Kalitko

*Heat-Mass Transfer Institute, HMTI, Belarus National Academy of Science, Minsk, Belarus* 

## **1. Introduction**

212 Material Recycling – Trends and Perspectives

S.Murugan, M.C. Ramaswamy, G.Nagarajan, "The Use of Tyre Pyrolysis Oil in Diesel

Scrap Tire Management Council, "The use of scrap tires in cement rotary kilns", 1992.

Turer, A., Ozden, B., Golalmis, M., World Bank DM2003 "Seismic Performance Improvement of Masonry Houses" (SPIM-1451) project final report, 2005. Wikipedia, Cement kiln, cited on 2011 at http://en.wikipedia.org/wiki/Cement\_kiln Wikipedia, recycling Available from http://en.wikipedia.org/wiki/Recycling, 2011.

William Sheehan, "Tires an d Glass Markets for Rural Georgia", 1995; cited on 2011 at

 http://www.rma.org/scrap\_tires/scrap\_tire\_markets/cement\_ kiln\_report.pdf Sharma et. al., "Disposal of waste tyres – review", Elsevier, Energy Convers. Mgmt Vol. 39,

Engines", Waste Management, Volume 28, Issue 12, December 2008, Pages 2743-

Ruben Tire and Auto Service, Available from

No. 5/6, pp, 511-528, 1998.

2749.

Available from

http://www.rabentire.com/?PageData=37134 2011.

http://www.p2pays.org/ref/24/23747.pdf

Waste tires pyrolysis is well known method for their thermal recycling by heating at near 500°C with purpose of liquid oil and carbon black by-production as near 50% and 35% yield correspondingly, including about 10% combustible off-gas residual after oil condensing and 5% wire steel cord in rest (all relatively to tire mass). There are many patents claimed in the world such as [1-20] and others, as well as many research papers published in this field such as [21-42] and others since the 1980s mainly. Not considering such simplest as batch-battery type and such complicated as fluidized bed one and some others, the drum-kiln and screw-auger type of pyrolysis reactor should be noticed as most preferable for commercial use, being both of them operated continually with tire shreds as 2-3 inch size. The tire material is gasifying in a sealed pyrolysis reactor and volatile hydrocarbons (pyrolysis gases or simply pyrogas,) are piping from reactor to condenser for the liquid pyrolysis oil. A few of the oil as 5-10% is burning for heating the reactor, provided with all the off-gas fuel after condensing the oil is afterburning too. As a solid rest the tire carbon char is continually discharging from reactor for its powdering, separating off steel wires and producing the carbon black.

But even in 2000s with reference to [32] it has been concluded as there was not an operating commercial plant in the world that could be recognized as operated successfully with a high commercial productivity and quality of both by-products. Particularly, for the carbon black could be used commercially in the rubber industry again, its quality must be as 1-2 % tire oil volatile matters residual content. In recent years the tire pyrolysis plants of rotary-batch type are many referenced in the net as an alternative and widely used in China, Malaysia, Taiwan, etc., operating simply with a whole tire bulk and producing so way the carbon black of low quality as 5-6% and more of the residual content above, operating a priory with a low productivity as the batch-type.

In connection with the carbon black quality and with reference to [1, 2] the vacuum tire pyrolysis method should be mentioned as claimed in the 1980s, being performed under the low-pressure and resulted in 4% and less of oil residual content. It should be noticed as well

Waste Tire Pyrolysis Recycling with Steaming:

Heat-Mass Balances & Engineering Solutions for By-Products Quality 215

In this connection with reference to [33-38] a new pyrolysis system for waste tire commercial recycling in the reactor of double-screw type with steam has been elaborated in HMTI (Belarus) for ENRESTEC Co. (Taiwan) in 2006, being next installed and applied by author's guidance in 2007-2008. The plant has been designed as a double-line pyrolysis system per 1 t/hr every (Pict.1, Fig.1) with carbon black quality as 1-2% oil residual matters, including more proof-explosion safety inside the reactor due to diluting the pyrolysis gases (pyrogas) with steam, as well as more sealing the reactor with steam feeding against air penetration into reactor under the low-operating pressure as required. Steam is self-producing in a second-heat boiler after heating the reactor provided by own pyrolysis oil-fuel combustion in a special furnace apart of reactor, including the pyrolysis off-gas afterburning therein too. For processing the steam is super-heating up to pyrolysis operating temp 400-450°C, being that performed in a steam coil tube around and along with reactor heating together, and feeding into reactor as shown and considered next bellow. With reference to [36] for all of unit numbers to be observed, the general design overview of the plant is shown in Pict.2 where only the units above are noticed in caption.

Pict. 1. ENRESTEC thermal units for waste tire pyrolysis with steam: 1 – oil fuel burner, 2 – furnace, 3 – pyrolysis reactor heating box, 4 – double-screw reactor in the box, 5 – second heat

steam boiler.

corresponded to the theoretical solution on such of dependence with pressure and pyrolysis temp condition considered just in the next part of the article. And specially concerning the steam use for tire pyrolysis in connection with that and with reference to U.S. Patent 866 758, it had been first claimed even in 1907, resulting in the pure carbon char yield with heating directly by steam at 315°C that was well enough for such of recycling (reclaiming in original), provided with the rubber particles intensively piping by the same steam flow. Much more late with reference to [9, 10, 33] the direct heating pyrolysis method by superheated steam feeding into reactor at 500-600°C has been claimed and published as a new idea of that in the 2000s. In accordance with that a multi-batch pyrolysis tunnel system has been elaborated in HMTI for recycling the whole tires in cartridges which continually moving through the long tunnel heating by this way. The idea was realized in a large scale commercial plant per 120 t/day in Lithuania, 2004-2005 but it was not effective as both low productivity and quality of carbon black because of low operating conditions as for heating the bulk of whole tires in cartridge, as for heating the large-long tunnel by steam feeding at all.

Independently the reactor type and heating system with references to [25, 28, 30, 31] some of catalytic pyrolysis methods could be noticed as proposed for enhancing the oil productivity and provided with such of solid or liquid additives as Na2CO3, AlCl3, KOH, Y-, USY- or ZSN- zeolites etc. Being restricted in detail consideration on that for sake of the present article, it can be shortly characterized as no radical catalytic dependence was obtained for commercial use so as a little of addition could be used for its action without contamination of the oil or carbon black with rest of the same addition in kind of solid or gas. Proposing the steam actually is not a catalyst, but simply a carrier gas, nevertheless with reference to [24] it is interesting to notice that the oil yield with steam pyrolysis of the oily shale (in a laboratory scale) was increased by 34%, comprising that with nitrogen at the same operating and thermal conditions. In contrast, no real difference for oil yield rate was obtained with olefins or tires pyrolysis in [22, 27], but excluding only a high steam reactivity with tire char for its next purification with carbon black by-production.

As for the steam pyrolysis in the present article, it is obviously proposed that oil residual content in the carbon black is objectively corresponded to the pyrogas concentration in pyrolysis reactor where the gas is saturating all inside, including the carbon black porous structure too as considered next in the present article. Even the tire pyrolysis would be first performed ideally as 100% oil volatile matters gasified entirely, next pyrogas inside the carbon porous structure will be cooling and condensing there in kind of the same oil residual matters after the carbon discharge from reactor. To replace the pyrogas from the carbon and so way to clean that simply, it is also well known as an inert gas (e.g. nitrogen as most available) could be feeding into pyrolysis reactor finally, provided the gas feeding rate to be corresponded to the tire pyrolysis rate. If no such of inert gas blowing up the reactor theoretically it is about 3% oil residual matters in the carbon by-product by this way. But really it is not commercial solution because of high cost for any inert gas supply relatively to price of the carbon black by-product. A second thermal processing (firing) of the carbon black at 750-800°C is required after pyrolysis so to purify that off the oil residual for next treatment with commercial use, or even for its storage to be clean off the specific smell which is steady appeared at the oil residual content 5-6% and more.

corresponded to the theoretical solution on such of dependence with pressure and pyrolysis temp condition considered just in the next part of the article. And specially concerning the steam use for tire pyrolysis in connection with that and with reference to U.S. Patent 866 758, it had been first claimed even in 1907, resulting in the pure carbon char yield with heating directly by steam at 315°C that was well enough for such of recycling (reclaiming in original), provided with the rubber particles intensively piping by the same steam flow. Much more late with reference to [9, 10, 33] the direct heating pyrolysis method by superheated steam feeding into reactor at 500-600°C has been claimed and published as a new idea of that in the 2000s. In accordance with that a multi-batch pyrolysis tunnel system has been elaborated in HMTI for recycling the whole tires in cartridges which continually moving through the long tunnel heating by this way. The idea was realized in a large scale commercial plant per 120 t/day in Lithuania, 2004-2005 but it was not effective as both low productivity and quality of carbon black because of low operating conditions as for heating the bulk of whole tires in cartridge, as for heating the large-long tunnel by steam feeding at

Independently the reactor type and heating system with references to [25, 28, 30, 31] some of catalytic pyrolysis methods could be noticed as proposed for enhancing the oil productivity and provided with such of solid or liquid additives as Na2CO3, AlCl3, KOH, Y-, USY- or ZSN- zeolites etc. Being restricted in detail consideration on that for sake of the present article, it can be shortly characterized as no radical catalytic dependence was obtained for commercial use so as a little of addition could be used for its action without contamination of the oil or carbon black with rest of the same addition in kind of solid or gas. Proposing the steam actually is not a catalyst, but simply a carrier gas, nevertheless with reference to [24] it is interesting to notice that the oil yield with steam pyrolysis of the oily shale (in a laboratory scale) was increased by 34%, comprising that with nitrogen at the same operating and thermal conditions. In contrast, no real difference for oil yield rate was obtained with olefins or tires pyrolysis in [22, 27], but excluding only a high steam reactivity with tire char

As for the steam pyrolysis in the present article, it is obviously proposed that oil residual content in the carbon black is objectively corresponded to the pyrogas concentration in pyrolysis reactor where the gas is saturating all inside, including the carbon black porous structure too as considered next in the present article. Even the tire pyrolysis would be first performed ideally as 100% oil volatile matters gasified entirely, next pyrogas inside the carbon porous structure will be cooling and condensing there in kind of the same oil residual matters after the carbon discharge from reactor. To replace the pyrogas from the carbon and so way to clean that simply, it is also well known as an inert gas (e.g. nitrogen as most available) could be feeding into pyrolysis reactor finally, provided the gas feeding rate to be corresponded to the tire pyrolysis rate. If no such of inert gas blowing up the reactor theoretically it is about 3% oil residual matters in the carbon by-product by this way. But really it is not commercial solution because of high cost for any inert gas supply relatively to price of the carbon black by-product. A second thermal processing (firing) of the carbon black at 750-800°C is required after pyrolysis so to purify that off the oil residual for next treatment with commercial use, or even for its storage to be clean off the specific smell

for its next purification with carbon black by-production.

which is steady appeared at the oil residual content 5-6% and more.

all.

In this connection with reference to [33-38] a new pyrolysis system for waste tire commercial recycling in the reactor of double-screw type with steam has been elaborated in HMTI (Belarus) for ENRESTEC Co. (Taiwan) in 2006, being next installed and applied by author's guidance in 2007-2008. The plant has been designed as a double-line pyrolysis system per 1 t/hr every (Pict.1, Fig.1) with carbon black quality as 1-2% oil residual matters, including more proof-explosion safety inside the reactor due to diluting the pyrolysis gases (pyrogas) with steam, as well as more sealing the reactor with steam feeding against air penetration into reactor under the low-operating pressure as required. Steam is self-producing in a second-heat boiler after heating the reactor provided by own pyrolysis oil-fuel combustion in a special furnace apart of reactor, including the pyrolysis off-gas afterburning therein too. For processing the steam is super-heating up to pyrolysis operating temp 400-450°C, being that performed in a steam coil tube around and along with reactor heating together, and feeding into reactor as shown and considered next bellow. With reference to [36] for all of unit numbers to be observed, the general design overview of the plant is shown in Pict.2 where only the units above are noticed in caption.

Pict. 1. ENRESTEC thermal units for waste tire pyrolysis with steam: 1 – oil fuel burner, 2 – furnace, 3 – pyrolysis reactor heating box, 4 – double-screw reactor in the box, 5 – second heat steam boiler.

Waste Tire Pyrolysis Recycling with Steaming:

matters of its content).

μ

residual matters:

where *Vi* is volume of the particle,

objectively proposed as not bellow

Heat-Mass Balances & Engineering Solutions for By-Products Quality 217

As for some history, the first steam use for rubber waste pyrolysis by U.S. Patent 866758 had been tested even in 1907, being concluded that the temp 600 F (315°C) is well enough for rubber vulcanized particles to be full pyrolized in the steam pneumatic flow condition at this temp. Comparing that to pyrolysis at 450–500°C as required without steam now, that is good evidence of steam effect by its diffusion with heat penetration inside every of the particles even at the lower temp. Being not so porous initially, with pyrolysis process in time the rubber is destructing and becoming as the carbon black of its fine porous structure that finally is well suitable for its cleaning by steam diffusion inside. In this connection it is all reason first to consider and evaluate even theoretically why and what is a limit on the carbon black quality by scrap tire pyrolysis recycling without steam (in terms of residual oil

By usual pyrolysis way as without steam, even all the tire volatile matters are proposed to be initially gasified, next there is to be objectively some of tire oil matters residual in carbon black (CB) because of its secondary contamination with the same volatized matters that recondensed in the CB porous structure after its cooling with discharge from reactor. Being some idealized and simplified, such of contamination can be theoretically formulated and estimated as bellow here. Let use the ideal gas law equation for the tire pyrolysis volatile matters (hydrocarbon vapors and inherent gases or simply pyrogas) which are proposed to be heated finally up to the temp *T* = 450°C (723 K) which is rather above all of pyrolysis liquid-gas phase transition points, and so allows the pyrogas can be considered as a superheated one similar to an ideal gas, which molecular weight is proposed to be equal to that of tire pyrolysis oil condensed from the pyrogas as the same. With reference to [1.2] it is about

= 210 and we have the next pyrogas mean-total density in tire pyrolysis reactor at the

*m pV RT* μ

> <sup>5</sup> 10 210 8314 723

Pyrogas of the density above is saturating all inside the reactor operating volume, including the bulk between CB particles and inside every of the particles too, being these of the inner porous structure. By this consideration we have the next pyrogas quantity discharged with anyone particle of CB porous product which will be next condensed therein as the oil

> *m V oil i i* ( ) = ⋅ ρ σ

σ

σ

structure is a light as conveniently proposed by density not above

<sup>=</sup> , (1)

, (3)

*cb* = 100 kg/m3:

is factor of the particle structure porosity which is

ρ

= 90%, and the pure mass of the particle solid-porous

<sup>⋅</sup> == = ≅ ⋅ 3.4 kg/m3. (2)

temp 450°C and near the normal pressure operating conditions ( *p* = 105 Pa):

*m p V RT* μ

ρ

**2. Theoretical limit on carbon black quality without steam** 

Fig. 1. Steam pyrolysis equipment and system flow diagram: 1 – pyrolysis reactor, 2 – reactor heating box, 3 – oil condenser, 4 – steam condenser, 5 – off-gas fan, 6 – second heat steam boiler, 7 – steam super-heating coil, 8 – oil Laval-separator, 9 – oil-water gravity separating tank, 10 – gas-oil furnace.

Pict. 2. Design overview of the ENRESTEC plant: 1,2 – both furnaces with oil fuel burners at front; 3, 4 – both heating boxes with every of double-screw reactor inside; 5 – heat utilizing steam boilers.

Fig. 1. Steam pyrolysis equipment and system flow diagram: 1 – pyrolysis reactor, 2 – reactor heating box, 3 – oil condenser, 4 – steam condenser, 5 – off-gas fan, 6 – second heat steam boiler, 7 – steam super-heating coil, 8 – oil Laval-separator, 9 – oil-water gravity

Pict. 2. Design overview of the ENRESTEC plant: 1,2 – both furnaces with oil fuel burners at front; 3, 4 – both heating boxes with every of double-screw reactor inside; 5 – heat utilizing

separating tank, 10 – gas-oil furnace.

steam boilers.

As for some history, the first steam use for rubber waste pyrolysis by U.S. Patent 866758 had been tested even in 1907, being concluded that the temp 600 F (315°C) is well enough for rubber vulcanized particles to be full pyrolized in the steam pneumatic flow condition at this temp. Comparing that to pyrolysis at 450–500°C as required without steam now, that is good evidence of steam effect by its diffusion with heat penetration inside every of the particles even at the lower temp. Being not so porous initially, with pyrolysis process in time the rubber is destructing and becoming as the carbon black of its fine porous structure that finally is well suitable for its cleaning by steam diffusion inside. In this connection it is all reason first to consider and evaluate even theoretically why and what is a limit on the carbon black quality by scrap tire pyrolysis recycling without steam (in terms of residual oil matters of its content).

### **2. Theoretical limit on carbon black quality without steam**

By usual pyrolysis way as without steam, even all the tire volatile matters are proposed to be initially gasified, next there is to be objectively some of tire oil matters residual in carbon black (CB) because of its secondary contamination with the same volatized matters that recondensed in the CB porous structure after its cooling with discharge from reactor. Being some idealized and simplified, such of contamination can be theoretically formulated and estimated as bellow here. Let use the ideal gas law equation for the tire pyrolysis volatile matters (hydrocarbon vapors and inherent gases or simply pyrogas) which are proposed to be heated finally up to the temp *T* = 450°C (723 K) which is rather above all of pyrolysis liquid-gas phase transition points, and so allows the pyrogas can be considered as a superheated one similar to an ideal gas, which molecular weight is proposed to be equal to that of tire pyrolysis oil condensed from the pyrogas as the same. With reference to [1.2] it is about μ = 210 and we have the next pyrogas mean-total density in tire pyrolysis reactor at the temp 450°C and near the normal pressure operating conditions ( *p* = 105 Pa):

*m pV RT* μ<sup>=</sup> , (1)

$$
\rho = \frac{m}{V} = \frac{p\mu}{RT} = \frac{10^5 \cdot 210}{8314 \cdot 723} \equiv 3.4 \text{ kg/m3.} \tag{2}
$$

Pyrogas of the density above is saturating all inside the reactor operating volume, including the bulk between CB particles and inside every of the particles too, being these of the inner porous structure. By this consideration we have the next pyrogas quantity discharged with anyone particle of CB porous product which will be next condensed therein as the oil residual matters:

$$m\_{oil(i)} = V\_i \rho \cdot \sigma \,, \tag{3}$$

where *Vi* is volume of the particle, σ is factor of the particle structure porosity which is objectively proposed as not bellow σ = 90%, and the pure mass of the particle solid-porous structure is a light as conveniently proposed by density not above ρ*cb* = 100 kg/m3:

Waste Tire Pyrolysis Recycling with Steaming:

heat-mass balance solution on that as following:

*s t <sup>G</sup> <sup>Y</sup>*

follows:

*GAS*min ≅ 10%:

( )

excessive supply index for fuel combustion,

*oil t*

*<sup>G</sup>*<sup>=</sup> ( ) () 2 3

where *<sup>a</sup> g* ≈ 15 kg/kg is air stoichiometry index per 1 kg of liquid fuel,

*c T Tg X GAS*

<sup>−</sup> <sup>=</sup> + =

α

( ) ( ) *pg g g a pw s a s*

*c TT h*

( )( ) *<sup>t</sup> <sup>p</sup> <sup>t</sup> <sup>p</sup> a t q* = −+ *c TT h* is a specific heat capacity per 1 kg pyrolysis, ( )( ) *ss <sup>p</sup> <sup>s</sup> <sup>p</sup> <sup>s</sup> q* = − *c TT* is a specific heat per 1 kg steam super-heating, ( )( ) *<sup>s</sup> <sup>p</sup> ws a s q* = −+ *c TT h* is a specific heat per 1 kg steam producing,

() 2 3 ( ) *g pg g g qc T T* = − is an enthalpy per 1 kg furnace gas flow.

*<sup>G</sup> <sup>X</sup>*

Heat-Mass Balances & Engineering Solutions for By-Products Quality 219

burning. It is a novel question on the tire pyrolysis recycling because even without steam there is not such of general analysis in this field until now. With all references to [35, 36] the question on the oil fuel quantity to be combusted with pyrolysis off-gas together for heating the process with steam feeding and self-producing at the same time, it was answered by the

*<sup>G</sup>* <sup>=</sup> ( ) <sup>2</sup>

*t gas r f*

*q g A q*

1 2

combustion, *E E <sup>f</sup>* = *<sup>r</sup>* = 0.95–0.97 is the furnace and reactor thermal efficiency by every heat emission to outside 3–5% proposed, including the supplementary specific calculations as

With the same references to [35, 36] the question what is the off-gas burning rate to be for heating the pyrolysis reactor without oil fuel, it has been simply obtained from (7) with proposition 0 *X* = which numerical solution at the pyrolysis conditions above is

The testing-operating data on the process with max 10% approximation are presented in the Table 1, including the standard analysis data on the pyrolysis oil and carbon black products quality referenced to [36]. It should be noted initially that testing the commercial process as considered above, as well as any other of such thermal processes with heat-mass balance calculation too, it is performed as 5–10 % discrepancy usually to be allowed. At the same time, concerning the carbon black recycling up to 1–2% of CnHm-residual quality as required for the market, it is clear that the latter can not be the subject for modeling, but only testing at the thermal parameters of the process under question. As for the non-calculating parameters which could be important for the carbon black quality, it is also clear that the

2

<sup>=</sup> <sup>−</sup> , (8)

*t gas r f*

*Q EE A* α

min

*<sup>q</sup> GAS*

 α

*oil r f*

*g a ss s*

*q Q E E A GAS Q EE A*

1

− −⋅ <sup>=</sup> <sup>−</sup> , (6)

*<sup>q</sup>* <sup>=</sup> , (6')

*<sup>q</sup> GAS <sup>X</sup>*

 α

<sup>+</sup> , (7)

<sup>1</sup> = 1.3–1.35 is air

α

<sup>2</sup> = 1.05–1.1 is the index for gas fuel

α

− + 1 2 100

α

*g s*

*q* α

α

$$m\_{cb(i)} = V\_i \rho\_{cb\\_\nu} \tag{4}$$

by which relation the next simple estimation is obtained:

$$\frac{m\_{\rm oil(i)}}{m\_{cb(i)}} = \sigma \frac{\rho}{\rho\_{cb}} = 0.9 \frac{3.4}{100} \equiv 3\%. \tag{5}$$

Concerning the theoretical limit on steam dilution with pyrogas as for its proof-explosive condition in reactor, with author's reference to [34] it is above 5 kg steam per 1 kg tire required so to provide such of condition with air. It is too much for real observation, comparing that to available steam self-producing rate by second heat after heating the reactor. And it is the question for analytical consideration and formulation bellow as it was realized in the operating process with steam in Taiwan.

#### **3. Heat-mass balance analysis on waste tire pyrolysis with steam**

Referencing namely to [35], the first version of the thermal units and flow diagram of the tire-steam pyrolysis process in Taiwan in 2007-2008 is shown in Fig.1, where steam is selfproducing in the second heat boiler 6 with flue gas flow after heating the double-screw reactor 1 in the hot gas box 2 connected with the furnace 10 for oil combustion with off-gas after-burning together. Steam is super-heating in the tube coil 7 inserted as along-around the reactor in the hot box too, and next steam is feeding into the reactor for steaming the tire pyrolysis as considered above. The pyrogas with used steam flow together is piping to the oil and steam condenser 3-4 in line correspondingly, being provided by suction performance of the gas fan 5 that pipes the combustible pyrolysis off-gas residual after oil-steam condensing into the furnace. Flue gas from the furnace is piping for heating both reactor and steam boiler in line, and next to exhaust scrubber. The real view on these thermal units (furnace, reactor, steam boiler) is shown in Pict.1.

The tire scrap is moving and mixing by screw along-inside the reactor by usual way of such processing, being pyrolyzed and discharged to outside with the carbon black to be next cooling, screening and crashing for magnetic separation against some of steel cord wire residual. Pyrolysis oil is separating by Laval centrifugal unit 8 so to produce the own light oil for burning in the furnace and so heating the reactor and boiler. Ideally the pyrolysis oil and steam were proposed to be condensing in 3-4 separately and next steam water to be cycling and pumping to the boiler again simply as it is shown in Fig.1. Really it was not of such ideal proposition and steam was partially condensing with oil together, as well as all different benzene's and low-temp aromatic fractions of the pyrolysis oil were condensable and soluble with steam water too. Considering that especially for development next bellow in p.6, here we formulate and calculate simply the heat-mass balance of reactor and other thermal equipment above, not including the condenser as not involved with pyrolysis process. Due to the reactor heating is based on the off-gas afterburning, being the latter well available and corresponded to the pyrolysis rate, as well as the steam for the process is selfproduced after heating the reactor and next super-heated along with reactor heating too, all of that is evidently depended on each other and so we can formulate analytically and calculate numerically the oil fuel specific consumption per 1 kg tire additively to the off-gas

*m V cb i i cb* ( ) = ρ

Concerning the theoretical limit on steam dilution with pyrogas as for its proof-explosive condition in reactor, with author's reference to [34] it is above 5 kg steam per 1 kg tire required so to provide such of condition with air. It is too much for real observation, comparing that to available steam self-producing rate by second heat after heating the reactor. And it is the question for analytical consideration and formulation bellow as it was

Referencing namely to [35], the first version of the thermal units and flow diagram of the tire-steam pyrolysis process in Taiwan in 2007-2008 is shown in Fig.1, where steam is selfproducing in the second heat boiler 6 with flue gas flow after heating the double-screw reactor 1 in the hot gas box 2 connected with the furnace 10 for oil combustion with off-gas after-burning together. Steam is super-heating in the tube coil 7 inserted as along-around the reactor in the hot box too, and next steam is feeding into the reactor for steaming the tire pyrolysis as considered above. The pyrogas with used steam flow together is piping to the oil and steam condenser 3-4 in line correspondingly, being provided by suction performance of the gas fan 5 that pipes the combustible pyrolysis off-gas residual after oil-steam condensing into the furnace. Flue gas from the furnace is piping for heating both reactor and steam boiler in line, and next to exhaust scrubber. The real view on these thermal units

The tire scrap is moving and mixing by screw along-inside the reactor by usual way of such processing, being pyrolyzed and discharged to outside with the carbon black to be next cooling, screening and crashing for magnetic separation against some of steel cord wire residual. Pyrolysis oil is separating by Laval centrifugal unit 8 so to produce the own light oil for burning in the furnace and so heating the reactor and boiler. Ideally the pyrolysis oil and steam were proposed to be condensing in 3-4 separately and next steam water to be cycling and pumping to the boiler again simply as it is shown in Fig.1. Really it was not of such ideal proposition and steam was partially condensing with oil together, as well as all different benzene's and low-temp aromatic fractions of the pyrolysis oil were condensable and soluble with steam water too. Considering that especially for development next bellow in p.6, here we formulate and calculate simply the heat-mass balance of reactor and other thermal equipment above, not including the condenser as not involved with pyrolysis process. Due to the reactor heating is based on the off-gas afterburning, being the latter well available and corresponded to the pyrolysis rate, as well as the steam for the process is selfproduced after heating the reactor and next super-heated along with reactor heating too, all of that is evidently depended on each other and so we can formulate analytically and calculate numerically the oil fuel specific consumption per 1 kg tire additively to the off-gas

ρ σ

ρ

3.4 0.9 100

by which relation the next simple estimation is obtained:

realized in the operating process with steam in Taiwan.

(furnace, reactor, steam boiler) is shown in Pict.1.

( ) ( )

*cb i cb*

**3. Heat-mass balance analysis on waste tire pyrolysis with steam** 

*oil i*

*m m* , (4)

== ≅ 3%. (5)

burning. It is a novel question on the tire pyrolysis recycling because even without steam there is not such of general analysis in this field until now. With all references to [35, 36] the question on the oil fuel quantity to be combusted with pyrolysis off-gas together for heating the process with steam feeding and self-producing at the same time, it was answered by the heat-mass balance solution on that as following:

$$X = \frac{G\_{oil}}{G\_t} = \frac{q\_t - \left(Q\_{gas}E\_rE\_f - \alpha\_2 A\right) \cdot \text{GAS}}{Q\_{oil}E\_rE\_f - \alpha\_1 A},\tag{6}$$

$$A = q\_{ss} \frac{q\_{\mathcal{g}} g\_a}{q\_s} \, , \tag{6'}$$

$$Y = \frac{G\_s}{G\_t} = \frac{c\_{p(g)}(T\_{g2} - T\_{g3})g\_a}{c\_{p(w)}(T\_s - T\_a) + h\_s} (\alpha\_1 X + \alpha\_2 GAS) = \frac{q\_g}{q\_s} \left(\alpha\_1 X + \alpha\_2 \frac{GAS}{100}\right),\tag{7}$$

where *<sup>a</sup> g* ≈ 15 kg/kg is air stoichiometry index per 1 kg of liquid fuel, α<sup>1</sup> = 1.3–1.35 is air excessive supply index for fuel combustion, α<sup>2</sup> = 1.05–1.1 is the index for gas fuel combustion, *E E <sup>f</sup>* = *<sup>r</sup>* = 0.95–0.97 is the furnace and reactor thermal efficiency by every heat emission to outside 3–5% proposed, including the supplementary specific calculations as follows:

( )( ) *<sup>t</sup> <sup>p</sup> <sup>t</sup> <sup>p</sup> a t q* = −+ *c TT h* is a specific heat capacity per 1 kg pyrolysis, ( )( ) *ss <sup>p</sup> <sup>s</sup> <sup>p</sup> <sup>s</sup> q* = − *c TT* is a specific heat per 1 kg steam super-heating, ( )( ) *<sup>s</sup> <sup>p</sup> ws a s q* = −+ *c TT h* is a specific heat per 1 kg steam producing, () 2 3 ( ) *g pg g g qc T T* = − is an enthalpy per 1 kg furnace gas flow.

With the same references to [35, 36] the question what is the off-gas burning rate to be for heating the pyrolysis reactor without oil fuel, it has been simply obtained from (7) with proposition 0 *X* = which numerical solution at the pyrolysis conditions above is *GAS*min ≅ 10%:

$$\text{GAS}\_{\text{min}} = \frac{q\_t}{Q\_{\text{gas}} E\_r E\_f - \alpha\_2 A} \,'\,\tag{8}$$

The testing-operating data on the process with max 10% approximation are presented in the Table 1, including the standard analysis data on the pyrolysis oil and carbon black products quality referenced to [36]. It should be noted initially that testing the commercial process as considered above, as well as any other of such thermal processes with heat-mass balance calculation too, it is performed as 5–10 % discrepancy usually to be allowed. At the same time, concerning the carbon black recycling up to 1–2% of CnHm-residual quality as required for the market, it is clear that the latter can not be the subject for modeling, but only testing at the thermal parameters of the process under question. As for the non-calculating parameters which could be important for the carbon black quality, it is also clear that the

Waste Tire Pyrolysis Recycling with Steaming:

Heat-Mass Balances & Engineering Solutions for By-Products Quality 221

The factor of steam feeding rate as required for pyrolysis reactor of the screw tubular type has been some tested in connection with the carbon black dusting by an excessive steam flow, being the pyrolysis oil next condensed with much of the carbon sludge after its centrifugal separation from the oil finally. To prevent the carbon dusting the steam feeding rate is appropriated as max 200–250 kg/hr with reactor diameter 0.6 m, or simply 1 t/hr per 1 m2 of cross-section square of that in specific terms. So way it is enable to provide the steam

With reference to [35, 36] it was a few as 1–2% of wet carbon-oil slurry after its gravity and centrifugal separation from the pyrolysis oil with water. After the separation slurry was well marketable in Taiwan for use as the asphalt component in the road construction as they doing there. Otherwise, the slurry is proposed to be mixing with the scrap tire and recycling with pyrolysis too. The question concerning what is max possible sludge mixing-recycling rate with tire pyrolysis together (in percent relatively to tire), it has been obtained in [35, 36]

> <sup>Δ</sup> = ⋅ ( ) *Q E E A GAS gas r f* <sup>2</sup> *wB* − ⋅ α

where *ΔX* is an additional oil fuel consumption for sludge pyrolysis together with tire by

As an imperfection of the first plant the steam was condensed with pyrolysis oil together and steam water after its gravity or centrifugal separation from the oil it was contaminated with different benzene and other low-temp aromatic fractions of the tire pyrolysis oil as well soluble with water. Such of contaminated steam water has become a regulation problem for its normal cycling to steam boiler again and so for the new process to be certificated in Taiwan and elsewhere, including some other operating problems considered in [36, 37] and being all the problems resulted simply from the water tube condensers applied and operated with water at 35-40°C. Moreover, operating by this way it was resulted in a lowquality of pyrolysis oil fuel in terms of the flash point temp which was about 40°C

With reference to [36, 37] in project for ALPHA RECYCLAGE FRANCHE COMTE (France) in 2009-2010 the tire-steam pyrolysis system has been developed and modernized so as a new condenser of venturi type with steam too is used (Fig.2), being first and only one referenced as without steam but namely for such of application in [2]. The new steam pyrolysis system is operating with oil condensing at near 100°C, proposing so way its quality in terms of the flash point temp to be high as near 80°C. Steam is not condensing and all piping with residual off-gas to furnace by which way only the oil condenser 4 is required (see Fig.2). And so way the furnace gas flow is rather enhanced with steam for heating reactor and next boiler where steam is acting in a new manner as a heating agent too which analyzed here.

( ) ( ) (100 ) ( 100) *Bc T h c T* = − + ++ − *pw a s ps p* , (9')

, (9)

feeding rate for carbon black purification and so on as considered next in p.6.

by the similar heat-mass balance solution as following:

max *<sup>X</sup> SLU*

*X*

which calculation with conditions above it is obtained as *SLU*max ≅ 6%.

**4. Process development with oil venturi condenser** 

correspondingly.

pyrolysis exposition time and tire chips-shreds size, and more exactly even the scrap thickness size, are both of most important, provided the size of the shreds was used as min 2 inches and some more. Really and simply the low, middle and high temp pyrolysis condition in range 350–450°C had been tested with tire processing rate within 0.5–1 t/hr, provided the reactor length and screw rotary speed resulted in the tire processing time as max 13 min so as carbon black quality to be near the same in specification range 1–2%. As for the scrap tire thickness, it was supplied in range of 5–15 mm.


Table 1. Testing-Operating Data on Tire Pyrolysis Recycling With Steam (Taiwan-2008).

The process calculation by (6)–(8) is presented in Table 2 as carried out with low, middle and high-temp pyrolysis condition at 350, 400 and 450°C inside reactor correspondingly, correlating that to the tire shreds thickness 5, 10 and 15 mm proposed. The subject and result of the calculation is the oil fuel consumption and steam self-producing rate per 1 kg tire which is well corresponded to the testing data at the high-temp pyrolysis condition.


Table 2. Calculating Data (6)-(7) on Oil Burning (*X*) And Steam Self-Producing Rate (*Y*) With Variable Pyrolysis Off-Gas Burning Rate at the Different Operating Temperatures .

pyrolysis exposition time and tire chips-shreds size, and more exactly even the scrap thickness size, are both of most important, provided the size of the shreds was used as min 2 inches and some more. Really and simply the low, middle and high temp pyrolysis condition in range 350–450°C had been tested with tire processing rate within 0.5–1 t/hr, provided the reactor length and screw rotary speed resulted in the tire processing time as max 13 min so as carbon black quality to be near the same in specification range 1–2%. As

Off-gas burning rate (10% tire mass at 55 C), m3/hr 50 75 100 Light pyrolysis oil mean-daily burning rate, kg/hr 40 30 20 Steam self-producing rate (feeding to reactor), kg/hr 200 250 300 Off-gas-oil furnace max operating temperature, °C 950 1100 1150 Furnace gas temp Tg1 for reactor heating inlet, °C 850 900 950 Furnace gas temp Tg2 for reactor heating outlet, °C 450 480 510 Pyrolysis operating temp Tp inside reactor, °C 350 400 450 Sulfur content in pyrolysis oil, % - 1.15 - Carbon content in pyrolysis oil, % - 1.1 - CnHm-content in carbon black, % - 1.5 - Sulfur content in carbon black, % - 2.3 - Table 1. Testing-Operating Data on Tire Pyrolysis Recycling With Steam (Taiwan-2008).

The process calculation by (6)–(8) is presented in Table 2 as carried out with low, middle and high-temp pyrolysis condition at 350, 400 and 450°C inside reactor correspondingly, correlating that to the tire shreds thickness 5, 10 and 15 mm proposed. The subject and result of the calculation is the oil fuel consumption and steam self-producing rate per 1 kg tire

> Middle-temps: 10 mm shreds, *Tg1* = 900°C, *Tg2* = 500°C, *Tp* = 400°C

> > *Y*, kg/kg

*X*, kg/kg

6 (35-40 C) 0.00896 0.164 0.0199 0.236 0.0333 0.330 7 (40-45 C) 0.00261 0.162 0.0111 0.232 0.0245 0.326 8 (45-50 C) - 0.159 0.0024 0.229 0.0157 0.322 9 (50-55 C) - - - 0.226 0.0069 0.318 10 (55-60 C) - - - - - 0.314

Table 2. Calculating Data (6)-(7) on Oil Burning (*X*) And Steam Self-Producing Rate (*Y*) With Variable Pyrolysis Off-Gas Burning Rate at the Different Operating Temperatures .

which is well corresponded to the testing data at the high-temp pyrolysis condition.

*Y*, kg/kg

Low-temps: 5 mm shreds, *Tg1* = 850°C, *Tg2* = 450°C, *Tp* = 350°C

*X*, kg/kg

Tire pyrolysis rate, kg/hr 500 750 1000

> High-temps: 15 mm shreds: *Tg1* = 950°C, *Tg2* = 550°C, *Tp* = 450°C

> > *Y*, kg/kg

*X*, kg/kg

for the scrap tire thickness, it was supplied in range of 5–15 mm.

Pyrolysis oil condensed heat value: 42 МJ/kg Off-gas heat value (without steam): 39 MJ/m3

GAS (oil condensing corresponded temperature), %

The factor of steam feeding rate as required for pyrolysis reactor of the screw tubular type has been some tested in connection with the carbon black dusting by an excessive steam flow, being the pyrolysis oil next condensed with much of the carbon sludge after its centrifugal separation from the oil finally. To prevent the carbon dusting the steam feeding rate is appropriated as max 200–250 kg/hr with reactor diameter 0.6 m, or simply 1 t/hr per 1 m2 of cross-section square of that in specific terms. So way it is enable to provide the steam feeding rate for carbon black purification and so on as considered next in p.6.

With reference to [35, 36] it was a few as 1–2% of wet carbon-oil slurry after its gravity and centrifugal separation from the pyrolysis oil with water. After the separation slurry was well marketable in Taiwan for use as the asphalt component in the road construction as they doing there. Otherwise, the slurry is proposed to be mixing with the scrap tire and recycling with pyrolysis too. The question concerning what is max possible sludge mixing-recycling rate with tire pyrolysis together (in percent relatively to tire), it has been obtained in [35, 36] by the similar heat-mass balance solution as following:

$$SLLI\_{\text{max}} = \frac{\Delta X}{X} \cdot \frac{\left(Q\_{\text{gas}}E\_rE\_f - \alpha\_2A\right) \cdot GAS}{wB} \,, \tag{9}$$

$$B = c\_{p(w)}(100 - T\_a) + h\_s + +c\_{p(s)}(T\_p - 100) \, , \tag{9'}$$

where *ΔX* is an additional oil fuel consumption for sludge pyrolysis together with tire by which calculation with conditions above it is obtained as *SLU*max ≅ 6%.
