Evaluation of the Tire Industry of China based on Physical Input-Output Analysis
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R E S E A R C H A N D A N A LY S I S
Evaluation of the Tire
Industry of China based
on Physical Input–Output
Analysis
Ning YANG, Dingjiang CHEN, Shanying HU, Yourun LI,
and Yong JIN
Keywords:
Summary
industrial ecology
material flow analysis (MFA) With the rapid development of the rubber industry and its
reuse downstream sectors in China, the resulting sharp increase in
scrap tires the number of scrap tires is creating great environmental pres-
sustainable development sure. By considering the tire production, consumption, collec-
waste rubber
tion, and reuse processes as a whole system of tire material
flows, and based on physical input–output analysis (IOA), this
article analyzes the status quo of China’s tire industry and per-
forms a comparative study between China and Europe. The
study shows that the tire industry of China in 2005 and that of
Europe in 1996 are similar in material-flow characteristics. To
make the best use of materials, it is necessary to strengthen
the reuse of scrap tires in China. A scenario analysis is pre-
sented to show the effects of improving the reuse process
from the viewpoint of IOA.
Address correspondence to:
Ning Yang
Center for Industrial Ecology
Department of Chemical Engineering
Tsinghua University
Beijing 100084, China
yangning99@tsinghua.org.cn
c 2010 by Yale University
DOI: 10.1111/j.1530-9290.2010.00223.x
Volume 14, Number 3
www.blackwellpublishing.com/jie Journal of Industrial Ecology 457R E S E A R C H A N D A N A LY S I S
Introduction
Currently, reusing waste materials has become
one of the most important ways to meet the
rapidly growing demands for resources and to
achieve sustainable development. In 2007, the
world’s rubber consumption reached nearly 23
million tonnes (IRSG 2008) and generated much
waste rubber—of which about 60%–70% was
from waste tires. It is estimated that by 2010,
China will have produced more than 300 million
tires, which has resulted in more than 200 mil-
lion waste tires, the weight of which is around 5.2
million tonnes (Wen and Xu 2006).
Today the tire industry brings with it much
more pressure on the environment and threats
to human health. The expansion of the scale of
tire production is leading to a growing demand Figure 1 Input–output modeling. i, j, k = nodes of
for energy and materials, and the release of much processes; fkj = flow (money, mass, or energy per
more waste to the environment. The accumula- unit time) from process j to process k; fjk = flow
tion of large quantities of scrap tires has taken (money, mass, or energy per unit time) from process
up considerable space because they are not easily k to process j; zk0 = inflow to process k from
compacted. Disposing of scrap tires in landfills is outside the system; y0k = outflow from process k to
the most common solution (Fullana et al. 2000). outside the system.
But long-buried scrap tires can result in vicious
fires that are very difficult to extinguish, and can in a given economic system. A group of re-
allow mosquitoes or bacteria to breed and trans- searchers (Patten et al. 1976; Finn 1977) ex-
mit disease. tended this approach to study material and energy
To achieve the sustainable development of flows in natural ecosystems. Based on their work,
the tire industry, especially in China, it is neces- Bailey (2000) used this approach to study mate-
sary to study its current status and recognize the rial flows in industrial systems. One of Bailey’s
characteristics of the system from a macroscopic case studies was the tire material flow system of
perspective. This article analyzes the status quo of Europe in 1996. This article follows Bailey’s path
China’s tire industry from a systematic perspec- by applying IOA to studying the tire industry of
tive, in which we view it as a system composed China. We have slightly improved Bailey’s six-
of the tire production, consumption, collection, node model of the system by reclassifying the
and reuse processes. This allows us to reorganize nodes into four processes, and studied the im-
all of the processes of the tire industrial system pacts of each process on the whole system.
and operate analogous to the way in which natu-
ral ecosystems operate to some extent, in which
materials are recycled and efficiently used. Input– Analysis Approach and Model of
output analysis (IOA) is applied in this study Tire Industrial System
in order to obtain a better understanding of the
Physical Input–Output Analysis
characteristics of the complex material flows in
this system, and to quantitatively reveal the im- Figure 1 is a general illustration of a system
portance of each process in the system. composed of processes and linkage flows, in which
IOA, originally developed by Leontief (1966), processes are represented by nodes i, j, k, . . .; fkj
has been successfully applied to the study of stands for the flow (of money, mass, or energy,
monetary flows, with the ability to trace all of all per unit time) from process j to process k; zk0
the direct and indirect flows between all nodes stands for the inflow to process k from outside
458 Journal of Industrial EcologyR E S E A R C H A N D A N A LY S I S
the system; and y0k stands for the outflow from each process.
process k to outside the system.
w = (w1 , w2 , . . . , wn )
The throughflow Tk , defined in equation (1)
n
below, calculates all flows passing through node n
n
∗ ∗ ∗
k, and means “the rate of the flow through process = ni 1 , ni 2 , . . . , ni n
k” (Finn 1977). If the sum of all outputs is not i =1 i =1 i =1
⎛ ⎞
equal to that of all inputs, this means that the n
n
accumulation changes as the flows pass through ⎝ n i∗j ⎠ (5)
process k; x· k+ represents the increase of the ac- j =1 i =1
cumulation, and x· k− represents the decrease of
the accumulation.
w∗ = w1∗ , w2∗ , . . . , wn∗
n
n ⎛ ⎞
Tk = f k j + z k0 − x· k− = fi k n n
n
j =1 i =1 =⎝ n ∗1 j , n ∗2 j , . . . , n ∗n j ⎠
+ y0k + x· k+ , k = 1, 2, . . . n (1) j =1 j =1 j =1
⎛ ⎞
The instantaneous outflow fraction qij (Bailey n
n
⎝ (6)
2000; Bailey et al. 2004) is defined in equation n i∗j ⎠
j =1 i =1
(2), and Q∗ in equation (3) is the matrix form of
qij ∗ , which represents all direct outflows from each
process to other processes per unit of product.
Model of Tire Industrial System
q i∗j = f i j /Tj , i = 1, 2, . . . n (2)
The model shown in figure 2 was presented by
Bailey (2000) and has been revised here to in-
Q∗ = [q i∗j ]n×n , i , j = 1, 2, . . . n (3) clude nodes for retreading, recycling, and other
uses of scrap tires as subprocesses of the reuse pro-
The Leontief inverse matrix N∗ is represented cess. According to this model, the tire industrial
by equation (4). In this matrix, all direct and system is divided into four processes. These are
indirect flows are accounted for. node 1 for production, node 2 for consumption,
node 3 for collection, and node 4 for reuse, which
N∗ = [n i∗j ]n×n = (I − Q∗ )−1 (4)
includes nodes 4 for retreading, 4 for recycling,
From the point of view of the contribu- and 4 for other uses.
tions to the processes, the column vector of N∗ , Node 4 represents the production of new tires
n∗j = (n ∗1 j , n ∗2 j , . . . n ∗n j ) , represents the contri- by retreading whole scrap tires, which provides
butions of process j to every process, and the the highest added value and emits the least pol-
sum of the column vector elements, in=1 n i∗j , lution. Node 4 represents the mixing of regener-
represents the contribution of process j to the ated rubber into new tires during the production
whole system. From the point of view of the de- process, which provides a lower added value than
mands of the processes, the row vector of N∗ , 4 . Node 4 represents other reuse of scrap tires,
ni∗ = (n i∗1 , n i∗2 , . . . n i∗n ), represents the demands such as to produce rubber cushions and rubber
placed by process i on every process, and the overshoes or for use as architectural materials,
sum of the row vector elements, nj=1 n i∗j , repre- which provides the lowest added value. Many
sents all of the demands of process i on the whole scrap tires are thermally decomposed or used as
system. fuel; here, no rubber—but other materials such
n ∗
Since the relative sizes of i =1 n i j and as steel—is reused. We do not consider this pro-
n ∗
n
j =1 i j reflect the relative contributions of a portion to be part of the reuse process, because it
given process to the system and the demands of is targeted primarily at energy production and
that process on the system, we use the vectors w not at reuse of materials, and could generate
and w∗ defined in equations (5) and (6) to nor- large amounts of poisonous gases and environ-
malize the relative contributions and demands of mental pollution. In order to obtain the highest
Yang et al., Evaluation of the Tire Industr y of China based on Physical IOA 459R E S E A R C H A N D A N A LY S I S
Figure 2 Model of the tire
industrial system. The tire industrial
system is divided into four processes
of production, consumption,
collection, and reuse, which includes
retreading, recycling, and other uses.
added value and least pollution, it is necessary to in 1996. The data for China was reconstructed
strengthen the reuse process, especially retread- from disparate sources; some was obtained di-
ing and recycling. rectly from yearbooks, websites, or other refer-
In this model, tires are made from virgin ma- ences, and the rest was obtained mainly through
terial (z10 ) and recycled rubber (f 14 ) in node 1. indirect calculation by the law of conservation of
During production, some manufacturing waste is mass or estimated using technological process pa-
generated and lost to outside the system (y01 ), the rameters, and reasonable assumptions, if needed.
amount of which depends on the production ca- Because the material flow data was difficult to
pacity. Some tires that do not meet quality spec- collect, we have collected data for China for the
ifications are collected to be treated as scrap tires year 2005 only, which may represent the current
(f 31 ). The products are used domestically in the status quo to some extent. The data sources and
manufacture of automobiles (f 21 ); exports are ex- flow calculations are presented in table 2 and
cluded in the model. Some rubber is lost to the table 3 of this paper. The data investigated here
environment by wear and tear (y02 ) during the for Europe in 1996 was taken from Weaver
tires’ use phase. There may be an accumulation (1996); data for other years is unavailable to us at
x· 2+ at node 2 when the number of motor ve- present. In Weaver’s analysis, accumulation x· 2+
hicles increases sharply. The remaining material had not been considered, so it is blank here in
flows into the collection process (f 32 ) as scrap the last row, second column of table 1.
tires, some of which are in good condition and
are retreaded (f 4 3 ) with the use of virgin mate-
rial (z4 0 ) and a small amount of recycled rubber
Material Input–Output Analyses of Cases
(f 4 4 ), and then reflowed to consumption (f 24 ).
and Comparative Study
Some of the materials recycled from scrap tires
proceed to other uses (f 4 3 ). The waste flowing The data in table 1 was used to calculate w
out from node 4 is emitted to the environment and w ∗ according to equations (1–6). A com-
(y04 ). The recycled material is also used to pro- parison of w and w∗ between China (2005)
duce regenerated rubber (f 4 3 ) and flows to the and Europe (1996) is shown in table 4. The el-
process of production (f 14 ) or retreading (f 4 4 ). ement representing the reuse process is the sum
Most of the materials flowing out from node 3 of the elements representing the processes repre-
(y03 ) are sent directly to a landfill or for inciner- sented by 4 (retreading), 4 (recycling), and 4
ation. (other uses). The data is visualized as bar charts in
figure 3.
Case Studies Although the tire industrial systems of China
in 2005 and of Europe in 1996 are significantly
Data on the Material Flow for China
different in the details of the flow data, IOA
in 2005 and for Europe in 1996
shows similar results for the two systems in terms
Table 1 shows material flow data for the tire of both the relative contributions of the four
industrial systems of China in 2005 and of Europe processes to the system (w ) and their relative
460 Journal of Industrial EcologyR E S E A R C H A N D A N A LY S I S
Table 1 Data on the material flow in the tire industrial systems of China in 2005 and of Europe in 1996
(kilotons per year)
Flow Brief description China Europe
z10 Virgin material to production 3,282 2,506
z4 0 Virgin material to retreading 28 74
y01 Manufacturing waste to environment 50 50
y02 Consumption wear and tear to environment 317 275
y03 Scrap tires to landfill or incineration 1,710 2,125
y04 Reused tire materials to environment 20 130
f14 Recycled rubber to production 173 19
f21 Tire products to consumption 3,307 2,400
f24 Retreaded tires to consumption 175 375
f31 Production wastes to be collected 99 75
f32 Scrap tires after consumption to be collected 1,950 2,500
f4 3 Recycled material to other use 20 130
f4 3 Scrap tires to be retreaded 140 300
f4 4 Recycled rubber to retreading 7 1
f4 3 Recycled material to regenerated rubber 180 20
x· 2+ Tire products accumulation 1,215 —
demands on the system (w ∗ ). From the point scrap truck tires can be retreaded, but this has
of view of the contributions, figure 3(a) shows been done for only 20–40%. In developing coun-
that the production process plays the most im- tries, for various reasons, tires become seriously
portant role in the system, the consumption pro- frayed at early stages of use. This means that the
cess the second most important role, and then fraction of scrap tires that can be retreaded rela-
the collection process. The reuse process makes tive to the total number of scrap tires is 10–20%
the least important contribution to the whole sys- lower than the value for developed countries. In
tem. From the point of view of demand, as shown China, 20–30% of scrap tires can be retreaded,
in figure 3(b), the reuse process obviously places but this has been done for only 8–15% (Yu 2006).
the greatest demands on the system, which indi- From a technical point of view, the percentage of
cates that the input from the system to the reuse regenerated rubber mixed into the new material
process is much more than the output from that used to produce new tires can be at least 10% us-
process to the system. ing ordinary regenerated rubber powder and 20%
The percentage of scrap tires used for retread- using a modified regenerated rubber powder (Hu
ing (f 4 3 /T3 ) is 12% for Europe and 7% for China, et al. 2007). The real situation is far from what
and the percentage of regenerated rubber used to current technology can achieve.
produce new tires (f 14 /(f 14 + z10 )) is 1% for
Europe and 5% for China. These data represent
Scenario Analysis of Tire
the average reuse levels of tire material in the
Industrial System of China
two regions. For the purposes of sustainability, it
is crucial to make the best use of waste material Based on the case of the Chinese tire indus-
by raising the percentage of scrap tires used for try in 2005, we present two scenarios in which
retreading and by increasing the amount of re- we suppose that the percentage of scrap tires
generated rubber used in the production of new used for retreading (f 4 3 /T3 ) and the percentage
tires. of regenerated rubber used to produce new tires
In developed countries, 60%–70% of scrap car (f 14 /T1 ) are increased in small steps. We then
tires can be retreaded, but only 3–6% of scrap car study the corresponding changes in the perfor-
tires have actually been retreaded; 50–60% of mance of reuse processes in the system using IOA.
Yang et al., Evaluation of the Tire Industr y of China based on Physical IOA 461R E S E A R C H A N D A N A LY S I S
Table 2 Equations used for calculating the material flows in the Chinese tire industrial system
Value
Flow Brief description From To Equation (kt/y)
z10 Virgin material to 0: Environment 1: Production z10 = f 21 + f 31 3,282
production + y01 − f 14
z4 0 Virgin material to 0: Environment 4 : Retreading z4 0 = f 4 4∗ x4 28
retreading
y01 Manufacturing waste to 1: Production 0: Environment y01‘ = M9 50
environment
y02 Consumption wear and 2: Consumption 0: Environment y02 = M10 317
tear to environment
y03 Scrap tires to landfill or 3: Collection 0: Environment y03 = f 32 + f 31 − f 4 3 1,710
incineration − f 4 4 − f 4 3
y04 Reused tire materials to 4 : Other uses 0: Environment y04 = M6 20
environment
∗
f 14 Recycled rubber to 4 : Recycling 1: Production f 14 = (f 21 + f 31 173
production + y01 )∗ x7 (1)
f 21 Tire products to 1: Production 2: Consumption f 21 = M8 3,307
consumption
f 24 Retreaded tires to 4 : Retreading 2: Consumption f 24 = f 4 4 + f 4 4 175
consumption + z4 0
f 31 Production waste to be 1: Production 3: Collection f 31 = M7 99
collected
f 32 Scrap tires after 2: Consumption 3: Collection f 32 = M4 1,950
consumption to be
collected
f 4 3 Recycled material to 3: Collection 4 : Other uses f 4 3 = M6 20
other uses
f 4 3 Scrap tires to be retreaded 3: Collection 4 : Retreading f 4 4 = M5 140
f 4 4 Recycled rubber to 4 : Recycling 4 : Retreading f 4 4 = f 4 4∗ x5 7
retreading
f 4 3 Recycled material to 3: Collection 4 : Recycling f 4 3 = f 14 + f 4 4 180
regenerated rubber
x· 2+ Tire products x· 2+ = f 21 + f 24 1,215
accumulation − f 32 − y02
(1) Imports and exports were not considered, for the sake of simplicity.
In these scenario studies, some of the flow ingly by a certain proportion, and then f 4 3 in-
parameters were fixed, including y01 , y02 , y04 , creases by the law of conservation of mass at node
f 31 , f 32 , f 4 3 , and x· 2+ . Since the flows in the 4 , and at the same time, y03 decreases. The in-
system are heavily mutually dependent, it was crease in f 24 reduces the consumption of new tires
reasonable—and it simplified the problem—to from production (f 21 ) and consequently reduces
set these flows as invariable when new tire pro- the use of virgin material (z10 ) in new tire pro-
duction capacity does not change very much and duction. The changes of the flows are presented
the tire consumption pattern is stable. in table 5.
In scenario 1, the percentage of scrap tires used In scenario 2, the percentage of regenerated
for retreading (f 4 3 /T3 ) was increased from 10% rubber used to produce new tires (f 14 /T1 ) was
to 30% in increments of 5%. When f 4 3 increases, increased from 5% to 30% in steps of 5%. The
the flows f 24 , f 4 4 , and z4 0 increase correspond- other flows at all of the nodes were unchanged
462 Journal of Industrial EcologyR E S E A R C H A N D A N A LY S I S
Table 3 Parameters used for calculating the material flows in the Chinese tire industrial system
Parameter Symbol Value Data source
∗ 8
Amount of new tires (/y) N1 3.18 10 China rubber market yearbook, 2005
Average weight per tire (kg) P1 26 Statistical estimate
Percentage of rubber in a tire (%) x1 60 Statistical estimate
Total rubber in new tires (kt/y) M1 4,961 M1 = N1 ∗ P1 ∗ x1
Amount of new tire imports (/y) N2 0.02∗ 108 China rubber market yearbook, 2005
Amount of new tire exports (/y) N3 1.08∗ 108 China rubber market yearbook, 2005
Total rubber in new tire imports (kt/y) M2 31 M2 = N2 ∗ P1 ∗ x1
Total rubber in new tire exports (kt/y) M3 1,685 M3 = N3 ∗ P1 ∗ x1
Amount of scrap tires (/y) N4 1.25∗ 108 China tyre retreading, repairing &
recycling association
Total rubber in scrap tires (kt/y) M4 1,950 M4 = N4 ∗ P1 ∗ x1
Amount of retreaded tires (/y) N5 0.09∗ 108 China tyre retreading, repairing &
recycling association
Total rubber in retreaded tires (kt/y) M5 140 M5 = N5 ∗ P1 ∗ x1
Percentage of other uses relative to x2 1 Expert survey
total scrap tires (%)
Total rubber for other uses of scrap tires M6 20 M6 = M4 ∗ x2
(kt/y)
Percentage of production waste to be x3 2 Expert survey
collected (%)
Total rubber to be collected in the form M7 99 M7 = M1 ∗ x3
of waste (kt/y)
Percentage of fresh rubber used in x4 20 Reasonable assumption
retreading (%)
Percentage of recycled rubber used in x5 5 Reasonable assumption
retreading (%)
Total rubber in new tires to M8 3,307 M8 = M1 − M3 + M2
consumption (kt/y)
Percentage of production rubber x6 1 Expert survey
emitted to environment (%)
Total rubber emitted to environment M9 50 M9 = M1 ∗ x6
from tire production (kt/y)
Percentage of consumption rubber x7 10 Expert survey
emission to environment (%)
Total rubber emitted to environment M10 317 M10 = (M4 + x· 2+ ) ∗ x7
from tire consumption (kt/y)
Percentage of regenerated rubber used x7 5 Expert survey
to produce new tires (%)
Table 4 Comparison of the relative contributions of the four processes to the system (w ) and their relative
∗
demands on the system (w ), shown comparatively between China (2005) and Europe (1996)
Production Consumption Collection Reuse
w China 0.315 0.267 0.228 0.190
Europe 0.297 0.276 0.230 0.196
w∗ China 0.065 0.123 0.171 0.640
Europe 0.054 0.125 0.175 0.647
Yang et al., Evaluation of the Tire Industr y of China based on Physical IOA 463R E S E A R C H A N D A N A LY S I S
Figure 3 Comparison between tire
industrial systems of China (2005)
and of Europe (1996): (a)
Comparison of systems in terms of
the relative contributions of the four
processes to the system (w ); and (b)
the relative demands of the four
∗
processes on the system (w ).
except for T4 . The increase in f 14 leads to Vectors w corresponding to the scenarios de-
an increase in f 4 3 and a decrease in y03 and scribed above were calculated, and are visualized
z10 . The changes of the flows are presented in in figure 4. In figure 4(a), when the percentage
table 6. of scrap tires sent to be retreaded rises from 10%
Table 5 Material flow data in kilotons per year for the Chinese tire industrial system when the percentage
of scrap tires used for retreading is changed
Percentage of
scrap tires
used for
retreading
(f4 3 /T3 ) z10 z4 0 Y01 Y02 y03 y04 f14 f21 f24 f31 f32 f4 3 f4 3 f4 4 f4 3 x· 2+
10% 3205 41 50 317 1646 20 169 3225 256 99 1950 20 205 10 179 1215
15% 3084 61 50 317 1544 20 162 3097 384 99 1950 20 307 15 178 1215
20% 2962 82 50 317 1443 20 156 2969 512 99 1950 20 410 20 176 1215
25% 2840 102 50 317 1342 20 149 2841 640 99 1950 20 512 26 175 1215
30% 2719 123 50 317 1241 20 143 2713 768 99 1950 20 615 31 174 1215
464 Journal of Industrial EcologyR E S E A R C H A N D A N A LY S I S
Table 6 Material flow data in kilotons per year for the Chinese tire industrial system when the percentage
of regenerated rubber used to produce new tires is changed
Percentage of
regenerated
rubber used
to produce
new tires
(f14 /T1 ) z10 z4 0 y01 y02 y03 y04 f14 f21 f24 f31 f32 f4 3 f4 3 f4 4 f4 3 x· 2+
5% 3,282 28 50 317 1,710 20 173 3,307 175 99 1,950 20 140 7 180 1,215
10% 3,110 28 50 317 1,537 20 346 3,307 175 99 1,950 20 140 7 353 1,215
15% 2,937 28 50 317 1,364 20 518 3,307 175 99 1,950 20 140 7 525 1,215
20% 2,764 28 50 317 1,191 20 691 3,307 175 99 1,950 20 140 7 698 1,215
30% 2,419 28 50 317 846 20 1,037 3,307 175 99 1,950 20 140 7 1044 1,215
to 30%, the relative contribution of the produc- creases from 5% to 30%, the relative con-
tion process to the system decreases from 0.312 to tributions of the collection process and reuse
0.274, and that of the reuse process increases from process increase—particularly the latter, which
0.191 to 0.214; meanwhile, the contributions of increases from 0.188 to 0.210; meanwhile, the
the consumption process and the collection pro- relative contributions of the production process
cess both increase distinctly. and the consumption process decrease, particu-
In figure 4(b), when the percentage of re- larly the former, which decreases from 0.317 to
generated rubber used to produce new tires in- 0.294.
Figure 4 Scenario analysis of tire
industrial system of China when the
reuse process is strengthened.
Yang et al., Evaluation of the Tire Industr y of China based on Physical IOA 465R E S E A R C H A N D A N A LY S I S
Discussion and Conclusions time, developing standardized and integrated
regulations.
Although material input–output analysis al-
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About the Authors
for safety reasons and also for tire protection dur-
ing use, well-timed scrap tire collection, and so Ning Yang is a Ph.D. candidate, Dingjiang
on, all of which would have to work in coor- Chen is a researcher, Shanying Hu is a profes-
dination with each other and be supported by sor, Yourun Li is a professor, and Yong Jin is a
government policies. The Chinese government professor, all at the Center for Industrial Ecology
should encourage enterprises to make good use of in the Department of Chemical Engineering at
waste materials by cutting taxes and, at the same Tsinghua University, Beijing, China.
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