LCA Car Tire

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Life

Cyc

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Life cycle assessment is a technique for recording and assessing ecological aspects of theinteractions between a product and the environment. Under this life cycle assessment, the authorshave examined the complete life of a car tire comprising the

• extraction of mineral and fossil raw materials like crude petroleum, coal, natural gas, iron and other ores

• manufacture of the tire’s raw materials like rubber, carbon black, chemicals, steel cord, bead wire and carcass fabric

• production of the tire at the tire plant• use of the tire on the road• utilization of the old tire as a raw material or energy provider

The authors have endeavored to find a way of portraying the results that, on the one hand, meets thestrict requirements of the relevant standards – in particular those of ISO 14 040 ff – and yet, on theother hand, supplies easy-to-follow information, both for internal purposes and for interested personsoutside the company.

The present life cycle assessment is the result of many individual contributions. The authors would like to express their thanks to the following companies and institutions forproviding data:

• Bayer AG, • Degussa-Hüls AG, • Grillo Zinkoxid GmbH, • Institut für Kunststoffprüfung und Kunststoffkunde, University of Stuttgart• Shell AG and • Textilcord Steinfurt S.A.

(now part of Glanzstoff Austria GmbH).

The authors would also like to thank the following individuals for their contributions:

• Dr. P. Entmayr (Continental AG), • H. Fehrenbach (ifeu), • H. Huinink (Continental AG), • Dr. H. Krähling (Solvay Deutschland GmbH), • Dr. Röhl (Continental AG), • K.-D. Schoppe (Volkswagen AG),• Dr. M. Schuckert (IKP), • Dr. G.W. Schweimer (Volkswagen AG).• D. Reinke (Vergoelst Runderneuerungen GmbH & Co KG)

Authors: Dr. Silke Krömer, freelance contributorDr. Eckhard Kreipe, Continental AGDr. Diethelm Reichenbach, Continental AGDr. Rainer Stark, Continental AG

Continental AG, P.O. Box 169, 30001 Hannover, Germany

AcknowledgementAcknowledgement

Publication DataPublication Data

ForewordForeword

ContentContent

1. Reasons for conducting the study...............................................................................................2

1.1. Individual goals.............................................................................................................................2

2. Scope of study...............................................................................................................................3

2.1. Assessment modules ...................................................................................................................42.2. General framework, boundaries and data sources ......................................................................42.3. Degree of detail ............................................................................................................................72.4. Special methodological features ..................................................................................................7

3. Life cycle inventory analysis.........................................................................................................8

3.1. Input .............................................................................................................................................83.1.1.Resource requirements ..........................................................................................................83.1.2.Air requirements .....................................................................................................................83.1.3.Water requirements ................................................................................................................9

3.2. Output ........................................................................................................................................103.2.1.Atmospheric emissions ........................................................................................................103.2.2.Emissions into water.............................................................................................................103.2.3.Overburden and waste .........................................................................................................113.2.4.Tire abrasion.........................................................................................................................12

4. Impact assessment .....................................................................................................................14

4.1. Impact categories/environmental potential ................................................................................144.1.1.Cumulative energy input.......................................................................................................144.1.2.Global warming potential......................................................................................................144.1.3.Acidification potential ...........................................................................................................154.1.4.Nutrification potential ...........................................................................................................164.1.5.Ecotoxic and human toxic potential .....................................................................................16

5. Tire variant comparison (life cycle inventory analysis and impact assessment) .................17

5.1. Comparison of carbon black and silica as fillers........................................................................175.2. Comparison of rayon and polyester as textile fabrics................................................................17

6. Recycling of worn tires (life cycle inventory analysis and impact assessment) ..................20

6.1. Cement plant..............................................................................................................................206.2. Tire power plant..........................................................................................................................216.3. Retreading ..................................................................................................................................22

6.3.1.Manufacture of new tires versus retreading of worn tires ....................................................246.3.2.Service life of a new tire versus service life of a retread.......................................................24

7. Interpretation ...............................................................................................................................28

7.1. Dominance analysis ...................................................................................................................287.2. Significance analysis ..................................................................................................................287.3. Sensitivity analysis .....................................................................................................................29

7.3.1.Possible sources of error......................................................................................................297.3.2.Impact of possible errors on the outcome of the assessment ............................................30

8. Opportunities for influencing the impact on the environment ................................................32

8.1. Raw materials acquisition ..........................................................................................................328.2. Tire production ...........................................................................................................................328.3. Tire use.......................................................................................................................................338.4. Recycling of worn tires...............................................................................................................33

9. Bibliography .................................................................................................................................34

10. Annex............................................................................................................................................35

11. Critical review of the life cycle assessment................................................................................36

Approx. 200 million car tires arecurrently in use in Germany.Each year approx. 600,000 tonsof worn tires are removed andreplaced by a correspondingnumber of new or retreadedtires1. Throughout its servicelife, from the acquisition of theraw materials through to the re-cycling of the worn tire, the tireconstantly interacts with theenvironment. Approaches toeffectively reducing the negativeenvironmental impact can bedemonstrated only on the basisof detailed knowledge of thisinteraction. This is why a lifecycle assessment quantifies thematerial and energy turnover inthe different stages of a tire’slife (life cycle inventory analysis)and describes the interactionwith the environment (impactassessment and interpretation).

1.1. Individual goals

The goals of the present lifecycle assessment are thefollowing:

1. Presentation of the materialand energy flows in the var-ious stages of a tire’s life

2. Quantification and evaluationof emissions and waste thatcould have an impact on theenvironment (determination ofthe “ecological backpack”borne throughout the life ofthe tire)

3. Identification of the main im-pact on the environment during the life of a tire asstarting point for a targetedand efficient reduction in themagnitude of the potentialenvironmental impact.

4. Development of a tool forevaluating the resource re-quirement and the environ-mental impact of alternativetire types (alternative rawmaterials and materials)

5. Quantification of the environ-mental impact of using worntires in recycling processesin comparison with the re-spective equivalence proc-esses.

6. Development of a standard-ized method for assessingrubber products

The life cycle assessment forpassenger car tires has beenprepared in compliance withDIN EN ISO 14040 ff. (Figure 1)(2,3,4,5). At appropriate pointsreference is made to specialfeatures in the assessment ofpassenger car tires.

1. Reasons for conducting the study1. Reasons for conducting the study

2

FIGURE 1: COMPONENTS OF A PRODUCT LIFE CYCLE ASSESSMENT (LCA) TO DIN EN ISO

14040.

Scope of a Product Life Cycle Assessment

Applications

1.) Product development and improvement

2.) Strategic planning

3.) Public policy making

4.) Marketing

5.) Other

Impact assessment

Inventory analysis

Definition of the goaland the

scope of study

Interpretation

2. Scope of study2. Scope of study

3

FIGURE 2: SCOPE OF ASSESSMENT

* The energy input is included in the scope of the assessment.

** In the case of recycled worn tires, the requisite energy input and likely raw material requirement have likewise been taken into consideration.

Input OutputResource acquisition

andmanufacture of

feedstockfor tires

Resources

Energy*

Atmospheric emissionsEmissions into waterOverburden and waste

Atmospheric emissionsEmissions into waterOverburden and waste

Atmospheric emssionsEmissions into waterOverburden and waste




Energy*

Energy*

Energy*

Energy*

Energy*

Atmospheric emissionsEmissions into water

Overburden and waste

Transport (1)

Tireproduction

Transport (2)

Transport (3)

Tireuse

Raw materials of the tire

Raw materials of the tire

New tire

New tire

Old tire

Old tire

Worn tire recycling**as retreads

Worn tire recycling**in

cement production

Worn tire recycling** in

tire power plants

(Energy recycling)(Recycling of materials)

Retreaded tire

The general frame-work of analysis iscom-prised of all theinputs and outputs ofthe various phases inthe life of a tire, asshown here in dia-gram form.

2.1. Assessment modules

2.1.1. Manufacture of rawmaterials for tires, incl.resource acquisition

The feedstock for tires is manu-factured from fossil, mineraland replenishable resources.On the basis of its physical andchemical properties, this feed-stock subsequently providesthe performance potential forthe functioning tire.

2.1.2. Production of the tire

The structural parts are manu-factured from the feedstock andassembled to form the greentire, which is then vulcanized toyield the functioning tire.

2.1.3. Use of the tire

The tire is the link between thevehicle and the road, transmittingto the latter all forces acting onthe vehicle and emitted by thevehicle. This function determinesits design and chemical makeup.Assessment of tire use wasbased on a standard size vehicledriven by the motorist in theaverage manner for the averagemileage on roads correspond-ing to the European standard.The tire is assumed to be ex-posed to the climatic conditionsprevailing in central Europe.While in operation, the tire issubjected to constant wear dueto tread abrasion. Eventually itforfeits its functional value dueto lack of sufficient tread depthand is withdrawn from service.

2.1.4. Recycling of worn tires

The original tire’s materialcomposition and its energycontent determines the value ofthe worn tire – and the recyclingpossibilities open to it. InGermany worn tires are prima-rily retreaded or used in cementplants. This study will also takea look at the recycling of worntires in tire power plants.Rubber powder produced fromworn tires and rubber granulateconsistute less significant usesfor worn tires and will not beconsidered here.

2.1.5. Transport

Between the various life stages– during which the constituentmaterials undergo changes –the tires must be transported.The transport of the tires isstrictly for the purpose of mov-ing the materials under consid-eration from one location to an-other. The transport modulesummarizes all transport opera-tions with the exception of thetransport of worn tires to the re-cycling point. The transport ofworn tires is taken into consid-eration in analyzing the recy-cling processes.

2.2. General framework,boundaries and datasources

2.2.1. Object of assessment

The object under assessmenthere is the passenger car tire.The material composition of thetire corresponds to that of asummer tire in Continental’smain line. To the extent pos-sible, data from the 175/70 R 13tire is used. All input material isgrouped together in type-related substance categories.Data is compiled for a represen-tative member of each of thesesubstance categories (e.g. arepresentative antioxidant forthe anti-aging substancegroup). 100% of the constituentelements of a tire are covered.Material alternatives are treatedin Chapter 5.


4

2.2.2. Reference variable

The reference variable/functionalunit is a single tire with anaverage service life of 50,000km over a four-year period.

2.2.3. Assessment boundaries

The assessment boundaries aredrawn in such a way as to ren-der the tire assessment easy tograsp and reproducible without,for all that, sacrificing its essen-tial integrity. A detailed study isconducted within these bound-aries.

For processes carried out inGermany, the electric energyrequirement enters into theassessment on the basis of theenergy mix in Germany6 (e.g.data records from raw materialmanufacturers located inGermany). The cumulativeenergy input (CEI), which pre-sents the entire energy quantityregardless of the type of energyacquired, takes into accountonly the energy required tomanufacture the tire but not thecalorific value of the product.

The resources category citesboth the resources used as ma-terial and the resources used asenergy. The energy content ofthe energetically used resourcesis shown again separately as pri-mary energy input. The acquisi-tion of resources is included inthe assessment.

The assessment does not takeinto account the construction,maintenance and servicing ofplant, tools, machines andtransport vehicles. Nor does ittake into account the expenseof producing the cars to befitted with the tires or of roadconstruction. Nor are the fol-lowing included in the assess-ment: noise emissions, tire abrasion during truck transportand expenditures for personnel,administration, planning, re-search and development.

2.2.4. Allocation

In the case of coupled produc-tion, information on the distribu-tion of inflows and outflows isnot available for the data drawnfrom non-corporate sources(e.g. manufacture of feedstockfor the tire). For this reason it isnot possible to say anythingabout the allocations made inthese data records. No creditingtakes place in the case ofcoupled production. For datafrom in-house surveys, the allo-cation is made on the basis ofmass distribution of the prod-ucts of coupled production (e.g.for prior chains of petroleumproducts). The inflows and out-flows in the recycling of worntires in cement plants is basedon the energetic contribution ofworn tires to overall energy ex-penditure.

2.2.5. Special allocation forthe use phase

The allocation of the inflowsand outflows to and from thetire occurring while the car isbeing used has an important in-fluence on the results of the as-sessment. The charges incurredin operating the car are distribut-ed on the basis of the savingspotential to be achieved bychanging the tire properties.

The fuel consumption requiredto move the vehicle is compos-ed of the share needed to over-come the tire’s rolling resist-ance, the vehicle’s air drag, thedrive resistance of the engineand gears and the accelerationresistance of the vehicle.Rolling resistance is determinedby the tire’s coefficient of rollingresistance and the mass of thevehicle including the tires. Theair drag value is dependent onthe driving speed and thegeometry of the vehicle and thetire. The drive resistance isdetermined by the internal fric-tion of the drivetrain.


5

The acceleration resistance isdependent on the individual driving style and on the mass ofthe vehicle.

Table 1 shows and explains thecategory assignments.


6

TABLE 1: ALLOCATION AND EVALUATION OF ROAD RESISTANCE.

The vehicle is assumed to weigh approx. 1250 kg and a tire approx. 6.5 kg. Road resistance is calculated using reference quantities valid for the

whole vehicle and thus for four tires per vehicle (7). The functional unit of the present study being a single tire, fuel consumption is calculated per

tire. The values shown in the table are calculated on the basis of Continental AG readings. There is a fluctuation of approx. 4% in the determination

of rolling resistance.

Total share ofvehicle fuel

consumption[%]

Reference to the tire

Total resistance

Share of fuelconsumptionattributable to

the 4 tires

Contribution ofone tire to

fuel consumption [%]

Rolling resistance Vehicle weight

Aerodynamicresistance

Wheel and wheelhouse account forapprox. 25% of thevehicle’s aerodynamicresistance; about 50%of that amount isassignable to the tires

Propulsionresistance

(internal friction)No reference to the tire

Accelerationresistance(loss due tobraking)

Tire weight andmoment of inertia

16 16 4

36

32

16

100

4.5 1.1

0.4 0.1

5..220.9

- -

All told, the tires account forapprox. 21% of a car’s fuelconsumption – or approx. 5.2%per tire to be taken into consid-eration here as environmentalimpact.

As Table 1 shows, the allocationis influenced not only by tire-specific characteristics but alsoby car-specific characteristics(e.g. weight).

2.2.5. Data sources

The data has been furnished byContinental AG, the raw mate-rial manufacturers (Bayer AG,Degussa-Hüls AG, GrilloZinkoxid GmbH, Shell AG,Textilcord Steinfurt S.A. (now Glanzstoff Austria GmbH)),publications[6,8,9,10] andpersonal communications fromDr. Entmayr (Continental AG),Mr. Huinink (Continental AG),Mr. Schoppe (Volkswagen AG)and Dr. Schuckert (IKP)). Dataon literature is derived fromUllman’s encyclopedia[11]. Thedata is taken from the years1990 to 1997.

2.2.6. Critical review

A critical review in accordancewith the requirements of DINEN ISO 14040 has been con-ducted by TÜV NORD (Dr. J.Hanel and Dr. W. Hirtz).

2.3. Degree of detail

The parameters recorded allflow into the life cycle inventoryanalysis. All relevant andrecorded parameters are like-wise taken into account for thecalculation of the environmentalpotential. Unless therwisespecified (see Table 2), no cut-off criteria have been applied.

2.4. Special methodologicalfeatures

• After use the worn tires areavailable for material orenergetic recycling. As sec-

ondary raw materials, worntires either provide the basisfor new products (e.g. re-treaded tires, cement clinkerblocks) or are used for acompletely different purposethan the original one (e.g. inagriculture or ports).Recycling of the old tire thusleads to an expansion of itsutility. This natural interfacebetween the car tire lifecycle assessment through tothe end of its use and theassessment of the respectiverecycling process is used forthe conception of thepresent study.

• The most realistic approxi-mation of the results of aworn tire assessment would

probably be a recycling mixincorporating all recyclingchannels with the capacitiesthey make available to themarket. This kind of recy-cling mix is not of much as-sistance in identifying wherethe main environmental im-pact is. The composition ofa recycling mix is, moreover,strongly dependent on themarket situation and the re-spective national laws. Forthese reasons, no assess-ment of a recycling mix willbe made here. Instead, themost important recyclingchannels for worn tires areregarded separately andcompared with the respec-tive equivalence processes(Chapter 6).


7

The life cycle inventory analysisand the impact assessment arebased on an operative carbonblack/rayon tire. Other tire typesare considered in a separatechapter (Chapter 5).

3.1. Input

The input of the life cycle inven-tory analysis covers the re-sources expended and the airand water required.

3.1.1. Resource requirements

The mining of so-called mineraland fossil resources gives riseto so-called dead heap.Although dead heap does notrepresent a raw material, it isusually classified as one [12]. Inthis assessment dead heap isnot listed under resources,however; there are 232 kg ofresources per tire and 28 kg ofdead heap.

Approx. 88% of all the re-sources consumed in the life ofa tire are required for the use ofthe tire by the car (Figure 3).

Approx. 6.9 % of the overall re-source requirement in the life ofa tire is consumed in the courseof extracting the raw materialsfor the tire. The raw materialssilica, synthetic rubber, carbonblack and steel account for thelargest share of the raw materi-als consumed in this phase ofthe tire’s life. The resource pe-troleum, which is used materi-ally and energetically, makes uproughly 24% of the overall

resource consumption in theacquisition of raw materials.Natural gas accounts foraround 18% of the energyrequirement in this phase of atire’s life.

Resources are required in theproduction of a tire to makeavailable the energy carriersnatural gas, petroleum and coal.These energy carriers make upapprox. 29% of the resourcesconsumed in tire manufacturing.

All told, approx. 4.8% of thetotal resources expended in thelife of a car tire are used for theproduction of the tire. The con-sumption of resources is lowestin the transport phase of the ti-re’s life (about 0.2%).

3.1.2. Air requirements

The air requirement is relatedmainly to the need for oxygenwhen burning the fossil resour-ces to obtain energy. The cartire’s use phase accounts forthe largest share of overall airconsumption (approx. 96.5%) inthe life of a tire. The other modules of tire life account forthe remainder as follows: raw materials extractionapprox. 2.2%,

production approx. 1.0% and transport approx. 0.2% (Figure 4).

3. Life cycle inventory analysis3. Life cycle inventory analysis

8

FIGURE 3: PRESENTATION OF RESOURCE CONSUMPTION AND THE QUANTITY OF

DEAD HEAP.

168

0.5 0.00811 7

204

13

0

50

100

150

200

Acquisi

tion o

f raw

mat

erial

sTr

ansp

ort

Product

ion

Use

Resource requirement Dead heap

Co

nsum

pti

on

of

reso

urce

s an

d d

ead

hea

pp

er c

ar t

ire

[kg

]

3.1.3. Water requirements

The water consumption ismade up of cooling water(approx. 68%), process water(approx. 31%) and servicewater (approx. 0.2%). Coolingwater is usually fed into circuitsand can thus be used over along period of time.

It exhibits a low negative im-pact factor. Process water isdirectly involved in the manu-facturing processes and isdisposed of as waste water.The term service water refers tothat portion of the water con-sumed that cannot easily beclassified as either coolingwater or process water.

Water is used in all phases thata tire passes through in its life.The largest share – approx.90% – is required for the acqui-sition of raw materials for thetire. The remainder is distribut-ed as follows among the otherphases of a tire’s life: approx.7.0% during use, approx. 3.8%during production and approx.0.2% for transport (Figure 5).

The water consumption in con-junction with the acquisition ofraw materials for the carbonblack/rayon tires under consid-eration here is as follows: ap-prox. 63% for the manufactureof synthetic rubber (SBR), ap-prox. 18% to obtain rayon, ap-prox. 3.1% for the manufactureof natural rubber, approx. 5.6%for the production of steel andapprox. 6.5% for the manufac-ture of chemicals.


9

FIGURE 4: PRESENTATION OF

AIR CONSUMPTION.

FIGURE 5: PRESENTATION OF WATER CONSUMPTION.

46 5 22

2027

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Acquisition of rawmaterials

Transport Production Use

Air

co

nsum

pti

on

per

car

tir

e [k

g]

560

1.324

44

0

100

200

300

400

500

600



Wat

er c

ons

ump

tio

n p

er c

ar t

ire

[kg

]

3.2. Output

The output of the life cycle in-ventory analysis is made up ofthe atmospheric emissions,emissions into water, waste andoverburden and tire abrasion.

3.2.1. Atmospheric emissions

Atmospheric emissions are de-termined primarily by the outputof carbon dioxide (approx.97%). The remainder consistsof carbon monoxide (approx.1.2%) and water vapor (approx.1.3%). Other emissions are me-thane (approx. 0.05%), nitrogenoxide (approx. 0.04%), volatileorganic hydrocarbons with theexception of methane (NMVOC) (approx. 0.06%), sulfurdioxide (approx. 0.04%),ammonia (approx. 0.02%),nitrous oxide (approx. 0.01%)and dust (approx. 0.17%).

Of all the phases in the life of atire, the car use phase accountsfor the greatest negative impacton the atmosphere (approx.95.4%) (Figure 6). This negativeimpact is due almost completely(approx. 98%) to the carbondioxide emitted when the car isin operation. Carbon monoxidemakes up approx. 1.2% of thenegative impact on the atmos-phere in the use phase.

The other phases in the life of atire have a considerably weakerinfluence on atmospheric emis-sions: tire production approx.2.5%, obtaining raw materialsfor the tire approx. 1.8% andtransport another 0.3% or so(Figure 6).

Dust is generated almost exclu-sively in the use phase andconsists primarily of particles ofvarious sizes produced by tireabrasion. The particles escapeinto the air and gradually fall to

the ground (see Chapter 3.2.4for details). Water vapor is re-leased when the tire is manu-factured. It is produced as a re-sult of cooling processes in thecourse of the manufacture ofthe rubber compounds as wellas of components.

3.2.2. Emissions into water

The negative impact on wastewater occurs almost entirely inconjunction with the acquisitionof raw materials for the tire(approx. 94.4%)(Figure 7). In the other phasesof life the negative impact onthe waste water is much lower:approx. 2.8% during transport,approx. 2.8% during use andapprox. 0.008% during produc-tion.

The negative impact on wastewater is due to chloride ions(approx. 58.2%), sulfate ions(approx. 24.6%) and natriumions (approx. 14.8%). Theseions get into the waste waterprimarily during the manufactureof silica, rayon and syntheticresins.


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FIGURE 6: PRESENTATION OF ATMOSPHERIC EMISSIONS.

10.8 1.515

567

0

100

200

300

400

500

600



Atm

osp

heri

c em

issi

ons

per

car

tir

e [k

g]

3.2.3. Overburden and waste

Dead heap accumulates in theprocess of mining mineral andfossil resources. Dead heap,which remains largely un-changed during ore dressingand during the acquisition ofraw materials, is referred to asoverburden[12]. A share of thedead heap is chemically chan-ged by ore dressing and rawmaterial extraction. This residueis classified as waste, for whichreason all further analyses willmake a distinction betweenoverburden and waste.

Roughly 76.2% of the overbur-den can be ascribed to the usephase of the tire – due to theextraction of crude oil for useas fuel and the provision ofelectric energy for petroleumrefining. 0.23 kg overburden isproduced per kg of normal gas-oline. The fact that the tire’s usephase accounts for such a pre-ponderant share of the totaloverburden quantity producedin the life of a tire is due to afuel consumption of approx.186 kg gasoline per tire forevery 50,000 km.

Approx. 11.9% of the totaloverburden amount occurs dur-ing tire production, while an-other 11.8% or so occurs inconjunction with the acquisitionof raw materials for the tire(Figure 8). In these phases ofthe tire’s life, the preponderantshare of overburden is due tothe mining of coal as energycarrier.

Coal is used either to obtainelectric energy or directly in therespective process of obtainingenergy.

Little petroleum is needed forthe transport of a single tire;consequently the lowestamount of overburden occurs inthis phase of a tire’s life (approx. 0.01%).

Waste arises in connection withthe extraction of raw materialsfor the tire (approx. 69.4%) and

tire production (approx. 26.0%)(Figure 8). Approx. 62% of thewaste from raw materialsextraction consists of residuefrom ore dressing. Large quanti-ties of ore dressing residue arisein the production of steel (al-most 80% of the entire oredressing residue incurred in theacquisition of raw materials forthe tire). About 64% of tire pro-duction waste is household rub-bish. The use phase accountsfor 4.6% of the total volume ofwaste in the life of a tire.


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FIGURE 7: PRESENTATION OF THE NEGATIVE IMPACT ON WASTE WATER.

1.85

0.0540.00016

0.055

0

0.5

1

1.5

2



Neg

ativ

e im

pac

t o

n w

aste

per

car

tir

e [k

g]

FIGURE 8: PRESENTATION OF OVERBURDEN AND WASTE.

Overburden

6.76

3.2

0.006 0.004

6.82

1.2

43.5

0.210

5

10

15

20

25

30

35

40

45



Waste

Ove

rbur

den

and

was

te p

er c

ar t

ire

[kg

]

3.2.4. Tire abrasion

Tire abrasion is already includ-ed in the assessment as outputin Chapter 3.2.1, “Atmosphericemissions”; a number of addi-tional peculiarities should alsobe dealt with here. Some of theabrasion is found in the groundand rain water. Emissions ofthis kind are hard to integrateinto the specified systematicsof a life cycle assessment.

The quantity of tire wear occur-ring in the life of a tire – i.e. inthe course of the average mile-age performance of 50,000 kmor in a four-year period – worksout to approx. 1 kg per tire; thiscorresponds to approx. 20 mgabrasion per tire and kilometertraveled (9).

Tire abrasion is composed ofrubber (approx. 42%), carbonblack (approx. 34%), and min-eral oils (approx. 17%) (Figure 9).

The remaining 7% or so ismade up of various treadingredients and substances ari-sing as a result of chemicalconversion of the ingredientsduring vulcanization of the tirerubber compounds.

The tire abrasion is first spreadtemporarily over the road sur-face and in the ground to bothsides of the road.

Abrasion is subject to thefollowing processes:

• It is washed off the road byrain water.

• Water-soluble substancesare eluted.

• Chemical and biological de-composition occurs.

In the analysis of a single tire,the 1 kg of tire abrasion isassumed to be evenly distribut-ed to either side of the roadover a period of four years anda distance of 50,000 km.Assuming a biological-chemicaldecomposition rate of 0.7% perday [13], the abrasion decom-poses almost completely withintwo years of termination of theuse of the tire[17]).

To the extent that inorganiccomponents are not convertedto metal soap in the course ofvulcanization, they remain in thetread of the tire and are the partof abrasion remaining in theground. This works out toapprox. 4 g of zinc oxide – plusapprox. 2.3 mg of cadmiumoxide and approx. 11 mg oflead(II) oxide as escort sub-stances of zinc oxide – per tire .


12

FIGURE 9: INGREDIENTS REFERRED TO AS "OTHER” ARE: SULFUR, WAX, PHENYLENEDIAMINE, CYCLOHEXYLTHIOPHTHALIMIDE,

SULFENAMIDES, ANILINE, BENZTHIAZOLE, MERCAPTOBELETHIAZOLE AND MERCAPTOBENZTHIAZOLDISULFIDE. PCA = POLYAROMATIC

HYDROCARBONS.

PCA

Other

3.0%

Lead oxide0.001%

Zinc oxide0.46%

Zinc soap

3.4%

Cadmium oxide0.01%0.0002%

Carbon black34%

Rubber42%

Miscel-laneous

6.9%Aromaticmineral oils

17.1%

Of interest in this connection isthe cumulative negative impacton the ground of the total abra-sion from all of the car tires inuse in Germany. On the basis ofthe continuous input and theconstant chemical and biologi-cal decomposition an equilib-rium concentration is estab-lished in the ground[17].

46,000 tons of abrasion is lefton Germany’s 228,000 km ofinterurban roads each year[2]

and distributed in a groundvolume[18] of 1.14*109 m3. In amodel calculation, the concen-tration and decomposition ofthe abrasion works out to aground abrasion concentration

of 16 g/m3. Each year the groundabsorbs approx. 0.16 g/m3 ofzinc oxide, approx. 0.09 mg/m3

of cadmium oxide and approx. 0.4 mg/m3 of lead(II)oxide.

Some of the abrasion compo-nents are washed away by rainwater parallel to their chemical-biological decomposition.Elution of the components andreaction products of vulcaniza-tion contained in abrasion de-pends, inter alia, on parameterslike ground particle absorptionof the substances, size of theabrasion particles, compositionof the ground, climatic condi-tions, solubility of the substances

in water under ground condi-tions, migration speed of thewater through the ground andthe length of the migration routeto the ground water. There is agreat deal of uncertainty in thedetermination and impact ofthese variables on the eluationbehavior of the various sub-stances. For this reason, thepresent study refrains fromengaging in any detailed quanti-tative examination of the elutionof tire abrasion.


13

An input-output list (resources,emissions, waste etc.) is pre-pared for each phase in the lifeof the tire. The quantities andenvironmental impact of theindividual components of theinput-output list vary. To allowfor a comparison of the indivi-dual phases in the life of a tire,it is a good idea to define acommon reference size. Theenvironmental impact that canproceed from the release of asingle component is evaluatedon the basis of equivalence fac-tors [12]. The environmental po-tential is determined on thebasis of the quantity and theequivalence factor of the com-ponents.

4.1. Impact categories/environmental potential

The environmental potential generally recognized in the cur-rent discussion and taken intoaccount here are: cumulativeenergy input[14], global warm-ing effect, acidification andnutrification. By selecting thisenvironmental potential, onetakes into account global criteria(global warming effect), regionalcriteria (acidification) and localcriteria (nutrification)[12].Possible contributions to theecotoxic and human-toxicpotential are likewise dealt with.

4.1.1. Cumulativeenergy input

It should be noted again at thispoint that the cumulative energyinput shown here does not con-tain the calorific value (i.e. thefeedstock energy).

The largest share in the cumula-tive energy input of a tire ismade in the use phase (approx.95.8%). This energy consump-tion arises as a result of thecar’s fuel consumption to over-come the tire-incited travelingresistance. The remaining shares of the energy input aredistributed over the remainingmodules of a tire’s life: rawmaterials acquisition approx.2.7%, production approx. 1.3%and transport approx. 0.2%(Figure 10).

4.1.2. Global warmingpotential

The global warming potential isexpressed in CO2 equivalentswith reference to a time horizonof 100 years. Takes into ac-count the components CO2,CO, methane and nitrous oxide(N2O).

The global warming potential ofa tire is determined almost en-tirely by the carbon dioxideemissions, CO2 representingthe dominating atmosphericemission in all phases of a tire’slife (Chapter 3.2.1.). The highestquantities of CO2 and CO arereleased in the use phase. Inthe life of the tire, they contri-bute approx. 96.3% to theglobal warming potential (Figure 11),

4. Impact assessment4. Impact assessment

14

FIGURE 10: PRESENTATION OF THE CUMULATIVE ENERGY INPUT.

211 16 104

7520

0500

10001500200025003000350040004500500055006000650070007500

Rohstoffgewinnung Transport Produktion Nutzung

Cum

ulat

ive

ener

gy

inp

ut p

er c

ar t

ire

[MJ]

7000

6000

5000

4000

3000

2000

1000

0Acquisition of raw

materialsTransport Production Use

4. Impact assessment4. Impact assessment

15

while the other phases in thelife of a tire contibute the follo-wing shares: raw materials ac-quisition approx. 2.2%,production approx. 1.2% andtransport approx. 0.2%.

4.1.3. Acidification potential

The acidification potential refersto the pollution gases released(sulfur oxide, nitrogen oxide,acids e.g. HCl, HF, H2SO4).They are expressed in SO2

equivalents.

The use phase of the tire showsthe greatest share of acidifica-tion potential at approx. 85.1%(Figure 12) and is due mainly tothe emission of SO2 (approx.32.5%), ammonia (approx.30.9%) and NOx (approx.20.8%). Raw materials acquisi-tion for the tire accounts forapprox 11.3% of the total acidi-

fication potential, due essen-tially to SO2 emissions (approx.5.1%), NOx (approx. 2.9%) andCS2 (approx. 2.9%). The trans-port phase contributes approx.1.9% to the acidification poten-tial. These amounts are dueprimarily to SO2 and NOx emis-sions (approx. 0.4% andapprox. 1.5% respectively)

during the operation of thetransport vehicle.

Tire production shows an acidi-fication potential of approx.1.6%, due mainly to SO2 (ap-prox. 0.7%) and NOx (approx.0.9%).

FIGURE 12: PRESENTATION OF THE ACIDIFICATION POTENTIAL.

14 1.5 7.3

601

0

100

200

300

400

500

600


Transport Production UseGlo

bal

war

min

g p

ote

ntia

l per

car

tir

e [k

g C

o2

equi

vale

nt]

FIGURE 11: PRESENTATION OF THE GLOBAL WARMING POTENTIAL.

0.07180.0123 0.0103

0.54

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1



Aci

difi

cati

on

po

tent

ial p

er c

ar t

ire

[kg

So

2 eq

uiva

lent

]

4.1.4. Nutrification potential

Nutrification refers to the sup-plying of nutrients to the eco-logical system. This can occur either via the eluviation frompollution gases out of the air orvia water. The nutrification po-tential is expressed in phos-phate equivalents.

All told, the use phase accountsfor approx. 89.8% of the nutrifi-cation potential in the life of atire (Figure 13) and is due to theemissions of the pollution gasesammonia (approx. 51.4%) andNOx (approx. 36.6%). Raw ma-terials acquisition for the tire ac-counts for approx. 5.5% of thenutrification potential (with air-borne NOx contributing 5.0%and the chemical oxygen re-quirement (COR) in waste water0.4%) . Nitrogen oxides are themain chemicals released in thetransport phase and accountsfor approx. 3.1% of the nutrifi-cation potential. Tire productionmakes the smallest contributionto nutrification potential with ap-prox. 1.5% (nitrogen emissions).It should be noted that thenutrients supplied during the lifeof a tire are almost completelyrelated to the release of nitrogenoxides and ammonia. The inputfrom phosphate or phosphatecompounds is minimal.

4.1.5. Ecotoxic and human-toxic potential

To date there is only a very rudi-mentarily developed standard-ized method for recording andevaluating the numerous poten-tial toxicological effects of pollu-tion emissions. This is due tothe difficulty of pinpointing andqualitatively evaluating the vari-able factors (exposition, limitedlocal occurrence of the pollu-tants, metabolization and/or ac-cumulation of pollutants, thresh-old concentrations, the sensi-tivity of organisms in ecologicalsystems, the reversability of theeffect of the impact). Data onecological and human toxicitythus represents a risk estimateand should in no case be re-garded as an absolute state-ment of impact potential.

Because of these methodologi-cal ambiguities in recording thepotential, no quantification isattempted here.

In tire raw materials acquisition,chloride ions and zinc ions arereleased into the water. Thesesubstances can contribute toecological and human toxicitypotential. In the tire’s transport,production and use phases,atmospheric emissions of SO2

and NOx (from energy input) cancontribute to the human toxicitypotential and the heavy-metalemissions into the air or wastewater (e.g. mercury from energysupply) to the ecotoxic potential.

Tire abrasion can likewise con-tribute to ecotoxicity and humantoxicity (see also Chapter 3.2.4).

4. Impact assessment 4. Impact assessment

16

FIGURE 13: PRESENTATION OF THE NUTRIFICATION POTENTIAL.

0.00370.0021 0.001

0.06

0

0.02

0.04

0.06



Nut

rific

atio

n p

ote

ntia

l per

car

tir

e [k

g P

O4

equi

vale

nt]

Tire raw materials research hasresulted in the development ofa number of different tire vari-ants, with diverse properties, inthe last few years. The assess-ment data for four different tirevariants is compared here (Table2). The variants differ in their tireraw materials composition.

5.1. Comparison of carbonblack and silica asfillers

By partially substituting silicafor carbon black as filler, it ispossible to reduce the tire’s rol-ling resistance, among otherthings. This leads to a decreasein a car’s energy consumptionand to a reduction in consump-tion of petroleum as resource.As a consequence, the quantityof pollutants released drops,with a concomitant lessening ofthe global warming, acidificationand nutrification potential.What’s more, the amount ofoverburden produced is alsolower. Production of the fillersilica increases the negativeimpact on the waste water,however.

Subsituting silica leads to a re-duction in the global warmingpotential of around 9.5%. Thisis due to a drop in pollutant gasemissions – CO2 and CO (ap-prox. 9.5% and 9.8% respect-ively). With the release of thepollution gases SO2, NOx andammonia declining at the sametime, the acidification potentialis reduced by approx. 6.3%.Nitrogen oxides and ammonia

are the main causative factorsfor the nutrification potentialduring the life of a tire. The re-duction in the release of thesechemical compounds thusleads to a reduction in the nutri-fication potential (approx.7.5%).

By partially substituting silicafor carbon black as filler, it ispossible to effect a 9.3% or soreduction in the cumulativeenergy input over the entire lifeof the tire .

Mention is made here of thefollowing complementaryimpact:

• All in all, a reduction of ap-prox. 8.7% in the consump-tion of resources is achieved,thanks to petroleum savingsof approx. 9.8%.

• The incidence of sulfate ionsin waste water increases bya factor of 4.3, while the in-cidence of sodium ions in-creases by a factor of 2.7.

• The amount of waste in-creases by approx. 3.4%,due to an increase in thequantities of solid and liquidwaste and of ash and slag.

5.2. Comparison of rayonand polyester as textilefabrics

The substitution of polyester forrayon leads to an increase inthe global warming potential inthe raw materials acquisitionphase, thereby increasing thecontribution to the global warm-ing effect by about 0.3%, dueto the higher level of CO2 emis-sions. The acidification poten-tial, on the other hand, declinesby approx. 1.6%. This reductionis based on lower atmosphericemissions of CS2 and H2S,which are released during themanufacture of rayon. AlthoughSO2 releases go up, there is areduction in the overall acidifi-cation potential. The nutrifica-tion potential is not influencedby substituting polyester forrayon.

5. Tire variant comparison 5. Tire variant comparison(Life cycle inventory analysis and impact assessment)

17

Textile fabric ply of a tire

The environment potential doesnot record all input and outputparameters. For this reason,further factors having an impactare additionally cited:

• By using polyester instead ofrayon as textile fabric, theresource requirement climbsand the energy input in-creases slightly (approx.0.1% and approx. 0.2%).

• The quantity of processwaste water declines byabout 52.8%. This reductionin the waste water amount isthe result of the raw materialsacquisition phase. The nega-tive impact on the wastewater likewise decreases(approx. 0.73 kg). This de-crease works out to around37.2% for a carbon blacktire and approx. 17.3% for asilica tire.

• The total amount of waste isreduced by about 9.6%.This is related to a decreasein the amount of solid andfluid waste occurring as aresult of the wood residueleft over in rayon manufac-ture.

The manufacture of cellulose forthe production of rayon is char-acterized by high water con-sumption and a high ion-relatednegative impact on wastewater. Considerably less wateris consumed in the manufactureof polyester and there is less ofa negative impact on wastewater. The substitution of poly-

ester for rayon leads to aconsiderable reduction in waterconsumption and in the nega-tive impact on waste water.These reductions are not reflec-ted in environmental potentialvalues, as the correspondingparameters do not flow into theenvironmental potential valuescited.

The decrease in chloride andsodium ions and in zinc can,however, lead to a reduction inthe eco- and human toxicity.

5. Tire variant comparison5. Tire variant comparison (Life cycle inventory analysis and impact assessment)

18

TABLE 2: (see page 19) PRESENTATION OF THE ASSESSMENT DATA FOR FOUR DIFFERENT

TIRE VARIANTS.

The values are obtained by totaling the individual data from the raw materials acquisition, transport,

production and use phases. They cover the entire life of a functioning car tire. Recycling of the

worn tire is not included in the data. All input contributing more than 1% to the total input sum

is shown. 99.1% of all input is recorded. The cut-off criterion for the three output categories

was set at 1% of the total of the respective output category. 99.7% of the atmospheric emissions,

98% of the negative impact on water and 99.9% of waste (incl. overburden) are recorded. This

cut-off limit gives rise to an inaccuracy of 2%. Raw materials that are relevant for the tire are

shown even if they account for less than 1% (e.g. sulfur). Standard emissions (e.g. dust, N2O,

BOD and COD, especially waste that must be monitored) are included even if they make up less

than 1%. BOD stands for biological oxygen demand, COD for chemical oxygen demand.

5. Tire variant comparison5. Tire variant comparison (Life cycle inventory analysis and impact assessment)

19

Inputs

Raw materials (kg): Carbon black/rayon Silica/rayon Carbon black/polyester Silica/polyester

Process water 194.81 195.70 94.77 92.12Cooling water 434.25 455.44 434.25 455.44Hard coal 2.16 2.24 2.16 2.24Lignite 3.46 3.48 3.46 3.48Natural gas 5.41 5.73 5.36 5.69Petroleum 205.52 185.43 206.02 185.94Sulfur 0.20 1.01 0.04 0.84Dead heap 28.06 26.92 28.06 26.92Latex 2.57 2.51 2.57 2.51Iron ore 1.17 1.00 1.17 1.00Air 2099.37 1904.57 2100.60 1905.85

Outputs

Products: Carbon black/rayon Silica/rayon Carbon black/polyester Silica/polyester

Mileage (km) 50,000 50,000 50,000 50,000Worn tire (kg) 5.47 5.68 5.47 5.47

Atmospheric emissions (kg): Carbon black/rayon Silica/rayon Carbon black/polyester Silica/polyester

Water vapor 7.83 7.83 7.83 7.83Polluted air 1464.53 1329.60 1465.59 1330.69Dust 1.02 0.95 1.02 0.95SO2 0.25 0.23 0.25 0.24CO 6.81 6.14 6.81 6.14CO2 576.74 522.01 578.65 523.99NOX 0.24 0.22 0.24 0.23N2O 0.057 0.052 0.057 0.052Methane 0.32 0.29 0.32 0.29NM VOC 0.35 0.33 0.345 0.32

Water pollution (kg): Carbon black/rayon Silica/rayon Carbon black/polyester Silica/polyester

Waste water 270.31 310.13 174.29 210.71Waste water - cooling water 422.83 436.14 422.83 436.14BOD 0.0080 0.0079 0.0062 0.0060COD 0.02 0.02 0.01 0.01Sulfate ions 0.48 2.07 0.054 1.63Sodium ions 0.29 0.77 0.20 0.68Chloride ions 1.13 1.17 0.94 0.97Calcium ions 0.000018 0.27 0.000018 0.27

Waste (kg): Carbon black/rayon Silica/rayon Carbon black/polyester Silica/polyester

Overburden 57.08 53.56 57.09 53.57Ore dressing residue 2.18 2.21 2.18 2.21Waste. solid and liquid 1.33 1.49 0.97 1.11Rubber waste 0.19 0.19 0.19 0.19Waste particularly subject to monitoring 0.055 0.067 0.055 0.067Household waste 0.80 0.80 0.80 0.80Slurry 0.081 0.084 0 0Ash and slags 0.047 0 0.049 0

Environmental potential: Carbon black/rayon Silica/rayon Carbon black/polyester Silica/polyester

Cumulative energy input (MJ) 7851.12 7117.16 7863.48 7113.67Global warming effect (kg CO2 equiv.) 623.25 564.15 625.17 566.14Acidification (kg SO2 equiv.) 0.63 0.59 0.62 0.57Nutrification (kg PO2 equiv.) 0.067 0.062 0.067 0.062

A car tire qualifies as a worn tirewhen, after a certain period ofuse, it has forfeited its originalfunctional capability (taken hereto be the carbon black/rayonversion of a size 175/70 R 13tire). The worn tire can berecycled for its material valueand/or as energy carrier.Recycling thus represents anexpansion in the use benefit ofa car tire. This natural interfaceis used to functionally separatethe life cycle assessment of acar tire from the life cycleassessment of a worn tire.

The recycling of worn tirestakes place in different recy-cling processes. Alongside rawmaterial recycling processes –the suitability of which is estab-lished in tests – there are anumber of material and energyrecycling processes that havebeen tested in real life situa-tions. This study takes a look atthe most significant worn tirerecycling processes as caseexamples.

The three recycling processesunder study here – full retread-ing, cement production, andenergy generation in tire powerstations – are compared withthe corresponding equivalentprocesses: new tire production,cement production using stand-ard fuels and energy generationin power plants with the help ofstandard fuels[8]. In a systemscomparison of this kind, theuniformity and equivalency ofbenefits must be guaranteed.The benefit achieved by using

the worn tire thus always servesas reference quantity; i.e. the mileage of the retreadedtire, the amount of cement pro-duced or the amount of energyobtained. This makes possiblea direct comparison of resourceconsumption and the relatedenvironmental impact withstandard and equivalent processes.

It is important to note that thismanner of analyzing a worn tire,which concentrates on its in-put as feedstock or energy car-rier in the recycling process, neglects the negative impact(resources expended, emis-

sions into the air and water,waste and overburden) duringits life as a functioning tire).

6.1. Cement plant

The material and energy inflowsfor the use of worn tires in a ce-ment plant are compared withthe same inflows when the stan-dard fuel – hard coal – is used.Fuel engineering considerationslimit the use of worn tires to nomore than 20% to 25% of thetotal quantity of energy carriers.

6. Recycling of worn tires 6. Recycling of worn tires (Life cycle inventory analysis and impact assessment)

20

Worn tires being fed into the rotary tubular kiln

The use of worn tires in the ce-ment plant generates consider-ably lower amounts of deadheap and overburden (14% ineach case) (Figure 14). This isbecause the use of worn tiresinstead of standard fuel meansthat less coal needs to bemined.

The use of worn tires leads to alower level of atmospheric emis-sions than is the case withstandard fuels (about 1.4%),with the global warming poten-tial reduced by approx. 1.9%,

the acidification potential by ap-prox. 1.9% and the nutrificationpotential by approx. 1.7%. As arule, the worn tire has a lowercarbon, sulfur and nitrogen con-tent than the hard coal used,which explains the reduced levelof pollution gas emissions (CO2,SO2 and NOx).

In view of the fact that worntires have a higher specific calo-rific value than hard coal, asmaller quantity of raw materialscan be used (0.5%). Reducingthe quantity of raw materials

used also reduces the amountof ash and slag generated dur-ing combustion. The amount ofwaste drops by approx. 4.2%.

Using worn tires instead of hardcoal does not affect the otherinput and output parameters toany great extent. Much of the en-vironmental impact is even re-duced slightly by using worn tires(see Figure 14 for details). Theenvironmental effect of usingworn tires in a cement plant canthus be regarded as “neutral”.


21

FIGURE 14: RECYCLING OF A WORN TIRE (CARBON BLACK TYPE) IN A CEMENT PLANT VS. USE OF A STANDARD FUEL.

In the cement plant, a worn tire share of 25% is assumed. The individual parameters are presented in summary form in the categories shown. The

categories for the use of standard fuel are set at 100% and the data for the use of worn tires as fuel is shown relative to that. The figures for the

individual columns indicate the absolute value of the summarized parameters in the categories. They are to be regasded independently of the

figures given on the % axis. Results of the life cycle inventory analysis and of the impact assessment are shown in the same chart. Input flows and

output flows in the life cycle inventory assessment are overwritten as “Input” or “Output”. The calculated environmental potential of the impact

estimate is overwritten as “Impact”.

150.

49

151.

23

62.0

5

62.3

0

30.4

0

30.7

6

9.62

11.1

4

76.7

1

77.7

8

0

9.52

11.0

3

0.02

29

0.02

40

197.

28

197.

01

78.3

2

79.8

3

0.01

16

0.01

18

0.10

6

0.10

8

0

10

20

30

40

50

60

70

80

90

100

110

Cement plant with worn tires Cement plant with standard fuel

Resourc

es (k

g)

Dead

heap (k

g)

Overb

urden

(kg)

Global

warm

ing

potentia

l (kg)

Air (k

g)

Wat

er (k

g)

Atmosp

heric

emiss

ions (

kg)

Emiss

ions i

nto

water

(kg)

Was

te (k

g)

Energy (

MJ)

Acidifi

catio

n

potentia

l (kg)

Nutrific

atio

n

potentia

l (kg)

0

Input Output Impact

6.2. Tire power plant

There are both negative and po-sitive effects on environmentalpollution when one opts for burning worn tires in tire powerplants rather than combustingfossil resources (the Germanenergy mix of hard and lignitecoal, petroleum and naturalgas), as is the case in conven-tional power plants (Figure 15).

For process-related reasons,the energy input in the formercase is higher than for conven-tional power plants using fossil

resources as fuel. The energyconversion efficiency of tirepower plants amounts to only25-30%; the efficiency of con-ventional power plants is muchhigher.

In comparison to conventionalpower plants, the tire powerplant under study has acid fluegas scrubbing, in addition toSO2 flue gas scrubbing. Thishas the effect of increasing thetire power plant’s water con-sumption and, in particular, thequantity of waste produced aswell. The resulting quantity of

waste is, however, very small incomparison to the resultingquantity of overburden. Thiswaste involves sludge (with awater content of approx. 50%)containing heavy metals. Part ofthe water consumed for fluegas scrubbing escapes into theatmosphere as water vapor(approx. 37%).


22

FIGURE 15: RECYCLING OF A WORN TIRE IN A TIRE POWER PLANT VS. ENERGY GENERATION IN CONVENTIONAL POWER PLANTS.

The individual parameters are shown summarized in categories. The categories for energy generation in conventional power plants are set at

100% and the data for the recycling of worn tires in a tire power plant is shown relative to that. The figures for the individual columns reflects the

absolute value of the summarized parameters in the categories. They are to be regarded independently of the figures given on the % axis. Results

of the life cycle inventory analysis and impact assessment are shown in the same chart. Input flows and output flows for the life cycle inventory

analysis are overwritten as “Input” or “Output”. The calculated environmental potential of the impact assessment is overwritten as “Impact”.

Resourc

es (k

g)

Dead

heap (k

g)

Overb

urden

(kg)

Global

warm

ing

potentia

l (kg)

Air (k

g)

Wat

er (k

g)

Atmosp

heric

emiss

ions (

kg)

Emiss

ions i

nto

water

(kg)

Was

te (k

g)

Energy (

MJ)

Acidifi

catio

n

potentia

l (kg)

Nutrific

atio

n

potentia

l (kg)

o%

20%

40%

60%

80%

100%

5.82

10.56

51.3

6

61.78

111.74

106.39

0.00

673

57.26 19.05 19.54

1.38

E-0

6

6.92E-06

0.00

666

56.7

0.03599

7.17E-04

152.18

95.91

16.2

1

20.410.00149

0.00145

0.01

186

0.01780

Tire power plant Conventional power plant

Input Output Impact

The tire power plant uses asmaller quantity of resources(45%) because worn tires havea higher specific calorific valuethan hard or lignite coal. Hardlyany dead heap and overburdenis produced in generatingenergy from worn tires. This isbecause the use of secondaryraw materials does not requirethe mining of any fossil resour-ces.

There are fewer atmosphericemissions (without water vapor)in a tire power plant than inconventional power plants.Insofar as the quantity of re-sources used in a tire powerstation is smaller than in con-ventional power stations, lessCO2 is released (approx. 17%)and a weaker global warmingpotential generated (approx.20%). Worn tires release so-mewhat less SO2 than coal,thereby reducing the acidifica-tion potential (approx. 33%).Reductions in the amounts ofthe SO2 and cadmium releasedcan lead to a reduction in theecotoxic and human-toxicpotential.

6.3. Retreading

A comparative ecological evalua-tion of a retreaded tire with anew tire poses certain metho-dological problems. A retreadedtire and an original new tire arenot equivalent products in thestrict sense of the word. This isbecause it is not technicallypossible for a retreaded tire to

simultaneously obtain the samelevel as the base product – anew tire – as regards propertieslike safety, durability, handlingand service life. (This notwith-standing, retreaded tires canattain a high technical level).

Some of the causes are:

• technical limits in roughingthe old tread components

• the inevitable additional tem-perature stressing of the car-cass during tread vulcaniza-tion

• the varying tire contours ofdifferent tire types and/ormakes

• the varying growth of thecarcass in the tire’s first lifeas a function of serviceperiod, load, air pressureand temperature. Nowadaysthe retreading industry iscapable of manufacturingretreaded tires that approxi-mate a new tire in almost allproperties – with the excep-tion of rolling resistance. Therolling resistance of a tire ofthis kind is at least 3% higherthan that of a new tire.


23

Tire power plant

Feeder shaft for worn tires

Feed grid

Additional burner

Combustion and irradiationchamber

Flue gas dust collector

Ash removal

For this comparison, one as-sumes the most favorable casefor a retreaded tire, namely arolling resistance 3% higherthan that of a new tire butotherwise the equal of a newtire property-wise.

6.3.1. Manufacture of newtires versus fullretreading of worn tires

Considerably more energy isrequired to manufacture a newtire than to retread a worn tire

(approx. 2.3 times more),approx. 1.85 times as much airis required, approx. 25 times asmuch water and approx. 1.4times as many resources (Figure16).

Atmospheric emissions, wastewater pollution and the amountsof overburden and waste produ-ced are also markedly higherthan for a retreaded tire (by ap-prox. factors of 2.2, 139, 4.4 and187 respectively).

This means that manufacturinga new tire has a much greaterenvironmental impact thanretreading a worn tire: the globalwarming potential is 1.8 timesthat of a retread, the acidificationpotential approx. 1.75 times andthe nutrification potential ap-prox. 1.07 times higher.

There is a trivial explanation forthese major differences: asalready mentioned, a worn tireenters into the present assess-ment as “raw material available”,

6. Recycling of worn tires6. Recycling of worn tires (Life cycle inventory analysis and impact assessment)

24

FIGURE 16: MANUFACTURE OF A NEW TIRE VS. RETREADING OF A WORN TIRE.

The individual parameters are shown summarized in categories. The categories for new tire manufacture are set at 100%, with the data for worn-tire

retreading presented relative thereto. The figures for the individual columns reflect the absolute value of the summarized parameters in the

categories. They are to be regarded independently of the figures given an the % axis. Results of the life cycle inventory analysis and of the impact

assessment are shown in the same chart. Input flows and output flows for the life cycle inventory analysis are overwritten as “Input” or “Output”.

The calculated environmental potential of the impact assessment is overwritten as “Impact”.

Resourc

es (k

g)

Dead

heap (k

g)

Overb

urden

(kg)

Global

warm

ing

potentia

l (kg)

Air (k

g)

Wat

er (k

g)

Atmosp

heric

emiss

ions (

kg)

Emiss

ions i

nto

water

(kg)

Was

te (k

g)

Energy (

MJ)

Acidifi

catio

n

potentia

l (kg)

Nutrific

atio

n

potentia

l (kg)

21.8

131.33

35.6

5

65.96

22.9

5

578.86

2.9

14.93

11.3

2

24.94

0.01

372

1.903

2.90

9

12.727

0.02

325

4.353

147.

45

331.65

11.4

5

20.40

0.00

640 0.00683

0.05

295

0.093

0

10

20

30

40

50

60

70

80

90

100

Retreading Manufacture of a new tire

Input Output Impact

without the expense for itsmanufacture being taken intoconsideration.The only rawmaterials needed in retreadingare those required for the newtread.

6.3.2. Service life of a newtire versus service lifeof a retread

A comparison of new tire manu-facture and worn tire retreadingyields very favorable results forretreads. This is relativized so-mewhat when the expense forthe use of new tires and retreadsis also considered. This mannerof viewing things actually violatesthe assessment framework

defined for the present study.The authors regard the inclusionof the use phase in the presen-tation of the retread as very im-portant, however, and thus viewthe deviation from the assess-ment framework as acceptable.

In what follows, two differentscenarios are considered: a roll-ing resistance increase of 3%corresponds to the value thatcan be obtained with the bestretreading technology available;a 10% increase in rolling resi-stance is average for retreads.In a first step, one compares theenvironmental impact of usingretreads with the impact ofusing a new tire. In a second

step, the environmental impactof the retreading process and ofusing a retread is comparedwith the corresponding impactof manufacturing and using anew tire.

6.3.2.1. Use of a retreadversus use of a newtire

As Figure 17 shows, the factthat rolling resistance is 3% or10% higher in the case of aretread means that the overallenvironmental impact in theretread’s use phase is approx.3% or 10% higher than a newtire’s use phase


25

6.3.2.2. Retreading and useof a retread versusmanufacture and useof a new tire

As Figure 17 shows, the life of aretread exhibits a much lowerwater consumption rate (approx.89%) and a much smallernegative environmental impacton waste water (approx. 96%).

This effect is due to the resourcesavings, especially for rayonand SBR. The reduction in thequantities of dead heap(approx. 42%) and overburden(approx 17%) result from alower consumption of electricenergy. On the other hand, theretread’s higher rolling resis-tance gives rise to greater fuelconsumption. This in turn leadsto increased overburden inconjunction with the drilling andrefining of petroleum.The reduc-

tion in overburden is thussmaller than the reduction indead heap. Waste (approx.95%) decreases because aretreaded tire makes use of theworn tire’s casing; as less steelis used, considerably less oredressing residue accumulates.

As even the quality car retreadexhibits more rolling resistancethan a new tire, it consumesmore energy and air during itsphase of use. The increased


26

FIGURE 17: USE OF A NEW TIRE VERSUS USE OF A RETREAD (3% OR 10% HIGHER ROLLING RESISTANCE).

The individual parameters are shown summarized in categories. The categories for the use of a new tire are set at 100%, with the data on the re-

tread being shown relative thereto. The figures for the individual columns reflect the absolute value of the summarzied parameters in the catego-

ries. They are to be regarded independently of the figures given on the % axis. Results of the life cycle inventory analysis and of the impact as-

sessment are shown in the same chart. Input flows and output flows for the life cycle inventory analysis are overwritten as “Input” or “Output”.

The calculated environmental potential of the impact assessment is overwritten as “Impact”.

0

10

20

30

40

50

60

70

80

90

100

110

Luft (k

g)

Was

ser (

kg)

atm

os.

Emiss

ionen

(kg)

Emiss

ionen

in

Was

ser (

kg)

Abfall (

kg)

Energ

ie (M

J)

Vers

auer

ungs-

potentia

l (kg)

Eutrophier

ungs-

potentia

l (kg)

232,

18 1226

8,06

71,3

6

17,3

2

635,

5

0,07

17,5

4

8429

,45

0,26

669,

22

0,64

0,07

2

2092

,94

623,

3

28,0

4

591,

72

1,96

26,0

7

4,57

7851

,87

621,

25

0,63

0,06

7

225,

97

216,

15

2108

,54

67,8

7

16,2

9

590,

89

0,07

16,4

9

0,24

7837

,62

639,

97

0,61 0,

069

Resso

urcen

(kg)

Taubes

Ges

tein

(kg)

Abraum

(kg)

Treib

haus-

potentia

l (kg)

Runderneuerter Reifen mit 3% höherem Rollwiderstand Runderneuerter Reifen mit 10% höherem Rollwiderstand Neureifen

Input Output I mpact

consumption of energy and airis more than offset by thesavings at-tained in retreading.The consumption of resourcesdrops by about 4.4%. Theresource savings attained inretreading is virtually canceledout by the higher petroleum(fuel) consumption .

With the car consuming morefuel, emissions of pollutant gas(CO2, NOx and SO2) andmethane are also higher. This isoffset by the savings realized inretreading. The consequence isnonetheless an increase in theglobal warming potential(approx. 3.0%) and the nutrifi-cation potential (approx. 3.0%).The acidification potential dropsby approx. 2.7%.

The environmental impact as aconsequence of higher rollingresistance is particularlymarked when the increase inrolling resistance is assumed tobe 10%. The energy and airrequirement rises by approx.8% or approx. 9% respectively.The lower resource requirementfor retreading is more thancanceled out by the increasedfuel consumption in the usephase; there is an increase inthe resource demand of approx.3%. With the increase in fuelconsumption, pollutant emiss-ions also rise (approx. 7%). Asa consequence the globalwarming potential also grows(approx. 8%), as do the acidifi-cation potential (approx. 1%)

and the nutrification potential(approx. 8%).

The ecological advantages anddisadvantages of the two variantsunder study do not becomeevident until the tire is viewed inan overall system.

The sum ecological effect of ahigh-quality retreaded tireexhibiting a moderate increasein rolling resistance can be saidto be virtually neutral, while aretreaded tire of average qualitycan be expected to generate agreater environmental impact.

6. Recycling of worn tires6. Recycling of worn tires(Life cycle inventory analysis and impact assessment)

27

One main goal of this life cycleassessment is to pinpoint whatcan be done to avoid environ-mental effects in the life of atire.

7.1. Dominance analysis

Because of the plethora of para-meters under consideration inthis assessment, no one phasecan be expected to exercisegeneral dominance for all para-meters. The greatest negativeimpact on the atmosphere, forexample, is in the use phase(Figure 7); in the case of wastewater, on the other hand, rawmaterial acquisition has thegreatest negative impact (Figure7). A summarized comparisoncan be made on the basis of thecumulative energy input and theenvironment potential in thevarious life phases.

The cumulative energy inputand the environmental potentialvalues are shown in Figure 18.

In all categories the greatestnegative impact on the environ-ment is shown to occur in theuse of the tire. Next in impor-tance – with a considerablylower impact – are the rawmaterials phase and the trans-port phase. Tire production hasthe weakest negative impact onthe environment. On the basisof the clear dominance of theuse phase vis-à-vis raw materi-als acquisition, production andtransport, it is evident that thegreatest potential for a reduc-tion in the environmental impactis there: even a relatively slightreduction in rolling resistancecan have a major effect.

7.2. Significance analysis

As the use phase of the tiregives rise to the greatest envi-ronmental impact (Chapter 7.1),it is the starting point for an ef-fective reduction of environ-mental effects by means of ma-terial variations. The compari-son of different variants showsclearly that the impact on theatmosphere can be lessened bysubstituting silica for carbonblack in the tread compound.This is because the changelowers the tire’s rolling resi-stance (Chapter 5.1). While thissubstitution increases, in fact,the negative impact on wastewater, the overall effect on thecumulative energy input and onthe environmental potential isadvantageous. A comparison ofthe rayon and polyester variants(Chapter 5.2) points to a clearsignificance with respect to thewater requirement and to emis-sions into water in favor of thepolyester variant.

For lack of any unambiguouscomparative criteria, no compa-rative evaluation will be madehere of the three worn-tire recy-cling alternatives studied. It isto be noted, however, that allthree recycling possibilitiesallow for savings of mineral orfossil resources to the extentthat these resources are repla-ced by worn tires.

7. Interpretation7. Interpretation

28

FIGURE 18: RELATIVE COMPARISON OF ENERGY CONSUMPTION AND VARIOUS FACTORS

OF IMPACT POTENTIAL IN THE PHASES OF A TIRES LIFE.

Acquisition of raw materials Transport Production Use

2.69 1.87

11.26

5.58

0.21 0.241.95 3.11

1.33 1.17 1.64 1.53

95.78 96.72

85.15

89.78

0

10

20

30

40

50

60

70

80

90

100

Cumulative energy input Nutrification potentialAcidification potentialGlobal warming potential

Worn tires are used as a secon-dary raw material in other pro-duct systems. The inherent pro-perties of these worn tires thusyield expanded benefits allowworn tire recycling to fulfill therequirements of the RecyclingManagement and Waste Act.

7.3. Sensitivity analysis

For methodological reasons,product life cycle assessmentsare always inevitably subject toa certain degree of “fuzziness”and subjectivity. The reason forthis is primarily uncertainty andinaccuracy in recording thedata, the delimitation of thescope of the assessment andthe weighting and evaluation ofthe environmental impact. Thesensitivity analysis should in-clude an estimate of the impactof possible errors on the resultsof the assessment.

7.3.1. Possible sources oferror

7.3.1.1. General framework ofanalysis

To ensure the reproducibility ofthe assessment, it was neces-sary to define the scope of theassessment (Chapter 2).Indirect and personnel expen-ses lie outside the systemlimits. This is because there isstill no agreement as to whetherthese expenses should flow intoan assessment. Construction,

maintenance and servicing ofsystems and auxiliary processesare not included in the assess-ment. This is firstly because theproportional assessment ofthese expenses relative to asingle tire would be minisculeand secondly because theseexpenses should be taken intoconsideration in assessing thesystems.

Possible noise emissions from atire are dependent on variousparameters. There are differencesin the existence and efficiencyof noise control measures, thetransmission of noise, thedistance from the source of thenoise, local conditions and thenoise-sensitivity of living beingsto noise. It is therefore difficultto quantify noise emissions, forwhich reason they are notincluded in the assessment.

One can therefore assume thatany error that may result fromexcluding the expenses cited issmaller than the impact that im-precise data and eroneous allo-cations would have (e.g. in use).

7.3.1.2. Allocations

No information is available onany allocation samples as mayhave been applied or withrespect to data records fromexternal sources. It can beassumed, however, that alterna-tive allocations would not haveany significant impact on theassessment results. On theother hand, the allocation of

material and energy flows in thetire’s use phase is of majorsignificance to the assessment.Distribution on the basis of theroad resistance generated bythe tire seems plausible be-cause it reflects the tire’s effecton the car’s fuel consumption. Itseems advisable to measurethe cement plant’s inflows andoutflows on the basis of theenergy contribution made byworn tires.

7.3.1.3. Cut-off criteria

With the exception of the datain Chapter 5 (caption to Table2), the data shown in thisassessment covers all the indi-vidual parameters. In this wayerrors due to the application ofcut-off criteria are avoided.

The assessment drawn up alsoincorporates data from raw ma-terial manufacturers and recycl-ing organizations. As none ofthe data suppliers indicates thecut-off criteria applied, it isassumed that all essential datahas been recorded.

7.3.1.4. Data gaps

Not all the data provided by theraw material suppliers exhibitsthe degee of integrity this as-sessment was aiming at. Thesegaps are filled in by calculations,database records and estimatesof our own as derived fromchemical processes. It must beassumed, however, that this


29

approach does not take full ac-count of the material and energyflows occurring. The remainingdata gaps involve only sectionsof the respective raw materialassessments and raw materialsthat only make up a small shareof the tire as a whole.

7.3.1.5. Assumptions/Averages

For some parameters readingswere available or different eithernot so that assumptions or cal-culations had to be made onthe basis of averages. Due tothis approach, the results mayfluctuate. There is, however, nodanger of this influencing theassessment’s core statements.

7.3.1.6. Effects related toprocesses andtechniques

The technical process andprocedural conditions prevailingin raw materials acquisition,energy generation and tireproduction differ from one manu-facturer to the next and thus arenot absolutely identical in allcases. The data used in this as-sessment, however, was viewedas representative. Proceeding inthis manner does, of course,lead to a certain “fuzziness” inthe assessment results; e.g. theuse of process data for Germanor European areas can lead tochanges in the absolute magni-tudes; this does not, however,

significantly influence theassessment’s core statements.

7.3.1.7. Data acquisition

The data acquisition for the pre-sent assessment covered a pe-riod of six years. Changes inmaterials preparation, technicalprocedures or new system de-signs occurring in the timespanthrough to completion of theassessment can affect the re-sults of the assessment. As faras is known, changes of thiskind did not transpire in the as-sessment timespan.

7.3.1.8. Evaluation method

The environmental impact isevaluated on the basis of equi-valence coefficients that deter-mine the contribution made bythe relevant pollutant to the re-spective environmental potential.Those environmental potentialvalues are studied whoseweighting coefficients are gene-rally recognized nowadays[15].It is, on the other hand, hardlypossible to scientifically ascer-tain the weighting coefficientsused to determine ecotoxicityand human toxicity (Chapter4.1.5). For this reason thepotential values are describedverbally instead of being repres-ented absolutely. In this way itis possible to avoid errors andmisinterpretations that couldarise as the result of a scientifi-cally unfounded evaluation

7.3.2. Impact of possibleerrors on the outcomeof the assessment

The tires’s use phase displaysthe highest global warming,acidification and nutrificationpotential in the overall life of atire (figure 21). This potential isdetermined primarily by therelease of CO2, SO2 und NOx inall phases of a tire’s life. Achange in the weighting ofthese pollutant gases in thecontributions to the variouspotential effects would impactevenly on all phases.

Consequently, the tire’s usephase would form the phase inthe life of a tire in which the evi-ronmental impact is strongest.

The dominance of the usephase over all other phases inthe life of a tire is quite marked.Even halving the use phase’scontribution to the environmen-tal potential observed (cumula-tive energy input, global warmingpotential, acidification potentialand nutrification potential) andat the same time doubling thecontribution made in the rawmaterials acquisition phasewould not lead to a shift in thephasal topography of theenvironmental impact. Theresults of this assessment canthus be regarded as tenable.

The consumption of water andthe negative impact on wastewater is highest during tire rawmaterials acquisition (Figure 19).To alter this assessment result it


30

would be necessary to halvewater consumption during theraw materials phase while at thesame time doubling water con-sumption during the tire pro-duction phase. Changes in thenegative impact on waste waterwould have to be more markedto influence this tire assessmentstatement.

The basic statements arisingfrom a comparison of the diffe-rent tire variants (energy savings,reduction in atmosphericemissions, changes in waterconsumption and the negativeimpact on waste water)(Chapter 5) are not significantlyinfluenced by the possiblesources of error cited here.

In the present assessment, therolling resistance of car retreadsis assumed to be 3% or 10%higher (Chapter 6.3.2). Changesin this value have a marked in-fluence on how the ecologicaladvantages and disadvantagesin the car retread use phasecompare with those in the newtire use phase (Chapter 6.3.2).

The results concerning the envi-ronmentally neutral use of worntires in cement plants is ob-tained from a comparison ofidentical plants within the scopeof the assessment. The state-ments arrived at are based onthe inherent properties of theworn tires versus those of hardcoal, the standard fuel. The dif-

ference between energy gene-ration in tire power plants and inconventional power plants isdue to differences in the proce-dural techniques and to theinherent properties of the diffe-rent energy carriers. There isvirtually no possibility that thesources of error cited will in anyway influence the resultsobtained here.


31

FIGURE 19: RELATIVE COMPARISON IN THE PHASE OF A TIRES LIFE.

Acquisition of raw materials Transport Production Use0

10

20

30

40

50

60

70

80

90

100

88.74

7.96

28.63

94.41

22.6

3

67.99

0.210.2 0.032.78

0.02 0.09

3.924.68

24.57

0.01

26.17 27.25

7.13

87.16

46.77

2.8

51.18

4.68

Water consumptionResource requirements

Dead heap

Negative impact on waste water

WasteOverburden

In this section, the phases inwhich the environmental impactis greatest – as determined bythe study – are to investigatedwith a view to pinpointing anypossible improvements. On thisbasis recommendations can bederived for corrective action.

8.1. Raw materialsacquisition

Raw materials acquisition for acar tire is characterized by ahigh water requirement (Figure 5and Chapter 3.1.3). The use ofcooling water poses less of aproblem from an ecologicalviewpoint as the negativeimpact resulting therefrom ismuch lower than from processwater (Chapter 3.1.3). Toachieve an efficient reduction inthe use of process water, it isadvisable to aim at substitutingthe raw materials rayon andsilica. Polyester has, to a certainextent, already replaced rayonin car tires, resulting in amarked reduction in the waterrequirement (Chapter 5.2).While it is true that a lot ofwater is required for the manu-facture of silica, using silica asfiller does lead to a clear reduc-tion in a car tire’s rolling resis-tance. Ranking the environmen-tal impact of using silica is thusa question of evaluation.

Raw materials acquisition is thephase in the life of a tire whenthe negative impact on wastewater is highest (Figure 7 andChapter 3.2.2). In the geogra-

phical area on which this as-sessment is based, water hasnot been a scarce resource todate so that reductions in thenegative impact on water arenot classified as an ecologicalpriority. Substituting polyesterfor rayon can, however, lead toa reduction in the negative im-pact on waste water.

The raw materials acquisitionphase is characterized by ahigh incidence of waste (Figure 8and Chapter 3.2.3). The highcontribution made by ore dres-sing residue to the overall inci-dence of waste does not reallypresent much of a problem, thewaste consisting, for the mostpart, of tailings that need not bemonitored. Using synthetic fi-bers instead of steelcord couldrepresent the right approach inreducing the amount of wastegenerated, assuming that theenvironmental impact from theproduction of fibers does notcancel out the benefits of wastereduction.

8.2. Tire production

The production of car tires ge-nerates large quantities of deadheap and overburden (Figure 3and Figure 8). As this negativeimpact results more fromenergy generation than directlyfrom tire production, it is notpossible to directly influence itin any way.

The waste generated in the pro-duction of car tires (Figure 8)can largely be classified as notrequiring any particular monitor-ing. An attempt should none-theless be made to differentiatethe waste quantities and to thenspecifically reduce certain typeswhile increasing the share ofwaste recycled.

8. Opportunities for influencing the impact on the environment8. Opportunities for influencing the impact on the environment

32

Rubber extraction

Tire production at Continental

8.3. Tire use

Tire use is accompanied by ahigh consumption of energyand resources (Chapters 3.1.1and 4.1.1), thereby contributinglargely to the global warming,acidification and nutrificationpotential (Chapters 4.1.2 to4.1.4). At the moment ecologi-cal concern focuses on the de-pletion point of these resourcesand the climate[16]. Tire manu-facturers can take action toreduce the negative environmen-tal potential by developing cartires with lower rolling resi-stance. The partial substitutionof silica for carbon black asfiller has already effected impro-vements allowing for greaterfuel efficiency in this area (seealso Chapter 5.1). Automakerscan also contribute to a furtherreduction in the environmentalpotential – for example, bycutting back the weight of thevehicle – as can motorists byadopting a more economicaldriving style and by payingmore attention to the conditionof their tires (e.g. by makingsure that the tires are correctlyinflated). Tire makers can be ofassistance here.

8.4. Recycling of worn tires

When worn tires are used in thecement industry they someti-mes replace the standard fuelor other raw materials, therebyhelping to conserve natural re-sources. As recycling is envi-ronmentally neutral, and withthe law imposing an upper limitof 25% for substitute fuels,there is no possibility of this in-fluencing the environmental im-pact.

When worn tires are fired wholein tire power plants, the resul-ting specific energy consump-tion is higher than for conven-tional power plants. Appropriatemilling of the worn tires to allowfor more effective firing systemswould eliminate this deficiency.At the moment a lot of waste isproduced in the power plantsstudied due to additional smokepurification facilities. The latterare necessary, however, toreduce gaseous emissions.

An immediately apparentadvantage of retreading is the“raw material bonus” that worntires offer. This advantage isoffset, however, by the disad-vantage of the retread’s higherrolling resistance and the ove-rall balance is even negative insome cases.

The general picture would beenvironmentally neutral if theincrease in rolling resistancecould be held to a moderatelevel of around 3%. It is clearthat further development is

necessary to achieve parity inthe use of new tires and worntires (Chapter 6.3).

8. Opportunities for influencing the impact on the environment8. Opportunties for influencing the impact on the environment

33

WORN TIRES ARE DELIVERED AND FED

INTO THE FURNACE AT THE CEMENT

PLANT.

1 WdK (Wirtschaftsverband der deutschen Kautschukindustrie), 1996, Mitteilung des WdK, Frankfurt

2 Umweltmanagement - Ökobilanz - Prinzipien und allgemeine Anforderungen - ISO 14040, 1997, International Standardization Organization, Genf

3 Umweltmanagement - Ökobilanz - Festlegung des Ziels und des Untersuchungsrahmes sowie Sachbilanz - ISO 14041 (Entwurf), 1997, International Standardization Organization, Genf

4 Umweltmanagement - Ökobilanz - Wirkungsabschätzung - ISO 14042 (Entwurf), 1999, International Standardization Organization, Genf

5 Umweltmanagement - Ökobilanz - Auswertung - ISO 14043 (Entwurf), 1999, International Standardization Organization, Genf

6 IKP (Institut für Kunststoffprüfung und Kunststoffkunde, Universität Stuttgart), Software zur Ganzheitlichen Bilanzierung ((GaBi 3), Stuttgart

7 Baumgarten R, 1993, Der ökologische Reifen - Ein Versuch einer ganzheitlichen Bewertung, VDI Bericthe Nr. 1088, Düsseldorf

8 IFEU (Institut für Energie- und Umweltforschung), 1997, , Ökologische Bilanzen in der Abfallwirtschaft, Fallbeispiel: Verwertung von Altreifen, Nr. 103 10 606, Heidelberg

9 INFU (Institut für Umweltforschung), 1996, Emissionen beim bestimmungsgemäßen Gebrauch von Reifen,

10 Schweimer GW, Schuckert M, 1996, Sachbilanz eines Golf, VDI Bericthe, Nr. 1307, 235-255, Düsseldorf

11 Ullman’s Encyclopedia of Industrial Chemistry, 1988, Vol. A11, 5. Auflage, Weinheim

12 Saur K, Eyerer P, 1996, Bewertung zur Ganzheitlichen Bilanzierung, In “Ganzheitliche Bilanzierungen” P Eyerer, Hrsg., Springer Verlag, Heidelberg

13 Cadle SH und Williams, 1980, Enviromental degradation of tire wear particles, Rubber Chem. Technol. 53, 903/914

14 VDI-RL 4600, 1997, Kumulierter Energieaufwand, Richtlinie des Verbands der Deutschen Ingenieure, Düsseldorf

15 IPCC (Intergovernmental Panel on Climatic Change), 1995, 1994 IPCC supplement. IPPC Secretariat, World Meterological Organisation, Genf

16 Bundesumweltministerium, 1998, Nachhaltige Entwicklung in Deutschland - Entwurf eines umweltpolitischen Schwerpunktprogramms, Berlin

weitere Datenquellen siehe Chapter 2.2 Punkt 5 Bezugsquellen der Daten

a To calculate the change in abrasion (A) over time , the following equations and constants were used:

Enrichment ‡ d(A)/dt = k1 (1)

Degradation ‡ d(A)/dt = - k2(A) (2)

Law of time ‡ (A) = (k1/k2){1 - exp(-k2t)} (3)

State of equilibrium ‡ (A)( = k1/k2 für t = ( (4)

Constants: k1 = 1000/(4*365) = 0,685 [g/Tag] for one tire

k1 = 46*109 /365 = 0,126*109 [g/Tag] for all car tires on interurban

k2 = 0,007 [1/Tag] roads in Germany

b Soil volume V (=tire-mileage*abrasion-width of deposit*2*wear-depth of penetration)

V = 228*106*25*2*0,1 = 1,14*109 [m3]

9. Bibliography9. Bibliography

34

Contributions to global warming potential (timeframe 100 years)

COMPOUND GLOBAL WARMING POTENTIAL[KG CO2 EQUIVALENT]

Carbon dioxide (CO2) 1

Methane (CH4) 24.5

Dinitrogen monoxide (nitrous oxide, N2O) 320

Carbon monoxide (CO) 3

Contributions to acidification potential

COMPOUND ACIDIFICATION POTENTIAL[KG SO2 EQUIVALENT]

Sulfur dioxide (SO2) 1

Nitrogen oxides (NOX) 0.7

Hydrogen sulfide (H2S) 1.88

Hydrogen fluoride (hydrofluoric acid, HF) 1.6

Hydrogen chloride (hydrochloric acid, HCl) 0.88

Ammonia/ammonium (NH3/NH4) 1.88

Contributions to nutrification potential

COMPOUND NUTRIFICATION POTENTIAL[KG PO4-EQUIVALENT]

Emissions into the air:

Phosphate (PO4) 1

Ammonia (NH3) 0.33

Nitrate (NO3) 0.42

Nitrogen oxides (NOx) 0.13

Emissions into water:

Phosphate (PO4) 1

Chemical oxygen demand (COD) 0.022

Ammonia/ammonium (NH3/NH4) 0.33

10. Annex10. Annex

35

ReportCritical Review of the Life Cycle AssessmentLife Cycle Assessment (LCA) of a Car Tire

ZERTIFIZIERUNGS- UNDUMWELTGUTACHTER GESELLSCHAFT

Order number: 328 227 01

Reporton the critical review of the life cycle assessment

to DIN EN ISO 14040 ff.

Life Cycle Assessment (LCA) of a Car Tire

Commissioned by:Continental AGPostfach 1 69

30001 Hannover

LCA prepared by:

Continental AGEnvironmental Protection/Recycling DepartmentDr. Silke Krömer, Dr. Eckhard Kreipe, Dr. Diethelm Reichenbach, Dr. Rainer Stark

External experts:TÜV Nord Zertifizierungs- und Umweltgutachter Gesellschaft mbH,accredited by the DAU-Deutsche Akkreditierungs- und Zulassungsgesellschaft für UmweltgutachtermbH, registration no. DE-V-0158Dr. Johann Josef Hanel, environmental reviewer, DE-V-0058Dr. Winfried Hirtz, environmental reviewer, DE-V-0151

Order no.: 328 227 01 Date of order: Feb. 24, 1999

Review based on: DIN EN ISO 14040ff. : 1997

DIN EN ISO 14041ff. : 1997

DIN EN ISO 14042ff. : 1999

DIN EN ISO 14043ff. : 1999

Critical review of the life cycle assessmentCritical review of the life cycle assessment

36

1. General remarks

1.1. Object and definition ofthe assignment

Continental AG’s environmentalprotection function worked outa comparative life cycle assess-ment (LCA) of a car tire. In aletter dated February 24, 1999Continental AG commissionedTÜV Nord Zertifizierungs- undUmweltgutachter GesellschaftmbH (TÜV Nord ZUG), asindependent external agency, to critically review the LCA incompliance with DIN ISO 14040 ff.

At TÜV Nord ZUG the reviewwas carried out by the environ-mental reviewers approved inaccordance with the environ-mental audit statute: Dr.-Ing.Johann Josef Hanel, Dr.-Ing.Winfried Hirtz.

As specified by the customer,the objective of the review wasone of verifying the reliability,transparency, relevance and re-presentativeness of the metho-dology used in the LCA submit-ted for review with respect to

• objective and scope of theassessment

• life cycle inventory analysis

• impact assessment and the

• interpretation/evaluation ofthe assessment..

1.2. Approach

Taking into consideration theoverriding quality criteria (trans-parency, reproducibility, qualityof data used, identification ofsource of data), the critical re-view was carried out as follows:

• review of objective andscope of assessment

- function and functionalequivalence

- system limits/scope ofassesssment (place, time,technology)

- allocation process with thespecific assignment/distribu-tion rules selected

- selection of significantparameters and materials

• review of the performed lifecycle inventory analysis

- input/output analysis (mainchains)

- input/output data used incl.the reliability of same

- systematic methods,integrity and plausibility ofthe input/output analysis

- sensitivity analysis andestimation of errors

- plausibility and soundnessof the calculations

- consideration of priorprocess chains, coupledproduction and secondarypost-use effects

• review of impactassessment

- selection of impact catego-ries (inventory- and problem-oriented)

- aggregation of data withrespect to impact categories

• review of the interpretation/comparative statements as aconsequence of impactassessment

For this review, relevant metho-dological processes and docu-ments as well as data acquisi-tion and calculation steps wereviewed in a representativescope, directly on the computerand elsewhere. Within the limitsof what is reasonable, pertinentprofessional literature on LCAtechniques was considered.


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2. Outcome of the criticalreview

2.1. Objective of the study

The objectives of the LCA areclearly and unambiguously defi-ned; external and internal targetgroups were likewise named forthe study. The introductory(concise) description for con-ducting a life cycle assessmentof a tire provides a sufficientamount of relevant informationto elucidate the targeted, ecolo-gically holistic mode of analysisin such a way as to render itreproducible.

2.2. Scope of study

The object of this assessmentwas seen to be a summer cartire in Continental’s main pro-duct line. It is compared withdifferent tire variants and the re-cycling of worn tires. The scopeof the assessment (boundaries)are defined and delimited withinthe system as a whole withrespect to area, time and tech-nology. The assessment limitsare compatible with the selectedfunctional unit of the assessmentobject, which is defined as amileage of 50,000 km in the lifeof a tire (standard mileage).

For the following life cycle in-ventory analysis, all relevantcomponents, structural partsand processes within the as-sessment area are ascertained,analyzed and finally consolidated

into five main modules typicalfor the assessment object:

- manufacture of raw materi-als for tires

- tire production

- tire use

- recycling of worn tires

- transport.

The technologically-relatedmultiplicity in the components,structural parts, and processescomposing the modules aretransformed to standard com-ponents in the current techno-logy generation without effec-ting any changes in the condi-tions. We regard this as areasonable and purposeful ap-proach. The presentation of theindividual modules in graphsand tables backs up the syste-matic procedure and integrity ofthe approach chosen. A 100%assessment is attained.

The effects and influences thatcan be overlooked in definingthe assessment system arediscussed and – to the extentrelevant – listed.

By way of summary, the scopeof assessment decided uponcan be said to ascertain andtake into account all relevantvariables within the limits of therelevant assessment space li-mits, in accordance with thepresent state of ecological as-sessment techniques.

2.3. Life cycle inventoryanalysis

The input/output analysis andthe documentation of the lifecycle inventory assessment of acar tire were effected with theassistance of a computer onthe basis of the aforementionedkey modules.

2.3.1 Data sources

The processes in the mainchains of the individual modulesare described realistically. Thedata used rely partly on gene-rally recognized files (PE/IKP1998: Holistic AssessmentTechniques, GaBi, Version 3)and partly on Continental AGsources. The data base is ascomprehensive as the DPsystems employed allow.Additional data was addedwhere necessary to ensure datasymmetry. This affected, forexample, overburden in thecase of oil extraction or rubbertransports. The data is reprodu-cible and representative for thisassessment. All manufacturerdata on individual ingredientsnot contained in the database –e.g. carbon black, silica – wassubjected to critical review. It isinherently conclusive.


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2.3.2. Plausibility andintegrity review

The computer imagery of thesystem boundaries is alsosystematic and in compliancewith the defined assessmentareas. The boundaries aredrawn wherever no (major)influence on the partial resultsand no influence on the overallresults are to be expected anymore (see the sensitivity analy-ses carried out). A high degreeof data quality and data sym-metry can be attested to. Thedata is complete within thelimits cited.

Sampling was carried out for allfive LC inventory analysis areas(main modules). In so doing, theaccuracy of the assessmenttechniques and the plausibilityof the calculations and resultswere checked for selectedparameters (e.g. CO2 emissions,material input, waste etc.)throughout the assessment.Within the assessment the cor-rect linkage of process chains,the incorporation of partial as-sessments and the basis for thedata was checked. In the caseof module changes, the recal-culation was actively monitored,as, for example, the calculationof the module “zinc production”instead of “iron production”.

To ensure the retraceability ofdata back to its source, boththe related calculations and thedocumentation was examined.

Within the framework of the ite-

rative review, the suggestionsmade by the environmental ex-perts with respect to the com-plementation of the documen-tation (100% reproducibility)were incorporated. This concer-ned, for example, the calorificvalue of worn silica and carbonblack tires or the nonusablethermal energy in tire powerplants. Upon termination of theproject, all data was completelyreproducible.

All significant parameters are inplace, representative, systema-tically designed and completelyassessed. The assessmentsand the data acquisition andcalculation processes are trans-parent and reproducible.

2.3.3. Allocations

Allocations occur primarily inthe use phase. They are notavailable in a generally accessi-ble database and were there-fore prepared by ContinentalAG. They are presented in thedocumentation in a completelyunderstandable and plausibleform. To the extent that alloca-tions from the databases areimported into the process plan,the basis of the data is sufficient.

Allocations from the databaseswere already taken into consi-deration there.

Other allocations were made forthe recycling of worn tires in ce-ment plants and in the event ofprior oil product chains. Theyare plausible.

2.3.4. Error assessments andsensitivity analysis

Separate uncertainty analysesfor the individual parameterswere demonstrated to havebeen carried out and are con-tained in the documentation.The assertions derived fromthese possible errors are tenable.

The sensitivity calculations andthe appurtenant requisite para-meterization were reviewed,with the key use-phase criteriaof relevance here being rollingresistance and aerodynamicdrag. Other materials added tosafeguard the assessementlimits – silica, for example – werelikewise covered. Thesensitivities were plausiblycalculated.

2.4. Impact assessment

The impact assessment isbased on the data in the lifecycle inventory analysis. The lifecycle inventory and impact as-sessments were separated fromone another both as regardstext and image. The impactindicators were selected incompliance with the reviewboundaries of the product lifecycle assessment.

To even be able to interpret – bymeans of an impact estimate –the data and information that itwas possible to study in thecourse of the life cycle inven-tory analysis, the data first hasto be summarized using prede-fined impact categories.


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Taking into consideration thegoals of the study, the functio-nal unit selected and the (stan-dard) technologies used in theassessment area, the followingimpact categories were definedin the study:

• resource consumption in theform of primary energy input

• Global warming potential(GWP)

• Acidification potential (AP)

• Nutrification potential (NP)

• Ecotoxic and human-toxicpotential.

These quantifiable impact cate-gories represent the assess-ment object, including the tech-nology employed, in terms oflocal, regional and global im-pact indicators (key categories).The assignment of individualdata to the impact indicatorshas been provided for. The datais grouped by respective envi-ronmental impact and is speci-fied in accordance with thescientifically established, data-based dose-impact relationship(Saur + Eyerer 1996). The calcu-lations were subsequentlycarried out. The factors in theDP system are internationallyrecognized.

The specific problem of humantoxicity and ecotoxicity – in thestrict sense of the word – hasalso been covered in the as-sessment in the form a risk

analysis. The use phase is themain exposition path for humanand ecotoxicity. Alongside theinhalation of abrasion particles(individual negative impactpath), deposits of toxic sub-stances were also observed onvegetation and along the shoul-der of the road. The assess-ment was not able to arrive at ahuman and toxicity evaluationscore summarizing the toxicitydata and substance groups.Because the data was gatheredfor a large area and incorporatedindividually, toxicity can bediscussed only in the form ofmodels.

Further impact categories are ofonly secondary importance withrespect to the objectives of theassessment.

The study did not consider rawmaterial depletion (petroleum,rubber). We feel this isappropriate in view of theassessment boundaries and theprimarily industrial use of theseraw materials.

The data was grouped underkey categories on the basis ofgenerally recognized equiva-lence factors in a clear, reliableand easily reproducible fashion.The results for the cases obser-ved in the LCA are presented in abalanced and conclusive manner.The cases in question are:

• manufacture of the rawmaterials for tires

• production of the tire

• use of the tire

• recycling of the tire

• transport.

2.5. Interpretation

The present interpretation ofresults of the inventory analysisand the impact assessment isconsistently and appropriatelyfocused on the goals definedfor the LCA. Recommendationswere made with respect tospecific users and targetgroups. The scope of therecommendations was appro-priately restricted in line withthe current configuration ofstandard tire manufacturing andthe alternatives on which theproduct life cycle assessmentwas based.

The recycling of worn tires isaddressed in three options re-presenting the major possibili-ties at the moment. The majorenvironmental effects arisingfrom the recycling of worn tiresare analyzed and discussed.This is especially true for the“retread” option. Due to thelack of functional equivalence,a direct comparison is possiblehere only to a limited extent.The appropriate separate as-sessment analysis carried outfor retreads and new tires provi-des valuable results and indica-tions in this regard, in particularfor the respective use phase ofeach.


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Because certain newer proces-ses – the use of rubber granu-late and powder, for example –do not currently enjoy the mar-ket relevance we feel theymerit, they are not treated inthis assessment.

Recommendations are labeledas such and clearly separatedfrom the life cycle inventoryanalysis and impact assess-ment.

3. Summary of the criticalreview

We have critically reviewed thecar tire life cycle assessment onthe basis of the requirementslaid down in DIN EN ISO 14040ff. The review can be summa-rized as follows:

• The methods used for theproduct life cycle assess-ment comply with the requi-rements laid down in DIN ENISO 14040 1999. They arescientifically founded andcorrespond to what is state-of-the-art with respect toproduct life cycle assess-ment techniques.

• The data employed is ade-quate, useful and qualifiedwith respect to the goal ofthe study.

• The interpretations take intoaccount the goal of thestudy and the restrictions re-cognized.

• The study submitted is in-herently conclusive andtransparent.


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A validity declaration has been issued with regasd to the critical review submitted.

Hannover, July 23, 1999

Dr.-Ing. Johann Josef Hanel Dr.-Ing. Winfried HirtzEnvironmental reviewer Environmental reviewer

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LCA Car Tire

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