�Environmental Benefits ofUsing Alternative Fuels in

Cement Production�

A LIFE-CYCLE APPROACH

CEMBUREAU - the European Cement Association, based in Brussels, is therepresentative organisation for the cement industry in Europe. Its Full Members are thenational cement industry associations and cement companies of the European Union andthe European Economic Area countries plus Switzerland and Turkey. Associate Membersinclude the national cement associations of Czech Republic, Hungary, Poland and SlovakRepublic and the sole cement company in Estonia.

The Association acts as spokesman for the cement sector towards the European Unioninstitutions and other authorities, and communicates the industry�s views on all issuesand policy developments likely to have an effect on the cement market in the technical,environmental, energy and promotion areas. Permanent dialogue is maintained with theEuropean and international authorities and with other International Associations asappropriate.

Serviced by a multi-national staff in Brussels, Standing Committees and issue-relatedProject Groups, established as required, enable CEMBUREAU to keep abreast of alldevelopments affecting the cement industry.

CEMBUREAU also plays a significant role in the world-wide promotion of cement andconcrete in co-operation with member associations, and the ready-mix and precastconcrete industries. The Association regularly co-hosts conferences on specific issuesaimed at improving the image of concrete and promoting the use of cement and concreteproducts.

Since its foundation in 1947, CEMBUREAU has developed into the major centre for thedissemination of technical data, statistics and general information on the cement industryworld-wide. Its publications serve as the principal source of information on the cementindustry throughout the world. It is the editor of the �World Cement Directory� providingdata on cement companies and works based in some 150 countries.

Rue d�Arlon 55 - B-1040 Brussels � Tel.: + 32 2 234 10 11 - Fax: + 32 2 230 47 20E-mail: secretariat@cembureau.be � http://www.cembureau.be

AssociationEuropéennedu CimentThe EuropeanCementAssociation

CEMBUREAU

INTRODUCTION

PREAMBLE

POLICY BACKGROUND

THIS REPORT

CARBON DIOXIDE REDUCTION AND STABILISATION

ISSUES

STRATEGY 1: IMPROVING THE EFFICIENCY OF CEMENT KILNS

STRATEGY 2: USE OF ALTERNATIVE FUELS

STRATEGY 3: SUBSTITUTION OF RAW MATERIALS

CONCLUSIONS

DISPOSAL VERSUS RECOVERY IN CEMENT KILNS

INTRODUCTION

SYSTEM DEFINITION

ENVIRONMENTAL IMPACTS

RECYCLING VERSUS RECOVERY IN CEMENT KILNS

INTRODUCTION

RECYCLING VERSUS UTILISATION OF WASTE PLASTICS

RECYCLING VERSUS UTILISATION OF WASTE OILS

SUMMARY OF ENVIRONMENTAL BENEFITS

CONTENTS� Page �

1

1.1

1.2

1.3

2

2.1

2.2

2.3

2.4

2.5

3

3.1

3.2

3.3

4

4.1

4.2

4.3

5

4

4

4

5

5

5

6

6

7

7

7

7

8

9

13

13

13

14

15

3

1. INTRODUCTION

1.2 POLICY BACKGROUND

The cornerstone of currentEuropean policy in theenvironmental arena is the Treatyon European Union, signed inFebruary 1992 at Maastricht andratified in 1993. The key issues ofrelevance to the cement industryarising from the Treaty are asfollows:

(1) Sustainable growth inEurope, respecting theenvironment, is establishedas a principal objective ofthe European Union.

(2) Integration of environmentalimperatives into other areasof policy is seen as anotherkey requirement.

(3) Flexibility in decision makingis promoted, with decisionsbeing taken at Communitylevel if objectives cannot beappropriately met atMember State level.

The European cement industryfully endorses these goals and,through CEMBUREAU, is activelyengaged in assessing thecontribution it can make towardsachieving these goals.

With respect to wastemanagement, in 1997 theEuropean Commission publisheda review of the CommunityStrategy for Waste Managementoriginally established in 1989. Thereview endorses the concept ofsustainable development andthe principles of the wastemanagement hierarchy, namely:

• prevention of waste;

• recovery of waste (includingmaterial recycling and energyrecovery);

• safe disposal of waste;

• application of the proximityprinciple and self-sufficiency inwaste management outlets.

CEMBUREAU concurs with theprinciples embodied in the wastemanagement hierarchy, whichrightly places waste preventionand recovery/reuse in a pre-eminent position relative toultimate disposal. CEMBUREAUbelieves that every opportunityshould be explored to preventand minimise waste generationand to maximise its recovery andreuse.

The utilisation of wastes in thecement industry, principally asalternative fuels but also assupplementary raw materials, iscompatible with the generalprinciples of waste managementat both European Union andnational levels, and with existingEU and national policies onenergy efficiency, climatechange and wastemanagement. There are tworeasons why the use of suchmaterials is considered by theindustry to be fully compatiblewith the principles of sustainabledevelopment:

(1) In terms of the cementmanufacturing process, theuse of alternative fuels andraw materials has thepotential to reduceemissions to the environmentrelative to the use ofconventional fossil fuels, andconserves non-renewableresources.

(2) In terms of the wastemanagement system,cement kilns offer a safealternative to conventionaldisposal of waste indedicated waste incineratorsor in landfills, again resultingin overall benefits byreducing environmentalburdens and reducing theneed for dedicatedtreatment capacity.

1.1 PREAMBLE

The principle of sustainabledevelopment has beenaccepted as a central policyobjective of the European Union.The European cement industry,through CEMBUREAU, hasengaged in proactive andpositive debate with decisionmakers on how the industry canbest put these principles intopractice.

Hitherto, decision making in theenvironmental arena has tendedto be on a piecemeal basiswhereby each industrial sector�sresource needs, energyrequirements and environmentalimpacts of each pollutant wereconsidered individually.CEMBUREAU believes thisapproach fails to maximiseopportunities for generalenvironmental improvements, nordoes it provide an adequateframework for the optimisation ofthe costs and benefits of policyoptions. In its place, CEMBUREAUadvocates a holistic, integratedview of industrial activity and theenvironment. Using this broaderconcept, the present reportexplores one facet of sustainabledevelopment: namely, how theEuropean cement industry cancontribute towards theimplementation of theCommunity Strategy for WasteManagement by substitutingconventional fossil fuels withalternative and suitable wastematerials. Using a life cycleapproach, the reportdemonstrates the overallenvironmental benefits that fuelsubstitution can deliver when thecement industry participates as alegitimate player within theCommunity�s wastemanagement infrastructure.

The use of waste in Europeancement kilns saves fossil fuelsequivalent to 2.5 million tonnesof coal per year.

4

2. CARBON DIOXIDE REDUCTIONAND STABILISATION

These two aspects of wastemanagement are interlinked.They are best examined by thetechnique known as Life CycleAssessment (LCA). An LCAdescribes the impact on theenvironment during the stages aproduct goes through from thetime the raw materials areobtained until the final disposal ofthe product.

1.3 THIS REPORT

In this report LCA techniques areused to examine two relatedtopics:

(1) The production of cementby the use of two differenttypes of fuel: coal, and non-fossil fuels made from waste.

(2) The management of wasteby two different routes:utilisation in cement kilns,and disposal or reuse byother operations.

The environmental benefits ofutilising waste materials incement kilns is examined underthree headings:

2.1 ISSUES

The European cement industry isalready recognised as beinghighly energy efficient, andadditionally there is little scope fortechnological changes which willreduce emissions of carbondioxide from the productionprocess. However, the industryhas demonstrated that thesubstitution of conventional fossilfuels with alternative fuels basedon waste can make animportant contribution tosustainable developmentthrough the reduction of theglobal burden of greenhousegases such as carbon dioxide.

The manufacture of cement isan energy intensive operation,and the cost of energyrepresents a significant part ofthe total production costs. On anEU wide basis, cementproduction totals approximately170 million tonnes per year. Withan average energy consumptionequivalent to the combustion of120 kg of coal per tonne ofcement, this level of productionutilises the equivalent of 20 milliontonnes of coal.

During the manufacture ofcement, CO2 is generated fromthree sources:

• combustion of fuel in the kiln,to maintain the required kilntemperature;

• decarbonation of limestonewithin the kiln;

• use of electricity ininstallations such as grindingmills.

A total of 0.83 tonne of CO2 isemitted per tonne of finishedproduct (80% clinker), and ismade up as follows:

• CO2 from decarbonation is0.45 tonne per tonne ofcement;

• CO2 from the combustion ofcoal is 0.28 tonne pertonne of cement;

• electricity produced in coalfired power plants to operateon-site installations contributea further 0.1 tonne of CO2per tonne of cement.

Of the three sources, thedecarbonation of limestonegenerates the greater proportion(60%) of the CO2 emissionsliberated from the kiln. It shouldbe noted that these threesources of emissions areessentially independent of eachother.

There are three main strategiesby which the cement industrymay contribute to a reductionin CO2 emissions:

(1) Improve the energyefficiency of cementmanufacture;

(2) Substitute fossil fuels used incement kilns by fuels derivedfrom waste;

(3) Modify the composition ofcement by using cementconstituents which requireless energy to produce thancement clinker.

Each strategy is discussed below.

• climate change and carbondioxide reductions;

• disposal versus recovery incement kilns;

• recycling versus recovery incement kilns.

Information under the last twoheadings is based on studiescarried out by TNO (TheNetherlands) and the FraunhoferInstitute (Germany).

5

2.2 STRATEGY 1:IMPROVING THE

EFFICIENCY OF

CEMENT KILNS

Dealing first with Strategy 1,emissions of CO2 from cementkilns are closely linked withprocess and energy efficiency.Over the past four decades, theEuropean cement industry hasadopted a policy of continuousimprovement in plant, equipmentand operation. For example, lessefficient kilns are being replacedby more fuel-efficient preheaterand precalciner kilns and ball millsfor cement grinding have beenreplaced by more efficientgrinding systems. Presently, 78%of Europe�s cement production isfrom dry process kilns, 16% isfrom semi-dry or semi-wet kilns,and only 6% is from wet processkilns mainly in geographical areaswith wet raw materials. Theseand other energy efficiencymeasures adopted within theindustry have resulted insignificant reductions in fuel use,and hence of CO2 emissions.

The industry will continue alongthe same lines to further improveenergy efficiency. There is,however, now limited scope forfurther improvements in energyefficiency, although the ongoingprogramme of modernisation willcontinue to result in lower CO2emissions per tonne of cementproduced.

2.3 STRATEGY 2:USE OF ALTERNATIVE

FUELS

This leads directly to Strategy 2,and the use of alternative fuels incement kilns. This practice has awider benefit than merelyreducing CO2 emissions at thepoint of cement production. Theglobal CO2 emissions arereduced, but the reductionsoccur in other industry sectorsthan the cement industry. Toanalyse the benefits of the use ofalternative fuels in cement kilns,we have applied LCA techniquesto two scenarios:

(1) Scenario 1: Waste iscombusted in a dedicatedincinerator, with energy

recovery, and the powergenerated is fed into thenational electricity gridsystem. The cement kilnoperates with a conventionalfossil fuel, coal.

(2) Scenario 2: Waste istransferred to the cementkiln, displacing an amount ofcoal in proportion to its heatcontent. Since theincinerator is no longeroperational, the electricity itoriginally produced is nowgenerated by a coal firedpower station.

For each scenario, we havecalculated the burden of CO2 toatmosphere, and thencompared the two scenarios forthe net effect on CO2 emissions.The calculations are presented inAnnex A.

The net CO2 burden of the twoscenarios is obtained bysubtracting the total burden ofScenario 2 from the burden ofScenario 1. The benefit(reduction) in CO2 emissionsfrom burning waste in cementkilns as opposed to dedicatedincinerators is summarised inTable 1 and Table 2.

Summary of CO2 emissions from burning 1 tonne of waste in a dedicatedincinerator with energy recovery or in a cement kiln, discounting the baseloadoperation of the power plant

Table 1

The above analysis coversoperating practice observed bymany incinerators in the EU:namely, the recovery of energyalongside the waste destruction

Activity Biofuel (16 GJ/t) Solvent Waste (26 GJ/t)

Incineration in dedicated incinerator

Combustion in cement kiln, displacing coal

Net benefit due to combustion in cement kiln

3,379 kg CO2

2,778 kg CO2

601 kg CO2/t waste

4,429 kg CO2

3,462 kg CO2

967 kg CO2/t waste

process. However, there remainsome incinerators which have noheat or energy recovery facilities.In this case, the power plant iseffectively decoupled from each

of the scenarios. The netreduction in CO2 emissions whenwaste is combusted in thecement kiln is greater, as shownin Table 2.

6

3. DISPOSAL VERSUS RECOVERY INCEMENT KILNS

3.1 INTRODUCTION

LCA techniques have been usedto compare the environmentaleffects of processing thefollowing wastes in a cement kilnas opposed to destruction indedicated waste incineratorsspecially designed for eachwaste type:

• spent solvents (in a rotary kilnincinerator);

• filter cake (in a rotary kilnincinerator);

• paint residues (in a rotary kilnincinerator);

• sewage sludge (in a fluidisedbed incinerator).

The project was commissionedby the Dutch Government aspart of their analysis of the DutchNational Hazardous WasteManagement Plan 1997 - 2007,

and was undertaken on theirbehalf by the NetherlandsOrganisation for Applied ScientificResearch (TNO)1).Two methods of allocation wereconstructed. The first methodtreated the cement kiln anddedicated waste incinerators asisolated units, and apportionedemissions and their environmentaleffects solely to the function ofwaste processing. In otherwords, upstream and

1) � Tukker A (1996). LCAs for Waste: The Dutch National Waste Management Plan 1997-2007. Paper presented at the4th Symposium for Case Studies, SETAC Europe, Brussels, December 1996.

� Keevalkink J A and Hesseling W F M (1996). Waste Processing in a Wet Cement Kiln and a Specialised Combustion Plant.Report No. TNO-MEP-R 96/082, TNO Institute of Environmental Sciences, Energy Research and Process Innovation,Apeldoorn, Netherlands.

By burning waste in a cement kilnand substituting for coal, a non-renewable resource, savings aremade through resourceconservation and associatedCO2 emissions. The cement kilnalso makes more efficient use of

Summary of CO2 emissions from burning 1 tonne of waste in a dedicated incineratorwithout energy recovery or in a cement kiln

Table 2

Activity Biofuel (16 GJ/t) Solvent Waste (26 GJ/t)

Incineration in dedicated incinerator

Combustion in cement kiln, displacing coal

Net benefit due to combustion in cement kiln

3,379 kg CO2

1,760 kg CO2

1,619 kg CO2/t waste

4,429 kg CO2

1,820 kg CO2

2,609 kg CO2/t waste

the intrinsic energy of the wastematerial. Specialist wasteincinerators are very inefficientconverters of the heat content ofwastes, whereas a cement kilnapproaches 100% efficiency. Anet decrease in the quantity of

CO2 released, relative to ascenario in which waste iscombusted in a dedicatedincinerator, reduces theenvironmental impact of thegreenhouse effect during thecombustion of wastes.

2.4 STRATEGY 3:SUBSTITUTION OF RAW

MATERIALS

The use of materials such aspulverised fly ash or slag toreplace raw materials such asclay in cement kilns has thepotential to reduce CO2emissions at the point of cementproduction, as these productsuse less energy than clay.

A much more efficient way ofusing industrial by-products andnatural materials is to mix these

with cement clinker and grindboth materials to a cement.Such cement consequentlyconsists of cement constituentsother than ground clinker. Theadditional cement constituentsoften provide additionalbeneficial properties to thecement. The modification of thecement composition by theusage of additional cementconstituents results inconsiderable reductions in CO2emissions as not only fuel relatedCO2 is reduced but also theprocess related CO2(decarbonation).

2.5 CONCLUSIONS

The analyses demonstrate theclear benefits the cementindustry can provide in CO2reduction through integratingcement kilns within an overallwaste management strategy,either through the use ofalternative fuels, or through theuse of materials such asindustrial by-products asadditional cement constituents.

7

Summary of inputs and outputs to the cement kiln and dedicated incineratorsTable 3

Input Materials

Input Utilities

Airborne Emissions

Waterborne Releases

Solid Wastes

Avoided Products

Dedicated Incinerators Cement Kiln

• Spent solvents• Filter cake• Paint residues• Sewage sludge

• Electricity• Lime• Sodium hydroxide• Ammonia

• Acid gases• Metals• CO2• CO• Dioxins• Hydrocarbons

• Metals in effluent

• Solid residue• Fly ash• Bottom ash

• Steam• Electricity

• Spent solvents• Filter cake• Paint residues• Sewage sludge

• Electricity at the kiln• Electricity for waste processing• Transport to kiln

• Acid gases• Metals• CO2• CO• Dioxins• Hydrocarbons

None (no liquid effluent)

None (recycled within kiln)

• Input coal• Input crude• Input raw material

downstream operations such ascoal mining and transportation (inthe case of the cement kiln) andelectricity generation (in the caseof the dedicated incinerator)were not considered, nor werethe avoided burdens resultingfrom fuel substitution in thecement kiln. However, it wasrealised that this method ofallocating environmental effectspenalised waste processing,since emissions from cement kilnsare regulated separately to thosefrom dedicated incinerators, withhigher emissions of acid gasessuch as sulphur dioxide beingpermitted in cement kilnoperation due to the fact thatthey are associated with the rawmaterials. Further, the widerimplications of fuel substitution

could not be assessed.The alternative method of systemenlargement was thereforeagreed with the Dutch authoritiesand applied to the LCA.Conceptually, this method isidentical to that described inSection 2 for the assessment ofCO2 emissions during the burningof waste, and illustrated in Figures1A and 2A in Annex A. In systemenlargement, the additionalupstream activity of fossil fuelprocurement and thedownstream activity of electricitygeneration are considered inconjunction with the incineratorand the cement kiln operations.The latter is offset with the burdenassociated with the generation ofelectricity as a result of the wastebeing transferred from the

incinerator to the kiln, while theincinerator system is offset withthe burden of procuring fossil fuelfor the cement kiln. The results ofthe LCA, as applied to thespecific case of a cement kiln inBelgium, are discussed below.

3.2 SYSTEM DEFINITION

The basis of the LCA was onetonne of waste, eitherincinerated in a dedicatedincinerator, or combusted in acement kiln as a substitute forconventional fuels, in the presentcase coal (90%) and crude(10%). The inputs and outputs tothe two systems are summarisedin Table 3.

The system definitions werebased on data obtained onactual, operating incinerators inthe Netherlands and a wetcement kiln in Belgium. In theincinerator systems, the flue gas iscleaned in a wet scrubber,resulting in a release of liquideffluent from the plant.

Additionally, in the case of thefluidised bed incinerator forsewage sludge, an SNCR deNOxsystem was installed,necessitating an input ofammonia. Solid residuesrequiring disposal included fly ash,filter sludge and bottom ash.

In the case of the cement kiln,there was neither a release ofliquid effluent nor a release ofsolid residue, since cement kilndust was recycled back into thekiln, a practice that is standard inthe industry.

8

3.3 ENVIRONMENTAL

IMPACTS

In an LCA, the environmentalimpacts resulting from thereleases to air, water and landfrom the incinerator systems orthe cement kiln are grouped intocategories. Each chemicalreleased can contribute to oneor more impact categories andconversely an impact categorycan contain contributions from anumber of releases - forexample, a release of sulphurdioxide can contribute both toacidification and to humantoxicity, while the latter impactcategory can containcontributions from emissions ofacid gases, metals, dioxins, andhydrocarbons. The LCA studyfocused on the following impactcategories:

(1) Depletion of mineralraw materials (DRM):For the incinerator systems,depletion of raw materialresults from the use of utilitiessuch as lime. The DRMscore can be positive (i.e.the resource is procured andused) or negative (i.e.avoided, when consideringnet emissions within theoverall waste managementoption).

(2) Depletion of fossilenergy carriers (EDP):This burden relates to theenergy input for wastehandling and utility input forflue gas cleaning. Again,the net EDP score relative totwo different options forwaste management can beboth positive or negative.

(3) Global warmingpotential(GWP):This impact arises fromemissions of CO2 duringcombustion, and fromemissions of methane frombiodegradable wastedeposited in landfills.

Avoiding the generation ofenergy or avoiding the useof fossil fuels in the cementkiln can result in a significantnet avoided GWP score.

(4) Depletion of theozone layer (ODP):This impact arises fromemissions of volatilehydrocarbons, and isrelatively small in magnitudecompared to other impacts.

(5) Human Toxicity (HT):This impact category arisesfrom emissions of acidgases, CO, hydrocarbons,dioxins, metals, etc.

(6) Aquatic Ecotoxicity(AT): For the incinerator systems,AT results from releases ofeffluent containing heavymetals. For the fossil fuels,AT arises from effluentsgenerated during the miningor refining processes.

(7) PhotochemicalOzone CreationPotential (POCP):This impact is caused byreleases of hydrocarbons toatmosphere, and can ariseat any stage of the lifecycle.

(8) Nutrification (NP):Nutrification results from theaddition of nutrients to a soilor water system, causing anincrease in biomass. Anynutrient can have this effect,but nitrogen and phosphorusare the most crucial species.

(9) Acidification (AP):This impact is caused bydeposition of acid gasessuch as sulphur and nitrogenoxides onto water bodies.

(10) Solid wastegeneration:Depending on the type ofsolid waste, theenvironmental impacts will

be different. The LCAdifferentiated between thefollowing waste types: non-hazardous waste (NW)arising from mining and othersimilar activities; hazardouswaste (HW) comprisingbottom ash, fly ash and filtersludge, and radioactivewaste (RW) comprising thewaste produced by theproportion of the nationalelectricity system generatedby nuclear power (6%).

Each impact category wasscored for each of the wastemanagement options. Theindividual scores were weightedby the �Distance to Target�method relative to the impactcreated by GWP, and thentotalled to obtain a compositescore.

The results of the LCA arepresented in Table 4 and inFigure 1. In Table 4, theenvironmental burden scoresassociated with burning waste inthe incinerator system (addingthe burdens associated withburning fossil fuel in the cementkiln) and the scores associatedwith burning waste in cement kilns(adding the burdens associatedwith generating additional heatand electricity) have beensummed to provide an overallsub-score for resource depletionand releases to air and water,and an overall sub-score forwaste production. These scoresare then added to provide atotal score for each wastemanagement option, theassumption having been madethat the impact categories areall of equal importance.

9

LCA scores for waste management optionsTable 4

Waste Incinerators Cement Kiln Net Benefitto Cement

Kiln

Resources/Air/Water

Spent solvent

Filter cake

Paint residues

Sewage sludge

SolidWaste

TotalScore

Resources/Air/Water

SolidWaste

TotalScore

154

44

91

59

24

500

362

80

178

544

453

139

116

43

71

53

44

11

26

20

160

54

97

73

-18

-490

-356

-66

The higher the score thegreater the potentialenvironmental impact of aparticular waste managementoption. Therefore a netenvironmental benefitrelative to the cement kilnoperation is represented bya negative net score, while anet environmental disbenefit willbe represented by a positive netscore. The table shows thatregardless of the type of waste,there is a net benefit to thecement kiln option, in terms ofall the impact categoriesconsidered (i.e. resourceconservation, releases to air,releases to water and theproduction of solid waste). Theimpact category of solid waste isperhaps the most significant netbenefit accrued to the cementkiln disposal option. Whereas inthe case of combustion indedicated incinerators solid

waste disposal fly ash, filtersludge, etc. is a majorconsideration within the overalllife cycle, and involves landfillingand its associated impacts ofleachate generation and healtheffects, the cement kiln optiondoes not generate liquid or solidwaste. The small score assignedto solid waste impacts relates tothe waste associated with thegeneration of the additionalelectricity and heat needed toreplace the power produced bythe incinerator.

TNO has also developed a�standardised environmentalprofile� for each disposal option.In this method of presentation,scores for the base caseenvironmental burdens arecalculated when one tonne ofwaste is combusted in anincinerator, and when one tonneof waste is combusted in a

cement kiln. From each basecase the scores for the avoidedenvironmental burdens aresubtracted. In the case of wastecombustion in incinerators, theavoided burdens relate toexternal electricity and heatproduction. In the case ofcombustion in a cement kiln, theavoided burdens relate to thesavings in fossil fuel and rawmaterial use at the kiln. A netdecrease in emissions isrepresented by negative scoresfor the impact categories,whereas a net addition toenvironmental burdens isrepresented by positive scores.Net scores for individual impactcategories are shown in Figure 1for each waste type. Thesummation of individual scoresinto a single overall score foreach waste management optionis presented in Table 5.

Net scores and environmental profiles for waste management optionsTable 5

Waste

Resources/Air/Water

Spent solvent

Filter cake

Paint residues

Sewage sludge

SolidWaste

TotalScore

Resources/Air/Water

SolidWaste

TotalScore

-5

7

2

-5

-20

487

330

60

-25

494

332

55

-42

7

-19

-9

-1

-1

-0.2

-1

-26

6

-19.2

-10

Incinerators Cement Kiln

10

4.1 INTRODUCTION

As stated in Section 1, theEuropean cement industry firmlysupports the principle of thewaste management hierarchy,and the need firstly to conservenon-renewable resources, andsecondly to recover, reuse andrecycle materials to their fullestpotential. In this regard thecement industry can play avaluable role in maximising theutilisation of latent energy withina waste material, providing anenvironmentally beneficialalternative to materialsrecycling. Two examplesillustrate this theme:

• the recycling of wasteplastics versus the utilisationof waste plastic in cementkilns as a heat source;

• the recycling of waste oilsversus the utilisation of wasteoils in cement kilns as a heatsource.

Since each activity (i.e. recyclingand use in a cement kiln) hasassociated upstream anddownstream implications in termsof energy use, resourcerequirements and avoidedburdens, LCA is again used todefine and analyse the twosystems.

4.2 RECYCLING VERSUS

UTILISATION OF WASTE

PLASTICS

The Fraunhofer Institute2) has

analysed the environmentalperformance of the followingactivities with respect toemissions of CO2, energy use,

4. RECYCLING VERSUS RECOVERY INCEMENT KILNS

and the generation of hazardouswaste:

• utilisation of 1 kg of wasteplastics in cement kilns,displacing an equivalentamount of fossil fuel inthermal units. This results inavoided emissions relating tothe mining, handling,transportation and use ofcoal at the kiln;

• incineration of 1 kg of wasteplastics in an incinerator,along with other municipalsolid waste. Fossil fuel is nowused in the cement kiln, inthe absence of asupplementary fuel;

• recovery by conversion of1 kg of waste plastic intogaseous and liquid synthesisproducts using processessuch as hydrogenation.

As the base case, it wasassumed that 1 kg of wasteplastics was landfilled along withother municipal solid waste. Thisis still the predominant route ofdisposal for unsorted municipalsolid waste within the EU.

The environmental impacts of thewaste management optionsrelative to landfilling wereassessed for a range of impactcategories, including globalwarming potential, nutrification,acidification potential, solidwaste generation, etc. Aselection of environmentalburdens are displayed in Figure2 and can be summarised asfollows:

(1) CO2 Generation:The use of waste plastics incement kilns as a substitutefuel results in the largest net

reduction in CO2 generationof the three managementoptions, relative to landfilling.For waste incineration, theoffset from avoiding externalenergy generation isinsufficient to counterbalancethe avoided burden throughnot having to mine, transportand use coal at the cementkiln. Hydrogenation andconversion of waste to plasticgoods itself is an activity thatuses energy, resulting in asmall net saving in CO2

generation.

(2) Energy Recovery:Apart from waste incineration,which is a relatively inefficientconverter of latent energy,the other managementoptions offer comparablebenefits in energy utilisationrelative to landfill.

(3) Hazardous WasteProduction:The cement kiln,hydrogenation and conversionoptions do not producehazardous waste, since anywaste products arerecyclable. However, wasteincineration will produce0.03 kg of hazardous wasteper kg of plastics, in the formof fly ash and bottom ash.This waste will require disposal,generally by landfilling.

Overall, the cement kiln optionoutperforms the remainingoptions, maximising thebeneficial use of waste plasticsrelative to conventionalincineration or conversion intochemical goods.lubricating oil products would

2) � Life Cycle Analysis of Recycling and Recovery of Households Plastics Waste Packaging. Fraunhofer Institute, Munich, 1996

� Verwertung von Kunststoffabfällen aus Verkaufsverpackungen in der Zementindustrie. Fraunhofer Institute, Munich, 1997

13

Environmental burdens associated with the management of waste oilsTable 6

Activity

Reprocessing of Waste Oil• Mining & transport of coal• Waste oil refining• Coal in cement plants• TOTAL

551149

4,0234,732

CO2 Emitted(kg/t waste oil)

Energy Used(MJ/t waste oil)

4,3002,115

4626,877

Waste Oil in Cement Kilns• Crude oil procurement• Crude oil refining• Waste oil in cement kilns• TOTAL

124246

2,5362,905

1,4342,676

174,121

5. SUMMARY OF ENVIRONMENTALBENEFITS PROVIDED BY CEMENTKILNS

mean the continuation of fossilfuel procurement and use at thecement kiln. Therefore theenvironmental burdensassociated with coal extraction,

processing and use in cementkilns were added to theenvironmental burdens resultingfrom reprocessing operations.

The LCA results for CO2 emissionsand energy use are displayed inTable 6.As with the utilisation of waste

plastics in cement kilns, the useof waste oils as supplementaryfuel outperforms the alternativewaste management option of

with energy recovery andmaterial recovery within acement kiln represents anattractive waste managementoption. With an excess of 300cement plants spread throughoutthe European Union, the industryis particularly well placed torespond to Society�s needs in thisregard. Waste materials whichthe industry has utilised asalternative fuels include usedtyres, rubber, paper waste, wasteoils, sewage sludge, plastics andspent solvent. In all cases thesewaste materials would eitherhave been landfilled orcombusted in dedicatedincinerators. Their use in cementkilns replaces fossil fuels: • maximises the recovery of

reprocessing. Emissions of CO2and overall energy utilisation areapproximately 60% lower for thecement kiln option than when

the waste oil is reprocessed intolubricating oil products.Controlled processing of waste

energy while ensuring theirsafe disposal;

• produces overallenvironmental benefits byreducing releases to air,water and land;

• prevents resource depletionof valuable non-renewablefossil fuels;

• obviates the need to builddedicated incinerationfacilities.

The important contribution thatthe cement industry can maketo a nation�s waste managementinfrastructure has been explicitlyrecognised by several European

governments. The practice ofemploying alternative fuels incement plants does not hinderthe establishment of a soundwaste management industry.This practice can co-existalongside a vigorous and thrivingmaterials recovery and recyclingand incineration industry, withoutdistorting the essential principlesof the EU�s waste managementhierarchy.

To this end the cement industrycontinues to contribute to thefurtherance of sustainabledevelopment in Europe.

15

Annex A

CO2 EMISSIONS

WHEN BURNINGWASTE

The purpose of this note is to develop scenarios describing the emissions of CO2 during the combustion of

waste material in a cement kiln rather than in a dedicated incinerator. The calculations are intended asindicative, to establish broad order of magnitude of net emissions rather than precise emission estimates.

Two scenarios are constructed. In Scenario 1 the waste is combusted in a dedicated incinerator, and thepower generated is fed into the national electricity grid system. The cement kiln operates with a conventionalfossil fuel (coal). The releases of CO

2 from this system comprise the following:

· CO2 from the mining and transportation of coal used at the cement kiln;

· CO2 from the combustion of coal at the cement kiln;

· CO2 from the combustion of waste in the dedicated incinerator.

In addition to the above, there are emissions of CO2 from the power plant, when the latter is operating at

reduced load owing to the addition of electricity into the grid from an external source downstream of thepower plant. These emissions do not need to be computed if the objective is to examine the net differencebetween Scenario 1 and Scenario 2.

In Scenario 2 the waste is now transferred to the cement kiln, displacing an amount of coal in proportion to itsheat content. Since the incinerator is no longer operational, electricity is not produced. In order to maintainthe overall supply of electricity to the grid, the power plant has to generate an additional amount of electricityequivalent to that previously generated by the incinerator. In most EU Member States this marginal power isgenerated via the combustion of coal. The releases of CO

2 from this system comprise the following:

· CO2 from the mining and transportation of coal used at the power plant;

· CO2 from the combustion of coal at the power plant;

· CO2 from the combustion of waste in the cement kiln.

The scenarios are described below.

A1. INTRODUCTION

A summary of the assumptions and their sources is presented in Table A1. The assumptions are discussed inmore detail below.

A2. ASSUMPTIONS

Summary of Data Input and Other InformationTable A1

BiofuelSolventCoalCoal miningCoal transportationIncinerator efficiencyPower plant efficiency

Heat Content

16 GJ/t26 GJ/t26 GJ/t----

CO2 Emissions Plant Design Reference

(a)(b)(a)(c)(c)(d)(c)

110 kg/t 70 kg/t 93 kg/t 24.3 kg/MWh 0.045 kg/km/t--

-----23%37%

Notes:(a) Nystrom K L E (1993). Incineration waste and the greenhouse effect. ISWA Times, 1993/4 Yearbook.

Emission factor for biofuels is the average of emission factors for wood 112 kg/GJ) and domesticwaste (108 kg/GJ).

(b) Emission factor estimated on the basis of 55% carbon content, relative to coal with 75% carboncontent.

(c) European Commission, DGXII, Science, Research and Development, JOULE (1995a). Externalities ofFuel Cycles �ExternE� Project.

(d) Wallis M K and Watson A (1994). MSW incineration: a critical assessment. Energy World, pp 14-16,December 1994.

17

A2.1 FUEL AND WASTE TYPES

We assume that the conventional fossil fuel used in the cement kiln and in the power plant is coal with a heatcontent of 26 GJ/t and a CO

2 emission factor of 93 kg CO

2/GJ.

We assume two waste types broadly representative of a biofuel made from waste materials (sewage sludge,refuse derived fuel (RDF), etc.) and a solvent waste derived from chemical wastes. For the biofuel we assumea heat content of 16 GJ/t (typical of RDF) and for the solvent waste we assume a heat content of 26 GJ/t,typical of the specifications for supplementary liquid fuels delivered to cement kilns. The CO

2 emission factor

for the biofuel is taken as 110 kg CO2/GJ, between that of domestic waste (108 kg CO

2/GJ) and a woody

waste (112 kg CO2/GJ). The CO

2 emission factor for the solvent waste is taken as 70 kg CO

2/GJ, assuming a

lower carbon content (55%) relative to that of coal (75%).

A2.2 DISPLACEMENT OF COAL

When combusting waste in the cement kiln, the amount of coal displaced will be proportional to the heatcontent of the waste. Therefore 1 tonne of biofuel will displace 0.62 tonne of coal, and one tonne of solventwaste will displace 1 tonne of coal. Assuming an energy consumption of 4 GJ/t of cement, 1 tonne ofbiofuel will produce 4 tonnes of cement, while 1 tonne of solvent waste will product 6.5 tonnes of cement.

Under Scenario 2, additional coal required in the power plant to supply the energy withdrawn from theelectricity grid due to the closure of the dedicated incinerator. Assuming a conversion efficiency at theincinerator of 23%, a conversion efficiency at the power plant of 37%, and a conversion factor of 280 kWhper GJ of heat content, 1 tonne of biofuel will produce 1,030 kWh of electrical energy in the incinerator,equivalent to 0.39 t of coal at the power plant. 1 tonne of solvent waste will produce 1,674 kWh of electricalenergy in the incinerator, equivalent to 0.63 t of coal at the power plant.

A2.3 MINING AND TRANSPORTATION OF COAL

CO2 is released during the mining and transportation of coal. The emission factors used are 24.3 kg CO

2/MWh

electric from coal mining, and 0.045 kg CO2/km/t for transportation by rail. It is assumed that coal

transportation from the mine to the cement kiln or to the power plant involves a round trip of 300 km.

A3.1 CONSTRUCTION OF SCENARIO 1

For Scenario 1, we assume the following:

• 1 tonne of waste is combusted in a dedicated incinerator.

• The cement kiln uses coal as the conventional fuel.

• Electricity from the incinerator offsets an equivalent amount of electricity produced at the power plant,enabling the power plant to operate at reduced load.

Two situations are defined:

· Scenario 1(a): Burning of biofuel in dedicated incinerator.

· Scenario 1(b): Burning of solvent waste in a dedicated incinerator.

A3. SCENARIO 1 - BURNING WASTEIN INCINERATORS

18

The CO2 burden to atmosphere comprises the following:

• (A) CO2 generated during the mining and transportation of coal.

• (B) CO2 generated during burning of coal in the cement kiln.

• (C) CO2 generated during burning waste in the incinerator.

• (D) CO2 generated at the power plant when the incinerator is on-line.

The total CO2 burden is therefore:

A + B + C + D

It is not necessary to compute the CO2 burden defined by (D).

A3.2 CO2 GENERATED DURING MINING AND TRANSPORTATION OF COAL (A)

With an emission factor of 24.3 kg CO2/MWh electric from coal mining, 0.045 kg CO

2/km/t for transportation by

rail and a round trip of 300 km for transportation to the kiln, the CO2 burdens are as follows:

· Scenario 1(a): CO2 emissions from mining of 0.62 t coal is 110 kg and transportation of 0.62 tonne of coal is

9 kg. Total is 119 kg.

· Scenario 1(b): CO2 emissions from mining of 1 t coal is 177 kg and transportation of 1 tonne of

coal is 13.7 kg. Total is 191 kg.

A3.3 CO2 GENERATED DURING BURNING OF COAL IN THE CEMENT KILN (B)

With an emission factor of 93 kg CO2/GJ, the CO

2 burdens are as follows:

· Scenario 1(a): CO2 emissions from combustion of 0.62 t coal is 1,500 kg.

· Scenario 1(b): CO2 emissions from combustion of 1 t of coal is 2,418 kg.

A3.4 CO2 GENERATED DURING BURNING OF WASTE IN THE INCINERATOR (C)

With an emission factor of 110 kg CO2/GJ for biofuel, and 70 kg CO

2/GJ for the solvent waste, the CO

2

burdens are as follows:

· Scenario 1(a): CO2 emissions from combustion of 1 t biofuel is 1,760 kg.

· Scenario 1(b): CO2 emissions from combustion of 1 t solvent waste is 1,820 kg.

A3.5 TOTAL CO2 BURDEN

The total CO2 burden from Scenario 1 is (A + B + C + D) kg.

· Scenario 1(a) = 119 + 1,500 + 1,760 + D = (3,379 + D) kg

· Scenario 1(b) = 191 + 2,418 + 1,820 + D = (4,429 + D) kg

19

A4.1 CONSTRUCTION OF SCENARIO 2

For Scenario 2, we assume the following:

• Waste is combusted in the cement kiln, displacing a (thermal) equivalent of coal.

• The incinerator does not function. An equivalent amount of energy is produced in the power plant bymining, transportation and combustion of coal.

Two situations are defined:

· Scenario 2(a): Burning of biofuel in the cement kiln

· Scenario 2(b): Burning of solvent waste in the cement kiln

The CO2 burden to atmosphere comprises the following:

• (D) CO2 released when the power plant is operating as in Scenario 1.

• (E) CO2 generated during burning of additional coal in power plant.

• (F) CO2 generated during mining and transportation of additional coal.

• (G) CO2 generated during burning of waste in the cement kiln.

The total CO2 burden for Scenario 2 is therefore:

D + E + F + G

A4.2 ADDITIONAL CO2 AT THE POWER PLANT (E)

· Scenario 2(a): 1 t of biofuel will generate 1,030 kWh electrical energy, equal to 0.39 t coal at thepower plant, giving an additional CO

2 burden of 943 kg at the power plant.

· Scenario 2(b): 1 t of solvent waste will generate 1,674 kWh electrical energy, equal to 0.63 t coal atthe power plant, giving an additional CO

2 burden of 1,523 kg at the power plant.

A4.3 ADDITIONAL CO2 EMISSIONS FROM COAL USE AT POWER PLANT (F)

• For Scenario 2(a), 1 t of biofuel is equivalent to 0.39 t coal. CO2 emissions from mining is 69 kg and from

transportation is 5.3 kg. Total CO2 emissions is 75 kg.

• For Scenario 2(b), 1 t of solvent waste is equivalent to 0.63 t coal. CO2 emissions from mining is 110 kg

and from transportation is 9 kg. Total CO2 emissions is 119 kg.

A4.4 CO2 EMISSIONS FROM BURNING WASTE IN THE CEMENT KILN (G)

These emissions are identical to CO2 generated during the combustion of the waste in the dedicated

incinerator.

A4. SCENARIO 2 - BURNING WASTEIN CEMENT KILNS

20

Therefore, burning of waste in a cement kiln results in the following benefits:

(1) Substitution of coal, a non-renewable resource, with waste, an unwanted material that will require safetreatment and/or disposal. Savings are made through resource conservation and associated CO

2

emissions.

(2) Making more efficient use of the intrinsic energy of the waste material. Specialist waste incinerators arevery inefficient converters of the heat content of wastes, whereas a cement kiln approaches 100%efficiency.

(3) Provision of combustion capacity for incinerable wastes in existing thermal plants which areenvironmentally safe and secure, obviating the need for dedicated, specialist combustion capacity tobe constructed.

(4) A net decrease in the quantity of CO2 released, relative to a scenario in which waste is combusted in a

dedicated incinerator, thereby reducing the environmental impact of the greenhouse effect during thecombustion of wastes.

Summary of CO2 emissions from burning 1 tonne of waste in a dedicated incinerator

or in a cement kilnTable A5

Incineration in dedicated incineratorCombustion in cement kiln

Net benefit due to combustionin cement kiln

Biofuel (16 GJ/t) Solvent Waste (26 GJ/t)

3,379 + D kg CO2

2,778 + D kg CO2

601 kg CO2/t waste

4,429 + D kg CO2

3,462 + D kg CO2

967 kg CO2/t waste

A5. NET CO2 BURDEN

The net CO2 burden of the two scenarios is obtained by subtracting the total burden of Scenario 2 from the

burden of Scenario 1. The benefit (reduction) in CO2 emissions from burning waste is cement kilns as opposed

to dedicated incinerators is summarised in Table A2.

· Scenario 2(a): CO2 burden due to combustion of 1 tonne of biofuel in the cement kiln is 1,760 kg.

· Scenario 2(b): CO2 burden due to combustion of 1 tonne of solvent waste in the cement kiln is 1,820 kg.

A4.5 TOTAL CO2 BURDEN

The total CO2 burden from Scenario 2 is (D + E + F + G) kg.

· Scenario 2(a) = D + 943 + 75 + 1,760 = (2,778 + D) kg

· Scenario 2(b) = D + 1,523 + 119 + 1,820 = (3,462 + D) kg

A6. BENEFITS OF BURNING WASTE INCEMENT KILNS

21

Copyright: CEMBUREAUN° Editeur: D/1999/5457/February

All rights reserved. No part of this publicationmay be reproduced, stored in a retrieval system

or transmitted in any form or by any means,electronic, mechanical, photocopying,

recording or otherwise, without the prior writtenpermission of the publisher.

Published by CEMBUREAU The European Cement Association

Rue d�Arlon 55 - B-1040 BrusselsTel.: + 32 2 234 10 11Fax: + 32 2 230 47 20

E-mail: secretariat@cembureau.beInternet: http//www.cembureau.be

Layout & Printing by

CEMBUREAU