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CCMECanadian Council Le Conseil canadien

of Ministers des ministresofthe Environment de I'environnement

NATIONAL EMISSION GUIDELINEFOR CEMENT KILNS

Initiative N306

March. 1998PN 1284

u

Th~ Canadian Council of Ministers of the Environment (CCME) is the major intergovernmel'1talforum in Canada for discussion and joint action on environmental issues of m~jor national,international and global concern. The 13 member governments work as partners in developing

. nationallyconsistentenvironmentalstandards,practicesandlegislation.

. .

Canadian Council of Ministers of the Environment Secretariat123 Main Street, Suite 360

Winnipeg, Manitoba R3C1A3Tel.: (204) 948-2.090Fax: (204) 948-2125

Prepared by theN306 MultistakeholdersWorking Group and Steering Committee

PN 1284 .ISBN: 1-895925-96-7

For additional copies, please contact:CCME Documents

cId Manitoba Statutory Publications. 200 Vaughan Street

Winnipeg, Manitoba R3C 1T5Tel.: (204) 945-4664Fax: (204) 945-7172

..

Table of Contents

Glossary of Terms iii

Abbreviations v

Preface 1

Introduction 3Cement Kilns 3

National Emission Guideline for Cement Kilns 4Applicability 4Emissionsof NitrogenOxides 4EmissionsofOtherPollutants 5MeasurementandMonitoring 5

Appendix A - Working Group Members 7

Appendix B - Technical Background Document: Assessment of NOxEmissionControlTechnologiesfor Cementand LimeKilns:ExecutiveSummary... 9

Glossary of Terms

Within the context of the Guideline, the meaning of certain terms is as described below.

Calcination:

Cement:

Cementltious Additives:

Clinker:

Clinker Cooler:

Greenhouse Gases:

Low-NOx Burner:

Nitrogen Oxides (NOx):

Rotary Cement Kiln:

Preheater Kiln:

Precalclner Kiln:

Staged Air Combustion:

Selective Non-Catalytic Reduction:

Selective Catalytic Reduction:

The liberation of carbon dioxide gas from limestone material (calcium carbonate)through the addition of heat in the cement or lime kiln.

A powdered product used in construction that is produced by combining, in a high-temperature kiln, materials containing calcium oxide, alumina, iron oxide and silica,to form a combination of calcium silicates.

Materials used as a substitute for clinker in the production of cement, includingblast fumace slag, flyash, bottom ash or slag from power plants, and other lime-stone and ferrous by-products from various industries.

An intermediate product in cement manufacture, consisting primarily of calciumoxide pellets formed by high-temperature chemical transformation of the rawmaterial feed; the pellets are subsequently cooled and ground into a fine powder.

A heat exchange device located at the clinker discharge end of the kiln to cool theclinker pellets and to provide preheated combustion air for the main kiln burner.

A collection of gases, including carbon dioxide, methane and nitrous oxide, knownto trap heat from the sun that has been reflected by the earth, thereby keeping thelower atmosphere warm.

A bumer designed to provide fuel and air staging and mixing to minimize peak

flame temperatures and so reduce NOx emissions.

Refers collectively to nitric oxide (NO) and nitrogen dioxide (N02), expressed as anitrogen dioxide equivalent.

A large rotating horizontally sloped steel cylinder. Raw material consisting of a wetor dry limestone and clay mixture is fed into one end of the kiln, and is calcined by

hot exhaust gases (CaC03 forms calcium oxide and C02)' It is then partiallymelted, or sintered, into clinker by additional intense heat input.

A type of cement or lime kiln that has a multistage heat exchange tower at the feedend to preheat incoming raw material, to aid in calcination and to increase overallenergy efficiency.

A cement kiln incorporating an additional burner at the kiln inlet to provide calcina-tion shortly after the preheater portion of the kiln. These are often shorter kilnswith higher energy efficiency and production capacity.

NOx control technology that uses more than one stage of combustion at theprecalciner kiln inlet to form a reducing atmosphere followed by an oxidizingregion.

An emission control method utilizing injection of ammonia (NHJ, or ammonia-containing compounds, into the flue gas at an appropriate high temperature, toconvert NOx into nitrogen and water vapour.

An emission control method whereby ammonia (NHJ is injected into the flue gasupstream of a catalyst structure, at an appropriate moderate temperature, to

convert NOx into nitrogen and water vapour.

iii

Abbreviations

CCME Canadian Council of Ministers of the Environment

CEM Continuous Emissions Monitoring

kg kilogram

nitrogen oxides

sulphur dioxide

co carbon monoxide

carbon dioxide

CaO calcium oxide

CaC03 calcium carbonate

NH3 ammonia

VOCs volatile organic compounds

v

Preface

In May 1991, the Canadian Council of Ministers ofthe Environment (CCME) issued Phase 1 of theManagement Plan for Nitrogen Oxides (N0x) andVolatile Organic Compounds (VOCs). The aim ofthe Plan is consistent attainment of the Canadian

maximum acceptable one-hour air quality objectivefor ozone of 82 parts per billion by the year 2005.This Guideline responds to initiative N306 of thePlan, oneof a seriesof initiativesaimedatpreventingfutureincreasesin emissionsthrough emissionlimitsfor new sources. The Guideline addresses emissionlimits for new high-temperature kilns in the cementmanufacturing industry, and makes recommen-dations for emission reductions from existingplantsthat are being modified or upgraded. While thisGuideline establishes maximum broad nationalemission limits, it is acknowledged that federal,provincialor regional environmentalauthoritiesmayimpose more stringent limits in response to regionalor local problems.

Principles considered to be important in developingthe Guideline were pollution prevention, energyefficiency, cost effectiveness and a comprehensiveapproach to minimizing various emissions. Whilethe Guideline NOx emission targets are aimed atnew kilns, certain emission reduction strategiesapplied to modified existing kilns could also bebeneficial. Where thereare opportunitiesto improvethe environmental performance and energyefficiency of kilns for which major modificationsare planned, emission rates and control methodsshould be evaluated in close consultation with theappropriate regulatory authorities.

For the overall benefit of the environment, theGuideline encourages the use of substitutes forcement materials and for fossil fuels, where it can

be demonstrated by the proponent that NOxemissionswouldnotbe increased. It also encouragesthe implementation of energy efficiency measuresin cement production.

The Guideline was developed through amultistakeholderconsultationprocess, by a workinggroup consisting of representatives from the cementand lime industry, equipment manufacturers,environmental groups, and provincial, regional andfederal governments. The contributions of allparticipantswho assistedin the establishmentofthisGuideline are gratefully acknowledged.

InquiriesabouttheGuidelinemaybe directedto:

ManagerOil,GasandEnergyBranchAir Pollution Prevention DirectorateEnvironment Canada351 81.Joseph Blvd.Hull, Quebec KIA OH3

Tel.: (819) 953-1120Fax: (819) 953-8903

1

Introduction

The National Emission Guideline for Cement Kilns

was developed to provide a consistentnationalbasisfor restricting emissions of nitrogen oxides (N0x)and other pollutants, while encouraging greaterenergy efficiency in the industry. A TechnicalBackground Document was also prepared, throughthe consultation process, to describe the Canadiancement industries and available NOx reductionmethods. A summary ofthis document is presentedin Appendix B to aid in the assessment of reductionstrategies for new, existing and modified kilns.

In this National Emission Guideline,NOx limits forcement kilns are expressed as weight of allowableemissions per unit of clinker production (kg/tonne).In determiningallowableemissionlevels forcementkilns where major modifications are planned,considerationshouldbe given to the offsetof clinkerproduction through the use of additives to clinkerto produce cement, and the increase in energyefficiency available by the recovery of waste heatenergyfrom cementkiln stack gases. TheGuidelinealso addresses issues related to other common air

pollutants, as well as monitoring of emissions.

Cement Kilns

The cement industry is based on the conversion of amixture oflimestone (CaC03) and clay, into clinkermaterial consisting of compounds of calcium oxide(CaO), by the addition oflarge quantities of heat ina coal- or gas-fired rotary kiln. NOx formationresults mainly from this high-temperaturepyroprocessing stage which sinters the material intoa cement clinker, as well as during initial limestonecalcination. Carbon dioxide (C02) is also liberatedin this calcination process. Clinker production cantake place in a wet-process long kiln with a slurryraw material feed, with a dry-process feed in a longkiln, or with a dry feed in more modern andefficientpreheater and precalciner kilns.

Several methods of NOx reduction were assessedduring the development of the Guideline, althoughonly some of these have been proven commercially.These include both combustion technologies whichreduce or prevent emissions at their point of

generation, and post-combustion methods whichreduce emissions already generated, as indicatedbelow and explained in detail in the TechnicalBackground Document:

· combustion operation modifications

· low-NOx burners

· staged air combustion

· selective non-catalytic reduction

· selective catalytic reduction.

Process optimization through combustionmodifications is one of the first options to beconsidered for improving process efficiency and forreducing emissions. The use oflow-NOx burnersis being studied internationally, with a wide varietyof results on installedsystems.Theseburners usuallyrequire an indirect-fired system, whereby mostcombustion air is provided independently of theburner. Selective non-catalytic reduction usinginjection of ammonia compounds is also beinginvestigated as a feasible post-combustiontechnology. There has been very limited experienceon flue gas control methods such as selectivecatalyticreduction,or on technologiessuch as stagedair combustion forprecalciner kilns. Experience hasshown that NOx emissions from coal-burning kilnsare often lower than from natural gas-burning kilns.

This Guideline recognizes that optimized andenergy-efficient kiln processes, such as preheaterand precalciner kilns with modem process andparticulate controls, are the most effective means ofminimizing the majority of emissions from cementkilns. These methods focus on cost-effective

pollution prevention measures, and also address avariety of emissions including greenhouse gases.

NOx emissions can also be minimized throughreductions in the clinker/cementratio, and tests withwaste-derived fuels have in some cases shown a

positive impact on reducing emissions. Regulatoryauthorities should consider the overallenvironmental impacts of incorporating flyash orslag mixed into the finished cement product toreduce the need for clinker, and of using substitute

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waste fuels such as solvents, tires and landfill gasesto supplement traditional fuels. For technicalguidance on operating and performance standards,reference is made to a separate CCME publicationentitled National Guidelines for the Use ofHazardous and Non-Hazardous Wastes asSupplementary Fuels in Cement Kilns.

National Emission Guideline forCement Kilns

Applicability

The emission limits of this Guideline apply to alllarge new cement kilns with a permitted capacitygreater than 1 500 tonnes per day, which receivefinal regulatory approval for construction afterJanuary 1, 1998. The Applicability clauses aresubject to alteration by the appropriate regional orprovincial regulatory authority.

For an existing large cement kiln, the Guidelinelimits statedbelow shall apply when a modificationresults in a 25-percent increase in permitted kilncapacity. Modifications that result in capacityincreases below this level should be allowed onlyonce, to avoid the use of multiple kiln upgrades tocircumvent the intent of the Guideline.

For modifications associated with one-time lesser

increases in permitted capacity, a program toimproveperformance shouldtake advantageof cost-effective technologies to achieve feasible emissionreductions. The resultingemission levels fromthesemodifiedkilns donot necessarilyhave to meet limitsstated for new kilns. Where there are opportunitiesto improve environmental performance and energyefficiency on kilns for which major modificationsare planned, emission rates and control methodsshould be evaluated in close consultation with theappropriate regulatory authorities.

Approval for special dispensation may be soughtfrom the appropriate regulatory authority indeveloping appropriate emission guidelines for thefollowing cases:

· for new small cement kilns with capacities ofless than 1 500 tonnes per day, where it can be

shown that the installation of a facility such as along dry kiln is justifiable,

· where it can be demonstrated that the kiln is

occasionally operated under uniquecircumstances.

Emissions of Nitrogen Oxides

The emissions from new natural gas or coal-firedcement kilns should not exceed 2.3 kg of NOx pertonne of clinker production, based on a monthlyaveragetime period. Shortertime averagingperiodswith a somewhat higher emission rate, to reflectunsteady emissions, could be chosen by permittingauthorities for site-specific reasons, if deemedappropriate.

For the use of other fuels such as oil or petroleumcoke on a temporary basis, or for the use ofalternative fuel mixes including landfill gas on anongoing basis, approval should be sought from theappropriate regulatory authority.

Where the proponent can demonstrate that clinkerproduction can be offset by the addition ofcementitious additives such as flyash or slag, ahigher NOx limit (kg/tonne clinker) could beconsidered by regulatory authorities. This limitwould be based on the portion of clinker producedfrom primary raw materials, excluding anycementitious additives such as flyash or slag. Suchan allowance would serve to increase the kg/tonneof clinker emission level for the kiln, and torecognize a reduction in overall net emissions for agiven amount of cement produced. The use of suchadditives should not result in an increase in total

NOxemissions (at full capacity) from the kiln wherethe allowance is used.

A similarapproachcouldbe considered ifwaste heatfrom the stack exhaust or clinker cooler was shownto be used for any other heating or industrialprocesses not normally associated with kilnoperation. The emission allowance wouldcorrespond to the emissions savings that wouldresult from reduced fuel combustion for that heatingor process application.

4

Emissions of Other Pollutants

When considering the installation of processmodifications to reduce emissions of NOx' cautionshould be exercised to minimize the adverseenvironmental impacts of other pollutants, whilemaintaining acceptable clinker quality. New kilnsystems should be designed, and raw materialsselected, to minimize sulphur dioxide (S02) andcarbon monoxide (CO) emissions while remainingin compliancewith NOxemission guidelines. Theseemissions shouldbe assessed on a site-specificbasisas determined by the appropriate regulatoryauthority.

Particulates

The fineparticulate dust contained in the kiln gasesexiting from the main stack or from the clinkercooling system can be controlled by the use ofequipment such as an electrostatic precipitator or afabric filter baghouse. Particulate emissions in theexhaustgases fornew kilns shouldnot exceed0.2 kgper tonne of clinker from the stack, and 0.1 kg pertonne from the clinker cooling system.

Sulphur Dioxide

Sulphur dioxide generated from the raw materialfeed into the process, and from the sulphur contentin the fuel, is usually captured to a large extent inthe preheater tower and in the raw clinker grindingmill. Since raw material composition is very site-specific,and S02emissions are sometimesinverselyrelated to NOx emissions, new kiln systems shouldbe designed to minimize S02 concentrations in theflue gas, while staying in compliance with NOxemission guidelines.

Carbon Monoxide

The presence of carbon monoxide in the kiln exitgas or in the downstreamparticulate control systemsshould be monitored to prevent unsafe conditions,and to allowthe fuel supplyto the kiln to be curtailedshould CO concentrations rise higher thanequipment specifications permit. Kiln systemsshould be designed to minimize CO concentrationswhile staying in compliance with NOx emissionguidelines.

Measurement and Monitoring

In order to confirm that the plant is operated in amanner consistent with this Guideline, all newcement kilns should measure NOx and S02emissions using a continuous emissions monitoring(CEM) system. If the measurement system usedfor process control at the kiln exit is to be used foremissions reporting, the proponent shoulddemonstrate a method that shows these emissions

to be representative of those exiting the stack.

In all cases,measurement, monitoringand reportingrequirements are subject to approval by theappropriate regulatory authority. Measurementmethods should be generally consistent with thosedeveloped and published for this purpose byEnvironment Canada.

On existing kilns which are to undergo majormodifications, measurement should be done with aCEM system, or by a method of comparableeffectiveness to continuous monitoring asdetermined by the appropriate regulatory authority.Such methods could include mass balance

calculations for S02 or predictive/parametricmonitoring. These methods could be supplementedby periodic source sampling and analysis.

Plants that intend to seek emission allowances forcementitious additives or waste heat utilization

should provide adequate mass balance and energycalculations.

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Appendix A

Working Group Members

Provincial and Regional Governments

Martin LecoursHanna Corinthios

Chow-Seng LiuKamal Bhattacharyya

Ministere de l'Environnement et de la Faune du QuebecOntario Ministry of the EnvironmentAlberta Environmental Protection

Greater Vancouver Regional District

Industry

Allan Moore

Peter DarbyshireMurray Smith(l)Charles Coles(2)

Jacques DenizeauSteve Prahacs(3)Richard PlantePaul Arsenault<4)

Tilbury CementContinental Lime (Canadian Lime Institute)Union Gas (Canadian Gas Association)St. Lawrence Cement (Canadian Portland Cement Association)Lafarge CanadaPulp and Paper Research Institute of CanadaGraybec LimePillard Combustion

Environmental Non-Government Organization

Bruce Walker<5) STOP

Federal Government

Horace WhaleyHugh DibbsManfred Klein

CANMET Energy Research LaboratoryEnvironment CanadaEnvironment Canada

(1) Replaces Ron Brintnell, Union Gas(2) ReplacesMichaelNisbet,LafargeCanada(3) Replaces Iver Simonsen, PAPRICAN(4) ReplacesGillesUguen,Pillard(5) Replaces Ellen Schwartzel, Pollution Probe

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Appendix B

Technical Background DocumentAssessment of NOx Emission Control Technologies for

Cement and Lime KilnsRadian Canada Inc., April 1995

Executive Summary

As part of the Canadian Council of Ministers of theEnvironment (CCME), Environment Canada isaddressingthe issueof NOxemissions,togetherwithother air pollution matters, by coordinating a multi-stakeholderconsultationprocess to developnationalemissionguidelinesformajor stationarycombustionsources. Initiative N306 of the CCME Planaddresses the cement and lime manufacturingindustries, and will result in the publication of anitrogen oxides (N0x) emission guideline for newand modified plants.

This report by Radian Canada Inc. is intended toprovide Environment Canada and members of theN306 Working Group on Cement and Lime Kilnswith a review and evaluation of the state of the art

in NOx emission control technology as applicableto cement and lime kilns. The report is based oninformation available from the two industries

concerned; regulatory agencies in Canada, theUnited States and Europe; and experience withinRadian itself of direct investigations of NOx controlsystems. This assessment will be used by CCMEin making recommendations for national emissionguidelines. It may also become a part of a CCMEbackground publication for the application ofremedial measures for existing facilities.

The report provides background information on theCanadian cement and lime industries, giving bothan economic andproductiontechnologiesoverview.It presents the available NOx emission data fromboth Canadian and other sources, and gives aworldwide view of NOx guidelines and targets forthe two respective industries. The mainstay of the

report is a detailed review of existing NOx controltechnologies: a technical description of them, andan assessment of their applicability to cement andlime kilns, from both an engineering and economicperspective. NOxemissionmonitoring is consideredas well. Conclusionsand recommendations identifypossible approaches to be taken in consideringapplicable control technologies and developingnational emission guidelines for the new andmodified kiln operations.

As there are significant differences between the twoindustries, as well as differences in the amount ofrelevant informationavailable on the subject ofNOxemissions and their control, the cement and limeindustries are addressed separately in this report.

Cement Kilns

During the past 20 years, considerable knowledgeof NOx generation, emission and control has beenobtained from research into the combustion of fossilfuels and from combustion in utility boilers andindustrial processes. Although many researchershave tried, these data cannot be extrapolated to thePortland cement manufacturing process. There is alimited amount of published data regarding NOxemissions from cement kilns. However, even onthe basis of this limited information, there is anindication of a strong dependence of the amount ofNOx emissions generated and the type of the kilnand the fuel used (Table AI).

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Table A1. NOx Emissions From Cement Kilns*

Modern preheater and precalciner kilns usuallygenerate lower NOx emissions than older, lessenergy efficient wet and long dry kilns, when allare fired using the same type of fuel. At the sametime, long dry kilns do not necessarily have lowerNOx emissions than wet kilns.

Using the sametype of kilnprocess technology,coalgenerates substantially less NOx than both naturalgas and bunker oil, strongly confirming that incement kilns due to their high combustiontemperature regimes (l630-1900°C vs. 1150°Cforutility boilers), thermal NO is the dominant factor,x

and fuel NO only a secondary one. In terms ofx

NOx generation, the dominance of coal as a fuel asopposed to natural gas or oil is a major differencebetween cement kilns and most of the other

stationary NOx emission sources such as utility andindustrial boilers.

There is a strong indication that use of some wastederived fuels (WDF) has a beneficial effect onreducing NOx emissions. This approach could beusefulprovided thereareno negativeeffects on otheremissions, clinker quality and kiln operation/maintenance.

Cement kiln emission limitsand regulationsenactedor proposed in different countries indicate not onlyconcern about NOx emissions and their effects onthe environment, but in some cases also a certainmisunderstandingwith respect to what is practicallyand economically achievable. The current limitsvary widely, dependingon the country or the districtwhere the cement plant is situated. There are alsodifficulties in comparingvarious data and limits due

Precalciner

1.7- 3.0

nda

1.35 - 1.95

to the different units in which emissions are given.Most European data is reported either inppmv or inmg of NOxper Nm3. Measurements can also bereported either dry or wet, as well as at various 0zlevels. Alternately,and this is the usual case inNorthAmerica, especially when it comes to the units usedby the regulatory bodies, mass measurements ofemissions per unit of finished product, specificallykg NOx /tonne, are preferred. The EuropeanCommunity, where the cement industry has beenmodernized faster than in North America, and mostof the kilns are either of the preheater or precalcinercoal-fired type, appears to be heading to a two-tierregulatorysystem, inwhich the majority of countrieswill have a standard in the 2.75-3.6 kg NO/tonneof clinker range, and environmental leaders likeGermany and Switzerland will aim at 1.3-2.0 kgNOx /tonne of clinker. Japan also appears to havea low NOx emission standard.

A number of NOxreduction technologieshave beenconsidered for application in cement kilns. Theseinclude both combustion and post-combustiontechnologies, many of which have already beentested, commercially used and proven in otherindustries. Combustion NOx control technologiesare dependent on the NOx formation mechanisms,and they attempt to control and reduce NOxemissions at the point of their generation; whereaspost-combustiontechnologiesare independentof themanner in which NOx is created, and act on alreadygenerated NOx'

It has to be stressed that not all NOx controltechnologies ~own andused in other industrial andutility applications are applicable to cement kilns.

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Fuel Wet Long Dry I Preheater

Natural Gas 9.0 7.0 - 9.5 5.65

Oil nda 3.3 - 4.6 nda

Coal 1.45;.4.33 2.4 - 4.6 1.5- 2.85

* kg NOz/ tonneof clinker;nda = no dataavailable

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Even if a given NOx control technology is provento be highly successful in, for example, industrialboilers, it doesnot meanthat itwill workin the dusty,high-temperature atmosphere of the cement kiln. Aspecific kilnprocessing technology, kilnprocessingconditions (especially temperature regime andexcess/lack of oxygen), finished productspecifications, and the relationship with the otheremissions,determinethe feasibilityandapplicabilityof a specific NOx control technology to a specificcement operation.

NOxcontroltechnologiesconsideredforapplicationin cement kilns and discussed in some detail in thereport include:

· combustion operation modifications (COM),

· low NOx burners (LNB),

· staged air combustion (SAC),

· selective non-catalytic reduction (SNCR),

· selective catalytic reduction (SCR).

From an extensive survey ofthe current state of theart, the study has drawn the following specificconclusions concerning these NOx controltechnologies and their general applicability to thecement industry.

Overall, the applicationofNOx control technologiesis kiln- and site-specific. Success of a particularNOx reduction technology on a particular kiln doesnot guarantee similar results in an apparently"similar" cement kiln elsewhere.

In the published literature, there seems to be a

consensus that of the various NOx controltechnologies, the combustion operationmodifications (COM), low NOx burners (LNB),staged air combustion (SAC) and selective non-catalytic reduction (SNCR) approaches appearfeasible for cement kiln applications. The last twotechnologies (SAC and SNCR), however, have notas yet been reduced to proven industrial practice.

The NOx reduction potential of the controltechnologiesis 15-30%forCOM, 15-30%forLNB,20-50% for SAC, and 40-70% for SNCR. (If two

technologies are implemented at the same time, theoverall reduction efficiency does not equal theirsum.) Technical feasibility, in descending order, isCOM> LNB > SAC> SNCR; and relative costsand cost effectiveness, in ascending order, rangeCOM < LNB :::::SAC < SNCR.

Any COM action leading to a reduced fuelconsumption and to an improved process stabilitywill contribute to minimizing NOx emissions(potential 15-30% NOx reduction). Kiln operatingparameters- such as the burning zone temperature,the amountof excess air and flame shape- aresome ofthe factorsgreatlyaffectingthe level ofNOxemissions. All actions taken to improve fuelefficiency, process stability and the reduction of theburning zone temperatures should have a positiveeffect onproduct quality. On the otherhand, actionstaken to alter the combustion and to enhance local

reducing conditions in the burning zone may affectthe clinker quality and kiln operation.

Among the available NOx control technologies,LNBs appear to be considered and tried most, atleast for applications in indirectly coal-fired longdry, preheater and precalciner kilns (potential 15-30% NOx reductions). There are a number ofcommercial vendors of LNBs. Their performanceis site specific, and at a number oflocations they donot perform up to full expectations. Longer termexperience in the cement industry with LNBs ismixed, and there are still a number of questionsregarding their efficiency in cement kilns. Thecapital costs of LNBs are relatively low; however,the capital investment can be significantly higher,if a simultaneousconversionfrom adirectcoal-firedto indirect coal-fired system is required. LNBoperation is site specific and the clinker quality andkiln operation can be affected; CO and THC mayIncrease.

SAC is applicable primarily to precalciner andpreheater kilns (potential 20-50% NOxreductions),although it can be adopted, to some extent, in mid-kiln firing of secondary fuels in long kilns as well.There has been only one full-scale cement plantindustrial installation of SAC reporting on theexperience. The findings, covering SAC installed

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in 1987/88,confirmeda reductionin NOxemissions;however, simultaneous and significant increases inCO and S02 levels were experienced. Althoughunder ideal circumstances, SAC could be fitted onto

existingpreheaters/precalciners,in realitytheseNOxcontroltechnologiescan be incorporatedonly duringthe design stages for new installations. SAC capitalcosts could be limited to those of additional burners

plus the cost of any incremental, site-specificadditional modifications. However, majorconversion of an existing wet or long dry operationto a modern preheater/precalcinerkiln incorporatingSAC could be in the multi-million dollar range. Itis not expected that SAC would affect clinkerquality; however, CO, S02and THC emissions mayincrease. Due to the small number of existing trialsand installations, further testing of SAC is needed;nevertheless, this technology seems to hold somepromise for cost-effectiveNOx controlin the cementindustry.

SNCR is also applicable only to modem preheaterand precalciner kilns (potential 40-70% NOxreductions). Although a few short-term trials bothin the V.S. andEurope using either ammonia or ureainj ection have been reported recently, thistechnology is not fully proven as yet. There hasbeen no full-scale SNCR installation in the cementindustry. Implementation of SNCR will result inadditional operational costs due to reagent costs.SNCR is not expected to affect clinker quality, as itis located downstream of the clinkering zone. Apotential for NH3, CO and PM10emissions exists,as well as the formation of a plume containingammonium salts. Although SNCR seems to be arather promising NOx control technology forpreheater and precalciner cement kiln applications,due to a limited number of existing trials and nofull-scale installations, as well as considerablecapitaland operationalcosts involved,furthertestingand proof of its long-term feasibility is needed.

SCR may provide high (70-90%) NOx reductionfor all kilns at very high capital and operationalmaterials/labour costs, but its technical feasibilityis still uncertain. There has been no trial ofSCR ona cement kiln.

As far as a potential target for NOx emissions fromnew or modified cementkilns is concerned, itwouldappear that for modem preheater/precalciner coal-fired kilns (these constitute the majority of the kilnsbuilt in Canada and elsewhere in the world over thelast 15-20 years, and would also be, with highprobability, built in the future), a range of 2.0-2.5kg NO/tonne of clinker could be considered.

The main features of the NOx control technologiesas applied to cement kilns are summarized inTable A2.

Lime Kilns

There is virtually no information about NOxemissions from lime kilns available in the literature.

This is perhaps due to the fact that the lime industryis much smaller than the cement industry, that itskilns operateat lowertemperaturesthan cementkilns(-1200°C vs. 1500°C), thus possibly generatinglower NOx emissions, and that the lime industry,unlike the cement industry does not monitor NOxlevels forprocess control. TheEPA AP-42 emissionfactors are 1.4-1.7 kg of NO/tonne of lime forrotary kilns, depending on the type of fuel, whilethe limited data reported by the Canadian limemanufacturers range ftom 0.5 to 3.5 kg NO/tonneof lime. There is an indication that shaft and

Calcimatickilns generate lessNOxthan rotary kilns.

Due to some similarities between the cement and

lime processes, while at the same time recognizingthe differences between the two materials andprocesses, it would appear that those controltechnologies identified as the most promising forcement kilns would be, with necessarymodifications, applicable to the rotary lime kilns,should the need arise, i.e.:

· combustion operation modifications (COM),

· low NOx burners (LNB),

· staged air combustion (SAC),

· selective non-catalytic reduction (SNCR).

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Table A2. Comparison of NOxControl Technologies for Cement Kilns

However, it seems that none of these controltechnologies have been tried as yet on rotary limekilns, and that the industry at this time questionstheir applicability. It would appear that at this stagethere is no need to consider specific NOx controlsteps for the shaft and Calcimatic kilns due to theirinherently low NOx generation, but this should stillbe confirmed through independent measurements.

Recommendations

The following recommendations are made withrespect to the application of NOx controltechnologies to cement and lime kilns:

Cement Kilns

· A survey should be conducted to generate adatabase for the total emissions and emissions

per unit of production of NOx in Canadiancement kilns per type of kiln and type fuel used.

· Full advantage of COMs and processoptimizationshould be taken for all cement kilnsbefore any other NOx control technology isconsidered.

· Furthertesting ofLNBs is requiredby the cementindustry to assess their long-term ability toproduce consistent lowNOx emissions and highquality clinker at the same time, withoutadversely affecting other emissions.

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Control Technical Potential NO Annualized Cost Cost Effect on Effect on

Feasibility Reductionx

Effectiveness Clinker Quality other EmissionsTechnology RangeOOO$/yr $/t of NO

removed x

COM High 15-30% - - may be either SO ,CO,x(all types positive or THC mayof kilns) adverse increase

LNB High 15-30% may vary with may vary with

indirect-fired* (all types 110-160* 340-570* installation; type installation, CO,

direct-fired** of kilns) 370-590** 1,280-2,050** of fuel; may THC may increase

kilns be detrimental

SAC High 20-50% none CO, THC may

(precalciner, increaset 120-160t 250-400tpreheater

and long' kih1 ) 180-220' 660-940'

SNCR Medium 40-70% 610-1,250 1,220-1,690 none potential for NH ,3

(precalciner PM emissions10

kilns)

SCR Low 70-90% 3,510-10,050 4,840-7,500 none potential for NH ,3

(all types of PM emissions;10

kilns) SO may increase3

· While SAC and SNCR hold promise forsignificant cost-effective NOx control, the fullenvironmental and process impacts still need tobe further ascertained, due to the small numberof trials and existing installations.

· The effect ofNOx emission regulations on otherpollutants (S02' CO, vac, particulates) shouldbe carefully investigated, and their negativeimpact weighted.

· As older wet and long dry kilns approach theend of their life-cycle, they could be convertedto preheater/precalciner kilns, if marketconditions and technical and economicalfeasibilities support this conversion.

· Use of waste derived fuels (WDF), known togenerally reduce NOx emissions, could beconsidered, provided that there are no adverseenvironmental impacts and negative effects onclinker quality or kiln operation/maintenance.

Table A3.

· Continuous emission monitoring systems(CEMs), located either at the stack or at the kilnexit, might be necessary to meet the monitoringprovisions on all large kilns. Alternate systems,such as PEMs, could be used on smaller kilns.

Based on information from the most recent long dryor preheater/precalcinerinstallationsthat burn either

coal or gas and for which there were reliable NOxemissions data available, representatives of thecement industry prepared a first draft of guidelinesfor the N306 Cement and Lime Working Group'sconsideration. For new or significantly modifiedcement kilns, based on the best demonstrated NOxcontrol technologies, the industry is proposing twosets of guidelines: one for short-term periods basedon daily averages plus two standard deviations (forcompliance 95% of the time); the other based onlonger term averages, yearly or monthly.

Proposal for the guidelines, as presented by theindustry, are given in Tables A3 and A4.

Cement Kilns NOxEmission Guidelines, Daily Averages

(kg NOjtonne of Clinker)

Long Dry Kiln

Gas-fired kiln

Coke/Coal-fired kiln5.0 + 2 x 0.35 = 5.73.0 + 2 x 0.5 = 4.0

Table A4.

Preheater/

Precalciner Kiln

2.1 + 2 x 0.2 = 2.52.1 + 2 x 0.2= 2.5

Cement Kilns NOxEmission Guidelines, Annual Basis

(kg NOjtonne of Clinker)

Long Dry Kiln

Gas-fired kiln

Coke/Coal-fired kiln

Preheater/

Precalciner Kiln

5.03.0

2.1

2.1

14

- -

Lime Kilns

...

... · Only once sucha databaseis established,could

... firmtargetsbe consideredfor NOxreduction.

... Intheabsenceofsuchinformation,therange1.5-

.. 2.0kg NOx/tonneof lime is suggestedas a

.. preliminarytargetformodemlimerotarykilns

.. withpreheatersat thistime.

.........,-,.,.,.,.".".".;lA,.~~;lAFP,.;JIA;JIA

~~,.,.,.....,.,.,.........~ 15,.

· There is a need for NOx emissions testing anddevelopment of a Canadian database relatingNOx generation to the type of lime kiln and thetype of fuel used.

Long Wet and Dry Cement Kiln Process

GAS

COKE...

COAL WATER FUEL

BURNER FAN

COOLER

CLINKER

TO

STORAGE

TIRE FEED

I:

CLINKERlNG ZONE

KILN DRIVE

CALCINING ZONEDRYING ZONE

KILN FEED

Courtesy of Canadian Portland Cement Association

Preheater and Precalciner Kiln Process

GAS

COKE

COAL WATER FUEL...

BURNER FAN

COOLER

CLINKER

TO

STORAGE

PREHEATER

TOWER

PRECALCINER

KILN DRIVE

CLINKERlNG ZONE CALCINING ZONE

16

GASES

TO

PRECIPIT ATOR

_ TIREFEED..,-..,,-y