planners guide for clean coal technology for power plants

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WORLD BANK TECHNICAL PAPER NO. 387am-, f W~~~~~ATP397

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RECENT WORLD BANK TECHNICAL PAPERSNo. 310 Elder and Cooley, editors, Sustainable ettlementand Development f the Onchocerciasis ontrolProgrammeArea:Proceedings f aMinisterialMeetingNo. 311 Webster, Riopelle and Chidzero, WorldBankLendingfor Small Enterprises 989-1993No. 312 Benoit,ProjectFinance t the WorldBank:An Overviewof Policies nd InstrumentsNo. 313 Kapur, Airport Infrastructure: heEmergingRoleof the PrivateSectorNo. 314 ValdWs nd Schaeffer n collaboration with Ramos, Surveillance f AgriculturalPriceand TradePolicies:HandbookforEcuadorNo. 316 Schware and Kimberley,InformationTechnology nd NationalTradeFacilitation:Making the Most of GlobalTradeNo. 317 Schware and Kimberley,InformationTechnology nd NationalTradeFacilitation:Guide o Best PracticeNo. 318 Taylor, Boukambou, Dahniya, Ouayogode, Ayling, Abdi Noor, and Toure,StrengtheningNationalAgricul-tural Research ystems in theHumid and Sub-humidZones of West and CentralAfrica:A Frameworkfor ctionNo. 320 Srivastava, Lambert, and Vietrneyer,MedicinalPlants:An ExpandingRole n DevelopmentNo. 321 Srivastava, Smith, and Forno, Biodiversity ndAgriculture: mplicationsforConservation nd DevelopmentNo. 322 Peters, TheEcologyand MAanagementf Non-TimberForestResourcesNo. 323 Pannier, editor, CorporateGovernance f PublicEnterprises n Transitional conomiesNo. 324 Cabraal, Cosgrove-Davies, and Schaeffer,Best Practicesor PhotovoltaicHouseholdElectrification rogramsNo. 325 Bacon,Besant-Jones, and Heidarian, Estimating ConstructionCostsand Schedules: xperiencewith PowerGenerationProjects n DevelopingCountriesNo. 326 Colletta, Balachander, and Liang, The Conditionof Young Children n Sub-Saharan frica:TheConvergence fHealth,Nutrition, and EarlilEducationNo. 327 Vald6s and Schaeffer in collaboration with Martin, Surveillance f AgriculturalPriceand TradePolicies:HandbookforParaguayNo. 328 De Geyndt, SocialDevelopment nd AbsolutePoverty n Asia and LatinAmericaNo. 329 Mohan, editor, Bibliography f Publications: echnicalDepartment,AfricaRegion,July 1987 o April 1996No. 330 Echeverria, Trigo, and Byerlee,Institutional Change nd EffectiveFinancing f AgriculturalResearch n LatinAmeri*caNo. 331 Sharma, Damhaug, Gilgan-Hunt, Grey, Okaru, and Rothberg, African WaterResources:Challenges ndOpportunitiesor SustainableDevelopmenitNo. 332 Pohl, Djankov, and Anderson, RestructuringLarge ndustrialFirms n Central ndEastern urope:.An mpiricalAnaoysisNo. 333 Jha, Ranson, and Bobadilla,Measuring he Burdenof Diseaseand the Cost-Effectivenessf Health nterventions:Case Study in GuineaNo. 334 Mosse and Sontheimer,PerformanceMonitoring ndicatorsHandbookNo. 335 Kirmani and Le Moigne,FosteringRiparianCooperationn InternationalRiver Basins:The WorldBank at Its Bestin DevelopmentDiplomacyNo. 336 Francis, with Akinwumi, Ngwu, Nkom, Odihi, Olomajeye, Okunmadewa, and Shehu, State, Community,and LocalDevelopment n NigeriaNo. 337 Kerf and Smith, PrivatizingAfrica'sInfrastructure: romiseand ChangeNo. 338 Young,MeasuringEconomicBenefitsfor WVaternvestmentsandPoliciesNo. 339 Andrews and Rashid, TheFinancing f PensionSystems n Centraland EasternEurope:An Overviewof MajorTrendsand Their Determinants, 990-1993No. 340 Rutkowski, Changes n the WageStructureduring EconomicTransition n Centraland EasternEuropeNo. 341 Goldstein,Preker, Adeyi, and Chellaraj,Trends n Health Status, Services, nd Finance: he Transition n Centraland EasternEurope,VolumeNo. 342 Webster and Fidler, editors, Le secteur nformelet les nstitutions de microfinancementn Afriquede l'OuestNo. 343 Kottelat and Whitten, Freshwater iodiversity n Asia, with SpecialReferenceo FishNo. 344 Klugman and Schieber with Heleniak and Hon, A Survey of HealthReformn CentralAsia

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WORLD BANK TECHNICAL PAPER NO. 387

A Planner's Guide forSelecting Clean-CoalTechnologies forPower Plants

KarinOskarssonAndersBerglundRolf DelingUlrikaSnellmanOlleStenbackJack J. FritzTheWorldBankWashington,.C.


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Copyright 1997The International Bank for Reconstructionand Development/THE WORLD BANK1818H Street, N.W.Washington, D.C. 20433,U.S.A.All rights reseivedManufactured in the United States of AmericaFirst printing November 1997

TechnicalPapers are published to cornmunicate the results of the Bank's work to the development community withthe least possible delay. The typescript of this paper therefore has not been prepared in accordance with the proce-dures appropriate to formal printed texts, and the World Bank accepts no responsibility for errors. Some sources citedin this paper may be informal documents that are not readily available.The findings, interpretations, and conclusions expressed in this paper are entirely those of the author(s) andshould not be attributed in any manner to the World Bank, to its affiliated organizations, or to members of its Board ofExecutive Directors or the countries they represent. The World Bank does not guarantee the accuracy of the data in-cluded in this publication and accepts no responsibility whatsoever for any consequence of their use. The boundaries,colors, denominations, and other information shown on any map in this volume do not imply on the part of theWorld Bank Group any judgment on the legal status of any territory or the endorsement or acceptance of such bound-aries.The material in this publication is copyrighted. Requests for permission to reproduce portions of it should be sentto the Office of the Publisher at the address shown in the copyright notice above. The World Bank encourages dissem-ination of its work and will normally give permission promptly and, when the reproduction is for noncommercialpurposes, without asking a fee. Permission to copy portions for classroom use is granted through the CopyrightClearance Center, Inc., Suite 910,222 Rosewood Drive, Danvers, Massachusetts 01923,U.S.A.Cover artwork: Lange Art Arkitektkontor AB, Stockholm, Sweden.ISSN: 0253-7494

Karin Oskarsson, Anders Berglund, Rolf Deling, Ulrika Snellman, and Olle Stenback work for Swedpower/VattenfallEnergisystem AB n Stockholm, Sweden. Jack J. Fritz is an environmental engineer in the Urban Develop-ment Sector Unit of the World Bank's East Asia Department.Library of Congress Cataloging-in-PublicationDataA planner's guide for selecting clean-coal technologies for powerplants / Karin Oskarsson ... let al.].p. cm. - (World Bank technical paper; no. 387)Includes bibliographical references.ISBN0-8213-4065-41. Coal-fired power plants-Asia, South-Environmental aspects.2. Coal-fired power plants-Asia-Environmental aspects. 3. Coal-fired power plants-Waste disposal. 4. Coal preparation-Technological nnovations. 5. Flue gases-Purifications-Equipmentand supplies. 6. Greenhouse gases. I. Oskarsson, Karin.II. Series.TK1302.9.P553 1997621.31'2132-dc2l 97-38022CIP


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7. BY- PRODUCTSAND WASTE HANDLING ......................................................... 91UTILIZATION........................................................ 92DISPOSAL........................................................ 95COOLINGWATER......................................................... 102WASTEWATER......................................................... 103REFERENCES........................................................ 106

8. LOW-COST REFURBISHMENT NCLUDING O&M IMPROVEMENTS..........................................109INSTRUMENTATIONNDCONTROL YSTEMS........................................................ 110BOILER YSTEMS..................................................... 113COOLINGWATERYSTEMS............................. 114AUxiLIARYYSTEMS.............................. 115OPERATIONNDMAINTENANCE............................. 116

9. TECHNOLOGY SELECTION MODEL ............................. 117FAST RACK ODEL............................. 117STEP1. PROJECT EFINITION............................................................................................................... 119STEP . TECHNOLOGYCRRENIN122STEP . POSSIBLE LTERNATIVES124STEP . COSTCALCULATIONNDRECOMMENDATION125

10. CASE STUDIESUSING FAST TRACK MODEL 131GREE NFIELDLANT131BOILERRETROFIT138

11. ENVIRONMENTALGUIDELINESAND REQUIREMENTS 147PROPOSEDWORLDBANK REQUIREMENTS147CHINESEREQUIREMENTS149INDIANREQUIREMENTS...... ...................EQUIREMENTS............................................................................................151SUMMARYOF ENVIRONMENTALEQUIREMENTS153REFERENCES.154

APPENDDL COAL CLEANINGMETHODS 155

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FOREWORDAs East and South Asia continue o develop economically, roductionof electrical energymust keeppace with demands of growing industriesand burgeoningpopulations. Roughly three-fourths of theenergy in Asian cities will come fromthermal power plants burningindigenous coals. Some of theseplants will be modem, state-of-the-artunits, owned and operatedby private interests, but most will bestate owned and operated under less than optimal conditions. Resulting air pollution, creation ofgreenhouse gases and solid residuals will have ever greater environmental mpact. In order to keepemissions at an absoluteminimum,new powerplants will have to include air pollution control devices.Older plants may have to be shuttered or retrofitted accordingly. Eventually, all new and retrofittedplantsmust meet the highest efficiency tandards so that coal burning can be kept to a minimum.Unforhmately, or many Asian countries, he costs of high efficiency,state-of-the-artpollution controlsystems are prohibitive. More often, less costly control systems will have to be employed. Typicaldecisions o be made by planners and engineersare whetherto implement95 percent sulfur removalata prohibitive cost, 70 percent sulfur removal at modest cost or no control at all. Important factors inthis equation include coal quality, power plant and mine location, ocal air quality standards, ambientair quality conditions,and waste transport and disposal. Few analytical tools exist to assist powersector planners and engineers n such a complexexercise. To add to the configurationof options, thecommercialavailability f several new combustion echnologies,such as fluidized beds, have made thechoice of technologyeven more challenging.The World Bank has been involved in the power sector and with the institutional, financial andregulatory issues that affect its environmentalperformance. The Asia Environment and NaturalResources Division (ASTEN) seeks to assure that investmentsmeet environmentalguidelines set outby the Bank's Board of Directors. In this effort, ASTEN initiated the preparation of A Planner'sGuide for Selecting Clean-Coal Technologies or Power Plants. We hope it willassist plannerschoosing among competingcombustionand pollution controltechnologies. Several existing reportsprovide detaileddescriptionsof these technologies;few incorporate an organized analytical approachto examining he options from the standpointof cost and performance. The particular value of thisguide is to provide a synthesis of available combustionand pollution control technology informationdeveloped o date.This reportoffers a step-by-stepmodel for selecting he appropriate echnologybased on the resourcesand objectives. It is the hope of the authors that it will be widely circulated among power sectorplanners, engineer and environmental pecialistsand encouragefuirtherwork along these lines. Theimportanceof this topiccannotbe overstressedsince electricalgenerationwill continueto grow rapidlyin conjunctionwith overalleconomicdevelopment n the two regions of Asia.

Maritta Koch-WeserChief, Asia Environment and Natural Resources DivisionWorld Bank

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ABSTRACT* Coal will continue to play a role in future energy supply in China and India, where today from70 to 75 percent of electric power is coal based.* The negative effects of coal on global environment, eco-systems and public health are welldocumented; its use must be balanced between the development needs of a country and thewelfare of its people and land.* The most widely used combustion technology in China and India are the subcritical pulverizedcoal boilers with low efficiencies resulting in the combustion of extra quantities of coal.* Greater efficiencies will reduce emissions and prevent waste generation, and must beimplemented n the short term. Planning should strive for increased utilization of by-productsand waste. And if disposal is the only alternative, protection of waterways must be enforced.* Washed-coal use in power production is the most cost-effective mean to reduce environmentalimpact. Coal cleaning reduces the ash content of coal and of substances such as inorganicsulfur and sodium associated with corrosion and deposition in boilers. Besides the use ofwashed coal offers several other advantages to the plant owner, such as increase efficiencyand availability, less wear and lower maintenance cost, and reduced waste generation at theplant.* Switching to coals with low sulfur content is the simplest method for reducing SO2 emissions.However, ultra-low sulfur coals may not be readily available. Nevertheless, low- to medium-sulfur coals are available in both China and India. However, with the large quantities of coalburned for power, industry and at the household level, particulate and SO2 emissions remainhigh, especially n industrial and urban areas.. The procedure outlined in the report for selecting environmentally friendly technologiesrequires evaluation and optimization of several technical, environmental and economic factors,including quality of coal, requirements on waste product, yearly operating time and operatinglifetime of the plant.

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ACKNOWLEDGMENTSThe authors would like to thank Anna-KarinHjalmarsson, AF-Energikonsult,Stockholm AB,Sweden, for her assistancewith the coal cleaning chapter; Zhang Li, Hunan Electric PowerDesign Institute, Changsha,China; and Ajay Mathur, Dean, Energy Engineering& TechnologyDivision, TERI, New Delhi, India, for their contributions. Review of the draft report wasprovidedby FrederickPope of Foster-WheelerEnvironmentalCorporationand Bernard Baratz,ShigeruKataoka, and StratosTavoulareas,WorldBank. Jack Fritz was the task manager or thisreport. Sheldon . Lippmancompleted he final editingand publicationmanagement f the report.

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ABBREVIATIONS,CRONYMS, NDDATANOTEACFB atmospheric circulatingfluidized bedBOT build-operate-transferCaO limeCa/S sorbent to sulfur ratioCO2 carbon dioxideESP electrostatic precipitatorsFGD flue gas desulfurizationFOB free-on-boardGJ gigajouleGT gigatonI&C instrumentationand controlsIGCC integrated gasification combined cycleIPP independentpower producerkg kilogramLHV lower heating valueLNB low NOx burnersMJ megajouleMt megatonMW megawattNDG normal dry gasNO. nitrogen oxidesNSPS new source performance standardO&M operation and maintenanceOFA over fire airPC pulverizedcoalPLF plant load factorPFBC pressurizedfluidized bed combustionSCR selective catalyticreductionSNCR selective non catalytic reductionSO2 sulfur dioxideTWh terawattData Note: Unlessnoted, all tables and figures were originated by the authors.

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EXECUTIVE UMMARYIn 1994, 374 TWh of electric power were generated in India and 886 TWh in China. Electricitydemand is growing rapidly in both countries and the annual growth rate from now until 2010amounts to approximately 7% in India and 6% in China. Both countries rely heavily on coal forpower production, industrial energy, and household heating and cooking. Approximately70-75%of the electric power is coal-based. Coal is expected to continue to play a major role in futureenergy supply scenarios in these countries.The use of coal negatively affects the global environment, local eco-systems and public health withemissions of carbon dioxide (CO2 ), sulfur dioxide (SO2), nitrogen oxides (NO.) and particulates.In addition to these emissions, the ash residue and the wastewater from coal combustion raisesignificant environmental issues. The very important task for both India and China is to balance theconflicting demands of economic growth and increased demand for power with environmentalimpact that can be considered reasonable for sustainable development.This report has been prepared as a technology selection guide for the use of power systemplanners and engineers to facilitate the selection of cost-effective, environmentally friendlytechnologies for coal-based power generation in countries grappling with impending power andcapital shortages in the face of stricter environmental regulations. The report focuses on plantsgreater than 100MWe in India and China.

COAL QUALITYAND COAL CLEANINGStarting with the coal itself, the use of washed coal is the most basic cost-effective and appropriatemeans of reducing the environmental impact of coal-based power production. Coal washingreduces the ash content in the coal. In India and China, coal washing is not widely used. Thissuggests that there is considerable potential for cost-effective environmental improvements.Following are some of the properties of washed-coal use:

* increases the efficiency of power generation, mainly due to a reduction in the energyloss associated with the attempted combustion of inert material;* increases plant availability;* reduces investment costs, less cost for fuel and ash handling equipment;* reduces operation and maintenance costs as a result of reduced plant wear and tear andreduced costs for fuel and ash handling;* energy savings in the transportation sector and lower transport costs;* reduces impuritiesand results in more even coal quality;* reduces the load on the particulate removal equipment in existing plants; and* reduces the amount of solidwaste that has to be taken care of at the plant.

For the power plant owner, there is a substantial economic incentive for firing washed coal. Thishas been proven by earlier calculations made for specific Indian power stations. In these stations, apremium of US$0.40-$0.55/metric ton (ton) coal could be paid for each percentage pointix


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reduction in ash content of the purchased coal. Although sulfur removal is not the primary aim,coal washing is also the cheapest way to remove inorganic sulfur from the coal. Coal washing canbe used as the primary cost-effective way to reduce emissions of S02 by 10 to 40%.

COMBUSTIONTECHNOLOGIESA new coal-fired power plant aims for high efficiency, high availability, low emissions and theproduction of a by-product that can be utilized, avoiding the need for disposal. By far the mostused combustion technology in India and China is subcritical pulverized coal (PC) boilers withplant efficiencies in the range of 33-36%. By striving for higher efficiencies, the emissions and thewaste per MWhe produced is reduced. The coal consumption per MWh, produced is also reduced.Higher efficiency is also the only way to reduce C02 emissions from a coal-fired power plant.Large supercritical boilers with high efficiencies have proven competitive on the internationalmarket. However, there are still no supercritical boilers in operation in India and just a few inChina. Introducing this technology requires a transfer of technology know-how to domesticmanufacturers and utilities from international manufacturers.Atmospheric circulating fluidized bed boilers (ACFB) represent a newer technology, withimproved environmental performance compared to PC boilers. In addition to the low emissions ofS0 2 and NO., the fuel flexibilityof ACFB boilers is extremely wide. Subcritical ACFB boilers withmoderate efficiencies are commercial in sizes up to approximately 100 MWe. There are a fewplants greater than 100 MWe in operation in the world and some are under construction. In Indiaand China, only small-scale fluidized bed boilers are in operation. The major drawback is thattoday there are only limited means of utilizing the waste, which means disposal is still necessary.Other technologies like pressurized fluidized bed combustion (PFBC) and integrated gasificationcombined cycle (IGCC) which offer high efficiencies and low emissions should be chosen onlywhen the requirements on commercial readiness are not so high.

SO2 EMISSIONCONTROLTECHNOLOGIESThe simplest way to reduce SO2 emissions is to switch to a coal with a lower sulfur content. Whencoal switching is not possible or not sufficient to reach acceptable emission levels, physical coalcleaning is still the most cost-effective route to reduction of S02 emissions. When further sulfurreduction is required, some S02 removal technology must be introduced. The choice of technologyis affected by the sulfur content in the coal, required emission level, requirement on waste product,yearly operating time of the plant and plant lifetime. When selecting sulfur removal technology, itis vital to make correct assumptions regarding these factors in order to select the best technology.Generally, the investment cost for technologies with low sulfur removal efficiencies, such assorbent injection processes, are low; the investment for high efficiency technologies, such as wetscrubbers, is high. Spray dry scrubbers fall somewhere between these technologies with regard toboth investment and efficiency.Today, sorbent injection processes and spray dry scubbers are usedmainly in relatively small-scale units burning low sulfur coal, in peak load plants and in retrofitapplications where the remaining operating time is short. Wet scrubbers are by far the most usedtechnology worldwide.

A Planner'sGuide or SelectingClean Coal Technologiesor Power Plants


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In India and China, where there is a need for immediate reduction of SO2 emissions and economicmeans are limited, a step-by-step approach can be considered. A low-cost sorbent injectionprocess can be installed rapidly, followed by further upgrading to a hybrid sorbent injectionprocess or a wet scrubbing system. Neither China nor India has significant experience with sulfurremoval technologies and only a few plants in each country have some kind of sulfur removalequipment installed. The fact that the sulfur content in the coals burned in India is low does notmean that SO2 emissions are not a problem since the total amount of S02 emitted from Indianplants is considerable.

NOXEMISSION ONTROLECHNOLOGIESOperation with low excess air, fine tuning of the boiler and staged combustion are veryinexpensive ways to reduce NO, emissions. NO, emissions should always be reduced, in the firstinstance, by optimizing the combustion process. Optimization needs to be related specificallytocoal and plant. A reliable system for 02 and NO. monitoring is required. Up-grading orreplacement of coal pulverizers can also be considered to minimize NO, emissions in existingboilers. These measurescan be combined with other low NO, technologies.Combustion modifications that can be made to reduce NO, emissions further include theinstallation of low NO, burners, over fire air (OFA), flue gas recirculation and coal reburning.Post-combustion measures include selective catalytic reduction (SCR) and selective non-catalyticreduction (SNCR). Combustion modifications show a lower increase in electricity production costthan post-combustion technologies, but they can only achieve a reduction of NO, emissions up to60%. SCR is the most efficient and most expensive technology and should only be chosen whenvery low emission levels are essential. After optimizing the combustion process, combustionmodification measures should be made to reduce NO, emissions.Typically n India, burners are designed for emissionsof 600 ppm NO,. Recently burners with NO.emissions less than 400 ppm have been developed. In China, more than 20% of the power plantsuse some kind of low NO, combustion, most are low NO. burners. SCR and SNCR technologiesfor low NO, emissions are not in use in either country.

PARTICULATEMISSION ONTROLECHNOLOGIESParticulates can be removed with a great degree of efficiency either in electrostatic precipitators(ESP) or in baghouse filters. ESPs are used in all large plants in India and in most Chinese plants,while fabric filters (baghouse) are extremely rare. ESP is by far the most commonly usedtechnology worldwide for particulate removal. ESPs are competitive for medium and high sulfurcoals with low to medium ash resistivity when an efficiencyup to and above 99.5% is required.They are also competitive for low sulfur coals and coals with high fly ash resistivity when lowerefficiencies are accepted. Due to their robust design, ESPs can also handle erosive high ash coals.Baghouse filters are suitable in combination with some sulfur removal technologies, such assorbent njectionand spraydryscrubbers.

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xiiBY-PRODUCTSAND WASTE

Utilization of residues is an essential part of a successfulenvironmentalmanagementstrategywhich embraces he concept of sustainable evelopment.Preventionshould be the priority for awaste management chemefollowedby utilization,with safe disposal as a final resort. Residuesfrom coal-use n India and Chinaare limited o fly ash and slag since flue gas desulfurization shardlyused. Only a smallportion of the fly ash and slag residue is utilized, hus, leaving he majorpart for disposal. Increased utilization as building material, for rnine reclamationand for civilengineering urposes s promoted both in India and China.Protectionof water sources s the most importantconcem associatedwiththe disposalof coal-useresidues.Wet disposal n disposalponds is the technology sed in most plants n India and it is alsothe predominantechnology n the southempart of China. ts main advantage s the ease by whichresidues can be transported and placed. However, the disadvantagesare obvious; the need foradditionalwater, increasedgenerationof leachate and greater land requirementscomparedwithdry disposal in landfills.There are also risks of overflow of the pond, during heavy rainfalls orexample. nternationally, tilities end to favor dry disposal n landfills,since problems ike waterpollution nd consumption re mninimnized.Analysisof the characteristics f the residue, ncluding eachate ests to determine he potential orleaching, s essentialbefore deciding on utilizationor disposal. Waste from coal-based powerproductionis not restricted to solid waste. A large amountof waste water is producedwhichneeds suitablehandling.

LoW-COST REFURBISHMENTRefurbishment f existingpower plants can be carried out to reduce operating and maintenancecosts, increase plant efficiency, ncrease availability, educe environmental mpact, increase plantlifetimeor increase plant load. There are several low-cost measures available or achieving heabove, someof whichare summarizedn this report. These nclude he installation f 02 measuringequipment or optimizationof the combustionprocess and installationof mechanical ondensercleaning ystems or increasedefficiency.

TECHNOLOGYSELECTIONMODELAND CASE STUDIESSuccessful electionof technology equires hat all project specificenvironmental, conomicandtechnical aspects are considered. A structured working procedure is necessary. Therefore, thisreport includes a technology selection model which is intended to be used as a guideline operform a technologyselectionduring the prefeasibility hase of a project. By using the model,suitablepower plantconcepts canbe developedwith clear data on:

* investment osts,* electricity roductioncosts,* flue gas cleaning osts, and* costs per ton emission emoved.A Planner's uide or Selecting leanCoalTechnologiesor PowerPlants


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The model is applied n two realisticcase studies;a greenfieldplant anda boiler retrofit.In thesecase studies he step-by-step pproach o technology election s demonstrated.

ENVIRONMENTALGUIDELINESAND REQUIREMENTSEmerging environmentalproblems are rapidly changing the way the authorities look uponenvironmentalquestions. It is important when selecting suitable power plant technologies oconsider not only today's environmental equirements,but to plan for future more stringentrequirementsand standards. Today's environmental equirements or coal-fired power plants inIndia and China are not very stringent compared with those operating in the United States,Western Europe and Japan. NeitherIndia nor China stipulatesreduction of NO, emissionsandthey both, to a great extent,rely on stackheight and dispersion ffects for emissionof particulatesand SO2. There are, as yet, no legislative nstruments o reduce the emissions n either country.The World Bank has developedenvironmentalguidelines o be applied to the planningof coal-fired power plants greater than 50 MWX, restricting emissionsof SOx, NOx and particulates.Water pollution is governedby Indian, Chinese and World Bank requirements and guidelines.Regulationscover, among other factors, suspendedsolids, oil and grease, heavy metals, pH andtemperature ncrease.

SUSTAINABLEDEVELOPMENT ND SOCIO-ECONOMIC LANNINGIn the strive for a sustainable developmentwith minimizedenvironmental mpact of powerproduction,an integratedpollutionmanagement pproachshouldbe adopted hat does not involveswitchingone form of pollution o another. For example,wet flue gas desulfurization FGD)wastes could lead to contaminationf the water supplyand sorbent njectionprocesses could leadto greater emissions f particulatematter. These factors have o be avoided.The socio-economicspectsof planning lso have to be considered.Pollutioncontrol echnologieswith an apparentlygreater capital cost may produce a by-product that can be utilized in thebuilding ndustryor the infrastructure onstructionsector, hus avoiding he need for disposal,andresulting n a net financial ain.

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1. INTRODUCTIONCOAL DEMAND NDTHEASIANENVIRONMENT

Today, approximately 70% of the installed electricity generation capacity in the developingcountries of Asia is concentrated in India and China. In 1994, 374 TWh of electric power weregenerated in India and 886 TWh in China.Electricity demand is growing rapidly in the region andplanners forecast an annual growth of around 7% in India and 6% in China from 1995 until 2010to keep pace with regional development objectives. India and China rely heavily on coal for powerproduction; between 70% and 75% of the generated power is coal based. Both countries havelarge indigenous coal supplies, and coal continues to play a major role in all future energy supplyscenarios. In China, hard coal production amounts to more than 1,100 megatons (Mt) per year;while in India, annual coal production exceeds 225 Mt.' Coal production will increase to satisfygrowing domestic demand.An enormous amount of capital investment will be required to reach the development goals fornew electricity capacity in the developing countries of Asia, i.e. China, Taiwan, Malaysia, SouthKorea, Indonesia, Philippines, Thailand and India. It is estimated that capital investment of $1,500billion will need to be made in the region between 1994 and 2010. These expenditures will beconcentrated in China and India. Obtaining the required capital will be a major problem, andadding the increasinglyessential pollution control equipment to a planned plant will increase theamount of capital that needs to be raised still further.The need for capital comes at a time when principal issues facing power sector planners includebrownouts, high transmission and distribution losses, and a stock of plants which are not wellmaintained and generally without pollution control. In addition, alternative approaches such asenergy conservation and demand-side management have only been partially successful in reducingdemand for new generation capacity. Another drawback is revealed when it is understood thatcurrent low electricity tariffs result in financial shortfalls in the utilities with a consequent lack ofcapital for new investment. Even government funding of the power sector is becoming moredifficultsince there is intense competition for funds between different industry sectors. As a result,private participation in power projects is emerging introducing IPP (independent power producer)and BOT (build-operate-transfer) projects into the market.The use of coal in the electricity generation sector negatively affects the global environment, localecosystems and public health. Mining is associated with problems of subsidence, aqueousdischarges requiring treatment and emissionsof methane. The coal-firing process causes emnissionsof CO2 , S02, NO, and particulates. Furthermore, it produces wastewater and considerableamounts of ash and other solid waste. Picturing the amount of emissions and waste from a coal-fired power plant is best done by looking at a flow diagram. Figure 1.1 shows a 200-MW plantwithout any pollution control equipment with its different flows of fuel, emissions, cooling waterand waste. As can be seen from the flow diagram, a single plant produces several tons per hour of1 Ton refers to metric ton throughout his report.


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2SO2, NO,, solid waste and dust. Plants with once-throughcoolingwater systemsas in Figure 1.1also needconsiderable mountsof fresh water for the condenser. n the past, environmentalssueswere given ittle consideration n selectingcoal technology n both India and China,but emergingenvironmental roblemsare changing his attitude. Technologies elected oday and over the nextseveral years will prevailfor 20 to 30 years and so will their associatedemissionsof S02, NO.,particulates nd greenhousegases.

Figure 1.1: A 200-MWcoal-firedpower plant withoutany pollutfoncontrolequipment

200 MWe ;7< ~~~~~S032:3.2 VhBottom sh:2.6 Vh NOx: .6 Vh

s ~~~~~~~~~Dust:4 tVhC02: 220 VhCoolingwater: 30 000 Vh

Note: Data used -- efficiency= 37%,sulfur content,S= 2%, ash content=32.8%.In the short term, the challenge comes from having to balance the conflicting demands ofeconomicgrowth and increasingdemand or power with the requirement or an acceptable evelofenvironmental mpact. Clean coal technologies with enhanced power plant efficiency, fuelswitching, use of washed coal, the introduction of pollution control equipment and emissionmonitoring nstruments,and proper by-product and waste handling, are all ways to a cleanerfuture. Choosing he most cost-effectiveway to reduce the environmentalmpactof coal firing sthe first vital step.

THEWORLDBANK'SROLEThe World Bank has been involved in power sector projects for many years with investmenttotaling some $40 billion hrough fiscal year 1991 or some 15 percent of total lending.A largeportion was obligated n the period 1985 hrough 1993. In addition, new projects continue o bedeveloped n anticipation f future energy requirements. nvestment n the sector will continue nspite of resistance rom environmental roups becauseof the need for additional apacity.A Planner'sGuideor Selecting lean-Coal echnologiesor PowerPlants


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As the World Bankbegins o grapplewith institutional,inancialand regulatory ssues in the hopeof improving he sector's performance, he issue of regional environmentalmpact needs to beexaminedas well. Efforts such as the RAINS-Asiawill provide an overviewof sulfur dioxideimpacts based on source definition.However,the issue of technologychoice and its impact oncost andenvironment ave not beenaddressed,especially romthe standpointof the powersystemplanner.

USEOF THEPLANNER'SGUIDEThis report is a technology and strategy guide for power system planners grappling withimpendingpower and capital shortages in the face of stricter environmental egulations.It isintended o facilitatehe selectionof cost-effective, nvironmentallyriendly echnologies or coal-based power generation.The focus is on coal-fired plants greater than 100 MWe in India andChina.In addition, as privatelyownedand operated power plants are being ntroduced, hereis aneed for planners o have an understandingof what is being offered. This guide aimsto helpunderstanding ower and associatedpollution ontrol echnologies,heir cost and performance.In separatechapters, echnical, nvironmental ndsome economiccriteriafor the technologyareasshown n Figure 1.2 are provided. Informations intended o be used duringa prefeasibilityhaseof a project.Fl ure1.2: Coaltechnologies epresentedn the Planner'sGuide

Ch3: Combustion echnologies-PCACFB- FPBC- IGCC

Ch5: NOxemission control- low NOx combustion-SCRK,l

CH6:ParticulatemissioncontrolCh 2: Coal quality/coalcleaning Fabric iEters

S02NoxDustC02Ch7: Waste andling Ch4.S02emissionontrolsolidwaste - sorbent njection processescooling water - spray dry scrubberswaste water wet FGDcombined SOx/NOxNote: Technical, conomic,and environmentalnformations provided n separatechapters ortechnologyreasand echnologieshownn this igure.

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Also, to get a first quick impression f the performanceof the different echnologiesdescribed nthis strategyguide, simplifiedlow diagrams ike the one in Figure 1I.1 ave been developed.Suchflow diagramsare included n the introduction o the coal cleaningchapter and at the end of eachcombustion,SO2, NO". nd particulateemissioncontrol sub-chapter.By looking at these figures,the reader can get an impressionof the impact of each technology as far as ernissions,coalconsumption nd waste productionare concerned.The guide also contains a technology selectionmodel, the Fast Track Model, and two realisticcase studies. The model gives a working procedure for the technology selection phase of aprefeasibility tudy. By using information n this report and from suppliers, etc., the followingimportantdata can be established t a prefeasibilityevel:

* suitablepower plant concepts,* investment ost,* electricity roductioncost,* flue gas cleaning osts, and- emissionsof SO2, NO,,and particulates.

Also included n the strategyguide are descriptionsof low cost refurbishment ptions that can becarriedout to increaseefficiency,ncreaseavailability,educe operatingand maintenance osts etc.in an existing power plant. References marked throughout the text are listed at the end ofrespectivechapters. Figure 1.3 shows he structureof the report and he linkageof the chapters oeach other.Figure 1.3. Structure of the report and linkage of chapters to each other

l Chapter 3 |I Chapter4

_ I - Rocommended FeasibilityChapter S Technology StudyIt@ 6 W Concepts

Chapter 6

t Pequirlments C f o P

L - - - - - - -

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2. COALQUALITYAND COALCLEANINGTECHNOLOGIESThis chapter focuses on the advantages of using washed coals and the effect coal quality has onthe overall cost of power production. How much more is it worth paying for a high quality coalthan for a low quality coal? Basic information regarding quality of Indian and Chinese coals, coalcleaning technologies and their suitabilityfor use is also discussed.Coal cleaning reduces the ash content of coal and of substances such as sodium associated withcorrosion and deposition in boilers. The selection of coal cleaning equipment is often notconsidered in the design of coal-fired power plants, since the most conmmon ocation of thecleaning plant is at the coal mine. However, coal quality is a major influencing factor in the designof the power plant, especially if high ash coals have to be used.An additional benefit of coal cleaning is the removal of inorganic sulfur. As shown in Figures 4.2and 4.3 in Chapter 4, coal cleaning is the cheapest way to reduce the sulfur emissions. A 10-40%reduction of sulfur content can be achieved by coal cleaning. The larger the percentage ofinorganically bound sulfur in the coal, the higher the percentage of sulfur that can be removed.Hence, the use of washed coal is a primary cost-effective way to reduce the environmental impactof coal-based power production. Currently, coal cleaning is not widely used in India or China;therefore, there is a significant opportunity for introducing coal cleaning.Following are some of the benefits of using washed coal:

* increased generation efficiency, mainly due to the reduction in energy loss as less inertmaterial passes through the combustion process;

? increased plant availability;reduced investment costs due, as an example, to reduced costs for fuel and ash handlingequipment;* reduced operation and maintenance (O&M) costs due to less wear and reduced costs forfuel and ash handling;* energy conservation in the transportation sector and lower transportation costs;* less impurities and a more even coal quality;reduced load on the particulate removal equipment in existing plants; and* reduction in the amount of solid waste that has to be taken care of at the plant.

When very low grade coals are used, coal cleaning may not be technically and economicallyjustified. In such cases, a mine mouth power plant is the best solution.Figure 2.1 shows a 200-MW subcritical pulverized coal-fired (PC) plant, without any flue gascleaning equipment, firing washed coal. The reduction in coal quantity and waste production

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Figure2.1: A 200-MW. ubcritical Cplant withno fluegascleaningequipment,lringwashed oal

Coal:70Vh = = \

200MWe) Sf if ~~~~~~~~~~~S02:.6 Vhh

NOx:0.6 /hBottom sh: 1.4 Vh Dust:14VhC02: 220 tVh

Note: Data used - plant efficiency= 37%,ash contentP 0%.achievedcan be seen by comparisonwith Figure 1.1. which shows the sameplant firinga high ashcoal.Whenproducing a high qualitycoal, the first objective s to minimize he impurities n the run-of-mine coal. The second is to try to avoid contaminationduring handlingand the third is to selectthe most appropriateplace to remove he various unwanted components rom the system. Somemechanizedmining methods mix more dirt in with the run-of-minecoal than others. Some dirtaddition and high ash coal can be avoided by careful exploration and selectivemining. Theseoptionsfor removing he impurities re shown n Figure 2.2.Different coal cleaning echnologiesare used in a series of unit operations in a cleaningplant.These could include classifying (by size), other separation processes, size reduction(milling/grinding),nd dewateringafter separation. The cleaningcosts generally ncrease as theparticle size decreases.The assessmentof any coal cleaningprocess is essentiallyempirical nnature. The separationachievable ependson the coal, the equipment nd the conditions.

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Figure .2: Optionsor minimizingand removingunwantedmpurities* dots/Sd eealgon ~~~~ProblemreanEXTRACTION d- taleivexmoratin -Nrelease- iurface selecivemining CH4rel,e- undergrounrd managingtheminingr _ - preliminary operationorqualty - groundvwatersize re uction z - separationfdirton disturbaancendhor anding - transportystems possible5- eparateRetorage contamnmalion- rock/overburden----------- _ * Zdisposal5 ' N - exdusion f foreign' fugitve ust. a , 1 matenai by good designandmaintenancef - acid un-offSTORAGE stodtyardndransport inaeaseduseof water, HOMOGENSATION systemsegcovered o>-lneanaJysis slurry. ANDrOR __, ~~~~~~~storage,cencreteND/OR --- oceewasteTRANSPORT a hardstands,goo imapoundments* ~~~~~~~~~~~housekeeping)

ii ra' a

i 5. PREPARATION i separationnd emoval___- sizing i of ol npunbes nioro use mainpathi - cdeaning._.._.__ - blenaing i pOssUl path

Source: Singer (1991).

COAL QUALITY

Coal in IndiaCoal has been produced in India for over 200 years. Output has been accelerating sinceindependence, particularly since the formation of the nationalized coal company in the early970s.Annual production is over 225 Mt from coal fields that are located mainly in the east of thecountry in the states of Assam, Bihar, Uttar Pradesh, Madhya Pradesh, Andhra Pradesh, Orissaand West Bengal. India's total coal reserve base is estimated to be near 160 Gt (gigaton). Coalranks range from lignites to bituminous coals with most being in the bituminous category. Thereare no anthracite or peat reserves. India has little good quality coal. Some 60% of the reserveshave an in situ ash content of 25-45%. As most of this ash is embedded dirt, coal cleaning is oftendifficult. As a result calorific values of the coal are low; for saleable coal averaging is under 20 GJ(gigajoule) per ton, or about two thirds that of a good quality internationally traded coal. Sulfurcontents are comparatively low by interational standards, typically under 1%, but are not so goodwhen expressed per unit of energy. Inherent moisture contents are unexceptional: typically 8-15%.The coal, which is hard, generally has a low swelling index and low volatile content. Much of thecoal has a crushing strength of 200-300 kg/cm3. Compared to other countries only a small part ofIndian coal is screened or washed for impurities.

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An unenforced ndiangovernmentpolicystates that coal should be washed whenever he distancebetween he mine and the end-user s greater than 1,000 kilometers.An attainableand reasonablegoal for the washingof Indianraw coal is to reduce the ash contentfrom as high as 50% o at least30%-40% ash or even down to 25%. Table2.1 presents examplesof typical coals from severalareas in India.Table 2.1: Analysesof typical Indian coals from several re ionsJharia Jharia UttarPradesh Renusagar Singrauli NeyveliRank Medium Highvolatile High olatile volatile Sub- Sub- Lignitebituminous bituminous bituminous bituminous bituminousAs receivedAsh, % 38.9 31.6 28.0 28.6 31.5 4.5Moisture,% 1.1 6.9 10.0 14.9 7.9 53.1Moisture ashfreeVolatile,% 25.3 37.2 41.0 45.1 47.4 57.1Carbon,% 83.6 74.1 71.9 70.3Hydrogen,% 4.5 4.8 5.0 5.2Oxygen,% 9.9 18.6 20.3 23.1Nitrogen,% 1.3 1.4 2.0 0.5Sulphur,% 0.7 1.8 0.8 1.1 0.8 0.9Lowerheating 33.0 30.4 30.7 28.4 27.3 26.4value,MJ/kgHardgrove 63 60 50 56 50 95+grindability,OHSource: Singer 1981).Coal n ChinaChina s the world's largest hard coal producerwith an annualproductionover 1,100Mt. Chinesecoal resources are vast. Official Chinese figures suggest a total geological resource of over770,000 Mt. The coals range from hard anthracite o lignite with ash contents between 10 and40%. The bituminous oals are of mediumand highvolatile ank; the mediumvolatilebeing ratherhigh in ash. The sulfur content is low in many coals, less than 1%, but there are also areas withover 2% sulfur. Compared o other countries,a smallproportion of Chinese coal is screenedorwashedfor impurities.Table 2.2 presentsexamplesof some typicalChinesecoals.

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9Table 2.2: Analysis of Chinese coals _ High volatile Mediumvolatile LowvolatileRank Sub-bituminous bituminous bituminous bituminousAs receivedAsh, % 32.8 37.0 29.7 27.7Moisture,% 22.6 3.3 10.3 9.6Moisture ndash reeVolatile, % 46.8 39.3 22.7 17.0Carbon, % 74.7 79.6 80.8 83.9Hydrogen,% 4.8 5.4 6.0 4.5Oxygen,% 18.6 12.4 10.7 5.1Nitrogen,% 1.3 1.7 1.4 1.4Sulphur,% 0.6 0.9 1.1 5.1Lower heating alue, 24.2 29.2 30.8 31.6MJ/kgHardgrovegrindability,H 52 45 50 48Source: Singer 1981).

COSTSCostof coal cleaningCoal cleaning plants are commonly located close to the mine and the cost of cleaning is included inthe coal price. The costs for coal cleaning vary from case to case, as does the impact on coalquality. Therefore there are hardly any published costs specific to different cleaning methods,however some are shown in Table 2.3.

Table 2.3 Examples of published costs for coal cleaningCleaning method Cleaning costsUS$/tonConventional cleaning* coarse fraction 2-3* fine fraction 3-10* jig, dense-medium or froth (for the US) 4-8Advanced physical separation 15-30Source: Couch 1995a)and Sachdev 1992).

Coal quality mpacton power generationcostThe degree of coal cleaning (e.g. ash content) has an impact on power plant economics. Theinvestment cost and the O&M costs are affected by the coal quality. In India and China, therewould be an economic advantage in many existing plants for firing washed coal. This has beenproven by calculations made for specific Indian power stations using two American state-of-the-artcomputer models (Ref 9). Using data from four representative Indian units in three power stationsand typical coal data, a substantial economic incentive for firing washed coals in these powerplants was identified. A break-even cost analysis established the following:

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* premiumof about $0.55/ton could be paid for each percentagepoint reduction in theash contentof the typicalhigh ash bituminous oals fired in older, existingpower plants(Ref.9).* Cleaninghigh ash coals for use in newer plants that were designed or high ash coalswas projected o be somewhat ess attractive.A premiumof about $0.40/ton for eachpercentagepoint reduction n a coal's ash content could be paid (Ref. 9).

Projectedsavingsderive mainly,rom reducedmaintenance ostswithin he power plant, increasedplant availability, nd reduced fuel transportationcosts. Figure 2.3 showsthe results of the ashsensitivity nalysis or the four differentpower plants in India on the break-even free on boardmine fuel cost. When the coal is purchased at a price following he slopes in Figure 2.3, theelectricityproductioncost is constant. If the coal can be obtained at a lowercost than its break-even cost, then the power plant's electricity roductioncost can be reduced.Figure2.3: Ash sensiftity analyis or four differentpowerplants (A-D)

32-30

_20 22 A,6 2 0 2 3d3 8 4AsRecivedshContent,Col

00

m24*20

1820 22 24 26 28 30 32 34 36 38 40As-ReceivedshContent~

Note: The igure hows he coalpnce hatcanbepaidas a finctionof ashcontentn the coal n orderto reach he samecost orelectricity roduction. heigures based n model alculations ade or ourIndian ower lants.Source: Sachev1992).Productioncost savingswhen reducing he ash content are illustratedby the break-even uel costsin Figure 2.3. Savings are split into differentparts; fuel-relatedcosts (e.g. more fuel needed),transportationcosts, operationcosts, maintenance osts, derate (e.g. high ash content may resultin restrictedmill hroughputand higher energyconsumption n mills)and increase in overallplantavailability.Table2.4 presents he savingsdue to reducedash content split into these areas for thedifferentplantspresented n Figure2.3.

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Table 2.4: Savings due to reduced ash content split into different powerplantsA, old B, newer C, old D, oldFuel (free on board) 2 6 2 4Transportation 49 27 19 68Operation 0 0 11 0Maintenance 39 27 14 23Derate 0 22 34 0Availability 10 18 20 5Total 100 100 100 100Note: Basedon Figure2.3.Source: Sachdev 1992).As shown in Table 2.4, the ash content of the coal has an effect on:

* fuel costs,* fuel transportation costs,* operational costs (e.g. ash handling, operation of pulverisers),* maintenance costs,* generation capacity, and* availabilityand forced outage rate.When deciding which coal quality to purchase, all the savings should be added and calculated perton coal. The savings should be compared to the costs for cleaned or cleaner coal. This was donein Figure 2.3 and Table 2.4.An example from an Indian mine with an annual capacity run-of-mine of 6.5 million ons shows thefollowing: the specific investment cost for coal cleaning was $24/ton, the ash content in washedcoal was 34% and the moisture content was 8% (Ref 8). The effect of using washed coal (with areduction in ash content from about 40 to 34 %), compared to run-of-mine coal, was evaluated.The plant load factor was anticipated to increase in the order of 5-10% when the ash content wasreduced from 40 to 34%. Data relating to the improvement in plant performance, distance fromthe mine and the cost of generation was analyzed. Figure 2.4 shows the decrease in operationcosts with the increase in the plant load factor (PLF), due to the use of washed coal, for a giventransportation distance from the mine. This is another proof of the importance coal quality has onoperating costs.

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12Figure 2.4: Operational cost decreasewith PLF increaseOperation ostUSC/kWh4,2-

43,8-~ 0< 800km

1000km3.6 v =1200m-*-1400 kml . 1600km3,4- . 800km

3,61 63 65 67 69 71 73Plant oad actor,%Note: Decrease n the generation ost with the mprovementn the PLFdue to theuse of washedcoal. Operational ost data are calculated or differentdistancesbetweenpowerplant andmine,$1=Rs35.Source: Quingruet al (1991).

Significant investment cost savings can also be realized for new plants if they are designed forfiring washed coal. The equipment affected by the ash content includes:coal receiving, preparation, handling and storage equipment;

3 steam generation;combustion air and flue gas systems;particulate removal system;* flue gas desulfurization system;* bottom ash system; and* waste disposal system including transportation system and disposal area requirements.When designing a plant for lower ash content or for washed coal, the reliability of the coalwashing plant has to be close to 100%. For as long as coal cleaning technology is not widespreadin India and China, and in cases where 100% coal cleaning cannot be guaranteed, it isrecommended that power plant is designed in anticipation of there being no positive influence frorhcoal cleaning. It is also important to strive for a correlation between the contracted coal price andthe quality of the coal.

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COALCLEANINGMETHODSConventional preparation/cleaning involves the separation of coal-rich from mineral-matter richparticles in different size ranges. A simple plant will only separate the coarse sizes, while morecomplex operations undertake separations of coarse, intermediate and fine. Different levels ofcleaninginvolve progressively separating finer size ranges.The physical methods are based on the differences in either density or surface properties betweenthe organic matter and the minerals it contains. A few separation methods which are underdevelopment depend on differences between the magnetic or electrostatic properties of thematerials. Chernical and biological methods have been tested on a small scale, but are not seen ashaving economic potential over the next 5-10 years in connection with power generation and theyare not covered by this guide.Physical coal cleaning may consist of the following stages:

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14Cleaningprocesses produce effluents uch as wastewater and solid residues. Figure 2.5 gives anexampleof how quantitiesand concentrations f effluentsvary for differentmethods.

Figure .5: Effluent rom coal cleaningParliculates Water vaporaDoar

200kt Coa 146ktmhining ooal deaning. deaied coalmining b ~~~~~~~~~~~~~~~~~73Gield41 \ #400kt _ } . 14001ktT -Dra-n.gl wer coaOo kd waste LicuidI Mt _-> Cleaning -90 kt Waste34 toverburden astoge -a 346t

OranageUndergrou.id water 200ktcooa:mNining

SdAd aste Drainagewater

346ktCoal

Source: Couch 1995a).Differentcoal cleaningmethods(described n the Appendix)are comparedregarding he state oftechnology,performance, dvantagesand disadvantages, osts and suitability n Tables 2.4 and2.5.Table2.4: Corn risonof differentcoal clea ing methodMethods Jigs Dense-mediumeparators HydrocyclonesState of technology * Commercial * Commercial * CommercialAdvantages * Large apacity * Good eparation* Inexpensive * Secondmost ommon* Most ommonypeworld methodwideDisadvantages * Lower eparationhan * Smallcapacities * Waterconsumption

dense-mediumCosts * Inexpensive * ExpensiveSuitability * Intermediatefficiency * Fordifficultor most * Forcoarseodevice. ormoderately difficulto clean oal. intermediatedifficulto cleancoal * Specific ravity 1.3-1.9 particles.* Specific ravity>1.5-1.6 * Size: .5-150mm * Size:0.5-150mm* Size: .5-150mm .-

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Table 2.5: Comparison f different coal cleaning methodsMethods Concentrationables Froth lotation Dry cleaningStateof technology * Commercial * Commercial * Closeo commercialAdvantages * Inexpensive * Goodresultson fines * No water required* Good pyrite separationDisadvantages * Quite smallcapacities * Complex * Not for difficult o cleanof 10-15 onslhr; * Poor pyriteseparation coal* Poor dewateringcharacteristicsCosts * Inexpensive * Expensive * Lowerhan wetprocessesSuitability * Used or fine coal * Used or fines. Mainly * Requires asycoal.;containinga greatdeal used or metallurgical size>10mmof pyrite. coals * Roughseparation* Specificgravity>1.5 * Size:


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3. COMBUSTIONECHNOLOGIESThe rapid growth of electric power consumption in India and China callsfor planning and buildingof cost-efficient power plants. Available combustion technologies include conventional PC-firedunits, with subcritical steam data and, hence, moderate efficienciesand supercritical PC units withhigher efficiencies. Pulverized coal-fired technology is the most widely used coal combustiontechnology for boiler sizes up to 1000 MWe. Atmospheric circulating fluidized bed combustion(ACFB) is a relatively mature technology which will likely contribute to new coal-fired units.There are also several new coal combustion technologies i.e. pressurized fluidizedbed combustion(PFBC) and integrated gasificationcombinedcycle (IGCC).In order to be cost-effective, new plants should have high efficiencies, high availability, lowemissions, and produce a by-product that can be utilized, avoiding the need for disposal. Asdiscussedin Chapter 2, the use of washed coal is a first cost-efficient step towards increased plantefficiencyand availability,reduced investment and O&M costs. The use of washed coal with lowash content also reduces the amount of solid waste disposal at the plant. This is further discussedin Chapter 7.A major concern in both India and China is the inefficientuse of coal in the power industry due tolow plant efficiencies (33 to 36%). Older power plants might have efficiencies as low as 25%.Higher plant efficiencieswill reduce the emissions of SO, NO. and particulates and the wasteproduction per MWhb. In addition to these advantages, coal consumption is reduced per MWheproduced. This is illustrated in Figure 3.1 where the hard coal consumption per kWh of electricityproduced is shown as a function of unit efficiency. For example, the figure shows that when theefficiency of a hard coal-fired power plant is increased from 34-42%, coal consumption isdecreased from 0.42-0.34 kg/kWh of electricity produced, or around 20%, if the hard coal has alower heating value (LHV) of 25 MJ/kg. Not only the coal consumption is decreased, butemissions and waste are also reduced by 20%. Another consequence of reduced consuption is thelessened amount of coal being transported on the already overloaded railways.Internationallythe current trend in base load PC-fired power plants is to build large, supercriticalplantswith efficienciesaround 42%, which could be the high efficiencytechnology alternative forIndia and China. This calls for transfer of technology know-how to manufacturers and utilities inIndia and China. As mentioned above, supercritical boilers with increased steam parameters arevery competitive on the international market for large PC plants. Most large PC boilers built inWestern Europe are supercritical. Although the investment cost is higher for a supercriticalboiler,the gains in reduced power generation costs and decreased emissions are obvious. Until recently,steam temperatures have been limited to 540C since high temperature steels, normally used inboilers and turbines, do not allow for higher temperatures. Today, there are materials available atacceptable costs which permit higher steam temperatures. In the future, efficiencies of around50% will be possible with ultra supercritical steam parameters.

17


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18Figure 3.1 Hard coalconsumptfon er kWh of electricityproduced orthree differentcoalswith LHV 20, 25 and 30 MJ/kg

800600- -

500 ~~~~~~~~~20JIkg400 2-25 MJ/kg300 - - - - 30MJAkg200 .~100

20% 30% 40% 50% 60%Net efficiency based on LHV

Pulverized coal-fired units cannot meet moderate emission standards without pollution controlequipment. Since reducing emissions from a PC unit is not without cost, other technologies havebeen developed. The ACFB technology has a low-cost advantage of a wide fuel flexibility and lowemissions of both NO. and SO2. Sulfur is captured directly in the boiler bed and NO,. formation islow due to the low combustion temperature. The drawbacks of today's ACFB technology is thatits waste of mixed ash and desulfiirization products is difficult to utilize. An ACFB plant alsoemits significant amounts of N2 0 which has a potential for global warming. The efficiency isrelatively low due to the use of subcritical steam parameters. Currently subcritical ACFB boilersare commercial in sizes up to approximately 100 MWe. Developmental work is underway onlarger size units, with possibilities for waste utilization and even increasing steam parameters.Market prices are difficult to predict, but a cost comparison between a PC plant equipped withwet FGD and an ACFB plant usually shows a lower investment cost for the ACFB plant.Offering high efficiencies and low emissions, PFBC and IGCC are technologies underdevelopment with few or no commercial plants in the world. Further demonstration is neededbefore they reach commercial status. Improving efficiency in existing power plants must beconsidered as an important, achievable first step to increased, cost-effective power generation.Since plants in India and China currently operate mainly at low efficiencies, there is substantialpotential for improvement. Some of these efficiency improving measures are discussed in Chapter8 on Low Cost Refurbishment.



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PULVERIZEDCOAL COMBUSTIONPulverized coal technology is the oldest and most commonly used technology for thermal powergeneration worldwide. It can be used for boiler sizes up to and above 1,000 MWe. Pulverizedcoal technology requires flue gas cleaning in order to be environmentally friendly, since theemissions of SO2 and NO, become unacceptably high. Fly ash and bottom ash from PC firing canbe used in the buildingindustry. Pulverized coal boilers can be divided into two groups based onsteam data: subcritical PC boilers, where the live steam pressure and temperature are below thecritical values 221.2 bar absolute pressure and 374.15C; and supercritical PC boilers with steamdata above the critical values. The current trend is to increase the steam data in order to increaseplant efficiency.Figure 3.2: A typical PC boiler system

IURNANCEP REHEATEXIT STEAM STEAMCOAL ILC

XBIRNERS FLRNANCE

l PLVERIZER 4, C > FD F1N _ C FLYASHSLOE FD FAN~~~~~~~~~ ~~~~~~~~~~~~~~ ~~~~SL

SuitabilityBoth sub- and supercritical PC boilers can be used for all boiler sizes up to 1,000 MW0. They canbe designed for any coal from lignite to anthracite, but a given boiler must be designed for onetype of coal (lignite, bituminous or anthracite). This means that once designedfor a specific coal,PC units are somewhat more sensitive to changes in fuel quality than fluidized bed combustiontechnology. Uncontrolled emissions from PC firing are high compared to other technologies,which means that emissionreduction equipment is necessary and can be rather expensive.

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SubcriticalPC boilersThe moderatesteam data used in subcriticalPC boilersresults in rather low plant efficiencies. headvantageof subcriticalboilers is that they are fairly simple to operate and maintain, elative oother combustion echnologies.The availability f subcriticalPC-boiler plants is very high as aresultof the simpledesignand long ime experience.SupercriticalPC boilersSupercritical echnology s newer than subcritical. n the industrializedworld, there are now manysupercriticalPC plants in operation, and most plants that are under construction will also besupercritical.There are no supercriticalboilers in operation in India and just a few in China, sothere is limited practical experience n supercriticalPC firing in both countries. Currently, nosupercritical oilersare manufactured n either ndia or China. The efficiencies f supercriticalPCplants are higher than those of subcriticalones and of ACFB plants. When plants with highefficiencyare wanted, supercriticalboilers should be selected. The higher efficiencyhas majoradvantages such as reduced coal consumption nd reduced emissionsof NO., S02, particulatesand waste per MWIICroduced.In boilers operating at high steam temperatures (above 540C), corrosion becomes more of anissue.When highsteam emperatures re used, coals with a high corrosionpotentialare less suitedand shouldbe avoided. Due to the more complexdesign of supercritical oilers, he requirementson O&M routinesare higher han those for a subcriticalboiler. Also the demandson water qualityand instrumentation nd controls (I&C) equipment re high.State of technologySubcritical boilersSubcriticalPC boilers have been used for more than 50 years. Unitsizes vary from less than 100to above 1,000MNWe.he technology s well proven and hur.dredsof units are in operation inIndia and China.SupercriticalboilersThe technology s well-proven n the industrializedworld with more than 200 units in operation.There are no supercritical oilers in operation in India today (Ref 1). In China here are only asmallnumberof supercritical lants; hey includeShanghai 2x600MNWe);iaoning 2x500MWV),and Hebei (2x500MWe), llbuilt in the 1990s(Ref. 2).Future developmentThe major future technical development will be to increase efficiencies and improve theenvironmentalperformanceof PC boilers. Improvement n efficiency s achieved by increasingsteam conditionsand potentially y the introductionof doublereheat. To date, the use of ferriticmaterials has limited steamtemperatures o 5400C. Higher steam temperaturesused to requireausteniticmaterials. Development f new ferriticmaterialnow allows steam conditionsup to 248bar and 593C. Plants with steamnata of 300 bar and 580-600C re currentlyplanned.

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Plant sizeUnit sizes over 1,000 MWeare possible. Normal sizes for new units are 250-600 MWe. Currently,all units being installed in India are either of 210-250 MWVor 500 MWe capacity. In China, largeboilers of 300 MWe and 600 MWe are projected.Fuel flexibilityPulverized coal-firing technology can handle a wide range of coals, from anthracite to lignite.However, combustion stability problems might occur if high ash and moisture coals are fired.Anthracite firing requires special boiler design due to the very low volatile compound content. Fora particular plant, the boiler and auxiliaryequipmentmust be optimizedfor its design-specificcoal.The flexibility or each PC boiler to handle a range of coal qualities is limited. Table 3.1 belowshows the limits for some coal parameters for a normal PC boiler.

Table3.1: Limitsfor coalparameters or PC boilerdesigned ornormalbituminouscoalCoalparameter Limit approximate alues)Lower HeatingValue >20 MJ/kgAsh content 1,100CMoisture


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Figure 3.3: Plant net efficiency increase achieved by increasing steam parameterNet efficiency50-49. Steam dab_ . | :3;ll~~~~~~~~~~Iar48 i+3,2% 700/720C4746- 45 ________ |I +1,0% Improved urtne

4 +12% Double reheat l43 +1 3M Increased steam data43 - ~~~~~~270ar sta dt

42- 585100C41 Suiercrtical

+4,5% 545i545'C I i40 - Ii39 -II38- Subcritical I37 ba40tr36 ondensor oressure.05 bar |Conventionalcoal fired I upercritical high temperaturepower plants IUltrasuper criticalpowerplants %A=r r1I1ntcNote: Thisdiagram hows ormal et efficienciesn conventional owerplants left),the efficiencies in supercritical igh temperatureplants (middle) and future efficienciesof ultra supercritical ower plants (right).Source: VGBKraftwerkstecknik1996).

Load rangeThe minimum oad is in the range of 25-40% of maximum continuous rating. However, oil or gasmight be required as a support fuel in this low load range. The practical limit for commercial partload operation is usually at a load determined by the need to introduce oil or gas firing to maintainPC combustion stability. This boundary is determined by the fuel composition and boiler islanddesign, but normally occurs between 40 and 60% of maximum continuous rating.Load change rateChanges of load (ramping) can be extremely rapid at up to 8% per minute. However, a normalload change rate required by the grid for coal-fired plants is circa 4% per minute within the wholeload range.Start- up timeCold start: 4-8 hours depending on type of circulation; once through is the fastest;natural circulation requires the longest time.Restart of a hot unit: 1-1.5 hours.

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Environmental performanceSulfur: Corresponds o the sulfurcontent of the coal.Particulates: 10-25mg/Nm usingESP or bag filter.NO.: New bituminous oal-firedboilerscan be designed or NO, emissions rom150-250mg/MJf,,l f the boiler is equippedwith low NOx burners;anthracite-fired oilersmay produce emissions round 500 mg/MJfi,,,.

Fig 3.4 below shows the uncontrolledNOx emission rom coal combustiondependingon firingtechniqueand boiler size. Note that burnerswith new source performancestandards(NSPS) forwall-firedboilers,using staged combustionwhich produces ower NO. emissions han pre- NSPSburners,have been developed.Figure3.4: Effect of boiler iring types and unitsize onuncontrolledNOxemission rom coal-firedplantsNOxemis orn,mg/MJ

1000 wall-firedwet bottom_w ~~~~cyclone

/ , z ~~pre-NSPS750.-

roof-fired

500 -= = r ~~~~tangentialy fi red

250-

0 100 200 300 400 500 600 700 8W0Unit apacity, WeSource: Takeshita1995).

WasteproductionPC-firingproduces fly ash (80-95% of the total ash flow) and bottom ash (5-20%). The ash isproducable without further treatment and can be used in the building or cement industry.Chapter3. CombustionTechnologies


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24However, t is important hat the content of unburnt carbonin the ash is low (normally ess than5%). Ash utilization s further developed n Chapter7.AvailabilityAvailabilityigures are high both for subcriticaland supercriticalplants. The availability s in therange of 86-92%, ncluding lannedoutages of 4 weeks per year.Construction issuesConstruction timeThe normal construction time is 36 months from contract award to commercial operation.Becauseof the large boilersizes, most of the plant has to be erected on site.Possibilitiesfor domestic manufacturing! licensing agreements for subcritical boilersBoth India and Chinahave very experiencedmanufacturersof subcriticalPC boilers. There arealso some licensing greementsbetween arge boiler manufacturers n industrialized ountriesanddomesticmanufacturers n Chinaand India (Ref. 1 and 2).Possibilities or domestic manufacturing! licensing agreementsfor supercritical boilers.Chinese boiler manufacturersdo not currently have the capability o design and manufacturesupercritical oilers. Cooperationactivitiesbetween internationaland Chinese manufacturers reunderwayand localmanufacturingwillbe possible n the near future (Ref.2). Supercritical oilerscannot be manufacturedcurrently n India, but international companies are investing in localmanufacturing Ref. 1). Already,part of a PC plant with a supercritical oilercan be manufacturedlocally f the design s carriedout by an internationalmanufacturer.

MaintenanceNormally, yearly overhaulperiod of four to five weeks is required. Equipment hat needs morefrequent maintenancedue to excessivewear and tear, such as coal pulverizers,must be maderedundant.Units with drum boilers can be maintainedby ordinarymaintenance ersonnel. Someparts in supercritical nce through boilers equire maintenance y specially rainedstaff.Complexityof technologyThe design of a power plant with PC boilers has a low degree of complexity.A unit consists ofboiler, urbine,fuel and ash handlingequipment nd flue gas cleaningequipment.A subcriticalPCunit with a drum boiler is fairlysimple o operate because the drum serves as a water magazineand compensates or deviationsbetween he firing rate and the feedwatersupply.This makes loadchanges airlyeasy o control.In a once-through upercritical oiler, the firing ate must alwaysbe in balancewith the feedwatersupply. Evaporation surfaces and superheatersmight otherwise become dry with no water orsteam in them. This kind of drying damages the surfaces. That makes the operationof once-throughboilersmore complex han that of drum boilers.

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CostsInvestment costsThe investment cost ranges from 1,000-1,600 USD/kWe for subcriticalboiler plants for unit sizesbetween 75 and 600 MWe. In Figure 3.5, the cost is given for a complete one-unit plant thatincludes everything from fuel storage to waste handling. No emission reduction equipment isincluded with the exception of low NO. burners. The investment cost for a boiler only amounts toapproximately 30% of the investment cost for a complete plant. Supercritical boiler plants areonly slightly more expensive (around 5%) than subcritical, if steam temperatures are kept atordinary levels. The cost is highly dependent on the state of the market, the size of the plant,number of units, the extent to which manufacturing can be carried out in low wage rate areas etc.

Figure 3.5: Investment costs or PC-boiler plants1600

0 1500-1400-X 1300-C 1200-0E 1100

1000-900-i) 800-0acL 700-600 0 100 200 300 400 500 600

Unit net electric output MWeNote: Investmentcosts for PC boiler plants including everything rom coalstorageandhandling o wastehandlingexceptemission eductionequipment.Source: US Dept. of Energy (1994).

Operation and maintenance costsIn Table 3.3, O&M costs for various sizes of PC boiler units are listed (Ref 5). The costs includethe boiler system, steamturbine system and auxiliarysystems.



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Table3.3 O&M osts or PCboiler units includingsteam urbinesystem and balancef plantUnit size Fixed O&M costs Variable O&M costsMW. USDlkWlyr UScentslkWh500 27 0.2150 36 0.575 53 0.6Source: USDeptof Energy1994).

A 200-MWePC plantFigure 3.6 shows a 200-MW subcritical ower plantwithout any flue gas cleaningequipment ndFigure 3.7 shows a supercriticalPC plant. The reduction n waste production,emissionsand coalconsumption hat are achievedby increasingplant efficiency re shown by comparingFigure 3.6and Figure 3.7.Figure3.6: 200-MW,ubcriticalplant withoutanypollution control equipment

200 MWe I _v ~~~~S02:.2 t/hBottomash:2.6 /h NOx:0.6 tlhr s ~~~~~~~~~~~~~~~Dust:4 t/h( 4~~~~~~ ~C02:20 /h

b ooling ater: 0 000 lh

Note: Data used - efficiency= 37%; sulfurcontent,S= 2%; ash content=32.8%.

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Figure3.7: 200-MW,supercritical plant without any pollution control equipment

Col3 t200 MWe ,

4S02:.9hBottom ash: 2.4 t/h NOx: 0.5 t/hC02: 200 tVh

Note: Data used -- efficiency= 41%;sulfur content,S= 2%; ashcontent=32.8 %.

Screening criteriaTables 3.4 and 3.5 are used for the technology screening in Chapter 9.Table3.4: Screening criteria forsubcritical boiler unitsMaturityof technology * More han 100 units n operation n India andChina,respectivelyMaxunit size . Over 1,000-MWe etWasteproduct * Possible o usewithout processing

Table 3.5: Screening criteria for supercrtical boiler unitsMaturityof technology * More han 100 units n operation n the world;none n Indiaand ess han 5 in China.Max unit size * Over 1,000-MWenetWaste product * Possibleo use withoutprocessing



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ATMOSPHERIC IRCULATINGLUIDIZED EDCOMBUSTIONAtmosphericcirculating fluidizedbed combustion s a relativelynew combustion technologywhich has been used most commonly in small-scale plants of less than 100 MWe. The technologyhas some major advantages including low emissions of SO. and NO,. Sulfur can be captured cost-effectively and directly in the furnace by limestone injection.

SuitabilityACFB boilers have an extremely high fuel flexibility and will accept a very wide range of differentfuels including low grade fuels. SO, emissions are low since sulfur can be captured directly in thefurnace by limestone injection. Because of the low combustion temperatures (circa 850C) theNO. emissions are comparatively low. However, significant amounts of N20 emissions have beendetected from ACFB boilers. Currently, all ACFB plants use subcritical steam data which meansthat plant net efficiencies are relatively low compared to those of supercritical PC boiler plants.The amount of waste is larger than for PC boiler units and a major drawback is that with currentstandards, there are only limited means to utilize the waste produced. Normally the investmentcost for a ACFB plant is lower than that of a PC boiler plant equipped with wet scrubber for fluegas desulfurization.There are only a few companies in the world supplying large ACFB boilers today. The technologyis commerciallyviable for boiler sizes up to 100MWe.State of technologyDuring the past ten years, fluidized bed technology has been extensively used for burning low-grade fuels in small plants. ACFB plants are commerciallyviable in sizes up to 100 MWe. Its useat a utility scale to date is limited. Currently, the largest plant in operation is rated at 250 MWe,although plants in sizes up to 350 MWe are under construction. There are less than 10 ACFBboilers with an output of 100 MWe or more in operation in the world.There are numerous small-scale fluidized bed boilers in operation in India today, but no largeACFBs (Ref 1). In China, there are numerous small-scale fluidized bed boilers, but almost nolarge-scale units. In Neijang Power Station, Sichuan Province, a ACFB boiler with a capacity of100 MWV upplied by an international supplier was commissioned in 1996 (Ref 2). There are alsoa number of ongoing projects in China for 50-MWe ACFBs. Today's ACFB boilers usesubcritical steam data and, hence, plant efficienciesare moderate.Future developmentA major future development of ACFB technology is scaling up to larger unit sizes in order toprovide utilities with a complete range of unit sizes. Sizes up to 650 MWVare currently planned.By-product utilization and N20 emissions are other issues that are being investigated. The use ofhigher steam data to compete with PC plant efficiencies ies in the future.



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Figure3.8: TYDpical CFBboilerplantFeed-water Cyclones

Turbineffeea o; - Arhatertack|_l

: V F~~~~~~~~~~~~~~~~D fanL

Coalsilo Limestoneiloe yasaryairlyash ecircuIatioIDpread~ ~ ~ ~ ~ ~ ~ ~~~rmoa|a Coalsio CoLieesngan fas

i1 fI~~~~~~~~Sreaduer fanJ.sil,S,e...Scondaryir 5n.eIfeder ' -Coal S Ash

S.~ recculationPiayair,.rTramp-material bres[rmr~' separator Fluidized-bedchamberBe-s

J!q ~ ~~~~~~~~~ ~~~~~~reinjectioiemovalWe-sBed-ashemoval revaCoalcrusherSource:Coalndustry dvisory oard1995).

co


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30PlantsizeToday, ACFB boilers are common in sizes below 100 MW.. Unit sizes up to 250 MWe are inoperation. However, he major internationalACFBsupplierwill offer commercialguarantees orunits up to 400 MWe. n the future, unit sizesup to 650 MWVwill be available.Fuel flexibilityThe fuel flexibilityof ACFB boilers is extremelywide, probably the widest of any powergeneration echnology.One singleboiler can be designed or a wide range of fuels. Various ypesof fuels such as biomass, peat, lignite, and hard coal can be burned in the same ACFB boilertogether or separately.Even coal cleaningwastes can be fired in a ACFBboiler. Table 3.6 showsthe possiblevariations n some chosen coal parameters or a normal ACFB boiler equippedwithfluegas ecirculation.

Table 3.6 Acceptablevalues for some coalparameters or normalACFB boilerwith flue gas recirculationCoal parameter Limit (a proximate values)LowerHeatingValue >5 MJ/KgAshcontent 900CMoisture


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Start-up tmeCold start: 8 - 12 hours depending n type of circulation.Restart of a hot unit: I - 1.5 hours.Restart after a weekendshut-down: 2 - 3 hours.EnvironmentalperformanceNO,: 80-150mgfMJfuel or bituminous oal withoutNO, reductionequipment.N20: significant missionsof N20 have been observed.Particulates:10-25mg/Nmwith ESP or bag filter.Sulfur: 90-95%removalof sulfur.Sulfur is captured in the bed by the injectionof limestone. The sulfur removalrate is highlydependenton the sorbent to sulfurratio (Ca/S). Increased sorbentto sulfur ratio improvestheS02-removal.At a Ca/S ratio of 2, a 90% sulfurremoval is possible.At a slightlyhigher Ca/Sratio, 95% sulfur removalis feasible. However, at higher sorbent ratios the sorbent utilizationdecreases, esulting n increasedsorbent consumption nd higheroperatingcosts.Figure 3.9 showsthe cost for the last ton of sulfur removed in a ACFB boiler. The molar ratiobetweencalciumand sulfur ncreasesdrasticallywithincreasing ulfur emovalefficiency.

Figure 3.9 Costs or last ton of sulfur removedas a functionof the sulfur removalefficiency16001400

i 1200:,l 1000

800o 600

400200

0% 20% 40% 60% 80% 100%Sulfur removal efficiency

Note: The imestonecost used s 20 USDper ton.



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WasteproductionSolid residues from ACFB combustion using limestone injection for SO2 control consist of amixture of coal ash oxides, calcium sulfate, high levels of lime (CaO) and low levels ofcarbonates. Of the residues, 80-90% are removed as fly ash and the rest as bottom ash. Today,ACFB wastes normally are landfilled. Development work on the use of ACFB wastes is ongoing.AvailabilityAvailability data is limited, but a sample of five fluidized bed boilers in the size range 80-160 MWeincluding both bubbling and circulating beds, all less than six years old, shows an averageavailabilitybetween 87-88% with planned outages of 4 weeks per year.Construction ssuesConstruction timeThe construction time for a ACFB plant is 36 months- from contract award to commercialoperation. Because of the large boiler sizes, most of the plant has to be erected on site.The possibilitiesfor domestic manufacturingToday, BBEL in India manufactures ACFB boilers with an output of 30 MVe. Some Chineseboiler manufacturers cooperate with foreign companies in order to implement the ACFBtechnology in China.Complexityof technologyThe complexity of the design of a power plant with ACFB boilers is low compared to that of, forexample, an IGCC plant. A unit consists of a boiler, a turbine, fuel and ash handling equipmentand flue gas cleaning. The operation of a ACFB boiler plant is more complex than that of a PCboiler plant. The temperature in the fmrnacemust be kept within a narrow span in order to ensureas efficient sulfur reduction. The distribution of air to the furnace must be well controlled.MaintenanceNormally, a yearly overhaul period of four to five weeks is required. The manufacturingcompanies provide regular inspection and maintenance services to their clients.CostsInvestment costThe investment cost for a ACFB boiler plant lies in the range of 1,300-1,800 USD/kW

planners guide for clean coal technology for power plants

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