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Since its first use in the early twentieth century, pulverised coal combustion (PCC) has maintained a dominant role in power generation from coal, and currently represents over 90% of global capacity. Circulating fluidised bed combustion (CFBC) is a more recent boiler technology whose higher tolerance to fuel quality has favoured niche application in small-scale and industrial power generation, often firing unconventional fuels such as waste coal and biomass. Despite also attaining status as a ‘cleaner’ coal technology due to more easily controllable NOx and SOx emissions, use of CFBC at the utility scale has long been restricted by smaller boiler sizes and lower efficiencies than PCC. However, scale-up and optimisation over the last ten years have allowed CFB boilers to benefit from economies of scale and begin to provide a viable alternative to PCC for utility power generation. Crucial to this progress has been the successful operation of the first supercritical CFB boiler at Lagisza power plant in Poland. In China, even 300 MW subcritical CFB boilers have managed to capture around 10% of the country’s rapidly growing coal capacity, and the recent commissioning of the world’s largest supercritical CFBC unit at 600 MW may mark the beginning of similar growth at this scale. Elsewhere, ongoing construction of a multiple unit 4400 MW CFBC plant in South Korea is further evidence that this technology may be in the process of acquiring a more prominent share of global coal power. Of the two advantages associated with CFBC, fuel flexibility has become the principal impetus for recent utility projects, as increasingly deregulated markets have encouraged utilities to seek cheaper fuel sources and the ability to easily change supply has become more attractive. Several recent power plants in the USA have employed CFBC as a means of cofiring locally available ‘opportunity fuels’ such as petcoke and waste coal, whilst in China the technology is seen as ideal for firing high-ash anthracite and lignite, as well as waste coal. In Poland, two major CFBC utility projects have been aimed at firing lignite and bituminous coals with variable properties or a tendency for slagging. Conversely, South Korea’s dependency on imported coal has made CFBC an attractive option for acquiring flexibility in the global coal market and avoiding dependence on a single supply chain. Aside from being the sole means of firing some challenging fuels, CFBC can therefore also provide a significant financial saving on fuel costs for plants which are in a position to switch or supplement supply with a cheaper alternative when necessary. On the other hand, the low NOx emissions and in situ desulphurisation capability of CFBC primarily represent a means of reducing plant capital expenditure by avoiding the costly installation of selective catalytic reduction (SCR) and wet flue gas desulphurisation (FGD). Estimation of PCC and CFBC plant costs for general, equivalent cases is challenging, but assessments from the past few years clearly indicate a closing of the financial gap between the two technologies as larger and more optimised CFB boilers have become available. Nevertheless, CFB boiler costs have remained higher, and the substantial savings derived from avoiding SCR and wet FGD installations are therefore significant in staying economically competitive with PCC plant. For this reason, future growth of the CFBC market share could be hindered by increasingly strict emissions limits which challenge the levels of desulphurisation practically achievable by addition of limestone to the furnace. All large CFB boilers in the USA have been obliged to add a form of downstream FGD, and it is likely that the recently introduced limit of 100 mg/m 3 in China will require similar investment. Whilst SNCR has proved sufficient NOx control for existing CFBC plant in regulated regions, the incorporation of SCR with four 550 MW boilers in South Korea suggest that this saving may also be lost for larger boilers and very low NOx limits. Operational cost savings associated with flue gas treatment in CFBC plant are small due to the less efficient use of reagents compared to SCR and wet FGD processes. However, addition of limestone to the CFB boiler also has the undesirable side effect of producing a much larger quantity of solid waste which has unsuitable chemistry for use as a cement substitute. This is in contrast with the separate streams of relatively saleable fly ash and gypsum produced by a PCC boiler with wet FGD. CFBC ash has instead been widely used for mine reclamation activity, but has also proved suitable for lower value construction applications such as as flowable fill and road base, or as a Profiles No 13/14 November 2013 Techno-economic analysis of PC versus CFB combustion technology IEA Clean Coal Centre is a collaborative project of member countries of the International Energy Agency (IEA) toprovide information about and analysis of coal technology, supply and use. IEA Clean Coal Centre has contracting parties and sponsors from: Australia, Austria, Brazil, Canada, China, the European Commission, Germany India, Italy, Japan, Republic of South Korea, New Zealand, Poland, Russia, South Africa, Switzerland, Thailand, the UK and the USA.
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PC VERSUS CFB
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Since its first use in the early twentieth century,pulverised coal combustion (PCC) has maintained adominant role in power generation from coal, and currentlyrepresents over 90% of global capacity. Circulatingfluidised bed combustion (CFBC) is a more recent boilertechnology whose higher tolerance to fuel quality hasfavoured niche application in small-scale and industrialpower generation, often firing unconventional fuels such aswaste coal and biomass. Despite also attaining status as a‘cleaner’ coal technology due to more easily controllableNOx and SOx emissions, use of CFBC at the utility scalehas long been restricted by smaller boiler sizes and lowerefficiencies than PCC. However, scale-up and optimisationover the last ten years have allowed CFB boilers to benefitfrom economies of scale and begin to provide a viablealternative to PCC for utility power generation. Crucial tothis progress has been the successful operation of the firstsupercritical CFB boiler at Lagisza power plant in Poland.In China, even 300 MW subcritical CFB boilers havemanaged to capture around 10% of the country’s rapidlygrowing coal capacity, and the recent commissioning ofthe world’s largest supercritical CFBC unit at 600 MWmay mark the beginning of similar growth at this scale.Elsewhere, ongoing construction of a multiple unit4400 MW CFBC plant in South Korea is further evidencethat this technology may be in the process of acquiring amore prominent share of global coal power.Of the two advantages associated with CFBC, fuel
flexibility has become the principal impetus for recentutility projects, as increasingly deregulated markets haveencouraged utilities to seek cheaper fuel sources and theability to easily change supply has become more attractive.Several recent power plants in the USA have employedCFBC as a means of cofiring locally available ‘opportunityfuels’ such as petcoke and waste coal, whilst in China thetechnology is seen as ideal for firing high-ash anthraciteand lignite, as well as waste coal. In Poland, two majorCFBC utility projects have been aimed at firing lignite andbituminous coals with variable properties or a tendency forslagging. Conversely, South Korea’s dependency onimported coal has made CFBC an attractive option foracquiring flexibility in the global coal market and avoidingdependence on a single supply chain. Aside from being the
sole means of firing some challenging fuels, CFBC cantherefore also provide a significant financial saving on fuelcosts for plants which are in a position to switch orsupplement supply with a cheaper alternative whennecessary.On the other hand, the low NOx emissions and in situ
desulphurisation capability of CFBC primarily represent ameans of reducing plant capital expenditure by avoidingthe costly installation of selective catalytic reduction(SCR) and wet flue gas desulphurisation (FGD).Estimation of PCC and CFBC plant costs for general,equivalent cases is challenging, but assessments from thepast few years clearly indicate a closing of the financialgap between the two technologies as larger and moreoptimised CFB boilers have become available.Nevertheless, CFB boiler costs have remained higher, andthe substantial savings derived from avoiding SCR and wetFGD installations are therefore significant in stayingeconomically competitive with PCC plant. For this reason,future growth of the CFBC market share could be hinderedby increasingly strict emissions limits which challenge thelevels of desulphurisation practically achievable byaddition of limestone to the furnace. All large CFB boilersin the USA have been obliged to add a form ofdownstream FGD, and it is likely that the recentlyintroduced limit of 100 mg/m3 in China will require similarinvestment. Whilst SNCR has proved sufficient NOxcontrol for existing CFBC plant in regulated regions, theincorporation of SCR with four 550 MW boilers in SouthKorea suggest that this saving may also be lost for largerboilers and very low NOx limits.Operational cost savings associated with flue gas
treatment in CFBC plant are small due to the less efficientuse of reagents compared to SCR and wet FGD processes.However, addition of limestone to the CFB boiler also hasthe undesirable side effect of producing a much largerquantity of solid waste which has unsuitable chemistry foruse as a cement substitute. This is in contrast with theseparate streams of relatively saleable fly ash and gypsumproduced by a PCC boiler with wet FGD. CFBC ash hasinstead been widely used for mine reclamation activity, buthas also proved suitable for lower value constructionapplications such as as flowable fill and road base, or as a
ProfilesNo 13/14 November 2013Techno-economic analysis of PC versus CFB
combustion technology
IEA Clean Coal Centre is a collaborative project of member countries of the International Energy Agency (IEA)to provide information about and analysis of coal technology, supply and use. IEA Clean Coal Centre has contractingparties and sponsors from: Australia, Austria, Brazil, Canada, China, the European Commission, Germany India, Italy,
Japan, Republic of South Korea, New Zealand, Poland, Russia, South Africa, Switzerland, Thailand, the UKand the USA.
lime substitute in waste stabilisation and soil amendment.High efficiency and reliability are also important
criteria which must be met by CFBC for its widespreadadoption for utility power plant. The move to supercriticalsteam conditions first implemented at Lagisza representsthe most significant advance in increasing CFBC thermalefficiencies, with the 43.3% (LHV) efficiency reached bythis plant competitive with equivalent PCC boilers.Relatively high auxiliary power consumption associatedwith fluidisation air fans remains the principal barrier toraising CFB efficiencies, but research in China has shownthat reductions can be achieved by minimising the bedmaterial whilst optimising the fluidisation state. Thistechnique has also proved useful for reducing erosiondamage which can afflict CFB boilers with some fuels.Although generally regarded as highly tolerant to high ashloadings, many early utility CFBC units have sufferedseverely reduced availability as a result of both ash erosionand agglomeration. As experience with the technology atlarge scales has grown, many of these problems appear tohave been resolved by improved design and operationalpractice, and highly reliable operation has been achievedby boilers firing conventional fuels. However, maintainingsuch optimum levels of reliability and efficiency for largeunits is likely to require the sacrifice of some degree offuel flexibility.
As international policy moves towards mitigating theCO2 emissions from power generation, biomass cofiringand carbon capture technologies are two developmentswhich will have an increasing impact on coal plants and inwhich CFBC could play an important role. In contrast toits role in coal-firing, CFBC is an established technologyfor biomass-firing, and many of the recent utility CFBboilers have incorporated the capability of burning up to20% biomass with little design alteration required. On theother hand, as the practice of co-firing biomass in PCCrapidly grows and experience is gained, it appears that themore established boiler technology will become equallycompetitive for cofiring wood wastes for which relativelystandard PCC equipment can be used. CFBC isnevertheless likely to retain an advantage for difficult highslagging biomass types such as agricultural wastes.Oxyfuel combustion, in which elimination of nitrogen
from the furnace produces a more easily captured streamof relatively pure CO2, is emerging as one of the mostviable carbon capture technologies. Both oxyfuel PCC andCFBC have been successfully tested at the pilot scale, butit is thought that CFBC may have greater potential forcombustion at higher oxygen concentrations, thuseconomising on boiler size. Research into the viability ofthis idea is in its early stages, and both boiler technologiesawait scaling up to the demonstration plant scale.
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2012201020082006200420021994 2016
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Foster Wheeler
Alstom
Harbin
Dongfang
Gardanne
Northside
Sulcis
Baima
Lagisza SC
Baima SC
Samcheok SC550
500
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300
The scale-up of CFB boiler capacity in the last twenty years, with significant plants labelled
Each issue of Profiles is based on a detailed study undertaken by IEA CleanCoal Centre, the full report of which is available separately. This particularissue of Profiles is based on the report:
Techno-economic analysis of PC versus CFB combustiontechnologyToby LockwoodCCC/226, ISBN 978-92-9029-546-4, 69 pp, October 2013
This report is free to organisations in member countries.£100 to organisations in non-member countries for six months afterpublication, and free thereafter.
Gemini House10-18 Putney HillLondon SW15 6AAUnited Kingdom
Tel: +44 (0)20 8780 2111Fax: +44 (0)20 8780 1746e-mail: [email protected]
> Internet: www.iea-coal.org
SC - supercritical
