Prospects for upgrading coal-fired power plants Herminé Nalbandian, Anne M Carpenter CCC/41 December 2000 Copyright © IEA Coal Research 2000 ISBN 92-9029-353-5 Abstract Upgrading ageing power plants can be a cost-effective option for extending their residual life, increasing capacity, efficiency and performance, reducing operating and maintenance costs, enhancing reliability and availability, and/or securing compliance with stricter environmental legislation. This report discusses the prospects and market opportunities for upgrading conventional pulverised coal-fired plants. It covers the retrofitting and upgrading of pulverisers and their fuel distribution system, particulate control, flue gas desulphurisation, and NOx abatement and control measures. Process optimisation to minimise pollutant formation and improve boiler efficiency is also described. The two repowering options covered are circulating fluidised bed boilers and the integration of a natural gas turbine to form a combined cycle. A case study of a refurbished or repowered plant for each of these options is included. However, the requirements and technical condition of each power plant are likely to be different. Each candidate plant therefore requires detailed technical, economic, financial, legal and environmental analyses before any major performance improvement plan is proposed. Acronyms and abbreviations A/C air to cloth ratio SIP State Implementation Plans (USA) BACT Best Available Control Technology SKB South Kalimantan Basin (Indonesia) CAAA Clean Air Act Amendments (USA) SNCR selective non-catalytic reduction CEC Commission of the European Communities SOAPP State-of-the-Art Power Plant CEM continuous emissions monitoring T/R Transformer/Rectifier CFB circulating fluidised bed UNECE United Nations Economic Commission for CFBC circulating fluidised bed combustion Europe CFD computational fluid dynamics VOC volatile organic compound(s) CIA carbon-in-ash CIS Commonwealth of Independent States (Russia, Ukraine, etc) COHPAC Compact Hybrid Particulate Collector DBA dibasic acid DCS digital/distributed control system EC European Commission EDF Electricité de France (France) EPA Environment Protection Agency (USA) EPRI Electric Power Research Institute (USA) ESP electrostatic precipitator(s) FBC fluidised bed combustion FBHE fluidised bed heat exchanger FF fabric filter(s) FGD flue gas desulphurisation GNOCIS Generic NOx Control Intelligent System HGI Hardgrove Grindability Index HP high pressure HRSG heat recovery steam generator(s) IPPC Integrated Pollution Prevention and Control LCPD Large Combustion Plants Directive L/G liquid to gas ratio LIFAC Limestone Injection into the Furnace and reActivation of Calcium LHV lower heating value LNB low NOx burners LOI loss on ignition LP low pressure LRTAP Long-Range Transboundary Air Pollution MIMO Multi Input/Multi Output MP medium pressure MWe megawatt electric MWth megawatt thermal NEC national emission ceilings NOx nitrogen oxides (NO and NO2) NSR normalised stoichiometric ratio NSR New Source Reviews (USA) NSPS New Source Performance Standards OFA overfire air pc pulverised coal PC personal computer PJBH pulse jet baghouse PLC programmable logic controller PRB Powder River Basin (USA) PSD Prevention of Significant Deterioration (USA) RH reheater SCR selective catalytic reduction 2 IEA Coal Research Contents 1 Introduction 5 2 Why upgrade? 6 2.1 The need to upgrade 6 2.2 Factors to be considered 7 2.3 Emission legislation 10 2.3.1 International and bilateral agreements 10 2.3.2 National standards 12 3 Opportunities for upgrading 15 3.1 Country survey 16 3.2 Questionnaire results 19 4 Milling and fuel distribution system 23 4.1 Pulverisers 23 4.1.1 Mill upgrade at Talcher power plant 23 4.1.2 Rotary classifier upgrade 24 4.1.3 Fuel switch in fan mills 26 4.1.4 Mill inerting 26 4.2 Coal and air distribution system 27 5 Primary pollution control 30 5.1 Process optimisation 30 5.2 Low NOx burners and overfire air 35 5.2.1 Retrofitting 36 5.2.2 Prospects 38 5.3 Reburning 39 5.3.1 Retrofitting 39 5.3.2 Prospects 41 6 Secondary pollution control 42 6.1 Particulate control 42 6.1.1 Electrostatic precipitators 42 6.1.2 Other particulate control technologies 46 6.2 Flue gas desulphurisation 47 6.2.1 Wet scrubbers 48 6.2.2 Spray dry scrubbers 51 6.2.3 Sorbent injection systems 52 6.3 Flue gas treatment for NOx control 54 6.3.1 Selective non-catalytic reduction 54 6.3.2 Selective catalytic reduction 56 7 Repowering 60 7.1 Circulating fluidised bed boilers 60 7.1.1 Why repower with CFB boilers? 60 7.1.2 Turów power plant 63 7.1.3 Prospects 64 7.2 Adding gas turbines 65 7.2.1 Why add gas turbines? 65 7.2.2 Modes of repowering coal-fired boilers 65 7.2.3 Prospects 70 8 Conclusions 73 9 References 76 Appendix 1 84 Appendix 2 89 Prospects for upgrading coal-fired power plants 3 4 IEA Coal Research 1 Introduction There are over 1600 pulverised coal (pc)-fired power plants for various countries on the size, age and pollution control in the world (>4000 units) with a total capacity of more than capability of their major coal-fired units is given in 1000 GWe currently in operation (to end 1999) accounting Chapter 3. The results of a questionnaire sent to selected for almost 40% of total electricity production. As plants age electric utilities and equipment manufacturers to determine they tend to become less reliable. Their performance and where they see the prospects for upgrading are also included. efficiency decline, and operating and maintenance costs increase. Derating of the plant due to equipment ageing and Coal pulverisers are critical elements of successful efforts to changes in operating regimes may also have occurred. The reduce operating costs of power plants, meet emission control power plants may be burning coals for which they were not requirements and provide boiler system flexibility. The size originally designed, further affecting their performance. distribution of the pulverised coal affects the combustion Current environmental legislation is usually stricter than in efficiency and hence the amount of unburnt carbon in fly ash, the past; consequently older power plants may not be meeting and the stability of the combustion process. The upgrading of the new environmental requirements. Options to continue pulverisers and the transport of the pulverised coal to the cost-effective power generation from these ageing units burners are described in Chapter 4. include: ● retirement and replacement with new capacity; Primary pollution control measures, that is at the combustion ● upgrading to extend their life; stage, are covered in Chapter 5. This chapter also discusses ● repowering, for example, by adding modern gas turbines process optimisation which can improve plant efficiency, as to produce more electricity than the original design. well as helping to lower emissions. Process optimisation is probably the most cost-effective approach for making This report will look at the last two options. Trends in the improvements in the short term. Retrofitting pollution control planning and construction of new power plants have been equipment for treating the flue gas downstream of the boiler discussed in other reports produced by The Clean Coal is discussed in Chapter 6. One of the driving forces for Centre (Couch, 1997, 1999). retrofitting pollution control is to meet stricter emission regulations. For example, the USA is currently undergoing a In this report, the terms upgrading, retrofitting and major retrofit programme, especially for NOx, in order to repowering will be used to describe modifications that may achieve compliance with the 1990 Clean Air Act be made at existing power plants. Upgrading (also called Amendments. Technologies for controlling CO2 emissions rehabilitation or refurbishment) is used to describe the non- are not yet in widespread commercial use and are therefore routine replacement of components, such as pulverisers, not covered in this report. More information on reducing CO2 burners, superheater tubing, turbine blading or other items, emissions can be found in The Clean Coal Centre reports by with the specific intention of improving the efficiency, Smith (1999) and Vernon (1999). increasing potential output or extending the useful life of an existing system. Retrofitting is limited to the installation of Repowering existing power plants with circulating fluidised modern pollution control or abatement devices in order to bed (CFB) boilers or by integrating a gas turbine to form a meet emission limits provided it does not involve making combined cycle is covered in Chapter 7. There are cases major changes in plant design. Repowering involves much where it may be more cost-effective to install CFB boilers, more substantial changes to the plant. These changes might such as when emission limits need to be met and there is no involve complete replacement of major systems such as room to fit flue gas desulphurisation equipment. This option boilers or turbines, and often includes significant changes to is most feasible when low cost coal, especially low grade cycle design. Conversion to combined cycle operation, and coal, is available to justify the heavy investment in a new the introduction of fluidised bed combustion (FBC) boiler. As well as reducing CO2 emissions, adding natural technology comes into this category. Repowering projects are gas-fired turbines can increase plant capacity. typically more extensive than upgrading, are more expensive and require a longer period of plant inactivity when no A case study for each of the options discussed in the report is revenue is being generated. included in each chapter, where appropriate. However, the upgrading requirements of each power plant are likely to be This report will discuss the prospects for upgrading different and so solutions will be site specific. conventional pc-fired plants у50 MWe. It begins by briefly looking at some of the factors that need to be considered when evaluating a refurbishment project. One of the driving forces for upgrading power plants is to meet stricter pollution regulations.