Circulating fluidized bed technology for utility-scale lignite power plants

Transcription

1 Circulating fluidized bed technology for utility-scale lignite power plants Vesna Barišić 1, Kalle Nuortimo 1, Bogusław Krzton 2 1 Foster Wheeler Energia Oy, Varkaus, Finland 2 Foster Wheeler Energia Polska, Warszawa, Poland Presented at International Conference Power Plants 2014 Zlatibor Serbia 28 1 October, 2014

2 CIRCULATING FLUIDIZED BED TECHNOLOGY FOR UTILITY-SCALE LIGNITE POWER PLANTS V. Barišić,* K. Nuortimo* and B. Krzton** Foster Wheeler Energia Oy, Varkaus, Finland* Foster Wheeler Energia Polska, Warszawa, Poland** Abstract: Circulating fluidized bed (CFB) has emerged among the leading combustion technologies for utility-scale, solid-fuel-fired power plants, especially when multi-fuel capabilities are required. Established benefits of high efficiency and reliability, supreme fuel flexibility, with low emissions and installation costs, have been demonstrated on nearly 440 Foster Wheeler s CFB boilers including both, subcritical and once-through supercritical boilers. The largest operating boiler is the PKE's owned Lagisza power plant in Poland, 460 MW e, which celebrates already five years of successful commercial operation. This paper will present three recent Foster Wheeler s CFB projects for utility-size boilers, all firing lignite or sub-bituminous coal as the main fuel: 1) Samcheok Green Power Plant, 4 x 550MW e, South Korea the world s largest power plant based on CFB technology that fires subbituminous coal and up to 5% biomass, 2) Harbin Electric International Co. Ltd. (HEI) Soma, 2 x 255 MWe, Turkey the biggest CFB boiler on Turkish lignite, ) Kladno, 15 MW e, Czech Republic smaller-scale CFB boiler for mid-european lignite with biomass co-firing capability. Key words: Utility CFB technology, Lignite, Biomass 1. INTRODUCTION Circulating fluidized bed (CFB) has emerged among the leading combustion technologies for utility-scale, solid-fuel-fired power plants, especially when multi-fuel capabilities are required. Established benefits of high efficiency and reliability, supreme fuel flexibility, with low emissions and installation costs, have been demonstrated on nearly 440 Foster Wheeler s CFB boilers including both, subcritical and once-through supercritical boilers (Figure 1). The largest operating boiler is the PKE's owned Lagisza power plant in Poland, 460 MW e, which celebrates already five years of successful commercial operation. CFB technology is currently available in large-scale sizes (up to 800 MWe) for a wide range of solid fuels.

3 Total number of units as by Jun 2014: 46 Peat Petcoke Oil-shale Waste 5% 11% 1% 4% Cumulative Steam Capacity [GW th ] Biomass 11% Coal 68% Delivery Year Figure 1. Foster Wheeler CFB reference (as by Jun, 2014). During the past 40 years Foster Wheeler has supplied around 00 CFB boilers designed for coal including lignite with total thermal capacity of 71 GW th (Figure 1). All the boilers share the same circulating fluidization principle; however, depending on the quality of fuel, the boilers differ significantly in design and operation. As shown in Figure 2, the size of CFBs designed for lignite/coal as primary fuel can vary in a broad range of steam capacity, form industrial to largescale utility boilers. Additionally, many of the boilers designed for coal feature the well known fuel flexibility capability, and additional fuels such as biomass and various types of waste are co-fired simultaneously. Steam Capacity [MW th ] Foster Wheeler Lignite/Coal References Total number of units: 298 Cumulative steam capacity: 71 GW th Samcheok, South Korea Soma, Turkey 2 x 255 MW e Kladno, Czech Rep. 15 MW e Delivery Year Figure 2. Foster Wheeler references for lignite/coal (as by Jun, 2014).

4 This paper will present three recent Foster Wheeler s CFB projects for utility-size boilers, all firing lignite as the main fuel: 1. Kladno, 15 MW e, Czeck Republic smaller-scale CFB boiler for mid-european lignite with biomass co-firing capability 2. Harbin Electric International Co. Ltd. (HEI) Soma, 2 x 225 MW boiler on Turkish lignite,. Samcheok Green Power Plant, 4 x 550MWe, South Korea the world s largest power plant based on CFB technology that fires lignite/subbituminous coal and up to 5% biomass. e, Turkey the biggest CFB 2. NATURAL CIRCULATION CFB TECHNOLOGY FOR UTILITY POWER PRODUCTION 2.1. Kaldno,15 MWe, Czeck Republic In 2010, the Swiss utility company Alpiq awarded a 15 MW e lignite fired EPC power plant contract to Kraftanlagen München (KAM) for the Kladno power plant in the Czech Republic. The project was designed to replace old technologies with a more efficient and environmentally cleaner plant, producing energy for the local community while meeting the strict requirement for flexibility from the electrical grid system. For the boiler at the Kladno power plant, Alpiq required CFB boiler technology that was specifically designed to co-fire lignite and biomass. The new Kladno K7 CFB boiler replaced an old coal-fired unit, which was commissioned at the Kladno power plant in the late 1970s. As the new boiler operates alongside two older 15 MW CFB units (commissioned in the 1990s), it can utilize many of the existing plant systems, such as the coal handling and water treatment plant. Scope of Foster Wheeler for the new Kladno CFB boiler included the design of the boiler; the delivery of the Figure. Kladno K7 CFB boiler design. boiler house enclosure with its steel structures, the boiler pressure parts, the auxiliary equipment, the lignite crushers, the fuel silos for solid biomass fuel and lignite, the fuel feeding equipment for biomass fuel and lignite, and the bag e

5 filter; the erection and construction of the boiler; and the start-up, performance testing and commissioning of the boiler. Commercial operation of the new boiler started in December 201. New Kladno CFB boiler belongs to the next generation of utility power boilers with capability of adapting to sudden load change requirements from the electricity grid. The design of the new Kladno CFB boiler (Figure ) incorporates the latest design of solids separators build from steam cooled panels integrated with the combustion chamber. The steam cooled separator design avoids the occurrence of heavy refractory linings in the separator. The final superheating stage and the final reheating stage are INTREX TM heat exchangers located in special enclosures at the bottom of the furnace (adjacent to the main combustion chamber). The INTREX TM heat exchangers are located outside the main combustion area, which enables them to be used as the last superheating and reheating stages. This results in higher steam temperatures because the INTREX TM heat exchangers are protected from the fouling and corrosive environment of the boiler s hot flue gas. The INTREX TM heat exchangers also provide high load-following capabilities and turndown ratios. The high performance of the solids separator leads to a high solids circulation rate and a uniform combustion temperature profile across the whole operation range. The design basis of the Kladno boiler is presented in tables 5 7. Table 1. Kladno fuel data Lignite Biomass LHV, MJ/kga.r Moisture% a.r Ash, % dry Sulphur, % dry Nitrogen, % dry % Table 2. Kladno boiler steam data Steam data Total Heat Output, MWth 0 Steam Flow, kg/s 105/102 Steam Pressure, bar(a) 1/ Steam Temperature, C 541/541 Feedwater Temperature, C 251 Table. Kladno boiler design performance Flue Gas Exit Temperature, C 10 Boiler Efficiency, % 9.2 Emission* Guarantees 40 % to 100 % BMCR ½ hour average NO x, mg/nm 190 SO 2, mg/nm 190 CO, mg/nm <95 NH, mg/nm (slip catalyst installed) <10 NH, mg/nm (w/o slip catalyst) <20 Particulate Matter, mg/nm <20 *) Emissions expressed in dry flue 6%O 2 The main fuel utilized in the new CFB boiler at the Kladno power plant is lignite obtained from the local mine Bilina. In addition, the boiler is designed to co-fire biomass up to 10% heat

6 input. Despite the fact that the lignite is obtained from only one source, there is substantial variation in the lignite quality, especially in terms of inorganic matter, which results in ash content range of 1% to 0% on dry basis. For biomass, the variation is even wider, giving a moisture range of 25% to 55%. The CFB boiler s ability to use fuel with such a wide variation in quality clearly demonstrates its excellent fuel flexibility. Commercial operation of the new Kladno K7 CFB boiler started in December 201, and it proved to be excellent. According to the performance tests, all performance guarantees have been fulfilled within a large margin, demonstrating that CFB boiler technology is able to meet and surpass all the requirements set for a modern utility power unit Harbin Electric International Co. Ltd. (HEI), Soma, 2 x 225 MW e, Turkey In January 2014, Foster Wheeler has been awarded a contract by Harbin Electric International Co. Ltd. (HEI) for the design and supply of two circulating fluidized-bed (CFB) boiler islands and flue gas scrubbers for HIDRO-GEN Energy Import, Export, Distribution and Trading Inc., a subsidiary of Kolin Group of Companies. HEI is acting as EPC contractor for HIDRO-GEN s power project to be built close to lignite mines near the town of Soma, in west part of Turkey. Foster Wheeler s scope includes design and supply of two 255 MW e (gross megawatt electric) steam generators and auxiliary equipment for the boiler islands, flue gas cleaning systems with Foster Wheeler CFB scrubbers, and technical advisory services during erection and commissioning. This is the largest CFB project awarded in Turkey until today. The CFB boilers will be designed to burn local lignite, due to the significant economic benefit of using this fuel for power generation. Local lignite reserves are located near Soma town, with design heating value of 6.77 MJ/kg (see Table 4). The boilers are of a natural circulation drum-type boilers with reheat (see steam parameters in Table 10). The CFB boilers design incorporates solids separators built from steam cooled panels integrated with the combustion chamber. The final superheating stage is in INTREX TM heat exchangers. The boiler layout is shown in Figure 4a. To reach required emission values (Table 6) in economic way, the circulating fluidized bed scrubbing (CFBS) technology has been applied in the Soma power plant. This is a viable pathway for addressing multi-pollutant control in a cost effective manner. There are two identical flue gas cleaning lines, which consist of CFB scrubber including bag-house with solids re-circulation (Figure 4b).

7 (a) (b) Figure 4. Soma CFB boilers: a) overall layout; b) CFB scrubber. Table 4. Soma fuel data Lignite LHV, MJ/kga.r Moisture, % a.r. 2. Ash, % dry 42.9 Sulphur, % dry Nitrogen, % dry 0.5 Table 5. Soma boiler steam data SH flow, kg/s SH pressure, bar(a) 17 SH temperature, C 565 RH flow, kg/s 17 RH pressure, bar(a) 5 RH temperature, C 565 Feed water temperature, C 262 Table 6. Soma design performance Boiler efficiency, % Emissions NO x, mg/nm <200 SO 2, mg/nm <200 CO, mg/nm <200 Particulate Matter, mg/nm <0 *) Emissions expressed in dry flue 6%O 2 Construction costs of CFB scrubber can be reduced as the major system components can be pre-assembled on the ground and lifted into place during system erection. This technology provides high pollutant removal efficiencies up to 99 % for SO 2, SO, HCl and HF. Further the absorber/fabric filter arrangement is highly adaptable for sorbent injection, which removes heavy metals including mercury. The main advantages of this technology combined with CFB boiler is reduced operating cost due to lower limestone consumption. Commercial operation of the new steam generators is scheduled for the beginning of 2017.

8 . FOSTER WHEELER LARGE-SCALE OTU CFB TECHNOLOGY The basic once-through (OUT) CFB concept is based on a CFB process that provides high plant efficiency. The concept incorporates supercritical steam parameters accompanied by Benson vertical tube technology and is based on in-line boiler arrangement (Figure 5). Figure 5. CFB boiler in-line concept. The furnace and the separators form a compact hot loop package and the convection pass consists of a steam-cooled enclosure containing the convection superheaters and reheaters. This is then followed by the economizer and the rotary regenerative air heaters. The design of the convection pass follows the same principles used in large two-pass PC boilers. The hot loop and convection pass are connected with steam cooled cross over ducts (CODs). The water and steam design of the OTU CFB boiler is based on the low mass flux BENSON once-through technology licensed by Siemens AG. This technology is ideal for the CFB design because it utilizes vertical furnace tubes instead of the spiral wound tubing that is used in many other once-through designs. In proven CFB designs, natural circulation is achieved by using vertical tubing as the normal arrangement and it is beneficial to use a similar design for supercritical OTU boilers. The heat transfer rate in CFB boilers is very low and is uniform in comparison to Pulverised Coal (PC) boilers, and the required water mass fluxes are relatively low. The low heat fluxes also allow the use of normal smooth tubes in the furnace walls with a mass flux of kg/m 2 s at full load. The fluid temperatures were carefully analyzed after each evaporator tube system in different load conditions when creating the OTU CFB design and it was found that the low and

9 uniform heat flux of the CFB furnace, and the BENSON low mass flux technology makes the fluid temperatures very uniform. Figure 6.. Steam circuitry. The OTU CFB design requires the plant to be operated with sliding steam pressure, so that the boiler pressure follows the turbine load. At lower loads (below ca. 70%), the main steam pressure is typically below the critical pressure (221 bar), and at higher loads the boiler operates at supercritical pressures. During boiler start-up and shut down a circulation pump is used to ensure that water flow through the evaporator is maintained to ensure proper cooling. The two-phase flow from the outlet headers of the evaporator walls is collected in the vertical water/steam separators where the water is then separated from the steam and led to a single water-collecting vessel (Figure 6). When the boiler load exceeds the BENSON point at approximately 0% load, the steam exiting the evaporator walls is slightly superheated. At this point, the circulation system can be closed and the boiler will achieve the once-through operation mode..1. Samcheok Green Power 4 x 550 MW e, South Korea In July 2011, Foster Wheeler received full notice to proceed by Hyundai Engineering and Construction for the design and supply of supercritical Circulating Fluidized Bed (CFB) steam generators for the Samcheok Green Power Project in South Korea. The contract included the design and supply of four 550 MW e advanced vertical tube, once-through supercritical CFB steam generators (Figure 7) feeding two steam turbines. The CFB steam generators have been designed to burn imported coal mixed with biomass while meeting all environmental requirements. Once the

10 Samcheok CFB units will enter commercial operation in 2015, they will be the world's most advanced CFBs and will provide a new level of fuel flexibility, reliability and environmental performance. The Samcheok boiler design is based on OTU CFB concept and follows the same basic design features used in the Łagisza plant. The boiler material requirements for most sections of the Samcheok boilers are very conventional and Figure 7. Samcheok Green Power 4 x 550 MW e. normal boiler materials have been used. The CFB steam generators at the Samcheok plant will be designed to burn imported coals mixed with biomass while at the same time meeting strict environmental requirements. The fuel that will be primarily used for the Samcheok plant is sub-bituminous coal sourced from several international coal mines (mainly in Indonesia). The boilers have also been designed to be able to cofire up to 5% wood pellets (Table 7). The steam pressure and temperature selected for the Samcheok plant have been shown to be viable in other supercritical units, and the conventional boiler steel materials can be used for the boiler s construction. Table 8 presents the main design steam parameters of the 4 x 550 MW e (gross) CFB boilers that will be built at Samcheok. Table 7. Samcheok fuel data Coal Biomass LHV, MJ/kga.r Moisture, % a.r Ash, % a.r Sulphur, % a.r Table 8. Samcheok boiler steam 100% load SH flow, kg/s 47.7 SH pressure, bar(a) 257 SH temperature, C 60 RH flow, kg/s 56.4 RH pressure, bar(a) 5 RH temperature, C 60 Feed water temperature, C 297

11 Table 9. Samcheok - design emission values Unit Limit value Method to meet SOx ppm (as SO 2 ) Max. 50 (6% O2) Limestone injection to furnace; no backend desulphurization equipment needed NOx ppm (as NO 2 ) Max. 50 (6% O2) SCR between economizer and air heaters Particulate matter mg/nm Max. 20 (6% O2) ESP The CFBs will meet the stringent emission values shown in Table 9 without needing any additional back-end flue gas desulphurization equipment for SO x control. The normal operating mode of the Samcheok unit is co-ordinated control with sliding pressure operation. The boilers will normally be operated at the same load level and any load change requests will be forwarded to the boilers simultaneously and with similar control parameters. The steam temperatures will be individually controlled in order to ensure that the required temperatures in the main steam and reheated steam systems are achieved. Reheated steam share between the boilers will be continuously monitored and controlled in accordance with the applicable firing rates. 4. SUMMARY CFB technology development has undergone extensive development since the 1970s and Circulating Fluidized Bed (CFB) technology has now established its position as a viable and efficient utility-scale boiler technology. When considering whether to build new plants, or to repower old plants, efficiency, environmental performance and operational flexibility are the key issues that developers need to consider. High efficiency means lower fuel consumption and lower levels of ash and air emissions, including lower emissions of carbon dioxide (CO 2 ). CFB technology has been proven to be capable of achieving these goals by means of both supercritical steam parameters and specialised boiler designs for biomass firing in the utility scale. CFB boiler designs have also achieved a high level of operational flexibility, which represents the next generation in utility power generation. New more tighten capabilities e.g. for low load operation and fast load following, are expected from current and new power generation capacity. These aims have been directly taken into account when undertaking CFB development programs in order to ensure compliance with future load control requirements. All of these achievements, as well as the further development efforts currently being undertaken, make CFB technology the optimum choice to meet the market s demands both now and in the future to utilise a broad range of fuels in large scale power generation.