Samcheok Green Power 4 x 550 MW e Supercritical Circulating Fluidized-Bed Steam Generators in South Korea Timo Jäntti, Kalle Nuortimo, Marko Ruuskanen, Juha Kalenius Foster Wheeler Energia Oy Finland
Abstract The proven high efficiency supercritical circulating fluidized-bed (CFB) technology offers excellent solutions for high efficiency electricity production and CO 2 reduction. The first high efficiency CFB power plants to utilize the supercritical steam parameters in coal firing with once-though steam cycle technology are Łagisza, 460MW e in Poland, Novocherkasskaya, 330MW e in Russia and Samcheok Green Power, 4 x 550MW e in South Korea. Furthermore, Foster Wheeler has developed its CFB technology to commercially offer the 600-800 MW e size, with a net efficiency of about 45 % (LHV). A full notice to proceed was given by Hyundai Engineering and Construction for the design and supply of four 550 MW e (gross megawatt electric) supercritical circulating fluidized-bed (CFB) steam generators for the Samcheok Green Power Project for Korea Southern Power Co., Ltd. (KOSPO). Contract includes the design and supply of four 550 MW e advanced vertical tube, once-through supercritical CFB steam generators feeding two steam turbines. The CFB steam generators will be designed to burn coal mixed with biomass while meeting the stringent environmental requirements. When these CFB units enter commercial operation in 2015, they will be the world's largest and most advanced CFB s providing KOSPO with a new level of fuel flexibility, reliability and environmental performance. This paper presents the Foster Wheeler supercritical CFB technology focusing on Samcheok Green Power 4x550 MW e CFB boiler design, operating mode and project status. Introduction to supercritical OTU CFB technology Technology development background CFB technology development has been a steady path from small demonstration unit in 1970 s to industrial sizes in 1980 s. The utility size of over 200 MW e was reached in the 1990 s and since then CFB technology has challenged the PC technology in large scale energy generation. Today, there are around 20 CFB units of over 200 MW e scale in operation or under construction with a wide range of fuels. Furthermore, the technology development advanced to once through units utilizing supercritical steam parameters with Łagisza reference entering commercial operation in 2009. Now CFB power plants to utilize the supercritical steam parameters with once-though steam cycle technology are Łagisza, 460 MW e in Poland, Novocherkasskaya, 330 MW e in Russia and the latest award in 2011, Samcheok 4 X 550 MWe in South Korea. These references are shown in Table 1.
Table 1. Foster Wheeler OTU CFB references Country Into production MW e Main fuel Łagisza, Poland 2009 460 Bituminous coal Novocherkasskaya, Russia 2014 (Estimate) 330 Anthracite, Bituminous coal Samcheok, South Korea 2015 4 x 550 Bituminous coal, biomass Foster Wheeler has truly taken CFB technology a step further, to utility sizes with supercritical steam parameters and once-through technology. This is the result of continuous and determined development work including an experience database of over 380 reference boilers in operation. Emphasis has been given to mechanical design issues and understanding the process conditions affecting heat transfer, flow dynamics, combustion characteristics, gaseous emission control and thermohydraulics among others. Understanding these processes has been gained by the work done in bench-scale test rigs, pilot plants, field testing of operating units, model development, and simulation using developed semi-empirical models or more theoretical models. Design criteria for larger units have been developed and successfully implemented on the basis of data collected, model development work, and correlations with conventional boiler design. Figure 1 shows the development CFB boiler size. Figure 1. Increase of the size of CFB boilers CFB technology and its main design components are well demonstrated in utility scale power production. As a next step, scale-up of CFB technology with super-critical steam parameters up to
800 MW e is feasible in the near future. Special features of Foster Wheeler CFB technology with supercritical steam parameters are presented in the next chapter. Foster Wheeler OTU CFB technology Basic boiler concept Basic OTU CFB concept, utilized in Samcheok boilers, is based on proven and efficient CFB process with high plant efficiency and supercritical steam parameters. With Benson vertical tube technology, heat transfer rate is very low and uniform. Concept is based on in-line boiler arrangement, which is presented in Figure 2. Furnace and separators form a compact hot loop package. The convection pass consists of a steam-cooled enclosure containing the convection superheaters and reheaters. This is followed by the economizer and rotary regenerative air heaters. The design of the convection pass follows the same principles employed in large two-pass PC boilers. Hot loop and convection pass are connected with steam cooled cross over ducts (CODs). Figure 2. CFB boiler in-line concept Water/steam circuit The water and steam side design is based on the low mass flux BENSON once-through technology licensed by Siemens AG, Germany. This technology is ideal for CFB conditions as it utilizes vertical furnace tubes, opposed to spiral wound tubing used in many other once-through designs. For the CFB technology, the vertical tubing is the normal arrangement in natural circulation designs and hence the similar design can now be used for supercritical, once-through boilers. The heat transfer rate in CFB and boilers is very low and uniform compared to pulverized coal (PC) and therefore the required water mass fluxes are rather low. The low heat fluxes also allow the use of normal smooth tubes in furnace walls with a mass flux of 550-650 kg/m 2 s at full load. The fluid temperatures after
each evaporator tube system were analyzed in different load conditions. Due to low and uniform heat flux of the CFB furnace and the BENSON low mass flux technology the fluid temperatures are very uniform. The plant is operated with sliding steam pressure so the boiler pressure is following the turbine load. Hence at lower loads (below ca. 70%) the main steam pressure is typically below the critical pressure (221 bar) and at higher loads the boiler is operating at supercritical pressures. During boiler start-up and shut down a circulation pump is used to secure minimum water flow through the evaporator. The two-phase flow from the outlet headers of the evaporator walls is collected to vertical water/steam separators where the water is separated from the steam and led to a single the water-collecting vessel (See Figure 3). When the boiler load exceeds so called BENSON -point at approximately 35% load- the steam exiting the evaporator walls is slightly superheated. Hence the circulation system can be closed and the boiler has achieved once-through operation mode. Figure 3. Steam circuitry The steam superheating takes place in different heat exchangers, located to flue gas flow as well as solids return (INTREX TM superheater). Steam temperature is controlled with spray desuperheaters. After the high pressure turbine the steam is brought back to the boiler for reheating. The reheater is typically divided to two stages. Reheater I (RH I) is equipped with a steam side bypass which is used for reheat steam temperature control. At higher loads part of the reheat steam is bypassed the RH I which reduces the heat pick-up and hence the inlet steam temperature to RH II is decreased. This
patented reheat steam control method avoids using a spray control for reheat side and therefore does not cause a decrease in plant efficiency. There are over 20 CFB boilers utilizing this control method, e.g. Turow and Łagisza CFB boilers in Poland. Flue gas side design of boiler The design of flue gas side of OTU CFB boilers is based on extensive analysis of the fuels and limestones that are going to be used. These have given the required data for the design models to make predictions for circulating material particle size distribution, solids densities and finally the heat transfer with adequate gas temperatures. The operation of the furnace has been verified with measurements in the largest units in operation as well as with 3D computer modeling, see Figure 4. The furnace is very insensitive for operational disturbances such as unbalanced fuel feeding. Reason for this feature of excellent stability is the nature of CFB combustion process; combustion takes place within the bed material which equalizes the heat release inside furnace. Figure 4. Furnace heat flux kw/m 2 The solids separator design of FW OTU CFB boilers is based on steam cooled panel wall construction. The solids separator design is optimized for high separation efficiency with low flue gas pressure loss. The high separation efficiency secures the optimum performance of the CFB boiler with respect to low emissions, low limestone consumption, and high combustion efficiency. The larger the CFB boiler, the greater the number of solids separators needed. As the size of individual separators does not have to be increased, there are no scale-up issues in this area, see Figure 5. The layout of four solids separators on opposite walls, giving a total of eight separators in all, has already been successfully used in five commercial CFB boilers.
400-800 MW e 200-300 MW e Module 300-400 MW e 150-200 MWe 100 MW e Figure 5. CFB Furnace and Separator Arrangement: Modularization and Scale-up INTREX Heat Exchanger Design INTREX is fluidized bed heat exchanger extracting heat from the hot circulating bed material that is collected in the solid separators. Additional bed material is taken to INTREX chambers directly from the lower part of the furnace (see Figure 6). This provides a sufficient amount of bed material at wide load range. A unique feature of the INTREX superheater is its ability to control the heat transfer by changing the fluidization velocities. This special capability is utilized for example during load changes to trim the steam temperatures and to control reheat steam temperature. Also in case of fuels having high chlorine contents INTREX superheater provides enhanced protection against corrosion. INTREX TM heat exchangers may serve either as superheater or as reheater surface. The refractory linings can be minimized due to water cooled casing of the INTREX surfaces. This allows the integration of the INTREX casings to the furnace thus eliminating expansion joints and minimizing distances to transfer hot solids. Controlling the flow of hot solids is done only with fluidization, therefore no valves or other mechanical devices are required. Another benefit of the INTREX heat exchanger is a high heat transfer rate, which decreases the amount of heat surface required thus making the actual dimensions smaller.
Figure 6. INTREX Heat Exchanger Boiler materials The material requirements for most sections of the boiler are very conventional and normal boiler materials can be used. For example furnace and solids separator panels can be manufactured of materials that do not require post-weld heat treatment. Steel materials are available up to 620 o C steam temperatures. Auxiliary equipment Auxiliary equipment do not differ from large-scale CFB boilers with natural circulation. Solutions have been developed and secured over the decades of successful operation of such plants. Combustion air system for OTU CFB boiler consists of primary and secondary air system and separate air system for fluidizing the INTREX heat exchangers and sealing devises. Typically radial fans with inlet guide vane control are used for primary and secondary air fans, 2 pcs each. For induced draft (ID) fans two axial fans are used. A flue gas recirculation system can be provided to accommodate the larger variations in the fuel quality. Downstream the economizer flue gases are cooled in rotary air heater, which enables low flue gas end temperature and compact structure. Electrostatic precipitator (ESP) is used to control dust emissions as required by the local authorities. The separated fly ash is conveyed to fly ash silo using a dense phase ash conveying system. Fuel feeding system consists typically of 2-4 independent fuel feed lines, divided equally to front and rear walls of the furnace. One fuel feeding line includes fuel boiler silo, drag chain feeder, drag chain conveyor and discharge to the feeding points. Each feed point has a dosing screw, slide gate and screw/ dropping chute to the furnace.
OTU CFB boilers in Poland and Russia The PKE Łagisza CFB boiler Figure 7. Łagisza Power Plant The boiler design for Łagisza plant (Figure 7) is based on well proven CFB technology. The fuel data is shown in Table 2. The main fuel for the boiler is bituminous coal. The fuel is sourced from 10 local coal mines with a wide range of coal parameters, proving once more the fuel flexibility of the CFB technology. Table 2. Fuel specification Bituminous Coal Design fuel Range LHV (a.r.) MJ/kg 20 18 23 Moisture % 12 6 23 Ash (a.r.) % 23 10 25 Sulfur (a.r.) % 1.4 0.6-1.4 Chlorine (dry.) % < 0.4 < 0.4 a.r. = as received The steam parameters for the boiler were specified by the PKE. The selected steam pressure and temperature are proven in other supercritical units and conventional boiler steel materials can be used. Table 3 presents main design steam parameters of this 460 MW e CFB boiler.
Table 3. Design Steam parameters at 100 % load SH flow kg/s 361 SH pressure MPa 27.5 SH temperature C 560 RH flow kg/s 306 RH pressure MPa 5.48 Cold RH temperature C 315 Hot RH temperature C 580 Feed water temperature C 290 The plant net efficiency is naturally dictated by the selected steam parameters, steam cycle configuration, cooling tower conditions and boiler efficiency. In Łagisza design the boiler efficiency is improved by flue gas heat recovery system, which cools the flue gases down to 85 C thus improving the plant net efficiency. The calculated LHV net plant efficiency for Łagisza is 43.3 % and net power output is 439 MW e. Łagisza Commercial Operation When the Łagisza power plant began commercial operations in late June 2009, it marked a new era in the evolution of circulating fluidized bed (CFB) technology. Operation experience of the Łagisza boiler has been excellent. Over the whole load range the boiler has performed as designed and operation has been steady and easily controllable. Based on the analysis result from Łagisza CFB, heat flux profiles to furnace walls have been low and uniform during coal firing. Due to uniform heat fluxes to furnace walls, steam temperature variation after evaporator has been minimal when operating above Benson-point. Emissions have been lower than set by the Large Combustion Plant (LCP) directive and a low flue gas exit temperature together with good combustion efficiency are guaranteeing high thermal efficiency. Control concept chosen for the Łagisza boiler has turned out to be a success. The CFB is behaving well on transient conditions and on the other hand all the parameters are stable as the boiler is operated on steady state conditions. Novocherkasskaya project In year 2007 The Sixth Wholesale Power Producer OGK-6 made a decision to take a step forward in their power producing capacity in terms of combustion technology and steam parameters. A selection of supercritical CFB combustion technology with 565/565 o C steam temperatures was made to be used in a new Novocherkasskaya GRES Unit No 9 (Figure 8).
Figure 8. Novocherkasskaya GRES Unit No 9 Foster Wheeler was selected as a supplier of the 330 MW e CFB boiler(table 4) to PJSC Energo Mashinostroitelny Alliance (EM Alliance). Manufacturing of pressure parts within FW s scope of supply furnace walls, grid and wingwall superheaters took place on FW s Fakop workshop in Sosnowiec (Poland), cyclones, furnace roof and Intrex superheaters were manufactured in WarkausWorks (Finland). The boiler is capable of combusting wide selection of fuels including anthracite, bituminous coal and coal slurry. Table 4. Design values of Novocherkasskaya GRES Unit No 9 Plant Electrical Output (Gross/Net) MWe 330/312 Net Plant Efficiency (LHV/HHV) % 41,5/39,9 Net Plant Heat Rate (LHV/HHV) kj/kwh 8681 SH flow kg/s 278 SH pressure bar(g) 247 SH temperature C 565 RH flow kg/s 227 RH pressure bar(g) 37 RH temperature C 565 Feed water temperature C 280 Current status of Novocherkasskaya project Scope of delivery; basic design, followed by detail design as well as purchasing procedures are ready and all engineering activities have been finished. Manufacturing of pressure parts was completed in
April 2010. Pressure parts' as well as other equipment's deliveries to customer have been completed in May 2010. Latest milestone in OTU CFB technology: Samcheok Green Power 4 x 550 MW e Full notice to proceed was given by Hyundai Engineering and Construction for the design and supply of four 550 MW e (gross megawatt electric) supercritical circulating fluidized-bed (CFB) steam generators for the Samcheok Green Power Project for Korea Southern Power Co., Ltd. (KOSPO). Contract includes the design and supply of four 550 MW e advanced vertical tube, once-through supercritical CFB steam generators (Figure 9) feeding two steam turbines. The CFB steam generators will be designed to burn coal mixed with biomass while meeting stringent environmental requirements. Full NTP for the project was received in July 2011, and when these CFB units enter commercial operation in 2015, they will be the world's largest and most advanced CFB s providing KOSPO with a new level of fuel flexibility, reliability and environmental performance. Figure 9. Samcheok Green Power 4 x 550 MW e Design details Samcheok boiler design is based on proven OTU CFB concept and follows the basic design features presented before. Boiler design is based on modular structure with identical separator and solids return designs. Steam circuit is generally the same as in Łagisza with advanced steam parameters (temperature) and optimized steam circuitry design. Boiler material requirements for most sections of the boiler are very conventional and normal boiler materials can be used. Furthermore, the design is free of T24-steel.
Design fuel The CFB steam generators will be designed to burn coal mixed with biomass while meeting stringent environmental requirements. Boiler design fuel is sub-bituminous coal from several international coal mines, mainly from Indonesia. Boilers can also co-fire wood pellets (Table 5). Table 5. Fuel specifications Bituminous Coal Design fuel Range LHV (a.r.) MJ/kg 16,3 14,2 24,9 Moisture % 33,5 20 43 Ash (a.r.) % 3,76 1,1 15,3 Sulfur (a.r.) % 0,1 0.1-1 Chlorine (dry.) % < 0.03 < 0.03 Wood pellets Design fuel Range LHV (a.r.) MJ/kg 17 15,8-18 Moisture % 10 5 15 Ash (a.r.) % 1 0,7 5 Sulfur (a.r.) % 0,03 0-0,16 Chlorine (dry.) % < 0.01 < 0.05 Auxiliary equipment Fuel and limestone feeding systems are based on volumetric equipment that has proven to be reliable in reference plant operation. Feeding points are located symmetrically to each furnace section to ensure uniform combustion in furnace. Bottom ash extraction system is based on water cooled screw and chain conveyors, also a proven technology used in various coal fired units. Equipment capacities are selected so that single feeding or extraction line failure does not effect to plant energy availability. Primary air fans are inlet vane controlled radial fans which is proven solution in number of large scale units. Secondary air as well as flue gas fans are axial type in order to gain high fan efficiency.
Steam parameters The selected steam pressure and temperature are proven in other supercritical units and conventional boiler steel materials can be used. Table 6 presents the main design steam parameters of these 4 x 550 MW e (gross) CFB boilers. Table 6. Design Steam parameters at 100 % load SH flow kg/s 437,7 SH pressure bar(g) 257 SH temperature C 603 RH flow kg/s 356,4 RH pressure bar(g) 53 RH temperature C 603 Feed water temperature C 297 Emission limits The CFB s will meet stringent emission values presented in Table 7 without additional back-end flue gas desulphurization equipment for SOx control. Table 7. Emission values Item Unit Limit value Method to meet SOx ppm (as SO 2 ) Max. 50 (6% O 2 ) Limestone injection to furnace; no back-end desulphurization equipment needed NOx ppm (as NO 2 ) Max. 50 (6% O 2 ) SCR between economizer and air heaters Particulate matter mg/m 3 n Max. 20 (6% O 2 ) ESP Unit Operation The one Samcheok unit consists of one steam turbine and two similar FW OTU-CFB boilers. Normal operation mode of the unit is coordinated control with sliding pressure operation. The boilers are normally operated at same load level and load change requests are forwarded for the boilers simultaneously and with similar control parameters. Steam temperatures are individually controlled to meet required temperatures in main steam and reheated steam systems. Reheated steam share between the boilers is continuously monitored and controlled according to firing rates. Normal operation range of the unit is from 50% to 100%.
Design study of a 800 MW e CFB Łagisza has validated supercritical CFB design platform providing a solid base for the further scale-up of the CFB technology. Today supercritical CFB up to scale 800 MW e in size is offered for bituminous coal, meeting the highest requirements for plant efficiency and environmental performance. Summary CFB technology development has been a one steady path beginning from 1970 s. Currently, circulating fluidized bed (CFB) technology has established its position as a utility-scale boiler technology. When considering either new plants or repowering old plants, efficiency and environmental performance are the key issues. High efficiency means lower fuel consumption, and lower levels of ash and air emissions, including lower emissions of carbon dioxide (CO 2 ). To achieve these goals, supercritical steam parameters have been applied. First high efficiency CFB power plants to utilize the supercritical steam parameters in coal firing with once-though steam cycle technology are Łagisza, 460MW e in Poland, and Novocherkasskaya, 330 MW e in Russia. As a latest milestone, full notice to proceed was given by Hyundai Engineering and Construction for the design and supply of four 550 MW e (gross megawatt electric) supercritical circulating fluidized-bed (CFB) steam generators for the Samcheok Green Power Project for Korea Southern Power Co., Ltd. (KOSPO). Contract includes the design and supply of four 550 MW e advanced vertical tube, oncethrough supercritical CFB steam generators feeding two steam turbines. Boiler design follows the basic design features of Łagisza project. Initial operating experiences of the world s first CFB, Łagisza project, utilizing supercritical steam parameters have been excellent. Extensive development work combined with Łagisza, Novocherkasskaya and Samcheok Green Power project experiences provides a solid knowledge base to propose CFB technology with super-critical steam parameters up to scale 800 MW e.