The Latest CFB Technology Developments for Flexible Large Scale Utility Power Production

The Latest CFB Technology Developments for Flexible Large Scale Utility Power Production Ari Kettunen, Jenö Kovács, Kalle Nuortimo, Riku Parkkonen, Timo Jäntti Presented at PowerGen Europe June 3-5, 2014 Cologne, Germany

THE LATEST CFB TECHNOLOGY DEVELOPMENTS FOR FLEXIBLE LARGE SCALE UTILITY POWER PRODUCTION Ari Kettunen, Jenö Kovács, Kalle Nuortimo, Riku Parkkonen, Timo Jäntti Foster Wheeler Energia Oy P.O.BOX 201, FI-78201 Varkaus, Finland ari.kettunen@fwfin.fwc.com ABSTRACT In recent years, Circulating Fluidized Bed (CFB) technology is increasingly becoming the market-leading technology used in the large scale utility solid fuel power production sector. In comparison with the conventional Pulverised Coal (PC) technology, CFB technology is a much more efficient method with which to generate large scale power with a broad variety of solid fuels. This makes CFB technology ideal to meet the current challenges in the power production markets. This paper will discuss the background behind, and reasons for, the success of CFB technology. This will be achieved by highlighting the key market drivers behind CFB technology s development, and the technical challenges that needed to be overcome during its development in the past 30 years. CFB technology is currently available in large scale sizes (up to 800 MW e ) for a wide array of solid fuels. After introducing the main market drivers behind the development of CFB technology, and the technical challenges of firing solid fuels in utility boilers, this paper will present the advanced technical features that have been developed for CFB boilers. CFB technology has proven to be ideal for firing a variety of solid fuels, such as bituminous and anthracite coals, lignite, petroleum coke, peat and biomass. This fuel flexibility, the possibility of fuel switching, and the possibility of co-firing are some of the significant economic advantages behind the technology. Users of CFB technology are able to choose/use the most cost effective fuel at any given time. This opens up the opportunity to use lower cost local fuels for power generation instead of high quality fuels with higher transportation costs. Furthermore, CFB technology is well positioned to meet the current pressure for increased flexibility in the power production sector that has been caused by the rise of renewable power, such as solar and wind. Finally, this paper will present real world examples of the latest utility CFB technology built to meet the requirements of the current power production market, such as the Łagisza plant (the world s first supercritical once-through CFB boiler (460 MWe)), the Samcheok Green Power plant (the world s largest CFB technology based power plant (4x550 MWe) that both fires coal and co-fires biomass), the Połaniec plant (the world s largest 100 % solid biomass firing CFB boiler (205 MWe)), and the Kladno plant (the next generation in utility power generation with wide operational and fuel flexibility (135Mwe)). Keywords: Utility CFB technology, Renewable Energy, Boiler dynamic performance

1 INTRODUCTION New boundaries for power plant operation are being set in the European energy production markets. Several international factors have led to increased pressure to develop power plant technology that is capable of both flexible and highly efficient operation. Several factors have caused the pressure to achieve these new requirements. Firstly, the shale gas boom in the US has lowered the coal price in Europe, making coal plants more economical than gas plants. At the same time, coal firing is also being encouraged by the low price of CO 2 in the emission trading system (below 5 /ton). Furthermore, European initiatives for the reduction of greenhouse gas emissions, as well as Environmental legislation (such as the Industrial Emission Directive (IED)), have encouraged the use of mixtures of biomass with other solid fuels and have tightened the emission limits for large combustion plants. In addition, RES (Renewable Energy Sources) targets have been implemented as a way to encourage the use of renewable energy production, such as solar and wind power. However, the use of RES remains relatively low and both the RES subsidies and the European long term energy policy are currently still under discussion. This means that reliance on RES power alone is not yet possible and so instead further requirements are being set for the operation of solid fuel fired power plants. Capacity market systems are also being considered as a way to compensate for the idle time in thermal capacity. These international factors have meant that European utility sized power plants now have new requirements and expectations for their operational capability. It is no longer enough for large coal, lignite and biomass fired power plants to operate solely as base load plants. Instead, power plants need to be able to support grid operators with a new type of flexibility. This is a significant challenge, as it means that boiler and turbine technology needs to be rapidly developed in order to be able to increase flexibility, fulfil the load change requirements, and meet the stringent emission limits. To achieve this goal, supercritical steam parameters and specialised boiler designs for firing biomass and RDF have been developed. In particular, CFB technology has been a focus of development due to its capacity for economical large utility power production and its enhanced environmental and operational performance in terms of reduced fuel needs, reduced pollutants emitted and the capability to adapt to sudden changes in the power demand.

Circulating Fluidized Bed (CFB) boiler technology, presented in the following chapters, has been growing in size and number over the past three decades and it has now established its position as a viable and ideal utility scale boiler technology. 2 DEVELOPMENT STEPS TO ACHIEVE A UTILITY SIZE CFB Technology development background CFB technology began development with small demonstration units constructed in the 1970s. Following this, the size of the technology increased, with industrial size units constructed in the 1980s and utility size units of over 200 MW e constructed in the 1990s. Since the 1990s, CFB technology has increasingly challenged the popularity of Pulverised Coal (PC) technology in large scale energy generation. Today, there are over 30 Foster Wheeler CFB units firing a wide range of fuels of a scale of over 200 MW e in operation, or under construction, worldwide. Furthermore, CFB technology has now advanced to the point where it is possible to construct once through units (OTU) utilising supercritical steam parameters. Foster Wheeler has built up extensive experience of CFB power plants which utilise supercritical steam parameters with once-though steam cycle technology. Examples of this are the Łagisza power plant (460 MW e ) in Poland, the Novocherkasskaya power plant (330 MW e ) in Russia, and the latest Samcheok power plant (4 X 550 MW e ) in South Korea. These references are shown in Table 1 below. Table 1. Foster Wheeler OTU CFB references Country In production MW e Main fuel Łagisza, Poland 2009 460 Bituminous coal Novocherkasskaya, Russia 2015 (Estimate) 330 Anthracite, Bituminous coal Samcheok, South Korea 2015 4 x 550 Bituminous coal, biomass These examples demonstrate that Foster Wheeler is on the cutting edge of CFB technology development and has the capability to design and construct utility size CFB technology boilers with supercritical steam parameters and once-through technology. Knowledge and experience has been achieved by committing to CFB technology and its continuous and determined development work, which has included an experience database of over 400 reference boilers in operation. Emphasis has been on the mechanical design issues of CFB technology and on understanding the process conditions affecting heat transfer, flow dynamics, combustion characteristics, gaseous emission control, and thermo hydraulics. By carrying out work in bench-scale test rigs and pilot plants, field testing of operating units, model development, and simulations carried out using developed semi-empirical models or more theoretical models, a detailed understanding of these processes has successfully been built up. This has led to development of detailed design criteria

for larger units, which has been successfully implemented in boiler projects. Design criteria has also been supported by data collected, model development work, and correlations with conventional boiler design. Figure 1 below shows the development of the size of CFB boilers. Figure 1. Increase of the size of CFB boilers The viability of CFB technology and its main design components has been proven in utility scale power production. The scale-up of CFB technology with super-critical steam parameters of up to 800 MW e is now technically ready and commercially available. The special features of CFB technology with supercritical steam parameters are presented in the next chapter. For the combustion of challenging solid biomasses on the utility scale, Advanced Bio CFB (ABC) technology has been developed and is now the state-of-the-art technology for biomass combustion. This technology will also be presented in detail in the following chapters. 3 FOSTER WHEELER OTU CFB TECHNOLOGY Basic boiler concept The Basic OTU CFB concept, which was utilised in the boilers in both the Łagisza and the Samcheok power plants, 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 (presented in Figure 2). The furnace and the separators in the design 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). Figure 2. CFB boiler in-line concept Water/steam circuit 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 utilises 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 550-650 kg/m 2 s at full load. The fluid temperatures were carefully analysed after each evaporator tube system in different load conditions when creating the OTU CFB design and it was found that the low and uniform heat flux of the CFB furnace and the BENSON low mass flux technology makes the fluid temperatures very uniform. 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 minimised. 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 (see Figure 3).

When the boiler load exceeds the BENSON point at approximately 30% load, the steam exiting the evaporator walls is slightly superheated. At this point, the circulation system can be closed and the boiler will have achieved the once-through operation mode. Figure 3. Steam circuitry Flue gas side design of the boiler The design of the flue gas side of OTU CFB boilers is based on an extensive analysis conducted of the fuels and limestone that are used in the boiler. This extensive analysis provided the required data to construct design models that are able to make predictions for the distribution of the circulating material particle size, the densities of the solids, and the heat transfer when adequate gas temperatures are achieved. The operation of the furnace has been verified with measurements that have been taken from the largest OTU CFB units currently in operation, as well as with 3D computer modelling (see Figure 4). The furnace is very stable and does not suffer from sensitivity for operational disturbances such as unbalanced fuel feeding. The reason for the excellent stability in OTU CFB units is because the very nature of the CFB combustion process means that the combustion takes place within the bed material, which equalises the heat release inside furnace.

kw/m 2 Figure 4. Furnace heat flux The solids separator design of OTU CFB boilers is based on the inclusion of a steam cooled panel wall. The solids separator design is also optimised in order to achieve high separation efficiency and low flue gas pressure loss. The high separation efficiency secures the optimum performance of the CFB boiler and leads to low emissions, low limestone consumption, and high combustion efficiency. 4 DEVELOPMENT OF LARGE SCALE CFB FOR BIOMASS COMBUSTION ABC TECHNOLOGY Environmental regulations and government subsidies have driven the demand for larger biomass boilers with increased efficiency, extended availability, and broadened fuel flexibility. Due to its inherent fuel flexibility, CFB boiler technology is ideal for large scale power generation from a broad range of biomass fuels, either used alone or co-fired with fossil fuels. CFB technology has progressively advanced and scaled-up for biomass firing since the 1980s, starting from small multi-fuel boilers firing residue from Nordic wood in the pulp and paper industry. Advanced Bio CFB (ABC) technology is now the state-of-the-art technology for biomass combustion. The development of ABC is the result of knowledge on biomass firing boilers, gained knowledge and experience from constructing over 400 CFB boilers, and continuous research in the field. The ABC technology has been applied successfully in both the Połaniec and the Kladno power plants. The Key design features of the ABC technology are summarised below in Figure 5.

Integrated Steam Cooled Solid Separator and Return Leg Control of Fouling & Corrosion Correct flue gas temperature Correct design for convective heat transfer surfaces Features to Control Agglomeration & Fouling Active Bed Material During Operation Fuel quality management FW SmartBoiler datalog & Diagnostic tools Optional additives with worst quality agros Conservative flue gas velocity Effective temperature control Step Grid Final SH & RH as INTREX Figure 5. Key features of ABC technology. 5 STATE OF THE ART CFB TECHNOLOGY BASED UTILITY POWER PLANT Foster Wheeler has successfully designed both OTU CFB boilers and ABC boilers at a utility size. Examples of OTU plants include the Lagisza power plant, a 460 MWe CFB boiler firing bituminous coal, and the Samcheok power plant, 4x550 MWe CFB boilers in South-Korea designed to fire bituminous coal and co-fire biomass. Examples of the utility size ABC technology include the Połaniec power plant, a 205 MW e / 447MW th CFB boiler located in Poland, which fires 100 % biomass including a considerable share of demanding agricultural residue, and the Kladno power plant, a 135 MW e /303 MW th CFB boiler located in the Czech Republic near Prague, which co-fires biomass and lignite. The PKE Łagisza CFB boiler Figure 6. Łagisza Power Plant The boiler design for the Łagisza plant (Figure 6) is based on well proven CFB technology.

The fuel data for the Łagisza plant is shown in Table 2 below. The main fuel used for the CFB boiler is bituminous coal. The fuel is sourced from 10 local coal mines with a wide range of coal parameters. The CFB boiler has shown that it is fully capable of operating using this fuel, thus demonstrating the fuel flexibility of the CFB technology. Table 2. Fuel specification a.r. = as received Bituminous Coal Design fuel Range LHV (a.r.) MJ/kg 20 18 23 Moisture % 12 6 23 Ash (a.r.) % 23 10 25 Sulphur (a.r.) % 1.4 0.6-1.4 Chlorine (dry.) % < 0.4 < 0.4 The steam parameters for the Łagisza boiler were specified by the PKE. The selected steam pressure for the Łagisza plant, as well as the temperature, has been proven to be viable in other supercritical units and conventional boiler steel materials can be used for construction. Table 3 below presents the main design steam parameters of the Łagisza 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 Łagisza plant s net efficiency is dictated by the selected steam parameters, the steam cycle configuration, the cooling tower conditions and the boiler s efficiency. The Łagisza boiler was also designed to utilise a flue gas heat recovery system, which cools the flue gases down to 85 C to improve efficiency. The calculated LHV net plant efficiency for the Łagisza plant is 43.3 % and the 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. The operation of the Łagisza boiler has thus far been excellent. Over the whole load range the boiler has performed as designed and its operation has been both steady and easily controllable. The results obtained from the operation of the Łagisza CFB show that the heat flux profiles of the furnace walls have been low and uniform during coal firing. Emissions have also been lower than the levels set by the Large Combustion Plant (LCP) Directive, and the low flue gas exit temperature achieved, as well as high combustion efficiency have guaranteed high overall thermal efficiency at the plant. This has clearly demonstrated that the control concept chosen for the Łagisza boiler has been a success. The CFB is behaving exactly as expected in transient conditions and all of the parameters are stable when the boiler is operated in steady state conditions. Latest milestone in the OTU CFB technology: Samcheok Green Power 4 x 550 MW e In July 2011, full notice to proceed was given 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 coal mixed with biomass whilst at the same time meeting all environmental requirements. Once the Samcheok CFB units enter commercial operation in 2015, they will be the world's largest and most advanced CFBs and will provide a new level of fuel flexibility, reliability and environmental performance. Design details Figure 7. Samcheok Green Power 4 x 550 MW e The Samcheok boiler design is based on OTU CFB concept and follows the same basic design features used in the Łagisza plant. The boiler design is based on a modular structure with separator and solids return designs that are identical to those used in the Łagisza plant. Steam

circuit is also generally the same as in the Łagisza plant, incorporating advanced steam parameters (temperature) and optimised steam circuitry design. The boiler material requirements for most sections of the Samcheok boilers are very conventional and normal boiler materials have been used. Furthermore, the design for the Samcheok boilers is free of T24-steel. Design fuel The CFB steam generators at the Samcheok plant will be designed to burn coal mixed with biomass whilst 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 co-fire wood pellets (Table 4). Table 4. Fuel specifications Bituminous Coal Biomass LHV (a.r.) MJ/kg 14,2 24,9 15,8-18 Moisture % 20 43 5 15 Ash (a.r.) % 1,2 15,3 0,7 5 Sulphur (a.r.) % 0.1-1 0-0,16 Steam parameters The steam pressure and temperature that has been selected for the Samcheok plant has been shown to be viable in other supercritical units and conventional boiler steel materials can be used for the boiler s construction. Table 5 below presents the main design steam parameters of the 4 x 550 MW e (gross) CFB boilers that will be built at Samcheok. Table 5. 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 CFBs will meet the stringent emission values given below in Table 6 without needing any additional back-end flue gas desulphurisation equipment for SOx control. Table 6. 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 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.. Połaniec CFB 205 MW e / 447 MW th, Poland for Agro and Virgin Biomass Solid Fuels There has recently been an increase of the use of biomass in energy production. In particular, the use of agricultural biomass in addition to virgin biomass has seen a growth in popularity. This has created a corresponding demand for large scale biomass firing power plants. In line with this increase in demand, in April 2010, GDF Suez Energia Polska S.A. awarded Foster Wheeler with a contract to design a CFB biomass firing boiler for the Połaniec Power plant (Figure 8). The combustion technology design is based on Advanced Bio CFB (ABC) technology (Figure 5). The Połaniec boiler is a 205 MW e /447 MW th, 158.3/135.1 kg/s, 535/535 ºC and 127.5/19.5 bar(a) utility boiler that operates on a broad range of biomass fuels, achieves the highest efficiency and availability currently possible, and operates in accordance with Polish regulations (Tables 7, 8 & 9). The Polish regulations set the proportion of agro biomass used for firing to a minimum of 20 % for plants in operation by the end of 2012.

Figure 8. Advanced Bio CFB in Połaniec site. Table 7. Połaniec fuel data Wood Residue Agro Biomass Sulphur 0.04% d.s. 0.04...0.16% d.s. Nitrogen 0.05% d.s. 0.49...1.27% d.s. Moisture 42.4% 9.7...13.0% Ash 0.5% d.s. 2.20...6.90% d.s. LHV 9.4 MJ/kg 14.7...17.9 MJ/kg

Table 8. Połaniec boiler design performance DESIGN PERFORMANCE, O 2 6% in dry gases Flue Gas Exit Temperature 148 C Boiler Efficiency 91.0% Emission Guarantees 50% 24h average - NO x - SO 2 - CO Particulate Matter (dry) MCR...BMCR <150 mg/nm 3 <150 mg/nm 3 <50 mg/nm 3 <20 mg/nm³ Table 9. Połaniec boiler steam data STEAM DATA Total Heat Output 447 MW th Steam Flow 158/135 kg/s Steam Pressure 127/20 bar(a) Steam Temperature 535/535 C Feedwater Temperature 242 C The delivery comprises of a CFB boiler island including designing and supplying the steam generator, auxiliary equipment, biomass yard and carrying out civil works, erection and commissioning of the boiler island. The fuel that was considered when designing the CFB boiler in the Połaniec power plant was comprised of 80 % wood and 20 % agro-biomass. The Wood fuel is clean wood from forestry and the Agro biomass fuel includes a variety of agro biomass such as straw, sunflower pellets, dried fruit (marc) and palm kernel shell (PKS). The alkali content of the fuel mixture with 20 weight-% of agro biomass was much higher than experienced earlier in commercial CFB boilers with a capability of firing solid biomass fuels. The fuel mix properties are presented below in Table 10. Table 10. Połaniec fuel mix properties Fuel: 80% Wood Chips & 20% AGRO (Straw, Sunflower, dry fruits, Palm kernel) Moisture [%] ar 35.9 Ash [%] dry 2.8 Nitrogen [%] dry 0.25 Sulphur [%] dry 0.05 LHV [MJ/kg] ar 10.5 Połaniec CFB Boiler Design The Advanced Bio CFB Design of the Połaniec boiler utilises the main design concept and features that are shown above in Figure 7. However, risks related to high temperature chlorine corrosion, fouling and agglomeration were also taken into account when designing the boiler and its operation. The design of the Połaniec CFB boiler (Figure 9) incorporates solids separators built from steam cooled panels integrated with a combustion chamber. The steam cooled separator design is effective because it avoids heavy refractory linings from occurring in the separator. The final superheating stage as well as the final

reheating stage comprises of INTREX TM heat exchangers, which are located in special enclosures at the bottom of the furnace (adjacent to the main combustion chamber). Figure 9. Advanced Bio CFB s in Połaniec boiler. The Połaniec CFB boiler utilises moderate fluidising velocity in the furnace. This is an important characteristic of Advanced Bio CFB technology utilised in order to achieve boiler efficiency. Furthermore, the design features a full step grid design in order to transfer any heavy unfluidised particles into the bottom ash removal system. In order to control the boiler s emissions, the boiler design utilises the well known benefits of CFB combustion, such as the low and uniform temperature profile in the furnace and the staged combustion. In addition to these combustion process related measures, the boiler has also been designed to include an ammonia injection system and catalyst (SNCR+SCR), which controls the nitrogen oxide emission, as well as an electrostatic precipitator (ESP), which controls particulate emission. With the inclusion of these measures in its design, the Połaniec CFB boiler can meet all of the relevant emission limits (150 mg/m 3 n NO x, 150 mg/m 3 n SO 2, 50 mg/m 3 n CO and 20 mg/m 3 n particulates). As can be seen by the above, this project clearly demonstrates the advantages of state-of-the-art Advanced Bio CFB design. The design allows co-firing high alkaline agro biomasses with wood-based biomass in utility-size power production. Initial operation experiences The Initial operational experiences at the Połaniec power plant have been excellent and the boiler was commissioned in accordance with the schedule in the fourth quarter of 2012. In fact, the commercial operation date was reached a full six weeks ahead of the contractual schedule on November the 15 th of 2012. Since that time, the boiler has operated as expected with various fuel mixes and has achieved the high efficiency that was expected. The boiler meets the requirements of electricity production at a full

load range and is in use on a weekly basis. The boiler also fulfils all of the relevant Polish grid requirements with a 4 % min. load change rate using only solid biomass fuels. The typical fuel mixture used for the boiler is 20 % PKS (Palm Kernel Shell) and 80 % forestry wood chips. An agro firing test using sunflower pellets, straw pellets and fruit dried chips each comprising 20 % along with wood chips took place in the beginning of February 2013. The results of this test showed successful operation with all of the tested agro qualities. Kladno CFB boiler design The Kladno boiler represents the next generation of utility power boilers. The Kladno CFB boiler has been designed to co-fire lignite and biomass with the capability of adapting to sudden load change requirements in the electricity grid. The design of the new Kladno CFB boiler (Figure 10) incorporates solids separators built 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. Figure 10. Kladno K7 CFB boiler design The design basis of the Kladno boiler is presented in tables 11-13.

Table 11. Kladno fuel data DESIGN FUEL DATA Lignite Biomass Sulphur 1,35% d.s. 0.13% d.s. Nitrogen 0,67% d.s. 1% d.s. Moisture 26,6% a.r 40% a.r Ash 19,78 % d.s. 3,33% d.s. LHV 15,61 MJ/kg 9,7 MJ/kg Table 12. Kladno boiler design performance DESIGN PERFORMANCE Flue Gas Exit Temperature 130 C Boiler Efficiency 93,2% Emission * Guarantees 40 % to 100 % BMCR ½ hour average - NO x <190 mg/nm 3 - SO 2 <190 mg/nm 3 - CO <95 mg/nm 3 - NH 3 <10 mg/nm 3 (slip cat. installed) - NH 3 <20 mg/nm 3 (w/o slip cat.) Particulate Matter <20 mg/nm³ *) Emissions expressed in dry fluegases @ 6%O2 Table 13. Kladno boiler steam data STEAM DATA Total Heat Output 303 MW th Steam Flow 105/102 kg/s Steam Pressure 133/33 bar(a) Steam Temperature 541/541 C Feedwater Temperature 251 C The new Kladno K7 lignite firing CFB boiler unit replaced an old coal-fired unit, which was commissioned at the Kladno power plant in the late 1970s. The new unit will be operated alongside two 135 MW e CFB units, which were previously commissioned in the 1990s, and is located adjacent to the old boilers. This allows the new boiler to utilise many of the existing plant systems, such as the coal handling and water treatment plant. Scope of work for the CFB boiler included the design of the boiler; the delivery of the 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 filter; the erection and construction of the boiler; and the start-up, performance testing and commissioning of the boiler. The time schedule that was adopted for the project is presented in Table 14. Table 14. Project execution schedule Contract Award December 2010 Start of Erection November 2011 Commercial Operation December 2013 The main fuel utilised for the new CFB boiler at the Kladno power plant is lignite obtained from a local mine (Bilina). The CFB Boiler is designed for biomass co-firing of a maximum of 10 % heat input. Despite the fact that the lignite is obtained from only one source, there is substantial variation in the fuel quality, especially in terms of in-organic matter, which results in a dry solids range of 13 to 30 %. 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. The Kladno CFB boiler incorporates the latest design of solids separators build from water or steam cooled panels integrated with the combustion chamber. The design also features INTREX TM superheaters. 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. After commencing commercial operation in December 2013, the operation of the Kladno power plant has been excellent. According to the preliminary results, 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. 6 DYNAMIC BOILER PERFORMANCE When designing a CFB boiler, it is important to ensure safe and efficient steady-state operation, high flexibility in fuel or fuel mixtures to be combusted, and high flexibility in the boiler s operational range. The increased requirements for solid fuel fired power plant operation and control dynamics in the European power market have resulted in a particular focus on the development of flexible operation with fast load following in order to fulfil the load change requirements. There has also been an increased emphasis on boiler designs needing to meet stringent emission limits. When designing a boiler, it is also equally important to carry out dynamic boiler optimisation. The purpose of dynamic boiler optimisation is primarily to achieve the performance required in order to achieve primary and secondary control of the electric grid frequency over the whole load range. On the other hand, dynamic optimisation aims to ensure that the boiler meets the requirements set for the boiler

controls (e.g. the main steam temperature and pressure control and the reheated temperature control), and, most importantly, dynamic optimisation helps to ensure that the boiler meets the emission limits in transient conditions. CFB boilers, whether equipped with once-through, or drum-type steam generators, and whether fired with fossil or solid biomass fuels, are a viable means of power generation and achieve fast and stable operation. Figure 11 demonstrates the load change (4% MCR/min) capability of the Kladno plant (lignite/biomass, constant pressure drum boiler) while simultaneously extracting steam for district heating. The primary grid support of the same plant was tested at low (30%) and high (100%) load levels (see Figure 12). The Kladno unit is fitted with the possibility for condensate throttling during load changes. These tests were part of grid code certification tests completed in late November 2013. Figure 11: Kladno new CFB unit load changes of 4% MCR/min. Figure 12: Kladno new CFB unit grid Primary Support tests at full and minimum load The Boiler dynamic performance of the 100% biomass fired Polaniec plant (constant pressure drum boiler) was also tested and the results are given in Figure 13. The Polaniec plant was also operated with a 4% MCR/min ramp. Furthermore, the Łagisza (coal combusted OTU boiler) dynamic operation with grid support capability at low load level is shown in Figure 14.

Figure 13: Polaniec new CFB unit load change from of 1% MCR/min, grid Primary Support and Secondary Support tests. Figure 14: Łagisza OTU-CFB load changes and grid Primary Support tests. Considerations to meet the current and future flexibility requirements The trend of needing to increase flexibility requirements in the European power market will set new targets for the development of conventional solid fuel based power plants. New functions and capabilities, such as low load operation and fast load following, are expected to result from this rapid development, particularly within the field of CFB technology.

In comparison with conventional PC technology, CFB technology provides the possibility to utilise various fuel blends. This includes lignite together with dried lignite, coal, and mixtures of biomass. Not only can these fuels be used, but when firing these fuels CFB technology is able to meet all of the relevant emission requirements as well as the boiler minimum load/load change requirements. Consequently, the need for dynamic capability is constantly increasing. Furthermore, there is also an increasing need to be able to shut down the plant for the night and achieve a fast start up in the morning. There have been various targets set by the power and utilities market. The commercially requested minimum load capability of CFB technology is currently app. 30%. However, the future target set is app. 15-20%. The currently requested primary load control capabilities are 2-5% (MCR)/30 s. However, a future development target has been set to increase the primary load control capabilities up to 10 %(MCR)/30 s in coordination with the steam turbine. Finally, secondary control capabilities are currently requested to be 2,5-4% (MCR)/min. However, in the future up to 5%(MCR)/min is targeted. Foster Wheeler is currently undertaking extensive development work in order to achieve these targets. 7 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 functions and capabilities, such as 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.