Marko Natunen, Timo Jäntti, Damian Goral, Kalle Nuortimo Foster Wheeler Energia Oy P.O.BOX 201, FI Varkaus, Finland

Transcription

1 FIRST OPERATING EXPERIENCES OF 55 MW e KONIN AND 205 MW e POŁANIEC CFB BOILERS FIRING 100 % BIOMASS Marko Natunen, Timo Jäntti, Damian Goral, Kalle Nuortimo Foster Wheeler Energia Oy P.O.BOX 201, FI Varkaus, Finland timo.jantti@fwfin.fwc.com ABSTRACT: Nations worldwide are taking initiatives to counteract global warming by reducing their greenhouse gas emissions. The European Union is playing a leading role by setting targets to reduce its greenhouse gas emissions by 20 %, from 1990 level, increasing its share of renewable energy to 20 % in its primary energy consumption and improving energy efficiency by 20 % with all three targets met by the year Efforts to increase boiler efficiency and the use of biomass and other solid renewable fuels are well in line with these objectives. Circulating Fluidized Bed boilers (CFB) are ideal for efficient power generation, capable of firing a broad variety of solid biomass fuels from small CHP plants to large utility power plants. After introducing the market drivers and technical challenges of firing solid biomass and residue in utility boilers, this paper presents the advanced technical features developed by Foster Wheeler in their CFB biomass boilers, which all together embody Advanced Bio CFB technology. This paper also reviews relevant boiler references in commercial operation, and finally reveals the range of applicability and performance of the latest CFB designs available on the market, supported by data from the commercial references, including Konin Poland (55 MW e ) and Połaniec - Poland (205 MW e ) that is the world s largest 100 % solid biomass firing CFB boiler today. First operational experiences of Połaniec and Konin boilers are highlighted. Keywords: CFB, Biomass, Renewable Energy

2 INTRODUCTION Nations worldwide are taking initiatives to counteract global warming by reducing their greenhouse gas emissions. The European Union is playing a leading role by setting targets to reduce its greenhouse gas emissions by 20 %, from 1990 level, increasing its share of renewable energy to 20 % in its primary energy consumption and improving energy efficiency by 20 % with all three targets met by the year Efforts to increase boiler efficiency and the use of biomass and other solid renewable fuels are well in line with these objectives. Circulating Fluidized Bed boilers (CFB) are ideal for efficient power generation, capable of firing a broad variety of solid biomass fuels from small CHP plants to large utility power plants. Advanced Bio CFB (ABC) technology represents the stateof-the-art for large scale power generation from solid biomass fuels. The Advanced Bio CFB technology further improves the well known benefits of earlier CFB technologies such as superior fuel flexibility, inherently low emissions, and high availability. Today, the Advanced Bio CFB technology offers efficient sub-critical boilers up to 600 MW e for 100 % biomass firing. This technology also offers supercritical steam parameters for biomass and coal cofiring applications up to 800 MW e. This is the result of continuous and determined development work, based on experience and data from nearly 400 CFB reference boilers, of which over 50 are designed for biomass, and nearly 50 for waste containing biodegradable fractions, which are effectively CO 2 - neutral. After introducing the market drivers and technical challenges of firing solid biomass and residue in utility boilers, this paper presents the key technical features adopted in CFB boilers to overcome such challenges, ultimately defining the Advanced Bio CFB technology. The paper reviews relevant boiler references in commercial operation, focusing on Konin and Połaniec CFB s operational experiences, and finally reveals the range of applicability and performance of latest CFB designs available on the market. BIOMASS AS ENERGY SOURCE IN UTILITY BOILERS Market Drivers Biomass is considered a carbon-neutral fuel in many countries, and its utilization in utility power boilers can result in reduction in carbon dioxide emissions (CO 2 ) since the biomass captured atmospheric carbon during its growth cycle. Until recently, the size of the biomass fired plants was limited to small industrial units. This was mainly due to a combination of limited high quality

3 biomass, as well as the availability of a large scale efficient boiler technology capable of reliably burning a wide spectrum of biomass fuels. Today, the biomass market has changed from local to global. Biomass fuels are dried and compressed into pellets to improve the economics and logistics of moving them around the globe. Pellets are currently being produced in Brazil, US, and Canada as well as other countries for transport to Europe and Asia. Some countries promote the use of biomass by granting environmental incentives that compensate for the additional costs of biomass transportation and logistics, while other countries only permit new plants that can operate on biomass. Such government policies have amplified the interest for large scale biomass fired units. As a clear sign of booming biomass market, in 2010 the global production of wood pellets reached 14.3 million tons, and its consumption approached 13.5 million tons, recording an increase of over 110 % compared to 2006 (IEA 2011). To date, biomass combustion systems fire mainly residue from the forest industry, such as wood chips, sawdust, bark, and forestry residue. However, as the demand for biomass fuels grows and the price for wood-based biomass increases, there is a growing interest to use biomass fuel from other sources, e.g. agricultural biomass, biomass residue and biomass wastes (Figure 1). Figure 1. Increasing diversity of solid fuels available on the global market

4 Technical Characteristics Biomass properties vary considerably depending on their biological origin, regional origin, seasonality, farming and harvesting practices, and ultimately on their preparation and processing. This leads to broad variations in chemical composition and physical properties across different biomass types and even within the same type (Table 1). Their wide property differences are one of the key challenges of using biomass as a fuel for power and steam production. Table 1. Properties of selected biomasses Timber Timber Saw Bagasse Straw Peat Recycled RDF pellets chips dust briquette pellets wood fluff Moisture % Lower Heating Value MJ/kg 17 7,5-13, ,7 9, Bulk Density kg/m Energy density MWh/m3 3 0,55 0,45-0,7 2,9 2,7 0,9 1,4 0,4 Ash % ds 0,9 0,4-5,3 0,4-0, , S % ds <0,1 <0,1 <0,05 <0,05 0,01-0,03 0,22 0,1 0,1-0,5 Cl % ds <0,03 <0,05 <0,03 <0,03 0,1-0,8 0,02-0,06 0,1 0,3-1,2 Alkali % ds 0,1-0,3 0,1-0,3 0,1-0,3 0,4-0,7 0,3-1,7 0,1 0,1-0,5 0,4-1 P % ds <0,05 <0,05 <0,04 <0,05 0,05-0,8 <0,35 <0,3 <0,5 Physical properties such as bulk density, heating value and moisture content affect plant design in terms of fuel handling, feeding systems and overall boiler dimensioning. Generally, boilers sized to handle the modest amounts of flue gas from dry pellets may have difficulties managing the considerably larger volumes of flue gas from wet chips. Conversely, furnaces designed to handle the moderate heat from wet chips may suffer overheating from drier and more calorific biomass and residue. Concerning the ash related problems, these may include furnace slagging, bed agglomeration, boiler fouling, localized erosion, and extended corrosion. Elevated levels of alkalis metals like sodium and potassium, as well as chlorine in biomass become concentrated in the boiler ash cause fouling and corrosion within the boiler. Challenges presented by woody biomass fuels were reasonably predicted on such bases. However, the broader variety of biomass fuels currently marketed demand more complex fuel evaluations, which take the overall fuel composition into account. Among the marketed biomass fuels, agricultural residue (agros) such as some straws, olive residue, and rapeseed residue are identified as the most problematic. These hold the highest potential to create operational difficulties such as agglomeration of fluidized beds, as well as fouling and corrosion of convective heat surfaces. These problems can be traced back to elevated concentrations of alkali, phosphorous and chlorine, which are typically much higher in most agros than in wood. This

5 unfavorable composition is the main reason why the utilization of novel biomass fuels has been limited in energy production so far. Detailed knowledge of biomass specifications and full understanding of their variability of supply are paramount to design boilers with highest efficiency and availability, and to operate them in the most economical way. 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 their inherent fuel flexibility, CFB boiler technology is ideal for large scale power generation from a broad range of biomass fuels, either alone or co-fired with fossil fuels. Foster Wheeler has progressively advanced and scaled-up CFB technology 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 today s state-of-the-art for biomass combustion. ABC is the result of corporate knowledge on biomass and experience from over 400 CFB commercial references combined with continuous research. The ABC technology not only addresses the fuel issues related to biomass firing, but also adopts plant requirements and optimizes its investment factors. Plant requirements include the type of the boiler i.e. utility or industrial boiler, capacity, operational load range, steam data, emission limits and other requirements set by legislation. Investment factors include plant availability, fuel flexibility requirements, the investment costs and operation costs. Consequently, economical boiler designs have been developed to fire easy-to-burn biomass, while more robust solutions are implemented as the biomass quality degrades and becomes more challenging to burn reliably. Key design features of the ABC technology are summarized in Figure 2. This concept has been utilized in the operating references described in the next chapter.

6 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 2. Key features of ABC technology. LARGE SCALE CFB FOR BIOMASS COMBUSTION EARLY OPERATING EXPERIENCES Examples of the ABC technology are i) Konin CFB boiler (55 MW e /154 MW th ) and ii) Połaniec (205 MW e / 447MW th ) located in Poland, which fire 100 % biomass including a considerable share of demanding agricultural residue. Konin 55 MW e / 154 MW th CFB, Poland July 2009, ZE PAK SA signed a contract with Foster Wheeler Energia Polska for the turnkey construction of a biomass-fired circulating fluidized bed boiler at the Konin Power Plant with a steam output of 215 t/h. In February 2010, the owner formally handed over the construction site to Foster Wheeler for the preparation of site facilities, and on March 15th in 2010 FW started civil engineering work relating to foundations for the boiler house and the auxiliary buildings and structures.

7 Foster Wheeler s scope of work included a CFB boiler island including designing and supplying the steam generator, auxiliary equipment and carrying out civil works, erection and commissioning of the boiler island. The main project constrains were the erection area and the project schedule. This brown field project is located inside The Konin Power Plant (Figure 3). Figure 3. Konin Power Plant The Konin CFB boiler is a state-of-the-art biomass firing unit designed for firing clean woody biomass and up to 20 % of the agricultural biomass including energy willow, straw, rapeseed residue, cherry stones and oat husk. The boiler design consists of the furnace and two high efficiency solid separators. Advanced design (Figure 4) follows the features in ABC technology presented before (Figure 2). Heat output capacity M 154 Steam flow t/h 215 Steam temperature C 540 Feedwater temperature C 210 Guaranteed efficiency % 91 NOx mg 200 SOx mg 200 Dust mg 30 Figure 4: Konin CFB Boiler

8 Fuel management High alkali fuels require advanced fuel handling (Figure 5) to avoid sudden changes in fuel composition. Konin CFB unit was designed with high availability in mind and this sets design basis for all key processes of the power plant. Design fuels differ from each other not only by chemical composition, but also by physical properties like bulk density, moisture content or particle size. All types biomass are transported to the site by trucks and they go to storage silos through an unloading station. There are three separate storage silos, each dedicated for forest and woody biomass and five separate silos for agro biomass. Each agro fuel is fed from separate silo, since the fuel mixture consist of straw pellets, oat husk, cherry stones, rapeseed cake and energy willow the dosing is made by screw reclaimers. System allows the dosing of different types of biomass in order to feed homogenous fuel mixture to boiler day silos. Figure 5. Konin biomass yard The mixture of different types of biomass is distributed evenly to boiler by four feeding points. The fuel is fed to solid return chutes from external integrated heat exchangers and mixed with circulating material before entering the furnace. Initial experience First steam to turbine went in on April 28 th 2012 and power block was synchronized two weeks later. The first operational experiences have been very good. Data from performance test shows that all guaranteed parameters have been met.

9 Połaniec CFB 205 MW e / 447 MW th, Poland for Agro and Virgin Biomass Solid Fuels The increase of biomass utilization in energy production has created a demand for large scale biomass firing power plants and the demand to utilize the agricultural biomass in addition to virgin biomass in energy production. GDF Suez Energia Polska S.A. has awarded the utility Połaniec Power plant project in April Combustion technology is based on the Advanced Bio CFB (ABC) technology (Figure 6). Połaniec 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 while targeting highest efficiency and availability achievable in accordance with Polish regulations (Tables 2, 3 & 4). Such regulations set the proportion of agro biomass to a minimum of 20 % under the condition that the plant is in operation by the end of Figure 6. Advanced Bio CFB in Połaniec site. Table 2. Połaniec fuel data FUEL DATA Wood Residue Agro Biomass Sulphur 0.04% d.s % d.s. Nitrogen 0.05% d.s % d.s. Moisture 42.4% % Ash 0.5% d.s % d.s. LHV 9.4 MJ/kg MJ/kg

10 Table 3. 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% MCR...BMCR, 24h average - NO x <150 mg/nm 3 - SO 2 <150 mg/nm 3 - CO <50 mg/nm 3 Particulate Matter (dry) <20 mg/nm³ Table 4. 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 considered for the new boiler in the Połaniec power plant is comprised of 80 % wood and 20 % agro-biomass. The Wood fuel is clean wood from forestry. 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 is clearly higher than experienced earlier in large scale commercial CFB boilers with biomass fuels. To enable the use of this challenging fuel mixture with high efficiency and availability in the CFB boiler, a demonstration of the advanced agro CFB concept was carried out in a development program with adequate pilot testing. The results show the CFB feasibility for the Połaniec project with the requested fuel range. The fuel mix properties are presented in Table 5.

11 Table 5. 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 Sulfur [%] dry 0.05 LHV [MJ/kg] ar 10.5 Połaniec CFB Boiler Design The Advanced Bio CFB Design of Połaniec utilizes the main design concept and features as shown in Figure 2. Risks related to high temperature chlorine corrosion, fouling and agglomeration potential were taken into account in the boiler design and operational concept. The design of the new Połaniec CFB boiler (Figure 7) has solids separators built from steam cooled panels integrated with the combustion chamber. The steam cooled separator design avoids heavy refractory linings in the separator. The final superheating stage as well as the final reheating stage are INTREX TM type 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, resulting in higher steam temperatures since it is protected from the fouling and corrosive environment of the boiler s hot flue gas. INTREX TM heat exchangers also provide good load-following capabilities and turndown ratios.

12 Figure 7. Advanced Bio CFB s in Połaniec boiler. The Połaniec CFB boiler utilizes moderate fluidizing velocity in the furnace which is an important characteristic of Advanced Bio CFB technology. Furthermore, the design features a full step grid design in order to transfer heavy unfluidized particles effectively into the bottom ash removal system. For controlling the emissions, the CFB utilizes well known benefits of the CFB combustion like low and uniform temperature profile in the furnace and staged combustion. In addition to these combustion process related measures, the boiler is equipped with ammonia injection system and catalyst (SNCR+SCR) for controlling the nitrogen oxide emission. Electrostatic precipitator (ESP) is used for controlling particulate emission. With these measures, the Połaniec CFB boiler can meet the emission limits set for it (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). This project further demonstrates the capability of state-of-the-art Advanced Bio CFB concept that allows co-firing high alkaline agro biomasses with wood-based biomass in utility-size power production. Initial operation experiences Initial operational experiences have been excellent with a smooth boiler commissioning in 4Q, The commercial operation date was reached six weeks ahead of the contractual milestone on November 15th. The boiler has operated well with various fuel mixes, and with high efficiency. Boiler

13 operation responds to requirements of electricity production, full load range is in use on weekly basis. The boiler fulfils all Polish grid requirements with 4 % min. load change rate demonstrated with solid biomass fuels only. Chipped clean wood from forestry is transported with trucks or with trains to the site where it is stored in the A-barn and unloaded with screw reclaimers to belt conveyors. Agro fuels are stored in a silo beside A-barn and led to the same conveyor belt above wood chips layer. Boiler day silos (2 pcs) feed biomass mixture to front and rear walls of the furnace, where 8 feeding points ensure excellent fuel distribution and thus good mixing for efficient combustion process. Since the beginning of hot commissioning the boiler has been operated under process values very close to the design figures and on load levels from minimum of 40 % MCR to maximum. Expected low emission levels have been confirmed during initial operation clearly fulfilling the set requirements. The initial boiler availability has turned out to be good while still improving. Especially there have been improvements in fuel logistic and handling essentially reducing amount of foreign particles while more operation experience has been gathered. Typical fuel mixture for the boiler is 20 % PKS (Palm Kernel Shell) with 80 % forestry wood chips. Agro firing test with sunflower pellets, straw pellets and fruit dried chips of 20 % portion each with wood chips took place in the beginning of Feb The initial results showed successful operation with all tested agro qualities. There was a special focus for high-alkaline straw co-firing which was completed successfully too. Official grid tests were completed during 1Q of Performance tests will be performed during spring LARGE SCALE CFB FOR BIOMASS COMBUSTION STATE-OF-THE-ART The increase of biomass utilization in energy production has created a demand for extremely large biomass firing power plants. Current prospects stretch out to 400 MW e biomass-fired units. Based on continuous development work and extensive reference data, the Advanced Bio CFB boiler concept has been developed to this scale and beyond. The highly efficient design offered for 100% biomass is available up to 600 MW e size for clean woody biomass, and up to 400 MW e when including 20-30% agro in the biomass.

14 The boiler scale is well within the existing CFB experience range. The CFB boiler design is based on CFB design for clean biomass fuels utilizing the fully integrated steam cooled solids separator and return leg, INTREX TM superheater and reheater, and partial step grid designs. The conceptual design of this high efficient MW e scale Advanced Bio CFB is market-ready MW e utility CFB for co-combustion of solid biomass fuels and coal Sub-critical ABC CFB boiler design is available up to 600 MW e with steam temperatures of over 560 ºC. Supercritical CFB is offered up to 800 MW e for bituminous coal with a possibility to co-fire 20 % biomass, meeting the highest requirements for plant efficiency and environmental performance. SUMMARY Biomass has an important role in reducing the environmental effects of energy production both in pure biomass plants and in coal and biomass co-combustion. Circulating Fluidized Bed boilers (CFB) are ideal for efficient power generation, capable of firing a broad variety of solid biomass fuels for small industrial plant as well as large utility power plants. The current state-of-the-art design is based on FW s extensive knowledge of biomass firing based on approximately 200 CFB and BFB units sold firing solid biomass fuels. Today, Advanced Bio CFB technology represents the state-of-the-art for large scale solid biomass fuel firing. The technology provides solutions for effective CO 2 reduction in large scale power generation with a broad range of solid biomass fuels. The award from GDF Suez Energia for a CFB boiler island for the PołaniecPołaniec Power Station in Poland confirms the competitive edge of CFB technology to fire 100% biomass to ever larger scale. After starting commercial operation in November 2012, this is the world s largest 100% biomass CFB boiler, burning wood residue with 20% agricultural residue. The ABC technology is the ideal choice in meeting the market s demand for fuel flexibility now and in the future to utilize a broad range of solid biomass fuels in large scale power generation.