STATE-OF-THE-ART CFB TECHNOLOGY FOR UTILITY-SCALE BIOMASS POWER PLANTS

Transcription

1 STATE-OF-THE-ART CFB TECHNOLOGY FOR UTILITY-SCALE BIOMASS POWER PLANTS Vesna Barišić*, Edgardo Coda Zabetta*, Bogusław Krztoń** *Foster Wheeler Energia Oy, R&D Department, Relanederinkatu, Varkaus, Finland **Foster Wheeler Energia Polska, Global Sales & Marketing, Aleja Jana Pawla II 15, Warszawa, Poland Utilization of biomass fuels in energy production continues to grow worldwide as a response to climate change concerns induced by anthropogenic emissions of CO. Over the last years, an increasing demand is emerging for highly efficient utility-scale power plants capable to co-fire woody biomass with large shares of agricultural residues, residues from production of bio-derived fuels for the transport sector (i.e. biodiesel, bioethanol), and/or wastes. However, properties of biomass fuels are more challenging comparing to conventional fossil fuels. The quality of biomass varies seasonally and regionally, moisture can be high, fuel handling and feeding are more demanding, and above all fouling, slagging, and superheater corrosion are common problems in biomass-fired boilers. With respect to these problems, circulating fluidized bed combustion has proven to be an ideally suited technology for large-scale power production utilizing broad range of biomass fuels. This paper summarizes the features of Foster Wheeler s biomass fired CFBs, with emphasis on the Advanced Biomass CFB (ABC) concept developed for utility-size CFBs targeting steam temperatures higher than 56 C. In particular, the paper will discuss the technical difficulties to be expected in co-combustion of woody biomass with agricultural residues, and the adequate countermeasures. Finally, the paper will give an overview on reference data from commercial biomass CFB projects. Key word: agricultural residues, wood-derived biomass, ash, agglomeration, fouling, corrosion 1. INTRODUCTION Utilization of biomass fuels in energy production continues to grow worldwide as a response to climate change concerns induced by anthropogenic emissions of CO. -derived fuels have been traditionally the main biomass sources fired in small/medium-scale boilers, and mostly connected to the pulp and paper industry and forestry exploitation. As the demand for biomass fuels is growing while the concern about forests availability and prices are increasing, other types of biomass are gaining in popularity. Over the past few years, the biomass market has developed into a global network offering a wide variety of opportunity fuels such as agricultural residues (agro-), residues from production of biofuels for the transport sector (e.g. bioethanol, biodiesel), dedicated energy crops, etc. This growth in fuel availability has led to an increasing demand for highly efficient utility-scale power plants capable to co-fire woody biomass with large shares of opportunity biomass, and/or wastes. When biomass or waste is considered, fluidized bed boilers are often the technology of choice offering supreme fuel flexibility and low emissions while boiler availability and efficiency are high. Bubbling fluidized bed boilers (BFB) have often been favored in small-scale industrial applications, while circulating fluidized bed boilers (CFB) are most advantageous in larger applications. During the past 3 years Foster Wheeler has booked over 36 CFB boilers ranging from 7 to nearly 1 MWth. Of these, over 5 are designed for biomass (or bio-mix) and nearly 5 for waste (or wastemix) containing biodegradable fractions. This paper summarizes the features of Foster Wheeler s biomass fired CFBs, with emphasis on the Advanced Biomass CFB (ABC) concept developed for utility-size CFBs targeting steam

2 temperatures higher than 56 C. In particular, the paper will discuss the technical difficulties to be expected in co-combustion of woody biomass with agricultural residues, and the adequate countermeasures. Finally, the paper will give an overview on reference data from commercial biomass CFB projects.. ASH RELATED CHALLENGES IN BIOMASS AND WASTE COMBUSTION Properties of biomass and waste fuels are more challenging compared to conventional fossil fuels. The quality of biomass varies seasonally and regionally, moisture can be high, energy content low, fuel handling and feeding are more demanding. Furthermore, the extremely complex biomass ash-chemistry is often a major cause for operational problems in biomass-fired boilers, and the content and concentration of ash forming elements differs substantially among biomass fuels. Si Al Fe Ca Mg K Na P Ash concentration Concentration [g/kg fuel, dry] Ash 54 g/kg Stem Forest Residue Recycled 5 Coal Peat Stem Forest Residue Sunflower Husk Wheat Straw Olive Rapeseed Recycled RDF Fossil Fuel Biomass Fuel Fuel 3 Concentration [g/kg fuel, dry] Sulfur Na, week acid soluble Chlorine K, week acid soluble 5 Coal Peat Stem Forest Residue Sunflower Husk Wheat Straw Olive Rapeseed Recycled RDF Fossil Fuel Biomass Fuel Fuel Figure 1. Comparison of fossil, biomass, and waste fuels in respect to the content and concentration of ash forming elements. As shown in Figure 1, compared to fossil fuels, most biomass and waste fuels contain a smaller amount of aluminosilicates, but higher shares of alkali elements that are in reactive form. Furthermore, within biomass there are large variations in composition of ash-forming elements depending on specie, part of plant, harvesting and processing practice [1].

3 Typically, woody biomass fuels have low content of ash,.1 6 % wt, dry, rich in Ca and K. Straw/stalk of herbaceous biomass contains 3 17 % wt, dry of ash, and their ash chemistry is governed by the share of Si, K, Cl, and occasionally Mg and P. Husk of oil/cereal crops may vary considerably depending on specie, for example ash content of sunflower husk vary approximately in the range 3 8 % wt, dry while rice husk 17 3 % wt. Furthermore, more than 55% of ash-forming elements (excluding O) in sunflower husk are K and Cl, while in rice husk Si. from olive oil extraction contains even up to 14% wt of ash with share of K and Cl of nearly 6% of ash-forming elements (excluding O). Seeds of oil/cereal crops, such as rapeseed, contain considerable amount of P together with high K and Mg in proportions that have a detrimental impact on boiler operation. Compared to biomass, waste fuels typically contain more Na, trace elements (Zn, Pb, Cu, metallic Al, etc.) and soil/concrete contaminations. In summary, each biomass and waste fuel has distinct features, which are results not only of chemical, but also physical properties, such as moisture content, density, particle size, form of fuel (pellet, fluff, etc.). Utilization of biomass and waste fuels in highly efficient CFB boilers is often connected with elevated risk of bed agglomeration, fouling, and corrosion. Agglomeration of bed material may occur during combustion of some biomass and waste fuels, and it is more intense with agro- than with wood-derived biomass. Agglomeration is caused by the formation of low-temperature melting compounds and/or eutectics. The reactions between alkali from fuel and quartz particles from the bed material have been identified as key events in formation of sticky alkali-silicate coating layers that lead to agglomeration. The agglomeration progresses by one or a combination of the two well-known mechanism: melt-induced, and coatinginduced. Moreover, in addition to alkali, also phosphorous is known to have a major role in the agglomeration mechanisms during (co-)combustion of agro-biomass in FBC conditions []. Owing to the elevated concentration of alkali and phosphorous, many agro-biomass fuels present a considerably higher risk than e.g. woody biomass to agglomerate, and are likely to suffer synergic agglomeration by both mechanisms [3]. 1 Concentration [g/kg fuel, dry] AgglPI FoulPI CorrPI LOW MEDIUM HIGH VERY HIGH Coal Peat Stem Forest Residue Sunflower Husk Wheat Straw Olive Rapeseed Recycled RDF Fossil Fuel Biomass Fuel Fuel Figure. Comparison of fossil, biomass, and waste fuels in respect to agglomeration, fouling and corrosion (AFC) probability. Fouling occurs as gaseous or liquid compounds that are formed during a combustion process deposit on colder surfaces, e.g. on convective heat exchangers. Ash-forming elements from fuel react with flue gases or with the solids suspended in the flue gas forming fouling components via complex mechanisms that are not yet fully understood. Compared to woody biomass, fouling during combustion of agro can be high and form deposits more enriched in alkali halides, which makes them more difficult to soot-blow.

4 Corrosion is most frequently a problem when firing biomass fuels in fluidized bed boilers via the so-called chlorine-induced mechanism. Chlorine corrosion occurs mainly at the convective heat exchangers. It follows high fouling rates associated with the presence of alkali and water vapor, and therefore is a bigger risk with certain agro-biomass as compared to woody-biomass. The biomass corrosion mechanism has been investigated for a long time [4] and, although its basic aspects are well accepted, the complexity of its details does not find general consensus. Predicting fuel propensity towards agglomeration, fouling and corrosion is a demanding task due to numerous ash-forming elements involved (Na, K, Ca, Mg, Si, Al, P, S, Cl, Zn, Pb), and complex mechanism of ash-transformation reactions under dynamic combustion conditions. During the years, tools have been successfully developed at Foster Wheeler to help with such predictions Probability index [ ] Probability index [ ] Probability index [ ] Agglomeration Fuel 1 + Fuel Coal + Stem Coal + Wheat Straw Stem + Wheat Straw Fouling Fuel 1 + Fuel Coal + Stem Coal + Wheat Straw Stem + Wheat Straw Corrosion Fuel 1 + Fuel Coal + Stem Coal + Wheat Straw Stem + Wheat Straw Fuel [% wt ] Figure 3. AFC tendency of fuel mix as by corporate model described in [5]. low medium high very high low medium high very high low medium high very high for the most commercial fuels. As the share and variety of fired biomass and waste fuels increases, Foster Wheeler s corporate models and tools are continuously upgraded to cover the new scenarios and to improve their predictive performance. Figure shows predictions from recently upgraded agglomeration, fouling, and corrosion (AFC) model, which are semi-empirical computer tools that combine theoretical description of agglomeration/fouling/corrosion phenomena with empirical correlations. The correlations are derived from Foster Wheeler s experience in fluidized beds including nearly 1, fuel samples and over 1, tests in about 15 CFB units [5]..1. Challenges and opportunities of cofiring As the availability of biomass fuels in large quantities are both regional and seasonal, and subjected to frequent variation in quality and quantity, utility-scale CFB boilers are inevitable designed for highest fuel flexibility. Such flexibility comes to a technical advantage when the co-fired fuel is coal, because many coals contain plenty of ash that dilute and often react with the biomass ash in such a way that the risk of agglomeration, fouling, and corrosion are minimized [6]. The use of coal, however, is somewhat unattractive these days, when green certificates and permits only support firing 1% biomass. Co-combustion of challenging agro-biomass with woody-biomass may also relieve some technical difficulties, but the advantages brought by woody-biomass are far lower than those brought by coal, and care must be placed to avoid unfavorable synergies between the agroand the woody-biomass. In other words, the challenges of co-firing an agro- and a woody-biomass cannot be deduced by linear interpolation between the challenges from each fuel fired alone, as demonstrated in Figure 3.

5 3. DESIGN OPTIONS A number of designs have been developed at Foster Wheeler to address the combustion of different fuels in efficient and economical ways. In short, easy-to-fire fuels are handled in economical boilers, and increasingly complex solutions are implemented as the fuel quality deteriorates [7]. Such complex solutions may include (see also Figure 5): a. Step grid The step grid is a grid developed since the 199 s to handle fuels that contain large fractions of inert material, such as stones and metallic debris. This grid features flat nozzles arranged into stepped rows, usually separated by refractory pre-casts. This design does not offer any appendages onto which fuel debris can hang, and creates an air flow that force large inert fractions to evacuate the furnace via the bottom ash chutes, thus assuring the effective removal of un-fluidized material. This design is essentially standard in Foster Wheeler CFBs firing biomass and/or waste. b. INTREX TM Intrex is a proprietary heat exchanger located in the return legs from the separators, where circulating material is returned to CFB furnaces. This heat exchanger is constantly immerged in the returning material, which is fluidized like the bed of a bubbling fluidized bed, but more gently. As a result, this heat exchanger benefit from more effective heat transfer than an exchanger in the convective pass, it does not suffer erosion while remaining free from deposits, and it is not exposed to corrosive flue gases. Therefore, higher steam temperatures can be attained with INTREXTM when firing corrosive fuels such as biomass and waste. c. Empty pass and water cannons Empty passes are empty sections of the flue gas backpass located upstream of the convective cage, where are located bundles of convective heat exchangers. With such passes, flue gases are cooled before hitting onto exchanger tubes, thus decreasing the formation of deposits, plugging of backpass, and corrosion of heat exchangers. The side panels of empty passes are water-cooled, and experience some fouling, which is easily removed. Water cannons can be used for effective and targeted cleaning, especially when fouling is localized. An ash hopper at the base of the empty pass helps removing fly ash and detached deposits. The need and length of the empty pass is evaluated based on the quality of (co-)fired fuels. d. Interchangeable superheaters and soot-blowing equipment Interchangeable superheaters are heat exchangers fabricated into bundles of easy assembly, and mounted into horizontal convective passes above which cranes can be maneuvered. This solution reduces considerably the down-time and maintenance costs resulting from exchanger failures. The alloys used for these superheaters are selected according to steam data and fuel quality, and include austenitic grades for corrosion resistance. Low flue gas velocities can be set to further reduce fouling problems. In case of high dust, individual ash hoppers can be arranged. For soot-blowing, either spring hammers or fully retractable soot-blowers can be used in corrosive flue gas. e. Chemical counteractions Numerous chemical countermeasures have been developed to control agglomeration, fouling, and corrosion in CFB boilers firing challenging fuels such as agro-biomass [8]. Among those, two are discussed here: alternative bed materials and additives. During years, a variety of alternative bed materials have been tested in the attempt to contain the reactions between fuel alkali and quartz particles leading to agglomeration. A number of CFB boilers delivered by Foster Wheeler are or have been operated commercially with alternative bed materials. These materials typically contain a lower amount of quartz as compared to sand

6 (inert), or contain other particles that preferentially capture alkali from the system without forming agglomerates (active). Among the tested materials, ash originating from certain pulverized coal boilers (PC-ash) has proven to be extremely effective when firing some highly agglomerating fuels. If proven effective also against agro-biomass, PC-ash would constitute an excellent alternative to sand as makeup material, especially for those utilities that own PC boilers and do not have easy access to sand. Besides alternative bed materials, agglomeration can be contained by means of additives that react with alkali under fluidised bed conditions, forming high-temperature melting alkalialuminium-silicates. Typically the additives contain one or a mix of the oxides of silicon, aluminium, and iron (SiO, Al O 3, Fe O 3 ) that in presence of water vapour produce HCl in fluidised bed combustion. Since chlorine is released as gaseous HCl rather than alkali chlorides, these additives are also supposed to reduce fouling and corrosion. Among the most effective of these additives is kaolinite, which is abundant in kaolin. Sulfur-based additives have grown in popularity against the corrosive effect of alkali halides, mainly potassium and sodium chlorides (KCl and NaCl). The composition, form, and feeding strategy dependents on the fuel. Nevertheless, granular elementary sulfur fed into the furnace has been recently favored at Foster Wheeler. Figure 4 summarize schematically the mechanisms discussed above. The key factor is always fuel ash, in the middle of the scheme. The figure should be read from the centre along the arrows and clockwise. In presence of inert bed material agglomeration can occur by melt-induced mechanism, while the un-reacted portion of fuel ash continues to foul the backpass. With highquartz sand agglomeration progresses via melt- and coating-induced mechanisms, while reducing the fouling ash. PC-ash captures most ash-forming elements from fuel, which is removed from the system with bottom ash and non-fouling fly ash. Kaolin captures problematic ash elements from the fuel and distributes them to bottom and fly ash. The portion to fly ash increases with the surface wear of reacted kaolin. Limestone has a dual effect: provides calcium to form high-temperaturemelting calcium phosphates, and coats silica preventing reactions leading to agglomeration. However, it can increase calcium-based fouling. Finally, sulphur causes the sulphation of alkali halides which are fouling but less corrosive. non fouling (FA) fouling/non corrosive fouling/corrosive limestone S u lfu r kaolinite agglomerating coating melt non agglomerating (BA) Figure 4. Scheme of interactions among fuel ash, bed materials, and additives [8].

7 Integrated Steam Cooled Solid Separator and Return Leg Control of Fouling & Corrosion Correct flue gas temperature Correct design for convective heat transfer surfaces During Operation Features to Control Agglomeration & Fouling Active Bed Material 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 Foster Wheeler s ABC technology [9]. 4. ADVANCED BIO CFB (ABC) TECHNOLOGY Foster Wheeler s Advanced Bio CFB is today s most advanced CFB technology for biomass combustion. It results from the corporate knowledge on biomass and the experience from over 35 commercial references combined with continuous research. This technology provides high efficiency boilers up to 3 MW e for a broad range of clean and challenging biomass fuels, and boilers up to 6 MW e co-firing 5% biomass with coal. With this technology superheated steam can approach 18 bar(a) at 57 C for clean biomass, and 9 bar(a) at 585 C for 5% coal. The ABC technology not only addresses the fuel issues discussed above, 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 requirement, the investment cost and operation costs. Consequently, economical boiler designs have been developed to fire easy biomass, while more demanding solutions are implemented as the biomass quality is more challenging [7,9]. Key design features of the ABC technology are summarized in Figure 5. The basic design for all kind of biomass fuels features fully integrated water or steam cooled solids separator and return leg, INTREXTM superheater and/or reheater, and Step Grid. For challenging fuels such as agro biomass one of more of the following design features are added to control the increased risk for agglomeration, fouling and corrosion. Heat transfer surfaces, fuel feeding systems and locations, as well as air distribution and velocities are designed to keep adequate and stable temperature profile in furnace. Convective heat surfaces are designed with suitable steam parameters, tube pitches and tube materials, and are located at optimum flue gas temperature. Alternative bed materials and various additives can be adopted to overcome agglomeration, fouling, and/or corrosion of the most challenging biomass fuels. Two CFB boilers have been recently booked by Foster Wheeler to fire 1% biomass of which as much as wt% agro-biomass: Konin (Poland), 154 MWth, 15 ton/h, 97 bar(a), 54 C, and Połaniec (Poland), 447 MWth, 158/135 kg/s, 18/ bar(a), 535/535 C. Fuels include rapeseed residue, straw briquettes, energy willow, cherry stones, oat husk for Konin, and straw, sunflower pellets, dried fruit (marc), and palm kernel for Połaniec.

8 .. Igelsta CFB 4MWth, Sweden for and Clean Biomass fuels One of the advanced CFB references highlighting the multi fuel capability and high steam parameters with high availability Foster Wheeler Advanced Bio CFB design is the Igelsta CFB owned by Söderenergi AB and located in Södertälje Sweden (Figure 6). Igelsta is a CFB boiler designed for a total plant output of 73 MW e (net), 151 MW district heating from the turbine condenser, and 58 MW district heating from the flue gas condenser, resulting in nearly 11 % LHV total plant efficiency, corresponding to >9% HHV. The steam flow is 9 kg/s, at 9 bar pressure and 54 ºC. The boiler is designed to co-fire mixtures of biomass (mainly wood residues) with maximum 5% en of waste (REF pellets). The boiler is also designed to co-fire up to 7% en recycled wood with biomass. Properties of the main fuel mixtures are listed in Table 1. The fuels to be co-fired in Igelsta differ substantially in chlorine content, ash components, heavy metals, and large inert bodies (e.g. stones and nails), which are higher in recycled wood than in clean wood, and even higher in waste. These properties make recycled wood and especially waste more corrosive. When co-fired with biomass, such corrosive propensity is further enhanced by the additional supply of biomass alkali (especially potassium) that favor the formation of troublesome compounds. The plant will meet the emission values presented in Table. Such emissions are controlled primarily utilizing the high combustion efficiency provided by the CFB. Secondarily, the boiler is equipped with ammonia injection in the furnace and the separator, and is also equipped with bag filters. The bag filter captures dust, HCl, HF, SO, heavy metals, and PCDD/F. Calcium hydroxide and sodium bicarbonate are added in optimized shares from independent feeding equipment to enhance sulfur capture at all times. Active carbon is fed from another silo to reduce mercury (Hg) and PCDD/F. The Igelsta CFB Foster Wheeler ABC boiler concept combines the conventional technology with features from our experiences of firing fuels like demolition wood and RDF [7]. The outcome is a concept suitable for co-firing a larger amount of challenging fuels, while still having a high steam temperature output of 54 C. Igelsta CFB boiler was handed over to the client on after a successful trial run ahead of schedule. Figure 6. Igelsta CFB cross-section.

9 Table 1. Igelsta main fuel mixtures Fuel Mix 1 Mix Mix 3 Biomass, [%] LHV Demol.wood, [%] LHV 7 REF pellets, [%] LHV 5 Moisture, [%] ar Ash, [%] dry Nitrogen, [%] dry Sulfur, [%] dry Chlorine, [ppm] dry 1 8 LHV, [MJ/kg] ar Table. Igelsta design performance (6%O,dry) Emissions - NOx [mg/mj] 35* SO [mg/m 3 n] 75 CO [mg/m 3 n] 5* Dust [mg/m 3 n] 1 NH 3 ppm 1 TOC [mg/m 3 n] 1 HCl / HF [mg/m 3 n] 1 / 1 Cd+Tl / Hg / HMs [mg/m 3 n].5 /.5 /.5 PCDD+F [ng/m 3 n].1.3. Połaniec CFB 447 MWth, Poland for Agro and Virgin Biomass Fuels In April 1, Foster Wheeler has been awarded a contract by GDF Suez Energia Polska S.A. for the design, supply and erection of a 19 MW e 1% biomass-fired CFB boiler island for the Połaniec Power Station in Poland. Połaniec is a 447 MW th, 158.3/135.1 kg/s, 535/535ºC and 17.5/19.5 bar(a) utility boiler based on Advanced Bio CFB (ABC) technology. It will operate on a broad range of biomass fuels while targeting high efficiency and availability achievable in accordance to Polish regulations. According to Polish law the share of agro-biomass is set to a minimum of % under the condition that the plant is in service by the end of 1. Once complete, this will be the world s largest biomass boiler burning wood residues with up to % agro biomass. The fuel considered for the new boiler in Połaniec power plant is comprised of 8% wt virgin wood and % wt agro-biomass including straw, sunflower pellets, dried fruit (marc), and palm kernel. The alkali content of the fuel mixture with % wt of agro biomass is clearly higher than experienced earlier in large-scale commercial CFB boilers with biomass fuels. Combined with inherited properties of the inquired biomass fuel mix, high risks of bed agglomeration, fouling and high temperature chlorine corrosion were expected. 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 described in [8]. The Advanced Bio CFB boiler design and operational concept with Połaniec type of the fuel mixtures is available today up to a scale of 3 MW e with the most advanced steam parameters available. 5. SUMMARY Changes in fuel market and ever-growing demand for utilization of biomass and waste fuels in energy production are the main driving force for the development of Foster Wheeler s Advanced Bio CFB (ABC) technology. Combustion properties of biomass fuels are a complex function of fuel s physical and chemical properties, whereas composition of ash-forming elements plays a major role. When cofired the behavior of fuel mixture including agro-biomass and/or waste cannot be deduced from linear interpolation of component fuels. The biggest challenges encountered in biomass CFB firing are the tendency towards bed agglomeration and fouling of convective heat surfaces, often associated to corrosion. Such

10 challenges are marginal with certain woody biomass, but they intensify when more challenging biomass fuels like agro biomass or waste are fired, and further grow when boilers must operate at the highest efficiency with irregular fuel mixtures. As the prediction of agglomeration, fouling, and corrosion tendency of fuels is essential to the CFB design, improving the predictive performance of related corporate tools and models is under permanent development. Measures to counteract challenges in firing a broad range of biomass fuels differ from project to project depending on costs, local regulations, and the preferences of the boiler owner. Countermeasures favored in recent Foster Wheeler Advanced Bio CFB (ABC) technology are briefly described in this paper together with references from Foster Wheeler Advanced Bio CFB portfolio. Based on extensive corporate knowledge on fluidized beds including nearly over 35 commercial references, combined with continuous research programs, ABC technology provides state-of-the-art solutions for effective CO reduction in large scale power generation with a broad range of biomass fuels. Two boilers have been recently booked by Foster Wheeler to fire 1% biomass, of which as much as wt% agro-biomass including energy willow, oat husk, palm kernel, straw, dried fruits, sunflower, and rapeseed residues. The largest of these units (447 MW th ) is designed to produce 158 kg/s of superheated steam at 18 bar(a) and 535 C. This technology also provides high efficiency boilers up to 3 MW e for a broad range of biomass fuels, and boilers up to 6 MW e co-firing 5% biomass with coal. With this technology superheated steam can approach 18 bar(a) at 57 C for clean biomass, and 9 bar(a) at 585 C for 5% coal. REFERENCES [1] Hiltunen, M., Barišić, V., Coda Zabetta, E., Combustion of Different Types of Biomass in CFB Boilers, Proceedings, 16 th European Biomass Conference, Valencia, Spain, 8. [] Barišić, V., Åmand, L.-E., Coda Zabetta, E., The role of limestone in preventing agglomeration and slagging during CFB combustion of high-phosphorous fuels, Proceedings, World Bioenergy, Jönköping, Sweden, 8. [3] Coda Zabetta, E., Barišić, V., Peltola, K., Hotta, A., Foster Wheeler experience with biomass and waste in CFBs, Proceedings, 33 rd International Technical Conference on Coal Utilization & Fuel Systems, Clearwater, Florida, 8. [4] Pettersson, J., Folkeson, N., Froitzheim, J., Jonsson, T., Halvarsson, M., Johansson, L.-G., Svensson, J.-E., Effects of Alkali Salts on the High Temperature Corrosion of the Austenitic Stainless Steel 34L, Proceedings, Impact of Fuel Quality on Power Production & Environment, Saariselkä, Finland, 1. [5] Barišić, V., Coda Zabetta, E., Sarkki, J., Prediction of agglomeration, fouling, and corrosion tendency of fuels in CFB co-combustion, Proceedings, th Fluidized Bed Combustion Conference, Xi an, China, 9. [6] Coda Zabetta, E., Hotta, A., Moulton, B., Hiltunen, M., biomass and Co-combustion European Experience, Proceedings, Electric power 9, Rosemont, Illinois, USA, 9. [7] Coda Zabetta, E., Kauppinen, K., Slotte, M., Foster Wheeler Experience with Biomass and other CO -neutal fuels in large CFBs, Proceedings, 4 th International Bioenergy Conference 9, Jyväskylä, Finland, 9. [8] Coda Zabetta, E., Barišić, V., Peltola, K., Sarkki, J., Jäntti, T., Advanced Technology to Co-fire Large Shares of Agricultural Residues with Biomass in Utility CFBs. Proceedings, Impact of Fuel Quality on Power Production & Environment, Saariselkä, Finland, 1. [9] Jäntti, T., Sarkki, J., Lampenius, H., The utilization of CFB technology for large-scale biomass firing power plants, Proceedings, Power-Gen Europe, Amsterdam, The Netherlands, 1.