Foster Wheeler Advanced Bio CFB Technology for Large Scale Biomass & Peat Firing Power Plants

Transcription

1 Foster Wheeler Advanced Bio CFB Technology for Large Scale Biomass & Peat Firing Power Plants Timo Jäntti Kalle Nuortimo Foster Wheeler Energia Oy Varkaus, Finland Presented at Russia Power Moscow, Russia March 5-7, 2012

2 Abstract Circulating Fluidized Bed technology is an ideal technology to be used for large scale power generation with a broad variety of biomass fuels. The well known benefits of CFB technology, such as the superior fuel flexibility, inherently low emissions and high availability can be fully utilized for this purpose. Today the biomass fired CFB technology offers a high efficiency boiler scale-up to 400MW e and fuel flexibility from clean biomass to RDF. This presentation describes the status of Foster Wheeler Advanced Bio CFB technology that represents the state-of-the-art for large scale Biomass and Peat Firing. The well proven technical features for large scale biomass and Peat fired CFB s are discussed with applicable reference data from latest commercial CFB projects firing very different type of biomass, peat and waste fuels. INTRODUCTION The European Union has set an objective to reduce at least 20 % of the European greenhouse gas emissions by 2020 from the 1990 level, and increase the share of renewable energy to 20 % of energy consumption, by the same year. The target is to also improve energy efficiency by 20 % from the current level by Foster Wheeler s objectives to increase the boiler efficiency using supercritical steam values and increase the use of biomass and other renewable fuels are well in line with the objectives set by the European Union, and globally. Foster Wheeler has extensive knowledge of utilizing a broad range of Biomasses in energy production. Today the Foster Wheeler CFB technology provides the high efficiency boiler scale-up to 300MW e for biomass firing, fuel flexibility from clean biomass to RDF and the scale-up to 800MW e with supercritical steam parameters for biomass and coal co-combustion applications. This is a result of continuous and determined development work, based on an experience database of over 350 reference CFB boilers sold. Of these, over 50 CFB boilers are designed for biomass (or bio-mix) and nearly 50 CFB boilers for waste (or waste-mix) containing biodegradable fractions, which are considered CO 2 -neutral. When including the biomass fired Bubbling Fluidized Bed boilers (BFB) into the reference base, Foster Wheeler can utilize lessons learnt from nearly 200 biomass fired fluidized bed projects.

3 The paper shows that Foster Wheeler Advanced Bio Circulating Fluidized Bed technology is an ideal technology to be used for large scale power generation with a broad variety of biomass fuels. The well known benefits of CFB technology, such as superior fuel flexibility, inherently low emissions and high availability can be fully utilized for this purpose. This paper underlines that the combustion properties of biomass and waste may vary considerably, sometimes demanding complex design options. An adequate knowledge of the biomass fuel characteristics, their range of variability, along with a proper understanding of how such variables influence the combustion process are paramount to design and operate a boiler in a most economical and efficient way. Biomass fuels To reduce emissions of greenhouse gases such as carbon dioxide (CO 2 ), boilers for heat and power production will be operated with increasingly high shares of biomass. Earlier, the size of the biomass fired plants has been limited for the locally available biomass fuel sources. Today the biomass market has changed from Local to Global. The green tariffs provided by most countries in the EU are making it possible to procure biomass globally using large biomass resources in America and Asia. This has created an interest for the large scale biomass fired units. To date, biomass combustion systems use mainly forest industry biomass resources such as wood and wood residues. As the demand for biomass fuels grows and the price for woodbased biomass fuels increases, there is a growing interest to utilize not only wood-based fuels but also agricultural biomass, biomass residues and biomass wastes as fuel. The quality of biomass fuels vary considerably due to fuel supply, preparation and processing, as well as local conditions such as soil chemistry, rainfall, and farming practices. In Table 1 properties of selected biomass fuels are shown. Table 1. Properties of selected biomasses

4 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 If biomass as a fuel is compared with different kinds of fossil fuels, the most important differences can be found in the variability of fuel characteristics, low energy density, higher moisture contents and low nitrogen and Sulfur contents of biomass fuels. Ash content is low but ash has a low melting temperature. The main constituents of ash are alkali and earth alkali elements and additionally Phosphorous in agro biomass. The moisture content of biomass has a large influence on the combustion process and on the resulting efficiencies. All biomass fuels have their own special characteristics that are related to the chemistry and physical properties of the fuel. For example, Chlorine (Cl) and alkaline contents are key parameters affecting corrosion and fouling in the boiler. Particle size and the earlier mentioned moisture content are examples of the physical properties having an effect on the combustion characteristics of the fuel. Agricultural and field crop residues including straw, shells and hulls are identified as the most problematic fuels having the strongest potential to create operational difficulties, such as agglomeration of fluidized bed, fouling and corrosion of the convective heat surfaces. Such high potential is not only dependent on the ash content of fuels, since the ash in biomass fuels is frequently low. Agro biomasses contain elevated concentrations of alkali, phosphorous and chlorine compounds, which produce low melting eutectics during combustion. The concentrations of these elements tend to be at the upper range of typical fuel specifications for biomass fuels, and are higher than commonly used in wood-fired boilers. The unfavourable composition of the ash is the main reason why so far the utilization of novel biomass fuels has been limited in energy production. The flue gases originating from the combustion of certain fuels contain vaporized salts and ash particles that can condense and stick on cooler surfaces, leading to fouling of heat

5 exchangers. Fouling during combustion of wood-based fuels is typically low and easy to clean with steam soot blowers. However, fouling during combustion of agro biomass can be very intense, resulting in the formation of thick deposits. Such deposits are difficult to clean with normal soot blowing. Fouling leads to reduced performance of the boiler and in severe cases causes shut down for manual cleaning. The most frequent corrosion problem occurring in biomass combustion is chlorine-induced high temperature corrosion, which occurs mainly in the convective heat surfaces. Such corrosion is connected to high fouling rates in the presence of elevated alkali and chlorine contents in the fuel Probability index LOW MEDIUM HIGH VERY HIGH 0 Aggl Foul Corr Aggl Foul Corr Aggl Foul Corr Aggl Foul Corr Aggl Foul Corr Wood chips Sawdust Husk (rice) Husk (sunflower) Straw Figure 1. Agglomeration, fouling and corrosion tendency for various types of biomass fuels (Foster Wheeler classification). As mentioned earlier, high concentrations of alkalis and chlorine lead to a high probability of agglomeration, fouling and corrosion. Biomass alkalis that are readily released into the vapour phase during combustion can undergo complex reactions with flue gas constituents and fly ash, leading to the formation of low-melting species. The concentration of these reactive alkalis is determined by their solubility during weak-acid leaching of the fuel, and can be used as an index of agglomeration and fouling potential. For biomass fuels, most of the alkalis are typically in a reactive form. Other species contained in the fuel ash can

6 influence the ability of these reactive alkalis to promote agglomeration and fouling. Accordingly, in fuels with elevated ash content the alkali species tend to be diluted and may not reach sufficient concentrations in the bed to cause agglomeration. Corrosion is connected to high fouling rates in the presence of elevated alkali and chlorine contents in the fuel. Understanding of the biomass fuel characteristics is the key issue to correctly address the fuel specific requirements in the boiler design. The Foster Wheeler fuel characterization models are based on the database including nearly 10,000 fuel samples and over 1,000 tests in about 150 CFB units. The model prediction for agglomeration, fouling and corrosion tendency is shown in figure 1 for wood biomass and selected agro biomass fuels. Advanced boiler design features for biomass firing Biomass as a CO 2 neutral fuel has an essential role in reducing CO 2 emissions in energy production and to meet the objective set by the European Union to reduce at least 20 % of the European greenhouse gas emissions by 2020 from the 1990 level, and increase the share of renewable energy to 20 % of energy consumption by the same year. The increase of biomass utilization in energy production has created a demand for large scale pure biomass firing power plants. These demands have given Foster Wheeler a reason to develop efficient large scale biomass firing technology and to improve the fuel flexibility in pure biomass and biomass co-combustion applications. Circulating Fluidized Bed technology is an ideal technology to be used for large scale power generation with a broad variety of biomass fuels. The well known benefits of CFB technology, such as the superior fuel flexibility, inherently low emissions and high availability can be fully utilized for this purpose. Today the biomass fired CFB technology offers a high efficiency boiler scale-up to 300MWe for pure biomass firing, fuel flexibility from clean biomass to RDF and the scale-up to 800MWe with supercritical steam parameters for biomass and coal co-combustion applications. Foster Wheeler s Advanced Bio CFB (ABC) is today s most advanced CFB technology for biomass combustion. It results from the corporate knowledge on biomass and the experience from over 350 commercial references combined with continuous research. This technology provides high efficiency boilers up to 300 MW e for a broad range of clean and challenging biomass fuels, and boilers up to 600 MW e co-firing 50% biomass with coal. With this

7 technology superheated steam can approach 180 bar(a) at 570 C for clean biomass, and 290 bar(a) at 585 C for 50% coal. Foster Wheeler s 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 requirement, the investment cost and operation costs. Consequently, economical boiler designs have been developed to fire easy-to-burn biomass, while more demanding solutions are implemented as the biomass quality is more challenging. Key design features of the ABC technology are summarized in figure 2. Figure 2. Key features of Foster Wheeler s ABC technology. CFB Technology for clean Biomass Fuels Kaukaan Voima CFB, Finland 385 MWth One of the largest biomass fired Foster Wheeler Advanced Bio CFB s is Kaukaan Voima power plant located UPM-Kymmene Paper Mill site in Lappeenranta, Finland. The Plant

8 produces electricity and process steam for the paper mill site and district heat for the City of Lappeenranta. The nominal capacity of the CFB boiler is 125 MW e (net), 385 MW th, designed to produce 149 kg/s of superheated steam at 115 bar(a) pressure and 550 C temperature. The boiler contract was awarded on April 2007 and the boiler was taken into commercial operation in 22 February 2010 (Figure 3). Figure 3. Foster Wheeler Advanced Bio CFB s in Kaukaan Voima site and boiler concept. The owner of the Kaukaan Voima plant is Kaukaan Energia Oy that is 46% owned by Lappeenrannan Energia Oy and 54% by Pohjolan Voima Oy. The main economical drivers of the project were more effective utilization of paper mill by-products and replacing gas with biomass fuels for Lappeenranta City s electricity and district heat production. The Kaukaan Voima boiler is designed to fire peat and pulp and paper mill by-products (mainly clean biomass fuels like bark, forest residue, sludge, etc.) as detailed in Table 2. The peat and biomass fuel can be fired separately or co-fired.

9 Table 2. Kaukaan Voima CFB plant fuel data Fuel Peat Biomass Moisture [%] ar Ash [%] dry Nitrogen [%] dry Sulfur [%] dry LHV [MJ/kg] ar The plant shall meet the following emission limits corresponding to (6% O 2, dry): 150 mg/m 3 n NO x, 200 mg/m 3 n SO 2, 200 mg/m 3 n CO and 20 mg/m 3 n particulates with primary measures. The boiler is equipped with an electrostatic precipitator (ESP) and ammonia injection both in the furnace and the separator (SNCR). Limestone injection in the furnace is included for DeSO x purposes. The Kaukaan Voima CFB boiler design is based on advanced Foster Wheeler CFB design for clean biomass fuels utilizing the fully integrated water cooled solids separator design and return leg designs, INTREX TM superheater and partial step grid design. Excellent first year performance Kaukaan Voima CFB s operational hours between 2/2010 and 2/2011 were over 7100, annual downtime including two months of planned shutdown. During commissioning period and first year of the commercial operation Kaukas boiler has demonstrated its capacity to operate on full load range with large variety of fuels and fuel mixtures in reliable and environmentally friendly manner. The excellent operation for the boiler s first year was good news to me. Co-operation between Foster Wheeler and Kaukaan Voima personnel has been very good. Despite some challenges related to fuel quality, wet and icy biomass feeding, plant automation system and minimum load running during summer time (boiler load under 40 %) we were very happy to achieve the title of being Finland s biggest wood based biomass user(1488 GWh) in Our new plant brings many benefits to us. Natural gas has been replaced by cheaper fuels, mainly wood based fuels and peat, the new plant is also very cost

10 effective and has an excellent capability to fight against tight emission limits including green house gases : says Plant Manager Jukka Kiuru. Large Scale Utility CFB 300 MW e Today there is a market demand for large scale biomass firing CFB plants in scale 300MW e. The Foster Wheeler Advanced Bio CFB boiler concept has been developed for this scale (Figure 4). Steam parameters for the plant are 179/43.6 bar(a), 568/566 C. Figure 4. Conceptual design of 300 MW e CFB for virgin wood pellets and wood chips. The boiler fires slightly dried virgin wood chips and/or high heating value wood pellets presented in Table 4. Table 4. Design fuels of the clean biomass fuel fired conceptual 300 MW e CFB boiler Fuel Wood Pellets Wood Chips Moisture [%] ar Ash [%] dry 0,4 2.5 < 4 Nitrogen [%] dry < 0.7 < 0.5 Sulfur [%] dry Chlorine [ppm] dry < 500 < 500 LHV [MJ/kg] ar

11 The boiler scale is well within the existing CFB experience range. The CFB boiler design is based on standard Foster Wheeler CFB design for clean biomass fuels utilizing the fully integrated steam cooled solids separator design and return leg designs, INTREX TM superheater and reheater design and partial step grid design. Based on similar key design features that are used in the earlier presented Kaukas CFB, the conceptual design of this high efficient 300MW e scale Foster Wheeler Advanced Bio CFB is market-ready. CFB technology for Challenging Biomass Fuels Połaniec CFB 447 MW th, Poland for Agro and Virgin Biomass 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 of virgin biomass for energy production. GDF Suez Energia Polska S.A. has awarded the utility Połaniec Power plant project in April Combustion technology is based on the Foster Wheeler Advanced Bio CFB (ABC) technology (Figure 5). Połaniec is a 447 MW th, 158.3/135.1 kg/s, 535/535ºC and 127.5/19.5 bar(a) utility boiler that will operate on a broad range of biomass fuels while targeting high efficiency and availability achievable in accordance to Polish regulations. Such regulations set the proportion of agro biomass to a minimum of 20 % under the condition that the plant is in service by the end of Once complete, this will be the world s largest biomass boiler burning wood residues and up to 20% agro biomass. Figure 5. Foster Wheeler Advanced Bio CFB s in Polaniec site location and boiler concept. 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

12 biomass fuel includes a variety of agro biomass such as straw, sunflower pellets, dried fruit (marc), and palm kernel. The alkali content of the fuel mixture with 20weight-% 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 Advanced Bio CFB Design of Połaniec utilizes the main features of the design solutions described before. Risks related to high temperature chlorine corrosion, fouling and agglomeration potential were taken into account in the boiler design and operational concept. The Foster Wheeler ABC design in Połaniec represents the state-of-the-art combustion technology for wood and agro biomass firing. The Advanced Bio CFB boiler technology with the Połaniec type of the fuel mixtures is available today up to a scale of 300MW e with the best steam parameters available. Igelsta CFB 240MW th, Sweden for Waste and Clean Biomass fuels One of the best 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 110 % LHV total plant efficiency, corresponding to >90% HHV. The steam flow is 92 kg/s, at 90 bar pressure and 540 ºC. The main investment drivers of the project were to secure long term competitiveness of district heat, replace fossil fuels with biomass and waste fuels and high fuel flexibility to reduce dependency of a single fuel source.

13 Figure 6. Foster Wheeler Advanced Bio CFB s in Igelsta site and boiler concept. The boiler is designed to co-fire mixtures of biomass (mainly wood residues) with max 25% en of waste (REF pellets). The boiler is also designed to co-fire up to 70% en recycled wood with biomass. Properties of the main fuel mixtures are listed in Table 5. 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). Table 5. Igelsta main fuel mixtures Fuel Mix 1 Mix 2 Mix 3 Biomass [%] LHV Rec.wood [%] LHV REF pellets [%] LHV Moisture [%] ar Ash [%] dry Nitrogen [%] dry Sulfur [%] dry Chlorine [ppm] dry LHV [MJ/kg] ar

14 The plant will meet the emission values presented in Table 6. 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 2, 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. Table 6. Igelsta emission performance (6%O 2,dry) at 100% load with Mix 1, 2, and 3 Emissions Performance NOx [mg/mj] 35 SO 2 [mg/m 3 n] 75 CO [mg/m 3 n] 50 Dust [mg/m 3 n] 10 NH 3 ppm 10 TOC [mg/m 3 n] 10 HCl / HF [mg/m 3 n] 10 / 1 Cd+Tl / Hg / [mg/m 3 n] 0.05 / 0.05 / PCDD+F [ng/m 3 n] 0.1 The ABC Design of Igelsta also widely utilizes the design solutions described before. 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. The outcome is a concept suitable for co-firing a larger amount of challenging fuels, while still having a high steam temperature output of 540 C. Igelsta CFB boiler was handed over to the client on after a successful trial run ahead of schedule. CFB Technology for Co-firing of Biomass and Coal Despite of the focus on bioenergy, other renewables and nuclear energy, coal will remain an important part of the global fuel pallet. Co-firing biomass in larger coal fired power plants

15 enables high efficiency power production from biomass fuels. Moreover, co-firing provides flexibility to robust use of biomass depending on its seasonal availability. CFB Technology with subcritical steam parameters is available today to burn 100% coal and 100% biomass fuels by utilizing the design features presented earlier. CFB Technology with supercritical steam parameters for biomass firing is available today with coal co-firing only. The limiting factors to meet the supercritical steam parameters with biomass fuels are only related to the high furnace tube material temperatures and to the lack of technically feasible tube materials against corrosion. As a state of art supercritical co-firing design, Samcheok Green Power 4 x 550 MWe is presented. Samcheok Green Power 4 x 550 MWe Supercritical Circulating Fluidized-Bed Steam Generators in South Korea Foster Wheeler has been given a full notice to proceed by Hyundai Engineering and Construction for the design and supply of four 550 MWe (gross megawatt electric) supercritical circulating fluidized-bed (CFB) steam generators for the Samcheok Green Power Project for Korea Southern Power Co., Ltd. (KOSPO). Contract includes the design and supply of four 550 MWe advanced vertical tube, once-through supercritical CFB steam generators feeding two steam turbines. The CFB steam generators will be designed to burn coal mixed with biomass while meeting stringent environmental requirements. When these CFB units enter commercial operation in 2015, they will be the world's largest and most advanced CFB s providing KOSPO with a new level of fuel flexibility, reliability and environmental performance in co-firing. Currently, a boiler scale up to 800MW e is technically feasible with a 20% share of clean virgin biomass fuel with clean coal and a scale up to 600MW e is technically feasible with a 50% share of clean virgin biomass fuel with clean coal. Summary Foster Wheeler has an extensive knowledge of biomass firing based on the knowledge of nearly 200 CFB and BFB units sold. The modern Foster Wheeler Advanced Bio CFB

16 technology provides state-of-the-art solutions for effective CO 2 reduction in large scale power generation with a broad range of biomass fuels. The biggest challenges encountered in biomass firing are the tendency towards bed agglomeration and fouling of convective heat surfaces, often associated to corrosion. Such 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. This paper underlines that the combustion properties of biomass and waste fuels may vary considerably, sometimes requiring demanding design features. An adequate knowledge of the fuel characteristics, their range of variability, along with a proper understanding of how such variables influence the combustion process are the key issues to design and operate a suitable boiler while avoiding unnecessary complexities and costs. 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 to illustrate the latest achievements in the combustion of CO 2 -neutral fuels. This paper also presents the flexibility of Foster Wheeler CFB design to burn the most challenging fuels used in energy production like RDF waste. Biomass based combustible fraction is 60 % of RDF. The co-firing of biomass in larger coal fired power plants with high efficiency power production is discussed in this paper. As a state of art supercritical co-firing design, Samcheok Green Power 4 x 550 MWe is presented. The Foster Wheeler ABC technology is the optimum choice to meet the market s demand now and in the future to utilize a broad range of biomass fuels in large scale power generation.