Advanced CFB Technology for Large Scale Biomass Firing Power Plants

Transcription

1 Advanced CFB Technology for Large Scale Biomass Firing Power Plants Teemu Nevalainen Timo Jäntti Kalle Nuortimo Foster Wheeler Energia Oy Finland Presented at Bioenergy from Forest 2012 Jyvaskyla, Finland August 29, 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 400 MW e and fuel flexibility from clean biomass to RDF. This paper describes the status of Foster Wheeler Advanced Bio CFB technology that represents the state-of-the-art for large scale Biomass Firing. The well proven technical features for large scale biomass fired CFB s are discussed with applicable reference data from latest commercial CFB projects firing very different type of biomass and agro-biomass fuels. Paper takes a special focus to the award from GDF Suez Energia of a CFB boiler island for the Polaniec Power Station in Poland, 100% biomass design advances to 190 MW e (gross) size range. The project further demonstrates the capability of state-of-the-art Advanced Bio CFB concept that allows the cofiring of high alkaline agro biomass fuels with wood-based biomass fuels in utility-size power production. Once operational (expected 4Q, 2012) this will be the world s largest 100% biomass boiler burning wood residues and up to 20% agro biomass fuel. Furthermore, key design features of the CFB boiler concept up to 400 MW e for pure biomass and agro-biomass fuels co-firing is presented. 1. 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 400 MW e for biomass firing, fuel flexibility from clean biomass to RDF and the scale-up to 800 MW 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 nearly 400 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. 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.

3 2. 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 wood-based 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 (see Table 1). For example, Chlorine (Cl) and alkali contents are key parameters affecting corrosion and fouling in the boiler. Bulk density and moisture content are examples of the physical properties having an effect on the combustion characteristics of the fuel. 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 Table 1: Properties of selected biomasses 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. Understanding of the biomass fuel characteristics is the key issue to correctly address the fuel

4 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. 3. 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 400 MW e for pure biomass firing, fuel flexibility from clean biomass to RDF and the scale-up to 800 MW e 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 nearly 400 commercial references combined with continuous research. This technology provides high efficiency boilers up to 400 MW e for a broad range of clean and challenging biomass fuels. With this technology superheated steam can approach 180 bar(a) at 570 C for clean biomass. 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 1. Figure 1: Key features of Foster Wheeler s ABC technology.

5 4. CFB Technology for Cofiring Peat and Biomass Fuels 4.1 Jyvaskylan Energia CFB, Finland 458 MW th The largest peat fired Foster Wheeler CFB is Jyvaskylan Energia power plant located at Keljonlanti by lake Päijänne in the city of Jyväskylä located in central Finland (Figure 2). The Plant produces up to 200 MW electricity and up to 240 MW of district heat to the City of Jyväskylä. The boiler is designed to produce 160/143 kg/s steam with steam parameters 164/43 bar(a) and 560/560 C. The boiler contract was awarded in August 2007 and the boiler was taken into commercial operation in summer Figure 2: Foster Wheeler CFB for Jyvaskylan Energia Oy site and boiler concept. The Jyvaskylan Energia boiler is designed to fire peat and wood chips as shown in Table 2. The maximum share of design wood chips is 70% of heat input. Fuel Peat Wood chips Moisture [%] ar Ash [%] dry Nitrogen [%] dry Sulfur [%] dry LHV [MJ/kg] ar Table 2: Jyvaskylan Energiaa CFB plant fuel data

6 The plant meets the following emission limits corresponding to (6% O 2, dry): 150 mg/m 3 n NOx, 200 mg/m 3 n SO 2, 200 mg/m 3 n CO and 30 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 DeSOx purposes. The CFB boiler design is based on standard Foster Wheeler CFB design utilizing the fully integrated steam cooled solids separators design and return leg designs, INTREX TM superheater and reheater design and partial step grid design. The Jyvaskylan Energia boiler performance has been as expected. Furthermore the availability of the CFB boiler has been excellent. 5. CFB Technology for Clean Biomass Fuels 5.1 Kaukaan Voima CFB, Finland 385 MW th 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 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 3. The peat and biomass fuel can be fired separately or co-fired.

7 Fuel Peat Biomass Moisture [%] ar Ash [%] dry Nitrogen [%] dry Sulfur [%] dry LHV [MJ/kg] ar Table 3. Kaukaan Voima CFB plant fuel data The plant meets the following emission limits corresponding to (6% O 2, dry): 150 mg/m 3 n NOx, 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 DeSOx 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. 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 operation of Kaukaan Voima CFB has continued with excellent availability and performance also during the second operational year. 5.2 Large Scale Utility CFB 400 MW e Today there is an interest for the large scale up to 400MW e biomass fired units. 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.

8 Figure 4: Conceptual design of 400 MWe 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. 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 Table 4: Design fuels of the clean biomass fuel fired conceptual 400 MW e CFB boiler 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 400MW e scale Foster Wheeler Advanced Bio CFB is market-ready.

9 6. CFB Technology for Challenging Biomass Fuels 6.1 Połaniec CFB 447 MWth, 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 Figure 5: Foster Wheeler Advanced Bio CFB s in Polaniec site. The Foster Wheeler s delivery comprises 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. 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 fuel mix properties are presented in Table 5. The plant shall meet the following emission limits corresponding to (6% O2, dry): 150 mg/m 3 n NOx, 150 mg/m 3 n SO2, 50 mg/m 3 n CO and 20 mg/m 3 n particulates. The boiler is equipped with an electrostatic precipitator (ESP), ammonia injection both in the furnace and the separator and catalyst in the second convective pass (SNCR+SCR).

10 6.2 Połaniec CFB Boiler Design 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 design of the new Połaniec CFB boiler 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 first superheating stage of the Połaniec CFB boiler, SH I is located inside the furnace as a Wingwall superheater and the second stage of superheating (convective SH II) is located in the first convective pass. The first reheating stage (convective RH I) is also located in the first convective pass. The third and final superheating stage as well as the second and final reheating stage are INTREX TM type heat exchangers located in a 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 it 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. Figure 6: Foster Wheeler Advanced Bio CFB s in Połaniec boiler concept. The Połaniec CFB boiler utilizes moderate fluidizing velocity in the furnace which is an important characteristic of Foster Wheeler Advanced Bio CFB technology. Further, the design features a full step grid design in order to transfer heavy unfluidized particles effectively into the bottom ash removal system.

11 Fuel feeding system of the Połaniec CFB boiler consists of two similar feeding lines, one feed line at both of the long walls of the furnace. Boiler has two fuel day silos for biomass. Fuel is fed into the furnace via eight feeding chutes providing good fuel mixing among whole bed area of the furnace. Combustion air system consists of primary and secondary air systems and separate air system for fluidizing the INREX TM heat exchangers and sealing devices. Radial fans with speed control are used to provide air for properly staged combustion of the biomass. For Induced Draft (ID) fan two axial fans are used. A flue gas recirculation system is provided to accommodate the larger variations in the fuel quality. For controlling the emissions, boiler 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. Electro Static Precipitator (ESP) is used for controlling particulate emission. With these measures Połaniec CFB boiler can meet the emission limits set for it (150 mg/m 3 n NOx, 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 Foster Wheeler s state-of-the-art Advanced Bio CFB concept that allows the co-firing of high alkaline agro biomasses with wood-based biomass in utility-size power production. Once Operational (expected 4Q, 2012) this will be the world s largest biomass boiler burning wood residues and up to 20% agro biomass. 6.2 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 7). 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 540ºC. 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. Figure 7: Foster Wheeler Advanced Bio CFB s in Igelsta site and boiler concept.

12 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 6. 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 Table 6: Igelsta main fuel mixtures The plant will meet the emission values presented in Table 7. 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.

13 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 Table 7: Igelsta emission performance (6%O 2,dry) at 100% load with Mix 1, 2, and 3 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. The Igelsta combined heat and power plant is Sweden s largest biomass fired co-generation plant. The Igelsta CFB has proven to be high performing boiler and a high availability has been achieved since the start-up of the boiler. 7. 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 technology provides state-of-theart 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.

14 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 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.