The CFB Technology Benefits in Comparison with Conventional Solid Fuel Generation Technologies for Utility and Cogeneration Applications

Transcription

1 The CFB Technology Benefits in Comparison with Conventional Solid Fuel Generation Technologies for Utility and Cogeneration Applications Kalle Nuortimo Harry Lampenius Anna Khryashcheva Tobias Boensel Presented at Russia Power 5-6 March 2013 Moscow, Russia Foster Wheeler All rights reserved.

2 THE CFB TECHNOLOGY BENEFITS IN COMPARISON WITH CONVENTIONAL SOLID FUEL GENERATION TECHNOLOGIES FOR UTILITY AND COGENERATION APPLICATIONS ABSTRACT Kalle Nuortimo, Harry Lampenius, Anna Khryashcheva, Tobias Boensel Foster Wheeler Energia Oy Relanderinkatu 2, P.O.BOX 201, 78201Varkaus, Finland In recent years, Circulating Fluidized Bed (CFB) technology is becoming the market leader in solid fuel power production sector. In comparison with conventional PC, Grate and BFB technology, CFB is most ideal candidate to be used for large scale power generation and industrial/municipal combined steam and power production with a broad variety of fuels. This paper will discuss the background and reasons for this success. In this paper, we will present the financial and environmental benefits of the technology, available for wide array of Russian solid fuels, by using some examples from Foster Wheeler s reference base of over 400 CFB boilers, delivered to 36 countries, ranging from smaller industrial units to utility units in the size of 4 x 550 MW e (Samcheok Green Power Project). CFB boilers are ideal for firing solid fuels, such as bituminous- and anthracite coals, lignite, petroleum coke, peat and biomass many of which are used in Russia. The fuel flexibility and fuel switching, as well as co-firing capability give significant economic advantage, allowing to choose/use the most cost effective fuel at any time, firing lower cost local fuels instead of high quality fuels with far transportation. This advantage is especially useful in municipal Heat and Power stations. Moreover, the emission control equipment avoidance benefits in the smaller district heating (CHP) and industrial plants often located in cities are significant. Due to the new requirements for flue gas acids like SO x, HCl, HF, dust and many other multipollutants, owners of coal fired, oil fired and RDF fired power plants are continuously evaluating the merits of adding back-end air quality control systems (AQCS). This paper introduces the Basin Dry Fork station project, which entered commercial operation 2011, featuring the best available dry flue gas scrubbing technology (BAT) for the first time worldwide in single unit size for a MW e coal fired boiler plant. Keywords: CFB, Biomass, Renewable energy, Coal firing, Petroleum coke firing, Flue Gas cleaning

3 INTRODUCTION Over the past 35 years, Circulating Fluidized Bed (CFB) boiler technology has evolved from industrial boiler technology used to burn difficult fuels in the late 1970s to the successful installation and commercial operation of the world s largest CFB boiler, Lagisza, rated at 460 MW e and supercritical steam conditions in Established benefits of improved efficiencies, reduced emissions, fuel flexibility, and lower costs all combined make CFB technology a highly competitive option for large-scale utility applications to include both subcritical biomass and petroleum coke boilers as well as once through supercritical (OTSC) technology for coal-based thermal power generation with a biomass co-firing possibility (Figure 1). Figure 1. CFB technology scale-up CFB TECHNOLOGY BENEFITS IN LARGE SCALE COAL COMBUSTION CFB technology is now challenging pulverized coal technology in large scale energy generation with currently over 80 CFB units of over 200 MW e, a 460 MW e supercritical unit in operation, and 4 x 550 MW e ultra supercritical CFB units under construction.

4 C F Fuel Air High temp, uneven radiant heat transfer Melting ash Fast burn Open flame High NOx No SOx capture Fuel specific designs Fuel Air Low, even tempera ture solids heat transfer Long burn No flame Low NOx SOx capture fuel flexible designs CFB Technology offers Fuel Flexibility and Low Emissions without SCR or FGD Air Flue 800 Figure 2. Principles and Benefits of CFB(right) Combustion compared to PC As indicated in Figure 2, the features of CFB combustion provide major benefits over pulverized coal steam generators. Circulating fluidized bed (CFB) process provides an ideal burning environment for a wide variety of fuels. The advantages of CFB technology can be summarized as follows: Fuel flexibility and multi-fuel firing, Low SO 2 emissions due to efficient sulfur capture with limestone in the furnace, Low NO x emission due to low combustion temperature and air-staging, Low CO and C x H y due to turbulent conditions and good mixing, Secondary flue gas clean-up systems typically not needed, Stable operating conditions and good turn-down ratio, Support firing is not needed except during start-up periods, Increased capacity possible within the same footprint as old boilers, No need for fuel preparation (e.g. pulverizing).

5 Utility scale PC fired steam generators are designed for a narrow range of fuels, typically coals with heating values above 6000 kcal/kg. As indicated in Figure 3, CFB steam generators afford the maximum flexibility in fuel selection covering all coal types including low rank coals, petroleum coke, coal slurries, anthracite culm, biomass, and peat in addition to a vast array of refuse derived solid fuels. Figure 3. Fuel Range Comparison for CFB vs PC Consequently, the fuel procurement flexibility for CFB steam generators provides long term fuel security and full access to the arbitrage in the global fuel market. The combustion temperature in a CFB is about 850 ⁰C vs ⁰C for a PC boiler. In a PC boiler, melting ash can cause slagging and corrosion in the furnace and soot blowing is required. Slagging and corrosion are minimized in a CFB furnace and soot blowing, if required at all, is only necessary in the heat recovery area of the unit. Another major feature of CFB is simple control of NO x and SO 2 emissions in the boiler. This avoids the EPC capital costs associated with Selective Catalytic Reduction (SCR) and Flue Gas Desulphurization (FGD) equipment. For a 600 MW e plant, Capex savings can exceed US$100 million. In addition, operating costs for ammonia and SCR catalyst management for SCR and lime for dry FGD can be avoided.

6 Latest milestone in OTU CFB technology for coal: Samcheok Green Power 4 x 550 MW e Foster Wheeler currently has a contract to design and supply four 550 MW e (gross megawatt electric) CFB steam generators to Hyundai Engineering and Construction for the Samcheok Green Power Project for Korea Southern Power Co., Ltd. (KOSPO). Contract includes the design and supply of four 550 MW e advanced vertical tube, once-through supercritical CFB steam generators (Figure 4) feeding two steam turbines. Full NTP for the project was received in July Figure 4. Samcheok Green Power 4 x 550 MW e Design details Samcheok boiler design is based on proven OTU CFB concept. Boiler design is based on modular structure with identical separator and solids return designs. Steam circuit is generally the same as in Łagisza, Poland, 460 MW e boiler with advanced steam parameters (temperature) and optimized steam circuit design. Boiler material requirements for most sections of the boiler are very conventional, and normal boiler materials can be used. Furthermore, the design is free of T24-steel. The CFB steam generators will be designed to burn coal mixed with biomass while meeting stringent environmental requirements. Boiler design fuel is sub-bituminous coal from several international coal mines, mainly from Indonesia. Boilers can also co-fire wood pellets.

7

8 Auxiliary equipment The fuel and limestone feeding systems are based on volumetric equipment that has proven to be reliable in reference plant operation. Feeding points are located symmetrically to each furnace section to ensure uniform combustion in furnace. The bottom ash extraction system is based on water cooled screw and chain conveyors, also a proven technology used in various coal fired units. Equipment capacities are selected so that single feeding or extraction line failure does not effect to plant s availability. The primary air fans are inlet vane controlled radial fans which is proven solution in number of large scale units. Secondary air as well as flue gas fans are axial type in order to gain high fan efficiency. Steam parameters Table 1 presents the main design steam parameters of these 4 x 550 MW e (gross) CFB boilers. Table 1. Design Steam parameters at 100 % load SH flow kg/s 437,7 SH pressure bar(g) 257 SH temperature C 603 RH flow kg/s 356,4 RH pressure bar(g) 53 RH temperature C 603 Feed water temperature C 297

9 Emission limits The CFBs will meet stringent emission values presented in Table 2 without additional backend FGD equipment for SO x control. Table 2. Emission values Item Unit Limit value Method to meet SO x (as SO 2 ) Max., 142,5 mg/nm 3 (6% O 2 ) Max. 102,65 NO x (as NO 2 ) mg/nm 3 (6% O 2 ) Particulate mg/nm 3 Max. 20 (6% matter O 2 ) Limestone injection to furnace; no back-end desulphurization equipment needed SNCR in CFB followed by SCR in HRA ESP Unit Operation One Samcheok unit consists of two similar FW OTU-CFB boilers operating to one steam turbine. This provides a major reliability advantage in comparison with a single 1100 MWe boiler to 1 turbine. If the boiler 1 is under the maintenance, unit can operate ca. 50% load. The power unit can also achieve a minimum load of ca 18% in case one boiler is shut down and second boiler is running at minimum load. The normal operation mode of the unit is coordinated control with sliding pressure operation. The boilers are normally operated at same load level, and load change requests are forwarded for the boilers simultaneously and with similar control parameters. Steam temperatures are individually controlled to meet the required temperatures in main steam and reheated steam systems. Reheated steam share between the boilers is continuously monitored and controlled according to firing rates.

10 Project status The project is proceeding well, and when the first CFB unit enters commercial operation in 2015, it will be the world's largest and most advanced CFB, with a new level of fuel flexibility, reliability and environmental performance. Design study of a 800 MW e CFB Łagisza 460MW e OTU boiler has validated supercritical CFB design platform by providing a solid base for the further scale-up of the CFB technology. Today, supercritical CFB up to scale 800 MW e in size is offered for bituminous coal, meeting the highest requirements for plant efficiency and environmental performance. CFB TECHNOLOGY ADVANTAGES IN FIRING RUSSIAN SOLID FUELS CFB boilers are ideal for firing solid fuels, such as bituminous and anthracite coals, lignite, petroleum coke, peat and biomass many of which are used in Russia. The fuel flexibility and fuel switching capability gives significant economic advantage, allowing flexibility to choose the most cost effective fuel at any time, firing lower cost local fuels instead of high quality coals with high transportation cost. In the following chapters, suitability and Foster Wheelers s experience of CFB technology for various fuels are highlighted.

11 Bituminous coals The use of CFB technology is largest for bituminous coals (like Kuznetsk and Ekibastuz coals) with over 200 references worldwide. In several projects the possibility to fire a multitude of different coals from different mines has been one of the main drivers for using CFB in these power plants. A good example of this is the largest CFB in operation, the 460 MW e Lagisza power plant in Poland. In some cases the co-firing of biomass, peat, petroleum coke, RDF, sludges etc., has also been used. The latest and most advanced project in this group is the Samcheok project presented earlier in this paper. Low volatile solid fuels (e.g. Rostov area anthracite) The circulation of the bed with the fuel in the combustion chamber in a CFB provides the possibility for a good burn out even for low volatile coals. FW has gained a good experience from the delivery of 35 boilers firing anthracite or anthracite waste coal. The size range of these references start from industrial sizes (12 MW e ) up to 330 MW e supercritical unit in Novocherkasskaya GRES Unit No 9. The partnership of Russian boiler supplier EM-Alliance and Foster Wheeler was awarded the Novocherkasskaya CFB boiler (Figure 5) by the OGK 6. In the selection of supercritical CFB combustion technology with 565/565 ⁰C steam temperatures (Table 3) the important goals for OGK 6 were to choose a technology that can burn the low volatile anthracite efficiently without any support fuel while meeting the environmental requirements. In addition to this, the boiler had to be able to fire Kuznetsk coal and co fire anthracite coal washery waste (Table 4). The boiler deliveries are completed and the boiler is under construction.

12 Figure 5. Novocherkasskaya GRES Unit No 9 Table 3. Design values of Novocherkasskaya GRES Unit No 9 Plant Electrical Output (Gross/Net) MWe 330/312 Net Plant Efficiency (LHV/HHV) % 41,5/39,9 Net Plant Heat Rate (LHV/HHV) kj/kwh 8681 SH flow kg/s 278 SH pressure bar(g) 247 SH temperature C 565 RH flow kg/s 227 RH pressure bar(g) 37 RH temperature C 565 Feed water temperature C 280

13 Table 4. Fuel specification Anthracite Coal LHV (a.r.) MJ/kg 21 Moisture % 9,0 Ash (a.r.) % 26 Sulfur (a.r.) % 1,3 Petroleum coke firing in utility scale Petroleum coke, a solid residue by-product of the crude oil refining processes, mostly delayed coking, is a very attractive fuel for large-scale power production due it s high carbon content, low hydrogen and almost free of ash qualities. Foster Wheeler is the market leader in petcokefired CFB boilers with over 70 references and over 80 % market share in petroleum coke fired boilers. CFB is a suitable technology also for firing other refinery by-products. For petroleum coke firing, commercial scale of 300 MW e is achieved with 2 x 300 MW e and 2 x 330 MW e references in USA. An example of European delivery is 70 MW e Lukoil Energy & Gas boiler in Ploesti, Romania. Petroleum coke is a hard to burn fuel due to the low volatile content, so the CFB technology advantage is the same as for the anthracite coals and provides a good fuel burn out and ability to efficiently capture the high level of sulfur in petcoke. Vanadium content in the petroleum coke is high causing a risk of corrosion and fouling of the heat surfaces in combustion of the fuel. Due to the low combustion temperature in the CFB these problems can be avoided. Lukoil Energy & Gas For petroleum coke firing, Foster Wheeler delivered a CFB boiler at Lukoil s refinery in Ploiesti, Romania (Figure 6). The delivery included a 70 MW e boiler, which entered into commercial operation in October Dependency on crude oil as boiler fuel was reduced (Table 5), plant capacity increased (Table 6), emissions were lower (Table 7), and fuel sourcing capabilities flexible.

14 Figure 6. Lukoil CFB boiler in Romania Table 5. Design fuel for Lukoil boiler Design fuel: Petroleum Coke LHV (a.r.) MJ/kg 31,14 Moisture % 10,2 Ash (a.r.) % 0,55 Sulfur (a.r.) % 3,53 Table 6. Design steam data for Lukoil boiler Total Heat Output 185 MWth SH flow 72 kg/s SH pressure 100 bar SH temperature 540 C Feed water temperature 214 C Table 7. Emissions for Lukoil boiler Emission (6% O 2, dry) mg/m 3 n SO NO x 200 Particulates 30

15 Lignite firing in utility scale Lignites are typically high ash and high moisture fuels which lend themselves very well for the use of the CFB technology. Foster Wheeler has lignite fired boiler experience ranging from 15 MW e small industrial boiler to large 315 MW e unit. In the Turow power station located in Bogatynia, Poland, six old pulverized-coal boilers (210 MW e ) were replaced in the first phase with three 235 MWe CFB units and later with three 262 MW e CFB units using the more compact new Foster Wheeler CFB design. (Figure 7). CFB BOILER 3x557 MWth, 3x262 MWe, 195/181 kg/s, 170/39 bar, 568/568 C Figure 7. Lignite firing in utility scale (Turow units 4-6)

16 Biomass firing In Europe, biomass is promoted because it is a renewable fuel source and CO 2 neutral. Biomass, in the form of wood chips, forestry waste, agricultural waste, and wood pellets can be utilized by using Fluid bed technologies, bubbling bed (BFB) and Circulating Fluidized bed (CFB). For small scale projects with only wood or wood waste the BFB technology is normally used. At the larger scale, where efficiency becomes important and the flexibility for co-firing coals or agricultural waste is needed, the CFB technology is more suitable. A good example project for the latter case is the power plant Polaniec described below. Polaniec biomass project 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 8). 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. 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 8. Advanced Bio CFB s in Polaniec site.

17 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. New agro biomass fuels are being continuously tested with customer.

18 True benefits of fuel flexibility: co-firing One of the important advantages of CFB technology that could be valuable in Russia, is the possibility of burning a diverse range of fuels alternately and simultaneously. Fuel flexibility includes both a wide range of heating values and the possibility of burning fuels with very different physical and chemical properties. The types of fuels used in CFB boilers include coal of various degrees of carbonification, waste coal, petroleum coke, peat, wood-derived fuels, agricultural and agro-industrial wastes, sludge, refuse derived fuels, tires, etc (see Figure 9). Coal Anthracite Bituminous Sub-bituminous Lignite Wood residue Bark Chips Wood dust Forest residue Recycled Wood Tire Derived Fuel Solid Recovered Fuel Waste coal Bituminous gob Anthracite culm Coal slurry Petroleum coke Delayed Fluid Peat Agricultural waste Straw Olive waste Sludge Paper mill De-inking Municipal Waste paper Gas Natural Off gases Oil Oil shale Figure 9. Type of fuels (co-) fired in Foster Wheeler s CFB boilers. CFB boilers can effectively deal with wide variations in coal quality, which can exist even within coals from a single mine. In an attempt to minimize the operational costs, utilities seek possibilities to utilize cheaper, lower-grade coals with high moisture, ash and sulfur content. Low-grade coals that have been already used in power production, have been local lignite coals or lower-rank bituminous coals, which do not have an export market due to low quality. At present, most CFB installations are designed for multi-fuel firing capability, i.e. for more than one solid fuel. CFB SCRUBBER FOR REACHING TIGHT EMISSION LIMITS Tightening environmental regulations are lowering the requirements for emissions from power plant and industrial facilities around the world. Newer, stricter standards are being required by more governments for pollutants that are already being regulated SO x, NO x and

19 particulate matter. In addition, metals, acid gases, and organic compounds are setting requirements for flue gas cleaning systems. Due to the new requirements for flue gas acids like SO x,hcl, HF, dust and many other multipollutants, owners of coal fired, oil fired and waste fired power plants are continuously evaluating the merits of adding back-end air quality control systems (AQCS). The dry technology of Circulating Fluidized Bed Scrubbing (CFBS) is a viable pathway for addressing multi-pollutant control in a cost effective manner and is well suited for retrofitting of existing power plants. Construction costs can be reduced as the major system components can be pre-assembled on the ground and lifted into place during system erection. The technology provides high pollutant removal efficiencies up to 99 % for SO 2, SO 3, HCl and HF. Further the absorber/fabric filter arrangement is highly adaptable for sorbent injection for removal of heavy metals including mercury. Basin Dry Fork station project, located in Gillette, Wyoming, USA (Figure 10), which entered commercial operation 2011, featured best available dry flue gas scrubbing technology (BAT) for the first time worldwide in single unit size for a 420 MW e coal fired boiler plant (520 MWe equivalent at sea level condition). Compared to wet FGD, the main advantages of this technology are up to 30 % less water consumption, the high removal efficiencies of SO 2, SO 3 and H 2 SO 4 in particular, the assured product utilization for landfill at the nearby opencast coal mine and significantly lower investment costs (up to 50 %).

20 Figure 10. CFB Scrubber Process Flow schematic, Dry Flow Station As presented in Figure 10, the absorber vessel is a self cleaning CFB upflow reactor wherein all reactants are introduced at the bottom of the vessel along with a large portion of particulate solids collected from a downstream fabric filter. SO 2 and SO 3 enter with the boiler flue gas, and the hydrated lime reagent is then introduced to the absorber above the entry point of the flue gas. The turbulator absorber wall surfaces provide high mixing and pollutant capture efficiency as reactants move to the top of the absorber. The gas is cooled by evaporation of a spray of low quality water injected into the absorber. The ratio of hydrated lime, recycled particulate, and, if necessary, fly ash solids to spray water is approximately 20:1 translating into extremely high surface area for conversion of SO 2 and SO 3 to calcium sulfate and calcium sulfite. The process does not require peripheral equipment such as rotary atomizers, spray spargers, or mist eliminators utilized in conventional dry or wet scrubbers. From the fabric filter clean flue gas is directed to the stack with almost no emissions left. Commercial operation of the FWGW Dry CFB began in June The first operation experiences of Basin Dry Fork station project have been excellent. The technology is able to meet the strict emission requirements and even more.

21 Summary Over the past 35 years, circulating fluidized bed (CFB) boiler technology has evolved from industrial boiler technology used to burn difficult fuels to utility size, latest reference being Samcheok 4 x 550 MW e project. Established benefits include fuel flexibility and multi-fuel firing in addition to low SO 2, and NO x emissions without secondary flue gas clean-up systems. When Russian solid fuels are considered, CFB boilers are ideal for several solid fuels, such as bituminous- and anthracite coals, lignite, petroleum coke, peat and biomass. The fuel flexibility and fuel switching, as well as co-firing capability give significant economic advantage, allowing to choose/use the most cost effective fuel at any time, firing lower cost local fuels instead of high quality fuels with far transportation. Basin CFB scrubber entered commercial operation 2011, featuring best available dry flue gas scrubbing technology (BAT) for the first time worldwide in single unit size over 500 MW e for a coal fired boiler plant. First operation experiences of Basin Dry Fork station project have been excellent.