CIRCULATING FLUIDIZED BED TECHNOLOGY UTILITY-SCALE UNIT EXPERIENCES Stephen J. Goidich Foster Wheeler Energy Corporation Perryville, New Jersey, USA ABSTRACT Foster Wheeler has been supplying circulating fluidized bed boilers to industrial clients for over two decades. The technology has now evolved into large scale utility size units with units as large as 250 MWe in operation, two (2) 300 MWe units in the construction phase and nearing start-up, and designs developed for units as large as 600 MW e in size. The successful operating experience of conventional CFB boilers with cyclone separators, as well as the more recently developed Compact CFB boilers, have demonstrated the ability to scale-up unit size to meet the requirements for utility power generation. Technology improvements are continually being developed and incorporated into the designs to enhance performance, increase operational flexibility, and improve reliability in a cost effective way. Described in this paper is the operating experience of current large scale conventional and Compact CFB boilers, the design and status of the next generation of utility CFB boilers which are scheduled to go into operation in the near term, and what lies ahead with integration of the state-of-the-art supercritical oncethrough utility boiler technology with CFB boiler technology.
1. INTRODUCTION As shown in Figure 1, commercialization of CFB technology began back in the late 1970’s. Since that time there has been a steady scale-up into the utility boiler size range with implementation of many new design features to increase reliability and operational flexibility to meet utility boiler standards. Examples of these enhancements include : o Steam-cooled solids separators and cross-over ducts in combination with advanced refractory systems to minimize refractory maintenence and enhance unit performance o In-duct start-up burner systems to shorten start-up times and save fuel o Fluidized bed ash coolers to reliably discharge spent bed material and recover heat o INTREXTM heat exchangers to increase operational flexibility to adjust furnace temperature and extend the steam temperature control range o Reheat steam bypass system for reliable and cost effective reheat steam temperature control During the early 1990’s, a new generation of CFB boilers was introduced by Foster Wheeler, the Compact CFB (see Figure 2). Experiences of conventional CFB combustors was applied in the scale-up of Compact units. Presently, scale-up of Compact boilers has reached the maximum capacity level of today’s conventional CFB boilers. As shown in Figure 1, the more rapid scale-up of the Compact CFB was possible UNIT CAPACITY (MWe) because of experience and lessons learned in 350 A A E E 1 J J scale-up of the conventional CFB boilers. W 300
The progress made in the development of CFB technology can be seen in the rehabilitation of Turow Power Station which is located in Bogatynia, Poland. Old pulverized-fuel boilers were replaced by three(3) conventional 235 MWe CFB boilers, which are currently in operation, and three(3) 262 MWe Compact CFB units which are in the fabrication/construction phase and are scheduled to go into operation starting in late 2002. Operating experiences experiences of Units 1,2, and 3, firing brown coal, have proven the
250 200 150 100 50 0 1970
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M A K Y E L
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N O D O U L I K I S N A A V A J A T T K N N
A I T O C S A V O N
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L N A S P I O N T N T E V T F N A C C O R
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A L O K O O K M M O H H K
K I A H T
5 W O R U T
A P M O C
U U K K
1 99 5
2000
YEAR OF INITIAL OPERATION
Figure 1. CFB Boiler Scale-up Chronology (Ref. 1)
2 0 05
technology to be a mature and advanced solution at the utility scale meeting the requirements of high reliability, performance and economy. Further improvements will be achieved in Units 4, 5, and 6 using Compact boiler technology with integrated cooled panel structures for the furnace, solids separator, and INTREX heat exchangers. Experiences from the scale-up and success of the Compact technology make it possible to provide the most advanced configurations for the utility scale CFB boilers. With the current status of CFB units, commercially feasible options for power production are available in the capacity range of 300 – 600 MW e. Further advantages in plant efficiency will be achieved by applying once-through steam cycle with supercritical steam parameters.
Figure 2. Compact CFB Boiler
2. EXPERIENCE FROM TUROW UNITS 1, 2, AND 3 Turow Units 1, 2, and 3 are the largest Foster Wheeler CFB boilers currently in operation. Table 1 lists the basis for design of these 235 MW e brown coal fired units. Because of the high moisture content of the fuel, the ratio of volumetric flue gas flow rate to the steam duty produced is high. As a result, the physical size of these units is the largest in the world. Table 2 lists the basic dimensions of the furnace and cyclones. Figure 3 is an isometric view of one of the units.
Steam Output Capacity, MWt Steam Flow, t/h (SH/RH) Steam Pressure, bar (SH/RH) Steam Temperature, °C (SH/RH)
529 665/593 132/25 540/540
Fuel As a repowering project, there was a financial incentive to utilize the existing foundations and the majority of structural steel columns. The space restrictions imposed by these requirements necessitated configuring the boiler with two (2) large diameter cyclone separators which represented a significant scale-up from previous experience. A three (3) cyclone design would have required an additional 30% increase in boiler island width for which there was not sufficient space. Performance with the large diameter cyclones was as expected with all performance guarantees achieved as noted in Table 3.
Moisture, wt%
44.0
Ash, wt%
22.5
Sulfur, wt% HHV, kcal/kg
• • • • •
2330
Emission Limits NOx, ppm
210
SO2, ppm
140
Table 1. Turow 1, 2, 3 Design Parameters
Before the units were turned-over to the customer, each had to complete a rigorous 30-day trial run program. All plant performance guarantees had to be demonstrated including the requirements of the Union for the Coordination of Production and Transmission of Energy (UCPTE) which is the European utility power plant standard that contains strict guidelines for load ramp changes and plant dispatching (Ref. 2). These requirements included: •
0.6
72 hour full load test +/- 4% MCR load ramp between 40% and 100% +/- 5% MCR step load changes load rejection to house load followed by resynchronization in a specified time load run back to 50% on loss of HP heaters, fans, condensate or primary cooling water pumps minimum time to reach full load from cold, warm, and hot restart conditions
All units met or exceeded the trial run requirements, demonstrating that large scaleup CFB boilers can meet utility market requirements for cycling and that the scale-up of the furnace solids circulation loop beyond previous experience was successful.
Boiler No.
1
Design
Steam Output, kg/s
184.06
183.62
185.4
Boiler Efficiency, %
90.12
91.27
90
Thermal Output, MWt
524.9
523.1
528.9
Gross Power, MWe
237.8
240.5
235
Heat Rate, kJ/kWh
9686
9472
9795
1.29
2.17
2.6
135
133
150
115
26
140
17.5
3.5
50
85
85
85
Limestone, Ca/S
Furnace
2
Emissions: Height, m
42.5
NOx, g/GJ
Width, m
21.1
SOx, g/GJ
Depth, m
9.9
3
Dust, mg/Nm Noise, dBA
Cyclones Table 3. Turow 1, 2, 3 Performance Results
Number Diameter
2 10.3
Table 2. Turow 1, 2, 3 Dimensions
3. THE JEA PROJECT APPROACHES THE COMMISSIONING PHASE When the 300 MW e JEA Northside Units 1 and 2 start-up in early 2002, this U.S. Department of Energy (DOE) funded demonstration project will provide a benchmark against which the utility, independent power, and financial industries can assess large scale application of CFB technology. The plant will demonstrate CFB technology for coal firing in the largest capacity units to date while providing reduced emissions, and a wide range of fuel firing flexibility. The Northside Generating Station in Jacksonville, Florida includes three heavy oil- and natural gasfired boilers. Units 1 and 3, which came on line in November 1966 and June 1977, respectively, are operating at limited capacity due to the high cost of fuel. Unit 2, which came on line in March 1972, has not operated since 1983 due to boiler availability problems.
Figure 3. Turow Unit No. 1
The JEA Northside demonstration project involves repowering the existing steam turbine at Unit 2 with a 297.5 MWe CFB boiler. The DOE cost sharing for the project includes two years of demonstration test runs during which Unit 2 will be operated on several different types of coal and coal/petroleum coke blends. Unit 1 is also being repowered with an identical CFB boiler which will be privately financed. Construction began in mid1999. Unit 2 is scheduled for initial operation in January 2002; Unit 1 will follow three months later.
Table 4 lists the steam capacity, design fuels, and emission limits for each boiler. The basic dimensions for the units are listed in Table 5. Figure 4 illustrates the unit design. Key design features of the boiler include a single, watercooled furnace, steam-cooled cyclone separators, INTREXTM heat exchangers, a parallel pass heat recovery area (HRA), in-duct start-up burners, fluidized bed ash coolers, and an air swept fuel feed system. A detailed description of these design features can be found in Reference 3.
Furnace Height, m
35.1
Width, m
26.1
Depth, m
6.7
Steam Output Capacity, MWt Steam Flow, t/h (SH/RH)
906/806
Steam Pressure, bar (SH/RH)
172/37.7
Steam Temperature,°C (SH/RH)
540/540
Fuel
Coke
Coal
Moisture, wt%
9.0
5.2
Ash, wt%
0.4
12.8
Sulfur, wt%
6.7
2.8
7780
7050
HHV, kcal/kg Emission Limits NOx, mg/Nm3
220
3
130
SO m /Nm
Cyclones
689
Table 4. JEA Design Parameters
Number Diameter
3 7.3
Table 5. JEA Dimensions
Figure 4. JEA Unit No. 2
4. UTILITY SIZE COMPACT CFB BOILERS In 1994 Foster Wheeler put into operation the first commercial size Compact CFB boiler for the 25 MW t Kokkola facility in Finland. This design combined the cooled, thin layer of refractory design developed for the steam-cooled cyclone, simplified fabrication and construction with flat wall panels, and provided a “compact” configuration by integrating the separator and sealing device adjacent to the furnace enclosure. To date there are 28 Compact CFB boilers in operation burning a range of fuels. An additional ten (10) units are in the design construction phase. The largest Compact units currently in operation are the two (2) 150 MWe National Power Supply units. The next largest units to come on line will be the 262 MWe Turow Units 4, 5, and 6. The following is a description of these units. 4.1 National Power Supply Company In 1998 two (2) 150 MW e Compact CFB boilers went into operation for the National Power Supply (NPS) Company, Limited, in Tha Toom, Thailand. The units fire imported coals (bituminous, anthracite) and provide power and heat to nearby industrial customers. These units were the first reheat cycle Compact CFB boilers and include the Foster Wheeler patented reheat steam bypass system for reheat steam temperature control (Ref. 5).
Steam Output Capacity, MWt
370.3
Steam Flow, t/h
*483/440
Steam Pressure, bar
162/55
Steam Temperature,°C
542/542
*SH/RH
Table 6 includes the design parameters to which the boilers were configured. Table 7 includes the results from performance acceptance tests.
Fuel
Anthracite
Capacity, MWt Steam Flow, t/h
Fuel Type
Bituminous
Anthracite
Moisture, wt%
8.0
8.0
Ash, wt%
9.9
12.4
Sulfur, wt%
0.4
0.4
6382
6714
HHV, kcal/kg
Steam Pressure, bar Steam Temperature, °C
357 *469/399 156/32 538/541
*SH/RH Boiler Efficiency, %
92.0
Emissions, ppmvd@6%O2 NOx
Emissions Limits NOx, ppmvd@6%O2
180
SO2, ppmvd@6%O2
450
Table 6. NPS Design Parameters
SO2 (w/o limestone)
34 339
Table 7. NPS Performance Results
Figure 5. NPS Boiler Arrangement
The boiler configuration for these units (see Figure 5) was the first to include a pair of double vortex Compact Separators on both the furnace front and rear walls. Internal furnace heat transfer surface in the form of superheat and reheat omega panels were included to achieve the desired furnace operating temperature.
Boiler Thermal Power, MWt
555
Gross Output, Mwe
261.8
Net Output, Mwe
238.0
Main Steam Flow, kg/s 4.2 Turow Units No. 4,5,6
565
Main Steam Pressure, bar
The two (2)-sided Compact CFB boiler arrangement developed for the NPS project was the basis for scale-up to the 262 MW e Turow Units 4,5, and 6 configuration which is shown in Figure 6. The design fuels, emission and performance requirements defined for Units 1, 2, and 3 are the same for Units 4, 5, and 6 except for the steam conditions defined in Table 6.
166.5
Main Steam Temperature, °C
565
Reheat Steam Flow, kg/s
180
Reheat Steam Pressure, bar
38.5
Reheat Steam Temperature, °C
565
Table 8. Turow No. 4, 5, 6 Steam Conditions
HOIST
STEAMDRUM
RH II CONVEYOR BRIDGE
RH I
COAL SILOS ECO LIMESTONE SILO
LIMESTONE SILO
TUBULAR AIRPREHEATER
FURNACE 22042 X 10074
ESP
AIRPREHEATER
Figure 6. Turow Unit No. 5 An enhancement included in the Turow Compact units are the eight (8) INTREX cells which include intermediate and finishing superheater heat transfer surface; four (4) cells per front and rear wall positioned to accommodate a well distributed arrangement of fuel feeders . The ability to control the rate of solids flow through the INTREX tube bundles provides increased operational flexibility for furnace and steam temperature control. The layout of the NPS and Turow units includes Compact separators on both sides of the furnace and a series pass heat recovery area with the FW reheat steam bypass arrangement for reheat steam temperature control. Project specific details will dictate if a one-sided Compact separator design is required and which type of reheat steam temperature control system will be used (reheat steam bypass, parallel pass HRA with gas flow proportioning, or INTREX reheat with solids and fluidization control.
5. ONCE-THROUGH UTILITY CFB BOILER CFB boilers, with a few exceptions, have primarily been configured as “drum” type units which utilize natural circulation as the means for cooling the furnace enclosure tubes. As CFB boilers move into the large-scale (300-600 MW e) utility market, there is a strong incentive to take advantage of the cycle efficiency improvement that supercritical steam conditions offer. As shown in Figure 7 there can be a significant improvement in plant heat rate with supercritical steam conditions. The current state-of-the-art of about 600°C steam temperature with pressures up to 300 bar can increase plant efficiency close to 3 percentage points. To utilize once-through supercritical operating conditions, the steam/water pressure parts of the CFB boiler must be configured to accommodate the selected circulation method. The selection of the circulation method dictates not only the boiler configuration, but also the selection of auxiliary systems as well as the modes and methods of operation and control
) 7 % ( T 6 N E M 5 E V O 4 R P M 3 I E T 2 A R T 1 A E H 0
538/538 565/565 593/593
) 300 a r b ( E 250 R U 165 S S E R P
STEAM TEMPERATURE (C)
Figure 7 Heat Rate Improvement (Ref.
As illustrated in Figure 8, in a drum type unit which operates at a subcritical pressure, large diameter tubes are used to minimize flow resistance so that a sufficient amount of steam and water can flow through the tubing by natural circulation. By designing for a sufficiently high circulation rate, the water passing through the tubing never completely evaporates to steam and a liquid film is maintained on the tube wall to keep it at essentially at the saturation temperature for the operating pressure of the boiler. In a once-through boiler which operates at supercritical pressure, there is no distinction between liquid and vapor phases and there is a continual increase in fluid temperature. With unbalances in heat absorption and variations in flow rate due to hydraulic resistance differences from tube to tube, variations in tube temperatures can occur. If the unbalance is not limited, high thermal stresses will result which can lead to tube failure.
Figure 8. Evaporator Tube Temperature
Historically, conventional pulverized coal (PC) OTU units have been designed for high steam/water mass flow rates through the furnace enclosure tubes to minimize peak tube metal temperatures and limit the differential temperature between adjacent tubes. To provide high mass flow rates, the evaporative furnace walls were designed in a multiple pass or spiral arrangement. While meeting the thermal/hyraulic requirements for reliable operation, these arrangements require increased auxiliary power because of the pressure loss resulting from the high mass flow rates and also, some increased mechanical complexity because of the pressure part circuitry.
5.1 BENSON Vertical Technology The current state-of-the-art technology for once-through boiler design is the BENSON Vertical technology developed by Siemens. This technology offers significant functional and economic advantages for OTU power generation such as: •
Low Pressure Loss. A single upflow evaporative pass with low mass flow rates results in low steam/water pressure losses and therefore, low auxiliary power consumption.
•
Simple Support System. With vertical tubing, the furnace enclosure tubes are self supporting and do not require special support straps to account for thermal growth.
•
Minimum Tube Temperature Unbalance. With low mass flow rates, the strongest heated tubes gets the highest flow rate because of a “natural circulation” flow characteristic.
•
Full Variable Steam Pressure. Since a single upflow evaporative pass is used, full variable pressure over the operating load range can be used to better match steam and turbine blade temperature for cycling operation.
In order to incorporate these advantageous features into Foster Wheeler conventional and CFB boilers, FW became a licensee of the BENSON Vertical technology. (A more detailed description of the BENSON Vertical technology and its integration with the Compact CFB boiler can be found in Reference 7.) 5.2 600 MWe OTU CFB Using the BENSON Vertical technology, Foster Wheeler has developed a design for a 600 MWe supercritical CFB boiler which is illustrated in Figure 9. The design is similar in configuration to that described for the Turow Units No. 4,5,and 6 in that includes a double-sided arrangement with a pair of double vortex Compact Figure 9. 600 MWe CFB Boiler Separators on each side of the unit, INTREX heat exchangers (8), and a series pass HRA with reheat steam bypass system for reheat steam temperature control. The development and analysis of the 600 MWe unit has shown that there are no technical reasons to limit the boiler size to the existing capacities and that the benefits of CFB technology can be achieved in large scale utility size units.
6. CONCLUSIONS The successful operation of large scale-up CFB boilers, such as Turow 1,2,and 3, has demonstrated the operational flexibility and reliability required for utility power production. The design enhancements incorporated in the soon to operate JEA Units 1 and 2, and Turow 4,5,and 6 will further demonstrate the capabilities of CFB technology. Future integration of supercritical once-through boiler technology with CFB technology will provide the best combination of features for efficient, cost effective, and environmentally safe power production.
7. REFERENCES 1. S.J. Goidich and T. Hyppanen, “Foster Wheeler Compact CFB Boilers for Utility Scale,” 16th International Conference on Fluidized Bed Combustion, Reno, Nevada, May 13-16, 2001. 2. J. Jablonski, W. Nowak, T. Ozimowski, “Rehabilitaiton of Turow Power Plant,” The Sixth Foster Wheeler Fluidized Bed Customers’ Conference, San Diego, CA, August 18-20, 2000. 3. R.A. Dyr, J. Hebb, and S.L. Darling, “The JEA CFB Demonstration Project: An Update,” 16th International Conference on Fluidized Bed Combustion, Reno, Nevada, May 13-16, 2001., 4. S.J. Goidich, T. Hyppanen, K. Kauppinen, “CFB Boiler Design and Operation Using the INTREXTM Heat Exchanger,” 6th International Conference on Circulating Fluidized Beds, Würzburg, Germany, August 2227, 1999.
5. P.K. Gounder, J.P. Risse, “Circulating Fluidized Bed with Reheat,” Joint Power Generation Conference, Atlanta, FL, October 19-21, 1992. 6. K. M. Retzlaff and G. Schlottner, “Steam Turbines for Ultrasupercritical Power Plants,” POWER-GEN ’98 Europe, Milan, June 9-11, 1998. 7. S. J. Goidich, “Integration of the BENSON Vertical OTU Technology and the Compact CFB Boiler,” POWER-GEN International 2000, Orlando, FL, November 14-16, 2000.
