1. Circulating Fluidized Bed Boilers
Experience, Capabilities & Performance

2. Fluidized Bed Combustion (FBC) technology…achieved through efforts of government initiatives in US and Europe
Applied to small and mid-size industrial and utility plants…
Why CFB?
Wide range of coals & heating values
Opportunity fuels (biomass)
Hard-to-Burn fuels (petroleum coke, tires)
- Excellent emission performance
Minimizes DeSOx / DeNOx systems
CFB has reached utility scale
Sizes over 300 MWe in operation
460 MWe under construction
Control strategies perfected over 25 years of collaboration between Metso Automation and Kvaerner Power (now Metso Power)
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3. Metso Automation FBC Experience – over 100 units…up to 460 MWe
Lagizsa
Xia Lang Tan 1 &2
Alholmens
Unit Size MWe
Yi Bin
Scrubgrass
Mt Poso
Xin Jian Si 1 & 2
Rauhaladati
Control systems on over 300,000 MW worldwide.
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4. Circulating Fluidized Bed Combustion (CFBC) technology recognized as a competitor to pulverized coal firing…
Demand is driven by:
Local availability of low cost fuel e.g. gob, culm, anthracite
Ability to capture harmful emissions in the furnace
Ability to burn a combination of fuels with varying heating values, ash content and moisture content
Low operating cost
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5. A notable example of utility sized CFBC - Alholmens, Finland … world’s largest single bio-fired CFBC boiler
Output: 240MWe plus + 165MW of process steam (1.5 millions #/hr)
Fuel: bark, wood chips, recycled paper & plastic, peat, coal
Single CFBC boiler from Metso Power
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6. Alholmens Control Room
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7. Metso Automation System for Alholmens
System functions:
Boiler Control
Burner Management
Information Management
Energy Management
Fuel Handling
Information Management System
Performance calcs – loss method & input output method, fuel heating value
Condition monitoring – boiler, turbine and auxiliaries
Emission monitoring – CEMS (European)
Boiler & turbine life – stress calculations
10,000 point process historian – DNAreplay analysis
20,000 point event historian – DNAalarm analysis
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8. Another notable installation - Narva, Estonia
Balti Elektrijaam
2 Foster Wheeler CFB Boilers
215 MWe
/ lb/h,1842/348 PSI
995/995F
Fuel: Oil shale
District heating 160 MWth
Eesti Elektrijaam
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9. Xiao Long Tan 2X300 MW CFB…Yunnan, PRC Largest CFB in China
Owner: Guodian IPP
Commercial operation: 2006
Fuel: Lignite
Boiler: Shanghai Boiler Works (Licensee of CE Alstom)
Controls: Metso Automation
Yunnan Xiao Long Tan Power Plant
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10. Lagizsa, Poland… world’s first supercritical CFB
Single Foster Wheeler CFBC
Unit size 460 MW
Fuel: anthracite
Pressure: 3988 PSIA
Temperature: 1040°F
Efficiency: 45.3%
Startup: 2007/08
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11. Lagisza – world’s first supercritical CFB
Emissions per EU directive:
SO lb/mbtu
NOx lb/mbtu
CO lb/mbtu
Dust lb/mbtu
Without DeSOx or DeNOx
equipment
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13. Circulating Fluidized Bed Boilers
Unique Issues and Challenges

14. Typical CFB plant with cyclone separator…
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15. FBC Issues and challenges…
Disturbances are caused by…
Low quality fuels with varying heating values
Multiple fuel firing with varying mixture and moisture
Load demand requirements from steam host and/or generation requires fast response and greater turndown
The consequences…
Higher emissions
Lower efficiency
Imbalance between demand and supply
All lead to higher operating costs!
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16. Objectives dependent upon only a few controlled variables…
lower emissions
higher efficiency
process parameters
within permitted limits
easy operation
automatic control
throughout entire
load range
can be achieved...
NOx SO2 T
O2 CO
T, p dT
F, P, T
by controlling...
fuel feed
combustion air
air distribution
limestone injection
The challenge… only a relatively few controlled variables to effect change
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17. Circulating Fluidized Bed Boilers
Control strategies to meet objectives…

18. What control strategies are required to meet overall objectives?
Coordinate boiler with turbine
Match generation to demand – AGC capability to trade in energy market
Advanced Model Predictive Control (MPC) – provides correct demand to turbine and boiler under all conditions
Match boiler inputs with turbine energy requirement – maximize efficiency
Compute and control true “heat release”
Detect changes in fuel heating value – maintain constant steaming rate
Totalize “heat release” from all sources – maintain constant overall fuel flow
Maintain proper fuel air ratio over entire load range – maximize efficiency
Optimize bed/furnace temperature
Maintain temperature within operating range - lower limestone usage
Maximize sulfur calcium association – lower SOx emissions
Lower overall combustion temperature – lower NOx emissions
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19. Typical CFBC power boiler control system…
Requires the addition of smart control strategies…
Coordinate “front end” with highly responsive generation control
Maintain generation equal to demand under all conditions
Compute and control “heat release” from all fuels being burned
Maintain constant boiler output under all conditions
Compute and control bed temperature
Lower emissions and limestone usage
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20. Circulating Fluidized Bed Boilers
Advanced Control Strategy 1…
Coordinated Control

21. Let us not forget the main purpose of this plant… generate electricity
Must control generation to demand
Must provide AGC capability
Must operate at maximum rate of change
Must protect the unit when equipment is not performing at optimal conditions
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22. Strategy 1 - Coordinate boiler with turbine… proven coordinated front end with Model Predictive Control.
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23. Closed loop generation control provides a linear response…
11:47am Stop
11:07pm Start Down
9:55am Start 50
100
150
200
250
MEGAWATTS
Inc.
Dec.
ADS
Inc.
Limit
Dec.
Limit
Rate
Limit ò A A A
Turbine
Base
Mode
Unit Demand T H D L D v S
Frequency
Bias MW D
PID
Main Steam
Pressure
Boiler Demand
Coordinated Mode
FIRST STAGE PRESSURE D
Pressure
Set Point PI D L D PI T ò
The solution to the governor linearization problem is the cascade strategy as shown here. Use of the first stage feedback control loop provides immediate correction of boiler disturbances with minimal upset to generation control. It is this fast loop that provides the linearized control response as shown on the right.
Note that by addition of the throttle pressure control of turbine follow mode and by the throttle pressure deviation high/low blocks and overrides that coordination between boiler and turbine is provided under all operating conditions.
Block
Override
Position Demand
to E-H-C
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24. Fast accurate response to AGC commands..
Unit 1 without new system (blue)
Unit 2 with new system (Red)
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25. Constraint coordinator protects unit… slows rate of change in the event equipment or process is not operating at optimum
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26. Circulating Fluidized Bed Boilers
Advanced Control Strategy 2…
Fuel Power Compensator®

27. Strategy 2 - Advanced application to compute and control true “heat release” from all fuel sources and detect changes in heating value
Fuel Power Compensator® –
Computes true “heat release” and corrects fuel and airflow demand.
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28. Fuel Power Compensator®
Calculation derived by back-calculating energy content of fuel – on-line and in real time
Heat balance calculation based upon steam, feedwater enthalpies and flow measurements
Oxygen consumption calculation
Stabilizes combustion process during:
Normal operation
Fuel feed disturbance situations
Variations in fuel quality or mixture
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29. Typical CFB with Fuel Power Compensator®…
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30. Fuel Power Compensator® developed in cooperation with Kvaerner…
INTELLIGENT FUEL FEEDING AND
CONTROL SYSTEM FOR
HETEROGENEOUS FUELS
Dr. Tero Joronen Research Scientist
University of California Berkeley Metso Automation Lentokentänkatu 11, PO Box 237, FIN Tampere, Finland Tel: (0) Fax: (0) Jani Lehto Product Engineer Kvaerner Power Kelloportinkatu 1 D, PO Box 109, FIN Tampere, Finland Tel: (0) Fax: (0)
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31. Fuel Power Compensator®...performance at Alholmens 240MW CFB plant
steam flow O2
coal
Increasing coal content in coal/bio-fuel mixture
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32. Circulating Fluidized Bed Boilers
Advanced Control Strategy 3…
Combustion Optimizer

33. Bed/furnace temperature and fuel/air ratio directly effect emissions, performance, operating cost… and are a function of many different variables…
SO2
Opacity
Slagging
CO2
NOX Hg
CaCo3
Air heater fouling
Carbon in flyash CO
Process is difficult to model
Process defined by multiple differential equations
Process changes over time
Feedforward / feedback control cannot deal with all scenarios
Requires input based upon operating experience
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34. Date
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35. Bed material and temperature management:
Good bed management:
Lower emissions
Lower agglomeration
Greater turndown
Stable combustion
Poor bed management:
Higher emissions
Forced outages
Less stable combustion
Higher agglomeration due to hot spots
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36. An important reason to optimize bed temperature…it can cost you!
Operating outside of the optimum temperature range can cost big bucks for extra limestone!
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37. NOX formation vs temperature and nitrogen content of the fuel…
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38. SNCR…Selective Non-catalytic Reduction is temperature sensitive
Ammonia (NH3) or urea (NH22CO) sprayed into the flue gas in the presence of oxygen to produce N2
Reaction produces water and urea in addition to CO2
If temperature is too low the ammonia does not completely react with the NO2 and causes ammonia to be released into the atmosphere …
…called “ammonia slip”
Requires precise furnace temperature control!
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39. The best solution is to…
Utilize all available process data
Make calculations that describe and predict performance
Incorporate operator know-how, expertise and intuition
and use
Fuzzy Logic
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40. Fuzzy logic for Fluidized Bed Boilers What, why...?
Fuzzy control is...
used to control processes for which
it is difficult to create mathematical models
an advanced control method in which
operator experience is utilized to develop
(automatic) control algorithms,
which are created ‘linguistically’ (verbally)
easy for operators to understand
how the higher level, fuzzy controls work
In power, cogeneration and energy-from-waste plants
fuzzy control...
is suitable for instance to optimize the operation of fluidized bed (and grate) boilers
fuzzy logic control can be installed after the start-up of the plant to improve operation
and solve problems
0.6
0.4 oC
Bed temperature- fuzzyfication
low normal high
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41. Control of primary/secondary air
Advanced Controls
Fuzzy logic for Fluidized Bed Boilers
Control of primary/secondary air
Rule base
Measurements Fuzzyfication
bed temperatures
NOx
Defuzzyfication
cyclone
temperatures
Fuzzy-
Inferenz
Control
increase
decrease
Presentation of linguistic variables
bed-temperatures (membership functions)
0.6
0.4 C
low normal high
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42. Implementation Fuzzy logic for Fluidized Bed Boilers
Advanced Controls
Fuzzy logic for Fluidized Bed Boilers
Implementation
Air flow / fuel power
Calculation of fuel-power
Setpoint for
controller
total air
primary air
secondary air
NOx SO2 T
O2 CO
T, p dT
F, P, T
Correction coefficients
fuel/air
primary /secondary air
secondary /tertiär air
setpoint for O2-controller
Corrections
Fuzzy
Fuzzy-logic
Fuzzy-logic
bed-temperature
cyclone temperature
total air
O2/CO-Optimization
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43. Principal structure... Fuzzy logic for Fluidized Bed Boilers T F, P, T
Advanced Controls
Fuzzy logic for Fluidized Bed Boilers
Principal structure...
3. Operator know-how T
F, P, T
2. Measurements
Fuzzy
(control/
Compensation/
Filtering / Recipe)
Fuzzy-logic T
O2 CO T T
NOx SO2
T, p dT
Tuning parameters
fuel/air
prim./sec. air
lower/upper sec. air
O2-controller setpoint
fuel distribution
1. Calculated variables
fuel heating value
oxygen consumption
flue gas flow
emissions mg/MJ
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44. Bed Temperature before (upper chart) and after optimization (lower Chart)…
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45. Typical CFB with Combustion Optimizer
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46. A performance story… Alholmens availability
On-line (%)
Forced Outages (hrs)
Avail (%)
2001
96.2
none
100
2002
93.0
276
96.7
2003
None
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47. Metso’s goal... To be the outstanding supplier for environmentally driven energy solutions.
Over 100 FBC boilers under control
Over 400,000 MW under control
Fast responsive generation control
Advanced control applications for FBC boilers
Fuel Power Compensator® computes true Heat Release
Fuzzy logic controller for bed temperature optimization
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