Circulating Fluidized Bed Boilers

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Circulating Fluidized Bed Boilers

• Experience, Capabilities Performance

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Fluidized Bed Combustion (FBC) technologyachieved
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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Metso Automation FBC Experience over 100
unitsup 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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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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A notable example of utility sized CFBC -
Alholmens, Finland worlds 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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Alholmens Control Room
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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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Another notable installation - Narva, Estonia

• Balti Elektrijaam
• 2 Foster Wheeler CFB Boilers
• 215 MWe
• 714 000/599 000 lb/h,1842/348 PSI
• 995/995?F
• Fuel Oil shale
• District heating 160 MWth
• Eesti Elektrijaam
• 2 Foster Wheeler CFB Boilers
• 215 MWe
• 714 000/599 000 lb/h,1842/348 PSI
• 995/995?F
• Fuel Oil shale

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Xiao Long Tan 2X300 MW CFBYunnan, PRCLargest
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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Lagizsa, Poland worlds first supercritical CFB

• Single Foster Wheeler CFBC
• Unit size 460 MW
• Fuel anthracite
• Pressure 3988 PSIA
• Temperature 1040F
• Efficiency 45.3
• Startup 2007/08

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Lagisza worlds first supercritical CFB

• Emissions per EU directive
• SO2 0.16 lb/mbtu
• NOx 0.16 lb/mbtu
• CO 0.16 lb/mbtu
• Dust 0.025 lb/mbtu
• Without DeSOx or DeNOx
• equipment

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Circulating Fluidized Bed Boilers

• Unique Issues and Challenges

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Typical CFB plant with cyclone separator
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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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Objectives dependent upon only a few controlled
variables

• Objectives...
• lower emissions
• higher efficiency
• process parameters
• within permitted limits
• easy operation
• automatic control
• throughout entire
• load range
• can be achieved...

• 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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Circulating Fluidized Bed Boilers

• Control strategies to meet objectives

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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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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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Circulating Fluidized Bed Boilers

• Advanced Control Strategy 1
• Coordinated Control

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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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Strategy 1 - Coordinate boiler with turbine
proven coordinated front end with Model
Predictive Control.
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Closed loop generation control provides a linear
response
Generation Control
Inc.
Dec.
ADS
Inc. Limit
Dec. Limit
Rate Limit
ò
A
A
A
Unit Demand
Turbine Base Mode
T
H
D
L
D
v
Frequency Bias
S
MW
D
PID
Main Steam Pressure

Boiler Demand Coordinated Mode
FIRST STAGE PRESSURE
D
Pressure Set Point
D
L
PI
D
PI
T
ò
Block
Override
Position Demand to E-H-C
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Fast accurate response to AGC commands..
Unit 1 without new system (blue) Unit 2 with new
system (Red)
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Constraint coordinator protects unit slows rate
of change in the event equipment or process is
not operating at optimum
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Circulating Fluidized Bed Boilers

• Advanced Control Strategy 2
• Fuel Power Compensator

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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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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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Typical CFB with Fuel Power Compensator
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Fuel Power Compensator developed in cooperation
with Kvaerner
INTELLIGENT FUEL FEEDING AND CONTROL SYSTEM FOR
HETEROGENEOUS FUELS Dr. Tero JoronenResearch
Scientist University of California
BerkeleyMetso AutomationLentokentänkatu 11, PO
Box 237, FIN-33101 Tampere, FinlandTel 358
(0)20 483 8807 Fax [phone]Jani
LehtoProduct EngineerKvaerner
PowerKelloportinkatu 1 D, PO Box 109, FIN-33101
Tampere, FinlandTel 358 (0)20 1412 432 Fax
358 (0)20 1412 210
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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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Circulating Fluidized Bed Boilers

• Advanced Control Strategy 3
• Combustion Optimizer

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Bed/furnace temperature and fuel/air ratio
directly effect emissions, performance, operating
cost and are a function of many different
variables
Opacity
SO2
Slagging
CO2
Hg
NOX
CaCo3
Carbon in flyash
Air heater fouling
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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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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An important reason to optimize bed
temperatureit can cost you!
Operating outside of the optimum temperature
range can cost big bucks for extra limestone!
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NOX formation vs temperature and nitrogen content
of the fuel
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SNCRSelective 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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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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Fuzzy logic for Fluidized Bed BoilersWhat,
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

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Advanced Controls
Fuzzy logic for Fluidized Bed Boilers Control of
primary/secondary air
Rule base
Measurements Fuzzyfication
Defuzzyfication
Fuzzy- Inferenz
cyclone temperatures

• Control
• increase
• decrease

Presentation of linguistic variables bed-temperatu
res (membership functions)
low normal
high
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Advanced Controls
Fuzzy logic for Fluidized Bed Boilers Implementati
on
Air flow / fuel power
Calculation of fuel-power

• Setpoint for
• controller
• total air
• primary air
• secondary air

• 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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Advanced Controls
Fuzzy logic for Fluidized Bed Boilers Principal
structure...
3. Operator know-how
F, P, T
T
T
O2 CO
NOx SO2
T
T
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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Bed Temperature before (upper chart) and after
optimization (lower Chart)
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Typical CFB with Combustion Optimizer
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A performance story Alholmens availability
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Metsos 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