Circulating Fluidized Bed Boilers Experience, Capabilities & Performance

Circulating Fluidized Bed Boilers

Experience, Capabilities & Performance

© Metso Automation Inc. 2003 Title/AuthorDate2

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

CFB BOILER2x274 MWth, 112 kg/s, 135 bar, 538 °C

EC Chorzów Elcho Sp. zo.o., Chorzów, Poland

Control strategies perfected over 25 years of collaboration between Metso Automation and Kvaerner Power (now Metso Power)


Metso Automation FBC Experience – over 100 units…up to 460 MWe

050

100150200250300350400450500

1988 1993 1995 2000 2001 2002 2003 2005 2006 2007

Un

it S

ize

MW

eLagizsa

Xia Lang Tan 1 &2

Alholmens

Xin Jian Si 1 & 2Scrubgrass Yi Bin

Rauhaladati

Mt Poso

Control systems on over 300,000 MW worldwide.


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


Alholmens Control Room


Another notable installation - Narva, Estonia

Balti Elektrijaam• 2 Foster Wheeler CFB Boilers• 215 MWe • 714 000/599 000 lb/h,1842/348 PSI • 995/995F• 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• 995/995F• Fuel: Oil shale


Xiao Long Tan 2X300 MW CFB…Yunnan, 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


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



Unique Issues and Challenges


Typical CFB plant with cyclone separator…

Convection Pass

Superheater

Economizer

Steam Drum

Secondary AirPorts

BedTemperature

CycloneSeparator

High Density

GovValves

Primary AirFan

GasRecirc

Fan

Secondary AirDamper

Secondary AirFlow

AirPreheater

Steam CoilAir Heater

FD Fan

ID Fan

Bag House

FuelFeeder

Turbine

Stack

PrimaryAir Flow

Primary SH locatedin Loop Seal


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!


Objectives dependent upon only a few controlled variables…

NOx SO2

T

TO2 CO

T, pdT

F, P, TT

T

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

by controlling...• fuel feed• combustion air• air distribution• limestone injection

by controlling...• fuel feed• combustion air• air distribution• limestone injection

The challenge… only a relatively few controlled variables to effect change


Control strategies to meet objectives…


What control strategies are required to meet overall objectives?

1.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

2.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

3.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


Advanced Control Strategy 1…

Coordinated Control


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


Strategy 1 - Coordinate boiler with turbine… proven coordinated front end with Model Predictive Control.

Furnace Pressure toID Fan Control

Convection Pass

Superheater

Economizer

Steam Drum

Secondary AirPorts

BedTemperature

CycloneSeparator

High Density

O2Correction

FuelControl

EnergyDemand

GovValves

Bed TempControl

Primary AirControl

Primary AirFan

GasRecirc

Fan SecondaryAir Control

Secondary AirDamper

Secondary AirFlow

Forced DraftAir FlowControl

PressureSetpoint

AirPreheater


FD Fan

FurnacePressureControl

FurnacePressure

ID Fan

Bag House

FuelFeeder

Fuel FeedDemand

Feedforward

AirflowDemand

Pri Air /Sec AirRatio

FuelDemand

GenerationControl

Turbine

Frequency

StackMPC

MW


L

H

PID

PI

FIRST STAGE

PRESSURE

v

AAUnit Demand

Generation ControlInc. Dec.

ADS

A

T

FrequencyBias

PI

L

MW

Inc.Limit

Dec.Limit

RateLimit

TurbineBaseMode

Position Demandto E-H-C

BlockOverride

Main SteamPressure

PressureSet Point

Boiler DemandCoordinated Mode

T

11:47am Stop

11:07pm Start Down

9:55am Start

50 100 150 200 250 MEGAWATTS

Closed loop generation control provides a linear response…


Unit 1 without new system (blue)

Unit 2 with new system (Red)

Fast accurate response to AGC commands..


Constraint coordinator protects unit… slows rate of change in the event equipment or process is not operating at optimum

D-E-BGeneration

ControlAlgorithm

1st StagePressure

GrossGeneration

Frequency

MW Demand fromLoad Dispatch

Office

MW Demand Setby Plant Operators

Interfaceto

TurbineGovernor Valves

D-E-BUnit Demand

Algorithm

Rate LimitingHigh/ LowLimiting

ConstraintCoordinatorAlgorithm

Process Variables& Auxiliaries

Status

Overrides fromBoiler Control

Maximum ramp rate3% per minute

Constraint coordinator cutsramp rate to 1.5% per minutebecause of process orequipment limitations.

Constraint coordinatorstops ramp until conditionclears

Constraint coordinatorresumes normal ramp.

LO

AD

Time



Fuel Power Compensator®


Strategy 2 - Advanced application to compute and control true “heat release” from all fuel sources and detect changes in heating value

Steam Flow Steam Pressure Steam Temperature Feedwater Flow Feedwater Temperature Air Flow Air temperature Flue Gas Flow Flue Gas Temperature Oxygen Level Solid Fuel Flow

Heat BalanceCalculation

OxygenConsumption

Bias for Changein EnergyContent

Fuel Power Compensator® –

Computes true “heat release” and corrects fuel and airflow demand.


Typical CFB with Fuel Power Compensator®…


Convection Pass

Superheater

Economizer

Steam Drum

Secondary AirPorts

BedTemperature

CycloneSeparator

High Density

O2Correction

FuelControl

EnergyDemand

GovValves

Bed TempControl

Primary AirControl

Primary AirFan

GasRecirc

FanSecondaryAir Control

Secondary AirDamper

Secondary AirFlow


PressureSetpoint

AirPreheater


FD Fan


FurnacePressure

ID Fan

Bag House

FuelFeeder

Fuel FeedDemand

FeedforwardAirflowDemand


FuelDemand

GenerationControl

Turbine

Frequency

Stack

Fuel PowerCompensator

Steam Flow

Steam Temp

FW Temp

Air Temp

Flue Gas Temp

Fuel Flow

Steam Pres

FW Flow

Airflow

Flue Gas Flow

Oxygen

MPC


Increasing coal content in coal/bio-fuel mixture

coal

O2

steam flow

Fuel Power Compensator®...performance at Alholmens 240MW CFB plant



Combustion Optimizer


Bed/furnace temperature and fuel/air ratio directly effect emissions, performance, operating cost… and are a function of many different variables…

SO2

HgNOX

CO2

Opacity

CO

Carbon in flyash

Slagging

Air heater fouling

• 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

CaCo3



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

Bed material and temperature management:


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!


NOX formation vs temperature and nitrogen content of the fuel…


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!


The best solution is to…

• Utilize all available process data

• Make calculations that describe and predict performance

• Incorporate operator know-how, expertise and intuition


Tuning parameters• fuel/air• prim./sec. air• lower/upper sec. air• O2-controller setpoint• fuel distribution

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

1. Calculated variables• fuel heating value• oxygen consumption• flue gas flow• emissions mg/MJ

NOx SO2T

T O2 CO

T, pdT

F, P, T

T

T

3. Operator know-how3. Operator know-how

2. Measurements2. Measurements

(control/Compensation/

Filtering / Recipe)

Fuzzy-logic

Ad

van

ced

Co

ntro

lsFuzzy logic for Fluidized Bed BoilersPrincipal structure...


Bed Temperature before (upper chart) and after optimization (lower Chart)…


Typical CFB with Combustion Optimizer


Convection Pass

Superheater

Economizer

Steam Drum

Secondary AirPorts

BedTemperature

CycloneSeparator

High Density

O2Correction

FuelControl

EnergyDemand

GovValves

Bed TempControl

Primary AirControl

Primary AirFan

GasRecirc

Fan

SecondaryAir Control

Secondary AirDamper

Secondary AirFlow


PressureSetpoint

AirPreheater


FD Fan


FurnacePressure

ID Fan

Bag House

FuelFeeder

Fuel FeedDemand

Feedforward

AirflowDemand


FuelDemand

GenerationControl

Turbine

Frequency

Stack

Fuzzy LogicController

Tbed

dTbed

Pair

Load

Pri Air Flow

Recyle GasFlow

Fuel PowerCompensator

Steam Flow

Steam Temp

FW Temp

Air Temp

Flue Gas Temp

Fuel Flow

Steam Pres

FW Flow

Airflow

Flue Gas Flow

Oxygen

MPC


A performance story… Alholmens availability

On-line (%) Forced Outages (hrs)

Avail (%)

2001 96.2 none 100

2002 93.0 276 96.7

2003 96.2 None 100


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

Documents

Circulating Fluidized Bed Boilers Experience, Capabilities & Performance