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Circulating Fluidized Bed Boilers

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Presentation on theme: "Circulating Fluidized Bed Boilers"— Presentation transcript:

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) Date Title/Author

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. Date Title/Author

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 Date Title/Author

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 Date Title/Author

6 Alholmens Control Room
Date Title/Author

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 Date Title/Author

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 Date Title/Author

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 Date Title/Author

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 Date Title/Author

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 Date Title/Author

12 Date Title/Author

13 Circulating Fluidized Bed Boilers
Unique Issues and Challenges

14 Typical CFB plant with cyclone separator…
Date Title/Author

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! Date Title/Author

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 Date Title/Author

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 Date Title/Author

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 Date Title/Author

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 Date Title/Author

22 Strategy 1 - Coordinate boiler with turbine… proven coordinated front end with Model Predictive Control. Date Title/Author

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 Date Title/Author

24 Fast accurate response to AGC commands..
Unit 1 without new system (blue) Unit 2 with new system (Red) Date Title/Author

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

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. Date Title/Author

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 Date Title/Author

29 Typical CFB with Fuel Power Compensator®…
Date Title/Author

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) Date Title/Author

31 Fuel Power Compensator®...performance at Alholmens 240MW CFB plant
steam flow O2 coal Increasing coal content in coal/bio-fuel mixture Date Title/Author

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 Date Title/Author

34 Date Title/Author

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 Date Title/Author

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! Date Title/Author

37 NOX formation vs temperature and nitrogen content of the fuel…
Date Title/Author

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! Date Title/Author

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 Date Title/Author

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 Date Title/Author

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 Date Title/Author

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 Date Title/Author

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 Date Title/Author

44 Bed Temperature before (upper chart) and after optimization (lower Chart)…
Date Title/Author

45 Typical CFB with Combustion Optimizer
Date Title/Author

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 Date Title/Author

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 Date Title/Author

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