MODELING OF BARK BOILERS a valuable tool in the design and operation of power boilers

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MODELING OF BARK BOILERS a valuable tool in the
design and operation of power boilers
Process Simulations Limited
March 12th, 2001 Cincinnati, Ohio
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PRESENTATION

• Mathematical modelling in the pulp and paper
  industry
• Mathematical modelling of boilers
• Examples of modelling of bark boilers
• Process simulators in operations, training and
  safety

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PROCESS MODELING GROUP
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PROCESS MODELLING
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STAGES OF ANALYSIS
IN PROGRESS
INDUSTRIAL APPLICATION
PROCESS SIMULATORS
INITIAL STAGE
Literature review Mill interaction Industrial
innovators Process knowledge Commitment of
industry
Physical model Numerical model Model
development Model validation Industrial testing
Industrial application Parametric
studies Solve problems Model proposed
retrofits Improve operations Reduce costs
Envelope calculations Interpolation Operational
simulator Training safety Interacts with
control system Technology transfer
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MODELLING EXAMPLES
Jet engines
Weather
Computer
Harrier jet
Automotive
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CFD PROCESS MODELLING
IN
OUT
OUT
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EFFECTIVE 3-D PROCESSMODELING REQUIRES

• Detailed knowledge of the process
• Sound understanding of the physics involved
• Expertise in computational methods
• Ability to collect information from operators and
  process engineers that have an understanding of
  the operation of the equipment

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MODELING STATEGY

• Use modeling as measurements resolution is low
  and environment severe
• Can evaluate what if scenarios
• Supplements operator equipment knowledge
• Assists mills to make informed decisions
  regarding upgrades to reduce risk
• Provide comprehensive information and 3-D view
  of equipment

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USAGE OF PROCESS MODELING

• Project Engineering
• reduce capital investment risks
• testing of design before committing funds
• train operators beforehand
• Process Engineering
• determine and solve immediate problems
• training of operators reduce variations
• avoid customers being beta test site for
  equipment or retrofits

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WHY RECOVERY BOILER 3-D PROCESS MODELING

• Recovery boiler environment is too severe for
  measurement
• Model provides comprehensive information
  throughout the entire boiler at relatively low
  cost
• Can evaluate what if scenarios to improve
  operation and design
• Supplements steam chief and operator knowledge of
  recovery boiler operations
• Assists mill managers in making informed
  decisions regarding boiler refits and replacements

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DETAILS OF BOILER MODEL

• Advanced and verified solution algorithm
• Black liquor combustion model
• Drying
• Pyrolysis CO, CO2, CH4, H2, H2O
• Char gasification
• Gas phase combustion model
• Advanced radiation model
• Convective section model
• Char bed model

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ISSUES ADDRESSED

• Improve flow and heat distribution
• High excess air
• Emissions CO, CO2, TRS, NOx,
• Mechanical carryover plugging
• Superheater and waterwall tube thermal stress
  failures
• Boiler stability capacity increase

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MODEL PREDICTIONS

• Gas species distributions
• H2, O2, N2, CO, CO2, H2O, CH4, NOx
• Gas flow velocity fields
• Temperature distributions and heat transfer to
  wall surfaces
• Liquor spray combustion and droplet trajectories
• Carryover characteristics

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MODEL VALIDATION

• Isothermal flow validation
• Water model measurements
• Full scale measurements

CE Boiler Model

• Hot flow validation
• Temperature measurements at bullnose
• Carryover prediction trends
• CO emission trends
• Velocity measurements

BW Boiler Model
Different aspects of model results have been
validated against data from operating boilers
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RETROFIT EXAMPLE

• Issue
• High plugging rates
• High gas temperature at superheater
• Bed growth control
• Objective
• Recommend modifications to air system

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RETROFIT EXAMPLE
Test Case Geometries
Tertiary Air Ports (20)
Secondary Air Ports (30)
Primary Air Ports (50)
Base Case
Modified Air System
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RETROFIT EXAMPLE
SECONDARY AIR SYSTEM PROBLEM AND SOLUTION
Base Case
Modified Air System
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RETROFIT EXAMPLE
Velocity Profiles
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RETROFIT EXAMPLE
Fuel Particle Trajectories
Modified Air System
Base Case
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RETROFIT EXAMPLE
Carryover Mass Flux
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RETROFIT EXAMPLE

• Larger air ports provides better jet penetration
• Increases gas mixing
• Breaks up the vertical air core
• Significantly reduces plugging rates
• Reduces gas temperatures at superheater

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PROBLEM SOLUTION
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FUEL AND GAS FLOW
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DESIGN MODIFICATIONS
Current
Modified
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MANUFACTURE DESIGN VS REALITY
Intended Interlace of Secondary Jets
Actual Interlace of Secondary Jets
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EXAMPLE OF BENEFITS OBTAINED

• Improve jet penetration
• Increase gas mixing
• Breaks up the vertical air core
• Significantly reduce plugging rates
• Reduces gas temperatures at superheater
• Helps mill managers make informed decisions
  regarding boiler refits/replacements
• Reduce capital expenditure risks

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BARK BOILERS
ISSUES ADDRESSED BY MODEL

• High excess air
• Emissions
• Mechanical carryover plugging
• Bed Issues
• Air flow distribution optimization
• Tubes thermal stress failures
• Boiler stability and capacity

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MODELING BENEFITS

• Reduce your operational costs
• Increase the range of operational conditions
• Improve controllability of the boiler
• Increase the capacity of the boiler
• Optimize air system
• Lower excess air necessary for complete
  combustion
• Improve overall thermal efficiency

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MODELING BENEFITS

• Increase the efficiency of boiler
• Analyse the existing air and fuel system
• Improve gas mixing and combustion effectiveness
• Optimise firing strategies for different
  loads/fuels
• Minimise danger of blackouts
• Analyse the possibility of air/fuel system
  upgrade
• Lessen the environmental impact
• Minimise particulate carryover, unburned char
• Minimise emission of CO2, CO, Nox

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BARK BOILERS
Upward gas velocity in a bark boiler (1)
base case (2) interlaced overfire air system
Base Case
Interlaced Case
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BARK BOILERS
Examples of carryover particulate trajectories
in different combustion stages
Base Case
Interlaced Case
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BARK BOILER
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POWER BOILERS

• Developed tools to predict with high resolution
  complex processes occurring in power boiler
• Model air system, fuel injection, fuel/air
  interaction, coal combustion, particle flight
  trajectories, convection sections, emissions,
  chemical species

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WHAT MODEL CAN DO FOR YOU

• Increase the load and efficiency of boiler
• Reduce operational costs
• Significantly reduce decision making risks for
  retrofits
• Minimise pollutants emissions
• Provide valuable information for operator
  training
• Minimize flue gas emissions
• Address fuel variability (ash, heating value)

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PROCESS MODELING ADDRESSES

• Low combustion efficiency
• Unstable combustion process (especially at lower
  load and for lower grade coal)
• Slagging on furnace walls and fouling on heater
  surfaces
• Local overheating
• High pollutants (NOx, SOx) emissions
• High temperature corrosion issues
• Optimisation of air and fuel delivery system

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HOW IT MAKES A DIFFERENCE

• Improve combustion efficiency by optimising air
  and fuel system
• Improve combustion stability through retrofitting
  of burner structure and adjusting of air and fuel
  system
• Lighten slagging through retrofitting of burner
  structure and adjusting of air and fuel system
• Predict optimal operation systems for different
  kinds of coal
• Reduce Pollutants emissions by introducing
  advanced combustion techniques

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POWER BOILERS EXAMPLE

• Solve high temperature corrosion at wall

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POWER BOILERS
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BOILER PROCESS MODELING

• Recovery Boilers
• Bark Boilers
• Power Boiler

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PROCESS SIMULATORS
Operator experience
Process knowledge
Operational Simulators
Training Simulators
Simulator Core
Measurements
Safety Simulators
Virtual Cameras
Physical Model
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PROCESS SIMULATORS
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PROCESSCAM

• 1000s of cameras inside the equipment
• Ability to predict equipment behavior for any
  configuration
• Scientific method for process design and
  optimization
• A simulator can assist with operational decisions
  based on some predetermined values
• Almost real time access

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PROCESSCAM TECHNOLOGY
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PROCESSCAM TECHNOLOGY

• Highly scalable and modular
• Provide process engineers, project engineers and
  operators more information for analyzing
  equipment operations
• Displays detailed 3-D results of a process in
  almost real time
• Application training, simulator, control

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SIMULATOR BENEFITS

• Simplified technology transfer to mills
• Reduce equipment operating costs
• Provide more rapid solutions to operating
  problems
• Improve operator training and safety
• Modelling available in real time
• Supporting a What If mode of operator
  interaction
• Reduce variability in operations

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VIRTUAL CAMERA

• 3-D view of process occurring inside recovery
  boiler
• For selected inputs
• immediate and easy to see variations
• effect on flow, temperatures, chemical species,
  liquor combustion
• Compliments, enhances, and challenges ways to
  view process

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TRAINING TOOL

• Operators can understand why some modes of
  operation are better than others
• Provide insight that would be impossible to
  obtain with traditional methods
• Enable realistic training outside the envelope of
  parameters characterizing normal operation
• New training scenarios can be programmed remotely
• Tool can significantly shorten startups

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SAFTEY TOOL

• Simulate various accident scenarios
• Display interactively in a class room setting
  effects of various accident conditions and impact
• Identify ways to prevent accidents before they
  occur

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INPUT CONTROLS 3D VIEWER
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ADVANCED ANALYSIS
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EASY ANIMATION OF FLOW FUEL
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COMPARISON STATES WITH SYNOPSIS
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PROCESS MODELLING

• Questions
• Comments
• Feedback
• Safety issues