Recovery Boiler Modeling

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Recovery BoilerModeling

• Process Simulation Ltd.

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Objectives

• Develop modeling tools to improve existing
  designs and operating procedures, and to lower
  carry over and environmental impact
• Analyse performance of different air systems and
  liquor firing strategies

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Introduction

• Process and equipment design was, until recently,
  based on experience
• Advances in numerical methods and computer speed
  and memory
• increased possibility of using more scientific
  methods, called mathematical modeling, for
  process design and optimization

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Mathematical Modeling Applications in Other
Industries
Jet engines
Weather
Computer
Harrier jet
Automotive
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Equipment Modeling Capabilities
Time
gt30
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We have active projects on this equipment
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Client List

• Weyerhaeuser USA
• Weyerhaeuser Canada
• Canfor
• Kvaerner
• Scott Paper
• Anthony Ross
• Weldwood

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Why Use Modeling?

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

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Details of the Recovery 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 by the Model

• High excess air
• CO, CO2, and other emissions
• Mechanical carryover plugging
• Bed blackouts
• Superheater and waterwall tube thermal stress
  failures
• Boiler stability and capacity

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Input Data Required

• Boiler geometry
• Bed shape
• Convective section layout
• Air temperature and flow rate at each port
• Liquor characteristics

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Model Predictions

• Gas species (e.g. H2,O2,N2,CO,CO2,H2O,CH4)distrib
  utions
• 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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Recovery Boiler Refit Example
The Issue

• High plugging rates
• High gas temperature at superheater
• Bed growth control

The Objective

• To recommend modifications to air system

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Test Case Geometries
Tertiary Air Ports (20)
Secondary Air Ports (30)
Primary Air Ports (50)
Base Case
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Secondary Air System Problem and Solution
Base Case
Modified Air System
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Air/Liquor System Data in Plan View
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Temperature Profiles
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Velocity Profiles
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Fuel Particle Trajectories
Modified Air System
Base Case
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Carryover Mass Flux
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Conclusions

• The modified air system
• 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
• In general, modeling
• Provides detailed data to facilitate efficient
  operation of Recovery Boilers.
• Helps mill managers make informed decisions
  regarding boiler refits/replacements