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Recovery Boiler Modeling

Recovery Boiler Modeling. Process Simulation Ltd. 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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Recovery Boiler Modeling

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  1. Recovery BoilerModeling Process Simulation Ltd.

  2. 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

  3. 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 Introduction

  4. Mathematical Modeling Applications in Other Industries Jet engines Weather Computer Harrier jet Automotive

  5. Preliminary Developing Mature Recovery Boiler Bark Boiler Hydrocyclone BFB Bark Boiler Head box Digester Lime kiln Gasifier Equipment Modeling Capabilities: Time 4 >30 1 6 1 We have active projects on this equipment

  6. Weyerhaeuser USA Weyerhaeuser Canada Canfor Kvaerner Scott Paper Anthony Ross Weldwood Client List

  7. 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 Why Use Modeling?

  8. 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 Liquor Combustion Model Details of the Recovery Boiler Model

  9. High excess air CO, CO2, and other emissions Mechanical carryover & plugging Bed blackouts Superheater and waterwall tube thermal stress failures Boiler stability and capacity Issues Addressed by the Model

  10. Boiler geometry Bed shape Convective section layout Air temperature and flow rate at each port Liquor characteristics Input Data Required

  11. Gas species (e.g. H2,O2,N2,CO,CO2,H2O,CH4)distributions Gas flow velocity fields Temperature distributions and heat transfer to wall surfaces Liquor spray combustionand droplet trajectories. Carryover characteristics Model Predictions

  12. Water Model Measurements Full Scale Measurements Model Validation Isothermal flow validation CE Boiler Model Hot flow validation • Temperature measurements at bullnose • Carryover prediction trends • CO emission trends • Velocity measurements B&W Boiler Model Different aspects of model results have been validated against data from operating boilers

  13. High plugging rates High gas temperature at superheater Bed growth control Recovery Boiler Refit Example The Issue: The Objective: • To recommend modifications to air system

  14. Modified Air System Test Case Geometries Tertiary Air Ports (20%) Secondary Air Ports (30%) Primary Air Ports (50%) Base Case

  15. Carryover Liquor guns Uniform flow Core forms Secondaryjets Jets Interlace Secondaryjets Jets collide Secondary Air System Problem and Solution Base Case Modified Air System

  16. Primary V = 30 m/s Liquor Guns 50% Air T = 423 K HV=15000 kJ/kg M = 46 kg/s T = 400 K z = 1.2 m M = 18 kg/s z = 7 m Common Secondary Secondary V = 85 m/s V = 85 m/s 30% Air 30% Air T = 423 K T = 423 K M = 27.6 kg/s M = 27.6 kg/s z = 3 m z = 3 m BaseCase ModifiedAirSystem Tertiary Tertiary 20% Air 20% Air V = 50 m/s V = 50 m/s T = 423 K T = 423 K M = 18.4 kg/s M = 18.4 kg/s z = 10 m z = 10 m Air/Liquor System Data in Plan View

  17. Temperature Profiles

  18. Velocity Profiles

  19. Fuel Particle Trajectories Modified Air System Base Case

  20. Carryover Mass Flux

  21. 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

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