1. Recovery Boiler Modeling
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. 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

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

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

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

7. 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

8. 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
Liquor Combustion Model

9. 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

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

11. Model Predictions
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 combustion and droplet trajectories.
Carryover characteristics

12. Model Validation Isothermal flow validation Hot 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
B&W Boiler Model
Different aspects of model results have been validated against data from operating boilers

13. 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

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

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

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

17. Temperature Profiles

18. Velocity Profiles

19. Fuel Particle Trajectories
Base Case
Modified Air System

20. Carryover Mass Flux

24. Conclusions The modified air system: In general, modeling:
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