www.psl.bc.ca
Recovery Boiler
Modeling
Process Simulation Ltd.
www.psl.bc.ca
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
Computing Hardware Trends
1000
10000
1000
100
Speed
(MIPS)
100
Memory
(MB)
10
10
1
1
Memory
Speed
0.1
1980
1985
1990
1995
0.1
2000
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Mathematical Modeling Applications
in Other Industries
Jet engines
Weather
Computer
Automotive
Harrier jet
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Equipment Modeling Capabilities:
Preliminary
Time
1
Developing
1
4
Mature
6
>30
Recovery Boiler
Bark Boiler
Hydrocyclone
BFB Bark Boiler
Head box
Digester
Lime kiln
Gasifier
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
Liquor Combustion 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)
distributions
• 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
•
•
•
•
B&W Boiler Model
Temperature measurements at bullnose
Carryover prediction trends
CO emission trends
Different aspects of model results
Velocity measurements
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
Modified Air System
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Secondary Air System Problem and Solution
Carryover
Liquor guns
Core forms
Secondary
jets
Jets collide
Base Case
Uniform flow
Secondary
jets
Jets Interlace
Modified Air System
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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
Secondary
V = 85 m/s
30% Air
T = 423 K
M = 27.6 kg/s
z=3m
Common
Liquor Guns
HV=15000 kJ/kg
T = 400 K
M = 18 kg/s
z=7m
Secondary
V = 85 m/s
30% Air
T = 423 K
M = 27.6 kg/s
z=3m
Modified
Air
System
Base
Case
Tertiary
20% Air
V = 50 m/s
T = 423 K
M = 18.4 kg/s
z = 10 m
Tertiary
20% Air
V = 50 m/s
T = 423 K
M = 18.4 kg/s
z = 10 m
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Temperature Profiles
T[K]
T[K]
1600
1500
1400
1300
1200
1100
1000
900
800
700
600
1600
1500
1400
1300
1200
1100
1000
900
800
700
600
Base Case
M odified Air System
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Velocity Profiles
20m/s
20m/s
Upward
velocity
W [m/s]
Upward
velocity
W [m/s]
16
14
12
10
8
6
4
2
0
-2
-4
Base Case
16
14
12
10
8
6
4
2
0
-2
-4
M odified Air System
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Fuel Particle Trajectories
Z
Z
Y
Y
X
X
---- drying
---- pyrolysis
---- char
---- smelt
Base Case
Modified Air System
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Carryover Mass Flux
Z
Z
Y
Y
Total Carryover
at Superheater
4.06%
Total Carryover
at Superheater
0.03%
X
Carryover
mass flux
2
[g/s/m ]
Carryover
mass flux
2
[g/s/m ]
200
160
140
120
100
80
60
40
20
5
0
Base Case
X
M odified Air System
200
160
140
120
100
80
60
40
20
5
0
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Black Liquor Particulate Distribution
(% of total liquor input)
Bed
15
12
9
6
3
0
Water
Pyro.
Char
Smelt
InFlight
30
20
18
16
14
12
10
8
6
4
2
0
Wall
Base Case
Modified Air System
Water
Char
Smelt
Carryover
5
25
Pyro.
4
20
3
15
2
10
1
5
0
Water
Pyro.
Char
Smelt
0
Water
Pyro.
Char
Smelt
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Oxygen Concentration Distribution
Modified Air System
Base Case
Z
Z
Y
Y
X
X
O2
0.16
0.14
0.12
0.1
0.08
0.07
0.06
0.05
0.04
0.02
O2
0.16
0.14
0.12
0.1
0.08
0.07
0.06
0.05
0.04
0.02
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Carbon Monoxide Concentration Distribution
Modified Air System
Base Case
Z
Z
Y
Y
X
X
CO
0.1
0.05
0.01
0.005
0.003
0.001
0.0005
0.0001
5E-05
CO
0.1
0.05
0.01
0.005
0.003
0.001
0.0005
0.0001
5E-05
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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