Www.psl.bc.ca Recovery Boiler Modeling Process Simulation Ltd.

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Recovery BoilerModeling

Process Simulation Ltd.

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• 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

Objectives

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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

0.1

1

10

100

1000

10000

1980 1985 1990 1995 2000

Memory(MB)

0.1

1

10

100

1000

Speed(MIPS)

Memory

Speed

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Mathematical Modeling Applications in Other Industries

Computer

Jet engines Weather

AutomotiveHarrier jet

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Equipment Modeling Capabilities:

MatureDevelopingPreliminary

Time Time

Bark Boiler

BFB Bark Boiler

Hydrocyclone

Head boxDigester

Lime kiln

Gasifier

Recovery Boiler

We have active projects on this equipment

>306411

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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

Liquor Combustion Model

• Advanced and verified solution algorithm

• Black liquor combustion modelDryingPyrolysis CO, CO2, CH4, H2, H2OChar 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)

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

• Water Model Measurements• Full Scale Measurements

Isothermal flow validation

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

CE Boiler Model

B&W Boiler Model

Different aspects of model results have been validated against data from operating boilers

Different aspects of model results have been validated against data from operating boilers

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Recovery Boiler Refit Example

• High plugging rates

• High gas temperature at superheater

• Bed growth control

The Issue:

The Objective:

• To recommend modifications to air system

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Tertiary Air Ports (20%)

Secondary Air Ports (30%)

Primary Air Ports (50%)

Base Case Modified Air System

Test Case Geometries

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Secondary Air System Problem and Solution

Jets collide

Carryover

Core forms

Secondaryjets

Liquor guns

Jets Interlace

Uniform flow

Secondaryjets

Base Case Modified Air System

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PrimaryV = 30 m/s

50% Air T = 423 K

M = 46 kg/sz = 1.2 m

Liquor Guns

HV=15000 kJ/kgT = 400 K

M = 18 kg/sz = 7 m

BaseCase

SecondaryV = 85 m/s

30% Air T = 423 K

M = 27.6 kg/sz = 3 m

Tertiary20% Air

V = 50 m/sT = 423 K

M = 18.4 kg/sz = 10 m

ModifiedAir

SystemTertiary20% Air

V = 50 m/sT = 423 K

M = 18.4 kg/sz = 10 m

SecondaryV = 85 m/s

30% Air T = 423 K

M = 27.6 kg/sz = 3 m

CommonAir/LiquorSystem Data in

Plan View

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1600150014001300120011001000900800700600

T[K]

Base Case

1600150014001300120011001000900800700600

T[K]

Modified Air System

Temperature Profiles

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Velocity Profiles

1614121086420

-2-4

20m/s

UpwardvelocityW [m/s]

Base Case

1614121086420

-2-4

20m/s

UpwardvelocityW [m/s]

Modified Air System

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X

Y

Z

X

Y

Z

---- drying---- pyrolysis

---- char

---- smelt

Fuel Particle Trajectories

Base Case Modified Air System

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Y

Z

X

2001601401201008060402050

Modified Air System

Total Carryoverat Superheater0.03%

Carryovermass flux[g/s/m

2]

Y

Z

X

2001601401201008060402050

Carryovermass flux[g/s/m

2]

Base Case

Total Carryoverat Superheater4.06%

Carryover Mass Flux

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02468

101214161820

Base Case

Modified Air System

Water SmeltPyro. Char

Wall

0

5

10

15

20

25

30

Water SmeltPyro. Char

InFlight

0

1

2

3

4

5

Water SmeltPyro. Char

Carryover

0

3

6

9

12

15

Water SmeltPyro. Char

Bed

Black Liquor Particulate Distribution(% of total liquor input)

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X

Y

Z

O20.160.140.120.10.080.070.060.050.040.02

X

Y

Z

O20.160.140.120.10.080.070.060.050.040.02

Oxygen Concentration Distribution

Base Case Modified Air System

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X

Y

Z

CO0.10.050.010.0050.0030.0010.00050.00015E-05

X

Y

Z

CO0.10.050.010.0050.0030.0010.00050.00015E-05

Carbon Monoxide Concentration Distribution

Base Case Modified Air System

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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