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Recovery Boiler Modeling

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Presentation on theme: "Recovery Boiler Modeling"— Presentation transcript:

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

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