Download - MASc Defense Presentation V2
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Understanding Rapid Dewatering of
Cellulose Fibre Suspensions
Daniel Paterson
MASc. Thesis Defense
Mechanical Engineering
April 18, 2016
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Outline
• Introduction to Industrial Problem
• Background: Past Dewatering Modeling Efforts • Problem: Past Methods• Project Objectives
• Part I: Extending the Modeling Approach• Part II/III: Determining Material Parameters• Part IV: Modeling Dewatering Trends• Part V: Validating Dewatering Models
• Conclusion
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Introduction
• Dewatering: Important unit process in industry
• Pulp and paper, ceramics, mining, etc.
• Examples in pulp and paper:
• Paper machine: Forming and pressing sections
• Thickeners, screw presses, wash presses
• Twin roll presses
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• Understand dewatering in twin press rolls
• Used to optimize design
• Focused on “nip point”
• Modelled as 1D, constant dewatering rate consolidation
4(Hi – Hf) << L
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Background
• Geometry
• Permeable piston at 𝑧 = ℎ 𝑡
• Closed base at 𝑧 = 0
• Compressive load: 𝜎 𝑡
• We want to model varying dewatering rates
• Varying 𝑑 ℎ 𝑡
𝑑 𝑡
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• Modeling Approach
• Follow work of Landman, Buscall, and White [1].
• Assumptions:
• Neglect gravity, inertial, and viscous terms
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(1)
(2)
(3)
(4)
(5)
Solid
Continuity
Fluid
Continuity
Darcian
Expression
Total Compressive
Stress Conservation
Constitutive
Equation
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• Governing Equation (Base Model)
• What is needed?
• Permeability:
• Compressive Yield Stress:
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• Material Parameters
• Compressive Yield Stress : The maximum network stress (effective solid stress) that can be withstood without solid network consolidation.
• Increasing function with (solidity)
• Permeability : A measurement of the resistance fluid flow experiences flowing through a porous media
• Decreasing function with
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• Model Solutions
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Slow Compression Fast Compression
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Problem: Preliminary Results
• Source?
• Suggested in the literature to be due to cellulose fibres porous, hollow structure [2]
• Viscous component to compaction due to fluid escaping fibres
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Nylon Fibres Cellulose Fibres
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• Expand the modeling efforts of Landman, Buscall, and White
• In conjunction with math postdoc
• Develop equipment and protocol for collecting material parameters
• Compressive Yield Stress
• Permeability
• Validate base model and test suitability of extended model for various suspensions of cellulose fibres
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Project Objectives
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• Suggested in the literature the source of discrepancy comes from porous cellulose fibres
• Consolidation:
• Dynamic Compressibility:
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= 0Base Model
Instantaneous
particle compaction
Base Model
Remove this assumption
Part I: Extending the Modeling Approach
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• Functional Form
• Proportional to fibre wall permeability?
• Proposed Functional Form:
• Crude model of flow out of a porous fibre to find fibre permeability:
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L
2r
Suggested Form Only!
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• Governing Equation (Extended Model)
• What is needed?
• Permeability:
• Compressive Yield Stress:
• Fitted Parameter: 14
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• Compressive Yield Stress: The maximum network stress (effective solid stress) that can be withstood without consolidation
• Techniques:
Permeation Trials
• Approximation neglecting
flow induced compaction:
• Control error
Part II: Material Parameter
Slow Speed Compaction
• Simplified continuity:
• Uniform consolidation
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• Experimental Apparatus
• Movement: 100 mm
• Load: 1.3 MPa
• Rate 0.001 – 10 mm/s
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• Materials
• Varying species, pulping process, refinement, and flocculation state
• Ideal fibre suspension for base model validation
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• Equipment Validation
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: Softwood chemical pulp [2]
: Softwood chemical pulp [3]
: Coal-mining tailing [4]
: Zirconia suspension [5]
: Water treatment sludge [6]
: Alumina suspension [7]
: Series 1 (NBSK) Slow Speed Technique
: Series 1 (NBSK) Permeation Technique
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• Representative Results
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Account: Fit a Functional Form
• Model equations
• Fit functional form
• Permeability: A measurement of the resistance fluid flow experiences flowing through a porous media
• Concern: Flow induced compaction
Part III: Material Parameter
Neglect: Manage Error
• Evaluate at
• Control error20
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• Experimental Apparatus
• Movement: 160 mm
• Load: 1.0 MPa
• Pressure: 1.0 MPa
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• Equipment Validation
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: Series 1 (NBSK)
: Softwood chemical pulp [8]
: Softwood chemical pulp [9]
: Softwood chemical pulp [10]
: Nylon fibre suspension [11]
: Nylon fibre suspension [11]
: Glass fibre suspension [11]
: Acrylamide polymer gel [11]
: Lattice-Boltzmann simulation [12]
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• Representative Results
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• Experimental dewatering trends collected for varying rates
• 0.001 – 10 mm/s
• Load versus solid volume fraction trends
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Part IV: Model Dewatering Trends
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• Nylon Fibre Experimental Results:
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• Discussion• Increased difficulty in dewatering with higher rates• Initial load growth with high dewatering rates
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• Nylon Fibre Model Results:
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Base Model
Experiment
• Discussion• Predictive trends (no free parameters)• Base model works well with “solid” nylon fibres
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• Discussion• Increased difficulty in dewatering with higher rates• Dewatering curves do not trend back to
• NBSK (Series 1) Experimental Results:
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• NBSK (Series 1) Model Results:
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Base Model
Extended Model
Experiment
• Discussion• Extended model trends fitted• Improved with extended model
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• Investigate models effectiveness in representing solid phase movement during consolidation
• Nylon Fibres Base Model
• NBSK (Series 1) Extended Model
• Film dewatering events to develop velocity profiles
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Part V: Validating Models
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Experimental Base Model
3.0 mm/s
0.25 mm/s
• Nylon Fibre Velocity Profiles:
• Discussion
• 0.25 mm/s: Closer to linear, small solidity gradients
• 3.0 mm/s: Nonlinear velocity, large solidity gradients
• Base models provides good representation
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• NBSK (Series 1) Velocity Profiles:
• Discussion
• Both velocities quite linear, small solidity gradients
• Base model provides poor representation
• Extended model provides improved representation
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Experimental Base Model Extended Model
10.0 mm/s
1.5 mm/s
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• Equipment and experimental protocol developed for collecting material parameters and
• Extended model provided improved representation of cellulose fibre dewatering over the base model
• Acceptable form of
• Base model provided good representation of nylon fibre suspension
• Constitutive function is well suited to hard particles
• Both models represented their corresponding suspensions well in capturing the movement of the solid particles
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Conclusions
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Thank You,Questions
Sponsors
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References
[1]
[2]
[3]
[4]
[5]
[6]
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[7]
[8]
[9]
[10]
[11]
[12]
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• Further cellulose trials
• Assess the continued suitability of dynamic compressibility function:
• Continue cataloging dewatering behaviours of various cellulose fibre suspensions
• Investigate a few experimental concerns
• Temperature impact on compressed cellulose fibres
• Retention challenges: TMP 36
Future Work
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Functional form of Dynamic Compressibility
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