Transcript No Slide Title

MODELLING OF KRAFT TWO-PHASE
DIGESTER PULP PROCESSES
*
P. He
M. Salcudean
I. Gartshore
E.L. Bibeau*
Engineering / Process & Product Quality
Conference & Trade Fair
September 12-16, 1999
Hilton Anaheim
OUTLINE
 Introduction
- Continuos Kamyr Digester
 Previous numerical models
 New process model
 Simulation results
 Conclusions
CONTINUOUS DIGESTER
Chips and
Liquor
Chips
Steam
Impregnation
Zone
Chips
Silo
Steam
Screens
Liquor
White Liquor
High
Pressure
Feeder
Cooking
Zone
Liquor
Washing
Zone
Blow Line
DIGESTER
 Wood
- Lignin (glue that binds fibres)
- Carbohydrates
• cellulose and hemi-cellulose
 White liquor
- NaOH and Na2S
 Weak black liquor
- Contains the degradation products
 Wash flow
DIGESTER
 Wood
- Lignin (glue that binds fibres)
- Carbohydrates
• cellulose and hemi-cellulose
 White liquor
- NaOH and Na2S
 Weak black liquor
- Contains the degradation products
 Wash flow
DIGESTERS MODELLING
OBJECTIVES
 Model the delignification processes
occurring within a digester
 Calculation of solid and liquid conservation
equations for simulating the dynamic
industrial pulping process in a digester
WHY DIGESTER MODEL
 Huge capital investment for mill
- Heart of Kraft operation
 Improve ROR
- Fluid mechanics
• Fibre property variations
- High corrosion rates
- Improve process control and knowledge
- Enhance equipment performance and reliability
- Reduce risk in capital expenditures
PREVIOUS MODELS
 1-D Block Flow “0 order models”
- Control of Kappa number (lignin concentration)
 1-D Models
- Model free liquor + impregnated chips
- Simple assumptions for flow
 One 2-D model (Harkonen)
- No convection terms; partial diffusion terms
- Irrotational flow
- Interaction between phases: Ergun’s equation
PREVIOUS MODELS
 Delignification models (NaOH + Na2S)
- 3 stages: initial, bulk, residual
- Model different wood components
• Lignin and carbohydrates
• Low/high reactive lignin, cellulose, 2 components
of hemi cellulose
Chips Liquor
 Diffusion process
-
HS
OH
Convection
-
OH
Wood Components
OH
Diffusion
-
HS
Degradation
Products
-
OH
-
-
HS
HS
-
HS
Degradation
Products
-
OH
Degradation
Products
Wood Components
Carbohydrates +
residual lignin
DIFFICULTIES
 Complex 3-D two-phase flow with high solid
fraction
 Some constitutive relationships difficult to
obtain
 Variation of solid pressure with solid fraction
and kappa number
 Tangential stress in both phases
 Reaction rates and diffusion characteristics
 Poor characterisation and variability of chip
UBC DIGESTER MODEL
MODEL CHARACTERISTICS
 3-D and two-phase solid-liquid flow
- two-phase treatment implemented
 Curvilinear grids with segmentation
 Quasi-steady mass, chemical reaction, and
heat transfer calculation
- option to expand to transient
 Liquid-solid flow model coupled with the
energy and conservation of species equations
UBC DIGESTERS MODEL
MODEL CHARACTERISTICS
 Both free and entrapped liquor
- mass exchange accounted
 Energy equation
- includes heat generation through
chemical reactions
 Transport equations for
- lignin and carbohydrates
MODEL ASSUMPTIONS
 Flow is two-phase, solid-liquid, 3D
quasi-steady flow
1: Volume fractions of solid
1  2  1
 2 : Volume fraction of
1  0.35  (083
.  014
. ln k ) p
0.6
s
ps :
liquid
Solid pressure
 The liquor occurs in two forms
2
-
free liquor
liquor entrapped into the chips
1
11
12
12 :
11:
11  12  1
Volume fraction of liquid in a chip
Volume fraction of wood material in a chip
DIGESTER MODEL
 MASS CONSERVATION EQUATIONS
Liquid   2  f V f    112  f Vs  m 12  0
Solid
 12  0
  111sVs  m
 MOMENTUM EQUATIONS
Liquid
D 2  f V f
Dt
Convection
Solid
1
1
    2 f    f V f (V f  u )  f dS    dS   2  f F f
U 0 S fs
U 0 S fs
Stress
tensor
Convection phase
momentum exchange
Phase momentum
exchange by
diffusion
Body
force
D1  sVs
1
1
   1 s    sVs (Vs  u)  s dS    dS  1  s Fs
Dt
U 0 Ssf
U 0 Ssf
DIGESTER MODEL
 Sample Equations
Liquid Momentum Equation
   2  f Vf Vf   f  2 2 Vf  ( p f  ps )  Vf (  112  f Vs  Vf    2  f )  Vf m 12
 [111 (  f   s )   f ]g  z  Vs   (1  s Vs )  F
Solid Pressure Equation
111 s
111 s

  ps   
{ ij Vf  1[11 (  s   f )   f ]g  z
 ij  m 12
 ij  m 12
 Vs   (1  s Vs )  1  p f  F }  m 12
DIGESTER MODEL
 ENERGY BALANCE
Liquid
  2 (  f c f V f Tf   f   Tf )  ksf (Tf  Ts )  k fw (Tf  Tw )  0
Solid
  1 ( scsVsTs  s  Ts )  ( s  hr r )  k sf (Ts  Tf )
 k sw (Ts  Tw )  0
 = thermal conductivity
 hr heat of reaction
r = reaction rate
k = heat conduction
c = heat capacity
Subscript w indicates the side walls
DIGESTER PULPING MODEL
 COMPONENT BALANCES
  (Vslig  Ds  lig )  Rlig  0
  (Vscarb  Ds  carb )  Rcarb  0
where


Ds  5.7 102 T 0.5e( 4870/ RT )  0.02lig  0.13[OH ]0.55  0.58
Ds = diffusion coefficient [OH] = concentration of effective alkali
Initial:
[OH ]  4.7lig  73.6
for 21.8  lig  28.0
Bulk:
[OH ]  0.85lig  10.41
for 1.5  lig  21.8
Residual:
[OH ]  4.7lig  73.6
for 0  lig  1.5
DIGESTER PULPING MODEL
 DELIGNIFICATION REACTION RATES
Stage
Rlig
1
2  4807.69 T
 36.2T e
Initial
Bulk
Residual
Rcarb
 {e
35.19
17200
T
[OH ]  e
19.64
e
29.23
10804
T
14400
T
 lig
[OH ]0.5 [ S ]0.4 } lig
[OH ]0.7 Rlig
2.53[OH ]0.11 Rlig
0.47 Rlig
2.19 Rlig
lig = carbohydrate content
 carb = lignin content
 sulf = sulfide sulfur content [S] = concentration of sulfide sulfur
NUMERICAL SCHEME
 Finite volume
 Curvilinear grids
 Block structured
 Second order accurate for
cross derivative terms
 Steady and unsteady
DIGESTER MODEL HISTORY
 Year 1
- Define fundamental 3-D two-phase equations
 Year 2
- Implement model
•
•
•
•
Liquid flow
Solid flow
Energy
Kraft pulping process
- Starting point
• UBC 3-D curvilinear flow solver
DIGESTER MODEL HISTORY
 Current Year
- Validation
• experimental digesters
• in-situe measurements
• compare to other numerical predictions
- Investigate first commercial digester
- Add sub-models
• discharge pipe, rake, chip level
- Constitutive relationships
• solid shear
• compaction
Chips - 26.5 l/s
White Liquor - 40 l/s
Wash Discharge - 25 l/s
Wash Nozzles - 15 l/s
Impregnation
Zone
Wash
Zone
Quench Discharge - 4 l/s
Extraction Screens - 45 l/s
Cooking
Zone
Upper Cook Discharge - 85 l/s
Upper Cook Screens -85 l/s
Lower Cook Discharge - 120 l/s
Lower Cook Screens - 120 l/s
0.44 m
54.4 m
950 t/D
5.359 m
Brown Stock
BOUNDARY CONDITIONS
Boundary Condition
Inlet Liquor
Inlet Chips
Upper cook discharge
Lower cook discharge
Cold blow quench discharge
Cold blow wash discharge
Cold blow nozzle water wash
Upper cook screens (2)
Lower cook screens (2)
Cold blow extraction screens (2)
Outlet
Direction In/Out
Axial
Axial
Radial
Radial
Radial
Radial
Radial
Radial
Radial
Radial
Axial
In
In
In
In
In
In
In
Out
Out
Out
Out
Q (l/s)
40
26.5
85
120
4
25
15
85
120
42
outflow
o
Porosity Temp ( C)
1
1
0.12
0.15
0.15
0.25
0.05
0.15
0.15
0.09
1
118
118
152.2
166.6
65
65
65
outflow
outflow
outflow
outflow
Chips (26.5 l/s)
Liquor (40 l/s)
Chips (26.5 l/s)
Liquor (40 l/s)
Axial Chip
Velocity
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Wash
Discharge
(25 l/s)
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Lower Cook
Discharge
(120 l/s)
Lower Cook
Discharge
(120 l/s)
ws
0.0010
0.0002
-0.0006
-0.0014
-0.0021
-0.0029
-0.0037
-0.0045
-0.0053 Quench
-0.0061 Discharge
-0.0069 (4 l/s)
-0.0076
-0.0084
-0.0092
-0.0100
Axial
Liquor
Velocity
Lower
Cook
Screens
(120 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
w
0.0020
0.0015
0.0010
0.0005
0.0000
-0.0005
-0.0010
-0.0015
-0.0020
-0.0025 Quench
-0.0030 Discharge
-0.0035 (4 l/s)
-0.0040
-0.0045
-0.0050
Wash
Discharge
(25 l/s)
Lower
Cook
Screens
(120 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
Chips (26.5 l/s)
Liquor (40 l/s)
NO SOLID SHEAR (Paper)
Chips (26.5 l/s)
Liquor (40 l/s)
Axial Liquor
Velocity
Axial Chip
Velocity
0.046
0.040
0.035
0.030
0.024
0.019
0.014
0.008
0.003
-0.002
-0.008
-0.013
-0.018
-0.024
-0.029
Upper Cook
Discharge
(85 l/s)
Lower Cook
Discharge
(120 l/s)
Quench
Discharge
(4 l/s)
Wash
Discharge
(25 l/s)
Upper
Cook
Screens
(85 l/s)
Lower
Cook
Screens
(120 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
0.058
0.052
0.046
0.040
0.034
0.028
0.022
0.016
0.010
0.003
-0.003
-0.009
-0.015
-0.021
-0.027
Upper Cook
Discharge
(85 l/s)
Lower Cook
Discharge
(120 l/s)
Quench
Discharge
(4 l/s)
Wash
Discharge
(25 l/s)
Upper
Cook
Screens
(85 l/s)
Lower
Cook
Screens
(120 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
Chips (26.5 l/s)
Liquor (40 l/s)
WITH SOLID SHEAR
Chips (26.5 l/s)
Liquor (40 l/s)
Axial Chip
Velocity
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Wash
Discharge
(25 l/s)
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Lower Cook
Discharge
(120 l/s)
Lower Cook
Discharge
(120 l/s)
ws
0.0010
0.0002
-0.0006
-0.0014
-0.0021
-0.0029
-0.0037
-0.0045
-0.0053 Quench
-0.0061 Discharge
-0.0069 (4 l/s)
-0.0076
-0.0084
-0.0092
-0.0100
Axial
Liquor
Velocity
Lower
Cook
Screens
(120 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
w
0.0020
0.0015
0.0010
0.0005
0.0000
-0.0005
-0.0010
-0.0015
-0.0020
-0.0025 Quench
-0.0030 Discharge
-0.0035 (4 l/s)
-0.0040
-0.0045
-0.0050
Wash
Discharge
(25 l/s)
Lower
Cook
Screens
(120 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
Chips (26.5 l/s)
Liquor (40 l/s)
Chips (26.5 l/s)
Liquor (40 l/s)
Radial
Chip
Velocity
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Wash
Discharge
(25 l/s)
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Lower Cook
Discharge
(120 l/s)
Lower Cook
Discharge
(120 l/s)
us
0.0010
0.0006
0.0001
-0.0003
-0.0007
-0.0011
-0.0016
-0.0020
-0.0024
Quench
-0.0029 Discharge
-0.0033 (4 l/s)
-0.0037
-0.0041
-0.0046
-0.0050
Radial
Liquor
Velocity
Lower
Cook
Screens
(120 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
u
0.0050
0.0046
0.0041
0.0037
0.0033
0.0029
0.0024
0.0020
0.0016
0.0011 Quench
0.0007 Discharge
0.0003 (4 l/s)
-0.0001
-0.0006
-0.0010
Wash
Discharge
(25 l/s)
Lower
Cook
Screens
(120 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
PARTICLE TRACKING
Chips
Liquor
Chips (26.5 l/s)
Liquor (40 l/s)
Chips (26.5 l/s)
Liquor (40 l/s)
Liquor
Temperature
Chip
Temperature
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Lower Cook
Discharge
(120 l/s)
Lower Cook
Discharge
(120 l/s)
Ts
165
158
151
144
136
129
122
115
108
101
94
86
79
72
65
Lower
Cook
Screens
(120 l/s)
Quench
Discharge
(4 l/s)
Wash
Discharge
(25 l/s)
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
Tf
165
158
151
144
136
129
122
115
108
101
94
86
79
72
65
Lower
Cook
Screens
(120 l/s)
Quench
Discharge
(4 l/s)
Wash
Discharge
(25 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
Chips (26.5 l/s)
Liquor (40 l/s)
Chips (26.5 l/s)
Liquor (40 l/s)
Kappa
Number
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Wash
Discharge
(25 l/s)
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Lower Cook
Discharge
(120 l/s)
Lower Cook
Discharge
(120 l/s)
200
187
175
162
150
137
125
112
100 Quench
87 Discharge
75 (4 l/s)
62
50
37
25
Slip
Velocity
Lower
Cook
Screens
(120 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
u-us
0.010
0.009
0.007
0.006
0.004
0.003
0.001
0.000
-0.001
-0.003 Quench
Discharge
-0.004 (4 l/s)
-0.006
-0.007
-0.009
-0.010
Wash
Discharge
(25 l/s)
Lower
Cook
Screens
(120 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
Chips (26.5 l/s)
Liquor (40 l/s)
Chips (26.5 l/s)
Liquor (40 l/s)
Solid
Pressure
Upper Cook
Discharge
(85 l/s)
Solid
Fraction
Upper
Cook
Screens
(85 l/s)
Lower Cook
Discharge
(120 l/s)
Lower Cook
Discharge
(120 l/s)
Ps
3355
3136
2917
2698
2479
2261
2042
1823
1604 Quench
1385 Discharge
1166 (4 l/s)
947
728
509
290
Wash
Discharge
(25 l/s)
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Lower
Cook
Screens
(120 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
e1
0.52
0.51
0.50
0.49
0.48
0.47
0.46
0.45
0.44
0.43
0.42
0.41
0.40
0.38
0.37
Lower
Cook
Screens
(120 l/s)
Quench
Discharge
(4 l/s)
Wash
Discharge
(25 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
CONCLUSIONS
 3-D digester model
- fairly advanced state of development
- can predict flow channelling
 Computations are feasible with ability to
capture essential features of the process
 Effective tool to improve operations, obtain
better performance, and address mill issues
 Need for extensive collaboration with
industrial partners and research players to
address issues of measurements and validation
ACKNOWLEDGEMENT
NSERC
Canfor Forest Products
COPY OF PRESENTATION
 Copy of results with solid shear and
movies
- Go to www.psl.bc.ca
- Press on “Public Download” button
- Go to directory “Anaheim”
- Download file “Digester.ppt”
Support Slides
Axial Chip Velocity
ws
0.0000
-0.0005
-0.0011
-0.0016
-0.0021
-0.0026
-0.0032
-0.0037
-0.0042
-0.0047
-0.0053
-0.0058
-0.0063
-0.0068
-0.0074
-0.0079
-0.0084
-0.0089
-0.0095
-0.0100
Chip 5 mm/s
Radial Chip Velocity
Radial Chip Velocity
Axial Liquor Velocity
us
0.0010
0.0007
0.0004
0.0001
-0.0003
-0.0006
-0.0009
-0.0012
-0.0015
-0.0018
-0.0022
-0.0025
-0.0028
-0.0031
-0.0034
-0.0037
-0.0041
-0.0044
-0.0047
-0.0050
Chip 5 mm/s
w
0.0020
0.0016
0.0013
0.0009
0.0005
0.0002
-0.0002
-0.0006
-0.0009
-0.0013
-0.0017
-0.0021
-0.0024
-0.0028
-0.0032
-0.0035
-0.0039
-0.0043
-0.0046
-0.0050
Liquor 5 mm/s
Radial Liquor Velocity
u
0.0050
0.0047
0.0044
0.0041
0.0037
0.0034
0.0031
0.0028
0.0025
0.0022
0.0018
0.0015
0.0012
0.0009
0.0006
0.0003
-0.0001
-0.0004
-0.0007
-0.0010
Liquor 5 mm/s
Chip Temperature
Ts
165.0
159.7
154.5
149.2
143.9
138.7
133.4
128.2
122.9
117.6
112.4
107.1
101.8
96.6
91.3
86.1
80.8
75.5
70.3
65.0
Liquor Temperature
Tf
165.0
159.7
154.5
149.2
143.9
138.7
133.4
128.2
122.9
117.6
112.4
107.1
101.8
96.6
91.3
86.1
80.8
75.5
70.3
65.0
Carb
65.2
63.6
61.9
60.3
58.7
57.1
55.4
53.8
52.2
50.6
49.0
47.3
45.7
44.1
42.5
Chip 5 mm/s
Lign
27.2
25.5
23.8
22.1
20.4
18.7
16.9
15.2
13.5
11.8
10.1
8.4
6.6
4.9
3.2
Liquor 5 mm/s
Kapp
200.0
187.5
175.0
162.5
150.0
137.5
125.0
112.5
100.0
87.5
75.0
62.5
50.0
37.5
25.0
Ps
3355
3136
2917
2698
2479
2261
2042
1823
1604
1385
1166
947
728
509
290
1
0.52
0.51
0.50
0.49
0.48
0.47
0.46
0.45
0.44
0.43
0.42
0.41
0.40
0.38
0.37
u-us
0.010
0.009
0.007
0.006
0.004
0.003
0.001
0.000
-0.001
-0.003
-0.004
-0.006
-0.007
-0.009
-0.010
Chips (26.5 l/s)
Liquor (40 l/s)
Chips (26.5 l/s)
Liquor (40 l/s)
% Lignin
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Wash
Discharge
(25 l/s)
Upper Cook
Discharge
(85 l/s)
Upper
Cook
Screens
(85 l/s)
Lower Cook
Discharge
(120 l/s)
Lower Cook
Discharge
(120 l/s)
Lign
27.2
25.5
23.8
22.1
20.4
18.7
16.9
15.2
13.5 Quench
11.8 Discharge
10.1 (4 l/s)
8.4
6.6
4.9
3.2
% Carbo
Lower
Cook
Screens
(120 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
Carb
65.2
63.6
61.9
60.3
58.7
57.1
55.4
53.8
52.2
50.6
49.0
47.3
45.7
44.1
42.5
Lower
Cook
Screens
(120 l/s)
Quench
Discharge
(4 l/s)
Wash
Discharge
(25 l/s)
Extraction
Screens
(42 l/s)
Cold Blow
Nozzles
(15 l/s)
Blowline
DIGESTER INPUT BC
WHITE LIQUOR INPUT (from side/top only)
White liquor density
White liquor temperature
White liquor
White liquor
AA liquor strength
AA liquor strength
%S [Na2S/(NaOH+Na2S)]
AA / BD W [NaOH + Na2S]
EA / BD W [NaOH + 0.5Na2S]
Calculated charge (Production * AA)
Calculated white liquor volumetric flow
Calculated white liquor flow rate
1050
118
40.00
42.00
96
5.99
0.30
0.19
0.16
29429
4912
38.6
kg/m3
C
l/s
kg/s
g/l Active
lb/Ft3 Active
by weight
by weight
by weight
lb/Hr AA charge
ft3/Hr
l/s
DIGESTER INPUT BC
CHIPS INPUT (from top only)
Chips inlet temperature at bin
23.4
C
Chips inlet temperature in Digester
Chip feed
Moisture
Fill Factor (F)
Wood usage factor
Chips Density (wet)
118.0
23
0.56
0.84
1.87
1150
C
kg/s
BD
ADtBS/rpm
BDU/ADtBS
kg/m3
Chip meter rpm (R)
11
rpm
Production
950
ADtBS
Original Design Production
720
ADtBS
12
ft3/rev
Chip Meter Volume (V)
Chip Weight (W)
26.37
OD lb/ft3
Yield (Y)
0.46
BD pulp/wood
Calculated production [(R F V W Y)/1.25]
1076
Adt/D
Production per hour (assume 0.9 BD/AD)
71250
lb/Hr BD
Calculated production in chips
Calculated chip feed rate
154891
20
lb/Hr Wood BD
kg/s