Effects of extended cooking times in the production
of eucalytus pulps
Miguel A. Osses, Env. Mgr, Valdivia Pulp Mill /Arauco – Chile, [email protected]
Abstract
Trying to explain the industrial behavior of Eucalyptus pulps produced with extended cooking
times, a laboratory study was carried out to investigate thise kind of pulps and correlate the results
with the pulp mill performance. Long cooking time pulps are produced in a mill when some of the
production areas stop and there is no enough capacity for storage in the high density towers of
unbleached or bleached pulps.
Eucalyptus globulus and Eucalyptus. nitens chips in the proportion of 80/20 were obtained
directly from the pulp mill wood yard. Chips where cooked in a conventional kraft batch digestor
using a laboratory MK System. Pulps produced with different cooking times where evaluated and O2
delignified to obtain a constant kappa. The results showed that long cooking time pulps, Presented
significant degradation, loosing chemical yield and affecting the production cost because of higher
wood consumption, black liquor presented higher solids content. For line 1 of Arauco pulp mill, it can
affect pulp production because the recovery boiler is deficient in black liquor burning capacity. In
spite of the pulp degradation, measured through the viscosity loss, the strength properties were not
affected, but the Gurley porosity increased significantly. This behavior could explain a lot of the pulp
drainage problems in the rotary filters, presses and Fourdrinier when these pulps are involuntarily
produced. Finally the production cost of these pulps increase directly with the retention time,
because de higher wood consumption and higher chemicals bleaching.
Key-Words: Eucalyptus kraft cooking, Effects of long cooking times
Introduction
Celulosa Arauco y Constitución S. A. produces in Chile around three millions tons per year
of market pulps. The main experience of the company was producing softwood pulps (Radiata
Pine). After a program of eucalyptus plantations of E. globules and E. nitens, the wood was used to
produce market bleached kraft pulps. Line 1 in the Arauco pulp mill was decided and adapted for
this. Some production trials were also done, but at the beginning a lot of production problems
occurred traduced in a discontinue operation and with pulps remaining more time in the digestors,
because the pulp tank were totally full. To understand the behavior of eucalyptus pulps produced
with these involuntary long retention time in conventional kraft cooking, laboratory pulps were
produced at kappa 15 constant, using E. globulus and E. nitens industrial chips coming from the
wood yard in the proportion of 80/20. The pulps were delignified up to kappa around 10 and
bleached with the short ECF sequence D0EpD1, that is used in the line 1 of the Arauco pulp mill in
Chile.
The mains objectives were to study the cooking yield variations, solids black liquor
production, changes in the pulps viscosity, in the drainage, bleachability and finally to use these
results for a better comprehension of the production problems with these pulps like poor filtration in
the washer filters and foudrinier, presses and the big quantity of breaks. Also the economics effects
were evaluated.
5TH International Colloquium on Eucalyptus Pulp, May 9-12, 2011. Porto Seguro, Bahia, Brazil
Experimental
The alkali charge and time to temperature of 165 ºC were maintained constant, changing
only the time to the cooking temperature. For cooking trials was was used a 5 liter MK System
digester with indirect heating. Were used times of 25, 60, 120,180 and 240 minutes. The pulps
obtained with kappa 15 were delignified up to kappa 10 and bleached with the short sequence of
D0EpD1 up to 90 % ISO.
In the cooking the following analysis were done. Kappa, screened yield, rejects at slots of
0,005 mm width, viscosity, hexenuronics acid, hemicelluloses, brightness and black liquor solids. For
O2 delignification and bleaching were determined the normal and standards parameters for these
experiences and showed in the following tables. All the analysis were conducted using TAPPI
standards
.
Results and discussion
The following tables show the results of the different laboratory experiences for wood
chips, brown pulp, delignified and bleached pulps. Also an estimation of the increased
production cost is presented, mainly focused in the higher consumption of wood and chemicals
for bleaching, when these kind of pulp are produced.
Wood chips characteristics
Table 1 – Some basic characteristics of pulps from E globulus y E nitens
E. globulus
Unidad
% bms
22 – 23
% bms
52
% bms
24
% bms
1,5
3
kg/m s
510 - 530
% bms
53 - 54
mm
0,9 – 1,0
vessels/gr
200 -300
Source: Arauco pulp mil labs
parameter
Insoluble lignin
Celullose
Hemicelullose
extractables
Basic density
Screened yield
Fiber lengh
vessels
E. nitens
26 - 28
50
26
1.0 – 1,5
450 - 460
47 - 48
0,6 – 0,7
400 - 600
Here is possible to see de big difference between the two Eucalyptus globulus has much lower
insoluble lignin content and higher cooking yield.
Table 2 - Chemical characteristics of mixed wood
Component
Glucans
Xilan
Galactanes
Mananes
M1
46,7
14,6
1,0
1,9
M2
46,1
14,3
1,2
2,1
mean
46,4
14,5
1,1
2,0
Component
Arabinanos
Soluble lignin
Insoluble lignin
Lig Total
Extraíbles
M1
0,3
4,3
21,2
25,5
1,7
M2
0,2
4,5
20,8
25,3
1,8
mean
0,3
4,4
21,0
25,4
1,8
These values are refered to 80/20 E Globulus y E Nitens mixture.
5TH International Colloquium on Eucalyptus Pulp, May 9-12, 2011. Porto Seguro, Bahia, Brazil
Table 3 – Cooks of eucalyptus mixture
Cooking time
kappa
Screened yield
Rejects
Brighness
viscosity
BL solids
BL pH
Residual alkali
Glucans
Xilan
Galactans
Manans
Source: Arauco pulp mil labs and
min
25
14,5
% bms
56,1
% bms
0,2
% ISO
41,2
cm3/gr
1412
%
19,3
12,9
gr/lt
6,7
% bps
80,4
% bps
17,1
% bps
0
% bps
0
Vicosa University
60
12,5
55,9
0,01
40,0
1274
19,8
12,5
3,6
80,1
16,9
0
0
120
11,9
54,8
0,001
39,2
1150
20,2
12,3
1,4
80,2
16,9
0
0
180
11,6
53,9
0,001
38,1
1072
20,4
11,7
0,0
80,4
17,1
0
0
240
10,7
53,4
0,001
36,0
1016
20,6
11,5
0,0
80,4
17,3
0
0
As was espected with same alkali charge, changing only the cooking time were obtained pulps
with lower kappa, lower yield, lower brightness, lower viscosity, showing the unwanted of this
practice that is possible to have in a mill, when there are operations problems after cooking
stage. Galactans and manans were totally dissolved because initial pH was similar for all the
cooks.
Table 4 – Pulps delignification results
Cooking time
O2 pressure
Temperature
kappa in
kappa out
Deslignification
Brighness
viscosity
Viscosity drop
Source: Arauco pulp mil labs
min
bar
°C
%
% ISO
3
cm /gr
3
cm /gr
25
4,5
95
14,5
9,8
32,4
55,6
1244
417
60
2,0
85
12,5
10,1
21,1
49,3
1231
302
120
2,0
75
11,9
10,0
16,0
48,0
1119
234
180
2,0
75
11,6
9,9
14,7
44,7
1090
212
240
2,0
50
10,7
10,1
6,5
39,9
1100
166
5TH International Colloquium on Eucalyptus Pulp, May 9-12, 2011. Porto Seguro, Bahia, Brazil
Talble 5 - Bleaching results
Cooking time
Do stage
time
Temperature
Multiple chlorine
ClO2 charge
Ep stage
NaOH charge
H2O2 charge
kappa
D1 stage
ClO2 charge
Viscosity
Brighness
ClO2 residual
Total consumptions
Chlorine dioxide
Soda caustic
Hidrogen peroxide
Source: Arauco pulp mil labs
min
25
60
120
180
240
min
°C
Kg/Bdt
50
60
0,24
9,0
50
60
0,24
9,2
50
60
0,24
9,1
50
60
0,24
9,0
50
60
0,24
9,3
kg/Bdt
kg/Bt
-
11,5
5,2
2,1
11,5
5,2
2,1
11,5
5,2
2,5
11,5
5,2
2,5
11,5
5,2
2,5
kg/BDt
3
cm /kg
%
kg/BDt
2,1
1051
90,1
traces
6,4
1052
90,1
traces
9,0
990
90,2
0,2
11,0
915
90,3
0,6
112,0
906
89,3
0,9
kg/BDt
kg/BDt
kg/BDt
11,1
11,5
5,2
15,6
11,5
5,2
18,1
11,5
5,2
20,0
11,5
5,2
21,3
11,5
5,2
This table clearly shows the difficult for bleaching of the pulps produced with high cooking time. The
main chemical as the chlorine dioxide increases almost the double.
Table 6 – Refining of unbleached pulps
Cooking time
min
PFI rev @ 30 °SR
2
Tear
mNm /g
Burst
kPa/g
Tensile
Nm/g
TEA
J/g
Porosity (Gurley)
seg/100ml
Elongation
%
Ref energy consump
Wh
3
Specific volume
cm /g
Water absortion
mm
Opacity
%
Fiber length
mm
Source: Arauco pulp mil labs
25
625
8,5
4,5
76
1,1
7,0
2,1
6,0
1,6
51,4
95,9
0,89
60
1200
9,4
5,2
87
1,4
10,0
2,5
12,5
1,5
52
96,0
0,89
120
1350
9,6
5,9
90
1,7
13,0
2,7
15,0
1,5
36
97,5
0,87
180
2200
9,5
6,3
95
2,0
18,0
3,1
22,5
1,5
36,5
97,0
0,83
240
1400
9,4
5,5
88
1,7
21,5
2,7
15,0
1,5
33
97,0
0,85
5TH International Colloquium on Eucalyptus Pulp, May 9-12, 2011. Porto Seguro, Bahia, Brazil
Table 7 – Refining of bleached pulps
Cooking time
PFI rev to 30 °SR
Tear
burst
tensile
TEA
Porosity Gurley
Elongation
Refining energy
Specific volume
Water absortion
Opacity
Fiber lenght
min
25
1950
9,7
5,9
83
2,2
9,0
3,9
21,0
1,49
50
68
0,78
2
mNm /g
kPa/g
Nm/g
J/g
seg/100ml
%
Wh
3
cm /g
mm
%
mm
60
2950
9,8
5,9
83
2,2
9,0
3,7
35,0
1,46
39
68
0,77
120
3000
10,0
5,7
81,9
2,1
9,9
3,5
36,0
1,43
38
69,8
0,77
180
3100
9,8
5,3
80
2,0
8,0
3,5
37,0
1,43
40
69,5
0,78
240
2950
10,0
5,3
80
1,9
8,0
3,4
36,0
1,41
37
69,5
0,78
Table 8 – Estimated Wood consumptions
Cooking time
min
25
60
120
180
240
Cooking yield
%
55,2
52,7
52,3
51,9
51,5
O2 delig. yield
%
98
98
98
98
98
Bleaching yield
%
98
98
98
98
98
Final yield
%
53,0
50,6
50,2
49,8
49,5
Wood consumption
tms/BDT
1,89
1,98
1,99
2,01
2,02
Wood consumption
m3/BDt
3,912
4,097
4,129
4,161
4,193
Wood consumption
US$/BDt 154,9 162,3
Source: calculations from cooking yield results
163,5
164,8
166,0
Table 9 Estimated bleaching and final cost
ClO2
kg/BDt
11,1
11,5
15,6
11,5
18,1
11,5
20
11,5
21,3
11,5
NaOH
kg/BDt
H2O2
kg/BDt
5,2
5,2
5,2
5,2
5,2
kg/BDt
3
3
3
3
3
Bleaching cost
US$/BDt
39,0
49,1
54,7
58,9
61,8
Final cost
US$/BDt
193,9
211,3
218,2
223,7
227,9
%
0
9,0
12,5
15,4
17,5
H2SO4
Increasing of cost
Conclusions
The obtained results show the problems that is possible to have, when the pulps are produced
with extended cooking times and batch conventional technique. The main direct problem are
the following: higher wood consumption and associated cost, because the lower yield, less
brightness, lower viscosity, higher chemical consumption in bleaching.
The lower porosity of unbleached pulps can help to understand the drainage problems in the
rotary vaccum filters used in the unbleached and bleached washing stage.
The strength properties of bleached pulps remain almost without changes.
5TH International Colloquium on Eucalyptus Pulp, May 9-12, 2011. Porto Seguro, Bahia, Brazil
Acknowledgements
To the research laboratory people of the Arauco pulp Mill in Chile, they needed to do twice
these lab experiences, because the laboratory pulps were lost with the big 2010 hearthquake.
5TH International Colloquium on Eucalyptus Pulp, May 9-12, 2011. Porto Seguro, Bahia, Brazil