SAWDUST - Pulp and Paper Canada

SAWDUST
TABLE I. Cooking conditions used for the four mill sawdust
furnishes examined.
Mill A B C D M&D
Wood charge (o.d.), g 200 200 200 200
L:W ratio* 3.5:1; 4.5:1 3.5:1 4.7:1 3.6:1
AA, % (on o.d. wood) 21.5 17.0 21.0 20.0
Sulphidity % (Kraft)** 33.0 38.0 24.5 30.0
Sulphidity, % (PS) 16.0 19.0 12.3 15.0
PS, % (on o.d. wood) 1.8 1.7 1.3 1.6
AQ, % (on o.d. wood) 0.05 0.05 0.05 0.05
Time to T (185°C), min 14 14 *** 12
*** This ratio includes the moisture in the wood
*** Sulphidity is expressed on an AA basis
*** Time-temperature profile of conventional cooking (~90 min to
170°C)
TABLE III. Yield benefits in sawdust cooking from anthraquinone
and polysulphide.
Mill A* B C D M&D D conv ***
PS, %** 1.8 1.7 1.3 1.6 1.6
Yield benefit (%) at kappa number 30****
KAQ 1.3 0.9 1.5 1.1 1.1
PS 3.5 2.3 2.8 2.7 3.1
PS-AQ 4.1 4.4 4.5 3.5 5.1
Synergy –0.7 1.2 0.2 –0.3 1.0
Yield benefit (%) at kappa number 20****
KAQ 0.9 0.7 0.6 1.0 1.0
PS 2.7 2.6 1.9 2.3 2.6
PS-AQ 4.1 3.6 3.8 3.4 4.4
Synergy 0.5 0.3 1.3 0.1 0.8
*** L:W = 3.5:1
*** PS charge, as sulphur, expressed on o.d. wood
*** Time-temperature profile of conventional cooking (~90 min to 170°C)
**** Yield benefit is relative to kraft process
TABLE II. Pulp yields for sawdust cooking using anthraquinone
and polysulphide.
Mill A* B C D M&D D conv ***
PS, %** 1.8 1.7 1.3 1.6 1.6
Total yield (%) at kappa number 30
Kraft 45.0 45.5 45.8 45.1 44.9
KAQ 46.3 46.4 47.3 46.2 46.0
PS 48.5 47.8 48.6 47.8 48.0
PS-AQ 49.1 49.9 50.3 48.6 50.0
Total yield (%) at kappa number 20
Kraft 42.8 42.9 44.4 43.4 42.7
KAQ 43.7 43.6 45.0 44.4 43.7
PS 45.5 45.5 46.3 45.7 45.3
PS-AQ 46.9 46.5 48.2 46.8 47.1
*** L:W = 3.5:1
*** PS charge, as sulphur, expressed on o.d. wood
*** Time-temperature profile of conventional cooking (~90 min to
170°C)
TABLE IV. Approximate H-factors required to reach 20 and
30 kappa number.
Mill A* B C D M&D D conv ***
PS, %** 1.8 1.7 1.3 1.6 1.6
H-factor to reach kappa number 30
Kraft 1250 2425 1225 1650 1425
KAQ 1100 2050 1000 1500 1225
PS 1200 1925 1225 1750 1350
PS-AQ 1000 1550 950 1500 1225
H-factor to reach kappa number 20
Kraft 1775 4000 1900 ≥2600 2500
KAQ 1725 3800 1650 ≥2600 2150
PS 1725 3500 1975 ≥2600 2500
PS-AQ 1475 3100 1575 ≥2600 2400
*** L:W = 3.5:1
*** PS charge, as sulphur, expressed on o.d. wood
*** Time-temperature profile of conventional cooking (~90 min to
170°C)
Effect of Chip Thickness on PS Performance:
Furnish Preparation: A Domtar
classifier was used to segregate the black
spruce chips (obtained from whole logs
debarked and chipped in Paprican’s pilot
plant) into 2 to 4 mm and 6 to 8 mm
thickness fractions. These chips were used
in their wet form and cooking liquor was
added under vacuum. Hand-cut black
spruce chips (2 mm and 4 mm in thickness,
20 mm in width and 20 mm in
length) were also generated from whole
logs. These handcut chips were air-dried,
and prior to cooking, were steamed, followed
immediately by a cold-water soak to
ensure effective liquor impregnation/
penetration. The cooking liquor was not
added under vacuum. A Wiley mill
equipped with a 3.2 mm screen was used
to produce the sawdust; excess flour was
removed from the sawdust using a 250-
micron screen. The procedure for introducing
cooking liquor was identical to
that described for the mill sawdust experiments
described above.
RESULTS, DISCUSSION
The softwood furnishes of four Canadian
kraft mills (1 Eastern, one coastal BC, and
two interior BC) that pulp sawdust were
evaluated in this study. For each mill furnish,
the yield benefits of polysulphide
(PS), anthraquinone (AQ) and PS-AQ were
examined, relative to kraft. To make our
results relevant to mill-scale application,
mill cooking conditions were reproduced
as closely as possible in our pilot plant.
Complete sets of yield and delignification
data are presented as figures for the
work done with the furnish from Mill A
and comparison data at kappa numbers
20 and 30 are given in Tables II to IV for
all the furnishes.
Mill A: The yield vs. kappa number relationships
for the four types of cooks, over
the kappa number range 18 to 30, are
shown in Fig. 1. Despite the rapid rise-totemperature
of the sawdust cooking operation,
polysulphide is clearly able to protect
yield effectively. At a kappa number of
30, the yield increase for PS (charged at
1.8% on o.d. wood) relative to the kraft
process, was 3.5%; at 20 kappa, the yield
advantage decreased to 2.7% (Table III).
The corresponding yield benefits of
AQ at these two kappa targets were 1.3
and 0.9%. For the combined application
of PS and AQ, the yield increases at the
higher and lower kappa numbers were
both 4.1%. While a small synergistic effect
[5] of PS-AQ (0.5%) was apparent at the
lower kappa numbers, at kappa 30, the
combined application of PS and AQ was
neither additive nor synergistic (–0.7%).
The delignification rates of the four
types of cooks are compared in Fig. 2 and
Table IV. For both kraft and polysulphide
cooks, AQ addition resulted in enhanced
delignification at kappa 30; at kappa 20 its
benefit was variable. The data in Table V
indicate that, if kraft cooking provides the
mill’s target kappa number of 28, the addition
of AQ, PS and PS-AQ to the cook
would decrease the kappa number to 25.5,
27.0 and 21.5, respectively. As shown in an
Pulp & Paper Canada T 2 105:1 (2004) ❘❘❘ 33