Optimizing shavings for reduced energy

Transcription

Optimizing shavings for
reduced energy consumption in
TMP production
Silvia Viforr, Rune Ziethén, Helmut Roll, Lennart Salmén
Innventia Report No. 400
2013
Optimizing shavings for reduced energy consumption in TMP production
Acknowledgements
Lars-Åke Hammar, Innventia, is gratefully acknowledged for the refining experiments
made.
The Swedish Energy Agency is gratefully acknowledged for the financial support to the
project.
Table of contents
Page
1 Summary ................................................................................................................. 1 2 Background ............................................................................................................ 3 3 Objectives ............................................................................................................... 5 4 Project description................................................................................................. 6 5 Materials and methods .......................................................................................... 7 6 5.1 Wood ............................................................................................................ 7 5.2 Wood shavings ............................................................................................. 7 5.2.1 Laboratory experiments at SP ...................................................................................7 5.2.2 Pilot plant experiments at Pallmann ..........................................................................9 5.2.3 Microscopic characterization of the raw materials ...................................................10 5.3 Wood chips ................................................................................................. 11 5.4 Refining ...................................................................................................... 12 5.5 Fibre and handsheet testing ....................................................................... 13 5.5.1 Pulp tests .................................................................................................................13 5.5.2 Paper tests ...............................................................................................................13 Results .................................................................................................................. 14 6.1 Laboratory shaving tests ............................................................................ 14 6.1.1 Test 1 .......................................................................................................................14 6.1.2 Test 2 .......................................................................................................................14 6.1.3 Test 3 .......................................................................................................................15 6.1.4 Test 4 .......................................................................................................................17 6.1.5 Test 5 .......................................................................................................................18 6.1.6 Test 6 .......................................................................................................................19 6.1.7 Energy measurements.............................................................................................19 6.2 Pilot plant experiments ............................................................................... 21 6.3 Refining trials .............................................................................................. 21 6.4 Pulp properties ........................................................................................... 22 7 Conclusions.......................................................................................................... 26 8 References ............................................................................................................ 27
Appendix 1. Co-operative partners - a description ....................................................... 28 Innventia Database information................................................................................. 29 Optimizing shavings for reduced energy consumption in TMP production
1
1 Summary
Chips used in the manufacturing of mechanical pulp were originally taken from
chemical pulp production and still have dimensions similar to those used for the
chemical pulping processes. Such chips may not be optimal for mechanical pulp
production. Laboratory experiment, based on the concept of pre-deformation of wood,
has also shown that by using wood shavings instead of traditional wood chips
considerable savings in energy consumption may be achieved without any loss of pulp
properties. Thus in order to investigate the possibilities of producing wood shavings in
industrial scale with sufficient quality for mechanical pulp production this study was
conducted.
In order to optimise knife angles for industrial cutting a pilot disc moulder was utilised.
Large difficulties with uneven production and slot jams were encountered. Using a
cutting angle of 50o, with a rather large space to the chip breaker, a production of
shavings with sufficiently good deformation was possible to reach.
In the industrial production a flaker was used. The set up finally decided on allowed for
a cutting angle of 70 o producing shavings with cell wall distortions that from a
microscopic point of view looked promising.
Refining turned out to be difficult due to feeding problems of the shavings. It was
finally concluded that in order to handle shavings a different design of the refiner
feeding system is necessary. Refining was instead made in a batch Wing refiner.
As compared to wood chips no energy savings with regard to freeness or tensile
strength was possible to achieve with the shavings material here used. Also light
scattering properties were similar. However it turned out that the shavings produced a
pulp with severe fibre cutting resulting in a substantial loss in tear strength. Probably the
cutting of the shavings have under industrial conditions not been possible to be made
under enough soft/moist conditions that the fibre structure itself has escaped damages
leading to the fibre rupture seen in the subsequent refining.
2
1 Sammanfattning
Den flis som idag används vid TMP tillverkning är ursprungligen framtagen för kemisk
massa och är inte optimerad i dimensioner för vad som skulle vara bäst för mekanisk
massatillverkning. Grundläggande studier har även visat på att man förbrukar onödigt
mycket energi på den första komprimeringen som sker vid raffinering varför mekaniska
förbehandlingar under mer gynnsamma förhållanden visat sig vara effektiva. Tidigare
laboratoriestudier har visat att om flisen mekaniskt förbehandlas i skjuvning/kompression så kan energiförbrukningen vid raffinering reduceras med ca 10 %. Om samtidigt
flisutseendet förändras till deformerade spånor, ”skjuvspån”, kan energi-minskningen
uppgå till hela 25 %. I syfte att ta spåntillverkningsprocessen närmare industriell
tillämpning har försök gjort med att skala upp tillverkningen av skjuvspån och utvärdera
dessa spånor för mekanisk massaframställning.
Skjuvspånstillverkning i större skala optimerades först i en pilotutrustning för
tillverkning av kutterspån vid SP-Trä i Borås. Utrustningen modifierades avseende
inmatningsbord, knivhållare, knivar, mm. och olika skärvinklar hos knivarna testades. I
de fall som medgav skjuvspånstillverkning utvärderades deformationen av fibrerna i
spånen med mikroskopiska studier.
Fullskaleförsök gjordes i en ”Flaker” hos Pallmann i Zweibrücken, Tyskland med 70o
skärvinkel där skjuvspån med önskade celldeformationer kunde produceras. Försök med
raffinering visade på stora matningsproblem av skjuvspånen till raffinören, så stora att
det inte gick att genomföra en kontinuerlig raffinering. I stället utfördes raffinering
satsvis i en Wingdefibrör där raffineringskurvor freeness mot energiförbrukning togs
fram för skjuvspån respektive flis från samma granvedsparti. Vid Wingdefibreringen
uppnåddes ingen energibesparing jämfört med normalflis vid raffinering till samma
freeness. Styrkeegenskaper och ljusspridning var likvärdiga för de olika massorna
medan fiberlängd och rivindex var kraftigt försämrade för skjuvspånen. Detta berodde
troligen på de alltför torra förhållanden som rått vid skjuvspåntillverkningen vilket lett
till fiberskador.
3
2 Background
Mechanical pulp of high quality requires a substantial degree of mechanical treatment
and consequently a high energy input during the refining. The energy consumption is
high for all mechanical pulping processes, with TMP production having an energy
consumption of between 2.0 and 3.5 MWh/t to freeness levels of 120- 30 CSF to obtain
suitable printing quality pulps. Due to the increasing costs of electrical energy, there is
an urgent need to improve the efficiency in the mechanical treatment in the refining
process and thus to reduce the energy demand.
Chips used in the manufacturing of mechanical pulp were originally based on those
adapted to chemical pulp production and still have dimensions similar to those used for
the chemical pulping processes. Such chips may not be the optimal ones for mechanical
pulp production. Considering the process conditions of mechanical pulping, the most
suitable chips might be somewhat longer than those currently used to preserve fibre
length, and considerably thinner to facilitate a fast heat transfer in the refining.
Most of the refining energy in the production of a mechanical pulp is used to increase
the flexibility and bonding ability of the fibres. This topic has for a long time been of
interest for researchers. Fundamental studies on the mechanical fatigue in wood under
conditions simulating refining have shown that only deformations of high amplitude are
beneficial for an effective mechanical treatment (Salmén et al. 1985), and that a precompression of the chips to a high degree might be a way of reducing the energy
consumption in the subsequent refining. Already in the 1960s, it was observed by Meret
and Fisher at the Powell River Company that, superior pulp strength could be achieved
by a pre-compression of wood blocks both parallel to and perpendicular to the long axis
of the fibres (Frazier and Williams 1982).
Uhmeier (1995) suggested, based on the laboratory deformation of wood blocks, that
large deformations across the fibre direction could be obtained by pressing a cutting tool
at a suitable angle through the wood to produce a different kind of "chips" or wood
shavings. It is also known that, during veneer cutting, large compressive strains occur
both in the directions parallel (mostly tangential in the case of rotary peeling) and
normal (mostly radial in the case of rotary peeling) to the cutting path in the case of
0°/90° orthogonal cutting (Thibaut and Beauchene 2004) which may be beneficial with
regard to refining processes. In addition, the new surfaces produced by the cutting
process have been subjected to high deformation levels in the cells in contact with the
tool tip, deformations that cause a delamination between fibres in the compound middle
lamella. Thus, the idea based on the pre-deformation achieved in such processes was
here conceived that refining of wood shavings might require less energy than the
refining of conventional chips.
Experimental work (Viforr and Salmén 2005), based on the concept of pre-deformation
of wood, has shown that using wood shavings instead of traditional wood chips for the
production of TMP in a laboratory scale refiner considerable savings in energy
consumption may be achieved without any loss of pulp properties. The potential for
energy savings at a given tensile index using wood shavings instead of the traditional
chips was estimated to be up to 25 %. As no optimisation of the refining process of the
wood shavings with respect to temperature and intensity has been performed, the
potential for energy savings may be even higher. This fact has though to be evaluated in
4
industrial refiners where feeding and refining are somewhat different from that in small
pilot scale equipment.
5
3 Objectives
The aim of the project has been to investigate the potential for reducing energy demand
in TMP production to printing grade paper with 20 % by:

developing an industrial manufacturing concept for producing wood shavings for
TMP production in industrial scale;

evaluating the energy saving potential for TMP production in a pilot refiner by
comparing the use of wood shavings with that of traditional wood chips.
6
4 Project description
The project consists of the following main tasks:
1. To develop and adapt cutting knives to a laboratory cutter for obtaining wood
shavings with suitable deformation.
2. Characterisation and evaluation of the deformations of the produced shavings.
3. Layout for adjustment of the knives of an industrial cutter for industrial
production of wood shavings with desired deformation characteristics.
4. Pilot scale refining trials of the industrially produced shavings.
5. Evaluation of the energy savings to printing paper grade properties when using
wood shavings as raw material compared to normal wood chips.
The co-operation partners in this project has been two Swedish institutes (Innventia and
SP) and PALLMANN - one machinery manufacturing company from Germany, see the
technical profile descriptions in Appendix 1.
7
5 Materials and methods
5.1
Wood
Fresh logs of pine wood collected in southern Sweden were used in all pre-experiments
for knife design adjustment.
Fresh logs of spruce wood, Picea Abies, collected in Germany were used for industrial
production of shavings as well as for traditional chip material for refining trials.
5.2
Wood shavings
In order to find out the most suitable cutting conditions for producing industrial wood
shavings with high fiber quality, pre-experiments were performed both in a laboratory
equipment at SP and after that at Pallmann on a large-scale semi-industrial equipment.
5.2.1
Laboratory experiments at SP
Fresh never dried pine-logs from the south-west of Sweden wee cut in pieces with
approximate dimensions of 180 x 120 x 25 mm. Both the sap-wood and the heart-wood
from the log were used. The wood blocks were stored in frozen conditions after sawing
until they were used in cutting of the shavings. The sawing of the pieces used for
making the shaving was aimed for a uniform direction of the annual rings, Figure 1.
Figure 1. Typical orientation of the annual rings in the wood blocks to be used for cutting of
shavings.
Obviously wood gives a natural curvature to the annual rings why it was not possible to
cut all wood blocks according to the outline as shown in, Figure 1. Such pieces were
mainly used in the initial trials where no energy measurements were made.
The equipment used at SP was a disc-moulder, Figure 2a. The diameter of the disc is
400 mm. The disc is equipped with 8 knives (Figure 2b) covering the distance between
140 mm and 380 mm from the centre of the disc. The maximum speed of the moulder is
1,000 RPM. During the project, the moulder was rebuild and equipped with a frequency
control that made it possible to adjust the rotational speed. The construction of the
moulder with radially placed knives implies that the cutting speed is variable depending
on the distance from the centre. With a maximum speed of 1000 RPM the cutting speed
is between 15 - 40 m/s. The most common rotation speed of the moulder used during
the production of shavings resulted in cutting speeds between 10-20 m/s.
8
a)
b)
Figure 2. a) Disc moulder used at SP; b) Detail of knifes
Figure 3 shows how knifes were placed in the moulder at SP. Originally, the knifes
were mounted with an angle of 45° towards the disc, giving a cutting angle equally
large. The angle between the knife and chip breaker was 45° providing for a good flow
of the shavings through the moulder.
Cutting knife, fix
mounting angle 45°
Ch
ip
br
ea
ke
r
Disc
Kn
if e
Disc
Figure 3. Detail of the mounting of knifes in relation to the disc in the moulder used at SP.
9
The definition of the cutting angles used in the following text is illustrated in Figure 4.
Cutting knife
Cutting angle
Chip
breaker
Angle between chipbreaker and knife
Figure 4. Definition of cutting angle as used in this report
During the final trials for producing shavings the energy used was measured using a
Fluke Power Logger 1735. The energy requirement was sampled during the production
of the shavings and results were corrected with the idling energy used for keeping the
moulder running at the set speed without cutting.
5.2.2
Pilot plant experiments at Pallmann
At Pallmann shavings were produced from German fresh spruce wood, 96 % moisture
ratio (based on absolute dry wood), in an industrial pilot flaker of type PZUL 8-300
(PALLMANN), Figure 5. In this equipment the knives are placed at the periphery of
the rotating disc, see Figure 6, providing for a constant cutting speed. The wood log is
moved with a constant speed towards the periphery defining the thickness of the
shavings produced. After producing the shavings they were stored frozen until refining.
The cutting speed was 35 m/s (rotation speed of knife ring), the feed rate 375 mm/s (log
against knives) and the knife protrusion 1.5 mm.
10
Figure 5. Flaker at Pallmann used for producing wood shavings.
Figure 6. Knife and rotary disc of the Flaker at Pallmann.
5.2.3
Microscopic characterization of the raw materials
Quantification of the structural and mechanical changes in the shavings being different
between to normal chips, and for evaluating the effectiveness of the shavings properties,
was evaluated using light microscopy.
In previous work, the degree of compression of shavings and wood chips has been
examined by ESEM (Environmental Scanning Electron Microscope) on cross-sections.
11
ESEM-micrographs in Figure 7 illustrate the type of changes of the wood structure
caused by the manufacture of the wood shaving to be expected. In comparison with the
wood chips, the fibers in the wood shavings are considerably deformed, especially close
to edges of the shavings.
Sample from the edge of a shaving
Sample from the middle of a shaving
Sample from a chip
Figure 7. Structural differences between wood chips and shavings observed on cross section
using electron microscopy. Bars indicate a length of 100 m.
5.3
Wood chips
Wood chips were produced in a pilot plant shipper from logs provided from Pallman.
These were taken as remaining pieces from logs used for producing wood shavings and
had a length of 80 cm and diameters of around 15-20 cm, see Figure 8. Chipping was
made in a pilot chipper, BRUKS 982 MT, Bruks AB and screened in a Rader JB 88
1182 disc screen classifier, Rader Company Inc. The 2-8 mm chip fraction was used.
12
Figure 8. Wood logs of spruce, Picea Abies, grown in Germany and used to produce chips for
refining comparisons.
5.4
Refining
Refining was originally intended using the STFI's pilot plant refiner, a Sunds Defibrator
RPM300. After several initial trials were the shavings totally plugged the feeding
system it was decided impossible to perform the refining in the equipment available
without an extensive rebuilding and a new construction design for the feeding screw. As
such trials would be rather costly and could not be motivated in the current project it
was decided to refine the material in a Wing refiner instead.
Both wood chips and shavings were refining using a Wing-refiner see Figure 9. The
impregnated wood materials were portioned into 125 g batches 8dry mater content) and
refined in the low-intensity wing refiner. The wing refiner chamber consisted of a 20
counter blade cylinder with a distance of 1 mm from 4 wing-like rotating blades to the
counter blades. Three empty runs of the steam heat treated refiner were used as a blank.
Chips were steam treated at a temperature of 124 °C±0.6 °C for 5 minutes, during which
the 4 wing-like blades were rotated 90° every 1.25 minutes to heat the chips evenly.
After 2 minutes of steaming the condensate was let out during 10 seconds. After 4
minutes and 50 seconds of steaming the valve was closed, the pulse-meter zeroed and
the run started after the 5 minutes of steaming. Refining was performed for 2, 6, 7, 8
and 10 minutes respectively. The pressure in the chamber was during refining 1.9-2.6
bars with the temperature rising from about 124 °C to 136 °C; the temperature
depending on how long the experiment was continued. All trials were run in singles.
Unrefined/less refined wood chips/pulp between the wing refiner body and the wing
refiner cap was removed.
13
The pulps were centrifuged and freeness and DMC were recorded where after the pulps
were transported to Innventia and stored in a fridge until pulp testing.
Figure 9. View of the Wing refiner from the side.
5.5
Fibre and handsheet testing
The pulp samples from the refining trials were tested with respect to dry solids content,
freeness; Canadian Standard Freeness, fibre width, length and shape using STFI
FiberTester.
Laboratory sheets were tested with regard to mechanical and optical properties
according to the following methods.
5.5.1
Pulp tests
Dry matter content chips (DMC)
Dry matter content pulp (DMC)
Freeness
5.5.2
SCAN-CM 39:94
SCAN-CM 3:78
SCAN-M 4:65
Paper tests
Hot desintegration
Laboratory sheets
Testing of lab. sheets
Basis weight
Structural density
Tensile index
Light scattering
Fibre length
ISO 5263-3:2004
ISO 5269-1:2005
ISO 5270:1999
ISO 536:1995
SCAN-P 88:01
ISO1924-3:2005
ISO 9416:2009
L&WFiber-Tester
14
6 Results
6.1
Laboratory shaving tests
6.1.1
Test 1
The first test was mainly made to serve as a reference for the original posting of the
knives in the moulder at SP. The cutting angle was 45°. The angle between the knife
and the chip breaker was 45°. The breaker was mounted with a distance between the
breaker and the edge of the knife of about 15 mm. The knifes were posted with a cutting
depth of 1.2±0.1 mm. Two different speeds were used a high speed 15-40 m/s and a low
speed app. 5-15 m/s.
6.1.2
Test 2
After the characterization of the shavings made with the original posting of the moulder
the knifes were re-sharpened with a new angle and new chip breakers were made. The
cutting angle with the re-sharpened knifes was 55°. The angle between the knife and the
chip breaker was 75°. The breaker was mounted with a distance between the breaker
and the edge of the knife of 3 mm. The knifes were posted with a cutting depth of
1.2±0.1 mm. Testing conditions are given in Table 1.
Table 1. Testing conditions in test 2.
Sample
Cutting speed
Cutting direction
2:1
30 - 40 m/s
Radial
2:2
30 - 40 m/s
Tangential/Radial
2:3
10 - 20 m/s
Tangential
2:4
10 - 20 m/s
Radial
2:5
10 - 20 m/s
Mixed
Comments
Tangential cutting direction
coincide with the cutting direction
used on a rotating log
Figure 10. Normal shavings to the left and shavings destroyed into stick to the right side.
The resulting material was severely destroyed from shavings into sticks, Figure 10. The
reason was most likely a much smaller angle between the knife and the chip breaker.
The mounting of the breaker very close, only 3 mm; from the edge of the knife resulted
in a more affective breaking of the shavings. But it also gave a narrow opening of the
15
slot were the knifes were mounted. The result of that was a sever destruction of the
shavings into sticks and a jam of the sticks in the moulder, Figure 11.
Figure 11. Jam in the moulder due to a to narrow opening to transport the cut shavings.
6.1.3
Test 3
In test 3 the sever destruction of the shavings using was tried to be avoided. The cutting
angle used was still 55°. The angle between the knife and the chip breaker was 75°. The
knifes were posted with a cutting depth of 1.2±0.1 mm. The cutting speed was 1020 m/s. Testing conditions are given in Table 2.
Sample
Distance between
chip breaker and
knife edge
Cutting direction
3:1
13 mm
Tangential/Radial
3:2
7 mm
Tangential/Radial
Comments
Material destroyed. Slots jammed
with sticks.
With the distance 13 mm there was a free transport of shavings through the moulder
preventing that the jam crushing the shavings into sticks. The distance of 7 mm was not
enough to avoid this phenomenon.
The shavings produced were examined at Innventia using light microscopy. Comparing
two of the cases examined, tests 2:2 and 3:1 with wood cuts with a very high angle that
do not deform the wood clear differences may be seen, see Figures 12-14.
16
Figure 12. Structure of undeformed wood shavings observed by light microscopy.
Figure 13. Structure of deformed wood shavings observed by light microscopy; experiment 2:2
17
Figure 14. Structure of deformed wood shavings observed by light microscopy; experiment 3:1
The light microscopy examinations revealed that shavings from both the testing 2:2 and
3:1 showed proper cell wall deformation degree pointed to that these running conditions
with a cutting angle of 55° should be preferable.
However the possibility to use these parameters for an economic production of shavings
also has to be considered. After discussion with Pallmann where Pallmann expressed
concerns about the cutting angle being too sharp and would require shorter interval
between changes and sharpening a new angle was decided upon. New trials were
therefore made with a cutting angle of 50°.
6.1.4
Test 4
Again the knifes were re-sharpened with a new angle. The cutting angle with the resharpened knifes was now 50°. The angle between the knife and the chip breaker was
75°. The knifes were posted with a cutting depth of 0.9±0.1mm. The thickness of the
shavings was intended to be 1.2 mm and the previous tests had shown a compression
during the cutting of about 0.3 mm. The cutting speed was 10 -20m/s. Testing
conditions are given in Table 3.
18
Sample
Distance
between chip
breaker and knife
edge
Cutting direction
Comments
4:1
13 mm
Mainly Tangential
Material destroyed. Slots jammed with
sticks.
4:2
16 mm
Mainly Tangential
Material partly destroyed. Some slots
jammed with sticks. Will cause problem
if continued
4:3
20 mm
Mainly Tangential
No jamming in the slots. Material not
affected.
The thinner cutting thickness required a wider slot for the transportation of shavings
from the moulder. A distance of 20 mm between the edge of the knife and the chip
breaker was needed. However in this case the wood shavings were not affected, i.e. no
sign of the desired cell wall deformation was seen.
6.1.5
Test 5
An alternative to the longer distance between the chip breaker and the edge of the knife
is to open the angle. In test 5 the angle between the knife and the chip breaker was
opened to 60°. The cutting angle was kept at 50°. The knifes were posted with a cutting
depth of 0.9±0.1 mm. The cutting speed was 10 - 20 m/s. Testing conditions are given
in Table 4.
Sample
Distance
between chip
breaker and knife
edge
5:1
10 mm
5:2
13 mm
5:3
16 mm
5:4
20 mm
Cutting direction
Comments
Mainly Tangential
sticks.
Mainly Tangential
sticks.
Mainly Tangential
affected.
Mainly Tangential
affected.
Also in this case the wood shavings were in some cases jammed in the moulder.
19
6.1.6
Test 6
In test 6 the angle between the knife and the chip breaker was opened to 45°. The
cutting angle was kept at 50°. The knifes were posted with a cutting depth of 0.9±0.1
mm. The cutting speed was 10 -20 m/s. Testing conditions are given in Table 5.
Sample
Distance
between chip
breaker and knife
edge
Cutting direction
Comments
6:1
10 mm
Mainly Tangential
No jamming in the slots. Some sticks in
the material.
6:2
13 mm
Mainly Tangential
No jamming in the slots.
6:3
16 mm
Mainly Tangential
No jamming in the slots.
6:4
5 mm
Mainly Tangential
No jamming in the slots. Some sticks in
the material.
Microscopic examination at Innventia indicated that when using the smaller distances
between the chip breaker and the knife edge deformed wood shavings were possible tyo
produce.
6.1.7
Energy measurements
For tests 4, 5 and 6 also measurements of the energy required to cut the material was
performed, Figure 15. Some comments to the test are that the most energy consuming
activity was the start-up of the moulder. There were also a base level of the energy
consumption to keep the moulder rotating also without any material into it. That energy
has been removed from the figures for the required energy in producing shavings. From
these measurements one could not see any differences between different posting
alternatives. However one could observe an increased need of energy when the slots
were jammed, Figure 16.
20
7000
6000
5000
4000
3000
2000
1000
0
0
20
40
60
80
100
120
Figure 15. Energy consumption for a normal cutting.
8000
7000
6000
5000
4000
3000
2000
1000
0
0,000
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
450,000
Figure 16. Energy consumption for cutting with jammed slot.
Table 6 below summarizes the energy consumption for trials with different angles and
distances between the knife and the chip breaker. All figures are based on two runs with
the same posting. The cutting angle was 50°. The knifes were posted with a cutting
depth of 0.9±0.1 mm. The cutting speed was 10 – 20 m/s.
Table 6. Energy needed to produce shavings from 1 000 g of pine
Distance between edge of
the knife and the chip
breaker
Angle between knife and chip breaker
80°
60°
5 mm
45°
6.0 Wh
10 mm
87.7 Wh
5.2 Wh
13 mm
17.9 Wh
16.0 Wh
5.6 Wh
16 mm
6.6 Wh
5.7 Wh
5.9 Wh
20 mm
5.7 Wh
4.4 Wh
21
6.2
Pilot plant experiments
The knives adjustments studies made in laboratory scale where used as input for the
pilot plant trials in a flaker at Pallmann. Originally the mounting of the knifes in the
Pallmann flaker will give a cutting angle of 35o, see Figure 17. In Figure 18 Pictures of
the original knives with an angle between the chip breaker and the knife of 30o is
shown.
Cutting angle 35o
Cutting knife
Figure 17. Schematic picture showing the cutting angle for the original mounting of knives in the
flaker at Pallmann.
22
Figure 18. The knives used by Pallmann in the first experiment where wood shavings were
produced; the cutting angle was 35° with an angle between the chipbreaker and the knife of 30°.
23
The shavings produced with the standard settings in the Pallmann flaker did not produce
any deformation to the fibres of the shavings as seen from the light microscopic pictures
of Figure 19. As a first step of modifying the cutting the angle between the chip breaker
and the knife was changed to 80o, see Figure 20. However, also in this case the
deformation of the cell walls of the fibres was rather small; see Figure 21, and not what
was hoped for if energy savings should be possible to reach in the subsequent refining
trials.
Figure 19. Micrographs illustrating the wood cell deformation of the wood shavings produced
when using knives with a cutting angle of 35° and an angle between the chip breaker and the
knife of 30°.
Figure 20. The knives used by Pallmann in the second experiment where wood shavings were
produced; the cutting angle was 35° with an angle between the chip breaker and the knife of
80°.
20
when using knives with a cutting angle of 35° and an angle between the chip breaker and the
knife of 80°.
In order to decrease the cutting angle, without affecting the mounting of the knives, a
possible way is to grind the knife edge in order that it appears blunter. This strategy was
chosen as sketched out in Figure 22 producing knives with a cutting angle of only 15 o.
When testing knives with this cutting angle in the Pallmann flaker shavings with
promising fibre deformations were produced as seen from Figure 23.
Cutting angle 70o
Figure 22. Schematic picture showing the cutting angle for the knives modified by grinding off
the knife tip to a cutting angle of 70o with an angle between the chip breaker and the knife of
75°, for mounting in the flaker at Pallmann.
21
when using knives with a cutting angle of 70° and angle between the chip breaker and the knife
of 75°.
These settings were subsequently used for the production of shavings to be tested in
TMP production with respect to energy demand and property development.
6.3
Refining trials
Refining experiments were carried out on the chips and shavings in a Wing-refiner at
Aalto University in Helsinki, Finland. As of experience the refining in this equipment is
highly reproducible at least from the power consumption versus time and freeness levels
reached. As seen for the freeness – energy curves in Figure 24 this was also the case in
these trials. Only a rather small difference in energy requirement could be seen between
the pulps produced from shavings as compared to those from normal chips. At the most
an energy savings of 200 kWh/t can be seen. This amounts only, at these high energy
22
levels in the wing refiner to an energy savings of 6 %. Due to financial restraints only
single point refining trials were possible.
600
500
CSF, ml
400
chips
300
200
shavings
100
0
0
1000
2000
3000
4000
5000
Energy consumption, kWh/t
Figure 24. Energy consumption versus time for Wing-refining of batches of chips and shavings
respectively.
6.4
Pulp properties
Pulp properties were evaluated for the different pulps having a freeness level between
540 and 120 in CSF as refined. Prior to paper making shives were removed from these
pulps in a Metso screen also resulting in a decreased freeness of the screened pulps.
As seen in Figure 25 the shaving did not result in any improved strength properties at a
specific energy consumption. A similar result is apparent in viewing the tensile freeness relationship as in Figure 26.
23
45
Tensile index, Nm/g
chips
40
shavings
35
30
25
20
1000
1500
2000
2500
3000
3500
Figure 25. Tensile index as a function of energy consumption in a Wing-refining of batches of
chips and shavings respectively.
Tensile index, Nm/g
45
40
chips
35
shavings
30
25
20
50
100
150
200
250
300
Freeness, ml CSF
Figure 26. Tensile index as a function of freeness after chives removal of Wing-refined batches
of chips and shavings respectively.
When considering optical properties it is apparent that for both wood materials the light
scattering coefficient followed a similar improvement when plotted against tensile
index, Figure 27; no apparent difference between the qualities could be discerned.
With respect to fibre length it was apparent that the cutting to shavings had resulted in a
severe fibre shortening indicating that the industrial cutting had not been able to
produce this material in an optimal way, Figure 28. This fact also resulted in a
substantially lower tear index for the pulp produced from the shavings as compared to
standard chip material, Figure 29.
Light scattering coeffisient, m2/kg
24
60
chips
55
50
shavings
45
40
20
25
30
35
40
45
Tensile index, Nm/g
Figure 27. Light scattering coefficient as a function of tensile index for Wing-refined batches of
chips and shavings respectively.
Fibre length,
length weigthed mean, mm
1.8
chips
1.6
1.4
shavings
1.2
1.0
1000
1500
2000
2500
3000
3500
Figure 28. Fibre length as a function of energy consumption in Wing-refining of batches of chips
and shavings respectively.
25
2
Tear index, mNm /g
7.5
chips
7.0
6.5
6.0
5.5
5.0
1000
shavings
1500
2000
2500
3000
3500
Figure 28. Tear index as a function of energy consumption in Wing-refining of batches of chips
and shavings respectively.
26
7
Conclusions
The possibilities of producing shavings in larger scale for industrial production of
mechanical pulp using refiners have been investigated. Flakers have a design that
potentially could fulfil such a requirement. However it was proven to be difficult to
have knives positioned in such a way that large deformations on the wood material
could be achieved still providing for a good runnability in the flaker and not providing
too large wear on the knives. In the end it was shown that although deformed shavings
were produced they were too much destroyed with regard to preserving the fibre length
in the refining operation.
Another problem encountered with the use of the shavings was that the feeding to the
refiner was obstructed. Obviously if shavings or shavings like materials would be
possible to be produced without fibre cutting the feeding operation has to be solved.
This probably means that the feeding system to the refiner has to be somewhat modified
allowing the material to be transported forward without the severe compression
occurring in present systems.
Due to the sever fibre cutting occurring when refining shavings it seems as the
production of the shavings have resulted in fracture initiations within the material that
have resulted in this destruction during the refining. In the shavings themselves no such
fibre shortening was observed. It could thus be that the shaving had not been possible
to produce under optimal conditions as was the case previously when producing
shavings under laboratory conditions. The difficulty presumable lies in the fact that it is
difficult to keep the desired climate providing for a soft flexible wood material during
the industrial production.
27
8 References
Frazier W C and Williams G J (1982)
Reduction of specific energy in mechanical pulping by axial precompression of wood.
Pulp Paper Can., 83:6, T162-T167
Salmén L, Tigerström A, Fellers C (1985)
Fatigue of Wood – Characterization of Mechanical Defibration.
J. Pulp Paper Sci., 11:3, J68-J73
Thibaut B and Beauchene J (2004)
Links between wood mechanics phenomena and wood mechanical properties: The case
of 0°/90° orthogonal cutting of green wood.
Proceedings of the 2nd Int. Symposium on Wood Machining, July 5-7, Vienna, Austria,
pp 149-160
Uhmeier A (1995)
Some aspects on solid and fluid mechanics of wood in relation to mechanical pulping.
Ph. D. thesis, Royal Insitute of Technology, Div. of Paper Technology, Stockholm
Viforr S and Salmén L (2005)
From wood shavings to mechanical pulp – a new raw material?
Nordic Pulp Paper Res. J., 20:4, 418-422
28
Appendix 1. Co-operative partners - a description
PALLMANN, Germany (www.pallmann.eu) is a typical, medium size family run
business with a historical background of over 100 years. PALLMANN is manufacturing
customer tailored size reduction machines for the plastic, food, recycling and in
particular for the timber industries. The company is market leader for machines to
produce wooden chips, flakes and particles and has a considerable market share in the
refiner business.
It has the world biggest research and development facility for many different types of
size reduction machines. The machines in this facility have a semi-industrial scale. Due
to its rather big size the results of customer trials and industrial developments can easily
be adopted on an industrial scale.
PALLMANN combines the construction and design of the machines, the complete
manufacturing process of the machines and research and development on the same
premises. All expertise and metal working machines and processes are in house that
giving PALLMANN the best flexibility to react on technical requirements and customer
wishes by ongoing iterative processes between the different departments. New
developments and improvements can easily be realized by the close linkages between
design department, manufacturing and research facility.
PALLMANN will contribute with its expert knowledge to the project for the production
of the new raw material for the TMP or CTMP process, respectively. Due to the
company’s long and vast expertise and extended production and trial facilities for size
reduction machines it will pool up the scientific team with industrial and practical
knowledge, machine manufacturing and large scale semi-industrial production options.
SP Technical Research Institute of Sweden (www.sp.se) is Sweden's largest industrial
research institute. SP is accredited for testing and certification of a number of wood
products. The research of SP Trä covers a wide range of areas within the wood
production and utilization of wood. So far the efforts of SP have been mostly connected
to production and use of solid timber and wood based panel. A closer cooperation
between SP and INNVENTIA will benefit all parts. The Ecobuild centre of excellence
which as a goal has to increase knowledge, production and use of coefficient wood
based materials and processes is coordinated from SP.
INNVENTIA AB, Sweden (www.Innventia.com) is a world leader in research and
development relating to pulp, paper, graphic media, packaging and biorefining.
Innventia’s unique ability to translate research into innovative products and processes
generates enhanced value for our industry partners. This approach is called “boosting
business with science”. Having Partner Customers in several countries worldwide,
Innventia is working globally, growing continually in know-how and knowledge.
Innventia has an extended co-operation with other research organisations and
universities, both national and international. Innventia posted revenues of SEK 330
million year 2009 and employs 270 people, based in Stockholm, Trondheim and
London.
29
Innventia Database information
Title
Author
Silvia Viforr, Rune Ziethén, Helmut Roll, Lennart Salmén
Abstract
Chips used in the manufacturing of mechanical pulp were originally taken from
chemical pulp production and still have dimensions similar to those used for the
chemical pulping processes. Such chips may not be optimal for mechanical pulp
production. Laboratory experiment, based on the concept of pre-deformation of wood,
has also shown that by using wood shavings instead of traditional wood chips
considerable savings in energy consumption may be achieved without any loss of pulp
properties. Thus in order to investigate the possibilities of producing wood shavings in
industrial scale with sufficient quality for mechanical pulp production this study was
conducted.
In order to optimise knife angles for industrial cutting a pilot disc moulder was utilised.
Large difficulties with uneven production and slot jams were encountered. Using a
cutting angle of 50o, with a rather large space to the chip breaker, a production of
shavings with sufficiently good deformation was possible to reach.
In the industrial production a flaker was used. The set up finally decided on allowed for
a cutting angle of 70 o producing shavings with cell wall distortions that from a
microscopic point of view looked promising.
Refining turned out to be difficult due to feeding problems of the shavings. It was
finally concluded that in order to handle shavings a different design of the refiner
feeding system is necessary. Refining was instead made in a batch Wing refiner.
As compared to wood chips no energy savings with regard to freeness or tensile
strength was possible to achieve with the shavings material here used. Also light
scattering properties were similar. However it turned out that the shavings produced a
pulp with severe fibre cutting resulting in a substantial loss in tear strength. Probably the
cutting of the shavings have under industrial conditions not been possible to be made
under enough soft/moist conditions that the fibre structure itself has escaped damages
leading to the fibre rupture seen in the subsequent refining.
Keywords
energy consumption, mechanical pulping, strength properties
Classification
1151
Type of publication
Innventia report
Report number
400
30
Publication year
March 2013
Language
English
INNVENTIA AB is a world leader in research and development relating to pulp, paper,
graphic media, packaging and biorefining. Our unique ability to translate research into
innovative products and processes generates enhanced value for our industry partners.
We call our approach boosting business with science. Innventia is based in Stockholm,
Bäckhammar and in Norway and the U.K. through our subsidiaries PFI and Edge
respectively.
INNVENTIA AB
Box 5604, SE-114 86 Stockholm, Sweden
Tel +46 8 676 70 00, Fax +46 8 411 55 18
[email protected]
www.innventia.com

Optimizing shavings for reduced energy

Transcription

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