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Permi by© ACA Systems all rights reserved1
Online Porosity Measurement
and Control
Permi by© ACA Systems all rights reserved
“Porosity is the best indicator for the balance
of pulp quality and machine settings”
2
Permi by© ACA Systems all rights reserved
Advantages
The very fast machine direction measurement enables a new kind of
control of paper and paperboard processes.
Increase from 576 ton/day up to 648 ton/day (12,5 %) in production
of liquid board.
Speed increase of cigarette paper machine from 300 m/min to 400
m/min (25 %).
100 000 euros savings/a when chemical (retention and defoaming
agent) proportioning was optimized by Permi.
3
Permi by© ACA Systems all rights reserved
System configuration
4
Measuring UnitControl Unit
Permi by© ACA Systems all rights reserved
Measuring head
Durable and low friction coating against paper web.
Outer vacuum ring with a separate vacuum control
prevents errors caused by the air pressure from the
moving web.
Using the optimised sensor geometry PERMI can
recalculate several porosity values according to
different standards.
Grade independent.
Accurate online readings, which help optimise
machine setting, furnish mix and especially get
faster grade changes with minimum broke.
5
Vacuum ringMeasurement slot
Permi by© ACA Systems all rights reserved
Measuring head 2
6
Vacuum ring
(outer circle)
Measurement slot
(inner circle)
Permi by© ACA Systems all rights reserved
Installation pictures
7
Permi by© ACA Systems all rights reserved
Installation pictures
8
Permi by© ACA Systems all rights reserved
Installation pictures
9
Permi by© ACA Systems all rights reserved
Installation pictures
10
Permi by© ACA Systems all rights reserved
Measuring range
Bendtsen, ml/min 10 – 20 000
Coresta 1 – 10 000
Gurley, s 6 000 – 1
Others are available on request
11
Permi by© ACA Systems all rights reserved
Process control and Permi
Key benefits of Permi
High sampling rate, 500 per second.
Continuous online operation.
Wide measuring range.
Best correlation to laboratory results.
Controlled vacuum levels.
Quick change of measuring method.
Minimum calibration on grade changes – short grade changes.
Reduces the need for laboratory testing.
12
Permi by© ACA Systems all rights reserved
Process control and Permi
Key benefits of Permi (continues)
Splendid real time information for refining control.
Optimizing base paper porosity for coating.
Quicker grade change - less broke.
Improved vacuum control in wire section.
Better wet-end chemistry management.
Superb control of calendering for uncoated papers.
Better wire and felt management.
Improved roll grinding management.
13
Permi by© ACA Systems all rights reserved
Process control and Permi
Monitoring of fast porosity variation
Reasons for variation Refining variation
Control of deculator
Proportioning of retention agent
Consistency of headbox
Control of vacuum box
Control of vacuum rolls
Foil angles
Dosage of antifoaming agent
14
Permi by© ACA Systems all rights reserved
Process control and Permi
Increased porosity (decrease in Gurley seconds) due to a small addition of uncoated broke
Very small changes in the broke
levels can have a big effect on paper
porosity (increasing or decreasing). In
this case addition of uncoated broke
has increased porosity
15
Permi by© ACA Systems all rights reserved
Process control and Permi
Uncoated broke vs. Porosity
16
Porosity [ml/min]
Broke [m³/h]
Permi by© ACA Systems all rights reserved
Process control and Permi
Couch vacuum and online porosity
Papermakers know that changes in couch
vacuum correlate quite well with changes in
final paper porosity.
The graphs from a kraft paper machine show
that high couch vacuum results in low porosity
(mirror curves).
However, sometimes the correlation is not
perfect due to variations in couch solids, press
and dryer section parameters as well as in
surface sizing and calendering when applicable.
17
Permi by© ACA Systems all rights reserved
Process control and Permi
refining
retention
vacuums
pH levels
foil angles
deaerators
hitting points
starch content
pulping process
consistency of head box
adding of coated broke
adding of uncoated broke
adding points of retention agent
retention agents as well as fillers
etc.
18
Some examples of use of Permi results to optimization work
Permi by© ACA Systems all rights reserved
Refining and Porosity
Refiner control systems
The most common refiner control is
Specific Energy Control. This cannot
compensate any changes in raw
materials or processes after refining.
Slightly better are CSF-control and
couch roll control. However, there are
so many processes after forming
section having effect on paper quality
and porosity that the only correct way
is to measure the final paper before
calendering and adjust or control
refining according to that.
19
Permi by© ACA Systems all rights reserved
Refining and Porosity
Wet end control with Permi
Fibres , refining, fines, fillers and wet end chemistry have effect on drainage, flocculation and retention.. All these effect on porosity, which is a good measure of paper quality.
Formation is a measure of small scale variations. Porosity measures variations as well as the level of paper quality.
By measuring paper porosity online it is possible to control wet end including raw materials, refining, wet end chemistry and wire section performance to get better paper quality..
20
Permi by© ACA Systems all rights reserved
Refining and Porosity
Adding refining energy will
decrease the size and number
of pores in the paper.
Fiber network tightening in the
refining is based in the
increase of fines content and
fiber bonded area, thus
resulting in a lower air
permeability level.
21
Lumiainen, J., Refining of chemical pulp, Papermaking Science and Technology, Book 8, Stock
Preparation and Wet End, Paulapuro, H. (Ed.),Fapet, Jyväskylä, CD-Rom (v.11.01).
Permi by© ACA Systems all rights reserved
Refining and Porosity
Conventional Control of Refining SRE control of refiners cannot decrease pulp quality variations
With on-line porosity measurement this can be corrected!
22
SRE = Specific Refining Energy
Pe = Effective Power, Pt = Total Power, Po = Idle Power
m = Fibre flow (Bone Dry)
Permi by© ACA Systems all rights reserved
Refining and Porosity
Freeness, porosity and refining
It has been interesting to note that the load distribution
between two softwood kraft refiners in series has effect on
porosity.
Specific energy consumption (SEC) in the first refiner was
reduced as much as it was increased in the second refiner.
Total SEC was constant as well as freeness (CSF).
However, paper porosity decreased about 25%. This shows
that CSF control cannot be correct in all situations.
It seems that only fines content has effect on freeness while
also internal fibrillation of fibres and fibre flexibility have
effect on porosity.
23
CSF
Porosity
Refiner loads (kWh/t):2.
1.
Permi by© ACA Systems all rights reserved
Refining and Porosity
Example of filter paper machine
A very small change in
refining control can be
clearly seen in the porosity
measurement. The units of
porosity numbers are l/m2/s.
24
Permi by© ACA Systems all rights reserved
Refining and Porosity
Refining control with porosity In series refining fibres are stiffer in the first refiner. If the load is too high, fibre cutting
and fines formation will increase. This decreases freeness and drainage on the wire.
In the second (and third refiner) fibres are more flexible and specific edge load can be higher without fibre cutting and fines formation. However, internal fibrillation will advance more and more flexible fibres compensate the binding power of fibre fines.
Same porosity can be achieved with higher CSF when using increased loading order. Total energy can be saved, drainage on the wire is increased and lower headboxconsistency can be used to get better formation even if the fibres are longer and paper strength is better.
Loading shares between refiners is only one example how online porosity can be utilised to optimise refining. This would not be possible by using freeness measurement, which mostly reflects fines content.
25
Permi by© ACA Systems all rights reserved
Refining and Porosity
High porosity sack kraft paper
Porosity control must be accurate for a high porosity sack kraft paper to reach the optimal combination of tensile strength and porosity.
26
Permi by© ACA Systems all rights reserved
Refining and Porosity
Energy savings Customer informed, that they get 6,25 % energy savings, when they used Permi
results to control refiners. Savings came, because pulps were not refined too much.
Production: > 50 000 t/a
Average energy consumption (before): 160 kWh/t
Price of kWh: 0,06 €/kWh
Price of consumption per year: 480 000 €
Savings using automated control of refiners: 6,25 %
Price of savings: 30 000 €/a
Speed: > 900 m/min
Product: fine papers
27
Permi by© ACA Systems all rights reserved
Refining and Porosity
TEA and Refining
Refining is always a compromise
between porosity and strength
properties.
Quick filling of valve sacks require
Gurley porosity between 5 and 10
seconds. This is the range, where TEA
(Tensile Energy Absorption) and tensile
drop very fast.
It is important to have a good control on
porosity to be able to make these
grades with acceptable combination of
the critical properties.
28
Permi by© ACA Systems all rights reserved
Refining and Porosity
Feedback Porosity for SEC* control
29
SEC Correction
Pulp from storage chest
Permi set pointfrom Operator
Controller
Pulp to mixing chest
Permi OnlinePorosity Analyser
SEC set point from Operator
SEC set point selection
SEC controller loop
Permi supervisory
predictive control
can give remote
set-point to SEC-
control about 6
times per hour or
faster
+/-
± 15 kWh/t
Dry paper web
*SEC = Specific Energy Consumption (kWh/t pulp)
Permi by© ACA Systems all rights reserved
Fillers, Fines and Porosity
Retention and porosity
There is a clear correlation
between retention and porosity.
Stabilizing long term retention
variations would reduce paper
quality variation.
30
Permi by© ACA Systems all rights reserved
Fillers, Fines and Porosity
Filler Type and Porosity
31
Permi by© ACA Systems all rights reserved
Fillers, Fines and Porosity
Filler Type and Porosity
Plate-like fillers, such as kaolin and
talc decrease bulk and porosity.
Carbonates such as PCC and GCC
increase bulk and porosity.
32
Permi by© ACA Systems all rights reserved
Fillers, Fines and Porosity
Effect of Filler on Porosity
Coarse carbonate fillers increase porosity,
but fine clay decreases it.
By using two fillers it could be possible to
control porosity of paper and filler content
independently.
33
Permi by© ACA Systems all rights reserved
Fillers, Fines and Porosity
Fibre fines and porosity
More fines at the edges – better Scott bond and lower porosity (more fibre bonding).
34
Permi by© ACA Systems all rights reserved
Drying and Paper Porosity
Filtration and Porosity
35
Liimatainen, H., et. All; Furnish
Consepts, Metso Paper
Technology Days 2003, Lahti, June 10
– 12, pp. 18 – 29.
Permi by© ACA Systems all rights reserved
Drying and Paper Porosity
Vacuum in Forming Roll and Porosity
36
Permi by© ACA Systems all rights reserved
Drying and Paper Porosity
Porosity and drying shrinkage
It is easy to see that on the left picture (freely dried) porosity is higher than on the right (restrained drying).
37
Freely dried paper Restrained drying shrinkage
Picture: Fapet, Paper Drying
Permi by© ACA Systems all rights reserved
Wet pressing and porosity
Wet pressing has a strong effect on the properties of paper. The press geometry, rolls and their covers, felts and linear pressure combinations must be selected to conform to the running speed and the paper grade to be produced.
38
Metso Paper
Permi by© ACA Systems all rights reserved
Wet pressing and porosity
Dry Content and Porosity with Shoe Press and Roll Press
39
KnowPap 4.0 (2002)
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Wet pressing and porosity
Press Draw and Porosity
A high press draw is not only question of runnability but also paper quality is lower when low porosity is needed.
Porosity measurement is also a good tool for evaluating what is a too high press draw
40
Permi by© ACA Systems all rights reserved
Formation and Porosity
Normalized ß-formation as a function of paper openness measured as Bendtsen air
permeability for the reference (kraft 60% and TMP 40%), DIP-based, and mechanical
virgin pulp-based furnishes.
41
Bad
Good
Permi by© ACA Systems all rights reserved
Formation and Porosity
Generally the porosity is low when the formation is good.
42
Good base paper
Bad base paper
Ari Puurtinen:MULTILAYERING
OF FINE PAPER WITH 3-
LAYER HEADBOX
AND ROLL AND BLADE GAP
FORMER, Espoo 2004
Permi by© ACA Systems all rights reserved
Formation and Porosity
43
Permi by© ACA Systems all rights reserved
Coating and Paper Porosity
Porosity and Coating Coverage
Dense sheet – small penetration of coating color and good coating coverage and gloss.
Porous sheet – deep penetration of coating color and poor coating coverage and gloss. Misting problems in film coating.
44Forsström et al. TAPPI Coating Conference, 2002
http://www.kcl.fi/news/link12004/link12004s4.html
Permi by© ACA Systems all rights reserved
Coating and Paper Porosity
Coating Coverage in Film Coating
Due to nip pressure coating coverage depends on porosity not on roughness.
45
U.Forsström et al. Tappi Coating
Conference, 2002
http://www.kcl.fi/news/link12004/link1
2004s4.html
Permi by© ACA Systems all rights reserved
Coating and Paper Porosity
Coat Weight and Gloss vs. porosity in Film Coating
Due to pressure penetration coat weight increases as porosity increases and gloss decreases. In blade coating gloss increases, when coat weight increases.
46
U.Forsström et al. Tappi
Coating Conference, 2002
http://www.kcl.fi/news/link12004/
link12004s4.html
Permi by© ACA Systems all rights reserved
Coating and Paper Porosity
Porosity versus Opacity
Opacity of Coated Paper (on-line coater)
Porosity of Base Paper
47
Permi by© ACA Systems all rights reserved
Coating and Paper Porosity
Coating and web breaks
It seems that higher porosity predicts web break in a blade coater.
48
Porosity, s Basis Weight, gsm
BREAK BREAK
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Porosity control before headbox
Porosity decreases with: More refining
More low freeness mechanical pulp
More coated broke (normally) or DIP
More fibre fines (better retention)
Less anionic trash (less hydrophobic material)
More hardwood pulp
Less softwood kraft pulp
More wet end starch
Less fillers or more platelike fillers (talc, delaminated clay)
Less air in stock
49
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Porosity control on paper machine
Porosity decreases with: Higher grammage
Better formation (usually)
Good retention
Slow drainage
More wet pressing
Less press draw or drying shrinkage
More surface size
More film forming size (PVA, CMC)
Less surface size penetration
Pigmented surface size
50
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Reasons and effects of low porosity
51
High internal bond
Low press to dryer drawWet Pressing
Good formation
Low air content
Good refining Good bonding
Corrugating medium
Low oil absorption
No pinholes
Good runnability
No print through
Dense sheet
Rotogravure printability
Offset printability
Low silicone pick-up
Limit: Set-off in CSWO
Low porosity
correlates with:Root cause:
Final benefit of low
porosity:
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Process Control by Permi
52
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Constant porosity – Consistent quality
Papermakers know that final porosity of cigarette, filter and sack papers is very
important but also printability and runnability properties of printing papers correlate
well with final paper porosity.
Most on-line instruments measure and control only one paper property. In addition to
final paper porosity, which is an important property for some paper grades, Permi is a
universal analyzer of paper quality for most paper grades due to the fact that almost
all process parameters have a clear effect on porosity.
On the other hand, porosity correlates with almost all physical paper properties. If
porosity is constant, paper process performs well and paper quality is consistent.
53
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Porosity and Paper Quality
54
Decreased
bulk
Better
formation
Lower
caliper
Lower
stiffness
Better
ply bondBetter
smoothness
Less print-
through
Less
pin holes
Higher
opacity
Better
print gloss
Lower ink
absorption
Increased
basis weight
Increased
moistureDecreased Porosity
More fibre
bonding
Higher
strength
Lower tear
strength
Lower light
scattering
Lower opacity
and brightness
Less
dusting
Lower ink
demand
Lower
fluting
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Process parameters increasing porosity
55
Higher Porosity
Lower
retention
Less broke
Lower fibre
fines content
More pin holesLower fibre
bonding
Softer windingDecreased wet
pressing
Coarser fibre
type
Less surface
size
More
carbonate
fillers
Less platey
fillers
Less wet end
starch
Less reject in
screening
Reduced
refining
Wet end
chemistry
Pulsating
drainage
More
shrinkage at
web edges
Reduced
calendering
Higher press
draw
More
flocculation
Higher air
content
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Advantages of single-point measurement A normal scanner covers only a tiny fraction of the web area. With a scan speed
of 0.5 m/s, web width of 10 m and web speed of 25 m/s web travels 500 m during
one scan. It is impossible to separate cross directional and machine directional
variations from a scanned measurement. However, there are separate CD and
MD controls, which cannot work very well in the wavelength range of 1 to 100
seconds.
This range is the most common problematic area related to variations in the
approach flow and short circulation of the paper machine. These variations are
mainly fluctuations in stock consistency but there can be other sources of
variation like raw material mixture, fines content or chemical condition of the
stock.
With a fast Permi porosity analyzer it is possible to improve the process so that
basis weight and moisture controls work better and the fast peak-to-peak
variation, which cannot be seen in the scanner measurement, is lower and thus
runnability is better.
56
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Advantages of single-point measurement One of our customers is using our sensor in a scanning system and our fixed
point Permi analyzer in another paper machine. They told us that they have done
quite a lot of research work with the both units and at least in their case the MD-
profile measurement with the Permi helps them much more than the CD-profiles.
The reason is that if there are short trend machine direction changes, they cause
wrong CD-profiles with the scanning sensor even though the sensor itself makes
the measurements correctly. They told that the same happens with all other
scanning sensors, too (grammage, ash etc.). They also told that the CD-porosity
profile changes in their machine only if they change a felt or a wire.
This customer uses always the Permi results to control the paper machine and
they told that with light weight grades they run the paper machine following only
the MD-porosity profile. From the Permi readings they can see how well the wet
end and the head box are working. They also pointed out that the quality of their
papers is better, but especially the runnability of the paper machine is nowadays
better than before the Permi installation.
57
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Typical CD and MD variation in porosity
Usually, there is a lot of CD
variation, but it is quite stable
from reel to reel. This could
be measured in the
laboratory and corrected if
possible.
Machine direction variation of
reel averages seems to be in
this case about ± 15 ml/min
(>10% range). This could be
corrected by using online
porosity measurement.
58
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Wet end control According to Metso Paper the most important measurements for wet end process control are
formation and porosity. With these on-line measurements the optimum running window can be found.
59
TARGE
T AREA
Porosity, ml/min
Fo
rmation
, %
Determining process
operation point
Control action rules:
• Headbox slice opening
• Former vacuums
Quality set points:
• Formation
• Porosity
Controls
Dewatering
Dryness
after press Porosity
Formation
Process Paper
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
PM wet end control
60
Metso’s opinion of the most important measurements to control wet
end process are moisture after presses, formation and porosity.
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Effect of increasing actuator set point in film coated paper
61
Actuator increase Dry weight Moisture Caliper Porosity Coat weight Gloss
Ba
se
Pa
pe
r Headbox Dilution
Press section steam
Water spray
Calender nip pressure
Co
ate
d Rod pressure
SC steam
SC nip pressure
= main actuator for each property
Permi by© ACA Systems all rights reserved
Total Process Control with Permi
Porosity is an overall measure of process performance. Porosity
measurement is like Freeness in stock preparation. When porosity is
stable process is performing well.
Permi is an excellent analyzer before surface sizing and coating.
Permi not only shows the history of the paper web but also predicts
how good coverage of size or coat weight can be achieved in the
following process.
Film coating and cases where the positive effects should be made with
a minimum coat weight are well suited for Permi.
When porosity is low, size or coating penetration is reduced and the
effect of coating on the paper surface is better. This is important when
basis weight is low, coating colour cost is high or when coating low
brightness base paper e.g. linerboard.
62
Permi by© ACA Systems all rights reserved
Total Process Control with Porosity
Process Optimization and Paper Quality Fast porosity measurement is the best link between process performance and total paper quality.
Stable porosity is a good guarantee of well working process and consistent paper quality.
63
Tensile
Bulk
Formation
Caliper Stiffness
Scott Bond Roughness
Print throughPin holes Opacity
Print gloss Ink demand
Basis weight Moisture
Drainage
Fillers
Wet pressing
Retention
Fibres
Press draw
Air content
Chemicals
Flocculation
Refining Screening
Web shrinkage
Calendering Winding
Permi
Permi by© ACA Systems all rights reserved
Paper Grades and Permi
Sack paper
Filter paper
Office paper
Medical paper
SC base paper
MG-kraft paper
Cigarette paper
Release papers
Envelope paper
Bank note paper
Photo base paper
Corrugated medium
Saturating base paper
Base paper for coating
Base paper for siliconizing
Uncoated calendered papers
64
Permi by© ACA Systems all rights reserved
Board Grades and Permi
Plasterboard
Gypsum board
Special boards
Release boards
Cigarette board
Graphical boards
Food service board
Base board for coating
Liquid packaging board65
Permi by© ACA Systems all rights reserved
Board Grades and Permi
Linerboards and Closed Water System
Closed water system is problematic because there is lot of fine material
circulating in the process.
Sometimes there is more fines in the sheet and the properties are
different. It is important to know the porosity because more fines means
more fibre bonds and better strength properties.
One is able to control fines better and learn about the process what is
causing variation of fines. Things like retention, web breaks, broke
amount, OCC quality, wire suctions wet pressing, condition of wires
and felt etc. all have effect on porosity and fines content.
66
Permi by© ACA Systems all rights reserved
Paper Grades and Permi
Base Paper for Coating
Coaters need to have the correct porosity of base
papers, because solids content of coating color is
low. With a high amount of water there is a risk
that too much binders migrate with water into the
base paper (poor water retention).
Binder migration results in lower surface strength
and mottled printing product.
Due to pressure penetration coat weight increases
in film coating, when porosity increases. However,
coating coverage and paper gloss decrease.
67
Permi by© ACA Systems all rights reserved
Paper Grades and Permi
Photo and Printing Papers
The printing quality of papers as well as the
runnability of printing machines depends on the
porosity of the paper.
If the porosity is too high, printing ink is
absorbed too deep into the paper structure and
the print quality is not sharp.
If the porosity is too low, printing ink stays on
the paper surface and the result may be
smudgy.
68
Permi by© ACA Systems all rights reserved
Paper Grades and Permi
Office Papers
One of the most used office paper is copy
paper. Porosity has a good correlation to the
runnability of office papers in printers, faxes and
copying machines.
If porosity is too low there is risk for multifeed,
which can even damage the machine. If
porosity is too high, paper machine runnability
and printing quality may suffer.
69
Permi by© ACA Systems all rights reserved
Paper Grades and Permi
Corrugating Medium (Fluting)
The corrugating medium is the fluted
layer of corrugated board made for
package and container boxes.
The porosity level of corrugating
medium correlates with refining and
has a good correlation to the board
strength, which is one of the most
important factors of packing materials.
70
Fluting
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Paper Grades and Permi
SC Papers SC papers (supercalendered uncoated magazine and
cataloque papers) must a have dense structure which
means a low air porosity. Porosity has a good
correlation with the printability of SC grades. Porosity is
one of the most important quality factors to be
measured.
The final porosity is a combination of the base paper
porosity and supercalendering process. The porosity
after supercalendering is very low, which means that
the accuracy of the porosity measurement must be
extremely good.
The porosity of the uncalendered base paper is
reasonable high and easy to measure.
71
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Paper Grades and Permi
Newsprint Porosity has a good correlation with the
printability of newspaper grades.
If the MD porosity profile is stable the runnabilityof printing machines will be excellent. The porosity (=structure of paper) variation is the main reason for the runnability problems in printing machines caused by newspapers.
When the MD porosity profile is stable, the runnability of a paper machine will be fine, too, there is a certain possibility to increase a speed of the paper machine.
72
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Paper Grades and Permi
Sack Paper
If permeability of sack paper is
too low air cannot pass the
walls of a paper when pouring
powder into a sack.
If the porosity is too high
strength problems may appear,
for instance, a sack filled with
heavy powder can break.
73
Permi by© ACA Systems all rights reserved
Paper Grades and Permi
Cigarette Papers The porosity has an influence on the temperature of combustion of
cigarette papers, which has an effect on the tar level of a cigarette.
The porosity has an influence on the taste of cigarettes, on dust content and on temperature of the burning process. Air must also pass the walls of the paper to dilute and cool the smoke of a cigarette.
Easy and fast on-line measurements help to keep the porosity of cigarette paper on the correct level and save time and money in grade changes.
The biggest problem is to keep the small scale variation as low as possible.
The most used measuring standard is Coresta. The usual air permeance of cigarette paper is 30 – 50 Coresta (about 25 – 15 Gurley seconds).
74
Permi by© ACA Systems all rights reserved
Paper Grades and Permi
Security Papers
The quality requirements of security papers
are high. The porosity is an important factor
in controlling the process.
The porosity of bank notes must be correct
for proper function of automatic counting
machines. If the porosity is too high air
cannot pass between the bank notes and
the counting machine may take two (or
even more) bank notes at the same time.
75
Permi by© ACA Systems all rights reserved
Paper Grades and Permi
Filter Papers
Depending on the porosity of the
paper, very small particles can be
trapped.
The price of filter papers can be very
high, so it is important to keep the air
porosity constant to avoid broke and
to keep the total efficiency of the
production high.
76
Permi by© ACA Systems all rights reserved
Permi versus competitors
Permi system configuration Air is vacuumed through the web with constant pressure
Flow rate is continuously measured
77
Electronic flow rate signal
Permi
Control
BoxEjector
Preset
leakage
vacuum
Air flow
Paper web
Preset measuring vacuum
Vacuum
controller
Sensor head and measuring
device are integrated
DCS
Two porosity
signals
Permi by© ACA Systems all rights reserved
Permi versus competitors
78
Measured
volume
100 ml
Leakage
vacuum
~ 1 kPa
Measuring
vacuum
~ 1 kPa
Paper web
Air flow
Long pneumatic distance between sensor
head and measuring device
100 g
Preset
leakage
vacuum
Preset
measuring
vacuum
Paper web
Air flow
Flow meter
Ejector
Vacuum
controller
PERMI measures air flow Multiperm, Microperm and Porolog
measure time
Permi by© ACA Systems all rights reserved
Permi versus competitors
Comparison Permi vs. conventional on-line porosity analyzers
79
Conventional on-line porosity analyzers
One measurement/
1 000 m
One measurement/
1 000 m
Web speed 1 200 m/min, Porosity 50 Gs
Dead time
600 m
80 000 measurements/ 3200 mPermi
Permi• One measurement 2 ms - 0,04 m
• Continuous measurement
• 80 000 measurements - 3200 m
Dead time
600 m
Conventional on-line porosity analyzers
• One measurement 50 s - 1000 m
• Dead time 30 s - 600 m
• Two (2) measurements - 3200 m
Permi by© ACA Systems all rights reserved
Permi versus competitors
80
Permi:
Normally one calibration is enough for one paper machine. If 70 grades => one (1) calibration.
Recalibration in every 2nd year.
Measuring time 2 ms.
Changes in roughness or web tension or speed do not have affect the results.
0.95 correlation or better to lab analyzers.
Competitors:
Usually every grade needs own calibration. If 70 grades => 70 calibrations.
Recalibration in every week.
Measuring time 5 ... 120 s
Changes in roughness, or web tension or speed have influence in results.
Poor correlation to lab analyzers without frequent recalibration.
Permi by© ACA Systems all rights reserved
Permi versus competitors
81
Permi:
Normally one calibration is enough for one paper machine. If 70 grades => one (1) calibration.
Recalibration in every 2nd year.
Measuring time 2 ms.
Changes in roughness or web tension or speed do not have affect the results.
0.95 correlation or better to lab analyzers.
Competitors:
Usually every grade needs own calibration. If 70 grades => 70 calibrations.
Recalibration in every week.
Measuring time 5 ... 120 s
Changes in roughness, or web tension or speed have influence in results.
Poor correlation to lab analyzers without frequent recalibration.
Permi by© ACA Systems all rights reserved
Users’ Experiences
The shortest pay back periods have been 4 – 8 weeks even though the Permi replaced a competitor’s unit.
The accurate and high-speed results have helped customers to control refining, shorten grade changes, control and minimize quality problems.
Kruger Wayagamack has informed that they have managed to improve both quality of papers and runnability of paper machine with the on-line porosity analyzer made by ACA Systems.
82
Permi by© ACA Systems all rights reserved
Users’ Experiences
Energy savings up to 10 Kwh/ton with better control of refining.
The personnel of Stora Enso Varkaus Mill voted the Permi to be the best investment in 2004-2005.
100 000 euros savings/a when chemical (retention and defoaming agent) proportioning was optimized by Permi.
Increase from 576 ton/day up to 648 ton/day (12,5 %!) in production of paper board when the proportion of fines was optimized by Permi (if drying is a bottleneck).
83
Permi by© ACA Systems all rights reserved
Users’ Experiences
15 % average shortening in grade changes.
Over 3 % increase in production in a Finnish LWC machine.
5 % increase in production in a Finnish office paper machine.
84
Permi by© ACA Systems all rights reserved
Users’ Experiences
Permi On-Line Porosity Analyzer gives us very reliable online information
for controlling the refiners, and the fines content in our furnish. It has
helped us optimize the paper quality and mechanical fiber treatment
consistently, and save energy in refining.
The online information provided by Permi – together with some other activities - has also helped us shorten grade change time by 15 - 20 %.
- Mill Manager Juha Kovanen, Savon Sellu, Finland
85
Permi by© ACA Systems all rights reserved
Users’ Experiences
We noticed, that we have sometimes very unstable porosity level. Things, which can swing the porosity, are the amount of fines, the refining, the unstable pH-level, the levels of tanks and very many others. But we can’t solve this kind problems, if we haven’t an equipment like the Permi.
Permi can give us very interesting and reliable possibility to control and optimize for example the pulping processes.
I believe that every process has many things, which are swinging the stability of process and which can be seen and solved with the Permi.
Grammage and moisture measurements are important ones, but with the fast porosity measurement one is able to make profit!
I ordered the Permi too late!
- Production Manager Seppo Karine, Stora Enso Imatra PM 1
86
Permi by© ACA Systems all rights reserved
Users’ Experiences
With Permi, we have reduced energy consumption in refining, and seen a reduction in product waste.
Permi allows us to maintain the product quality
After two years of having Permi on our paper machine, it is not possible to operate without it!
Porosity feedback allows us to control refining intensity on each paper grade, and the operators follow it all the time.
- Production Manager Luc AUBRIOT, Ahlstrom La Gere, France
87
Permi by© ACA Systems all rights reserved
Users’ Experiences, Engine Filters
The measurement values of our essential parameters of porosity and air permeability are showing very convincing results.
Permi produces a continuous and very clear picture of the sheet.
It allows us to anticipate changes before each parent reel change, so it is a very powerful tool in process management.
- Production Manager Yves MELOTTE, Ahlstrom Malmédy, Belgium
88
Permi by© ACA Systems all rights reserved
Correlations
On-Line Permi vs. Lab. in MD LWC Base Paper
89
Permi by© ACA Systems all rights reserved
Correlations
Average 15 % - 20 % shorter Grade Changes.
One linear calibration makes possible to follow grade changes in real time.
90
Permi by© ACA Systems all rights reserved
Correlations
91
Permi by© ACA Systems all rights reserved
Correlations
92
Permi by© ACA Systems all rights reserved
Correlations
93
Permi by© ACA Systems all rights reserved
Correlations
94
Permi by© ACA Systems all rights reserved
Correlations
95
Permi by© ACA Systems all rights reserved
Correlations
96
Permi by© ACA Systems all rights reserved
Correlations
97
Permi by© ACA Systems all rights reserved
Correlations
98
Permi by© ACA Systems all rights reserved
Correlations
99
Results by Ahlstrom Glassfibre, Karhula, Finland
Permi by© ACA Systems all rights reserved100 Thank You for Your Attention!
"Know structure of your paper in order to better run your
machine!"
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