Peak Total TCR-2512 (top) and TCR-2502 (bottom)

Revolutionizing consistency measurement across a whole range of papermaking applications, BTG’s new TCR-2502 in-line transmitter delivers the industry’s most accurate, cost-effective solution.

BTG’s Peak Total sensor TCR-2502 has been designed by pulp and paper experts to overcome the limitations of traditional consistency measurement instruments, delivering greater accuracy, better overall process control, and significant cost savings.

The new in-line transmitter’s ground-breaking approach won BTG this year’s prestigious Paper Industry Technical Association (ATIP) Innovation ‘Gold Prize’, in recognition of its clear advantages over conventional consistency measurement devices.

Until now, approaches to measuring consistency in the 0.5-14% range have been based on a number of different measuring principles:

• Total consistency is usually measured via the optical or microwave principle, using in-line measurement. The optical principle can measure all filler content, while the microwave principle only measures around 60% of filler.
• Ash content can be measured by different optical principles, some in-line but most on-line.
• Fiber consistency is measured using the shear-force principle (rotating or blade) with in-line measurement. This is the most frequently used type of consistency measurement.

In practice, this has meant that accurate, reliable measurement of total consistency and ash content has necessitated the use of more than one type of measurement probe.

BTG engineers decided there must be a better way – a system that would yield highly accurate, reliable measurement of stock consistency based around a single, easy to use system.

The result is the Peak Total transmitter TCR-2502 which uses just one unique measurement principle to precisely and separately evaluate:

• Total consistency from 0.5 -12%
• Filler content from 1 – 70%
• Fiber consistency from 0.4 – 10%.

The heart of the Peak Total innovation is a light-emitting system that measures reflectance from the slurry at a very high frequency, using advanced signal processing. The resulting data provides accurate information about the fiber, fines, and filler content of the pulp. Pulp brightness and color have no impact on the results.

The TCR-2502 comes with pre-calibration curves, but can also be very easily adapted to each mill’s actual process conditions. Normally, one sample is enough to adjust the slope (amplification) of the measurement signal, but it is also possible to calibrate using more samples, to pick up behavior from different process conditions – for example, different pulp grades.

Calibration is performed via the user-friendly interface on the connection box (CPM), but if desired can also be undertaken using BTG’s own purpose-built PC software package – which has the advantage of also being able to log data and show trends.

Installation is very easy. The extremely sturdy in-line transmitter is mounted directly in the pipe, either in a sluice valve for retraction while the process is running, or directly in a stud. It can be installed in virtually any position, without sensitivity to temperature, vibration or other factors, and features state-of-the-art electronics, including a long-life LED and photo detector.

Suitable for every stage of the papermaking process, from the pulper to the machine chest, BTG’s revolutionary technology can save mills anywhere from € 50,000-300,000 per year, depending on the size of their operation. Applications include:

• After the pulper: filler control through raw material selection.
• Waste water treatment, deinking: productivity optimization through filler content management.
• Refining: energy savings through precise calculation of the specific energy on the fiber.
• Mixing chest: precise substitution of fibers by filler, and improved use of broke through the control of filler content.
• Headbox: reduced basis weight variation.
• Effluent treatment: precise evaluation of fiber loss and slurry optimization.

The transmitter is available in two different versions:

• The TCR-2502 with a retraction system so it can be taken out of the line while the process is running – useful for example in applications where dirt builds-up.
• The TCR-2512 – a ‘light’ version without the retraction system.

Sensor technology in DIP line

Tamil Nadu Newsprint and Papers Limited (TNPL) will commission a new DIP line in order to expand its production capacity. The new DIP line is built by Andritz and furnished with state-of-the-art measurement and control technology from BTG to be used for sampling, consistency & brightness.

TNPL is one of the largest bagasse-based paper manufacturers in Asia. The three-loop DIP plant will be the first of its kind in India and will supply 300 t/d deinked pulp to produce high-quality writing and printing paper.

The scope of BTG instrumentation supplied to the plant includes a number of consistency transmitters; two MEK-2500 rotating transmitters, six MBT-2500 moving blade transmitters, and three SBT-2400 static blade transmitters. L*a*b* color and four ERIC (residual ink count) BT-5400 brightness transmitters will be used to control brightness, with the order being completed by seven MPS-1000 sampling valves and four MCS-1000 medium consistency sampling valves. BTG will also take over local service and support.

Jasna S. Stevanic

Increased knowledge about wood polymer interactions opens for a more sustainable future

By creative use of a combination of advanced analytical and evaluation methods, Swedish scientist Jasna S. Stevanic has managed to reach a new level of understanding of the ultrastructure and of the polymer interactions in the cell wall of spruce wood. This research project, carried out at Swedish research institute of Innventia, can make way for development of new types of renewable materials e.g. for the packaging industry, as well as a more energy efficient production of newsprint.

Over the years, paper makers have tried a number of methods for pretreating wood chips to save energy in refining. Many scientists have also tried to figure out how the strong and durable wood fibre could be imitated to produce new types of renewable materials. One obstacle in both cases has been the extreme complexity of the wood fibre. The understanding on the interactions between the different kinds of wood polymers is still incomplete. In her research, Jasna Stevanic has used a number of methods, e.g. dynamic mechanical analysis, DMA, imaging FTIR spectroscopy and dynamic FTIR spectroscopy.

Dynamic FTIR spectroscopy in combination with dynamic 2D FTIR spectroscopy was used to examine how the lignin, protein pectin, xyloglucan and cellulose interact in the primary cell wall. The creative combinations of techniques being used proved very useful for studying molecular interactions in the complex polymeric systems of cell walls. By introducing minor stress to the material, and analyse the results with methods such as DMA and 2D FTIR spectroscopy, it proved possible to produce a complete map of the molecular interactions in both the primary and secondary cell wall. Based on the results, schematic pictures of the cross-linkages could be produced.

Imaging FTIR microscopy proved a very useful method in analysing the orientation of cellulose, glucomannan, xylan and lignin in the secondary cell wall.

New materials for the packaging market

Trying to build renewable materials for packaging, using wood fibre as the starting point, has been a goal for R&D within paper industry for a long time. Wood science, nano technology and other research areas have taken major steps forward, being close to the point where knowledge can be transferred into a number of new products. Maybe we are closing up on this point today.

• There is a great potential in using the interactions of the cell wall to build new materials, once we have a clear picture of the ultrastructure and polymer interactions, says Jasna S. Stevanic.

  The results from the analytical part of the project indicated a parallel orientation of polysaccharides with respect to each other and the fibre axis and a partial parallel orientation of lignin. The results also indicated a strong interaction between cellulose and the hemicellulose glucomannan.

  The next step of Jasna S. Stevanic’s research was to create a biocomposite film based on cellulose reinforced hemicellulose, thus utilizing the previous findings about the strong interaction between these polymers. Bacterial cellulose & rye arabinoxylan were used as model compounds in these experiments because of their purity, but the goal is obviously to use materials from waste material streams in pulp mills for industrial production of biocomposite products and therefore spruce galactoglucomannan and microfibrillated cellulose were also used.

  The interactions were studied, using among other methods the DMA method mentioned above, based on the understanding of the ultra-structural organisation of the primary and secondary walls from earlier stages of the research.

• This research may prove to teach us to synthetically build renewable materials with the unique material structures that give wood and other plant material such excellent qualities, says Jasna S. Stevanic. Plant materials show extreme resistance against variations in climatic conditions. By producing synthetic biocomposite materials, we can use the new knowledge about ultra-structure and polymer interactions in cell walls at the same time as we design materials to specific needs and also make them more homogenous.

Energy efficient newsprint with softening of cell wall

It is known from earlier trials that a low degree of sulphonation has a positive effect on energy efficiency of the refining process, and that a negative effect will occur if the sulphonation is taken too far. Jasna S. Stevanic managed to show exactly why this is, and describe the mechanisms involved. This new and deeper knowledge may lead to the development of efficient industrial procedures to considerably lower the energy demand in refining.

Jasna S. Stevanic managed to show that with a low degree of sulphonation, selective reactions caused a weakening of the interactions between three pair of polymers: lignin and pectin, lignin and protein, pectin and protein. The treatment resulted in an increased softening and swelling of the material, and contributed to a looser bond between the primary wall and middle lamella.

This explains the reasons behind the noted energy savings from a low sulphonation. The explanation of the negative effect from a higher degree of sulphonation seams to be that such a treatment moves into the secondary cell wall, where it causes effects on the lignin which makes the wood chips more difficult to refine. The strength of the secondary cell wall is not depending on the same polymer interactions that are weakened by sulphonation.

• The primary wall has always been very difficult and costly to analyze, says Jasna S. Stevanic. We may look at 10 000 € per gram just to isolate it. This has contributed to the fact that the interactions in this part of the wood cell walls have been insufficiently known. At Innventia I have had advanced microscopical and spectro-scopical instruments and methods available. We have also managed to utilize and combine analytical methods that helped us to put together an improved picture of polymer interactions in the primary wall.

Advancement through wide co-operations

Jasna S. Stevanic points to the fact that research in wood chemistry, nano technology and other material sciences now has advanced enough to be combined into common projects with the goal to produce new renewable materials with very interesting qualities. Jasna Stevanic work is also an example of wide cooperation, being largely financed by Formas Wood Wisdom NET and the Wallenberg Wood Science Centre, a research centre shared between the leading Swedish technical universities of Chalmers in Gothenburg and KTH In Stockholm.

• One example of promising combinations of research is the pilot scale plant for energy efficient production of nano cellulose now in operation at Innventia. This operation, combined with new knowledge in wood chemistry and Innventia’s competence in pulp and paper processes, may lead to interesting developments in the near future.
• Both aspects of Jasna S. Stevanic’s research will be subjects to further research at Innventia, says Lennart Salmén, Jasna’s supervisor, head of Fibre and Material Science group at Innventia and President of IAWS (International Academy of Wood Science).

About Jasna Stevanic

• Researcher at Innventia, Stockholm, since 2004

• PhD at Chalmers University of Technology 2011

• Licentiate at Royal Institute of Technology 2008

• Civ. Engineer at Sarajevo University 1998

About Innventia

Innventia is a leading R&D centre working with pulp, paper, graphic media, packaging and biorefining. Innventias aim is to translate research into innovative products and processes. Since April 2009 the name has been changed from STFI-Packforsk to Innventia.

Written by: Nils Lindstrand

M.Maria Francis*

At first sight, a centrifugal pump seems to be one of the simplest machine. In practice however, it is capable of posing an enormous spectrum of different problems. The selection of the right pump for the right job is very important and results in minimum maintenance of pumps. But this calls for knowledge of not only what happens within the pump but also what happens behind and beyond the pump. Therefore it has to be a joint effort between the hydraulic expert and the process specialist. Selection of the right pump itself rewards. Start up, operating problems, maintenance cost etc are minimized. The performance of the pump is very much dependent on the performance of the overall system.

Effects of Pump Running Away From BEP

One can compare man as a machine with a man made machine say pump. The performance of man can be measured by his consistent output. To have consistent output, one has to see that the man is working at or near his expected capacity, that is, he is neither overloaded or otherwise. Overloading may lead to fatigue and under expectation develops frustration. This condition is monitored by his behavior, mistakes in work and losing temper. So is the case of pump. The pump has to be selected and operated at or near its best efficiency point. Over expectation may lead to overloading of the motor, cavitations, increased vibrations. Operating the pump at part capacity may lead to increased loading on the bearings thereby increasing bearing temperatures, increased vibrations and noise. The performance of the pump can be monitored by its behavior, mistakes and temperature.

Effects of Over sizing pumps

The system head curve is developed by plotting total system head (static and friction loss) as the flow varies from zero to maximum. System head curve analysis helps define the operating relationship between the pump head and the system head. Efficient and trouble free operation depends on a close match of pump curve and system curve. Otherwise pumps may be picked that are improperly sized and do not run at the conditions for which they are selected/purchased.

At design flow 350cum/hr, the Engineer calculates the head as 32m. Erroneously believing that using a safety factor will ensure his reaching D, he adds 12 m, to obtain total head of 45 m. Assuming the user needs a pump to operate 350cum/hr, and 45m, pump manufacturer selects a pump with curve A,B,C. The pump curve intersects the system head curve at BEP- Best Efficient Point.

However, the actual system curve is E,D,C and the pump will run at C rather than B. Because with discharge valve fully open, pump seeks equilibrium with the system and operate at the intersection of pump curve and system head curve. At point C the pump will produce a flow of 480cum/hr. Not only the user is getting different conditions than he wants, he is also operating at a less efficient point on the pump curve & spending more on energy.

To get 350 cum/hr, the valve is gradually closed, steepening the system head curve. The pump produces 350 cum/hr and 45 m. But head at 350 cum/hr is 32 m. The pump thus produces 45m and 350 cum/hr but delivers only 32 m and 350 cum/hr to the system. The additional head 12 m, is thus wasted across the valve as heat and noise.

The effects of over sizing the pumps are:

• Operation at excess capacity requires greater NPSH®
• High pressure drop through foot valve
• Cavitation leading to efficiency drop and premature failure of rotor
• Greater power consumption
• High initial purchase cost
• Internal loading and hydraulic radial thrust and
• Vibration and dehydration.

The solutions are:

• Reduce impeller dia
• Reduce speed and
• Go for new correct sized pump.

Excessive throttling pulp stock pumps leads to dehydration due to high velocity, vibrations, greater internal radial load reducing life of rotating element. Hence, the pumps are not to be operated for extended periods, less than 1/4th of BEP capacity.

It is needless to mention that for any machine preventive and routine maintenance is mandatory for its successful operations.

* General Manager - Marketing, Sam Turbo Industry Private Limited

The ADR consists of a closed cylindrical reservoir inbuilt with a pipe as an entry point for the liquid situated in the upper part of the reservoir. It also consists of a point for the gas to enter from and a pipe for the liquid to exit situated in the lower part of the reservoir.

The liquid’s entry is designed in such a way that it enters the reservoir at a specific velocity. It is set at a tangent to the cylindrical body of the reservoir in such a way that when the liquid is introduced into the reservoir, under the effect of the centrifugal force the liquid creates a spiral, rotational movement around the reservoir’s axis of revolution.

Advantageously, in upper zone of the side wall on the inside of the reservoir are placed a number of slides which extend to the inside of the reservoir and towards the aforementioned inner wall. These slides act as obstacles in the path of the liquid circulating in spirals on the inner wall of the reservoir.

How ADR works

The liquid is introduced into the reactor through the entry point placed in the upper part of the reactor. The liquid is introduced at a determined speed which owing to the centrifugal force allows the liquid to be plastered onto the inner wall of the reactor and thereby be spread in a thin layer. The gas to be dissolved is introduced into the reservoir. This gas forms a pocket in the upper part of the reservoir. The lower part of this gas pocket is defined by the end of the pipe that drains out excess gas.

Regulatory valves are located on the pipe of the liquid’s exit point and on the point from where the excess gas is drained out. This allows the reservoir to be maintained under pressure and to regulate respectively the flow of the liquid flowing through the reactor and the flow of the gas being drained out. This is done in a way to maintain the level of liquid.

While circulating in spirals on the lateral inner wall of the reservoir, the liquid comes in contact with slides which disperse the liquid into the gas pocket. This is how, a larger quantity of liquid dispersed in small drops into the gas pocket offer a much higher surface area of exchange than by dispersing smaller amounts of gas into large quantities of liquid.

Advantages:

• Lower power consumption by approx 25%

• Reduction of head of high pressure pump

• Reduction of recycle flow rate of the high pressure pump

• Higher air dissolution- higher by 20% compared to any air dissolving devise.

Center Press Sheet Removal Double Doctor

Abstract:

There are many applications on a paper machine where the installation of double doctors will help to improve machine efficiency through reduction of sheet breaks and elimination of rewetting. This paper will discuss the history of double doctors, the principles of how this technology works and the many benefits associated with the installation of double doctors. It will describe the many different applications where this technology can be successfully installed on paper machines and results from various installations.

Introduction:

Doctors tend to be one of the most neglected pieces of equipment on a paper machine which is quite surprising considering they are highly critical pieces of equipment in maintaining and improving paper machine runnability. For many years there were 3 main reasons for doctoring a roll on a paper machine:

• Sheet Removal: The Doctor System must be correctly located for removal of the sheet from the surfaces of rolls and cylinders and to assist the machine operators in transferring/transporting the sheet of paper from the wet-end to dry-end of the machine prior to the reel.

• Roll Cleanliness: The Doctor System must be correctly designed to help with the removal of fiber and dirt from the surface of rolls and cylinders, thus maintaining roll cleanliness and improving paper quality and machine efficiency.

• Roll Conditioning: The Doctor System must be correctly designed to ensure that the doctor constantly conditions the roll and cylinder surfaces, without causing damage, so ensuring that a top quality product is produced on the machine. For example using an abrasive type fiberglass blade to polish a rusty old drying cylinder that has been put back in service.

In recent years, another very important reason for doctoring has come to light.

Couch Roll rewetting on fourdrinier machine

• Water removal: There are many areas on a paper machine where we can see rewetting. Installation of double doctors on couch rolls and suction press rolls helps eliminate this rewetting and improve paper machine runnability.

In most of the Indian paper mills couch rolls and suction press rolls do not have double doctors and we can clearly see a rewetting problem with most of these applications.

History:

Due to the surface texture of granite it is possible for dirt and fiber to get inside small cracks and fissures on the roll surface and get below the level of the doctor blade making it impossible to doctor off.

Similar to a foil blade on the fourdrinier of a paper machine, when the surface of the roll passes a doctor blade at high speed a partial vacuum is created behind the doctor blade. This vacuum pulls fine and dirt particles off the roll surface and they build up on the back of the doctor blade until they form “crumbs” that become heavy enough to fall off, go through the press nip and cause a sheet break. Sometimes these crumbs are actually sticky and don’t fall off but continue to build up until the blade actually starts to lift away from the roll, if there is a sheet break when this is happening it will cause sheet passing and potential damage to the doctor and press felt.

In addition to this problem, most paper mills were installing steam showers to try to increase machine production and to improve moisture profile control. This caused additional heat distortion problems for single doctors on press applications. The solution to all of these problems: Double Doctors

For press roll double doctors, the second blade holder and blade act as a crumb catcher to prevent “crumbs” from going back into the nip and causing a sheet break. A shower is installed between the two doctor blades and is directed behind the lead blade to prevent dirt build-up thus preventing the lead blade from lifting away from the roll. Cladding and insulation can also be included on this type of double doctor to eliminate any heat distortion problems associated with steam showers in close proximity. The end result of this type of double doctor is reduction of sheet breaks and improved efficiency. Many machines in India today are being upgraded to have a binip (or similar) press arrangement. Double doctors for these types of upgrades are a must.

Water removal Double Doctors:

Double doctors for water removal can be installed in many applications such as suction press rolls, suction pick-up rolls, blind drilled press rolls, suction pressure rolls for tissue machines, but the most common place is the suction couch roll application upon which we will base the following discussions. As mentioned above, water removal double doctors are not common in the Indian pulp and paper market and most couch rolls in this market do not have double doctors. Most machines have a simple rubber wipe as shown below. Please notice the amount of water that gets past the wipe and rewets into the wire and paper web.

Heavy duty style K Flex holder for sheet removal applications

The same principles apply to water removal double doctors that apply to sheet removal press double doctors. The “foil effect” of the roll surface passing a doctor blade at high speed creates a partial vacuum behind the doctor blade. For water removal, this vacuum pulls water and fiber from within the drilled holes. Therefore, the lead doctor blade removes rimming surface water and cleans the roll surface, but it also creates a partial vacuum behind the lead blade which pulls water out of the drilled holes. A second blade is needed to remove this water ejected or pulled out of the drilled holes, hence there is a need for double doctor technology, for water removal.

Benefits derived based on the installations of water removal double doctors:-

• Rewetting is eliminated and most installations have experienced 1-3% increase in sheet dryness post couch with a double doctor as compared to the old rubber wipe mounted on the save-all.

• The rubber wipe i s not consistently touching with the same pressure therefore rewetting is inconsistent resulting in wet streaks. With a double doctor, all the water is removed therefore no wet streaks and improved moisture profile.

• A dryer stronger sheet entering the press section usually results in a reduction of sheet breaks.

• Some of the installations have resulted in improvement in wire life and pick up felt life.

• Partial vacuum created by the blades keeps the holes open and clean, with less risk of hole plugging which in some instances results in less time between roll changes.

Important Design Considerations: Doctor Support

When designing a doctor support, we normally try to design so that the blade line passes as close as possible to the centre of the doctor pivot point. This will ensure that the energy transmitted into the doctor passes through the stronger point of the construction and at the same time, minimizes the effect of turning moments around the pivot.

The centre of gravity should be located as close as possible to the pivot, so that the support always has a turning moment towards the surface of the roll or cylinder. This is to produce a very safe doctor installation. If holding restraints, such as pneumatic cylinder or turnbuckles are removed or fails, the doctor will rest up on roll surface and not fall away from roll causing possible injury.

A doctor beam is normally supported in two bearings at the tending and drive sides of the machine and it will have some natural deflection. Careful engineering calculations are required with any doctor design, to minimize this deflection and to ensure maximum allowable deflection on any support is not exceeded. In addition to minimizing the natural deflection in the design of the structure, it is important that the doctor beam is machined to compensate for this calculated (verified by measurement) deflection. It is also important to ensure that when the doctor is in its operating position that net deflection with respect to the roll surface being doctored is zero.

K Flex Klean self cleaning and self sealing blade holder for water removal applications

Another extremely important consideration regarding doctor support design is the natural frequency of the doctor. If the doctor natural frequency is the same frequency at which the roll rotates, then the doctor will vibrate and give very poor doctoring results and risk damage to the roll cover. To ensure the doctor will not vibrate due to the resonant critical speed of the roll, computer simulation is used to calculate the doctor deflection, moment of inertia, and natural frequency. The roll rotational frequency at maximum paper machine design speeds should never exceed75% of the doctor’s natural frequency.

Stress relieving of the support structure after welding and prior to machining is essential. This is usually done by vibration method.

Important Design Considerations: Blade Holders

For both sheet removal and water removal type double doctors, self contouring flexible type blade holders are a must. The “K” Flex double tube type holder is shown in figure # 6.

With this type of blade holder the blade is held by a flexible top plate with bolted on fingers on 2” (or 50 mm) centers. These fingers are individually pivoted from the bottom tube tray bolted directly on the machined surface of the doctor support structure. Between the bottom tray and the fingers, there are two air tubes on either side of a pivoting rod. Inflating the right hand tube (shown on figure 6) pushes the blade against the roll. Since this tube itself and the top plate are flexible the blade will self contour and follow exactly the shape of the roll surface. This is especially important on sheet removal applications as any point where the blade does not contact the roll could be a potential place where the sheet could get past the blade potentially causing a sheet wrap or even damage to a felt or to the doctor. By regulating the air pressure in the load tube we can easily adjust blade loading pressure to the desired level and ensure uniform blade contact pressure across the roll face. Exhausting the air flow from the right hand tube and switching air flow into the left hand tube (as shown on figure 6) allows the blade to lift away from the roll for easy blade changing.

Sheet removal positions, especially press doctors, are very demanding applications and often see the highest blade loading pressures of any doctor on a paper machine. It is critical that the blade holder is of very heavy duty design, while still maintaining its flexibility.

For water removal double doctors, the lower profile “finger on top” K Flex Klean design blade holder (see figure 7) is preferred. This blade holder operates exactly the same way as the K Flex. The only difference is we move the finger from the underside of the top plate to the top side. This allows the air loading tube to fully contact the underside of the top plate and the tube tray thereby completely sealing the blade holder and not allowing water to flow through the blade holder.

Conclusions:

Proper and effective doctoring is critical in providing good paper machine runnability. Double doctors are a cost effective way in realizing improvements in efficiency. The addition of double doctors to critical sheet removal press applications can result in a reduction in the number of sheet breaks and improved paper quality. Similarly water removal double doctors help to prevent sheet rewetting and improve sheet dryness at the couch, suction press and suction pick up roll applications.

When setting circular blades, special attention is to be paid to overlapping of blades, contact pressure, shear plane angle, and forward slip.

When users detect that cutting quality starts to deteriorate or that the service life of machine knife becomes shorter, this is quite often due to the technical condition of the cutting section which is less than ideal and not due to the tool itself. Well trained repair staff and machine operators have to be able to detect, analyze, and eliminate sources of disturbance. However, corresponding knowhow and experience are often missing.

Training and Practice

In order to be able to respond to cutting problems appropriately and quickly, operators have to dispose of a vast knowledge of the influencing factors on the cutting process. Theoretical and practical training regarding troubleshooting forms a solid basis to be able to analyze and solve problems accurately.

Preventive Maintenance – Avoiding Emergencies

In many companies, it has been customary for some time to take preventive actions because everyone knows that emergencies bear risks which are always connected with resulting costs, too.

• On the one hand, this includes the availability of the machine. Regarding machine downtimes, stocks can always be justified.

• Regrinding intervals of the knives are to be selected in a favorable way to avoid bottlenecks right from the beginning. Here, the grinding quality should have priority over the quickest possible return of the knife.

• An internal or external grinding service guaranteeing manufacturer’s quality is to be ensured to provide reproducibility of the cutting performance.

• But it is even more essential to perform regular preventive maintenance of the equipment consistently and in good time. In the day-to-day business, this is often neglected due to deadlines or capacity bottlenecks which may be connected therewith.

• Defective knife supports or worn bearings may entail significantly longer downtimes or quality problems and customer complaints.

Operators, knife manufacturers, and service providers equally profit from talking openly about homemade problems such as machine failures by material jam (crash) which may damage knife support or transverse blade drums.

Operating errors should also be discussed openly as making mistakes is human and all of us can learn from them. Common efforts and team spirit in this respect do not only ensure the sustainable efficiency of the production process but also enhance it.

Turn some employees into your in-house experts holding the company’s know-how!

Preventive maintenance and repair ensure your product quality, avoid customer complaints, and increase the
efficiency of your production processes and the profit situation connected therewith.

The cross-direction moisture profile of paper and board is often the most critical quality parameter since it  affects so many other sheet properties – strength, dimensional stability and, most importantly, how the sheet runs in customers’ printing and converting machines. Running at the right average moisture is important, but even point-to-point quality is the vital requirement.

So with improved customer quality and a good return on investment in mind, the Cascades East Angus mill in Québec’s Eastern Townships installed a Metso IQAquaPro CD moisture profiler on their number 4 kraft paper machine. The new moisture profiler and associated cross-direction controls were added to an existing Metso PaperIQ QCS and system and Damatic XDi DCS system.

Normand Langlais, Paper Mill Superintendent, provides statistics which show the good return on investment for the profiler and controls.

These include:

• Moisture profile rejects were reduced by about 84% in 2008 compared to 2007.

• The cost of claims was down by 40% in 2008 compared to 2007. This was mainly related to the IQAquaPro start up.

• Average sheet moisture increased from 5.0% to 5.7%.

• Steam consumption was reduced by about 2.7%, as a result of improved profiles and other dryer section improvements, and machine speed was increased about 2.9%.

On the all-important quality side, he reports much improved uniformity of paper properties – notably moisture and related strength properties – and Cascades East Angus’ customers have noticed the improvements.

Moisture uniformity affects strength uniformity

Langlais explains why moisture uniformity is so important to the mill and its customers. “A big difference in point-to-point moisture in a roll affects the sheet tear and tensile strength. Some of our clients slit our paper into 1 inch (2.5 cm) bands. If there is a big difference in moisture it is difficult to slit.”

Number 4 machine is a 122 inch (310 mm) trim specialty machine making about 55 kraft and recycled paper grades with grammage ranging from 37 to 120 GSM. These grades include kraft envelope papers, butcher wrap, grease resistant paper for pet food bags and extensible paper, which is used for construction. The machine is equipped with a Clupak unit for stretchy extensible paper and a size press for flat papers.

Stability needed quickly

With typically 4 grade changes per day, the machine is often in a state of transition and it takes some time to stabilize the process and product quality. Minimizing the time required to level the moisture profile and achieve prime quality is critical and that is why the mill needed a quick, responsive way to control. Adding the profiler and controls to the existing Metso equipment was a technically sound way to go, the mill staff reasoned. The new profiler was interfaced to the existing control system via a new metsoACN module.

The expected ROI would come from reducing mill waste and customer claims. Also, some energy savings could be possible if the sheet could be run with higher moisture content. The mill had previously invested in machine upgrades to improve the moisture profiles and save energy – including a uni-run felt section, new siphons and changed press crowns. But Langlais says they needed to do more to get better results.

The IQAquaPro is located on the first top drying cylinder after the machine’s size press and Clupak unit. This location gives the moisture lots of time to penetrate the sheet before it reaches the reel. It was a tight fit in an older machine, but the installation logistics were effectively worked out by the mill staff & Metso. Felt roll positions were changed to maintain the same dryer felt length.

Serge Tremblay, project engineer, reports that the complete profiler support equipment package provided by Metso, including atomizing air and water supply and treatment equipment, helped to minimize the mill’s engineering requirements. “It was easy to connect; we just had to supply the platform,” he says. The profiler on the machine was installed during the Christmas 2007 shut and was up and running in early 2008. Tremblay reports the project was under budget.

“Instant good results”

Normand Langlais says the results – much improved moisture profiles – were noticed almost instantly. “It has made a big difference in the control of the machine. The operators accepted the system very quickly“, he says. The operation of the unit is trouble free as no streakiness or dripping problems were noted after the startup.

Metso guaranteed the control performance on certain key grades. The results are shown in Figure 1.

2-sigma CD moisture variation has been reduced by about 90% on two key grades. Most importantly, the peak to peak variation has been reduced to 0.5% or under. This means the sheet strength properties across a small span are uniform as well. And, as the final proof of perfor-mance, that uniform sheet runs well in customers’ converting machines.

Normand Langlais “The results – much improved moisture profiles – were noticed almost instantly. “It has made a big difference in the control of the machine. The operators accepted the system very quickly, “he says.

The new moisture profiler and associated cross-direction controls were added to an existing Metso PaperIQ QCS and system and Damatic XDi DCS system.

Serge Tremblay reports that the complete profiler support equipment package provided by Metso, including atomizing air and water supply and treatment equipment, helped to minimize the mill’s engineering requirements. “It was easy to connect; we just had to supply the platform,” he says.

IQAquaPro control hardware is located in cabinets on the machine drive side.

The IQAquaPro is located on the first top drying cylinder after the machine’s size press and Clupak unit. This location gives the moisture lots of time to penetrate the sheet before it reaches the reel. It was a tight fit in an older machine, but the installation logistics were effectively worked out by the mill staff & Metso.

Within the scope of research project a test procedure was developed for the accelerated light-induced ageing of inkjet prints based on studies conducted on the ageing behaviour of coloured inkjet prints under realistic environmental conditions. The first part of this article is devoted to discussing ageing phenomena under realistic environmental conditions which laid the foundations on which the test procedure was subsequently developed.

Ageing under realistic environmental conditions

The studies were based on prints made using four representative inkjet printing systems designed for home, office and archive use. Comparisons were based on two bubble inkjet printers (printer A with an aqueous inkjet ink; printer B with an aqueous alternative inkjet ink), a piezoelectric printer with solvent wax ink (printer C) as well as a piezoelectric printer with an aqueous inkjet ink (printer E). The prints made by a colour laser printer (printer D) served as the reference for comparison purposes. A wide selection of different papers was printed in order to cover different applications.

To simulate application-oriented conditions, the prints were subjected to the following ageing conditions for approximately one year:

• Climatised room 23°C / 50% rel. humidity, in darkness (in a closed folder),

• Office (artificial light, dry),

• Behind a window pane (with incident sunlight).

A testo 545 light meter with a measuring range from 0 to 100,000 Lux was used to determine the amount of radiation the print samples were exposed to while they were being stored in the office and behind the window pane. The colour changes in the prints were evaluated at predetermined time intervals.

Storage in darkness

The trials simulated the type of long-term storage that is most common both in archives and in the home, i.e. storage of documents in folders without incident light. The trials were intended to show the extent to which prints fade even under such storage conditions and how properties such as legibility or surface strength change.

The results showed that colour changes occurred in the prints in the visually barely noticeable range (change in chromaticity coordinates ÄE to 5) irrespective of the paper grade or printer. Even here, it became clear that findings regarding the stability of the prints are always dependent on the printerpaper- ink system and therefore cannot be generalised (see Figure 1.) Under these ageing conditions, the stability of the inkjet prints was equal to or better than the stability of the laser prints (see , laser printer = printer D). It is absolutely essential to systematically select papers that match the corresponding printer-ink system to obtain prints that are as resistant to ageing as possible.

When the prints stored in darkness were evaluated visually a year later, their photo quality showed no changes that would disturb the human eye (change in chromaticity co-ordinates of ÄE < 1). Even legibility, surface strength and resistance to agents did not change at all during the year of storage compared to the original state. Moreover, these results were totally independent of the printer or paper used. The only exceptions were the prints that had been made on recycling paper (papers 8 and 9) using printer E, as these prints were found to have suffered a slight deterioration in print contrast after a year of storage.

The results of these trials demonstrated that storage of inkjet prints in darkness under constant climatic conditions did not exhibit any disadvantages compared to prints produced by electrophotographic printing.

Office storage not in direct daylight

Prints frequently lie on desks or hang on wall charts for longer periods of time in offices and are thus exposed to artificial light in a day-night rhythm. The results of these trials demonstrated that inkjet printers achieved results comparable to those of laser printers even under such storage conditions. The changes in chromaticity co-ordinates in most of the printer-paper combinations were generally less than one ÄE of max. 5. The colours yellow and magenta showed the greatest reaction to the office light situation.

The storage of prints in the office, however, resulted in visible colour changes in those prints that had been printed using wax ink (printer C). All of the other prints produced by printers A and E (except for the yellow colour of printer E) and the laser prints (printer D) remained significantly less than ÄE = 3 in most cases (see Figure 4). In the case of the prints made by printer C (wax ink), the most significant changes were found in the colours magenta and cyan, e.g. on paper 3 (inkjet, standard matte) with as much as ÄE = 8, whereas only slight changes in chromaticity co-ordinates were observed in the case of black and yellow with a ÄE from 1.5 to 2. The results were highly dependent on the paper grade used.

It is evident from Figure 4 that the ageing stability of the prints can be optimised by selecting an appropriate grade of paper. The trial findings revealed that prints made on special inkjet printing paper (papers 1 to 4) did not necessarily achieve the best ageing stability. The prints made with printer A (bubble inkjet) on multipurpose papers 6, 10 and 12 proved to have much greater light stability than the prints made on special inkjet printing paper. Under the storage conditions described above, inkjet prints thus achieved virtually the same good light stability as coloured laser prints when the printers and papers were selected appropriately.

Storage behind a window pane in direct daylight

Prints are often exposed to direct sunlight for long periods of time behind a window pane as notices or announcements, placards or posters or as documents mounted in glass picture frames. This ageing situation was simulated in another set of trials.

When prints were stored behind a window pane, much higher irradiation energy including part of the daylight UV radiation acted on the prints. The colour differences were accordingly greater after a year of storage. Significant differences again became evident depending on the printer-ink-paper combination that was used (see Figure 5).

The colour stability of the inkjet prints was significantly poorer in the case of yellow and magenta when compared with the stability of the laser prints (printer D). The results obtained with the colours black and cyan, on the other hand, were comparable to those produced by electrophotographic printing (see Figure 6).

Conclusions

When inkjet printing technology is used to produce coloured prints, both the fields of application and the resulting requirements and storage conditions must also be taken into consideration. Systematic selection of the three components of the printing system, i.e. the printer, printing ink and paper, is essential to achieve optimum ageing and light stability. PTS can provide effective support when a decision is pending for a specific print system using the requirements profile developed in the project for different fields of application and with the help of the test method developed for accelerated light-induced ageing of coloured inkjet prints.

In this endeavor of the paper mills towards reducing operational costs and increasing operational efficiency, the selection and use of appropriate design of forming fabrics plays a silent but very vital role. Even though the cost of machine clothing is below 2% of total manufacturing cost, the loss to a paper mill due to improper selection of a fabric or its usage or due to its poor performance can be colossal. Forming fabric is the first point of sheet forming. Any mistake here can hardly be erased from the final sheet.

Mr. D. K. Raina

Here we present an overall synopsis of the Paper Machine Clothing industry with the help of expert insight provided by , who has over 25 years of industry experience and currently heads the marketing at Wires & Fabriks (SA) Lt. He joined the industry in 1983 as Management Trainee in BILT. Thereafter he was the Sales & Export Manager in Porritts & Spencer (Asia) Ltd for 10 years till 1993.

Mr. D.K. Raina

Trends in Paper Machine Clothing (PMC) industry

The PMC industry has followed the usual evolutionary trend in terms of new designs and value added features but the main change has been in the papermakers’ outlook towards its role. It is no more just a conveyor carrying fibers from the headbox to the press section forming a quality sheet and giving a good life. It is no more just a “production” related item but a consumable which affects the “productivity” and helps in reducing costs.

Key drivers leading to Transformation in Indian Paper industry

Printing industry in general drives the Paper industry regarding the quality parameters of papers which then translates this requirement to machine clothing suppliers. Apart from heavy R&D related activities and technological developments done by PMC manufacturers all over the world, including us to satisfy the same, the main credit goes to the Indian papermakers. They have started looking at things beyond just the fabric life. Rather they now analyze it as a fabric which can help in improving the overall machine operational efficiencies. Even the medium and small paper machines are employing qualified paper technologists and engineers which has brought a sea change in the outlook adopted towards forming fabrics or machine clothing in general.

As a result, now with regard to forming fabrics, papermakers talk about their customized requirements as dictated by the market scenario as there are specific designs available which help in reducing costs, improve retentions, low sheet breaks ,longer life etc.

Forming fabrics reduce costs.How?

Forming fabric designs have been developed over the years from single layer to triple layer. But now with new generic designs, like our newly developed Shute-Support Triple Layer or STL, which belongs to SSB range of fabrics, it is possible to save on overall costs. This is done by lowering energy costs by reducing drag load, optimize retention aid chemical cost by improving mechanical retention, lower operational costs due to less sheet breaks etc.

Change in Forming Fabric Design along with the Change in Paper Machine Speed

In recent years, paper machine speeds have got a lot faster and much of this progress can be traced back to massive strides undertaken in gap forming technology. But, as machines get faster, ever greater pressure is placed on the forming fabrics to perform to equivalent or even higher standards at increased machine speeds. Clearly, this has a profound impact on the forming fabrics performance. For example, in a classic fourdrinier design, the number of wire revolutions per minute might be 16. But for the top wire of a gap former, the number of revolutions per minute jumps to 64, which means that dewatering times have dropped dramatically, from some 1.5 seconds to 0.17 seconds today. Clearly, if forming fabrics are to meet the challenges imposed by such changes, further improvements are crucial.

R&DFocus of Forming Fabric Suppliers

The R&D department of various companies is targeting design improvements on a number of performance characteristics that are critical in increasing formation quality at increased machine speeds. Some of the main areas to be tackled include: reducing water carrying and misting parameters, creating a finer surface that provides more support points and helps reduce sheet marking, increasing the level of mechanical retention and providing better cross-direction profiles.

With this in mind, we have developed STL forming fabrics in our plant in Jaipur, manufactured first time in India, which reduce water carrying as well as generate a higher fiber support index. High speed forming requires good drainage characteristics, especially for fast initial dewatering in the gap and the fabric structure needs to be very stable for even paper profiles, but at the same time fine enough for good mechanical retention. And in order to get the full benefit, good flexibility of the fabric in the machine direction is essential. STL fabrics fulfill all these requirements successfully. High wire tension and high dynamic forces also require very good stability properties from fabrics. As a result forming fabrics including the STL variants are becoming finer, more uniform, and more stable to match the developments seen to date in high speed forming and this trend will continue.

Chinese Competition

Well Chinese manufacturers have been there for many years yet they are visible in India in recent times only. But, the Indian papermaker is smart enough to distinguish between a “cheap” product, an “economic” product and a “premium” product. So whosoever is able to meet his “specific quality demand” and can successfully convert his “wants” into “needs” by providing required application support and technical services will be the preferred supplier, whether from China, India or Europe. We have often seen that so called cheap consumables prove very expensive at the end and sometimes the so-called high-end international designs also prove an overkill for average paper mills. The wisdom of a reliable machine clothing supplier lies in recognizing the difference between the two.

Fluoropolymer-lined systems based on PTFE/PFA prove to be economical and useful alternatives to metallic alloy piping in many applications like handling corrosive solvents in Chemical and Pulp & Paper industry like transfer of Chlorine dioxide (Cl02), NaOH, H2S04 acid etc. Few key points of this technology along with critical success factor has been discussed in this paper after having intensive experience in using Fluoropolymer lined pipes and components for handling corrosive chemicals. In Certain applications Fluoropolymer PTFE /PFA has become alternative choice to exotic material like Titanium, Tantalum, and Zirconium etc. Paper companies in India like TNPL, ITC, Century, West Coast, Abhishek Industries and many more have been benefited with this technology based solution.

TEFLON* Lined "T"

The Pulp & Paper industries face a continued and growing need for the containment of corrosive or harmful products and intermediates that reduce the service life of conventional piping and vessels. Fluoropolymers has opened the door of all new opportunities to handle corrosive solvents like Acids (H2SO4), Bleaching chemicals, Chlorine dioxide (CLO2) in Fiberline. Our R&D invented first Fluoropolymer Teflon® PTFE in 1938 which became prime material for handling corrosions in early 50’s.

Critical success factors for Fluoropolymer Lined components in Pulp & Paper Industry

The items listed below must be considered during the selection, design, and operation of Fluoropolymer-PTFE/PFA lined pipe in pulp&paper applications.

Key Operations:

• Chlorine Di Oxide Transfer Line

• Chemical handling in Fiber line&Bleaching Cycles

• Acid (H2SO4) Handling&Caustic extraction.

Liner Selection

Industrial polymers have been used since the 1950s to handle both aggressive and extremely pure process fluids. These fluoropolymers have been used in applications such as corrosion-resistant lining for process equipment which includes Lined metallic piping, fittings columns, vessels, pumps, and valves.

TEFLON* Lined Column

PTFE-lined systems offer more cost-effective service than many metal systems. This is due to their comparable installed cost coupled with lower life-cycle cost. Fluoropolymer liners are often used in chemical services with aggressive chemicals at temperatures approaching 235-250° C. The plastic lining also eliminates concern about chloride stress cracking of stainless steel.

Definition of Lined components & Liner Material selection

Fluoropolymer-lined piping combines a structurally sound metallic shell with a corrosion-resistant plastic liner. The most common plastic liners are polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polypropylene (PP), Perfluoroalkoxyalkane copolymer (PFA), perfluoro ethylene propylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE). Liner selection is primarily dependent upon the Types & concentration of chemicals, Vacuum/ Pressure conditions and normal operating temperature. The maximum temperature rating for the plastic liner may be lower for installations handling highly aggressive chemicals. PTFE has highest popularity for liner material because of high chemical inertness to nearly all chemicals, Higher temperature stability & economically feasible.

Process Operations-Thermal Cycling

For Vacuum application, Generally PTFE lined pipes up to 8 inch size works fine. For larger sizes thicker liners and counter Vacuum arrangement can be considered. Minimizing the occurrence of thermal cycling in hightemperature permeating applications and controlling the cool down cycle of the process can maximize service life of the plastic-lined piping system.

Selection of right Fabricator

TEFLON* lined valves

Selection of right fabricator is equally important for successful application of Fluoropolymer lined piping & components in chemical handling. Fabricator should follow the right guidelines during processing and handling of fluoropolymers. Their facility should meet general good manufacturing practices and products must be qualified inline with internationally recognised standards.

ASTM Qualification Standard for Lined Piping and Components

The American Society for Testing Materials (ASTM) has established standards for common plastic-lined piping products. The ASTM F1545 specifications cover requirements for workmanship, dimensions, design, construction, working pressures and temperatures, test methods, identification markings, and the materials used in the construction of the final product.

Installation & Maintenance

The successful use of lined system also depends upon installation process. Various factors like selection of right flange design, gaskets, applying torques during installation should be followed as per suppliers engineering manual. In case of Fluoropolymer lined systems, specific torque ranges to be implemented & Re-torquing is required after 24 hrs to avoid any chances of leakages. Periodical visual inspections are recommended to check any Liner, flanges, gasket failure etc. Destructive testing can be performed by statistical sampling method.

Chemical compatibility testing and Failure Analysis

Generally, fully fluorinated polymers like PTFE, PFA are almost resistant to all known solvents except few alkali metals, whereas in case of new solvent mixtures & different temperature conditions, it is recommended to check chemical compatibility with material supplier.

Design considerations

Common venting systems used by plastic-lined pipe manufacturers are a series of

1.6 mm (1 16 in) to 4.0 mm (5 32 in) diameter holes in the metallic shell, or a helical groove system inside the housing that connects flange vents (Figure 1). The venting system provides a pathway for permeating chemicals (vapor) to escape.

Case Histories

Case 1: As an alternative to stainless steel, non-metallic materials such as “TEFLON PTFE“ have gained increasing acceptance in paper industry due to their excellent chemical resistance and successful long term performance. As per above figure, verification of excellent performance is in D stage chlorine dioxide bleach stage seen at TAPPI USA where after 10 years of continuous service, TEFLON shows no evidence of cracking or failure. The inside surface of the liner was smooth and clean.

Case 2 (TNPL): Tamilnadu Newsprint & Papers Ltd located in southern India where Metso had supplied the fibreline. In Year 2007-08, complete TEFLON® lined pipes and fittings for fiber line as well as for Chlorine dioxide line were manufactured and supplied by a Fluoropolymer lined component supplier from India. They are member of DIPPN network and their facilities were qualified by DuPont Engineering USA.

Conclusion:

Fluoropolymer-lined systems prove to be both useful and economical in Pulp & Paper applications. Such systems help protect the process equipment and minimize loss of the chemical process fluids, which protects the environment. Use of proper engineering designs will offer large amount of cost saving & safety of handling corrosive solvents like ClO2 , H2SO4, NaOH etc in fiberline pulp & paper industry. These designs should acknowledge the major factors namely: service conditions, process fluid chemistry, and liner material. Indian Pulp & Paper industry is getting benefited with this technology in a big way.