Summaries of April 2005 peer-reviewed papers.

TAPPI JOURNAL is a monthly publication that includes full-text, peer reviewed research papers exploring every aspect of pulp and papermaking. Each issue presents technically sound, applications-based research; special insights from the authors; and more. TAPPI Membership includes access to all TAPPI JOURNAL content online at www.tappi.org. In addition, convenient print and electronic subscription options are available; TAPPI members receive substantial subscription discounts.

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FIBER PROPERTIES

HYDRODYNAMICS OF INDIVIDUAL PULP FIBERS

APPLICATION: The Rotating Tank Hydrodynamometer (RTH) is a new device designed to measure the hydrodynamics of different pulp fibers, which may help to predict the separation of different pulp fibers in hydrocyclones.

Designed to measure the hydrodynamics of different pulp fibers, a new device may help predict the separation of different pulp fibers in hydrocyclones. The Rotating Tank Hydrodynamometer (RTH) was previously validated with spheres, copper wires, and nylon fibers. Now it has been used to test softwood kraft, softwood TMP, hardwood kraft, and hardwood CTMP fibers. The testing led to a number of observations.

The orientation of a fiber in the rotating tank depends strongly on its initial orientation, which fibers tend to maintain during the entire radial settling process. The orientation of a pulp fiber largely determines how fast it settles, whereas the shape of the fiber has little to do with it. In general, the settling velocities of pulp fibers vary widely, probably because of variations in fiber diameter and wet density.

In these experiments, the hydrodynamic characteristics of individual wood fibers were measured under conditions simulating those in a real hydrocyclone. Hydrocyclones are used to group fibers by their characteristics to improve sheet formation. View this paper online at http://www.tappi.org/index.asp?pid=32003&ch=1

Sheldon I. Green and Brad Wong are with the Dept. of Mechanical Engineering, University of British Columbia. 2324 Main Mall, Vancouver, BC, V6T 1Z4, Canada. Email Green at [e-mail].

FELTS

THE STRENGTH OF PERIODIC PRESS SECTION MARKS IN PAPER

APPLICATION: Press fabric manufacturers can use this method to design tailored solutions for mark-sensitive press positions, and papermakers can use these ideas to run their press sections more efficiently.

Manufactured by methods that involve periodic or repeating patterns, the press felt passes through the press nip of the paper machine with the weak, partially consolidated fiber web. The surfaces of the two are pushed together with a pressure of up to 10 MPa. The press fabric produces periodic variations in the paper structure and surface, which may be imperceptible or may not be acceptable at all.

What is the relationship between the degree of marking and fabric structure and paper machine conditions? A new method has been devised to allow papermakers to predict the felt marking quantitatively by taking into account felt construction, sheet furnish, and pressing conditions.

In this technique, a pressure map is created for the load distribution arising from the press felt's structure under constant applied load. This pressure map is converted to a digital image and analyzed with fast Fourier transform (FFT) image analysis techniques to quantify its separate periodic and stochastic components. Next, the components of pressure distribution are analyzed with regard to how they affect the structure of the sheet. Machine and furnish variables are also considered, particularly the in-going moisture content, grammage, pressing pressure, and machine speed.

By comparing the likely degree of marking for an uneven first press felt with that for a much smoother final press felt, we showed that marking is always more likely to occur in the downstream presses. We were surprised to find that higher pressure can actually lead to less marking. View this paper online at http://www.tappi.org/index.asp?pid=32004&ch=1

Formerly at the University of Manchester, Michael R. Dowling is currently with Hugh Baird College, Liverpool, UK. Stephen J. I'Anson and Richard W. Hoyland are with the School of Materials, University of Manchester, Sackville Street, Manchester, M60 1QD, UK. Sharon M. Hoole is with Voith Fabrics Blackburn Ltd. Blackburn, UK. Email Dowling at [e-mail]. I'Anson at [e-mail], Hoyland at [e-mail], and Hoole at [e-mail].

RECYCLING

THE ATTACHMENT FORCE OF INK TO PAPER IN PAPER RECYCLING OPERATIONS

APPLICATION: The findings of this study may help recycling mills increase their deinking efficiency.

A range of ink and paper combinations find their way into the feed furnish of a newspaper deinking plant, in addition to ONP (old newspaper). That includes OMG (old magazines) and a wide range of advertisement inserts and office paper. A change in furnish composition can create problems attaining pulp quality targets. This is apparent during certain periods of the year, such as peak advertising periods. One reason for this problem is an increase in the portion of furnish having a high ink-fiber attachment strength. The ability to measure the ink-fiber attachment force allows these differences to be quantified. In this study, we used a Couette device to measure ink removal as a function of applied force for various ink-paper combinations found in a typical ONP feed furnish. The quantity of ink removed was measured using image analysis.

This study showed that the ink-fiber attachment force for aged magazines, advertisement inserts, and xerography printed paper is significantly higher than that of newsprint grades. Due to the magnitude of force required to detach these highly bonded inks from the fiber surface, a significant quantity likely remains attached to fiber following repulping. Reducing the ink-fiber attachment force can reduce the quantity of recalcitrant ink. This can be achieved by increasing the process temperature or adding appropriate chemicals to the pulper. Extending the repulping time may also increase removal of the highly bonded ink, but can also lead to redeposition. This ink can also be detached by applying higher shear forces during dispersion, for example. View this paper online at http://www.tappi.org/index.asp?pid=32005&ch=1

Frantisek Ruzinsky and Chad P.J. Bennington are with the Department of Chemical and Biological Engineering and Pulp and Paper Research Institute of Canada Pulp and Paper Centre, The University of British Columbia, Vancouver, BC, Canada V6T 1Z4. Email Bennington at [e-mail].

PULP YIELD

ESTIMATING THE PULPING YIELD BY CARBOHYDRATE ANALYSIS

APPLICATION: Kraft mills with continuous digesters can use this method to estimate the yield gain when additives are introduced or to control the yield when process parameters are changed.

Determining the pulping yield for a continuous digester is not easy. It usually involves determining the pulp mill mass balances over at least three months of production. A simple and precise method for quantifying carbohydrates in pulps should prove helpful to mills when process parameters are changed or when yield-increasing additives are introduced.

Such a method has now been developed. It is based on using HPLC to determine the glucomannan content of the pulp. Easy to use and fairly inexpensive, the method involves an enzymatic hydrolysis of the pulp followed by a second hydrolysis with trifluoroacetic acid (TFA). The results are comparable to the TAPPI method T 249 cm-85. The utility of this method has been confirmed in both laboratory experiments and full-scale mill experiments. View this paper online at http://www.tappi.org/index.asp?pid=32006&ch=1

David Vaaler is a Ph.D. student and Storker T. Moe is an associate professor at the Dept. of Chemical Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway. Kristin Syverud is a senior research scientist at the Paper and Fibre Research Institute (PFI), Trondheim, Norway. Berit Seem is a process engineer at Peterson Linerboard, Moss, Norway. Email Moe at [e-mail].

WOOD CHIPS

EFFECTS ON CHIP SIZE DISTRIBUTION WHEN AN EXTRA SCREEN IS ADDED IN SCAN-CM 40:01

APPLICATION: When an extra screen is introduced, the new chip distribution will require the mill to revise the quality control system used to evaluate the chips it purchases.

Chip dimensions are commonly characterized by laboratory screening methods. The most commonly used method in Scandinavia has been SCAN-CM 40:94. A new method has been introduced, SCAN-CM 40:01, in which an extra screen has been added. With 13 mm round holes, this screen divides the F3 accept class of 40:94 into two new classes, F3a and F3b, for large and small accepts.

When the analysis method is changed, mill personnel should know what to expect in terms of differences in the chip distribution. The differences in the accept fraction should be taken into account when a new quality control system is developed. The quality index affects the payment schedule for purchased chips. One of the objects of this study was to analyze the differences in chip size distribution between the old and new SCAN methods.

When chips were screened according to SCAN CM 40:94, the F3 accept class held about 86% of the chips. When screened according to the new method, the accept amount for the same chip sample increased by 1%, split into 65% F3a and 22% F3b. Accordingly, the pin chip class (F4) decreased by 1% when the chips were screened by the new method. The new method cannot screen out pin chips as effectively as the old method can, and more pin chips are left in the accept fractions trays. No differences could be detected for oversize chips (F1), overthick chips (F2), or fines (F5).

The results of this study showed that the amounts of large and small accept chips are relatively consistent for chips from a single sawmill, but large differences can be found among different sawmills in the proportion of these chip classes. View this paper online at http://www.tappi.org/index.asp?pid=32007&ch=1

Anders Bjurulf is with Norske Skog, P.O. Box 329, 1326 Lysaker, Norway. Email Bjurulf at [e-mail].

ONLINE EXCLUSIVE PROCESS CONTROL

MONITORING PARTICULATE MATERIAL FORMATION IN A KRAFT FURNACE RECOVERY BOILER

APPLICATION: This work advances efforts to enhance recovery boiler operations and control.

This study considers the potential use of neural networks to monitor particulate material formation during recovery boiler furnace operation. We built neural networks using 12 months of normal industrial operation data. The networks inputs were chosen according to available industrial information and process knowledge. The networks output describes the number of particles produced per minute. We initially used feed-forward neural networks, but the results were unacceptable because the information from normal operation data was inadequate. As an alternative approach, we investigated using discrete radial basis function networks to classify the amount of particles in size intervals. The results show that the proposed methodology can satisfactorily describe the particulate material formation, mainly as a monitoring tool for plant operation. View this paper online at http://www.tappi.org/index.asp?pid=32008&ch=1

Andrea O.S. Costa is with Curso de Engenharia Sanitaria e Ambiental, Diretoria da Area de Ciencias Exatas, UnilesteMG, Av.; Mauricio B. de Souza Jr. is with the Departamento de Engenharia Quimica, Escola de Quimica, Universidade Federal do Rio de Janeiro; Evaristo C. Biscaia Jr. and Enrique L. Lima are with the programa de Engenharia Quimica (PEQ), COPPE, Universidade Federal do Rio de Janeiro. Email Costa at [e-mail] and Lima at [e-mail].