TAPPI JOURNAL summaries.

SUMMARIES OF DECEMBER 2003 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.

SILVICULTURE 

GENETIC VARIATION OF JUVENILE WOOD PROPERTIES IN A LOBLOLLY PINE PROGENY TEST

APPLICATION: Genetic testing and selection could improve cellulose yield, fiber length, fiber coarseness, and reduce lignin content in Loblolly pine.

Forest biologists and wood, paper scientists, and forest company have collaborated to study the genetic variation of several important physiochemical wood properties of loblolly pine (Pinus taeda L.). Taking cores from 11-year-old trees, these scientists studied the genetic variation and the breeding potential to improve cellulose yield, fiber length, fiber coarseness, and lignin content for pulp and paper production. Earlywood and latewood of juvenile wood (Ring 3) and transition wood (Ring 8) were analyzed separately for these key traits.

Early and latewoods of Rings 3 and 8 were significantly different for [alpha]-cellulose content, average fiber length, and coarseness but not for percent lignin content. Latewood of both rings had higher [alpha]-cellulose, average fiber length, and coarseness than earlywood. Transition wood had significantly higher [alpha]-cellulose, average fiber length, and coarseness but lower lignin content than juvenile wood had. Loblolly pine families differed significantly for [alpha]-cellulose, average fiber length, and coarseness but not for lignin content.

In general, additive genetic effects explained greater percentages of family variation than dominance genetic effects. For all the traits, genetic variation increased from juvenile wood to transition wood. Although weak individual and family heritabilities were found for [alpha]-cellulose, average fiber length, and coarseness for the juvenile wood, heritability estimates for the transition wood were moderately high. Positive genetic correlations of wood density with [alpha]-cellulose, average fiber length, and coarseness indicated that breeding for wood density could help to improve the traits studied for pulp and paper production. View this paper online at http://www.tappi.org/index.asp?pid=28282

Robert Sykes, Fikret Isik, Bailian Li, John Kadla, and H-m. Chang are affiliated with North Carolina State University, College of Natural Resources. Sykes, Isik, and Li are in the Dept. of Forestry, and Kadla and Chang are in the Dept. of Wood and Paper Sciences. Please address correspondence to Dr. Bailian Li, Dept. of Forestry, Campus Box 8002, North Carolina State University, Raleigh, NC 2769-8002. Email Li at [e-mail].

RECOVERY BOILERS

MODIFYING BOILER OPERATION TO REDUCE PRIMARY AIR PORT CRACKING IN A RECOVERY BOILER

APPLICATION: Mills that experience this type of primary air port cracking problem might want to try this approach; other mills may gain insights on boiler operating parameters to avoid.

This systematic study examined the cause of severe cracking of SS304L/SA210 composite waterwall tubes at primary air ports, membrane bar wastage, and cracking of butt welds located between the bottom of the primary air ports and the floor in the recovery boiler at the Irving Pulp & Paper's Saint John mill. The results show that the severity of the problem was strongly related to the frequency and the magnitude of tube temperature excursions at the air ports, which were greatly affected by the char bed dynamics near the air ports.

The mill significantly reduced the cracking problem by operating the boiler at a lower black liquor solids content and at a higher primary air flow. These conditions appear to keep the char bed away from the air ports and help reduce tube temperature excursions.

Computational fluid dynamic modeling was used to examine the air flow and liquor spray patterns in the lower furnace. Based on the modeling results, two additional air ports were installed for the secondary air system in an effort to eliminate the recirculation flow patterns in both corners of the furnace. The additional ports would help minimize carryover, while maintaining low thermocouple activity to avoid the primary air port cracking. The data obtained to date shows that the number of temperature spikes in these corners of the boiler has been drastically reduced. View this paper online at http://www.tappi.org/index.asp?pid=28283

Honghi Tran and Shery Vafa are with the University of Toronto, Toronto, Ontario, Canada; Cindy Milbury, Bobbie Blaney, Farshad Piroozmand, Arnie Roherty, and Dan Mott are with Irving Pulp & Paper Ltd., Saint John, New Brunswick, Canada; and Blaine Anderson and Keith Rivers are with Babcock & Wilcox Canada, Cambridge, Ontario, Canada. Email Tran at [e-mail].

BLEACHING

FORMATION OF DISSOLVED HIGH MOLECULAR ORGANIC SUBSTANCES IN THE BLEACHING OF SOFTWOOD KRAFT PULP

APPLICATION: Mill personnel can use the information in this study for pollution abatement assessments, either when planning new lab studies or when designing new bleach plants, modifying an existing bleach plant, or modifying an external effluent system. The results can also provide background when developing models for bleach plants.

This study focused on the possibility of influencing the formation of dissolved high molecular substances after D(EP)DD and D(EP) bleaching of softwood kraft pulp. In laboratory experiments, we used ultrafiltration to separate molecules of different sizes from the generated filtrates. We knew that the biological degradation rate in the receiving water decreased with increasing molecular weight. The cut-off for the membranes used were 1000, 3000, and 10,000 g/mol (Dalton). We used COD and ultraviolet absorbance at 280 nm to analyze total organic substance and the amount of dissolved lignin.

The study showed that filtrates could not be stored deeply frozen before ultrafiltration. The study also showed that the cut-off value of a membrane increases during ultrafiltration. That prompted us to develop a special design for the ultrafiltration experiments.

We demonstrated that it is possible to influence the formation of high molecular material in the different bleaching stages. Conditions in the chlorine dioxide and the extraction stages must be modified to obtain the best mix between the amount of generated COD, the formation of high molecular COD, and bleaching efficiency. View this paper online at http://www.tappi.org/index.asp?pid=28284

Ulf Germgard is professor and Irene Boren and Sasha Aleksic were graduate students, Department of Chemistry, Karlstad University, SE-651 88 Karlstad, Sweden. Email Germgard at [e-mail].

RETENTION

VINYLFORMAMIDE-BASED CATIONIC POLYMERS AS RETENTION AIDS IN ALKALINE PAPERMAKING

APPLICATION: Paper mills can use the new cationic polymers as effective retention aids with conventional rosin sizes in alkaline papermaking.

Our research group has been trying to explore new retention aids and retention systems for alkaline papermaking. N-vinylformamide has an active formamido group that has some interesting interactions with cellulose fibers and rosin size particles. Its homopolymer and copolymers with cationic monomers are considered to be effective novel retention aids in the wet-end of papermaking.

In this study, the researchers synthesized two vinylformamide-based cationic polymers and characterized them by using GPC and polyelectrolyte titration. These polymers were then used as retention aids in rosin sizing under alkaline papermaking conditions.

The cationic polymers were found to be efficient retention aids for alkaline sizing of paper with conventional emulsion rosin size. Each polymer's performance in retention depends on its molecular weight and the chemical structure of its cationic portion.

Scanning electron microscopy (SEM) and electron spectroscopy for chemical analysis (ESCA) were employed to interpret the interactions between polymer molecules and rosin size particles. The results showed that the polymer molecules can cover the rosin size particles well enough to form stable complex particles. Consequently, these polymers prevent the alkaline conditions from reacting with the rosin size, and the upshot is good sizing of paper under alkaline conditions. View this paper online at http://www.tappi.org/index.asp?pid=28285

Fei Wang, Takuya Kitaoka, and Hiroo Tanaka are with the Department of Forest and Forest Products Science, Kyushu University, Fukuoka 812-8581, Japan. Email Tanaka at [e-mail].

ONLINE EXCLUSIVE PROCESS SIMULATION

ENHANCING GRADE CHANGES USING DYNAMIC SIMULATION

APPLICATION: Simulator helped to understand grade change dynamics in a multilayer board machine, and to re-tune the automatic grade change program.

Paper mills have adopted dynamic simulation as a powerful training tool, when not considered too expensive, but other applications have faced many practical difficulties at mill sites. This paper describes how dynamic simulation was used in a Finnish paper mill in developing operations in grade changes. The mill makes a minimum of one grade change per day.

The process model covers the board making process from the pulp chests to the end of the 7th dryer group of a 3-layer board machine. For many years, a specific grade change automation program (AGC) has assisted operators at the mill. AGC calculates targets for operating variables, coordinates mutual delays, and handles ramping of the variables.

The aim of the simulation study was to minimize production losses by shortening the grade change time. The simulator serves as a test bench to find better values for AGC parameters. This requires that the simulator confidently predicts the effects of the inputs (simultaneous ramps of the various operating variables) on the outputs (critical variables like moisture and basis weight). In addition, the functionality of the AGC was modeled in detail to enable what-if studies with new parameter settings.

All together, we present our experiences in using dynamic simulation to improve efficiency of a multi-grade, multi-ply board machine. The target is not to invest in new equipment in the process or control system, but to optimize operation of the present system. The paper describes the structure of the simulation model and the basic calculation principles of the simulation tool. It also includes illustrative simulation results. Today, the mill process engineers use the simulator in the mill and the first parameter changes have been carried out to the real machine. View this paper online at http://www.tappi.org/index.asp?pid=28286

Lappalainen and Juslin are with VTT Technical Research Centre of Finland, P.O. Box 1301, Fin-02044 VTT, Finland; Myller is with Stora Enso Oyj, Fin-55800 Imatra, Finland; Vehvilainen is with Metso Paper Inc., Service; Tuuri is with Andritz Oy, Pulp Mill Automation; Email Lappalainen at [e-mail].

WET PRESSING

THE BEHAVIOR OF FIBERS IN WET PRESSING

APPLICATION: Research offers a better understanding of the mechanisms of densification in wet pressing by quantifying the way individual fibers change in a sheet.

The researchers define a fiber shape factor and the twist angle of fiber cross section in paper to help quantify the changes that a sheet of paper goes through in wet pressing. Using resin embedding and confocal laser scanning microscopy, they measured the fiber shape factor and twist angle directly.

Fiber twist, fiber collapse, and gap closure were found to be the main mechanisms in the densification of the paper structure. At low pressing pressures, all three mechanisms are at work, but gap closing predominates. Increasing the pressure increases the apparent density only slightly. At high pressures, the density increase is attributable primarily to the additional twisting and collapsing of the fibers.

The analysis of the fiber shape factor showed that the degree of collapse of fibers in the handsheets is symmetrically distributed in lightly pressed sheets. Even at very high pressures, fibers in the handsheets cannot be totally collapsed by wet pressing. Furthermore, the out-of-plane fiber deflection angle of fiber segments is independent of wet-pressing pressure. View this paper online at http://www.tappi.org/index.asp?pid=28287

Warren Batchelor is senior lecturer, Jihong He is a PhD student, and Robert Johnston is a professor, all with the Australian Pulp and Paper Institute, PO Box 36, Department of Chemical Engineering, Monash University, VIC 3800. Email Batchelor at [e-mail].

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