Summaries of June 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.

For more information about joining TAPPI, or to subscribe to TAPPI JOURNAL, contact the TAPPI Member Connection Center: Phone: [phone] (USA), 1 800 446-9431 (Canada), [phone], by email at [e-mail], or visit www.tappi.org.

PITCH CONTROL

PITCH REDUCTION IN A KRAFT ASPEN INTEGRATED MILL PULPING FRESH CHIPS

APPLICATION: This research outlines how pulp producers can achieve goals including low ash pulp, low dichloromethane (DCM) pulp, or elimination of talc from their process, through use of the proprietary pitch dissolver dispersant tested.

A kraft mill running aspen as its furnish uses approximately 20 metric tons/day of talc. The mill wanted to replace talc in its process because the handling and preparation took 6 work-hours per day. The mill had tried various dispersants, but none performed to its expectations. The mill wanted to prevent the brown stock screens from plugging and either maintain or reduce the final pulp dirt counts, without affecting pulp quality.

The mill decided to try a proprietary pitch dissolver/dispersant other than nonyl/alkyl phenol ethoxylates or ethoxylated alcohols. (The latter two pitch dispersants are considered to be carcinogenic.) Results obtained include a 68% decrease in colloidal pitch in the final bleached pulp filtrate, and 3.3% more DCM extractives removed from the bleached pulp during the trial phase; also, the paper machine efficiency improved by 30 h/month and the wire life increased by 15%. View this paper online at http://www.tappi.org/index.asp?pid=32459&ch=1

Amin Manji is technical manager/process and project engineer; John Karagiannis is vice president sales; Satish Salgar is technical director; Jim Constant is CEO and president, Constant America Inc., Montreal, Quebec, Canada. Email Constant at [e-mail].

DILUTION

FLOW REGIME EFFECTS ON THE SPREADING RATE OF A NYLON FIBER SUSPENSION JET IN A RECTANGULAR CHANNEL

APPLICATION: Concentration, fiber length, and flow parameters affect the behavior of fiber suspensions in a confined shear flow.

How can we measure and control the process of diluting thick stock? Thick stock is diluted when a stream of dilution water mixes with a concentrated jet of fiber suspension. Dilution reduces the mass concentration of the fibers in the suspension and leads itself to better formation. As this research shows through both qualitative and quantitative evidence, it also helps to disrupt the fiber network prior to mixing.

In a fiber suspension jet introduced symmetrically to a dilution water flow, the suspension was disrupted by a flow restriction placed in the nozzle. Digital imaging was used to observe the growth of the shear layer and the quality of the mixing field. The purpose was to separate the effects of the velocity ratio and shear on the mixing efficiency.

The growth in the shear layer was correlated to the pressure drop across the restriction. The growth in the mixing layer was found to be affected primarily by the difference in velocity between the fiber flow and the water flow when the jet was highly turbulent. The mixing layer became less uniform when the fiber length and fiber concentration were increased and when the pressure drop was decreased across the flow restriction. These results show that mixing is improved when the fiber network is disrupted prior to mixing. View this paper online at http://www.tappi.org/index.asp?pid=32460&ch=1

At the time of this research Eric Andrew Schmidt was with the Institute of Paper Science and Technology; he is now with the Swedish Pulp and Paper Research Institute. Junyong Zhu is with the USDA Forest Products Laboratory. Email Schmidt at [e-mail].

BLACK LIQUOR GASIFICATION 

PRESENTATION OF A DRY BLACK LIQUOR GASIFICATION PROCESS WITH DIRECT CAUSTICIZATION

APPLICATION: With the new process, the efficiency of producing electrical power is expected to be 30-35%.

A new type of black liquor gasification process promises significant advantages over Tomlinson boilers and wet gasification processes. In this new process, black liquor is injected into a circulating fluidized bed, with sodium titanate ([Na.sub.2]O*(Ti[O.sub.2])[.sub.3]) as the fluidizing medium. The organics are gasified mainly by steam reforming, because the temperature is relatively low (below 870[degrees]C) and the water content of the black liquor is relatively high (>20% water). The black liquor inorganics consist mainly of sodium carbonate and sodium sulfate.

In the reactor, sodium carbonate is converted into [Na.sub.2]O*Ti[O.sub.2], which is removed from the bed and dissolved in water to give 4 NaOH + [Na.sub.2]O*(Ti[O.sub.2])[.sub.3]. After dewatering, this material is reinjected into the fluidized bed. The sulfate is first reduced to [Na.sub.2]S, and then most of the sulfur is evaporated as [H.sub.2]S after [Na.sub.2]S reacts with C[O.sub.2] + [H.sub.2]O. The hydrogen sulfide is absorbed in a scrubber from the exhaust gas, after dust is filtered out. Sodium hydroxide and sodium carbonate constitute the absorbent, and the process equipment is designed in such a way that [H.sub.2]S is selectively absorbed from C[O.sub.2], giving a 1M solution of NaHS.

The sulfide-rich solution is used to pre-impregnate the wood chips, allowing modified cooking, which gives stronger and brighter fibers out of the digester. The gas is reheated after dust is removed and then combusted in a gas turbine/steam turbine cycle, to produce 2-3 times more electricity than currently produced in steam cycles with conventional recovery boilers. View this paper online at http://www.tappi.org/index.asp?pid=32461&ch=1

Erik Dahlquist is with Malardalens Tech. University, 721 23 Vasteras, Sweden 46-70-6212680. Andrew Jones is with International Paper, 6285 Tri-Ridge Blvd., Loveland, OH 45206. Email Dahlquist at [e-mail] or Jones at [e-mail].

LIME KILN

EFFECTS OF PROCESS VARIATION ON RING FORMATION IN LIME KILNS

APPLICATION: Mills can reduce the operating costs associated with ring formation.

A number of lime kilns were studied to find connections between process variations and the tendency for rings to form. Ringing problems are linked to the temperature profile inside the kiln, which is affected by variations in lime mud dryness. Repeated fluctuations in temperature cause rings to grow thicker.

NIR spectroscopy was used to measure lime mud dryness in a mill trial in an effort to reduce the fluctuations in dryness. Some deviations arose in the measurements, however, because the lime mud had a tendency to cover the NIR optic. If this problem could be remedied, the dryness measurements could be used to determine how much water to add to the lime mud.

When rings form, the operation of the lime kiln has to be interrupted for cleaning. However, some practical steps can be taken to reduce ring formation. Mill personnel can add crushed limestone, monitor the shell temperature, and inspect the kiln frequently. A power shot system that releases vaporized liquid C[O.sub.2] has also proven effective in reducing the costs associated with ring formation. View this paper online at http://www.tappi.org/index.asp?pid=32462&ch=1

Maria Bjork is with Stora Enso Pulp Competence Centre, Box 9090, S-650 09, Karlstad, Sweden. Email Bjork at [e-mail].

FIBER BONDING

A NEW METHOD FOR DETERMINING THE RELATIVE BONDED AREA

APPLICATION: A new method has been developed for calculating the relative bonded area from sheet density and fiber cross-sectional shape.

The relative bonded area (RBA) is the fraction of total available fiber surface that is bonded. It is a quantity widely used in regard to paper mechanical properties. There are two methods for measuring RBA, the BET method, which is based on nitrogen absorption, and the light-scattering method. The light-scattering method is quicker and is generally preferred.

The main difficulty with this technique lies in determining the value of [S.sub.0]. In the light-scattering method, RBA = ([S.sub.0] - S)/[S.sub.0], where S is the light-scattering coefficient of a sheet and [S.sub.0] is the light-scattering coefficient for a completely unbonded sheet. If a papermaker could make an unbonded sheet, then the instruments could measure [S.sub.0] directly. Since that isn't possible, different values of S first have to be determined from sheets made to have different tensile strengths or different sheet densities. The values of S correlated with either tensile strength or density can then be used to extrapolate the value of [S.sub.0].

We found that neither correlation was useful because the fiber shape changes with wet pressing. Therefore, we developed a new method for calculating the RBA in which the scattering coefficient and sheet density are corrected for changes in the fiber cross-sectional shape. With the data corrected, there is a linear correlation between the scattering coefficient and sheet density. Based on this correlation, a simple new formula was derived for calculating the RBA. View this paper online at http://www.tappi.org/index.asp?pid=32463&ch=1

Warren Batchelor and Jihong He are with the Australian Pulp and Paper Institute, Monash University, Australia. Email Batchelor at [e-mail]

SIZING

PET POLYESTER RESINS USED IN THE WET END AT NEUTRAL-ALKALINE PAPERMAKING CONDITIONS

APPLICATION: This study will help in developing new technologies for PET polyester resin or other anionic sizes to be used in neutral-alkaline papermaking systems.

This study reports efforts to develop new technologies for PET polyester anionic resin and rosin to be used in neutral alkaline papermaking conditions and associated technologies.

We tested a new PET polyester alone and in combination with rosin as a wet-end additive in acid and neutral-alkaline papermaking systems. The results showed that the PET is a good size for products intended to be water repellent or resistant. Compared to conventional sizing processes under neutral-alkaline condition, premixing the resin and rosin improved their sizing efficiency, water resistance, and strength. The results compared favorably with sizing results obtained under acid conditions.

We found that rosin or polyester, or both, reacted with alum to form a carbonic-aluminum complex directly. The complex not only avoids the hydrolysis of alum, but also changes the rosin or polyester, or both, from anionic to cationic. The order of premixing processes affected size efficiency. We noted that the polyester favors acid conditions, because it is anionic. View this paper online at http://www.tappi.org/index.asp?pid=32464&ch=1

Yong Zou and Jeffery S. Hsieh are with the Pulp and Paper Engineering, School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0100; Eric Mehnert and John Kokoszka are with EvCo Research, LLC, 1575 Northside Drive, NW, 400 Atlanta Technology Center, Suite 450, Atlanta, GA 30318; Tim S. Wang is affiliated with Georgia Tech and EvCo. Email Hsieh at [e-mail].

ONLINE EXCLUSIVE PROCESS AUTOMATION

AUTOMATIC CONTROL OF ADDITIVES WITH MODERN ONLINE MEASUREMENT TECHNOLOGY

APPLICATION: This paper describes control strategies adopted in different areas of the paper mill and the benefits related to automatic closed loop control of wet-end additives using the latest available measuring technologies.

Advanced online measuring technology enables automatic control of wet-end additives in paper and paperboard machines. In this study, doses of fixatives (coagulants), retention aids, and deaerator chemicals were automatically controlled with online measuring devices on a high-speed newsprint machine in Sweden. On the basis of online cationic demand measurements, fixatives were controlled to a specific anionic trash set point. This control substantially increased chemical performance, while simultaneously improving retention aid chemical performance and control.

On the paper machine, in-line consistency transmitters controlled retention aid chemical dosages, resulting in more stable paper machine performance. Online measurements of dissolved and entrained gases in the approach system enable mills to control additions of deaerator chemicals into the white water. When reviewing the overall results of the study, we found that modern online measuring technology enables significant productivity increases for papermakers. View this paper online at http://www.tappi.org

Roland Berger is senior applications specialist, BTG Americas, Point Claire, Canada; Daniel Watzig is technical specialist, BTG Muetek Germany, Herrsching; Heinz Ziegler is professor doctor, Munich University of Applied Sciences, Germany; and M. Fasth is production engineer, Holmen Paper Braviken, Sweden. Email Berger at [e-mail].