Summaries of February 2006 peer-reviewed papers.

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COATINGS

THREE-DIMENSIONAL OBSERVATION OF COATED PAPER BY CONFOCAL LASER SCANNING MICROSCOPE

APPLICATION: A confocal laser scanning microscope with the new fluorescence stain technique can show the three-dimensional distribution of a coating binder.

The distribution of coating components and the depth to which coating penetrates into paper are important attributes in determining the final product quality. Many analytical techniques have been proposed to characterize the coating layer, but most are limited in some way or entail difficult procedures for preparing the samples.

A new method uses a confocal laser scanning microscope (CLSM) to image the coating layer after it is stained with a fluorescent dye. Rhodamine B is used as the dye because of its fluorescence at the excitation wavelength of 514 nm. Sample preparation is minimal, and no artifacts from cross sectioning methods are introduced.

The method was found to be useful in quantifying the depth of coating penetration into the paper. The coating binder was stained with Rhodamine B, but kaolin, calcium carbonate, and the base paper were stained only slightly or not at all. Because of this selective adsorption, the distribution and position of latex in the coating layer can be characterized.

Bubbles in the coated layer could be imaged by this technique. For a lightweight coated paper, it was found that coating binder penetrated into the base paper. Two coated layers of the double-coated paper could be observed by the difference in contrast. View this paper online at http://www.tappi.org/index.asp?pid=34025&ch=1

Yasushi Ozaki is with Research Institute of National Printing Bureau, 6-4-20 Sakawa, Odawara-city, Kanagawa 256-0816, Japan. Douglas W. Bousfield, and Stephen M. Shaler are with the Paper Surface Science Program, University of Maine, Orono, Maine, 04469-5737. Email Ozaki at [e-mail].

BLEACHING

DECREASING CALCIUM OXALATE SCALING BY PARTIAL SUBSTITUTION OF Mg(OH)[.sub.2] FOR NaOH IN THE PEROXIDE BLEACHING OF MECHANICAL PULPS

APPLICATION: By partially replacing NaOH with Mg(OH)[.sub.2], papermakers may be able to decrease oxalate-related scaling without sacrificing brightness in bleached mechanical pulp.

The formation of scale deposits leads to operational problems in a bleach plant. Forms of scaling include calcium oxalate, calcium carbonate, barium sulfate, and pitch. The alkaline peroxide process generates oxalate and oxalate-related scaling in the production lines of bleached mechanical pulps.

Therefore, we wanted to study the potential of partially replacing NaOH with Mg(OH)[.sub.2] as the alkali source during the peroxide bleaching of mechanical pulps. They examined its effect on oxalate formation and brightness and found that the amount of precipitated oxalate was negligible when 30-50% of NaOH was replaced with Mg(OH)[.sub.2] during bleaching. They also found that a higher brightness was achieved than reached with the NaOH-based peroxide process.

Therefore, a partial replacement of NaOH with Mg(OH)[.sub.2] should be a practical solution to oxalate-related scaling in production lines for bleached mechanical pulp. The addition of MgS[O.sub.4] to a peroxide stage can also decrease the amount of precipitated oxalate, but the addition of MgS[O.sub.4] is not as effective as the partial replacement of NaOH with Mg(OH)[.sub.2]. View this paper online at http://www.tappi.org/index.asp?pid=34026&ch=1

Li Yu and Yonghao Ni are with Limerick Pulp and Paper Research and Education Centre, University of New Brunswick, Fredericton, N.B., Canada, E3B 6C2. Email Ni at [e-mail].

PULPING

MEDIUM CONSISTENCY OXYGEN DELIGNIFICATION PERFORMED WITH A CONTROLLED CAVITATION REACTOR

APPLICATION: This work demonstrates the importance of mass transfer in oxygen delignification and how mills can benefit from working to improve it. This work also showcases an easy oxygen delignification retrofit for mills.

A U.S. mill has conducted a pilot-scale medium consistency oxygen delignification (MCOD) trial using a proprietary reactor as part of an integrated delignification system. Delignification responses were obtained for various operating conditions and multiple chemical charges. Delignification levels of 35% or more were obtained for hardwood pulp. The trials were designed to determine potential operating costs, energy consumption, operational conditions, and benefits associated with a low capital cost installation of this system into an existing washer line. Material and energy balances in conjunction with pilot plant and lab data were used to predict potential net effects of the MCOD system upon operating costs. The effects of the oxygen delignification operation upon pulp physical properties were also determined. View this paper online at http://www.tappi.org/index.asp?pid=34027&ch=1

Peter W. Hart is with MeadWestvaco Corporation, Chillicothe, OH 45601. Douglas Mancosky and Daniel Armstead are with Hydro Dynamics, Inc., Rome, GA 30165. Email Hart at [e-mail], Mancosky at [e-mail], or Armstead at [e-mail].

BLACK LIQUOR GASIFICATION 

A LOW-TEMPERATURE, BLACK LIQUOR GASIFIER MODEL FOR USE IN WinGEMS

APPLICATION: The model can be used in full mill simulations to explore the potential impact of implementing BLG technology.

Black liquor gasification (BLG) is moving closer to commercial realization. Tools to simulate its effects on pulping operations could help mill decision makers in evaluating its implementation. WinGEMS[TM] is a simulation tool that is often used in the pulp and paper industry, but it has not had a BLG block.

These researchers developed a BLG model in WinGEMS[TM] to simulate black liquor gasification and determine its effects on mill operations. Several obstacles were overcome in the creation of the block, including the need to support user-defined stream components.

To validate the model, the developers compared the results to process data. The process model generates values for output streams and back-calculates values for input streams. These values were in close agreement with data provided by the manufacturer. The BLG block is currently being used in case studies to determine the effects of varying the rates of carbon conversion. View this paper online at http://www.tappi.org/index.asp?pid=34028&ch=1

Mathias Lindstrom, Ved Naithani, Adrianna Kirkman, and Hasan Jameel are with the Dept. of Wood and Paper Science, North Carolina State University, Raleigh, NC 27695-8005. Email Lindstrom at [e-mail].

TESTING

CHARACTERIZATION OF CHEMICAL PULP FINES

APPLICATION: This study presents several simple methods for characterizing chemical pulp fines, allowing better control of fines quality.

This study presents a number of new methods for characterizing chemical pulp fines. The methods are used to measure the dewatering rate, settling rate, and viscosity of a fines suspension, which are closely related to the specific surface area of fines. The dewatering rate of the fines suspension measured with a gravimetric water retention meter that used pressure filtration coincided with the results obtained with a conventional method for measuring the drainage time in a sheet mold. The settling rate measured with a Turbiscan device, which is equipped with an optical head for scanning the sample automatically, correlated with the results of conventional visual observation. The Brookfield viscosity of the fines suspension may be dependent on the degree of hydration of the fines network. All of these new methods were found to be simple, fast, and accurate for measurement. The finer the fines fractions, the more it contributed to slowing down the settling and increasing the viscosity of the fines suspension. View this paper online at http://www.tappi.org/index.asp?pid=34029&ch=1

Taegeun Kang is a research associate and Hannu Paulapuro is a professor at the Laboratory of Paper Technology, Helsinki University of Technology, P.O.Box 6300, FIN-02015, Finland. Email Kang at [e-mail].

ONLINE EXCLUSIVE CORROSION

MATERIALS ISSUES IN BLACK LIQUOR STEAM REFORMING/GASIFICATION

APPLICATION: This research will help improve the safety and reliability of black liquor steam reforming/gasification systems.

Steam reforming/gasification of the black liquor produced during wood pulping offers the potential for more efficient energy recovery, reduction of emissions, and improved safety. This technology is currently being implemented in two North American semichemical pulp mills. As might be expected in scaling up any process system, a number of problems have been encountered.

Degradation of metallic and refractory components has been observed in several areas. This paper presents the results of the examinations of a number of these damaged metallic components. It describes some of the material failures in the two low-temperature reformer/gasifier systems and then presents the solutions being applied or the approaches to finding a solution. View this paper online at http://www.tappi.org/index.asp?pid=34068&ch=1

James R. Keiser and Bruce A. Pint are with Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA; Robert DeCarrera is with Georgia-Pacific Corporation, Atlanta, Georgia, USA; David G. Newport is with ThermoChem Recovery International, Baltimore, Maryland, USA; and Robert S. Rowbottom, now retired, was with Norampac, Mississauga, Ontario, Canada. Email Keiser at [e-mail].