Summaries of January 2006 peer-reviewed papers.

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PROCESS SIMULATION

CONSEQUENCES OF LIGNIN PRECIPITATION IN THE PULP AND PAPER INDUSTRY 

APPLICATION: The research from this program will lead to more economic, ecological, and energy efficient processes for making pulp and paper.

We evaluated the overall economic and energy consequences of the lignin precipitation process proposed by the Swedish national EcoCyclic Pulp Mill research program. The study compared four different bleached kraft pulp model mills, representing greenfield mills with different steam demands and varying surpluses of thermal energy that can be precipitated as lignin. The results suggest that 37%-50% of the lignin in the black liquor must be removed if the thermal energy surplus generated by the model mills is to be exported as lignin. From an energy savings perspective, the most important consequence is that the power balance changes significantly when precipitating lignin, in some cases even leading to a power deficiency in the mill. Other important consequences include an increased live steam demand for evaporation and a decreased load in the recovery boiler. We concluded that it is reasonable from an energy perspective to precipitate lignin in the evaluated model mills.

At the given economic conditions, the model mills with lignin precipitation have similar total costs as the model mill without lignin precipitation, if the lignin price is approximately US$ 12/MWh. At today's pricing of biomass fuel, this means that it must be possible to sell the lignin at a higher price than bark to make lignin precipitation interesting from an economic perspective.

The lignin price at which the model mills with lignin precipitation have similar total costs as the model mill without lignin precipitation changes with changing economic conditions; the most important parameters are the electricity price and the cost for carbon dioxide (C[O.sub.2]). If the cost for C[O.sub.2] is eliminated, the lignin price necessary decreases to below US$ 9/MWh, and the possibility to use flue gases instead of pure C[O.sub.2] for the precipitation must therefore be studied further. View this paper online at http://www.tappi.org/index.asp?pid=33846&ch=1

Ulrika Wising is with the NSERC Design Engineering Chair, Process Integration in the Pulp & Paper Industry, Chemical Engineering Department, Ecole Polytechnique, Montreal Canada; Jessica Algehed and Thore Berntsson are with the Department of Chemical and Biological Engineering, Chalmers University of Technology, Goteborg, Sweden; Lennart Delin is with AF-IPK AB, Stockholm, Sweden. Email Wising at [e-mail].

COATING

COATING IMPROVES THE BRIGHTNESS STABILITY OF WOOD-FREE COATED PAPERS CONTAINING HIGH-YIELD PULP

APPLICATION: Mills have an opportunity to use more high-yield pulp in wood-free coated papers by adjusting the coat weight to improve the brightness stability.

Mills can increase bulk and reduce costs by replacing hardwood kraft with high-yield pulp in wood-free coated papers. However, there is some concern about the effects of high-yield pulp on brightness stability.

The researchers studied how the brightness stability of coated wood-free paper is affected by pigment coating and the substitution of high-yield pulp for hardwood kraft pulp. In this work, they sought the answers to two specific questions:

1. Can coating improve the brightness stability of coated papers containing high-yield pulp and, if it can, by how much?

2. Can a paper containing high-yield pulp have brightness stability equal to that of a wood-free coated paper?

Light-induced brightness loss occurred as a result of both high-yield pulp substitution and yellowing of the coating color. However, coating does improve the brightness stability. How much improvement occurs depends on the high-yield pulp substitution and the coat weight. For a 15% substitution of high-yield pulp, a coat weight of 20 g/[m.sup.2] gave the same brightness stability as a 100% kraft sheet coated at 4 g/[m.sup.2].

An empirical model was developed to estimate the effects of high-yield pulp and coat weight on the brightness stability of wood-free coated papers. This model proved quite accurate in predicting the brightness stability. View this paper online at http://www.tappi.org/index.asp?pid=33847&ch=1

Zhirun Yuan, John Schmidt, Cyril Heitner, and Xuejun Zou are with Paprican, Pointe-Claire, QC, Canada, H9R 3J9. Email Yuan at [e-mail], Schmidt at [e-mail], Heitner at [e-mail], or Zou at [e-mail].

RECYCLING

THE EFFECTS OF CHANGING ONP QUALITY ON A NEWSPRINT MILL

APPLICATION: This report highlights the need to prepare for changes in raw materials and to work with suppliers to address quality issues.

One of the most significant changes in the recycling industry in the last several years has been the shift from source-separated to commingled collection systems. The NORPAC newsprint mill in Longview, Washington, USA, has used recovered fiber as a part of its raw material furnish for 14 years and now consumes more than 250,000 tons annually. During this time, as more and more of the mill's old newsprint (ONP) suppliers have switched to commingled collection, the quality of the raw material has decreased substantially. To maintain the high newsprint quality standards required of the mill's customers, additional maintenance, reject disposal, and fiber costs of more than US$2.5 million per year have been incurred. Increased equipment wear, due primarily to glass and other abrasive contamination, has increased maintenance costs more than 300%. Pulper rejects, which are landfilled and consist primarily of plastics, tin, glass, and aluminum, have increased 800%. Other fiber-related costs have increased by 740%. In the drive to reduce recycling collection costs the recovered fiber-consuming mill has been substantially and adversely affected. There is a strong need for more balance in this system. View this paper online at http://www.tappi.org/index.asp?pid=33848&ch=1

William K. Sacia is with Weyerhaeuser Company and Jay Simmons is with Weyerhaeuser Company, NORPAC. Email Sacia at [e-mail].

CORROSION

SOOT BLOWER LANCE TUBE CORROSION IN RECOVERY BOILERS

APPLICATION: This report may help mills identify and resolve recovery boiler lance tube corrosion problems.

Severe internal corrosion of soot blowers lances in two recovery boilers was likely a result of flue gas infiltration into the lance tubes, which formed an acidic condensate that rapidly attacked the lance material. The problem was rectified by improvements to the low pressure air system that ensure continuous purging of the soot blower lances to keep the flue gases out. The experience highlights the importance of a properly functioning purge air system for soot blowers. View this paper online at http://www.tappi.org/index.asp?pid=33849&ch=1

At the time of this work M. Ishaq Jameel and Nelson Oliveira were with Clyde Bergemann, Inc., they are now with the Anthony Ross Co.; Honghi Tran is with Pulp & Paper Centre, University of Toronto; Augusto C. Lovo was with Aracruz Cellulose S.A., now with Kvaerner Pulping. Email Jameel at [e-mail].

ENZYME TREATMENT

APPLICATION: Mills can apply xylanase enzyme to reduce the total equivalent chlorine demand in the bleaching process, to reduce the AOX generated.

Market and environmental demands are pressuring pulp mills to reduce the consumption of chlorine and chlorine dioxide in their bleaching processes. At the mill that was the focus of this study, xylanase enzyme was already being used as a semipermanent prebleaching chemical. The purpose of this study was to lend support to the understanding that enzymes are effective in reducing the total equivalent chlorine with hydrogen peroxide applied in the first extraction stage.

Enzyme treatment decreased the bleaching chemical load by about 8 kg of total equivalent chlorine per ton of pulp, which slightly reduced the AOX in the effluent discharge. The enzyme treatment did not significantly affect either the production rate or the pulp strength. However, substitution increased in the chlorination stage by 8%. Consequently, it appears that enzymes can be used to lower the total equivalent chlorine demand in the bleach plant and the bleaching costs with little impact on the pulp quality. View this paper online at http://www.tappi.org/index.asp?pid=33850&ch=1

At the time of this work Amin H. Manji was with Skeena Cellulose, he is now with A.H. Lundberg, Vancouver, BC. Email him at [e-mail].

POLYMER COATINGS

THE RECYCLABILITY OF PAPERS TREATED WITH ENVIRONMENTALLY FRIENDLY PET POLYESTERS

APPLICATION: By changing its wet-end chemistry to include recycled PET, a mill can maintain the paper's performance while making it easier to repulp broke.

New water-dispersible polyesters made with recycled polyethylene terephthalate (PET) have been used successfully as paper coatings for their barrier properties against water, vapor, and oil. Used soda bottles, polyester film, and PET fibers are the primary sources of recycled PET. The polyester water-barrier coating has replaced wax coatings, making it possible to repulp and recycle coated papers.

We studied papers made with these polyesters to determine how well the paper can be repulped and recycled at different dosages and under different repulping conditions. We also studied how these polyesters can be used as wet-end additives to increase the paper's strength and water resistance.

The polyesters can be used with wet-strength chemicals such as polyamide epichlorohydrin to strengthen paper while maintaining its capability of being repulped. The polyester and PAE mixture forms a new high-molecular-weight resin, PET-PAE. PET-PAE forms covalent bonds and adhesive bonds with fibers. This adhesive bonding helps increase the paper's repulpability. By changing its wet-end chemistry to include recycled PET, a mill can maintain the performance of its paper while making it easier to repulp broke. View this paper online at http://www.tappi.org/index.asp?pid=33851&ch=1

Tim S. Wang, Jeffrey J. Krueger, and Jeffery S. Hsieh are with Pulp and Paper Engineering, School of Chemical and Bimolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0100. Peter Pellitier and John Kokoszka are with EvCo Research, LLC, 1575 Northside Drive, NW, 400 Atlanta Technology Center, Suite 450, Atlanta, GA 30318. Email Wang at [e-mail].