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    Articles techniques évalués par des pairs PAPTAC - Décembre 2009

    DEMONSTRATION OF THE PRECIPITATOR DUST PURIFICATION (PDP) SYSTEM AT TEMBEC’S SKOOKUMCHUCK KRAFT PULP MILL

    N. Jemaa, G. Tan, A. Thibault, M. Paleologou, R. Adderley, G. Baxter, M. Sheedy, D. Swaine, J. Wearing, and J. Lockhart

    The Precipitator Dust Purification (PDP) chloride removal system was demonstrated at Tembec’s Skookumchuck kraft pulp mill. The system was able to treat about 1 t/d of ESP dust. The resin bed removed sodium chloride with an efficiency ranging from 90 to 99% depending on the chloride level in the feed solution and the mode of operation. The recovery of sodium sulphate and sodium carbonate was over 97% during the recycle mode of operation. Some of the metal ions (e.g. zinc and iron) slowly accumulated on the resin bed but a periodic acid wash was able to displace them.Demonstration of the Precipitator Dust Purification (PDP) System at Tembec’s Skookumchuck Kraft Pulp Mill.

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    EFFECTS OF EXTRACTIVES FROM MOUNTAIN PINE BEETLE-ATTACKED LODGEPOLE PINE ON KRAFT MILLS

    L. Allen, A. Gagné, and P.Watson

    This report addresses the impact of mountain pine beetle infestation on several extractives-related issues in kraft pulp mill operation: extractives in pulp, pitch control, and effluent treatment. The work, funded by the Mountain Pine Beetle Initiative of Natural Resources Canada, involved visits to five western Canadian kraft mills to observe operating conditions, collection of samples for subsequent laboratory measurements, and overall analysis of the combined information. Work in separate reports has shown that the use of infested wood usually causes higher extractives (especially increased resin acid content) in the wood to the digester and this results in an increased solubility of fatty and resin acid soaps in black liquor. Hence the use of infested wood resulted in a greater extractives load to be removed in brownstock washing for good pitch control. Use of green- and red-stage wood did not cause a significant change in the normal quantities of extractives in pulp across the bleach plant and at the pulp machine. In the mill using gray-stage wood, the solubility of extractives in black liquor was even higher and brownstock washing was more important for their removal. The quantity of extractives, especially the unsaponifiables, in the final pulp was significantly higher in the mill using gray-stage wood. In this mill, the resin acid concentration in the final effluent was high. The gray-stage results require further confirmation in more mills.

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    EFFECTS OF EXTRACTIVES FROM MOUNTAIN PINE BEETLE-ATTACKED LODGEPOLE PINE ON TMP PLANTS AND PAPER MILLS

    L. Allen, A. Gagné, and P.Watson

    This report assesses the impact of using mountain pine beetle infested wood in integrated TMP and paper mills on extractives-related issues, such as: extractives in pulp, pitch control, friction properties of paper, and effluent treatment. Use of infested wood in TMP pulp and paper mills did not seem to cause significant changes in the normal amounts of extractives and their chemical composition across the mills. Use of a pitch dispersant for pulping of green and red stage infested wood to prevent plugging of grooves in refiner plates may be necessary due to the high variability in extractives levels. The friction properties of newsprint from infested wood were within the normal range for newsprint. Effluent treatment plants successfully reduced the extractives of effluents during use of infested wood to near-zero values. As only three mills were involved and none was using gray-stage wood, the results are preliminary.

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    IMPACT OF A KRAFT MILL CLOSURE ON AMBIENT LEVELS OF PARTICULATE MATTER (PM2.5) IN THE COMMUNITY

    B. O’Connor

    Ambient PM2.5 monitoring and chemical characterization was conducted in a kraft mill town during operation and after the permanent shutdown of the mill. Analysis of the data collected during this period indicated that the mill emissions were not contributing significantly to the elevated levels of PM2.5 in the community on an hourly or a daily basis. For the 1-h data points, the range of PM2.5 concentrations for winds coming from the direction of the mill was similar before and after the mill shutdown. With regards to the composition of the ambient PM2.5, the closure of the mill did result in some minor changes. However, for the two largest PM2.5 components, comprised of sulphate and the organic fraction, the mill shutdown did not change the relative amounts, indicating that there are other significant contributing sources in the area.

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    NEUTRAL PH CONVERSION IN MECHANICAL GRADES – FINE BALANCE OF CHEMICAL AND MECHANICAL CONTRIBUTIONS

    P. Pruszynski, C. Smith, and P. Sturtevant

    After most alkaline conversions in wood-free grades were completed in the late 1990’s, neutral pH conversions in mechanical grades emerged as the next major industry trend. Converting mechanical grades of paper to higher operating pH is in most cases driven by the desire to introduce calcium carbonate based fillers, which offer a number of cost and quality advantages to the papermaker.  In addition, higher operational pH is known to increase web strength development, which allows for higher filler loadings and a reduction of expensive Kraft fiber, commonly added to improve wet web and finished product strength. This increased potential for fiber substitution and the resulting reduction in furnish costs were primary drivers for neutral pH conversions in their early stages. Geographical differences in availability and cost between kaolin and calcium carbonate filler explain the regional differences in advancement of converting of mechanical paper grades production to neutral pH.  

    Neutral pH applications in mechanical grades are defined by the introduction of reactive fillers, which raise the operating pH to a level that can be potentially harmful to brightness development.  Successful neutral pH conversions and neutral pH operation require knowledge, technology and cooperation between the papermaker, the filler supplier and the wet-end retention, sizing and microbiological control supplier.

    In this paper the focus will be placed on the recent neutral conversions that, contrary to earlier projects driven mainly by economics, require constant attention to the quality benefits. In such conversions a team of mill personnel and the filler supplier would benefit strongly from a partnership with a quality oriented solutions provider. Evans [1] calls for a “holistic approach” to such conversions - from the pulping/bleaching plant to the printing press. We will discuss the most important elements of neutral pH conversions and illustrate how proper chemical program selection and its application may contribute to successful outcome of these important projects.

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    THE HALF-LIFE OF BIOLOGICAL KNOTS IN KRAFT PULPING

    M. MacLeod, and A. Dort

    How many times do you have to cook biological knots and the knotter rejects derived from them in a bleachable-grade kraft mill before they are reduced completely to fibrous material and dissolved organics? And what is the yield of pulp from such material? To find the answers, we experimented with stockpiled knotter rejects and with fresh biological wood knots. With either material, re-cooking demonstrated that knotter rejects continued to beget further knotter rejects. Relative to normal wood chips, biological knots cooked far slower and to lower pulp yields; after re-cooking, the pulps became progressively worse in average fibre length and overall strength. Re-cooked knotter rejects from biological knots had a half life of two complete cooks in bleachable-grade kraft pulping. Because mixing biological knots or their knotter rejects descendants with normal chips makes kraft pulping much more heterogeneous and impairs pulp yield and product quality, they should be purged as efficiently as possible from chip furnishes going to digesters, and knotter rejects containing them should go to hog fuel boilers or landfills rather than digesters.

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    EFFECT OF THE FINAL ECF BLEACHING STAGE ON EUCALYPTUS KRAFT PULP PROPERTIES – A COMPARISON BETWEEN HYDROGEN PEROXIDE AND CHLORINE DIOXIDE

    P.E.G. Loureiro, P.J. Ferreira, D.V. Evtuguin, and M.G.V.S. Carvalho

    The factors contributing to the differences between chlorine dioxide and hydrogen peroxide final ECF bleaching stages are discussed with respect to the properties of Eucalyptus globulus kraft pulps. The higher beatability of pulps bleached with a final peroxide stage was assigned to the better fibre swelling capacity. For laboratory beaten fibres, dry zero-span tensile strength is a more suitable predictor of fibre strength than wet zero-span or intrinsic viscosity, at least when comparing pulps with different bleaching history. A comparison between laboratory and industrial bleached pulps is also provided.

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    USING PROCESS-BASED COST MODELING TO EVALUATE PROCESS MODERNIZATION ALTERNATIVES

    M. Janssen, P. Naliwajka, and P.R. Stuart

    This paper presents a methodology for design decision making based on a cost accounting model that incorporates the principles of Activity Based Costing (ABC). Such an approach provides a process-based view on the operating costs of the mill process, both direct and overhead costs. Furthermore, the presented cost modeling approach significantly increases the granularity and transparency of the results when compared to a classical techo-economic study, and permits the examination of some critical design scenarios. A case study demonstrates this approach by evaluating several process design alternatives for increased deinked pulp (DIP) production and cogeneration at an integrated newsprint mill.

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    POLYMER CONFORMATION EFFECT ON THE FIBRE RETENTION PROCESS — STUDY OF BLOCKING AGENT SYSTEMS

    O. Oulanti, B. Chabot, F. Brouillette, and C. Daneault

    Bridging polymer conformation effect on retention was investigated by a sequential addition of two cationic polymers using a blocking agent system. The linear non-bridging polymers improved the bridging polymer retention efficiency at certain pre-adsorbed polymer dosages. Maximum retention levels corresponded to an optimum surface neutralization. The pre-adsorbed polymers promote an expanded bridg¬ing polymer conformation improving the retention process. Increasing the pre-adsorbed polymer dosage strongly disturbed the system and decreased the bridging polymer retention efficiency. The pre-adsorption of a branched non-bridging polymer presents a similar trend to linear polymers.

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    INCREASING FLEXIBILITY FOR TIME OF DAY PULPING AT ALBERTA NEWSPRINT COMPANY

    S. Singh, C. Mills, and N. Wild

    In 2005, ANC undertook a capital project, known as the TMP Production Project, to increase the TMP plant production rate in order to better manage electrical power costs and to improve the heat recovery. The TMP plant in its previous configuration had more than adequate capacity to meet the day-to-day pro¬duction requirements of the paper machine. However, ANC operates in a fully deregulated electrical power market and rigorously practices time-of-day (TOD) pulping to minimize electrical power costs. Lately, the higher pulp demand due to increased paper machine production reduced the flexibility and subsequent cost effectiveness of TOD pulping. The goals of the project were to de-bottleneck the TMP in order to increase the peak production rate from 800 to 900 bdmt/d, while utilizing refiner steam for clean steam production.

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