Showing papers in "Appita Journal in 2010"

TCF bleaching of eucalypt kraft pulp with oxone.

Abstract: TCF delignification and bleaching of kraft eucalypt pulp using ozone and oxone under alkaline conditions has been investigated. The pulp samples were bleached in two stages of oxone (Ox) treatment using an AZOx1Ox2 sequence. Pulp brightness greater than 84% ISO was achieved. The effects of oxone charge, alkali charge, bleaching temperature and time on the bleaching response were studied. The colour removal was determined from the chromaticity coordinates (L*, a* and b*) and 98% colour removal was achieved. Accelerated ageing experiments showed excellent brightness stability with very little brightness reversion (or thermal degradation) of the oxone treated pulp. Improvements in pulp strengths compared to ozone and acid treatments were achieved along with significant HexA removal demonstrating the feasibility of oxone in TCF bleaching.

Recent trends in research, development and application of membrane technology in the pulp and paper industry

Abstract: (2). Even though water constitutes less than 10% of the final product, it acts as a carrier throughout the production process. Depending on the type of process, water is used from the initial stage of debarking, through pulping, washing, bleaching and papermaking with between 1 and 16 m3/tonne used at any stage. In addition to water, chemicals, fillers and sizing agents are also extensively used. As a result, the final amount of effluent or wastewater is significant (6 to 200 ML/tonne) and because of this the pulp and paper industry has historically been labelled as one of the most polluting industries. The characteristics of pulp and paper mill effluents such as high biological and chemical oxygen demand (BOD and COD), colour, suspended solids, additive content (including fillers, acids, bases and starch) all contribute to environmental pollution if discharged without treatment (3). With increasingly stringent environmental regulations and cost of fresh water, especially in developed countries, the pulp and paper industry is looking for improved options for treating its incoming water and effluents. Conventional methods such as using clarifiers and biological treatments are being replaced or improved using membrane technology. This paper is based on a literature review of more than 150 publications over the period of 1999 to 2008 using three databases, the ScienceDirect, Scopus and Compendex, as well as proceedings from annual conferences of pulp and paper technical associations such as those of Appita (Australia and New Zealand) and Tappi (Atlanta based).

Study of pitch colloidal stability using a Photometric Dispersion Analyser

Abstract: This paper describes the use of a photometric dispersion analyser (PDA) to study and quantify the effect of wood resin preparation and salt on the colloidal stability of wood resin dispersions. The PDA technique has two major benefits over other techniques in that it can quantify the aggregation kinetics under dynamic shear conditions and at low concentrations of colloidal material. It is very sensitive to small changes in the solution and provides information about the floc structure and homogeneity. To ensure reproducible results when analysing colloidal wood resin dispersions, conditioning of the tubing and a constant flow rate and stirring rate were required. The PDA signal response with time for the wood resin dispersions shows three distinct regions: a growth region, a peak region, and a decay region. The slope of the initial growth region was used to measure the kinetics of coagulation and to determine the stability ratio, W. The critical coagulation concentration of different salts was also determined. The timeweighted variance of the PDA output showed that potassium salts resulted in more homogeneous aggregates than those formed with the addition of magnesium salts.

The effect of process conditions on pulp quality development in low consistency refining of mechanical pulp - TMP

Abstract: High consistency (HC) defibration followed by secondary stage low consistency refining (LC) is an energy efficient process in mechanical pulping that has been explored for some time. In this study ...

Effect of Printing Parameters on Delamination of Board in Sheet Fed Offset Printing

Abstract: Delamination of board in sheet fed offset printing has become a frequent source of complaints. Both printing parameters and structural properties of board affect delamination tendency however little attention has been given to the printing parameters. The purpose of this study was, through printing trials and physical simulation, to find out the effect of printing parameters on delamination. High printing speed promotes delamination. Similarly, high ink viscosity at low shear rate, among other ink and printing parameters, had an obvious effect on delamination. Both printing speed and ink properties affect the maximum ink tack in ink splitting. The force at the delaminating interface is proportional to this ink tack. Other printing parameters which contributed to delamination of board to a certain degree were printing press configuration, number of dry backtrap nips, ink density, printing blanket compressibility, blanket smoothness, nip pressure, nip indentation, and fibre-orientation in the printing sheet.

Mg(OH)(2)-based hydrogen peroxide refiner bleaching: influence of extractives content in dilution water on pulp properties and energy efficiency

Abstract: Two refiner bleaching trials on TMP and SGW rejects using magnesium hydroxide and hydrogen peroxide were conducted in a reject refiner. Clear filtrate from a disc filter was used as dilution water during the first trial (normal mill operation) and fresh water was used during the second trial. Refiner bleached pulp had approximately nine %ISO higher brightness than reference pulps in both trials using a peroxide charge of 25 kg/t pulp. The brightness gain increased to 12 %ISO after high consistency storage at 755 degrees C for 30 minutes. The bleached pulp from the first trial had 10% lower tensile index compared to reference at similar refining energy. The extractives content on the surfaces of the bleached fibres (surface coverage measured by ESCA) was 20% higher compared to the unbleached reference pulp when clear filtrate was used as dilution water. Within this surface extractives content increase, the increase of triglycerides and steryl esters was largest, almost doubling in value. Acetone extraction of the pulps led to higher apparent sheet strength. The increase was equal for both the reference and the bleached samples but the bleached pulp still had inferior strength properties compared to the reference pulp. When a second trial was carried out with fresh water as dilution, much less difference in the strength properties of bleached and unbleached pulp was observed. It is suggested that addition of alkali to the refiner caused extractives in the clear filtrate to destabilise and re-deposit onto fibre surfaces. The fact that removal of extractives with acetone did not bring the strength of bleached pulp up to the level of the reference pulp suggests that extractives may have influenced the fibre development process of the bleached pulp fibres in the refiner.

Optimization of pressure filter performance by refractometer - Mill investigations

Abstract: The performance of a pressure filter was studied under mill conditions using refractometers as measurement devices. The measurement results were utilized for the optimization of washer performance by calculating real-time displacement ratio (DR) values. The variables selected for the experiments were: the amount of wash liquid, feed consistency of pulp, feed pressure, pulp production, temperature of feed pulp, amount of vacuum filtrate and the distance of the seal bars from the drum. Research work was carried out by installing 4 refractometers (7 measurement points) on the pressure filter after the digester in the brown stock washing line at a Finnish kraft pulp mill. The results indicated that changes in the concentration of incoming flows to the washer can be detected online by real-time refractometer measurements. The results can be also used as a tool for monitoring the condition of pressure filters, for example by adjusting the distance of the seal bar from the drum.

Between-tree Variation in Stem Volume, Wood Density, Fibre Length and Kraft Pulping Properties of 'Eucalyptus globulus' and the Utility of Field-portable NIR Spectroscopy and Wood Cores in Evaluating Pulpwood Quality Properties of Standing Trees

Abstract: Pulpwood quality characteristics of 75 individual trees of 10 to 11-year-old Eucalyptus globulus were evaluated to assess their suitability for inclusion in a clonal tree improvement program. The trees were phenotypically selected for good growth and form from three commercial plantations in contrasting rainfall zones in south-western Western Australia. All sampled trees were assessed for merchantable tree volume, heartwood proportion, bark proportion, basic density and Kraft pulping properties. Simulated wood core samples extracted at breast height from each tree were evaluated for basic density and near infrared spectroscopy (NIRS) predicted pulp yield. The application of a field-portable NIRS system as a tool for rapid determination of pulp yield in standing trees was tested as was the reliability of Pilodyn penetration in predicting basic density at breast height. The selected trees showed a considerable degree of variation within and between sites for all the evaluated properties, indicating a potential for tree improvement through cloning of individual trees matched to specific sites. Across the three sites, individual tree values ranged from 451 to 658 kg/ m3 for chip basic density; 0.78 to 1.12 mm for fibre length; 47.8 to 58.8% for screened pulp yield at Kappa number 18, with an active alkali from 10.5 to 15.8% and 264 to 371 kg/m3 for pulpwood productivity. Core samples were better predictors of whole tree chip basic density compared to Pilodyn penetration, with respective coefficients of determination of 0.83 and 0.61. The field-portable NIRS spectra taken from bark free surfaces on standing trees produced moderately high predictions of total pulp yield (R2 = 0.70) but poorer predictive capacity for screened pulp yield (R2 = 0.61). In contrast, the laboratory-based NIRS method using wood core samples was found to be a superior predictor with R2 values of 0.85 and 0.88 respectively for screened and total pulp yield.

Low-effluent Recycled Paper Mills

Abstract: With increasing pressure on discharge quality and uncertainty of water supply in many parts of the world, the pressure to move towards effluent-free papermaking is increasing. The advantages of operating an effluent-free mill are that it requires no discharge licence, requires very little fresh water and can offer a product with good environmental credentials. Closure of a mill water system can result in a range of problems, the severity of which will depend on the nature of product being produced, the quality of the raw material and the degree of closure attempted. In most cases some additional treatment will be required before recycling the water. Commonly this will include at least one stage of biological treatment, but membrane processes, evaporation and other steps may also be required. Poorly applied, such processes can be very expensive and to be most cost effective the treatment process must be tailored to the needs of the mill and designed into the basic mill flow scheme. The types of problem that might be encountered are described and how these have been tackled in cases from mills employing very simple closure, through extensive biological treatment up to fully liquid effluent free mills.

The relationship between hygroexpansion, tensile stiffness, and mechano–sorptive creep in bleached hardwood kraft pulps

Abstract: Hygroexpansion coefficient and tensile stiffness are important parameters in many paper applications. This study compares several bleached industrial hardwood kraft pulps, comprising five eucalypt ...