Showing papers in "Appita Journal in 1995"

Rapid measurement of variation in tracheid transverse dimensions in a radiata pine tree

Abstract: Variation in tracheid cross-section dimensions has been mapped in a 19 year old radiata pine tree. An instrument recently developed for the rapid estimation of transverse tracheid dimensions was used for the analysis. Sixty radii (four directions at each of fifteen heights) were processed. Variation was mapped for properties important to the pulp and paper industry: wood density, tracheid perimeter, coarseness and wall thickness. In this tree, coarseness, wall thickness and density trends were approximately linear from pith to bark, and the rate of rise was similar at all sampling heights. As a result, variation of these properties in the three was approximately cylincrically symmetric. Average coarseness, density and wall thickness fell by 25% from the 0.8 metre level to the 20 metre level in the tree. Average tracheid perimeter was almost independent of sampling height. At breast height, coarseness rose by 86% from pith to bark (350 to 650 μg m -1 ), density rose by 45% (380 to 550 kg m -3 ) and wall thickness by 57% (2.1 to 3.3 μm). Unweighted breast height core properties for this tree were similar to volume-weighted whole tree properties above breast height. Correlations between properties such as coarseness and wall thickness were strong when ring averages or trends were considered, but poor within individual tree rings. Understanding of the mechanisms of short term regulation of tracheid properties should allow increased selectivity in the silvicultural and genetic control of individual properties

Pulpwood quality estimation by near-infrared spectroscopic measurements on eucalypt woods

Abstract: Near-infrared spectroscopy has been examined as a method for providing a rapid estimate of pulpwood quality based on small samples. The woods were drawn from three trees in ten provenances of Tasmanian Eucalyptus globulus. The measures of pulpwood quality were yield, soda charge at Kappa number 15, total lignin, and hot water and alkali solubles. The samples were divided to provide 24 which were used in obtaining the calibrations and six which served as unknowns. The calibrations were obtained by using standard. Norris and partial least squares regressions. Predictions of the various pulpwood quality measures were obtained with residual standard deviations in the range 0.8-2.6 units.

X-ray diffraction estimation of the microfibril angle variation in eucalypt wood

Abstract: X-ray diffraction of wood was investigated as a technique suitable for the development of an automated method to estimate the variation of microfibril angle in eucalypt increment cores. Existing methods such as polarized light microscopy, requiring individual fibres, are very time consuming and cannot be readily automated. Radial and tangential eucalypt samples removed from a radial section of a disc were used for the measurement of x-ray diffraction parameters related to microfibril angle, using a modified method. Similar results were obtained for the two directions of measurement. Microfibril angle was calculated to be in the range 10-20 degrees, decreasing from pith to bark, and was consistently smaller for latewood than earlywood

Use of enzymes to improve drainability of secondary fibres

Abstract: Several commercial cellulases and hemicellulase enzymes were evaluated for their effectiveness to improve the drainage of secondary fibres. Drainage improvement over the control was substantial with 'Pergalase' (a mixture of cellulase and hemicellulase) and Maxazyme (a cellulase) followed by a smaller but still significant increase with Lyx. A. niger (cellulase). The effect of 'Pergalase' treatment on pulps of different initial freeness showed that the lower the initial freeness, the higher the gain. The drainage improvement was 11.7% (0.1% enzyme) and 21.3% (0.2% enzyme) at a residence time of 30 minutes for low freeness pulp. Increase of residence time to 180 minutes improved the drainage by 25.4% (0.1% enzyme) and 31.7% (0.2% enzyme). The pulp retained most of the required strength properties when treated with 'Pergalase' either at 0.1% enzyme addition and residence time of 45 minutes or 0.2% enzyme addition and residence time of 30 minutes. Increase of residence time beyond 30 minutes with 0.2% enzyme resulted in deterioration of strength properties.

Incorporation of xylanase in total chlorine free bleach sequences using ozone and hydrogen peroxide

Abstract: Laboratory studies on processes combining enzyme with new bleaching technologies are described. The application of xylanase as one bleaching stage enhances the bleachability of eucalypt kraft pulp and reduces the quantities of bleaching agents in subsequent stages. Methods combining xylanase treatment (X), ozone (Z), acidification (A), and hydrogen peroxide (P) have been investigated in a variety of sequences. Hardwood kraft pulps bleached in the XAZZP 1.2% sequence exhibit a brightness of 90 Photovolt compared with 85.2 Photovolt for the AZZP 1.7% . The physical properties of the bleached pulps are comparable to those of commercial pulps. These findings suggest that it is possible to produce pulps exhibiting a high degree of brightness without chlorination

The potential application of non-wood fibres in papermaking: an Australian perspective

Abstract: Most of the non-wood material readily available for papermaking is short fibred and generally deficient compared with short fibred woodpulp. Australia in particular is richly endowed with hardwood resources suitable for the production of pulps of excellent papermaking quality and this severely restricts the viable papermaking opportunities for short fibred non-wood pulps. Greater opportunities exist for the utilisation of long fibred nonwood pulp in both specialty and commodity paper grades and as a replacement for imported long fibred chemical wood pulps. This paper reviews the papermaking properties of a variety of long fibred non-woods pulps including hemp, flax, abaca and sisal. Potential applications are discussed as well as issues to be addressed to facilitate the establishment of viable non-wood pulp production in Australia

Flow of medium consistency wood pulp fibre suspensions

Abstract: The various mechanisms of flocculation and the predominant mechanisms of flow of medium concentration (8-20%) wood pulp fibre suspensions are reviewed and discussed. Various definitions of fluidization and fluid-like behaviour are analysed and compared in a critical literature review. It is shown that care must be taken when interpreting explanations and data from the literature because of the differences in definition. It is also shown that rotational viscometers produce tangential and radial motion with back-mixing which do not occur in ordinary pipeline flow, and hence comparative data and observations must be interpreted carefully. The published friction loss correlations are presented together with some practical design considerations

The effect of laboratory mixing at medium pulp concentration on radiata pine kraft pulp

Abstract: Medium pulp concentration (MC) treatment of radiata pine pulp in a high intensity laboratory mixer modified pulp and handsheet properties compared with untreated control pulp. The treatment had little effect on pulp viscosity and freeness while Kappa number decreased. Pulp was weaker as indicated by reductions in tear tensile, and wet zero span tensile compared with untreated control pulp. Treatment increased fibre wall dislocations and enhanced fibre curl, and thus improved stretch. Reaction temperature and pH were identified as significant. Increasing reaction pH increased sheet density and tensile, but elevated temperatures during treatment had the opposite effect. The relative contribution of either refining and/or curling of the fibres appears to be controlled by the process conditions during treatment. Unrefined pulp handsheet properties induced by MC treatment were maintained following PFI mill refining when compared with control pulps. However as refining proceeded the magnitude of the differences were reduced.

Effect of vacuum level and suction time on vacuum assisted drainage of a paper machine wire section

Abstract: The effect of various vacuum levels and their effective dwell times on the solids content of the paper web was studied. The study was made with a specially designed laboratory drainage tester, in which suction time and vacuum levels could be dynamically varied. The results were compared to the drainage measurements taken on a pilot machine. The initial change in moisture content versus time of effective suction is very rapid. After the rapid initial dewatering a nearly constant level of moisture content is obtained; the airflow through the web does not continue to efficiently remove water The experimental results are also described by a simple empirical formula. The predictive capability of this formula is examined with a case study of a pilot machine. An example of suction profile optimization, based on laboratory measurements, is presented for a commercial machine.

TMP fibre and fines qualities of thirteen radiata pine wood types

Abstract: The fibre and fines properties of TMP made from 13 radiata pine wood types with double and/or single disc refiners are related to kraft fibre and TMP quality. TMP+14 and +30 fraction fibre properties of length and coarseness can be predicted from those of corresponding kraft pulps. Fines, short fibre fragment and fibrillation qualities of TMP to a large extent determine handsheet light scattering and bonding properties. High proportions of particulate fines with slender short fibres of low coarseness form handsheets with high packing densities, open surfaces and good light scattering properties. High proportions of fibrillar fines with large, long fibres of high coarseness form handsheets with closed and bonded surfaces and low light scattering properties. TMP rich in coarse fibrillar fines with large fibres of high collapse potential form handsheets with closed and bonded surfaces of high micro roughness, and good light scattering properties. Double disc refining can give more fibre damage, fibrillar fines which are more coarse, and improved handsheet light scattering properties, compared with single disc refining.

Peroxide bleaching of radiata pine TMP and eucalyptus regnans cold caustic soda pulps with sodium hydroxide and magnesium oxide

Abstract: Sodium hydroxide and magnesium oxide have been compared as alkali sources in single-stage and two-stage bleaching of eucalypt cold caustic soda (CCS) and radiata pine TMP. In contrast to using sodium hydroxide, addition of DTPA, sodium silicate or magnesium sulfate to magnesia produces a reduction in pulp brightness gain. Possibilities of internal recycling of liquor during two-stage peroxide bleaching process using either sodium hydroxide or magnesium oxide as an alkali, have also been investigated. Utilization of residual peroxide in a sequential two-bleaching of radiata pine TMP and eucalypt CCS pulps, although some exceptions show encouraging results. Under certain conditions, recycling residual peroxide produces detrimental effects on the bleaching response of radiata pine TMP

Fouling during heat transfer to kraft pulp black liquor. II: Analysis of deposit and modelling

Abstract: In Part I of this investigation, the authors reported experimental results on the fouling of heat transfer surfaces from kraft pulp black liquor. In this paper the fouling deposits are analysed with respect to appearance, composition and process conditions from which they were obtained. Assuming chemical reaction controlled fouling, a deposition model is developed and compared to the experimental data.

Effect of deinking on optical and physical properties of secondary fibre after pulping and flotation

Abstract: Furnishes of mixed magazines and newsprint and all-magazines and all-newsprint were used to investigate changes in properties of secondary fibre during deinking. In most cases, optical and physical properties showed reverse trends after pulping and flotation stages. These differences can be explained by the change in proportions of mechanical and chemical fibres, filler, fines and ink during flotation. After the pulping stage, trends in strenght properties were influenced by detrimental effects of filler from magazines. However, after the flotation stage, due to loss of most of the filler and fines, an enhancement in all strenght properties occured. Brightness and light absorption coefficient appeared to be more influenced by ink content, when large amounts of filler are present. The light scattering coefficient was dominated by the fibre type. After flotation, despite the highest brightness value, the all-magazine furnish had the highest ink speck count. Extended periods of flotation (greater than ten minutes) had no significant effect on properties of the waste paper investigated.

Process effects on the response of softwood kraft pulp to enzyme assisted bleaching

Abstract: The effects on enzyme assisted bleaching of pulp type, extent of delignification and enzyme source were studied. Radiata pine kraft and kraft-oxygen pulps each al two Kappa number levels, were pretreated with different commercial enzyme products then DEoD bleached. Improvements to bleaching effectiveness as well as changes in important physical and chemical properties of pulp were measured before and after enzyme treatment. Results are discussed in relation to the proposed mechanisms of enzyme assisted bleaching

Fouling during heat transfer to kraft black liquor. I: Experimental results

Abstract: The present paper reports results of an investigation into fouling from New Zealand Forest Products kraft pulp liquor. A large number of experiments were performed in a specially designed test loop to measure fouling rates as a function of surface temperature bulk temperature, velocity and solids concentration. Results from experiments with two chemical fouling inhibitors and with Teflon surface coating are also presented

Mixing gases and pulp suspensions in a continuous laboratory mixer

Abstract: The ability to mix gases and pulp suspensions was studied with a laboratory rotary mixer adapted for continuous operation. The laboratory mixer had a concentric-cylinder geometry consisting of a vaned rotor and baffled housing, similar in design to some commercial mill-scale and laboratory pulp mixers. Air was mixed into kraft pulp suspensions having mass concentrations up to 4% to give suspensions with gas contents up to 50% by volume. Pulp flows to the mixer were varied from 75 to 125 L/min. This gave nominal residence times varying from 0.8 to 2.7 s depending on the volume of gas added. Mixing effectiveness was evaluated based on the flow pattern observed in the mixer and the power drawn by the rotor. The flow pattern and power consumed in mixing were affected by suspension composition (pulp concentration (p.c.) and gas content), rotor speed, and flow rate through the mixer. Changes in flow rate could result in a step change in the power drawn by the rotor and flow pattern produced. The gas capacity of the mixer was reduced over the case of batch operation due to gas hold-up within the mixer. The gas hold-up was reduced as the flow velocity through the mixer increased, as the rotor speed was decreased, and as the suspension p.c was reduced. The ability to sustain effective mixing in this particular device was limited to gas contents of below 10% once the suspension p.c. reached 3%.

Analysis of performance of a multicylinder dryer, using computer simulation model and experimental data

Abstract: A mathematical model is presented that describes the operation of a high speed multicylinder paper machine dryer with a single tier configuration. The model uses input parameters such as cylinder diameters, dryer geometry, steam temperature, air humidity, and temperature, etc, to calculate the number of cylinders required, felt temperatures, paper web temperatures, moisture content and drying rate along the length of the dryer section. The program has been verified by comparing its output with data from production paper machines. The model can be used to predict the effect of various design parameters on the dryer performance, such as dryer cylinder and vacuum roll diameters, and roll spacing. It can be used to predict the conditions required for uniform drying of the paper web, taking into account the differences in heat and mass transfers occurring at the opposite sides of the paper dried on a single tier dryer. To increase the dryer performance, use of air impingement systems is suggested

Enzyme pretreatment of kraft pulp to reduce consumption of bleach chemicals

Abstract: The use of chlorine in the bleaching of chemical pulps has to be minimized to meet environmental requirements for the disposal of adsorbable organic halogens (AOX) The study deals with the production and characterization of the enzyme preparation used and the optimization of enzyme pretreatment prior to the bleaching sequence is discussed The results show that pH has the greatest effect on enzyme effectiveness compared to time and temperature Optimum conditions improved the enzyme efficiency by 94% The study describes the effect of the enzymes on various bleaching sequences such as (C/D)EDED, DEDED, ODED, OZEQP and OAQPAP For sequences containing chlorine compounds, the use of enzymes decreases Kappa number but with a lower effectiveness of 5% on average and enhances final brightness, with a slight reduction in chlorine dioxide consumption

A new may of measuring the effect of fluorescent whitening agents

Abstract: Although the concept of whiteness is well understood, the measurement of whiteness is complex and is made more difficult by human psychological biases and the effects of fluorescent whitening agents. The whiteness of optically brightened papers is strongly dependent upon the conditions of illumination when either viewing or measuring such papers. For meaningful measurement, which agree with visual assessments, the measuring instrument's light source must be calibrated and controlled particularly in the ultraviolet range of its emission spectrum. A fully automatic means of adjusting and calibrating the instrument to simulate three different standard sources of illumination (i.e., outdoor daylight, indoor illumination, and ultraviolet excluded illumination) has been described. This procedure facilitates more extensive analysis of the effect of fluorescent whitening agents than was previously possible

Peroxymonosulfate and dimethyldioxirane as interstage treatments in two-stage oxygen delignification

Abstract: Dimethyldioxirane (DMD) a selective bleaching agent is most conveniently formed in situ by adding peroxymonosulfate (Ps) to pulp impregnated with acetone. This study investigated whether DMD formed in situ is more effective than Ps alone as an interstage treatment for two-stage oxygen delignification. Kraft-oxygen pulp from radiata pine was treated with a range of peroxymonosulfate in the presence or absence of acetone then oxygen delignified. Addition of acetone improved the overall selectivity when peroxymonosulfate (2.5% HSO 5 - ) or greater was applied. At 5 Kappa number pulp treated with 5% HSO 5 - and acetone had a viscosity 1.2 mPa.s higher than that of corresponding pulp treated with only peroxymonosulfate. Brightness after final oxygen delignification improved by up to two ISO units with acetone in the interstage treatment (5% HSO 5 - ). Final bleaching of the 5% Ps-acetone interstage treated pulp with 1.6% chlorine dioxide improved brightness by a further 17% ISO. These improvements in selectivity and brightness, however, were relatively small compared with the increased costs and additional process complexity required for acetone addition.

A new simulator for paper forming using neural network methods

Abstract: A new simulation package is described for the paper forming process, using neural networks paradigms. Various parameters involved in paper forming are taken into consideration. These include fibre concentration, fibre propensity to flocculate, fibre flexibility and fibre length, as well as parameters describing the forming conditions, like geometry of the fabric, drainage speed, turbulence intensity and turbulence decay. Generated structures resemble those found in commercial papers and may be useful in interpreting physical processes in the forming operation

The effects of total sulfur concentration and reactor pH on the anaerobic co-treatment of CTMP wastewater and domestic sewage

Abstract: Anaerobic digestion is relatively new for the treatment for CTMP effluents; it offers many potential advantages over conventional aerobic treatment. Reactor pH and effluent sulfur concentration were studied for their influence on the performance of laboratory scale anaerobic reactors, treating a combined CTMP and sewage wastewater. Operating under conditions, typical of full-scale installations, good treatment performance was observed. lowering the acidogenic reactor pH to about 5.5, did not result in increased sulfide inhibition, partly because, at this pH, less sulfate reduction was observed compared with that at pH 7.3. Feed wastewater sulfate-S concentrations up to 590 mg S/L did not have any adverse effects on performance over the acidogenic reactor pH range of 5.0-7.3. When both reactor phases were maintained at pH 7.3, the treatment system no longer behaved as a two phase system, but, as two single phase reactors in series. Concern about possible adverse consequences due to high sulfide concentrations or variations in reactor pH values, seem unfounded; these results indicate that anaerobic treatment of the combined CTMP and sewage wastewater is extremely robust and should give good overall effluent treatment

Totally chlorine-free bleaching of eucalypt kraft pulp incorporating a UV-peroxide stage

Abstract: A commercial eucalypt kraft pulp (Kappa no. 13.2) was bleached with totally chlorine-free (TCF) sequences involving oxygen delignification (O), acid treatment (A), chelation (Q), UV-peroxide treatment (Up) and pressurized peroxide treatment (PO). The pulps were compared with a pulp bleached by the elemental chlorine-free (ECF) sequence OD(EO)DD. Acid treatment before and after oxygen delignification gave pulps with Kappa numbers as low as 3.0, with reduced yields. Brightness after a (Up) stage was higher for pulps treated with acid and a chelant (EDTA). With either lower peroxide applications or higher pulp concentrations in the (Up) stage, lower brightnesses resulted. A subsequent pressurized peroxide stage in the sequence OQ(Up)(PO) with a total peroxide charge of 4% gave brightness 91.1% ISO. Sequences with (PO) but without (Up) stages gave lower brightness, an AOQ(PO)(PO) sequence gave 88.1% ISO brightness. The fibre strengths of the TCF pulps were lower than those of the ECF bleached pulp: TCF bleaching without the (Up) stage gave the lowest fibre strength. However the TCF pulps developed tensile strength more rapidly The study demonstrates that TCF sequences involving a (Up) stage enable eucalypt kraft pulps to be bleached to high brightness while requiring only moderate amounts of peroxide.

Infrared energy transfer mechanism in constant and falling rate periods of paper drying and its correlation to drying efficiency

Abstract: A medium intensity medium frequency infrared system has been developed by converting the heat of combustion of natural gas to infrared flux using a series of ceramic emitters. A region of operation has been found where this system produces a surprising improvement in drying efficiency of newsprint grade paper on the paper machine brought about by prolongation of the constant drying rate period to a relatively low moisture content. The fact that the drying rate remains relatively constant even in a partially dry porous paper surface leads to analysis of diffusion processes near a solid surface. A modification of a previously proposed model includes the experimental observation that a partially wetted paper can yield practically the same drying rate as that of the completely wetted paper under certain conditions encountered in drying. The validation of the model considers the infrared spectrum divided into small intervals. The IR energy flux generated by natural gas combustion was calculated and its efficiency was determined separately for IR internal absorption, IR energy generation, and total heat of combustion using a numerical illustration.

Fracture toughness of paper

Abstract: The effects of fibre length and some papermaking variables on plane stress fracture toughness were studied. Fracture toughness, Elmendorf tear and tensile strength were compared. It was shown that the fracture toughness of paper varied linearly with the average fibre length, and that fracture toughness was more strongly dependent on fibre length than tensile strength or tearing resistance. Fracture toughness was somewhat more strongly dependent on sheet density than tensile strength when fibre-fibre bonding was changed with additives or the pulp was dried under different conditions before sheetmaking. As the bonding was changed by changing the wet-pressing pressure during sheetmaking, the changes in both fracture toughness and tensile strength with density diminished. It was also demonstrated that there was good agreement between the measured and the estimated fracture toughness.

Factors influencing the treatment of Australian pulp mill effluent

Abstract: The use of chlorine to bleach paper pulp results in the formation of organochlorines, which, if not degraded by effluent treatment have the potential to cause harmful environmental effects. This paper describes the results of a study aimed at determining the factors important in the degradation of organochlorines, toxicity, colour and chemical oxygen demand (COD) in bleached kraft effluent. Factors investigated included the effects of pH, Eh and nutrient supplementation. Biological activity was found to be important in treating pulp mill effluent. About 10% of the organochlorines in the effluent were removed in sterile controls compared with 40 to 60% in the presence of aerobic and anaerobic microbial activity. BOD and COD reduction were favoured by aerobic conditions. Reduction of all properties tested was approximately the same, whether the effluent was amended with defined nutrients or not, however the addition of raw sewage to the effluent improved the removal of COD and AOX under aerobic conditions, but not under anaerobic conditions. Colour removal was poor in most experiments.

MCC Pulping with Additives and Modified Sulfidity Profiles

Abstract: The effects of delignification rate, yield and pulp properties of several modifications to MCC pulping were studied in the laboratory. All the sulfide normally charged over the course of MCC pulping was added during the impregnation stage to avoid sulfide starvation during the initial phases of delignification. This increased the delignification rate while maintaining the strength benefits of MCC pulping. The addition of 2% polysulfide to the impregnation stage of MCC pulping increased the pulp yield by two percentage points allowing Kappa number to be reduced from 26 to 15 while maintaining the same yield. No effect on pulping rate or final pulp strengths was observed. The addition of 0.1% anthraquinone to MCC pulping resulted in moderate increases in delignification rate, but no improvements to pulp yield.

Ozone bleaching of eucalypt kraft pulps

Abstract: Kraft pulps from plantation and mature eucalypt wood samples were bleached with the sequences OZ and OZQ(PO). The ozone stage was done at high pulp concentration. The aim of the study was to bleach pulps to a brightness of 90% ISO without reducing their strenght properties. Pulps prepared by conventional and extended delignification procedures were used. The use of xylanase with the OZ sequence gave higher pulp brightness levels (about 2% ISO) but with the OZQ(PO) sequence the increase was much smaller. The bleaching yield was about 1-3% units lower, depending on the wood sample and the pulping procedure. Conventional pulps were bleached to about 88% ISO brightness with the OZQ(PO) sequence. The tearing resistance was equal to that of the unbleached pulp. The extended delignification pulps were bleached to levels in the range 89.5-90.5% ISO but tearing resistances were slightly lower.

Wastewater management at Australian Newsprint Mills Albury : responding to community expectations

Abstract: Australian Newsprint Mills Ltd (ANM) Albury mill is near the headwaters of the Murray River, Australia's most important waterway. Because of its location, the mill has had to practise a high level of environmental compliance and develop innovative practices for minimizing environmental impact. The water conservation practices built into the original mill design have been enhanced over the years and through monitoring community opinion about ANM's discharges, the Company has decided to implement off-river disposal of its treated water water. The paper discusses developments since the mill was commissioned, investigations leading to off-river disposal and the developoment of the disposal scheme

Deinked pulp and the Netbond retention aid system

Abstract: Alkyloxylated based surfactants used in deinking recycled fibre have been found to interfere with the Netbond retention aid system. The interference that occurs appears to be dependent on pulp pH, temperature and PFR:PEO ratio. The surfactant forms an insoluble complex with the phenolic resin (PFR) in the Netbond system. PFR is incorporated into the interior of the surfactant micelles and is thus unavailable for interaction with polyethylene oxide (PEO), the second component of the Netbond system. Only when sufficient PFR is added to provide an excess is PFR available to interact with PEO. Fatty acid based surfactants generally do not exhibit the same behaviour as the alkyloxylated versions with respect to the Netbond retention aid system.