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Editorial: Art Ragauskas: Eyes on the future, TAPPI JOURNAL
Editorial: Art Ragauskas: Eyes on the future, TAPPI JOURNAL October 2012
Journal articles
Magazine articles
Editorial: TAPPI’s 2022 Nanotechnology Conference convenes in Finland, TAPPI Journal June 2022
ABSTRACT: TAPPI’s International Conference on Nano-technology for Renewable Materials was finally held in person this past June 13-17 in Helsinki, and more than 200 attendees gathered to participate in the 36-session program. A total of 24 countries were represented at the event and more than one-third of attendees were first-time participants.
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Effects of rings on flow and temperature in lime kilns, TAPPI Journal June 2022
ABSTRACT: A steady state, two-dimensional (2D) axisymmetric model has been developed to help understand how rings form and grow in a typical lime kiln. Rings of varying length, thickness, and geometry at the front and back faces were modeled to study the effects on flue gas flow and temperature. The results show that ring growth causes the gas velocity to increase and insulates the adjacent refractory, resulting in a lower kiln shell temperature. The results also reveal the formation of recirculation zones immediately down-stream of the rings, as well as temperature deviations upstream and downstream of the rings that might promote recarbonation and further ring growth. The model was applied to a kiln from a kraft mill with front-end and mid-kiln rings and good agreement was obtained between the measured and predicted kiln shell temperatures, providing confidence in the modeling.
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Water chemistry challenges in pulping and papermaking • fundamentals and practical insights: Part 1: Water chemistry fundamentals and pH, TAPPI Journal June 2022
ABSTRACT: Water is an essential component of the papermaking process. Nevertheless, papermakers often overlook its importance compared to fibers and chemical additives. A better understanding of water properties and chemical interactions associated with water at the wet end leads to a sound foundation for high-quality paper production and smooth operation. Not all fresh water and process water is the same. Fresh water varies from mill to mill, primarily due to the location and availability of water sources. Some industrial trends, such as enhancing water conservation and production yield, gradually shift process water quality over time. The current work serves as a primer on water and water chemistry fundamentals to help the papermaker prepare for the future challenges of increased contamination of process water associated with reduced fresh water usage. This paper focuses on basic water chemistry definitions and discusses the impact of pH on wet-end operation. It is clear that pH is a fundamental factor that directly affects the process and impacts other factors relevant to the papermaking process. It is crucial to understand what pH represents, how it is measured, how to select the proper pH and carefully control it, and how to closely maintain the process at target setpoints. Understanding the sensitivity of operation to pH change will lead to an appropriate focus on these issues. In addition to basic theory, we also review onsite experience and practical mill cases. It is imperative to stress that, although critical, pH is not the only chemical parameter impacting papermaking operations. Other factors, such as ionic concentration measured by conductivity, surface, soluble charge, and hardness, are critical and will be discussed in Part II of this series. As pH is a primary and independent factor that impacts various forms of charge and conductivity, the authors decided to start the current series of papers by discussing pH.
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Rewet suppression through press felt engineering, TAPPI Journal June 2022
ABSTRACT: Due to the immense energy and associated financial cost of drying paper, achieving a drier web entering the dryers is a key objective in paper manufacture. One major research thrust has been finding a way to increase press solids by mitigating or eliminating rewet in the press section. For decades, solutions to this problem have remained elusive. In this work, we develop a novel approach that significantly reduces rewet by rupturing the liquid channels between felt and web. We illustrate the effects that altering the mechanical and surface properties of the press felt matrix have on the stability of these liquid channels. In a laboratory-scale platen press, a 40% reduction in the residual water of 120 g/m2 southern bleached softwood kraft (SBSK) pulp handsheets after pressing was observed, corresponding to an increase in press solids from 48% to 61%. For reference, pressing under identical conditions with paper blotters, in which minimal rewet is presumed to occur, resulted in 64% solids. Furthermore, we observed enhanced dewatering across a range of basis weights, applied pressures, and felt types. In addition to measuring the solids content of pressed sheets, we capture and analyze video evidence of the mechanisms at play in our improved dewatering technology.
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The Influence of the Fine Structure of Cellulose on the Action of Cellulases, TAPPI Journal June 2022
ABSTRACT: In the hydrolysis of cellulose with enzymes of Aspergillus niger at 47°C., it shown that a great decrease in the rate occurred in the late stage of the reaction, usually with considerable cellulose still reamaining undissolved.
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Rheological characteristics of platy kaolin, TAPPI JOURNAL September 2019
ABSTRACT: Platy kaolin can provide significant value in the coating of paper and paperboard. It can be used in multiple applications and can provide benefits such as titanium dioxide (TiO2) extension, smoothness improvement, improved print gloss or ink set rates, calendering intensity reduction, and improved barrier properties. It is not a pigment that can be simply substituted for traditional hydrous kaolin without some adjustment to the coating formulation. These adjustments can be as simple as reducing solids, but may require binder changes as well. The coater setup may need to be adjusted because of the unique rheological behaviors these pigments exhibit.The unique rheological characteristics of platy kaolin are explored here. Measurements of the water retention of platy kaolin containing coatings confirm that water retention is not reduced in comparison to more blocky kaolin pigments, despite the lower coating solids at which they need to be run. This means that the rheological characteristics are the most important in understanding the runnability. An extensive analysis reveals some unique behaviors that need to be understood when utilizing these materials. Viscoelastic measurements indicate that, for this binder system, Tan d is mainly a function of solids. This may explain how weeping is initiated on a blade coater. The degree of shear thinning behaviors is investigated using the Ostwald de-Waele power law. The immobilization point was determined using the Dougherty-Krieger equation and related to the work of Weeks at the University of Maine on blade coater runnability. An indirect measure of particle shape and size synergy is also demonstrated using the Dougherty-Krieger equation parameters.
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Flow characteristics of drag-reducing natural bamboo fiber suspensions with minimal environmental load, TAPPI Journal September 2019
ABSTRACT: The reduction of pipe friction loss by adding drag-reducing agents has attracted attention as an aid to energy conservation. Drag-reducing agents induce drag reduction (DR) effects and should have a minimal environmental load, with natural resource-saving potential. This study demonstrates bamboo fiber as a drag-reducing agent that saves natural resources and has a low environmental load. Using pressure drop measurements, we report DR with suspensions of bamboo fibers with the average diameter of 13.3 µm and aspect ratio of 98.7. The maximum DR obtained in this experiment is 43% at the concentration of 4000 ppm and pipe diameter of 30 mm; DR is affected by the Reynolds number, suspension concentration, and pipe diameter. In addition, the bamboo fibers can be easily removed from the suspensions by filtration. We found that low-environmental-load bamboo fiber has DR effects like those of other fibers; its effects are greater than those of conventional synthetic fibers and wood pulp. Furthermore, it is resistant to mechanical degradation, recoverable, and recyclable. Therefore, DR effects can be selectively obtained by adding the fibers only when DR is needed; the fibers can then be collected when DR is no longer necessary. This method might greatly expand the application range of DR agents. The results demonstrate the usefulness of bamboo fibers as DR additives.
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How to use total dissolved solids measurements to evaluate the performance of diffuser washers—A mill study, TAPPI Journal April 2020
ABSTRACT: Various types of pulp washing equipment are available. Each washing device has a unique mechanical construction, and the washing principle is often a combination of dilution, thickening, and displacement washing. In this work, the performance of the pressure diffuser washer is studied. In stepwise trials, the effect of the feed and discharge consistencies on the performance of the diffuser was studied. The effect of the downward velocity of the screen on the pressure diffuser’s washing efficiency was also studied. The measurement of total dissolved solids (TDS) by a process refractometer was used as a wash loss measurement unit and the refractometer’s results were used in the calculations of standardized Nordén efficiency (E10) values. The chemical oxygen demand (COD) and conductivity values were also measured and their results compared to the TDS results.The results indicated that feed consistency has a significant effect on the performance and effectiveness of the diffuser washers in the mill. It can also be stated that when the downward velocity of the screen is adjusted to too high a level, the washing efficiency of the pressure diffuser decreases. As a conclusion from the mill tests, it can be stated that even small process parameter changes can provide enhanced diffuser washing at the beginning of the washing line, which has a direct effect on the performance of post-oxygen washing.
Journal articles
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A novel unit operation to remove hydrophobic contaminants, TAPPI Journal April 2020
ABSTRACT: For mills making paper with recovered fiber, removal of hydrophobic contaminants is essential for trouble-free operation of paper machines. Significant cost savings on paper machine operation can be achieved by reducing deposits, which results in better quality, reduced downtime, increased fiber yield, and reduced energy consumption. Bubble nucleation separation (BNS) is a relatively new process for removing hydrophobic particles. When vacuum is applied to a slurry, dissolved gas bubbles nucleate on hydrophobic particles and drag them to the surface for easy removal. We constructed a 16-L batch unit to evaluate the effect of operating parameters on removal of hydrophobic particles, using statistical design of experiments. These results were used to guide our design of a 16-L continuous unit. We tested this unit on laboratory and mill samples. The removal of 60%•80% of hydrophobic particles was achieved with a low reject rate of < 2%.Following on this success, we built a 200-L pilot unit and tested it in our pilot plant. With promising results there, we installed the pilot unit at a commercial paper recycling mill. Over the course of several mill trials, we showed that it was possible to remove a considerable amount of suspended solids from paper machine white water with less than 2% rejects. Unfortunately, due to the unit only treating 50 L/min and the mill flow being 12000 L/min, we were not able treat a sufficient portion of the white water to know whether a large-scale implementation of BNS would improve paper machine runnability.