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Flow rheology of light foams generated from aqueous solutions of polyvinyl alcohol, TAPPI Journal January 2023
ABSTRACT: Recent studies have shown that foam-assisted application of additives into a wet web has advantages over the conventional way of adding the chemicals into the pulp suspension before forming, e.g., increased mechanical retention as well as high dosage giving increased wet strength without impairing the sheet uniformity. To engineer processes utilizing this new technology, the complex flow behavior of applied foams must be quantified. At the minimum, the foam viscosity and the slip velocity at the solid surfaces need to be known to build practical models that can be used in analyzing and upscaling unit processes of the foam-assisted application.In this study, the rheological behavior was quantified for foams having polyvinyl alcohol (PVOH), a widely used strength additive chemical, as the surfactant. The foam density was varied between 100 g/L and 300 g/L, and the concentration of the PVOH solution was varied between 0.5% and 6.0% (w/w). The foams were generated with a commercial foam generator, and the rheological properties of the foams were measured by using a horizontal pipe bank. At the outlet from the generator, the volumetric flow rate, the absolute pressure, and the bubble size distribution of the foam were measured. In the measurement pipe section, the viscous pressure gradient and the slip velocity were measured, after which the foam was discharged to ambient air pressure. The viscosity and the dynamic surface tension of the PVOH solutions were quantified with commercial laboratory devices. In the viscosity analysis, the apparent shear rate was calculated from the volumetric flow rate, and the resulting apparent viscosity was translated to real material viscosity data by applying the Weissenberg-Rabinowitsch correction. The results indicated that PVOH foams can be described with high accuracy as shear-thinning power-law fluids where the detailed behavior depends on the foam density and the PVOH concentration. Slip flow, as usual, increased with increasing wall shear stress, but it was also dependent on the PVOH concentration, the air content, and the bubble size. For both the foam viscosity and the slip flow, a correlation was found that described the quantitative behavior of all the studied foams with good accuracy.
Magazine articles
Forklift emissions - some solutions, TAPPI JOURNAL, December 1993, Vol. 76(12)
Forklift emissions - some solutions, TAPPI JOURNAL, December 1993, Vol. 76(12)
Magazine articles
Corrosion in lower furnace of kraft recovery boilersâ??in-situ characterization of corrosive environments, Solutions! & TAPPI JOURNAL, February 2004, Vol. 3(2) (179KB)
Corrosion in lower furnace of kraft recovery boilers–in-situ characterization of corrosive environments, Solutions! & TAPPI JOURNAL, February 2004, Vol. 3(2) (179KB)
Journal articles
Magazine articles
Recovery boiler back-end heat recovery, TAPPI Journal March 2023
ABSTRACT: Sustainability and efficient use of resources are becoming increasingly important aspects in the operation of all industries. Recently, some biomass-fired boilers have been equipped with increasingly complex condensing back-end heat recovery solutions, sometimes also using heat pumps to upgrade the low-grade heat. In kraft recovery boilers, however, scrubbers are still mainly for gas cleaning, with only simple heat recovery solutions. In this paper, we use process simulation software to study the potential to improve the power generation and energy efficiency by applying condensing back-end heat recovery on a recovery boiler. Different configurations are considered, including heat pumps. Potential streams to serve as heat sinks are considered and evaluated. Lowering the recovery boiler flue gas temperature to approximately 65°C significantly decreases the flue gas losses. The heat can be recovered as hot water, which is used to partially replace low-pressure (LP) steam, making more steam available for the condensing steam turbine portion for increased power generation. The results indicate that in a simple condensing plant, some 1%•4% additional electricity could be generated. In a Nordic mill that provides district heating, even more additional electricity generation, up to 6%, could be achieved. Provided the availability of sufficient low-temperature heat sinks to use the recovered heat, as well as sufficient condensing turbine swallowing capacity to utilize the LP steam, the use of scrubbing and possibly upgrading the heat using heat pumps appears potentially useful.
Journal articles
Magazine articles
Multilayering of conventional latex-based dispersion coatings containing small amounts of silica nanospheres: Runnability on a pilot scale flexographic coater and barrier performance, TAPPI Journal November 2023
ABSTRACT: The addition of functional coatings to packaging materials is a key requirement for increasing their performance and creating innovative packaging solutions. Flexography, a cost-effective printing method commonly used to print information and graphics directly onto a wide variety of packaging substrates, shows good potential for applying functional coatings. In this study, conventional clay-latex coating formulations containing approximately 1.3 wt% silica nanospheres were applied to a linerboard using a pilot scale flexographic printing web press. The performance of multilayered silica nanosphere-based coatings was compared with conventional coatings containing talc and/or wax dispersion in terms of coating grammage, runnability, and barrier performance. Coating grammage increased with an increased number of coating layers and a significant decrease in both the water vapor transmission rate (WVTR) and the direct water uptake of water (Cobb 120 wettability test) was observed for coatings containing silica nanoparticles. In general, the silica nanosphere-based coatings performed better than talc-based coatings. Talc/wax-based coatings had the highest variation in surface roughness due to an uneven distribution and variations of coating layers.
Journal articles
Magazine articles
Improving paper wet strength via increased lignin content and hot-pressing temperature, TAPPI JOURNAL October 2020
ABSTRACT: It is known that the strength properties of wood-based paper materials can be enhanced via hot-pressing techniques. Today, there is a desire not only for a change from fossil-based packaging materials to new sustainable bio-based materials, but also for more effective and eco-friendly solutions for improving the dry and wet strength of paper and board. Against this background, hot pressing of paper made from high yield pulp (HYP), rich in lignin, becomes highly interesting. This study investigated the influence of pressing temperature and native lignin content on the properties of paper produced by means of hot pressing. Kraft pulps of varied lignin content (kappa numbers: 25, 50, 80) were produced at pilot scale from the same batch by varying the cooking time. We then studied the effect of lignin content by evaluating the physical properties of Rapid Köthen sheets after hot pressing in the temperature range of 20°C•200°C with a constant nip pressure of 7 MPa. The pilot-scale cooked pulps were compared with reference samples of mill-produced northern bleached soft-wood kraft (NBSK) pulp and mill-produced chemithermomechanical pulp (CTMP).Generally, the results demonstrated that lignin content had a significant effect on both dry and wet tensile index. All of the pilot cooked pulps with increased lignin content had a higher tensile index than the reference NBSK pulp. To obtain high tensile index, both dry and wet, the pressing temperature should be set high, preferably at least 200°C; that is, well above the glass transition temperature (Tg) for lignin. Moreover, the lignin content should prefera-bly also be high. All kraft pulps investigated in this study showed a linear relationship between wet strength and lignin content.
Journal articles
Magazine articles
Equilibrium moisture content in wet pressing of paper, TAPPI Journal July 2020
ABSTRACT: Equilibrium moisture is a limiting factor in achieving high solids in the later stages of pressing or pressing low basis weight grades. We have developed a model that relates equilibrium moisture directly to the pore size distribution of fibers as measured by the solute exclusion technique. The model shows that chemical pulping and refining increase equilibrium moisture by increasing pore volume at given pore sizes in fibers, which leads to lower pressed solids and greater energy expenditure in the dryer section. Means to increase equilibrium moisture without compromising pulp strength are briefly discussed.
Journal articles
Magazine articles
Novel test method for measuring defects in barrier coatings, TAPPI Journal November 2022
ABSTRACT: In the last several years, activity to develop water-based barrier coatings (WBBCs) that meet challenging packaging performance requirements has increased dramatically. Cellulose-based packaging solutions can provide a more sustainable packaging option for replacing single-use plastic-based options like extrusion-based and laminated materials. An advantage of WBBCs is the opportunity to reduce the coating thickness applied, as long as the barrier requirements can be met. A challenge that must be overcome is the ability to maintain a defect and pin-hole-free coating layer after coating and drying to retain the barrier performance. Many formulation and coating parameters can affect the barrier coating layer quality; however, methods for detecting more subtle differences in these types of studies are not widely available. Work was carried out to develop a quantitative technique for detecting and measuring the quantity and size of defects in the barrier coating layer. A test method has been developed using a combination of dyed oil and image analysis to be able to characterize the imperfections in the coating surface. The use of dyed oil serves two purposes. First, it better simulates the types of materials, in this case, oils and grease, for which the barrier coating is expected to hold out. Second, it also provides contrast between the coating and failure points for testing. An image analysis technique is employed to characterize the number and size of the imperfections. For the former, it reduces the testing time required if a quality control or laboratory technician counts the dots. For the latter, it assists with judgment on the source of the root cause of the imperfection, such as base sheet defects, coating dispersion issues, or perhaps micro-blisters in the coating, as some examples.To show the benefit of this technique, several pilot coating studies were designed to see if the new technique could be utilized to detect differences in WBBC performance. Both process and chemical variables were evaluated. With refinement, it is believed this technique can be utilized in development work, as well as for a potential quality control technique for manufacturing of coated paper and paperboard products.
Journal articles
Magazine articles
Improving monochloramine performance with innovative sensor-controlled dosing, TAPPI Journal January 2024
ABSTRACT: Monochloramine (MCA) has become one of the major oxidant chemistries for biological control in the paper industry. Feedback control, such as oxidative-reductive potential (ORP), is often used to provide better control of a dosing scheme. The trademarked Ackumen MCA-i is a chemical-digital solution that uses artificial intelligence with actionable insights to stabilize the wet-end process, providing improved performance and reduction in overall chemical costs. Accurate sensor-controlled dosing can be tied to multiple inputs, such as production rates, grade changes, pH, ORP, chlorine residual, freshwater usage, and more. In this study, a case history will be presented to demonstrate how this technology provided a more consistent MCA molecule throughout the process, resulting in a higher level of efficacy and reduction in chemical costs.
Journal articles
Magazine articles
Spraying starch on the Fourdrinier— An option between wet end starch and the size press, TAPPI Journal January 2021
ABSTRACT: Technology to apply suspensions of starch grains to the wet surface of paper, during the dewatering process, is reviewed. Though the technology is not new, it continues to attract the attention of papermakers as a means to increase bonding strength. Starch grains that are sprayed onto the wet-web of paper can be retained at levels exceeding what can be effectively added to the fiber suspension at the wet end. Unlike adding a starch solution at a size press, no additional drying capacity is required on the paper machine. To be effective, the starch needs to be able to swell and develop bonding during the paper drying process. Paperboard applications with recycled fibers appear to be a good fit. There is potential to increase bonding by processes that favor fuller gelatinization of the starch grains by the time the paper becomes dry.