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Improving refining efficiency with deflocculation, TAPPI Journal May 2022
ABSTRACT: The ability to load a refiner requires the formation of a fiber mat between opposing refiner bars. One of the consequences of this is the formation of flocs that persist through the refiner grooves and exit the refiner. These flocs interfere with sheet strength, requiring additional energy to make up the strength deficit. In addition, flocs can initiate string formation, resulting in machine efficiency issues such as cross-machine profile deterioration and the downtime required to correct it. Novel refiner plate modifications have been shown to improve refining efficiency in otherwise identical refiner plates. Energy savings are typically around 15% of gross refining energy on the basis of the treated stock, although much higher reductions have also been seen. Addressing this previously underappreciated flaw in conventional refining enables greenhouse gas reduction and other benefits related to sheet strength and machine efficiency.
Journal articles
Magazine articles
Low consistency refining of mechanical pulp — system design
Low consistency refining of mechanical pulp — system design, TAPPI JOURNAL July 2017
Journal articles
Magazine articles
Fiber-based characterization of pulp refining, TAPPI Journal September 2022
ABSTRACT: Fiber development in pulp refining can be characterized by three parameters: number of impacts on pulp, N; energy per impact, I, and bar force on fibers, F. These parameters enable comparisons of radically different refining conditions; determination of intensity for hardwoods and softwoods; assessment of effect of bar width on fiber shortening; and predictions of tensile strength increases.
Journal articles
Magazine articles
Effect of pH and enzymes on strength of recycled fibers during refining, TAPPI JOURNAL July 2018
Effect of pH and enzymes on strength of recycled fibers during refining, TAPPI JOURNAL July 2018
Journal articles
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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
In-process detection of fiber cutting in low consistency ref
In-process detection of fiber cutting in low consistency refining based on measurement of forces on refiner bars, TAPPI JOURNAL April 2017
Journal articles
Magazine articles
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.
Journal articles
Magazine articles
In-process detection of fiber cutting in low consistency ref
In-process detection of fiber cutting in low consistency refining based on measurement of forces on refiner bars, TAPPI JOURNAL April 2017
Journal articles
Magazine articles
Large data set analysis to determine refiner plate total cost of ownership, TAPPI Journal June 2019
ABSTRACT: Efficient process data storage and its subsequent analysis are vital to the profitable operation of a paper mill. An evaluation of refiner plate performance was conducted for an integrated paper mill. Trials with two new plate patterns were compared with the incumbent pattern; the goal was to increase refiner plate life. Plate life increased with both new design patterns, and the mill selected one of the two new choices. However, addi-tional impacts to paper machine performance and mill maintenance costs were not considered in the selection deci-sion. A large data set analysis tool was used to identify unrealized savings of 1.5% with reduced fiber usage (basis weight) on the paper machine’s most prevalent grade. The large data analysis indicated that this unrealized benefit with the alternate plate design was not attainable with the chosen plate design.
Journal articles
Magazine articles
Energy saving potential of interstage screen fractionation for production of board grade BCTMP, TAPPI Journal August 2023
ABSTRACT: Over the last few decades, the continuing decline in mechanical pulp-based grades has led pulp producers to modify operations and implement measures to reduce production costs in order to stay competitive. In spite of a considerable effort to reduce energy consumption, the latter is still a major portion of production costs in the process of making bleached chemithermomechanical pulp (BCTMP). In this study, we evaluated the impact of interstage screening fractionation (ISSF) and secondary refining strategy for producing BCTMP with the objective of reducing refining energy consumption while maintaining or improving bulk and strength properties. In the first step and to establish a baseline for a mill’s existing configuration, the collected primary refined pulp and reject streams from the ISSF were refined in a high consistency (HC) refiner to target freeness levels. The accepts and refined rejects streams were recombined, and their properties were compared to those of the refined primary pulp. The results showed that, at a given freeness of 400 mL and compared to the control case (without fractionation), the ISSF using an 0.070 in. basket followed by rejects refining could lead to about 25% energy saving in the second stage HC refining. Handsheet properties showed that utilization of ISSF could produce BCTMP with higher bulk and similar average fiber length and tear index. However, a slight reduction in tensile strength was observed. In the second set of trials, the primary refined pulp and the rejects from the ISSF using the 0.070 in. basket were refined by a low-consistency (LC) refiner. The results showed that, at the same freeness of 400 mL and compared to refined primary pulp, the ISSF saved about 26% in net LC refining energy. At a specific edge load (SEL) of 0.4 J/m, the produced pulp had similar bulk and strength properties compared to those of the control sample. A higher SEL of 0.6 J/m in LC refining could further decrease net refining energy consumption; however, it also led to reduction in fiber length, bulk, and strength properties.
