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Characterizing rheological behavior and fluidization of highly refined furnishes, TAPPI Journal April 2024
ABSTRACT: In this work, highly refined softwood bleached kraft pulp (SWBKP) furnishes, referred to here as XFC, were studied from the perspective of fiber suspension handling in processing. The rheology of the furnishes was studied with a rotational rheometer using a non-standard flow geometry to understand the viscosity development at different consistencies and the impact of temperature. For fluidization analysis during pipe flow, two optical methods were implemented; namely, optical coherence tomography (OCT) and high-speed video (HSV) imaging. The OCT was used to determine the small-scale floc structures near the pipe wall where the shear stress is highest, and the HSV imaging was applied for observing flow instabilities and XFC suspension uniformity at the pipe scale. All these issues can be significant in deciding the minimum flow rate required for a process pipe to get sufficient fluidization of XFC suspensions.
Journal articles
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Editoral: Investing in the future: Writing and peer-reviewing for TAPPI Journal, TAPPI Journal July 2024
ABSTRACT: Those who actively participate in TAPPI realize how much there is to gain from the networking, educational resources, career development, and other opportunities that come with this involvement. One important opportunity is the ability to share your work and expertise with others in your field, and an excellent way to do this is by taking part in the TAPPI Journal peer-review process, either as an author or a reviewer or both.
Journal articles
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Comparing a linear transfer function-noise model and a neural network to model boiler bank fouling in a kraft recovery boiler, TAPPI Journal, July 2024
ABSTRACT: Boiler bank fouling reduces heat transfer efficiency in kraft recovery boilers. Here, we model the relationships between boiler parameters and boiler bank pressure drop, an indicator of fouling, based on recovery boiler operating data. We compared two models: an autoregressive integrated exogenous (ARIX) model and a feedforward neural network. The ARIX model better simulates boiler bank pressure drop compared to the neural network (R2 of 0.64 vs. 0.58). Based on the ARIX model, we identified six boiler parameters that significantly influence boiler bank fouling and their relative contributions. Finally, we demonstrate how the models can simulate boiler bank pressure drop given artificial perturbations in boiler parameters.
Journal articles
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A model black liquor formulation for use in development and evaluation of membranes for concentrating weak black liquor, TAPPI Journal February 2022
ABSTRACT: As part of a larger program to develop robust membranes for concentrating weak black liquor prior to the evaporation step, several commercially available membranes were tested for suitability in this application. Given the variation in kraft black liquor for various wood species, the mill-to-mill variations, and the challenges of obtaining fresh samples, the need became apparent for a synthetic reference black liquor that would allow any membrane developer to test a new prototype membrane and compare the results with others. We present a formulation for a model black liquor (MBL) similar to real kraft black liquor in the composition of the major species that can be formulated from readily available reagents. The MBL was tested with two commercial membranes and resulted in similar levels of lignin retention as the real black liquor. It also showed similar viscosity behavior to real black liquor as a function of solids content.
Journal articles
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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
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New learnings and strategies for meeting future recovery boiler particulate emission limits with existing electrostatic precipitators, TAPPI Journal June 2021
ABSTRACT: It is foreseeable that recovery boiler particulate emission limits in the United States and Canada will continue to get more stringent with time. Because of this, continued improvement of emission control equipment, as well as a better understanding of how operating parameters affect performance, are necessary. Although electrostatic precipitators (ESPs) are often viewed as a mature technology, many improvements in ESP technology continue to be developed. In recent years, academic efforts have improved the understanding of recovery boiler operating conditions on ESP performance. Additionally, advancements in materials, power supplies, and design continue to improve the efficiency and reliability of ESPs.This paper discusses how recovery boiler and electrostatic precipitator (ESP) operating factors affect ESP perfor-mance based on process simulations and practical experience, and how these learnings can be implemented to improve future operation of existing ESPs.
Journal articles
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Repulping of wet strength paper towel with potassium monopersulfate, TAPPI Journal September 2020
ABSTRACT: Potassium monopersulfate (KMPS) was used in repulping of polyamide-epichlorohydrin (PAE)-containing paper towel. The effectiveness of the repulping aid was compared with that of sodium hypochlorite. Addition of a 2.4% KMPS repulping aid achieved complete repulping of the paper towel, resulting in 88% screen yield and about 5% rejects. To reach a similar pulping result, two times the oxidative equivalent amount of sodium hypochlorite had to be used. Compared to the pulp fibers obtained from sodium hypochlorite repulping, those obtained from KMPS repulping had higher physical strength, longer fiber length, and lower fines content. This study demonstrated that KMPS was superior to sodium hypochlorite in repulping of PAE-containing paper towel in terms of effectiveness and pulp quality.
Journal articles
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External fibrillation of wood pulp, TAPPI Journal June 2023
ABSTRACT: Pulp refining produces external fibrillation consisting of fibrils tethered to fiber surfaces, in addition to loose fibrils and fines. Both contribute to a larger bonding area that increases paper strength, but tethered fibrils have less likelihood of being washed out during papermaking. This study postulates the mechanism by which refining produces external fibrillation and the optimum conditions for doing so.The postulated mechanism is surface abrasion during sliding of fibers in refiner gaps. External fibrillation occurs when forces are great enough to partially dislodge fibrils from fiber surfaces, but not large enough to break the fibrils. The refining intensities to achieve these forces were determined by a mathematical model and experiments using a laboratory disc refiner. The optimum intensities in terms of specific edge load (SEL) for chemical pulps were about 0.1 J/m for hardwoods and 1.0 J/m for softwoods. An extension of this study suggested that abrasion may also account for most of the energy consumed in the mechanical pulping process.
Journal articles
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Evaluating the effect of recovery boiler operation on green liquor dregs concentration using multivariate analysis, TAPPI Journal June 2023
ABSTRACT: Poor settling and filterability of green liquor dregs has been a persistent problem in many kraft pulp mills. While the concentration and settling/filtering behaviors of dregs are expected to be related to how black liquor is burned in recovery boilers, the effect of boiler operation is not well understood. A systematic study was conducted to examine how recovery boiler operation may affect the dregs concentration in the raw green liquor (RGL) at three kraft pulp mills using SIMCA, a multivariate data analysis (MVDA) program. Daily average boiler operating data from three kraft mills were analyzed over a 3-year period. Results of both principal component analysis (PCA) and partial least squares regression (PLS) suggest that the main boiler operations contributing to high dregs concentrations in RGL are low liquor firing load, low bed temperature, poor char burning, and unstable char bed.
Journal articles
Magazine articles
Combatting lime kiln ringing problems at the Arauco Constitución mill, TAPPI Journal July 2020
ABSTRACT: The lime kiln at the Arauco Constitución mill experienced severe ringing problems requiring it to be shut down for ring removal every 3 to 6 months. The mill controlled the problems by blasting ring deposits off during operation with its existing industrial shotgun and a newly installed Cardox liquid carbon dioxide (CO2) cartridge system. Various ring blasting procedures were tested to determine the optimum ring location and thickness to blast; the optimum depth to insert the CO2 cartridge into the kiln; and the most effective blasting frequency and sequence to employ. The best strategy was found to be the weekly blasting operation that alternated between the liquid CO2 cartridge and the industrial shotgun, with the CO2 cartridge inserted into the ring mass, 20 cm (8 in.) away from the refractory brick surface, and the shotgun aimed at rings at about 28 m (92 ft) from the kiln discharge end. With each blasting event removing considerably more rings than before, it takes a longer time for rings to rebuild, allowing the kiln to run continuously between annual maintenance shutdowns with only a few short (< 4 h) downtimes for ring removal. This substantially reduces the costs associated with ring removal and lime replacement during unscheduled shutdowns.