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TAPPI Journal Summaries, Paper360º July/August 2023

TAPPI Journal Summaries, Paper360º July/August 2023

Facing the Pressures of Cutting the Maintenance Budget, Paper360º July/August 2023

The Future of Pulp and Paper Investments in the PNW, Paper360º July/August 2023

TAPPI News, Paper360º July/August 2023

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.

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.

Water chemistry challenges in pulping and papermaking • fundamentals and practical insights: Part 2: Conductivity, charge, and hardness, TAPPI Journal June 2023

ABSTRACT: Although water is essential to the papermaking process, papermakers often overlook its importance and focus on fibers, fillers, 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. Water is an excellent solvent for ionic substances, both organic and inorganic. These substances contribute to system conductivity, charge, and hardness and significantly impact the papermaking process. Part 1 of this paper, published in TAPPI J. 21(6): 313(2022), discussed fundamental water properties, water chemistry, and the impact of pH on pulping and papermaking operations. In this paper, we review definitions, sources, and the typical symptoms of the effect of conductivity, charge, and hardness on the productivity of the papermaking process. Sources of conductivity, charge, and hardness impacting these factors, measurement methods, and available correction strategies for their control are also discussed.

Editorial: Progress continues in recovery cycle optimization, TAPPI Journal March 2023

ABSTRACT: Travel came to a halt just before the 2020 International Chemical Recovery Conference (ICRC) was to take place in Brazil. The ICRC was to be co-hosted in 2021 with TAPPI PEERS, but PEERS was eventually cancelled for that year as travel for many had not resumed. In early 2022, The University of Toronto hosted an online meeting in order to bring together the community of researchers and industrial engineers for an ICRC event. At this event, 19 research papers were presented.

Eucalyptus black liquor properties in a lignin extraction process: density, dry solids, viscosity, inorganic, and organic content, TAPPI Journal March 2023

ABSTRACT: Extracting lignin from black liquor is becoming more common, although only a few research papers discuss the impact of the process on the liquor’s primary properties. This work aims to determine the changes in black liquor properties as it undergoes a lignin extraction process using carbon dioxide (CO2). A diluted eucalyptus black liquor sample (DBL) was acidified with CO2 to a final pH of 8.5. After filtration, the kraft lignin was removed, and the filtrated lignin lean black liquor (LLBL) was collected. Five acidified black liquors (ABL) samples were collected during acidification at pH 10.5; 10.0; 9.5; 9.0; and 8.5. The samples were analyzed regarding lignin content in solution, sodium carbonate (Na2CO3), sodium sulfate (Na2SO4), density, dry solids content, and viscosity. While Na2SO4 remained almost constant, Na2CO3 presented an enormous increase in its concentration when comparing DBL with LLBL. As pH decreased, the lignin content in the solution was also reduced due to lignin precipitation. The results showed similar behavior for dry solids, density, and viscosity of the supernatant, but an increase in density was observed around pH 9.00. In light of this, the density of LLBL turns out to be closer to the one in the initial DBL. The significant increase in carbonate content could explain this behavior during acidification with CO2 once the inorganic content significantly influences the property. The viscosity was determined from 10 s-1 to 2000 s-1. We observed a Newtonian behavior for all samples. The increase in carbonate content in the sample is crucial information to the recovery cycle, especially for calculating the mass and energy balance when targeting the use of the LLBL.

On the diagnosis of a fouling condition in a kraft recovery boiler: combining process knowledge and data-based insights, TAPPI Journal March 2023

ABSTRACT: Fouling is still a major challenge for the operation of kraft recovery boilers. This problem is caused by accumulation of ash deposits on the surfaces of heat exchangers in the upper part of the boiler over time. The first consequence is the reduction of steam production due to loss of heat transfer and, finally, the shutdown of the boiler due to clogging. The present work investigated the operational condition of a modern kraft boiler under a critical fouling condition. This boiler had even faced a manual cleaning due to a clogging event. This analysis combined process knowledge, plant team experience, and a data-driven approach, given the complexity of the process. In this sense, historical data covering this critical period of operation were collected. After a cleaning procedure, they were used to obtain a predictive neural network model for the flue gas pressure drop in the boiler bank, which is an indirect measure of ash deposit accumulation. Once validated, it was used for sensitivity analysis, with the aim of quantifying the effects of the model inputs. Five variables out of eighteen accounted for nearly 60% of the total effect on pressure drop. Namely, primary air temperature (21.6% of the total effect) and flow rate (11.1%), black liquor flow rate (9.9%) and temperature (8.4%), and white liquor sulfidity (8.6%). The analysis of these results mainly suggested an excess of carryover, which composes the ash deposits. Recommended actions to mitigate the fouling condition involved adjustments to the primary air system before the more drastic solution of reducing the boiler load.