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Saving Money in Wastewater Treatment, Paper360º March/April 2024

Summaries from TAPPI Journal, Paper360º May/June 2024

Use of fines-enriched chemical pulp to increase CTMP strength, TAPPI Journal April 2021

ABSTRACT: In this study, fines-enriched pulp (FE-pulp)—the fine fraction of highly-refined kraft pulp—was benchmarked against highly-refined kraft pulp (HRK-pulp) as a strength agent in eucalyptus chemithermomechanical pulp (CTMP). Both the FE-pulp and the HRK-pulp were produced from unbleached softwood kraft pulp, and equal amounts of those strength agents were added to the original CTMP, as well as to washed CTMP, where most of the fines had been removed. The effects of the added strength agents were evaluated with laboratory handsheets.The FE-pulp proved to be twice as effective as HRK-pulp. Both HRK-pulp and FE-pulp increased the strength of the CTMP handsheets. The bulk of the handsheets decreased, however, as well as the drainability. The addition of 5% FE-pulp resulted in the same strength increase as an addition of 10% HRK-pulp, as well as the same decrease in bulk and CSF. For the handsheets of washed CTMP, the strengths were not measurable; the CTMP lost the sheet strength when the CTMP-fines content was reduced through washing. The reduced strength properties were compensated for by the addition of chemical pulp fines that proved to be an efficient strength agent. The addition of 5% FE-pulp restored the strength values, and at a higher bulk and higher drainability.

Ultrastructural Behavior of Cell Wall Polysaxxharides, TAPPI Journal April 2022

ABSTRACT: Considerable information on the ultrastructural organization of the plant cell wall and the supermolecular arragement of the cell wall components, in particular of cellulose, has been obtained with the electron microscope.

A feasibility study of using the organic Rankine cycle for power generation from the flue gases of recovery boilers, TAPPI Journal August 2022

ABSTRACT: Almost 415 tons/h of flue gases with a temperature of 160°C are released to the atmosphere from the recovery boiler of a pulp mill with capacity of 1000 air dried (a.d.) metric tons of pulp per day. This is a large waste heat stream that can be used to generate power, to decrease the operating costs of a pulp mill, and to save carbon dioxide (CO2) emissions. In this work, the feasibility of using an organic Rankine cycle (ORC) with ammonia as the working fluid to generate power from the flue gases of recovery boilers is studied. CHEMCAD and Taguchi methods are used for simulation of the process and for optimization of operating conditions, respectively. The temperature of the ammonia and flue gases at the exit of evaporator, exit pressure of the pump and turbine, and the degree of subcooling of ammonia at the exit of the condenser are five operating parameters that are manipulated to optimize the process. Three different scenarios are defined: minimizing the net power cost, maximizing the ORC efficiency, and maximizing the net profit. Different aspects of these scenarios, such as net power generation, cost, efficiency, and CO2 emission savings are discussed, and optimum operating conditions are reported.

Causes of poor dregs settling in a green liquor clarifier, TAPPI Journal August 2022

ABSTRACT: A study was conducted to examine the most likely parameters responsible for poor dregs settling at a kraft mill over a 2.5-year period, using multivariate data analysis (MVDA) and machine learning (ML) techniques. The dregs settling behavior seems to be seasonally influenced, implying that wood quality variation can be a factor. The results from the MVDA/ML analysis show that poor dregs settling is correlated to incomplete combustion and/or low load conditions in the recovery boiler, low sulfidity in the causticizing plant, and high flow in the green liquor•weak wash cycle. Compositions of dregs and black liquor were also examined to identify correlations with impaired dregs settling. The results show that poor dregs settling strongly correlates with high silicon (Si) content in dregs and moderately correlates with high iron (Fe) and high aluminum (Al) contents, and with low bulk density in dregs. For mills that experience dregs settling or green liquor filtering issues, regular compositional analyses of dregs, green liquor, weak wash, and black liquor are recommended in order to monitor the dynamics of silicon and other constituents in the recovery cycle.

Utilization of kraft pulp mill residuals, TAPPI Journal February 2022

ABSTRACT: Kraft pulp mills produce on average about 100 kg of solid residuals per metric ton of pulp produced. The main types of mill waste are sludge from wastewater treatment plants, ash from hog fuel boilers, dregs, grits, and lime mud from causticizing plants and lime dust from lime kilns. Of these, about half is disposed of in landfills, which highlights the need and potential for waste recycling and utilization. Sludge is either incinerated in hog fuel boilers to generate steam and power or used in various forms of land application, including land spreading, composting, or as an additive for landfill or mine waste covers. The majority of hog fuel boiler ash and causticizing plant residues is landfilled. Alkaline residuals can be conditioned for use in land application, manufacture of construction materials, and production of aggregates for road work. This technical review summarizes residuals utilization methods that have been applied in pulp and paper mills at demonstration- or full-scale, and therefore may act as a guide for mill managers and operators whose goal is to diminish the costs and the environmental impact of waste management.

Preparing prehydrolyzed kraft dissolving pulp via phosphotungstic acid prehydrolysis from grape branches, TAPPI Journal January 2022

ABSTRACT: Dissolving pulp was successful prepared via phosphotungstic acid (PTA) prehydrolysis kraft (PHK) cooking followed by an elementary chlorine-free (ECF) bleaching process from grape branches. The effects of prehydrolysis temperature, reaction time, and PTA concentration that potentially affect the quality of dissolving pulp product on chemical components of pulp were studied via an orthogonal experiment. The structure of lignin was activated during the PTA prehydrolysis phase, and lignin was easily removed during the following cooking process. Thus, relatively mild conditions (140°C, 100 min) can be used in the cooking process. During the prehydrolysis phase, temperature exhibited the most significant influence on the cellulose purity of the obtained pulp fiber, followed by reaction time and PTA concentration. The optimized prehydrolysis conditions were as follows: prehydrolysis temperature, 145°C; reaction time, 75 min; and PTA concentration, 1 wt%. Whether the excessively high prehydrolysis temperature or prolonging the reaction time did not favor the retention of long chain cellulose, the delignification selectivity for the cooking process could not be further improved by excessive PTA loading. Under these prehydrolysis conditions, 94.1% and 29.0% for a-cellulose content and total yield could be achieved after the given cooking and bleaching conditions, respectively. Moreover, the chemical structure and crystal form of cellulose were scarcely changed after PTA prehydrolysis, which could be confirmed by results from Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). PTA prehydrolysis could be considered as an alternative method for preparing PHK dissolving pulp under relatively mild cooking conditions.

Understanding the risks and rewards of using 50% vs. 10% strength peroxide in pulp bleach plants,TAPPI Journal December 2024

Authors: Alan W. Rudie and Peter W. Hart | TAPPI J. 17(11): 601(2018) - ABSTRACT: The use of 50% concentration and 10% concentration hydrogen peroxide were evaluated for chemical and mechanical pulp bleach plants at storage and at point of use. Several dangerous occurrences have been documented when the supply of 50% peroxide going into the pulping process was not stopped during a process failure. Startup conditions and leaking block valves during maintenance outages have also contributed to explosions. Although hazardous events have occurred, 50% peroxide can be stored safely with proper precautions and engineering controls.  For point of use in a chemical bleach plant, it is recommended to dilute the peroxide to 10% prior to application, because risk does not outweigh the benefit. For point of use in a mechanical bleach plant, it is recommended to use 50% peroxide going into a bleach liquor mixing system that includes the other chemicals used to maintain the brightening reaction rate. When 50% peroxide is used, it is critical that proper engineering controls are used to mitigate any risks.

Wheat straw as an alternative pulp fiber, TAPPI Journal December 2024

Author: Peter W. Hart | TAPPI J. 19(1): 41(2020) - ABSTRACT: The desire to market sustainable packaging materials has led to an interest in the use of various fiber types as a raw material. It has been suggested that the use of annual crops for partial replacement of wood fiber would result in more sustainable products. Several life cycle analyses (LCA) have been performed to evaluate these claims. These LCAs provided conflicting and contradictory results because of the local conditions and the specific pulping processes investigated. Selected LCAs are reviewed and the underlying reasons for these conflicting results are analyzed.