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Peracetate/singlet oxygen chemistry used in post-bleaching of kraft pulp as a practical oxidant for paper machines, TAPPI Journal May 2021
ABSTRACT: The use of a novel sodium peracetate/singlet oxygen chemistry for brightening bleached kraft pulp shows exciting potential for technical performance, supply logistics, safety, and cost reduction. Potential chemical carryover to the paper machine raises questions about whether peracetate will impact paper machine performance, such as metal corrosion, useful press felt life, and interference with existing biocide programs or paper machine chemistry. Sodium peracetate/singlet oxygen chemistry can be used in high-density storage chests for brightening/whitening and to increase color stability. Any oxidant used directly before the paper machine has the possibility of impacting paper machine operations. Traditional oxidants used in bleaching, such as chlorine dioxide and hydrogen peroxide, are known to cause corrosion on machinery metals and press felts. Hydrogen peroxide residuals can interfere with common biocide programs. Traditional oxidants used in biocide treatments themselves significantly degrade press felt life when the rule-of-thumb concentration thresholds are exceeded. Sodium peracetate is evaluated in this paper for its impact on nylon press felt fiber degradation, metal corrosion, and interference with typical biocide programs.Laboratory results indicate that sodium peracetate/singlet oxygen chemistry is less corrosive than chlorine, bromine, and hydrogen peroxide on press felt nylon fiber and can therefore be used at higher levels than those chemistries to increase brightness without increasing negative downstream impact. Sodium peracetate can also be used with current biocide programs without negative impacts such as consumptive degradation. Higher residuals of peracetate going to the paper machine may be useful as a biocide itself and can complement existing programs, allowing those programs to stay within their safe operating levels and thereby extend press felt useful life.
Journal articles
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Gas dispersion in the oxygen delignification process, TAPPI Journal May 2021
ABSTRACT: There has been very little knowledge about the state of gas dispersion in the oxygen delignification process, even though this has a major impact on the performance of the reactor. This paper presents a new continu-ous inline method for measuring oxygen bubble size distribution in the reactor, as well as results from studies con-ducted in softwood and hardwood lines. This new measurement worked well, and new information about oxygen bubble size, as well as how different reactor conditions affected the distribution, was obtained. For example:œ In the softwood line, the mean volume-weighted bubble size was about 0.1 mm, whereas in the hardwood line, this size was almost 10 times higher. For both lines, there was considerable variation in the measured bubble size over the long term.œ For both lines, an increase in mixer rotation speed caused a discernible decrease in the bubble size, and an increase in oxygen charge caused a discernible increase in the bubble size.œ In the softwood line, no coalescence of the bubbles in the reactor was observed, but in the hardwood line, some coalescence of the larger bubbles occurred.œ In the test conducted in the hardwood line, the use of brownstock washer defoamer caused a discernible increase in oxygen bubble size.œ In the hardwood line, reactor pressure had a noticeable effect on the amount of delignification, which indicated that improving mass transfer of oxygen (e.g., by decreasing the oxygen bubble size, in this case) should also have an increasing effect on the delignification.
Journal articles
Magazine articles
The role of gas dispersion in the oxygen delignification process, TAPPI Journal May 2021
ABSTRACT: Oxygen delignification is an essential part of the pulp production process. Delignification occurs with the aid of alkali and dissolved oxygen. Dissolved oxygen is obtained by dispersing oxygen gas into the pulp suspension by using efficient mixers. Little is known about the state of oxygen gas dispersion and its effect on oxygen delignification kinetics and efficiency. This paper will present the results for the effect of gas bubble size on the performance of oxygen delignification. The results are mainly based on detailed studies made in a Finnish hardwood mill where the oxygen bubble size distribution could be altered at the feed of the reactor. An essential aspect of these studies was the use of a new continuous inline gas bubble size measurement system to simultaneously determine the bubble size distribution at the feed and top of the reactor. Information about oxygen consumption in the reactor could also be obtained through the bubble size measurements. Accordingly, these studies quantify the effect of oxygen bubble size on the kappa reduction of the pulp. The effect of different chemical factors on the oxygen bubble size is also studied.Finally, the relationship between the gas bubble size and the liquid phase oxygen mass transfer coefficient (kLa) is presented. This connects the bubble size to the kappa reduction rate. Based on the presented modeling approach and the evaluation of practical factors that are not taken into account in the modeling, it was concluded that the volumetric average oxygen bubble size should preferably be smaller than 0.2 mm in practice.The information obtained with the new gas bubble size measurement system and the presented modeling approach give a very new basis for understanding, monitoring, adjusting, and designing oxygen delignification processes.
Journal articles
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Understanding the pulping and bleaching performances of eucalyptus woods affected by physiological disturbance, TAPPI Journal November 2018
Understanding the pulping and bleaching performances of eucalyptus woods affected by physiological disturbance, TAPPI Journal November 2018
Journal articles
Magazine articles
Lignin-based resins for kraft paper applications, TAPPI Journal November 2019
ABSTRACT: We investigated miscanthus (MS) and willow (W) lignin-furfural based resins as potential reinforce-ment agents on softwood and hardwood kraft paper. These resins might be sustainable alternatives to the commercial phenolformaldehyde (PF) resins. Phenol is a petrochemical product and formaldehyde has been classified as a carcinogen by the U.S. Environmental Protection Agency. The lignin used in this study was derived from hot water extraction (160ºC, 2 h) of MS and W biomass, and may be considered sulfur-free. These biorefinery lignins were characterized for their chemical composition and inherent properties via wet chemistry and instrumental techniques. The resin blends (MS-resin and W-resin) were characterized for their molecular weight, thermal behavior, and mechanical properties. Mechanical properties were measured by the resin’s ability to reinforce softwood and hard-wood kraft papers. The effect of adding hexamethylenetetramine (HMTA), a curing agent, to the resin was also examined. Mixtures of PF and lignin-based resins were investigated to further explore ways to reduce use of non-renewables, phenol, and carcinogenic formaldehyde. The results show that lignin-based resins have the potential to replace PF resins in kraft paper applications. For softwood paper, the highest strength was achieved using W-resin, without HMTA (2.5 times greater than PF with HMTA). For hardwood paper, MS-resin with HMTA gave the highest strength (2.3 times higher than PF with HMTA). The lignin-based resins, without HMTA, also yielded mechanical properties comparable to PF with HMTA.
Journal articles
Magazine articles
Kinetics of sulfur dioxide-alcohol-water (SAW) pulping of su
Kinetics of sulfur dioxide-alcohol-water (SAW) pulping of sugarcane straw (SCS), TAPPI JOURNAL June 2017
Journal articles
Magazine articles
Mechanical modification of softwood pulp fibers using a novel lightweight vertical bar plate, TAPPI Journal April 2021
ABSTRACT: Refiner plates made using sand casting have a draft angle, which results in a trapezoidal bar shape. These trapezoidal bar plates have a limited throughput compared to the vertical bar plates, and eventually the edges of the bars become dull, resulting in longer time to reach the target freeness and shorter service life. The new light-weight refiner plate with a bar insertion method into a plate base was developed by selecting an aluminium-based alloy as the plate base material and a stainless steel alloy with high wear resistance as the bar material. The light-weight plate with sharp bar edges was very effective in reducing refining energy by reaching the target freeness faster than the sand-cast bar plate. Finally, the lightweight sharp bar plate, which weighed only about half the weight of the cast bar plate, was expected to significantly contribute to easy replacement, improved paper quality, and larger throughput without excessive loss of fiber length.
Journal articles
Comparative evaluation of conical and double disk refiners: Effects of operating mode, refining intensity, and device geometry on energy consumption and paper properties, TAPPI Journal August 2026
ABSTRACT: This study investigates the effects of refiner operating mode and refining intensity adjusted via pulp flow rate, applied power, and refiner speed on the refining characteristics of high-yield southern softwood. We compared Valmet’s OptiFiner PRO (conical) and DD6700 (double disk) refiners under matched specific edge load (SEL) conditions. Batch and one-pass modes were evaluated for their impact on energy efficiency and physical paper properties. The results showed that while SEL provides a useful baseline, it does not fully account for differences in refiner geometry, particularly angular parameters. With the chosen plate sets, C-factor analysis revealed that the OptiFiner PRO delivers a lower number of fiber impacts at a higher intensity per impact compared to DD6700 at similar SEL, influencing fiber length, short-span compression test (STFI) index, and tear strength development. These findings offer actionable insights for mills seeking to optimize refining efficiency and cost. In summary, conical refiners may provide advantages in compression strength at mid-range energies, while double disk refiners maintain higher tear strength at elevated energies due to better fiber length preservation.
Journal articles
Simplified modeling of a complete rotary lime kiln at a pulp mill, TAPPI Journal February 2026
ABSTRACT: Rotary lime kilns are essential and complex components in pulp mills using the kraft process. They are primarily used to produce lime (CaO), which is then employed to make white liquor, the reagent used to separate wood fibers. To understand and improve the performance of the kiln, modeling its behavior is essential. However, the kiln operates through a complex combination of thermal and chemical phenomena. That is why a simplified approach was used to tackle this challenge. A zero/one-dimensional steady-state analysis was performed based on first principles to simplify the modeling process and reduce the need for experimental data. Additional assumptions, such as steady-state operation and the absence of a refractory lining, were introduced to further simplify the model so that it can be used for daily analysis. Moreover, the auxiliary equipment of the plant, such as the intercooler and preheat cyclone, is also modeled. The final model was validated using data from the literature and a two-month analysis of experimental measure-ments from the Burgo Ardennes lime kiln in Virton, Belgium. It shows good agreement with the available data, with a 6% deviation for the adiabatic flame temperature and a 17% average error in predicting the kiln shell outside temperature. For the fuel and lime flow rate predictions, also validated over the same two-month period, the errors were -6.6% and 0.6%, respectively.
Journal articles
Full-scale operation of a membrane-based black liquor concentrator, TAPPI Journal January 2026
ABSTRACT: For years, black liquor concentration by reverse osmosis has been an aspiration for reducing mill energy consumption and costs. Building on a 2023 report of an 81% reduction in the energy intensity for concentrating black liquor using its membrane platform at the pilot scale, this paper reports on the fabrication, installation, startup, and operation of the world’s first full-scale membrane-based black liquor concentration system at the International Paper Grande Prairie mill in Canada. The majority of the membrane modules in this system have reliably exceeded permeability expectations by more than 50%. In addition to strong membrane performance, the system has been a significant source of learnings for material specifications and system design. Incorporating these learnings and comparing to typical multiple effect evaporators, the system demonstrates a 43% reduction in capital cost for the same capacity, a 30% reduction in the lifetime cost of removing water from black liquor, and an 86% reduction in energy use. The impact on washer optimization was also considered, and net energy and chemical costs were reduced by US$3.8 and US$6.8/a.d. metric ton for a typical brown and bleach mill, respectively, when incorporating this technology. Completed in less than 12 months, the facility has demonstrated successful black liquor concentration at the 500 gpm scale with monthly uptime as high as 96%.