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Journal articles
Optimization of energy efficiency and condensate production in evaporation plants for a modern softwood pulp mill, TAPPI Journal April 2026
ABSTRACT: To meet the need to further improve thermal efficiency and environmental performance of kraft pulp mills, new systems and techniques have been developed within the evaporation plant. This paper describes these novel approaches and how they were implemented in a project completed in 2018 for a new evaporator and condensate treatment system supplied by Valmet at the SCA Östrand market pulp mill in Sweden. This project was part of a stepwise upgrade of the complete mill to increase the production capacity of the mill from 430,000 to 900,000 air-dried metric tons/year (ADt/y). As part of this upgrade, the mill had the objectives to increase the energy efficiency of the pulp mill and to minimize the air emissions as much as possible, the effluent volume, and the water usage in the mill. The mill also wanted to have the disposal of the biosludge in the black liquor, and the production of tall oil from black liquor soap, liquid methanol, and turpentine. This required that the new evaporation and condensate treatment system be very closely integrated into the other process departments of the mill, including integration of the hot weak black liquor flash vapor from the digester directly into the evaporator train and the production of multiple streams of clean evaporation plant condensate at the correct temperature for the bleach plant. Heat and mass balance calculation values, which were found to do very well in predicting the effect on actual mill operation, are also presented in this paper.
Journal articles
A systems approach for process debottlenecking towards a sustainable pulp and paper industry, TAPPI Journal April 2026
ABSTRACT: Increasing the competitiveness of the pulp and paper industry requires an effective optimization of its existing assets in line with a long-term vision for process transformation, production upgrade, and product diversification. Currently, pulp production increase is one of the main sources of additional revenue for the kraft industry. Likewise, energy efficiency is often employed as a cost-effective approach to reduce operating costs, enhancing the possibilities to lower fossil fuel consumption and contributing to a low-carbon economy. On the other hand, reaching higher production targets and facilitating process transformation, such as biorefinery implementation, heavily depend on the status and performance of a mill’s current infrastructure; therefore, a system analysis is needed to assess the new production requirements, the bottlenecks, and the interactions across departments. In order to obtain practical improvement solutions, direct and indirect impacts on process performance and resource utilization should be considered. This work provides an overview of the key challenges that need to be addressed for production increase and energy efficiency improvement. The methodology starts by a scope analysis for debottlenecking and screening capacity limitations vs. mill targets, followed by their ranking (bottleneck ranking diagram). Benchmarking, gap analysis, and root-cause techniques are applied to diagnose system inefficiencies. This mill-wide debottlenecking assessment is then used to guide the selection of a long-term sustainable operation and design a portfolio of improvement projects by avoiding cross effects of the short-term projects on the long term. A case study of a kraft pulp mill is used to illustrate the proposed methodology.
Journal articles
Examination of scoring parameters of corrugated fiberboard, TAPPI Journal August 2026
ABSTRACT: One of the less interrogated aspects of corrugated packaging are scoring and scoring profiles, the intentional localized crushing of flutes to accommodate package folding and closure. This study explores the effect of scoring parameters on box compression test strength (BCT) of two balanced corrugated boards. Scoring differences produced BCT that varied by 10% for one board and less for the other board. Parameters from 4-point bending of scored specimens showed some correlation with BCT, while eccentricity and torsion parameters had less correlation. Different scores produced BCT differences that were not strongly predicted by most standard tests in the current study, implying other tests may be needed to examine the actual boundary conditions on a box during compression. In a few cases, aggressive scoring produced cracked score lines, and those containers had lower BCT than containers with uncracked score lines.
Journal articles
Investigating the causes of severe economizer tube thinning in a spent sulfite liquor (SSL) boiler, TAPPI Journal August 2026
ABSTRACT: In this study, the causes of tube thinning in the economizer of an ammonia-based spent sulfite liquor (SSL) boiler in a Canadian pulp mill are investigated. The tube thinning was most severe in the upper tube rows of the lowest economizer sections where the tube surface temperature ranges between about 180°C and 210°C. The location, the temperature range, and the results of a tube failure analysis indicate that some form of corrosion- erosion is the main cause for the tube thinning. The process is likely initiated by the formation of potassium bisulfate in tube deposits. We hypothesize that some areas in the economizer, including gaps in tube shields, have allowed for temporary buildup of deposits that were not fully removed by sootblowing. Potassium bisulfate is highly hygroscopic, so it readily absorbs moisture, forming an acidic solution leading to corrosion. The corrosion products are removed by the erosive effects of high velocity gas movement, causing the tube thinning. The high-speed fluid flow may be a result of sootblower action and/or enhanced flue gas velocity due to channeling. The tube thinning eventually leads to perforation and leakage.
Journal articles
Editorial: TAPPI Journal research themes in 2025 highlighted sustainability and process efficiency, TAPPI Journal February 2026
Each year, the pages of TAPPI Journal offer more than a collection of technical papers -- they provide a sanpshot of where our industry is appling its intellectual energy in research. Looking back at the January through November 2025 issues, there was a distant focus on improving materials performance, strenghtening process efficiency, and integrating sustainability considerations into existing manucaturing processes. A majority of this focus was centered on packaging for a variety of applications.
Journal articles
Beyond the machine: Decoding process water microbes behind odor in papermaking, TAPPI Journal February 2026
ABSTRACT: Paper manufacturing processes create an ecosystem conducive to microbial growth, characterized by abundant water, nutrients, and optimal temperatures, fostering diverse microbial habitats. With the increased use of recycled fibers and greater water system closure, the industry now faces amplified microbiological challenges, particularly odor generation. These odor problems have raised community concerns, as shown by resident com-plaints, and have led to significant economic impacts, including costly lawsuits against major paper manufacturers. Based on earlier studies showing that microbes in papermaking systems can generate odor-causing volatile com-pounds, this study is guided by the hypothesis that recycle paper mill process water harbors odor-causing microbial communities and thus represents a primary source of malodor. To test this hypothesis, process water samples from commercial recycle paper mills were analyzed using high-throughput Illumina sequencing to characterize microbial communities in one complete analysis. The study results revealed fifteen major microbial populations, dominated mainly by the genus Pseudomonas. The identified microbes were further linked to prior literature to determine their functional roles in odor generation, including the production of haloanisoles (2-monochloroanisole, 2,4-dichloroanisole, 2,3,6-trichloroanisole, 2,4,6-tri-bromoanisole), geosmin, 2-methylisoborneol, and volatile organic sulfur compounds such as dimethyl polysulfides, hydrogen sulfide, and methylmercaptan. This study introduces a microbiological community-profiling approach that enables papermakers to assess whether process water represents a potential source of malodor. Earlier studies have not examined microbial com-munities in recycle paper mill process water specifically from the perspective of identifying malodor sources, nor have they integrated such findings with an extensive literature-based assessment. The findings of this study advance both science and practice by offering a method that can serve as an early diagnostic tool for papermakers, supporting effective future odor management and deepening understanding of microbial ecology in paper mill environments.
Journal articles
Editorial: New research sheds light on critical processes in the recovery cycle, TAPPI Journal July
The chemical recovery cycle has been called the backbone of a kraft pulp mill, making modern paper production both economically and environmentally sustainable. It regenerates pulping chemicals (primarily sodium hydroxide and sodium sulfide) used to separate wood fibers, allowing them to be reused rather than continuously replaced, while also recovering energy by burning the organic components of black liquor to produce steam and electricity that supply much of the mill’s power needs. In addition, the recovery cycle minimizes waste, reduces emissions, and recovers valuable by-products, creating a highly efficient closedloop system. Without this process, chemical costs, energy consumption, and environmental impacts would increase, making large-scale kraft pulping significantly less economical and sustainable.
Journal articles
Alternative disposal methods for pulp mill biosludge
ABSTRACT: The chemical pulp production process produces notable amounts of biosludge, mostly in the wastewater treatment system. Biosludge is a problematic waste stream due to its properties, and recently, its amounts have been on the increase. The most used disposal processes are incineration in a bark boiler or a recovery boiler now that landfilling is no longer permitted by legislation in many countries. Incineration of wet sludges with poor drying characteristics decreases the energy efficiency of the process. Biosludge is typically mixed with black liquor in the evaporation plant before feeding to the recovery boiler. Although the recovery boiler is designed to handle challenging fuels, biosludge disposal requires consideration of its behavior during evaporation and accumulation of non-process elements in the recovery cycle. This study discusses the currently used sludge handling methods and presents two novel methods, hydrothermal carbonization and anaerobic digestion, to convert sludge into a usable form. Production of hydrochar or biogas offers new usage possibilities for biosludge and improves the energy efficiency of the mill when the new methods replace incineration. The processes are still developing, and thus their economic feasibility is uncertain; however, depending on the case details, they can be considered promising alternatives to be implemented in the future.
Journal articles
Modern NCG practice, TAPPI Journal July 2026
ABSTRACT: New innovations have been put in operation for collection and handling systems of noncondensable gases (NCGs) in modern kraft pulp mills. This work investigates technologies in new pulp mills that aim to achieve the benefits of odor-free processes while enhancing chemical circulation within the mill. It describes and discusses both past and current systems for collecting and handling NCGs. The mills studied have designed and implemented their NCG systems within the past 10 to 15 years. New innovations have emerged, offering promising methods to further reduce occasional sulfurous odor emissions from the kraft process. These methods explore pretreatment and sulfuric gas stream reuse options in process units where these gases are generated or during the transportation of these side streams to their final destruction site. Using modern practices outlined in this paper, malodorous gases can be collected to the extent that a kraft pulp mill is essentially odor-free pending operator errors or major equipment malfunctions. One of the difficult aspects is that NCG systems in kraft mills are often designed case-by-case, as well as by various equipment vendors and with varying numbers of destruction sites. The actual detailed design depends on the chosen layout, process configuration depending on individual equipment purchased, and even on the design practices of individual suppliers.
Journal articles
Effects of calcium on sodium salt scaling with the presence of resin acids and fatty acids, TAPPI Journal June 2026
ABSTRACT: Reintroducing tall oil soap or its related products into high dry solids black liquor has been found to reduce sodium salt scaling in falling film evaporators. Aside from resin acids and fatty acids, which are the likely scale inhibitors, calcium is reintroduced into black liquor because of the relatively high calcium content of tall oil soap. One concern is that this increase in calcium content might lead to the formation of additional calcium and sodium scales in evaporators. In this work, we investigated the relationship among trace amounts of calcium, sodium salts, resin acids, and fatty acids in a controlled system using a model salt solution and a benchtop setup. We studied the effects of the calcium carbonate addition and calcium carbonate scales on sodium salt scaling in the presence of resin acids and fatty acids. We found that some calcium carbonate is incorporated in the precipitated sodium crystals, and the suspended sodium crystals become larger and more compact with increasing calcium carbonate concentration. Experiments in the benchtop setup show that precipitating calcium carbonate scale on the heat exchanger does not lead to a higher rate of sodium salt scaling. The solubility of calcium carbonate is not affected by the addition of resin acids and fatty acids. These findings indicate that the reduction in sodium salt scaling through the addition of tall oil soap is primarily related to resin acids and fatty acids, rather than to calcium or to interactions between calcium and mixtures of resin and fatty acids.