Search
Use the search bar or filters below to find any TAPPI product or publication.
Filters
Content Type
Publications
Level of Knowledge
Committees
Collections
Journal articles
Magazine articles
Continuous digester rapid thinning, TAPPI Journal June 2024
ABSTRACT: Carbon steel continuous digesters built after the early 1980s are fully stress relieved, so stress corrosion cracking has been less of a concern. However, these newer digesters were designed to run modified cooking processes that have turned out to be much more corrosive than those running with conventional cooking. This corrosion is mainly associated with softwood digesters and appears to be flow related. Average corrosion rates of 40 mil/year are possible on the exposed shell between the wash and extraction screens. The corrosion patterns are visually distinct from surfaces in the upper digester and below the wash screens. This paper goes into practical detail on where it occurs, the causes, visual identification, inspection planning and results evaluation, and finally, how to mitigate this damage, which consists of applying a corrosion resistant barrier. Some discussion on dealing with general corrosion throughout the digester is included.
Journal articles
Magazine articles
Online monitoring of the size distribution of lime nodules in a full-scale operated lime kiln using an in-situ laser triangulation camera, TAPPI Journal June 2024
ABSTRACT: To maximize efficiency of the recausticizing process in a pulp mill, producing a reburned lime with high and consistent reactivity is process critical. Prior investigations have demonstrated a correlation between the reactivity of lime and its nodule size, as well as the dusting behavior of the kiln. Therefore, monitoring the nodule size produced in the lime kiln could be a promising indirect method to measure the performance of the lime kiln. The objective of this investigation was to evaluate the utility of a laser triangulation camera for online monitoring of nodule size distribution for the lime kiln. A series of full-scale trials were performed in a lime kiln of a kraft pulp mill in which a camera was installed at the exit conveyor to analyze the lime discharging from the kiln. The nodule size distribution was analyzed for correlation with the lime temperature, flue gas temperature, and rotational speed of the kiln. The monitoring demonstrated temporal stability, and the results showed that the lime temperature had the most significant effect on the nodule size. The rotational speed of the lime kiln and the flue gas temperature showed limited effect on nodule size, but they had significant impact on the specific energy demand. The overall conclusion of the study is that the camera methodology effectively correlates lime temperature with nodule size distribution, and it advocates for the methods of implementation in automating lime temperature control, facilitating the production of consistently reactive lime at a lower specific energy consumption.
Journal articles
Magazine articles
Optimizing OCC refining with defloccing, TAPPI Journal April 2025
ABSTRACT: Subjecting pulp to a high shear zone immediately after refining results in more efficient refining. This phenomenon was originally observed to benefit softwood pulp refining. It was attributed to floc reduction based on floc measurements in mill refiners and the observation of reduced headbox plugging. Hence, this phenomenon has been termed “defloccing.” The present work shows this technology also benefits refining of North American old corrugated containers (OCC). The combined results of several mill trials with OCC defloccing demonstrate the interactions between OCC refining intensity, defloccing technology, and other state-of-the-art refining improvements. At the same refining intensity, defloccing OCC on 100% recycled machines increases OCC refining efficiency by 15%, with greater efficiency improvement on machines that use softwood as well as OCC. Furthermore, it is shown that the benefits of defloccing are additive to refining improvements made in the refining zone of a refiner plate. Most OCC refiner plate designs can therefore benefit from the addition of a defloccing feature.
Journal articles
Gap mechanics in pulp refiners, TAPPI Journal June 2025
ABSTRACT: Studies of pulp refining have shown that a single bar impact on pulp has only a 1%•5% probability of producing a successful refining effect. This study has explored the reason why. An analysis of refining kinetics suggested that small segments of a fiber length, about a fiber diameter in size, are treated during each impact. Measurements of localized swelling along fiber lengths caused by refining supported this finding. Based on these findings, it was postulated that force transmittal through fiber networks occurred primarily at fiber crossings. The small size of fiber diameters relative to fiber lengths accounts for the low probability of a successful refining event at each impact. This probability, and the probability of fibers being captured and impacted during passage through a refiner, account for the need for multiple bar crossings to refine pulps.
Journal articles
Effect of pulp refining on thixotropy of cellulose fiber suspensions, TAPPI Journal September 2025
ABSTRACT: This paper presents results on the thixotropic behavior of low-consistency bleached eucalyptus fiber suspensions that had been mechanically treated. The pulps were refined in a PFI mill at different numbers of revolutions (0, 3000, and 6000) to study the effect of refining intensity on the viscosity time-response of fiber suspensions. In steady rheological tests, all the suspensions exhibited shear thinning behavior and no significant differences were observed after mechanical treatment. Stepwise experiments showed that viscosity continuously increased with time when shear rate was suddenly reduced. Additionally, a delay in time evolution of viscosity was observed as the pulp was more refined. A stretched exponential model was fitted to the experimental results of viscosity.
Journal articles
Toward environmental resilience in pulp and paper manufacturing: Water consumption and carbon dioxide emission reductions, TAPPI Journal September 2025
ABSTRACT: Pulp and paper manufacturing is a water- and energy-intensive industrial sector, necessitating improvement of its operational efficiency, as well as reduction of emissions to the maximum extent possible. This review focuses on the reduction of water consumption and carbon dioxide (CO2) emissions that originate in the pulp and paper industry (PPI). First, process simulation and optimization techniques used for water consumption reduction are reviewed. Then, techno-economic analyses of solvent-based CO2 capture from PPI are discussed. Additionally, key actions are proposed for enhancing water consumption reduction and CO2 capture in PPI.
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
Support for innovation and workforce development, TAPPI Journal August 2026
Advanced manufacturing is gaining attention in developed economies due to national security issues, calls for developing domestic supply chains, and more importantly, the need for creating jobs. COVID-19 exposed vulnerabilities in the manufacturing of lifesaving and critical items such as N95 masks. Tariffs are considered one avenue to protect domestic manufacturing, but in the case of manufactured products like commodity textiles, a tariff barrier alone will not be able to bring back manufacturing. It is a beneficial move by the U.S. government to boost manufacturing through investments in research and development (R&D), enhancing the advanced manufacturing sector focusing on defense and medical items through the establishment of centers like the Advanced Functional Fabrics of America. Additionally, schemes to grow a skilled workforce both at factory and R&D levels will be valuable.
Journal articles
Black liquor spray properties in-furnace conditions for swirl cone nozzles, TAPPI Journal July 2026
ABSTRACT: Recovery boiler furnace operation is controlled for high chemical recovery, high steam production, and low emissions. Good control allows long runs with minimum cleaning without expensive shutdowns. An essential variable affecting boiler operation is black liquor spraying into the furnace. Poorly controlled black liquor spraying causes difficulties, e.g., in chemical recovery, fouling of heat transfer surfaces, and decreased energy production. A challenging measurement strategy with three different swirl cone nozzles . types A, C, and T . was carried out at a mill in the United States. Black liquor spray properties were measured under in-furnace conditions for flow rates of 2.0 L/s to 3.0 L/s. Three spraying temperatures of 119™‹C, 122™‹C, and 126™‹C, which were 2™‹C, 5™‹C, and 9™‹C above the boiling point (ƒ¢Te), were tested. These flow rates and temperatures are typical for industrial nozzle sizes with exit orifice sizes of 17 mm and 22 mm. An imaging method to measure droplet size in a highly challenging furnace environment was developed. Droplet volume median diameter (Dv50) for nozzles A, C, and T varied between 7 mm to 4 mm, 7 mm to 5 mm, and 8 mm to 6 mm, depending on the flow rate and temperature. The high number of droplets detected by the analysis program enabled data fitting into statistical correlations. The size and width parameters for the Rosin™]Rammer droplet size distribution function could be defined. The droplet size distribution was found to be surprisingly wide, probably because of swollen droplets. Spray velocity was measured in two locations, 5 cm from the nozzle and 1.8 m from the nozzle. Near the nozzle, the average velocity increased from 7.3 m/s to 13 m/s when the flow rate was increased from 2 L/s to 3 L/s. Increase of black liquor temperature increased spray velocity in most of the cases. At the distance of 1.8 m from the nozzle, average spray velocities varied between 4.0 m/s to 11 m/s, depending on nozzle geometry, flow rate, and temperature. The opening angles of the spray for nozzles A and C varied between 57™‹ to 78™‹. The opening angle of nozzle T with flow guide varied between 48™‹ to 56™‹. The highest penetration of the spray was estimated for nozzle T because of the narrow spray and large droplets.
Journal articles
Controlling sulfidity by recycling sulfur in CNCG, TAPPI Journal July 2026
ABSTRACT: Pulp and paper mills have faced a major dilemma. On one hand, mills should not dispose of the side streams by mixing them with effluent water. On the other hand, there has been no other way to dispose of excess sulfur than getting rid of recovery boiler electrostatic precipitator (ESP) ash and buying sodium hydroxide to replace lost sodium. A new, yet old, process has been introduced to alleviate the problem. An alternative is the onsite production of sulfuric acid (H2SO4) to significantly reduce, or to even eliminate, the need for recovery boiler fly ash dumping. A sulfuric acid plant produces concentrated commercial quality H2SO4 from concentrated non-condensable gases (CNCGs). Up to 99.9% of the sulfur in CNCGs can be converted into concentrated sulfuric acid with this wet-gas sulfuric acid (WSA) process. There are already references on pulp mills highlighting that the process is straightforward to use. Mills can increase the amount of sulfur in CNCGs by controlling the heavy back liquor storage time and temperature. This opens up a new way to control the mill sulfidity by recycling sulfur. The effect of recycling sulfur is highlighted with reference mills. Due to integrated paper production, the Northern Mill is a large energy consumer, producing mostly softwood-based end products. The Eucalyptus Mill is a large standalone hardwood (eucalyptus) pulp mill where electricity is produced substantially in excess of its own use. As a sample case, lignin production with and without sulfur recycling is presented.