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A guide to eliminating baggy webs, TAPPI Journal June 2021
ABSTRACT: Slack or baggy webs can cause misregistration, wrinkles, and breaks in printing and converting operations. Bagginess appears as non-uniform tautness in the cross direction (CD) of a paper web. The underlying cause is uneven CD tension profiles, for which there are few remedies once the paper is made. Precision measurements of CD tension profiles combined with trials on commercial paper machines have shown that uniform CD distribution of moisture, basis weight, and caliper profiles at the reel are key to avoiding bagginess. However, the most important but infrequently measured factor is the CD moisture profile entering the dryer section. Wetter areas entering the dryers are permanently elongated more than dry areas, leading to greater slackness in the finished paper. In storage, wound-in tension can amplify baggy streaks in paper near the surface of a roll and adjacent to the core. Unwrapped or poorly wrapped rolls exposed to low humidity environments may have baggy centers caused by moisture loss from the roll edges.All of the factors that impact bagginess have been incorporated in a mathematical model that was used to interpret the observations from commercial trials and can be used as a guide to solve future problems.
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Using novel DNA methods to achieve higher process efficiency and performance, TAPPI Journal January 2023
ABSTRACT: Uncontrolled microbiological activity is a challenge for recycled fiber (RCF) mills as it can have negative effects on production and end-product quality. The microbes that exist in these systems have been largely unknown, and the strategies employed to control microbiology have been non-specific. Understanding the specific microbial groups present in RCF mills, their properties, and where they exist, as well as having the ability to accurately measure the true troublemakers, are key to targeted control of the bad actors. In this study, we present the results of a global survey of over 40 RCF paper machines. The same RCF-specific problem-causing bacterial groups were found on different continents, including large densities of newly identified bacteria in paper processes. Those can degrade cellulose and starch, produce acids and odorous substances, and have a significant impact on fiber strength and additive consumption. We also demonstrate how modern DNA tools can quantify the impact of biocidal countermeasures against the actual troublemakers, including bacteria found to degrade cellulose during RCF pulp storage, which may be linked to a negative impact on end-product strength. These novel DNA tools give producers updated biocide program key performance indicators (KPIs) and actionable information to more effectively design and adjust microbiological control to achieve higher process efficiency and performance.
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Non-process elements in the recovery cycle of six Finnish kraft pulp mills, TAPPI Journal March 2023
ABSTRACT: In this work, the aim was to study the distribution and accumulation of the non-process elements (NPEs) in the recovery cycle of Finnish pulp mills and look at whether the geographical location (North vs. South) correlates with the current Finnish NPE levels. In addition, a comparison to older similar Finnish measurements was made with an attempt to analyze the reasons behind differences in the most typical non-process elements, aluminum (Al), silicon (Si), calcium (Ca), phosphorus (P), magnesium (Mg), manganese (Mn), chlorine (Cl), and potassium (K), taking into account the main elements in the white liquor, sodium (Na) and sulfur (S). The extensive laboratory results gained in this study are from seven sampling points at six pulp mills and present analytical data of metal concentrations. The data obtained presents an update to previous NPE studies. The levels found did not statistically differ between North and South Finland. The NPE levels, apart from phosphorus, found in Finnish pulp mills today have not changed considerably compared to the levels in earlier investigations in the 1990s. In the newest data, the phosphorus concentration was consistently higher in the as fired black liquor, electrostatic precipitator (ESP) ash, lime mud, and green liquor than in the previous results. In addition, the levels of Al, Si, Ca, P, and Mg in recovery boiler ESP ash were consistently higher compared to the older results. As the mills start to close their systems more, a stronger accumulation of NPEs can be expected, increasing the likelihood of more operational problems in the process. Further understanding of where the NPEs accumulate and how they can be most effectively removed will be valuable knowledge in the future.
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Paper bending stiffness and web tension measurement from a running web using a vacuum and computer imaging, TAPPI Journal May 2023
ABSTRACT: A novel method for measuring the bending stiffness of paper online during manufacturing is introduced. The method uses photometric stereo imaging to detect the shape of the deflection surface caused by a controllable pressure difference over the paper’s surfaces. The hardware for the measurement is based on a combination of two existing sensors, which has accelerated and facilitated the development of the implementation. The deflection and loads are tied together by the governing differential equation for the bending of an orthotropic elastic plate with selected simplifications. An approach to resolve material parameters and in-plane loads without knowledge of traditional boundary conditions is suggested. The presented method was tested in a paper mill during manufacturing. For bending stiffnesses measured online, correlation coefficients 0.88 and 0.92 were obtained compared to state-of-the-art laboratory measurements. However, the results gained from a moving web are noisy and the data requires correction of the slope and an off-set. Although several issues remain to be resolved before the method can be considered as an accurate measurement for industrial use, the theoretical background, the performance of online implementation, and the results are promising. Possible causes for the observed discrepancies and the future development of the method are discussed.
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Black liquor evaporators upgrade — How many effects?, TAPPI Journal April 2023
ABSTRACT: Black liquor evaporation is generally the most energy intensive unit operation in a pulp and paper manufacturing facility. The black liquor evaporators can represent a third or more of the total mill steam usage, followed by the paper machine and digester. When considering an evaporator rebuild or a new system, the key design question is how many effects to include in the system. The number of effects is the main design feature that deter-mines the economy of the system and the steam usage for a given evaporation capacity. A higher number of effects increases steam economy and reduces energy cost to a point, but additional effects also have higher initial capital cost and increased power costs. This research paper uses life-cycle cost analysis (LCCA) as a method to determine the optimum number of evaporator effects for a new evaporator system. The same basic principles and method can also apply to existing evaporator rebuild projects.
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Numerical investigation of the effect of ultrasound on paper drying, TAPPI Journal March 2022
ABSTRACT: The paper drying process is very energy inefficient. More than two-thirds of the total energy used in a paper machine is for drying paper. Novel drying technologies, such as ultrasound (US) drying, can be assessed numerically for developing next-generation drying technologies for the paper industry. This work numerically illustrates the impact on drying process energy efficiency of US transducers installed on a two-tiered dryer section of a paper machine. Piezoelectric transducers generate ultrasound waves, and liquid water mist can be ejected from the porous media. The drying rate of handsheet paper in the presence of direct-contact US is measured experimentally, and the resultant correlation is included in the theoretical model. The drying section of a paper machine is simulated by a theoretical drying model. In the model, three scenarios are considered. In the first scenario, the US modules are positioned in the dryer pockets, while in the second scenario, they are placed upstream of the drying section right after the press section. The third case is the combination of the first and second scenarios. The average moisture content and temperature during drying, enhancement of total mass flux leaving the paper by the US mechanism, total energy consumption, and thermal effect of heated US transducers are analyzed for all cases. Results show that the application of the US can decrease the total number of dryer drums for drying paper. This numerical study is based on the US correlation obtained with the US transducer direct-contact with the paper sample. Thus, future work should include US correlation based on a non-contact US transducer.
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Furnishing autohydrolyzed poplar weakly alkaline P-RC APMP to make lightweight coated base paper, TAPPI Journal February 2022
ABSTRACT: This work investigated the effects of autohydrolysis pretreatment severity on poplar (Populus tomentosa Carr.) woodchips used to make a type of high-yield pulp (HYP) known as preconditioning followed by refiner chemical treatment, alkaline peroxide mechanical pulp (P-RC APMP). It also investigated the ratios for partially replacing sodium hydroxide (NaOH) with magnesium oxide (MgO) in the high-consistency (HC) retention stage of the P-RC APMP process on the obtained HYP’s properties. The results show that the pretreatment severity of autohydrolysis at combined hydrolysis factor (CHF) = 10.77 and the 50 wt% ratio for partially substituting NaOH with MgO were the optimum conditions for making light-weight coated (LWC) base paper. Compared to the conventional P-RC APMP, the optimized P-RC APMP had similar bulk and higher tensile, burst, and tear indices, as well as opacity, but a slightly lower ISO brightness. When the optimized P-RC APMP and commercial softwood bleached sulfate pulp (SBKP) were blended to make LWC base paper, the most favorable pulp furnish was comprised of 50% optimized P-RC APMP and 50% commercial SBKP. The obtained LWC base paper handsheet had better bulk, and its other properties could also meet the require-ments of LWC base paper.
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How to use total dissolved solids measurements to evaluate the performance of diffuser washers—A mill study, TAPPI Journal April 2020
ABSTRACT: Various types of pulp washing equipment are available. Each washing device has a unique mechanical construction, and the washing principle is often a combination of dilution, thickening, and displacement washing. In this work, the performance of the pressure diffuser washer is studied. In stepwise trials, the effect of the feed and discharge consistencies on the performance of the diffuser was studied. The effect of the downward velocity of the screen on the pressure diffuser’s washing efficiency was also studied. The measurement of total dissolved solids (TDS) by a process refractometer was used as a wash loss measurement unit and the refractometer’s results were used in the calculations of standardized Nordén efficiency (E10) values. The chemical oxygen demand (COD) and conductivity values were also measured and their results compared to the TDS results.The results indicated that feed consistency has a significant effect on the performance and effectiveness of the diffuser washers in the mill. It can also be stated that when the downward velocity of the screen is adjusted to too high a level, the washing efficiency of the pressure diffuser decreases. As a conclusion from the mill tests, it can be stated that even small process parameter changes can provide enhanced diffuser washing at the beginning of the washing line, which has a direct effect on the performance of post-oxygen washing.
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Decreased water usage in a softwood ECF bleaching sequence— full mill simulations, TAPPI JOURNAL June 2018
Decreased water usage in a softwood ECF bleaching sequence— full mill simulations, TAPPI JOURNAL June 2018
Journal articles
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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.