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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.
Journal articles
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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.
Journal articles
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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.
Journal articles
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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
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Can carbon capture be a new revenue opportunity for the pulp and paper sector?, TAPPI Journal August 2021
ABSTRACT: Transition towards carbon neutrality will require application of negative carbon emission technologies (NETs). This creates a new opportunity for the industry in the near future. The pulp and paper industry already utilizes vast amounts of biomass and produces large amounts of biogenic carbon dioxide. The industry is well poised for the use of bioenergy with carbon capture and storage (BECCS), which is considered as one of the key NETs. If the captured carbon dioxide can be used to manufacture green fuels to replace fossil ones, then this will generate a huge additional market where pulp and paper mills are on the front line. The objective of this study is to evaluate future trends and policies affecting the pulp and paper industry and to describe how a carbon neutral or carbon negative pulp and paper production process can be viable. Such policies include, as examples, price of carbon dioxide allowances or support for green fuel production and BECCS implementation. It is known that profitability differs depending on mill type, performance, energy efficiency, or carbon dioxide intensity. The results give fresh understanding on the potential for investing in negative emission technologies. Carbon capture or green fuel production can be economical with an emission trade system, depending on electricity price, green fuel price, negative emission credit, and a mill’s emission profile. However, feasibility does not seem to evidently correlate with the performance, technical age, or the measured efficiency of the mill.
Journal articles
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Investigation of the influencing factors in odor emission from wet-end white water, TAPPI Journal October 2020
ABSTRACT: Emission of malodorous gases, such as volatile organic compounds (VOCs), hydrogen sulfide (H2S), and ammonia (NH3) during pulping and papermaking has caused certain harm to the air environment and human health. This paper investigated the influencing factors of odor emission from wet-end white water during the production of bobbin paper in a papermaking mill using old corrugated containers (OCC) as raw material. The concentration of malodorous gases emitted from wet-end white water was determined with pump-suction gas detectors. The results indicated that low temperature could limit the release of malodorous gases from white water. Specifically, no total volatile organic compounds (TVOC), H2S, and NH3 was detected at a temperature of 15°C. The concentrations of malodorous gases were slightly increased when temperature increased to 25°C. When temperature was 55°C, the released concentrations of TVOC, H2S, and NH3 were 22.3 mg/m3, 5.91 mg/m3, and 2.78 mg/m3, respectively. Therefore, the content of malodorous gases significantly increased with the temperature increase. The stirring of white water accelerated the release of malodorous gases, and the release rate sped up as the stirring speed increased. However, the total amount of malodorous gases released were basically the same as the static state. Furthermore, the higher the concentration of white water, the greater the amount of malodorous gases released. The pH had little influence on the TVOC release, whereas it significantly affected the release of H2S and NH3. With the increase of pH value, the released amount of H2S and NH3 gradually decreased. When pH reached 9.0, the release amount of H2S and NH3 was almost zero, proving that an alkaline condition inhibits the release of H2S and NH3.
Journal articles
Magazine articles
Modeling and parameter optimization of the papermaking processes by using regression tree model and full factorial design, TAPPI Journal February 2021
ABSTRACT: One of the major challenges in the pulp and paper industry is taking advantage of the large amount of data generated through its processes in order to develop models for optimization purposes, mainly in the papermaking, where the current practice for solving optimization problems is the error-proofing method. First, the multiple linear regression technique is applied to find the variables that affect the output pressure controlling the gap of the paper sheet between the rod sizer and spooner sections, which is the main cause of paper breaks. As a measure to determine the predictive capacity of the adjusted model, the coefficient of determination (R2) and s values for the output pressure were considered, while the variance inflation factor was used to identify and eliminate the collinearity problem. Considering the same amount of data available by using machine learning, the regression tree was the best model based on the root mean square error (RSME) and R2. To find the optimal operating conditions using the regression tree model as source of output pressure measurement, a full factorial design was developed. Using an alpha level of 5%, findings show that linear regression and the regression tree model found only four independent variables as significant; thus, the regression tree model demonstrated a clear advantage over the linear regression model alone by improving operating conditions and demonstrating less variability in output pressure. Furthermore, in the present work, it was demonstrated that the adjusted models with good predictive capacity can be used to design noninvasive experiments and obtain.
Journal articles
Magazine articles
Black liquor evaporator upgrades— life cycle cost analysis, TAPPI Journal March 2021
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. Evaporator steam economy is defined as the unit mass of steam required to evaporate a unit mass of water from black liquor (i.e., lb/lb or kg/kg.) The economy is determined by the number of effects in an evaporator train and the system configuration. Older systems use four to six effects, most of which are the long tube vertical rising film type. Newer systems may be designed with seven or even eight effects using falling film and forced circulation crystallization technology for high product solids. The median age of all North American evaporator systems is 44 years. Roughly 25% of the current North American operating systems are 54 years or older. Older systems require more periodic maintenance and have a higher risk of unplanned downtime. Also, older systems have chronic issues with persistent liquor and vapor leaks, shell wall thinning, corrosion, and plugged tubes. Often these issues worsen to the point of requiring rebuild or replacement. When considering the age, technology, and lower efficiency of older systems, a major rebuild or new system may be warranted. The intent of this paper is to review the current state of black liquor evaporator systems in North America and present a basic method for determining whether a major rebuild or new installation is warrant-ed using total life cycle cost analysis (LCCA).